Heptachlor structure

Heptachlor and cw-chlordane, both of which are chiral, produce caged or half-caged structures (Figure 1.8) on irradiation, and these products have been identified in biota from the Baltic, the Arctic, and the Antarctic (Buser and Muller 1993). 

Figure 13.1 Chemical structure of chlordane-related compounds 1, chlordene (4,5,6,7,8,8-hexachloro-3a,4,7,7a-tetrahydro-4, 7-methanoindene) 2, c/ s-chlordane, also known as alpha-chlordane (1-exo, 2-exo, 4,5,6,7,8,8-octachloro-2,3,3a,4,7,7a-hexahydro-4,7-methanoindene) 3, trans-chlordane, also known as gamma-chlordane (1-exo, 2-endo, 4,5,6,7,8,8-octachloro-2,3,3a,4,7,7a-hexahydro-4,7-methanoindene) 4, heptachlor (1,4,5,6,7,8,8-heptachloro-3a,4,7,7a-tetrahydro-4,7-methanoindene) — technical heptachlor contains about 15% c/s-chlordane and 2.5% trans-chlordane 5, heptachlor epoxide (1,4,5,6,7,8,8-heptachloro-2,3-epoxy-3a,4,7,7a-tetrahydro-4,7-methanoindene) and 6, oxychlordane, also known as octachlor epoxide (1-exo, 2-endo, 4,5,6,7,8,8-octachloro,2,3-exo-epoxy-2,3,3a,4,7,7a-hexahydro-4,7-methanoindene). 

Technical chlordane consists of about 45 components, primarily m-chlordane (19%), trans-chlordane (24%), heptachlor (10%), cis- and iran.v-nonachlor (7%), and various chlordane isomers (22%). Chemical analysis of technical chlordane is difficult because of analytical interferences from other organochlorine compounds, nonstandardization of analytical techniques, variations in the number and relative composition of components in weathered chlordane, and uncertainty of the structural formulas and other properties of several compounds present. 

There are few studies that specifically describe the effects of heptachlor or heptachlor epoxide in humans following exposure via the oral, inhalation, or dermal routes. There are data on the health effects of chlordane from occupational studies of pesticide applicators and manufacturers, and from studies of people who consumed food contaminated with chlordane and heptachlor. Chlordane is a pesticide that is structurally similar to heptachlor, and technical-grade preparations may contain... 

Cyclodienes. These are polychlorinated cyclic hydrocarbons with endomethylene-bridged structures, prepared by the Diels-Alder diene reaction. The development of these insecticides resulted from the discovery in 1945 of chlordane, the chlorinated adduct of hexachlorocydopentadiene and cyclopentadiene (qv). The addition of two Cl atoms across the double bond of the five-membered ring forms the two isomers of chlordane /12789-03-6] or l,2,4,5,6,7,8,8-octachloro-2,3,3, 4,7,7 -hexahydro-4,7-methano-ll1f-indene, a-trans (mp 106.5°C) and p-cis (32) (mp 104.5°C). The p-isomer has significantly greater insecticidal activity. Technical chlordane is an amber liquid (bp 175°C/267 Pa, vp 1.3 mPa at 25°C) which is soluble in water to about 9 //g/L. It has rat LD5Qs of 335, 430 (oral) and 840, 690 (dermal) mg/kg. Technical chlordane contains about 60% of the isomers and 10—20% of heptachlor. It has been used extensively as a soil insecticide for termite control and as a household insecticide. 

As seen from the structural formulas in Figure 16.4, the organochlorine insecticides are of intermediate molecular mass and contain at least one aromatic or nonaromatic ring. They can be placed in four major chemical classes. The first of these consists of the chloroethylene derivatives, of which DDT and methoxychlor are the prime examples. The second major class is composed of chlorinated cyclodiene compounds, including aldrin, dieldrin, and heptachlor. The most highly chlorinated members of this class, such as chloredecone, are manufactured from hexachlorocyclo-pentadiene (see Section 16.3). The benzene hexachloride stereoisomers make up a third class of organochlorine insecticides, and the third group, known collectively as toxaphene, constitutes a fourth. 

Uses Chlordane is a viscous, amber-colored liquid. Technical-grade chlordane is a mixture of many structurally related compounds including trans-chlordane, cis-chlordane, chlordane, heptachlor, and /ran.v-nonachlor.14,15 Chlordane was used as a broad-spectrum pesticide in the United States from 1948 to 1988. Its uses included termite control in homes and pest control on agricultural crops (e.g., com, citrus, home lawns, gardens, turf, ornamental plants). 

The detectability (1) of hydrocarbon pesticides varies because of their differing chemical structure and physical properties. The practical minimum limits of analysis by this procedure are (a) 10 p.p.t. or less for aldrin, DDD, DDT, dieldrin, endrin, heptachlor, heptachlor epoxide,... 

Figure 4.3 Structures of some chiral chlordane constituents. The (+)-enantiomers and absolute configurations of heptachlor, heptachlor exo-epoxide, cis-chlordane, trans-chlordane, and oxychlordane are shown [16, 17], Only one enantiomer of each compound is depicted...

The older cyclodiene insecticides like aldrin, dieldrin, heptachlor, chlordane, endrin, and endosulfan act also as antagonists on the GABA channels. These substances still represent some problems as environmental pollutants because many of them are very stable in organisms, soil, and sediments. They all have a characteristic "clumsy" structure. Endosulfan was introduced in 1956 and is still in use, whereas the other compounds were introduced between 1948 and 1950. 

Fig. 2 Molecular structures of the Dirty Dozen. 1 - Polychlorinated dibenzo-p-dioxines, PCDD 2 - Polychlorinated dibenzofuranes, PCDF 3 - Polychlorinated biphenyls, PCB 4 - Hexachlorobenzene, HCB 5 - 2,2-Bis(4-chlorophenyl)-l,l,l-trichloroethane, DDT 6 - Toxaphene 7 - Aldrin 8 - Dieldrin 9 - Endrin 10 -Chlordane 11 - Heptachlor 12 - Mirex.

In the insect organisms, it is metabolised to the heptachlor epoxide of structure 46. Heptachlor epoxide is more active than the parent compound, therefore this... 

Heptachlor 76-44-8 none termiticide termiticide in structures of houses termiticide (subterranean) wood treatment + ... 

Heptachlor [76-44-8], another cyclodiene insecticide of chemical structure similar to chlordane is a chlorination product of chlordane. Technical grade heptachlor contains about 73% heptachlor, 22% fran -chlordane and 5% nonachlor. This pesticide was extensively used until 1970s for the control of soil insects, cotton insects, grasshoppers and termite control. The use of this pesticide for underground termite control was banned in the United States in 1988. Its application after that was restricted to controlling fire ant in power transformers. The U.S. EPA has classified heptachlor as a Group B2 probable human carcinogen. 

Although the toxic properties are more or less the same for structurally similar compounds, such as Heptachlor and Chlordane, the degree of toxicity may vary significantly with chlorosubstitution in the compound. For example, substitution of chlorine atoms with methoxy group in the aromatic rings in DDT decreases the latter s toxicity. Thus, the methoxy derivative, Methoxychlor, is significantly less toxic than DDT. Similarly, ethyl-substituted Perthane is much less toxic than p,p -DDD. 

More recently, Dearth and Hites (1991b) measured the half-lives of depuration of 14 different chlordane components (e.g., c/s- and /rans-chlordane and cis- and trans- nonachlor) and metabolites (e.g., heptachlor epoxide, oxychlordane) from the fat of rats fed chlordane in the diet for 28 days. Half-lives ranged from 5.92 days (c/s-chlordane) to 54.1 days (nonachlor III) and were apparently related to the metabolism rate of the various compounds. Structural characteristics associated with slowed depuration included an increasing number of chlorines on ring 1, the chlorine on Cl existing in an endo- (compared with an exo-) configuration, and the presence of two chlorines on C2. In mice treated once or every other day for 29 days, the whole body content of cis- and frans-chlordane remained at very low levels the content of cis- and frans-nonachlor and oxychlordane continued to increase with continued treatment (Hirasawa and Takizawa 1989). The investigators concluded that the chlordane isomers were readily metabolized, but that the nonachlor isomers were not. Oxychlordane, a metabolic intermediate of both chlordane isomers, is very slowly metabolized and tends to persist. 

Because the life cycles of insects are short, they can evolve an immunity to insecticides within a short period. As early as 1948, several strains of DDT-resisfant insects were identified. Today, fhe malaria-bearing mosquitoes are almosf completely resistant to DDT, an ironic development. Other chlorocarbon insecticides were developed to use as alternatives to DDT against resistant insects. Examples of fhese chlorocarbon materials include Dieldrin, Aldrin, Chlordane, and the substances whose structures are shown here. Heptachlor and Mirex are prepared using Diels-Alder reactions. 

In Spite of structural similarity, Chlordane and Heptachlor behave differently than DDT, Dieldrin, and Aldrin. Chlordane, for instance, is short-lived and less toxic to mammals. Nevertheless, all the chlorocarbon insecticides have been the objects of much suspicion. A ban on the use of Dieldrin and Aldrin has also been ordered by the EPA. In addition, strains of insects resistant to Dieldrin, Aldrin, and other materials have been observed. Some insects become addicted to a chlorocarbon insecticide and thrive on it ... 

The polychlorinated cyclodienes Aldrin 400) and Heptachlor 402) are converted in vitro by rabbit liver microsomes to their corresponding epoxides (Figure 12). The epoxidase has the characteristics of the mixed-function oxidase system in that it requires both NADPH and oxygen and it is inhibited by SKF 525-A. Dieldrin 401) is detoxified in vivo in the rat through hydrolysis of the epoxy group to a rarzi -dihydrodiol, which subsequently is oxidized to the dicarboxylic acid other metabolites include 9-hydroxydieldrin and a pentachloroketone structure. 

---