Direct Trisazo Dyes

Direct Blue 218 had reported sales of 623 t valued at 4.4 million ia 1987. It is produced from Direct Blue 15 (76) by metallizing and elimination of methyl groups from the methoxide to form the copper complex. Direct Blue 15 (76) is prepared by coupling o-dianisidine [119-90-4] to two moles of H-acid (4-amiQO-5-hydroxy-2,7-naphthalenedisulfonic acid) under alkaline pH conditions. Other important direct blues iaclude Direct Blue 80 (74), (9-dianisidine coupled to two moles of R-acid (3-hydroxy-2,7-naphthalenedisulfonic acid [148-75-4]) followed by metallizing to form a bis copper complex, and Direct Blue 22 (77), an asymmetrical disazo dye, prepared by coupling o-dianisidine to Chicago acid [82-47-3] and 2-naphthol. Direct Blue 75 (78) is an example of a trisazo dye represented as metanilic acid — 1,6-Q.eve s acid — 1,6-Q.eve s acid — (alb) Ai-phenyl J-acid. 

Numerous linear diamines, such as many of those in the survey mentioned above, have been evaluated as potential replacements for benzidine, an inexpensive and highly versatile intermediate that was banned in the 1970s because it posed a carcinogenic threat. Two trisazo dyes have been synthesised recently using 4,4, diaminodiphenyl thioether instead of the benzidine component of Cl Direct Black 38 (3.112 X = Y = NH2) and Cl Direct Green 1 (3.112 X = OH, Y = H). These new dyes exhibited higher substantivity and fastness to washing than the two traditional products on cellulosic fibres [119]. 

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). 

Disazo and trisazo dyes (containing two and three azo groups, respectively) can be treated with COClj to give mostly red or brown shades. For example. Direct Red 80 (4.18 C.I. No. 35780) is prepared by treating (4.19) with phosgene [992a] ... 

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). 

TrisaZO and Polyazo Dyes. These are mostly direct dyes, the hues ate predominandy brown, black, or dark blue or green. Some are leather dyes. Benzidine, which used to be an important bisdiazo component, has been replaced by 4,4 -diaminobenzanilide [785-30-8] ... 

All azo dyes contain one or more azo groups (-N=N-) as chromophore in the molecule on the basis of the number of azo groups in each molecule, they are named monoazo-, disazo-, trisazo-, etc. The azo groups are in general bound to a benzene or naphthalene ring, but they can also be attached to heterocyclic aromatic molecules or to enolizable aliphatic groups. On the basis of the characteristics of the processes in which they are applied, the molecule of the dye is modified to reach the best performances so they can be acid dyes, direct dyes, reactive dyes, disperse dyes, or others. 

It is in the direct dye class that the more complex polyazo dyes come into their own, and trisazo structures such as Cl Direct Blue 78 (4.64), Cl Direct Brown 222 (4-65) and Cl Direct Black 38 (4.66) are classic examples of this type of dye. The last-named dye is now known to be carcinogenic [72]. Generally, the A—>M2— E type (such as 4-64) afford reasonably bright blue shades whilst dyes prepared according to other sequences, such as the E<—D— Z<—A type (examples 4.65 and 4-66) yield drab shades. 

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... 

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. 

Diazotised benzidine is coupled with 8-amino-a-naphtliol-8 C-disulphonic acid (H acid) in acid solution and the resulting dyestuff in sodium carbonate solution added to diazotised p-aminophenylarsinic acid. The resulting trisazo-dyestuffis a brownish-black powder, soluble in water, giving a blue solution, which dyes cotton directly in blue tones. 

Azo dyes are classified according to a color index system based on usage and chemical constituents. These are subdivided into monoazo, disazo, trisazo, and polyazo derivatives with a specific assigned range of color index number. Another classification system involves dividing dyes into dyeing classes such as acid, basic, disperse, direct, mordant, and reactive dyes. Azo compounds are used extensively as dyes to color varnishes, paper, fabrics, inks, paints, plastics, and cosmetics. They are used in color photography. 

---