Azetidinium-based Hypergolic Ionic Liquids with High Strain Energy

A class of azetidinium-based hypergolic ionic liquids was synthesized and characterized by H-1 and (CNMR)-C-13, IR spectroscopies, and electrospray ionization mass spectrometry. The properties of six synthesized ionic liquids were characterized with respect to liquid range (-80-200 degrees C), density (0.99-1.05 gcm(-3)), heat of formation (0.70-2.17 kJg(-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 (9a: 0.41 kJg(-1), 156.5 s; 9 b: 0.36 kJg(-1), 155.3s), 9 exhibited a much higher heat of formation (0.78 kJg(-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 kJg(-1), 184.5 s), 12 has a greater potential to be employed as green propellants.