Process for the manufacture of a hair dye product containing 5,6-dihydroxyindole

A process for the manufacture of a shelf stable hair dye product comprising a container and an essentially air-free hair dye composition containing at least one indolic melanin precursor, the process comprising the steps of:

• (a) preparing an aqueous hair dye composition containing the melanin precursor 5,6-dihydroxyindole by (i) reacting dopa and salts thereof with an alkali metal ferricyanide oxidant in an aqueous medium to obtain dopachrome, (ii) permitting the dopachrome to undergo a rearrangement reaction in the aqueous medium to form 5,6-dihydroxyindole, said rearrangement being conducted in the substantial absence of oxidant, the aqueous medium being buffered by a buffering agent suitable to maintain the pH of the aqueous media between about 4.5 to about 9 during the reactions (i) and (ii), and (iii) removing ferrocyanide produced during the reaction (i) and the rearrangement reaction (ii);
• and
• (b) charging a container with the aqueous hair dye composition from step (a),
• said process being conducted under substantially anaerobic conditions to avoid incorporation of oxygen into said hair dye product, said hair dye product having a 5,6-dihydroxyindole concentration of at least 2 mg/ml by weight of the hair dye composition.