Particularly valuable dyestuffs are obtained from those wherein D represents a sulphonated phenyl or naphthyl radical, especially those which contain a SO H group in ortho position to the azo link; the phenyl radical may be further substituted for example, by halogen atoms such as chlorine, alkyl radicals such as methyl, acylamino groups such as acetylarnino and alkoxy radicals such as methoxyv (2