Dechlorination of DDT catalyzed by visible-light-driven system composed of vitamin B₁₂ derivative and Rhodamine B

The visible-light-driven dechlorination of 1,1-bis(4-chlorophenyl)-2,2,2- trichloroethane (DDT) was carried out in the presence of a hydrophobic vitamin B₁₂, heptamethyl cobyrinate perchlorate and Rhodamine B. DDT was successfully dechlorinated to form 1,1-bis(4-chlorophenyl)-2,2-dichloroethane (DDD) as the mono-dechlorinated product upon visible light irradiation with a tungsten lamp (λ > 440 nm). Upon prolonged visible light irradiation to DDT, DDMU (1-chloro-2,2-bis(4-chlorophenyl)ethylene), DDMS (1-chloro-2,2-bis(4-chlorophenyl)ethane) and DCS (trans-4,4′- dichlorostilbene) were obtained as the di- and tri-dechlorinated products. The use of the photostable organic sensitizer enabled prolonged photocatalysis via a noble-metal-free process. The vitamin B₁₂ derivative was replaced by an imine/oxime-type cobalt complex although the cobalt complex system showed a lower catalytic activity than the B₁₂ derivative system. The dechlorination mechanism in the B₁₂-Rhodamin B system was investigated by various methods such as UV-vis absorption and fluorescence quenching.