The Photochemical Oxidation Reaction of Benzylic Alcohols in Dimethyl Sulfoxide

A new photochemical oxidation reaction of benzylic alcohols has been developed by using DMSO as a solvent. The oxidation, which has been performed in an oxygen atmosphere, can be carried out under neutral conditions at room temperature. Detailed studies on the role of DMSO as the solvent were carried out by using benzyl alcohol; it has been established that, in the photo-oxidation in DMSO, the uptake of oxygen was much facilitated compared with the reactions using other solvents, and also that, the benzaldehyde formed was well protected from further oxidation by a complex formation. Three secondary benzylic alcohols gave moderate yields of the corresponding ketones. The same experiments on ten substituted benzyl alcohols have revealed that the presence of an electron-releasing group facilitates the oxidation affording benzaldehydes, whereas an electron-attracting group retards it.