Organoarsenic chemistry
In general these applications are declining in step with growing concerns about their impact on the environment and human health.
[2] Arsenic typically occurs in the oxidation states (III) and (V), illustrated by the halides AsX3 (X = F, Cl, Br, I) and AsF5.
Compounds of arsenic(V) containing only organic ligands are rare, the pre-eminent member being the pentaphenyl derivative As(C6H5)5.
Akin to the Direct process in organosilicon chemistry, methyl halides react with elemental As, as illustrated in the following idealized equation:[5] Such reactions require copper catalysts, are conducted near 360 °C.
Symmetrical organoarsenic(III) compounds, e.g. trimethylarsine and triphenylarsine, are commonly used as ligands in coordination chemistry.
They are observed in the gas phase but considerable steric protection is required to inhibit their conversion to oligomers as liquids or solids.
[6]: 318 For example, methylarsine oxidizes first to cyclo-methylarsine(I): These compounds have structures similar to the phosphorus sulfides.
Arsenic-arsenic bonds are very weak, and oligomeric arsenic compounds are even more liable to oxidize than their hydrogenated precursors.
[6]: 662–672 Organoarsenic compounds, especially those featuring As-Cl bonds, have been used as chemical weapons, especially during World War I. Infamous examples include "Lewisite" (chlorovinyl-2-arsenic dichloride) and "Clark I" (chlorodiphenylarsine).
As arsenic is toxic to most life forms and it occurs in elevated concentration in some areas several detoxification strategies have evolved.
[9] For example, the mold Scopulariopsis brevicaulis produces significant amounts of trimethylarsine if inorganic arsenic is present.
[12] Arsenobetaine was first identified in the Western rock lobster[13][14] Saccharides bound to arsenic, collectively known as arsenosugars, are found especially in seaweeds.
The only polyarsenic compound isolated from a natural source is arsenicin A, found in the New Caledonian marine sponge Echinochalina bargibanti.
