2-amino-8-hydroxynaphthalene-6-sulfonic

A particularly important class of coupling components are the aminohydroxy-naphthalenesulfonic acids. Appropriate variation of the disazo component permits the development of shades ranging from orange to black. Orange and scarlet are achieved with I-acid (6-amino-l-hydroxy-naphthalene-3-sulfonic acid) and y-acid (7-amino-1-hydroxynaphthaIcne-3-sulfonic acid), whereas H-acid (8-amino-l-hydroxynaphthalene-3,6-disulfonic acid) and K-acid (8-amino-l-hydroxy-naphthalene-3,5-disulfonic acid) derivatives are useful for red to bluish-red hues. Extremely lightfast red shades are also accessible with disazo dyes ( brown dyes ). For chemical structures see Section 3.1.5). 

The most important coupling component for the Di—D and D 1- K<-D2 types is 6, which is produced by treatment of 6-amino-l-hydroxynaphthalene-3-sulfonic acid (I acid) with phosgene. 

Anilinesulfonic acids are chiefly used as starting component D, naphthylamine and Cleve acids as middle components Mi and M2, and I acid, its /V-phenyl derivatives, H acid, 2-amino-8-hydroxynaphthalene-6-sulfonic acid (y acid), and their derivatives as final component K. This type mainly possesses blue and green shades. Example C. I. DirectBlue 78, 34200 (16) [2503-73-3],... 

The synthesis of the 1 1 complex 8 is an example of [10] demethylative chroma-tion. It is prepared by diazotization of 5-amino-2-chlorohydroquinone dimethyl ether and coupling onto 1-hydroxynaphthalene-5-sulfonic acid. The reaction product and Cr203 in formic acid are heated in an autoclave at 130 °C. The chromium complex 8 [80004-31-5] is obtained as a black powder that gives grayish blue dyeings on wool and leather. 

In the stepwise synthesis of the unsymmetrical complex dye 13 [ 70236-60-1] [10], the azo dye made from diazotized l-amino-2-hydroxy-5-nitrobenzene and 1-phenyl-3-methyl-5-pyrazolone and the 1 1 chromium complex obtained from 6-nitro-l-diazo-2-hydroxynaphthalene-4-sulfonic acid and 2-naphthol are heated together at 80 °C for 5 h. The adduct is salted out with NaCl. A black powder is obtained that dyes wool and leather in dark brown shades. The resulting colors are fast, particularly on shrink-resistant wool. 

Alkaline glucose converts the diazonium salts of l-amino-2-hydroxy-naphthalene-4-sulfonic acid and its halogen, nitro, carboxyl, or sulfonic acid derivatives into the corresponding 2-hydroxynaphthalene-4-sul-fonic acids.126 According to this patent, the yields are nearly quantitative. 

The azo compounds are important chromophores because of extended electronic delocalisation between the two aromatic rings via the azo bond. The darkness of the dye is enhanced by extensive delocalisation combined with several sulfonic acid groups which function as auxochromes. An example is provided by Naphthol Blue Black B (10), prepared from 8-amino-l-hydroxynaphthalene-3,6-disulfonic acid (H-acid) (11) by coupling it in the 7-position with diazotised p-nitroaniline in acidic solution and subsequently coupling in the 2-position with diazotised aniline in alkaline solution (Scheme 3). The H-acid (11) is a very versatile component in dye manufacture because it can couple with diazonium salts in either the 2-position or 7-position depending on the pH of the reaction medium, as indicated in Scheme 3. 

Isolation of the sulfonic acids as salts is usually carried out in one of two ways. In one the sulfonation mixture is taken up in water, neutralized with slaked lime, and filtered from the precipitated calcium sulfate, whereafter the filtrate, which contains the calcium salt of the sulfonic acid, is treated with sodium carbonate which converts the calcium into the sodium salt after filtration from calcium carbonate the solution is concentrated until crystallization occurs or, if necessary, evaporated to dryness. This procedure, termed chalking in industry, can be applied to all sulfonic acids except for the few cases such as l-amino-4-hydroxynaphthalene-2-sulfonic acid that give sparingly soluble calcium salts however, it is inconvenient because of the large volumes of liquid that must later be evaporated to avoid this precipitation of... 

A dye component that is used frequently is H acid (l-amino-8-hydroxynaphthalene-3,6-disulfonic acid). Production of this comparatively complex substitution pattern requires a series of different chemical reactions. The known side reactions and subsequent reactions on sulfonation and nitration of the naphthalene system and high-pressure hydrolysis of its substituents reduce the yield of the target product. If, as a consequence, intermediate isolations are unavoidable during the course of the process to prevent a gradual increase in the amount of by-products, additional product losses in mother and wash liquors will occur. Management of the often considerable quantities of solid waste and wastewater is therefore an important consideration in the production of H acid. 

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