Stabilization of anionic indole dyestuffs

摘要

Azo dyestuffs which contain, as the coupling component an indole of the formula <IMAGE> wherein R denotes an optionally substituted alkyl radical, an optionally substituted aryl radical or an optionally substituted aralkyl radical, and the benzene ring A can be further substituted, frequently exhibit an undesired irreversible change in the color shade in acid solutions, which surprisingly can be prevented by adding nitrogen-containing complex-forming substances.