Methoxychlor, atomization

Many chlorinated hydrocarbon alternatives to DD T have been developed. One of the earliest substitutes was methoxychlor, shown in Figure 15.18. This compound has a much lower toxicity in most animals and, unlike DDT, is not readily stored in animal fat. Look carefully at the structures of methoxychlor and DDT, and you ll see that they are identical except that methoxychlor has two ether groups where DDT has two chlorine atoms. Because the structures are nearly identical, they have nearly the same level of toxicity in insects. In higher... 

Many xenobiotics contain alkyl groups, such as the methyl (-CH3) group, attached to atoms of O, N, and S. An important step in the metabolism of many of these compounds is replacement of alkyl groups by H, as shown in Figure 7.6. These reactions are carried out by mixed-function oxidase enzyme systems. Examples of these kinds of reactions with xenobiotics include O-dealky-lation of methoxychlor insecticides, N-dealkylation of carbary 1 insecticide, and S-dealkylation of dimethyl mercaptan. Organophosphate esters (see Chapter 18) also undergo hydrolysis, as shown in Reaction 7.3.12 for the plant systemic insecticide demeton ... 

Strategy. The only structural difference between these two molecules is the replacement of two chlorine atoms on DDT with two methoxy (also written as OCH3) moieties on methoxychlor. Thus, we can use the pi-values of these two groups to first remove the two chlorines and then add the two methoxys. 

The groups on the phenyl rings appear to have some effect on the reductive dechlorination of the trichloroethane. Thus, o,p -DDT is de-chlorinated reductively to o,p -DDD by mechanisms and rates similar to the reductive dechlorination of p,p -DDT 17, 25). In contrast, Mendel et al. 17) were unable to obtain reductive dechlorination when the phenyl chlorine atoms of p,p -DDT were replaced by ethyl or methoxy groups. It is interesting, however, that they were unable to recover completely the methoxychlor. This indicates anaerobic degradation of this compound by some other route. 

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. 

Mono-OH-MXC is a chiral conq>ound in which the carbon atom bridging two benzene rings is the chiral center (Figure 4). It is known that the enzymatic 0-demethylation of methoxychlor into mono-OH-MXC in rat and human livers is enantioselective (10,11). In this metabolic reaction, the (5) enantiomer is predominantly produced by human liver microsomes at n-%1%. The activity of... 

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