Instances of non-electrolyte solvation leading to less pronounced rate enhancements of ester hydrolyses in dipolar aprotic solvents: the possibility of hydrolysis via conjugate base formation in the case of ethyl indole-2-carboxylate and methyl 4-pyridylacetate

Abstract

The kinetics of alkaline hydrolysis of various heterocyclic esters (I)–(X), ethyl benzoate (XI), and ethyl phenyl-acetate (XII) have been investigated in binary solvent mixtures of dimethyl sulphoxide (DMSO)–water and ethanol–water. The rate data for esters (I) and (II) indicate the possibility of an E1 cb route for their hydrolysis. The hydrolysis of heterocyclic esters constitute a unique case in which the rate enhancements of ester saponifications on transfer from protic to dipolar aprotic solvents are governed by the solvation of the non-electrolyte (ester) molecule by DMSO, a factor hitherto relegated to the background.