Parathion

in xylene and butanolParathion, also called parathion-ethyl or diethyl parathion and locally known as 'Folidol', is an organophosphate insecticide and acaricide. It was originally developed by IG Farben in the 1940s. It is highly toxic to non-target organisms, including humans, so its use has been banned or restricted in most countries. The basic structure is shared by parathion methyl. Parathion, also called parathion-ethyl or diethyl parathion and locally known as 'Folidol', is an organophosphate insecticide and acaricide. It was originally developed by IG Farben in the 1940s. It is highly toxic to non-target organisms, including humans, so its use has been banned or restricted in most countries. The basic structure is shared by parathion methyl. Parathion was developed by Gerhard Schrader for the German trust IG Farben in the 1940s. After World War II and the collapse of IG Farben due to the war crime trials, the Western allies seized the patent, and parathion was marketed worldwide by different companies and under different brand names. The most common German brand was E605 (banned in Germany after 2002); this was not a food-additive 'E number' as used in the EU today. 'E' stands for Entwicklungsnummer (German for 'development number'). It is an irreversible acetylcholinesterase inhibitor. Safety concerns have later led to the development of parathion methyl, which is somewhat less toxic. When pure, parathion is a white crystalline solid. It is commonly distributed as a brown liquid that smells of rotting eggs or garlic. The insecticide is somewhat stable, although it darkens when exposed to sunlight. Parathion is synthesized from diethyl dithiophosphoric acid (C2H5O)2PS2H by chlorination to generate diethylthiophosphoryl chloride ((C2H5O)2P(S)Cl), and then the chloride is treated with sodium 4-nitrophenolate (the sodium salt of 4-nitrophenol). As a pesticide, parathion is generally applied by spraying. It is often applied to cotton, rice and fruit trees. The usual concentrations of ready-to-use solutions are 0.05 to 0.1%. The chemical is banned for use on many food crops. Parathion acts on the enzyme acetylcholinesterase indirectly. After an insect (or a human) ingests parathion, an oxidase replaces the double bonded sulfur with oxygen to give paraoxon. The phosphate ester is more reactive in organisms than the phosphorothiolate ester, as the phosphorus atoms become much more electropositive. Degradation of parathion leads to more water-soluble products. Hydrolysis, which deactivates the molecule, occurs at the aryl ester bond resulting in diethyl thiophosphate and 4-nitrophenol.