Boronium-cation-based ionic liquids as hypergolic fluids

Abstract

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. Ignition! Bis(1-allyl-1H-imidazole-3-yl) dihydroboronium dicyanoborohydride (see figure) exhibits one of the lowest viscosities (35 mPa s) and the shortest ignition-delay times (14 ms) of any reported ionic-liquid fuel component of a hypergolic mixture with white-fuming nitric acid. These remarkable properties seem to be due to the highly reactive reducing nature of the B-H bonds present in both the cation and anion. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.