Neutral hydrolysis of substituted phenyl trifluoroacetates in water–acetonitrile mixtures with low content of water

Abstract

The neutral hydrolysis of substituted phenyl trifluoroacetates has been studied in water–acetonitrile mixtures in the region 0.56–3.89M water. The large solvent deuterium isotope effect (kH2O/kD2O) of 2.3 and the thermodynamic activation parameters for the hydrolysis of 4-nitrophenyl and 2,4-dinitrophenyl trifluoroacetates are consistent with a reaction mechanism in which one water molecule acts as a nucleophile and one as a general base. A linear correlation with a slope of 3.4 is found between log kobs and log [H2O] for the hydrolysis of 4-nitrophenyl trifluoroacetate. This indicates the incorporation of several water molecules in the transition state. The effect of the structure of the leaving group on the rate of the reaction is best explained by a rate-limiting attack on the carbonyl group.