2-Hydroxynaphthalene-3,6,8-trisulfonic acid [6259-66-1]. (7-hydroxynaphthalene-1,3,6-trisulfonic acid), C10H8O10S3, Mr 384.3, and its alkali-metal salts are readily soluble in water; nevertheless, the sodium salt is obtainable by salting out. Amination at 240℃ gives 2-aminonaphthalene-3,6,8-trisulfonic acid. Alkali fusion gives a mixture of dihydroxynaphthalenedisulfonic acids and finally 4,6,7- trihydroxynaphthalene-2-sulfonic acid. Diazo coupling occurs slowly in the 1-position.
2-Naphthol is heated with sulfuric acid monohydrate at 115℃ for 3 h. The reaction mixture is cooled and 65 % oleum is added, followed by heating at 115℃ for 12 h, after which it is poured into water. Salt is then added to the hot solution and the sodium salt of the product crystallizes. Further purification is effected by redissolving in water and salting out.
