Investigations of bis(methyltetrazolyl)triazenes as nitrogen-rich ingredients in solid rocket propellants – Synthesis, characterization and properties

Abstract

The energetic nitrogen-rich compounds 1,3-bis(1-methyltetrazol-5-yl)triaz-1-ene ( 4) and 1,3-bis(2-methyltetrazol-5-yl)triaz-1-ene ( 5) were synthesized by diazotation of 1-methyl-5-aminotetrazole ( 2) and 2-methyl-5-aminotetrazole ( 3), respectively, by using half an equivalent of sodium nitrite. The reaction of 4 and 5 with diluted ammonia solution yields ammonium bis(1-methyltetrazol-5-yl)triazenate ( 6) and ammonium bis(2-methyl-tetrazol-5-yl)triazenate ( 7). Treating of 4 and 5 with aqueous sodium hydroxide solution yields sodium bis(1-methyltetrazol-5-yl)triazenate ( 8) and sodium bis(2-methyltetrazol-5-yl)triazenate ( 9) almost quantitative. Compounds 8 and 9 were methylated using methyl iodide and dimethyl sulfate, respectively, originating bis(1-methyltetrazol-5-yl)-3-methyltriaz-1-ene ( 10) and bis(2-methyltetrazol-5-yl)-3-methyltriaz-1-ene ( 11). The products 4– 11 were characterized by Raman, IR, multinuclear NMR and UV–Vis spectroscopy, mass spectrometry, elemental analysis and differential scanning calorimetry. The structures of the crystalline state of 4 · H 2O, 5, 8 · MeOH, 10 and magnesium bis(2-methyltetrazol-5-yl)triazenate ( 12) were determined by low temperature single crystal X-ray diffraction. The heats of formation Δ f H ∘ of 4– 7, 10 and 11 were calculated using energies of combustion Δ c U ∘ determined by bomb calorimetry, resulting in strongly endothermic values. With these data and by using calculated ( 4, 5, 10) as well as measured ( 6, 7, 11) crystal densities, several detonation parameter (heats of explosion, detonation pressure, detonation velocity, explosion temperature) were calculated by the explo5 software. In addition, the specific impulse of different propellant mixtures of the most promising compound 6 with ammonium dinitramide (ADN) were computed. Furthermore the n-octanol/water partition coefficients of 4, 5, 6 and 7 were determined and the long-term stability of 6 was tested by thermal safety calorimetry. Lastly the sensitivities toward impact and friction as well as electrical discharge were determined by the BAM drophammer, friction tester and a small scale electrical discharge tester.