Visible light-triggered vanadium-substituted molybdophosphoric acids to catalyze liquid phase oxygenation of cyclohexane to KA oil by nitrous oxide

[Display omitted] •Using nitrous oxide to oxidize cyclohexane to KA oil under visible light irradiation.•Using V(V)-substituted molybdophosphoric acids as effective catalysts.•Using concentrated HCl solution as an efficient promoter.•Providing an excellent selectivity for KA oil (especially for cyclohexanone).•The donor–acceptor interaction between catalyst and HCl is responsible for the present photooxidation. The development of a mild and highly efficient process for utilization of nitrous oxide (N2O) as a green oxidant has very important academic and applied values in the synthesis of oxygenated products. This paper first discloses that a series of vanadium-substituted molybdophosphoric acids (PMo12−nVn, n=1–3), assisted by HCl aqueous solution, can efficiently catalyze the visible light-driven liquid phase oxygenation of cyclohexane by N2O in acetonitrile (MeCN), providing ca. 26.2% cyclohexane conversion and 90.2% selectivity for cyclohexanol and cyclohexanone (KA oil) under optimized conditions, along with a small quantity of chlorination. Among the catalysts examined, PMo10V2 and especially PMo9V3 showed a higher activity for this photocatalytic oxygenation than PMo11V. Furthermore, the amount of water added strongly influenced this HCl-promoted photocatalysis oxygenation. The selectivity of cyclohexanone was continuously and significantly improved from 21.8 to 82.7% with increasing water amount from 0 to 0.15mL, but the conversion of cyclohexane obviously decreased when the amount of water added was higher than 0.12mL. The promoting effect of HCl on the present photocatalysis reaction is probably due to the fact that the donor–acceptor (D–A) adduct between HCl and PMo12−nVn can be excited by visible light to achieve its intra-molecular electron transfer from Cl− to PMo12−nVn anions, which leads to the generation of Cl radicals and the reduction of catalysts. The subsequent reactions initiated by the Cl radicals result in the oxygenation of cyclohexane by N2O to KA oil and the regeneration of catalysts, as supported by UV–vis spectral and cyclic voltammetric measurements.