1-Amino-8-hydroxynaphthalene-3,6-disulfonic acid [90-20-0]. (4-amino-5-hydroxynaphthalene-2,7-disulfonic acid), H acid, C10H9NO7S2, Mr 319.3, is usually isolated as its monosodium salt [5460-09-3], a gray powder that is slightly soluble in cold water and readily soluble in hot water; the disodium salt is very soluble in water. With diazo compounds, H acid couples ortho to the amino group under acid conditions and ortho to the hydroxyl group under alkaline conditions. Bisazo derivatives are formed by stepwise acid and alkaline coupling, with the much slower acid coupling being performed first.
4-Amino-5-hydroxy-2,7-naphthalenedisulfonic Acid is useful for preparing reactive dyes.
A slightly alkaline solution of Na2CO3 (ca 22g) in water (litmus) is added to a solution of 100g of the dry acid in 750mL of hot distilled water, followed by 5g of activated charcoal and 5g of Celite. The suspension is stirred for 10minutes and filtered by suction. The acid is then precipitated by adding ca 40mL of conc HCl (solution is blue to Congo Red), then filter it by suction through a shark skin filter circular sheet (or hardened filter paper) and wash it with 100mL of distilled water. The purification process is repeated. The acid is dried overnight in an oven at 60o and stored in a dark bottle The diethylamine salt has m 306-307o(dec, from aqueous EtOH). [Post & Moore Anal Chem 31 1872 1959]. [Beilstein 14 H 840, 14 I 758, 14 II 502, 14 III 2292, 14 IV 2824.]
