Kinetics and mechanism of the hydrolysis of diethyl thioacetals of substituted benzaldehydes in aqueous perchloric acid

Abstract

Substituent effects, activation parameters, acidity dependencies and solvent isotope effects suggest that the acid-catalysed hydrolysis of diethyl thioacetals of meta- and para-substituted benzaldehydes, and of acetophenone, proceed via an essentially A1 scheme. The extent of C–S bond cleavage in the transition state may become progressively greater on moving from the least to the most reactive acetals. The use of the èxcess acidity as a criterion of mechanism is briefly discussed. Activation enthalpies and entropies are significantly larger for the meta-substituted acetals. Our results are compared with existing data for the O,O- and O,S-analogues.