Cacodylic acid: Difference between revisions

{{Chembox

| Verifiedfields = changed

| Watchedfields = changed

| verifiedrevid = 459990955

| ImageFile = Cacodylic acid.svg

| ImageSize = 160px

| ImageAlt = Structural formula

| ImageFile1 = cacodylic-acid-3D-balls.png

| ImageSize1 = 160px

| ImageAlt1 = Ball-and-stick model

| ImageCaption1 = [[Ball-and-stick model]]<ref>{{ Cite journal | url = https://dx.doi.org/10.5517/ccx73mv | title = CSD Entry: CADYLA01 : Dimethylarsinic acid | website = [[Cambridge Structural Database]]: Access Structures | year = 2011 | publisher = [[Cambridge Crystallographic Data Centre]] | doi = 10.5517/ccx73mv | access-date = 2021-12-21 | last1 = Betz | first1 = R. | last2 = McCleland | first2 = C. | last3 = Marchand | first3 = H. }}</ref><ref name="Betz">{{ cite journal | title = The monoclinic polymorph of dimethylarsinic acid | first1 = R. | last1 = Betz | first2 = C. | last2 = McCleland | first3 = H. | last3 = Marchand | journal = [[Acta Crystallographica Section E: Structure Reports Online|Acta Crystallogr. E]] | year = 2011 | volume = 67 | issue = 8 | pages = m1013 | doi = 10.1107/S1600536811025505 | pmid = 22090811 | pmc = 3212109 }}</ref>

| PIN = Dimethylarsinic acid

|Section1={{Chembox Identifiers

| ChemSpiderID_Ref = {{chemspidercite|correct|chemspider}}

| PubChem = 2513

| EINECS = 200-883-4

| ChEBI_Ref = {{ebicite|changed|EBI}}

| ChEBI = 29839

| ChEMBL = 1231644

| RTECS = CH7525000

| DrugBank_Ref = {{drugbankcite|correct|drugbank}}

| UNNumber = 1572

| Gmelin = 130562

| Beilstein = 1736965

| InChI = 1/C2H7AsO2/c1-3(2,4)5/h1-2H3,(H,4,5)

|Section2={{Chembox Properties

| Formula = C₂H₇AsO₂

| MolarMass = 137.9977 g/mol

| Appearance = White crystals or powder

| Odor = odorless

| Density = > 1.1 g/cm³

| MeltingPtC = 192 to 198

| MeltingPt_notes =

| BoilingPt= >

| BoilingPtC = 200

| Solubility = 66.7 g/100 ml

| SolubleOther = soluble in [[ethanol]], [[acetic acid]] <br /> insoluble in [[diethyl ether]]

| pKa = 6

| MagSus = -79.9·10⁻⁶ cm³/mol

|Section3={{Chembox Structure

| CrystalStruct = triclinic,<ref>{{ cite journal | first1 = J. | last1 = Trotter | first2 = T. | last2 = Zobel | journal = [[Journal of the Chemical Society|J. Chem. Soc.]] | year = 1965 | pages=4466–4471 | title = 826. Stereochemistry of arsenic. Part XVI. Cacodylic acid | doi = 10.1039/JR9650004466 }}</ref> monoclinic<ref name="Betz" />

}}

|Section7={{Chembox Hazards

| GHSPictograms = {{GHS06}}{{GHS09}}

| GHSSignalWord = Danger

| HPhrases = {{H-phrases|301|331|410}}

| PPhrases = {{P-phrases|261|264|270|271|273|301+310|304+340|311|321|330|391|403+233|405|501}}

| NFPA-H = 4

| NFPA-F = 0

| NFPA-R = 0

| ExternalSDS = [https://web.archive.org/web/20030802230345/http://ptcl.chem.ox.ac.uk/MSDS/CA/cacodylic_acid.html External MSDS]

| FlashPt =

| AutoignitionPt =

| LD50 = 23-100 mg/kg (rat and mouse, oral)

'''Cacodylic acid''' is an [[organoarsenic compound]] with the [[chemical formula|formula]] (CH₃)₂[[Arsenic|As]]O₂H. With the formula R₂As(O)OH, it is the simplest of the [[arsinic acids]]. It is a colorless solid that is soluble in water.

Neutralization of cacodylic acid with base gives '''cacodylate''' salts, e.g. '''sodium cacodylate'''. They are potent [[herbicide]]s. Cacodylic acid/sodium cacodylate is a [[buffering agent]] in the preparation and fixation of biological samples for [[electron microscopy]] and in [[protein crystallography]].

In the 18th century it was found that combining {{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 "[[cacodyl]]s" was reported by [[Robert Bunsen]] at the [[University of Marburg]]. Bunsen said of the compounds,

<blockquote>"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".</blockquote>

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 [[herbicide]]s by a large variety of manufacturers under numerous brand names. APC Holdings Corp. sold cacodylic acid and its salts under the [[Agent Blue|Phytar]] brand name.<ref name="Greene2005">{{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}}</ref> 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]]".<ref name="HerbicidesMedicine1994">{{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}}</ref>

==Reactions==

Cacodylic acid is a [[weak acid]] with a pK_a of around 6.25.<ref>{{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}}</ref>

Cacodylic acid can be reduced to dimethylarsine , which is a versatile intermediate for the synthesis of other organoarsenic compounds:<ref>{{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}}</ref><ref>Burrows, G. J. and Turner, E. E., "A New Type of Compound containing Arsenic", Journal of the Chemical Society Transactions, 1920, 1374-1383</ref>

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

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

== Health effects ==

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.<ref name="EPA1">{{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}}</ref> Arsenic is classified as a Group-A [[carcinogen]].<ref name="EPA1"/>

{{reflist}}

==Further reading==

* {{cite journal |author1=Kenyon, E. M. |author2=Hughes, M. F. | title = A Concise Review of the Toxicity and Carcinogenicity of Dimethylarsenic Acid | journal = [[Toxicology (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 }}

* [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]

[[Category:Organoarsenic compounds]]

[[Category:IARC Group 2B carcinogens]]