Effect of ion pairing on the reactivity of solvated electrons in ethyl alcohol

The effect of inert divalent cations Mg2+ and Ca2+ on the rate of reaction of the solvated electron with nitrate and zinc ions in ethanol has been studied by pulse radiolysis. In ethanol the rate of reaction of solvated electrons with the nitrate anion is comparatively slow due to the Coulombic repulsion between the two ions. Addition of Mg2+ or Ca2+ which do not react with e-/sub s/ increases the rate of the reaction. It can be shown that this catalytic effect is due to the formation of ion pairs between the nitrate anion and the inert divalent cation which, by shielding the electrostatic repulsion between the reactants, facilitate the establishment of the transition state. Conversely the rate of reaction between e-/sub s/ and Zn2+ is decreased by addition of Ca2+ but in this case the slowing down of the reaction can be accounted for by a normal salt effect. The possibility of formation of ion pairs between solvated electrons and inert divalent cations and their influence on the kinetics are discussed. 8 figures, 2 tables