BENZENE DERIVATIVES IN OXIDATIVE HAIR DYEING 199 4.0 3.0 c M+P- pH I I 12 Figure 3. Effect of pH on the rate of reaction ofp-benzoquinone monoimine with 2,6-xylenol at 30øC. The full line shows the theoretical curve calculated from equation (1) and the broken lines show the contributions of the reactions between the various ionic species to the total rate. The open circles represent the experimental results. monoimine with 2,5-xylenol we get k a = 50.7 X 0.039 X 29 X 10 = 5.74 x 102 which compares well with the experimental value of 5.3 x 102l mol -• min -• Table VII shows that C-methylation of monoimine decreases the reactivity about twentyfold, while C-chlorination has the opposite effect. Conversely, C-methylation of

200 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS Table VII Effect of Substituents on the Reactivity ofp-Benzoquinone Monoimines and Phenolate Ions at 30øC Substituent Factor 2 Substituent • Monoimine Phenolate 2-Me 0.039 29.0 3-Me 0.059 10.0 2-Cl 40.0 0.12 3-Cl 22.0 0.22 •The imine is numbered with the imino-group in position 4. 2Substituent factor is the factor by which the reactivity is changed by introduction of the designated substituent. 0 o / / / / / / / I i I i-- 8 10 12 pH Figure 4. Effect of pH on the rate of reaction of 2-methyl-p-benzoquinone-4-imine with 4-chlororesorci- nol at 30 ø. The experimental points (circles) are superimposed on the line calculated for reaction of neutral monoimine with resorcinol dianion.

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