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Methamidophos Basic information
Product Name:Methamidophos
Synonyms:Acephate-met;BAY 71628;bay71628;Bayer 5546;bayer5546;Chevron 9006;Chevron ortho 9006;chevron9006
Product Categories:Amines, Agro-Products, Sulfur & Selenium Compounds;Alpha sort;Endocrine Disruptors (Draft)Pesticides&Metabolites;EPA;H-MAlphabetic;Insecticides;Agro-Chemicals;INSECTICIDE;M;META - METHPesticides;Method Specific;Oeko-Tex Standard 100;OrganophorousMethod Specific;Pesticides
Mol File:10265-92-6.mol
Methamidophos Structure
Methamidophos Chemical Properties
Melting point 44.5°C
Boiling point 208.7±23.0 °C(Predicted)
density d44.5 1.31
vapor pressure 2.3×10-3Pa (25°C)
refractive index nD40 1.5092
Fp 212 °C
storage temp. 0-6°C
Water Solubility  >200 g l-1 (20°C)
form solid
Stability:Stable. Incompatible with strong oxidizing agents, copper, copper alloys.
CAS DataBase Reference10265-92-6(CAS DataBase Reference)
NIST Chemistry ReferencePhosphoramidothioic acid, o,s-dimethyl ester(10265-92-6)
EPA Substance Registry SystemMethamidophos (10265-92-6)
Safety Information
Hazard Codes T+;N,N,T+,Xn,F
Risk Statements 24-26/28-50-36-20/21/22-11
Safety Statements 1/2-28-36/37-45-61-26
RTECS TB4970000
HazardClass 6.1(a)
PackingGroup II
Hazardous Substances Data10265-92-6(Hazardous Substances Data)
ToxicityLD50 in adult male, female rats (mg/kg): 25, 27 orally (Gaines, Linder)
MSDS Information
Methamidophos Usage And Synthesis
Chemical PropertiesMethamidophos is a colourless crystalline solid with a pungent odour. It is readily soluble in water, alcohols, ketones, and aliphatic chlorinated hydrocarbons but sparingly soluble in ether and practically insoluble in petroleum ether. Methamidophos is also a breakdown product of another OP, namely, acephate. Methamidophos is slightly corrosive to mild steel and copper alloys.
Chemical PropertiesMethamidophos is a colorless crystalline solid with a pungent odor. It is readily soluble in water, alcohols, ketones, and aliphatic chlorinated hydrocarbons, but sparingly soluble in ether and practically insoluble in petroleum ether. It is highly toxic, systemic with properties of an insecticide, acaricide, and avicide. The US EPA has grouped methamidophos as an RUP, meaning use and handling of this chemical substance requires qualifi ed, certifi ed, and trained workers. Methamidophos is effective against chewing and sucking insects and is used to control aphids, fl ea beetles, worms, white-fl ies, thrips, cabbage loopers, Colorado potato beetles, potato tube-worms, army-worms, mites, leafhoppers, and many others. Crop uses include broccoli, brussels sprouts, caulifl ower, grapes, celery, sugar beets, cotton, tobacco, and potatoes. It is used on many vegetables, hops, corn, peaches, and other crops. Methamidophos is also a breakdown product of another OP, namely, acephate. Methamidophos is slightly corrosive to mild steel and copper alloys.
Chemical PropertiesMethamidophos is an off-white crystalline solid.
UsesInsecticide and acaricide.
UsesMetamidophos is an organophosphate insecticide used in great quantities in rice fields in rice-producing countries.
UsesInsecticide; acaricide.
UsesMethamidophos is used to control a wide range of insects and mites in a very large number of crops.
General DescriptionCrystalline solid, technical product is off-white with a pungent odor. Used as an insecticide on a number of vegetables and on cotton.
Reactivity ProfileOrganophosphates, such as Methamidophos, are susceptible to formation of highly toxic and flammable phosphine gas in the presence of strong reducing agents such as hydrides. Partial oxidation by oxidizing agents may result in the release of toxic phosphorus oxides. Avoid strong acids or alkalis. [EPA, 1998].
Health HazardMethamidophos is harmful or fatal if swallowed, inhaled, or absorbed through the skin.
Health HazardMethamidophos is highly toxic to mammals. Inhalation of methamidophos causing weakness, tightness in the chest, wheezing, headache, blurred vision, pinpoint pupils, tearing,and runny nose are common early symptoms. On accidental ingestion and with severe poisoning, methamidiophos causes nausea, vomiting, diarrhea, and cramps, sweating and twitching, weakness, shakiness, blurred vision, pinpoint pupils, dyspnea (shortness of breath), tightness in the chest, sweating, confusion, changes in heart rate, convulsions, coma, respiratory failure, and death. People with health disorders, such as high blood pressure, problems of the gastrointestinal, heart, liver, lung, or nervous system, have been reported to be more sensitive to methamidophos-induced toxicity. Reports have indicated that occupational workers exposed to methamidophos who developed poisoning with symptoms such as pain (needle type) in the feet, legs, and hands, high blood pressure, gastrointestinal disorders, heart, liver, lung, or nervous system problems, may be more sensitive to methamidophos.
Fire Hazard(Non-Specific -- Organophosphorus Pesticide, n.o.s.) Container may explode in heat of fire. Fire and runoff from fire control water may produce irritating or poisonous gases. (Non-Specific -- Phosphoramidothioic Acid, O-Ethyl S-Methyl Ester) Emits very toxic fumes of nitrogen oxides, phosphorus oxides, and sulfur oxides when heated to decomposition. Stable at neutral pH. Avoid strong acids or alkalis.
Agricultural UsesInsecticide, Miticide: Methamidophos is a highly active, systemic, resid-ual organophosphate insecticide/acaricide/avicide with contact and stomach action. Its mode of action in insects and mammals is by decreasing the activity of an enzyme important for nervous system function called acetylcholinesterase. This enzyme is essential in the normal transmission of nerve impulses. Methamidophos is a potent acetylcholinesterase inhibitor. It is effective against chewing and sucking insects and is used to control aphids, flea beetles, worms, whiteflies, thrips, cabbage loopers, Colorado potato beetles, potato tubeworms, armyworms, mites, leafhoppers, and many others. Crop uses include broccoli, Brussels sprouts, cauliflower, grapes, celery, sugar beets, cotton, tobacco, and potatoes. It is used abroad for many vegetables, hops, corn, peaches, and other crops. Generally, methamidophos is not considered phytotoxic if used as directed, but defoliation has occurred when applied as foliar spray to deciduous fruit. It is compatible with many other pesticides, but do not use with alkaline materials. Methamidophos is slightly corrosive to mild steel and copper alloys. This compound is highly toxic to mammals, birds, and bees. Do not graze treated areas, and be sure to wear protective clothing including respirator, chemical goggles, rubber gloves, and impervious protective clothing. A U.S. EPA restricted Use Pesticide (RUP). Not approved for use in EU countries .
Safety ProfilePoison by ingestion, inhalation, sh contact, subcutaneous, and intraperitoneal routes. Human systemic effects by ingestion: fasciculations, pupdlary constriction, and sweating. A cholinesterase inhbitor type of insecticide. When heated to decomposition it emits very toxic fumes of NOx, POx, and SOx. See also PARATHION.
Potential ExposureA potential danger to those involved in the manufacture, formulation, and application of this insecticide on vegetables and cotton
Environmental FateChemical/Physical. Emits toxic fumes of phosphorus, nitrogen and sulfur oxides when heated to decomposition (Sax and Lewis, 1987).
Metabolic pathwayMethamidophos is a contact insecticide which is particularly effective against caterpillars and aphids. It also has some systemic action although much less than acephate. There is some uncertainty concerning the nature of the leaving group when the compound inhibits acetylcholinesterase although most evidence suggests that it is methanethiolate. There are claims that it requires metabolic activation to a more active inhibitor (Eto et al., 1977) and yet other evidence that it does not (Khasawinah et al., 1978). Most studies which have examined the biotransformation of acephate have identified methamidophos as one of its metabolites and the latter is considered to be the active metabolite. The main route of biotransformation in soil is through deamination. In mammals, metabolism involves de-O-methylation, de-S-methylation and deamination, with de- O-methylation in the liver probably being the most important route. There is no evidence as to whether demethylation is hydrolytic or oxidative. Methamidophos and its metabolites are highly polar and no conjugates have been identified. There is some evidence that the compound can lead to delayed neurological degeneration in mammals through inhibition of 'neuropathy target esterase'.
MetabolismAcute oral LD50 for rats is about 20 mg/kg. Inhalation LC50 (4 h) for rats is 0.2 mg/L air. NOEL (2 yr) for rats is 2 mg/kg diet (0.1 mg/kg/d). ADI is 4 μg/kg b.w. Methamidophos itself shows only a poor anti-AChE activity, oxidative activation being suggested. It appears to cause delayed neuropathy. The major part of administered methamidophos in animals is rapidly eliminated from the body through urine and respiration. The major metabolic routes are O-demethylation, S-demethylation, and deamination. In plants, deaminated methamidophos is a major metabolite. Methamidophos is degraded rapidly in soil by deamination and demethylation, to eventually form carbon dioxide and phosphoric acid.
ShippingUN2783 Organophosphorus pesticides, solid, toxic, Hazard Class: 6.1; Labels: 6.1-Poisonous materials
DegradationMethamidophos is stable at pH 3-8 but it is hydrolysed in acids and alkalis. Photodegradation is of minor importance (PM). The physicochemical, electronic and molecular-orbital properties of methamidophos have recently been described and the compound is apparently nonionised at physiological pH (Singh et al., 1998).
The alkaline hydrolysis of methamidophos and its two N-methylated derivatives was examined by Fahmy et al. (1972). In aqueous KOH the main product was S-methyl phosphoramidothioate (2), whereas in less polar media such as aqueous MeOH or acetone the route was via de-Smethylation to give methyl phosphoramidate (3). It was concluded that the two competing mechanisms for methamidophos hydrolysis were (i) addition-elirnination on phosphorus leading to P-O bond cleavage, loss of methoxide and formation of product 2, (ii) an elimination reaction involving the amido proton to give P-S bond cleavage, loss of methanethiolate and formation of product 3. Proposed routes for the hydrolysis of methamidophos are shown in Scheme 1.
IncompatibilitiesIncompatible with strong acids or alkali. Attacks mild steel and copper-containing alloys (technical grade)
Waste DisposalIn accordance with 40CFR 165 recommendations for the disposal of pesticides and pesticide containers. Must be disposed properly by following package label directions or by contacting your local or federal environmental control agency, or by contacting your regional EPA office.
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