| abstract |
The present invention is directed to the preparation of an aqueous hair dyeing composition containing an effective hair dyeing amount-at least 2 mg/ml-5,6-dihydroxyindole (DHI). An aqueous hair dyeing composition is produced by reacting under essentially anaerobic conditions dopa or a salt thereof with an alkali metal ferricyanide oxidant in an aqueous reaction medium to obtain dopachrome, and permitting the dopachrome to undergo rearrangement 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 sufficient buffering agent to maintain a pH of from about 4.5 to about 9 for the reaction medium throughout the series of reactions that take place thereafter, removing the ferrocyanide species present in the aqueous system, and lastly, charging the composition into a suitable container. |