Some photoinduced decarboxylation reactions.

Some of the fundamental aspects of photochemistry have been discussed. The photoinduced decarboxylation of carboxylic acids and carboxylate anions is reviewed, as well as decarboxylations sensitised by salts (e.g. cerium(IV) salts), heterocyclic compounds(e.g. acridine), and carbonyl compounds (i.e. biacetyl). Decarboxylations sensitised by 'biochemically- active' molecules e.g. flavins, are also reviewed. The photoinduced decarboxylation of carboxylic acids of type RXCH2CO2H (where 'R' is an alkyl or aryl group, and 'X' =O, S, or NH), sensitised by various ketones and quinones, has been studied. Yields of carbon dioxide and substituted hydrocarbons, of type RXCH3, have been obtained. Other product studies have shown that with a few quinones e.g. tetrachloro-p-benzoquinone, stable adducts are formed, whereas aromatic ketones give the corresponding pinacols. Quenching studies have been carried out to determine the rate constants for decarboxylation, and a kinetic scheme is proposed. Evidence in support of a mechanism involving an electron transfer, from the acid to the excited carbonyl group, is presented. The photoinduced decarboxylation of carboxylic acids, sensitised by quinoxalines, has been briefly considered. (Vi) Yields of anisole from the decarboxylation of phenoxyacetic acid, under nitrogen, have been obtained; other products, from reactions carried out in the presence of air, were also obtained. Possible reaction mechanisms are considered.