Demeton-S-methyl

Demeton-S-methyl is an organic compound with the molecular formula C6H15O3PS2. It was used as an organothiophosphate acaricide and organothiophosphate insecticide. It is flammable. With prolonged storage, Demeton-S-methyl becomes more toxic due to formation of a sulfonium derivative which has greater affinity to the human form of the acetylcholinesterase enzyme, and this may present a hazard in agricultural use. Demeton-S-methyl is an organic compound with the molecular formula C6H15O3PS2. It was used as an organothiophosphate acaricide and organothiophosphate insecticide. It is flammable. With prolonged storage, Demeton-S-methyl becomes more toxic due to formation of a sulfonium derivative which has greater affinity to the human form of the acetylcholinesterase enzyme, and this may present a hazard in agricultural use. Demeton-S-methyl was first described in 1950 by Schrader and was widely adopted as a pesticide because of the lower toxicity to humans than the previously used demeton. In its beginning days, it was mostly used together with demeton-O-methyl in an O:S ratio of 70:30. From 1957 onward, only pure demeton-S-methyl was used. Because of its high toxicity and severe toxic effects to humans, demeton-s-methyl is now classified as a highly toxic substance by the World Health Organisation and is banned from agricultural use worldwide. Demeton-S-Methyl is a compound that is closely related to VX in terms of structure. The structure is C6H15O3PS2. Demeton-S-Methyl has a molecular weight of 230.28 g/mol. It appears as a colourless to slightly yellow coloured oily liquid with a garlic like odor. Its density is 1.2 g/cm3, which makes it slightly heavier than water. The melting points and boiling points are <25 °C (<77 °F) and 118 °C (244 °F) respectively, although the compound decomposes before reaching the boiling point. The relatively low 0,0004 mmHg (at 20 °C) means Demeton-S-Methyl wil vaporize very slowly and mostly stay as a liquid. Demeton-S-Methyl is less stable than its predecessor Demeton, but it is used instead because of the lower toxicity to humans. Demeton-S-methyl is hydrolyzed quickly in alkaline media. Demeton-S-methyl is readily soluble in water and most organic compounds. There are three ways of synthesizing Demeton-S-methyl. It can be made by a reaction between Thiodiglycol and dimethyl thiophosphate. Here the sulfur in dimethyl thiophosphate attacks on one of the oxygens of thiodiglycol. One of the oxygens of dimethyl thiophosphate in turn forms a double bond with the phosphate and losing its hydrogen which forms water with the hydroxyl on the other side of the thiodiglycol. The second synthesis route is by alkylation of Dimethyl dithiophosphoric acid with 2-(ethylmercapto)-ethyl chloride. The third way is through  the reaction of 2-(ethylthio)-ethanol, which is similar to thiodiglycol minus one of the hydroxyl groups, and O,O-dimethyl phosphochlorothioate. This happens through alcohol chlorination, hydrolysis and dehydrochlorination respectively.