Solvolysis of esters of trifluoracetic acid

Abstract

Although the spontaneous hydrolysis of simple alkyl esters related to halogenoacetic acids has frequently been studied, no systematic body of rate data is presently available concerning the reactivity of these substances in light and heavy water. The purpose of the present study is to survey the temperature dependence of the rates of hydrolysis in water and deuterium oxide of four esters derived from triflouoracetic acid (CF₃COOR: R = methyl, ethyl, i-propyl and tertiary butyl). -- On the basis of ¹⁸O tracer Bunton and Hadwick (1) have concluded that the spontaneous hydrolysis of methyl trifluoroacetate in pure water takes place by acyl-oxygen fission (B Ac² mechanism). On the other hand, Moffat and Hunt (2) have concluded that tertiary butyl trifluoroacetate reacts by an SN1 mechanism in acetone-water mixtures. These observations suggest that a change in mechanism (B Ac² → SN1) is to be expected in the hydrolysis of the series of trifluoroacetates mentioned above. The aim of this work is to attempt to locate the region of mechanistic change by using the thermodynamic parameters characteristic of the activation process (ΔG⁺, ΔH⁺, ΔS⁺, and ΔC⁺p) as well as the ratio of the rates of hydrolysis of each substrate in light and heavy water. An attempt has also been made to assess the significance of the parameter, ΔC⁺p, in cases where a reaction is occurring by more than one mechanism.