Synthesis and characterization of energetic salts based on the new propan-2-ylidene methanetriamium cations

Abstract

Development of new hypergolic ionic liquids is the key in replacing toxic N,N-dimethylhydrazine as green liquids propellants. Three salts based on the new propan-2-ylidene methanetriamium cations and dicyanamide anion were synthesized and characterized by 1H and 13C NMR, IR and Raman spectroscopy, elemental analysis, and TG/DTA. In addition, their crystal structures were determined by X-ray single crystal diffraction. N-(propan-2-ylidene) methanetriamium dicyanamide (1) crystallizes in the monoclinic space group P21/n, N,N′-bi(propan-2-ylidene) methanetriamium dicyanamide (2) in triclinic P−1, and N,N′,N″-tri(propan-2-ylidene) methanetriamium dicyanamide (3) in monoclinic C2/c. With heats of formation (from 1.56 to 1.80kJg−1) and densities (from 1.19 to 1.31gcm−3) in hand, the detonation pressure (P) and velocity (D), and specific impulse (Isp) values of salts were calculated as 8.94GPa, 4989ms−1 and 174.3s (1), 7.91GPa, 4815ms−1 and 179.0s (2), and 7.33GPa, 4693ms−1 and 180.6s (3), respectively. Impact sensitivities of 1, 2 and 3 were measured to be no less than 40J by hammer tests, which places these salts in the insensitive class. Moreover, the resulting salts are hypergolic with white fuming nitric acid and exhibit potential as bipropellants.