| Abstract: | A study was made of the mechanism of benzene polymerization by aluminum chloride-cupric chloride. Our main effort was devoted to propagation with the aim of resolving a literature conflict as to whether a cationic or radical pathway is involved. When equimolar mixtures of benzene and haloarene are polymerized, the resulting copolymers are composed almost exclusively of benzene monomer. This approach is based on the known relative reactivities of the monomers toward electrophilic and radical species. The amount of haloaromatic present in the copolymer was determined by elemental analyses and confirmed by infrared spectroscopy. These results are strongly indicative of propagation by an electrophilic moiety. The presence of oxygen in the reaction mixture was found to have no significant effect on the rate or yield of the polymerization, in contrast to a previous published report. The progress of the reaction was followed by titration of the evolved hydrogen chloride. Phenyl radicals, obtained by the thermal decomposition of benzoyl peroxide in benzene, were found to be incapable of initiating the polymerization in the presence of cupric chloride. Increased yields of biphenyl and the presence of chlorobenzene point to oxidation of intermediate radicals by cupric chloride. None of the experimental evidence is satisfactorily interpreted by radical propagation. The data are nicely rationalized on the basis of cationic chain extension, apparently via a radical cation initiator. |
