Hydroxyl Group (V)¹ and Imidazole (X)² Catalysis. The General Base Catalysis of Ester Hydrolysis by Imidazole and the Influence of a Neighboring Hydroxyl Group

Imidazole has been found to be a catalyst for the hydrolysis of alkyl acetyl esters (CH₃COOR') in which the pK_a of HOR' is less than pK_w. The catalytic coefficient for imidazole catalysis in these cases has been found to be associated with a deuterium solvent kinetic isotope effect (i.e., R^H/k^D) of 2 to 4. It is suggested that the mechanism represents an imidazole general base or general acid-catalyzed hydrolysis. The rate of alkaline hydrolysis of the cyclopentyl ester of dichloroacetic acid has been shown to be only about half as sensitive to facilitation by a neighboring hydroxyl group as previously found for the corresponding acetyl ester. In addition, the rate of imidazole general base-catalyzed hydrolysis of cyclopentyl dichloroacetate has been found to be completely insensitive to the presence of a neighboring hydroxyl group.