NEW EVIDENCE IN FAVOR OF THE ENOL MECHANISM FOR THE ALKALINE-HYDROLYSIS OF ETHYL ACETOACETATE

The enol mechanism is proposed to account for the rapid alkaline hydrolysis of ethyl acetoacetate in water and for its first-order kinetics. The mechanism first involves the establishment of base-catalyzed keto-enol equilibria via the enolate anion between the ester and the enoles CH3C(OH) = CHCO2Et and CH3 COCH = C(OH)OEt. Of these enols only the former is reactive toward nucleophilic addition of water to form the intermediate dipolar ion [GRAPHICS] whose breakdown leads to the products. Four different types of evidence are presented in favor of this mechanism on the basis of: a) the observed kinetics at various water concentrations, b) the measured deuterium solvent isotope effect, c) the measured activation parameters and d) the observed kinetics in water when ionization of the ester into the enolate anion is low.