2‐Fluoroanthraquinone‐Catalyzed Photooxidation of Benzylic Hydrocarbons and Aliphatic Alcohols With O 2 in Supercritical CO 2 , Accelerating Effect of Water

A greener process for the oxidation of hydrocarbons containing primary, secondary, and tertiary benzylic carbon atoms, as well as aliphatic alcohols (e.g., cyclohexanol, menthol, and 4‐heptanol) with molecular oxygen in supercritical carbon dioxide (scCO 2 ) medium under the visible‐light irradiation in the presence of 2‐fluoroanthraquinone (2‐FAQ) as a photocatalyst (1 mol%) has been developed. The photooxidation reactions have been found to be accelerated by the addition of small amounts (1 equiv.) of water to the system. Plausible pathways for the promotion of the oxidation process have been identified: The most prominent is the cleavage of H─O bonds in the added water molecules under the action of the photocatalyst that results in extra reactive oxygen species generation. Also, a radical‐chain mechanism for the photocatalytic process has been proposed. It is the first time that experimental data on the photophysical properties of 2‐FAQ, including the redox potential of this promising photocatalyst in the photoexcited state, have been obtained.