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

Abstract

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.