Methamidophos derivatization

As in the case of the methyIcarhamate esters, the organophos-phorus insecticide methamidophos (0, -dimethyl phosphoramidothi-oate) may be derivatized by substitution of a hydrogen atom on the phosphoramido nitrogen atom. An outstanding example of the benefit from this type of substitution is found in acephate, the... 

The reaction between a phosphoramidothioate and N-chlorosulfenylcarbamate described in Figure 2 has been applied to methamidophos. In Figure 2, the reaction was used to derivatize a toxic me thyIcarhamate ester by a non-toxic phosphora-midothioate however, in the case of methamidophos the reaction was used to derivatize a toxic phosphoramidothioate with a nontoxic carbamate moiety. The IJ-alkoxycarbonyl-IJ -alkylamino-sulfenyl derivatives of methamidophos thus prepared, where R... 

Attempts to react methamidophos with the corresponding chlorosulfinylcarbamate intermediate, however, resulted in products which were unstable and of no value as proinsecticides. In general, phosphoramidothioates such as methamidophos are more difficult to derivatize than the methylcarbamate esters and therefore are less useful as precursors to proinsecticides. 

Tomaszewaska and Hebert (2003) reported a method for the analysis of ( , -dimethyl hydrogen phosphorothioate (0,5-DMPT) in urine. 0,5-DMFT is a specific metabolite of methamidophos, The urine sample was extracted with a CIS column, and the sample was lyophilized at low temperature to prevent loss of highly volatile and thermally unstable metabolite (0,5-DMPT). The lyophilized residue was derivattzed using MTBSTFA and 1% terl-butyl-dimethylchlorosilane in acetonitrile. After filtration, the derivatized product was analyzed with GC/FPD (pulse FPD) in the phosphorus mode. The limit of detection for the method is reported as 0.004 ppm, with a mean recovery of 108%. 

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