Reactions of carbonyl compounds in basic solutions. Part IV. The mechanism of the alkaline hydrolysis of methyl 3-benzoylacrylates

Abstract

Rate coefficients for the alkaline hydrolysis of a series of 3′- and 4′-substituted methyl cis- and trans-3-benzoyl-acrylates, 3′- and 4′-substituted methyl cis- and trans-3-benzoyl-3-methylacrylates, and 4′-substituted methyltrans-3-benzoyl-2-methylacrylates have been measured in 70%(v/v) dioxan–water at 1·0 °C. Rate coefficients for the unsubstituted parent esters were measured at several temperatures, from which the entropies and enthalpies of activation were evaluated. The effects of substitution were assessed by means of the Hammett equation. The reaction constants, ρ, for the two series of cis-esters are comparable to those for the hydrolysis of methyl benzoates under the same conditions. Those for the three series of trans-esters were only about one third those for the cis-esters and are compatible with simple transmission of the substituent polar effect to the ester group. Three criteria for the occurrence of intramolecular catalysis in the alkaline hydrolysis of keto-esters, i.e., activation parameters, relative rates, and substituent effects, all indicate its presence in the hydrolysis of cis-3-benzoylacrylates.