190 REPORT— 1902. 



follows that intramolecular rearrangement must have occurred during one 

 or other or both of these condensations. This problem, which was for 

 some years attacked by purely chemical methods/ has more recently been 

 approached from the physico-chemical side, but even now the question can 

 scarcely be said to be definitely settled. The cryoscopic determinations 

 made by Auwers and his pupils - indicate that only the ortho-hydroxy- 

 azo-compounds are quinone-hydrazones, the para-derivatives being phe- 

 nolic. Chemical evidence in support of the azo-formula for the para- 

 hydroxy-compounds is furnished by Hewitt,^ whilst Noelting's results 

 show that these substances may also react as hydrazones.'' 



The question has again been revived by Hantzsch, who places the 

 hydroxyazo-compouuds within the category of pseudo-acids. These are 

 acidic substances which have a configuration differing from that of their 

 salts, tautomeric change taking place during the formation of the metallic 

 derivatives ; 



CgHsNHN : C.K^ : 

 (-fNaOH) / \ (-H2O) 



"^ .ONa \ 



C,H5NH.N:CoH, -> CgH^NH.N : CcH,(OH)., 



^ ^OTT abnormal hydrate. 



(_ H^O) % 



C,;H5.N : N.C,;H,ONa. 



The substance CgHr.NNH : C,;H4 : O is a non-electrolyte, and hence its 

 salt, when disisolved, should exhibit hydrolytic dissociation ; this however 

 is not the case, the metallic derivative behaving as the salt of a negatively 

 substituted phenol. The hydrates of the azo-phenols, isolated by Hewitt,'' 

 contain only half a molecule of water, but the compound C1.C(3H4NH.N: 

 C5H3CH3(OH).2 has been ol)tained '' which corresponds with the 

 abnormal hydrate required by Hantzsch's hypothesis. 



The manufacture of hydroxyazo- and aminoazo-compounds has acquired 

 considerable importance, owing to the fact that the products of the action 

 of diazotised benzidine, tolidine, and o-dianisidine on the sulphonic acids 

 of the naphthalenoid amines and phenols have the valuable property of 

 dyeing unmordanted cotton ; a quality which is also shared by the azo- 

 derivatives of primulin and dehydrothio-^j-tolidine, two amines containing 

 sulphur, which were discovered by Green.' 



The sodium salt of sulphonated primulin can itself be dyed on cotton, 

 and after being diazotised on the fibre and treated with a solution of 

 a suitable phenol or amine, it gives rise to an insoluble azo-compound 

 which, on account of the method of formation, is called an ' ingrain ' 

 colouring matter. 



These insoluble azo-compounds may also be produced by first im- 

 pregnating a textile fabric with a phenol, and then treating the material 

 with the solution of a diazonium salt. It was in the course of an investi- 



' Liebermann, Ber.. 18S3, 16, 2858 ; Zincke, Her., 1884, 17, 3026 ; 3 887, 20, 3171 ; 

 Meldola, Trans., 1889, 55, 114, 603. 



- Zeit.fiir Phys. CJiem., 21, 355, and £er., 1900, 33, 1302. 

 3 Trans., 1900. 77, 99, 712, 810. ^ Bcr., 1887, 20. 2997. 



'' Ber., 1895, 28, 799; 1898, 31, 2118. " Ber., 1899, 32, 3089. 



' Tra7is., 1889, 55, 227. 



