First Example of 1,2,5‐Oxadiazole‐Based Hypergolic Ionic Liquids: A New Class of Potential Energetic Fuels

Abstract

The development of liquid energetic fuels with improved properties is an important topic in space propulsion technologies. In this manuscript, a series of energetic ionic liquids incorporating a 1,2,5‐oxadiazole ring and nitrate, dicyanamide or dinitramide anion was synthesized and their physicochemical properties were evaluated. The synthesized compounds were fully characterized and were found to have good thermal stabilities (up to 219 °C) and experimental densities (1.21–1.47 g cm−3). Advantageously, 1,2,5‐oxadiazole‐based ionic liquids have high combined nitrogen‐oxygen contents (up to 64.4 %), while their detonation velocities are on the level of known explosive TNT, and combustion performance exceeds those of benchmark 2‐hydroxyethylhydrazinium nitrate. Considering the established hypergolicity with H2O2 in the presence of a catalyst, and insensitivity to impact, synthesized ionic liquids have strong application potential as energetic fuels for space technologies.

Controlling the Energetic Properties of N-Methylene-C-Linked 4-Hydroxy-3,5-dinitropyrazole- and Tetrazole-Based Compounds via a Selective Mono- and Dicationic Salt Formation Strategy

“…New-age energetic materials are primarily composed of nitrogen-rich heterocyclic rings including pyrazole, tetrazole, oxadiazole, etc., due to the desired energetic performance arising from many N–N and N–C energetic bonds. − 3,5-Dinitropyrazole-based compounds, for instance, have been extensively explored owing to their high nitrogen and oxygen contents, high heats of formation, and adequate densities. − Some stability features could be introduced to these nitropyrazole-based HEDMs to fine-tune their overall performance. One of the most common techniques is the introduction of alternating electron-withdrawing and -donating groups, like in the case of TATB, 2,4,6-triamino-5-nitropyrimidine-1,3-dioxide (ICM-102), triazolo–triazine explosive (TTX), etc. ,, This causes internal charge separation, which slows the creation of hotspots after exposure to external stimuli and hence enhances physical stability .…”

“…A subsequent upfield shift in the 1 H NMR of the protons corresponding to the methylene bridge was observed in all salts, with peaks in the range of 5.92−6.03 ppm in the case of monocationic salts 3−7 and 5.75−5.86 ppm in the case of dicationic salts 8−12. The carbon of the methylene bridge showed successive downfield shifts in monosalts ( 49 Compounds 2, 4, 9, and 11 were also analyzed by 15 N NMR spectra, and nitromethane was used as a reference for assessing the chemical shifts (Figure 4). The peaks were assigned in reference to similar compounds reported in the literature.…”

“…By controlling the stoichiometric equivalents of the bases added, we successfully obtained a series of monocationic (3−7) and dicationic salts(8−12).Spectral Studies of Compounds. Compounds 2−12 were characterized by IR, NMR [ 1 H, 13 C{ 1 H}, in a few cases,15…”

“…C{1 H} NMR (125 MHz, DMSO-d 6 , ppm): δ 153.0 142.6, 137.3, 134.0, 49.0 ppm 15. N NMR (DMSO-d 6 + 1 drop of D 2 O, ppm): −199.2, −99.2, −81.6, −33.5, −28.3, −16.4.…”