The dehalogenation of lindane by a range of hemoproteins, porphyrins, and corrins has been tested under reducing conditions in the presence of dithiothreitol. In addition, a series of porphyrin-metal ion complexes have been prepared and have also been screened for the capacity to dehalogenate lindane. Hemoglobin, hemin, hematin, and chlorophyll alpha all catalyzed the dehalogenation of lindane, as did all of the corrins tested. The porphyrins which did not contain metal centers--coproporphyrin, hematoporphyrin, protoporphyrin, and uroporphyrin--were inactive. However, when these porphyrins were then complexed with Co, Fe, Mg, Mo, Ni, or V, lindane dehalogenation was observed. In all cases, the reaction proceeded by an initial dechlorination to produce tetrachlorocyclohexene, which was further dehalogenated to yield chlorobenzene as the end product.

Dehalogenation of lindane by a variety of porphyrins and corrins.

Vitamin B12, reduced by titanium (III) citrate to vitamin B12s, catalyzes the reductive dechlorination of chlorophenols. Reductive dechlorination of pentachlorophenol and of all tetrachlorophenol and trichlorophenol isomers was observed. Reaction of various chlorophenols with vitamin B12 favored reductive dechlorination at positions adjacent to another chlorinated carbon, but chlorines ortho to the hydroxyl group of a phenol were particularly resistant to reductive dechlorination, even if they were also ortho to a chlorine. This resulted in a reductive dechlorination pattern favoring removal of para and meta chlorines, which differs substantially from the pattern exhibited by anaerobic microbial consortia.

Regiospecificity of Chlorophenol Reductive Dechlorination by Vitamin B12s

We found that in-situ preparation of Ni2B with the addition of excess NaBHa was--6ff--ective in the extensive dechlorination of DDT (DENNIS-and COOPER, 1975), heptachlor and chlordane (DENNIS and COOPER, in press). Similar systems have been used to reductively dehalogenate aromatic systems (EGLI, 1968) and as a site specific method for deuteration (BOSIN, et a l . , 1973). This catalytic system was found to rapidly and comp-Te~ly dechlorinate lindane (the gamma isomer of 1,2,3,4,5,6 hexachlorocyclohexane) to benzene, cyclohexene, cyclohexane and chloride ions. In a similar reduction of lindane described by Bieniek e t a l . (1970), lindane, Co2B and an excess of NaBH4, in various solvents, produced tetrachlorocyclohexane as the major product.

D. Bienik

Papers

Beitraege zur oekologischen chemie 29. mitt. reduktive dehalogenierung von chlorierten cyclischen kohlenwasserstoffen