Ester containing aggregates in the autocatalytic biphasic hydrolysis of ethyl alkanoate

Autocatalytic kinetics are observed during the biphasic alkaline hydrolysis of C-4, C-6 and C-8 (butanoate, hexanoate and octanaoate) ethyl esters. Ethanol and alkanoate anions are the products of the reaction. A kinetic model including spontaneous dissolution of the organic phase into the aqueous phase, aqueous hydrolysis of the ester, formation of ester containing aggregates and micellisation has been proposed. For C-4, taking into account salting-in and solvent effects is sufficient to reproduce the autocatalytic behaviour. For C-8, the major autocatalytic process is an ester containing aggregates (ECA) mediated phase transfer. For C-6, it appears that the role of ECA is double. Small sized ECA which are formed at the beginning of the reaction do not perform rapid phase transfer and trap surfactant molecules. Larger ECA which appear at the end of the reaction are the main phase transfer agent. Using an empirical formula to describe the size of the interface, the model is able to reproduce the effect of a variation of the volumic ratio of the two phases as well as the effect of stirring rate and non-emulsified experiments.