Phenol is an important precursor for many chemicals and industrial products. One of the dream chemical reactions is the one-step oxygenation of benzene to phenol. However, challenges to overcome are low yield, poor selectivity, and the requirement of high temperature.

Shunichi Fukuzumi, Osaka University, Japan, and colleagues examined the direct oxygenation of benzene to phenol under visible-light irradiation of 2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ) in an oxygen-saturated acetonitrile solution of benzene. They activated a highest quantum yield of 45 %.

Their photocatalytic reaction is initiated by photoinduced electron transfer from benzene to the triplet excited state of DDQ. This gives phenol and 2,3-dichloro-5,6-dicyanohydroquinone (DDQH). DDQ acts as a stoichiometric oxidant. Tert-Butyl nitrite (TBN) then converts DDQH to DDQ under aerobic conditions.

• Visible-Light-Induced Oxygenation of Benzene by the Triplet Excited State of 2,3-Dichloro-5,6-dicyano-p-benzoquinone,
  Kei Ohkubo, Atsushi Fujimoto, Shunichi Fukuzumi,
  J. Am. Chem. Soc. 2013.
  DOI: 10.1021/ja402303k