Metal complex dyes classes

Another class of metal complex dyes is derived from the formazan stmcture. These dyes are appHed to wool and nylon from a neutral or weakly acidic dyebath analogous to the 2 1 premetallized OjO -dihydroxyazo complexes. The bluish-gray dye Cl Acid Black 180 [11103-91-6] (61) (Cl 13710) is a 2 1 cobalt complex of the formazan type. 

Chromium Complexes. Because of their high stability chromium complexes of tri-dentate azo dyes are the most important class of metal-complex dyes. This is due to the reluctance of hexacoordinated chromium(m) complexes to exchange ligands, which, however, complicates the preparation of chromium complex dyes from hexaaqua chromium(m) salts, and makes it possible to prepare triaqua 1 1 chromium complex dyes. Generally, 1 1 chromium complexes can be made in... 

These laked 1 2 metal-complex dyes belonging to the generic class of solvent dyes have a broad application range, including transparent lacquers, wood stains, numerous office products, foil printing, and recently ink-jet printing [59],... 

An EPA survey has shown that leather tanneries typically ( rate 10 to 12 d [15] and are specialized in dyeing either grain or suede sides. The most common dyeing method applied is so-called drum-dyeing in which the dye preparation is mechanically pumped into rotation wheels. Environmental releases occur during the opening of the wheel batch and dumping the wet and rinsed dyed sides. Major dye-classes applied in the leather industry are acid dyes (which account for about 90% of the leather market), metal complex dyes and, to a lesser extent, cationic dyes. 

Acid and metal complex dyes belong to different groups of chemical substances. Thirty-eight commercial dyes of these classes are studied on silica gel TLC plates (116). The best results for the separation of acid dyes are shown in Table 5. The data on 1 1 metal complex dyes are recorded in Table 6 and for 1 2 complex dyes in Table 7. The different solvent systems used are given in each table. It was observed that the well-shaped spots without tailing were obtained for acid dyes and 1 2 metal complex dyes. The separation of 1 1 metal complex dyes was also clear, but the spots were diffuse and showed tailing. The best solvent systems were 5 and S2 for the acid dyes, S2 and 4 for the 1 1 metal complex dyes, and 5 and S3 for the 1 2 metal complex dyes. 

Most mordant dyes are monoazo stmctures. The most important feature of this class of dyes is excellent fastness to light and washing. Mordant dyes are available ia aU shades of the spectmm with the exceptioa of bright violets, blues, and greens. To be useful, the metal complexes must be stable, ie, must not demetallize when subjected to dyebath conditions and aU aftertreatment processes, especially repeated washings. Chromium forms stable chelate rings with mordant dyes which are not affected by treatment with either weak acid or alkaU (see Coordination compounds). 

Acid Dyes. These water-soluble anionic dyes ate appHed to nylon, wool, sUk, and modified acryHcs. They ate also used to some extent for paper, leather, food, and cosmetics. The original members of this class aU had one or mote sulfonic or catboxyHc acid groups in thein molecules. This characteristic probably gave the class its name. Chemically, the acid dyes consist of azo (including preformed metal complexes), anthraquiaone, and ttiaryHnethane compounds with a few azHie, xanthene, ketone imine, nitro, nitroso, and quHiophthalone compounds. 

Forma n dyes bear a formal resemblance to a2o dyes, since they contain an a2o group but have sufficient stmctural dissimilarities to be considered as a separate class of dyes. The most important forma2an dyes are the metal complexes, particularly copper complexes, of tetradentate forma2ans. They are used as reactive dyes for cotton (81) is a representative example. 

The ability of transition metal ions, and especially chromium (as Cr3+), to form very stable metal complexes may be used to produce dyeings on protein fibres with superior fastness properties, especially towards washing and light. The chemistry of transition metal complex formation with azo dyes is discussed in some detail in Chapter 3. There are two application classes of dyes in which this feature is utilised, mordant dyes and premetallised dyes, which differ significantly in application technology but involve similar chemistry. 

Another important class of pigment are the so-called toner pigments. These are water-soluble dyes containing sulfonic acid groups which are insolubilized by forming a salt with a divalent cation such as calcium and barium5 (Scheme 2). Until recently the toner pigments were perceived merely as insoluble salts but X-ray studies have shown them to exist as supramolecular metal complexes (see Section 9.12.4.2). 

Azo dyes and azo pigments are the most important class of both non-metallized and metallized colorants. Therefore, this section is devoted entirely to metal complex azo dyes and pigments. 

This small class of blue copper-complex dyes has made a significant contribution to the acid and reactive ranges in recent years (sections 5.4.2, 5.4-3 and 7.5.8). The essential chromogen is the bicyclic 1 1 chelated grouping illustrated (1.20). Trivalent metals such as chromium, nickel or cobalt will give tetracyclic 1 2 complexes with a central metal atom, analogous to conventional 1 2 metal-complex azo dyes. 

Direct dyes have only modest fastness to washing, which may be improved by after-treatments such as metal-complex formation (section 5.5.3) or by diazotisation of the dye on the fibre and further coupling of the diazonium salt with an insoluble coupling component (section 1.6.14). In addition to their use on cotton and viscose, direct dyes are important in the dyeing of leather. The cheapest members of this class are also used in the coloration of paper, since for this purpose fastness properties are largely irrelevant and price is all-important. 

Complexes derived from medially metallizable, tridentate azo compounds represent the single most important class of metal complex dyestuffs in commercial terms. Some indication of this is afforded by the fact that in 1983 the world consumption of premetallized dyes of this type was of the order of 20 000 tons. 

This chapter is devoted to the chemical chromophores of dyes, but the term chromophore is used here in a somewhat extended manner that also considers dye classes such those as based on cationic, di- and triarylcarbonium, and sulfur compounds, and metal complexes. 

The term phthalocyanine was first used by R. P. Linstead in 1933 [1] to describe a class of organic dyes, whose colors range from reddish blue to yellowish green. The name phthalocyanine originates from the Greek terms naphtha for mineral oil and cyanine for dark blue. In 1930-1940, Linstead et al. elucidated the structure of phthalocyanine (H2Pc) and its metal complexes [1-11]. The basic structure is represented by phthalocyanine (1) itself ... 

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