Phenylarsonic acid

Phenylarsonic acid is the chemical compound with the formula C₆H₅AsO(OH)₂, commonly abbreviated PhAsO₃H₂. This colourless solid is an organic derivative of arsenic acid, AsO(OH)₃, where one OH group has been replaced by a phenyl group. The compound is a buffering agent and a precursor to other organoarsenic compounds, some of which are used in animal nutrition, e.g. 4-hydroxy-3-nitrobenzenearsonic acid.

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Preparation and structure

PhAsO₃H₂ can be prepared in several routes, but a common one entails treatment of phenyl diazonium salts with sodium arsenite (prepared from arsenious acid and base) in the presence of a copper(II) catalyst.^[1]

C₆H₅N₂⁺ + NaAsO₃H₂ → C₆H₅AsO₃H₂ + Na⁺ + N₂

Related derivatives are prepared similarly.^[2] It was first prepared by Michaelis and Loenser.^[3][4][5] X-ray crystallography indicates that the molecules are connected by hydrogen-bonds consistent with short distance of 2.5 Å separating the oxygen atoms. The arsenic center is tetrahedral.^[6]

Related phenylarsonic acids

Several derivatives of phenylarsonic acid have been used as additives for animal feeds. These include 4-hydroxy-3-nitrobenzenearsonic acid (3-NHPAA, or Roxarsone), p-arsanilic acid (p-ASA), 4-nitrophenylarsonic acid (4-NPAA), and p-ureidophenylarsonic acid (p-UPAA).

References

1. ^ Bullard, R. H.; Dickey, J. B. “Phenylarsonic Acid” Organic Syntheses, Collected Volume 2, pages 494 (1943). http://www.orgsyn.org/orgsyn/pdfs/CV2P0494.pdf
2. ^ Ruddy, A. W.; Starkey, E. B. “p-Nitrophenylarsonic Acid” Organic Syntheses, Collected Volume 3, pp. 665 (1955). http://www.orgsyn.org/orgsyn/pdfs/CV3P0665.pdf
3. ^ A. Michaelis, H. Loesner (1877). "Ueber nitrirte Phenylarsenverbindungen". Berichte der deutschen chemischen Gesellschaft 27: 263-272. doi:10.1002/cber.18940270151.
4. ^ A. Michaelis (1875). "Ueber aromatische Arsenverbindungen". Berichte der deutschen chemischen Gesellschaft 8: 1316-1317. doi:10.1002/cber.187500802125.
5. ^ A. Michaelis, W. La Coste, A. Michaelis (1880). "Ueber die Verbindungen der Elemente der Stickstoffgruppe mit den Radicalen der aromatischen Reihe. Dritte Abhandlung: Ueber aromatische Arsenverbindungen". Annalen der Chemie 201 (2-3): 184-261. doi:10.1002/jlac.18802010204.
6. ^ Struchkov, Yu T. “Crystal and molecular structure of phenylarsonic acid” Russian Chemical Bulletin 1960, Volume 9, 1829-1833. doi:10.1007/BF00907739