Disperse Monoazo Dyes

Commercial Disperse Azo Dyes. The first proposal to use insoluble dyes in suspension in an aqueous foam bath, ie, disperse dyes, to dye cellulose acetate was in 1921 (60). Commercialization of disperse dyes began in 1924 with the introduction of the Duranol dyes by British Dyestuffs Corporation (61) and the SRA dyes by British Celanese Company (62). In contrast to the acid monoazo dyes, derivatives of benzene rather than of naphthalene are of the greatest importance as coupling components. Among these components mono- and dialkylariifines (especially A/-P-hydroxyethyl-and A/-(3-acetoxyethylanifine derivatives) are widely used couplers. Nitrodiazobenzenes are widely used as diazo components. A typical example is CeUiton Scarlet B [2872-52-8] (91) (Cl Disperse Red 1 Cl 11110). 

Disperse reds are second only to blues as the most important disperse color manufactured. AU. commercial disperse reds are monoazo dyes. In 1988, Disperse Red 73 (98, R = CN) had production of 270 tons valued at nearly 1.6 million. Disperse Violet 24 (99) is produced from diazotized 2-hromo-4,6-dinitroani1ine by coupling with 2-(A/-butyl-y -toluidine)ethanol. 

Monoazo dyes such as Disperse Blue 11 (102) and Disperse Black 1 (103) are appHed to cellulose acetate as a dispersion and dyed in the usual way, then diazotized in situ and coupled in this instance, to 3-hydroxy-2-naphthoic acid forming the blue and black shades, respectively. 

Much of the available published data on the aqueous solubility of disperse dyes was accumulated during the 1960s in the course of studies of the mechanism of dyeing cellulose acetate with disperse dyes. Most of the dyes examined were low-energy types for dyeing acetate (Table 3.5). Particular attention was given to monoazo dyes derived from aniline or... 

The main aromatic amines used as diazo components are substituted anilines or naphthylamines and the coupling components substituted iV-aUcylanilines, phenols, naphthylamines and naphthols. Heteroaromatic diazo and coupling components are widely used in commercial azo dyestuffs. The main heterocyclic conpling components are pyrazalones (2.6) and, especially, pyridones (2.8). These are nsed to prodnce bright yellow and orange monoazo dyes, such as Cl Acid Yellow 72 (2.7) and Cl Disperse Orange 139 (2.9). ... 

Solvent dyes are really intermediate between dyes and pigments being insoluble in water but soluble in solvents, especially hydrocarbons. Structurally many solvent dyes bear a close similarity and relationship with disperse dyes. The Colour Index has an issne on Solvent Dyes, where several hundred dyes are described, unfortunately many of the strnctnres remain confldential. The structures of the disclosed dyes range from very simple monoazo dyes, e.g. Cl Solvent Yellow 14 (2.78) to the higher performing anthraquinones, e.g. Cl Solvent Yellow 163 (2.79) and Blue 36 (2.80), quinophthalones... 

Using these and other design principles, very large increases in the valnes of chro-mophores have been obtained since the original work on the simple red monoazo dyes of the disperse dye class. These new NLO chromophores are known as high pP chromophores , a selection of which are shown in Figure 5.31, the pP values quoted being measnred by electric field induced second harmonic at (EFISH) 1.9 It... 

Mo no azo Dyes. About 50 % of all disperse dyes are monoazo dyes, which thus represent the largest single group [9], Relatively simple syntheses enable a range of shades from greenish yellow to cyan to be produced with this chromophore system. 

Monoazo dyes derived from aromatic amines as coupling components and carbo-cyclt aromatic amines as diazo components are the class of disperse azo dyes with the greatest economic importance. Commercial products are most often represented by structure 2, in which 4-nitroaniline [100-01-6] and its substituted derivatives constitute the diazo component. 

About 10 % of all disperse dyes are disazo compounds [9], Even the simplest hydroxy disazo dyes, such as 4-aminoazobenzene coupled to phenol and 4-ami-noazobenzene coupled to o-cresol. have a good affinity for polyester fibers and yield lightfast reddish yellow hues. However, these shades are frequently less bright than those obtained with monoazo dyes. 

Conventional treatment processes for these dyes prior to discharge involve ozonation. While a simple water-soluble monoazo dye such as A07 is easily oxidized by ozone, the larger diazo dyes such as NBB are difficult to destroy by ozonation. While oxidative ozonation is a popular treatment process, the sodium borohydride catalyzed reductive decolorization of these dyes is also used. The other example shown above, DB79, is water insoluble and is finding increased application in the dyeing of polyester and other synthetic fabrics. Traces of the disperse dye have been reported in river bed sediments in Quebec, Canada, receiving dye waste from upstream manufacturers. 

The polymer investigated here is a polymethylmethacrylate (PMMA) copolymerised with methacrylate esters of a dicyanovinyl-terminated bisazo dye derivative. A nitro-terminated version of the bisazo dye derivative and a typical monoazo dye. Disperse Red 1 (DRl), derivative is also discussed in [47]. These azo dyes are hereafter referred as 3RDCVXY, 3RNO2, and 2RNO2, respectively. The molecular structure of 3RDCVXY is shown in Figure 3.12a. 

Dyestuffs. The use of thiophene-based dyestuffs has been largely the result of the access of 2-amino-3-substituted thiophenes via new cycHzation chemistry techniques (61). Intermediates of type (8) are available from development of this work. Such intermediates act as the azo-component and, when coupled with pyrazolones, aminopyrazoles, phenols, 2,6-dihydropyridines, etc, have produced numerous monoazo disperse dyes. These dyes impart yeUow—green, red—green, or violet—green colorations to synthetic fibers, with exceUent fastness to light as weU as to wet- and dry-heat treatments (62-64). 

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. 

The discovery in 1979 of the benzodifuranone chromogen (1.14) and its exploitation in red disperse dyes for polyester fibres [23,24] emerged from ICI research towards new chromogens of high colour value, brightness and substantivity to overcome the relative weakness of anthraquinones and dullness of monoazo alternatives in the red disperse dye area. A striking improvement in build-up properties was found by introducing asymmetry... 

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]. 

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]. 

An aqueous dispersion of a disperse dye contains an equilibrium distribution of solid dye particles of various sizes. Dyeing takes place from a saturated solution, which is maintained in this state by the presence of undissolved particles of dye. As dyeing proceeds, the smallest insoluble particles dissolve at a rate appropriate to maintain this saturated solution. Only the smallest moieties present, single molecules and dimers, are capable of becoming absorbed by cellulose acetate or polyester fibres. A recent study of three representative Cl Disperse dyes, namely the nitrodiphenylamine Yellow 42 (3.49), the monoazo Red 118 (3.50) and the anthraquinone Violet 26 (3.51), demonstrated that aggregation of dye molecules dissolved in aqueous surfactant solutions does not proceed beyond dimerisation. The proportion present as dimers reached a maximum at a surfactant dye molar ratio of 2 5 for all three dyes, implying the formation of mixed dye-surfactant micelles [52]. 

Figure 3.4 Colour yield of acylamino-substituted blue monoazo disperse dyes [89]...

Only a limited range of nitro, azo and anthraquinone disperse dyes exhibit adequate fastness to dry heat, light and weathering for application on polyester automotive fabrics. The structure of Cl Disperse Yellow 86 was modified to incorporate UV absorbers of the benzophenone, benzotriazole or oxalanilide types into the dye molecule. The derived dyes showed better fastness properties than the parent unsubstituted dye. Positioning of the photostabilising moiety within the dye molecule had little influence on the light fastness obtained, however. Built-in benzophenone residues were more effective than the other two types [177]. Nevertheless, several further monoazo and nitrodiphenylamine disperse dye... 

In order to facilitate satisfactory dye uptake, the molecular size of a disperse dye must be kept small monoazo structures are therefore exceptionally important, particularly in the coloration of polyester and cellulose triacetate. In the yellow shade area, molecular size generally poses no problem and the various available coupling components can all be used without making the molecule too large. A very simple example of the type of structure employed using a phenolic coupling component is Cl Disperse Yellow 3 (4-72). This dye is known to cause skin sensitisation when on nylon [85] and can also provoke an allergic reaction [86]. 

In addition to benzenoid diazo components, diazotised heterocyclic amines in which the amino group is attached to a nitrogen- or sulphur-containing ring figure prominently in the preparation of disperse dyes [87,88], since these can produce marked bathochromic shifts. The most commonly used of these are the 6-substituted 2-aminobenzothiazoles, prepared by the reaction of a suitable arylamine with bromine and potassium thiocyanate (Scheme 4.31). Intermediates of this type, such as the 6-nitro derivative (4.79), are the source of red dyes, as in Cl Disperse Red 145 (4.80). It has been found that dichloroacetic acid is an effective solvent for the diazotisation of 2-amino-6-nitrobenzothiazole [89]. Subsequent coupling reactions can be carried out in the same solvent system. Monoazo disperse dyes have also been synthesised from other isomeric nitro derivatives of 2-aminobenzothiazole [90]. Various dichloronitro derivatives of this amine can be used to generate reddish blue dyes for polyester [91]. 

The widespread adoption of high-temperature dyeing methods has also allowed the use of simple disazo structures, such as Cl Disperse Orange 13 (4.89) and Cl Disperse Orange 29 (4.90), as economic dyes giving chiefly yellow and orange hues. The latter dye is known to exist in the syn conformation in the crystal [95] the unsubstituted parent dye prefers the anti conformation. A few monoazo and disazo disperse dyes have absorption bands in the near infrared [96]. 

Considerable research effort has been devoted to developing a new generation of disperse dyes designed to optimise fastness to washing and minimise cross-staining of the cellulosic component of polyester/cellulosic blends [97,98]. Diester-containing monoazo disperse dye structures (4.91) that yield a dicarboxylic acid on hydrolysis and certain thienylazo blues... 

The synthesis of monoazo disperse dyes by diazotization and coupling is described under Azo Dyes (see Section 2.2). Additional chemical treatment subsequent to synthesis of the azo compounds is performed only rarely. 

Fig. 13.91. Monoazo cationic (1), disperse (2-4), 1 1 chromium complexed (5), and mordant (6) dyes prepared via an A -> E process.

Examples of dyes made via an A —> M — E synthesis are shown in Fig. 13.98. Although most azo disperse dyes are based on monoazo structures, disazo structures such as 15 (C.I. 

Sommer, K. and Kruse, H. (1979). Modification of monoazo dispersion dye of benzene series-with improved dyeing stability. Hoechst AG Patent DE 2 835 544. [260t]... 

The monoazoic compound Disperse Blue 124 (Figure 7) is the most frequently positive dye on patch testing with the textile series, particularly in women. It is probably the main cause of textile contact dermatitis today. It is closely related to another azo dye, Disperse Blue 106 (Figure 8), marketed since 1985, and both are frequently used together. This latter dye seems to have the stronger sensitizing potential and can provoke infiltrated lesions. Concomitant positive reactions to both Disperse Blue 106 and 124 are expected because of their structural similarity, and are very consistent. 

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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