\ 



JACKSON AND FULLER. DIPARABROMBENZYLCYANAMIDE. 283 



constitution (Ag 2 NCN) must be ascribed to this substance and to cyan- 

 amide. If, on the other hand, these compounds are formed by successive 

 additions of the alkyl bromide with splitting off of argentic bromide, the 

 disubstituted cyanamides could be formed from a silver salt with a 

 carbodiimide formula, as is shown by the following reactions: — 



R 

 NR Br NR NR 2 



// \ / / 



C + RBr = C = C + AgBr. 



NAg NAg N 



Our results, therefore, prove nothing in regard to the true formula of 

 cyanamide. 



Preparation of Diparabrombenzylcyanamide, 

 (C G H 4 BrCH 2 ) 2 NCN. 



The yellow silver salt of cyanamide, Ag.,NCN, prepared according to 

 Walther,* was mixed with a benzol solution of parabrombenzylbromide 

 in the proportion of two molecules of the bromide to one of the salt, 

 which should be finely powdered. The mixture was heated in a flask 

 with a return-condenser on the steam-bath, until after four or five hours 

 the full yellow color of the argentic cyanamide had been completely 

 replaced by the yellowish white color of argentic bromide. The precipi- 

 tate was then filtered out and washed thoroughly with hot benzol, and 

 the filtrate and washings evaporated to dryness, when a thick reddish 

 yellow oil was left. To purify this it was dissolved in hot alcohol, and 

 the strong solution allowed to cool slowly ; a yellow oil was deposited 

 at first followed by a white crystalline substance, which was obtained by 

 pouring the solution off from the oil as soon as the crystals began to 

 appear. By repeated recrystallizations of this sort the melting-point of 

 the substance was raised to 133°, where it remained constant. It was 

 dried in vacuo and analyzed with the following results : — 



* Journ. prakt. Chem., 1896, 510. 



