Disperse Methine Dyes

Another compound of interest is adenine [73-24-5] or 6-aminopurine (53) derived from pheny1a 2oma1ononitri1e (92). The introduction of the dicyanostyryl moiety has led to the industriali2ation of several methine dyes such as the Cl Disperse Yellow [6684-20-4] (54) (93). The Cl Disperse Blue 354 [74239-96-6] (55) also represents a new class of anTinoarylneutrocyariine dyes with a brilliant blue shade (94). The dimer of malononitrile is also used for the synthesis of new dyes (95). 

Methine Dyes. The condensation products of 4-dialkylaminobenzaldehydes with cyano acetic esters have long been used to dye acetate fibers. Brilliant greenish yellow dyes with excellent lightfastness are obtained on polyester fibers with the corresponding condensation products of malonodinitrile. The sublimation fastness of this dye type can be improved by introducing suitable substituents into the alkyl residue of the amino group or by doubling the molecular size, e.g., C.I. Disperse Yellow 99, [25857-05-0] (11) [12,30,31],... 

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. 

Azo and anthraquinone compounds comprise the two principal stmctural types which are used as disperse dyes. Other compounds used to a much lesser extent include methines, cyanostyryls, hydroxyquinophthalones, and ifitrodiarylarnines. 

The structures of a number of neutral and anionic polymethine dyes are illustrated in Figure 6.3. There are many types of neutral poly-methines, utilising a wide range of electron donor and acceptor groups. For example, C. I. Disperse Yellow 99 (114) and C. I. Disperse Blue 354... 

The name of this structural class ( quinoline ) in the Colour Index is not ideal because quinoline derivatives feature in other related classes, such as the methine basic dyes with a quinolinium cationic group. The class is more precisely associated with quinophthalone (1.15), the characteristic chromogen derived by condensation of quinoline derivatives with phthalic anhydride. This small class of yellow compounds contributes to the disperse, acid, basic and solvent ranges of dyes. 

Uncharged styryl (methine) disperse dyes were originally introduced to provide greenish yellow colours on cellulose acetate fibres. One such dye still in use is Cl Disperse Yellow 31 (6.226), which is made by condensing 4-(N-butyl-N-chloroethylamino)benzaldehyde with ethyl cyanoacetate. Suitable compounds for polyester usually contain the electron-accepting dicyanovinyl group, introduced with the aid of malononitrile. An increased molecular size leads to improved fastness to sublimation, as in the case of Cl Disperse Yellow 99 (6.227). A novel polymethine-type structure of great interest is present in Cl Disperse Blue 354 (6.228), which is claimed to be the most brilliant blue disperse dye currently available [85]. 

Quinophthalone (6.229) and its derivatives [86] also fall into the methine category, although they appear in the Colour Index under quinoline colouring matters. The parent compound was discovered in 1882 by Jacobsen, who condensed 2-methylquinoline (quinaldine) with phthalic anhydride. The product, quinoline yellow, is used as a solvent dye (Cl Solvent Yellow 33). The light fastness is improved by the presence of a hydroxy group in the quinoline ring system. Derivatives of this type provide greenish yellow disperse dyes for polyester. The moderate sublimation fastness of Cl Disperse Yellow 54 (6.230 R = H) is improved by the introduction of an adjacent bromine atom in Cl Disperse Yellow 64 (6.230 R = Br). 

A new cross-conjugated methine-type chromogen was introduced in 1984. The dye Cl Disperse Red 356 (6.232) exemplifies this system, which contains two a,co-donor-acceptor dienone segments. The development of such benzodifuranone disperse dyes has been described [87]. 

Simple methines, often called styryl dyes, were once important as yellow disperse dyes bnt are now only nsed to prodnce bright bine and tnrqnoise dyes. Examples are the mono-methine (2.21), the dimethine (2.22) and the azamethine (2.23). Indophenols (2.24), another class of azamethines, have been nsed as bright bines for transfer printing onto polyester and in digital imaging by dye diffnsion thermal trans-... 

The largest usage is in polyester and many dyestuff companies have disperse dye ranges for this purpose, some of which are also applied to polyamide fibres. The main colours are in the yellow, orange, red, pink and violet areas with coumarins, methines and perylene dominating the structural classes. 

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],... 

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). 

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... 

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