Trinitromethyl Energetic Groups Enhance High Heats of Detonation

Employing Nitrogen-Sulfur Synergy: 1,2,3-Triazole-Thiadiazole-Based Energetic Materials

In this study, we synthesized energetic materials integrating thiadiazole and triazole moieties. The newly developed compounds were thoroughly characterized using NMR, IR, elemental analysis, TGA-DSC, and single-crystal X-ray diffraction (for compound 3). These compounds exhibited acceptable properties, including high densities (1.88-1.92 g cm-3), moderate to good detonation performance (VOD: 6383-8128 m s-1), good thermal stability (143-238 °C), and less sensitivity to impact (>15 J) and friction (360 N). Notably, compounds 4 and 8 achieved superior detonation velocities compared to nearly all reported sulfur-based energetic materials to date. This work highlights the significance of triazole-thiadiazole frameworks in the development and fine-tuning of energetic materials.

Promising Energetic Asymmetric Bistetrazoles Synthesized via Sequential Cycloaddition Reactions

Herein, we report the successful synthesis of a series of asymmetric bistetrazole-based energetic compounds (4, 8, 4a-c, and 5a-c) starting from 2-(5-amino-4-nitro-1H-pyrazol-3-yl)-2H-5-cyanotetrazol (3), which was obtained via the reaction of 3,5-diamino-4-nitropyrazole hydrochloride with diazoacetonitrile using a [3 + 2] cycloaddition strategy. All newly synthesized compounds displayed superior detonation performances, particularly 2'-(5-amino-4-nitro-1H-pyrazol-4-yl)-2H,2'H-5,5'-bistetrazole (4), which exhibited exceptional overall performances. These findings underscore the potential of asymmetric bistetrazole derivatives as promising candidates for the development of advanced energetic materials.

Based on 124-Oxadiazole: Design and Synthesis of a Series of Insensitive Energetic Materials and Discovery of Another Route for the Synthesis of DNAF via Rearrangement

Compounds containing dinitromethyl groups are ideal structural units for energetic materials due to their high density and good oxygen balance. However, these compounds often have drawbacks, such as low decomposition temperatures and high mechanical sensitivity, which limit their practical applications in energetic materials. In order to address these issues, a series of novel nitrogen- and oxygen-rich energetic compounds 7-11 have been successfully designed by incorporating amino groups to enhance hydrogen bonding. Among them, compound 8 exhibited an excellent overall performance (Tdec = 215 °C, ρ = 1.81 g cm-3, D = 8603 m s-1, IS > 40 J, FS > 360 N) and displayed good typical secondary explosive characteristics. During the synthesis process, a new and safe method was developed to synthesize 3,4-di(nitramino)furazan and its ion salts. The conversion from 1,2,4-oxadiazole to 1,2,5-oxadiazole via rearrangement was explored through multiple experiments to investigate its mechanism. This new transformation is a valuable complement to the azole-azole rearrangement of the Boulton-Katritzky type.

Azobis(polynitrophenyl-1,2,5-oxadiazoles) as Heat-Resistant Friction-Insensitive Energetic Materials

The evolution of energetic materials science presents new challenging tasks associated with the creation of advanced technologies for sustainable development of the future. In this work, a set of new heat-resistant high-energy materials incorporating the polynitrophenyl-1,2,5-oxadiazole scaffold enriched with azo/azoxy moieties have been designed and synthesized. Due to a smart combination of explosophoric groups and 1,2,5-oxadiazole rings, the prepared high-energy substances have excellent thermal stability (up to 300 °C), good densities (up to 1.75 g cm-3), high enthalpies of formation (340-538 kJ mol-1), and high combined nitrogen-oxygen content (63-68%). In-depth structural analysis revealed the presence of strong intra- and intermolecular hydrogen bonds in aminodinitrophenyl derivatives, which in combination with the small deviation of electrostatic potential values explains the low mechanical sensitivity of these materials. At the same time, trinitrophenyl-1,2,5-oxadiazoles incorporating three adjacent non-coplanar nitro groups demonstrated higher sensitivity to impact, albeit retaining complete insensitivity to friction. The overall performance of the thus prepared high-energy substances exceeds that of the known heat-resistant explosive hexanitrostilbene. Therefore, the newly synthesized family of energetic polynitrophenyl-1,2,5-oxadiazoles provides a fruitful foundation for the creation of the advanced heat-resistant energetic materials of the future.

Energetic Methylene-Bridged Furoxan-Triazole/Tetrazole Hybrids

Design and synthesis of new energetic materials retains its urgency in chemistry and materials science. Herein, rational construction and regioselective synthesis of a series of energetic compounds comprising of a methylene-bridged combination of 1,2,5-oxadiazole and nitrogen-rich azoles (1,2,4-triazole and tetrazole) enriched with additional explosophoric functionalities (nitro and azo moieties) is presented. All target materials were thoroughly characterized using IR and multinuclear NMR (1H, 13C, 14N, 15N) NMR spectroscopy, high-resolution mass spectrometry, X-ray diffraction, and differential scanning calorimetry. All synthesized energetic substances showed good thermal stability (up to 239 °C) and low mechanical sensitivity, while their performance reached or exceeded the level of TNT.

First Alliance of Pyrazole and Furoxan Leading to High-Performance Energetic Materials

Nitrogen heterocyclic scaffolds retain their leading position as valuable building blocks in material science, particularly for the design of small-molecule energetic materials. However, the search for more balanced combinations of directly linked heterocyclic cores is far from being exhausted and aims to reach ideally balanced high-energy substances. Herein, we present the synthetic route to novel pyrazole-furoxan framework enriched with nitro groups and demonstrate a promising set of properties, viz., good thermal stability, acceptable mechanical sensitivity, and high detonation performance. In-depth crystal analysis showed that the isomers having lower-impact sensitivity values in both types of regioisomeric pairs are those with the exocyclic furoxan oxygen atom being closer to the pyrazole ring. Owing to the favorable combination of high crystal densities (1.83-1.93 g cm-3), positive oxygen balance to CO (up to +13.9%), and high enthalpies of formation (322-435 kJ mol-1), the synthesized compounds show high calculated detonation velocities (8.4-9.1 km s-1) and excellent metal accelerating abilities. The incorporation of the 3-nitrofuroxan moiety increases the thermal stability (by ca. 20 °C) and decreases the mechanical sensitivity of target hybrid materials in both types of regioisomeric pairs. Simultaneously, the detonation performance of 3-nitrofuroxans is almost identical to that of 4-nitrofuroxans, highlighting the potential of the regioisomeric tunability in the future design of energetic materials.

Symmetric Refunctionalization of Diaminodinitropyrazine with Hydrazine and Aminotetrazole: Strategy for Enhancing Detonation Performance and Safety in Energetic Materials

Two novel nitrogen-rich green energetic compounds were synthesized for the first time from readily available and cost-effective pyrazine starting materials. All newly synthesized molecules were comprehensively characterized, including infrared spectroscopy, nuclear magnetic resonance, elemental analysis, mass spectrometry, and thermogravimetric analysis-differential scanning calorimetry. All compounds have additionally been validated by single-crystal X-ray diffraction analysis. The physicochemical properties of compounds 2, 4, and 5 were thoroughly investigated. Notably, all compounds exhibit remarkable performance, such as a high density (>1.84 g cm-3), excellent detonation properties (VOD > 8582 m s-1, and DP > 31.3 GPa), outstanding thermostability (>205 °C), and high insensitivity (IS > 35 J, and FS = 360 N). These attributes are quite comparable to those of secondary benchmark explosives such as TATB, RDX, LLM-105, and FOX-7. This tuned performance evidences that the incorporation of hydrazine, nitro, and aminotetrazole into the pyrazine framework fosters robust nonbonded interactions, ultimately enhancing thermal stability and reducing sensitivity. The findings of this study not only signify that compounds 2 and 5 have excellent detonation properties and stability but also prove that the strategy of replacing amino groups with hydrazine and aminotetrazole is a practical means of developing new insensitive energetic materials.

Assembling of Nitropyrazoles into Tetranitroacetimidic Acid (TNAA): A Pathway to High-Performance Energetic Oxidizers through Dual C/N-Functionalization

In this work, incorporating nitropyraozles into tetranitroacetimidic acid (TNAA) resulted in two analogues of isomeric TNAA-like compounds (3 and 5). These compounds exhibit excellent densities, detonation performance, and high specific impulse, which are promising high-energy oxidizers that are comparable to AP and ADN. This structural modification strategy may have the potential to contribute significantly to the development of versatile, high-performance energetic oxidizers.

Preparation of Highly Energetic Coordination Compounds with Rich Oxidants and Lower Sensitivity Based on Methyl Groups

Revamping the structure of energy storage is an efficient strategy for striking a balance between the performance and sensitivity of energetic materials to achieve high energy and reduced sensitivity. In continuation of prior research, this study utilized the ligand 3,5-dimethyl-1H-pyrazole-4-carbonhydrazide (DMPZCA) and innovatively designed and synthesized the compound ECCs [Cu(HDMPZCA)2(ClO4)2](ClO4)2·2H2O (ECCs-1·2H2O). Compared with the former research, solvent-free compound ECCs-1 refers to an innovative material characterized by a dual structure involving ionic salts and coordination compounds. Due to these unique structures, ECCs-1 exhibits an increased [ClO4-] content, a higher oxygen balance constant (OB = -7.9%), and improved mechanical sensitivity (IS = 8 J, FS = 32 N). Theoretical calculations support the superior detonation performance of ECCs-1. Additionally, experimental results confirm its ignition capability through lower-threshold lasers and highlight the outstanding initiation potential and explosive power, making it a suitable candidate for primary explosives.

Pushing the limits of the heat of detonation via the construction of polynitro bipyrazole

The trinitromethyl group is a highly oxidized group that is found as an active functionality in many high-energy-density materials. The most frequently used previous synthetic method for the introduction of the trinitromethyl group is the nitration of heterocyclic compounds containing an acetonyl/ethyl acetate/chloroxime group. Now a novel strategy for constructing a trinitromethyl group (5) via nitration of an ethylene bridged compound, dipyrazolo[1,5-a:5',1'-c]pyrazine (2), is reported. In addition, the other two nitrated products (3 and 4) were obtained under different nitrating conditions. Compound 5 has excellent detonation performance (Dv = 9047 m s-1, P = 35.6 GPa), and a low mechanical sensitivity (IS = 10 J, FS = 216 N), with an especially attractive heat of detonation of 6921 kJ kg-1, which significantly exceeds that of the state-of-the-art explosive CL-20 (Q: 6162 kJ kg-1).

Thermal stability of azole-rich energetic compounds: their structure, density, enthalpy of formation and energetic properties

Energetic compounds, as a type of special material, are widely used in the fields of national defense, aerospace and exploration. Their research and production have received growing attention. Thermal stability is a crucial factor for the safety of energetic materials. Azole-rich energetic compounds have emerged as a research hotspot in recent years owing to their excellent properties. Due to the aromaticity of unsaturated azoles, many azole-rich energetic compounds have significant thermal stability, which is one of the properties that researchers focus on. This review presents a comprehensive summary of the physicochemical and energetic properties of various energetic materials, highlighting the relationship between thermal stability and the structural, physicochemical, and energetic properties of azole-rich energetic compounds. To improve the thermal stability of compounds, five aspects can be considered, including functional group modification, bridging, preparation of energetic salts, energetic metal-organic frameworks (EMOFs) and co-crystals. It was demonstrated that increasing the strength and number of hydrogen bonds of azoles and expanding the π-π stacking area are the key factors to improve thermal stability, which provides a valuable way to develop energetic materials with higher energy and thermal stability.

Enhanced Energetic Performance via the Combination of Furoxan and Oxa-[5,5]bicyclic Structures

Three new compounds based on the combination of furoxan (1,2,5-oxadiazole N-oxide) and oxa-[5,5]bicyclic ring were synthesized. Among them, the nitro compound showed satisfactory detonation properties (Dv, 8565 m s^-1; P, 31.9 GPa), which is comparable to the performance of RDX (a classic high-energy secondary explosive). Additionally, the introduction of the N-oxide moiety and oxidation of the amino group more effectively improved the oxygen balance and density (d, 1.81 g cm^-3; OB%, +2.8%) of the compounds compared to furazan analogues. Combined with good density and oxygen balance as well as moderate sensitivity, this type of furoxan and oxa-[5,5]bicyclic structure will open up a platform for the synthesis and design of new high-energy materials.

High-performing, insensitive and thermally stable energetic materials from zwitterionic gem-dinitromethyl substituted C-C bonded 1,2,4-triazole and 1,3,4-oxadiazole

A series of gem-dinitromethyl substituted zwitterionic C-C bonded azole based energetic materials (3-8) were designed, synthesized, and characterized through NMR, IR, EA, and DSC studies. Further, the structure of 5 was confirmed with SCXRD and those of 6 and 8 with ¹⁵N NMR. All the newly synthesized energetic molecules exhibited higher density, good thermal stability, excellent detonation performance, and low mechanical sensitivity to external stimuli such as impact and friction. Among all, compounds 6 and 7 may serve as ideal secondary high energy density materials due to their remarkable thermal decomposition (200 °C and 186 °C), insensitivity to impact (>30 J), velocity of detonation (9248 m s^-1 and 8861 m s^-1) and pressure (32.7 GPa and 32.1 GPa). Additionally, the melting and decomposition temperatures of 3 (T_m = 92 °C, T_d = 242 °C) indicate that it can be used as a melt-cast explosive. The novelty, synthetic feasibility, and energetic performance of all the molecules suggest that they can be used as potential secondary explosives in defence and civilian fields.