Description
Paraquat dichloride is a dark blue liquid, non-combustible, stable herbicide chemical. It is
incompatible with strong oxidising agents. On contact with fire paraquat decomposes gives
off irritating or toxic fumes (or gases), nitrogen oxides, and hydrogen chloride. Paraquat
dichloride contact and storage destroys metal. Paraquat dichloride hydrolyses in alkaline
media and reacts with aluminium to produce hydrogen gas.
Paraquat (N,N′-dimethyl-4,4′-bipyridinium dichloride) is one of the most widely used herbicides
in the world. Paraquat dichloride is a herbicide currently registered to control weeds
and grasses in many agricultural and non-agricultural areas. It is used preplant or preemergence
on vegetables, grains, cotton, grasses, sugar cane, peanuts, potatoes, and tree plantation
areas; post-emergence around fruit crops, vegetables, trees, vines, grains, soybeans,
and sugar cane. It is also used on non-crop areas such as public airports, electric transformer
stations, and around commercial buildings to control weeds. It has been reported that about
seven pesticide products are registered which contain the active ingredient paraquat dichloride
and classified as restricted use pesticides (RUPs). Paraquat dichloride and the products
are primarily intended for ‘Occupational Use’. In the United States, Paraquat is classified as
‘restricted commercial use’, and people must obtain a license to use the product.
Chemical Properties
Paraquat is a yellow solid with a faint,
ammonia-like odor.
Chemical Properties
off-white powder
Uses
Paraquat dichloride acts as an electron acceptor and transfer catalyst in redox reactions.
Production Methods
Paraquat dichloride is commercially produced by the quaternization of pyridine with methyl chloride to form methyl viologen, followed by oxidation and neutralization with hydrochloric acid to yield the dichloride salt. The process begins with the reaction of pyridine with methyl chloride under pressure to produce 1,1′-dimethyl-4,4′-bipyridinium dichloride (methyl viologen). This intermediate is then oxidised to its active herbicidal form and neutralised with hydrochloric acid to stabilise the salt.
Definition
ChEBI: Paraquat dichloride is an organic chloride salt. It has a role as a herbicide and a photosystem-I inhibitor. It contains a paraquat.
General Description
Colorless to yellow crystalline solid. Used as a contact herbicide and desiccant.
Air & Water Reactions
Water soluble.
Reactivity Profile
Paraquat dichloride is stable in acidic media, but unstable in alkaline media. Paraquat dichloride is photochemically decomposed by UV irradiation in aqueous solutions and is rapidly inactivated by soil. The neat chemical may be sensitive to light. Paraquat dichloride is corrosive to metal and Paraquat dichloride can react with strong acids, bases, and oxidizing agents. Paraquat dichloride is hydrolyzed by alkali compounds and Paraquat dichloride is inactivated by inert clays and anionic surfactants.
Health Hazard
Can cause death due to severe injury to the lungs. The lowest lethal oral dose reported in humans is 43 mg/kg.
Fire Hazard
Avoid strong oxidizers.
Flammability and Explosibility
Not classified
Contact allergens
Paraquat is a quaternary ammonium compound with herbicide
properties, as diquat. It is contained in Cekuquat or
Dipril. It can cause contact and phototoxic contact dermatitis,
acne, and leukoderma mainly in agricultural workers.
Mechanism of action
Broad-spectrum, non-residual activity with contact and some desiccant action. Photosystem I (electron transport) inhibitor.
Safety Profile
A human poison by ingestion. Poison experimentally by ingestion, skin contact, intraperitoneal, intravenous, and subcutaneous routes. Human systemic effects by ingestion: acute renal failure, acute tubular necrosis, cough, diarrhea, dyspnea, headache, hyp
Potential Exposure
Those engaged in manufacture,
formulation and application of this herbicide. Classified
for restricted use: limited to use by a certified applicator, or
those under applicator’s direct supervision.
Shipping
UN2781 Bipyridilium pesticide, solid, toxic,
Hazard Class: 6.1; Labels: 6.1-Poisonous materials.
Purification Methods
Recrystallise the dichloride from MeOH/acetone mixture. It has also been recrystallised three times from absolute EtOH [Bancroft et al. Anal Chem 53 1390 1981]. Dry it at 80o in a vacuum. [Beilstein 23/8 V 30.]
Incompatibilities
Incompatible with oxidizers (chlorates,
nitrates, peroxides, permanganates, perchlorates, chlorine,
bromine, fluorine, etc.); contact may cause fires or explosions.
Keep away from alkaline materials, strong bases,
strong acids, oxoacids, epoxides (hydrolysis), alkylarylsulfonate
wetting agents. Corrosive to metals. Decomposes
in presence of ultraviolet (UV) light. Decomposes in heat
(see physical properties, above) and in the presence of UV
light, producing nitrogen oxides, hydrogen chloride.
Waste Disposal
Paraquat is rapidly inactivated
in soil. It is also inactivated by anionic surfactants.
Therefore an effective and environmentally safe disposal
method would be to mix the product with ordinary household
detergent and bury the mixture in clay soil. 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. Consult
with environmental regulatory agencies for guidance on
acceptable disposal practices. Generators of waste containing
this contaminant (≥100 kg/mo) must conform with
EPA regulations governing storage, transportation, treatment,
and waste disposal.
