KINETICS AND MECHANISM OF THE HYDROLYSIS OF DIETHYL THIOACETALS OF SUBSTITUTED BENZALDEHYDES IN AQUEOUS PERCHLORIC-ACID

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 excess 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.