Kinetics of the reversible hydration of 1, 3-dichloroacetone in dioxan and acetonitrile solution

The kinetics of the reversible hydration of 1, 3-dichloroacetone have been studied spectrophotometrically in solutions of water in dioxan and in acetonitrile, over a wide range of water concentrations, with and without the addition of catalysts. The results in both solvents strongly suggest that in the uncatalysed reaction the transition state contains one molecule of ketone and three molecules of water; in the catalysed reaction a molecule of triethylamine or benzoic acid can replace one or two molecules of water respectively. A cyclic transition state is proposed, and model calculations suggest that the reaction takes place by the step-wise transfer of three protons rather than by their synchronous motion. The same conclusion is reached by considering the observed kinetic hydrogen isotope effect of kH/kD = 2·7.