Bacterial dehalogenation of a PCB derivative

Polychlorinated biphenyls (PCBs) are compounds that were once used in a variety of electrical devices, industrial applications, and polymers. Their use and production were banned in 1979, however, owing to the toxicity of PCBs and their tendency to accumulate in the food chain. 

4-Chlorobenzoic acid is a degradation product of some PCBs. It is now known that certain bacteria are able to 

Some key features of this enzymatic S Ar mechanism are the following. The nucleophile that attacks the chlorinated benzene ring is a carboxylate anion of the enzyme. When the carboxylate attacks, positively charged groups within the enzyme stabilize the additional electron density that develops in the thioester carbonyl group of the Meisenheimer intermediate. Collapse of the Meisenheimer intermediate. 

11B Nucleophilic Aromatic Substitution through an Elimination-Addition Mechanism Benzyne 

Although aryl halides such as chlorobenzene and bromobenzene do not react with most nucleophiles under ordinary circumstances, they do react under highly forcing conditions. Chlorobenzene can be converted to phenol by heating it with aqueous sodium hydroxide in a pressurized reactor at 350°C (Section 21.4B)  

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Polyketide Anticancer Antibiotic Biosynthesis 954 The Bombardier Beetle s Noxious Spray 958 Bacterial Dehalogenation of a PCB Derivative 961... 

As late as 1975, industrial concerns were legally discharging PCBs into the Hudson River. In 1977, the EPA banned the direct discharge into waterways, and since 1979 their manufacture, processing, and distribution have been prohibited. In 2000 the EPA specified certain sections of the Hudson River for cleanup of PCBs. In 2009, a plan to decontaminate parts of the Hudson River by dredging was finally implemented. See "The Chemistry of. . . Bacterial Dehalogenation of a PCB Derivative" (Section 21.1 IB) for a potential method of PCB remediation. 

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