Sulfanilic acid

• 4- aminobenzenesulfonic
• 4- Aminobesilat
• Aniline -4-sulfonic
• P- aminobenzenesulfonic
• P- aniline sulfonic acid

White crystalline solid

Fixed

1.485 g · cm -3 ( 25 ° C)

Decomposition at 288 ° C

Slightly soluble in water: 10 g · l -1 ( 20 ° C)

Attention

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Sulfanilic acid is the common name for 4- aminobenzenesulfonic. Aminobenzenesulfonic acids are important industrial intermediates in the synthesis of organic, water-soluble dyes. Because of the high acidity of the sulfonic acid is, in contrast to the aminocarboxylic acids, its isoelectric point (IEP ) in the acid.

Synthesis

It is obtained by sulfuric acid with aniline heated to 190 ° C. So that a sulfonic acid in an electrophilic substitution in the para position to the amino group is bound to the benzene ring.

Through a pre-equilibrium of the autoionization of sulfuric acid H3SO4 ions arise:

This can eliminate water and it forms HSO3 as electrophile can attack the ring in ortho- or para -position to the amino group protonated.

Use

Sulfanilic acid is required for the production of Lunges reagent for nitrite and nitrate detection.

In addition, it is used in the synthesis of azo dyes, such as methyl orange. It is also a primary standard, according to pharmacopoeia.

Of special importance is sulfanilic acid as a starting material for the preparation of chemotherapeutic agents from the group of sulfonamides.