| IUPAC name
|Appearance||Off white or purple crystalline solid|
|Melting point||288 °C (550 °F; 561 K)|
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Sulfanilic acid is an arylsulfonic acid that is mainly used for making azo dyes, such as methyl orange, and sulfa drugs, such as sulfanilamide. It is also used in the quantitative analysis of nitrate and nitrite ions. It can be synthesized easily by sulfonation of aniline.
Sulfanilic acid is zwitterionic. It is highly soluble in basic solutions, and moderately soluble in strongly acidic solutions. Its isoelectric point is 1.25, which would be the optimum pH for precipitating and recrystallizing it. It crystallizes from water as a dihydrate, but can be dehydrated by heating.
Sulfanilic acid is a white solid when pure, but commercial and home made samples are usually off-white or even purple, due to contamination with trace amounts of strongly colored polyaniline compounds.
Sulfanilic acid may be available from some online chemical suppliers, but is not usually sold to the general public. It is more practical to make if one has access to aniline.
Synthesis of azo dyes:
Synthesis of sulfanilamide
Sulfanilic acid is not particularly dangerous but should be handled with gloves.