Green Synthetic Approach for High-Performance Energetic Nitramino Azoles

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 Advanced Pyrazole and N-N-Bridged Bistriazole-Based Secondary High-Energy Materials

In this work, we have synthesized 3,5-dihydrazinyl-4-nitro-1H-pyrazole (2), 9-nitro-1H-pyrazolo[3,2-c:5,1-c']bis([1,2,4]triazole)-3,6-diamine (3), and N-N-bonded N,N'-{[4,4'-bi(1,2,4-triazole)]-3,3'-diyl}dinitramide (5) and its stable nitrogen-rich energetic salts in one and two steps in quantitative yields from commercially available inexpensive starting material 4,6-dichloro-5-nitropyrimidine (1). Along with characterization via nuclear magnetic resonance, infrared, differential scanning calorimetry, and elemental analysis, the structures of 2 and 4-8 were confirmed by single-crystal X-ray diffraction. Interestingly, 5-8 show excellent thermal stability (242, 221, 250, and 242 °C, respectively) compared to that of RDX (210 °C). Detonation velocities of 2, 4, 6, and 7 range from 8992 to 9069 m s-1, which are better than that of RDX (8878 m s-1) and close to that of HMX (9221 m s-1). All of these compounds are insensitive to impact (10-35 J) and friction (360 N) sensitivity. These excellent energetic performances, stabilities, and synthetic feasibilities make compounds 2, 4, 6, and 7 promising candidates as secondary explosives and potential replacements for the presently used benchmark explosives RDX and HMX.

Combining the advantages of 1,3,4-oxadiazole and tetrazole enables achieving high-energy insensitive materials

Combining the advantages of energetic heterocycles to achieve high-energy insensitive explosives is a significant challenge. Herein, based on high-energy tetrazole rings and highly stable 1,3,4-oxadiazole rings, a series of novel nitrogen rich energetic compounds 5-9 were successfully constructed. The related compounds were fully characterized by EA, FT-IR, NMR, DSC, and MS, and compounds 6-9 were further confirmed by X-ray single crystal diffraction. Among them, the energetic ion salts 6-8 show high thermal stability (Tdec > 250 °C) and low mechanical sensitivity (IS > 40 J, FS > 360 N), as well as good energy properties (7552-8050 m s-1, 19.4-23.3 GPa). In particular, the azo compound 9 exhibits competent comprehensive performances (Tdec = 226.2 °C, D = 8502 m s-1, P = 28.9 GPa, IS = 32 J, FS = 320 N). These results suggest that the strategy of integrating tetrazole and 1,3,4-oxadiazole and employing an azo structure as a bridging unit are effective approaches to construct high-energy insensitive materials.

A multi-fused heat-resistant energetic compound constructed by hydrogen bonds

The design of heat-resistant energetic compounds generally employs symmetry, planarity, and multi-hydrogen bonds to obtain compounds with high density, good thermal stability, and low sensitivity. In this paper, a heat-resistant hydrazine-bridged compound, 6,6'-(hydrazine-1,2-diyl)bis(5-nitropyrimidine-2,4-diamine) (PHP), was designed and synthesized with the strategy of multi-fused conjugated structure constructed by hydrogen bonds. The compound featured high symmetry, high planarity, and strong conjugation with good thermal stability (364 °C). This strategy provides a basis for the design of heat-resistant energetic compounds.

Alkaline metal and alkaline earth metal salts of di(1H-tetrazol-5-yl)methanone (DTO): energetic catalysts for ammonium perchlorate decomposition

Six new coordination complexes were obtained and fully characterized; complexes 4 and 5 exhibit good catalytic performances on AP.

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 (D_v = 8272 m s^-1, P = 28.1 GPa). Compound 4 shows moderate thermal stability (161 °C), decent mechanical sensitivity and higher detonation performance (D_v = 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.

Arylpentazoles with surprisingly high kinetic stability

The more-than-one-century-old arylpentazoles can only be used in situ in generating the pentazole anion due to their unfavourable kinetic stability. We successfully increased the N2-leaving barrier to reach hitherto the highest value of 40.83 kcal mol-1 at the CBS-QB3 level via a newly proposed co-stabilization method, making the broader applications of arylpentazoles feasible.

Theoretical study of effects of introducing varying linkages into bis-triazoles on energetic performance

A series of novel bis-triazole compounds was designed by combining high-energy functionalities (nitro and nitramino groups) as substituents with each triazole and incorporating of varying linkages into the bis-triazoles. Then, their heats of formation (HOFs), energetic properties, HOMO-LUMO, electrostatic potential, and impact sensitivity were studied theoretically to facilitate further developments. In general, all the designed compounds possess much higher HOFs than RDX, -CH₂-CH₂-, -N=N-, or -NH-NH- linkages contribute to increase the HOFs, while incorporation of the bridge group -O-CH₂-CH₂-O- shows negative effect on HOFs. Detonation properties of most of the designed compounds can be comparable with or even better than ones of RDX, suggesting that designing the bridged bis-triazoles-based derivatives with energy-rich substituents is an efficient method to obtain potential energetic compounds. Considering the detonation performance and impact sensitivity, -NH-(I), -N=N- (V), and -NH-NH- (VI) are favorable bridged groups between energetic moieties for designing efficient energetic materials (EMs).

Sandwich-like low-sensitive nitroamine explosives stabilized by hydrogen bonds and π–π stacking interactions

Sandwich-like low-sensitive nitroamine explosives were developed which expand the structural category of low-sensitive energetic materials and could give references to the design of new low-sensitive energetic materials.

Recent Advances in Synthesis and Properties of Nitrated-Pyrazoles Based Energetic Compounds

Nitrated-pyrazole-based energetic compounds have attracted wide publicity in the field of energetic materials (EMs) due to their high heat of formation, high density, tailored thermal stability, and detonation performance. Many nitrated-pyrazole-based energetic compounds have been developed to meet the increasing demands of high power, low sensitivity, and eco-friendly environment, and they have good applications in explosives, propellants, and pyrotechnics. Continuous and growing efforts have been committed to promote the rapid development of nitrated-pyrazole-based EMs in the last decade, especially through large amounts of Chinese research. Some of the ultimate aims of nitrated-pyrazole-based materials are to develop potential candidates of castable explosives, explore novel insensitive high energy materials, search for low cost synthesis strategies, high efficiency, and green environmental protection, and further widen the applications of EMs. This review article aims to present the recent processes in the synthesis and physical and explosive performances of the nitrated-pyrazole-based Ems, including monopyrazoles with nitro, bispyrazoles with nitro, nitropyrazolo[4,3-c]pyrazoles, and their derivatives, and to comb the development trend of these compounds. This review intends to prompt fresh concepts for designing prominent high-performance nitropyrazole-based EMs.

1,3,4-Oxadiazole based thermostable energetic materials: synthesis and structure–property relationship

A combination of 1,3,4-oxadiazole and pyrazole produces a series of new compounds with satisfactory energetic properties.

Nitro compounds as the core structures of promising energetic materials and versatile reagents for organic synthesis

This review addresses some promising areas of chemistry of nitro compounds extensively developed in recent years in Russia (particularly at the N.D.Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences) and worldwide. The most important results in the synthesis of novel energetic N-, C- and O-nitro compounds are summarized. New environmentally friendly approaches to the preparation of known compounds of this series, used as components of energetic compositions, are considered. Methods for selective transformations of various nitro compounds to valuable products of organic synthesis, primarily biologically active products and their precursors, are systematically analyzed.

The bibliography includes 446 references.

Versatile functionalization of 3,5-diamino-4-nitropyrazole for promising insensitive energetic compounds

Variation of functional groups offers an efficient approach for tuning properties of materials such as thermal stability, and detonation performance while improving sensitivities to mechanical stimuli. Now versatile functionalization of 3,5-diamino-4-nitropyrazole involving the introduction of a tetrazole ring, or a guanyl group, or ring expansion is described. All of the compounds were fully characterized and some of them (2, 9 and 13) were verified by single crystal X-ray diffraction. Based on their good thermal stabilities and high detonation performance as well as insensitive properties, they are potentially insensitive energetic compounds.