116-63-2

solid

1-Amino-2-naphthol-4-sulfonic acid can be used in determination of phosphate.

ChEBI: 4-amino-3-hydroxynaphthalene-1-sulfonic acid is a naphthalenesulfonic acid and an aminonaphthalene. It has a role as a mutagen. It is functionally related to a 2-naphthol.

2-Naphthol is dissolved in dilute aqueous sodium hydroxide and precipitated in finely divided form by addition of sulfuric acid at 5℃. Sodium nitrite solution is added to the slightly alkaline suspension, followed by sulfuric acid to effectthe nitrosation while the temperature is held at 5 – 8℃. The suspension of 1-nitroso2-naphthol is neutralized with aqueous sodium hydroxide; a solution of sodium bisulfite is then added. The temperature is allowed to rise to 20℃, and the soluble bisulfite addition complex is formed. Excess sulfuric acid is then added and the temperature is raised to 40℃, whereupon reductive rearrangement takes place and the product slowly crystallizes at 50℃. Filtration and washing give the product as a 25 % paste in 80 % yield. All plant items and reactants must be free from iron to avoid complex formation.

Purify it by warming 15g of the acid, 150g of NaHSO3 and 5g of Na2SO3(anhydrous) with 1L of water to ca 90o, shaking until most of the solid had dissolved, then filtering hot. The precipitate obtained by adding 10mL of conc HCl to the cooled filtrate is collected, washed with 95% EtOH until the washings are colourless, and is dried under vacuum over CaCl2. It is stored in a dark-coloured bottle, in the cold [Chanley et al. J Am Chem Soc 74 4347 1952]. [Beilstein 14 IV 2825.]