COLOR REACTIONS OF OXIDATION DYE INTERMEDIATES 147 the rate of color development, intensity of color on the hair and bleaching action on the natural pigment. 7. Bleaching action on the natural pigment. Ammoniacal hydrogen peroxide will oxidize intermediates to dyes but at the same time may bleach the natural hair pigment. This may or may not be de- sirable. 8. Peroxide stability of the dye bath: Catalytic decomposition of the developer when mixed with the product can adversely affect the rate and completeness of color development. 9. Rate of color development: Ideally, color development should start leveling off in fifteen or twenty minutes so that there will be little difference in hue and intensity between a thirty and a forty-five- minute color development. This so that the first strands of hair colored will not be deeper in shade than the last strands to which dye was applied. 10. Staining of the scalp: Since the skin surface is also keratinous in nature it can also be dyed. Measures must be taken, however, so that such stains will readily shampoo out. 11. Condition of the hair after application: Oxidative dyeing of hair re- sults in undesirable physical and chemical changes. Careful formulation can keep these to a minimum. 12. Levelness ofdyeing: Certain shades (reds, silver, smoke, steel) have a tendency not to level on the hair but steps can be taken to mini- mize this. This is only a partial list and yet each one of these could easily be the subject of a technical paper. There are other variables which merit the concern of the cosmetic chemist but over which he excercises no control. These are with the consumer. Affecting the end color result are such factors as the condition of the user's hair, has it previously been dyed, tinted, bleached or permanent waved and what other preparations have been applied to the hair. It is no wonder that the instructions for the application of oxidation dyes are so complicated. Many of these problems were discussed in detail in a series of articles by Kass (1, 2, 3). In addition to these the cosmetic chemist must cope with some peculiar color problems when he starts to develop the many hair shades. Oxidation hair dyes are complicated products that may contain as many as 12 to 20 ingredients. They can be classified into several groups: dye vehicle or solvent, dye intermediates and modifiers, stabilizers and anti- oxidants, alkalizing and swelling agents. The composition of these groups, the interrelation of individual components, and the complexities of for- mulation and performance have been reviewed (1, 2, 3). It is the purpose of this paper to explore the interaction of dye intermediates in relation to color effects on the hair. Our findings and observations are primarily in the area of hair dye technology and we will delve only briefly into the theoretical aspects of the problems. The scope of this presentation is limited to dye intermediates commercially available for use in oxidation dyes.

148 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS HAIR COLORS or INDIVIDUAL INTERMEDIATES Dye intermediates can be divided into two groups-primary interme- diates and secondary intermediates. The primary intermediates are chem- ical compounds which by themselves will form a dye upon oxidation. These are the para and ortho benzene diamines, amino phenols and their derivatives. The secondary dye intermediates, also referred to as color couplers and modifiers, are for the most part meta diamines, meta amino phenols, polyhydroxy phenols and naphthols. The phenols may or may not color the hair upon oxidation but their primary function is to modify. and often stabilize colors resulting from the oxidation of primary inter- mediates. Their use may also result in drastic color changes. Complica- tions now arise. As we will shortly show, certain of the primary inter- mediates may and often do react with other primary intermediates during oxidation to produce unexpected color changes. It will be helpful at this time to quickly review colors produced on hair by the principal dye inter- mediates. The aromatic diamines produce the following colors: p-phenylene diamine ................................ brown m-phenylene diamine ................................ gold p-toluylene diamine sulfate ........................... reddish brown p-aminodiphenyl amine .............................. gray 2,4-diamino anisole .................................. ash blonde 2,4-diamino diphenyl amine .......................... violet brown m-toluylene diamine ................................. blonde These color descriptions are only approximate because the actual shade re- sulting under specific conditions may vary greatly due to concentrations, alkalinity, composition of the dye base and many other factors. The intermediates available today are generally of high purity although cer- tainly not of CP grade. For example, the four meta diamines in the above list all yield light dyeings on hair although when chemically pure they will not dye the hair at all. Meta diamines will not form a quinoid upon oxida- tion and this is essential to dye formation. This will be made clear when we examine briefly the chemistry of the oxidation reaction. In the case of the meta diamines, color formation is due to the presence of very small amounts of the para or ortho isomers. The meta diamines are valuable intermediates when used with para diamines, and we will examine this color reaction in greater detail. The second important group of intermediates are the amino phenols. 0-amino phenol ................................ deep gold m-amino phenol ................................ no color p-amino phenol ................................ light auburn 2,4-diamino phenol hydrochloride ................. light reddish brown p-methyl amino phenol sulfate ................... pale blonde