6-Nitro-2-naphthol-8-sulfonic acid

The Sn+ ion reduces the nitro group and the resulting product fluoresces strongly. The 6-nitro-2-naphthol-8-sulfonic acid seems to be the best of all reagents for tin ions. 

Procedure. One drop of the test solution is placed on a filter paper and sprayed with a 0.1 % solution of 6-nitro-2-naphthol-8-sulfonic acid followed, after 6 minutes, with cone, ammonia. Under u.v. light, an intense blue fluorescence indicates the presence of Sn i ions. 

Sodium Bisulfite. Sodium bisulfite [7631-90-5] NaHSO, is occasionally used to perform simultaneous reduction of a nitro group to an amine and the addition of a sulfonic acid group. For example, 4-amino-3-hydroxyl-l-naphthalenesulfonic acid [116-63-2] C qH NO S, is manufactured from 2-naphthol in a process which uses sodium bisulfite (59). The process involves nitrosation of 2-naphthol in aqueous medium, followed by addition of sodium bisulfite and acidification with sulfuric acid. 

Nitro-l-diazo-2-naphthol-4-sulfonic acid prefers the 2-position in spite of the nitro group, and increasing alkalinity favors ortho coupling with diazophenols. 1-Naphthalenesulfamic acid [24344-19-2] (ArNHSO H) and N-nitro-1-naphthylamine [4323-69-7] (ArNHNO ) couple exclusively in the para position. The substitution of resorcinol [108-46-3] and y -phenylenediamine [108-45-2] is compHcated and has been discussed (29,30). The first azo dyes from aniline, eg. Aniline Yellow [60-09-3] (19) (Cl Solvent Yellow 1 Cl 11000) were manufactured in 1861 and Bismark Brown [10114-58-6] (20) (Cl Basic Brown 1 Cl 21000) appeared in 1863. The reaction is as follows ... 

Naphthol-7-sulfonic acid, 2-amino-6-(2-hydroxy-6-nitro-... 

A similar argument can be applied to the results of later work by Idelson et al.i9 In this they prepared the chromium complex (133) by interaction of the 1 1 chromium complex of 1-phenyl-3-methyl-4-(2-hydroxy-4-cyanonaphth-l-ylazo)-5-pyrazolone and diethylenetriamine and by reaction of the azo compound with [Cr(CO)3dien]. Identical products were obtained and, since the diethylenetriamine occupies9 a facial position in [Cr(CO)3dien], it was concluded that the complex (133) had a facial configuration. Similarly, the reported77 separation of isomeric 2 1 chromium complexes of 2-amino-6-(2-hydroxy-6-nitro-4-sulfonaphth-l-ylazo)-5-naphthol-7-sulfonic acid is... 

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. 

Action of bisulfite on a nitro compound or on a quinone or quinonemo-noxime, in which the nitro and nitroso groups are simultaneously reduced to amino groups. Examples are the preparation of l-naphthylamine-2,4-disulfonic acid from o-nitronaphthalene and bisulfite (naphthionic acid as by-product), and the manufacture of l-amino-2-naphthol-4-sulfonic acid from nitroso- -naphthol and bisulfite (page 201). 

Nitrophthalic acid has usually been prepared by nitration of phthalic add or phthalic anhydride, followed by separation from the accompanying 3-nitrophthalic acid. It has also been prepared from 6-nitro-2-naphthol-4-sidfonic acid (obtained from the technical diazo-anhydride of 6-nitro-i-amino-2-naphthol-4-sulfonic acid). The present procedure is more convenient than any of the earlier methods. 

Eriochrome black T was one of the first and most widely used of the metal indicators. Unfortunately, it is unstable in solution, probably because the molecule has both an oxidizing (nitro) and a reducing (azo) group. Lindstrom and Diehl developed as a replacement the indicator l-(l-hydroxy-4-methyl-2-phenylazo)-2-naphthol-4-sulfonic acid, called calmagite, with the structure... 

The (x-substituted naphthalenes, like substituted benzenes, are ihpst commonly prepared by a sequence of reactions that ultimately goes back to a nitro compound (Sec. 30.8). Preparation of / -substituted naphthalenes, on the other hand, cannot start with the nitro compound, since nitration does not take place in the j3-position. The route to /3-naphthylamine, and through it to the versatile dia-zonium salts, lies through /9-naphthol. /9-Naphthol is made from the /3-sulfonic acid it is converted into /8-naphthylamine when heated under pressure with ammonia and ammonium sulfite (the Bucherer reaction, not useful in the benzene series except in rare cases). 

The nitro and nitroso derivatives of a few aromatic hydroxy compounds are used as yellow-green dyes. The nitro compounds are prepared by direct action of nitric acid in presence of sulfuric acid, or by first sulfonating and then nitrating the sulfonic acid. In the preparation of naphthol yellow, a-naphthol is first sulfo-nated to the 2,4,7-trisulfonic acid, which on nitration undergoes replacement of the sulfonic acid groups at positions 2 and 4 by nitro groups. 

Nitroso compounds are formed as intermediates in this reaction. Yields from sulfonic acids, carboxylic acids, and nitro compounds, amongst others, are poor,424 but those from tertiary amines and phenols are often very good,423,426 although naphthols give only the nitroso derivatives for example, yields are 70% from A,iV-diethylaniline,423 96% from phenol,426 98% from o- or 7W-cresol,426 95% from chlorophenol,426 and 75-85% from o-hydroxybenzene-sulfonic acid 428 the diazonium group enters para to the NR2 or OH group. 

CAS 846-70-8 EINECS/ELINCS 212-690-2 Synonyms Acid yellow 1 2,4-Dinitro-1-naphthol-7-sulfonic acid disodium salt Disodium 5,7-dinitro-8-oxidonaphthalene-2-sulfonate 8-Hydroxy-5,7-dinitro-2-naphthalenesulfonic acid disodium salt Classification Nitro color Empirical CioH6N2Na208S Formula C10H6N2O8S 2Na Toxicology TSCA listed Uses Colorant in cosmetics, external pharmaceuticals... 

Red lake P n. Made by coupling diazotized p-nitro aniline-0-sulfonic acid with fi-naphthol. 

Sulfonic acids of naphthols and naphthylamines show a very strong fluorescence the nitro derivatives of these compounds do not fluoresce. 

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