The most important reactions used for the manufacture of 0-naphthylaminesulphonic acids are (a) sulphonation of naph thylamine, (b) amination of naphtholsulphonic acids in presence of ammonium bisulphite, and (c) reduction of 0-nitronaphthalene sulphonic acids. As sources of azo-dyes these acids are not so important as the a-amino-compounds; many of the dyestuffs de rived from them are of little worth and, moreover, once they have coupled (in the a-position) with other diazotized amines, the contiguous j3-amino-group cannot be itself diazotized. f3-Naph thylamine-6-sulphonic acid (Bronner acid ) and f3-naphthylamine 3 :6-disulphonic acid are among the more important. One valuable property, however, which the j3-naphthylamine-di- and tri-sul phonic acids possess is that of exchanging an a-sulphonic group for a hydroxyl group when digested with caustic soda, thus pro ducing the valuable aminonaphtholsulphonic acids; -a-naphthyl amine-di- (though not tri-) sulphonic acids under the same con ditions exchange the amino-group for a hydroxyl group giving merely naphtholdisulphonic acids. The naphthylaminesulphonic acids of both the a- and 0- series may be estimated by titration with diazotized para-nitraniline.
An important feature of sulphonic groups, not only in the naph thylamine and naphthol series, but also in naphthalenesulphonic acids, is the frequency with which they "migrate" from one posi tion to another during the sulphonation process. This apparent shifting is due largely to hydrolysis of the sulphonic group, fol lowed by resulphonation in another position under the altered con ditions. For example, sulphonation of f3-naphthol at the ordinary temperature gives the 1-, at 6o° C the 8-, and at Ice C the 6 sulpho-derivative.
The ten possible diaminonaphthalenes have all been prepared, most of them by heating the corresponding aminonaphthol or dihydroxynaphthalene with ammonia under pressure, but reduc tion of nitronaphthylamines, of dinitronaphthalenes, or of azo dyes furnishes others which would otherwise be difficult of access.
They have found little application in the colour industry. :8- Naphthylenediamine, melting point 67° C, is of interest because, like the true ortho-diamines (1 :2- and 2 :3-), it readily forms another ring by condensation with such sub stances as acetone, acetic anhydride, phosgene, ethyl oxalate and nitrous acid. The diaminonaphthalenesulphonic acids are unim portant.
any appreciable extent. The naphthols are said to occur in very small amount in high-boiling coal-tar fractions. Many tests have been devised for detecting and estimating traces of a- and /3 naphthols in each other. Moreover, certain colour reactions are available : (I) ferric chloride, with which the a- isomeride gives an opalescence changing to a violet precipitate of ace-dinaphthol, whereas the /3- gives a pale green colour changing to a white precipitate of 00'-dinaphthol; (2) bleaching powder solution, a- giving a violet colour, and /3- a pale yellow; (3) sodium hypoiodite (a- gives a purple colour, and 0- nil), and (4) titanyl sulphate (a- gives an intense green colour changing to reddish violet on addition of acetic acid, and (3- nil). Both a- and 0 naphthols develop Prussian blue colorations with chloroform and caustic potash solution.
a-Naphthol, is usually manufactured by adding so dium naphthalene-a-sulphonate to fused caustic soda in an open vessel at about 300° C, or by heating it with strong caustic soda solution in an autoclave at about 280° C for hours, whereby the formation of oxidation products attendant upon open pot fusions is avoided. If required quite free from 0-naphthol (which is always present in a-naphthol prepared by fusion processes), it may be obtained by heating a-naphthylamine sulphate or hydro chloride with water at 200° C under pressure for four hours. An other method consists in heating under pressure a-chloronaphtha lene, caustic soda and methyl alcohol at C for several hours. a-Naphthol crystallizes in white, lustrous prisms, melting point C, boiling point 278-280° C. It is readily soluble in most organic solvents and in caustic alkali solutions, but only sparingly in hot water. Unlike 0-naphthol, it is volatile in steam at ioo° C, and possesses a phenolic odour. a-Naphthol is more poisonous than 0-haphthol, and finds no medicinal application. Nitrous acid converts it into a mixture of 2- and 4-nitroso-a-naphthol, the former preponderating. One chlorine atom can be introduced by using sulphuryl chloride to give 4-chloro-a-naphthol, but chlori nation with chlorine leads to the formation of the 2 :4-dichloro derivative. Nitration gives, in the same way, not a mononitro compound, but 2 :4-dinitro-a-naphthol. The sodium salt of this substance, known variously in commerce as Martius yellow, Man chester yellow, or naphthalene yellow, was formerly used as a golden-yellow dye for silk and wool. It is easily removed from the fibre, however, and has been superseded. A closely related dyestuff of greater importance is naphthol yellow S (2 :4-dinitro a-naphthol-7-sulphonic acid).