Water-soluble azo dyes

G. M. Shaul, R. J. Lieberman, C. R. Dempsey, and K. A. Dostol, "TreatabiUty of Water Soluble Azo Dyes by the Activated Sludge Process,"... 

Shaul GM, Holdsworth TJ, Dempsey CR, Dostal KA (1991) Fate of water-soluble azo dyes in the activated sludge process. Chemosphere 22 107-119... 

Sulfonated azo dyes are widely used in different industries [16]. Some structure of sulfonated and unsulfonated azo dyes is shown in Fig. 1. These water-soluble azo dyes will enter the environment generally with wastewater discharge. Also, these sulfonated and unsulfonated azo dyes have a negative aesthetic effect on the wastewater, and some of these compounds and biodegraded products are also toxic, carcinogenic, and mutagenic [17]. There exists clear evidence that sulfonated azo dyes show decreased or no mutagenic effect compared to unsulfonated azo dyes... 

A very noticeable feature has been the use of a wider range of heterocyclic coupling components than in water-soluble azo dyes. An early example of this trend was Cl Disperse Yellow 5 (4.74), which used 4-hydroxy-1-methylcarbostyril as coupling component. It was in... 

Shaul, G.M., Lieberman, R.J., Dempsey, C.R., and Dostal, K.A. Treatability of water soluble azo dyes by the activated sludge process, in Proceedings of the Industrial Wastes Symposium, 59" Water Pollution Control Conference, October 1986. 

Shaul, G., Dempsey, C., and Dostal, K., Fate of Water Soluble Azo Dyes in the Activated Sludge Process, EPA/600/S2-88/030, U.S. Environmental Protection Agency, Research and Development Office, Washington, D.C., 1988. 

By far the most predominant metabolic pathway for water-soluble azo dyes is cleavage of the azo linkage by azoreductase of the liver and extrahepatic tissue or by intestinal microflora in the body [25,26], Oxidative metabolism occurs for lipid-soluble dyes, e.g., solvent dyes. Three oxidation pathways are known for such dyes (1) C-(ring-)hydroxylation, (2) A-hydroxylation at a primary or secondary amino group or (3) by stepwise oxidation of the methyl groups of dimethylamino compounds (demethylation). All three oxidative degradation ways leave the azo bond intact. For further details of the mechanisms, see [27,28],... 

The introduction of polar groups, such as the sulfonic acid or carboxyl group, increases the solubility sufficiently to yield rather useful indicators. We shall see in Chapter Ten that these water-soluble azo dyes are especially valuable because their salt error is negligible. 

Fate of Water Soluble Azo Dyes in the Activated Sludge Process... 

M. Tachibana, T. Imamura, M. Saito, and K. Kina, Rapid Determination of Copper in Serum by Flow Injection Analysis with Water Soluble Azo Dye [in Japanese]. Bunseki Kagaku, 32 (1983) 776. 

In the classic Griess test, use is made of sulfanilic acid (I), with subsequent coupling of the resulting diazonium compound with a-naphthylamine (II), to give the red -benzene sulfonic acid-azo-a-naphthylamine (HI), here shown in its baso-form, to produce the red, water-soluble azo dye (IV). 

There is a wide variety of dyes unique to the field of hair coloring. Successive N-alkylation of the nitrophenylenediamines has an additive bathochromic effect on the visible absorption to the extent that violet-blue dyes can be formed. Since the simple A/-alkyl derivatives do not have good dyeing properties, patent activity has concentrated on the superior A/-hydroxyalkyl derivatives of nitrophenylenediamines (29,30), some of which have commercial use (31). Other substituents have been used (32). A series of patents also have been issued on substituted water-soluble azo and anthraquinone dyes bearing quaternary ammonium groups (33). 

OIL SOLUBLE AZO DYES The oil soluble, water-iasoluble, azo dyes dissolve ia oils, fats, waxes, etc. Generally, yellow, orange, red, and brown oil colors are azo stmctures and greens, blues, and violets are primarily anthraquiaones (see Dyes, anthraquinone). Blacks are usually nigrosiaes and iaduhnes of the aziae type (see Azinedyes). An example is Oil Red [85-83-6] (127) (Cl Solvent Red 24 Cl 26105). Uses iaclude the coloring of hydrocarbons, waxes, oils, candles, etc. 

The soluble azo dyes contain one or more sulfonic acid groups. Their degree of water solubiUty is determined by the number of sulfonic groups present and their position in the molecule. FD C Red No. 40 (5) and D C Orange No. 4 (16) belong in this class. 

Acid Dyes. These water-soluble anionic dyes ate appHed to nylon, wool, sUk, and modified acryHcs. They ate also used to some extent for paper, leather, food, and cosmetics. The original members of this class aU had one or mote sulfonic or catboxyHc acid groups in thein molecules. This characteristic probably gave the class its name. Chemically, the acid dyes consist of azo (including preformed metal complexes), anthraquiaone, and ttiaryHnethane compounds with a few azHie, xanthene, ketone imine, nitro, nitroso, and quHiophthalone compounds. 

Chen H, Xu H, Heinze TM (2009) Decolorization of water and oil-soluble azo dyes by Lactobacillus acidophilis fermentum. J Ind Microbiol Biotechnol 36 1459-1466... 

The relative and absolute configurations of diepoxydicarbazoles involving the 2,6-dioxa-4,8-diazaadamantane system were determined in the course of a study on indole and indole alkaloids.242 Water-soluble azo, anthraquinone, and phthalocyanine dyes which are substituted by a 4-chloro-s-triazin-2-ylamino group can be quaternized with a l-aza-3-methyl-4,6,10-trioxa-adamantane unit in aqueous medium at 40 50"C.243 Dyes mixed with... 

Oil-soluble azo dyes, 9 420-421 Oil soluble sulfonates, 23 530 recent developments in, 23 534 Oil-water separation, 22 68... 

Cationic substituents can also be introduced into preformed azo dyes. In this manner, mixtures of isomers are obtained which may carry one to four cationic groups in various positions. The multiplicity of isomers is a cause for good water solubility. These dyes are predominantly used for coloring paper. 

Fat- and oil-soluble dyes are also soluble in waxes, resins, lacquers, hydrocarbons, halogenated hydrocarbons, ethers, and alcohols, but not in water. It is not possible to differentiate clearly between them and the alcohol- and ester-soluble dyes. With the exception of blue anthraquinone derivatives, fat- and oil-soluble dyes are azo dyes, generally based on simple components. According to their degree of solubility they usually contain hydroxyl and/or amino groups, but not sulfonic acid and carboxylic acid groups. Examples of fat- and oil-soluble azo dyes are C.I. 

Individual pH Indicators. The most commonly used pH indicators include azo dyes, nitrophenols, phthaleins, and sulfophthaleins. Varying the substituents on the chromophores yields pH indicators with different transition ranges, and the complete pH range between 0 and 14 can thus be covered, as shown in Table 5.17 and Figure 5.2. Introducing acid groups (sulfo or carboxyl) leads to water-soluble indicator dyes. 

Furthermore, cationic dyes 179 of the diazahemicyanine class are derived from indolizines. This invention related to water-soluble azo dyestuffs is useful for the colorations of synthetic polymeric materials particularly polymers and copolymers of acrylnitrile and dicyanoethylene as well as modified polyesters and polyamides (81GBP2075540, Scheme 64). 

To study quantitatively the kinetics of lipid oxidation and antioxidation, a standard way of controlling and measuring the rate of free radical initiation is to use thermally labile azo compounds. These artificial initiators generate radicals at a reproducible, well-established and constant rate. In the presence of initiators such as a,a-azobisisobutyronitrile (AIBN) or benzoyl peroxide, the overriding initiation can be directly related to the rate of production of the initiator radical. Also, by using either water-soluble or lipid-soluble azo dyes, these compounds can initiate radicals at known specific micro-environments. 

Water-insoluble azo dyes soluble in fats (Sudan dyes), or disperse dyes can usually be easily chromatographed on papers impregnated with organic solvents. For example, Sudan dyes are well separated in systems with paraffin oil as stationary phase (impregnation) and ethanol-water mixture (8 2) or ethanol-ammonia (8 2) as the mobile phase for obtaining rapid information papers impregnated with 50% dimethylformamide and hexane as the moving phase may be used. Dyes can be applied onto the paper in acetone solution in an amount up to 20 pg (48). 

Sudan 1 dye was extracted from chilli powder and detected using Au NPs in concentration as low as 48 ng in 1 g of powder (Cheung et al. 2010). Recently, Jahn and co-workers employed enzymatically generated Ag NPs prepared by a bottom-up and self-organizing procedure (see Sect. 3.4.2.1), in combination with a lipophilic sensor layer for the detection of water-insoluble azo-dye Sudan III in real food matrix, paprika products (Jahn et al. 2015). The surface modification consisted of self-assembled aliphatic hydrocarbons with a thiol moiety forming hydrophobic monolayer on the SERS substrate. The resulting layer repelled unwanted water-soluble analytes from the surface whereas water-insoluble ones were adsorbed and detected by SERS. The riboflavin was introduced as a water-soluble competitor, which is part of the relevant food matrices. Sudan 111 dye was detected down to 9 pmol 1 concentration from paprika powder extract in the methanol. Beside this, lipophilic sensor layer can also be applied for further analytical tasks for which it is beneficial to discriminate water-soluble from insoluble substances. 

In order to study the photo-reorientation of the azo-dye molecules (water-soluble sulfonic dye SDl) by linearly polarized UV exposure, the polarized absorption spectra of the layer before and after irradiation with linearly polarized UV light were measured, using incident light with polarization directions parallel and perpendicular to the polarization direction of the activated linearly polarized UV light [18, 47]. Figure 2.12 shows the polarized absorption spectra (absorbance or optical density) before (curve 1) and after (curves 2 and 3) UV irradiation. 

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