662 TRANSACtlON^ OP sfeCtlON B. 



G. The Action of Halogens upojt Aromatic Hydrazines. 

 Bij F. D. Chattaway, D.Sc, F.R.S. 



The actions which take place when the halogens are brought into contact with 

 primary aromatic hydrazines are so violent, unless special precautious are taken, and 

 such large amounts of tarry matters are formed, that they have been investigated 

 comparatively little, and in consequence the formation of the many ditfei'ent 

 substances which are produced when the conditions of interaction are altered 

 has never been accounted for satisfactorily. 



Tbe complicated changes which occur all depend, however, upon a progressive 

 substitution of hydrogen attached to the nitrogen, followed by a breaking down 

 or iutra-molecular rearrangement of the N-substituted hydrazuies thereby pro- 

 duced. 



AVhen a halogen acts upon an aromatic hydrazine one of the hydrogen atoms 

 of tlie — NH — NH.j group, probably one in the — NHo group is replaced,' a nitrogen 

 halogen derivative being produced which at once undergoes what is in fact the 

 typical diazo decomposition — for example : — 



C,H,-N-H C,H,-N-H C„H, N H 



I -* I -^ I + III + I 



H-N-H H-N-Br H N Br 



Hydroxyl ions mucii accelerate the rate at which this decomposition occurs, 

 vvhiJe hydrogen ions correspondingly diminish it. 



When halogens therefore act upon aromatic hydrazines in presence of alkalis, 

 hydrocarbons, the hydrides of tbe aromatic groups present in the hydrazines, are 

 almost exclusively produced. When, however, an excess of halogen is employed 

 a relatively small amount of the N-mono-substituted hydrazine undergoes further 

 substitution before disruption can take place and a dihalogen N-substitution pro- 

 duct is formed, which, like the mono-substitution product, is unstable in presence 

 of alkali and breaks down similarly, a mono-substituted halogen derivative of 

 the hydrocarbon formed in the first action being produced — for example :— 



The N-mono-substituted hydrazines being far more stable in presence of acids, 

 when these are present this replacement of a second halogen atom takes place to 

 11 much greater extent, and the whole of the hydrazine may thus be converted into 

 tbe N-disubstituted derivative, which then may, according to conditions, undergo 

 the diazo decomposition or yield a diazonium salt, thus : — 



HBr. 



The diazonium salt may, if suitable means are adopted, be isolated,' but, as the 

 interaction of h ilogen and hydrazine is usually very vigorous and accompanied by 

 considerable evolution of heat, it is generally decomposed, giving rise to tarry 

 matters. 



In presence of a considerable excess of hydrochloric or other strong acid the 

 NH^ group is to a large extent |)rotected ^ against the action of the halogen 

 and substltutiou takes place most readily in the — NH— group. The nitrogen 

 halogen compound thus produced is of the type of the acyl amino compounds, and 



' This, as iu other similar cases, is without doubt effected by the addition of two 

 atoms of the halogen, followed by the elimination of a molecule of halogen hydride. 



- Ohattaway, Trans. Ckem. Soc, 1908, 98, 852. 



' This is probably due to the addition of halogen necessary for substitution to 

 take place being prevented by the combination of the NH^ group with the acid. 



