Hypergolic Behavior of Pyridinium Salts Containing Cyanoborohydride and Dicyanamide Anions with Oxidizer RFNA

Abstract

AbstractA series of low‐cost, pyridinium cation‐based hypergolic ionic liquids (HIL) containing amine, butyl, or allyl substituents with cyanoborohydride [BH3CN]− and dicyanamide [DCA]− anions were developed and characterized. The investigated physicochemical properties include melting and decomposition temperature, viscosity, density, heat of formation (ΔHf) and specific impulse (Isp). The ignition delay (ID) of all HILs was tested with the oxidizer RFNA. The HIL, 1‐allyl 4‐amino pyridinium dicyanamide, exhibited highest density (1.139 g cm−3) amongst the known pyridinium HILs. The heats of formation predicted on the basis of Gaussian 09 suit programs were within the range of − 30 to 356 kJ mol−1. The structure of HIL, 1‐butyl 4‐aminopyridinium cyanoborohydride, was examined by single‐crystal X‐ray diffraction, which revealed hydrogen bonding between anion and cation as N1−H1N⋅⋅⋅N3=2.07 Å, N1−H2N⋅⋅⋅H1B1=2.18 Å, and N1−H2N⋅⋅⋅H2B1=2.21 Å, respectively. HIL (1‐allyl 4‐aminopyridiniun cyanoborohydride) exhibited highest Isp of 228 s amongst the designed series.