PHOTOCHEMICAL DECARBOXYLATION OF ACIDS WITH THALLIUM(3)

T1(III) carboxylates generated by the facile metathesis of T1(III) acetate and a variety of carboxylic acids are photolyzed at 2537 and 3500 A in benzene solutions. Photolysis yields T1(I) carboxylate and CO2 quantitatively together with products derived from the alkyl moiety of the acid. These are alkane, alkene, dialkyl and alkyl esters, and alkylbenzene. The relative amounts of each depend on the irradiating source. Alkyl dimers are formed in high yields with 2537-A light, whereas at 3500-A alkanes are the major products. These products are considered to arise from free alkyl radicals generated by photolytic homolysis of T1(III) carboxylates stepwise to T1(II) carboxylates, followed by further fragmentation to the T1(I) product. The good yields of dimers particularly from primary acids using 2537-A irradiation is attributed to high local concentrations of radicals due to the instability of the T1(II) species generated in an excited state. These alkyl radicals can be trapped by hydrogen donors of scavenged by Cu(II). The rearrangement of 5-hexenyl radical from 6-heptenoic acid to cyclopentylmethyl radical is not reversible and direct molecular processes do not obtain in the dimerization. © 1968, American Chemical Society. All rights reserved.