Reactions of palladium(II) with organic compounds. Part II. Oxidation of some benzenoid compounds in trifluoroacetic acid

Benzene, some monosubstituted benzenes, and di- and poly-methylated benzenes are readily oxidised by palladium(II) in trifluoroacetic acid. Benzene and most monosubstituted analogues give mainly or solely biaryls, as do o-xylene, m-xylene, and hemimellitene (1,2,3-trimethylbenzene). Most of the possible isomers were found in each case but the predominant ones are those in which one of the aryl groups is bonded to the second through the position most susceptible to electrophilic attack. Toluene, ethylbenzene, p-xylene, and pseudocumene (1,2,4-trimethylbenzene) give, in addition, diarylmethanes, and from mesitylene and durene (1,2,4,5-tetramethylbenzene) these latter compounds were the only products detected. Diarylmethane formation, in most cases, was of necessity selective but, even in those instances where more than one such compound might have been expected, only the anticipated product of electrophilic arylmethylation was observed. Mechanisms which account for the formation of the two types of product are discussed.