Process for preparing dye compositions containing 5,6-dihydroxyindole

A process for preparing a storage stable hair dye composition containing a 5,6-dihydroxyindole of the formula ##STR2## the process comprising the steps:

• (a) forming a reaction mixture in a container, said reaction mixture consisting essentially of about 0.25 to about 2% of an O-protected 5,6-dihydroxyindole of the formula ##STR3## wherein R.sup.1 and R.sup.2 vary independently and are hydrogen, methyl or ethyl;
• R.sup.3 and R.sup.4 vary independently and are C.sub.1 to C.sub.6 alkyl;
• X is carbon or sulfur, and n=1 when X is carbon or n=2 when X is sulfur;
• an alkaline hydrolyzing agent, and water or an aqueous/alcoholic vehicle;
• (b) rapidly sealing the container in such manner as to provide an anaerobic environment in said container, and
• (c) allowing the O-protected 5,6-dihydroxyindole of formula (I) present in the reaction mixture to hydrolyze slowly in said anaerobic environment to obtain the hair dye composition.