Оранжевый II

Orange-red powder

ChEBI: Acid orange 7 is a member of naphthalenes. Orange allergenic extract is used in allergenic testing.

Acid Orange 7, commonly known as acidic orange II. 4-Aminobenzenesulfonic acid diazo, and Naphthalen-2-ol coupling. It is produced by azo coupling of β-naphthol and diazonium derivative of sulfanilic acid.

Purification is as for Orange I. Its solubility in H2O is 40g/L at 25o. [Müller et al. Helv Chim Acta 35 2579 1952.] Also purify it by extracting it with a small volume of cold water, then crystallising it by dissolving in boiling water, cooling to ca 80o, adding two volumes of EtOH and cooling. When cold, the precipitate is filtered off, washed with a little EtOH and dried in air. It can be salted out from aqueous solution with sodium acetate, then repeatedly extracted with EtOH. Meggy and Sims [J Chem Soc 2940 1956], after crystallising the sodium salt twice from water, dissolved it in cold water (11mL/g) and added conc HCl to precipitate the acid dye which was separated by centrifugation, redissolved and again precipitated with acid. After washing the precipitate three times with 0.5M acid, it was dried over NaOH, recrystallised twice from absolute EtOH, washed with a little Et2O, dried over NaOH and stored over conc H2SO4 in the dark. It can then be converted to the pure salt with the calculated amount of NaOH or Na2CO3. [Beilstein 16 IV 408.]