Photocatalytic metal‐free oxidation of alcohols with molecular oxygen in supercritical CO2 medium

Abstract

AbstractNear‐UV‐light‐induced oxidative conversion of cyclic and linear alcohols into corresponding carbonyl compounds was achieved in the supercritical CO2 medium under the action of molecular oxygen in the presence of 2‐fluoroanthraquinone (1 mol %), a simple and available metal‐free photocatalyst. A thorough examination of the impact of various process parameters on the reaction outcome allowed to identify a narrow density area at ~0.3 g/cm3 in the vicinity of the medium critical point and optimal reaction conditions (~45 °C, ~8.4 MPa) where up to 99 % conversions and 65–93 % yields of the oxidation products could be attained. Furthermore, it has been shown that compressed atmospheric air, a far cheaper and safer oxidizer than pure oxygen, can be applied to the reaction. Based on the experimental data, a plausible mechanism of the photocatalytic process has been proposed comprising photocatalyst excitation with near‐UV light followed by the hydrogen atom transfer (HAT) as the key stages.