2-Aminonaphthalene-1-sulfonic acid

Chemical properties

Grey white to light pink powder. 2-Aminonaphthalene-1-sulfonic acid [81-16-3].  Tobias acid, C10H9NO3S, Mr 223.24, is sparingly soluble in water but the sodium salt is readily soluble. Coupling with diazo compounds takes place in the 1-position with elimination of the sulfonic acid group.

The Uses of 2-Aminonaphthalene-1-sulfonic acid

Azo dye intermediate, optical brighteners.

The Uses of 2-Aminonaphthalene-1-sulfonic acid

2-Amino-1-naphthalenesulfonic acid has been used in the preparation of 2-(2-naphthylamino)benzoxazole by reacting with 2-chlorobenzoxazole.

Production Methods

2-Hydroxynaphthalene-1-sulfonic acid is heated with a mixture of ammonia and ammonium sulfite in an autoclave at 150 ℃ and 1 MPa for 30 h. The reaction mixture is added to a slurry of lime, and excess ammonia is driven off. Inorganic calcium salts are filtered off at 80℃, and the filtrate is acidified with hydrochloric acid at 40℃ to precipitate Tobias acid in 95 % yield. Care must be taken throughout the process to avoid desulfonation and formation of 2- naphthylamine.

General Description

2-Amino-1-naphthalenesulfonic acid is a manufacturing intermediate in the monosulfo monoazo color additive D&C Red No. 34 and its lakes.

Purification Methods

Crystallise the acid under nitrogen from boiling water and dry it in a steam oven [Bryson Trans Faraday Soc 47 522, 527 1951]. [Beilstein 14 III 2240, 14 IV 2792.]