Crystallization thermodynamics of 2,4(5)-dinitroimidazole in eleven pure solvents

2,4(5)-Dinitroimidazole(2,4(5)-DNI) is an important energetic material, and it is also an important precursor for the preparation of drugs and energetic materials. In this study, the solubility of 2,4(5)-DNI in eleven pure solvents(chlorobenzene, benzene, 1,2-dichloroethane, toluene, water, isopropyl alcohol,ethyl acetate, acetonitrile, methanol, 1,4-dioxane and acetone) were measured by using a dynamic test method from 278.15 K to 323.15 K under 101.1 kPa. Four solubility models were used to fit the experimental data, which were ideal model, modified Apelblat equation, polynomial empirical equation, and λh equation. Meanwhile, the relative average deviation and root-mean-square deviation between the experimental data and the fitted data were also calculated. Furthermore, the three thermodynamic parameters,i.e., dissolution enthalpy, dissolution entropy and Gibbs energy were obtained based on solubility data.Finally, the crude product of 2,4(5)-DNI was crystallized with acetone as solvent, and the purity of the crystalline product was greater than 99.5%.

2,4-DNI的研究进展

综述了高能不敏感单质炸药———2,4-二硝基咪唑的两种合成方法:2-硝基咪唑硝化法、1,4-二硝基咪唑(1,4-DNI)的热重排法;详细介绍了其热分解性能、晶体结构特征、爆炸性能、摩擦感度、撞击感度等方面的性能;简述了其在合成和含能材料方面的应用前景。

Theoretical predict structure and property of the novel CL-20/2,4-DNI cocrystal by systematic search approach

Cocrystallization integrates the merits of high energy and insensitivity between energetic molecules to obtain energetics with satisfying performance.However,how to obtain supramolecular synthons accurately and rapidly for predicting the structure and property of cocrystal remains a challenging problem.In this research,an efficient systematic search approach to predict CL-20/2,4-DNI cocrystal has been proposed that 2,4-DNI revolves around CL-20 with a stoichiometric ratio of 1:1 in accordance with the specified rules(hydrogen bond length:2.2-3.0 Å;search radius:6.5 Å;the number of hydrogen bond:1-3).Eight possible supramolecular synthons were obtained by combining quantum chemistry with molecular mechanics.Crystal structure prediction indicated that there are four structures in cocrystal,namely P21/c,P212121,Pbca and Pna21,and CL-20/2,4-DNI cocrystal is likely to be P21/c and the corresponding cell parameters are Z=4,a=8.28 Å,b=12.17 Å,c=20.42 Å,α=90°,β=96.94°,γ=90°,and ρ=1.9353 g/cm^(3).To further study the intermolecular interaction of CL-20/2,4-DNI cocrystal,a series of theoretical analyses were employed including intermolecular interaction energy,electrostatic potential(ESP),Density of State(DOS),Hirshfeld surface analysis.The C-H…O hydrogen bonds are demonstrated as the predominant driving forces in the cocrystal formation.The mechanical properties and detonation properties of CL-20/2,4-DNI cocrystal implies that the cocrystal shows better ductility and excellent detonation performances(9257 m/s,39.27 GPa)and can serve as a promising energetic material.Cocrystal structure predicted was compared with the experimental one to verify the accuracy of systematic search approach.There is a less than 8.8%error between experiment and predict results,indicating the systematic search approach has extremely high reliability and accuracy.The systematic search approach can be a new strategy to search supramolecular synthons and identify structures effectively and does have the potential to promote the development of energetic cocrystal by theoretical design.

2,4-二硝基咪唑热分解机理的理论研究

运用密度泛函理论在B3LYP/6-311G(d,p)水平上计算了2,4-二硝基咪唑(2,4-DNI)的几何结构。基于自然键轨道理论,分析了Wiberg键级、Mulliken电荷和NBO电荷,进而得到各键的中点静电势。运用了从头算分子动力学(AIDM)方法对2,4-DNI分子的热分解轨迹进行模拟,并以B3LYP/6-311G(d,p)方法计算的反应能垒为依据,计算了硝基断裂和异构化反应在400~4000 K下的速率常数。结果表明:2,4-DNI主要起始热分解方式是C-NO_(2)断裂;异构化反应在热力学上是允许可行的,但动力学却难以进行;2,4-DNI分解生成的NO_(2)对其热分解会产生影响。