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

Near‐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.