ISOMERIC CHANGE 219 



A typical and very important case amongst aromatic com- 

 pounds is the transference of a halogen atom from the side 

 chain into the ring in the conversion of phenylchloroacetamide, 

 C 6 H 3 .NCl.CO.CH 3 , into />-chloroacetanilide, C1.C 6 H 4 .NH. 

 CO.CH3. In presence of alkalis the former compound is 

 stable, but it undergoes change very readily in presence of 

 hydrochloric (but not of any other *) acid. This isomeric 

 change takes place very readily and smoothly, and may be 

 regarded as a process of self-chlorination, effected through the 

 electrolysis of a hydrochloric acid circuit joining the >NC1 to 

 the — C 6 H 5 group. The discharge of two atoms of electrolytic 

 hydrogen at the )>NC1 group would suffice to reduce it to )NH, 

 whilst the two atoms of electrolytic chlorine set free simul- 

 taneously at the — C fi H 5 group would convert it into — C 6 H 4 .C1. 



It is, however, of interest to note that the original chlorina- 

 tion of the amino group of the acetanilides R . NH . CO . CH S 

 + C1 2 $HC1 + R.NCI.CO.CH3 has been shown by Orton 

 and Jones 2 to be a reversible process in which the extent of 

 the interaction may be ascertained accurately by passing a 

 current of air through the liquid and determining the amount 

 of chlorine carried forward by a known volume of air. As 

 this action is reversible it is evident that the addition of 

 hydrogen chloride as a catalyst to the chloro-amine would be 

 followed immediately by the liberation of chlorine, so that if 

 the original anilide were capable of being chlorinated in the 

 benzene ring a secondary chlorination might ensue as repre- 

 sented by the equation 



C 6 H 5 . NH . CO . CH 3 + Cl a -> CI . CgH^ . NH . CO . CH 3 + HC1 



1 " Hydrochloric acid is the only catalyst. Hydrofluoric, sulphuric acids, etc., 

 have no effect ; hydrochloric acid can always be detected when a change begins 

 in the presence of these acids. Chlorine and bromine are without effect untiL 

 hydrochloric acid is formed." — Orton, Brit. Assoc. Report, Winnipeg, 1909. 

 2 Proc. Chem. Soc. 1909, 25, 196. 



