Bistetrazolylamines—synthesis and characterization

Abstract

The acid-catalyzed cyclization reaction of sodium dicyanamide and sodium azide in the ratio of 1 : 2 afforded 5,5′-bis(1H-tetrazolyl)amine (H₂bta, 2) in high yield (88%) as the monohydrate. Dehydration of 2·H₂O at elevated temperature and reduced pressure gave anhydrous 2, while recrystallization from DMSO yielded 2·H₂O·DMSO. 2 was converted into 5,5′-bis(2-methyltetrazolyl)methylamine (Me₃bta, 6) in two steps. In the first step, 2 was twice deprotonated with sodium hydroxide and alkylated with MeI producing 5,5′-bis(2-methyltetrazolyl)amine (Me₂bta, 5) in moderate yield (55%). The second step involved the alkylation of 5 with dimethyl sulfate in alkaline solution (72%). In all cases, the obtained colorless, crystalline compounds were fully characterized by vibrational (IR, Raman) spectroscopy, multinuclear NMR spectroscopy, mass spectrometry, elemental analysis, X-ray structure determination, and initial safety testing (impact, friction and electrical spark sensitivity). According to the UN Recommendations for the “Transport of Dangerous Goods”, compounds 2·H₂O, 5, and 6 are classified as “insensitive” while 2 is described as “sensitive”. The thermal behaviors were investigated using differential scanning calorimetry (DSC). The heats of formation (Δ_fH_m° (2*H₂O) = 203 kJ mol⁻¹, Δ_fH_m° (2) = 633 kJ mol⁻¹, Δ_fH_m° (5) = 350 kJ mol⁻¹, Δ_fH_m° (6) = 583kJ mol⁻¹) were calculated using heats of combustion (Δ_comb.H (2·H₂O) = −1714 kJ mol⁻¹, Δ_comb.H (2) = −1858 kJ mol⁻¹, Δ_comb.H (5) = −2932 kJ mol⁻¹, Δ_comb.H (6) = −3843 kJ mol⁻¹) obtained from oxygen bomb calorimetry. In addition, explosion parameters such as the detonation velocity (D(2·H₂O) = 7792 m s⁻¹, D(2) = 9120 m s⁻¹, D(5) = 7291 m s⁻¹, D(6) = 7851 m s⁻¹) and detonation pressure (P(2·H₂O) = 220 kbar, P(2) = 343 kbar, P(5) = 172 kbar, P(6) = 205 kbar) were calculated using the program EXPLO5. “Koenen tests” were successfully performed for compound 2 using critical diameters of 8 mm and 10 mm.