Proton transfer from disulphonyl-activated carbon acids

Abstract

Rates of the water catalysed detritiation of six disulphonyl-activated carbon acids, with acidities in the range 11 < pK0 < 15, have been measured in aqueous solution. A Bronsted exponent α= 1·1 ± 0·1 has been calculated. The rates of recombination of the carbanions with hydronium ion have values close to 2 × 1010 l mol–1 s–1. It is shown that the association step included in Marcus' theory of proton transfer is necessary to explain the results. The transition state for proton transfer from disulphones to weak bases resembles an encounter complex between the carbanion and conjugate acid of the base catalyst. A comparison is made with other carbon acids and it appears that the behaviour of disulphones approaches more closely to the ‘normal’ proton transfer of oxygen acids.