L-Naphthol-3,6-disulfonic acid

Technologically, the most important examples of such couplers are 1-naphthylamine, 1-naphthol, and sulfonic acid derivatives of 1-naphthol (Fig. 2). Of great importance in the dyestuff industry are derivatives of l-naphthol-3-sulfonic acid, such as H-acid (8-amino-l-naphthol-3,6-disulfonic acid [90-20-0])... 

Various types of dyes are prepared from dehydrothiotoluidine. The free base or its sulfonic acid is diazotized and coupled with various naph-tholsulfonic acids such as, for example, e acid (l-naphthol-3,8-disul-fonic acid). The resulting dye is characterized by its high purity of color and can be discharged to a pure white. Such red direct dyes are sold under various names, and are usually referred to as dyes of the erika red type. (Erika Z is the combination from dehydxothioxylidine and e acid. l-Naphthol-3,6-disulfonic acid gives a very similar dye.) In addition to the true azo dyes from dehydrothiotoluidine, two other products are made which are important yellow dyes. One of these dyes is the naphthamine yellow NN (also called chloramine yellow) (Kalle), formed from dehydrothiotoluidinesulfonic acid by oxidation with sodium hypochlorite. The other is thiazole yellow or Clayton yellow, which is made by combining the diazo compound of dehydrothiotoluidinesulfonic acid with a second molecule of the same compound to form a diazoamino compound. 

Dinitrophenylazo)-l-naphthol-3,6-disulfonic acid, disodium salt 6.0-7.0... 

Five impurities of 8-amino-l-naphthol-3,6-disulfonic acid (e.g., l-naphthol-4-sulfonic acid, 8-aminonaphthalene-l,3,6-trisulfonic acid, chromotropic acid) were resolved on a C,g column (A = 235 nm) using an aqueous 0.3 M sodium sulfate mobile phase [1561]. All compounds eluted in <8 min. Detection limits of... 

The rate constants in Figure 5-3 were measured by injecting the solution of the (E)-diazoate into a buffer solution that also contained a highly reactive coupling component (2-naphthol-3,6-disulfonic acid, except at pH values below 2.5, where l,8-dihydroxynaphthalene-3,6-disulfonic acid was used instead). The diazonium ion formed reacts rapidly with these naphthols, and the concentration of the corresponding azo compounds was determined spectrophotometrically. 

The pK values for azolediazonium ions (Scheme 12-4) refer to the heterolysis of the NH bond, not to the addition of a hydroxy group. Therefore, these heteroaromatic diazo components may react either as a cation (as shown in Scheme 12-4) or as the zwitterion (after loss of the NH proton). Diener and Zollinger (1986) investigated the relative reactivities of these two equilibrium forms (Scheme 12-5) in the azo coupling reaction of l,3,4-triazole-2-diazonium ion with the tri-basic anion of 2-naphthol-3,6-disulfonic acid. 

The yellow ink jet dyes (and pigments) are metal-free azo dyes, such as Cl Direct Yellow 132 and Cl Acid Yellow 23 (Tartrazine).48,49 Most of the magentas are azo dyes derived from H-acid (l-amino-8-naphthol-3,6-disulfonic acid), such as (62), and xanthenes, such as Cl Acid Red 52 and Cl Acid Red 289.48,49 Where high lightfastness is a requirement, a copper complex azo dye, Cl Reactive Red 23 (63), is used. However, such dyes are dull (see Section 9.12.3.2). Nickel complex PAQ dyes, such as (22), are claimed to be brighter and to have similar high lightfastness... 

Ion-pair HPLC (194,195) was used to separate amaranth from its subsidiary dye l-(4-sulfo-l-naphthylazo)-2-naphthol-6-sulfonic acid disodium salt (fast red E) and from its intermediates 1-naphthylamine 4-sulfonic acid (naphthionic acid) and 2-naphthol-3,6-disulfonic acid disodium salt (R-salt). Ion-pair HPLC was also used for the determination of total free and bound nonsul-fonated aromatic amines in amaranth after diazotization and coupling with R-salt (198). 

Sunset yellow was separated from its subsidiary dye l-p-sulfophenylazo-2-naphthol-3,6-disulfonic acid trisodium salt (195) and from its intermediates sulfanilic acid and Schaeffer s salt (194) by means of ion-pair HPLC. Ion-pair chromatography has also been used to determine free and bound nonsulfonated aromatic amines in sunset yellow after reduction with dithionite, diazotization with sodium nitrite, and coupling with R-salt (202). 

Azo Dyes. The dye obtained by coupling diazotized 4-(2-sulfooxyethylsulfonyl)ani-line with l-amino-8-naphthol-3,6-disulfonic acid at pH 1 - 2 is coupled at pH 6 - 7 with a diazonium compound synthesized from the condensation product derived from l,3-diaminobenzene-6-sulfonic acid and 2,4,6-trifluoro-5-chloropyrimidine. The crude material is salted out of the solution and isolated. This product (24) gives a blue solution in water and dyes cotton in a marine blue to black color ... 

DISODIUM (2,4-DIMETHYLPHENYLAZO)-2-HYDRO-XYNAPHTH.ALENE-3,6-DISULFONATE DISODIUM (2,4-DIMETHYLPHENYLAZO)-2-HYDROXYNAPHTRAL-ENE-3.6-DISULPHONATE DISODIUM SALT of l-(2,4-XYLYLAZO)-2-NAPHTHOL-3,6-DISULFONIC ACID DISODIUM SALT of l-(2,4-XYLYLAZO)-2-NAPHTHOL-... 

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. 

FIGURE 15. Absorption spectra at 20 °C of 5-cyano-l-naphthol (5C1N), l-naphthol-3,6-disulfonate (3,6DS1N), 2-naphthol-3,6-disulfonate (3,6DS2N), 2-naphthol-6,8-disulfonate (6,8DS2N) and 1,6-dibromo-2-naphthol (l,6DBr2N) measured in water at acidic pH values from 4 to 7 ... 

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