Advanced tetracyclic heat-resistant energetic materials based on bis(4-nitropyrazole) bridged 1,2,4-triazole.

In recent years, with the development of deep coal mines and petroleum resources and the expansion of the aerospace industry, the pursuit of heat-resistant energetic materials with high thermal stability and high energy has been increasing. Bis(4-nitropyrazole) was employed as an energy bridge to link 1,2,4-triazole, thereby constructing a sophisticated tetracyclic framework in this study. A tetracyclic heat-resistant explosive 5,5'-(4,4'-dinitro-2H,2'H-[3,3'-bipyrazole]-5,5'-diyl)bis(4H-1,2,4-triazole-3,4-diamine) (3) and its derivatives 6-8 with excellent comprehensive performance have been successfully prepared. Particularly noteworthy is that compound 3 has a detonation velocity of 8604 m s-1, which exceeds that of the conventional heat-resistant explosive HNS with a velocity of 7164 m s-1. Furthermore, compound 3 has higher thermal stability (Td = 340 °C) than HNS (Td = 318 °C). In addition, the tetracyclic compound 3 also exhibited extraordinarily low sensitivity (IS > 40 J; FS > 360 N). These unique characteristics make it a potential candidate for novel heat-resistant and insensitive energetic materials.

Synthesis of fused energetic compounds using structural modification from local carbonyl to hydroxylamine/hydrazone.

This work presents the successful synthesis of a series of fused energetic compounds using the strategy of structural modification from local carbonyl to hydroxylamine, hydrazone or methylamine. Hydroxylamine-substituted compound 2 exhibits high density, high detonation performance and low sensitivities as a secondary explosive.

An Efficient One-Step Reaction for the Preparation of Advanced Fused Bistetrazole-Based Primary Explosives.

The first example of [5,6,5]-tricyclic bistetrazole-fused energetic materials has been obtained through a one-step reaction from commercial and inexpensive 4,6-dichloro-5-nitropyrimidine. This one-step reaction including nucleophilic substitution, nucleophilic addition, cyclization, and electron transfer is rarely reported, and the reaction mechanism and scope is well investigated. Among target compounds, organic salts exhibit higher detonation velocities (D: 8898-9077 m s-1) and lower sensitivities (IS: 16-20 J) than traditional high energy explosive RDX (D = 8795 m s-1; IS = 7.5 J). In addition, the potassium salt of 5-azido-10-nitro-bis(tetrazolo)[1,5-c:5',1'-f]pyrimidin (DTAT-K) possesses excellent priming ability, comparable to traditional primary explosive Pb(N3)2, and ultralow minimum primary charge (MPC = 10 mg), which is the lowest MPC among the reported potassium-based primary explosives. The simple synthesis route, free of heavy metal and expensive raw materials, makes it promising to quickly realize this material in large-scale industrial production as a green primary explosive. This work accelerates the upgrade of green primary explosives and enriches future prospects for the design of energetic materials.

Toward High-Energy and Low-Sensitivity Energetic Materials Based on a Fused [5,5,5,6]-Tetracyclic Backbone.

A route for fused [5,5,5,6]-tetracyclic energetic compounds based on the facile cyclization reaction has been explored. Fused [5,5,5,6]-tetracyclic compound 4 shows a high measured density (1.924 g cm-3), a low sensitivity (IS = 10 J, and FS = 144 N), and an excellent detonation velocity (9241 m s-1), which are much better than those of RDX. The results indicate that compound 4 is a potential candidate as a secondary explosive and provide new insight into the construction of fused polycyclic heterocycles.

A Synthetic Strategy for the Preparation of Fused [5,6,5,5]-Tetracyclic Energetic Compounds.

This study explores a straightforward synthetic strategy for preparing fused [5,6,5,5]-tetracyclic energetic compounds. Compound 4 has a high thermostability (Td = 307 °C), which is comparable to that of traditional heat-resistant explosive HNS (Td = 318 °C), but a higher detonation velocity (8262 m s-1) than HNS (7612 m s-1). These results indicate that compound 4 deserves further investigation as a potential heat-resistant explosive.

The design and synthesis of new advanced energetic materials based on pyrazole-triazole backbones.

A series of derivatives of the nitropyrazole-triazole backbone were designed through units' screening of 219 N-heterocycle compounds and were synthesized. Among them, the thermal stability of DNPAT (Tdec = 314 °C) is close to that of traditional heat-resistant explosive HNS (318 °C) while the detonation performance and sensitivity (D = 8889 m s-1; IS = 18 J) are better than those of HNS (D = 7612 m s-1; IS = 5 J) and traditional high-energy explosive RDX (D = 8795 m s-1; IS = 7.4 J), which is rarely reported in heat-resistant explosives. Moreover, compounds 4 and 6 show excellent performances (IS > 15 J, D > 9090 m s-1, P > 37.0 GPa), illustrating that compounds 4 and 6 may be used as secondary explosives. All these results enrich prospects for the development of energetic materials.

An advanced primary explosive and secondary explosive based on a zwitterionic pyrazole-triazole derivative.

Two zwitterionic energetic materials containing a pyrazole-triazole backbone were synthesized and fully characterized. Compound 3 can serve as an ideal secondary explosive due to its high decomposition temperature (>200 °C), low impact sensitivity (>40 J), and excellent calculated detonation velocity (9090 m s-1). The good priming ability of compound 4 demonstrates that it is a potential candidate as a primary explosive, which was confirmed in the test. These results indicate that zwitterionic molecules are an efficient promising class for the future design of new high-energy density materials.

C-C bonded bis-5,6 fused triazole-triazine compound: an advanced heat-resistant explosive with high energy and low sensitivity.

It is still an urgent problem in the field of energetic materials to explore the synthesis of heat-resistant compounds with balanced energy and thermal stability through simple synthetic routes. Recently, fused compounds are considered to provide a promising framework for the construction of ideal heat-resistant compounds. In this study, three novel C-C bonded bis-5,6 fused triazole-triazine compounds, 3,3'-dinitro-[7,7'-bi[1,2,4]triazolo[5,1-c][1,2,4]triazine]-4,4'-diamine (2), 4,4'-diamino-[7,7'-bi[1,2,4]triazolo[5,1-c][1,2,4]triazine]-3,3'-dicarbonitrile (3), and 3,3'-di(1H-tetrazol-5-yl)-[7,7'-bi[1,2,4]triazolo[5,1-c][1,2,4]triazine]-4,4'-diamine (4), were synthesized by a simple method. Compound 2 exhibited an approaching detonation velocity of 8837 m s-1 compared with that of the traditional high energy explosive RDX velocity of 8795 m s-1, while its thermal stability (Td = 327 °C) was comparable to that of the heat-resistant explosive HNS (Td = 318 °C). At the same time, the double fused compound 2 also realized high density (1.90 g cm-3) and extremely low sensitivity (FS > 360 N, IS > 40 J). The above good comprehensive properties prove that compound 2 can be used as a potential insensitive high-energy heat-resistant explosive. In addition, the effects of the crystal structure on the sensitivity and thermal stability were studied using the quantum chemical methods. These results imply that the formation of double fused ring compounds by the ring closing reaction at symmetrical positions is an ideal strategy for the development of advanced heat-resistant explosives.

Series of Azido and Fused-Tetrazole Explosives: Combining Good Thermal Stability and Low Sensitivity.

The introduction of azido groups into the energetic skeleton has the advantages of increasing the energy level. In this work, a series of azido compounds with good stability and low sensitivity as well as tetrazole-fused compounds based on energetic salts are synthesized. The detonation pressures and velocities of these new compounds fall in the ranges of 18.9-27.3 GPa and 7153-8450 m s-1, respectively. The detonation velocity of the tetrazole-fused compounds based on the potassium salts 3, 6, and 7 are 7810, 7153, and 7989 m s-1, respectively. Also, their decomposition temperatures (244, 237, and 240 °C, respectively) are higher than that of traditional explosive RDX (204 °C). Notably, two representative compounds 2 and 5 possess higher decomposition temperature (2: 196 °C and 5: 178 °C) and overall detonation properties (2: D = 8129 m s-1 and P = 26.6 GPa and 5: D = 8336 m s-1 and P = 27.3 GPa) as well as relativity lower sensitivities (2: IS = 12 J and FS = 240 N and 5: IS = 10 J and FS = 144 N) than that of primary explosive 2-diazo-4,6-dinitrophenol (Td = 157 °C, D = 6900 m s-1, P = 24.7 GPa, IS = 1 J, and FS = 24.7 N). Moreover, the initiation capacity of compounds 2 and 5 was also assessed through the initiation tests. The results indicate that the two compounds could be a promising environmentally friendly primary explosive.

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.

Novel polynitro azoxypyrazole-based energetic materials with high performance.

Novel polynitro azoxypyrazole-based energetic compounds 1,2-bis (4-nitro-1H-pyrazol-5-yl) diazene 1-oxide (3) and 1,2-bis (1,4-dinitro-1H-pyrazol-3-yl) diazene 1-oxide (4) were synthesized from 5-amino-pyrazole-4-carbonitrile by optimized reactions. Their structures were characterized by elemental analysis and single-crystal X-ray diffraction techniques. Compound 3 exhibits high thermal stability (239 °C), low mechanical sensitivity (IS = 22 J, FS = 240 N) and moderate detonation performance (Dv = 8272 m s-1, P = 28.1 GPa). Compound 4 shows moderate thermal stability (161 °C), decent mechanical sensitivity and higher detonation performance (Dv = 9228 m s-1, P = 38.7 GPa) compared to that of RDX. These newly developed strategies for constructing novel energetic compounds enrich the content of the ever-expanding energetic materials.

Synthesis of nitrogen-rich and thermostable energetic materials based on hetarenecarboxylic acids.

Two series of both nitrogen-rich and thermostable energetic materials as well as their energetic salts based on hetarenecarboxylic acids are now described. Among these new compounds, neutral compounds 3 and 10 have higher nitrogen contents (69.66% and 63.05%) than their energetic salts, which suggests that they could be used as green energetic materials. In addition, compound 3 shows a good decomposition temperature (Td = 281 °C), which is close to that of TNT (Td = 295 °C). Nitrogen-rich salt 6 exhibits better integrated energetic-properties (D = 8913 m s-1, IS = 24 J, FS = 320 N) than RDX (D = 8795 m s-1, IS = 7.5 J, FS = 120 N).

Response to "What Shall We Do with Computed Detonation Performance? Comment on '1,3,4-Oxadiazole Bridges: A Strategy to Improve Energetics at the Molecular Level'".

The values obtained for detonation performance are a function of the computational methods utilized. Since there are many such methods, the literature may contain a range of values for a single compound.

1,3,4-Oxadiazole Bridges: A Strategy to Improve Energetics at the Molecular Level.

Many energetic materials synthesized to date have limited applications because of low thermal and/or mechanical stability. This limitation can be overcome by introducing structural modifications such as a bridging group. In this study, a series of 1,3,4-oxadiazole-bridged furazans was prepared. Their structures were confirmed by 1 H and 13 C NMR, infrared, elemental, and X-ray crystallographic analyses. The thermal stability, friction sensitivity, impact sensitivity, detonation velocity, and detonation pressure were evaluated. The hydroxylammonium salt 8 has an excellent detonation performance (D=9101 m s-1 , P=37.9 GPa) and insensitive properties (IS=17.4 J, FS=330 N), which show its great potential as a high-performance insensitive explosive. Using quantum computation and crystal structure analysis, the effect of the introduction of the 1,3,4-oxadiazole moiety on molecular reactivity and the difference between the sensitivities and thermal stabilities of mono- and bis-1,3,4-oxadiazole bridges are considered. The synthetic method for introducing 1,3,4-oxadiazole and the systematic study of 1,3,4-oxadiazole-bridged compounds provide a theoretical basis for future energetics design.

Derivatives of 3,6-Bis(3-aminofurazan-4-ylamino)-1,2,4,5-tetrazine: Excellent Energetic Properties with Lower Sensitivities.

To find a balance between energy and safety, a series of compounds based on azo-, azoxy-, 1,4,2,5-dioxadiazene-, and 3,6-diamino-1,2,4,5-tetrazine-bridged bis(aminofurazan) were designed and synthesized. These compounds were analyzed by nitro group charges (Qnitro) and bond dissociation energy (BDE) calculations, which are related to sensitivity and stability. Based on the calculated results, derivatives of 3,6-bis(3-aminofurazan-4-ylamino)-1,2,4,5-tetrazine have the largest values for -Qnitro and BDE of all of the bis(aminofurazan) compounds. This shows that compounds based on 3,6-bis(3-aminofurazan-4-ylamino)-1,2,4,5-tetrazine have the lowest sensitivities and best stabilities, which has been substantiated by experiments. Additionally, their explosive properties remain essentially competitive with compounds based on azo-, azoxy-, and 1,4,2,5-dioxadiazene-bridged bis(aminofurazan). Hirshfeld surface calculations were also performed to better understand the relationship between the molecular structure and stability/sensitivity. This work highlights the value of 3,6-diamino-1,2,4,5-tetrazine as a linker to achieve good balance between safety and energy.

Studies on the synthesis and properties of nitramino compounds based on tetrazine backbones.

In this paper, a series of novel energetic compounds based on the backbone of the tetrazine-triazole structure were successfully synthesized. N,N'-((1,2,4,5-Tetrazine-3,6-diyl)bis(1,2-dihydro-3H-1,2,4-triazole-5-yl-3-ylidene))dinitramino (4) was prepared by the nitration of 5,5'-(1,4-dihydro-1,2,4,5-tetrazine-3,6-diyl)bis(1H-1,2,4-triazol-3-amine) (3) with 100% nitric acid and its energetic salts (6-14) were also prepared. All the compounds were fully characterized. The structures of 4 and 5 were further confirmed by single crystal X-ray diffraction analysis. The results show that these compounds have high heats of formation ranging from 2.09 to 3.95 kJ g-1, good detonation pressures and detonation velocities and acceptable sensitivities. Among them, compound 4, with low sensitivities (IS: 20 J and FS: 270 N) and excellent detonation properties (vD = 9100 m s-1; P = 34.1 GPa) shows potential for application in the field of highly energetic and insensitive explosives. The hydroxylammonium salt (7) exhibits promising energetic properties, which, in some cases, are superior to those of octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX).

A novel energetic framework combining the advantages of furazan and triazole: a design for high-performance insensitive explosives.

A series of tetracyclic furazan-triazole compounds have been synthesized and fully characterized. The predicted detonation performance and tested mechanical sensitivities showed their high-energy performance and insensitive features. Quantum chemical calculations and crystal structure analysis were applied to study the intrinsic structure-property relationship among these compounds. In addition, the detonation test shows their promising potential as secondary explosives.

Energetic Derivatives of 8-Nitropyrazolo[1,5-a][1,3,5]triazine-2,4,7-triamine: Achieving Balanced Explosives by Fusing Pyrazole with Triazine.

Using the triazine ring as the stabilizing factor, a series of energy-safety balanced fused ring compounds were successfully studied. Compounds 1, 7, and 9·H2O were further confirmed by single-crystal X-ray diffraction analysis. The detonation performance and safety parameters associated with impact and friction sensitivities were investigated by using EXPLO5 (version 6.01) and BAM methods, respectively. Based on their good detonation properties and high thermal and mechanical stabilities, these materials are potentially high performance insensitive explosives.

New pyrazole energetic materials and their energetic salts: combining the dinitromethyl group with nitropyrazole.

In this work, a series of pyrazole-derived energetic compounds were successfully synthesized. These energetic compounds were fully characterized by NMR spectroscopy, IR spectroscopy, and elemental analysis. The structures of compounds 5, 6, 7 and 7a were determined by single crystal X-ray diffraction. The physicochemical and energetic properties of all synthesized energetic compounds, including density, thermal stability and energetic performance, were investigated. The structure-property relationship was illustrated using two-dimensional fingerprint plots based on Hirshfeld surfaces, NCI plots and ESP of 7 and 7a. Among these energetic compounds, the hydroxylammonium salt 7b exhibited satisfactory calculated detonation performance (8700 m s-1), which was comparable to the commonly used highly explosive RDX (8748 m s-1). The potassium salt 5 was tested for its detonation ability by detonating RDX. The result indicates that compound 5 could be used as a potential green primary explosive.

Combinations of furoxan and 1,2,4-oxadiazole for the generation of high performance energetic materials.

Several energetic materials, which are composed of furoxan and 1,2,4-oxadiazole backbones, were synthesized by nitrating 3,3'-bis(5-amino-1,2,4-oxadiazol-3-yl)-4,4'-azofuroxan (2) under 100 wt% HNO3 or 100 wt% HNO3/Ac2O followed by a cation metathesis. All synthesized compounds were fully characterized by multinuclear NMR spectroscopy, IR spectroscopy, and elemental analysis, while 3,3'-bis(1,2,4-oxadiazol-5(4H)-one-3-yl)-4,4'-azofuroxan (3) and diammonium 3,3'-bis(5-nitramino-1,2,4-oxadiazole-3-yl)-4,4'-azofuroxan (4a) were confirmed by single crystal X-ray diffraction. The physicochemical and energetic properties of these compounds including density, thermal stability and sensitivity were investigated. Compounds 3 and 4 have high densities (3: 1.90 g cm-3, 4: 1.92 g cm-3), which are comparable to that of HMX (1.91 g cm-3). All energetic compounds show relatively high calculated heat of formation in the range from 504.79 kJ mol-1 to 1405.62 kJ mol-1. Their detonation properties were evaluated by EXPLO5 code using the measured density and calculated heat of formation. Among them, compounds 3 and 4 have good detonation performance (3: D = 8891 m s-1, P = 34.7 GPa, 4: D = 9505 m s-1, P = 41.3 GPa) and acceptable sensitivities (3: IS = 10 J, 4: IS = 4 J), which indicate their potential applications as high-performance energetic materials.