Naphthol disulfonic acids from

Sulfurous acid and its salts are inexpensive reducing agents which are, however, usable only in special cases. These reagents frequently give sulfonation simultaneously with reduction (cf. the preparation of l-naphthylamine-2,4-disulfonic acid from 1-nitronaphthalene, and of l-amino-2-naphthol-4-sulfonic acid from nitroso- -naphthol, pages 178 and 201). Also, in the reduction of diazobenzene to phenylhydrazine, a N-sulfonic acid is formed first and this must be split by vigorous treatment with hydrochloric acid (see pages 96 and 128). 

The over-all yield from 2-naphthol is about 90 peA cent of theory. This method is also used for the preparation of 4-amino-l-phenol-3,5-disulfonic acid from p-nitrosodimethylanihne by the following reaction ... 

Diazo coupling involves the N exocyclic atom of the diazonium salt, which acts as an electrophilic center. The diazonium salts of thiazoles couple with a-naphthol (605). 2-nitroresorcinol (606), pyrocatechol (607-609), 2.6-dihydroxy 4-methyl-5-cyanopyridine (610). and other heteroaromatic compounds (404. 611) (Scheme 188). The rates of coupling between 2-diazothicizolium salts and 2-naphthol-3.6-disulfonic acid were measured spectrophotometrically and found to be slower than that of 2-diazopyridinium salts but faster than that of benzene diazonium salts (561 i. The bis-diazonium salt of bis(2-amino-4-methylthiazole) couples with /3-naphthol to give 333 (Scheme 189) (612). The products obtained from the diazo coupling are usuallv highly colored (234. 338. 339. 613-616). 

Zollinger (1971) calculated the actual rate constant referring to the monomeric diazo component from the (overall) measured rates and the dimerization equilibrium constant. The ratio of rates of the first to the second azo coupling reaction of the biphenyl-4,4 -bis-diazonium ion with the trianion of 2-naphthol-3,6-disulfonic acid at 15 °C, k /k2 9 is 80. 

Micellar catalysis of azo coupling reactions was first studied by Poindexter and McKay (1972). They investigated the reaction of a 4-nitrobenzenediazonium salt with 2-naphthol-6-sulfonic and 2-naphthol-3,6-disulfonic acid in the presence of sodium dodecylsulfate or hexadecyltrimethylammonium bromide. With both the anionic and cationic additives an inhibition (up to 15-fold) was observed. This result was to be expected on the basis of the principles of micellar catalysis, since the charges of the two reacting species are opposite. This is due to the fact that either of the reagents will, for electrostatic reasons, be excluded from the micelle. 

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). 

Bailey et al. (199) and Singh (200) used ion-exchange HPLC for the separation of amaranth from the intermediates naphthionic acid and R-salt, as well as the side reaction products 2-naph-thol-6-sulfonic acid sodium salt (Schaeffer s salt), 2-naphthol-6,8-disulfonic acid disodium salt (G-salt), and 2-naphthol-3,6,8-trisulfonic acid trisodium salt (NTSA). 

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 ... 

The l-naphthol-5-sulfonic acid is prepared by alkali fusion, at 160-190 C., of naphthalene-1,5-disulfonic acid (see page 219) it can also be prepared by the Bucherer reaction from l-naphthylamine-5-sulfonic acid (see page 214). 

The reaction of di- and polysulfonic acids can usually be carried out so that the replacement of the sulfo groups by hydroxyls takes place stepwise (partial alkali fusion). Thus, phenol-m-sulfonic acid is obtained from benzene-m-disulfonic acid under mild conditions, while resorcinol is formed under more vigorous conditions (see page 144) similarly, naphthalene-l,5-disulfonie acid yields, first, l-naphthol-5-sulfonic acid, then l,5 dihydroxynaphthalene, both valuable azo dye... 

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. 

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. 

Orange G (l-phenylazo-2-naphthol-6,8-disulfonic acid di-Na salt) [1936-15-8] M 452.4, pKj st 9. Recrystallise this dye from 75% EtOH, dry it for 3hours at 110° and keep it in a vacuum desiccator over H2SO4. The free acid crystallises from EtOH or cone HCl in deep red needles with a green reflex. [Conant Pratt J Am Chem Soc 48 2483 1923, Drew Landquist J Chem Soc 292 1938, Beilstein 16 H 301, 16 I 305, 16 II 141,16 III 327.]... 

As a result of extensive screening, a growing number of nitrogen containing compounds were also found to mediate pulp delignification with laccase. Apart from ABTS and HBT, they include l-nitroso-2-naphthol-3,6-disulfonic acid (NNDS) and... 

The superiority of the negative-ion mode was also clear from the FD mass spectra of 9a and 17 and of the potassium salts of benzenesulfonic acid, 1-methylphenanthrenesulfonic acid and perylenesulfonic acid13,29, where the unclustered anions were the only significant species desorbed from the respective salts, dissolved in a polyethylene oxide matrix. Only weak negative-ion signals could be obtained from the application of electrodynamic ionization mass spectrometry to the disodium salts of 2-naphthol-3,6-disulfonic acid (24a) and of 4,5-dihydroxy-2,7-naphthalenedisulfonic acid (24b)30. 

Naphthols. Of the four important naphtholmonosulfonic acids, only two are produced by direct sulfonation of the naphthol. 2-Naphthol-l-sulfonic acid (Armstrong s acid) is formed by treatment with 97 per cent sulfuric acid at low temperature with a short reaction time or with SO3 using a solvent, w hile 2-naphthol-6-sulfonic (Schaeffer s acid) is produced at 120-125 C with 78 per cent sulfuric acid. The two major naphtholdisulfonic acids [2-naphthol-6,8-disulfonic acid (G acid) and 2-naphthol-3,6-disulfonic acid (R acid)] are formed together by direct sulfonation of 2-naphthol, using sulfuric acid followed by oleum and raising the temperature in steps from 15 to 80 C. They are isolated as the potassium and sodium salts, respectively, by differential salting out. 

In our laboratory, this method was appUed to the purification of food mono-azo dyes. Amaranth, New Coccine, and Sunset Yellow FCF were purified at 99.7%, 99.5%, and 99.3%, respectively, from 1-23 g of commercial dyes. Continued research has led to the purification of impurities present in commercial Sunset Yellow FCF that include RS-SA (trisodium salt of 3-hydroxy-4-[sulfophenyl] azo-2,7-naphthalene disulfonic acid), GS-S A (1 -[4-sulfophenyl]azo)-2-naphthol-6,8-disulfonic acid), DONS (disodium salt of 6,6 -oxybis-2-naphthalene sulfonic acid), and 2N-SA (sodium salt of 4-[(2-hydroxy-l-naphthalenyl)azo]benzenesulfonic add). The method successfully isolated GS-SA from Sunset Yellow FCF. " ... 

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