Sulfanilic acid


Sulfanilic 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.

Synthesis

Sulfanilic acid can be produced by sulfonation of aniline:

Applications

As the compound readily forms diazo compounds, it is used to make dyes and sulfa drugs. This property is also used for the quantitative analysis of nitrate and nitrite ions by diazonium coupling reaction with N-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.

Derivatives

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.