To a beaker immersed in an ice bath add 21.7 mL of 15% nitric acid and 3.4 g of aminoguanidine bicarbonate, start an addition of 1.7 g of sodium nitrite dissolved in 3.5 mL of water and maintain the temperature below 25°C. Allow the solution to stand for 20 minutes and add 4.6 grams of sodium bicarbonate, reflux the solution for 4h. After the reflux, bring the pH down to 4 with some sulfuric acid and let the solution crystallize while cooling down to room temperature. Filter the mixture and wash with some cold ethanol. Recrystallize from hot ethanol.
Addition of the reagents
The color of the solution is because of nitrous acid formation
Refluxing the mixture
The pure 5-aminotetrazole monohydrate