CHAPTER II. 



Preparation and Properties of Cyanamide. 



PREPARATION. 



Free cyanamide, CN.NHg, was first obtained by Bineau, in 

 1838, by the action of ammonia on chlorcyan, but it was not 

 isolated by him from the ammonium chloride with which it 

 was formed. The Italian chemists Cloez and Cannizzaro,^ in 

 1 85 1, effected the separation, and gave the first description of 

 the compound. 



Their method consists in passing chlorcyan into a solution 

 of ammonia in absolute ether, filtering off the crystalline am- 

 monium chloride and evaporating the solution in vacuo below 

 40°. The reaction takes place according to the following 

 equation : 



2NH3 + CNCl «-- CNCl, NH, 4- NH. 



It can also be prepared by the action of freshly precipitated 

 mercuric oxide on thio-urea, in the presence of a little am- 

 monium thiocyanate, which dissolves some of the mercuric 

 oxide as the double thiocyanate, and so renders it more active : 

 NH, NH, 



S:C/ "^ ^\ + ^«^ 



NH, N 



It is most conveniently prepared from either commercial 

 sodium cyanamide or commercial calcium cyanamide. 



From Commercial Sodium Cyanamide.^ — Twenty-five grams 

 of the salt are gradually added to 37 grams of hydrochloric 

 acid (sp. gr. 1.19) with strong cooling, and the water is re- 

 moved by distillation in vacuo below 40° C. The residue 

 solidifies on cooling; it is extracted with ether, the ether dis- 

 tilled off from the solution, and the cyanamide caused to 



^ Compt. rend., XXXII, 62. A, 78, 229, and Leibig's Annalen 78, 229. 



^ Caro, Schiick, Jacoby, Zeit Angew Chem. 1910, XXIII, 2405, 2417. 



