TRANSFORMATION OF AROMATIC NITROAMINES, ETC. 99 



various ways in which the facts may be accounted for. He points 

 out that the migrating group is always present in the system, whenever 

 isomeric change is taking place. 



II. — Bromination of Anilides and the Conversion of Bromoamincs. 

 (With W. J. Jones, B.Sc.) 



The interaction between bromoamines and hydrobromic acid only 

 differs in degree from that between chloroamines and. hydrochloric 

 acid. Tintomeiric measurements have shown that in acetic acid of 

 all dilutions the reaction is quantitatively 



Ar.NBrAc + IIBr = Ar.NHAc + Br 2 . 



The direct bromination of the anilide is therefore always identical 

 with the conversion of a bromoamine under the influence of hydro- 

 bromic acid. 



The bromination which results when a chloroamine is treated with 

 hydrogen bromide (or a bromoamine with hydrogen chloride) is a far 

 more rapid process. In both these cases bromine chloride is formed 

 and is the brominating agent. 



Bromination, ^however, differs in one respect very markedly from 

 chlorination in that hydrobromic acid and bromide exert a powerful 

 retarding influence. Thus in the presence of four molecular pro- 

 portions of hydrobromic acid, bromine does not act on acetanilide in 

 glacial acetic acid at 16°. Hydrochloric acid, even when present at 

 8 to 10 times the concentration of the chlorine, has a scarcely percep- 

 tible effect. 



The bromide exerts its maximum effect in glacial acetic acid. 

 Addition of water reduces the effect, and as Fries x has shown, dilute 

 acetic acid is the best medium for bromination of anilides. Thus in 

 one of our experiments, in 75 per cent, acetic acid, using the molecular 

 ratio, 8HBr:Br 2 :C G H..NHAc, three-quarters of the acetanilide was 

 brominated in twenty minutes. p-Chloroacetanilide in glacial acetic 

 acid is brominated too slowly for easy measurement; in 50 per cent. 

 acetic acid, ft u = 0"36, and in water = 12. 



The cause of this influence lies in the union of the bromine with 

 bromidion forming Br' 3 . We have shown by the method of aspiration 

 that in glacial acetic acid, when bromine and hydrobromic acid are 

 in molecular proportions, 75 per cent, of the bromine is combined witli 

 bromidion, but as the acetic acid is diluted the percentage of free 

 bromine rapidly increases. In water we obtained by our method for 

 the equilibrium, K= [Br,] [Br'J / [Br' 3 ] , values similar to those found 

 by Jakowkm 2 (by measurement of the distribution ratio between water 

 and carbon tetrachloride); our value for K 15 ° is 62, and Jakowkin's 

 K"° = 0-63. 



. l Antiakn, 1900, 346, 128. . 2 Zrit. Plvjs. CJum., 1SP0, 20, 38. 



