An efficient access to (1H-tetrazol-5-yl)furoxan ammonium salts via a two-step dehydration/[3+2]-cycloaddition strategy

Exploring the energetic potential of 2,5-disubstituted tetrazoles: a case of 2,5-bis(oxadiazolyl)tetrazoles

Exploration of new possible molecular combinations for the preparation of energetic materials remains a challenging task. Herein, the construction of new azole assemblies incorporating the poorly studied 2,5-disubstituted tetrazole motif in combination with oxadiazole moieties is presented. A complete set of experimentally defined properties including thermal stability and mechanical sensitivity, as well as the calculated detonation performance, was evaluated. All target energetic substances have high densities (1.72-1.74 g cm-3) and high combined nitrogen-oxygen content (55-73%). Azo-bridged hexaheterocyclic entities showed high friction sensitivity (on the level of primary explosives), while the introduction of two amino groups improved the sensitivity up to a nitro ester's level, considered as the lowest acceptable level for manufacturing.

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.

Recent progress in synthesis and application of furoxan

This review highlights recent developments in the synthesis and application of furoxan. The chemistry of furoxan is relatively underdeveloped compared to that of other heterocycles owing to its difficult synthesis, which is ascribed to the labile nature of this molecule under various reaction conditions. Nevertheless, recent studies have conducted a variety of bond-forming reactions on the furoxan ring via a post-ring introduction of substituents (PRIS) strategy. This strategy enables the synthesis of furoxan molecules of interest more directly than the conventional methods that rely on the pre-installation of substituents on the furoxan ring precursors. In this review, the PRIS strategy for furoxan synthesis is classified and discussed according to the type of bond formed. Additionally, recent progress in the application of furoxan molecules, predominantly facilitated by the development of new synthetic methods, is covered in this review.

(2-Vinyltetrazolyl)furoxans as New Potential Energetic Monomers

A regioselective approach toward the synthesis of a set of new (2-vinyltetrazolyl)furoxans as potential energetic monomers has been realized. All target energetic materials were thoroughly characterized by spectral and analytical methods. Moreover, crystal structures of two representative heterocyclic systems were studied by single-crystal X-ray diffraction. Prepared high-energy substances have high combined nitrogen-oxygen content (63-71 %), high enthalpies of formation and good detonation parameters (D: 6.7-7.8 km s-1; P: 18-28 GPa). Mechanical sensitivities of the synthesized vinyltetrazoles range these explosives from highly sensitive to completely insensitive. Using calculations of molecular electrostatic potentials (ESP), structural factors influencing the impact sensitivity were revealed. Overall, newly synthesized (2-vinyltetrazolyl)furoxans are of interest as promising energetic monomers due to the presence of the vinyl moiety and explosophoric heterocyclic combination, while their performance exceeds that of benchmark explosive TNT.

Novel family of nitrogen-rich energetic (1,2,4-triazolyl) furoxan salts with balanced performance

Nitrogen-rich energetic materials comprised of a combination of several heterocyclic subunits retain their leading position in the field of materials science. In this regard, a preparation of novel high-energy materials with balanced set of physicochemical properties is highly desired. Herein, we report the synthesis of a new series of energetic salts incorporating a (1,2,4-triazolyl) furoxan core and complete evaluation of their energetic properties. All target energetic materials were well characterized with IR and multinuclear NMR spectroscopy and elemental analysis, while compound 6 was further characterized by single-crystal X-ray diffraction study. Prepared nitrogen-rich salts have high thermal stability (up to 232°C), good experimental densities (up to 1.80 g cm⁻³) and high positive enthalpies of formation (344–1,095 kJ mol⁻¹). As a result, synthesized energetic salts have good detonation performance (D = 7.0–8.4 km s⁻¹; p = 22–32 GPa), while their sensitivities to impact and friction are quite low.

Synthetic Strategies Toward Nitrogen-Rich Energetic Compounds Via the Reaction Characteristics of Cyanofurazan/Furoxan

The structural units of amino-/cyano-substituted furazans and furoxans played significant roles in the synthesis of nitrogen-rich energetic compounds. This account focused on the synthetic strategies toward nitrogen-rich energetic compounds through the transformations based on cyanofurazan/furoxan structures, including 3-amino-4-cyanofurazan, 4-amino-3-cyano furoxan, 3,4-dicyanofurazan, and 3,4-dicyanofuroxan. The synthetic strategies toward seven kinds of nitrogen-rich energetic compounds, such as azo (azoxy)-bridged, ether-bridged, methylene-bridged, hybrid furazan/furoxan-tetrazole–based, tandem furoxan–based, hybrid furazan-isofurazan–based, hybrid furoxan-isoxazole–based and fused framework–based energetic compounds were fully reviewed, with the corresponding reaction mechanisms toward the nitrogen-rich aromatic frameworks and examples of using the frameworks to create high energetic substances highlighted and discussed. The energetic properties of typical nitrogen-rich energetic compounds had also been compared and summarized.

Nitrogen-rich metal-free salts: a new look at the 5-(trinitromethyl)tetrazolate anion as an energetic moiety

A series of energetic nitrogen-rich salts comprised of a 5-(trinitromethyl)tetrazolate anion and high-nitrogen cations was synthesized by simple and efficient chemical routes from readily available commercial reagents. These energetic materials were fully characterized by IR and multinuclear NMR (¹H, ¹³C, ¹⁴N) spectroscopy, elemental analysis, and differential scanning calorimetry (DSC). Additionally, the structure of an energetic salt containing the 3,6,7-triamino-7H-[1,2,4]triazolo[4,3-b][1,2,4]triazolium cation was confirmed by single-crystal X-ray diffraction. The synthesized compounds exhibit decent experimental densities (1.648-1.845 g cm^-3) and positive enthalpies of formation (up to 725.5 kJ mol^-1) and, as a result, superior detonation performance (detonation velocities 8.2-9.2 km s^-1 and detonation pressures 28.5-37.8 GPa), which is comparable to or even exceeding those of commonly used booster explosive PETN. On the other hand, high mechanical sensitivity of several novel 5-(trinitromethyl)tetrazolate salts along with their high combined nitrogen-oxygen content (>81%) and excellent detonation performance render them environmentally friendly alternatives to lead-based primary explosives.

Design and Synthesis of Nitrogen-Rich Azo-Bridged Furoxanylazoles as High-Performance Energetic Materials

A series of novel energetic materials comprising of azo-bridged furoxanylazoles enriched with energetic functionalities was designed and synthesized. These high-energy materials were thoroughly characterized by IR and multinuclear NMR ( 1 H, 13 C, 14 N) spectroscopy, high-resolution mass spectrometry, elemental analysis, and differential scanning calorimetry (DSC). The molecular structures of representative amino and azo oxadiazole assemblies were additionally confirmed by single-crystal X-ray diffraction and X-ray powder diffraction. A comparison of contributions of explosophoric moieties into the density of energetic materials revealed that furoxan and 1,2,4-oxadiazole rings are the densest motifs while the substitution of the azide and amino fragments on the nitro and azo ones leads to an increase of the density. Azo bridged energetic materials have high nitrogen-oxygen contents (68.8-76.9%) and high thermal stability. The synthesized compounds exhibit good experimental densities (1.62-1.88 g cm -3 ), very high enthalpies of formation (846-1720 kJ mol -1 ), and, as a result, excellent detonation performance (detonation velocities 7.66-9.09 km s -1 and detonation pressures 25.0-37.7 GPa). From the application perspective, the detonation parameters of azo oxadiazole assemblies exceed those of the benchmark explosive RDX, while a combination of high detonation performance and acceptable friction sensitivity of azo(1,2,4-triazolylfuroxan) make it a promising potential alternative to PETN.

Nitro-, Cyano-, and Methylfuroxans, and Their Bis-Derivatives: From Green Primary to Melt-Cast Explosives

In the present work, we studied in detail the thermochemistry, thermal stability, mechanical sensitivity, and detonation performance for 20 nitro-, cyano-, and methyl derivatives of 1,2,5-oxadiazole-2-oxide (furoxan), along with their bis-derivatives. For all species studied, we also determined the reliable values of the gas-phase formation enthalpies using highly accurate multilevel procedures W2-F12 and/or W1-F12 in conjunction with the atomization energy approach and isodesmic reactions with the domain-based local pair natural orbital (DLPNO) modifications of the coupled-cluster techniques. Apart from this, we proposed reliable benchmark values of the formation enthalpies of furoxan and a number of its (azo)bis-derivatives. Additionally, we reported the previously unknown crystal structure of 3-cyano-4-nitrofuroxan. Among the monocyclic compounds, 3-nitro-4-cyclopropyl and dicyano derivatives of furoxan outperformed trinitrotoluene, a benchmark melt-cast explosive, exhibited decent thermal stability (decomposition temperature >200 °C) and insensitivity to mechanical stimuli while having notable volatility and low melting points. In turn, 4,4′-azobis-dicarbamoyl furoxan is proposed as a substitute of pentaerythritol tetranitrate, a benchmark brisant high explosive. Finally, the application prospects of 3,3′-azobis-dinitro furoxan, one of the most powerful energetic materials synthesized up to date, are limited due to the tremendously high mechanical sensitivity of this compound. Overall, the investigated derivatives of furoxan comprise multipurpose green energetic materials, including primary, secondary, melt-cast, low-sensitive explosives, and an energetic liquid.

Properties and Promise of Catenated Nitrogen Systems As High-Energy-Density Materials

The properties of catenated nitrogen molecules, molecules containing internal chains of bonded nitrogen atoms, is of fundamental scientific interest in chemical structure and bonding, as nitrogen is uniquely situated in the periodic table to form kinetically stable compounds often with chemically stable N-N bonds but which are thermodynamically unstable in that the formation of stable multiply bonded N₂ is usually thermodynamically preferable. This unique placement in the periodic table makes catenated nitrogen compounds of interest for development of high-energy-density materials, including explosives for defense and construction purposes, as well as propellants for missile propulsion and for space exploration. This review, designed for a chemical audience, describes foundational subjects, methods, and metrics relevant to the energetic materials community and provides an overview of important classes of catenated nitrogen compounds ranging from theoretical investigation of hypothetical molecules to the practical application of real-world energetic materials. The review is intended to provide detailed chemical insight into the synthesis and decomposition of such materials as well as foundational knowledge of energetic science new to most chemists.

Development of a safely handleable synthetic equivalent of cyanonitrile oxide by 1,3-dipolar cycloaddition of nitroacetonitrile

Cyano-aci-nitroacetate serves as a safely handleable precursor of nitroacetonitrile that undergoes 1,3-dipolar cycloaddition to form 3-cyanoisoxazol(in)es.

Design of hybrid heterocyclic systems with a furoxanylpyridine core via tandem hetero-Diels–Alder/retro-Diels–Alder reactions of (1,2,4-triazin-3-yl)furoxans

Synthetic strategy for the synthesis of hybrid heterocyclic systems with the furoxanylpyridine core based on the tandem hetero-Diels–Alder/retro-Diels–Alder reactions of (1,2,4-triazin-3-yl)furoxans with enamine and norbornadiene has been developed.

Metal-assisted addition of a nitrate anion to bis(oxy)enamines. A general approach to the synthesis of α-nitroxy-oxime derivatives from nitronates

α-Nitroxy oxime derivatives have been synthesized by a metal-assisted addition of nitrate anion to bis(oxy)enamines.