Influence of the Solvents on Some Radical Reactions

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CHEMISTRY RESEARCH AND APPLICATIONS SERIES

INFLUENCE OF THE SOLVENTS ON SOME RADICAL REACTIONS 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.

CHEMISTRY RESEARCH AND APPLICATIONS SERIES Applied Electrochemistry Vijay G. Singh (Editor) 2010. ISBN: 978-1-60876-208-8 Heterocyclic Compounds: Synthesis, Properties and Applications Kristian Nylund and Peder Johansson, (Editors) 2010. ISBN: 978-1-60876-368-9 Influence of the Solvents on Some Radical Reactions Gennady E. Zaikov, Roman G. Makitra, Galina G. Midyana, and Lyubov I. Bazylyak 2010. ISBN: 978-1-60876-635-2

CHEMISTRY RESEARCH AND APPLICATIONS SERIES

INFLUENCE OF THE SOLVENTS ON SOME RADICAL REACTIONS

GENNADY E. ZAIKOV ROMAN G. MAKITRA GALINA G. MIDYANA AND

LYUBOV I. BAZYLYAK

Nova Science Publishers, Inc. New York

Copyright © 2010 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. 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. LIBRARY OF CONGRESS CATALOGING-IN-PUBLICATION DATA Influence of the solvents on some radical reactions / editors, Gennady E. Zeikov ... [et al.]. p. cm. Includes index. ISBN 978-1-61728-243-0 (eBook) 1. Solvents. 2. Chemical kinetics. 3. Free radical reactions. I. Zaikov, Gennadii Efremovich. QD544.I54 2009 541'.3482--dc22 2009041993

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

CONTENTS Preface Chapter 1

vii Complications Existing at Consideration of Factors Influencing on Kinetics of Radical Reactions

1

The Medium Influence on Thermolysis of Diacyl – and Dialkylperoxides

15

Chapter 3

Decomposition of Peracids Esters

41

Chapter 4

Decomposition of the Hydroperoxides and Reactions of the Phenoxy Radicals

55

Chapter 5

Effects of the Solvents in the Oxidation Reactions

67

Chapter 6

The Medium Influence on some other Homolytic Reactions

95

Chapter 2

Conclusions

117

Appendix

119

Index

125

PREFACE This book is based on results of a series of experimental investigations it was proved that the nature of medium has an essential influence both on the rate and the chemical mechanism of homolutical reactions. This influence can be quantitatively connected with the physical–chemical characteristics of medium based on the principle of linearity of free energies with the use of multiparametric equations.

Chapter 1

COMPLICATIONS EXISTING AT CONSIDERATION OF FACTORS INFLUENCING ON KINETICS OF RADICAL REACTIONS Regularities of kinetics for homolytical radical processes are essentially intricater, than in a case of the heterolytical reactions. That is why, in spite of their more practical importance, in particular for the oxidizing processes, their successful studies have been realized appreciably later, and the first successful generalizations were obtained for the reactions in gaseous phase. However, the attempts to obtain the quantitative connections between the rate of radical reactions in liquid phase and properties of this phase up to the latest time were unsuccessful. Linearity equations of free energies (LFE) by Hammet–Taft and Koppel–Palm types have a much wide application for the generalization of substituents influence, or, respectively, medium properties, on the rate of the heterolytical reactions. However, the works considering an application of the linearity equations of free energies for homolytical reactions are seldom to be found in reference due to both experimental and conceptual difficulties. In comparison with the heterolytical processes, the medium influence on kinetics of the homolytical processes was studied essentially a lesser degree, and appropriate investigations were usually carried out only in not large quantity of solvents that complicates their quantitative interpretation. Here it is necessary to notify, that in the last edition of the well–known Reichardt’s monograph [1] only 16 (!) pages amongst total 630 ones are dedicated to reactions with the participation of free radicals. The same situation is observed in the old review of O. Pytela [2] concerning to the generalization of solvents influence on kinetics: only 6 amongst 80 considered reactions are radical. The reason of such situation is, first of all, the low sensibility of the radical processes rates to the medium properties. If the

Gennady E. Zaikov, Roman G. Makitra, Galina G. Midyana et al.

2

heterolytical reactions rate constants changes depending on medium are usually observed within the limits of some orders and achieve even 1010, then the homolytical processes rate constants changes via medium usually not exceed the 1–2 order. Moreover, an investigation of the medium properties influence on the rate of the homolytical processes is lead onto other difficulties, namely: i)

Complication and multi–stage of the majority of reactions with the participation of radicals. As a rule, the chain radical reactions are realized via some stages, that is why, usually determinate experimentally constant rate is resulting and depends on the separate stages rates ratio. In consequence of the experimental difficulties there are few data permitting quantitatively to compare the influence of solvents or substituents on the rates of separate elementary stages of radical reactions. However, in some cases when the chemical mechanism of the reaction permits for sure to determine the limitative stages, the numerical approximation of the most probable expression for the rate and quantitative treatment of data on the basis of obtained constants rate are possible in different media. Such constants rates are approximately equal to the constants rate of limiting stage as it was proposed, for example, in a case of butyric aldehyde oxidation in different solvents [3]. ii) Often there are possible two (or more) parallel paths of the reaction proceeding during the radical–forming process. This why, in a case of benzoyl peroxide thermolysis [4] or peracids thermolysis [5] along with the monomolecular cleavage parallel the decomposition induced by the forming radicals is realized, and it is characterized by absolutely another kinetic and energetic parameters. Total rate of these compounds decomposition can be presented by the following equation:

[ ROOR' ] dt

k1 [ ROOR' ] k ind [ ROOR' ]n

(1)

Since the effective process rate constant, (usually determinate in a case of the peroxy compounds decomposition upon –O–O– groups content decrease), is resulting and the effects of solvation or substituent influence have an effect on both reactions accordingly to different regularities, that, as a rule, the generalization of values keff. via LFE equations does not lead to success. In such a case, when the reaction proceeds in the presence of inhibitors or in the medium of solvents suppressing the

Complications Existing at Consideration of Factors Influencing…

3

radical transitions, it is possible to determine of rate constants of the non– initiated process; the rate constants of the initiated decomposition is determined as the disparity of the total and inhibited thermolysis rates. Each of these processes can be characterized by means of the separate LFE equation. This fact will be demonstrated hereinafter. Also it is necessary to indicate that generally the hydrocarbons as the solvents promote to the initiated radical processes. iii) The role of the solvent is not only to inhibit or to propagate the reaction radical stages. In a number of cases the solvent can influences on the chemical mechanism of the process. Thus, at the inhibited decomposition of the azelaic acid polymeric peroxide [6] the rates of its decomposition in ethers (dibutyl ether, tetrahydrofurane, dioxane) are beyond the general dependence for 15 others solvents that permit to suppose for them the other chemical mechanism of transition, maybe – partial bimolecular interaction of peroxide and solvents. Decomposition reaction in pyridine has an autocatalytic character. Deviations from general regularities of the medium action for ethers [7] were notified also for reaction of tert– butylperformate thermal decomposition catalyzed by pyridine. iv) The rate constants of transitions with the participation of radicals often depend on the concentration of an initial substrate. As a result of parallel realization of the reactions by different orders, the observed experimentally order is differed from the first one and can be changed with the concentration, that is observed, for example, at some peracids [8] or benzoyl peroxide [9, 10] decomposition. The same situation is observed during the ion–radical transformations. This peculiarity, and also outermost sensibility of the homolytic transformations even to the traces of the additives, especially to the ions of heavy metals by variable valency, dithers to be careful at the selection and comparison of data by different authors, that in the case of heterolytic reactions, as a rule, is not a problem. v) In a number of homolytical transformations the diffusive processes can play the specified role – especially in a case of the oxidization by molecular oxygen. So–called “cage” effects also have a significant influence; these effects caused by medium ability for self–association around the reacting particles that correspondingly increases the radicals “activity”. This phenomenon has a much wide practical application in polymer chemistry [11].

4


That is why in equations, which tie together the process rate and the medium properties, not only the “solvation” parameters from the “classic” Koppel–Palm equation [1] can be significant, but also some others, for example, the density of cohesion energy

2

H vap. RT / Vm , which is proportional to the medium

self–association and is responsible for the “cage” effect or molar volume of solvents Vm. It was shown in the work [12], that the decomposition rates of p– nitrophenyldiazotriphenylmethane in alkanes are in good correlation with their viscosity. The presence of linear connection between the constant rate logarithm for dicumyl peroxide thermolysis into alkanes and their viscousity was determined also in [13]. Say the truth, this comparison was carried out only among the hydrocarbons homologous series and the data in other solvents are beyond the obtained dependence; that is why it’s impossible to exclude the possibilities of influence on the rate of any other characteristic, which is also routinely changed with the molecular weight. For example, it is well–known, that is for the homologous series of solvents the density of the cohesion energy proportional to their activation energy of viscos flow [14]. Detailed analysis of possible transformations of peroxy group –O–O– under the action of different factors has been presented recently in the work [15]. The homolytic decomposition of this group is the most studied at high temperatures or at irradiation with the formation of two radicals RO•. However, there are possible parallel also others ways of this group transformations, namely peroxy compounds represent by themselves the oxidizing agents in the reactions with active electrophiles and nucleophiles. Nevertheless, in a number of cases the multiparametric equations were found as effective for the generalization and analysis of medium properties influence on kinetics of homolytical processes. An analysis of the references permitted to establish, that the quantitative connection between the medium properties and radical processes rate can be determined in those cases, when there is the possibility to determine the rate of every stage or limiting stage of reaction. 2

1. HOMOLYTICAL NON–INITIATED (INHIBITED) REACTIONS OF DECOMPOSITION [6, 7, 16, 17] However, it is impossible to generalize the data concerning to the medium influence on the effective rate constants of the benzoyl peroxide thermolysis with the use of one equation, since these magnitudes are constituent. Total rate of the


5

process represents by itself the result of the simultaneous proceeding both homolytic and induced processes:

d [ Bz 2 O2 ] dt

khomol [ Bz 2O2 ] k ind[ Bz 2O2 ]

3

(2)

2

In consequence of different character of solvation for the initial peroxide and for the intermediate radicals forming as a result of it decomposition, the medium influence on the rate of this process cannot be described by means of one equation. However, the rates of inhibited and initiated processes separately are generalized by LFE equations. An analysis of the corresponding data showed, that different solvation types achieve an increase of the homolytical decomposition. This fact, in spite of the irreversibility reaction of the peroxide molecule decomposition is not connected with the solvation of the reaction products (radicals), but with the –O–O– bond weakening at the solvation of initial peroxide. The “cage” effects determining by the value of the medium cohesion practically have not the influence on the rate of the inhibited energy density decomposition. At the same time, the influence of the solvents parameters on the rate of benzoyl peroxide decomposition reaction is opposite: the solvation of formed radical stabilizes this process, and the medium self–association in consequence of the “cage” effect increases the interaction probability thereby increases the process rate. 2

2. THE CASE, WHEN THE LIMITATIVE IS ONLY ONE STAGE AMONG OTHER STAGES OF THE RADICAL PROCESS Thus, it was determined at the butyric aldehyde oxidation in the presence of ferrocene [3], that in spite of the multistage process only two stages, namely initiation one and the chain transfer one represent by themselves the limiting stages:

RCHO Men 1

RCO

3

RCHO

RCO

H

RCOOH

Me n (

RCO

2

O2

RCO 3 )

6


Respectively, the rate of this process can be described with the sufficient exactness by following equation:

d [ RCHO] dt

(3)

k[ RCHO][ Me n 1 R ]1 / 2

The attempts of authors to connect the obtained values of the sum rate constants with the Kirkwood function of solvents or with the oxygen solubility in them didn’t lead to positive results. At the same time, the multiparametric equation LFE satisfactorily generalizes the experimental data from the work [3] and permits sensibly to interpret the role of the solvation effects. In spite of the visible value of the pair correlation coefficient (r = 0,865) of logarithms values of the rate constants with the medium polarity, the influence of this characteristic can be neglected. That is why the conclusion of authors [3] as to different polarity of base and reacting states can not be admitted as sufficiently well–reasoned. Factors determining the rate of a process are only polarization and the medium cohesion energy density of solvents [18]:

lg k N = 11;

0,058 1,12 R = 0,986:

n2 1 n2 2

0,00159

(4)

2

s = 0,05

Positive influence of aromatic solvents polarization (toluene and chlorobenzene) is compensated by comparatively great negative influence of their cohesion energy density and that is why the oxidation rate in weakly polarized but little associated alkanes is near to the oxidation rate in aromatic hydrocarbons. In some cases for oxidizing processes the rate of the oxygen consumption is proportional to the rate of limiting stage. Data [19] concerning to the medium influence on the acrolein oxidization rate catalyzed by Cobalt acethylacetonate in 12 solvents are good generalized by three–parametric equation:

lg W

0,531 1,67 f

0,021ET

0,026

2

(5)

R = 0,963; s = 0,133 Similarly to previous case, the heightened medium cohesion energy density slows down the process and determines its rate [20].


7

3. THE CASE, WHEN THERE ARE KNOWN THE RATE CONSTANTS OF SEPARATE ELEMENTARY STAGES OF RADICAL REACTIONS, FOR EXAMPLE, IN A CASE OF STYRENE, CUMENE, METHYLETHYLKETONE, TETRALIN OXIDATION Consideration of the values and the signs of coefficients at separate terms of the regression equations permits to estimate the differences in solvation degree of neutral molecules and interim forming radicals, which are formed on separate stages and thereby determine the reaction direction in different solvents [21].

4. REACTIONS WITH THE PARTICIPATION OF LOW–ACTIVITY RADICALS, FOR EXAMPLE, IN A CASE OF PHENOXYL RADICALS DIMERIZATION [22] At the attempts to connect the rate constant of the 2,4,6–triphenylphenoxyl radicals dimerization with the ET electrophilicity parameter of Reichardt it was determined the presence of V–like dependence. Hydrocarbons and halogenhydrocarbons are on the same dependence sidetrack; at ET increasing the dimerization rate is decreased and it is increased in polar alcohols, acetone and dimethylformamide at ET increasing. At the same time, the generalization of data [22] via multiparametric equation permits adequately to generalize them by one linear equation [23]. Hence, the influence of medium on the rate of a series radical processes can be described analogously as same as in a case of the heterolytical reactions via multiparametric LFE equations taking into account the different solvation processes proceeding in solution. Such generalization is favourable to deeper understanding the chemical mechanism of the processes and peculiarities of the solvents selection with different properties. The indispensable condition of the LFE equations application is the availability of the rate constants of separate elementary stages of complex [composite] reaction or, as a last resort, of limiting stages. At the same time, using the effective total rate constants of the gross– process is inadmissible. This conclusion will be considered below on examples of different radical reactions. When generalizing the data of the correlation between the ζ –constants of substituents and the rate of conversion for homolytical reactions, a number of

8


deviations from the Hammett equation may be found which cannot be explained, thus leading to the supposition that with a sharp change of the electron density on the reaction center caused by the influence of some substituents, especially the NO2 group, the reaction mechanism most probably changes. The following examples can be adduced. It has been shown in [24] that the non–induced decomposition of tert–butyl perbenzoates in the diphenyl ether at 120 0C for the five substituents (OMe, Me, H, Cl, NO2) may be excellently described by the Hammett equation with the r = 0,990–0,996 (at various temperatures). The decomposition rate diminishes with the growth of the attraction of electron to the phenyl cycle in consequence of the decrease of the electron density at the oxygen atom being connected with the carbonyl group and the increase of the –O–O– bond polarity (ionic character) and correspondingly the increase of their stability. This result was confirmed in [25] for the reaction in n–undecane at 110 0C. However, the thermolysis of peresters in chlorobenzene and toluene obeys the Hammett equation with the exception of the data for the p–NO2 substituent in chlorobenzene and for those of p–OMe in toluene [26]: see Figure 1.

Figure 1. Thermolysis of tert–butylphenylperacetates in chlorobenzene at 90 0C according to [26]. The dependence of log k(min-1) vs. ζ. The data for p–OMe extrapolated.


Figure 2. The thermal decomposition of substituted benzoylperoxides in acetophenone at 80 0C accordingly to [27]. The dependence of log k (min–1) vs. ζ.

Figure 3. The thermal decomposition of substituted benzoylperoxides according to [29]. The dependence of logk on ζ. The N0 of experimental points according to Table 1.

9

10


Table 1. Thermolysis of Substituted Benzoyl Peroxides in Styrene at 70 0C according to [29] N0 1 2 3 4 5 6 7 8 9 10 11 12 *

Substituent H m–Me m–OMe m–F m–Cl m–Br m–I m–NO2 p–Me p–OMe p–Oct p–F

logk -5.155 -5.222 -5.046 -5.444 -5.444 -5.420 -5.444 -6.155 -4.963 -4.773 -4.731 -5.276

ζ+ 0.000 -0.069 0.115 0.337 0.337 0.391 0.352 0.710 -0.170 -0.268 -0.240 0.062

N0 13 14 15 16 17 18* 19 20 21 22 23 24

– data excluded from calculations.

substituent p–Cl p–Br p–I p–NO2 p–Et p–CN p–i-Pr p–t-Bu p–C6H5 p–OCOCH3 3,5–(CH3)2 3,4–(OMe)2

logk -5.268 -5.284 -5.268 -6.699 -5.004 -5.268 -4.975 -4.896 -5.071 -5.222 -5.114 -5.052

ζ+ 0.227 0.232 0.180 0.778 -0.151 0.660 -0.280 -0.197 -0.010 0.310 -0.140 -0.153

Still more substantial deviation for the nitro–groups has been observed in the case of monoinduced decomposition of substituted benzoylperoxides in acetophenone in [27] (Figure 2). The correlation coefficient for all substituents is according to review [28] equal to 0,687 only, or after checking the ζ values, it is 0,769. Even after the exclusion from our calculations of the most deviating data for the nitrosubstituted peroxydes (o– and p–nitro, and 3,5–dinitro) r = 0,835 only. Nevertheless, the iso–kinetic dependence in this reaction is unexpectedly well realized: ΔH# = (26,66 ± 0,30) + (0,617 ± 0,64)ΔS# N = 11;

R = 0,955;

(6) s = 0,25

The authors do not find a satisfactory explanation for the V–like dependence of logk on ζ, i. e. for the effect of the rate increase of strong electronegative nitro groups. However, the decomposition rates for the same peroxydes determined dilatometrically at 70 0C in styrene according to its polymerization rate, correlate with the ζ values considerably better, though some deviations can also be found [29]. For the 24 points (see Table) R = 0,819 only but when we exclude the data for p–cyanocompound which deviates the most, we receive an equation with an acceptable, though small degree of concordance:

Complications Existing at Consideration of Factors Influencing… logk = (–5,098 ± 0,044) – (1,410 ± 0,136)ζ N = 23;

R = 0,925;

11 (7)

s = 0,179

For the ζ+ constants of para–substituents the correlation is only slightly worse: for 14 substituents R = 0,816 and after the exclusion from the calculations of the data for the p–CN compound, R = 0,904. The decomposition rate (and, probably the initiation of styrene polymerization) for the substitud benzoyl peroxydes increases in case of the electron–drawing substituents and decreases in case of electron–attracting ones [30]. According to Walling’s opinion the transition state depends on the electron effects. It is necessary to mention the fact stated by the authors of ref. [31] that the orto–substituted peroxydes decompose significantly faster especially in the case of substituents of large volume as the result of combination of the steric and polarizability effects. This observation agrees with the same results about the influence of the sterically hindered substituents on the decomposition of tert– butyl esters of the aliphatic peracids [25]. When the authors found for the II unbranched peresters an excellent correlation between the rates of thermolysis at 110 0C and the Taft’s constants (R = 0,995, ρ = 1,237), the branched peracids as well as those containing the voluminous substituents in the α– or β–positions (Cl, phenyl) deviate from the rectilinear dependence on ζ and the rate of their decomposition was found to be on the average for one order higher. The common Es –scale at steric constants is in this case unapplicable. The above mentioned examples illustrate the difficulties appearing in the application of the LFER equations even in relatively simple cases of generalization of electron effects. One may anticipate more substantial complications caused by the above considered reasons in case of examination of medium effects. Nevertheless, in a number of cases such a qualitative examination is possible and this permits to foresee the rates of the process in other solvents not investigated yet and to present the mechanism of homolytic reactions in a more detailed way. Here it is necessary to note that for analysis of the solvents influence on the rate of reactions we have used mainly the widen Koppel–Palm equation in accordance with [32, 33]: lgk = a0 + a1

n2 1 1 + a2 + a3Ет + a4B + a5δH2 + а6VМ 2 2 1 n 2

(8)

12


in which n and ε are refractive index and permittivity of the solvents, determining of their polarizability and polarity, and they are responsible for the ability to non– specific solvation of the substrates; В is the basicity upon Koppel–Palm and Ет is electrophilicity upon Reichardt which determine the possible acid–base (specific) interactions in system, δН is a solubility parameter upon Hildebrant which is proportional to the medium cohesion density, that is to the energy expenses for the formation of cavity in it; VМ is a molar volume of the solvents connected with their structural peculiarities. Accordingly to [34] the equation was assumed as adequate if the value of multiple correlation coefficient R ≥ 0,95. In order to determine the influence of separate solvation factors on the processs rate, that is the significance of the separate terms of equation, it was carried out their alternating exclusion with every one determination of R for obtained equations with less quantity of the terms (in accordance with the recommendations of [34]). If the value R at this was decreased unsignificantly respective term was considered as insignificant. As a rule, for obtaining of the adequate connection between lgk of rate and medium properties, 3–4 terms of equation it is enough, that is dependently on the substrate properties only some characteristics of medium are essential. Applied in a work characteristics of the solvents obtained based on the works [35, 36], are represented in Appendix.

REFERENCES [1]

Ch. Reichardt Solvents and Solvent Effects in Organic Chemistry // Wiley – VCH, Weinheim (2003), 630 p. [2] O. Pytela // Collect. Czech. Chem. Commun. (1988), vol. 53 (7), p. 1333. [3] J. Vcelak, V. Chavalovsky // Chem. Prom., (1980), vol. 30 (2), p. 76. [4] K. Nozaki, P. D. Bartlett // J. Am. Chem. Soc., (1946), vol. 68, p. 1686. [5] D. Lefort, J. Sorba, D. Roillard // Bull. Soc. Chim. France (1961), p. 2219. [6] N. S. Tsvietkov, V. Ya. Zhukovsky, R. G. Makitra, Ya. N. Pyrig // Reakts. Sposobn. Org. Soed. (1978), vol. 15, p. 68. [7] R. E. Pincock // J. Am. Chem. Soc., (1964), vol. 86 (9), p. 1820. [8] A. K. Meteliev, M. K. Shchennikova // Trudy po Khimiji i Khimtechnologiji (Gorkyj), (1968), issue 1, p. 70. [9] E. R. Sarukhanyan // Sci. Notes of Erevan University, Natural Sciences, (1984), issue 3, p. 88. [10] S. Molnar // Period. Polytehn. Chem. Eng., (1973), vol. 17, p. 257.


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[11] F. Bilmeyer // Introduction to Chemistry and Technology of Polymers, (1958), p. 220. [12] W. A. Pryor, K. Smith // J. Am. Chem. Soc., (1970), vol. 92, p. 5401. [13] T. Yamamoto, H. Onishi, M. Hirota, Y. Nakashio // J. Chem. Soc. Jap., Chem. and Ind. Chem., (1985), vol. 7, p. 1459. [14] M. P. Raetsch, B. Friedel // Z. Phys. Chem. (DDR), (1975), vol. 256, p. 829. [15] S. Baj, M. Dawid // Wiadom.Chemiczne (2000), vol. 54 (11–12), p. 1023. [16] V. S. Dutka, N. S. Tsvietkov, R. F. Markovska // Kinetika and Catalysis (1982), vol. 23, issue 5, p. 1071. [17] E. M. Havryliv, R. G. Makitra, Ya. M. Pyrig // Reakts. Sposobn. Org. Soed., (1987), vol. 24 (1), p. 5. [18] Ya. M. Pyrig, R. G. Makitra, Y. Y. Yatchyshyn // Kinetika and Catalysis (1991), vol. 32 (5), p. 1040. [19] J. Ohkatsu, M. Takeda, T. Hara, O. Tetsuo, A. Misiko // Bull. Chem. Soc. Japan (1967), vol. 40 (6), p. 1413. [20] Y. Y. Yatchyshyn, Ya. M. Pyrig, R. G. Makitra // Organic Reactivity (1988), vol. 24 (3), p. 340. [21] R. V. Kucher, Y. O. Opeyda, L. G. Nechytaylo, V. А. Symonov // Intermolecular Interactions and Reactive Ability of Organic Compounds / Edn: “Naukova Dumka”, Kiev (1983), p. 82. [22] P. P. Levin, I. V. Khudyakov, I. A. Khardina, K. N. Rygalov // Izv. АS USSR (1977), issue 11, p. 2605. [23] R. G. Makitra, V. Ya. Zhukovsky, Ya. M. Pyrig // Kinetics and Catalysis (1982), vol. 23 (5), p. 1262. [24] A. T. Blomquist, J. A. Bernstein // J. Am. Chem. Soc. (1951), vol. 73, p. 5546. [25] V. L. Antonovsky, L. D. Bezborodova, M. E. Yaselman // Zh. Phys. Chem. (1969), vol. 43, p. 2281. [26] P. D. Bartlett, Ch. Ruchard // J. Am. Chem. Soc., (1960), 82, p. 1756. [27] A. T. Blomquist, A. J. Buselli // J. Am. Chem. Soc., (1951), 73, p. 3883. [28] H. H. Jaffe // Chem. Revs., (1953), 29, p. 191. [29] W. Cooper // J. Chem. Soc., (1951), p. 3106. [30] F.R.Mayo, C. Walling // Chem. Revs., (1950), 45, p. 269. [31] I. S. Voloshanovsky, S. S. Ivanchov // Reports of ASci. USSR,, (1974), 3, p. 252. [32] Kucher R. V., Vasyutyn Ya. M., Makitra R. G., Pyrig Ya. M. // Reports of ASci. USSR, Ser. «B», (1988), № 6, p. 47. [33] Makitra R. G., Turovsky A. A., Zaikov G. E. Correlation Analysis in Chemistry of Solutions // Utrecht-Boston, VST Ed., 2004, 320 p.

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[34] Recommendations for Reporting the Results of Correlation Analysis in Chemistry using Regression Analysis // Quant. Struct., Act. Relat., (1985), vol. 4, № 1, p. 29. [35] R. G. Makitra, Ya. M. Pyrig, R. V. Kyvelyuk // Dep. VINITI № 628–V86 (1986). [36] Abboud J. L. M., Notario R. // Pure and Appl. Chem., (1999), vol. 71, № 4б p. 645.

Chapter 2

THE MEDIUM INFLUENCE ON THERMOLYSIS OF DIACYL – AND DIALKYLPEROXIDES A number of investigations have been dedicated to the decomposition of diacylperoxides. Benzoyl peroxide is the classical object for studies of radical reactions. This is connected both with its accessibility and purification simplicity and also with its wide application as initiator of different radical processes including the polymerization ones. However, this reaction is sufficient complicated, proceeds parallel upon two paths, namely monomolecular path and induced one; that is why dependently on the conditions its kinetics is enough complicated. Correspondingly, the descriptions of medium properties influence on the process in more early works are contradictory. In accordance with the [1, 2] the reaction of benzoyl peroxide decomposition is monomolecular, but the kinetics is complicated in consequence of lapping the bimolecular induced decomposition: (PhCOO)2

2PhCOO

(1)

2PhCOO

PhCOOPh + CO2

(2)

PhCO2 + (PhCO2)2

d [ Bz 2 O2 ] dt

PhCOOPh + CO2 + PhCO2

k1[ Bz 2 O2 ] k[ Bz 2O2 ]

3

2

(3) (4)

Evidently, a disagreement of the decomposition constant rates for substituted benzoyl peroxides with ζ–constants of the Hammet’s equation caused by the

16


availability of two alternative paths of the reaction and mentioned in the works [3, 4]. There were presented data [1, 2] concerning to the benzoyl peroxide decomposition depth in 40 solvents for the same periods of time. Accordingly to proposed chemical mechanism, the rate constants by the first order found on the basis of these data are not correlated with the properties of the solvents, since they are by the constants of the gross process and this is to be expected that the solvation effects will be determined by the ones factors for molecular process and by others factors for induced process. An impossibility to determine the quantitative connection between the gross constants of benzoyl peroxide decomposition and properties of the solvents is confirmed by the results of work [5]. Depending on the medium character the total rate of the benzoyl peroxide decomposition at 30 0C is under the regularities of the first (aromatic hydrocarbons, nitrobenzene, chloroform), the second (acetone, butyric aldehyde) and the third (acetic acid, ethyl acetate, dichloroethylene) orders or has the autocatalytic character (CCl4, chlorobenzene). From the first group it can be obtained the general three–parametric dependence for five of the same type aromatic solvents and CHCl3:

lg k 10 4 12,57 74,70 f n N=6

0,0056 B 0,065

R = 0,995

(5)

2

s = 0,032

The deciding influence on the decomposition rate has a parameter of the nucleophilic solvation B (r = 0,825). However, the data concerning to the rates in cumene are not within the hyperplane of the regression assigned by the equation (2.5) and the decomposition rates constants values for the four aromatic solvents (except the anisole) are differed one from another only on ± 10 %; that is why the excerpt can not characterize adequately the influence of the solvent on the total rate constant of the benzoyl peroxide decomposition. Table 1. Constants rate of the BP decomposition № 1 2 3 4 5 6 7

Solvent Ethylbenzene Benzene Toluene Chloroform Nitrobenzene Cumene Anisol

f(n2) 1.4933 1.4979 1.4963 1.4433 1.5526 1.4915 1.5179

B 58 48 58 14 67 56 155

2

, kJ/mole 325.7 349.7 331.2 353.1 479.4 302.1 380.0

k1 104, h–1 1,30 1,73 1,78 1,97 2,38 2,63 5,12

The Medium Influence on Thermolysis of Diacyl– and Dialkylperoxides

17

Table 2. The rate of acetyl peroxide decomposition into n–alkanes at 80 0С accordingly to [6] Solvent

lg k

δ2, kJ/mol

n2 1 n2 2

2

Heptane Octane Decane Dodecane Tetradecane Hexadecane

–4,1124 –4,1343 –4,1643 –4,2111 –4,2291 –4,2684

228,0 234,9 243,8 256,9 260,1 263,3

0,2304 0,2411 0,2488 0,2536 0,2666 0,2596

0,191 0,193 0,199 0,203 0,207 0,206

1 1

, sP 0,417 0,546 1,000 1,492 2,089 3,451

Table 3. Constants of rate at 80 0С and energies of activation for the reactions of benzoyl peroxide and furoyl peroxide decomposition [8] Benzoyl peroxide Solvent

ktotal 106, s–1

Еtotal, kJ/mol

khomol 106, s–1

Benzene Dichloroethane Cyclohexane Dioxane Ethylacetate Acetic acid Methanol

34,0 37,0 41,6 113,1 71,0 60,0 62,0

125,6 122,7 124,8 108,0 115,5 111,0 112,6

34,0 35,4 19,0 43,7 51,9 42,2 ––

kind 106, l1/2 / (mol1/2·s) 0 62,5 610 1700 450 436 ––

Furoyl peroxide ktotal 106, s–1

Еtotal, kJ/mol

61 118 62 144 79 1290 ––

115,1 108,9 116,0 108,9 122,3 89,6 104,7

Functions of the viscosity 1/η and (η/Avis)1/2 were proposed in work [6] as the parameters characterizing the effects of the medium influence on the benzoyl peroxide decomposition rate. However, at the dicumenyl peroxide decomposition the linearity between the rate constants of the decomposition and f(η) is observed only in the series of n–alkanes C8 – C14; in a case of polar solvents or aromatic hydrocarbons kdecomp. are beyond the straight line given by the regression equation and are better generalized by the polarity function (ε – 1)/(2ε + 1) or by the electrophilicity ET function [7]. However, from our point of view, the cohesion energy density δ2 = (ΔHevap. – RT)/Vmol is better right for the characteristics of the medium action on the kinetics of radical processes than the viscousity one, since the rate of radical processes is determined not so much by diffusion of radicals as the cell effect related with the


18

solvents ability to self–association. With the aim of this assumption check–up the data [6] were parallel correlated with the values η and δ2 (see Table 2): Appropriate pair correlation coefficients are equal at η – 0,958 and δ2 – 0,982, that is the δ2 parameter in comparison with the viscosity functions is characterized by higher degree of relationship with the decomposition rate. Additional taking into account the factors of non–specific solvation f(n2) and f(ε) practically not increases the value R, since into alkanes the specific solvation does not proceed:

lg k

3,313 0,0053

N=6 R = 0,985 r3 = 0,958

2

0,872 f n s = 0,0164

(6)

1,111 f r1 = 0,982

r2

=

0,908

In order to confirm the signification of medium cohesion energy density factor in kinetics of radical processes of homolysis, the data [8] concerning to the kinetics of benzoyl peroxide and furoyl peroxide have been generalized by us via the fifth–parametric LFE equation. The values of used characteristics of solvents were taken from the review [9]. In considered communication it were determined the rates both of total and homolytical inhibited processes and the rate of the induced decomposition was determined on the basis of their difference. Since the values ktotal were calculated in slope of the straight line [Bz2O2] / time] in most cases they increase with the substrate concentration increasing as a result of extension the induced thermolysis part contribution into the general process. With the aim of investigations the values corresponding to minimal concentration of peroxide 2·10–3 mole/l (see Table 3) were used by us. Decomposition of these diacyl peroxides proceeds on two ways (namely, homolytic and initiated) and observed rate is total [4]:

W

k homol Bz 2O2

kind Bz 2O2

3/ 2

(7)

With the diacylperoxide concentration increasing the gross constants of its decomposition are changed. This gave the possibility to obtain separately khomol and kind [8] by means of kinetic analysis of experimental data. The generalization of corresponding data from Table 3 leads to the following equations [10]:

lg k homol

5,543 3,00 f n

1,13 f

0,0018B 0,0024

2

(8)

The Medium Influence on Thermolysis of Diacyl– and Dialkylperoxides N=6 R = 0,977 s = 0,051 r3 = 0,807 r4 = 0,655

r1 = 0,403

r2

=

19

0,527

It is necessary to note, that the cohesion energy density practically does not influence on the rate of homolytical non–induced by radicals decomposition:

lg k homol R = 0,968

5,49 2,34 f n

0,924 f

(9)

0,0156 B

s = 0,049

An exclusion of others parameters decreases the value R till 0,9 and lower. Especially is aloud the influence of the basicity B – without taking into account of this factor R is decreased till 0,73.At the same time in a case of the induced decomposition the factor δ2 already has significance and is favourable to decomposition process. Simultaneously the influence of the polarity is insignificant:

lg kind

41,62 178,8 f n 2

R = 0,991 s = 0,684 r4 = 0,156

0,0257 B 0,565ET r1 = 0,798

r2 – 0,419

0,273

(10)

2

r3

=

0,230

An exclusion of the rest parameters decreases the value R till < 0,9, especially has significance the influence of non–specific solvation caused by the polarizability: without f(n2) R = 0,54. Thus, conducted analysis points out the different influence of the solvation effects in reactions of homolytical and induced thermolysis of benzoil peroxide. Homolytical decomposition is accelerated by any types of the solvation, which is related, evidently, not with the radicals solvation – reaction products, but with the solvation of benzene rings of the starting peroxide, that leads to weakening the broken –O–O– bond. It is possible also that the solvation with the nucleophilic solvents of electron–deficitive hydrocarbon atom of carbonyl group proceeds. Really, the maximal rate of decomposition is observed in the most basic among all studied solvents – ethylacetate. At the same time, the cell effects determined by δ2 practically do not influence on the rate of homolytical decomposition. An influence of the solvents properties on the rate of induced decomposition is contrary: the solvation of formed radical stabilizes of it and decreases the possibility of its attack on the molecule of benzoyl peroxide, and the medium

20


self–association is favourable to the cell effect, increases the possibility of particles interaction and increases the process rate. However, in the work [8] was shown, that the action of induced decomposition on total rate of the process is relatively of a little significance and the values of gross–constants are near to those for the homolytic decomposition (with the exception of ethylacetate and dioxane). That is why, it is possible to obtain the equations connecting the solvents properties and rate constants and energies of activation of the gross–process:

lg ktotal

3,772 1,78 f n

0,48 f

N=7 R = 0,973 s = 0,073 r3 = 0,89 r4 = 0,21

0,0019 B 0,0011 r1 = 0,520

r2

(11)

2

=

0,80

Nucleophilic solvation as same as in the cases of homolytical decomposition increases the rate of the gross–process, however the influence of others solvation parameters is opposite as a result of decreasing the significance of rate of initiated decomposition [10]. These calculations point out the advisability of separate considering the present data concerning to non–initiated and initiated decomposition of Bz2O2 with the use of equations including the factor of cohesion energy density for more quantity of solvents. The values of rate constants for homolytical non–initiated decomposition of Bz2O2 at 80 0C in 21 solvents are presented in Table 4 on the basis of works [1, 3, 4, 11–14, 16]. Obtained correlation of all data accordingly to the fifth–parametric LFE equation although corresponds to the trustworthiness requests accordingly to Fisher’s criterium, however it is characterized by extremely low value of general correlation coefficient R = 0,824. Indeed, here it is necessary to take into account, that in Table 4 there are data of the eight authors and these data obtained under different experimental conditions at different purity of reactants, concentration and that is the most important under the different inhibition method of initiated reaction. Thus, in works [4, 11] the rate of homolytic decomposition was determined graphically from the comparison of experimental rates at different concentrations of benzoil peroxide; in works [3, 4, 14] the decomposition was carried out under excess of styrene and etc. Even under near conditions of the experiment carrying out there are visible divergences in determined values of constants (k1) in different authors. Data of Table 5 can be presented as example:


21

Table 4. Logarithms of the rate constants for homolytic non–initiated decomposition of benzoyl peroxide at 80 0С (k, h–1) №

Solvent

Ref.

lg kexp.

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21

Carbon tetrachloride Benzene Toluene Nitrobenzene Tert–Butanol Cyclohexene Cyclohexane Ethylacetate Acetic acid Acetic aldehyde Methylcyclohexane n–Octane Chlorobenzene Brombenzene Acetone Dioxane Acetophenone Styrene Cumene Ethylbenzene p–Xylene

1 1 11 1 1 1 1 1 1 1 11 11 12 12 13 14 3 4 16 16 16

–4,6812 –4,4844 –4,4844 –4,4844 –4,4844 –4,7143 –4,1965 –4,0478 –4,0895 –4,1249 –4,2231 –4,4260 –4,6144 –4,6596 –4,0400 –4,4000 –4,3400 –4,5000 –4,7100 –4,7328 –4,7570

lg kcalc. (eq.13) –4,6459 –4,7093 –4,6845 –4,4967 –4,6722 –4,5599 –4,5918 –4,1149 –4,1320 –4,0995 –4,5838 –4,5332 –4,5767 –4,6603 –3,9486 –4,4236 –4,4090 –4,7989 –4,6711 –4,6769 –4,6880

lg k -0,0353 +0,2249 +0,2001 +0,0123 +0,1878 -0,1544 +0,3953 +0,0678 +0,0425 –0,0254 +0,3607 +0,1072 –0,0377 +0,0007 –0,0914 +0,0236 +0,0690 +0,2989 –0,0389 –0,0559 –0,0690

Table 5. Data for non–initiated decomposition of benzoyl peroxide №

Solvent

С [BP], mol/l

1 2 3

Benzene Benzene tert–Butylbenzene

0,050 0,025 0,012

k1, min–1 [11] 0,00199 0,00218 0,00268

[4] 0,00219 0,00240 0,00303

At such divergences of experimental data by different authors even low value of R permits in principle positively to solve the question about possibility of generalization of medium physical–chemical properties influence on the rate of the same type of homolytic reactions [15]. And exclusion from the consideration

22


of the most deviating from general dependence data concerning to the decomposition in benzene (№ 2), toluene (№ 3), cyclohexane (№ 7), methylcyclohexane (№ 11) and styrene (№ 18) permits to obtain the equation with the acceptable degree of relationship:

lg k1

3,830 4,321 f n 2

N = 16;

1,355 f

0,00063B 0,00672ET 0,0022

2

(12)

R = 0,953;

r1 = 0,717; r2 = 0,621;

s = 0,097; r3 = 0,654;

r4 = 0,703;

r5 = 0,428

Check–up of the significance of separate parameters of the regression equation points out the practically negligible influence of specific solvation and cohesion energy density on the process of peroxide decomposition; an exclusion of ET parameter from the equation decreases the value R till 0,950, additional exclusion of δ2 parameter from the equation decreases the value R till 0,948. At the same time, the removal from the calculation of any among all parameters characterizing the non–specific solvation practically destroys the correlation: without f(n2) R = 0,784; without f(ε) R = 0,874. Finally, the influence of medium on the rate of non–initiated decomposition with the adequate accuracy is described by three–parametric equation:

lg k1 N = 16 F(0.05, 3, 12) 4.

3,650 4,724 f n 2 R = 0,948

1,325 f

0,000558B

s = 0,097

(13)

FS = 7,22 > 3,49 =

Comparison of calculated and experimental values lgk is represented in Table

Thus, the nucleophilic solvation of benzoyl peroxide facilitates to its non– induced decomposition, probably, as a result of weakening the –O–O– group as a consequence of the electrons drawing off on carbonyl groups:


23

Table 6. The rate constants of the initiated decomposition of benzoil peroxide at 80 0С, k, (mol/l)–1/2 №

Solvent

Ref.

lg kexp.

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

ССl4 Benzene Toluene Nitrobenzene Nitrobenzene Tert-Butylbenzene Cyclohexene Cyclohexane Ethylacetate Acetic acid Acetic anhydrous Chlorobenzene Brombenzene Cumene Ethylbenzene p-Xylene

4 4 4 4 12 4 4 4 4 4 4 9 9 16 16 16

–4,4325 –4,3688 –43688 –4,3688 –4,2247 –3,8144 –4,3336 –3,4881 –3,4357 –3,2915 –3,5149 –4,7282 –4,2247 –4,0223 –4,0164 –4,1396

lg kcalc. (eq.15) –3,6803 –4,2936 –4,2336 –4,2193 –4,2193 –4,0722 –4,1271 –3,4193 –3,3850 –3,4252 –3,5194 –3,9634 –4,3404 –4,1359 –4,1873 –4,2771

lg k –0,7522 –0,0752 –0,1353 –0,1495 –0,0054 +0,2578 –0,2065 –0,0688 –0,0507 +0,1437 +0,0045 –0,7648 +0,1157 +0,1136 +0,1709 +0,1375

At the same time, the high–polarizable solvents via the interaction with the electrons of benzene nucleus of benzoyl peroxide suppresses the tendency to the decomposition. It is necessary to notify that since the decomposition is homolytic and proceeds without the participation of free radicals, the “cage” effects determined by the medium self–association are of little significance. As contrasted to above presented dependencies the initiated decomposition of benzoyl peroxide is subjected to others regularities. The results of the works [4, 9, 12, 16] (see Table 6) were used for the consideration. In these works the rate of the initiated decomposition was determined as the difference between the total rate of the process and the rate of non–initiated decomposition. The initiated thermolysis is the best of all described in accordance with the above–presented chemical mechanism by the equation with the kinetic order 3/2. The generalization of data for the solvents from Table 6 gives the reasonable degree of relationship only under condition of the exclusion from the consideration the most diverting values concerning to the decomposition in Carbon tetrachloride and chlorobenzene (R = 0,947). The divergences from general regularities in a case of CCl4 were mentioned also in the work [17] at the

24


investigations of solvents effects on the radicals PhCOO· transformation. With the aim of the degree of relationship increasing we had excluded from the consideration also the results concerning to decomposition in tert–butylbenzene. It was obtained the equation:

3,3414 13,148 f n 2

lg k3 / 2

3,372 f

0,0051B 0,020ET 0,0154

2

(14) N = 12 (0,05; 5; 6).

R = 0,959

s = 0,159

FS = 6,79 > 4,39 = F

Electrophilic solvation has a little influence on the process rate, however more appreciably than in a case of homolytical decomposition; that’s why the following expression is acceptable:

lg k3 / 2

0,2649 13,92 f n 2

R = 0,948

s = 0,161

3,834 f

0,0048B 0,0133

2

(15)

FS = 5,40 > 4,12 = F (0,05; 4; 7)

As same as in a previous case, the medium polarizability decreases the rate of a process that evidently is a result of the stabilization of free radicals C6H5CO· forming at the peroxides decomposition due to non–specific solvation of the aromatic ring by high–polarizable solvent and, as a result by shrinking the unshared electron of forming radical on the nucleus. The similar effect gives rise also the nucleophilic solvation of free radical with the participation of unshared electron. As contrasted to the non–radical homolytical decomposition noticeably becomes aware of influence of the medium ability for self–association, since the effect of a cage formed by the molecules of the solvent in presented case decreases the probability of attack by radicals of the peroxide molecule. Thus, the medium action on the rate of benzoyl peroxide decomposition of radical processes can be satisfactory generalized via LFE equations, however, only under the separate consideration of the rates of every elementary reaction (or its stage). Such generalization permits more deeply to delve into the chemical mechanism of the reaction and to explain the nature of separate solvation effects [15]. Above–mentioned approach can be applied also for others diacylperoxides and also for the polymeric peroxides of dibasic acids. Thus, if in a gaseous medium the decomposition of diacetylperoxide is subjected to the kinetics of the


25

first order in a wide range of temperatures [18], then in the liquid phase at 55 – 85 C the first order is observed only at it low concentrations and at higher temperatures the deviations are observed as a consequence of the “cage” effect demonstration. Depending on the nature of solvent the values of constants are changed insignificantly, no more than in 1,5 times at constant value of process activation energy ≈ 30 – 33 ccal/mole [19]. However, in more later works it was notified more essential influence of the solvent on the rate of decomposition – since at the iso–butyrylperoxide decomposition in the presence of inhibitor the values of constants rate are changed in the range of one order and are increased from hydrocarbons to nitrobenzene. It was determined the presence of approximately linear dependencies lgk on Kirkwood’s function, however separately for hydrocarbons and polar substances [20]. As it was shown in Chapter I, the similar peculiarity is notified also for decomposition of tert– butylperformate. In detail the decomposition of iso–butyryl and benzoyl peroxides were investigated in work [21]. However, the authors carried out the investigations only in 4 solvents (cyclohexane, CCl4, benzene and acetonitrile), that not gives the possibility quantitatively to generalize the data. In theoretical aspect it was important to determine: are conclusions obtained by us applicable for others diacylperoxides? That is why, the references data of Smid, Rembaum and Szwarc [22] were analogously mathematically treated by us upon the rate of propionyl and butyryl peroxides thermolysis in different solvents. The numerical values of the constants rates are represented in Table 7. It turned out, that these data are also good described by tetra–parametric linear Koppel– Palm equation. Let us note, that in following calculations (eqs. 16–21, and also eqs. 29–30) the electrophilicity Е proposed in Koppel and Palm’s works was used as the electrophilicity factor instead of the Ет upon Reichardt; in other words, this is Ет “released” from the possible influence of the non–specific solvation [23]. Under taking into account the all four parameters, the influence of the medium on the reaction rate for the propionyl and butyryl peroxides can be described by following equations (16) and (17) respectively: 0

lg k 6 0,80 0,44 f n 2 R = 0,965

0,80 f

0,00198B 0,0048E

(16)

s = 0,086

Pair correlation coefficients are respectively equal to: f(n2)r = 0,23; f(ε)r = 0,71; f(E)r = 0,42; f(B)r = 0, 85 and

26


lg k 6 0,65 0,88 f n 2 R = 0,985

0,84 f

0,00195B 0,013E

(17)

s = 0,071

The values of paired correlation coefficients are following: f(n2)r = 0,16; f(ε)r = 0,74; f(E)r = 0,56; f(B)r = 0, 89. The calculations of the series of tri– and di–parametric correlation equations showed, that the thermolysis of propionyl and butyryl peroxides are described with the adequate accuracy by two–parametric equations taking into account only polarity and basicity of medium respectively:

lg k 6 0,94 0,86 f R = 0,962

(18)

0,0022 B

(19)

s = 0,080

lg k 6 0,93 0,95 f R = 0,968

0,0021B

s = 0,088

Particular interest presented by itself the treatment of Lamb and co–workers [20] data concerning to the influence of solvents on the decomposition rate of iso– butyryl peroxide since the proposed by them dependence lgk = f(ε–1)/(2ε+1) points out the clear difference between the effects in polar and non–polar media. Thus, in non–polar solvents the constant of the decomposition rate linearly connected with the modification of the solvent polarizability and in the polar ones it correlates with the dielectric penetration of medium. Mathematical treatment of data (see Table 7) in accordance with the Koppel– Palm equation showed, that the rate of iso–butyryl peroxide decomposition depends on the medium properties as follow:

lg k 5 R = 0,982

2,45 8,73 f n 2

0,693 f

0,00199 B 0,0533E

(20)

s = 0,0855

the values of pair correlation coefficients are as following: f(n2)r = 0,48; f(ε)r = 0,764; f(E)r = 0,28; f(B)r = 0,65.


27

Maximal pair correlation coefficient is observed from the medium polarity, however the exclusion of separate parameters with the aim of determination of their significance points out the insignificant role of this parameter and the deciding influence has the polarizability and the medium basicity. Thus, general correlation coefficients for the respective tri–parametric equations are equal to: f(n2, E, B)R = 0,972; f(ε, E, B)R = 0,811; f(ε, n2, B)R = 0,962; f(ε, n2, E)R = 0,952. Henceforth, the all solvents have been divided into two groups as same as in the work [20], namely, into polar and non–polar ones. In non–polar solvents under taking into consideration of the four parameters the general correlation coefficient hits in “splendid” field f(ε, n2, E, B) R = 0,992; s = 0,0912, and the values of the paired correlation coefficients are respectively equal to: f(n2)r = 0,97; f(ε)r = 0,90; f(E)r = 0,76; f(B)r = 0,83. Really, as our results in non–polar media (iso–octane, cyclohexane, carbon tetrachloride, m–xylene, toluene, benzene)) showed, the dependence of constant of iso–butyryl peroxide decompositon satisfactory correlates with the medium polarizability. In polar solvents: f(ε, n2, E, B)R = 0,989; s = 0,0785; f(n2)r = 0,39; f(ε)r = 0,96; f(E)r = –0,03; f(B)r = 0,49. It turned out, that the iso–butyryl peroxide decomposition rate constant dependence on polarity and polarizability of medium can be described with “good” correlation in polar media as follow:

lg k 5

1,58 1,62 f n 2

R = 0,982

s = 0,082

5,5693 f

(21)

Thus, whereas the polarity and share and share a like electrophilicity and medium basicity have the main influence on the polymer peroxide of azelaic acid decomposition rate, in a case of iso–butyryl peroxide decomposition the important role plays also the polarizability of the solvents. Such peculiarity of this peroxide decomposition is probably caused by fact that the peroxide regrouping to “inversion” product (ROC(O)OC(O)R) proceeds parallel to radical decomposition (as it indicated by authors [20]). Positive values of the coefficients into correlation equations in all cases point out the stabilization of transition state of the peroxides as a result of their molecules interaction with the solvent or point out the destabilization of structure of starting peroxide as a result of solvation, besides, this interaction connected both with the non–specific and with the specific solvation (π–complexes, donor– acceptor complexes, etc.).

28


Table 7. Rate constants of the propionyl and butyryl peroxides thermolysis in accordance with the data [22] and iso–butyryl peroxide thermolysis accordingly to data [20] and also characteristics of the used solvents at 20 0С № 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19

Solvent ССl4 iso–Octane Cyclohexane n–Hexane Benzene Toluene m–Xylene p–Xylene Chloroform Chlorobenzene Fluorobenzene Dichlorethane Acetic aldehyde Acetic acid Dioxane iso–-Propyl alcohol tert–Butyl alcohol Benzonitrile Nitrobenzene

k·105, s–1 peroxide propionyl

butyryl

9,8

11,1

14,8 19,0 18,3

11,4 22,4 21,4

f(n2)

f( )

Е

В

0,3615 0,3189 0,3408 0,3081 0,3852 0,3828 0,3822 0,3822 0,3357 0,3968 0,3647 0,3524 0,3181

0,2261 0,1925 0,2027 0,1862 0,2306 0,2395 0,2292 0,2292 0,3587 0,3775 0,3733 0,4309 0,4643

0,0 0,0 0,0 0,0 2,1 1,3 0,0 0,0 3,28 0,0 0,0 3,0 3,7

0 0 0 0 48 58 68 68 14 38 50 40 100

305,0

0,3059 0,3385 0,3096

0,3872 0,2231 0,4601

14,6 4,2 8,7

131 237 236

251,0

0,3145

0,4342

5,2

247

420,0 580,0

0,4004 0,4147

0,4708 0,4788

0,0 0,0

155 67

iso–butyryl 78,0 32,0 45,0 240,0 143,0 140,0 75,0 173,0 123,0

35,0

43,0

38,0 45,0

47,0 46,0

39,0 37,0

43,0

Carried out kinetic investigations of the diacil peroxides thermal decomposition reactions give the grounds to conclude about the chemical mechanism of their thermolysis – radical or ionic one. Since the reaction rate is increased with the medium penetration dielectric increasing, in accordance with the Kirkwood–Leidler–Erich equation the dipole moment of the transition state should be more than the dipole moment of the starting molecule of peroxide. It is necessary to conclude from this, that along with the radical mechanism the ionic mechanism also takes place, that is “ion–radical pair” is formed in transition state:

RCOO

2

[ R CO2 OCOR

R CO2 OCOR]

This conclusion is agreed with the results of the work obtained in a different way by Walling and co–workers [21] and also by Shatkina and co–workers [23].


29

Naturally, medium polarity increasing leads to increasing the part of the heterolytic decomposition. However, in the work [24] on the basis of which the presented material was given, the possible influence of the “cage” effect was not taken into account, i. e. the term with δ2 is absent in equations. In later investigations under consideration of data concerning to the di–tert–butylperoxide decomposition this lack has been putted out. It was used also more universal electrophilicity parameter ET by Reichardt. Since in a series of the later works as to LFE method it was determined also the significance of the molar volume VM influence, this parameter was also introduced into calculation, i. e. the primary calculations have been carried out in accordance with the six–parametric equation. In a case of the most simple representatives of these compounds, namely di– tert–bytulperoxide, the data of the work [25] concerning to its thermal monomolecular decomposition were considered at 120 – 135 0C in 10 solvents unable to promote the induced decomposition. It was determined by authors, that both the energy consumption for the cavity formation in liquid (it self– association) and solvation factors have an influence on the formation of the activated transition state, however the quantitative treatment of data were not carried out. Table 8. Logarithms of the experimental first order rate constants for di– tert–butylperoxide decomposition (lgk 10–6 s–1) in solvents at 120 and 130 0C in accordance with the [25] and also the calculated values of lgk obtained accordingly to equations (23) and (24) № 1 2 3 4 5 6 7 8 9 10 11 12

Solvent Cyclohexane Triethylamine Dimethylaniline Cyclohexene Tetrahydrofuran tert–Pentanol Nitrobenzene Ethylbenzoate Benzene tert–Butanol Acetic acid Acetonitrile

120 0С lgkexp. –0,2007 –0,1024 –0,0177 –0,1192 –0,0132 0,1004 0,1173 0,0294 0,0414 0,1492 0,3404 0,3444

lgkcalc. –0,1430 –0,1507 –0,0118 –0,1277 0,0211 0,1386 0,1478 0,0476 –0,0457 0,1806 0,3283 0,2841

lgk 0,0577 –0,0483 0,0059 –0,0085 0,0343 0,0383 0,0305 0,0182 –0,0871 0,0314 –0,0122 –0,0602

130 0С lgkexp. 0,4133 0,4983 0,5328 0,4487 0,5302 0,6503 0,6314 0,5302 0,5079 0,6335 0,7987 0,7505

lgkcalc. 0,4334 0,4466 0,5334 0,4544 0,5522 0,6329 0,6288 0,5671 0,4982 0,6625 0,8012 0,7150

lgk 0,0201 –0,0517 0,0007 0,0057 0,0220 –0,0174 –0,0027 0,0369 –0,0096 0,0290 0,0025 –0,0355


30

Table 9. The values of experimental (accordingly to work [25]) and calculated in accordance with the equation (26) di–tert–butylhydroperoxide decomposition activation enthalpies into organic solvents, and also corresponding experimental values of enthalpies of its dilution ΔHsolv (ccal/mole) and calculated accordingly to equation (28)

*

Н#exp.

Solvent

№

Calculated accordingly to eq. (26) Н#calc.

( Н# )

solut. H exp .

Calculated accordingly to eq. (28) solut. H exp .

( Нsolut.)

1

Triethylamine

40,600

39,910

–0,690

0,000

0.109

0,109

2 3 4 5 6 7 8 9 10 11 12

Dimethylaniline Cyclohexene Tetrahydrofuran tert–Pentanol Nitrobenzene Ethyl benzoate Benzene tert–Butanol Acetic acid Acetonitrile Cyclohexane

37,600 37,300 37,100 35,700 35,600 35,500 35,300 34,300 33,400 31,000 40,800**

37,589 38,010 37,544 34,405 35,038 36,244 35,175 34,611 33,566 31,309 37,063

–0,011 0,710 0,444 –1,295 –0,562 0,744 –0,125 0,311 0,166 0,309 –3,737

0,866 0,000 0,236 0,949 1,150 0,575 0,400* 1,330 1,080 1,550 0,307

0,653 0,012 0,483 1,139 1,250 1,086 0,381 1,192 1,034 1,489 0,127

–0,213 0,012 0,247 0,190 0,100 0,511 –0,019 –0,138 –0,046 –0,061 –0,180

– the data havn’t been taken into account under calculation by equation (26); – the data havn’t been taken into account under calculation by equation (28).

**

Respective values of the logarithms of the rates constants decomposition for di–tert–butylperoxide in 12 solvents at 120 and 130 0C and also activation enthalpies into ccal/mole are represented in Tables 8 and 9. Generalization of data at 120 0C leads to the six–parametric equation (22):

lg k

0,978 0,64 0,35 f n 2

1,08 0,25 10 3

2

0,76 0,25 f

0,24 0,08 10 3 B 0,020 0,003 ET

1,00 0,55 10 3VM (22)

with the value of multiple correlation coefficient R = 0,985, pair correlation coefficients with separate parameters rO1 = 0,374; rO2 = 0,745; rO3 = 0,137; rO4 = 0,948; rO5 = 0,862; rO6 = 0,687 and mean–square error s = 0,129. As we can see, the defining impact on the t–Bu–OO–t–Bu decomposition rate has its electrophilic solvation ET; the cohesion energy density 2 influence evidently also will be of a great significance. In order to check up this assumption it was determined the significance of separate terms of equation by their alternate exclusion with every


31

time R determination. In this way it was determined the insignificance of the equation term with VM, however, quite adequate description of the medium properties influence on the t–Bu–OO–t–Bu decomposition rate can be achieved by means of the equation (23) including only two factors, namely ET and 2, at that both of them are favourable to the reaction:

lg k

0,872

R = 0,964

0,019 0,004 ET

s=

3

0,456 0,212 10

2

(23)

0,087

The values lgk calculated in accordance with the equation (23) and the divergence of the experimental and calculated data Δlgk = lgkcalc. – lgkexp. are presented in Table 8. The values Δlgk are in the error limits s = 0,087 and only lightly exceeds this value. The generalization of data concerning to the decomposition rate constants at 130 0C leads to the similar results (and even better statistically). For six– parametric equation R = 0,990, s = 0,030 and is possible its simplification to two–parametric equation (24):

lg k

0,120

R = 0,975

0,017 0,002 ET

0,105 0,123 10

3

2

(24)

0,026

s=

Somewhat worse results were obtained at generalization of data from the same work concerning to the decomposition activation enthalpies ΔH* (see Table 9). For all 12 solvents the correlation is unsatisfactorily low (R = 0,928), however at the exclusion of the most diverting data for cyclohexane it were obtained the equations (25) and (26) adequately generalizing the medium properties influence on the ΔH# value, ccal/mole: H#

41,403

5,598 7,015 f n 2

0,094 0,053 ET

R = 0,977

0,022 0,005

s = ± 0,526

11,867 4,603 f 2

0,004 0,010 VM

2,700 1,572 10 3 B

(25)


32

H # 45,427 17,940 4,223 f R = 0,967

0,127 0,054 ET

0,029 0,004

2

(26)

s = ± 0,629

Here we observe the coordination of the solvation effects: an increase of the ET and δ2 characteristics elevating the decomposition rate constant simultaneously decreases the ΔH# value, that is energy barrier of the process. Table 10. Effective rate constants for polymeric peroxide of azelaic acid thermal decomposition in solvents. Starting concentration 0,05 mole/l

№

Solvent

1 2 1 Cyclohexane 2 m–Xylene 3 ССl4 4 Cumene 5 Caproic acid 6 Chloroform 7 Benzonitrile continuation on page 27 1 2 8 Chlorobenzene 9 Dichlorethane 10 Amyl acetate 11 Acetic acid 12 Anisole 13 Butyl ether 14 Dioxane 15 n–Butyl ether 16 Nitrobenzene 17 Dimethylformamide 18 Dimethylsulphoxide 19 Benzyl alcohol 20 Tetrahydrofuran

k·108, s–1 k·105, s–1 Temperature, 0С 20 65 70 3 4 5 1,19 1,47 4,30 1,61 3,39 1,79 4,30 2,25 2,71 3,40 7,08 4,72 4,80 8,50

75 6 8,30 8,72 5,78 8,24 9,25 13,4 17,0

80 7 16,0 18,3 12,7 17,2 17,1 24,6 31,5

85 8

3 5,66 5,88 6,90 9,37 10,0 14,0 15,0 21,7 24,2 26,0 46,6 54,7 71,9

6 12,5 22,4 14,0 24,3 24,5 30,0 24,7 29,5 33,8 39,0 68,9 106,0 89,5

7 22,4 40,3 24,9 42,7 45,6 53,0 36,2 51,0 60,6 66,5 115,0

8 40,5

4 5,88

5 7,08 12,3

7,40

13,5

7,28

13,3 17,0 19,8 22,7 40,3 59,0 47,0

11,3 11,6 21,0 32,6 28,1

29,6 20,8 28,1 31,8

43,3 78,0

73,2 104,5 110,0


33

Electrophilic solvation is realized, evidently, upon the oxygen atoms of peroxide group thanks to which the –O–O– bond is weaken. The data obtained in work [25] are agreed with this assumption. These data are concerned to the heat solution of t–Bu–OO–t–Bu (ΔHsolv., ccal/mole) in the same solvents, in which the kinetics was studied; the maximal values are achieved into solvents containing the hydroxy group and also into electrophilic nitrobenzene and acetonitrile (see Table 9). At the assumption to generalize these data by means of Koppel–Palm equation the value R is low, namely 0,949, however after the exclusion of the most diverting data for ethyl benzoate it is possible their adequate generalization by means of the equations (27) and (28) at defining role of the factors ET (r = 0,822) and δ2 (r = 0,920): H solut.

3,53 0,947 1,652 f n 2

5,293 1,142 10 3 ET

R = 0,971

H solut.

1,566 1,166 f

3,955 0,035 10 3 B 0,043 0,013 ET

8,825 3,444 10 3VM

(27)

s = ± 0,132

2,866 0,032 0,013 ET

4,217 0,744 103

2

7,471 2,634 10 3VM (28)

R = 0,962

s = ± 0,150

Calculated in accordance with the equation (28) values ΔHsolut. and also their divergence with the experiment are represented in Table 9. Developed approach was turned out by effective also for the generalization of data concerning to the decomposition of polymeric peroxides of acids. For example, in work [26] it was studied the inhibited by styrene decomposition of polymeric peroxide of azelaic acid in 20 solvents. Corresponding values of the constants are represented in Table 10. As we can see from the experimental data (see Table 10), the values of lgk are increased with increasing the polarity and basicity of solvents (Figure 1 and Figure 2), however, the strict functional dependence is absent here.

34


Figure 1. Dependence of lgk on Kirkwood’s parameter of solvents.

Figure 2. Dependence of lgk on basicity of solvents.

Evidently, this is explained by combined influence of these factors and also is caused by the impact of two others parameters of the solvents, namely polarizability and electrophilicity. Since in the references there are no data for the basicity of caproic acid, this solvent (№ 5 in Table 10) was excluded from the calculations (the numbers of all points on Figures and in the text correspond to the numeration of the solvents in Table 10). The calculation of pair correlation coefficients upon separate parameters of the solvents gives the following


35

numerical values: for f(ε) R = 0,680; f(n2) R = 0,033; f(B) R = 0,806; f(E) R = 0,363. The all four parameters of the solvent have an influence on the value of lgk; however, this influence by no means the same. At the fourth–parametric dependence the correlation coefficient is equal to 0,900. The most deviations from the linear dependence (greatly more than the confidence probability) give the points №№ 7, 13, 14, 20 (benzonitrile, butyl ether, dioxane, tetrahydrofuran). An exclusion of the benzonitrile (№ 7) increases R from 0,900 till 0,932; an exclusion of tetrahydrofuran (№ 20) increases R from 0,932 till 0,953; an exclusion of dioxane (№ 14) increases R from 0,953 till 0,969 and the exclusion of butyl ether (№ 13) increases R from 0,969 till 0,985. This points out the possibility of staining the unaccounted disturbing factors taking place at the reaction carrying out in the above–mentioned four solvents; that is why, they have been also excluded from the following consideration. It was notified in [26] that the polymeric peroxide of azelaic acid decomposition rate in dioxane greatly more than in other solvents that was explained by the effect of the induced decomposition. Possibly is also other explanation: it is well–known, that the ethers including also the dioxane and tetrahydrofuran are exceptionally easily oxidized by the oxygen with the formation of peroxides. Although the interaction of these solvents with peroxides was not investigated, one ought not to exclude the possibilities of proceeding the bimolecular or chain reaction that makes conditional upon great rate of the process in these solvents and their falling out from the general series of the solvents as a result of other chemical mechanism of the reaction. For the residuary 15 solvents general correlation coefficient is equal to 0,985 that make a “good” correlation [27]. At this, regression equation is as follow:

lg k 108

10,240 3,178 f

4,489 f n 2

0,0249 E 0,00186 B (29)

R = 0,985

s = 0,116

The values of paired correlation coefficients: f(ε) R = 0,916; f(n2) R = 0,167; f(B) R = 0,803; f(E) R = 0,494 show that in solution both non–specific and specific solvations proceed. Polarizability of the solvent practically does not influence on the solvation of peroxide. Positive values of the regression coefficients at all parameters point out the stabilization of activated state as a result of its interaction with the solvent and point out the absence of such stabilization for the starting

36


peroxide; i. e., the stronger is interaction of peroxide in transition state with the solvent, the easier proceeds its decomposition. As it was expected, at the exclusion of the basicity, the correlation is made worse – multiplying correlation coefficient is decreased till 0,945. An exclusion of the polarity parameter still more makes worse the correlation: for lgk = f(n, E, B) R = 0,903. Function lgk is less sensible to the exclusion of other parameters: lgk = f(ε, E, B) R = 0,955 and lgk = f(n, ε, B) R = 0,970, i. e., the influence of the electrophilicity is respectively of little significance. It was determined, that the influence of a solvent on the rate of a polymeric peroxide of azelaic acid thermal decomposition process is determined mainly by its polarity and basicity and with the satisfactory accuracy is described by two–parametric equation:

lg k 108 R = 0,952

8,759 3,847 f

(30)

0,00172 B

s = 0,192

The dependence lg k 10

8

0,00172B

f

is represented on Figure 3.

Figure 3. Two−parametric correlation of the PPAA thermolysis rate.


37

Figure 4. Dependence of ΔН# on ΔS# for the PPAA thermolysis reaction.

Activation energy is decreased (on 6 ccal/mole at transition from the cyclohexane to tetrahydrofuran) and the pre–exponential multipliers are also decreased (on three orders) symbate to the polarity and the basicity of the solvents; although, similar to a case of lgk the linear dependence is not discovered. Between the values ΔH# and ΔS# the linear dependence is observed. The presence of corresponding compensating effect points out the indivisible chemical mechanism (despite the different force of the solvation effects) in monomolecular reaction of thermal decomposition of polymeric peroxide of azelaic acid in a whole series of investigated solvents. The presence of specific nucleophilic solvation of polymeric peroxide of azelaic acid by donor solvents is in good agreement with the data of works [28, 29], in which with the use of the physical–chemical methods of analysis it was shown that the benzoyl peroxide forms the low–stable complexes with such donors as pyridine and piperidine. Since at the complex formation a partial transition of electrons by n–electron pairs proceeds on the non–stable peroxy group, its stability at the solvation is more decreased that leads to the decreasing of ΔH# value of peroxy thermolysis reaction. Simultaneously with the solvent polarity increasing and solvates formation the peroxide modifies its conformation that facilitates it following decomposition.

38


Let note, that in the strong donor, namely in pyridine, which can oxidized with the formation of N–oxides, the reaction of polymeric peroxide of azelaic acid thermolysis proceeds quicker than in other investigated solvents and the peroxide rating curves have complicate, probably, autocatalytic character. Experimental data are not under the reaction rate equations by the first or the second orders and could not took into account under presented consideration. In above–mentioned work the parameter δ2 was not taking into account; however, in later investigation [30], in which the data from the above–said work concerning to the energies and enthalpies of decomposition activation were generalized, it was determined the insignificance of this factor that is in good agreement with fact that the decomposition proceeded monomolecularly since it was carried out in the presence of inhibitor. The correlation connection between the activation energy and its characteristics for 18 solvents shows, that though the multiple correlation coefficient R = 0,823 is low, however it’s increased to the satisfactory value R = 0,958 after an exclusion from the calculations of the most diverting data for nitrobenzene, chlorbenzene and carbon tetrachloride. Maximal value of the paired correlation coefficient is observed upon the basicity parameter rB = 0,920. In this case the regression equation will as follow: Eact. 132,9 37 42 f n 2

N = 15

9 16 f

R = 0,958

0,062 0,011 B 0,33 0,28 ET

s

0,004 0,02 2 (31)

3,20

At the sequential exclusion of separate factors, that is for corresponding four– parametric equations the values of multiplying correlation coefficients are decreased: on 0,948 without f(n2); on 951 without f(ε); on 0,953 without (δ2); on 0,757 without B; on 0,945 without ET. Least ponderable of all is the influence of the cohesion energy density and the impact of the solvent polarity. Without taking into account of these factors we obtain the following three–parametric equation:

Eact. 132,3

38 30 f n 2

0,061 0,007 B

0,28 0,12 ET (32)

N = 15

R = 0,951

s

2,95


39

The analogous dependence we obtain also for the enthalpy of activation:

H 13,80 N = 15

0,062 0,007 B

(33)

0,28 0,13 ET

R = 0,943

s

3,02

The same in a case of others polymeric peroxides of dibasic acids the influence of the solvents on the rate of above–mentioned compounds decomposition can be adequately generalized via multiparametric equations [31]. Thus, in a case of peroxides of acids the impact of the solvents on the rate of above–mentioned compounds decomposition and also activated parameters of process can be adequately generalized via multiparametric equations LFE, but only under condition of separate consideration of data for inhibited and initiated processes.

REFERENCES [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14]

Nozaki K., Bartlett P. // J. Am. Chem. Soc. (1946), vol. 68 (9), p. p. 1686– 1694 Bartlett P., Nozaki K. // J. Amer. Chem. Soc. (1947), vol. 69, p. 1686 Blomquist A., Buselli A. // J. Amer. Chem. Soc. (1951), vol.73 (8), p. p. 3883–3888 Cooper N. // J. Amer. Chem. Soc. (1951), vol. 11, p. p. 3106–3111 Cass W. // J. Amer. Chem. Soc. (1946), vol. 68 (10), p. 1976 Pryor W., Smith K. // J. Am. Chem. Soc. (1970), vol. 92, p. p. 5401–5412 Yamamoto T., Onishi H., Hirota M., Nakashio Y. // J. Chem. Soc. Jap., Chem. and Ind. Chem. (1985), 7 (11), p. p. 1459–1461 Molnar S. // Period. Polytechn. Chem. Eng. (1973), 17 (3), p. 257 Makitra R., Pyrig Ya., Kivelyuk R. // Dep. VINITI № 628–В86 (1986), 51 p. Havryliv Ye., Makitra R., Pyrig Ya. // Dopovidi Akademiji Nauk Ukajiny (1991), № 2, p. p. 98–101 Hartmann P., Sellers H., Turnbull D. // J. Amer. Chem. Soc. (1947), vol. 69 (11), p. 2416 Gill G., Williams G. // J. Amer. Chem. Soc. (1965), vol. 12, p. p.7127 Denisov E. // Izv. Akademiji Nauk Ukajiny (1960), vol. 24, p. 812 Swain G., Stockmayer W., Clarke J. // J. Amer. Chem. Soc. (1950), vol. 72 (12), p. 9426

40


[15] Makitra R., Pyrig Ya., Havryliv E. // Dep. VINITI / М.: (1988), № 8418– В88, 11 p. [16] Foster W., Williams G. // J. Amer. Chem. Soc. (1962), p. 2862 [17] Walling C., Azar J. // J. Org. Chem. (1968), vol. 88 (10), p. 3885 [18] Rembaum A., Szwarc M. // J. Amer. Chem. Soc. (1954), vol. 76 (12), p. p. 5978–5981 [19] Levy M., Steinbergh M., Szwarc M. // J. Amer. Chem. Soc. (1954), vol. 76 (12), p. p. 5975–5978 [20] Lamb R., Pacifici J., Ayers P. // J. Amer. Chem. Soc. (1965), vol. 87 (17), p. p. 3928–3935 [21] Walling C., Waits H., Milovanovic J., Pappiaonnoy Ch. // J. Amer. Chem. Soc. (1970), vol. 92 (16), p. p. 4927–4932 [22] Smid J., Rembaum A., Szwarc M. // J. Amer. Chem. Soc. (1970), vol. 92 (16), p. p. 4927–4932 [23] Shatkina T., Lovtsova A., Mazel K., Peh T., Lippmaa E., Reutov O. // Reports of USSR Academy of Sciences (1977), 237, p. 368 [24] Tsvietkov N., Zhukovsky V., Pyrig Ya., Makitra R. // Kinetika and Catalysis (1979), vol. 20 (6), p. p. 1418–1422 [25] Huyser E., Van Scoy R. // J. Org. Chem. (1968), vol. 33, p. 3524 [26] Tsvietkov N., Zhukovsky Ya., Markovska R. // Ukr. Khim. Zhurn. (1976), vol. 42, p. 1294 [27] Palm V. Principles of Quantitative Theory of Organic Reactions // L. «Khimiya» (1977) [28] Vartapetyan O., Chaltykyan O., Khachitryan S. // Armenian Chem. J. (1972), vol. 25, p. 731 [29] Vartapetyan O., Khachitryan S. // Sci. Notes of Yerevan State University (1973), p. 50 [30] Kucher R., Havryliv Ye., Zhukovsky V., Makitra R., Pyrig Ya., Turovsky A. // Reports of USSR Academy of Sciences (1989), series “B” (11), p. p. 31–34 [31] Dutka V., Tsvietkov N., Markovska R. // Kinetika and Catalysis (1982), vol. 23 (5), p. p. 1071–1073

Chapter 3

DECOMPOSITION OF PERACIDS ESTERS Peracids esters can be decomposed in two ways – first is homolytical decomposition of –O–O– bond and the second one is simultaneous decomposition of –O–O– and –C–C– bonds, at that the second way usually predominates [1]:

Although the predominance of the reactions 1 or 2 depends on the radical nature R•, however the essential influence here has also both the nature of solvent, in which the decomposition proceeds, and possible presence of the reaction initiator, so–called active radical forming at the decomposition of more reactive compounds (induced way of reaction) or possible presence of catalyst of metal ions by variable valency. In R. E. Pincock [2] classical investigation concerning to tert–butylperformate (TBPF) thermolysis catalyzed by pyridine in 20 solvents at 90 0C it was determined that the rate of this process is increased in twice orders at the transition from non–polar n–heptane to nitrobenzene. However, the values for only some solvents are laid on the linear dependence of lgk on Kirkwood parameter; at that, it was determined the presence even of two linear dependencies, namely for polar solvents and for hydrocarbons (Figure 1).

42

Gennady E. Zaikov, Roman G. Makitra, Galina G. Midyana et al. O HC

C (CH3) 3

O O Table 1. Rate constants of the decomposition in the presence of pyridine in different solvents accordingly to [2] and parameters of Koppel–Palm equation for solvents

№

Solvent

k·103 mole–1·s–1

lgk

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18

Nitrobenzene Nitromethane Dichloromethane Chloroform Chlorobenzene p–Chlorotoluene Tetrahydrofurane Dioxane Benzene Toluene Cumene p–Xylene p–Cymene Dibutyl ether ССІ4 Cyclohexene Cyclohexane n–Heptane

212 167 69 45,2 40,9 39,7 30,8 23,0 21,5 17,7 15,1 13,7 11,7 7,01 6,08 3,79 2,11 1,52

2,3263 2,2227 1,8388 1,6551 1,6117 1,5988 1,4886 1,3617 1,3324 1,2480 1,1790 1,1367 1,0682 0,8457 0,7839 0,5786 0,3222 0,1818

2

1 1

0,4147 0,3126 0,3398 0,3357 0,3968 0,3954 0,3292 0,3385 0,3852 0,3829 0,3806 0,3822 0,3791 0,3239 0,3615 0,3531 0,3408 0,3164

n2 1 n2 1

В

Е***

0,4788 0,4808 0,4217 0,3587 0,3775 0,3860 0,4049 0,2231 0,2306 0,2395 0,2396 0,2292 0,2277 0,2893 0,2261 0,2243 0,2027 0,1906

67 65 23 14 38 38* 287 237 48 58 56 68 60** 285 0 97 0 0

0 5,1 2,7 3,28 0 (0) 0 4,2 2,1 1,3 (1) (1) (1) 0 0 (0) 0 0

* – the value was took for chlorobenzene; ** – the value was took for tert–butylbenzene; *** – values accordingly to [3].

Author does not discuss the last possibility. For low–polarity solvents in [2] the linear dependence of lgk on medium polarizability is also notified. It was determined also the connection between the rate constants of TBPF decomposition in some solvents and rates of amines quaternization in the same media. Author supposes that the decomposition has an ionic character due to catalytic influence of the pyridine on hydrogen atom of formyl group in accordance with the following scheme:


43

Figure 1. Dependence of the tert–butylperformate decomposition rate on polarity accordingly to [2] (1); alternative dependence for hydrocarbons (2).

However, an independence of the process rate on concentration of the substrate disagrees with this assumption. In a number of the solvents (for example, ethers) other chemical mechanism of the process is possible, namely with the formation of an oxygen that is more typical for induced radical decomposition of the peroxy compounds. Data of the work [2] have been quantitatively generalized by V. A. Palm and I. A. Koppel [3], who confirmed that the rate of this reaction is determined accordingly to assumptions of author [4] by non–specific solvation. However, the achieved multiple coefficient of correlation for this dependence is sufficiently low R = 0,895. It was determined by us later in work [5], that the all data of work [2] for 18 solvents (after the exclusion of styrene and diphenylmethane) are ideally generalized by four–parametric LFE equation

lg k 10 3

3,429 8,738

n2 1 4,247 2 n2 1

1 0,00078B 0,171E 1 (1)

with R = 0,994 and S = 0,042 and pair coefficients of correlation r01 = 0,275; r02 = 0,862; r03 = 0,059; r04 = 0,484. In this equation: n is the light refraction index of


44

the solvents, ε is their permittivity, B and E are the basicity and the electrophilicity accordingly to Palm [3]. At alternating exclusion of separate parameters accordingly to [6] the values of multiple coefficients of correlation are respectively decreased to 0,909; 0,716; 0,987; 0,900. Thus, both the value of corresponding pair coefficient and the treatment of results in accordance with [6] indicate on the practical insignificance of the basicity parameter. The decomposition process of perester O HC C (CH3) 3 O O with satisfactory accuracy can be described by three– parametric equation:

lg k 103

3,056 7,824

n2 1 4,348 2 n2 1

1 0,165E 1

(2)

with R = 0,987 and S = 0,105. Investigations row was dedicated to studies of solvents influence on the tert– butylperbenzoate (TBPB) decomposition rate. For this compound the catalysis by bases accordingly to proposed in [2] scheme is impossible in consequence of the absence of formyl hydrogen atom while the decomposition process should be characterized by homolytical character. The decomposition of tert– butylperbenzoate was studied at 119,4 0C in a number of solvents [7]. It was determined, whereas in aliphatic media the rate constants are visibly differential, that in 8 aromatic hydrocarbons, halogen hydrocarbons, methyl benzoate they are differed only in 1,5 time and are decreased with the nucleophylicity increase. These data upon total rate constants by first order k h–1 can be generalized via three–parametric equation, at that the medium polarity increases the decomposition rate and its ability to specific solvation, on the contrary, decreases this decomposition rate, probably in consequence of the relative stabilization of the perester:

lg k

1,105

4,66 0,41 f

0,914 0,084 10 3 B 1,83 0,18 10 2 ET (3)

N = 8; R = 0,993; s = ± 0,736·10–2.

Table 2. Tert–butylperbenzoate decomposition rate constants at 110 0С and 119,4 0С and the parameters of solvents* №

Solvent

Ref.

n2 1 n2 1

2

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

Chlorobenzene n–Butanol Dibutyl ether Acetic acid Benzene Xylene n–Chlorotoluene Diphenyl ether Butyl acetate Cumene Undecane Brombenzene Ethylbenzene t–Butyl benzene Methyl benzoate

7 7 7 7 7 7 7 10 7 12 12 7 7 7 7

0,3064 0,2421 0,2421 0,2270 0,2947 0,2968 0,3037 0,3340 0,2393 0,2898 0,2536 0,3232 0,2921 0,2905 0,3025

0,377 0,457 0,289 0,387 0,231 0,256 0,386 0,321 0,364 0,239 0,203 0,373 0,242 0,239 0,394

1 1

δ2

В

ЕТ

k·104 (110 0)

k·104 (119,4 0)

lgk (110 0)

lgk (119,4 0)

385,9 553,9 250,4 427,1 349,8 327,2 388,6 358,8 302,3 319,1 250,0 422,4 325,7 289,0 408,8

38 231 285 139 48 68 41 123 158 56 0 40 58 60 160

157,0 210,2 139,8 214,4 144,4 143,6 161,6 147,8 155,8 141,6 129,4 157,0 142,3 141,1 164,2

0,384 7,440 1,800 1,140 0,350 0,380** 0,342 0,228 1,056 0,396 0,425 –– –– –– ––

1,115 18,400 3,793 9,058 1,041 1,092 1,010 0,900 2,676 –– 4,170 1,325 1,065 1,032 0,784

–4,4157 –3,1284 –3,7447 –3,9431 –4,4559 –4,4202 –4,4660 –4,6421 –3,9763 –4,4023 –4,3716 –– –– –– ––

–3,9527 –2,7352 –3,4210 –3,0430 –3,3825 –3,9618 –3,9957 –4,0458 –3,5725 –– –3,3799 –3,8778 –3,9727 –3,9863 –4,1073

parameters of the solvents δ2 and ЕT in kJ/mole in accordance with [13]. starting value К119,4 = 1,10 10–4 has been recalculated on temperature 110 0С on the basis of Еact. = 33,8 ccal/mole.

46


Essentially less legible results have been obtained at the attempt to generalize the data from monograph [8] on the basis of decomposition rate of the same compound in 8 both aliphatic and aromatic solvents – obviously because the results of different authors were used in it. The best results have been obtained by us in [9] at generalization of data for 15 solvents from works [7, 10, 12] on the basis of tert–butylperbenzoate decomposition rate at 110 0C and 119,4 0C in 15 solvents (Table 2). The neutralization of the induced decomposition in those works was realized by diphenyl ether addition. Data presented in Table 2 with a high authenticity degree are generalized via five–parametric LFE equation taking into account the solvation parameters of the Koppel–Palm equation [3] and also the cohesion energy density upon Hildebrand δ2 in view of possible influence of the cell effect on the decomposition process. The ET parameter upon Reichardt the proportionality of which to E parameter proved in [14] was used as the electrophilicity characteristic with the aim of comparison in [9], since in the work [2] the possibility of the effect on the decomposition of the Kosower’s parameter Z = ET is supposed. There were obtained the following expressions: A) for 110 0C

lg k 104

1,406 10,566 f n

0,355 f

0,0054

2

0,00218B 0,0135ET (4)

N = 11, r1 =0,765,

R = 0,966, r2 = 0,563, r5 = 0,646

S = 0,055 r3 = 0,494,

r4 = 0,798,

B) for 119,4 0C

lg k 104

1,174 10,931 f n 0,555 f

0,0032

2

0,00057 B 0,00393ET (5)

N = 13, r1 =0,843,

R = 0,954, r2 = 0,342, r5 = 0,653

S = 0,167 r3 = 0,354,

r4 = 0,523,


47

Thus, the conclusion of works [2, 3, 15] about determining effect of the medium polarizability on the tert–butylperbenzoate decomposition rate is confirmed, however, the relatively low value of pair coefficient of correlation upon this parameter r = 0,764 points out the significant effect of others factors upon the process rate. At the consideration of equation for 119,4 0C the byturn testing of their significance permits to exclude the polarity factor:

lg k

f n,

2

, B, ET ,

and

R = 0,996

The process can be described with the acceptable exactness by four– or even three–parametric equations:

lg k 10 4

1,484 10,375 f n

2

0,00548

0,00227 B 0,012ET

(6)

R = 0,996,

lg k 10 4 R = 0,961,

S = 0,054

3,370 6,350 f n

2

0,00197

0,00220 B

(7)

S = 0,146

At the same time, the exclusion of other solvation factors decreases the value more substantially: f(n) till 0,87 and δ2 or B till 0,92. General dependencies are the same for 119,4 0C: the polarity of medium does not influence on the lgk value, at its exclusion R is decreased only from 0,954 till 0,953. The effect of electrophilic solvation is also of little significance, the exclusion of which leads to three–parametric equation with R = 0,948:

lg k 10 4

1,057 11,216 f n

0,00345

2

0,00044 B 0,004812 ET (8)

R = 0,953

lg k 10 4 R = 0,948

S = 0,158

1,795 9,655 f n S = 0,166

0,00217

2

0,00041B

(9)

48

Gennady E. Zaikov, Roman G. Makitra, Galina G. Midyana et al. An influence of the basicity parameter is also relatively of little significance:

lg k 10 4

1,620 10,224 f n

2

0,00224

(10)

R = 0,146 At the same time, an elimination from the calculations of energy outlay for the loculus into reactive medium formation

2

destroys the correlation: R =

0,854. The connection between lgkcalc. (calculated upon three–parametric equations taking into account n, B and δ2) and lgkexp. is represented on Figures 2 and 3 for temperatures 110 0C and 119,4 0C. The points numbering corresponds to Table 2. At the comparison of calculated data of obtained equations with the data for tert–butylperformate (TBPF) thermolysis first of all it is necessary to draw attention on appreciable influence of the medium basicity with increasing of which the decomposition rate is increased. Thereby, the presumption stated in [4] as to catalysis of peresters decomposition by bases solvating their molecule and favorable to this reaction as a result of electronic shifts, is confirmed. However, since the formyl hydrogen is absent in a case of TBPB that is why it is necessary to consider the solvation of acyl fragment more probable. Indeed, amongst studied solvents there are not strong bases as same as pyridine.

Figure 2. Dependence of lgkcalc. on lgkexp. for tert–butylperbenzoate decomposition at 110 0 С.


49

Figure 3. Dependence of lgkcalc. on lgkexp. for tert–butylperbenzoate decomposition at 119,40С.

Table 3. Constants rate of the t–butyl–o–thiophenylperbenzoate decomposition [15] № 1 2 3 4 5 6 7 8 9 10 11

Solvent Cyclohexane Tetrahydrofurane Chlorbenzene Nitrobenzene Acetone Tert–butanol Acetonitrile DMSO Isopropyl alcohol Ethanol Methanol

k·104 , s–1 0,0686 0,300 0,490 0,880 1,220 3,240 5,440 6,020 7,250 16,500 47,500

ET 31,2 37,4 37,5 42,0 42,2 43,9 46,0 45,0 48,6 51,9 55,5

Unlike to TBPF, the medium polarizability increasing here not increases decomposition of TBPB, but decreases it, that is possibly connected with aromatic character of TBPB and due to this fact stabilizing solvation of starting molecule prevails. Specified though insignificant influence of

the the the the


50

cohesion energy density factor on the decomposition rate caused by fact, that the diphenyl oxide is weaker inhibitor than the pyridine, and the induced decomposition of TBPB can also partially proceeds as a consequence of this fact. Insignificance of the medium polarity parameters and its electrophilicity points out the less polar character of the activated state of TBPB in comparison with TBPF or, that is more probably, with complex “TBPF–pyridine”. Higher decomposition rates of “TBPF–pyridine” complex in comparison with the TBPB decomposition rate are in good agreement with the above–said assumption. Thus, for example, for the reaction in benzene the decomposition constant rate for TBPF at 90 0C is equal to 21,5·10–3 l/mole·s, and the constant rate of the first order for TBPB at 110 0C is equal only to 0,35·10–4 s–1. Decomposition of tert–butyl ether of o–thiophenylperbenzoic acid inhibited by styrene additive has been investigated in work [15] at 40 0C. It has been notified by authors the presence of linearity between lgk of decomposition in alcohols, acetone, DMSO, acetonitrile and Kosower Z parameter. On the basis of registered rate propagation with Z increasing and also on the basis of data concerning to the salt effect and the influence of substituents, authors assume, that the first stage of the homolytic decomposition is the formation of polar transition state:

However, a series of the experimental values are disagreed with this dependence. At the same time, the generalization of data from [15] (Table 3) by means of five–parametric equation leads to the equation, which with the sufficiently trustworthiness of connection covers the results for the all 11 investigated solvents [9].

lg k

8,421 0,174

n2 1 1 0,0903 0,0006 B 0,017 ET 0,00263 2 2 1 n 1

(11)

2

Decomposition of Peracids Esters N = 11

R = 0,176

r1 = 0,506 r2 = 0,769 r5 = 0,930

51

S = 0,989 r3 = 0,560

r4

=

0,985

Practically, the value lgk is determined by the influence of only one factor, namely by electrophilic solvation ET upon Reichardt (Figure 4). Relatively low values of the pair coefficients of correlation with others factors do not permit to make some suppositions in view of their insignificance. At the non–specific solvation factors exclusion from the calculation, the general coefficient of correlation is remained as unaltered: lgk = f(B, ET, δ2), R = 0,989; whereas the electrophilic solvation parameter exclusion decreases the multiple coefficient of correlation to 0,973. Taking into account the nucleophilic solvation and cohesion energy density of medium only extremely lightly corrects the dependence between lgk and ET. However, it is necessary to notify the high degree of connection between lgk and δ2 and possible acceptable description of medium effects by combination of parameters δ2 and B: lgk = f(B, δ2), R = 0,948. Evidently, such peculiarities are result of the distinctive selection of the solvents, in preference strong polar ones.

Figure 4. Dependence of lgk. on ET [9] for the t–butyl–o–thiophenylperbenzoate decomposition.

52

Gennady E. Zaikov, Roman G. Makitra, Galina G. Midyana et al. Table 4. Regrouping of CPB in solvents with different dielectric transmissivity ( ) Solvent Acetic acid Methanol Ethanol n–Butanol tert– Butanol Furfurol Nitromethane Nitrobenzene Cyclohexanone

(25 0С) 6,19 32,63 24,44 17,1 10,9 41,7 38,6 34,82 18,3

k·105, s–1 (50 0С) 131,0 39,4 17,8 9,4 1,9 4,55 4,1 1,25 0,44

Еact, ccal/mole 20,7 21,5 22,2 21,3 21,2 22,6 22,4 22,6 22,0

Temperature, 0 С 30–60 20–50 40–60 40–70 50–70 50–80 50–80 60–80 60–90

Determinative role of the electrophilic solvation, contributory (in accordance with the [15]) to the appearance of positive charge on the Sulfur atom and also the independence of the process rate on polarity of medium (r = 0,769) point out the abruptly different decomposition mechanism in considered two cases. General for them is only the influence of nucleophilic solvation contributing to polarization of –O–O– bond and medium self–association effect. So abrupt difference in responsivity to solvation effects of not too different upon structure substrates permits in similar reaction of the perester thermolysis to make the observations on the one hand about the advisability of following widening of such investigations and from the other hand about the effectiveness of the LFE methods application for their studies. Thermolysis of cumylperbenzoate (CPB) at 60 – 80 0C in the presence of acid catalysts proceeds, however, not via the peroxy group decomposition, but in accordance with the regrouping mechanism as follows:


53

In accordance with [16] the reaction rate is increased with the medium polarity increasing, however a series of exceptions is observed (see Table 4). At the same time, the generalization of these data upon sixth–parametric equation which takes into account not only the solvation parameters δ2 but also the molar volume of solvents, permits to obtain the equation with R = 0,999, and consecutive exclusion of little significance parameters permits to determine that the decomposition rate depends only on two parameters ε and ET of solvents:

lg k

1,073

R = 0,978,

8,94 2,11 f

0,126 0,012 ET

(12)

S = 0,17

Thus, the opinion of authors [16] about favourable for the reaction role of medium polarity mismatches to the reality – although this parameter is significant, however at its increase the regrouping process become slower; here defining factor is the electrophilic solvation of perester, probably upon carboxyl group. The value of paired correlation coefficient with this parameter r = 0,920 and f(ε) has only the certain corrective influence. Let us notify, that the insignificance of δ2 (that is the cell effect absence) confirms the heterolytic, but not homolytic, reaction path. It is known a series of other works dedicated to the kinetics of peracids esters decomposition, however, as a rule, the number of investigated solvents 6–8 it’s not enough for reliable statistical treatment of results via multiparametric LFE equations. Thus, the generalization of data concerning to the constants rates of peresters decomposition via LFE equations with the following determination of significance of their separate terms can give the certain guidelines as to predominant chemism of the process.

REFERENCES [1] [2] [3]

S. Baj, M. Dawid // Wiadom.Chemiczne (2000), vol. 54 (11–12), p. 1023– 1061. R. E. Pincock // J. Am. Chem. Soc., (1964), vol. 86 (9), p. 1820–1826. I. A. Koppel, V. A. Palm // In “Advances in Linear Free Energy Relationships” / Ed. N. B. Chapman and J. Shorter, Pergamon Press, London – New York (1972), p. 203.

54 [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16]

Gennady E. Zaikov, Roman G. Makitra, Galina G. Midyana et al. V. S. Dutka, N. S. Tsvietkov, R. F. Markovska // Kinetika and Catalysis (1982), vol. 23, issue 5, p. 1071–1073. N. S. Tsvietkov, V. Ya. Zhukovsky, R. G. Makitra, Ya. N. Pyrig // Reakts. Sposobn. Org. Soed. (1979), vol. 16 (2), p. 273. N. B. Chapman, M. R. J. Dack, D. J. Newman, J. Shorter, R. Wilkinson // J. Chem. Soc. (1974), Perkin Trans. 2, p. 962. A. T. Blomquist, A. F. Ferris // J. Amer. Chem. Soc. (1951), vol. 73, p. 3412. V. L. Antonovsky // Organic Initiators (1972), p. 242. E. M. Havryliv, R. G. Makitra, Ya. M. Pyrig // Reakts. Sposobn. Org. Soed., (1987), vol. 24 (1), p. 5. A. T. Blomquist, T. A. Bernstein // J. Amer. Chem. Soc. (1953), vol. 73, p. 5346. H. Hock, F. Depke // Chem. Ber., (1951), vol. 84, p. 356. V. L. Antonovsky, L. D. Bezborodova, M. E. Yaselman // Zh. Phys. Chem. (1969), vol. 43, p. 2281. R. G. Makitra, Ya. M. Pyrig, R. V. Kyvelyuk // Dep. VINITI № 628–V86 (1986). T. M. Krygowsky, E. Milczarek, P. K. Wrona // J. Chem. Soc. (1980), Perkin Trans. Part 2, p. 1563. D. L. Tuleen, W. G. Bentradem J. P. Martin // J. Amer. Chem. Soc. (1963), vol. 85, p. 1938. N. V. Yablokova, V. A. Yablokov, А. V. Badyanova // Kinetika and Catalysis (1967), vol. 8 (1), p. 49.

Chapter 4

DECOMPOSITION OF THE HYDROPEROXIDES AND REACTIONS OF THE PHENOXY RADICALS The hydroperoxides decomposition has been investigated in detail since they have a much wide technological application. First of all, here it is necessary to indicate on the cumene hydroperoxide (isopropylbenzene), which is an intermediate product at the obtaining of phenol via cumene method; this method for a long time was one among the main methods for obtaining of this important product for the chemical industry. It was developed the technique of obtaining in the same way also for other aromatic oxy–compounds. And a series of hydroperoxides, for a example hydroperoxide of 1, 1–diphenylethane, has applied as effective initiators of polymerization. As same as in a case of peroxides, also the connection between the rates of hydroperoxides decomposition and the properties of the solvents, in which the reaction proceeds, can be adequately described in a number of cases by means of the multi–parametric equations. As an example, the data concerning to the hydroperoxide of tetralin and Lithium salt of tert–butylhydroperoxide decompositions can be presented. An essential influence of the electrophilic solvation on the rate of the hydroperoxide decomposition can be noted on the basis of data [1]. Authors studied the rate of hydroperoxide of tetraline decomposition in 9 aromatic solvents in the presence of inhibitor N–phenyl–β–naphthylamine at 90 0C. Since about from 2,5 till 19 molecules of hydroperoxide are decomposed per one molecule of the consumed amine, authors conclude about the predominantly catalysing role of the amine forming initially with the hydroperoxide the complex with the contact ion pair. The reaction is subordinated to the regularities of the

56


first order reaction; however, since in the [1] the corresponding constants rates were determined not for the all solvents, only the decomposition rates WROOH·106 mole/l s (see Table 1) have been taken by us as a corrected value. Authors note, that the decomposition rate increases with the medium polarity, however, clear dependence between lgW and ε is not observed. At the generalization of data from Table 1 accordingly to six–parametric equation it was obtained the expression with R = 0,922. An exclusion from the consideration the most diverting data for quinoline permits to obtain the equation (1) with the excellent correlation degree:

lg W 12,730 25,217 5,125 f n 2 0,185 0,048 ET

2,653 2,091

8,153 2,360 f 2

1,758 0,393 10 3 B

0,014 0,002 10 3 VM (1)

R = 0,992

s

r01 = 0,229; r02 = 0,654; r06 = 0,447

0,039 r03 = 0,154;

lg W 14,690 18,620 3,187 f n 2

r04 = 0,589;

13,346 2,088 f

r05 = 0,482;

0,322 0,062 ET

3

0,013 0,003 10 VM (2) R = 0,965

s

0,080

Unlike to below considered case as to Lithium salt of hydroperoxide decomposition, here is insignificant the factor of cohesion energy density and significant is molar volume of the solvent with the “minus” sign: the it more (that is, the more sizes of molecule), the less for it the possibility to solvate the peroxy group edged by voluminous structures of tetralin and naphthylamine. It’s no wondering the discordance with general dependence of data upon decomposition rates in quinoline – observed decomposition rate in it almost in twice higher than the calculated one as a result of, probably, parallel proceeding side reaction of the quinoline oxidation into its N–oxide or, possibly itself quinoline being by amine has catalytic impact.

Decomposition of the Hydroperoxides and Reactions…

57

Table 1. Logarithms of experimental rate constants of the first order decomposition for tetralin hydroperoxide lgk·10–6s–1 (in accordance with [1]) and calculated values lgk accordingly to equation (2) № 1 2 3 4 5 6 7 8 9

Solvent Cumene Tetralin n–Decane Decalin Anisole Acetophenone Nitrobenzene Chlorobenzene Quinoline*

lgkexp. –0,1192 –0,1135 0,2304 0,3010 0,2041 0,3617 0,6532 0,6990 0,7482

lgkcalc. –0,2001 –0,0700 0,2557 0,2527 0,3380 0,4237 0,5539 0,6629 –0,4067

lgk –0,0809 0,0435 0,0252 –0,0483 0,1339 0,0620 –0,0993 –0,0361 –1,1549

Note: – * data for quinoline were not taken into account at the calculation accordingly to equation (2).

Table 2. Logarithms of experimental rate constants of the first order decomposition for Lithium tert–butylhydroperoxide lgk·10–6s–1 (in accordance with [2]) and calculated values lgk accordingly to equation (4) №

Solvent

lgkexp.

lgkcalc.

1 2 3 4 5 6 7 8

Benzene Cumene Ethylbenzene Toluene p–Xylene Mesitylene n–Butylbenzene tert–Butylbenzene

0,8633 0,9445 0,9823 1,0000 1,0682 1,1614 0,9731 0,9191

0,8652 0,9328 0,9841 1,0083 1,0699 1,1592 0,9560 0,9364

lgk 0,0019 –0,0117 0,0019 0,0083 0,0017 –0,0022 –0,0171 0,0173

Similar influence of the solvation factors was determined at the generalization of data from the work [2] upon kinetics of Lithium tert–butylhydroperoxide decomposition in 8 solvents at 80 0C (see Table 2). Authors inform that whereas at the decomposition of this compound in low– polarity media the rate is determined by non–specific solvation, that in aromatic hydrocarbons defining is the influence of the specific solvation; the last fact is confirmed by high correlation coefficient r = 0,990 lgk with the basicity parameter


58

B by Palm. Practically the same value of r is observed in a case of the complications steric parameter ES of the Hammet’s equation. However, in both cases the all needed characteristics were known only for 5–6 solvents. That is why in presented work it was done the re–calculation of values lgk from the work [2] in accordance with the Koppel–Palm equation. At that, it was obtained the equation (3):

lg k 10,317

9,253 5,141 f n 2

0,293 0,046 ET

3,416 0,316

9,246 1,400 f 2

0,977 2,393 10 3 B

0,147 0,339 10 3 VM (3)

R = 0,998

s

r01 = 0,352; r02 = 0,377; r06 = 0,230

0,006 r03 = 0,942;

r04 = 0,899;

r05 = 0,026;

Although for the hydrocarbons №№ 1–6 really the linear increase of the rate with their basicity increasing is observed, however, at the introduction into the ring of more volumetric groups, the rate is essentially decreased that leads to decreasing the R, and, that is the most important to the sign change at this parameter, the influence of which on lgk finally is turned out of a little significance; the rate of substrate decomposition is determined not by the basicity, but by the combined influence of electrophilic solvation and cohesion energy density of medium at the definite correcting influence of the polarity:

lg k

6,741

R = 0,993

9,316 1,195 f

s

0,260 0,013 ET

9,316 1,195

2

(4)

0,011

In Table 2 there are values of lgk calculated in accordance with the equation (4) and their deviation with the experiment. Obviously, the decomposition rate is decreased at the electrophilic solvation of oxygen atoms of ~OOH group. At the same time, since the investigation object is the salt of peroxide, supposed by authors of work [2] nucleophilic interaction is improbably. Comparison of the results permits to conclude that the processes of peroxy compounds decomposition depend on summary influence both of the cohesion


59

energy density of the solvents and also their solvation ability, at that the measure of significance of separate factors depends on the chemical structure of the substrate. Electrophilic solvation of the peroxy group can both favorite and hinder the decomposition process. As it was above–mentioned, the multi–parametric equations were turned out also suitable for generalization of data concerning to the rates of phenoxy radicals recombination (their “death”) including the polyphenylphenoxyloles:

2 RO

2 k1 2k 1

(5)

D

Polyparametric equation is also suitable for the description of the solvent influence on the rate of reversible dimerization reaction of 2,4,6– triphenylphenoxy radicals and decomposition of dimmers [3] and also on the value of the equilibrium constant “K” of this reaction. Table 3. Logarithms of the dimerization constants rate (k∙10–7 mole/l∙sec) and dissociation (k–1∙10–3sec–1) for triphenylphenoxyl radicals accordingly to [4] in solvents and also the parameters of solvents № 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17

Solvent Hexane ССl4 Toluene Benzene Dioxane Chlorobenzene Chloroform Pyridine Dimethylformamide tert–Butanol Acetonitryle Isopropanol n–Butanol n–Propanol Ethanol Methanol Ethyleneglycol

lg k1 1.7324 1.2430 0.8451 0.8129 0.2788 0.0414 –0.3010 –0.6576 –0.2228 0.2430 0.4150 0.7404 0.7924 0.9085 0.9345 0.7782 0.1761

lg k–1 0.2041 0.2430 0.3222 0.4150 0.4771 0.3010 0.0414 –0.2696 0.1461 –0.2798 0.4624 0.2175 0.3979 0.5052 0.4150 0.6233 –0.3468

lg K∙105 –0.5229 0.0000 0.4771 0.6021 1.2041 1.2553 1.3424 1.3979 1.1761 0.4771 1.0414 0.4771 0.6021 0.6021 0.4771 0.8451 0.4771

60


Solvents: 1 – hexane; 2 – CCl4; 3 – toluene; 4 – benzene; 5 – dioxane; 6 – chlorobenzene; 7 – chloroform; 8 – pyridine; 9 – dimethylformamide; 10 – tert–butanol; 11 – acetonitrile; 12 – isopropanol; 13 – n–butanol; 14 – propanol; 15 – ethanol; 16 – methanol; 17 – ethylenglycol. Figure 1. Dependence of the rate constant logarithm for the reaction of 2,4,6– triphenylphenoxy radicals [6] dimerization on Reichardt’s electrophilicity parameter ET [4].

Authors of the work [3] at the attempt to correlate the value lgk1 with the Raichardt’s electrophilicity parameter ET [4] including into itself partially also the factors of non–specific solvation [5] determined the presence of V–shaped like dependence (see Figure 1). Hydrocarbons and halogen hydrocarbons are located on the same branch of the dependence where the rate is decreased with the ET increasing; in polar solvents (namely, alcohols, acetone, and dimethylformamide) the dimerization rate is increased with the ET increasing. Minimal rate of the process is observed in pyridine; some solvents (methanol, ethanol, glycol) are not located on the proposed dependence at all. Authors [6] explain these peculiarities by possible resolvation, but the character of the radical solvation by donor pyridine and acceptor chloroform should be different, although they are located on the same branch of dependence. An attempt to generalize the all body of data [6] accordingly to five– parametric linear equation including besides the polarity, polarizability, basicity and electrophilicity parameters also the cohesion energy density:


lg k

a0

a1 f (n 2 ) a2 f

a3 B a4 ET

a5

61 (6)

2

leads to low general correlation coefficient R = 0,847. However, an exclusion from the consideration only three points, namely chloroform, dioxane and tert– butanol permits to increase the R value respectively to 0,942, 0,978 and 0,981; that is, to get over into the field of good correlation. It was obtained the equation:

lg k 10

7

4,693 8,660 f n 2

0,991 10 3 B

4,294 f

0,073ET 3,562

2

(7)

R = 0,981

s

r01 = 0,411; r02 = 0,562;

0,151 r03 = 0,267;

r04 = 0,682;

r05 = 0,777

Negative signs of the regression coefficients at all parameters except for the electrophility, show, that both non–specific and nucleophilic solvation stabilize the radical RO∙ and hinder to it dimerization reaction; at the same time, the electrophilic solvation favorites to the dimerization that is corresponds to the right branch of the V–shape like dependence lgk1 on ET [6]. The presence of such V– shape like dependence evidently is caused by the summation of two opposite tendencies of the solvent influence. By turn exclusion of the separate parameters in accordance with [7] leads to the five four–parametric equations with R = 0,921; 0,910; 0,960; 0,973 and 0,932 respectively. Thus, the least significant are parameters of the basicity B and the cohesion energy density δ2. At their exclusion the following equations were obtained:

lg k 10

7

5,111 9,404 f n

5,446 f

3,295

2

0,075E (8)

R = 0,973

lg k 10

7

R = 0,954

s

0,170

5,478 11,183 f n

s

0,209

and

5,838 f

0,075E

(9)

62


Five–parametric equation is suitable also for description of the solvent influence on the reverse reaction of the forming peroxide dissociation (lgk–1) and, respectively, on the constant of equilibrium of reaction lgK = lgk1/k–1. However, the correlation here is worse possibly due to the less accuracy of the value k–1 determination. The following equations have been obtained for 13 points:

lg k 10

3

0,234 0,197 f n

0,934 f

1,253

2

0,00145B 0,0326E (10)

R = 0,939

s

lg K 105

3,397 10,02 f n

0,097

and

4,355 f

2,226

2

0,0001B 0,0027 E (11)

R = 0,911

s

0,271

For the first equation insignificant is polarizability, for the second one is the basicity. Finally, the dissociation process is satisfactory described by the following equations:

lg k 10

3

0,179 0,956 f

1,303

2

0,00147 B 0,0337 E (12)

R = 0,939

lg K 105

s

0,097

3,438 10,094 f n

and

4,468 f

2,251

2

0,0025E (13)

R = 0,911

s

0,271

Kinetics of this process has been studied for other phenoxyl radicals (I. 4–Ph– PhO•; II. 2–Ph–PhO•; III. 2,4–Ph2–PhO•; IV. 2,6–Ph2–PhO•; V. 2,6–(tert– Bu)2PhO•) in a series of the solvents in works [6, 8, 9]. However, the attempts of authors to determine the one–parametric dependence on parameter of the solvents ET [10] were not successful: in some cases it was observed the V–shaped like dependence of lgk on ET (recombination of 2,4,6–triphenylphenoxyl, 4–


63

phenylphenoxyl), and in others cases (recombination of 2,6–di–tert– butylphenoxyl) on the whole is impossibly to determine the clear dependence of this parameter. Authors explain the presence of such V–shaped like dependence by the influence of specific solvation of radicals which decreases their ability to the recombination in consequence of ∆H≠ of reaction increasing; however, at the same time, at the radical desolvation ∆S≠ is increased, and at great values of ET parameter this effect becomes by predominant, as a consequence of which the rate of recombination reaction is increased again. In all cases for 12 points the general correlation coefficient is low (R = 0,82 – 0,92), however, an exclusion from the consideration of one or more the most deviative points, for example: 7 – СНСl3 for k1, 2.7 – ССl4, СНСl3 for k2 and etc., increases the value R till acceptable values 0,95–0,98 [12]. In most cases the non–specific solvation of radicals caused by polarity and polarizability of the solvents mainly contributes in this process. The influence of specific solvation and self–association of solvents is less essential (with the exception of radical (II), where the rate of dimerization is determined by electrophilic solvation). Negative signs at regression coefficients point out the recombination rate decreasing both at specific and at non–specific solvation of radicals that is in good agreement with the conclusions of work [9]; besides, the influence of non–specific solvation is more essential than the specific one. Solvation of radial increases of its stability and the destruction of the solvation sphere requires the energy expenses. This leads to decreasing the recombination rate. At the same time, an increase of the recombination rate in strong associative solvents, especially in alcohols, is connected not so much with factor ∆S# increasing as with the energy advantage obtained at the self–association of the releasing molecules of solvent. The same results have been obtained under consideration of data concerning to the reverse recombination of 2–(4’–diphenylaminophenyl)indadione–1,3–yle radical (а0 = 5,093; a1 = –14,417; a2 = –2,205; a3 = –0,00081; a4 = –0,0012; a5 = 4,410. R = 0,953; s = 0,214). Authors [11] explain the V–shaped like dependence of lgk7 on ET by fact that as same in a case of arylphenoxyl radicals, the recombination of radicals is accompanied by the dissociation of their solvate complexes needing the energy consumption. An increasing of the recombination rate starting from ET = 39 is admittedly connected with the specific salvation by these solvents which is favorable for the achievement of needed orientation of radicals in solvation net. However, the results of calculations for the rates constants k7 accordingly to above proposed equation show, that both specific and non–specific solvation of radical slows down the recombination, and the self– association of solvents (term δ2) accelerates of it [12].


64

Logarithms of The Rates Constants for Phenoxyl Radicals Decay in Different Solvents (Accordingly To [9, 11]) And Characteristics Of The Solvents № 1 2 3 4 5 6 7 8 9 10 11 12

Solvent Hexane Carbon tetrachloride Toluene Benzene Tetrahydrofurane Chlorobenzene Chloroform Methylene chloride Acetone Acetonitrile Acetic acid Formic acid

lgk1+8 1,7404 1,1461 0,8451 0,8129 0,7782 0,5051 0,3010 0,5798 0,9031 1,000 0,5563 0,6532

lgk2+8 1,2553 0,7404 0,7782 0,6628 0,4771 0,6990 0,4914 0,6990 0,5911 1,0792 0,1761 0

lgk3+8 1,2553 0,4914 0,5315 0,4771 0,3424 0,3424 0,1461 0,3424 0,3802 0,7404 0,3010 0,4771

lgk4+8 0,9031 0,3617 0,3979 0,3010 0,4771 0,1139 0,4437 0,0414 0,5798 0,8451 0,3424 0,4771

lgk5+8 0,9294 0,5441 0,7782 0,5911 0,2788 0,5441 0,6990 0,7782 0,5315 0,7404 0,4150 0,1461

lgk6+8 1,1139 0,8513 1,7404 1,3802 1,4771 1,3617 1,8195 1,9031 1,8129 1,9868 2,2304 –

lg[k·1010] = 5,093 – 14,417f(n2) + 2,205f(ε) – 0,0012В + 4,410ET – 0,81·10– 3 2 δ (14) R = 0,953; s = ±0,097 Of course, here it can be taken into account both the energetic advantage of the remissive molecules of the solvent at the self–association and the “cage” effect and also the influence of the entropy factor. Interestingly, that the electrophilic solvation of radicals practically does not proceed (insignificance of the term with E parameter), a little influence has also the nucleophilic solvation. The main influence on the stabilization of radical has its non–specific solvation connected with the polarisability of the solvent.

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

Ivanov S., Katieva Y. // Kintika and Catalysis (1983), vol. 24, p. 277 Shekunova V., Sokolov N., Alexandrov Yu. // Journal of Organic Chemistry (1984), vol. 54, p. 1163 Tsvietkov N., Zhukovsky V., Makitra R., Pyrig Ya. // Reaktsionnaya Sposobnost’ Organicheskikh Soyedienienij (1978), vol. 15, p. 68 Lievin P., Khudyakov I., Khardina I., Rygalov L. // Doklady Akademiji Nauk USSR (1977), vol. 11, p. 2605

Decomposition of the Hydroperoxides and Reactions… [5]

65

Reichardt Ch., Dimroth K. // Losungsmittel und Empiriasche Parameter zur Charakterisierung Ihrer Polaritat / In “Fortschritte der Chem. Forschung” (1968), vol. 11 (1), p. 556 [6] Koppel I., Payu A. // Reaktsionnaya Sposobnost’ Organicheskikh Soyedienienij (1974), vol. 11, p. 139 [7] Chapman N., Dack M., Newman D., Shorter J., Wilkinson R. // J. Chem. Soc. (1974), Perkin Trans. 2, p. 962 [8] Khudyakov I., de Young K., Lievin P., Kuzmin V. // Doklady Akademiji Nauk USSR (1977), vol. 2, p. 444 [9] Lievin P., Khudyakov I., Kuzmin V. // Doklady Akademiji Nauk USSR (1980), vol. 2, p. 255 [10] Reichardt Ch. // Solvents in Organic chemistry / L.: “Khimiya”, 1973, 124 p. [11] Yasmenko A., Khudyakov I., Kuzmin V. // Doklady Akademiji Nauk USSR (1980), vol. 3, p. 529 [12] Makitra R. G., Zhukovsky V. Ya., Pyrig Ya. N. Kinetika and Catalysis (1982), vol. 23, № 5, p. 1262.

Chapter 5

EFFECTS OF THE SOLVENTS IN THE OXIDATION REACTIONS A numbers of works [1−4] were dedicated to an influence of the medium on kinetics of the hydrocarbons oxidization. In accordance with the generally accepted scheme of the process its rate is determined by the following expression:

V

d O2 dt

Vin

k2 RH k6

Vin

(1)

that is, depends on the initiation rate Vin., chain transfer (k2) and the rate of its termination (k6). However, a number of attempts to characterize both general rate and partial k2/k6 by any properties of the solvent, in particular by their polarity, were unsuccessful. This is no wonder taking into account the complicated character of the process, probable solvation of the intermediate forming radicals and also possible influence of the “cage” effect. Additionally it is necessary to notify that the oxygen itself can form the complexes both with the hydrocarbons and some substrates and with the solvent. Let us notify here, in particular the work [5], in which it was considered the formation of complexes between the oxygen and organic molecules on the basis of their UV−spectra, the work [6] − on the basis of NMR data in like systems, the work [7] − in which it was determined the formation of unstable complex of aldehyde with the oxygen, ect. That is why the possibilities of description of the medium properties influence on the oxidation rate of organic substrates by multi−parametric equations have been studied by us. Since it concerned to the hydrocarbons, in work [8] it was realized by us the successful attempt to generalize the data of work [4] as to initiated by AIBN (azo–di–isobutyronitryle) oxidation with the use of molecular


68

oxygen a series of olefins, namely cyclohexane, n−methylcyclohexene, α−methylstyrene.

5.1. OXIDATION OF UNSATURATED CYCLIC HYDROCARBONS In Table 1 there are values of general rate for cyclohexene oxidation by oxygen at 60 0C in the presence of 0,05 mole/l of azo−bis−isobutyronitrile taken from the work [9]; these values are numerically equal to the rates of the oxygen absorption d[O2]/dη mole/(l·h) by 2 M hydrocarbon solution except for ½ initiation rate, that is the rate of the initiator decomposition. Table 1. Experimental [9] and calculated accordingly to equation (3) values of the rates for cyclohexene oxidation in different solvents

*

№

Solvent

1 2 3 4 5 6 7 8 9

Cyclobenzene tert−Butylbenzene Benzene Diphenyl Ether Tetrachlormethane Acetic acid tert−Butanol Chlorbenzene 1−Chloronaphthali ne Diethylketone 2−Propanol Nitrobenzene Ethanol Nitroethane Methylethylketone Nitromethane Acetonitrile Dimethylsulfoxide

10 11 12 13 14 15 16 17 18

Wexp. Wcalc. mole/(l·s) 0,036 0,0294 0,0315 0.0308 0,0342 0,0329 0,0353 0,0428 0,0364 0,0320 0,0373 0,0381 0,0445 0,0598 0,0461 0,0501 0,0464 0,0538

lgWexp

lgWcalc

.

.

−1,51 −1,50 −1,47 −1,45 −1,44 −1,43 −1,35 −1,34 −1,33

−1,53 −1,51 −1,48 −1,37 −1,50 −1,42 −1,22 −1,30 −1,27

−0,02 −0,01 −0,01 +0,08 −0,06 +0,01 +0,13 +0,04 +0,06

0,48 0,54 0,54 0,67 0,72 − − 0,67 0,75

0,0500 0,0613 0,0636 0,0693 0,0749 0,0752 0,0878 0,0921 0,105

−1,30 −1,21 −1,20 −1,16 −1,13 −1,12 −1,06 −1,04 −0,98

−1,25 −1,18 −1,14 −1,12 −1,14 −1,25 −1,05 −1,10 −1,06

+0,05 +0,03 +0,06 +0,04 −0,01 −0,13 +0,01 −0,06 −0,08

− − 0,93 − − − 1,31 1,28 −

0,0563 0,0663 0,0731 0,0753 0,0720 0,0560 0,0901 0,0961 0,0878

lgW

k3/ k6*

In original of work [9] k3/ k6 was used instead of the accepted indication k2/ k6.


69

Taking into account the rate increasing in 1,5 order at the transition from low−polarity hydrocarbons to such strongly polarity solvents as nitromethane, acetonitrile, dimethylsulfoxide authors conclude that “although this rate increasing is not great, however it can be important in synthetic reactions” and come out with a suggestion that the nature of a solvent can influences both on the chain transfer and the chain termination stages, however more sensitive to possible solvation effects will be evidently the rate of the termination stage in consequence of the polar character of R−O−O· radical. However, at plotting the dependence on Kirkwood’s function the suitable linearity was not determined that permits to suppose more complicate influence of the polarity on a process evidently due to others solvation effects and others properties of the solvent. This supposition is confirmed at the generalization of data from the Table 1 accordingly to five−parametric equation. For all 18 solvents the value of multiple correlation coefficient R = 0,948 although is significant upon Fisher criterion (Fsign. = 19,58 > FT(0,95; 12; 5) = 4,68), however is some lower than recommended one by IUPAC [10] R ≥ 0,950. After an exclusion from the calculations the most divergent from the regression hyperplane point for tertiary butyl alcohol the R value for 17 solvents increases up to 0,968. As a result, it was obtained the expression (2) describing with the adequate accuracy the connection of rate sum logarithm for cyclohexene oxidation in different solvents with their physical chemical parameters: lg W

1,175 0,92 0,39 f n 2

0,85 0,18 10

3

1,28 0,23 f

0,24 0,18 10 3 B 18,6 4,6 10 3 ET

2

(2) In spite of the description adequacy of mentioned data by this equation, some its coefficients, for example, at the basicity factor and polarizability, are not differed from zero upon the Student’s criterion. At the same time, the values of paired correlation coefficients lgW with separate parameters ri (i = 1, 2 … 5) are equal respectively to 0,415; 0,888; 0,621; 0,659; 0,830 and permit only indirectly to confirm a small contribution of the polarisabilty and basicity into the value lgW. In accordance with the recommendations of Group of Correlation Analysis at IUPAC [10], in order to determine the value of separate factors contribution it was carried out their alternate exclusion with every time calculation of R. These calculations confirmed the insignificant influence of the basicity and polarizability factors, an exclusion of which decreases R only to 0,963 and 0,946 respectively. Finally, the dependence of the cyclohexene oxidation process rate on the

70


properties of solvents can be described with the adequate accuracy by three−parametric equation (3) accordingly to which increasing the polarity and medium cohesion energy density increases the rate of a process, and an ability for the electrophilic solvation decreases it:

lg W

1,652 1,32 0,26 f

11,6 4,6 10 3 ET

0,76 0,21 10

3

2

(3)

with significant R = 0,946 (Fsign. = 36,71 > FT(0,95; 13; 3) = 8,73), and s = 0,063, which adequately describes the data of experiment (Fad. = 42,41 > FT(0,95; 2; 13) = 3,81). Among the residuary three factors in equation (3) the most influence has the polarity of the solvents − at its exclusion the value R is decreased to 0,839 whereas an exclusion of any from two others factors is manifests itself is not aloud: without δ2 R = 0,890 and without ET R = 0,918. In Table 1 there are experimental and calculated accordingly to equation (3) values of lgW and also their divergences ∆lgW and the values Wcalc. The comparison of lgWcalc. and lgWexp. is represented on Figure 1.

Figure 1. Interrelation between the calculated accordingly to eqn. (3) and experimental values of cyclohexene oxidation rate. Numbers of the points correspond to Table 1.


71

Table 2. Comparison of Experimental and Calculated Ratios k 3

k 6 for

Oxidation of α–Methylstyrene Accordingly to Data [3] №

Solvent

1 2 3 4 5 6 7 8 9 10 11

Decane tert–Butylbenzene Tetrachloromethane Benzene Chlorobenzene Acetic acid tert–Butylalcohol o–Dichlorobenzene Nitrobenzene Nitromethane Acetonitrile

k3 exp. 24,0 33,1 38,1 48,8 50,1 55,5 52,0 55,7 63,2 85,1 85,5

k 6 10 3 calc. 29,0 35,3 36,8 42,5 47,8 47,7 53,7 55,6 65,6 101,1 75,7

lg k 3

k6

exp. –1,62 –1,48 –1,42 –1,31 –1,30 –1,26 –1,28 –1,25 –1,20 –1,07 –1,07

calc. –1,54 –1,45 –1,43 –1,37 –1,32 –1,32 –1,27 –1,25 –1,18 –1,00 –1,12

lg k 3

k6

+0,08 +0,03 –0,01 –0,06 –0,02 –0,06 +0,01 0,00 +0,02 +0,07 –0,05

As we can see, these values for majority of the solvents are coagreed in the limits of obtained root−mean−square deviation s ≈ ± 0,063 or only some exceeds it (for methylethylketone, dimethylsulfoxide and, of course, tert−butanol). Taking into account the peculiarities of the power function, the divergences between Wcalc. and Wexp. would be more essential, but nevertheless the obtained generalization can be reasonable. An analysis of the equation (3) confirms the conclusion of the author’s work [9] about favourable influence of polarity upon cyclohexene oxidation rate, however direct dependence between them here is absent in consequence of visible influence of two factors, namely cohesion energy density of the solvent and its ability to the electrophilic solvation. An influence of the first factor is positive since it in consequence of the “cage” effect is favourable to more effective chain transfer. Electrophilic solvation of the cyclohexene upon its π−bond decreases the ability of the molecule to interaction with radicals. If to compare the equations (2) and (3) with corresponding expressions describing the solvents influence on the unsaturated cyclic hydrocarbon (namely, tetraline (on the basis of data [11]) oxidation rate, than it is possible to mark both some likeness and some differences. First of all, this is absence of visible influence on the process of nucleophilic solvation (basicity), and also the influence of medium polarity f(ε) elevating the oxidation rate and the cohesion energy density (δ2). Obviously, the influence of polarity is caused by general peculiarities of chemical mechanism of radical oxidation − preferred cooperation

72


of chain transfer stage, efficiency of which is reinforced also by the “cage” effect connected with cohesion of the solvent. At the same time the ability of solvents to electrophilic solvation at tetraline oxidation leads to decreasing the process rate; wholly, this influence has a little significance, but in a case of cyclohexene oxidation it essentially decreases the rate that is caused by unsaturated character of the substrate. Above presented conclusions about possibility of generalization of medium influence on the cycloalkenes oxidation rate is confirmed by analysis of less representative data array concerning to medium influence on proportion of k3/√k6. In Table 1 there are experimental data taken from the work [9] as to cyclohexene oxidation under the same conditions as in a case for W. Similarly to values W, tunes k3/√k6 increase with medium polarity increasing from ≈ 0,5 (cyclohexane, benzene) till ≈ 1,3 (nitromethane, acetonitrile), that is approximately in 2,5 time. Analysis of data [9] as to medium influence on kinetics of 4−methylcyclohexene and α−methylstyrene oxidation at 65 0C leads to fundamentally like conclusions. In this work there are data for 11 solvents at the ratio of reactants volumes: solvent, 1 : 20, in the presence of 0,07 mole/l of azo−bis−isobutyronitrile used as initiator. In a case of 4−methylcyclohexene the taking into account of all solvents leads to low value of R = 0,919, however an exclusion from the consideration (as in a case of cyclohexane) of data for tert−butanol permits to increase its value up to 0,979. Here is visible mutual correlation of some parameters: f(ε) with δ2 r = 0,822; B with ET r = 0,805 and ε with ET r = 0,779. Nevertheless, after an exclusion of insignificant factors it is possible the suitable description of the dependence by three−parametric equation:

lg k3 / k 6

1,80 1,75 0,59 10 3 B 17,1 6,1 10 3 ET

1,66 0,23 10 3

2

(4) s = 0,059; (Fsign. = 23,2 > FT(0,95; 6; 3) = 8,94); R = 0,979 at paired correlation coefficients with separate parameters ri = 0,653; 0,639 and 0,912 respectively. Equation adequately describes the experimental data at the significance level α 0,05 (Fad. = 60,05 > FT(0,95; 9; 6) = 4,10). As we can see, the signs of coefficients at separate parameters are the same as in a case of the cyclohexene, that are marked the influence of δ2 factor (self−association of medium) accelerating the process and the decelerating one, namely the electrophilic salvation. In consequence of the observed artificial constraint of f(ε) and δ2 parameters, it is impossible to estimate their separate influence on the rate of process since the coefficient at f(ε) is formally


73

insignificant in the five−parametric equation, that, evidently are not agreed with the general results. This is, obviously, artefact, conditioned by mutual correlation of f(ε) and δ2 parameters into investigated set of the solvents. Thus, in the presented case, the same influence of the solvation factors as in a case of the cyclohexene oxidation is kept; this permits to suppose the same chemical mechanism of their oxidation. The same results have been obtained at generalization of data concerning to α−methylstyrene oxidation. For all 11 solvents the data are generalized by five−parametric equation:

lg k 3 / k 6

2,53 1,81 0,15 f n 2

8,0 4,0 10 3 ET

1,42 0,27 10

0,52 0,32 f 3

0,38 0,28 10 3 B

2

(5) s = 0,039;

R = 0,971

at the values of pair correlation coefficients lgk3/√k6 with separate factors ri = 0,235; 0,875; 0,471; 0,767 and 0,938 respectively. As same as in the previous cases, by defining here is the influence of the medium cohesion energy density or so−called the “cage” effect. Here also the great correlation of the separate parameters is manifested itself: f(ε) with δ2 r = 0,878 and f(ε) with ET r = 0,788, as a result of which the influence of this factor the same as the influence of a medium basicity B is insignificant. Insignificant also is the coefficient at the electrophilicity factor. Finally, the medium influence on the rate of the α−methylstyrene oxidation process can be satisfactory described by two−parametric equation (6) taking into account the influence of the polarizability and cohesion energy:

lg k 3 / k 6

2,05

0,76 0,44 f n 2

1,30 0,14 10

3

2

(6) with s = 0,039 and significant (Fsign. = 39,12 > FT(0,95; 8; 2) = 19,4), R = 0,952 which is adequately (Fad. = 65,6 > FT(0,95; 10; 8) = 3,35) describes the data of experiment. It was interesting to compare the relative influence of the solvents at uninhibited and inhibited oxidation of hydrocarbons. For this purpose the data


74

concerning to the styrene oxidation in 18 solvents at 65 0C were taken from work [3] (see Table 2). Concentration of the styrene was 0,42 mole/l, concentration of the initiator (AIBN) consisted of 0,07 mole/l. It was determined by authors, that the rate of a process W determining in the main proportion k2/k61/2 upon the comparison with the oxidation of pure styrene is decreased in low−polar solvents (hydrocarbons, CCl4) and is increased in polar ones. The turn−down is approximately in three times (see Table 3). However, the attempts to determine the unique dependence between the process rate and such functions of the medium polarity as (ε−1)/(2ε+1) or (ε−1)/(2ε+1)d∙M do not lead to success: at the general symbasis of these values for a set of the solvents, especially for aromatic ones, the essential deviations from the linearity are observed. Authors supposed, that “such deviations, probably conditioned by the non−electrostatic forcers, including the effects of non−specific solvation determined both by the high polarizability of CCl4 and by the presence of π−electrons in aromatic rings”; however, the quantitative account of these deviations has not be done. That’s why, it was very interesting to check up the possibility of these data generalization by Koppel−Palm’s equation and to compare of obtained results with those for others hydrocarbons and first of all like to the structure of cumene and α−methylstyrene [8, 13]. The values of the rate for inhibited oxidation process W·106 mole/(l·s) and lgW and the ratios k2/k61/2·102 (l·mole/s)1/2 and also the logarithms of this magnitude are represented in Table 3 on the basis of work [3]. Generalization of data concerning to the rate of a process W for all investigated 18 solvents leads to the equation with unsatisfactorily low value of multiple correlation coefficient R = 0,874 [12]. However, an exclusion from the consideration of data only for one solvent, namely p−xylene, permits to obtain the five−parametric equation (7) with reasonable degree of connection R = 0,950 and root−mean−square error s = ± 0,46: lg W

5,96 1,33 0,61 f1 n 2

0,46 0,28 10

3

0,82 0,29 f 2

0,19 0,32 10 3 B

2,72 4,60 10 3 ET

2

(7) Here, as same as in the all following cases the adequacy of the equation is confirmed in accordance with the recommendations [10] by coordination of the calculated Fisher’s criterion value with tabular one for corresponding number of degrees of freedom at reliability α = 0,95.


75

Positive signs at the all terms of equation show, that both the solvation of the starting molecule of a styrene by the solvent and the “cage” effect determined by the medium cohesion are favourable to the oxidation process. It was determined the insignificance for contribution of specific solvation factors: for 17 solvents an exclusion of the term with B decreases the R only to 0,949 and the following exclusion of ET to R = 0,946. Thus, the influence of the solvents properties on the styrene oxidation rate can be described with the adequate accuracy by the three−parametric equation (8) excluding the influence of the effects of the specific solvation with R = 0,946 and s = ± 0,06:

lg W

5,79

0,92 0,45 f1 n 2

0,92 0,26 f 2

0,52 0,25 10

3

2

(8)

The following exclusions more visibly impair the correlation − for two parametric equation without δ2 or without f1(n2) R = 0,926, and without f2(ε) R = 0,890. Factor determining the styrene oxidation rate in different media is, first of all, their polarity; this fact is confirmed by visible value of paired correlation coefficient r between lgW and f2(ε): r = 0,921 (without taken into account of p−xylene); at the same time, the influence of the polarizability and cohesion energy density is less significant, although it aloud. In Table 3 there are values of lgW calculated in accordance with the equation (5) and also their deviations with the experimental values ∆lgW. As we can see, either they are in the errors limits s ± 0,06 or they are only slightly outside of these limits (styrene, n−decane, acetic acid); an exclusion is p−xylene, which is not taken into account in the calculations. Theoretically, the rate of the radical processes is proportional to the value k2/k61/2, however, in reality that is marked by authors [3], the character of a solvent also influences on the initiator decomposition rate, that is, on the value k1, and as a result, at the symbasis of the values W and k2/k61/2 the obligated proportionality between them is not observed. That is why, in the similar way the presented in work [3] data upon k2/k61/2 (see Table 3) were generalized. The calculation for all 18 solvents gives the adequacy dependence with R = 0,947, and exclusion from the consideration of data for the acetonitrile permits to obtain the equation with R to 0,963 (equation (9) with s ± 0,04):

lg k 2 / k 6

1/ 2

2,41 1,03 0,96 f1 n 2

2,84 3,52 10 3 ET

0,45 0,28 10

0,68 0,21 f 2 3

0,07 0,23 10 3 B

2

(9)

Table 3. Comparison of experimental (accordingly to data [3]) and calculated rates for non−inhibited oxidation of the styrene Experiment Solvent

2

1 1

Calculation accordingly to eq. (8)

, k2 102 k6

W·106,

mole l s

−lgW

−lgW

Calculation accordingly to eq. (10)

Experiment

ΔlgW

l mole s

lg

1/ 2

k2 k6

lg

k2 k6

lg

1

2

3

4

5

6

7

8

9

10

Styrene n−Decane CCl4 tert−Butylbenzene p−Xylene Toluene Benzene Propionic acid Chlorobenzene Bromobenzene Acetic acid о−Dichlorobenzene 2−Propanol tert−Butanol Ethanol Nitrobenzene Nitromethane Acetonitrile

0,244 0,195 0,226 0,238 0,229 0,240 0,231 0,297 0,379 0,373 0,398 0,428 0,463 0,472 0,471 0,479 0,481 0,480

9,8 4,6 6,1 6,8 8,0* 8,2 8,7 9,0 10,5 11,2 12,0 12,4 12,5 13,1 13,9 15,8 16,3 17,0

5,009 5,337 5,215 5,167 5,523 5,086 5,061 5,046 4,979 4,951 4,921 4,907 4,903 4,886 4,857 4,801 4,787 4,770

5,083 5,250 5,162 5,150 5,442 5,124 5,123 5,044 4,957 4,925 4,998 4,877 4,854 4,921 4,796 4,800 4,777 4,841

−0,074 0,087 0,053 0,017 0,081 −0,038 −0,062 0,002 0,022 0,026 −0,077 0,030 0,049 −0,035 0,061 0,001 0,010 −0,071

2,33 1,35 1,79 1,66 1,95 2,10 2,23 2,20 2,63 2,73 2,93 3,10 3,05 3,02 3,39 3,68 4,18 4,59**

1,633 1,870 1,747 1,780 1,710 1,678 1,652 1,658 1,580 1,564 1,533 1,509 1,516 1,520 1,470 1,435 1,379 1,338

1,656 1,819 1,739 1,730 1,723 1,705 1,702 1,638 1,568 1,536 1,608 1,499 1,483 1,544 1,428 1,434 1,411 1,473

−0,023 0,051 0,008 0,050 −1,013 −0,027 −0,050 0,020 0,012 0,028 −0,075 0,010 0,033 −0,024 0,042 0,001 −0,032 −0,135

Notes: * − data excluded from the calculation accordingly to equation (8). ** − data excluded from the calculation accordingly to equation (9).

k2 k6


77

As same as in a case of W, the factors of the specific solvation here are insignificant (for equation (5) R = 0,961, s ± 0,04:

lg k 2 / k 6

1/ 2

2,31 0,89 0,33 f1 n 2

0,72 0,19 f 2

0,51 0,18 10

3

2

(10) Maximal influence on the ratio k2/k61/2 has again the medium polarity with r = 0,929 and the influence of polarizability and cohesion energy density like to W is only correcting one − at the admittance of any among these parameters corresponding to two parametric equations R is decreased only to 0,935−0,937. In Table 3 there are corresponding values of lg(k2/k61/2) calculated accordingly to equation (10) and their deviations from the experimental values. Thus, qualitative conclusions of the authors [3] about deciding influence of the medium polarity on the styrene oxidation rate are quantitatively confirmed; an increase of this polarity is favourable to the formation of the dipole in substrate. However, the assumption of authors [3] as to considerable influence in a case of aromatic hydrocarbons of specific solvation does not correspond to reality − the most probably here plays the role their highest polarizability. Significantly also is the influence of the medium self−association with increase of which the oxidation rate is increased as a result of “cage” effect visualization promotional to the radical processes proceeding. Table 4. Comparison of experimental (accordingly to [3]) and calculated accordingly to equation (12) rates for inhibited oxidation of styrene Solvent Styrene n−Decane CCl4 p−Xylene Chlorobenzene Bromobenzene Acetic acid о−Dichlorobenzene tert−Butanol* Nitrobenzene Nitromethane Acetonitrile

Basicity В [14] 43 0 0 68 38 40 139 28 247 67 65 178

Experiment k2/k6·103 8,47 3,10 3,77 5,08 5,01 4,92 5,42 6,55 6,68 8,18 14,77 23,75

Notes: * − data excluded from the calculation.

−lg(k2/k6) 2,072 2,509 2,424 2,294 2,300 2,308 2,266 2,184 2,175 2,087 1,831 1,624

Calculation −lg(k2/k6) 2,239 2,505 2,410 2,219 2,285 2,191 2,265 2,239 1,640 2,089 1,818 1,638

Δlg(k2/k6) −0,167 0,004 0,014 0,075 0,015 0,117 0,001 −0,055 0,535 −0,002 0,013 −0,014

78


The same, at the cumene oxidation [13] the determining and increasing the process rate are factors of the polarity and solvents cohesion energy density, but not the ability of the solvents to the specific solvation. At the comparison of the equation (10) with corresponding generalization for similar upon the structure α−methylstyrene in work [8] it was shown, that analogously insignificant are factors of specific solvation, however, despite the relatively high value of r (correlation of the rate process with the medium polarity 0,875) for adequate description in a case of α−methylstyrene it is enough of two others significant parameters, namely polarisability and cohesion energy density increasing the oxidation rate. In that way it can be said about the uniformity of the solvents influence on the oxidation process of the all these three hydrocarbons, the base of which is the non−specific solvation of the substrate related with the medium polarity. Significantly is also the influence of the “cage” effect. In the same work [3] it was investigated the kinetics of a styrene oxidation inhibited by phenols. In Table 4 there are vales k2/k6 for the oxidation of 1,74 M styrene solutions into 12 solvents in the presence of 4,8·10−4 M of AIBN and 9,8·10−5 M of inhibitor, namely di−2,6−tert−butyl−4−methylphenol. Under general essential deceleration of the process, its rate in polar solvents is relatively more, that is explained by the authors by formation of the hydrogen bond between the solvent and phenol and, correspondingly, by decreasing the effective concentration of the latter. However, both data for aromatic hydrocarbons and for MeCN and MeNO2 are deviated from the linear dependence with the Kirkwood’s function. At the same time, it was notified the symbate increase of the values k2/k6 with the displacement into IR−spectrum of the phenol band OH in corresponding solvents (that is basicity upon Palm B PhOH [14]), that points out the significance of the specific interaction in presented case. Сorrelation analysis of data from Table 4 by means of five parametric equation for all 12 solvents leads to the dependence with relatively low degree of relationship: R = 0,907, however, after exclusion of data for tert−butanol it was obtained (as same as in a number of others cases) the equation (11) with the acceptable value R = 0,964 and s = ±0,10:

lg k 2 / k 6

2,44

0,02 0,01 ET

0,56 1,15 f1 n 2 2,37 0,61 10

3

0,43 0,79 f 2

3,09 0,98 10 3 B

2

(11)

Analysis of the separate terms of equation significance points on the relative insignificance of the non−specific solvation factor in presented case. Dependence


79

of the styrene inhibited oxidation rate on the solvents properties can be with the adequate accuracy described by three parametric equation (12) with R = 0,961 and s = ± 0,09:

lg k 2 / k 6

2,20

3,01 0,81 10 3 B

2,69 0,85 ET

2,11 0,34 10

3

2

(12) Corresponding calculated values of lg(k2/k6) in accordance with equation (12) and their deviations from the experiment are represented in Table 4. Comparison of the equations (10) and (12) for non−inhibited and inhibited oxidation of the styrene points on the principally discriminate role of the solvents properties in these two processes. In a case of the inhibited process its rate depends on the specific binding together of inhibitor−phenol by the basic solvents with the formation of complex; this fact is agreed with the authors’s point of view [12]. However, although the basicity of a solvent is a factor determining the process rate, the value of pair correlation coefficient with this factor is equal only to 0,704 and adequate description of the process is impossible without additional taken into account the factor of the solvents electrophilicity in turn decreasing the process rate, probably, as a result of the antibate to their basicity effect of weakening ability to H−bond formation. Significant is also the role of the cohesion energy density of medium. The influence of specific solvation is also determining one for the heterolytic oxidizing dimerization of styrene under the trimer palladium acetate Pd3(OAc)b [15]. Thus, using the correlation analysis permits quantitavely to generalize the data concerning to the rates of the styrene oxidation under different conditions and to clear up the influence on the process of separate solvation factors.

5.2. OXIDATION OF SATURATED CYCLIC HYDROCARBONS Consideration of data concerning to the oxidation of saturated aromatic hydrocarbons of tetraline and cumene leads to the same conclusions. In order to propagate the above−said approach concerning to the saturated hydrocarbons oxidation, the data of work [11] concerning to the tetraline oxidation were considered in different solvents at 70 0C. In this work solutions contained 1,47 M of tetraline at AIBN concentration 0,01 M; the process rate W [mole/(l·s)] was determined upon the rate of oxygen absorption. It was marked by authors the

80


absence of the correlation between the reaction rate and polarity of the solvents determined by the Kirkwood’s function. Among studied in [11] 34 solvents it were considered data only for 30 ones (see Table 5) having the all needed characteristics in references [16]. For all 30 solvents the value of the multiple correlation coefficient R = 0,793, that is achieved degree of relationship is low than the usually accepted as satisfactory one at R ≥ 0,95. However, an exclusion from the consideration the most deviating results only for three solvents, namely propanol, pentanol and octanol, increases the value R up 0,859; 0,928 and 0,968 respectively, that is permits to achieve the acceptable value of the correlation degree. As it well−known, alcohols in the oxidation processes are inhibitors. Data for the residuary 27 solvents can be generalized by means of five parametric equation (13):

lg W

5,287

0,59 0,17 f n 2

0,19 1,7 10 3 ET

1,02 0,09 f

0,24 0,11 10

3

0,16 0,11 10 3 B

2

(13) at correlation paired coefficient with separate factors ri = 0,078; 0,930; 0,222; 0,507 and 0,749 respectively, multiple correlation coefficient 0,969 and mean square deviation s = ± 0,03 from the calculated lgk. As we can see, the coefficients at the items reflecting the influence of specific solvation B and ET statistically significantly don’t differ from zero (accordingly to the Student’s criterion). By sequential exclusion of these factors it was shown, that the multiple correlation coefficient R at this is decreased insignificantly and the tetraline oxidation rate in liquid is satisfactory described by three parametric equation (14):

lg W

5,302

0,54 0,16 f n 2

0,95 0,08 f

0,288 0,075 10

3

2

(14) s = ± 0,03, which adequately describes the data of experiment: in accordance with the Fisher’s criterion (Fad. = 128,7 > FT(0,95; 26; 23) = 1,99). The value R = 0,964 is also significant upon the Fisher’s criterion (Fsign. = 103,5 > FT(0,95; 23; 3) = 8,653). Values lgW calculated in accordance with the equation (14) and also their deviations from the experimental ones ∆lgW = lgWcalc. − lgWexp. are represented in Table 5.


81

Table 5. Values of general rate for tetraline oxidation [11] W = d[O2]/d [mole/l·s] and comparison of lgW for experimental values with the calculated ones in accordance with the equation (15) № 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

Solvent tert−Butylbenzene m−Dichlorobenzene Bromobenzene −Chloronaphthalene Chlorobenzene Nitrobenzene Decane Nonane Octane Tetrachloroethelene 2−Nitropropane 1−Nitropropane Nitroethane Nitromethane iso−Valeric acid Valeric acid Butyric acid Acetic acid Propanol Pentanol Octanol Acetophenone Anisole Amyl acetate Butyl acetate Ethyl benzoate Methyl benzoate Ethyl propionate Propyl acetate Diethyl malonate

W·105 0,779 0,946 0,999 1,00 1,05 1,34 0,639 0,662 0,666 0,743 1,36 1,42 1,54 1,84 0,798 0,814 0,909 1,21 0,671* 0,704* 0,790* 0,998 1,04 0,878 1,01 1,04 1,04 1,06 1,07 1,12

Note: *data excluded from the final calculation.

−lgWexp. 5,1085 5,0241 5,0004 5,0000 4,9788 4,8729 5,1945 5,1791 5,1765 5,1290 4,8665 4,8477 4,8125 4,7352 5,0980 5,0894 5,0414 4,9172 5,1733 5,1524 5,1024 5,0009 4,9830 5,0565 4,9957 4,9830 4,9830 4,9747 4,9706 4,9508

−lgWcalc. 5,1488 5,0109 5,0008 5,0214 4,9977 4,8814 5,1754 5,1790 5,1796 5,1371 4,8804 4,8180 4,8314 4,7769 5,0664 5,0727 5,0348 4,9334 4,8183 4,8610 4,9043 4,9019 5,0261 5,0077 4,9984 4,9840 4,9740 4,9764 4,9812 4,9737

lgW −0,0404 0,0132 −0,0004 −0,0214 −0,0189 −0,0086 0,0191 0,0001 −0,0031 −0,0081 −0,0139 0,0297 −0,0189 −0,0417 0,0316 0,0167 0,0066 −0,0162 0,3550 0,2914 0,1981 0,0989 −0,0432 0,0488 −0,0027 −0,0011 0,0089 −0,0017 −0,0106 −0,0230

We can see from the equation (14) that the defining and increasing of the process rate influence has only two factors, namely the polarity of medium and its cohesion energy density. The influence of the polarizability factor decreasing the general rate of a process in essence is of little significance, since under its exclusion the value R is decreased only to 0,952. Deciding significance of δ2

82


factor points on the visualization in oxidation process of the “cage” effect increasing the probability of the chain transfer (in accordance with the general scheme of the oxidation processes chemical mechanism). However, at the same time, this factor decreases the solubility of gases in liquids on the whole and of the oxygen in particular [17]. If the coefficient of the equation at δ2 has the sign “+” than it points on the absence of the diffusion resistance in presented process proceeding evidently in the kinetic field. Experimental constants of the rate in alcohols are essential lower than the calculated ones (see Table 5) owing to some alcohols are not blended with the obtained regularities that is possible caused by the extremely low solubility in them of the oxygen [17] and, as the consequence, by the influence on general oxidation rate of the interface transition or diffusion rate which is inessential in a case of the less associated solvents than the alcohols. Nevertheless the conclusions about the favourable role of the medium polarity increasing are also important, that, however, needs of more careful investigation and also the conclusions about insignificance of the specific solvation factors are important that, however, could be expected for the homolytic reactions. As same as in a case of the olefins oxidation [8], the defining and increasing of the process rate factors are medium cohesion energy density, that is, its self−association, and polarity. Decelerating influence has the solvation of a substrate by the solvent defining of its polarizability, that is the effect of non−specific solvation of aromatic ring; electrophilic solvation as same as in a case of the cyclohexene is possible in tetraline in consequence of the double bond absence. At the same time, the medium influence on the tetraline oxidation is differed from the oxidation of aldehydes [18−19] (where the coefficient at the factor of medium association δ2 has the sign “−”)it may be because the oxidation transformation of aldehydes proceeds greatly quicker than the hydrocarbons oxidation and, that is why in that case the rate of the oxygen dissolving in liquid plays the essential role. In a case of the electron donor molecules of aldehydes the ponderable positive introduction into general rate of the process has also their specific electrophilic solvation, and the factor of medium polarity decreases the total rate of a process. Let us note, that the results of the work [11] have been generalized also in a work [20] by means of four parametric equation, that is, without taking into account the factor of cohesion energy density. Such generalization permitted, however, to cover the considerably less number of data (13 solvents) and with the worst correlation coefficient (R = 0,953). It is important to note, that such approach lead of the authors to the conclusion about the significance of all four factors, that is, about the influence of both specific and non-specific solvation


83

processes; this fact is not taken the convincing explanations in a case of the radical oxidation. Above−mentioned analysis is relatived to the rate of a gross process; such rate is determined by the oxygen consumption rate, on which the diffusion processes can be partially imposed. That is why the following question is appeared: in which manner the medium properties will be influence on the rate of the separate stages of hydrocarbons oxidation? In accordance with the generally accepted scheme the rate of uninhibited process is determined by following expression:

W

k3 / k6

RH

k1 I

(15)

where [I] is the concentration of an initiator; k1 is the constant of its decomposition; k3 and k6 respectively the constants of chain transfer and chain termination. Unfortunately, in work [11] there are not enough data as to the values of k3/√k6 in different solvents. As same as in a case of the general rate of oxidation, the defining and favourable factor for the process is medium polarity increasing which evidently promotes the chain transfer in consequence of the non−specific solvation of the aryl ring of tetraline by polar solvents. Electrophilic solvation of π−electronic system of benzene ring also promotes to this process, although in a lesser degree. Simultaneously, in accordance with the donor character of tetraline, its nucleophilic solvation does not proceed. Defining influence of the cohesion energy density factor on the rate of tetraline oxidation is observed also in the presence of decanoates of Cobalt or Manganese [21].

5.3. OXIDATION OF ALDEHYDES Here is advisably to note, that the generalization of medium influence by means of multiparametric equations is effective also under consideration of non−radical oxidation reactions. For example, in work [22] it was shown, that the rate of acrolein and α−alkylacroleines with peracetic acid interaction in 12 solvents by different polarity (from water to benzene) does not depend indirectly on the “polarity” (electrophilicity) Reichardt’s parameter ET, but it can be satisfactory generalised by three parametric equations taking into account the influence of polarity and electrophilicity favourable to the process proceeding and cohesion energy density decreasing its rate. Evidently, in a case of the aldehydes

84


oxidation the first stage is the formation of complex with hydrogen bond between aldehyde and acyclic form NUK [23−25]. Next, fitting the oxygen atom of the peroxy group to electron−deficit carbon atom of aldehyde takes place and regrouping the complex into reaction products [26] proceeds. Both electrophilic solvation by the solvent of carbonyl atom of peacid oxygen and non−specific solvation favourable to the charges separation in complex promote this regrouping:

Unlike to the reaction of olefins NUK epoxidation [27] in our case the role of the medium basicity is insignificant. Low rate of the process in aromatic solvents and insignificance of the medium basicity influence permit to assume about some difference in chemical mechanisms for the aldehydes NUK oxidation reaction and for the olefins epoxidation reaction. Whereas under an epoxydation process the complex−formation takes place upon double bond of the olefin with the cyclic form of peracetic acid (so−called chemical mechanism “butterfly”) and basic solvents decrease the rate of an interaction as a consequence of the transformation of active cyclic form peracetic acid into the non−active one, then carbonyl group of the aldehydes is greatly stronger donor of the electrons than the double bond C=C of olefins, and the bond with peracetic acid is easy realized, probably with the formation of hydrogen bond upon the unshared electronic pair. Nevertheless, insignificant decrease of the rate in more basic solvents (ethyl acetate, acetone) and the sign “minus” at the term with the basicity parameter permit to suppose the possibility of some competition for the molecule peracetic acid between the oxidized aldehyde and basic solvent. Probably, that in the solvents by more basicity than the investigated ones, for example, dimethylformamide, the process rate is decreased some more visible. However, the oxidation of aldehydes by molecular oxygen proceeds in another way.


85

Table 6. Cohesion energy densities for solvents (δ2, kJ/m3) and rate constants of butyric aldehyde oxidation at 35 0C №

Solvent

δ2

1 2 3 4 5 6 7 8 9

Acetonitrile Dimethylformamide Acetic acid Dioxane Ethyl acetate Chlorbenzene Toluene Isooctane n−Heptane

593,1 612,9 427,1 418,7 342,1 385,9 336,0 196,4 228,0

ka, l·mole−1/2·h−1 experiment calculation 0,153 0,175 0,199 0,183 0,372 0,333 0,389 0,372 0,435 0,454 0,459 0,483 0,544 0,559 0,725 0,791 0,780 0,701

kb, l·mole−1·h−1 experiment 0,080 0,109 0,208 0,185 0,217 0,246 0,311 0,359 0,453

calculation 0,092 0,098 0,175 0,198 0,238 0,264 0,303 0,416 0,369

In number of works [29−31] it was carried out the systematical investigation of the kinetics and it were determined the gross constants of oxidation for some aldehydes in different solvents. Authors consider, that the general rate of a process is determined mainly by the rate of the limitative stage and on the basis of proposed by them mechanisms assume the presence of qualitative relation between determined properties of the solvents and their influence on the oxidation rate. In connection with fact, that the number of the investigated solvents is large enough, it was very interesting the attempt to apply for their generalization of correlated analysis methods with the aim of the check the approach qualified only under the presence of united interaction mechanism and sufficient approximation of the gross process constants to the constants of the limitative stage. In work [29] it was investigated the catalytic oxidation of 50 % solutions of butyric aldehyde in the presence of 0,5 % ferrocene at 35 0C. For this process it was proposed the following multistage chemical mechanism: i)

initiation

RCHO + M(n+1)+ → RCO● + H+ + Mn+

(16)

ii) chain transfer RCO● + O2 → RCO3●

(17)

RCO3● + RCHO → RCOOH + RCO2●

(18)

RCO3● + RCHO → RCO3H + RCO●

(19)

86

Gennady E. Zaikov, Roman G. Makitra, Galina G. Midyana et al. RCO2● + RCHO → RCOOH + RCO●

(20)

iii) catalyzed oxidation RCO3H + Mn+ → RCO2● + OH− + M(n+1)+

(21)

iv) peracid decomposition RCO3H + RCHO → 2RCOOH

(22)

It was shown by authors that the rate of a process can be approximated by general empiric equation d[RCHO]/dη = k0[O2]n[RCHO]m[M(n+1)++R]p

(23)

where exponents n, m and p have been determined by fitting from the possible values (0; ½; 1; 3/2) up to achievement of adequate description of the experimental data; [R] is the concentration of products providing the autocatalysis and which are formed in accordance with the reactions (18) − (20). Under condition that [O2] = const the most like congruence with the experiment give the calculated expressions at m = 1, p = ½ (a) or worse at m = 3/2, p = ½ (b). It have been calculated the gross constants ka and kb represented in Table 6 on the basis of experimental curves till the 50 % conversation of aldehyde and with the use of proposed values m and p by authors [29]. On the basis of comparison with the oxidation chemical mechanism of benzaldehyde and by analogy with the radical oxidation chemical mechanism of hydrocarbons authors postulated that a rate of the stage (17) will be visible higher than the initiation stage (16) and following stages of the chain transfer. They suppose that the initiation stage (16) and especially the stage of a chain transfer (18) will be by the limitative stages. In order to confirm this conclusion, authors [29] have done the comparison of the rate constants obtained in 10 solvents with the Kirkwood’s function and the comparison of the rate constants obtained in 8 solvents with the solubility in them of the oxygen with obtaining the following one parametric dependencies with degrees of relationship:

ln k a

f

2

1 r = 0,878 1

ka = f([O2])

r = 0,959

(24)


ln k b

f

2

1 r = 0,833 1

kb = f([O2])

r = 0,935

87 (25)

On the basis of this authors concluded about the influence of medium polarity on the rate of the oxidation process along with the oxygen solubility. Since the coefficient at f(ε) is minus, then the transition state on a stage of the chain transfer is assumed to be less polar than the starting reagents. It is neseccary to notify, however, that the alternative path of the process via the stages (17)−(19)−(22) was not taken into account by authors; besides, the stage (17) will be evidently by the limitative one, in favour of which the determined by authors statistical authenic relationship between the process rate and the oxygen solubility [32] would be point out. Data of [29] have been generalized by us via LFE five parametric equation taking into account along with the solvation parameters of the Koppel−Palm’s equation also medium cohesion energy density upon Hildebrandt δ2 = (∆Hevap. − RT)/VM. As it was determined, this parameter is determinative for the process of gases dissolving into liquids [33] and at the same time essentially influences on the rate of induced benzoil decomposition in consequence of the „cage” effect [34].

Figure 2. Dependence of the rate constant for the process of butyric aldehyde catalytic oxidation on the solvents cohesion energy density; numbers of points corresond to data in Table 6.


88

Parameters of the solvents were taken from the work [16], ET and δ2 in kJ/mole. It was obtained the following equation:

lg k a

0,218 1,41 0,60 f n 2

0,28 0,33 f

1,69 0,32 10

3

2

2,2 2,8 10 4 B

5,1 4,4 10 4 ET

(26)

At number of solvents N = 9, R = 0,992, s = 0,048, the values of paired correlation coefficients which characterize the contribution of separate factors into the constant of the process rate consist of: r01 = 0,252; r02 = 0,872; r03 = 0,975; r04 = 0,749; r05 = 0,744. Determinative role plays the δ2 parameter, dependence of which on lgka represented on Figure 2. In accordance with the conclusion of authors [29] the polarity of medium decreases the process rate whereas its polarization and ability to the specific solvation, on the contrary, increases. However, checking the significance of separate factors points out the trifling contribution of the polarity and specific solvation. Finally, the dependence of the oxidation process rate on the medium properties can be satisfactory described by three and even two parametric equations:

lg k a

0,165

1,28 0,57 f n

1,68 0,18 10

3

2

2,8 3,8 10 4 ET (27)

R = 0,988

lg k a R = 0,986

s = 0,046

0,058

1,12 0,50 f n

1,58 0,11 10

3

2

(28)

s = 0,045

Thus, factors determining the butyric aldehyde oxidation rate are the medium cohesion energy density and its polarizability. Despite the relatively great value of the pair coefficient of the correlation with the medium polarity r02 = 0,865 (or 0,840), the influence of this factor on the process rate is insignificant and the conclusion of authors [29] about the differences into polarity of the base and reacting states can not be recognized as sufficiently well−reasoned. At the same time, the medium polarizability distinctly influences on the process rate; in spite of the high degree of the association δ2 in strong polarizable toluene and


89

chlorbenzene (in 2 times), the rate constants in them and especially the half reaction times (accordingly [29]) are near to those in weakly polarizable alkanes having the low cohesion energy density. One parametric correlation between the process rate in different solvents and solubility in them of oxygen is worse than at the combined taking into account of some factors; this fact also points out the complicate character of the medium influence. In order to check the conclusion of the author’s work [18] about possible determinate influence of the oxygen solubility on the process rate it were determined by us the dependencies «solubility of oxygen (PN, mol. parts) on the properties of studied solvents», and also dependencies of lgk and lgPN on PN. The following expressions have been obtained:

lg PN 0,968 4,22 0,79 f n

3,3 4,1 10 4

2

1,9 0,4 10 3 B 2,4 0,4 10 2 ET (29)

R = 0,997

lg k a

1,46 0,26

R = 0,942

ka

s = 0,035

0,590 0,086 lg PN

(30)

218 36 PN

(31)

s = 0,067

0,251 0,048

R = 0,927

r02 = 0,951

s = 0,077

Thus, polarizability and electrophilicity of the medium decrease the solubility in it of oxygen, but at the same time they visible increase the aldehyde oxidation rate. Hence, the ability of medium to the non−specific solvation determined by its polarizability plays an essential role on the stages determining the process rate (namely, chain transfer or initiation). At the same time, negative role of the cohesion energy density increasing can be explained either by decrease of the oxygen solubility due to the medium association increasing or by the posible increase of the chain termination probability via the recombination of radicals in «cage» of the associated solvent. Evidently, here the total influence of these two factors takes place. In work [31] it was investigated the influence of medium on the rate of catalyzed by Cobalt acethylacetonate the acrolein oxidation at 30 0C. The attempts of the authors to determine the dependence between the properties of the solvents

90


and the process rate calculated upon the rate of the oxygen adsorbtion do not lead to success; it was marked only the deceleration of the process in water, methanol, formic acid and hexene in comparison with the rate in aromatic hydrocarbons, nitrobenzene, dimethylformamide (see Table 7). Maximal rate of the oxygen adsorption is observed in the medium of carbonic acids C3−C5, that is agreed with the data of work [30] concerning to the non−catalytic oxidation of the butyric aldehyde. Data of the work [31] is also good generelized via the multiparametric equation:

lg WO2

4,764 3,95 1,20 f n

2,88 0,44 f

7 0,7 10 4

2

4,5 3,8 10 4 B

3,67 0,61 10 2 ET (32) For a number of solvents N = 12, R = 0,988, s = 0,089; paired correlation coefficients: r01= 0,295; r02= 0,648; r03= 0,868; r04= 0,264; r05= 0,484. Maximal (decelerating) influence on the rate of the oxygen adsorption has also as same as in a case of the butyric aldehyde oxidation the medium cohesion energy density. Practically is insignificant the influence of the basicity and relatively is unimportant the influence of the medium polarizability. Polarity and electrophilicity have the definite correcting action on the rate of catalytic oxidation of the acrolein, which is good described by the following equation:

lg WO2

3,512

1,84 0,50 f

7,7 1,1 10

4

2

2,5 0,7 10 2 ET (33)

R = 0,960

s = 0,137

The adequacy of an equation and the significance of R are confirmed by the check accordingly to Fisher’s criterion: Fad. = 21,3 > FT(0,05; 2; 8) = 4,46)

FR = 31,4 > FT(0,05; 8; 3) = 8,84

Calculated values WO2 obtained in accordance with this equation are represented in Table 7.


91

Table 7. An influence of the solvents on the rate of acrolein oxidation (WO2·104, mole/l·s [31]) Solvent Formic acid Acetic acid Propionic acid Butyric acid Benzene Toluene

Experiment 1,80 6,36 7,63 8,72 5,82 6,36

Calculation 3,02 5,63 6,98 7,68 4,56 4,44

Solvent Tetrachlormethane Cyclohexane n−Hexane Nitrobenzene Dimethylsulfoxide Water

Experiment 4,45 3,09 4,36 2,18 2,06 0,26

Calculation 4,49 4,47 5,71 1,89 1,76 0,26

An influence of the medium on the process rate is like to those at non−catalytic oxidation of the butyric aldehyde. In addition to the influence of medium self−association, it’s also observed the profitable influence of electrophilic solvation of the reactive complex, whereas at the non−catalytic oxidation the role of electrophilic solvation is insignificant and the ability of the medium to nucleophilic solvation decelerates the process. Since the nucleophilic solvation of the starting aldehyde is low−probability, then the stabilization by the solvent of primarily forming radicals RCO• evidently proceeds. It is more difficult to interpretate the role of the non−specific solvation; in generally, this process is directed in sideways of the oxidation deceleration in consequence of the solvation of starting substances or radicals forming on the initial stages. Thus, in the presented work it was shown, that the medium influence on the aldehydes oxidation rate in some cases can be generelized via the polyparametric LFE equations. However, in a case of using the rate constants of gross process the satisfactory results can be obtained only in a case when they are neared to those for the limitative stage and the influence of others possible reactions is unnoticeable. Multiparametric equations have been successfully applied also for the generalization and an interpretation of the medium role in non−radical oxidation by peracetic acid the series of sulfides, sulfoxides [35], nitrosobenzene, octin−4 and others compounds [36].

REFERENCES [1] [2]

A. Howard, K. Ingold // Canad. J. Chem., (1964), vol. 2 (5), p. p. 1250−1253 G. Kamiga, K. Ingold // Canad. J. Chem., (1964), vol. 42 (11), p. p. 2424−2433

92 [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18] [19] [20] [21] [22] [23]

Gennady E. Zaikov, Roman G. Makitra, Galina G. Midyana et al. J. Howard, K. Ingold // Canad. J. Chem., (1964), vol. 42 (5), p. p. 1044−1056 D. Hendry, G. Russel // J. Amer. Chem. Soc., (1963), vol. 85 (12), p. p. 2368−2371 H. Tsubomura, R. Mullinen // J. Amer. Chem. Soc., (1960), vol. 82 (23), p. p. 5966−5974 N. Mukhin // Dep. VINITI № 2792−80, (1980) A. Rieche // Ang. Chemic, (1938), vol. 51, p. p. 707−709 R. Makitra, Ya. Pyrig // Z. Org. Khim., (1996), vol. 32 (10), p. p. 1468−1472 D. Hendry, G. Russel // J. Amer. Chem. Soc., (1969), vol. 86 (12), p. 368 Quant. Struct. Acta. Relat. (1985), vol. 4, p. 29 (translation in Ukr. Khim. Z., (1992), vol. 58 (3), p. 260) E. Niki, J. Kamiya, N. Ontu // Bull. Chem. Soc. Japan, (1969), vol. 42 (11), p. p. 3324−3329 R. Makitra // Z. Org. Khim., (2005), vol. 76 (6), p. p. 958−962 R. Makitra, Ya. Pyrig, Y. Yatchyshyn // Z. Org. Khim., (1999), vol. 35 (7B) p. 1073 N. Koppel, A. Palm // Reatsyonnaya Sposobnost’ Organicheskikh Soyedinienij, (1974), vol. 11 (1), p. 121 A. Yatsymirsky, A. Ryabov, V. Zagorodnikov et al. // Inorg. Chim. Acta, (1981), vol. 48 (2), p. 163 R. Makitra, Ya. Pyrig, H. Kivelyuk // Dep. VINITI № 828−В86 (1986) D. Bryk, R. Makitra, Ya. Pyrig, Yu. Stefanyk // Zhurn. Prikladn. Khimiyi, (1988), vol. 60 (1), p. p. 91−97 S. Maslov, E. Blumberg // Uspiekhi Khimiji, (1976), vol. 45 (2), p. p. 303−328 G. Zaikov, A. Vigutynsky, Z. Mayzus, N. Emmanuel // Doklady Akademiji Nauk USSR, (1966), vol. 168 (5), p. p. 1096−1099 R. Kucher, Y. Opeida, L. Nechytailo, M. Symonov // Book: Intermolecular Interactions and Reactive Ability of Organic Compounds / К.: «Naukova Dumka» (1983), p. p. 82−93 R. Makitra, R. Prystansky, R. Sheparovych // Zhurn. Phys. Chim., (2004), vol. 78 (4), p. p. 622−625 Y. Yatchyshyn, Ya. Pyrig, R. Makitra // Reatsyonnaya Sposobnost’ Organicheskikh Soyedinienij, (1987), vol. 24 (3), p. p. 336−344 R. Vasilyev, N. Emmanuel // Doklady Akademiji Nauk USSR (1956), vol. 4, p. p. 378−396


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[24] R. Vasilyev, A. Terenin, N. Emmanuel // Doklady Akademiji Nauk USSR (1956), vol. 4, p. p. 397−402 [25] R. Vasilyev, A. Terenin, N. Emmanuel // Doklady Akademiji Nauk USSR (1956), vol. 4, p. p. 403−409 [26] M. Fedevych, Y. Yatchyshyn, Y. Pyrig, M. Kaspruk // Nieftiekhimiya, (1975), vol. 15 (3), p. p. 449−453 [27] R. Makitra, Ya. Pyrig // Zhurn. Phys. Chim., (1978), vol. 52, 3, p. p. 785−787 [28] B. Lynch, K. Pausacker // J. Chem. Soc., (1955), vol. 5, p. p. 1525−1531 [29] J. Vcelak, J. Chvalovsky // Chem. Promysl., (1980), vol. 30 (2), p. 76 [30] A. Mirus, Y. Mokryj // Visnyk of Lviv Polytechnic Institute, (1983), vol. 171, p. 133 [31] J. Ohkatsu, M. Takeda, T. Hara et al. // Bull. Chem. Soc. Japan, (1967), vol. 40 (6), p. 1411 [32] Ya. Pyrig, R. Makitra, Y. Yatchyshyn // Kinetika and Catalysis, (1991), vol. 32 (5), p. p. 1040−1047 [33] R. Makitra, Y. Pyrig, T. Polytanska // Zhurn. Prikladn. Khimiyi, (1981), vol. 54 (1), p. 54 [34] V. Ushkalova, E. Kolmakova // Nieftiekhimiya, (1970), vol. 10 (2), p. 246 [35] Y. Vasiutyn, R. Makitra, Y. Pyrig // Ukr. Khim Zhurn., (1985), vol. 51 (4), p. p. 381−384 [36] R. Makitra, O. Makogon, Ya. Pyrig // Reatsyonnaya Sposobnost’ Organicheskikh Soyedinienij, (1987), vol. 24 (1), p. p. 25−29

Chapter 6

THE MEDIUM INFLUENCE ON SOME OTHER HOMOLYTIC REACTIONS 6.1. THE MEDIUM INFLUENCE ON AZOBISISOBUTYRONITRILE (AIBN) DECOMPOSITION Azobisisobutyronitrile (AIBN) is one among widely used applied initiators of radical processes, especially, polymerization processes including the industrial ones. It is no wonder, that a numbers of works are dedicated to its decomposition including those which are concerned to the influence of the solvents on the kinetics of decomposition. However, as a rule, these investigations have been carried out in not great numbers of solvents that does not permit to make the quantitative conclusions. For example, in work [1] it was determined the linear dependencies between lgk and electrophilicity Reichardt’s parameter ET only on the basis of data concerning to the AIBN decomposition rate into 5 solvents. At the same time, in work [2] it is informed about practically the same values of AIBN decomposition constants in different media. The same conclusion has been done by authors [3], in particular, conclusion about practical stationary k values of rate into solutions by different viscosity. Also the reference concerning to AIBN decomposition in different media represented in [4] points out only insignificant changes of the rate k − 1,40∙104s−1 in tert−amyl alcohol up to 1,98·104s−1 in nitrobenzene [5, 6]. The same investigation was carried out in [7] and also in different media the constant value of process activation energy Ea ≈ 30,5 ÷ 31,5 ccal/mole is kept as constant. The same conclusion has been done by the authors of work [8].


96

The most completely a decomposition of azobisisobutyronitrile in different solvents has been studied in work [9] under investigation of styrene oxidation initiated by this compound. Corresponding rate constants by the first order (k) for the reaction of azobisisobutyronitrile decomposition at its concentration 0,07 mole/l and 65 0C are represented in Table 1. Generalization of data from Table 1 in accordance with six parametric equation leads to the equation with enough high value of multiplying correlation coefficient R = 0,9495; at this, any among taking into account parameters have not determine influence on the value lgk, since the values of pair correlation coefficients (ri) are in the limits 0,18−0,55. An additional exclusion from calculations the most deviating data for nitromethane permits to obtain the expression (1), which excellently describes the connection between the values lgk of decomposition in 12 solvents and the their properties: lg k

5,609

2,19 0,14 f n 2

0,23 0,09 10

3

0,10 0,07 f

1,04 0,08 10 3 B

6,89 0,88 10 3 ET

2

(1) N = 12

R = 0,9869

s = ± 0,011

Determination of the significance of separate terms of equation contribution into the value lgk was done in accordance with the recommendations [10] by their alternate exclusion with every time determination of R values for resulting equations with a less number of terms. Thus, it was determined the insignificance of polarity factor, that is agreed with bigger standard deviation of a coefficient at this term and it was obtained the equation (2).

lg k

5,574

2,09 0,14 f n 2

0,324 0,07 10

3

1,014 0,089 10 3 B

6,82 0,98 10 3 ET

2

(2) N = 12

R = 0,9840

s = ± 0,012

However, the following exclusion of any residuary parameters either essentially makes worse the correlation (R = 0,953 at exclusion of δ2 or R = 0,910 at exclusion of ET) or on the whole destroys of it. Especially insignificantly is the influence of the parameter f(n2), although the value of its pair correlation


97

coefficient with the value lgk is ri = 0,172 and is extremely low, however, after its exclusion the value R for three parametric equation lgk = f(B, ET, δ2) is equal only to 0,575. Obtained results mean that the monomolecular decomposition of azobisisobutyronitrile complicatedly depends on different properties of medium: both specific (B and ET) and non−specific (f(n2)) solvation of molecule of this compound are favourable to the decomposition. Correspondingly, the maximal rate of the decomposition is observed in the most electrophilic solvents, namely in carbonic acids, nitrocompounds, alcohols, probably, in consequence of the azobisisobutyronitrile cyanic groups solvation leading to weakening of the −N=N− bond. At the same time, the medium self association increasing counteracts to the decomposition. It can be supposed, that this is result of the complication into the attack of other azobisisobutyronitrile molecules by forming radicals. Table 1. Experimental [9] and calculated accordingly to equation (1) logarithms of rate constants for decomposition of azobisisobutyronitrile at 65 0C № Solvent 1 2 1 Decane 2 Tetrachlormethane 3 p−Xylene 4 Toluene 5 Benzene 6 Propionic acid 7 Chlorobenzene 8 Acetic acid continuation on page 74 1 2 9 о−Dichlorobenzene 10 tert−Butanol 11 Nitrobenzene 12 Acetonitrile 13 Nitromethane

k·105, s−1 [9] 3 1,2 1,3 1,8 1,7 1,6 1,8 1,7 1,8

−lgkexp. [9] 4 4,921 4,886 4,745 4,770 4,796 4,745 4,770 4,745

−lgkcalc. 5 4,923 4,875 4,771 4,780 4,792 4,753 4,763 4,744

lgk 6 0,002 −0,011 0,026 0,010 −0,004 0,008 −0,007 −0,001

3 1,7 2,0 2,0 1,5 1,6b

4 4,770 4,699 4,699 4,824 4,796

5 4,756 4,685 4,712 4,831 4,925

6 −0,014 −0,014 0,013 0,007 0,129

98


Figure 1. Correlation between experimental [9] and calculated accordingly to equation (2) values of the rate constants logarithms for the decomposition of azobisisobutyronitrile at 65 0C (N = 12; R = 0,9840; s = ± 0,012). Numbers of points correspond to presented ones in Table 1.

In Table 1 there are values of lgk constants logarithms of azobisisobutyronitrile decomposition at 65 0C − experimental [9] and calculated accordingly to equation (2), and also their divergence ∆lgk. The values ∆lgk are insignificant even for excluded from the calculations nitromethane (∆lgk = 0,129) at the equation (2) obtaining. The all other deviations practically are not outside the errors s = ± 0,012 (see Figure 1). Obtained results are confirmed by the analysis of data from two others works concerning to the kinetics initiated by the azobisisobutyronitrile decomposition, hydrocarbons oxidation, however, the experiment has been carried out in less number of solvents; that is why their generalization is statistically less trustworthy. Data of work [11] obtained at 60 0C are represented in Table 2. Constants of azobisisobutyronitrile decomposition rate (0,097 mole/l) at 60 0C determined in binary systems “solvent − oxidized hydrocarbon (1,9 mole/l) of cumene or cyclohexene”, are visibly differed, especially into polar and electrophilic solvents such as acetonitrile and nitromethane, evidently in consequence of the possible complex forming with the donor of electrons which is the cyclohexene.

Table 2. Experimental [11] and calculated in accordance with the equations (3) and (4) rate constants logarithms for the azobisisobutyronitrile decomposition (0,097 mole/l) at 60 0С in the presence of hydrocarbons (1,9 mole/l)

№

Solvent

1 2 3 4 5 6 7 8

Acetonitryle Tetrachloromethane Chlorobenzene 1−Chloronaphthalene tert−Butylbenzene Diphenyl ether Nitrobenzene Nitromethane

Cumene k1·106, s−1 [11] 7,09 4,00 6,54 5,26 4,75 3,90 6,46 6,51

−lgk1(exp) [11] 5,149 5,398 5,184 5,279 5,323 5,409 5,190 5,186

−lgk1(calc) 5,166 5,377 5,208 5,330 5,315 5,383 5,162 5,157

а

lgk1 0,017 −0,021 0,024 0,051 −0,008 −0,026 −0,028 −0,029

Cyclohexene k2·106, s−1 [11] 10,40 5,05 6,49 5,87 4,93 4,11 6,87 11,90

−lgk2(exp) [11] 4,983 5,297 5,188 5,231 5,307 5,386 5,163 4,924

−lgk2(calc)б 5,036 5,338 5,199 5,214 5,340 5,334 5,098 4,929

lgk2 0,053 0,041 0,011 −0,017 0,033 −0,052 −0,065 0,005

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Generalization of data obtained in the presence of cumene (k1) by means of five parametric equation leads to the expression with R = 0,9615. The signs at the all terms of this equation (with the exception of the basicity) are the same as in an equation (1). Neared are also the values of the majority regression coefficients, however, on the contrary to the previous case here insignificant was turned out also the parameter of the polarizability f(n2). As a result, the character of the medium influence on the rate of the azobisisobutyronitrile decomposition is acceptably described by three parametric equation (3) at defining influence of electrophilic solvation on the decomposition (pair correlation coefficient lgk with ET r = 0,831).

lg k1

6,878 0,890 0,270 10 3 B

N=8

61,62 11,0 10 3 ET

R = 0,9574

1,59 0,40 10

3

2

(3)

s = ± 0,030

Similar results have been obtained also at the generalization of other data set from Table 2, namely the decomposition rate constants of azobisisobutyronitrile in system “solvent − 1,9 M solution of cyclohexene”. Their generalization by five parametric equation leads to the expression with R = 0,9911 at maximal influence of the electrophilicity: r4 with ET is equal to 0,939. Factors f(ε) and δ2 were turned out in the presented case insignificant since at their exclusion R practically is not decreased (0,9908 and 0,9905). Insignificantly is also the polarisability influence for these data; that’s why it was obtained two parametric equation (4).

lg k 2 N=8

6,403

0,736 0,347 10 3 B R = 0,9635

32,9 3,7 10 3 ET

(4)

s = ± 0,043

In number of other works [5, 7−8] the azobisisobutyronitrile decomposition was studied in less number of solvents (4−6), that it is not enough for the reliable statistical analysis or it were used media for which unknown the solvation characteristics. However, the main conclusions above obtained, namely about the defining rate of the azobisisobutyronitrile decomposition, the role of electrophilic solvation and the absence of the connection with the polarity of solvent are confirmed also by these results.


101

Here is advisably to note that in references there are results of investigations concerning to the medium influence on the decomposition rate of other azocompounds, however, the quantity of investigated solvents as a rule is insignificantly for the reliable statistical treatment, especially that the vales of the process rate constants are changed relatively not enough. This was determined for phenylazotriphenylmethane [12, 13] and p−nitrophenylazotriphenylmethane [14] (decrease of k with medium viscosity increasing, and also others phenyl substituted derivatives [15], some cyclic azoderivatives [16] etc.).

6.2. THE MEDIUM INFLUENCE ON HYDROCARBONS HALOGENATION The nature of solvents also essentially influences on reactions of organic compounds halogenation −dependently on medium even the direction of the reaction is changed. And in this case the multiparametric equations were turned out by effective for the determination of the connection between properties of the solvents and the ratio of separate products yields. The data from [17] were used by us for the consideration; in these data were presented the results of studying the selectivity of photochemical chlorination of 2,3−dimethylbutane in different media as the ratio of Q yields of tertiary 2−chloromethylbutane to the first isomer of 1−chlorodimethylbutane, which practically are determined by the ratio of corresponding processes rates. Statistically such ratio should be equal to 1 : 6, however, in consequence of hydrogen great reactive ability near the tertiary atom of carbon the opposite effect is observed − from 4 : 1 in aliphatic solvents to 20−30 : 1 in aromatic media; this fact author [17] explains by intermediate formation of complex with charge transfer (“π−complex”) between chlorine atom and benzene ring in result of which its reactive ability is decreased in comparison with the unbound chlorine atom leading to the process selectivity increasing. It was determined by author of this work, that the concentration change of the chlorinating hydrocarbon can be enough visibly influences on the selectivity Q. Since the hydrocarbon was taken in a great excess relatively to the chlorine, di−substituted compounds are practically not formed, however, the author notes, that some solvents can interact with the chlorine. Evidently, partial chlorine consumption for side reactions can also influences on the determined value Q that decreases the trustworthiness of the presented data. Let us notify also, that the


102

temperature of a process also has the influence on the value Q: it is decreased at the temperature increasing. For aromatic solvents it was determined the linear increasing of logarithm selectivity lgQ at their basicity increasing determined as the constant logarithm of hydrocarbon complex forming with the gas like HCl equilibrium at −78,5 0C [18] and also with ζ constants of Hammet’s equation that was explained as a consequence of π−complex stability increasing at increasing the electronic density on aromatic ring. However, such comparisons have been obtained only for 10−15 aromatic solvents, in preference for alkyl− and halogenobenzenes and do not include the aliphatic solvents. Also others attempts to determine for the all data array from the work [17] the unified dependence on the medium properties do not lead to success − in work [19] there are results concerning to total their generalization via mutliparametric equations; it was determined that the factor defining the selectivity is the polarizability of solvents, however, the application of four parametric Koppel−Palm’s equation for 15 solvents leads to the expression with extremely low value of multiplying correlation coefficient R = 0,621. Therefore advisably it was to check the possibility to generalize of data [17] by means of six parametric equation, taking into account along with the solvation characteristics of the solvents also the square of their solubility Hildebrandt’s parameter δ2 and the molar volume VM characterizing the structural peculiarities of the medium. In Table 3 on the basis of work [17] presented the values of Q obtained at 55 0 C and concentration of solvent 4 mole/l for 28 solvents for which there are all needed characteristics. However, calculated for all data array multiple correlation coefficient value R is low and equal to 0,827. Therefore, in accordance with the recommendations [10] it was done the sequential exclusion from the calculations the most deviating values of Q up to the achievement of R > 0,95. It was necessary to exclude also from the consideration also data for five solvents, namely: nitrobenzene (R = 0,880); methylbenzoate (R = 0,908); chlorobenzene (R = 0,927); trichloroethylene (R = 0,945) and CCl4 (R = 0,961). Thus, it was obtained the six parametric equation (6), which with the adequate accuracy describes the influence of the solvents on the selectivity of a process: Q

49,21 182,75 22,91 f n 2 8,96 11,70 10

R = 0,962

3

2

21,12 9,91 f

0,10 0,03 VM

s = ± 2,53

18,58 8,88 10 3 B 0,18 0,21 10 3 ET

(5)


103

By the sequential exclusion of separate parameters it was determined, that the dependence of the yields ratio of tertiary to the primary halogen derivative of dimethylbutane at its photochemical chlorination at 55 0C with the adequate accuracy is described by three parametric equation (7):

Q

61,00

216,03 19,07 f n 2

17,80 7,88 f

0,088 0,24 VM (6)

R = 0,953

s = ± 6,35

In this equation the role of a factor f(n2) is defining − at its exclusion the correlation destroys (R = 0,610), whereas at the exclusion of any from others factors the decrease of R is less significant: without f(ε) R = 0,942, without VM R = 0,923. It is necessary to draw attention into the insignificance of δ2 parameter, i. e. in presented case on the contrary to others radical reactions the selectivity of the process does not depend on the “cage” effect, probably in consequence of high reactive ability of Cl• radical. Increase of the solvents polarity and their molar volume promote the selectivity displacement in side of the tertiary halogen derivatives formation, however really the value Q is determined by the sum influence of all significant factors and first of all by the ability of the solvent to the non−specific solvation. In Table 3 there are values of Q calculated accordingly to equation (7) and their deviations from the experimental values. As we can see, these deviations are not exceed 25 % with the exception of calculation results for the five excluded from the consideration solvents and also for the cyclohexene and dibutyl ether. It is necessary to notify, that in principle the correlation of lgQ values is possible, however, the result here is visibly worse: at practically the same as for Q value R for all 28 solvents equal to 0, 821 the acceptable value R ≥ 0,95 is achieved only after an exclusion of data for all six solvents and achieved at that time value R = 0,952 is visibly lower, then in a case of the calculations upon Q: R = 0,962. It more essentially, that practically the all parameters of this equation are significant: an exclusion from the consideration of term with δ2 decreases R till 0,946; an exclusion of any other term of this equation practically destroys of the correlation: value R is decreased till 0,74−0,91.


104

Table 3. Experimental [17] and calculated accordingly to equation (7) values of the selectivity Q for the reaction of photochlorination of 2,3−dimethylbutane and their divergence ΔQ № 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28

Solvent Nitromethane Methyl acetate Butyric acid Cyclohexene Propionitrile Butyronitrile tert−Butanol 1,4−Dioxane Dibutylether Dimethylformamide Fluorobenzene Benzene Toluene о−Xylene Ethylbenzene Anizole p−Xylene Cumene m−Xylene tert−Butylbenzene Mesitylene Iodobenzene 1−Chloronaphthalene Tetrachloromethane‫٭‬ Trichloroethylene‫٭‬ Chlorobenzene‫٭‬ Methylbenzoate‫٭‬ Nitrobenzene‫٭‬

Qexp. 3,30 4,30 4,10 3,60 4,00 4,00 4,80 5,60 7,20 9,10 16,20 14,60 15,40 15,00 16,30 18,40 18,60 20,30 22,40 24,00 25,00 31,00 33,00 3,50 3,60 10,20 10,20 4,90

Qcalc. 2,5216 0,6912 6,2539 9,5359 1,7652 5,4232 6,1643 5,5424 11,4424 10,1980 13,6861 14,2072 15,8051 18,2436 16,8521 20,2103 16,9757 18,1112 22,6902 19,5608 18,6547 31,1138 34,5510 11,3189 13,4168 20,8410 22,7262 25,5753

ΔQ −0,7784 −3,6088 2,1539 5,9359 −2,2348 1,4232 1,3643 −0,0576 4,2424 1,0980 −2,5139 −0,3928 0,4051 3,2436 0,5521 1,8103 −1,6243 −2,1888 0,2902 −4,4392 −6,3453 0,1138 1,5510 7,8189 9,8168 10,6410 12,5262 20,6753

Note: *Data have not taken into account under the calculation accordingly to equation (7).

It was interesting to compare the efficiency of proposed approach to other reactions of radical chlorination and bromination. It was studied by authors [20] the flourbromination of mixtures consisting of cyclopropylbenzene and toluene or p−chlorotoluene proceeding with the cyclopropylic ring breaking in the first case


105

(C−C reactivity) or with the formation of benzyl bromide in the second case (C−H reactivity). These data are essentially differed into approach in comparison with the work [17], since the authors studied the reaction mainly in the medium of halogenohydrocarbons unable to the specific interactions and, respectively, to the formation of the π−complex that permitted to consider the results with the application of intrinsic pressure conception. Corresponding data are represented in Table 4. It was determined by authors the absence of clear dependence between the values of selectivity Q = ks/kn and viscosity or Kirkwood’s function of the solvents. Although in both cases it is observed definite symbacy, however, the values of correlation coefficients are low, correspondingly 0,79 (for 17 media) and 0,8 (for 14 media). Essentially better agreement is observed between Q and δ2 parameter − r ~ 0,95 (for 15 media). Higher degree of relationship is observed with the intrinsic pressure parameter, however, it known only for nine among all studied solvents. Since the parameters required for the generalization of data [20] accordingly to equation are known not for all solvents (first of all for fluorochlorohydrocarbons), it were generalized by us the values Q only for 11 media (see Table 4). Obtained six parametric equation (8) is characterized by high value of R = 0,978, however, in accordance with the conclusions [20] the factor defining (and increasing) the selectivity value is medium cohesion energy density; the value of paired correlation coefficient r between Q and δ2 is equal to 0,728. Table 4. Experimental [20] and calculated accordingly to equation (9) seletcivities Q for reaction of photobromination of blend consisting of cyclopropylbenzene and toluene № 1 2 3 4 5 6 7 8 9 10 11

Solvent Pentane 1,2−Dibromomethane Dichloromethane Chloroform Tetrachloromethane 1,2−Dichloroethane Benzene Chlorobenzene Bromobenzene 1−Bromonaphthalene Carbon disulfide

Qexp. 0,570 4,300 3,900 3,300 1,800 4,200 2,900 3,600 4,000 9,700 2,900

Qcalc. 0,5948 5,3066 2,9950 2,4179 2,2276 3,4733 2,8121 4,3440 5,6131 8,3180 3,0675

ΔQ 0,0248 1,0066 −0,9050 −0,8821 0,4276 −0,7267 −0,0879 0,7440 1,6131 −1,3820 0,1675


106

Unlike to above considered case of the chlorination reaction, here insignificant is the factor of the polarizability, that possibly conditioned by specific selection of solvents − from 11 only 9 are halogen substituted for which the higher polarizability is typical. At the exclusion of this factor R is decreased insignificantly:

Q

38,62 34,28 9,61 f

38,11 9,24 10 3 B 0,92 0,22 ET

36,70 9,24 10 3

7,64 0,81 10 2 VM R = 0,976

2

(7) s = ± 0,491

Following exclusion of any among terms of the equation decreases of R to undesirable low limits < 0,95. Here the sign “minus” notices upon oneself the attention at the parameter of solvent basicity. It is well−known, that the halogen hydrocarbons form the π−complexes with the aromatic hydrocarbons [21, 22] playing the role of electrons donors. Increasing the halogenohydrocarbons basicity decreases their ability to procrastinate upon themselves π−electrons of aromatic ring of the reagent, i. e. decreases the constant of complex formation between the components of the system. Decrease (in accordance with the equation (9)) the value Q, i. e. the ratio kcyclopropylbenzene/kbenzene with the acceptor basicity increasing points out the relative increasing of the toluene bromation rate with respect to one of the cyclopropylbenzene, that permits to assume the preferable interaction of bromine atom not with the pure hydrocarbon, but with its solvation form − π−complex with the solvent − halogen hydrocarbon. However, similar to the chlorination reaction the factors of basicity and electrophilicity characterizing the specific solvation have relatively less influence on the selectivity. The connection between the value Q and the medium properties can be described although with a low degree of accuracy by two parametric equation:

Q

11,28

R = 0,915

26,15 4,16 10

3

2

5,57 1,28 10 2 VM

(8)

s = ± 0,918

As we can see, the selectivity of the studied reaction of photochemical bromation is determined by not only medium cohesion and structural peculiarities of the solvents, but also by their ability to the solvation. Probably, it is connected


107

with the visibly great sizes of the bromine atom in comparison with the chlorine [23]. Thus, an application of multiparametric equations permits not only quantitatively to generalize of rate data for hydrocarbons radical halagenation, but also permits to do some conclusions about chemical mechanism of these reactions. That is why it was interesting to check the application of six parametric equation for the generalization of data in others works concerning to medium influence on the ratio of reaction products, i. e. on the rate of radical processes which can proceed in two alternative ways. In work [24] presented the data concerning to interaction of 2,3−dimethylbutane (0,8 M) (I) with tert−butylhypochloride (0,2 M) initiated by UV−radiation in 16 solvents in a temperatures range 0−100 0C. It is known, that the tert−butylhypochloride under light is decomposed with the formation of radicals Cl• and (CH3)3CO• which in turn can either to be regrouped with the methyl radical detachment or interact with others compounds, in presented case with the hydrocarbons: (СН3)3СО + RH (СН3)3СО

kд

k

(9)

(СН3)3СОН + R

(10)

СН3СОСН3 + СН3

In a case of 2,3−dimethylbutane (I) the chlorination by chlorine atom proceeds with the formation of tertiary 2−chloro−2,3−dimethylbutane (II) and parallel with the formation of primary 1−chloro−2,3−dimethylbutane (III), quantities of which are determined by corresponding processes rate with the constants kt and kp. Dependently on the solvents nature the ratio Q = kt/kp can be varied approximately in four times, for example, at 25 0C from 17 for methyl acetate till 72 for anisole.

kt

.

CH3 CH CH CH3 + Cl CH3 CH3

kp

CH3CH3 CH3 C C CH3 Cl H

(II)

CH3CH3 Cl CH 2 C C CH3 (III) H H

108


Table 5. Ratio of yields of 2−chloro−2,3−dimethylbutane and 1−chloro−2,3−dimethylbutane Q in different solvents at 0; 25; 40 and 70 0С [24] №

Solvent

0 0С

1 2 3 4 5 6 7 8 9 10 11 12 13 14

Anisole Bromobenzene tert−Butyl benzene Benzene trans−Dichloroethylene cis−Dichloroethylene Chlorobenzene о−Dichlorobenzene Benzonitrile tert−Butanol Acetone Acetonitrile Acetic acid Methyl acetate

106 104 96 89 75 60 94 91 67 − 128 − 53 25

25 0С exp. 72,0 78,0 75,0 70,0 61,0 47,0 66,0 66,0 48,0 38,0 76,0 47.0 28.0 17.0

calc. 68,3 80,8 63,7 75,7 63,2 42,0 65,4 71,2 − 36,7 − 40,8 35,0 22,3

Q −3,7 2,8 −11,3 5,7 2,2 −5,0 −0,6 5,2 − −1,3 − −6,2 7,0 5,3

40 0С

70 0С

65 64 63 55 50 40 54 50 40 30 51 33 20 14

45 47 44 − 40 29 35 34 25 20 30 17 − 10

Ер−Ет kcalor/mole 2,25 2,13 2,05 1,99 1,74 1,89 2,58 2,63 2,57 3,06 3,77 4,57 4,21 2,35

In Table 5 there are values for the ratios kt/kp at temperatures: 0; 25; 40 and 70 0C, and also the differences in activation energies for both processes (Ep − ET) (ccal/mole) taken from the work [24]. Since at 100 0C the ratio Q determined only for some solvents, these data are not presented. In maximal number of solvents (N = 16) the reaction was studied at 25 and 40 0C, however, the values obtained in 80 % acetone and also in absence of the solvent, that is, in pure 2,3−dimethylbutane, have been excluded from the data presented in work [24]. Accordingly to free energies linearity principle their change in process is proportional to the logarithms of the reaction rate constants. Generalization of data from Table 5 accordingly to lgQ = lgkt/kp for 14 solvents at 25 0C upon six parametric equation leads to the expression with the multiplying correlation coefficient R = 0,672. After an exclusion of the most deviating data for the acetone and methyl acetate for the residuary 12 solvents R is equal to 0,951. In work [23] it was shown by us that for the generalization of data concerning to medium influence on the ratio of two products forming at photochemical chlorination of 2,3−dimethylbutane, better to start not from the logarithms values Q, but from the value itself. That is why this approach has been used by us also in the presented case. Really, generalization of data obtained at 25 0C in 14 solvents leads to the equation with higher value of multiplying correlation coefficient R = 0,704. This value also is unsatisfactorily low; the sequential exclusion from the consideration (in accordance with the IUPAC recommendations [10]) the most


109

differing data for the acetone and benzonitrile permits to increase of R respectively to 0,929 and 0,977 (equation (11)).

Q

75,86 330,5 67,4 f n 2 0,20 0,03

N = 12

2

144,7 28,6 f

0,03 0,03 B

0,18 0,46 ET

0,23 0,09 VM

(11)

R = 0,977

s = ± 4,26

An adequacy of the equation as same as in the all others cases is confirmed by its Fisher’s criterion agreement with the tabled value for corresponding number of points at degree of reliability α = 0,95. It is necessary to note here, that in work [19] the reliable correlation was not determined at generalization of data from work [24] upon lgkt/kp in accordance with the Koppel−Palm’s equation; at the same time, the value R = 0,898 was obtained at generalization accordingly to the Swain’s equation [25] for 9 solvents, besides, the defining factor here was the “acidity” of the solvent. Values of pair correlation coefficients r between Q and separate parameters (after an exclusion of deviating data) are respectively equal to 0,872; 0,490; 0,718; 0,328 and 0,647, although point out the probable predominant influence of the polarizability and medium electrophilicity factors on the ratio of reaction products, however, do not permit to determine quantitatively their significance. That is why in accordance with the technique [10] the significance of the separate parameters has been determined as same as in others cases by their alternative exclusion with the calculation every time the values R for obtained equations with less number of terms. Thus, it was determined a low significance of the ability to the specific nucleophilic solvation B and molar volume VM factors. At exclusion of B, R is decreased only to 0,974 and the following exclusion of VM leads to the four parametric equation with R = 0,962.

Q

55,71 422,8 58,7 f n 2

127,6 35,1 f

0,16 0,04

2

0,58 0,55 ET (12)

R = 0,962

s = ± 5,42

Factor ET is also of little significance: dependence of the yields ratio of tertiary and primary isomers upon the properties of the solvent can be acceptably described by three parametric equation (15).


110

Q

81,67

460,5 48,7 f n 2

144,6 32,5 f

0,16 0,04

2

(13) R = 0,958

s = ± 5,68

Following exclusion of any terms from the equation decreases of R till the values less than 0,90; a function is especially sensible to the exclusion of polarizability parameter. As same as in a case of photochemical chlorination (I) [23], a factor determining the ratio of isomers Q is the non−specific solvation of the substrate connected with the ability of the solvent to the polarization − the pair correlation coefficients between Q and f(n2) at 25 0C are correspondingly equal to 0,887 [23] and 0,872. In both cases it is marked also the insignificance of possible specific interactions. At the same time, the influence of two others parameters f(ε) and VM in the first case and f(ε) and δ2 in the second case has only the corrective character: at the exclusion of f(n2) from the three parametric equation, R is decreased to 0,6; the correlation is wholly destroyed whereas an exclusion of f(ε), VM or δ2 leads to the two parametric equations with R in a ranges 0,90−0,94. It is necessary to pay the attention in fact that in both cases (photochemical chlorination of compound (I) [23] by chlorine and the reaction with tert−BuOCl) the term of equation with the Hildebrand’s parameter δ2 has the sign “plus” since the medium self association determines the “cage” effect promotional to the radical reactions proceeding. The same dependencies have been obtained under the generalization of data [24] by means of six parametric equation for temperatures 0; 40 and 70 0C. The difference of the activation energies Ep−Et for different media can be also generalized by means of multiparametric equation. For all 14 solvents R is equal to 0,878; an exclusion from the consideration of data for cis−dichloroethylene and methylacetate permits to obtain the expression with the satisfactory degree of relationship. Analysis of the presented equations shows, that the ability of the solvents to the self association promotes the interaction of radicals (CH3)3CO• with the exceeded cyclohexane, probably, in consequence of staining the “cage” effect; some less effect is observed at increasing the molar volume of the solvent. At the same time, the ability of organic solvents to the non−specific (f(ε)) or to the specific (ET) solvation of radicals (CH3)3CO• promotes their dissociation. On the contrary, the analysis of data concerning to the photochemical bromination of the mixture consisting of cyclopropylbenzene and toluene in medium of organic


111

solvents [20] showed, that increase of δ2 and VM favors to break up of cyclopropyl ring and the polarity increasing raises the yield of the bromide benzyl [23]. Determined by us insignificance of the solvents basicity B (their ability to the nucleophilic solvation) in reactions of the halogenation is in good agreement with the qualitative conclusion of authors [24]: charge transfer plays only the insignificant role into transition state at hydrogen atom break by alkoxy radical, since the maximal differences into selectivity are observed in polar media and in aromatic solvents a less effect is observed. Our results contradict to the Russell’s point of view about possible influence of the complex forming between the chlorine atom and π−electron system of aromatic ring [17]. Authors [24] supposed also the possibility of the polarity and polarizability of the solvents influence on the process, but they obtained only the qualitative correlation Q with ε, dipole moment µ or polarity Kosover’s parameter Z. Presented here calculations confirm the assumption about the defining role of non−specific solvation in studied process from the one hand, and explain the reason of the clear relationship absence on the other hand: quantitative generalization of the solvents properties influence on the selectivity can be obtained only by means of multiparametric equations taking into account the common influence of the different factors. Here it would be appropriately notified, that the Z parameter determines not the solvents polarity, but their electrophilicity − it is proportional to the Raichardt’s parameter ET [26]. An absence of the satisfactory correlation between the selectivity of the radical bromination and separate characteristics of the solvents, in particular, with the polarity, was shown also in the work [20]. However, proposed by authors the cohesion energy density (“intrinsic pressure”) as optimal characteristic also gives only the approximated agreement; in work [23] it was shown by us the expediency of the multiparametric equations application also for this case. Also the data from ref. [27] concerning to the influence of the solvents on the selectivity of the electrophilic addition of halogen hydrocarbons and olefins can be generalized by multiparametric equations [27].

6.3. THE EXAMPLES OF OXIDATION BY PERACETIC ACID On a basis of the solvents effects investigations in the work [28] it was uttered an opinion that the chemical mechanism of reactions epoxidation and oxidation by peracids of sulphides, thiocompounds, nitrogencompounds and alkines is the same: in accordance with the Lynch’s and Pausacker’s points of view [29] the active form is the cyclic form of the peracid with intramolecular hydrogen bond,

112


forming via reaction the chelate complex upon unshared pair of electrons of the substrate. In accordance with this chemical mechanism the rates of reactions are decelerated in the base solvents by reason of transformation of the peracid into low–activity form with intermolecular hydrogen bond. However, the strict proportionality between the rates of the corresponding reactions is absent. Under comparison of the rates [28] for p– dinitrodibenzylsulphide oxidation by perbenzoic acid and for natrozobenzene oxidation by m–chloroperbenzoic acid, the data concerning to oxidation into benzene and ethanol are deviated from the linear dependence. Some deviations are observed also under comparison between themselves of the rates for oxidation of nitrozobenzene and epoxidation of cyclohexene by peracetic acid accordingly to data [30] or for reactions of epoxidation by peracids of different substrates [31]. The reason of this behaviour should be searched evidently in different sensitivity of the substrates to solvation effects of medium, the full considering of which is possible only due to application of multiparametric free energies linearity equation proposed by Koppel and Palm [32]. Although the factor determining the reaction rate of substrates with peracids is the basicity of medium, however some contribution into this value has also other solvation effects. Thus, we have showed [31, 33], that in epoxidation reactions the correlation coefficient between the process rate and decelerating it the basicity of medium is in the ranges 0,86 – 0,95; multiple correlation coefficient is visibly increased under taking into account of other solvation effects, first of all, electrophilic solvation. At oxidation of the sulphides more significant is additional considering the non–specific solvation [34]. For the purpose of clearing up the relative role of the different solvation effects at interaction of peracids with other substrates we have treated the data concerning to oxidation of nitrozobenzene [35] and 4–octyne [36] by m– chloroperbenzoic acid (see Table 6) with the use of the Koppel–Palm equation (with the additional considering of the cohesion energy density). We have obtained the following equations for nitrozobenzene:

lg k1 10 4

m = 11;

0,665 9,507

n2 1 1 0,251 0,045 2 2 1 n 2

R = 0,986;

r1 = 0,746; r2 = 0,321;

2

0,00357 B 0,24 E (14)

s = 0,123;

r3 = 0,262;

r4 = 0,925;

r5 = 0,444.


113

Table 6. Rate of nitrosobenzene oxidation (k1) and 4–octyne oxidation (k2) by m–chloroperbenzoic acid in different media upon data [35–36] №

Solvent

1 1 2 3 4 5 6 7 8 9 10 11 12

2 CHCl3 CCl4 Benzene Nitrobenzene Sulpholane DMFA Dioxane Tert–butanol Isopropanol Ethanol Methanol CH2Cl2

lgk1∙104, exp. 3 2,556 2,117 2,299 2,539 2,0414 1,029 1,441 1,301 1,425 1,537 1,660 –

lgk1∙104, calc. 4 2,425 2,284 2,282 2,550 2,027 1,207 1,356 1,233 1,372 1,485 1,722 –

Δlgk

lgk2∙104, exp.

5 0,131 –0,167 0,017 –0,011 0,015 –0,178 0,085 0,068 0,053 0,052 –0,062 –

6 1,3263 0,7300 0,8407 – – – –0,4089 – –0,4815 – –0,4089 1,0867

Therefore, as same as in a case of the interaction with other substrates, the basicity of medium although is a factor determining and decelerating the process rate, however the value of the correlation coefficient between lgk1 and B it is enough low – only 0,925; and the additional considering of other solvation factors permits to achieve the best correlation. Check of significance of the coefficients at separate factors points out the insignificance of medium polarity and quite low sensitivity of reaction to the electrophilicity of medium – the consecutive exclusion of the corresponding parameters in the regression equation decreases R till 0,985 and 0,982 respectively. At the same time, an exclusion from the calculations of polarity parameter decreases R till 0,955; an exclusion of the cohesion energy density decreases R till 0,965. Adequate description of the process can be realized via three–parametrc equation:

lg k1 10 4

0,029 6,83

n2 1 n2 2

R = 0,982; s = 0,119 Fcalc. = 19,4 > 8,89 = FT(0,05; 7;3).

0,0051

2

0,0388B

(15)

114


Thereby, the medium influence on reaction of nitrozobenzene oxidation like to the sulphide oxidation. For dinitrodibenzylsulphide oxidation we have obtained in work [34] the following expression: 2+ lg k m = 12;

0,164 8,580

n2 1 1,496 n2 2

R = 0,984;

2

0,00426 B

s = 0,132;

(16)

r(OB) = 0,953.

Some deviations from the linearity indicated by authors [28] between the rates of these processes caused by less influence of non–specific solvation in the second reaction, although in both cases the role of the polarity factor is the same and is opposite to the decelerating influence of the basicity. The influence of the cohesion energy density (energy consumption for cavity formation for the location of reactive complex) is less significant, especially in the first case. For octyne oxidation in consequence of the less number of studied solvents (namely, seven), the calculation upon five–parametric equation is statistically improbable, however, after rapid estimation of the significance for some factors it was determined the insignificance of the cohesion energy density and electrophilic solvation. The process is good described by three–parametric equation:

lg k 2 10 4 m = 7;

2,523

n2 1 n2 2

R = 0,998;

r1 = 0,793; r2 = 0,247;

2,050

2

1 0,0050 B 1

(17)

s = 0,172;

r3 = 0,463.

Fcalc. = 20,8 > 9,28 = FT(0,05; 3;3). As same as in a previous case, the factor determining the process rate is the basicity of medium and an ability of the solvents to the non–specific solvation is favourable to the process proceeding as a consequence of the active complex solvation. However, here both factors f(n2) and f(ε) are equivalent – an exclusion of any among them decreases the value R till 0,968. It’s interesting to notify, that the oxidation reactions unlike to the epoxidation ones practically are insensitive to the possible electpophilic solvation of the reactive complex.


115

Presented here analysis once more confirm the opinion that the influence of medium even on similar reactions can visibly differed as a result of differences in solvation processes and the full description of these inluences is possible only under condition of taking into account the all solvation effects via multiparametric free energies linearity equations.

REFERENCES [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18] [19] [20]

Schulz, C. Ruckurdt // Tetrahedron Lett. (1976), vol. 43, p. p. 3883−3886 Overberger, M. Oishaughnessy, H. Shalit // J. Amer. Chem. Soc. (1949), vol. 71 (8), p. p. 2661−2666 L. Shcherbina, B. Heller, V. Chirgilov // Reports of Insts.: “Chemistry and Chemical Technology” (2001), vol. 43 (5), p. p. 141−144 Ch. Cholling // Free Radicals in Solutions / М.: (1962), p. p. 404−405 L. Arnett // J. Amer. Chem. Soc. (1952), vol. 74 (8), p. p. 2027−2031 Petersen, J. Markgraf, S. Ross // J. Amer. Chem. Soc. (1961), vol. 83 (18), p. p. 3819−3823 Moroni // Makromol. Chemie (1967), vol. 105 (2412), p. p. 43−49 M. Kulkarni, R. Mashelkar, L. Doraiswamy // Chem. Eng. Sci. (1980), vol. 35 (4), p. p. 828−830 J. Howard, R. Ingold // Canad. J. Chem. (1964), vol.43 (611), p. 1044 Quant. Struct. - Act. Relat. (1985), vol. 4 (1), p. 29 Hendry, G. Russel // J. Amer. Chem. Soc. (1964), vol. 86 (12), p. 2368 J. Leffler, R. Hubbard // Contrib. Dept. of Chemistry, Florida Univ. (1954), p.p. 1089−1096 M. Alden, J. Leffler // J. Amer. Chem. Soc. (1994), vol. 76 (105), p. p. 425−1427 W. Pryor, K. Smith // J. Amer. Chem. Soc. (1970), vol. 12 (18), p. p. 5403−5412 R. Neumann, G. Lockyer // J. Amer. Chem. Soc. (1983), vol. 105 (12), p. p. 3892−3897 W. Duismann, C.Ruchardt //. Chem. Ber. (1978), vol. 11, p. p. 596−605 G. Russel // J. Am. Chem. Soc. (1958), vol. 80, p. 4987. H. Brown, J. Brady // J. Am. Chem. Soc. (1952), vol. 74, p. 3570 Pytela // Coll.Czech. Chem.Commun. (1988), vol. 53, p. 1333 M. Tanko, M. Suleman, G. Hulvey, A. Park, J. Powers // J. Am. Chem. Soc. (1993), vol. 115, p. 4520

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[21] Guryanova, I. Goldshtein, I. Romm // Donor−Acceptor Bond / М.: „Chemistry”(1973), 323 p. [22] R. Makitra, Ya. Tsykanchuk, O. Melnychuk // Journ. of Org. Chem. (1973), vol. 43, p. 146 [23] R. Makitra, G. Midyana, Е. Palchykova // Journ. of Org. Chem. (2005), vol. 41 (7), p. p. 967−972 [24] C. Walling, P. Wagner // J. Am. Chem. Soc. (1964), vol. 87, p. 3368 [25] C. Swain, M. Swain, A. Powel, S. Alumni // J. Am. Chem. Soc. (1983), vol. 105, p. 802 [26] T. Griffiths, D. Pugh // Coord. Chem. Rev. (1979), vol. 29, p. 129 [27] M. Capka, V. Bazant, V. Chvalovsky // Collect. Czech. Chem. Commun. (1968), vol. 33 (9), p. p. 2886−2894. [28] K. M. Ibne–Rasa, J. O. Edwards // Intern. J. Chem. Kinetics, vol. 7, 575 (1975.) [29] B. M. Lynch, K. H. Pausacker // J. Chem. Soc., 1525 (1955). [30] P. Renolen, J. Ugelstad // J. Chim. Phys., vol. 8, 634 (1960); R. Curci, R. A. Di Prete, J. O. Edwards // J. Org. Chem., vol. (35), 740 (1970). [31] Ya.. M. Vasyutyn, R. G. Makitra, Ya. M. Pyrig, V. I. Tymokhin, G. G. Shemray // J. Org. Chem., vol. 21, 471 (1985). [32] A. Koppel, V. A. Palm // In: Advances in Linear Free Energy Relationships, Plenum Press, London – New York (1972), p. 202. [33] Ya.. M. Vasyutyn, G. G. Midyana, R. G. Makitra, Ya. M. Pyrig,, V. I. Tymokhin // Reports of AS USSR, vol. 39 (1985). [34] Ya.. M. Vasyutyn, R. G. Makitra, Ya. M. Pyrig // Ukr. Khim. Journ., vol. 51, 381 (1985). [35] M. Ibne–Rasa, J. O. Edwards, M. T. Kost, A. R. Gallopo // Chem. Ind., 964 (1973). [36] M. Ibne–Rasa, J. O. Edwards, R. H. Pater, J. Ciabattoni // J. Amer. Chem. Soc., vol. 95, 7894 (1973).

CONCLUSIONS The nature of solvents has an essential influence on the rate of the heterolytical reactions, namely, the changes of their rate constants can achieve till the ten orders. At the same time, the change of the rate constants for homolytical reactions with medium relatively insignificantly is varied and, as a rule does not exceed one or two orders. That is why up to the present time it was widespread the point of view about the practical insignificance of the medium influence on such processes. With a storage of the experimental data this statement was contradicted, however the attempts to determine the reliable dependencies between the value of rate constant of radical processes and the properties of the solvents were as a rule unsucssessful (some correlations, for example were obtained only for homologous series of the solvents). The reason of which was the complexity and multi–stage of the homolytic reactions. Based on the analysis of a number of referencees by different authors it was shown in the presented handbook that such point of view does not correspond to reality. The value of the rate constants for a series of the radical reactions can be adequately connected with the solvents characteristics via the multiparametric linear equations, however uder following conditions: i)

such generalization is possible when the total rate of the radical process is determined only by the one limited stage and the influence of other is low significant or when possible is the separate interpretation of individual stages, for example, at separate consideration of initiative stages of process and its proceeding; ii) the reaction proceeds into the one way or possible is the experimental separate determination of the constants for individual directions, for

118

Gennady E. Zaikov, Roman G. Makitra, Galina G. Midyana et al. example, determination the rate of parallely proceeding reactions of initiated and non–initiated decomposition; iii) since in the radical reactions a so–called “cage” effect plays an important role, which increases the probability of the effective blows of the radicals with the substrate, then the linear equations taking into account only the solvation ability of the medium should be added by the term which takes into account of this factor; effectve taking into account of the medium self–association is possible via including the Hilderbrandt solubility parameter into calculations.

An effective application of such approach it was shown mainly on examples of series of oxidation reactions, peroxy compounds decomposition and also for redical decomposition of azocompounds or galogenization reactions. In the last case is possible also the quantitative generalization of data with respect to the products yields forming as a result of realization of different possible ways of reactions.

APPENDIX THE MAIN CHARACTERISTICS OF THE SOLVENTS № 1 1 2 3 4 5 6 7 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 33 34

Solvent 2 Pentane Isоpentane Hexane n–Heptane Heptene–1 n–Octane Isooctane n–Nonane n–Decane Undecane n–Dodecane Tridecane Tetradecane Pentadecane Hexadecane Cyclopentane Cyclohexane Methylcyclohexane Cyclohexene Decalin (mix) Benzene Toluene o–Xylene m–Xylol p–Xylol Mesytelene Ethylbenzene Cumene n–Butylbenzene t–Butylbenzene Tetraline trans–Decaline α– Methylnaphthalene β– Methylnaphthalene

n 3 1.35748 1.35373 1.37486 1.38765 1.39980 1.39743 1.39145 1.40542 1.41189 1.41720 1.42150 1.42560 1.42900 1.43150 1.43450 1.40363 1.42623 1.42312 1.44650 1.47580 1.49790 1.49693 1.50543 1.49721 1.49581 1.49837 1.49330 1.49146 1.48979 1.49266 1.54135 1.46950

ε 4 1.8440 1.8450 1.8900 1.9240 2.0685 1.9480 1.9400 1.9725 1.9930 2.0050 2.0160 2.0261 2.0368 2.0452 2.0518 1.9650 2.0230 2.0200 2.2140 2.2600 2.2840 2.3837 2.5740 2.3740 2.2690 2.2790 2.4030 2.3833 2.3590 2.3660 2.7730 2.1515

δ2 5 210.3 182.8 222.0 231.0 251.2 240.3 196.4 243.4 249.6 256.0 254.2 260.8 262.4 265.7 269.0 275.6 281.5 255.4 255.4 323.2 349.7 331.2 338.6 320.4 313.3 324.2 325.7 302.1 309.0 289.0 381.4 323.2

B 6 0 0 0 0 90 0 0 0 0 0 0 0 0 0 0 0 0 0 97 0 48 58 68 68 68 77 58 56 56 60 0 0

ET 7 31.0 30.9 31.0 31.1 30.0 31.1 30.3 31.0 31.0 31.0 31.1 31.0 31.2 31.0 30.8 30.4 30.9 30.7 32.3 31.8 34.3 33.9 34.3 33.3 33.1 32.9 34.0 33.9 33.8 33.7 33.5 31.8

VM 8 114.5238 116.1836 130.5000 146.4912 140.8608 162.5600 165.0578 178.6212 194.9300 210.9312 227.4600 243.5271 260.0900 275.8571 294.0300 94.1342 108.1000 127.6723 101.4074 156.5572 88.8500 106.2400 120.6500 122.8900 123.3400 139.0972 122.4900 139.4316 155.6961 154.7982 135.8684 154.4581

1.61755

2.9150

408.6

64

35.3

138.7219

1.60192

2.7470

392.4

54

34.8

143.0483

120 № 1 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73

Gennady E. Zaikov, Roman G. Makitra, Galina G. Midyana et al. Solvent 2 Styrene Dichloromethane Chloroform Tetrachloromethane Ethylchloride 1,2–Dichloroethane 1,1–Dichloroethane 1,1,1– Trichloroethane Tetrachloroethane Pentachloroethane Vinyliden chloride Trichloroethylene Tetrachloroethylene 1–Chloropropane n–Butylchloride tert–Butylchloride Chlorocyclohexane Chlorobenzene o–Dichlorobenzene p–Chlorotoluene Benzylchloride 1–Chloronaphtaline Bromoform Bromoethane 1,2– Dibromomethane Cyclohexylbromide Bromobenzene m–Bromotoluene 1–Bromonaphtaline Iodobenzene Flourobenzene Methanol Ethanol n–Propanol Isopropanol n–Butanol Isobutanol Butanol–2 tert–Butanol

n 3 1.54690 1.42456 1.44330 1.46603 1.36760 1.44480 1.41640

ε 4 2.4257 9.1400 4.7960 2.2400 9.4500 10.663 10.860

δ2 5 361.0 410.5 353.1 311.2 396.4 396.4 398.0

B 6 43 23 14 0 34 40 53

ET 7 34.8 40.7 39.1 32.4 41.6 41.9 39.4

VM 8 115.3267 64.0000 80.5000 96.4900 70.0543 80.1600 84.2298

1.43790

5.6400

305.6

92

36.2

100.6943

1.49400 1.50250 1.42490 1.47730 1.50566 1.38790 1.40210 1.38570 1.46260 1.52480 1.55145 1.51990 1.53910 1.63260 1.59760 1.42481

8.0800 3.8330 4.6700 3.4090 2.3000 7.7000 7.3980 9.5740 8.1500 5.6900 9.9300 6.0800 6.4300 5.0500 4.3850 9.3700

403.6 350.9 367.3 354.6 362.1 300.7 297.9 259.2 336.3 381.0 424.4 388.6 450.0 439.1 468.9 385.9

29 12 18 10 2 46 59 64 67 38 28 41 40 37 32 79

38.7 35.4 37.0 35.9 31.9 37.4 39.4 40.7 36.2 37.5 38.1 38.7 38.5 37.0 37.7 37.6

104.9125 121.0712 82.5000 89.6317 102.1244 88.2472 106.2801 109.2916 121.4023 101.6802 112.6513 118.2991 115.0727 136.1893 87.4637 76.1565

1.53880

4.8600

449.9

85

38.3

86.6000

1.49530 1.56010 1.55140 1.60000 1.62130 1.46573 1.32663 1.36139 1.38556 1.37760 1.39922 1.39390 1.39240 1.38779

7.9200 5.3910 5.3600 5.1150 4.6250 5.4500 33.600 25.090 20.330 19.520 17.510 17.800 17.460 12.470

359.3 422.4 416.0 452.0 391.9 374.3 876.2 676.0 590.5 563.5 542.9 530.4 517.9 461.8

68 40 53 37 38 38 218 235 223 236 231 230 240 247

39.6 37.5 38.1 37.5 37.9 37.0 55.4 51.9 50.7 48.4 50.2 48.6 47.1 43.3

123.1571 105.0301 121.3049 139.7233 111.8531 93.8477 40.4300 58.4100 74.8000 76.5100 91.5300 92.4400 91.9000 93.9500

The Medium Influence on some other Homolytic Reactions № 1 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114

Solvent 2 n–Amyl alcohol Isoamyl alcohol n–Hexanol Isohexanol n–Heptanol n–Octanol Nonanol Decanol Undecanol Dodecanol Cyclohexanol Benzyl alcohol Allyl alcohol 2–Chloroethanol Ethyleneglycol 2–Methoxyethanol Diethyleneglycol Triethyleneglycol Glycerin Phenol Diethyl ether Dipropyl ether Isopropyl ether Dibutyl ether Chlorex Dimethoxyethane Diglyme Tetrahydrofurane 1,4–Dioxane Dibenzyl ether Anisol Phenetol Diphenyl ether Acetone Methylethylketone Diethylketone Cyclopentanone 2–Hexanone Cyclohexanone Acetophenone Benzophenone

n 3 1.40999 1.40853 1.41816 1.44900 1.42490 1.42913 1.43330 1.43720 1.43920 1.44550 1.46290 1.54033 1.41345 1.44200 1.43180 1.40240 1.44790 1.45310 1.47470 1.55090 1.35555 1.38320 1.36888 1.39925 1.45750 1.37960 1.40970 1.40762 1.42241 1.51680 1.51791 1.50840 1.58260 1.35880 1.37850 1.39240 1.43680 1.40070 1.45097 1.53718 1.60770

ε 4 13.900 15.640 12.500 12.500 11.100 10.340 9.1700 8.1000 5.9800 5.7030 15.000 16.300 20.600 25.800 37.700 15.950 31.690 23.190 41.140 8.1000 4.3350 3.3940 4.0400 3.0830 21.200 3.5000 5.5000 7.5800 2.2940 3.8210 4.4100 4.2160 3.6860 21.240 18.510 17.000 13.600 14.560 18.300 17.390 13.300

δ2 5 519.4 510.8 486.5 501.0 435.0 444.2 429.7 417.0 404.6 394.8 514.5 612.9 633.4 656.3 868.3 542.2 612.9 786.4 1200 755.0 228.0 243.5 220.2 250.4 443.9 306.1 362.0 363.8 408.0 416.2 380.0 412.0 358.8 397.2 361.7 339.1 453.7 312.3 431.2 464.3 434.8

B 6 235 227 237 226 239 237 236 236 237 237 242 208 204 183 224 238 242 260 230 130 271 279 293 285 178 238 240 305 236 233 155 158 123 193 209 187 230 210 242 202 192

ET 7 49.1 49.0 48.8 49.8 48.5 48.3 48.0 47.7 47.2 46.7 46.9 50.4 52.1 55.5 56.3 52.3 53.8 53.5 57.0 61.4 34.5 34.0 34.0 33.0 42.6 38.2 38.6 37.4 36.0 36.3 37.1 36.6 35.3 42.2 41.3 39.3 39.4 40.1 39.8 40.6 40.4

121 VM 8 108.1800 108.8700 125.2600 125.6900 141.3800 157.4400 174.2149 190.6988 209.6107 224.2238 104.1000 103.6721 68.0300 67.0700 56.0100 78.8800 94.7800 133.4844 73.0873 87.8711 103.8000 138.8600 141.1400 169.3000 117.0376 104.4200 142.9000 81.1400 85.2200 191.3610 109.2222 126.3289 158.6207 73.5500 89.5200 105.8000 88.9900 123.5100 103.7500 116.3020 168.2456

122 № 1 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154

Gennady E. Zaikov, Roman G. Makitra, Galina G. Midyana et al. Solvent 2 Formic acid Acetic acid Propionic acid Butyric acid Acetic anhydride Ethylformiate Methylacetate Ethylacetate Ethylchloroacetate Ethyldichloroacetate Ethyltrichloroacetate n–Propylacetate n–Butylacetate Phenylacetate Ethylpropionate Diethylcarbonate Methylbenzoate Ethylbenzoate Dibutylphtalate Propylenecarbonate 4–Butyrolactone Formamide N–methylformamide Dimethylformamide Dimethylacetamide Diethylacetamide N– Methylpyrrolidone Acetonitrile Propionitryle Butyronitryle Benzonitryle Phenilacetonitryle Nitromethane Nitroethane Nitrobenzene Propylamine n–Butylamine Diethylamine Dibutylamine Triethylamine

n 3 1.37140 1.37160 1.38690 1.41580 1.39040 1.35980 1.35930 1.37239 1.42050 1.43840 1.45050 1.38440 1.39406 1.50300 1.38385 1.38456 1.52050 1.50680 1.49250 1.41890 1.43530 1.44754 1.43190 1.43050 1.43720 1.43740

ε 4 57.900 6.1900 3.2000 2.9700 20.500 8.0800 6.7900 6.0530 11.400 10.400 7.8000 5.6040 5.0100 5.2900 5.6500 2.8200 6.5900 6.0170 6.6300 65.100 39.000 111.50 190.50 37.650 38.930 30.400

δ2 5 627.2 427.1 483.3 461.5 562.4 355.9 375.4 342.1 437.7 353.7 324.7 309.3 302.8 381.6 322.4 324.1 408.8 392.1 361.0 739.8 696.5 368.6 875.0 613.6 479.1 411.6

B 6 131 139 139 139 100 185 170 164 125 119 45 185 158 121 174 145 160 142 38 176 207 270 287 294 343 335

ET 7 54.3 51.7 50.5 50.5 43.9 40.9 40.0 38.1 39.4 41.1 39.4 37.5 38.5 38.2 38.8 37.0 39.2 38.1 39.5 46.6 44.3 56.6 54.1 43.8 43.7 41.4

VM 8 37.7295 57.2449 74.6774 91.3900 94.3530 80.8200 79.3200 97.8600 105.7377 122.4649 138.4309 115.0000 131.6700 126.8779 114.5000 121.1589 125.2438 142.8966 266.3541 85.1000 76.5000 39.5435 58.4851 77.4000 92.3860 124.5081

1.46840

32.000

534.2

341

42.2

96.6000

1.34423 1.36390 1.38420 1.52823 1.52086 1.38189 1.39200 1.55257 1.39006 1.40090 1.38637 1.41770 1.40101

37.500 29.700 20.400 25.200 16.700 38.570 29.500 35.720 5.3100 4.8800 3.7800 2.9980 2.6400

590.5 479.4 437.9 515.0 471.3 675.3 515.3 479.4 324.1 309.8 288.5 269.2 213.5

178 162 164 155 155 65 66 67 661 537 637 691 650

45.6 43.7 43.1 42.0 42.7 46.3 43.6 41.2 38.5 38.4 35.4 34.5 32.1

52.4266 70.3448 87.0277 102.5968 115.5000 53.6379 71.3593 102.1659 82.3259 98.9716 102.6826 174.4129 138.8066

The Medium Influence on some other Homolytic Reactions № 1 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192

Solvent 2 Ethylenediamine Piperadine Pirydine Tetramethylurea α–Picoline Анiлiн N–Methylaniline Dimethylaniline Diethylaniline Quinoline Triethylphosphate tri–n–Butylphosphate Hexamethapol Carbon bisulfide Diethylsulfide Thionyl chloride Dimethylsulfoxide Sulfolane Diethylmethanesulfamide Dimethylethansulfamide Diethylethanesulfamide Tetraethylsulfamide Water m–Chlorotoluene Amylodide Benzaldehyde 2–Chlorobutane 2–Ethylhexanol–1 Kerosene А Kerosene F 2–Nitropropane Pentanol–2 n–Amylacetate iso–Amylacetate Diethylmalonate Amyl ether iso–Amyl ether Valeric acid

123

n 3 1.45677 1.45340 1.51000 1.45070 1.50100 1.58545 1.57020 1.55819 1.54178 1.61480 1.40530 1.42240 1.45790 1.62760 1.44233 1.52710 1.47700 1.48170

ε 4 14.200 5.8000 12.300 23.100 9.8000 6.8900 5.9600 4.4800 5.2000 8.8000 8.3000 8.0500 29.600 2.6430 5.9600 9.2500 48.900 44.000

δ2 5 633.5 375.0 427.1 408.3 444.0 454.7 410.3 330.1 333.4 482.9 341.5 282.2 467.0 420.3 308.2 444.0 634.9 689.5

B 6 560 706 472 348 502 346 452 422 316 494 332 336 471 0 250 26 362 181

ET 7 42.0 35.5 40.5 41.0 38.3 44.3 42.5 36.5 38.0 39.4 41.7 39.6 40.9 32.8 33.3 55.0 45.1 44.0

VM 8 66.7778 99.4000 80.5499 119.5062 98.0211 91.1155 108.3418 126.7573 159.7752 117.9452 170.5618 272.9000 175.7000 60.2771 107.7419 71.8912 71.4000 95.1000

1.44700

52.000

468.8

152

43.6

137.5729

1.44770

74.000

490.0

158

43.8

119.9584

1.44810

49.000

441.3

159

43.5

153.8031

1.44790 1.33300 1.52140 1.49550 1.54550 1.39410 1.43000 1.44240 1.44000 1.39440 1.40530 1.40290 1.40120 1.44160 1.40985 1.40850 1.42550

30.000 80.310 5.5500 5.8100 17.800 7.0900 7.7000 2.0700 2.1400 25.520 13.710 4.7900 4.7200 7.5600 2.7980 2.8170 2.6610

359.2 2290 388.6 327.2 368.6 280.0 440.0 257.0 258.0 360.0 475.4 298.1 301.4 293.6 388.0 388.0 408.9

152 156 38 74 180 61 238 0 0 67 230 190 194 190 275 280 139

41.0 63.1 38.3 40.0 40.0 40.0 48.5 31.0 31.1 42.8 46.5 38.0 38.0 35.0 32.0 32.0 48.5

198.9859 18.0000 118.0784 131.1656 101.4532 106.2801 156.5100 0 0 87.0019 108.7300 148.7000 149.2100 151.8199 202.0900 203.5500 108.7646

124 № 1 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209

Gennady E. Zaikov, Roman G. Makitra, Galina G. Midyana et al. Solvent 2 iso–Valeric acid o–Nitrotoluene m–Dichlorobenzene 1–Nitropropane tert–Amyl alcohol 1,2,4– Trichlorobenzene Furan Methylacrylate Vinylacetate Tetrahydropirane cis–Dichloroethylene trans– Dichloroethylene Morpholine Methylformiate 4–Picoline N–Ethylanilyne o–Toluidine

n 3 1.40330 1.54710 1.54586 1.40180 1.40580

ε 4 2.6610 26.260 5.0200 26.740 5.8200

δ2 5 408.9 479.4 402.7 580.0 438.0

B 6 139 67 17 67 264

ET 7 48.5 41.1 37.0 43.0 41.7

VM 8 109.6992 117.9106 114.1382 88.8235 108.4256

1.57100

4.1500

412.1

40

36.2

125.2000

1.42140 1.40400 1.39580 1.42000 1.44900

2.9420 7.1200 2.3000 5.6800 9.2000

346.0 295.8 342.3 327.6 384.2

103 163 143 290 18

36.0 38.8 38.0 36.2 41.9

72.6200 90.5300 93.0700 98.2100 76.0000

1.44600

2.2700

346.0

18

34.2

77.8000

1.45400 1.34330 1.50500 1.55590 1.57280

7.6800 8.5000 12.280 5.8700 6.3400

475.2 420.0 432.6 410.0 410.0

345 170 495 203 197

41.0 41.9 39.5 42.6 42.6

87.5600 61.6500 98.0000 125.9000 107.3000

INDEX A absorption, 68, 79 acceptor, 27, 60, 106 accessibility, 15 accuracy, 22, 26, 36, 44, 62, 69, 70, 75, 79, 102, 103, 106 acetate, 16, 32, 45, 79, 81, 84, 85, 104, 107, 108 acetic acid, 16, 75 acetone, 7, 16, 50, 60, 84, 108 acetonitrile, 25, 33, 50, 60, 69, 72, 75, 98 acetophenone, 9, 10 achievement, 63, 86, 102 acid, 3, 12, 16, 17, 21, 23, 27, 28, 29, 30, 32, 33, 34, 35, 36, 37, 38, 45, 50, 52, 64, 68, 71, 75, 76, 77, 81, 83, 84, 85, 90, 91, 97, 104, 108, 112, 113, 122, 123, 124 acidity, 109 activation, 4, 17, 20, 25, 30, 31, 38, 95, 108, 110 activation energy, 4, 25, 38, 95 additives, 3 adsorption, 90 agents, 4 AIBN, 67, 74, 78, 79, 95 alcohol, 28, 32, 49, 69, 95, 121, 124 alcohols, 7, 50, 60, 63, 80, 82, 97 aldehydes, 82, 83, 84, 85, 91 alkanes, 4, 6, 17, 18, 89 alternative, 16, 43, 87, 107, 109

amide, 123 amine, 55, 56 amines, 42 application, 1, 3, 7, 11, 15, 52, 55, 102, 105, 107, 111, 112, 118 aromatic hydrocarbons, 6, 16, 17, 44, 57, 77, 78, 79, 90, 106 aromatic rings, 74 assumptions, 43 atoms, 33, 58 authenticity, 46 autocatalysis, 86 availability, 7, 16 B barrier, 32 basicity, 12, 19, 26, 27, 33, 34, 36, 37, 38, 44, 48, 57, 58, 60, 61, 62, 69, 71, 73, 78, 79, 84, 90, 100, 102, 106, 111, 112, 113, 114 benzene, 19, 22, 23, 25, 27, 45, 50, 60, 72, 83, 101, 108, 112 benzoyl peroxide, 2, 3, 4, 5, 15, 16, 17, 18, 19, 21, 22, 23, 24, 25, 37 binding, 79 bonds, 41 Boston, 13 bromination, 104, 110, 111 bromine, 106, 107 butterfly, 84 butyl ether, 35, 50

Index

126 butyric, 2, 5, 16, 85, 87, 88, 90, 91 C

carbon, 27, 38, 84, 101 Carbon, 21, 23, 64, 105, 123 carbon tetrachloride, 27, 38 carbonic acids, 90, 97 carbonyl groups, 22 carboxyl, 53 catalysis, 44, 48 catalyst, 41 cell, 17, 19, 20, 46, 53 chain termination, 69, 83, 89 chain transfer, 5, 67, 69, 71, 72, 82, 83, 85, 86, 87, 89 chemical industry, 55 chemical properties, 21 chloride, 64, 120, 123 chlorination, 101, 103, 104, 106, 107, 108, 110 chlorine, 101, 107, 110, 111 chlorobenzene, 6, 8, 16, 23, 42, 60, 102 chloroform, 16, 60, 61 cis, 108, 110, 124 classical, 15, 41 cleavage, 2 CO2, 15 cohesion, 4, 5, 6, 7, 12, 17, 18, 19, 20, 22, 30, 38, 46, 50, 51, 56, 58, 60, 61, 70, 71, 73, 75, 77, 78, 79, 81, 82, 83, 87, 88, 89, 90, 105, 106, 111, 112, 113, 114 communication, 18 competition, 84 complexity, 117 complications, 11, 58 components, 106 compounds, 2, 4, 29, 39, 41, 43, 55, 58, 91, 101, 107, 118 concentration, 3, 18, 20, 32, 43, 74, 78, 79, 83, 86, 96, 101, 102 conception, 105 concordance, 10 confidence, 35 congruence, 86

constant rate, 2, 4, 15, 50 consumption, 6, 29, 63, 83, 101, 114 conversion, 8 correlation, 4, 6, 8, 10, 11, 12, 18, 20, 22, 25, 26, 27, 30, 31, 34, 35, 36, 38, 43, 44, 47, 48, 51, 53, 56, 57, 61, 62, 63, 69, 72, 73, 74, 75, 78, 79, 80, 82, 88, 89, 90, 96, 100, 102, 103, 105, 108, 109, 110, 111, 112, 113 correlation analysis, 79 correlation coefficient, 6, 10, 12, 18, 20, 25, 26, 27, 30, 34, 35, 36, 38, 53, 57, 61, 63, 69, 72, 73, 74, 75, 79, 80, 82, 88, 90, 96, 97, 100, 102, 105, 108, 109, 110, 112, 113 correlations, 117 CPB, 52 cyclohexane, 22, 25, 27, 31, 37, 68, 72, 110 D data set, 100 death, 59 decane, 75 deficit, 84 degrees of freedom, 74 density, 4, 8, 12, 59, 78, 89, 102 derivatives, 101, 103 destruction, 63 detachment, 107 deviation, 10, 58, 71, 80 diffusion, 17, 82, 83 diffusion process, 83 dimerization, 7, 59, 60, 61, 63, 79 dimethylformamide, 7, 60, 84, 90 dimethylsulfoxide, 69, 71 dipole, 28, 77, 111 dipole moment, 28, 111 discordance, 56 displacement, 78, 103 dissociation, 59, 62, 63, 110 disulfide, 105 divergence, 31, 33, 98, 104 DMFA, 113 donor, 27, 37, 38, 60, 82, 83, 84, 98

Index E electron, 8, 11, 19, 24, 37, 82, 84, 111 electron density, 8 electron pairs, 37 electrons, 22, 23, 37, 74, 84, 98, 106, 112 electrostatic force, 74 energetic parameters, 2 energy, 4, 5, 6, 7, 12, 17, 18, 19, 20, 22, 29, 30, 32, 37, 38, 46, 48, 50, 51, 56, 58, 59, 60, 61, 63, 70, 71, 73, 75, 77, 78, 79, 81, 82, 83, 85, 87, 88, 89, 90, 105, 111, 112, 113, 114 energy consumption, 29, 63, 114 energy density, 5, 6, 7, 17, 18, 19, 20, 22, 30, 38, 46, 50, 51, 56, 58, 59, 60, 61, 70, 71, 73, 75, 77, 78, 79, 81, 82, 83, 87, 88, 89, 90, 105, 111, 112, 113, 114 enthalpy of activation, 38 entropy, 64 equilibrium, 59, 62, 102 esters, 11, 41, 53 Ethanol, 49, 52, 59, 68, 76, 113, 120 Ether, 68 ethers, 3, 35, 43 ethyl acetate, 16, 84 exclusion, 10, 11, 12, 19, 21, 22, 23, 27, 30, 31, 33, 35, 36, 38, 43, 44, 47, 51, 53, 56, 61, 63, 69, 70, 72, 74, 75, 78, 80, 81, 96, 100, 102, 103, 106, 108, 109, 110, 113, 114 experimental condition, 20

127

gene, 1 generalization, 1, 2, 4, 7, 11, 18, 21, 23, 24, 31, 33, 46, 50, 53, 56, 57, 59, 69, 71, 72, 73, 74, 78, 82, 83, 85, 91, 98, 100, 102, 105, 107, 108, 109, 110, 111, 117, 118 generalizations, 1 glycol, 60 groups, 2, 10, 22, 27, 58, 97 growth, 8 guidelines, 53 H halogen, 44, 60, 103, 106, 111 halogenation, 101, 111 heat, 33 heavy metal, 3 heavy metals, 3 heptane, 41 hexane, 60 high temperature, 4 homolytic, 3, 4, 5, 11, 18, 20, 21, 23, 50, 53, 82, 117 hydro, 3, 4, 6, 16, 17, 25, 41, 43, 44, 57, 58, 60, 67, 69, 73, 74, 77, 78, 79, 82, 83, 86, 90, 98, 99, 106, 107, 111 hydrocarbon, 19, 68, 71, 98, 101, 102, 106 hydrocarbons, 3, 4, 25, 41, 43, 44, 58, 60, 67, 69, 73, 74, 78, 82, 83, 86, 98, 99, 106, 107, 111 hydrogen, 42, 44, 48, 78, 84, 101, 111 hydroperoxides, 55

F I

flow, 4 France, 12 free radical, 1, 23, 24 free radicals, 1, 23, 24 freedom, 74 G gas, 102 gases, 82, 87

in transition, 28, 36 inadmissible, 8 independence, 43, 52 indication, 68 industrial, 95 industry, 55 inhibited oxidation process, 74 inhibition, 20 inhibitor, 25, 38, 50, 55, 78, 79 inhibitors, 2, 80

Index

128

initiation, 5, 11, 67, 68, 85, 86, 89 interaction, 3, 5, 20, 23, 27, 35, 58, 71, 78, 83, 84, 85, 106, 107, 110, 112, 113 interactions, 12, 105, 110 interface, 82 intermolecular, 112 intrinsic, 105, 111 inversion, 27 Investigations, 44 ionic, 8, 28, 42 ions, 3, 41 irradiation, 4 isomers, 109, 110 J Japan, 13, 92, 93 K kinetics, 1, 4, 15, 17, 18, 24, 33, 53, 57, 67, 72, 78, 85, 95, 98 L linear, 4, 7, 25, 35, 37, 41, 42, 58, 60, 78, 95, 102, 112, 117, 118 linear dependence, 35, 37, 41, 42, 78, 112 liquid phase, 1, 25 liquids, 82, 87 Lithium, 55, 56, 57 location, 114 London, 53, 116 M Manganese, 83 media, 2, 26, 27, 42, 44, 57, 75, 95, 100, 101, 105, 110, 111, 113 medium formation, 48 metal ions, 41 metals, 3 methanol, 60, 90 methylcyclohexane, 22

molar volume, 4, 12, 29, 53, 56, 102, 103, 109, 110 mole, 16, 18, 25, 30, 31, 32, 33, 37, 42, 45, 50, 52, 56, 59, 68, 72, 74, 79, 81, 85, 88, 91, 95, 96, 98, 99, 102, 108 molecular oxygen, 3, 68, 84 molecular weight, 4 molecules, 7, 24, 27, 55, 63, 64, 67, 82, 97 N neutralization, 46 New York, 53, 116 nitrobenzene, 16, 25, 33, 38, 41, 90, 95, 102 NMR, 67 nucleophiles, 4 nucleus, 23, 24 O observations, 52 octane, 27 olefins, 68, 82, 84, 111 organic, 30, 67, 101, 110 organic compounds, 101 organic solvent, 30, 110 organic solvents, 30, 110 orientation, 63 oxidation, 2, 5, 6, 56, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 96, 98, 111, 112, 113, 114, 118 oxidation rate, 6, 67, 70, 71, 72, 75, 77, 78, 79, 80, 82, 85, 88, 89, 91 oxide, 50, 56 oxides, 38 oxygen, 3, 6, 8, 33, 35, 43, 58, 67, 68, 79, 82, 83, 84, 86, 87, 89, 90 oxygen absorption, 68, 79 oxygen consumption, 6, 83 oxygen consumption rate, 83

Index P palladium, 79 parameter, 7, 12, 16, 18, 22, 27, 29, 34, 36, 38, 41, 44, 46, 47, 48, 50, 51, 53, 57, 58, 60, 62, 64, 83, 84, 87, 88, 95, 96, 100, 102, 103, 105, 106, 110, 111, 113, 118 particles, 3, 20 permit, 3, 51, 69, 84, 95, 109 permittivity, 12, 44 peroxide, 3, 4, 5, 15, 16, 17, 18, 19, 20, 22, 23, 24, 26, 27, 28, 32, 33, 35, 36, 37, 38, 58, 62 Peroxides, 10 phenol, 55, 78, 79 phenoxyl radicals, 62 PhOH, 78 photochemical, 101, 103, 106, 108, 110 play, 3 polar media, 26, 27, 111 polarity, 6, 8, 12, 17, 19, 26, 27, 29, 33, 36, 37, 38, 42, 43, 44, 47, 50, 52, 53, 56, 57, 58, 60, 63, 67, 69, 70, 71, 72, 74, 75, 77, 78, 80, 81, 82, 83, 87, 88, 96, 100, 103, 111, 113, 114 polarizability, 11, 12, 19, 24, 26, 27, 34, 42, 47, 49, 60, 62, 63, 69, 73, 74, 75, 77, 81, 82, 88, 89, 90, 100, 102, 106, 109, 110, 111 polarization, 6, 52, 88, 110 polymer, 3, 27 polymerization, 10, 15, 55, 95 polymerization processes, 95 power, 71 preference, 51, 102 pressure, 105, 111 probability, 5, 24, 35, 82, 89, 91, 118 propagation, 50 proportionality, 46, 75, 112 purification, 15 R radiation, 107 radical mechanism, 28

129

radical reactions, 1, 2, 8, 15, 103, 110, 117, 118 range, 25, 107 reactants, 20, 72 reaction center, 8 reaction mechanism, 8 reaction rate, 25, 28, 38, 53, 80, 108, 112 reaction rate constants, 108 reaction time, 89 reactivity, 105 reagent, 106 reagents, 87 reality, 53, 75, 77, 117 recombination, 59, 62, 63, 89 rectilinear, 11 refraction index, 43 refractive index, 12 regression, 7, 16, 17, 22, 35, 38, 61, 63, 69, 100, 113 regression equation, 7, 17, 22, 35, 38, 113 relationship, 18, 22, 23, 78, 80, 86, 87, 105, 110, 111 reliability, 74, 109 resistance, 82 rings, 19 S salt, 50, 55, 56, 58 saturated hydrocarbons, 79 selectivity, 101, 102, 103, 104, 105, 106, 111 sensitivity, 112, 113 separation, 84 series, vii, 4, 7, 17, 26, 29, 35, 37, 40, 50, 53, 55, 62, 68, 91, 117, 118 shape, 61 sign, 56, 58, 82, 84, 106, 110 significance level, 72 signs, 7, 61, 63, 72, 75, 100 solubility, 6, 12, 82, 86, 87, 89, 102, 118 solvent, 3, 16, 24, 25, 26, 27, 34, 35, 36, 37, 38, 41, 56, 59, 61, 62, 63, 64, 67, 69, 71, 72, 74, 75, 78, 79, 82, 84, 89, 91, 98, 100, 102, 103, 106, 108, 109, 110 spectrum, 78

Index

130

stability, 8, 37, 63, 102 stabilization, 24, 27, 35, 44, 64, 91 stabilize, 61 stages, 2, 3, 5, 7, 69, 83, 86, 87, 89, 91, 117 standard deviation, 96 statistical analysis, 100 steric, 11, 58 storage, 117 styrene, 10, 11, 20, 22, 33, 43, 50, 74, 75, 76, 77, 78, 79, 96 styrene polymerization, 11 substances, 25, 91 substrates, 12, 52, 67, 112, 113 T temperature, 45, 102 tetrahydrofuran, 35, 37 tetrahydrofurane, 3 thermal decomposition, 3, 9, 28, 32, 36, 37 thermolysis, 2, 3, 4, 8, 11, 18, 19, 23, 25, 26, 28, 36, 37, 38, 41, 48, 52 toluene, 6, 8, 22, 27, 60, 88, 104, 105, 106, 110 trans, 108, 119, 124 transfer, 5, 67, 69, 71, 72, 82, 83, 85, 86, 87, 89, 101, 111 transformation, 3, 4, 24, 82, 84, 112 transition, 3, 11, 27, 28, 29, 37, 41, 50, 69, 82, 87, 111 transitions, 3 translation, 92 trichloroethylene, 102 trimer, 79

trustworthiness, 20, 50, 101 U USSR, 13, 40, 64, 65, 92, 93, 116 UV, 67, 107 V values, 2, 6, 7, 10, 16, 18, 20, 22, 23, 25, 26, 27, 29, 30, 31, 33, 35, 37, 38, 41, 42, 44, 50, 51, 57, 58, 63, 68, 69, 70, 71, 72, 73, 74, 75, 77, 78, 79, 81, 83, 86, 88, 90, 95, 96, 98, 100, 103, 104, 105, 108, 109, 110 viscosity, 4, 17, 18, 95, 101, 105 visible, 6, 20, 71, 72, 75, 84, 86, 89 visualization, 77, 82 W water, 83, 90 workers, 26, 28 X xylene, 27, 74, 75 Y yield, 111

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