Acid dyes

Dyes Containing Anionic Functional Groups Acid dyes Direct dyes Mordant dyes Reactive dyes 

Dyes Requiring Chemical Reaction before Application Vat dyes Azoic dyes Sul fur dyes 

Special Colorant Classes Disperse dyes Solvent dyes Pigments Natural dyes 

Dyes classified by this scheme are assigned standard designations according to dye class, color, and overall constitution by the Society of Dyers and Colorists in the Color Index (e.g Acid Blue 141, Vat Green 17, Disperse Red 17). 

A number of dyes, including acid, direct, mordant, and reactive dyes, contain functional groups that are sodium salts of sulfonic or carboxylic acids. These functional groups provide water solubil ity to the dyestuff. The dyes differ in subclassification in their affinity for fibers and/or the presence of special functional groups. 

Acid dyes are used for dyeing wool, synthetic polyamides, and silk in aqueous media. They may be subdivided into the following basic types  

The arylamino residue may be altered subsequently by sulfonation, halogena-tion, acylation, or by the Einhom reaction. Substitution of anthraquinone in the 5-, 6-, 7-, or 8-positions offers an additional possibility to change the characteristics of the dye. For instance, halogen atoms and sulfonic acid groups cause bath-ochromic effects that are most pronounced when the substituents are introduced in the b-position. The solubility of the 2,6- (or 2,7-) disulfonic acids is higher than that of the 2,5- (or 2,8-) series. 

Diamino dihydroxyanthraquinonesulfonic Acids. These dyes belong to the oldest synthetic acid wool dyes, but their importance has decreased considerably An example for this class is 62, C.I. Acid Blue 43, 63000 [2150-60-9] [6, p. 42], 

1-Amino -4-hydmxyanthraquinones with External Sulfonic Acid Groups. By onesided reaction of quinizarin with aiylamines, followed by sulfonation, violet level- 

Other Acid Anthraquinone Dyes. In addition to the dyes in the preceding classes, a whole series of specially developed products is available. For instance, derivatives of the anthrimide or carbazole series are known to be very light-fast gray and brown wool dyes. The post-sulfonation products of 1,5- and 1,8-diarylami-noanthraquinones are violet dyes commonly applied as mixtures. 

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Mordant acid dyes combine simultaneously with the mordanting agent (generally Cr(OH)j) and the fibre the dyestuff generally contains ortho OH -azo or OH-OH groups. 

Premetallized acid dyes are similar to the simple acid dyes but are already complexed to a metal. 

Most xanthene dyes are classified as basic dyes by their method of appHcation acid dyes can be produced by introduction of sulfonic acid groups. The fluoresceins, which contain carboxy and hydroxy substituents, are also acid dyes for coloration of silk. Some of the fluoresceins in which the carboxy group has been esterified, are soluble in alcohol or other organic solvents and can be classified as solvent dyes. Mordant dyes can be produced by introducing o-dihydroxy or sahcyhc acid groups (2), which when metallised can have very good lightfastness. 

Another group of halogenated fluorescein dyes is prepared by condensing chloro derivatives of phthalic anhydride with resorcinol, followed by bromination or iodination. Thus Phloxine B /78472-87-2] (Acid Red 92, Cl45410) (42) is prepared by condensing tetrachlorophthaUc anhydride with resorcinol followed by tetrabromination. Phloxine B undergoes ethylation to yield the yellowish ted acid dye Cyanosine B [6441-80-1] (43). 

As improvements over P-methylumbeUiferone (55—57), 4-methyl-7-amino-coumarin [26093-31-2] (12a) and 7-dimethylamino-4-methylcoumarin [87-014] (12b) (58—61) were proposed. These compounds are used for brightening wool and nylon either in soap powders or detergents, or as salts under acid dyeing conditions. They are obtained by the Pechmaim synthesis from appropriately substituted phenols and P-ketocarboxyflc acid esters or nitriles in the presence of Lewis acid catalysts (see Coumarin). 

Chrome-tanned leather has chromium bonded to the leather fibers. This chromium can act as a mordant for acid dyes resulting in fast colors and intense shading at the surface of the leather. 

In dye-binding tests, milk is mixed with excess acidic dye solution where the protein binds the dye in a constant ratio and forms a precipitate. After the dye—protein interaction takes place, the mixture is centrifuged and the optical density of the supernatant is determined. Utilization of the dye is thus measured and from it the protein content determined. Several methods for appHcation of dye-binding techniques to milk are given (24,25). 

Many aminonaphthalenesulfonic acids are important in the manufacture of azo dyes (qv) or are used to make intermediates for azo acid dyes, direct, and fiber-reactive dyes (see Dyes, reactive). Usually, the aminonaphthalenesulfonic acids are made by either the sulfonation of naphthalenamines, the nitration—reduction of naphthalenesulfonic acids, the Bucherer-type amination of naphtholsulfonic acids, or the desulfonation of an aminonaphthalenedi-or ttisulfonic acid. Most of these processes produce by-products or mixtures which often are separated in subsequent purification steps. A summary of commercially important aminonaphthalenesulfonic acids is given in Table 4. 

Parameter Basic dyes Acid dyes Direct dyes... 

The amine ends also react with atmospheric contaminants, such as SO2 and oxides of nitrogen and ozone, under ambient storage conditions (50). This phenomenon is referred to as aging and results in reduced acid dye affinity. 

Effect of Fiber Properties. Acid dyes are attracted to the accessible amine ends of the nylon chains located in the amorphous regions of the fiber. Acid dye affinity of nylon can be adjusted by a dding excess diamine or diacid to the polymer salt or by changing the molecular weight in polymerization. A light acid-dyeable nylon-6,6 is spun with 15—20 amine ends, expressed in terms of gram equivalents per 10 g of polymer. A medium or... 

The major use of this compound is in the production of mordant and acid dyes. 2-Amino-4-nitropheno1 also has found limited use as an antioxidant and light stabilizer in butyl mbbers and as a catalyst in the manufacture of hexadiene. The compound has been shown to be a skin irritant and continuous exposure should be avoided. Toxicological studies indicate that it is nonaccumulative (162). 

Dyes, Dye Intermediates, and Naphthalene. Several thousand different synthetic dyes are known, having a total worldwide consumption of 298 million kg/yr (see Dyes AND dye intermediates). Many dyes contain some form of sulfonate as —SO H, —SO Na, or —SO2NH2. Acid dyes, solvent dyes, basic dyes, disperse dyes, fiber-reactive dyes, and vat dyes can have one or more sulfonic acid groups incorporated into their molecular stmcture. The raw materials used for the manufacture of dyes are mainly aromatic hydrocarbons (67—74) and include ben2ene, toluene, naphthalene, anthracene, pyrene, phenol (qv), pyridine, and carba2ole. Anthraquinone sulfonic acid is an important dye intermediate and is prepared by sulfonation of anthraquinone using sulfur trioxide and sulfuric acid. 

The dyes used on wool can be divided into the following groups acid dyes, chrome dyes, premetallized dyes and reactive dyes (88,89,92—94,97—99). Strictly speaking, all types of wool dyestuffs can be described as acid dyes, but in practice this term is confined to leveling acid dyes, half-milling dyes, milling dyes, and supermilling dyes (94,97). This subclassification of acid dyes arises out of the methods used for their appHcation and their fastness properties on wool. 

Chrome dyes are acid dyes (mol wt 300—600) that contain groups capable of forming complexes by reaction with a metal salt, usually sodium or potassium dichromate (94,97). The chrome/dye complex has lower solubiUty, and hence better wetfastness, than the parent dyestuff. Reaction between the... 

The incorporation of metal salts of amphoteric surface active agents (Mostat Series) as internal antistatic agents in polypropylene fibers has been reported (95). Metal salts of alanine, amidoamine, and imida2oiine-type amphoteric surface-active agents show excellent performance as internal antistatic agents and also improve the dyeing abiUty of the fibers with acid dyes. 

Dyes in these classes are generally basic dyes ie, the chiomophoie is cationic. Some stmctures have been sulfonated to acid dyes, eg, the Nigrosine, (Cl Solvent Black 5 Cl 50415), (8) to Cl Acid Black 2 [8005-03-6] (Cl 50420) (9). 

ACID DYES Commercial acid dyes contain one or more sulfonate groups, thereby providing solubility in aqueous media. These dyes are apphed in the presence of organic or mineral acids (pH 2—6). Such acids protonate any available cationic sites on the fiber, thereby making possible bonding between the fiber and the anionic dye molecule. Wool, an animal fiber, is an amphoteric coUoid, possessing both basic and acidic properties because of the amino and carboxylic groups of the protein stmcture. In order to dye such a system, coulombic interactions between the dye molecule and the fiber must take place ie, H2N" -wool-COO + H2N" -wool-COOH. The term acid dye is appHed to those that are capable of such interactions. Acid dyes... 

There are three general classifications of acid dyes depending on their method of apphcation acid dyes that dye direcdy from the dyebath, mordant dyes that are capable of forming metallic lakes on the fiber when aftertreated with metallic salts, and premetallized dyes. 

The data in Table 1, as reported by the U.S. International Trade Commission (39), show the extent of acid dye production and sales in the United States in 1988. In addition, the Trade Commission Import (40) data shows that 2753 t of acid dyes valued at 24.9 million was imported in 1983. Table 2 shows the important acid dyes for which production and sales data are revealed by the manufacturers. 

Table 2. Commercial Acid Dyes, U.S. Production and Sales., 1988 ...

Mordant Dyes. MetaUizable azo dyes are appHed to wool by the method used for acid dyes and then treated with metal salts such as sodium chromate [7775-11-5] sodium dichromate [10588-01-9] and chromium fluoride [1488-42-5] to form the metal complex in situ. This treatment usually produces a bathochromic shift ia shade, decreases the solubUity of the coloring matter, and yields dyeiags with improved fastness properties. The chromium salts can be appHed to the substrate before dyeiag (chrome-mordant or chrome-bottom method), together with the dye ia a single bath procedure (metachrome process), or as a treatment after dyeiag (afterchrome process). 

Barium chloride finds use in the production of barium colors, such as the diazo dyes barium hthol ted [50867-36-2] and barium salt of Red Lake C [5160-02-1], a mordant for acid dyes and dying of textiles. Other uses include aluminum refining and boiler water treatment. 

Other minor uses of ethyl chloride iaclude blowiag agents for thermoplastic foam (51) and styrene polymer foam (52), the manufacture of polymeric ketones used as lube oil detergents (53), the manufacture of acetaldehyde (qv) (54), as an aerosol propellent (55), as a refrigerant (R-160), ia the preparation of acid dyes (56), and as a local or general anesthetic (57,58). 

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