ON OUR PRESENT KNOWLEDGE OF AROMATIC DIAZO-COMPOUNDS. 195 



The corresponding diazo-oxides would be thus represented : — 



R.N E.N 



»S^2/wdiazo-oxide || Antidia.zo-OKide \\ 



KON NOK. 



(normal series) (iso series) 



The assumption involved in both cases is the same — namely, that the' 

 third affinity of doubly linked trivalent nitrogen may be exerted in one 

 or other of two definite directions. If this be granted, then there can be 

 little doubt that the labile normal diazo-oxides possess the /S^/ra-configura- 

 tion, for in this series the coalescence of the contiguous associated radicles 

 readily occurs with the elimination of nitrogen. The stable ■isodiazo- 

 derivatives should by exclusion have the Anti-structure.^ 



There is one point, however, in which the analogy between oximes and 

 diazo-oxides breaks down ; the stereo-isomeric oximes give rise to isomeric 

 oxygen-ethers, whereas both the isomeric diazo-oxides yield the same 

 C-ether. These 0-ethers are explosive and combine with bases and 

 phenols in the presence of alkali hydroxides or carbonates yielding azo- 

 compounds. They are accordingly placed by Bamberger in the Syn or 

 normal series. ^ Hantzsch, on the contrary, points out that in their 

 capacity for forming azo-derivatives they do not diffisr markedly from the 

 iso- or an<i-diazo-derivatives. The exact relationship of these ethers to 

 the metallic diazo-oxides can scarcely be considered as finally settled. 



The iso- or «w<i-diazo-oxides undoubtedly exhibit the phenomenon of 

 tautomerism, and, under certain conditions, react in accordance with the 

 formula R.NH.NO, the formation of iV- ethers, B,N(alk).NO (secondary 

 aromatic nitrosamines), being a case in point. 



Structural Forniuke for the Isomeric Diazo-oxides. — The hypothesis 

 that the isomeric diazo-oxides are structurally different has been defended 

 by Bamberger ^ and Blomstrand,'* who maintain that the normal diazo- 

 oxide is a diazonium derivative, having the same configuration as the 

 original diazonium salts. There is no longer any difference of opinion 

 with respect to the oxime formula of the isodiazo-oxides, and accord- 

 ingly the second hypothesis may be thus graphically illustrated 



KN.Cl R.N.OK R.N : NOK 



-> • -> 



N N 



diazonium chloride. normal diazo-oxide. iso-diazo-oxide. 



One grave objection to the theory is at once detected from this diagram 

 which indicates that the diazonium hydroxide 



R.N.OH 



N 



is capable of acting not only as an acid, but also aa a strong base, The 

 difficulties attending this assumption will be considered at greater length 

 in the sequel. 



Existence of Syn-diazo-Sidphonates, Cyanides, <&c. — Hantzsch, who 

 obtained a very unstable red potassium benzenediazo-sulphonate isomeric 



» Hantzsch, Ber., 1894, 27, 1702; 1895, 28, 676, 1734. 



= Ber., 1895, 28, 225. » Ber., 1895, 28, 444, 826, 1218. 



« Jov/rn. pralit. Chem., 1896, 63, 169; 1897, 64, 305 ; 1897, 65, 480. 



02 



