Reactions of carbonyl compounds in basic solutions. Part 8. Mechanism of alkaline hydrolysis of methyl pseudo-8-(3- or 4-substituted benzoyl)-1-naphthoates and pseudo-2-(3- or 4-substituted benzoyl)benzoates

Abstract

Rate coefficients have been measured for the alkaline hydrolysis of a series of methyl pseudo-8-benzoyl-1-naphthoates and pseudo-2-benzoylbenzoates in 70%(v/v) dioxan–water at 60.0 °C. The entropies and enthalpies of activation for the parent pseudo-esters have been evaluated, as have the solvent isotope and solvent (aqueous dioxan and dimethyl sulphoxide) effects for these esters. The reaction constants, ρ, for the naphthoates and benzoates are ca. 0.6 and 0.8, respectively. The evidence is consistent with hydrolysis occurring by a stepwise mechanism, with rate-determining attack of hydroxide ion. The greater reactivity of the five- than of the sixmembered ring arises from greater ring strain in the former.