Acid 1:2 Metal-Complex Dyes

Unmodified Carpet printing/dyeing acid, metal-complex dyes... 

Depolymerised Carpet printing/dyeing acid, metal-complex dyes Cotton, viscose vat, direct, azoic dyes Polyester disperse dyes Nylon acid, metal-complex dyes Acrylic fibres basic dyes... 

Acid metal complex dyes are used for dyeing wool and polyamide fibres. They are suitable also for preparing coloured, transparent cellulose nitrate varnishes, partly then as their dye acids. 

Changes in the backbone of the sulfonic acid azo dyes often produce drastic changes in properties of the materials. The disulfonic acid (5) is somewhat similar to (3), but is used to color leather red (77). More esoteric dyes have also been developed based on sulfonic acid metal complexes and chitosan-derived materials (78,79). 

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. 

Manufacture of alkylsulfones, important intermediates for metal-complex dyes and for reactive dyes, also depends on O-alkylation. An arylsulphinic acid in an aqueous alkaline medium is treated with an alkylating agent, eg, alkyl haUde or sulfate, by a procedure similar to that used for phenols. In the special case of P-hydroxyethylsulfones (precursors to vinylsulfone reactive dyes) the alkylating agent is ethylene oxide or ethylene chlorohydrin. 

The 1 2 metal complex dyes are dyed either at neutral pH or with ammonium acetate, and the exhaustion achieved by the effect of van der Waals forces. The pH is then aUowed to go slightly acidic to form salt linkages between the dye anion and the protonated primary amine groups in the wool (NH3 ). AU the dyes have similar dyeing properties and the conditions of appHcation do not damage the wool. 

Where high wetfastness is needed, for example in hotel lobbies and bars where Hquid spillages are likely, the higher fastness acid dyes (Groups 2 and 3) and even metal complex dyes are used. 

The major problem of these diazotizations is oxidation of the initial aminophenols by nitrous acid to the corresponding quinones. Easily oxidized amines, in particular aminonaphthols, are therefore commonly diazotized in a weakly acidic medium (pH 3, so-called neutral diazotization) or in the presence of zinc or copper salts. This process, which is due to Sandmeyer, is important in the manufacture of diazo components for metal complex dyes, in particular those derived from l-amino-2-naphthol-4-sulfonic acid. Kozlov and Volodarskii (1969) measured the rates of diazotization of l-amino-2-naphthol-4-sulfonic acid in the presence of one equivalent of 13 different sulfates, chlorides, and nitrates of di- and trivalent metal ions (Cu2+, Sn2+, Zn2+, Mg2+, Fe2 +, Fe3+, Al3+, etc.). The rates are first-order with respect to the added salts. The highest rate is that in the presence of Cu2+. The anions also have a catalytic effect (CuCl2 > Cu(N03)2 > CuS04). The mechanistic basis of this metal ion catalysis is not yet clear. 

Approach (a) is normally the easiest to control, and is used in the application of levelling acid and 1 1 metal-complex dyes to wool or nylon, and of the reactive, sulphur or vat dyes to cellulosic fibres. The agents traditionally used are the stronger acids and alkalis such as sulphuric, hydrochloric and formic acids, sodium carbonate and sodium hydroxide. In... 

The dye-fibre systems of obvious interest for approach (b) are milling acid and 1 2 metal-complex dyes on wool or nylon, basic dyes on acrylic fibres and disperse dyes on various fibres. With wool and nylon there is often some overlap with approach (c) (section 12.2). 

Levelling acid dyes and particularly 1 1 metal-complex types generally require an exceptionally low pH in order to promote exhaustion and levelling up to 3% o.w.f. sulphuric acid is most commonly used for levelling acid dyes, although hydrochloric, formic and phosphoric acids are also effective. In the case of conventional 1 1 metal-complex dyes it is essential to use a sufficient excess of acid over and above the typical 4% o.w.f. sulphuric acid normally absorbed by the wool, otherwise there may be a tendency towards tippy dyeings and lower wet fastness. The actual excess required depends on applied depth and liquor ratio [2] typical recommendations are given in Table 12.2. 

Table 12.2 Amounts of sulphuric acid used with conventional 1 1 metal-complex dyes [2]...

For generation of acidic conditions, a non-volatile acid such as citric acid (12.7), or an acid donor such as ammonium tartrate (12.8) or ammonium sulphate, is preferred. An acid or acid donor is not used with 1 2 metal-complex dyes of high neutral-dyeing affinity,... 

Synthetic alizarin (5.1), Cl Mordant Red 5 (5.2) and Cl Mordant Orange 1 (5.3), the first azo dye capable of forming a metal complex, in this case via the salicylic acid residue, are examples of the simple mordant dyes in widespread use at the time when Werner propounded his theory. The first metal-complex dyes to be prepared in substance, rather than within the fibre, were discovered by Bohn of BASF in 1912 by treating hydroxyanthraquinonesulphonic acids with a warm solution of a chromium(III) salt. In the... 

The presence of residual unbound transition-metal ions on a dyed substrate is a potential health hazard. Various eco standards quote maximum permissible residual metal levels. These values are a measure of the amount of free metal ions extracted by a perspiration solution [53]. Histidine (5.67) is an essential amino acid that is naturally present as a component of perspiration. It is recognised to play a part in the desorption of metal-complex dyes in perspiration fastness problems and in the fading of such chromogens by the combined effects of perspiration and sunlight. The absorption of histidine by cellophane film from aqueous solution was measured as a function of time of immersion at various pH values. On addition of histidine to an aqueous solution of a copper-complex azo reactive dye, copper-histidine coordination bonds were formed and the stability constants of the species present were determined [54]. Variations of absorption spectra with pH that accompanied coordination of histidine with copper-complex azo dyes in solution were attributable to replacement of the dihydroxyazo dye molecule by the histidine ligand [55]. 

The major problem of these diazotizations is oxidation of the initial aminophenols by nitrous acid to the corresponding quinones. Easily oxidized amines, in particular aminonaphthols, are therefore commonly diazotized in a weakly acidic medium (pH 3) so-called neutral diazotization or in the presence of zinc or copper salts. This process, which is due to Sandmeyer, is important in the manufacture of diazo components for metal complex dyes, in particular those derived from l-amino-2-naphthol-4-sulfonic acid. 

Thus, RP-HPLC-MS has been employed for the analysis of sulphonated dyes and intermediates. Dyes included in the investigation were Acid yellow 36, Acid blue 40, Acid violet 7, Direct yellow 28, Direct blue 106, Acid yellow 23, Direct green 28, Direct red 79, Direct blue 78 and some metal complex dyes such as Acid orange 142, Acid red 357, Acid Violet 90, Acid yellow 194 and Acid brown 355. RP-HPLC was realized in an ODS column (150 X 3 mm i.d. particle size 7 /.an). The composition of the mobile phase varied according to the chemical structure of the analytes to be separated. For the majority of cases the mobile phase consisted of methanol-5 mM aqueous ammonium acetate (10 90, v/v). Subsituted anthraquinones were separated in similar mobile phases containing 40 per cent methanol. The flow rate was 1 ml/min for UV and 0.6 ml/min for MS detection, respectively. The chemical structure of dye intermediates investigated in this study and their retention times are compiled in Table 3.28. It was found that the method is suitable for the separation of decomposition products and intermediates of dyes but the separation of the original dye molecules was not adequate in this RP-HPLC system [162],... 

Metal Complexation. Azo dyes containing hydroxy or carboxylic acid gronp substituents adjacent to the azo gronp react with transition metal ions, e.g. chromium, cobalt and copper to produce complexes, e.g. Cl Acid Violet 78 (2.15)7 These metal complex dyes are more stable to light than their unmetallised precursors and have been widely nsed as dyes for polyamide and wool fibres. However, there is now a move away from chrominm complexes due to toxicity concerns (see section 2.3.2.). 

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. ... 

Metal Complex Dyes. T he 1 2 metal-dye complexes are of commercial interest because of their excellent lightfastness in pale shades. These macromolecules arc dillicult to apply level and arc sensitive to both chemical and physical variations. In their application they are treated as the Group 3 acid dyes. 

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