Chemical structures of dyes

The RP-TLC behaviour of some common food dyes was investigated in detail. The chemical structure of dyes are listed in Fig. 3.2. Measurements were carried out on RP-18 silica plates using aqueous ammonium sulphate (0.1 0.5 1.0 M), ethanol and acetone in various volume ratios. Developments were performed at room temperature (22 2°C) in chambers previously saturated with the vapours of the mobile phase. It was found that the presence of dissociable anorganic salt modifies markedly the RP retention behaviour of dyes. The retention of dyes generally decreases with increasing concentration of the organic modifier in the mobile phase. It was further concluded that RP-TLC can be successfully used for the separation of this class of synthetic food dyes [81]. 

TLC coupled with mass spectrometry employing desorption electrospray ionization has been used for the separation of synthetic dyes. The chemical structures of dyes included in the investigation are shown in Fig. 3.7. ODS HPTLC plates (10 X 10 cm) were used as the stationary phase the mobile phase consisted of methanol-tetrahydrofuran (60 40, v/v) containing 50-100 mM ammonium acetate for the positive-ion test and of methanol-water (70 30, v/v) for the negative-ion test. Test mixtures for negative- and positive-ion mode detection consisted of methyleneblue, crystal violet, rhodamine 6G... 

The carcinogenic aromatic amines released from azo dyes in leather were investigated by using microwave-assisted extraction (MAE) or supercritical fluid extraction (SFE) followed by RP-HPLC. The chemical structures of dyes and aromatic amines are listed in Fig. 3.69. The flow schemes for SFE and MAE are shown in Figs 3.70. and 3.71. 

Fig. 3.76. Chemical structures of dyes employed as target substrates in the Ti02-assisted photocatalysis. Reprinted with permission from R. Comparelli et al. [143].

RP-HPLC found application in the monitoring of the alkali hydrolysis kinetics of alkali-clearable azo disperse dyes containing a fluorosulphonyl group. The chemical structures of dyes included in the experiments are shown in Fig. 3.85. Samples for RP-HPLC analysis were neutralized to pH 4.0 - 4.5 with diluted HC1 mixed with five volumes of ACN and injected without any other sample preparation step. Separation was carried out in an ODS column at ambient temperature. The isocratic mobile phase consisted of ACN-water (80 20, v/v) and dyes were detected at their absorption maxima. HPLC measurements indicated that dyes are easily hydrolysed under relatively mild alkaline conditions, and the hydrolysis follows a pseudo first-order kinetics [148],... 

The effect of the electrochemical treatment on the degradation of some textile dyes was monitored by RP-HPLC. The chemical structures of dyes investigated are shown in Fig. 3.86. 

Thus, RP-HPLC-MS has been employed for the analysis of sulphonated dyes and intermediates. Dyes included in the investigation were Acid yellow 36, Acid blue 40, Acid violet 7, Direct yellow 28, Direct blue 106, Acid yellow 23, Direct green 28, Direct red 79, Direct blue 78 and some metal complex dyes such as Acid orange 142, Acid red 357, Acid Violet 90, Acid yellow 194 and Acid brown 355. RP-HPLC was realized in an ODS column (150 X 3 mm i.d. particle size 7 /.an). The composition of the mobile phase varied according to the chemical structure of the analytes to be separated. For the majority of cases the mobile phase consisted of methanol-5 mM aqueous ammonium acetate (10 90, v/v). Subsituted anthraquinones were separated in similar mobile phases containing 40 per cent methanol. The flow rate was 1 ml/min for UV and 0.6 ml/min for MS detection, respectively. The chemical structure of dye intermediates investigated in this study and their retention times are compiled in Table 3.28. It was found that the method is suitable for the separation of decomposition products and intermediates of dyes but the separation of the original dye molecules was not adequate in this RP-HPLC system [162],... 

CZE was also employed for the analysis of sulphonated azo dyes in river samples. The chemical structures of dyes are shown in Fig. 3.150. Separations were performed in a fused-silica capillary (total length 57 cm effective length, 50 cm 75 pm i.d.). Activation of the capillary was carried out by washing it with 1.0 M NaOH for 15 min, followed by water (5 min) and the running buffer (5 min). The buffer was prepared from 10 mM... 

A principle focus of this book is the classification of dyes by chemical structure. This is certainly not the only possible classification scheme for dyes ordering by application properties, e.g., naming according the substrate to be dyed is another alternative. Neither of these two categories can be used with the exclusion of the other one, and overlap is often inevitable. Nevertheless, for this book it was decided to make the chemical structure of dyes the main sorting system. 

Guiflard, C., Lachheb, H., Houas, A., Ksibi, M., Elaloui, E. and Herrmann, J.-M. (2003b) Influence of chemical structure of dyes, of pH and of inorganic salts on their photocatalytic degradation by Ti02 comparison of the efficiency of powder and supported Ti02. J. Photochem. Photobiol. A Chem. 158, 27-36. 

A.R. Khataee, M.B. Kasiri, Photocatal3 tic degradation of organic dyes in the presence of nanostructured titanium dioxide Influence of the chemical structure of dyes . Journal of Molecular Catalysis A Chemical, 328, 8-26, (2010). 

Fig. 7.22 Chemical structures of dyes used for sentinel blue. The latter dye is not tilways approved for sentinel lymph node biopsies—the tiiarylmethane dyes, patent lymph node localization blue V and isosulfan blue, and the thiazine dye, methylene...

Glassification and Structure. Litde is known about the structure of sulfur dyes, and therefore, they ate classified according to the chemical Structure of the starting materials. 

Table 13-2. Chemical structures of representative small molecule transport materials ami luminescent dyes.

Structural hybrid, in resonance theory. 69 Structures, of dyes, in relation with elecuo-chemical potential. 75 extreme of cyanine dyes, 69 Styryl compounds, nomenclature of, 29 Styryl dyes, in basicity scale, 71 with dialkylamino group, 77 as models in relation with pKa, 50 and role of anhvdrobases. 50 as sensitizers, in photography. 79 stereo aspect of condensation. 50 synthesis of, 49... 

There is a wide diversity of chemical structures of anthraquinone colorants. Many anthraquinone dyes are found in nature, perhaps the best known being alizarin, 1,2-dihydroxyanthraquinone, the principal constituent of madder (see Chapter 1). These natural anthraquinone dyes are no longer of significant commercial importance. Many of the current commercial range of synthetic anthraquinone dyes are simply substituted derivatives of the anthraquinone system. For example, a number of the most important red and blue disperse dyes for application to polyester fibres are simple non-ionic anthraquinone molecules, containing substituents such as amino, hydroxy and methoxy, and a number of sul-fonated derivatives are commonly used as acid dyes for wool. 

The chemistry of the three most important chemical classes of organic colorants, the azo, carbonyl and phthalocyanine classes, has been dealt with individually in Chapters 3-5 respectively. In this chapter, the chemistry of a further five chemical classes which are of some importance for specific applications is discussed. These classes are the polymethines, arylcarbonium ion colorants, dioxazines, sulfur dyes and nitro dyes. A section of this chapter is devoted to each of these, each individual section contains a description of the principal structural features which characterise the particular colorant type, together with an outline of the chemistry of the main synthetic routes. There are many other chemical types of dyes and pigments that do not fall into the categories previously mentioned, but which are neglected in this text either because they are commercially of little importance or because they have been less extensively investigated. 

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 chemical structures of some typical disperse dyes are illustrated in... 

Figure 8.5 Some typical chemical structures of reactive dyes...

Fig. 17 Chemical structure of the styryl dye (dibutylamino) stilbazolium butylsulfonate...

Fig. 10 (a) Chemical structure of PEG-6-PCL copolymer, (b) CLSM image of PEG-6-PCL polymersomes containing membrane-encapsulated Nile Red (2 mol%) and aqueous entrapped Calcein dyes. Scale bar 5 pm. (c) Cryo-TEM image of PEG-6-PCL polymersomes. Scale bar 100 nm. Reprinted from [228] with permission... 

The color index (Cl) number, developed by the society of dyers and colorists, is used for dye classification. Once the chemical structure of a dye is known, a fivedigit Cl number is assigned to it. The first word is the dye classification and the second word is the hue or shade of the dye. For example, Cl Acid Yellow 36 (Cl 13065) is a yellow dye of the acid type. Additionally, a dye mixture may consist of several dyes for example, Navy 106 is composed of three reactive azo dyes remazol black B (Reactive Black 5), Remazol Red RB (Reactive Red 198), and Remazol Golden Yellow 3. 

Luangdilok W, Paswad T (2000) Effect of chemical structures of reactive dyes on color removal by an anaerobic-aerobic process. Water Sci Technol 42(34) 377-382... 

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