Photodegradation behaviors of polychlorinated biphenyls in methanol by UV-irradiation: Solvent adducts and sigmatropic arrangement

Abstract

This study has investigated the photolysis of polychlorinated biphenyls (PCBs) in methanol solution under UV irradiation. The results showed that the PCBs containing ortho-chlorine can generate both hydroxylated and methoxylated PCBs (HO-PCBs and MeO-PCBs), while the PCBs with a meta-chlorine but without ortho-chlorine can only generate MeO-PCBs as the only solvent adducts. No solvent adducts were detected during the photochemical reaction of 4-chlorobiphenyl (PCB-3), indicating the para-chlorine cannot be attacked by solvent molecule to form correspondent solvent adducts. The sigmatropic rearrangement was found during the photochemical reaction of ortho-substituted PCBs, but cannot occur in the reaction of PCBs with only meta- or para-chlorine, indicating that ortho–chlorine played a vital role in the sigmatropic rearrangement reaction. In addition, the seteric hindrance can also lead to the generation of sigmatropic rearrangement products. The effect of solvent was investigated in the case of photochemical reaction of 2-chlorobiphenyl (PCB-1), the results showed that sigmatropic rearrangement can occur in different solvents, and corresponding solvent adducts were generated in the photochemical reaction of PCB-1 in different solvents.