HYDROLYSIS OF ELECTRON-ACCEPTING ESTERS CATALYZED BY ELECTRON-DONATING AZOLES - NONCLASSICAL MICHAELIS-MENTEN MECHANISM

The hydrolyses of electron-accepting esters catalyzed by electron-donating azoles were investigated. 1,2,3-Benzotriazole accelerated the hydrolysis of 1-naphthyl 3,5-dinitrobenzoate in the pH range of 7 to 11, whereas the hydrolysis above pH 12 was retarded by the azole. The retardation was attributed to the formation of a charge-transfer complex between the ester and the anionic deprotonated 1,2,3-benzotriazole ; the nucleophilic attack by hydroxide ion on the ester is inhibited by the formation of the anionic complex. This inhibition is expected to take place over all the pH region above neutrality ; therefore, the acceleration by the azole below pH 11 can be ascribed to bimolecular nucleophilic attack of free 1,2,3-benzotriazolide anions on the free ester molecules that overrides the inhibition. The kinetics is expressed by a hyperbolic function which is similar to that for the Michaelis-Menten mechanism in enzymic reactions ; however, this catalytic reaction is explained by the "nonclassical" Michaelis-Menten mechanism proposed by Menger.