100% Selective Oxygenation of Alkyl Substituted Benzenes

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A ring-substituted toluene with an electron-withdrawing substituent, p-tolunitrile, is oxygenated with molecular oxygen to yield the corresponding aldehyde using tetrafluoro-p-dicyanobenzene as a photosensitizer under photoirradiation with an Hg lamp (λ > 300 nm). The 100 % selective oxygenation of p-xylene to p-tolualdehyde is achieved using 10-methyl-9-phenylacridinium ion as a photosensitizer under visible light irradiation, leading to yield p-tolualdehyde exclusively as the final oxygenated product. Both oxygenation reactions are initiated by photoinduced electron transfer from the ring-substituted toluene to the singlet excited state of the photosensitizer. The reason for the high selectivity in the photocatalytic oxygenation of various toluene derivatives is discussed based on the photoinduced electron transfer mechanism.