Sulfanilic acid

Sulfanilic acid

Names
Preferred IUPAC name 4-Aminobenzene-1-sulfonic acid
Other names 4-Aminobenzenesulfonic acid p-Aminobenzenesulfonic acid Sulfanilic acid (not retained)
Identifiers
CAS Number	121-57-3 Y
3D model (JSmol)	Interactive image
ChEBI	CHEBI:27500 N
ECHA InfoCard	100.004.075
PubChem CID	8479
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
SMILES C1=CC(=CC=C1N)S(=O)(=O)O
Properties
Chemical formula	C6H7NO3S
Molar mass	173.19
Density	1.485
Melting point	288 °C (550 °F; 561 K)
Solubility in water	12.51 g/L
Acidity (pKa)	3.25 at 298K
Related compounds
Related sulfonic acids	Benzenesulfonic acid p-Toluenesulfonic acid
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
N  (what is YN ?)
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.

Sulfanilic acid can be produced by sulfonation of aniline:

As the compound readily forms diazo compounds, it is used to make dyes and sulpha drugs. 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.

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

Sulfanilic acid has four primary end uses. It is used as an intermediate in the production of yellow food dye, specific pharmaceutical applications, optical brighteners for white paper and as a concrete additive. The sulfanilic acid intermediate can be purchased in four different grades - technical grade, pure grade, sodium sulfanilate solution and sodium sulfanilate dry powder.