Study On Synthesis And Properties Of Imidazolium Energetic Ionic Liquids

As a kind of unique energetic materials, energetic ionic liquids tend to exhibit important research values and practical application potentials in the field of novel explosives and green bipropellant fuels. Compared with traditional molecular energetic compounds, such as 2,4,6-trinitrotoluene(TNT), 1,3,5-trinitro-1,3,5-triazacyclohexane(RDX), and 1,3,5,7-tetranitro-1,3,5,7-tetraazacyclooctane(HMX), energetic ionic liquids have advantages of negligible volatility, environmental friendliness, low melting point, high thermal stability, and low sensitivity to external stimulus such as friction, impact and electrostatic discharge.Imidazolium-based energetic ionic liquids, as a kind of important energetic ionic salts, exhibit some attractive properties including high thermal stability and energy density. Energetic ionic liquids based on imidazolium compounds can be prepared by metathesis reaction or acid-base neutralization reaction of imidazolium cations and energetic anions. In addition, in order to achieve a better balance between energy and security, ionic liquids can be customized by proper selection of the energetic component ions due to their structural designability.In this thesis, twelve N-hydroxyethylimidazolium energetic ionic liquids(3a~3f and 4a~4f) were synthesized via quaternization and metathesis reactions, starting from N-methylimidazole, 1,2-dimethylimidazole, and 2-chloroethanol, and were characterized by UV-Vis, FT-IR, ESI-MS, 1H NMR, and 13 C NMR. Besides, the structures of 1-(2-hydroxyethyl)-3-methylimidazolium 3,5-dinitro-1,2,4-triazolate(3a) and 1-(2-hydroxyethyl)-3-methylimidazolium picrate(3b) were further confirmed by single-crystal X-ray diffraction. Studies show that all the energetic ionic liquids dissolved easily in polar solvents. The decomposition temperatures of the N-hydroxyethylimidazolium energetic ionic liquids were measured in the range of 124~293 °C, and most of the energetic ionic liquids exhibited excellent thermal stabilities with decomposition temperatures above 200 °C. The densities and molar formation enthalpies of the energetic ionic liquids were calculated by Gaussian software based on the designed isodesmic reactions. The densities and molar formation enthalpies were in the range of 1.42~1.59 g·cm-3 and-256.07~-15.84 k J·mol-1 and 39.21~123.63 k J·mol-1, respectively. The detonation velocities and detonation pressures of these ionic liquids were predicted by the Kamlet-Jacobs formula to be 5.97~7.20 km·s-1 and 13.57~20.57 GPa, respectively. Among them, 1-(2-hydroxyethyl)-3-methylimidazolium dinitramide(3e) exhibited excellent detonation properties with a detonation velocity of 7.20 km·s-1 and a detonation pressure of 20.57 GPa, which was superior to TNT(D = 6.84 km·s-1, P = 20.29 GPa).In this thesis, starting from 1-(2-hydroxyethyl)-3-methylimidazole chloride(1) and 1-(2-hydroxyethyl)-2,3-dimethylimidazole chloride(2), fourteen novel N-nitrooxyethylimidazolium energetic ionic liquids(5, 6, 9a~9f and 10a~10f) were synthesized via nitration and metathesis reactions. All of the compounds were characterized by UV-Vis, FT-IR, ESI-MS, 1H NMR, and 13 C NMR. The crystal structures of 1-(2-nitrooxyethyl)-3-methylimidazolium picrate(9b) and 1-(2-nitrooxyethyl)-2,3-dimethylimidazolium picrate(10b) were determined by single-crystal X-ray diffraction. The solubility study of the ionic liquids was carried out with commonly used organic solvents, showing that the energetic ionic liquids dissolve easily in polar solvents. All the N-nitrooxyethylimidazolium energetic ionic liquids decomposed in the range of 110~198 °C. N-nitrooxyethylimidazolium nitrate(5 and 6), N-nitrooxyethylimidazolium 3,5-dinitro-1,2,4-triazolate(9a and 10a), N-nitrooxyethylimidazolium picrate(9b and 10b), N-hydroxyethylimidazolium dinitramide(9e and 10e), and N-nitrooxyethylimidazolium 5-nitrotetrazolate(9f and 10f) showed excellent thermal stabilities with decomposition temperatures above 165 °C. The calculated densities of the synthesized N-nitrooxyethylimidazolium energetic ionic liquids ranged between 1.49 and 1.64 g·cm-3. The molar formation enthalpies of the ionic liquids were calculated to be in the range of-321.91~-5.63 k J·mol-1 and 43.88~185.43 k J·mol-1 by Gaussian software based on the designed isodesmic reactions. Their detonation velocities and detonation pressures were calculated to be 6.62~7.63 km·s-1 and 17.40~23.84 GPa, respectively. The theoretical densities of 1-(2-nitrooxyethyl)-3-methylimidazolium 3-nitro-1,2,4-triazolate-5-one(9c), 1-(2-nitrooxyethyl)-3-methylimidazolium 5-nitrotetrazolate(9f), and 1-(2-nitrooxyethyl)-2,3-dimethylimidazolium 3,5-dinitro-1,2,4-triazolate(10a) were above 1.54 g·cm-3, and the calculated detonation velocities were slightly higher than TNT. The theoretical detonation velocities and detonation pressures of N-nitrooxyethylimidazolium nitrate(5 and 6), N-nitrooxyethylimidazolium picrate(9b and 10b) and N-nitrooxyethylimidazolium dinitramide(9e and 10e) were above 7.00 km·s-1 and 20.00 GPa. Among them, 1-(2-nitrooxyethyl)-3-methylimidazolium dinitramide(9e) possessed an excellent detonation performance with the highest detonation velocitiy(D = 7.63 km·s-1) and detonation pressure(p = 23.84 GPa).