84-86-6

slightly greyish to beige powder and granules

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.

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.]