A large variety of twice-deprotonated nitrogen-rich 5,5'-bistetrazolates, that is, the ammonium (1), hydrazinium (2), hydroxylammonium (3), guanidinium (4), aminoguanidinium (5), diaminoguanidinium (6), triaminoguanidinium (7), and diaminouronium (8) salts, have been synthesized. Energetic compounds 1-8 were fully characterized by single-crystal X-ray diffraction (except 8), NMR spectroscopy, IR and Raman spectroscopy, and differential scanning calorimetry (DSC) measurements. With respect to their potential use in propellant applications, the sensitivity towards impact, friction, and electrical discharge were determined. Several propulsion and detonation parameters (e.g., heat of explosion, detonation velocity) were computed by using the EXPLO5 computer code based on calculated (CBS-4M) heats of formation and X-ray densities. Additionally, the performance of 1-8 in various formulations was investigated by calculating the specific energy and specific impulse of the compounds under isochoric conditions.
Sodium 5‐cyanotetrazolate sesquihydrate (1) was prepared from sodium azide and two equivalents of sodium cyanide under acidic conditions. Its hydrolysis, when treated with an excess of 6 M nitric acid yields tetrazole‐5‐carboxamide (4), whereas stoichiometric amounts of 2 M nitric acid yields the free acid 5‐cyanotetrazole (2). 5‐Cyanotetrazole readily reacts with hydroxylammonium chloride to form the oxime of tetrazole‐5‐carboxamide (6). Both compounds, the tetrazole‐5‐carboxamide (4) and its oxime (6), bear an acidic proton, which can be abstracted with bases such as aqueous ammonia or hydroxylamine, to form the respective hydroxylammonium (5, 7) or ammonium salts (8). Also the guanidinium (9) and the triaminoguanidinium salt (10) were prepared using guanidinium and triaminoguanidinium chloride, respectively. All mentioned compounds, including the silver salt of 5‐cyanotetrazole (3), were structurally characterized by low‐temperature single‐crystal X‐ray analysis. In additional, the materials were characterized using NMR and vibrational (IR, Raman) spectroscopy as well as mass spectrometry and elemental analysis. The thermal behavior was studied from DSC measurements and the sensitivities of the compounds towards shock, friction, and electrostatic discharge were determined. Moreover, the heats of formation were calculated (atomization method, CBS‐4M enthalpies) and several detonation/propulsion parameters computed with the EXPLO5 code.
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