GENERAL ACID CATALYSIS IN BENZOPHENONE KETAL HYDROLYSIS

Benzophenone diethyl ketal, 2,2-diphenyl-1,3-dioxolane, 2,2-di(p-methoxyphenyl)-1,3-dioxolane, 2,2-di- (p-tolyl)-1,3-dioxolane and 2,2-di(p-chlorophenyl)-1,3-dioxolane were prepared and their kinetics of hydrolysis studied in aqueous dioxane formate, chloroacetate and diehloroacetate buffers. General acid catalysis was observed for hydrolysis of ketals of benzophenone, 4,4′-dimethoxybenzophenone and 4,4′-dimethylbenzophenone in chloroacetate and diehloroacetate buffers. Catalytic coefficients for the buffer acids and for hydrogen ion were derived from the kinetic data. Hydrogen ion catalytic coefficients correlate closely with Hammett’s substituent constants for the para substituents. The entropy of activation for hydrogen ion catalyzed hydrolysis is near zero for benzophenone diethyl ketal and slightly negative for the 2,2-diary 1-1,3-dioxolanes. The relationship between acetal and ketal structures and the mechanisms (Al or SE2) by which they hydrolyze are discussed. © 1969, American Chemical Society. All rights reserved.