Triphenodioxazine Dyes

Like phthalocyanine dyes, triphenodioxazine dyes are large molecules, and therefore their use is restricted to coloring the more open-structured substrates such as paper and cotton. 

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Table 3.1 summarizes observed absorption maxima as a function of various substituents. In particular, blue triphenodioxazines have very high molar extinctions e, comparable to those of bisazo and phthalocyanine dyes. Until recently, anthraquinone dyes (e ca. 15 000) were predominant in most applications requiring brilliant blue dyes, but the much stronger triphenodioxazine dyes now represent a less expensive alternative in many applications. 

Copper complexes of the formazan dye series (see Sections 2.10 and 3.11) are another alternative to reactive anthraquinone dyes they produce red to greenish-blue shades. Like triphenodioxazine dyes, copper formazans exhibit high molar extinctions ( e = 25 000 -30 000). These materials are derived from l-(2-hydroxyphe-nyl)-3-phenyl-5-(2-carboxyphenyl)formazan (22), in which all three rings are capable of supporting groups that increase the compound s reactivity and solubility. 

Table 3.2 Examples of triphenodioxazine dyes 19 with different reactive anchors...

Triphenylimidazole. See Lophine Triphendioxazine dyes, 9 259-261 Triphenodioxazine chromophores, 9 320... 

Triphenodioxazine compounds have been used to make brilliant blue direct and reactive dyes for cellulosic fibres, but only one pigment in this chemical class, Cl Pigment Violet 23 (2.43), is widely used. It is prepared by condensing 3-amino-9-ethylcarbazole with chloranil in trichlorobenzene [29]. As with many other pigments, manufacturers offer it in many physical forms adapted to the intended end-use. 

The dioxazine ring system is the source of some valuable violet pigments, such as Cl Pigment Violet 23 (6.211). This colorant is obtained by condensing 3-amino-9 ethylcarbazole with chloranil. Sulphonation of the pigment gives the dye Cl Direct Blue 108. Triphenodioxazines have recently been the source of some blue reactive dyes [241-Examples are known of symmetrical bifunctional structures (6.212 NHRNH = alkylenediamine, Z = haloheterocyclic system) and unsymmetrical monofunctional types such as 6.213 [37]. 

These dyes are invariably monoazo compounds with the reactive system attached to the diazo component, owing to the ready availability of monosulphonated phenylenediamine intermediates. Pyrazolone couplers are most commonly used, as in structure 7.82 (where Z is the reactive grouping), and this is particularly the case for greenish yellow vinylsulphone dyes. Catalytic wet fading by phthalocyanine or triphenodioxazine blues is a characteristic weakness of azopyrazolone yellows (section 3.3.4). Pyridones (7.83), barbituric acid (7.84) and acetoacetarylide (7.85 Ar = aryl) coupling components are also represented in this sector, with the same type of diazo component to carry the reactive function. 

These chromophores have declined significantly in importance as textile dyes bnt have remained of interest becanse of their fluorescent behaviour, as discussed in Chapter 3, section 3.5.1.5. One exception is the triphenodioxazine ring system, which is used to produce valuable blue dyes in the Direct (2.19) and Reactive dye classes (2.20) as well as pigments (see section 2.4.1.7). The dyes from this chromogen have a very high molar absorption coefficient (ca. 80 000) versus typical anthraquinone dyes (ca. 15 000) and have therefore replaced some of the dyes from this latter chromogen in the reactive dyeing of cotton. ... 

The carbocyclic azo dyes are highly cost-effective and have good all-around fastness properties. However, they generally lack brightness and consequendy cannot compete with anthraquinone dyes in this respect. This shortcoming of carbocyclic azo dyes is overcome by heterocyclic azo dyes, as well as other dye classes such as triphenodioxazines and benzodifuranones. 

Virtually every conceivable chromophore has been used in the synthesis of reactive dyes, including monoazo and disazo species, metal complexes of azo dyes, formazan dyes, anthraquinones, triphenodioxazines, and phthalocyanines. The product lines offered by the major dye producers in most cases feature comparable chromophores, differing primarily in the nature of the reactive systems and the particular substitution patterns adopted. 

Dyes derived from the triphenodioxazine ring system (18) have been commercially available since 1928 when Kranzlein and coworkers discovered dyes with this basic structure augmented by sulfonic acid groups. The unsubstituted triphenodioxazine (which is of no importance as a colorant) was first obtained by G. Fischer in 1879 [39], and its structure 18 was elucidated in 1890 [40],... 

The triphenodioxazine chromophore was tested in almost every class of dyes, but only recently has it been introduced into reactive dyes. Dioxazines were investigated in some of the earliest work on reactive dyes in the late 1950s, and they are included in some of the first patents covering reactive anchors and reactive dyes [42], In particular, compound 21 was invoked as a chromophore, with reactive anchors attached to the free amino groups of the molecule. 

The triphenodioxazine chromophore can be converted to a reactive dye by incorporating anchors that are attached to the dioxazine core either directly or via bridging groups. The first patents, like the first commercial products, were based almost exclusively on the use of bridging groups. The usual starting material is 2-chloro-5-nitrobenzenesulfonic acid (27), which is treated with a diamine (28). 

Because of their symmetry, all such triphenodioxazine reactive dyes feature double or even fourfold anchor systems. However, dyes with only one anchor group can be prepared by adding a single equivalent of acylating agent. Most asymmetric products of this type are based on l,4-phenylenediamine-2-sulfonic... 

Stability of the Dye-Fiber Bond. Because of the large variety of reactive dyes, generalizations about colorfastness are difficult. While wetfastness is determined mainly by the anchor system used, most other fastness properties depend on the dye as a whole or the chromophore present. Most reactive dyes are azo or anthra-quinone derivatives whose standard of fastness varies greatly. Phthalocyanine, formazan, and triphenodioxazine derivatives are also very important. In addition, application conditions and finishing processes of the dyed goods can affect fastness properties. Thus, with some resin-finished textiles (dimethylolpropyleneurea finish) a decrease in lightfastness is observed. 

Special Processes and Development Trends [36, 37], Many attempts have been made to remedy the weak points of the reactive dyeing system. Lightfastness could be significantly improved over a wide range of shades by development of effective chromophores (e g., triphenodioxazine and copper formazan for blues). However, in the red range, reactive dyes are still inferior in lightfastness to vat and naphthol dyes. 

The sulfonated derivatives of the parent structure, discovered in 1928 (Kranzlein et al., Farbewerke Hoedist), afford colorants which can be used as direct dyes on cotton, but the parent triphenodioxazine, an orange solid, has no technical importance as a colorant. It was not until 1952, however, that a tinctorially strong violet pigment derived from a 9,10-dichlorotriphenodioxazine was patented and ultimately designated as Pigment Violet 23. 

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