1-Amino-2-naphthol-4-sulfonic acid [116-63-2-A] C10H9NO4S
In an 800-ml beaker, dissolve 4.1 g of sodium hydroxide and 14.4 g of 2-naphthol in 450 ml of water. After everything is dissolved, cool to room temperature and add 7 g of sodium nitrite while stirring. The mixture is then cooled in an ice water bath to 5 °C and within 5 hours, a mixture of 6.5 ml concentrated sulfuric acid and 100 g ice is added. During these 5 hours, vigorous stirring is necessary to achieve fine distribution of 1-nitroso-2-naphthol. This is essential for the subsequent reduction and sulfonation. After the time has elapsed, the formed 1-nitroso-2-naphthol is filtered off and washed with 10% sodium chloride solution. The filter cake is then mixed in a 400-ml beaker with 110 ml of water and 25 g of sodium bisulfite. The mixture warms to 35 °C and the 1-nitroso-2-naphthol dissolves, being simultaneously reduced and sulfonated. Then, 60 ml of concentrated hydrochloric acid is added, and the reaction mixture is heated to 40 °C. The temperature then rises to 50 °C by itself and the sulfonic acid begins to precipitate. To complete the precipitation of the product, the solution is left to stand overnight. The next day, the product is filtered off and dried in a vacuum desiccator.
Description: 1-Amino-2-naphthol-4-sulfonic acid forms gray needles, usually containing 0.5 mol water. The crystals can turn pink upon exposure to light, especially when moist. 1-Amino-2-naphthol-4-sulfonic acid is insoluble in water, ethanol, ether, and benzene. It is soluble in hot sodium bisulfite solutions and alkalis; however, the alkaline solution oxidizes in air to a brown substance, which dissolves in hot water to form a green solution. Controlled oxidation of 1-Amino-2-naphthol-4-sulfonic acid with nitric acid yields the ammonium salt of 1,2-naphthoquinone-4-sulfonic acid. The neutral sodium salt solution of 1-Amino-2-naphthol-4-sulfonic acid fluoresces weakly blue. The acid is used for the manufacture of various indicators as well as red, blue, and black azo dyes.
Source: Organic Syntheses, Coll. Vol. 2, p. 42
Delivered by: Mephisto
Last update: 19/12/2005
Other names: 4-Amino-3-hydroxy-1-naphthol-4-sulfonic acid; Boeniger acid