Kinetics of the oxidation of hydrogen peroxide by aquocerium(IV) ions in aqueous perchlorate media

The rapid reaction of aquocerium(IV) ions with hydrogen peroxide has been investigated in perchlorate media by the stopped-flow technique. Oscilloscope traces show a rapid initial rise in optical density followed by a rapid decay. The initial rise is ascribed to the formation of cerium(IV)–hydrogen peroxide complexes and the subsequent decay is explained by an inner-sphere electron transfer. The rate of decay is independent of the initial [CeIV], of [H2O2], of [Ce]III, and of acidity, confirming that an intermediate complex with a high formation equilibrium constant exists, The activation energy for the rate-determining electron transfer is very low.