202 PROCEEDINGS OF THE AMERICAN ACADEMY 



XV. 



CONTRIBUTIONS FROM THE CHEMICAL LABORATORY OF HAR- 

 VARD COLLEGE. 



RESEARCHES ON THE SUBSTITUTED BENZYL COM- 

 POUNDS. 



By C. Loking Jacksox. 



THIRD PAPER. 



ON PARAIODBENZYL COMPOUNDS. 



C. F. Mabery. 



Presented May 9, 1877. 



The preparation of paraiodbenzylbromide, C^H^ICHMr, has been 

 described in the first article of this series ; * but the method there 

 given did not invariably yield good results, the [)roduct often being 

 mixed with a black tar which it was very hard to remove com[)lctely by 

 crystallization. A more careful study of the conditions of the reac- 

 tion has shown that this was due to an oily impurity of the iodtoluol, 

 a very small amount of which was sufficient to destroy a great part 

 or even the whole of the paraiodbenzylbromide : if the paraiodtoluol 

 purified by distillation was carefully pressed between filter-paper, this 

 oil was absorbed, and then the product of the bromiriug was nearly 

 white after the first crystallization. When the purified paraiodtoluol 

 was used, the yield was very nearly the same, averaging 4.7 grs. of 

 pure bromide from 10 grs. of iodtoluol, when the bromiriug took 

 place at 115'=', 130°, or 150^ (one-half of the thermometer-bulb dipping 

 in the liquid), while at temperatures below 115° the bromiring was 

 slow, and the amount of paraiodbenzylbromide formed small. These 

 observations are important, because they tend to fix, in the case of 

 paraiodtoluol, the limit at which bromine ceases to enter the main 

 ring in any great amount, and thus one step is taken toward giving a 



* These Proceedings, Vol. XII. (n. s. IV.) p. 219. 



