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Carbaryl

Carbaryl

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Encyclopedia
Carbaryl is a chemical in the carbamate
Carbamate
Carbamates are organic compounds derived from carbamic acid . A carbamate group, carbamate ester, and carbamic acids are functional groups that are inter-related structurally and often are interconverted chemically. Carbamate esters are also called urethanes.-Synthesis:Carbamic acids are derived...

 family used chiefly as an insecticide
Insecticide
An insecticide is a pesticide used against insects. They include ovicides and larvicides used against the eggs and larvae of insects respectively. Insecticides are used in agriculture, medicine, industry and the household. The use of insecticides is believed to be one of the major factors behind...

. It is a white crystalline solid commonly sold under the brand name Sevin, a trademark of the Bayer
Bayer
Bayer AG is a chemical and pharmaceutical company founded in Barmen , Germany in 1863. It is headquartered in Leverkusen, North Rhine-Westphalia, Germany and well known for its original brand of aspirin.-History:...

 Company. Union Carbide
Union Carbide
Union Carbide Corporation is a wholly owned subsidiary of The Dow Chemical Company. It currently employs more than 2,400 people. Union Carbide primarily produces chemicals and polymers that undergo one or more further conversions by customers before reaching consumers. Some are high-volume...

 discovered carbaryl and introduced it commercially in 1958. Bayer purchased Aventis CropScience in 2002, a company that included Union Carbide pesticide operations. It remains the third most-used insecticide in the United States for home gardens, commercial agriculture, and forestry and rangeland protection. Approximately 11 million kilograms were applied to U.S. farm crops in 1976.

Production


Carbaryl is produced by treating methyl isocyanate
Methyl isocyanate
Methyl isocyanate is an organic compound with the molecular formula CH3NCO. Synonyms are isocyanatomethane, methyl carbylamine, and MIC. Methyl isocyanate is an intermediate chemical in the production of carbamate pesticides . It has also been used in the production of rubbers and adhesives...

 (3) with 1-naphthol
1-Naphthol
1-Naphthol, or α-naphthol, is a colorless crystalline solid with the formula C10H7OH. It is an isomer of 2-naphthol differing by the location of the hydroxyl group on naphthalene. The naphthols are naphthalene homologues of phenol, with the hydroxyl group being more reactive than in the phenols....

 (4).


Alternatively, 1-naphthol (1) is first converted to its chloroformate
Chloroformate
Chloroformates are a class of chemical compounds which are esters of chloroformic acid. They are widely used as reagents in organic chemistry. For example, benzyl chloroformate is used to introduce the CBZ protecting group and fluorenylmethyloxycarbonylchloride is used to introduce the FMOC...

 (3), which is then treated with methylamine to give the desired product (4):


The former process was carried out in Bhopal, which ultimately ended in disaster
Bhopal disaster
The Bhopal disaster also known as Bhopal Gas Tragedy was a gas leak incident in India, considered one of the world's worst industrial catastrophes. It occurred on the night of December 2–3, 1984 at the Union Carbide India Limited pesticide plant in Bhopal, Madhya Pradesh, India...

. In comparison, the latter synthesis uses exactly the same reagents, but in a different sequence. This synthesis avoids the preparation of methyl isocyanate, and the comparison is often used as a case study in green chemistry
Green chemistry
Green chemistry, also called sustainable chemistry, is a philosophy of chemical research and engineering that encourages the design of products and processes that minimize the use and generation of hazardous substances...

. That said, the second synthesis still uses phosgene
Phosgene
Phosgene is the chemical compound with the formula COCl2. This colorless gas gained infamy as a chemical weapon during World War I. It is also a valued industrial reagent and building block in synthesis of pharmaceuticals and other organic compounds. In low concentrations, its odor resembles...

, which is toxic and reacts with water, and methylamine
Methylamine
Methylamine is the organic compound with a formula of CH3NH2. This colourless gas is a derivative of ammonia, but with one H atom replaced by a methyl group. It is the simplest primary amine. It is sold as a solution in methanol, ethanol, THF, and water, or as the anhydrous gas in pressurized...

, which is a toxic and flammable gas.

Biochemistry


Carbamate insecticides are reversible inhibitors of the enzyme acetylcholinesterase
Acetylcholinesterase
"Acetylcholinesterase, also known as AChE or acetylcholine acetylhydrolase, is an enzyme that degrades the neurotransmitter acetylcholine, producing choline and an acetate group. It is mainly found at neuromuscular junctions and cholinergic nervous system, where its activity serves to terminate...

. They resemble acetylcholine
Acetylcholine
The chemical compound acetylcholine is a neurotransmitter in both the peripheral nervous system and central nervous system in many organisms including humans...

, but do not undergo the final hydrolysis. In this way, they interfere with the nervous system and cause death.

Applications


The development of the carbamate insecticides has been called a major breakthrough in pesticide
Pesticide
Pesticides are substances or mixture of substances intended for preventing, destroying, repelling or mitigating any pest.A pesticide may be a chemical unicycle, biological agent , antimicrobial, disinfectant or device used against any pest...

s. The carbamates do not have the persistence of chlorinated pesticides. Although toxic to insects, carbaryl is detoxified and eliminated rapidly in vertebrates. It is neither concentrated in fat nor secreted in the milk. For the latter reasons, carbaryl is favored for food crops, at least in the US. It is the active ingredient in Carylderm shampoo used to combat head lice until infestation is eliminated.

Risk


Carbaryl kills both targeted (e.g. malaria-carrying mosquitos) and beneficial insects (e.g. honeybees), as well as crustaceans.

Although approved for more than 100 crops in the US, carbaryl is illegal in several countries, including the United Kingdom, Austria, Denmark, Sweden, Germany, and Angola.

Carbaryl is often produced using methyl isocyanate
Methyl isocyanate
Methyl isocyanate is an organic compound with the molecular formula CH3NCO. Synonyms are isocyanatomethane, methyl carbylamine, and MIC. Methyl isocyanate is an intermediate chemical in the production of carbamate pesticides . It has also been used in the production of rubbers and adhesives...

 (MIC) as an intermediary. A leak of MIC used in the production of carbaryl caused the Bhopal disaster
Bhopal disaster
The Bhopal disaster also known as Bhopal Gas Tragedy was a gas leak incident in India, considered one of the world's worst industrial catastrophes. It occurred on the night of December 2–3, 1984 at the Union Carbide India Limited pesticide plant in Bhopal, Madhya Pradesh, India...

, the largest industrial accident in history. This accident caused around 11,000 deaths and over 500,000 injuries.

Safety


Carbaryl is a cholinesterase inhibitor and is toxic to humans. It is classified as a likely human carcinogen
Carcinogen
A carcinogen is any substance, radionuclide, or radiation that is an agent directly involved in causing cancer. This may be due to the ability to damage the genome or to the disruption of cellular metabolic processes...

 by the United States Environmental Protection Agency
United States Environmental Protection Agency
The U.S. Environmental Protection Agency is an agency of the federal government of the United States charged with protecting human health and the environment, by writing and enforcing regulations based on laws passed by Congress...

(EPA.)

Oral :
  • 250 mg/kg to 850 mg/kg for rats
  • 100 mg/kg to 650 mg/kg for mice

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