298 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS "difficult to perm" nature), and the kinetic behavior, but none have been found. It is clear that the kinetic pathway can be altered by changing the properties of the reducing agent solution (pH, concentration) and is also highly sensitive to various hair types. It is hoped that further work will provide a clearer picture of this complex issue. Nevertheless, despite the reservations expressed concerning the basic assumptions of the method, it is shown that the reduced-time treatment is very useful in analyzing the information that is obtained from the SFTK experiments. Results have shown that the reason a hair type may be described as "difficult to perm" is a slower rate of reduction, which then results in a breaking of an insufficient amount of disulfide bonds to give a good curl strength. It has also been postulated by Wickett that a diffusion-controlled process will impart more damage to the hair as a result of the reaction being concen- trated in the outer portions of the fibers. As such, the SFTK technique, together with the ABD-F fluorescence microscopy, can be very valuable in designing new and more effective perms. ACKNOWLEDGMENTS The authors thank Loralei Brandt, Dr. Craig Herb, Elaine LaMarre, Vera Stulov, and Dr. Priscilla Walling. REFERENCES (1) R. R. Wickett, Kinetic studies of hair reduction using a single fiber technique,J. Soc. Cosmet. Chem., 34, 301-316 (1983). (2) C. E. Reese and H. Eyring, Mechanical properties and the structure of hair, Textile Res. J., 20, 743-750 (1950). (3) R. R. Wickerr and R. Mermelstein, Single fiber stress decay studies of hair reduction and depilation, J. Soc. Cosmet. Chem., 37, 461-473 (1986). (4) R. R. Wickett and B. G. Barman, Factors affecting the kinetics of disulfide bond reduction in hair, J. Soc. Cosmet. Chem., 36, 75-86 (1985). (5) J. Sikorski and H. J. Woods, The effect of rate of extension on the Young's modulus of keratin fibers, Leeds Phil. Soc., 5, 313 (1950). (6) E.G. Bendit, There is no Hookean region in the stress-strain curve ofkeratin,Jo Macrotool. Sci.-Phys., B17(1), 129-140 (1980). (7) C. M. Bamford and C. F. H. Tipper, Eds., Comprehensive Chemical Kinetics, Vol. 22 (Elsevier, Am- sterdam, Oxford, New York, 1980). (8) J. H. Sharp, C. W. Brindley, and B. N. N. Achar, Numerical data for some commonly used solid state reaction equations, J. Am. Ceram. Soc., 49, 379-382, (1966). (9) L. F. Jones, D. Dollimore, and T. Nicklin, Comparison of experimental kinetic decomposition data with master data using a linear plot method, Thermochim. Acta, 13, 240-245, (1975). (10) T. Toy'oka and I. Kazuhiro, New fluorgenic reagent having halogenbenzofurazan structure for thioIs: 4-(aminosulfonyl)-7-fluoro-2,1,3-benzoxadiazole, Analyt. Chem., 56, 2461-2464 (1984). (11) D. J. Evans, A method for determining the penetration of reducing agents into wool using fluores- cence microscopy, Textile Res. J. 59, 569-579 (1989).

j. Soc. Cosmet. Chem., 45, 299-308 (November/December 1994) Kinetics and mechanism of indo-aniline dye formation in aqueous peroxide solution YAN FENG and ALEXANDER CHAN, Clairol R&D Research Laboratories, 2 Blachley Road, Stamford, CT, 06922. Received August 5, 1994. Synopsis Oxidation of a mixture of para-phenylenediamine (PPD) and phenols generates indo-aniline dyes. The process is of special interest with hydrogen peroxide (H202) , which is used commercially to induce permanent hair coloring formation. Although limited reports can be found to discuss the mechanism of indo-aniline formation by other oxidants, e.g., K3Fe(CN)6 and 02, little is known about the mechanism of indo-aniline formation in aqueous peroxide solution. Kinetic studies of indo-aniline formation by H20 2, recently carried out in our laboratories, indicate that indo-aniline is formed through a multiple-step scheme. The rate of indo-aniline formation was limited by PPD consumption, a kinetically slow step. Both promotion and inhibition of H202 on indo-aniline formation were observed and were accounted for by a mechanism developed based on kinetic modeling. INTRODUCTION Indo-anilines (I) are a series of colored compounds. These compounds, formed by the peroxide oxidation of a mixture of p-phenylenediamine and phenols, have been found to be very useful for hair coloring (1). Understanding the mechanism of indo-aniline formation is of interest to the hair coloring industry because of its particular values in the development of permanent hair coloring products. A detailed mechanistic study of indo-aniline dye formation was reported by J. F. Corbett (2-4) in the early 70s, using ferricyanide as the oxidizing agent. He reported stoichiometrical conversion of PPD to indo-aniline at pH 8.5 in excess of phenols. The kinetics of indo-aniline formation in the presence of ferricyanide is fast, and the indo-aniline formation is instant after the reactants are mixed. On the contrary, forma- tion of indooaniline under similar conditions, except for the use of hydrogen peroxide as the oxidant, was found to be a very slow process. Our studies indicate that multiple steps are responsible for indo-aniline formation in the hydrogen peroxide system. The efficiency of converting PPD to indo-aniline, which is defined as the ratio of the amount Address correspondence to Yan Feng at 4020 Yorktown Dr. #5, Fairfax, VA 22030. Alexander Chan's current address: Helene Curtis, Inc., R&D Dept., 4401 W. North Ave., Chicago, IL 60639. 299