Ma Yu, He Xudong, Meng Liya, Xue Xianggui, Zhang Chaoyang
Institute of Chemical Materials, China Academy of Engineering Physics (CAEP), P. O. Box 919-311, Mianyang, Sichuan 621900, China.
Phys Chem Chem Phys. 2017 Nov 22;19(45):30933-30944. doi: 10.1039/c7cp03801a.
Energetic ionic salts (EISs) are attracting extensive attention because of their ready preparation and some excellent properties and performances that are comparable to those of common explosives with neutral molecules. Hydroxylamine (HA) is protonated or ionized as H-HA and preferred to be introduced into EISs to form HA-based EISs with almost all kinds of anions since these EISs possess higher packing densities and thus more excellent detonation performances than others with the same anions. Moreover, relative to that of pure HA, the thermal stability of HA-based EISs is significantly enhanced. This significantly enhanced thermal stability can extend the application of HA via deprotonation of H-HA back to HA; however, the mechanism for stabilization of HA by salification remains unclear. Herein, we employed thermodynamic and kinetic calculations and molecular dynamics simulations to reveal the thermal stability mechanisms of many currently synthesized HA-based EISs and some previously reported EISs with inorganic anions as well as those of pure HA and its aqueous solution. As a result, we have found that the enhanced stability of HA-based EISs is mainly due to the ionization and separation of HA molecules themselves. That is, H-HA, as an ionized product, is more molecularly stable than HA, with significantly strengthened covalent bonds. The separation of H-HA ions or HA molecules makes decomposition more difficult as decomposition initiation varies from bimolecular to unimolecular reactions of HA, with a significant increase in the energy barrier. We have, therefore, proposed a strategy for the stabilization of unstable systems, such as neutral N-rich energetic compounds, by ionization and separation to strengthen these systems and change the decomposition mechanism by increasing the energy barriers of trigger steps such that these barriers become more difficult to overcome, respectively.
高能离子盐（EISs）因其易于制备以及一些与中性分子的普通炸药相当的优异性能而备受广泛关注。羟胺（HA）被质子化或离子化为H-HA，并且由于这些EISs具有比具有相同阴离子的其他EISs更高的堆积密度以及更优异的爆轰性能，所以它更倾向于被引入EISs中以与几乎所有种类的阴离子形成基于HA的EISs。此外，相对于纯HA，基于HA的EISs的热稳定性显著增强。这种显著增强的热稳定性可以通过将H-HA去质子化变回HA来扩展HA的应用；然而，通过成盐稳定HA的机制仍不清楚。在此，我们采用热力学和动力学计算以及分子动力学模拟来揭示许多目前合成的基于HA的EISs以及一些先前报道的含有无机阴离子的EISs以及纯HA及其水溶液的热稳定性机制。结果，我们发现基于HA的EISs稳定性增强主要是由于HA分子自身的电离和分离。也就是说，H-HA作为一种离子化产物，比HA分子更稳定，其共价键显著增强。H-HA离子或HA分子的分离使得分解更加困难，因为分解起始从HA的双分子反应变为单分子反应，能垒显著增加。因此，我们提出了一种通过电离和分离来稳定不稳定体系（如中性富氮高能化合物）的策略，以强化这些体系并通过增加触发步骤的能垒来改变分解机制，从而使这些能垒分别更难被克服。
