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J. Soc. Cosmet. Chem., 30, 191-211 (July/August 1979) The role of meta difunctional benzene derivatives in oxidative hair dyeing. II. Reactions with p-aminophenols KEITH C. BROWN and JOHN F. CORBETT Clairol Research Laboratories, 2 Blachley Road,, Stamford, CT 06902. Received.January 5, 1979. Presented at IOth IFSCC Conference, October 1978, Sydney, Australia. Synopsis A study of the REACTIONS OF P-AMINOPHENOLS with m-diamines, m-aminophenols, and resorcinol, under OXIDATIVE conditions, is described. Oxidation of p-aminophenol to p-benzoquinone monoimine is followed by coupling to the meta compound and oxidation to give N-(p-hydroxyphenyl) aminobenzoquinone diimines, aminoindophenols and hydroxyindophenols, respectively. Visible spectra of the dyes are related to DYE COLOR ON HAIR and stability in solution is related to color stability on hair. INTRODUCTION Oxidative hair dyeing involves the in-fiber formation of dyes from colorless interme- diates. The essential chemical process involves primary intermediates, generally p-diamines and p-aminophenols, couplers, generally meta-difunctional benzene deriva- tives such as m-diamines, m-aminophenols, and resorcinol, and hydrogen peroxide. In the first paper in this series (1), the reactions ofp-phenylenediamine with a variety of couplers were described and mechanisms were proposed. In general, dye formation was shown to involve slow oxidation ofp-phenylenediamine by hydrogen peroxide to give p-benzoquinone diimine which, in the form of its highly reactive conjugate acid, reacts with the coupler by electrophilic attack on the most nucleophilic site on the benzene ring of the coupler. The resulting leuco dye is then oxidized to the indamine, indoaniline, or indophenol. In certain cases, further reaction of diimine with the indo dye resulted in the formation of tri-nuclear or polynuclear dyes. Some indo dyes undergo rapid intramolecular cyclization to phenoxazines others undergo slow cyc!ization to phenazines, which is partly responsible for the instability of the color on hair. The present paper describes the reaction of p-aminophenols with couplers and discusses properties of the resulting dyes. 191