Naphtholsulphonic Acids

This displacement is accomplished by heating the sulphonated derivative at a high temperature with sodium or potassium hydroxide [64]. Typical is the preparation of 2-naphthol (4.15) from naphthalene-2-sulphonic acid (Scheme 4.21). Displacement of the sulphonic acid group occurs more readily when it is located at the a- rather then at the P-position, the former requiring a fusion temperature of about 200 °C and the latter one of about 250 °C. This difference in reactivity can be exploited to prepare naphtholsulphonic acids by fusion of suitable naphthalenedisulphonic acids. 

The preparation of 2-naphthol by high-temperature sulphonation of naphthalene followed by alkali fusion of the resulting naphthalene-2-sulphonic acid has been mentioned previously. Further sulphonation of 2-naphthol yields several useful naphtholsulphonic acids and conditions can be chosen to make one or other of these compounds the main product. The initial product is the unstable 2-naphthol-l-sulphonic acid, which readily rearranges to 2-naphthol-6-sulphonic acid (4-36 Schaeffer s acid). Further sulphonation leads to 2-naphthol-6,8-disulphonic acid (4-37 G acid) at low temperature and 2-naphthol-3,6-disulphonic acid (4.38 R acid) at higher temperature. 

The case is different when these positions are already occupied by other groups, for example, by the sulpha-group. With a-naph-tholthe azo-chain enters into the adjacent/3-position for instance, with a-naphtholsulphonic acid azo-compounds of the general formula... 

The Schoellkopf Aniline Co. have patented an acid obtained by nitration of a-naphthalenemonosulphonic acid, reduction to amido-acid, and conversion into naphtholsulphonic acid by the diazo-reaction. It is so far characteristic as it gives a scarlet with diazotoluene, while its isomers give oranges. [D.P. 15871.]... 

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 yet the 8-naphtholsulphonic acid corresponding to y3-naph-thylamine-7-sulphonic acid has not been isolated from the acids formed in sulphonating /3-naphthol. The constitutions of the acids, according to the most recent researches, may be graphically demonstrated by the following formulm —... 

Diamond Yellow G.. Diamond Yellow R.. Cloth Brown R. Cloth Brown G. Cloth Orange il-amidobenzoic acid. 0-amidobenzoic acid. Benzidine.. . 1 1 Salicylic acid. Salicylic acid. 1 mol. salicylic acid, 1 mol. a-naphtholsulphonic acid. 1 mol. salicylic acid, 1 mol. /3 3-dioxynaphthalene. 1 mol. salicylic acid, 1 mol. resorcin. 

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. 

Benzo-grey.—Tetrazodiphenyl is combined with equal molecules of salicylic acid and a-naphthylamine, the product diazotised and combined with a-naphtholsulphonic acid (Nevile and Winther). 

Wool Greys.—These dyestuffs are obtained by action of aniline and analogous bases on the condensation-products of nitroso-dimethyl- and diethyl-aniline on Schaeffer s jS-naphtholsulphonic acid. 

Otto Nikolaus Witt (St. Petersburg, 31 March i853 Charlottenburg, 22/23 March 1915), at first educated in Russia, studied (1871) in Zurich Polytechnic under J. Wislicenus and E. Kopp. In 1875 became chemist to the dye firm of Williams, Thomas, and Dower in Brentford, near London, where he discovered the azo-dyes chrysoidine and tropaeoline. In 1882 he became chemist to the Verein Chemischer Fabriken in Mannheim, where he introduced 1 4-naphtholsulphonic acid as an azo-dye intermediate. In 1885 he... 

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