Diazinon (IUPAC name: O,O-Diethyl O-[4-methyl-6-(propan-2-yl)pyrimidin-2-yl] phosphorothioate, INN - Dimpylate), a colorless to dark brown liquid, is a thiophosphoric acid ester developed in 1952 by Ciba-Geigy, a Swiss chemical company (later Novartis and then Syngenta). It is a nonsystemic organophosphate insecticide formerly used to control cockroaches, silverfish, ants, and fleas in residential, non-food buildings. Diazinon was heavily used during the 1970s and early 1980s for general-purpose gardening use and indoor pest control. A bait form was used to control scavenger wasps in the western U.S. Diazinon is used in flea collars for domestic pets in Australia and New Zealand. Residential uses of diazinon were outlawed in the U.S. in 2004 because of human health risks but it is still approved for agricultural uses. An emergency antidote is atropine. History Diazinon was developed in 1952 by the Swiss company Ciba-Geigy (now Novartis) to replace the formerly dominant insecticide DDT. In 1939, the chemist Paul Hermann Müller from the then-independent Geigy company had discovered that DDT was effective against malaria-bearing insects. This capability made use of DDT important enough that Müller even received the 1948 Nobel Prize in Medicine. However, as the decades following the award passed, DDT was found to be such an environmental danger that developed countries and eventually world-level organizations banned the insecticide for all purposes except for combating disease-vector insects, leading Ciba-Geigy to research alternatives. Diazinon became available for mass use in 1955, while DDT production tapered. Before 1970, diazinon had issues with contaminants in its solution; but by the 1970s, alternative purification methods were used to reduce the residual, unwanted materials. After this processing improvement, diazinon became an all-purpose, indoor-and-outdoor, commercial pest control product. In 2004, the US outlawed residential use of diazinon when the EPA determined that its ability to damage the nervous system posed a risk to human health (especially the health of children). The chemical is still used for industrial agricultural purposes. Synthesis According to the German Patent bureau, the industrial synthesis of diazinon is as follows: β-isobutyrylaminocrotonic acid amine was cyclized with NaOR (R is either a hydrogen or aliphatic chain of 1 to 8 carbons) in a mixture of 0 to 100% by weight of water and an alcohol having 1 to 8 carbon atoms, above 90°C (but below the boiling point of the mixture used). Sodium pyrimidinolate was precipitated out in an inert solvent, such as benzene, with simultaneous removal of the