Hexachlorocyclohexanes

Hexachlorocyclohexanes (HCHs) have not caused the problems of bioconcentration or bioaccumulation associated with DDT or the cyclodienes, and they have not been implicated in large-scale environmental problems. They will only be discussed briefly here, drawing attention to certain differences from the foregoing groups. 

Of the other HCH isomers, the alpha and beta forms are less toxic than the gamma form. However, the beta form is more persistent than the gamma form, and unacceptably high residues have sometimes been reported in foods originating from countries where technical HCH is still used (Environmental Health Criteria 123). 

Organic Pollutants An Ecotoxicological Perspective, Second Edition 

Resistance to DDT has been developed in many insect species. Although there are some cases of metabolic resistance (e.g., strains high in DDT dehydrochlorinase activity), particular interest has been focused on kdr and super kdr mechanisms based upon aberrant forms of the sodium channel—the principal target for DDT. There are many examples of insects developing resistance to dieldrin. The best-known mechanism is the production of mutant forms of the target site (GABA receptor), which are insensitive to the insecticide. 

Brooks, G.T. (1974). The Chlorinated Insecticides, Vols 1 and 2—A detailed and authoritative standard reference work on the chemistry, biochemistry, and toxicology of organochlo-rine insecticides. 

These are usually abbreviated as HCHs for obvious reasons. The most well known of these compounds is lindane, which is also known as the gamma isomer of HCH or y-HCH. Its structure is given below. 

Note the orientation of the chlorines relative to the cyclohexane ring this is the aaaeee-isomer, where a is axial and e is equatorial. HCHs are abundant in the Love Canal dump because the Hooker Chemical Corp. in Niagara Falls, NY, made them. HCHs have environmental half-lives of a few years, and they have been found in mammals from the Arctic. Lindane s use in the United States is being phased out starting in 2009. 

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Cm.OROCARBONSANDCm.OROHYDROCARBONS - TOXIC AROMATICS] (Void) b-Hexachlorocyclohexane... 

The performance of SCWO for waste treatment has been demonstrated (15,16). In these studies, a broad number of refractory materials such as chlorinated solvents, polychlorinated biphenyls (PCBs), and pesticides were studied as a function of process parameters (17). The success of these early studies led to pilot studies which showed that chlorinated hydrocarbons, including 1,1,1-trichloroethane /7/-T5-6y,(9-chlorotoluene [95-49-8] and hexachlorocyclohexane, could be destroyed to greater than 99.99997, 99.998, and 99.9993%, respectively. In addition, no traces of organic material could be detected in the gaseous phase, which consisted of carbon dioxide and unreacted oxygen. The pilot unit had a capacity of 3 L/min of Hquid effluent and was operated for a maximum of 24 h. 

Lindane is one of eight different hexachlorocyclohexane (HCH), C H Cl, isomers and its Chemical Abstract n.2cniQ is la, 2a 3P, 4a, 5a 6P-hexachlorocyclohexane [58-89-9] (y-HCH or y-BHC, ben2ene hexachloride) (80). Commercial products containing lindane are marketed as either a mixture of isomers or as the pure y-BHC isomer. Not unexpectedly, lindane is a highly stable lipophilic compound and it has been used extensively worldwide as an insecticide. In contrast, hexachloropentadiene, C Cl, is an extremely reactive industrial intermediate used as a chemical intermediate in the synthesis of a broad range of cyclodiene-derived pesticides, which include endosulfan, endrin, heptachlor, and several different organohalogen flame retardants (81). 

Chemical Designations - Synonyms BHC, 1,2,3,4,5,6-Hexachlorocyclohexane Lindane Chemical Formula C,sH,sCl[Pg.38]

HERBAZIN 500 BR , siniazine, 74 HERBI D-480 , 2,4-D, 74 HERBIMIX SC , atraziiie + semazine, 74 HERBIPAK 500 BR , ametryn, 74 HERBITRIN 500 BR , atraziiie, 74 HERBOXONE , 2,4-D, 74 HERBURON 500 BR , diui-on, 74 Hercules Eic., 232 Herdillia Chemicals Ltd., 172 Heterene Iiic., 232 Hexachlorobenzene, 74 Hexachlorobutadiene, 74 Hexachlorocyclohexanes, 74 Hexachlorocyclopentadiene, 74 Hexachloroethane, 75 Hexachloronaphthalene, 75 Hexachlorophene, 75 Hexafluoroacetone, 75 Hexafluoroethane, 75 Hexaniethylenedianiine, 75 Hexaniethylene diisocyanate, 75 Hexaniethylphosphoric trianiide, 75 n-Hexane, 75 Hexanol, 75 Hexazinone, 75 1-Hexene, 75... 

That benzene hexachloride isomer mixture is then the raw material for lindane production. The production of lindane per se is not a chemical synthesis operation but a physical separation process. It is possible to influence the gamma isomer content of benzene hexachloride to an extent during the synthesis process. Basically, however, one is faced with the problem of separating a 99%-plus purity gamma isomer from a crude product containing perhaps 12 to 15% of the gamma isomer. The separation and concentration process is done by a carefully controlled solvent extraction and crystallization process. One such process is described by R.D. Donaldson et al. Another description of hexachlorocyclohexane isomer separation is given by R.H. Kimball. 

There are eight diastereomers of 1,2,3,4,5,6-hexachlorocyclohexane. Draw each in its more stable chair conformation. One isomer loses HC1 in an E2 reaction nearly 1000 times more slowly than the others. Which isomer reacts so slowly, and why ... 

Gamma hexachlorocyclohexane, radiation resistance, 196 Gamma-rays, 188, 193, 194, 197, 202 Gamma-space, 320 Gas hydrates, 3, 20, 22, 25, 34 mechanism of formation, 4 thermodynamic properties, 15 x-ray work, 3... 

Heterogeneous polymerization, 163 Hexachlorobenzene, influence of radiation on, 198, 200 quadrupole spectrum, 197 Hexachlorocyclohexane resonance lines, 191... 

Rings with more than two differently substituted carbons can be dealt with on similar principles. In some cases, it is not easy to tell the number of isomers by inspection. The best method for the student is to count the number n of differently substituted carbons (these will usually be asymmetric, but not always, e.g., in 68) and then to draw 2" structures, crossing out those that can be superimposed on others (usually the easiest method is to look for a plane of symmetry). By this means, it can be determined that for 1,2,3-cyclohexanetriol there are two meso compounds and a dl pair and for 1,2,3,4,5,6-hexachlorocyclohexane there are seven meso compounds and a dl pair. The drawing of these structures is left as an exercise for the student. 

The mechanism is usually electrophilic (see p. 972), but when free-radical initiators (or UV light) are present, addition can occur by a free-radical mechanism. Once Br-or Cl- radicals are formed, however, substitution may compete (14-1 and 14-2). This is espiecially important when the alkene has allylic hydrogens. Under free-radical conditions (UV light) bromine or chlorine adds to the benzene ring to give, respectively, hexabromo- and hexachlorocyclohexane. These are mixtures of stereoisomers (see p. 161). ... 

Lastly, we will describe how these methods have been used to characterize the effects of hexachlorocyclohexanes on neutrophil functions. Although we are limiting this to a discussion of neutrophils, these approaches are completely generalizable to other cell types and have already been applied to some. We hope this summary will be useful to workers who wish to extend these techniques to the cell systems of interest to them. 

There are several isomers of 1,2,3,4,5,6-hexachlorocyclohexane (HCH). The Y isomer is insecticidally active, whereas most of the others are relatively inactive. These compounds have been shown to activate inflammatory functions of neutrophils (35,36). Using Indo-1, we have characterized intracellular Ca mobilization in response to these compounds. Figure 9 shows the responses of cells labeled with Indo-1 to stimulation by y, < " P , and 6-HCH at a concentration of 260 pH. 

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