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

• Propan-2-ylidene methanetriamium is the new structures.
• Bond homogenization of the salts suggests delocalization of the charge.
• The salts are hypergolic with white fuming nitric acid.

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 1.80 kJ g−1) and densities (from 1.19 to 1.31 g cm−3) in hand, the detonation pressure (P) and velocity (D), and specific impulse (Isp) values of salts were calculated as 8.94 GPa, 4989 m s−1 and 174.3 s (1), 7.91 GPa, 4815 m s−1 and 179.0 s (2), and 7.33 GPa, 4693 m s−1 and 180.6 s (3), respectively. Impact sensitivities of 1, 2 and 3 were measured to be no less than 40 J 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.