Direct Disazo Dyes

Fastusol Yellow 66 [91-34-9] (25) (Cl Direct YeUow 4 Cl 24890) is a symmetrical primary disazo dye from a tetrazo component (4,4 diamino-2,2 stilbene-disulfonic acid [81-11-8],... 

Amidine Fast Red F [2429-84-7] (26) (Cl Direct Red 1 Cl 22310) is an iinsymmetrical primary disazo dye from a tetrazo component (benzidine... 

Direct dyes are defined as anionic dyes substantive to ceUulosic fibers (cotton, viscose, etc), when applied from an aqueous bath containing an electrolyte. Before the discovery of Congo Red in 1884, only mordanted cotton could be dyed. Congo Red [573-58-0] (62) (Cl Direct Red 28 Cl 22120) a primary symmetrical disazo dye, which is made readily from bisdiazotized benzidine and naphthionic acid [84-86-6] (4-arnino-l-naphthalenesulfonic acid), was the precursor of a most important line of dyes, including all shades, derived from benzidine and its homologues. Today, no benzidine dye is produced because benzidine is carcinogenic. 

Direct Reds. The principal commercially produced direct reds, with revealed chemistry, are of disazo or polyazo composition (Table 6). Direct Red 81 (68) is manufactured by couplingp- -aminopheny1azo)henzenesu1fonic acid to A/-benzoyl J-acid Other important direct red dyes iaclude those shown ia Figure 5. 

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. 

Direct Black 22 [6473-13-8] (84) (Cl 35435) is produced first by coupling 4,4 dianainodiphenylainine-2-sulfonic acid to two moles of gamma acid to form a primary disazo dye, which is then bisdiazotized and coupled to two moles of y -phenylenediartiine (MPD). 

The 1 1 copper complex azo dyes are used both as reactive dyes for cotton and as direct dyes for paper. (For definitions of reactive dyes, which form covalent linkages with the substrate, and direct dyes, which bind more weakly, see refs. 23 and 24, respectively.) Typical monoazo dyes are Cl Reactive Violet 1 (23) and Cl Reactive Blue 13 (25), and the bis-copper-ed dye, Cl Direct Blue 80 (26). The navy blue dye, Cl Reactive Blue 82 (27), is a typical disazo dye. 

A full interpretation of the relationships between direct or vat dye structure and substantivity for cellulose must take into account the contribution of multilayer adsorption of dye molecules within the pore structure of the fibre [71]. The great difference in substantivity between Cl Direct Red 28 (3.66) and the monoazo acid dye (3.67) that is the half-size analogue of this symmetrical disazo dye may be interpreted in terms of their relative tendencies to form multilayers within the fibre pores as a result of dye-dye aggregation. Saturation adsorption values of these two dyes on viscose fibres at pH 9 and 50 °C corresponded to monolayer coverage areas of approximately 90 and 11 m2/g of internal surface respectively [72]. In view of the smaller molecular area and greater mobility of the half-size acid dye, higher uptake than the direct dye would be anticipated if there were only a limited area of internal surface available for true monolayer adsorption. 

Affinity values of the symmetrical disazo dyes Cl Direct Yellow 12 (3.6), Red 2 (3.8 X = CH3, Y = H) and Blue 1 (3.2) on cellophane have been measured recently under hydrostatic pressures up to 600 Mpa [120]. The affinity of Yellow 12 increased slightly but values for the other two dyes decreased considerably with increasing hydrostatic pressure (Table 3.23). The sulpho groups on the central stilbene nuclei of the Yellow 12 molecule tend to inhibit aggregation, whereas Red 2 and Blue 1 aggregate much more readily. The small increase in the affinity observed with Yellow 12 may indicate that isomerisation from the cis to the more stable Linns form may occur as the hydrostatic pressure is increased. 

The required long planar shape is more readily supplied by simple disazo structures such as Cl Direct Blue 1 (4.60). Copper complexes of such disazo compounds are important and are dealt with elsewhere (section 5.5.3). A widely used method of producing A—A type disazo dyes relies on treating J acid with phosgene (COCl2) to give the bis-coupling component carbonyl J acid (4.61). 

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. 

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. 

Currently used water soluble yellow ink-jet dyes include monoazo dyes C.I. Acid Yellow 17, 18965 [6359-98-4] and C.I. Acid Yellow 23, 19140, [1934-21-0] which exhibit symmetrical narrow absorption bands, as well as the disazo dyes C.I. Direct Yellow86, 29325 [50925-42-3] and C.I. Direct Yellow 132 [61968-26-1]. Recently developed, improved yellow dyes include disazo dye 5 of the type C.I. Direct Yellow 86, 29325, but modified by introducing carboxyl groups. Similar to C.I. Direct Black 195, this dye shows a high waterfastness on uncoated paper due to differential, pH-dependant solubility [3,12],... 

Type E1 D-+E1 Synthesis. Dyes of this type require the conversion of an aryldiamine to a tetrazonium compound (one that has two diazonium groups), in a process know as tetra-zotization. See Fig. 13.93, which involves environmentally friendly alternatives to benzidine. Following tetrazotization, one tetrazonium molecule reacts with two coupler molecules to produce the target dye, examples of which are provided in Fig. 13.94 (11 C.I. Direct Red 28 (Congo Red), 12 C.I. Direct Yellow 12, and 13 C.I. Acid Yellow 42). Disazo dyes prepared this way include dye 14 (C.I. Direct Blue 15), which is converted to the important bis-copper complex, C.I. Direct Blue 218 (see Fig. 13.95). 

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... 

Disazo dyes such as C.I. Direct Yellow 44 are prepared according to the sequence shown in Fig. 13.101. In this example, a pair of monoazo dyes is reacted with phosgene. 

The fastness to light of direct dyes often is improved by the formation of copper chelates. Direct Red 83 is the copper complex of the disazo dye prepared by coupling two moles of diazotized 2-aminophenol-4-sulfonic acid to one mole of J acid urea. 

Direct Blues. Direct Blue 86, a phthalocyanine direct dye, represents a small but important segment of the direct dye stmcture groups. The dyes are brilliant greenish blue or turquoise shades. Sales of nearly 2 million were reported in the United States in 1988. Among the disazo blues. Direct Blue 80 (74) and Direct Blue 98 (75) were sold in 152 t and 107 t quantities at an average cost of 2.22 and 1.81/kg, respectively, in 1988. Table 7 and Figure 6 show some direct blues. 

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. 

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