Integration of Carbonyl Groups with 1,3,4-Oxadiazoles: A Heat-Resistant Energetic Compound with Well-Balanced Performance via Heterocycle Transformation

The exceptional combination of high density and superior thermal stability renders ketone-based energetic compounds particularly attractive for heat-resistant explosives. While extensive research has demonstrated successful carbonyl functionalization of azoles, such as pyrazoles, triazoles, 1,2,4-oxadiazoles, and imidazoles, the potential of carbonyl-substituted 1,3,4-oxadiazole systems has surprisingly never been explored in energetic materials. In this study, the tetrazole-based energetic material 2,2'-bis(dinitromethyl)-2<i>H</i>,2'<i>H</i>-5,5'-bitetrazole (<b>BDNBT</b>) reacted with nitrosulfur mixed acid, successfully yielding the ketone-based energetic compound [2,2'-bi(1,3,4-oxadiazole)]-5,5'(4<i>H</i>,4'<i>H</i>)-dione (<b>OXO-9</b>) featuring a bis(1,3,4-oxadiazole) skeleton. <b>OXO-9</b> demonstrates balanced overall properties. It exhibits a high density of 1.91 g cm^-3 and superior detonation performance (<i>D</i>_v = 8283 m s^-1 and <i>P</i> = 29.3 GPa) comparable to HNS (<i>D</i>_v = 7612 m s^-1 and <i>P</i> = 24.3 GPa). Additionally, it possesses a high decomposition temperature (<i>T</i>_d = 317 °C) similar to that of HNS (<i>T</i>_d = 318 °C), while its impact sensitivity (IS = 32 J) is lower than that of TNT (IS = 15 J). This work demonstrates a strategic transformation from tetrazole to 1,3,4-oxadiazole, offering new synthetic routes in heterocyclic chemistry for energetic materials. Significantly, the synthesis of <b>OXO-9</b> provides a theoretical foundation for future exploration of diverse nitrogen heterocycle transformations.