Synthesis and Properties of Azide‐Functionalized Ionic Liquids as Attractive Hypergolic Fuels

Abstract

Hypergolic ionic liquids (ILs) have shown a great promise as viable replacements for toxic and volatile hydrazine derivatives used as propellant fuels, and hence, have attracted increasing interest over the last decade. To take advantage of the reactivity and high energy density of the azido group, a family of low‐cost and easily prepared azide‐functionalized cation‐based ILs, including fuel‐rich anions, such as nitrate, dicyanamide, and nitrocyanamide anions, were synthesized and characterized. All the dicyanamide‐ and nitrocyanamide‐based ILs exhibited spontaneous combustion upon contact with 100 % HNO3. The densities of these hypergolic ILs varied in the range 1.11–1.29 g cm−3, and the density‐specific impulse, predicted based on Gaussian 09 calculations, was between 289.9 and 344.9 s g cm−3. The values of these two key physical properties are much higher than those of unsymmetrical dimethylhydrazine (UDMH). Among the studied compounds, compound IL‐3b, that is, 1‐(2‐azidoethyl)‐1‐methylpyrrolidin‐1‐ium dicyanamide, shows excellent integrated properties including the lowest viscosity (30.9 M Pa s), wide liquid operating range (−70 to 205 °C), shortest ignition‐delay time (7 ms) with 100 % HNO3, and superior density specific impulse (302.5 s g cm−3), suggesting promising applications with potential as bipropellant formulations.

Theoretical Study on Hydrolytic Stability of Borohydride-Rich Hypergolic Ionic Liquids

“…Considerable efforts have been devoted to the development of new high-performance HILs with heterocyclic and open-chain cations in combination with highly reactive anions. To date, a large number of room-temperature HILs have been developed as promising hypergolic fuels, − which are considered as potential green replacements for hydrazine-based fuels in future chemical propellants.…”

Hybridization of Dinitramide and Dicyanamide: Evaluation of Nitrocyanamide in Energetic Salts and Coordination Compounds

“…Several salts of nitrocyanamide including alkaline, alkaline earth, and transition metal salts are already known in the literature, as well as nitrogen-rich derivatives including ammonium, and the already mentioned guanidinium, aminoguanidinium, and triaminoguanidium (TAG + ) salts, , as well as several ionic liquids. − Since the series of nitrogen-rich derivatives of NCA anions has not been fully investigated, we have focused on the synthesis and investigation thereof, as they tend to be promising compounds, which emerges from the structural hybridization of DCA and DN. Moreover, there are no energetic calculations or crystallographic studies on the known structures of nitrogen-rich NCA salts .…”

“…The main research on this anion, however, focused on the reaction of nitrocyanamide as a nucleophile, − resulting in isocyanates, and later the implementation of the anion into transition metal complexes. − These were mainly based on pyrazole − and imidazole ,− ligands and were largely part of spectroscopic studies. Further energetic investigations were carried out rather recently, focusing on nitrocyanamide as part of ionic liquids used in hypergolic mixtures. − In this area, the group of Shreeve has been leading the way, whereas mostly dialkylated imidazolium cations ,, or other alkylammonium salts ,− were used. However, some energetic salts, such as aminoguanidnium or triaminoguanidinium, which are solids at ambient temperature, have also been investigated …”

Synthesis and properties of borane‐containing ionic liquids based on biferrocene

“…[4,5] In recent years, numerous environmentally friendly EILs based on different energetic anions [6][7][8] have displayed short ignition delay (ID) times with white fuming nitric acid (WFNA) and were expected to replace the toxic fuel such as monomethylhydrazine (MMH) [9] and unsymmetrical dimethylhydrazine (UDMH) [10,11] in liquid propellants. By appraising the properties of EILs, it is notable that energetic anions have a significant impact on their hypergolicity such as N(CN) 2 À , [12][13][14] BH 3 CN À , [15][16][17] BH 4 À , [18] and BH 3 (CN) BH 2 (CN) À . [19] To examine the impact of energetic anions on the properties of EILs, Tang et al [20] calculated the energy gap between 10 energetic anions and WFNA; then, they confirmed that the smaller the energy gap, the shorter ID times EILs have.…”