Aerobic oxidation of saturated hydrocarbons into alkyl hydroperoxides induced by visible light and catalysed by a ‘quinone–copper acetate’ system

Abstract

Irradiation in air of an alkane solution in MeCN in the presence of catalytic amounts of quinone and copper(II) acetate (ratio 5 : 1) affords mainly alkyl hydroperoxide which by the action of triphenylphosphine may be easily converted into the corresponding alcohol and ketone (aldehyde)(in the case of cyclohexane oxidation the ratio cyclohexanol : cyclohexanone was 50:1 after 10 h). The main peculiarities (the rate dependencies on initial concentrations of a substrate and the catalyst as well as of some additives and the effective activation energy) of the reaction are described. The proposed mechanism includes the abstraction of the hydrogen atom from alkane, RH, by photo-excited quinone to produce radicals R˙ and HOC₆H₄O˙. The former then reacts rapidly with O₂ to give RO₂˙, and the latter may be reoxidized by copper(II). A copper(I) derivative thus formed may be converted into copper(II) when oxidized either by RO₂˙ or O₂.