Dyes, anthraquinone classes

Disperse dyes from the monoazo and anthraquinone classes have been implicated in cases of contact dermatitis. Circumstances common to such cases appear to be heavy depths of these dyes on nylon rather than polyester and occurring in articles of clothing that are in direct contact with the skin, often in areas that are likely to become moistened by perspiration. Hosiery, socks, blouses and close-fitting athletic or fashion wear, such as velvet leggings, are representative of the types of garment where this problem has arisen [1]. 

Because azo dyes, as amaranth, are the most widely used food colorants and are water soluble, they were bonded to selected polymers via a sulfonamide linkage. However, the azo linkages in the dyes themselves were unstable to intestinal microbial action and do not meet the requirements of biological stability because they are cleaved in the gut to yield absorbable aromatic amines. Hence a variety range of chromophore classes have been reported to be incorporated into polymers. For the anthraquinone class of chromophores, the basic water insolubility was changed by converting a portion of the backbone to sulfonic acids that impart anionic solubilizing functions. However, this meant that fewer chromophores could be attached and less intense colors would result. 

There are only a few publications in the field of TLC of disperse dyes, although this method provides better resolution and is more time-economical than PC. WoiJiENWEBEB [84] has separated Celliton Fast Red Violet RN (C. I. 61100), CelHton Fast Pink B (C. I. 60710) and qumizarin (C. I. 58050) through TLC on acetyl-ceUulose powder of 10% acetyl content he used the solvent ethyl acetate-tetrahydrofuran-water (6 + 35 + 47) which is suitable also for PC-separations on acetyl-paper (43). Many azo- and anthraquinone disperse dyes have been separated by Rettie and Haynes [61] with the help of TLC on the same adsorbent, using tetrahydrofuran-water-4N acetic acid (80 + 54 + 0.05) and mixtures of similar composition. Better separations of disperse dyes of the anthraquinone class can be obtained by TLC on silica gel 6, using chloroform-acetone (90+ 10) [61] 1-Amino-, 2-amino-, 1,2-diamino- and 1,4-diamino-anthraquinones could be thus separated. 

In the dyestuff industry, anthraquinone still ranks high as an intermediate for the production of dyes and pigments having properties unattainable by any other class of dyes or pigments. Its cost is relatively high and will remain so because of the equipment and operations involved in its manufacture. As of May 1991, anthraquinone sold for 4.4/kg in ton quantities. In the United States and abroad, anthraquinone is manufactured by a few large chemical companies (62). At present, only two processes for its production come into consideration manufacture by the Friedel-Crafts reaction utilizing benzene, phthahc anhydride, and anhydrous aluminum chloride, and by the vapor-phase catalytic oxidation of anthracene the latter method is preferred. 

The carbocychc azo dye class provides dyes having high cost-effectiveness combined with good all-around fastness properties. However, they lack brightness, and consequendy, they cannot compete with anthraquinone dyes for brightness. This shortcoming of carbocychc azo dyes is overcome by heterocychc azo dyes. 

Anthraquinone Dyes. This second most important class of dyes also iacludes some of the oldest dyes they have been found ia the wrappiags of mummies dating back over 4000 years. In contrast to the a2o dyes, which have no natural counterparts, all the important natural red dyes were anthraquiaones (see Dyes, natural). However, the importance of anthraquiaone dyes is declining due to their low cost-effectiveness. 

Acylaminoanthraquinones. This dye class consists mainly of ben2oyl derivatives of aminoanthraquinones. Due to the relatively low molecular weight, this dye class is appHed in dyeing at low temperature. Yellow, orange, red, and even violet colors are covered by acylamino anthraquinones. 

Anthraquinone dyes have been produced for many decades and have covered a wide range of dye classes. In spite of the complexity of production and relatively high costs, they have played an important role in the areas where excellent properties ate requited, because they have excellent lightfastness and leveling properties with brUhant shades that ate not attainable with other chtomophotes. However, recent increases in environmental costs have become a serious problem, and future prospects for the anthraquinone dye industry ate not optimistic. Some traditional manufacturers have stopped the production of a certain dye class or dye intermediates that were especially burdened by environmental costs, eg, vat dyes and their intermediates derived from anthraquinone-l-sulfonic acid and 1,5-disulfonic acid. However, several manufacturers have succeeded in process improvement and continue production, even expanding their capacity. In the forthcoming century the woddwide framework of production will change drastically. 

Consumption. Anthraquinone dyes are the most important dye class after azo dyes. Wodd textile production is estimated in Table 14. Estimates of the consumption of dyes for textiles ate given in Figure 14, together with the figures for fiber consumption. This shows that the consumption of each dye class or classes is approximately parallel to the consumption of fibers to which they ate apphed. 

Indigo is the most important vat dye, dating back to ancient times and produced on an industrial scale since 1880. To replace the indigo dyes, the indanthrone (21) class of dyes was developed. Indanthrone has superior characteristics as a vat dye and became a key material for further development of anthraquinoid vat dyes. There exist a variety of anthraquinone vat dyes differing in the chromophoric system. The color-structure relationship of vat dyes have been rationalized by the Pariser-Parr-Pople molecular orbital (PPP MO) method. Some examples of commercialized anthraquinoid vat dyes are shown in Scheme 6.14... 

The valence-bond approach may be used to provide a qualitative account of the /lmax values, and hence the hues, of many dyes, particularly those of the donor acceptor chromogen type. The use of this approach to rationalise differences in colour is illustrated in this section with reference to a series of dyes which may be envisaged as being derived from azobenzene, although in principle the method may be used to account for the colours of a much wider range of chemical classes of dye, including anthraquinones (see Chapter 4), polymethines and nitro dyes. 

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