Methamidophos is an off-white crystalline solid. Molecular weight= 141.12; Freezing/Melting point=44.5℃; Vapor pressure= 8 3 104 mmHg at 20℃. Hazard Identification (based on NFPA-704 M Rating System): Health 3, Flammability 1, Reactivity 0. Slightly soluble in water.
Methamidophos 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.
Methamidophos is an off-white crystalline
solid.
Methamidophos 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.
Insecticide and acaricide.
Methamidophos is used to control a wide range of insects and
mites in a very large number of crops.
Metamidophos is an organophosphate insecticide used in great quantities in rice fields in rice-producing countries.
ChEBI: Methamidophos is an organic thiophosphate resulting from the N-deacylation of the proinsecticide acephate. It has a role as an acaricide, an agrochemical and an avicide. It is an organic thiophosphate, a phosphoramide and an organothiophosphate insecticide.
The commercial production of methamidophos typically begins with the synthesis of O,S-dimethyl phosphoramidothioate, its active chemical structure. This involves reacting dimethyl phosphorochloridothioate with ammonia or an amine derivative under controlled conditions to introduce the amidothioate group. The process requires careful temperature regulation and the use of solvents to ensure purity and yield. After synthesis, the crude product undergoes purification steps such as distillation or crystallisation to remove impurities and stabilise the compound.
Crystalline solid, technical product is off-white with a pungent odor. Used as an insecticide on a number of vegetables and on cotton.
Organophosphates, 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].
Methamidophos is harmful or fatal if swallowed, inhaled, or absorbed through the skin.
Methamidophos 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.
(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.
Insecticide, 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
.
ACEPHATE-MET®; BAY 71625®; BAYER
71628®; CHEVRON 9006®; CHEVRON ORTHO 9006®;
FILITOX®; GS-13005®; HAMIDOP®; METAFOS®;
MONITOR®; MTD®; NITOFOL®; NURATRON®;
ORTHO 9006®; PATROLE®; PILLARON®; SRA
5172®; SUPRACIDE®; SWIPE®; TAHMABON®;
TAMARON®; VITARON®
Systemic with contact and stomach action. Acetylcholinesterase (AChE) inhibitor.
Poison 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.
A potential danger to those involved
in the manufacture, formulation, and application of this
insecticide on vegetables and cotton
If this chemical gets into the eyes, remove anycontact lenses at once and irrigate immediately for at least15 min, occasionally lifting upper and lower lids. Seek medical attention immediately. If this chemical contacts theskin, remove contaminated clothing and wash immediatelywith soap and water. Speed in removing material from skinis of extreme importance. Shampoo hair promptly if contaminated. Seek medical attention immediately. If thischemical has been inhaled, remove from exposure, beginrescue breathing (using universal precautions, includingresuscitation mask) if breathing has stopped and CPR ifheart action has stopped. Transfer promptly to a medicalfacility. When this chemical has been swallowed, get medical attention. Give large quantities of water and inducevomiting. Do not make an unconscious person vomit.Obtain authorization of an antidote or performance of otherinvasive procedures. The effects may be delayed. Medicalobservation recommended. Note to physician: 1,10 -trimethylenebis(4-formylpyridinium bromide)dioxime (a.k.a TMB-4 dibromide and TMV-4) has been used as an antidote for organophosphate poisoning.
Chemical/Physical. Emits toxic fumes of phosphorus, nitrogen and sulfur oxides when
heated to decomposition (Sax and Lewis, 1987).
Methamidophos 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'.
Acute 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.
Color Code—Blue: Health Hazard/Poison: Store in a secure poison location. Prior to working with this chemical you should be trained on its proper handling and storage. Store in tightly closed containers in a cool, wellventilated area
UN2783 Organophosphorus pesticides, solid,
toxic, Hazard Class: 6.1; Labels: 6.1-Poisonous materials
Methamidophos 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.
Incompatible with strong acids or alkali.
Attacks mild steel and copper-containing alloys (technical
grade)
In 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.
Insecticide; Acaricide; Metabolite
