?slightly greyish to beige powder and granules. 1-Aminonaphthalene- 4 -sulfonic acid [84- 86-6]. (4-aminonaphthalene-1-sulfonic acid), naphthionic acid, Piria’s acid, C10H9NO3S, Mr 223.24, is sparingly soluble in water (0.25 % at 100℃), but the sodium, potassium, calcium, and barium salts are all readily soluble. Chlorination of 1-Aminonaphthalene- 4 -sulfonic acid with copper(II) chloride produces 4-chloro-1-aminonaphthalene, whereas the action of chlorine on an aqueous sulfuric acid solution gives 2,3-dichloro-1,4-naphthoquinone. High-temperature bromination gives 2,4- dibromo-1-aminonaphthalene, whereas vigorous nitration yields 2,4-dinitro-1-hydroxynaphthalene. Sulfonation with 25 % oleum gives 1-aminonaphthalene-4,6- and 4,7-disulfonic acids, whereas prolonged heating with sulfuric acid at 130℃ leads to 1-aminonaphthalene-5- and 6- sulfonic acids. Hydrolysis of the 1-amino group to give 1-hydroxynaphthalene-4-sulfonic acid is best achieved by a reverse-Bucherer reaction but also results from prolonged heating with 50 % sodium hydroxide.
4-Amino-1-naphthalenesulfonic acid has potent therapeutic applications. Its sodium salt has been used as non-toxic hemostatic. It is also a metabolite of azo dyes.
Intermediate for azo dyes, e.g., Congo red. Naphthionic acid is used as an intermediate in the production of 1-hydroxynaphthalene-4-sulfonic acid, 1-aminonaphthalene-2-sulfonic acid, and 1-aminonaphthalene-4,6- and 4,7-disulfonic acids. Use as a diazo component has been previously described, e.g., C.I. Food Red 3, C.I. Food Red 7, C.I. Food Red 9, and C.I. Acid Red 25.
ChEBI: Naphthionic acid is an aminonaphthalenesulfonic acid.
Naphthionic acid was first prepared by PIRIA by heating 1-nitronaphthalene with ammonium sulfite; however, the formation of 1-aminonaphthalene-2,4-disulfonic acid and other byproducts makes this route unattractive for large-scale production. Although it can also be prepared by direct sulfonation of 1-naphthylamine, it is more conveniently produced by a solvent-bake process. 1-Naphthylamine is dissolved in o-dichlorobenzene and H2SO4 (molar ratio 1 : 1) added to form a suspension of the sulfate. After being heated gradually to 180℃, the reaction is completed by maintaining this temperature until all the water of reaction has been distilled off with solvent recycle. The product is extracted from the final mixture by addition to aqueous sodium carbonate solution. After separation, the aqueous layer is steam distilled to remove residual solvent, and the product is salted out, filtered, and washed with brine to give sodium naphthionate as a paste in 90 % yield.
4-Amino-1-naphthalenesulfonic acid is a diazo compound. It is also known as Piria′s acid.
It crystallises from H2O as needles of the 0.5 hydrate. Salt solutions fluoresce strongly blue. The S-benzylisothiuronium salt has m 195o (from aqueous EtOH). [Beilstein 14 IV 2793.]
