Radical cations of polychlorinated and polybrominated biphenyls in 1,2-dichlorethane: a pulse radiolysis study

Abstract

The pulse radiolysis of polychlorinated (PCBs) and polybrominated biphenyls (PBBs) in 1,2-dichloroethane has been investigated. The radical cations exhibit specific absorption spectra with one or two bands in the u.v., and one weak transition in the near i.r. region. The latter are red shifted relative to the corresponding absorption band of the plain biphenyl radical cation. ortho-Substitution leads to a blue shift while meta-substitution exerts only a weak effect on the absorptions in the u.v. The life-times of both meta- and ortho-substituted biphenyl radical cations are decreased relative to that of the unsubstituted biphenyl species. Radical cations of ortho-substituted PCBs and PBBs, as well as those containing many vicinal halogen atoms, decay by approximately first-order kinetics. The underlying reaction is assumed to be deprotonation. Radical cations of biphenyls with para-substituents show a red shift in the u.v. absorption and an increase in life-time relative to the corresponding properties of the unsubstituted biphenyl species. Their decay occurs mostly by second-order kinetics. On the basis of these physico-chemical characteristics a probable structure is suggested for the radical cations of halogenated biphenyls.