The photosensitised oxidation of amines. Part IV. The use of aromatic hydrocarbons as sensitisers

Abstract

The photo-oxidation of tertiary amines, but not of primary and secondary amines, is sensitised by aromatic hydrocarbons (anthracene, naphthalene, perylene, and phenanthrene) in acetonitrile. Reaction does not occur in benzene. The reactions are interpreted as occurring via the formation of hydrocarbon radical anions and amine radical cations from the singlet states of the hydrocarbons. Amine radicals, which subsequently react with oxygen to give the products (imines, aldehydes, and secondary amines) may be formed by proton transfer from the amine radical cation to the hydrocarbon anion. Alternatively, proton transfer to the superoxide anion (O₂^–˙), formed by electron transfer from the hydrocarbon radical anion to oxygen, may occur. Quantum yields for the photoreduction of aromatic hydrocarbons by triethylamine and NN-dimethylaniline are reported.