Studies in solvolysis. Part 4. Substituent and solvent isotope effects in the solvolysis of a series of benzyl trifluoroacetates

The rates of neutral hydrolysis of a series of 4-substituted benzyl trifluoroacetates 4-X-C 6 H 4 CH 2 OCOCF 3 , X = NO 2 , Cl, H, CH 3 , and OCH 3 have been studied in water and deuterium oxide, both solvents containing 0.012 mol fraction of acetone. The alteration of the rates with the nature of the 4-substituent and the kinetic solvent isotope effect (k(H 2 O)/k(D 2 O)) are consistent with the proposal that the esters with X = NO 2 , Cl, H, and CH 3 all react by an acyl–oxygen B Ac 2 mechanism. On the other hand, the same mechanistic criteria indicate that the 4-methoxybenzyl ester reacts by both the B Ac 2 and the S N 1 alkyl–oxygen fission paths in equal amounts.