ON OUR PRESENT KNOWLEDGE OF AROMATIC DIAZO-COMPOUNDS. 189 



X NH2 



/ ^NjCftH,, + NaCl + CH3CO2H, 



takes place with considerable difficulty, and the yield of azo-compound is 

 small ; moreover the complete alkylation of the amino-radicles altogether 

 prevents this condensation. ' 



In the case of the naphthylamines and their sulphonic acids, the 

 formation of ortho- and para-aminoazo-compounds takes place with equal 

 readiness ; /3-naphthylamine, 



3 NH2 



< > 



6 7 



however, only yields azo-derivatives when the positions 1 and 8 are 

 unoccupied. The presence of substituent radicles in either of these posi- 

 tions leads to the formation of diazoamines,^ and there appears to be no 

 tendency for the diazo-group to migrate into position 3. 



2. Hijdroxi/azo-compounds.— The formation of benzeneazophenol by the 

 action of benzenediazonium chloride on an alkaline solution of phenol is 

 a typical example of the method of preparing this important class of 

 substances. Goldschmidt (loc. cit.) found that the essential reagents in 

 this reaction are the diazo-hydroxide and the phenol set free by the 

 hydrolysis of its alkali-derivative. Excess of alkali hinders the condensa- 

 tion, the velocity of which diminishes as the concentration of the phenol 

 or diazo-compound increases. 



Although at first sight the mode of formation of hydroxyazo-compounds 

 seems to leave little room for doubt as to the constitution of the products, 

 yet this point has, for many years, been the subject of considerable contro- 

 versy. This discussion arose from the fact that certain of these hydroxyazo- 

 compounds can also be prepared by condensing the aromatic hydrazines with 

 quinones ; 4-benzene-azo-ii-naphthol, for example, can be obtained either 

 from benzenediazonium chloride and a-naphthol, or from phenylhydrazine 

 and a-naphthoquinone. Similarly the corresponding 2-benzene-azo a- 

 naphthol is produced either as a by-product in the former of these reactions, 

 or by the action of phenylhydrazine on ^-naphthoquinone, and the alternative 

 methods of formation may be represented in the following manner : — 



(i) Azo-condensation, 

 CH^NaiOH + H:C,oH60H = H20-fCeH5.N2.C,oH60H. 



(ii) Hydrazone condensation, 



CCH5NHNH2 + O \ CioHfiO = H20-i-C6H5NHN iCioHgO. 



Since the two reactions give rise to identically the same substance, it 



' Trans., 1902, 81, f.50. 



» Witt, Ber., 1888, 21, 3483 ; Morgan Trans., 1902, 81, 91. 



