The Dechlorination of Polychlorinated Biphenyls by UV-irradiation. VIII. Reactions of 2,3- and 3,4-Dichlorobiphenyl in a 2-Propanol Solution

Abstract

Abstract The photodechlorinations of 2,3-dichlorobiphenyl (2,3-DCB) and 3,4-dichlorobiphenyl (3,4-DCB) in 2-propanol gave 3-chlorobiphenyl and 4-chlorobiphenyl respectively. The quantum yields of monochlorobiphenyl formation were 0.2 for 2,3-DCB and 0.06 for 3,4-DCB, independent of the substrate concentration and the wavelength of the exciting light. On the basis of the results obtained in quenching experiments using cis-1,3-pentadiene, it was concluded that 2,3-DCB was photodechlorinated exclusively in the excited singlet state, while 3,4-DCB was photodechlorinated in both excited singlet and triplet states. In the case of 3,4-DCB, the relative contributions of excited singlet and triplet states to the total dechlorination were evaluated as 0.8 and 0.2 respectively. The participation of the excited triplet state in the photodechlorination of 3,4-DCB was ascertained both by quenching reactions with biacetyl as a quencher and by photosensitized dechlorinations with acetone and acetophenone as sensitizers.