Reactive dyes synthesis

Fluorination and iodination reactions are used relatively littie in dye synthesis. Fluorinated species include the trifluoromethyl group, which can be obtained from the trichi oromethyl group by the action of hydrogen fluoride or antimony pentafluoride, and various fluorotria2iQyl and pyrimidyl reactive systems for reactive dyes, eg, Cibacron F dyes. 

Phenazine leucos until now are usually substituted at their 3 and 6 positions by amino groups due to the normal method of synthesis of the parent phenazine dyes. These types of leuco dyes are reactive. An alternative method of dye synthesis allows access to phenazine dyes with just one substituent at the 3-position.20 The resulting leuco dyes are called half diazine leucos. The loss of one exocyclic amino group leads to higher redox potential and results in less reactive leuco dyes, more useful in applications such as thermographic and photothermographic imaging, particularly Color Dry Silver. 

In Chapters 3-6, the commercially important chemical classes of dyes and pigments are discussed in terms of their essential structural features and the principles of their synthesis. The reader will encounter further examples of these individual chemical classes of colorants throughout Chapters 7 10 which, as a complement to the content of the earlier chapters, deal with the chemistry of their application. Chapters 7, 8 and 10 are concerned essentially with the application of dyes, whereas Chapter 9 is devoted to pigments. The distinction between these two types of colorants has been made previously in Chapter 2. Dyes are used in the coloration of a wide range of substrates, including paper, leather and plastics, but by far their most important outlet is on textiles. Textile materials are used in a wide variety of products, including clothing of all types, curtains, upholstery and carpets. This chapter deals with the chemical principles of the main application classes of dyes that may be applied to textile fibres, except for reactive dyes, which are dealt with exclusively in Chapter 8. 

The most commonly employed routes for the preparation of the / -sulfatoethylsulfone group, which is the essential structural feature of vinylsulfone reactive dyes, are illustrated in Scheme 8.5. One method of synthesis involves, initially, the reduction of an aromatic sulfonyl chloride, for example with sodium sulfite, to the corresponding sulfinic acid. Subsequent condensation with either 2-chloroethanol or ethylene oxide gives the / -hydroxyethylsulfone, which is converted into its sulfate ester by treatment with concentrated sulfuric acid at 20 30 °C. An alternative route involves treatment of an aromatic thiol with 2-chloroethanol or ethylene oxide to give the /Miydroxyethylsulfonyl compound which may then be converted by oxidation into the /Miydroxyethylsulfone. 

Heavy metals are widely used as catalysts in the manufacture of anthraquinonoid dyes. Mercury is used when sulphonating anthraquinones and copper when reacting arylamines with bromoanthraquinones. Much effort has been devoted to minimising the trace metal content of such colorants and in effluents from dyemaking plants. Metal salts are used as reactants in dye synthesis, particularly in the ranges of premetallised acid, direct or reactive dyes, which usually contain copper, chromium, nickel or cobalt. These structures are described in detail in Chapter 5, where the implications in terms of environmental problems are also discussed. Certain basic dyes and stabilised azoic diazo components (Fast Salts) are marketed in the form of tetrachlorozincate complex salts. The environmental impact of the heavy metal salts used in dye application processes is dealt with in Volume 2. 

Three major approaches have been followed to provide reactive dyes in this important sector. One category is closely related to the reddish blue monoazo 1 1 copper complexes already described (section 7.5.8). To provide the higher substantivity and deeper intensity for build-up to navy blue shades, a second unmetallised azo grouping is introduced. As with the brown dyes, the A—>M—>E pattern is adopted for their synthesis. Component A is normally a sulphonated aniline, M an aminophenol or aminocresol and E a sulphonated naphthol or aminonaphthol. The reactive system (Z) is usually, but not invariably, located on the E component and the copper atom always coordinates with an o,o -dihydroxyazo grouping provided by the M and E components (7.109). 

Koprivanac, N, Loncaric Bozic, A, Papic, S. Cleaner production processes in the synthesis of blue anthraquinone reactive dye. Dyes and Pigments, 2000 44, 33-40. 

Scheme 4.3 Synthesis of vinyl sulfones. The vinyl sulfone is highly electrophilic (reactive) and frequently used in fiber-reactive dyes.

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. 

The synthesis of selected reactive dyes is illustrated by the following examples taken from the patent literature. 

To provide an overview chemical constitution and synthesis are combined in this section. The various application media for metal-complex dyes are a further ordering principle, which generates overlap of some sections with reactive dyes (Section 3.1), leather dyes (Section 5.1), and paper dyes (Section 5.3), demonstrating the typically complex interrelationship of constitution and application of dyes. 

The chlorosulfonation of the CuPc system opens the door to the synthesis of reactive dyes, as shown in Fig. 13.137. In this case, aminochlorotriazine 56 reacts with a CuPc-S02Cl intermediate to give a mono-chlorotriazine reactive dye (57), which in turn can be used to make the cationic reactive dye 58. 

A classic illustration of scaffold decoration is the trisubstituted 1,3,5-triazine. The starting material trichloro-l,3,5-triazine is inexpensive, and the halogens can be displaced by nucleophilic aromatic substitutions one by one. Such chemistry was well precedented in pre-combinatorial days, and used on a large scale for the synthesis of colour-fast reactive dyes. The overall reaction sequence has an appeal in its simplicity, and both academic and industrial practitioners have reported a steady trickle of such triazine-based libraries over the last 20 years. Novelty will come either from the particular set of nucleophiles employed or the assay targets. 

Shen X M, FT-IR andNIR FT-Raman On-line Measurement of the Synthesis of Reactive Dyes, PhD Thesis, University of Leeds, 1998. 

The starting material for many of the triazine-based fibre-reactive dyes is cyanuric chloride (cf. Houben-Weyl, Vol. 10/3, p 391 ff Vol. 11/1, p 70ff>- These dyes are prepared by nucleophilic displacement of one or two chlorine atoms with one or two dye molecules. As the last step, the product is bound to the textile by reacting the third chlorine with the hydroxy groups in cellulose fibre or with the amino functions in polyamides, wool, and silk. Many reviews are available.85 95 Cyanuric chloride is also used in the synthesis of optical brighteners.92 94... 

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