Methylarsonic acid

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Methylarsonic acid
MeAsO3H2.png
Names
Preferred IUPAC name
Methylarsonic acid [1]
Other names
Methanearsonic acid
Monomethylarsonic acid
Identifiers
3D model (JSmol)
4-04-00-03682
ChemSpider
ECHA InfoCard 100.004.278 OOjs UI icon edit-ltr-progressive.svg
EC Number
  • 204-705-6
PubChem CID
RTECS number
  • PA1575000
UNII
UN number 1557
  • InChI=1S/CH5AsO3/c1-2(3,4)5/h1H3,(H2,3,4,5)
    Key: QYPPRTNMGCREIM-UHFFFAOYSA-N
  • C[As](=O)(O)O
Properties
CH5AsO3
Molar mass 139.970 g·mol−1
Appearancewhite 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).

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 herbicides and fungicides in growing cotton and rice. [2]

Contents

Reactions

Near physiological pH, methanearsonic acid converts to its conjugate bases, the methylarsonates. These include CH3AsO3H− and CH
3AsO2−
3.

Synthesis and biosynthesis

Reaction of arsenous acid with methyl iodide gives methylarsonic acid. This historically significant conversion is called the Meyer reaction: [3]

As(OH)3 + CH3I + NaOH → CH3AsO(OH)2 + NaI + H2O

The then-novel aspect of the reaction was that alkylation occurs at arsenic, leading to oxidation of arsenic from oxidation state +3 to +5.

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. [4]

Safety

Like most arsenic compounds, it is highly toxic. [4]

References

  1. ↑ International Union of Pure and Applied Chemistry (2014). Nomenclature of Organic Chemistry: IUPAC Recommendations and Preferred Names 2013. The Royal Society of Chemistry. pp. 916, 918. doi:10.1039/9781849733069. ISBN   978-0-85404-182-4.
  2. ↑ Grund, S. C.; Hanusch, K.; Wolf, H. U. "Arsenic and Arsenic Compounds". Ullmann's Encyclopedia of Industrial Chemistry . Weinheim: Wiley-VCH. doi:10.1002/14356007.a03_113.pub2. ISBN   978-3-527-30673-2.
  3. ↑ G. Meyer (1883). "Ueber einige anomale Reaktionen". Berichte der deutschen chemischen Gesellschaft. 13: 1439–1443. doi:10.1002/cber.188301601316.
  4. 1 2 Styblo, M.; Del Razo, L. M.; Vega, L.; Germolec, D. R.; LeCluyse, E. L.; Hamilton, G. A.; Reed, W.; Wang, C.; Cullen, W. R.; Thomas, D. J. (2000). "Comparative toxicity of trivalent and pentavalent inorganic and methylated arsenicals in rat and human cells". Archives of Toxicology. 74: 289–299. doi:10.1007/s002040000134.
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