Hydrophobic Hydrolytic‐Stable N‐Alkylimidazole‐Cyanoborane Complexes as Ultrafast‐Igniting Hypergolic Fuels

Abstract Introduction of cyano group into the molecules of borane‐based hypergolic fuels can greatly reinforce the hydrolytic stability. By the formation of complex between BH 2 CN and imidazole, six complexes were readily prepared from N ‐alkyl substituted imidazole hydrochloride salts and NaBH 3 CN in THF and fully characterized by 1 H and 13 C NMR, IR spectroscopy, high‐resolution mass spectrum, and differential scanning calorimetry (DSC). Among them, 1‐allylimidazole‐cyanoborane complex ( 5 ) displayed some attractive properties such as water immiscibility and good hydrolytic stability, high density (>1.0 g cm −3 ), good thermal stability ( T d , 193 °C, onset), high calculated density impulse ( ρI sp , 358 s g cm −3 ), ultra‐short ignition delay time (WFNA, 3 ms), and super low viscosity (8.4 mPa s), showing the real application potential as a fuel and an efficient fuel additive in bipropellants.