A labeled form of alpha-Naphthol Orange, also known as Acid Orange 20, which is an organic azo dye.
ChEBI: CI Acid Orange 20 is an organic molecular entity.
4-Aminobenzenesulfonic acid diazo, and Naphthalen-1-ol?coupling.
Purify the dye by dissolving it in the minimum volume of H2O, adding, with stirring, a large excess of EtOH. The salt separates as orange needles. It is collected by centrifugation or filtration, washed with absolute EtOH (3x) and Et2O (2x) in the same way and dried in a vacuum desiccator over KOH. The free acid can be recrystallised from EtOH. [Slotta & Franke Chem Ber 64 86 1931, Beilstein 16 H 275, 16 II 117, 16 IV 410.] The purity can be checked by titration with titanium chloride [Klotz J Am Chem Soc 68 2299 1946].
Properties and Applications
orange. Soluble in water for palm light orange, slightly soluble in ethanol, acetone, insoluble in most organic solvents. The strong sulfuric acid for purple, diluted into palm orange, red with purple precipitation. Its water solution to join strong hydrochloric acid for orange brown; Add sodium hydroxide in red. Used for wool, silk fiber dyeing, etc. Also used in leather dyeing and indicator.
