Hair Dyeing with Oxidation Dyes

Permanent Hair Colorants. Permanent colorants produce hair coloration that lasts until the hair grows out. Color is formed inside the hair by hydrogen peroxide-induced coupling reactions of colorless dye precursors. A hiU range of shades can be obtained with this system and the permanent or oxidative hair colorants are considered to be the most important class of hair dyes. 

Melanin Drying. One development (ca 1993) in hair coloring involves the formation of pigments within the hair that are very similar to natural melanin. Thus either catalytic or air oxidation of 5,6-dihydroxyindole [3131-52-0] can be effectively used to permanently dye hair within a short time (38). The formed color can, if required, be further modulated with dilute H2O2 or can be even totally removed from hair by this oxidant. 

J. Zhou, H. Xu, G.-H. Wan, C.-F. Duan and H. Cui, Enhancing and inhibiting effects of aromatic compounds on luminol-dimethylsulfoxide-OH chemiluminescence and determination of intermediates in oxidative hair dyes by HPLC with chemiluminescence detection. Talanta, 64 (2004) 467—477. 

Frequent inflammation of the pharynx and larynx has heen reported in exposed workers. Very small quantities of the dust have caused asthmatic attacks in workers after periods of exposure ranging from 3 months to 10 years. Sensitization dermatitis has heen reported from its use in the fur dyeing industry. In this process, oxidation products of p-phenylenedi-amine are generated that are also strong skin sensitizers. Many instances of inflammation and damage of periocular and ocular tissue have been reported from contact with hair dyes containing p-phenylenediamine, presumably in sensitized individuals. ... 

Before dyeing with oxidation dyes, the furs are treated with the appropriate killing agents and then mordanted with metal salts. Iron, chromium, and copper salts, alone or in combination, are used for mordanting, and the uptake process requires several hours. Adjustment of the pH is effected with formic, acetic, or tartaric acid. The final dyeing process is carried out in paddles with the precursors and hydrogen peroxide until the actual dye lake is developed and adsorbed within the hair fiber. It takes quite a few hours at room temperature until the dyeing process is finished. 

Disperse and other synthetic dyes can only be taken up by the hair at elevated temperatures, and for this reason the skins must be chrome-tanned. The shrinking temperature of suede has to be at least 20° C higher then the dyeing temperature. No mordant is required, unlike with oxidation dyes, and killing need be far less intensive, too. In actual fact the operation is more hair cleaning than a killing process. The suede portion is not dyed and can be cleaned very easily with standard washing auxiliaries. 

Permanent hair colors can be achieved with tint shampoos. The shampoo base is adjusted to an alkaline pH and contains oxidation dye intermediates. Before application, it is mixed with hydrogen peroxide or a hydrogen peroxide addition compound. In comparison with oxidation hair dyes, tint shampoos employ lower concentrations of base and oxidant. This suppresses the simultaneous bleaching process that occurs during dyeing (see Section 5.4.2). As a result, damage to the keratin in hair is diminished, but the uniform coloring action is lost. 

Early oxidation hair dyes were used in solution form these have been replaced by cream- or gel-based formulas. The oil-in-water emulsions commonly used can be supplemented with auxiliary ingredients, such as polymers to improve combing ability, as well as other conditioning additives. Extensive patent literature is available on this point [35], Gel formulations may be based on alcoholic solutions of nonionic surfactants or fatty acid alkanolamide solutions, which form a gel when mixed with the oxidant. The type (emulsion or gel) and the basic composition of the preparation strongly influence dyeing [47], Different base formulations with the same dye content yield varying color depths and shading due to the distribution of the dye between the different phases of the product, interaction with surfactants, and diffusion from the product into the hair. 

In addition to cream and gel formulations, powder hair dyes are also marketed, but to a lesser extent. Besides the dye intermediates, they contain thickeners and oxidants in powder form. They are stirred with water before use. 

Hair dyes must meet a number of conditions related to their end use. Color can be assessed by colorimetry [49], The limits of precision are set by the substrate on which the measurement is performed. Studies on test subjects are difficult because of the uneven natural hair color and the background color of the scalp. Tresses are hard to prepare at a constant quality level. Measurements on wool cloth give reproducible results, but for oxidation dyes the shades are not identical to those produced on hair. Colorimetric methods are therefore useful only for comparative measurements on the same object, for example, in lightfastness tests. Because hair must be redyed after four to six weeks due to growth, the fastness required of hair dyes is generally less than that needed for textiles. However, stability is still a problem with many indo dyes (see Section 5.4.3). Some of them... 

Many of the organic aromatic amines used in hair dyes are strong sensitizers and oxidative dyes should be used with extreme caution. 

A 45-year-old woman developed extensive urticarial lesions 30 minutes after the application of a hair dye, starting on the scalp and face, followed by abdominal cramps, watery diarrhea, vomiting, dysphonia, and loss of consciousness. A prick test with a 1/128 dilution of the hair dye showed a positive reaction, but individual dye constituents did not. Prick testing with the oxidation products of the individual dye constituents showed a strongly positive reaction to oxidized paratoluenediamine, which was weaker after addition of an antioxidant to the mixture. 

Oxidation dyes are often referred to as permanent hair dyes and are the most important of the commercial hair dyes. Permanent hair dyes generally consist of p-diamines and p-aminophenols that are oxidized by hydrogen peroxide to active intermediates [3]. These active intermediates then react inside the hair with color couplers to provide shampoo-resistant hair dyes. 

One might speculate that (XXIII) functions only as a dye coupler however, related V,V-dialkyl p-phenylenediamines have been used with common dye couplers (in the absence of unsubstituted p-phenylenediamines), suggesting that this type of species does act as a dye precursor in oxidative hair dyeing [8,26,27]. 

Resorcinol is one of the components of most oxidation dyes and, as such, is probably the most commonly used oxidation dye coupler. Brody and Bums [21] have shown that p-phenylenediamine, in the absence of hair and phenols, is oxidized to Bandrowski s base. However, when resorcinol is present, polyindophenols (XX) are formed, and the formation of Bandrowski s base is effectively prevented [21]. These brown polymeric polyindophenol pigments have been identified by elemental analysis, acetyl values, and hydrolysis to p-phenylenediamine. Low-molecular-weight di-and trinuclear species were not detected by Brody and Burns, but Shah et al. [22] have isolated a green pigment from hair dyed with mixtures of p-phenylenediamine and resorcinol. This pigment was identified as the trinuclear indophenol (XXI). 

An intense black eumelanin-type pigment is produced by reacting DOPA with controlled amounts of potassium ferricyanide. Simple analogs of intermediates of the melanic pathways such as 8-hydroxy-l,4-dihydrobenzoth-iazine or thio-substituted catechols when oxidized with different oxidants at specific pH conditions and sometimes in the presence of oxidation dye nucloephiles provide different colors similar to those of permanent hair dyes [10]. These systems are still developmental and have not been commercialized to date, but they do appear to offer promise for the future. 

The primary toxicological concerns of hair dyes, primarily oxidation hair dyes, are with contact dermatitis and long-term potential systemic effects [5]. Of all hair products, the most sensitizing are the paradiamine oxidation dyes [63], and the most sensitizing ingredients of these products are p-phenylenediamine, p-toluenediamine sulfate, and o-chloro-p-phenylenedi-amine, although other related aromatic amines have also been shown to provide some sensitizing potential [62]. 

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