Formation of polychlorinated biphenyls from the pyrolysis of hexachlorocyclohexane in the presence of Fe2O3.

Abstract

Industrial manufacture of polychlorinated biphenyls (PCBs) was based on the chlorination of biphenyl by anhydrous chlorine on heating in the presence of suitable catalysts synthesized all 209 PCB congeners by diazo coupling of chloroanilines and chlorobenzenes. Other than the commercial production or laboratory synthesis of PCBs as mentioned above, there were few additional reports on the formation of PCBs. Buser observed the formation of small quantities of higher chlorinated biphenyls from the pyrolysis of chloro-benzenes at 620{degrees}C, but the mechanism of the formation of PCBs had not been investigated. Zinburg et al. reported the formation of chloro-benzenes and chlorophenols by heating hexachlorocyclohexane (HCH) in the presence of H{sub 2}SO{sub 4} or H{sub 2}O{sub 2} in water, but pyrolysis of HCH in the presence of iron(III) oxide (Fe{sub 2}O{sub 3}) had not been reported. Bao et al. reported findings about 10% of PCBs in the waste from reaction stills affiliated to a large chemical factory in northern of China for production of trichlorobenzenes by pyrolysis of non-gamma HCH. To investigate the mechanism of the formation of PCBs, a series of experiments was performed. We discovered that hydrogen chloride can catalyze the condensation reaction of chlorobenzenes with chlorophenols into PCBs. The resultsmore » provided a mechanism of formation of PCBs from the pyrolysis of HCH in the chemical factory. 7 refs., 5 figs.« less