N-Acetonitrile Functionalized Nitropyrazoles: Precursors to Insensitive Asymmetric N-Methylene-C Linked Azoles.

Properties of energetic compounds obtained by linking energetic pyrazoles to tetrazoles by means of N-methylene-C bridges can be fine-tuned. Reactions of pyrazole derivatives with chloroacetonitrile followed by conversion of the cyano group to tetrazole using click reactions in the presence of zinc chloride result in asymmetric N-methylene-C bridged azole-based energetic compounds. All the compounds were thoroughly characterized by IR and NMR [1 H, 13 C {1 H}, 15 N] spectroscopy, elemental analysis, and differential scanning calorimetry (DSC), and for two compounds, further supported by single-crystal X-ray diffraction studies. Heats of formation and detonation performances were calculated using Gaussian 03 and EXPLO5 v6.01 programs, respectively. Initial studies show that this new approach is promising for synthesizing less sensitive energetic compounds with fine-tuned properties.

Energetic Di- and Trinitromethylpyridines: Synthesis and Characterization.

Pyridine derivatives based on the addition of trinitromethyl functional groups were synthesized by the reaction of N2O4 with the corresponding pyridinecarboxaldoximes, then they were converted into dinitromethylide hydrazinium salts. These energetic compounds were fully characterized by IR and NMR spectroscopy, elemental analysis, differential scanning calorimetry (DSC), and X-ray crystallography. These pyridine derivatives have good densities, positive enthalpies of formation, and acceptable sensitivity values. Theoretical calculations carried out using Gaussian 03 and EXPLO5 programs demonstrated good to excellent detonation velocities and pressures. Each of these compounds is superior in performance to TNT, while 2,6-bis(trinitromethyl)pyridine (D = 8700 m·s-1, P = 33.2 GPa) shows comparable detonation performance to that of RDX, but its thermal stability is too low, making it inferior to RDX.

Fully C/N-Polynitro-Functionalized 2,2'-Biimidazole Derivatives as Nitrogen- and Oxygen-Rich Energetic Salts.

Through the use of a fully C/N-functionalized imidazole-based anion, it was possible to prepare nitrogen- and oxygen-rich energetic salts. When N,N-dinitramino imidazole was paired with nitrogen-rich bases, versatile ionic derivatives were prepared and fully characterized by IR, and 1 H, and 13 C NMR spectroscopy and elemental analysis. Both experimental and theoretical evaluations show promising properties for these energetic compounds, such as high density, positive heats of formation, good oxygen balance, and acceptable stabilities. The energetic salts exhibit promising energetic performance comparable to the benchmark explosive RDX (1,3,5-trinitrotriazacyclohexane).

Potassium 4,4'-Bis(dinitromethyl)-3,3'-azofurazanate: A Highly Energetic 3D Metal-Organic Framework as a Promising Primary Explosive.

Environmentally acceptable alternatives to toxic lead-based primary explosives are becoming increasingly important for energetic materials. In this study, potassium 4,4'-bis(dinitromethyl)-3,3'-azofurazanate, comprising two dinitromethyl groups and an azofurazan moiety, was synthesized and isolated as a new energetic 3D metal-organic framework (MOF). Several attractive properties, including a density of 2.039 g cm(-3) , a decomposition temperature of 229 °C, a detonation velocity of 8138 m s(-1) , a detonation pressure of 30.1 GPa, an impact sensitivity of 2 J, and friction sensitivity of 20 N make 4 a good candidate as a green primary explosive.

Energetic salts based on furazan-functionalized tetrazoles: routes to boost energy.

Based on the backbone of the furazan-tetrazole structure, routes were developed to improve the properties of energetic materials. Two types of high-density energetic salts were designed, prepared, and fully characterized. Single-crystal X-ray analyses support the structural characteristics for two amino salts. A majority of the salts exhibited good detonation properties, high thermal stabilities, and relatively low impact and friction sensitivities. Hydroxylammonium and hydrazinium salts, 1-3 and 1-4, which have relatively high densities (1.84 and 1.74 g cm(-3,) , respectively), acceptable impact and friction sensitivities (14 J, 160 N and 28 J, 360 N), and good detonation pressures (38.3 and 32.2 GPa) and velocities (9323 and 9094 m s(-1) ), have performance properties superior to 1,3,5-trinitro-1,3,5-triazinane (RDX) and triaminotrinitrobenzene (TATB).

Combination of 1,2,4-Oxadiazole and 1,2,5-Oxadiazole Moieties for the Generation of High-Performance Energetic Materials.

Salts generated from linked 1,2,4-oxadiazole/1,2,5-oxadiazole precursors exhibit good to excellent thermal stability, density, and, in some cases, energetic performance. The design of these compounds was based on the assumption that by the combination of varying oxadiazole rings, it would be possible to profit from the positive aspects of each of the components. All of the new compounds were fully characterized by elemental analysis, IR spectroscopy, (1)H, (13)C, and (in some cases) (15)N NMR spectroscopy, and thermal analysis (DSC). The structures of 2-3 and 5-1⋅5 H2O were confirmed by single-crystal X-ray analysis. Theoretical performance calculations were carried out by using Gaussian 03 (Revision D.01). Compound 2-3, with its good density (1.85 g cm(-3)), acceptable sensitivity (14 J, 160 N), and superior detonation pressure (37.4 GPa) and velocity (9046 m s(-1)), exhibits performance properties superior to those of 1,3,5-trinitroperhydro-1,3,5-triazine (RDX).

Energetic Materials with Promising Properties: Synthesis and Characterization of 4,4'-Bis(5-nitro-1,2,3-2H-triazole) Derivatives.

Using a variety of functionalization strategies, derivatives of 4, 4'-bis(5-nitro-1,2,3-2H-triazole) were designed, synthesized, and characterized. The isomers were separated, their structures were confirmed with single-crystal X-ray analysis, and their properties were determined by differential scanning calorimetry, density, impact sensitivity, heat of formation, and detonation velocity and pressure (calculated by EXPLO5 V6.01). Those materials were found to exhibit superior detonation performance when compared with the other fully carbon-nitrated bis(azoles).

Theoretical study of a series of 1,2-diazete based trinitromethyl derivatives as potential energetic compounds.

CONTEXT: Explosive properties of novel potential high energy density materials of a series of 1,2-diazete-based molecules with trinitromethyl functional group were investigated computationally. All the sixty seven molecules were optimised to obtain their molecular geometries and electronic structures. Electrostatic potential analysis was also carried out in the determination of different parameters. The calculations indicate that the majority of the compounds have high positive heat of formations, high density and good detonation performance greater than that of traditional energetic materials like RDX and HMX. They are also having comparable values of impact sensitivity. These features promise their potential to be used as energetic materials for future applications. Most of the designed molecules are having high positive oxygen balance values so that the study of these molecules can also be extended as potential candidates for oxidisers in solid propellants. METHODS: Optimisation and vibrational frequency analysis of the studied molecules were done with density functional theory using B3LYP/aug-cc-pVDZ as the basis set to zero imaginary frequencies using Gaussian 09. Electrostatic potential analysis were carried using the Multiwfn program.

Lithium-Promoted Formation of M-2AZTO-Li (M = N2H5+ or NH3OH+ and AZTO = Anion of 1-Hydroxytetrazole-5-hydrazide)-Type "Quaternary" Complexes with Nitrogen-Rich Characteristics: Construction of Novel Insensitive Energetic Materials.

Lithium-based nitrogen-rich complexes are important research objects in the field of high-energy materials. However, the weak coordination abilities of lithium ions relative to those of other metal ions with greater atomic numbers have hindered their applications in the field of nitrogen-rich complexes. Herein, we successfully prepared novel lithium-based nitrogen-rich complexes (N2H5-2AZTO-Li and NH3OH-2AZTO-Li) by exploiting the structural properties of 1-hydroxytetrazolium-5-hydrazine (HAZTO). Both N2H5-2AZTO-Li and NH3OH-2AZTO-Li were found to exhibit physicochemical parameters (including the density, stability, and energetic properties) that were intermediate between those of the simple ionic compounds (3 and 4) and the complexes (5) that formed them, enabling a favorable balance between high energy, high stability, and environmental friendliness (for N2H5-2AZTO-Li: detonation velocity (D) = 9005 m s-1, detonation pressure (P) = 35.5 GPa, decomposition temperature (Tdec) = 238.1 °C, impact sensitivity (IS) = 24 J, friction sensitivity (FS) = 210 N, and detonation product (DP) (CO) < 2%; for NH3OH-2AZTO-Li: D = 9028 m s-1, P = 35.7 GPa, Tdec = 211.2 °C, IS = 20 J, FS = 180 N, and DP (CO) < 2%). This study transcends the conventional structural forms of nitrogen-rich complexes, opening new horizons for the design of novel insensitive energetic materials.

Molecular design and theoretical study of oxadiazole-bifurazan derivatives.

CONTEXT: The design and synthesis of new high energy density materials is an important part of the research in the field of high energy materials. However, the synthesis of high-energy materials is very difficult and dangerous. Therefore, it is necessary to design the compounds in advance and evaluate the performance of the designed compounds, so as to screen the high-energy candidate compounds with excellent performance and provide reference for future synthesis and application. 1,2,5-oxadiazole (furazan) and 1,2,4-oxadiazole are five-membered nitrogen-oxygen heterocycles. Because their structures contain high-energy N-O, C=N bonds, they can effectively improve the energy density and oxygen balance of compounds, which has attracted widespread attention. In this paper, 42 kinds of oxadiazole-bifurazan energetic derivatives were designed by inserting different functional groups and changing the parent bridging groups with 1,2,4-oxadiazole and furazan as the basic structural units. Their electronic structures, aromaticity, heats of formation (HOFs), detonation properties, thermodynamic properties and electrostatic potential were systematically studied by density functional than theory (DFT). The results show that -C (NO2)3 has the greatest improvement effect on HOFs among all the substituent groups. The detonation performance of -N=N- bridged oxadiazole-bifurazan derivatives is better than that of -NH-NH- bridged derivatives. And -C(NO2)3 is the most effective group to improve the detonation performance and density of compounds. Compared with the parent compounds, when a -C(NO2)3 was introduced, the density increased by about 5.5%. A6 (D = 10.30 km·s-1, P = 48.86 GPa) and D6 (D = 9.57 km·s-1, P = 42.31 GPa) are the compounds with the best D and P among the designed compounds, which are higher than RDX and HMX, and are potential candidates for new high-energy materials. METHODS: With the help of Gaussian16 software and Multiwfn 3.8 package, the B3LYP method in density functional theory was selected. The 6-311G (d, p) basis set was used to optimize the structure of the 42 derivatives, and the high-precision def2-TZVPP basis set was used to calculate the energy.

Synthesis, thermal behaviors, and energetic properties of asymmetrically substituted tetrazine-based energetic materials.

1,2,4,5-tetrazine ring is a common structure for the construction of energy-containing compounds, and its high nitrogen content and large conjugation effect give it the advantage of a good balance between energy and mechanical stability as a high-nitrogen energy-containing material. However, most of the reported works about tetrazine energetic materials (EMs) are symmetrically substituted tetrazines due to their easy accessibility. A small number of reports show that asymmetrically substituted tetrazines also have good properties, such as high density and generation of enthalpy and energy. Herein, two asymmetrically substituted tetrazines and their five energetic salts were prepared and fully characterized by IR spectroscopy, NMR spectra, elemental analysis, and differential scanning calorimetry (DSC). The structure of the two compounds was further confirmed by single-crystal X-ray diffraction studies. The thermal behaviors and thermodynamic parameters were determined and calculated. In addition, the energetic properties and impact sensitivities of all the compounds were obtained to assess their application potential. The results show that compounds 2-4 and 7-9 show higher detonation velocities than TNT, and the hydrazinium salt 9 possesses the best detonation properties (D = 8,232 m s-1 and p = 23.6 GPa). Except for 4 and 3, all the other compounds are insensitive, which may be applied as insensitive explosives. Noncovalent interaction analysis was further carried out, and the result shows that the strong and high proportion of hydrogen bonds may contribute to the low-impact sensitivity.

Polynitro-Functionalized Azopyrazole with High Performance and Low Sensitivity as Novel Energetic Materials.

The development of energetic materials is still facing a huge challenge because the relationship between energy and sensitivity is usually contradictory: high energy is always accompanied with low sensitivity. Here, a high-energy, low-sensitivity energetic polynitro-functionalized azopyrazole (TNAP) and its energetic salts have been synthesized. The structural characterization of these compounds was analyzed by elemental analysis, 1H and 13C NMR spectroscopies, and infrared spectroscopy. The single-crystal structure of compounds K2TNAP, TNAP, 5, and 6 was obtained by X-ray diffraction, and K2TNAP is a novel energetic metal-organic framework. The calculated detonation properties of TNAP (9040 m s-1 and 36.0 GPa) are superior to that of RDX (8796 m s-1 and 33.6 GPa). In addition, TNAP also has lower mechanical sensitivity (IS > 40 J, FS = 244 N) and higher decomposition temperature (Td = 221 °C) than RDX (IS = 7.4 J, FS = 120 N, and Td = 204 °C). These experimental results suggest that TNAP may become a new candidate for secondary explosives.

Theoretical studies of novel high energy density materials based on oxadiazoles.

In this study, 32 energetic compounds were designed using oxadiazoles (1,2,5-oxadiazole, 1,3,4-oxadiazole) as the parent by inserting different groups as well as changing the bridge between the parent. These compounds had high density and excellent detonation properties. The electrostatic potentials of the designed compounds were analyzed using density functional theory (DFT). The structure, heat of formation (HOF), density, detonation performances (detonation pressure P, detonation velocity D, detonation heat Q), and thermal stability of each compound were systematically studied based on molecular dynamics. The results showed that the -N3 group has the greatest improvement in HOF. For the detonation performances, the directly linked -N=N- and -NH-NH- were beneficial when used as a bridge between 1,2,5-oxadiazole and 1,3,4-oxadiazole, and it can also be found that bridge changing had little effect on the trend of detonation performance, while energetic groups changing influenced differently. In general, the introduction of nitro groups contributes to the improvement of the detonation performance of the compounds. In this study, the compounds containing the highest amount of nitro groups were found to have better detonation performance than their counterparts and were not significantly different from RDX and HMX.

Detonation properties and impact sensitivities of trinitromethane derivatives of three-membered heterocyclic ring compounds.

We have carried out the design and theoretical investigation of a series of trinitromethane derivatives of three-membered heterocyclic ring compounds - aziridine, 1H-azirine, diaziridine, 1H-diazirine, triaziridine, 1H-triazirene, oxaziridine, oxadiaziridine, dioxaziridine, oxirane, and dioxirane - in search for new high energy density materials (HEDM). We have estimated the properties relevant to HEDMs of the proposed molecules using Density Functional Theory (B3LYP/aug-cc-pVDZ). The results show that most of the molecules have a high value of solid-phase heat of formation, crystal density, detonation velocity and pressure with satisfying values for impact sensitivities. We have identified some of these molecules, 1-(triinitromethyl)diaziridine, 2-(trinitromethyl)-1-nitro-1H-azirine, and (2-(trinitromethyl)-3-nitrooxirane) are potential candidates of energetic molecules among the 60 molecules we investigated. As most of them are having a high positive oxygen balance, they can be recommended for use as oxidisers in solid propellants.

Computational studies on nitro derivatives of BN indole as high energetic material.

Nitrogen-rich heterocycles and their nitro derivatives are one of the important classes of energetic materials. In the present study, the computational methods have been applied to determine the thermodynamic and detonation properties of nitro derivatives of BN indole molecule. Structure optimization and electronic energy of the designed molecules are determined using the density functional theory. The gas-phase heat of formation of the species concerned is determined by the atomization method. Wave function analysis-surface analysis suite (WFA-SAS) has been applied to determine the condensed phase heat of formation and crystal density of designed molecules. Bond dissociation energy (BDE) is determined to identify the trigger bond. The energy gap between highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) has been calculated to predict the stability of the molecule. Impact sensitivity and detonation properties of designed species are calculated. The calculated parameters show that among all the designed molecules, the molecule A6 (1,2,3,5,6,7-Hexanitrobnindole) has the properties to be considered as a high density energetic molecule.

A promising energetic biopolymer based on azide-functionalized microcrystalline cellulose: Synthesis and characterization.

In the current investigation, azidodeoxy-microcrystalline cellulose nitrate (AMCCN) as a novel promising nitrogen-rich energetic biopolymer was synthesized, and its features were compared to those of azidodeoxy-pristine cellulose nitrate (APCN), conventional cellulose nitrate (PCN) and microcrystalline cellulose nitrate (MCCN). The produced nitrated samples and their precursors were fully characterized using various analytical techniques. In addition, the heats of combustion and mechanical sensitivities of all nitrated biopolymers were evaluated, and their energetic performances were predicted by EXPLO5 V6.04 software. The obtained results provide evidence for the effectiveness of the applied chemical functionalization approach to synthesize the relatively insensitive AMCCN and APCN with nitrogen content of 22.75 % and 22.50 %, density of 1.718 g/cm3 and 1.706 g/cm3, and detonation velocity of 7707 m/s and 7533 m/s, respectively, which are higher than those of PCN. This work opens avenues to design promising energetic biopolymers based on renewable microcrystalline cellulose for potential application in advanced high performance solid propellants and explosives.

High-substitute nitrochitosan used as energetic materials: Preparation and detonation properties.

In order to develop new high-energy materials utilizing natural products, a high-substitute nitrochitosan was prepared with different methods. Prepared processes and detonation properties of the nitrochitosan samples were systematically studied. The nitration substitute degree, nitrogen content, exothermic decomposition enthalpy, heat of combustion, impact sensitivity, detonation velocity and detonation pressure of the prepared high-substitute nitrochitosan were 2.01, 16.67 %, -2226 J g-1, -7831.6 ±â€¯116.3 J g-1, >14.2 J, 7.81 km s-1, and 24.03 GPa, respectively. Compared with nitrocellulose (NC), the nitrogen content, impact sensitivity and detonation properties of the prepared nitrochitosan were significantly improved. Nitrochitosan and RDX can form a uniform composite in acetone. With the increase of RDX content, the impact sensitivity of composite increased, but the composite was more stable and not easy to decompose. High-substitute nitrochitosan presents a potential application in solid propellants.

Design of Energetic Materials Based on Asymmetric Oxadiazole.

A new family of asymmetric oxadiazole based energetic compounds were designed. Their electronic structures, heats of formation, detonation properties and stabilities were investigated by density functional theory. The results show that all the designed compounds have high positive heats of formation ranging from 115.4 to 2122.2 kJ mol-1. -N- bridge/-N3 groups played an important role in improving heats of formation while -O- bridge/-NF2 group made more contributions to the densities of the designed compounds. Detonation properties show that some compounds have equal or higher detonation velocities than RDX, while some other have higher detonation pressures than RDX. All the designed compounds have better impact sensitivities than those of RDX and HMX and meet the criterion of thermal stability. Finally, some of the compounds were screened as the candidates of high energy density compounds with superior detonation properties and stabilities to that of HMX and their electronic properties were investigated.

Theoretical investigation of the structure, detonation properties, and stability of bicyclo[3.2.1]octane derivatives.

A series of nitro group and aza nitrogen atom derivatives, based on bicyclo[3.2.1]octane, were designed and studied by theoretical methods. The geometric structure calculations were performed at B3LYP/6-311G(d,p), B3P86/6-311G(d,p), B3LYP/6-31G(d), and B3PW91/6-31G(d,p) levels. The electrostatic potential analysis, heats of formation, densities, heats of sublimation, detonation performances, bond dissociation energies (BDEs), and impact sensitivities of the designed compounds were calculated by reasonable calculation methods to evaluate their comprehensive properties and establish the relationship between structure and performance. Results show that density and detonation properties always increase with the increasing number of nitro groups and aza nitrogen atoms. BDEs generally decrease with the increasing number of nitro groups. Except for BDEs of A9, B9, and D8, BDEs of all designed compounds are larger than 20 kcal mol-1 and meet the requirement for new high energy density compounds (HEDCs). Two theoretical prediction methods show all the designed compounds have an acceptable impact sensitivity. Detonation velocity and detonation pressure were predicted in the range of 5.24-9.59 km/s and 9.97-43.44 GPa, respectively. Eleven compounds have better detonation properties than HMX, and seven compounds meet the criteria for HEDCs. Taking thermal stability and impact sensitivity into consideration, four compounds (C9, E8, F8, and G7) may be considered as new potential HEDCs, and C9, E8, and F8 may have similar detonation properties to the famous CL-20. Graphical abstractFour new HEDCs with acceptable impact sensitivity (C9, E8 and F8 may have similar detonation properties to the famous CL-20).

DFT studies on nitrogen-rich pyrazino [2, 3-e] [1, 2, 3, 4] tetrazine-based high-energy density compounds.

By using the density functional theory method, we investigated the heats of formation (HOFs), electronic structure, detonation properties, thermal stability and sensitivity for a set of pyrazino [2, 3-e] [1, 2, 3, 4] tetrazine derivatives with different substituents and different numbers of N-oxides. Our findings reveal that the HOFs of the derivatives decrease dramatically with the increasing number of N-oxides. The effects of the substituents on the HOMO-LUMO gaps are coupled with those of the N-oxides. The calculated detonation properties point out that -NF2, -ONO2 and an increasing number of N-oxides are very helpful for improving the detonation performance of the designed derivatives. The bond dissociation energies of the weakest bonds indicate that a majority of our designed compounds have better thermal stability. The -NH2 group is very useful to decrease the free space value. Most of the derivatives have higher h50 values compared with parent molecules. Considering the sensitivity, thermal stability and detonation performance, four compounds could be considered as potential candidates of high-energy density compounds.