Nitrification Progress of Nitrogen-Rich Heterocyclic Energetic Compounds: A Review

As a momentous energetic group, a nitro group widely exists in high-energy-density materials (HEDMs), such as trinitrotoluene (TNT), 1,3,5-triamino-2,4,6-trinitrobenzene (TATB), cyclo-1,3,5-trimethylene-2,4,6-trinitramine (RDX), etc. The nitro group has a significant effect on improving the oxygen balance and detonation performances of energetic materials (EMs). Moreover, the nitro group is a strong electron-withdrawing group, and it can increase the acidity of the acidic hydrogen-containing nitrogen-rich energetic compounds to facilitate the construction of energetic ionic salts. Thus, it is possible to design nitro-nitrogen-rich energetic compounds with adjustable properties. In this paper, the nitration methods of azoles, including imidazole, pyrazole, triazole, tetrazole, and oxadiazole, as well as azines, including pyrazine, pyridazine, triazine, and tetrazine, have been concluded. Furthermore, the prospect of the future development of nitrogen-rich heterocyclic energetic compounds has been stated, so as to provide references for researchers who are engaged in the synthesis of EMs.     

Energetic Salts Based on Tetrazole N‐Oxide

Energetic materials (explosives, propellants, and pyrotechnics) are used extensively for both civilian and military applications and the development of such materials, particularly in the case of energetic salts, is subject to continuous research efforts all over the world. This Review concerns recent advances in the syntheses, properties, and potential applications of ionic salts based on tetrazole N‐oxide. Most of these salts exhibit excellent characteristics and can be classified as a new family of highly energetic materials with increased density and performance, alongside decreased mechanical sensitivity. Additionally, novel tetrazole N‐oxide salts are proposed based on a diverse array of functional groups and ions pairs, which may be promising candidates for new energetic materials.     

Kinetic Stability and Propellant Performance of Green Energetic Materials

A thorough theoretical investigation of four promising green energetic materials is presented. The kinetic stability of the dinitramide, trinitrogen dioxide, pentazole, and oxopentazole anions has been evaluated in the gas phase and in solution by using high‐level ab initio and DFT calculations. Theoretical UV spectra, solid‐state heats of formation, density, as well as propellant performance for the corresponding ammonium salts are reported. All calculated properties for dinitramide are in excellent agreement with experimental data. The stability of the trinitrogen dioxide anion is deemed sufficient to enable synthesis at low temperature, with a barrier for decomposition of approximately 27.5 kcal mol^?1 in solution. Oxopentazolate is expected to be approximately 1200 times more stable than pentazolate in solution, with a barrier exceeding 30 kcal mol^?1, which should enable handling at room temperature. All compounds are predicted to provide high specific impulses when combined with aluminum fuel and a polymeric binder, and rival or surpass the performance of a corresponding ammonium perchlorate based propellant. The investigated substances are also excellent monopropellant candidates. Further study and attempted synthesis of these materials is merited.     

Novel Highly Energetic Pyrazoles: N‐Trinitromethyl‐Substituted Nitropyrazoles

A new family of energetic compounds, nitropyrazoles bearing a trinitromethyl moiety at the nitrogen atom of the heterocycle, was designed. The desirable high‐energy dense oxidizers 3,4‐dinitro‐ and 3,5‐dinitro‐1‐(trinitromethyl)pyrazoles were synthesized in good yields by destructive nitration of the corresponding 1‐acetonylpyrazoles. All of the prepared compounds were fully characterized by multinuclear NMR and IR spectroscopy, as well as by elemental analysis. Single‐crystal X‐ray diffraction studies show remarkably high density. Impact sensitivity tests and thermal stability measurements were also performed. All of the pyrazoles possess positive calculated heats of formation and exhibit promising energetic performance that is the range of 1,3,5‐trinitroperhydro‐1,3,5‐triazine and pentaerythritol tetranitrate. The new pyrazoles exhibit positive oxygen balance and are promising candidates for new environmentally benign energetic materials.     

含能盐和含能离子液体

近年来含能盐和含能离子液体由于其独特的性质而受到广泛关注。本文综述了多种含能盐和含能离子液体（阳离子包括三唑、四唑、双环唑、六次甲基四胺等;阴离子包括硝酸根、高氯酸根、硝基唑、叠氮根、四硝基铝、多腈基化合物、二硝基尿素等）的合成;结合其表征结果分析了阳离子上的取代基以及阴阳离子对它们的性能如熔点、生成焓、密度等的影响。对含能盐和含能离子液体在炸药和推进剂方面的应用进行了展望。     

Synthesis of Energetic Polyethers from Halogenated Precursors

In the solid rocket propellant formulations an important component is the polymeric binder. Actually, the most used binder is hydroxyl-terminated polybutadiene. However, the research is oriented toward the use of energetic polymers which, in addition to the binder function, should improve the propulsion capability of the propellant. In this respect, good candidates are oxetanic polyethers with azidic functionalities in their side chains. Considering the explosive character of such materials, their synthesis must be designed with attention to the safety of the process. In this note, the preparation of azidic copolymers is described and different synthetic strategies are discussed and compared.     

3-氨基-4-硝基氧化呋咱含能化合物的设计合成研究

在氧化呋咱环上引入氨基或硝基等功能基团,可提高含能化合物的能量密度和爆炸性能。为了获得更高能量密度的新型含能化合物,本文利用密度泛函理论（DFT）和单、双激发的耦合簇（CCSD）方法探索了以3-酰基叠氮基-4硝基氧化呋咱为起始材料,在二氧六环和水混合溶剂中合成3-氨基-4硝基氧化呋咱的反应机理,给出了反应的势能曲线。结果表明,该反应主要分为两个阶段：3-酰基叠氮基-4硝基氧化呋咱脱N₂后进行Curtious重排产生异氰酸酯;异氰酸酯经水解、羟基扭转、CO₂的脱离形成产物。反应的决速步为CO₂的脱离,能垒为44kcal/mol。因此,加热是实现该合成反应的必要条件。水既绿色环保,又参与反应,是该反应的最佳溶剂。这些结果为3-氨基-4-硝基氧化呋咱的实验合成提供了必要的理论依据。     

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).     

共晶含能材料研究进展

共晶是不同种类的分子(两种或两种以上)通过氢键等分子间相互作用,形成具有特定结构和性能的多组分分子晶体,不同含能材料形成共晶可以有效改善炸药的感度、安全性等性能。针对目前高能炸药的改性需求,共晶在含能材料领域中的应用具有巨大的潜力。综述了共晶的形成原理及生长特性,总结了常见共晶的制备方法和表征方法,评述了含能材料共晶的研究现状和发展前景。     

An Alliance of Polynitrogen Heterocycles: Novel Energetic Tetrazinedioxide-Hydroxytetrazole-Based Materials

Energetic materials constitute one of the most important subtypes of functional materials used for various applications. A promising approach for the construction of novel thermally stable high-energy materials is based on an assembly of polynitrogen biheterocyclic scaffolds. Herein, we report on the design and synthesis of a new series of high-nitrogen energetic salts comprising the C-C linked 6-aminotetrazinedioxide and hydroxytetrazole frameworks. Synthesized materials were thoroughly characterized by IR and multinuclear NMR spectroscopy, elemental analysis, single-crystal X-ray diffraction and differential scanning calorimetry. As a result of a vast amount of the formed intra- and intermolecular hydrogen bonds, prepared ammonium and amino-1,2,4-triazolium salts are thermally stable and have good densities of 1.75–1.78 g·cm⁻³. All synthesized compounds show high detonation performance, reaching that of benchmark RDX. At the same time, as compared to RDX, investigated salts are less friction sensitive due to the formed net of hydrogen bonds. Overall, reported functional materials represent a novel perspective subclass of secondary explosives and unveil further opportunities for an assembly of biheterocyclic next-generation energetic materials.     

Study of Furoxan Derivatives for Energetic Applications

Two novel energetic compounds, 3,4‐bis(1′,2′,4′‐triazole‐3′‐yl)furoxan (BTAF) and 3,4‐bis(1′‐nitro‐1′,2′,4′‐triazole‐3′‐yl)furoxan (BNTAF), were prepared and their structures were characterized by IR, ¹H NMR, ¹³C NMR, MS techniques and elemental analysis. The properties of BTAF and BNTAF were estimated. The predicted performance data of BTAF are as follows: density (measured) is 1.75 g/cm³, nitrogen content 50.9%, detonation velocity 7277 m/s, detonation pressure 20.1 GPa and enthalpy of formation +419.7 kJ/mol. The predicted performance data of BNTAF are as follows: density is 1.84 g/cm³, nitrogen content 45.2%, enthalpy of formation +841.5 kJ/mol, detonation velocity 8490 m/s and detonation pressure 32.4 GPa. The main themal properties of BTAF and BNTAF were analyzed by DSC and TG techniques, the results show that BTAF melts with concomitant decomposition at 188.8°C, the melting point of BNTAF is at 99.2°C and its first decomposition temperature is 139.2°C.     

Dense Energetic Nitraminofurazanes

3,3′‐Diamino‐4,4′‐bifurazane ( 1 ), 3,3′‐diaminoazo‐4,4′‐furazane ( 2 ), and 3,3′‐diaminoazoxy‐4,4′‐furazane ( 3 ) were nitrated in 100 % HNO₃ to give corresponding 3,3′‐dinitramino‐4,4′‐bifurazane ( 4 ), 3,3′‐dinitramino‐4,4′‐azofurazane ( 5 ) and 3,3′‐dinitramino‐4,4′‐azoxyfurazane ( 6 ), respectively. The neutral compounds show very imposing explosive performance but possess lower thermal stability and higher sensitivity than hexogen (RDX). More than 40 nitrogen‐rich compounds and metal salts were prepared. Most compounds were characterized by low‐temperature X‐ray diffraction, all of them by infrared and Raman spectroscopy, multinuclear NMR spectroscopy, elemental analysis, and by differential scanning calorimetry (DSC). Calculated energetic performances using the EXPLO5 code based on calculated (CBS‐4M) heats of formation and X‐ray densities support the high energetic performances of the nitraminofurazanes as energetic materials. The sensitivities towards impact, friction, and electrostatic discharge were also explored. Additionally the general toxicity of the anions against vibrio fischeri, representative for an aquatic microorganism, was determined.     

Energetic heterocyclic N-oxides: synthesis and performance

Novel synthetic strategies toward construction and functionalization of nitrogen-rich energetic compounds bearing at least one heterocyclic N-oxide scaffold are briefly overviewed. The present focus review summarizes main recent advances (published in the period 2017–2022) in the chemistry of five- and six-membered heterocyclic N-oxides as well as their linear combinations and fused bi-, tri- and tetraheterocyclic frameworks which are of paramount importance for the development of next-generation energetic materials. Physicochemical properties along with detonation performance and mechanical sensitivities of the reported high-energy substances are discussed and their application potential is especially emphasized.     

Syntheses of Energetic cyclo‐Pentazolate Salts

Three energetic salts of cyclo‐N₅^? were synthesized via a metathesis reaction of barium pentazolate and sulfates which was driven by the precipitation of BaSO₄. All the energetic cyclo‐N₅^? salts were characterized by single‐crystal X‐ray diffraction, infrared (IR), ¹H and ¹³C multinuclear NMR spectroscopies, thermal analysis (TGA and DSC), and elemental analysis. The salts exhibit relatively good detonation performance with low sensitivities and good thermal stabilities. This new method opens the door to exploring more pentazolate anion‐containing high‐performance energetic materials.     

十二烷基苯的硝化选择性

借助气相色谱发现正十二烷基苯在硝硫混酸和硝磷混酸中硝化时，一硝化产物中对位异构体可达６０％，较在硝酸乙酸酐中硝化时的对位选择性高１０％，利用１ＨＮＭＲ测定了工业十二烷基苯和正十二烷基苯在高浓度硫酸（９８％）的硝硫混酸中的硝化选择性，发现前者的硝化中对位异构体的高达８０％。     

Selective Nitration of Phenolic Compounds by Green Synthetic Approaches

Aromatic nitration is one of the most important unit processes in synthetic organic chemistry and in the chemical industry. Particularly, nitrophenols are important precursors for the production of dyestuffs, pharmaceuticals, agrochemicals, explosives, plastics, and other industrially important products. Many commercial processes are available for the production of these important nitro precursors, but some processes are commonly lead to mixtures of regioisomers and are not environmentally friendly. Thus, in recent years many scientists have been developed new methodologies to improve selectivity and yield of the products. In this review, we summarize recent advances in the synthesis of nitrophenols by green chemistry approaches.     

Dimethoxycarbonyl Groups Surrounding a Symmetric Diaminobistetrazole Ring: Exploring New Green Energetic Materials

A novel oxygen‐containing dimethoxycarbonyl diaminobistetrazole ( 1 ) was synthesized via a facile strategy. The sodium salt ( 2 ) based on this ligand was prepared and these two compounds were fully characterized by using elemental analysis, IR and mass spectrometry and single‐crystal X‐ray diffraction. Their density, heats of formation, thermal stability and sensitivity, as well as the energetic properties from EXPLO5 code were investigated. These newly synthesized compounds possess high positive heats of formation and detonation heats. Compound 1 exhibits good detonation performance and acceptable stability, and might be a potential eco‐friendly alternative of lead azide. The present study contributes to the development of tetrazole derivatives as new energetic materials.     

吡唑及吡嗪类含能化合物研究进展

吡唑和吡嗪分别为分子中含两个氮原子的五元和六元杂环,是富氮杂环化合物的理想结构单元.部分具有生成焓高、热稳定性好和感度较低等特点.介绍了吡唑、吡嗪类高氮杂环含能化合物的合成、性能以及在含能材料中的应用研究进展,其中LLM-105和ANPZ-i在钝感炸药中应用前景良好,预测了两类含能化合物的发展前景.