On the Mechanism of Ester Hydrolysis:  Trifluoroacetate Derivatives

The hydrolysis rate of trifluoacetates of ArX (X = p-CH3, H, p-F, p-Cl, and m-Cl) was measured as function of pH and buffer concentration. All the reactions were catalyzed by the buffer bases, and the Bronsted plot showed a small upward curvature. The kinetic isotope effect is ca. 2.5−2.3 for the reactions of water. The Hammett plots as well as the plots of log kB vs pKlg are linear. The slopes of these plots are remarkably similar to those corresponding to the hydrolysis of aryl acetates and aryl formates. From these results, we conclude that the reaction corresponds to general base-catalyzed addition of water and break of the leaving group with no intermediate with finite lifetime despite the fact that the trifluoromethyl group stabilized the intermediate considerably.