Lewis acid activated oxidation of alkanes by barium ferrate

Abstract

In the presence of a few equivalents of a metal chloride, barium ferrate (BaFeO₄) has been found to oxidize cyclohexane at room temperature in acetic acid–dichloromethane to give a mixture of chlorocyclohexane, cyclohexanol and cyclohexanone. The rates of oxidation for the various metal chlorides follow the order AlCl₃>FeCl₃>MgCl₂>LiCl>ZnCl₂. The best yield was obtained with MgCl₂, which represents a balance between reactivity and stability. Oxidation of other organic substrates has also been carried out using the BaFeO₄–LiCl system. Notably the system is able to oxidize propane and ethane to give a mixture of chloroalkanes and carbonyl products. The deuterium isotope effect for the oxidation of cyclohexane was found to be 2.1, 1.8, and 3.0 for chlorocyclohexane, cyclohexanol and cyclohexanone, respectively. The active intermediate is proposed to be a Lewis acid–ferrate adduct formed by coordination of an oxo ligand of the ferrate to the metal ion. It is suggested that the reactivity of this adduct is reminiscent of a radical species that oxidizes alkanes ia a hydrogen atom abstraction pathway.