Methanearsonate

Methylarsonic acid

Names
Other names methanearsonic acid
Identifiers
CAS Number	124-58-3
3D model (JSmol)	Interactive image
Beilstein Reference	4-04-00-03682
ChemSpider	8604
EC Number	204-705-6
PubChem CID	8948
RTECS number	PA1575000
UNII	J37VJ5709S
UN number	1557
InChI InChI=1S/CH5AsO3/c1-2(3,4)5/h1H3,(H2,3,4,5) Key: QYPPRTNMGCREIM-UHFFFAOYSA-N
SMILES C[As](=O)(O)O
Properties
Chemical formula	CH5AsO3
Molar mass	139.97 g·mol−1
Appearance	white solid
Melting point	160.5 °C (320.9 °F; 433.6 K)
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references

Methylarsonic acid is an organoarsenic compound with the formula CH₃AsO₃H₂. It is a colorless, water-soluble solid. Salts of this compound, e.g. disodium methyl arsonate, have been widely used in as a herbicides and fungicides in growing cotton and rice.

Near physiological pH, methanearsonic acid converts to its conjugate bases, the methylarsonates. These include CH₃AsO₃H⁻ and CH₃AsO₃²⁻. The biomethylation of arsenic compounds is thought to start with the formation of methanearsonates. Thus, trivalent arsenic compounds are methylated to give methanearsonate. S-adenosylmethionine is the methyl donor. The methanearsonates are the precursors to cacodylates, again by the cycle of reduction (to methylarsonous acid) followed by a second methylation.

Like all arsenic compounds, it is highly toxic.