Methyl nitrate energetic compounds based on bicyclic scaffolds of furazan–isofurazan (isoxazole): syntheses, crystal structures and detonation performances

Two energetic bicyclic scaffolds (furazan–isoxazole and furazan–1,3,4-oxadiazole) were constructed via different cyclization reactions. Based on the energetic bicyclic scaffolds, the energetic compounds, 3-(4-nitraminofurazan-3-ly)-isoxazole-5-methylnitrate 1c and 5-(4-nitraminofurazan-3-ly)-1,3,4-oxadiazole-2-methylnitrate 2c, were designed and synthesized in good yields. Because of the acidity of nitramine, the corresponding energetic ionic salts, ammonium 3-(4-nitraminofurazan-3-ly)isoxazole-5-methylnitrate 1d and ammonium 5-(4-nitraminofurazan-3-ly)-1,3,4-oxadiazole-2-methylnitrate 2e, were also obtained and well characterized, their structures were further determined by X-ray single crystal diffraction. To have a better understanding of the structure–property relationships of furazan-bicyclic scaffolds and nitrate groups, their thermal behaviors, detonation performances and the sensitivities were investigated via differential scanning calorimetry (DSC), ESP analysis, Hirshfeld surfaces calculation, EXPLO5 program and BAM standard techniques. Compared with those of ammonium 5-(4-nitraminofurazan-3-ly)-1,2,4-oxadiazole-2-methylnitrate 3e, the results show that all these methyl nitrate energetic compounds based on bicyclic scaffolds of furazan–isofurazan exhibit good detonation performances and extraordinary insensitivities. As supported by experimental and theoretical data, the formation of energetic ionic salts causes an increase of the weak interactions, significantly improving the thermal performance over 110 °C.