Cacodylic acid

Cacodylic acid
Structural formula
Ball-and-stick model
Names
IUPAC name
Dimethylarsinic acid
Other names
Dimethylarsenic acid, Cacodylic acid, Hydroxydimethylarsine oxide, Arsecodile, Ansar, Silvisar, Phytar 560, DMAA, UN 1572
Identifiers
3D model (JSmol)
ChEBI
ChemSpider
DrugBank
ECHA InfoCard 100.000.804
EC Number 200-883-4
KEGG
RTECS number CH7525000
UNII
Properties
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)
66.7 g/100 ml
Solubility soluble in ethanol, acetic acid
insoluble in diethyl ether
Acidity (pKa) 6
-79.9·10−6 cm3/mol
Structure
triclinic
Hazards
Safety data sheet External MSDS
T+
R-phrases (outdated) R26/27/28, R40
Lethal dose or concentration (LD, LC):
700 mg/kg (rat, oral)
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

Cacodylic acid is the organoarsenic compound with the formula (CH3)2AsO2H. With the formula R2As(O)OH, it is the simplest of the organoarsinic acids. Derivatives of cacodylic acid, cacodylates, were frequently used as herbicides. For example, "Agent Blue," one of the chemicals used during the Vietnam War, is a mixture of cacodylic acid and sodium cacodylate. Sodium cacodylate is frequently used as a buffering agent in the preparation and fixation of biological samples for electron microscopy. Its molecule includes an atom of the highly-toxic metalloid arsenic.

History

Significant early research into cacodyls was done 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 large variety of manufacturers under numerous brand names. APC Holdings Corp. sold cacodylic acid and its salts under the Phytar brand name.[1] The variety used in Vietnam (as Agent Blue) was Phytar 560G.[2]

Synthesis

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.

Reactions

Cacodylic acid is a weak acid with a pKa of 6.[3]

Cacodylic acid can be reduced to dimethylarsine(III) derivatives, which are versatile intermediates for the synthesis of other organoarsenic compounds:[4][5]

(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.[6] Arsenic is classified as a Group-A carcinogen.[6]

See also

References

  1. ↑ Stanley A. Greene (2005). Sittig's Handbook of Pesticides and Agricultural Chemicals. William Andrew. p. 132. ISBN 978-0-8155-1903-4.
  2. ↑ 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.
  3. ↑ Henry B.F.Dixon (1996). "The Biochemical Action of Arsonic Acids Especially As Phosphate Analogues". Advances in Inorganic Chemistry. 44. pp. 191–227. doi:10.1016/S0898-8838(08)60131-2.
  4. ↑ Feltham, R. D.; Kasenally, A.; Nyholm, R. S. (1967). "A New Synthesis of Di- and Tri-Tertiary Arsines". Journal of Organometallic Chemistry. 7: 285–288.
  5. ↑ Burrows, G. J. and Turner, E. E., "A New Type of Compound containing Arsenic", Journal of the Chemical Society Transactions, 1920, 1374-1383
  6. 1 2 Dibyendu, Sarkar; Datta, Rupali (2007). "Biogeochemistry of Arsenic in Contaminated Soils of Superfund Sites". EPA. United States Environmental Protection Agency. Retrieved 25 February 2018.
  • Kenyon, E. M.; Hughes, M. F. (2001). "A Concise Review of the Toxicity and Carcinogenicity of Dimethylarsenic Acid". Toxicology. 160 (1–3): 227–236. doi:10.1016/S0300-483X(00)00458-3.
  • Elschenbroich, C; Salzer, A. (1992) Organometallics, 2nd Edition
  • Bunsen Biography
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