Hair Couplers

Amin ophen o1 has been used as a stabilizer of chlorine-containing thermoplastics (153), although its principal use is as an intermediate in the production of 4-aniino-2-hydroxybenzoic acid [65-49-6] a tuberculostat. This isomer is also employed as a hair colorant and as a coupler molecule in hair dyes (154,155). 

In patented hair dyes the mentioned 5-5 bicyclic ring systems such as 94 and 95 (Figure 9) are used as oxidative couplers <1999EUP923929, 1997W09735551, 2003FRP2830192, 2004EUP1428510>. 

The main dye prodncing system nsed in hair coloration involves the oxidation of a primary intermediate in the presence of a colonr coupler to produce the coloured molecule. The primary intermediates are 1,4-phenylenediamines or 1,4-aminophe-nols and the colonr conplers are 1,3-phenylenediamines or 1,3-aminophenols. The primary intermediates are oxidised by peroxides to give the colonred benzo-quinonediimines or monoimines, which react with the couplers to give indoamines or indophenols, e.g. (2.52) and (2.53), depending on the natnre and ratio of the reactants, as shown schematically in Fignre 2.20. ... 

Oxidation Hair Colorant. Color-forming reactions are accomplished by primary intermediates, secondary intermediates, and oxidants. Primary intermediates include the so-called para dyes, -phenylenediamine, -to1nenediamine, -aminodiphenylamine, and -aminophenol, which form a quinone monoimine or diimine upon oxidation. The secondary intermediates, also known as couplers or modifiers, couple with the quinone imines to produce dyes. Secondary intermediates include -diamines, w-aminophenols, polyhydroxyphenols, and naphthols. Some of the more important oxidation dye colors are given in Figure 1. An extensive listing is available (24,28). 

The use of primary intermediates as sole dye precursors severely limits the range of shades some couplers are therefore sometimes added. They do not themselves develop a significant color effect as such but if present in primary intermediates they modify the resulting colors. The usual couplers are 1,3-diami-nobenzene (blue), 3-aminophenols (red), and resorcinol (yellow-green). This technique is mostly used for human hair (see Section 5.4.2), the oxidation steps being performed at around pH 9.5 with hydrogen peroxide. 

This size enlargement is largely responsible for fixing the dye in the hair. With the proper choice of substituents, any color from yellow to blue can be obtained [9, pp. 279-283], [26] and Scheme 5.2. If one or two primary intermediates are mixed with various (usually three to five) couplers, a range of colors is produced in the hair, giving the desired shade as an overall impression. 

The principal red couplers are 3-aminophenol [591-27-5], 5-amino-2-methyl-phenol [2835-95-2], and 1-naphthol [90-15-3]. Yellow-green couplers include resorcinol [108-46-3], 4-chlororesorcinol 195-88-5, benzodioxoles, and 2-methyl-resorcinol [608-25-3] and its derivatives. The importance of the yellow-green couplers lies in the broad-band absorption of the dyes produced, which makes natural-looking hair shades possible. Table 5.4 lists a range of colors obtained by reaction of primary intermediates with different couplers. 

Table 5.4 Combinations of primary intermediates and couplers used in hair colorants...

A dye is considered permanent if it penetrates into the hollow hair shaft. Coloring of hair starts with a treatment of substances such as hydrogen peroxide and ammonia. The ammonia causes hair shafts to swell and open, allowing dye intermediates and couplers to penetrate. Dyes applied during the second step of coloring react with the precursors to form pigments that remain in the hair. 

When used alone, the primary intermediates give a quite limited shade range following oxidation on hair. To enhance the range of available hair colors, the primary intermediates are oxidized in the presence of suitable couplers ) Whereas most couplers do not... 

A furylmethyl group has been incorporated into a dye developer-coupler combination which has been shown to be useful for the oxidative dyeing of keratin fibers, especially human hair <2002W02072568>. The regioisomeric furans 29 and 30 belong to this class of compounds and are easily synthesized from the corresponding aldehydes and a previously generated aminophenyl carbamate. 

Permanent hair dyes are often derivatives of an aromatic amine, discovered as a hair dye in 1883, called /Mra-phenylenediamine (H2N-C6H4-NH2), including primary intermediates such as pcirci-aminophenol, dihydroxybenzene, 4-methylaminophenol, tetraaminopyrimidine, 2-aminomethyl-4-aminophenol, and / ara-aminodiphenylamine. The / zrra-phenylenedi-amine compound produces a black color, with its derivative parci- mmo-diphenylaminesulfonic acid used in blond formulations. Couplers are generally aromatic phenols or amines that have an available site that is subject to electrophilic interaction. Typical couplers include chemicals such as resorcinol, wrte-phenylenediamine, 2,4-diaminoanisole, mrm-aminophenol,... 

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). 

To formulate the foregoing hair precursor-coupler bases, add the sulfonate and neodol to water by stirring at room temperature. Add the... 

Snip a small strand of hair about % in. wide, cutting it close to the scalp. Apply tape to the cut ends to hold the hairs together during treatment. Mix a small amount ( tsp.) of precursor-coupler base and oxidizer base, apply the dye solution to the strand of hair and wait 20 min then wipe the dye from the strand to check the color. If the desired shade is not dark enough, apply more dye and recheck. Continue until the desired depth of shade is achieved. 

Now the consumer is ready to use the product. Mix lOOg of the precursor-coupler base with 75 g of the oxidizer base and spread it through the hair, allowing the reaction to proceed for 10 to 20 min or the time indicated by the strand test before rinsing thoroughly with water. 

Hair dyes. Primary intermediates and couplers used in semi-permanent and permanent hair-colouring procedures. Allergies were described to ... 

Uses coupler for hair dyes dye intermediate in the manufacturing of 4-aminosalicylic acid Cross para groups of compounds. M-AMINOPHENOL A... 

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