环四甲撑四硝胺(HMX)结构和性质的DFT研究

用密度泛函理论(DFT)B3LYP方法,取6-31G基组,求得环四甲撑四硝胺分子的几何构型、电子结构、 IR谱和298～1200 K的热力学性质.全优化几何构型和电子结构均具有Ci对称性.在相邻原子之间以N-NO2键的Mulliken集居数最小,表明其间电子分布较少,预示其为热解和起爆的引发键.IR谱与实验结果良好相符.     

NO2, OH和OH-对环四甲撑四硝胺初始热解的影响

在密度泛函理论的(DFT)B3LYP/6-31g(d)水平上, 优化得到了环四甲撑四硝胺(β-HMX)及其与高氯酸铵(AP)裂解产物NO2、OH及OH-分别形成复合物的各种稳定构型, 计算了β-HMX及各复合物中最弱的N—NO2键解离能. 结果发现: β-HMX与NO2、OH结合后构型变化不是很大, 但对称性降低; β-HMX与OH-结合后, HMX构型发生较大变化, 原有的对称性明显遭到破坏. 计算表明: NO2易与HMX骨架环上亚甲基(—CH2—)中的H作用,“置换”出H而引发HMX的热解, 从而改变了HMX的初始分解通道; OH对HMX的N—NO2键解离影响不大, 而OH-与β-HMX结合后其N—NO2键解离能比β-HMX降低近200 kJ·mol-1, 表明OH-对其裂解有明显的促进作用. NO2、OH-的存在可使HMX的分解温度大大降低.     

Method optimization for quantitative analysis of octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) by liquid chromatography-electrospray ionization mass spectrometry

A simple, sensitive LC-ESI-MS method was optimized for quantitative analysis of octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) in environmental samples. Under negative ionization mode, HMX can form adduct ions with various organic acids and salts, including acetic acid, formic acid, propionic acid, ammonium nitrate, ammonium chloride, sodium nitrite, and sodium nitrate. Acetic acid was chosen as additive and the ion, [M + CH₃COO]⁻ with m/z = 355 was used for selective ion monitoring (SIM) in this study. Good sensitivity was achieved with low acetic acid concentration in the mobile phase and relatively low capillary temperature. The method detection limit was 0.78 pg for HMX in standard solution. Linearity (R² > 0.9998) was obtained at low concentrations (0.5-50 μg/L). This method has been used to determine HMX concentrations in water samples and lizard egg samples from an animal exposure study.     

Initial chemical events in shocked octahydro-1,3,5,7-tetranitro-1,3,5,7- tetrazocine: a new initiation decomposition mechanism

We have performed ab initio molecular dynamics simulations in conjunction with the multiscale shock technique to study the initial chemical processes of octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) under shock wave loading. The results show that the initial decomposition of shocked HMX is triggered by the N-O bond breaking and the ring opening. This will initiate many decomposition reactions and lead to the production of many small radicals at a moment. As the shock compression continues, these small radicals recombine to produce many large radicals and further form ring-shaped radicals. Then, these radicals begin to further decompose. It is also found that the system transiently produces a large number of metallic states under the shock compression. Our simulations thus suggest a new mechanism for the initial chemical processes of shocked HMX and provide fundamental insight into the initial mechanism at the atomistic level, which is of important implication for understanding and development of energetic materials.     

Detection of the cyclic nitramine explosives hexahydro-1,3,5-trinitro- 1,3,5-triazine (RDX) and octahydro- 1,3,5,7-tetranitro- 1,3,5,7-tetrazine (HMX) and their degradation products in soil environments

The cyclic nitramine explosives hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) and octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazine (HMX) were examined in field and microcosm soil samples to determine their patterns of degradation and environmental fates. A number of analytical techniques, including solid-phase microextraction with on-fiber derivatization, gas chromatography-mass spectrometry, gas chromatography with electron-capture detection, liquid chromatography-mass spectrometry, and micellar electrokinetic chromatography were required for the analyses. Two different classes of intermediates were detected, both of which lead ultimately to the formation of nitrous oxide (N2O) and carbon dioxide (CO2). The first class was identified as the nitroso derivatives formed by the sequential reduction of -NO2 functional groups. The second class of intermediates, which was favored at higher humidities and in the presence of anaerobic sludge amendments, consisted of ring cleavage products including bis-(hydroxymethyl)-nitramine and methylenedinitramine. Rye-grass (Lolium perenne) present in field samples was found to extract and accumulate HMX from soil without further degradation. In all cases (excepting the plant samples), the indigenous microbes or amended domestic anaerobic sludge consortia degraded the cyclic nitramine explosives eventually to produce N2O and CO2.     

Density functional theory studies of effects of boron replacement on the structure and property of RDX and HMX

In this study, based on two model nitramine compounds hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) and octahydro-1,3,5,7-tetranitro-1,3,5, 7-tetrazocine (HMX), two series of new energetic molecules were designed by replacing carbon atoms in the ring with different amounts of boron atoms, their structures and performances were investigated theoretically by the density functional theory method. The results showed that the boron replacement could affect the molecular shape and electronic structure of RDX and HMX greatly, and then would do harm to the main performance like the heat of formation, density, and sensitivity. However, the compound RDX-B2 is an exception; it was formed by replacing two boron atoms into the system of RDX and has the symmetric boat-like structure. Its oxygen balance (4.9%), density (1.91 g/cm³), detonation velocity (8.85 km/s), and detonation pressure (36.9 GPa) are all higher than RDX. Furthermore, RDX-B2 has shorter and stronger N NO₂ bonds than RDX, making it possesses lower sensitivity (45 cm) and better thermal stability (the bond dissociation energy for the N NO₂ bond is 204.7 kJ/mol) than RDX. Besides, RDX-B1 and HMX-B4 also have good overall performance; these three new molecules may be regarded as a new potential candidate for high energy density compounds.     

Liquid chromatography/electrospray ionization tandem mass spectrometry analysis of octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX)

A quantitative liquid chromatography/electrospray ionization tandem mass spectrometry (LC/ESI-MS/MS) method was developed for the analysis of the explosive, octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX). In negative ionization mode, HMX forms an acetate adduct ion [M + CH(3)COO](-), m/z 355, in the presence of a small amount of acetic acid in the mobile phase. The ESI collision-induced dissociation (CID) spectrum of m/z 355 was acquired and the transitions m/z 355 --> 147 and m/z 355 --> 174 were chosen for the determination of HMX in samples. Using this quantification technique, the method detection limit was 1.57 microg/L and good linearity was achieved in the range 5-500 microg/L. This method will help to unambiguously analyze environmentally relevant concentrations of HMX.     

New theoretically predicted RDX‐ and β‐HMX‐based high‐energy‐density molecules

Theoretically new high‐energy‐density materials (HEDM) in which the hydrogens on RDX and β‐HMX (hexahydro‐1,3,5‐trinitro‐1,3,5‐triazine and octahydro‐1,3,5,7‐tetranitro‐1,3,5,7‐tetrazocine, respectively) were sequentially replaced by (N NO₂)x functional groups were designed and evaluated using density functional theory calculations in combination with the Kamlet–Jacobs equations and an atoms‐in‐molecules (AIM) analysis. Improved detonation properties and reduced sensitivity compared to RDX and β‐HMX were predicted. Interestingly, the RDX and β‐HMX derivatives having one attached N NO₂ group [RDX‐(NNO₂)1 and HMX‐(NNO₂)1] showed excellent detonation properties (detonation velocities: 9.529 and 9.575 km·s⁻¹, and detonation pressures: 40.818 and 41.570 GPa, respectively), which were superior to the parent compounds. Sensitivity estimations obtained by calculating impact sensitivities and HOMO‐LUMO gaps indicated that RDX‐(NNO₂)1 and HMX‐(NNO₂)1 were less stable than RDX and HMX but more stable than any of the other derivatives. This method of sequential NNO₂ group attachment on conventional HEDMs offers a firm basis for further studies on the design of new explosives. Furthermore, the newly found structures may be promising candidates for better HEDMs.     

Enhanced extraction of octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) and hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) in the presence of sodium dodecyl sulphate and its application to environmental samples

A method for enhanced extraction of octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) and hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) from environmental samples is developed with the assistance of sodium dodecyl sulphate (SDS) surfactant. In this study, the concentration of SDS surfactant and other analytical parameters are optimized on a high-performance liquid chromatography-UV system. An isocratic flow of 1.0 mL/min with mobile phase acetonitrile-water; 70:30 (v/v) at 230 nm wavelength on a reverse-phase amide column is used for baseline separation of explosives and making calibration curves. The amount of recovered explosives from spiked soil and water samples are calculated. The limits of detection obtained for HMX and RDX standards are 1.5 and 3.8 ppb (S/N=3), respectively, which are much better than obtained by the Environmental Protection Agency method 8330. The recoveries are found to be enhanced by 1.7 and 1.6-fold with SDS solution as compared to water for HMX and RDX, respectively, from soil samples.     

Identification of octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) pyrolysis products by simultaneous thermogravimetric modulated beam mass spectrometry and time-of-flight velocity-spectra measurements

The pyrolysis products formed during the isothermal decomposition of HMX at 211°C are H₂O, HCN, CO, CH₂O, NO, N₂O, methylformamide, C₂H₆N₂O, octahydro-1-nitroso-3,5,7-trinitro-1,3,5,7-tetrazocine, and a nonvolatile residue. The temporal behaviors of these products during the decomposition are presented. The method for using time-of-flight (TOF) velocity spectra to assist mass-spectrometry measurements in identifying the different gaseous products formed from the pyrolysis of a material by determining the approximate molecular weights of the different gaseous products contributing to the different m/z values in the mass spectrum of the mixture is described. The ion fragmentation of HMX as a function of electron energy shows complete fragmentation of the HMX molecular ion for electron energies ≥ 12.4 eV. No fragments from the pyrolysis of HMX other than those mentioned above are observed.     

Intermolecular Vibration Energy Transfer Process in Two CL-20-Based Cocrystals Theoretically Revealed by Two-Dimensional Infrared Spectra

Inspired by the recent cocrystallization and theory of energetic materials, we theoretically investigated the intermolecular vibrational energy transfer process and the non-covalent intermolecular interactions between explosive compounds. The intermolecular interactions between 2,4,6-trinitrotoluene (TNT) and 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (CL-20) and between 1,3,5,7-tetranitro-1,3,5,7-tetrazocane (HMX) and CL-20 were studied using calculated two-dimensional infrared (2D IR) spectra and the independent gradient model based on the Hirshfeld partition (IGMH) method, respectively. Based on the comparison of the theoretical infrared spectra and optimized geometries with experimental results, the theoretical models can effectively reproduce the experimental geometries. By analyzing cross-peaks in the 2D IR spectra of TNT/CL-20, the intermolecular vibrational energy transfer process between TNT and CL-20 was calculated, and the conclusion was made that the vibrational energy transfer process between CL-20 and TNTII (TNTIII) is relatively slower than between CL-20 and TNTI. As the vibration energy transfer is the bridge of the intermolecular interactions, the weak intermolecular interactions were visualized using the IGMH method, and the results demonstrate that the intermolecular non-covalent interactions of TNT/CL-20 include van der Waals (vdW) interactions and hydrogen bonds, while the intermolecular non-covalent interactions of HMX/CL-20 are mainly comprised of vdW interactions. Further, we determined that the intermolecular interaction can stabilize the trigger bond in TNT/CL-20 and HMX/CL-20 based on Mayer bond order density, and stronger intermolecular interactions generally indicate lower impact sensitivity of energetic materials. We believe that the results obtained in this work are important for a better understanding of the cocrystal mechanism and its application in the field of energetic materials.     

Dissociative Electron Attachment to the Nitroamine HMX (Octahydro-1,3,5,7-Tetranitro-1,3,5,7-Tetrazocine)

In the present study, dissociative electron attachment (DEA) measurements with gas phase HMX, octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine, C₄H₈N₈O₈, have been performed by means of a crossed electron-molecular beam experiment. The most intense signals are observed at 46 and 176 u and assigned to NO₂ ^? and C₃H₆N₅O₄ ^?, respectively. Anion efficiency curves for 15 negatively charged fragments have been measured in the electron energy region from about 0–20 eV with an energy resolution of ~0.7 eV. Product anions are observed mainly in the low energy region, near 0 eV, arising from surprisingly complex reactions associated with multiple bond cleavages and structural and electronic rearrangement. The remarkable instability of HMX towards electron attachment with virtually zero kinetic energy reflects the highly explosive nature of this compound. Substantially different intensity ratios of resonances for common fragment anions allow distinguishing the nitroamines HMX and royal demolition explosive molecule (RDX) in negative ion mass spectrometry based on free electron capture.      

Potentiometric microdetermination of 1,3,5-trinitro-1,3,5-triazacyclohexane and 1,3,5,7-tetranitro-1,3,5,7-tetrazacyclooctane in several solvents

Pyridine, tetramethylguanidine, and hexamethylphosphoramide were evaluated as solvents for the microdetermination of two weakly acidic compounds of ordnance interest, 1,3,5-trinitro-1,3,5-triazacyclohexane (RDX) and 1,3,5,7-tetranitro-1,3,5,7-tetrazacyclooctane (HMX). The titrant was tetrabutylammonium hydroxide in methanol/ toluene. Endpoints were determined potentiometrically by a glass/modified calomel electrode system or by two polarized platinum electrodes.The largest potentiometric break was found in the very basic solvent tetramethylguanidine. Endpoint detection using two polarized platinum electrodes significantly enhanced the precision of the analysis.     

1,3,5,7-四乙酰基-1,3,5,7-四氮杂环辛烷合成反应中间体的制备分离

1,3,5,7-四乙酰基-1,3,5,7-四氮杂环辛烷(TAT)是高能炸药奥克托今(HMX)重要的合成反应前体之一,1,5-二乙酰基-1,3,5,7-四氮杂环辛烷(DAPT)醋酐酰解法和乙腈甲醛小分子缩合法均能制备得到TAT.采用半制备高效液相色谱制备分离了上述两种制备方法反应原液中的六种中间体,分别是1-乙酰氧甲基-3,5,7-三乙酰基-1,3,5,7-四氮杂环辛烷、1,3,5-三乙酰基-1,3,5,7-四氮杂环辛烷、1-乙酰氧甲基-3,5,7-三乙酰基-1,3,5,7-四氮杂环辛烷、N,N’-亚甲基二乙酰胺、三乙酰胺二亚甲基三胺和四乙酰胺三亚甲基四胺,为反应机理研究提供了有力的证据.DAPT醋酐酰解法反应原液样品的最佳制备色谱条件为:正相硅胶柱(20 mm×250 mm,10～20μm),流动相:V(乙腈)∶V(甲醇)=95∶5,流速为10 mL·min-1,检测波长为215 nm,进样量为1 mL,样品浓度30 mg/mL.乙腈甲醛小分子缩合法反应原液样品的最佳制备色谱条件为:正相硅胶柱(20 mm×250 mm,10～20μm),流动相:V(乙腈)∶V(水)=90∶10,流速为10 mL·min-1,检测波长为215 nm,进样量为1 mL,样品浓度30 mg/mL.制备得到的中间体经HPLC分析知纯度均在97%以上,可直接作为结构鉴定的标准样品.     

高能混合物的感度理论判别—— 不同配比和不同温度AP/HMX的MD研究

为了寻求高能复合材料的感度理论判据, 对高氯酸铵(AP)和HMX(环四甲撑四硝胺)所构成的不同质量比的二元混合体系, 用分子动力学(MD)方法和修正的PCFF力场, 作正则系综(NVT)下的周期性模拟计算, 求得其结合能和HMX热解引发键(N—NO2)的平均键长和最大键长. 结果表明, 结合能随质量比不同呈复杂变化趋势; HMX(N—NO2)引发键的最大键长随体系中HMX配比增加先增后减, 而当AP/HMX为1∶1时其值最大, 恰与此配比下感度最大的实验事实相一致. 选择质量比为1∶1的AP/HMX作不同温度下的NVT-MD模拟, 发现引发键(N—NO2)最大键长随温度升高而递增, 与感度随温度升高而增大的实验事实相符. 为此我们建议, 把高能复合材料中易爆燃组分引发键的最大键长作为其热和撞击等感度的理论判据, 借以阐明、比较或预示它们的相对安全性.     

Development of an extraction and cleanup procedure for a liquid chromatographic-mass spectrometric method to analyze octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine in eggs

An efficient sample extraction and cleanup method was developed for determination of octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) in eggs. The procedure included solvent extraction of HMX from eggs followed by cleanup using florisil and styrene-divinylbenzene (SDB) cartridges. Homogenized egg aliquots were thoroughly mixed with 10 mL acetonitrile and extracted with ultrasonication for 1 h. Each sample was centrifuged and all liquid was collected for cleanup. After concentration by N₂ evaporation, each extract was cleaned by florisil and SDB cartridges to remove endogenous interfering compounds. Finally, each extract was filtered through a 0.2 μm PTFE membrane and stored for liquid chromatographic-mass spectrometric (LC-MS) analysis. Chromatographic separation was achieved on a reverse phase (RP) C18 column, with a mobile phase containing 60% methanol + 40% 1.0 mM acetic acid aqueous solution. Acetic acid was employed as mobile phase additive to form negatively charged adduct ions [M + CH₃COO]⁻, and m/z = 355 was quantified by selective ion monitoring (SIM). Overall recoveries from eggs containing 10, 50, 250 and 1000 ng/g of HMX were 84.0%, 88.0%, 90.6% and 87.4%. A method detection limit (MDL) of 0.15 ng/g was achieved.     

Intermolecular interactions,thermodynamic properties,crystal structure,and detonation performance of HMX/NTO cocrystal explosive

Previous studies have shown that the design of cocrystal explosives is one of the most promising approaches to decrease the sensitivity and maintain the detonation performance of existing explosives. As is well‐known, octahydro‐1,3,5,7‐tetranitro‐1,3,5,7‐tetrazocine (HMX) is a high energy density material (HEDM). But the application of HMX is limited, due to its high sensitivity. Thus, an insensitive explosive 5‐nitro‐1,2,4‐triazol‐3‐one (NTO) is proposed as a cocrystal former (CCF) to cocrystallize with HMX in the present work. The binding energies, heat of formations (HOFs), thermodynamic properties, atoms in molecules, and natural bond orbital analysis of four HMX/NTO complexes have been calculated using density functional theory methods, including meta‐hybrid functional (M062X) and dispersion‐corrected density functionals (B97D, ωB97XD). In addition, the crystal structure of HMX/NTO cocrystal has been investigated using Monte Carlo simulation and first principles methods. The HMX/NTO cocrystal is most likely to crystallize in triclinic crystal system with P1 space group, and corresponding cell parameters are Z = 2, a = 9.06 Å, b = 8.19 Å, c = 10.27 Å, α = 81.94^°, β = 98.42^°, γ = 82.03^°, and ρ = 1.92 g/cm³. The detonation velocity and detonation pressure of HMX/NTO cocrystal are 8.73 km/s and 35.14 GPa, respectively, a little lower than those of HMX. Finally, bond dissociation energies (BDEs) of the weakest trigger bond in HMX/NTO complexes are calculated. The results show that HMX/NTO complexes are thermally stable and meet the thermal requirement of HEDMs (BDE > 120 kJ/mol). © 2012 Wiley Periodicals, Inc.     

Solid phase microextraction-high performance liquid chromatographic determination of octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) and hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) in the presence of sodium dodecyl sulfate surfactant

A simple and sensitive method has been developed using preconcentration technique solid phase microextraction (SPME) and analytical technique HPLC-UV for the determination of octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) and hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) from the environmental samples. Aqueous solution of anionic surfactant SDS was used for the extraction of both nitramine high explosives, viz., HMX and RDX from soil samples which were subsequently sorbed on SPME fiber. The static desorption was carried out in the desorption chamber of the SPME-HPLC interface in the presence of mobile phase ACN/methanol/water (30:35:35) and the subsequent chromatographic analysis at a flow rate of 0.5 mL/min and detection at 230 nm. For this purpose, a C(18), 5 microm RP analytical column was used as a separation medium in this method. Several parameters relating to SPME, e.g., adsorption/desorption time, concentration of salt, stirring rate, etc., were optimized. The method was linear over the range of 20-400 ng/mL for HMX and RDX standards in the presence of surfactant in aqueous phase, respectively. The correlation coefficient (R(2)) for HMX and RDX are 0.9998 and 0.9982, respectively. With SPME, the detection limits (S/N = 3) in ng/mL are 0.05 and 0.1 for HMX and RDX, respectively in the presence of the SDS surfactant. The developed method has been applied successfully to the analysis of real environmental samples like bore well water, river water, and ground alluvial soil.     

Structural studies on some 1,3,5,7-tetraazabicyclo-[3.3.1]-nonane derivatives

From a study of the ¹H NMR spectra of a number of 3,7-disubstituted derivatives of 1,3,5,7-tetraazabicycio - [3.3.1] - nonane it is concluded that these molecules exist in either chair-chair or flattened chair-chair conformations. The derivatives containing COCH₃ and NO substitutents have room temperature spectra consistent with restricted rotation about their NC and NN bonds respectively. High temperature spectra reveal an activation energy, for the rotational barrier of the NC bond in the diacetyl derivative, of 23±2K.Cal/mol.     

Anharmonic vibrational properties of explosives from temperature-dependent Raman

Raman spectra from 50 to 3500 cm(-1) and 4-296 K are analyzed for molecular crystal powders of the explosives pentaerythritol tetranitrate (PETN), beta-octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX), and 1,3,5-triamino-2,4,6-trinitrobenzene (TATB) and the inert naphthalene. Temperature-dependent Raman spectroscopy is utilized for its sensitivity to anharmonic couplings between thermally populated phonons and higher frequency vibrations relevant to shock up-pumping. The data are analyzed with anharmonic perturbation theory, which is shown to have significant fundamental limitations in application to real data. Fitting to perturbation theory revealed no significant differences in averaged anharmonicities among the three explosives, all of which exhibited larger averaged anharmonicities than naphthalene by a factor of 3. Calculations estimating the multiphonon densities of states also failed to correlate clearly with shock sensitivity. However, striking differences in temperature-dependent lifetimes were obvious: PETN has long lived phonons and vibrons, HMX has long lived phonons but short lived vibrons, while TATB has short lived phonons and vibrons at low temperature. Naphthalene, widely used as a model system, has significantly different anharmonicities and density of states from any of the explosives. The data presented suggest the further hypothesis that hindered vibrational energy transfer in the molecular crystals is a significant factor in shock sensitivity.