Uses
Monocrotophos is an organophosphorous insecticide. Monocrotophos is used mainly against cotton pests but it is also used in the protection of citrus, rice, potatoes, vegetables and other crops.
Definition
ChEBI: An alkenyl phosphate that is the 4-(methylamino)-4-oxobut-2-en-2-yl ester of dimethyl phosphate.
General Description
Colorless crystals with a mild ester odor, commercial product is a reddish-brown solid. Used as a fast acting insecticide with both systemic and contact action against a wide range of pests on cotton, sugar cane, tobacco, potatoes, peanuts, tomatoes, and ornamentals. Very toxic.
Air & Water Reactions
Water soluble. Rapidly hydrolyzed.
Reactivity Profile
Monocrotophos is incompatible with the following: Metals, low molecular weight alcohols & glycols [Note: Corrosive to black iron, drum steel, stainless steel 304 & brass. Should be stored at 70-80°F.] . Incompatible with alkaline compounds.
Health Hazard
Monocrotophos is an organophosphorus pesticide. It is a cholinesterase inhibitor and acts on the nervous system. Extremely toxic; probable oral lethal dose to humans 5-50 mg/kg or between 7 drops and 1 teaspoon for a 70 kg (150 lb.) person. Repeated inhalation or skin contact with Monocrotophos may, without symptoms, progressively increase susceptibility to poisoning.
Fire Hazard
Wear positive pressure breathing apparatus and full protective clothing. Container may explode in heat of fire. Toxic fumes evolved when heated to decomposition. Incompatible with alkaline compounds. Unstable in aqueous solution above pH 7.0; in low molecular weight alcohols and glycols. Stable in ketones and higher molecular weight alcohols and glycols. Stable when stored in glass or polyethylene containers. Relatively stable in sunlight. Keep away from temperatures above 80F; do not store below 70F. Corrosive to black iron, drum steel, stainless steel 304 and brass, but not to glass, aluminum, or stainless steel 316.
Hazard
Flammable, dangerous fire risk. Use
may be restricted. Toxic via ingestion, inhala-
tion, and skin absorption. Questionable carcinogen.
Cholinesterase inhibitor.
Potential Exposure
The liquid form is a severely hazardous
pesticide formulation. A potential danger to those
involved in the manufacture, formulation, and application
of this insecticide.
First aid
If this chemical gets into the eyes, remove any
contact lenses at once and irrigate immediately for at least
15 minutes, occasionally lifting upper and lower lids. Seek
medical attention immediately. If this chemical contacts the
skin, remove contaminated clothing and wash immediately
with soap and water. Speed in removing material from skin
is of extreme importance. Shampoo hair promptly if
contaminated. Seek medical attention immediately. If this
chemical has been inhaled, remove from exposure, begin
rescue breathing (using universal precautions, including
resuscitation mask) if breathing has stopped and CPR if
heart action has stopped. Transfer promptly to a medical
facility. When this chemical has been swallowed, get medical
attention. Give large quantities of water and induce
vomiting. Do not make an unconscious person vomit.
Obtain authorization and/or further instructions from the
local hospital for administration of an antidote or
performance of other invasive procedures.
Shipping
UN2783 Organophosphorus pesticides, solid,
toxic, Hazard Class: 6.1; Labels: 6.1-Poisonous materials.
Incompatibilities
Alkaline pesticides. Attacks black iron,
drum steel; stainless steel; brass.
Description
Monocrotophos is a colorless to reddish-brownsolid with a mild ester odor. Molecular weight = 223.19;Specific gravity (H2O:1)= 13; Boiling point= 125℃; Freezing/Melting point = 53.9℃ (pure); 25- -30℃ (thereddish brown technical product); Vapor pressure =7X10-mm at 20^C; Flash point= >93*C. HazardIdentification (based on NFPA-704 M Rating System):Health 3, Flammability 1, Reactivity 0. Soluble in water.Commercially available as a water-miscible solution.
Chemical Properties
Monocrotophos is a colorless to reddishbrown
solid with a mild ester odor.
Waste Disposal
Small amounts may be
hydrolyzed with water. Incineration in a unit with
effluent gas scrubbing is recommended for larger amounts.
In accordance with 40CFR165, follow 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.
Production Methods
The commercial production of monocrotophos involves a multi-step synthesis that begins with the preparation of the key phosphorus intermediate, dimethyl phosphite, produced by reacting phosphorus trichloride with methanol in the presence of a base such as triethylamine or ammonia in an inert solvent like toluene. Concurrently, the organic precursor, N-methylacetoacetamide, is synthesised via the condensation of diketene with methylamine in aqueous or methanolic solution, yielding the beta-keto amide through nucleophilic ring-opening of the lactone. This amide is then reacted with dimethyl phosphite in a base-catalysed Michaelis-Arbuzov-type addition across the enone system, typically in methanol, forming the intermediate dimethyl 1-methyl-2-(methylcarbamoyl)ethylphosphonate. The final step involves selective dehydrogenation and isomerisation using chlorine gas or sulfuryl chloride in a chlorinated solvent like dichloromethane, followed by dehydrochlorination with a tertiary amine to generate the αlpha,βeta-unsaturated vinyl phosphate with predominant (E)-configuration.
Mechanism of action
Broad-spectrum, systemic with stomach and contact action. Acetylcholinesterase (AChE) inhibitor.
Environmental Fate
Plant. Decomposes in plants forming the N-hydroxy compound in small amounts
(Hartley and Kidd, 1987).
Chemical/Physical. Hua et al. (1995) studied the titanium dioxide-mediated photooxidation
of monocrotophos using a recirculating photoreactor. The initial concentration and
flow rate used were 50 nM and 30 mL/minute, respectively. The irradiation
Emits toxic fumes of phosphorus and nitrogen oxides when heated to decomposition
(Sax and Lewis, 1987; Lewis, 1990).
Metabolic pathway
Technical monocrotophos contains 75-80% of the Ε-isomer and 9% of the
2-isomer, the balance being various impurities. Most studies on the metabolic
fate of this compound have used purified material containing >99%
E-isomer. Monocrotophos is a systemic vinyl phosphate insecticide with
a particularly high water solubility and low log Kow. This hydrophilic
property influences its metabolism and environmental fate in that it
tends to remain in the water phase and does not bioaccumulate.
The main routes of metabolic degradation are demethylation to des-
O-methylmonocrotophos and hydrolysis to dimethylphosphate and
N-methylacetoacetamide. Hydroxylation of the N-methyl group in animals
and plants followed by N-demethylation are also important from
a toxicological points of view, since these metabolic steps yield active
acetylcholinesterase inhibitors.
storage
Color Code—Blue: Health Hazard/Poison: Storein a secure poison location. Prior to working with thischemical you should be trained on its proper handling andstorage. Store in tightly closed containers in a cool, wellventilated area. Sources of ignition, such as smoking andopen flames, are prohibited where this chemical is handled,used, or stored. Metal containers involving the transfer of 5gallons or more of this chemical should be grounded andbonded. Drums must be equipped with self-closing valves,pressure vacuum bungs, and flame arresters. Use only nonsparking tools and equipment, especially when opening andclosing containers of this chemical. Wherever this chemicalis used, handled, manufactured, or stored, use explosionproof electrical equipment and fittings
Degradation
Monocrotophos is thermally labile, decomposing exothermically at
>55°C (PM). This thermo-instability has been known to cause manufacturing
problems. It is relatively stable at acidic and neutral pH values
but it is hydrolysed in alkaline solutions (PM). The DT50s at pH 3, 6 and
9 were 131, 134 and 26 days, respectively. Products of hydrolysis were
N-methylacetoacetamide (2), the main product at alkaline pH values, and
O-desmethylmonocrotophos (3), which predominated in acid and neutral
solutions (Lee et al., 1990). Further decomposition of N-methylacetoacetamide
(2) then gave acetone (4), CO2 and methylamine (5), whereas
under acidic conditions the O-desmethylmonocrotophos was shown to
decompose to inorganic phosphate (6), monomethyl phosphate (7), methanol
(B), acetone (4) and N-methylacetoacetamide (2) (Beynon et al., 1973).
Since monocrotophos does not significantly absorb light at wavelengths
greater than 300 nm, little photolysis would be expected to take place in
sunlight. Photolysis experiments in which aqueous solutions of monocrotophos
were exposed to sunlight in quartz tubes showed no products
other than the hydrolysis products 2 and 3, neither was their rate of
production accelerated. A soil surface photolysis experiment indicated
loss of monocrotophos, probably as CO2, due to microbial action. No
particular photolytic degradation products were detected apart from
minor amounts of the hydrolytic products 2 and 3 (Lee et al., 1990) (see Scheme 1).
Pesticide Type
Insecticide; Acaricide
