Dye Salts with Complex Anions

Prints containing Alkali Blue are not fast to the standard DIN 16524 solvent mixture, but they are fast to acid, paraffin, butter, and other materials. Tested in accordance with normative testing standards (Sec. 1.6.2.2), the prints unexpectedly also show fastness to alkali. It should be noted, however, that at higher alkali concentrations the tinctorial strength of the system declines and the shade becomes duller. This is a result of the fact that the pigment reacts with alkali. 

In terms of lightfastness, Alkali Blue performs moderately. 1/1 SD letterpress proof prints equal step 3 on the Blue Scale, while 1/3 to 1/25 SD formulations equal only step 2. However, as shading components their lightfastness is excellent and satisfies the requirements for all types of applications. This is due to the fact that a large portion of the incident light is absorbed by carbon black. 

Alkali Blue pigments are used in large volume to color office articles, especially ribbons for typewriters and computers, as well as blue copy paper. Other areas of application, such as the plastics industry, do not employ Alkali Blue pigments because of their lack of fastness. 

This class of pigments consist of salts of the anions of complex inorganic acids with dye cations, primarily with triarylcarbonium cations. 

The shortage of tungsten and molybdenum during the 1930s in Germany necessitated the use of copper ferrocyanide as anion. Some of these salts have maintained their commercial position to the present time. Besides, silicomolybdates are also used to produce this type of pigments. 

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Eq. (a) shows that the quaternary salt gets quantitatively precipitated by sodium tetraphenyl boron as the complexing agent. Eq. (b) depicts that quaternary compounds shall readily react with certain anionic dye, such as bromophenol blue, to yield a blue, chloroform-soluble complex. 

As claimed (Mihara et al. 1997), it is possible to improve significantly the light resistance of the organic dye used by combining the organic dye with a nitrogen-containing cation radical salt with metal complex anion. One such cation radical salt is shown in Scheme 7-2. 

Direct Dyes. These water-soluble anionic dyes, when dyed from aqueous solution in the presence of electrolytes, are substantive to, i.e., have high affinity for, cellu-losic fibers. Their principal use is the dyeing of cotton and regenerated cellulose, paper, leather, and, to a lesser extent, nylon. Most of the dyes in this class are polyazo compounds, along with some stilbenes, phthalocyanines, and oxazines. Aftertreatments, frequently applied to the dyed material to improve washfastness properties, include chelation with salts of metals (usually copper or chromium), and treatment with formaldehyde or a cationic dye-complexing resin. 

Solvent dyes [1] cannot be classified according to a specific chemical type of dyes. Solvent dyes can be found among the azo, disperse, anthraquinone, metal-complex, cationic, and phthalocyanine dyes. The only common characteristic is a chemical structure devoid of sulfonic and carboxylic groups, except for cationic dyes as salts with an organic base as anion. Solvent dyes are basically insoluble in water, but soluble in the different types of solvents. Organic dye salts represent an important type of solvent dyes. Solvent dyes also function as dyes for certain polymers, such as polyacrylonitrile, polystyrene, polymethacrylates, and polyester, in which they are soluble. Polyester dyes are principally disperse dyes (see Section 3.2). 

In the initial description of the cationic dye-borate system [24, 76], it was postulated that electron transfer was possible because, in nonpolar solvents, dye/borate salts exist predominantly as ion pairs. Since the lifetime of the cyanine singlet excited state is quite short [24, 25], this prerequisite is crucial for eflfective photo-induced electron transfer. Recently initiator systems in which neutral dyes are paired with triarylalkylborate anions have appeared in the literature [77]. In the latter case, the borate ion acts as the electron donor while neutral merocyanine, coumarin, xanthene, and thioxanthene dyes act as the electron acceptors. It is obvious that these initiating systems are not organized for effective electron transfer processes. The formation of an encounter complex (EC) between excited dye and electron donor is required. 

Analytical flotation, i.e. shaking out with organic liquids, may be used to advantage when colored or colorless precipitations are conducted in a test tube. Minute amounts of a colored precipitate produced in a colored solution can often be made visible if the test is made as a drop reaction on filter paper or, in case this is not feasible because of the need of warming, etc., a drop of the suspension (after dilution if necessary) can be placed on filter paper. The precipitate will be retained in the center of the fleck while the colored liquor diffuses away through the capillaries of the paper and can be effectively separated from the precipitate by repeated treatments with one to three drops of water. However, it must be remembered that not all colored solutes may be washed away in this manner, because certain soluble colored substances (usually with colored anions) are irreversibly adsorbed on filter paper. Examples include the red solutions of complex ferrous salts of a,a -dipyridyl and phenanthroline, and likewise solutions of acid or amphoteric dyes (for instance rhodamine dyes). 

Cationic azo dye occurs as salt with halide or other anion. Used as aq. soln. Forms extractable ion-pairs with Co, Ni and other metals (as anionic complexes) which are used in sensitive extraction-photometric detn. of metals. Cryst. Sol. H2O. 

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. 

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. 

As the range of components available for use in the azoic dyeing process expanded, research was simultaneously targeted on improvements designed to make the process more attractive to the commercial dyer. The necessity for the dyer to diazotise the Fast Base was removed with the introduction of stabilised diazonium salts [111], known as Fast Salts. Stabilisation was achieved by a judicious selection of the counter-ion to the diazonium cation various anions have found use in commercial Fast Salts and some examples are listed in Table 4-4. Particularly effective is the diazonium tetrachlorozincate, which can be readily prepared by adding an excess of zinc chloride solution to a solution of the diazonium salt. The precipitated complex diazonium salt is usually admixed with an inert diluent, which enhances its stability, and in use the dyer only needs to dissolve the powder in water to prepare the necessary diazonium salt solution. 

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