Acylation. Part XXXVI. The kinetics and mechanism of the alkaline hydrolysis and the n-butaminolysis of ethyl thiolbenzoate in aqueous solution

Abstract

The hydrolysis of ethyl thiolbenzoate in aqueous solution between pH 9·80 and 10·75 obeys the rate equation –d[Ester]/dt=k_OH–[OH^–][Ester], with k_OH–= 1·6 ± 0·1 l mol^–1 s^–1 at 56 °C. The activation energy is 21·0 ± 0·2 kcal mol^–1. The n-butaminolysis of the same ester at 33·4 °C is general base-catalysed. Its rate displays dependencies upon [OH^–] and [amine] which point to the involvement of a carbonyl addition intermediate in the reaction, the breakdown of this intermediate to products being the only step catalysed by bases present. The rate constant for formation of the intermediate has a value (8·1 ± 0·2)× 10^–3 l mol^–1 s^–1. The relationships between the rate constants for the remaining steps of the mechanism have been evaluated. The other types of intermediate mechanism, and synchronous mechanism, normally considered in ester aminolysis appear to be excluded in the present instance.