Triazole-Substituted Nitroarene Derivatives: Synthesis, Characterization, and Energetic Studies

Synthetic manifestation of trinitro-pyrazolo-2H-1,2,3-triazoles (TNPT) as insensitive energetic materials

This study showcases the design and development of a facile method for synthesizing trinitro-pyrazolo-triazole (TNPT) and its derivatives. The synthesized compounds are analysed using multinuclear NMR [1H, 13C, and 15N] and HRMS analyses. Furthermore, X-ray diffraction studies confirm the structure of some TNPT derivatives. Notably, compounds 8, 9, 11, and 12 exhibit good thermal stability with a decomposition threshold above 250 °C, and show a high level of insensitivity towards impact and friction [impact sensitivity (IS) is more than 25 J and friction sensitivity (FS) is above 180 N]. Compound 12, in particular, displays excellent performance characteristics [density 1.76 g cc-1 (at 298 K), a high detonation velocity (Dv = 8550 m s-1), and good thermal stability (Td = 280 °C), with high insensitivity towards impact and friction (IS = 35 J; FS = 180 N)]. The Hirshfeld surface analysis study provides further insight into the sensitivity of the TNPT derivatives.

Computational Manifestation of Nitro-Substituted Tris(triazole): Understanding the Impact of Isomerism on Performance-Stability Parameters

Density functional theory (DFT) methods were used to design a series of energetic dinitro-tris(triazole) isomers by altering the triazole rings and -NO2 groups. The impact of three nitrogen atoms' position in the tris(triazole) scaffold on energy content, performance, and stability was discussed. Based on computed heats of formation and densities, the detonation properties were predicted using the thermochemical EXPLO5 (v6.06) code. Using the bond dissociation energy of the longest C-NO2 bond, the thermal stability was investigated. The mechanical sensitivities were estimated and correlated with RDX and HMX using maximum heats of detonation (Q), free void (ΔV) in the lattice of the crystalline compound, and total -NO2 group charge. Among the designed series, compounds O4, R1, R3, and R4 display high heats of formation (>450 kJ/mol), high densities (>1.92 g/cm3), good detonation performances (D > 8.76 km/s and P > 32.0 GPa), and low sensitivities. Our findings suggest that the isomeric tricyclic triazole backbone could be a promising platform for developing new high-performing and thermostable energy materials.

Reduction of stress responses in honey bees by synthetic ligands targeting an allatostatin receptor

Honey bees are of great economic and ecological importance, but are facing multiple stressors that can jeopardize their pollination efficiency and survival. Therefore, understanding the physiological bases of their stress response may help defining treatments to improve their resilience. We took an original approach to design molecules with this objective. We took advantage of the previous identified neuropeptide allatostatin A (ASTA) and its receptor (ASTA-R) as likely mediators of the honey bee response to a biologically relevant stressor, exposure to an alarm pheromone compound. A first series of ASTA-R ligands were identified through in silico screening using a homology 3D model of the receptor and in vitro binding experiments. One of these (A8) proved also efficient in vivo, as it could counteract two behavioral effects of pheromone exposure, albeit only in the millimolar range. This putative antagonist was used as a template for the chemical synthesis of a second generation of potential ligands. Among these, two compounds showed improved efficiency in vivo (in the micromolar range) as compared to A8 despite no major improvement in their affinity for the receptor in vitro. These new ligands are thus promising candidates for alleviating stress in honey bees.

Polynitro-N-aryl-C-nitro-pyrazole/imidazole Derivatives: Thermally Stable-Insensitive Energetic Materials

A wide array of methoxy-substituted-polynitro-aryl-pyrazole/imidazoles with readily oxidizable -NH₂/NO₂/NHNO₂/diazo functional groups is synthesized. Single crystal X-ray diffraction (XRD) analysis confirms the molecular structure of the compounds. Energetic properties of the synthesized compounds are determined by theoretical and experimental studies. Most of the compounds are thermally stable and insensitive to impact and friction. Some of the molecules possess better detonation velocity and detonation pressure over TNT.

Mutually Isomeric 2- and 4-(3-nitro-1,2,4-triazol-1-yl)pyrimidines Inspired by an Antimycobacterial Screening Hit: Synthesis and Biological Activity against the ESKAPE Panel of Pathogens

Starting from the structure of antimycobacterial screening hit OTB-021 which was devoid of activity against ESKAPE pathogens, we designed, synthesized and tested two mutually isomeric series of novel simplified analogs, 2- and 4-(3-nitro-1,2,4-triazol-1-yl)pyrimidines, bearing various amino side chains. These compounds demonstrated a reverse bioactivity profile being inactive against M. tuberculosis while inhibiting the growth of all ESKAPE pathogens (with variable potency patterns) except for Gram-negative P. aeruginosa. Reduction potentials (E_1/2, V) measured for selected compounds by cyclic voltammetry were tightly grouped in the -1.3--1.1 V range for a reversible single-electron reduction. No apparent correlation between the E_1/2 values and the ESKAPE minimum inhibitory concentrations was established, suggesting possible significance of other factors, besides the compounds' reduction potential, which determine the observed antibacterial activity. Generally, more negative E_1/2 values were displayed by 2-(3-nitro-1,2,4-triazol-1-yl)pyrimidines, which is in line with the frequently observed activity loss on moving the 3-nitro-1,2,4-triazol-1-yl moiety from position 4 to position 2 of the pyrimidine nucleus.

Time-Domain Terahertz Spectroscopy and Density Functional Theory Studies of Nitro/Nitrogen-Rich Aryl-Tetrazole Derivatives

The paper reports the time-domain THz spectroscopy studies of noncentrosymmetric energetic nitro/nitrogen-rich aryl-tetrazole high-energy molecules. The fingerprint spectra in the THz domain reveal the role of different functional groups attached to position "1" of the tetrazole moiety, which controls the energetic properties. These responses are deliberated through density functional theory (DFT) calculations. The synthesized aryl-tetrazoles exhibit high positive heat of formation (369-744 kJ/mol), high detonation velocities, and pressures (D _v: 7734-8298 m·s^-1; D _p: 24-28 GPa) in comparison to the noncentrosymmetric 2,4,6-trinitrotoluene (TNT). These compounds exhibit variation in the refractive indices and absorption between 0.1 and 2.2 THz range. The DFT studies at the molecular and single-crystal level (using plane wave pseudo potential method) endorse in detecting these bands (with ∼1% deviation). The calculated vibrational frequencies and linear optical properties are found to have good agreement with the experimental data in UV-visible and THz regions.

A novel energetic framework combining the advantages of furazan and triazole: a design for high-performance insensitive explosives

Combining energetic furazan and triazole rings to achieve a series of high performance and insensitive energetic compounds.

A comparative study of thermal stability of TNT, RDX, CL20 and ANTA explosives using UV 266 nm-time resolved photoacoustic pyrolysis technique

The paper reports the potential use of UV based pulsed photoacoustic spectroscopy to study the thermal stability of some well-known premier explosives such as TNT, RDX, CL20, and ANTA between 30 and 350 °C range. The thermal PA spectra of samples were recorded using fourth harmonic wavelength i.e. 266 nm of pulse duration 7 ns and repetition rate 10 Hz obtained from Q-switched Nd: YAG laser system. Under the influence of UV radiation, the explosive molecules in vapor phase follow the photodissociation process and converted into their byproducts such as NO, NO₂ and N₂O etc. due to π* ← n transitions, which are responsible for the generation resultant PA signal at 266 nm wavelength. The results obtained from PA spectra as a function of temperature are cross verified with Thermo gravimetric-differential thermal analysis (TG-DTA) to ascertain the thermal stability of these samples. The comparative PA spectra of samples were analyzed and shown the behavior of acoustic modes with respect to incident laser energy, and data acquisition time. Finally, the thermal quality factor "Q" is measured to test the stability of reported explosives.

Synthesis and performance study of methylene-bridged bis(nitramino-1,2,4-oxadiazole) and its energetic salts

A series of new energetic compounds based on methylene-bridged bis(nitramino-1,2,4-oxadiazole) was synthesized through a simple, safe and efficient route and fully characterized.

Estimating the densities of benzene-derived explosives using atomic volumes

The application of average atomic volumes to predict the crystal densities of benzene-derived energetic compounds of general formula C _a H _b N _c O _d is presented, along with the reliability of this method. The densities of 119 neutral nitrobenzenes, energetic salts, and cocrystals with diverse compositions were estimated and compared with experimental data. Of the 74 nitrobenzenes for which direct comparisons could be made, the % error in the estimated density was within 0-3% for 54 compounds, 3-5% for 12 compounds, and 5-8% for the remaining 8 compounds. Among 45 energetic salts and cocrystals, the % error in the estimated density was within 0-3% for 25 compounds, 3-5% for 13 compounds, and 5-7.4% for 7 compounds. The absolute error surpassed 0.05 g/cm³ for 27 of the 119 compounds (22%). The largest errors occurred for compounds containing fused rings and for compounds with three -NH₂ or -OH groups. Overall, the present approach for estimating the densities of benzene-derived explosives with different functional groups was found to be reliable. Graphical abstract Application and reliability of average atom volume in the crystal density prediction of energetic compounds containing benzene ring.

3-Amino-1,2,4(4H)-oxadiazol-5-one (AOD) and its nitrogen-rich salts: a class of insensitive energetic materials

The 3-amino-1,2,4(4H)-oxadiazole-5-one and its nitrogen-rich salts are synthesized in good yield. The compounds show promise as insensitive energetic ingredients.

Synthesis and properties of 5,5′-dinitramino-3,3′-bi(1,2,4-oxadiazole) and its energetic salts

In order to develop high energy density materials, 5,5′-dinitramino-3,3′-bi(1,2,4-oxadiazole) (3, DNABO), a new heterocyclic energetic compound, was synthesized by the simple nitration of 5,5′-diamino-3,3′-bi(1,2,4-oxadiazole) (2) with 95% fuming nitric acid.

Comparative Study of Ultraviolet Laser-Based Time-Resolved Photoacoustic Fingerprint Spectra and Thermal Decomposition Mechanisms of Energetic 1,2,3-1H-Triazole Derivatives Under Controlled Pyrolysis

We report the comparative study of photoacoustic (PA) fingerprint spectra, thermal decomposition, and stability mechanism of some phenyl and bis series energetic compounds named 1-(2-methoxy,-3,5-dinitrophenyl)-1H-1,2,3-triazole ( S₅), 1-(3-methoxy, 2, 6 dinitrophenyl) 1H-1, 2, 3 triazole ( S₁₀), 1-(4-nitrophenyl)-1H-1,2,3-triazole ( S₈), and 2,6-bis ((4-(nitromethyl)-1H-1,2,3-triazol-1-yl)methyl) pyridine ( S₉). Fourth harmonic wavelength, i.e., 266 nm of pulse duration 7 ns and 10 Hz repetition rate obtained from Q-switched Nd: YAG laser, was used to record the thermal PA spectra of these compounds under controlled pyrolysis condition in the range of 30-350 ℃. The PA fingerprint spectra are produced due to entire molecule vapor along with principal functional byproduct NO₂ molecule. NO₂ molecule is a major gas released during thermal decomposition due to weakest nature of C-NO₂ bond. Further, NO₂ molecules are involved in photodissociation process due to π*← n transition and converted into NO molecules inside the PA cell due to excitation by 266 nm wavelength. The combined results of PA and gas chromatography-mass spectrometry (GC-MS) spectra along with thermo gravimetric-differential thermal analysis (TG-DTA) data confirm the thermal decomposition mechanism process that can be completed in multiple steps. In addition, GC-MS spectra also confirm the release of NO and NO₂ molecules. The effect of incident laser energy and data acquisition time has been carried out for understanding the behavior of acoustic modes. Finally, the thermal quality factor "Q" is measured to test the stability of compounds.

Structures and properties of energetic cations in energetic salts

Energetic cations play important roles in energetic performance, which may attribute to the diverse backbones and substituted groups of energetic cations. This review emphasizes the roles of backbones and substituted groups in the energetic performance of energetic salts.

Theoretical studies on the derivatives of tris([1,2,4]triazolo)[4,3-a:4′,3′-c:4′′,3′′-e][1,3,5]triazine as high energetic compounds

Tris([1,2,4]triazolo)[4,3-a:4′,3′-c:4′′,3′′-e][1,3,5]triazine inherited from triazole and triazine is suggested theoretically as a new framework for insensitive and high-energetic materials.

Investigation of the thermal decomposition and stability of energetic 1,2,4-triazole derivatives using a UV laser based pulsed photoacoustic technique

The paper reports PA fingerprint spectra, thermal stability and efficiency as rocket fuel for nitro rich energetic materials labeled as p-Me-DNPT, p-OMe-DNPT and p-NH₂-DNPT using UV 266 nm based pulsed photoacoustic pyrolysis technique between 30–350 °C range.

Evaluation of thermal stability and acoustic fingerprint spectra of energetic 1,2,4-triazoles based on bond lengths of chemical substituents using pulsed photoacoustic technique

We investigated the effect of the bond lengths of the chemical substituents on the thermal stability of newly synthesized nitro rich 1,2,4-triazoles such as P-Me-DNPT, P-OMe-DNPT, and P-NH₂-DNPT using pulsed photoacoustic pyrolysis technique.

A DFT study of five-membered nitrogen-containing fused heterocycles for insensitive highly energetic materials

A suitable combination of aromatic rings, hydrogen bonds and layered crystal packing can be applied to obtain new compounds with both power and safety aspects.

Site-selective arene C-H amination via photoredox catalysis

Over the past several decades, organometallic cross-coupling chemistry has developed into one of the most reliable approaches to assemble complex aromatic compounds from preoxidized starting materials. More recently, transition metal-catalyzed carbon-hydrogen activation has circumvented the need for preoxidized starting materials, but this approach is limited by a lack of practical amination protocols. Here, we present a blueprint for aromatic carbon-hydrogen functionalization via photoredox catalysis and describe the utility of this strategy for arene amination. An organic photoredox-based catalyst system, consisting of an acridinium photooxidant and a nitroxyl radical, promotes site-selective amination of a variety of simple and complex aromatics with heteroaromatic azoles of interest in pharmaceutical research. We also describe the atom-economical use of ammonia to form anilines, without the need for prefunctionalization of the aromatic component.

New 1-(3-nitrophenyl)-5,6-dihydro-4H-[1,2,4]triazolo[4,3-a][1,5]benzodiazepines: synthesis and computational study

Triazole derivatives constitute an important group of heterocyclic compounds have have been the subject of extensive study in the recent past. These compounds have shown a wide range of biological and pharmacological activities. In this work, new fused tricyclic 1-(3-nitrophenyl)-5,6-dihydro-4H-[1,2,4]triazolo[4,3-a][1,5]-benzodiazepines have been synthesized by the thermal cyclization of N'-(2,3-dihydro-1H-1,5-benzodiazepin-4-yl)-3-nitrobenzohydrazides. After screening ethanol, toluene and 1-butanol as solvents, butanol-1 was found to be the best choice for the cyclization reaction in order to obtain the highest yields of tricyclic derivatives. The chemical structures of the synthesized compounds were elucidated by the analysis of their IR, 1H- and 13C-NMR spectral data. For tentative rationalization of the reaction processes, the global and local reactivity indices of certain compounds, taking part in the reaction pathway, were assessed by means of quantum mechanical calculations using the conceptual density functional theory (DFT) approach. This work could be useful for the synthesis of new heterocyclic compounds bearing a fused triazole ring.

Energetic salts prepared from phenolate derivatives

Energetic salts with 1 : 1, 2 : 1, and 3 : 1 charge ratios (cation : anion) based on various nitrogen-rich cations and phenolate anions have been synthesized by a straightforward and simple method.