AZO PIGMENTS AND THEIR INTERMEDIATES - EFFECT OF SUBSTITUTION ON THE DIAZOTIZATION AND COUPLING REACTIONS OF O-HYDROXYANILINES

The effects of substituents on the diazotization and coupling reaction s of o-hydroxyanilines have been studied. When the substituent is a st rong electron-withdrawing group, e.g. NO2, the resulting substituted 2 -hydroxy-1-benzenediazonium chloride is highly acidic, even in aqueous hydrochloric acid solution. It deprotonates and forms the correspondi ng substituted 1,2-benzoquinone-1-diazide. For less electron-withdrawi ng or even electron-releasing substituents, the so-generated diazonium chlorides are soluble in the aqueous hydrochloric acid solution. Thes e diazotized products are isolated as hexafluorophosphate salts. The c oupling reactions between various diazotized products of o-hydroxyanil ines and 2-hydroxy-3-naphthanilide are shown to proceed through the 1, 2-benzoquinone-1-diazide intermediate, regardless of their original st ructure. Synthetic results show that the substituted 1,2-benzoquinone- 1-diazide intermediate is only reactive when it is activated by a subs tituent that is more electron-withdrawing than the chloro group.