110 JOUBNAL OF THE SOCIETY OF COSMETIC CHEMISTS .•N••Me H2N' •'"•.• HzN•O (XIII) Table I The nmr Spectra of the Aminoindoanilines in Deuterated Dimethylsulfoxide Before deuteration a g-Aminoindoaniline After deuteration r No. of H r No. of H Assignment 3.32 2 b ...... NH.o (quin.) 4.37 2 b ...... NH. (benz.) 2.88 • 2.77 • lpairortho 3.06 2.96 CH (quin.) 3.67 j•' 2 3.61 • 2 (J: 111 cps) 3.86 3.79 3.00 '• 2.88'[ 2 pairs ortho 3.14 3.02 • CH (benz.) 3.20 • 4 3.12 • 4 (J:S4cps) 3.34 TM 3.26 4.37 TM 1 b 4.31 lone CH a (quin.) Before deuteration • 2-Amino-5-methylindoaniline (XIII) After deuteration r No. of H r No. of H Assignment 3.37 2 • ...... NH2 (quin.) 4.47 2 ...... NH2 (benz.) 3.00 1 3.13 1 lone CH (quin.) 3.00'[ 2.92 • 2 pairs ortho 3.14 3.07 CH (benz.) 3.gl • 4 3.14 • 4 (J-90cps) 3.35 TM 3.29 4.40 i 4.31 1 ]one CH c (quin.) 8.13 s 3 8.11 3 CHo m -- masked peak, s = slight splitting to doublet. Obtained by difference on deuteration. Ortho to NH• group. When an equimolar mixture of p-phenylenediamine and m-aminophenol is oxidized with potassium ferricyanide, a similar dye (mp 131 ø ) is produced having an elemental analysis (C, 67.9 H, 4.92 N, 19.4%) corresponding to the molecular formula C•2H•NaO, and having an nmr spectrum consistent with the 2-aminoindoaniline structure (Table I). When less reactive oxidants, such as molecular oxygen or hydrogen peroxide, are used for the oxidation of

OXIDATIVE HAIR DYEING 111 concentrated p-phenylenediamine/m-aminophenol mixtures, the magenta color again develops, but the black crystalline precipitate, which forms as the reaction proceeds and which has a melting point of 237øC, does not give a magenta color on dissolution in water. Elemental analysis and the molecular weight of this product (C, 68.2 H, 5.62 N, 5.62% tool wt = 319.1433 high resolution mass spectrometer) point unequivocally to a molecular formula C•8Hx7N50. Since such a compound could be formulated as arising from the addition of a molecule of p-phenylenediamine to the 2-aminoindoaniline, we assigned the structure (XIV). This assignment is supported by the fact that acid hydrolysis gives 2.5-dihydroxybenzoquinone and p-phenylenediamine and reaction products thereof, and by consideration of the percentage con- version of p-phenylenediamine when various molar ratios of reactants are employed in its synthesis (Table II). Final confirmation is supplied by the nmr spectrum (Table III). (xiv) Table II Yields of Compound (XIV) for Various Reactant Ratios p-Diamine m-Aminophenol Temp Time Yield (M) (M) (øC) (hr) (%)• 0.01 0.01 30 24 82 0.05 0.05 30 24 93 0.05 0.05 75 5 96 0.08 0.04 40 24 91 • % of p-phenylenediamine converted. Oxidation of mixtures of 2,5-toluenediamine and m-aminophenol gave com- pounds analogous to (XIII) and (XIV). Oxidation of mixtures of p-phenylenediamine and 4-methyl-3-aminphenol (where the position para to the hydroxy group is blocked) gives rise to a ma- gena dye which could not be isolated in the pure state due to the ease with which it undergoes conversion, in concentrated solution, to a violet dye (Table IV). This latter was isolated and shown to be a 3,7-diamino-2-methyl- phenoxazinium salt (XV) by elemental analysis, its characteristic spectrum (Fig. 2) and its high pK• value of 11.2 (44,45). The magenta dye is pre- sumably 2-hydroxy-5-methylindamine (XVI). It is noteworthy that, in dilute solution, (XVI) undergoes decomposition without forming any of the phenox- azinium salt (Fig. 3) and hair dyeing experiments suggest that while the ma- genta indamine (XVI) is formed in the hair, little if any of the phenoxazinium salt (XV) is formed at the time of dyeing or subsequently.