Vapour phase chemistry of arenes. Part II. Thermolysis of chlorobenzene and reactions with aryl radicals and chlorine and hydrogen atoms at 500

Pyrolysis of chlorobenzene is interpreted as a radical (chain) process with the radicals ·C6H4Cl, ·Cl, and H· as carriers. Chlorobenzene, with added sources of R·(Cl·, H·, or Ph·) gives the biaryls chlorobiphenyl and bichlorophenyl, the ratio being highly dependent on R·. Thus, Cl· mainly abstracts H from PhCl to give o, m, and p-·C6H4Cl radicals (20 : 55 : 25) forming bichlorophenyls as the main product, whereas H· replaces and abstracts chlorine; Ph· leads to chlorobiphenyls as the principal products. Isomer distributions have been determined and are discussed. It is also shown that ·C6H4Cl radicals are isomerically stable under our conditions (e.g.,m-·C6H4Cl + PhH → 3-ClC6H4Ph only). With o-·C6H4Cl, naphthalene is formed in addition to 2-chlorobiphenyl. However, benzyne is rejected as an intermediate. ortho-Dichlorobenzene and biphenyl are found to react with H· at comparable rates.