1-Aminonaphthalene-3,8-disulfonic acid [129-91-9]. (8-aminonaphthalene-1,6- disulfonic acid), amino epsilon acid, C10H9NO6S2, Mr 303.3, and its sodium salt are very soluble in water, but the barium salt is only sparingly soluble. Reduction with zinc and alkali (or with sodium amalgam) desulfonates to give 1-aminonaphthalene-3-sulfonic acid. The amino group is hydrolyzed by water at 180℃ to give 1-hydroxynaphthalene-3,8-disulfonic acid. Caustic fusion results in 1-amino-8-hydroxynaphthalene-3-sulfonic acid, whereas reaction with 10 % sodium hydroxide at 250℃ produces 1,8-dihydroxynaphthalene-3-sulfonic acid. Amination produces 1,3-diaminonaphthalene-8-sulfonic acid, but the production of 6,8- di(phenylamino)naphthalene-1-sulfonic acid (diphenyl epsilon acid) by reaction with aniline is more important.
Naphthalene is sulfonated under conditions that give predominately the 1,6- disulfonic acid. The sulfonation mass is nitrated with H2SO4–HNO3 at 30 – 40 ℃. After addition of dolomite and neutralization with lime, the liquor is reduced with iron and basified with magnesia, and the iron residues are removed. Careful adjustment of temperature and acidity precipitates the product as the acid magnesium salt, which is purified by dissolution in aqueous sodium carbonate and removal of magnesium carbonate; the diacid is precipitated with acid in 32 % overall yield.
