Thiophosphate insecticides

Thiirane, 2-keto- — see a-Thiolactones Thiirane, 2-mercaptomethyl-thiophosphate insecticide, 7, 183 tuberculosis inhibition by, 7, 183 Thiirane, 2-methyl-adducts... 

Titanium(III) chloride (particularly in slightly alkaline medium) reduces the p-nitro groups of the thiophosphate insecticides to amino groups, which are then reacted with nitrite in acid mediiun in a second step to yield a diazonium compound as intermediate. This is then coupled to N-(l-naphthyl)-ethylenediamine dihydrochloride to yield an azo dye [3]. In the case of benzodiazepines the first reaction step includes an additional acid hydrolysis to the corresponding benzophenone derivative [2]. 

The detection limits for thiophosphate insecticides are 40-100 ng substance per chromatogram zone [1],... 

Fig. 1 chromatogram of the thiophosphate insecticides (each ca. SOO ng) after treatment with dipping solutions I and II (A) before and (B) after complete drying of the TLC plate. TVacks 1 and S mixture Track 2 azinphos ethyl Track 3 malathion Track 4 diazinone. 

The hydrolytic action of alkalis on the thiophosphate insecticides, such as parathion, yields free phenols that then couple with the diazonium salt to yield azo dyes. 

The chromatograms are freed from mobile phase in a stream of warm air for 3 min, then immersed in dipping solution I for 3-5 s or uniformly sprayed with spray solution I. Then, except in the case of thiophosphate insecticides, the plate is immediately immersed in dipping solution II for 3-5 s or homogeneously sprayed with spray solution II. In the case of thiophosphate insecticides there is a delay of 2 min [4] or the plates are heated to 70-110 °C for 10-15 minutes before the plates are erposed to the second reagent solution. 

Note It is occasionally recommended that sodium acetate be added to the reagent [2]. Thiophosphate insecticides with a simple P—S bond yield yellow chromatogram zones and those with a P=S double bond yield brown ones on a light brown background [10]. Further treatment of the stained chromatogram with iodine vapors increases the detection sensitivity [7] more than does spraying afterwards with caustic soda solution, which is also occasionally recommended [16, 17, 20, 21]. 

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. 

The reaction course has not been elucidated (cf. also sodium hydroxide reagent). Hydrolyzation reactions and aromatizations are probably primarily responsible for the formation of colored and fluorescent derivatives. Substituted nitrophenols - e.g. the thiophosphate insecticides — can probably be hydrolyzed to yellow-colored nitro-phenolate anions by sodium hydroxide or possibly react to yield yellow Meisenheimer complexes. Naphthol derivatives with a tendency to form radicals, e.g. 2-naphthyl benzoate, react with hydrolysis to yield violet-colored mesomerically stabilized 1,2-naph-thalenediol radicals. 

Note Methanolic sodium hydroxide solution can replace potassium hydroxide solution [16] (q.v.). The production of color tones and fluorescence is very dependent on the duration and temperature of heating hence optimal conditions must be determined empirically [16]. Some thiophosphate insecticides do not form fluorescent derivatives [16]. The natural fluorescence of various cumarin derivatives is intensified [1]. 

Uchiyama M, Yoshida T, HommaK, etal. 1975. Inhibition of hepatic drug-metabolizing enzymes by thiophosphate insecticides and its drug toxicological implications. Biochem Pharmacol 24(11-12) 1221-1225. 

A few of the estimated 50,000 organophosphates are shown in Figure 7-6. Many of the organophosphates (echothiophate is an exception) are highly lipid-soluble liquids. Echothiophate, a thiocholine derivative, is of clinical value because it retains the very long duration of action of other organophosphates but is more stable in aqueous solution. Soman is an extremely potent "nerve gas." Parathion and malathion are thiophosphate insecticides that are inactive as such they are converted to the phosphate derivatives in animals and plants and are used as insecticides. 

Murphy, S.D., Liver metabolism and toxicity of thiophosphate insecticides in mammal, avian and piscine species, Proc. Soc. Exp. Biol. Med., 123, 392,1966. 

Singh, A.K., Jiang, Y. (2003). Lipopolysaccharide (LPS) induced activation of the immune system in control rats and rats chronically exposed to a low level of the organo-thiophosphate insecticide, acephate. Toxicol. Ind. Health 19 93-108. 

Thiophosphate insecticides are protoxins, as they are unable to phosphorylate the serine until after the first liver passage, during which the thiono group is replaced by an 0x0 group. Therefore, they are called indirect acetylcholinesterase inhibitors. 

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