Kinetics and mechanism of catalytic oxidation of alcohols to carbonyl compounds with dioxygen in the Pd-containing aqua system

The oxidation of lower aliphatic alcohols C₁–C₄ with dioxygen to form the corresponding carbonyl compounds in the presence of the PdII tetraaqua complexes and Fe^II-Fe^III aqua ions in an aqueous medium was studied at 40–80 °C. The introduction of an aromatic compound (acetophenone, benzonitrile, phenylacetonitrile, o-cyanotoluene, nitrobenzene) and Fe^II aqua ion instead of the Fe^III aqua ion into the reaction system increases substantially the catalytic activity and the yield of the carbonyl compound. The key role of the Pd species in the intermediate oxidation state stabilized by the aromatic additive in the catalytic cycle of alcohol oxidation with dioxygen to the carbonyl compound was shown. An increase in the kinetic isotope effect with an increase in the temperature of methanol oxidation indicates a change in the rate-determining step of alcohol oxidation with dioxygen in the presence of Pd^II-Fe^II-Fe^III and the aromatic compound. At temperatures below 60 °C, the catalytically active palladium species are mainly formed upon the reduction of the Pd^II tetraaqua complex with the Fe^II aqua ion, whereas at higher temperatures the reaction between the alcohol and Pd^II predominates. The mechanism and kinetic equation of the process were proposed. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 842–848, May, 2007.