NH2C6H4SO3H

NH2C6H4SO3H is the chemical formula for sulfanilic acid, also known as 4-aminobenzenesulfonic acid. It is an organic compound consisting of a benzene ring substituted with both an amino group (NH2) and a sulfonic acid group (SO3H). The amino group is typically in the para position relative to the sulfonic acid group, hence the name 4-aminobenzenesulfonic acid.

Sulfanilic acid is a white crystalline solid that is sparingly soluble in water. It is amphoteric, meaning it can act as both an acid and a base due to the presence of the acidic sulfonic acid group and the basic amino group. It exists primarily as a zwitterion in solid form and in neutral aqueous solutions, where the proton from the sulfonic acid group transfers to the amino group.

This compound is an important intermediate in the synthesis of many dyes, pharmaceuticals, and other organic chemicals. Its diazonium salt, formed by reaction with nitrous acid, is crucial in the azo coupling reaction to produce azo dyes, a large and commercially important class of colorants. Sulfanilic acid is also used in some analytical chemistry procedures, such as the determination of nitrite ions. Its production typically involves the sulfonation of aniline.