Alkane hydroperoxidation with peroxides catalysed by copper complexes

Abstract

Various copper(I) and copper(II) derivatives, both “simple” ones (copper acetate, perchlorate and a complex with CH₃CN) and compounds containing N,O-chelating ligands, catalyse very efficient (turnover numbers attain 2200) oxidation of saturated hydrocarbons with peroxyacetic acid (PAA) or tert-butyl hydroperoxide (TBHP) in acetonitrile solution at 60 °C. Alkyl hydroperoxide, alcohol and ketone are formed, the main product being an alkyl hydroperoxide in the oxidation with PAA and an alcohol for the case of TBHP. It has been proposed that the oxidation with PAA is induced via the attack of species r˙ [HO˙ or CH₃C(O)O˙] on the alkane, RH. A competitive attack of r˙ on the solvent, CH₃CN, also occurs. It has been assumed that in the case of the reaction catalysed by complex Cu(CH₃CN)₄BF₄, copper is present mainly in the form of Cu⁺ cation, and the rate-limiting step of the oxidation process is the formation of r˙ viareaction (1): CH₃C(O)OOH + Cu⁺ → CH₃C(O)O˙ + HO⁻ + Cu²⁺ or/and CH₃C(O)OOH + Cu⁺ → CH₃C(O)O⁻ + HO˙ + Cu²⁺ with initial rate W₁ = k₁[PAA][Cu(CH₃CN)₄BF₄] and k₁ = 1.7 mol⁻¹ dm³ s⁻¹ at 60 °C. The activity of the Cu-catalyst is dramatically changed on a small modification of N,O-chelating ligands in the catalyst.