Comprehensive assessment of physicochemical properties of new energetic materials

The review presents original methodological approaches and summarizes the results of research into the assessment of relationships between the structure of energetic organic compounds and their main physicochemical properties. A large number of experimental values of these parameters were statistically analyzed, and a database of the properties of explosives and rocket propellant ingredients was created. Based on the analysis and integration of these data, approaches were developed to evaluate the fundamental properties of energetic compounds of different chemical classes, such as the enthalpy of formation, the molecular crystal density, and the sensitivity to mechanical impacts. The explosive and ballistic characteristics were calculated. The comprehensive assessment was made of the possible applications of new substances and those poorly characterized by experimental methods.     

Qualitative estimation of the dependence of the number of energetic compounds on their oxygen coefficient

The ratio between the numbers of structural formulas of C,H,N,O-containing energetic compounds belonging to the classes of fuels (low values of the oxygen coefficientA), explosives (mediumA), and oxidants (highA values) was studied by a computer generation procedure. The number of the theoretically possible structural formulas was found to decrease rapidly on going from fuels to explosives and then to oxidants; this observation agrees with the data on the numbers of various energetic compounds currently used and proposed. The strategy of the search for new compounds with the specified properties is described in brief, and its applicability to the search for explosives and oxidants with a small (up to 12) number of atoms in a molecule is evaluated. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1304–1310, July, 1998.     

Assessment of the Strength of Energetic Compounds Through the Trauzl Lead Block Expansions Using Their Molecular Structures

The strength of energetic materials can be expressed as the expansion of the cavity of a standard lead block through explosion of the sample. A new method is introduced for prediction of the Trauzl lead block expansions for some of the important classes of pure and mixture of energetic compounds, with the general formula of C_aH_bN_cO_d. This model needs only the molecular structure of the energetic materials without using the detonation characteristics of different explosives. The model uses the ratios of the number of carbon to oxygen (a/d) and hydrogen to oxygen atoms (b/d). The effects of intra‐ and intermolecular interactions are applied to the model by assignment of some correcting parameters upon considering certain molecular fragments. This model gives more reliable results with respect to three of the best available methods.     

Reliable Prediction of Shock Sensitivity of Energetic Compounds based on Small‐scale Gap Test through Their Electric Spark Sensitivity

The sensitivity of an energetic compound gives its vulnerability to accidental detonation, which is caused by an unintended stimulus. Shock and electric spark sensitivities of energetic compounds are two important sensitivity parameters for assessment of their safety in working places. Several correlations are introduced for reliable prediction of shock sensitivities of energetic compounds at 90, 95, and 98 % of theoretical maximum density (TMD) according to NSWC using Navy small‐scale gap test through their electric spark sensitivities. For 11 explosives, where experimental data of both shock and electric spark sensitivities were available, the predicted results at 90 % of TMD are compared with the quantum mechanical approach. The root‐mean‐square (rms) deviations of the new and complex quantum mechanical methods at 90 % TMD are 2.38 and 3.95 kbar, respectively, which confirmed the high reliability of the new method. For high explosives with 90, 95, and 98 % TMD, it will be shown that the predicted results of the new method are also much more reliable than one of the best available empirical approaches. A correlation between shock sensitivities on the basis of aluminum gaps with different thicknesses and the pressure required to initiate material pressed to 90 % TMD is also derived.     

Methylated Azoles, 2‐Tetrazenes,and Hydrazines

This report is a summary of our work on energetic materials. Herein, triazole‐, tetrazole‐, 2‐tetrazene‐ and hydrazine‐based energetic compounds are described. An overview of the synthetic methods and of the problematic around the quest of new explosives is given. Hydrogen‐bonding formation and alkylation (methylation) reactions were studied as a mean to decrease the sensitivities towards classical stimuli and increase their thermal and chemical stability. ¹⁵N NMR spectroscopy is a valuable tool for the assignment of the methylation site in keeping with the results of the crystal structure analysis. Lastly, the thermal/chemical stability, sensitivity data and energetic performance of the compounds is described.     

Molecular design of all nitrogen pentazole‐based high energy density compounds with oxygen balance equal to zero

We designed a new family of pentazole‐based high energy density compounds with oxygen balance equal to zero by introducing −NH₂, −NO₂, −N₃, −CF₂NF₂, and −C[NO₂]₃, and the properties including density, heats of formation, detonation performances, and impact sensitivity were investigated using density functional theory. The results show that half of these new energetic molecules exhibit higher densities than RDX (1.82 g/cm³), in which H5 gives the highest density of 2.09 g/cm³. Among all the 54 designed molecules, 22 compounds have higher D and P than RDX and eleven compounds have higher D and P than HMX, indicating that designing the pentazole‐based derivatives with oxygen balance equal to zero is a very effective way to obtain potential energetic compounds with outstanding detonation properties. Taking both the detonation performance and stability into consideration, nine compounds may be recognized as potential candidates of high energy density compounds. It is expected that our results will contribute to the theoretical design of new‐generation energetic explosives.     

Structural,thermochemical and detonation performance of derivatives of 1,2,4,5-tetrazine and 1,4 <Emphasis Type="Italic">N</Emphasis>-oxide 1,2,4,5-tetrazine as new high-performance and nitrogen-rich energetic materials

In this study, density functional theory calculations are used to estimate enthalpy of sublimation, enthalpy of formation and crystal density of some important derivatives of 1,2,4,5-tetrazine and 1,4 N-oxide 1,2,4,5-tetrazine. These data were used for predicting their detonation properties including heat of detonation, detonation pressure, detonation velocity, detonation temperature, spark sensitivity, deflagration temperature and power of energetic using appropriate methods. The results show that the title compounds exhibit high positive solid-phase enthalpy of formation. It is found that detonation pressure and detonation velocity of these compounds are high because of the large values of crystal density and solid-phase enthalpy of formation. Detonation temperature and spark sensitivity of some derivatives are higher than octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine as one of the high-performance explosives.     

1,1′‐Nitramino‐5,5′‐bitetrazoles

1,1′‐Dinitramino‐5,5′‐bitetrazole and 1,1′‐dinitramino‐5,5′‐azobitetrazole were synthesized for the first time. The neutral compounds are extremely sensitive and powerful explosives. Selected nitrogen‐rich salts were prepared to adjust sensitivity and performance values. The compounds were characterized by low‐temperature X‐ray diffraction, IR and Raman spectroscopy, multinuclear NMR spectroscopy, elemental analysis, and DTA/DSC. Calculated energetic performances using the EXPLO5 code based on calculated (CBS‐4M) heats of formation and X‐ray densities support the high performances of the 1,1′‐dinitramino‐5,5′‐bitetrazoles as energetic materials. The sensitivities toward impact, friction, and electrostatic discharge were also explored. Most of the compounds show sensitivities in the range of primary explosives and should only be handled with great care!     

三、四唑高能离子盐的研究概况

为满足火炸药等领域对多功能含能材料的需求,高生成焓、高密度、钝感、稳定和环境友好的三、四唑高能离子盐的研究受到广泛关注。 本文综述了10年来三唑和四唑高能离子盐的合成及性能研究概况,为含能离子盐的研究提供参考。     

Collision cross section measurement and prediction methods in omics

Omics studies such as metabolomics, lipidomics, and proteomics have become important for understanding the mechanisms in living organisms. However, the compounds detected are structurally different and contain isomers, with each structure or isomer leading to a different result in terms of the role they play in the cell or tissue in the organism. Therefore, it is important to detect, characterize, and elucidate the structures of these compounds. Liquid chromatography and mass spectrometry have been utilized for decades in the structure elucidation of key compounds. While prediction models of parameters (such as retention time and fragmentation pattern) have also been developed for these separation techniques, they have some limitations. Moreover, ion mobility has become one of the most promising techniques to give a fingerprint to these compounds by determining their collision cross section (CCS) values, which reflect their shape and size. Obtaining accurate CCS enables its use as a filter for potential analyte structures. These CCS values can be measured experimentally using calibrant-independent and calibrant-dependent approaches. Identification of compounds based on experimental CCS values in untargeted analysis typically requires CCS references from standards, which are currently limited and, if available, would require a large amount of time for experimental measurements. Therefore, researchers use theoretical tools to predict CCS values for untargeted and targeted analysis. In this review, an overview of the different methods for the experimental and theoretical estimation of CCS values is given where theoretical prediction tools include computational and machine modeling type approaches. Moreover, the limitations of the current experimental and theoretical approaches and their potential mitigation methods were discussed.     

A New Method for Predicting Decomposition Temperature of Imidazolium‐based Energetic Ionic Liquids

Two novel correlations are introduced to predict decomposition temperatures of imidazolium‐based energetic ionic liquids. The first simple model is based only on the number of some of atoms in cationic and anionic structures. Meanwhile, a suitable correction term was added in the second correlation to adjust the predicted results for the presence of some specific cation/anion moieties. The measured data of 164 different types of imidazolium‐based energetic ionic liquids were used to derive the new correlations. The calculated mean absolute percent errors (MAPEs) of the first and second models are 6 and 4, respectively. The predicted results have confirmed that insertion of correcting function in the second correlation can provide better estimations. These models were also tested and compared with one of the best available group contribution methods, where group contribution method can be applied, for 17 further imidazolium‐based energetic ionic liquids containing complex molecular structures. Furthermore, the predicted values of MAPEs of the new models are close to that of obtained by group contribution method.     

Chelate Coordination Compounds as a New Class of High-Energy Materials: The Case of Nitro-Bis(Acetylacetonato) Complexes

The existence of areas of strongly positive electrostatic potential in the central regions of the molecular surface of high-energy molecules is a strong indicator that these compounds are very sensitive towards detonation. Development of high-energy compounds with reduced sensitivity towards detonation and high efficiency is hard to achieve since the energetic molecules with high performance are usually very sensitive. Here we used Density Functional Theory (DFT) calculations to study a series of bis(acetylacetonato) and nitro-bis(acetylacetonato) complexes and to elucidate their potential application as energy compounds with moderate sensitivities. We calculated electrostatic potential maps for these molecules and analyzed values of positive potential in the central portions of molecular surfaces in the context of their sensitivity towards detonation. Results of the analysis of the electrostatic potential demonstrated that nitro-bis(acetylacetonato) complexes of Cu and Zn have similar values of electrostatic potential in the central regions (25.25 and 25.06 kcal/mol, respectively) as conventional explosives like TNT (23.76 kcal/mol). Results of analysis of electrostatic potentials and bond dissociation energies for the C-NO₂ bond indicate that nitro-bis(acetylacetonato) complexes could be used as potential energetic compounds with satisfactory sensitivity and performance.     

Energetic materials based on poly furazan and furoxan structures

Furazan and furoxan represent fascinating explosophoric units with intriguing structures and unique properties. Compared with other nitrogen-rich heterocycles, most poly furazan and furoxan-based heterocycles demonstrate superior energetic performances due to the higher enthalpy of formation and density levels. A large variety of advanced energetic materials have been achieved based on the combination of furazan and furoxan moieties with different kinds of linkers and this review provides an overview of the development of energetic poly furazan and furoxan structures during the past decades, with their physical properties and detonation characteristics summarized and compared with traditional energetic materials. Various synthetic strategies towards these compact energetic structures are highlighted by covering the most important cyclization methods for construction of the hetercyclic scaffolds and the following modifications such as nitrations and oxidations. Given the synthetic availabilities and outstanding properties, energetic materials based on poly furazan and furoxan structures are undoubtedly listed as a promising candidate for the development of new-generation explosives, propellants and pyrotechnics.     

Thermal decomposition properties and compatibility of CL-20, NTO with silicone rubber

The new polycyclic nitramine 2,4,6,8,10,12-hexanitrohexaazaisowurtzitane (HNIW) has been focused as a considerable amount of research recently on investigating its polymorphs, relative stability, and respective reaction chemistry. It is known as CL-20 popularly, CL-20 is a very high-energy and relatively high oxygen balance value crystalline compound whose method of synthesis and detailed performance data are still classified. 5-oxo-3-nitro-1,2,4-triazole (NTO, or nitrotriazolone) was an insensitive molecule comparison general explosives, and the NTO based polymer bonded explosives (PBX) was a low vulnerability explosive. Both energetic materials are all very important high explosives, which is used in a variety of military formulations widely owing to the properties of high energy and desensitization of PBX, many researchers have demonstrated the usefulness of above two energetic materials in explosive component. In this work, the thermal decomposition characteristics of explosives CL-20 and NTO were studied using thermal analytical techniques (TG, DSC), then the compatibility of above two explosives with silicone rubber, and the decomposition kinetic parameters such as activation energies of decomposition, the frequency factor of the decompose reaction are also evaluated by non-isothermal DSC techniques.     

High-pressure studies of pharmaceutical compounds and energetic materials

The effects of high pressure on pharmaceutical compounds and energetic materials can have important implications for both the properties and performance of these important classes of material. Pharmaceutical compounds are frequently subjected to pressure during processing and formulation, causing interconversion between solid forms that may affect properties such as solubility and bio-availability. Energetic materials experience extremes of both pressure and temperature under conditions of detonation and deflagration, causing changes in properties such as sensitivity to shock and chemical reactivity. This tutorial review outlines the various methods used to study these materials at high pressure, describes how pressure can be used to explore polymorphism, and provides examples of compounds that have been studied at high pressure.     

Simple relationship for predicting onset temperatures of nitro compounds in thermal explosions

Nitro compounds are capable of rapid chemical decompositions with a large amount of energy releases and hence pose significant thermal explosion hazards. Molecular simulation has been well established and demonstrated as an effective tool to predict physical and/or chemical properties of energetic materials, such as onset temperature, heat of reaction, and shock sensitivity. In this work, a simple relationship for predicting the onset temperature of nitro aromatic compounds containing other functional groups is developed based on their molecular structures. The results have shown that the thermal onset temperature of a specific nitro aromatic compound is strongly related to its excitation energy (a singlet state to triplet state). The predicted onset temperatures show very good agreement with respect to the measured onset temperatures by differential scanning calorimetry. Deviations compared to the experimental values are very small. These correlations can be used to computationally screen new nitro compounds for their thermal explosion hazards. These correlations can also be applied as a preliminary thermal analysis method and expedite the evaluation process of new energetic materials.     

RDX基PBX的模型、结构、能量及其与感度关系的分子动力学研究

以RDX（环三亚甲基三硝胺）为基、PS（聚苯乙烯）为粘结剂构成PBX（高聚物粘结炸药）的MD（分子动力学）模拟初始模型.比较分别以1根46链节和2根23链节PS置于RDX（001）晶面上的两种（PBX1和PBX2）模型下的MD模拟结果,发现二者的结构、相互作用能和力学性能均很接近.取PBX2进行5种温度（195,245,295,345和395 K）下的NPT系综、MD模拟系统研究,发现随温度依次升高,各体系中RDX引发键N NO2键的最大键长（Lmax）递增,N–N键连的N与N之间的双原子作用能（EN-N）和内聚能密度（CED）递减,与感度随温度升高而增大的实验事实相一致.综合已有工作,对高能复合材料（如PBX和固体推进剂等）的感度理论研究,建议关注其中易爆燃组分在外界刺激下的结构和能量变化,其引发键Lmax和作为引发键强度度量的双原子作用能（如EN-N）,可作为热和撞击感度相对大小的理论判据.     

A Facile and Versatile Synthesis of Energetic Furazan-Functionalized 5-Nitroimino-1,2,4-Triazoles

An analogue-oriented synthetic route for the formulation of furazan-functionalized 5-nitroimino-1,2,4-triazoles has been explored. The process was found to be straightforward, high yielding, and highly efficient, and scalable. Nine compounds were synthesized and the physicochemical and energetic properties, including density, thermal stability, and sensitivity, were investigated, as well as the energetic performance (e.g., detonation velocities and detonation pressures) as evaluated by using EXPLO5 code. Among the new materials, compounds 4 – 6 and 11 possess high densities, acceptable sensitivities, and good detonation performances, and thereby demonstrate the potential applications as new secondary explosives.     

Synthesis of 5‐Aminotetrazole‐1 N‐oxide and Its Azo Derivative: A Key Step in the Development of New Energetic Materials

1‐Hydroxy‐5‐aminotetrazole ( 1 ), which is a long‐desired starting material for the synthesis of hundreds of new energetic materials, was synthesized for the first time by the reaction of aqueous hydroxylamine with cyanogen azide. The use of this unique precursor was demonstrated by the preparation of several energetic compounds with equal or higher performance than that of commonly used explosives, such as hexogen (RDX). The prepared compounds, including energetic salts of 1‐hydroxy‐5‐aminotetrazole (hydroxylammonium ( 2 , two polymorphs) and ammonium ( 3 )), azo‐coupled derivatives (potassium ( 5 ), hydroxylammonium ( 6 ), ammonium ( 7 ), and hydrazinium 5,5′‐azo‐bis(1‐N‐oxidotetrazolate ( 8 , two polymorphs)), as well as neutral compounds 5,5′‐azo‐bis(1‐oxidotetrazole) ( 4 ) and 5,5′‐bis(1‐oxidotetrazole)hydrazine ( 9 ), were intensively characterized by low‐temperature X‐ray diffraction, IR, Raman, and multinuclear NMR spectroscopy, elemental analysis, and DSC. The calculated energetic performance, by using the EXPLO5 code, based on the calculated (CBS‐4M) heats of formation and X‐ray densities confirm the high energetic performance of tetrazole‐N‐oxides as energetic materials. Last but not least, their sensitivity towards impact, friction, and electrostatic discharge were explored. 5,5′‐Azo‐bis(1‐N‐oxidotetrazole) deflagrates close to the DDT (deflagration‐to‐detonation transition) faster than all compounds that have been investigated in our research group to date.     

New Correlation between Electric Spark and Impact Sensitivities of Nitramine Energetic Compounds for Assessment of Their Safety

Electric spark and impact sensitivities of nitramine energetic compounds are two important sensitivity parameters, which are closely related to many accidents in working places. For nitramines, in contrast to electric spark sensitivity, their impact sensitivity can be easily measured or predicted by various methods. A new approach is introduced to correlate electric spark and impact sensitivities of nitramine energetic compounds by the use of three structural parameters. The predicted results of the novel model for 20 nitramines are compared with two of the best available models, which are based on complex quantum mechanical approach and the measured values of activation energies of thermolysis. The root‐mean‐square (rms) and maximum deviations of the new model are 1.06 and 2.41 J, respectively. For further 14 nitramines, where the measured electric spark or impact sensitivities were not available, the estimated electric spark sensitivities by the new model are close to those predicted based on experimental data of activation energies of thermolysis.