Direct Monoazo Dyes

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. 

Klabisiella sp. VN-31 Reactive Yellow 107, Reactive Red 198, Reactive Black 5, Direct Blue 71 Monoazo dyes RY107 and RR 198 were decolorized in 72 and 96 h the diazo dyes (RB5 and triazodye DB71) decolorized in 120 and 168 h [39]... 

Pseudomonas luteola Reactive azo dyes, Direct azo dyes and leather dyes The 59-99% color removal after 2-6 days static incubation, at dye concentration of 100 mg L 1, monoazo dyes showing fastest rate of decoloration [78]... 

Direct dyes of the disazo diarylurea type, such as Cl Direct Orange 26 (3.5) and Cl Direct Red 79 (3.21), are particularly prone to decomposition in high-temperature dyeing because molecular breakdown can occur by hydrolysis as well as by the reductive mechanism under alkaline conditions. Thus the ureido linkage in this red dye may be broken by hydrolysis to give two monoazo dye fragments (3.22), or the azo groups can be reduced to yield a diaminodiphenylurea (3.23) and two molecules of H acid (Scheme 3.3). 

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). 

Only a few monoazo dyes possess the necessary substantivity to render them suitable for direct dyeing of cellulosic fibers. 

Coupling diazotized dehydrothio-p-toluidinesulfonic acid to resorcinol and subsequent coupling of diazotized aniline to the monoazo dye formed gives C. I. Direct Orange 18, 20215 [5915-59-3] (11), an important substantive dye. 

Substantive yellow monoazo dyes with very good light fastness are also obtained by oxidation of dehydrothio-p-toluidine and its derivatives. Oxidation of the sodium salt of the monosulfonic acid of the primulin base in the alkaline pH range with sodium hypochlorite results, for example, in C. I. Direct Yellow29, 19556 [6537-66-2] (22). 

The trialkylammonium alkyl residue may also be attached directly to the aryl residue of the diazo component [110], Dyes that derive from aminomethylated 2-aminonaphthalene and contain acetoacetarylides, naphthols, or pyrazolones as the coupling components are suitable for dyeing paper. An example is the yellow monoazo dye 38. 

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],... 

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. 

This dye is one of the most widely used direct azo dyes as it is an extraordinarily strong dye. It is not fast to acid or to light. The first step in its preparation involves the preparation of the monoazo dye, sulfo chrysoidine G ... 

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. 

Disperse dyes from the monoazo and anthraquinone classes have been implicated in cases of contact dermatitis. Circumstances common to such cases appear to be heavy depths of these dyes on nylon rather than polyester and occurring in articles of clothing that are in direct contact with the skin, often in areas that are likely to become moistened by perspiration. Hosiery, socks, blouses and close-fitting athletic or fashion wear, such as velvet leggings, are representative of the types of garment where this problem has arisen [1]. 

The application range designated by this generic name in the Colour Index incorporates those acid, direct and mordant dyes with substantivity for leather and satisfactory fastness on that substrate [55]. It is a commercially important sector, the number of products listed being exceeded only by the complete acid or direct dye ranges. As expected from the sources of this selection, about 85% of leather dyes are azo compounds (35% disazo, 30% monoazo, 20% metal-complex monoazo) and the remainder are mainly yellow to orange stilbene dyes and anthraquinone or triarylmethane types in the violet to green sectors. 

Commercially viable systems for the decolorisation of spent dyebaths can be based on hydrogen peroxide treatment initiated by UV radiation. A representative selection of six disulphonated monoazo acid dyes and two disazo disulphonated types was exposed for various times in a pilot-scale photochemical reactor of this kind. The controlling parameters were dye structure, pH, peroxide dosage and UV light intensity [39]. In a wider survey of the response of various classes of dyes to the combination of UV radiation and hydrogen peroxide, viable candidates for further in-plant treatment trials were the water-soluble reactive, direct, acid and basic classes. On the other hand, water-insoluble colorants such as disperse and vat dyes did not appear to be viable [40]. 

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. 

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. 

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. 

Compound 1 is obtained by melting /Moluidinc with sulfur at 130 - 230 °C. The derivatives 2-5 are used to produce monoazo direct dyes. 

Direct Blue 106 and C.I. Direct Blue 108), and phthalocyanine (e.g., C.I. Direct Blue 86 and C.I. Direct Blue 199). About 82% of all direct dyes have disazo or polyazo structures, with stilbene and monoazo structures occupying about 5% each and thiazole, phthalocyanine, and dioxazine structures covering the remaining few percent.18... 

Azo Compounds Azo dyes are widely used in the food, pharmaceutical, cosmetic, textile, and leather industry. They are synthetic compounds characterized by one (monoazo) or several intramolecular N = N bonds. Azo dyes, if they are systemically absorbed, can be metabolized by the way of azoreductases of intestinal microflora by liver cells and skin surface bacteria. This metabolism leads to aromatic amines that can be hazardous. In the 1930s, some azo derivatives like 4-dimethyl aminoazoben-zene (Butter Yellow, Cl Solvent Yellow 2, Cl 11020) and o-aminoazotoluene were experimentally found to be directly carcinogenic to liver and bladder after feeding. Other complex azo dyes like Direct Black 38 or Direct Blue 6 (Figure 28) release the aromatic amine benzidine. Some examples of azo dyes metabolized in benzidine and benzidine-congeners are listed in Table 3. 

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. 

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