Oxidation dye precursors

Substituted 2-Aminoalkyl 1,4-Diaminobenzene Compounds and Oxidation Dye Precursor Containing the Same L. Chassot etaU US 6,436,152 (August 20, 2002)... 

Oxidation dye precursors are derivatives of aniline (see Table 6-1). Precursors are difunctional ortho- or para-diamines or aminophenols that are capable of oxidizing to diiminium (IX) or quinoniminium (X) ions, proposed by Corbett [3] as the active intermediates of this process. This article by Corbett [3] is an excellent review of the chemistry of oxidative dyeing. 

Oxidation dye couplers are electron-rich aromatic species. They are commonly substituted resorcinols or meta-phenylenediamines, usually containing a vacant position para to the amine or phenolic group (see Table 6-2). Oxidation dye precursors, when oxidized in the absence of couplers, form colored compounds, usually gray or brown-black shades. On the other hand, couplers themselves usually produce little or no color, but in the presence of precursors and oxidizing agent, they modify the color formed by the precursor. 

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. 

Attempts to broaden the range of materials available as dye precursors have been made (34,35). Oxidative dyes based on pyridine derivatives produce less sensitization than those based on benzene derivatives (36) however, they lack tinctorial power, lightfastness, and availabihty. Derivatives of tetra am in opyrim i din e are claimed to act as primary intermediates to give intense shades with good fastness and excellent toxicological properties (37). 

Dye release may relate either directly or inversely to the image-related reduction of silver halide. Release of the dye or dye precursor may be accomphshed or initiated by the oxidized developing agent or the unoxidized developing agent or by alkali or silver salts. 

Arylmethane leuco dyes are converted into di- or triarylmethane dyes on oxidation. This class of dye precursors sometimes is referred to as leuco di- or triphenylmethane dyes, or di- or triphenylmethane leuco dyes. The use of the term di- or triarylmethane dyes can be misleading as the central carbon atom is a carbonium ion. Instead, the term di- and triarylmethine dye is recommended for this class as it correlates with the well-known polymethine dyes. Nevertheless, it has not been commonly used. 

For oxalate detection, authors proposed a similar detection approach for recognition of oxalate via an immobilized oxalate oxidase/peroxidase couple and dye precursors MBTH (3-methyl-2-benzothiazolinone hydrazone) and DMAB (3-dimethylaminobenzoic acid). The peroxide generated by oxidation of oxalate to CO2 reacted with the dye precursors in a peroxidase-catalyzed reaction to yield an indamine dye with absorption maximum at 590 nm. The concentration of oxalate was correlated with increased absoiption from dye. 

Uses. Oxidative dye developing agent for photographic processes precursor for pharmaceuticals used in hair dyes... 

As with oxidation dyes, the actual dye in the Phthalogen process-the insoluble phthalocyanine pigment-is formed in the fiber itself. The dyeing is performed with precursors. There are two main processes. 

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. 

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. 

In spite of the importance of bleaches in oxidation dyeing, very few technical improvements apart from formulation aspects have occurred recently in this field. The selective adsorption of metal ions [21], especially of iron(n) salts [22], on melanin has been proposed for gentler bleaching of human hair. This process has achieved no more acceptance than the use of peroxocarboxylic acids or their precursors, which are important as bleaching intensifiers in textile bleaching. 

With direct dyes (see Section 3.3), as opposed to oxidation dyes, the actual dye (and not its precursor) is applied to the hair. It imparts a semipermanent or temporary color that lasts for a variable time. Lightening is not possible. 

Most oxidation dye formulations contain two or three or more ingredients that act as either dye precursors or couplers. Therefore, several reac-... 

Modern oxidation dyes sometimes contain coloring agents in addition to dye precursors and couplers for example, direct dyes like disperse blue 1 and nitro-phenylenediamines are sometimes included. 

Table 6-3 summarizes a scheme for formation of oxidation dyes and provides some examples of the types of dyes that have been isolated from these reactions. This scheme shows that a dye precursor (e.g., p-phenylenediamine) is oxidized to its corresponding diiminium ion (IX), and this active intermediate condenses with an electron-rich dye coupler, forming a dinuclear product that is oxidized to an indo dye. This reaction may stop at the dinuclear dye stage, or additional condensation-oxidation... 

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]. 

The literature on the interactions of oxidation dyes shows that dye precursors and dye couplers are both involved. Dye precursors are oxidized to... 

Because most oxidation dyes contain three to seven components capable of acting as either dye precursors or dye couplers, and most contain p-phenylenediamine and resorcinol, several di-, tri-, and polynuclear colored species of this general type are formed in these reactions. 

Pyrene is used commercially to make dyes and dye precursors. It was used by Jarroux et al. [37] as a MALDI matrix for the analysis of a poly(ethylene oxide) sample terminated with pyrene on both sides. trans-2-[3-(4-tert-Butylphenyl)-2-methyl-2-propenylidene]malononitrile is a relatively new matrix (it was introduced in 2003). This matrix possesses a very low threshold, probably lower than HABA. 

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