Demeton

Metasystox A trade name for demeton-methyl, C[Pg.257]

Fig. 1 Absorption scan of a chromatogram track with 150 ng of each substance per chromatogram zone 1 = demeton-S-methylsulfone, 2 = dimethoate, 3a = transmevinphos,...

Delta Chemical Corporation, 225 Deltech Corporation, 225 Demeton-methyl, 50... 

Metabolites in the degradation of Demeton S-methyl sulfoxide by soil... 

An unknown analytical response in lettuce was detected61 and thought to contain P and S. The initial GC/MS Cl CH4 data were dominated by ions at m/z 121, 197 and 291 (equation 40). The GC/MS Cl NH3 data, however, indicated that perhaps the molecule had a higher molecular weight of 306 (MH+ equal to m/z 307, cf. equation 40). Comparison with the Cl CH4 and Cl NH3 spectra of demeton-S- (199) and demeton-O-sulfones showed, however, that the retention time and mass spectra of the former only matched the unknown (except the omission of the ion at m/z 307). On another stationary phase (OV-101) limited mass scanning of the ion at m/z 121 revealed a second unknown (200) eluting at 4.2 min (the major unknown, i.e. demeton-S-sulfone at 3.0 min). The molecular weight of 200 was believed to be 306. Because of the presence of ions at m/z 121,... 

Decarbonylation, photochemical 885 Decarboxylation 605 Dehydrohalogenation 417 n-Delocalization 392 Demeton sulphones, mass spectra of 155... 

Demeton-S-methyl sulfone (hRf 0-5), dimethoate (h/ f 5-10), demeton-S-metlq (hRf 20-25), triazophos (h/ f 40-45), azinphos-methyl (hRf 40-45), azinphos-ethj (hRf 50-55), malathion (h/ f 60-65), parathion-methyl (hRf 75-80) and parathioo ethyl (h/ f 80-85) yielded yellow to brown chromatogram zones on a light brown bact ground, with thiophosphate insecticides with P = S double bonds appearing as brow zones and those with single P — S bonds as yellow zones. 

Mechanism of action can be an important factor determining selectivity. In the extreme case, one group of organisms has a site of action that is not present in another group. Thus, most of the insecticides that are neurotoxic have very little phytotoxicity indeed, some of them (e.g., the OPs dimethoate, disyston, and demeton-5 -methyl) are good systemic insecticides. Most herbicides that act upon photosynthesis (e.g., triaz-ines and substituted ureas) have very low toxicity to animals (Table 2.7). The resistance of certain strains of insects to insecticides is due to their possessing a mutant form of the site of action, which is insensitive to the pesticide. Examples include certain strains of housefly with knockdown resistance (mutant form of Na+ channel that is insensitive to DDT and pyrethroids) and strains of several species of insects that are resistant to OPs because they have mutant forms of acetylcholinesterase. These... 

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