To a beaker immersed in an ice bath 55 mL of cold conc. sulfuric acid is added, with vigorous stirring 58 g of guanidine nitrate is added to the solution while maintaining the temperature below 20°C. After the addition, the mixture is stirred for additional 3h and let stand for 24h at room temperature. Then pour the solution to 500 mL of ice and water slush, filter and wash with some cold water. Recrystallize from hot water-ethanol solution.
Addition of the guanidine nitrate to the sulfuric acid
Pouring the mixture into ice water slush
The recrystallized product