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.     

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.     

Structural and functional diagnostics of ultrafine components in condensed high-energy systems

The study deals with octogen (HMX) and aluminum, which are among the most widely used components of condensed high-energy systems. The structure, thermal behavior and combustion parameters were determined for the octogen-based monofuels and octogen-aluminum binary systems at different dispersity of components. Irrespective of differences in thermal behavior, monofuels obtained with standard and ultrafine octogen powders were shown to have virtually identical combustion parameters. In the binary systems, replacement of standard microsized aluminum by ultrafine one increases the combustion rate by a factor of 2.5, and completeness of the metal reaction (oxidation) by a factor of 4.     

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 (¹H, ¹³C, ¹⁴N) 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.     

High-energy 4(10)-2-fluoro-2,2-dinitroethyl and 4(10)-2,2-dinitropropyl derivatives of polynitrohexaazaisowurtzitanes

Russian Chemical Bulletin - Methods for the syntheses of a series of high-energy 4(10)-2-fluoro-2,2-dinitroethyl and 4(10)-2,2-dinitroethyl derivatives of polynitrohexaazaisowurtzitanes were...     

The structure of particles and combustion parameters of compositions with nanoaluminum

Aluminum nanoparticles modified with various additives (Ba, gasoline, and organosilicon resin) were obtained by arc plasma recondensation. The chemical composition, morphology, and thermal properties of nanoparticles and the characteristics of combustion of energy-producing condensed systems containing nanoaluminum were studied experimentally. The structure of the particles was determined by X-ray diffraction (a Rigaku Geigerflex diffractometer), transmission electron microscopy (JEM 2000 EX-II), scanning electron microscopy (JEOL JSM 7401F), atomic force microscopy (SOLVER P-47), and differential scanning calorimetry (NETZSCH STA 409). The replacement of aluminum powder with micron particles with nanodisperse aluminum increased the rate of combustion of stoichiometric compositions on the basis of ammonium perchlorate by an order of magnitude at a pressure of 40 atm. Simultaneously, the mean linear diameter of agglomerates collected from the surface of combustion decreased from 28 to 2 μm. The results are evidence that the use of energy-producing condensed compositions with nanoaluminum offers much promise for increasing the effectiveness of solid fuel rocket engines.     

Comparative study of HMX and CL-20

This study deals with a well-known monocyclic nitramine HMX and a relatively new polycyclic strained-cage nitramine CL-20. Experimental data on the powder morphology, simultaneous thermal analysis (STA) and burning rate of binary formulations Al/HMX and Al/CL-20 are presented. Kinetic modelling for HMX and CL-20 are considered based on analysis of STA data obtained for low heating rates. The processing of STA data by the Kissinger method was shown to need to be supplemented with the construction of a thermokinetic model. The thermal decomposition of HMX is reliably described by the reaction of the first order with the autocatalysis. Obtained kinetic parameters of the HMX thermal decomposition correlate with literature-known data on kinetics of the lead stage of HMX combustion. Two types of aluminium powder, i.e. micron-sized and ultrafine, are used to investigate the interaction with both nitramines. Thermal analysis revealed the higher Al oxidation ability of the solid compounds produced at CL-20 thermolysis, than that one of HMX. Burning rate experiments show the differences in the combustion parameters between CL-20- and HMX-based formulations, specifically along with the burn rate level increase for CL-20 monopropellant as compared to HMX one, the pressure exponent and effect of the aluminium particle size variation are also distinct. Results are analyzed and compared to available literature data.     

Effect of polymorphic phase transitions on stability of energetic compounds. Thermal transformations of 2,4,6-tris(2,2,2-trinitroethylnitramino)-1,3,5-triazine

Russian Chemical Bulletin - The kinetics of thermal transformations of the energetic compound 2,4,6-tris(2,2,2- trinitroethylnitramino)-1,3,5-triazine (1) and products of this reaction were studied...     

Physicochemical characteristics of the components of energetic condensed systems

The physicochemical characteristics of nanosized energetic materials (aluminum, ammonium nitrate, RDX) are studied and the burning rate of energetic condensed systems containing nanosized components is determined. The morphology, chemical purity, and thermal properties of nanosized powders produced by vacuum and plasma recondensation were examined. The materials obtained are identical to the precursors and are characterized by an increased reactivity compared to their microsized counterparts. At a pressure of 100 atm, a monopropellant prepared from nanosized RDX particles is found to have twice as high the burning velocity as a microsized RDX propellant. For nanoaluminum-ammonium perchlorate compositions, the burning velocity is demonstrated to be an order of magnitude higher than that for similar compositions with microsized aluminum. An important feature of nanoaluminum-based formulations is a decrease in the degree of agglomeration of metal fuel products and, hence, in two-phase losses in solid-propellant rocket engines.     

3-(4-R-3-Furazanyl)-5-nitropyrazolyl-1,2,4-oxadiazoles as a new class of energy rich ensembles

A number of new energetic compounds were synthesized based on a combination of pyrazole, furazan, and 1,2,4-oxadiazole. Density, temperature of decomposition, and mechanical sensitivity of the compounds obtained were experimentally determined. Their detonation parameters were calculated.