Sulfanilic acid

Description

Sulfanilic acid (4-amino benzene sulfonic 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.

Chemical properties

Sulfanilic acid is a greyish-white crystals or powder. As the compound readily form 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) ethylene diamine , 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.

The Uses of Sulfanilic acid

Sulfanilic Acid (Sulfadimethoxine EP Impurity D) is a toxic metabolite of Tartrazine (T007700). Used as Ehrlich’s reagent, for detecting of nitrites. Antibacterial.

The Uses of Sulfanilic acid

Sulfanilic acid may be used for the functionalization of single-walled carbon nanotubes (SWNTs) with aryl sulfonate groups.

Definition

ChEBI: An aminobenzenesulfonic acid that is aniline sulfonated at the para-position.

General Description

White powder with faint purple tinge. Grayish-white flat crystals. Becomes anhydrous at around 212°F. Low toxicity (used medicinally).

Air & Water Reactions

Insoluble in water.

Reactivity Profile

Sulfanilic acid is an amino acid. Reacts weakly with both acids and bases.

Fire Hazard

Flash point data for Sulfanilic acid are not available, however Sulfanilic acid is probably combustible.

Synthesis

Sulfanilic acid can be produced by sulfonation of aniline.

Purification Methods

Crystallise the acid (as dihydrate) from boiling water. Dry it at 105o for 2-3hours, then over 90% H2SO4 in a vacuum desiccator. The S-benzylisothiuronium salt has m 187o (from aqueous EtOH). [Beilstein 14 IV 2655.]