Preparation and characteristics of 1,2,4-oxadiazole-derived energetic ionic salts with nitrogen linkages

Abstract

A new family of energetic ionic salts containing a 1,2,4-oxadiazole ring and an amino or triazene linkage were synthesized by the oxidation of 3-nitro-5-amino-1,2,4-oxadiazole (NOA) with sodium dichloroisocyanurate (SDCI) affording sodium bis(3-nitro-1,2,4-oxadiazol-5-yl)amide (2) and sodium 1,3-bis(3-nitro-1,2,4-oxadiazol-5-yl)triaz-2-en-1-ide (3) followed by cation metathesis. Their molecular structures were fully characterized by ¹H and ¹³C NMR, MS and IR spectroscopy, while three ionic salts 4, 5 and 7 along with two sodium salt precursors 2 and 3 were confirmed by single-crystal X-ray diffraction. Differential scanning calorimetry (DSC) was employed to investigate the thermal stability of these ionic salts, revealing moderate onset decomposition temperatures ranging from 166 °C to 249 °C. By using a fall hammer test, most salts were found to exhibit low impact sensitivities. Guanidinium bis(3-nitro-1,2,4-oxadiazol-5-yl)amide (4) exhibits good performance with acceptable detonation properties (D: 8351 m s⁻¹, P: 29.0 GPa), good stability (T_d: 241 °C, onset) and low impact sensitivity (IS > 40 J).