DDT-reductive dechlorination catalyzed by cobalt phthalocyanine, 2,3- and 3,4-tetrapyridoporphyrazine complexes in non-aqueous media

Abstract

Neutral cobalt(II) phthalocyanine and 2,3- and 3,4-tetrapyridoporphyrazine complexes were examined in pyridine, dimethyl sulfoxide and N,N-dimethylformamide to evaluate their catalytic properties in the reductive dechlorination of 1,1-bis(4-chlorophenyl)-2,2,2-trichloroethane (p,p'-DDT). Cyclic voltammetry, controlled potential bulk electrolysis and thin-layer UV-visible spectroelectrochemistry of each compound in the presence of DDT indicated that both the singly and doubly reduced species, [Co(I)]- and [Co(I)]2- , can catalyze the dechlorination of DDT through the formation of, and a photoinduced or electrochemically induced cleavage of, the Co-C bond in the organometallic intermediates. GC-MS analysis revealed that DDT was converted to 1,1-bis(4-chlorophenyl)-2, 2-dichloroethane (p,p'-DDD), 1,1-bis(4-chlorophenyl)-2,2-dichloroethylene (p,p'-DDE) and 1,1-bis(4-chlorophenyl)-2-chloroethylene (p,p'-DDMU), upon dechlorination. The catalytic performance of the three cobalt complexes depends upon the reactive nature of each compound, the solvent, the reaction time and the equivalence of DDT. In addition, either DDD or DDE can be catalytically dechlorinated to generate DDMU, possibly through a similar mechanism.