Electron spin resonance studies. Part XVI. Photochemical reactions of biacetyl with some benzenoid compounds

Abstract

The photoexcitation of biacetyl in the presence of phenylacetic acid or phenoxyacetic acid is aqueous acid results in the liberation of carbon dioxide, the appearance of the monoprotonated biacetyl semidione radical, and the formation of products derived from the benzyl or the phenoxymethyl radical, respectively. A study of the factors which determine the reactivity in these processes provides evidence that reaction occurs by addition of biacetyl in its n,π* triplet state to the aromatic ring followed by acid-catalysed fragmentation. The bearing of the results on the deactivation of photoexcited ketones by benzenoid compounds, and on some reactions of photoexcited flavins, is discussed.