90-40-4

2-Amino-8-hydroxynaphthalene-3,6-disulfonic acid [90-40-4]. (3-amino-5-hydroxy2,7-disulfonic acid), RR acid, 2 R acid, Columbia acid, C10H9NO7S2, Mr 319.3, and its alkali salts are readily soluble in water. Coupling with diazo compounds takes place under alkaline conditions in the position ortho to the hydroxyl group.

The RR acid is used as a coupling component in azo dyes, e.g., C.I. Food Black 2 and C.I. Direct Brown 151.

2-Aminonaphthalene-3,6,8-trisulfonic acid liquor is concentrated by evaporation and heated with sodium hydroxide liquor in an autoclave [7]. The temperature is raised to 195℃ over 10 h and held at 195℃ for another 8 – 10 h until completion of the reaction is determined by working up a test sample and obtaining a strength by alkaline coupling equal to the diazotization titer. After dilution, acidification, and stirring while hot until all sulfur dioxide is expelled, the product is filtered off as its monosodium salt at 55℃ and washed with brine. Most of the isomeric 2-amino-3-hydroxynaphthalene-6,8-disulfonic acid impurity is removed in the filtrate. Crude RR acid is obtained in 65 % yield and is suitable for certain outlets. Further purification is necessary for critical derived dyes, and this is achieved by dissolving in dilute alkali, filtering at 80℃, and reprecipitating by addition of sodium chloride and hydrochloric acid. Filtration at 55℃ gives 90 % recovery of product.

Notclassified