Polyazido-methyl Derivatives of Prominent Oxadiazole and Isoxazole Scaffolds: Synthesis, Explosive Properties, and Evaluation

Azidomethyl-bisoxadiazol-linked-1,2,3-triazole-(ABT)-based potential liquid propellant and energetic plasticizer

A scalable synthesis of azidomethyl bisoxadiazol linked-1,2,3-triazole-(ABT) based potential liquid propellant and energetic plasticizer is obtained from commercially available diaminomaleonitrile in excellent yield. Newly synthesized compounds were fully characterized by various spectroscopic techniques. These materials exhibit good densities (1.77 g cm-3) and high thermal stabilities (Td = 181 °C). Compound 5 has good detonation properties (5, P = 20.81 GPa, D = 7516 ms-1) and propulsive properties (Isp (neat) = 210 s). These are superior to TNT and GAP and comparable to BAMOD, making them potential green liquid rocket propellants and energetic plasticizers.

Single Pd-doped arsenene coordinated with nitrogen atoms as an electrocatalyst for effective chlorine evolution reaction: DFT and machine learning studies

We designed a series of single transition metal-anchored arsenene coordinated with nitrogen atoms (TMNx@As) as electrocatalysts for chlorine evolution reaction (CER). Density functional theory (DFT) and machine learning were employed to investigate the catalytic activity of TMNx@As. It is found that the performance of TMNx@As is the best when the transition metal is Pd and the nitrogen coordination content is 66.67%. The catalytic activity of TMNx@As for chlorine evolution reaction is mainly determined by the covalent radius (Rc) and atomic non-bonded radius (Ra) of the transition metal and the fraction of N atoms in metal's coordinating atoms (fN).

Synthesis and Characterization of Azido- and Nitratoalkyl Nitropyrazoles as Potential Melt-Cast Explosives

Desirable advancements in the field of explosive materials include the development of novel melt-castable compounds with melting points ranging from 80 to 110 °C. This is particularly important due to the limited performance and high toxicity associated with TNT (trinitrotoluene). In this study, a series of innovative melt-castable explosives featuring nitratoalkyl and azidoalkyl functionalities attached to the 3-nitro-, 4-nitro-, 3,4-dinitropyrazole, or 3-azido-4-nitropyrazole scaffold are introduced. These compounds were synthesized using straightforward methods and thoroughly characterized using various analytical techniques, including single-crystal X-ray diffraction, IR spectroscopy, multinuclear nuclear magnetic resonance (NMR) spectroscopy, mass spectrometry, elemental analysis, and DTA. Furthermore, the energetic properties such as (theoretical) performance data, sensitivities, and compatibilities of the compounds were evaluated and compared among the different structures.

Design and Synthesis of Energetic Melt-Castable Materials by Substituent-Specific Modification

With the increase in the demand for high-performance composite explosives, the search for advanced energetic melt-castable compounds has attracted increasing attention in the field of energetic materials. Herein, two new energetic materials with nitromethyl and azidomethyl substituents (1-(nitromethyl)-3,4-dinitro-1H-pyrazole (NMDNP) and 1-(azidomethyl)-3,4-dinitro-1H-pyrazole (AMDNP) were prepared by the substituent modification of a potential melt-castable molecule ((3,4-dinitro-1H-pyrazol-1-yl) methyl nitrate, MC-4), respectively. NMDNP exhibited a suitable melting point (90 °C), good thermal stability (Td : 185 °C) and excellent detonation performance (8484 m s-1 ) and impact sensitivity (25 J), thereby demonstrating promise as an energetic melt-castable material. Simultaneously, compared with the nitrato-methyl and azidomethyl substituents, the nitromethyl substituent exhibited greater advantages in regulating performance.

Design and synthesis of phenylene-bridged isoxazole and tetrazole-1-ol based energetic materials of low sensitivity

A variety of phenylene-bridged isoxazole and tetrazole-1-ol based green energetic materials was synthesized, for the first time, in good to excellent yields. The structures of the newly synthesized compounds were confirmed by spectroscopic techniques, elemental analysis, and single-crystal X-ray analysis. The value of the present work is that all newly synthesized compounds have good thermal stabilities ranging between 167-340 °C and acceptable densities between 1.51 g cm^-3 to 1.82 g cm^-3. Detailed computational insight into the energetic properties of the new compounds shows that they have good energetic properties (propulsive and ballistic) with excellent thermal and mechanical stabilities which makes them promising candidates for solid propulsion systems. Compounds 5, 12 and 14 are the superior candidates as melt-castable energetic materials.

Methyl nitrate energetic compounds based on bicyclic scaffolds of furazan-isofurazan (isoxazole): syntheses, crystal structures and detonation performances

Two energetic bicyclic scaffolds (furazan-isoxazole and furazan-1,3,4-oxadiazole) were constructed via different cyclization reactions. Based on the energetic bicyclic scaffolds, the energetic compounds, 3-(4-nitraminofurazan-3-ly)-isoxazole-5-methylnitrate 1c and 5-(4-nitraminofurazan-3-ly)-1,3,4-oxadiazole-2-methylnitrate 2c, were designed and synthesized in good yields. Because of the acidity of nitramine, the corresponding energetic ionic salts, ammonium 3-(4-nitraminofurazan-3-ly)isoxazole-5-methylnitrate 1d and ammonium 5-(4-nitraminofurazan-3-ly)-1,3,4-oxadiazole-2-methylnitrate 2e, were also obtained and well characterized, their structures were further determined by X-ray single crystal diffraction. To have a better understanding of the structure-property relationships of furazan-bicyclic scaffolds and nitrate groups, their thermal behaviors, detonation performances and the sensitivities were investigated via differential scanning calorimetry (DSC), ESP analysis, Hirshfeld surfaces calculation, EXPLO5 program and BAM standard techniques. Compared with those of ammonium 5-(4-nitraminofurazan-3-ly)-1,2,4-oxadiazole-2-methylnitrate 3e, the results show that all these methyl nitrate energetic compounds based on bicyclic scaffolds of furazan-isofurazan exhibit good detonation performances and extraordinary insensitivities. As supported by experimental and theoretical data, the formation of energetic ionic salts causes an increase of the weak interactions, significantly improving the thermal performance over 110 °C.

Nitrene formation is the first step of the thermal and photochemical decomposition reactions of organic azides

In this work, the decomposition of a prototypical azide, isopropyl azide, both in the ground and excited states, has been investigated through the use of multiconfigurational CASSCF and MS-CASPT2 electronic structure approaches. Particular emphasis has been placed on the thermal reaction starting at the S₀ ground state surface. It has been found that the azide thermally decomposes via a stepwise mechanism, whose rate-determining step is the formation of isopropyl nitrene, which is, in turn, the first step of the global mechanism. After that, the nitrene isomerizes to the corresponding imine derivative. Two routes are possible for such a decomposition: (i) a spin-allowed path involving a transition state; and (ii) a spin-forbidden one via a S₀/T₀ intersystem crossing. Both intermediates have been determined and characterised. Their associated relative energies have been found to be quite similar, 45.75 and 45.52 kcal mol^-1, respectively. To complete this study, the kinetics of the singlet and triplet channels are modeled with the MESMER (Master Equation Solver for Multi-Energy Well Reactions) code by applying the RRKM and Landau-Zener (with WKB tunnelling correction) theories, respectively. It is found that the canonical rate-coefficients of the singlet path are 2-orders of magnitude higher than the rate-coefficients of the forbidden reaction. In addition, the concerted mechanism has been investigated that would lead to the formation of the imine derivative and nitrogen extrusion in the first step of the decomposition. After a careful analysis of CASSCF calculations with different active spaces and their comparison with single electronic configuration methods (MP2 and B3LYP), the concerted mechanism is discarded.

Synthesis of heterocyclic (triazole, furoxan, furazan) fused pyridazine di-N-oxides via hypervalent iodine oxidation

Use of a mild PIDA oxidation strategy to access heterocyclic (triazole, furoxan, furazan) fused pyridazine di-N-oxides.

N-Functionalisation of 5,5'-bistetrazole providing 2,2'-di(azidomethyl)bistetrazole: a melt-castable metal-free green primary explosive

N-Hydroxymethylation of heterocyclic compounds offers a promising starting procedure to ultimately introduce nitratomethyl- as well as azidomethyl-moieties. Applied to 5,5'-bistetrazole, the resulting 2,2'-di(azidomethyl)bistetrazole (3) and 2,2'-di(nitratomethyl)bistetrazole (4) are high-performing melt-castable energetic materials. Sensitivities were predicted by Hirshfeld analysis and explored in detail by experimental analysis. Because of their increased values towards mechanical stimuli and a short deflagration to detonation transition (DDT), the diazidomethyl derivative especially shows promise as a new melt-castable primary explosive.

Synthesis and Characterization of the Potential Melt-Castable Explosive 3-(1,2,4-Oxadiazolyl)-5-Nitratomethyl Isoxazole

The synthesis of 3-(1,2,4-oxadiazolyl)-5-nitratomethyl isoxazole (C₆ H₄ N₄ O₅ ), its physical properties, and its theoretical performances are described. This energetic material was found to have a melting point range of 76.6-79.2 °C, and a thermal onset decomposition temperature of 184.5 °C. These thermal features put this material into the standalone melt-castable explosive class. The material was found to have TNT performance, and was found to be insensitive to impact, friction, and electrostatic discharge, despite having a nitric ester functionality. A critical reaction in making this molecule was the desymmetrization of diaminoglyoxime. The optimization of this transformation is described. Previous reports of this desymmetrization were found to be inaccurate, as the desymmetrization reaction produces a co-crystal of mono- and bi-1,2,4-oxadiazole products.