2- Naphthol-l-sulfonic 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])... 

J-acid (6-amino-l-naphthol-3-sulfonic acid [87-02-5]) (16), and gamma acid (7-amino-1-naphtho1-3-su1fonic acid [90-51-7]) (17). 

The ratio between the isomers obtained in coupling with 1,3- and 1,5-naphtholsulfonic acids depends on the reactivity of the diazo component. Energetic ones, such as the 2,4-dinitrobenzenediazonium compound, essentially couple only with l-naphthol-3-sulfonic acid [3771-14-0] in the para position, but 4-chloro-benzenediazonium salt (a weaker diazo) attacks the ortho position. Both isomers result when mononitrobenzenediazonium compounds are used. The tendency to couple para is greater in l-naphthol-5-sulfonic acid [117-59-9] C QHgO S (21). For the combination of... 

The azo coupling reaction proceeds by the electrophilic aromatic substitution mechanism. In the case of 4-chlorobenzenediazonium compound with l-naphthol-4-sulfonic acid [84-87-7] the reaction is not base-catalyzed, but that with l-naphthol-3-sulfonic acid and 2-naphthol-8-sulfonic acid [92-40-0] is moderately and strongly base-catalyzed, respectively. The different rates of reaction agree with kinetic studies of hydrogen isotope effects in coupling components. The magnitude of the isotope effect increases with increased steric hindrance at the coupler reaction site. The addition of bases, even if pH is not changed, can affect the reaction rate. In polar aprotic media, reaction rate is different with alkyl-ammonium ions. Cationic, anionic, and nonionic surfactants can also influence the reaction rate (27). 

Direct Oranges. AU principal commercially produced direct oranges are of disazo or stUbene chemical composition (Table 5). Direct Orange 102 (65) (R = COO Na+ ), is manufactured by first coupling aniline to 6,6 -ureylenebis-l-naphthol-3-sulfonic acid foUowed by a second coupling with /)-aminobenzoic acid [150-13-0]. 6,6 -Ureylenebis-l-naphthol-3-sulfonic acid [134-47-4] is the coupling component in many of the most important direct colors. It is produced by phosgenation of two moles of J-acid (6-ainino-l-naphthol-3-sulfonic acid). 

Other commercially important direct oranges iaclude Direct Orange 26 (66) (R = H) (2 mol aniline coupled to 6,6 -ureylenebis-l-naphthol-3-sulfonic acid), and Direct Orange 72 (67) which is obtained by phosgenatiag two moles of 7-amiQO-l,3-naphthalenedisulfonic acid coupled to cresidine [120-71 -8]. 

Fig. 5. Direct red dyes, (a) Direct Red 81 described ia text (68) (b) Direct Red 2 (o-toLidiae coupled to two moles of naphthionic acid) (69) (c) Direct Red 23 (aniline coupled to 6,6 -ureylenebis-l-naplitliol-3-sulfonic acid with a second coupling with j aminoacetanilide) (70) and Direct Red 80 (2 mol 6-amino-3,4 -azobenzenedisulfonic acid coupled twice to 6,6 -ureylenebis-l-naphthol-3-sulfonic acid) (73). Direct Red 24 (4-aniino-y -toluenesulfonic acid coupled under acidic conditions to 6,6 -ureylenebis-l-naphthol-3-sulfonic acid followed by an alkaline coupling of o-anisidine) (71) (d) Direct Red 72 (Broenner s acid, ie, 6-artiino-2-naphthalenesulfonic acid coupled under acidic conditions to 6,6 -ureylenebis-l-naphthol-3-sulfonic acid followed by an...

The Colour Index (up to June 1991) Hsts 21 direct violets with disclosed chemical constitutions. Commercially important are Cl Direct Violet 9 [6227-14-1] (79) (Cl 27885) (sulfanihc acid coupled to cresidiue followed by alkaline coupling to V-phenyl J-acid) and Cl Direct Violet 66 [6798-03-4] (80) (Cl 29120) (a copper complex of 2-arniao-l-phenol-4-sulfonarnide (2 mol) coupled to 6,6 -imiQobis-l-naphthol-3-sulfonic acid). 

In a broader context, but based on his own investigations of general acid- and based catalyzed additions to carbonyl groups, Jencks classifies a reaction like the azo coupling of l-naphthol-3-sulfonic acid dianion catalyzed by water molecule(s) hydrogen-bonded at the naphtholate oxygen as a pre-association mechanism. 

The small increase of the reaction rate for the 1-position (dotted line) at pH 9.5 to 10.0 reflects experimental results obtained by Ikeda et al. 255-257) paper these authors determined the relative rate constants for azo coupling reactions of 6-amino-l-naphthol-3-sulfonic acid (J-acid, 153) with 4-methyl- and 4-chlorobenzenediazonium ions in competitive experiments to the azo coupling reaction of l-naphthol-4-sulfonic acid at pH 5.5-9.1. The rate at the 2-position of J-acid, i.e. the reaction directed by the O -group, is 300-4000 times faster than that at the 5-position, which is directed by the amino group. These authors made two interesting observations ... 

As we found more recently , these orientation effects can be disguised by mixing effects of the type discussed in Section 4.2. In reactions of 3-trifluoromethyl-benzenediazonium ions with 7-amino-l-naphthol-3-sulfonic acid 154, rates and product ratios which would be predicted from Figure 3 are obtained only in very dilute solutions (<10 mol/1). In systems with higher concentrations of the reactants the product with the 3 -trifluoromethylphenylazo group in the 8-position is not only dominant in acidic solution, as expectal, but also up to pH 9. In this pH range also considerable amounts of bisazo product are obtained. These are observations which are typical for mixing eff ts observed in very fast reactions. With the unsubstituted benzenediazonium ions, a less reactive electrophile, however, rates and products are determined only by equilibria of the type of (70). 

DNSA [2-(2,4-Dinitrophenylazo)-6-(N-Me-N-(2-hydroxysulfonyloxyethyl-sulfonyl)-amido]-l-naphthol-3-sulfonic acid... 

J Acid n Fusion product of beta-naphthylamine-3,6-bisulfonic acid with caustic. Used in the manufacture of dyes. Also known as 2-Amino-5-Naphthol-7-Sulfonic Acid and 6-Amino-l-Naphthol-3-Sulfonic Acid. 

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