Pigments, azo

Perchloric acid Acetic acid, acetic anhydride, alcohols, antimony compounds, azo pigments, bismuth and its alloys, methanol, carbonaceous materials, carbon tetrachloride, cellulose, dehydrating agents, diethyl ether, glycols and glycolethers, HCl, HI, hypophosphites, ketones, nitric acid, pyridine, steel, sulfoxides, sulfuric acid... 

Because the heat distortion temperature of cured epoxy resins (qv) increases with the functionality of the curing agents, pyromellitic dianhydride is used to cross-link epoxy resins for elevated temperature service. The dianhydride may be added as a dispersion of micropulverized powder in liquid epoxy resin or as a glycol adduct (158). Such epoxies may be used as an insulating layer in printed circuit boards to improve heat resistance (159). Other uses include inhibition of corrosion (160,161), hot melt traffic paints (162), azo pigments (163), adhesives (164), and photoresist compounds (165). 

Many of the pigments carry a nitro group ia the diazonium component, usually ia the ortho position (R = NO2). Among the acetoacetaryUde components the o-methoxy derivative (R2 = OCH, R3 = H) is one of the most important ia the production of azo pigments. The colors of these pigments range from red to green-shade yellows. Commercially important products ate shown ia Table 3. 

In the metal-free class of azo pigments it is remarkable that the simplest derivatives of 2-naphthol such as Hansa Red B [2425-85-6] (139) (Cl Pigment Red 3 Cl 12120 Toluidine Red) and Para Red [6410-10-2] both known since 1905, are still of importance. 

The alternative approach is to pad the fabric with the alkaline naphthol and dry, foUowed by printing directly onto this prepared fabric diazonium salts or stabilized diazonium salts. Coupling is instant and the only further treatment needed is to remove aU the uncoupled naphthol and surface azo pigment in a subsequent washing treatment. Because the choice of colors is limited from one naphthol component, other shades are obtained by using other classes of dye alongside the azoic colors, eg, reactives. This approach is widely used in the production of African prints. 

Benzothiazin-4-ones, dihydrosynthesis, 3, 1028 Benzothiazole, acetoacetylamino-azo pigments from, 1, 334 Benzothiazole, 2-acyl-synthesis, 6, 265 Benzothiazole, 2-alkoxy-synthesis, 6, 323 Benzothiazole, 2-alkyl-synthesis, 6, 265 Benzothiazole, 2-alkyl-6-nitro-reactions... 

Benzotriazine, 6-amino-3-methyl-4-oxodihydro-azo pigments from, 1, 334... 

Pyrazol-5-one, 3-methyl-1 -phenyl-4-phenylazo-methylation, 5, 264 Pyrazol-5-one, pyridyl-biological activity, 5, 295 Pyrazol-5-one, l-(4 -carbamoylphenyl)-3-methyl-azo pigments from, 1, 334 Pyrazol-5-one, 3-methyl-l-phenyl-azo dyes from, 1, 330 azo pigments from, 1, 334 Pyrazolones acetylated acylotropy, 5, 264 analytical applications, 5, 300 anions... 

Quinoline, amino-2-hydroxy-4-methyl-azo pigments from, 1, 334 Quinoline, 8-amino-6-methoxy-as antimalarial, 2, 517 Quinoline, 4-amino-2-methyl-protonation, 2, 341 Quinoline, anilino-3-substituted... 

By the use of microstructured mixers, pigment and other particulate syntheses can be improved. In this way, finer particles with more uniform size distribution were yielded for the commercial azo pigment Yellow 12 (see Fig. 2) [11]. The particles formed in the microstructured mixer have better optical properties such as the glossiness or transparency at similar tinctorial power. Since the micro-mixer made pigments have more intense colour, lower contents of the costly raw material in the commercial dye products can now be employed which increases the profitability of the pigment manufacture. 

The potential described above is not only of a scientific nature, as all these publications impressively prove. Indeed, it has been applied to bench-scale, pilot-scale and production-scale processing. Examples refer to the fields of Grignard reactions [11], polymerizations [21], boron chemistry ]317], and azo pigment generation ]136]. 

Coupled with the latter investigations, it was shown that a diazo suspension can be fed through a micro device without leading to plugging [55]. This broadens the scope of micro processing applicability towards azo pigment formation. 

Two commercial azo pigments, one yellow and one red, were prepared following the scheme given above the nature of the substituents was not disclosed [55]. 

OS 39] ]R 25] ]P 27] A 24 h run of a pilot-scale micro reactor for azo pigment production was performed using a diazo suspension [55], At the end of this period, the pressure loss of the micro reactor increased exponentially. Special means were developed to prevent clogging and unstable operation. By partial removal of the deposits, the pressure loss was brought back to normal. 

Azoic dyeing of cellulosic fibres is a process that is used only to a small extent today. In this process, an azo pigment is formed by chemical reaction within the fibre. The cotton fibres are first impregnated with an appropriate coupling component such as the anilide of 3-hydroxy-2-naphthoic acid, 156, under aqueous alkaline conditions. The fibre is then treated with a solution of a stabilised diazonium salt, in which the... 

Figure 9.1 Chemical structures of some important classical azo pigments...

Figure 9.3 Intermolecular association in the crystal structure of a benzimidazolone azo pigment...

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