On the Anomalous Decomposition and Reactivity of Ammonium and Potassium Dinitramide

Abstract

Mechanistic pathways for the thermal decomposition of the solid-state energetic oxidizers ammonium dinitramide (ADN) and potassium dinitramide (KDN) have been deciphered by carefully considering previously performed experimental studies and using state of the art quantum chemical modeling of molecular clusters. Decomposition is governed by surface chemical processes, involving polarized (twisted) dinitramide anions of reduced stability. Under atmospheric and low-pressure conditions, the rate-determining step for the decomposition of these dinitramide salts is the dissociation into NO(2) and NNO(2)(-) radicals. The activation barriers for these steps are estimated to be 30 and 36 kcal/mol for ADN and KDN, respectively. The known stabilizing effect of water is explained by its hydrogen bonding ability, which counteracts polarization of surface dinitramides. The reactivity of ADN toward various chemical environments is likely explained through metastable decomposition radical intermediates. Donation of hydrogen bonds, antioxidant character, and basicity are properties believed to correlate with a compound's ability to act as a stabilizer for dinitramide salts.

Kinetic Stability and Propellant Performance of Green Energetic Materials

“…[6][7][8][9][10] However, the decomposition barrier for the free dinitramide anion (c.f. 1 in Scheme 1) has been theoretically estimated to be 47 kcal mol À1 .…”

“…1 in Scheme 1) has been theoretically estimated to be 47 kcal mol À1 . [9,10] The large barrier can be attributed to stabilization of the anion through considerable electronresonance delocalization. The actual real-life stability of 1 is strongly coupled to its ability to polarize charge, and its chemical environment has been shown to be of great importance.…”

“…The actual real-life stability of 1 is strongly coupled to its ability to polarize charge, and its chemical environment has been shown to be of great importance. [9,10] In addition, phase transitions due to eutectics of dinitramide salts with their corresponding nitrate decomposition products further complicate the thermal behavior. [8][9][10] The stability of dinitramide anions in common solvents is typically good.…”

“…[9,10] In addition, phase transitions due to eutectics of dinitramide salts with their corresponding nitrate decomposition products further complicate the thermal behavior. [8][9][10] The stability of dinitramide anions in common solvents is typically good. However, theoretical estimations of solvated decomposition kinetics have not been reported.…”

Experimental Detection of Trinitramide, N(NO2)3

“…The barrier heights are underestimated by 8-11 kcal mol À1 compared to CBS-QB3 (extrapolated CCSD(T)) and SCS-MP2 calculations, which are in very good agreement. As we know from previous studies that B3LYP, B2PLYP, and highlevel ab initio methods (such as CCSD(T) and SCS-MP2) behave very similarly when treating N(NO 2 ) 2 À and its radical, [16] and, given the high accuracy of the latter methods, we can safely assume that the error by DFT stems from an overestimation of the TNA ground state energy. Thus, the limited interest in TNA might be caused by the wide use of B3LYP, which underestimates its stability.…”