Cacodylic acid

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Cacodylic acid
Structural formula
Ball-and-stick model
IUPAC name
Dimethylarsinic acid
Other names
Dimethylarsenic acid, Cacodylic acid, Hydroxydimethylarsine oxide, Arsecodile, Ansar, Silvisar, Phytar 560, DMAA, UN 1572
3D model (JSmol)
ECHA InfoCard 100.000.804
EC Number 200-883-4
RTECS number CH7525000
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) 1.57
-79.9·10−6 cm3/mol
Safety data sheet External MSDS
Very Toxic 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R-phrases (outdated) R26/27/28, R40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 chemical compound with the formula (CH3)2AsO2H. 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.


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 and reactions[edit]

In the 18th century it was known 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.

Cacodylic acid can be reduced to dimethylarsine (III) derivatives, which are versatile intermediates for the synthesis of other organoarsenic compounds:[3][4]

(CH3)2AsO2H + 2 Zn + 4 HCl → (CH3)2AsH + 2 ZnCl2 + 2 H2O
(CH3)2AsO2H + SO2 + HI → (CH3)2AsI + SO3 + H2O

Health effects[edit]

Cacodylic acid is highly toxic by ingestion, inhalation, or skin contact. Once thought to be a byproduct of inorganic arsenic detoxification, it is now believed to have serious health consequences of its own. It has been shown to be teratogenic in rodents, most often causing cleft palate but also fetal fatality at high doses. It has been shown to be genotoxic in human cells, causing apoptosis and also decreased DNA production and shorter DNA strands. While not itself a strong carcinogen[citation needed], cacodylic acid does promote tumors in the presence of carcinogens in organs such as the kidneys and liver.

The 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.[5] Arsenic is classified as a Group-A carcinogen.[5] The EPA states[6] that:

Arsenate (AsV) is the oxidized form and occurs in well-aerated soils, whereas in chemically-reduced soil environments, arsenite (AsIII) is the prevalent As form. Although arsenite is more toxic than arsenate, arsenate can also have deleterious effects on humans, plants, and microorganisms. Arsenic-contaminated soils pose serious risk to human health.

The EPA also states that, while contaminated soil poses a serious risk to health, arsenic frequently mobilizes from soils and other sources, ending up in water where it is even more of a toxicity issue.[5]

See also[edit]


  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. ^ Feltham, R. D.; Kasenally, A. and Nyholm, R. S., "A New Synthesis of Di- and Tri-Tertiary Arsines", Journal of Organometallic Chemistry, 1967, volume 7, 285-288.
  4. ^ Burrows, G. J. and Turner, E. E., "A New Type of Compound containing Arsenic", Journal of the Chemical Society Transactions, 1920, 1374-1383
  5. ^ a b c Dibyendu, Sarkar; Datta, Rupali (2007). "Biogeochemistry of Arsenic in Contaminated Soils of Superfund Sites". EPA. United States Environmental Protection Agency. Retrieved 25 February 2018. 
  6. ^ Carelton, James (2007). "Final Report: Biogeochemistry of Arsenic in Contaminated Soils of Superfund Sites". EPA. United States Environmental Protection Agency. Retrieved 25 February 2018. 

External links[edit]