Dissolve 20 g of isocyanogen tetrabromide in 200 mL of acetone, cool down to 0°C in an ice bath. Then dissolve 18 g of sodium azide in 120 mL of water and cool down to 0°C. Then slowly over the course of 2 h add the azide solution to the tetrabromide while stirring the solution, the temperature must be kept at 0°C. After addition, stir the mixture vigorously for 4 h at room temperature, then pour the mixture into 750 mL of water and stir for 1 h, cool the solution in an ice bath. Filter and wash with 500 mL of water then dry in open air.