Thermal Decomposition Studies on Ammonium Dinitramide (ADN) and 15N and 2H Isotopomers

The thermal decomposition of ammonium dinitramide (ADN) and potassium dinitramide (KDN) were examined neat and in solution. Isothermal kinetics were measured (160−220 °C) by monitoring dinitramidate loss and were found to be first-order. Ammonium ion loss and gas formation were not good measurements of ADN decomposition since they reflect the fate of the ADN decomposition product ammonium nitrate. Kinetics of decomposition were nearly identical for ADN neat (proteo- and deutero-), ADN in water (1 or 20 wt %), ADN in various pH aqueous buffers, and for aqueous KDN (1 wt % in water or deuterium oxide). The activation energy, calculated for ADN, was about 40 kcal/mol (167 kJ/mol) for neat ADN and 37 kcal/mol (155 kJ/mol) for aqueous solutions of ADN. Decomposition of ADN in aqueous buffers suggested that under the conditions of these studies decomposition of dinitramidate or its parent acid proceeds at about the same rate at pH 3, pH 5, and unbuffered but decreased by about 40% at pH 9. Neat KDN was unique in that it decomposed about an order of magnitude slower than ADN, but its decomposition increased to be comparable to that of ADN when KDN was aqueous or when any ammonium salt was mixed with KDN. Nitrous oxide and nitrate (or nitric acid) were the principal decomposition products of dinitramide. Nitrogen gas was also formed, to a significant extent in the decomposition of ADN and to a small extent in that of KDN. Nitrogen gas resulted from the interaction of ammonium or ammonia with the nitrate or gaseous nitrogen oxides. Studies of 15 N-labeled ADN confirm that one N−NO 2 bond remains intact, forming nitrous oxide, while the other nitro group combines with the nitrogen from ammonium to form nitrogen gas. Several decomposition pathways consistent with these findings are considered.