Names | |
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Preferred IUPAC name S-[2-(Ethylsulfanyl)ethyl] O,O-dimethyl phosphorothioate | |
Other names 1-(Dimethoxyphosphorylthio)-2-(ethylthio)ethane S-[2-(Ethylthio)ethyl] O,O-dimethyl phosphorothioate, Demeton methyl; O,O-Dimethyl 2-ethylmercaptoethyl thiophosphate; Metasystox; Methyl mercaptophos; Methyl systox | |
Identifiers | |
3D model (JSmol) | |
1707311 | |
ChEBI | |
ChEMBL | |
ChemSpider | |
ECHA InfoCard | 100.011.866 |
EC Number |
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KEGG | |
PubChem CID | |
RTECS number |
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UNII | |
UN number | 3018 |
CompTox Dashboard (EPA) | |
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Properties | |
C6H15O3PS2 | |
Molar mass | 230.28 g/mol |
Appearance | Oily, colorless to pale-yellow liquid [2] |
Density | 1.2 g/cm3 |
Boiling point | 118 °C (244 °F; 391 K) |
0.33 g/100 ml (20 °C (68 °F; 293 K)) | |
Vapor pressure | 0.0004 mmHg (20 °C (68 °F; 293 K)) [2] |
Hazards | |
GHS labelling: | |
Danger | |
H301, H311, H411 | |
P264, P270, P273, P280, P301+P310, P302+P352, P312, P321, P322, P330, P361, P363, P391, P405, P501 | |
NIOSH (US health exposure limits): | |
PEL (Permissible) | N.D. [2] |
REL (Recommended) | TWA 0.5 mg/m3 [skin] [2] |
IDLH (Immediate danger) | N.D. [2] |
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). |
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. [3]
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. [4] [5] 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. [6] 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 Organization and is banned from agricultural use worldwide. [7] [8]
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. [9] It appears as a colourless to slightly yellow coloured oily liquid with a garlic like odor. [10] 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, [11] although the compound decomposes before reaching the boiling point. The relatively low 0,0004 mmHg (at 20 °C (68 °F; 293 K)) [12] means Demeton-S-Methyl will 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. [13] 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. [14] 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. [15] 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. [16]
Demeton-S-methyl is still available as a solution, however its use is banned in most countries because of the severe toxicity.
Demeton-S-methyl inhibits cholinesterase, which takes care of the breakdown of acetylcholine (AChE). In the presence of Demeton-S-methyl, an accumulation of AChE occurs, which can result in impeded neurotransmission. [17] This can lead to impaired muscle function and even suffocation resulting in death. [18]
Animal experiments show that almost all demeton-S-methyl derivatives are excreted through urine. Most of the demeton-S-methyl is converted to demeton-S-methyl sulfoxide, where an oxygen group is added to the sulfur in the side chain. This sulfoxide can then be further metabolised by adding another oxygen group, creating demeton-S-methyl sulfone. Another pathway to metabolise demeton-S-methyl is to demethylate the oxygen group(s) of demeton. Again, this demethylated form can occur in an sulfoxide and sulfone form. Lastly, de-esterification of the O-methylphosphoric ester group can occur which will be followed by methylation and sulfoxidation. This will lead to the formation of methyl sulfinyl-2-ethyl sulfinyl ethane and methyl sulfinyl-2-ethyl sulfonyl ethane. [19]
Demeton-S-Methyl is an organic phosphorus compound that has been used as an effective insecticide and acaricide in agriculture, mainly against plant-sucking arthropod pests. [20] [21] It was applied for control of aphids, mites, and whiteflies on fruit, vegetables, potatoes, beet and hops. [22] Demeton-S-Methyl is absorbed and distributed within the plant, allowing concentrations to reach high enough levels to kill the insects that feed on the plant by sucking its juices.
In agriculture, methyl demeton was used in a mixture of the O-isomer and the S-isomer in an approximate ratio of 70:30. [23] However, the S-isomer was found to be more toxic against insects than the O-isomer. [24] When the purified S-isomer form was introduced and availability rose, it replaced the mixture in agriculture.
A lot of data on the toxicity of methyl-S-demeton comes from case studies, often with persons who have been exposed to the chemical occupationally. Methyl-S-demeton was sprayed on the plants by sprayers, who were often temporarily employed. In a study with sprayers that used methyl-S-demeton occupationally the health implications were assessed. [25] The sprayers worked 8 hours a day, and symptoms of intoxication occurred after one to 18 days of exposure. The main signs of toxicity included drowsiness, vomiting, abdominal pain, diarrhoea, nausea, fatigue, headache, respiratory problems, salivation and lachrymation. Serum-cholinesterase levels were lowered by 64% in 25 sprayers when compared to control persons.
In one case of poisoning, ingestion of 50 to 500 mg of methyl-S-demeton/kg body weight resulted in acute cardiovascular collapse and death 83 hours after exposure. [23] A second case-study involves a farmer who was exposed to the chemical on at least 23 occasions for periods varying from 20 minutes to 6+3⁄4 hours, mostly during his work as a marker in aerial spraying but also during the preparation of the chemical. [26] He developed headaches, nausea and dizziness during the working week which subsided during the weekend. Later, he developed anorexia and had difficulty performing simple cognitive tasks. He was admitted to the hospital where it was found that his serum-cholinesterase levels were very low. He was discharged when these levels rose to acceptable levels. In another case, a two-year-old boy was admitted to the hospital after ingestion of 10 ml (0.35 imp fl oz; 0.34 US fl oz) of demeton-S-methyl. Symptoms included excessive salivation, vomiting, bronchial hypersecretion, muscarinic effects on pulse rate and pupil size, and slight bradycardia. [27] In this case, too, serum-cholinesterase levels were significantly lowered, but returned to baseline after admission to the hospital. Lastly, one case of lethal suicide intoxication with demeton-S-methyl has been reported. [28]
The Joint FAO/WHO Meeting on Pesticide Residues (JMPR) concluded that demeton-S-methyl is a highly toxic organophosphorus insecticide. Effects due to chronic exposure are unlikely to occur. Furthermore, demeton-S-methyl does not persist in the environment and is not accumulated by organisms. However, demeton-S-methyl has a high acute toxicity towards aquatic invertebrates and is also toxic to birds and fish. [17] The JMPR recommended ADI (acceptable daily intake) is 0.0003 mg/kg body weight. The LD50 values of demeton-S-methyl for mammals range from 7 to 100 mg/kg body weight, depending on the route of administration and species. [17]
Oral LD50 values of demeton-S-methyl in rats were between 33 and 129 mg/kg body weight. [17] When the toxin was inhaled, the LC50 with 4 hours of exposure for Wistar rats was found to be 310 mg/m3 air for males, and 210 mg/m3 air for females. [17] In dietary studies on dogs, mice and rats, NOAEL (No Observed Adverse Effect Level) values of 1 mg/kg diet were found. These values are equal to a NOAEL range of 0.036 to 0.24 mg/kg body weight per day.
Hrynko et al. 2021 provides an analysis method for detection of Demeton-S-methyl and Demeton-S-methyl-sulfone intoxication of bees. [29]
Carbaryl is a chemical in the carbamate family used chiefly as an insecticide. It is a white crystalline solid previously sold under the brand name Sevin, which was a trademark of the Bayer Company. The Sevin trademark has since been acquired by GardenTech, which has eliminated carbaryl from most Sevin formulations. Union Carbide discovered carbaryl and introduced it commercially in 1958. Bayer purchased Aventis CropScience in 2002, a company that included Union Carbide pesticide operations. Carbaryl was the third-most-used insecticide in the United States for home gardens, commercial agriculture, and forestry and rangeland protection. As a veterinary drug, it is known as carbaril (INN).
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.
Malathion is an organophosphate insecticide which acts as an acetylcholinesterase inhibitor. In the USSR, it was known as carbophos, in New Zealand and Australia as maldison and in South Africa as mercaptothion.
Chlorfenvinphos is an organophosphorus compound that was widely used as an insecticide and an acaricide. The molecule itself can be described as an enol ester derived from dichloroacetophenone and diethylphosphonic acid. Chlorfenvinphos has been included in many products since its first use in 1963. However, because of its toxic effect as a cholinesterase inhibitor it has been banned in several countries, including the United States and the European Union. Its use in the United States was cancelled in 1991.
Aldicarb is a carbamate insecticide which is the active substance in the pesticide Temik. It is effective against thrips, aphids, spider mites, lygus, fleahoppers, and leafminers, but is primarily used as a nematicide. Aldicarb is a cholinesterase inhibitor which prevents the breakdown of acetylcholine in the synapse. Aldicarb is considered "extremely hazardous" by the EPA and World Health Organization and has been banned in more than 100 countries. In case of severe poisoning, the victim dies of respiratory failure.
Aldrin is an organochlorine insecticide that was widely used until the 1990s, when it was banned in most countries. Aldrin is a member of the so-called "classic organochlorines" (COC) group of pesticides. COCs enjoyed a very sharp rise in popularity during and after World War II. Other noteworthy examples of COCs include dieldrin and DDT. After research showed that organochlorines can be highly toxic to the ecosystem through bioaccumulation, most were banned from use. Before the ban, it was heavily used as a pesticide to treat seed and soil. Aldrin and related "cyclodiene" pesticides became notorious as persistent organic pollutants.
Iodomethane, also called methyl iodide, and commonly abbreviated "MeI", is the chemical compound with the formula CH3I. It is a dense, colorless, volatile liquid. In terms of chemical structure, it is related to methane by replacement of one hydrogen atom by an atom of iodine. It is naturally emitted by rice plantations in small amounts. It is also produced in vast quantities estimated to be greater than 214,000 tons annually by algae and kelp in the world's temperate oceans, and in lesser amounts on land by terrestrial fungi and bacteria. It is used in organic synthesis as a source of methyl groups.
Azinphos-methyl (Guthion) is a broad spectrum organophosphate insecticide manufactured by Bayer CropScience, Gowan Co., and Makhteshim Agan. Like other pesticides in this class, it owes its insecticidal properties to the fact that it is an acetylcholinesterase inhibitor. It is classified as an extremely hazardous substance in the United States as defined in Section 302 of the U.S. Emergency Planning and Community Right-to-Know Act, and is subject to strict reporting requirements by facilities which produce, store, or use it in significant quantities.
Organothiophosphates or organophosphorothioates are a subclass of organophosphorus compounds and of thiophosphate compounds. They are the organic compounds that contain a phosphate group in which one or more oxygen atoms is substituted by sulfur. Many are used as pesticides, some have medical applications, and some are used as oil additives. They generally have the chemical formula (RO)3PS, [(RO)2P(S)O]−, R(RO)2PS, etc.
Phosmet is a phthalimide-derived, non-systemic, organophosphate insecticide used on plants and animals. It is mainly used on apple trees for control of codling moth, though it is also used on a wide range of fruit crops, ornamentals, and vines for the control of aphids, suckers, mites, and fruit flies.
Methiocarb is a carbamate pesticide which is used as an insecticide, bird repellent, acaricide and molluscicide since the 1960s. Methiocarb has contact and stomach action on mites and neurotoxic effects on molluscs. Seeds treated with methiocarb also affect birds. Other names for methiocarb are mesurol and mercaptodimethur.
Chlorethoxyfos is an organophosphate acetylcholinesterase inhibitor used as an insecticide. It is registered for the control of corn rootworms, wireworms, cutworms, seed corn maggot, white grubs and symphylans on corn. The insecticide is sold under the trade name Fortress by E.I. du Pont de Nemours & Company.
Disulfoton is an organophosphate acetylcholinesterase inhibitor used as an insecticide. It is manufactured under the name Di-Syston by Bayer CropScience. Disulfoton in its pure form is a colorless oil but the technical product used in vegetable fields is dark and yellowish with a sulfur odor. Disulfoton is processed as a liquid into carrier granules, these granules are mixed with fertilizer and clay to be made into a spike, designed to be driven into the ground. The pesticide is absorbed over time by the roots and translocated to all parts of the plant. The pesticide acts as a cholinesterase inhibitor and gives long lasting control.
Demeton, sold as an amber oily liquid with a sulphur like odour under the name Systox, is an organophosphate derivative causing irritability and shortness of breath to individuals repeatedly exposed. It was used as a phosphorothioate insecticide and acaricide and has the chemical formula C8H19O3PS2. Although it was previously used as an insecticide, it is now largely obsolete due to its relatively high toxicity to humans. Demeton consists of two components, demeton-S and demeton-O in a ratio of approximately 2:1 respectively. The chemical structure of demeton is closely related to military nerve agents such as VX and a derivative with one of the ethoxy groups replaced by methyl was investigated by both the US and Soviet chemical-weapons programs under the names V.sub.X and GD-7.
Carbophenothion also known as Stauffer R 1303 as for the manufacturer, Stauffer Chemical, is an organophosphorus chemical compound. It was used as a pesticide for citrus fruits under the name of Trithion. Carbophenothion was used as an insecticide and acaricide. Although not used anymore it is still a restricted use pesticide in the United States. The chemical is identified in the US as an extremely hazardous substance according to the Emergency Planning and Community Right-to-Know Act.
Tetraethyl pyrophosphate, abbreviated TEPP, is an organophosphate compound with the formula [(C2H5O)2P(O)]2O. It is the tetraethyl derivative of pyrophosphate (P2O74-). It is a colorless oil that solidifies near room temperature. It is used as an insecticide. The compound hydrolyzes rapidly.
Terbufos is a chemical compound used in insecticides and nematicides. It is part of the chemical family of organophosphates. It is a clear, colourless to pale yellow or reddish-brown liquid and sold commercially as granulate.
Triamiphos (chemical formula: C12H19N6OP) is an organophosphate used as a pesticide and fungicide. It is used to control powdery mildews on apples and ornamentals. It was discontinued by the US manufacturer in 1998.
Ethiofencarb is a carbamate insecticide which is useful in controlling aphids on hard and soft fruits and some vegetables. It is not as dangerous as organophosphorous pesticides, but is considered highly toxic to humans in the UK, moderately toxic under US EPA classification, and highly toxic to aquatic life.
EPN is an insecticide of the phosphonothioate class. It is used against pests such as European corn borer, rice stem borer, bollworm, tobacco budworm, and boll weevil.
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