Abstracto
- The second-order rate constant for the saponification of ethyl acetate at 30.0°C in H2O/D2O mixtures of deuterium atom fraction n (a proton inventory experiment) obeys the relation k2(n) = 0.122 s-1 M-1 (1 - n + 1.2n) (1 - n + 0.48n)/(1 - n + 1.4n) (1 - n + 0.68n)3. This result is interpreted as a process where formation of the tetrahedral intermediate is the rate-determining step and the transition-state complex is formed via nucleophilic interaction of a water molecule with general-base assistance from hydroxide ion, opposite to the direct nucleophilic collision commonly accepted. This mechanistic picture agrees with previous heavy-atom kinetic isotope effect data of Marlier on the alkaline hydrolysis of methyl formate (Marlier, J. F. J. Am. Chem. Soc. 1993, 115, 5953).