The densities of high energetic molecules in the solid state were calculated with a simplified scheme based on molecular surface electrostatic potentials (MSEP). The MSEP scheme for density estimation, originally developed by Politzer et al., was further modified to calculate electrostatic potential on a simpler van der Waals surface. Forty-one energetic molecules containing at least one nitro group were selected from among a variety of molecular types and density values, and were used to test the suitability of the MSEP scheme for predicting the densities of solid energetic molecules. For comparison purposes, we utilized the group additivity method (GAM) incorporating the parameter sets developed by Stine (Stine-81) and by Ammon (Ammon-98 and -00). The absolute average error in densities from our MSEP scheme was 0.039 g/cc. The results based on our MSEP scheme were slightly better than the GAM results. In addition, the errors in densities generated by the MSEP scheme were almost the same for various molecule types, while those predicted by GAM were somewhat dependent upon the molecule types.
We have reinvestigated the synthesis of 1-methyl-2,4,5-trinitroimidazole (MTNI; 1), and further characterized its physical properties. It is a promising candidate as an insensitive high explosive. Compound 1 was synthesized from the imidazole (2), via a 5-step sequence of reactions, and subjected to various sensitivity tests for explosives. The structure of 1 was characterized by X-ray diffraction. The crystal is orthorhombic; C 4 H 3 N 5 O 6 , M = 217.11, Z = 8, Pca2 1, a = 8.6183(6) Å, b = 17.7119(12) Å, c = 10.6873(7) Å, V = 1631.38(19) Å 3 , Dc = 1.768 g/cm 3 . The structure was refined to R = 0.0284 for 3201 independent reflections with I > 2σ(I). The molecular structures calculated by high levels of ab initio and density functional theories were in good agreement with those observed by X-ray experiment. According to our preliminary sensitivity tests, 1 was characterized to be intermediate in sensitivity between RDX and TNT. The explosive performances were evaluated theoretically, and were found to be comparable to those of RDX. In addition, owing to its low melting point (82 °C), 1 is believed to be an excellent candidate for inclusion in melt-castable explosives, and may lead to increased explosive power.
We synthesized 4,4',5,5'-tetranitro-2,2'-bi-1H-imidazole (TNBI), which may serve as a new energetic filler for high explosive formulations. TNBI was synthesized by treating an excess amount of sodium nitrate with 2,2'-bi-1H-imidazole (BI), which was produced from glyoxal and ammonia gas. The overall synthetic yield was 32%. The synthesized TNBI was characterized by performing various chemical analyses including NMR, IR, and CHN analyses. Small scale sensitivity tests were carried out at both research institutes (ADD and ARDEC). The sensitivity results varied from more sensitive than RDX to substantially less sensitive than RDX according to the purity and conditions of the test samples. Based on our careful characterizations, this large variation in sensitivity was attributed to the moisture content that was present in the test samples due to a hygroscopic nature of TNBI. We also found that the hygroscopic nature of TNBI changed significantly due to the amount of impurities, especially sulfates.
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