Yellow azo dye

The l-arylpyrazol-5-ones (4.9), prepared by the two-step condensation of an arylhydrazine with ethyl acetoacetate, are the most commonly used coupling components for the synthesis of greenish yellow azo dyes. Coupling occurs at the 4-position of the pyrazolone ring which, as in the case of the acetoacetarylamides discussed above, is activated towards electrophilic attack by the two flanking unsaturated carbon atoms (Scheme 4.14). 

The indazolin-3-ones (55) yield magenta dyes formulated as zwitterionic structures (56) (69USP3486894). On the other hand, the related benzisoxazolones (57) give yellow azo dyes (58) with p-phenylenediamines (57BRP778089). 

With regard to heterocyclic compounds as coupling components, the importance of the formerly widespread pyrazolone-, aminopyrazole-, and 4-hydroxy -quinolone-based yellow azo dyes has greatly diminished with the advent of the tinctorially superior and therefore more economical pyridone azo dyes. Only a few examples have survived and then only for special applications such as for dyeing of acetate fibers. Examples are C.I. Disperse Orange 56 and C.I. Disperse Yellow5. (for structure, see Section 3.2.5). 

Compared to direct azo dyes, the direct anthraquinone dyes have lower tinctorial strengths and are therefore far less economical to use. They have lost most of their importance. Only a few special green dyes have retained their importance. Direct green cotton dyes can be produced by coupling a blue bromamine acid dye and a yellow azo dye via ureido or diaminotriazine bridges. 

Early in the twentieth century a very hazardous chemical was used as a food colourant 4-dimethylaminoazobenzene, so-called butter yellow , was a yellow azo dye used in some countries to colour butter, before extensive testing was required. When it was studied in 1947, the dye was shown to be a potent carcinogen capable of causing liver tumours in experimental animals, and it was rapidly withdrawn. Fortunately, the treatment of food with additives, which has now become more extensive, is now safe. 

A colorimetric method for microdetermination of sulfonamides based on diazotization of the drug with sodium nitrite and hydrochloric acid has been reported (59). The diazonium salt is then coupled with 8-hydroxyquinoline in alkaline medium and the absorbance of the developed color measured at its maximum wavelength. A similar method involves diazotization and coupling of the sulfonamide with indole in alkaline solution to form an intense yellow azo dye which exhibits maximum absorption at 449 nm. Beer s law is obeyed over the concentration range 1-32 /ig/ml with a relative standard deviation of less than 2% (60). The reaction of sulfonamides with chloramine-T in sulfuric acid gives a yellow product which is suitable for the determination of sulfonamides in different formulations. It has an accuracy similar to that of the Bratton and Marshall method (61). 

The mechanism of the catalytic photofading of yellow azo-dyes by blue anthraquinone dyes has attracted much interest. Two independent groups of... 

Azo dyes find use as acid-base indicators. For example. Methyl Red prepared in this experiment. Methyl Orange, and Congo Red are well-known acid-base indicators. Azo dyes are commonly used in the textile, food, and cosmetic industries FD C Yellow No. 6, a yellow azo dye is used to color candy, ice cream, beverages, and so on. Several azo dyes (including Butter Yellow and FD C Red No. 2) have been banned by the FDA from use in foods, drugs, and cosmetics in the United States because of suspected carcinogenic properties. 

A yellow azo dye once used to color margarine has been outlawed because it is carcinogenic. Outline a synthesis of this dye, butter yellow, starting from benzene and N,N-dimethylaniline ... 

Richter discover the element indium. German chemist Joseph Wilbrand discovers TNT (trinitrotoluene). Production of aminoazobenzene (aniline yellow), the first yellow azo dye. German chemist Adolf von Baeyer develops the first barbiturate. 

An advance was made in 1934 by CIBA in introducing the Chlorantine Greens formed by linking a blue anthraquinone dye and a yellow azo dye by means of a substituted triazinyl ring system (Figure 2.28). 

The formation of colored salts can also take place in alkaline media. For example, the yellow azo dye (VIII) formed in the colorimetric determination of phenol dissolves in alkali with a red color with the formation of ions (IX). Addition of alcohol produces additional solvatochromic color changes to violet (22). 

Figure 27.8 A molecule of a yellow azo dye. instead of phenol, CH,-OH, the reactant used in the coupling reaction is...

Stilbene-azo dyes of more precise constitution prepared in the usual way by tetrazotization and coupling of 4,4 -diamino-2,2 -stilbenedisulfonic acid [81-11-8] (7). The product in this example is ZDkect Yellow 4 (Cl 24890) [3051 -11 -4] (8) ... 

Nitro-l-diazo-2-naphthol-4-sulfonic acid prefers the 2-position in spite of the nitro group, and increasing alkalinity favors ortho coupling with diazophenols. 1-Naphthalenesulfamic acid [24344-19-2] (ArNHSO H) and N-nitro-1-naphthylamine [4323-69-7] (ArNHNO ) couple exclusively in the para position. The substitution of resorcinol [108-46-3] and y -phenylenediamine [108-45-2] is compHcated and has been discussed (29,30). The first azo dyes from aniline, eg. Aniline Yellow [60-09-3] (19) (Cl Solvent Yellow 1 Cl 11000) were manufactured in 1861 and Bismark Brown [10114-58-6] (20) (Cl Basic Brown 1 Cl 21000) appeared in 1863. The reaction is as follows ... 

In this way, many green azo dyes have been made by combining separate conjugated systems in the same molecule, eg, one yellow and the other blue. The blocking or the insulating group prevents the electronic interaction of one chromophore system with the second. Chloramine Fast Scarlet 4BS... 

OIL SOLUBLE AZO DYES The oil soluble, water-iasoluble, azo dyes dissolve ia oils, fats, waxes, etc. Generally, yellow, orange, red, and brown oil colors are azo stmctures and greens, blues, and violets are primarily anthraquiaones (see Dyes, anthraquinone). Blacks are usually nigrosiaes and iaduhnes of the aziae type (see Azinedyes). An example is Oil Red [85-83-6] (127) (Cl Solvent Red 24 Cl 26105). Uses iaclude the coloring of hydrocarbons, waxes, oils, candles, etc. 

Basic Red 22 (134), which contains 1 part ia 7 of the yellowish red 1,4-dimethyl isomer, Basic Red 29 (135), and Basic Yellow 25 (136) are all examples of delocalized cationic azo dyes. Dyes of this type can also be synthesized by Hbnig s oxidative coupling reaction of heteroaromatic hydrazones with tertiary aromatic amines. 

Monoazo Pigments. In combination with other groups, the a2o linkage, —N=N—, imparts color to many dyes and pigments (see Azo Dyes). The simplest of these, ie, the Hansa yellows, toluidine reds, and naphthol reds, do not have the lightfastness and heat stabiUty required for plastics. Permanent YeUow FGL and Permanent Red 2B are stable enough for vinyls, polyethylene, polypropylene, and ceUulosics (11). Permanent Red 2B is available as the calcium, barium, or manganese salt. 

Azo Dyes. The Colourindex classifications of dyes depend more on their historical eady use than on their stmctures, eg. Oil Orange is named Solvent Yellow 14, and a yellow for synthetic fibers is Disperse Yellow 23. 

In general, the azo colors are useful for coloring polystyrene, phenoHcs, and rigid poly(vinyl chloride). Many are compatible with poly(methyl methacrylate), but in this case the weatherabiUty of the resin far exceeds the life of the dyes. Among the more widely used azo dyes (qv) are Solvent Yellows 14 and 72 Orange 7 and Reds 1, 24, and 26. 

Pyrazolone dyes are particularly versatile yellow chromophores the yellow dye developer used in Polacolor, the first instant color film, was based on a pyrazolone dye. The stmctures of the three Polacolor dyes are shown in Figure 3. The study of azo dyes derived from 4-substituted 1-naphthols led to the chromophore used in the Polacolor magenta dye developer. The Polacolor cyan dye developer contained a 1,4,5,8-tetra-substituted anthraquinone as chromophore (20). 

C rbocyclic Azo Dyes. These dyes are the backbone of most commercial dye ranges. Based totally on benzene and naphthalene derivatives, they provide yellow, red, blue, and green colors for all the major substrates such as polyester, cellulose, nylon, polyacrylonitrile, and leather. Typical stmctures (26—30) are shown in Figure 4. 

Fig. 4. Carbocychc azo dyes. Disperse Yellow 3 [2832-40-8] (Cl 11855) (26) is used to dye polyester Reactive Orange 1 [6522-74-3] (Cl 17907) (27) is a cotton dye Direct Orange 26 [25188-23-2] (Cl 29150) (28) is a dye for paper Synacril Fast Red 2G [48222-26-0] (Cl 11085) (29) dyes acrylic fibers Acid...

Although it has been reported (138) that decolorization of wastewater containing reactive azo dyes with sodium hydrosulfite is possible only to a limited extent, others have demonstrated good reduction (decolorization). For example, using zinc hydrosulfite for the decolorization of dyed paper stock (139) resulted in color reduction of 98% for azo direct dyes (139). A Japanese patent (140) describes reducing an azo reactive dye such as Reactive Yellow 3 with sodium hydrosulfite into its respective aromatic amines which ate more readily adsorbable on carbon than the dye itself. This report has been confirmed with azo acid, direct, and reactive dyes (22). 

Many other azo dyes with fluorotriazine reactive groups have been synthesized, eg, scadet [70255-11-7] (78), orange [70239-79-1] (79), yellow [71942-72-8] (80), and orange [73900-71-7] (81). 

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