ISOMERIC CHANGE 223 



hydrogen chloride, but when kept in a dry atmosphere slowly 

 changes into the nitroaniline. The formation of this additive 

 compound is evidently an essential stage in the process — a view 

 that receives strong support from the fact that isomeric change 

 is not brought about by hydrogen chloride at pressures below 

 ^ atmosphere nor by aqueous hydrogen chloride at concen- 

 trations below N/200. It will be noticed that the additive 



uri 



compound contains the group — N t_jktq ; it is therefore not 



improbable that it may be partially resolved into the chloro- 

 amine and nitrous acid, and that — whatever the nature of the 

 added catalyst may be — the isomeric change really depends on 

 the presence of a trace of nitrous acid. The fact that nitrous 

 acid is always formed during the transformation has recently 

 been demonstrated by Orton 1 and affords important confir- 

 mation of the view that this acid is the only directly-efficient 

 agent in bringing about the transference of a nitro group. The 

 actual transference could be effected by electrolysing the acid in 

 such a way as to discharge two atoms of electrolytic hydrogen 

 at the — NH.N0 2 group, thus reducing it to — NH 2 + HN0 2 , 

 at the same time delivering two equivalents of — N0 2 at the 

 adjacent ^CH group and so converting it into )>C.N0 2 + HN0 2 . 

 In the case of dibromo-o-nitrophenol and the related com- 

 pounds the formation of an additive product is probably again 

 the first stage in the action. From such a compound a trace of 

 nitrous acid might easily be split off, and if this were electrolysed 

 in such a way as to discharge its H — and — N0 2 groups at the 

 " 2 " and at the "4" positions in the benzene ring an isomeric 

 compound would result from which dibromo-/>-nitrophenol could 

 be produced by merely removing a molecule of bromine — 



HO Br HO Br 



OH V V OH 



Br/\NO, Br r ^v^/Br Br ^^\ Br Br/\Br 



+ Br., ^NO, -Br.. 



<J ■* "O v? kJ -* 



Br Brt : (<\ \ /\ 



•-•'--.^ Br NO., 



Dibromo-o-nitrophenol Bromine additive compounds Dibromo-/>-nitrophenol 



The ease and smoothness with which this and many other 



1 British Assoc. Report, Winnipeg, 1909. 



