2-Naphthylamine-6,8-disulfonic acid

Bagal et al. (1975) investigated in more detail the role of donor-acceptor complexes in the azo coupling reaction of the 4-nitrobenzenediazonium ion with 2-naphthylamine-3,6-disulfonic acid and that of the 4-chlorobenzenediazonium ion with 2-naphthol-6-sulfonic acid. Their kinetic results are, as would be expected, compatible with the mechanisms shown in Schemes 12-74 or 12-75. 

Amido -R -Acid. 3-A mi no-2.7-nupht ha l enedi sulfonic add 2-naphthylamine-3,6-disulfonic acid. C H,-NOA mol wt 303.32. C 39.60%, H 2.99%, N 4.62%, O 31.65%, S 21.14%, Prepd by treating 2-hydroxy-3,6-naph-thalenedisulfonie acid with ammonium sulfite and ammonium hydroxide Pelitcolas, Josue. Bull. She. Chim. France 1952, 89. 

A mixture of 35.0 g a-nitronaphthalene (0.2 mol), 200 mL 52 N NaHS03 (75% excess), and 250 mL H2O was heated under a return condenser until the mixture was completely homogeneous. The contents of the flask were evaporated to 300 mL and treated with 50 mL 12 iV HCI to give a heavy white precipitate, which was filtered from the cooled solution. This mixture was warmed with 300 mL water, which dissolved the salts present, leaving the naphthionic acid (solubility of0.024 g in 100 mL water) 13.5 g aminosulfonic acid was thus obtained, in a yield of 29%. The combined filtrates were saturated with NaCl, and the precipitate produced was filtered off. It was nearly free from inorganic salts. When dry, it weighed 31 g, which, on the basis of a monosodium salt of a naphthylamine disulfonic acid is equivalent to a yield of 66%. 

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])... 

M acid ORG chem NH2CioH5(OH)S03H A sulfonic acid formed by alkaline fusion of a disulfonic acid of a-naphthylamine used as a dye intermediate. em, as-3d Macquer s salt See potassium arsenate. mo kerz, s6lt ... 

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). 

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). 

It is to be observed that other m-nitrosulfonic acids also form very insoluble fenous salts. One example is 2-nitro-4,8-naphthalenedisulfonic acid wmch can be obtained in a pure state very easily by this method. This method of separation has long been known in the industry. For information about 2-naphthylamine-4,8-disulfonic acid, see page 219 ff. 

The solution is held for 2 days at 0° during which the 2,5,7 acid separates. The product, after filtering and pressing, weighs about 170 grams. The mother liquor, which is about 40 per cent sulfuric acid, contains about 22 grams of sulfonic acids per liter, which is not recovered. The 2-naphthylamine-5,7-disulfonic acid corresponds to about 26 grams of NaNOa. 

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). 

Since such light fast, direct dyes are usually trisazo dyes, a possible structure is synthesized from 2-naphthylamine-4,8-disulfonic acid, o-naphthylamine, Cleve acid, and y acid (acid coupling). 

Determination of 2 Naphthylamine>5,7>disulfonic Acid in the Presence of 2>Naphthylamine-6,8 disulfonic Acid... 

Derivation (3-naphthylamine sulfate is sulfonated with 66% oleum the precipitate, 2-naphthylamine-6,8-disulfonic acid, is heated with 65% sodium hydroxide solution at 210C and 210 psi. 

C acid. (2-naphthylamine-4,8-disulfonic acid). C10H5(NH)2(SO3H)2. 

Derivation l-Naphthylamine-8-sulfonic acid is reacted with sulfuric acid to yield 1-naphthylamine-4,8-disulfonic acid further reaction with 25% oleum gives l,8-naphthosulfam-2,4-disulfonic acid, which melts at 155C with 40% NaOH. 

Derivation Naphthalene-1,5- and 1,6-sulfonic acids are nitrated and reduced, giving 1-naphthylamine-3,8- and 4,8-disulfonic acids. Separation is effected by crystallizing out the acid sodium salts of 1-naph-thylamine-3,8-disulfonic acid. 

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