24 октября, 2015 
Pokraskin The filter cake of sodium 2-naphthol-l-sulfonate, obtained under
(a) , is placed in an enameled autoclave of about 1-liter capacity with 250 cc. 20 per cent ammonia and an ammonium bisulfite solution prepared by saturating 60 cc. 20 per cent ammonia with S02 with cooling. The mixture is heated in the autoclave for 8 hours at 145-150°C. (internal temperature). In large scale preparations, the ammonia is then distilled off and reused in the next run. It is more convenient in laboratory preparations to saturate the solution with salt, whereupon the sodium salt of 2-naphthylamine-l-sulfonic acid is precipitated almost completely. The mixture is allowed to stand overnight, and then the sulfonate is filtered off and washed well with saturated salt solution to remove ammonia and ammonium salts. The resulting filter cake is dissolved in hot water and the solution is filtered and treated with sufficient concentrated hydrochloric acid to make it distinctly acid to Congo red. After cooling the solution thoroughly, the precipitate, consisting of the free 2-naphthylamine-l-sulfonic acid in the form of needles, is filtered off, washed with cold water, and dried. The yield is 98 grams, or 83 per cent of the theoretical amount based on /3-naphthol.
As mentioned earlier (page 192), 2-naphthol-l-sulfonic is the first product formed by the reaction of concentrated sulfuric acid on /З-naphthol. It is rearranged so rapidly by the unavoidable excess of sulfuric acid, however, that it cannot be prepared by direct sulfonation with sulfuric acid.
The procedure described above involves sulfonation in the absence of free sulfuric acid at low temperatures, land avoids the use of an appreciable excess of the sulfonating agent. Similar procedures are generally applicable to the preparation of sulfonic acids which cannot be prepared satisfactorily by the ordinary sul — fonation methods, because they are easily isomerized or sulfonated further by concentrated sulfuric acid. Even compounds which are ordinarily converted directly into disulfonic acids, such as carbazole, 4,4’-dihydroxydiphenylmethane, etc., can be monosulfonated in this way.
2- Naphthol-l-sulfonic acid does not couple with diazo compounds under ordinary conditions, because the single reactive position in the 0-naphthol nucleus is occupied. However, at higher temperatures ana in acid media, the sulfo group is replaced by the azo radical and the dye that is formed is the same as that from /З-naphthol. This property is made use of in developing paranitraniline red on the fiber.[41]
The chief use of 2naphthol — 1-sulfonic acid is as an intermediate in the preparation of 2-naphthylamirie-l-sulfonic aeid. The latter, when diazotized and coupled with /З-naphthol, yields the valuable lake dye, lithol red R, which is used in large quantities.
The conversion of 2-naphthol-1-sulfonic acid’into the corresponding naphthyl- aminesulfonic acid is another example of the Bucherer reaction which was discussed in connection with the preparation of l-naphthol-4-sulfonic acid (page 182).
1- Am ino-2-па phthol -4-sulfonic Acid from /3-Naphthol
Preparation of an Aminonaphthol*ulfonic Aeid from the Hydroxy-
nitroso Compound (Quinonemonoxime)
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