Description
1-Aminonaphthalene-3,6-sulfonic acid [6251-07-6]. (4-aminonaphthalene-2,7- disulfonic acid), Freund’s acid(1,3,6), C10H9NO6S2, Mr 303.3, and its salts are readily soluble in water. Caustic fusion results in a mixture of aminonaphtholsulfonic acids, but amination occurs selectively, producing 1,3-diaminonaphthalene-6-sulfonic acid.
Production Methods
Naphthalene is sulfonated with sulfuric acid at 160℃ for 14 h to give a mixture of mainly 2,6- and 2,7-disulfonic acids. The reaction mass is nitrated with H2SO4–HNO3 at 30℃, poured into water, and limed out. The filtrate is then reduced with iron and hydrochloric acid, and the reduction liquor is worked up to selectively salt out the sodium salt of 1-aminonaphthalene-3,7-disulfonic acid in 17.5 % yield. The filtrates and brine wash are then acidified to precipitate crude 1-aminonaphthalene-3,6-disulfonic acid, which is purified by dissolution in aqueous potassium hydroxide and precipitation with acid; the yield is 35 %.
