Polyhalogenated aromatic compounds

The toxicities of polyhalogenated aromatic hydrocarbons are elaborated upon in the chapters of Part 3 of this book. 

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The influence of electron density distiibution in the radical-anioa on the rate of carbon-halogen bond cleavage was discussed on page 94. This effect makes possible the selective dehalogenation of polyhalogen aromatic compounds. Examples... 

SANDERSON J T, AARTS J M M J G, BROUWER A, FROESE K L, DENISON M S and GIESY J P, Comparison of Ah-receptor-mediated luciferase and ethoxyresorufin O-deethylase induction in H4IIE cells implications for their use as bioanalytical tools for the detection of polyhalogenated aromatic compounds , Toxicol Appl Pharmacol 1996 137 316-25. 

The data available suggest that 2,3,7,8-TCDD is a dermal toxicant both in humans and animals. Erythematous skin rashes and chloracne are considered one of the hallmarks of 2,3,7,8-TCDD toxicity, although it can be caused also by exposure to other polyhalogenated aromatic compounds. It is also worth mentioning that although in humans chloracne indicates exposure to chlorinated or halogenated aromatics, lack of chloracne does not indicate that exposure has not occurred. 

HillRHJr. 1985. Effects of polyhalogenated aromatic compounds on porphyrin metabolism. Environ... 

Wallbaum, U., and K. Zunker. 1998. Process for reducing the concentration of polyhalogenated aromatic compounds or polynuclear aromatic hydrocarbons in a flue gas. US Patent, Patent Number WO9803247. 

Direct oxidation of polyhalogenated aromatic compounds to phenols or quinones, or para-substituted phenols to quinones, is thought to occur by a variant of ipso-substitution. Pentaf-luorochlorobenzene is thus oxidized to tetraflu-... 

When substitution occurs in polyhalogenated aromatic compounds, such as the pentafluorobenzene derivatives, QF5X, the extent of the replacement of F or X by the nucleophile and the product orientation must be determined. 

The loss of the X halide is in competition with the corresponding X radical that supplies the [M-X] ion. This last mechanism is presented in Figure 9.60 in the case of a tetrachlorodioxin. Unlike the elimination of halide ions that results from homo-lytic cleavage of the C-X bond, the formation of [M-X]- results from a heterolytic cleavage. For polyhalogenated aromatic compounds, the relative proportions of M-, [M-X]-, and X- in the mass spectrum depend on the conditions of the spectrometer source (temperature, pressure) and also and especially on the nature of the thermal-ization gas used."... 

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