Studies in homogeneous catalysis: Copper‐phenanthroline complexes as catalysts for the oxidation of methanol

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AbstractCopper phenanthroline complexes are catalysts for the oxidation of methanol by oxygen at 30‐45 °.A feature of the reaction is that it shows an induction period unless started with small amounts of H2O2 or cuprous ion. During the reaction the system contains a considerable amount of cuprous complex, the presence of which appears to be an essential condition for the continuation of the oxidation.Hydrogen peroxide, in contrast to other hydroperoxides, rapidly forms cuprous complex when added to a cupric‐phenanthroline system. This reaction probably proceeds via formation of O2−. from HO2− ion and cupric complex. The radical ion \documentclass{article}\pagestyle{empty}\begin{document}\[{\rm O}_{\rm 2}^{-\bullet}\]\end{document} would then abstract a hydrogen atom from methanol (or methoxide) coordinated to cupric‐phenanthroline complex, while simultaneously the cupric ion would abstract an electron from the methanol ligand, thus giving rise to formaldehyde and a proton without the intervention of free methanol radicals. The HO2− ion formed in this reaction would either be reoxidized by cupric complex (chain propagation) or reductively split by a cuprous‐phenanthroline complex (termination).The reactions leading to the hydrogen peroxide‐induced formation of cuprous complex probably constitute an essential part of the mechanism of the copper‐phenanthroline‐catalysed oxidation of methanol by oxygen. In this latter reaction \documentclass{article}\pagestyle{empty}\begin{document}\[{\rm O}_{\rm 2}^{-\bullet}\]\end{document} is supplied by the reaction of cuprous complex with oxygen.