Solvolysis of some alkyl esters of fluorosulphuric acid in water and aqueous solvents

Abstract

The solvolysis of methyl, ethyl, and isopropyl fluorosulphates in pure water and aqueous organic solvents has been studied. The extrapolated reactivity at 25 °C of these compounds is 10⁴ to 10⁶ times higher than that of halides, alkanesulphonates, and benzenesulphonates but is similar to that shown by chlorosulphates and perfluoroalkane-sulphonates.

The kinetics and medium and nucleophile effects have been investigated to establish the mechanism of the reactions. The effect of a variation in the dielectric constant of the medium has also been discussed. The activation parameters of these solvolytic reactions were correlated through a ΔH^‡vs.ΔS^‡ plot.

It is concluded that even when methyl and ethyl fluorosulphates show behaviour typical of compounds reacting by a S_N2-type mechanism, some evidence of a slight difference between both processes was found. The solvolysis of isopropyl fluorosulphate has a high contribution from a unimolecular ionization mechanism.