Mechanisms of the reductive denitration of pentachloronitrobenzene (PCNB) and the reductive dechlorination of hexachlorobenzene (HCB)

The reductive denitration of PCNB and the reductive dechlorination of HCB are complex, and begin with reaction of both fungicides with glutathione, with elimination of the nitro group and/or of chlorine, respectively. The glutathione conjugates are further metabolized by cleavage of the glycine and glutamate residues to give cysteine conjugates or N-acetylcysteine conjugates by acetylation in mammals. The cysteine derivatives are further metabolized by cleavage of the C-S bond to produce thiophenols, which after reductive desulphuration form pentachlorobenzene, or minor chlorinated benzenes, respectively.