Carbaryl

Carbaryl (1-naphthyl methylcarbamate) is a chemical in the carbamate family used chiefly as an insecticide. It is a white crystalline solid previously sold under the brand name Sevin, which was a trademark of the Bayer Company. Union Carbide discovered carbaryl and introduced it commercially in 1958. Bayer purchased Aventis CropScience in 2002, a company that included Union Carbide pesticide operations. Carbaryl was the third-most-used insecticide in the United States for home gardens, commercial agriculture, and forestry and rangeland protection. As a veterinary drug, it is known as carbaril ( INN).

Production

Carbaryl is often inexpensively produced by direct reaction of methyl isocyanate with 1-naphthol.
:C₁₀H₇OH + CH₃NCO → C₁₀H₇OC(O)NHCH₃

Alternatively, 1-naphthol can be treated with excess phosgene to produce 1- naphthyl chloroformate, which is then converted to carbaryl by reaction with methylamine. The former process was used in the chemical plant that caused the Bhopal disaster. In comparison, the latter synthesis uses exactly the same reagents required for the synthesis of methyl isocyanate. This route avoids the potential hazards of methyl isocyanate, allbeit at a higher cost.

Biochemistry

Carbamate insecticides are slowly irreversible inhibitors of the enzyme acetylcholinesterase. They resemble acetylcholine, but the carbamoylated enzyme undergoes the final hydrolysis step very slowly (minutes) compared with the acetylated enzyme generated by acetylcholine (microseconds). They interfere with the cholinergic nervous system and cause death because the effects of the neurotransmitter acetylcholine cannot be terminated by carbamoylated acetylcholinesterase.

Applications

The development of the carbamate insecticides has been called a major breakthrough in pesticides. 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 milk, so is favored for food crops, at least in the US.Robert L. Metcalf "Insect Control" in Ullmann's ''Encyclopedia of Industrial Chemistry'' Wiley-VCH, Weinheim, 2002. It is the active ingredient in Carylderm shampoo used to combat head lice until infestation is eliminated.

Ecology

Carbaryl kills both targeted (e.g., malaria-carrying mosquitos) and beneficial insects (e.g., honeybees), as well as crustaceans.Carbaryl General Fact Sheet - National Pesticide Information Center
/ref> Because it is highly toxic to zooplankton, the algae they feed on experience blooms. Boone & Bridges 2003 find that larger algae eaters such as '' Bufo woodhousii'' benefit from this effect. 5.4.1 Taxon-Wide Impacts — Pesticides and Contaminants, and Their Roles in the Decline of Amphibian Populations. Moore, Robin D.; Claude Gascon. pp.111-145.

Although it can increase survival rates for organisms that benefit from consequential algae blooms, the long term effects of these changes in competition levels and predation can be detrimental to many aquatic ecosystems, particularly those dominated by Anurans.

It is approved for more than 100 crops in the US. Carbaryl has been illegal in the EU since 21 November 2007 and Angola.Carbaryl Insecticide Hazard Data

Safety

Carbaryl is a cholinesterase inhibitor and is toxic to humans. It is classified as a likely human carcinogen by the United States Environmental Protection Agency (EPA.)Interim Reregistration Eligibility Decision for Carbaryl
, U.S. EPA, June 2003. The oral is 250 to 850 mg/kg for rats and 100 to 650 mg/kg for mice.

Carbaryl can be produced using methyl isocyanate (MIC) as an intermediary. A leak of MIC used in the production of carbaryl caused the Bhopal disaster, the most lethal industrial accident in history.

References

External links

Carbaryl Technical Fact Sheet - National Pesticide Information Center
* ttp://extoxnet.orst.edu/tibs/cholines.htm Cholinesterase Inhibition - Extension Toxicology Networkbr>EPA infoEPA factsheet
*

{{Authority control

Acetylcholinesterase inhibitors
Carbamate insecticides
IARC Group 3 carcinogens
Endocrine disruptors
Naphthol esters
Veterinary drugs
Aromatic carbamates
1-Naphthyl compounds