Direct dyes coupled

Azo-stilbene dyes formed by diazotization of a condensation product containing primary amino groups and coupling with azo dye coupling components, eg. Direct Brown 29 (Cl 40505) (6) ... 

The advantage of fluorescent dyes coupled to primary antibodies is the fast result obtained with the direct method. Another advantage is the possibility to label more than one antigen at the same time. In plant material, it is important to take into account the possible autofluorescence of the tissue. Disadvantages can be the lack of orientation in the tissue and photobleaching of the dyes. The latter problem can often be... 

The simplest monoazo dyes fail to meet these requirements, but by choosing intermediates known to confer substantivity and by building up the molecule to provide the necessary length and coplanarity (section 3.2.1), direct dyes can be produced from this class. Thus the highly substantive character of the benzothiazole nucleus is exploited in Cl Direct Yellow 8 (4-58), as is the alignment of the azo, ureido and acylamino groups in the substituted J acid coupling component of Cl Direct Red 65 (4-59). 

Direct dyes have only modest fastness to washing, which may be improved by after-treatments such as metal-complex formation (section 5.5.3) or by diazotisation of the dye on the fibre and further coupling of the diazonium salt with an insoluble coupling component (section 1.6.14). In addition to their use on cotton and viscose, direct dyes are important in the dyeing of leather. The cheapest members of this class are also used in the coloration of paper, since for this purpose fastness properties are largely irrelevant and price is all-important. 

Many of the premetallised direct dyes are symmetrical structures in the form of bis-1 1 complexes with two copper(II) ions per disazo dye molecule. Scheme 5.12 illustrates conversion of the important unmetallised royal blue Cl Direct Blue 15 (5.43), derived from tetrazotised dianisidine coupled with two moles of H acid, to its much greener copper-complex Blue 218 (5.44) with demethylation of the methoxy groups as described above. Important symmetrical red disazo structures of high light fastness, such as Cl Direct Red 83 (5.45), contain two J acid residues linked via their imino groups. Unsymmetrical disazo blues derived from dianisidine often contain a J acid residue as one ligand and a different coupler as the other, such as Oxy Koch acid in Cl Direct Blue 77 (5.46), for example. 

In contrast to direct dyes, metal-complex azo reactive dyes are almost always monoazo chromogens coordinated to one copper(II) ion per molecule. The important structural types include phenylazo J acid reds (5.47), phenylazo H acid violets (5.48) and naphthylazo H acid blues (5.49), where Z represents the reactive system attached through the imino group in the coupling component. Less often the reactive system is located on the diazo component, as in Cl Reactive Violet 5 (5.50) and analogous red to blue members of various ranges. 

The group of direct dyes with aftertreatment includes direct dyes that, after being applied to the fiber by the usual method, are subjected one of the following aftertreatments (1) Aftertreatment with cationic auxiliaries, (2) aftertreatment with formaldehyde, 3) diazotization of the dye on the fiber and coupling with suitable components (diazotization dyes), and (4) aftertreatment with metal salts. 

Acetoacetic acid arylides and pyrazolone derivatives are the coupling components mainly used. Naphtbolsulfonic acids are of only minor importance here. Dehydrothio- p-toluidine sulfonic acid (2) and the sulfonated primulin base are also used as diazo components for certain orange disazo direct dyes. 

The possibility of first converting suitable azo compounds into copper complexes, and subsequently using them as coupling components for the synthesis of azo direct dyes, was also described. 

The urea bridge can also be introduced into direct dyes with 4,4 -diaminodi-phenylurea derivatives by means of bis-diazotization and coupling (see 25). 

Direct dyes containing one or more diazotizable amino groups in the dye molecule permit further diazotization on the fiber and subsequent coupling with a developer. 3-Naphthol can be used as a developer for orange, red, brown, blue, and black shades, and 1,3-phenylenediamine and 2,4-diaminotoluene for brown, gray, and black shades. 

Direct dyes (see Section 3.3) that contain aromatic amino groups can be diazo-tized on the fiber after dyeing and then coupled with a developer (a phenol, naphthol, or aromatic amine). Wetfastness, in particular, is improved by such an enlargement of the molecule, and the shade also changes (see Section 2.2). Conversely, water-soluble, substantive azo dyes which bear amino or hydroxyl groups capable of coupling can also be used, followed by aftertreatment with a diazo-nium compound. The resulting polyazo dye shows excellent wetfastness (see also Section 4.8). 

The direct dyes that are most suitable for leather have the following features predominantly long-chain dye molecules, sulfonate groups at the ends of the molecule, additional non-dooble-bonded groups, a balanced ratio of double bonds to solubilizing groups, and predominantly meta -substituted azo coupling components. These empirical observations have been used to enhance the technical properties of anionic polyazo leather dyes. 

Because many direct dyes do not have good washfastness and lightfastness, their dyeings on cotton are often treated with a chemical agent, in what is commonly known as an aftertreatment process. The most widely used aftertreatment methods involve (1) cationic fixatives, (2) copper sulfate, or (3) diazotiza-tion and coupling reactions. The first and third methods are designed to enhance wash-... 

Type A1 — Z X Z-t—A1 Synthesis. Disazo dyes of this type are produced from coupling twice to dye intermediates such as those shown in Fig. 13.99, and are largely direct dyes for cotton. A representative synthesis is shown in... 

Primuline, discovered by Green, was the first commercial yellow direct dye which could be diazotized on the fiber and coupled with washing is good, but its light fastness is unsatisfactory. Also, it is not... 

Since such light fast, direct dyes are usually trisazo dyes, a possible structure is synthesized from 2-naphthylamine-4,8-disulfonic acid, o-naphthylamine, Cleve acid, and y acid (acid coupling). 

Various types of dyes are prepared from dehydrothiotoluidine. The free base or its sulfonic acid is diazotized and coupled with various naph-tholsulfonic acids such as, for example, e acid (l-naphthol-3,8-disul-fonic acid). The resulting dye is characterized by its high purity of color and can be discharged to a pure white. Such red direct dyes are sold under various names, and are usually referred to as dyes of the erika red type. (Erika Z is the combination from dehydxothioxylidine and e acid. l-Naphthol-3,6-disulfonic acid gives a very similar dye.) In addition to the true azo dyes from dehydrothiotoluidine, two other products are made which are important yellow dyes. One of these dyes is the naphthamine yellow NN (also called chloramine yellow) (Kalle), formed from dehydrothiotoluidinesulfonic acid by oxidation with sodium hypochlorite. The other is thiazole yellow or Clayton yellow, which is made by combining the diazo compound of dehydrothiotoluidinesulfonic acid with a second molecule of the same compound to form a diazoamino compound. 

In producing the developed colours, the direct dyestuff is diazotized on tile fibre, and the diazonium compound couples with a suitable developer. With the coupled dyes the process is reversed. The cotton is dyed with a direct dye containing an amino or hydroxyl group and the dyed fibre is then treated with a solution of a diazotized base. An example is Benzo Para Deep Brown G (C.I. direct brown 152), (24),... 

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