Diazotization of sulfanilic acid

The indirect method Diazotization of sulfanilic acid 2495 A solution of sodium sulfanilate (23 g) and sodium nitrite (7 g) in water (120 ml) is cooled to 0° and dropped with stirring into an ice-cold solution of concentrated sulfuric acid (17 ml) in water (100 ml). The diazonium salt separates instantaneously. 

A) Diazotization of Sulfanilic Acid.—A mixture of 105 g. (0.5 mole) of sulfanilic acid dihydrate, 26.5 g. (0.25 mole) of anhydrous sodium carbonate, and 500 cc. of water is heated and stirred until all the sulfanilic acid has dissolved, and the solution is then cooled in an ice bath to 15° (sodium sulfanilate begins to crystallize at this temperature). A solution of 37 g. (0.54 mole) of sodium nitrite in 100 cc. of water is added and the resulting solution is poured at once onto a mixture of 106 cc. (1.25 moles) (Note 1) of concentrated hydrochloric acid (sp. gr. 1.18) and 600 g. of ice contained in a 2-1. beaker. The solution, from which />-benzenediazonium sulfonate separates on stirring, is allowed to stand in an ice bath for fifteen to twenty-five minutes, during which time the naphtholate solution is prepared. 

Monoaminoarenesulfonic acids exist in acid solution as zwitterions (2.3 in the case of sulfanilic acid), which are relatively insoluble in contrast to the corresponding bases (such as 2.4). For this reason the indirect method of diazotization is often employed in such cases. The aminoarenesulfonic acid is dissolved as the anion (2.4) by introducing the required amount of sodium carbonate or hydroxide, and nitrite is added to the approximately neutral solution, which is then run into mineral acid. Indirect diazotization is particularly recommended for the aminosulfonic acids of greater molecular mass but, contrary to some statements in the literature, the three anilinesulfonic acids themselves can be diazotized directly in suspension, the reaction proceeding quite smoothly after some practice. 

These diazonium salts are good electrophiles for activated aromatic rings, such as amines and phenols, and this is how azo dyes are prepared. Diazotization of the salt of sulfanilic acid, which we have just made by sulfonation of aniline, gives an inner salt that combines with N,N-dimethylaniline to form the water-soluble dye, methyl orange. 

A solution of sulfanilic acid, equivalent to 17.3 grams (0.1 mole) of 100 per cent material, in 100 cc. water containing 5.5 grams of soda (if the sulfonate is used instead of the free sulfonic acid, the soda is omitted, of course) is treated with 25 cc. concentrated hydrochloric acid and then, with good stirring, with 35 cc. 20 per cent sodium nitrite solution. The diazotization requires about 10 minutes, during which the temperature should not exceed 15°. 

Oval (egg-shape) channels occur along [001] of sulfanilic acid monohydrate 16 that exhibits a layered structure with hydrogen bond connection of the layers (Fig. 2.1.36) and additional rectangular channels along [100] and [010] ( zeolitic interpenetration). Its quantitative gas-solid diazotization has been studied prepara-tively, by AFM, and GID [15, 18, 32, 33]. Also the diazotization of water-free crystalline sulfanilic acid (P21/c) [78] profits from prominent channels along [001] [33], whereas 4-nitroaniline has only a flat channel along [001] and its diazotization profits from its (101) cleavage plane [79]. 

A more selective modification, with concomitant loss of activity, has been achieved using diazotized [ °S]sulfanilic acid (130,194). The free thiol groups were protected by mercuric chloride before the tyrosine modification was performed. It was found that an incorporation of 1.5 radioactive sulfur atoms per subunit inhibited the activity. The labeled peptide was isolated and partially sequenced. By comparison with the dogfish LDH sequence the labeled tyrosine corresponds to residue 220. However, this tyrosine is nowhere near the active center of the subunit. It is most improbable that it can be associated with catalysis. 

Nitrite alternatively may be determined via the diazotization with sulfanilic acid followed by the coupling with N-(l-naphthyl)ethylenediamine dihydrochloride, detection limits being 10 moll . Possible enhancement of the sensitivity could be achieved by adsorptive cathodic stripping of this complex. 

A new spray reagent, dapsone, was described for the detection of baygon, carbaryl, and carbofuran. ITie detection was based on the alkaline hydrolysis of the carbamates forming the corresponding phenols, which can be reacted in the para position with the diazotized aryl amines. The sensitivities of several diazotized anilines, sulfanilic acid, p-toluidine were compared with dapsone. The limits of the detection were about 0.1 pg range (72e) (Table 4). 

If this oxidation is carried out in the presence of sulfanilic acid, the latter is diazotized and there is no redox reaction between the nitrous acid and the hydriodic acid (compare page 366). After removal of the excess iodine with thiosulfate, the diazonium salt may be coupled with a-naphthylamine to give a red azo dye. (See page 364 regarding this sensitive Griess test for nitrites.)... 

Recently, layer-by-layer assemblies of polystyrene-based diazonium salt (DPS) and sulfonated reduced graphene oxide (SRGrO) were deposited on quartz, silicon, and ITO substrates [300]. The DPS was prepared from polystyrene (PS) through nitration, reduction, and diazotization reaction, whereas SRGrO was prereduced with NaBH4, modified with diazonium salt of sulfanilic acid, and reduced by hydrazine. Besides a spontaneous reaction between DPS and SRGrO, the... 

Hydroxylamine, oximes, and hydroxamic acids can be oxidized with iodine quantitatively to nitrous acid. If this oxidation takes place in the presence of sulfanilic acid, the latter is diazotized so that it can be detected, after the excess of iodine had been eliminated with thiosulfate, by coupling it with 1-naphthylamine. 

Other disazo dyes of this kind are Acid Red 115 (Cloth Red B), which is made by coupling diazotized aminoazotoluene with R acid, and Acid Black 18. Acid Black 18 will be recognized as having been made by the combination, through diazotization and coupling, of sulfanilic acid, a/p/ia-naphthyl-amine, and H acid. 

Most of the thiazoles studied absorb in the ultraviolet above 254 nm, and the best detection for these compounds is an ultraviolet lamp (with plates containing a fluorescent indicator). Other indicator systems also exist, among which 5% phosphomolybdic acid in ethanol, diazotized sulfanilic acid or Pauly s reagent (Dragendorff s reagent for arylthiazoles), sulfuric anisaldehyde, and vanillin sulfuric acid followed by Dragendorff s reagent develop alkylthiazoles. Iodine vapor is also a useful wide-spectrum indicator. 

Alkaline Coupling Process. Orange II [633-96-5] (21) (Cl Acid Orange 7 Cl 15510) a monoazo dye discovered ia 1876, serves as an example of the production of an azo dye by alkaline coupling. A suspension of diazotized sulfanilic acid (0.1 mol) is added to a solution (cooled to about 3°C) of 14.4 g 2-naphthol dissolved ia 15 g 30% sodium hydroxide, 25 g sodium carbonate, and 200 mL of water. The temperature should not be allowed to rise above 5°C. The reaction is heated until solution occurs and the dye is precipitated with 100 g sodium chloride. The mixture is cooled and filtered, and the product is dried. 

Of these dyes, Acid Yellow 151 (37) still has the greatest market among the yellows. As reported by USITC, production had increased to 1989 tons in 1985 from 706 tons in 1975. It is produced by coupling diazotized 2-amino-l-phenol-4-sulfonamide to acetoacetanilide followed by metallizing with cobalt to obtain a 1 2 cobalt complex. Acid Orange 24 (38), which is sulfanilic acid coupled to resorcinol to which diazotized mixed xyUdines have been coupled, is an unsymmetrical primary diasazo dye with a bihinctional coupling component. 

It has long been known that pyrroles can be used as coupling components (see, for example, Schofield, 1967, p. 76). More recently Butler and coworkers have studied the reactions of arenediazonium ions with pyrroles (Butler et al., 1977 Butler and Shepherd, 1978, 1980). 1-Methyl- and 2,5-dimethylpyrrole react with diazotized sulfanilic acid to give 12.34 and 12.35 respectively. The formation of 12.34 is in accordance with the a-positions in pyrrole being more susceptible to elec-... 

Phenols (capable of coupling) Fast blue salt B, fast blue salt BB, fast black salt K, diazotized sulfanilic acid (Pauly s reagent) diazotized sulfanilamide or 4-nitroaniline Intensely colored azo dyes are formed. Catecholamines [20, 3S], imidazoles [21] and amines capable of coupling also react. [3, 17]... 

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