Use of heterocyclic compounds as photosensitisers for the decarboxylation of carboxylic acids

Abstract

Irradiation of solutions of substituted acetic acids ArX·CH₂·CO₂H (X = O, S, or NH) in the presence of acridine, phenazine, benzophenazines, and dyes such as Methylene Blue and eosin, leads to decarboxylation of the acids. Reaction occurs in the presence of oxygen and products derived from the substituted methyl radicals ArX·ĊH₂ are isolated. Under these conditions the heterocyclic compounds are recovered unchanged at the end of the reaction. Possible reaction mechanisms are discussed and the proposal is made that reaction occurs via electron transfer from the acid to an excited state of the sensitiser.