Reductive dechlorination and degradation of mirex and kepone with vitamin B12s

Abstract

Vitamin B_12s effects the reductive dechlorination of mirex (dechlorane) in protic solvent systems, under both catalytic and stoichiometric conditions, mainly to yield compounds of composition C₁₀Cl_12-nH_n, with n = 1–8, in which the basic dihomocubane cage structure is retained; the formation of cage-opened, reductively dehalogenated derivatives of 4,7-methanoindene occurs only to a very minor extent.

The corresponding reactions of kepone (chlordecone), in contrast, occur with predominant formation of indene derivatives C₉Cl_8-nH (with n = 3–5), presumably via 4,7-methanoinden-8-one derivatives. Under certain mild conditions, vitamin B_12s induces a fragmentation of kepone leading to the destruction of the dihomocubane moiety and the formation of an isolable organocobalamin having a C₃Cl₃H₂ residue attached to the cobalt atom. In strongly alkaline media, the reaction of kepone with vitamin B_12s may in addition yield high-molecular-weight condensation products of unknown constitution. Reactions of this type are of interest as prototypes of soil-decontamination processes.