Boronium-Cation-Based Ionic Liquids as Hypergolic Fluids



Two series of boronium-cation-based ionic liquids were prepared and fully characterized by 1H, 13C, and 11B NMR and infrared spectroscopy, differential scanning calorimetry (DSC), and elemental analysis. The structure of bis(1-methyl-1H-imidazole-3-yl)dihydroboronium dicyanoborohydride (5 a) was determined by single-crystal X-ray diffraction. The densities of these ionic liquids range from 1.05 to 1.28 g cm−3, and the heats of formation, predicted on the basis of Gaussian 03 calculations, fall between −164.6 and 430.5 kJ mol−1. Compound 5 b, bis(1-allyl-1H-imidazole-3-yl)dihydroboronium dicyanoborohydride, exhibits the lowest viscosity (35 mPa s) and shortest ignition-delay time (14 ms) in combination with 100 % HNO3.