Dyeing Behaviors of Amino Heterocyclic Compounds as Blue Oxidative Hair Dye Precursors Applied to Keratin Fibers

The study investigated novel heterocyclic compounds, specifically 1,2,3,4-tetrahydroquinoline and 2,3-dihydroindole, as blue oxidative dye precursors for keratin fibers, particularly human hair. The experiments involved mixing these compounds with H2O2 gel at a 1:1 ratio and a pH of 8-11. It was found that 1,2,3,4-tetrahydroquinoline derivatives, especially N-methyl-7-amino-1,2,3,4-tetrahydroquinoline, were excellent candidates for blue dyes due to their color purity, stability, and fastness. In contrast, 2,3-dihydroindoles produced similar colors but lacked stability and brilliance.