ISOMERIC CHANGE 233 



after the liquid had changed to only about one-half of the usual 

 extent. It was therefore evident that the chloroform either 

 contained or produced some substance which was capable of 

 destroying the catalytic action of a basic impurity. 



The acid chloroform solutions were also anomalous in that 

 the acids, which at higher concentrations produced an accelera- 

 tion, were found at a lower concentration to produce an actual 

 arrest of isomeric change, the rotatory power in one instance 

 (a millinormal solution of trichloracetic acid) remaining abso- 

 lutely constant during twenty-four days. These solutions were 

 evidently not pure, as they soon acquired a pungent and 

 unpleasant odour, which proved to be due to carbonyl chloride 

 formed by oxidation from the chloroform 



CHCl, + O = COCl, + HCl 



In view of the marked catalytic action of neutral salts, and 

 the entirely different behaviour of acid solutions in chloroform 

 and in benzene, it was evident that the arrest of isomeric 

 change in the chloroform solutions could not be due merely 

 to neutralisation of basic impurities by an acid. But carbonyl 

 chloride, which is usually present in the chloroform and 

 possesses the property of converting amines into ureas, e.g. 



COCl, + 2NH 3 = CO(NH), + 2HCI 

 COCl, + 2NQH„ = CO(NC 5 H, ) + 2HCI, 



would be able to transform these bases into compounds from 

 which the nitrocamphor would be unable to recover them, so 

 that their catalytic action would be permanently destroyed. 

 Direct experiments soon proved that this was the case, as by 

 the addition of either carbonyl chloride or acetyl chloride, the 

 isomeric change of nitrocamphor could be checked, and to all 

 intents and purposes arrested altogether, not only in chloro- 

 form but in benzene, in carbon disulphide and in ether. No 

 retardation could be produced, however, by acetyl chloride 

 in presence of acetic acid and acetic anhydride. Phenyl 

 isocyanate, which, like carbonyl chloride, possesses the property 

 of converting organic bases into ureas, was found to be of no 

 value in retarding the change in benzene, probably because 

 it was itself eliminated as a urethane by interacting with the 

 hydroxylic form of the nitrocamphor. Finally, as carbonyl 

 chloride has no special action on mineral bases, it was found 

 that an efficient arrest of the change could only be brought 



