Phosphorothionate ester

Data presentations should include the parent compound and all toxic transformation products. This is particularly important for oxidation of sulfide linkages to sulfoxides or sulfones. These products are often equally toxic to the parent with increased availability. Attention should also be given to oxidative desulfuration of phosphorothionate esters. 

The discovery of prontosil was fortuitous and was not based on rationale design. There are a large number of pesticides which fall in the same category as prontosil, i.e., they are active by virtue of their susceptibility to metabolic or chemical modification to active intermediates. The classical example of an insecticide of this type is parathion, a phosphorothionate ester which in animals or plants is oxidatively desulfurated to the potent anticholinesterase paraoxon O). The insecticidal activity of parathion was known for several years before the purified material was shown to be a poor anticholinesterase and that metabolic activation to paraoxon was necessary for intoxication. 

One of the most extensively studied phosphorothionate esters from the standpoint of mammalian metabolism is the insecticide parathion. The majority of this paper will center on what is known of the mechanism of mammalian microsomal metabolism of this compound. 

Smolen, J. M., and A. T. Stone, Divalent metal ion-catalyzed hydrolysis of phosphorothionate ester pesticides and their corresponding oxonates , Environ. Sci. Technol., 31, 1664-1673 (1997a). 

Torrents, A., and A. T. Stone, Oxide surface-catalyzed hydrolysis of carboxylate esters and phosphorothionate esters , Soil Sci. Soc. Am. J., 58, 738-745 (1994). 

Figure 18.9 gives the structural formulas of some typical phosphorothionate esters and the general formula of this type of organophosphate insecticide. 

Insecticidal parathion is a phosphorothionate ester first licensed for use in 1944. Pure parathion is a yellow liquid that is insoluble in kerosene and water, but stable in contact with water. Among its properties that make parathion convenient to use as an insecticide are stability in contact with neutral and somewhat basic aqueous solutions, low volatility, and toxicity to a wide range of insects. It was applied as an emulsion in water, dust, wettable powder, or aerosol. Even before it was banned for general use, it was not recommended for applications in homes or animal shelters because of its toxicity to mammals. 

Many insecticides and herbicides are in a sense designer chemicals, which can be engineered to degrade within a specified time period. The substituent groups chosen determine which degradation pathways will be most favorable and the magnitude of rate constants. Chlorpyrifos, ronnel, and several other insecticides share a common phosphorothionate ester group, which is subject to hydrolysis ... 

Monothiopyrophosphates (9.494) can be obtained from salts of phosphorothionic esters and dial-kylphosphorochloridates (9.501), or by reaction (9.502). 

Phosphorothionate esters such as parathion, for which the structural formula is, are effective as insecticides because they. ... 

---