I. Soc. Cosmet. Chem., 24, 103-134 (February 2, 1973) The Role of Meta Difunctional Benzene Derivatives in Oxidative Hair Dyeing. I. Reaction with p-Diamines JOHN F. CORBETT, Ph.D.* Synopsis-A study of the reactions of P-DIAMINES with RESORCINOLS, M-DIAMINES, and M-AMINOPHENOLS, under oxidative conditions, is described. The resulting major colored species are shown to be di-, tri-, and polynuclear indoanilines or indamines, and only rarely, in specific cases, do these undergo intramolecular cyclization to phenoxazines or phenazines under the conditions pertaining in oxidative dyeing. COLOR EFFECTS on hair and the visible spectra of the dyes are described and the IONIC SPECIES present in DYED HAIR is designated. The mechanism of the color- forming reaction is shown to involve initial OXIDATION of the p-diamine to the diimine which reacts, as its conjugate acid, with the neutral amino and/or phenoxide form of the coupler. High relative humidity is shown to be particularly deleterious to the stability of indo dyes on hair. The mechanism of off-shade fading of oxidatively dyed hair is discussed. INTRODUCTION It is well established that there are three classes of components which are important to the color development process of oxidative hair dyeing. These are the primary intermediates, the oxidant, and the couplers. The primary intermediates are difunctional derivatives of benzene which are capable of undergoing oxidation with the concomitant development of color. These intermediates are usually aromatic ortho or para aliamines or ami- nophenols. It has been shown that p-diamines and p-aminophenols undergo oxidation to colorless p-benzoquinone imines (1) which are the essential re~ active species in the color-forming reactions (2). *Clairol Inc., 1 Blachley Rd., Stamford, Conn. 06902. Investigation conducted at Gil- lette Co., Personal Care Division, Chicago, Ill. 103

104 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS Ox. Ox.• NH• NH OH O Oxidation of the individual primary intermediates gives rise to colored products since the resulting imines are capable of reacting with unoxidized intermediate to produce dye species (Fig. 1). Thus, the reaction of p-benzo- quinone diimine with p-phenylenediamine results in the formation of the brown dye Bandrowski's base (I)(3-5). An analogous product (II) may re- sult from the oxidation of p-aminophenol, but this has not yet been estab- lished. Oxidation of o-aminophenol and of o-phenylenediamine gives rise to 2-aminophenoxazinone (1II) (6,7) and 2,3-diaminophenazine (IV) (8), re- spectively. However, the mechanism, and even the intermediacy of the corre- sponding o-benzoquinone imines, has not yet been established for the latter two oxidations (9). NH• NH z (1•) brown-black N Ox.• HO OH OH N ,•,OH (II) brown N H• Ox, OH (III) orange NH• Ox,) N H•. N H• (IV) red orange Figure 1. Self-coupling products of primary intermediates