Experimental Detection of Trinitramide, N(NO₂)₃

Abstract

There is an incentive for research directed towards new environmentally friendly oxidizers and energetic materials. [1][2][3] Recent examples for advances in polynitrogen chemistry are the bulk synthesis of the V-shaped N 5 + , [4,5] the tetrazole-based CN 7 , À[6] and the detection of cyclic N 5 À . [7,8] Compounds containing exclusively oxygen and nitrogen are desirable for applications such as environmentally benign rocket propulsion. Of those, the dinitramide anion (N-(NO 2 ) 2 À ) [9][10][11] is the heaviest compound known to date. Trinitramide (TNA; N(NO 2 ) 3 ) constitutes a possible energetic green oxidizer that could be suitable for future high-performance propellants. Only a few theoretical works have previously dealt with this hitherto unknown nitrogen oxide. [12][13][14] The heat of formation (DH 0 f(gas) ) of TNA has been estimated at between 38 and 71 kcal mol À1 , [12][13][14] and the N À N bond dissociation energy has been estimated to be 20-27 kcal mol À1 . [13,14] The existence of an N 4 O 6 intermediate has also been speculated to explain observed decomposition kinetics of dinitraminic acid (HN(NO 2 ) 2 ) in nitric acid. [15] To the best of our knowledge, no synthetic effort toward TNA has been attempted. Herein we present the first experimental detection of this exotic molecule.We initially subjected TNA to a thorough quantum chemical analysis. The aim of this study was to decipher the kinetic stability and different decomposition pathways in gas phase and in solution. We also performed calculations on two possible synthesis routes, and estimated physical properties such as density, heat of formation, vaporization, sublimation, and performance characteristics of TNA as a rocket-propellant component.Proposed self-decomposition pathways available to TNA are shown in Scheme 1. The NÀN bond dissociation enthalpy in the gas phase is calculated to be 28.2 kcal mol À1 . Owing to the favorable change in entropy, this dissociation is likely the [*] Dr. M. Rahm, Dr.

Theoretical Design of Green Energetic Materials: Predicting Stability, Detection, Synthesis and Performance

“…Trinitramide (TNA, N(NO 2 ) 3 , 1), or trinitroamine, which is the systematic name, was first prepared and detected in 2010 by Rahm et al after a thorough computational analysis [37]. It is one of only nine nitrogen oxides that have been observed experimentally, and by far the largest to date.…”

“…The first theoretical study on TNA was published in 1987 [38], but after that only a few studies appeared in the 1990s [39,40] before the 2010 detection. The reason for the loss of interest in TNA was probably that the bonding of this molecule is poorly described by standard DFT methods [37]. The common B3LYP method predicts a bond dissociation enthalpy (BDE) for the N N bond of only 20 kcal/ mol; a value that would render TNA much too unstable to be of interest for any application.…”

“…Our original interest in this molecule stemmed from its proposed role in the decomposition of dinitraminic acid. However, as we were investigating the molecule by the gold standard of quantum chemistry methods, CCSD(T), within the CBS-QB3 scheme, we were surprised to see that the BDE went up to more than 28 kcal/mol [37]. This led to a more thorough analysis of the kinetic stability of TNA, and Figure 2.1 shows our current best estimate of the gas phase decomposition energetics for this molecule [37] (Brinck, T. and Rahm, M., 2013, unpublished results).…”

“…However, as we were investigating the molecule by the gold standard of quantum chemistry methods, CCSD(T), within the CBS-QB3 scheme, we were surprised to see that the BDE went up to more than 28 kcal/mol [37]. This led to a more thorough analysis of the kinetic stability of TNA, and Figure 2.1 shows our current best estimate of the gas phase decomposition energetics for this molecule [37] (Brinck, T. and Rahm, M., 2013, unpublished results). Compared to our 2011 study [37], some of the energies have been corrected for the effect of optimizing geometries using coupled-cluster (CCSD) instead of B3LYP.…”

“…This led to a more thorough analysis of the kinetic stability of TNA, and Figure 2.1 shows our current best estimate of the gas phase decomposition energetics for this molecule [37] (Brinck, T. and Rahm, M., 2013, unpublished results). Compared to our 2011 study [37], some of the energies have been corrected for the effect of optimizing geometries using coupled-cluster (CCSD) instead of B3LYP. In addition to the homolytic N N bond cleavage, there is a second decomposition channel that involves a transfer of a NO 2 -group to form the higher lying intermediate 4.…”