Can N-oxidation alleviate the energy-safety contradiction of energetic materials?

Abstract

The introduction of the N-oxide functional group to the heterocyclic structure is deemed as an effective strategy to construct highly energetic and lowly sensitive materials. Nevertheless, the detailed influence of N-oxidation on the detonation performance and sensitive properties of energetic materials (EMs) is still fragmentary. Herein, a total of 34 experimental known crystals of energetic N-oxides and their analogues were screened, and the detonation performances along with sensitivities were comparatively analyzed to reveal the role of N-oxidation. The results show that crystal density and packing coefficients increase as the introduction of N-oxide groups in most cases, leading to high detonation performances. Compared with analogues, conversely, the decomposition temperatures and sensitivities of energetic N-oxide decrease and rise, respectively, indicative of poor safety. Hence, it is difficult to both promote energy and safety by N-oxidation relative to the analogues. However, the introduction of N-oxide groups is still helpful for the creation of novel EMs since some energetic N-oxides can possess high energy and low sensitivity comparable to HMX. Additionally, several theoretical approaches of sensitivity estimation were tested and inconsistent prediction results were obtained, demonstrating that sensitivity prediction only at the molecular level is not enough for N-oxide systems.