Halogenated Arenes and Carboxylates with Chlorine, Bromine, or Iodine Substituents

PART 1 HALOGENATED ARENES AND CARBOXYLATES WITH CHLORINE, BROMINE, OR IODINE SUBSTITUENTS 

These industrial chemicals are widely used as the precursors for a wide range of products, which include agrochemicals, pharmaceutical products, polychlorinated biphenyls (PCBs), and polybro-minated diphenyl ether flame retardants. For almost all of them, serious concern has arisen over their adverse environmental effects. 

Since the aerobic degradation of halogenated phenols takes place by monooxygenation and is discussed in Part 2 of this chapter, it is not discussed here except to note the production of chlorocat-echols from chlorophenols and chloroanilines. Emphasis is placed on chlorinated substrates, and reference may be made to a review (Allard and Neilson 2003) for details of their brominated and iodinated analogs. The degradation of aromatic fluorinated compounds is discussed in Part 3 of this chapter. 

Aerobic degradation of chlorinated arene hydrocarbons, including the important group PCBs, and chlorobenzoates that are produced from them as metabolites, is generally initiated by dihy-droxylation of the rings to dihydrodiols followed by dehydrogenation to catechols. Halide may be lost simultaneously and for 2-halogenated benzoates, both halide and carboxyl. Salient aspects are summarized, and attention drawn to selected aspects of enzyme inhibition. 

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