Aldicarb sulfoxide, reduction

The oxidation of pesticide compounds usually generates products with aqueous mobilities that are either similar to or greater than that of the parent compound. The oxidation of aldicarb, for example, produces aldicarb sulfoxide and aldicarb sulfone, both of which have lower A/qc values than aldicarb (Moye and Miles, 1988). Similarly, because most phototransformations involve either the hydrolysis or oxidation of the parent compound, they yield products that are generally more polar (Mill and Mabey, 1985), and thus more water soluble than the parent compound. Reduction reactions, by contrast, may result in products that are less water soluble than their parent compound. Examples include the reduction of aldicarb sulfoxide to aldicarb (Miles and Delfino, 1985 Lightfoot et al, 1987) and the reduction of phorate sulfoxide to phorate (Coats, 1991). The reactivity of transformation products may be either higher or lower than that of their parent compounds. However, those in the former category (i.e., reactive intermediates) are, of course, much less likely to be detected in the hydrologic system than more stable products. 

The reduction of aldicarb sulfoxide, which is the major metabolite in aerobic soils, has been observed in groundwater systems (Miles and Delfino, 1985 Lightfoot et al., 1987). 

Its systemic effect is related to its metabolism. In plants it is converted to its sulfoxide (41), which is water soluble and therefore easily translocated in the transport system. The sulfoxide is a 10-20 times stronger cholinesterase inhibitor than aldicarb. However, when applied directly to insects it is less toxic because, due to its hydrophilic nature, it can hardly penetrate the insect cuticle. Presumably, a similar bioactivation takes place also in the insect organism. As metabolism proceeds, the sulfoxide derivative 41 is hydrolysed to 2-methyl-2-methylsulfinyl-propionaldehyde (42), which is partly converted by oxidation to 2-methyl-2-methysuffinylpropionic acid (43), and partly by reduction to the corresponding alcohol (44), as shown in Scheme 1.8. Part of the sulfoxide is converted to sulfon... 

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