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Carbaryl

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Carbaryl
Names
IUPAC name
1-naphthyl methylcarbamate
Other names
Sevin
Identifiers
3D model (JSmol)
ChemSpider
ECHA InfoCard 100.000.505 Edit this at Wikidata
EC Number
  • 200-555-0
RTECS number
  • FC5950000
UN number 2757
  • InChI=1/C12H11NO2/c1-13-12(14)15-11-8-4-6-9-5-2-3-7-10(9)11/h2-8H,1H3,(H,13,14)
    Key: CVXBEEMKQHEXEN-UHFFFAOYAZ
  • O=C(Oc2cccc1ccccc12)NC
Properties
C12H11NO2
Molar mass 201.225 g·mol−1
Appearance Colorless crystalline solid
Density 1.2 g/cm3
Melting point 142 °C (288 °F; 415 K)
Boiling point decomposes before boiling
very low
Hazards
Flash point 193–202 °C
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Carbaryl (1-naphthyl methylcarbamate) is a chemical in the carbamate family used chiefly as an insecticide. It is a white crystalline solid commonly sold under the brand name Sevin, 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. It remains the third most-utilized 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.[1]

Production

Carbaryl is produced by treating methyl isocyanate (3) with 1-naphthol (4).[2]

Alternately, 1-naphthol (1) is first converted to its chloroformate (3), which is then treated with methylamine to give the desired product (4):[2]

The former process was carried out in Bhopal, which ultimately ended in disaster. In comparison, the latter synthesis uses the exact same reagents but in a different sequence. This synthesis avoids the preparation of methyl isocyanide, and the comparison is often used as a case study in green chemistry. That said, the second synthesis still uses phosgene, which is toxic and reacts with water, and methylamine, which is a toxic and flammable gas.

Biochemistry

Carbamate insecticides are reversible inhibitors of the enzyme acetylcholinesterase. They resemble acetylcholine 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 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 the milk. For the latter reasons, carbaryl is favored for food crops, at least in the US.[1] It is the active ingredient in Carylderm shampoo used to combat head lice. 7 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.[3]

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.)[4]

Oral LD50:

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

References

  1. ^ a b Robert L. Metcalf “Insect Control” in Ullmann’s Encyclopedia of Industrial Chemistry” Wiley-VCH, Weinheim, 2002. doi:10.1002/14356007.a14_263
  2. ^ a b Thomas A. Unger (1996). Pesticide synthesis handbook (Google Books excerpt). William Andrew. pp. 67–68. ISBN 0815514018.
  3. ^ Carbaryl Insecticide Hazard Data
  4. ^ Interim Reregistration Eligibility Decision for Carbaryl, U.S. EPA, June 2003.
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