Unimolecular Decomposition Reactions of Picric Acid and Its Methylated DerivativesA DFT Study

To handle energetic materials safely, it is important to have knowledge about their sensitivity. Density functional theory (DFT) has proven a valuable tool in the study of energetic materials, and in the current work, DFT is employed to study the thermal unimolecular decomposition of 2,4,6-trinitrophenol (picric acid, PA), 3-methyl-2,4,6-trinitrophenol (methyl picric acid, mPA), and 3,5-dimethyl-2,4,6-trinitrophenol (dimethyl picric acid, dmPA). These compounds have similar molecular structures, but according to the literature, mPA is far less sensitive to impact than the other two compounds. Three pathways believed important for the initiation reactions are investigated at 0 and 298.15 K. We compare the computed energetics of the reaction pathways with the objective of rationalizing the unexpected sensitivity behavior. Our results reveal a few if any significant differences in the energetics of the three molecules, and thus do not reflect the sensitivity deviations observed in experiments. These findings point toward the potential importance of crystal structure, crystal morphology, bimolecular reactions, or combinations thereof on the impact sensitivity of nitroaromatics.为安全处理含能材料，掌握其感度特性至关重要。密度泛函理论（Density functional theory, DFT）已被证实为含能材料研究中的宝贵工具，本研究即采用该方法对2,4,6-三硝基苯酚（苦味酸，PA）、3-甲基-2,4,6-三硝基苯酚（甲基苦味酸，mPA）以及3,5-二甲基-2,4,6-三硝基苯酚（二甲基苦味酸，dmPA）的热单分子分解过程展开研究。上述化合物分子结构相似，但据文献记载，mPA的撞击感度远低于另外两种物质。本研究在0 K与298.15 K条件下，对三种被认为对引发反应至关重要的反应路径开展了探究。我们通过对比各反应路径的计算能量学数据，旨在阐释该反常的感度行为。研究结果显示，三种分子的能量学特征即便存在显著差异也寥寥无几，因此无法反映实验中观测到的感度差异。上述发现表明，晶体结构、晶体形貌、双分子反应或其组合，可能对硝基芳香族化合物的撞击感度具有重要影响。