Heterogeneous Catalysis and Fine Chemicals II: Proceedings of the 2nd International Symposium, Poitiers, October 2-5, 1990 (Studies in Surface Science and Catalysis)

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Studies in Surface Science and Catalysis 59 HETEROGENEOUS CATALYSIS AND FINE CHEMICALS II

This Page Intentionally Left Blank

Studies in Surface Science and Catalysis Advisory Editors: B. Delmon and J.T. Yates

Vol. 59

HETEROGENEOUS CATALYSIS AND FINE CHEMICALS II Proceedings of the 2nd International Symposium, Poitiers, October 2-5, 199 0

Editors

M. Guisnet, J. Barrault, C. Bouchoule, D. Duprez, G. Pbrot, R. Maurel and C. Montassier Laboratoire de Catalyse en Chimie Organique (URA CNRS 3501,UFR Sciences, Universitb de Poitiers, 40 Avenue du Recteur Pineau, 86022 Poitiers, France

ELSEVIER

Amsterdam - Oxford - New York

-Tokyo

1991

ELSEVIER SCIENCE PUBLISHERS B.V. Sara Burgerhartstraat 25 P.O. Box 21 1 , 1000 AE Amsterdam, The Netherlands Distributors for the United States and Canada. ELSEVIER SCIENCE PUBLISHING COMPANY INC 655, Avenue of the Americas New York, NY 10010, U.S.A.

L i b r a r y o f Congress C a t a l o g i n g - i n - P u b l i c a t i o n

Data

Heterogeneous c a t a l y s i s and f i n e c h e m i c a l s I 1 p r o c e e d i n g s o f t h e 2nd i n t e r n a t l o n a l s y m p o s i u m . P o l t i e r s . O c t o b e r 2-5, 1 9 9 0 / e d i t o r s . M. Guisnet Let al.1. 59) p. cm. -- ( S t u d i e s i n s u r f a c e s c i e n c e a n d c a t a l y s i s P a p e r s from t h e 2nd I n t e r n a t i o n a l Symposium on H e t e r o g e n e o u s C a t a l y s i s and F i n e Chemicals. I n c l u d e s b i b l i o q r a p h i c a l r e f e r e n c e s and i n d e x e s . ISBN 0 - 4 4 4 - 8 8 5 1 4 - 5 1. G u i s n e t . M . 1. H e t e r o g e n e o u s c a t a l y s i s - - C o n g r e s s e s . 11. I n t e r n a t i o n a l S y m p o s i u m o n H e t e r o g e n e o u s C a t a l y s i s a n d F i n e 111. S e r i e s . Chemicals (2nd 1990 Poltiers. Francel 00505.H463 1991 541,3'95--dc20 9 1-9044

...

.

CTP

ISBN 0-444-885 14-5

0 Elsevier Science Publishers B.V.. 199 1 All rights reserved. No part of this publication may be reproduced, stored in a retrieval system or transmitted in any form or by any means, electronic, mechanical, photocopying, recording or otherwise, without the prior written permission of the publisher, Elsevier Science Publishers B.V./ Academic Publishing Division, P.O. Box 330, 1000 AH Amsterdam, The Netherlands. Special regulationsfor readers in the USA -This publication has been registered with the Copyright Clearance Center Inc. (CCC), Salem, Massachusetts. Information can be obtained from the CCC about conditions under which photocopies of parts of this publication may be made in the USA. All other copyright questions, including photocopying outside of the USA, should be referred t o the publisher. No responsibility is assumed by the Publisher for any injury and/or damage t o persons or property as a matter of products liability, negligence or otherwise, or from any use or operation of any methods, products, instructions or ideas contained in the material herein. Although all advertising material is expected t o conform to ethical (medical) standards, inclusion in this publication does not constitute a guarantee or endorsement of the quality or value of such product or of the claims made of it by its manufacturer. This book is printed on acid-free paper Printed in The Netherlands

V

CONTENTS

Foreword ...................................................................

XI11

Preface ......................................................................

XV

Scientific Committee .......................................................

XVII

Organizing Committee .......................................................

XVII

Financial Support .........................................................

XVIII

PLENARY

LECTURES AND

INVITED

PAPERS

Gas-1 iquid-solid reactors for hydrogenation in fine chemicals synthesis J.F. Jenck ...........................................................

1

Structure-reactivity in the hydrogenation of alkenes. Comparisons with reductions by diimide and the formation of a Ni(0) complex S. Siege1 ............... ............................................

21

Heterogeneous catalytic oxidat on and fine chemicals R.A. Sheldon.. .......... ............................................

33

Solids for catalysis and control in organic synthesis K. Smith .............................................................

55

Enantioselective catalysis by chiral sol ids : approaches and results H.U. Blaser and M. Muller.. ..........................................

73

Catalysis with immobilized enzymes : hydrolysis and esterification by Rhizopus arrhizus C. Gancet ............................................................ 93

\' I

RESEARCH PAPERS

I . HYDROGENATION AND RELATED REACTIONS Hydrogenation o f benzaldehyde t o b e n z y l a l c o h o l i n a s l u r r y and f i x e d - b e d reactor

M. H e r s k o w i t z .......................................................

105

S t r u c t u r e and c a t a l y t i c p r o p e r t i e s i n h y d r o g e n a t i o n o f v a l e r o n i t r i l e o f Raney n i c k e l prepared f r o m C r and Mo doped Ni2A13 a l l o y s

M. Besson, 0. Djaouadi, J.M. Bonnier, S. H a m a r - T h i b a u l t and M. J o u c l a ...........................................................

113

Selective preparation o f c h l o r o a n i l i n e s from chloronitrobenzenes over s u l f i d e d hydrotreating catalysts C . Moreau, C . Saenz, P. Geneste, M. Breysse and M. L a c r o i x

..........

121

The a p p l i c a b i l i t y o f d i s p e r s e d m e t a l s as c a t a l y s t s f o r o r g a n o m e t a l l i c r e a c t i o n s R.L. Augustine, S.T.

O'Leary, K . M . Lahanas and Y.-M.

Lay ............ 129

S u r f a c e organometall i c c h e m i s t r y on m e t a l s : s e l e c t i v e h y d r o g e n a t i o n o f c i t r a l i n t o g e r a n i o l and n e r o l on t i n m o d i f i e d s i l i c a s u p p o r t e d rhodium

B. O i d i l l o n , A . El Mansour, J.P. Candy, J.P. B o i i r n o n v i l l e and J.M. Basset .........................................................

137

S e l e c t i v e h y d r o g e n a t i o n o f u n s a t u r a t e d aldehydes o v e r z e o l i t e - s u p p o r t e d m e t a l s D.G.

Blackmond, A. Waghray, R . Oukaci, B. Blanc and P. G a l l e z o t . .

...

145

The mechanism o f h y d r o g e n o l y s i s and i s o m e r i z a t i o n o f o x a c y c l o a l k a n e s on m e t a l s .

X. Nature o f t h e a c t i v e s i t e s i n the r e g i o s e l e c t i v e hydrogenation o f oxiranes F . Notheisz, A.G.

Zsigmond, M. Barto'k, 0. Ostgard and G.V.

Smith .... 153

Chemo-, r e g i o and s t e r e o s e l e c t i v i t y i n s t e r o i d h y d r o g e n a t i o n w i t h Cu/A1203. Intra-

and i n t e r m o l e c u l a r hydrogen t r a n s f e r r e a c t i o n s

N. Ravasio, M. Gargano, V . P .

q u a t r a r o and M. Rossi .................. 161

S e l e c t i v e h y d r o g e n a t i o n o f a r o m a t i c and a1 i p h a t i c n i t r o compounds b y hydrogen t r a n s f e r over MgO

J. K i j e < s k i , M. G l i i s k i , R . WiSniewski and S. Murghani .............. 169

VII

Mass t r a n f e r c o n s i d e r a t i o n s f o r t h e e n a n t i o s e l e c t i v e h y d r o g e n a t i o n o f a - k e t o e s t e r s c a t a l y z e d b y cinchona m o d i f i e d Pt/A1203

M. Garland, H.P. J a l e t t and H.U. B l a s e r ..............................

177

S e l e c t i v e carvone hydrogenat i o n on Rh supported c a t a l y s t s

R. Gomez, J. Arredondo, N. Rosas and G. Del Angel ....................

185

S e l e c t i v e h y d r o g e n a t i o n o f c i t r a l i n t h e 1 i q u i d phase o v e r unsupported n i c k e l molybdenum c a t a l y s t s N i l - x Mo, J. Court, F. J a n a t i - I d r i s s i and S. V i d a l

.............................

193

S u l f u r removal f r o m terpenes by h y d r o d e s u l f u r i z a t i o n on c a r b o n - s u p p o r t e d catalysts

F . Casbas, D. Duprez and J. O l l i v i e r .................................

201

S t u d i e s on t h e c a t a l y t i c h y d r o g e n a t i o n o f r e s i n a c i d s d e r i v a t i v e s : s y n t h e s i s o f a benzoxazol e B. Gigante, A.M.

Lobo, S. Prabhakar, M.J. M a r c e l o - C u r t o and

D.J. W i l l i a m s ........................................................

209

The i s o m e r i s a t i o n o f l a c t o s e t o l a c t u l o s e c a t a l y s e d by a l k a l i n e ion-exchangers

B.F. K u s t e r , J.A.W.M.

Beenackers and H.S.

van d e r Baan ............... 215

F u r a n i c d e r i v a t i v e s s y n t h e s i s f r o m p o l y o l s b y heterogeneous c a t a l y s i s o v e r metals C . Montassier, J.C. Menezo, J . Moukolo, J. Naja, J. B a r b i e r and

J.P. B o i t i a u x

........................................................

223

A c t i v i t y and s t a b i l i t y of promoted Raney-nickel c a t a l y s t s i n g l u c o s e hydrogenation P.J. Cerino, G. Fleche, P. G a l l e z o t and J.P. Salome

.................. 231

T r a n s f o r m a t i o n o f sugar i n t o g l y c o l s on a 5 % Ru/C c a t a l y s t P. M u l l e r , P. Rimmelin, J.P. Hindermann, R. K i e f f e r , A. Kiennemann and J. C a r r e .........................................................

237

S e l e c t i v e h y d r o g e n a t i o n o f acetophenone on unpromoted Raney n i c k e l : influence o f the reaction conditions J. Masson,

P. C i v i d i n o , J.M. Bonnier and P. F o u i l l o u x ................ 245

VIIl

Chemoselective r e d u c t i o n o f enones t o a l l y 1 i c a l c o h o l s J. Kaspar, A. T r o v a r e l l i , F . Zamoner, E. F a r n e t t i and M. G r a z i a n i

... 253

Comparison o f homogeneous and heterogeneous p a l l a d i u m c a t a l y s t s i n t h e c a r b o n y l a t i o n o f a1 l y l e t h e r s M.M. Barreto-Rosa, M.C. Bonnet and I . Tkatchenko ....................

263

L i q u i d - p h a s e s e l e c t i v e h y d r o g e n a t i o n o f 1 , 4 - b u t y n e d i o l on s u p p o r t e d N i and N i Cu c a t a l y s t s

F.M. B a u t i s t a , J.M. Campelo, A. G a r c i a , R. GuardeKo, D. Luna and J.M. Marinas ........................................................

269

C a t a l y t i c p r o p e r t i e s o f t r a n s i t i o n metal s u l p h i d e s f o r t h e d e h y d r o g e n a t i o n o f s u l p h u r c o n t a i n i n g molecules

M. L a c r o i x , H. M a r r a k c h i , C. C a l a i s , M. Breysse and C . Forquy

....... 277

React i o n s o f u n s a t u r a t e d e t h e r s on a copper-chromium c a t a l y s t

R . Hubaut and J.P. B o n n e l l e .

........................................

287

Hydrogenation o f methyl -3 b u t e n a l on p o l y c r y s t a l l i n e p l a t i n u m C.-M. P r a d i e r , E. Margot, Y. B e r t h i e r , G. C o r d i e r ................... 295 Surface c h e m i s t r y and c a t a l y s i s w i t h o r g a n i c n i t r o compounds. L o o k i n g f o r t h e key t o h i g h e r s e l e c t i v i t i e s

P.A.J.M.

Angevaare, A. Maltha, T.L.F.

Favre, A . P . Zuur and V . Ponec. 305

P r e p a r a t i o n o f orthophenylenediamine f r o m 4 - c h l o r o - 2 - n i t r o a n i l i n e J.L. M a r g i t f a l v i , M. Hegedus, S. Gdbolos and E. Talas ............... 313 Chemoselective h y d r o g e n a t i o n o f a r o m a t i c c h l o r o n i t r o compounds w i t h amidine modified nickel catalysts P. Baumeister, H.U.

B l a s e r and W . S c h e r r e r ..........................

321

Intermediates formation i n t h e c a t a l y t i c hydrogenation o f n i t r i l e s Ph. Marion, P. G r e n o u i l l e t , J. Jenck and M. J o u c l a . ................. 329 R e d u c t i v e a m i n a t i o n o f acetone on t i n m o d i f i e d s k e l e t a l n i c k e l c a t a l y s t s S. Gdbolos, E. Talas, M. Hegedus, J.L. M a r g i t f a l v i and J. Ryczkowski 335

IX

S y nt h es is o f d i m e t h y l a l k y l a m i n e s f r o m a c i d s and e s t e r s over promoted copper catalysts J. B a r r a u l t , G. Delahay, N. Essayem, Z. G a i z i , C. Forquy and

R. Brouard

..........................................................

343

T e r t i a r y amine p r e p a r a t i o n by r e d u c t i v e a l k y l a t i o n o f a1 i p h a t i c secondary amines w i t h ketones R.E.Malz, Jr. and H. G r e e n f i e l d

.....................................

351

E f f e c t o f promoters on Pt/SiO2 c a t a l y s t s f o r t h e N - a l k y l a t i o n o f s t e r i c a l l y hindere d a n i l i n e s i n t h e vapor phase M. Rusek

............................................................

359

P o l y f u n c t i o n a l i t y o f Zn-Cr-0 (Pd) c a t a l y s t f o r t h e s y n t h e s i s o f p y r a z i n e s f rom diamines and g l y c o l s L. F o r n i and R. M i g l i o

.............................................. 11.

367

OXIDATION

From s urf ac es t o d i s c r e t e molecules as c a t a l y s t s f o r alkene e p o x i d a t i o n K.A. J ~ r g e n s e n

......................................................

377

On t h e oxygen t o l e r a n c e o f n o b l e metal c a t a l y s t s i n l i q u i d phase a l c o h o l o x i d a t i o n s . The i n f l u e n c e o f t h e s u p p o r t on c a t a l y s t d e a c t i v a t i o n P. Vinke, W. van d e r Poel and H. van Bekkum.........................

385

I r o n - p h t h a l l o c y a n i n e s encaged i n z e o l i t e Y and VPI-5 m o l e c u l a r s i e v e as c a t a l y s t s f o r t h e o x y f u n c t i o n a l i z a t i o n o f n-alkanes R.F. Parton, L. Uytterhoeven and P.A.

Jacobs..

......................

395

M i l d o x i d a t i o n o f c y c l i c C6-clO hydrocarbons i n l i q u i d phase a t room temperature b y heterogeneous p h o t o c a t a l y s i s J.M. Herrmann,

W. Mu and P. P i c h a t ..................................

405

O x i d a t i v e dehydrogenation o f 3-hydroxy-4-methyl-4-penten-2-one t o 4-met hyl-4pent e n-2 , 3 -d ion e over CuO-based c a t a l y s t s H.G.-J. Lansink R o t g e r i n k , G. Penn, P.C. A. B a i k e r

F u n f s c h i l l i n g and

...........................................................

413

P a r t i a l o x i d a t i o n o f t o l u e n e t o benzaldehyde M. A i ...............................................................

423

New p o l y d e n t a t e M o ( V 1 ) - g r a f t e d p o l y ( amido amine) r e s i n s as heterogeneous epoxidation c a t a l y s t s P. F e r r u t i , E . Tempesti, L. G i u f f r e , R . Ranucci and C . Mazzocchia ... 431

S e l e c t i v e o x i d a t i o n o f methyl e t h y l k e t o n e t o d i a c e t y l o v e r vanadium phosphorus oxide c a t a l y s t s E. McCullagh, J.B. McMonagle and B.K. H o d n e t t

.......................

437

(Heterogeneous) p h o t o c a t a l y t i c o x i d a t i o n o f t o l u e n e u s i n g p u r e and i r o n - d o p e d t i t a n i a catalysts J.A. Navio, M. G a r c i a Gomez, M.A.

Pradera A d r i a n and J. Fuentes Mota 445

S y n t h e s i s o f n i t r i l e s b y r e a c t i o n o f p - x y l e n e w i t h NO o v e r Cr203-Al203 catalysts S. Z i n e and A. Ghorbel

..............................................

455

S e l e c t i v e e l e c t r o c a t a l y t i c o x i d a t i o n o f g l y o x a l i n aqueous medium E.M.

B e l g s i r , H. Huser, C . Lamy and J.-M. Leger .....................

463

111. ACID-BASE CATALYSIS N i t r i c a c i d a s s o c i a t e d w i t h i n o r g a n i c s o l i d s : a v e r s a t i l e r e a g e n t and c a t a l y s t i n t h e chemistry o f aromatics M.H.

Gubelmann, C . Doussain, P.J. T i r e l , J.M. Popa .................. 471

D e h y d r a t i o n o f carboxamides t o n i t r i l e s u s i n g s u l p h a t e d z i r c o n i a c a t a l y s t R.A.

Rajadhyaksha and G.W.

J o s h i ....................................

479

S a t u r a t e d and u n s a t u r a t e d ketones manufactured b y heterogeneous c a t a l y s i s W . R e i t h , M. Dettmer, H. Widdecke and B . F l e i s c h e r .................. 487

Condensation o f methyl N-phenyl carbamate w i t h sol i d a c i d c a t a l y s t s J.S. Lee, C.W.

Lee, S.M.

Park ................. 495

Lee, J.S. Oh and K.H.

Z e o l i t e s as base c a t a l y s t s . P r e p a r a t i o n o f c a l c i u m a n t a g o n i . s t s i n t e r m e d i a t e s b y condensation o f benzaldehyde w i t h e t h y l a c e t o a c e t a t e

A . Corma, R.M. M a r t i n - A r a n d a and ,F. Sa'nchez..

.......................

503

XI

Mechanism o f p h e n y l a c e t a t e t r a n s f o r m a t i o n on z e o l i t e s Y. P o u i l l o u x , J.P. Bodibo, I. Neves, M. Gubelmann, G. P e r o t and M. Guisnet ..........................................................

513

O r t h o s e l e c t i v e a l k y l a t i o n o f 2 - e t h y l a n i l i n e w i t h methanol on f e r r i c o x i d e catalysts J. Valyon, R.M. M i h a l y i and 0. K a l l o ................................

523

Rearrangement o f c y c l ohexanone oxime t o c a p r o l actam o v e r s o l i d a c i d c a t a l y s t s

T. C u r t i n , J.B. McMonagle and B.K. H o d n e t t ..........................

531

Beckmann rearrangement r e a c t i o n s on a c i d i c s o l i d s

E . G u t i e r r e z , A.J. Aznar and E . R u i z - H i t z k y .........................

539

S e l e c t i v e r i n g - o p e n i n g o f i s o m e r i c 2-methyl - 3 - p h e n y l o x i r a n e s on o x i d e c a t a l y s t s

A. Molna'r, I . Bucsi and M. B a r t i k . .

.................................

549

Mono and t r i d i r e c t i o n a l 12-membered r i n g z e o l i t e s as a c i d c a t a l y s t s f o r c a r b o n y l group r e a c t i o n s M.J. Climent, A.Corma, H. Garcia, S. I b o r r a and J . Primo

....... ....

557

T r i p l e bond h y d r a t i o n u s i n g z e o l i t e s as c a t a l y s t s

A. F i n i e l s , P. Geneste, M. Lasperas, F. Marichez and P. Moreau.

.... 565

Rearrangement o f epoxides u s i n g m o d i f i e d z e o l i t e s M. Chamoumi, 0. Brunel, P. Geneste, P. Moreau and J . S o l o f o

..... ..... 573

The gas phase i s o m e r i z a t i o n o f s u b s t i t u t e d halobenzenes on z e o l i t e s 6. Coq, J. P a r d i l l o s and F. Figueras

................................

581

K a o l i n promoted W i t t i g o l e f i n a t i o n and a r o m a t i c n i t r a t i o n

.............................................

589

A u t h o r Index ..............................................................

597

S u b j e c t Index .............................................................

601

S t u d i e s i n Surface Science and C a t a l y s i s ( o t h e r volumes i n t h e s e r i e s )

.... 605

C . C o l l e t and P. L a s z l o


XI11

FOREWORD

The Second International Symposium on Heterogeneous Catalysis and Fine Chemicals was held in Poitiers (Futuroscope), France, October 2-5, 1990. Just as in the first symposium (held in Poitiers, March 1988) the aims were to illustrate the present day role played by heterogeneous catalysis in the synthesis of functional compounds and to discuss methods of research in this field. Since the first Symposium was held, research activities have rapidly expanded as has the support provided by industry. Thus 104 Abstracts were submitted (an increase of 44 on the first symposium), closely related to the symposium theme. Moreover, the scientific contribution made by industry was also greater than at the previous symposium since this time a third of the papers was presented by researchers solely from industry (5 papers) or in collaboration with researchers from Universities (16 papers). The transformations studied were this time much more complex, covering all aspects of selectivity : chemo, regio and stereo-selectivity having been frequently considered. The three themes of the symposium : selective hydrogenation, selective oxidation and acid-base catalysis were introduced by four plenary lectures and two invited communications, A panel concerned with the future of zeolites and other shape-selective materials for fine chemical synthesis was conducted by specialists in the field : 0. Barthomeuf (University of Paris 6 ) , E. Derouane (University of Namur), L. Forni (University of Milan), M. Gubelmann (RhBnePoulenc, St Fons), W. Hoelderich (BASF, Ludwigshafen) and G. Perot (University of Poitiers). An exhibition of equipment was held during the symposium on October 3 and 4 . Over 20 firms exhibited equipment, chemicals and catalysts which were of interest to researchers involved with the synthesis of functional compounds by heterogeneous catalysis. The Organizing Committee would 1 ike to thank all the participants, particularly the authors of the communications, the various session chairmen and the members of the panel on zeolites. Special thanks are due to the members of the Scientific Committee who accomplished the difficult task of selecting the communications and reviewing the papers. Their suggestions allowed us to improve the quality and presentation of the communications. We would also like to thank all the members of the Laboratory of Catalysis in Organic Chemistry and the members of Atlas (the Association of postgraduate students and doctors of this laboratory) for their enthusiastic help. We hope the symposium provided all the participants with an opportunity to establish fruitful social and scientific ties.


xv PREFACE

Le second Colloque International CNRS sur le theme Catalyse Heterogene et Chimie Fine s’est tenu a Poitiers (Futuroscope) du 2 au 5 octobre 1990. Comme pour le premier Colloque (Poitiers 15-17 mars 1988), l’objectif etait de montrer le r6le joue aujourd’hui par la Catalyse Heterogene dans la Synthese des composes fonctionnels et de discuter des strategies de recherche a developper dans ce domaine. Depuis le premier Colloque, 1 ’activite de recherches s’est fortement accrue et le soutien de 1’Industrie est alle croissant. C’est ainsi que 104 resumes (au lieu de 60 lors du premier Symposium) en rapport etroit avec le theme nous ont ete soumis. Par ailleurs, la contribution scientifique de 1‘Industrie a enormement progresse puisqu’a ce Colloque, 5 communications venaient de 1’Industrie et 16 resultaient de collaborations entre chercheurs de 1’Industrie et de 1’Universite. Enfin les reactions presentees deviennent de plus en plus complexes, tous les aspects de la selectivite : chimio, regio et stereoselectivite etant souvent examines. Les trois grands themes du Symposium : hydrogenation, oxydation et catalyse acidobasique furent introduits par 4 conferences plenieres et 2 communications invitees. Une table ronde sur l’avenir des zeolithes et des autres materiaux a selectivite de forme en synthese organique a ete animee par des specialistes du domaine : D. Barthomeuf (Universite de Paris 6 ) , E. Derouane (Universite de Namur), L. Forni (Universite de Milan), M. Gubelmann (RhBnePoulenc, St Fons), W . Hoelderich (BASF, Ludwigshafen), G. Perot (Universite de Poitiers). Une exposition de materiel s’est tenue en parallele avec le Symposium les 3 et 4 octobre. Plus de 20 Societes y ont presente materiel, produits chimiques et catalyseurs de grand inter6t pour les chercheurs concernes par la synthese de composes fonctionnels par Catalyse Heterogene. Le Comite d’organisation remercie tous les participants et particul ierement les auteurs de communication, les Presidents de Seance et les animateurs de la table ronde. Des remerciements particuliers sont dijs aux membres du Comite Scientifique qui ont eu la tiche delicate de choisir les communications et d’examiner les articles. Leurs suggestions et leurs critiques ont incontestablement permis d’amel iorer la qua1 it6 et la presentation des communications. Nos remerciements vont aussi a tous les membres du Laboratoire de Catalyse en Chimie Organique et d’Atlas (Association des Chercheurs et Anciens Chercheurs de ce Laboratoire) qui ont participe avec enthousiasme et efficacite a l’organisation de ce Symposium. esperons que ce Colloque a donne l‘opportunite a tous les participants d’etablir des relations a la fois amicales et scientifiques. Nous


XVII

SCIENTIFIC COMMITTEE J.E. BACKWALL, U n i v e r s i t y o f

P . C . GRAVELLE, PIRSEM (CNRS), P a r i s ,

Uppsal a, Sweden

France

G. BALAVOINE, Departement Chimie

G. HECQUET, NORSOLOR, Mazingarbe,

CNRS, France

France

J. BARBIER, U n i v e r s i t y o f P o i t i e r s ,

W. HOELDERICH, BASF, Ludwigshafen, RFA

France

M. BLANCHARD, U n i v e r s i t y o f P o i t i e r s , France

J.C. JACQUESY, U n i v e r s i t y o f

H.U.

G. MARTINO, I n s t i t u t F r a n c a i s du

BLASER, Ciba-Geigy, Basel,

P o i t i e r s , France

S w i t z e r l and

P e t r o l e , Rueil-Malmaison, France

J. BOUSQUET, E l f A q u i t a i n e , P a r i s ,

G. MATTIODA, Hoechst, S t a i n s , France

France

C. MERCIER, Rhijne-Poulenc, S a i n t -

A. CORMA, I n s t i t u t e o f C a t a l y s i s ,

Fons, France

Madrid, Spain

D. O L I V I E R , I n s t i t u t de Recherches

B. DELMON, U n i v e r s i t y o f L o u v a i n - l a -

sur l a Catalyse,Villeurbanne,

France

Neuve, Belgium

Y. ONO, I n s t i t u t e o f Technology,

G. DESCOTES, Un i v e r s it e C1 aude

Tokyo, Japan

Bernard, Lyon, France

K. SMITH, U n i v e r s i t y o f Swansea,

G. FLECHE, Roquette, Lestrem, France

L. FORNI, U n i v e r s i t y o f M i l a n , I t a l y

U n i t e d Kingdom H. VAN BEKKUM, U n i v e r s i t y o f D e l f t ,

P. GENESTE, U n i v e r s i t y o f

The Netherlands

M o n t p e l l i e r , France

ORGANIZING

COMMITTEE

M. GUISNET

Chairman

3. BARRAULT and 0 . DUPREZ

Secretaries

C . BOUCHOULE, R. MAUREL, C. MONTASSIER and G. PEROT

Members

ATLAS 86 ( A s s o c i a t i o n o f s t u d e n t s o f t h e C a t a l y s i s Group o f P o i t i e r s )

XVlll

F I N A N C I A L SUPPORT

The O r g a n i z e r s a r e g r a t e f u l t o t h e i r Generous Sponsors :

- CENTRE NATIONAL DE LA RECHERCHE S C I E N T I F I Q U E (CNRS) - CONSEIL GENERAL DE LA VIENNE - SOCIETE FRANCAISE DE C H I M I E - D I V I S I O N CATALYSE - UNIVERSITE DE P O I T I E R S AND UFR SCIENCES FONDAMENTALES E l

APPLIQUEES - ATOCHEM - BASF - CIBA-GEIGY

-

DEGUSSA

- DERIVES RESINIQUES ET TERPENIQUES - I N S T I T U T FRANCAIS DU PETROLE - JONHSON MATTHEY - RHONE-POULENC - ROQUETTE FRERES

M. Guisnet et al. (Editors), Heterogeneous Catalysis andFine Chemicals II

1

0 1991 Elsevier Science Publishers B.V.,Amsterdam

-

-

GAS LIQUID SOLID REACTORS FOR HYDROQENATION IN FINE CHEMICALS SYNTHESIS

Jean F. JENCK Unit6 Mixte CNRS - R h h e Poulenc (UMR BP 166 F 69151 DECINES (FRANCE)

-

45)

ABSTRACT :

Although the presence of a liquid phase in heterogeneous hydrogenation catalysis is useful for chemical reactivity COIItrol, it introduces considerable engineering complexity. Different types of triphasic hydrogenation reactors, with moving or immobilized catalyst, in continuous or batch mode, are compared. Coupling of intrinsic kinetics with mass and energy transfer determines reactor performances, in rate as well as in selectivity. Reactor design and scale-up require the knowledge of numerous physico-chemical parameters, whose acquisition by measurement or correlation is briefly presented. INTRODUCTION :

Solid catalysts are commonly used in reactions of gaseous dihydrogen with liquid substrates, particularly in the field of fine chemicals. By I1fine" , we usually mean organic molecules exhibiting structural complexity, related to polyfunctionality and/or the presence of heteroatoms (O,S,N,P,X, etc ...), involved in small production processes (less than a few thousand T/yr, and down to the kg/yr scale), with a high production cost (over 20 FF/kg). The question of selectivity in these fine hydrogenations is frequently raised : for instance, in the last symposium in this series (Poitiers, March 1988), the following topics were presented : hydrogenation of unsaturated aldehydes [la], of sugars [lb] : alcaloid modifiers to introduce chirality on a Pt catalyst [lc] ; regioselective hydrodechlorination of polychloroaromatics [Id] : Pb alloying to modify Pd [le] or Ni [If] hydrogenation catalysts. Concerning activity, most studies focus on intrinsic (chemical) kinetics, with little consideration to the apparatus and its possible physical limitations. In fact,the design and selection of a catalytic hydrogenation reactor (hydrogenator) is not a trivial problem at all, owing to the broad range of process conditions encountered.

2

The presence of liquid phase introduces engineering complications : the interactions between transport phenomena, both for mass and energy, and intrinsic kinetics play a vital role in determining reactor performances, both for activity and selectivity, catalyst stability, etc...

-

/ BOLID BYBTEMB Although other methods, such as stoechiometric iron reduction [2], are still practised, gaseous dihydrogen is widely used, as documented in the reference books by Augustine [ 3 ] , Freifelder and Cerveny [6]. Recent patents and articles [ 4 1 Rylander [ 5 ] will be quoted throughout this article, more by way of illustrative examples than for the sake of exhaustivity. 1-1 Polyphasic systems in catalytic hydroqenations 1

TRIPHABIC GAB / LIQUID

Hydrogen

I

substrate

!catalyst

I

field :

It is worthwhile mentioning that : - triphasic also means G / L / L , for instance in homogeneous catalysis where H2 is contacted with two immiscible liquids [ 7 ] ) - G / L / S processes exist where S is a reagent or a G / L contact promotor. Here we will discuss G / L / S reactors with S solid catalysts (almost always a supported or massive metal). 1-2 A liquid medium in conjunction with G reactant and S catalyst : Two major reasons can be put forward for the presence of a liquid. First, a high temperature may not be suitable : to prevent damages to thermosensitive fine molecules or catalysts : to improve hydrogenation selectivity. Low volatility and/or high concentration of the organic sustrate, under reaction conditions, then lead to the appearance of a liquid phase Example [ E l : hydrogenation a bulky molecule of like

X

W

0

"

X

Fine chemical hydrogenations are G / S processes : Ar

H2 + A r d o

H2

+

NQ

sometimes still carried out

JoH Cu/Borosilicate N

COOR

zrOz CHO

+

,260.C

Cr203 3 4 0 ' C

[9]

[lo]

in

3

The second reason is that a liquid layer may be desired, either to provide an environment around the catalytic sites avoiding deposits and thus ensuring higher effectiveness, even chemically modifying the site, or to improve temperature control (no "hot spots11because liquids have a much higher conductivity and heat capacity than gases). Furthermore, a liquid layer can also help to control the reactivity scheme, for instance by inhibiting or promoting secondary reactions inside the L phase. Among the considerable number of cases, here are some intentional additions of L component : for acido-basic properties : acidity for hydrodehalogenations [Id], pyridine-ring protection [llJ, p-aminophenol from nitrobenzene [12], basicity for triazoles [13] for dielectric properties : hydrogenolysis (of C - 0 , C-X bonds) increases vs hydrogenation (of double bonds) with higher z [14] for site modification : control of hydrogenolysis by sulfides [15], formamidine acetate [16] ; partial reduction of nitro to hydroxylamines in presence of sulfoxide [17], of alkynes with quinoline promotor [18] ; enantioselective a-ketoesters hydrogenation with alkaloid modified catalysts [lc] water, even in small quantities, sometimes promotes (dinitriles hydrogenation on Raney cobalt [19]), sometimes poisons (acetophenone hydrogenation on Raney nickel [20]). Dilution with a solvent causes however a lower productivity and, at times, downstream purification problems : solventless I1neat1l processes are occasionally claimed [21]. Besides these positive effects, a major disadvantage is introduced : a liquid barrier to direct access of gaseous Ha to the catalyst particle ! The rheological properties of the fluid are also deeply modified, because the viscosity of liquids is many orders of magnitude higher than for gases. Finally, properties such as solubility, molecular diffusivity, etc.. of H2 in organic mixtures, difficult to measure and even to estimate, have a vital influence on the mass transport phenomena, which can be schematized as follows :

'

-

Energy transfer limitations can also appear, as all tions are fairly to highly exothermic,

hydrogena-

4

-

G / L /S HYDROGENATION REACTOR8 To understand and ultimately to forecast the performance of a reactor, it is essential to study the coupling of lltruell(intrinsic) kinetics with mass and energy transport, and to determine the flow regimes of the three phases (hydrodynamics). Modelling a reactor involves :

2

r

Nature of p W s conversion Ploducldislribulicn

Hydrodynamics : solid +

llua phases circulation

2-1 Classification of G/L/S hydroqenators The fundamental discrimination lies in the flow of solid phase : - moving catalyst (fine particles) : stirred @Is1urryg1 tank reactor STR jet-loop llVenturill reactor JLR bubbling column reactor BCR fluidized slurry reactor FSR - fixed bed (large pellets) : submerged fixed bed reactor FBR trickle-bed reactor TBR A second consideration is the operating mode : continuous, batch, or semi-continuous. An extensive textbook on theory, design and scale-up of multiphase reactors was published by Gianetto and Silveston in 1986 [ 2 2 ] , supplementing "Three-phase catalytic reactors1' (1983, by Ramachandran and Chaudhari [ 2 3 ] ) . General books on reactor engineering 1 2 4 1 give few details on G/L/S systems. 2 - 2 Characteristics of G/L/S hydroqenators : 2.2.1 stirred slurry tank reactor BTR This llworkhorsell for industry is extensively used for batch hydrogenations (1 to 100+ m3, up to 100 bar). Very fine (1 to 2 0 0 pm) solide particles are suspended in L, almost perfectly mixed by a mechanical agitator. STR .. can accommodate different agitators : the 6-bladed Rushton turbine is very popular [ 2 5 ] . Recent developments focus on hollowshaft turbines.

. . .

.

.

.

:.

.

,

5

Heat removal is accomplished by internal cooling coils or wall jacket exchangers. Hydrodynamic regimes are complex, because of complicated flow patterns, prone to quick and dramatic changes. Usually a few overall parameters are considered, such as : gas residence time and holdup, solid suspension, energy input, volumetric mass transfer coefficient (sec 5 3.2.3). 2.2.2.

Jet-loop (venturi) reactor JLR

Using the same slurry, JLRs tend to replace S T R s in the most recent fine chemical hydrogenations [26]. The L/S slurry is circulated back at high flow in a loop connected to a Venturi. The local underpressure in the neck causes gas to be sucked in : the intense turbulence achieves a very large interfacial area between tiny bubbles and the slurry. An external heat exchanger on the loop enables an almost unlimited heat removal, convenient for extremely high exothermic reactions, and isothermal operations. On the other hand, JLRs are restricted to a batch mode and can only accommodate catalysts compatible with the pump (low hard ness, low attrition). 2.2.3.

Bubbling column reactor BCR c

Also called "gas sparged reactor", it is little used in hydrogenations. Gas is fed, with partial recycling to increase turbulence, at the bottom of a virtually stationary L phase. Mixing is by far less efficient than in S T R or JLR. BCR is preferred only when the overall reaction is slow ; it is an alternative for TBR ( 5 2.2.6) with better temperature control as a result of higher liquid holdup.

C

2.2.4

Fluidized slurry reactor FBR

L

a

It only operates in continuous mode and uses catalyst particles of a slightly larger size than in BCR : an upward flow of L maintains S in suspension, but the L velocity should be slower than the S settling velocity. Stability also requires a very narrow particle size distribution. Hydrodynamics and mass transfer depend on G/L flow ratio. G velocity is usually rather slow, with bubbles rising through a continuous L phase. Heat removal is restricted to use of wall exchangers.

6

Submerged fixed bed reactor FBR S is immobile : fixed bed reactors always operate in continuous mode, which is not quite suitable for small fine chemicals pro0x0; 0 duction. 280 -80" In F B R s , particles are significantly larger than in slurry (1 to 10 mm) and packed in a fixed bed. A slowly moving L wholly wets the catalyst bed, giving excellent temperature stability and a close to perfect piston flow, whereas small gas bubbles ascend through the bed. The low gas flow makes F B R s not quite adapted for hydrogenation St.*"."t Liquid 2.2.6 Trickle-bed reactor TBR ton. flov TBR is in fact a version of FBR without submersion, but with a downward flow of L through the bed, in most cases co-currently to G. dry ,pot Quite different is the wetting of particles : here G is the continuous phase and the 5 to 5 0 mm particles may not be completely wetted by the downstream rivulets, and thus may develop "dry spotsp8. Stagnant pockets fill the interstices. Other operating difficulties are : wall-bypassing and, above all, stiff temperature control related to intricate hydrodynamic behavior. On the other hand, intense fluid phases interaction is achieved, (at the cost of increased energy consumption) and TBRs are more and more used in fine chemicals, for hydrogenations at higher pressures than in STRs. 2.2.5

B

:3

,

2-3 Which technology in industrial hydroqenation ? [ 2 7 1 FBR : commonly applied in petrochemicals and bioprocesses, it only has few applications in hydrogenations : phenylacetylene,

dinitriles. TBR : widely used for all sorts of hydrotreatments in petro and

chemicals. commodity chemicals, it is now adopted in fin= Intermediates hydrogenation includes : quinones, sugars, lactones, functional aromatics, etc... Despite continuous operation, small size TBR can be adapted to batch-wise synthesis by multiple recycling of L product. Example : trifluoracetic acid hydrogenation [ 2 8 ] . STR and JLR : batch hydrogenators are generally used : a technological comparison is given in J 2 . 6 below.

7

The difficulty of making the right choice is illustrated by the following table : continuous high pressure hydrogenation of adiponitrile in ammonia (obviously not fine chemistry) gives a meaningful example : company

raactor

BASP

trickle-bad

Philips Du Pont

slurry-loop reactor co-current upflow FBI?

ICI

fixed bed

VickersZimmr

downward cocurrent tube-bundla reactor

tamperature control by cooling and partial recycling of L serial arrangement of beds vith intermediate L cooling by cooling oe racyclad offgases evaporative cooling by inert diluant

2-4 Slurry or fixed bed ? advantages and disadvantages Glucose hydrogenation to sorbitol, ester hydrogenolysis to alcohols are good examples to depict the dilemma : formerly performed in a slurry technology (Raney nickel or copper chromite powders), they are now processed in TBRs, with new supported precious metal catalysts. Advantages are said to be : - no loss of metal, better quality of product (no contamination) - reduced side-reactions in L layer, due to smaller L holdup. The big drawback is the risk of a glpathologicalll loss of temperature control, related to the appearance of "hot spotsf1. Other examples of this : - in cyclohexene hydrogenation, benzene is coproduced [29] - due to decarboxylation risk of cyclohexane carboxylic acid, STR cascade is preferred to FBR in (old) benzoic acid + H2 process. The following table gives a selection of advantages and drawbacks [30] : techno

slurry phase

advantages

disadvantages

. continuous or batch mod, . mechanical stirring : E . T stability, easy heat expenditure, maintenance removal catalyst crushing . handling of viscous . high L hold-up, side liquids reactions . good L/S wetting. good . operation at outlet concatalyst life centration poor productl . good G/L L/S mass Vity (CSTR) transfer . difficult catalyst sepa. possible removal of ration expensive Filtracatalyst

. plug-Flow operation close to : high proFixed bed

. . .

..

ductivity low catalyst loss, precious metals low maintenance cost higher P and T, larger volumes low liquid holdup lower investment

tion product pollution by fines

. no viscous liquids . poor catalyst effectiveness (size) . risks of pressure drop . performances depend dramatically on hydrodynamics (narrow range) strength of catalyst + especially eor TBR difficult heat removal, difficult T control incomplete catalyst wetting

. mechanical . .

8

2-5 Consequences of technological choices on catalyst design Blurry phase (BTR, JLR, BCR, FBR)

2.5.1 A

good powder catalyst has the following properties :

- high resistance to attrition, to avoid the generation of fines - suspension characteristics (size, shape, density, material base. .)

- filterability (narrow and mono-dispersity, agglomeration,...) which is conflicting with suspension ! Especially important in JLR is a low hardness to preserve the fragile recirculation pump : a carbon support is favored. It should also be recalled that even in a L environment, the nature of the support can exert a chemical influence ; examples from patents : Na-exchanged silica + alumina is preferred to carbon for hydrogenation of trimethylquinone 1311 ZnO is preferred to alumina in long chain aldehydes hydrogenation 1321 2 . 5 . 2 Fixed bed (FBR, TBR) catalyst pellet requirements are : high mechanical strength, compatible with packing homogeneity in shape (spheres, cylinders, extrudates,...) control of metal impregnation Alumina under &form is the most common support. For hydrogenation in fine chemistry, in small scale TBRs, granular carbon increasingly raises interest on account of better heat conductivity, better wetting and also easy metal recovery in ashes after catalyst burning. 2 - 6 Batch hydrogenators For the reasons explained in the 2 previous paragraphs, most applications in fine chemicals are run in batch mode, where STR, JLR and BCR may be chosen [ 3 3 ] : the performances of these batch hydrogenators, as shown below in 5 3 , hinge on G/L mass transfer capability, and above all, on interfacial area a : m2 of bubbles area per m3 slurry :

. .

. . .

reactor

movement of bubbles

Venturi neck to reaction zone

2000 to 3000

For exothermal reactions like hydrogenations, usually the second limiting parameter :

heat transfer

~~

reactor BCR STR

JLR

cooling system

wall jacket and cooling coil, poor mixing same, with Intense m ixin g tube and shell exchanger on external loop

h (WU-~K-~)

=

500

900 > 1300

is

9

2-7 Laboratory G/L/S hydrogenators Hereafter is a random selection of lab hydrogenators : type hydroqenation of

STR BCR

FSR FBR TBR

STR

3 As

-

nitrobenzene cottonseed oil a-methylstyrene acetone 1-heptene styrene, phenylacetylene cyclohexene a-methylstyrene crotonal

pressure ranqe 2

to 21 bar 5 bar 1 bar c 1 bar 2 bar

1 to 1 1 to 1

5 bar bar 15bar bar

catalyst (size, conc.) a 1 2 to 7 dp-SSyn, dp = 10 dp 100

dp dp

--

gl-1 8 w/w 0 . 4 to 3 q1-1 to 65 pm to 200 pn

dp * 3 . 5 10111 0 , s to 4 mP 0,4 to 2 om dp-5nm

ref (341

(351 (361

137) (381 (391 1401 ~ 4 1 1 (421

DESIGN AND MODELLING OF Q/L/B HYDROGENATION REACTORS

mentioned in the introduction, the liquid medium negatively acts on the transport of H2. 1

L

The overall process cdnsists of the following successive steps : 1 - mass transfer from the bulk bubble to the interface 2 - mass transfer from interface to the bulk liquid phase 3 - mixing and diffusion in the bulk liquid 4 - mass transfer to the external surface of particle 5 - mass transfer inside the particle porosity 6-7-8 - catalysis (adsorption, reaction, desorption) Obviously the L substrate and product(s) follow similar processes (3 to 8 ) . Reactor design requires extensive knowledge of 3 aspects, wh i.ch are raised in this chapter : chemical kinetics

...................

(E and m transfer)

'4 reactor

hydrodynamics 1

-

1

a pratical illustration, experiments performed in our lab (UMR CNRS-Rh6ne Poulenc) will be pointed out as an approach to global modelling of industrial G/L/S hydrogenators.

As 45

10

3-1 Hydrodynamics By hydrodynamics, we mean the movements of L and G phases through the S packing or with the S particles inside the reactor ; it - firstly the flow regime deals with : - then for STR : interfacial area, gas holdup, pumping flow of stirrer, power input, etc.. for TBR : pressure drop, solid wetting, liquid holdup etc. Physical properties ( L density, viscosity, tension,. . . ) strongly affect hydrodynamics,which in turn affect mass and heat transfer. For the flow regime, the most useful notion is "residence time distributiong1(R.T.D). A small STR is perfectly mixed and a lab TBR is perfectly piston plug-flow, but for larger equipments, inadequate baffling or stirring, the presence of coils, wall bypassing, axial and radial dispersions, etc.. make the real reactor far from ideal ! An assembly of ideal plug-flow reactors and continuous stirred reactors in series and parallel can be derived by a "simulation" procedure (see e.g. [ 4 5 ] ) to give the same R.T.D as the actual reactor. In our lab, R.T.Ds are experimentally determined for the 3 phases by pulse injections of radioactive tracers in the real medium : gaseous Ar or Kr : liquid organometallic complexes, or halides : solid neutron-irradiated metal catalysts. 3-2 Mass-transfer The organic sustrate is normally at much higher molar concentration than H2 dissolved in L. Therefore, the first limitation can be predicted to be on &, especially at low pressure : it is called the "limiting reactant". 3.2.1 Overall model Concentration profile, for limiting HZ :

C ( i s constant

due

to excellent

mixing in liquid

:

By definition of steady rates : r = kla (ci -c1) = to bulk L transfer

G

mass : rng

state, all ksas (cl

steps take

- c,)

L to S surface

transfer

=

place at

equal

msq k* OH eL overall grain reaction

11

The physical significance of the parameters will be briefly discussed later. kl, ks : mass transfer coefficients a, as : interfacial areas q : efficiency factor (see : 5 3.2.6)k* : rate constant 0 : coverage of active surface, with hypothesis of Langmuir Hinshelwood. It is essential here to focus not only on the rate, but on understanding that the H2 local concentration at the catalytic site, where selectivity is also settled, totally depends on preliminary transport phenomena. A striking example is [ 4 6 ] :

H2+cH30a - cH'0aN c1

c1

NO2

it is better not to have any H2 transfer limitations, because the site depletion in H2 would cause more C-0 and C-C1 hydrogenolysis, lower activity and more Pt detachment from carbon support. The overall model, too complex, can be converted in the case of limited Ha pressure, where Langmuir-Hinshelwood kinetics simplify to 1st order [ 4 7 ] (more complicated mathematical treatments can nevertheless be made, as shown by Aris [ 4 8 ] ) . Ci 1 1 1 1 - =

r r e s i stames :

- + kla

(-

ms

gas absorption

kSaS

+ -

1 '1 k*

external and i n t e r m l catalyst

Knowing r, the overall (slurry phase) hydrogenation rate for various catalyst loading, the plot of 1 vs 1 , if linear, allows r mg to calculate kla, the volumetric G/L mass transfer coef. We used this method in our lab for Raney metals catalyzed hydrogenation of ____................. cyano functions, but with rather I l/m, large imprecision. 3.2.2. G/L mass tranefer The vital and sometimes overlooked factor is the equilibrium solubility of H2 in L : Ci = P/& (Henry's law). The Henry constant is a function of temperature and the nature of the liquid. Values can be found, or estimated by "solubility parameters of Hildebrand" found in classical engineering handbooks [ 4 9 ] . P d,

ci'rPpl CI

12

On mixtures, except for one review [50], little information is available and measures are required : both indirect (physical absorption) and direct (chromatographic) methods are possible. In UMR45, by high pressure adjustment of a chromatographic method, we proved that water in organic media, even in trace amount, has a dramatic negative influence on H2 solubility. H2 is generally poorly soluble ; among the best solvents are : apolar (low E , [14]), volatile, low cohesion energy density. Unlike for other gases, HI for hydrogen decreases with T. The G/L resistance is "film" : r = kla . (Ci-Cl)

located only

on the

liquid side, in

kl : ms-1

a: m-1

c: mol. m-3

a

represents film thickness and properties : mass transfer coefficient. Different physical models corroborate experimental findings : kl cc D1 1/2. D1 molecular diffusivity (from first Fick law) is a function of L viscosity and temperature. Adapting the Stockes-Einstein law to real media led to WilkeChang correlation [51], among others : 1 D1 p . - = f (physical L parameters) T Direct D1 measuring remains more accurate, but expensive : we used Taylor's method [52] (pulse injections in capillary column). The rheological properties of L exert a huge influence on kl and hence must be apprehended in the model. A s a striking example, we discovered that adding a catalyst promotor made the L behavior change from ideal (Newtonian) to pseudo-plastic : viscosity p , very high at the beginning of the stirring, only goes down with increasing shear.

.

@ interfacial area (m2 par m3) gives a picture of how bubbles are spread. Extensive litterature is available on methods to measure kl, a and kla : see e.g. [53]. The physical absorption / desorption method was developped in UMR45 for H2 in organic L + catalyst S medium (see I 3.2.4. below). Typical values in G/L contactors are : cyclones

Vanturi

STR

2 0 to 50

100 t o 2500

100 t o 2000

[541 FBR 50 t o 1 7 0 0

(a in m - 1 )

13

The volumetric mass transfer coefficient can be correlated with EL the energy dissipation. A wealth of scattered data for G/L/S hydrogenation reackla’s’l [ I tors [ 551 , are summarized in the following graph. EL reaches a few kW.m-3 on plant, but 10 times that level 10-1 in lab reactors. kla is sometimes correlated 1 0 -2 , for with ( E L D L ) ~ / ~ especially - 1 ( 0 . 3 1 .-

3.2.3

10.1

100

101

Scaling-up G/L mass transfer

STRs are frequently used, and often limited by G/L transfer.

Extrapolation raises serious questions : which is the best scaling-up criterion ? rotation of stirrer N ? diameter D of the turbine ? a function N a D P ? Typical design (even for lab hydrogenators) of a 6-bladed Rushton turbine 4-baffle equipped STR : optimal geometry is : 0.3 < D/T < 0.5 H/T = 1 T/B = 10 H/S = 3 H/P = 6 The power input of such agitation is : P* = ct. N3D5 EL being P*/Volume, and kla being best n correlated to ( E l ) 1 / 2 , it is concluded that a I1good1lextrapolation criterion is constant N3/2D.

.

-

4

0

.

:

3.2.1 Influence of suspended 8 on kla : There is strong experimental evidence, but no agreement on effects [56] that S loading (and size, shape, density ...) affects G/L transfer in slurry. For these uppermost important effects, two lltheoriesll have been put forward : for decrease of kia : a decrease of kl through increased film viscosity or a reduction of area (surface phenomena, coalescence, turbulence dampening, bubble surface rigidity) for increase in kla : by collision effects, by stretching otherwise spherical bubbles by llshuttlegl effect, where adsorbing S (with dp < film) penetrates the film, loads transferring H 2 , returns to bulk L , then desorbs H2, thus enhancing the transfer process.

14

We recorded dramatic, reverse and still unforeseable effects ; the tendency of S to act either as an isolated particle or to agglomerate seems to be a key factor. This is connected to recent work on the adhesion of S to G bubbles [ 5 7 ] ; it is shown that i 20 pm Pd/C considerably enhances G/L transfer, since Pd/A1203 is inert. 3.2.5

L/B

mass transfer r = ksas . (C1

-

Cs)

L/S interfacial area can be calculated from loading, particle size and geometry H

m

A

L

a

turbulent liquid lamina film

Solid

can (seldom) be measured, but dimensionless group correlations are available

As conventional Re # cannot be computed, a concept of local tropic turbulence is introduced :

Rei #

iso-

T : energy dissipation dp : particle size y : L viscosity Practically, in STRs with dp < 5 0 pm, L/S transfer is almost never limiting even with viscous liquids. In TBRs, as k, is down to 10-5 ms-1, it may become limiting ; but in general, when limitation appears at the S level, the intragranular phenomenon prevails.

= T

dp4 Y-3

3.2.6 Intragranular mass transfer The approach is similar to G / S hydrogenation, but here the pores are filled with a stagnant liquid. H2 molecules move by a pure diffusional process : no Knudsen diffusion. Modelling remains basically the same as in G/S, with notorious differences : - D1 around 10-9 m2s-1, some 104 times less than in G phase ; - H2 concentration in L lower than the equivalent pressure G ; - 102 times better thermal conductivity in L : with the exception of ##dryspotsi8in TBR, beds and particles in G/L/S/ reactors can reasonably be assumed to be isothermal. The procedure for checking intraqranular diffusion is : - record apparent rate r, measure (or estimate) C1 and Deff, the effective diffusivity (see next 5 3.2.7) - record S characteristics : diameter dp, specific area Sp, density Pp

15

- suppose 1st order kinetics (other mathematical treatments are available), compute : 4 = (dp2.sP*pp.r)/ (Deff-C1) Thiele modulus and the effectiveness factor +I (--> l/+ when +anh

+

-->

m)

- the "truell (non diffusion disturbed) rate is r*

= r/,, : use with care for q < 0.7 due to errors on Deff. r.c dp2 ! It is The pratical usefulness is straightfoward : experimentally found that : - for dp < 100 pm, intragranular transport is very rarely 1imiting - for dp > 5 mm, intragranular transport always limits, which is the reason for the "egg shell8*design of catalyst for TBR Carberry et a1 [58] found for a-methylstyrene hydkogenation on = 0.007 with 8.25 mm Pd/A1203: q = 1 with 30 pm slurry (STR), pellet (TBR) Recall that kinetics are tgfalsifiedol in diffusion regime [59]. 3.2.7 Effective diffusivity in catalyst pores Deff can be measured, either directly by the flux through a catalyst pellet (Wicke-Kallenbach diffusion cell [60]), or by transient pulse method [61]. It is easier, but less accurate, to relate Deff to molecular diffusivity. E : porosity (fraction of S consisting of void) Deff = E / r ( 7 : tortuosity (can be viewed as the angle any pore makes with a straight line Usual values are : 0.25 < E < 0 . 5 ) ) => Deff g D1/10

+

.

3 < r < 3

)

In fine chemistry hydrogenation, the diffusional limitation

can

result not from H2 but from bulky (slowly diffusing) organic substrate ! Two examples [62] : linoleate (18 carbon chain) + H2 : preferably on a Itegg shellg1 Pd on granular carbon . 12 to 22 C nitriles t H2 : on a high porosity, large pores (low tortuosity) Ni -+ MgO + Si02 catalyst. The consequence of low diffusivity can be detrimental in the (common) case of consecutive hydrogenation : A --> B --> C : if the movement of desired B out of the porosity is slow, C by-product will increase, with a rapid selectivity drop in B. "Egg shelltt,uniform and "egg yolko8Ni/AlzOj catalysts [63] behave very differently for alkyne --> alkene (--> alkane) hydrogenations

.

16 3 . 3 Kinetics of G/L/S hydroqenations Transition from G/S to G/L/S cannot be done in a formal way, a detailed and comprehensive analysis is necessary [64]. Gathering reliable data, designing kinetic experiments taking into account side-reactions occurring homogeneously in the L medium, demands strenuous work. Then, if one wants to investigate liquid-phase effects and their kinetic complications, analysis of the results is laborious : even the mathematical data treatment is often difficult, because most experimental data is collected in closed systems (integral). Open (differential) reactors would be more adapted although costly and arduous to operate cleanly. Also, this time-consuming process to establish intrinsic kinetics is rarely realistic for a small company involved in fine chemicals [65]. It appears that Langmuir-Hinshelwood models frequently fit the data from serious studies, i.e with variety range of operating conditions ( P I TI concentrations) [64]. Dissociative adsorption of hydrogen is common, but in many instances on a different site than that which adsorbs the organic substrate

[661.

In our own lab experiments with various cyano compounds and nickel catalysts, we concluded on a l-site L.H type catalysis [67] but we had to introduce corrective parameters for substrate interactions, indicating failure of the basic assumption of surface ideality, i.e equal adsorption energy whichever coverage is reached. 3 . 4 Mass transfer eliminatin in laboratory hydroqenation To know how transport phenomena intervene, the criterion is to compare the observed rate to the maximum possible rates for G/L, L/S, S/pore mass transfer, as shown in 5 3.2. This procedure requires knowledge of a large set of values : diffusivity, Henry constant, kla etc.. The detection of intragranular diffusion is the most difficult path : - the Koros-Novak test [68] proposes dilution of the catalyst particles with inert material : it is however unable to discriminate an extragranular L/S transfer limitation - the Madon-Boudart test [ 6 9 ] works with constant size but different metal loading ("dispersion") on the support : it requires preparations of reproducible catalysts. - lately, methods based on increased poisoning of one single catalytic material have been proposed [ 7 0 ] . mfunnhr

I--\-

In our group, for slurry-phase hydrogenations, we use the wing diagram to check experimental regimes [71] :

-

follo-

17

.. . .. .. . . - ,

inIragranular

US lransler or US intragranular

-

l/dp

CONCLUSION

The use of solid catalysts, mostly supported and massive metals, for liquid phase hydrogenation of functional, complicated, expensive, fragile fine chemicals, has already led organic synthetic chemists t o cooperate w i t h catalysis experts, in order to design highly specific materials and reaction conditions, and tune-up the catalytic site activity and selectivity in the light of coordination chemistry concepts. The engineering complexity of triphasic gas-liquid-solid media makes the catalytic hydrogenation reactors troublesome to model and scale-up. The goal of this paper is to convince that a reactor engineering specialist must be involved in a "tri-expertll cooperation.

18

REFERENCES

6

M-Guisnet, J.Barrault, C.Bouchoule, D.Duprez, C. Montassier and G.PBrot (Eds.), Heterogeneous Catalysis and Fine Chemicals, Elsevier, Amsterdam, 1988 a) p.123 and 171 b) p.165 and 189 c) p.153 d) p.19 e) p.197 f) p. 145 Eastman Kodak, EP 347136 (14.6.88) RL.Augustine, Catalytic hydrogenation, Marcel Dekker, New York, 1985 M.Freifelder, Practical catalytic hydrogenation, Wiley, New York, 1971 PN.Rylander, Catalytic hydrogenation in organic syntheses, Academic Press, New york, 1979 : PN.Rylander, Hydrogenation methods. Academic Press, London. 1985 L.Cerveny (Ed.) , Catalytic hydrogenation, Elsevier, Amsterdam,

7 8

RhBne Poulenc EP320339(1.12.87); Henkel DE 3841698(10.12.88) R.Jacquot(Rh6ne Poulenc), communication at GECAT, Belgodere,

9 10 11 12 13 14

BASF, EP 325141(16.1.88) Mitsubishi Kasei, EP 343640(25.5.88) F.W.Vierhapper and E.L.Elie1, J.Org.Chem40(1975)2729 Technical Research Institute, US 4885289(8.6.87) Ciba Geigy, EP 363318(28.9.88) PN.Rylander, Chemical Catalyst News, Engelhardt Corp., October 89 and ref. herein Bayer, EP 355351(20.7.88) and DE 3824625(20.7.88) Ciba Geigy, EP 325892(31.12.87) M.Von Pierre, Helv. Chim. Acta 72(1989)1554 J.G.Ulan and W.F. Maier, J.Mol.Cat. 54(1989)243 Du Pont, US 4885391(14.1.88) Hoechst Celanese, EP 358420(7.9.88) Hoechst Celanese, EP 353898(19.7.88) A.Gianetto and P.Silveston (Eds.),Multiphase chemical reactors, Hemisphere, Washington, 1986 P.A.Ramachandran and R.V.Chaudhari, Three phase catalytic reactors, Gordon and Breach, New york, 1983 CG.Hi11 Jr, An introduction to chemical engineering kinetics and reactor design, Wiley, New york, 1977 : GF.Froment and KB. Bischoff, Chemical reactor analysis and design, Wiley, New york, 1979 : O.Levenspie1, The chemical reactor omnibook, OSU Book, 1979 : J.Villermaux, Genie de la reaction chimique, Lavoisier, Paris, 1982 : H.I.De Lasa (Ed.), Chemical reactor design and technology, NATO AS1 Serie E 110, Martiniis Nijhoff,

1

2 3 4 5

1986 1990.

15 16 17 18 19 20 21 22 23 24

1986. 25 26 27 28 29 30 31 32 33 34 35

JH.Rushton, Chem.Eng.Progr. 46 (1950), 395 RJ.Malone (Herzog-Hart Corp), CEP june 1980, 53 A.Gianetto and P.L.Silveston, chapter 16 in ref. 22 Rh6ne Poulenc, EP 365403(21.10.88) V.Stanek and J.Hanika,Eth Congress CHISA,Prag, September 84 J.Hanika and V.Stanek, chapter 16 in ref. 6 Mitsubishi, EP 264823(1986) Eastman Kodak, US 4837368(6.6.89) J.J.Concordia (Herzog-Hart Corp), CEP, march 90, 50 F.Turek and R.Geike, Chem.Technik 33 (1981) 24 J.Marangozis, 0B.Keramidas and G.Paparisvas, IEC PRD 16 (1977)

36 37 38

T.K.Sherwood and E.J.Farkas, Chem.Eng.Sci 21(1966)573 N.O.Lemcoff and G.J.Jameson, AIChE J. 21(1975)730 A.N.Gareman, A.Emakova, V.P.Bachvalova and N.I. Rassadnikova, Hung.J.Ind.Chem. 3(1975)37 S.Mochizuki and T.Matsui, AIChE J. 22(1976)904

361

39

19

40 J.Hanika,K.Sporta,Z.Ulbrichova,J.Novak and V.Ruzicka, Coll. Czech. Chem. Comm. 39(1974),240 41 F.Turek, R.Lange, A.Busch and R.Loewe, Chem.Technik 27 (1975), 149 42 C.N.Kenney and W.Sedriks, Chem.Eng.Sci. 27(1972),2029 43 F.Turek, R.Chakrabarti, R.Lange, R.Geike, W.Flock, Chem.Eng. Sci 38(1983),275 44 JM.Lambert Jr, in D.W.Blackburn (Ed.), Catalysis in organic Reactions, Marcel Dekker, New york, 1990, p. 97 45 JM.Smith, Chemical engineering kinetics, Mac Graw Hill, New York, 1981 46 G.Leuteritz, ACHEMA, Frankfurt a.M., june 1985 47 C.N.Satterfield, Mass transfer in heterogeneous catalysis, MIT Press, Cambridge USA, 1970 48 R.Aris, Mathematical theory of diffusion and reaction in permeable catalysis, Clarendon, Oxford, 1975 49 Perry, Chemical Engineering Handbook, Mac Graw Hill, New York; R.C.Reid,J.M.Prausnitz, B.E.Poling, Properties of gases and liquids, Mac Graw Hil1,New york, 1987 50 H.Battino and H.Clever, Chem.Rev. 60(1966)395 51 C.R. Wilke and P. Chang, AIChE J. 1(1955)264 52 G.Taylor, Proc. Royal SOC. London, GB A 219(1953)186 and 225 (1954)473 53 J.C.Charpentier, chapter 4 in ref. 22 54 A.Laurent and J.C.Charpentier, 1ntern.Chem.Eng. 3(1983) 265 ; 55 H.J.Warnecke and P. Hussmann, Chem.Eng.Comm.78(1989)131 J.Voigt and K.Schueger1, Chem.Eng.Sci. 34(1979)1221 ; LL.Van Dierendonck, G.W.Meindersma and GM.Leuteritz, 6 th Euro Conf. on Mixing, Pavia, may 1988 56 J.C.Lee, S.S.Ali and P.Tasakorn, 4 th Euro Conf. on Mixing, Noordwijkerhout, april 82 : G.E.Joosten, JG. Schilder and J.J.Jansen,Chem.Eng.Sci. 32(1977)563 : E.Alper, T.Wichtendah1 and D.Deckwer, Chem.Eng.Sci.35(1980)217 : S.K.Pa1, MM. Sharma and VA Juvekar, Chem.Eng.Sci.37(1982)327 : E.Sada, H.Kumazawa and I.Hashizume, Chem.Eng.J.26(1983)239 ; E.Alper, Chem.Eng.Comm.36(1985)35 57 0.J.Wimmers and J.M.Fortuin, J.Eng.Sci. 43(1988)313 58 N.D.Sylvester, K.I.Kulkami and J.J.Carberry,Can.J.Chem. Eng. 53 (1975)313 59 A.Wheeler in Advances in Catalysis, vol. 3, Academic Press, New york, 1951 60 E.Wicke and P.Kallenbach, Kolloid 2. 97(1941)135 61 N.Wakao and S.Kaguei, Heat and mass transfer in packed beds, Gordon and Breach, New york 1980 62 W.A.Cordova and P.Harriott, Chem.Eng.Sci.(1975)1201 Unilever, EP 340848(6.5.88) 63 Y.Uemura and Y.Hatate, J.Chem.Eng.Jap. 22(1989)287 64 S.L. Kiperman, chapter 1 in ref. 6 65 H.J.Janssen,AJ.Kruithof,G.J.Steghuis andK.R. Westerterp, Ind. Eng.Chem.Res 29 (1990) 754 66 OM.Kut, F.Yuecelen and G.Gut, J.Chem.Tech.Biotech 39 (1987),107 67 C.Mathieu, E.Dietrich, S.Indey, H.Delmas and J.Jenck, RQcents Progres en Genie des ProcQdBs, Lavoisier, Paris, in press 68 R.M.Koros and E.J.Novak, Chem.Eng.Sci. 22(1967)470 69 R.J. Madon and M. Aoudart, 1nd.Eng.Chem.Fund. 21(1982) 438 70 G.W.Smith,D.J.Ostgard,F.Notheisz,A.Zsigmond,I.Palinko and M.Bartok, in D.W. Blackburn (Ed.) Catalysis in Organic reactions, Dekker, New york, 1990, p. 157 71 J.Breysse, RhBne Poulenc Industrialisation, private communication


M. Guisnet et al. (Editors), Heterogeneous Catalysis and Fine @ 1991 Elsevier Science Publishers B.V., Amsterdam

Chemicals I1

STRUCTURE-REACTIVITY IN THE HYDROGENATION OF ALKENES. COMPARISONS WITH REDUCTIONS BY DIIMIDE AND THE FORMATION OF A Ni(0) COMPLEX

S . SIEGEL

Department of Chemistry and Biochemistry, University of Arkansas, Fayetteville, Arkansas, 72701 (USA)

ABSTRACT The effect of structure on the rates of hydrogenations catalyzed by Pt, Pd, and Ni is compared with the effects upon the rates of reduction by diimide (diazene) (Garbisch) and the association constants with a Ni(0) complex (Tolman). These later reactions serve as models for the effect of structure on certain of the elementary reactions of catalysis by metals. Some of the factors which determine the selectivity of a catalyst are reviewed including the kinetics, the metal, and the importance of isomerization as a competing reaction. INTRODUCTION The rate of hydrogenation of an alkene depends upon the catalyst, the reaction conditions, and the structural environment of the double bond. That substituting alkyl groups for vinyl hydrogens lowers reactivity has been known for many years (refs. 1-3). The individual and competitive rates of hydrogenation (Pt/SiOz) of alkenes which represent a broad range o f structure has been reported by Tellier and Maurel (ref. 3 ) . Other structural effects on reactivity have been recognized but no comparable study embraces structures which include vinyl substituted polar groups as well as unsaturated hydrocarbons. In this paper we shall compare the effect of structure on hydrogenations on Pt, Pd and Ni catalysts with the structural effects on reductions with diimide (diazene) (ref. 6) and the equilibrium constants for the association of substituted ethylenes with a Ni(0) complex (ref. 7). These particular reactions were chosen because of our perception of their relation to the mechanisms of catalytic hydrogenation, and the insightful analysis of the relationship between structure and reactivity provided by the authors of these studies. KINETICS AND MECHANISM ON Pt AND Pd Maurel and Tellier showed that the variation in the structure of alkenes has a much smaller effect on the individual rates than on the competitive rates of hydrogenation on Pt/SiOz (refs. 4 . 5 ) . For a group of 24 compounds, the individual rate constants, kA differ by less than 10 whereas the competi-

21

22 6 tive rates span a range of 10 . Following the procedure of Wauquier and Junger

(ref. 8). they extracted the relative adsorption constants, KA, from the competitive rates of hydrogenation with the aid of the individual rate constants, eqn. (l), where I is the slope of the plot of log[A] vs log[B]. Seven alkyl

substituted ethylenes furnish a linear plot of log

K.4

against the summation of

the Taft polar substituent constants, sigma* (ref. 4 ) . But the polar and steric substituent constants of alkyl groups are intercorrelated and therefore the result does not reveal the relative contributions of these effects (refs. 2,3). The method of Wauquier and Jungers assumes Langmuir-Hinshelwood kinetics in

which the fraction of the surface, which is occupied by an adsorbed reactant, is governed by the Langmuir adsorption isotherm. Hussey et al., however, argue that the relative competitive rates on platinum catalysts are measures of the competitive rates of alkene adsorption (ref. 9). They note the near absence of isomerization in Pt catalyzed hydrogenations and, when Dz is used in place of

Hz, little of the exchanged alkene is formed although the distribution of deuterium in the product alkane indicates a rapid interconversion of the alkyl intermediate and the adsorbed alkene. These interpretations of the kinetics differ in that in one, the rate of desorption of the alkene is assumed to be fast relative to the conversion of adsorbed alkene to the alkyl intermediate, while in the other, desorption is assumed to be relatively slow. The appropriate interpretation is likely to depend upon the structure of the unsaturated compound, the catalyst and the conditions employed, all variables which affect the product controlling step. The mechanisms of hydrogenating cyclohexene on Pt and Pd differ. Madon, O'Connell and Boudart found the kinetics of hydrogenation of cyclohexene on platinum in the liquid phase is zero order in cyclohexene and first order i n Hz; the rate constant is independent of the solvent providing that the concentration of Hz is used in the rate expression (ref. 10). They concluded that the rate is determined by the dissociative adsorption of HZ which reacts rapidly with the alkyl intermediate, presumed to be the main form of adsorbed cyclohexene on the surface. I n contrast, Gonzo and Boudart showed that the rate of the gas-phase or the liquid-phase hydrogenation of cyclohexene on palladium, supported on silica gel or alumina, is zero order in cyclohexene but one half order in hydrogen pressure (ref. 11). Recalling that a large amount of exchanged alkene and some HD is formed when deuterium is used in place of hydrogen (ref. 1 2 ) they showed that the results are consistent with a mechanism in which adsorption of Hz is reversible and the reaction of an

23

adsorbed hydrogen atom with the alkyl intermediate is the rate controlling step. Similar conclusions were drawn by Lee, Inoue and Yasumori from their studies of the kinetics of the gas-phase hydrogenation of cyclohexene on highly dispersed Pd on ZrOz or A1203 (ref. 13). The distribution of deuterium in the products when Hz was replaced with either Dz or mixtures of Hz and Dz furnished supporting evidence for their mechanism. From studies of the Pt/SiOZ and Pd/SiOz catalyzed reactions of various alkenes and alkynes with Hz and Dz in a liquid-phase batch reactor, Kung and Burwell, Jr. concluded that "adsorbed hydrogen was in preequilibrium on neither catalyst and adsorbed olefin was not in preequilibrium on Pt/SiOz and probably not on Pd/SiOz except for trans-di-t-butylethylene", the most sterically hindered olefin in their study (ref. 1 4 ) . Their conclusions do not deny that the elementary reactions which precede the rate or product controlling reaction are reversible; only that they are not in equilibrium. The Langmuir-Hinshelwood treatment of the kinetics of surface catalyzed reactions affords a useful representation of some of the characteristics of catalytic hydrogenation. It is a limiting form of more exact equations which recognize that, even though the elementary steps are reversible, few if any will be at equilibrium (ref. 15). Not surprisingly, alternative assumptions regarding the relative rates of the forward and reverse elementary reactions can lead to approximate equations of the same form. Individual rates usually are determined under conditions in which the rate is zero order in alkene. In the competitive reactions, however, the relative

rates are proportional to the relative concentrations of the competing unsaturated compounds, i.e. first order. Presumably, the mechanisms are unchanged by the competitor, and accordingly, the relative individual rates and the relative competitive rates are determined by the difference in energy of the same transition states but different ground states; in the former the alkene is bound to the catalyst, in the latter it is free. The effect of alkene structure on relative reactivity indicates that a much greater structural change in the alkenic moiety occurs on adsorption than in the change from adsorbed alkene to the transition state of the rate controlling surface reaction. Moreover, where measures indicate appreciable differences in adsorption energy, the more strongly adsorbed compound often exhibits the smaller zero order rate. STRUCTURE-REACTIVITY IN RELATED REACTIONS Some understanding of the effect of structure on the rate of catalytic hydrogenation has been sought through comparisons with structural effects in other types of reactions. The attempt to find linear free energy relationships

24 between recorded substituent constants and either the reaction rates or the apparent relative adsorption constants have had some success (refs. 2,3). We believe, however, that the effect of structure on the association constants of substituted ethylenes with Ni[P(O-o-toly1)3]3 and the reduction of the double bond by diimide are particularly useful models. The first models the effect of structure upon the adsorption of substituted ethylenes on a metal, the second involves the

syll

transfer of hydrogen to the carbon-carbon double bond and

models either the adsorption of the alkene or the transfer of the first hydrogen atom to the adsorbed alkene to form the alkyl intermediate (ref. 16). These hypotheses are supported by recent ab initio quantum mechanical calculations for reductions by diimide (refs. 17,18), and for hydrogenations catalyzed by ClRh(PH3)3

(ref. 19). In both reactions, electron density is trans-

ferred to the alkenyl double bond, the bond is lengthened and the attached groups are bent out of the plane in an eclipsed conformation. Because in both model reactions the rate is proportional to the concentration of the unsaturated compound, neither reaction represents directly the effect of structure upon the individual rates of hydrogenation when zero order in alkene; correlations with the model reactions are seen within groups of structurally related compounds. Complexation with Ni[P(O-o-tolyll& Tolman has shown that the equilibrium constants for the reactions of 38 substituted ethylenes with Ni[P(O-o-tolyl3)]3 in benzene, to form (ENE)bis(tri-o-toly1phosphite)nickel complexes, is sensitive to the ethylene's struc-

ture, eqn. (2) (ref. 7 ) . Values of

NiL3 + ENE

Ki =

(ENE)NiL2

+L

K1

at 25'

where L

=

-4 vary from 10 for cyclohexene to

P(O-o-tolyl)s.

8 4 x 10 for inaleic anhydride. The stability of the complex is enhanced by electron withdrawing substituents, such as cyano and carboxyl, and lowered by alkyl groups. That resonance involving unshared electrons on the oxygen of an alkoxy group overpowers the inductive effect is indicated by the relative values of K1 for ally1 methyl ether, 1-hexene, and vinylbutyl ether which diminish in that order by factors of 3:1:0.006. Log K1 correlates well with the sum of the substituent parameters, sigmap+,as defined by Swain and Lupton (ref. 20). Tolman notes that the high sensitivity of the Ni(0) equilibrium constants to structural modifications of the alkene is due to the low ionization potential of Ni(0)

and the resulting small energy separation between the HOMO

of the metal and the pi* orbital of the alkene. Steric effects of substituents

25 are relatively unimportant compared to electronic effects and resonance is more important than inductive interactions. The ability of the metal to back bond is lowered progressively in the series Ni(0) > Pt(0) > Rh(1) > Pt(I1) > Ag(1) which reduces the importance of resonance and decreases the selectivity of the metal for different substituted alkenes. The relative importance of sigma donation from the occupied pi orbital of the alkene to an empty metal orbital compared to back donation from the metal to the alkene‘s pi* orbital determines the geometry of the alkene moiety which can vary from close to the planer alkene to a structure best described as a rnetallacyclopropane (ref.

21). The later structure might explain why trans- disubstituted ethylenes form more stable complexes than their

cis- isomers (see following section).

Diimide reductions 6

The relative reactivities toward diimide cover a range of -10 , from 1 , 2 dimethylcyclohexene to norbornene (ref. 6). Electron attractive substituents increase the reactivity of the double bond towards diimide although the data to place compounds such as maleic acid or acrylonitrile on the scale for Garbisch’s hydrocarbons is lacking (ref. 21b). Garbisch et al. found that the main factors that contribute to the observed reactivities in diimide reductions of unsaturated hydrocarbons, eqn. ( 3 ) , are torsional strain, bond angle

+ H

‘N_N/

H

,

,

NEN

NEN 3)

strain, and alpha-alkyl substituent effects as indicated by the good agree ent between calculated and observed relative reactivities. In their calculations, they assumed that the transition state occurred early along the reaction coordinate, about one third of the change to the saturated product, and that the pi-bond order is fairly large. Steric effects, between diimide and the alkene, are assumed to be negligible. Resonance or polar interactions between vinyl substituents and the double bond affect the ground state energy which decreases to zero in the product. Using the same structural parameters in the calculations, the agreement with the observed relative reactivities of cycloalkenes for different addition reactions indicates that the model is qualitatively correct (ref. 22). This treatment was applied also to stereo

26

selectivities (refs. 6,16). The effect of polar groups on the diimide reaction is sensitive to the configuration of the attached groups. For example, fumaric acid (trans) is ten times as reactive as maleic acid (&)

and the ratio of reactivities of the

geometrical isomers of cinnamic acid, trans/cis, is 10:3 (ref. 21b). In comparison, &-and trans-2-butene have almost identical reactivities. The difference may be explained by a change in the degree of advancement of the transition state towards the saturated product where the eclipsed conformation would result in a greater non-bonded repulsive interaction between the

a-

substituents than the trans. A correlation of the effect of structure on the Ni(0) association constants

and reductions by diimide is displayed in Fig. 1. Unfortunately, none of the negatively substituted ethylenes in Tolman’s series are included in Garbisch et al.’s study.

Log k (Diimide)

Fig. 1. Correlation of l o g k (Diimide). (a) vs l o g I (Pt/A1203) ( * ) ; (b) vs log KAB ( P t / A l z 0 3 ) (0). ComDarison of catalytic hydrogenation on metals with the model reactions The correlation between the apparent association constants, KA, which are derived from the competitive rates on Pt and reductions by diimide indicates that structural changes in the alkene generally have parallel effects on these reactions, Fig. 2 .

Because the diimide reduction is essentially free of

steric effects, this effect is liable to account for some of the differences which are observed in extended groups of compounds. The small range of individual reactivities on Pt, which are zero order in alkene, can be understood in that the variation in structure which increases the driving force towards

27

Log k (Diimide)

Fig. 2 . Correlation of log k (Diimide) vs l o g K (Ni(0) complex). the addition of hydrogen, also increases the strength of adsorption on the metal. The latter is a function of the metal that apparently diminishes in the order Pt> P&

Ni (refs. 3 , 1 4 , 2 3 ) .

Within a limited group of hydrocarbons, cycloalkenes, the kinetically derived association constants on Pt/Alz03 correlate with both model reactions and the strain in the double bond which suggests that the relief of strain is a principal factor in determining relative reactivity in this series, Table 1. TABLE 1 Structure-Reactivity of cycloalkenes. Comparisons of individual and competitive hydrogenation rates on Pt with related reactions.

Hz,Pt'

Ni(ENE)b

STRAINh

Diimidec

~~

Compound

h

Bicycloheptene Cis-cyclooctene Cyclopentene Cycloheptene Cyclohexene

223 10 121

78 113

KAB

--25. 7.5 6.3 (1.0)

Keq

4.4

6.Z X ~ O - ~ 2.6~10-~ 2.3~10-~

3.5~10-~

a0.52% Pt/Alz03 at 250C, 1 atm, (ref. 3 ) . b(Ref. 5 ) . c(Ref. 4 ) .

H ,Kcal

krel

27.2 7.4

4 . 5x102 17.

6.8 6.7 2.5

12.

15.5 (1.0)

28

Interestingly, the order of the reactivity in the individual rates on Pt, Pd, and Ni exhibit similar patterns except for the placement of cyclohexene and cyclooctene, Table 2 . The relative reactivity of cyclooctene is low because, other than norbornene, it is more strongly attracted to the metal than are the others in the group. TABLE 2 . Effect of structure of cycloalkenes on the individual rates of hydrogenation (relative to cyclopentene) on metal catalysts compared to diimide reductions. Compound Bicycloheptene Bicyclooctene Cyclopentene Cyclohexene Cycloheptene Cyclooctene

Diimidea

Pt/AlzO~b

Pd/SiOzb

29 1.9

1.8

1.9 2.0

1.4

1.4

(1.0)

(1.0)

(1.0)

(1.0) 0.43 0.96 0.13

0.90 0.64 0.08

0.065 0.078

1.1

0.5

___

0.05

NiCc

___

NiBd 3.8

___

(1.0) 0 .O l e

0.6 0.2

'(Ref. 1). b(Ref. 14). c(Ref. 27). d(Ref. 23). RRelative to cyclooctene, the value would be 0.16 from ref. 29 Although alkenes appear to be less tightly bound to Pd than to Pt, the relative individual rates in the two series differ little. The competitive rates on Pd were not determined so a comparison with the kinetically derived relative adsorption constants on Pt is unavailable. The zero order rate of norbornene relative to cyclohexene on 1-5% Pd/A1203 at 30 OC is 3.4 while the relative competitive rate is 4.7 which increases to 7 . 6 in the presence of triphenylphosphine (ref. 24). STRUCTURE AND REACTIVITY ON NICKEL Nickel affords selective catalysts for the hydrogenation of alkenes, dienes, and alkynes. When catalyzed by C. A. Brown's P - 2 nickel, prepared by the reduction of Ni(0Ac)z

with NaBHb in ethanol, the individual rates as well

as the competitive rates appear to be sensitive to the alkene structure as judged by the reported initial rates of hydrogen addition (ref. 23). Alkene isomerization is relatively slow. Except for the most reactive alkenes such as norbornene. the individual hydrogenations seem to be first order in alkene. This indicates that alkenes are more weakly bound to Ni than to Pt or Pd. Similar selectivities are reported by Brunet, Gallois, and Caubere for a catalyst prepared by the reduction of Ni(0Ac)z (ref. 27).

with NaH and t-amyl alcohol in THF

29

The order in which the reactivity of these cycloalkenes fall on these nickel catalysts may be compared with the relative reactivities on Pt, with diimide and with the Ni(0) association constants measured by Tolman, Tables 1 and 2. The place of cyclooctene in these orderings is particularly noteworthy. Recall that cyclooctene is the better competitor in hydrogenations on Pt which is reflected in the relative apparent adsorption constants, Table 1. The two nickel catalysts mentioned above show opposite relative reactivities for these cycloalkenes although the illustrated plots of the progress of the reactions on both catalysts suggest that the rates are approximately first order in alkene. Interestingly, Brown reports that over his P-2 Ni, the selectivity of cyclooctene over cyclohexene is larger in competitive hydrogenations than in individual reductions (ref. 23). An explanation for this difference in selectivity of the Ni catalysts is suggested by the studies of Okamoto et al. who correlated the difference in the X-ray photoelectron spectra of various nickel catalysts with their activity and selectivity in hydrogenations (ref. 28,29). They find that in individual as well as competitive hydrogenations of cyclohexene and cyclooctene on Ni-B, cyclooctene is the more reactive while the reverse situation occurs on nickel prepared by the decomposition of nickel formate (D-Ni). On all the nickel catalysts the kinetically derived relative association constant favors cyclooctene (ref. 29). The boron of Brown’s P-2 nickel donates electrons to the nickel metal relative to the metal in D-Ni. The association of the alkene with the metal is diminished which indicates that, in these hydrocarbons, the electron donation from the HOMO of the alkene to an empty orbital of the metal is more important than the reverse transfer of electron density from an occupied d-orbital of the metal into the alkene’s pi* orbital. APPLICATIONS TO SYNTHESIS There is general recognition that selectivity for the addition of hydrogen to one compound rather than another in a mixture, or to a particular double bond in a compound which has multiple unsaturation, depends upon the catalyst and the conditions. The illustrated structure-reactivity correlations afford an estimate of the degree of selectivity which may be achieved when adsorption is adequately reversible. The later is aided by a weakening of the attraction between the double bond and the metal center of the catalyst. There are circumstances when the opposite selectivities are desired and kinetic control of adsorption may be required. This aspect of selectivity is not addressed here. For example, Tolman found that the Ni(0) association constant of vinyl 6

methyl ketone is 5 x 10 greater than 2-methyl-1-pentene.Accordingly, it is

30

not surprising that Pd catalyzes the highly selective addition of hydrogen to the double bond in eremophilone which is conjugated with the carbonyl group leaving the methylene group untouched, eqn. (4) (ref. 3 2 ) . In contrast, tristriphenylphosphinerhodium(1) chloride, (PhsP)RhCl, catalyzes the

hydrogenation of the methylene group exclusively. This illustrates Tolman’s note that the oxidation state of the metal affects the selectivity of a metal for different alkenes (ref. 7).

0

0

Eremophi lone

The possibility that isomerization may effect the selectivity is important to note. A convenient method o f removing 1,9-octalin from a mixture of the 1 , 9 - and the 9,lO-octalinsis to hydrogenate the mixture over a Pt catalyst.

Pd is ineffective because it is more active than Pt in catalyzing the inter-

conversion of the isomers, eqn. (5) (procedure suggested by Hussey given in ref. 3 0 ) .

11 [HI

031 , g - o c t a l i n

(5)

Double bond migration can be inhibited by amines and other nucleophilic agents and lead to higher selectivities in the reduction of dienes such

as

1,4-cyclooctadieneor 1,3-cyclopentene to their respective monoenes (ref. 33)

31

If alkene isomerization is not possible or degenerate as in cyclohexene, the relative individual rates are not greatly different (Table 1) (ref. 14). The literature indicates that selectivity often can be improved, particularly with Ni and Pd catalysts by the use of promoters such as amines (ref. 34). Presumably, the amine competes for reactive sites with the alkenes and is effective if its adsorption constant lies between the constants of the competing alkenes. The effectiveness of the promoter is not diminished with the depletion of the more reactive alkene and is most useful with a supported catalyst where the concentration of molecules near a reactive site may be limited by pore diffusion. Selectivity would also improve if the promoter increases the rate of desorption of the alkenes (ref. 35). An interesting means of improving the selectivity of Pd for the conversion o f unconjugated dienes, such as 1,4-cyclooctadieneto the monoene is to add

phenylacetaldehyde to the mixture undergoing reaction (ref. 36). The mechanism of action is not established but it may involve aldehyde decarbonylation to form adsorbed CO; but the addition of small amounts of CO to the reactants does not reproduce the effect of the aldehyde (ref. 37). Means to modify the metal suface in other ways can prove effective, the studies of Ni catalysts by Okamoto et al. afford an interesting example of an attempt to reach a more fundamental understanding of catalyst selectivity. SUGGESTIONS FOR FURTHER STUDY Some suggestions are in order for anyone beginning a kinetic study of the effect of structure on reactivity. Aside from the precautions to assure that the rates are free from transport limitations, consideration should be given to the effect of alkene concentration on the individual rates as well as the competitive rates in light of the studies of Boitiaux et al. who found that the more strongly bound unsaturated compounds inhibit reduction at high concentrations, particularly on catalysts with low metal loadings and high dispersions (ref. 25). Furthermore, Kung et al. have shown that the competitive reactivity of sterically hindered hydrocarbons relative to cyclopentene on Pt catalysts is sensitive to the dispersion of the metal (ref. 26). REFERENCES 1 2

3

4 5 6

S. V. Lebedev, G. G. Kobliansky and A. 0. Yakubchik, J. Chem. SOC., 127 (1925) 417. M. Kraus, Adv. Catal., 29 (1980) 151. L. Cerveny and V. Ruzicka, Adv. Catal., 30 (1981) 335. R. Maurel and J. Tellier, Bull. SOC. Chim. France (1968) 4650. R. Maurel and J. Tellier, Bull. SOC. Chim. France (1968) 4191. E. W. Garbisch, Jr., S . M. Schildcrout, D. B. Patterson and C. M. Sprecher, J . Am. Chem. SOC., 87 (1965) 2932.

32

7 8 9

10 11 12 13 14 15

16 17 18 19 20 21 21b 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37

C. A . Tolman, J . Am. Chem. SOC., 96 (1974) 2780. J. P. Wauquier and J . C. Jungers, Bull. SOC. Chim. France, 24 (1957) 1280. A. S. Hussey, R. H. Baker and G. W. Keulks, J. Catal., 10 (1968) 258. R. J. Madon, J . P. O'Connell and M. Boudart, AIChE J., 24 (1078) 904. E. E. Gonzo and M. Boudart, J. Catal., 52 (1978) 462. R. L. Burwell, Jr., Acc. Chem. Res., 2 (1969) 289. B. Y. Lee, Y. Inoue and I. Yasumori, Bull. Chem. SOC. Jpn., 54 (1981) 13. H. H. Kung and R. L. Burwell, Jr., J. Catal., 63 (1980) 11. M. Boudart and G. Djega-Mariadassou,Kinetics of Heterogeneous Catalytic Reactions, Princeton University Press, Princeton, N.J., 1984, Chap. 3. S . Siegel, G. M. Foreman and D. Johnson, J. Org. Chem., 45 (1975) 3589. E. Flood and P. N. Skancke, Chem. Phys. Letters, 54 (1978) 53. D. J. Pasto and D. M. Chipman, J . Am. Chem. SOC., 101 (1979) 2290. N. Koga, C. Daniel, J. Han, X. Y. Fu and K. Morokuma, J. Am. Chem. SOC., 109 (1987) 3455. C. G. Swain and E. C. Lupton, Jr., J. Am. Chem. SOC., 90 (1968) 4328. J. P. Collman, L. S . Hegedus, J . R. Norton and R. G. Finke, Principles and Applications o f Organotransition Metal Chemistry, University Science Books, Mill Valley, California, 1987. S. Hunig, H. R. Miller and W. Thier, Angewandte Chemie, Int. Edn., 4 (1965) 271. E. W. Garbisch, Jr., J . Am. Chem. SOC., 87 (1965) 505. C. A . Brown and V. K. Ahuja, J. Org. Chem., 38 (1973) 2226. J. A . Hawkins, Doctoral Dissertation, University, University of Arkansas, Fayetteville, AR, 1983, pp. 87, 102, 136. J. P. Boitiaux, J. Cosyns and E. Robert, Applied Catal., 32 (1987) 145. H. H. Kung, R. Pellet and R. L. Burwell, Jr., J. Am. Chem. SOC., 98 (1976) 5603-56117 J - J . Brunet, P. Gallois and P. Caubere. J. Org. Chem., 45 (1980) 1937. Y. Okamoto, Y. Nitta, T. Imanaka and S . Teranishi, J . C. S . Faraday I , 75 (1979) 2027. Y. Okamoto, Y. Nitta, T. Imanaka and S . Teranishi, J . Catal., 64 (1980 397. G. V. Smith and R. L. Burwell, Jr., J . Am. Chem. SOC., 84 (1962) 925. A. W. Weitkamp, J . Catal., 6 (1966) 431. M. Brown and L. W. Piszkiewicz, J . Org. Chem., 32 (1967) 2013. H. Hirai, H. Chawanya and N. Toshima, Bull. Chem. SOC. Jpn., 58 (1985) 682. P. N. Rylander, Hydrogenation Methods, Academic Press, Inc. (London) Ltd., 1979. J. P. Boitiaux, J . Cosyns and S . Vasudeuan, Applied Catal., 15 (1985) 317326. S . Nishimura, M. Ishibashi, H. Takamiya, N. Koike and T. Matsunaga, Chem. Lett., (1987) 167. S . Nishimura, personal communication.

M. Guisnet et al. (Editors), Heterogeneous Catalysis and Fine Chemicals II 0 1991 Elsevier Science Publishers B.V., Amsterdam

33

HETEROGENEOUS CATALYTIC OXIDATION AND FINE CHEMICALS R.A.

Sheldon

5900 AB

R&D D e p a r t m e n t , Andeno B.V.,

VENLO (The N e t h e r l a n d s )

ABSTRACT The use o f s o l i d c a t a l y s t s i n l i q u i d p h a s e o x i d a t i o n s o f r e l e v a n c e t o f i n e chemicals manufacture i s reviewed. Heterogeneous c a t a l y s t s o f f e r obvious a d v a n t a g e s : ease o f p r o d u c t a n d c a t a l y s t r e c o v e r y a n d s u i t a b i l i t y f o r continuous processing. Moreover ' s i t e i s o l a t i o n ' o f redox m e t a l i o n s i n o x i d a t i v e l y r e s i s t a n t inorganic matrices a f f o r d s s t a b l e c a t a l y s t s w i t h unique a c t i v i t i e s a n d s e l e c t i v i t i e s . The v a r i o u s t y p e s o f o x i d a t i o n p r o c e s s e s a r e r e v i e w e d on t h e b a s i s o f t y p e o f mechanism, o x i d a n t a n d c a t a l y s t . The l a t t e r i s d i v i d e d i n t o t h r e e categories : supported metals, metal i o n s and o x i d i c ( o x o m e t a l ) c a t a l y s t s . Emphasis i s p l a c e d on s y s t e m s e x h i b i t i n g u n u s u a l substrate, chemo-, regioand s t e r e o s e l e c t i v i t i e s , e s p e c i a l l y on new developments such as redox z e o l i t e s and redox p i l l a r e d c l a y s . INTROOUCTION C a t a l y t i c o x i d a t i o n i s t h e most i m p o r t a n t technology f o r t h e c o n v e r s i o n o f hydrocarbon feedstocks ( o l e f i n s , a r o m a t i c s and alkanes)

t o a variety of bulk

I n g e n e r a l , two t y p e s o f processes a r e used : h e t e r o -

i n d u s t r i a l chemicals.'

geneous, gas p h a s e o x i d a t i o n and homogeneous l i q u i d p h a s e o x i d a t i o n . The f o r m e r tend

to

involve

supported

metal

o r metal

oxide

catalysts

e.g.

in

tne

maflUfaCtUre o f e t h y l e n e o x i d e , a c r y l o n i t r i l e a n d m a l e i c a n h y d r i d e w h i l s t t h e l a t t e r generally

employ d i s s o l v e d m e t a l

salts,

e.g.

i n the production of

t e r e p h t h a l i c a c i d , b e n z o i c a c i d , a c e t i c a c i d , phenol and p r o p y l e n e o x i d e . I n t h e f i n e c h e m i c a l s i n d u s t r y t h e r e i s a l s o c u r r e n t l y much i n t e r e s t i n t h e use o f c a t a l y t i c o x i d a t i o n a s an e n v i r o n m e n t a l l y more a c c e p t a b l e a l t e r n a t i v e f o r o x i d a t i o n s e m p l o y i n g c l a s s i c a l s t o i c h i o m e t r i c o x i d a n t s such a s p e r m a n g a n a t e and d i c h r o m a t e .

Since the m a j o r i t y o f

f i n e c h e m i c a l s a r e complex,

multi-

f u n c t i o n a l molecules h a v i n g h i g h b o i l i n g p o i n t s and l i m i t e d thermal s t a b i l i t y , processing i s l a r g e l y

limited to the

l i q u i d phase.

E i t h e r homogeneous o r

h e t e r o g e n e o u s C a t a l y s t s can b e employed a n d b o t h h a v e t h e i r a d v a n t a g e s and disadvantages : HOMOGENEOUS ADVANTAGES

-

Mild conditions

HETEROGENEOUS

- Easy s e p a r a t i o n o f

- High a c t i v i t y / s e l e c t i v i t y DISADVANTAGES

catalyst & product

- E f f i c i e n t heat t r a n s f e r

-

-

C a t a l y s t recovery

- Heat t r a n s f e r problems

Not r e a d i l y adapted t o

-

continuous processing

Continuous processing Low a c t i v i t y l s e l e c t i v i t y

34

Indeed, t h e i d e a l c a t a l y s t s a r e t h o s e t h a t combine t h e h i g h a c t i v i t y and s e l e c t i v i t y u s u a l l y a s s o c i a t e d w i t h homogeneous c a t a l y s t s w i t h t h e ease o f r e c o v e r y and r e c y c l i n g t h a t i s c h a r a c t e r i s t i c o f s o l i d c a t a l y s t s . F u r t h e r m o r e , heterogeneous c a t a l y s t s a r e g e n e r a l l y s t a b l e towards d e a c t i v a t i o n by o x i d a t i v e d e s t r u c t i o n o f the ligands surrounding the metal i o n and/or the formation o f unreactive

p-0x0

dimers

(oligomers)

that

characterizes

many

homogeneous

o x i d a t i o n c a t a l y s t s ( s e e l a t e r f o r a more d e t a i l e d d i s c u s s i o n ) . Hence, i n t h e Context o f f i n e chemicals m a n u f a c t u r e t h e r e i s c o n s i d e r a b l e i n t e r e s t i n t h e development o f o x i d a t i v e l y s t a b l e , s o l i d c a t a l y s t s t h a t e x h i b i t h i g h a c t i v i t i e s and s e l e c t i v i t i e s i n l i q u i d phase o x i d a t i o n s . TYPES OF

MECHANISM

Both homogeneous and heterogeneous

c a t a l y t i c o x i d a t i o n s can be d i v i d e d

i n t o t h e same t h r e e c a t e g o r i e s based on t h e t y p e o f mechanism i n v o l v e d : ( a ) autoxidation,

(b)

direct

oxidation

of

(coordinated)

substrates

and

(c)

c a t a l y t i c oxygen t r a n s f e r . Autoxidation

In c o n t r a s t t o c a t a l y t i c h y d r o g e n a t i o n , where no r e a c t i o n t a k e s p l a c e i n t h e absence o f a c a t a l y s t ,

c a t a l y t i c o x i d a t i o n s w i t h m o l e c u l a r oxygen a r e

c o m p l i c a t e d by t h e f a c t t h a t oxygen r e a c t s w i t h o r g a n i c s u b s t r a t e s even i n t h e absence o f a c a t a l y s t . T h i s i n v o l v e s t h e s o - c a l l e d f r e e r a d i c a l a u t o x i d a t i o n mechanism w i t h t h e f o l l o w i n g as key s t e p s :

R.

r

0, fast

ac,.

(2)

A m a j o r problem a s s o c i a t e d w i t h such a u t o x i d a t i o n s i s t h a t t h e y a r e l a r g e l y

i n d i s c r i m i n a t e , i.e.

t h e y e x h i b i t p o o r chemo- and r e g i o - s e l e c t i v i t i e s .

They

a r e s y n t h e t i c a l l y u s e f u l o n l y w i t h r e l a t i v e l y s i m p l e s u b s t r a t e s c o n t a i n i n g one r e a c t i v e p o s i t i o n , e.g.

the o x i d a t i o n o f toluene t o benzoic a c i d o r p-xylene

t o t e r e p h t h a l i c a c i d . Any c a t a l y t i c o x i d a t i o n has t o complete w i t h t h i s nonc a t a l y t i c pathway. Moreover, t h e s i t u a t i o n i s f u r t h e r c o m p l i c a t e d b y t h e f a c t that

transition

decomposition

of

metal trace

ions

also catalyze

amounts

of

a u t o x i d a t i o n s by m e d i a t i n g t h e

hydroperoxides

r a d i c a l s , v i a t h e s o - c a l l e d Haber-Weiss mechanism :

into

chain-initiating

35

Metal(i0n) oxidations o f coordinated substrates The key s t e p i n t h i s c a t e g o r y i n v o l v e s t h e o x i d a t i o n o f a c o o r d i n a t e d s u b s t r a t e by a m e t a l i o n or an oxometal s p e c i e s (see l a t e r ) . Examples i n c l u d e t h e p a l l a d i u m ( I 1 ) - c a t a l y z e d o x i d a t i o n of

olefins

(Wacker p r o c e s s ) and t h e

o x i d a t i v e dehydrogenation o f a l c o h o l s , where t h e key s t e p s a r e r e a c t i o n s ( 5 ) and ( 6 ) , r e s p e c t i v e l y . RCH-CHz

+

Pd"X,

+

H,O

___)

RCCCH,

I

2HI

Fin

The o x i d i z e d f o r m o f t h e metal i o n i s subsequently r e g e n e r a t e d by r e a c t i o n o f t h e reduced f o r m w i t h m o l e c u l a r oxygen. A s p e c i a l case o f r e a c t i o n ( 6 ) i s

i n v o l v e d i n t h e o x i d a t i v e dehydrogenation o f a l c o h o l s o v e r supported m e t a l s (see l a t e r ) . C a t a l y t i c oxygen t r a n s f e r 3 T h i s i n v o l v e s t h e r e a c t i o n o f an oxygen donor w i t h an o r g a n i c s u b s t r a t e i n t h e presence o f a metal c a t a l y s t a c c o r d i n g t o t h e g e n e r a l scheme :

s +

x-0--y

X-0-Y

=

*

oxygen donor; S

so =

c

(7)

Tf

substrate; H

=

catalyst

When t h e oxygen donor i s H202 o r ROZH, t h e a c t i v e o x i d a n t i n these processes i s an oxometal o r a peroxometal s p e c i e s formed as shown below : M-O,?.

&

PEROXOMETAL

HX + RG,H

HOR

T

30

36 I n t e r e s t i n g y, the so-called

the f i r s t

examples o f c a t a l y t i c oxygen t r a n s f e r i n v o l v e d

reagent^,^

Milas

formed b y m i x i n g heterogeneous metal

c a t a l y s t s with a s o l u t i o n o f hydrogen p e r o x i d e i n t e r t - b u t a n o l .

oxide

These r e a g e n t s

w e r e u s e d f o r -he v i c i n a l h y d r o x y l a t i o n o f o l e f i n s ( r e a c t i o n 1 0 ) . OH

I I

cdtalyst R'CIH-CHR'

H,O?

t

OH

b

(10)

RICH-CHR-

Many a c i d i c m e t a l o x i d e s s u c h a s Os04, Moog, W03, V205 a n d Cr03 c o n s t i t u t e effective catalysts f o r t h i s reaction.

A l t h o u g h many o f t h e s e o x i d e s , 2.3. t h e a d d i t i o n o f H202 r e s u l t s i n t h e

Moo3, V2O5, a r e i n s o l u b l e i n t e r t - b u t a n o l f o r m a t i o n o f s o l u b l e p e r a c i d s (e.g.

I t was s u b s e q u e n t l y f o u n d t h a t many

HV04).

o f these reactions proceed v i a epoxide intermediates t h a t a r e hydrolyssd t o v i c i n a l d i o l s u n d e r t h e a c i d i c r e a c t i o n c o n d i t i o n s . When c e r t a i n c a t a l y s t s . e.g.

o r Na2Mo04, w e r e u s e d u n d e r b a s i c o r n e u t r a l c o n d t i o n s s e l e c t i v e

Na2W04

e p o x i d a t i o n was ~ b s e r v e d . ~ Thus,

t h e M i l a s r e a g e n t s may b e c o n s i d e r e d t o b e t h e p r o g e n i t o r s o f t h e

metal c a t a l y s t / a l k y l

hydroperoxide reagents5-8 t h a t were l a t e r developed oy,

i n t e r a l i a , Halcon, Arco and S h e l l w o r k e r s and c u l m i n a t e d i n t h e r e a l i z a t i o n o f c o m n e r c i a l p r o c e s s e s f o r t h e e p o x i d a t i o n o f p r o p y l e n e ( r e a c t i o n 11). T n 2 s 2 r e a g e n t s i n v o l v e t h e v e r y same m e t a l c a t a l y s t s , e.g.

Movl,

W"',

V v and

Ti"',

as t h e M i l a s r e a g e n t s and t h e y a r e m e c h a n i s t i c a l l y c l o s e l y r e l a t e d .

CH,CH==CH,

+

c a t a I ys t

RO,H

b

CH,CH-CH,

ROH

A R C 0 P r o c e s s : Homogeneous c a t a l y s t (Mo")

RO,H

=

(CII,),CO,H

(TBHP)

SHELL P r o c e s s : Heterogeneous c a t a l y s t ( T i T V / S i 0 2 ) R02H

=

PhCIf(CH,)O2i1

(E3HP)

B i o c a t a l y t i c oxygen t r a n s f e r The c y t o c h r o r n e P 4 5 0 - c o n t a i n i n g m o n o ~ x y g e n a s e s ~c a t a l y z e t h e o x i d a t i o n o f a w i d e v a r i e t y o f o r g a n i c s u b s t r a t e s v i a t h e g e n e r a l scheme :

S

-

s u b s t r a t e ; DH,

=

hydrogen d o n o r ( N A D H , e t c . )

The p r o s t n e t i c g r o u p o f t h e s e enzymes c o n t a i n s a n i r o n ( I I 1 ) p o r p h y r i n complex a n d t h e a c t i v e o x i d a n t can b e f o r m a l l y r e g a r d e d a s a h i g h - v a l e n t o x o i r o n ( V -

37 p o r p h y r i n species formed as shown i n f i g u r e 1. PFe I : I

peroxide shun t

PFs"

IRO,H

or tlaOC1

!02

p-o:io (inactive)

FIGURE 1. Mechanism of cytochrome P450 catalyzed oxidation. A l t e r n a t i v e l y , t h e a c t i v e o x o i r o n ( V ) s p e c i e s can be g e n e r a t e d d i r e c t l y f r o m r e a c t i o n o f t h e i r o n ( I I 1 ) p o r p h y r i n w i t h an oxygen donor'', NaOCl, e t c . ,

such as H202. ROzH,

o b v i a t i n g t h e need f o r a c o f a c t o r as hydrogen donor.

Although

these model systems, employing i r o n ( 111) o r manganese( I 1 I ) p o r p h y r i n s , o b v i a t e t h e need f o r a r e d u c i n g agent ( c o f a c t o r ) t h e y v i r t u a l l y a l l s u f f e r f r o m t h e same

disadvantage

as

the

in

vivo

system,

i.e.

they

contain

expensive,

o x i d a t i v e l y u n s t a b l e 1 igands. Moreover, t h e model systems tend t o s u f f e r from an e x t r a

disadvantage

: active

f o r m a t i o n of d i m e r i c p-0x0

oxornetal

comp1exes.l'

species are deactivated v i a We s h a l l

the

r e t u r n t o these problems

later. O b v i o u s l y i t would be advantageous i f i t was p o s s i b l e t o d e v i s e a C a t a l y s t that

i s able t o mediate the transfer

of b o t h oxygen atoms o f d i o x y g e n t o

o r g a n i c s u b s t r a t e s , w i t h o u t r e q u i r i n g t h e consumption o f a r e d u c i n g agent. I n p r i n c i p l e , t h i s can be achieved a c c o r d i n g t o r e a c t i o n 13.

Indeed, t h i s pathway i s f o l l o w e d i n many gas phase o x i d a t i o n s o v e r metal oxide Catalysts.

such as vanadium p e n t o x i d e and b i s m u t h molybdate.

It

i S

g e n e r a l l y r e f e r r e d t o as t h e Mars-van K r e v e l e n mechanism a f t e r i t s o r i g i n a l Such a scheme i s f e a s i b l e i n gas phase o x i d a t i o n s where adsorbed s u b s t r a t e m o l e c u l e s can r e a c t w i t h s u r f a c e oxometal s o e c i e s t o f o r m r a d i c a l

38 intermediates t h a t are r a p i d l y f u r t h e r converted t o products.

I n l i q u i d phase

o x i d a t i o n s , i n c o n t r a s t , any r a d i c a l s t h a t a r e formed w i l l r e a c t r a p i d l y w i t h surrounding substrate molecules and/or dissolved dioxygen i n the b u l k l i q u i d leading

to

difference

free

radical

between

autoxidations.

heterogeneous

gas

This phase

is

an

important

oxidations

and

fundamental liquid

phase

oxidations. Nevertheless,

there

are

scattered

reports o f

homogeneous

systems

that

appear t o i n v o l v e t h e t r a n s f e r o f b o t h oxygen atoms o f d i o x y g e n t o o r g a n i c s u b s t r a t e s . Thus, Groves and Q u i n n r e p o r t e d 1 3 t h e c a t a l y t i c a e r o b i c e p o x i d a t i o n o f o l e f i n s mediated b y a d i o x o (tetramesitylporphyrinato)ruthenium(VI) complex Two e q u i v a l e n t s o f epoxide w e r e formed

a t ambient temperature and pressure.

for each m o l e c u l e o f d i o x y g e n consumed.

F u r t h e r m o r e , i t was shown t h a t t h e

d i o x o r u t h e n i u m ( V 1 ) complex was a competent s t o i c h i o m e t r i c o x i d a n t under anaer o b i c c o n d i t i o n s . The f o l l o w i n g mechanism was proposed t o e x p l a i n t h e r e s u l t s :

PRu"

11-

/"

[

+ 0,

PRII:",

t Interestingly,

V i

P[u=o 0

lc=c t h e analogous t e t r a - p - t o l y l

p o r p h y r i n a t o complex, which i s

known t o f o r m a p-0x0 dimer upon o x y g e n a t i o n , was i n a c t i v e as an o x y g e n a t i o n Catalyst.

T h i s l e d t h e a u t h o r s t o c o n c l u d e t h a t i n h i b i t i o n o f p-0x0 dimer

formation, v i a s t e r i c hindrance f r o m bulky s u b s t i t u e n t s i n the porphyrin r i n g , i s essential f o r c a t a l y t i c a c t i v i t y . More

recently,

Ellis

and

Lyons

have

i r o n ( I 1 I ) p o r p h y r i n complexes a r e s t a b l e , that

reported14

that

polyfluorinated

highly a c t i v e oxidation Catalysts

c a t a l y z e t h e unprecedented s e l e c t i v e h y d r o x y l a t i o n

of

isobutane w i t h

m o l e c u l a r oxygen a t ambient temperature. TFe'

Temp. 2 4 O

TPPF,,

Time (h)

Conversion

Selectivity

143

18%

95%

17%

8 7 "6

3

80' =

(TPPF,,)OH]

trtr~kis:pentafLuorophenyl)p~~phyKln~to

39 I n o r d e r t o e x p l a i n t h e i r h i g h a c t i v i t y and s t a b i l i t y i t was p o s t u l a t e d t h a t p o l y h a l o g e n a t i o n o f t h e p o r p h y r i n r i n g system n o t o n l y s t a b i l i z e s t h e l a t t e r towards o x i d a t i v e d e s t r u c t i o n b u t a l s o s t a b i l i z e s t h e o x o i r o n i n t e r m e d i a t e w i t h r e s p e c t t o p-0x0 dimer f o r m a t i o n .

I n p r i n c i p l e , i t should a l s o

be p o s s i b l e t o d e s i g n s t a b l e s o l i d c a t a l y s t s capable o f m e d i a t i n g analogous s e l e c t i v e o x i d a t i o n s i n t h e l i q u i d phase. TYPES

OF OXIDANT

In bulk chemicals manufacture economic c o n s i d e r a t i o n s u s u a l l y d i c t a t e t h e use o f m o l e c u l a r oxygen as t h e o x i d a n t . o t h e r o x i d a n t s may be c o m n e r c i a l l y o x i d a n t s (e.g.

I n f i n e chemicals, on t h e o t h e r hand,

feasible

(see t a b l e

1).

Indeed,

other

30% hydrogen p e r o x i d e ) may even be p r e f e r r e d for reasons o f

s e l e c t i v i t y and ease o f h a n d l i n g ,

i.e.

i t is not a question o f p r i c e

per

b u t p r i c e / p e r f o r m a n c e r a t i o . A l t h o u g h m o l e c u l a r oxygen i s t h e l e a s t expensive o x i d a n t i t r e q u i r e s e l a b o r a t e s a f e t y p r e c a u t i o n s , and t h e a s s o c i a t e d c o s t s , i n order t o avoid working w i t h i n explosion l i m i t s . TABLE 1. Single oxygen donors. % ACTIVE OXYGEN DONOR

-

COPRODUCT

H202

47.01

H20

03 t -Bu02H

33.3 17.8

02 t BuOH ~

NaClO

21.6

NaC1

NaC102

19.2

NaCl

NaBrO

13.4

NaBr

HN03

25.4

NOX

13.7

C5H1 lNO

KHS05

10.5

KHSOL

NaI04

7 . 2’

Na I

PhIO

7.3

PhI

C

~ 1 H~ 0 2~ 3

1. Based on 100% H,O,; 2. Assuming that onLy one oxygen a t o m is utilized; 3. N-Nethylmorpholine-N-oxide

In a d d i t i o n t o p r i c e and ease o f h a n d l i n g t h e n a t u r e o f t h e c o p r o d u c t and t h e Percentage a v a i l a b l e oxygen a r e i m p o r t a n t c o n s i d e r a t i o n s .

The f o r m e r i s

i m p o r t a n t from an environmental v i e w p o i n t and t h e l a t t e r i n f l u e n c e s t h e volume y i e l d ( k g p r o d u c t p e r u n i t r e a c t o r volume p e r u n i t t i m e ) .

The o x i d a n t o f

c h o i c e f o r f i n e chemicals manufacture i s o f t e n 30% H202 s i n c e i t i s r e l a t i v e l y

40

cheap, easy t o h a n d l e and i t s c o p r o d u c t i s water.

Moreover, u n l i k e m o l e c u l a r

oxygen i t g e n e r a l l y does n o t r e a c t w i t h o r g a n i c s u b s t r a t e s i n t h e absence o f a catalyst. CATALYST TYPES Heterogeneous c a t a l y s t s f o r l i q u i d phase o x i d a t i o n s can be d i v i d e d i n t o t h r e e d i f f e r e n t c a t e g o r i e s : ( a ) s u p p o r t e d m e t a l s (e.9. m e t a l i o n s (e.g.

Pd/C),

( b ) supported

i o n exchange r e s i n s , m e t a l i o n exchanged z e o l i t e s ) and ( c )

s u p p o r t e d oxometal

( o x i d i c ) c a t a l y s t s (e.g.

TiIV/SiO2,

redox z e o l i t e s ,

redox

p i l l a r e d c l a y s ) . T h i s d i v i s i o n o f t h e v a r i o u s c a t a l y s t t y p e s w i l l be used as a framework f o r t h e ensuing d i s c u s s i o n .

SUPPORTED METALS AS CATALYSTS

-

O X I D A T I V E DEHYDROGENATION

I n 1845 D o b e r e i n e r noted15 t h a t e t h a n o l i s o x i d i z e d t o carbon d i o x i d e and w a t e r by oxygen i n t h e presence o f aqueous a l k a l i and a p l a t i n u m C a t a l y s t . The c a t a l y t i c e f f e c t o f p l a t i n u m on t h e a e r o b i c o x i d a t i o n o f cinnamyl a l c o h o l d e s c r i b e d 1 6 by S t r e c k e r

Wieland

t h a t f i n e l y divided palladium catalyzes

showed''

i n 1855.

I n t h e p e r i o d 1912-1921

was subsequently

the o x i d a t i o n of

p r i m a r y a l c o h o l s and aldehydes t o aldehydes and c a r b o x y l i c a c i d s , r e s p e c t i v e l y , i n aqueous s o l u t i o n . S i n c e oxygen c o u l d be r e p l a c e d b y o t h e r hydrogen a c c e p t o r s

i t was concluded t h a t these r e a c t i o n s i n v o l v e a d e h y d r o g e n a t i o n mechanism, f o l l o w e d by o x i d a t i o n o f h y d r i d e by oxygen, e.g.

More r e c e n t l y , n o b l e m e t a l - c a t a l y z e d widely

appiied

to

che

selective

o x i d a t i v e d e h y d r o g e n a t i o n s have been

oxidations

of

alcohols18

and

(18)

.. 0

OH

vicinal

C a t a l y s t : Pt. Pb/C o r Pt. Bi/C

In

particular,

catalytic

aerobic

oxidations

of

carbohydrates,

using

s u p p o r t e d n o b l e m e t a l s i n t h e l i q u i d phase, have been e x t e n s i v e l y s t u d i e d by

41 Heyns and c o w o r k e r s 2 2 7 2 3 a n d , m o r e r e c e n t l y , b y g r o u p s a t t h e u n i v e r s i t i e s o f E i n d h c ~ v e n ~a ~n d- ~D~e l f t . 3 2 - 3 6

I n p r i n c i p l e , t h e s e r e a c t i o n s can i n v o l v e f o u r

d i f f e r e n t types o f chemoselective o x i d a t i o n : 1. C1 a l d e h y d e ( h e m i a c e t a l ) o x i d a t i o n CHO

2 . P r i m a r y CH20H

+

3. S e c o n d a r y CHOH

C=O

their

C=O

+

+

r e s u l t s with Pt/C

O=C as

proposed the f o l l o w i n g r e a c t i v i t y scale COCH20H

>

CH20H

>

C02H

C02H

+

4. D i o l c l e a v a g e -CH(OH)CH(OH)

Based on

+

CHOHaxial

>

catalyst,

Heyns a n d P a ~ l s e n ~ ~ ? ~ ~

for t h e d i f f e r e n t g r o u p s : CHO

)

CHOHeaUatorial

C1 o x i d a t i o n One

reaction that

has

been e x t e n s i v e l y

studied,

as

established i n d u s t r i a l processes i n v o l v i n g fermentation, catalyzed oxidation o f

0-glucose

to

D-gluconate

an a l t e r n a t i v e

to

i s the noble metal-

( r e a c t i o n 19)

i n aqueous

a1 k a l i.22-25

Palladium selectivity trimetallic

is in

superior this

(Pd, P t ,

to

process.

platinum with More

respect

recently,

bi-

to (e.g.

both Pd,

activity

ana

Bi/C)37

and

B i / C ) 3 8 c a t a l y s t s have been d e s c r i b e d t h a t a f f o r d v e r y

high s e l e c t i v i t i e s t o gluconic acid.

F o r e x a m p l e , Degussa w o r k e r s 3 * o b t a i n e d

g l u c o n i c a c i d i n 96% s e l e c t i v i t y u s i n g a 4% Pd, c a t a l y s t a t pH 10, 55°C a n d 1 0 mbar O2 p r e s s u r e .

1% P t ,

5% B i - o n - c h a r c o a l

P t enhances t h e a c t i v i t y and

B i t h e s e l e c t i v i t y o f t h e Pd c a t a l y s t . T h a t C1 o x i d a t i o n p r o c e e d s v i a i n i t i a l d e h y d r o g e n a t i o n , a s shown i n r e a c t i o n

42 19, was d e m o n s t r a t e d some y e a r s ago by t h e D e l f t g r o u p who showed32i33

that

t r e a t m e n t o f a l d o s e s w i t h n o b l e m e t a l c a t a l y s t s ( P t a n d Rh w e r e s u p e r i o r t o Pd, N i a n d

R u ) a t h i g h pH ( > 1 2 ) r e s u l t s i n t h e s i m u l t a n e o u s f o r m a t i o n o f t h e

corresponding a l d o n i c a c i d and m o l e c u l a r hydrogen.

i t was shown t h a t

Indeed,

t h e a l d o s e can f u n c t i o n a s a n e f f i c i e n t h y d r o g e n d o n o r f o r c a t a l y t i c h y d r o g e n t r a n s f e r reactions. C1-oxidation

o f aldoses i s a general

reaction3'

and has

been s u c c e s s f u l l y a p p l i e d t o t h e o x i d a t i o n o f g a l a c t o s e , mannose a n d xylOSe to

the

corresponding

aldonic

acids.

More

recently,

the

oxidation o f the disacharide lactose t o lactobionic acid, PdiC c a t a l y s t ,

impregnated i n - s i t u

with Bi,

selective

(>99%)

u s i n g a commercial

h a s been d e m o n s t r a t e d b y

the

E i ndhoven g r o u p . 2 9

C g vs C2 o x i d a t i o n F u r t h e r r e a c t i o n o f g l u c o n i c a c i d w i t h o x y g e n o v e r P t / C o r Pd/C C a t a l y S t S l e a d s t o t h e o x i d a t i o n o f t h e c 6 p r i m a r y CH20H g r o u p t o a f f o r d D - g l u c a r i c a c i d v i a t h e c o r r e s p o n d i n g a l d e h y d e ( L - g u l o r o n i c a c i d ) a s i n t e r m e d i a t ? (See f i g u r e 2). due Tne

t3

Unfortunately,

t h e r e a c t i o n e x h i b i t s o n l y moderate s e l e c t i v i t i e s

competing degradation o f t h e carbon c h a i n t o lower d i c a r b o x y l i c acids.

best

results

(55-60%

selectivity

to

glucarate)

obtain

with

?t/C

c a t a 1 ys t 5.30 931

i"

HC HO

-+Hy/ co,-

CHC

OH

co, -

L-guloronate

HO

OH

D-glucarate

2-keto-D-gluconate

FTGvRE 2. 3:tidation of D-gluconate. E f f o r t s t o increase t h e s e l e c t i v i t y of

t h i s r e a c t i o n by doplng the Pt/C

c a t a l y s t w i t h Pb r e s u l t e d i n t h e s e r e n d i p i t o u s d i s c o v e r y , group,

o f t h e s e l e c t i v e Pt,Pb/C-catalyzed

b y :he

Eindhoven

o x i d a t i o n o f g l u c o n i c a c i d t o 2-

43 k e t o g l u c o n i c a c i d i n a l k a l i n e medium.z6-z8

The r e a c t i o n i s a g e n e r a l one a n d

can b e a p p l i e d t o t h e s e l e c t i v e o x i d a t i o n o f a v a r i e t y o f a - h y d r o x y a c i d s t o t h e c o r r e s p o n d i n g 2 - k e t o a c i d s , e.g.

l a c t i c a c i d a f f o r d s p y r u v i c a c i d i n >95%

s e l e c t i ~ i t y . * ~ The * ~ ~r a t i o o f C2 t o C6 o x i d a t i o n i n g l u c o n i c a c i d i n c r e a s e d b y a f a c t o r o f 140 on d o p i n g t h e P t / C c a t a l y s t w i t h a n i n s o l u b l e l e a d S a l t . 2 7 The s e l e c t i v i t y e n h a n c i n g e f f e c t o f

t h e l a t t e r was p o s t u l a t e d z 6 t o i n v o l v e

c h e l a t i o n o f t h e a-hydroxy a c i d t o l e a d ( I 1 ) on t h e s u r f a c e o f t h e C a t a l y s t thus

facilitating

transfer

of

the

hydrogen

of

the

hydroxyl

at

C2

to

platinum(0). Catalyst deactivation

A l l o f t h e r e a c t i o n s d e s c r i b e d above s u f f e r f r o m t h e same d r a w b a c k : r a p i d catalyst deactiviation.

I n noble metal-catalyzed o x i d a t i v e dehydrogenations

t h e m e t a l must p e r f o r m two f u n c t i o n s : s u b s t r a t e dehydrogenation and subsequent o x i d a t i o n o f t h e s u r f a c e m e t a l h y d r i d e s p e c i e s b y a d s o r b e d oxygen. The s u c c e s s o f a p a r t i c u l a r c a t a l y s t depends on a d e l i c a t e b a l a n c e b e t w e e n t h e s e t w o Steps. U n f o r t u n a t e l y , t h e m o l e c u l a r oxygen t h a t i s n e c e s s a r y f o r t h e d e s i r e d r e a c t i o n i s a l s o responsible f o r the d e a c t i v a t i o n of

the catalyst,

t h e mechanism o f

w h i c h i s b y no means f u l l y u n d e r s t o o d . I t i s g e n e r a l l y n o t o b s e r v e d w i t h gas phase r e a c t i o n s b u t i s c h a r a c t e r i s t i c of

(aqueous)

l i q u i d phase o x i d a t i o n s

o v e r n o b l e m e t a l c a t a l y s t s , w h e r e a d s o r b e d o x y g e n atoms r e a c t w i t h W a t e r t o form adsorbed hydroxyl species. a d s o r b e d o x y g e n atoms,

I t i s thought30i31

t o i n v o l v e m i g r a t i o n of

v i a t h e formation of adsorbed h y d r o x y l species,

the P t l a t t i c e , a process r e f e r r e d t o as 'dermasorption'. minimized,

but not eliminated,

into

D e a c t i v a t i o n can be

by u s i n g l o w oxygen p a r t i a l p r e s s u r e s ,

low

s t i r r i n g speeds a n d s o - c a l l e d d i f f u s i o n - s t a b i l i z e d c a t a l y s t s . 3 4 ~ 3 5 The l a t t e r c o n c e p t i n v o l v e s t h e u s e o f l a r g e u n i f o r m p a r t i c l e s (e.9.

e x t r u d a t e s ) i n which

oxygen d i f f u s i o n l i m i t a t i o n leads, a t a c e r t a i n d e p t h i n t h e p a r t i c l e ,

to a

p r o p e r t u n i n g o f r e a c t i o n s and consequently t o a h i g h e r s t e a d y s t a t e a c t i v i t y . Recently,

van

Bekkum a n d

coworkers39

studied the

oxygen

tolerance

of

v a r i o u s n o b l e m e t a l / c a r b o n c a t a l y s t s i n l i q u i d phase o x i d a t i v e dehydrogenation o f a l c o h o l s . The o r d e r o f s t a b i l i t y t o w a r d s p o i s o n i n g by o x y g e n was f o u n d t o be P t

> Ir >

Pd

>

Rh

>

Ru (Ru/C was i n a c t i v e ) . O f p r a c t i c a l i m p o r t a n c e

i S

the

maximum t u r n o v e r number d i v i d e d b y t h e p r i c e o f t h e m e t a l a n d i t was s u g g e s t e d that

Pd p r o b a b l y has a b e t t e r p r i c e / p e r f o r m a n c e

ratio,

i.e.

' v a l u e f o r money' t h a n P t even t h o u g h t h e l a t t e r i s more s t a b l e .

gives

better

44

V i c i n a l d i o l cleavage In

the

noble metal-catalyzed

oxidations

described

above

vicinal

diol

cleavage i s sometimes observed as a s i d e - r e a c t i o n b u t never as a main r e a c t i o n . Oxidative

diol

periodate

(Malaprade

cleavage

usually

oxidation)

involves

stoichiometric

and t h e r e

oxidants

i s a g r e a t need f o r

such as catalytic

p r o c e d u r e s employing i n e x p e n s i v e , c l e a n o x i d a n t s such as O2 o r H202. Recently,

heterogeneous

catalytic

systems were

described41 t h a t

employ

m o l e c u l a r oxygen f o r t h e l i q u i d phase o x i d a t i v e c l e a v a g e o f v i c i n a l d i o l s . A l t h o u g h t h e c a t a l y s t s appear t o be m i x e d m e t a l o x i d e s r a t h e r t h a n supported metals

t h e method

resembles

closely

the

noble metal-catalyzed

oxidations

d e s c r i b e d above, hence t h e i r i n c l u s i o n i n t h i s s e c t i o n . The c a t a l y s t s a r e h i g h s u r f a c e a r e a r u t h e n i u m p y r o c h l o r e o x i d e s h a v i n g t h e g e n e r a l f o r m u l a A2+XRu2-X07-y (A = Pb, B i ; 0

< x
synclyst 25 (25% t

alumina) > synclyst 13 > H Mordenite, Amberlyst A125, silica > Amberlite IRA 120 >> Nafion

+

(H ). The order suggests that surface acidity is a major factor in the catalysis, but the mordenite

and Nafion were far less active than their acidities would suggest. Presumably this results from failure of the reagent to penetrate the catalyst interiors to reach the active sites in these cases. Under comparable conditions with the same catalyst (silica), the order of activity of various brominating agents was acetyl hypobromite > TBH, bromine, N&-dibromamine-T > 1,3-

dibromo-5,5-dimethylhydantoin (DBDMH) > NBS > Nfl-dibromo-ten-butyylamine. Thus, it is now possible to select a combination of reagent and catalyst to provide a highly active system, a very weakly active system, or an intermediate system according to the needs of the substrate. Some of the difficult brominations encountered previously can now be tackled. For example, tetrabromination of carbazole occurs readily at ambient temperature with silica as catalyst if DBDMH is used instead of NBS.19 In another example, attempts to polybrominate indole-3-acetonitrile with NBS over a silica catalyst give rise to complex mixtures but use of the more active catalyst, montmorillonite K10, allows the clean production of an unstable

64

intermediate. Depending upon the work-up conditions good yields of either of two stable 19 products can be obtained (Fig. 11).

3NBS

@ H C Z JN

KlO

H

Figure 11. Brornination of indole-3-acetonitrilewith NBS-K10. The range of brominated indoles now available provides opportunities for convenient syntheses of a number of potentially useful compounds. For example, many marine natural products contain a bromoindole fragmen?'

derivable from 6-bromotryptamine, but 6-

bromotryptamine has been obtained in only 6% yield following a multistage synthesis involving build up of the indole nucleus2l Reduction of the products in Figure 11 may provide a much more direct approach and we are currently investigating this po~sibility.'~In addition, catalytic tritiation of bromoindoles provides an opportunity for synthesis of radiolabelled compounds (e.g.

19

Fig. 12).

rnBr CH&N

Br

T,, complex catalyst*

wNH

i t \

H

H (76 Ci rnmol-')

Figure 12. Synthesis of tritiated tryptamine. Reagent systems suitable for bromination of deactivated aromatics such as nitrobenzene can be devised, as can mild reagent systems suitable for selective bromination of highly activated 19 aromatics such as phenols (Fig. 13).

Supported Bromine

6'

*

65

OIH

+

dr (80% - 100~0)

(X=H, OMe. CH, CI)

(0- 20%)

Figure 13. Selectivepara-brominationof phenols. Other Electrophilic Substitution Reactions The principle of combination of an organic reagent and a solid acid catalyst can be usefully applied in different types of electrophilic substitutionreactions. For example, we have found that use of an acyl nitrate in combination with the proton or aluminium form of mordenite or zeolite X leads to good yields of nitroarenes having much higher para:ortho isomer ratios than those obtained via traditional nitration methods (Fig. 14)22 Laszlo's group have achieved similar 23 results by use of metal nitrates supported on K10 clay in the presence of acetic anhydride. R

6

R

PhC02N02 AI3+,H+Mord.

=-

I

o : m : p

Yield (%)

time

99

10 rnin

32 : 1 : 67

97

80 rnin

25 : 2 :73

86

2h

26 : 2 : 72

86

70 rnin

14:2:84

96

70 rnin

5 : 3 :92

Figure 14. Selective para-nitrationof alkylbenzenes. The group of Geneste in Montpellier has studied Friedel-Crafts acylation of aromatic hydrocarbons by carboxylic acids in the presence of solid acid ~atalysts?~ whilst Friedel-Crafts alkylationhas receivedextensive study over both

andclays26 It is clear that such solid

66

acid catalysts have substantial potential for electrophilic aromatic substitution. It would be of interest to know if similar benefits could be obtained in nucleophilic aromatic substitution reactions by means of solid bases.

The Ullmann Synthesis of Diary1 Ethers A useful reaction for investigation is the Ullmann synthesis of diaryl ethers:7

which has

potential importance for synthesis of a number of commercial products in the agrochemical and pharmaceutical fields, but which suffers from serious drawbacks, particularly high temperatures o 28 (typically 180-220 C) or long reaction times (up to 20 hours) and modest yields (typically 4030 60%).29We hoped that a powerful solid base such as fluoride-impregnated alumina might prove advantageous. However, in practice it appeared that simple, solid potassium carbonate was as good a base as any. Nevertheless, we have been successful in developing conditions which give

substantial practical advantages by using ultrasonic irradiation of solventless reaction mixtures (Fig. 19.”

Ultrasound has previously been found to effect rate enhancement in the Ullmann 31 synthesis of biaryls.

(excess) (X,y = H, OMe, CH3)

(70- 95%)

Figure 15. Ultrasound-assisted synthesis of diaryl ethers. Applications of Solids in Aliphatic Chemistry Although this review has concentrated primarily on aromatic chemistry, there are numerous potential applications of heterogeneous catalysts in aliphatic chemistry. Any acidcatalysed reaction may in principle be catalysed by the acid of a zeolite or clay and many such examples have been reported. 8’32-34 Base-catalysed reactions could benefit from utilization of fluoride-impregnated alumina3’ However, few of the reported examples in aliphatic chemistry appear to have made use of the shape-selectivity properties of the catalysts. One example where such a factor might be useful is in the Diels-Alder reacti0n.3~ For example, if the reaction between acrylonitxile and cyclopentadiene could be catalysed within the

67

pores of an appropriate zeolite it might be possible to gain control of the exo:endo ratio and cause the em-product, unusually, to predominate. Our first attempt at this reaction seemed to give complete selectivity in favour of the e~o-product,'~but the yield was only ca. 35%. However, breakdown of the zeolite liberated further adduct, which turned out to be almost entirely endoproduct. Thus, the reaction itself did not produce the desired selectivity (no transition state control), but there was impressive separation of the products, which may warrant further investigation.

In one final example from the work carried out in our laboratories, it is interesting to consider the possibility of shape selection between chemically similar functional groups. This would be especially useful when catalytic sites within the pores of a zeolite were essential for reaction, but the selectivity could still be demonstrated even on uncatalysed reactions. We therefore considered the addition of bromine to alkenes.

In principle, a zeolite with an appropriate pore structure should be able to select between a straight chain and a branched or cyclic alkene because only the straight chain compound could enter the pores. If an equimolar mixture of the two alkenes were treated with one equivalent of bromine in different ways differences should become evident. In the absence of zeolite, little selectivity would be expected. If the zeolite were present in sufficient quantity to absorb all of the straight chain alkene and then the bromine were added, preferential reaction should take place on the alkene not absorbed. On the other hand, initial absorption of the bromine followed by addition of the alkene mixture should give rise to preferential reaction on the alkene which can enter the pores to meet the bromine. The validity of this proposition is demonstrated in Figure l6.l' successfully applied to a range of other examples.

the process has been

68

0

+

+ Br

65 : 35

no zcolitc prcsciit

zeolite p r e s c i i t , re;iclioii 'iiulsitle' pores 96 : 4 aviililc ~ i r c s c i i l , rc;icliiiii 'iiisidc'

Iiiirvh

17 : X 3

Figure 16. Selective bromination of alkenes in the presence of a zeolite. A selective bromination of styrene with bromine absorbed into a molecular sieve was we believe this to be the f i s t claimed once befor?6 but the claim was later r e f ~ t e d . 3 Thus, ~ genuine demonstration of this effect. Conclusion Zeolites and clays are extensively used as catalysts in the bulk chemicals and petrochemicals industries. temperatures.

Typically, reactions are carried out in the gas phase at high

Such conditions become unreasonable when liner chemicals are involved.

Instead, low temperatures and liquid phase reactions become necessary. The costs of the reagents and catalyst are also less important as the product values increase, but product selectivity and good yields are more important. Thus, there is considerable interest in the development of mild, selective, liquid phase reactions such as those described here. Although this review has concentrated particularly on the work of our own gronp, many others are working in the field and their contributions are referred to in the review articles cited. Acknowledgements The contributions of an able group of research students - Michael Butters, Karl Fry, Mark Hammond, Anil Mistry, Martin James, Lysanne Pearce, Vincent Boschat and Dennis Jones - and of industrial collaborators

-

Barry Nay, David Walker, Martin Atkins (BP), Martin Bye

(Amersham International), Derek Basset, Paul Ashworth and Janet Chetland (Associated Octel) are gratefully acknowledged. The companies and the S.E.R.C. are thanked for financial support.

69

Finally, I am grateful to Professor M. Guisnet and the organizers of the Conference on Fine Chemicals and Catalysis for the invitation to present this work in Poitiers.

References 1.

V. B. Jigajinni, W. E. Paget and K. Smith, J. Chem. Res. (S),1981, 376.

2.

K. Smith, M. Butters, W. E. Paget and B. Nay, Synthesis, 1985, 1155.

3.

C. Yaroslavsky, Tetrahedron Lett., 1974,3395.

4.

M. Hojo and R. Masuda, Synth. Commun., 1975,5, 169.

5.

M. Butters, Ph.D. Thesis, Swansea, 1986.

6.

K. Smith, M. Butters and B. Nay, Tetrahedron Lert., 1988,29, 1319; see also UK Patent 2 165 244A (1986).

7.

P. Laszlo, Accounts Chem. Res., 1986,19, 121; Science, 1987,235, 1473.

8.

W. Holderich, M. Hesse and F. Nlumann, Angew. Chem. Int. Ed. Engl., 1988, 27, 226; H. van Bekkum and H.W. Kouwenhoven, Recl. Trav. Chim. Pays-Bas, 1989,108,283.

9.

D. W. Breck, '2eolite Molecular Sieves", Wiley, New York, 1974.

10.

K. Smith, M. Butters and B. Nay, Synthesis, 1985, 1157; see also U.K. Patent 2 155 009A (1985).

11.

J. Van Dijk, J. J. Van Daalen and G.P. Paerels, Recl. Trav. Chim. Pays-Bas, 1974, 93,72; see also H. van Bekkum, T. Huizing, J. J. F. Schotten and T. M. Wortel, Terrahedron Letr., 1980,21,3809.

12.

For an extensive discussion of the use of zeolites for catalysis of aromatic chlorinations see L. Delaude and P. Laszlo, J . Org. Chem., in press. We thank Professor Laszlo for a preprint of this publication.

13.

See A. G. Mistry, K. Smith and M. R. Bye in D. Price, B. Iddon and B. J. Wakefield, Ed., "Bromine Compounds: Chemistry and Applications", Elsevier, Amsterdam, 1988 (contains reports of a conference held in Salford, September 1986), p.277. The process has recently been developed into a general method for para-selective bromination of aromatic ethers; H. Konishi, K. Aritoni, T. Okano and J. Kiji, Bull. Chem. Soc. Japan, 1989,62,591.

70

14.

See

Th. M. Wortel, D. Oudijn, C. J. Vleugel, D. P. Roelofsen and H. van Bekkum, J.

Caral., 1979, 60, 110, and references cited therein; F. de la Vega and Y. Sasson, J.C.S. Chem. Comm., 1989,653. 15.

T. Hino, M. Nakagura and S. Akaboshi, Chem. Phurm. Bull (Japan). 1967,15, 1800; R. L. Hinman and C. P. Bauman, J. Org. Chern., 1964, 29, 1206; J. Parrick, A. Yahya and Y.

Jin, Terrahedron Lerr., 1984, 25, 3099, W. B. Lawson, A. Patchornik and B. Witcop, J. Am. Chem. SOC.,1960,82,5918; T. Hino and M. Nakagawa, Heterocycles, 1977.6, 1680.

16.

N. Putokhin, J. Gen. Chem., (U.S.S.R.), 1945, 15, 332; R. S. Phillips and L. A. Cohen,

Tetrahedron Lerr., 1983,24,5555; and references cited therein. 17.

A. G. Mistq, K. Smith and M. R. Bye, Terrahedron Lerr., 1986,27,1051.

18.

D. J. Evans, H. F. Thimm and B. A. W. Collier, J . Chem. SOC.Perkin Trans. 11, 1978,865.

19.

Unpublished observations.

20.

See D. J. Faulkner in D. Price, B. Iddon and B. J. Wakefield, Ed., "Bromine Compounds:

Chemisrry and Applications", Elsevier, Amsterdam 1988, p. 121. 21.

C. Grgn and C. Christophersen, Acra Chem. Scand. B , 1984,38,709.

22.

K. Smith, K. Fry, M. Butters and B. Nay, Terrahedron Len., 1989, 30, 5333; see also European Patent Number EP 0356091 (1990).

23.

A. Cornelis, L. Delaude, A. Gerstmans and P. Laszlo, Terrahedron Lerr., 1988, 29, 5657; A. Cornelis, A. Gerstmans and P. Laszlo, Chem. Lerr., 1988, 1839; P. Laszlo and J.

Vandormael, ibid, 1988, 1843. 24.

B. Chiche, A. Finiels, C. Gauthier, P. Geneste, J. Graille and D. Pioch, J. Mol. Caral., 1987, 42 , 229; B. Chiche A. Finiels, C. Gauthier and P. Geneste, J. Org. Chem., 1986, 51,2128.

25.

N. S. Gnep, J. Tejada and M. Guisnet, Bull. SOC.Chim. Fr., 1982,5.

26.

For a recent example, see J. A. Clark, A. P. Kybett, D. J. Macquarrie, S. J. Barlow and P. Landon, J. Chem. SOC.Chem. Commun., 1989, 1353.

27,

A. A. Moroz and M. S. Shvarstberg, Usp. Khim., 1974,43, 1443.

28.

T. Y'amamoto and Y. Kurata, Can. J. Chem., 1983,61, 86.

29.

H. E. Ungnade and E. F. h o l l , Org. Synrh., 1946,26,50.

71

30.

T. Ando, S. J. Brown, J. H. Clark,D. G . Cork, T. Hanafusa, J. Ichihara, J. M. Miller and M. S. Robertson, J . Chem. SOC.Perkin Trans. II, 1986, 1133.

31.

J. Lindley, J. P. Lorimer and T. J. Mason, Ultrasonics, 1987,25,45; 1986,24,292.

32.

P. Laszlo, Science, 1987,235, 1473.

33.

P. Laszlo, Accounts Chem. Res., 1986,19, 121.

34.

F. Figueras, Caral. Rev. Sci. and Eng., 1988,30,457.

35.

J. Ipaktschi, Z. Natutforsch. B;Anorg. Chem., Org. Chem., 1986,41B, 496.

36.

P. A. Risbood and D. M.Ruthven, J . Am. Chem. SOC.,1978,100,4919.

37.

R. M. Dessau,J. Am. Chem. SOC.,1979,101, 1344.


M. Guisnet et al. (Editors),Heterogeneous Catalysis and Fine Chemicals I1 0 1991 Elsevier Science Publishers B.V., Amsterdam

73

ENANTIOSELECTIVE CATALYSIS BY CHIRAL SOLIDS: APPROACHES AND RESULTS. HANS-ULRICH BLASER* and MANFRED M a L E R Central Research Laboratories, CIBA-GEIGY AG, R 1055.6, CH-4002 BASEL

ABSTRACT The application of solid chiral catalysts for the enantioselective synthesis of chiral molecules is reviewed. An attempt has been made to classify the different types of catalytic systems and to discuss the approaches and methods which have been used for the investigations. Enantioselectivities observed for several reaction types (hydrogenation/hydrogenolysis/dehydrogenation; electrochemical reactions; base catalysis; miscellaneous reactions) are summarized according to substrates and catalytic systems. The influence of system parameters and mechanistic investigations are reviewed for the following catalyst systems: Tartrate modified catalysts, cinchona modified catalysts and electrochemical systems. Conclusions concerning synthetic and commercial-scale applications of chiral solid catalysts are presented. I. INTRODUCTION /SCOPE

Enantioselective synthesis is a topic of undisputable importance in current chemical research and there is a steady flow of articles, reviews and books on almost every aspect involved. The present overview will concentrate on the application of solid c h i d catalvsts for the enantioselective synthesis of chiral molecules which are a special class of fine chemicals. Included is an account on our own work with the cinchona-modified Pt catalysts. Excluded is the wide field of immobilized versions of active homogeneous complexes or of bio-catalysts. During the preparation of this survey, several reviews have been found to be very informative [l-141. if its Let us start off with a few fundamental concepts and definitions. A molecule is image and mirror-image are not superimposable and therefore enantiomeric. A reaction or a catalyst is called enantioselective (or asymmetric or enantioface-differentiating [4]) if one of the enantiomers is produced preferentially starting from non-chiral substrates. If a reaction occurs faster with one enantiomer of a racemic substrate we speak of kinetic resolution (or enantiomerdifferentiation [4]). Enantioselectivity (or enantiomeric excess (ee) or optical yield) is only possible if a chiral agent is present during the reaction and interacts with the substrates in the product-determining step. It is a kinetic phenomenon, due to the difference in activation energy between the diastereomeric transition states leading to the two enantiomers (distinguished by the prefix R and S or d and 1). The enantioselectivity is defined as ee (%) = 100 x I[R]-[S]l/ ([R]+[S]). At 25 OC, an energy difference of 1.5 kcal/mol and 3 kcal/mol leads to about 80% (90%:10%) and 98% (99%:1%) enantiomeric excess, respectively. The observed ee will be below the inherent catalyst selectivity if the racemic reaction occurs uncatalyzed or on non-chiral sites as well. An enantioselective catalyst has two functions: First, it has to perform what one could call the chemical catalysis, here named activating function. In addition, it has to control the

74

stereochemical outcome of the reaction and we term this the controlling function. The two functions can be performed by the same or by two different agents. In the following scheme we have tried to classify the different types of catalytic systems described in Section I1 where an inherently chiral or a chirally modified solid catalyst is involved. At least two extreme cases can be distinguished, one where reactions are being catalyzed only at the surface of a "hard" solid (e.g. a metal) and the other where the reaction occurs inside a "soft" material (e.g. an organic polymer). An attempt will be made to discuss critically the approaches and methods which have been applied during various phases of the investigations, because each phase has its own type of problems and therefore requires a different strategy. Actkratlng function

Controlllng tunctlon

Reactlon type

metallic surface

modifier or polymer

metallic surface

chiral support

metal salt or oxide

modifier or polymer

chiral metal salt

chiral metal salt

chiral polymer

chiral polymer

none

crystal

hydrogenation erectrochemistry hydro enation de h ycfogenat ion isomerization polymerization isornerization pol merization caAene addition SN2 reaction nucleophilic addition oxidation bromination dimerization h drogenolysis

Our review will be organized as follows: 11

I11 IV V VI

EARLY INVESTIGATIONS / EXPLORATORY PHASE: THE SEARCH FOR CATALYTIC SYSTEMS. INFLUENCE OF SYSTEM PARAMETERS: THE SEARCH FOR BETIER ENANTIOSELECTIVITIES. SYNTHETIC AND COMMERCIAL-SCALE APPLICATIONS. MECHANISTIC INVESTIGATIONS: THE SEARCH FOR UNDERSTANDING. CONCLUSIONS.

11. EARLY INVESTIGATIONS / EXPLORATORY PHASE: THE SEARCH FOR CATALYTIC

SYSTEMS. During the early phase of an investigation there is usually very little information available and therefore, the goal is to find a "lead" which then can be developed and improved further to give e.g. a synthetically useful system. The approach most often used is what one could call "screening with a concept": experiments are set up in order to test an intuitive idea or a more or less well defined hypothesis. A good illustration for this approach is described by Izumi [4]: "we expected simply that an optically active product should be produced from the influence of the optically active environment, like baking a waffle. We used silk fibroin as a 'waffle iron"'.

75

Random screening is usually too time consuming but a certain randomness is desirable during the exploratory phase because unexpected effects are bound to occur. Again a citation: Tai [I] says regarding the discovery of the Ni/tartrate/NaBr catalyst and its application to 0-keto ester hydrogenation: "It was sheer luck that methyl acetoacetate was employed as a substrate...". The first reported attempts of what was then called "absolute or total asymmetric synthesis" with chiral solid catalysts used nature (naturally!) both as a model and as a challenge. Hypotheses of the origin of chirality on earth and early ideas on the nature of enzymes strongly influenced this period [15]. Two directions were tried: First, chiral solids such as quartz and natural fibres were used as supports for metallic catalysts and second, existing heterogeneous catalysts were modified by the addition of naturally occuring chiral molecules. Both approaches were successful and even if the optical yields were, with few exceptions, very low or not even determined quantitatively the basic feasibility of heterogeneous enantioselective catalysis was established. We carried out a thorough literature search and the results are summarized in Figs. 1-4 (substrates), Fig. 5 (important modifier structures) and Tables 1-4 (catalytic systems). We are confident that most of the relevant investigations and catalytic systems are reported here. Some papers are available only in Russian or Japanese and in these cases we either cite the Chemical Abstract reference or a review. Results are classified according to reaction type: a) Hydrogenation/hydrogenolysis/dehydrogenation;b) Electrochemical reactions; c) Base catalysis; d) Miscellaneous reactions. If available, the best optical yield for a substrate type is included in the Figures, together with the best catalyst system. a) Hydrogenation / hydrovenolysis / dehydrogenation This is clearly the most important application of chiral solid catalysts and Fig. 1 and Table 1 show an impressive number of entries. As will be seen in Sections In.-V., much of the available information is concentrated on very few catalyst systems and substrates. The first successful experiments were reported by Schwab [ 161: Cu, Ni and Pt on quartz were used to dehydrogenate racemic 2-butanol 2. At low conversions, a measurable optical rotation of the reaction solution indicated that one enantiomer of 2 had reacted preferentially (ee 0.4 give lower optical yields and lower turnover numbers. However, the platinum dispersion is not a sufficient parameter to explain the enantioselectivities observed for the different catalysts. Other factors such as texture of the support, morphology and size distribution of the platinum particles may affect the catalyst performance as well [30,58,59,61]. Catalyst stability. Under the conditions used for preparative experiments, the optical yield remains constant up to complete conversion, suggesting that the modified catalyst is rather stable [62]. However, experiments at low modifier concentration indicate that the cinchona alkaloid deteriorates slowly and its enantioselectiveeffect is lost [33,63]. Solvent and additives. Several systems have been studied concerning solvent effects. Fig. 6 shows that quite small changes in substrate, modifier or reaction conditions can lead to rather different results. Generally, very good results are obtained in apolar solvents with dielectric constants of 2-6. But in some cases alcohols can give equally high ee's. An important conclusion is that the optimal modifier concentration is dependent on solvent, modifier and substrate type [33]. The addition of amines and weak acids can affect the enantioselectivity [31,33].

ee (%) 80

a)

60 40

20 20 40 60 80 100

20 40 60 80 100

20 40 60 80 100

20 40 60 80 100

dlelectrlc constant

Fig. 6. Influence of the solvent polarity on the optical yield of various a-ketoester hydrogenations. a),b) catalyst not pre-modified, cinchonidine (Cd) added to the reaction mixture [33, 621; c) catalyst pre-modified with Cd, no Cd added, d) catalyst pre-modified with Cd and Cd added [31].

Reaction conditions. Temperatures between 20-50 OC and pressures >10 bar give good results. Usually higher pressures lead to slightly higher ee's and an increase in rate, while an increase of the temperature also leads to higer rates but to a decrease in selectivity. Typical results are depicted in Fig. 7 where it can be seen that the situation is sometimes more complex [30,33].

84

ee (%)

rate (m0Vmin.g)

80

60

.

40

lobar 100 bar

-

(XI

ao 60 40

20

20

0

20

40

60

80

I 0

OC

20

40

60

80

*c

Fig. 7. Influence of temperature and pressure on rate and optical yield. Catalyst not pre-modified, cinchonidine (Cd)and dihydrocinchonidine ( H a ) added to the reaction mixture. a) solvent EtOH 1301,-ee, --- rate; b) -benzene, 75 bar; toluene, 50-150 bar [33].

---

Modifier concentration. Preliminary experiments indicated that catalyst and modifier concentration have a strong effect on rate and ee [30]. In a detailed investigation this was confirmed (see Section V). Dehalogenation of 22 with cinchona modified Pd catalysts. Here we give a brief illuswtion of how we proceeded in order to improve the enantioselectivity for this hydrodehalogenation. Our first experiments using Pd/C/cinchonidine resulted in ee's of 2-4%, while the chemoselectivity (total dehalogenation) was >90%.Based on our experience with dehalogenation reactions and enantioselective catalysts we investigated the following parameters: catalyst type (Pd/C, Pd/CaC03, Pd/BaS04, Pt/13aS04, Pt/C), modifier (several cinchona derivatives), solvent (THF,methyl acetate, EtOH, MeOtBu) and base (NaOAc, N ( B u ) ~ MgO). , In a first series only cinchonidine was used as modifier and 15 of the 60 possible catal yst/solvent/base combinations were chosen randomly. Optical yields between 0 and 30% were obtained and first trends indicated that P ~ / B ~ S O J H F / N ( B U was ) ~ the best combination to continue. Screening of ca. 20 cinchona derivatives and a brief paxameter optimization resulted in an enantioselectivity of 50% (Pd/BaSO&inchonine/ THF/N(Bu)3,25 "C, 4 bar) [33]. c) Electrochemical systems. Again we refer to the review by Tallec 1361 where the effect of system parameters on enantioselectivity is summarized. For a given substrate, the most important factors are electrode material, electrode pretreatments, modifier structure, solvent, electrolyte, pH and buffer system, voltage and temperature.

IV. SYNTHETIC AND COMMERCIAL-SCALE APPLICATIONS. While the former three sections deal with investigations of model substrates and reactions, this part is dedicated to applications of enantioselective heterogeneous catalysts to solve "real" synthetic problems both on a laboratory and on a commercial scale. With one exception, all the

85

examples reported here are hydrogenation reactions, the only reaction type developed to any kind of maturity. As a rule, synthetic chemists will consider only those new reactions and catalysts for preparative purposes where the enantioselectivityreaches a certain degree (e.g. S O % ) and where both the catalyst and the technology are readily available. For heterogeneous catalysts this is not always the case because the relevant catalyst parameters are often unknown. It is therefore of interest that two types of modified Nickel catalysts are now commercially available: a Raney nickeVtartrateMaBr from Degussa [64] and a nickel powder/tartrate/NaBrfrom Heraeus [65, 661. It was also demonstrated that commercial Pt catalysts are suitable for the enantioselective hydrogenation of a-ketoesters [30, 311. With some catalytic experience, both systems are quite easy to handle and give reproducibleresults. In addition to good enantioselectivity and availability, a viable production catalyst has to meet further requirements e.g. activity, productivity, price, handling and separation (for a discussion of these problems see [67, 681). Heterogeneous catalysts have an inherent advantage concerning handling and separation. But in the case of the nickeutartrate system productivity and price of the modified catalyst can be a problem and successful attempts have been made in order to re-use the catalyst either by coating with a polymer [56] or by adding certain amines [57]. We have found that the development of such a process is more demanding than a classical heterogeneous hydrogenation reaction because so many additional reaction parameters are involved. The use of statistical optimization methods can be of advantage and in addition, rigorous quality control (substrates,catalyst, solvent etc.) is necessary to garantee reproducibility. The first example, a multistep synthesis of several isomers of the sex pheromone of the pine sawfly, starts with the nickel catalyzed hydrogenation of methyl 2-methyl-3-oxobutyrate(1) with fair stereoselectivitywhich later was further improved [69,70]. 1. Niltartrate 100°C, 100 bar

L

(l)

ervthro/threo = 3/1 ee = ca. 60%

'

and stereoisomers

The same catalyst system was also reported to lead to biologically active Cl&,6 3-hvdroxvacids starting from the corrresponding ketoesters with optical yields of 83-87%, which can be increased to >99% with a simple crystallization [71]. Cu-tartrate has been used to catalyze a carbene addition (seereaction 43 in Section XI) with 46% optical yield, giving an intermediate in a steroid synthesis [49]. A convenient and efficient ligand synthesis for homogeneous enantioselective hydrogenation is described [72] starting with the stereoselective hydrogenation of acetylacetone (2)

--

1. Raney nickeVtartrate/NaBr d

ee > 97% de not given

& x

x

X = OPPh2, PPh2

86

that was developed by Izumi's group and commercialized by Wako Pure Chemicals Ind. [l , 731. Kawaken Fine Chemicals Co. has also indicated that similar catalytic reactions are under development and that certain optically pure intermediates will be produced [74]. The next example originates from our own laboratory: Two potential intermediates for the angiotensinconverting enzyme inhibitor benazevril can be synthesized using cinchona modified noble metal catalysts (3). While the hydrogenation of the a-ketoester has been developed and scaled-up into a production process (10-200 kg scale, chemical yield >98%, ee 79-82%), the novel enantioselective hydrodechlorination reaction (see Section In) could be a potential alternative to the established synthesis where the racemic a-bromobenzazepinon is used [75]. At the moment both selectivity and productivity of the catalyst are too low and substitution reactions occur less readily with the chloro analog.

Finally, Raney nickel modified by (R,R)-tartaric acid/NaBr has been shown to be an efficient catalyst for the asymmetric hydrogenation of an intermediate in the synthesis (4) of tetrahydrolipostatin, a pancreatic lipase inhibitor developed by Hoffmann-LaRoche (100% chemical yield, ee 90-92%,6-100 kg scale) [76].

(CH2)FH3

1. Raney NiRarIratelNaBr

V. MECHANISTIC INVESTIGATIONS: THE SEARCH FOR UNDERSTANDING. Even though it is quite obvious that the empirical strategies described above are very effective for improving a catalytic system, understanding how a catalyst works is certainly the ultimate challenge. This is difficult for any heterogeneous catalyst and even more so for an enantioselective one. For the tartrate modified catalysts a large series of investigations have been reported by several research groups. These are summarized and commented in the following reviews [ l, 4, 6, 12, 14, 551. We will attempt to compare some aspects investigated for both the

87

NVtartrate and the Pt/cinchona systems and describe the pmposed conclusions concerning their mode of action. As usual the first hypotheses were based on qualitative and unsystematic observations as described in Section III. These were then refined or rejected in the course of further investigations. Effect of modifier and substrate structure. Very often structural effects are the first factors to give an idea on the mode of action of an enantioselective catalyst. From the observed dependence of the optical yield on modifier (see Fig. 8) and substrate structure (see Table 1) it was soon concluded that the interactions in the product determining step must be very specific. For Ni catalysts the two carboxyl and at least one OH group are essential for an effective modifier while preferred substrates must have an oxygen function in P-position of the keto group 11, 41. For the cinchona modified Pt catalysts the quinuclidine-nitrogen is considered essential and the configuration at C, of the alkaloid determines which enantiom of the a-hydroxyester is formed preferentially. Substrates with an additional carboxyl group a to the ketone (or the CClz-group in are suitable [30,581. COOH

COOH

ee(%) 75

COOH COOH 83

COOH

COOH

COOH

COOH

CH,

OMe

H

OMe

OH COOH

OH COOH

OM.

COOH

COOH

OH OH COOH

H OH OH COOH

65

68

61

0.2

1.2

0.0

ee(%) HOCH,

79

clnchonldlne derlvatlves excess R-lactate

-

-

clnchonlnederlvatlves excess Slactate

Fig. 8. Effect of the modifier structure on the optical yield for the hydrogenation of methyl acetoacetate [4] and ethyl pyruvate 1581. Adsorption of modifier and substrate. This aspect has been very well studied for the nickel catalysts: IR,UV, X P S , EM, electron diffraction and electrochemical investigations were carried out, very often using model catalysts. But also more conventional investigations like the effect of pH on the amount of adsorbed tartrate have been reported. There is a general consent that under the optimized conditions a corrosive modification of the nickel surface occurs and that the tartrate molecule is chemically bonded to Ni via the two carbonyl groups. There is also agreement that during the hydrogenation (which is carried out in an organic solvent) the adsorbed tartrate does

88

not leave the surface. There are two suggestions as to the exact nature of the modified catalyst: Sachtler [55] proposes an adsorbed [Ni2tartrate.J, complex; japanese [l, 41 and russian [14] groups prefer a direct adsorption of the tartrate on the Ni surface. In the gas phase, it has been shown that methyl acetoacetate is adsorbed as enolate and there are indications that the adsorption of the substrate is stronger if the catalyst is modified [55]. For the Wcinchona catalysts only preliminary adsorption studies have been reported [30]. From the fact that in situ modification is possible and that under preparative conditions a constant optical yield is observed we conclude that in this case there is a dynamic equilibrium between cinchona molecules in solution and adsorbed modifier. This is supported by an interesting experiment by Margitfalvi [63]: When cinchonine is added to the reaction solution of ethyl pyruvate and a catalyst pre-modified with cinchonidine. the enantiomeric excess changes within a few minutes from (R)-to (S)-methyl lactate, suggesting that the cinchonidine has been replaced on the platinum surface by the excess cinchonine. Kinetic studies and mechanistic schemes. With this paragraph we will conclude our survey on the mechanism of chirally modified hydrogenation catalysts. Several kinetic studies have been carried out using various Ni catalysts both in the liquid and the gas phase [l, 4, 551. Activation energies were found to be 10-15 kcal/mol. The reaction was first order in catalyst. Reaction orders for H2 ranged from 0 to 0.2 in the gas phase and from 0 to 1 in liquid phase while for methyl acetoacetate values of 0.4-1 (gas phase) and 0.2-0.8 (liquid phase) were determined. Based on these findings and on many other observations two mechanistic schemes were proposed: Izumi's and also Klabunovskii's groups favor a classical Langmuir-Hinshelwood approach: the adsorbed substrate reacts with activated hydrogen on the nickel surface in a stepwise fashion. The orientation of the adsorbed f3-ketoester is controlled by the tartrate via hydrogen bonding. There are results which suggest that the enantio-differentiation is determined in the adsorption step of the ketoester and not by the addition of hydrogen, but without structural evidence this is just a hypothesis. The important NaBr effect is explained as blocking of non-modified sites since the ratio of modified and non-modified sites determines the resulting optical yield [ 1.4, 141. Sachtler proposes a "dual site" mechanism where the hydrogen is dissociated on the Ni surface and then migrates to the substrate which is coordinated to the adsorbed nickel-tartrate complex. In this context it is of interest that the well known Sharpless epoxidation probably takes place on a dimeric tartrate complex of Ti. Sachtler suggests that both the anion and the cation have a function which vanes according to the conditions used. It is not clear whether the spillover mechanism is also proposed for the reaction in solution [55]. In our laboratory a kinetic study is in progress with a Pt/A1203 catalyst, modified with 10.1 1-dihydrocinchonidine(HCd) using ethyl pyruvate (Etpy) as substrate and ethanol or toluene as solvent. We are studying both the modified and the unmodified systems and it was demonstrated in both cases that the rate of reaction was not transport controlled [77]. The reaction for the unmodified catalyst was found to be first order in the Pt/A1203 catalyst. Depending on H2 pressure the following reaction orders were determined:

89

Unmodified WAI 03

Hp pressure 40 bar

4

WA1203/HCd

Etpy

EtPY

H2

0 0-0.4

>O

0

0.8 0.8

0

0-0.5

In addition, we are investigating the influence of low modifier concentration. Because of problems with the stability of the hydrocinchonidine, rates and optical yields have to be determined at very low conversions. During these studies the large accelerating effect by the cinchona modifier was confirmed. Fig. 9 summarizes our first results which show that, especially in toluene, extremely low modifier concentrations (corresponding to a ratio of HWP&,,& OS!) are necessary to obtain maximum ee and rate. The dependence of both rate and optical yield can be explained by a "ligand accelerated" type of catalysis [78] where a slow unselective (unmodified catalyst) and a fast enantioselective reaction cycle (adsorbed cinchona modifier) are assumed to be in a dynamic equilibrium. This mechanistic scheme predicts an interdependence between enantioselectivity and reaction rate either as ee vs l/rate (linear) or ee vs rate (hyperbole). Fig. 10 shows two cases where we find just this type of correlation: for the experiments with varying modifier concentrations and - interestingly enough - also for the turnover frequencies (TOF)of the various Pt/Al2O3catalysts tested (see Section HI). One possible explanation for this difference in catalyst performance is that the portion of the metal surface which can be modified is dependent on the nature of the Pt crystallites. At the moment we have no good explanation for the observed acceleration except that it has a connection to the basic character of the quinuclidine part and the adsorption behavior of the cinchona molecule. In addition, we think that the rate and product determining steps occur on the platinum surface and that well defined interactions between the platinum surface (ensembles), one cinchona molecule and the a-ketoester are crucial. There are, of course, other possible explanations for the observed enantioselection. Wells and Thomas [80] have proposed that an array of

ee (%)

0.1

0.2

1

1

0.3 0.4 1

,

HCdlPt 0.5

,

40 20

toluene

robs

ee (%I

0.2 0.4

0.6 0.8

HWlPl 1.0 robs

(mow

. 8~1O-~

70

. 6

50

. 4

30

. 2

0.02 0.04 0.06 0.08 0.1

[HW] (mmol/l)

10

' 4

ethanol

' 2

0.04 0.080.12 0.16 0.2

[HWl (mmolfl)

Fig. 9. Dependence of initial rate (.) and optical yield (+) on 10,lldihydrocinchonidine concentration and H W t ratio in toluene and EtOH (Pt/Al2O3, RT, 20 bar) [78b].

90

wate (simol)

ma(%)

8

4

12

x104

80 60

40 20 I 2

4

6

8

10 x10-5

rate (mous)

. . 20

.

60

.

. . 100 TOF (1/s)

Fig. 10. Interdependence of rate and enantioselectivity for the hydrogenation of ethyl pyruvate with WAI2O3 catalysts. a) For varying HCd concentrations (results from Fig. 9) --- ee versus l/rate and -ee versus rate; b) For different Pt/A1203 catalysts modified with cinchonidine [59]. cinchona molecules controls the stereochemistry. Interactions between substrate and modifier could also occur in solution. We think that especially the results with the very low dihydrocinchonidineconcentrations make these alternatives less likely. VI. CONCLUSIONS From a theoretical or conceptional point of view, enantioselective catalysis with chiral solids is a fascinating and challenging area of chemistry. The polymeric heterogeneous catalysts described in this review can be regarded as enzyme models. The catalysis very likely occurs inside the chiral mamx and the reaction is controlled by supramolecular interactions. For the case of the

rnodi3ed hydrogenation catalysts we propose that the metal surface must have a suitable structure to allow exactly the right interactions between the metal, the adsorbed modifier and the adsorbed substrate. This would explain the observed requirements for high enantioselectivity: two functional pans for the modifier (for adsorption on the catalytic surface and for interactions with the substrate) as well as for the prochiral subsfrate (binding function and reaction site). From a synthetic point of view, there are a few reaction types catalyzed by chiral heterogeneous catalysts which are useful for preparative chemists. But it is also evident that the scope of most catalytic systems is rather narrow and very high substrate specificity is observed. Compared to homogeneous or bio-catalysis, enantioselectivities are usually lower but there are exceptions. From a technical or commercial point of view, enantioselective heterogeneous catalysts would be preferable to homogeneous catalysts because of their handling and separation properties, but only if their catalytic performance is satisfactory. It has been demonstrated that this is indeed possible. ACKNOWLEDGMENTS We would like to thank E. Broger. K. Deller and J. Smtz for providing information on technical aspects of asymmetric hydrogenations, M. Garland and J. Margitfalvi for preliminary

91

results and R. Bader, H.P. Jalett, I. Mergelsberg, B. Pugin and A. Togni for critical discussions and support during the preparation of this manuscript. REFERENCES A. Tai and T. Harada, in Y. Iwasawa (Ed.), Taylored Metal Catalysts, D. Reidel, Dordrecht, 1 1986, p. 265. J. D. Momson (Ed.), Asymmetric Synthesis, Vol. 5, Academic Press Inc., London, 1985. 2 J.D. Momson and H.S. Mosher, Asymmetric Organic Reactions, Amer. Chem. Soc., 3 Washington DC, 1976. 4 Y. Izumi,Adv. Cat., 32 (1983) 215. H. Brunner, Topics in Stereochemistry, 18 (1988) 129. 5 M. Bartok, in Stereochemistry of heterogeneous metal catalyts, chapt. XI, J. Wiley, New 6 York, 1985, p. 511. H. Pracejus, Fortschr. Chem. Forsch., 8 (1967) 493. 7 E.I. Klabunovskii, "Asymmetric Synthesis", Goskhimizdat, Moscow, 1960, german 8 translation by G. Rudakoff, VEB Deutscher Verlag der Wissenschafkn, Berlin, 1963. C. Carlini and F. Ciardelli, in Y. Yermakov and Likholobov (Eds.), Homogeneous and 9 Heterogeneous Catalysis, VNU Science Press, Utrecht, 1986, p. 471. For a review see P. Pino and R. Miihlhaupt, Angew. Chem. 92 (1980) 869. 10 S. Inoue, Adv. Polym. Sci., 21 (1976) 78. 11 M. Aglietto, E. Chinellini, S. D'Antone, G. Ruggeri and R. Solaro, Pure & Appl. Chem., 60 (1988) 415. 12 M.J. Fish and D.F. Ollis, Cat. Rev.-Sci. Eng., 18 (1978) 259. 13 J. Mathieu and J. Weill-Raynal, Bull. Soc.Chim. Fr., (1968) 1211. 14 E.I. Klabunovskii, Izv. Akad. Nauk. SSSR. Ser. Khim., (1984) 505 (engl. 463). 15 F. Rost, Angew. Chem. 48 (1935) 73. 16 G.M. Schwab and L. Rudolph, Natunviss., 20 (1932) 362; G.M. Schwab, F. Rost and L. Rudolph, Kollooid-Zeitschrift, 68 (1934) 157. 17 D. Lipkin and T.D. Stewart, J. Amer. Chem. Soc.,61 (1939) 3295. 18 Y. Nakamura, Bull. Chem. Soc.Jpn., 16 (1941) 367. 19 T.D. Stewart and D. Lipkin, Amer.Chem.Soc., a(1939) 3297. 20 M. Nakazaki, J. Chem.Soc. Japan, Pure Chem. Sect., 25.(1954) 831. 21 S. Akabori, Y. Izumi, Y. Fuji and S. Sakurai, Nature, 178 (1956) 323. 22 T. Isoda, A. Ichikawa and T. Shimamoto, Rikagaku Kenkyusho Hokuku, 34 (1958) 134, 143. C.A., 54 (1958) 285. See also [4]. 23 A.A. Balandin, E.I. Klabunovskii and Y.I. Petrov, Dokl. Akad. Nauk. SSSR, 127 (1959) 557 (engl. 57 l), 24 T. Yoshida and K. Harada, Bull. Chem. Soc.Jpn., 44 (1971) 1062. 25 E.S. Neupokoeva, E.I. Karpeiskaya, L.F. Godunova, E.I. Klabunovskii, Izv. Akad. Nauk SSSR, Ser. Khim., (1975) 2354 (engl. 2241). 26 Asahi Patent, JP 13307 (1963). C.A., 60 (1966) 3092. 27 H. Hirai, J. Polymer. Sci. B (Polymer Letters), 9 (1971) 459. 28 R.L. Beamer, R.H. Belding and C.S. Fickling, J. Pharm. Sci., 58 (1967) 1142 and 1419. 29 K. Harada and T. Yoshida, Natunviss., 57 (1970) 131 and 306. 30 H.U. Blaser, H.P. Jalett, D.M. Monti, J.F. Reber and J.T. Wehrli, in Studies in Surface Science and Catalysis 41 (Heterogeneous Catalysis and Fine Chemicals), M. Guisnet et al. (Eds.), Elsevier, Amsterdam, 1988, pp. 153-163. 31 Y. Orito, S. Imai, S. Niwa and Nguyen G-H, J. Synth. Org. Chem. Jpn., 37 (1979) 173. Y. Orito, S. Imai and S. Niwa, J. Chem. Soc.Jpn., (1979) 1118., (1980) 670 and (1982) 137. 32 J.R.G.. Perez, J. Malthete and J. Jacques, C. R. Acad. Sc. Paris Sene 11, (1985) 169. 33 H.U. Blaser, M. Garland, H.P. Jalett, M. Miiller and U. Pittelkow (Ciba-Geigy), unpublished work. 34 R.M. Dessau, Mobil Oil Co. US 4,554,262 (1985). 35 R. Fomasier, F. Marcuzzi and D. Zorzi, J. Mol. Catal., 43 (1987) 21. 36 A. Tallec, Bull. Soc. Chim. Fr., (1985) 743. 37 F. Beck, Chem.-1ng.-Tech., 48 (1976) 1096. 38 M.P. Soriaga, E. Binamira-Soriaga, A.T. Hubbard, J.B. Benziger and K.W.P. Pang, Inorg. Chem., 24 (1985) 65 and 73.

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39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81

E. Erlenmeyer and H. Erlenmeyer, Biochem. Zeitschr., 233 (1922) 52. G. Bredig and F. Gersmer. Biochem. Zeitschr.. 250 (1932) 414. A.P. Teren’tev and E.I. Klabunovskii, C. A., 49 (1955) 5263. T.L. Jacobs and D. Danker, J. Org. Chem.. 22 (1957) 1424. S. Tsuboyama, Bull. Chem. Soc. Jpn., 35 (1962) 1004. A.G. Osinovski and B.V. Erofeev, Dokl. Akad. Nauk. BSSR, 28 (1984) 006. C. A. 102 (1985) 95926. H. Yamashita. Bull. Chem. Soc.Jpn., 61 (1988) 1213. K. Penzien and G.M.J. Schmidt. Anpew. Chem.. 81 (1969) 628. M. Lahav, F. h u b , E. Gati, L. his&witz and.Z. Ludmer, J. Amer. Chem. Soc.,98 (1976) 1620. M. Marchetti, E. Chiellini, M. Sepulchre and N. Spassky. M h m o l . Chem.. 180 (1979) 1305. A.R. Daniewski and T. Kowalczyk-Przewloka, J. Org. Chem.. 50 (1985) 2976. Y. Tanaka, H. Sakuraba and H. Nakanishi. J. Org. Chem., 55 (1990) 564. B.S. Green, R. Arad-Yellin and M.D. Cohen, Topics in Stereochemistry, 16 (1986) 131. R. Lamartine, R.Pemn, A. Thozet and M. Pemn. Mol. Cryst. Liq. Cryst.. 96 (1983) 57. J.M. Brown, Further Perspective in Organic Chemistry, Ciba Foundation Symp. 53, Elsevier, Amsterdam, 1978, p. 149. V.A. Pavlov. N.I. Spitsina and E.I. Klabunovskii, Dokl. Akad. Nauk. SSSR, Ser. Khim., (1983) 1653(engl. 1501). W.M.H. Sachtler, in L.Augustine (Ed.), Catalysis in Organic Reactions, Chem. Ind., 22 (1985) 189. A. Tai, K. Tsukioka, Y. Imachi, Y. Inoue, H. Ozaki, T. Harada and Y.Izumi, Proc. 8th Int. Congr. Cat. (1984) 531 A. Tai, K. Tsukioka, H. Ozaki, T. Harada and Y.Izumi, Chem. Lett., (1984) 2083. H.U. Blaser, H.P. Jalett, D.M. Monti, A. Baiker and J.T. Wehrli, ACS Symposium on Structure-Activity Relationships in Heterogeneous Catalysis, 1990, Boston. Manuscript in print. J.T. Wehrli, A. Baiker, D.M. Monti, H.U. Blaser, J. Mol. Catal.. 61 (1990) 207. H.U. Blaser, H.P. Jalett, D.M. Monti and J.T. Wehrli. Appl. Catal., 52 (1989) 19. J.T. Wehrli, A. Baiker. D.M. Monti and H.U. Blaser, J. Mol. Catal., 49 (1989) 195. J.T. Wehrli, A. Baiker, D.M. Monti, H.U. Blaser and H.P. Jalett, J. Mol. Catal., 57 (1989) 245. J. Margitfalvi, Federal Institute of Technology, Ziirich, personal communication. K. Deller, Degussa, Hanau, personal communication. J. Strutz, W.C. Heraeus GmbH, Hanau, personal communication. H. Brunner, M. Muschiol. T. Wischert and J. Wiehl, Tetr. Asymm., 1 (1990) 159. J.W. Scott, Topics of Stereochemistry, 19 (1989) 209. R. Sheldon, Chem. Ind. (London), (1990) 212. A. Tai, M. Imaida, T. Oda and H. Watanabe, Chem. Lett.,(1978) 61. A. Tai, H. Watanabe and T. Harada, Bull. Chern. Soc.Jpn., 52 (1979) 1468. M. Nakahata, M. Imaida, H. Ozaki, T. Harada and A. Tai, Bull, Chem. Soc.Jpn., 55 (1982) 2186. J. Bakos, I. Toth and L. Marko, J. Org. Chem, 46 (1981) 5427. Catalogue of Wako Pure Chemicals Indusaies (Osaka), 22. Ed. p.471 and 547 (cited in [l]). M. Ishii, Kawaken Fine Chemicals Co., personal communication, S.K. Boyer, R.A. Pfund, R.E. Pomnann, G.H. Sedelmeier and Hj. Wetter, Helv. Chim. Acta, 71 (1988) 337. G.H. Sedelmeier, H.U. Blaser and H.P. Jalett, EP 206993 (1986). E. Broger, Hoffmann-LaRoche, Basel, personal communication. M. Garland, H.P. Jalett and H.U. Blaser, these prepxints. a. E. N. Jacobsen. I. Marko, W. S. Mungall. G. Schrijder and K. B. Sharpless, J. Amer. Chem. Soc., 110 (1988) 1968 and 111 (1989)737. b. M. Garland and H.U. Blaser, J. Amer. Chem. Soc., 112 (1990) 7048. R.M. Laine, G. Hum, B.J. Wood and M. Dawson, Stud. Surf. Sci. Catal., 7 (1981) 1478. P.B. Wells, Faraday Discuss. Chem. Soc.. 87 (1989) 1; J.M. Thomas, Angew. Chem. Adv. Mater., 101 (1989) 1105. M. Bartok, G. Wittmann, G.B. Bartok and G.Gondos, J. Organomet. Chem., 384 (1990) 385.


93

CATALYSIS WITH IMMOBILIZED ENZYMES : HYDROLYSIS AND ESTERIFCATION BY RHlZOPUS ARRHlZUS

C. GANCET Groupement de Recherches de Lacq. Elf Aquitaine, BP 34,64170 Artix, France

SUMMARY The dead cells of the mycelium of Rhizopus arrhizus constitute a naturally immobilized lipase very active in organic solvents. This immobilized enzyme was used for hydrolysis and synthesis of ester bonds : triglycerides hydrolysis. and interesterification, esters and glycerides synthesis. More recently, the catalytic system has been applied in drug synthesis to the resolution of racemic esters with a good enantioselectivity. Under non-aqueous or micro-aqueous conditions, this fungal catalyst shows high efficiency and good operational stability. As neither purification, nor immobilization step are needed, total cost is low, and fully compatible with industrial uses.

INTRODUCTION In standard aqueous media, hydrolases are enzymes which are able to hydrolyse

covalent bonds (Fig. 1.). Three classes of hydrolases are used industrially : osidases (glycosidic linkage hydrolysis). proteinases (peptidic linkage hydrolysis) and esterases (ester linkage hydrolysis). Lipases are triglyceride esterases, and as these substrates are insoluble in water, lipases are interfacial enzymes. Under these conditions, the hydrolytic reaction versus the synthetic reaction is favoured'. However. ester bond synthesis in aqueous conditions has been reported, but low yields were obtained. Since 1978, numerous works that show the ability of lipolytic enzymes to be active in organic solvents have been ~ u b l i s h e d ~Moreover. -~. it appears that in certain conditions the stability of the enzyme is enhanced b y the low content of water. In such conditions, as the organic substrates are soluble in the reactional media which is therefore homogeneous, continuous processes can be designed in a very classical way.

94

Fig. 1. Hydrolases

Lipases, Esterases E.C.3.3.1,

Most of the lipases are Serine enzymes, and it is clearly admitted today that the mechanism of the enzyme includes an acyl-enzyme intermediary which occurs between the fatty acid of one substrate and the Serine hydroxyl group of the active site (Fig. 2,). Following the reaction. this intermediary is attacked by a nucleophile which is for example water in the case of hydrolysis. Alcohols. thiols. and sometimes amines have been used according to the same scheme. Lipases are proteins which molecular weight is in most cases between 40 and 50 kDa. which corresponds about 300 amino-acid residues. Isoelectric points are between 4 and 7. and optimal p H values are between 5 and 8. according to the origin. On the other hand, lipases are glycoproteins which glycosylated hydrophile part is located opposite to the hydrophobic zone around the active site. The lipase from the yeast Candido. for example, contains 4.2 % b y weight of sugars. Lipases may show different types of specificity towards their substrates. Position on the alvcerol The enzyme can be 1.3 specific. like the mammals pancreatic lipase. or aspecific. like the Pseudomonos fluorescens one. Chain lenath of the fattv

a

The formation of the acyl-enzyme intermediary is more or less rapid according to the affinity between the lipase site and the considered chain. For example, Penicillium and Aspergillus lipases prefer short chains, when Rhizopus or Pseudomonas have broader

mectra.

95

R-C-OH

8

Fig. 2. Acyl-enzyme mechanism

Chain unsaturation of the fattv acid In a very similar way. acyl-enzyme formation depends upon the unsaturation level of the chains, and upon the position of the double bond(s) on the chains. Geotrichum condidum lipase is known to prefer fatty acids with a double bond on the C9, like oleic acid. Nature and structure of the nucleoDhile In the case of Rhizopus arrhizus, primary alcohols have a good reactivity when they are not too much sterlcally hindered, but secondary alcohols are less reactive and tertiary ones do not react at all. Enantioselectivity As lipases are proteins, they are able to act as chiral catalysts, and for example to

hydrolyse specifically one of the isomers in a racemic mixture of esters. Lipases can be found in animals, vegetals and microorganisms. Historically the pancreatic lipase of mammals was the first to be studied, but today, only the enzymes produced by microorganisms are susceptible to industrial development, under different forms according to the considered process.

RHlZOPUS ARRHlZUS MYCELIAL LIPASE

Rhizopus arrhizus (ATCC 24563) is a filamentous fungus, known to be producer of an exocellular lipase. According to the culture medium and especially to the carbon and nitrogen sources the lipolytic activity can remain bound to the cells.

96 After drying and delipidation this biomass c a n be considered as a naturally immobilized enzyme (Fig. 3.). The hydrolytic activity measured on olive oil in di-isopropylether is around 75 to 200 micromoles per g of dry mycelium and per mn. The chain length specificity spectrum is broad. as shown before (from C14 to C22)

300

5 250

c 1 mn

Oil Water Acetone MTBE

10 01.5 15 73.5

10 ml

. Mycelium

0

10

20

30

40

50

60

Time, mn 1 Unit = 1 Frnole FA / rnn (typically,75-200 U/g)

Fig.3. Mycelium activity ORGANIC MEDIA Organic solvents used must be compatible with the enzymatic activity. not take place in the reaction, be good solvent of the substrates, have a low cost, and be the more harmless possible. The solvents commonly used in the literature are aliphatic alkanes, or similar compounds of low polarity. Aliphatic ethers that were used in this work, show less hydrophobicity than alkanes, and thus allow introduction of water for hydrolysis reactions. For interesterification experiments, trichloro-trifluoro-ethane was used, as water is not a substrate for the reaction (Fig. 5,). Tertio-amylic alcohol was retained for glycerides synthesis, as a solvent able to dissolve either fatty acids or triglycerides and glycerol. ENZYMATIC VERSUS CHEMICAL CATALYSIS Enzymes must be preferred in the following situations : -low stability of the substrateW -needed cleanliness of the reaction -needed "natural" character of the reaction6

97 Fig. 4. Production of fatly acids by triglycerides hydrolysis

Triglycbrides + H20

Fatty acids + glycerol

-b

MTBEIAcetone 85-1 5 v/\ 30°C 4 x 7 5 m n Yield : 88-97 Yo

1

b

Water

T..

n

Segmented reactor : (a) triglycerides solution : tallow 20, water 1.5, acetone 15, MTBE 63.5(Yop/p) ; (b) adjustment of water content.

.*.....

807

; !i

a >

C

8

3 20 1

ol

1

0

0.5

1

1.5

2

2.5

3

3.5

4

Time, months Operational stability of Rhizopus arrhizus mycelium on continuous hydrolysis of triglycerides

98

-needed selectivity Fig. 5. Relative activity of Rhizopus arrhizus mycelium in organic solvents I

?rificationof oleic acid and octar Solvent Freon 11

Activity %

103

Freon 112

995

Freon 113

97,2

Perfluoroheptane

55

Diphenyl ether

89

Dibutyl phtalate

79.6

Hexane

732

Methyl-t-butyl ether (MTBE)

66.2

Dimethoxy propane

52.6

Tributyl phosphate

51,7

Dioxane

132

DMF

0

TRIGLYCERIDES HYDROLYSIS The reaction is carried out in a continuous fixed-bed reactor with several segments. Each segment contains a load of dry Rhizopus arrhizus mycelium added with silica to ensure good flow properties. The substrate solution is injected through the first segment, then water content is adjusted as water solubility increases when diglycerides appear, and the reaction goes on through the following segments (Fig. 4.). Estimated residence time is about 1 hour per segment. and obtained conversion rates are as follow. Total water added reaches about 5 times the stoechiometry; e.g. in case of primrose oil hydrolysis, water added at each step was 7.5. 11, 5.6 and 4.4 g per 100 g of triglycerides. Operational stability was tested through tallow hydrolysis. It appears that constant yield was maintained during several months, showing the high stability of the mycelial lipase in these conditions4. Initial water solubility in the reactional medium is a key point, and two systems were designed to increase this parameter. The first solution is to use micro-emulsions of water in the solvent with the help of di-octyl-sulfosuccinate(AOT) as tensio-active agent. Good results con be obtained, but separation and recycling of the detergent are difficult to extrapolate at larger scales.

99 The solution we use is the addition of a polar co-solvent as a ketone. In this case, the activity of the catalyst is decreased by the co-solvent, but a convenient compromise with the increase of water solubility can be found.

INTERESTERIFICATIONOF TRIGLYCERIDES5 The interesterification of fats and oils is the only way to create new hybrid products with new physical, and especially

new rheologlcal properties. Chemical

interesterification is well known, but has no position or chain specificity, and is not very clean. With lipases in micro-aqueous media, the exchange of acyl groups between the different triglycerides may be oriented, and designed according to the specificity of the enzyme. A single segment mycelium reactor was used with trichloro-trifluoro-ethane as

solvent (Fig. 5.). For a concentration of 25 % (V/V) of triglycerides, full interesterification was obtained within 1 hour of residence time. The productivity of the system can be estimated to 1.5 kg of interesterifiedproduct per hour and per kg of dn/ mycelium. The operational stability was measured through monitoring of a triglyceride probe during 2.5 months on a continuously running reactor. The decrease of activity was about 15 % per month.

As in the case of hydrolysis, water plays a role. But here, it's only a catalytic role, and the water concentration needed is about 100 ppm for good results. If it increases, hydrolysis takes place, and if it decreases, the activity of the enzyme can literally be switched off.

MONO AND DIGLYCERIDES SYNTHESIS For hydrolysis or synthesis of esters, and for interesterification of triglycerides, solubility of the substrate is good in the usual low polarity solvents. When dealing with glycerides synthesis either by direct esterification of fatty acids b y glycerol or by glycerolysis of triglycerides, glycerol is poorly soluble in these solvents, and another medium must be used. Tertiary alcohols, and especially tertio-amylic alcohol were found to give homogeneous solutions of both glycerol and fatty acids.

100 Fig. 6. Mono and diglyceridessynthesis by direct coupling of acid and glycerol or by glycerolysis of triglycerides

Fatty acid + glycerol or Glycerol + triglycerides

-

Mono and diglycerides

t-amyl alcohol

Direct svnthesk 1 mole C18:l for 3 moles glycerol

Conversion in monoolein : 44.7 %(molar) diolein : 2.0 %

1 "mole" of tallow for 10 moles of glycerol

Conversion in monolein : 38.8 %(p/p, monoolein/suif) Operational stability Glycerolysis of tallow

$2

50

0

20

40

60

Time, days

00

I

101 Two segments of the same fixed bed reactor were used. with dehydration of the reactional medium on molecular sieve between each of them. With oleic acid, and an excess of 3 moles of glycerol per mole of acid, the yield was 44.7 % (molar) of monoolein after 2 hours. At the same time, only 2 % of di-olein were obtained (Fig. 6,). With the same system applied to the transesterification of tallow, and an excess of 10 moles of glycerol per mole of triglyceride. a conversion of 38.8 % (weight) in

monoglycerides was observed, the rest being diglycerides from the initial substrate. The stability of the mycelium under these conditions is also very interesting : a glycerolysis reactor was run continuously during 3 months with very little loss of activity.

RESOLUTION OF RACEMICESTERS~

Enzymes can be stereospecific. and lipases as esterases can act as very efficient catalysts even on molecules which ester groups are not glycerides. The hydrolysis of such esters is not always possible, especially if they are sterically hindered, or if the carboxylic acid involved is aromatic, and the carbonyl group conjugated. Esters of benzo'ic acid, for example are very difficult to hydrolyse. The stereospecificity may be carried. either by the carboxylic acid moiety, or by the alcohol part of the molecule. There is no rule up to now to predict if a given molecule will be a substrate, and if the enzyme will express its stereospecificity toward it. Screening of lipases and esterases is the only method to select firstly the active enzymes, and secondly the specific ones that give the wanted isomer. Very often, the enantiospecificity is not absolute, and kinetics play a major role in the efficiency of the enantiomer selectivity. The example we show here is the resolution of a racemic mixture of epoxy-esters according to the following reaction :

0

Lipase

RLCOOCH3 H20 O H Rl,/-kOOCH3 H

+

H O R q o C O O H H

102

Fig. 7. Resolution of a racemic mixture of esters

0 R ~ ~ C O O C --w H ~

H H

0 R-/~_H

+...

mycelium MTBEIAcetone 85-15

Best enantioselectivity factor E in these conditions :

E = k+k-

Ln(1- p ) (1- ee ) =

Ln(1- p ) (l+ee )

avec ee = enantiomeric excess of the substrate et p = global hydrolysis yield

Variation of the enantioselectivity factor E

103 Among the 50 enzymes screened, Rhizopus arrhkus mycelial lipase showed the best results in terms of E, which is the enantioselectivity coefficient depending of the enantiomeric excess and the conversion (Fig. 7J7. Methyl-tertiobutyl-ether1 acetone was found to be a good solvent of the racemic

epoxy-ester, and thus is used for the reaction, as for triglycerides hydrolysis. Batch conditions are used with a ratio enzyme/substrateof 2 (weight), during 1 to 24 hours at 25 "C. Progress of the reaction is measured b y proton NMR with an internal standard, and enantiomeric excess is obtained through chiral HPLC analysis of the product. A coefficient E as high as 37 has been obtained with a yield of 02 % of the theoretical

maximum, and an enantiomeric excess of 99.9b.

CONCLUSION Rhizopus arrhizus dead mycelium was found to be very active in organic solvents as a naturally immobilized lipase. Triglycerides hydrolysis and interesterification, esters and glycerides synthesis, natural flavour esters preparation and racemic mixtures resolution in pharmaceutical drugs synthesis are among the successfully designed processes, each of one with a specific reactional medium. Under these different conditions, the fungal catalyst shows high efficiency and stability, and as either purification, or immobilization are avoided, operational cost is low, and thus compatible with industrial use.

REFERENCES P. Desnuelle, The Enzymes, P. Boyer (Ed.),Vol. VII, 1972,575. G. Bell, J.A. Blain, J.D.E. Patterson, C.E.L. Show and R. Todd, Ester and glyceride synthesis b y Rhizopus arrhizus mycelia, Fems Microbiol. Lett., 3, 1978,223-225. G. Bell, R. Todd, J.A. Blain, J.D.E. Patterson and C.E.L. Show, Hydrolysis of triglycerides by solid phase lipolytic enzymes of Rhizopus orrhizus in continuous reactor systems, Biotech. Bioeng., 23,1981,1703-1719. C. Gancet and C. Guignard. Proc. Int. Symp. Biocat. in Org. Media, Wageningen. The Netherlands, December 7-10,1986.Studies in organic Chemistry, C. Laone (Ed.),Elsevier, 29,1987,261-266. C. Gancet. C. Guignard and P. Fourmentraux. Process for carrying out enzymatic reactions in an organic solvent, US. Pat. 4855233,1989.

C. Gancet, Synthese enzymatique d'esters naturels, Societt5 Francaise de

104

Chimie, Third national meeting, Nice, France, 1988. 7

C.S. Chen. Y. Fujimoto, G. Girdaukas and C.J. Sih. Quantitative analysis of

biochemical kinetic resolution of enontiomers. J. Am. Chem. SOC.. 104. 1982, 7294.

7299. 8

C. Gancet, J.A. Laffitte. C and C. Soccol, Procede de preparation d'un

diastereoisomere de derives glycidiques, Demande de Brevet Francais 8914938.1989.


105

HYDROGENATION OF BENZALDEHYDE TO BENZYL ALCOHOL IN A SLURRY AND FIXED-BED REACTOR M. Herskowitz

Dept of Chem. Eng., Ben Gurion University , Beer Sheva, Israel ABSTRACT A kinetic model was developed based on data obtained over a range of temperatures and hydrogen pressures. The kinetic parameters were expressed as a function of temperature. The kinetic model was applied to the analysis of the trickle-bed data. Predictions of a matheniatical model of the trickle-bed reactor were compared with data obtained at two temperatures and a range of pressures. The intraparticle mass transfer resistance was very important. INTRODUCTION The catalytic hydrogenation of benzaldehyde is a model reaction of hydrogenations of aromatic aldehydes. The principal reaction is: C7H,0+H2

+ C,H,O

There are two side reactions which are thermodynamically feasible: C,H,O

+ 2H2 + C7H, + M, 0

C7H8+ Id2

-+

C,H,

+ CH,

Benzaldehyde has been hydrogenated on Pd/C( l), Raney nickel and nickel boride (2) catalysts. Baltzly (Ref. 1) measured the rate of hydrogen pressure decrease as a function of time in a batch reactor. He found that the rate of reaction was zero order for both reactants at hydrogen pressures above 3 atm. and benzaldehyde concentrations above 1.O gniol/l. The rate data was obtained at 22°C in various solvents. No measurements of the products and the benzaldehyde were reported. For the 3% Pd/C catalyst, the rate of reaction was 1.6 x gniol/g.min, independent of thc type of solvent. Schreifels et al.( Ref. 2) measured the rate of benzaldehyde hydrogenation at 70°C and 6 atm., using Raney nickel. They found that the rate of reaction

106

depended strongly on the reactant to catalyst ratio. The reported rate of reaction was in the range 1.7 x

-

1.3 x 10-3 gmol/g.min. No information on the

selectivity of the products was given. Industrial gas-liquid hydrogenation reactions are carried out in slurry and trickle-bed reactors (Ref. 3). Modeling of the latter has been advanced significantly in the last two decades (Refs. 4-6). Predictions of trickle-bed reactors performance were in good agreement with experimental data (Ref.7). The purpose of this study is twofold: to develop a kinetic expression for nickel catalysts and to test the perfomiance of a trickle-bed reactor as compared with model predictions. EXPERIMENTAL Hydrogenation runs were carried out in a dead-end 300 cm3 batch autoclave manufactured by Autoclave Engineers, Erie, Pa. Description of the experimental setup has been given elsewhere (Ref. 8). The bakh -recycle

Q I

Figure I : Schematic diagram of trickle-bed system: 1. trickle-bed. 2. separator.

3. liquid pump. 4. back pressure regulator. 5 . thermostatic bath.

107

trickle-bed reactor is described schematically in Figure 1. The liquid was pumped from a 2-liter glass separator through a rotameter to the reactor, a 2.54 ID stainless steel tube equipped with a jacket. The reactor was packed with a layer of alumina pellets, a layer of nickel catalyst pellets and another layer of alumina pellets. The pressure in the reactor was controlled by a back pressure regulator. The reactor temperature was maintained by circulating oil through the jacket from a themiostatic bath and it was measured by a thermocouple. The benzaldehyde was 99.5% pure, as measured by GC and HPLC. Its contact with air was avoided so as to eliminate the possibility of oxidation. The purity of hydrogen was better than 99.7%. Two nickel catalysts were used, both provided by Engelhard, de Meem B.V. Their properties are given in Table 1. RESULTS AND DISCUSSION Kinetic Study: The operating conditions in the kinetic study are given in Table 2. In all experiments the overall mass balance was checked, retaining only samples which gave deviations of less than 3%. Plots of the benzaldehyde concentration against time of reaction yielded a linear dependency at concentrations above about 1.5 g.mol/l. Below this value, the pseudo-zero-order with respect to benzaldehyde changed to a pseudo-first-order, as illustrated in Figure 2. The kinetic data was obtained only in the zero-order range. The kinetic data were measured at an impeller speed of 2000 RPM. In the range of 1200-2000 RPM no changes in the rate of reaction were measured indicating that the gas-liquid mass transfer resistance was negligible. Furthermore, the rate of reaction increased linearly with catalyst concentration, as shown in Figure 3. The catalyst particle size was in the range of 35-70 pm. Several runs carried out with 10 pm particles gave similar rates of reaction, which means that intraparticle mass transfer resistance was negligible. A semilogarithmic plot of the rate constant against the reciprocal of the absolute temperature presented in Figure 4 yielded an activation energy of 13.2 kcal/gmol. Kinetic model The rate of reaction order with respect to benzaldehyde was found to

108

Tn353.1 K P:446 kPa 2.5 56 catalyst

0.024 I

Time

20

, min

.

. 30

.

, 40

,

50

catalyst concentration, g/l

2.Typical hydrogenation run. 3.Effect of catalyst concentration on reaction rate change from zero to one. Benzyl alcohol has no effect on the rate. The effect of hydrogen concentration was studied by measuring the rate of reaction as a function of hydrogen pressure. The rate data are plotted in Figure 5 . On the basis of those results, a kinetic Langniuir-Hinshelwood model is proposed, which assumes that the surface reaction is rate limiting.

r=

KHPH 1 + KB CB (1 +.I KH PH)2 kKBCB

where C , is the benzaldehyde concentration, P, is the hydrogen pressure, K, and KH are the benzaldehyde and hydrogen adsorption constants, respectively and k is the rate constant. In the range of conditions studied here, K, is of the order of 1 (gmol/l)-' which yields a zero-order at high benzaldehyde concentration. r=k

K H pH

(1

+ .IKH PH)'

= k,,

This expression was employed in the analysis of the rate data in Figure 5. The two parameters k and KH were expressed as a function of temperature, by

109

fitting simultaneously the rate data at three temperatures (Figure 5). The lines in Figure 5 are the predicted rate constants using the best values of the constants:

(3)

k = 2.18 x lo8 exp (-lOOOO/T) kgnio1kg.s

temperature ,K C

,013

-E

I

C C

I

E

P=446 kPa 2.5 % catalyst

.

353.1 343.1

CI

5

A

5

-

2

0

2

.MoI i 0.0028

.

, 0.0027

.

,

.

0.0028

,

.

0.0029

0.0030

0

200

400

800

1000

BOO

-1

1IT ,K

4. Rate constant dependency on temperature.

Hydrogen pressure, kpa

5. Effect of hydrogen pressure

on the reaction rate.

K,

= 1.85 x 1O-Io exp (5500/T) kPa-'

(4)

As expected, k increases significantly with temperature while K,

decreases with temperature. Trickle-bed studv The operating conditions are listed in Table 2. The results given in Table

3 were obtained with one batch of catalyst packed in the reactor. The liquid was drained from the system and replaced with pure benzaldehyde three times. After an initial decrease in catalyst activity - of about 30% -no significant decay was measured during the run. The limiting reactant in the reactor is hydrogen. All mass transfer resistances have to be accounted for. The hydrogen flux from the gas to the liquid, to the external pellet surface and inside the pellet are equal, assuming complete wetting of h e pellets, as expected under those conditions (Ref. 4).

1200

110

CH, and CHs are the hydrogen concentration in the liquid and the external pellet surface, respectively.

H is the Henry’s constant, estimated to be 2.3 x 1 0 4

kPa/(kmol/m3) (9). k,a, and k, as are the gas-liquid and liquid-solid mass transfer coefficients, respectively. q is the effectiveness factor, which can be expressed as a function of the Thiele modulus:

- 6 (KH H CHs)l/2 + 6 (1 + K H H CHS)

- 112 112

) In (1+ (KIj H CHS) 1’2

1

(7 1

The details are given elsewhere (Ref.lO). The mass balance for the benzaldehyde is:

where m is the mass of the catalyst and V is the liquid volume. Over the range of zero-order with respect to benzaldehyde, equation (Ref.9) can be integrated to give:

The calculation of ro in equation (9) requires the estimation of k,a,,

D,. kLaL and k, as

k, as and

were estimated using the correlations recommended

elsewhere (Ref. 4). The value of D, was calculated from the equation:

(10) where

E,,

is the pellet porosity, DH is the hydrogen diffusivity and T is the

tortuosity factor. Their values are given in Table 3. The predicted values are in

111

TABLE 1 Properties of nickel catalysts Name

Composition %Ni

Surface Area m2/g

Pellet density kg/m3

Porosity

1404 5852

68 56.7

130 239

1.72 1.34

0.67 0.66

TABLE 2 Range of operating conditions 1. kinetic studv: catalyst conc. (kg/m3) :25 - 50 Temp (K) 1343 - 373 Pressure (kPa) A70 - 1120 2.trickle-bed study: Liquid velocity (m/s) :0.004 Gas velocity (m/s) :0.004 -0.008 Temp.(K) :353 - 373 Pressure (kPa) 1220- 580 170 g catalyst and 1000 cm3 liquid.

TABLE 3 Comparison of trickle-bed data with model predictions k,a, = 0.12 s-l ksaS= 0.70 s-l D, =8 x m2/s

T,K

353.1

373.1

P, kPa

360 580 220 360 580

z =3

- AC/At, measured

kmol/m3.s predicted

17

7.8 x 1.3 x 8.8 x 1.5 x 2.5 x

8.2x 1.1 x 9.0 x 1.4 x 2.2 x

0.042 0.04 1 0.043 0.04 1 0.040

10-2 10-1

lo-' 10-1

10-2 10-2 10-1 10-1

112

good agreement with the data. The effectiveness factor is very low, indicating that intraparticle mass transfer resistance is vcry significant. The gas-liquid mass transfer resistance is also important, as expected. On the other hand, the liquid-solid mass transfer resistance is negligible. As a result, the rate of reaction i n the slurry reactor is about 50 times higher than that in the trickle-bed. Thereforc, i n cases of such high rates of reaction, the slurry reactor is a better choice, although the gas-liquid mass transfer and the filtration of the catalyst may be a problem. CONCLUSIONS The kinetic model developed in this study can be used to design and analyze various chemical reactors for the hydrogenation of benzaldehyde. Although it is based on a Langmuir-Hinshelwood mechanism, it does not prove that this is the correct mechanism. The analysis of the trickle-bed runs indicate that intraparticle mass transfer resistance is very significant. Gas-liquid mass transfer

may ~ I S O have a

significant resistance. This is an important consideration in the decision proccss of using a slurry or a trickle-bed reactor. REFERENCES 1. R. Baltzly, Studies on catalytic hydrogenations, J. Org. Cheni., 41 (G), (1976), 920-28. 2. J.A. Schreifels, P.C. Maybury and W.E. Swartz, Comparison of the activity and lifetime of Raney nickel and nickel boride in the hydrogenation of various functional groups, J. Org. Chem., 46(7), (1 98 I ) , 1263-69. 3. P.A. Ramachandran and R.V. Chaudhari, Three-Phase Catalytic Reactors, Gordon and Breach Science Publ., New York, 1983. 4. M. Herskowitz and J.M. Smith, Trickle-bed reactors: a review, AIChE J., 29, (1983), 1-18. 5 . R.M. Koros, Engineering aspects of trickle-bed reactors, in :H.I. dc Lasa (Ed.), Chemical Reactor Design and Technology, M. Nijhoff Publ., Dordrecht, 1986, pp.579-630. 6. A. Gianetto and F. Berruti, Modelling of trickle-bed reactors, ibid., pp.631-685. 7. S. Goto and J.M. Smith, Trickle-bed reactor performance, AIChE J., 21, (1975), 706-19. 8. J. Wisniak, M. Herskowitz, K. Leibowitz and S. Stein, Hydrogenation of xylose to xylitol, Ind. Eng. Chem., Prod. Res. Dev., 13, (1974), 75-80. 9. M. Herskowitz, J. Wisniak and L. Skladman, Hydrogcn solubility in organic liquids, J. Chem.Eng. Data, 28, (1 983), 164-6 10. M. Herskowitz, Modelling of a trickle-bed reactor - the hydrogenation of xylose to xylitol, Chem. Eng. Sci., 40(7), (1983, 1309-1 1.

M. Guisnet et al. (Editors), Heterogeneous Catalysis and Fine Chemicals I1 o 1991 Elsevier Science Publishers B.V., Amsterdam

113

STRUCTURE AND CATALYTIC P R O P E R T I E S I N HYDROGENATION OF VALERONITRILE OF RANEY NICKEL PREPAKED FROM C r AND Mo DOPED Ni2A13 ALLOYS.

M. BESSON',

D. DJAOUADI',

J.M. BONNIER',

S. HAMAR-THIBAULT'

and M. JOUCLA3

' L a b o r a t o i r e d ' E t u d e s Dynamiques e t S t r u c t u r a l e s de l a S e l e c t i v i t e ( L E E S 1 ) CNRS URA 332 - U n i v e r s i t 6 Joseph F o u r i e r - BP 53X - 38041 GRENOBLE CEDEX (France). L a b o r a t o i r e Therrnodynamique e t P h y s i c o - C h i m i e M e t a l l u r g i q u e s (LTPCM) - CNRS URA 29 - BP75 - 38402 SAINT-MARTIN-D'HERES CEDEX ( F r a n c e ) . l l n i t e M i x t e Rh6ne-Poulenc I n d u s t r i a l i s a t i o n 166 - 69151 DECINES-CHARPIEU CEDEX ( F r a n c e ) .

-

24, Avenue Jean J a u r e s - BP

SUMMARY Raney n i c k e l c a t a l y s t s , unpromoted o r doped w i t h molybdenum o r chromium, The s t r u c t u r e and were p r e p a r e d f r o m t h e p r e c u r s o r a l l o y s o f t h e t y p e N i A1 phase c o m p o s i t i o n o f t h e c a t a l y s t s have been d e t e r d n e 3 d . H y d r o g e n a t i o n o f v a l e r o n i t r i l e a t 90°C and 1 . 6 MPa i n c y c l o h e x a n e was p e r f o r m e d t o e v a l u a t e c a t a l y s t a c t i v i t i e s and t h e r e l a t i v e amounts o f amines f o r m e d . D o p i n g c a t a l y s t s b y chromium i m p r o v e d r e a c t i o n r a t e s and y i e l d s o f p r i m a r y amine, whereas molybdenum a d d i t i o n was i n e f f e c t i v e .

.

INTRODUCTION The h e t e r o g e n e o u s c a t a l y t i c h y d r o g e n a t i o n o f n i t r i l e s has been u s e d i n amine p r e p a r a t i o n f o r a l o n g t i m e . G e n e r a l l y t h e p r o d u c t s a r e a m i x t u r e o f p r i m a r y , s e c o n d a r y and t e r t i a r y amines,

t h e n a t u r e o f w h i c h depends on t h e

c a t a l y s t used as w e l l as on r e a c t i o n c o n d i t i o n s ( r e f s . 1,Z).

The s e l e c t i v i t y

o f n i t r i l e hydrogenation i s o f importance, p a r t i c u l a r l y i n the production o f p r i m a r y amines. I n such r e a c t i o n s t h e c a t a l y s t s most o f t e n p r o p o s e d a r e Raney nickel catalysts (refs. 1-3). To promote

the

activity

and

selectivity

of

Raney n i c k e l

catalysts,

a l l o y i n g o f t h e s t a r t i n g Ni-A1 a l l o y w i t h m e t a l was o f t e n used. F o r i n s t a n c e , Montgomery ( r e f . 4 ) p r e p a r e d c a t a l y s t s b y a c t i v a t i n g t e r n a r y a l l o y powders o f A1 ( 5 8 w t % ) - N i ( 3 7 - 4 2 w t

X) -

M (0.5 w t % ) where M

A l l promoted c a t a l y s t s t e s t e d were

=

Co, C r ,

Cu, F e and Mo.

more a c t i v e t h a n t h e r e f e r e n c e c a t a l y s t ,

i n h y d r o g e n a t i o n o f b u t y r o n i t r i l e . Molybdenum was t h e most e f f e c t i v e p r o m o t e r . W i t h Cr o r T i ,

h y d r o g e n a t i o n o f i s o p h t a l o n i t r i l e on Raney n i c k e l o c c u r r e d a t

l o w e r optimum t e m p e r a t u r e t h a n w i t h non a c t i v a t e d n i c k e l

(ref.

5).

I t was

shown t h a t a d d i t i o n o f T i o r Co t o Raney n i c k e l s u p p r e s s e d t h e f o r m a t i o n o f secondary amine ( r e f . 6 ) . T h i s work has been u n d e r t a k e n t o compare promoted Raney n i c k e l c a t a l y s t s

114

( M = Cr o r Mo). The

o b t a i n e d f r o m s t a r t i n g a l l o y s of c o m p o s i t i o n N i 2 - x M x A 1 3

m i c r o s t r u c t u r e o f t h e c a t a l y s t s was determined and t h e b e h a v i o u r o f t h e s e c a t a l y s t s i n terms o f r a t e o f h y d r o g e n a t i o n and s e l e c t i v i t y was i n v e s t i g a t e d i n t h e h y d r o g e n a t i o n o f v a l e r o n i t r i l e as a model m o l e c u l e . EXPERIMENTAL

Preparation o f c a t a l y s t s The undoped c a t a l y s t was prepared f r o m t h e monophasic c r y s t a l l i z e d Ni2A13 a l l o y ( r e f . 7 ) . The molybdenum and chromium promoted c a t a l y s t s were prepared from a l l o y s w i t h t h e composition Ni2-xMxA13 M = C r ( x = 0.07 o r 0.11)

where M = Mo (0.05,(x,(0.4)

and

( r e f . 8 ) . The c a t a l y s t s were t h e n prepared

d e s c r i b e d p r e v i o u s l y ( r e f . 91,

as

by l e a c h i n g t h e crushed a l l o y s i n a 6N sodium

h y d r o x i d e s o l u t i o n a t b o i l i n g temperature.

The c a t a l y s t s were k e p t under a

molar s o l u t i o n o f NaOH. Characterization o f catalysts The

specific

adsorption

and

surface the

areas

metallic

were

determined

surface

areas

by

by

means

using

of

nitrogen

adsorption

of

3 - m e t h y l t h i o p h e n i n l i q u i d phase ( r e f . 9 ) . The b u l k c o m p o s i t i o n o f each sample was determined by chemical a n a l y s i s and expressed by t h e atomic r a t i o s A l / N i and M / N i

.

The c a t a l y s t s were observed by t r a n s m i s s i o n e l e c t r o n microscopy

(JEOL 200 C X - T E M )

and analysed e i t h e r g l o b a l l y

o r at point

-

l a t e r a l r e s o l u t i o n o f 1 . 5 nm by means o f a STEM ( V G energy

-

level with a

HB 501) connected t o an

d i s p e r s i v e X-ray a n a l y s e r ( E D A X ) .

V a l e r o n i t r i l e hydrogenation The procedure was d e s c r i b e d i n d e t a i l i n a p r e v i o u s work ( r e f s . 1 0 - 1 1 ) . Hydrogenation was c a r r i e d o u t i n l i q u i d phase i n a 250 m l a u t o c l a v e w i t h a magnetic s t i r r e r (1600 rpm), a t c o n s t a n t p r e s s u r e ( 1 . 6 MPa) and t e m p e r a t u r e (90°C).

The

catalyst

was

carefully

washed

with

cyclohexane. A f t e r l o a d i n g t h e c a t a l y s t ( 0 0 . 5

water,

isopropanol

and

g ) and cyclohexane (135 m l ,

HPLC grade and d i s t i l l e d ) t h e a u t o c l a v e was f l u s h e d w i t h hydrogen. The m i x t u r e was p r e t r e a t e d under hydrogen p r e s s u r e (1.6. MPa) a t room t e m p e r a t u r e f o r 1 h. Temperature was r a i s e d t o 90°C and f r e s h l y d i s t i l l e d v a l e r o n i t r i l e ( 1 0 m l ) was i n t r o d u c e d . The s t a r t o f hydrogenation.

Samples

of

s t i r r i n g was c o n s i d e r e d t o be t h e s t a r t o f t h e 0.5

ml

were

taken

chromatography equipped w i t h a 10 % Carbowax 20 M

and 7-

analysed

by

FID

gas

10 % KOH on Chromosorb WHP

80-100 packed column ( 4 m x 1 / 8 " ) . Hexadecane was u s i d as i n t e r n a l s t a n d a r d .

115 RESULTS Characterization o f c a t a l y s t s The d e t a i l e d c h a r a c t e r i z a t i o n o f t h e c a t a l y s t s was d e s c r i b e d elswhere ( r e f s . 12,13). We summarize some o f t h e s e r e s u l t s . (i ) Composition o f p r e c u r s o r a1 l o y s

I n t h e s e doped a l l o y s , t h e major phase (P,) t h e N i 2 A 1 3 phase and a small amount o f d i s s o l v e d C r (

had t h e c o m p o s i t i o n of

'L

W)

1.5 a t

and Mo ('L

0.2 a t % ) . T h i s p r i m a r y phase was surrounded by a small amount o f a b i n a r y

i n t h e case o f C r a d d i t i o n , and o f two phases i n t h e case o f

phase (-Cr4A19)

+ 0.3 % Mo and a t e r n a r y phase P3

= NiAl

Mo a d d i t i o n (P,

(NiMo)A13). The

=

p r o p o r t i o n s o f t h e v a r i o u s phases i n t h e a l l o y s v a r i e d and t h e q u a n t i t y of phase P1 decreased s i g n i f i c a n t l y when t h e Mo c o n t e n t i n c r e a s e d . (ii) Composition o f c a t a l y s t s -

When t h e s e doped a l l o y s were leached, t h e d i f f e r e n t phases p r e s e n t i n t h e p r e c u r s o r a l l o y gave r i s e t o d i f f e r e n t agglomerates i n t h e c a t a l y s t . EDX m i c r o a n a l y s i s performed on Cr-doped c a t a l y s t showed a l a r g e number o f

agglomerates formed f r o m t h e p r i m a r y N i 2 A 1 3 phase.

(Al/Ni

0.22,

Cr/Ni-

0.08). However some C r r i c h zones were a l s o observed, formed f r o m t h e C r - A 1 rich

phase mentionned.

The c a t a l y s t s

contained

oxidized

chromium

(Cr

+3

s t r o n g l y segregated a t t h e s u r f a c e . On t h e

contrary,

i n t h e case o f

Mo a d d i t i o n ,

three well

defined

agglomerates were analysed and were r e l a t e d t o t h e phases observed a l l o y . The A1 and A,

-

0.60, Mo/Ni 0.2-2.0)

0.04).

-

agglomerates i s s u e d r e s p e c t i v e l y f r o m t h e P1

phases, had a low molybdenum c o n t e n t ( A l / N i

CL

0.25,

Mo/Ni

CL

The A 3 t y p e s were r i c h i n Mo ( A l / N i

and were r e l a t e d t o t h e P 3 phase.

i n the and P,

0.05 and A l / N i 0.3,

'L

Mo/Ni%

The amount o f t h e s e d i f f e r e n t

agglomerates depended on t h e c o m p o s i t i o n o f t h e p r e c u r s o r a l l o y ,

and t h e

amount o f A1 decreased when t h e Mo c o n t e n t i n c r e a s e d . The o t h e r physico-chemical s u r f a c e area SBET,

metallic

characteristics of the catalysts (specific

s u r f a c e area SNi

and chemical c o m p o s i t i o n i n

volume) a r e g i v e n i n Table 1. The i n t r o d u c t i o n o f C r i n c r e a s e d b o t h SBET and SNi Mo had h a r d l y any e f f e c t on t h e s e s u r f a c e areas, increasing,

they

decreased

considerably.

With

Cr,

b u t w i t h promoter l e v e l t h e r e was

promoter d u r i n g t h e l e a c h i n g t r e a t m e n t ; i n t h e case o f promoter was d i s s o l v e d ,

; small additions o f

Mo, -65-80

no l o s s o f % of the

confirming observations o f o t h e r i n v e s t i g a t o r s ( 4 ) .

The e x t e n t o f removal o f aluminium was v e r y low and decreased w i t h i n c r e a s i n g promoter c o n t e n t .

116

TABLE 1 Physicochemical c h a r a c t e r i s t i c s o f t h e c a t a l y s t s Ni2A13

Precursor a l l o y

-1) *g 2 -1 SNi(m .g 1 Chemical c o m p o s i t i o n at % Al/Ni a t % M / N i x 100

Ni2-xMoxAl

0.07

0.11

0.05

0.1

0.17

0.4

80

122

113

78

74

68

23

65

83

77

59

56

42

6

0.51 5.4

0.28 0.49

0.36 1.07

0.62 3.70

1.02 8.70

X

2

N i 2-xCrxA1

0.28

0.38 4.0

_C_a_ _t a_ _l y- t i c h y d r o g e n a t i o n o f v a l e r o n i t r i l e C a t a l y t i c h y d r o g e n a t i o n o f v a l e r o n i t r i l e w i t h a commercial Raney n i c k e l c a t a l y s t under d i f f e r e n t r e a c t i o n c o n d i t i o n s was d e s c r i b e d i n p r e v i o u s papers ( r e f s . 10,111.

I t occurs as f o l l o w i n g ( s e e F i g . 1 ) .

@PA)

PENTYLAMINE(PA)

Fig. 1

TRI PENTYLAM I NE (TPA 1

ENAMINE

.

Reaction network o f v a l e r o n i t r i l e h y d r o g e n a t i o n

The r e d u c t i o n o f t h e n i t r i l e proceeds s t e p w i s e w i t h f o r m a t i o n o f a p r i m a r y a l d i , n i n e which t h e n i s hydrogenated t o t h e p r i m a r y amine ( p e n t y l a m i n e ) . P a r t o f t h e a l d i m i n e condenses w i t h p r i m a r y amine a l r e a d y formed t o produce t h e unstable aldimine

aminal.

This

intermediate

(dipentylimine)

(dipentylamine).

which

looses

ultimately

ammonia leads

to to

yield

a

secondary

secondary

amine

The r e a c t i o n o f t h e same p r i m a r y i m i n e w i t h t h e secondary

amine g i v e s r i s e t o the

t e r t i a r y amine ( t r i p e n t y l a m i n e ) , a f t e r h y d r o g e n a t i o n .

The p r o d u c t s d i s t r i b u t i o n as a f u n c t i o n o f t i m e i s i l l u s t r a t e d i n F i g . 2 f o r t h e unpromoted c a t a l y s t d e r i v e d f r o m t h e N i 2 A 1 3 a l l o y . The r a t e o f disappearance o f v a l e r o n i t r i l e remained c o n s t a n t w i t h t i m e up to-75

% c o n v e r s i o n . As soon as t h e r e a c t i o n s t a r t e d ,

t h e presence o f PA and

D P I were observed. D P I reached a maximum and was g r a d u a l l y hydrogenated t o DPA

117

or

r e a c t e d back t o g i v e p e n t y l a m i n e ( r e f . 1 1 ) . When t h e r e was n o more VN,

DPI

had d i s a p p e a r e d . The amount o f TPA f o r m e d was s m a l l .

Fig.2. Hydrogenation o f valer o n i t r i l e : p r o d u c t s d i s t r i but i o n as a f u n c t i o n o f t i m e o n the catalyst derived from N i *A1 3 .

40

20

60

reaction t i m e (min) I n f l u e n c e o f t h e promoters A s shown i n F i g . 3, t h e k i n e t i c s o f v a l e r o n i t r i l e h y d r o g e n a t i o n on t h e d i f f e r e n t c a t a l y s t s d i f f e r e d w i t h a d d i t i o n o f a p r o m o t e r . The i n i t i a l s p e c i f i c r e a c t i o n r a t e s were determined by t h e slopes o f t h e conversion c u r v e s o f v a l e r o n i t r i l e a t i n i t i a l time. E f f e c t o f chromium a d d i t i v e s on h y d r o g e n a t i o n a c t i v i t y was r a t h e r good : t h e i n i t i a l s p e c i f i c a c t i v i t y i m p r o v e d w i t h a d d i t i o n o f C r ( x = 0.071, f u r t h e r increase o f C r ( x

=

0.11)

but

d i d n o t change s i g n i f i c a n t l y t h e i n i t i a l

r a t e . A s t h e a d d i t i o n o f chromium i n c r e a s e d , t h e t i m e n e c e s s a r y t o o b t a i n h a l f c o n v e r s i o n and a l s o t h e t o t a l t i m e o f h y d r o g e n a t i o n i n c r e a s e d m a r k e d l y . Jhen t h e v a l e r o n i t r i l e had been c o m p l e t e l y t r a n s f o r m e d , t h e r e r e m a i n e d DPI. The m o d i f i c a t i o n o f t h e Raney n i c k e l w i t h l o w

Mo amount ( x

= 0.05

o r 0.1)

l e a d t o c a t a l y s t s w h i c h had r o u g h l y t h e same k i n e t i c b e h a v i o u r as t h e undoped. F u r t h e r i n t r o d u c t i o n o f molybdenum i n t h e Ni2A13 a l l o y had a s u b s t a n t i a l n e g a t i v e e f f e c t on t h e p r o p e r t i e s o f t h e c a t a l y s t s ,

w i t h a drop

a c t i v i t y o f t h e c a t a l y s t w i t h t h e h i g h e s t Mo c o n t e n t ( x = 0 . 4 ) .

i n the

Though t h e

amount o f c a t a l y s t was s i x t i m e s more t h a n f o r t h e o t h e r c a t a l y s t s ,

the

c o m p l e t i o n o f h y d r o g e n a t i o n was n o t o b t a i n e d . T a b l e 2 summarizes t h e r e s u l t s o f t h e hydrogenation r a t e s surface area),

(based on weight

o f c a t a l y s t and

on

t h e t i m e s f o r 50% c o n v e r s i o n and f o r t o t a l r e a c t i o n ,

s e l e c t i v i t i e s expressed

as

percentage

of

VN transformed

into

a

metallic and t h e reaction

product. The t a b l e 2 shows moreover t h a t t h e e f f e c t s o f chromium ( x molybdenum a d d i t i v e s were b e n e f i c i a l f o r t h e i n t r i n s i c a c t i v i t y

=

0 . 1 1 ) and o f

Via.

The chromium doped c a t a l y s t s had a l s o a marked i n f l u e n c e o n t h e p r o d u c t s obtained,

a f f o r d i n g a h i g h e r s e l e c t i v i t y i n p e n t y l a m i n e : i t was i n c r e a s e d

118 from 79% (undoped c a t a l y s t ) chromium ( x = 0.11)

t o 83% ( x = 0.07)

resulted s t i l l

; further

introduction o f

i n an improvement (85% i n PA)

and t h e

f o r m a t i o n o f t e r t i a r y amine was n o t d e t e c t e d . I n t r o d u c t i o n o f molybdenum i n t o t h e N i 2 A 1 3 a l l o y r e s u l t e d i n d e c r e a s i n g o f t h e s e l e c t i v i t y i n p r i m a r y amine t o ~ 7 7 6%.The c o n t e n t o f molybdenum had no a p p r e c i a b l e e f f e c t on t h i s s e l e c t i v i t y , ( x = 0.4).

even i n r e l a t i v e l y l a r g e amounts

I n t h i s l a t e case, D P I accumulated i n t h e r e a c t i o n medium and

reached 17 % o f VN transformed i n t o D P I a t t h e maximum, compared t o 8-9.5 w i t h t h e o t h e r Mo promoted c a t a l y s t s .

A Ni1.93cr0,07A13 NiI.B9Cr0.11 A'3

A -6 -4

20

1ooa

io

$0

ioo

n n

-

1-20

reaction time ( m i n 1

reaction t i m e ( m i n )

F i g . 3. E v o l u t i o n o f v a l e r o n i t r i l e (-1 and d i p e n t y l i m i n e (---I t i m e o v e r C r and Mo promoted c a t a l y s t s . R e a c t i o n c o n d i t i o n s : 0.5 g c a t a l y s t , T = 9O"C, PH* = 1.6 MPa.

with reaction 0.1 mol VN,

%

119 TABLE 2

Hydrogenation o f v a l e r o n i t r i l e

on t h e c a t a l y s t s

prepared f r o m Ni2-xMxA13

p r e c u r s o r a1 l o y s .

v0

A1 l o y precursor

mmo1.s N i2Al

Nil .93Cr0.07A13 N i .89Cr0.

lAl

-1

103

.g

-1

vlOx mmol .s

103

-

t50%tlO0% S e l e c t i v i t y

-2

-1

(min)

" Ni

%PA

%DPA

%TPA

79

1.215

20

-

65

79.2

20.7

100

1.205

15

-

70

83.1

16.9

1.43

18

-

120

85.1

14.9 t r a c e s

2,110

C

hydrogenation

of

(scheme 1 ) a l l o w s t o c a l c u l a t e t h e c o n c e n t r a t i o n

in

c h l o r o a n i l i n e intermediate, maximum c o n c e n t r a t i o n

(61,

for

f r o m which i t can be deduced b o t h t h e

i n t h e intermediate,

when d ( B ) / d t = O . t i m e tmax

observed

(Blmax,

and t h e c o r r e s p o n d i n g

125

The d i f f e r e n t e x p r e s s i o n s l e a d i n g t o (BImax and tmax a r e g i v e n below :

Thus t h e maximum c o n c e n t r a t i o n i n 4 - c h l o r o a n i l i n e

( g i v e n as

molar

p e r c e n t ) i n c r e a s e s f r o m 72% a t 250°C t o 86% a t 200°C and 95% a t 150°C o v e r t h e s u l f i d e d NiMo HR 348 c a t a l y s t . The r e s u l t s a r e b e t t e r o v e r t h e CoMo HR 306 c a t a l y s t ,

77% a t 250"C,

94% a t 200°C

and 98% a t

150°C.

A

better

i l l u s t r a t i o n o f t h e i n c r e a s e i n s e l e c t i v i t y i s g i v e n i n F i g . 3 and F i g . 4 w i t h

Fig.3. A r r h e n i u s p l o t f o r h y d r o -

Fig.4. Arrhenius p l o t f o r hydro-

processing o f 4-chloronitrobenzene

processing o f 4-chloronitrobenzene

over s u l f i d e d CoMo HR 306 c a t a l y s t .

o v e r s u l f i d e d NiMo HR 348 c a t a l y s t .

126

the Arrhenius p l o t s obtained f o r both c a t a l y s t s .

The apparent

activation

e n e r g i e s c a l c u l a t e d f r o m t h e s e p l o t s a r e o f t h e same o r d e r o f magnitude f o r t h e two c a t a l y s t s , 6-7 kcal.mo1-'

f o r t h e h y d r o g e n a t i o n o f t h e n i t r o group

f o r t h e h y d r o g e n o l y s i s o f t h e C - C 1 bond.

and 18 kcal.mo1-'

The l a r g e d i f -

f e r e n c e s i n t h e apparent a c t i v a t i o n e n e r g i e s i l l u s t r a t e unambiguously t h e increase i n t h e s e l e c t i v i t y t o c h l o r o a n i l i n e , t h e e f f e c t o f t h e temperature b e i n g more i m p o r t a n t f o r t h e h y d r o g e n o l y s i s t h a n f o r t h e h y d r o g e n a t i o n r e a c tion. A t lOO"C,

o n l y c h l o r o a n i l i n e was d e t e c t e d .

The v a l u e o f t h e apparent a c t i v a t i o n energy i s r a t h e r low f o r t h e hydrogenation s t e p . T h i s v a l u e i s o f t h e same o r d e r o f magnitude t h a n t h o s e encountered f o r alkenes h y d r o g e n a t i o n o v e r m e t a l o r s u l f i d e d c a t a l y s t s , k c a l .mol-'

(refs.4,5).

3-8

Alkenes a r e w e l l known t o be r e a d i l y hydrogenated.

The low a c t i v a t i o n energy observed f o r t h e h y d r o g e n a t i o n o f t h e n i t r o group can t h u s be r e l a t e d t o i t s g r e a t a b i l i t y t o undergo h y d r o g e n a t i o n r a t h e r than t o d i f f u s i o n a l phenomena except maybe a t h i g h t e m p e r a t u r e s where some d e v i a t i o n s f r o m t h e A r r h e n i u s e q u a t i o n a r e observed. to

avoid d i f f u s i o n

considered,

limitation

in

the

liquid

Classical requirements

phase

have

already

been

p a r t i c u l a r l y the proportionality o f the reaction r a t e t o t h e

c a t a l y s t w e i g h t , t h e c o n c e n t r a t i o n o f t h e a c t i v e component, speed, and c a l c u l a t i o n s made w i t h t h e T h i e l e modulus, 0

the agitation

r (k/D)"

=

assuming

a p a r t i c l e r a d i u s r o f .0045 cm and a d i f f u s i o n c o e f f i c i e n t 0 f o r t h e l i q u i d phase l y i n g between

and

cm2/s ( r e f s . 6 , 7 ) .

Another p o i n t w o r t h m e n t i o n i n g i s t h e r e d u c t i o n o f s u b s t i t u t e d n i t r o benzenes by sodium d i s u l f i d e i n aqueous m e t h a n o l i c s o l u t i o n . T h i s r e a c t i o n was shown t o be l a r g e l y i n f l u e n c e d by t h e presence o f e l e c t r o n - d o n a t i n g o r electron-withdrawing substituents ( r e f . 8 ) .

The e f f e c t o f s u b s t i t u e n t s f i t s

t h e Hammett e q u a t i o n w e l l , t h e s l o p e 0 - v a l u e b e i n g a u t h o r s t o propose t h e d i s u l f i d e a n i o n S2-

thus leading t h e

i. 3.55,

as t h e r e d u c t i v e s p e c i e s . 2- and

3 - c h l o r o n i t r o b e n z e n e s have been s t u d i e d over t h e CoMo HR 306 and NiMo HR 348 c a t a l y s t s under o p e r a t i n g c o n d i t i o n s s i m i l a r 4-chloro

derivative.

No s i g n i f i c a n t

t o those

difference

observed from i n d i v i d u a l o r c o m p e t i t i v e e x p e r i m e n t s . absence

of

substituent

effects

that

the

reported

for

the

i n t h e r e a c t i v i t i e s was It r e s u l t s from t h e

hydrogenation

mechanism

over

s u l f i d e d CoMo HR 306 and NiMo HR 348 c a t a l y s t s d i f f e r s f r o m t h e r e d u c t i o n mechanism over

sodium d i s u l f i d e .

As

a

consequence,

the

S2-

species,

sometimes i n v o k e d as t h e a c t i v e s p e c i e s o f s u l f i d e d c a t a l y s t s l i k e RuS2 and NbS3 ( r e f s . 9,101,

would n o t be t h e a c t i v e s p e c i e s f o r t h e s u l f i d e d h y d r o -

t r e a t i n g NiMo and CoMo c a t a l y s t s . The presence o f d i s u l f i d e i o n s p e c i e s f o r both l a t t e r c a t a l y s t s c o u l d n o t be supported by any e x p e r i m e n t a l method.

127

Experiments a r e b e i n g c o n s i d e r e d t o complete t h e s e

preliminary results

concerning t h e e f f e c t o f s u b s t i t u e n t s . CONCLUSION Hydrogenation

of

chloronitrobenzenes

to

chloroanilines

achieved over c o n v e n t i o n a l s u l f i d e d h y d r o t r e a t i n g c a t a l y s t s .

is

easily

Large d i f f e -

rences i n t h e a c t i v a t i o n e n e r g i e s a r e observed f o r h y d r o g e n a t i o n o f t h e n i t r o group o f c h l o r o n i t r o b e n z e n e and c l e a v a g e o f t h e C-C1 bond o f c h l o r o a n i l i n e . It i s thus possible t o increase t h e s e l e c t i v i t y t o c h l o r o a n i l i n e by o p e r a t i n g a t low temperatures.

T h i s s e l e c t i v i t y i s i n c r e a s e d a g a i n by

u s i n g t h e Co-promoted r a t h e r t h a n t h e Ni-promoted c a t a l y s t . properties

of

sulfided

hydrotreating

catalysts

can

be

The s e l e c t i v e advantageously

compared t o t h o s e o f o t h e r c a t a l y t i c systems ( r e f . 1 1 ) .

REFERENCES 1. C.Moreau, R.Durand, P . G r a f f i n and P.Geneste, Stud.Surf.Sci.Catal., 41 (1988) 139. 2. n o r e a u , J . J o f f r e , C.Saenz and P.Geneste, J.Catal.,122 (1990) 448. 3. J . J o f f r e , P.Geneste, A.Guida, G.Szabo and C.Moreau, 5 d . P h y s . Theor. Chem., ,71 990) 409. 4. S. J .Thornson a n d T . Webb, J.Chem.Soc. ,Chem.Commun., ( 1976) 526. 5. Z . P o l t a r z e w s k i , S.Galvagno, R . P i e t r o p a o l o and P . S t a i t i , J.Catal., 102 (1986) 190. 6. %.Bond, "Heterogeneous C a t a l y s i s : p r i n c i p l e s and a p p l i c a t i o n s " , 2 e d i t i o n , Clarendon P F ~ S S , Oxford, 1987, p.48. 7. P.B.Weisz, Proceedings 7 I n t e r n a t i o n a l Congress on C a t a l y s i s , T.Sziyama and K.Tanabe, Eds., Kodanska-Elsevier, Tokyo,1981,p.3. 8. M.Hojo, Y.Takagi and Y.Ogata, J.Am.Chem.Soc., 82 (1960) 2459. 9. J.B.Goodenough, Proceedings o f t h e F o u r t h I n t e r n a t i o n a l Conference on t h e Chemistry and Uses o f Molybdenum (M.F.Barry and P.C.H. M i t c h e l l , Eds.) Ann Arbor, M I , Climax Molybdenum Company, 1982,p.19. 10. M.Vrinat, C . G u i l l a r d , M.Lacroix and M.Breysse, Bull.Soc.Chim.Belg., 96 (1987) 1017. 11. 6-r e c e n t r e v i e w s on h y d r o g e n a t i o n o f n i t r o groups, see f o r example : Compendium o f o r g a n i c s y n t h e t i c methods, J.Wiley, N.Y., Vo1.6 (1988) and p r e c e d i n g volumes i n t h e s e r i e s , and J.R.Kozak i n " C a t a l y s i s o f Organic Reactions", P.N.Rylander, H . G r e e n f i e l d and R.L. Augustine, Ed., M.Dekker, N.Y. , 1 9 8 8 , ~ . 135.


M. Guisnet et al. (Editors), Heterogeneous Catalysis and Fine Chemicals I1 0 1991 Elsevier Science Publishers B.V., Amsterdam

129

THE APPLICABILITY OF DISPERSED METALS AS CATALYSTS FOR ORGANOMETALLIC REACTIONS R.L. Augusthe*, S.T. O'Leary,K.M. Lahanas and Y.-M. Lay Department of Chemistry, Seton Hall University, South Orange, New Jersey 07079 USA SUMMARY Initial work indicates that dispersed metals may be used to promote a variety of organometallic reactions. The Heck Arylation proceeds smoothly over supported Pd catalysts while diene cyclizations can be catalyzed by dispersed Rh metal. The use of these heterogeneous species facilitates product isolation and permits the application of flow systems rather than batch reactors for these reactions. Frontier Molecular Orbital and mechanistic considerations indicate that these reactions take place on the coordinately unsaturated comer atoms on the metal surface.

INTRODUCTION The use of heterogeneous catalytic reactions in the fine chemical industry is usually limited to the modification of functional groups by hydrogenation or oxygenation reactions. If, however, heterogeneous catalysts could also be used to promote synthetically useful C-C bond forming reactions, such processes would have significant practical, economical and environmental importance. At the present time there are a number of these synthetically useful reactions which are catalyzed by soluble organometallic complexes (ref. 1) but, the large scale use of such soluble species to make compounds of interest to the fine chemical industry is not practical. The primary problem associated with the use of these homogeneous catalysts is the separation of the product not only from the organometallic species but also from ligands which may have dissociated from the catalyst during the reaction. If one could use heterogeneous catalysts such as dispersed metals to promote this type of reaction, product separation would be facilitated and the more efficient flow processes could be used instead of the commonly employed batch mode. There are, however, a number of problems which must be overcome before such systems can be used practically. In the first place it must be shown that dispersed metals can promote these reactions and, secondly, a more detailed knowledge must be acquired of substrate adsorption on the catalyst and the interaction of the adsorbed species to give the product. The first of these problems appears to have a reasonable expectation of solution. There are a few publications which state that supported metals can be used to promote some of the organometallic reactions commonly run with soluble catalysts (refs. 2-4). In these reports, though, the use of the supported metal is generally included only as an entry in a table describing the effect of changing reaction parameters on product yield and/or selectivity. The fact that a heterogeneous catalyst was used is seldom discussed. When it is mentioned, it is

130

usually assumed that the metal promotes the reaction because some of it is "solubilized" to give the active catalytic species. We describe here some of our initial efforts concerned with the use of dispersed metals as catalysts for organometallic reactions and the development of a Frontier Molecular Orbital description of the reactions taking place on the metal surface. RESULTS AND DISCUSSION

Oreanometallic reactions An interesting organometallic reaction is the Heck Arylation (Eqn. 1) (ref. 5 ) , which is commonly run using a Pd(OAc)2 catalyst. This reaction is used to prepare aryl enol ethers which can be valuable synthetic intermediates in that they can be hydrolyzed to aldehydes or ketones, species which can be useful themselves or as intermediates in further reactions. The influence of reaction parameters on the rate and selectivity of this reaction was reported in a series of papers (refs. 2, 3). In these a brief mention in some tables was made that Pd/C was able to catalyze this reaction but no discussion of the use of this catalyst was included, We have found, though, that this reaction is readily promoted over dispersed Pd catalysts. When run with Pd(OAc)2 as the catalyst, the Heck reaction gives as the primary products the E (1) and Z (2) aryl /3 enol ethers in about a 2: 1 ratio. The u isomer, 3, and ester, 4, are also produced but in much smaller amounts. When the reaction is run over Pd/A1203, the same products are obtained but the /3 enol ethers 1 and 2 are produced in nearly a 3:l ratio. Table 1 lists the product compositions of these reactions. TABLE 1 p-Nitrobenzoyl Chloride Reaction Run Over Various Palladium Catalystsa Percent Yield Catalyst P~(OAC)~~ Pd/ y- A12 0 3

b-E (1)

b-Z (2)

E/Z Ratio

a (3)

Ester(4)

50.4 42.9

27.1

1.86 2.75

6.3 5.8

4.4

15.6

3.2

aThe reactions were run with 2.5 mmol of p-nitrobenzoyl chloride, 5.0 mmol of butyl vinyl ether, 3.75 mmol of n-ethylmorpholine, and catalyst in 0.25 mol % (based on p-NBC) in 25 ml of dioxane. Dodecane was used as an internal standard. The experiment was performed under a blanket of N2 at the reflux temperature of the solvent. bl mol % (based on p-NBC). Xylene was the solvent. The most striking comparison between the homogeneous and heterogeneous catalysts was that four times more palladium was required in the homogeneously catalyzed reaction to give about the same rate as that of the Pd/A1203 promoted reaction. A tertiary amine is present in the reaction mixture to remove the HCl from the catalyst and regenerate the catalytically active

131

species. When the heterogeneously catalyzed reaction was run in toluene, the solvent commonly used in homogeneously catalyzed reactions, the catalyst was rapidly deactivated by the precipitation of the amine hydrochloride. To prevent this, dioxane was used as the solvent to keep the salt in solution. To establish that the Pd/A1203 was responsible for the reaction and not some "solubilized" species, the catalyst was separated from the reaction mixture after 10% conversion and the resulting solution heated under conditions known to promote the homogeneous reaction. No further reaction was observed until the Pd/A1203 was reintroduced to the reaction mixture.

ICOJ 5

- WtHtM Rh

0

0

0

6

7

8

Eqn.

1

Eqn.

2

The diene cyclization shown in Eqn. 2, has been reported to take place only over RhC13 and Wilkinson's catalyst (ref. 6). We have found that it also occurs when run over supported Rh catalysts. The heterogeneously catalyzed reaction is particularly sensitive to the nature of the solvent used. With alcohols or other solvents which can adsorb on the catalyst, there is an apparent competition with the adsorption of the double bonds and the cyclization does not take place. In alkane solvents, which do not interact with the catalyst, the reaction occurs with reasonable facility. This cyclization is run routinely at 145°C in a flow system with a decane solution of 5 passing through a small column containing a Rh/A1203 catalyst. The product composition was related to the time 5 was in contact with the catalyst. With fast flow rates (short contact times) 6 was the primary product of the reaction but the isornerized species, 7 and 8, were produced when slower flow rates were used. This indicates that 6 was the primary product of the reaction but that it was isomerized over the catalyst to 7 and 8.

132

In neither of these reactions was it necessary to add any ligands or modifiers to the system to promote the reaction. Active sites While these results indicate that a supported metal can be used to promote organometallic reactions, there are a number of questions which must be answered before their use in this way can become routine. One of the most important of these considerations concerns the nature of the "active site" on the metal which promotes the reaction and the process by which the reaction takes place on this site. Data are available which indicate that groups or "ensembles" of surface atoms are used to promote reactions involving C-C bond cleavage or hydrocarbon rearrangements while single atom sites are responsible for C-H bond forming and breaking reactions (refs. 7, 8). Further results show that the "ensemble" sites responsible for C-C bond breaking are primarily groups of atoms on the 111 faces of the metal particles (ref. 9). The single atom sites which promote C-H bond formation or cleavage, on the other hand, are the more coordinately unsaturated corner atoms (refs. 10, 11). Other single atom sites are the edge atoms which presumably can promote double bond isomerizations (ref. 11).

X

Side

V i e w

Z

X

Top

-Y

V i e w

Fig. 1. Top and side views of a bulk atom in an fcc crystalline lattice shown as a twelve coordinate complex.

133

Most catalytically active metals have the fcc crystal lattice. Examination of crystal models shows that there are at least 13 different types of surface atoms possible with the fcc crystal arrangement (ref. 12). In these metals each bulk atom is surrounded by twelve nearest neighbors as depicted in Fig. 1 for that orientation viewed from the 100 face. This entity can be thought of as a twelve coordinate "complex" of the central atom, M, surrounded by twelve "ligand" atoms. The different single atom surface sites can be derived from this twelve coordinate species by removing varying numbers of the "ligand" atoms. The 100 face atom "complex" is produced by removing "ligands" 4, 9, 10, and 12 from the species shown in Fig. 1. This results in a surface "complex" composed of the central atom, M, surrounded by "ligands" 1, 2, 3, 5, 6, 7, 8, and 11. The octahedral comer atom depicted in Fig. 2 is composed of the metal atom with "ligands" 2, 3, 6, and 7. We have used our Single Turnover (STO) reaction sequence to characterize dispersed metal catalysts with respect to the numbers of alkene saturation sites, double bond isomenzation sites, and hydrogenation inactive sites they have present on their surfaces (ref. 13). Comparison of the product composition observed when a series of STO characterized Pt catalysts were used for cyclohexane dehydrogenation with those observed using a number of instrumentally characterized Pt single crystal catalysts has shown that the STO saturation sites are comer atoms of one type or another on the metal surface (ref. 10).

X

-:j

l p z

Top

Vi e w

e v

5PX

5 P x 5P, 5s

-1 0

4 d X42d- ,=22

-

#

S i d e

View

I

Fig. 2. Energy levels of the 5s, 5p, and 4d electrons of a Pd octahedral comer atom

- 1

134

When a series of STO characterized PdlA12Q catalysts were used to promote the Heck reaction (Eqn. 1) the amount of the /? aryl enol ethers, 1 and 2, formed after a 60 minute reaction was directly related to the comer site densities on these catalysts. Thus, this reaction and presumably, others such as the diene cyclization shown in Eqn. 2, which require the adsorption of two reactive species on a single surface atom, must take place on the more coordinatively unsaturated comer atoms. Frontier Molecular Orbital mechanistic treatment In order to utilize these heterogeneously catalyzed reactions more fully it is necessary to develop an understanding of the mode of substrate adsorption and interaction on these sites. While the octahedral orientation is common to most soluble organometallic catalysts, surface species with this arrangement are not possible on fcc metals. Surface complexes having the octahedral orientation cannot be produced regardless of which "ligands" are removed from the twelve coordinate species shown in Fig. 1. However, if the electronic character of these sites were determined, it should be possible to use reaction sequences similar to the mechanisms proposed for the soluble species as long as the surface orbitals of the site which are involved in the interactions have the correct symmetry and are available for substrate bonding. Scheme

1

10 Slde

Vlew

111 ' ' Q

13

12

EHMO calculations on 111 and 100 metal planes have indicated that the surface electron orbitals are quite localized (refs. 14-16). This supports the premise that these surface sites can be considered as "surface complexes". With this assumption classical inorganic techniques can

135

be used to determine the electron distribution at each of these sites. We have developed an Angular Overlap Method (ref. 17) approach to this problem and have calculated the s, p, and d electron energies for each of the possible surface sites on a number of different fcc metals. The s, p, and d electron orbital energy values for the Pd octahedral comer atom is shown in Figure 2 along with the side and top views of the d orbital arrangement for this site. Using Frontier Molecular Orbital considerations it can be seen that the 5 s orbital is the LUMO and the degenerate 4dx, and 4dyz orbitals are HOMO. Thus, a substrate can adsorb on this site by electron donation to the 5s orbital with back bonding from either the 4dx, or 4dYr Only one of these can be used since when adsorption occurs further interaction with another species from the z direction is blocked. The adsorption of a second species must take place in the x-y plane and involves electron donation to the LUMO 5px or 5py. Backbonding from the HOMO 4d,2 orbital is not possible since it is out of the x-y plane. The 4d,2.y2 orbitals are coincident with the px and py so they cannot take part in the adsorption either. Instead the 4dxy orbitals which do have the proper orientation are used for backbonding. Scheme 1 illustrates these points for an alkene hydrogenation on a Pd octahedral comer site, 9. Adsorption of H2 occurs with D donation to the 5s orbital and back bonding from the 4dx, to the D* orbitals of the b,as in 10, to give the dihydride, 11, shown in both top and side views. Alkene adsorption now can only take place by IT donation to the 5py with backbonding to the IT*orbital from the 4d,, as in 12. Hydrogen insertion gives the hydrido metalalkyl, 13, again depicted in both side and top views, Reductive elimination gives the alkane and regenerates the active site, 9. Scheme 2 shows a similar mechanistic pathway for a Heck reaction taking place on a Pd octahedral comer. This mechanism is based on that established for soluble Pd catalysts (ref. 5). Adsorption of the aryl halide (or aryl acid chloride after decarbonylation) gives the aryl Pd halide, 15, by way of the adsorbed intermediate, 14. Vinyl ether adsorption, as in 16, takes place as described in Scheme 1. Aryl insertion gives the halometalalkyl, 17, which on B elimination to the available 4dxy orbital gives the aryl enol ether, 2 (or 1 depending on which hydrogen is eliminated in 17). The resulting halo palladium hydride, 18, then reacts with the tertiary amine to give the amine hydrochloride and regenerates the octahedral comer for further reaction. CONCLUSIONS

It appears that supported metal catalysts can be used to promote synthetically useful organometallic reactions. The utilization of such reactions can be of practical, economic, and environmental importance to the fine chemical industry. Frontier Molecular Orbital and mechanistic considerations indicate that these reactions, along with hydrogenations and, presumably, oxygenations, take place on the coordinately unsaturated comer atoms present on the surface of these dispersed metal catalysts.

136

2

s c heme

9

R,NH+

14 Side

Vlew

11 '

Ill

HZ

uo E

H

2

18

16

ACKNOWLEDGEMENT

This research was supported by Grant DE-FG02-84ER45120 from the U.S. Department of Energy, Office of Basic Energy Science. The metal salts were obtained through the JohnsonMatthey Precious Metal Loan Program. REFERENCES 1 J.P. Collmann, L.S. Hegedus, J.R. Norton and R.G. Finke, Principles and Applications of Organotransition Metal Chemistry, University Science Books, Mill Valley, CA, 1987. 2 C.M. Andersen, A. Hallberg and G.C. Daves, J. Org. Chem., 52 (1987) 3529. 3 C.M. Andersen and A. Hallberg, J. Org. Chem., 53 (1988) 235. 4 D.L. Bergbreitner and B. Chen, J. Chem. Soc., Chem. Commun. (1983) 1238. 5 R.F. Heck, Acc. Chem. Res., 12 (1979) 146. 6 A. Bright, J.F. Malone, J.K. Nicholson, J. Powell and P.L. Shaw, J. Chem. SOC.,Chem. Commun. (1971) 712. 7 J.H. Sinfelt, J.L. Carter and D.J.C. Yates, J. Catal., 24 (1972) 283. 8 P.S. Kirlin and B.C. Gates, Nature (London), 325 (1987) 38. 9 D.W. Goodman, Chem. Ind. (Dekker) 22 (Catal. Org. React.) (1985) 171. 10 R.L. Augustine and M.M. Thompson, J. Org. Chem., 52 (1987) 1911. 11 M.J. Ledoux, J. Catal., 70 (1981) 375. 12 R.L. Augustine and P.J. O'Hagan, Chem. Ind. (Dekker) 40 (Catal. Org. React.) (1989) 11 1. 13 R.L. Augustine and R.W. Warner, J. Catal., 80 (1983) 358. 14 J.Y. Saillard and R. Hoffmann, J. Am. Chem. Soc., 106 (1984) 2006. 15 S.S. Sung and R. Hoffmann, J. Am. Chem. SOC.,105 (1985) 578. 16 J. Silvestri and R. Hoffmann, Langmiur, 1 (1985) 621. 17 R.S. Drago, Physical Methods in Inorganic Chemistry, Saunders NY 1977.

M. Guisnet et al. (Editors ), Heterogeneous Catalysis and Fine Chemicals II 0 1991 Elsevier Science Publishers B.V., Amsterdam

SURFACE

ORGANOMETALLIC

CHEMISTRY

ON

METALS:

137

SELECTIVE

HYDROGENATION OF CITRAL INTO GERANIOL AND NEROL ON TIN MODIFIED SILICA SUPPORTED RHODIUM.

B. DIDILLON*, A~ EL MANSOUR**, J.P. CANDY*, J.P. BOURNONVILLE*** 2nd J.M. BASSET I.R.C. 69626 Villeurbanne Cedex, France ** Universiti? Mohamed V, Facult6 des Sciences de Rabat, Maroc *** I.F.P. 92506 Rueil-Malmaison Cedex, France ABSTRACT

A bi-metallic Rh-Sn(n-C4Hg)2/SiO2 catalyst, obtained by the organometallic route, has been found to be extremely active and selective in the hydrogenation of citral ( A : geranial and b: neral) to the corresponding unsaturated alcohols (geraniol and nerol). The synthesis of the Ilbimetallic catalyst" from the organometallic precursor as well as the kinetics of hydrogenation is described. A tentative explanation for the extremely high chemoselectivity (96% at 100% conversion) for the hydrogenation of the C=O double bond is given. INTRODUCTION

Surface organometallic chemistry on metals is a new method to obtain well defined bimetallic catalysts (1). For example, the reaction of tetra-n-butyl tin with the surface of group VIII metals leads to bimetallic catalysts which exhibit very high selectivities and activities for the hydrogenolysis of ethyl acetate into ethanol (2-4). However the high temperature treatment of the solids obtained by this way totally removes the butyl groups and the catalytic active phase is a new bimetallic material, which is very likely an alloy. Careful studies of the reaction between tetra-n-butyl tin and silica supported group VIII metal M ( M = R h ( ' ) , Ru(O) or Ni(')) catalysts (5), indicate that the reaction proceeds stepwise via a surface intermediate complex which can be formulated as MaSn(C4Hg)x (1<xl). To our knowledge, such surface organometallic complex was never mentioned or even characterized. Consequently, no catalytic studies have ever been carried out on metallic surfaces modified on DurDose by a grafted organometallic fragment In this work, we report the catalytic activities and selectivities of Rh,Sr~(cqHg)~ in the selective hydrogenation of citral. Citral is a member of the alpha-beta unsaturated aldehydes family; It offers three kinds of unsaturations: (i) an aldehydic

138

function, a conjugated double bond and an isolated double bond. Rhodium or platinum supported on silica are totaly unselective for the hydrogenation of citral to unsaturated alcohols (6-12). EXPERIMENTAL The silica support (small pellets, 1 nun in diameter, surface area of 250 m2.g-l) was purchased from SHELL. Rhodium was grafted on silica by cationic exchange between [RhC1(NH3)5I2+ ions and surface GSi-O'NH4' groups at pH 10. The SSi-O-NH4+ groups were obtained by exchange between fSi-0-H+ groups and NH4' ions in ammonia solution. [RhCl(NH3)5](0H)2 was obtained by contact of [RhC1(NH3)5]C12 with an anionic exchange resin (IRA 400) in aqueous solution. The surface complex obtained by this route was decomposed by calcination at 570K in flowing dry air and then reduced in flowing hydrogen at 570K to give catalyst A. This catalyst contains 1 wt% of rhodium. A could be transformed into B by treatment with dry air at 300K for 1 hour. The particle size of B was in the range of 1.0-1.5 nm as determined by electron microscopy. Hydrogen-oxygen interaction on B indicates (13) that reduction of B occurs at 300K and could be complete at 400K. The reaction between tetra-n-butyl tin [Sn(n-C4H9)4] and B is achieved in the liquid phase, directly in the reaction vessel (stainless steel autoclave, well stirred by a magnet). A given amount of B (typically 250 mg, 2.5.10-5 no1 of Rh) is placed, under argon, in the autoclave, with 10 ml of n-heptane and x ml of Sn(n-C4H9)4. The slurry is then stirred under 6 MPa of hydrogen, at 370K, during 60 mn, to obtain catalyst C. The reduction of citral is performed in situ, in the same autoclave, without any exposure of the catalyst to air. After cooling down the reactor to room temperature and reducing the hydrogen pressure, a solution of 0.9 nl of citral and 0.4 nl of tetradecane (internal standard) in 10 ml of n-heptane is introduced under hydrogen in the autoclave. The temperature and the hydrogen pressure are then raised to respectively 340K and 7.6 MPa. The kinetic of the reaction is followed with time by analysis of samples of the liquide phase. The selectivity for a product X at 100% conversion (S,) is defined by: Sx = [X]100/[Citra1]0. [Citral]~ represents the initial concentration of Citral ( 2 and E) and and [XI100 represents the concentration of X at 100% conversion.

139

RESULTS

a) Prevaration and characterization of the surface orsanometallic catalvst. Catalyst C is obtained by reaction of Sn(n-C4H9)4 with B in the liquid phase (n-heptane) under a hydrogen atmosphere (vide supra). The amount of tin fixed on the catalyst depends on the amount of Sn(n-C4H9)4 introduced (Table 1).

The maximum quantity of tin fixed corresponds to a Sn/Rh ratio of ca. 1. During this reaction n-butane is evolved. The amount of remaining butyl groups has been quantitatively measured by subsequent hydrogenolysis at 630K which leads to the formation of n-butane. The value obtained was found to be 2.1 C4/Sn fixed on the cat.alyst. The catalyst C seems to be best described by the formula: RhaSn(C4Hg)2/Si02. Such surface organometallic fragment has been characterized by M.A.S H' and 13C NMR (14) as well as volumetric measurements, electron microscopy and IR spectroscopy (15). It has been checked that during catalysis the butyl groups are not removed from the surface : after catalytic reaction a subsequent hydrogenolysis at 630K indicates that 1.93 C4 equivalent/Sn still remain on the catalyst. b) Citral hvdrosenation on catalvst C The overall reaction path for citral Z is represented in scheme 1. Typical kinetic measurements for citral (2 and E mixture 35/65) hydrogenation on catalyst C (Sn/Rh=l) are shown on figure la. In every case, a first order in citral is observed (figure lb), assuming that: d[citral]/dt = k[citral]. The constant (k) is directly proportional to the amount of catalyst (figure 2a) and to the hydrogen pressure PH2 (figure 2b). The apparent activation energy calculated from the slope of the Arrhenius plot in the temperature range 273-313K is 49 kJ.mol-l. The overall reaction rate can be represented by the following equation: d[citral]/dt

=

-K.e-49/RT[citral].

[c].pH2

(1)

140

2pi$j

[Citr.] (mol/l)

-Ln [Citr.] 1

3

0

1

2

3

4

5

0

1

2

3

time (h)

4

5

time (h)

Figure 1: Kinetics measurements of citral hydrogenation T=310K; RhlCitral=O.005; Hydrogen pressure:

(*I

3 MPa, (+) 2 MPa, (x) 1 MPa

1.0 0.8

0.6

(Rh/Cit r a I).10

Py(MPa)

Figure 2 Variation of the constant (k) versus: (a) RhlCitral ratio; T=310K; Hydrogen pressure=5 MPa (b) Hydrogen pressure; T=310K; RhlCitral=0.005

Sn /Rh Figure 3: Selectivity and activity of citral hydrogenation, versus SnlRh ratio Hydrogen pressure=7.6 MPa, T=350K. RhlCitral=0.005

141

Scheme 1 trans DIMETHYL-3.7

OCTENE-2 AL

DIMETHYL-3.7 OCTANAL

-A+B

/

CITRAL TRANS

A

-

roH-B+C trans DIMETHYL-3.7

OCTENE-2 OL

CITRONELIAL

/

DIMETHYL-3.7 OCTANOL

CITRONELLOL

The chemoselectivity of the reaction depends on the Sn/Rh ratio (Table 2 and Figure 3).

The selectivity for citronella1 increases up to a value of (at 100% conv.) for a Sn/Rh ratio of 0.12. Above these values, the selectivity for citronella1 decreases and the selectivity for geraniol and nerol increases up to 96% (at 100% conv.) for a Sn/Rh ratio of 0.92. Significant variations of activities are simultaneously observed suggesting selective metallic surface poisoning followed by enhanced catalytic activity due to a new catalytic material which contains a tin din-butyl fragment. It is possible to transform this kind of organometallic catalyst in an bimetallic rhodium-tin alloy by treatment under 81%

142

hydrogen at 630K ( 3 ) . Citral hydrogenation on this catalyst is totally unselective (Table 2) It is interesting to discuss those results in the light of the various hypothesese which were previously proposed for the selective hydrogenation of alpha-beta unsaturated aldehydes. It is known that Pt-Sn, Pt-Fe, Pt-Ru, Pt-Co or Pt-Ge supported on nylon (7-9) or carbon (10-11) give for certain compositions high yields of unsaturated alcohols. In addition to a geometric effect of the second metal, which prevents hydrogenolysis by decreasing (16), two hypothesese based on a the size of the Pt @@ensembles@@ possible electronic effect of the second metal are proposed to explain the high selectivities and activities. In the case of PtFe (10), the authors suggest that the two metals are in the metallic state and belong to an alloy. They observe, by EXAFS, an electron transfer from Fe to Pt (12) and suggest that the aldehydic double bond is then more easily adsorbed on the Ilinduced sites@@. In the case of Pt-Sn and Pt-Ge (7-9), the authors propose that the Snn+ or Gen+ ions (Lewis acids) activate the carbonyl group by enhancing the positive charge of the C=O carbon atom. The effect of electrophiles on the lone pair of electrons of a carbonyl group is a well known process in coordination chemistry (18); Electrophiles are known to increase the rate of CO insertion in metal alkyl bonds. In the hydrogenation of alpha-beta unsaturated aldehydes they would favor the coordination of the multifunctionnal molecule by its aldehydic fragment. These ions would then be responsible for the increase of selectivity for the C=O hydrogenation In our case a similar explanation can be advanced. Preliminary IR data (15) indicate that CO can be chemisorbed on catalyst C (RhSn(C4H9)2/SiO2) in a linear and bridged manner, suggesting that the dialkyl tin fragment and CO could be adsorbed on rhodium in a close vicinity. It is also reasonnable to assume that tin is in the divalent oxidation state. In this case, the mechanism of the citral hydrogenation could be the following:

143

In conclusion this paper reports, for the first time, that an organometallic fragment grafted on the surface of a metal particle can render the metallic catalyst selective for a given reaction The implications in catalysis can be very wide since it could be possible to change the organometallic fragment at will for a given reaction as it is currently done in homogeneous catalysis.

.

REFERENCES Y.A. Ryndin and Y.I. Yermakov in Surface Organometallic Chemistry: Molecular Approaches to Surface Catalysis, NATO AS1 Series, J.M. Basset et al. (Edit.), Kluwer (Publ.), 1987,pp 127-1 55 O.A. Ferretti, L.C. Bettega de Pauli, J.P. Candy, G. Mabilon and J.P. Candy, in Preparation of Catalysts IV, B. Delmon et al. (Edit.), Elsevier (Publ.), 1987 pp 713-723 (3) J.P. Candy, O.A. Ferretti, G. Mabilon, J.P. Bournonville, A. El Mansour, J.M. Basset and G. Martino, J. Catal., 112,210 (1988) (4) P. Louessard, J.P. Candy, J.P. Bournonville and J.M. basset, in Structure and Reactivity of Surfaces, C. Morterra, A. Zechina and G. Costa (Edit.), Elsevier (Publ.), 1989, pp 591-600 M. Agnelli, P. Louessard, A. El Mansour, J.P. Candy, J.P. Bournonville and J.M. Basset, Catalysis Today, 5,63 (1989) P.N. Rylander, Catalytic Hydrogenation in Organic Syntheses, Academic Press, New York, 1979, pp 72-80 S. Galvagno, 2. Poltarzewski, A. Donato, G. Neri and R. Pietropaolo, J. Chem. SOC., Chem. Comm., 1729 (1986) 2 . Poltarzewski, S. Galvagno, R. Pietropaolo and P. Saiti, J. Catal., 190 (1986) S. Galvagno, 2. Poltarzewski, A. Donato, G. Neri and R. Pietropaolo, J. Mol. Cat., 35, 365 (1986) D. Goupil, P. Fouilloux and R. Maurel, React. Kinet. Catal. Lett., 35, 185 ( 1 987) P. Fouilloux, in "Heterogeneous Catalysis and Fine Chemicals", M. Guisnet e t al. (Edit.), Elsevier Science, Amsterdam (Publ.), 1988, pp 123-129. 6. Moraweck, P. Bondot, D. Goupil, P. Fouilloux and A.J. Renouprez, Journal de Physique, 48,297 (1987) J.P. Candy, O.A. Ferretti, G. Mabilon, J.P. Bournonville, A. El Mansour, J.M. Basset and G. Martino, J. Catal 112,201 (1988) B. Didillon, P. Lesage, J.P. Candy, J.P. Bournonville and J.M. Basset, to be published B. Didillon, J.P. Candy, J.M. Basset, F. Lepeltier and J.P. Bournonville, to be published in Preparation of Catalysts V. M. Ichikawa, A.J. Lang, D.F. Shriver and W.H. Sachtler, J. Amer. Chem. SOC.107,7216 (1985) A. El Mansour, J.P. Candy, J.P. Bournonville, O.A. Ferretti, G. Mabilon and J.M. Basset. Angewandte Chemie, 361 (1989) Angew. Chem. Int. Engl. 28, 347 (1989) (18) F. Correa, R.Nakamura, R.E. Stimson, R.L. Burwell Jr. and D.F. Schriver, J. Am. Chem. SOC.lJ22, 5112 (1980)

m,

m,


M . Guisnet et al. (Editors), Heterogeneous Catalysis and Fine Chemicals II 0 1991 Elsevier Science Publishers B.V., Amsterdam

145

SELECTIVE HYDROGENATION OF UNSATURATED ALDEHYDES OVER ZEOLITESUPPORTED METALS

D.G. BLACKMOND,' A. WAGHRAY,' R. OUKACI,', B. BLANC,' and P. GALLEZOT' 'Department of Chemical and Petroleum Engineering, University of Pittsburgh, Pittsburgh, PA 15261 (USA) *Institut de Recherches sur la Catalyse, CNRS, 2 Avenue Albert Einstein, 69626 Villeurbanne Cedex (FRANCE)

SUMMARY The hydrogenation of 3-methyl crotonaldehyde was investigated over Ru supported on NaY and KY zeolites in both liquid- and gas-phase reactions. Significant effects of the nature of the support on the product selectivity were observed. It was suggested that increased basicity of the zeolite resulted in increased selectivity towards the unsaturated alcohol product. INTRODUCTION Selectivity in the hydrogenation of =,p-unsaturated aldehydes has become an important topic in heterogeneous catalysis (refs. 1-4). Unsaturated alcohols, important in the synthesis of fine chemicals, may be produced selectively over certain supported group VIII-metal catalysts (refs. 5,6), but the general problem of the selective intramolecular hydrogenation of carbonyl groups remains a challenging task. Studies by this group have suggested (ref. 7) that an electronic interaction between a functionalized graphite support and small Pt or Ru particles enhances the selectivity of these metals towards the production of unsaturated alcohols, the desired product. Comparison with results f o r these metals on a carbon support demonstrated the significance of the support in this electronic effect. This paper discusses an extension of those studies to investigate the selectivity of Ru supported on NaY and Kexchanged NaY zeolites in the hydrogenation of 3-methyl

146

crotonaldehyde. Support effects have been observed for similar Ru/Y catalysts in the Fischer-Tropsch synthesis (ref. 8 ) , where modifications in the zeolite resulted in changes in catalyst activity for hydrogenation of olefins formed as primary products. EXPERIMENTAL Supported Ru catalysts were prepared using NaY zeolite (Strem Chemicals) as a support. The Ru/NaY catalyst was prepared using the zeolite directly as received. Potassium-exchanged NaY (KY) was prepared by ion-exchange of the NaY zeolite with potassium nitrate (Alpha Products, ultrapure) (refs. 10,ll). Ru-loaded catalysts were then prepared by ion-exchange of the two zeolite supports with Ru(NH,),Cl, (Strem Chemicals) to a nominal weight loading of 3% as described in detail in (9,ll). Samples were pretreated by heating in hydrogen at 75 cc/min to 573 K at 0.5 K/min and holding there for two hours. Samples were passivated and stored in air until use. Crystallite size was examined by TEM (JEOL 100 CX equipped with high-resolution pole pieces). The high pressure, liquid-phase hydrogenation of 3-methyl crotonaldehyde was carried out in a well-stirred batch autoclave under 4 MPa H, (Air Liquide, 99.995% purity) pressure using 0.1 mol of 3-methyl crotonaldehyde (UAL) (Merck) and 0.6 g catalyst. Isopropanol (37.5 cc) was used as a solvent. The catalyst was activated by stirring under 4 MPa H, pressure at 373K for two unsaturated aldehyde UAL hours prior to introduction of the reactant at the same temperature. The reaction products were monitored by repetitive sampling and gas chromatographic analysis. Since this was a batch reaction, data are reported as selectivity vs. conversion. Time of reaction to reach about 30% conversion was close to 6 0 minutes for Ru/NaY and 150 minutes for Ru/KY. Gas phase studies were performed at 0.1 MPa total pressure with a flow rate of 100 cc/min H, and 100 cc/min He (Linde). The helium stream was diverted through a saturator containing the liquid reactant UAL (Aldrich) such that its volume fraction in the inlet to the reactor was 0.5%. The gas hourly space velocity was 120 lh'lg'' catalyst. Prior to reaction, the catalyst was pretreated at 673 K for at least 2 hours following a 1 K/min rise to the reduction temperature. The reactor was cooled under

147

flowing hydrogen to 313 K prior to introduction of the UALsaturated He stream. Reaction products were analyzed by repetitive sampling and chromatographic analysis. After one hour on stream, the catalysts reached a steady state of about 1-3% conversion of UAL to three products, the unsaturated alcohol (UOL), the saturated alcohol (SOL), and the saturated aldehyde (SAL)

.

RESULTS AND DISCUSSION Characterization of the Ru/KY and Ru/NaY catalysts used in this study by transmission electron microscopy showed that the metal was well-dispersed within the zeolite as particles small enough to fit inside the supercages, less than 1 nm in diameter. Figure 1 compares the selectivities of hydrogenation products as a function of UAL conversion for liquid-phase reaction over the two RU catalysts. Both catalysts produced significant amounts of SAL. However, selectivity towards UOL, the desired product, increased threefold for the K-exchanged catalyst compared to Ru/NaY, Results of the continuous flow gas-phase reaction of UAL over the two Ru zeolite catalysts are given in Figure 2 , where the product selectivity is plotted against time of reaction. In this reaction mode the differences in product selectivity between the two catalysts were even more striking than those observed in the liquid-phase reactions described above. Once again the K-exchanged catalyst offered higher selectivity towards UOL compared to Ru/NaY. In fact, UOL was the major product for Ru/KY, surpassing SAL in contrast to the results for the liquid-phase reaction on these catalysts. Modification of the zeolite appears to have affected the selectivity of Ru in these hydrogenation reactions. Exchange of K cations for Na cations in Y zeolite increases the basicity of the support (ref. 9). In Fischer-Tropsch reactions over similar catalysts, Ru/Y catalysts so modified yielded significant increases in -the olefinic product fraction at the expense of paraffins. Olefins are believed to be primary products in F-T synthesis, with paraffins being produced from olefins in secondary hydrogenation reactions. In an analogous fashion, the Ru/KY catalyst used in the present study might also be expected to

148

inhibit intramolecular C=C hydrogenation reactions in molecules such as 3-methyl crotonaldehyde. This was indeed the case for both gas- and liquid-phase reactions, as can be seen from Figures 1 and 2. In accordance with interpretation of the F-T data, the increased basicity of the KY compared to Nay, possibly resulted in a transfer of charge from the support to the metal which in turn decreased the capability of C=C hydrogenation. Similar electronic effects were invoked in previous work by this group (7) to explain high selectivity of cinnamaldehyde to cinnamyl alcohol over Ru supported on functionalized graphite. A promoting effect on both the activity and selectivity for the production of unsaturated alcohol was also observed previously by this group (refs. 13,14) for hydrogenation of cinnamaldehyde over Pt-Fe catalysts. It was suggested that a dual-site mechanism operated in the bimetallic system whereby cationic Fe electron acceptor species preferentially activated the C=O bond while hydrogenation of the reduced Pt sites provided hydrogen for aldehyde to the alcohol. A similar mechanism might explain the increased UOL formation over Ru/KY. If the small crystallites of Ru are located within the zeolite supercages in close proximity to the K' neutralizing cations, the result may be a system with both metallic sites to provide hydrogen and a cationic site to activate Interactions between CO and alkali species whereby the CO bond. a direct K--O=C interaction causes weakening of the C=O bond have been suggested for alkali-promoted single crystal (refs. 15,16) and supported metal (refs. 17-19) systems. Recent gas-phase studies of crotonaldehyde hydrogenation over Pt/TiO, by Vannice and Sen (ref. 20) suggested a similar mechanism for TiO, moieties interacting with CO on Pt. The reaction network for hydrogenation of the unsaturated aldehyde crotonaldehyde was studied extensively by Simonik and They observed isomerization of the unsaturated Beranek ( 2 0 ) . alcohol to the saturated aldehyde at a reaction temperature of 433 K:

149

80

. A

-D

SAL

-+SOL

-

4ucc

91

Q u)

V

T

.

0

1

10

.

I

20

-

I

30

-

I

40

’

I

513

Conversion (“A)

. B 60

Q

SAL

+see 4 L K x

Figure 1. Product selectivities as a function of conversion in liquid-phase hydrogenation of 3-methyl crotonaldehyde over A ) Ru/NaY: and B) Ru/KY. UOL = unsaturated alcohol: SOL = saturated alcohol: SAL = saturated aldehyde. Pressure = 4 MPa; Temperature = 373K.

150

0

I

I

I

I

I

60

100

160

200

260

300

Tlrne (rnlna) too

13

10 -

a

ro

A A

90

-

-

M

UOL SOL SAL

Figure 2. Product selectivities as a function of time in gas-phase hydrogenation of 3-methyl crotonaldehyde over A ) Ru/NaY; and B) Ru/KY. UOL unsaturated alcohol; SOL = saturated alcohol; S A L = saturated aldehyde. Pressure = 0.1 MPa, Temperature = 313K.

-

151

In the present study, liquid-phase reactions over both NaY and KY showed significant production of SAL compared to the gas-phase studies. The higher temperature of the liquid-phase work might account for this increased SAL production through UOL isomerization as shown above. Another possibly important factor is the residence time of the products in the batch liquid-phase reactions. In the continuous flow mode, products may not be in contact with the catalyst long enough to undergo significant secondary isomerization reactions, a limitation which does not exist in batch reactions. Further work is underway in both liquid- and gas-phase hydrogenation studies aimed at achieving a better understanding of both the kinetics of the reaction network and the role of the zeolite support in altering the product selectivity of the metal. CONCLUSIONS Preliminary results for Nay- and KY-supported Ru catalysts demonstrate significant effects of the nature of the zeolite cation for the selectivity of 3-methyl crotonaldehyde hydrogenation. It was suggested that increased basicity of the zeolite resulted in increased selectivity toward the unsaturated alcohol product. These results agree with earlier suggestions that the nature of the support can have significant influence on the product distribution in the hydrogenation of -,p-unsaturated aldehydes. ACKNOWLEDGMENTS Support from NATO Scientific Affairs Division (Brussels, Belgium), the Centre International des Etudiants et Stagiaires (C.I.E.S., Paris, France) and the U.S. National Science Foundation (Presidential Young Investigator Program, CBT-8552656) is gratefully acknowledged.

152

REFERENCES

9

P.N. Rylander, IIHydrogenation MethodsI1l Academic Press, London, 1985. J.E. Germain, I1Catalytic Conversion of Hydrocarbons,I1 Academic Press, New York, 1969. R.L. Augustine, Catal. Rev. Sci.-Eng., u,285 (1976). R.L. Augustine, in IIAdvances in CatalysisI1l (D.D. Eley, P.W. Selwood, and P.B. Weisz, Eds.), V o l . 25, p. 56, Academic Press, New York, 1976. M.L. Khidekel, A.S. Bakhanov, A.S. Astakhova, K.A. Brikenshtein, V.I. Savchenko, I.S. Monakhova, and V.G. Dorokov, Izv. Akad. Nauk. SSR, Ser. Chem. (1970), p. 499. P.N. Rylander, and D.R. Steele, Tetr. Lett., 1579 (1969). A . Giroir-Fendler, D. Richard, and P. Gallezot, in tlHeterogeneousCatalysis and Fine Chemicals,1o (M. Guisnet et al., Eds.), p.171, Elsevier, Amsterdam, 1988. F.A.P. Cavalcanti, D.G. Blackmond, R . Oukaci, A. Sayari, A. Erdem-Senatalar, and I. Wender, J. Catal. , 113,1 (1988). Y.W. Chen, H.T. Wang, and J.G. Goodwin, Jr., J. Catal., B,

10

R. Oukaci,

1 2 3 4 5 6 7 8

499 (1984). A.

Sayari, and J.G. Goodwin,

Jr., J. Catal.,

102, 126 (1985). 11 12 13 14

15 16 17 18 19 20 21

J.Z. Shyu, E.T. Skopinski, A . Sayari, and J.G. Goodwin, Jr., Appl. Surf. Sci., a,297 (1985). Jacobs et al. JCS Far. 1 7 4 , 403 (1980). D. Richard, J. Ockelford, A. Giroir-Fendler, and P. Gallezot, submitted to Catal. Lett. D. Richard, P.Fouilloux, and P. Gallezot, in IICatalysis: Theory to Practice,Il Proc. 9th Intl. Congr. Catal., (M. J. Phillips and M. Ternan, Eds.), Vol. 3, p. 1074, The Chemical Institute of Canada, Ottawa, 1988. D. Lackey, M. Surman, Jacobs, S . Grider, D. and D.A. King, Surf. Sci. , 152-153, 513 (1985). K.J. Uram, L. Ng, and J.T. Yates, Jr., Surf. Sci., 177, 253

.

(1986) S. Kesraoui, R. Oukaci, and D.G. Blackmond, J. Catal., 432 (1987).

105,

P.A.J. Angevaare, H.A.C. Hendrickx, and V. Ponec, J. Catal. , 110, 11 (1988). P.A.J. Angevaare, H.A.C. Hendrickx, and V. Ponec, J. Catal. , 110, 18 (1988). M . A . Vannice, and B. Sen, J. Catal., 115, 65 (1989). J. Simonik, and L. Beranek, Collection Czechoslov. Comm.,

z, 353

(1972).


153

THE : lECHANISM OF HYOROGENOLYSIS AN0 I S O M E R I Z A T I O N OF OXACYCLOALKANES ON METALS, PART X? NATURE OF THE A C T I V E S I T E S I N THE REGIOSELECTIVE HYDROGENATION OF OXIRANES F. NOTHEISZ’,

A.G.

ZSIGMOND1,

M. BARTOKI, 0. OSTGARO 2 and G.V.

SMITH2

‘Oepartment o f Organic Chemistry, A t t i l a Jozsef U n i v e r s i t y , 06m t e r 8, H-6720 Szeged (Hungary) 20epartment o f Chemistry and Biochemistry and Molecular Science Program, Southern I l l i n o i s U n i v e r s i t y , Carbondale, I L 62901 (USA)

SUMMARY The hydrogenolysis and i s o m e r i z a t i o n of methyloxirane were s t u d i e d over various P t c a t a l y s t s i n order t o determine t h e number and nature of the act i v e s i t e s . The steps were found t o be t h e probable a c t i v e s i t e s and the transformation i s s t r u c t u r e - s e n s i t i v e . The r e g i o s e l e c t i v i t y is n o t a f f e c t e d by v a r i a t i o n i n the c a t a l y s t s t r u c t u r e , so i t i s determined by t h e nature of t h e metal.

INTRODUCTION

It are

i s w e l l known t h a t n o t a l l o f the exposed atoms of a metal

catalytically

tual

active

crystallite

a c t i v e . Establishment of the number and nature o f t h e

s i t e s i s an important step i n the determination of the

ac-

ccmplete

of surface r e a c t i o n s and i n p r e d i c t i o n and p r e p a r a t i o n of nore ac-

riiechanisms

t i v e and s e l e c t i v e metal c a t a l y s t s . Outing

studies

cycloalkanes

o f the hydrogenolysis and i s o m e r i z a t i o n o f

the

2-Me-oxa-

on t r a n s i t i o n metal c a t a l y s t s , i t was found t h a t d i f f e r e n t

met-

a l s have d i f f e r e n t r e g i o s e l e c t i v i t i e s ( r e f s 1,2). On Cu and N i c a t a l y s t s , p r i marily mation lysts

the C-0 bond adjacent t o the s u b s t i t u e n t is s p l i t , l e a d i n g t o t h e for-

of

a primary alcohol or aldehyde ( r e f . 3 ) , w h i l e on P t and

secondary a l c o h o l or ketone (Scheme

MeC(0)Me + MeCH(0H)Me

1).

mMe

+!!!k a

a ’ g b

Scheme 1 8

Pd

cata-

mainly t h e more d i s t a n t C-0 bond undergoes cleavage (ref. 4 ) y i e l d i n g a

Part I X . :

ref. 6

+PrOH

+ EtCHO

154

An explanation o f why the r e g i o s e l e c t i v i t y on Cu and N i i s d i f f e r e n t

from

on P t or Pd demands a knowledge o f the mechanism o f the r e a c t i o n . On

that and

Pd

c a t a l y s t s , a C-0 bond i n the oxiranes undergoes cleavage through

participation of site

chemisorbed hydrogen; the r e g i o s e l e c t i v i t y i s

governed

f a c t o r s . On N i and Cu, i o n i c i n s e r t i o n takes p l a c e and

stereochemical

regioselectivity

i s observed. Through deoxidation, o x i r a n e i s

Pt the by

oppo-

able

to

the Cu and N i surfaces, r e s u l t i n g i n i o n i c s u r f a c e s i t e s (Lewis acid-

oxidize

base s i t e s ) . I n t h e cases o f P t and Pd, the oxide formed i n t h i s way i s r a p i d l y reduced i n t h e presence o f hydrogen. results

Our

explained

by

show t h a t the observed d i f f e r e n c e i n r e g i o s e l e c t i v i t y can

regioselectivity

is

determined

oxygen,

by t h e n a t u r e o f the metal.

However,

other

r e g i o s e l e c t i v e r i n g opening on P t c a t a l y s t s ? This paper r e p o r t s

the

be the

responsible

metal by v a r y i n g i t s s t r u c t u r e ? What k i n d of s u r f a c e s i t e s are

for

i.e.

questions a r i s e : Is i t p o s s i b l e t o a f f e c t t h e r e g i o s e l e c t i v i t y o f

interesting a

d i f f e r e n t a f f i n i t i e s of t h e metals f o r

the

new

r e s u l t s concerning the above questions. EXPERIMENTAL Methods The

investigations o f 175 cm3

volume

. The

were performed i n a closed c i r c u l a t i o n r e a c t o r with a 3 volume o f the r e a c t a n t sample was 0.3 cm The c a r r i e r

.

was helium, f r e e d from oxygen with an A l l t e c h Oxy-Trap. The hydrogen used

gas in

the

measurements was produced by a Matheson 8326

equipped

electrolysis

apparatus

with a Pd d i f f u s i o n c e l l . 2-5 mg c a t a l y s t samples were used. D e t a i l s

on the experimental procedure were r e p o r t e d e a r l i e r ( r e f s . 5,6). Catalysts 0.48%, 0.83%, 1.17%, and 1.91% Pt/Si02 c a t a l y s t s o r i g i n a t e d from

The

laboratories o f pregnating

Burwell and B u t t ( r e f . 7). They were prepared e i t h e r by

H2PtC16

or by ion-exchanging Pt(NH3)4C12 on Davison s i l i c a

o f exposed P t atoms was determined by hydrogen

the im-

gel.

chemisorption

The

percentage

and

H2-02 t i t r a t i o n . The 0.13% Pt/Si02 c a t a l y s t was prepared i n our l a b o r a t o -

ry

from

platinum acetylacetonate ( r e f . 8). I t s d i s p e r s i o n was determined

CO

chemisorption and H2-02 t i t r a t i o n . A d d i t i o n a l l y , t h e p a r t i c l e s i z e s o f a l l

catalysts

were

examined

by e l e c t r o n microscopy on a H i t a c h i H

by

500H t r a n s -

mission e l e c t r o n microscope. For other d e t a i l s , see r e f s . 7,8. Analysis

A The 1.5m

Carlo

Erba Fractovap 2150 gas chromatograph was used f o r the

chromatographic

columns were 0.5 m 20% OOPN/Chromosorb

15% Reoplex 400/Chromosorb

W a t 293

analysis. K,

and

W a t 313 K.0ata were processed with a Perkin-

155

Elmer Sigma 10 integrator. Material The methyloxirane used in this study was a product of BOH (GC purity: 9 9 % ) ; prior to use, it was double distilled. RESULTS AN0 DISCUSSION Metal surfaces have a variety of sites which differ in the extent of coordinative unsaturation. The various sites are planes ( 1MI, steps (’M) and corners (3M) (ref. 9 ) . Much work has been done to correlate these surface sites with a set of interrelated reactions occurring simultaneously on the same surface (refs. 8,10,11). In order to determine the active sites in the transformations of methyloxirane, we studied its hydrogenation and isomerization on a set of Pt/Si02 catalysts with different dispersions. The results can be seen in Table 1. (Data were obtained at a hydrogen pressure of 33.3 kPa. The partial pressure of methyloxirane was 1.6 kPa.) TABLE 1 Turnover frequencies in transformations of methyloxirane and correlation between the fraction of active sites and the rate of transformation on Pt/Si02 catalysts. Loading Oispersion

(%I

(%)

1.91 1.17 0.48

7.1 40.7 62.1

0.28

0.83 0.13

80.9 100.0

0.22 0.04

MP Ac 2P

IP Na

= =

= = =

Ns =

MP 0.17

1.52

Ac Turnover 2Pfrequencies 1P (s-l) Total

10.10 1.54

1.23 5.22 11.70 2.36

0.19

0.18

0.88 2.86

0.19

0.37 0.60

0.19 0.03

2.47 8.73 23.90 4.31 0.44

N,”S

0.09 0.20

0.34 0.14 0.04

turnover frequency of the minor products. turnover frequency of acetone. turnover frequency of 2-propanol. turnover frequency of 1-propanol. number of active sites, determined by carbon disulfide poisoning in alkene hydrogenation. number of surface sites, determined by chemisorption methods.

The data in Table 1 show that the transformation of methyloxirane is a structure-sensitive reaction, since the total turnover frequency (TOF) in the transformation of methyloxirane varies appreciably with increasing dispersion. The rate of transformation passes through a maximum as a function of dispersion. Since the theoretical calculations of van Hardeveld and Hartog (ref. 12) indicate that the number of step sites changes via a maximum curve a? a function of the dispersion, this maximum curve may be an indication that

156

the steps are the a c t i v e s i t e s i n t h i s r e a c t i o n . found ( r e f . 5 ) t h a t t h e hydrogenolysis o f methyloxirane on

We e a r l i e r

Pt

c a t a l y s t s takes place v i a an a s s o c i a t i v e mechanism (Scheme 2). Me CH M e

Scheme 2 mechanism i n v o l v e s an a s s o c i a t i v e a d s o r p t i o n o f the oxirane; the r a t e -

The

step i s t h e r i n g opening, with t h e p a r t i c i p a t i o n o f hydrogen. The

determining following

steps

acetone.

are

relatively

I n deuterium, acetone-dl

rapid, resulting i n

secondary

was the main product, t h a t

is

or

alcohol

intramole-

H-migration does n o t p l a y a s i g n i f i c a n t role i n acetone formation.

cular

reduction

of

acetone t o 2-propanol does n o t take p l a c e as l o n g as

The

unreduced

methyloxirane i s present i n t h e m i x t u r e . The observed i n v e r s i o n o f t h e c o n f i g u r a t i o n is i n good accordance w i t h t h e p a r t i c i p a t i o n o f hydrogen i n t h e t r a n s i t i o n complex ( r e f . 1 3 ) . This two

mechanism can proceed e a s i l y on t h e s t e p s i t e s . Since t h e steps

c o o r d i n a t i v e unsaturations, they are a b l e t o adsorb hydrogen and

have

methyl-

oxirane simultaneously. The

same

Pt/Si02

c a t a l y s t s were poisoned by CS2;

the

hydrogenation

(+)-apopinene was used as an i n d i c a t o r r e a c t i o n ( r e f . 1 4 ) . The amount o f necessary t o e l i m i n a t e the hydrogenation a c t i v i t y p e r m i t s c a l c u l a t i o n o f fraction between in

CS2 the

corre-

t h e number o f s t e p s i t e s . S i m i l a r l y , a good c o r r e l a t i o n i s

found

t h i s f r a c t i o n and t h e r a t e o f methyloxirane t r a n s f o r m a t i o n (Table 1).

results

These

tion

o f metal s i t e s a c t i v e i n o l e f i n hydrogenation. This f r a c t i o n

with

lates

of

r e v e a l t h a t t h e s t r u c t u r e - s e n s i t i v i t y i s caused by t h e

the

number o f a c t i v e s i t e s , and t h e steps appear t o be

the

variaactive

s i t e s f o r the r e g i o s e l e c t i v e hydrogenation o f methyloxirane. Burwell propane

and coworkers ( r e f . 15) s t u d i e d t h e t r a n s f o r m a t i o n o f methylcyclo-

on t h e same series o f P t c a t a l y s t s , and found i t t o be m i l d l y

ture-sensitive. continuously

struc-

The TOF i n t h e hydrogenolysis of methylcyclopropane increased

as a f u n c t i o n o f the dispersion. The t o t a l TOF v a r i e d by a

two, w h i l e t h e a c t i v a t i o n energy of t h e r e a c t i o n was

independent

fac-

tor

of

the

percentage o f metal exposed.These f a c t s o f f e r e d a simple geometric expla-

of

157 nation of TOF.

t h e i r r e s u l t s : the more numerous the a c t i v e s i t e s , t h e h i g h e r

persion,

the

the numbers o f step and k i n k s i t e s increase with i n c r e a s i n g

Since

they

considered t h a t the hydrogenation o f methylcyclopropane

distakes

place on these s i t e s . In

s p i t e o f i t s close s i m i l a r i t y t o methylcyclopropane, methyloxirane

hibits sites

different are

behavior.

The observed maximum curve means t h a t

i n a c t i v e s i t e s i n t h e transformation of oxiranes. The

ex-

the

kink

reason

for

i n a c t i v i t y is n o t completely c l e a r , b u t i t i s very probable t h a t CO

the

poi-

soning i s responsible. The on

main minor product i s ethane. (The d i s t r i b u t i o n of t h e minor

0.48% Pt/Si02

catalyst:

CH4 = 2.6%, CO = 10.6%, C2H4 =

products

32.4%, C2H6

=

54.4%.) The minor products are produced by t h e decarbonylation o f methyloxirane,

but

is

sur-

only t h e hydrocarbons desorb, the CO remaining adsorbed on t h e

During the decarbonylation process, C-0 and C-C bond r u p t u r e s occur. I t

face.

w e l l known t h a t k i n k s i t e s are the a c t i v e s i t e s o f C-C hydrogenolysis,

SO

i t i s understandable t h a t decarbonylation w i l l poison t h e k i n k s i t e s . have a l s o s t u d i e d the change i n r e g i o s e l e c t i v i t y and t h e s e l e c t i v i t y o f

We

acetone

of

I t i s seen t h a t the r e g i o s e l e c t i v i t y does n o t depend on t h e d i s p e r s i o n :

data. on

formation as f u n c t i o n s o f the dispersion. Table 2 shows b o t h s e t s

all

c a t a l y s t s , the s t e r i c a l l y less hindered bond breaks. I n o t h e r

words,

r e g i o s e l e c t i v i t y i s n o t affected by the v a r i a t i o n i n t h e metal s t r u c t u r e .

the

This observation c o r r e l a t e s w e l l w i t h our former r e s u l t s : the d i f f e r e n t r e g i o selectivities nisms

are

due t o t h e d i f f e r e n t types o f mechanism, and these

mecha-

are governed by the d i f f e r e n t a f f i n i t i e s o f the metals f o r oxygen ( r e f s

3,4). TABLE 2 R e g i o s e l e c t i v i t y data f o r the transformation o f methyloxirane and s e l e c t i v i t y of acetone formation, Catalyst 1.91% P t / S i O 2 1.17% Pt/Si02 0.48% Pt/Si02 0.83% Pt/Si02

Hydrogen pressure (kPa 1

Regioselectivity

33.3.

0.92

33.3

0.96

1.8

1.8

33.3 1.8 33.3 1.8

1.00

1.00 0.97

1.00 0.95

Acetone selectivity

0.38 0.66 0.34 0.51 0.45 0.62

1.00

0.38 0.57

0.93

0.48 0.61

1.00 R e g i o s e l e c t i v i t y = TOFAc+TOF2p/TOFAc+TOF2p+TOFlp. S e l e c t i v i t y of acetone formation = TOFAc/TOFAc+TOF2p.

the

158

The

selectivity

of

acetone f o r m a t i o n e x h i b i t s a

curve

with

a

slight

minimum

character as a f u n c t i o n o f t h e d i s p e r s i o n ( F i g u r e 1, curve "a").

possible

e x p l a n a t i o n o f the minimum curve is r e l a t e d t o t h e mechanism.

the

two

main products (acetone and 2-propanol) have a

the

selectivity

(the

higher

prove at

common

intermediate,

is determined by t h e hydrogen a v a i l a b i l i t y on the s u r f a c e

the hydrogen pressure, t h e h i g h e r t h e a l c o h o l

selectivity).

the correctness o f t h i s explanation,we a l s o determined the availability,

the

a more c h a r a c t e r i s t i c change should be observed a t

lower

hydrogen pressure.) The r e s u l t s ( F i g u r e 1, curve "b") c o n f i r m t h e

idity

of

curve

"a".

the

the explanation: t h e minimum i n curve "b" is deeper, than

curves.

dispersion). others,

this

I n b o t h cases t h e r e is an experimental p o i n t which does

hythe val-

that

in

not

These are the s e l e c t i v i t y data on t h e most a c t i v e c a t a l y s t Since

To

selectivity

hydrogen pressure. ( I f t h i s s e l e c t i v i t y is determined by

lower

drogen

The Since

fit (62%

t h e r e a c t i o n is much f a s t e r on t h i s c a t a l y s t than on

leads

t o a hydrogen d e p l e t i o n on t h e surface, which

the

causes

a

higher 0x0 s e l e c t i v i t y .

SAC

0.7

: I

J

1.6 kPa

0.5

a

-

1

0.3

0.1

3 33.3 kPa

20

40

60dispersion 80 (%)

100

F i g . 1. The s e l e c t i v i t y o f acetone formation as a f u n c t i o n o f the d i s p e r s i o n . The sites surface

d i s s o c i a t i o n o f the hydrogen molecule i s thought t o occur on t h e (ref.

16) and t h e hydrogen atoms can m i g r a t e t o any o t h e r s i t e on

step the

( r e f . 17). I n other words t h e hydrogen a v a i l a b i l i t y on t h e s u r f a c e i n

connected w i t h the number o f s t e p s i t e s .

159

The experimental r e s u l t s p e r m i t the f o l l o w i n g conclusions: -The transformation of methyloxirane on various P t c a t a l y s t s i s a s t r u c ture-sensitive curve

reaction.

t o t a l TOF o f the r e a c t i o n e x h i b i t s

The

a

maximum

as a f u n c t i o n of dispersion. The s t r u c t u r e s e n s i t i v i t y i s caused by the

change i n the number o f a c t i v e s i t e s . -The

hydrogenolysis

and i s o m e r i z a t i o n o f methyloxirane take p l a c e

via

a

mechanism i n which hydrogen i s i n v o l v e d i n t h e rate-determining step. This rea c t i o n occurs on the step s i t e s . -The pendent The

regioselectivity

of

the transformation o f

methyloxirane

is

inde-

o f the c a t a l y s t s t r u c t u r e , b u t i t depends on t h e nature o f t h e metal.

selectivity

character

as

of acetone formation e x h i b i t s a curve with a s l i g h t minimum

a f u n c t i o n o f dispersion, since t h i s s e l e c t i v i t y i s

determined

by the hydrogen a v a i l a b i l i t y on the surface. REFERENCES

1 F . Notheisz, M. Bartok and A . G . Zsigmond, React. K i n e t . Catal. L e t t . , 29 (1985) 339-343. 2 G. Senechal a?d 0. Cornet, 81. SOC. Chim. France, (1971) 773-783. 3 F. Notheisz, A. Molnar, A.G. Zsigmond and M. Bartok, J. Catal., 98 (1986) 131-137. 4 F . Notheisz, A.G. Zsigmond, M. Bartok and G.V. Smith, J. Chem. SOC., Faraday Trans. l . , 83 (1987) 2359-2363. 5 M. Bartok, F. Notheisz, A.G. Zsigmond and G.V. Smith, J. Catal., 100 (1986) 39-44. 6 0. Ostgard, F . Notheisz, A.G. Zsigmond, G.V. Smith and M. Bartbk, J.Catal., (submitted f o r p u b l i c a t i o n ) . 7 T. Uchijima, J.M. Hermann, Y . Inoue, R.L. Burwell,Jr., J.B. Butt and J.B. Cohen, J. Catal., 50 (1977) 464-478. 8 F. Notheisz, M. Bartok, 0. Ostgard and G.V. Smith, J. Catal., 101 (1986) 212-217. 9 S. Siegel, J. Outlaw,Jr. and N. G a r t i , J. Catal., 52 (1978) 102-115. 10 M.J. Ledoux. Nouv. J . Chim.. 2 (1978) 9-15. 11 G.V. Smith, ' A . Molnar, M.M. 'Khan, 0.. Ostgard and T . Yoshida, J. Catal., 98 (1986) 502-512. 1 2 R. van Hardeveld and F. Hartog, Adv. Catal., 22 (1972) 75-113. 13 M.Bartdk, Stereochemistry of heterogeneous metal c a t a l y s i s , Wiley (1985) 14 G.V. S m i t h , F. Notheisz, A.G. Zsigmond, 0. Ostgard, T. Nishizawa and M. Bartok, i n : M.J. P h i l l i p s and M.Ternan (Eds), Proc. 9 t h I n t . Congr. Catal., Calgary, Canada, June 26-July 1, 1988, The Chem. I n s t . o f Canada, Ottawa, 1988, Vol. 4, pp 1066-1072. 15 P.H. Otero-Schipper, W.A. Wachter, J.B. B u t t , R.L. Burwel1,Jr. and J.B. Cohen, J. Catal., 50 (1977) 494-507. 16 G.A. Somorjai, Chemistry i n Two Dimensions: Surfaces, C o r n e l l U n i v e r s i t y Press, I t h a c a , N.Y., 1981. 17 K. Tanaka, Adv. Catal., 33 (1985) 99-158.


M. Guisnet et al. (Editors), Heterogeneous Catalysis and Fine Chernicak I1 0 1991 Elsevier Science Publishers B.V., Amsterdam

161

CHEMO-, REGIO- AND STEREOSELECTIVITY IN STEROID HYDROGENATION WITH CdA1203. INTRA- AND INTERMOLECULAR HYDROGEN TRANSFER REACTIONS.

N.RAVASIO1, M.GARGANO1, V.P.QUATRARO1 and M.ROSS12 1 Centro C.N.R. sulle Metodologie Innovative di Sintesi Organiche, Dipartimento di Chimica dell'Universita, via Amendola 173, 701 26 BAR1 (Italy) 2 Centro C.N.R. e Dipartimento di Chimica lnorganica e Metallorganica, Universita di Milano, via Venezian 21, 20133 MILANO (Italy)

SUMMARY The hydrogen transfer from different secondary alcohols to a steroidic conjugated enone and a saturated ketone in the presence of Cu/A1203 has been investigated. The stereochemical pathway of the reaction has been studied and the results are compared with those obtained by conventional molecular hydrogen addition in the presence of the same catalyst. While chemo- and regioselectivity are essentially unaffected by the hydrogen source, the stereoselectivity of the hydrogen addition to the conjugated olefinic moiety depends upon the alcohol used as hydrogen donor, and 5p:5cr isomer ratios ranging between 48 and 85% were observed. In the second step of H2 addition, the reduction of the 3-keto-group, a strong effect of the donor molecule on the stereochemistry was observed moving from 2-propano, to 2-octanol. However, an excess of the equatorial alcohol was obtained in every case. INTRODUCTION Supported copper catalysts are widely used in industrial chemical processes for the hydrogenation of different compounds. Of great importance are the synthesis of methanol in the presence of CuO/ZnO/A1203 catalyst and hydrogenation of fat oxo-aldehydes to alcohols with mixed copperchromium oxides. On the other hand, the use of copper catalysts in laboratory scale hydrogenations is little known. We recently found that prereduced 7.5% Cu on Al2O3, easy to prepare by conventional techniques, can b e conveniently used under very mild conditions (60°C, 1 atrn of H2) for the selective hydrogenation of steroidic enones. Thus, Cu/A1203 allows the chemospecific reduction of a,p

162

unsaturated carbonyl groups when other saturated keto-groups or isolated olefinic bonds are also present in the moleculel. Moreover, the enone olefinic bond is reduced with total regioselectivity and AIB cis, 5P-3-0XO derivatives are produced with stereoselectivity values up to 89%. The % O X 0 group is hydrogenated according to a subsequent, well separated step (mono:dihydrogenation selectivity up to 95%), giving equatorial alcohols. In the particular case of 1,4-androstadien-3,17-dioneregioselectivity promoted by copper was better than that exhibited by any catalytic system previously reported, giving up to 72% of 4-androsten-3,17-dione (93% regioselectivity).

However, during this study we have discovered, besides the expected hydrogenation produced by gaseous He activation, a secondary hydrogen source originated from alcoholic groups present in the substrate molecule or in the solvent. The formal hydrogen transfer from the alcoholic function to the enone one, parallels the conventional hydrogenation reaction as both processes are catalyzed by the same copper catalyst. Catalytic hydrogen transfer reactions are well known2 but they have been underutilized in the reduction of organic compounds with respect to the conventional use of molecular hydrogen or metal hydrides. These reactions promise potential advantages if compared with catalytic hydrogenations as the absence of gaseous hydrogen which involves considerable hazards. Moreover, transfer methods could afford new and not yet explored selectivities in the reduction of organic molecules. Direct comparison of reaction products by using gaseous H2 or a hydrogen donor are needed not only to get an insight into the reaction mechanism but also to evaluate the advantages or disadvantages of the two methods. Preliminary investigation on the reduction of steroidic molecules via hydrogen transfer showed new and interesting features of selectivity3. We report here the results obtained by using secondary alcohols as hydrogen donors towards steroidic conjugated enones and saturated ketones in the presence of 7.5% Cu on alumina.

163

RESULTS Unsaturated A5-3P-hydroxy steroidic molecules undergo a facile isomerization in toluene solution at 60°C in the presence of Cu on alumina under inert atmosphere. The saturated ketones derived through a formal hydrogen transfer from the alcoholic to the olefinic moiety are formed, besides small amounts of A4-3-ketone.

The internal hydrogen exchange favours the formation of the 50 (A/B cis) isomer which was obtained with 72-88% stereoselectivity, w h e r e a s conventional catalytic hydrogenation of A 5 olefinic bonds in the presence of Pd catalysts gives only the 5a isomer and homogeneous hydrogenation catalysts are totally inactive4. This observation can be used to derive a possible reaction mechanism for the hydrogen transfer process. We assume that the first step is the dehydrogenation of the alcoholic group, followed by isomerization of the unsaturated ketone to the conjugated one:

&-& CU/A1203

0

0

This latter point was experimentally proved by converting As-cholesten3-one into the conjugated A 4 isomer in the presence of Cu/A1203. The subsequent hydrogen addition to the A4-3-one follows the stereochemistry expected in the presence of heterogeneous catalysts as Cu/A1203 which produces an excess of the 5p isomer also with gaseous H2. The synthetic value of this reaction can be outlined.

164

In fact, the production of 5P-steroids from A5-3P-ols, readily available and cheap starting materials, requires preliminar oxidation through the Oppenauer reaction or, more recently, fermentation to the A 4 - 3 - k e t o derivatives. From this one 5p steroids are readily obtained through catalytic hydrogenat i o n4. On the other hand, the use of Cu/A1203 allows the production of 5p derivatives (cardioactive agents) in one step. Moreover this result suggests the investigation of the role of different external hydrogen donors on the selectivity in the hydrogenation reaction of steroidic molecules. Therefore we used 4-androsten-3,17-dione 1 and 5 a - a n d r o s t a n - 3 , 1 7 d i o n e 2 as model substrates to investigate the chemo- regio- and stereoselectivity of hydrogen transfer from different secondary alcohols , 2-propano1, 2-octano1, cyclohexanol, 1-phenyl-ethanol and diphenylmethanol in the presence of Cu/A1203. In particular, hydrogenation of 1 allowed to determine the selectivity towards 5p isomers, whereas the percent of axial alcohol was derived from the hydrogenation of 2 . These results can be compared with those obtained with the same catalyst in the presence of molecular hydrogen.

All the examined alcohols were active as hydrogen transfer reagents both towards the olefinic and the carbonylic double bond in a wide range of temperatures (60"-140°C). Under these conditions preliminar tests showed that selectivity does not depend on the temperature. Blank experiments using A1203 pretreated as the Cu containing catalyst at 270°C showed that the hydrogen transfer in the presence of the support alone is negligible. On the other hand prereduced Cu on Si02 gave the same results as Cu/A1203 in the hydrogenation of 2. All hydrogen transfer reactions were carried out under N2 at 90°C. According to GLC analysis the time required for the reduction of 1 to the corresponding ketones ranged between 20 min and 1.5 hours, whereas the reduction of 2 to the corresponding alcohols required 2-4 hours. Table I and Fig.la and b collect the experimental results obtained in the hydrogenation of 1 and 2 in the presence of 7.5% Cu/A1203.

165

The chemoselectivity in the hydrogen transfer reaction is the same already observed in H2 addition conditions in the presence of Cu/AI203. Thus, the conjugated enone is selectively hydrogenated while the saturated keto-group remains unchanged. Also regioselectivity is the same and the olefinic bond is reduced before the carbonylic one. However mono:dihydrogenation selectivity is very poor and saturated alcohols begin to form almost at the same time as saturated ketones. This situation is very different from that observed in the presence of molecular H2, when two well separated hydrogenation steps are present, as evidenced by Fig.la and Fig.1b. By comparing the results on stereochemistry obtained in the reduction of 1 and 2 by using alcohols and molecular hydrogen, a great flexibility of the hydrogen transfer reaction is apparent. Thus, selectivity towards the formation of 5p isomer can be modified from 48% to 85% and towards the formation of the axial alcohol from 15 to

45%.

0

1

Fig.1. Products distribution vs. equivalents of H2 or alcohol consumed during the hydrogenation of 1 in the presence of Cu/A1203 and molecular H2 (a) or 1-Ph-ethanol (b). ~ = 1 , 0 = 5 ~ - d i o n e , ~ = 2 , r = 5 ~ -x=5a-ols, ols, n=5P-diols.

166

Therefore by changing the nature of the reagent we can move the reaction from non selective conditions to highly directed stereo addition of hydrogen. In particular, 85% of the 5p isomer with respect to the 50: one represents the highest observed value which can not be obtained with gaseous H2 either changing operative conditions (T and P) or the nature of the copper catalyst. .................................................................. Table la Stereochemical course during the hydrogenation of 1 and 2 by hydrogen transfer in the presence of Cu/A1203

2-propanol 2-octanol cyclo hexanol 1(Ph)ethanol diphenylmethanolb

48 55 85 72 73

15 45 42 16 15

a = donor alcohol as solvent, 90°C b = l g in toluene (5 mL), 900c

Concerning the hydrogen transfer mechanism, the formation of surface copper hydrides as intermediates can be suggested also in the case of alcohols as donors1 This would explain the observed regioselectivity according to a 1 , 4 addition process followed by a prototropic rearrangement, as discussed by Bonnelle et al. for the hydrogenation of simpler molecules on copper chromites. Unfortunately, not simple correlations between molecular structure of the donor alcohol and stereoselectivity can be actually derived and more experiments with different alcohols are required. However, the products stereochemistry found when using 1-phenylethanol and diphenylmethanol as donors is close to that observed in H2 addition conditions, thus suggesting the occurrence o f two consecutive steps,

167

dehydrogenation of the donor alcohol and hydrogenation of the sterooid substrate: donor ketone + H2 Substrate + H2---+ Substrate.H2

--------,

In the case of 2-propanol and 2-octanol a direct surface hydrogen transfer reaction may take place, as was demonstrated by Burwell for the reaction between 2-propanol and 2-butanone on copper oxide’. According to this hypothesis, it is not surprising that the donor size influences the product stereochemistry. It is worth saying that both lacking of selectivity in the A 4 olefinic moiety hydrogenation and increasing of the axial epirner in 3 ketoderivatives saturation following the donor steric demand are typical aspects of steroid reduction by means of complex hydridess.

EXPERIMENTAL IR spectra were recorded on a Perkin-Elmer 577 instrument; 1 H and 1% NMR spectra were recorded on a Varian XL 200 instrument. GC analysis were performed on a Hewlett-Packard 5880 instrument, FI detector, equipped with a Methyl Silicone fluid capillary column (35 m), by using n-esadecane as internal standard. GC-MS analysis were performed using a HewlettPackard 5995 C instrument. Reaction products were identified by comparison with authentic samples, 1% NMR and MS data. Catalyst preparation: to a solution of Cu(N03)2.3H20 (16g ) in 150 ml H20, 30% NH40H was added till dissolution of the hydroxide initially formed. To the clear solution 20 g of alumina (Riedel-De-Haen), pH 4.5, surface area 200 m2/g, particle size 70-290 mesh, were added. The suspension was stirred for 10 minutes and diluted, very slowly,to 2L volume, stirred for 30 minutes and filtered off. The solid was dried at 120°C for 4 hours and heated in air at 350°C for 6 hours. The catalyst was pretreated at 270°C with H2 at atmospheric pressure (prereduced catalyst: Cu/A1203) following the procedure previously reported for copper chromiteg. Thus, a sample of CuO/A1203 was introduced in a glass reactor and heated at 270°C in a thermostattic device for 20 min with the reactor open, then under vacuum for 20 min. Hydrogen at 1 atm was carefully introduced: a fast reduction took place as indicated by water condensation on the cold arm of the reactor. Water was removed from time to time under vacuum and finally the catalyst was cooled under H2 to the

168

temperature choosen for the reaction. Hydrogen was removed under vacuum and the reaction vessel washed several times with N2 before its use in the hydrogenat ion react io n . Cu/AI203 obtained in this way has a copper content of 7-8%, determined by atomic absorption, surface area before the reduction treatment 220-250 m*/g (BET methodlo), specific Cu(0) area after pretreatment 20-30 m2/g (N20 decomposition1 '). Hydrogenation procedure. The steroid (0.2 mmoles) was dissolved in the donor alcohol (6 ml) and the solution heated to 90°C, transferred, under N2, in the reaction vessel where the catalyst (150 mg) had been previously pretreated and stirring was begun. To monitor the products distribution versus the alcohol equivalents consumed (Fig.l), 20 p L samples were withdrawn from the reacting solution through a viton septum and analyzed by GC. EquatoriaVaxial ratio was determined on the mixtures coming from the hydrogenation of 2 , by digitonide precipitation1 2, GC quantitative determination after silyl derivatives formationi 3 and CAD-MIKE spectroscopy following the procedure already described14 . REFERENCES 1) N.Ravasio and M.Rossi, J. Org. Chem. submitted for pubblication 2) R.A.W.Johnstone, A.H.Wilby and I.D.Entwistle, Chem. Rev. 85 (1985) 129 3) M.Gargano, V.P.Quatraro, N.Ravasio and M.Rossi, V IUPAC Symposium on Organometallic Chemistry directed towards Organic Syntheses, October 1-6, Firenze (Italy), Abstracts P S I -55 4) R.L.Augustine, in J.Fried and J.Edwards (Eds.), Organic Reactions in Steroid Chemistry, Van Nostrand-Reinhold, New York, 1972, chapt. 3. 5) D.Lednicer and L.A.Mitscher, Organic Chemistry of Drug Synthesis, vol.1 and Vol. II, John Wiley &Sons, New York, 1977 and 1980 6) a)R.Hubaut, M.Daage and J.P.Bonnelle, Applied Catalysis 22 (1986) 231 ; b) R. Hubaut, J.P.Bonnelle and M.Daage, J. Mol. Catalysis 55 (1989) 170. 7) J.Newham and R.L.Burwell, Jr., J. Am. Chem. SOC.86 (1964) 1179 8) D.M.S.Wheeler and M.M.Wheeler in ref.4, chapt.2 9) C.Fragale, M.Gargano and M.Rossi, J. Am. Oil Chem. SOC.59 (1982) 465 10) S.Brunauer, P.H.Emmett, E.Teller, J. Am. Chem. SOC. , 60 (1938) 309 11) T.J.Osinga, B.G.Linsen, W.P. Van Beek, J. Catalysis 7 (1967) 277 12) L.F Fieser,.M. Fieser, "Natural Products Related to Phenanthrene", Reinhold Pub. Corp., New York (1949), 3rd Ed., pp. 102-104 13) E. M. Chambaz, E. C. Homing, Analyt. Biochem. 30 (1969) 7 14) B. Pelli, P.Traldi, M. Gargano, N. Ravasio, M. Rossi, Org. Mass Spectrom. 22 (1987) 183.

169


SELECTIVE HYDROGENATION OF AROMATIC AND ALIPHATIC NITRO COMPOUNDS BY HYOROGEN TRANSFER OVER MgO

J. KIJENSKI, M. GLINSKI, R. WTSNIEWSKI and S. MURGHANI The Laboratory of Catalytic Synthesis, Institute of Organic Technology Warsaw Technical University (Politechnika), 00 662 Warsaw, Poland SUMMARY The possibility of using of aliphatic alcohols as hydrogen donors for the catalytic transfer reduction of nitro group over MgO was examined. Catalytic hydrogen transfer was found to be effective and selective method f o r reduction of nitrobenzene, 4-nitrotoluene, 4-chloronitrobenzene, 4-nitro-m-xylene, -nitrostyrene, 3-nitrobenzaldehyde, 1-nitropropane, and 1-nitrobutane. Conversion of starting nitro compound into desired product depended on the alcohol used as a donor. Adsorption of reactant and catalyst deactivation were studied by esr. New aspects of a role of one-electron donor sites in hydrogen transfer over MgO were demonstrated.

p

INTRODUCTION Commercially nitroarenes arid nitroalkanes are reduced to corresponding amines on nun-catalytic (using Bechamp o r Zinin method) or on catalytic way (hydrogen gas over metals). The catalytic transfer hydrogenation is an effective alternative for the above methods. Reductions of nitroarenes to aminoarenes by hydrogen transfer was reported for a wide range of metallic catalysts such as Pd, Cu, Fe, Ni, Rh and Ru (ref. 1). In a search for active hydrogen donors, it was found that formic, phosphinic and phosphorous acids, and their salts, unsaturated hyddrocarbons as cyclohexene, and especially hydrazine would reduce nitro compounds to amines with satisfying yield (ref. 1). The only but important limitation of the process is the high price of donors used. In the present paper we have examined the possibility of using of alcohols as hydrogen donors for catalytic transfer reduction (CTR) of nitro group. This paper is the continuation of our previous efforts at studying the synthetic application of hydrogen exchange on oxides. Our recent results concerned the reduction of aldehydes (saturated and unsaturated), epoxides, and nitriles, as well as the dehydrogenation of long chain aliphatic alcohols and alkylaromatics (ref. 2 ) . The reduction of a series of aromatic and aliphatic nitro compounds with various alcohols was studied over magnesium oxide as the catalysts. The hydrogen transfer reaction between alcohols and nitrocompounds should proceed according to the following equations:

170

RN02

+

RNOz

+ 3R1R2CHOH-RNHz

3R1CH20H-RNH2

”

3R C H‘

+

+

+ 2H20 f o r primary and

3R1RzC = 0

+

2H20

f o r secondary a l c o h o l s .

I n b o t h cases the minimum donor - acceptor molar r a t i o demanded f o r t h e reduct i o n o f n i t r o - t o amino group equals 3.

EXPERIMENTAL Reactions were c a r r i e d o u t i n a continuous f i x e d bed r e a c t o r a t atmospheric pressure i n t h e temperature range 350-450°C w i t h MgO as a c a t a l y s t . The r a d i c a l p r o p e r t i e s of the f r e s h , deactivated and regenerated c a t a l y s t , as w e l l as t h e adsorbed s t a t e s o f r e a c t a n t s were s t u d i e d by esr u s i n g Radiopan SE/X 2547 spectrometer. The adsorption o f r e a c t a n t s was performed according t o t h e procedure described elsewhere ( r e f . 3 ) . The magnesia c a t a l y s t p r e p a r a t i o n was described p r e v i o u s l y ( r e f . 3 ) . The l i q u i d product mixtures were analysed by gc (Chrom 5) using 4-m g l a s s column f i l l e d with 20 % OV-101 on Gas Chrom Q . Products were characterized by comparison w i t h a u t h e n t i c samples !ir, gc) and by m e l t i n g p o i n t s o f t h e i r hydrochlorides. RESULTS AND DISCUSSION values f o r the r e a c t i o n s of hydrogen t r a n s f e r between primary and seP condary alcohols and n i t r o compounds were c a l c u l a t e d u s i n g Van Krevelen and The K

Chermin procedure ( r e f . 4 ) . S i m i l a r l y as the simple r e d u c t i o n w i t h hydrogen the c a t a l y t i c hydrogen t r a n s f e r from alcohols t o n i t r o d e r i v a t i v e s is s t r o n g l y favor e d thermodynamically. For a l l s t u d i e d r e a c t i o n s w i t h primary a l c o h o l s the K values were o f the range o f h o l s K N 1044 P

P w h i l e f o r processes i n v o l v i n g secondary a l c o -

.

Reduction o f n i t r o a r e n e s Magnesium oxide e x h i b i t e d h i g h a c t i v i t y and h i g h s e l e c t i v i t y i n t h e hydrogen t r a n s f e r from alcohols t o s t u d i e d n i t r o a r e n e s . Because o f t h e l i m i t e d space o f the paper t h e complete amine y i e l d

-

temperature dependence was shown only

for

nitrobenzene r e d u c t i o n (Table 1). However, a l s o f o r o t h e r r e a c t a n t s the y i e l d o f the aminic product increased c o n t i n o u s l y between the values obtained a t the l o west (350°C) and the h i g h e s t (450°C) r e a c t i o n temperatures. Below 350°C t h e comp l e t e l a c k of a c t i v i t y o f MgO i n the s t u d i e d t r a n s f o r m a t i o n was noted. The same was observed by us e a r l i e r ( r e f . 2) i n the case t h e c a t a l y t i c t r a n s f e r r e d u c t i o n

of o t h e r f u n c t i o n a l groups. (i) Reduction o f nitrobenzene. The conversion o f nitrobenzene i n t o a n i l i n e depended s t r o n g l y on t h e a l c o h o l used as a hydrogen donor. Unexpectedly, methan o l was the most e f f e c t i v e donor molecule (91.4 % o f a n i l i n e ) . The order of ac-

171

tivity for hydrogen donation was found to be methanol-isopropanol > s-butanol n-butanol > i-butanol. >n-propanol >ethanol (ii) Reduc-tionof other nitroarenes. Table 2 depicts the yields of amines formed by reduction of the studied nitroarenes. No general rule of usefulness of particular alcohols for the reduction process was observed. Maximum yield of p-tohidine (39.8 % ) was gained in the reaction of 4-nitrotoluene with n-butanol. Highest conversion of 4-nitro-m-xylene into 4-amino-m-xylene was obtained using isopropanol as a donor molecule, while the most effective action of ethanol was noted in the reduction of 4-chloronitrobenzene (62.8 % of 4-chloroaniline). It should be wnderlined that all studied reactions occured with the selectivity higher than 99 %, only traces of condensation tar-like products were detected in the products mixture. The ease of reduction decreased in the order 4-chloronitrobenzene > 4-nitrotoluene >2,4-dimethylonitrobenzene. The above observation led us to the preliminary conclusion that the electronegative character of the substituent diminishes fitness of nitro group in nitroarene on the reduction. (iii) Reduction of nitroarenes possessinq second reducible group. The p r o ducts distributions of the redilction of -nitrostyrene and 3-nitrobenzaldehyde with various alcohols are listed in Table 3. -Phenylethylarnine (I) - the product of total reduction of side chain as well as both products of its partial reduction: -phenylvinylamine (11) and p-phenylnitroethane (111) were obtained in the reaction of P-nitrostyrene. The type of a donor used strongly affected the reaction selectivity. E.g. using methanol as hydrogen donor the ratio of I : II : I11 (450'C) was 41.2 : 49.0 : 8.4 (at the conversion of reactant - 100 a), the same ratio was 12.1 : 67.1 : 18.8 (at the reactant conversion of 98.0 % ) €or isopropanol (35OoC), and 30.1 : 42.3 : 15.4 (at the conversion of /3-nitrostyrene of 97.8 %) for s-butanol. The greater ease of reduction of nitro group in comparison with C=C bond reduction is obvious, however, the presence of remarkable amounts of -phenylethylamine in reaction products indicates that exchange of -NO2 group accelerates the reduction of a neighbour vinyl group. It should be emphasized that the reduction of 13-nitrostyrene by catalytic transfer reduction leads to the products completely different than these obtained in hydrogen transfer over metals. Namely, reduction of -nitrostyrene with formic acid over palladium gave the oxime of phenylacetaldehyde (ref. 5). Much more spectacular were the selectivity variations in the case of 3-nitrobenzaldehyde reduction (Table 3 ) . Depending on the hydrogen donor used 3-nitrobenzyl alcohol (methanol, 450°C) or 3-aminobenzaldehyde (i-propanol, 450°C) were the main reaction products.

>

/3

p

P

Reduction of nitroalkanes The effectiveness of catalytic transfer hydrogenation of nitroparaffins over MgO is demonstrated in the Table 4. At 450°C 1-nitropropane yielded 94.9 % of

TABLE 1

F

N 4

The y i e l d s of a n i l i n e formed i n t h e r e a c t i o n of n i t r o b e n z e n e w i t h v a r i o u s a l c o h o l s o v e r MgO, HLSV-1 Reaction temperature "C

Y i e l d of a n i l i n e u s i n g a g i v e n donor mol %

Oonor/acceptor ratio methanol

ethanol

n-propanol

i-propanol

n-butanol

s-butanol

12.3 18.2 22.6 25.6 37.1

30.0 33.1 41.2 50.0 54.4

i-butanol

______

350 375 400 425 450

3 3 3 3 3

: : : : :

77.3 77.8 78.4 81.5 91.4

l l l l l

15.8 26.5 33.6 39.3 51.3

26.1 30.9 38.3 39.1 47.3

62.5 73.9 74.5 78.3 91.0

tr 5.9 12.3 14.1 29.9

~~

TABLE 2

The y i e l d s o f amines formed i n t h e r e a c t i o n s of c o r r e s p o n d i n g n i t r o a r e n e s w i t h v a r i o u s a l c o h o l s o v e r MgO, donor : a c c e p t o r ratio-3,

HLSV-1

Reactant

Reaction temperature "C

Y i e l d o f amine u s i n g a g i v e n donor rnol % methanol

ethanol

n-propanol

i+ropanol

n-butanol

i-butanol

~~

4-nitrotoluene

350 450

18.1 24. 2

14.4 33.1

28.3

12.5 29.6

13.9 39.8

2,4-dimethylnitrobenzene

350 450

7.3 13.7

16.6 31.0

6.3 18.2

tr 16.0

tr 20.7

4-chloronitrobenzene

350 450

19.0 32.4

38.0 58.1

11.7

25.1 63.6

13.8 27.4

18.4 45.1

TABLE 3 The p r o d u c t s of t h e r e d u c t i o n of n i t r o a r e n e s p o s s e s s i n g a second r e d u c i b l e group w i t h v a r i o u s a l c o h o l s over MgO, donor : a c c e p t o r r a t i o - 6 , Hydrogen donor

React i o n temperature

"C

HLSV-1 P r o d u c t s of

pe t h-phenylylamine

P-nitrostyrene reduction mol %

P r o d u c t s of 3 - n i t r o b e n z a l d e h y d e r e d u c t i o n rnol %

P-phenylvinylamine

3-aminobenz y l alcohol

lI)-phenylnitroethane

3-aminobenzaldehyde

3-nitrobenzyl alcohol

methanol

350 450

41.3 41.2

35.8 49.0

14.3 8.4

2.8 13.6

-

82.6

ethanol

350 450

18.7 20.4

44.0 49.9

21.2 29.0

2.0 35.1

5.7 8.9

36.0

n-propanol

350 450

19.4 36.4

45.1 28.2

30.5 20.3

i-propanol

450 350

12.1 22.1

61.1 47.1

18.8 25.2

2.7 14.8

1.5 51.6

7.0

15.4 20.2

42.3 46.4

30.1 32.3

s-butanol

350 450

-

-

TABLE 4 The y i e l d s of c o r r e s p o n d i n g arnines formed i n r e a c t i o n s of 1 - n i t r o p r o p a n e and 1 - n i t r o b u t a n e w i t h v a r i o u s a l c o h o l s ,

donor

: acceptor r a t i o - 3 ,

Reactant

HLSV-1 Reaction temper a ture

Y i e l d of amine u s i n g a g i v e n donor rnol % methanol

350

1-nitropropane

450

4.3 67.5

1-nitrobutane

350 450

11.1 83.7

ethanol

n-propanol

i-propanol

n-butanol

s-butanol

i-butanol

16.5

10.6 41.2

9.3 94.9

35.5 84.9

3.7 76.3

21.7 90.0

23.8 87.9

9.6 90.9

9.8 79.0

8.7 16.9

6.3 53.8

13.6 93.5

18.6

W

174

1-propylamine with ~ 1 0 %0 selectivity (isopropanol). At the same temperature 1-nitrobutane was converted to 1-butylamine with yield of 93.5 % and 100 % selectivity (isobutanol). Catalyst deactivation and regeneration The catalyst decay during nitrobenzene reduction was studied in long-time experiments. The gradual poisoning of the catalyst was observed (Table 5) which led in 4-5 hrs to the significant diminishing of reactant conversion. TABLE 5 The decrease of aniline yields (mole %) during nitrobenzene reduction with various alcohols, temperature - 450°C, donor : acceptor ratio-3, HLSV-1 Time on stream hr 0

1.0

2.0

3.0

4.0

5.0

20.0

91.4 91.0 91.0 91.0 51.3 54.4

69.1 46.5 91.3 90.7 31.4 32.6

57.7 25.3 90.8 91.4 16.5 17.4

36.0 13.8 54.0 90.3 15.3 11.2

18.6 12.0 32.1 91.0 9.5 8.8

10.6 9.6 21.0 90.9

10.0 10.4

Hydrogen donor methanol isopropanol 1 isopropanol(N2)2 isopropanol(02) n-propanol s-butanol

90.7 9.1 8.3

1-catalyst regenerated by nitrogen (450°C) treatment during 10 min after each 33 min of reaction, 2-catalyst regenerated by air treatment according the same procedure Tndepending on the used alcohol the deactivation profiles reached the plateau corresponding the yield of aniline in the range of 8-10 mol %.Various regeneration procedures have been applied to preserve the catalyst activity on the high level. The calcination of used catalyst during 10 min in air at 450°C following each 0.5 hr of catalyst work was found to be the optimum regeneration mode (Table 5). The heating in neutral gas (nitrogen or argon) did not result in satisfying activity stability. The same regeneration procedure as f o r nitrobenzene was successfully adopted in reduction of other investigated nitroarenes. Esr studies of surface intermediates In our previous paper (ref. 2) we demonstrated the particular role played by one-electron donor centres on magnesia surface in catalytic transfer hydrogenation. Moreover, nitroarenes exhibit high tendency to convert themselves into corresponding anion radicals during adsorption on MgU. Thus, it was expected that esr spectroscopy would reveal new data concerning the reactants activation.

175

Esr i n v e s t i g a t i o n s were done of c a t a l y s t s samples with r e a c t a n t s adsorbed a t room and a t r e a c t i o n temperature. Also the p r e p a r a t i o n s o f d e a c t i v a t e d and regenerated c a t a l y s t were studied. From a l l s t u d i e d n i t r o compounds o n l y t h e f o l l o wing: nitrobenzene (parameters o f esr s i g n a l : g = 2.0031; A Hmax = 7 Gs; i n t e n -

.

1

.

spin g- 1, m-dinitrobenzene (2.0043; 9 Gs; 1.9 10" s p i n s i t y 1.2 g-'), 4 - n i t r o t o l u e n e (2.0051; 10 Gs; 6.1 10" s p i n . g -1), 4-nitro-m-xylene (2.0031;

-

1

13 Gs; 1 . 8 . 1019 s p i n - g- ) , formed t h e corresponding anion r a d i c a l s .

None from the used a l c o h o l s was converted i n t o paramagnetic species on MgO s u r f a ce. New evidence for t h e importance o f one e l e c t r o n donor centres f o r c a t a l y t i c t r a n s f e r r e d u c t i o n has a r i s e n from esr i n v e s t i g a t i o n s . Both, h e a t i n g o f anion r a d i c a l o f nitrobenzene on MgO surface from room temperature t o 350"C, or a d s o r p t i o n o f nitrobenzene a t 350°C on f r e s h MgO r e s u l t e d i n the new paramagnetic species. Esr s i g n a l ( A on F i g . 1) o f t h i s species d i f f e r e d i n shape ( l a c k o f h . f . c .

s t r u c t u r e ) and i n g va-

l u e (g = 2.0023) from t h e s i g n a l o f t h e par e n t i o n r a d i c a l , i n t e n s i t y remained o n l y s l i g h t l y changed. During t h e r e a c t i o n o f n i trobenzene with a l c o h o l surface species un'

1

derwent f u r t h e r e v o l u t i o n and

esr spectrum o f

MgO a f t e r 5 h r s o f r e a c t i o n revealed t h e preF i g . 1. E s r o f paramagnetic spesence o f a narrow s i g n a l ( A H m a x = 4 Gs, c i e s on deactivated and regeneg = 2.0023) o f the i n t e n s i t y c.a. 600 times r a t e d c a t a l y s t surface. higher than.the one measured f o r t h e i o n r a d i c a l (B on F i g . 1). Most probably the new s i g n a l d e r i v e d from r a d i c a l s formed i n a surface c h a i n r e a c t i o n o f adsorbed reactants. During regeneration by a i r treatment the number o f s u r f a c e r a d i c a l species remarkably diminished, the esr spectrum (C on F i g . 1) o f regenerat e d c a t a l y s t consisted from t h e narrow s i g n a l (AHmax = 3 Gs, g = 2.0030) which i n t e n s i t y corresponded t o only 8 . 10''

s p i n . g - I . The one-electron donor proper-

t i e s of deactivated and regenerated c a t a l y s t were c o n t r o l l e d u s i n g nitrobenzene ( e l e c t r o n a f f i n i t y 0.7 eV) and m-dinitrobenzene (E.A.

1 . 4 eV) adsorption. The

adsorption o f nitrobenzene on b o t h deactivated and regenerated surfaces d i d n o t l e a d t o the appearance o f a new paramagnetic surface species. The same r e s u l t was noted when n-dinitrobenzene adsorbed on deactivated magnesia. However, m-dinitrobenzene adsorption on regenerated MgO surface r e s u l t e d i n the formation o f 18 a t y p i c a l r a d i c a l species ( g = 2.0043,aHmax = 12 Gs, i n t e n s i t y 1.2. 10

1

s p i n . g- ) (0 on F i g . I ) . This observation l e d us t o the conclusion t h a t from s t r o n g and moderate donor s i t e s present on MgO surface (Ref. 31, o n l y t h e second one would be e a s i l y regenerated and e x h i b i t a c t i v i t y i n s t u d i e d r e a c t i o n s .

176

Strong centres, forming anion radical even from nitrobenzene molecule are poisoned irreversibly, however, their presence is not necessity for the preservation of catalytic activity. Taking into consideration that regenerated MgO which is not ahle to ionize nitrobenzene molecule is still active in its reductiori by hydrogen transfer and that only a few from reduced nitro compounds form ion radicals on catalyst surface one can ascertain that ion radicals formation is not necessary step in nitroarenes (or nitroparaffins) activation. Probably, one-electron donor sites take part only in activation of alcohol what was demonstrated by us earlier. CONCLUSION The main conclusions wolild be summarized as following: (i) the reduction of nitro compounds with alcohols by catalytic hydrogen transfer is a very selective process; (ii) the conversion of starting nitro compounds into desired products depends on the alcohol used as a donor. Each reaction should be individually optimized to find the most effective donor molecule. The substitution in nitroarene molecule diminishes its reactivity in catalytic transfer reduction (CTR); (iii) the previously demonstrated (ref. 2) action of one-electron donor sites on MgO surface is limited to the donating alcohol transformation; ionization of nitro compound molecule is not necessary step of its activation for CTR; (iiii) the simplicity of reaction, accessibility of reactants and ease of catalyst regeneration make CTR of nitro group with alcohols over MgO useful method for the commercial selective synthesis of aryl and alkylamines. REFERENCES 1 R.A.W. Johnstone, A.H. Wilby and 1.0. Entwistle, Heterogeneous catalytic transfer hydrogenation and its relation to other methods f o r reduction of organic compounds, Chem. Rev., 85 (1985) 129-1.70. 2 J. Kijehski, M. Glifiski and J. Reinhercs, Hydrogen transfer over MgO. An alternative method for hydrogenation-dehydrogenation reactions, in: M. Guisnet, J. Barrault, C. Bouchoule, 0. Ouprez, C. Montassier and G. Perot ( E d s . ) , Studies on Surface Science and Catalysis, V o l . 41, Elsevier Amsterdam, 1388, pp. 231-240. 3 J. Kijefiski, 5. Malinowski, Influence of sodium on physico-chemical and catalytic properties of MgO, J.C.S. Faraday I, 74 (1978) 250-262. 4 G.J. Janz, Estimation of Thermadynarnic Properties of Organic Compoimds, Academic Press, New York, 1958, pp. 183-197. 5 1.0. Entwistle, A.E. Jackson and R.A.W. Johnstone, Reduction of nitro-compounds, J.C.S. Perkin I, (1977) 443-444.

M. Guisnet et al. (Editors), Heterogeneous Catalysisand Fine Chemicals IZ 0 1991 Elsevier Science Publishers B.V., Amsterdam

177

MASS TRANSFER CONSIDERATIONS FOR THE ENANTIOSELECTIVE HYDROGENATION OF a-KETO ESTERS CATALYZED BY CINCHONA MODIFIED Pt/A1203 M. GARLAND*, H.P. JALElT and H.U. BLASER Central Research Laboratories, R-1055, Ciba-Geigy AG, 4002 Basel, Switzerland

ABSTRACT For the enantioselective hydrogenation of ethyl pyruvate catalyzed by a commercially available Pt/A1203 powder catalyst modified with dihydrwinchonidine, turnover frequencies of up to 50 s-' at 20 OC and 10.0 MPa were observed. Generally, the optical yields were S O % but under certain conditions lower enantioselectivities were observed. An integrated program of catalyst characterization, transport calculations and kinetic experiments was undertaken to quantify the mass transfer parameters. Catalyst characterization suggested that the powder catalyst was in fact of 'eggshell' design. By using catalyst fractions of varying mean particle diameter, negligible intraparticle resistance was found (Koros/Nowak and Madofloudart criterion). Further, calculations and experiments indicated that, under specific conditions, the lower ee's were due to liquid-solid transport resistance. Conditions can now be identified where intrinsic kinetics, not affected by transport problems, can be measured for future mechanistic studies. INTRODUCTION Recently, the enantioselective hydrogenation of ethyl pyruvate catalyzed by cinchona modified Pt/A1203 (ref. 1) was shown to be a ligand accelerated reaction (ref. 2). The rate of reaction for the fully modified system is more than 10 times faster than the racemic hydrogenation using unmodified catalyst. Under certain reaction conditions, this liquid phase hydrogenation exhibits a turn-over frequency of up to 50 s'l (3.4 mol/kg-cat s). Emphasis until now has been directed at empirically increasing optical yields (ref. 3,4).

CATALYST

CH3q o \ c * H s

0 Ethyl Pyruvate

+

H2

MODIFIER

'so

H+*+o, OH CH,

OH

C2HS

0 (R)-Ethyl Lactate

+

CH,

\

CZHS

0 (S)-Ethyl Lactate

Such a high reaction rate strongly suggested the potential for mass transport problems. Indeed, a turn-over frequency on the order of 1 s-l is considered appropriate for the purpose of mechanistic studies normally conducted in the gas phase (ref. 5). At higher rates, various complications including intraparticle diffusion problems, often arise. The situation is even more severe in the liquid phase where the bulk diffusivity of species is considerably reduced. A

178

thorough discussion of the inherent transport problems in heterogeneous hydrogenations in the liquid phase can be found in the literature (ref. 6). The goal of the present study was to identify regions of negligible transport control for future mechanistic studies. In the following, a systematic approach to the current transportlreaction problem is presented. EXPERIMENTAL Reactions All kinetic experiments were carried out in a double-walled 50 ml batch reactor (3.2 cm diam.). The reactor was equipped with baffles, a 3 cm magnetic stimng bar, a thermocouple, and a capillary sampling line. The reactor was connected to a 45 ml reservoir, pressure regulators, transducers. and a cryostat. The system was designed to operate at reaction conditions of T=273-303K, A T d . 3 C and P=O-15.OMPa, AP=kO.lIWa. Typically, the reactor was loaded with 50 mg of 5% Pt/A1203 catalyst (prereduced 2 hours at 400OC under Hi),and 10 mg dihydrocinchonidine (Hcd). 10 ml ethyl pyruvate (freshly distilled) and 20 ml toluene (Fluka puriss) were then added to the reactor. The autoclave was sealed and the system was purged with argon (2.0 MPa) 5 times while stimng. Reactions were initiated by pressurizing both the reservoir and reactor with hydrogen in the absence of stimng, waiting for 2-3 minutes for thermal effects to subside and then starting the stirrer. Approximately 30 second were needed to saturate the liquid phase with dissolved hydrogen. Rates were measured from the pressure drop in the reserviour after this initial saturation period. Optical yields were determined by derivatizing the ethyl lactate with isopropyl isocyanate followed by glc on a Chirasil-Val column (ref. 9). This method has been shown to give accurate and reproducible results (ref. 10). Catalyst A commercially available 5% Pt/AI2O3 catalyst (Engelhard Industries 4759) was used in this study. The catalyst sample had a mean particle size of 55 pm as measured by light scattering, a BET surface area of 140 m2/g, a mean pore radius of 50 A and a density of 5.0 dml. The platinum loading was 4.65%, and the platinum dispersion was 0.28 as measured by static CO titration (ref. 11). RESULTS AND DISCUSSION Catalyst Characterization For subsequent tests of intraparticle transport resistance, the catalyst was dry sieved into seven fractions. The mean particle size of these seven fractions were 18,29, 35.44.57,81, and 93 pm. The particle size distributions of these seven fractions are shown in Figure 1, the platinum loading and dispersion are depicted in Figure 2. It is clear from Figure 2 that the platinum loading is a strong function of the catalyst particle size i.e. 5.42% for the 18 pm fraction and 3.25% for

179

the 93 pm fraction. The dispersion varies less than 10% over the seven fractions. The remaining physical properties of the fractions are listed in Table 1. Incidence %

70 I

e

60

0.3

I

5-

- 0.25

4-

- 0.2 0.15

3-

0

50 100 150 Particle Diameter (micron)

2-

-

1-

- 0.05

0'

'0

200

0.1

0 20 40 60 80 100 Mean Particle Diameter (micron)

Fig. 1. Particle size distributions of the sieved catalyst fractions. Fig. 2. Platinum loading and dispersion of the sieved catalyst fractions. Platinum %.

----

Dispersion, -

TABLE 1 Texture parameters of the individual catalyst fractions Mean Particle Size

Pt

(Pm)

%

18 29 35 44 57 81 93

5.46 5.19 4.95 4.76 4.30 3.83 3.25

Dispersion

0.257 0.274 0.276 0.283 0.286 0.281 0.288

Surface Area

Real Density

Apparent Density

Pore Volume

Mean Pore Radius

(m%)

(S/ml)

(@mi)

(ml/g)

(A)

1.17 1.66 1.84 1.90 1.91 1.94 1.92

0.61 0.37 0.34 0.36 0.31 0.29 0.30

122 145 151 159 144 130 116

4.10 4.25 4.84 5.94 4.61 4.52 4.56

100 51 44 45 42 45 52

The decreasing platinum loadings with increasing particle diameter strongly suggest that the catalyst is of "egg-shell'' design. In other words, there is an enhanced concentration of the metal in the outermost layer of the catalyst particles. The preferential deposition close to the exterior surface of A1203 particles is well documented for a variety of metal salts (ref. 12). This is

180

particularly the case for catalysts prepared from HzPtCI, (ref. 13). However, as far as we are aware, the preparation of egg-shell Pr/A1203 catalysts with particle sizes of 20-100 microns has not been documented in the open literature. Attempts to verify this structure by direct measurements ( E M ) were inconclusive, but by using simple geometrical arguments we estimate that a shell thickness of approximately 10 pm is consistent with the observed platinum loadings. The mechanical strength of the unsieved catalyst was tested in stirring experiments. These attrition tests were canied out with 200 mg catalyst in 30 ml toluene at 900 RPM. The tests were conducted for 0, 1, 2, 5, 10, and 30 minutes, the stimng stopped and the suspension filtered over a 5 km porous glass filter. The results as mean particle size versus stimng time are presented in Figure 3. A 50% reduction in the mean particle size occured in approximately 8 minutes. In order to check whether the high rate of attrition also occurs under normal catalyst loadings (50 mg), we collected the individual fractions after 15-30 minutes of reaction (see Fig. 6-8) and the particle size distributions were determined. The 18,28, 35,44,57,81 and 93 pm particles were reduced to 18, 30, 33, 35, 38, 36 and 41 pm respectively. Clearly, there is attrition of the bigger catalyst particles but a significant difference in size still existed between the smallest (18 pm) and largest (93/41 pm) fractions even at reaction times considerably greater than the 1-5 min that were used to determine the initial rates and optical yields. Mass Transfer Studies Suspension of Catalyst Particles. There were concerns about complete catalyst suspension due to the density of the particles. Calculations indicated that total suspension of the dense A1203 particles should occur by 600 RPM (ref. 14). Such calculations are normally valid for agitated reactors with 1:l height to diameter ratios, and a turbine impeller at 1/4 height. Lower clearance in the reactor (the present case) will decrease the impeller speed required for complete suspension of the particles. Visual inspection of the open reactor confirmed complete suspension of the catalyst at 450-600 RPM. Gas-Liquid Hydrogen Transport. Using a dynamic method (ref. 15), the gas-liquid mass transfer coefficient KLa for hydrogen into toluene was measured in the 50 ml reactor. The autoclave was pressurized to an initial pressure PI and then stimng was started. The rate of mass transfer as a function of time and in terms of P, and the final pressure P2, is given by Equation 1.

(P2/pl)ln[(Pl-Pi)/(P~-P2)1= KLa x t

(1)

Four experiments were conducted under an initial pressure of 10.0 MPa hydrogen at 150, 300, 450, and 600 RPM. Plots of the left hand side of equation 1 versus time for these experiments are shown in Figure 4. The resulting numerical values of KLa (slope of the straight lines) were 0.0025, 0.005, 0.015, and 0.06 s1respectively. The data shows that the mass transfer coeffent is roughly proportional to (WM)2. Thus at 900 RPM. a stimng speed which will be subsequently used, the predicted value of KLa is calculated to be 0.14 s-'. This corresponds to a maximum rate of hydrogen transfer of 1 . 2 ~ 1 mol/s. 0~

181

In order to avoid mass transfer effects in an agitated reactor, the rate of reaction should not exceed 10% of the maximum rate of gas-liquid mass transfer, KLaxC(H2), where KLa is the diffusion coefficient and C(H2) is the solubility of hydrogen (ref. 16a). This guarantees that the liquid phase is essentially saturated with hydrogen. Preliminary experiments at low concentrations of modified catalyst gave an activity of 8.5~10"mol/(g-cams) at 10 MPa and 20 OC. Assuming a H, solubility in toluene of 0.3 mom (ref. 17). we calculate that the maximum loading of catalyst should not exceed 0.14 grams at 900 RPM. Size (micron)

60 I

0 0

5

10

15

20 25

30 35

Time (minutes)

0' 0

I

100

200

300

400

500

Time (seconds)

Fig. 3. Mean particle size versus stirring time (200 mg unsieved catalyst; toluene). Fig. 4. Determination of KLa (toluene; 10.0 MPa; 2OOC) Liquid-Solid Transport. The transport of hydrogen from the bulk liquid phase through the liquid film to the external catalyst surface was also a concern. Again, the rate of reaction inside a catalyst particle should not exceed 10% of the maximum liquid-solid mass transfer rate (a,,k,C(Hz)) (ref. 16b). For the unsieved catalyst (mean particle size = 55 km, apparent density = 2 g/cm3) the external surface area % was estimated to be 600 cm2/g and the liquid-solid mass transfer coefficient k,(Hz) was calculated as 0.12 cm/s at a stirring speed of 900 RPM (ref. 16~). After taking into account the hydrogen solubility, the measured rate of reaction represents 4% of the corresponding maximum mass transfer rate. Therefore the condition for negligible liquid-solid mass transfer resistance is met. To confirm these calculations, stirring experiments were conducted under the standard conditions at 300, 450, 600, 900, and 1200 RPM. The results presented as pressure drop in the reservoir versus time together with the optical yields are shown in Figure 5. There is no increase in the reaction rate for the system above 600 RPM, consistent with the assumption that rates determined at 900 RPM should be essentially free of both gas-liquid and liquid-solid mass transport control. However, significantly lower reaction rates and optical yields were observed for

182

the experiments conducted at stirring speeds less than 600 RPM.Since we have observed that lower hydrogen pressures lead to lower enantioselectivities (ref. 18). the stirring experiments indicate that there is a lower effective hydrogen concentration at low impeller speeds. Given the previous transport considerations, this could be due to gas-liquid resistance and/or liquid-solid resistance. Intrauarticle Resistance. The Koros/Nowak (ref. 7) or Madofloudart (ref. 8) criterion states that, in the absence of mass transfer influences, the activity of a heterogeneous catalyst should be proportional to the number of active sites. In other words, the observed turn-over frequency (TOF) should be independent of the particle size if there is negligible intraparticle resistance since all active sites are fully effective. Such experiments with the different catalyst fractions were conducted in toluene at both 2.0 and 10.0 MPa hydrogen and at 900 RPM. The initial rates of the reaction as well as the initial ee’s for these two sets of experiments are shown in Figures 6 and 7. In both cases, essentially constant TOF’s as well as constant ee’s are obtained, indicating a complete absence of intraparticle control.

Pressure Drop (bar)

30 I

25 20

09 (yo)

---Iioo 0

0 v

-90

0

- 80

15 A

10

5

0

10

20 30 40 50 Time (minutes)

60 70

-50

-0

20 40 60 80 100 Initial Particle Size (micron)

Fig. 5 . Influence of stirring on rate of hydrogen uptake and optical yield (unsieved catalyst; toluene; 10.0 MPa; 20T) Fig. 6.Effect of mean particle size on optical yields and turnover frequencies (individual catalyst fractions; toluene; 2.0 MPa; 2OoC; 900 RPM).---- TOF; -ee.

In addition to these experiments, the effectiveness factors (ref. 20) were also calculated for the smallest and largest catalyst particles (assuming a uniform distribution of active sites). The

183

effective diffusivity of Hz ( 2 . 5 ~ 1 0cm2/s) ~ was calculated using the Wike-Chang equation (ref. 19) and a tortuosity of 3 (ref. 16d). The reaction is first order in hydrogen (ref. 18). For particle diameters of 18. 55 and 93 pm, effectiveness factors of q(l8 Fm) 1, q(55 pn) = 0.7 and q(93 pm) < 0.5 were obtained which means that the TOF's observed for the smallest particles should be about 2 times higher than those measured for the largest particles. This is clearly not what we find experimentally! Either abrasion or a non-uniform distribution of platinum could be responsible for this discrepancy. Since the observed rates are determined during initial reaction times (1-5 min), abrasion can not be the main reason for the independence of TOF on particle size. Hence, these experiments suggest that the catalyst used has indeed an "egg-shell" structure. Hydrogenations were also carried out in 100% ethyl pyruvate and the results are shown in Figure 8. It should be noted that the turnover frequencies are lower than those observed in toluene (compare Fig. 7. with Fig. 8.). But more importantly. both TOF and ee's increase with particle size! Gas-liquid resistance can be excluded since KLa for H2 transfer into ethyl pyruvate has been measured and is also about 0.06 s-l at 600 RPM.Further, intraparticle control is unlikely because the TOF's should decrease with particle size. Hence, we think that these observations can be explained by liquid-solid mass transport effects as follows. The apparent density of the catalyst

-

ee (%) I100

TOF (11s) 1001

80 -

0

0

n u

1

TOF(l/s) 0 0

~

ee (%) 1

0

90

TL:

0

0

60 -

A

_ _A_ A

40 -

A

- 80 - 70

20 -

- 60

0 0

50 40 60 80 100 Initial Particle Size (micron) 20

Oo:/:ll 40 60 20

0

--

01

0

-A-

0

pi'

A A"

70

a- 60

'50 20 40 60 80 100 Initial Particle Size (micron)

Fig. 7. Effect of mean particle size on optical yields and turnover frequencies (individual catalyst fractions; toluene; 10.0 MPa; 20°C; 900 RPM).---- TOF; -ee. Fig. 8. Effect of mean particle size on optical yields and turnover frequencies (individual catalyst fractions; no solvent; 10.0 MPa; 20% 900 RPM).---- TOF; -ee.

0

184

particles decreases with decreasing particle size (see Table 1). Therefore, the density difference between reaction medium and catalyst particles decreases with decreasing size as well, leading to a reduced relative velocity and consequently to a reduced H2 transfer (ref. 21). The observed effect on the optical yield also points to an apparent lower hydrogen concentration on the catalyst, analogous to the effects observed for the stimng experiments. CONCLUSIONS We have identified reaction conditions where intrinsic kinetics can be obtained for the very fast enantioselective hydrogenation of ethyl pyruvate using a commercially available Pt/Al203 powder catalyst, modified with dihydrocinchonidine. We conclude that this is in part due to i) the egg-shell structure of the catalyst, ii) the high turbulence achieved in the reactor and iii) the density and/or the viscosity of the solvent used. In solvents like ethyl pyruvate, liquid-solid transport problems can arise. ACKNOWLEDGMENTS We would like to thank Dr. H.H. Fuldner and Mr. R. Miiller for the determination of the texture parameters, Ms. R. Gosteli for the measurements of the platinum dispersion and Dr. O.M. Kut for valuable discussions. REFERENCES 1 Y. Onto, S . Imai and S . Niwa, J. Chem. SOC. Jpn., (1979) 1118. M. Garland and H.U. Blaser, J. Amer. Chem. SOC., 112 (1990) 7048. 2 3 J.T. Wehrli, A. Baiker, D.M. Monti and H.U. Blaser, J. Mol. Catal., 49 (1989) 195. 4 H.U. Blaser, H.P. Jalett, D.M. Monti, J.F. Reber and J.T. Wehrli, in: M. Guisnet (Ed.) Heterogeneous Catalysis and Fine Chemicals, Elsevier, Amsterdam, 1988, pp. 153-163. M. Boudart, and R.L. Burwell, Jr., in: E.S, Lewis (Ed.) Techniques in Chemistry, Vol. VI, 5. Wiley, New York, 1974, pp. 693-740. 6. G. Gut, O.M. Kut, F. Yuecelen and D. Wagner, in: L. Cerveny (Ed.) Catalytic Hydrogenation, Elsevier, Amsterdam, 1986, pp. 5 17-545. R.M. Koros and E.J. Nowak, Chem. Eng. Sci., 22 (1967) 470. 7 8 R.J. Madon and M. Boudart, Ind. Eng. Chem. Fundam., 21 (1982) 438. W. A. Konig, I. Benecke and S. Sievers, J. Chromatogr. 238 (1982) 427. 9 10 J.T. Wehrli, Dissertation No. 8833, ETH-Zurich, 1989. 11 R.J. Farrauto, AIChE J. Symp. Ser., 70 (1978) 9. 12 R.L. Moss, in: R.B. Anderson, P.T. Dawson (Eds.), Experimental Methods in Catalytic Research, Vol. II., Academic, New York, 1976, pp. 43-91. 13 C.N. Satterfield, Heterogenous Catalysis in Practice, McGraw-Hill, New York, 1980. 14 G . Baldi, R. Conti and E. Alaria, Chem. Eng. Sci., 33 (1978) 21. 15 A. Deimling, B.M. Karandiker, Y.T. Shah, and N.L. Cam, Chem. Eng. J., 29 (1984) 127. 16 P.A. Ramachandran and R.V. Chaudhari, Three-Phase Catalytic Reactors, Gordon and Breach, New York, 1983. a) p. 190, b) p. 191, c) p. 179. 17 E. Brunner, J. Chem. Eng. Data, 30 (1985) 269. 18 M. Garland, H.P. Jalett and H.U. Blaser, Manuscript in Preparation. 19 R. Wilke and P. Chang, AIChE J., 1 (1955) 264. 20 C.G. Hill Jr, An Introduction to Chemical Engineering Kinetics and Reactor Design, Wiley, New York, 1977, p. 448. 21 C.N. Sattertield, Mass Transfer Effects in Heterogeneous Catalysis, MIT Press, Cambridge, 1970, p. 115.

M.Guisnet et al. (Editors),Heterogeneous Catalysis and Fine ChemicalsII

185

0 1991 Elsevier Science Publishers B.V., Amsterdam

SELECTIVE CARVONE HYDROGENATION ON Rh SUPPORTED CATALYSTS

R. Gomez, J. Arredondo, N. Rosas and G. Del Angel Universidad Autonoma Metropolitana-Iztapalapa Dept. of Chemistry, P. 0. BOX 55-534. Mexico 09340 D.F.

SUMMARY The catalytic properties of rhodium supported on MgO, SiOz and Ti02 had been studied for the carvone hydrogenation reaction. Catalysts prepared in basic medium result to be more active than the ones prepared in acid medium. The main reaction products are carvotanacetone, carvomenthone and carvomenthol. In all cases, the main product is carvotanacetone, when the support is MgO the selectivity towards that product is even higher (92YY). The hydrogen stereoaddition towards the axial-equatorial carvomenthol formation is higly selective in Rh/MgO catalysts (100%). The particular Rh/MgO behavior can be explained by a deposit of MgO support over the metallic particles, diminishing the size of the Rh atoms ensembles.

INTRODUCTION

It is well known that catalytic processes employing soluble catalysts are more selective in the hydrogenation of poly-unsaturated compounds than those using solid catalysts. However the continuous demand of chemical products obtained by selective hydrogenation of unsaturated molecules, invite

to

study

solid catalysts, since their advantages for industrial application are well known. Nevertheless few attempts in this way have been done, eventhough the promising results reported with metal supported catalysts: high selectivity in the partial hydrogenation of 1,4 cyclohexanedione (ref. 1 ) employing Ru/SiOz

catalysts (up to 70% of 4-hydroxycyclohexanone), and up to 90%

selectivity in the hydrogenation of the double bond of 2-cyclohexenone for Pt/SiO

2

catalysts (ref. 2). Additional examples for selective hydrogenation

on supported catalysts are given elsewhere (refs. 3-61. In the mentioned studies the selective hydrogenations were made with the aim to obtain kinetical data, and the catalysts characterization was scarce. On the other hand, it is known that metal supported catalysts exhibit important particle size and support effects in the selectivity patterns (ref. 7).

Therefore it seems to be interesting to study such effects in the selective hydrogenation of a poly-unsaturated molecule as carvone. It was reported that the partial hydrogenation of this molecule is very sensitive to different homogeneous catalysts: organometallic compounds (refs. 8-10), Zn/OH (re:.

111,

NaBH

(ref.121, and Zn-NiC1

(ref. 13) as examples.

186 The purpose of the present work is to study: the precursor (metallic chlorides or carbonyl compounds), particle size

and support (silica,

magnesia and tltania) effects in the selective hydrogenation of carvone employing rhodium as active metal. EXPERIMENTAL Preparation. The catalysts were prepared by impregnation from aqueous solution of RhC13.3 H20 (ICN Pharmaceuticals) and n-hexane solutions of the complexes, Rh2(CO)4C12, Rh4(CO)12 and Rh6(CO)16. prepared in our laboratory (ref 14). The supports were silica (KetJen F-2, 380 m2/g), Titania (Degussa, 60 m2/g) and MgO (ICN, Pharmaceuticals, 40 m2/g).

The supports had been

previously calcined in air at 450 OC for 12 h, and reduced in flowing hydrogen for 2 h at 400 OC. Dispersion Measurements. chemisorption at' 25

Dispersions

were

determined

by

hydrogen

0

C in a conventional glass volumetric apparatus. The

amount of uptaken hydrogen was obtained by extrapolating to zero pressure the linear portion of the isotherm. The stoichiometric ratio H/Rh = 1 . 0 , was used for dispersion calculations in agreement with previous results (ref. 7 ) . The mean crystallite size was calculated assuming a simple spherical particle shape and equipartition of the dense crystal planes (1.33

x

10''

atoms/m2).

For carbonyl clusters impregnated type catalysts, the particle size was determlnated by electron microscopy (only particles smaller than 20

A

were

observed). Catalytic Experiments. Activities were performed

in a 1 liter Parr

reactor. A typical experiment was performed as follows: at a temperature of 100 OC, 100 mg of the catalyst and 1.5 X wt of (-1-carvone (Aldrich) in

n-hexane solution (100 ml) were introduced in a high pressure Parr reactor equipped with mechanical stirring and automatic temperature control. Before introducing the hydrogen the system was purged 2 or 3 times with N2, The total hydrogen pressure was 21 atm. The reaction products were analysed by gas chromatography, M41 Hnd Mass Spectrometry and ldentifled as: unreacted carvone, carvotanacetone, carvomenthone and three carvomenthol stereoisomers (axial-equatorlal, equatorial-equatorial and equatorial-axial). RESULTS The dispersion values, particle size and metal content for the various catalysts are reported in Table 1. The results show a high dispersion on most of the cataysts and particle sizes going from 11 to 42 A. It can also be seen that the two ammonlacal preparations of Rh/SIO do not change the 2 dispersion.

187 The initial rate (ro) and activity per site (TOF) are reported in Table 1. In contrast with the dipersion results, the low values obtained for the ammoniacal preparations show an important precursor effect and a small one on the nature of the support. However, the selectivity values for the formation of the three hydrogenated products reported in Table 2, demonstrate that selectivity depends on the nature of the support. Magnesia support presents the highest selectivity (90%) to the carvotanacetone formation. Particle size effects in selectivity were not detected, since, the small changes observed

TABLE 1 Dispersion, particle size and activity of Rh catalysts for carvone hydrogenation. Catalysts

Rh

Dispersion

(wt % I

(XI

0.5 1.0 1.0 2.0 1.0 2.0 1.0 2.0

94 79 93 46 42 25 57 44

RNSiOza RNSiOza Rh/SiOz Rh/si02 Rh/MgO Rh/MgO RNTiOz RWTiOz

TOF. 10'

Particle

ro.10'

(A)

(b)

(C)

0. 18 0.27 2.70 2.50

0.26 0.35 3.06

size 11 13 11 23 25 42 19 26

0.96

2.75 2.32

1.85

3.38

__

__

a) Sol. NHrOH. b) mol/g cat min. c) molecule/site min.

TABLE 2 Selectivity

(XI

Catalysts

Rh/SiOz RWS102 Rh/SiOz Rh/SiOz Rh/MgO Rug0 Rh/TiOz RNTi02

for carvone hydrogenation on Rh catalysts.

Carvotanacetone

Carvomenthone

0.5a 1. Oa 1.0 2.0 1.0

79 83 83 75 92

2.0 1.0 2.0

90

19 15 16 18 6 6 15 20

a) Sol. NHiOH

75 71

Carvomenthol

2

2 1 7 2 4 10 9

188

on silica and magnesia supports at different dispersions do not justify any speculation about it; two catalysts with the same dispersion value (SiO 2.0% and MgO 1.0%) have different selectivity patterns. The support effect in terms of selectivity can be observed in Table 3. The results show that the axial-equatorial carvornenthol is the only product when the support is magnesia. Rh/MgO catalysts results stereoespecific for the hydrogen carbonyl addition.

to

be

highly

DISCUSSION The results of Table 1, show that the preparation method does not affect the metallic dispersion

.

However, the catalysts prepared

in ammoniacal

solution have the lowest activity per site, showing that

in carvone

hydrogenation an important precursor effect in activity is obtained. Nevertheless, in the hydrogenation of poly-unsaturated molecules the catalyst effects are more evident in the selectivity patterns, as is shown in Table 2 and 3. The selectivity behavior for the various catalysts, show that R M g O is the most selective for carvotanacetone formation. The addition is mainly limited, in these catalysts, to one hydrogen molecule, although in carvone there are three possible sites at which reduction can occur. Though the magnesia effect is detected in hydrogen addition, this effect is most remarkable in the stereospecificity towards the axial-equatorial

carvomenthol formation (Table 3 ) . TABLE 3 Stereoisomers selectivity (%I of carvomenthol of carvone hydrogenation on Rh Catalysts. Catalysts

(a)

Rh/SiOz 1.Od RWSi02 1.0

29 30 100

Rh/MgO

RWMgO

1.0 2.0

100

a) axial-equatorial carvomenthol. b) equatorial-equatorial carvomenthol. c) equatorial-axial carvomenthol. dl s o l . NHIOH.

71 70

--

189

Fig. 1. Consecutive mechanism in carvone hydrogenation. In

carvone

hydrogenation a

consecutlve

mechanism without

desorption from the surface is expected (Fig. 1).

molecule

The high selectivity

towards the carvotanacetone observed in magnesia supports suggest that the consecutive mechanism is not completed in this support. Addition of three hydrogen molecules to carvone to obtain the cavomenthol without desorption of the molecule requires at least three adjacents sites, resulting in a particle size sensitive reaction; this sensitivity could not be observed in our catalyts, probably because the particle size in SiO supports are very close. However two catalysts showing comparable dispersions, Rh/Si02 2% and Rh/MgO 1%

give

different

selectivity

to

carvotanacetone

and

carvomenthol

stereoisomers. This implies that an unusual effect operates in magnesia support.

TABLE 4

Selectivity ( X )

for carvone hydrogenation on Rh catalysts prepared

from carbonyl clusters. Catalysts (a)

Carvotanacetone

a) 1% wt Rh content.

Carvomenthone

Carvomenthol

20 27 76 16

68

95

1

2

3 13

190

TABLE 5 Stereoisomers selectivity (%I of carvomenthol in carvone hydrogenation on Rh catalysts prepared from carbonyl clusters. Catalytst

(a)

(b)

(C)

e OH

Rh4(CO)iz/Si02 Rh6 (CO)16/SiO2 Rhz(CO)rCla/MgO Rhr (CO112AgO

13 51

4

--

--

--

---

87 49 96 100

a) axial- equatorial. b) equatorial-equatorial. c) equatorial-axial. Recently Poels et a1 (ref. 151, in the "syngas" reaction study shown that over Rh/MgO catalysts, a partial blocking of the metal surface occurs by effect of MgO hydrolysis. Similar effects have been also reported in benzene hydrogenation and methylcyclopentane hydrogenolysis (refs. 16,171 over Ru/MgO catalysts. It could then be possible that the same effect operates in carvone hydrogenation over the magnesia support. In this case the hydrogen addition stops at the first step and the stereospeclficlty to the axial-equatorial carvomenthol formation could be due to the blockage of the adjacents sites by MgO support deposited on the metallic particles. Additional evidence of that hypothesis is given in Tables 4 and 5. The catalysts prepared with carbonyl clusters ln n-hexane medium must avoid the MgO

hydrolysis. The selectivity patterns for such catalysts show notable

differences in comparison with the aqueous impregnated type catalysts. The carvotanacetone formation is largely dlmlnlshed and the stereospecificity to axial-equatorial carvomenthol is totaly inhlbited. However in Rhodium silica supported catalysts the selectivity to carvotanacetone practically does not change. The effects in stereospeciflty towards the carvomenthol product may be due to a small silica hydrolysis effect. CONCLUSIONS

The following important conclusions emerge from this study: ( i ) precursor effect is exhibited in carvone hydrogenation activity, ( i i l

the R W g O

catalysts results to be more selective towards carvotanacetone formation than

191 Rh/Si02and

Rh/T1O2

catalysts.

(ill)

the

stereospecificity

to

hydrogen

addition in the carvomenthol formation is higher in MgO supported catalyst. (iv) magnesia support effect is found due to the blockage of the metal particles by the MgO. REFERENCES 1 M. Bonnet, P. Geneste and M. Rodriguez, J. Org. Chem., 45 (19801 40. P. Geneste, M.Bonnet and C. Frouin, J. Catal., 64 (1980) 371. 2 3 P. Geneste, M Bonnet and M. Rodriguez, J. Catal., 57 (1979) 147. 4 A. A. Pavia, P. Ceneste and J. L. OLive, Bull. Soc. Chim., (1981) 24. 5 G. C. Accrombessi, P. Ceneste, J. L. Olive and A. A. Pavia, Tetrahedron, 18 (1981) 3135.

6

G. C. Acrombessi, P. Ceneste, J. L. Olive and A. A. Pavia, J. Org. Chem. 45 (1980) 4139.

7

G. Del Angel, B. Coq, R. Dutartre and F. Figueras, J. Catal., 87 (1984) 27.

R. E. Ireland and P. Bey, Org. Synth., 53 (1973) 63. Ch. Larpent, R. Dabard and H. Patin, Tetrahedron Lett., 28 (1987) 2507. A. J. Birch and K. A. M. Walker, J. Chem. SOC., (c) (1966) 1894. 11 J. C. Fairlle, C. L. Hdgson and T. Money, J. Chem SOC., Perkin I (1973)

8

9 10

2109. 12 13 14

N. R. Natale, Org. Prep. Proc. Int., 15 (1983) 389. Ch. Petrler and J. L. Luche, Tetrahedron Lett., 28 (1987) 2351. N Rosas, C. Marquez, H. Hernandez and R. Comez, J. Mol. Catal., 48 (1988) 59.

E. K. Poels, P. J. Mangnus, J. Van Welzen and V. Ponec, In Proc. Int. Cong. Catal., 8 th Berlin, 1984, 2 (1984) 59. 16 M. Viniegra, R. Comez and R. D. Conzalez, J. Catal., 111 (1988) 429. 17 P. Villamil, J. Reyes, N. Rosas and R. Gomez, J. Mol. Catal., 54 (1989) 15

205.


M. Guisnet et a]. (Editors),Heterogeneous Catalysis and Fine Chemicals II 0 1991 Elsevier Science Publishers B.V., Amsterdam

S E L E C T I V E HYDROGEii,iTlO,i

C!T,hL

df

N I C K E L - k O L Y B D E ~ ~ U ! .C~t \ T A L Y S T S N i

J.COUHT,

F.JUNATI-IDKISSI

111 T H E

193

L I Q U I D P H A S E OVER

UIWIPPORTED

-x~40x.

and S . V I D A L

L a o o r a s o i r e d ' E i u d e s Dynawiques ec S.ti-ucturales de l a S e l e c - i i v i . i @ (LEOSS-1) CIWS g?A 332 - U n i v e r s i - i 6 Joseph F o u r i e r - BP 53X - 38041 G R E i W B L t C E X X (France).

SUII;YA t? Y The h y d r o g e n a i i o n o f ci.;ral has 3een i n v e s c i g a c e d i n cyclohexane and i n Sy c o - r e d u c c i o n o f 2-propanol , w i ih un-supported ili d-x i40x ca'ialys-is, prepared m i x t u r e s o f i o d i d e s o f a p p r o p r i a L e d conposi,ion w i t h napnchalene-sodium as r e d u c i n g agent. i i i g h y i e l d s i n c i ; r o n e l l o l were observed i n 2 - p r o q a n o l . The s e l e c t i v i s y o f t h e d i f f e r e n t steps i n so;h s o l v e n t s i s d i s c u s s e d u s i n g as s e l e c t i v i t y c r i , e r i a ,he r a i i o s k . D /k .o f o r each r e a c t i o n s i e p ( c o m p e x i ' i i v e N o r c o n s e c u z i v e ) . These r a t i o s $a& deen conpuied oy f i . i . i i n g t h e neasured produc-c conposiLions t o .ihe f u n c t i o n s obzained by a n a l y x i c a l i n t e g r a t i o n o f .the LkNGivlUIX-HIl\lSELi1OUD raee expressions.

INTROOUCTION Lie prepared a se:-ies o f o i n e x a l l i c , co-reduction

of

mixiures

sodiua-napniAalene

as

of

dry

reducing

un-supporeed

iodides agen'i.

of

Nii40x

appropiaie

Catalyst

ca,:alys';s

oy

comqosi-Lion w i ;h

cnaracieriza.iion

and

.

20

I 0-

-0-

e-

0

I

I

10

20

--rh

0

Fig.1 Selectivities of the main isomerization products during the P-pinene HDS on the bare supports (200"C, 1 atm). a-pinene ;0 dipentene ; ncamphene.

*

206

product, whereas this is a-pinene on alumina and silica. The protonic mechanism of ppinene isomerization is likely to proceed through the carbocation intermediates shown in Fig. 2 [Ref.8]. C-C bond shifts in the pinenium ion leading to the A ion and then to the camphenium ion are relatively difficult to occur. This explain why the selectivity to camphene remains low. On the contrary the p scission leading to the B ion is much more probable since the constraint in the pinene bicycle is then suppressed.

a pinene

p pinene

I\

6z=+b 0.Q A

B

II

*

d ipen t e n e

- H' c--

Camphene

Fig2 Protonic mechanism for P-pinene isomerization. It is not easy, however, to correlate the nature and the surface state of support with the selectivity to dipentene : a plausible hypothesis would be that, for steric reasons, the dipentenium is favoured in the microporosity of the transformation pinenium -> carbons.

..

c t i v u c a r b o n - W t e- d c The results obtained on the CoMo/Carbon VII catalysts are given in Table 5.

207

Table 5 Activity of CoMo/C catalysts in 8-pinene HDS (200"C, 1 atm).

I Catalyst

Time-on-stream (h)

DEG %

I

HDS %

I

CO-MO

6 30

99 99

60 64

Co-Mo-Na

6 30 50

53 32 24

71 77 78

Na-Co-Mo-Na

6 30

26 10

74 77

Impregnation of cobalt and molybdenum (without sodium) increases largely the isomerizing activity of the catalyst : the p-pinene is then completely converted. The catalysts prepared with sodium molybdate and sodium hydroxide (Co-Mo-Na and Na-CoMo-Na) have lower isomerizing activities while their HDS activities are significantly increased. As in the case of alumina supported catalysts the sulfided CoMo phase protected by a double layer of alkaline ions on the carbon support gives the best results in HDS of p-pinene. The behaviour of this catalyst was examined in desulfurization of the turpentine oil (40% a-pinene, 25% p-pinene, 25% A3-carene and 10% camphene t dipentene + myrcene, 1500 ppm S). The results are recorded in Table 6. Table 6 Desulfurization of a turpentine oil. Time a-pinene 6

-1 + 1.2 +8

DEG % p-pinene

+ 15 + 26 + 30

HDS % 3-carene

- 2.6 + 0.8 + 1.5

77 77 79

The negative values for the degradation of a-pinene and of A3-carene at 6h-onstream correspond to an increase of these terpenes in the products. After 30 h-on-stream all the main terpenes are degraded during the HDS treatment. It should be noted that the conversion of p-pinene is higher in the turpentine oil than in the 8-pinene fraction. This is not due to a change in the terpene concentration : in an experiment of HDS carried out with a mixture of a-pinene, p-pinene and A3-carene (in the same proportion as in the turpentine oil), the conversion of p-pinene was 12%, very close to the conversion recorded

208

with the p-pinene fraction. It seems that the turpentine oil contain impurities increasing the isomerization activity of the catalysts. ACKNOWLEDGEMENTS The authors thank Mr Agouri (CETRA) for constant interest concerning this work. Thank are due to the Ministtre de la Recherche et de la Technologie for financial support (Contracts 84-F-0963 and 84-F-0964). REFERENCES 1 2 3 4 5

6 7 8

F. Casbas, D. Duprez, J. Ollivier and R. Rolley, Eur. Pat. 243238 (A1 . F. Casbas, D. Duprez, J. Ollivier and R. Rolley, Eur. Pat. 267833 (All. F. Casbas, D. Duprez and J. Ollivier, Appl. Catal., 50 (1989) 87. J.C. Duchet, E.M. van Oers, V.H.J. de Beer and R. Prins, J. Catal., 80 (1983) 386. F.E. Massoth, in "Adv. in Catalysis (D.D. Eley, H. Pines and P.B. Weisz, Eds.) Vo1.27 p265. Acad. Press, New York (1978). K.S. Chung and F.E. Massoth, J. Catal., 64 (1980) 320 and 332. M. Guisnet, J.L. Lemberton, G. Perot and R. Maurel, J. Catal., 48 (1977) 166. J.E. Germain and M. Blanchard, in "Adv. in Catalysis" (D.D. Eley, H. Pines and P.B. Weisz, Eds.) V01.20 p267. Acad. Press, New York (1969).

M. Guisnet et al. (Editors),Heterogeneous Catalysis and Fine Chemicals II 0 1991 Elsevier Science Publishers B.V., Amsterdam

209

STUDIES ON THE CATALYTIC HYDROGENATION OF RESIN ACIDS DERIVATIVES: SYNTHESISOFABENZOXAZOLE

B. GIGANTE,l A. M. LOB0,2 S. PRABHAKJ~R,~ M. J. MARCELO-CURTO,' and D. J. WILLIAMS3

Laboratbrio Nacional de Engenharia e Tecnologia Industrial, Departamento de Tecnologia de lndustrias Quimicas, ServiCo de Quimica Fina, Estrada das Palmeiras, 2745 Queluz (Portugal) 2SecC%ode Quimica OrgAnica Aplicada, Departamento de Quimica, FCT, Universidade Nova de Lisboa, Quinta da Torre, 2825 Monte da Caparica, and Centro de Quimica Estrutural, Complexo I, IST, Av. Rovisco Pais, 1096 Lisboa Codex (Portugal) 3Department of Chemistry, Imperial College of Science, Technology and Medicine, London SW7 2AY (United Kingdom)

SUMMARY In the course of reduction experiments of methyl 12,14-dinitrodehydroabietate3, a new benzoxazole resin acid derivative 6 was synthesized and its structure established by spectroscopic data, chemical derivatization and X-ray analysis. INTRODUCTION Dehydroabietic acid 1 , the main resin acid of disproportionated rosin, is a readily available hydrophenanthrene derivative and a useful starting material for the synthesis of industrial and/or physiologically important products (I), by introduction of suitable substituents in the aromatic ring, such as the nitro or amino groups. Nitration

of

dehydroabietic

acid

methyl

ester

2

yields

methyl

12,14-dinitrodehydroabietate3 (2-3). We have previously reported (4) that the reduction

of 3 with tin/hydrochloric acid (5) afforded essentially methyl 12,144iaminodehydroabietate 5. However, work up proved troublesome due to the formation of tin derivatives, consisting mainly of I)-stannic acid (6), and as a consequence gave low yields of isolated product. This led us to look for alternative reducing agents.

Me

1 R, 2 R, 3 R, 4 R, 5 R, 7 R,

= COOH,

R,

= R, = H

6

H = COOMe, R, = R,= NO, = COOMe, R, = NO, R3= NH, = COOMe, &, R, = NH, = COOMe, R, = NHCOMe, R, = NO, = COOMe,

= R,=

EXPERIMENTAL The following commercial powder catalysts (all from Degussa) were used in the screening runs: rhodium-platinum oxide (45,65% Rh, 19,8% Pt), rhodium oxide (58,2% Rh), platinum oxide (8O,6% Pt), palladium-on-carbon (5% Pd) and platinum-on-carbon(5% Pt). The reactions were carried out in the liquid phase in a well stirred reactor at room temperature and under hydrogen pressure (40 psi). a) For reactions with metal oxides as catalysts the standard conditions were: the catalyst (8.3% w/w) was reduced to metal with hydrogen in the glacial acetic acid (6 ml), the starting material 3 (0.25 mmoles) was added and shaken with hydrogen. b) For reactions with metal on carbon as catalysts the standard conditions were: the catalyst (16% w/w) and starting material 3 (0.5 mmoles) in glacial acetic acid (34 ml ) were shaken with hydrogen. During the course of the reaction samples were withdrawn at appropriate intervals and analysed by GLC.

211

RESULTS AND DISCUSSION

In the course of experiments conducted with other reducing agents (viz. Rh2O3, PtO2, Pd/C, PVC) on methyl 12,14-dinitrodehydroabietate 3,the formation of varying proportions

of

methyl

12-amino-14-nitrodehydroabietate

4 and methyl

12,14-diaminodehydroabietate 5, along with the benzoxazole derivative 6 (Fig. 1), was

detected. The formation of a benzoxazole ring under these conditions has not been hitherto reported and experimental conditions necessary for maximum yield were studied. The highest yield of 6, ca. 58%, was obtained with Rh203/Pt02.xH20 in acetic acid and took over 6 days. When acetic anhydride or mixtures

of acetic acid/acetic

anhidride were used as the solvent, only the acetamide derivative 7 was formed. The yield of 6 was not improved by the use of catalysts such as Rh2O3, Pt02, Pd/C or

W C in

acetic acid (Table 1). TABLE 1 Catalytic Hydrogenation of Methyl 12,14-Dinitrodehydroabietate3 Catalyst

Solvent

Time (h)

7

3 AcOH Ac20 AcOH/Ac20(1:2) AcOH AcOH glac. AcOH glac. AcOH

160 160 180 162 162 48 45

0 0 42 0 0 0 0

0 0 0 0 68

3 39

20

58

0 0

0 0

42 21 74 20

24 0 12c) 23c)

a) Relative percentages by gc analysis of the end product.

b) Below detection limits; c) Not observed when conc. H2SO4 (0.1O/O v/v) was added to the solvent (4).

212

It is interesting to speculate that the formation of 6 with Rh2O3 is a result of the intermediate phenylhydroxylamine 8, the precursor for the amine 5, being 0-acylated to

9 and suffering a 3,3'-azaoxy Cope rearrangement. The product, an o -acetoxyaniline 10, eliminates a molecule of water and generates 6 (Fig. 2).

All the compounds were identified by physical and spectroscopic data and comparison with literature data (3,6). The structure of the new benzoxazole 6 was based on spectroscopic data and synthesis of its acetylated derivatives, and confirmed by X-ray crystallographic analysis.

pgH2 Ho\ H , N

'C0,Me

COPMe

8

9

CO, Me

%OOMe

6

10

Fig. 2. Proposed pathway for the formation of the benzoxazole derivative 6.

213

REFERENCES E. Schroder, R. Albrecht and C. Rufer, Dehydroabietylamin-Derivate und ihre antibakteriellen Eigenschaften, Arzneim.-Forsch., 20 (1970) 737-743. L. F. Fieser and P. Campbell, Concerning Dehydroabietic Acid and The Structure of Pine Resin Acids, J. Am. Chem. Soc., 60 (1938) 159-170. E. R. Littmann. The Resin Acids. The Action of Palladium on Abietic Acid, J. Am. Chem. Soc., 60 (1938) 1419-1421. 8. Gigante, A. M. Lobo, S. Prabhakar and M. J. Marcelo Curto, Studies on The European Catalytic Hydrogenation of DehydroabieticAcid Derivatives, in: Proc. !jth Conference on Biomass for Energy and Industry, Lisbon, Portugal, October 9-13, 1989, Elsevier, Amsterdam, in press. H. Becker, W. Berger, G. Domschke, E. Fanghanel, J. Faust, M. Fisher, F. Gentz, K. Gewald, R. Gluch, K. Schwetlick, E. Seiler, and G. Zeppenfeld, in: P. A. Ongley (Ed.) Organicum: Practical Handbook of Organic Chemistry, Pergamon Press, New York, 1973, p. 552. A. Tahara, M. Shimagaki, M. Itoh, Y. Harigaya and M. Onda, Diterpenoids. XXXVIII. Conversion of I-Abietic Acid into Steroidal Skeletons: Formation of the D-Ring, Chem. Pharm. Bull., 23 (1975) 3189-3202.


M.Guisnet et al. (Editors), Heterogeneous Catalysis and Fine Chernicak II 0 1991 Elsevier Science Publishers B.V., Amsterdam

215

THE ISOMERISATION OF LACTOSE TO LACTULOSE CATALYSED BY ALKALINE ION-EXCHANGERS B.F.M. KUSTER, J.A.W.M. BEENACKERS, H.S. VAN DER BAAN, Laboratorium voor Chemische Technologie, Technische Universiteit Eindhoven,

P.O. Box 513, 5600 MB Eindhoven (The Netherlands). SUMMARY

Lactulose is industrially produced by the homogeneous alkali catalysed isomerisation of lactose. The use of heterogeneous alkaline ion-exchangers as catalyst can result in a simpler overall process and in higher selectivities. The effect of the type of ion-exchanger, particle diameter, temperature and sugar concentration on the kinetics has been studied. A kinetic model is given which can be used to describe the experimental results. Loss of selectivity can occur due to a limiting diffusion rate. High sugar concentrations are beneficial for a high yield. Some proposals are given for process improvements. INTRODUCTION Lactulose, 4-O-~-D-galactopyranosyl-D-fructose,

is a synthetic

disaccharide which is commercially produced from lactose, 4-0-P-Dgalactopyranosyl-D-glucose, by alkali catalysed isomerisation. Production

estimates are 8000 tons per year and prospects are steady expansion (ref.1). A recent review has been written by Mizota et.al.

(ref.2).

In

most commercial procedures homogeneous alkalis are added t o catalyse the isomerisation. The use of alkaline ion-exchangers as catalysts is described by Demaimay and Baron (ref.3).

Recently Shukla et.al. (ref.4)

mentioned the use of zeolites. Up to now most patents and publications only give recipees. We did some kinetic studies on the heterogeneous alkaline isomerisation of carbohydrates, which have been described in the thesis of Beenackers (ref.5).,

a part of which will be presented here.

Experimental procedures are given there. Details on the physical properties of the ion-exchangers used have been published before (ref . 6 ) . Reaction Network Sugars behave as weak acids (pKA

-

12) and at high pH ionisation

occurs. Ionisation in its turn induces enolisation of the aldehydo and keto functions in sugars and via these enolate intermediates sugars are mutually interconverted. The enolate intermediates not only reconvert t o

216

sugars but also enter into degradation reactions, ultimately leading to acidic products by splitting and rearrangement reactions. The enolate ions are unstable intermediates, hence the pseudo steady state approximation can be applied to these intermediates, resulting in a kinetic model in which only stable components figure. It also can be proven (ref.5) that such a model will be mathematically equivalent to the one as follows from the network presented in figure 1. LA \

kLA

LA-

Lu-

/

LU

LA(-) = lactose (anion) LU(-) = lactulose (anion)

ku.\

kLu/

kLUD

GAL

=

k

= rate constants

D-galactose

GAL

+ ACIDS Fig. 1.

Simplified reaction network of lactose isomerisation.

The network as depicted in the figure is a very simplified one. It does not incorporate epi-lactose (C-2 epimer of lactose, 4-0-P-D-galacto-

pyranosyl-D-mannose) and further reactions of D-galactose. However, it does describe the major events: the interconversion of lactose and lactulose, the formation of D-galactose by an elimination reaction and the simultaneous formation of acidic by-products from the glucose moiety. The major acidic product is iso-saccharinic acid. The consequence of the formation of acidic by-products is that the reaction is self-poisoning: the acids neutralize the alkaline catalyst and the reaction virtually stops as soon as an amount of acid has been formed equivalent to the amount of alkali added as catalyst. This is true for the commercial homogeneous alkali catalysed reaction as well as for the heterogeneous alkali catalysed reaction. RESULTS AND DISCUSSION Batch experiments have been carried out with several anion-exchangers in the OH--form, starting with lactose as well as with lactulose at temperatures in the range 303 to 363 K. Final conversions, which depend

on the catalyst to sugar ratio, generally were reached within 8 ks, depending on temperature. Using anion-exchangers as a heterogeneous

217 catalyst results in a neutral, ion-free sugar mixture as the product, while all degradation acids are retained within the catalyst. Samples of the sugar mixture were analysed at different reaction times by ionexchange chromatography (ref.7). The catalyst could be regenerated with alkali, washing out the degradation products. A typical composition of the washings, as determined with isotachophoresis (ref .5),

is presented in

table 1. TABLE 1 Composition (mol fraction) of acid product mixture washed out of the deactivated catalyst. Conditions: Lactose, 200 mourn3; Amberlite IRA 904, 40 mourn3; T, 333 K. formic acid

.21

dihydroxybutyric acid

.12

acetic/glycollic acid

.05

deoxypentonic acid

.04

lactic acid

.03

meta-saccharinic acid

.ll

glyceric acid

.01

iso-saccharinic acid

.43

From the reaction network we derive the following kinetic equations

(N = number of moles):

the initial selectivity for lactulose from lactose, S o , is given by:

In order to evaluate the rate constants from the analysed sugar concentrations, we need information on the amount of sugar present in the ionized form inside the ion-exchanger as a function of these external concentrations. These relations have been determined separately and we previously reported on ionisation (ref.8) and adsorption (ref.9).

Using

these relations rate constants were calculated from initial rate data (ref.5) and the results will be presented in the following sections.

218

I n f h n c e o f t h e tvDe o f a t - a l y s t Using s e v e r a l ion-exchangers ( r e f . 6 ) , s t a r t i n g w i t h l a c t o s e , t h e s e l e c t i v i t y f o r l a c t u l o s e has been determined. A t 313 K as well as a t 333 K t h e m a c r o r e t i c u l a r r e s i n s IRA 904 and IRA 938 gave t h e h i g h e s t v a l u e s ,

b o t h r e s i n s have an e x c e p t i o n a l l y h i g h p o r o s i t y .

TABLE 2 I n f l u e n c e of p a r t i c l e s i z e and p o r o s i t y of t h e ion-exchanger on t h e a p p a r a n t r a t e c o n s t a n t s and i n i t i a l s e l e c t i v i t y . C o n d i t i o n s : L a c t o s e , 600 m o l d ; Ion e x c h a n g e r , 40 mol/m3; T, 313 K.

IRA 401 (gel type) .47 .05

dp'

This f a c t

IRA 904 (macroporous) .50 .05

.21

.41

.54

-05

.022

-063 .052

.80

.95

.90

.51

.91

i d i c a t e s I a t s e l e c t i v i t y w i l l b e lowered due t o pore

d i f f u s i o n l i m i t a t i o n . T h i s i s i l l u s t r a t e d i n t a b l e 2 , where a p p a r a n t r a t e c o n s t a n t s and i n i t i a l s e l e c t i v i t y a r e g i v e n f o r IRA 401 g e l t y p e and IRA 904 macroporous type ion-exchanger i n normal s i z e ,

- 0.05

m. The macroporous ion-exchanger

-

0 . 5 mm, and ground,

as w e l l as t h e ground g e l t y p e

do n o t c a u s e d i f f u s i o n problems, however, t h e unground g e l t y p e does. Because l a c t u l o s e i s more s e n s i t i v e t o d e g r a d a t i o n t h a n l a c t o s e , a low d i f f u s i o n r a t e c a u s e s l a c t u l o s e t o b r e a k down b e f o r e i t l e a v e s t h e c a t a l y s t r e s u l t i n g i n a high a p p a r e n t v a l u e f o r kUD. The r e s u l t s a l s o show t h a t t h e g e l t y p e c a t a l y s t g i v e s a h i g h e r s e l e c t i v i t y provided t h a t d i f f u s i o n c o n t r o l can b e a v o i d e d . More d e t a i l s on d i f f u s i o n of s u g a r s i n ion-exchangers can b e found elswhere ( r e f . 1 0 ) .

Inf l u e n c e ~ f - ~ h ~ - ~ ~ m ~ ~ ~ r ~ u ~ Some d a t a on t h e e f f e c t of t e m p e r a t u r e a r e g i v e n i n f i g u r e s 2a and b . Below 313 K an a c t i v a t i o n energy of 90 KJ/mol i s e s t i m a t e d f o r b o t h kU and kLU. Above 313 K d i f f u s i o n l i m i t a t i o n o c c u r s , r e s u l t i n g i n a d e c r e a s i n g a p p a r e n t a c t i v a t i o n energy and a l s o i n a lower s e l e c t i v i t y a t higher temperature.

2 19

b

a -3

1.00

s,

C

-6

.

-7

.

W Y

Y

5

0.80

-8. -9

.

-

2.70

2.80

2.90

3.00

3.10

3.20

300 310

320 330 340 350 360

1000/T (T in K )

T (T in K )

Fig. 2a. Arrhenius plot of kU and kLU, 2b. Selectivity of the lactose isomerisation. Conditions: Amberlite IRA 9 0 4 , 40 m o u r n 3 ; lactose: 600 mourn3. Influence of the concentration At two different concentrations isomerisation experiments have been carried out with lactose as well as with lactulose. The results are shown in table 3 , together with the initial catalyst condition data as calculated from separate absorption and ionisation measurements (refs.8,9). It appears that a higher selectivity can be obtained at higher initial concentrations. TABLE 3 Influence of lactose/lactulose concentration on initial catalyst condition. apparent rate constants and initial selectivity. Conditions: Amberlite IRA 9 0 4 , 40 mol/m3; T, 313 K. c

~ in solution, , ~ mol/m-l ~

CLA,Lu in ion exchanger, mol/m3 CHz0 in ion exchanger/CH pure 2

90

5 70

250

5 70

0.94

0.87

13.43

13.15

0.60

0.54

0.20

0.27

0.15

0.064

0.67

0.51

0.81

0.90

220

From the rate constants it can be noticed that a lower C

and a H20 lower pH inside the ion-exchanger result in a shift of equilibrium backwards to lactose and it must be concluded that our system deviates from an ideal one. We further see that this slightly negative effect is overcompensated by a decrease of the rates for degradation. Apparently, the ratio of rates for reverse enolisation (sugar formation) and degradation of the enolate intermediates is influenced by CHz0 and pH. This is not yet accounted for in our kinetic model. INDUSTRIAL APPLICATION Because lactulose has a high degradation rate, good selectivities can only be obtained at low lactose conversions. In industrial practice concentrated lactose solutions are heated with approximately 0.04 mol alkali per mol lactose. This results in a final conversion of about 20% and a selectivity of 80’1. which is the point where the alkali is neutralized by the acid degradation products (i.e. 0.04 = 0.2 x (1-0.8)). By concentrating and cooling most of the residual lactose can be crystallized and recycled, leaving a product mixture consisting of lactulose, D-galactose, lactose, epi-lactose and salts. For further work-up the salts are removed by cation- and anion-exchange. Using alkaline ion-exchangers as the catalyst can result in a cheaper process because only one type of exchanger is needed. From our results it appears that good selectivities, generally higher than those reported in the patent literature, can be obtained, provided that diffusion control is avoided. Especially high sugar concentrations are beneficial and first trials in our laboratory have shown that also at high temperature and high concentration good selectivities are reached using less active catalysts which, therefore, do not cause diffusion problems. Although up to now the commercial product generally is a sugar mixture containing lactulose, there is a trend to further purification. We recently developed an oxidative procedure using a Pd-catalyst, in situ doped with Bi, as described elswhere (ref.11). Using this catalyst all aldose sugars i.e. D-galactose, lactose and epi-lactose, in an isomerisation mixture could be oxidized with air or oxygen to the corresponding aldonic acid salts, without any breakdown of lactulose. The salts could be removed by ion-exchange resulting in a high-purity lactulose solution.

221 REFERENCES

1.

2. 3. 4. 5.

6. 7. 8. 9. 10.

11.

H . Pluim, Duphar BV, p e r s o n a l communication. T. M i z o t a , Y. Tamura, M. Tomita, S. Okonogi, B u l l . I n t . D a i r y Fed., 212 (1987) 69-76. M. Demaimay, C. Baron, L a i t , 58 (575-576) (1978) 234-45. R. S h u k l a , X.E. V e r y k i o s , R. M u t h a r a s a n , Carbohydr. R e s . , 143 (1985) 97-106. J.A.W.M. B e e n a c k e r s , Ph.D. T h e s i s , May 1980, T e c h n i s c h e U n i v e r s i t e i t Eindhoven (The N e t h e r l a n d s ) . J.A.W.M. B e e n a c k e r s , B.F.M. K u s t e r , H.S. van d e r Baan, Appl. Catal., 16 (1985) 75-87. L.A.Th. V e r h a a r , M . J . M . v a n d e r Aalst, J.A.W.M. Beenackers, B.F.M. K u s t e r , J . of Chromatogr., 170 (1979) 363-370. J.A.W.M. B e e n a c k e r s , B.F.M. K u s t e r , H.S. van d e r Baan, Carbohydr. R e s . , 140 (1985) 169-183. J.A.W.M. B e e n a c k e r s , B.F.M. K u s t e r , H.S. v a n d e r Baan, Appl. C a t a l . , 23 (1986) 183-197. J.A.W.M. B e e n a c k e r s , B.F.M. K u s t e r , H.S. van d e r Baan, Appl. Catal., 23 (1986) 199-206. H.E.J. H e n d r i k s , B.F.M. K u s t e r , G.B. Marin, Carbohydr. R e s . , i n p r e s s .


M. Guisnet et al. (Editors), Hetrrogeneous Catalysis and Fine Chemicals I1 1991 Elsevier Science Publishers B.V., Amsterdam

223

Q

FURANIC DERIVATIVES SYNTHESIS FROM POLYOLS BY HETEROGENEOUS CATALYSIS OVER METALS. C. MONTASSIER, J.C. MENEZO, J. MOUKOLO, J. NAJA, J. BARBIER, URA CNRS 350 Laboratoire de chimie 4 40, Avenue du Recteur Pineau 86022 POITIERS CEDEX J.P. BOITIAUX Institut Fragais du Petrole 1-4 Avenue de Bois Preau 92506 RUEIL-MALMAISON CEDEX

ABSTRACT Raney copper catalyst is modified by mixing with aqueous salts of metals (Ir, Rh, Ru, Pd, Pt, Au) having a standard oxido-reduction potential higher than that of Cu. On pure Raney copper it is assumed that 10-15% of the surface copper atoms are hydroxylated and that these sites are responsible for the C-C and C - 0 bonds breakin observed during polyols conversion (dehydroxylation, retro-CLAISEN, retro-MICHAELf These sites are the first exchanged during the oxido-reduction modification, so that the above reactions are poisoned. For higher coverages of the additives, new sites appear that catalyze polyols cyclodehydration into furanic derivatives (glucitol is mainly converted into 1,43,6dianhydro-D-glucitol called isosorbide). This phenomenon is interpreted through an electronic transfer from copper to the second metal, leading to electrophilic copper. INTRODUCTION In a previous study (1) dealing with polyols conversion (glycerol, erythritol, glucitol) in neutral aqueous phase, between 453 and 533 K, under hydrogen pressure (3-6 MPa), we showed that ruthenium hydrogenolyses drastically both C-C and C - 0 bonds. Raney copper has not such a property but is able to convert polyols through its hydro-dehydrogenation activity according to the following scheme. Adsorption of polyols over copper surface and dehydrogenation, favoured at the end of the carbon chain, lead to unsaturated species strongly adsorbed which can undergo the nucleophilic attack of adsorbed hydroxyls ("OH), leading to dehydroxylation (DOH) :

224

H ., C=CH2

I OH /

I

2

H2C -CH

-CH,

I 1 OH OH

61

OH OH

If more intensive dehydrogenation occurs, for instance at 1 and 3 positions, the reaction of a "OH"group can lead to retro-CJAISEN products (RC) : H

OH

Formic acid is quickly dehydrogenated into carbon dioxide. If the carbon chain of the polyol contains 5 or more carbon atoms, a retroMICHAEL reaction (RM) can occur from a 1-5 didehydrogenated species :

Finally, unsaturated species are hydrogenated by copper and can desorb. This last reaction (RM) enables us to understand the formation of products containing 3 carbon atoms (glycerol, 1,Zpropanediol) from glucitol (sorbitol) but is always in competition with the two other ones (DOH, RC). The ratio of these three reactions, determining the conversion selectivity, depend widely on the copper origin (Raney, deposited on a support, impurities, activation process). So, we studied the influence of additives deposited on Raney copper on these reaction selectivities. EXPERIMENTAL The experiments were carried out in a static reactor (300 ml autoclave) with aqueous polyols solutions (0,ll to 0,44M). Hydrogen pressure was set in the 3,O-6,0 MPa range and temperature between 483 and 533 K. Samples drawn from the liquid and gaseous phases in

225

the course of the reaction were analyzed by HPLC (BIO-RAD HPX 87H and 87C columns, refractometric detector) and by CPV (PORAF'AK Q column). Raney copper is prepared by intensive leaching of a commercial copper-aluminum alloy (50-50 wt%) washed with water until neutral. Bimetallic catalysts are obtained using an oxido-reduction method : summarized as : n CU-s + 2 M"+ ---> n cu2+ + 2 M, in which M may be : Ir, Rh, Ru, Pd, Pt, Au whose standard oxido-reduction potentials are higher than that of Cu. This reaction is carried out by simply contacting (15 hours) an aqueous suspension of a known amount of Raney copper stirred by nitrogen bubbling with a known amount of a second metal salt solution. Knowing the number of copper surface mol.Cug-' mesured from N20reaction), the amount of salt (chlorides) atoms. (4,36 x is set so as to obtain the desired coverage : M/Cus, that is the atomic ratio second metal/initial surface copper. The following bimetallic catalysts were prepared : bimetals

Cu-Ir

Cu-Rh

M/Cus

0,lO

0,17

CU-RU

0 to 0,35

Cu-Pt

Cu-Pd

CU-AU

0 to l,o

0,80

0,90

RESULTS AND DISCUSSION Selectivitv of Dolyols conversion over the Cu -Ru bimetallic catalysts Ru/Cu, = 0.33 Glycerol (0,44M), at 533 K under 4MPa of hydrogen, is not converted after 6 hours of reaction (4g of catalyst). mol.min-I gIn the same conditions, erythritol (0,33M) is transformed (2,52 x 'cat) with a high selectivity (near 100%) into 1,4-anhydroerythritoI without any isomerisation.

mol.min-' g-l Likewise 1,4-butanediol is cyclised into tetrahydrofuran (2,93 x cat.at.493 K). Xylitol is transformed (2,O x 104mol.min-1g-1cat. at. 533 K) into 1,4-anhydro-(D,L)xylitol :

226

Glucitol ("sorbitol") is converted at the initial rates of 0,135 x 104mol.min-1g-1c;,t.nt 493 K and 8,8 x 104mol.min'1g-1cat. at 533 K. The main path is its cyclization into, first, (isosorbide) (figure 1). 1,4-anhydro-D-glucitol and then to 1,4-3,6-dianhydro-D-glucitol Two secondary ways of conversion are observed leading to 2,s-anhydro-L-iditol and 2,sanhydro-D-mannitol. All these cyclodehydration products are the result mainly of an inside chain oxygen attack on a primary carbon : the chiral carbon configurations remain unchanged. l h e only exception to this rule concerns the secondary products obtained from glucitol. 2.5-anhydro-L-iditol arises from the attack of the oxygen at C-2 on C-S which configuration is inversed. 2,s-anhydro-D-mannitol arises from the attack of the oxygen at C-5 on C-2 which configuration is inversed. In the case of glucitol conversion, the anhydroalditols total yield is 71% at 533 K, the other products obtained arising from degradations (breaking of C-C and C - 0 bonds). klectivity of b c i t o l conversion over the Cu-M bimetallic catalvsb Results are presented in table 2 for glucitol conversion at 493 K. TABLE 2 Glucitol (0,ll M) conversion over various bimetallic catalysts. Initial rate : molmin- lg- ]cat lo4. Products distribution in mole % of initial glucitol. GCL = glucitol, MAH = monoanhydrohexitols, ISOS = isosorbide. Catalyst

Cu-Pt CU-AU Cu-Pd CU-RU Cu-Rh Cu-Ir

M/Cu,

18 0,YO

0,80 0,35 0,17 0,lO

Initial rate 2,0 1,22 0,4 1 0,135 0,02

Products distribution after 360 min. %GCL %MAH 7,3 0 67 20.1 56,s 47,7

76,3 61,4 753 72,7 23,9 42,6

%lSOS 16,5 34,l 18,O 7,2 45

2,8

227

Figure 1 : Glucitol conversion over Cu-Ru (Ru/Cus = 0,33) at 533 K. The product distribution indicated is in mole percent in the mixture of all anhydrohexitols which total yield relative to initial glucital is 71 mole%

228

Initial conversion rates are not easy to compare because of the very different coverages obtained according to the second metal used. We can only notice that for M/Cus = 0,lO and 0,17 (Cu-Ir and Cu-Rh), these rates are very low. The main important feature i , that the same cyclodehydration reactions are observed, like that for Cu-Ru catalyst, whatever the nature of the second metal is. Activity and selectivitv variations according to &metal covera& As shown in figure 2 for glucitol conversion at 493 K for platinum and ruthenium as additives, the first atoms exchanged with copper are strong poisons for the copper catalyst until M/Cus = 0,lO to 0,15. In the range (A), the selectivity observed is that of Raney copper (DOH mainly, RC, RM). No cyclodehydration products have been detected. Above M/Cus = 0,lO to 0,15 (C) the activity increases and the cyclodehydration reaction leading to furanic products is the main one. This cyclodehydration is well known, especially for the synthesis of isosorhide (2-5) and is usually carried out in strongly acidic medium. Its mechanism was proved (4) to be a SN2 intramolecular reaction catalyzed by protonation of the alcoholic functions. The products distributions we obtained are close to those obtained by acidic catalysis.

?5

RU

Pt +

3 0 -

' 0

1

4

05

00

I

I

0

07

0

08

08

1

M/Cu (surf.)

I

A

0 4

c

Figure 2 : Initial rate variations of glucitol conversion at 493 K in function of M/Cus for M = Ru (m) and Pt (+). From all these results we suggest the following scheme :

229

OH

I

C u Raney

c u - c u - c u - c u - c u - c u CL-CU-CU-CU

A

+H,-H

DOH,RC,Xbl

CU-M M/Cu s

0,lO

CU-M M/Cu s > 3,lO

CU-CU-M CU Cu-C u - C U - C U - C U - C U

-

+H, H

Cu C U \, Gu-CU \: Cu-Cu-M-CU u -2

'\

B

C

//H.-H CDOIl I

,

In A, a Raney copper catalyst would be able to hydro-dehydrogenate alcoholic functions (-H, + H ) on metallic copper sites. About 10 to 15% of the copper would be hydroxylated copper able to catalyze the degradation reactions DOH, RC, RM. These sites would be more reactive than Cu towards Mn -t in the oxido-reduction modification of the initial Raney copper, so that, beeing first exchanged, the rates of DOH, RC, RM decrease. In C, further exchange between metallic copper and M"' would create new sites able to catalyze the cyclodehydration reaction (CDOH). These sites must be, as protons, electrophilic centers able to weaken C-0 bonds enough to allow intramolecular SN2 reactions mainly on primary carbon atoms. As the standard oxido-reduction potential of copper is lower than that of the second metals used in this work we suggest that an electronic transfer from copper to M (Ir, Rh, Ru, Pd, Pt, Au) could generate electrophilic copper M- - Cu' able to catalyze the cyclodehydration according to the scheme :

CONCLUSION The catalytic properties of copper during polyols conversion in aqueous phase may be drastically modified by some additives. Metals having a standard oxido-reduction potential higher than that of copper (Ir, Rh, Ru, Pd, Pt, Au) can be deposited on it by oxidoreduction reaction. The first atoms of second metal deposited exchange with hydroxylated

230

copper which amount to 10 to 15% of the initial superficial copper. The hydroxylated copper would be the sites active for dehydroxylation, retro-CLAISEN and retroMICHAEL reactions, that, so, are poisoned by the additive. When the exchange is higher than 10-15% of the surface copper, new sites appear, able to catalyze cyclodehydration reactions leading to furanic derivatives. We suggest that an electronic transfer from copper to the additive undergoes electrophilic copper sites able to adsorb alcohols and to initiate intramolecular SN2 reactions as it is well known for acidic catalysis of the cyclodehydration. Despite the practical interest of the good selectivity we obtained for these reactions (6) the variations in selectivity and activity according to the additive coverages show that relatively complex molecules such as natural polyols, which configurations are well established, are useful probe molecules able to bring out important informations about catalytic sites and their properties. ACKNOWLEDGMENTS We thank the Institut Francais du PCtrole for their financial support. REFERENCES 1 a) C. Montassier, D. Giraud, J. Barbier, Proc. “1st Int. Symp. Heterogeneous Catal. and Fine Chemicals”. Poitiers, France, 1988, Elsevier, Amsterdam, 41 (1988), 165-70. b) C. Montassier, D. Giraud, J. Barbier, J.P. Boitiaux, Bull. Soc. Chim. Fr. (1989, 148-55. R.M. Goepp, H.G. Fletcher, J. Am. Chem. SOC.,68 (1946), 939-41. 2 3 B.G. Hudson, R. Barker, J. Org. Chem. 32 (1967), 3650-8. 4 K. Bock, C. Pedersen, M. Thogersen, Act. Chem. Scand., B 35 (1981), 441-9. 5 F. Jacquet, A. Gaset, J.P. Gorrichon, Information Chimie, 246 (1984), 155-8. 6 J. Barbier, J.P. Boitiaux, P. Chaumette, S. Le Pors, J.C. Menezo, C. Montassier, Eur. pat. 90.400.177.3 (1990)

M. Guisnet et al. (Editors), Heterogeneous Catalysis and Fine Chemicals I I

231

Q 1991 Elsevier Science Puhlishers B.V., Amsterdam

ACTIVITY AND STABILITY OF PROMOTED RANEY-NICKEL CATALYSTS IN GLUCOSE HYDROGENATION P.J. CERlNOl , G. FLECHE2. P. GALLEZOTl and J.P. SALOMEZ lnstitut de Recherches sur la Catalyse, C.N.R.S.. 2 avenue Albert Einstein, 69626 Villeurbanne CBdex - (France) 2 Societe Roquette Freres, 62136 - Lestrem (France)

-

-

SUMMARY The activity and stability of Raney-nickel catalysts promoted with molybdenum, chromium and iron have been studied in glucose hydrogenation. There are several causes of deactivation. Sintering plays a minor role after four recyclings. Leaching of iron atoms from the nickel surface IS the main cause of the rapid deactivation of ironpromoted catalysts. Poisoning by organic fragments produced by glucose cracking on the nickel surface could be the main cause of deactivation. The presence of chromium or molybdenum on the nickel surface is beneficial for the stability because they decrease the crackin activity and favor the activation and hydrogenation of the carbonyl group of the aldehyjc form of glucose. INTRODUCTION It is well known, even from old literature data (ref. 1) that the presence of metal promotors like molybdenum and chromium in Raney-nickel catalysts increases their activity in hydrogenation reactions. Recently Court et al (ref. 2) reported that Mo, Cr and Fe-promoted Raney-nickel catalysts are more active for glucose hydrogenation than unpromoted catalysts. However the effects of metal promotors on the catalytic activity after repeated recycling of the catalyst have not been studied so far. Indeed, catalysts used in industrial operation are recycled many times, stability is then an essential criterion for their selection. From a more fundamental standpoint, the various causes of Raneynickel deactivation have not been established. This work was intended to address two essential questions pertinent to the stability of Raney-nickel in glucose hydrogenation namely what are the respective activity losses experienced by unpromoted or by molybdenum, chromium and iron-promoted catalysts after recycling and what are the causes for their deactivation ? EXPERIMENTAL Precursor alloys of composition Ni40-~M~A160 were prepared by cooling metal melts under argon atmosphere. The ingots were annealed for three weeks at 950°C under argon, then ground and sieved to keep grains smaller than 40 pm. Composition of the alloys are given in table 1. Batches of 100 g were leached by 500 cm3 of soda (6N) added slowly at room temperature. The suspension was refluxedfar two hours and washed with

232

Table 1 : Composition and characterizationof Raney-nickel catalysts

Catalysts

Alloy composition

MINI ( x i 02)

RNi Ni39.2Al60.8 RNiMo Ni38.2A160.8MOl 2.6 RNiCr Ni38.3A160.6Crl 2.7 RNiFe Ni34.gAI58.7Fe6.4 18.5 RNilndl a RNilnd2a -

Catalyst composition AI/Nib M/Nib X(I

0.19-0.1 8 0.25-0.21 0.28-0.24 0.45-0.34 0.11-0.09 0.13-0.1 1

02)

0.89-0.84 2.6-2.2 18.5-6.9 0.80-0.81 0.1 -0.1 1

BET areab (m2/g)

Crystallite sizeb (A)

82-64 79-70 116-73 97-75 77-74 101-61

43-47 38-45 34-39 45-36

a - industrial catalyst promoted with molybdenum b - before and after five hydrogenation cycles soda (1N). The powder was then submitted to three refluxing treatments in 6N, 4N and 2N soda solutions and finally kept under 1N soda. The composition of the different catalysts thus prepared and of two industrial catalysts are given in table 1. BET surface areas were measured after outgassing the catalysts under vacuum at 120°C for 4h. X-ray patterns were recorded with catalysts kept under water. Crystallite sizes were obtained with the Scherrer formula. The local composition of catalysts was measured by energy-dispersive X-ray emission (EDX) associated with a VG HB501 scanning transmission electron microscope (STEM). The spatial resolution of analysis is 1.5 nm. The STEM-EDX study was performed on ultramicrotome sections of Raney-nickel grains embedded in an epon resin. Before hydrogenation the pH of a D-glucose solution (3.37 mol-1) was adjusted at 6.5 with acetic acid. The solution was heated at 60°C and poured in an autoclave containing 2 wt % of Raney-nickel with respect to glucose monohydrate. The autoclave was pressurized under 45 bars of hydrogen and the temperature was increased from 60 to 130°C. The reaction was started after pressurization at 50 bar and stirring at 1400 rpm. Samples of the reaction medium were periodially taken for HPLC analysis (Column Biorad HPX 87C at 85°C). After the first hydrogenation the reactor was purged, the catalyst was washed and a new charge of glucose was hydrogenated. All these steps were conducted under H2-pressure. RESULTS Table 1 shows that the precursor alloys have the expected composition Ni40-~M,A160 within analytical errors. The X-ray pattern of the precursor alloy of RNi and RNiCr is characteristic of the Ni2A13 hexagonal phase. In the case of iron-promoted alloy there are weak additional reflections corresponding to the A15Fe2 phase. In the case of molybdenum, A13Mo and AlgMog phases are detected in agreement with literature data showing that molybdenum has a low solubility in the Ni2A13 phase (ref. 3). The fresh

233

catalyst RNiMo has lost a large amount of molybdenum with respect to its precursor alloy (table 1). This is in contrast with RNiCr and RNiFe where the M/Ni ratios did not change after soda attack. This lost is probably due to the large fraction of molybdenum not associated with nickel in the Ni2A13 phase. As noticed previously (ref. 3) the presence of a third metal increases the retention of aluminum. The local composition of the catalysts was measured by STEM-EDX on different zones of a given ultramicrotome section (edge, core), on different areas (1 nm2-1 pm2) and on different sections. In all catalysts except RNilnd2, the promotors are distributed throughout the nickel grain on a nanometer-sized scale. In RNiMo, inclusions of a Morich phase have been detected, they could result from the attack of the A13Mo and AlgMog phase detected in the precursor alloy. In RNilnd2, the concentration of molybdenum is very heterogeneous the promotor being concentrated near the external surface of the catalyst grains. Figure 1 (a-f) gives the conversion of glucose as a function of time for the different catalysts, fresh and during four successive recyclings. The initial rates expressed per catalyst weight are given for the first and fifth hydrogenation.The selectivity to sorbitol was always higher than 97 %. the less active catalysts giving the lowest selectivity because a fraction of dextrose isomerizes into fructose which is subsequently hydrogenated into mannitol. After five hydrogenation runs, the BET area decreases for all catalysts (table 1) which could be attributed to a partial sintering. However the area loss could be due to a poisoning of the catalyst. Indeed, the presence in Raney nickel grains of strongly bound organic residue, which could not be washed out or outgassed, would decrease the amount of physisorbed nitrogen. Table 1 gives the average sizes of nickel crystallites measured by X-ray line broadening analysis on (1 11) reflections, before and after the five hydrogenation runs. They increase moderately and even decrease for RNiFe. This confirms that the BET area loss could be due in part to a poisoning which reduces the capacity of nitrogen adsorption. However, measurements of the metallic surface area should also be done to confirm possible surface poisoning. DISCUSSION From figure 1 (a - e) it is clear that the activities of Raney-nickel catalysts increase with the addition of promotors, iron producing the largest rate enhancement in agreement with previous reports (ref. 3). These effects can be tentatively interpreted by the following mechanism. The promotor atoms on the surface of nickel crystallites are more electropositive than nickel since the electron affinities (ref. 4) are in the series Fe < Cr < Mo < Ni (15.7:64.2:71.9:115.5 kJ mol-1). Even under H2-pressure. they can be positively charged and act as adsorption sites for the glucose aldehydic form via the oxygen atom of the carbonyl group. The polarization of the C = 0 bond favors a

234 Conventon tx)

100 . I -

o

M

40

MI

60

100 im

140

160 IMI

Time (min) Conmnlon (X) -

loor

mo

--

~

80

60

i 40

lo

50

----

1

o

m

40

Conraalon

60

I%)

ro

1.375

1.96

01

7

(LO ioo I M Time (min)

160 180

140

lo

5O

2.98

0.59

ao

mo

o

1

T

I

r

m

40

60

MI

,

7- 7--,-7--

loo

im

140 ibo IM

mo

I

20

After indwtrlnl

0

30

00

80

120

I

1

160

180

1

1

I

8

0

30

Time (min)

- 1 Hydro.

+-

2 Hydro.

80

80

-

120

160

180

Time ( min ) --C

3 Hydro.

G --I

4 Hydro.

-

5 Hydro

Fig. 1 : Conversion of glucose as a function of time in five successive hydro enations for the different catalysts (a) RNi ; (b) RNYo ; (c) RNiCr ; (d) RNiFe ; (e) WNilndl ; (f) RNilnd2. The initial rates ro (mol h-lg- ) are given for the first and fifth reactions. The lower curve in (e) corresponds to a catalyst after many industrial hydrogenations.

235

nucleophilic attack of the carbon atom by hydrogen dissociated on neighbouring nickel atoms as suggested by the following scheme.

HO

After successive recyclings the catalyst activities decrease at different paces. Thus, during the fifth run the hydrogenation rate on RNiFe is five times smaller than during the first, whereas the rate of RNiMo and RNiCr are divided by 2 and 1.4 respectively. Catalyst RNilndl promoted with molybdenum deactivates almost like RNiMo (figures 1b, 1e) whereas RNilnd2 deactivates rapidly (figure 1f). One cause of catalyst deactivation is the sintering of the metal phase. This is obvious for RNilndl which after much recycling in industrial conditions has lost both its activity (lower curve in figure 1e) and its BET area (14 m2g-1). It was checked by electron microscopy that the nickel crystallites are large and agglomerated in this aged catalyst. Although in the other catalysts there is a simultaneous decrease of BET area and activity, it cannot be concluded that deactivation after five runs is due mainly to metal sintering. As mentionned above, the decrease in BET area could be partly due to the presence of organic residues indeed the little increase of nickel crystallite sizes points at a moderate sintering. Besides, there is no proportionality between the BET area and the activity, thus in RNiCr, there is a large apparent loss of BET area without much deactivation. Clearly there are other factors contributing to catalyst deactivation. Thus in RNiFe the rapid aging after successive recycling has nothing to do with sintering since the crystallite sizes even decrease. It can be attributed to an extraction of the iron atoms from the surface which are solubilized in the reaction medium as shown by the decrease of the Fe/Ni ratio after reactions (table 1). Then the activity is no longer promoted by the mechanism discussed above. Another cause of deactivation for all the catalysts and especially for the unpromoted ones is the poisoning of active sites by side reaction products. Indeed nickel is well known for its cracking activity producing organic fragments which remain adsorbed strongly on the nickel surface. The presence of chromium or molybdenum on the nickel surface (and also of aluminum which is in larger amount in

236

promoted-catalysts) could reduce this cracking activity either by geometric effect (size of nickel ensemble) or by electronic effects (electron transfer to nickel). Thus the RNilnd2 catalyst deactivates rapidly because molybdenum is not distributed throughout catalyst grains as shown by STEM-EDX analysis, whereas the other Mo-promoted catalysts and RNiCr keep their activities. The presence of organic fragments poisoning the surface has been confirmed by magnetic measurements which will be reported elsewhere. Indeed the magnetization of nickel was found smaller after reaction on RNi but not on RNiCr, indicating that surface nickel atoms in the former catalyst are "demetallized" by chemisorbed species. CONCLUSION Raney nickel catalysts promoted by molybdenum, chromium and iron exhibit higher initial activities in glucose hydrogenation because electropositive atoms on the nickel surface polarize the carbonyl group of the glucose molecule adsorbed via the oxygen atom. The larger the electropositivity, the larger the activation of the carbonyl group. The activities decrease progressively after successive recyclings. Threee factors are involved in the deactivation process (i) a leaching of the promotor atoms from the nickel surface. This process is specially marked on iron-promoted catalysts which deactivate rapidly after the first reaction. (ii) a poisoning of the catalyst by organic fragments produced by side cracking reactions. This would be the main cause of deactivation during the first few runs. However there is little deactivation for molybdenum and chromium promoted catalysts (iii) a decrease in the surface area due to nickel crystallite sintering. This is the major cause of deactivation after a large number of recycling e.g. after a long period of industrial operations. REFERENCES 1 2

3 4

R. Paul, Bull. SOC.Chim. Fr. 13 (1946) 208. J. Court, J.P. Damon, J. Masson and P. Wierzchowski in : M. Guisnet et al (Ed.), Heterogeneous catalysis and fine chemicals, Elsevier, Amsterdam, 1988, pp 189196. L. Kaufman and H. Nesor, Metallur ical Trans., 5 (1974) 1627. H. Hotop and W.C. Lineberger, J. Fhys. Chem. Ref. Data, 14 (1985) 731-750.

M.Guisnet et al. (Editors), Heterogeneous Catalysis and Fine Chemicals II

237

1991 Elsevier Science Publishers B.V., Amsterdam

TRANSFORMATION OF SUGAR I N T O GLYCOLS ON A 5% Ru/C CATALYST

P. MULLER, P. RIMMELIN, J.P. HINDERMANN, R . KIEFFER, A. KIENNEMANN L a b o r a t o i r e de Chimie Organique Appliquee E H I C S URA CNRS 469 1, r u e B l a i s e Pascal 67000 STRASBOURG FRANCE J . CARRE' SUCRERIES ET RAFFINERIES 67150 E R S T E I N FRANCE

SUMMARY Saccharose h y d r o g e n o l y s i s was performed i n a s l u r r y t y p e r e a c t o r i n presence o f a 5% Ru/carbon c a t a l y s t . M o d i f i c a t i o n o f pH d u r i n g t h e r e a c t i o n can i n c r e a s e t h e y i e l d o f 1,Z-propane d i o l and g l y c e r o l n o t i c e a b l y . An adsorbed complex i s proposed t o account f o r t h e d i f f e r e n c e i n s e l e c t i v i t y f o r v a r i o u s C 5 and C sugars. 6 INTRODUCTION

The p r o d u c t i o n excess o f saccharose i n t h e w o r l d i n g e n e r a l and i n Europe i n p a r t i c u l a r l e a d s t o t h e r e s e a r c h o f i t s v a l o r i z a t i o n by chemical methods. A p a r t t h e hydrogenation o f aldose o r c e t o s e t o t h e c o r r e s p o n d i n g p o l y o l s ( r e f s . 1-11) t h e o b t e n t i o n o f lower p o l y o l s l i k e g l y c e r o l , and

ethylene-glycol

is

also

an

interesting

process

1,2-propane

(refs.

12-15).

diol The

m u l t i p l i c i t y o f t h e r e a c t i o n s i n b a s i c media when saccharose i s c o n s i d e r e d (inversion

e.g.

hydrogenolysis

ose e.g.

formation, glycol

hydrogenation

formation,

e.g.

polymerization)

hexitol makes

formation, the

process

d i f f i c u l t t o c o n t r o l . Furthermore, t h e h y d r o g e n a t i o n process i s known t o be r i n g s t r u c t u r e dependant ( r e f s . 2,4,11)

i n aqueous s o l u t i o n . The s t u d y o f t h e

c a t a l y t i c h y d r o g e n o l y s i s o f saccharose was undertaken i n o u r l a b o r a t o r y i n a t h r e e phase s l u r r y t y p e r e a c t o r .

Monomers o f v a r i o u s

s t e r e o c h e m i s t r y were

s u b m i t t e d t o h y d r o g e n o l y s i s i n o r d e r t o g a i n some i n s i g h t i n t o t h e mecanism i n v o l ved. EXPERIMENTAL Experiments were c a r r i e d o u t i n a t h r e e phase s l u r r y t y p e r e a c t o r w i t h aqueous sugar s o l u t i o n s device

(A).

. Hydrogen was

f e d i n t o t h e r e a c t o r through a f l o w r e g u l a t i o n

The s t a i n l e s s s t e e l

r e a c t o r was

temperature c o n t r o l l e d by a p o w e r s t a t .

heated e l e c t r i c a l l y

and t h e

I t was equipped w i t h a m a g n e t i c a l l y

d r i v e n v a r i a b l e speed s t i r r e r . The equipment was f i t t e d w i t h i n s t r u m e n t s f o r measuring t e m p e r a t u r e (C) ( i n

238

Fig. 1 : Hydrogenolysis r e a c t o r

t h e r e a c t i o n medium and i n t h e h e a t i n g d e v i c e ) . Flow r a t e and p r e s s u r e were m o n i t o r e d by a computer. Hydrogenolysis r u n s were s t a r t e d by c h a r g i n g t h e r e a c t o r w i t h sugar s o l u t i o n s containing

the

appropriate

amount

of

catalyst.

predetermined p r e s s u r e and t h e f l o w was s e t on.

Hydrogen was

fed

to

the

Then h e a t i n g and s t i r r i n g

begun. A d d i t i v e s were l e d i n t o t h e r e a c t o r under p r e s s u r e .

A sampling t u b e

p e r m i t t e d w i t h d r a w a l o f l i q u i d a t s p e c i f i e d i n t e r v a l s and t h e e x i t hydrogen c o u l d be analyzed by on l i n e GPC t h r o u g h a sampling l o o p ( B ) . Chemically p u r e monosaccharides and d i s a c c h a r i d e s were used. The c a t a l y s t ( 5 $ Ruthenium on c a r b o n ) was purchased f r o m ALDRICH. Chromatographic c o n d i t i o n s : Sugar and p o l y o l s i n aqueous media were analyzed by HPLC. (column, sugar pack waters;

e l u a n t H20; f l o w r a t e 0.5 m l / m i n .

: t e m p e r a t u r e 90°C;

differential

refractometer d e t e c t o r ) . G l y c o l s and monoalcohols were s e p a r a t e d by c a p i l l a r y column GPC (column,

WAX 58 CHROMPAC,

flame i o n i s a t i o n detector,

CP

programmed t e m p e r a t u r e : 60 t o

.

250°C, 5"C/mi n ) . Gaseous samples were determined by GC (column s t a t i o n a r y phase,

carbosieve;

d e t e c t o r , catharometer, programmed t e m p e r a t u r e : 30 t o 230"C, 4"C/min.). The s t a r t i n g t i m e f o r t h e experiments was t a k e n a t t h e s t a r t o f t h e h e a t i n g o f t h e r e a c t o r . A f t e r one hour t h e r e a c t i o n t e m p e r a t u r e was reached (220°C). The

yields

are

given

as

the

following

ratio

:

weight

of

considered

239

p r o d u c t / w e i g h t o f s t a r t i n g p r o d u c t x 100. RESULTS AND D I S C U S S I O N Table 1 p r e s e n t s t h e r e s u l t s o b t a i n e d i n t h e saccharose h y d r o g e n o l y s i s . I n p a r t A,

i t means s t a r t i n g w i t h a b a s i c medium, t h e s t u d y shows t h a t many

r e a c t i o n s a r e r u n n i n g i n t h e same t i m e : f i r s t i n v e r s i o n o f saccharose t o f o r m glucose and f r u c t o s e , t h e n h y d r o g e n a t i o n o f t h e monosaccharides t o h e x i t o l s and u l t i m a t e l y h y d r o g e n o l y s i s i n t o 1,2-propane d i o l . The y i e l d s i n 1,2-propane d i o l and i n g l y c e r o l a r e n o t v e r y h i g h (17 and 7% r e s p e c t i v e l y ) a f t e r 4 hours. Table 1 : Y i e l d o f saccharose h y d r o g e n o l y s i s .

............................................................................. Time on stream ( h ) Remaining Saccharose % Yields G F

1 71 2 2

m A

S

3

M 1,2-PG GLY

2

3

4

5 3 2 10 1 15

2

1

7 2 23 17

2 1 17 7

12 5 26 6

5 24 7

17

8

46

35 12

____---_____--__________________________-----------------~-----~------

B

Remaining Saccharose % Yields G F m S M 1 ,Z-PG GLY

9 30 22

5

7 2 9

17 9 20

________________________________________---------------~-----------Remaining Saccharose % G Yields F m C

S

M 1,2-PG GL Y

5

a

2 1

3

52 30

26 10 27

________________________________________----------------------------A : Reaction c o n d i t i o n s : T = 220°C, P = 5,5 MPa, pH = 10 sugar c o n c e n t r a t i o n 40 g/L, s u g a r / c a t a l y s t w e i g h t r a t i o 16. B : Same as f o r A b u t s u g a r / c a t a l y s t w e i g h t r a t i o 32. C : Same as f o r A b u t pH = 6 f o r t h e f i r s t two hours t h e n a d j u s t e d t o pH = 10. G : glucose S : sorbitol 1,2-PG : 1,2-propylene g l y c o l F : fructose M : mannitol GLY : g l y c e r o l m : mannose

Some r e a c t i o n parameters were t h e r e f o r e changed i n influence o f t h e d i f f e r e n t steps

order

to

study

the

on t h e o b t a i n e d y i e l d s . Thus t h e c a t a l y s t

c o n c e n t r a t i o n was lowered and t h e i n v e r s i o n c o u l d p a r t l y be separated f r o m t h e h y d r o g e n a t i o n and t h e h y d r o g e n o l y s i s ( p a r t B ) . T h i s r e s u l t e d i n a b e t t e r y i e l d i n 1,2-propane d i o l (24% a f t e r 4 h o u r s ) . Decreasing t h e c a t a l y s t c o n c e n t r a t i o n

240

d i m i n i s h e s t h e h y d r o g e n a t i o n r a t e . The pH o f t h e s o l u t i o n d r o p s d u r i n g t h e f i r s t hour when s t a r t i n g a t PH

10. T h i s pH d r o p i s f a s t e r i n presence of

=

l e s s c a t a l y s t p r o b a b l y because o f secondary r e a c t i o n s .

Indeed t h e a n a l y s i s

shows t h a t much more a c i d i c compounds a r e p r e s e n t i n t h e case o f l o w c a t a l y s t c o n t e n t . T h i s can e x p l a i n t h a t saccharose i s much f a s t e r c o n v e r t e d t o g l u c o s e and f r u c t o s e and why saccharose i s a p p a r e n t l y t r a n s f o r m e d f a s t e r t o p o l y o l s i n presence o f l e s s c a t a l y s t . The h y d r o g e n o l y s i s o f t h e C 6 oses o r p o l y o l s i s thought

to

proceed

reaction i s thus

through

faster

an e n e d i o l

than

in

part

(ref.

A

15-1 7 ) .

since

one

dehydrogenate t h e h e x i t o l s . The y i e l d s i n 1,2-propane

The need

hydrogenolysi s not

at

first

d i o l and g l y c e r o l a r e

t h u s enhanced. The s e p a r a t i o n between h y d r o g e n a t i o n and h y d r o g e n o l y s i s can be o b t a i n e d by m o d i f i c a t i o n o f t h e pH d u r i n g t h e r e a c t i o n . a c i d i c pH (pH 5 t o 6 ) . F o r h y d r o g e n o l y s i s , e n e d i o l which s t a r t e d a t pH

Indeed h y d r o g e n a t i o n o c c u r s a t t h e r e a c t i o n i n t e r m e d i a t e i s an

i s u n f a v o r e d i n a c i d i c media. =

I n p a r t C,

t h e r e a c t i o n was

6. The base (Ca(OHI2) was added up t o pH 10 a f t e r two hours,

i t means a f t e r t h e h y d r o g e n a t i o n s t e p . I t can c l e a r l y be seen t h a t i n t h e f i r s t h o u r d u r i n g t h e t e m p e r a t u r e i n c r e a s e

f r o m 20 t o 220°C,

h y d r o l y s i s o f saccharose and h y d r o g e n a t i o n o f t h e formed

g l u c o s e and f r u c t o s e t o s o r b i t o l

and m a n n i t o l

p o l y o l s a r e hydrogenolysed t o 1,2-propane

proceeds.

Then,

t h e formed

d i o l and g l y c e r o l e s s e n t i a l l y . T h i s

r e s u l t s i n an i n c r e a s e o f t h e y i e l d i n 1,2

propane d i o l and g l y c e r o l .

This

enhancement can be e x p l a i n e d p a r t i a l l y by a decrease o f secondary r e a c t i o n (e.g.

p o l y m e r i s a t i o n o f t h e oses)

s i n c e now t h e p r o d u c t s a r e p r e s e n t

as

p o l y o l s and n o t as oses. A n e a r e r e x a m i n a t i o n o f t h e r e s u l t s ( T a b l e I , p a r t C ) shows t h a t t h e formed m a n n i t o l i s t r a n s f o r m e d more e a s i l y t h a n s o r b i t o l .

It

appears t h u s c l e a r l y t h a t t h e h y d r o g e n o l y s i s r e a c t i o n i s s e n s i t i v e t o t h e s t r u c t u r e o f t h e h e x i t o l . The h y d r o g e n o l y s i s o f p o l y o l s and t h e c o r r e s p o n d i n g oses has t h u s been undertaken t o g e t a b e t t e r i n s i g h t i n t o t h e r e a c t i o n process ( T a b l e 2 ) . TABLE 2. Y i e l d s of p o l y o l s and oses h y d r o g e n o l y s i s (1,2-propanediol g l y c e r o l 1. POLYOLS YIELDS % OSES YIELDS %

t

.....................................................

MANNITOL GALACTITOL SORBITOL IDITOL

56 44 35 35

ARABITOL X Y L ITOL

46 39

MANNOSE GALACTOSE GLUCOSE I DOSE FRUCTOSE ARABINOSE XYLOSE

57 49 41 48 43 37

......................................................

R e a c t i o n c o n d i t i o n s l i k e i n T a b l e 1 ( p a r t A) f o r t h e p o l y o l s and i n Table 1 ( p a r t C) f o r t h e oses. The p r o d u c t s ware analyzed a f t e r 4h.

241

0 II

0 II

Rnlacrirol

Fig.

2

: S ' r u c t u r r s of

the proposed complexes.

242

For t h e C 5 compounds e s s e n t i a l l y 1,2-propane

d i o l and g l y c e r o l a r e observed. T h i s w i l l be d i s c u s s e d

Only s m a l l amounts o f e t h y l e n e g l y c o l a r e d e t e c t e d . here

after.

From Table

2

clearly

it

results

that

the

oses

and

the

c o r r e s p o n d i n g p o l y o l s r e a c t i n t h e same manner. However t h e s e l e c t i v i t y o f t h e h y d r o g e n o l y s i s d i f f e r s f o r t h e v a r i o u s p o l y o l s used i n t h i s s t u d y . The problem remains t o e x p l a i n t h i s d i f f e r e n c e i n s e l e c t i v i t y .

I t would be d i f f i c u l t t o

g i v e h e r e a l l t h e d e t a i l s about t h e s t r u c t u r e o f sugars and r e l a t e d p o l y o l s . The i n t e r e s t e d r e a d e r m i g h t f o u n d more i n f o r m a t i o n s i n r e f . ( 1 8 - 1 9 ) . Andrews and K l a e r e n ( 2 0 ) have proposed a r e a c t i o n scheme w i t h a c o o r d i n a t e d sugar a l k o x y a n i o n as i n t e r m e d i a t e i n r u t h e n i u m based homogeneous c a t a l y s i s o f monosaccharide s e l e c t i v e h y d r o c r a c k i n g . However t h e p r o d u c t s o b t a i n e d i n t h e r e a c t i o n o f g l u c o s e ( e t h y l e n e g l y c o l and e r y t h r i t o l ) a r e n o t i n concordance w i t h our r e s u l t s .

In t h e h y d r o g e n a t i o n o f g l u c o s e and f r u c t o s e on copper

c o n t a i n i n g c a t a l y s t , Makkee e t a1 ( r e f . 4 ) proposed t h a t 0 - f r u c t o s e (and o t h e r k e t o s e s ) formed i o n i s e d f u r a n o s e s p e c i e s adsorbed on copper by c o o r d i n a t i o n o f 0-1, 0-2 and 0-5 t o t h e s u r f a c e . An a d s o r p t i o n o f t h e p o l y o l s on t h e c a t a l y s t s s u r f a c e i n a t h r e e f o l d c o o r d i n a t i o n s i m i l a r t o t h a t proposed by Makkee e t a1 ( r e f . 4 ) i s p o s s i b l e as shown on f i g . 2. I t can be seen t h a t t h e 2-0, 3-0, 4-0 and 3-0, 4-0, 5-0 c o o r d i n a t i o n s a r e most s t a b l e f o r m a n n i t o l . As shown on t h e f o l l o w i n g scheme ( f i g . give 2 C3

3 ) , t h e 2-0,3-0,4-0

4-0,

and 3-0,

5-0 complexes can

species.

OH

\ ri2 c -

OH

\I/

c;\

+ CHz OH-CHOH-CI10

4

I

I

C-

C-

I

M F i g . 3 : Proposed r e a c t i o n scheme.

CIlzOH

I

t

2

CHZ OH-CHOH-CHO

243

Experiments on t h e h y d r o g e n a t i o n o f g l y c e r o l show t h a t i t i s n o t c o n v e r t e d into

1,Z-propane

diol

in

our

reaction

conditions.

Unlike

glycerol,

g l y c e r a l d e h y d e i s c o n v e r t e d t o a m i x t u r e o f 1,2-propane d i o l and g l y c e r o l . I t seems t h u s t h a t g l y c e r a l d e h y d e which i s d e t e c t e d i n s m a l l amounts

i n our

h y d r o g e n o l y s i s experiments c o u l d be a r e a c t i o n i n t e r m e d i a t e . For g a l a c t i t o l t h e same c o o r d i n a t i o n s a r e p o s s i b l e b u t a s t e r i c i n t e r a c t i o n e x i s t s between t h e s u r f a c e and t h e CHOH-CH20H c h a i n . The 2-0,3-0,4-0

and 3-0,

4-0, 5-0 c o o r d i n a t i o n s a r e t h u s l e s s f a v o u r e d t h a n f o r m a n n i t o l . F o r s o r b i t o l , t h e 3-0,

4-0 and 5-0 c o o r d i n a t i o n i s t h e same as f o r m a n n i t o l .

However f o r t h e 2-0,3-0

and 4-0 complex t h e two c h a i n s (CH20H and CHOH-CH20H)

a r e on t h e

same

s i d e and

therefore

unfavoured.

It

results

from

these

c o n s i d e r a t i o n s t h a t t h e s e l e c t i v i t y t o 1,2 propane d i o l and t o g l y c e r o l s h o u l d be m a n n i t o l

galactitol

sorbitol.

T h i s i s what was

observed

i n our

experiments. The r e s u l t s f o r t h e C 5 p o l y o l s o r oses show t h e same v a r i a t i o n o f s e l e c t i v i t y w i t h s t r u c t u r e as f o r t h e C6 compounds. As f o r t h e C6 oses m o l e c u l a r models f o r C5 oses show t h a t t h e

proposed

c o o r d i n a t i o n i s a l s o f a v o u r e d f o r a r a b i t o l b u t n o t f o r x y l i t o l . The a r a b i t o l complex has t h e same c o n f i g u r a t i o n as m a n n i t o l , b u t t h e 3-C, 4-C bond cleavage g i v e s 1 C2 and 1 C3 i n s t e a d o f 2 Cj molecules. T h e r e f o r e t h e y i e l d o f 1,2propane d i o l and g l y c e r o l i s l o w e r f o r a r a b i t o l t h a n f o r m a n n i t o l . G l y c o l a l d e h y d e which would be i n o u r r e a c t i o n scheme a r e a c t i o n i n t e r m e d i a t e i n t h e f o r m a t i o n o f g l y c o l f o r C 5 compounds i s o n l y s l i g h t l y c o n v e r t e d t o g l y c o l b u t i s r a t h e r decomposed i n t o hydrocarbons (methane, c o u l d e x p l a i n why almost o n l y C 3

p o l y o l s are obtained.

ethane).

This

Comparing now t h e

r e a c t i v i t y t o t h e s t a b i l i t y o f t h e s e complexes a good c o r r e l a t i o n can be o b t a i n e d : mannose

galactose

arabinose

sorbose = i d o s e

xylose.

The

same r e s u l t s were o b t a i n e d f o r h e x i t o l s . F r u c t o s e which i s hydrogenated t o m a n n i t o l and s o r b i t o l has an i n t e r m e d i a t e s e l e c t i v i t y

(between g l u c o s e and

mannose 1. CONCLUSION The study o f t h e h y d r o g e n o l y s i s o f saccharose t o 1,2-propane

d i o l has shown

t h a t a b e t t e r y i e l d can be o b t a i n e d by t h e s e p a r a t i o n o f h y d r o l y s i s and hydrogenation steps, f r o m t h e bond cleavage. T h i s can be achieved by a d j u s t i n g t h e pH d u r i n g t h e r e a c t i o n . The h y d r o g e n o l y s i s o f d i f f e r e n t oses has shown a d i f f e r e n c e i n t h e s e l e c t i v i t y o f t h e r e a c t i o n . An adsorbed f o r m o f t h e p o l y o l s can account f o r these d i f f e r e n c e s . Indeed some oses l i k e mannose and g a l a c t o s e have no h i n d r a n c e t o f o r m t h e proposed complex.

244

A f u r t h e r improvement o f t h e t r a n s f o r m a t i o n o f saccharose t o 1,2-propane can p r o b a b l y be o b t a i n e d f r o m i t s s e l e c t i v e h y d r o g e n a t i o n t o m a n n i t o l e.g.

diol in

presence o f molybdate i o n s ( r e f . 21.

REFERENCES 1 J.W. Green, The carbohydrates, Chemistry and B i o c h e m i s t r y , Acad. Press, New York, 2nd Ed 16, 1980, 989. 2 M. Makkee, A.P.G. Kieboom, H. van Bekkum, S t a r c h / S t a r k e , 37, (19851, 133. 3 J. Wisniak, M. Hershkowitz, R. L e i b o w i t z , S. S t e i n , I n d . I n g . Chem. Prod. Res. Dev., 13, (19741, 75. 4 M. Makkee, A.P.G. Kieboom, H. van Bekkum, Carbohydr. Res., 138, (19851, 225. 5 J. Wisniak, R. Simon, I n d . Eng. Chem. Prod. Res. Dev., 18, (19791, 50. 6 F.B. Bishanov, R.B. Drozdova, React. K i n e t . C a t a l . L e t t . , 21, (19821, 35. 7 A.H. Germain, M.L. Wauters, G.A. L'Homme, Stud. S u r f . S c i . C a t a l . 7, (19811, 1492. 8 A.A. W i s m e i j r , A.P.G. Kieboom, H. van Bekkum, React. K i n e t . C a t a l . L e t t . , 29, (19851, 311. 9 J.M. Bonnier, J.P. Damon, J . Masson, Appl. C a t a l . 30, (19871, 181. 10 G. Vanling, A.J. Driessen, I n d . Engng. Chem. Prod. Res., 9, (19701, 212. 11 J. Ruddlesden, A. Stewart, 0. Thompson, R. Whelan, Faraday Discuss. Chem. SOC. , 72, (19811, 397. 12 C . M o n t a s s i e r , D. Giraud, J. B a r b i e r , Heterogeneous C a t a l y s i s and F i n e Chemicals M. GUISNET e t a l . ( E d i t o r s ) , 1988 E l s e v i e r Science P u b l i s h e r s B.V., Amsterdam p. 165 13 D. Ariono, C . Moraes, A. Roesyadi, G. Declercq, A. Z o u l a l i a n , B u l . SOC. Chim., 5, (19861, 703. 14 I . T . C l a r k , I n d . & Eng. Chem., 50, (19581, 1125. 15 I . D . Rozhdestvenskaya, T.N. Fadeeva, L.V. S h i l e i k o , K i n e t . C a t a l . 11, (19701, 568. 16 D.K. Sohounloue, C . M o n t a s s i e r , J. B a r b i e r , React. K i n e t . C a t a l . L e t t . , 22, (19831, 391. 17 A.P. Sergev, B.L. Lebedev, Uspekhi Khimi, 28, (19591, 669. 18 S.J Angyal, Angew. Chem. 81, (1969), 172. 19 S. J. Angyal, Adv. Carbohydr. Chem. Biochem. 42, (19841, 15. 20 M.A. Andrews, S.A. K l a e r e n , J. Am. Chem. SOC., 111, (1989), 4131.

M. Guisnet et al. (Editors),Heterogeneous Catalysis and Fine Chemicals II 0 1991 Elsevier Science Puhlishers B.V., Amsterdam

SELiCTIVE HYDROGENATION OF ACETOPHENWE GI1 I"O#OTtD

245

HAllEY INICKEL : 1i.IFLUENCE

OF THE ; l i A C T I O N CONDITIONS J. MASSON',

P . CIVIDINO',

J.W. BONNIER

1

and P . FOilILLOiJX

2

' L a o o r a t o i r e d ' E t u d e s Llynamiques e i S z r u c t u r a l e s de l a S e l e c c i v i i s (LtOSS-1 ) CiWS URA 332 - I l n i v e r s i ' c 6 Joseph F o u r i e r - BP 53X - 38041 GRENOBLE CEDEX (France). 2

U n i e e lvlixte } wavenumber (cm-')

Figure 2 . FT-IR spectra of (a) nitrocyclohexane (575K),( b ) nitrobenzene (575K),( c ) acetic acid (575K),and (d) nitrosobenzene (475K)adsorbed at a-Mn,O,. (Spectrum ( d ) is found to be assignable to surface azoxybenzene species.) The transformation of nitrocyclohexane into an azoxy surface complex needs a dehydrogenation step. The proven formation of a nitronate species indicates that dehydrogenation easily happens, indeed.

Discussion Information obtained from the systems studied, leads to the assumption that the time dependence of the product distribution of selective nitrobenzene oxidation (fig.1) has to be explained in the following way:

311

During the induction period, removable oxygen of the transition metal oxide attacks the ring of nitrobenzene and leads to the formation of the reducing fragments C, H, and CH, at the surface. Oxidation of these fragments produces carboxylate species at the surface. With nitrocyclohexane or nitromethane this oxygen leads also to the formation of carboxylate species. In the course of the induction period, the reducing fragments accumulate on the surface and create a situation at the surface, which leads to the formation of aniline. When reaching steady state conditions, the catalyst is partially reduced and selective removal of one of the oxygen atoms from the nitro group can be accomplished, resulting in nitrosobenzene production. During the period of selective reduction of nitrobenzene to

Q O \

nitrosobenzene, the most likely intermediate is a surface species of which only one of the two oxygen atoms interacts with the oxide surface, possibly as shown in smcture 11. Direct evidence for this adsorption mode could not be obtained by FT-IR spectroscopy, most probably because the lifetime of this mode is too short to allow its observation.

0

0

structure I1

It is likely that on highly reduced materials, like metals, a nitrene intermediate is formed upon reduction of nitr~benzene[~~. Although direct evidence for nitrene formation has not been obtained in this study, an indirect indication for such an intermediate can be found in the production of azobenzene and azoxybenzene. Coordination chemistry reveals how two ArN species can be coupled into one azobenzene molecule. In the case of the reaction of Fe,(CO),, with aromatic nitro compounds in benzene[I6’,formation of derivatives such as in structure I11

N

/.‘ (C0)s Fe

\

e(CO)s

.$e(co)3

has been proven by X-ray diffraction. Azoxybenzene can be formed by reaction of nitrene with nitrosobenzene, formed by reduction of nitrobenzene.

structure 111

The above mentioned process of the transformation of nitro compounds into nitroso compounds should also be possible for the other nitro compounds studied, nitromethane and nitrocyclohexane. However, no aliphatic nitroso compounds (or oximes obtained by isomerisation of the aliphatic nitroso compound) have been detected either in the gas or in the adsorbed phase. This is obviously caused by the easy migration of the a-hydrogen along

312

the molecules of nitroalkanes, which leads to the formation of a very reactive, easily oxidizable nitronate species. Once this pathway is opened, a very reactive C=N bond is formed and subsequently oxidized. This sequence of reaction steps prevents the competitive reduction to the corresponding nitroso compounds.

References [ 1] H.G.Zenge1, Chem.Ing.Tech. 2 (1983) 962

[2] [3] [4] (51 [6] [7] [XI [9] [ 101

1111 1121 [ 131 [ 141 [ 151

161

H.G.Zengel and M.Bergfeld, Ger.Offen 2939692 (1981) D.Dodman, K.W.Pearson, and J.M.Woolley, Brit.App1. 1322531 (1973) N.L.Holy, A.P.Gelbein, and R.Hansen, U.S.Patent 4585900 (1986) C.S.John, European Patent 0 178 718 A 1 (1986) K.Kishi, Surf.Sci. 192 (1987) 210 T.L.F.Favre, P.J.Seijsener, P.J.Kooyman, A.Maltha, A.P.Zuur, and V.Ponec, CataLLett. 1 (1988) 457 T.L.F.Favre, A.Maltha, P.J.Kooyman, A.P.Zuur, and V.Ponec, Proc.XI Symp.lberoam. (1988) 807 J.B.Benziger, Appl.Surf.Sci. (1984) 309 J.B.Benziger, Combust.Sci.Techno1. 29 (1982) 191 P.A.J.M.Angevaare, E.J.Grootendorst, A.P.Zuur, V.Ponec, Stud.Surf.Sci.Catal. 55 (1990) 861 Interscience J.H.Boyer, The chemistry of the nitro and nitroso group, H.Feuer (4.). Publishers, U.S.A. (1969) 244 H.A.C.M.Hendnckx, PhD Thesis 1988, Leiden, the Netherlands H.Feuer, C.Savides. C.N.R.Rao, Specmhim.Acta 19 (1963) 431 H.Knetenbrink and ILKnozinger, Zeitschr.Physik.Chemie, Neue Folge 102 (1976) 43 J.M.Landesberg, L.Katz, and C.Olsen, J.Org.Chem. 2 (1972) 930

M. Guisnet et al. (Editors),Heterogeneous Catalysis and Fine Chemicals I1 0 1991 Elsevier Science Publishers B.V., Amsterdam

313

T fi IJ A id I L I ‘1i I> 17 E P AK A T 1 UiJ U F I1[<TII0 1’ IE N Y LEN E D I A M IN E FROM 4 - C H LOR 0 - 2- N I

J.L.Margitfalvi,

M.HegedLis,

S.Gtlb616s

a n d E.TAlas

C e n t r a l R e s e a r c h I n s t i t u t e f o r C h e m i s t r y o f t h e H u n g a r i a n Academy o f S c i e n c e s , 1 5 2 5 B u d a p e s t , POB 1 7 , H u n g a r y

SUMMARY I n t h i s w o r k t h e p r e p a r a t i o n o f o r t h o p h e n y l e n e d i a m i n e (OPDA) f r o m 4 - c h l o r o - 2 - n i t r o a n i l i n e was s t u d i e d o n a l u m i n a s u p p o r t e d p a l l a d i u m c a t a l y s t s . H i g h OPDA y i e l d s w e r e o b t a i n e d o n c a t a l y s t s c o n t a i n i n g s t a b i l i z e d i o n i c palladium. I n the preparation o f t h e given palladium containing c a t a l y s t s anchoring type surface reactions were u s e d . The e x i s t e n c e o f p a l l a d i u m i n i o n i c f o r m was e v i d e n c e d b y X P S a n d EI’R m e a s u r e m i i n t s .

1N T R 0 OU C T I0N Urthophenylenediamine

(OPOAI

i s an i m p o r t a n t i n t e r m e d i a t e of

s e v e r a l b i o l o g i c a l l y a c t i v e compounds,

i n c l u d i n g t h e benzimidazene-

- c a r b a r n a t e t y p e f u n g i c i d e s [ I ] .T h e r e a r e d i f f e r e n t s y n t h e s i s o f UPUH.

I n t h e present work an d t t q i t

p a r e OPDA f r o m 4 - c h l o r o - 2 - n i t r o ~ n i l i n e ( C N A ) . by n i t r d t i o n and subsequent The p r e p a r a t i o n of i c steps,

i.e.

routes for the

was done t o p r e -

CNA c a n b e o b t a i n e d

a r n m o n o l y s i s o f p a r a - d i c h l o m - b e n z e n e [I].

UPOA f r o m CNA r e q u i r e s t w o d i f f e r e n t c a t a l y t -

d e c h l o r i n a t i o n and r e d u c t i o n .

Both o f these rcac-

t i o n s r e q u i r e s h y d r o g e n a n d a r e c a t a l y z e d b y Group V I I I m e t a l s . Supported p a l l a d i u m i s considered as one o f t h e most a c t i v e c a t a l y s t b o t h f o r hydrodehalogenation [ ‘ , 3 ] and r e d u c t i o n o f t h e n i t r o group 1-

1.

I t i s a l s o known,

that in addition t o the catalytic reaction

r o u t e t h e dehalogenation o f aromatic h a l i d e s can be c a r r i e d o u t stoichiometric reaction LiA1H4 o r NaBH4).

[;I

i n t h e presence o f metal hydrides

Further c h a r a c t e r i s t i c feature o f hydrodehaloge-

n a t i o n r e a c t i o n s is t h e r e q u i r e m e n t f o r a d d i t i o n o f the reaction

i n

le.g.

rree bases i n t o

m i x t u r e t o f i x t h e formed h y d r o c h l o r i c a c i d [ L I l ] .

CATALYST U E S I G N R e a c t i o n s i n v o l v e d i n t h e f o r m a t i o n o f OPDA a r e g i v e n i n Scheme I. T h e m o s t i m p o r t a n t i s s u e i n t h e p r e p a r a t i o n o f OPOA f r o m C N A i s t o find a specific catalyst,

which can c a t a l y z e b o t h t h e hydrodechlo-

r i n a t i o n and t h e r e d u c t i o n s t e p s .

I n t h i s case the conversion o f

314

qNo2 GNH2 L

by - products

slow

Cl

SCHEME I CNA to OPOA can be carried out in one step. Further technological improvement will be if the use of free base could be avoided. The basis for the design of catalysts f o r Scheme I was the need to obtain higher rates f o r the hydrodechlorination step than f o r the reduction of the nitro group of CNA. If rate of conversion of CNA to 4-chloro-1,2-orthophenylenediamine ( L P D A I is high i n this case the formation of OPDA is strongly hindred a s , due to the substituent effect, the rate of hydrodechlorination of Lr'UA is low. Characteristic feature of catalyst designed f o r the hydrodehalogenation and reduction is the p r e s e n c e of a stabilized, anchored form of ionic palladium o n the alumina support. T h e idea to have ionic forms of palladium on the support is tiased o n homogeneous catalytic analogies. It has been reported that i n hydrodehalogenation o f arylhalides the rate limiting step is the oxidative addition of the ArCl to the palladium [5]. Based on this knowledge it has been suggested that the introduction of palladium into the heterogeneous catalyst not i n metallic but i n ionic form should i n crease the rate of hydrodehalogenation reaction provided the mode of stabilization of the ionic form of palladium can b e found. SURFACE CHEMISTRY T h e r e are different approaches to introduce ionic species onto silica or alumina supports. In this work an anchoring process via lithiated alumina was used as follows:

315 S u r f a c e r e a c t i o n s ( 1 ) and (21 have been w i d e l y used t o p r e p a r e s i l i c a s u p p o r t e d m e t a l complex c a t a l y s t s [ 6 ] . The s t a b i l i z a t i o n o f i o n i c f o r m s o f p a l l a d i u m w a s strurif;ly i n c r e a s e d b y t h e p r e s e n c e of -0Li moiety. Simultaneous presence o f - O L i and (-0InPd s u r f a c e s p e c i e s r e s u l t e d i n a very a c t i v e hydrodehalogenation and r e d u c t i o n catalyst.

EXPERIMENTAL C a t a l y s t p r e p a r a t i o n and c h a r a c t e r i z a t i o n

I n t h i s w o r k K e t j e n CK 3 0 0 t y p e a l u m i n a w a s u s e d a s s u p p o r t . 0 i f f e r e n t p a r t i c l e s i z e were u s e d d e p e n d i n g o n t h e a p p l i c a t i o n ( 0 . 0 3 - 0 . 0 5 mm a n d 0 . 3 1 - 0 . 6 3 mm f o r s t i r r e d t a n k a n d t r i c k l e b e d r e a c t o r s , r e s p e c t i v e l y ) . P r i o r t o t h e c a t a l y s t p r e p a r a t i o n t h e s u p p o r t was t h e r m a l l y t r e a t e d i n v a c u u m a t I x I O - ~ b a r . S o l v e n t s a n d g a s e s were c a r e f u l l y d r i e d and

deoxygenated p r i o r t o t h e i r use.

R e a c t i o n ( 1 ) was c a r r i e d o u t i n n-hexane s o l v e n t . The e x c e s s but y l l i t h i u m was e i t h e r removed by w a s h i n g w i t h n-hexilne o r decompos e d b y t h e r m a l t r e a t m e n t . A n c h o r i n g o f p a l l a d i u m ( r e a c t i o n (2)) w a s c a r r i e d o u t i n a c e t o n e s o l u t i o n f o l l o w e d by w a s h i n g w i t h a c e t o n e and methanol.

T h e formed S u r f a c e Complex (SC) was s t a b i l i z e d by

t h e r m a l t r e a t m e n t i n n i t r o g e n a t 1O0-30O0C f o r 3 h o u r s . F u r t h e r d e t a i l s on c a t a l y s t p r e p a r a t i o n w i l l b e g i v e n i n t h e R e s u l t s a n d Uiscussion. S o m e o f t h e c a t a l y s t s a m p l e s p r e p a r e d were c h a r a c t e r i z e d b y E P R

a n d XPS.

E P R s p e c t r a were r e c o r d e d a t 2 0 a n d -196OC u s i n g a JEOL

JES-FE3X s p e c t r o m e t e r .

XPS m e a s u r e m e n t s were t a k e n by u s i n g a V G

ESCA 3 s p e c t r o m e t e r w i t h a n a l u m i n i u m K a

radiation source. A l l bin-

d i n g e n e r g i e s w e r e r e f e r r e d t o t h e A12p l i n e ( B E

=

74.7 eV).

Catalytic reactions

The conversion of 4-chloro-'-nitroaniline

(CNA)

( F l u k a , purum,

'98%) w a s c a r r i e d o u t i n s t i r r e d t a n k o r t r i c k l e b e d r e a c t o r s under r e l a t i v e l y mild reaction condtion (P =

35-120OC).

=

2-30 b a r and T =

Gas C h r o m a t o g r a p h y was used f o r p r o d u c t a n a l y s i s .

RESULTS AND DISCUSSI0N S u r f a c e r e a c t i o n s and c a t a l y s t p r e p a r a t i o n

I n order t o obtain different extent of lithiation i n reaction (1) t h e f o l l o w i n g experimental v a r i a b l e s were changed: t e m p e r a t u r e

o f d e h y d r o x y l a t i o n . t h e amount o f b u t y l l i t h i u m u s e d , t e m p e r a t u r e and t i m e o f t h e r e a c t i o n . The p a l l a d i u m c o n t e n t o f t h e c a t a l y s t was

316 Table 1 Condition of t h d preparation of ionic palladium c a t d l y s t s React ion (11

Ta

N o [OC]

1 2 3L

150 150 150

4c

300

5

200 150 150 150 150 250 150

6

7 8d gd 10 11

Reaction

EuLib A1203

time, min

2.3 2.3 2.3 0.9

60

1.5

90

2.3 1.5 2.5 2.5 2.3 2.3

60

60 60 60

time, min

XPS d a t a

Concentration

(2)

W%

Li

Pd

60 1440 60

0.31 0.61 0.46

60

0.52 0.51

60

30 135 900

85

60

0.92

85 85

60 60

85

GO

0.84 0.24 0.49

0.55 0.70

1.2 1.2 1.2 0.3 1.2 l.G 0.4 0.6 1.3 0.4 0.6

Pd3d5/2 binding FWHM energy

Cl n.a n.a n.a 0.3 0.3 n.a 0.5 n.a n.a n.a n.a

336.6 3 3 5 . ~ 3 3 ~ J.

3.7 3.0 3.2 -

336.6 336.3 334.9

11.0 4.3 2.8 -

Temperature of dehydroxylation; G i v e n i n mmol/g; A f t e r r e a c t i o n ( 1 ) t r e a t m e n t a t 150°C f o r 1 h o u r a t I x I O - ~ b a r P a r t i c l e s i z e t0.045 mm, i n o t h e r s a m p l e s : 0 . 3 1 - 0 . 6 3 mm c o n t r o l l e d by ( i ) t h e e x t e n t of

lithiation,

(ii) the temperature

a n d [ i i i ) t h e t i m e o f r e a c t i o n (21. C h a r a c t e r i s t i c p r o p e r t i e s o f c a t a l y s t s p r e p a r e d and c o n d i t i o n s o f p r e p a r a t i o n a r e g i v e n i n T a b l e I.

T h e i o n i c c h a r a c t e r o f c a t a l y s t s p r e p a r e d s t r o n g l y depended on t h e e x p e r i m e n t a l c o n d i t i o n s u s e d i n s u r f a c e r e a c t i o n s ( 1 ) a n d (2) and on t h e modes o f t h e removal o f t h e u n r e a c t e d b u t y l f a r a s i n reaction

i m p o r t a n t t o remove u n r t d c t e d b u t y l l i t h i u m ing w i t h n-hexane.

lithium.

As

( 1 ) a n e x c e j s b u t y l l i t h i u m was u s e d i t was v e r y by

washing o r e x t r a c t -

I n t h i s way u n d e s i r e d r e d u c t i o n o f rdCl2 u n d e r

c o n d i t i o n o f r e a c t i o n (21 c o u l d b e p r e v e n t e d .

T h e t h e r m a l t r e a t m e n t o f t h e l i t h i a t e d a l u m i n a dirnod t o d e c o m pose unrracted butyl lithium resulted

(see catalysts

NO3

i n reduction o f palladium

and 4 ) . I n t h i s c a s e u n d e s i r e d r e d u c t i o n o f pal-

l a d i u m w a s d t t r i b u t e d t o t h e p r e s e n c e o f h i g h l y d i s p e r s e d metallic l i t h i u m or l i t h i u m h y d r i d e f o r m e d f r o m C 4 H g L i

during the thermal

trcatment . T h e f o r m a t i o n o f m e t a l l i c p a l l a d i u m w a s a l s o o b s e r v e d in t h e p r e s e n c e o f s m a l l amount o f w a t e r i n t r o d u c e d i n t o t h e a c e t o n e t o i n c r e a s e t h e s o l u b i l i t y o f PdCl?. o f reaction

(LdtalySt5

S i g n i f i c a n t i n c r e a s e of t h e time

(2) resulted also i n partial reduction NOZ

and 31.

o f palladium

317 C h a r a c t e r i z a t i o n o f c a t a l y s t s b y EPR a n d XPS The EPR s p e c t r a o f a l i t h i a t e d a l u m i n a a n d t w o t y p e s o f p a l l a d -

1 . C a t a l y s t NO5

i u m c a t a l y s t a r e shown i n F i g . by a n c h o r i n g t e c h n i q u e , pregnation.

has been p r e p a r e d

w h e r e a s c a t a l y s t NO7 b y c o n v e n t i o n a l i m -

A n a r r o w EPR s i g n a l ( w i t h g = 2 . 0 0 4 1

was d e t e c t e d o n l y

on c a t a l y s t c o n t a i n i n g i o n i c p a l l a d i u m . B a s e d on t h e g v a l u e s a n d t h e absence of a n i s o t r o p y and h y p e r f i n e s t r u c t u r e i n s p e c t r a b and c t h e EI’R s i g n a l s c a n b e a t t r i b u t e d t o f r e e e l e c t r o n o r i g i n a t e d f r o m t h e e l e c t r o n i c i n t e r a c t i o n o f i o n i c p a l l a d i u m and t h e a l u m i n a

171. I t i s w o r t h f o r m e n t i o n i n g , t h a t t h e r e d u c t i o n

support

t a l y s t N O 5 i n h y d r o g e n a t 200°C

ance o f t h e n a r r o w l i n e i n s p e c t r u m c . s i g n a l s c o r r e s p o n d i n g t o Pd+’ spectra

.

o f ca-

does n o t r e s u l t i n t h e d i s a p p e a r -

I t i s a l s o noteworthy,

that the

a n d Pd+3 c a n n o t b e d e t e c t e d i n

H

I H

1 g = 2 ,0046 C

100 G

100G

U

I

Fig.

1 . Li’R sli e c t r a o f L i / A 1 , 0 3 and d i f f e r e n t P d - c o n t a i n i n ( a ) L i / A 1 2 0 3 p r e c u r o s o r o f C a t a l y s t N o 5 j ( b ) C a t a l y s t N 5 c ap trael py satrse. d b y a n c h o r i n g p a l l a d i u m ; ( c l C a t a l y s t N O 5 t r e a t e d i n H 2 a t 200°C;

i

( d ) C a t a l y s t p r e p a r e d b y i m p r e g n a t i o n l s p e c t r a t a k e n a t 20°C. X P S d a t a a r e g i v e n i n T a b l e 1 . B a s e d on l i t e r a t u r e d a t a [ d , g I

t h e b i n d i n g e n e r g i e s around 335.0 m e t a l l i c and i o n i c p a l l a d i u m . d i n g e n e r g y o f t h e Pd 3dSl2 lysts

NO1,

J ,

:I

and 336.7 eV were a t t r i b u t e d t o

respectively.

The v a l u e s o f t h e D i n -

bond s t r o n g l y i n d i c a t e t h a t i n c a t a -

palladium i s i n i o n i c form.

Contrary t o that,

c a t a l y s t NO7 m e t a l l i c p a l l a d i u m was e v i d e n c e d .

i n

I n t h e case o f c a t a -

l y s t NO7 t h e FWHM o f t h e Pd 3 d 5 / 2 b o n d h a d t h e l o w e s t v a l u e .

I n ca-

t a l y s t s a m p l e s c o n t a i n i n g i o n i c Pd t h e FWHM v a l u e s a r e much l a r g e r .

These d a t a r e v e a l t h e h o m o g e n i t y o f s u r f a c e s p e c i e s w i t h m e t a l l i c c h a r a c t e r and c e r t a i n i n h o m o g e n i t y o f t h e i o n i c p a l l a d i u m

introduLed

318

by anchoring. I n the latter case the inhomogenity can be attributed either to different valent states or ligand environment of the ionic palladium anchored to the alumina. It has also been reported that in the presence of chlorine the FWHM values o f the P d 3dSl2 bonding energy is higher than in its absence [ e l . Conversion of 4-chloro-2-nitroaniline to orthophenylenediamine Kinetic curves o f the products formation obtained on ionic palladium catalyst (NO91 are shown in Fig. 2. T h e formation of OPOA on catalysts containing both ionic and metallic palladium is shown i n Fig. 3. These results reveal the high activity of alumina supported ionic palladium catalysts both in the hydrodehalogenation reaction and reduction o f the nitro group. As seen i n Fig. 3.. the addition o f metallic palladium strongly dechreases the initial hydrodechlorination activity of catalysts containing ionic palladium. In the latter catalysts the metallic palladium was introduced prior t o the lithiation (reaction ( 1 ) ) .

0

20

40

60 80 time, rnin

100

0

20

40 60 time, min

80

Fig. 2. Kinetic curves of the products formation from CNA. D-OPDAI + - ONA; o - CPDA; Catalyst N09, isopropanol-water (90:10),?OO cm3, CNA: 5 g; CNA/catalyst: 8; P: 1 bar; T : GOOCJ stirred tank reactor. Fig. 3. Influence o f the metallic palladium on the formation of OPDA; Metallic palladium [w%l: - 0.0 [catalyst N o 8 1 , o - 0.05, 0 - 0 . 1 0 1 Conditions: s e e Fig. 2.; CNA/catalyst = 12.

319

100

s

40 -

D

a

b

A / -A-A

.-b)

1

SO 20

0

a

0

- A

time, min

time, min

F i g . 4. I n f l u e n c e o f t h e amount o f c a t a l y s t on t h e f o m t i o n o f OPDA and CPOAI A - 0 . 9 3 g, x - 1 . 8 6 g, # - 3 . 2 g~ C a t a l y s t N ' l l , CNA: 30 g P H ~ : 3 0 b a r ; T: 9 5 C; NH3-HzO ( 5 0 - 5 0 % ) , 3 0 0 cm3; s t i r r e d t a n k reactor.

100

1

100

1

w.

a 0 a U x-x-x

0

30

60

90

0

120

time, min

30

60

90

120

time, min

F i g . 5. R o l e o f t h e temperature o f pretreatment on t h e f o r m a t i o n o f OPDA and CPOA; o - 100°C, 0 - 200°C, x - 30OoC; c a t a l y s t : N O 1 O j c a t a l y s t : 1.86 gl CNA: 30 g; PH2: 30 bar; T: 95OC. NH3-H20 (50-50%) 300 cm3; s t i r r e d t a n k r e a c t o r . As shown i n F i g .

4.,the

r a t e s o f OPOA a n d CPOA f o r m a t i o n a n d

thus y i e l d s were s t r o n g l y i n f l u e n c e d by t h e amount o f c a t a l y s t optimized r e a c t i o n c o n d i t i o n

used.

Under

and a t 100 % o f conversion OPDA s e l e c t i v i t y around

96 % could be obtained. Heat treatment i s used t o s t a b i l i z e t h e i o n i c p a l l a d i u m formed i n s u r f a c e r e a c t i o n (2). A l l o f t h e c a t a l y s t s were t r e a t e d in

n i t r o g e n a t 100°C f o r 3 h o u r s .

of

treatment resulted i n s i g n i f i c a n t increase i n t h e hydrodechlo-

r i n a t i o n a c t i v i t y a s showri i n F i g . Results obtained i n a t r i c k l e

The i n c r e a s e o f t h e t e m p e r a t u r e

5. b e d r e a c t o r a r e s u m m a r i z e d i n Tab-

320 Table 2

Conversion of CNA in trickle bed reactor Catalysta'

v

T

Inlet, cmj.min-"

bar liquid"

OC

gas

Selectivity, 2

Conversion c

OPUA

CPUA

unknown

34.4 10.7

Ill.

~

~~~~

35

2

NU 5

10 70

NO5

70

2 2 5

NO5 N%

117

5

80

NO6

80

CJ 5

NO5 No5

0.7 0.7 0.7 0.7 0.4

0.7 0.7

110 110 110 110 110 120 60

100 100 100 100 Yti

100

100

b5.b

80.C

Y8.2 96.2 17.1 96.9 98.0

0.5 1.1 7.5 3.1 2 .0

U.Ci

1.3 2.7 75.4 U.L< I1.L

See T a b l e 1

Amount of catalyst: 5 g 5 wt% CNA i n ethanol l e 2. These investigations were aimed t o obtain high UPDA selectiv-

ities at I O U % of conversion. The selectivity of the OPUA formation strongly depended on the reaction temperature. A t temperature abovc llO°C condensation of the OPOA and CPDA wdb o b s t r v e d , howw,sI, dt rr lLitively low temperature and hydrogen pressure 1 0 0 % conversion and 98 % OPUA selectivity could be achieved. N o significant ageing of

the catalysts up to 1 0 0 hours rzartion t i n i t .

zuulu

tt:

ubsirvtd.

CONCLUSION

Results obtained in this work strongly indicate that catalyst design b a s e d on the primary knowledge o f the reaction network and the mechanism of the given reactions can be used to obtain highly active and selective catalysts f o r hydrodechiorination reaction and reduction o f the nitro group. It w a s also demonstrated that upon using anchoring type surface reaction palladium can b e stabilized on the alumina i n ionic form. REFERENCES

1

2 3

H.W.Layer, Arnines, aromatic-phenylenediamines, i n M.Garyson and 0.Eckroth ( E d s . ) "Kirk-IIthmtr Encyl.Chern.Technol., 3 r d Ed., Wiley. New York, 1 Y 7 6 , 2, 3 4 8 - 3 5 4 . A.R.Pinder, Synthesis, I Y t i U , 1125. P.h.Rylander "Catdlytic Hydrogenation i n Organic Synthesis", Academic Press, New York, 1979, p p . 2 3 5 - 2 4 6 . G.Elrieger and T.J.Nestrick, Chemical Reviews, 74 ( 1 9 7 4 ) 5 6 7 . J.K.Stille and K.S.Y.Lau, J.Am.Chem.So~., 98 ( 1 9 7 F ; I 5 8 4 1 . Yu.l.Yermakov and V.A.Likholobov, Kinet.Katal., 2 1 ( 1 9 8 0 ) 1206. P.A.Uerger and J.F.Roth, J.Catal., 4 ( 1 9 G 5 ) 7 1 7 . F.Ro7on-Verduraz, A.Omar, J.Escadr and B.Pontvainne, J.Cata1. 53 ( 1 9 7 0 ) 1 2 6 . A.I.Lapidus, V.V.Maltsev, E.S.Spiro, G.V.Antoshin, V.I.Garanin arid H.M.Minachev, 17v.Akad. N a u k S S S R , Ser.Khim. 1 9 7 7 , 2 4 5 4 .


32 1

CHEMOSELECTIVE HYDROGENATION OF AROMATIC CHLORONFTRO COMPOUNDS WITH AMIDINE MODIFIED NICKEL CATALYSTS. P. BAUMEISTER, H.U. BLASER and W. SCHERRER Central Research Laboratories, Ciba-Geigy AG, CH-4002 Basel, Switzerland

ABSTRACT The chemoselective hydrogenation of halogen substituted aromatic nitro compounds is described using Raney nickel modified with amidine derivatives. Screening of a wide variety of amidines suggests that the C- and N-substituents and the type of anion have a strong influence on the inhibiting properties of the modifier. Formamidine acetate has been shown to be the most effective dehalogenation inhibitor. With this modifier even very sensitive substrates like halogenated dinitro benzene can be hydrogenated with selectivities > 97%. Investigation of the over-all kinetics and measurements of the catalyst potential are reported. From these results it is concluded that the dehalogenation occurs as a consecutive reaction after the halogenated aniline has been formed and that the dehalogenation is suppressed either by the presence of the strongly adsorbing nitro compounds and the corresponding reaction intermediates or by the effective modifiers. INTRODUCTION The hydrogenation of halogen substituted aromatic nitro compounds to the corresponding halogen substituted anilines very often is accompanied by an undesired hydrodehalogenation reaction. Two strategies have been used in order to find selective catalytic systems which produce high yields of the halogenated product: either the properties of the catalyst were optimized using various production methods (ref. 1-3). or commercially available catalysts were made more selective by adding specific modifiers (or inhibitors) to the reaction solution (ref. 4-6). The following two factors have been shown to influence the sensitivity of the C-X bond to hydrogenolysis: the type of halogen (I>Br>Cl>>F) and the position of X in relation to the nitro group (ortho>para> meta) (ref. 5). Additional nitro groups in ortho and para position to the halogen increase the tendency for hydrogenolysis even further. To date, the best studied modified systems are Pt catalysts inhibited with sulfur compounds, morpholine or phosphorous compounds (ref. 5). Raney nickel modified with dicyandiamide has also been reported to be able to hydrogenate aromatic chloronitro compounds with very good selectivities and activities. Since nickel is an attractive alternative to precious metal catalysts we decided to search for other types of inhibitors and to investigate the stage at which dehalogenation occurs.

u R

Raney nickel ____)

modifier

322

EXPERIMENTAL Reaction conditions All experiments were carried out in well stirred three-phase-slurry reactors at constant temperature and hydrogen pressure. Hydrogen consumption and hydrogenation time were determined by recording the pressure drop in a reservoir of known volume as a function of time. In special cases the catalyst potential was also measured during the reaction using the following system: gold electrode / lithium acetate bridge / Ag-AgC1 reference electrode (ref. 7). Typical hydrogen uptake and potential curves are depicted in Figure 1. For the test of the various modifiers the following conditions were used: 300 ml stainless steel autoclave; 40.8 g (0.2 mole) l-chloro-2,4-dinitrobenzene;2.0 g Raney nickel (60% in water); 0.012 moles of modifier; 120 ml methanol; temperature 60°C; H2 pressure 10 bar; 1100 rpm. Different substrates have been tested under the following conditions: 300 ml stainless steel autoclave; 0.25 moles of substrate: 2.0 g Raney nickel (60% in water); 1.5 g (0.014 moles) of formamidine acetate; 120 ml methanol; temperature 80°C;H2 pressure 12 bar, 1500 rpm. The catalyst potential was measured using the following conditions: 750 ml glass reactor, 15.8 g (0.1 mole) 2-chloro-nitrobenzene; 3.0 g Raney nickel (60% in water); 0.02 moles modifier, 550 ml methanol; temperature 30°C; H2 pressure 1.1 bar; 1500 rpm. Reagents and catalysts The halonitro compounds and the methanol used were of purum or pract. quality from Fluka. The amidine derivatives (in the form of their salts) were purchased from Fluka or Aldrich (purum or pract.). The N,N-dialkyl-formamidine acetates were prepared by analogy to a published procedure (ref. 8) from cyanamide and used as isolated (containing ca. 10% ammonium acetate). Two commercially available types of Raney nickel were used as 60% aqueous suspensions: B 113 W (Degussa) and M (Doduco) with no difference in the hydrogenation performance. Analytics The reaction solutions were analyzed as follows: I-chloro-2,4-dinitrobenzene:the reaction mixture was treated with acetic anhydride and the acetylated products analyzed by HPLC (Hypersil ODS 5 pm; eluent water/acetonitrile; UV detector 254/300nm). The other reaction mixtures were analyzed by GLC (OV 101; FID). In these cases it was possible to identify the following compounds: substrate, dehalogenated nitro compound, desired aniline; dehalogenated aniline. Two reaction intermediates (hydroxylamine and azo- or hydrazo-compound) were determined as a sum. The selectivities given were determined at the end of the hydrogenation and are defined as S (%) = 100 x (desired aniline / I:anilines)

323

RESULTS AND DISCUSSION Influence of modifier structure We decided to use as a very sensitive model reaction the hydrogenation of I-chloro-2,4-dinitrobenzene in order to find new and efficient dehalogenation inhibitors. For comparison, dicyandiamide was used as standard inhibitor. We concentrated our search of new modifiers on nitrogen containing compounds and found the most interesting effects with compounds of the following general structure

-

i H

\

R2- NH

R2

general structure of

effective inhibitors

Some results of this inhibitor screening are summarized in Table 1. It is immediately clear that formamidine acetate and its N-alkylated derivatives are good dehalogenation inhibitors. The selectivity achieved is comparable to that of dicyandiamide while the hydrogenation time observed is considerably lower. Compared to the unmodified system, the other inhibitors do not show a significantly improved selectivity but have a positive effect on the activity. The following structural effects can be distinguished: - The substituent R1 at the central carbon atom has to be either H or NHCN. Replacing it by either a methyl, phenyl or amino group leads to a sharp decrease in chemoselectivity. - The N-substituents R2 are less critical as long as R2 = H or alkyl. The selectivity decreases when R2 is phenyl. - The anion also has some influence on the performance of the catalytic system and acetate is clearly the better choice. At the moment we do not have a convincing explanation for the observed influence of the inhibitor structure. The basicity can not account for the effect of the substituents because both the more basic guanidine and the less basic N,N’-diphenyl formamidine are less selective than formamidine itself. A positive cooperative effect of formamidine and acetic acid is possible because we have found that acetic acid acts as a promotor in various types of hydrogenations. It was shown in separate experiments that anilines can react with formamidines to give both N-mono- and N,N-diary1 formamidines which no longer are effective inhibitors. Another way of modifier deactivation is the hydrolysis to ineffective formamide by water formed during the hydrogenation of the nitro group. This could explain the rather high modifier concentration needed in order to get good selectivities. Similar observations of instability under reaction conditions have also been reported for dicyandiamide (ref. 4).

324

TABLE 1 Influence of the modifier structure on reaction time and chemoselectivity of the hydrogenation of

l-chloro-2,4dinitrobenzene(Raney nickel; methanol; 60°C; 10 bar). Modifier

Rl

Formamidine acetate

H

N,N'-Dibutyl- acetate formamidine

H

N,N'-Ditetbutylformamidine acetate

Reaction time [min]

Selectivity Remarks

acetate

75

97,5

(CHZ),CH3

acetate

80

97

CH3 d-CH3

acetate

80

96

acetate

120

R2

H

X

[%]

standard

LH3

N,N'-Dimethylformamidine acetate

H

CH3

N,N'-Diphenylformamidine

H

phenyl

75

94,5 82

Guanidine acetate

NHz

H

acetate

135

66

Acetamidine acetate

CH3

H

acetate

75

86

Benzamidine

phenyl

H

180

76

H

H

CI

140

86

CH3

H

CI

150

71

240

70

210

99

Formamidine hydrochloride Acetamidi ne hydrochloride no modifier

Dicyandiamide

NH-CN

H

free base

free base

Reference experiment Reference experiment

Effect of substrate structure Different substrates were hydrogenated in presence of formamidine acetate in order to test the scope of this new dehalogenation inhibitor. The results are summarized in Table 2. In all cases where comparable results are available, formamidine acetate performs with selectivities and activities as high as those of the catalytic systems described in the literature for Pt catalysts. The different sensitivity of the C-X bond towards hydrogenolysis for varying substitution patterns is also clearly seen with this modifier. In addition, the hydrogenation of a C=O bond is inhibited as well (4-chloro-3-nitroacetophenone).These results demonstrate that we have found a new, universal modifier for the selective hydrogenation of substituted aromatic nitro compounds. While for most halogenated nitro compounds investigated very selective catalysts (both platinum and nickel) can be found, this is not the case for the dinitro substrate. Here only Raney nickel modified by either dicyandiamide or formamidine has been described to give satisfactory selectivities.

325

TABLE 2 Reaction time time and chemoselectivity for the hydrogenation of different substrates (formamidine acetate; Raney nickel; methanol; 80°C; 12 bar)

Substrate 1-Chloro-2,4dinitrobenzene

l-Chloro-2nitrobenzene l,Chloro-2nitrobenzene l-Chloro-3nitrobenzene 1-Chloro-4nitrobenzene 1 2-Dichloro-3nitrobenzene 1,4-Dichloro-2nitrobenzene 1 2-Dichloro-4nitrobenzene l-Bromo-3nitrobenzene 1-Bromo-3nitrobenzene

Reaction time [ min ]

Selectivity

75

97,5

from Table 1

90

99,4

(98.3%;110°C) (ref. 5)

100

88,O

no modifier

90

99,4

95

99,7

70

99,7

65

[“/,I

”16

65

99,7

110

98,7

165

91,o

4-Chloro-3nitroacetophenone

60

97,2

4-Chloro-3nitroacetophenone

75

93,l

Remarks (literatureresults)

(99.6%;1lo°C) (ref. 5) (99.3%;40°c) (ref. 2) 99.1%;6OoC (ref. 2) /99.8%;13O0k) (ref. 1) (99.8%;10O0C) (ref. 5) (99.5%;6O0C) (ref.2) no modifier

IK)

modifier

Over-all kinetic studies The question at what stage of the nitro group reduction the undesired dehalogenation occurs has been addressed by several research groups (ref. 3,9). It has been demonstrated that the dehalogenation of bromo- and chloro-nitrobenzene using platinum or nickel catalysts mainly occurs as a consecutive reaction of the haloaniline. Palladium catalysts act differently and can even preferentially hydrogenolyze the C-Xbond (ref. 10). For both theoretical as well as practical reasons it was of interest to us to investigate this problem for the modified nickel catalysts. We decided to use 2-chloronitrobenzene as model substrate and to cany out carefully controlled experiments with several modifiers. In order to determine the composition of the reaction solution, samples were withdrawn during the reaction and analyzed by GLC. In addition, hydrogen uptake and the catalyst potential via a gold electrode were measured. This method is not applied widely and the theoretical basis is still not fully developed but there is agreement that the following statements can be made (see Figure 1) (ref. 7, 11): the potential which is measured using the electrode described above depends on the oxidation potential of the substrates present and on their adsorption on the catalyst surface. When there is no reducible substrate, the SO called

326

hydrogen uptake

catalyst potential (mW . .

[YO)

0

-400

4

:

+

:

. *: d

20

-500

40

-600

60

hydrogen uptake hydrogen uptake catalyst potential catalyst potential

.

(selective) (unselective) (selective) (unselective)

Fig. 1 80

-700

loo

I

I reaction time

Schematic representation of typical curves for hydrogen uptake and catalyst potential for the hydrogenation of aromatic halonitro compounds.

reversible potential is measured, which is attributed to a hydrogen covered catalyst. When for example a nitro compound is added, the potential shifts to positive values of about 400 rnV (( 1 ) in Figure 1). When all the nitro groups are converted it is sometimes possible to detect the partially reduced intermediates (hydroxylamine, azoxy, azo, hydrazo etc), indicated by a potential drop of 100-200 rnV (21. When these are completely reduced to the aniline the reversible potential is reached again (3).Since the observed potential is also influenced by the pH value. the final reading may be somewhat more negative because the anilines act as a weak base. If dehalogenation occurs, hydrogen consumption continues and the potential rises again [ 4). corresponding to the formation of HX. Figures 2a-d show plots of catalyst potential and substrate concentration (GLC) versus hydrogen consumption for the hydrogenation with formamidine acetate (a), with dicyandiamide (b), with guanidine acetate (c) and without modifier (d). This type of presentation allows to standardize and to compare reactions with different reaction times, which are indicated at the upper edge of the graphs. As expected by analogy with the results reported for the unmodified nickel catalysts (ref.9), no dehalogenation is observed as long as either nitro compounds or partially reduced intermediates are present in solution. Using the two most effective modifiers the reaction stops after consumption of the theoretical amount of hydrogen. This is indicated by a sharp decrease of the catalyst potential and no further hydrogen uptake. In the case of the 2-chloro aniline no dehalogenated products are detectable by GLC even after prolonged hydrogenation times. The unselective catalysts show different behavior: while again no hydrogenolysis occurs before all reducible species have disappeared, the reaction goes on and dehalogenated anilines are detected by GLC. If one interrupts the hydrogenation at this point, no dehalogenated aniline can be detected by GLC (c 0.1%). In addition, the catalyst potential rises again because of the HCL produced. This negative potential peak represents a much more precise endpoint for the nitro

327

reduction than the hydrogenation curve which shows only a slight inflection when 100% of the theoretical amount of H2is consumed.

readion Dime (min.) 36 75 90 150

reaction time (min.) 160 240 3001360

60

potential

I

I

DLC-area

GLC-area

I%)

(mv) -300

100

-400

80

100

I%)

60 -590 40

-600

M

A,.' 0

'

'

'

20

40

60

'X

80

x 100

'

-700

0

hydrogen uptake (%) a) formamidine acetate

c) guanidlne acetate

reaction time (min.)

r e a c h time (min.) 45

110

260 315 GLC-area 100

(%I

BO

-600 60

60 -700

40

40 -800

.

.. .. .

..,

20

20

0

0

0 2 0 4 0 6 0 B O l 0 0 hydrogen uptake (%)

b) dicyandiamide

8

* A

8

0

20

60 80 100 105 hydro(lm uptake (%) 40

d) without modifier

catalyst potential (selective) catalyst potential (unselective) intermediates chloronitrobenzene chloroaniline aniline

Fig. 2a-d: Hydrogenation of 2-chloro-nitrobenzene in presence of different modifiers. Catalyst potential and concentration of reactants and products versus hydrogen uptake (conversion). (Raney nickel; methanol; 30°C; 1.1 bar). The observation that no hydrogenolysis of the C-X bond takes place as long as either nitro compounds or reaction intermediates are present can be explained by the strong adsorption of these molecules, thereby preventing the interaction of the C-Cl bond with the catalyst. The mode of action of the modifiers is less clear. It could be due to a modification of the catalytic properties of the Raney nickel or also to a competitive adsorption between the effective modifiers and the

328

haloanilines. CONCLUSIONS Amidine derivatives are effective dehalogenation inhibitors for the chemoselective hydrogenation of aromatic halonitro compounds with Raney nickel catalysts. The best modifiers are unsubstituted or N-alkyl substituted fomamidine acetates and dicyandiamide which are able to prevent dehalogenation even of very sensitive substrates. Our results indicate that the dehalogenation occurs after the nitro group has been completely reduced i.e. as a consecutive reaction from the halogenated aniline. A possible explanation for these observations is the competitive adsorption between haloaniline, nitro compound, reaction intermediates and/or modifier. The measurement of the catalyst potential can be used to determine the endpoint of the desired nitro reduction very accurately. ACKNOWLEDGMENTS The authors would like to thank Mr. R. Miiller and Mr. R. Juanes for the experimental work, Ms. A. Lutterotti for the analytical support and Ms. E. Scherrer for critical comments. REFERENCES 1 J.B.F. Anderson, K.G. Griffin and R.E. Richards, Chemie-Technik, 18/5 (1989) 40-44. 2 J. Strutz and E. Hopf, Chem.-1ng.-Tech., 60/4 (1988) 297-298. 3 W. Pascoe, Catalysis of Organic Reactions, P.N. Rylander et al., Dekker Inc., NY, (1988) pp. 121-134. 4 DE 2’441’650 to Nippon Kayaku KK, (1973). 5 J.R. Kosak, Catalysis in Organic Synthesis, W.H. Jones ed., Academic Press, NY, (1980) pp. 107-117.

EP 325’892 to Ciba-Geigy, (1987). 7 F. Beck, Chem.-1ng.-Tech, 48/12 (1976) 1096-1105. 8 C. Kashima, M. Shimizu, T. Eto, Y . Omote, Bull. Chem. SOC. Jpn., 59 (1986) 3317-3319. 9 V.I. Savchenko, T.V. Denisenko, S. Ya. Sklyar, V.D. Simonov, Journal of organic chemistry of the USSR, 11 (1975) 2183-2186. 10 J. Margitfalvi, private communication, Chemisch-technisches Laboratorium, ETH Zurich, Switzerland. 11 F. Wolf, H. Fischer, Journal f. prakt. Chemie, 317/2 (1975) 247-251. 6

M. Guisnet et al. (Editors),Heterogeneous Catalysis and Fine Chemicals II

329


INTERMEDIATES NITRILES

FORMATION

IN

THE

CATALYTIC

HYDROGENATION

OF

by Ph. MARION, P. GRENOUIILET, J. JENCK and M. JOUCLA UMR

45

- CNRS - RP RHONE POULENC INDUSTRIALISATION 24 rue J. Jaures 69151 DECINES-CHARPIEU Cedex FRANCE

ABSTRACT :

In the course of the catalytic hydrogenation of u , w dinitriles over Raney nickel, by-products are obtained from C-N and C-C bond formation. The mechanism of the formation of these compounds was investigated. Cyclic and linear secondary amines can result from the same secondary imine through a transimination process involving a ring-chain tautomerism. Stereochemical results for 2-aminomethyl-cyclopentylamine (AMCPA) are in accordance with a specific cyclisation pathway favored by an intramolecular hydrogen bond giving rise to the cis isomer from aminocapronitrile, unfavored in the case of adiponitrile which leads to the trans AMCPA as the major isomer. INTRODUCTION : Catalytic hydrogenation of nitriles over Raney nickel leads to primary amines with variable amounts of secondary and tertiary amines depending on reaction conditions (Ref. 1). These by-products result from hydrogenation of secondary imines and enamines respectively. We have investigated the catalytic hydrogenation of u , w dicyanoalkanes and we report results with 1,4-dicyanobutane (ADN). Scheme 1 details the intermediates involved in a step-by-step addition of hydrogen to the dinitrile molecule adsorbed on the metal surface. Some of them are to be considered as precursors for the formation of by-products (detected in the liquid phase after desorption).

330

/

A ADN

c

ACN

(adiponilrile)

(aminocapronitrile)

HMD (hexam4lhyldne diamine)

Scheme 1

We will focus on two types of compounds arising from :

.

C - N bond formation hexamethylene triamine (BHT)

.C-

C

: 1-azacycloheptane

(HMI) and

bis

bond formation : 2-(aminomethyl)-cyclopentylamine

( AMCPA)

EXPERIMENTAL PART

Hydrogenation procedure : Adiponitrile was hydrogenated over Raney nickel catalyst in a 150 ml autoclave equipped with a magnetic stirring under constant pressure and temperature. The catalyst was washed then weighted by pycnometry and charged into the reactor with the solvent. The dinitrile was introduced in a special container. The reactor was closed and purged repeatedly with nitrogen first and then with hydrogen. The autoclave was heated to the reaction temperature and the nitrile was introduced. Gas chromatography was carefully carried on the liquid mixture at the end of the hydrogenation. Transimination : Pure 1-aza-1-cycloheptene was introduced in a NMR probe at a known concentration and primary amine was gradually added. The equilibrium was determinated by 1H and 13C NMR analysis.

331 RESULTSAND DISCUSSION :

-

N bond formation As secondary amines proceed from hydrogenation of secondary imines, the behaviour of these compounds is of importance in the reaction mixture. Secondary imines can result from the condensation of primary amino group with primary imines cornparables in reactivity with a carbonyl function. C

Only in the case of a , w - dicyanoalkanes hydrogenation, there is a possibility of intramolecular condensation of intermediate [&I between amino and imino group. Such a condensation leading to an aminal [z] prone to ammonia loss, gives rise to l-aza-l-cycloheptene 2. Hydrogenation of this intermediate leads to azacycloheptane 5 . 1-aza-1-cycloheptene is a key-intermediate for the formation of azacycloheptane 5 and bis hexamethylene triamine 8 [R = (CH2)6 NHz]. In fact 2. can react in three different ways : - Addition of hydrogen leading to secondary amine 5 Addition of ammonia going backwards to [L] - Addition of any amino group to give, via aminal [ 5 ] , amino imine (scheme 2).

-

Scheme 2

332

This last point has been examplified through transimination reactions and ring-chain tautomerism between cyclic aminals and open chain amino imines. We have prepared 2 following the synthetic sequence (scheme 3)

1 ) NaN3, DMSO, Nal cat.

Schema 3

Compound 1 polymerizes slowly at room temperature and can be kept in solution for several hours. Add tion of pr mary amine shows an equilibrium between 2 - and 7 -. Diamine 8 is obtained from hydrogenation of am no imine which can be formed by direct addition of primary arnine to amino imine [A] or to 1-aza-1-cycloheptene 3 . As it is generally accepted, formation of l-aza-l-cycloheptene in the course of the hydrogenation reaction leads to the cyclic amine 4. We have demonstrated its ability to generate also diamine 8 .

z

2-(aminomethyl)- cyclopentylamine (AMCPA) The well-known Thorpe-Ziegler condensation reaction (Ref. 2) involves the nucleophilic addition of a carbanion to an electrophilic center. Starting from adiponitrile, enamino nitrile 2 is recovered. Catalytic hydrogenation of this compound gives trans AMCPA as the major isomer (scheme 4 ) :

cis (minor) Scheme 4

333

In order to determine the course of the formation of AMCPA we have investigated the catalytic hydrogenation of amino capronitrile (ACN) over Raney nickel. GC analysis of the crude material indicates that AMCPA is present in small amount and moreover that the cis isomer predominates. The Thorpe-Ziegler reaction requires the presence of two electron withdrawing groups in the reactant. In accordance with the microreversibility principle, dehydrogenation of a primary amino group has been demonstrated (Ref. 3). Imino nitrile A can be the intermediate producing the cis observed. Two condensation products can arise starting from this compound : amino nitrile 11 and enamino imine lo (scheme 5 ) :

AMCPA

aNH2 CN

11

Lp Scheme 5

The cis stereochemistry observed is better supported starting from rather than from 11. In the first case intramolecular hydrogen bonding between amino and imino group favors the cis configuration leading to cis AMCPA as the major compound. Minor trans isomer can be issued from the slow isomerization of 12a (scheme 6). With enamino nitrile 2 intramolecular hydrogen bonding cannot take place so a rapid isomerization occurs between 13a and p J giving rise to the trans AMCPA as the major isomer after hydrogenation. Isomerization to 13b is reinforced also by the slower rate of hydrogenation of a nitrile group than an aldimine one.

334

AMCPA bans

AMCPA cI3

AMCPA cis

AMCPA lrans

Scheme 8

Conclusion The synthesis of 1-aza-1-cycloheptene and the study of its reactivity allows us to propose this compound as an important intermediate for the generation of secondary amines in the course of the catalytic hydrogenation of adiponitrile to hexamethylene diamine. Concerning 2-(aminomethyl)-cyclopentylamine formation, some dehydrogenation reaction of amino capronitrile can occur on the catalytic surface. Stereoselectivity can be interpreted in terms of chelating effect leading to the cis isomer. REFERENCES [l] RYLANDER P.N. "Hydroqenation Methods, Academic Press, 1985, p. 94 [2] J. March "Advanced Organic Chemistry" 3 th Ed. Wiley and

Sons,

(31

1985, p. a54 M. Besson, J.M. Bonnier and M. Joucla, Bul. Soc. Chim. F. Part. 1990, 127,5-12 and 13 19.

-


335

REOUCTIVE A M I N A T I O N OF A C E T O N E O N T I N M O O I F I E O SKELETAL N I C K E L CATALYSTS S.Gllbolos,

E.Tdlas,

M.HegedLis,

J.L.Margitfalvi

and J .Ryczkowski*

C e n t r a l R e s e a r c h I n s t i t u t e f o r C h e m i s t r y o f t h e H u n g a r i a n Academy o f S c i e n c e s , 1 5 2 5 B u d a p e s t , POB 1 7 , H u n g a r y ABSTRACT C o n t r o l l e d S u r f a c e R e a c t i o n s (CSKs) b a s e d on t h e r e a c t i v i t y o f a d s o r b e d hydrogen t o w a r d s t i n a l k y l compounds were used f o r t h e modification of a skeletal nickel catalyst. The modification of t h e s k e l e t a l n i c k e l c a t a l y s t w i t h t i n was a i m e d t o s u p p r e s s t h e formation of i s o p r o p y l a l c o h o l i n t h e r e d u c t i v e amination of acetone. The introduction of t i n t e t r a a l k y l s i n t o t h e c a t a l y s t res u l t e d i n an i n c r e a s e of t h e f o r m a t i o n o f d i i s o p r o p y l a m i n e and s l i g h t decrease of t h e formation of alcohol. Upon u s i n g t i n dibenzyl dichloride f o r the modification o f the c a t a l y s t s t r o n g supp r e s s i o n of t h e s e l e c t i v i t y towards isopropanol could be achieved. X-Ray d i f f r a c t i o n r e v e a l e d t h e p r e s e n c e o f A 1 3 N i 2 a n d A l N i a l l o y s , m e t a l l i c N i , N i O , Al(OH)3 and A l O [ O H I i n t h e h e a t t r e a t e d c a t a l y s t , t h e l a t t e r c o u l d be r e s p o n s i b l e f o r t h e entidii~.~cl s e l e c t i v i t y t o w a r d s t h e f o r m a t i o n o f s e c o n d a r y a m i n e a t 190-2OOOC.

INTRODUCTION Lower a l i p h a t i c a m i n e s a r e w i d e l y u s e d a s i n t e r m e d i a t e s f o r t h e synthesis of herbicides,

i n s e c t i c i d e s a n d d r u g s or c a n b e a p p l i e d

a s r u b b e r a c c t ~ l e r a t o r s ,c o r r o s i o n i n h i b i t o r s , etc.

[I].

surface active agents

T h e most w i d e s p r e a d method f o r t h e p r e p a r a t i o n o f l o w e r

a l i p h a t i c a m i n e s i n v o l v e s t h e r e a c t i o n o f ammonia w i t h a n a l c o h o l

o r a c a r b o n y l c o m p o u n d i n t h e p r e s e n c e o f h y d r o g e n . T h e m o s t common c a t a l y s t s u s e d f o r r e d u c t i v e a m i n a t i o n o f a l c o h o l s , a l d e h y d e s and k e t o n e s c o n t a i n n i c k e l , component 11-31.

platinum, palladium or copper as a c t i v e

One o f t h e m o s t i m p o r t a n t i s s u e s i n t h e r e d u c t i v e

amination is t h e s e l e c t i v i t y c o n t r o l a s t h e product d i s t r i b u t i o n , i.e.

the ratio

o f primary t o secondary

o r tertiary amines, is

s t r o n g l y a f f e c t e d by t h e r m o d y n a m i c s . I n t h i s work r e s u l t s o b t a i n e d i n a c a s e s t u d y , i . e .

the reduct-

i v e a m i n a t i o n o f a c e t o n e on a s k e l e t a l n i c k e l c a t a l y s t t o i s o p r o p y l a m i n e a n d d i i s o p r o p y l a m i n e w i l l b e g i v e n a n d d i s c u s s e d . Keact i o n s involved i n the r e d u c t i v e amination of a c e t o n e a r e g i v e n i n

*On l e a v e f r o m U e p a r t m e n t o f C h e m i c a l T e c h n o l o g y , Faculty of Chemistry, U n i v e r s i t y of Maria Curie-Sklodowska, 20-021 L u b l i n , Poland

336 Scheme 1.

+H 2

+NH3,

+HZ

(CH312CH-Otl

-H20

+H2

-

(CH.3 )' -2C = O

(ClH3)2C=NH

[Cli

+(CH3I2C=n, -H20 ( C H 3 1 2 C H - N H 2 +(CH3I2C=NH, - N H 3

+HZ

).C=N-CH(CH3)2

3.2

+I I

(CH312 CH-NH-CH(CH312 Scheme 1 .

I t i s known t h a t u p o n d i s t i l l a t i o n o f t h e r e a c t i o n m i x t u r e o f t h e r e d u c t i v e a m i n a t i o n o f a c e t o n e d i i s o p r o p y l a m i n e and i s o p r o p a n o l forms ficult.

i 7 ~ 1 1 t r om p~ aking t h e separation extremely d i f -

a binary

Therefore,

t h e g o a l o f t h i s w o r k was t o f i n d t h e modes a n d

ways f o r t h e s u p p r e s s i o n o f t h e f o r m a t i o n o f i s o p r o p a n o l t i v e poisoning the

shclital

nickel catalyst

via selec-

by a second m e t a l such

as t i n . I m p r e g n a t i o n w i t h t h e s o l u t i o n o f t h e compound o f a p o i s o n i n g element

[Sn,

Pb,

Bi,

P etc.)

t o poison n i c k e l catalysts.

i s c o n s i d e r e d a s t h e m o s t g e n e r a l way However,

upon u s i n g c o n v e n t i o n a l i m -

p r e g n a t i o n t e c h n i q u e s t h e o p t i m a l s e l e c t i v e p o i s o n i n g o f t h e supp o r t e d o r s k e l e t a l c a t a l y s t s c a n n o t b e g u a r a n t e i i l ~ 4[ 1 . I n t h i s w o r k t i n o r g a n i c compounds w i t h g e n e r a l f o r m u l a o f SnRnC14-n

[R =

dhyl

o r b e n z y l l were used f o r t h e s e l e c t i v e p o i -

soning o f the s k e l e t a l n i c k e l catalyst.

A c c o r d i n g t o o u r a, p r o a c h

t h e s e l e c t i v e p o i s o n i n g o f a Group VIII m e t a l can b e c o n s i d e r e d a s dn a n c h o r i n g p r o c e s s

a r e used t o

i n w h i c h C o n t r o l l e d S u r f a c e R e a c t i o n s (CSRs)

i n t r o d u c e t h e p r e c u r s o r o f t h e second m e t a l ( S n l

the surface o f the f i r s t

I:II~L~

one 151.

SURFACE CHEMISTRY Kecently,

we h a v e d e m o n s t r a t e d t h a t h y d r o g e n p r e a d s o r b e d o n p l a -

t i n u m o r n i c k e l can r e a c t w i t h t i n o r l e a d t e t r a d l k y l

compounds r e -

sulting i n the formation o f bimetallic surface e n t i t i e s w i t h metali n t e r a c t i o n [5-81.

-metal

CSRs l e a d i n g t o t h e f o r m a t i o n o f b i m e t a l -

l i c s u r f a c e s p e c i e s can b e w r i t t e n as f o l l o w s : xNitl

+

SnRnC14-n

-

solvent

Ni -SnR

-

(I1

(n-xIR1-l

+

- xC

1

+

xRkI

(1)

(4-n)HCl

(21

20 - 5OOC

Nix-SnKn-xC14-n

Nix-Sn

+

A

I n reaction

( 1 ) hydrugen adsurbed on n i c k e l r e a c t s s e l e ~ l i v e l y

337

w i t h t h e t i n o r g a n i c c o m p o u n d r e s u l t i n g i n a P r i m a r y S u r f a c e Comp lex (PSC)

( I ) , which can be decomposed i n hydrogen a t m o s p h e r e i n

t h e t e m p e r a t u r e i n t e r v a l b e t w e e n 50-3OO0C ( r e a c t i o n (2)I . EXPERIMENTAL C a t a l y s t p r e p a r a t i o n and m o d i f i c a t i o n Granular skeletal nickel catalyst w i t h p a r t i c l e s i z e of d mm w a s p r e p a r e d by l e a c h i n g a N i - A 1

=

3-5

a l l o y c o n t a i n i n g 50 w t % n i c k e l .

H a l f o f t h e a m o u n t o f a l u m i n i u m was l e a c h e d o u t w i t h 3 w t % N a O H w a t e r s o l u t i o n a t 50'C

f o r 12 hours. A f t e r leaching tbe c a t a l y s t

was washed w i t h d i s t i l l e d w a t e r a n d was k e p t u n d e r a n a q u e o u s s o l u t i o n h a v i n g pH

=

9.

Prior t o t h e m o d i f i c a t i o n w i t h t i n t h e c a t a l y s t w a s d r i e d i n f l o w i n g n i t r o g e n a t 120°C f o r 4 h o u r s . A f t e r d r y i n g t h e c a t a l y s t w a s t r e a t e d i n h y d r o g e n a t 200 or 3OO0C f o r 2 h o u r s f o l l o w e d b y c o o l i n g t o room t e m p e r a t u r e i n h y d r o g e n . t a l y s t w i t h t i n compounds, i . e . a t 50°C vent.

The modification of the ca-

surface reaction

( 1 ) was c a r r i e d out

u s i n g 2 0 g o f g r a n u l a r s a m p l e a n d 100 cm3 o f b e n z e n e s o l -

T h e c o n c e n t r a t i o n o f t i n c o m p o u n d s was

varied. Reaction

( I ) w a s m o n i t o r e d by g a s v o l u m e t r y a n d G C a n a l y s i s a s d e s c r i b e d e l s e w h e r e [ 6 ] . U e c o m p o s i t i o n o f PSC (11, i . e .

surface r e a c t i o n

(2

was p e r f o r m e d i n hydrogen i n t h e c a t a l y t i c r e a c t o r p r i o r t o t h e a c t i v i t y test u s i n g a h e a t i n g rate of Z°C/min

and a f i n a l tempera

t u r e o f Z5OoC. Catalyst characterization T h e n i c k e l a n d a l u m i n i u m c o n t e n t s o f t h e c a t a l y s t s were d e t e r m i -

ned by a t o m i c a b s o r p t i o n s p e c t r o s c o p y (AAS). T i n a n d c h l o r i n e c o n -

t e n t s o f t h e m o d i f i e d c a t a l y s t s g i v e n i n T a b l e 2 were d e t e r m i n e d by AAS a n d c h e m i c a l a n a l y s i s , r e s p e c t i v e l y . T h e p h a s e c o m p o s i t i o n o f c a t a l y s t s was s t u d i e d by X - r a y d i f f r a c -

tion

[ X R O ) t e c h n i q u e . X R O s p e c t r a were r e c o r d e d by u s i n g a P h i l l i p s

1700 powder d i f f r a c t o m e t e r equipped c h r o m a t o r a n d CuK,

w i t h a g r a p h i t e c r y s t a l mono-

radiation.

Catalytic reaction A s t a i n l e s s s t e e l f l o w r e a c t o r c h a r g e d w i t h 20 g c a t a l y s t was

used t o study t h e r e d u c t i v e amination o f a c e t o n e ( A C ) .

Further

d e t a i l s on e x p e r i m e n t a l c o n d i t i o n s c a n b e f o u n d i n T a b l e 2 . R e a c t i o n p r o d u c t s w e r e a n a l y s e d by g a s c h r o m a t o g r a p h y u s i n g a g l a s s column f i l l e d w i t h 18 w t % Carbowax 2000

+

5 w t % KOH o n C h r o m o s o r b P

338

NAW s u p p o r t . T h e f o l l o w i n g r e a c t i o n p r o d u c t s were a n a l y s e d : i - p r o pylamine (IPA), di-i-propylamine amine [ I P P A ) ,

i-propylalcohol

(DIPA), i - p r o p y l i d e n e - i - p r o p y l -

(IPALI.

KESULl'J ANU UISLUSSlUN

P r e p a r a l i r i n arid c h a r a c t e r i ~ a t i o no f t h e s k e l e t a l n i c k e l c a t a l y s t s

I t i s known t h a t s t a r t i n g a l l o y s o f s k e l e t a l n i c k e l c a t a l y s t s a r e u s u a l l y a m i x t u r e of A 1 3 N i , 19-11].

A13Ni2,

A l h i and e u t e c t i r . phdscs

D e p e n d i n g on t h e c o n d i t i o n s o f l e a c h i n g t h e c a t a l y s t s c o n -

g e n e r a l l y of m e t a l l i c n i c k e l , s m a l l a m o u n t o f N i O anti been found t h a t t h e

IIIUIL

UI

r e s i d u a l aluminium, A13r'li2

lks5 h y d r a t e d a l u m i n a [ 9 , I 1

1. It

alloy, has

lower t h e c o n c e n t r a t i o n o f a l k a l i n e s o l u t i o n

a n d t h e lower t h e t e m p e r a t u r e o f l e a c h i n g . t h e h i g h e r a r t ! t h e a a l l o y a n d A1(OHI3 p h a s e s r e m a i n i n g i n t h e c a t a l y s t mounts of A 1 N i 3 2 [ 9 - 1 1 ] . The c r y s t a l l i n i t i y and t h e e x t e n t o f h y d r a t i o n o f a l u m i n a p h a s e s c a n b e a l t e r e d by t h e r m a l t r e a t m e n t of t h e s k e l e t a l n i L k e l catalyst.

I t has a l s o been observed t h a t hydrated alumina can sup-

pressed the s i n t e r i n g of the c a t a l y s t s [12,

131.

A s t h e a i m of t h e p r e s e n t work was t o p r e p a r e a s k e l e t a l n i c h e 1

c a t a l y s t s t a b l e a t high temperature i n the reductive amination o f a c e t o n e , d i l u t e d NaOH s o l u t i o n w a s u s e d f o r l e a c h i n g o f t h e s t a r t i n g a l l o y . B a s e d on l i t e r a t u r e d a t a i t was e x p e c t e d t h a t t h e leached o u t c a t a l y s t would conkdin s u f f i c i e n t amount o f a l u m i n a p h a s e s f o r s t a b i l i z a t i o n of t h e c a t a l y s t . Indeed, t h e chemical a n a l y s i s o f t h e u n m o d i f i e d c a t a l y s t by AAS c o n f i r m e d t h a t o n l y a b o u t h a l f o f t h e a l u m i n i u m was l e a c h e d o u t u s i n g d i l u t e d NaOli s o l u t i o n . T h e A 1 a n d t h e N i c o n t e n t o f t h e c a t a l y s t w a s 2 2 a n d 54 w t % , r e s p e c t i v e l y . T h e presence of metallic A 1 i n s o l i d solu t i o n w i t h nickel. A1-Ni

residual

a l l o y s a n d h y d r a t e d a l u m i n a p h a s e s c o u l d a c c o u n t f o r t h e high

A 1 content of the catalyst.

I n t h e X R D s p e ~ t r u m( n o t s h o w n ) o f t h e

fresh catalyst lines characteristic of A13Ni2

a l l o y and A l ( O I i 1

p l i d s e s i n Ltie f o r m s o f D a y e r i t e a n d G i b b s i t e h a v e a p p e a r e d .

sencc o f A13Ni2

Thepre-

a l l o y i n t h e c a t a l y s t can b e e x p l a i n e d by t h e f a c t

t h a t t h i s a l l o y i s much m o r e p a s s i v e t h a n o t h e r s a n d r e a c t s v e r y s l o w l y i n d i l u t e d a l k a l i n e s o l u t i o n a t 50°L Al(Oli)

[lo].

The presence of

p h a s e s i n t h e c a t a l y s t can b e a t t r i b u t e d t o t h e h y d r o l y s i s

3 of a l u m i n a t e s formed i n t h e l e a c h i n g p r o c e s s [ 9 ] .

XRD d a t a g i v e n i n

T a b l e 1 i n d i c a t e t h e p r e s e n c e o f m e t a l l i c Ni, A l 3 N i 2 .

AlNi.

A1(011)3

a n d AlO(0H) p h a s e s i n t h e t h e r m a l l y t r e a t e d a c t i v i t y t e s t e d unmodi f i e d c a t a l y s t . The p r e s e n c e o f A l U l U H )

i n t h e c a t a l y s t can b e e x -

p l a i n e d by p a r t i a l d e c o m p o s i t i o n o f A l ( O H 1 3 p h a s e s d u r i n g

protmit-

339 TABLE 1 XRD d a t a o f u s e d u n m o d i f i e d s k e l e t a l n i c k e l c a t a l y s t a

I/Io

d,8

I/Io

6.13

27

2.35

15

AlO(0H)

A l ( O H 1 3(B1

Phases

d,a

Phases

4.85

57

2.22

15

4.73

29

2.10

4

4.3Y

29

2.05

92

A13Ni2,

AlNi

3.50

0

2.04

92

A13Ni2,

N i

3.35

5

2.02

100

A13Ni2

3.17

21

1.92

5

A13Ni2

2. 86

3

1.77

24

2.45

6

1.45

9

AlNi,

i. 39

10

1.42

9

A13Ni2

NiO

N i NiO

a A f t e r t r e a t m e n t i n h y d r o g e n a t 25OoC. B = Bayerite,

G = Gibbsite

m e n t i n h y d r o g e n a t 25OoC. Modification of the s k e l e t a l nickel c a t a l y s t with t i n I n t h i s series o f experiments t h e r e a c t i v i t y o f hydrogen c h e m i s o r b e d on g r a n u l a r s k e l e t a l n i c k e l c a t a l y s t t o w a r d s d i f f e r e n t t i n a l k y l compounds, i . e . =

e t h y l , Bu

=

S n E t 4 , SnBu4, SnEt2C12 a n d SnBz2C12 ( E t

b u t y l , Bz

=

=

b e n z y l ) h a s b e e n s t u d i e d . Upon m o d i

-

f y i n g t h e s k e l e t a l n i c k e l c a t a l y s t w i t h d i f f e r e n t t i n a l k y l s surface reaction

( 1 1 a p p e a r e d t o be v e r y s e l e c t i v e . Only s a t u r a t e d

h y d r o c a r b o n s c o r r e s p o n d i n g t o t h e a l k y l g r o u p o f t i n p r e c u r s o r compound h a s b e e n f o r m e d . D e t a i l s on s u r f a c e r e a c t i o n s i n v o l v e d i n t h e m o d i f i c a t i o n of t h e c a t a l y s t w i l l be g i v e n elsewhere [151. t.itlciu c t

i v e arni n d t i o n o f a c e t o n e I n the r e d u c t i v e amination of a c e t o n e c a r r i e d o u t i n t h e tempe-

r a t u r e r a n g e o f 169-21OoC t h e f o c u s w a s l a i d on t h e s e l e c t i v i t y changes a t high conversion l e v e l .

Experimental conditions, charac-

t e r i s t i c f e a t u r e s o f c a t a l y s t s and c o r r e s p o n d i n g a c t i v i t y and sel e c t i v i t y data obtained i n t h e reductive amination of acetone a r e given i n Table 2. It is noteworthy t h a t i n o r d e r t o d e c r e a s e the f o r m a t i o n o f i s o p r o p y l a l c o h o l b y - p r o d u c t a r e l a t i v e l y low h y d r o g e n / /ammonia m o l a r r a t i o ( H 2 / N H 3

=

0.5)

h a s t o b e c h o s e n . As s e e n i n

340

F i g . 1 . R e l a t i o n s h i p b e t w e e n s e l e c t i v i t i e s a n d H,/NH3 molar r a t i o i n t h e r e d u c t i v e a m i n a t i o n o f a c e t o n e o n u r i ~ i i u u l~tt d s k t i ~ . L d l r ~ i t : h 1 L a t a l y s t [T = 1 1 I " I , P = 0.0 MPa, WHSV = 0 . 0 h K 1 , N H 3 / A C = 2 1 .

Fig.

I , t h e s e l e c t i v i t i e s t o w a r d s aniines and i s o p r o p a n o l can b e

s t r - u r i t . 1 ~ a l t e r e d by li2/Nli3

c h a n g i n g t h c H /NH3 r a t i o . The h i g h e r the 2 r a t i o , t h e higher is the s e l e c t i v i t y towards isopropanol.

U a t a g i v u r i i n T a b l e 2. i n d i c a t e d t h a t u p o n i n c r e a s i n e t h e r c a c t i o n ternperaturc i n the reductive amination of acetone the s e l e c t i v i t y t1;wdrds

D I P A e s p e c i a l l y o n tiri m o d i f i e d c a t a l y s t s s i g n i f i -

caritly increased, whereas s e l e c t i v i t i e s towards o t h e r products dec r e a s e d i n d i f f e r e n t e x t e n t . S u c h an i n c r e a s e i n t h e s e l e c t i v i t y o f f o r m a t i o n o f UIF'A u p o n i n c r e a s i n g t h e r e a c t i o n t e m p e r a t u r e c a n n o t be e x p l a i n e d by thermodynamics 1 1 4 1 , and i t h a s n o t been o b s e r v e d

it is s u g g e s t e d t h a t t h e e r ~ l i a r i c e ds e l e c t i v i t y t o w a r d s U I P A o b t a i n e d a t on c o n v e n t i o n a l

1YU-?I3UUC

Cdfl

skeletal nickel catdlysts [ 2 , 1 4 ] . Therefore,

b e d L L r i b u t e d t o t h e h i g h AlO(0H) c o n t e n t o f t.tiF: cc3-

t a l y s t 1 2 1 . However,

the mechanism of t h e f o r m a t i o n o f t h e second-

a r y arriinil r e q u i r e s f u r t h e r e l u c i d a t i o n . A s seen from t h e d a t a g i v e n i n T a b l e 2 t h e s e l e c t i v i t y o f t h e

unmodified n i c k e l c a t a l y s t towards t h e formation o f isopropanol is higher than /

:.

Upun m o d i f y i n g t h e c a t a l y s t w i t h t i n ,

r e l a t i v e l y s m a l l amount o-f t i n i n t r o d u c e d ,

despite the

t h e amount o-f i s o p r o p -

a n u l formed d e c r e a s e d and s i g n i f i c a n t s e l e c t i v i t y c h a n g e s were obdecrease i n the activity. tin from t i n t e t r a a l k y l s t h e s e l e c t i v i t y t o -

s e r v e d w i t h o u t noticeable lJpon i n t r o d u c i n g

wards t h e furrnation o f secondary amine s i g n i f i c a n t l y i n c r e a s e d a t

341 Table 2 R e d u c t i v e a m i n a t i o n o f a c e t o n e on s k e l e t a l n i c k e l c a t a l y s t s a

'

Sn c1 wt% wt% oc

Catalyst

0

0

n. 082 0 N i -SnE t4- b

0.13

Ni-SnBu4-lC

0.025

bi-SnBua-2"

0.076

Ni-SnEt2C12- i t'

0.12

0.07

0.27

0.14

0.30

n. 17

170 190 172 192 200 171 192 170 191 169 193 200 190 1goe 210e 170 190 171 190 202

Conversion

0 98.6 99.3 59.1 99.2 99.5 58.1 Yii.4 98.0 58.5 98.2 98.5 99.0 98.2 98.9 99.0 95.6 96.9 93.4 95.0 96.2

se

1 e c t i v i t i e s,+ % IPA OIPA IPPA IPAL

85.1 83.' 78.1 68.2 64.7 75.4 66.3 83.6 74.7 84.5 70.9 68.0

82.11 85.3 71.6 83.3 84.7 86.4 87.0 85.4

3.6 8.6 11.6 24. ,, 27.5 14.5 26.6 7.e 20.6

5.2 20.7 25.4 12.6 9.5 23.2 7.0 9.4 3.4

8.8 12.1

1.0 0.5 3.4 1.7 1.4 4.6 2.3 1.0 n.6 5.0

2.9 1.9 1.4 0.6 0.6 6.9 3.4 10.2 4.2 2.5

10.3 7.3 5.9 6.0 6.0 5.5 4.8 7.5 4.0 5.3 5.5 4.7 4.0 4.2 4.6 2.8 2.5 C12H25NH2 t H 2 0

4 2 (ii) C12H25NH2 + (CH30H .$HCHO]

> C12H25NHCH3 -

+ H 2 0 ------>

In order to explain this hydrogen effect it can be supposed that i) the hydrogen coverage in normal conditions is not sufficient to maintain the catalyst in the adequate reduced state, ii) the excess of hydrogen inhibits the formation of carbonaceous deposits (and the modification of the catalyst) or the strong adsorption of some reagents and products ... In an effort to understand better the catalytic chemistry associated with this reaction, the reactivity of dodecylnitrile or dodecylamine was measured under the same experimental conditions. The results listed in Table 1 show that the nitrile and the primary amine are much more easily transformed into N-dimethylalkylamine than the ester or the acid (Table 2). The rate determining step in the methylation process is directly related to one of the first reactions converting the ester or the acid into nitrile. It can be assumed that: 1) The adsorption of the reagent is not quite effective on the catalyst or/and ii) the water formed during the reaction could lead to a superficial (or a bulk) modification of the catalyst and of the adsorption properties of some of the reagents.

346

TABLE 2 Influence of promoters in the amination of dodecanoic acid. P = 50 bars, T = 300"C, (LHSV),,id = 1/6 h-', Acid : NH3 : CH30H : H2 = 1 : 10 : 40 : 100 (ester) Catalyst

Selectivity (%)

Acid or estcr Conversion (%) RNH2

RNHCH3

RN(CH3)2

RCOOMe

others

Reaction : acid/NH3/CH30H/H2

I

CuO 43-Cr203 39

100

21.2

26.0

37.1

7 .0

8.7

Cu15 Crl5-AI2O3

100

20.0

32.4

26.0

8.0

13.6

Cu15Cr15 Ca2-AI-203

100

8.4

24.0

67.0

0.6

Cu15Cr15 Mn2-AI2O3

100

16.0

36.0

46.0

2.0

Cu15Cr15 Ca2-Ti02

100

27.0

31.0

35.6

Unsupported catalyst

2.1

4.3

Reaction : cstcr/NH3/CH30H/H2 Cu15Cr15 Ca2-AI2O3

100

10.0

20.8

65.7

3.5

2) Influence of (Ca or Mn) additives on the catalytic properties of CuCr/A1203 (Ti02) in the amination of dodecanoic acid : The effect of adding Ca or Mn to CuCr/Al203 (TiOZ) catalysts presented in Table 2 demonstrate that i) the selectivity in N-dimethyldodecylamine is much enhanced, the effect being rather more significant with alumina than with a titania support; ii) the total amine selectivity is particularly high, above 98% instead of 80% without promoter. A similar result also presented in Table 2 is obtained when the acid is replaced by methyl dodecanoate. 3) Effect of calcination pretreatment The influence of additives was investigated after changing the conditions of catalyst activation especially after modifying the calcination temperature. It can be seen in Table 3 that the selectivity varies very much with this activation step and also that the final result depends on the nature of the additive;

347

TABLE 3 Influence of calcination temperature on the catalytic properties of Cu-Cr/support catalysts in the amination of dodecanoic acid. P = 50 bars, T = 300"C, (LHSV),,id = 1/6 h-', Acid : NH3 : CH30H : H2 = 1 : 10 : 40 : 100

Catalyst

Selectivity (%)

Calcination temperature ("C) RNH2

Cu15 Cr15 Mn2/AI2O3

Cu15Cr15 Ca2/AI2O3

Cu15Cr15 Ca.-JTi02

RNHCH3

RN(CH3)2

RCOOCH3

others

120

9.0

23.0

66.5

1.5

380

16.0

36.0

46.0

2.0

120

10.0

28.0

54.0

330

8.4

24.0

67.0

120

21.0

48.0

27.0

1.0

3.0

330

27.0

31.0

35.6

2.1

4.3

3.2

5.0 0.6

* When the catalyst is promoted with manganese, an increase of calcination temperature from 120°C to 380°C (followed by the reduction step at 350°C) decreases the selectivity in methylated products. Moreover figure l a shows a rapid decrease, with time on stream, of the selectivity into N-dimethyldodecylamine. * Contrary to the previous situation when the catalyst is promoted with calcium, the selectivity into the desired product increases with the calcination temperature and there is no significant change of selectivity with reaction time (figure lb) if there is an increase of RN(CH3)z in the first hours of the reaction.

348

Fig1 Influence of calcination temperature on the catalytic properties of a) CulSCrlS Mn2A1203 ; b) Cu15Cr15 Ca2-Al203 catalysts in the amination of dodecanoic acid. (-_-_---_) calcinated at 120°C ) calcinated at 380°C (a) or 330°C (b). (

4)Catalyst characterization In table 4 the modifications of the reduction rate and of the adsorption properties after the addition of Ca or Mn are presented. If is evident from these results that the reducibility of the Cu-Cr-AI203 catalyst especially when promoted with manganese is reduced. Nevertheless the accessible copper surface and the hydrogen adsorption are not modified by additives; but the hydrogen storage, which appears from TPD measurment, is decreased by Ca and Mn. From the TPD curves, it appears that there are three hydrogen desorption steps at 130, 260 and 35OoC, the two last ones are preponderant with unpromoted catalysts while it is the contrary with promoted catalysts. Therefore the addition of Ca or Mn to Cu-Cr catalysts inhibits the adsorption of strongly bonded hydrogen. On the other hand these catalysts have been studied for other hydrogenation reactions and we have also observed a decrease of hydrogenation activity when Cu-Cr catalysts are modified with Ca or Mn (13).

349

TABLE 4 Influence of promoters on the reducibility and adsorption properties of Cu-Cr/Al203 catalysts. (a) The reduction is calculated in assuming that all Cu(I1) and Cr(VI) species are reduced into Cu(o) and Cr(II1) states. Catalyst Cu15-Cr15

Cu15-Cr15-Ca2

310-400

430

Cu15-Cr15-Mn2

Cu-Cr-X/Al203 TPR T m a i C'C) Reduction rate (%)

92

83

350-400 67

(a) Hydrogen adsorption pmo~eg - l catal.

3.4

2.7

4.1

Hydrogen TPD pmole g- 1 catal.

12.8

4.1

3.9

Copper area m2 g-1 catal.

2.6

2.0

2.0

Now the influence of water or ammonia on copper catalysts is being investigated. Previously A. BAIKER and coll. have shown that ammonia could modify the catalytic properties of copper catalysts used in the amination of alcohols (9). These authors noticed the formation of copper nitride after NH3 exposure at a temperature of about 300°C which is the reaction temperature of our study. The first results that we obtained in our study showed that both H 2 0 and NH3 decrease significantly the copper dispersion in unpromoted catalysts and that this modification is less significant when Ca or Mn are added to the Cu-Cr catalyst. We are now studying what are the superfical modifications consecutive to the addition of promoters or/and water and ammonia. 5) Conclusion To summarize, we demonstrated in this study that the addition of a small amount of calcium or manganese increases the rates of the amination of ester and of acid and the

350

N-methylation with methanol. These results can be obtained without increasing the partial hydrogen pressure as was observed for unpromoted catalysts. On the other hand we noticed that these compounds don't modify the metallic area but decrease the reducibility which means that copper oxide and chromium (VI) oxide are only partially reduced. Moreover as the highly adsorbed hydrogen is also inhibited and as these catalysts are more stable in the presence of H 2 0 or NH3 than unpromoted catalysts, one can also deduce that one of the important roles of the hydrogen during the reaction is to prevent the modification of catalysts or/and the amination reaction by ammonia and water. REFERENCES H. Adkins, "Reactions of hydrogen with organic compounds"; The university of 1 Winconsin Press, 1938,65. 2 J.C.J. Bart and R.P.A. Sneeden, Catal. Today, 1987,2, 1. a) P. Courty, D. Durand, E. Freund and A. Sugier; J. Mol. Catal. 1982, 17,241. 3 b) N. Mouaddib, Thesis, Lyon, 1989. H.W. Chen, J.M. White, J.G. Ekerdt, J. catal., 1986,99, 293. 4 J.W. Evans, M.S. Wainwright, N.W. Cant, D.L. Trimm, J. Catal. 1984,88, 203. 5 A.K. Agarwal, N.W. Cant, M.S. Wainwright, D.L. Trimm, J. Mol. Catal., 6 1987,43,79. J.C. Lee, D.L. Trimm, M.A. Kohler, M.S. Wainwright, N.W. Cant, Catal. Today, 7 1988,2, 643. J. Volf, J. Pasek, Studies in Surface Science and Catalysis 1987,27, 105 8 Ed. L. Cerveny. 9 A. Baiker, J. Kijenski, Catal. Rev. Sci. Eng., 1985,27-4, 653. J. Barrault, M. Seffen, C. Forquy, R. Brouard, "Heterogeneous Catalysis and Fine 10 Chemicals" in Stud. In Surf. Science and Catalysis, 1988,41,361. 11 M. Seffen, Thesis, Poitiers, 1986. 12 L. Jalowiecki, G. Wrobel, M. Daage, J.P. Bonnelle, J. Catal., 1987, 107,375. (and previous paper in Appl. Catal.). Z. Gaizi, Thesis, Poitiers, 1990. 13


351

TERTIARY AMINE PREPARATION BY REDUCTIVE ALKYLATION OF ALIPHATIC SECONDARY AMINES WITH KETONES R. E. MALZ, Jr.1 and

H. GREENFIELD2

SUMMARY This paper discusses the need for more stringent catalyst requirements for the reductive alkylation of secondary to tertiary amines. We illustrate the major importance of steric factors, with respect to both the amine and ketone and discuss the relative effectiveness of several catalysts. One obtains excellent yields with the more reactive and unhindered ketone, such as cyclohexanone and acetone, and relatively unhindered secondary amines.

INTRODUCTION We developed a process of preparative and potential commercial utility for the production of tertiary aliphatic amines by the reductive alkylation of dialkyl amines and of alicyclic secondary amines with ketones in the presence of hydrogen and a catalyst3. Such tertiary amines have at least one secondary alkyl group. The reductive alkylation of primary alkylamines with ketones is a well-known and useful method for the preparation of secondary amines4. Major side reactions are hydrogenation of the ketone to the alcohol and, at higher temperatures, condensation reactions of the ketones and of ketone-amine addition products. One may drastically reduce these side reactions by the proper choice of catalysts and conditions. There are many examples of the preparation of tertiary aliphatic amines by the reductive alkylation of dialkylamines or secondary non-aromatic heterocyclic amines with ketones using platinums-'3, palladium12-l7, mixtures of platinum and palladiuml*,and nickel12. 1 3 . 1 9 - 2 2 catalysts.

352

The literature reports yields which decrease with increasing size and complexity of the groups attached to the nitrogen atom of the amine and the carbonyl group of the ketone7.23. One sees much slower reductive alkylation of secondary amines with ketones to tertiary amines than the corresponding transformation of primary to secondary amines7. 2 4 . The increase in by-product formation is the result of the need for the more severe operating conditions, particularly higher temperatures. The reductive alkylation reaction consists of a sequence of steps in which the hydrogenation is preceded by chemical processes. For primary amines, one forms the alcoholamine, which could proceed on to the ketimine. Hydrogenation of either the alcoholamine or the ketimine produces the secondary amine product.

The secondary amine product probably is derived from the ketimine rather than by hydrogenolysis of the alcoholamine25.

353

Since ketimine formation is not possible in the reductive alkylation of secondary amines, this reaction must involve the hydrogenolysis of an alcoholamine. However, if either carbon a to the starting carbonyl has a hydrogen available, the enamine formation is possible.

This enamine can be reduced to the tertiary amine product.

Thus, two major differences between the reductive alkylation of primary and secondary amines are the increased steric hindrance in the latter case, and the fact that tertiary amine formation cannot proceed through a ketimine intermediate.

EXPERIMENTAL Dibutylamine, piperidine, N-ethylcyclohexylamine, N-ethyldicyclohexylamine, and the ketones were reagent grade chemicals. The 5% palladium on carbon, 5% platinum on carbon, sulfided 5% platinum on carbon and sulfided 5% rhodium on carbon catalysts were obtained from Engelhard Industries. The 2 0 % molybdenum sulfide on alumina (Girdler T-318) was obtained from the Chemetron Corp. Palladium chloride was obtained from Matheson, Coleman and Bell. Ruthenium trichloride was obtained from Ventron. A bulk ruthenium sulfide catalyst was prepared by bubbling

354

gaseous hydrogen sulfide for 1 h into a solution of 10.0 g of ruthenium trichloride hydrate (RuC1,.1-3 H,o) in 1 liter of distilled water. The black precipitate was filtered, washed with 2 liters of distilled water, then with 500 ml of 2-propanol, and then with 1 liter of cyclohexanone. A bulk palladium sulfide catalyst was prepared by substantially dissolving 10.0 g of palladium chloride dihydrate in 1 liter of 0 . 3 N hydrochloric acid with stirring and then bubbling in gaseous hydrogen sulfide for 0.2 h. The black precipitate was filtered, washed with 2 liters of distilled water, then with 5 0 0 ml of 2-propanol, and then with 500 ml of cyclohexanone. Example 1 N,N-Dibutylcyclohexylamine by reductive alkylation of dibutylamine with cyclohexanone. The results are shown in Table 1. A detailed description of one experiment illustrates the procedure. In all other experiments we list the starting materials, the autoclave and the experimental conditions. To a 1.7 liter autoclave were added 64.6 g ( 0 . 5 0 mole) of dibutylamine, 250 ml (ca. 2.4 mole) of cyclohexanone, and 3.5 g of 5% palladium on carbon. The autoclave was sealed, purged first with nitrogen and then with hydrogen, and hydrogen added to a pressure of 500 psig. The reaction mixture was heated with agitation for 4.3 h at 45-500 and 350-500 psig. The autoclave was cooled and depressurized, and the reaction product was removed. The catalyst was removed by filtration through Celite filter-aid. A pure sample of N,N-dibutylcyclohexylamine26 was obtained by preparative GC of a portion of the filtrate. Anal. Calcd for C,,H,,N: MW, 211. Found by titration with 0.1 N perchloric acid in acetic acid: 212. Analysis of the filtrate by quantitative GC indicated the presence of 103.5 g (98% yield) of N.N-dibutylcyclohexylamine, no detectable dibutylamine, and 14% reduction of the excess cyclohexanone to cyclohexanol. Example 2 N,N-Dibutyl-1,3-dimethylbutylamine by reductive alkylation of dibutylamine with methyl isobutyl ketone A _ We reacted 64.6 g ( 0 . 5 0 mole) of dibutylamine, 250 ml (ca. 2.0 mole) of methyl isobutyl ketone, and 3.5 g of a sulfided platinum on carbon catalyst in a 1-liter autoclave for 5.0 h at

355

2000 and 500-800 psig. A pure sample of N,N-dibutyl-1,3-dimethylbutylamine was obtained by preparative HPLC. Anal. Calcd for C,,H,,N: C , 78.79; H, 14.64; N, 6.56. Found C, 78.82; H, 14.58; N , 6.55. A quantitative GC analysis indicated the presence of 64 g (60% yield) of N,N-dibutyl-1,3-dimethylbutylamine and no detectable dibutylamine. We reacted 129.2 g (1.00 mole) of dibutylamine, 430 ml (ca. 3.4 mole) of methyl isobutyl ketone, and 12.0 g of a 5% palladium on carbon catalyst in a 1.7 liter autoclave for 2.6 h at 190-2050 and 600-800 psig. A quantitative GC analysis indicated the presence of 114 g (54% yield) of N,N-dibutyl-1,3-dimethylbutylamine and no detectable dibutylamine.

Example 3 N-Isopropylpiperidine by reductive alkylation of piperidine with acetone. We reacted 42.6 g (0.50 mole) of piperidine, 250 ml (ca. 3.4 mole) of acetone, and 3.5 g of a sulfided 5% platinum on carbon catalyst for 1.3 h at 90-1000 and 400-700 psig. A portion of the N-isopropylpiperidine27. 2 8 was distilled at 149-1500. Anal. Calcd for C,H,,N: MW 127. Found by titration with 0.1N perchloric acid in acetic acid: 127. A quantitative GC analysis indicated the presence of 59 g (93% yield) of N-isopropylpiperidine and no detectable piperidine. -B We reacted 85 g (1.0 mole) of piperidine, 515 ml (ca. 7.0 mole) of acetone, and 6.0 g of a 5% palladium on carbon catalyst for 1.0 h at 60-650 and 500-800 psig. GC analysis as in A indicated the presence of 107 g (84% yield) of N-isopropylpiperidine and no detectable piperidine. Example 4 N-Ethyldicvclohexylamine by reductive alkylation of N-ethylcyclohexylamine with cyclohexanone. The results are shown in Table 2.

RESULTS AND DISCUSSION The results summarized in Table 1 illustrate the successful preparation of a trialkylamine by the reductive alkylation of

356

dibutylamine, a dialkylamine, with cyclohexanone using a palladium catalyst and a number of metal sulfide catalysts. Excellent yields of the tertiary amine were obtained. ApproxTcble 1. REDUCTIVE ALKYLATION OF D18UTYLPbllblE WlTH CYCLOHEX!.NOt.Ifa

'lield, mJeX

Catalyst type

Pd

2d PtS,

Pt;,

wt,q

3.5 3.5 35 3.5

T47p %

FreTsUre (psiq)

Tim, h

%mineb

cyclohexandC

45-50 85-95 45-5C 195-1 10

350-m

4.3

600-800 509-800

14 lG.3

500-71'lfi

07

a5

---

r,

?,

0

96 84d

RhS, FdS,

3.5

95-100

500-800

1355145

RuS,

f

MOSX

70

75-80 240-253

500-800 500-800

3.8 7.0 33

I00

P

600-1000

43

14

6 '3

94

__

36

_-

89

II

a. Each experiment was run with 64.6 q (050) m d e of dihutvlornrne, 250 r r i (co. 2.4 m d e cysloherancre'l. b. N.N-dibutylcyclohex~lomine .: E k e d cr excess (1 9 d e ) cvclchhermme d. Dihitylamine, recovered cnly in this experiment, was 17%. Yield bfl5ed cn Cmver5icr was 101 Y e Prepwed frcm 10. q palladium chlor;de hydrate f prepared frm I09 ruthenlorn trichlwids hydrate

imately 5 to 15% of the excess cyclohexanone was hydrogenated to cyclohexanol. We estimate ketone condensation occurred accounting for about 5% of the excess ketone. Reacting acetone, MEK and MIBK at the same catalyst level and pressure, we observed it took a temperature of 9 5 o C with acetone, 145oC with MEK and 200OC for MIBK to achieve a significant reaction. The cycle time varied somewhat, but the general trend showed the more hindered gave a marked decrease in reaction rate. The details of the rection with dibutylamine with methyl isobutyl ketone (MIBK) are give in example 2. Experiments with MIBK required much higher temperature than with cyclohexanone and gave 54 and 60% yields of desired tertiary amine, using palladium and platinum sulfide catalysts, respectively. The absence of starting dibutylamine in the reaction product indicated that side reactions involved the amine as well as the ketone. Hydrogen absorption data showed that only about 5 to 10% of the excess MIBK had been reduced to the corresponding alcohol. Platinum sulfide appeared superior to palladium for the reductive alkylation of piperidine with acetone. A more carefully controlled comparison of platinum sulfide with palladium and with platinum is shown in Table 2 for the reaction of N-ethylcyclohexylamine with cyclohexanone. Platinum gave a very poor conversion of the starting secondary amine (27%) and a correspondingly low yield of the tertiary amine product (22%), although the yield based on conversion was good (81%). The

357 TABLE 2 REDUCTI r E ALh YLATION Of N-ELH (LCYCLGHEXYLAMINE WITH CYCLOHEXANONEa Yield, mde % recwwd 3O amneb rrcovaed Catalyst 2Quntne 3ctudc 6 0 C A cyclohexanme cyclohexade

0

PtS, Pt

49

42

73

22

Pd

56

30

51 51 68

16 16

35

23

35

61

Each Pxperimnt was run with 636 q 1050 mde) of N-ethylcylccheqlmne. 54 0 g (055 mde) r y c l d e i a n m g 1 15 nj nf mthand and 050 9 of 5%catalyst M r a r h fw7 5 h at 1620 and in the rarqe of 600-763 psi9 Eased on dirycld-texylamine E m 4 x starting ~ v c l o h ~ ~ o i c n ~ Eased wl cwgerted cvcloh~xannne Determtn,?l by quntitdiw 3' andysi:

of

b r

d e

undesired reduction of ketone to alcohol was much more pronounced with the platinum than with the palladium or platinum sulfide catalysts. The platinum sulfide gave 42% tertiary amine while the palladium resulted in 30% tertiary amine. Both gave the same amount of ketone reduction. These results illustrate the practicality of preparing trialkylamines by the reductive alkylation of dialkylamines with aliphatic ketones. Excellent yields are obtained, particularly with the more reactive and less hindered ketones, such as cyclohexanone and acetone, and with the less hindered secondary amines. Platinum sulfide, or other platinum metal sulfides, are the catalysts of choice when more hindered reagents require more severe operating conditions.

Uniroyal Chemical Co., Naugatuck, Conn., 06770, U.S.A. 2 Presently, First Chemical Corp., Pascagoula, Miss. 39581, U.S.A. 3 R.E. Malz, Jr.and H. Greenfield (to Uniroyal) Eur. Pat. Appl. 14985 (Sep. 3 , 1980); Chem. Abstr. 1981, 94, 102811y.) 4 W . S . Emerson, Organic Reactions, Vol IV, John Wiley and Sons, New York, 1948, pp 174 to 255 5 A . Skita, F. Keil with L. Boente, Chem. Ber. 1929, 62B, 1142. 6 A. Skita, F. Keil with H. Havemann, K.P. Lawrowsky, Chem-Ber. 1

1930, 638, 34. 7 8 9

A. Skita, F. Keil, H. Havemann, Chem. Ber. 1933, 66B 1400. R.V. Heinzelman, B.D. Aspergren, J. Am. Chem. SOC., 1953, 75, 3409. A. Skita, W. Stuhmer, Ger. 932,677 (Sep. 5, 1955), Chem.

358

Abstr.; 1958, 52, 20200h. 10 D.E. Ames, D. Evans, T.F. Grey, P.J. Islip, K.E. Richards, J.

Chem. SOC. 1965, 2636. 11 E. Seeger, A. Kottler (to Dr. K. Thomae G.m.b.H.) Ger. 1,255,646 (Sep. 29, 19661, Chem. Abstr. 1966, 65, 18564. 12 M. Freifelder, Practical Catalytic Hydrogenation, Wiley-Interscience, New York, 1971, p 376,377 (reference 3) 13 B.A.O. Alink, N.E.S. Thompson (to Petrolite) U.S. 3,994,975 (Nov. 30, 1976). B.A.O. Alink, N.E.S. Thompson, R.P. Hutton, (to Petrolite) U.S. 4,040,799 (Aug. 9, 1977). 14 A. Skita, F. Keil, E. Baesler, Chem. Ber. 1933, 66B. 858. 15 R.M. Robinson, (to Abbott) U . S . 3,314,952 (Apr. 18, 1957). 16 S. Wolownik, (to Abbott) U.S. 3,432,508 (Mar. 11, 1969). 17 P.F. Jackisch, (to Ethyl), U.S. 4,521,624 (Jun. 4, 1985) 18 W.B. Wright, Jr, J. Org. Chem. 1959, 24, 1016. 19 H.A. Shonle, J.W. Corse, (to Eli Lilly) U.S. 2,424,063, (July 15, 1947). 20 F.J. Villani, N. Sperber, (to Schering) U.S. 2,852,526 (Sep. 16, 1958). 21 L.F. Kuntschik, O.W. Rigdon, (to Texaco) U.S. 3,976,697 (Aug. 24, 1976). 22 Q.W. Decker, E. Marcus, (to Union Carbide) U.S. 4,190,601 (Feb. 26, 1980). 23 Ref. 4, p. 195. 24 Ref. 12, p. 359, 376. 25 Ref. 4, p. 181 26 0. Stichnoth, W. Schmidt, (to BASF) Ger. 851,189 (Oct. 2, 1952), Chem. Abstr. 1953, 47. 112394. 27 H. Thies, H. Schoenenberger. P.K. Qasba, Arch. Pharm. 1969, 302, 610, Chem. Abstr. 1969, 71, 124154 (bp 145-1480 at 720 mm). 28 R.A.Y. Jones, A.R. Katritzky, A.C. Richards. R.J. Wyatt, J. Chem. SOC. (B) 1970, 122 (bp 510 at 21 mm).


359

EFFECT OF PROMOTERS ON Pt/Si02 CATALYSTS FOR THE N-ALKYLATION OF STERICALLY HINDERED ANLINES IN THE VAPOR PHASE Milos Rusek, Central Research Laboratories, R 1055, CIBA-GEIGY AG, CH-4002 Basel, Switzerland ABSTRACT We have developed a multimetallic catalyst for the large scale synthesis of sterically hindered mono-N-alkylanilines with very good selectivity and high catalytic activity. In contrast to copper chromite catalysts which allow the N-alkylation only with primary alcohols, the doubly promoted Pt/SiO2 catalysts described here are useful for the reaction of ortho-substituted anilines with both primary and secondary alcohols. The catalyst must activate three reaction steps: Dehydrogenation of the alcohol, condensation of the aniline with the carbonyl compound produced and hydrogenation of the resulting imine to the desired N-alkylaniline. In the vapor phase the hydrogenation step is the most difficult to achieve under our reaction conditions. The effects of different metallic promoters (Sn, Ge, Re etc.) and of various basic additives on the performance of the catalyst are discussed. The best catalyst developed is a Pt-Sn/SiOl catalyst pretreated with Ca2+ which is able to catalyze the alkylation of several ortho-disubstituted anilines with high conversions and selectivities. INTRODUCTION Most multipromoted catalysts have been described for the catalytic reforming of petroleum. For this process it is typical, that several reactions take place simultaneously: dehydrogenation of cyclohexanes, dehydroisomerization of alkylcyclopentanes and dehydrocyclization of alkanes. Isomerization, hydrogenolysis, and hydrocracking are also involved in the process. In fine chemical manufacturing, the application of promoted platinum catalysts is less known. Maxted and Akhar have reported that the addition of stannous, manganous, ceric and ferric chloride to platinum oxide (Adams catalyst) facilitates the hydrogenation of aldehydes, ketones and olefins (ref. 1). The selective hydrogenation of unsaturated aldehydes or ketones to unsaturated alcohols has been achieved by the addition of ferrous sulfate and zinc acetate to platinum catalysts (ref. 2). Ortho substituted N-alkyl anilines are intermediates for an important class of pesticides. They can be synthesized by the reaction of the aniline with the appropriate alcohol:

‘Et

MEA

MOIP

‘Me

AA

The following multi-step mechanism is proposed for this transformation: First, the dehydro-

360

genation (2a) of the alcohol to the corresponding carbonyl compound takes place. Condensation (2b) of this carbonyl compound with the aniline follows and the last step is the hydrogenation (2c) of the imine. Ho\c/R1 H/

\

R2

R

@HC:R’ R

H

R2

A

All three steps are reversible under the conditions normally used. We found that with most catalysts the third step - the hydrogenation of the imine - is the slowest reaction. If this step is hindered, the first two steps will remain far from equilibrium. It is therefore important to find catalysts with enhanced hydrogenation activity because this leads to an increase of the over-all conversion. Experiments with catalysts which are known to catalyze the alkylation reaction in the liquid phase (ref. 3), showed that the desired gas-phase reaction of substituted anilines with alkoxyalcohols occurs, but with very low yield. Pd promoted copper chromite catalysts which are able to catalyze the alkylations of sterically hindered anilines with primary alkoxyalcohols (ref. 4, 5) showed only very low activity and selectivity when secondary alcohols were used. We found a solution with new, doubly promoted platinum catalysts on silica and reported their scope and limitations for the synthesis of various aniline derivatives (ref. 5). In the following communication we describe the development of the most effective catalyst using as model reaction the N-alkylation of 2-methyl-6-ethylaniline with methoxy-2-propanol. EXPERIMENTAL Materials. The catalysts were prepared by impregnation of SiOz with an aqueous solution of HzPtC16 and the appropriate promoting metal salts, using the incipient wetness technique. SiOz, type M from Chemische Werke Uetikon, Switzerland, was used (20-35 mesh (ASTM), BET surface area 470 m2/g, pore volume 0.38 ml/g, composition: 41.9% Si, 860 pprn Ca, 150 ppm Mg, -3.0). The latter type of sites are thought to be selective for the formation of caprolactam. Catalyst operation at high (>350"C) reaction temperatures has been reported (ref. 6) to give

decreased selectivity towards caprolactam, the suggested reason for this being an increase in side reactions rather than a change in the acid property of the catalyst. Catalyst deactivation as a function of operation time is perhaps the most serious limitation of this approach to the production of caprolactam from cyclohexanone oxime, and is a common problem with all calalyst types. Various reasons have been put forward to account for this effect including coke formation (ref. 6) and/or irreversible adsorption of basic reaction by-products (ref. 3). A detailed examination of the effects of operation conditions on boria on alumina catalyst performance and lifetime is reported in this paper, in an attempt to further elucidate the important parameters controlling optimisation and maintenance of caprolactam yield. EXPERIMENTAL The catalyst was made up according to established methods, (ref. 7), impregnating boric acid (BDH general purpose grade) on alumina (120m2/g surface area, pore volume o.95cm3/g) and calcining at 350'C before use. The percentage boria, as measured by Spectrophotometry, was found to be approx 13wt%. Characterisation by XRD showed that boria (B2O3), was the only crystalline phase present on the surface of the alumina after calcination.

The vapour phase Beckmann rearrangement reaction was carried out using a continuous flow system operated at ambient pressure. Helium was used to entrain the cyclohexanone oxime (Aldrich general purpose grade) into the vapour phase from a saturator. The vapour pressure of the oxime was controlled by adjusting the saturator temperature. The catalytic reaction took place in a fixed bed U-tube reactor. The temperature was controlled by a thermocouple placed in a thermowell in the catalyst bed. In normal operation the total gas flow rate was 30 ml min-l. On leaving the reactor the gas stream was cooled by passing it through a glass spiral trap immersed in an ice bath. At regular intervals the accumulated products in the trap were washed out with a known volume of methanol and analyzed by gas chromatography. The gas chromatography column, a 3m column of 3%. OV17, was operated at 170'C using a Flame Ionization Detector and nitrogen as carrier gas, with naphthalene as internal standard. Following testing, catalyst regeneration was attempted by heating in air at 500°C for 48 hours. All catalysts were crushed to a fine powder and analyzed by X-ray diffraction using a Phillips Diffractometer with nickel filtered CUK radiation as the source. Catalysts were analyzed for boria content according to the carminic acid spectrophotometric method (refA), using a Varian DMS 100s U.V. Visible Spectrophotometer. In preparation for total boria content analysis, 0.04g of crushed catalyst was added to 5mls of conc. H2SO4. lOmls of water was slowly added, stirring and heating until all the catalyst had dissolved. This solution was made up to 25mls with distilled water. Preparation for water soluble

boria analysis involved leachirig the boron oxide from the catalyst by stirring in warm water for 0.5 hours. RESULTS AND DISCUSSION Figure 1 shows the conversion, selectivity and yield when 0.lg of boria on alumina catalyst at 300'C is used to rearrange cyclohexanone oxime to caprolactam. Although a high oxime conversion was achievable on commencing the reaction, this was not matched by correspondingly high lactam yield and selectivities. Thus side reactions predominated at low values of reaction time. Lactam selectivity increased with time on stream, however, presumably as a result of rapid poisoning of the active sites for the faster non-selective side reactions. Similar "initiation" behaviour has been reported (ref. 9) for this reaction over zeolites. As time on steam increased further, decreases in both conversion and lactam selectivity were apparent due to further non-selective poisoning of all catalyst active sites.

40 -

30

I 1 0

1

2

3

1

I

1

I

I

4

5

6

7

8

9

Time (hours) Fig.1. (I) oxime conversion, (+) caprolactam selectivity and (u) caprolactam ield 00'(!. with time using 0.lg boria on alumina catalyst at a reaction temperature of 3

The effect of temperature on the conversion, selectivity and yield after 3 hours on stream is shown in figure 2. In each case a catalyst mass of 0.lg boria on alumina catalyst was tested. With increasing reaction temperature the oxime conversion increased, however, maxima in lactam selectivity and yield were observed at a reaction temperature of 300°C. At higher temperatures excessive coking and side reactions were thought to occur,

534

resulting in high conversion but poor lactam selectivity. Values of the latter parameter also decrease at low reaction temperatures. Although this is somewhat at variance with that reported by other workers (ref. 6), it is postulated that the longer residence times used in this study resulted in an increased likelihood of re-adsorption of the lactam on the catalyst at these temperatures. This hypothesis in borne out by the observation that total conversion at 250'C decreased much more rapidly than at higher reaction temperatures.

200

250

300

350

400

Reaction Temperature ('C) Fig.2. Diagram showing the effect of reaction temperature on ( I ) oxime conversion, (+) caprolactam selectivity and (*) caprolactam yield alter 3 hours on stream using 0.1 g boria on alumina catalyst. The effect of mass of catalyst on performance, shown in figure 3, indicated an optimum mass for maximum selectivity and yield. Small catalyst beds were observed to give a maximum in lactam yield at short reaction times, thus ending up predominantly in the deactivated state (both conversion and lactam selectivity low) after three hours on stream. On the other hand large catalyst beds required much longer to achieve maximum lactam production, and after three hours on stream are predominantly in the initiation phase (high conversion, low lactam selectivity).

535

100

80

60 O/O

40 'Ac

20

0 0

I

I

I

I

I

0.1

0.2

0.3

0.4

0.5

0.6

Mass of Catalyst (9) Fig. 3 Diagram showing the effect of catalyst mass on (.) oxime conversion, (+) caprolactam selectivity and ( J C ) caprolactam yield after 3 hours on stream, using boria on alumina catalyst at a reaction temperature of 300'C. Figure 4 is a plot of oxime conversion, caprolactarn selectivity and yield of different catalysts over a period of 30 hours. The three catalysts used were boria on alumina, alumina and a regenerated boria on alumina catalyst. The regenerated catalyst was previously on stream for 30 hours and then heated in air for 48 hours at 500'C in an effort to remove coke. The concept of an initiation period in which the non-selective, presumably strongly acidic, catalyst sites are initially deactivated (refs. 6,7)is given further credence by comparing the performance of the catalyst with that of the alumina support. It is obvious that the increased initiation period, in the latter case, is a result of the larger number of nonselective sites which must be deactivated. This is also indicated by the higher overall conversion of the alumina support. It is also noteworthy that there were a limited number of sites on the alumina which were selective for lactam formation. A comparison of the performance of the fresh and the regenerated catalysts can be made from figure 4. It is obvious that, although the regeneration process does not cause a large improvement in lactarn selectivity, the fact that higher overall conversions were attained means that lactam yield recovers somewhat. The increased conversions obtained with the regenerated catalyst is most likely due to the fact that loss of boron during the regeneration process (see tattle) results in the uncovering of additional nonselective sites on the alumina support.

536

100

C

90

0

n V

80

e r S

i

(4

7c

0

n 6(

o/o

S

e I

81

C

61

e t

(b) i V

i t Y

4

2

YO

E

%

(c)

y

t

e I d

1

F

0

ti

10

15

20

25

30

Time (h) Fig.4. (a) Oxime conversion, (b) Caprolactam selectivity, (c) Caprolactam Yield using 0.2g (.) boria on alumina, (u)regenerated boria on alumina and (+) alumina catalyst at 300'C for 30 hours.

537

TABLE Analysis of Catalyst Samples by Spectrophotometry %Boron (as B2O3)

Sample Total boron

Water soluble boron

Fresh BpO3lalumina

12.7

12.3

Regenerated catalyst1

11.1

7.0

Regenerated in air at 500'C for 48 hours.

In the case of the regenerated catalyst improved lactam yields (compared to that of the deactivated catalyst) were retained only for much shorter operating times compared to the performance of fresh catalyst, presumably because not all of the lactam-selective sites have been regenerated. There is ample evidence both from the present and other (refs. 3,6) work that both coking and re-adsorption of basic reaction by-products play a part in catalyst deactivation. In the former case the observed catalyst colour change on use and the fact that removal of the carbon by calcination increased both the lactam yield and total conversion would tend to indicate that coking is a fairly non-selective deactivation process. Spectroscopic evidence for the presence of aromatic amines on zeolite catalysts used for this reaction (ref. 3), as well as the fact that acidic carrier gases such as carbon dioxide are known (ref. 1) to give superior lactam selectivity, point towards the involvement of base readsorption in deactivation. Again in this case calcination would be expected to regenerate lactam yield. The melting and agglomeration of B203 has been proposed (ref. 10) as a deactivation mechanism for silica supported catalysts. This is not thought to be likely in the present case since XRD evidence on used catalysts showed little evidence of crystalline B2O3 being present. In addition boron analysis of the regenerated catalysts (see table) indicated a decrease in boron oxides (especially water soluble) present. Almost 100% of the total boron present in the fresh catalyst is in a water soluble form (B2O3), however only 70% of this latter form of boron is in the regenerated catalyst. It is apparent from the present results that coking and base re-adsorption cannot be the only catalyst deactivation mechanisms, since, if they were, it would be expected that the regenerated catalysts would have contained significant amounts of crystalline, water soluble B2O3 as did the fresh catalyst. The boron analyses (see table) and XRD data indicated that although crystalline water soluble B2O3 was present in the unused catalyst, it was significantly less in the regenerated samples, even though the total boron content (water soluble and water insoluble) was still high. This suggests a third deactivation mechanism (possibly linked to the other two) whereby the B2O3, present on the fresh

538

catalyst and partially responsible for the lactam selectivity, is converted during the catalytic reaction into an amorphous water-insoluble boron species which is not selective for lactam formation. This deactivation process is not thought to be caused by a temperature effect alone since unused catalyst samples which were prepared by calcination in air at 500'C (same conditions as for regeneration) showed lactam yields as good or better than conventional preparations (calcined at 350'C). In conclusion, decrease in cyclohexanone oxime yield and caprolactam selectivity with time on stream is a major factor in the use of boria on alumina catalyst in the rearrangement reaction. Coke deposition and basic by-product adsorption have been suggested as a means of deactivation. In addition the conversion of water soluble boron, which is selective to lactam formation, to an amorphous water insoluble boron species is another factor that can account for the catalyst deactivation.

REFERENCES

Sato,H., Ishii,N., Hirose,K. and NakamuraS., Studies in Surface Science and Catalvsis, . 28 (1 987)755 Aucejo,A., Burguet,M.C., Corma,A, and Fornes,V., ADDI.Catal.. 22 (1986)187 Bbrguet,M.C., Aucejo,A. and Corma,A., Can. J. Chern. Eng., 65 (1987)944 Izumi,Y., Sato,S. and Urabe,K., Chem. Letts. (Chem. SOC.JDn.1. I19831 1649 Sato,S., $akurai,H., Urabe,K. and Izumi,Y., Chem. Letts. (Chem. SOC.Jpn.), (1985)277 Sato,S., Hasebe,S., Sakurai,H., Urabe,K. and Izumi,Y., Ap LCatal., 29 (1987)107 Sakurai,H., ato,S., Urabe,K. and Izumi,Y., Chern Letts. Chern. SOC.Jpn.), (1985)1783 Pupha ,K.W., Merrill,J.A., Booman,G.L. and Rein,J.E., Anal. Chem,. 30 (1958)161 2 Landis,P.S. and Venuto,P.B., J.Catal., 6 (I 966)245 Sato,S., Urabe.K. and Izumi,Y., J. Catal., 99 (1986)102

\

l


539

BECKMANN REARRANGEMENT REACTIONS ON ACIDIC SOLIDS

E.GUTIERREZ, A.J.AZNAR and

E.RUI2-HITZKY

Instituto de Ciencia de Materiales, CSIC c/Serrano 115 bis.- 28006 Madrid (Spain) SUMMARY Oximes can be catalytically transformed to amides by different inorganic solid materials following molecular rearrangement processes (Beckmann reactions). These reactions take place in "dry media" conditions, i.e. without any solvent, at relative low temperature (10Oo-16O0C).The yield and the selectivity depend on the nature of the solids (structure, composition, texture, etc) differing, in some cases substantially, with respect to that obtained in the classical homogeneous conditions. Thus acidic solids, as alurninosilicates with layer structure (A13'-montmorillonite), proton-exchanged zeolite (HNaY) or amorphous silica-alumina materials, as well as sulphoarylcompounds (sulphopolystyrene and sulphoarylderivates of silica), have been employed as catalysts, showing good conversion rates and selectivities to the amide formation, in particular after elimination of adsorbed water molecules. The competitive reaction is the hydrolysis of the oxime to carbonyl compounds, which is enhanced by the presence of water at the surface of the solids, in particular when these materials are of less acidic character (silica, alumina, Na-exchanged zeolites and montmorillonites). INTRODUCTION We have recently reported (refs. 1-3) the catalytic rearrangement reactions of 1,2-glycols to carbonyl compounds ( "pinacol rearrangement") on different inorganic materials, the selectivity of the reactions being clearly dependent on the nature of the solid support. The topology of the solids shows a special influence in the development of those reactions. Thus, lamellar materials such as certain 2:l charged phyllosilicates ("clay minerals") give reaction products that are not obtained in the presence of other solids with different topology, or in homogeneous media. The selectivity of these molecular rearrangement processes is clearly determined by the layered structure of the solid catalysts. The purpose of the present work is to study comparatively the activity of different acidic solids as catalysts in other "classical" type of molecular rearrangement as it is the conversion of oximes to amides (Beckmann rearrangement, eqn. 1 ) , by adopting "dry media"

540

conditions and operating under soft experimental treatments. As it is well known these reactions, which are conventionally carried out in homogeneous media, are acid-catalyzed processes. H'

Rl( C=N-OH)R, oxime

R,-CO-NH-R, amide

(1)

Different attempts to use some solid acids -as zeolites and phosphates-as catalysts in gas-solid reactions, have been already described (refs. 4-6). Nevertheless, the control of the selectivity appears to be difficult because drastic experimental conditions are always required. EXPERIMENTAL PART The starting oximes (acetophenoneoxime and cyclohexanone oxime) were prepared by reaction of the corresponding carbonyl compound with hydroxylamine hydrochloride. The purity of the resulting oximes was checked by GC and IR spectroscopy after recrystallisation of the samples. The catalytic reactions were performed either on the hydrated solids (equilibrated with the relative humidity -about 55%- of the atmosphere) or on the dehydrated catalysts (heated at 160"C, during 3 hours). An intimate mixture of the inorganic solid (100 mg) and the oxime in solid state ( 2 0 mg) was introduced in a Pyrex glass reactor. Thus, the reaction was carried out in "dry media" conditions, i.e. without any solvent. The mixtures were either activated with a microwave oven or heated at 100, 130 or 160°C in a conventional oven, during variable times (in the standard procedure: 1 hour). The microwave oven used is a domestic (2450 MHz) Moulinex model FM 460, carrying out the experiments at 600 W of power and introducing a unic vessel in the oven in each experiment. The reaction products were extracted by treatment with a large excess ( 5 ml) of an appropriate solvent (methanol or chloroform), and the extracts were analyzed by GC. The GC analysis were effectued in a Perkin Elmer 8410 chromatograph with a 12 m capillary column of fused silica with associated BP-1 phase. IR spectra were recorded in the range of 40002 5 0 cm-l using K B r disks, fluorolube or nujol mulls on a Perkin-Elmer 580B spectrophotometer, coupled to a M-3500 data station.

54 1

The solids used as catalysts are: Al-mont and Cr-mont: homoionic A1 or Cr exchanged montmorillonite, prepared from a sample obtained from the sodium aluminosilicate of the natural deposit of Wyoming, USA, (sample 25 b, supplied by Word's Natural Science Stablishement Inc., Rochester, N.Y., USA). SAS: arylsulphonic derivative of silica obtained as described in ref.7. A15: commercial sulphopolystyrene resin (Amberlist-15), crosslinked with 8% divinylbenzene, obtained from Fluka. ZHY: partially proton-exchanged Y zeolite, supplied by Union Carbide. Si/A1 ratio=2.9. The exchange ratio of Na' by H': 40% Other solid catalysts: silica (silicagel 60, Merck, 230 mesh), alumina (neutral 90, Merck, 70-230 mesh), and silica-alumina (Akzo Chemie, Ketjen Catalysts, grade LA-3P, Al,O,= 13.8%, t200 mesh). RESULTS AND DISCUSSION Reactions of acetophenone oxime (1) When acetophenone oxime (1)is thermically treated with acidic solids in "dry media" under soft experimental conditions, two main products are obtained: the rearrangement one: acetanilide (N-phenyl acetamide) ( 2 ) obtained by Beckmann rearrangement with migration of the phenyl group, and the hydrolysis one: acetophenone ( 3 ) , obtained by the hydrolysis of the imino group (C=N) (eqn.2). N-OH Acidic solid I1 C,H,-C-CH, s acetoph.oxime

(1)

51

0 \\

CH,-C-NH-C,H, + CH,-C-C,H, acetanilide acetophenone

(2)

(3)

The yield of the reaction (Table 1) clearly depends or the nature of the solid and on the experimental conditions (temperature, time). Thus, with silica and alumina, amorphous solids with a relatively low acidity, the acetophenone oxime molecule reacts with a very low yield, being the only reaction product the hydrolysis one, acetophenone. With the synthetic mixed oxide silica-alumina, that possesses simultaneously Bransted and Lewis acidic centres, the conversion is quantitative, being also the major product the hydrolysis one (31, when the reaction is carried out at 160°C.

Nevertheless, at 130°C (3h), the silica-alumina does not produce appreciable conversion of 1. When the aryl sulphonic derivative of silica is selected as catalyst, quantitative yields are obtained for 3h at 130°C or for lh at 160'C, being in both cases the selectivity of the reaction directed to the hydrolysis product 3 . With the sulphonic resin Amberlist 15 the conversion of the oxime 1 depends on the temperature of the reaction: thus, at 130°C (3h) the yield is close to 50% being the major product the acetophenone ( z ) , while at 160°C (lh) the yield is 73%, and the two products 2 and 3 are detected. TABLE 1 Conversion ( % ) and selectivity ( % ) in the reaction of acetophenone oxime with different acidic solids (rate solid/oxime = 5:l) hydrated (50% r.h.). Reaction conditions: 160"C/lh and 130°C/3h.

Solid Silica Silica Alumina Alumina Si1-alum Si1-alum SAS SAS A15 A15 ZHY ZHY Al-mont Al-mont

Selectivity ( % ) Conditions Conversion (%) Acetanilide Acetophen.("C/hours) 160/1 130/3 160/1 130/3 160/1 130/3 160/1 130/3 160/1 130/3 160/3 130/3 160/1 130/3

6 0 8 0 100 6 100 98 73 50 100 15 100 100

2 2

100 0 88 0 82 50 78 98

57

40

2

90 65 100

0 0 0 0 0 25

33 0 68 17

22

81

-

0 0 12 0 18 25 20 0 3 8 2 0 10 2

In the same experimental conditions (lh, 160"C), the protonic zeolite NaHY gives rise to quantitative percentages of conversion, being the rate 2/3 = 33:65, while at 130'C, 3h, the conversion is of a 15% and the main product the ketone 3. Finally, when the lamellar phyllosilicate montmorillonite (homoionically exchanged with A13' cations) is selected as catalyst, great differences in the selectivity of the reaction are observed: thus when the reaction is carried out at 130°C, 3 hours, the rate of conversion is 100% and the selectivity acetanilide (z)/acetophenone ( 3 ) is 17/81, while at 16OoC, 1 hour, the conversion is likewise of 100% and the rate 2/3 is 68/22.

543

The obtained results point out that a great competition between the Beckmann rearrangement reaction and the hydrolysis one exists. Both reactions are acid catalyzed, but the rearrangement one is favoured when strong acidic solids are used as catalysts and when high reaction temperatures are selected. It is known from the literature that certain acidic solids as protonic zeolites (refs.4 and 5) or aluminium phosphates (ref.6) are used as solid catalysts in the Beckmann rearrangements reaction, but generally strong experimental conditions are required (temperatures higher than 300") In the present work we can deduce that the selectivity of the reaction can be easily changed by varying the experimental conditions (temperature/time) and/or the acidic solid used as catalyst. From Table 1 it can be observed that only the most acidic solids give rise to considerable conversion rates (silica-alumina, aryl sulphonic solids, protonic zeolite, A13*-montmorillonite), the selectivity of the reaction being in general favourable to the hydrolysis product 3. Only with the A13+-montmorillonitesolid at 160"C, the major product is the Beckmann rearrangement one, acetanilide ( 2 ) . This different behaviour of the selected substrates could be interpreted in terms of topology of them and of the strength of the acidic centres. Thus, it has been demonstrated that cations with high polarizing power (high charge and low radii) present in the interlayer space of phyllosilicates induce a great degree of dissociation in the water molecules coordinated with them (eqn.3) and give rise to selective reactions those does not take place with other acidic solids (refs. 1-3). A~(H,o),~+

A1(H20),-n(OH),'3-n'*+ nH'

(3)

In this case, it has been likewise demonstrated that with A13'montmorillonite as acidic solid, the selectivity of the reaction can be easily modified to obtain the ketone ( 3 ) or the amide ( 2 ) . The fact that with the lowest temperature the percentage of hydrolysis product increases, could be attributed to the greatest content of interlayer water (not directly coordinated) present at that temperature (130°C) compared with the highest one (160°C). On the contrary, the rearrangement product, acetanilide, is the principal one for the highest temperature, which is in good agreement with the fact that the rearrangement reaction needs a greater acidity, that is increased when the content of water is low, therefore being favoured at highest temperatures.

544

To demonstrate that the water molecules coordinated to the interlayer cations are the responsible of the hydrolysis reaction, we have carried out the dehydration of the A13*-montmorillonitefor 3h at 160°C previously to the reaction. In this case, we have selected two experimental conditions, 160°C for 1 hour and 100°C for 2 hours, in order to find great differences between both reactions. The obtained results (Fig. 1) clearly shows that when the water content diminishes by the dehydratation process, the percentage of ketone also diminishes, increasing the content of amide in the reaction mixture, especially when the reaction is carried out at the higher temperature (160°C). a)

b)

100°C/2 hours

16O"Cll hour

Fig. 1. Conversion ( % ) and selectivity ( % ) in the reaction of acetophenone oxime with A13'-montmorillonite (rate solid/oxime = 5: 1 ) hydrated (50% r.h.) and dehydrated (3h at 160°C). Reaction conditions: 100°C/2h (a) and 160"C/lh (b). The decrease in the water content by the dehydration process also have influence on the by-products, that mainly correspond to the products from the hydrolysis of acetanilide acetic acid and ani1ine Beside, the yield of the reaction at 100 "C increase for the dehydratated solid, due to the increase in the rearrangement yield. On the other hand, we have compared the yield and selectivity in the reactions of acetophenone oxime with A13* and Cr" exchanged montmorillonites activated thermically and by microwaves (Fig. 2). From the obtained results, we can deduce that microwaves enhance significatively the conversion rate, being the conversion practically quantitative for only 10 minutes of treatment at 600W. The selectivity of the reaction can be directly correlated with that of the thermal treatment at 160°C. The effect of microwaves could be attributed, as we have previously demonstrated (ref.8) to the rapid

.

(z),

545

activation and consequently loss of the water molecules in the solid, that gives rise to a great activation of the organic molecules. The selectivity of the reaction is in good agreement with the diminishing in the water content, which increases the acidity of the solid and, as we have previously demonstrated, favours the rearrangement reaction. a)

b) 10 8

6 4 2

Fig. 2. Conversion ( % ) and selectivity ( % ) in the reaction of acetophenone oxime with A13+ and Cr"-montmorillonites (rate solid/oxime = 5:l) actived thermically (160"C/lh) (a) and by microwaves ( 600W. 10min) (b). Reactions of cyclohexanone oxime ( 4 ) It has been described the reaction of cyclohexanone oxime with solids of different nature, as zeolites (refs. 4 and 5) and aluminum phosphates ( ref. 6 ) , giving rise to the Beckmann rearrangement product, E-caprolactame when the reactions are carried out in the gas phase at relatively high temperatures (>300"C). In the present work we have carried out the reaction of cyclohexanone oxime in the presence of the selected acidic solids in dry media under soft experimental conditions (16OoC, 1 hour). The obtained results show a great complexity due to the presence of significants amounts of differents products (by-products and subproducts), accompanying to the main ones: €-caprolactame ( 5 ) formed by Beckmann rearrangement and cyclohexanone ( 6 ) obtained by hydrolysis of the oxime (eqn. 4 ) . Among the other products present in the reaction mixture, the aminoacid, 6-aminohexanoic acid and the nitrile, 5-hexanenitrile have been detected. We have compared the yield and the selectivity in the reaction f o r the solids in equilibrium with a relative humidity of 50% and dehydrated at 160°C during 3 hours (Table 2). In all cases the conversion rate is close to 100% as much f o r the hydrated solids as for the dehydrated ones. The selectivity of the reaction can be directed by changing the solid

546

and the experimental conditions. Thus with the hydrated A13’montmorillonite the yield in cyclohexanone is 728, while the sulphopolyestyrene resin Amberlyst 15 dehydrated 3h at 160°C. yields E-caprolactame in a 61%.

beozo 0

0 = ” - O H

acidic solid

cyclohexanone oxime

n

e- caprolactame 5

4

4-

+

others

cyclohexanone

(4)

6

From the results presented in Table 2 it can be again deduced that the dehydration process increase in general the selectivity towards the amide, while the presence of certain amounts of water in the solid favours the hydrolysis reaction. With the present data is not possible to establish correlations between conversion and selectivity of the reaction with the nature and topology of the different acidic solids, therefore further investigations are needed to go deeply into the mechanism of the reaction. TABLE 2 Conversion ( % ) and cyclohexanone oxime solid/oxime = 5:1 ) (160°C/3h). Reaction

selectivity ( % ) in the reaction of with different acidic solids (rate hydrated ( 50% r. h. ) and dehydrated conditions: 160”C/lhour. ~

Selectivity Solid

(%)

Hydratation Conversion (%) Cyclohexa. E-caprolac.Others state ~

Sil-alum Sil-alum SAS SAS A1 5 A1 5 ZHY Z HY Al-mont Al-mont

50% r.h. dehydrated 50% r.h. dehydrated 50% r.h. dehydrated 50% r.h. dehydrated 50% r.h. dehydrated

95 97 100 98 99 100 99 98 100 96

~

14 33 15 24 2 5 32 14 72 26

38 47 24 48 47 61 24 29

8 21

43 17 61 26 50 34 43 55 20 49

CONCLUSIONS The acid catalyzed conversion of oximes over different acidic solids in “dry media“ under soft conditions gives as major products the amide (Beckmann rearrangement) and the ketone (hydrolysis). The

547

selectivity of the reaction can be easily directed towards the amide or the carbonyl compound by selecting the experimental conditions (temperature, time) and the acidic solid used. Thus, the nature, topology and hydration state of the solid have direct influence in the conversion and selectivity of the reactions. In the same way, the reaction can be activated by microwaves, reacting quantitative yields for only 10 min. of activation at 600w. ACKNOWLEDGEMENTS The authors acknowledge their very fruitful discussions with Prof. G. Bram and Prof. J.M. Serratosa. This work has been partially financed by the CICYT, Spain. REFERENCES 1 E. Gutierrez and E. Ruiz-Hitzky, Mol. Crvst. Lia. Crvst. Inc. Nonlin. Opt., 161 (1988), 453-458. 2 E. Gutierrez, A.J. Aznar and E. Ruiz-Hitzky, Studies in Surface Science and Catalysis: Heteroaeneous Catalysis and Fine Chemicals, M. Guisnet et a1 (Ed.), Elsevier Sci. Pub., B.V., Amsterdam (1988), 211-219. E. Gutierrez and E. Ruiz-Hitzky, Pillared Lavered Structures: 3 Current Trends and ApDliCatiOnS, I.V. Mitchell (Ed.), Elsevier Appl. Sci., London (1990), 199-208. P.S. Landis and F.B. Venuto, J. Catal., 6 (1966), 245-247. 4 A. Aucej0,M.C. Burguet, A. Corma and V. FornBs, ADD. Catal., 22. 5 (2) (1986), 187-200. I.A. Costa,P.M. Deya, J.V. Sinisterra and J.M. Marinas, An. 6 Quim.. Ser. C, 28 (1) (19821, 43-47. A.J. Aznar and E. Ruiz-Hitzky, Mol. Crvst. Lip. 7 Cryst.Inc.Nonlin. Opt., 161 (1988), 459-469. E. Gutierrez, A. Loupy, G. Bram and E. Ruiz-Hitzky, Tetrahed. 8 Lett., 30(2) (1989), 945-948.


M. Guisnet et al. (Editors), Heterogeneous Catalysis and Fine Chemicals I1

549


ON OXIDE CATALYSTS

SELECTIVE RING-OPENING OF I S O M E R I C 2-METHYL-3-PHENYLOXIRANES

ARPAD MOLNAR, IMRE B U C S I and MIHALY BARTdK Department o f Organic Chemistry, A t t i l a Jozsef U n i v e r s i t y , 06m t 6 r Szeged (Hungary)

8,

H-6720

SUMMARY The rearrangement o f l i g h t gnd deuterium-labelled cis- and trans-2-methyl-3phenyloxiranes (1, 2 and 1 , 2 ) was s t u d i e d on ZnO, A 1 0 and WO , and i n t h e presence of BF Both i n the gas phase (473-673 K) and ?he l i q u j d phase (298413 K ) , 1-phdyl-2-propanone ( 3 ) and 2-phenylpropanal (4) were formed with h i g h s e l e c t i v i t i e s (0-90% and 11-80%, r e s p e c t i v e l y ) . Ring-opening was found t o occur by s e l e c t i v e f i s s i o n o f the benzyl C-0 bond. Mechanistic s t u d i e s revealed t h e formation of an open carbenium i o n or a double-bonded surface intermediate. The a c i d i c ( e l e c t r o p h i l i c ) and basic characters o f the oxides determine the product d i s t r i b u t i o n s by a f f e c t i n g the r e l a t i v e importance o f the competing mechanisms.

i6

.

INTROOUCTION The

ring-opening o f oxiranes, leading t o the formation o f isomeric

compounds continuing the

carbonyl

the a c t i o n of a c i d c a t a l y s t s as a r e s u l t of rearrangement, i s

by

i n t e r e s t ( r e f s . 1-4).

of

However, most o f these s t u d i e s focus mainly on

transformations o f terpene oxides

or oxiranes with o t h e r f u n c t i o n a l groups

i n the l i q u i d phase, under homogeneous r e a c t i o n c o n d i t i o n s . The

present

paper r e p o r t s r e s u l t s on the ring-opening o f

ence

of

pres-

d i f f e r e n t oxides both i n the l i q u i d phase and i n t h e gas phase.

Oxide

are known t o catalyse the rearrangement o f oxiranes ( r e f s . 2-4).

catalysts literature pointed

cis- and trans-2-

(1 and 21, c a r r i e d o u t f o r the f i r s t time i n t h e

methyl-3-phenyloxirane

data

( r e f s . 5-7) and our own s t u d i e s with 2-methyloxirane ( r e f .

the importance of acid-base p r o p e r t i e s i n determining

to

selectivities.

Some

8)

ring-opening

For t h i s reason, the oxides used were ZnO, A1203 and W03,

which

cover a wide range of acid-base p r o p e r t i e s . The study o f these simple model compounds

can provide important i n f o r m a t i o n about the r e g i o s e l e c t i v i t y and stereo-

chemistry

of

the ring-opening. A c o r r e l a t i o n can a l s o be expected between

the

a c t i v i t y / s e l e c t i v i t y of the c a t a l y s t s and t h e i r acid-base p r o p e r t i e s . EXPERIMENTAL Materials The

isomeric oxiranes prepared by r i n g c l o s u r e o f 1-bromo-1-phenyl-2-propan-

01 (ref. plate

9)

were separated on a Fischer c o n c e n t r i c tube

number: 90) (b.p.:

cis (1) 355

K/13 mm Hg,

trans (2)

column

(theoretical

361 K/13 mm Hg,

ac-

550

coi~iing to

r e f . 10: 356-357 and 361 Kf13 mm Hg, r e s p e c t i v e l y ;

97%, y i e l d :

58%). The isomers o f 2-methyl-3-phenyloxirane-

isomer

purity:

r 211 1: 2-

(I* and

H

2*)

.

were synthesized i n a s i m i l a r way from 1-bromo-1-phenyl-2-propanol- 2- H 11 C h a r a c t e r i s t i c data on the oxides (Strem Chemicals) are g i v e n i n Table 1. TABLE 1. C h a r a c t e r i z a t i o n of oxide c a t a l y s t s

-n/K

BET surface

value

(m’9-I)

wo,

423K

573K

0 0.10 0.72

20

27.0

0.1s

100 17

58.8 96.8

0.72 1.67

ZnO

A1203

p y r i d i n eC

Acid-base p r o p e r t i e s a Me2Znd nBuNH2e

benzo&c acid

5.25 5.15 4.80

1.96 1.20 3.54 ~

0.90 2.77 0.53

~~

a

Values i n d i c a t e number o f surface a c i d i c or b a s i c s i t e s , nm-’. bn i s the formal charge, and i s the i o n r a d i u s . %umber o f p y r i d i n e molecules adsorbed, as determined by p u l s e chromatographic d t i t r a t i o n i n helium; c a t a l y s t pretreatment: 773 K , 2 h. Number o f surface OH groups as determined by pulse t i t r a t i o n w i t h d i m e t h y l z i n c tetrahydrofuranate complex i n helium a t 363 K according t o r e f . 11; c a t a l y s t pretreatment: 773 K , 2 h. e T i t r a t i o n i n absolute benzene according t o r e f . 1 2 . Methods Reactions

o-xylene tions

with

tions

in

with

i n the l i q u i d phase were c a r r i e d out i n 1,4-dioxane (373 K ) or

(413

K ) ( 0 . 1 g c a t a l y s t and 0.1 g r e a c t a n t i n 0.5 m l s o l v e n t ) .

lpl

8F3.Et20 as c a t a l y s t were r u n a t room temperature.

Transforma-

the gas phase were s t u d i e d a t 473-673 K by u s i n g t h e GC-pulse

catalyst

2

q u a n t i t i e s corresponding t o 0.5 m s u r f a c e

area

in

Reacmethod

(pretreatment:

700

K , 1 h i n helium; 1,411 pulses). The t r a n s f o r m a t i o n o f t h e

led

compounds was c a r r i e d out i n a continuous f l o w r e a c t o r a t 523 K (1 g

deuterium-labelcata-

l y s t , 1 g h - l feeding r a t e o f r e a c t a n t s , f l o w r a t e o f helium: 50 ml min-’1. Analyses 20% polyethylene g l y c o l succinate on Kieselguhr column (1.2 m, 443 K ,

A

ml min-’ helium c a r r i e r gas) was used f o r GC analyses. Deuterium-labelled pounds

50 com-

were analysed by NMR spectroscopy (JEOL C 60-HL equipment) a f t e r separaw i t h a Carlo Erba Mod P p r e p a r a t i v e GC. Mass spectrometric analyses o f the

tion

reaction

mixtures

were c a r r i e d out with a Hewlett Packard 5890A GC

instrument

(25 m HP-20M column, 353-473 K ) coupled with a 5970 MSD quadrupole mass spectrometer ( E I source, 70 eV, 1-s scans, HP 59970 MS ChemStation data system). RESULTS The in

the

experimental r e s u l t s on the t r a n s f o r m a t i o n s o f the two i s o m e r i c oxiranes gas phase (Table 2) i n d i c a t e the formation of t h r e e

isomeric

carbonyl

551

compounds (Fig. 1). Results in the liquid phase in solvents (2-xylene, 1,4-dioxane) often used in homogeneous reactions are given in Table 3. TABLE 2 Selectivity of transformations of and trans-2-methyl-3-phenyloxirane (1 and 2) on oxide catalysts in the gase p h x r e a c t i o n temperature: 523 K )

a-

Catalyst Oxirane

ZnO

1

Conversion (mol%) 2-Phenylpropanal ( 4 ) 1-Phenyl-2-propanone (3) 1-Phenyl-1-propanone (5) Decomposition 4/3 ratio

A1203 1 2

2

46 13 83 76 2 2 0.32 1.22 0.16 17 24

15 55 45

wo3

1

40 48 49

100 11 87

2 98 13 84

3 2 3 0.98 0.13 0.15

TABLE 3 Selectivity of transformations of 1 and 2 on oxides in the liquid phase Solvent (reaction temp., K ) Catalyst Oxirane Conversion (reaction time, h) 2-Phenylpropanal ( 4 ) 1-Phenyl-2-p~opanone( 3 ) Unidentified

o-Xylene (413) b

1,4-~ioxane( 3 7 3 1 ~ A1

1

1

73(24) 62(24) 14 26 79 70 7 4

32

20(12) 14(12) 75 25

50 50

1

78(3) 20 80

62(3) 47 50 3

aNo transformation was observed n ZnO and A1 0 after 24 h. bNo transformation was observed on ZnO after 24 h. ‘Mainly polym&?c material.

phwMe a O b

&/I

H-+/l

Ph-CH2-C-Me

Me Ph-tH-C,

6 3

4 H

4

Ph-C-C%-Me

1

5

Fig. 1. Transformation directions of 2-methyl-3-phenyloxirane. Data on the transformations under homogeneous conditions with BF3 as catalyst can be found in Table 4. Because of the significant side-reactions taking place mainly in 2-xylene, only the results in l,4-dioxane can be considered characteristic of rearrangement.

552

Further important data concerning t h e r e a c t i v i t i e s of l i g h t and deuterium-laisomers are given i n Table 4. Oata on t h e deuterium d i s t r i b u t i o n i n

belled carbonvl

comoounds formed i n t h e t r a n s f o r m a t i o n s o f t h e isomers o f

[

phenyloxirane- 2- H

'11

the

2-methvl-3-

are t o be found i n Table 5.

TABLE 4. isomeric 2') o f transformations o f l i g h t ( 1 , 2) and l a b e l l e d (l*,

Selectivity

2-methyl-3-phenyloxiranes catalysed by BF3 under homogeneous c o n d i t i o n s a 1

Oxirane

1*

Solvent

2*

1*

1

(3)

16 22 20

2

2*

o-Xylene

1,4-Dioxane

Conversion (mol%) :-Ph,nyl-~-~E-;~n3riL: Unidentified a

2

11

35

24

90

23

10

12

97 3

21 40 60

14 7c 30

3 22 78

4

23 71

Room temperature, r e a c t i o n time: 30 min. bblainly polymeric m a t e r i a l .

TABLE 5 Tracer s t u d i e s w i t h C a t a l y s t Substrate

cis (1')

and

trans (2*)

c

2-methyl-3-phenyloxirane- 2- H

2-Phenylpropanal (4*Ia

1-Phenyl-2 propanone (3*)a

deuterium distribution i n content l a b e l l e d p o s i t i o n s

deuterium distribution i n content l a b e l l e d p o s i t i o n s C1-0 C3-0

c1-0

c2-0

l*

0.97 0.97 0.83 0.71 0.70 0.60 0.82 0.93

2*

BF3 ZnO

1*

0.96 0.97 0.90 0.93 0.83 0.91

2*

1* A1203

2*

w03

2'

1*

*I1

0.91 0.91 0.86 0.89 0.80 0.87

0.05 0.05 0.04 0.04 0.03 0.04 ~

0.97 0.97 approximately equal amounts i n t h e two positions

~~

a A s t e r i s k s i n d i c a t e l a b e l l e d compounds. The above experimental r e s u l t s can be summarized as f o l l o w s . Under homogeneous c o n d i t i o n s , e x c l u s i v e formation o f 1-phenyl-2-propanone (i)

( 3 ) took place, regardless o f t h e stereochemistry o f t h e oxiranes. On the oxides i n the gas phase t h e (ii) phenyl-2-propanone ited

similar

cis isomer

(1) was transformed i n t o 1-

( 3 ) with h i g h s e l e c t i v i t y , w h i l e t h e

s e l e c t i v i t i e s i n the formation o f b o t h

trans isomer

(2) exhib-

1-phenyl-2-propanone

(3)

and 2-phenylpropanal (4).

(iii) The oxide c a t a l y s t s e x h i b i t e d an i n c r e a s i n g a c t i v i t y p e r u n i t surface a r ea

i n the sequence ZnO< A1203
,-tho

and t h e para p o s i t i o n s . In the f o r m e r c a s e , t h e

L

590

resulting Wheland

2.

product

intermediate

In t h e l a t t e r c a s e .

loses a proton e x p u l s i o n of

to yield

protonated

3. T h i s i p s o - s u b s t i t u t i o n f o r m s o n l y t r a c e s of p - n i t r o a n i s o l e 3 u n d e r homogeneous

carbon monoxide a f f o r d s product

reaction conditions

( T a b l e 1).

TABLE 1 Proportion o f p-nitroanisole function

formed

(21.2%) as a

the solid present.

01

Solid

support

( n o n eI

a

(%I

3

1.1

silica.

2.3

Kieselghur’

1. 6

Cu(N03)z.3HzOb

1.3

KIOa

9.6

”

C

1a y c op

10

”

K10-Cu’+

13

KlO-Al”

15

K10-Ti4+

16 a

21

Kaolinitem

27

K10-Zr4+

__---_--_-_-_--_------------------------------------a

1.5 g

the solid +

of

1 0 mmol

excess relative to HNOi clay

are

min., x

g

amount

0.5

of of

ml

+ 3.1

m l AczO

fuming HN03

(

i . e . an in

the

(25 ml)

and

plus the residual water

in t h a t o r d e r in C C l G

for 114 h while

refluxed %

introduced

L

~ . a - , Merck,

99.5

is a d d e d d r o p w i s e .

solid and

no HNO3

( x

value

i s function of

the

~03-/9).

CHO 2’ ~

The two Wheland

i n t e r m e d i a t e s 2’ a n d 3’ a r e h i g h l y

59 1

p o l a r , w i t h c a l c u l a t e d d i p o l e moment respectively

( r e f . 4-51.

The high acidity

(ref. 2 ) and the high electric a m o n t m o r i l l o n i t e clay

thus

diminishing

Electric

of 4.49 a n d 5.57 D

would

(

H o = -6 t o

-8)

f i e l d at t h e i n t e r f a c e of

increase the formation of

the a c t i v a t i o n e n e r g y b a r r i e r

a,

( r e f . 6).

f r o m G a u s s ’ s l a w , at a

field calculat3d

d i s t a n c e of o b, from a c l a y s h e e t w i t h a

charge density

a p p r o p r i a t e f o r a s m e c t i t e ( t h e U p t o n b e n t o n i t e ) of 6.8 m i l l i e l e c t r o n . ~ - ’ has a

l i m i t i n g v a l u e of 1.2

f o r a d i e l e c t r i c c o n s t a n t of u n i t y . e x p e c t e d f o r a n i n c r e a s e of p o l a r i t y

1Olo V . m - ’

The energy gain 1 D of

of

t r a n s i t i o n s t a t e s is t h u s 5.5 kJ.mol-’

the

for a local

d i e l e c t r i c c o n s t a n t of 5 (ref. d ) . In t h e

p r e s e n c e of m o n t m o r i l l o n i t e

K10,

the proportion

of P - n i t r o a n i s o l e 3 in t h e p r o d u c t m i x t u r e i n c r e a s e s by m o r e t h a n o n e o r d e r of m a g n i t u d e .

I t grows up a s the

B r s n s t e d a c i d i t y at t h e s u r f a c e is e n h a n c e d by acidic

surface intersticial

L i k e w i s e , yet

in a more

pronounced manner,

a kaolinite,

another clay with a strongly acidic s u r f a c e (Ho 6 ) ( r e f . 2).

a l s o favors ips0 nitration:

nitroanisole

a

compared

r i s e s t o 27%. b o o s t e d by

to homogeneous +

the Lewis-

c a t i o n s ( r e f . 7-81. = -3 t o

t h e y i e l d o f Pa f a c t o r 20 a s

reaction conditions!

Kaolin E T - 1 W/Q

0

Kaolin B.E.T=20m2/0

h (c

0

3

IGG

0 h h s s @f kaolin

Fig.

1.

Relationship

nitroanisole mass

L

3_

a m m t of anisaldehyde

between the Dercentage

formed and the ratio

of k a o l i n i t t

;in moll.

!

250

of P-

(g.mol-’) of

the

( i n J ) to t h e a m o u n t of p - a n i s a l d e h y d e

-

592

T h e proportion of ips0 n i t r a t i o n product first amount of clay present

depends u p o n the

mixture, then r e a c h e s a plate.

in the r e a c t i u n

This l i m i t c a n s q u a r e w i t h

a clay saturation. The r e s u l t s o b t a i n e d by X-ray s t u d i e s o n the k a o l i n i t e separated

diffraction reaction HNir3

mixture by

filtration

before

from

the

th+ acidition s ~ f

indicate that there is no i n t e r c a l a t i o n of

anisaldshyde r3r nitrating a g e n t , which would r-eiult in a n increase o f

d o o i , which

in our c a s e r e m a i n s .:onstant.

To sum u p , the adsorption of p-anisaldehyde particule o f the

clay r e s u l t s in a c o n s i d e r a b i t

z p s o substitution

on a

increase in

pathway during nitratiori.

WITTIG OLEFINATION Following S c h l o s s e r (ref. 9 ) . we divided alkylidene phosphoranes

(phosphorus

the

ylides)

L

used

in

W i t t i g r e a c t i o n s into three groups a c c o r d i n g to their

react i v i t Y -

+ RI-P-CH-R

1 0 m i n )

- for ~

=

0

.

2

,

1

~

~

~

~

~= -0.0176.t ~ ~ ~ ~

+ ~ 2.217 ~ ~ ~( 2~) ~

C b e n z a l d e h r d c ]

( t > 20minl T h i s t y p e of b e h a v i o u r s (ln---k’.t)

obtained assumes

C A I

steady-state

( d c e y - O )of

the ylide concentration.

One can

d t

account for the time necessary to reach the steady-state by

i n t r o d u c i n g a s e c o n d t e r m in e q u a t i o n s

This time is shorter when kaolinite How can

we

( 1 ) and

(2).

is p r e s e n t .

e x p l a i n t h e i n c r e a s e in r e a c t i o n r a t e :

1. T h e e q u a t i o n s

(11 and

(2) account

“macroscopic” observations.

for

They correspond t o the

a c c u m u l a t i o n o f t h e r e a g e n t s o n k a o l i n s u r f a c e , so that t h e i n c r e a s e of increase o f

local concentration c a u s e s a n

reaction rate. d C A

1

--kl

.[ A l l o s r l

d t

2. A n

interaction between the clay and the reagents

and/or the reactions intermediates causes a d i m i n u t i o n of

the activation energy

( k ’ k a o l L n = 1.65

* k ’ u i t h o u t

of

the reaction

k a o l i n ) .

F i g . 3 C o m p a r i s o n of t h e F T I R s p e c t r a

--- b e n z a l d e h y d e -benzaldehvde

adsorbed on kaolinite

(2.10-~mole) 0. rig

’

.

595 T h e c o m p a r i s o n of

the benzaldehyde

shift

the carbonyl

frequency, reflecting an increase o f

bond polarity, carbon.

That

of

1 5 cm-'

IR spectra shows a

hypsochromic

thus a higher

phenomenon

( 1 7 0 3 cm-'--->1688

c m - l ) of the

charge on the carbonyl

favors the reactions with

the

anions.

CONCLUSION The clay

surface increases

reagents meeting This dual

the probability

of

and modifies the reagents polarity.

influence

f a v o r a b l e to t h e

is s t r o n g l y

r e a c t i o n s t h a t we h a v e s t u d i e d .

REFERENCES T.J.

Pinnavaia,

P.L.

Hall,

S.S.

Cady.

M.M.

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Aromatic radical cation formation on the intracrystals s u r f a c e s ,of t r a n s i t i o n m e t a l

J.

Phys.

H.A.

Chem..

Benesi,

layers lattice silicates.

( 1 9 7 4 ) 994-999.

78

Acidity

of c a t a l y s t

strengh from colors adsorbed

I. A c i d

surfaces.

i n d i c a t o r s , J.

Am.

Chem.

S O C . 78 ( 1 9 5 6 ) 5 4 9 0 - 5 6 9 6 . H.A.

Benesi

a n d B.H.C.

solid catalysts.

A. A

C o r n e l i s , L.

Adv.

Winquest, Catal.

Delaude,

A.

27 (1978) 9 7 - 1 8 2 . C e r s t m a n s a n d P.

Lett.,

Collet,

R.C.

Tetr.

(1988) 5657-5660.

29

aromatic

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Laszlo,

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Surface acidity

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M.J.S.

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SOC. 97

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A.

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D u r a n , J.

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of

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153 ( 1 9 8 8 ) 8 2 - 8 6 .

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Lett.,

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reagents. P. L a s z l o ,

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solids, Acc.

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using

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19

A n ab

( 1 9 8 6 ) 121-127.

inorganic

596

9

M.

S c h l o s s e r , in : Methodicum Chimicum. Georg T h i e m e

Verlag. 10 E.

Stuttgart. 7 ( 1 9 7 6 ) 529.

Vedjs and C.F.

M a r t h , Mechanism

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J. Am. 11 E.

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Vcdjs, T .

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rrvsrsible W i t t i g r e a c t i o n

of

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52 ( 1 9 8 7 ) 6637-6639.

12 G. Gallagher and R . L .

W e b b , Tetrasubstitued

a c r v l a t e s : thc Wittig-Horner r e a c t i o n o f triethyl a-phosphonoPropionate,

k e t o n e s with

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-126. 13 Source Clay Minerals re posit or^. Dept.

University o f

of

Geology,

Missouri C o l u m b i a , Missouri 65201 U S A .

597

AUTHOR A

INDEX C a r r e , J.

237

A i , M.

423

Casbas, F .

201

Angevaare, P.A.J.M.

305

C e r i n o , P.J.

23 1

A r r e d o n d o , J.

Chamoumi, M.

573

Augustine, R . L .

1a5 129

Aznar, A.J.

539

C i v i d i n o , P. C l i m e n t , M.J.

245 557

Collet, C.

589

€3

Baiker, A.

413

Coq, 6 .

B a r b i e r , J.

223 343

Cordier, G.

Barrault, J. B a r r e t o - R o s a , M.M. Barto'k, M . B a s s e t , J.M.

263 153,549

Corma, A . C o u r t , J. C u r t i n , T.

58 1 295 503,557 193 53 1

Baumeister, P.

137 321

D

B a u t i s t a , F.M.

269

D e l a h a y , G.

343

Beenackers, J.A.

215

Del Angel, G.

185

B e l g s i r , E.M.

D e t t m e r , M.

B e r t h i e r , Y.

463 295

D i d i l l o n , 8.

487 137

Besson, M.

113

D j a o u a d i , D.

113

Blackmond, D.G. B l a n c , B. B l a s e r , H.U. Bodibo, J.P. B o i t i a u x , J.P. B o n n e l l e , J.P. Bonnet, M.C. B o n n i e r , J.M.

145 145 73,177,321 513 223 287 263

Doussain, C.

471

Duprez, D.

20 1

E E l Mansour, A

137

Essayem, N .

343

B o u r n o n v i l l e , J.P.

113,245 137

F a r n e t t i , E.

253

B r e y s s e , M.

121,277

F a v r e , T.L.F.

Brouard, R.

343

F e r r u t i , P.

305 43 1

Brunel , D.

573

Figueras, F .

Bucsi, I .

549

F

F i n i e l s , A. F l e c h e , G.

C Calais, C.

Fleischer, 6.

Campelo, J.M.

277 269

Forquy, C .

Candy, J . P .

137

F o u i l l o u x , P.

Forni, L.

58 1 565 23 1 487 367 277,343 245

Fuentes Mota, J. F u n f s c h i l l ing, P.C.

445 413

G

G a i z i , 2. G a l l e z o t , P. Gancet, C.

J Jacobs, P . A .

395

J a n a t i - I d r i s s i , F.

193

J a l e t t , H.P.

343 145,231

Jgrgensen, K.A.

Garcia, A.

93 269

G a r c i a , H.

557

G a r c i a Gomez, M.

445

K

Gargano, M.

161 177

K a l l o , D.

Garland, M. Geneste, P. Gigante, B. Ghorbel, A. G i u f f r g , L. G l i r f s k i , M. Gbbolos, S. Gomez, R .

121,565,573 209 455 43 1 169 313,335

177

Jenck, J.

1,329 377 479 113,329

J o s h i , G.W. J o u c l a , M.

523 253

Kaspar, J. K i e f f e r , R. Kiennemann, A. K i j e n ' s k i , J.

237 237 169 215

K u s t e r , B.F.

L

185

L a c r o i x , M.

G r a z i a n i , M.

253

Lahanas, K.M.

129

G r e e n f i e l d , H.

351 329

Lamy, C . Lansink R o t g e r i n k , H.G.J.

463 413

Lasperas, M.

565 129

G r e n o u i l l e t , P. Guardeco, R. Gubelmann, M. Guisnet, M. G u t i e r r e z , E.

269 471,513 513 539

H Hamar-Thibault, S. Hegedus, M. Herrmann, J.M. Herskowitz, M. Hindermann, J.P. Hodnett, B.K. Hubaut, R. Huser, H.

113 313,335 405 105 237 437,531 287 463

121,277

Lay, Y.M. Lee, C.W.

589 495

Lee, J.S.

495

L a s z l o , P.

Lee, S . M .

495

Leger, J .M.

463

Lobo, A.M.

209

Luna, D .

269

M M a l t h a , A. Malz, R.E.,

305 Jr.

M a r c e l o - C u r t o , M.J. Marg i t f a l v i, J. L.

I I b o r r a , S.

Margot, E.

557

Marichez, F .

351 209 313,335 295 565

599

Marinas, J .M. Marion, Ph.

269

Perot , G.

329

P i c h a t , P.

513 405

Ma rrak c hi, H. M a r t i n Aranda, R.M.

277 503

Ponec, V. Popa, J .M.

305 471

Masson, J .

245 43 1

P o u i l l o u x , Y. Prabhakar, S.

513 209

Pradera Adrian, M.A.

445

P r a d i e r , C.M.

295

Primo, J.

557

Mazzochia, C . McCullagh, E. McMonagle, J.B.

437 437,531

Menezo, J.C. M i g l i o , R.

223 367

M i h a l y i , R.M. Molnbr, A.

523 549

Montassier, C .

223 121

Moreau, C . Moreau, P. Moukolo, 3.

565,573 2 23

Q Q u a t r a r o , V.P

161

R Rajadhyaksha, R.A. Ranucci, R .

479 43 1

Mu, W. M u l l e r , M.

405 73

Ravasio, N. Reith, W.

161 487

M u l l e r , P. Murghani, S.

237 169

Rimmelin, P. Rosas, N.

231 185

Rossi, M. Ruiz-Hit zky, E .

539

Rusek, M. Ryczkowski, J.

359 335

N Naja, J. Navio, J.A. Neves, I . Notheisz, F.

223 445 513 153

S Saenz, C . Sal ome, J P.

.

0 Oh, J.S.

161

121 23 1

O’Leary, S.T

495 129

Sanchez, F. Scherrer, W .

321

011 i v i e r , J.

201

Sheldon, R.A.

33

Ostgard, 0.

153

Siegel, S.

21

Oukaci, R.

145

Smith, G.V. Smith, K.

153 55

Sol o f o , 3.

573

P

Pard ill o s , J.

581

Park, K.H. Parton, R.F.

495 395

T Ta’las,

Penn, G.

413

Tempesti, E.

E.

503

313,335 431

600

T i r e l , P.J.

47 1

W

Tkatchenko, I .

263

Waghray, A.

145

T r o v a r e l l i, A.

253

Widdecke, H.

487

W i l l i a m s , D.J.

209

Wigniewski, R.

169

U Uytterhoeven, L.

395

Z V

Zamoner, F .

253

Valyon, J.

523

Zine, S .

455

Van Bekkum, H.

385

Zsigmond, A . G .

153

Van d e r Baan, H.S

215

Zuur, A . P .

305

Van d e r Poel , W.

385

Vidal, S .

193

Vinke, P.

385

601

INDEX

SUBJECT

A Acyl a t i o n

Esterification

93,503,557

503,513,557

A1 k y l a t i o n o f

F

- , 2 - e t h y l a n i l ine

523

F r i e s rearrangement

513

N-alkylation o f -,amines w i t h ketones

351

H

-,anilines

359

Halogenation

Amination o f

55

Hydration o f

- , a c i d s and e s t e r s

343

- , a l k y n e s and n i t r i l e s

565

- ,acetone

335

Hydrodechl o r i n a t i o n

313

6 Beckmann rearrangement

531,539

Bromine a d d i t i o n t o alkenes

55

Hydrodeoxygenat ion

287

Hydrodesul f u r a t i o n

201

Hydrogen t r a n s f e r

161,169,253

Hydrogenation o f -,acetophenone

C Carbonyl a t i o n o f a1 l y l e t h e r s 263 C h i r a l sol i d s

73

Claisen-Schmidt condensation 557 Clays

55,471

- ,k a o l i n

589

-,montmorillonite -

539,589

, p i 11 ared

581

-,redox p i l l a r e d Condensation

33 495,503

245

- ,a1 kenes -,benzaldehyde -,butyned i o l - ,carvone - ,c h 1o r o n i t roaromat i c s - ,c i t r a l

21 105 269 185 121,321 137,193

-,glucose -

23 1

,a-ketoesters

177

- ,n itr i l e s

113,329

-,nitrocompounds

169

Conversion o f p o l y o l s

223

-,oxiranes

153

Cycl i z a t i o n o f dienes

129

-,resin acid derivatives

209

- ,s t e r o i d s

161

D Deactivation

- , u n s a t u r a t e d a1 dehydes 231,581

D e h y d r a t i o n o f amides

137,145,193,295

479

-,unsaturated ethers

277

Hydrogen01ys i s o f saccharose 237

Dehydrogenation o f

mass t r a n s f e r i n

- ,t e t r a h y d r o t h i o p h e n e

287 1,105,177

Hydrolysis

93

E E lectrocatalys i s

463

Enant i o s e l e c t i v e c a t a l y s i s

I I o n exchange r e s i n s

73,93,177 Enzyme Epoxidat ion

93 377,431

55,215,487,495 Isomerization o f - ,epox i d e

573

602

-,halobenzene

58 1

-,Ru/zeol i t e

145

,la c t o s e -,oxiranes

215

M o ( V 1 ) - g r a f t e d polymers

43 1

153,549

-,O-pinene

201

-,unsaturated ethers

287

-

Model r e a c t i o n s

21

N N i t r a t i o n o f aromatics

L

55,471,589

Label 1 i n g s t u d i e s

377,549

M

N i t r o x i d a t i o n o f p-xylene

455

0

Mechanisms

33,73,129,329,367,377

Organometallic r e a c t i o n s

129

Oxidation o f Metal c a t a l y s t s -

,Cu/A12O3

161

-,Cu, modi ied -

269,343

,I r/C

385

-,Ni -

21,269

,Ni/A1 PO4

-,Ni,

269

amid ne m o d i f i e d

- ,N i 1-xMox - ,Pd/A12O3 -

32 1

- ,a1 coho1 s

385

-,glyoxal

463

-,hydrocarbons

395,405,423,445

-,methyl e t h y l k e t o n e

437

O x i d a t i v e d e h y d r o g e n a t i o n 33,413 Oxide c a t a l y s t s Oxides o f

193

-,Ag

377

129,313,385

- ,A1

541,549

,Pd/C

- , Pd, unsupported - ,Pt/A12O3 - ,P t / C -,Pt,

cinchona m o d i f i e d

-,Pt,

polycrystall ine

263,385

-,B

53 1

129,385

-,Cr-A1

455

385

- ,cu

413

385

-,Cu-Cr

287

- ,Fe

523

73,177 295

- ,Ge

523

153

-,Mg

169,253

promoted

359

-,Mn

305

unsupported

209 223

- ,Mo - ,P t

423

-,Raney Cu, m o d i f i e d

- ,Pt/Si02 -,Pt/Si02,

-,Pt/Rh, - ,Raney

Ni

113,231,245,329

-,Raney N i , C r and Mo m o d i f i e d 113,231 -,Raney N i , Sn m o d i f i e d -

,Rh/A12O3

,Rh/C - ,Rh/Mg0

385

-

-,Rh/SiO2, -

,Ru/C

335 129,385

-,Si

55

-,Ti

405,445

-,v-P

137 237,385

437

- ,W

549

-,Zn

549

Poly-alumazane, as a s u p p o r t

185 Sn m o d i f i e d

463

385 Oxygen t r a n s f e r

33

603

P

Photocatalytic oxidation 405,445 Polyfunctional catalysis 367,487 Potential measurement 321

Synthesis of -,isosorbide -,pyrazines

R

W

Reactors, triphas ic 1,105 Reduction o f -,nitro to nitroso compounds 305 - ,enones 253

Witt ig olef inat ion

S Sol vent effects

193,245,495

Steric effects 351,359 Structure-react ivity 21,581 Sulphur removal from terpenes 201 Sulphated zirconia 479 Sulphided catalysts 121,201,277,351

Superacid sol ids 479 Surface organometallic chemistry 137

223 367

589

Z

Zeol ites 55,539,565 - ,1 arge pore zeol i tes 503,557 -,offretite 573 -,protonic zeolites 513,581 -,redox zeol ites 33 - , V P I 5 , iron phthallocyanines encaged in 395

- ,Y

513,573

-,Y, iron phthallocyanines encaged in 395 - ,ZSM5 513,573


605

STUDIES IN SURFACE SCIENCE AND CATALYSIS Advisory Editors: B. Delmon, Universite Catholique de Louvain, Louvain-la-Neuve, Belgium J.T. Yates, University of Pittsburgh, Pittsburgh, PA, U S A .

Volume 1 Preparation of Catalysts I.Scientific Bases for the Preparation of Heterogeneous Catalysts. Proceedings of the First International Symposium, Brussels, October 1417,1975 edited by B. Delmon, P.A. Jacobs and G. Poncelet Volume 2 The Control of the Reactivity of Solids. A Critical Survey of the Factors that Influence the Reactivity of Solids, with Special Emphasis on the Control of the Chemical Processes in Relation t o Practical Applications by V.V. Boldyrev, M. Bulens and B. Delmon Volume 3 Preparation of Catalysts II. Scientific Bases for the Preparation of Heterogeneous Catalysts. Proceedings of the Second International Symposium, Louvain-la-Neuve, September 4-7, 1978 edited by B. Delmon, P. Grange, P. Jacobs and G. Poncelet Volume 4 Growth and Properties of Metal Clusters. Applications t o Catalysis and the Photographic Process. Proceedings of the 32nd International Meeting of the Societe de Chimie Physique, Villeurbanne, September 24-28, 1979 edited by J. Bourdon Volume 5 Catalysis by Zeolites. Proceedings of an International Symposium, Ecully (Lyon), September 9- 1 1, 1980 edited by B. Imelik, C. Naccache, Y. Ben Taarit, J.C. Vedrine, G. Coudurier and H. Praliaud Volume 6 Catalyst Deactivation. Proceedings of an International Symposium, Antwerp, October 13-15,1980 edited by B. Delmon and G.F. Froment Volume 7 New Horizons in Catalysis. Proceedings of the 7th International Congress on Catalysis, Tokyo, June 30-July 4, 1980. Parts A and B edited by T. Seiyama and K. Tanabe Volume 8 Catalysis by Supported Complexes by Yu.1. Yermakov, B.N. Kuznetsov and V.A. Zakharov Volume 9 Physics of Solid Surfaces. Proceedings of a Symposium, Bechytte, September 29October 3, 1980 edited by M. GzniEka Volume 10 Adsorption at the Gas-Solid and Liquid-Solid Interface. Proceedings of an International Symposium, Aix-en-Provence, September 2 1-23, 198 1 edited by J. Rouquerol and K.S.W. Sing Volume 11 Metal-Support and Metal-Additive Effects in Catalysis. Proceedings of an International Symposium, Ecully (Lyon), September 14-1 6, 1982 edited by B. Imelik, C. Naccache, G. Coudurier, H. Praliaud, P. Meriaudeau, P. Gallezot, G.A. Martin and J.C. Vedrine Volume 12 Metal Microstructures in Zeolites. Preparation - Properties - Applications. Proceedings of a Workshop, Bremen, September 22-24, 1982 edited by P.A. Jacobs, N.I. Jaeger, P. Jirir and G. Schulz-Ekloff Volume 13 Adsorption on Metal Surfaces. An Integrated Approach edited by J. Benard Volume 14 Vibrations at Surfaces. Proceedings of the Third International Conference, Asilomar, CA, September 1-4, 1982 edited by C.R. Brundle and H. Morawitz

606 Volume 5 Heterogeneous Catalytic Reactions Involving Molecular Oxygen by G.I. Golodets Volume 6 Preparation of Catalysts Ill. Scientific Bases for the Preparation of Heterogeneous Catalysts. Proceedings of the Third International Symposium, Louvain-la-Neuve, September 6-9, 1982 edited by G. Poncelet, P. Grange and P.A. Jacobs Volume 17 Spillover of Adsorbed Species. Proceedings of an International Symposium, LyonVilleurbanne, September 12-1 6, 1983 edited by G.M. Pajonk, S.J. Teichner and J.E. Germain Volume 18 Structure and Reactivity of Modified Zeolites. Proceedings of an International Conference, Prague, July 9- 13, 1984 edited by P.A. Jacobs, N.I. Jaeger, P. Jirli, V.B. Kazansky and G. Schulz-Ekloff Volume 19 Catalysis on the Energy Scene. Proceedings of the 9th Canadian Symposium on Catalysis, Quebec, P.Q., September 30-October 3, 1984 edited by S.Kaliaguine and A. Mahay Volume 2 0 Catalysis by Acids and Bases. Proceedings of an International Symposium, Villeurbanne (Lyon), September 25-27, 1984 edited by B. Imelik, C. Naccache, G. Coudurier, Y. Ben Taarit and J.C. Vedrine Volume 2 1 Adsorption and Catalysis on Oxide Surfaces. Proceedings of a Symposium, Uxbridge, June 28-29, 1984 edited by M. Che and G.C. Bond Volume 22 Unsteady Processes i n Catalytic Reactors by YuSh. Matros Volume 23 Physics of Solid Surfaces 1984 edited by J. Koukal Volume 2 4 Zeolites: Synthesis, Structure, Technology and Application. Proceedings of an International Symposium, Portoroi-Portorose, September 3-8, 1984 edited by B. Driaj, S.HoEevar and S.Pejovnik Volume 25 Catalytic Polymerization of Olefins. Proceedings of the International Symposium on Future Aspects of Olefin Polymerization, Tokyo, July 4-6, 1985 edited by T. Keii and K. Soga Volume 26 Vibrations a t Surfaces 1985. Proceedings of the Fourth International Conference, Bowness-on-windermere, September 15- 19, 1985 edited by D.A. King, N.V. Richardson and S.Holloway Volume 27 Catalytic Hydrogenation edited by L. Cervenp Volume 28 New Developments in Zeolite Science and Technology. Proceedings of the 7th International Zeolite Conference, Tokyo, August 17-22, 1986 edited by Y. Murakami, A. lijima and J.W. Ward Volume 29 Metal Clusters in Catalysis edited by B.C. Gates, L. Guczi and H. Knozinger Volume 3 0 Catalysis and Automotive Pollution Control. Proceedings of the First International Symposium, Brussels, September 8-1 1, 1986 edited by A. Crucq and A. Frennet Volume 31 Preparation of Catalysts IV. Scientific Bases for the Preparation of Heterogeneous Catalysts. Proceedings of the Fourth International Symposium, Louvain-la-Neuve, September 1-4, 1986 edited by 6 . Delmon, P. Grange, P.A. Jacobs and G. Poncelet Volume 3 2 Thin Metal Films and Gas Chemisorption edited by P. Wissmann Volume 33 Synthesis of High-silica Aluminosilicate Zeolites by P.A. Jacobs and J.A. Martens Volume 3 4 Catalyst Deactivation 1987. Proceedings of the 4th International Symposium, Antwerp, September 29-October 1, 1987 edited by B. Delmon and G.F. Froment

607 Volume 35 Keynotes in Energy-Related Catalysis edited by S. Kaliaguine Volume 36 Methane Conversion. Proceedings of a Symposium on the Production of Fuels and Chemicals from Natural Gas, Auckland, April 27-30, 1987 edited by D.M. Bibby, C.D. Chang, R.F. Howe and S. Yurchak Volume 37 Innovation in Zeolite Materials Science. Proceedings of an International Symposium, Nieuwpoort, September 13-1 7, 1987 edited by P.J. Grobet, W.J. Mortier, E.F. Vansant and G. Schulz-Ekloff Volume 38 Catalysis 1987. Proceedingsof the 10th North American Meeting of the Catalysis Society, San Diego, CA, May 17-22, 1987 edited by J.W. Ward Volume 39 Characterization of Porous Solids. Proceedings of the IUPAC Symposium (COPS I), Bad Soden a. Ts., April 26-29, 1987 edited by K.K. Unger, J. Rouquerol, K.S.W. Sing and H. Kral Volume 40 Physics of Solid Surfaces 1987. Proceedings of the Fourth Symposium on Surface Physics, Bechyne Castle, September 7-1 1, 1987 edited by J. Koukal Volume 4 1 Heterogeneous Catalysis and Fine Chemicals. Proceedings of an International Symposium, Poitiers, March 15-1 7, 1988 edited by M. Guisnet, J. Barrault, C. Bouchoule, D. Duprez, C. Montassier and G. Perot Volume 42 Laboratory Studies of Heterogeneous Catalytic Processes by E.G. Christoffel, revised and edited by 2. Paal Volume 43 Catalytic Processes under Unsteady-State Conditions by Yu. Sh. Matros Volume 44 Successful Design of Catalysts. Future Requirementsand Development. Proceedingsof the Worldwide Catalysis Seminars, July, 1988, on the Occasion of the 30th Anniversary of the Catalysis Society of Japan edited by T. lnui Volume 45 Transition Metal Oxides. Surface Chemistry and Catalysis by H.H. Kung Volume 46 Zeolites as Catalysts, Sorbents and Detergent Builders. Applications and Innovations. Proceedings of an InternationalSymposium, Wurzburg, September 4-8, 1988 edited by H.G. Karge and J. Weitkamp Volume 47 Photochemistry on Solid Surfaces edited by M. Anpo and T. Matsuura Volume 48 Structure and Reactivity of Surfaces. Proceedings of a European Conference, Trieste, September 13-16, 1988 edited by C. Morterra, A. Zecchina and G. Costa Volume 49 Zeolites: Facts, Figures, Future. Proceedings of the 8th InternationalZeolite Conference, Amsterdam, July 10-14, 1989. Parts A and B edited by P.A. Jacobs and R.A. van Santen Volume 50 Hydrotreating Catalysts. Preparation, Characterizationand Performance. Proceedingsof the Annual InternationalAlChE Meeting, Washington, DC, November 27-December 2,1988 edited by M.L. Occelli and R.G. Anthony Volume 5 1 New Solid Acids and Bases. Their Catalytic Properties by K. Tanabe, M. Misono, Y. Ono and H. Hattori Volume 52 Recent Advances in Zeolite Science. Proceedings of the 1989 Meeting of the British Zeolite Association, Cambridge, April 17-1 9, 1989 edited by J. Klinowski and P.J. Barrie Volume 53 Catalyst in Petroleum Refining 1989. Proceedings of the First International Conference on Catalysts in Petroleum Refining, Kuwait, March 5-8, 1989 edited by D.L. Trimrn, S.Akashah, M. Absi-Halabi and A. Bishara

608 Volume 54 Future Opportunities i n Catalytic and Separation Technology edited by M. Misono, Y. Moro-oka and S. Kimura Volume 55 New Developments in Selective Oxidation. Proceedings of an International Symposium, Rimini, Italy, September 18-22, 1989 edited by G. Centi and F. Trifiro Volume 56 Olefin Polymerization Catalysts. Proceedings of the International Symposium on Recent Developments in Olefin PolymerizationCatalysts, Tokyo, October 23-25, 1989 edited by T. Kelli and K. Soga Volume 57A Spectroscopic Analysis of Heterogeneous Catalysts. Part A: Methods of Surface Analysis edited by J.L.G. Fierro Volume 578 Spectroscopic Analysis of Heterogeneous Catalysts. Part B: Chemisorption of Probe Molecules edited by J.L.G. Fierro Volume 58 Introduction t o Zeolite Science and Practice edited by H. van Bekkum, E.M. Flanigen and J.C. Jansen Volume 59 Heterogeneous Catalysis and Fine Chemicals II. Proceedings of the 2nd InternationalSymposium, Poitiers, October 2-5, 1990 edited by M. Guisnet, J. Barrault, C. Bouchoule, D. Duprez, G. Perot, R. Maurel and C. Montassier Volume 60 Chemistry of Microporous Crystals. Proceedings of the International Symposium on Chemistry of Microporous Crystals, Tokyo, June 26-29, 1990 edited by T. Inui, S. Namba and T. Tatsumi Volume 6 1 Natural Gas Conversion. Proceedings of the Natural Gas Conversion Symposium, Oslo, August 12- 17, 1990 edited by A. Holmen, K.-J. Jens and S. Kolboe Volume 62 Characterization of Porous Solids II.Proceedings of the IUPAC Symposium (COPS 11). Alicante, May 6-9, 1990 edited by F. Rodriguez-Reinoso,J. Rouquerol, K.S.W. Sing and K.K. Unger Volume 63 Preparation of Catalysts V. Proceedings of the Fifth International Symposium on the Scientific Bases for the Preparation of HeterogeneousCatalysts, Louvain-laNeuve, September 3-6, 1990 edited by G. Poncelet, P.A. Jacobs, P. Grange and B. Delmon

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