Cacodylic acid

In the 18th century it was found that combining arsenic trioxide ({{chem2|As2O3}}) and four equivalents of potassium acetate ({{chem2|CH3CO2K}}) gives a product called "Cadet's fuming liquid" which contains cacodyl oxide, {{chem2|((CH3)2As)2O}} and cacodyl, {{chem2|((CH3)2As)2}}.

Early research into "cacodyls" was reported by Robert Bunsen at the University of Marburg. Bunsen said of the compounds,

"The smell of this body produces instantaneous tingling of the hands and feet, and even giddiness and insensibility... It is remarkable that when one is exposed to the smell of these compounds the tongue becomes covered with a black coating, even when no further evil effects are noticeable".

His work in this field led to an increased understanding of the methyl group.

Cacodyl oxide, {{chem2|((CH3)2As)2O}}, is often considered the first organometallic compound to be prepared synthetically.

Cacodylic acid and its salts were incorporated into herbicides by a large variety of manufacturers under numerous brand names. APC Holdings Corp. sold cacodylic acid and its salts under the Phytar brand name.{{cite book|author=Stanley A. Greene|title=Sittig's Handbook of Pesticides and Agricultural Chemicals|url=https://books.google.com/books?id=hAoKEHpyu6wC&pg=PA132|year=2005|publisher=William Andrew|isbn=978-0-8155-1903-4|page=132}} The variety Phytar 560G, a mixture of cacodylic acid and sodium cacodylate, was used during the Vietnam War as a defoliant under the name "Agent Blue".{{cite book |author1=Committee to Review the Health Effects in Vietnam Veterans of Exposure to Herbicides |url=https://books.google.com/books?id=RjCHcoUE3B8C&pg=PA89 |title=Veterans and Agent Orange: Health Effects of Herbicides Used in Vietnam |author2=Institute of Medicine |publisher=National Academies Press |year=1994 |isbn=978-0-309-55619-4 |pages=89–90}}

Cacodylic acid is a weak acid with a pK_a of around 6.25.{{cite journal |vauthors=((Shin, T.-W.)), ((Kim, K.)), ((Lee, I.-J.)) |date=April 1997 |title=Spectrophotometric determination of the acid dissociation constants for cacodylic acid and p-Nitrophenol at elevated temperatures |journal=Journal of Solution Chemistry |volume=26 |issue=4 |pages=379–390 |doi=10.1007/BF02767677 |issn=0095-9782}}

Cacodylic acid can be reduced to dimethylarsine , which is a versatile intermediate for the synthesis of other organoarsenic compounds:{{cite journal|author1=Feltham, R. D. |author2=Kasenally, A. |author3=Nyholm, R. S. |title=A New Synthesis of Di- and Tri-Tertiary Arsines|journal=Journal of Organometallic Chemistry|year=1967|volume=7|issue=2|pages=285–288|doi=10.1016/S0022-328X(00)91079-9}}Burrows, G. J. and Turner, E. E., "A New Type of Compound containing Arsenic", Journal of the Chemical Society Transactions, 1920, 1374-1383

:{{chem2|(CH3)2AsO2H + 2 Zn + 4 HCl → (CH3)2AsH + 2 ZnCl2 + 2 H2O}}

:{{chem2|(CH3)2AsO2H + SO2 + HI → (CH3)2AsI + SO3 + H2O}}

When treated with hydrogen sulfide, dithiocacodylic acid results:{{cite journal |doi=10.1071/ch9701117 |title=Synthesis and infrared spectra of some dithiocacodylate complexes |date=1970 |last1=Casey |first1=AT |last2=Ham |first2=NS |last3=MacKey |first3=DJ |last4=Martin |first4=RL |journal=Australian Journal of Chemistry |volume=23 |issue=6 |page=1117 }}

:{{chem2|(CH3)2AsO2H + 2 H2S → (CH3)2AsS2H + 2 H2O}}

Cacodylic acid is highly toxic by ingestion, inhalation, or skin contact. The U.S. EPA states that all forms of arsenic are a serious risk to human health and the United States Agency for Toxic Substances and Disease Registry ranked arsenic as number 1 in its 2001 Priority List of Hazardous Substances at Superfund sites.{{cite web |url=https://cfpub.epa.gov/ncer_abstracts/index.cfm/fuseaction/display.highlight/abstract/6015 |title=Biogeochemistry of Arsenic in Contaminated Soils of Superfund Sites |last1=Dibyendu |first1=Sarkar |last2=Datta |first2=Rupali |date=2007 |website=EPA |publisher=United States Environmental Protection Agency |access-date=25 February 2018 |archive-url=https://web.archive.org/web/20200317143949/https://cfpub.epa.gov/ncer_abstracts/index.cfm/fuseaction/display.highlight/abstract/6015 |archive-date=17 March 2020 |url-status=dead}} Arsenic is classified as a Group-A carcinogen.

• Arsenic
• Arsine

{{reflist}}

• {{cite journal |author1=Kenyon, E. M. |author2=Hughes, M. F. | title = A Concise Review of the Toxicity and Carcinogenicity of Dimethylarsenic Acid | journal = Toxicology | volume = 160 | year = 2001 | issue = 1–3 | pages = 227–236 | doi = 10.1016/S0300-483X(00)00458-3|pmid=11246143 |url=https://zenodo.org/record/1259985 }}
• Elschenbroich, C; Salzer, A. (1992) Organometallics, 2nd Edition

• [https://www.atsdr.cdc.gov/csem/csem.html Case Studies in Environmental Medicine - Arsenic Toxicity]
• [http://www.corrosion-doctors.org/Biographies/BunsenBio.htm Bunsen Biography]

{{DEFAULTSORT:Cacodylic Acid}}

Category:Arsenical herbicides

Category:Organoarsenic compounds

Category:IARC Group 2B carcinogens