Kinetic and thermodynamic basicities of anions in mixed solvents

Abstract

The rates and equilibria for reactions involving proton transfer between several nitroalkanes and fluoride, acetate and hydroxide ions have been investigated in dimethylsulphoxide + water and trifluoroethanol + water mixtures. The results show that the effects of solvent variation on the rates are not simply related to the effects on the overall free energy changes occurring during the reactions. Recently observed anomalies in Brönsted β coefficients for reactions involving these substrates disappear as the fraction of water in the dimethylsulphoxide + water mixtures decreases. It is argued that the anomalous β values in water result from specific hydration effects on the acidity constants.