Preparation of Guanidine Nitrate

After having messed around with cyanamide, the synth for guanidine nitrate was pleasurably easy. No gas, no pH checking, no gel to filter. That's the way it worked:

75g lime nitrogen(*) and 190g ammonium nitrate where pulverized and placed in a 1L erlenmeyer. The mixture was heated on a boiling water bath and stirred from time to time with a glass rod. The black and white mixture became a thick black paste. After 6h of heating, 300 ml of hot water was added (evolution of NH3) and the resulting paste was filtered (again the lovely smell of NH3). The residue was washed with 100 ml of hot water and the combined washings were reduced by 200 ml and cooled to 4°C. First fell out red powder (reminding of FeO) of unknown composition and then lots of white crystals. The crystals were filtered. The filtrate was reduced to half volume and cooled to 4°C. Again red powder and some crystals (this time much less) fell out. The crystals contain up to 50% ammonium nitrate, so they were recrystallized from hot water (taking care to filter out the red powder). Yields up to 75% (from calcium cyanamide) can be expected. For more purity, product can be recrystallized from MeOH.

(*) Lime nitrogen is commercial calcium cyanamide, containing about 50% calcium cyanamide. It is important to use the commercial preparation because it contains Ca(OH)2 which is important in this reaction. The reaction can be scaled up to multi kg levels.

Reference: Inorganic Syntheses I, p97