Premetallised dyes

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. 

Only the products associated with acid and premetallised dyes are dealt with in this section. The auxiliaries used with mordant dyes are covered in section 5.8. Anionic acid dyes, applied principally to wool and nylon, vary widely in their fastness and level-dyeing properties (section 3.2.2) in general, the higher the wet fastness of a dye the more difficult it is to apply evenly. Hence it is not surprising that the use of auxiliaries with acid dyes is related mainly to level-dyeing properties. There are two basic aspects ... 

An appropriate ion-specific electrode was found to provide a convenient, precise and relatively inexpensive method for potentiometry of copper(II) ion in copper-complex azo or formazan dyes. Copper(II) ion in copper phthalocyanine dyes can be quantified after anion exchange. Twelve commercial premetallised dyes evaluated using this technique contained copper(II) ion concentrations in the range 0.007 to 0.2%. Thus many copper-complex direct or reactive dyes are likely to contribute low but possibly significant amounts of ionic copper to textile dyeing effluents [52]. 

Levelling agent for controlling strike and aiding migration when dyeing nylon with acid dyes. Not generally recommended for use with premetallised dyes. 

The use of liposomes as complexing agents in the application of premetallised acid dyes to wool has been investigated [21-24]. Liposomes are lipid structures containing aqueous compartments surrounded by bilayer membranes. However, the methods as yet available for the preparation of these agents are hardly practical in dyehouse terms (section 10.3.4). 

Heavy metals are widely used as catalysts in the manufacture of anthraquinonoid dyes. Mercury is used when sulphonating anthraquinones and copper when reacting arylamines with bromoanthraquinones. Much effort has been devoted to minimising the trace metal content of such colorants and in effluents from dyemaking plants. Metal salts are used as reactants in dye synthesis, particularly in the ranges of premetallised acid, direct or reactive dyes, which usually contain copper, chromium, nickel or cobalt. These structures are described in detail in Chapter 5, where the implications in terms of environmental problems are also discussed. Certain basic dyes and stabilised azoic diazo components (Fast Salts) are marketed in the form of tetrachlorozincate complex salts. The environmental impact of the heavy metal salts used in dye application processes is dealt with in Volume 2. 

Many of the premetallised 1 1 chromium-dye complexes introduced from 1915 onwards for the one-bath dyeing of wool at low pH were o,o -dihydroxyazo compounds containing chelated chromium (III) ions. Typical examples still in use today include Cl Acid Orange 74 (5.18) and other azopyrazolones ranging in hue from yellow to bluish red, as well as... 

Many of the premetallised direct dyes are symmetrical structures in the form of bis-1 1 complexes with two copper(II) ions per disazo dye molecule. Scheme 5.12 illustrates conversion of the important unmetallised royal blue Cl Direct Blue 15 (5.43), derived from tetrazotised dianisidine coupled with two moles of H acid, to its much greener copper-complex Blue 218 (5.44) with demethylation of the methoxy groups as described above. Important symmetrical red disazo structures of high light fastness, such as Cl Direct Red 83 (5.45), contain two J acid residues linked via their imino groups. Unsymmetrical disazo blues derived from dianisidine often contain a J acid residue as one ligand and a different coupler as the other, such as Oxy Koch acid in Cl Direct Blue 77 (5.46), for example. 

Symmetrical premetallised 1 2 metal-dye complexes of unsulphonated monoazo structures with aluminium (5.57) or trivalent iron (5.58) have been patented recently for use as solvent dyes [36]. They contain a polar methoxypropylaminosulphone grouping in each diazo component and are marketed as alkylamine salts. It remains to be seen, however, whether a full colour gamut of bright aluminium and iron complex dyes can be discovered with light fastness performance equivalent to that of currently available chromium and cobalt complex dyes. 

In spite of their long-recognised disadvantages, or as a result of the substantial efforts to overcome them, chrome dyes still represent about 30% of total dye consumption in wool dyeing (Table 3.10 in section 3.2.2). Premetallised acid dyes and reactive dyes for wool account for a further 40%, so it is not surprising that much attention has been given to... 

Leather can be dyed with acid, direct and mordant dyes. Many of the direct dyes were based on benzidine and its congeners but the German Ordinance, covered under the toxicity of certain azo dyes in section 2.3.1.1, has meant that this is no longer an option. To improve the light fastness of the dyed leathers, 1 2 premetallised azo dyes have also been used, but once again the use of metal complex dyes is becoming less favoured. ... 

Reserving agent for the dyeing of nylon in blends with wool or cotton. Effective on all acid dyes including milling and premetallised. 

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