Initial state and transition state solvation effects in the cobaltitungstate oxidation of iodide in binary aqueous solvent mixtures

Abstract

Rate constants are reported for 12-tungstocobaltate(III) [CoW12O40]5− oxidation of iodide in water and in binary aqueous solvent mixtures containing up to 40% methanol, 40% acetonitrile, or 60% dimethyl sulphoxide. From these kinetic results, solubility measurements on potassium 12-tungstocobaltate(III), and published data on Gibbs free energies of transfer of appropriate ions, it has been deduced that the dominant factor in determining the marked decrease in rate observed on going from water into the binary aqueous solvent mixtures is destabilisation of the transition state for the electron-transfer reaction.