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ADVANCES IN CHEMISTRY RESEARCH

ADVANCES IN CHEMISTRY RESEARCH VOLUME 8 No part of this digital document may be reproduced, stored in a retrieval system or transmitted in any form or by any means. The publisher has taken reasonable care in the preparation of this digital document, but makes no expressed or implied warranty of any kind and assumes no responsibility for any errors or omissions. No liability is assumed for incidental or consequential damages in connection with or arising out of information contained herein. This digital document is sold with the clear understanding that the publisher is not engaged in rendering legal, medical or any other professional services.

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ADVANCES IN CHEMISTRY RESEARCH

ADVANCES IN CHEMISTRY RESEARCH VOLUME 8

JAMES C. TAYLOR EDITOR

Nova Science Publishers, Inc. New York

Copyright ©2011 by Nova Science Publishers, Inc. All rights reserved. No part of this book may be reproduced, stored in a retrieval system or transmitted in any form or by any means: electronic, electrostatic, magnetic, tape, mechanical photocopying, recording or otherwise without the written permission of the Publisher. For permission to use material from this book please contact us: Telephone 631-231-7269; Fax 631-231-8175 Web Site: http://www.novapublishers.com

NOTICE TO THE READER The Publisher has taken reasonable care in the preparation of this book, but makes no expressed or implied warranty of any kind and assumes no responsibility for any errors or omissions. No liability is assumed for incidental or consequential damages in connection with or arising out of information contained in this book. The Publisher shall not be liable for any special, consequential, or exemplary damages resulting, in whole or in part, from the readers’ use of, or reliance upon, this material. Any parts of this book based on government reports are so indicated and copyright is claimed for those parts to the extent applicable to compilations of such works. Independent verification should be sought for any data, advice or recommendations contained in this book. In addition, no responsibility is assumed by the publisher for any injury and/or damage to persons or property arising from any methods, products, instructions, ideas or otherwise contained in this publication. This publication is designed to provide accurate and authoritative information with regard to the subject matter covered herein. It is sold with the clear understanding that the Publisher is not engaged in rendering legal or any other professional services. If legal or any other expert assistance is required, the services of a competent person should be sought. FROM A DECLARATION OF PARTICIPANTS JOINTLY ADOPTED BY A COMMITTEE OF THE AMERICAN BAR ASSOCIATION AND A COMMITTEE OF PUBLISHERS. Additional color graphics may be available in the e-book version of this book.

LIBRARY OF CONGRESS CATALOGING-IN-PUBLICATION DATA ISSN: 1940-0950 ISBN: 978-1-61324-936-9 (eBook)

Published by Nova Science Publishers, Inc. © New York

CONTENTS Preface

vii

Chapter 1

Association Nature of Dyes Chromaticity Yu. A. Mikheev, L. N. Guseva, Yu. A. Ershov andG. E. Zaikov

Chapter 2

Thermal Bhaviour and Enthalpy Relaxation in Aromatic Polycarbonate and Syndiotactic Poly(Methyl-Methacrylate) Maurizio Penco, Stefania Della Sciucca, Gloria Spagnoli and Luca Di Landro

Chapter 3

Chapter 4

About Geometrical and Electronic of the Structure of Molecular Insectitsid DDT (Nobel Award 1948, P. Muller) V. A. Babkin, V. U. Dmitriev and G. E. Zaikov Parameters of the Combustion of Differential Propellant in Mixture of Oxidants: Molecular Oxygen-Ozone V. A. Babkin, K. V. Sergeeva, E. S. Titova and G. E. Zaikov

Chapter 5

Cobaloximes with Functionalized Ligands Alexei A. Gridnev, Dmitry B. Gorbunov and Gregory A. Nikiforov

Chapter 6

The Tacticity Governed Stereomicrostructure in Poly(Methyl Methacrylate) (PMMA) as a Way to Explain its Physical Properties N. Guarrotxena

Chapter 7

The Modeling of Transition Metal Complex Catalysts in the Selective Alkylarens Oxidations with Dioxygen: The Role of Hydrogen – Bonding Interactions L. I. Matienko, L. A. Mosolova and G. E. Zaikov

1

29

47

51

55

67

75

vi Chapter 8

Chapter 9

Chapter 10

Chapter 11

Index

Contents New Carbofunctional Oligoisiloxanes for the Substrates of Antibiocorrosive Covers N. Lekishvili, Sh. Samakashvili, G. Lekishvili and Z. Pachulia Performance, Stability and Qualification of Developed Multifunctional Materials Jon Meegan, Mogon Patel, Anthony C. Swain, Jenny L. Cunningham, Paul R. Morrell and Julian J. Murphy

115

129

Molybdenum-Initiated Ring Opening Metathesis Polymerization of Noborn-5-ene-2-yl Acetate Solmaz Karabulut

145

The Co-Occurrence of Carrageenan and Agaran Structures in Red Seaweeds Marina Ciancia and Alberto S. Cerezo

155 193

PREFACE This book presents original research results on the leading edge of chemistry research. Each article has been carefully selected in an attempt to present substantial research results across a broad spectrum. Topics discussed include thermal behaviour and enthalpy relaxation in aromatic polycarbonate; cobalozimes with functionalized ligands; parameters of the combustion of differential propellant in mixture of oxidants and the modeling of transition metal complex catalysts. Chapter 1 - In the range of waves lengths 200-800 nm are studied absorption electronic spectra of individual molecules of triphenilmethane, xanthene and thiazene dyes. In triphenilmethane a number are studied the malachite green, crystal violet, diamond green and methyl violet. In xanthene number are studied rodamine B and rodamine G; in thiazene a number - methylene blue. Molecular solutions of dyes prepared by heptane extraction from commercial powders, and also by thermal processing of triacetate cellulose and the cellophane films, painted by these dyes. It is established, that individual molecules of dyes do not absorb light in visible range of a spectrum, i.e. have no chromogene groups. From here follows, that usually observable chromaticity of dyes is caused by supramolecular structures dimers and larger dyes molecules associates at mutual orientation favorable for molecular interaction. From here follows, that existing quantum-chemical theories of chromaticity of the studied dyes classes are incorrect and demand revision. Chapter 2 - The structural relaxation of polymers depends on the kinetic character of the glass-transition phenomenon: amorphous polymers below their Tg are not at equilibrium and their structures continuously relax in attempt to reach the equilibrium state. Several phenomenological and molecular approaches have been proposed to describe the structural relaxation but a universal model is still lacking. The enthalpy relaxation of glasses is usually described with models developed on the basis of Tool-Narayanaswamy-Moynihan (TNM) theory [1,2]: it is assumed that the instantaneous relaxation time(s) (τ) for enthalpy relaxation depends on both the temperature (T) and the structure of the glass, identified by its fictive temperature (Tf). This approach is able to describe the enthalpy relaxation in low-molecularweight glass-forming system fairly well [3,4], but discrepancies have been observed in several polymeric systems [5,6]. One of these discrepancies concerns the overestimation of enthalpy lost on aging the samples for long periods of time. Hodge [7], Gomez Ribellez [8] and Cowie [9] ascribed this features in polymers to the effect of topological constraints, such as chain entanglements, which are completely ignored in the TNM-based models.

viii

James C. Taylor

In this work, the enthalpy relaxation of aromatic polycarbonates and of syndiotactic poly(methyl methacrylate)s (PMMA) are investigated performing DSC experiments with the intention of characterize the effect of the composition and of the molar mass in aromatic polycarbonates and the relaxation dynamic as a function of the molecular mass and to highlight the effect of PMMA entanglement mass (Me) in syndiotactic poly(methyl methacrylate)s (PMMA). Chapter 3 - Quantum-chemical calculation of molecular of insectitsid DDT was done by method AB INITIO in base 6-311G**. Optimized by all parameters geometric and electronic structures of these compound was received. The universal factor of acidity was calculated (pKa=26.5). Molecular of insectitsid DDT pertain to class of very weak Н-acids (рКа>14). Chapter 4 - Calculation of the mixture of oxidants of differential propellant (molecular oxygen – ozone) was made by classical quantum-chemical semitheoretical method CNDO/2 in parametrization of Santri-Poppl-Segal. Optimized geometric and electronic structure of the combination of these oxidants was received. Parameters of the combustion of this mixture were evaluated. Parameters of the combustion of mixture of oxidants (O2+O3) practically do not differ from parameter of the combustion of the molecular oxygen. Chapter 5 - Cobaloximes, alkylcobaloximes and borofluoride adducts on the basis of asymmetric functionalized ligandes have been synthesized. These cobaloxime systems form geometric isomers. The presence of chiral center in axial ligand gives rise to the appearance of diastereotopics effect. Chapter 6 - Three industrial samples of Poly(methyl methacrylate) (PMMA), prepared under different conditions, have been extensively analyzed by means of 1H-NMR spectroscopy. Starting from the mm, rr and mrandrm triad contents, as given by the spectra, the type of tacticity statistics distribution has been deduced. Sample X appears to be completely Bernoullian, while samples Y and Z deviate somewhat from this behaviour exhibiting a tiny trend towards Markovian statistics. The fraction of mmrm and rrrm pentads and that of pure heterotactic and atactic triad moieties has been calculated by assuming either a Markovian statistics for samples Y and Z or a Bernoullian statistics for all the samples. On the other hand, the fraction of the same pentads has been determined by deconvoluting the overall triad signals of the spectra into the corresponding pentad signals. An appreciably good agreement with the values obtained assuming Bernoullian statistics for all the samples appears evident. As a result, the evolution of every pentad content from sample X to Sample Z could be stated. Thus the samples prove to be appropriate models to study the relationship between any physical property and the stereomicrostructure of PMMA as was done previously for Poly(vinyl chloride) (PVC) and Polypropylene (PP). Chapter 7 - The different methods of improvement of catalytic activity of transition metal complexes in the oxidations of alkylarens with molecular oxygen are stated briefly. The offered at first by authors and developed in their works the method of control of catalyst activity of transition metal complexes with additives of electron-donor mono- or multidentate exo ligands L2 in the oxidations of alkylarens (ethylbenzene, cumene) with molecular oxygen into corresponding hydroperoxides is presented. The modeling of catalytic nickel and iron complexes with use of ammonium quaternary salts and macro-cycle polyethers as exo ligands-modifiers is described in detail. The role of the Hydrogen–Bonding interactions in mechanisms of homogeneous catalysis is discussed. The modeling of catalyst activity of complexes Fe(II,III)(acac)n with R4NBr (or 18-crown-6) (18C6) in the ethylbenzene oxidation in the presence of small amounts additives of water (~10-3 mol/l) is analyzed. The role of

Preface

ix

micro steps of the chain initiation (O2 activation), and propagation in the presence of catalyst (Cat + RO2•→) in the mechanism of nickel- and iron-catalyzed oxidation of ethylbenzene is evaluated. Chapter 8 - New carbofunctional oligoisiloxanes containing trifluorinepropil and methacrylic groups at silicon atoms have been synthesized and studied. On the basis of the data of IR and NMR spectral analysis the process of hydrosilylatrion, composition and structure of synthesized compounds have been investigated. By using of diferential-thermal and thermogravimetric analisis method the thermal stability of sintesized oligomers have been studied. By the diferential-scanning calomerty method the phase transition temperatures of synthesized oligomers were determined. It was established that synthesized oligomers are amorphic one-phase systems. The preliminary ivestigation showd that the sybthesized carbofunctional oligomers in combination with polyepoxides and non-volatile bioactive organo-ellement arsenic complex compounds new composite materials of multifunctional application for individual and environmental protection of various materials may be created. Chapter 9 - In this article we will review the design, formulation and development of materials exhibiting simplified structure / property relationships, reversible cure mechanisms, increased resistance to physical property changes over time and stress sensitive behaviours. These properties are discussed within the context of the external literature. The article also provides a brief overview of the processes employed by AWE to qualify materials and further understand their storage, ageing and compatibility properties. Chapter 10 - MoCl5-e−-Al-CH2Cl2 catalyst system can efficiently polymerize noborn-5ene-2-yl acetate in moderate yields and in relatively high molecular weights. The analyses of the product by FTIR, 1H NMR and 13C NMR spectra give the verification of metathetical polymers. The polymer shows narrow molecular weight distribution and good solubility in common organic solvents. Chapter 11 - In the last seventeen years it has been shown that red seaweeds classified as “carrageenophytes” also biosynthesize agaran structures, while certain “agarophytes” produce small amounts carrageenan structures. No neat separation of these carrageenan/agaran systems was obtained, leading to the idea of “hybrid” molecules, called DL-hybrid galactans. Several points concerning these polysaccharide systems have been addressed: 1. Description of the systems of galactans, in which carrageenan and agaran structures were found (DL-galactan systems), as well as the methodology necessary for their detection. 2. Isolation of “pure” carrageenans or agarans from these systems using nondegrading conditions and the consequent new hypothesis of the formation of molecular complexes. 3. Evidences favoring each hypothesis, namely, the existence of hybrid molecules versus molecular complexes formation. Versions of these chapters were also published in Polymers Research Journal, Volume 3, Numbers 1-4, edited by Frank Columbus, published by Nova Science Publishers, Inc. They were submitted for appropriate modifications in an effort to encourage wider dissemination of research.

In: Advances in Chemistry Research. Volume 8 Editor: James C. Taylor

ISBN 978-1-61209-089-4 ©2011 Nova Science Publishers, Inc.

Chapter 1

ASSOCIATION NATUREOF DYES CHROMATICITY Yu. A. Mikheev1, L. N. Guseva1, Yu. A. Ershov2 and G. E. Zaikov* 1

N.M. Emanuel Institute of Biochemical Physics, Russian Academy of Sciences, 4 Kosygin str., 119334 Moscow, Russia 2 N.E. Bauman Moscow State Technical University, 2-rd Baumanskaya str. 5, 105005 Moscow, Russia

ABSTRACT In the range of waves lengths 200-800 nm are studied absorption electronic spectra of individual molecules of triphenilmethane, xanthene and thiazene dyes. In triphenilmethane a number are studied the malachite green, crystal violet, diamond green and methyl violet. In xanthene number are studied rodamine B and rodamine G; in thiazene a number - methylene blue. Molecular solutions of dyes prepared by heptane extraction from commercial powders, and also by thermal processing of triacetate cellulose and the cellophane films, painted by these dyes. It is established, that individual molecules of dyes do not absorb light in visible range of a spectrum, i.e. have no chromogene groups. From here follows, that usually observable chromaticity of dyes is caused by supramolecular structures - dimers and larger dyes molecules associates at mutual orientation favorable for molecular interaction. From here follows, that existing quantum-chemical theories of chromaticity of the studied dyes classes are incorrect and demand revision.

Keywords: nature of dyes, electronic spectra, supramolecular structures, quantumchemical calculations, chromaticity.

*

E-mail: [email protected]

2

Yu. A. Mikheev, L. N. Guseva, Yu. A. Ershov et al.

The big number of the works devoted to the nature of organic compounds chromaticity is published. Interest to a chromaticity problem is connected with requirements of development of technology of dyeing, and also with problems of photochemistry and sciences about photoconductivity and transformation of a solar energy to electricity [1-9]. All works devoted to the nature of organic compounds chromaticity, are based till now on achievements of quantum chemistry of individual molecules (see [1-4] and Internet search systems sites, for example, www.scirus.com). Thus the term «chromogene», used for a designation of the molecular structure which are giving rise to coloring, connect exclusively with the individual molecules. These possessing enough developed conjugated π-bonds system, and the term «chromophore» designates various chemical groups which are under construction chromogene [4]. However, in works [10, 11] at copper phtalocyanine research (a pigment of dark blue color) the important fact has been established, that chromogene of this dye are individual molecules, but supramolecular dimers and larger molecular associates are not. In these works applied extraction molecules of dye from powders by means of polymeric films (polyethylene, cellulose triacetate) and heptane. This method allows separating single molecules from pigment particles. It is established, that commercial copper phtalocyanine powders contain a cmall amount of an amorphous phase, heptane soluble. As a result did received solutions of individual molecules possess a characteristic spectrum with the developed system of electronic-oscillatory bands. These bands are in ultra-violet area, i.e. individual molecules do not absorb visible light and do not form the painted solutions. From here follows, that color of the given dye arises only as a result of compound of molecules in supramolecular dimers and larger associates. In the given work individual molecules of cation triphenilmethane, xanthene and thiazene classes dyes are releaseed by extraction and thermal processing. It has appeared, that, as well as in a case copper phtalocyanine, chromogenes of this dyes type are not individual molecules, and their supramolecular dimers and larger associates are chromogene. From the received results the urgency of working out of quantum chemistry methods follows with reference to supramolecular structures of dyes.

EXPERIMENTAL In this work used commercial powders of triphenilmethane (TPMD), xanthene (XD) and thiazene (TD) dyes (Shostkinsky chemical reactants plant). Are studied TPMD - malachite green (MG), crystal violet (CV), methyl violet (MV) and diamond green (DG) (in the form of 1% spirit solution). Are studied also XD – rodamins B and G, and representative of– methylene blue (MB). Molecules of the listed dyes contain developed positively charged π-systems and oxalateor chlorine anions. Extraction of MG, CV and MV molecules from powders carried out by spectroscopic pure heptane on a water bath. Extraction of DG and rodamine B molecules carried out from their spirit solutions at 25º C. To notice, that chromogene molecular associates of the studied dyes not soluted in heptane.

Association Nature of Dyes Chromaticity

3

For preparation of a rodamine B heptane molecular solution ~1mg dye sample dissolved in ethanol (2 ml), added heptane (4 ml). Then the received mix diluted with water. Water action consists, first, in heptane miscibility decrease with spirit, secondly, in heptane extraction strengthening of dye molecules from an aqueous-alcoholic layer. Heptane processing of rodamins and MG powders does not lead to formation of molecular solutions. Thus rodamine and the MG molecules was not possible extract as well from their specially prepared spirit solutions. Extraction subjected also solutions of immonium hydroxides TPMD which prepared, mixing powders or their spirit solutions with water solutions of alkali KOH (2-5%). Used also release ion of molecular fractions of dyes by absorption from aqueousalcoholic solutions of dyes by triacetate cellulose (TAC) films. Solutions of dyes for extraction prepared, mixing their spirit solutions (~10 mg in 10 ml of ethanol) with the distilled water (~10 ml). Influence of heating on electronic spectra of TAC and the cellophane films, containing XD and MG is studied. XD entered into TAC films (20 microns) from solutions in the mixed solvent (9 parts of chloroform on one part of ethanol), evaporating solvent in Petri dishes. XD and MG entered also into cellophane films (a thickness 40 microns) by absorption from aqueous-alcoholic solutions. For this purpose mixed solutions of dye of 3 mg in 1 ml of ethanol about 20 ml of the distilled water. As a result dyes concentration in films exceeded concentration in water approximately in 100 times. Solutions and films spectra registered on “Specord UV-VIS” and “Shimadzu UVmini1240” spectrophotometers.

DISCUSSION OF RESULTS Spectral Properties of Individual and Aggregated Cationic Triphenilmethane Dyes (TPMD) The Chromogene Nature of the Malachite Green TPMD molecules studied comprise grouping with developed π-system and a fragment with the chinoid structure bearing a positive charge on atom of nitrogen (immonium cation). Consider [1-4] what exactly such molecular structure serves as the reason of occurrence of coloring, i.e. is chromogene. The immonium cation structural formula of TPMD looks like:

4

Yu. A. Mikheev, M L. N. N Guseva, Yuu. A. Ershov ett al.

Here R = СН С 3 and R ' = H (MG); R = СН3 and R ' = N (CH3) 2 (C CV); R = С2H5 and a R ' = H (D DG); R = CH3 and R ' =NH (CH ( 3) (MV). TPMD anions are Cl - inn molecules CV C and MV, and a oxalate-annions Ox- in MG M and DG m molecules. Thu us MG and DG D moleculess include two organic imm monium cationns and two am mmonium catiions [12]. For example, MG formuula looks like (Ox–N+H(C CH3)2–Рh'–С(Р Рh)=Рħ=N+–OCO–) O 2, where Ox - oxaalate-anion, Рhh and Рh' - phenyl and phennylene radicals, Рħ - a cycloohexadiene w frragment of a chinoid radicall. The optical spectrum off a MG - oxalaate ethanol solution (1 molee/l) is resultedd on Figure 1аа, a curve 1. Maxima M spectrral positions (νν, cm-1 (λ, nm m)): 16 200 (617); 23 500 (4225 nm) and 31 600 (316 nm m) of absorptiion band of a MG oxalate ethanol e solutioon correspondd to literary V of the seeeming extinction coefficiennt, calculated for the main absorption daata [1, 13]. Value baand (617 nm) of MG chrom mogene particlees dissolved inn ethanol counnting on conceentration of inndividual arom matic fragmentts (Ar) makes ε617 = 4.4×104 l / (mole.cm)).

(a) Fiigure 1. Continu ued on next pagge.


5

(b) Figure 1. Changes of optical spectra ethanol (a) and heptane (b) solutions of commercial MG oxalate in the presence of KOH (a) and ethanol (b). Explanatory in the text.

On Figure 1а curves 2-4 represent transformation of a spectrum 1 in a MG carbinol leycoform spectrum at addition of alkali KOH in a solution. Curves 2 and 3 characterize change of a spectrum 1 in time (through 40 and 80 mines accordingly) at very low concentration KOH - 8·10-5 mole/l, and 4 - at 3·10-3 mole/l. It is necessary to underline, that for lack of alkali in a MG oxalate ethanol solution (Figure 1а, the curve 1) in a spectrum is not found out any signs of increase in time of an intensive carbinol leycoform band at frequency ν =38000 cm-1. It testifies to stability MG oxalate in ethanol solution. In alkaline environment MG oxalate is hydrolyzed finally with carbinol formation. It is necessary to notice, that MG and CV carbinols for the first time are received in work [14] by processing of these dyes chlorides by weak water solutions of alkalis. Thus MG and CV carbinols were released in the form of deposits, slightly solved in water. Pure carbinols received by recrystallization from heptane or ether, are steady and, contrary to representations of authors of work [13], do not dissociate in ethanol solutions on Ar-cations and hydroxylions [14, 15]. Observed on Figure 1а character of spectral transformation of MG solution under the influence of alkali finds out the step nature of this process. So, already at very low concentration of alkali there is an intensity decrease chromogene bands νmax = 16200 cm-1 of dye to simultaneous increase of a wide band νmax = 38 000 cm-1. Thus on curves 1-3 (Figure 1а) is available an isobiestic point at ν = 35 500 cm-1. From here follows, that at an intermediate stage of hydrolysis intermediate products with identical spectroscopic properties are formed which, however, are not carbinol. For reception of carbinol it is required to increase concentration of alkali. So, at increase in concentration KOH to 3×10-3 mole/l the isobiestic point disappears, and the UV-band arising thus (Figure 1а, a curve 4) an endproduct - carbinol keeps the form of a band of predecessors, but has higher intensity. It is necessary to notice, that at the first stage of MG oxalate-ions hydrolysis are replaced with hydroxide-ions with formation immonium-basis. I.e. immonium cations remain. At very low alkali concentration disappearance of dye band (Figure 1, curves 1-3) is accompanied by

6


simultaneous growth of an ultra-violet band (38 000 cm-1) which position in accuracy corresponds to the carbinol UV-band. At such low KOH concentration reaction stops at presence isobiestic point on a spectrum. Thus dye transforms in immonium hydroxide, carbinol precursor. The solution becomes colorless, that is rather essential. It testifies that in itself individual MG cations are not chromogenes. The MG oxalate hydrolysis end-product - leycocarbinol is formed at increase in alkali concentration with isobiestics infringement in a spectrum. Leycocarbinol has two alkilaniline groups absorbing UV-light at 38 000 cm-1 (263 nm) [13, 16]. Therefore its UV-band is more intensive in comparison with MG immonium cations, having one alkilaniline group. Received for carbinol value of extinction coefficient ε263 = 2.8×104 l/ (mole.cm), calculated on a spectrum 4 (Figure 1а), practically coincides with resulted in [15]. The same size turns out from parity D617/D263 = ε617 / ε 263, that corresponds to practically full transform of arils MG Ar-fragments in carbinol. On a low-frequency slope of a band of 38 000 cm-1 the excess in the range of 33 000 cm-1 (~ 300 nm) where according to [13, 15] there is a weak additional carbinol absorption band is observed. Simultaneously with carbinol UV- bands in a spectrum 4 (Figure 1а) is observed a weak band at 28 000 cm-1. It belongs not MG cations, but to by-product Х which is formed at MG synthesis. This collateral Х, too, as well as MG, is in an initial preparation of dye in oxalate form. That a band ~ 28 000 cm-1 in its spectrum appear at big enough maintenance of alkali (Figure 1а testifies to it, a curve 4) in that interval of frequencies, where a spectral curve of dye (Figure 1а, the curve 1) has a minimum. Oxalate product Х the group eliminates not only under the influence of alkali does not possess high firmness, and oxalate, but also at heating in heptaneе. On Figure 1б represented the spectrum (a curve 1) of compounds, heptane extracted (volume of 10 ml) from initial MG sample (~ 100 mg) at ~ 100 ºС. The received extract has been filtered through the paper filter and diluted in 2.5 times. In this spectrum the UV-band νmax = 30 300 cm-1 (~ 330 nm) of compounds Х have big enough intensity and is batohrome displaced to 28 000 cm-1 at replacement heptane by ethanol (Figure 1б, a curve 3). The maximum of the same band in heptane, saturated with ethanol, is located at 30 000 cm-1, and in the ethanol saturated heptane at 28 250 cm-1 (350 nm) (Figure 1б, a curve 2). (Heptane and ethanol limited mix up with each other, forming two layers). It is necessary to notice, that the compounds of type Х having the UV-bands with similar properties are found out in all investigated dyes. It testifies that admixture compounds molecules in them have identical chromophore groups. It is essential, that in spectra of solutions (Figure 1б, curves 1 - 3), received heptane extraction, are absent signs of bands of absorption of initial dye which practically we will not dissolve in heptane. There are no also band signs MG carbinol forms (38 000 cm-1, see Figure 1а, a curve 4). On Figure 1б the spectrum 3 characterizes ethanol solution received after heptane evaporation from heptane extract and the subsequent dissolution of the dry rest in ethanol. It is visible, that after transition in ethanol, the UV-band extracted compounds Х tests batohrome displacement concerning a heptane solution band. However, the characteristic band of carbinol MG forms at 33 000 cm-1 here is absent. This band appears only in the presence of alkali. For example, the spectrum 2 (Figure 1б) is transformed to a spectrum 4 (Figure 1б) at addition in a solution of 20 mg KOH. Alkali entering, apparently, is not reflected in the form and intensity of the UV-band at 28 250 cm-1, belonging to compound Х, however, thus there is characteristic for carbinol UV-band at 33 000 cm-1.


7

It is necessary to notice, that the spectrum 4 (Figure 1б) UV-light absorption is a little deformed in area ν>33 000 cm-1 by spectrum imposing turbidness from light-scattering KOH colloid particles. Light scattering deformed the widened band at 40 000 cm-1 represents the sum of bands from formed carbinol and, probably, high-frequency band of compound Х. It is necessary to pay attention also that in a spectrum heptane extract 1 (Figure 1б) the UV-band with νmax = 41 200 cm-1 (243 nm) is clear expressed. The considerable contribution to this band absorption not having bands in visible area of a spectrum bring passed in heptane individual MG molecules, including immonium cations, but. That fact testifies to presence of individual MG molecules in heptane extract, that band of 33 000 cm-1 arises under the influence of alkali (Figure 1б, a spectrum 4) at absence in the extract chromogene associates of MG molecules. Individual MG molecules can be a unique source of carbinol in this case only. Considering absence of visible bands of absorption of light at individual MG molecules, it is necessary to assume, that formation dye chromogene associates from nonchromogene (colorless) molecules take place probably in this case by self-assemblage of these associates. Such conclusion proves to be true that at evaporation colorless heptane solutions with a spectrum 1 (Figure 1б) on glass surfaces of vessels blue-green layers of dye are formed. Formation chromogene MG crystals from colorless MG molecules can be observed also by means of a band chromatographic paper absorbing heptane solution and painted during movement on it and evaporation of solvent. As MG chromogenes can act not only MG oxalate crystal particles, but also dimers, formed of nonchromogene individual MG molecules at the expense of enough strong intermolecular interactions. The proof of that a band with λmax = 617 nm belong dimers molecules of MG oxalate, is change of intensity of this band, observed at mixture of two parts spirit solution MG with one part of ice acetic acid. Value ε617 MG spirit solutions = 4.4×104 l / (mole.cm). In the mixed solution ε617 = 5.5·104 l / (mole.cm). Despite such increase, absorption coefficient oxalate MG in a mix of spirit with acetic acid approximately in 2 times it is less, than at chloride MG in 98 % acetic acid (ε617=1.04·105 l/mole·cm) [4]. The observable divergence of characteristics caused by distinction of the nature of solvents, is rather great. Such influence should be expected at enough cmall size molecular associates, such as dimers.

Heptane Extracts Spectra of Products of Malachite Green Hydrolysis Independent evidence is received in experiences with heptane extracts of products of water-alkaline hydrolysis initial MG oxalate that individual MG cations do not possess chromogene property. It is obvious, that thus chromogenes particles are formed only as a result of association of the molecules bearing on compensated electric charges of ionic pairs. As it was already marked, MG oxalate alkaline hydrolysis finds out, at least, two macroscopical kinetic stages clear observed on UV-spectra. From the kinetic point of view hydrolysis reaction proceeds through three consecutive stages [12]. The first stages of MG oxalate alkaline hydrolysis - fast reaction of an exchange of oxalate ions on HO- anions going from cmall energy of activation: (Ox–N+H(CH3)2–Ph'–С(Ph)=Pħ=N+–OCO–)2 + 2 HO– →

(I)

8

Yu. A. Mikheev, L. N. Guseva, Yu. A. Ershov et al. 2 Ox–N+H(CH3)2–Ph'–C(Ph)=Pħ=N+(CH3)2–OH + –OCOCOO– ,

(II)

After this the stage of neutralization of ammonium ions proceeds HO– + II → H2O + Ox– + N(CH3)2Ph'–C(Ph)=Pħ=N+(CH3)2–OH,

(III)

In it the saltless form of hydroxide immonium is formed. The final, third stage of process is carried out, most likely, by reaction hydroxydeа immonium with HO- anion, attacking the central atom of carbon: HO - + III → N (CH3) 2Ph '-C (OH) (Ph)-Ph '-N (CH3) 2 (carbinol) +-OH. Molecules II and III bear on one dimetilaniline group, whereas a carbinol molecule - two such groups. According to it, intensity of a band of UV-absorption at a carbinol molecule should be twice more in the event that quinoid groups of compounds II and III do not bring the considerable contribution to the given UV-band. Such situation it is possible to explain ν = 38 000 cm-1 band strengthening in the conditions of the step hydrolysis, observed on spectra Figure 1а at transition from curves 1-3 (with isobiestic point) to a curve 4. (That quinoid groups in II and III have rather weak absorption in the range of frequencies 32 000 - 42 000 cm-1, proves to be true properties of compound X which will be considered later.) UV-bands in the range of 33 000 cm-1 belonging immoniumе hydroxide (II, III) and carbinol, too differ on the intensity. The spectra presented on Figure 2а proof to it. So, the heptane extract spectrum in which forms immonium hydroxides II and III prevail, is presented on Figure 2а, a curve 1. The given solution has been prepared by heptane extraction (~ 10 ml) of the compounds formed at once after mixture spirit of a MG oxalate solution (~ 50 mg in 20 ml of ethanol) with a water solution of alkali (to a consistence of 4 % KOH) and then diluted in 100 times. At this spectrum there is implicitly expressed band at 33 000 cm-1. The subsequent extraction the compounds collecting in the same alkaline solution, has allowed to establish, that the band of 33000 cm-1 becomes more intensive during solution ageing.

Similarly Rise in Temperature Operates Also at Extraction On Figure 2а 2 and 3 spectra are presented of heptane extract received by heating (20 min) sample 54 mg MG oxalate to 10 ml of water alkali (5 %) at stirring about 10 ml heptane and filtering (dilution in 40 times and 320 times accordingly). In both spectra the clear maximum is observed at 33 200 cm-1, characteristic for a low-frequency band MG carbinol. Mixture heptane extract with ethanol leads to formation of two layers, one of which represents the spirit heptane saturated. The spectrum of such layer is presented on Figure 2а, a curve 4. In this spectrum the carbinol band at 33 000 cm-1 is washed away, losing a maximum and taking the form of a shoulder, practically repeating the form of the spectrum resulted in [13]. We will notice also, that present at spectra 1-3 (Figure 2а) heptane solutions in the form of an excess at 30 000 cm-1 the weak band of compound X, batochrome shift is in a spectrum spirit a solution heptane saturated, receiving clear expressed maximum at 28 000 cm-1 (350 nm).


9

There is one more important feature: freshly prepared heptane extracts colored by alkali MG oxalate form dye layers on glass ampoules and spectroscopic a ditch. During ageing of water-alkaline solutions of compound II and III gradually turn in carbinole, and received of them heptane extracts give ever less a dye deposit. In itself carbinole does not form the painted deposits. Formation of the painted deposits from molecules II and III proceeds with the big ease on the glass ampoules surface as adsorption of individual molecules gives them favourable mutual orientation. Thus it is possible to use and chromatographic papers bands, immersing them in heptane solution containing compounds II and III. Formed on a paper band during movement and evaporation heptane dye is easily washed off by spirit. The spectrum of eluate from a chromatographic papers band is presented on Figure 2б, a curve 1. It has not only a band of dye of 16 100 cm-1 (621 nm), but also rather intensive carbinol band at 37 900 cm-1 (264 nm) which too has been absorbed by chromatographic paper. Formation of dye particles at adsorption goes in a competition to carbinol formation, and easily proceeds also on a powder not polar polyethylene oxide, not soluble neither in heptaneе, nor in spirit.

(a) Figure 2. Continued on next page.

10


(b) Figure 2. Optical spectra гептановых extracts of products of alkaline hydrolysis оксалата МЗ (a) and spirit eluates (b) of the compounds formed at adsorption of colourless products of MG hydrolysis on a filtering paper and polyethylene oxide particles. Explanatory in the text.

On Figure 2б spectra of 2-4 heptane extract from the concentrated water-alkaline solution MG oxalate, after its mixture with ethanol (in the ratio 1:1) and entering into a mix of 2 mg polyethylene oxide powder are resulted. Long-wave absorption bands of the spectra 2-4, observed right after mixing and through 4 and 26 ч accordingly, practically do not differ by the spectral position from bands MG oxalate in spectra spirit solutions and MG cations in 98 % acetic acid [4].

Spectra of Solutions and Extracts of the Crystal Violet Spirit solution of CV sample spectrum, presented on Figure 3а (the curve 1), has a visible light absorption band at 17 380 cm-1 (575 nm), ε575 = 9.5×104 l / (mole.cm). We will notice, that in extinction coefficient calculations considered presence crystallization waters in CV powder: 18 molecules of water on 2 CV molecules [1, p.191]. In CV water solution (Figure 3а, the curve 2) a band maximum of dye is at 17 000 cm-1 (588 nm), ε588 = 8.8×104 l / (mole.cm), that will be co-coordinated with data [1, 17]. On spectra 1, 2 (Figure 3а) is present also a band not marked in the literature at 29 000 cm-1, belonging to admixture compound XCV which molecules have chromophore group of type X. Spectral CV bands are stable enough in time both in spirit, and in water solutions, however, their intensity decreases at hit in solutions even rather low quantities of alkali. Entering KOH to concentration of 10-3 mole/l in spirit solution with a spectrum 1 (Figure 3а) causes its decoloration during 1 – 2 sec. Simultaneously there is a band at 38 000 cm-1 with low intensive shoulder at 33 000 cm-1 (Figure 3а, a curve 3). The given transformation


11

reflects formation carbinol CV forms and actually repeats a situation with formation MG carbinol (Figure 1, a curve 4). Observed in spirit a solution at 28 000 cm-1 a band (Figure 3а, the curve 1), belonging to compound XCV, does not change in the presence of alkali. Dilution spirit heptaneом (spirit have evaporated to 0.3 ml and then have added heptane to 3 ml) has caused гипсохромное displacement of the given band to 29 000 cm-1 (Figure 3а, a curve 4). Initial samples CV contain an impurity not only XCV, but also the rests not reacted leycobase (triphenilmethane derivative), used for CV synthesis. Both compounds heptane extracted at heating on a water bath, however residual triphenilmethane it is dissolved at 25 ºС in heptaneе better, than XCV. The spectrum of freshly prepared heptane extract of both compounds is presented on Figure 3б, a curve 1. Curves 2, 3 (Figure 3б) represent spectra of heptane solution received after loss from it (through 20) a colorless XCV deposit (spectra wrote down after filtering and разбавления initial heptane extract accordingly in 140 (1), 100 (2) and 280 times (3).) Observed during ageing heptane extract spectral transformation testifies, that in a deposit passes mainly compound XCV (its band in heptaneе has νmax = 30 100 cm-1 (333) nm) whereas in a solution remains triphenilmethane with an intensive band at νmax = 37 800 cm-1 (264.5 nm) and a weak band at 32 600 cm-1 (306 nm). Repeated keeping in heptaneе parts of the deposit which has dropped out at 25 ºС, has given the solution of compound XCV close to saturation, with a spectrum 4 (Figure 3б) and νmax = 30 100 cm-1. Dissolution of other part of a deposit in spirit has given a spectrum 5 (Figure 3б) with a band displaced to 27 200 cm-1 (367 nm). In both cases practically there are no triphenilmethane absorption bands (with νmax = 37 800 and 32 600 cm-1) which has appeared will be better dissolved in heptaneе at 25 ºС, than XCV. It is necessary to notice, that the UV-absorption spectrum of heptane solution triphenilmethane is very similar to a spectrum of absorption of spirit solution CV carbinol [13]. However, as is known, carbinol is badly dissolved in heptaneе at 25 ºС [14, 15].

(a) Figure 3. Continued on next page.

12


(b) Figure 3. Optical spectra of crystal violet solutions in various mediums (a) both extract triphenilmethane residual and by-product XCF of synthesis of dye (b). Explanatory in the text.

Good solubility in heptane compounds with νmax = 37 800 and 32 600 cm-1 allows to identify it with triphenilmethane. Additional acknowledgment of that the given impurity is not carbinol, serves that processing spirit a solution (a spectrum 5, Figure 3б) chloride hydrogen does not lead to occurrence of spectral bands of dye - a reaction product carbinols with HCl. Meanwhile, at processing of the same solution weak сернокислым a dichromate solution калия it gets color, characteristic for CV, that corresponds to the mechanicm of synthesis of the given dye [3, 4, 6,]. Let's notice, that in heptane extracts of CV powders, as well as in a case with extracts of powders MG, are present nonchromogene molecules CV which band of absorption masks absorption initial triphenilmethane and compounds XCV. A presence nonchromogene molecule CV in heptane extracts is fixed on gradual release from heptane violet deposits on walls spectroscopic a ditch. Similar process as it was marked, proceeds and in initially colorless heptane solutions nonchromogene molecules MG oxalate. The painted layers especially quickly cover the ampoules glasses containing such extracts, in the conditions of heating on a water bath when molecules CV and MG have an opportunity to evaporate together with heptane and then are adsorbed on glasses. Presence nonchromogene molecules CV in heptane is easily defined the same as and in a case with MG, by means of a band chromatographic paper shipped in a colorless extract, on occurrence of violet coloring during moving of a solution and heptane evaporation.

Properties of Alkaline Solutions of the Crystal Violet The spectral picture of interaction CV with alkali qualitatively reproduces a situation with MG. So, an end-product of CV alkaline hydrolysis is corresponding carbinol, and formed at intermediate stages of hydrolysis individual molecules CV hydroxide immonium (type II and


13

III) it is possible extract by heptane. As it has appeared, heptane extracts in itself are colorless, however, being in them hydroxide immoniumя can, as well as in a case with MG, competely with carbinol formation to turn in supramolecularе dimers and larger units of violet color. Unlike immonium hydroxide, colorless CV carbinol, as well as MG carbinol, does not give the painted products without special acid processing. Formation of layers of dye, as well as in a case with MG, easily proceeds at adsorption of molecules CV immonium hydroxide on glass ampoules, especially at their evaporation simultaneously with heptane. Are evident as well experiences with a chromatographic paper band absorbing heptane extract immonium hydroxide. Let's notice, that considerable similarity of CV and MG hydroxides immonium spectra with spectra corresponding carbinols and their ability to form painted dimers, have served as the reason of occurrence of idea about carbinols dissociation on cation dyes and anions HO- at carbinol adsorption on firm surfaces [1, 13]. It was supposed [1], that such dissociation especially easily proceeds at presence on ionized centers of firm surfaces. Meanwhile, results of the present work proof, first, that cation dyes are not chromogene, secondly, that process of formation of layers of dyes does not depend on presence ionized centers on adsorbents surfaces. Really, the surface chromatographic papers contains only the HO- groups which polarity not bigger polarity of HO- groups of ethanol, and in ethanol CV and MG carbinols do not form chromogene structures in itself, without influence of acids. At the same time immonium hydroxides easily form layers of paints even on a surface of particles not polar polyethyleneoxyde, and especially quickly if particle preliminary to moisten with ethanol for the purpose of plasticification and increase in molecular-segmental mobility. It is necessary to notice, that all described above property are characteristic as well for heptane extracts and for studied by us samples of diamond green (a spirit medical preparation) and methyl violet, spectra of which spirit solutions qualitatively coincide with MG and CV spirit solutions spectra.

Spectra and Properties of Compounds with Quinoid Structure of Molecules As it was marked, all commercial dyes studied in the present work contain heptane extracted impurity, whose molecules possess chromophore groups responsible for occurrence in heptane solutions of similar UV-absorption bands in the range of 30000 - 31 000 cm-1 (333 - 320 nm). These bands are equally displaced at replacement heptane on ethanol to 28 000 cm-1 (357 nm). Batohrome displacement of UV-bands at carrying over of the molecules possessing conjugated π-electronic system, from the hydrocarbonic environment in hydroxyl one, as is known, stimulates to increase in polarity of molecules at electronic excitation and accordingly about increase in energy of interaction with environment in comparison with not exitated molecules [1]. Cmall amount admixture of molecules with similar spectra in all studied samples of dyes it is possible to explain, proposing the mechanicm applied in manufacture of dyes. This processing include oxidizing of triphenilmethane in case of MG, DG, CV and oxidizing of initial compound - dimetilaniline in case of MV [3, 6, 18]. Oxidation triphenilmethane (general formula PhH1 (Ph2) CH-Ph'-N (CH3)2, here Ph1 and Ph2 - phenyl groups having in para-position substitutants of corresponding dyes) - initiated

14


chain free radical process (the initiator - usually lead dioxide) which end-product is carbinol (Cb): Ph1 (Ph2) CH-Ph'-N (CH3) 2 + r• → Ph1 (Ph2) C•-Ph'-N (CH3) 2 (R•) + rH, R• + O2 → ROO•, ROO• + Ph1 (Ph2) CH-Ph'-N (CH3) 2 → ROOH + R•, ROOH → RO• + HO•, RO• + Ph1 (Ph2) CH-Ph'-N (CH3) 2 → Cb + R•; HO• + Ph1 (Ph2) CH-Ph'-N (CH3) 2 → H2O + R•; 2 ROO• → breakage, Here r• - a radical of the initiator. In parallel with carbinol formation chains of oxidation of CH3- (CH3CH2-) groups proceed: Ph1 (Ph2) CH-Ph'-N (CH3)2 + r• → rH + Ph1 (Ph2) CH-Ph'-N (CH3) CH2•, (R1•) R1• + O2 → R1OO•, R1OO• + Ph1 (Ph2) CH-Ph'-N (CH3) 2 → Ph1 (Ph2) CH-Ph'-N (CH3) CH2OOH + R1•, Ph1 (Ph2) CH-Ph '-N (CH3) CH2OOH → Ph1 (Ph2) CH-Ph'-N (CH3) CH2O• + HO•, HO• + Ph1 (Ph2) CH-Ph'-N (CH3)2 → H2O + R1•, Ph1 (Ph2) CH-Ph'-N (CH3) CH2O• → CH2O + Ph1 (Ph2) CH-Ph'-N• (CH3) (R2•). Formed nitric radical R2• enters disproportion reaction with ROO• with formation quinoid compounds ROO• (R1OO•) + R2• → ROOH (R1OOH) + Ph1(Ph 2) С=Pħ = NCH3 (X). In technological synthesis of MV dye use oxidation dimetilaniline PhN(CH3)2 in which in system formaldehyde is formed. Then consecutive condensation reactions of formaldehyde with molecules initial dimetilaniline and formed monometilaniline proceed. For monometilaniline formation in system enter phenol PhOH [18] which serves as the donor of hydrogen for the nitric radical formed during oxidation, differing low reaction ability PhN (CH3) 2 + r • → PhN (CH3) CH2 , PhN (CH3) CH2• + O2 → PhN (CH3) CH2OO•, PhN (CH3) CH2OO• + PhN (CH3) 2 → PhN (CH3) CH2OOH + PhN (CH3) CH2•, PhN(CH3)CH2OOH → PhN(CH3) CH2O• + HO•, HO• + PhN (CH3) 2 → H2O + PhN (CH3) CH2•, PhN (CH3) CH2O• → CH2O + PhN• (CH3), PhN• (CH3) + HOPh → PhNH (CH3) + •OPh, 2•OPh → breakage. As a result of condensation of formaldehyde with initial dimetilaniline and formed monometilaniline there is a mix carbinol with different number methyl groups in aniline fragments of molecules [3, 18]. At this mix inevitably there are by-products of oxidation with quinoidной structure of molecules. The subsequent carbinole chloride hydrogen or oxalate acid processing leads to formation of dyes with an impurity of corresponding salts of compounds X, for example,


15

Ph1 (Ph2) С=Pħ = NCH3 + HCl → Ph1 (Ph2) С=P ħ = N+H (CH3) Cl- (X+HCl-). Oxalates and chlorides of compounds X as shows experience, do not possess high stability and lose acid fragments at hot heptane extraction. Reversible character of reaction of HCl with X is clear shown in experiences with TAC films, absorbing compounds XMG and XCV from water dispersions of dye. On Figure 4 the spectrum of 2 films, containing absorbed XMG in comparison to a spectrum of 1 pure film is resulted. At absorption processing MG oxalate solution (1.6 %) volume 0.5 ml mixed a solution about 20 ml of water. In this mix immersed a film (a thickness 40 microns) for 20 days. Here the spectrum 3 received at keeping of a film with a spectrum 2 in HCl steams over hydrochloric acid within several minutes is presented. Apparently, as a result of reaction with HCl intensity of a band of 28 600 cm-1 (350 nm) compounds XMG sharply falls. Simultaneously with it intensity of a of UV-absorption band increases at 40 000 cm-1, belonging X+H cation. It is important, that thus it is not observed any signs of visible light absorption. The subsequent endurance of the hydrochlorinated film on air within days leads to practically full restoration of a 28 600 cm-1 band (Figure 4, a spectrum 4). The lung spontaneous dehydrochlorination of muriatic salt X+HCl- testifies about weak quinoid compounds nucleophylity. It is possible to explain presence at X the developed aromatic system interaction of π-electrons. Reversible hydrochlorination was observed as well with a spirit solution of compound XCV: its UV-band with νmax = 27 800 cm-1 strongly reduced the intensity under the influence of HCl, but again increased it at neutralization of acid by alkali.

Figure 4. Spectra of triacetate cellulose (TAC) film in the thickness 40 microns in an initial condition (1); after absorption of compound XMG (2); after 30 min of endurance in steams of hydrochloric acid (3) and after endurance on air within days (4). Explanatory in the text.

16


Experiments with reversible hydrochlorination of compounds XMG and XCV are important. That proof to absence chromogene properties both at initial quinoid compounds, and at quinoid cations, i.e. quinoid cations and electroneutral quinoid structures do not give to individual molecules of properties of dyes. Thus the fact of loss by compounds XMG and XCV the UV-bands at transition in cation form has a direct relation with the property known for aniline compounds. In this case occurrence of positive charges on atoms of nitrogen essentially complicates participation their electrons in aromatic π-systems photoexcitation [16]. Thus, single triphenilmethane dyes molecules, representing aromatic immonium cations with neutral aniline (or cation aniline groups), do not absorb visible light, as well as electroneutral phtalocyanine molecules. And the same as and in a case phtalocyanine, chromogene particles of these dyes are formed as a result of self-assemblage enough strong supramolecular dimers and larger units under intermolecular forces.

Spectral Properties of Individual and Aggregated Cation Xanthene Dyes As VIP-representatives xanthene dyes (XnD) used rodamine B and rodamine G, forming in water and spirit solutions of scarlet or raspberry-red color. The structure of their molecules is Y

+ O

N(C2 H5 ) 2

Cl

-

C COX O

Here symbols Y and X correspond: Y = (C2H5) 2N, X = H for rodamine B; Y = (C2H5) HN, X = H for rodamine G. Let's notice, that the rodamine B ethyl ether (X = C2H5), named rodamine 3B, forms solutions with similar coloring. It demonstrates that presence carboxyl (acid) group in xanthene molecules has no basic value for chromaticity display. Apparently, the structures of XnD molecules have certain similarity to molecules TFMD, such as the diamond green, malachite green and crystal violet. At the same time, they more flat owing to rigid fixing of two 6-cycles through atom of oxygen while in molecules TFMD 6-cycles are cut rather each other under a cmall corner (30º) on type a propeller [4]. In works [17, 19-21], carried out about 50 years ago, it is established, that XnD films, as well as TFMD, undergo transformations at heating in hydrazine steams with formation of the colorless compounds possessing only UV-spectra with similar bands. These transformations have been interpreted as consequence of similar chemical reactions. At the same time, possessing flat molecules rodamine B, G, 3B, unlike TFMD, form colorless films with the same UV-bands as well for lack of steams hydrazine. For this purpose enough simple heating in atmosphere of helium or sublimation in vacuum with the subsequent condensation on


17

quartz plates. At sublimation temperature 70ºС the spectrum of condensed layer rodamineа B is close to a spectrum of a film of the initial dye received by sedimentation from spirit solution. In this case a visible light absorption band is considerably above accompanying absorption UV-bands. However in process of sublimation temperature rise the sublimate spectrum changes, and at 145-160ºС received films possess three sharply expressed UVbands with maxima at 235, 277 and 315-317 nm, many times surpassing the visible band responsible for coloring. Precisely same bands are characteristic and for the films discolored at 120ºС in helium atmosphere (750 mm Hg). The important property of XnD films discolored in such a way is that they is reversible restore the initial color at storage on air, and not at the expense of reaction with oxygen, and under the influence of a moisture. Besides, dye color is restored at dissolution of colorless films in water. On the basis of the author results [17, 19-21] has excluded possibility of thermal disproportion of molecules XnD and has stated idea about course of their certain isomerisation. At the same time the concrete nature of such reaction, and also structure of a colorless product, remained not opened. The question on the nature received in [17, 19-21] colorless rodamine films receives the necessary answer taking into account results of works [10-12] and considered above a result on properties TFMD. According to stated above, individual TFMD molecules absorb only UV-light. At the same time, for chromaticity of the given dyes are responsible supramolecularе dimers and larger units consisting of mutually ordered molecules. Besides, quinoid cation (immonium fragment of TFMD molecule), offered in the literature as TFMD chromogene. Actually is not that as does not absorb light of a visible range. Similar quinoid cation till now it is considered chromogene as well in a case xanthene dyes. Considering the new facts concerning the chromaticity nature, it is natural to believe, that XnD chromogene and, in particular, rodamine B and G, individual molecules, and them supramolecularе and larger units are too not. In that case received in works [17, 19-21] rodamine colorless films should be considered as a film with amorphed structure consisting mainly from disorder placed individual molecules. Really, the fact chromogenity absence at individual molecules rodamine have established by means of two techniques. In one of them for registration of spectra of a rodamineа B molecules superseded water in heptane layer from a dye solution in spirit-heptane mixes. In other molecules received by heating of the dye entered into TAC and cellophane films.

Heptane Extracts Properties Used in a case with heptane extraction TFMD molecules from powders has not led to positive result in application to xanthene powders. Assuming, that xanthene individual molecules (or particles of an amorphous phase) can strongly enough occludates in a crystal lattice of dye, we used a technique with dissolution of powders in ethanol and the subsequent XnD molecules extraction from solutions. Optical spectra of rodamine B molecules heptane extracts are presented on Figure 5, curves 1, 2. For preparing of these solutions 1 mg of a dye powder dissolved in ethanol (2 ml) and diluted with pure heptane (4 ml). The received solution diluted with the distilled water (2 ml). Water action consisted, first, in heptane miscibility decrease with spirit, secondly, in extraction strengthening of rodamine molecules exfoliating heptaneом. We will underline,

188


thhat chromogen neые dye parrticles are noot dissolved in heptaneе, and a the extraact remains coolourless. Forr registration of o spectra recceived colourless heptaneоввый a layer diluted d pure heeptaneом in 3.5 times (Figuure 5, a curve 1) 1 and 10 timees (Figure 5, a curve 2). Absorption n bands of theese solutions are in spectruum UV-area. Optical densiity Dmax in m maxima of ban nds (λmax = 2300, 270 and 307 nm) graduallly decrease with w increase in i length of a wave. Characcteristic properrty of all heptaane solutions, including an initial extract,, is absence o absorption of o visible lightt and, accordinngly, color. att them bands of For comparrison on Figurre 5 the opticaal spectrum off 4 rodamineа B films, receiived in [19] by y dye sublimaation in vacuuum is resultedd at 145°C. By B the author opinion [17, 19-21], the giiven film reprresents certainn condensed issomerisation product p of roddamine B moleecules, lost cooloring as a issomerisation result. r It has UV-absorptio U n bands λmax = 235, 277 annd 317 nm w which many tim mes over surpaass intensity of o a visible bannd observed inn a spectrum with w λmax = 5550 nm. Preseence of a visiible band thee author [17, 19] connectss with grasped in cmall am mounts in thee conditions of condensattion by moleccules of the dye which not n in time issomerisate. It is necesssary to note fuull qualitative conformity of heptane soluutions UV-bannds (Figure 5,, curves 1, 2)) and sublimaated films (Figure 5, a cuurve 4). Somee quantitative difference coonsists that maaxima of subliimate UV-bannds are batohroome displacedd on 5-10 nm concerning heeptane solutions bands. Sim milar displacem ment is an everryday occurrennce at transitioon of lightabbsorbing moleecules from soolutions in a solid s [17]. It allows a considdering, that in both cases thhe absorbing liight centers arre identical chromogene grooups.

Fiigure 5. Opticall spectra of the discolored rodaamine B forms in i heptane (1, 2), 2 a sublimate layer (4) and fillm TAC (7), an nd also it chrom mogene forms inn water (5) and TAC T film: initiaal (6) and sustaiined in w water after therm mal discolorationn (8). Additionaal explanatory in the text.


19

As it was marked, the author [17, 19-21] has found out the fact of regeneration of dye from colorless rodamine sublimate films on restoration characteristic for dyes of a visible band λmax ~ 550нм at a premise of films in steams of water or dissolution in liquid water. On Figure 5 the spectrum 5 received at dissolution of a colorless rodamineа B film with a spectrum 4 in water [17] is resulted. Apparently, in water there is a sharp growth of a visible band and decrease in UV-bands. Similar inversion of the specified bands takes place and in a heptane solutions case, and it can be carried out in two various ways. We will underline, that in itself heptane solutions, being in glass ampoules, remain colorless long time (~ 4 months). At the same time it is enough to place a filtering paper band as its surface becomes covered by a layer of dye of raspberry-red color in such solution. The formed layer of dye, insoluble in heptaneе, is easily dissolved in spirit. Dyeing can be recycled and another by. For example, to colorless heptane to a solution (3 ml) with a spectrum presented on Figure 5, a curve 2, have added 4.5 ml of ethanol and 0.5 ml of water. As a result of it the mix at first became мутно pink, but through ~ 20 mines мутность has disappeared and was formed water-spirit layer which spectrum is resulted on Figure 5, a curve 3. Apparently, this layer has an intensive visible band with λmax = 548 nm, and characteristic for heptane the UV-band solution in it have considerably lowered the intensity. The result with heptane extraction colorless rodamineа B fraction and regeneration of dye from heptane solutions has great value for understanding of the mechanicm of formation of rodamine colorless forms. Really, extraction of the colorless rodamineа B form in experiences with heptane it was carried out at a room temperature, and experiment conditions excluded possibility dye molecules isomerisation. The idea such isomerisation has arisen at the author [17, 19-21] owing to similarity of the UV-spectrum colorless sublimates with alkilamine group spectra of aniline compounds. To what concern, in particular, rodamine leycobases (lactones). Meanwhile, lactone formation reaction (including intermediate compound formation previous lactone) proceeds only at very high alkali concentration [18] that is excluded in experiences with heptane extraction. Besides, as is known, lactones are intermediate compounds at xanthene dyes synthesis, and they transform in rodamine only with the assistance of protonic acids [18]. In our experiences with adsorption on a filtering paper bands shipped in heptane solutions, rodamine B dye was recycled for lack of acids. Thus the dye which molecules bear on themselves carboxyl groups does not turn spontaneously to the colorless form at a room temperature. On the basis of the told it is necessary to conclude, that being in heptane solution chromophore centers (with absorption UV-bands) belong to individual rodamine B molecules. Adsorption of these molecules bearing on flat chromophore groups, as well as adsorption of molecules TFMD, leads to fast regeneration chromogene rodamine particles thanks to that at adsorption is provided oriental conformity for chromophore groups dispose (which in an individual kind are colorless) against each other. At the same time, in liquid heptane the probability of realization such oriental conformity, apparently, is low. Adsorption processes stimulate dye regeneration as well at mixture heptane solutions with an aqueous-alcoholic composition. At initial stages of such mixture it is formed thin emulsion with the developed surface between aqueous-alcoholic medium and heptane microdrops. It is necessary to notice, that attempt repeated rodamine B molecules extraction from samples that have already been subjected such extraction, has shown practical absence of

20


individual molecules in heptane layer. From this follows, that initial crystal samples of dye contains the limited quantity of amorphous phase soluble in heptane. Similar attempts to release individual molecules from crystal rodamineа G samples have appeared unsuccessful. It is possible to explain it or absence in them of an amorphous phase, or specificity of a molecules structure. Really, rodamineа G molecules contain groups NHC2H5 that gives them higher hydrophility and ability to build polymeric chains at the expense of formation among themselves salt bridges-COONH2 +–. Such chain salts, naturally, should possess lowered heptane extrability. Received in [17] UV-spectra of solid colorless sublimate films of rodamine B, 3B and G practically coincide with heptane extract rodamine B spectra. On this basis it is possible to conclude, that sublimate films really represented amorphous state of dyes. A little intensive visible bands thus present at their spectra at 550 nm belonged to microunits into which molecules have been packed as crystals, and units were formed in cmall amounts at condensation of colorless rodamine molecules of a steam phase. Thus, received for XnD results confirm the conclusion drawn earlier [12] about quinoid immonium fragment nonchromogenity which is present and in molecules TFMD. Thus presence at individual molecules XnD and TFMD only UV-absorption bands as at leycobase molecules and leycocarbinoles, it is caused by that those and others bear on themselves aniline structures with alkilsubstituted amino groups.

Spectroscopy of TAC films Containing Rodamines Polymeric films used for thermal experiences which as a matter of fact represent updating of Vartanyan experiences [17, 19-21]. The spectrum of TAC film with rodamine B is presented on Figure 5, a curve 6. In this case the maximum of a visible band (557 nm) is batochrome displaced concerning value of 548 nm, characteristic dye for a solution in an aqueous-alcoholic mix (Figure 5, a curve 3). Heating of the given film at 160°С during 30 mines, carried out without pumping out, causes its practically full discoloration (Figure 5, a curve 7), connected with band disappearance λmax = 557 nm. The last is combined with appreciable growth of two UV-bands belonging to individual molecules (the most short-wave UV-band with λmax = 230 - 235 nm in this case mask own UV-absorption of TAC film). Containing rodamine B TAC film discolored as a result of heating does not change the spectrum (Figure 5, a curve 7) within a week. Meanwhile, at film immersing in water its spectrum is quickly transformed with practically full restoration of a visible band of dye and leveling of UV-bands (Figure 5, a curve 8). It is characteristic, that value λmax = 548 at the film shipped in water corresponds to this indicator of an aqueous-alcoholic solution of dye, whereas at a dry film λmax = 557 nm. It can be considered as the evidence of that chromogene rodamineа B particles in the placed in water film are in water nanodrops, formed as a result of water absorption. It is rather interesting, that water desorption from a wet film during its drying on air at Тroom again leads to its full discoloration and spectrum restoration heated a dry film (Figure 5, a curve 7). Repeated immersing of the dried up film in water causes again occurrence of a spectrum Figure 5, a curve 8, characteristic for chromogene particles. As it has appeared,


21

realization of several similar cycles does not lead to washing away chromogene particles from a film. The picture of spectral transformations representing specific effect of memory and observed at Тroom, it will completely be connected with that the colorless rodamine B form are its individual molecules. Really, in TAC films there are no both alkaline, and the acid compounds necessary for transfer of dye in leycoform and back with participation of corresponding intermediate compounds. It is necessary to notice, that the found out alternation at Тroom. processes of discoloration and coloring of films proofs that the colorless molecules formed as a result of painted units rodamineа B dissociation, remain in a polymeric matrix nearby with each other, without diffusing on a long distance. Only full restoration of particles of dye in which quality should act supramolecularе dimers will be observed in this case. It is possible to make a certain notion about structure rodamine B dimers. Most likely, in them molecules are focused flat quinoid fragments to each other whereas phenyl rings bearing carboxyl groups, are parted. Tightening of two molecules in dimers is not connected with formation of chemical bonds between them, and caused by the synchronized dispersive interactions arising between π-systems of both molecules and, probably, occurrence of synchronous electric currents in these systems providing a mutual electromagnetic attraction of molecules. On the basis of told it is possible to assume, that formed in initial films at solvent evaporation chromogene dimers are stabilized in a dry polymeric matrix in an environment of segments of the polymeric chains receiving certain mechanical pressure. This pressure relax somewhat at film heating, changing a spatial configuration of the polymeric chain segments forming the nearest environment dimers, and simultaneously displacing dye molecules from each other. As a result of such displacement it is broken rather weak noncovalent interaction of molecules in dimers, and molecules appear as independent (in optical sense) the centers with absorption bands in UV-area spectrum. Immersing of the colorless films comprising deformed supramolecularе dimers, in water leads to their humidifying and, in certain degree, to plasticization with formation of water nanodrops around dimers. Dye molecules inside water nanodrops become mobile and have an opportunity to realize power interaction among themselves, that leads to regeneration chromogene dimers. In the conditions of the subsequent drying of films rigidity of a polymeric matrix and chain segments of the nearest environment dimers is restored come back to that balance of mechanical pressure which has been received at heating of films. Character of mutual displacement of dye molecules, components chromogene dimers simultaneously comes back.. Thus, considering nochromogenety individual molecules rodamineа B and chromogenety its physical dimmers, it is possible to describe specific effect of structural memory observed on spectra that cannot be made proceeding from representation about chromogenityи individual molecules of dye. The similar effect of structural memory is reproduced in certain degree and on films TAC painted rodamine G by a technique described above. So, by heating (160ºС, more than 30 mines) can achieve practically full discoloration of such films that is presented on Figure 6 in the form of transition from a spectrum 1 to a spectrum 2 at considerable decrease in a visible band with λmax = 526 nm (νmax = 19 000 cm1 ). At the same time, a little big duration of heating for this purpose is required. Besides,

222


unnlike films wiith rodamineоом B, degree of o restoration of optical dennsity of a visibble band at im mmersing in water w reaches only half of optical densitty of thermallly discolored films with roodamine G (Fiigure 6, a specctrum 3). The lowered opticcal density of a visible band reached as a result of reggeneration lim mits a limit of o coloring of o films durinng realizationn of cycles midifying” “ddrainage – hum It is possibble to explain the given sittuation realizaation of two possibilities. p F First, in the coonditions of thhermal dissocciation of painnted dimers roodamine G in TAC matrix the part of thhe formed individual moleccules rodaminee G can dispeerse in the envvironment of polymer p on suuch distances which w excludee possibility of o their subseqquent meeting at plasticization of films by y water. Seco ondly, presencce of groups NHC N 2H5 and COOH at moolecules rodam mine G can leead at heatingg to formatioon between molecules m salt and amidee bridges, noot allowing acccepting structture necessaryy for chromogene.

Fiigure 6. Opticall spectra of variious rodamine G forms in filmss (1-3) TAC and (4, 5) cellophhane: 1, 4 beefore heating, 2, 2 5 - after heatinng at 160 ºС, acccordingly and 5 mines and 3 - after saturationn by water heeated TAC film ms (spectrum 2). Additional expplanatory in the text.


23

Spectroscopy of the Painted Cellophane Films The results considered above force to reconsider known treatment of the spectral transformations observed at change of concentration of painted XnD solutions. At dyes of this type the properties specifying in occurrence associates in concentrated solutions [1, 22, 23] are brightly shown. So, for example, at concentration increase rodamine visible light absorption band of their water solutions are deformed. Till now it is considered, that characteristic for very low concentration of dyes the basic maximum of a visible band belongs to individual molecules (monomers). The concentration increase leads to occurrence of the second maximum on short-wave recession of the basic visible band. This maximum attributes dimers [1, 23]. Rise in temperature causes decrease in a new maximum so the form of a absorption spectrum of the concentrated solutions approaches with the spectrum form of weak solutions. This spectral effect explains disintegration dimers. Now, on the basis of the new information that single molecules are not responsible for rodamine chromaticity, and them dimers, it is necessary to draw a conclusion, that occurrence of new, more short-wave visible band is caused by dimers aggregation, existing already at the lowest dyes concentration. For the purpose of the additional proof of the given statement have made experiments with use of cellophane films differing from TAC films by presence of micropores, containing in it not only XnD dimers, but also larger chromogene units. On Figure 6 is the spectrum of 4 of the cellophane films, absorbing rodamine G during 10 min from the mixed solution of 3.5 mg dye in 1 ml of spirit and about 20 ml of the distilled water. In a visible range of the given spectrum the dye band with λmax = 535 nm (ν=18 700 cm-1) which in the literature attribute to rodamine G monomers, and the short-wave band with λmax = 505 nm (ν = 19 800 cm-1) is lased on it, attributed dimers. Heating of a film with a spectrum 4 (Figure 6) at 160 ºС during 5 min causes practically full disappearance of a band at 505 nm, accompanied by considerable growth of a band with λmax = 535 nm (Figure 6, a spectrum 5). Simultaneously with it the UV-band with λmax = 350 nm (28 500 cm-1) considerably grows. During the further heating intensity of band at 350 and 535 nm synchronously decreases. The similar picture of spectral changes takes place as well at the cellophane films containing absorbed rodamine B. In the beginning, at heating of such films (160 ºС) there is a disappearance of a shortwave visible band with λmax=532 nm (attributed in the literature rodamineа B dimers) and growth of a long-wave visible band with λmax=562 nm (attributed to monomers). The UVband with λmax = 357 nm simultaneously considerably grows. It is necessary to notice, that cellophane films, unlike TAC films, strongly turn yellow in the conditions of the long heating, however the picture of spectral changes described above is fixed unequivocally. Thus, on an initial phase of heating of cellophane films there is a disintegration concerning large chromogene units to formation molecular dimers, possessing visible band at 535 nm (rodamine G) and 562 nm (rodamine B). On the second phase of heating of films both dyes dimers dissociate with formation of the individual molecules which are not possessing absorption of visible light. That leads to decrease in intensity of visible band like a situation with TAC films (Figure 5, curves 6,7;

24


Figure 6, curves 1,2). Thus visible band and long-wave UV-band (at 350 and 357 nm) of both rodamins decrease synchronously, that testifies to an accessory of these UV-band dimers the given dyes. Thus, for an explanation of the nature of chromaticity xanthene dyes, as well as in case of CuPc [10, 11] and TFMD [12], it is necessary to consider not only properties of individual molecules of these compounds, but also properties corresponding supramoleculare units. Spectroscopy of Individual Molecules and Chromogenes of Methylene Blue Dye Flat molecular chromophore of methylene blue dye (MB), as well as TFMD and XnD chromophores, includes quinoid structure with immonium cation:

(CH3)2 N

S

+ N(CH3)2

N The positive cation charge is compensated by a negative chloride anion charge. In elementary MG crystal cell 4 molecules of MG and 16 molecules of water contain [1, 24]. Forces of coupling in a crystal lattice do not allow to molecules of MG extract from a dye powder in all temperature interval of a liquid heptane (T X. By correlating the changes in all the above repeating stereosequences with those in any physical property of the samples, the understanding of the processes at molecular level, involved in that property should take a step further. A considerable amount of work on PVC and PP makes this prospect quite reliable.

REFERENCES [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13]

Vella, N.; Toureille, A.; Guarrotxena, N.; Millán, J. Macromol. Chem. Phys. 1996, 197, 1301-1309. Guarrotxena, N.; Vella, N.; Toureille, A.; Millán, JL. Macromol. Chem. Phys. 1997, 198, 457-469. Guarrotxena, N.; Millán, JL.; Vella, N.; Toureille, A. Polymer 1997, 38, 4253-4259. Guarrotxena, N.; Vella, N.; Toureille, A.; Millán, JL. Polymer 1998, 39, 3273-3277. Guarrotxena, N.; Toureille, A.; Millán, J. Macromol. Chem. Phys. 1998, 199, 81-86. Guarrotxena, N.; Millán, J.; Sessler, G.; Hess, G. Macromol. Chem. Phys. 2000, 21, 691-696. Guarrotxena, N.; Martínez, G.; Millán, J. Polymer 1997, 38, 1857-1864. Guarrotxena, N.; Martínez, G.; Millán, J. Polymer 2000, 41, 3331-3336. Guarrotxena, N.; del Val, J.J.; Millán, J. Polymer Bulletin 2001, 47, 105-111. Guarrotxena, N.; del Val, J.J.; Elicegui, A.; Millán, J. J. Polym. Sci. Polym. Phys. 2004, 42, 2337-2347. Hatada, K.; Kitayama, T. “NMR Spectroscopy of Polymers”, Chap 3, Springer 2004, ISBN: 3-450-40220-9. Guarrotxena, N.; Martínez, G.; Millán, J. Eur Polym J. 33, 1473 (1996) and referentes cited therein. Guarrotxena, N.; Schue, F.; Collet, A.; Millán, J. Polym Int. 52, 420 (2003).



Chapter 7

THE MODELING OF TRANSITION METAL COMPLEX CATALYSTS IN THE SELECTIVE ALKYLARENS OXIDATIONS WITH DIOXYGEN: THE ROLE OF HYDROGEN – BONDING INTERACTIONS L. I. Matienko∗, L. A. Mosolova and G. E. Zaikov Emanuel Institute of Biochemical Physics, Russian Academy of Sciences, 4 Kosygin str., Moscow, 119334 Russia

ABSTRACT The different methods of improvement of catalytic activity of transition metal complexes in the oxidations of alkylarens with molecular oxygen are stated briefly. The offered at first by authors and developed in their works the method of control of catalyst activity of transition metal complexes with additives of electron-donor mono- or multidentate exo ligands L2 in the oxidations of alkylarens (ethylbenzene, cumene) with molecular oxygen into corresponding hydroperoxides is presented. The modeling of catalytic nickel and iron complexes with use of ammonium quaternary salts and macrocycle polyethers as exo ligands-modifiers is described in detail. The role of the Hydrogen–Bonding interactions in mechanisms of homogeneous catalysis is discussed. The modeling of catalyst activity of complexes Fe(II,III)(acac)n with R4NBr (or 18crown-6) (18C6) in the ethylbenzene oxidation in the presence of small amounts additives of water (~10-3 mol/l) is analyzed. The role of micro steps of the chain initiation (O2 activation), and propagation in the presence of catalyst (Cat + RO2•→) in the mechanism of nickel- and iron-catalyzed oxidation of ethylbenzene is evaluated.

∗

E-mail:[email protected]

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L. I. Matienko, L. A. Mosolova and G. E. Zaikov

Keywords: homogeneous catalysis, oxidation, alkylarens, hydroperoxides, dioxygen, Ni(II)-, Fe(II,III) acetylacetonates, HMPA, DMF, MSt (Na, Li, K), ammonium quaternary salts, macro-cycle polyethers, PhOH, additives of small amounts of H2O.

1. INTRODUCTION The major developments in hydrocarbon oxidations have often been motivated by the need for the ever-growing polymer industry. The functionalization of naturally occurring petroleum components through reaction with air or molecular oxygen was naturally seen as the simplest way to derive useful chemicals [1]. The research of N.N. Semenov (gas-phase oxidation reactions) [2] and later N.M. Emanuel (liquid-phase hydrocarbon oxidation with molecular oxygen) [3] and others [4] clarified the concepts of chain reactions and put the theory of free-radical autoxidation on a firm basis. Industrial practice developed alongside. The development of the industrial processes depends mainly on the investigators ability to control these processes. The one of the methods of control of the rate and mechanism of the free-radical autoxidation processes is the change of medium, in which the autoxidation occurs (the pioneer works of Professor G.E. Zaikov) [5], followed by [1,6]. The homogeneous catalysis of liquid-phase hydrocarbon oxidation has played no fewer roles in the improvement of oxidation processes. The selective oxidation of hydrocarbons with molecular oxygen as an oxidant to desired products is now a foreground line of catalysis and suggests the use of metal-complex catalysts. In the last years the development of investigations in the sphere of homogeneous catalysis with metal compounds occurs in two ways – the chain free-radical catalytic oxidation and catalysis with metal-complexes, modeling the action of ferments. But the most of the reactions performed at the industrial scale are on autoxidation reactions mainly because of low substrate conversions at catalysis by biological systems models [1,7]. In works of N.M. Emanuel and his school it was established for the first time that transition metals compounds participated in all elementary stages of chain oxidation process with molecular oxygen [8-13]. Later these discoveries were confirmed and described in reviews and monographs [14-20]. However, there is no complete understanding of mechanism yet. Special attention was attended to investigation of role of metals compounds at stages of free radicals generation, in chain initiation reactions (O2 activation) and hydroperoxides dissociation. Reaction of chain propagation under interaction of catalyst with peroxide radicals (Cat + RO2•→) is studied insufficiently. Catalysis by nickel compounds (NiSt, Ni(acac)2) was studied in details only in works L.I. Matienko together with Z.K. Maizus, L.A. Mosolova, E.F. Brin [12, 21-23]. Solution of the problem of the selective oxidation of hydrocarbons into hydroperoxides, primary products of oxidation is the most difficult one. High catalytic activity of the majority of used catalysts in ROOH decomposition doesn't allow suggesting of selective catalysts of oxidation into ROOH to present day. Application of transition metals salts rarely leads to significant increase in process selectivity, since transformations of all intermediate substances are accelerated not selectively [20]. For alkylarens, hydrocarbons with activated C−H bonds (cumene, ethylbenzene) the problem of oxidation into ROOH at conditions of radical-chain oxidation process with degenerate branching of chain is solvable, since selectivity of oxidation into ROOH at not deep stages (∼1-2%) is high enough (S∼80-95%). In this case the

The Modeling of Transition Metal Complex Catalysts…

77

problem is in increase of reaction rate and conversion of hydrocarbon transformation into ROOH at maintaining of maximum reachable selectivity. Obviously, effective catalysts of oxidation into ROOH should possess activity in relation to chain initiation reactions (activation by O2) accelerating formation of ROOH and also should be low effective in reactions of radical decomposition of formed during oxidation process active intermediates [20]. It should be noted that except the catalytic systems developed by the authors nobody had proposed effective catalysts for selective oxidation of ethylbenzene into αphenylethylhydroperoxide (PEH) up to now in spite of the fact that ethylbenzene oxidation process was well studied and a large number of publications and books in the sphere of homogeneous and heterogeneous catalysis were devoted to it [20, 24-27]. At recent decades the interest to fermentative catalysis and investigation of possibility of modeling of biological systems able to carry out selective introduction of oxygen atoms by C−H bond of organic molecules (mono- and dioxygenase) is grown [28-30]. Both the alkylarens oxidations at catalysis by biological systems models, and the traditional transition metal catalyzed liquid-phase radical-chain oxidation of alkylarens with dioxygen occurs mainly into the alcohols and carbonyl compounds. The recently discovered molybdoenzyme ethylbenzene dehydrogenase (EBDH) catalyzes the oxygen-independent oxidation of ethylbenzene to (S)-1-phenylethanol [31] Unfortunately, dioxygenases able to realize chemical reactions of alkane’s dioxygenation are unknown [29]. In addition to the theoretical interest, the problem of selective oxidation of alkylarens (ethylbenzene and cumene) with dioxygen in ROOH is of current importance from practical point of view in connection with ROOH use in large-tonnage productions such as production of propylene and styrene (α-phenylethylhydroperoxide), or phenol and acetone (cumyl hydroperoxide) [1,32]. The method of transition metal catalysts modification by additives of electron-donor mono- or multidentate ligands for increase in selectivity of liquid-phase alkylarens oxidations into corresponding hydroperoxides was proposed by authors [33] for the first time. The mechanism of ligand –modifiers control of catalytic alkylarens (ethylbenzene and cumene) oxidation with molecular oxygen into ROOH was established, and new effective catalysts for ethylbenzene and cumene oxidation in ROOH were modeled [33].

2. HOMOGENEOUS CATALYTIC OXIDATIONS OF ALKYLARENS WITH MOLECULAR OXYGEN The various catalytic systems on the base of transition metal compounds have been used for the alkylarens oxidation with molecular oxygen. And all of them catalyzed alkylarens oxidations mainly to the products of deep oxidation [6, 34]. One of the most striking examples is the oxidation of alkylarens into carbonyl compounds and carbonic acids by dioxygen in the presence of so-called MC-catalysts (Co(II) and Mn (II) acetates, HBr, HOAc) [6]. Cobalt complexes with pyridine ligands, for example, catalyzed the oxidation of neat ethylbenzene to acetophenone in 70% conversion and 90% selectivity [35]. Mn porphyrin complex catalyzes the ethylbenzene oxidation with dioxygen to 3:14 mixture of methylphenylcarbinole and acetophenone in the presence of acetaldehyde [36]. The system

78


CuCl2–crown ether in the presence of acetaldehyde is efficient as catalyst of oxidation of ethylbenzene, indane, and tetralin by dioxygen (70°C) into the corresponding alcohols and ketones with high TON [37]. The oxidations were established to occur via a radical pathway and not by a metal–oxo intermediate. In the absence and in the presence of crown ether the hydroperoxide was established as the main product of the indane oxidation at room temperature [38]. The oxidation of ethylbenzene using iron-haloporphyrins in a solvent-free system under molecular oxygen at 70-110°C gives mixture of α-phenylethylhydroperoxide, methylphenylcarbinole, and acetophenone (1:1:1). The catalyst is (TPFPP=5,10,15,20-tetrakis (pentafluorophenyl)porphyrin). Ethylbenzene conversion does not more than 5%. The oxidation occurs via radical pathway [39]. The products of ethylbenzene oxidation with air under mild condition (T > 60°C, atmospheric pressure), catalyzed by [TPPFe]2O or [TPPMn]2O (μ-oxo dimeric metalloporphyrins, μ-oxo-bis(tetraphenylporphyrinato)iron (manganese)) without any additive are acetophenone and methylphenylcarbinole. The ethylbenzene oxidation is radical chain oxidation in this case also. The ketone/alcohol (mol/mol) rations are 3.76 ([TPPMn]2O, ethylbenzene conversion – 8.08%), 2.74 ([TPPFe]2O, ethylbenzene conversion – 3.73%) [40].

3. THE APPLICATION OF THE DIFFERENT METHODS FOR INCREASE IN ACTIVITY AND SELECTIVITY OF HOMOGENEOUS CATALYSTS IN THE OXIDATION PROCESSES The application of metal-complex catalysis opens possibility of regulation of relative rates of elementary stages Cat–O2, Cat–ROOH, Cat–RO2 and in that way to control rates and selectivity of processes of radical-chain oxidation [20]. Varying ligands at the metal center or additives, one can improve yields of the aim oxidation products, and control the selectivity of the reaction. Besides, initial catalyst form is often only the precursor of true catalytic particles and functioning of catalyst is always accompanied by processes of its deactivation. Introduction into reaction of various ligands-modifiers may accelerate formation of catalyst active forms and prevent or trig processes leading to its deactivation. The understanding mechanisms of the additive’s action at the formation of catalyst active forms and mechanisms of regulation of the elementary stage of the radical-chain oxidation may be resulted in new efficient catalytic systems and selective catalytic processes. The methods of heterogeneous catalysts modification with additives of different compounds, which increased catalytic activity and protected catalysts from deactivation, are known for a long time. But researches of action of various ligands-modifiers in homogenous catalysis are often rare and relate mainly to investigating of ligands-modifiers influence on catalyst activity in radical initial stages (O2 activation, ROOH homolytic decomposition) [20,24]. Besides this, the reaction of O2 activation by transition metal complexes in schemes catalytic radical chains oxidation is not taken into consideration in most cases. The additives, often being axial ligands for metal complexes, are considered in models, which mimic enzyme reaction center (mono- and dioxygenase). At now the numerous


79

examples of various catalytic reactions are known when addition of certain compounds in small amounts dramatically enhances the reaction rate and rarely the product yield. As a rule mechanisms of the additives’ action are not proved although the authors tentatively propose mechanistic explanations [41]. The works of Ellis and Lyons and more recently that of Gray and Labinger have identified the halogenated metal porphyrins – catalyzed oxidation of alkanes into alcohols by dioxygen at the mild conditions (100oC) [42-45]. However, substituted alkanes such as 2methylbutane, 3-methylpentane, 2,3-dimethylbutane, and 1,2,3-trimethylbutane are oxidized into a mixture of products due to oxidative cleavage of carbon- carbon bond [43]. The including of halogen, electron withdrawing substituents, into porphyrin ligand increases the stability and as result the activity of halogenated iron porphyrins [42,43]. Nevertheless the relative low conversion is due to the catalyst decomposition. It is now generally agreed that one-electron redox reactions and oxygen-centered free radical chemistry being about the oxidations in these systems are most probably than mechanisms similar to those proposed for biological oxidations by Cytochrome P-450 and methanemonooxygenase (through two-electron oxygen-transfer processes at participation of high valent metal-oxo oxidant) [44,45,46]. Perhalogenated iron porphyrins are known to be effective at decomposing alkyl hydroperoxides via free radicals formation [45,46].

3a. Immobilization of Homogeneous Catalyst on Heterogeneous Support for Increase in Activity and Selectivity of Catalyst in the Alkylarens Oxidations Several studies are focused on the silica-, zeolite- and polymer – supported metal – catalyzed oxidation [47-54]. The potential advantages of using a solid catalyst include the case of its removal from the oxidation mixture and subsequent reuse, and control of its reactivity through the microenvironment created by the support. The metal complexes, heterogenised in the zeolite pores, are prevented from deactivation; the oxidation of the ligand by another complex cannot be realized. The increase in stability encapsulated salen complex arises from the protection of the inert zeolite framework, making complex degradation more difficult by impeding sterically the attack to the more reactive parts of the ligand, and the life of salen catalyst is prolonging [48]. At the same time the zeolite influences on the formation of products by steric and electronic influences on transition state of the reaction, they also control the entry and departure of reagents and products. The one of the limitations of zeolites are that their tunnel and pore sizes are no large than about 10 Ǻ [50]. The occluded catalytic complexes require a zeolite with caves or intersections which are large enough to embed them. For these purposes faujasites, containing super cages, are most frequently used [48].The creation of mesopores in zeolite particles to increase accessibility to internal surface has been the subject of many studies (mesopore – modified zeolites). It is known that postsynthesis hydrothermal dealumination and other chemical treatments form defect domains of 5 – 50 nm (which are attributed to mesopores) in faujasites, mainly zeolite Y [48]. The low activity of these zeolite catalysts is connected with their highly hydrophility as result of low silicon to aluminum ration. The deactivation by sorption of polar products and

80


solvent on pores of zeolite still remained a serious issue for oxidation of alkanes (with low polarity). Even dealumination of the structure up to silicon to aluminium ratio above 100, increased the activity only twice [48]. The creation of a hydrophobic environment around the active site was required to circumvent the activity and sorption problems. In the case of the reaction of cyclohexane oxidation to adipic acid with air in the presence of Fe – aluminophosphate-31 (ALPO-31) (with narrow pore, 0.54-nm diameter) cyclohexane is easily adsorbed in the micro pores [51]. But desorption of initial products such as cyclohexylperoxide or cyclohexanone is slow. Consequently, subsequent radical reactions occur until the cyclohexyl ring is broken to form linear products that are sufficiently mobile to diffuse out of the molecular sieve. In contrast, with a large pore Fe – ALPO-5, cyclohexanol and cyclohexanone account for ~ 60% of the oxidation products. Thus, localization of a free radical reaction inside micro pores seems to give rise to particular selectivity. Often the catalytic activity is unchanged practically if supported metal complex is used. So the silica – and polymer – supported iron(III) tetrakis(pentafluorophenyl)porphyrins, FeTF8PP, [49] catalyzed the ethylbenzene oxidation reactions by dioxygen into the same three products, α-phenylethylhydroperoxide, methylphenylcarbinole, and acetophenone (1:1:1), as analogous homogeneous catalyst, suggesting that these catalytic oxidations proceed by the same mechanism. However, in general, the heterogeneous catalytic ethylbenzene oxidation is even slower. The products yields are limited by the stability/activity of iron porphyrin and these in turn are dependent mainly on catalyst loading and microenvironment provided by support. The “neat” and zeolite-Y-encapsulated copper tri- and tetraaza macrocyclic complexes exhibit efficient catalytic activity in the regioselective oxidation of ethylbenzene using tertbutyl hydroperoxide [52]. Acetophenone was the major product; the small amounts of o- and p-hydroxyacetophenones were also formed, revealing that C–H activation occurs at both the benzylic and aromatic ring carbon atoms. The latter is significant over the “neat” complexes in the homogeneous phase, while it is suppressed significantly in the case of the encapsulated complexes. Molecular isolation and the absence of intermolecular interactions (as revealed by EPR spectroscopy), synergism due to interaction with the zeolite framework and restricted access of the active site to ethylbenzene are the probable reasons for the differences in activity/selectivity of the encapsulated catalysts. The differences in selectivity are attributed to the formation of different types of “active” copper–oxygen intermediates, such as side-on peroxide, bis-μ-oxo complexes and Cu-hydroperoxo species, in different proportions over the “neat” and encapsulated complexes. Water soluble catalysts combining the properties of metal complexes and surfactants on the basis of terminally functionalized polyethylene glycols and block-copolymers of ethylene oxide and propylene oxide with various combinations of ethylene and propylene oxide fragments were investigated [53]. Polymers, functionalized by dipyridyl and acetyl acetone were used as ligands for preparation Co(II) complexes. Macro complexes PEG-acac-Co turned out to be more active than their non-polymeric analogues in oxidation of ethylbenzene by dioxygen under the same temperature (120°C). The only product was acetophenone. Cobalt remains fixed at the end of the polymer chain with acac-ligand and is surrounded by oxygen atoms of the PEG chain. Such surrounding is labile and does not preclude from activation of dioxygen.


81

The activity of the liquid phase polyhalogenated metalloporphyrins (Co, Mn, Fe) and supported catalysts (silica, polystyrene) and the cationic metalloporphyrins encapsulated in NaX zeolite are founded to be active for cyclooctane oxidation with molecular O2 into ketone and alcohol with primary ketone formation. At the last case the ration c-one/c-ol is higher than at the use supported on silica and polystyrene catalysts and in fact coincide with results, which are received with the cationic metalloporphyrins in solution [54].

3b. Modification of Metal Complex Catalysts with Additives of Monodentate Axial Ligands For the first time the phenomenon of significant rise of not only initial rate (w0), but also the selectivity (S = [PEH] / Δ[RH]·100%) and conversion degree (C = Δ[RH] / [RH]0·100%) of oxidation of alkylarens (ethylbenzene, cumene,) into ROOH by molecular O2 under catalysis by transition metals complexes М(L1)2 (M = Ni(II), Co(II), L1=acac-) in the presence of additives of electron-donor monodentate ligands (L2 = HMPA (hexamethylphosphorus triamide), dimethyl formamide (DMF), N-methyl pyrrolidone-2 (MP)), MSt (M = Li, Na, K) was found by authors of the articles [55-57]. On the example of ethylbenzene oxidation (120°C) the mechanism of control of М(L1)2 complexes catalytic activity by additives of electron-donor monodentate ligands L2 (L2 = HMPA, DMF, MP, MSt) was established [58-61]. The coordination of exo ligand L2 to М(L1)2 changes symmetry of complex and its oxidative-reductive activity. At that the catalytic activity of formed in situ primary complexes М(L1)2·L2 is increased that is expressed in the rise in the rate of free radical formation in chain initiation (activation by O2) and PEH homolytic decomposition, and increase in initial oxidation rate (I macro stage) [58,59]. In this connection at the first macro stage the selectivity of ethylbenzene oxidation into PEH is not high. With process development the increase in SPEH (SPEH,max ≈ 90%) in comparison with I macro stage (SPEH,max = 80%), and decrease in reaction w are observed (II macro stage). Ligands L2 control transformation of M(L1)2 complexes into more active selective particles. At that the rise in SPEH is reached at the expense of catalyst participation in activation reaction of O2, and inhibition of chain and heterolytic decomposition of PEH. Beside this the direction of formation of side products, acetophenone (AP) and methylphenylcarbinol, (MPC), is changed from consequent (under hydroperoxide decomposition) to parallel at the expense of modified catalyst in the chain propagation (Cat + RO2•→). At the III macro stage the sharp fall of the SPEH is accompanied by the increase in the rate of PhOH formation at the PEH heterolysis, catalyzed by the completely transformed catalyst [59-61]. We have established that in the case of use of nickel complexes Ni(L1)2 (L1=acac¯) selective catalyst is formed as result of controlled by L2 ligand regio-selective connection of O2 to nucleophilic carbon γ-atom of one of the ligands L1. Coordination of electron-donor exo ligand L2 by Ni(L1)2 promoting stabilization of intermediate zwitter-ion L2(L1M(L1)+O2¯) leads to increase in possibility of regio-selective connection of O2 to acetylacetonate ligand activated in complex with nickel(II) ion. Further introduction of O2 into chelate cycle accompanying by proton transfer and bonds redistribution in formed transition complex leads to break of cycle configuration with formation of (OAc-) ion, acetaldehyde, elimination of CO


82

and is completed by formation of homo- and hetero poly nuclear heteroligand complexes of general formula Nix(acac)y(L1ox)z(L2)n (L1ox= MeCOO-) ("А") (Scheme 1-3) [59-61]. Transformation of complexes Ni(acac)2·L2 (L2 = HMPA, DMF, MP, MSt)) leads to formation of homo bi- (L2 = HMPA, DMF, MP) or hetero three nuclear (L2 = MSt, M=Na, Li, K) heteroligand complexes "A": Ni2(OAc)3(acac)L2 (Scheme 1) [10]. The structure of the complex "A" with L2 =MP is proved kinetically and by various physical-chemical methods of analysis (mass-spectrometry, electron and IR-spectroscopy, element analysis). Transformation of Ni(L1)2 (L1=enamac-, chelate group (O/NH)) is realized in the absence of activating ligands (L2) [60] (L1ox=NHCOMe- or MeCOO-) (Scheme 2) by analogy withreactions of oxygenation imitating the action of L-tryptophan-2,3-dioxygenase [62, 63]. L2.L1Ni(COMeCHMeCO)2+O2 → L2.L1Ni(COMeCHMeCO)+…O2– L2.L1Ni(COMeCHMeCO)+…O2– → L2.L1Ni(MeCOO)+MeCHO+CO L1=(COMeCHMeCO)–

o

2 2 Ni(COMeCHMeCO)2 L2 ⎯⎯→ Ni2(MeCOO)3(COMeCHMeCO)L2+3MeCHO+3CO+L2 L2=N-метилпирролидон-2

Scheme 1.

Ni(COMeCHMeCNH)2 + O2 –→ .L1⋅Ni(COMeCHMeCNH)+…O2– L1⋅ Ni(COMeCHMeCNH)+…O2– –→ L1⋅Ni(NHCOMe) + MeCHO +CO (Q) ↓ H2O L1⋅Ni(MeCOO) + NH3 (P) Scheme 2.

Scheme 3. The principle scheme of oxygenation of ligand (acac)¯ in complex with Ni(II), initiated with exo ligand L2.


83

Similar change in complexes' ligand environment in consequence of acetylacetonate ligand oxidative cleavage under the action of O2 was observed in reactions catalyzed of the only known to date a Ni(II)-containing dioxygenase – acireductone dioxygenase, ARD [64], and in reactions of oxygenation imitating the action of quercetin 2,3-dioxygenase (Cu, Fe) [65, 66]. The similarity of kinetic dependences in the parent processes of ethylbenzene oxidation in the presence of {Fe(III)(acac)3+L2} and {Ni(II)(acac)2+L2} (L2=DMF) (120°C) is in agreement with assumption that transformation of Fe(II)(acac)2·DMF complexes, formed at initial stages of ethylbenzene oxidation at catalysis by {Fe(III)(acac)3+ DMF}, into more active selective catalytic species can be also the result of the regioselective addition of O2 to the γ-C atom of acetylacetonate ligand (controlled by L2 ligand) [67]. However due to the favorable combination of the electronic and steric factors appeared at inner and outer sphere coordination (hydrogen bonding) of ligand DMF with Fe(II)(acac)2 the oxygenation of the acetylacetonate ligand may follow another mechanism. Insertion of O2 into C−C bond (not the C=C bond as takes place for nickel(II) complexes with consequent break-down of cycle configuration through Criegee mechanism) can lead to the formation of methylglyoxal as the second destruction product in addition to the (OAc)⎯ ion via 1,2-dioxetane intermediate (by analogy with the action of Fe(II) containing acetylacetone dioxygenase (Dke 1) (Scheme 4) [68]. As in the case of catalysis by Ni complexes the active selective transformation products are hetero ligand complexes of probable structure: Fe(II)x(acac)y(OAc)z(L2)n (L2=DMF) [56,67].

Scheme 4. The principle scheme of dioxygen-dependent conversion of 2,4-pentandione catalyzed by acetyl acetone dioxygenase Fe(II).

84


The final product of the conversion of acetylacetonate ligands is Fe(II) acetate (Scheme 4). Both Fe(II) acetate, and Ni(II) acetate, catalyze heterolytic decomposition of PEH into phenol and acetaldehyde. At both cases the complete catalyst transformation is causing the sharp fall of SPEH [56,59,67]. The enzymatic cleavage of C – C bonds in β-diketones has growing significance for various aspects of bioremediation, biocatalysis, and mammalian physiology, and the mechanisms by which this particular cleavage is achieved are surprisingly diverse [69], ranging from metal-assisted hydrolytic processes [69] to those catalyzed by dioxygenases [68]. Carbon monoxide, one of the products of (acac)¯ - ion oxygenate breakdown path catalyzed with the only known to date a Ni(II)-containing dioxygenase – acireductone dioxygenase, ARD, and releasing at the oxygenation of Ni(L1)2·L2 (Scheme 1-3), previously considered biologically relevant only as a toxic waste product, is now considered a candidate for a new class of neural messengers [68].

3c. Modeling of Transition Metal Complex Catalysts upon Addition of Ammonium Quaternary Salts and Macro-Cycle Polyethers as LigandsModifiers: The Role of Hydrogen – Bonding Interactions Ammonium salts are well-known cationic surfactants. These amphiphilic molecules aggregate in aqueous solution to micelles and at higher concentrations to lyotropic (typical member is CTAB, cetyltimethylammonium bromide) (or thermotropic) mesophases. Beside this ammonium salts are used as phase transfer catalysts and as ionic liquids (ILs) in synthesis of nanopartickle catalysts [70-74]. It was established earlier that quaternary ammonium salts R4NX can play two different roles in various catalytic reaction in water – organic systems. These salts can act as catalysts of phase transfer but also R4NX salts are often directly involved in catalytic reaction itself. Thus, for example, in reactions of the oxobromination of aromatic compounds a lipophylic ammonium salt transfers H2O2 into the organic phase. At the same time, since it is a Lewis acid it forms R4NBr•(Br2)n or R4NBr•(HBr)n adducts thus activating Br2 or salts of HBr for electrophilic attack on the aromatic ring [75]. In the catalytic oxidation of styrene to benzaldehyde by H2O2 in water – organic solvent systems ammonium salts completely transfer H2O2 and catalyst (Ru, Pd) into the organic phase by forming hydrogen bonds. Moreover, the complex formation affects the properties of the catalyst by the changing its activity (rate and selectivity of the reaction) [75]. In the oxidation of p-xylene in a water – organic system in the presence of CoBr2 and R4NBr the catalytically active species are complexes CoBr2 with R4NBr [76]. It is known also that catalytic activity of CTAB in the ROOH decomposition in the presence of metals compounds is dependent on structural changes in the formed inverse micelles [77,78]. The ability of ammonium quaternary salts to complex formation with transition metals compounds was established. It was proved for example that М(acac)2 (M=Ni, Cu) form with R4NX (X=(acac)-, R=Me) complexes of [R4N][М(acac)3] structure. Spectral proofs of octahedral geometry for these complexes were got [79]. Complexes Me4NiBr3 were synthesized and their physical properties were studied [80].


85

The selective complexation ability of crown ethers is one of their most attractive properties. Crown ethers are of considerable interest in biologically modeling of enzyme catalysis, and as phase transfer catalysts [71,81]. Intermolecular and intramolecular hydrogen bonds and other noncovalent interactions are specific in molecular recognition [81]. Interest in studying of structure and catalytic activity of nickel complexes (especially nickel complexes with macrocycle ligands) is increased recently in connection with discovering of nickel-containing ferments [82-86]. So, they established that active sites of ferment urease are binuclear nickel complexes containing N/O-donor ligands [82]. Cofactor of oxidation-reduction ferment methyl-S-coenzyme-M-reductase in structure of methanogene bacteria is tetra-aza-macrocycle nickel complex with hydrocorfine Ni(I)F430 axially coordinated inside of ferment cavity [84]. Inclusion of transition metals cations into cavity of macrocycle polyether is proved by now by various physical-chemical methods. At that the concrete structure of complex is determined not only by geometric accordance of metal ion and crown-ether cavity but by the whole totality of electron and spatial factors created by metal, polyether and other ligand atoms and also by solvent [87]. The ability of the ammonium quaternary salts as well as macrocycle polyether to form complexes with transition metals compounds was used by us to design effective catalytic systems. It was established by us earlier, that at the relatively low nickel catalyst concentration the selectivity of the ethylbenzene oxidation into PEH, catalyzed by Ni(L1)2 (1,5·10-4 mol/l), was sufficiently high: SPEH,max = 90%. This fact may be expected from the analysis of the scheme of catalyzed oxidation including participation of catalyst in chain initiation under catalyst interaction with ROOH, in chain propagation (Cat + RO2•→) and assuming the chain decomposition of ROOH. In this case the rate of reaction should be decreased, and [ROOH]max should be increased with decrease of [Cat]0 [8]. But the growth in SPEH,max is not accompanied the growth in the conversion C. The value C into PEH in the ethylbenzene oxidation, catalyzed by Ni(L1)2 (1,5·10-4 mol/l), was not exceeded C = 2-4% [59,60]. The change in the direction of by products formation is observed. Products AP and MPC are formed in this case not from PEH but parallel with PEH, i.e. wP / wPEH ≠ 0 at t→0, and furthermore wAP / wMPC ≠ 0 at t→0 that indicates on parallelism of formation of AP and MPC (P = AP or MPC) [33]. At these conditions addition of electron-donor monodentate ligands turned to be low effective [33,56,59] and the change of SPEH,max and CS=90% under introduction of additives L2 (L2 = HMPA, MP) into system practically was not observed. Coordination of 18K6 or R4NX with Ni(II)(acac)2 was seemed to promote oxidative transformation of nickel (II) complexes (schemes 1–3) into catalytically active particles and result in increase in C at conservation of SPEH,max not less than 90%. This supposition was based on the next literature data. For example, the ability of crown-ethers to catalyze electrophilic reactions of connection to γ-C-atom of acac--ligand is known [71, 88]. It is known that R4NX in hydrocarbon mediums forms with acetylacetone complexes with strong hydrogen bond R4N+(X…HOCMe=CHCOMe)¯ in which acetylacetone is totally enolyzed [89]. The controlled by R4NX regio-selective connection of O2 by γ-C-atom of (acac)¯ ligand in complex М(acac)n·R4NX is probable enough. Various electrophilic reactions in complexes R4N+(X…HOCMe=CHCOMe)¯ proceed by γ-C-atom of acetylacetone [71, 89].

86


Obviously, the favorable combination of H-bonding and steric factors, appearing under coordination of 18K6 or R4NX may not only accelerate the active multi-ligand complex formation (Schemes 1-4) but also hinder the transformation of active catalyst into inactive particles. At the introduction of 18K6 or Me4NBr additives into ethylbenzene oxidation reaction catalyzed by complexes Ni(L1)2 the extraordinary results were received. Really significant increase in conversion degree of oxidation into PEH at maintenance of selectivity on level SPEH ~ 90% occurs. The degree of conversion into PEH is increased from 4-6 up to 12% for complexes of Ni(II)(acac)2 (Ni(O/O)2) with 18C6 (1:1 and 1:2) and from 12 up to 16% for complex of Ni(II)(enamac)2 (Ni(O/NH)2) (1:1). Besides this the increase in the initial rate of reaction w0 (Figure 1), and SPEH,max from 90% to 98-99% (18K6) are observed [33,90,91]. In the case of additives of Me4NBr into reaction of ethylbenzene oxidation catalyzed by Ni(II)(acac)2 the value of SPEH,max=95% is higher than under catalysis by Ni(II)(acac)2 without addition of L2. The SPEH,max is reached not at the beginning of reaction of ethylbenzene oxidation, as it occurs at the case of complexes with 18C6, but at C=2-3%. Selectivity remains in the limits 90% <S≤ 95% to deeper transformation degrees of ethylbenzene C≈19% than in the presence of additives 18K6 (C≈12%) [33,92,93]. Additives of 18K6 or Me4NBr to ethylbenzene oxidation reaction catalyzed by Ni(L1)2 lead to significant hindering of heterolysis of PEH with formation of phenol (PhOH) responsible for selectivity decrease. At that induction period of PhOH formation in the presence of Me4NBr is significantly higher than in the case of 18K6 [90-93]. Influence of quaternary ammonium salt on catalytic activity of Ni(II)(acac)2 as selective catalyst of ethylbenzene oxidation into PEH extremely depends on radical R structure of ammonium cation. If cetyltimethylammonium bromide (CTAB) is added, SPEH,max is reduced down to 80-82% [92,93]. The rate w0 is significantly increased, in ∼ 4 times in comparison with ethylbenzene catalysis by Ni(II)(acac)2 complex. The initial rate of PEH accumulation wPEH,0 is higher than in the case of ethylbenzene oxidation catalyzed by the system {Ni(II)(acac)2 + Me4NBr}. However initial rates of accumulation of side products of reaction of AP with MPC are also significantly increased (Figure 1b). The decrease in PEH selectivity connected with heterolysis of PEH. The phenol formation is observed at lower conversions of RH transformation. Analysis of consequence of ethylbenzene oxidation products formation catalyzed by systems {Ni(L1)2+18К6} and {Ni(II)(acac)2+R4NBr} showed that the mechanism of products formation is unchanged as compared with oxidations catalyzed by Ni(L1)2 or {Ni(L1)2+HMPA}. The products PEH, AP and MPC were established to be formed parallel (wP/wPEH ≠ 0 at t→0) in the course of the process, AP and MPC were formed also parallel (wAP/wMPC≠0 at t→0). Catalysis of ethylbenzene oxidation initiated by {Ni(II)(acac)2 + CTAB} system is not connected with formation of micro-phase by the type of inverse micelles since the micellar effect of CTAB revealing at t0 < 1000 [77] is as a rule not important at t0 ≥ 1200. Furthermore, as we saw the system {Ni(II)(acac)2 + CTAB} was not active in decomposition of ROOH. For estimation of catalytic activity of nickel complexes as selective catalysts of ethylbenzene oxidation into α-phenylethylhydroperoxide we proposed to use parameter S·C. The S is mean value selectivity of oxidation into PEH, which evaluated a change of S in the course of


87

oxidation from S0 at the beginning of reaction to some Slim, conditional value chosen as a standard.

a

Ni(O,0)2

I row-wPEH,0, II-wAP+MPC,0, III-wPEH, IVwAP+MPC

wo.105

Ni(O,NH)2

14 12 10 8 6 4 2 0

12.64 8.61 6.25

5.38

4.44

2.36 0 0

0 0

b 70 60 50 40 30 20 10 0

9.65 8.15

w0, w.106, mol l-1 s-1 61

29

27 21

16.7

17

2.2 2

1.8 1

2.6 1.3

11 0000

2.6 1.1

27

23

19

15 2.7

Figure 1a. Dependences of initial rates w0 (mol l-1 s-1) on [18К6] concentration in ethylbenzene oxidation reactions catalyzed by {M(L1)2+18К6} (M=Ni(II), L1=acac-1, enamac-1). [M(L1)2]=1,5·10-4 mol/l, 120°С. b. Dependences of initial rates w0 (mol l-1 s-1) and the rates w (mol l-1 s-1) in the process of ethylbenzene oxidations catalyzed by {M(L1)2+18К6} (M=Ni(II), L1=acac-1, enamac-1) on [R4NBr] (mol/l). [M(L1)2]=1,5·10-4 mol/l, 120°С.

For comparable by value systems selectivity as Slim was selected the value Slim = 80% approximately equal to selectivity of non-catalyzed ethylbenzene oxidation into PEH at initial stages of reaction. The value selectivity was carried out in the limits S0 ≤ S ≥ Slim (Smax >


88

80%), C − conversion at S = Slim [33, 60]. The system {Ni(II)(acac)2+Me4NBr} by the value of parameter S·C (S·C ~ 24·102 (%,%)) is the most active catalyst of ethylbenzene oxidation into PEH as compared with catalysis by systems {Ni(II)(L1)2+18C6(HMPA)} [91]. We established that in the presence of 18K6 or R4NBr only without nickel complex autocatalytic developing of process with initial rates by order lower was observed. The SPEH,max, equal to 85% (18K6) or 95% (Me4NBr) at the beginning of ethylbenzene oxidation was sharply reduced with the increase of ethylbenzene conversion degree. The PhOH formation is observed from the very beginning of reaction. Synergetic effects of increase in parameter w0 and S·C and indicated the formation of active complexes Ni(L1)2 with (L2) [94] structure 1:1 (L1= (acac)¯, L2=18C6, R4NBr), 1:2 (L1= (acac)¯, (enamac)¯, L2=18C6) [90-93] and also the products of their transformation (Figure 1(a, b), 2). The stability of homo polynuclear heteroligand complexes Nix(L1)y(L1ox)z(L2)n (L1ox= MeCOO-, L2=18C6, R4NBr) ("А") formed in the course of oxidation seems to be due to the intermolecular and intramolecular hydrogen bonds. The possibility of supra molecular structures formation in this case is high [95-97]. The formation of complexes Ni(L1)2 with L2=18C6 or R4NBr was also proved by spectrophotometry under analysis of UV spectra of absorption of Ni(L1)2 and R4NBr (18C6) mixtures solutions. At that L2 coordinate with metal ion with preservation of ligand L1 in internal coordination sphere of complex [90,92]. Under formation of complexes of Ni(L1)2 with L2 in spite of axial coordination by the fifth coordination place of nickel (II) ion the outer sphere coordination of L2 (H–bonding) with acetylacetonate-ion is also possible.

30

24.3

25

20.6

20 15

9.6

10 5

Br } {N

i(I I)( ac ac

)2 +M e4 N

)2 +1 8C 6} i(I I)( ac ac {N

{N

i(I I

)(a ca c

)2 +H M FA

}

0

Figure 2. Parameter S·C·10-2 (%,%) in the ethylbenzene oxidation upon catalysis by сatalytic systems {Ni(II)(acac)2+L2} with L2=Me4NBr, 18C6, HMPА. [Ni(II)(acac)2]=1.5·10-4 mol/l, 120°C.


-2

a

15

S· C ·10 (%,%) 18.12

20 11.9

89

16.2

15.9

11.9

17.47 11.89

10 5 0 0

2,0·10-4 4,6·10-4 1,0·10-3 1,6·10-3 3,0·10-3 5,0·10-3 [PhOH], mol/l

Figure 3. Continued on next page.

b

3

[PhOH].10 , mol/l

25 20 2

15

3

1

10 5 0 0

10 20 30 40 50 60

t, h Figure 3a. Dependence of parameter S·C·10-2(%,%) on [PhOH] in reaction of ethylbenzene oxidation catalyzed by {Ni(II)(acac)2+MP+PhOH}. [Ni(II)(acac)2] = const = 3·10-3 mol/l, [MP] = const = 7·10-2 mol/l. 120°C. 3b. Kinetics of accumulation of PhOH in reaction of ethylbenzene oxidation catalyzed by binary system {Ni(II)(acac)2+МP} (1) and two triple systems {Ni(II)(acac)2 + МP + PhOH} with variable values of [PhOH] = 4.6·10-4 mol/l (2) or 3·10-3 mol/l (3) and [Ni(II)(acac)2] = const = 3·10-3 mol/l, and [МP] = const = 7·10-2 mol/l. 1200C.

The possibility of outer sphere coordination of R4NX with β-diketonates (Ni(II), Fe(III)) was demonstrated by us using complexes Fe(III)(acac)3 in the presence of various R4NBX. In the UV spectrum Fe(III)(acac)3 exhibit an intense absorption band at ν = 37·10-3 cm-1 (CHCl3) of the π – π* transition of the conjugated cycle of the acetylacetonate ion [92,93]. In the presence of salts R4NX (Me4NBr, CTAB, (C2H5)4NBr, (C2H5)3C6H5NCl and the other) a

90


decrease in the intensity and a bathochromic shift of the absorption maximum to ν = 36·10-3 cm-1 (Δ λ ≈ 10 nm) are observed. Such a change in spectrum indicates the influence of R4NX coordinated in the outer sphere on conjugation in the ligand. The change in the conjugation in the chelate ring of acetylacetonate complex, when R4NX is coordinated in the outer coordination sphere of the metal can be caused by participation of the oxygen atoms of the acetylacetonate ion in the formation of coordination bonds with the ammonium ion or hydrogen bonds with alkyl substituents of the ammonium ion [92,93]. As in the case of ethylbenzene oxidation catalyzed by nickel complexes (Ni(L1)2), at the catalysis by Fe(III)(acac)3 the SPEH,max increases as [Cat] is reduced. However, this increase is less significant, from SPEH = 42-46% to SPEH = 65%. We also observed a reduction in the rate of ethylbenzene oxidation as [Fe(III)(acac)3] decreased. However, the dependence of [PEH]max on [Fe(III)(acac)3] shows an extremum, suggesting that the mechanism of catalysis is more complicated in this case [67,93,98]. Fe(III)(acac)3, and formed in the course of ethylbenzene oxidation Fe(II)(acac)2, are inactive in PEH decomposition [67,93,98]. In our articles it was established, that in ethylbenzene oxidation catalyzed by Fe(III)(acac)3 ([Cat]=(0.5÷5)·103 mol/l, (80, 120°С)) the oxidation products MPC and AP as well as PEH are the major products. They are formed parallel both at the beginning of reaction, and at deeper stages of oxidation: wP/wPEH is constant and nonzero at t → 0 (P=AP or MPC) [67,93,98]. The effects of electron-donor exoligands-modifiers on w, SPEH and C of the ethylbenzene oxidation catalyzed by Fe(III)(acac)3 were studied at [Cat] = 5·10-3 mol/l. In this case [PEH] = [PEH]max. In the presence of electron-donor monodentate ligand HMPA SPEH,max is increased from 42 up to ~57% (80°С), conversion degree C from 5 up to 15% ([Cat] = 5·10-3 mol/l). These were the maximum effects of electron-donor monodentate ligands on the SPEH and C of ethylbenzene oxidation at catalysis by Fe(III)(acac)3 [67,93]. In ethylbenzene oxidation in the presence of {Fe(III)(acac)3(5·10-3 mol/l)+ R4NBr(0.5·10-3 mol/l)} (R4NBr=CTAB) (80°С) the SPEH,max=65%, which is reached in the developed process (Figure 4a (1, 2)), is higher than in the case of use of additives of monodentate ligands HMFA, DMF [93]. The fast decrease in SPEH at the beginning steps of the process is connected with the transformation Fe(III) complexes in Fe(II) complexes in the course of ethylbenzene oxidation (the auto acceleration period of the reaction is observed), the increase in wPEH,0, decrease in wP,0, and [PEH]max at catalysis by complexes (Fe(II)(acac)2)x·(R4NBr)y are observed. Then the increase in SPEH occurs at the expense of significant decrease in AP and MPC formation rate in the process at parallel stages of chain propagation and chain quadratic termination (wP/wPEH ≠ 0 at t → 0, wAP/wMPC ≠ 0 at t → 0). The conversion degree is increased from C = 4 up to ~ 8% (at SPEH=40-65%) (Figure 4a). Additives of CTAB to ethylbenzene oxidation reaction catalyzed by Fe(III)(acac)3 lead to significant hindering of heterolysis of PEH with formation of phenol responsible for decrease in SPEH. The growth in S·C is ∼ 2.6, 2.36, 1.4 times for R4NBr=CTAB, (С2H5)4NBr), Me4NBr) respectively in comparison with catalysis by Fe(III)(acac)3 (S·C=2.1·102 (%,%)) (Figure 4b). In given case for value Slim as standard we accept Slim =40%, a value that approximately corresponds to the selectivity of ethylbenzene oxidation in the presence of ligand-free Fe(III)(acac)3 (5·10-3 mol/l) (80°С) under the steady-state reaction conditions, C is the conversion for which SPEH ≤ Slim. In the absence of a catalyst, the addition of L2 has


91

practically no effect on selectivity of ethylbenzene oxidation reaction and the reaction proceeds in the autocatalytic mode at w0 below that in the catalysis by Fe(III)(acac)3.

a 95

S PEH, %

85 75 65 55 45 35 25 0

5

10

C, % Figure 4. Continued on next page.

-2

b

5,46

4,97 3,43

2,9

H 2O +

CT AB

CT AB

H 2O +

NB r

M e4

NB r

1,14

M e4

(C

(%,%) 6,91

2H 5) (C 4N 2H Br 5) 4N Br + H 2O

8 7 6 5 4 3 2 1 0

S·C · 10

Figure 4a. Dependences SPEH от C in the ethylbenzene oxidation in the presence Fe(III)(acac)3 (1) and systems {Fe(III)(acac)3 + CTAB} (2) and {Fe(III)(acac)3 + CTAB + H2O} (3). 800C. b. Parameter S·C·10-2 (%,%) in the ethylbenzene oxidation at catalysis by Fe(III)(acac)3, and catalytic systems {Fe(III)(acac)3+R4NBr} and {Fe(III)(acac)3+R4NBr+H2O}. [Fe(III)(acac)3] = 5·10-3 mol/l, [R4NBr] = 0.5·10-3 mol/l, 80°C.

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The no additive (synergetic) effects of growth in S·C parameter and w0 observed in the reactions catalyzed by Fe(III)(acac)3 in the presence of R4NBr, and also obtained kinetic regularities of ethylbenzene oxidation indicate the formation catalytic active complexes [94] presumably of (Fe(II)(acac)2)x·(R4NBr)y as well as the complexes, produced as a result of the transformation of (Fe(II)(acac)2)x·(R4NBr)y during oxidation. The most effect of increase in S·C was got in the case of CTAB additives. As we saw at the catalysis by nickel complexes in the presence of the CTAB additives SPEH,max is reduced down from 90 to 80-82% as compared with increase in SPEH,max (94%) in the case of Me4NBr additives [93]. Due to the favorable combination of the electronic and steric factors appeared at inner and outer sphere coordination (hydrogen bonding) of CTAB with Fe(II)(acac)2 the oxidative degradation of the acetylacetonate ligand may follow “dioxygenase-like” mechanism, described by Scheme 4. There is a high probability of formation of stable complexes of structure Fe(II)x(acac)y(OAc)z(CTAB)n (“B”). Out-spherical coordination of CTAB evidently creates sterical hindrances for regio-selective oxidation of the (acac)¯− ligand, and the transformation of the intermediate complex (“B”) into the final product of dioxygenation. In the case of catalysis by the {Fe(III)(acac)3 + DMF} system the complexes Fe(II)x(acac)y(OAc)z(DMF)n, formed in the process, are not stable, though DMF like CTAB forms H-bonds with acetylacetonate ion [67]. The rapid decrease in SPEH was observed. SPEH,max at the catalysis by the {Fe(III)(acac)3 + DMF} system was not higher in fact than SPEH,max at the catalysis by the {Fe(III)(acac)3 in the absence of the additives. With the use of HMPA as exo ligand, that did not form H – bonds with chelate ring of Fe(II)(acac)2, the transformation of Fe(II)(acac)2)·HMPA was not observed, although HMPA as electron-donor ligand was characterized with a higher DN value (after V. Gutmann) as compared with DMFA [67]. Catalysis of ethylbenzene oxidation initiated by {Fe(III)(acac)3 + CTAB} system (80°С) in the case of application of the small concentrations R4NBr (0.5·10-3 mol/l) is not connected with formation of micro-phase by the type of inverse or sphere micelles. As we saw above the system {Fe(III)(acac)3 + CTAB} was not active in decomposition of PEH. wP/wPEH ≠ 0 at t → 0, wAP/wMPC ≠ 0 at t → 0. Analogous mechanism of formation PEH, AP and MPC is observed at the use of Me4NBr and (С2H5)4NBr additives which do not form micelles. At the concentration of [CTAB] = 5·10-3 mol/l the rate of the PEH accumulation and [PEH]max decreases significantly, since the probability of micelles formation obviously increases. Thus, we established the interesting fact – the catalytic effect of small concentrations of quaternary ammonium salts, [R4NBr] = 0.5·10-3 mol/l, which in 10 times less than [Fe(III)(acac)3]. It is known that salts QX can form complexes with metal compounds of variable composition which depends on the nature of solvent [93]. The formation of poly nuclear heteroligand complexes (Fe(II)(acac)2)x·(R4NBr)y (and Fe(II)x(acac)y(OAc)z(R4NBr)n also) seems to be probable.


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3d. Triple Catalytic Systems Including Bis (Acetylacetonate) Ni(Ii) and Additives of Electron-Donor Compound L2 and Phenol as Exo Ligands One of the most effective methods of control of selective ethylbenzene oxidation into αphenylethylhydroperoxide with dioxygen may be the application of the third component of catalytic system − phenol (PhOH) along with Ni(II)(acac)2 and the additives of electron-donor ligands L2 (L2= MSt (M=Na, Li), MP, HMPA) [99]. We discovered phenomenon of the considerable increase in the efficiency of selective ethylbenzene oxidation reaction into α-phenylethylhydroperoxide with dioxygen in the presence of triple systems {Ni(II)(acac)2+L2+PhOH}, parameters S·C, the conversion degree C (at SPEH ~85-90%), and the hydroperoxide contents ([PEH]max), in comparison with catalysis by binary systems {Ni(II)(acac)2+L2}. The obtained synergetic effects of increase in S·C under catalysis by {Ni(II)(acac)2 + L2} on [МP] ((S·C)max ~ 17,5·102 (%,%) at [МP]=const=7·10-2 mol/l), in the presence of inhibitor phenol ([PhOH]=const=3·10-3 mol/l) seems to be due to unusual catalytic activity of formed at mentioned conditions triple complexes [М(L1)2·(L2)n·(PhOH)m]. This presumption is confirmed by dependences of S·C on [Ni(II)(acac)2] at [PhOH]=const=3·10-3 mol/l and [МP]=const=7·10-2 mol/l ((S·C)max=17,47·102 (%,%), [Ni(II)(acac)2]=3·10-3 mol/l) and also of S·C on [PhOH] at [Ni(II)(acac)2]=const=3·10-3 М and [МP]=const=7·10-2 mol/l. In last case S·C reaches extremum (S·C)max=17,5 and 18,12·102 (%,%) at two values of [PhOH] = 3·10-3 и 4,6·10-4 mol/l accordingly (Figure 5a). Comparison of kinetic regularities of ethylbenzene oxidation catalyzed by triple systems {Ni(II)(acac)2(3·10-3 mol/l) + МP(7·10-2 mol/l) + PhOH} ([PhOH]= 3·10-3 or 4,6·10-4 mol/l) was carried out. Obtained data testify on the fact that in both cases selective catalysis of ethylbenzene oxidation into PEH is connected with formation in the course of oxidation of catalytically active complexes with structure 1:1:1 [94,99]. The some differences observed at the initial stages of two reactions are caused obviously by the different initial conditions of triple complexes Ni(II)(acac)2·(L2)·(PhOH) formation in the course of catalytic ethylbenzene oxidation in these cases. At catalysis by triple system {Ni(II)(acac)2+МP+PhOH} with small [PhOH] =4.6·10-4 mol/l the fast increase in the concentration of PhOH right up to [PhOH] = (3-5)·10-3 mol/l (at t=0-5 h) is observed. [PhOH] = (3-5)·10-3 mol/l ∼ corresponds to [PhOH] for the first combination {Ni(II)(acac)2 (3.0·10-3 mol/l) + МP (7.0·10-2 mol/l) + PhOH (3.0·10-3 mol/l)} and to the formation of complexes of structure [М(L1)2·(L2)·(PhOH)]. The increase in the rate of PhOH accumulation at the beginning of the process may be due to the function of PhOH as acid that becomes stronger because of outer sphere coordination of PhOH with nickel complex Ni(II)(acac)2·МP, and this effect favors to heterolysis of PEH with the formation of phenol [100]. This supposition is confirmed by the following facts. So the accumulation of PhOH, but not the consumption, at the maximum initial rate wPhOH,0=wPhOH,max is observed upon addition of PhOH (3.0·10-3 mol/l) into the reaction of ethylbenzene oxidation catalyzed by coordinated saturated complexes Ni(II)(acac)2·2MP ([Ni(II)(acac)2] = 3.0·10-3 mol/l, [МP] = 2.1·10-1 mol/l), and also in the case of the ethylbenzene oxidation catalyzed by binary system {Ni(II)(acac)2(3.0·10-3 mol/l) + PhOH(4.6·10-4 mol/l)} at [МP] = 0 [99]. Phenomenal results were obtained by us in the case of application of system, including NaSt as L2 {Ni(II)(acac)2 (3.0·10-3 mol/l) + NaSt (3.0·10-3 mol/l) + PhOH (3.0·10-3 mol/l)}.

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Parameters C > 35% at the SPEH,max =85-87%, concentration [PEH]max = 1.6 – 1.8 mol/l (∼27 mass ), S·C ∼ 30.1·102 (%,%) are much higher, than in the case of the other triple systems and the most active binary systems [99]. These data and some of other effective triple systems (L2=LiSt, MP, HMPA) are protected by patent RU (2004); the authors are L.I. Matienko, L.A. Mosolova, patent holder is Emanuel Institute of Biochemical Physics, Russian Academy of Sciences. Similarity of phenomenology of ethylbenzene oxidation in the presence of {Ni(II)(acac)2 (3.0·10-3 mol/l) + MP (7.0·10-2 mol/l) + PhOH (3.0·10-3 mol/l)} and {Ni(II)(acac)2 (3.0·10-3 mol/l) + NaSt (LiSt) (3.0·10-3 mol/l) + PhOH (3.0·10-3 mol/l)} allows assuming analogous mechanism of selective catalysis realizing by triple complexes formed in the course of oxidations.

a 80

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Figure 5a. Dependence of SPEH от С in the reactions of the oxidation of ethylbenzene catalyzed catalytic systems {Fe(III)(acac)3+18C6(5·10-3 mol/l)} and {Fe(III)(acac)3+18C6(0,5·10-3 mol/l)} without additives of water (1,2), and in the presence of 3.7·10-3 mol/l H2O. [Fe(III)(acac)3]=5·10-3 mol/l. 800C. b. The values of parameter S·C·10-2 (%,%) in the reactions of the oxidation of ethylbenzene catalyzed by Fe(III)(acac)3 or catalytic systems {Fe(III)(acac)3+18C6} without additives of water (1,2), and in the presence of 3.7·10-3 mol/l H2O. [Fe(III)(acac)3]=5·10-3 mol/l, 800C.


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Also, the parallel formation of PEH and side products AP and MPC is established in these two cases: wP/wPEH ≠ 0 at t→0 (P=AP or MPC) and wAP/wMPC≠0 at t→0 at the beginning of reaction and in developed reaction of ethylbenzene oxidation catalyzed by {Ni(II)(acac)2+L2+ PhOH} (L2 = NaSt (LiSt), MP). Increase in SPEH during the catalysis by complexes Ni(II)(acac)2·L2·PhOH (L2 = NaSt, MP) in comparison with non-catalyzed oxidation is connected with the change of direction of the formation of side products AP and MPC (AP and MPC are not formed from PEH, as it takes place in non-catalyzed oxidation) and also with hindering of heterolytic decomposition of PEH [99]. The advantage of the triple systems consists in the fact that the formed in situ complexes Ni(II)(acac)2·L2·PhOH are active for a long time, and are not transformed in the course of the process into inactive particles. Thus, the application of triple systems, including Ni(II)(acac)2, electron donor ligand L2 and PhOH, as homogeneous catalysts is one of the most effective methods of control of selective ethylbenzene oxidation by dioxygen into PEH.

4. THE ROLE OF HYDROGEN–BONDING INTERACTIONS IN MECHANISMS OF HOMOGENOUS CATALYSIS As a rule reactivity and selectivity of metal complex homogenous catalysts have been controlled by variations in axial ligands used, focusing mainly on steric and electronic properties of the latter. At that the interactions in the secondary coordination sphere and the role of hydrogen bonds are investigated least of all. An increasing number of synthetic catalysts and related systems show the benefits of secondary interactions [101,102], which are generally difficult to control. While nature’s metalloenzymes use secondary interactions, hydrogen bonding or proton transfers in active site. The importance of H-bonds in dioxygen O2 binding and O2 activation is well documented in metalloproteins [103]. For instance, removal of residues within the active sites that H-bond to the Fe–O2 unit in hemoglobins causes a loss in respiration [104]. In addition, dioxygen affinity in hemoglobins has been correlated with the H-bond network surrounding the iron center. Protein dysfunction is observed in Cytochrome P450 when the active site H-bond network proximal to the Fe–O2 moiety is disrupted [105]. H–bonding interactions are useful for design of catalytic systems, imitating enzymes activity. The participation of H-bonds in dioxygen binding to cobalt complexes and O2 activation was studied in [106]. The cobalt complexes [CoIIH22iPr]¯ (Potassium {Bis[(N’-tertbutylureayl)-N-ethyl]-(N’-isopropylcarbamoylmetyl)-aminato-cobaltate(II)}) and [CoIIH1iPr]¯ (Potassium {[(N’-tert-butylureayl)-N-ethyl]-bis(N’-isopropylcarbamoylmetyl)-aminatocobaltate(II)}) with multiple H-bond donors readily bind (Co–O2) and activate dioxygen (Co(III)–OH complexes). The greater number of intramolecular H-bonds produces the more stable Co(III)–OH complex. The complex [CoIIH0iPr]¯ (Potassium {bis[((N’isopropylcarbamoylmetyl)-aminato]cobaltate(II)}) with no intramolecular H-bond donors does not react with dioxygen. Investigated Co(II) complexes with rigid H-bond framework are not able to form intermolecular H-bonds. Mononuclear non-heme iron proteins are involved in various biological processes. Iron centers with terminal hydroxo ligands (Fe–OH) are proposed to be the active species in many catalytic cycles of enzymes including for example protocatechuate 3,4-dioxygenase [107].

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Synthesizing the mononuclear Fe–OH moiety is a challenge because of its strong propensity to form multinuclear hydroxo- and oxo-bridged complexes and the different methods are used for synthesis of stable mononuclear Fe–OH complexes [108,109,110]. So, bulky deprotonated urea-derived ligand (H3buea) stabilizes the Fe–OH units by steric hindrance and intramolecular hydrogen bonds forming a protective cavity [110]. In [107] it was reported the first mononuclear iron(II) hydroxo (1) and iron(III) dihydroxo (2) complexes (1=[Fe(II)(L)2(OH)](BF4), 2=[Fe(III)(L)2(OH)2](BF4), L=bis(N-methylimidazol-2-yl)-3methylthiopropanol) stabilized by an intermolecular hydrogen-bonding assembly. The principle of acceleration of chemical transformations by preliminary favorable orientation of reagent by virtue of molecular forces of the hydrogen bond type or hydrophobic interactions is widely involved in enzymatic catalysis [111]. An example of catalytic process for which the orientation of reagents in the outer coordination sphere of metal complexes is to be important is the formation of urethanes in the coordination sphere of Fe(III)(acac)3 [112]. The role of the catalyst in this process consists in the creation of favorable conditions for the formation of a co-planar complex between the reagents in which an optimal mutual orientation of isocyanide and alcohol, providing a noticeable decrease in activation energy, is accomplished. The numerous transition-metal β-diketonates undergo a wide range of substitution reactions common to aromatic systems. The methine protons on the complexes’ chelate rings can be displaced by many different unsaturated electrophilic groups ‘‘E” [114]. This is metalcontrolled process of C–C bond formation [115]. The most effective catalyst of those reactions is Ni(II)(acac)2. The reactions formally are analogy to electrophilic reactions of Michael addition [114]. The limiting stage of those reactions is the formation of resonance stabilized zwitter-ion {M(II)(L1)n+•E-}, in which proton transfer occurs [114,115]. The appearance of new absorption in electron specters of absorption of mixtures {Ni(II)(acac)2+ L2+E}, which may be explained as charge transfer from ligand donor systems of complex Ni(II)(acac)2•L2 to π-acceptors E= tetrtacyanethylene or chloranil, testify in the CTC L2Ni(II)(acac)2•E favor. The outer sphere reaction of connection of E to γ-C atom of acetylacetonate ligand is followed by the formation of L2Ni(II)(acac)2•E [33,59]. As above mentioned the axial coordination of electron-donor exo ligands L2 by M(II)(L1)2 controls the formation of primary M(II)(L1)2•O2 complexes and the following outer sphere coordination interactions. The coordination of L2 by Ni(L1)2 (L1=acac¯) promoting stabilization of intermediate zwitter-ion L2(L1M(L1)+O2¯) leads to increase in possibility of regio-selective connection of O2 to C–H methine bond of acetylacetonate ligand activated by the coordination with metal. The outer sphere reaction of insertion of O2 into chelate cycle is dependent on the metal and ligand-modifier L2. So the reaction of L1 oxygenation occurs by analogy with the action of the Ni(II)-containing dioxygenase – acireductone dioxygenase, ARD [64], with reactions of oxygenation imitating the action of quercetin 2,3-dioxygenase (Cu, Fe) [65,66], with the action of L-tryptophan-2,3-dioxygenase (nickel complexes (Scheme 1-3)) or by analogy with the action of Fe(II)-containing Acetylacetone dioxygenase (Dke 1) (iron complexes, Scheme 4). The role of H-bonding interaction in mechanism of catalytic active complexes formation was investigated by us by means of the introduction of small amounts of H2O into catalytic reaction [116,117].


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In the last years the interactions between enzyme molecules and surrounded H2O molecules, because of its importance for enzyme activity is in the centre of attention of many investigators [118,119]. Water in active site of protein can play more than a purely structural role: as a nucleophile and donor proton, it can be a reagent in biochemical processes [118]. So proton transfer facilitated by a bridging water molecule also seems to occur in horseradish Peroxidase, where it enables the transfer of a proton from iron-coordinated H2O2 to a His residue in the active site [120] – the first step in cleavage of the O–O bond. Ab Initio simulations without this bridging water arrive at an energy barrier considerably greater than that found experimentally, because of the large separation of the proton source and sink. In [121] the role of H-bonds of water in mechanism of action of Heme oxygenases (HO) is investigated. HO uses Heme (iron-protoporphyrin IX) as substrate and cofactor to cleave it at one meso position into biliverdin, CO, and free iron [122]. The additives of water can serve as mechanistic probes and aid in obtaining true mechanistic understanding in some organocatalytic reactions [123]. The water is nucleophile in palladium-catalyzed oxidative carbohydroxylation of allene-substituted conjugated dienes [124]. This is an example of Pd- catalyzed oxidation leading to C –C bond formation in water with subsequent water attack on a (π-allyl) palladium intermediate. The different effect of the water concentration on the intra- and extra-diol oxygenations of 3,5-di-tert-butylcatechol with O2, catalyzed by FeCl2 in tetrahydrofuran-water indicates that the intermediates for two reactions are different (model for Catechol-2,3-dioxygenases) [125]. We considered the possibility of the positive effect of small amounts of water on the rate of the transformation of iron complexes with L2 (L2 = R4NBr, 18C6) and, probably, on the parameters SPEH and C in the ethylbenzene oxidation, catalyzed {Fe(III)(acac)3 + L2}. Outer sphere coordination of H2O molecules may promote the stabilization of intermediate zwitterion L2(L1M(L1)+O2¯) and as a consequence the increase in the probability of the regioselective addition of O2 to nucleophilic γ-C аtom of (acac)¯ ligand one expected. It is well-known that the stability of zwitter-ions increases in the presence of the polar solvents [114]. The H – bond formation between H2O molecule and zwitter-ion may also promote the proton transfer inside of the zwitter-ion followed by the zwitter-ion conversion into the products via Scheme 4 [114,115]. It is known the cases of the increase in the ratio of alkylation’s products on γ-C atom of the R4N(acac) in the presence of insignificant additives of water (∼10-3 моль/л) as compared to the alkylation’s reaction in the non proton solvents [126]. It is mentioned analogy facts of increase in catalytic activity of 18C6 reference to electrophilic reactions on γ-C-atom of (acac)⎯ ligand in THF in the presence of mill moles of water [126]. Monodiamine complex Ni(II)-[(R,R)-N,N-dibenzylcyclohexane-1,2-diamine]Br2 catalyzes the Michael addition reactions in the presence of water [127]. Few examples are known to date about the influence of small additives of H2O (~10-3 mol/l) on the homogeneous catalysis by transition metal complexes in the hydrocarbon oxidation with molecular O2. The role of H2O as a ligand in metal complex-catalyzed oxidation has not been practically investigated [111,121,128]. And it is unknown examples of catalytic reactions, when addition of water in small amounts enhances the reaction rate and the product yield. Some of known facts are concerned of the use of onium salts QX together with metal catalyst. So the decrease in the rate of the tetralin oxidation, catalyzed with onium-

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decavanadate(V) ion-pair complexes in the presense of ~10-3 mol/l H2O was observed [129]. The oxidations are dependent on structural changes in the inverse micelles, in response to concentration changes of ion-pair complexes existing only in the presence of small amounts of H2O [130]. The most known facts are connected with the influence of small concentrations of H2O on the catalysis of the ROOH homolysis by onium salts (including quaternary ammonium salts). The acceleration of ROOH homolysis may be the consequence of H – bond formation between ROOH, H2O and QX [131]. Also it is important to understand the role of small amounts of water because some water is always formed during the catalytic oxidation of the hydrocarbon. The homogeneity of the hydrocarbon solution remains upon addition of small amounts H2O ([H2O] ∼ 10-3 mol/l) [130].

4a. The Effect of Small Amounts of H2O in the Ethylbenzene Oxidation, Catalyzed with {Fe(III)(acac)3+R4NBr} System We first established the increase in catalytic activity of system on basis of transition metal complex and donor ligand-modifier, namely, system {Fe(III)(acac)3 + CTAB}, as catalyst of the ethylbenzene oxidation to PEH at the addition of small amounts of H2O (~10-3 mol/l) [116]. It was found that the admixtures of H2O caused no additive (synergistic) effects of growth in selectivity SPEH,max, conversion degree C (SPEH,max ≈ 78.2%, C ≈ 12%) (parameter S·C). ∆ SPEH,max ≈ 14% and ∆C ≈ 4%, as compared with catalysis by {Fe(III)(acac)3 + CTAB} and ∆ SPEH,max ≈ 40% and ∆C ≈ 8% as compared with catalysis by Fe(III)(acac)3 (Figure 4a,b). The effect of small additives H2O depends significantly on radical R structure of ammonium cation. The decrease in the selectivity of systems {Fe(III)(acac)3 + R4NBr} (R = Me or C2H5) as catalysts of the ethylbenzene oxidation to PEH was observed. The dependence of SPEH on the C in the discussed ethylbenzene oxidation, catalyzed with iron complexes in the presence of small amounts of H2O has extremum as well in the absence of H2O additives. The decrease in values of SPEH,max was observed. Thus, SPEH,max ≈ 43% ({Fe(III)(acac)3 + (C2H5)4NBr + H2O}) < SPEH,max = 48% (at the catalysis with {Fe(III)(acac)3 + (C2H5)4NBr (5·10-4 М)} in the absence of H2O) and SPEH,max ≈ 43% ({Fe(III)(acac)3 + Me4NBr + H2O}) < SPEH,max = 64% ({Fe(III)(acac)3 + Me4NBr}). The fall in the parameters SPEH,max and S·C one can explain by high rates of oxygenation of intermediate complexes Fe(II)x(acac)y(OAc)z(R4NBr)p(H2O)q into final product (Figure 4b). The discovered fact of increase in parameters SPEH,max, C (and S·C) at catalysts of the ethylbenzene oxidation by {Fe(III)(acac)3 + CTAB + H2O(~10-3 mol/l)} seems to be due to the increase in stationary concentration of active selective heteroligand intermediate Fe(II)x(acac)y(OAc)z(CTAB)n(H2O)m, formed in the course of the ethylbenzene oxidation (Scheme 4). The out-spherical coordination of CTAB, may create sterical hindrances from H2O coordination and regio-selective oxidation of (acac)- − ligand by the described above mechanism, and the rate of oxygenation of intermediate “B” to inactive final product Fe(OAc)2 reduced. Besides that the part of H2O molecules may be absorbed by hydrophilic cation n-C16H33Me3N+, and as a result the lowering of the rate of the intermediate heteroligand complex “B” conversion to the end products was realized.


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In the oxidation in the presence of {Fe(III)(acac)3 + CTAB(5·10-4 mol/l) + H2O (3.7·10-3 mol/l)} system the PhOH as oxidation product was not found right up to 50 hours of the ethylbenzene oxidation. This fact is connected probably with the significant decrease in the activity of formed catalyst in the heterolytic decomposition of PEH with formation of phenol (PhOH) and also the inhibition of the rate of particles formation (Fe(OAc)2), responsible for PEH heterolysis [116]. The all reactions to investigate proceed in autocatalytic mode due to the transition Fe(III) to Fe(II). The products were formed with auto acceleration period longer than in the case of the H2O additives – free process. The reaction rates (as well as in the absence of the H2O additives [22]) rapidly becomes equal to w = wlim = wmax (w0). Under these steady – state reaction conditions the changes in oxidation rates in the both cases were due to the changes in PEH or P (AC+MPC) accumulations. The increase in w0 at catalysis by complexes (Fe(II)(acac)2)n(Me4NBr)m in the presence of the H2O is observed (as compared with catalysis by Fe(II)(acac)2, and catalysis by complexes (Fe(II)(acac)2)n(Me4NBr)m without H2O [93]). The rate w0 decreases insignificantly in the case of catalysis by (Fe(II)(acac)2)n((С2H5)4NBr)m and H2O additives (as compared with catalysis by complexes (Fe(II)(acac)2)n((С2H5)4NBr)m without H2O additives [93]. These are unusual results as compared with known facts of significant decrease in the hydrocarbon oxidation rate due the solvatation of radicals RO2• by molecules of water, forming in the course of the oxidation in the absence of Cat [24], or the deactivation of Cat with water in the processes of chain-radical catalytic hydrocarbon oxidation by O2 in no polar medium [25]. Unlike the catalysis by {Fe(III)(acac)3+CTAB+H2O} fall in initial rate w0, (in ∼ 2 times) is observed (Table). It was established that at the addition of 3.7·10-3 mol/l H2O into the ethylbenzene oxidation, catalyzed with {Fe(III)(acac)3+ R4NBr} (R4NBr= CTAB, Me4NBr, C2H5)4NBr} the mechanism of products formation is obviously unchanged. As in the absence of H2O the products AP and MPC formed parallel to PEH formation, at parallel stages of chain propagation and chain quadratic termination, AP and MPC formed in parallel stages also (wP/wPEH ≠ 0 at t → 0, wAP/wMPC ≠ 0 at t → 0 (here P= AP or MPC)) [116]. These data differed from known facts of catalysis with CTAB and systems, including CTAB, and transition metal complexes, consisting in the acceleration of PEH decomposition in the micelles of CTAB [78].

4b. The Effect of Small Amounts of H2O in the Ethylbenzene Oxidation, Catalyzed with {Fe(III)(acac)3+18C6} System In reaction of the oxidation of ethylbenzene with dioxygen in the presence of catalytic system {Fe(III)(acac)3(5·10-3 mol/l)+18К6} (80°С) in the absence of water the dependence of SPEH от С has extremum, as in the case of use of additives of ligands DMF or R4NBr. SPEH,max = 70% ([18К6]0 = 0.5·10-3 mol/l) and SPEH,max = 75.7% ([18К6]0 = 5·10-3 mol/l) in the process are higher than SPEH,max = 65% in the case of use of CTAB as exo ligand-modifier [91,93,117] (Figure 5a,b). The addition of 18C6 in the ethylbenzene oxidation with dioxygen


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catalyzed by Fe(III)(acac)3 result in the redistribution of the major oxidation products. The significant increase in [PEH]max is observed ~ 1.6 or 1.7 times at [18C6] = 5·10-4 mol/l, 5·10-3 mol/l, at that decrease in [AP] and [MPC] ~ 4, 5 times accordingly occurs (Figure 6a,b). 30 25

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40

t, h

Figure 6a. Kinetics of accumulation of PEH (1,2) and Ph (3,4) in the reactions of the oxidation of ethylbenzene catalyzed {Fe(acac)3+18C6} (1,3) and {Fe(acac)3+18C6+H2O} (2,4) [Fe(acac)3]=[18К6]=5·10-3 mol/l. [H2O]=3,7·10-3 mol/l. 800C. b. Kinetics of accumulation of AC (1, 3) и MPC (2, 4) in the reactions of the oxidation of ethylbenzene catalyzed {Fe(acac)3+18C6} (1,2) and {Fe(acac)3+18C6+H2O} (3,4). [Fe(acac)3]=[18К6]=5·10-3 mol/l. [H2O]=3,7·10-3 mol/l. 800C.

Additives of 18C6 lead to significant hindering of heterolysis of PEH with of the formation of phenol responsible for decrease in selectivity. In the presence of catalytic system {Fe(III)(acac)3+18К6} synergetic effect of increase in S·C parameter ~ 2,5 and 2,8 times at [18К6]0=0,5·10-3 mol/l and [18К6]0=5·10-3 mol/l correspondingly is observed in comparison with catalysis by Fe(III)(acac)3 (S·C =2,1·102 (%,%)) [91,117]. Obtained kinetic regularities of the oxidation of ethylbenzene testify to formation presumably of (Fe(II)(acac)2)p·(18К6)q complexes and products of their transformation in the course of oxidation. It is known that Fe(II) and Fe(III) halogens form complexes with crownethers of variable composition (1:1, 1:2, 2:1) and structure dependent on type of crown-ether and solvent [87]. Supposedly, due to the favorable combination of the electronic and steric factors appeared at inner and outer sphere coordination (hydrogen bonding) of 18C6 with Fe(II)(acac)2 (as also in the case of catalysis with complexes with CTAB [13]) there is a high probability of formation of sufficiently stable hetero ligand complexes of the common structure Fe(II)x(acac)y(OAc)z(18C6)n, the intermediate products of the oxygenation of (acac)ligands in the (Fe(II)(acac)2)p·(18C6)q complexes by analogy to the catalysis by acetyl acetone dioxygenase (M = Fe(II)) (Dke 1) (Scheme 4) that results in the SPEH,max and C increase: {Fe(III)(acac)3+18К6}→Fe(II)(acac)p·(18К6)q+O2→Fe(II)x(acac)y(OAc)z(18К6)n. (I)


101

At the addition of 3.7·10-3 mol/l H2O into the ethylbenzene oxidation, catalyzed with {Fe(III)(acac)3(5·10-3 mol/l)+18C6} system (80°С) the efficiency of system as selective catalyst, evaluated with parameters SPEH,max and S·C, decreases (Figure 5a,b). But the increase in C (at the SPEH,max ≥ 40%) from 4% into ~ 6,5% ({Fe(III)(acac)3+18К6(5·10-4 моль/л)+H2O}) and 9% ({Fe(III)(acac)3+18C6(5·10-3 моль/л)+H2O}) is observed. Analogy facts of decrease in parameters SPEH,max and S·C in the presence small amounts of water< as mentioned above were got by us at the use of systems ({Fe(III)(acac)3+ R4NBr(Me4NBr, (C2H5)4NBr)+H2O}as catalysts [116]. The observed kinetic regularities (Figure 5,6, Table) seems to be due to (Fe(III,II)(acac)n)m·(18К6)n complexes and dioxygenation products formations. Obviously at the coordination of H2O molecules the shift of 18К6 into outer coordination sphere of iron complex does not take place [132], as the fall of activity of catalytic system does not occur. It is known also that H2O molecules may form with crown-ethers the inclusion complexes through H-bonding [133], but enthalpy of its formation is small: ~ 2–3 kcal/mol [134]. The outer coordination of H2O molecules with iron complex with 18C6 [117] seems to promote the transformation of Fe(II)(acac)2)p·(18К6)q into particles of “B” type (Scheme 4), catalyzed the ethylbenzene oxidation to PEH, as the growth in SPEH occurs in the ethylbenzene oxidation. The fall in the SPEH,max at the use of water as ligand-modifier in this case seems to be due to the growth in the transformation rate of the active intermediate, polynuclear heteroligand complexes Fe(II)x(acac)y(OAc)z(18К6)m(H2O)n, into Fe(II) acetate [68], and the decrease in steady-state concentration of Fe(II)x(acac)y(OAc)z(18К6)m(H2O)n. The facts, which testify favor the increase in catalytic activity of {Fe(III)(acac)3 + 18C6} system as catalyst of the ethylbenzene oxidation into PEH in the presence of 3.7·10-3 mol/l H2O, were obtained. Table. The initial rates w0 and calculated rates of micro stages of chain initiation (wi,0), chain propagation (wpr,0) and (wi,0/wpr,0)·100% in the ethylbenzene oxidations catalyzed with Fe(III)(acac)3 and {Fe(III)(acac)3+L2} or {Fe(III)(acac)3+L2+L3} systems. [Fe(III)(acac)3]=5·10-3 mol/l. L2 = [CTAB] = 0.5·10-3 mol/l. L2 = [18C6] = 5·10-3 mol/l. L3= [H2O] = 3.7·10-3 mol/l. 80○ C L2, L3

w0 106

wi,0·107

wpr,0·106

(wi,0/ wpr,0) 100% 2.38

⎯

6.30

0.79

3.32

CTAB

7.65

1.63

3.14

5.19

CTAB+H2O

4.85

1.21

0.98

12.24

18C6

2.63

0.24

0.93

2.58

18C6 + H2O

6.94

0.15

5.58

0.27

The increase in the rate of the ethylbenzene oxidation catalyzed with ({Fe(III)(acac)3+18C6+H2O}) both at the initial stages of the process and in the course of the


102

oxidation was observed as compared with the catalysis in the absence of water. The growth in the initial rate is connected mainly with increase in the [AP] accumulation. The redistribution of the oxidation products takes place in the presence of water. At the early stages of the ethylbenzene oxidation in the presence of catalytic system {Fe(III)(acac)3(5,0·10-3 mol/l)+18C6(5,0·10-3 mol/l)+H2O(3,7·10-3 mol/l)} AP but not PEH becomes the major product of the reaction. The highest value of ethylbenzene oxidation selectivity to the AP, SАP,0 = 70%, and the lowest selectivity of ethylbenzene oxidation to the PEH, SPEH,0 ≈ 25%, are got in this case. The relation [АФ]/[МФК] increased from ~ 1,2 ({Fe(III)(acac)3 + 18C6 (5,0·10-3 mol/l)}) to 6,5 ({Fe(III)(acac)3 + 18C6 (5,0·10-3 mol/l) + H2O}). The additives of H2O do not change the order in which PEH, AP, and MPC form. As in the absence of water, the products PEH, AP and MPC form in parallel stages, AP and MPC result from parallel reactions also (wP/wPEH ≠ 0 at t → 0, wAP/wMPC ≠ 0 at t → 0) throughout the ethylbenzene oxidation process.

5. PARTICIPATION OF ACTIVE FORMS OF IRON AND NICKEL CATALYSTS IN ELEMENTARY STAGES OF RADICAL-CHAIN ETHYLBENZENE OXIDATION We suggest the original method for evaluation of catalytic activity of complexes formed in situ at the beginning of reaction and in developed process, at elementary stages of oxidation process [33,90-93] by simplified scheme assuming quadratic termination of chain and equality to zero of rate of homolytic decomposition of ROOH. In the framework of radical-chain mechanism the chain termination rate in this case will be (1): 2

⎧ w ⎫ wterm=k6[RO2 ] =k6 ⎨ PEH ⎬ ⎩ k2[RH]⎭ ⋅ 2

(1)

where wPEH − rate of PEH accumulation, k6 − constant of reaction rate of quadratic chain termination; k2 − constant of rate of chain propagation reaction RO2• + RH→. We established that complexes M(LI)n (M=Ni(II) ([Cat]=(0.5-1.5)·10-4 mol/l), Fe(III) ([Cat]=(0.5-5)·10-3 mol/l)) were inactive in PEH homolysis, products MPC and AP were formed at stages of chain propagation Cat + RO2•→ and quadratic termination of chain. Actually, w0~[Cat]1/2 and wi,0~[Cat] and linear radicals termination on catalyst may be not taken into account. In the case of quasi-stationarity by radicals RO2•⋅ the values wterm.= wi are the measures of nickel(II) and iron(II) complexes activity in relation to molecular O2. Discrepancy between wAP+MPC and wterm in the case of absence of linear termination of chain is connected with additional formation of alcohol and ketone at the stage of chain propagation Cat + RO2•→ (2): wpr.= wAP+MPC – wterm

(2)


103

The direct proportional dependence of wpr,0 on [Cat] testifies in favor of nickel(II) and iron(II) complexes participation at stage of chain propagation Cat + RO2•→. We suggest that these conditions w0~[Cat]1/2 and wi,0~[Cat] will be fulfilled also in the presence of additives of R4NBr, 18C6 and small amounts of water in the case of catalysis with iron complexes, as mechanism of catalytic reaction is not changed in the all examined cases wP/wPEH ≠ 0 at t → 0, wAP/wMPC ≠ 0 at t → 0. Except theoretical consideration in [24], activity of transition metals complexes M(L1)n (M=Ni, Co, Fe, L1 = acac-, enamac-) at stage of chain propagation (Cat + RO2•→) of ethylbenzene oxidation is estimated only in our works [33,90-93,116,117]. Investigation of reaction ability of peroxide complexes [LM−OOR] (M=Co, Fe) preliminary synthesized by reactions of compounds of Co and Fe with ROOH or RO2• radicals [135-137] confirms their participation as intermediates in reactions of hydrocarbons oxidation. Obviously, the schemes of radical-chain oxidation including intermediate formation [LM−OOR] [135-138] with further homolytic decomposition of peroxo-complexes ([LM−OOR]→R′C=O (ROH) + R•) may explain parallel formation of alcohol and ketone under ethylbenzene oxidation in the presence of M(L1)2 (L1 = acac¯, enamac¯) and their complexes with 18C6 (R4NBr). We established that mechanism of selective catalysis of complexes M(L1)n (M(L1)2•(L2)n) (M=Ni, Fe) and products of their transformation depended on both ratio of rates of chain initiation wi (activation by O2) and propagation (wpr) and on activity of Cat in PEH decomposition (homolysis, heterolysis of PEH, chain decomposition of PEH). In non-catalytic ethylbenzene oxidation at high temperatures the formation of active free radicals occurs in reaction of chain initiation (RH+O2→) and under chain decomposition of PEH, the value SPEH to a significant extent should be determined by factor of instability of PEH β = wPEH¯ / wPEH+ (wPEH¯ − sum rate of PEH decomposition (thermal (molecular) and chain), wPEH+ − rate of chain PEH formation). Actually, it turned out that value β in the course of non-catalyzed process of ethylbenzene oxidation is increased at the expense of rise of PEH chain decomposition rate that leads to reduction of SPEH [20, 24]. At conditions of ethylbenzene oxidation catalyzed by M(L1)2 (M=Ni(II), Fe(II)) and M(L1)2 complexes with R4NBr, 18C6 the value is β = wPEH¯/wPEH+ → 0 as at the beginning, so in developed process, the direction of AP and MPC formation is changed (consequent (from PEH decomposition) → parallel), SPEH depends on catalyst activity at stages of chain initiation (activation by O2) and chain propagation (Cat + RO2•→).

Catalysis with Nickel Complexes Calculation by formulas (1) and (2) show that high activity of "primary" complexes Ni(II)(LI)2•18C6n as selective catalysts of ethylbenzene into PEH oxidation is connected with five-(chelate group (O/NH)) and twenty-(chelate group (O/O))-fold growth of rate wi,0 in comparison with catalysis by Ni(LI)2, hindering of rate of chain propagation (wpr,0) (Cat + RO2•→). Under catalysis by complexes Ni(acac)2•18C6n (n=1,2) and Ni(enamac)2.18C6n (n=1) experimentally determined wAP+MPC,0 completely coincide with calculated ones by formula (1) values of wterm,0.

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4

5

2.92

3

3.08

s

2.56

1

2.36 1 -1

6

6

w Σ , 0.10 , w рr,0 .10 , w i,0 .10 , mol l-

Complexes Ni(O,NH)2•18C6n are twice as more active than Ni(O,O)2•18C6n at stage of free radicals origin (wi,0), although the "crown-effect" (increase of w0 and wi,0 under the effect of 18K6 additives) observed in the case of catalysis by Ni(II)(O,NH)2·18К6n is lower. It may be explained by reduction of acceptor properties of complex Ni(II)(O,NH)2 in comparison with Ni(II)(O,O)2 in relation to coordination 18K6 that is caused by covalent character of bonds Ni-NH and reduction of effective charge of metal ion. Conditions allowing estimation of wpr and wi (formulas 1 and 2) in developed process under catalysis Nix(LI)y(LIox)z и Nix(LI)y(LIox)z 18К6n (LI= enamac-1) are fulfilled. It turned out that the role of reaction of chain propagation in developed oxidation reaction of ethylbenzene is increased. In contrast to catalysis by complexes Ni(II)(L1)2 (L1=acac-1, enamac-1) with 18К6 in reaction of ethylbenzene oxidation catalyzed by Ni(II)(L1)2 in the absence of crown-ethers additives increase of initial rate of oxidation is connected mainly with participation of catalyst at stage of chain propagation. At that under catalysis by Ni(O,NH)2 complex the value wpr,0 is twice as much than under catalysis by Ni(O,O)2. at the same time the rate of chain initiation almost in order exceeds wi,0 in oxidation reaction catalyzed by Ni(II)(acac)2. As it obvious, presence of donor NH-groups in chelate group of nickel complex promotes significant increase of role of activation reaction of molecular oxygen in catalysis mechanism. [33]. High activity of "primary" complexes Ni(II)(acac)2•R4NBr as selective catalysts of ethylbenzene into PEH oxidation as well as the activity of Ni(LI)2.18C6n is connected with growth of rate wi,0 in comparison with catalysis by Ni(LI)2, hindering of rate of chain propagation (wpr,0) Cat + RO2•→ (Figure 7).

2.3

2

2.2

1.64 1.18

1

0.56

3

0.6

0.4

0.3

2

0 0

1

2 3

[Me4 NBr].10 , mol/l

Figure 7. The ethylbenzene oxidation rates at the beginning of reaction wΣ,0 (1), and calculated rates of chain initiation wi,0 (2), and propagation wпр,0 (3) as a function of [Me4NBr] in the ethylbenzene oxidation upon catalysis by {Ni(II)(acac)2+Me4NBr}. [Ni(II)(acac)2]=1.5·10-4 mol/l, 1200 C.


105

As is seen from Figure 7 that the minimum value of wрr,0 is at [Me4NBr] = 1·10-3 mol/l, which corresponds to the formation of the complex in 1:1 ratio. As [Me4NBr] increases further wрr,0 increases too. At [Me4NBr] = 2·10-3 mol/l the latter reaches the value of wpr,0 observed in the presence of Ni(II)(acac)2 only. It is evident that at the Me4NBr coordination (in the inner and in outer spheres) steric hindrances to coordination of RO2• with the metal ion can appear (wрr,0 drops). If [Me4NBr] is rather large, the probability of opening of the chelate ring of the (acac)- ion increases and coordination of the radical RO2• with the metal center becomes possible (wрr,0 increases). Under substitution of radical CH3 (Me4NBr) in cation R4N+ by radical n-C16H33 (CTAB) the activity of formed complexes Ni(II)(acac)2·CТАB at stages of chain initiation and propagation is increased in 4,6 and in 20,5 times correspondingly. At that the rate of PEH accumulation (wPEH,0) is increased only in 2 times, and wАP+MPC,0 in 15.4 times in comparison with catalysis by Ni(II)(acac)2·Me4NBr (Figure 1b).

Catalysis with Iron Complexes The chain initiation in ethylbenzene oxidation by dioxygen in the presence of Fe(III)(acac)3 and {Fe(III)(acac)3+ L2} (L2 = R4NBr, HMPA, DMF) can be represented by the following reaction: Fe(III)(acac)3 ((Fe(III)(acac)2)m·(L2)n)+ RH → → Fe(II)(acac)2 ((Fe(II)(acac)2)x·(L2)y) … Hacac + R•

(I)

The reaction of Fe(III) with RH and interaction of the resulting Fe(II) complex with dioxygen appear to be responsible for chain initiation in the reaction catalyzed by Fe(III)(acac)3 and {Fe(III)(acac)3+ R4NBr}. As is seen from the Table, the rate of chain initiation in the presence of {Fe(III)(acac)3+ R4NBr(CTAB)} is higher than in the reaction catalyzed by Fe(III)(acac)3 and much higher than in the no catalytic reaction (wi,0 ≈ 10-9 mol l-1 s-1). SPEH,0 depends on the catalyst activity at stages of chain initiation (activation by O2) and propagation Cat + RO2•→ at catalysis by Fe(III)(acac)3 in the presence of R4NBr. Thus, the rise of SPEH,0 from 45 up to ∼ 65% in ethylbenzene oxidation catalyzed by {Fe(III)(acac)3+R4NBr} (R4NBr=CTAB) system (Table) is connected with an increase in wi,0 (in 2 times) and a small decrease in wpr,0. The rate of PEH formation increases in ~1.5 times and the rate AP and MPC formation at stages of chain propagation Cat + RO2•→ increases insignificant. The analogous effects are observed with R4NBr=Me4NBr. In the case of (C2H5)4NBr the decrease in the SPEH,0 is due to the growth of the rates wАP+MPC,0 (wpr,0) as compared with an increase in the rates wPEH,0. The complexes Fe(II)x(acac)y(OAc)z(R4NBr)n formed in the process of ethylbenzene oxidation catalyzed by system {Fe(III)(acac)3+R4NBr} are likely to be inactive in the heterolytic decomposition of PEH and in the reaction with the RO2• radicals (Figure 3, 4). The reaction (I) appears to be responsible for chain initiation in the reaction catalyzed by (Fe(II,III)(acac)2)p·(18C6)q complexes.

106


As one can see from the Table the increase in SPEH,0 from ∼ 40 - 50 to ∼ 65 - 70% at the initial stages of the oxidation of ethylbenzene catalyzed by system {Fe(III)(acac)3+18К6} ([18К6]0=0.5·10-3 mol/l, 5.0·10-3 mol/l), at catalysis by (Fe(II)(acac)2)p·(18C6)q complexes, is connected mainly with decrease in the rates of the formation of AP and MPC at micro steps of chain propagation (Cat + RO2•→). The drop of wpr,0 and wi,0 occurs evidently due to electron and steric factors, appeared at the inner and outer sphere coordination (H-bonding) of 18C6 with Fe(II)(acac)2, that may decrease the probability of the coordination of RO2• and O2 with the metal ion and formation primary complexes with O2 and / or RO2• following the formation of the active particles of superoxide and peroxide types. The ratio wi,0/ wpr,0 ≈ 2-5% ({Fe(III)(acac)3+L2} L2=R4NBr, HMPA, DMF, and also 18C6 [15]) means that the iron complexes are more active in chain propagation (Cat + RO2•→) than in chain initiation. Furthermore, this value indicates that the reaction (Cat + RO2•→) plays a greater role in ethylbenzene oxidation catalyzed by the iron complexes than in the same reaction catalyzed by the Ni(II) complexes. In the latter case, the ratio wi,0/ wpr,0 ≈ 11-50%, and depends on the nature of the ligand environment of metal ion [33,91,93]. The estimated ratio wi,0/ wpr,0 ≈ 2-5% suggests that AP and MPC form mainly in the chain propagation step (conceivably, through the homolytic decomposition of the intermediate complex [L2Fe(L1)2— OOR] [135-138]). In the case of catalysis by iron complexes with HMPA, which does not transformed in the course of oxidation, it is possible to estimate the apparent activation energies for micro steps of ethylbenzene oxidation − chain initiation (activation by O2) and propagation (Cat + RO2•→) at two temperatures, 80 and 1200C. These are Ea(wi) =24.53 and 13.03 kcal/mol and Ea(wpr) =21.46 and 17.63 kcal/mol in the absence and presence of HMPA, respectively. The gain in activation energy of the initiation reaction 11.5 kcal/mol via the coordination of HMPA is approximately equal to the energy Ea ~ 10 kcal/mol of ligand addition to metal acetylacetonates [139]. The difference in Ea between the initiation and propagation reactions in the presence of HMPA is presumably responsible for tendency of oxidation selectivity SPEH to increase with decrease in temperature. The higher activity of Fe(II)(acac)2)·DMF complexes as compared with Fe(II)(acac)2)·HMPA complexes at the initiation (wi) and propagation (wpr) steps seems to be to π-donor properties of DMF and its ability to form H-bonds [140]. The coordination of DMF may increase the probability of formation of the primary O2 complexes O2·Fe(II)(acac)2)·DMF [141,142] and, presumably, enhance the activity of the nascent superoxide complexes [DMF·Fe(II)(acac)2) O2¯•] at the radical generation step (wi). As above the the schemes of radical-chain oxidation including intermediate formation [LM-OOR] peroxo complexes at the propagation step followed by the homolytic dissociation of the peroxo complexes ([LM-OOR]→R′C=O (ROH) + R•) are a likely explanation of the observed increase in the rate and MPC selectivity of the Fe(II)(acac)2)·DMF catalyzed ethylbenzene oxidation in the initial stages of the reaction SMPC,0 ≈ 58%. It is quite likely that the coordination of π-donor DMF will facilitate the stabilization of DMF·Fe(II)(acac)2)–O•, an oxo species that is produced upon the degradation of the intermediate [ROO-Fe–DMF] peroxo complexes via the homolytic O–O bond dissociation in propagation step ([L2Fe-O•– • OR]→ R′C=O (ROH) + R•), and a growth in the probability that RO• radicals escape from the solvent cage (cage “latent radical” mechanism).


107

As mentioned above the mechanism of the ethylbenzene oxidation catalyzed with {Fe(III)(acac)3+ R4NBr (18C6)} is obviously unchanged at the addition of 3.7·10-3 mol/l H2O. So we proposed that catalysis by complexes (Fe(II)(acac)2)x·(R4NBr)y·(H2O)n, (Fe(II)(acac)2)p·(18C6)q·(H2O)n satisfied the conditions w0~[Cat]1/2 and wi,0~[Cat] that allowed wi,0 and wpr,0 to be calculated by Eqs. (1) and (2) and the catalytic activity of complexes (Fe(II)(acac)2)x·(R4NBr)y·(H2O)n at the micro stages of chain initiation (activation of O2, wi,0) and chain propagation (Cat + RO2•→, wpr,0) can be evaluated. As follows from the data in Table the growth in SPEH,0 at the catalysis by complexes Fe(II)(acac)2)x·(CTAB)y·(H2O)n is connected mainly with the considerable fall in the value of wpr,0 ~ 3.2 times. The value of wi,0 decreases by a factor of ~ 1.3. At that the rate of {AP+MPC} accumulation wp,0 decreases ~ 3 times, and wPEH,0 decreases only by a factor of ~ 1.26. The decrease in the rate of chain propagation wpr,0 at the catalysis by complexes (Fe(II)(acac)2)x·(CTAB)y·(H2O)n seems to be caused by unfavorable steric factors for the RO2• coordination with metal centre appeared in this case. Beside this the part of H2O molecules may be absorbed with hydrophilic cation n-C16H33Me3N+, creating unfavorable conditions for RO2• coordination with metal ion. At the catalysis with complexes (Fe(II)(acac)2)x·(CTAB)y·(H2O)n the growth in ratio wi,0/ wpr,0 to a grate extent (by a factor of ~ 2.35 as compared with (Fe(II)(acac)2)x·(CTAB)y was received. In the case of the use of the other R4NBr as ligand-modifier L2 the decrease in parameter wi,0/ wpr,0 was observed at the H2O addition :~ 1.4 times (L2 = (C2H5)4NBr (mainly in consequence of the decrease in wi,0 ~ 1.5 times)); ~ 1.22 times (L2 = Me4NBr (mainly in consequence of the increase in wpr,0~ 1.7 times (wi,0 increases ~ 1.4 times))) as compared with catalysis by systems without admixed H2O. As seen from the data presented in Table, the reaction of the chain propagation (Cat + RO2•→) is evidently the principal reaction of the AP and MPC formation in the ethylbenzene oxidation in the presence of systems {Fe(III)(acac)3 + L2 + H2O} (L2=CTAB, 18C6). It took place also in the cases of use of composition of {Fe(III)(acac)3 + L2} or only Fe(III)(acac)3. The contribution of the reaction of chain quadratic termination in the mechanism of AP and MPC formation is inessential. In the ethylbenzene oxidation, catalyzed with (Fe(II)(acac)2)x·(18C6)y·(H2O)n complexes, the significant decrease in parameter wi,0/ wpr,0 is observed ~ 10 times as compared with catalysis with (Fe(II)(acac)2)p·(18C6)q. This fall of wi,0/ wpr,0 is evidently caused mainly with growth in the wpr,0 value. In this case the lowest SPEH,0 ≈ 25% and the highest selectivity of the ethylbenzene oxidation into AP SAP0 ≈ 70% values are got. The [AP]/ [MPC] ration increases from 1.2 ((Fe(II)(acac)2)p·(18C6)q) to 6.5 ((Fe(II)(acac)2)x·(18C6)y·(H2O)n). It is known for example that the ethylbenzene oxidation (70○ C, CH2Cl2, CH3CHO) upon catalysis by complexes of Cu(II) with 18C6 [(CuCl2)4(18C6)2(H2O)] occurs mainly with the formation of ketone (AP). The [alcohol]/ [ketone] ration is 6.5 [37]. As shown above, at catalysis by the system {Fe(III)(acac)3 + 18К6 (5,0·10-3 М) + H2O} (80○C) the oxidation selectivity SAP,0 =70 is sufficiently high at C=1%. But SAP,0 is lower than that at the catalytic oxidations, which imitate the action of monooxygenases, for example in the case of oxidations in the presence of Sawyer’s system, one of the MMO models [143,144]. At the ethylbenzene oxidation with O2 (24○C), catalyzed with Sawyer’s system {[(Fe(II)(Mn(III))Lx(Lx=bpy, py))+HOOH(R)], polar solvents MeCN, py+CH3COOH} SAP ∼

108


100%, but the conversion only C=0,4%. The catalytic particles were presented by the next hypothetic structure [ ]:

which oxygenate the ethylbenzene oxidation with the mainly formation of acetophenone. The particles (*) are formed at the reaction of O2 with peroxo complexes {LxFe(II)OOH(R) + pyH+}, which are formed at the initial stage of reaction as result of nucleophilic addition of HOOH(R) to LxFe(II).

CONCLUSION The problem of lowering in homogenous catalyst activity in the oxidation process is the major one, because the functioning of catalyst is always accompanied by processes of its deactivation. The homogenous catalysts heterogenised on silica-, zeolite-, polymer supports are prevented from deactivation and lifetime of catalyst increases. At that the increase in activity, mainly in the oxidation rate, and also in selectivity is observed. But these methods have the rage of limitations, connected with structure peculiarity of supports. As a rule mechanisms of the ligand – modifiers’ action in homogenous catalytic oxidation are not proved although the authors tentatively propose mechanistic explanations. The various catalytic systems on the base of transition metal compounds have been used for the alkylarens oxidation with molecular oxygen. And all of them catalyzed alkylarens oxidations mainly to the products of deep oxidation. The method of transition metal catalysts modification by additives of electron-donor mono- or multidentate ligands for increase in selectivity of liquid-phase alkylarens oxidations into corresponding hydroperoxides was proposed by us for the first time. On the basis of established (Ni) and assumed (Fe) mechanisms of formation of catalytic active particles and mechanisms of catalyst actions more active catalytic systems {М(L1)2 + L2} (L2 = crownethers or ammonium quaternary salts) for the ethylbenzene oxidation into αphenylethylhydroperoxide were modeled by us and so the mechanisms of selective catalysis were confirmed. Values of selectivity, SPEH, conversion С, and PEH yield reached at application of L2= crown-ethers or ammonium quaternary salts (Me4NBr) exceed analogous parameters in the presence of the other {Ni(II)(L1)2+L2} systems [33] and known catalysts of ethylbenzene oxidation into PEH [24-27]. The high activity of {М(L1)2 + L2} (L2 = crown-ethers or ammonium quaternary salts) as catalysts of the ethylbenzene oxidation into α-phenylethylhydroperoxide is connected with the formation active primary complexes (M(II)(L1)2)x·(L2)y, and homo poly nuclear hetero ligand complexes M(II)x(L1)y(L1ox)z·L2n, (“A” (Ni), “B” (Fe)) (formed through “dioxygenase-


109

like” mechanisms). The stability of “A” (“B”) to the L1 dioxygenation seems to be due to the intramolecular and intermolecular H-bonding interactions. The additions of small amounts of water into catalytic systems (M=Fe) are used as mechanistic probe. Results exceed all expectations. Not only is the role of H-bonding interactions in the mechanism of “B” formation confirmed. The increase in the catalytic activity of Fe systems at the addition of small additives of H2O are established also. The growth in the selectivity of the ethylbenzene oxidation into α-phenylethylhydroperoxide is observed at catalysis by {Fe(III)(acac)3+CTAB+H2O} system. The significant increase in the oxidation rate and the selectivity of the ethylbenzene oxidation into acetophenone at catalysis by {Fe(III)(acac)3+18C6+H2O} system are received. It is discovered unusual activity of mono- or hetero bi nuclear heteroligand Ni(II)(acac)2·L2·PhOH (L2=MSt (M=Na, Li), MP, HMPA) complexes, including phenol, as the very active catalysts of the ethylbenzene oxidation into α-phenylethylhydroperoxide. The H-bonding interactions are assumed in mechanism of formation of these catalytic complexes. The formation of stable supra molecular structures on the base of {Ni(II)(acac)2·NaSt·PhOH} as a result of intramolecular and intermolecular H-bonds is very probably [95-97]. The catalytic activity of nickel and iron complexes with 18K6 or R4NBr at micro stages of chain initiation (wi, activation О2) and propagation at the participation of Cat (wpr, Cat+RO2•→) in the ethylbenzene oxidation process is evaluated in the framework of radicalchain mechanism with original method, proposed by authors.

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Chapter 8

NEW CARBOFUNCTIONAL OLIGOISILOXANES FOR THE SUBSTRATES OF ANTIBIOCORROSIVE COVERS N. Lekishvili∗, Sh. Samakashvili, G. Lekishvili and Z. Pachulia Ivane Javakhishvili Tbilisi State University, 1, Ilia Chavchavadze Ave., 0128 Tbilisi, Georgia

ABSTRACT New carbofunctional oligoisiloxanes containing trifluorinepropil and methacrylic groups at silicon atoms have been synthesized and studied. On the basis of the data of IR and NMR spectral analysis the process of hydrosilylatrion, composition and structure of synthesized compounds have been investigated. By using of diferential-thermal and thermogravimetric analisis method the thermal stability of sintesized oligomers have been studied. By the diferential-scanning calomerty method the phase transition temperatures of synthesized oligomers were determined. It was established that synthesized oligomers are amorphic one-phase systems. The preliminary ivestigation showd that the sybthesized carbofunctional oligomers in combination with polyepoxides and non-volatile bioactive organo-ellement arsenic complex compounds new composite materials of multifunctional application for individual and environmental protection of various materials may be created.

Keywords: oligohydride siloxane, structure, hydrosilylation, antibiocorrosive covers, properties.

∗

E-mail: e-mail: [email protected]

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N. Lekishvili, Sh. Samakashvili, G. Lekishvili et al.

INTRODUCTION One of the ways for protection of synthetic materials is the creation of novel coating polymer materials of muliti-vectorial and directional bioactivity by physical and/or chemical modification of various polyfunctional film-obtaining adhesive polymer matrixes with biologically active compounds [1- 6]. Use of natural and synthetic biologically active compounds as modificating additives, unable to firm fixation in polymer matrix. Such polymers are characterized not only by contact [fungistatic] action, as the first ones, but can dosilly extract biologically active compounds to environmet. The latter is an important factor of guaranteed human protection during it long stay in a closed space. In many regions of the world is widely circulated some diseases of agricultural plants, caused by various phytopathogenic microorganisms. For example, roots cancer, caused by A. tunefacicus. Tumors, halles and nodes are formed as a result of intensive division of affected cells of meristem plant tissues. Roots’ and fruit-trees cancers are provoked by - А. tunefacicus; a cancer of root crops, beets is provoked by X. campestris pv. beticols etc. These diseases distractively damage plants, including grapevine and essentially decrease a crop yield. They also deteriorate quality of grape, water-melons, melons and gourds and other agricultural plants [7]. So the creation of new composites contained bioactive compounds with high biological activity, also conservers and compounds for anti-biocorrosive covers of various natural, synthetic and artificial materials, cultural veritiges is very actually and need of the further development [8].

EXPERIMENTAL Method of Analysis Spectral analysis: IR spectra were obtained from KBr pellets, using UR-20 (Karl Zeis®) spectrophotometers and a Nicollet Nexus 470 machine with MCTB detector [9]. NMR spectra were obtained with an AM-360 (Brucker®) instrument at an operating frequency of 360 MHz using CDCl3 as a solvent and tetramethylsilane as an internal standard [10]. Elemental analysis of the compounds obtained was carried out according to classic methods of microelemental analysis [11]. The quantitative determination of functional groups was performed by using procedures described in ref. [11]. The content of the active hydrogen in Si–H was determined according to the ref. [12]. Quantum-chemical calculations were performed on PC with AMD processor with the built-in coprocessor by using Mopac2000 and CS Chem3D Ultra, v8. We gave the following key-words to guide each computation: EF GNORM=0.100 MMOK GEO-OK AM1 MULLIK LET DDMIN=0.0 GNORM=0.1 GEO-OK. Thermogravimetric and differential-thermal analysis (TGA and DTA) was per-formed on a derivatograph (Paulic, Paulic and Erdey) at the speed of the heating 10Kmin-1. Chromatography analysis of original reagents and the reaction products were performed by using the device LKhM-80 (Russia), type 2 (the column 3000 x 4 mm, the head – “Chromosorb W, the phase-5 mass % SE-30, and gas-carrier-helium).

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Wide-angle X-ray diffractograms have been obtained by DRON-2 instrument (“Burevestnik”, Petersburg, Russia). Cu Kα was measured without a filter; the motor angular velocity was ω ≈ 2 deg.min-1.

GENERAL RESULTS Antibiocorrosive coatings contain two components at least – biologically active compound and polymer matrix where the biologically active compound is dropped (included) [13, 14]. There are described in the literature that some polyfunctional heterochain organic polymers, such as polyurethane elastomers, polyurethane-acrylate, ionomers, etc., succesfully are used as a matrix for creation of antibiocorrosive coatings from their solutions [14, 15]. The polymer carriers (matrix) for the antibiocorrosive coatings also may be obtained based on polyepoxide resins in mass in presence of the active diluents [16]. Application of the organic polyepoxide resin “ED-26” for creation of the matrix for antibiocorrosive coatings didn’t give good results. The obtained coatings crack during the exploitation and turn yellow. To modify the aforementioned coating material, we used silicon-organic oligomers with fluorinealkyl radicals at silicon atoms obtained by hydrosilylation oligo-organohydridesiloxane with perfluorinealkylacrylate (13FA) in presence of Speier’s catalyst (0.1 mole solution of H2PtCl6 in iso-propanole):

Scheme 1. General scheme of hydrosilylation of oligoorganohydridesiloxane with perfluorinealkylacrylate.

In IR spectra of synthesized compounds along with maximums of absorption related to SiOSi, SiCH3, SiC6H5, CH3, C6H5 groups (1040-1090 cm-1, 1425 cm-1, 1440 cm-1, 1330 cm-1, 2970 cm-1, 1605 cm-1, 3080 cm-1) there were found maximums of absorption related to H2C=C (in acrylic group), C=O (in ester goup) and C–F group (in CF2 and CF3 groups) (1640 cm-1, 1720 cm-1, 1330 cm-1)16. In IR spectra there was also observed a week maximum of absorption related to Si–H group, confirmed non-complete (100%) conversion of Si–H groups. Addition of the fluorine-containing oligomers to the composites based on “ED-26” results the solidifier effect, hydrophobicity and thermal-stability decreased but the hardening of the afore-mentioned oligomers is difficult. To facilitate the hardening of siliconorganic modifiers we have synthesized the new fluorine- containing carbofunctional oligoorganosiloxane with methacrylic groups at silicon atoms (MF-1-AMA-F3) by two stages according to the following scheme:


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I. Me3SiO[(Me2SiO)a(SiMeO)b(SiMePhO)c]mSiMe3 H + Scheme (Continued).

+ mb CH2 = CH

CH2

O(O)C

C = CH2 CH3

Me3SiO[(Me2SiO)a(SiMeO)b(SiMePhO)c]mSiMe3 (CH2)3O(O)C

C = CH2

CH3 II. Me3SiO[(Me2SiO)a(SiMeO)b(SiMePhO)c]mSiMe3 (CH2)3O(O)C + nF3

C = CH2 CH3

Me Me3SiO[(Me2SiO)a SiO R

(SiMeO)b(SiMePhO)c]mSiMe3 3n (CH2)3

O(O)C

C = CH2 , CH3

where

R = CH2CH2CF3

Scheme 2. General reaction scheme of obtaining of the oligomer MF-1-AMA-F3.

On the 1st stage we synthesized the comb-type oligosiloxane with side allyl methacrylate fragment (Scheme 2). The process was controlled by determination of the content of active Si–H groups′ in oligoorganohydridesiloxane by the method described in ref.12. During hydrosilylation, a decrease of concentration of active Si–H groups with time was observed. The corresponding kinetic curves were formed using these data. Based on kinetic curves of Si−H groups conversion (Figure 1), the reaction rate constants have been determined (k=0.13


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l.mol-1c-1, T=700C). The total reaction order equals to 2. In the IR spectrum there was not observed maximum of absorption for Si–H group (Figure 2). In Figure 1a is shown that hydrosilylation proceeds rapidly during the 1-1.5 hours and then slows down. The reaction proceeds at 700C with conversion of about 72-73-% by determination of the active Si–H groups, while at 90'C it reaches 80-82%. Figures 1a and 1b show that at the same temperature (70'C) we reach the higher conversation of Si–H groups in case hydrosylilation MF-1 with AMA than with 13FA.

Figure 1. Dependence of the conversion of Si−H group (a) and reciprocal value of the concentration (b) on time (1.- 700C; 2.- 800C; 3.- 900C), and logarithm of the reaction rate constant on the reciprocal value of temperature (c) during the reaction of MF-1 with AMA.

N. Lekiishvili, Sh. Sam makashvili, G. G Lekishvili ett al.

1220

Fiigure 2. IR specctrum of adductt obtained from the interaction of MF-1 and AMA. A

The syntheesized oligomeers are vitreouus liquids soluuble in acetonne, dioxane annd ordinary arromatic-type organic solvvents. Structuures and com mpositions of o the oligom mers were esstablished by elemental e anallysis, FTIR annd NMR specttral data. In the IR spectra of syynthesized oliigomers (Figuure 2) maxim mums of the absorptions a (11040−1080 cm m-1, 1440 cm m-1, 1450 cm-1, 2930 cm-1, 2970 cm-1, 1605 cm-1) rellated to the foollowing grouups Si−O−Si, Si−CH3, Si−C C6H5, CH2, CH C 3, C6H5 werre found . In IR spectra thhere were also o observed thhe absorption maximums related r to C= =O, C−O−C and a H2C=C grroups (1735 cm c -1, 1160 cm m-1, 1650 cm-1). In the 1H NMR N spectrum m of the hydroosilylation prooduct (Figure 5a) there weree identified thhe resonance signals s with chemical shiftss 1.92 ppm, 5.40 ppm and 6.99 ppm, rellated to the prrotons of the following f grouup: 5,40 ppm H 6,00 ppm H

C

C CH H3 1,92 ppm

In the speectrum one caan also obserrve the resonaance signals of phenyl prrotons with chhemical shiftss in the range 7.0-7.6 ppm.. There were also observedd resonance siignals with chhemical shifts 1.2 ppm of thhe methylene groups, 1.1 pppm of the metthyl groups annd complex m multiplet1 in th he range of 4-11.8 ppm relateed to the methine group connfirming formaation of the frragments CH2−CH2 (α) andd CH3−CH (β β) of feasible derivation off Markovnikovv and antiM Markovnikov a addition produucts. In the 13C NMR N spectrum m (Figure 3b)) of the same sample one can c observe thhe presence off the resonancce signal with the chemical shift 65.75 pppm related to the protons off the OCH2 grroup and the resonance r signnal with the chemical c shift 17.71 ppm reelated to the fragment f of C 3 that indicaates formation of both (Markkovnikov and anti-Markovnnikov) productts: CH


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In 13C NMR spectrum of the obtained oligomers we have identified four type Si–CH3contained groups, this is once again proves the presence of α and β adducts (Markovnikov and anti-Markovnikov) [17].

0,82 ppm CH3 CH3

Si CH3

,

0,51 ppm CH3 Si CH2

,

0,15 ppm

1,33 ppm CH3

CH3 Si

,

CH

CH3

Si C6 H 5

By the ratio of integral intensity of correspond resonance signals we determined the ratio of α and β adducts (39.13:60.87).

Figure 3a. 1H NMR spectrum of hydrosilylation product of oligomethylphenylhydridsiloxane and allyl metacrylate.

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Figure 3b. 13C NMR spectrum of of hydrosilylation product of oligomethylphenylhydridsiloxane and allyl metacrylate.

Semiempirical quantum methods we have used are simplified versions of the HartreeFock self-consistent field approach using empirical corrections derived from experimental data. These methods are usually referred to through acronyms encoding some of the underlying theoretical assumptions. We applied one of the most frequently used AM1 (Austin Model 1) methods [18]. It is based on the neglect of differential diatomic overlap (NDDO) integral approximation. This approach belongs to the class of zero differential overlap (ZDO) methods, in which all two-electron integrals involving two-center charge distributions are neglected [18, 19]. A number of additional approximations are made to speed up calculations and a number of parameterized corrections are made for corrections of the approximations in the quantum-mechanical model. For AM1, the parameterization performed so that we obtain enthalpies of formation ∆Hf instead of total enthalpies, as a function of the distance R–C-Si. The calculations provide us also with P1 values which represent bond orders [19]. We have performed calculations using a semiempirical AM1 method for modeling reaction between of oligomethylphenylhydrosiloxane (MF-1) to AMA using software Chem3D 18. Such calculations for polymethylhydrosiloxane and AMA are not doable since the software does not produce reliable results for systems with more than 100 atoms. Necessarily, numerical values for the model reaction will be different than for the polymers studied experimentally but will provide better understanding of the experimental results (Schemes 2 and 3).


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CH3 CH3

Si

O CH3

CH3

Si

CH3 C6H5

Si

CH3 H + H2C

CH

CH2 O

C

C

CH2

O

O

CH3

CH3 CH3 I

Si

O CH3

CH3

Si

CH3 C6H5

Si

CH3 (CH2)3 O

C

C

CH2

O

O

CH3 CH3 CH3 II C6H5

Si

O

CH3

CH3

CH3

Si

Si

O

CH3 CH CH3

CH2 O

C

C

CH2

O

CH3

Scheme 3. Model system for the calculation of ΔΔΗ# and ΔΔΗ for products of hydrosilylation of MF-1 with AMA.

We consider the hydrosilylation of (CH3)3SiOSi(CH3)(H)SiOSi(C6H5)(CH3)2 with AMA in view of the anti-Markovnikov and Markovnikov rules. According to the model reactions compounds I and II will be obtained (Scheme 3). The hydrosilylization is considered through the following model reaction: (CH3)3SiOSi(CH3)(H)SiOSi(C6H5)(CH3)2 + + CH2=CH–CH2–O–C(O)–C(CH3)=CH2 → β (I) and α (II) adducts The activation energy of α-adduct is ΔΔΗ#=124.8 kJ/mole (RSiC = 2.30 Å), and for β adduct is ΔΔΗ#=114.4 kJ/mole (RSiC = 2.25 Å). In the both cases the combination process is exothermic (ΔΔΗ = -199.3 kJ/mole and ΔΔΗ = -191.2 kJ/mole respectively). The low value of activation energy of β-product indicates the superiority of performing the reaction in this direction. Compare now ∆Hf values for compounds of addition taking also into account Figures 4 and 5. Clearly, hydrosilylation reaction of (CH3)3SiOSi(CH3) (H)SiOSi(C6H5)(CH3)2 to AMA is energetically more favorable according to the antiMarkovnikov rule behind to Markovnikov rule. This result is in good agreement with aforementioned NMR spectral data. On the second step we have carried out the catalytic coolygomerization reaction of obtained methacrylate with trimethyltri(trifluorinepropylene)cyclotrisiloxane in toluene at

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80°C, in presence of sulfocationit “CU 23“, 1.5_2 mass % (It is manufactured based on copolymer of divinylbenzene with styrene) and hydroquinone (inhibitor) (1 mas. %).

Figure 4. The dependence of enthalpy (ΔΗ) on the reaction coordinate (RSiC) for α-adduct.

Figure 5. The dependence of enthalpy (ΔΗ) on the reaction coordinate (RSiC) for β-adduct.

Investigation of the model reaction (Scheme 4) By CLC method20 show that for this reaction, in the conditions of the reaction of the co-oligomerization, is characterized the establishment of the equilibrium at room temperature (250C) during 8 hours. The conversion of the hexametyl-disiloxane (HMDS) reaches 50 % 20: by an increase of the temperature up to 700C the yield of the reaction product, by the conversion of the HMDS, increase till 80-85 %. [CH2=C(CH3)–COO(CH2)3 Si(CH3)2] + [(CH3)2Si]2O ↔ ↔ 2 CH2=C(CH3)–COO(CH2)3 Si(CH3)2–O– Si(CH3)3 Scheme 4. General scheme of the model reaction.


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The value of the specific viscosity of the product of co-oligomerization depends on the molar ratio of MF-1–AMA and cyclosiloxane (Tible 1) and on the reaction temperature. From the figure 8 it is evident that the corves of dependence of the value of specific viscosity ηsp on the time have an extreme character: in the begining, the ηsp reaches the maximal value for 2.53 hours at the organosiloxane conversion of 80-85%, increases and the value is kept constant for the obtained oligomers 6.0 hrs. After that, the ηsp decreases till certain constant value (Figure 6, Table 1). Table 1. The reaction conditions of cooligomerization of MF-AMA and F3, and some characteristics of reaction products #

Initial substances molar ratio MF-AMA F3

T,° C

Duration of the reaction, hr

ηspec.

1

1

4

80

6

0,035

2

1

6

80

6

0,028

Mη*

252 3 178 4

. Mη=[η 5000]1,515.

*

Figure 6. Dependence of the value of specific viscosity of co-oligomerization products of MF-1-AMA with F3 (1) at the 800C.

With the arising of the temperature (1000C) the value of the specific viscosity of products of co-oligomerization increases and became 0.460.

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It must be noted that the value of the specific viscosity of the products of co-oligomerization, in comparison with analogical systems16, increases slowly, what may be connected with the increasing of the steric factor at the silicon atoms in MF-1-AMA. The obtained co-polymers are white viscous products soluble in ordinar organic solvents (toluene, dimethyl formamide). The composition and structure of synthesized co-olygomers were studied based on data.of elememtal analysis and IR spectra. After degassing (t=100-1200C, Presid.=10-1 mm.merc.) of adducts the IR measurements was performed. In the IR spectrum the characteristic maximums of the absorption (1040-1080 cm-1, 1440 cm-1, 1450 cm-1, 1720 cm-1, 1645 cm-1, 2970 cm-1, 1600 cm-1) of Si–O–Si, Si–CH3, Si–C6H5, C=O, C=C, CH3, C6H5 groups and (1170 cm-1, 1270 cm-1), also maximums of the absorption to C-F(CF3) groups were observed [9]. We have determined for synthesized oligomers wide-angle X-ray scattering (WAXS). Figure 7 shows that the oligomers are amorphous one-phase systems. Diffraction patterns display two maxima. First 2Θ0≈10.5 corresponds to the maximum of the interchain distance d1≈8.85 Ǻ while the second (2Θ0≈21) corresponds to d2≈4.33 Ǻ which characterizes both intramolecular and interchain interactions [21]. By differential-scanning calorimetric (DSC) studies (Figure 10) we determined that synthesized oligomers are amorphic one-phase systems. (Figure 8). From analysis of DCS curves (Figure 7) is shown that the incorporation of perfluoromethacrylic radical in the chain of oligmethylphenylsiloxane (MF-1) modified with allyl methacrylate, results to the rise of the transition temperature (Tg) by 19°C.

Figure 7. Wide-angle X-ray patterns of synthesized oligomers: 1. MF-AMA/F3 (1:6), 2. MF-AMA (1:1), 3. MF-1-13FA (1:1).


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Figure 8. DSC curves of oligomers:. MF-AMA (1:1); 2. MF-1- AMA-F3 (1:1).

The thermooxidative stability of synthesized organosilicon was studied by DTA and TGA analysis methods. The destruction of polymers is starting at 280-290°C, and the intensive dest ruction proceeds above 450°C. Based on synthesized carbofunctional oligomers in combination of polyepoxides and non-volatile bioactive arsenic-containing complexes compounds, dropped (included) into the polymer matrix, we manufactured antibiocorrosion covers for surfaces of different materials [22]. The preliminary ivestigation showd that the elaborated composites may be recomended as: a) protective covers of multifunctional destination (film materials and impregnating compositions) stable to biocorrosion; б) materials with antimycotic properties for prophylaxis and treatment of mycosis and dermatomycosis: adhesive compositions in the form polymer systems for nail fungi diseases treatment; c) biologically active polymer materials; d) for protection some of archaelogical items and museum exibits.

REFERENCES [1] [2] [3] [4] [5]

Gu Ji-Dong. Int. Bioterior.andBiodegr. 2003, 52, 1, P 69-91. Howard G.T. Biodegradation of polyurethane: a review. Int. Bioterior.and Biodegr. 2002, 49, 4, 242-252. International Standard ISO 846:1997 (E). Plastics – Evaluation of the action of microorganisms. Second edition 1997-06-15. 22 p. Marphenina O.E. Spreading of potential dangerous micromycetes in environment. Problems of medical mycology. 2000, 2, 2, 36-37 (Rus.). Denyver S.P.. Blackwell Scientific Publications, 1991.

128 [6]

[7] [8]

[9] [10] [11]

[12] [13] [14]

[15]

[16] [17]

[18] [19] [20] [21] [22]

N. Lekishvili, Sh. Samakashvili, G. Lekishvili et al. Hazziza-Laskar, J., et al., Biocidal Polymers Active by Contact. IV. Polyurethanes Based on Polysiloxanes with Pendant Primary Alcohols and Quaternary Ammonium Groups. Journal of Applied Polymer Science, 1995, 58, 1, 77-84. Koval E.Z. and Sidorenko L.P. Mycodestructores of the industrial articles. Kiev: Naukova dumka, 1989. – 192 p. (Rus.). 41st IUPAC World Chemistry Congress. Chemistry Protection Health, Natural Enviroment and Cultural Heritage. Programme and abstracts. Turin (Italy), August 511. 2007. Nakamoto, K. IR and Combination scattering spectrum of inorganic and coordination compounds. Мир, 1991. Friebulin H. ‘Bask One- and two-dimensional NMR Spectroscopy’, VCH, Germany, 1991, 218. Kreshkov A.P., Bork V.A. Bondarevskaya E.A., Myshlyaeva L.V., Syavtsillo S.V. and Shemyatenkova V.T., "Manuel for Analysis of Organosilica Compounds", M. Goschimizdat, 1962 (Rus.). Iwahara, T., Kusakabe, M., Chiba, M. and Yonezawa, K. J. Polym. Sci. A 31, 1993, 2617. Pat. 14952А Ukraine. Grekov A.P., Veselov V.Ya. et. al. - Appl. 04.03.97 (Ukr.). Pat. 33837 Ukraine. Method of making polyurethane foams with biocompatibility and bactericidy. Savelyev Yu.V., Markovs’ka L.A, Savelyeva О.А. et al. - Appl. 17.03.2003 (Ukr.). Savelyev Yu., Akhranovitch E.R., Pissis P. et.al. Influence of chain extenders and chain end-groups on properties of segmented polyurethanes. I. Phase morphology. Polymer, 1998, 39, 15, 3425-3429. Lekishvili N., Kopilov V., Murachashvil D., Sokol'skaya I..and Kezherashvili M. Oxidation Communications, 2008 (submitted). Lekishvili N, Samakashvili Sh., Lekishvili G. Siliconorganic polyepoxides with side epoxy groups modified with chelates. Polymers and Polymer Composites, 2008, 16, 1, 35-45. Michael J. S. Dewar, Eve G. Zoebisch, Eamonn F. Healy, and James J. P. Stewart. J. Am. Chem. Soc. 1985, 107, 3902-3909. Allinger N.L. J. Am. Chem. Soc. 1977, 99, 8127-8134. Zubov V.P., Stavova S.D., Chikhacheva I.P., Budris S.V., Kopylov V.M., Zheneva M.V. and Obiedkova M.M. Plasticheskie Massi., 1993, 5, 3-5. Mukbaniani O., Titvinidze G., Tatrishvili T., Mukbaniani N., Brostow W.and Pietkievicz D. Journal of Applied Polymer Science, 2007, 104, 1176-1183. N. Lekishvili, Sh. Samakashvili, M. Kezherashvili, T. Lobzhanidze, M. Labartkava and Z. Pachulia. Aantibiocorrosive Covers Based on Carbofunctional Siliconorganic Oligomers and Biological Active Unvolatile Arsenic-Organic Complex Compoundes. Proceedings of Ivane Javakhishvili Tbilisi state University. Chemistry, 362, 2008, 4657.



Chapter 9

PERFORMANCE, STABILITY AND QUALIFICATION OF DEVELOPED MULTIFUNCTIONAL MATERIALS Jon Meegan, Mogon Patel∗, Anthony C. Swain, Jenny L. Cunningham, Paul R. Morrell and Julian J. Murphy Atomic Weapons Establishment, Aldermaston, Reading, RG7 4PR, UK

ABSTRACT In this article we will review the design, formulation and development of materials exhibiting simplified structure / property relationships, reversible cure mechanisms, increased resistance to physical property changes over time and stress sensitive behaviours. These properties are discussed within the context of the external literature. The article also provides a brief overview of the processes employed by AWE to qualify materials and further understand their storage, ageing and compatibility properties.

1. INTRODUCTION Molecular or nanofilled elastomers represent an area of interest for AWE, as through rational design and careful control over the choice and dispersion of filler phase, they can potentially provide simpler behaviours and greater sample homogeneity when compared to conventional particulate filled equivalents. These characteristics are advantageous as they facilitate component manufacture, qualification and fundamental understanding of the material properties. ∗

E-mail address: [email protected]

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Jon Meegan, Mogon Patel, Anthony C. Swain et al.

Foamed variants of the above systems have been studied as the presence of a continuous microstructure within the material allows for tailoring of the mechanical properties and performance to suit specific end applications or working environments. We have employed 3 Dimensional X-Ray Computer Tomography (XRCT) to further develop the qualitative understanding of foam microstructures within these materials. The utilisation of fundamental ‘click’ type chemical reactions such as Diels Alder cyclisation to introduce reversible cure functionality into crosslinking or polymer species has been of significant interest to AWE in recent years. Materials containing such functionalities can be designed to undergo a controlled and reversible crosslinking reaction on application of an external stimulus which can be triggered when the material is no longer required to perform its role. Thus, a material that reverts from a liquid to a solid and back to a liquid state on application of heat would theoretically allow components to be separated without the application of significant force. Also highlighted within this chapter is an overview of AWEs efforts to develop and formulate radiation and thermally stable polymeric materials through the incorporation of icosahedral closo-dicarbaborane cages. We also report a rationale for our recent studies into stress sensitive Poly DimethylSiloxane (PDMS) elastomers and a generic materials qualification overview.

2. PDMS INCORPORATING POLYOCTAHEDRAL OLIGOMERIC SILSESQUIOXANE AND GRAPHITE NANOFIBRE AS FILLERS PDMS elastomers are typically reinforced with a filler phase to improve the physical properties of the resulting composite material, this reinforcement is achieved through load transfer between the polymer and the filler components [1]. Historically the most commonly used fillers in PDMS systems have been particulate silica fillers due to their affordability, high surface area and compatibility with the polymer matrix [2]. However, the incorporation of these irregular shaped, hydroscopic, high surface area fillers is believed to lead to undesirable and often complicated degradation mechanisms in both the filler [3] and the polymer [4] phases as well as the exhibition of complex mechanical behaviours such as the Mullins effect [5] Unwanted interfacial effects in filled systems such as an enhanced Mullins effect can be inhibited or removed entirely from a material through the careful choice of filler phase or use of a polymer component with a narrow (weight averaged) molecular weight distribution; as the latter is both technically difficult and prohibitively expensive to achieve on a production scale much of the work in the available literature concentrates on modifying the filler component. Due to the versatile nature and commercial viability of many existing PDMS formulations there has been little published research in recent years into the effects of incorporation of other filler types into PDMS elastomers. Much of the current research indicates that the physical properties of other polymer networks, blends or melts are dramatically improved and / or simplified through the incorporation of particulate nanofillers [6,7,8,9]. Work within AWE has focused on the introduction of uniform nanotubular fillers or Polyoctahedral OligomericSilSesquioxane (POSS) moieties into PDMS elastomers in an effort to both modify and simplify the mechanical and ageing behaviours of these composite materials.

Performance, Stability and Qualification ...

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POSS [10,11] moieties represent an interesting class of filler material, formally they are recognised as molecules but are often classed as nanofillers due to the dimensions of the molecule and having a propensity to aggregate. The surface chemistry of the molecules is readily tailored to suit a range of applications, including acting as a reactive filler [12,13] or a mechanical filler via passivation of the surface. Incorporation of POSS fillers into polymeric materials has been shown to improve properties such as mechanical strength and increased glass transition or decomposition temperature [14] The molecular / nanoparticulate nature of POSS fillers also allows for them to act as potential probes to further develop the molecular nature of structure – property relationships which can then be exploited to optimise material properties for specific applications. Carbon nanotubes have been used as reinforcing agents within metals [15], ceramic composites [16] and polymers [17], in all cases the presence of nanotubes in the bulk material leads to improved physical properties such as mechanical strength or electric conductance when compared to the non reinforced material. One of the drawbacks of these materials is that until recently carbon nanotubes were difficult to produce and process in the quantities required for component manufacture; of greater interest are graphite nanofibres (GN) as they can be prepared in large quantities and display similar physical properties to carbon nanotubes. Incorporation of GN into polystyrene foams has been shown to influence the mechanical, heat transfer and thermal expansion coefficeint of the materials [18].

2.1. Preparation of Composites It is universally recognised that in order to maximise the effect of incorporating a filler into a polymer matrix, both components need to be homogenously distributed. To facilitate this process there are three commonly used methods [16]: • • •

Direct mixing –filler and polymer are directly mixed together prior to elastomer formation. Solution mixing –polymer and filler are dispersed in a common solvent which is removed after mixing. In situ polymersisation –the filler is mixed in with monomers which undergo condensation events to form the polymer phase or the filler phase is simultaneously formed during the evolution of the elastomeric network.

2.2. Structure Property Relationships of Selected Composites Figure 1 shows that in the case of GN filled PDMS the composite material is stiffer and exhibits a linear stress strain response, exhibiting more ideal mechanical behaviour than the particulate silica filled sample. The degree of flow within the polymer is also reduced when compared with the silica filled equivalent, this can been seen in the closer bunching of compression / release cycles. The increase in stiffness and reduced flow properties are empirically attributed to the combined reinforcing effect [19] of the nanofibres and their random distribution throughout the material (Figure 2). Of greater interest is the reduction in

132


non ideal behaviour and the resulting simplification of the bulk modulus when compared to the particulate filled material; closer examination of the stress strain curves would suggest that the inert surface of the GN and resulting decrease in polymer / filler interactions inhibits the Mullins effect in the material. The behaviour of the POSS filled materials is believed to be dependant on the dispersion of POSS within the polymer matrix. Scanning Electron Microscopy (SEM) and Confocal Raman (CFR) studies (Figure 2 and 3) indicated that the material comprised of polymer rich and POSS rich areas and also a region which showed an anomalous Raman band, assigned to a POSS / polymer composite rich zone.

Figure 1. SEM image of GN (top left), Molecular structure of POSS (top right) and Compressive Stress Strain Plots for POSS filled9, Particulate filled and GN Filled PDMS (bottom) prepared using the direct mixing protocol.


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Figure 2. SEM images of POSS filled (left) and GN filled (right) PDMS.

Figure 3. CFR study of POSS/PDMS composite (Octaphenyl POSS results shown) [21]. Optical micrograph of POSS/PDMS surface (top left), CFR map of boxed region in micrograph (top right) and Raman spectra of POSS (green) / PDMS (blue) and composite regions (red) in filled material.

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Examination of the stress strain traces for the POSS / PDMS composite demonstrates that for equiaxial nanofillers, where there is no beneficial reinforcement arising form the aspect ratio of the filler, the degree of non ideality and reinforcing behaviour can be qualitatively accounted for by the surface chemistry of the filler phase. Silicic acid functionalities present on dihydroxy POSS are known to readily incorporate into PDMS matrices [20], the associated decrease in polymer chain mobility of the polymer component and effective fixed location of the filler particles in this sample reduced the observed Mullins effect giving rise to simplified bulk moduli (Figure 1). POSS fillers with non reactive surfaces (Octaphenyl POSS) act as particulate fillers, offering improved mechanical reinforcement at the expense of increased filler and polymer chain mobility caused by the inhomogenous distribution of POSS through the polymer phase; this effect is evident in the increased non ideal character of this trace.

2.3. Development of PDMS Foams One approach used by AWE to control the mechanical properties of PDMS elastomers has been to introduce a foam structure into the material. Foamed PDMS elastomers generally play an important role in a number of specific stress absorbing applications. Examples of Polystyrene and Polyurethane foams have tended to dominate the market and open literature in recent years, generally exhibiting high stiffness to weight ratios and some unique mechanical properties. The mechanical properties are strongly related to both the microstructure of the foam and the properties of the polymer making up the cell walls [22]. In general, the desirable material property requirements of foams may be summarised as shown below: • • • • •

Uniform pore size/distribution. Controlled or tuneable load-deflection properties. Good batch to batch and sample reproducibility. Low compression set. Ability to control pore size leading to the development of scaled foam architectures.

The need to develop an overall understanding of how the microstructure in PDMS foams influences mechanical performance is therefore of importance to AWE, one method reported in the literature and used regularly by AWE is 3D X-Ray Computer Tomography (3DCT) [23]. The technique offers insight into the behaviour of the foam structure (Figure 4) with and without deformation and can be used, in conjunction with accurate baselining, to provide porosity measurements.


135

Figure 4. 3DCT model of a POSS filled foam.

If homogenous nano or molecular composite materials could be prepared many of the beneficial effects discussed within this section such as quantitative structure - property relationships or lower filler loadings to achieve a given mechanical strength may be realised. Such materials could find uses within more specific applications and hostile environments where reproducibility of mechanical behaviours, operation temperatures, stability and both longer more accurate lifetime predictions are highly desirable. In order to achieve this goal the authors believe that a significant amount of investigation must occur into the factors affecting filler dispersion within polymer melts and ultimately elastomers.

3. REVERSIBLY CURING POLYMERS Processes involving assembly and disassembly of complex components would be facilitated by adhesives which could be switched between adhesive and non adhesive states as required, one of the most elementary chemical reactions displaying this property is the pericyclic reaction between an electron rich diene and an electron poor dienophile [24] (Figure 5). Examples of this behaviour and its applicablility to functional materials are numerous in the literature, a specific case is the observed reaction between discrete polymer chains containing pendant furan (diene), or maleimide groups (dieneophile) groups [25] and complimentary difunctional crosslinking moities, such as a bismaleimide or difuran functionalised reagents to generate networks. The reproducablity and efficiency of reactions displaying thermal hysteris has been proven using cyclo addition chemistry [26] to develop a material which has found applications within the electronics industry [27] The Diels Alder reaction between furan and maleimide (Figure 5) is a thermally reversible process, the reaction occurs at room temperature to form a kinetically stable adduct which undergoes fragmentation at 90 °C, perturbing the equilibrium towards the entropically favoured starting materials. The fragmentation reactions generate two isomeric products; an endo product and an exo product.

136


The temperature at which thermal hysterisis occurs can be tuned through subtle modification of the diene and dienophile moieties. Making the the diene more or less electron-rich and the dienophile more or less electron-poor has been shown to alter the temperature at which the reaction proceeds and reverses [24]. O

E xo

H O

O

N

O O

N H

+ O

O

O

N

Endo

H O

Figure 5. Diels-Alder reaction between a diene (furan) and a dienophile (maleimide).

3.1. Model Systems Initial work conducted by AWE involved developing synthetic procedures to produce a series of small molecule model PDMS based materials which incorporated furan and maleimide units. Sufficient evidence was obtained to warrant extension of the study to generate low molecular weight, linear, PDMS polymers. Subsequently a series of difuran functionalised PDMS were generated and reacted with a bismaleimide to yield low molecular weight model polymeric systems (Figure 6). This simple approach allowed for the full characterisation of the core chemistry and facilitated the development of PDMS materials containing substituted maleimide or furan functionalities.

Figure 6. Generic functionalized PDMS species used in the reversible Diels Alder reaction, n = 1 to 3.


137

Figure 7. 1H VTNMR study, indicating the reversible nature of the Diels Alder reaction.

3.2. Novel Reversibly Curing Materials Using Diels-Alder Chemistry Variable Temperature Nuclear Magnetic Resonance (VTNMR) studies of the Diels Alder product in Figure 7 support the reversible nature of the reaction. Spectra obtained in the reversible temperature region (60 °C - 90 °C) indicate that peaks assigned to the Diels Alder linked product decrease in intensity while the peaks attributed to the momomeric products (δ 4.66, CH2 –difuran functionalised PDMS monomer, δ 6.88, CH -maleimide) are shown to undergo a corresponding increase in intensity. Spectra obtained outside of this temperature range do not show any increase or decrease of the monomer or product peaks. These conclusions were verified by a Differential Scanning Calorimetry (DSC) investigation into the material (not shown) which confirmed the presence of a broad endothermic event ranging from 60 °C to 92 °C. We believe that the reversible cure chemistry will give rise to a range of crosslinked elastomeric or adhesive materials with designed functionality and operating regimes. Physical characterisation of these potentially interesting systems will be of paramount importance, as will the quantification of molecular constitution on the overall mechanical and thermal stability of the materials in a range of operating environments.

138


4. POLY(M-CARBORANYL-SILOXANE): THE CARBORANYL UNIT AS A BIFUNCTIONAL POLYMER STABILISER A previously reported study by AWE detailed the increase in stiffness of a commercial silica filled PDMS formulation with increasing gamma dose3. The observed trend (Figure 8) displayed non linear behaviour at low doses (red region) of gamma radiation which indicated complex behaviour, believed to be caused by simultaneous degradation and radical mediated crosslinking reactions of the polymer and filler phases at the polymer / filler interface [28]. At low gamma doses the stiffness of the polymer decreases, this is likely to be due to a range of factors including chain scission and back biting to form cyclic materials. At high gamma doses the PDMS polymer shows an increase in stiffness, caused by an increase in crosslink density.

Figure 8. Polymer stiffness as a function of gamma dose.

The stability of polymers in a range of detrimental conditions including high temperature or radioactivity, could be improved through the incorporation of ‘radical sinks’ within the material., this approach has been shown to modify the glass transition temperature (Tg) and decrease the rotational freedom of the polymer backbone; both factors cause a decrease in net elasticity. Further investigation suggested that the physical and chemical properties of boron containing siloxane polymers within such environments could be retained or improved, relative to the non boron containing polymers [29] a generic structure for such a polymer is shown in Figure 9.

Figure 9. Generic carboranylsiloxane material.


139

4.1. Preparation of Poly(m-carboranyl-siloxane) Poly(m-carborane-siloxane) elastomers are most commonly prepared by a ferric chloridecatalysed bulk condensation co-polymerization of dichloro- and dimethoxy-terminated monomers with alkylchloro- or arylchloro-siloxanes. The nature of the substituent groups within the siloxane blocks can be controlled through introduction of the appropriate silane feedstock, phenyl and vinyl modified versions of poly(m-carborane-siloxane) have been prepared in this manner [30].

4.2. Thermal and γ Stability of Poly(m-carboranyl-siloxane) DSC investigations into the thermal behaviour of the materials showed that the Tg of carboranyl modified elastomers synthesised by AWE were located within the range -30 °C to -40 °C; this is significantly higher than that for standard PDMS [31]. The introduction of the sterically bulky carborane unit into the siloxane backbone clearly elevates the glass-transition temperature. However, although the carborane unit introduces conformational rigidity the polymer chains retain sufficient flexibility and mobility which is indicated by a Tg < -30 °C. Thermal Gravimetric Analysis (TGA) conducted in air showed that poly(m-carboranesiloxane) materials typically underwent 4 % cumulative mass loss up to 450 °C and that this mass loss reached 7 % at 600 °C (Figure 10). In comparison, unmodified siloxanes are known to undergo mass loss events of up to 50 % up to 450 °C caused by evolution of low molecular weight siloxanes generated by chain scission events (as evidenced in Figure 8). The ca. 1 % mass increase of the sample between 480 °C and 580 °C is attributed to the oxidative thermal degradation of the carboranyl units and subsequent formation of a mixed boron oxide / boron carbide surface coating. The rapid loss in mass above temperatures of 580 °C is due to the thermal degradation of the boron containing species within the material.

Figure 10. TGA trace for carboranyl modified siloxane.

140


Figure 11. with a*.

11

B MAS NMR spectra of carbornyl modified siloxane. Spinning side bands are marked

The impact of heat and ionising radiation on the carborane cage is evident in the [11] B Magic Angle Spinning NMR (MAS NMR) spectrum (Figure 11). At 580 °C the sacrifical conversion of the carboranyl unit into amorphous boron oxide or carbide is indicated by the presence of additional and enhanced shouldering of the signal which appears in the spectrum obtained after heating at 480 °C. The broad line shape and chemical shifts of the signal in the spectrum obtained at 580 °C and the resulting ceramic like residues observed in the sample cell are typical of mixed boron oxides / carbides. An 11B spectrum obtained for the irradiated sample closely resembles that of the pristine material, indicating the remarkable γ stability of the carboranyl cage. Our investigations have shown that the incorporation of carboranyl units into a polysiloxane tends to strengthen the siloxane bond to thermal degradation. The typical high temperature degradation process in siloxanes4 (depolymerisation or unzipping of the base siloxane) is modified through increased inductive dπ - pπ contributions from the carboranyl group.

5. STRESS SENSITIVE POLYSILOXANES [32,33] The ability of a material to provide diagnostic information relating to its condition or local environment is of particular interest to AWE. Through external collaborations we have sought to develop a range of fluorescent materials capable of providing qualitative information regarding the stress / strain forces experienced by the material.


141

The concept of correlating optical properties with deformation within a fluorophore doped gel is based on the following rationale: deformation of the gel causes changes within the molecular orientation of fluorophore doped polymer chains, which in turn alters the immediate environment of the bound fluorophore. If the fluorophore has a propensity to form excited monomer (excimer) states the degree of change in the emission or absorption spectrum of the fluorophore will be directly proportional to the degree of disruption experienced by the polymer chains. Pyrene has been extensively employed as a diagnostic probe to detect molecular-level changes occurring with a polymeric host. Various polymer systems containing pyrene have been investigated, including polyethylene [34], poly(methyl methacrylate) [35], polystyrene [36] and PDMS [37]. The fabrication and characterisation of PDMS thin film sensors containing pyrene [38] has been reported. The fluorescence response of the films was monitored in response to changes in film thickness or surface temperature. The advantages of using pyrene in such systems are based upon its sensitivity to its immediate environment as the wavelength of pyrene emission depends upon its solubility in a medium (local polarity) and its interaction with other pyrene molecules (concentration). A relatively long singlet excited state fluorescence lifetime and high fluorescence quantum yield also make pyrene a popular choice of fluorophore. Our development work on stress sensitive PDMS materials is currently focused on the investigation of the photophysical properties of pyrene and its incorporation into a crosslinked polysiloxane gel. Although our studies are at a relatively early stage of development regarding the synthesis of various siloxane/pyrene polymers and cross-linkers, as well as the formation of polysiloxane gels containing chemically bonded pyrene moieties within the polymer matrix, has been successfully achieved. The binding of pyrene to the network is especially important, since pyrene molecules are known to migrate through polysiloxanebased materials. Eventually these multifunctional materials may lead to an in situ (nondestructive) method for monitoring the age related changes (or health) of a structural material at a molecular level.

6. QUALIFICATION OF NEW POLYMERIC MATERIALS Qualification is an important process in the development of any new polymeric material and as such, requires the provision of sufficient evidence to ensure that the material meets the required specifications. Throughout this chapter we have described methods and techniques used to interrogate a material for information regarding mechanical and degradation phenomena; other considerations which form part of the qualification process include long term storage (LTS) and studies involving compatibility with other materials in the end application. Both of these issues require that long term, complex studies on the materials be performed. LTS trials on individual components are an important first step in qualification, AWE adopts two approaches: real time and accelerated ageing using elevated temperatures and Arrhenius kinetics [28]. These experiments assess the time dependant applicability or sensitivity of the component to the storage environment.

142


Accelerated ageing studies present a unique problem because the temperatures used not only accelerate the degradation of the material but also have the potential to activate mechanisms not witnessed during the lifespan or operating extremes of the material. Therefore the accelerating temperature and the ageing regime needs to be carefully considered to avoid activating and accelerating the undesirable ageing processes. The effects of humidity or stress may also be investigated depending on the conditions likely to be encountered during use. After completion of LTS trials attempts to mimic application specific conditions, known as a multimaterial experiments, are performed. Experimental configurations tend to be more complex and aim to duplicate (as close as possible) the mix in materials likely to be encountered during use. Ageing data is collected using temperature accelerated ageing and Arrhenius techniques. Data collected during this step helps determine the extent to which distinct materials are able to coexist both physically and chemically. Examples of such incompatibilities include corrosion of the material, evolution of gas, sensitisation of the material and adhesion problems. Following multimaterial experiments, the final stages in component qualification involve the much more complex simulations of complete systems and operational environments. These studies may typically involve a number of different investigations including vibrational effects, thermal cycling and specific system performance. The full system trials represent the ultimate proof of design performance under real environmental regimes. The timescales involved in the trialing of a new material to achieve full qualification are variable and highly dependant on the available resources, some trials can take 10-15 years depending on the information being gathered. However, the overriding strategy within AWE towards the development of simpler materials with improved manufacturing routes, has the benefit that materials and ageing processes may be more easily understood and predicted by suitable modelling routines. This in turn is likely to lead to reduced qualification timescales.

REFERENCES [1]

A. K. Bhowmick, H. L. Stephens, Handbook of Elastomers (Second Edition), Marcel Dekker Inc, 2001, ISBN 0-8247-0383-9. [2] W. Noll, Chemistry and Technology of Silicones (Second Edition), Academic Press, 1968. [3] M. Patel et al., Polymer Degradation and Stability, 91, 2006, 406. [4] A. Chapiro, Radiation Chemistry of Polymeric Systems, John Wiley and Sons, 1962. [5] D. E. Hanson et al, Polymer, 46, 2005, 10989. [6] J. G-I. Rodriguez et al., Journal of Thermal Analysis and Calorimetry, 87, 2007, 45. [7] A. Eisenberg, G. Tsagaropolous, Macromolecules, 28, 1995, 396. [8] A. Eisenberg, G. Tsagaropolous, Macromolecules, 28, 1995, 6067. [9] T. A. Martin, Unpublished, 2006. [10] D. W. Scott, Journal of the American Chemical Society, 68, 1946, 356. [11] G. Li et al., Journal of Inorganic and Organometallic Polymers, 11 (3), 2001, 123. [12] I. S. Isayeva, J. P. Kennedy, Polymeric Materials: Science and Engineering, 89, 2003, 645.

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F. J. Feher et al., Chemistry Communications, 1998, 399. G. Pan et al., Journal of Polymer Science: Part B: Polymer Physics, 41, 2003, 3314. M. Reibold et al., Nature, 444, 2006, 286. P. Ajayan et al., Nanocomposite Science and Technology, Wiley-VCH, 2004, ISBN 3527-30359-6. K. I. Winey, M. Moniruzzaman, Macromolecules, 39, 2006, 5194. J. Lee et al. , Journal of Cellular Plastics, 42, 2006, 105. J. R. Fried, Polymer Science and Tecnology, Prentice-Hall, 1995, ISBN 0-13-685561X. J. D. Wright, A. J. M. Sommerdijk, Sol-Gel Science and Technology, Gordon and Breach, 2001. Technical Reoprt, Horiba Jobin Yvon, S. Fitzgerald, 2006. H. R. Lin, Polymer Testing, 16, 1997, 429. J. H. Kinney et al , Journal of Applied Polymer Science, 80 (10), 2001, 1746. I. Flemming, Pericyclic Reactions, Oxford University Press, 1999, ISBN 0-19-850307-5. R. Gheneim et al., Macromolecules, 35, 2002, 7246. X. Chen et al. , Science, 2002, 295, 1698. D. A. Loy et al. , US Patent 6-403-753, 2002. M. Patel, A. R. Skinner, Synthesis and Properties of Silicones and Silicone Modifed Elastomers, 138, American Chemical Society, 2003, ISBN 0-8412-3804-9. H. Schroeder et al., Presentation: The American Chemical Society Division of Rubber Chemistry, 1966. M. Patel et al. , Polymer Degradation and Stability, 83 (3), 2004, 539. M. Aranguren, Polymer, 39 (20), 1998, 4897. N. Rossi et al., In press, 2006. I. Rushworth, Unpublished, 2006. M. Szadkowska-Nicze et al., Journal of Photochemistry and Photobiology A: Chemistry, 75, 1993, 125. R. B. Crenshaw, C. Weder, Chemistry of Materials, 15, 2003, 4717. G. E. Johnson, Macromolecules, 13, 1980, 839. J. Bisberg et al. , Macromolecules, 28, 1995, 386. S.D. Kim, J. M. Torkelson, Macromolecules, 35, 2002, 5943.



Chapter 10

MOLYBDENUM-INITIATED RING OPENING METATHESIS POLYMERIZATION OF NOBORN-5-ENE-2-YL ACETATE Solmaz Karabulut∗ Hacettepe University Faculty of Science Chemistry Department 06800 Beytepe-Ankara-Turkey

ABSTRACT MoCl5-e−-Al-CH2Cl2 catalyst system can efficiently polymerize noborn-5-ene-2-yl acetate in moderate yields and in relatively high molecular weights. The analyses of the product by FTIR, 1H NMR and 13C NMR spectra give the verification of metathetical polymers. The polymer shows narrow molecular weight distribution and good solubility in common organic solvents.

Keywords: norbornene derivatives; ring opening metathesis polymerization (ROMP); Mo-based initiator; electrocatalyst; polymer.

INTRODUCTION Cyclic olefins such as norbornene (NBE) and its derivatives can be polymerized via three different routes: ring-opening metathesis polymerization (ROMP) [1], cationic or radical polymerization [2], and vinylic polymerization [3]. The increasing interest in the ring-opening metathesis polymerization (ROMP) of norbornene derivatives containing functional groups has developed in recent years. Because these monomers are quite cheap and readily available [4,5] and obtaining polymer structures have attractive properties such as high glass transition ∗

E-mail address: [email protected]>[email protected]

146

Solmaz Karabulut

temperature, high optical transparency and low birefringence [6-9]. The functional derivatives of some cycloolefins cannot be polymerized but norbornene can be easily polymerized under the same conditions. Because the high ring strain of the norbornene structure may compensate to some degree for the retarding effect caused by the interaction of functional substituents with active centers of metathesis. The structure and properties of polymers received are dependent on the catalyst used. In the presence of catalysts on the basis of WCl6 [10], RuCl3 [11], and Re2O7/Al2O3 [12], as well as well-defined Schrock [13-15] and Grubbs [16-20] initiators ring-opening metathesis polymerization (ROMP) takes place with formation of cyclolinear structures. We previously reported many scientific studies on the application of WCl6-e--Al-CH2Cl2 catalyst system to olefin metathesis reactions [21-28] but until recently only one study on MoCl5-e--Al-CH2Cl2 catalyst system to ROMP of norbornene [29]. The generation of active moieties for metathesis of alkenes from WCl6 and MoCl5 via electrohemical technique was first studied by Gilet et al. and the electroreduction of these salts at a platinum cathode with an aluminum anode under controlled potential was reported to produce an active species for the metathesis of alkenes under mild conditions [30-32]. One of the most interesting aspects of the electrochemical technique is that the oxidation state of the reduced species can be stabilized at a controlled potential. Furthermore, the absence of cocatalyst avoids the side reactions such as isomerization, alkylation of the substrates occurring when chemical reducing agents are used. Moreover, the organoaluminic or organotin cocatalysts are, in practice, very dangerous to handle and very often give by-products arising from isomerization or alkylation of the substrates. The aim of this study is to test the catalytic activity of economical and easily prepared electrochemically generated Mo-based initiators on the ring opening metathesis polymerization of 5-norbornene-2-yl acetate (NB-OCOMe) without employing any cocatalyst under the mild polymerization conditions.

EXPERIMENTAL Chemicals MoCl5 and noborn-5-ene-2-yl acetate were supplied from Aldrich and used as received. Dichloromethane (Aldrich) was distilled over P2O5 under nitrogen. THF and methanol were supplied from Merck and used as received.

Electrochemical Instrumentation The electrochemical instrumentation consists of an EGG-PAR Model 273 coupled with a PAR Model Universal Programmer. The measurements were carried out under a nitrogen atmosphere in a three-electrode cell having a jacket through which water from a constant temperature bath was circulated. In the electrochemical experiments, the reference electrode consisted of AgCl coated on a silver wire in CH2Cl2/ 0.1 M tetra-n-butyl ammonium tetrafluoroborate (TBABF4), which was separated from the electrolysis solution by a sintered

Molybdenum-Initiated Ring Opening Metathesis Polymerization…

147

glass disc. Experiments were carried out in an undivided cell with a macro working platinum foil electrode (2.0 cm2) and aluminium foil (2.0 cm2) counter electrode. Electrolysis was carried out without a supporting electrode because of its deleterious effect on the catalyst system. For this reason, the distance between the platinum working and aluminium counter electrode was kept constant and as small as possible (i.e. 2.0 mm) in order to keep the solution resistance to a minimum.

Generation of Catalyst The catalyst was prepared according to previously described procedures [29].

Polymerization Reactions All reactions were carried out in an inert atmosphere with Schlenk techniques under nitrogen. 1 ml of the catalytic solution was added to 1.6 mmol monomer. The mixture was kept at room temperature under vigorous stirring. The reaction was quenched by methanol addition after 24 h. The polymer was further purified to remove the catalytic residues by dissolving it in THF and re-precipitating it with methanol and drying it overnight in a vacuum at room temperature. Polymerization reactions were repeated for different reaction times and monomer/catalyst ratios to optimize reaction conditions. The polymerization yield in percentage was calculated as the weight fraction of converted monomer over the total monomer.

Polymer Characterization NMR spectra of the polymer were recorded with a Bruker GmbH 400 MHz highperformance digital FT-NMR spectrometer using CDCl3 as solvent and tetramethylsilane as the reference. Infrared spectra were obtained from KBr pellets using a Perkin-Elmer FTIR spectrometer. Number molecular weight (Mn) and molecular weight distriution (PDI) were determined by gel permeation chromatography. GPC analysis was performed with a Shimadzu LC10ADVP liquid chromatograph equipped with a Shimadzu SPD-10AVP UV detector, relative to polystyrene standards. Samples were prepared in THF (w/v, %1) as eluent and passed through a Nucleogel GPC M-5 μ-styragel column. A constant flow rate of 1 ml min-1 was maintained at 25 °C. Glass transition temperature was measured by Shimadzu DSC-60 (10 ºC /min).

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Solmaz Karabulut

RESULTS AND DISCUSSION An O-substituted norbornene derivative, 5-norbornene-2-yl acetate (NB-OCOMe), was polymerized via ring opening metathesis polymerization with electrochemically produced Mo-based active species. The polymerization process is illustrated in Eq. (1).

1 The ring opening metathesis polymerization (ROMP) of noborn-5-ene-2-yl acetate was studied over some catalyst systems [7,8]. A comparison of the polymerization conditions and results of the polymer obtained by various catalyst systems with MoCl5-e−-Al-CH2Cl2 is given in Table 1. The number molecular weight Mn and molecular weight distribution (PDI) were measured as 92.7 x 103 and 1.32, respectively. As shown in Table 1, the electrochemical molybdenum-based system leads to polymers of higher molecular weight and lower polydispersity in comparison with the other catalyst systems. This electrochemical catalyst system seems to be very active, as shown by the moderate yields of polymerization and in the smaller reaction period. Thermal behaviour of the polymer was analyzed by DSC. DSC curve for the polymer is shown in Figure 1. Thermal analysis indicates that only one transition is observed between −50 and 100 ◦C. This transition is the glass transition temperature (Tg) is 60.9 °C. Microstructure of the resulting polymer was deduced from 13C NMR spectrum. The carbon atoms in polymer are numbered from 1 to 9 as indicated in Scheme 1. NMR spectroscopic data for the resulting polymer obtained in the presence of the MoCl5–e−–Al– CH2Cl2 catalyst system are consistent with the data previously reported for this polymer prepared via ROMP by other systems [8].

Scheme 1.

Table 1. ROMP of noborn-5-ene-2-yl acetate over some catalysts Cocatalyst

Cocatalyst / Catalyst

Reaction Time

Catalyst /Monomer

Reaction Temperatur e

(C2H5)3Al

2,65

48 h.

1:12

20 ºC

(CH3)4Sn

1

24 h.

1:9

(C2H5)3Al

1

10 min.

RuCl2(P(C6H5)3)3

-

-

RuCl2Py2(IMesH2)(CHPh)

-d

RuCl2Py2(IMesH2)(CHPh)

Catalyst ReCl57 7

WCl6

MoCl57 7

8

8

-

MoCl5-e -Al-CH2Cl2 a

Yield (%)

c

%cis

Mn (x10-3)

24

76

-

-

40 ºC

60

71

-

-

1:6

20 ºC

56

38

-

-

96 h.

1:25

40 ºC

29

16

-

-

-

4 min.

1: 100

55 ºC

81

-

177.4

1.81

-d

-

4 min.

1:100

55 ºC

83

-

80.9

3.09

-

-

9 h.

1:160

25 ºC

88

35

92.7

1.32

Determined by gravimetrically. Calculated from 13C-NMR spectra. c Determined by GPC, relative to polystyrene standard. d Some imidazolium salts were used as ionic liquids. b

a

b

c

PDI

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Solmaz Karabulut

NMR spectra confirm that there is no loss of C=C double bond during polymerization and indicate the formation of a mainly trans compound with one acyclic C=C double bond and one cyclopentane unit. The 13C NMR spectra of MoCl5–e−–Al–CH2Cl2 initiated polymer are shown in Figure 2 and Figure 3. These spectra of the polymer consist of a CO resonance at 170 ppm, a group of olefinic carbon peaks at 126–138 ppm, a group of ring-carbon peaks at 34-78 ppm and a group of upfield peaks at 21 ppm due to the methylene carbons. These line positions and assignments are listed in Table 2.

Figure 1. Partial DSC curve for polymer obtained by electrochemically generated metathesis catalyst.

Figure 2. Expansion of the olefinic region of 13C NMR spectrum of polymer.


151

Figure 3. Expansion of the non-olefinic region of 13C NMR spectrum of polymer.

Table 2. 13C NMR peak assignments (ppm from TMS) of polymer produced by MoCl5-e-Al-CH2Cl2 catalyst system Carbon

Position and Asssignment cis

trans

1

42. 04

C2 C3

77.98 39.93

C4

35.28 35.15 136.19 134.10 129.36 127.57 39.88 21.28

47.25 47.03 46.78 77.79 38.83 38.71 39.93 40.07 135.88 133.16 129.61 127.64 38.14 21.32

C

C5 C6 C7 C9

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Solmaz Karabulut

Figure 4. IR spectrum of polymer.

T he olefinic region clearly confirms the formation of polymers by metathesis. For C1 and C4 the differences for cis and trans chemical shifts are δt- δc= 4.65 and 5.18, respectively, as expected, while for C2, C3 and C7 the trans signals is upfield from cis, as in polymers of norbornenene derivatives. The rather tightly spaced fine structure and various overlaps make it difficult to obtain very precise values of cis content. So, the best that can be done from C-1 signals at around 47 ppm (trans) and 42 ppm (cis). Here, it is particularly important to note that no evidence of the addition chemistry is apparent in the NMR spectra except for the retention of the C=C double bonds during polymerization. IR spectroscopy was also used to support the retention of unsaturation in the polymer and high trans stereochemistry was assigned. Figure 4 illustrates the FTIR spectrum of the polymer. The trans content of the polymer is confirmed by the stronger absorption of the trans C=CH out-of-plane bending at 965 cm−1 with respect to the absorption at 745 cm−1 arising from the cis C=CH out-of plane bending. The absorption at 1650 cm−1, belonging to the C=C stretching, indicates the retention of the double bonds in the polymer obtained via the ROMP mechanism. The spectral features are consistent with the data reported in the literature (7,8). 1H NMR spectrum shows signals in both the olefinic region (5.1-5.4 ppm) and in the alkyl region (1.03.0 ppm). The results obtained by 13C NMR are consistent with the 1H NMR spectrum shown in Figure 5.


153

Figure 5. 1H NMR spectrum of polymer.

CONCLUSION This study shows that ROMP of noborn-5-ene-2-yl acetate to O-containing unsaturated polymer by MoCl5–e−–Al–CH2Cl2 catalyst proceeds with moderate yield. High trans polymer was obtained by this catalyst system with high molecular weight in a short periods. Further research will be performed using norbornene derivatives containing functional groups by ROMP in the presence of electrochemically generated W-and Mo-based active species.

ACKNOWLEDGMENT This work was supported by a grant provided by the TUBITAK (Scientific and Technological Research Council of Turkey, Grant No: 108T084).

REFERENCES [1] [2] [3] [4] [5]

[6] [7]

Gaylord, N.G.; Mandal, B.M.; Martan, M. J. Polym. Sci. Pol. Lett Ed 14, 1976; 555. Goodall, B.L.; McIntosh, H.; Rhodes, L.F. Marcromol. Symp. 89, 1995; 421. Haselwander, T.F.A.; Heitz, W.; Krugel, S.A.; Wendorff, J.H. Macromol. Chem. Phys. 197, 1996; 3435. Mol, J.C. J. Mol. Catal. A: Chem. 213, 2004; 39. Mol, J.C. Industrial applications of olefin metathesis, In Novel Metathesis Chemistry Designing Well-Defined Initiator Systems for Specialty Chemical Synthesis, Tailored Polymers and Advanced Materials Applications, İmamoğlu Y, Bencze L. (eds.). NATO ASI Series V122. Kluwer Academic Publishers: Dordrecht, 2003; 313. Grubbs, R.H., Handbook of Metathesis, Wiley-VCH Verlag GmbH and Co. KGaA, Weinheim, Germany Vol. 3, 2003; pp. 413–414. Ivin, K.J.; Mol, J.C. Olefin Metathesis and Metathesis Polymerization, Academic Press, Inc., London 1997, pp.302-303.

154 [8] [9] [10]

[11]

[12] [13] [14]

[15] [16] [17] [18] [19] [20] [21] [22] [23] [24] [25] [26] [27] [28] [29] [30] [31] [32]

Solmaz Karabulut Buchmeiser, M.R. Chem. Rev. 2000, 100, 1565. Khosravi, E.; Szymanska-Buzar, T. Ring Opening Metathesis Polymerization and Related Chemistry, Kluwer Academic Publishers, The Netherlands 2002; pp. 91–104. Finkelshtein, E.Sh.; Makovetskii, K.L.; Yampolskii, Yu.P.; Portnykh, E.B.; Ostrovskaya, I. Ya.; Kaliuzhnyi, N.E.; Pritula, N.A.; Golberg, A.I.; Yatsenko, M.S.; Plate, N.A. Makromol. Chem. 1991; 192, 1. Finkelshtein, E.Sh.; Portnykh, E.B.; Makovetskii, K.L.; Ostrovskaya, I.Ya.; Bespalova, N. B.; Yampolskii, Yu.P. In Metathesis Polymerization of Olefins and Polymerization of Alkynes; Imamoglu, Y., Ed.; NATO ASI Series C 506, Kluwer: Dordrecht, The Netherlands, 1998; pp 189-199. Kawakami, Y.; Toda, H.; Higashino, M.; Yamashita, Y. Polym. J. 1988, 20, 285-292. Schrock, R.R. Chem. Rev. 2002; 102, 14-179. Schrock, R.R. The Discovery and Development of High-Oxidation State Mo and W Imido Alkylidene Complexes for Alkene Metathesis. In Handbook of Metathesis; Grubbs, R. H., Ed.; Wiley-VCH: Weinheim, Germany, 2004; Vol. 1, pp 8-32. Schrock, R.R. Chem. Commun. 2005; 2773-2777. Grubbs, R. H. Handbook of Metathesis, 1st ed.; Grubbs, R. H., Ed.; Wiley-VCH: Weinheim, Germany, 2003; Vol. 1-3. Trnka, T. M.; Grubbs, R. H. Acc. Chem. Res. 2001; 34, 18-29. Ivin, K.J.; Kenwright, A.M.; Khosravi, E.; Hamilton, J.G. Macromol. Chem. Phys. 202 2001; 3624. Haigh, D.M.; Kenwright, A.M.; Khosravi, E. Tetrahedron 60, 2004; 7217. Haigh, D.M.; Kenwright, A.M.; Khosravi, E. Macromolecules 38, 2005; 7571. Çetinkaya, S.; Karabulut, S. and İmamoğlu, Y. Euro. Pol. J., 41, 2005; 467. Karabulut, S.; Çetinkaya, S.; Düz, B. and İmamoğlu, Y. Appl. Organometal. Chem. 18, 2004; 375. Karabulut, S.; Çetinkaya, S.; Düz, B. and İmamoğlu, Y. Appl. Organometal. Chem. 19, 2005; 997. Çetinkaya S, Karabulut S, Düz B and İmamoğlu Y, Appl. Organometal. Chem., 19, 2005; 347. Dereli, O.; Düz, B., Zümreoğlu, B.K. and İmamoğlu, Y. Appl. Organometal. Chem., 18, 2004; 130. Karabulut, S.; Aydogdu, C.; Düz, B.; İmamoğlu, Y., J. Inor. and Organometal. Pol. and Mat., 16, 2006; 115. Karabulut, S.; Aydogdu, C.; Düz, B.; İmamoğlu, Y.; J. Mol. Catal., 254, 2006; 186. Karabulut, S.; Aydogdu, C.; Düz, B.; İmamoğlu, Y., J. Inor. and Organometal. Pol. and Mat., 17, 2007; 517. Dereli, O.; Aydogdu, C.; Düz, B.; İmamoğlu, Y. Appl. Organometal. Chem., 19; 2005; 834. Gilet, M.; Mortreux, A.; Folest, J.C.; Petit, F., J. Am. Chem. Soc., 105, 1983; 3876. Gilet, M.; Mortreux, A.; Nicole, J.; Petit, F. J.C.S. Chem Comm., 1979; 521. Düz B.; Pekmez, K.; İmamoğlu, Y.; Süzer, Ş.; Yıldız, A. J. Organometal. Chem., 77, 2003; 684.



Chapter 11

THE CO-OCCURRENCE OF CARRAGEENAN AND AGARAN STRUCTURES IN RED SEAWEEDS Marina Ciancia1,2 and Alberto S. Cerezo2,∗ 1

Cátedra de Química de Biomoléculas, Departamento de Biología Aplicada y Alimentos, Facultad de Agronomía, Universidad de Buenos Aires, Av. San Martín 4453, 1417 Buenos Aires, Argentina 2 CIHIDECAR-CONICET, Departamento de Química Orgánica, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Ciudad Universitaria, Pabellón 2, 1428 Buenos Aires, Argentina.

ABSTRACT In the last seventeen years it has been shown that red seaweeds classified as “carrageenophytes” also biosynthesize agaran structures, while certain “agarophytes” produce small amounts carrageenan structures. No neat separation of these carrageenan/agaran systems was obtained, leading to the idea of “hybrid” molecules, called DL-hybrid galactans. Several points concerning these polysaccharide systems have been addressed: 4. Description of the systems of galactans, in which carrageenan and agaran structures were found (DL-galactan systems), as well as the methodology necessary for their detection. 5. Isolation of “pure” carrageenans or agarans from these systems using non-degrading conditions and the consequent new hypothesis of the formation of molecular complexes. 6. Evidences favoring each hypothesis, namely, the existence of hybrid molecules versus molecular complexes formation.

Keywords: carrageenan, agaran, DL-hybrid, red seaweed, galactan structure. ∗

E-mail address: [email protected], phone/fax: 54 11 4576 3346. (Corresponding author)

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Marina Ciancia and Alberto S. Cerezo

INTRODUCTION Galactose-containing polysaccharides are the main matrix polysaccharide components in the majority of the red seaweeds. These galactans have structures based on a linear chain of alternating 3-linked β-galactopyranosyl residues (A-units) and 4-linked α-galactopyranosyl residues (B-units). The A units always belong to the D-series, whereas the B units include residues of the D- or L-series, many times occurring as 3,6-anhydrogalactopyranosyl moieties (Stortz, Cases and Cerezo 1997a). The simplest classification is made according to whether the 4-linked residues belong to the D- or L-series: by this token, two different classes of galactans are defined, namely carrageenans and agarans, respectively. Classification of carrageenans takes into account the sulfation pattern of the A-unit; the κ-family comprises 4-sulfated polysaccharides, while the λ-family includes those with 2sulfation (Figure 1). Less important are the β-family, in which the A-unit is not sulfated and the ω-family with sulfation on C-6 of this unit. Classification of agarans is not so clear cut as that of carrageenans, but these products can be grouped between two extreme structures, one of them is agarose and the other is obtained replacing the 3,6-anhydro-derivative by L-galactose 6-sulfate (Figure 2), giving rise to the so called “Yaphe´s third extreme” (Duckworth and Yaphe 1971). The latter is important in porphyrans. Α−unit

-

O3SO

Β−unit O

O3SO

O

O

CH2OH

O

OR -

O3SO

O

O

OH

O

O

-

O

CH2OH

OR

C

OH

κ-carrageenan R=H ι-carrageenan R=SO3-

HO

μ-carrageenan R=H ν-carrageenan R=SO3-

(a) O

O OH

OH

OSO3-

CH2OH

O

-

O3SO

CH2OH

O O

C

O OSO3-

O

O OSO3-

HO

O OSO3-

cyclized λ-carrageenan (θ−carrageenan)

λ-carrageenan

(b) Figure 1. Idealized structures of carrageenans of the kappa-family (a) and of the lambda-family (b). OH CH2OH

a O O

+

R=H

b

O O O

O

O ROH2C

CH2OH

OH

HO

OH

OH

OH O

HO

O

or SO3- (porphyran)

Figure 2. Structure of the basic backbone of agarans (a) and of agarose (b).

The Co-Occurrence of Carrageenan and Agaran Structures ...

157

In addition, a third group, in which B-units with the D- and L-configuration are on the same molecule, is under discussion (Figure 3).

1

The letter codes refer to the nomenclature of Knutsen, Midlabodski, Larsen and Usov (1994). Figure 3. Possible structures of DL-hybrid galactans1.

They are usually known as “hybrid” or intermediate galactans (agaroid-carrageenan hybrids, according to Takano, Hayashi and Hara 1997). Nevertheless, the denomination “hybrids” has to be used with due care. In the field of carrageenans, it was used to describe products whose structures contain different idealized repeating units (i.e. κ/ι-carrageenans). To avoid name uncertainties, we use for them the term “carrageenan hybrids” and adopt the term “D/L-hybrid galactans” for galactans, in which B units with D- and L-configuration are assumed to be in the same molecule. We also define “DL-galactan system” as the system of galactans, in which the presence of D- and L-galactose or their 3,6-anhydro-derivatives, and consequently of carrageenan and agaran structures, can be experimentally detected. The division of red algal galactans in carrageenans and agarans led to call their parents seaweeds carrageenophytes and agarophytes, respectively. Carrageenophytes are usually members of some families of the order Gigartinales, while typical agarophytes usually belong to the orders Gelidiales and Gracilariales. This clear-cut separation has been upset because careful studies using enantiomeric analysis on the polysaccharide systems produced by seaweeds from the Gigartinales, known to yield carageenans, indicated that they also biosynthesize small amounts of L-galactose containing galactans (Ciancia, Matulewicz and Cerezo 1993, 1997, Estevez, Ciancia and Cerezo 2000, 2001; Storz, Cases and Cerezo 1997b). In time, it was also found that some agarophytes produce, not only agarans, but also small amounts of galactans with carrageenan structures (Errea and Matulewicz 2003). This means that if the division between carrageenophytes and agarophytes seaweeds is maintained, it should refer only to the major types of polysaccharides produced by the seaweeds. The “DL-hybrid” galactans that have a carrageenan predominant structure were called “DL-hybrid carrageenans” and those with a predominant agaran structures, “DL-hybrid agarans”. These are the limits between which the DL-hybrid galactans are defined with a molar ratio D-:L-galactose going from 1:0 in “pure” carrageenans to 1:1 in “pure” agarans. Intermediate values are interpreted as DL-hybrid galactans.

ENANTIOMERIC ANALYSIS In some cases, detection of the presence of carrageenans, agarans and DL-hybrids was carried out or at least aided by the regular use of 13C NMR spectroscopy for screening of

158


extracts or, in purified fractions, for structural determinations. This is possible due to the fact that carrageenan and agaran disaccharidic backbone units are diastereomeric (Figures 1 and 2). The position of the signal of C-1 of the galactose residues in these products depends not only of the type of bond with the neighboring unit [α-(1→3) or β-(1→4)], but also of the relative configurations of both, the residue under consideration, and the neighboring residue (Usov, Yarotskii, and Shashkov 1980, Usov 1984). Besides, substitution produces secondorder effects. For instance, an A-unit (3-linked β-D-galactose) of a non-cyclized agaran gives a signal at 103.7 ppm, while the same unit in a non-cyclized carrageenan appears around 104.8 ppm. For the B-unit, C-1 of an α-L-galactose unit appears at 100.9-101.1 ppm, while that of α-D-galactose, at 96.1 ppm; 3,6-anhydro-α-L-galactose, at 98.0-98.5 ppm and 3,6anhydro-α-D-galactose, at 95.1-95.7 ppm (Usov, Yarotskii, and Shashkov 1980, Usov 1984). However, the use of 13C NMR spectroscopy for the determination of enantiomeric forms of the monosaccharide units in these types of polysaccharides is difficult due to the complexity of these polymers and their high molecular weight. Several broad bands are usually found in the anomeric region and weak signals can be lost, even if more elaborated chemical analysis (see later) shows that the corresponding units are present. Besides, methoxyl and sulfate substitution on C-2 shifts greatly the anomeric signals. Given the low sensitivity inherent to 13C NMR spectroscopy and the complexity of the spectra in the anomeric zone, low percentages of minor enantiomers may not be detected. In fact, it is well documented that usually galactan structures present in 5-10 % together with other predominant structures, are poorly detected by 13C NMR spectroscopy. Thus, negative results in the spectra of carrageenans or agarans do not exclude the presence of small, but still significant, amounts of 4-linked α-L- or α-D-galactose moieties, respectively, or their 3,6anhydro-counterparts. The use of bidimensional techniques is beginning to overcome these difficulties. Several other methods have been developed to assign the D- or L-configuration of sugar units in galactans, as optical rotation determinations of the polysaccharide hydrolyzate or enzymatic methods (Aspinall 1982). The first one may only be used with homopolymers, which should be devoid of other optically active matter. The second, gives only gross results, and should be used with care with sugars for which the specificity of the enzymes is unknown. A method combining the use of infrared spectroscopy and partial methanolysis and further analysis of the fragments by liquid chromatography was proposed (Whyte, Hosford, and Engar 1985). The authors noticed a signal at 940 cm-1 in the spectra of agars, which represented at least 70 % of the intensity of that at 905 cm-1, and was small or absent in spectra from carrageenans. More elaborated determinations, which override the above described problems, involve acid hydrolysis of the polysaccharide to obtain the mixture of free monosaccharides, which are then treated with a chiral reagent to give a mixture of diastereomeric compounds. These compounds are analyzed using GLC with regular columns (Gerwig, Kamerling, and Vliegenthart 1978, Leontein, Lindberg, and Lonnngren 1978, Gerwig, Kamerling, Vliegenthart, 1979, Little 1982, Cases, Cerezo, Stortz 1995, Lindqvist and Jansson 1997) or high-field 1H NMR spectroscopy (York, Hantus, Albersheim, and Darvill 1997). In another approach, monosaccharide enantiomers are separated as different sugar derivatives using chiral GLC columns (Lindqvist and Jansson 1997, Heinrich, Konig, Bretting, and Mischnick 1997). However, the use of glycosides as chiral derivatives produces multiple peaks in the chromatogram for each component sugar that correspond to the anomers of the pyranosic,


159

furanosic and the open forms of the sugars, in a proportion determined by their equilibrium. Thus, overlapping of peaks makes their assignment difficult, even when using capillary GLC. This fact demands the use of routine GC/MS with ion monitoring for the analysis, as total ion chromatogramans are too complicated (Takano, Matsuo, Kamei-Hayashi, Hara, and Hirase 1993). Another drawback is that methylated products present in small but significant amounts may not be observed due to their partitioning in several peaks. This problem was overcome by transforming the anomeric carbon atoms of the sugars obtained during hydrolysis of the polysaccharide into another group, as amino (by reductive amination) or carboxylate (by oxidation). An HPLC method was developed, which involves a coupling reaction with (-)TBMB carboxylic acid and per-O-acetyl pyranosyl bromides to give diastereomeric 1-OTBMB carbonylated sugars, which could be separated by HPLC (Nishida, Bai, Ohrui, and Meguro 1994). Application of these methods to the analysis of carrageenans and agarans has still the drawback that during acid hydrolysis performed in the usual conditions, degradation of 3,6anhydrogalactose occurs. A qualitative analysis of the presence of both isomers of 3,6anhydrogalactose may be obtained by partial reductive hydrolysis of the polysaccharide sample and detection of the acetylated derivatives of agarobiitol and/or carrabiitol by GLCMS (Usov and Ivanova 1992). The absolute configuration of 3,6-anhydrogalactose units has also been assigned by partial methanolysis and determination of the presence of agarabiose and/or carrabiose derivatives (Takano, Matsuo, Kamei-Hayashi, Hara, and Hirase 1993). Later, this procedure was superseded by the development of a method that involves a partial oxidative hydrolysis to yield the 3,6-anhydrogalactonic acid chlorides, which are separated and quantified by GLC, after conversion to the acetylated diastereomeric sec-butyl esters (Errea, Ciancia, Matulewicz, and Cerezo 1998). Care should be taken when the 3,6anhydrogalactosidic linkages are hydrolyzed to carry out their oxidation or reduction, as their rates of hydrolysis may be markedly affected by the presence of substituents (methoxyl or sulfate groups) on C-2. Therefore, their quantitation may show large errors (Chiovitti, Bacic, Craik, Kraft, Liao, Falshaw, and Furneaux 1998). Many seaweed galactans contain not only galactose and 3,6-anhydrogalactose, but also their mono-O-methyl derivatives in one or more of the four available positions. Each of them may individually belong to the D- or L-series (Cases, Stortz, and Cerezo 1994). In this case, a reaction of the hydrolyzed mono-O-methyl-galactoses with chiral 1-amino-2-propanol by reductive amination followed by acetylation and GLC analysis was used successfully. The procedure resolves all enantiomeric pairs, but that of 2-O-methylgalactose, which can be separated if the amine is replaced by α-methylbenzylamine (Cases, Cerezo, and Stortz 1995). This method was then extended to determine the configuration of 3,6-anhydrogalactose and its 2-O-methyl-derivative, using also derivatization with one of the enantiomers of αmethylbenzylamine as chiral amine. Moreover, a one-pot technique was developed to determine the proportion of both enentiomers of 4-linked 6-sulfated α-galactose and their 3,6anhydro-derivative in a polysaccharide, and, as results of this analysis, the percentage precursor structures of carrageenan- and agaran-types (Navarro and Stortz 2003). Obviously, this method can be used also in the methylation analysis of polysaccharides, improving the structural information (Errea, Kolender, and Matulewicz 2001). With that purpose, the absolute configuration of tetra-, tri-, di- and mono-O-methylgalactoses was also assigned with the aid of GC/MS of trimethylsilylated derivatives of 2-octyl-L-glycosides (Takano, Matsuo,

160


Kamei-Hayashi, Hara, and Hirase 1992, Takano, Matsuo, Kamei-Hayashi, Hara, and Hirase 1993). Table 1 summarizes the methods available for enantiomeric analysis of red seaweed galactans by application of gas chromatographic techniques. Table 1. Summary of the methods available for enantiomeric analysis of red seaweed galactans by application of gas chromatographic techniques1 Reaction involved2 1. Hydrolysis, 2. Chiral ROH/H+

Glycosides3,4

1. Hydrolysis, 2. NaCNBH3/(S)-MBA

Aminoalditols5

1. Hydrolysis, 2. NaCNBH3/(S)-AP

Aminoalditols5

1. Mild hydrolysis, 2. MMB

Disaccharide alditols6

Comments Many peaks (anomeric forms) per sugar. Severe overlapping if methylated Gals are present Only for 2-O-Me-Gal enantiomers. Enantioselective for other Gal units 2-O-Me-Gal enantiomers are not Separated. Quantitation of acid-stable sugars is possible. Only for 3,6-AnGal in consecutive carrabiose or agarobiose units.

Esters7

Only for 3,6-AnGal

Aminoalditols8

3,6-AnGal and 2-O-Me-Gal enantiomers not separated. Quantitation of acid-stable sugars and 3,6-AnGal is possible.

Aminoalditols8

Only for 3,6-An-2-O-Gal, 3,6AnGal and 2-O-Me-Gal

1. Mild hydrolysis, 2. Br2, 3. H+, 4. NaBH4, 5. SOCl2, 6. s-BuOH 1. Hydrolysis, 2. NaCNBH3/(S)-AP Repeat twice, mild then strong hydrolysis 1. Hydrolysis, 2. NaCNBH3/(S)-MBA Repeat twice, mild then strong hydrolysis

Derivative

1

Adapted from Navarro and Stortz 2003. MBA=methylbezylamine, AP=aminopropanol, MMB 4-morpholine barane. 3 Gerwig, Kamerling, and Vliegenthart 1978. 4 Leontein, Lindberg, and Lonnngren 1978. 5 Cases, Cerezo, and Stortz 1995. 6 Usov and Ivanova 1992. 7 Errea, Ciancia, Matulewicz, and Cerezo 1998. 8 Navarro and Stortz 2003. 2

In spite of some remaining difficulties, at present, full chiral recognition of the monosaccharides in the original polysaccharide, as well as the partially methylated sugars in a permethylated galactan is an absolute requisite for a fine structural study of red seaweed galactan structures.

DL- GALACTAN SYSTEMS IN RED SEAWEEDS It has been found that carrageenophytes of related families of the order Gigartinales, as Gigartinaceae (i.e. Chondracanthus canaliculatus, Gigartina skottsbergii, G. canaliculata, G. leptorinchos, Sarcothalia crispata studied as Iridaea undulosa, Chondrus crispus),


161

Phyllophoraceae (i.e. Mastocarpus stellatus, Gymnogongrus torulosus, G. griffithsiae) and Solieriaceae (i.e. Anatheca dentata, Kappaphycus alvarezii) produce agarans usually in small amounts, but, at least in one case, up to ∼ 30% of the total galactans (Craigie and Rivero Carro 1992, Ciancia, Matulewicz, and Cerezo 1993,1997, Stortz and Cerezo 1993, Estevez, Ciancia, and Cerezo 2000, 2001, 2004, 2008, Chopin, Kerin, Mazerolle 1999, Talarico, Zibetti, Faria, Scolaro, Duarte, Noseda, Pujol, and Damonte, 2004, Nunn, Parolis, and Russell, 1971, 1981). On the other hand, agarophytes, like those of the Ceramiales (i.e. Rhodomela larix, Digenea simplex, both from the Rhodomelaceae), but also in some cases of the Bangiales (i.e. Porphyra columbina) and Gelidiales (i.e. Pterocladiella capillacea), were found to produce not only agarans, but also carrageenans as minor components (Takano, Yokoi, Kamei, Hara, and Hirase 1999, Takano, Shiomoto, Kamei, Hara, and Hirase, 2003, Navarro and Stortz 2003, Errea and Matulewicz 2003), while other groups of red algae of the orders Bonnemaisoniales, Halymeniales, Plocamiales, Rhodymeniales, biosynthesize both families of galactans in variable quantities (Usov 1992, Stortz and Cerezo 2000, Takano, Shiomoto, Kamei, Hara, and Hirase 2003). However, not only the biosynthetic role of these mixed systems, but also their molecular structures are still unclear. No evidence for neat separation of these DL-galactan systems into carrageenans and agarans has been achieved and variations in composition and substitution levels shown in different fractionations might be ascribed to high, but normal compositional and structural dispersion, suggesting the possibility of block copolymers. However, no proof of D/L-hybrid galactan structures has been found either. Whether these carrageenan- and agaran-structures are forming blocks in copolymers, or if they are different molecules forming molecular aggregates, is still not known. There is a strong need for verification of the existence of these types of molecules, however, until now they have only been made evident by the exhaustive usage of fractionation techniques and homogeneity determinations, before carrying out structural determinations. Considering the fact that partial hydrolysis has up-to-date produced only agaran or carrageenan fragments, it is possible that the agaran-carrageenan domain, if it exists, should correspond to a junction zone of a block copolymer (Figure 3). Thus, the yield of DL-hybrid oligosacharides (those which contain both α-D- and α-L-galactose units) in a random partial hydrolysis should be very low. Moreover, considering that agaran and carrageenan may self-complex in solution, the irregular junction zones might be slightly more susceptible to hydrolysis, and the yields of those oligosaccharides might be even lower than those expected in a random hydrolysis process. Taking into account that agarophyte taxa of the order Bangiophycidae are considered as ancestral pool from which the evolutionary higher taxa of the Florideophycidae have arisen (Oliveira and Bhattacharya 2000), the biosynthetic capacity to produce agarans may represent a primitive condition among the Florideophyceae, as suggested by the fact that seaweeds of the order Ahnfeltiales are agarophytes. These organisms would be interpreted as ancestral to taxa that contain carrageenans as major product in their cell walls (Fredericq, Hommersand, and Freshwater 1996). The most important types of galactans (i.e. agarans and carrageenans) are not always biosynthesized by monophyletic groups of red algae, but they are also present in paraphyletic or polyphyletic groupings of these seaweeds. This fact could be a consequence of the multiple origin of each type of polysaccharides along the red algal evolution. However, the chemical

162


structure of these products within the red seaweeds seems to be a stable chemotaxonomic character, useful for the characterization at genera or family level, but it is highly variable at ordinal or higher groupings (Estevez, Ciancia, and Cerezo 2008). Some DL-galactan systems from “classical” and “non-classical” carrageenophytes and agarophytes are discussed below, most of the examples were chosen to ilustrate fractionation methodology and enantiomeric analysis.

1. DL-Galactan Systems from “Classical” Carrageenophytes Seaweeds from three families of the order Gigartinales: Gigartinaceae, Solieriaceae and Phyllophoraceae produce the most valuable carrageenans and have been known as typical carrageenophytes. Craigie and Rivero-Carro (1992) were the first to show the presence of DL-galactan hybrids in a screening of galactans from gametophytes of the Gigartinaceae (Gigartina canaliculata, Chondrus crispus, G. leptorhynchos) and Phyllophoraceae (Mastocarpus stellata, previously included in the Petrocelidaceae1) and reported it in the XIVth International Seaweed Symposium, but these results were never published in detail. Several groups were working in the field at that time, and in 1993 two papers were published: One reported the presence of L-galactose containing galactans in the polysaccharide system biosynthesized by gametophytes of Gigartina skottsbergii (Ciancia, Matulewicz, and Cerezo 1993) and the other one, in the system from tetrasporophytes of Iridaea undulosa (Stortz and Cerezo 1993) and, in 1994, two Ph.D. Thesis appeared (Noseda 1994, Ciancia 1994), starting the detailed, chemical, enantiomeric and spectroscopic studies of these systems. a. DL-Galactan Systems from Cystocarpic Plants of the Family Gigartinaceae Matrix galactans from cystocarpic plants of the Gigartinaceae are completely extracted at room temperature and they are made up of similar amounts of polysaccharides gelling at low concentrations of KCl (κ/ι- carrageenans, together with small amounts of L-galactose- and 3,6-anhydro-L-galactose-rich galactans) and non-gelling galactans (partially cyclized μ/νcarrageenans, together with small amounts of L-galactose- and 3,6-anhydro-L-galactose-rich galactans) (Ciancia, Matulewicz, and Cerezo 1993, 1997, Flores, Cerezo, and Stortz 2002). Water-soluble polysaccharides from gametophytes of Gigartina canaliculata, Chondrus crispus, G. leptorhynchos were fractionated by precipitation with potassium chloride, and the KCl-soluble products (partially cyclized μ/ν-carrageenans, together with small amounts of Lgalactose- and 3,6-anhydro-L-galactose-rich galactans) were submitted to an alkaline treatment (cyclization of the μ/ν- to κ/ι-carrageenans, Figure 1). The cyclized derivatives were, again, precipitated with KCl separating new soluble fractions. Compositional and enantiomeric analysis of these fractions showed the presence of D- and L-galactose in molar ratios near unity, suggesting that these products were agarans (Craigie and Rivero-Carro 1992). The mixture of galactans from cystocarpic samples of I. undulosa (Cc) were fractionated (Table 2) and treated as depicted in Figure 4 (Flores, Cerezo, and Stortz 2002). Bulk precipitation of Cc with 2M KCl yielded 62 % of an insoluble product (Ci, κ/ι-carrageenans) 1

Names are given according to the currently accepted classification, as informed by Guiry & Guiry 2009.


163

and 31% of a soluble one (Cs, μ/ν-carrageenans). Alkaline treatment of Ci and Cs proceeded with excellent yields (93-95%), giving CiT and CsT in which the precursor units (4-linked αgalactose 6-sulfate and 2,6-disulfate) were cyclized. Both products were fractionated by precipitation with increasing concentrations of potassium chloride, yielding three fractions insoluble at 0.1M, 1M, and 2M KCl and one soluble at the latter concentration (Table 3).

Figure 4. Fractionation of the gametophytic carrageenan from I. undulosa.

Table 2. Yields and analyses of the native carrageenan (Cc) from Iridaea undulosa and from fractions obtained by precipitation with KCl1

1

Carrageena n

Yield %

Cc Ci Cs

62 31

Gal:3,6AnGal:sulfate Molar ratio 1:0.57:1.14 1:0.59:1.14 1:0.55:1.23

From Flores, Cerezo, and Stortz, 2002.

Ratio per 100 monosaccharide units 3,6-AnGal Sulfate 36 73 37 72 35 79

164

Marina Ciancia and Alberto S. Cerezo Table 3. Yields and analyses of the fractions obtained by alkaline treatment and fractionation of carrageenans Ci and Cs from Iridaea undulosa Range of Yield Carrageenan precipitation % M, KCl CiT CiTi-0.1 CiTi-1 CiTi-2 CiTs CsT CsTi-0.1 CsTi-1 CsTi-2 CsTs

0.0-0.1 0.1-1.0 1.0-2.0 2.0 sol. 0.0-0.1 0.1-1.0 1.0-2.0 2.0 sol.

932 92 5 1 2 953 81 9 90 %), while the fraction soluble in 2 M KCl (F3) ∼ 60 % of agaran structure (Table 6). A part of F3 (F3i) retrograded and the remaining soluble moiety (F3s) was submitted to alkaline treatment and KCl fractionation, to give a new soluble product (T4, 40 % of the alkali treated product). Although a small amount of κ-structure was still detected, T4 is mostly an agaran ([α]D= - 40º), constituted by 3-linked non sulfated β-Dgalactose and β-D-galactose sulfated on C-2 or C-2 and C-4, and 4-linked α-L-galactose, partially sulfated on C-3 and partially methylated on C-2; also, a significant quantity of 3,6anhydro-α-L-galactose 2-sulfate was detected. Other agarans extracted from this seaweed have structures similar to T4, with quantitative variations in the proportion of these structural units, in spite of their solubility behavior (Estevez, Ciancia, and Cerezo 2004). A 13C NMR spectroscopic study of the hot-water extract of G. torulosus from New Zealand (as Anhfeltia torulosa) showed κ- , ι- and μ/ν-structures in a ratio 32:46:22 (Furneaux and Miller 1985). Later, chemical studies with extensive use of fractionation procedures showed that the red seaweed G. torulosus biosynthetizes a system of carrageenans similar to that of cystocarpic plants of the Gigartinaceae (i.e. KCl-insoluble carrageenans of the κ/ιcarrageenan hybrid type, in this case, with predominance of ι-structure, together with KClsoluble μ/ν-carrageenans). Nevertheless, enantiomeric analysis of the component sugars and structural units of the fractions showed in all the cases the presence of L-galactose containing galactans. Sequential extractions with water at room temperature produced three fractions (A1-A3) in low yields. All of them contained significant amounts of L-galactose and 3,6-anhydro-Lgalactose, comprising 28-38 % of agaran structures. Further sequential hot water extractions also yielded products, in which both galactose and 3,6-anhydrogalactose were present in Dand L-configurations (Estevez, Ciancia, and Cerezo 2008).

Table 6. Analysis of the row extract obtained from Kappaphycus alvarezii (C), of fractions obtained from it by KCl fractionation (F1-F3) and fractions obtained from treated F3s by KCl-fractionation (T1-T4). Data for a commercial κ-carrageenan from the same seaweed (K) are also shown

Fraction

K C C´ F1 F2 F34 F3s T1 T2 T4 F3i 1

Range of precipitatio n M, KCl

Yield %

0.1-0.2 0.2-0.5 2.05 Insol.6 0.1-0.2 2.05 -

65.6 82.0 67.0 7.0 15.0 10.6 14.8 18.2 40.0 4.4

Monosaccharide composition (moles %)

Sulfate Carbohydrates as SO3K % % n.d.2 n.d. 45.0 47.1 49.1 n.d. 55.0 24.0 51.6 48.0 27.1

28.0 23.9 22.0 25.4 26.9 22.8 25.1 10.0 31.8 19.3 11.6

Gal D-

L-

49.5 50.2 47.8 49.9 48.8 41.6 35.9 39.4 43.9 29.0 33.3

1.0 3.1 tr. 1.3 1.6 18.4 19.2 31.2 4.5 14.2 24.1

2-L-Gal 6-D-Gal tr.3 tr. tr. tr. 5.4 4.3 2.3 6.1 5.5

tr. 1.2 tr. tr. 3.3 1.3 3.5 1.0 2.8 2.3

AnGal D-

L-

48.4 40.0 44.6 45.0 46.6 14.7

1.1 3.8 3.1 3.8 3.0 tr. 5.1

3.6 45.7 5.3 2.5

3.0 1.7 4.6 3.8

D-Xyl

D-Glc

1.1 1.3 tr. 10.5 26.9 12.9 1.4 18.9 14.7

1.8 2.0 tr. 6.1 7.3 4.1 1.8 16.2 13.8

[α]Dº

Mw KDa

+ 51.8 + 48.6 n.d. + 51.2 + 56.7 n.d. n.d. n.d. + 20.0 - 40.0 n.d.

140 30 125 42 42 n.d. 24 n.d. n.d. n.d. n.d.

From Estevez, Ciancia, and Cerezo 2004. 2n.d.=not determined. 3tr.=traces. 4By dissolution of F3 in water a soluble (F3s) and an insoluble product (F3i) were obtained. 5Soluble in 2.0 M KCl. 6Insoluble in water.

Table 7. Analysis of the hot water extracts C1-C4 from Gymnogongrus torulosus and of fractions obtained from C1 by KCl fractionation

Extract s C1 F1 F2 F33 C2 C33 C4

Range of precipitation M, KCl

Yield %

0.4-0.5 1.2-1.4 2.04 -

31.1 44.9 21.1 16.1 10.1 7.6 3.6

2

Sulfate as SO3K % 29.9 29.2 26.3 15.8 22.9 20.2 17.1

Monosaccharide composition (moles %)4 Gal

6-Gal

AnGal

Xyl

Glc

D-

L-

D-

D-

L-

D-

D-

54.2 47.4 54.8 36.5 54.5 54.7 42.6

6.1 1.4 tr.2 25.4 5.9 6.8 8.4

tr.3 2.5 3.3 2.7

28.7 38.1 36.7 16.8 22.4 14.2 26.9

9.6 11.4 6.0 5.8 11.0 15.7 3.7

1.4 1.7 2.5 8.6 1.4 1.0 6.4

tr. 4.3 2.4 4.3 9.3

[α]Dº

Mw KDa

Carrageenan5 %

Agaran

44 56 77 18 45 23 18

67 74 88 25 65 52 70

33 26 12 75 35 48 30

+ 25.0 + 40.0 + 47.9 - 15.5 + 18.4 + 13.8 - 3.5

5

%

1

From Estevez, Ciancia, and Cerezo 2001. 2Yield of C1-C4 are given for 100 g of the residue of exhaustive extraction at room temperature. Yields of fractions F1-F3 are given for 100 g of C1. 3tr.=traces. 42.6 % and traces of 3-Gal were found in F3 and C3, respectively. 5Considering Xyl and Glc as contaminants.

Table 8. Analysis of the fractions obtained by alkaline treatment of F3 from Gymnogongrus torulosus and further fractionation with KCl1 Range of Fraction precipitatio Yield3 2 % n M, KCl F3T1 F3T2 F3T4 F3T6 1

Ins. 0.1-0.2 0.6-1.0 2.05

12.9 16.7 12.5 34.6

Monosaccharide composition (moles %) Sulfate as SO3K % 8.6 27.3 19.0 16.1

Gal

AnGal D-3-Gal L-3-Gal

D-

L-

43.9 41.2 55.1 45.9

32.1 10.3 4.6 29.3

6.2

tr.4 tr.

4.2

-

D-Xyl D-

L-

31.2 19.2 8.3

10.0 15.8 19.8 4.2

7.8 1.4 1.3 8.1

[α]Dº

- 114.3 + 33.3 + 46.3 - 56.9

Mw KDa

Carrageena n6 %

Agaran

39.7 35.0 45.0 22.5

9 50 50 27

91 50 50 73

6

%

From Estevez, Ciancia, and Cerezo 2001. 2Fractions obtained in small yield are not shown. 3Yields of F3T1-F3T6 are given for 100 g of alkali-treated F3. 3tr.=traces. 4Soluble in 2.0 M KCl. 5Considering Xyl as contaminant.

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Fractionation of the first hot water extract (C1, Table 7) with KCl gave two insoluble fractions, F1 and F2 (Table 7), in which the 3,6-anhydrogalactose 2-sulfate units were in the D- and L-forms, while the 3,6-anhydrogalactose was in the D-form (Estevez, Ciancia, and Cerezo 2004). The KCl-soluble fraction (F3) was treated with alkali and the cyclized derivative was further fractionated with KCl. All the fractions contained D- and L-galactose (Table 8). An insoluble subfraction (F3T1) with 8.6 % sulfate and [α]D= - 114.3º contained 91 % of agaran structures, while other (F3T4) with 19.0% sulfate and [α]D= + 46.3º contained about 50% of each carrageenan and agaran structures; the soluble fraction (F3T6) was mostly agaran (73 %). Considering that F3T2 and F3T4 precipitated with KCl and that a chain of a few carrabiose units is too short for gelation (Rees, Williamson, Frangou, and Morris 1982), the carrabiose units should not be interspersed regularly in the backbone, but grouped. This is in agreement with the block-structure theory (Takano, Hayashi, Hara 1997) and with the isolation of carrageenan and/or agaran fragments from the partial hydrolysis of the polysaccharides from Anatheca dentata (Nunn, Parolis, and Rusell 1971) and Grateloupia divaricata (Cryptonemiales) (Usov and Barbakadze 1978). F3T1 and F3T6 are composed by similar structural units, although F3T1 is less sulfated: 3-linked non sulfated β-D-galactose and β-D-galactose substituted on C-4 or C-6 (possibly with sulfate on C-4 and with single stubs of β-D-xylose on C-6) or C-2 and C-4, and 4-linked α-L-galactose, partially sulfated on C-3 and, possibly, 3,6-anhydro-α-L-galactose 2-sulfate units. Carposporophytes of G. torulosus also biosynthesize small amounts of L-galactose containing galactans (about 4 % of agaran structures) (Estevez, Ciancia, and Cerezo 2002). Raw water extracts and their alkali-treated derivatives from six species of red algae of the genus Callophycus (Solieriaciae) were studied by Fourier Transform Infrared spectroscopy as well as 1H and 13C NMR spectroscopy without detecting any absorption that could be assigned to agaran structures (Chiovitti, Basic, Craik, Munro, Kraft, and Liao 1997). Also, hot water extracts of two seaweeds of the genus Rhabdonia (R. coccinea and R. verticillata) (Solieriaceae) showed 13C NMR spectra without any absorption corresponding to agarans, suggesting the necessity of the chemical determination of the absolute configuration of the galactose and derivatives (Chiovitti, Liao, Kraft, Munro, Craik, and Basic 1996). These are two examples of chemical work carried out with a different aim, where different information is obtained. c. DL-Galactan Systems from Tetrasporophytes of the Family Gigartinaceae Galactans from tetrasporic plants of the Gigartinaceae are also extracted at room temperature and they are mainly carrageenans of the λ-family. The galactans from tetrasporophytes of I. undulosa (Stortz and Cerezo 1993) and G. skottsbergii (Noseda 1994) gave, by fractionation with KCl, fractions which precipitated at high concentrations of this salt (λ-carrageenans), and a fraction soluble in 2 M KCl. These soluble fractions comprised structures of the λ-family, together with unusual units and L-galactose-containing galactans. By fractionation of the soluble product from I. undulosa, T3 (([α]D= +11.0º, 30% of galactose in the L-form, Table 2) by anion-exchange chromatography (Stortz, Cases, and Cerezo 1997) fractions containing the expected λ-carrageenans, together with mixtures of λ-structures and agarans (or DL-hybrids) and some unusual polysaccharides were isolated (Table 9).


171

Table 9. Analysis of fractions obtained from the soluble tetrasporic carrageenan (T3) from Iridaea undulosa by alkaline treatment and KCl-fractionation1 Fraction F2 F5 F10 F14 F17 F20 F30A F30B

Yield % 14.6 6.0 4.8 13.6 3.6 2.0 4.0 6.8

Sulfate as SO3Na % 21.1 6.7 15.2 23.3 22.3 29.1 19.9 27.8

[α]Dº - 20.3 + 4.4 - 26.6 - 29.2 - 10.8 + 37.6 + 10.6 + 43.7

Residues/100 sugar residues D-Gal 49.8 13.4 36.0 53.0 64.8 93.1 76.2 100

L-Gal 43.0 41.1 45.1 47.0 28.7 6.9 21.5 tr.

D-Glc 2

4.9 45.5 13.82 6.5 2.3 tr.

SO3Na 85 36 58 108 109 146 124 162

1

From Stortz, Cases, and Cerezo 1997b. 2F2 and F10 contain 2.3 and 5.1 % of L-Rham, respectively. tr.=traces.

2

These results suggest that there could also be some polysaccharide structure (F10) leaving the usual unit alternancy. The crude tetrasporic carrageenans from G. skottsbergii yielded also a fraction soluble in 2M KCl (T7), its analysis, as well as that of the alkali-treated derivative (T7T1), indicated a D-:L-galactose ratio of 4:1. Carrageenans from the tetrasporic plants of Gigartina lanceata and G. chapmanii have also been studied. 13C NMR spectra of the extracts and of the alkali-treated products gave no evidence of the presence of L-galactose or of its 3,6-anhydro-derivative which, according to the above described results, should be present (Falshaw and Furneaux 1998). These results suggest that this methodology may not be adequate to detect small, but still significant, percentages of minor diasteromeric structures, due to its inherent low sensitivity, as well as the low solubility and viscisity of the solutions, and the usual complexity of the spectra of these raw materials.

2. DL-Galactan Systems from Other Red Seaweeds of the Order Gigartinales Members of the family Kallymeniaceae produce complex, highly sulfated, non-gelling, D- and L-galactose containing galactans. Few reports of galactans from seaweeds of the genus Callophyllis informed the presence of carrageenans in C. rhynchocarpa (Usov and Klochkova 1992, Usov, Ivanova, and Shashkov 1983); carrageenans and agarans were found in C. rangiferina (Chopin, Kerin, and Mazerolle 1999) and in C. cristata (Usov and Klochkova 1992). Polysaccharides from C. hombroniana have mainly a θ-carrageenan structure (Figure 2), minor quantities of λ-carrageenans, and a galactan structure corresponding to a θ-carrageenan, desufated on C-2 of the 3,6-anhydrogalactose units. An agaran structure comprising α-L-galactose units was also found in significant amounts (Falshaw, Furneaux, and Stevenson 2005).

172


Carrageenans of the λ/θ/α-type were informed for C. variegata, based on infrared spectroscopy (Chopin, Kerin, and Mazerolle 1999). Further studies on poysaccharides from gametophytic samples of this seaweed extracted with water at room temperature (Rodriguez, Merino, Pujol, Damonte, Cerezo, and Matulewicz 2005) showed only traces of L-galactose or its derivatives. However, fractionation by precipitation with KCl yielded fractions with low positive optical rotations consistent with the presence of carrageenan and agaran structures. Accordingly, low but significant quantities of L-galactose (3,6-anhydrogalactose was always in the D-configuration) (Table 10) were detected. F3 was submitted to alkaline treatment giving, after fractionation of the modified polysaccharides with KCl, a major soluble fraction, F3T3 (Table 10). The agaran moiety in these fractions was constituted by 3-linked β-Dgalactose units, mainly sulfated on C-2 and non-sulfated α-L-galactose residues, similar to those found in C. hombroniana (Falshaw, Furneaux, and Stevenson 2005). Other seaweed of the family Kallimeniaceae, Cirrulicarpus gmelinii, was also found to produce DL-hybrid galactans ((Usov and Klochkova 1992). Hence, it was reported that the ratio agaran/carrageenan, as well as the major type of polysaccharides, might prove to be a significant chemotaxonomic marker for the genus and others of the family Kallymeneaceae, as there is still some taxonomic controvercy about these seaweeds (Miller 1997, Chopin, Kerin, and Mazerolle 1999). It was found that Endocladia muricata (Endocladiaceae) produces the expected carrageenans, but also 6 % of agaran (White, Hosford, and Engard 1985). On the other hand, funorans, a mixture of galactans from Gloiopeltis spp. also belonging to the family Endocladiaceae, now included in the order Gigartinales, have been considered sulfated agarans (Lawson, Rees, Stancioff, and Stanley 1973, Penman and Rees 1973), mainly constituted by 6-sulfated agarose and its precursor structure. However, fractionation of the galactans of G. complanata by precipitation with cetylpyridinium and redissolution with 4 M KCl at 4º C, allowed to isolate a highly sulfated fraction in small yield, mostly constituted by D-galactose residues and with a highly positive optical rotation ([α]D = + 64º). By redissolution of the remaining precipitate in the same solution, but at 100º C, an agaran was isolated; this product was further fractionated to give a fraction that precipitated in 0.5 M KCl, mostly 6-sulfated agarose, and a soluble fraction, rich in precursor units (Takano, Hayashi, Hara, and Hirase 1995). Later, a DL-hybrid galactan fraction obtained from another species of the same genus, G. furcata, obtained in a similar way (PS3, [α]D = + 23º), was studied in depth (Takano, Iwane-Sakata, Hayashi, Hara, and Hirase, 1998). By partial acid hydrolysis and fractionation di- and tri-saccharides containing only D-galactose or alternating D- and L-galactose (or their derivatives) were isolated and characterized (Table 11). No evidences of alternating carrageenan and agaran disaccharide units were found. Structural determination by methylation analysis and 13C NMR spectroscopy indicated that the carrageenan moiety was constituted by 3-linked β-D-galactose (4)2,4-disulfated units and 4linked 3,6-anhydro-α-D-galactose residues, or their precursor (α-D-galactose 6-sulfate). Some seaweeds of the family Dumontiaceae, like Constantinea rosa-marina, C. subulifera, and Cryptosiphonia woodii, were also found to produce DL-hybrid galactans (Chopin, Kerin, and Mazerolle 1999).

Table 10. Analysis of fractions isolated from the row extract otained from Callophyllis variegata by KCl-fractionation and of the main fraction obtained from alkali-treated F3 by further fractionation with KCl1 Range of precipitatio Fraction n M, KCl F1 F2 F3 F3T3 1

1.20-1.25 1.80-2.00 2.006 2.006

Yield % 9.7 11.0 73.3 94.0

2

Sulfate as SO3K % 33.6 40.9 31.6 29.4

Monosaccharide composition3(moles %) Gal D64 60 57 59

3-Gal L-

7 10 10 11

3 2

2 -

DAnGal4 15 16 20 23

D-Xyl 8 2 6 7

[α]Dº + 10.8 + 13.5 + 20.0 + 5.7

Mw KDa 185 356 95 n.d.

Carrageenan 5

% 84 77 77 76

Agaran5 % 16 23 23 24

From Rodríguez, Merino, Pujol, Damonte, Cerezo, and Matulewicz 2005. 2Yields are given as percentages of the total recovered for F1-F3 (65.1 %). 3 Small quantities of Glc and Man were detected in F1-F3. 4Only 3,6-anhydro-D-galactose was detected by 13C NMR spectroscopy; for F3 and F3T3 this was confirmed by an analytical procedure. 5Considering Xyl, Glc, and Man as contaminants. 6Soluble in 2.0 M KCl.

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Sulfated galactans from Schyzimenia binderi are DL-hybrids, with predominance of carrageenan structures devoid of 3,6-anhydrogalactose. Sulfation was found on C-2, C-4, or both positions, on the 3-linked β-D-galactose units and on C-3 on the 4-linked α-galactose residues (Matsuhiro, Conte, Damonte, Kolender, Matulewicz, Mejías, Pujol, and Zúñiga 2005). Polysaccharides obtained from other species of this genus had previously been found to be either carrageenans (Whyte, Foreman, and De Wreede 1984) or agarans (Bourgougnon, Lahaye, Quemener, Chermann, Rimbert, Cormaci, Furnari, and Kornprobst 1996). Significant quantities of uronic acids were detected in some cases. Table 11. Disaccharides and trisaccharides obtained by partial acid hydrolysis of PS3 from Gloiopeltis furcata1 1 2 3 4 5 6 7 8 9 10

β-D-Gal(1→4)L-Gal β-D-Gal(1→4)D-Gal α-L-Gal(1→3)D-Gal α-D-Gal(1→3)D-Gal β-D-Gal(1→4)3,6-anhydro-L-Gal 6-O-Me-β-D-Gal(1→4)D-Gal α-L-Gal(1→3)β-D-Gal(1→4)L-Gal α-D-Gal(1→3)β-D-Gal(1→4)D-Gal β-D-Gal(1→4)α-L-Gal(1→3)D-Gal β-D-Gal(1→4)α-D-Gal(1→3)D-Gal

1

From Takano, Iwane-Sakata, Hayashi, Hara, and Hirase, 1998

3. DL-Galactan Systems from Red Seaweeds of the Order Halymeniales Algae from the Halymeniales biosynthesize complex sulfated galactans. Most of them have sulfate at C-2 of the β-D-galactose units and they formally belong to carrageenans of the λ-family. The presence of D- and L-galactose residues has been reported in members of different genera of the order Halymeniales, as Grateloupia (Usov, Miroshnikova, and Barbakadze 1975, Usov and Barbakadze 1978, Usov, Yarotsky, and Shashkov 1980, Sen, Das, Sarkar, Suddhanta, Takano, Kamei, and Hara 2002, Wang, Bligh, Shi, Wang, Hu, Crowder, Branford-White, and Vella 2007) Halymenia (Fenoradosoa, T. A., Delattre, C., Laroche, C., Wadouachi, A., Dulong, V., Picton, L., Andriamadio, P., Michaud, P. 2009), Pachymenia, (Farrant, Nunn, and Parolis, 1971, 1972, Parolis, 1978, 1981, Miller, Falshaw, and Furneaux 1995), Phyllymenia (Nunn and Parolis 1969, Parolis 1981) and Aeodes (Allsobrook, Nunn, and Parolis 1971, 1974, 1975). Acetolysis of the polysaccharide of Aeodes ulvoidea (Grateloupiaceae) resulted in the isolation of ten oligosaccharides most of them arising from non-cyclized carrageenans, but one, obtained in small amount (about 0.1%) was 4-O-β-D-galactopyranosyl-2-O-methyl-Lgalactose and other, a tetrasaccharide, isolated in 0.03 % yield ( [α]D = - 60˚), was suggested to have alternating D- and L-galactose residues (Allsobrook, Nunn, and Parolis 1975).

Table 12. Analysis of some of the galactans obtained from Cryptonemia crenulata1

Fraction C1S4 C1S-1 C1S-2 C1S-3 C2S4 C2S-1 C2S-2 C2S-3 C2S-4 C2S-2c C2S-2d 1

Yield2 % 3.76 9.6 18.0 56.0 6.63 3.2 24.0 54.2 3.3 25.0 55.0

Sulfate as SO3Na % 26.0 22.3 26.5 16.0 27.7 20.1 25.1 28.3 17.5 14.0 20.4

Pyruvic acid % 7.9 n.d. 2.2 0.7 3.7 n.d. 1.9 0.5 n.d. 4.5 0.4

Monosaccharide units3 (moles %) [α]Dº G+D:L 1:0.17 1 1 1 1:0.17 1 1 1:0.09 1 1 1:0.11

DA:LA 0.18:0.04 0.21 0.02 0.15 0.04:0.14 0.12:0.01 0.06:0.04 0.09:0.20 0.09:0.06 0.14 0.01

LA2M 0.14 0.04

0.09 0.11 0.10 0.10 0.14 0.13 0.15 0.09

D2M:L2M 0.10:0.02 0.08 0.07 0.11 0.07:0.02 0.10 0.08 0.05:0.02 0.03 0.09 0.05:0.03

Xyl 0.17 0.16 0.05 0.18 0.06 0.05 0.14 0.05 -

+ 25.5 + 14.0 + 12.0 + 12.0 + 27.0 + 11.0 + 6.5 + 23.0 + 4.0 n.d. n.d.

From Zibetti, Noseda, Cerezo, and Duarte 2005. 2Yields of C1S and C2S are given per 100 g of dry seaweed, yields of fractions are given per 100 g of the parent compound. 3Knutsen´s nomenclature. G+D=β-D- plus α-D-galactose and L=α-L-galactose. 4Soluble in 2.0 M KCl.

176


Other major characteristics of the galactans from the genus Aeodes were: methylation on C-2 of the α-D-galactose units, substitution of the same units by single stubs of 4-O-methyl-α-Lgalactose residues, and sulfation, mostly on the β-D-galactose units, possibly on C-2, and also on C-6 of some of the α-galactose residues (Nunn and Parolis 1968, Allsobrook, Nunn, and Parolis 1975). Cryptonemia crenulata (Halymeniaceae) has been reported to produce ι-carrageenans (Saito and Oliveira 1990). Nevertheless, later preliminary results suggested highly complex polysaccharides (Chopin, Kerin, and Mazerolle 1999). In a more detailed research (Zibetti, Noseda, Cerezo, and Duarte 2005) the seaweed was extracted with water at room temperature (C1) and with a hot phosphate buffer (pH 6.5) (C2), these extracts were purified by precipitation with 2M KCl in which 94% of C1 and 97% of C2 remained soluble (C1S and C2S, Table 12). C1S and C2S were fractionated by ion exchange chromatography to give subfractions C1S-1 – C1S-3 and C2S-1 – C2S-4, respectively. C2S-2 was refractionated on the same column giving C2S-2a – C2S-2d. In all the fractions, when enantiomeric analysis was carried out, the D- and L-forms of galactose, 3,6-anhydrogalactose and 2-Omethylgalactose, together with the L-form of the 3,6-anhydro-2-O-methyl-galactose were found. The percentage of carrageenan structures was 28-38 %, while that of agaran structures was 62-72%.

4. DL-Galactan Systems from Agarophytes of the Order Ceramiales All the representatives of the Ceramiales studied contained agarans with a wide range of substituents. The first time that a carrageenan structure, even though in small quantity, was identified in the polysaccharide system from an algae belonging to the order Ceramiales was in a fraction of the extract from the red seaweed Rhodomela larix (Takano, Yakoi, Kamei, Hara, and Hirase 1999), previously considered as producing highly methylated agarans (Usov and Ivanova 1975). However, partial hydrolysis of a methanolysis-resistant moiety obtained from the main polysaccharide fraction from this seaweed afforded sets of the disaccharides [β-D-Gal(1→4)L-Gal, β-D-Gal(1→4)D-Gal, α-L-Gal(1→3)D-Gal, α-D-Gal(1→3)D-Gal] and trisaccharides [α-L-Gal(1→3)β-D-Gal(1→4)L-Gal, α-D-Gal(1→3)D-Gal(1→4)D-Gal, β-D-Gal(1→4)α-L-Gal(1→3)D-Gal, β-D-Gal(1→4)α-D-Gal(1→3)D-Gal], indicating that both agaran and carrageenan structures cooccur, even if the latter are small in quantity. Structural analysis showed that the 4-linked α-galactose units were partially methylated on C2 and sulfate groups were on C-6 of these units, C-2 of the cyclized derivatives, and on C-3 of the α-D-galactose units. The 3-linked galactose units were partially sulfated on C-6 (Takano, Yakoi, Kamei, Hara, and Hirase 1999). Fractionation of the galactans from the agarophyte from Digenea simplex (Rhodomelaceae) by ion-exchange chromatography led to the isolation of a sulfated product, which afforded, when subjected to partial methanolysis, disaccharide derivatives characteristic of agaran and carrageenan structures. The substitution pattern was similar to that of R. larix, although some 3-linked galactose units were sulfated on C-4 (Takano, Shiomoto, Kamei, Hara, and Hirase 2003). Both, R. larix and D. simplex have been considered as potential sources of agar or agarose (Chiovitti, Liao, Kraft, Munro, Craik, and Basic 1996). On the other hand, the sulfated galactan systems from other Rhodomelaceae, i.e.


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Bostrychia montagnei (Duarte, Noseda, Cardoso, Tulio, and Cerezo 2002), Polysiphonia nigrescens (Prado, Ciancia, and Matulewicz 2008), Acanthophora spicifera (Duarte, Cauduro, Noseda, Noseda, Gonçalves, Pujol, Damonte, and Cerezo 2004) showed to be composed by agarans with different substitution patterns, but, in spite of the fact that extensive fractionation procedures were carried out, results did not show the existence of carrageenan structures in significant quantities.

5. DL-Galactan Systems from Agarophytes of the Order Rhodymeniales Sulfated galactans were isolated from the red seaweed Lomentaria catenata (Takano, Nose, Hayashi, Hara, and Hirase 1994) by precipitation with cetylpyridinium salt. Redissolution with KCl solutions allowed to isolate a product that, by acid hydrolysis and fractionation gave the oligosaccharides indicated in Table 13. All these oligosaccharides had carrageenan or agaran structures, but in no case a mixed product was found. The ratio of agarose- to carrageenan-chains was estimated to be 1:0.56 for this fraction. A particular structural feature of these polysaccharides was the presence of D-glucose and D-glucuronic acid side chains, which were deduced to be linked as single stubs to C-3 of the 4-linked Dgalactose units and to C-4 of the 3-linked D-galactose units, respectively in the carrageenan backbone. Although these polysaccharides were highly sulfated, the sulfation pattern was not analyzed. Table 13. Neutral products obtained by partial acid hydrolysis of PS-2 from Lomentaria catenata1,2 Isolated fraction DP1 PD2a DP2b DP2e DP2d DP2c DP3a3 DP3b-1 DP3b-24 DP4a DP4b 1

Product identified 1 Gal+Xyl+Glc 2 β-D-Gal(1→4)L-Gal 3 β-D-Gal(1→4)D-Gal 4 α-L-Gal(1→3)D-Gal 5 α-D-Gal(1→3)D-Gal 6 -D-Glc(1→3)D-Gal 7 α-L-Gal(1→3)β-D-Gal(1→4)L-Gal 8 α-D-Gal(1→3)β-D-Gal(1→4)D-Gal 9 β-D-Gal(1→4)α-L-Gal(1→3)D-Gal 10 β-D-Gal(1→4)α-D-Gal(1→3)D-Gal 11 β-D-Gal(1→4)α-L-Gal(1→3) β-DGal(1→4)L-Gal 12 Unidentified tetrasaccharide(s) 13 Higher oligosaccharides

Relative yield 63.3 15.8 4.3 1.9 0.5 1.9 3.4 0.5 2.4 0.3 2.1 1.8 3.6

From Takano, Nose, Hayashi, Hara and Hirase 1994. 2Two acidic oligosaccharides were identified as: D-GlcA(β1→4)D-Gal and D-GlcA(1→4)D-Gal(1→4)D-Gal. 3Obtained as a mixture of trisaccharides 7 and 8. 4Obtained as a mixture with trisaccharide 9.

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On the other hand, galactans from Champia novae-zelandiae are also agar-rich DLhybrids, being mainly sulfated on C-2 of both alternating units, as well as on C-3 of the 4linked residues (Miller, Falshaw, and Furneaux 1996). Extracts obtained from samples of Hymenocladia sanguinea from different lacations and life stages were found to have essentially equivalent polysaccharides by 13C NMR spectroscopy. They contained 3-linked βD-galactose units sulfated on C-2; the B-units (D-galactose, L-galactose and 3,6-anhydro-Lgalactose, in ratio 0.57:0.38:0.05) were mainly 4-linked D-galactose 3-sulfate and 2,3disulfate, together with L-galactose units, sulfated in part on C-6 (Miller 2001), showing important substitution similarities with polysaccharides from C. novae-zelandiae.

6. DL-Galactan Systems from Seaweeds of the Order Bonnemaisoniales Galactans from gametic, carposporic and tetrasporic stages of red seaweed Asparagopsis armata (Bonnemaisoniaceae) are mainly non-cyclized carrageenans with heterogeneous sulfation pattern and certain degree of branching. In addition, agarans were also detected, as well as small amounts of uronic acids, only in significant quantities (15.9 %) in the carposporophytes (Haslin, Lahaye, and Pellegrini 2000).

7. DL-Galactan Systems Detected in Typical Agarophytes Galactans biosynthesized by seaweeds of the genus Porphyra (Bangiales) are usually known as porphyrans. They are agarans whose main structural characteristic is the presence of important amounts of precursor units (α-L-galactose 6-sulfate) (Morrice, McLean, Long, and Williamson 1983), which by alkaline treatment give 3,6-anhydro-L-galatose; in this way, an agarose structure is obtained from porphyran (Figure 2). The other structural characteristic of these polysaccharides is a certain degree of methoxylation on C-6 of the β-D-galactose units. Unexpectedly, the presence of a small quantity (3 %) of α-D-galactose 6-sulfate units was detected in the crude extract from Porphyra columbina, indicating the presence of a carrageenan structure (Navarro and Stortz 2003). After extensive fractionation procedures of the room temperature and 50 ºC water extracts from Pterocladiella capillacea, small amounts of galactans containing 4-linked α-Dgalactose substituted on C-3 possibly with sulfate, were found, showing the presence of DLhybrid galactans for the first time in a seaweed of the order Gelidiales (Errea and Matulewicz 2003).

DEVIATION OF THE STRUCTURE OF CARRAGEENANS (OR CARRAGEENAN BLOCKS) AND AGARANS (OR AGARAN BLOCKS) IN THE DL-GALACTAN SYSTEMS Structure of the backbone. The presence of unusual units, as well as that of branches of xylose, galactose and/or glucose, in carrageenan and agaran molecules, which are supposed to


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be lineal, suggested that the structure of carrageenan blocks (or molecules) and/or agaran blocks (or molecules) in DL-galactan systems may be somewhat different to that of the “classical” carrageenans or agarans (Zibetti, Noseda, Cerezo, and Duarte 2005). Nevertheless, it should be considered that: a) some of the samples, in which the unusual units or the side chains appear have been found after extensive fractionation and in very low yield, and they cannot be considered as representative of the galactan system and b) no enantiomeric analysis on the partially methylated galactoses from methylation analysis were carried out in the earlier research of galactans from typical carrageenophytes or agarophytes, difficulting the comparison with more recent studies on other seaweeds. A fraction (Fs) from the galactans of cystocarpic G. skottsbergii (Ciancia, Matulewicz, Cerezo 1993) showed major amounts of β-D-galactose 4-sulfate units and minor amounts of β-D-galactose 2-sulfate units, these are linked to the usual α-D-units in carrageenans, but also to non-substituted α-L-galactose residues. 3-linked 6-sulfated β-D-galactose units were found in the agaran moiety of the galactans from cystocarpic (Flores, Cerezo, and Stortz 2002) and tetrasporic stages (Stortz, Cases, and Cerezo 1997) of I. undulosa, together with 4-linked 3substituted galactose residues (Stortz, Cases, and Cerezo 1997), a pattern common to corallinans (Cases, Stortz, and Cerezo 1994) and other red seaweeds galactans obtained from several species of the Halymeniales (Miller, Falshaw, and Furneaux 1995, Miller, Falshaw, Furneaux, and Hemmingson 1997). The agaran moiety of tetrasporic G. skottsbergii contains, as above, 3-linked 6-substituted β-D-galactose units and 4-linked 3-substituted α-L-galactose residues, but in smaller amounts (Noseda 1994). Galactans extracted with water at room temperature from K. alvarezii have a basic κcarrageenan pattern, with small amounts of unusual residues, as non-sulfated 3-linked β-Dgalactose and its 2,4- and 4,6-disulfated forms and important amounts of 6-O-methyl β-Dgalactose (4-sulfate) in the polysaccharide backbone. Agarans are shown by the presence of 3-linked 2- and 6-substituted galactose residues and 4-linked non-substituted and 3substituted α-L-galactose units (Estevez, Ciancia, and Cerezo 2000). Those extracted with hot water are partially substituted on C-2 or C-4, or disubstituted in both positions of the β-Dgalactose units, and on C-3 or C-2 and C-3 of the α-L-galactose residues with sulfate groups or single stubs of β-D-xylopyranose, D-glucopyranose and galactose or with Dglucopyranosyl-(1→4)-D-glucopyranose side chains. Significant quantitites of 2-O-methyland 3-O-methyl-L-galactose units were also present (Estevez, Ciancia, and Cerezo 2004). Substitution on C-2 and C-3 of the 4-linked α-L-galactose units was also found in the agarrich DL-hybrids, Champia novae-zelandiae (Miller, Falshaw, and Furneaux 1996). Agarans that retrograded during fractionation of the hot-water extracts of K. alvarezii (F3i) or after alkaline treatment of the soluble fraction (T1), showed great structural dispersion, as the 3-linked β-D-galactose units are substituted in part on C-4 or C-2, or disubtituted on C-2 and C-4. The major B-units are 4-linked α-L-galactose substituted on C-3, nonsubstituted L-galactose, D/L-galactose substituted on C-2 and C-3 and 3,6-anhydro-L- and D-galactose and their derivative substituted on C-2. Agaran structures from G. torulosus have small amounts of β-D-galactose units nonsubstituted, sulfated on C-2, and substituted on C-6 with single stubs of xylose, together with small percentages of α-L-galactose 3-sulfate. Those extracted with hot water comprised 3sulfated α-L-galactose units and 2-sulfated 3,6-anhydro-α-L-galactopyranose residues in the agaran moieties. A small amount of β-D-galactose substituted on C-6 with stubs of β-D-

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xylose was found in both extracts. The presence of alkali-stable L-galactose 3-sulfate units, xylosyl side chains and traces of 3-O-methylgalatose were previously found in the galactans extracted from Anatheca dentata (Nunn, Parolis, and Rusell 1971, 1981). Galactans of C. variegata are mainly cyclized λ-carrageenans (θ-carrageenans), together with highly sulfated units, but they also comprise small amounts of non-substituted β-Dgalactose units, linked to 2,3-disulfated and non-substituted α-L-galactose residues (Rodriguez, Merino, Pujol, Damonte, Cerezo, and Matulewicz 2005). These are some examples, but similar structures were reported for other carrageenophytes. On the other hand, the carrageenan blocks of galactans from the agarophyte Cryptonemia crenulata are constituted by the major quantities of β-D-galactose, partially sulfated on C-2, linked to α-D-galactose 6-sulfate and their cyclized derivative, in the carrageenan- as well as in the agaran-moiety. The A-units contained also non-substituted, 2,6-disulfated and 4,6pyruvic acid ketal substitution. The agaran B-units appeared substituted on C-6 by single stubs of xylose and galactose and methylated on C-2 (Zibetti, Noseda, Cerezo, and Duarte 2005). 4-Linked α-D-galactose units substituted on C-3 were found in the carrageenan moiety from the agarophyte Pterocladiella capillacea (Errea and Matulewicz 2003). In summary, the unusual A-units are characterized by different sulfation patterns (nonsulfated or sulfated on C2 or C6), by higher sulfation (sulfated on 2,4- or 2,6-), and by methylation or branching (mainly single stubs of xylose on C-6). Unusual B-units are unsubstituted, 3-substituted with sulfate, xylose or galactose and 2,3-disulfated or substituted by sulfate and single stubs of xylose in the same way; methyl groups appear on C-2 or C-3 of the α-L-galactose residues. All these “unusual” structural units do not appear in carrageenans and/or agarans from “classical” carrageenophytes or agarophytes, but they are often found in carrageenan-like or agaran-like galactans from other seaweeds (i.e. Halymeniales, Ceramiales, Rhodimeniales). Counterions. Ca2+ showed high affinity for sulfated L-galactans from different ascidian species, and its concentration increased with increasing amounts of nonsulfated sugar branches. This affinity also increased as the mean distance between charged groups decreased, suggesting that Ca2+ binding requires more than one sulfate group per each calcium atom (Ruggiero, Fossey, Santos, and Mourao 1998). Similar results were reported for glycosaminoglycans; their sulfate groups are capable of binding Ca2+ with stronger affinity than that expected from simple salt formation (Hunter, Wong, and Kim 1988). The raw extract from K. alvarezii contains major amounts of divalent (Ca2+ and Mg2+) cations in agreement with the known capacity of the seaweeds to concentrate these salts (Kloareg and Quatrano 1988). These counterions were maintained in high percentages in fractions that were obtained through fractionation procedures involving contact with massive amounts of potassium chloride or hot and concentrated sodium hydroxide solutions, or sequences of both. It is worth noting that permethylation of the polysaccharides involved as first step the preparation of the triethylammonium salts by ion-exchange chromatography, nevertheless the methylated derivative contains as much inorganic cations as the parent polysaccharide. Similar difficulties to exchange the divalent counterions were found in a commercial sample of a κ-carrageenan from the same seaweed, which originally contained about 40 % of Ca2+. After cation-exchange chromatography at 80º C on a sodium preregenerated resin, it still showed about 15 % of Ca2+ (Chen, Liao, and Dunstan 2002).


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Consequently, Ca2+ binding in these polymers is not a simple function of availability of anion binding sites, but a more complex Ca2+-polysaccharide interaction (Chandrasekaran, Radha, and Lee 1994, Tibbits, MacDougall, and Ring 1998). Side chains. “Classical” carrageenans and agarans are linear molecules with no branching. Nevertheless, xylose, glucose and galactose have been found as single stubs or short chains in several agarans (Kolender and Matulewicz 2002, Duarte, Noseda, Cardoso, Tulio, and Cerezo 2002, Usov, Bilan, and Shashkov 1997, Cases, Stortz, and Cerezo 1994) or in the agarans (or agaran blocks) of DL-galactan systems (Ciancia, Matulewicz, and Cerezo 1993, Estevez, Ciancia, and Cerezo 2001, Takano, Shiomato, Kamei, Hara, and Hirase 2003, Estevez, Ciancia, and Cerezo 2000). Terminal galactose units were found in the soluble fraction of tetrasporic (Stortz, Cases, and Cerezo 1997) and cystocarpic (Fs) galactans of G. skottsbergii and I. undulosa. In Fs alternating 3- and 4-linked side chains and single stubs of xylose were also found (Ciancia, Matulewicz, and Cerezo 1993). Several fractions of the DL-galactan system of K. alvarezii (Table 6) contain small-tosignificant amounts of xylose, glucose and galactose as short chains or single stubs, linked to C-2 and/or C-4 of the 3-linked β-D-galactose and C-3 and/or C-2 and C-3 of the 4-linked αD- or α-L-galactose residues. In the galactan system of Bostrychia montagnei (Ceramiales), terminal β-D-xylose units are linked to C-6 of the β-D-galactose units and C-3 of the α-galactose residues (Duarte, Noseda, Cardoso, Tulio, and Cerezo 2002). They have also been found linked to C-6 of the βD-galactose units in the “corallinans” (Usov, Bilan, and Shashkov 1997, Cases, Stortz, and Cerezo 1994). On the contrary, the system of Cryptonemia crenulata showed no branching in the β-D-galactose units, but the α-galactose residues carry single stubs of β-D-galactose and β-D-xylose (Zibetti, Noseda, Cerezo, and Duarte 2005).

ISOLATION OF “PURE” CARRAGEENANS AND/OR “PURE” AGARANS FROM DL-GALACTAN SYSTEMS DL-galactan systems have never been totally resolved into carrageenans and agarans. Nevertheless, the use of solutions of high ionic strengh (KCl solutions), alkaline solutions or highly chaotropic media (LiCl/DMSO) at high temperature allowed isolation of “pure” carrageenans or agarans. Furthermore, carrageenan or agaran structures, sometimes to percentages as high as 95 %, have been obtained by spontaneous insolubilization or by ionexchange chromatography in systems where the amounts of sulfate in both types of structures were quite different. Alkaline treatment of the raw galactan obtained from K. alvarezii (C) and further dialysis in the same alkaline medium gave a “pure” kappa/iota-carrageenan (C’) (Estevez, Ciancia, and Cerezo 2004). Similar treatment of fractions A1 (Estevez, Ciancia, and Cerezo 2008) and C1 (Estevez, Ciancia, and Cerezo 2004) from G. torulosus also produced “pure” kappa/iotacarrageenan (Tables 6 and 7), suggesting that the kappa/iota-carrageenans biosynthesized by both seaweeds were forming complexes with agarans. In addition, during fractionation of the raw extract obtained with hot water of K. alvarezii some products retrograded spontaneously (F3i), or after alkaline treatment of the soluble

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fraction F3s (T1) (Estevez, Ciancia, and Cerezo 2004). These insoluble products were almost “pure” agarans (∼ 90 %) and had characteristics similar to those of the insoluble fraction obtained in comparable situation from the alkali-treated, KCl-soluble fraction of G. torulosus (F3T1), suggesting that these agarans are usual minor components of the polysaccharide system of the carrageenophytes. The above mentioned alkali-treated product from K. alvarezii gave, after precipitation of T1, two gelling fractions and a soluble one (T4), which is mostly an agaran with a substitution pattern similar to that of T1 and F3i. (Estevez, Ciancia, and Cerezo 2004). Ion-exchange chromatography on Sephadex DEAE A-25 of T4 gave six fractions eluted according their sulfate content. Even though 3,6-anhydrogalactose was not resolved into the D- and L-enantiomers in this work, all the data suggest that the first fraction (FI , 35.0 %, sulfate content, 5.8 %) was in ∼ 97 % an agaran, while the last one (FVI, 8%, sulfate content 27.8 %) was in ∼ 70-90 % a carrageenan. The fibrillar material from G. torulosus (RC4) contained major amounts of (glyco)proteins, galactans and cellulose, together with small amounts of xylose and mannose. Small amounts of L-galactose, together with traces of 3,6-anhydro-L-galactose units were detected. Extraction of RC4 with LiCl/DMSO at high temperature solubilized 34 % of the cell wall, from which only 16.5 % was isolated after dialysis. This product was a kappa/iotacarrageenan with a molecular weight of ∼ 11 kDa. Thus, about half of the extracted material was lost during dialysis in the chaotropic medium including the possible L-galactose containing polysaccharides. This result could be attributed to their low molecular weight (Estevez, Ciancia, and Cerezo 2008). It is not known whether these low Mw fragments are real or they are artifacts produced during the extraction procedure, even thought LiCl/DMSO reagent was reported not to cleave covalent linkages (Petrus, Gray, and BeMiller 1995).

FORMATION OF CARRAGEENAN, AGARAN AND CARRAGEENAN/AGARAN COMPLEXES In early investigations, it had been suggested (Pernas, Smidsrod, Larsen, and Haug 1967) that the solubility behaviour of carrageenan molecules in mixtures was the same as that in homogeneous fractions. In other words, that there were no intermolecular interactions and therefore, the KCl-precipitation range should define the chemical structure of the carrageenan. Later data demonstrated that carrageenan molecules associate forming transients, non-stequiometric complexes and the solubility of these complexes proved to be different from that of “pure” fractions (Stortz and Cerezo 1988, Ciancia, Matulewicz, and Cerezo 1993, 1995). Thus, three fractions of the carrageenan from unsorted I. undulosa precipitated at very sharp concentration ranges of KCl (1.20-1.25; 1.35-140; 1.55-1.65 M), nevertheless, they were mixtures of μ/ν- and λ-carrageenans. Both types of molecules, which isolated differ in solubility (μ/ν-carrageenans are totally soluble in 2M KCl, while λ-carrageenans precipitate at high concentrations of this salt), but have similar structures, differing only in the position of sulfation of the 3-linked units (Figure 2), could form some type of aggregates (Stortz and Cerezo 1988). The effects of complexation can be seen comparing yields, precipitation ranges, and analysis of the fractions obtained from cystocarpic and tetrasporic plants of I. undulosa


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(Stortz and Cerezo 1993) with those obtained in the same way from unsorted samples (Matulewicz and Cerezo 1980) of the same seaweed. Taking into account the amount of κ/ιstructure, the carrageenan system from the unsorted sample seems to be composed of a mixture of about two thirds of cystocarpic carrageenans and one third of tetrasporic carragenans. However, these carrageenans precipitated at higher KCl concentrations than those observed for samples separated according to the stage of the life-cycle, 0.75-1.05 M for κ/ι-structures in mixed samples vs. 0.50-0.70 M for those of isolated cystocarpic plants, and 1.20-1.65 for λ-carrageenan in mixed systems vs. 1.00-1.20 M for the tetrasporic samples. Another concern is that the potassium chloride-soluble material in the mixture is much less than that accounted for in the sorted samples, suggesting that part of the soluble structures had been precipitated with the KCl-insoluble fractions (Stortz and Cerezo 1993). Alkaline treatment of a partially cyclized μ/ν-carrageenan from cystocarpic G. skottsbergii and further fractionation of the alkaline derivative with potassium chloride yielded a fraction soluble in 2M KCl with negative rotation (Fs). Enantiomeric analysis showed the presence of about 88% of agarans. These agarans were present together with carrageenans through the extraction and all the fractionation and alkaline treatment steps and are only evident after an elaborate fraccionation procedure (Ciancia, Matulewicz, and Cerezo 1993). Comparison of the KCl-fractionations for alkali-modified derivatives of the above mentioned partially cyclized μ/ν-carrageenan obtained in three different batches showed different precipitation patterns, the corresponding recoveries were low and yields of the fractions and arbitrary subfractions, as well as their composition were different. The low recoveries suggest the presence in the alkali-treated derivatives of low molecular weight products forming composition-dependent complexes, which are dissociated during the fractionation with potassium chloride, and lost in the subsequent dialysis (Ciancia, Matulewicz, and Cerezo 1995). Hence, the variability of the results appears to be associated with temperature- , time- , and composition of molecular associations (Manzi, Mazzini, and Cerezo 1984, Blake, Murphy, and Richards 1971, McCleary, Amado, Waibel, and Neukon 1981). The product (C) extracted with hot water from K. alvarezii, after separation the fraction obtained at room temperature, showed clear differences with a commercial sample of κcarrageenan (K) obtained from the same seaweed (Table 6), namely: (a) it was soluble in 75 % iso-propanol; (b) it had much lower number-average molecular weight ; (c) it contained significant amounts of L-galactose and 3,6-anhydro-L-galactose units; (d) it also contained higher quantities of xylose and glucose and (e) it contained 77.9 % of divalent ions (Ca2+ and Mg2+), against 35.3 % in the commercial κ-carrageenan (Estevez, Ciancia, and Cerezo 2004). The most significant preparative difference between this sample (C) and the commercial κcarrageenan, was that the latter was extracted from a seaweed previously treated with alkali (Glicksman, M. 1993). On this basis, C was submitted to a short, non-degrading, alkaline treatment producing C´ (Table 6), which was similar to the commercial sample. The changes C → C´ were explained in terms of complexes of κ-carrageenans and small fragments of agarans formed, possibly through Ca2+ bridging two sulfate groups from different molecules. This arrangement would be stabilized by further complexation of the cation (Estevez, Ciancia, and Cerezo 2004). These complexes were broken, at least partially, by the alkaline treatment, and the agaran fragments were lost during alkaline dialysis. This scheme of aggregation of small agaran molecules with higher molecular weight carrageenans would be a general

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phenomenon between the galactan sulfates extracted from carrageenophytes belonging to the Phyllophoraceae and Solieriaceae, and it could be generalized to other carrageenophytes from the Gigartinales.

CONCLUSION DL-Galactan Hybrids or Molecular Complexes? The presence of both, carrageenan and agaran, structures in galactan systems of red seaweeds is not exceptional but a general fact, showing that red marine algae biosynthesize what has been called a DL-galactan system of polysaccharides. No neat separation of these systems into “pure” agaran and carrageenan polymers has been obtained, however, no proof of D/L-hybrid galactan structures has been found. Considering the fact that partial hydrolysis has up-to-date produced only agaran or carrageenan fragments, the possibility of carrageenan and agaran mixed diads in the “hybrid” molecule (Figure 3) is very small and so the agaran-carrageenan domains (if they exist) should correspond to juntion zones of a block copolymer. It is not actually known whether the above ‘block DL-hybrid galactan’ hypothesis is correct or whether the polysaccharide extracts constitute a mixture of carrageenan-type and agaran-type molecules. Attempts to fractionate of the raw extracts and/or different fractions or subfractions obtained by KCl precipitation, ion-exchange or gel-permeation chromatography, as well as by several other fractionation methodologies showed the complexity of the systems (Lechat, Amat, Mazoyer, Buleon, and Lahaye 2000), but failed to produce a neat carrageenan/agaran separation. Whether this is a proof of the existence of DLhybrid galactan molecules, or only shows the failure of present-day techniques to separate mixtures of ‘diastereoisomeric’ polysaccharides, is not known, but if the classical definition of homogeneity (Aspinall 1982) is applied, these products should be considered as DL-hybrid galactans until a successful fractionation demonstrates the contrary. No matter whether DL-hybrid galactans or DL-galactan mixtures are considered, the DLgalactose variation should be visualized as another form of structural dispersion in the family of seaweed galactans, in which the existence of only carrageenans and agarans would be just representatives of extreme structure systems.

ACKNOWLEDGMENTS This work was supported by grants from CONICET (PIP 5699) and the University of Buenos Aires (X016 and G048).


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INDEX A absorption spectroscopy, 28 accessibility, 79 acetaldehyde, 77, 81, 84 acetic acid, 7, 10, 166 acetone, 56, 57, 60, 63, 77, 80, 83, 100, 120 acetophenone, 77, 78, 80, 81, 108, 109 acetylation, 159 acid, 7, 13, 14, 15, 16, 21, 30, 47, 58, 59, 80, 84, 93, 134, 158, 159, 160, 166, 172, 174, 175, 177, 180, 189 acidity, viii, 47, 48 acrylate, 117 activation energy, 33, 34, 40, 42, 96, 106, 123 active centers, 146 active site, 80, 85, 95, 97 additives, viii, 75, 76, 77, 78, 81, 85, 86, 90, 92, 93, 94, 97, 98, 99, 102, 103, 104, 108, 109, 116 adhesion, 142 adhesives, 135 adsorption, 9, 10, 13, 19 agar, 176, 178, 179, 186, 187, 192 aggregation, 23, 183 alcohols, 58, 77, 78, 79, 188 algae, 161, 166, 170, 176, 184, 185, 187, 188, 190, 191, 192 alkaline hydrolysis, 7, 10, 12 alkane, 77 alkenes, 146 alkylation, 97, 146, 190 alters, 141 aluminium, 68, 80, 147 amine, 159 amines, 30, 58

ammonium, viii, 4, 8, 75, 76, 84, 85, 86, 90, 98, 108, 146 ammonium salts, 84 amorphous polymers, vii, 29 aniline, 14, 16, 19, 20, 58 annealing, 43, 44, 45 Argentina, 155, 186 aromatic compounds, 27, 84 arsenic, ix, 115, 127 ASI, 153, 154 atactic moieties, 72, 73 atmosphere, 16, 24, 64, 146, 147 atmospheric pressure, 78 atoms, ix, 16, 49, 77, 80, 85, 90, 115, 117, 122, 126 auto acceleration, 90, 99

B bacteria, 85 bending, 152 beneficial effect, 135 benefits, 95 Bernoullian statistics, viii, 67, 69, 70, 71, 72 biliverdin, 97 biocompatibility, 128 biological activity, 116 biological processes, 95 biological systems, 76, 77 biologically active compounds, 116 biomass, 192 bioremediation, 84 birefringence, 146 bisphenol, 30, 31, 32, 35 blends, 130 bonding, 95, 96

194

Index

bonds, 2, 76, 81, 84, 90, 92, 95, 97, 104, 106, 109, 152 branched polymers, 190 branching, 76, 178, 180, 181 breakdown, 84 by‐products, 14, 146

C calcium, 166, 180, 185, 188, 190 cancer, 116 capillary, 159, 187 carbides, 140 carbon, 8, 58, 79, 80, 81, 131, 148, 150, 159 carbon atoms, 80, 148, 159 carbon nanotubes, 131 carbonic acids, 58, 77 carboxyl, 16, 19, 21 carob, 189 catalysis, viii, 75, 76, 77, 78, 81, 83, 85, 86, 88, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99, 100, 102, 103, 104, 105, 106, 107, 108, 109, 113 catalyst, viii, ix, 58, 75, 76, 78, 79, 80, 81, 84, 85, 86, 88, 90, 96, 97, 98, 99, 101, 102, 103, 104, 105, 108, 117, 145, 146, 147, 148, 150, 151, 153 catalytic activity, viii, 75, 76, 78, 80, 81, 84, 85, 86, 93, 97, 98, 101, 102, 107, 109, 146 catalytic effect, 92 catalytic system, 77, 78, 85, 91, 93, 94, 95, 99, 100, 101, 102, 108, 109 cation, 2, 3, 13, 15, 16, 17, 24, 86, 98, 105, 107, 180, 183 cellulose, vii, 1, 2, 3, 15, 165, 182, 190 cellulose triacetate, 2 ceramic, 131, 140 CH3COOH, 58, 107 chain mobility, 134 chain propagation, 76, 81, 85, 90, 99, 101, 102, 103, 104, 105, 106, 107 chain scission, 138, 139 chain transfer, 55 Chavchavadze, Ilia, 115 chelates, 128 chemical, vii, viii, 1, 2, 16, 21, 27, 35, 47, 48, 51, 52, 54, 56, 58, 68, 77, 79, 82, 85, 96, 109, 116, 120, 130, 135, 138, 140, 146, 152, 158, 162, 167, 170, 182 chemical bonds, 21 chemical kinetics, 109 chemical properties, 138

chemical reactions, 16, 77, 130, 135 chemical structures, 35 chemicals, 76 chiral center, viii, 55 chiral recognition, 160 chloride anion, 24 chlorine, 2 chloroform, 3, 56, 59, 60 chromatographic technique, 59, 160 chromatography, 56, 164, 165, 170, 176, 180, 181, 182, 184, 188 clarity, 34 classes, vii, 1, 2, 156 classification, 156, 162, 185 cleavage, 79, 83, 84, 97 coatings, 117 cobalt, 95 cocatalyst, 146 coenzyme, 85 collateral, 6 colloid particles, 7 combustion, vii, viii, 51, 52, 54 compatibility, ix, 129, 130, 141 competition, 9, 62 complex carbohydrates, 187 complexity, 158, 171, 184 composites, 116, 117, 127, 131 composition, viii, ix, 19, 30, 31, 33, 37, 60, 62, 68, 92, 100, 107, 115, 126, 161, 164, 165, 167, 168, 169, 183, 185, 188, 192 compounds, ix, 6, 8, 9, 10, 11, 12, 14, 15, 16, 19, 21, 24, 52, 76, 77, 78, 79, 84, 85, 92, 103, 108, 115, 116, 117, 123, 127, 128, 158 compression, 131, 134 computation, 116 computer technology, 54 condensation, 14, 16, 18, 20, 24, 131, 139 conductance, 131 configuration, 21, 52, 53, 54, 81, 83, 157, 158, 159, 166, 167, 170, 172, 187, 188, 189, 192 conformity, 18, 19 conjugated dienes, 97 conjugation, 90 conservation, 85 constant rate, 33, 40 construction, 2 consumption, 93 contaminant, 169 COOH, 22 co‐oligomerization, 124, 125

Index cooling, 33, 34, 36, 37, 40, 41, 42 coordination, 81, 83, 86, 88, 89, 92, 93, 95, 96, 97, 98, 100, 101, 104, 105, 106, 107, 128 copolymer, 31, 33, 35, 39, 161 copolymerization reaction, 39 copolymers, 30, 31, 33, 35, 37, 39, 80, 161 copper, 2, 80 cornea, 189 correlation, 35, 39 correlations, 48 corrosion, 142 crops, 116 crown, viii, 75, 78, 85, 100, 101, 104, 108 crystallization, 10 crystals, 7, 20, 59, 63, 64 cuticle, 187 cycles, 16, 21, 22, 43, 95, 131 cycling, 142 cyclohexanol, 80 cyclohexanone, 80

D decomposition, 76, 78, 79, 81, 84, 85, 86, 90, 92, 95, 99, 102, 103, 105, 106, 131 decomposition temperature, 131 deconvolution, 69, 71 deformation, 134, 141 degenerate, 76 degradation, 79, 92, 106, 130, 138, 139, 140, 141, 142, 159 degradation mechanism, 130 degradation process, 140 dehydrochlorination, 15 deposits, 5, 9, 12 derivatives, 58, 59, 145, 152, 153, 157, 158, 159, 162, 167, 170, 172, 176, 183, 192 desorption, 80 destruction, 83, 127 detection, ix, 155, 157, 159 deviation, 43 dialysis, 181, 182, 183, 188 direct measure, 69 disorder, 17 dispersion, 129, 132, 135, 161, 179, 184 displacement, 6, 11, 13, 18, 21, 73 dissociation, 13, 21, 22, 26, 76, 106 distillation, 24, 25, 27, 59 distilled water, 3, 17, 23, 25 divergence, 7, 71

195

DMF, 76, 81, 82, 83, 90, 92, 99, 105, 106 DMFA, 92 donors, 95 double bonds, 152 drainage, 22 drying, 20, 21, 147 DSC, viii, 30, 31, 32, 33, 34, 40, 41, 43, 126, 127, 137, 139, 147, 148, 150 dyeing, 2 dyes, vii, 1, 2, 3, 5, 6, 13, 14, 16, 17, 19, 20, 23, 24, 27, 28

E elastomers, 117, 129, 130, 134, 135, 139 electric charge, 7 electric current, 21 electricity, 2 electrocatalyst, 145 electrolysis, 146 electromagnetic, 21 electron, viii, 75, 77, 79, 81, 85, 90, 92, 93, 95, 96, 106, 108, 122, 135, 136 electronic integrator, 69 electronic structure, viii, 47, 48, 51, 54 electrons, 15, 16 electroreduction, 146 e‐mail, 115 emission, 141 enantiomers, 158, 159, 160, 182 encoding, 122 endosperm, 188 endothermic, 137 endurance, 15 energy, 2, 7, 13, 34, 54, 97, 106, 123 entanglements, vii, 29 environmental protection, ix, 115 enzymes, 95, 158 epoxy groups, 128 EPR, 80 equality, 102 equilibrium, vii, 29, 33, 40, 42, 73, 124, 135, 159, 188 ester, 56, 58, 117 ethanol, 3, 4, 5, 6, 8, 10, 13, 17, 19, 25 ethers, 85, 100, 101, 104, 108 ethylene, 80 ethylene oxide, 80 evaporation, 6, 7, 9, 12, 13, 21, 27 excitation, 13

196

Index

exploitation, 117 extinction, 4, 6, 10 extraction, vii, 1, 2, 3, 6, 8, 15, 17, 19, 166, 167, 169, 182, 183, 189

F fabrication, 141 filler particles, 134 fillers, 130, 131, 134 film thickness, 141 films, vii, 1, 3, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 141 fixation, 116 flexibility, 139 fluid, 54 fluorescence, 141 fluorine, 54, 117 foams, 131, 134 formaldehyde, 14 formamide, 81, 126 formula, 3, 4, 13, 48, 82, 103 fragility, 35 fragments, 4, 6, 14, 15, 21, 80, 120, 158, 161, 170, 182, 183, 184 free radicals, 76, 79, 103, 104 free volume, 32, 68 freedom, 138 freshwater, 190 FTIR, ix, 120, 145, 147, 152 functionalization, 76 fungi, 127 furan, 135, 136

G gamma radiation, 138 garbage, 164 gel, 30, 141, 147, 164, 184, 185, 191, 192 gel permeation chromatography, 30, 147 gelation, 170 geometry, 84 Georgia, 115 Germany, 128, 153, 154 glass transition, 31, 35, 39, 40, 131, 138, 145, 148 glass transition temperature, 31, 39, 40, 138, 146, 148 glasses, vii, 12, 29 glucose, 164, 165, 177, 178, 181, 183

glycoproteins, 165 glycosaminoglycans, 180, 188 GPC, 30, 31, 147, 149 graphite, 131 grouping, 3

H halogen, 79 halogens, 100 Hartree‐Fock, 122 H‐bonding, 86, 96, 101, 106, 109 heat capacity, 36, 38, 44 heat transfer, 131 heating rate, 37 helium, 16, 116 heme, 95 heptane, vii, 1, 2, 3, 5, 6, 7, 8, 9, 10, 11, 12, 13, 15, 17, 18, 19, 20, 24 herpes, 191 herpes simplex, 191 heterogeneity, 165 heterogeneous catalysis, 77, 112 hexane, 59 HIV, 185, 192 homogeneity, 98, 129, 161, 184 homogeneous catalyst, 80, 95 homolytic, 78, 81, 102, 103, 106 homopolymers, 39, 158 Hong Kong, 110 host, 141 Hunter, 180, 188 hybrid, ix, 155, 157, 161, 166, 167, 172, 178, 184, 190, 191 hydrazine, 16 hydrocarbons, 76, 103 hydrogen, 12, 14, 24, 48, 83, 84, 85, 88, 90, 92, 95, 96, 100, 116, 166 hydrolysis, 5, 6, 7, 8, 10, 12, 158, 159, 160, 161, 166, 170, 172, 174, 176, 177, 184, 192 hydroperoxides, viii, 75, 76, 77, 79, 108 hydrophility, 20, 79 hydrophobicity, 117 hydroquinone, 124 hydrosilylation, 115, 117, 118, 119, 120, 121, 122, 123 hydroxide, 5, 8, 12, 13 hydroxyl, 5, 13 hypothesis, ix, 155, 184

Index

I ideal, 60, 131, 134 image, 132, 133 induction, 86 induction period, 86 industrial processing, 166 infrared spectroscopy, 158, 172 inhibition, 81, 99 inhibitor, 93, 124 initiation, ix, 75, 76, 77, 81, 85, 101, 103, 104, 105, 106, 107, 109 insertion, 96 interface, 138 intermolecular interactions, 7, 80, 182 inversion, 19 ion‐exchange, 176, 180, 181, 184 ions, 5, 7, 8, 97, 183, 185 IR spectra, 116, 117, 120, 126 IR spectroscopy, 30, 152 Ireland, 187 iron, viii, 75, 78, 79, 80, 95, 96, 97, 98, 101, 102, 103, 106, 109 IR‐spectroscopy, 82 isolation, 80, 164, 166, 170, 174, 176, 181, 188 isomerization, 146 isomers, viii, 55, 56, 57, 59, 159 Italy, 29, 128

J Japan, 192 Javakhishvili, Ivane, 115, 128

K KBr, 116, 147 ketones, 78 kinetic curves, 118 kinetic regularities, 92, 93, 100, 101 kinetics, 33, 45, 141 KOH, 3, 5, 6, 7, 8, 10

L lead, 3, 12, 14, 21, 22, 27, 83, 86, 90, 100, 130, 141, 142 lifetime, 108, 135, 141

197

ligand, viii, 55, 58, 60, 62, 77, 79, 80, 81, 82, 83, 85, 86, 88, 90, 92, 95, 96, 97, 98, 99, 100, 101, 106, 107, 108 linear molecules, 181 liquid chromatography, 158 liquid phase, 81 liquids, 35, 84, 120, 149 lithium, 68, 190 localization, 80

M magnitude, 37 majority, 55, 76, 156 manganese, 78 manufacturing, 142 MAS, 140 mass loss, 139 matrix, 21, 22, 117, 156, 188 mechanical properties, 130, 134, 190 mechanistic explanations, 79, 108 media, 181 melts, 130 memory, 21 meristem, 116 messengers, 84 metal complexes, viii, 75, 80, 96 metal ion, 85, 88, 104, 105, 106, 107 metalloenzymes, 95 metals, 76, 84, 131 methanol, 56, 58, 59, 63, 68, 146, 147 methodology, ix, 155, 162, 171 methyl groups, 14, 35, 62, 120, 180 methyl methacrylate, viii, 30, 67, 68 methylation, 159, 172, 176, 179, 180, 187, 191 methylene blue, 2, 24 micromycetes, 127 microstructure, 68, 130, 134 mixing, 3, 10, 25, 131, 132 modelling, 38, 142 models, vii, viii, 29, 52, 67, 76, 107 modulus, 132 moisture, 17 molar ratios, 162 mole, 4, 5, 6, 7, 10, 117, 123 molecular mass, viii, 30, 40, 42 molecular orientation, 141 molecular oxygen, viii, 51, 52, 54, 75, 76, 77, 78, 104, 108 molecular structure, 2, 3, 48, 88, 109, 161, 190

198

Index

molecular weight, ix, 30, 31, 32, 39, 40, 45, 69, 130, 136, 139, 145, 147, 148, 153, 158, 166, 182, 183 molecular weight distribution, ix, 69, 130, 145, 148 molecules, vii, ix, 1, 2, 3, 4, 6, 7, 9, 10, 12, 13, 14, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 77, 84, 97, 98, 99, 101, 107, 131, 141, 155, 161, 178, 182, 183, 184 molybdenum, 148 monomers, 23, 25, 55, 131, 139, 145 monosaccharide, 158, 163, 167 morphology, 128 Moscow, 1, 47, 51, 55, 75, 109, 110, 112 MP, 81, 82, 85, 89, 93, 94, 95, 109 mycology, 127

N NaCl, 165 NATO, 153, 154 neglect, 122 Netherlands, 154 New Zealand, 167, 189 nickel, viii, 75, 76, 81, 83, 85, 86, 88, 90, 92, 93, 96, 102, 103, 104, 109 nitrogen, 3, 16, 68, 146, 147 NMR, viii, ix, 30, 31, 40, 56, 57, 58, 59, 60, 62, 63, 64, 67, 68, 69, 70, 72, 73, 115, 116, 120, 121, 122, 123, 128, 140, 145, 147, 148, 149, 150, 151, 152, 153, 157, 158, 167, 170, 171, 172, 173, 178, 189, 192 nodes, 116 norbornene, 145, 146, 148, 153 Nuclear Magnetic Resonance, 137

O oil, 59 olefins, 145 oligomers, ix, 115, 117, 120, 121, 125, 126, 127 optical density, 22, 25 optical properties, 141 optimization, 47, 52, 54 organic compounds, 2, 27, 109 organic polymers, 117 organic solvents, ix, 120, 126, 145 overlap, 44, 122 oxalate, 2, 4, 5, 6, 7, 8, 9, 10, 12, 14, 15 oxidation, viii, 14, 75, 76, 77, 78, 79, 80, 81, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 97, 98,

99, 100, 101, 102, 103, 104, 105, 106, 107, 108, 109, 110, 146, 159 oxidation products, 78, 80, 86, 90, 100, 102 oxidation rate, 81, 99, 104, 108, 109 oxygen, viii, 16, 17, 51, 52, 54, 75, 76, 77, 79, 80, 90 ozone, viii, 51, 52

P Pacific, 192 paints, 13 palladium, 97 parallel, 14, 81, 85, 86, 90, 95, 99, 102, 103 parallelism, 85 parity, 6 passivation, 131 pentads, viii, 67, 69, 70, 71, 72 permeation, 184 peroxide, 76, 80, 103, 106 peroxide radical, 76 petroleum, 76 phenol, 14, 35, 77, 84, 86, 90, 93, 99, 100, 109, 166 phenomenology, 94 PhOH, 14, 76, 81, 86, 88, 89, 93, 95, 99, 109 photoconductivity, 2 physical properties, 68, 69, 71, 84, 130, 131, 188 physics, 28, 109 physiology, 84 plants, 116, 162, 167, 170, 171, 182, 190 plasticization, 21, 22 platinum, 146, 147 PMMA, v, viii, 30, 39, 40, 42, 45, 67, 68, 69, 70, 71, 72, 73 polarity, 13, 80, 141 poly(methyl methacrylate), viii, 30, 141 poly(vinyl chloride), 68, 69 polycarbonate, vii, 32 polycarbonates, viii, 30, 31, 32 polycondensation, 30 polydispersity, 39, 148 polyether, 85 polymer, ix, 22, 43, 68, 76, 79, 80, 108, 116, 117, 124, 127, 130, 131, 132, 134, 135, 138, 139, 141, 145, 147, 148, 150, 151, 152, 153 polymer chain, 80, 134 polymer chains, 135, 139, 141 polymer industry, 76 polymer materials, 68, 116, 127 polymer matrix, 116, 117, 127, 130, 131, 132, 141 polymer melts, 135

Index polymer networks, 130 polymer structure, 145 polymer systems, 127, 141 polymeric chains, 20, 21, 31 polymeric films, 2 polymeric materials, 130, 131 polymerization, 68, 139, 145, 146, 147, 148, 150, 152 polymerization process, 148 polymers, vii, ix, 29, 31, 68, 116, 122, 126, 127, 131, 136, 138, 141, 145, 146, 148, 152, 158, 181, 184 polypropylene, 68, 69 polysaccharide, ix, 155, 156, 157, 158, 159, 162, 165, 166, 171, 174, 176, 179, 181, 182, 184, 185, 187, 189, 190, 192 polystyrene, 31, 45, 81, 131, 141, 147, 149 polyurethane, 117, 127, 128 polyurethane foam, 128 polyurethanes, 128 porosity, 134 porphyrins, 79, 80 potassium, 162, 163, 180, 183, 191 precipitation, 162, 163, 164, 166, 167, 168, 169, 172, 173, 176, 177, 182, 183, 184 preparation, 3, 6, 80, 180 primary products, 76 probability, 19, 56, 69, 70, 92, 97, 100, 105, 106 probe, 109, 141 propagation, ix, 75, 102, 103, 104, 105, 106, 109 propane, 56 prophylaxis, 127 propylene, 77, 80 proteins, 95, 165, 182 protons, 56, 58, 60, 96, 120 PVC, viii, 68, 69, 71, 73

Q quantum chemistry, 2, 27 quantum‐chemical calculations, 1 quartz, 17, 24 quaternary ammonium, 84, 86, 92, 98

R radiation, 130, 140 Radiation, 142 radical formation, 81 radical polymerization, 55, 145

199

radical reactions, 80 radicals, 4, 99, 102, 103, 105, 106, 117 Raman spectra, 133 raw materials, 171 reactants, 2 reaction center, 78 reaction medium, 58 reaction order, 119 reaction rate, 77, 79, 97, 99, 102, 118, 119 reaction rate constants, 118 reaction temperature, 125 reaction time, 60, 62, 64, 147 reactions, 14, 30, 76, 77, 79, 80, 83, 84, 85, 87, 92, 93, 94, 96, 97, 99, 100, 102, 103, 106, 109, 123, 135, 138, 146, 147 reactivity, 79, 95 reagents, 79, 96, 116, 135 real time, 141 reception, 5 recession, 23 recognition, 85 recommendations, iv recrystallization, 5 Red Sea, vi, 155, 160, 171, 174, 187, 189, 191, 192 redistribution, 81, 100, 102 refractive index, 69 regeneration, 19, 21, 22, 26, 27 reinforcement, 130, 133 relaxation, vii, viii, 29, 30, 32, 33, 34, 35, 37, 38, 39, 40, 44, 45 relaxation process, 33, 44 relaxation processes, 33 relaxation rate, 44, 45 relaxation times, 33, 34, 38 requirements, 2, 134 residues, 95, 140, 147, 156, 158, 171, 172, 174, 176, 178, 179, 180, 181, 188 resins, 59, 117 resistance, ix, 129, 147 resolution, 187 resources, 142 respiration, 95 rheology, 185 Rhodophyta, 185, 186, 187, 188, 189, 191 rings, 21, 96 ROOH, 14, 76, 77, 78, 81, 84, 85, 86, 98, 102, 103 room temperature, 19, 59, 78, 124, 135, 147, 162, 166, 167, 169, 170, 172, 176, 178, 179, 183 rotations, 172 routines, 142

200

Index

S salt formation, 180 salts, viii, 14, 20, 75, 76, 84, 85, 89, 92, 97, 108, 146, 149, 180 SAP, 107 saturation, 11, 22 scattering, 7, 126, 128 sedimentation, 17 seed, 188 selectivity, 76, 77, 78, 80, 81, 84, 85, 86, 87, 90, 95, 98, 100, 102, 106, 107, 108, 109 semiconductors, 28 sensitivity, 141, 158, 171 sensors, 141 shape, 38, 140 signals, viii, 44, 56, 57, 60, 67, 69, 71, 120, 121, 152, 158 signs, 5, 6, 15 silane, 139 silica, 79, 80, 81, 108, 130, 131, 138 silicon, ix, 79, 115, 117, 126 silver, 146 simulations, 97, 142 Singapore, 112 SiO2, 56, 59, 60 sodium, 180, 190 sodium hydroxide, 180 software, 122 solubility, ix, 12, 60, 141, 145, 164, 167, 171, 182 solvents, 7, 97, 107 sorption, 79 Spain, 67 species, 80, 83, 84, 95, 106, 130, 136, 139, 146, 148, 153, 170, 172, 174, 179, 180 specific heat, 31, 35 specifications, 141 spectrophotometry, 88 spectroscopy, viii, 67, 68, 69, 80, 157, 158, 170, 172, 173, 178, 189, 192 stabilization, 81, 96, 97, 106 stable complexes, 92 states, 135, 141 statistics, viii, 67, 68, 69, 71 steel, 25 stereochemical composition, 40 stereosequences, 68, 72, 73 stimulus, 130 stoichiometry, 60 storage, ix, 17, 26, 129, 141

stretching, 152 strong interaction, 164 structural changes, 84, 98 structural relaxation, vii, 29 styrene, 77, 84, 124 substitutes, 58 substitution, 96, 105, 158, 161, 176, 178, 180, 182 substitution reaction, 96 substrates, 146 sulfate, 156, 158, 159, 163, 165, 166, 167, 170, 174, 176, 178, 179, 180, 181, 182, 183, 186, 189 surface area, 130 surface chemistry, 131, 134 swelling, 191 symmetry, 62, 81 syndiotactic sequences, 68, 71, 72 synthesis, 6, 11, 12, 14, 19, 28, 56, 58, 59, 60, 84, 96, 141

T tacticity, viii, 67, 68, 69, 71 Tbilisi, 115, 128 technologies, 52, 54 technology, 2, 28 temperature, vii, 17, 23, 24, 26, 29, 33, 34, 36, 38, 39, 40, 42, 43, 44, 64, 80, 106, 119, 124, 125, 136, 137, 138, 140, 141, 142, 146, 147, 181, 182, 183, 186 temperature dependence, 40 tetrahydrofuran, 68, 97 TGA, 116, 127, 139 theoretical assumptions, 122 thermal analysis, 116 thermal degradation, 139, 140 thermal destruction, 27 thermal expansion, 131 thermal properties, 30 thermal stability, ix, 115, 137 thermal treatment, 44 thermooxidative stability, 127 toluene, 30, 123, 126 toxic waste, 84 transformation, 2, 5, 10, 11, 25, 77, 81, 83, 84, 85, 86, 88, 90, 92, 97, 100, 101, 103 transformation degrees, 86 transformation product, 83 transformations, 16, 21, 23, 27, 76, 96 transition metal, vii, viii, 75, 76, 77, 78, 81, 84, 85, 97, 98, 99, 103, 108

Index transition temperature, ix, 35, 115, 126, 139, 147 transparency, 146 transport, 35 tryptophan, 82, 96 Turkey, 145, 153

U Ukraine, 128 uniform, 130 updating, 20 urea, 96, 166 US Department of Commerce, 46 USSR, 28 UV, 3, 5, 6, 7, 8, 11, 13, 15, 16, 17, 18, 19, 20, 21, 23, 24, 25, 27, 88, 89, 147

201

W Washington, 112 water, viii, 2, 3, 5, 8, 10, 11, 12, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 58, 59, 60, 64, 68, 75, 84, 94, 97, 99, 101, 103, 109, 146, 166, 167, 168, 169, 170, 172, 176, 178, 179, 181, 183 water absorption, 20 water desorption, 20 WAXS, 126 weight ratio, 134 withdrawal, 27

Y yield, 58, 62, 64, 108, 124, 136, 141, 147, 157, 159, 161, 169, 174

V vacuum, 16, 18, 68, 147 valence, 49 variations, 95, 161, 167 velocity, 117 vinyl chloride, viii, 68 viscosity, 30, 35, 125, 126

Z zeolites, 79

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