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Phenylarsonic acid

Phenylarsonic acid
IUPAC name Phenylarsonic acid
Other names Benzenearsonic acid
CAS number 98-05-5
Molecular formula C6H7AsO3
Molar mass 202.05
Appearance colourless solid
Density 1.76 g/cm3
Melting point

154–158° °C

Solubility in water low
Main hazards Toxic
Except where noted otherwise, data are given for
materials in their standard state
(at 25 °C, 100 kPa)

Infobox disclaimer and references

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 This colourless solid is an organic derivative of arsenic acid, AsO(OH)3, where one OH group has been replaced by a phenyl group.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.

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).


  1. ^ Bullard, R. H.; Dickey, J. B. “Phenylarsonic Acid” Organic Syntheses, Collected Volume 2, pages 494 (1943).
  2. ^ Ruddy, A. W.; Starkey, E. B. “p-Nitrophenylarsonic Acid” Organic Syntheses, Collected Volume 3, pp. 665 (1955).
  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
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Phenylarsonic_acid". A list of authors is available in Wikipedia.
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