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.

Strategy for Extending the Nitrogen Chain: The Bis(1,2,3-triazole) Formation Reaction from Tosylhydrazones and N-Amino Azole.

A facile and versatile synthesis strategy for the bis(1,2,3-triazole) formation reaction was developed from tosylhydrazones and N-amino (N-NH2) azole instead of C-amino amine derivatives. The novel energetic compounds containing the bicycle catenated six-nitrogen chain (N6) and the first example of N7 neutral compounds were synthesized in a moderate or high yield. The possible mechanism of bis(1,2,3-triazole) formation reaction based on amino azole of N-NH2 was verified by the X-ray crystal structure of key intermediates. In addition, four energetic compounds 4aa, 4ba, 4ac, and 4ad containing N6 and N7 structures possess acceptable decomposition temperatures (150.1-201.6 °C) and moderate calculated detonation performances (6850-7727 m/s). Among them, 4aa (N6 structure) and 4ad (N7 structure) could be used as the melt-cast explosive candidate and the gas generation agent candidate, respectively. This type of nitrogen-nitrogen bonding formation opens a new method for discovery of novel high-nitrogen energetic compounds containing catenated multiple nitrogen atoms especially odd number nitrogen compounds.

Synthesis and Characterization of 4-(1,2,4-Triazole-5-yl)furazan Derivatives as High-Performance Insensitive Energetic Materials.

3-Nitro-4-(5-nitro-1,2,4-triazol-3-yl)furazan (2), N,N'-bis(trinitroethyl)-3,5'-diamino-4-(1,2,4-triazol-3-yl)furazan (3), N,N'-bis(trinitroethyl)-3,5'-dinitramino-4-(1,2,4-triazol-3-yl)furazan (4) and eighteen nitrogen-rich salts (5 a, 5 b, 5 d-5 i, 5 g-1, 6 a-6 i) were designed and synthesized. These 4-(1,2,4-triazole-5-yl)furazan derivatives were fully characterized by IR and NMR spectra, elemental analysis, and differential scanning calorimetry (DSC). The solid-state structures of 2, 5 d, 5 e, 5 h, 5 g-1, 6 g, and 6 i were confirmed via single crystal X-ray analysis. Detonation performance (detonation velocities and pressures) of these energetic compounds was evaluated and the impact and friction sensitivities were measured using standard BAM technology. Some of the compounds, for example, 2 (D: 9152 m s-1 , P=37.1 GPa) and 4 (D: 9355 m s-1 , P=40.1 GPa) exhibit excellent detonation performance, which are comparable to the highly explosive benchmarks such as RDX (D: 8795 m s-1 , P=34.9 GPa) and HMX (D: 9144 m s-1 , P=39.2 GPa).

C8 N26 H4 : An Environmentally Friendly Primary Explosive with High Heat of Formation.

The synthesis and characterization of the metal-free polyazido compounds 3,6-bis-(2-(4,6-diazido-1,3,5-triazin-2-yl)-hydrazinyl)-1,2,4,5-tetrazine (2) and 3,6-bis-(2-(4,6-diazido-1,3,5-triazin-2-yl)-diazenyl)-1,2,4,5-tetrazine (4) are presented. Two compounds were characterized by NMR spectra, IR spectroscopy, mass spectrometry, and differential scanning calorimetry (DSC). Additionally, the structure of 2 was confirmed by single-crystal X-ray diffraction. Compounds 2 and 4 exhibit measured densities (1.755 g cm-3 and 1.763 g cm-3 ), good thermal stabilities (194 °C and 189 °C), high heat of formation (2114 kJ mol-1 and 2820 kJ mol-1 ), and excellent detonation performance (D, 8365 m s-1 and 8602 m s-1 ; P, 26.8 GPa and 29.4 GPa). Furthermore, compounds 2 and 4 have been tested for their priming ability to detonate RDX. The results indicate that the title compound 2 is a potential environmentally friendly alternative candidate to lead-based primary explosives.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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).

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.

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).

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.