The photosensitized decarboxylation of carboxylic acids by benzophenone and quinones

Benzophenone and a number of quinones have been found to photosensitize the decarboxylation of acids of the type R1XCH2·CO2H (where X = O, S, and NH). The yields of substituted hydrocarbons (R1XCH3) formed by hydrogen abstraction by the alkyl radicals (R1XĊH2) and of addition products formed by reaction of the radicals with tetrachloro-p-benzoquinone as well as reduction products of the quinones have been determined. The yields of substituted hydrocarbons were often considerably increased by the inclusion of the good hydrogen donor, thiophenol, in the reaction mixture. The amino-acid studied, was found to give a substantial yield of the related aniline as well as the expected N-methylaniline. The benzophenone-sensitized reactions were retarded by oxygen whereas those sensitized by quinones were not. Addition of acetic acid was found to retard the reaction of phenoxyacetic acid with tetrachloro-p-benzoquinone.