Reaction of the aquacopper(I) ion with hydrogen peroxide. Evidence for a CuIII(cupryl) intermediate

Abstract

Oxidation of CH₃OH to HCHO occurs as a chain reaction on γ-irradiation of deaerated aqueous CH₃OH + H₂O₂+ Cu²⁺_aq solutions. The reaction of Cu⁺_aq with H₂O₂ is a propagation step. The chain-length and the dependence of HCHO formation rate on radiation dose, CH₃OH concentration and pH are not compatible with a mechanism that includes production of the free hydroxyl radical, OH ˙, by the Cu⁺_aq+ H₂O₂ reaction. It is suggested that an intermediate is formed by this reaction that reacts with methanol with a rate constant not greater than 4 × 10⁵ dm³ mol^–1 s^–1, and the main features of the results are explained on this basis. The reactivity of the proposed intermediate is shown to be similar to that of the Cu^III_aq(cupryl) species, produced by reaction of OH ˙ with Cu²⁺_aq.