Naphthylaminesulphonic Acid

Congo red Diphenyldiazobis-1-naphthylaminesulphonic acid disodium salt 3.0-5.0 Blue Red —... 

A white powder, or small, lustrous, colorless needles (when crystallized from hot water), which carbonize but do not melt on being heated. Naphthylaminesulphonic acid is soluble in about 4000 parts of cold water, more readily in hot water, scarcely soluble in alcohol, and insoluble in ether. The solution in ammonia water exhibits a violet fluorescence. 

Diazoazonaphthalenesulphonic acid, obtained by combination of y8-naphthylaminesulphonic acid and a-naphthylamine, reacts with naphtholsulphonic acids, producing deep blue dyestuffs. One of these comes into commerce as Blue-black or Azo-black, and dyes wool a shade similar to that with nigrosine [68]. 

The free sulpbonic acid is blue, the salts are scarlet, and give the same shade on cotton. These shades, though fast to soap, are unfortunately turned blue -by weak acids. This property is less marked in the dyestuff known as Benzopurpurine B. It is obtained [69] from tetrazoditolyl (obtained from o-tolidine and nitrous acid) and the /3-naphthylaminesulphonic acid, obtained by Bronner from Schaeffer s S-naphtholsulphonic acid and ammonia. 

As the naphthylaminesulphonic acids are very numerous, only those of technical value will he considered here. 

It is known as naphthalidinesulplionic acid or simply as Laurent s acid. It is usedj but not to any great extentj in the manufacture of azo-colours. The more easily soluble sodium salt obtained above yields a-naphthylaminesulphonic acid S (peri-acid) on reduction. It has the constitution ... 

I. Schollkopf acid.—a-naphthylaminesulphonic acid S suprh) is sulphonated, and the resulting disulphonic acid converted into... 

A peculiar property possessed by -naphtholsulphonic acids which contain hydroxyl- and sulpho-groups in the peri (1 8) position, is that they yield anhydrides by elimination of water, and these anhydrides (called sultones) are frequently obtained in place of the acids, on decomposing the diazo-compounds with boiling water. Thus the naphtholsulphonic acid corresponding to ffl-naphthylaminesulphonic acid S yields naphtho-sultone. 

Naphthylaminesulphonic Acids.—A large number of isomeric sulphonic acids derived from a- and /3-naphthylamine are known and several of them are extensively used in the dye-stuff industry. 

These are reddish blue 1 1 copper-complex monoazo dyes derived from a 2-naphthylamine-or 2-aminonaphtholsulphonate as diazo component and another aminonaphtholsulphonate as coupler. Often such dyes are more easily prepared using a 2-naphthylaminesulphonate and oxidatively coppering the resulting monoazo dye (section 5.5.3). In orthodox structures the imino link of H acid carries the reactive system (7.99), but in other instances the naphthylamine diazo component provides the site of attachment of a haloheterocyclic (7.100) or sulphatoethylsulphone (7.101) grouping. 

The third acidj which has only recently been identified by its conversion into the corresponding /3-naphthylaminesulphonic acidj is identical with the F- or 8-acid. [Green B. B. 1889, p. 731.]... 

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