Benzene hexachloride isomers

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. 

Cristol, S. J. (1947) The kinetics of the alkaline dehydrochlorination of the benzene hexachloride isomers. The mechanisms of second-order elimination reactions. Journal of the American Chemical Society, 69, 338-342. 

Experimental data indicate that the anti pathway for E2 reactions is favored over the syn pathway. In one of the earliest studies of the stereochemistry of the E2 reaction, Cristol found the rate constant for the dehydrochlorination of the )3 isomer of benzene hexachloride (1,2,3,4,5,6-hexachlorocyclohexane, 6), in which each chlorine is cis to the hydrogen atoms on either side of it, to be only 10" times those of the other benzene hexachloride isomers. Since each of the other isomers has at least one hydrogen atom trans to a chlorine atom on an adjacent carbon atom, the low reactivity of 6 suggested that the E2 reaction occurs preferentially when there is a trans relationship for the hydrogen atom and chlorine atom on cyclohexane. ... 

Chlorine and bromine add to benzene in the absence of oxygen and presence of light to yield hexachloro- [27154-44-5] and hexabromocyclohexane [30105-41-0] CgHgBr. Technical benzene hexachloride is produced by either batch or continuous methods at 15—25°C in glass reactors. Five stereoisomers are produced in the reaction and these are separated by fractional crystallization. The gamma isomer (BHC), which composes 12—14% of the reaction product, was formerly used as an insecticide. Benzene hexachloride [608-73-17, C HgCl, is converted into hexachlorobenzene [118-74-17, C Clg, upon reaction with ferric chloride in chlorobenzene solution. 

HCH, sometimes misleadingly termed benzene hexachloride (BHC), exists in a number of different isomeric forms of which the gamma isomer has valuable insecticidal properties. These were discovered during the 1940s, and HCH came to be widely used as an insecticide to control crop pests and certain ectoparasites of farm animals after the Second World War. Crude technical BHC, a mixture of isomers, was the first form of HCH to be marketed. In time, it was largely replaced by a refined product called lindane, containing 99% or more of the insecticidal gamma isomer. 

The first commercially available HCH insecticide sometimes misleadingly called benzene hexachloride (BHC) was a mixture of isomers, principally alpha HCH (65-70%), beta HCH (7-10%), and gamma HCH (14-15%). Most of the insecticidal activity was due to the gamma isomer (Figure 5.1), a purified preparation of which (>99% pure) was marketed as lindane. In Western countries, technical HCH was quickly replaced by lindane, but in some other countries (e.g., China) the technical product, which is cheaper and easier to produce, has continued to be used. HCH has been used as a seed dressing, a crop spray, and a dip to control ectoparasites of farm animals. It has also been used to treat timber against wood-boring insects. 

Particularly the chlorinated compounds have enjoyed range of applications vinyl chloride (chloro-ethene) as monomer for the production of PVC, tetra- and trichloroethenes as solvents for degreasing, and the insecticides l,l,l-trichloro-2,2-bis(p-chlorophenyl)ethane (DDT) and isomers of hexachlorocyclohexane (HCH) (benzene hexachloride). The biodegradation of fluorinated aliphatic compounds is generally different from the outlines that have emerged from investigations on their chlorinated, brominated, and even iodinated analogues. They are therefore treated separately in Part 4 of this chapter. 

The Milwaukee, Wis., Health Department regulates the use of DDT, chlordan, and the gamma isomer of benzene hexachloride by permitting their use only when food, food working surfaces, and equipment are covered during the spraying process so as to prevent spray from being deposited thereon. 

Carter 12), of the Bureau of Entomology and Plant Quarantine, has adapted the total-chlorine method to the analysis of mixtures of DDT and benzene hexachloride in the following manner After determination of total chlorine in the mixture, the DDT is estimated by the Schechter-Haller colorimetric method 47), half this value is subtracted from the total chlorine (because DDT contains 50% of chlorine), and the difference is calculated as benzene hexachloride. This procedure gives no indication of the amount of the gamma isomer of benzene hexachloride. 

LaClair (43) has employed the dehydrohalogenation reaction to determine the gamma isomer of benzene hexachloride in the technical product and in dust mixtures. Two identical samples are dissolved in 95% ethyl alcohol and treated with 1 N ethanolic potassium hydroxide at 0° C. for 15 and 50 minutes, respectively. The 15-minute period is sufficient to dehydrochlorinate most of the alpha and the delta isomers without appreciably affecting the gamma. In 50 minutes the gamma isomer is also dehydrochlorinated. The beta isomer does not react under these conditions, and usually the epsilon isomer is present in quantities too small to interfere seriously. 

Methods utilizing characteristic physical properties have been developed for several chlorinated hydrocarbon insecticides. Daasch (18) has used infrared spectroscopy for the analysis of benzene hexachloride. By this means it is possible to determine the gamma-isomer content, as well as that of the other isomers of technical benzene hexachloride, provided the product is substantially free of the higher chlorinated cyclohexanes. 

The gamma isomer of benzene hexachloride can also be determined by polarography (24, 0). The method is based on the fact that, under the conditions used, the gamma isomer is the only one of the five isomers that is reduced at the dropping mercury electrode. 

A method for determining the gamma isomer of benzene hexachloride by partition chromatography has been developed by Aepli et al. (1). Nitromethane and n-hexane are used as the partition solvents, and silicic acid is the supporting medium. The method appears to be useful for routine product analyses. An accuracy of about 2% of the actual gamma isomer present is claimed. 

A mass-isotope dilution method for determining the gamma isomer of benzene hexachloride, in which gamma-hexadeuterobenzene hexachloride is used as a tracer molecule and the dilution is determined by use of infrared spectrophotometry, has been developed by Trenner et al. (52). Impurities have no effect on the accuracy of this method. 

It was also established in laboratory work that this product could be readily formulated into dusts, wettable powder, or liquid formulations. Liquid formulations were more readily made with this than with the commercial benzene hexachloride, because of the higher concentration of the gamma isomer. 

The residual toxicity of the pure gamma isomer was found to be equivalent to that of ordinary commercial benzene hexachloride. Commercial usage has shown that the residual action is effective for a longer time with dust or wettable powder spray applications than with emulsive solvent-type formulations. The over-all residual life of the chemical is on the order of 4 to 8 days as compared to 14 to 21 days for DDT. This is, of course, adequate residual life for good insect control in most cases and the shorter... 

The isomers of benzene hexachloride (1,2,3,4,5,6-hexachlorocyclohexane) also eliminate the elements of hydrogen chloride to alkali, and comparative data regarding the proposed hypothesis are available. Table II gives reaction-rate constants for dehydrochlorination (6) and comparative toxicities to larvae of A. quadrimaculatus (12). Here, of course, the compounds differ only in stereochemistry—that is, in spatial arrangement of the atoms—and there is no apparent relationship between reactivity and toxicity. 

Table II. Dehydrochlorination-Rate Constants and Toxicity to Anopheles quadrimaculatus Larvae of Isomers of Benzene Hexachloride...

The chemist should explore the fields of chemicals with structures related to compounds known to be effective. He should also study new classes of structures. Safety appears to lie in numbers. The failure of several members of a new class of compounds does not prove that there are no effective members in the group. Only certain of the analogs of DDT are good insecticides. Even DDT is not effective on some species of insects. Only the gamma isomer of benzene hexachloride is highly effective. 

Partition chromatography, developed by Martin and Synge (3) for the separation of amino acid derivatives, was employed by Ramsey and Patterson (4) for the separation of isomers of benzene hexachloride (1,2,3,4,5,6-hexachlorocyclohexane) in the technical product. The work of Ramsey and Patterson was extended by Aepli, Munter, and Gall... 

BHC in each technical BHC sample determined by partition chromatography. b The common name for the 7-isomer of benzene hexachloride of a purity of not less than 99%. c Calculated from total chlorine determination on DDT fraction. 

Fig. 5. Relationship between the distribution (partition) coefficient on dimethyl dihydrogenated tallow montmorillonite for a range of non-ionic organic pollutants and their corresponding solubility in water. BHC is benzene hexachloride, the y-isomer of which is known as lindane aroclor 1232 and aroclor 1252 denote mixtures of polychlorinated biphenyls containing about 32 and 52% chlorine, respectively. After Beall (2003).

Elimination of HC1 from the -isomer of benzene hexachloride in a series of water-alcohol mixtures.470 30... 

Synonyms AI3-09232 Benzene hexachloride-a-isomer a-Benzene hexachloride BRN 3195880 CCRIS 327 EINECS 206-270-8 ENT 9232 a-HCH a-Hexachloran a-Hexachlorane a-EIexachlorcyclohexane a-Hexachlorocyclohexane 1,2,3,4,5,6-Hexachloro-a-cyclohexane la,2a,3p,4a,5p,6p-Hexachlorocyclohexane a-1,2,3,4,5,6-Hexachlorocyclohexane a-Lindane ... 

Synonyms AI3-09233 te/js-a-Benzene hexachloride p Benzene hexachloride Benzene-cA-hexachloride BRN 1907338 CCRIS 328 EINECS 206-271-3 ENT 9233 p-HCH P-Hexa-chloran pHexachlorobenzene la,2p,3a,4p,5a,6p-Hexachlorocyclohexane pHexachloro-cyclohexane 1,2,3,4,5,6-Hexachloro-P-cyclohexane l,2,3,4,5,6-Hexachloro-to/3s-cyclohexane p i,2,3,4,5,6-Hexachlorocyclohexane P-Isomer P-Lindane TBH UN 2761. 

Benzenediol, see Hydroquinone p-Benzenediol, see Hydroquinone Benzeneformic acid, see Benzoic acid Benzene hexachloride, see Lindane Benzene hexachloride-a-isomer, see a-BHC Benzene-crs-hexachloride, see p-BHC Benzene-y-hexachloride, see Lindane a-Benzene hexachloride, see a-BHC p-Benzene hexachloride, see p-BHC 6-Benzene hexachloride, see 8-BHC y-Benzene hexachloride, see Lindane frans-a-Benzene hexachloride, see p-BHC Benzene hexahydride, see Cyclohexane Benzene methanoic acid, see Benzoic acid Benzene methanol, see Benzyl alcohol Benzene tetrahydride, see Cyclohexene Benzenol, see Phenol... 

Raghu, K. and MacRae, LC. Biodegradation of the gamma isomer of benzene hexachloride in submerged soils. Science (Washington, DC), 154(3746) 263-264, 1966. 

Chlorination of benzene gives an addition product that is a mixture of stereoisomers known collectively as hexachlorocyclohexane (HCH). At one time, this was incorrectly termed benzene hexachloride. The mixtnre has insecticidal activity, though activity was found to reside in only one isomer, the so-called gamma isomer, y-HCH. y-HCH, sometimes under its generic name lindane, has been a mainstay insecticide for many years, and is about the only example of the chlorinated hydrocarbons that has not been banned and is still available for general use. Although chlorinated hydrocarbons have proved very effective insecticides, they are not readily degraded in the environment, they accumulate and persist in animal tissues, and have proved toxic to many bird and animal species. 

Davidson (10) reported on the use of petroleum oil containing benzene hexachloride as a means of malaria control by adult mosquito destruction in western Africa. He concluded that an oil solution containing 0.5% of the gamma isomer of benzene hexachloride (Gammexane) sprayed on the inside wall surfaces of all houses at the rate of 10 mg. of gamma per square foot (2 quarts of solution to 1000 square feet) practically eliminated mosquitoes in those houses for about 6 months. 

Vast quantities of petroleum benzene have been used in the manufacture of such widely used agricultural chemicals as benzene hexachloride and lindane, the essentially pure gamma isomer of 1,2,3,4,5,6-hexachlorocyclohexane. 

The gamma isomer of hexachlorocyclohexane was commonly called gamma benzene hexachloride, a misnomer, since no... 

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