Organoarsenic

Organoarsenic chemistry is the chemistry of compounds containing a chemical bond between arsenic and carbon. A few organoarsenic compounds, also called "organoarsenicals," are produced industrially with uses as insecticides, herbicides, and fungicides. In general these applications are declining in step with growing concerns about their impact on the environment and human health. The parent compounds are arsine and arsenic acid. Despite their toxicity, organoarsenic biomolecules are well known.

Surprising for an area now considered of minor importance, organoarsenic chemistry played a prominent role in the history of the field of chemistry. The oldest known organoarsenic compound, the foul smelling cacodyl was reported in "cacodyl" (1760) and is sometimes classified as the first synthetic organometallic compound. The compound Salvarsan was one of the first pharmaceuticals, earning a Nobel prize for Paul Ehrlich. Various other organoarsenic compounds formerly found use as antibotics (Solarson) or other medical uses.

Arsenic typically occurs in the oxidation states (III) and (V), illustrated by the halides AsX₃ (X = F, Cl, Br, I) and AsF₅. Correspondingly, organoarsenic compounds are commonly found in these two oxidation states.

Arsenic(V) compounds typically feature the functional groups RAsO(OH)₂ or R₂AsO(OH) (R = alkyl or aryl). Cacodylic acid, with the formula (CH₃)₂AsO₂H, figures prominently throughout the chemistry of organoarsenic compounds. In contrast, the dimethylphosphonic acid is less significant in the corresponding chemistry of phosphorus. Cacodylic acid arises from the methylation of arsenic(III) oxide. Phenylarsonic acids can be accessed by the reaction of arsenic acid with anilines, the so-called Bechamp reaction.

...
Wikipedia