Leather Anthraquinone Dyes

The application range designated by this generic name in the Colour Index incorporates those acid, direct and mordant dyes with substantivity for leather and satisfactory fastness on that substrate [55]. It is a commercially important sector, the number of products listed being exceeded only by the complete acid or direct dye ranges. As expected from the sources of this selection, about 85% of leather dyes are azo compounds (35% disazo, 30% monoazo, 20% metal-complex monoazo) and the remainder are mainly yellow to orange stilbene dyes and anthraquinone or triarylmethane types in the violet to green sectors. 

In 1869 Caro succeeded in performing the sulfonation step, and the anthraqui-none dyes could be used to color leather. These bright acid dyes have excellent lightfastness and a bright, mostly blue to reddish shade. The arylaminoanthraqui-none types are chiefly utilized for coloring leather. The sulfo groups can be present in the anthraquinone or/and in the substituent. An example is C.I. Acid Blue 25, 62055 [6408-78-2] (6). 

Reactive dyes are colored compounds that contain groups capable of forming covalent bonds between dye and substrate. Approximately 80-90% of reactive dyes are azo dyes. The other chromogenic classes are anthraquinones, dioxazines, phthalocyanines, and some 1 1 copper azo complexes. Reactive 1 2 complex leather dyes were also commercially manufactured for a short time. Constitution and producer have not been disclosed. 

Acid dyes are employed above all for colouring wool, polyamide fibres, paper, leather and inks. Only certain acid dyes are permitted for colouring foodstuffs and such food colorants are therefore treated in a special section below (p. 623). The difficultly soluble salts of some acid dyes are used as pigments. Most acid dyes are azo-, triarylmethane-, xanthene-, or anthraquinone derivatives. Various investigators have reported PC-separations of acid dyes in detail [12, 31, 33, 40]. Such separations can be carried out more quickly with TLC and often with superior resolution. Table 131 summarises experimental conditions of the abundant work in this field. 

Anthraquinone Acid Dyes. Anthraquinone acid dyes are illustrated by Acid Blue 25 and Acid Green 25. These dyes are water-soluble anthraquinone derivatives that are used to dye wool, silk, nylon, leather, and paper. 

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