Acid and Metal-Complex Dyes

Acid and Metal-Complex Dyes on Wool and Silk... 

For printing with acid and metal-complex dyes on polyamide material see Section 4.10.2. 

Problems with the compatibility of the dyes can also arise in dyeing mixtures of PA and PAC fibers. Such blends are produced, e.g., for skiwear. The cationic dyes used for the PAC component do not dye normal PA fibers. Acid and metal-complex dyes leave PAC fibers practically white. Sulfo group containing 1 1 metal-complex dyes possess a zwitterionic character and therefore can be applied in low concentration in the same bath with cationic dyes, without the occurrence of precipitation. In this manner, one-bath dyeing can be carried out. The stability of... 

Teri et al. [169] report the highest depth of dyeing for sisal fibers relative to jute and coir in the case of direct, acid, and metal complex dyes, where, as in the case of cationic dyes, coir exhibited the highest depth of shade, followed by jute and sisal, due to absorption of the dye at localized sites in the fiber. ... 

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. 

Uses Reserving agent for polyamide fibers and wool against many acid and metal complex dyes in wet-on-wet printing... 

Practically all synthetic fibers can be printed with disperse dyes. Cationic dyes are used preferentially for acrylic fibers, and acid dyes and metal-complex dyes can be used for prints on polyamide fibers. The importance of printing with disperse dyes and the relative amount of different man-made fibers used for prints varies according to fashion and local requirements. Polyester fabrics alone or in combination with cotton are the most important. After precleaning, fabrics made from synthetic fibers must be heat-set to achieve dimensional stability and crease resistance. The usual setting conditions are 20-30 s at 190-210°C, and for texturized articles about 30°C lower. 

Dyes. In dyeing PES-wool mixtures, disperse dyes are used for the PES component, and acid or metal-complex dyes for the wool. Disperse dyes can soil wool to a great extent. Since they produce poorly fast dyeings on wool, the dyes selected must stain wool as slightly as possible or must be easily removable by a washing step, which may be reductive if necessary. Frequently used dyes are C.I. Disperse Yellow 23, 54, 64 C.I. Disperse Orange 30, 33 C.I. Disperse Red 50, 60, 73, 91, 167, 179 and C.I. DisperseBlue 56, 73, 87. Premixed dyes consisting of disperse and wool dyes are occasionally available. 

Traditionally, acid dyes have been categorized by dyers into four distinctive groups, based largely on their unique properties and dyeing characteristics leveling dyes, milling dyes, supermilling dyes, and metal complex dyes. An outline description of these four types follows ... 

Uses Leveling agent for dyeing wool with acid, chrome, and metal complex dyes Properties Yel. liq. misc. with water sp.gr. 1.08 33% act,... 

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. 

In the case of the naphthoquinone methine-type near-IR dye 55, reduction with tin(II) chloride under acidic conditions gives the leuco dye 56, which has weak absorption maxima at 350-359nm in methanol. The leuco dye 56 can be isolated as a stable pale yellow compound. The oxidation behavior of 56 has been studied by adding benzoquinone as oxidant in methanol solution. Compound 56 immediately produced new absorption at 760 nm which is consistent with the absorption maximum of 55 (Scheme 19).30 The absorption spectra of the leuco, quinone, and metal complex forms are summarized in Table 3. 

The physical and chemical properties of formazans have been reviewed in detail.1,2 In this discussion only those properties that directly or indirectly affect the choice of a tetrazolium salt as a leuco dye will be discussed. Spectral, acid—baseyedox, and metal complexing properties will be stressed. 

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. 

---