CH3AsO

CH3AsO, also known as methylarsonic acid or methanearsonic acid, is an organoarsenic compound with the chemical formula CH3AsO. It is a colorless solid that is soluble in water and ethanol. Methylarsonic acid is an intermediate in the environmental methylation and biomethylation of arsenic. It is a monomethylated arsenic species, meaning it contains one methyl group attached to the arsenic atom.

This compound is a derivative of arsenic acid (H3AsO4) where one hydroxyl group is replaced by a methyl group. In its pure form, it exists as CH3As(O)(OH)2. Methylarsonic acid is a weak acid. It can be found in the environment as a product of microbial metabolism of inorganic arsenic. It is also used as a herbicide, particularly in cotton farming, although its use has declined due to concerns about arsenic contamination.

Methylarsonic acid is considered moderately toxic. Exposure can occur through ingestion, inhalation, or skin contact. Symptoms of exposure can include gastrointestinal distress, skin irritation, and neurological effects. Due to its toxicity and environmental persistence, regulations exist in many countries regarding its production, use, and disposal. The environmental fate of methylarsonic acid is complex, involving further transformation by microbial activity into other arsenic species, including dimethylarsinic acid and inorganic arsenic.