Tetrakisazo dyes

Numerous syntheses are possible for these dyes, which all yield only dark shades. Here, too, only a few ty pes are of industrial importance. 

A further extension to the trisazo dyes on the principle of series coupling D— Mr M2— M3— K offers no advantages, because the intermediate isolation that is frequently necessary leads to yield losses, and a chain extension is therefore ruled out on economic grounds. This is also reflected in the number of poly-azo dyes listed in the Colour Index [5], Although 78 tetrakisazo dyes with eleven different synthesis principles are listed, only 14 dyes with five and more azo groups are mentioned, two of which are specified with eight azo groups. 

An example of type D - M1- M2- M3- K is the brown C. I. Direct Dye, 35850 [8002-98-0] (sulfanilic acid —m -toluidine — Cleve acid 6 — m -toluidine — 1-nitrophenylene-2,4-diamine). 

the disazo dye is initially prepared from bis-diazotized 4,4 sdiami-nodiphenylamine-2-sulfonic acid with 2 equivalents of c acid. Coupling is then again carried out stepwise to c acid and finally to m -phenylenediamine. 

Direct Black 19, 35255 [6428-31-5] (19) is also an important dye. It is obtained by coupling two equivalents of j9-nitraniline to H acid, sulfhydrate reduction of the two nitro groups, and coupling of the bis-diazotized intermediate compound with two equivalents of m -phenylenediamine. 

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Chemically, the azo class is subdivided according to the number of azo groups present into mono-, dis-, tris-, tetrakis-, etc. Mono- and disazo dyes are essentially equal in importance, trisazo dyes are less important, and tetrakisazo dyes, except for a few, are much less important. For this reason, substances with more than three azo linkages are generally included under the heading of polyazo dyes. The Colour Index]isX.s the azo dyes as follows ... 

Cl Direct Black 22 [6473-13-8] (Cl 35435) is an example of a tetrakisazo dye, (4,4 -dianainodiphenylainine-2-sulfoiiic acid bisdiazotized and coupled to 2 mol gamma acid which is then bisdiazotized and coupled to 2 mol y -phenylenediamine) which had production of 552 t in 1985. 

Tetrakisazo dyes (dyes containing four azo groups) are less common but some do find use, these products often arising from the phosgenation of an amino disazo dye. 

Conventional directdyes include monoazo, disazo. trisazo. and tetrakisazo dyes. It is advantageous to subdivide them according to the nature of their chemical structure. Disazo dyes, for example, can be divided according to chemical synthesis principles into primary and secondary. Conventional azo direct dyes further include symmetric urea derivatives, dyes obtained by oxidation of amines, and triazinyl and copper-containing dyes. 

Tetrakisazo dyes with good fastness properties prepared by tetrazotization of (7) coupling to 1-naphthylamine, letetrazotizing and coupling to, eg, 2-naphthol, have been reported (14). Limited use is also reported for both basic and reactive stilbene-containing dyes (10,13,32,33) (Fig. 2). Although it is reported that basic dyes are stiitable for dyeing paper, none is found in commerce. 

A few azo dyes containing four, five and six azo groups, referred to respectively as tetrakisazo, pentakisazo and hexakisazo dyes, are known although they are progressively less important commercially and, naturally, the synthetic strategies are more complex. Also, because of the... 

An evaluation of the macrocyclic ligand cucurbituril in powder form as a precipitant for direct dyes varying in molecular size, including Cl Direct Red 79 (disazo), Blue 71 (trisazo) and Red 80 (tetrakisazo), established the influence of pH and ligand concentration on adsorption [60]. The cucurbituril molecule contains six acetylenediurein units linked in... 

Browns are the most important shades for leather after blacks. Despite then-higher molecular weight and sole use on leather, these dyes are normally also classified as acid dyes. C.I. Acid Brown 123, 35030 [6473-04-7] (9), for example, although a tetrakisazo compound, is classified as an acid dye. The dyeing is more on the surface. 

Polyazo Dyes. Azo dyes can be made with three, four, or more azo linkages. Those with three (trisazo) and four (tetrakisazo) are quite common. An example of a trisazo dye for cotton is Direct Black 80. It is made by the following sequence p-aminoacetanilide is diazotized and coupled alkaline to Gamma Acid, the acetyl group is removed by hydrolysis, and the resulting diamine is tetrazotized and coupled with 1,6 Cleve s Acid to Gamma Acid (alkaline). 

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