Azetidinium‐based Hypergolic Ionic Liquids with High Strain Energy

Abstract

AbstractA class of azetidinium‐based hypergolic ionic liquids was synthesized and characterized by 1H and 13C NMR, IR spectroscopies, and electrospray ionization mass spectrometry. The properties of six synthesized ionic liquids were characterized with respect to liquid range (−80–200 °C), density (0.99–1.05 g cm−3), heat of formation (0.70–2.17 kJ g−1), specific impulse (164.0–184.5 s), and ignition delay time (23–130 ms). In order to better understand the relation between ring stains and energy of obtained compounds, the isomers of 9 were also synthesized for comparison. It is interesting to find that, compared with the isomers (9 a: 0.41 kJ g−1, 156.5 s; 9 b: 0.36 kJ g−1, 155.3 s), 9 exhibited a much higher heat of formation (0.78 kJ g−1) and specific impulse (164.8 s), which indicates that ring strains play an important role in the performance of energetic compounds. With the highest energetic properties (2.17 kJ g−1, 184.5 s), 12 has a greater potential to be employed as green propellants.