Cacodylic acid

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 defoliants in the Vietnam War, was 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 transmission electron microscopy.

History
Significant early research into cacodyls was done by R. W. 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 radical.

Cacodyloxide, ((CH3)2As)2O, is often considered the first organometallic compound to be prepared synthetically.

Synthesis and reactions
In the 1700s 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.

Cacodylic acid can be reduced to dimethylarsine (III) derivatives, which are versatile intermediates for the synthesis of other organoarsenic compounds:
 * (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. 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, cacodylic acid does promote tumors in the presence of carcinogens in organs such as the kidneys and liver.