Disperse Nitro Dyes

The nitro group is commonly encountered as a substituent in dyes and pigments of most chemical classes, but it acts as the essential chromo-phore in only a few dyes. Nitro dyes are a small group of dyes of some importance as disperse dyes for polyester and as semi-permanent hair dyes. Picric acid, 139, was historically the first nitro dye, although it was... 

The synthesis of nitro dyes is relatively simple, a feature which accounts to a certain extent for their low cost. The synthesis, illustrated in Scheme 6.5 for compounds 140 and 141, generally involves a nucleophilic substitution reaction between an aromatic amine and a chloronitroaromatic compound. The synthesis of C. I. Disperse Yellow 14 (140) involves the reaction of aniline with l-chloro-2,4-dinitroaniline while compound 141 is prepared by reacting aniline (2 mol) with compound 144 (1 mol). 

Nitro dyes exhibit benzenoid-quinonoid tautomerism (1.25) and their colour is attributed mainly to the o-quinonoid form, since this can be stabilised by hydrogen bonding. The tautomeric o-nitrosonaphthols (1.26) readily form chelate complexes with metals. A few yellow nitro disperse dyes, including Cl Disperse Yellow 1 (1.25), and brown acid dyes remain of significance. The remaining nitro and nitroso colorants, such as (1.26) and its 1 3 iron (II) complex (1.27), are no longer of commercial interest. 

Xitro and Nitraso Dyes. These dyes are now of only minor commercial importance, hut are of interest for their small molecular structures. The most important nitro dyes are the nitrodiphcnylamines. Their small molecules arc ideal for penetrating dense libers such as polyester, and are therefore used as disperse dyes for polyester. All the important dyes are yellow. Although the dyes are not terribly strong (fW- 20- 000). they are cosi-effective hecatise of their easy synthesis from inexpensive intermediates... 

Industrially applied disperse dyes are based on numerous chromophore systems. Approximately 60 % of all products are azo dyes, and ca. 25 % are anthraqui-none dyes, with the remainder distributed among quinophthalone, methine, naphthalimide, naphthoquinone, and nitro dyes [9],... 

Nitro Dyes. 2-Nitrodiphenylamines are readily obtained by condensation of derivatives of 2-nitrochlorobenzene 88-73-3] with suitable aromatic amines. Because of their accessibility and good lightfastness, these dyes became very important for dyeing cellulose acetate and, more recently, have gained a solid position as disperse dyes for polyester fibers. This is especially true for the reaction product of 1 mol of 3-nitro-4-chlorobenzenesulfonyl chloride [97-08-5] and 2 mol of aniline. An exhaustive review of the constitution and color of nitro dyes is given by Merian [40], The yellow nitroacridones may also be classified in this group. 

As the name suggests, this very small class of organic dyes has at least one nitro group as the chromophore. Nitro dyes invariably are yellow or orange and are important for their economical cost and good lightfastness. Examples include the dyes shown in Fig. 13.78-C.I. Acid Orange 3 (A), C.I. Disperse Yellow 42 (B), C.I. Acid Yellow 1 (C), and... 

C.I. Disperse Yellow 70 (D). A key disadvantage of nitro dyes is their low color strength (emax = 5000-7000). Improvements in color strength have been achieved by incorporating an azo group, as illustrated in dye D. 

According to their chemical structures and the Cl system, dyes can be classified into 17 groups nitro dyes, triphenylmethane derivatives, xanthenes, acridine derivatives, quinoline derivatives, azines, ant-hraquinones, indigoid dyes, phthalocyanines dyes, oxydation bases, insoluble azo dye precursors, and azo dyes (classes XII-XVII). In practice, dyes are classified into different application classes disperse, acid, basic, direct, vat, fiber-reactive, sulfur, preme-tallic, solvent dyes, and naphthols. 

Disperse Yellow 39, a no longer available methine dye, was implicated in trouser dermatitis. The nitro dye Disperse Yellow 9 was cited in some reports. 

In the manufacture of 2-naphthalenol, 2-naphthalenesulfonic acid must be converted to its sodium salt this can be done by adding sodium chloride to the acid, and by neutralizing with aqueous sodium hydroxide or neutralizing with the sodium sulfite by-product obtained in the caustic fusion of the sulfonate. The cmde sulfonation product, without isolation or purification of 2-naphthalenesulfonic acid, is used to make 1,6-, 2,6-, and 2,7-naphthalenedisulfonic acids and 1,3,6-naphthalenetrisulfonic acid by further sulfonation. By nitration, 5- and 8-nitro-2-naphthalenesulfonic acids, [89-69-1] and [117-41-9] respectively, are obtained, which are intermediates for Cleve s acid. All are dye intermediates. The cmde sulfonation product can be condensed with formaldehyde or alcohols or olefins to make valuable wetting, dispersing, and tanning agents. 

Brightener structures of only moderate molecular size are of interest for white grounds in the transfer printing of polyester fabrics. Derivatives of 6-acetamidoquinoxaline with an electron-donating substituent (X) in the 2-position (11.48) were prepared by converting quinoxalin-2-one to 2-chloro-6-nitroquinoxaline and condensation with amines (X = RNH), alcohols (X = RO) or phenols (X = PhO), followed by reduction and acetylation (Scheme 11.19). The nitro intermediates (11.49) are also of interest as low-energy disperse dyes for polyester [61]. 

A striking feature of disperse dye development in recent decades has been the steady growth in bathochromic azo blue dyes to replace the tinctorially weaker and more costly anthraquinone blues. One approach is represented by heavily nuclei-substituted derivatives of N,N-disubstituted 4-aminoazobenzenes, in which electron donor groups (e.g. 2-acylamino-5-alkoxy) are introduced into the aniline coupler residue and acceptor groups (acetyl, cyano or nitro) into the 2,4,6-positions of the diazo component. A PPP-MO study of the mobility of substituent configurations in such systems demonstrated that coplanarity of the two aryl rings could only be maintained if at least one of the 2,6-substituents was cyano. Thus much commercial research effort was directed towards these more bathochromic o-cyano-substituted dyes. 

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... 

Heterocyclic coupling components are widely used in the disperse dye field for the production of yellow dyes. Numerous conventional dyes are based on simple pyrazolones, often combined with an o-nitroaniline diazo component, the o-nitro group being particularly favourable in ensuring good light fastness. Cl Disperse Yellow 8 (4-73), which uses a very simple pyrazolone coupling component, is an example. 

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]. 

Baughman (1992) measured the disappearance rate constants for a number of solvent and disperse azo, anthraquinone, and quinoline dyes in anaerobic sediments. The half-lives ranged from 0.1 to 140 days. Product studies of the azo dyes showed that reduction of the azo linkages and nitro groups resulted in the formation of substituted anilines. The 1,4-diaminoanthraquinone dyes underwent complex reactions thought to involve reduction and replacement of amino with hydroxy groups. Demethylation of methoxyanthraquinone dyes and reduction of anthraquinone dyes to anthrones also was observed. 

Disperse polyester, polyamide, acetate, acrylic and plastics fine aqueous dispersions often applied by high temperature/ pressure or lower temperature carrier methods dye may be padded on cloth and baked on or thermofixed azo, anthraquinone, styryl, nitro, and benzodifiiranone... 

More than 50% of disperse dyes are simple azo compounds, about 25% are anthraquinones, and the rest are methine, nitro, and naphthoquinone dyes (see Sections 2.2, 2.3, 2.6, 3.12). 

Most of the chromophore systems common in dye chemistry (nitro, azo, anthraquinone, triphenylmethane, and azomethine) are currently used [37,39, pp. 526-533], Disperse, cationic (basic), and anionic (acidic) dyes are employed. 

Disperse dyes vary in the type of chromophore present and include azo, anthraquinone, nitro, methine, benzodifuranone, and quinoline based structures. Examples of the first three types are given in Table 13.4, and representative of the latter three types are C.I. Disperse Blue 354, C.I. Disperse Yellow 64, and C.I. Disperse Red 356. Most disperse dyes have azo ( 59%) or anthraquinone ( 32%) structures. Azo disperse dyes cover the entire color spectrum, whereas the important anthraquinone disperse dyes are mainly red, violet, and blue. The azo types offer the advantages of higher extinction coefficients (emax = 30,000-60,000) and ease of synthesis, and the anthraquinones are generally brighter and have better photostability (lightfastness). The key weaknesses associated with the anthraquinone dyes are their low extinction... 

Nitro-2-R-benzothiazoles DNA damage, against Staphylococcus aureus, Bacillus subtilis [362], Euglena gracilis [363], azo disperse dyes in textile [364]... 

If they are ingested, dyes and particularly those that have an azo group can be metabolized by the intestinal microflora or by the liver enzymes. So, their effects can occur in organs responsible for metabolism or elimination, like the liver and urinary tract. Skin metabolism may also be responsible for the transformation of dyes, for example, those from colored textiles that can leach from the fabric and migrate to the skin. For example Disperse Orange 3 is degraded to p-phenylenediamine (PPD) and nitro-aniline in the skin (Figure 1). Direct Blue 14 (Cl 23850), after azo reduction, converts to the aromatic amine o-toluidine and other amines when incubated with cultures of Staphylococcus aureus. 

Product studies of Disperse Red 1, another large volume textile dye, in anoxic sediment slurries demonstrates that reduction of nitro group substituents can occur prior to the reduction of the azo linkage (Equation 3.31) (Yen et al., 1991). 

Modern oxidation dyes sometimes contain coloring agents in addition to dye precursors and couplers for example, direct dyes like disperse blue 1 and nitro-phenylenediamines are sometimes included. 

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. 

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