Sulfanilic acid

Sulfanilic acid
IUPAC name p-aminobenzenesulphonic acid
Other names Sulphanilic acid
Identifiers
CAS number	121-57-3 Y
PubChem	8479
	ChEBI	CHEBI:27500 Y
Jmol-3D images	Image 1
SMILES C1=CC(=CC=C1N)S(=O)(=O)O
InChI InChI=InChI=1/C6H7NO3S/c7-5- 1-3-6(4-2-5)11(8,9)10/h1-4H, 7H2,(H,8,9,10)/f/h8H
Properties
Molecular formula	C6H7NO3S
Molar mass	173.19
Density	1.485
Melting point	288 °C; 550 °F; 561 K
Solubility in water	>20 g/l
Acidity (pKa)	3.01
Related compounds
Related sulfonic acids	Benzenesulfonic acid p-Toluenesulfonic_acid
Y (verify) (what is: Y/N?) Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
Infobox references

Sulfanilic acid (4-aminobenzenesulfonic acid ) is an off-white crystalline solid which finds application in quantitative analysis of nitrate and nitrite ions. The solid acid exists as a zwitterion, and has an unusually high melting point. ^[1]

Synthesis

Sulfanilic acid can be produced by sulfonation of aniline:^[2]

Applications

As the compound readily form diazo compounds, it is used to make dyes and sulpha drugs. ^[1] This property is also used for the quantitative analysis of nitrate and nitrite ions by diazonium coupling reaction with N-(1-Naphthyl)ethylenediamine, resulting in an azo dye, and the concentration of nitrate or nitrite ions were deduced from the color intensity of the resulting red solution by colorimetry. ^[3]

It is also used as a standard in combustion analysis.

References

1. ↑ 1.0 1.1 "Sulphanilic acid". A Dictionary of Chemistry. Oxford University Press, 2000. Oxford Reference Online. Oxford University Press.
2. ↑ Siegfried Hauptmann: Organische Chemie, 2nd Edition, VEB Deutscher Verlag für Grundstoffindustrie, Leipzig, 1985, p. 511, ISBN 3-342-00280-8.
3. ↑ G. H. Jerffery; J. Bassett; J. Mendham; R. C. Denney (1989). "Colorimetry and Spectrophotometry". Vogel's Textbook of Quantitative Chemical Analysis, 5th Edition. Longman. p. 702. ISBN 0-582-44693-7.