Ester hydrolysis of carbaryl

Microorganisms hydrolyze carbaryl to 1-naphthol, whereas in mammals different oxidation products are formed. 

Ester hydrolysis is the most important microbial degradation of diazinon, whereas mammals produce glutathione conjugates and oxidation products. 

---

Detoxification and Activation Reactions From an acute toxicity standpoint, the metabolism of pesticides by most organisms usually results in their conversion to products of lesser biological activity. There are several reasons v y such would be expected, not the least of which is the fact that the detoxification systems of living organisms have evolved for just such a purpose. Certainly, too, structure-activity relationships are usually so critical that toxicity, especially in the acute sense, is often greatly reduced or totally eliminated as the result of essentially any chemical transformation. Numerous examples of metabolic reactions leading to more-or-less complete pesticide detoxification could be cited, but the o-deethylation of chlorfenvinphos and the ester hydrolysis of carbaryl, both insecticides, are shown as somewhat representative examples (Figure 7). 

The difference is in the mechanism of reaction. In the case of carbaryl, the reaction proceeds by an elimination process in which the proton acidity on the nitrogen atom determines the reactivity. On the other hand, the chlorpropham reaction proceeds in a manner analogous to the hydrolysis of carboxylic acid esters. Much like carboxylic acid esters, electron-withdrawing substituents in carbamates accelerate the reaction by an amount that depends on whether the substituents are on N or O. Conversely, electron-donating substituents (methyl in the case of chlorpropham, above) slow the rate of hydrolysis. 

Substantial numbers of important agrochemicals contain the carbonyl groups noted earlier, so that abiotic hydrolysis may be the primary reaction in their transformation the example of carbaryl has already been cited (Wolfe et al. 1978a). The same general principles may be extended to phosphate and thiophosphate esters, although in these cases, it is important to bear in mind the stability to hydrolysis of primary and secondary phosphate esters under neutral or alkaline conditions that prevail in most natural ecosystems. On the... 

Post-column hydrolysis of carbamate esters, such as carbaryl, was discussed in Chapter 4, Section 2. Further consideration of anticholinesterase insecticides can be found in Chapter 7, Section 4. 

---