Solvent effects on the kinetics of redox reactions between ions and alcohols. Effect of solvent structure

Abstract

The effect of the solvent structure on the rates of redox reactions in alcohol + water mixtures is discussed. Collision number varies with the viscosity which is related to structural changes in the solvent. For a temperature-independent reaction, like the oxidation of isopropanol by the anthraquinone-2-sulphonate ion, the rate gives a direct measure for the collision number, and the rate constant for this reaction at 0°C in t-BuOH + water mixtures varies with viscosity as predicted by the collision number. In contrast, the variation with solvent composition of the rate constant for the temperature-dependent oxidation of isopropanol by Mn³⁺_aq is controlled by the effect of changes in the dielectric constant on the contribution of the ion-dipole interaction to the energy of activation. The application of collision theory and of transition state theory to this latter reaction are compared.