Kinetics of oxidation of isopropanol by aquocerium(IV) ions in perchlorate media

Abstract

The oxidation of isopropanol by Ce^IV in perchlorate media is an inner-sphere reaction involving two intermediate complexes Ce⁴⁺(CH₃)₂CHOH_aq and Ce⁴⁺(CH₃)₂CHO^–_aq. The latter is formed by the dissociation of a proton form the former and not via CeOH³⁺_aq and isopropanol. The heat and entropy of formation of Ce⁴⁺(CH₃)₂CHOH_aq, and the energy and entropy of activation for the first-order decomposition of both complexes, are determined. The energies and entropies of activation are compared with those for the outer-sphere oxidations of secondary alcohols where a concerted transfer of an electron to the cation and of a proton to the bulk solvent occurs. The value for the formation equilibrium constant for Ce⁴⁺(H₂O)_n(CH₃)₂CHOH, where n > 6, is compared with similar constants for octahedral alcoholaquocations and the trigonal-pyramidal alcoholaquoproton.