Carbaryl

Carbaryl is often inexpensively produced by direct reaction of methyl isocyanate with 1-naphthol.{{cite book | title = Pesticide Synthesis Handbook | author = Thomas A. Unger | publisher = William Andrew | year = 1996 | isbn = 0-8155-1401-8 | pages = 67–68 | url = https://books.google.com/books?id=blYN-_pY9_IC&pg=PA67 | format = Google Books excerpt}}

:C₁₀H₇OH + CH₃NCO → C₁₀H₇OC(O)NHCH₃

Alternatively, 1-naphthol can be treated with excess phosgene to produce 1-naphthylchloroformate, which is then converted to carbaryl by reaction with methylamine. The former process was used in the chemical plant that caused the Bhopal. 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.

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.

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. {{doi|10.1002/14356007.a14_263}} It is the active ingredient in Carylderm shampoo used to combat head lice until infestation is eliminated.[https://dtb.bmj.com/content/20/15/59 Carbaryl against lice]

Carbaryl kills both targeted (e.g., malaria-carrying mosquitos) and beneficial insects (e.g., honeybees), as well as crustaceans.[http://npic.orst.edu/factsheets/carbgen.pdf Carbaryl General Fact Sheet - National Pesticide Information Center] 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.{{cite book | editor-last1=Kendall | editor-first1=Ronald | editor-first2=Thomas E. | editor-last2=Lacher | editor-first3=George P. | editor-last3=Cobb | editor-first4=Stephen B. | editor-last4=Cox | title=Wildlife Toxicology: Emerging Contaminant and Biodiversity Issues | publisher=CRC | publication-place=Boca Raton | year=2010 | isbn=978-1-4398-1794-0 | oclc=646404494}} 5.4.1 Taxon-Wide Impacts — Pesticides and Contaminants, and Their Roles in the Decline of Amphibian Populations. Moore, Robin D.; Claude Gascon. pp.{{nbs}}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.{{Cite journal |last=Boone |first=Michelle D. |last2=Semlitsch |first2=Raymond D. |date=February 2002 |title=Interactions of an Insecticide With Competition and Pond Drying in Amphibian Communities |url=http://dx.doi.org/10.1890/1051-0761(2002)012[0307:ioaiwc]2.0.co;2 |journal=Ecological Applications |volume=12 |issue=1 |pages=307–316 |doi=10.1890/1051-0761(2002)012[0307:ioaiwc]2.0.co;2 |issn=1051-0761|url-access=subscription }}

It is approved for more than 100 crops in the US. Carbaryl has been illegal in the EU since 21 November 2007{{Cite web|url=https://eur-lex.europa.eu/legal-content/EN/TXT/HTML/?uri=CELEX:32007D0355|title=L_2007133EN.01004001.XML}} and Angola.[http://www.grandcountywater.com/CarbarylInsecticideHazardData.htm Carbaryl Insecticide Hazard Data] {{webarchive |url=https://web.archive.org/web/20100511193333/http://www.grandcountywater.com/CarbarylInsecticideHazardData.htm |date=May 11, 2010 }}

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.)[http://www.epa.gov/oppsrrd1/REDs/carbaryl_ired.pdf Interim Reregistration Eligibility Decision for Carbaryl] {{webarchive |url=https://web.archive.org/web/20080725202902/http://www.epa.gov/oppsrrd1/REDs/carbaryl_ired.pdf |date=July 25, 2008 }}, U.S. EPA, June 2003. The oral {{LD50}} 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.{{cite book |last=Eckerman |first=Ingrid |title=The Bhopal Saga—Causes and Consequences of the World's Largest Industrial Disaster |url=https://docs.google.com/file/d/0B0FqO8XKy9NRZDNzTkZQeVJQbE0/edit?pli=1 |year=2005 |publisher=Universities Press |location=India |isbn=81-7371-515-7 |doi=10.13140/2.1.3457.5364}}

{{Reflist|30em}}

• [http://npic.orst.edu/factsheets/archive/carbtech.pdf Carbaryl Technical Fact Sheet - National Pesticide Information Center]
• [http://extoxnet.orst.edu/pips/carbaryl.htm Carbaryl Pesticide Information Profile - Extension Toxicology Network]
• [http://extoxnet.orst.edu/tibs/cholines.htm Cholinesterase Inhibition - Extension Toxicology Network]
• [http://www.epa.gov/oppsrrd1/reregistration/carbaryl/ EPA info]
• [https://web.archive.org/web/20061006094739/http://www.epa.gov/oppsrrd1/REDs/factsheets/carbaryl_factsheet.pdf EPA factsheet]
• [http://www.inchem.org/documents/hsg/hsg/hsg78_e.htm IPCS (WHO) Health and Safety Guide]
• [http://www.inchem.org/documents/ehc/ehc/ehc153.htm Environmental Health Criteria - WHO]
• [http://www.exchemistry.com/sevin.html Exclusive Chemistry Ltd - routes of Sevin synthesis]
• [https://www.cdc.gov/niosh/npg/npgdcas.html CDC - NIOSH Pocket Guide to Chemical Hazards]
• {{PPDB|115}}

{{Insecticides}}

{{Acetylcholine metabolism and transport modulators}}

{{Authority control}}

Category:Acetylcholinesterase inhibitors

Category:Carbamate insecticides

Category:IARC Group 3 carcinogens

Category:Endocrine disruptors

Category:Naphthol esters

Category:Veterinary drugs

Category:Aromatic carbamates

Category:1-Naphthyl compounds