RESEARCHES UPON THE CHEMICAL PROPERTIES OP GASES. 213 



IV. PEEPARATION OF HALOGEN COMPOUNDS OF ALKYLS AND OLBFINES. 



The alkyl iodides serve as the most convenient source for the preparation of the 

 paraflSns by the Gladstone and Tribe reaction, to which reference has ah-eady been 

 frequently made, e. g.: 



The same compounds find application in forming the defines by the action of KOH 

 in alcoholic solution. Thus : 



CaHjI + KOH = CgHe + KI + H^O. 



The olefine dibromides are of service in the preparation of defines by means of 

 zinc which abstracts the halogen, liberating the olefine. The acetylenes are most 

 conveniently produced from the olefine dibromides, by the action of alcoholic potash, 

 according to the reaction : 



CjH.Br^ + 2 KOH = C^Hi + 2 KBr + H^O. 



Hence, the selection of convenient methods in forming these iodine and bromine 

 compounds has become a matter of much importance in the study of gas reactions. 



The alkyl iodides are most easily formed by the action of iodine upon a mixture 

 of red phosphorus and alcohol. 



Chancel {Ber., 1883, p. 2286 K, and Bull Soc. Ckim., XXXIX, p. 648) has given 

 a very convenient method for the preparation of propyl iodide and similar compounds. 

 127 gm. iodine, 60 gm, propyl alcohol and 10 gm. of red phosphorus are mixed in 

 a flask, and, after the reaction, which at once sets in, has subsided, the flask is to be 

 heated for an hour, connected with a reversed condenser. After cooling, the oily 

 liquid is decanted, washed with soda solution and dried by calcium chloride. On 

 distilling, nearly 90 per cent, of the theoretical yield is obtained. 



This method gives very satisfactory results, and is applicable in the case of 

 CH3I, C2H5I, C3HVI, etc. 



The process commonly recommended for the preparation of ethyl bromide by 

 the addition of bromine to a mixture of ethyl alcohol and red phosphorus, yields a 

 small and impure product and is difficult to control. Erlenmeyer (Jahresh., 1878, 

 p. 538) has given an excellent method for the preparation of ethyl bromide by the 

 distillation of a mixture of potassium bromide, sulphuric acid and alcohol. Both of 

 these processes yield a product largely contaminated by ether, which, although not 



A. P. S. — VOL. XVIL 2 B. 



