Heavy-atom isotope effects on the acid-catalyzed hydrolysis of methyl benzoate

Abstract

Results of the use of a previously reported technique of four-heavy atom isotope effects for study of the acid-catalyzed hydrolysis of methyl benzoate are reported. Ether oxygen and methyl carbon isotope effects on the reaction were measured by the usual natural-abundance isotope-ratio technique. The carbonyl oxygen isotope effect was measured by the pseudo-natural-abundance double-label method as was the carbonyl carbon isotope effect. The results led to the assumption that the hydrolysis of methyl benzoate proceeds by way of a tetrahedral intermediate. The small amount of oxygen exchange with the solvent that accompanies the hydrolysis indicated that it is intermediate formation rather than decomposition that is rate determining. The small magnitude of the observed carbon isotope effect on the acid-catalyzed hydrolysis of methyl benzoate compared to carbon isotope effects on other reactions of this compound indicate that the transition state is relatively reactant-like. (BLM)