Naphthol AS

Naphthol AS is an organic compound with the formula C10H6(OH)C(O)NHC6H5. It is the anilide of 3-hydroxy-2-carboxynaphthalene. Many analogous compounds are known, designated with a differing suffix. For example, in Naphthol AS-OL, the aryl substituent on nitrogen is C6H4-2-OCH3. These compounds are used as coupling partners in the preparation of some azo dyes.

History
In 1911, it was found to be a good precursor to dyes for wool by chemists at K. Oehler Anilin- und Anilinfarbenfabrik Offenbach.