Arsanilic acid

Arsanilic acid
Chemical structure of arsanilic acid
Ball-and-stick model of the solid-state zwitterionic structure of arsanilic acid
IUPAC name 4-aminophenylarsonic acid
Other names 4-Aminobenzenearsonic acid, 4-Aminophenylarsonic acid, 4-Arsanilic acid, Atoxyl
style="background: #F8EABA; text-align: center;" colspan="2" | Identifiers
CAS number	98-50-0
style="background: #F8EABA; text-align: center;" colspan="2" | Properties
Molecular formula	C6H8AsNO3
Molar mass	217.054 g/mol
Appearance	white solid
Density	1.957 g/cm3
Melting point	232 °C
Solubility in water	modest
style="background: #F8EABA; text-align: center;" colspan="2" | Hazards
R-phrases	R23-R25,R50-R53 23/25-50/53
S-phrases	S20S21S28S45S60-S61
NFPA 704	75px 0 2 0
style="background: #F8EABA; text-align: center;" colspan="2" | Related compounds
Related compounds	phenylarsonic acid
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

Arsanilic acid is the organoarsenic compound also called p-aminophenylarsenic acid. This colourless solid was used as a drug in the late 19th and early 20th centuries but is now considered prohibitively toxic. Arsanilic acid is a derivative of phenylarsonic acid with an amine in the 4-position. It exists as a zwitterion, H₃N⁺C₆H₄AsO₃H⁻, although it is typically represented with the non-zwitterionic formula, H₂NC₆H₄AsO₃H₂.

Synthesis

Arsanilic acid was first reported in 1859 by Antoine Béchamp. Béchamp optimistically chose the name Atoxyl, referring to its reduced toxicity compared to arsenic. The original synthesis, which involved the reaction of aniline and arsenic acid, remains useful today:

C₆H₅NH₂ + H₃AsO₄ → H₂O₃AsC₆H₄NH₂ + H₂O

History and uses

Arsanilic acid was initially used in medicine to treat simple skin diseases. In 1905, two British physicians, H.W. Thomas and A. Breinl, reported that atoxyl was active against the trypanosomes of sleeping sickness. The effect was however not very pronounced and the necessary dosage was so high that toxic side effects far outweighed the benefits. It frequently caused blindness by damaging the optic nerve and other varied disorders. Nevertheless, the discovery of arsanilic acid's activity against trypanosomes was the basis for a major advance by the bacteriologist Paul Ehrlich. Ehrlich, who believed that the formula was incorrect, and the organic chemist Alfred Bertheim revised the structural assignment. The correct formula suggested new ways that the atoxyl molecule could be modified, and a series of such derivatives were then synthesized. Testing for anti-syphilitic activity was performed by Sahachiro Hata who worked in Ehrlich's lab. The result of this collaboration was the discovery of the drug Salvarsan in 1909, which also was later abandoned but which accelerated the growth of medicinal chemistry.

Although the practice is controversial, arsanilic acid and related compounds are sometimes used in treating dysentery in swine.

External links

• Atoxyl at Chemical Heritage More about the origins and uses of the medicine.
• Explorers of the Body Some info about sleeping sickness and atoxyl.
• Arsonic Acid poisoning information.
• Ihde, Aaron J. The Development of Modern Chemistry, Dover, New York, 1984. pp. 697-698.ar:أتوكسيل

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