Dieldrin structure

The somewhat unexpected inertness of dieldrin toward mineral acids has great practical significance despite its structure it remains, under practical conditions of use, insec-ticidally active under both acidic and alkaline conditions. 

GC is coupled with many detectors for the analysis of pesticides in wastewater. At the present time the most popular is GC-MS, which will be discussed in more detail later in this section. The flame ionization detector (FID) is another nonselective detector that identifies compounds containing carbon but does not give specific information on chemical structure (but is often used for quantification because of the linear response and sensitivity). Other detectors are specific and only detect certain species or groups of pesticides. They include electron capture,nitrogen-phosphorus, thermionic specific, and flame photometric detectors. The electron capture detector (ECD) is very sensitive to chlorinated organic pesticides, such as the organochlorine compounds (OCs, DDT, dieldrin, etc.). It has a long history of use in many environmental methods,... 

The peak period for the use of aldrin and dieldrin was between the late 1960s and the early 1970s throughout various parts of the world (WHO, 1989). The use pattern of aldrin and dieldrin are quite similar. They act as effective contact and stomach poisons for insects. They are used to control soil insects (e.g. grasshoppers and corn rootworm), and protect crops and wooden structures from termites (WHO, 1989). The production of aldrin and dieldrin has decreased since the early 1960s. In the United States, the peak use of aldrin from 19 million pounds in 1966 decreased to 10.5 million pounds in 1970 (USEPA, 1980). During this same period (1966-1970), annual dieldrin use dropped from 1 million to 670,000 pounds. These decreases were primarily due to increased insect resistance to the aldrin and dieldrin, and to the development and availability of more effective and environmentally friendly pesticides (USEPA, 1980). 

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. 

At this time I was interested in the natural tolerance of houseflies to structural analogues of dieldrin and, with Harrison, I soon showed that whereas tolerance to cyclodienes was often related to oxidative detoxication and could be reduced or eliminated by benzodioxole synergists, dieldrin-resistance in houseflies did not respond to synergism and was apparently not a consequence of oxidative detoxication (33) Several laboratories (for their subsequent reviews see 34-36) confirmed the importance of oxidative biotransformations in insects and in 1964-5, at Slough, J. W Ray showed that microsomal preparations from houseflies and other insects contained cytochrome P450 (37) Thus, the links between insect and mammalian biochemical pharmacology were finally and firmly established. 

Several investigations (38-40) between i960 and 1965 finally dispelled the myth of dieldrin s metabolic inertness in mammals and since then numerous laboratories have shown that cyclodienes conform to the established principles of drug metabolism (4l). Molecular structure has a profound influence on the exposure of the non-chlorinated portions of these molecules to enzymatic attack and the low persistence of endrin, as compared to dieldrin, in mammalian tissues appears largely due to the stereochemical difference (42). The biotransformations of dieldrin are summarised in Figure 5 ... 

Figure 8. Planar structure of dieldrin and partial structures of some dieldrin analogs (each containing six chlorine atoms) referred to in the text. Table below gives toxicities for dechlorinated derivatives of dieldrin (see key in figure) to adult female blowflies, Calliphora erythrocephala. Similar superscripts indicate significant difference at 95%...

Photolysis of 2-bromo-4,4-dimethyl-2-cyclohexenone only affords reduction, even in a nucleophilic medium343,344. Apparently, this substrate is structurally not suitable to form a vinyl cation. Formation of vinyl radical-derived products is also the main process for all vinylic halides, if their irradiation is performed in an apolar medium. Such photochemical reductive dehalogenation and especially dechlorination reactions have been extensively studied in the past, not in the least because of their importance as abiotic transformation of persistent polychlorinated environmental pollutants. Examples are the cyclodiene insecticides aldrin and dieldrin, which contain a vicinal dichloroethene chromophore. In recent... 

The crystals composing the deposits of lindane and dieldrin were upright and easily dislodged by the insect, though markedly different in structure (Figure 1). Lindane crystals were platelike, usually 20-200/x wide and 50-300/x long. Dieldrin crystals were extremely fine and needlelike, usually 20-500/ long and less than 5/x wide. 

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,... 

Ln(tfc)3 chelates were used to probe the meso structure of dieldrin (32) " and meso and chiral isomers of cis- (32 ) and frawi-4,5-dihydroxy-4,5-dihydroaldrin (32") . For the me o-compounds 32 and 32" in the presence of Ln(tfc)3 chelates, prochiral pairs of hydrogen atoms such as H4-H5 and H3-H6 exhibit distinct resonances. The H4-H5 pair also couple to each other. For each enantiomer of the chiral compound (32c), the H4-H5 pair is equivalent and these appear as a singlet. In the presence of Ln(tfc)3, two singlets are observed, one each for the H4-H5 pair of the (R)- and (5 )-isomers. A similar analysis of the meso and rfZ-isomers of cis- and frawi-2,3-butylene oxide was facilitated through the use of Ln(tfc)3 chelates. ... 

Cyclodienes are chlorinated hydrocarbon insecticides with a polycyclic structure and, as the name implies, two unsaturated bonds. Not all of the insecticides in this class meet these criteria. Chlordane, for example, contains only one double bond in its polycyclic structure. Endrin and dieldrin are epoxides of the cyclodienes isodrin and aldrin, respectively. 

Organochlorine insecticides may be divided into three broad groups dichlorodiphenylethanes, such as DDT and methoxychlor cyclodienes, such as chlor-dane and dieldrin and hexachlorocyclohexanes, such as lindane. Mirex and chlordecone, however, are organochlorine insecticides whose caged structures do not fit well into the previous groups. 

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.

Dieldrin in concentrated solution or in the solid state is converted by the action of light to photo-dieldrin (54) of the structure 4,5-eJco-epoxy-l,9,10,10,ll-ejco-12-hexachloro-8,3,7,6-enacute toxicity to warm-blooded organisms is also higher than that of dieldrin. 

Photo-dieldrin (54), which is also formed by the action of sunlight on the plant surfaces treated with dieldrin, is converted in the organism of male rats predominantly to the keto derivative of structure 55, while in the organism of female rats other, more polar, metabolites are formed (Klein et al., 1970 Matthews and Matsumura, 1969). 

Structural wood and new wood insecticides that have proven to be effective are solutions of Toxaphene, Dieldrin, Lindane, and Dursban. Most are controlled toxins and should be used only with the advice of a professional applicator. 

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