Azo-based dyes

Azo-based dyes, known to be carcinogenic, contain easily hydrolyzed azo bonds. In the GI tract, these bonds are cleaved to yield the free aromatic amine(s) [20]. Azo reduction may also take place in the liver of humans and other mammals by reductase enzymes, but it is likely that hydrolysis in the GI tract is predominant [21]. The resultant aromatic amines are easily absorbed in the intestines. It was found that inclusion of sulfonate moieties on the aromatic amine feedstocks mitigates the toxicity, as illustrated with the azo dye Brilliant Black BN (Cl Food Black 1) in Figure 13.6. The sulfonate moieties are highly ionized in the GI tract and at environmental pHs (5-9), and their reduction products cannot penetrate the GI endothelial membranes following oral exposure. Consequently, the chemicals are poorly absorbed, and any portion that is absorbed is rapidly excreted in the urine [22, 23]. 

Conversation with the dye manufacturer revealed a mistake had been made in recommendation of the disperse dye to be used in conjunction with the high-energy reactive dye. The recommended dye was an azo-based dye that was not stable to base at high temperatures, and degradation caused the purplish shade shift observed in the research. For future investigations, an anthraquinone-based disperse dye that is base-stable at 170°C has been recommended by the manufacturer for use with the high-energy reactive dye. 

A number of common azo based dyes are known to be possible carcinogens. This results from their metabolism to more labile products in the liver. Analysis of these metabolites is obviously an important in a number of areas. Radzik et al. have utilised LC-DED in both in the redox mode and in parallel for the determination the metabolites of Disperse Orange 3 (viii) liver microsomal fractions. No prior extraction, preconcentration or derivatisation was required for the analysis of the principle metabolites 4-nitroaniline (ix), 2-amino-5-nitrophenol (x) and N-hydroxy-4-nitroaniline (xi) in the sub-pM range. 

Finally, it should be mentioned that the chiral additive used to create a chiral nematic phase does not have to be a mesogen itself - it has to be soluble at reasonable concentration levels to produce the desired pitch, but since it is now acting equally as an impurity, the normal phase transition properties of the host material may also be altered. Chiral nematic liquid crystals are highly sensitive in their optical properties, and may therefore be used as contaminant detectors. Equally photoresponsive additives, such as azo-based dyes, may be incorporated into a chiral nematic structure and on photoexcitation they change shape since they then behave as an impurity they can easily alter the pitch or selective reflection properties. Such effects are normally reversible because of the trans-cis and cis-trans back reactions available. This gives a simple imaging device. 

In metabolism studies of azo dyes and pigments in the hamster, in vivo cleavage of the benzidine-based dye, Direet Black 38, to benzidine was shown by analysis of the urine. However, studies of the 3,3 -diehlorobenzidine-based pigment. Pigment Yellow 12, showed no evidenee for in vivo cleavage to release 3,3 -diehlorobenzidine (Nony et al. 1980). 

The only published method available for the determination of personal exposure to benzidine-based dyes utilized the analysis of urine for benzidine and benzidine metabolites (JO, J 1 ). This method does not allow for quantitation of a daily exposure, since benzidine and its metabolites have been found in the urine of hamsters fed a benzidine-based dye up to 168 hours after a single dosing (J 2). A method for the determination of personal exposure to azo dyes and diazonium salts has been developed (J 3), but it is not specific enough to determine an exposure to a benzidine-based dye. 

This method has been used to analyze both symmetrical (C.I. Direct Red 28 and C.I. Direct Blue 6) and unsymmetrical (C.I. Direct Black 38 and C.I. Direct Brown 95) benzidine-based dyes. Based on this work, the application of the method to other benzidine-based dyes should be straightforward. When field samples are submitted for benzidine-based dye analysis, bulk samples of the dyes present in the sample also should be submitted. With these bulk samples, the analyst should be able to determine if this method is applicable to the various dyes submitted and if any interferences are present. The method presently has not been tested on field samples. An existing sampling method (J 3) for azo dyes and diazonium salts should be directly applicable to this method with a change from a cellulose ester to a Teflon filter. This change is necessary to insure quantitative recovery of the sample from the filter. 

Azo dyes made from 47, and also their cleavage products from azo reduction, are appreciably less genotoxic than the corresponding benzidine-based dyes. An example is the mutagenic (and carcinogenic) benzidine-based dye Direct Violet 43 (48) and its corresponding isosteric analog (49), in which the benzidine moiety is replaced with 47. Other examples are available [84]. 

Such dye salts are converted to azo bases by alkali. Alkylating agents attack the nitrogen atom of the azo bond, forming alkylarylhydrazone dyes which dye polyacrylonitrile in lightfast, yellow to orange shades [26],... 

Heterocyclically substituted acetic acids (e g., benzothiazolyl-, benzimidazo-lyl- [34], and pyrimidylacetic acids [35]) are also suitable as coupling components for preparing cationic hydrazone dyes. In these compounds the methyl group in the 2-position is additionally activated. The carboxyl group is split off after coupling and the azo base is methylated. 

Disperse dyes vary in the type of chromophore present and include azo, anthraquinone, nitro, methine, benzodifuranone, and quinoline based structures. Examples of the first three types are given in Table 13.4, and representative of the latter three types are C.I. Disperse Blue 354, C.I. Disperse Yellow 64, and C.I. Disperse Red 356. Most disperse dyes have azo ( 59%) or anthraquinone ( 32%) structures. Azo disperse dyes cover the entire color spectrum, whereas the important anthraquinone disperse dyes are mainly red, violet, and blue. The azo types offer the advantages of higher extinction coefficients (emax = 30,000-60,000) and ease of synthesis, and the anthraquinones are generally brighter and have better photostability (lightfastness). The key weaknesses associated with the anthraquinone dyes are their low extinction... 

Examples of dyes made via an A —> M — E synthesis are shown in Fig. 13.98. Although most azo disperse dyes are based on monoazo structures, disazo structures such as 15 (C.I. 

This is a kind of naphthol dye which contain one azo base, -N=N-, in the molecule. It is a bright red powder, insoluble in water. and alcohol, it melts at 21C G, vaporized from about 230 0, and boils at 280°C being partly carbonized. As a component of smoke compositions, it is easily damaged by heat even at relatively low temperatures this is a defect of this dye and it may be caused by the NO base contained in the molecule. 

Dyeing of PP fibers with some azo disperse dyes of basic character has been intensively studied via the chlorination route. The results of dye uptake and fastness properties are explained as based on the inductive effect, electrostatic interaction, and steric effect of these dyes. 

The chemicals responsible for the colour are not able to penetrate the cortex and are deposited on the surface of hair to give the colouring effect. Different chemicals are used in this type of products, such as azo compounds, triphenylmethane-based dyes, indoamines, and indophenols. 

Basic, forms a stable water-soluble dihydrochloride. Diazotization gives brown azodyes (Bismarck brown) owing to the coupling of the partially diazotized base with the excess of diamine. Is also used as an end component of many azo-dyes, readily coupling with one or two molecules of diazo compound. 

The behavior of insoluble monolayers at the hydrocarbon-water interface has been studied to some extent. In general, a values for straight-chain acids and alcohols are greater at a given film pressure than if spread at the water-air interface. This is perhaps to be expected since the nonpolar phase should tend to reduce the cohesion between the hydrocarbon tails. See Ref. 91 for early reviews. Takenaka [92] has reported polarized resonance Raman spectra for an azo dye monolayer at the CCl4-water interface some conclusions as to orientation were possible. A mean-held theory based on Lennard-Jones potentials has been used to model an amphiphile at an oil-water interface one conclusion was that the depth of the interfacial region can be relatively large [93]. 

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