The thermal decomposition of azodicarbonamide (1,1′-azobisformamide)

When azodicarbonamide is decomposed in the temperature range 165–195°, gas is evolved and a white sublimate and a white residue are formed. The gas consists of nitrogen and carbon monoxide together with a third component, which is isocyanic acid at lower and ammonia at higher temperatures. The sublimate consists of cyanuric acid, cyamelide, and urea, and the residue is a mixture of biurea, cyanuric acid, and urazole. Two main primary reactions appear to take place concurrently. In the first azodicarbonamide decomposes to form biurea, nitrogen, and isocyanic acid, and in the second to form urazole, nitrogen, isocyanic acid, and ammonia. At 171. 5° the first mode of decomposition is twice as frequent as the second. Cyanuric acid, cyamelide, carbon monoxide, and ureal all appear to be products of secondary reactions involving isocyanic acid. On prolonged heating at higher temperatures the biurea initially formed decomposes into urazole and ammonia. When the quantity of gas evolved is determined as a function of time, and S shaped cureve is obtained with a long linear centre portion. This near constant rate of decomposition over the main part of the reaction has an activation energy of 228 kJ mol–1 and is accounted for by a one-dimensional propagation of the decomposition through the crystal lattice.