9,10-Dihydroanthracene auto-photooxidation efficiently triggered photo-catalytic oxidation of organic compounds by molecular oxygen under visible light

The development of mild and efficient process for the selective oxidation of organic compounds by molecular oxygen (O2) can be one of the key technologies for synthesizing oxygenates. This paper discloses an efficient and mild synthesis protocol for the O2-involved ethylbenzene (EB) photooxidation triggered by 910-dihydroanthracene (DHA) auto- photooxidation in acetone under visible light illumination, which can achieve 87.7 % EB conversion and 99.5 % acetylacetone (ACP) selectivity under ambient conditions. Also, 62.9 % EB conversion and 96.3 % ACP selectivity is obtained in air atmosphere. Furthermore, this protocol has a good adaptability for the photooxidation of other organic substrates such as tetrahydronaphthalene, diphenylmethane, toluene, cyclohexane, cyclohexene, alcohol, methylfuran and thioether to their corresponding oxygenates. A series of control and quenching tests, combined with EPR spectra, suggest that the photo-excited DHA can transfer its photo-electron to O2 to yield a superoxide radical anion (O2⚫−), then DHA is preferentially oxidized to anthraquinone (AQ) by the active O2⚫− owing to its high reactivity. Finally, the in situ generated AQ as an active photo-catalyst can achieve the photooxidation of EB and other organic compounds by O2. The present photo-autoxidation protocol gives a good example for the O2-based selective oxidation of inert hydrocarbons under mild conditions.