Sulfanilic acid

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Sulfanilic acid
Skeletal formula of sulfanilic acid
Ball-and-stick model of sulfanilic acid
Sample of Sulphanilic acid.jpg
IUPAC name
p-aminobenzenesulphonic acid
Other names
Sulphanilic acid
121-57-3 YesY
Jmol-3D images Image
PubChem 8479
Molar mass 173.19
Density 1.485
Melting point 288 °C (550 °F; 561 K)
12.51 g/L
Acidity (pKa) 3.01
Related compounds
Related sulfonic acids
Benzenesulfonic acid
Except where noted otherwise, data is given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
 N verify (what isYesY/N?)
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]


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

Synthetic route of sulfanilic acid from aniline.png


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]

Diazo coupling of sulfanilic acid and N-1-(Naphthyl)ethylenediamine.png

It is also used as a standard in combustion analysis and in the Pauly reaction.


  1. ^ a b "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.