Cacodylic acid

Cacodylic acid
	; Ball-and-stick model
Names
	Preferred IUPAC name Dimethylarsinic acid
	Other names Dimethylarsenic acid, Cacodylic acid, Hydroxydimethylarsine oxide, Arsecodile, Ansar, Silvisar, Phytar 560, DMAA, UN 1572
Identifiers
CAS Number	75-60-5 ;
3D model (JSmol)	Interactive image;
Beilstein Reference	1736965
ChEBI	CHEBI:29839 ;
ChEMBL	ChEMBL1231644;
ChemSpider	2418 ;
DrugBank	DB02994 ;
ECHA InfoCard	100.000.804
EC Number	200-883-4;
Gmelin Reference	130562
KEGG	C07308 ;
PubChem CID	2513;
RTECS number	CH7525000;
UNII	AJ2HL7EU8K ;
UN number	1572
CompTox Dashboard (EPA)	DTXSID7020508 ;
	InChI InChI=1S/C2H7AsO2/c1-3(2,4)5/h1-2H3,(H,4,5) Key: OGGXGZAMXPVRFZ-UHFFFAOYSA-N ; InChI=1/C2H7AsO2/c1-3(2,4)5/h1-2H3,(H,4,5) Key: OGGXGZAMXPVRFZ-UHFFFAOYAP;
	SMILES O=[As](O)(C)C;
Properties
Chemical formula	C2H7AsO2
Molar mass	137.9977 g/mol
Appearance	White crystals or powder
Odor	odorless
Density	> 1.1 g/cm3
Melting point	192 to 198 °C (378 to 388 °F; 465 to 471 K)
Boiling point	> 200 °C (392 °F; 473 K)
Solubility in water	66.7 g/100 ml
Solubility	soluble in ethanol, acetic acid ; insoluble in diethyl ether
Acidity (pKa)	6
Magnetic susceptibility (χ)	-79.9·10−6 cm3/mol
Structure
Crystal structure	triclinic, monoclinic
Hazards
	GHS labelling:
Pictograms
Signal word	Danger
Hazard statements	H301, H331, H410
Precautionary statements	P261, P264, P270, P271, P273, P301+P310, P304+P340, P311, P321, P330, P391, P403+P233, P405, P501
NFPA 704 (fire diamond)	4 0 0
	Lethal dose or concentration (LD, LC):
LD50 (median dose)	23-100 mg/kg (rat and mouse, oral)
Safety data sheet (SDS)	External MSDS
	Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). verify (what is ?) Infobox references

Cacodylic acid is an organoarsenic compound with the formula (CH₃)₂AsO₂H. 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 herbicides. Cacodylic acid/sodium cacodylate is a buffering agent in the preparation and fixation of biological samples for electron microscopy and in protein crystallography.

History

In the 18th century it was found that combining As₂O₃ and four equivalents of potassium acetate (CH₃CO₂K) gives a product called "Cadet's fuming liquid" which contains cacodyl oxide, ((CH₃)₂As)₂O and cacodyl, ((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, ((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.^[4] 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".^[5]

Reactions

Cacodylic acid is a weak acid with a pK_a of around 6.25.^[6]

Cacodylic acid can be reduced to dimethylarsine , which is a versatile intermediate for the synthesis of other organoarsenic compounds:^[7]^[8]

(CH₃)₂AsO₂H + 2 Zn + 4 HCl → (CH₃)₂AsH + 2 ZnCl₂ + 2 H₂O

(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.^[9] Arsenic is classified as a Group-A carcinogen.^[9]

References

^ Betz, R.; McCleland, C.; Marchand, H. (2011). "CSD Entry: CADYLA01 : Dimethylarsinic acid". Cambridge Structural Database: Access Structures. Cambridge Crystallographic Data Centre. doi:10.5517/ccx73mv. Retrieved 2021-12-21.
^ ^a ^b Betz, R.; McCleland, C.; Marchand, H. (2011). "The monoclinic polymorph of dimethylarsinic acid". Acta Crystallogr. E. 67 (8): m1013. doi:10.1107/S1600536811025505. PMC 3212109. PMID 22090811.
^ Trotter, J.; Zobel, T. (1965). "826. Stereochemistry of arsenic. Part XVI. Cacodylic acid". J. Chem. Soc.: 4466–4471. doi:10.1039/JR9650004466.
^ Stanley A. Greene (2005). Sittig's Handbook of Pesticides and Agricultural Chemicals. William Andrew. p. 132. ISBN 978-0-8155-1903-4.
^ Committee to Review the Health Effects in Vietnam Veterans of Exposure to Herbicides; Institute of Medicine (1994). Veterans and Agent Orange: Health Effects of Herbicides Used in Vietnam. National Academies Press. pp. 89–90. ISBN 978-0-309-55619-4.
^ Shin, T.-W., Kim, K., Lee, I.-J. (April 1997). "Spectrophotometric determination of the acid dissociation constants for cacodylic acid and p-Nitrophenol at elevated temperatures". Journal of Solution Chemistry. 26 (4): 379–390. doi:10.1007/BF02767677. ISSN 0095-9782.
^ Feltham, R. D.; Kasenally, A.; Nyholm, R. S. (1967). "A New Synthesis of Di- and Tri-Tertiary Arsines". Journal of Organometallic Chemistry. 7 (2): 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
^ ^a ^b Dibyendu, Sarkar; Datta, Rupali (2007). "Biogeochemistry of Arsenic in Contaminated Soils of Superfund Sites". EPA. United States Environmental Protection Agency. Archived from the original on 17 March 2020. Retrieved 25 February 2018.

External links

[1] Betz, R.; McCleland, C.; Marchand, H. (2011). "CSD Entry: CADYLA01 : Dimethylarsinic acid". Cambridge Structural Database: Access Structures. Cambridge Crystallographic Data Centre. doi:10.5517/ccx73mv. Retrieved 2021-12-21.

[Betz-2] Betz, R.; McCleland, C.; Marchand, H. (2011). "The monoclinic polymorph of dimethylarsinic acid". Acta Crystallogr. E. 67 (8): m1013. doi:10.1107/S1600536811025505. PMC 3212109. PMID 22090811.

[3] Trotter, J.; Zobel, T. (1965). "826. Stereochemistry of arsenic. Part XVI. Cacodylic acid". J. Chem. Soc.: 4466–4471. doi:10.1039/JR9650004466.

[Greene2005-4] Stanley A. Greene (2005). Sittig's Handbook of Pesticides and Agricultural Chemicals. William Andrew. p. 132. ISBN 978-0-8155-1903-4.

[HerbicidesMedicine1994-5] Committee to Review the Health Effects in Vietnam Veterans of Exposure to Herbicides; Institute of Medicine (1994). Veterans and Agent Orange: Health Effects of Herbicides Used in Vietnam. National Academies Press. pp. 89–90. ISBN 978-0-309-55619-4.

[6] Shin, T.-W., Kim, K., Lee, I.-J. (April 1997). "Spectrophotometric determination of the acid dissociation constants for cacodylic acid and p-Nitrophenol at elevated temperatures". Journal of Solution Chemistry. 26 (4): 379–390. doi:10.1007/BF02767677. ISSN 0095-9782.

[7] Feltham, R. D.; Kasenally, A.; Nyholm, R. S. (1967). "A New Synthesis of Di- and Tri-Tertiary Arsines". Journal of Organometallic Chemistry. 7 (2): 285–288. doi:10.1016/S0022-328X(00)91079-9.

[8] Burrows, G. J. and Turner, E. E., "A New Type of Compound containing Arsenic", Journal of the Chemical Society Transactions, 1920, 1374-1383

[EPA1-9] Dibyendu, Sarkar; Datta, Rupali (2007). "Biogeochemistry of Arsenic in Contaminated Soils of Superfund Sites". EPA. United States Environmental Protection Agency. Archived from the original on 17 March 2020. Retrieved 25 February 2018.

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