Reactions of carbonyl compounds in basic solutions. Part 12. The mechanism of the alkaline hydrolysis of 3-substituted phenyl 2-acetyl- and 2-benzoyl-benzoates

Abstract

Rate coefficients have been measured for the alkaline hydrolysis of 3-substituted phenyl 2-acetyl-and 2-benzoyl-benzoates in 70%(v/v) dioxane–water at several temperatures. The enthalpies and entropies of activation have been evaluated. The effects of substitution have been assessed by means of the Hammett equation. Comparison of the reaction constants with those for model systems, as well as the relative rates and activation parameters, indicate that the rate-determining step for the 2-acetyl esters is attack by hydroxide anion at the keto-carbonyl group and for the 2-benzoyl esters it is the intramolecular attack on the ester-carbonyl group, which follows equilibrium addition of the hydroxide anion at the keto-carbonyl group.