Epoxy carboxy reaction kinetics

Main Teciiniques Used in Kinetic Studies of Epoxy-Carboxy Reactions. . . . 156... 

Before studying epoxy-carboxy esterification kinetics, it must be remembered that side reactions can interfere with the main reaction. These must either be avoided by well-defined experimental conditions or taken into account in kinetic calculations. 

Amine consumption in reaction II could make it difficult to use the epoxy-carboxy reaction to prepare esters or polyesters. In fact, most of the zwitterion Z, which is formed from E and the amine, is transformed into the ester P and, at least in solution, only a small quantity of side product is formed. Moreover, titrations carried out during the reaction show that epoxy and acid groups are consumed at roughly the same rate, demonstrating that even if the contribution of reaction II to overall kinetics and mechanism is important it does not forbid the use of this method for preparation of polyesters. 

As shown in Table 1, many metal derivatives can be used for catalyzing the epoxy-carboxy reaction. Unfortunately, in most cases, there is no study of the kinetics and of the mechanisms of the reaction. 

Chromium III derivatives have been used for catalyzing epoxy-carboxy reactions (see Table f). Unfortunately, most publications are patents which describe the process without any information on the mechanisms and the kinetics. Let Cr(OOC R ) be an activated chromium tricarboxylate salt , i.e., a chromium salt having readily available coordination sites. Steele et al. propose the following mechanism ... 

Table 3. Kinetic parameters of epoxy-carboxy esterification and polyesterification reactions — Table is in two parts Part I (page 182 to 198 for experimental conditions. Part 2 (page 199 to 208 for results and references, r = initial molar ratio of epoxide (or diepoxide) to acid (or diacid) when r is given (third column), no solvent is present. [Al, and are acid and epoxide initial concentrations, reflectively... 

Epoxy-carboxy esterification has many applications, mainly in polymer chemistry. It is not only used to build polymer chains but also for chemical modification. Its most important advantage is that it can be carried out at moderate temperature with the formation of P-hydroxyester linkages and without elimination of volatiles. However, it can be spoiled by side reactions, and it is important to define the conditions which decrease the contribution of these latter. Most of the works that we have reviewed describe the reactional systems under different experimental conditions (catalyzed or non-catalyzed reaction, in solution or in the bulk) and, sometimes, give the values of kinetic parameters (partial or global orders, activation parameters). 

First of all, we collected the main techniques used in the kinetic studies of the reaction (reaction procedures, analytical methods, treatment of experimental data). In fact, unambiguous results can be obtained only if some basic conditions are observed. The survey of the literature shows a great diversity of the catalysts used in epoxy-carboxy esterifications or polyesterifications however, at least in the case of kinetic studies, tertiary amines and ammonium salts are largely predominant. From the fundamental studies carried out with organic models, and mostly in solution, several mechanisms were proposed involving the formation of a complex which can be cyclic or not. 

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