Energetic materials based on poly furazan and furoxan structures

Preparation of a benziodazole-type iodine(III) compound and its application as a nitrating reagent for synthesis of furazans via a copper-catalyzed cascade process

The existing hypervalent I(III) reagents bearing ONO2 group are limited in types and their applications primarily focused on the nitrooxylation reactions featuring a fully-exo fashion. Herein, a benziodazole-type O2NO-I(III) compound was prepared and its reaction with β-monosubstituted enamines in the presence of CuI could trigger a radical nitration/cyclization/dehydration cascade to provide a series of less explored but biologically interesting furazan heterocycles. Mechanistically, the benziodazole-type O2NO-I(III) compound acts as a nitrating reagent and incorporates its NO moiety into the final furazan product in a fully-endo model, a process of which was proposed to involve nitration, cyclization and dehydration.

Revealing the Electro-oxidation Mechanism of 5-Aminotetrazole on Nickel-Based Oxides and Synthesizing 5,5'-Azotetrazolate Salts

With the gradual expansion of the application of organic electromechanical synthesis in the field of energetic materials, it is necessary to explore deeply the mechanisms behind the organic electromechanical oxidation of energetic materials in order to develop efficient electrocatalysts. Electrochemical synthesis of 5,5'-azotetrazolate (ZT) salts is not only environmentally friendly and efficient but also can replace oxygen evolution reaction (OER) combined with hydrogen production, significantly reducing the battery voltage of overall water splitting (OWS) and achieving low energy consumption hydrogen production. Here, we prepared the Co-modified nickel-based oxide electrodes (Ni3-xCoO4/carbon cloth (CC), x = 1, 2) as a medium to reveal the oxidative coupling mechanism of 5-aminotetrazole (5-AT). Experimental and theoretical calculations verified that Ni-catalyzed oxidative coupling of 5-AT is a proton-coupled electron transfer (PCET) process, including electron transfer of electrocatalytic intermediates (Ni2+-O + OH- = Ni3+-O(OH) + e-) and spontaneous dehydrogenation process (Ni3+-O(OH) + X-H = Ni2+-O + X•). The Ni3+-O(OH) is an extremely fast nonreducing electron transfer center that serves as a chemical oxidant to directly abstract hydrogen atoms from the 5-AT. Simultaneously, the synergistic effect of Co doping on the electric cloud around Ni causes the upshift of the d-band centers, which is conducive to the easier adsorption of OH*, forming the generation of active intermediate Ni3+-O(OH). Thus, Ni2CoO4/CC has higher Faraday efficiency (FE) and yield for the oxidation reaction of 5-AT, with a yield of approximately 72.3% after electrolysis at 1.7 V vs reversible hydrogen electrode (RHE).

Improvement of Thermal Stability and Sensitivity of Furazan/Furoxan via Ring Closure Generation of Vicinal Amino-Nitro Structure

Energetic compounds that display high thermal stability and insensitivity properties are essential for applications in mining, gas drilling, etc. In this work, a novel 4-nitro-5-aminoisoxazole energetic moiety oriented to enhance thermal stability and decrease the sensitivity of furazan/furoxan analogues was constructed. The generation of a vicinal amino-nitro structure can be effectively realized in one step by a green and mild ring-closing reaction of nitroacetonitrile potassium salt with chloroxime in aqueous solution. Seven new energetic compounds with good thermal stability (Td: 155.8∼270.3 °C) and low sensitivity (IS: >40 J, FS: 96∼192 N) were synthesized. The nitro-furazan and isoxazole combined product exhibits the advantages of both skeletons, with energetic properties (Dv = 8350 m s-1, P = 30.1 GPa) that may find value in insensitive energetic materials. This strategy promises to achieve a balance between energy levels and stability of furazan/furoxan analogues and offers a new way for the design and synthesis of highly thermally stable compounds that meet special applications.

Bistriazolotriazole-tetramine: commendable energetic moiety and cation

CONTEXT

Various 7H,7'H-[6,6'-bi[1,2,4]triazolo[4,3-b][1,2,4]triazole]-3,3',7,7'-tetramine (A) based nitrogen-rich energetic salts were designed and their properties explored. All energetic salts possess relatively high nitrogen content (> 48%), positive heats of formation (> 429 kJ/mol) and stability owing to a significant contribution from fused backbone. The cationic component shows a very high heat of formation (2516 kJ/mol); therefore, it is highly suitable for enthalpy enhancement in new energetic salts. The cation was paired with the energetic anions nitrate (NO3-), perchlorate (ClO4-), dinitromethanide (CH(NO2)2-), trinitromethanide (C(NO2)3-), nitroamide (NHNO2-), and dinitroamide (N(NO2)2-) to improve oxygen balance and detonation performance. Designed salts show moderate detonation velocities (7.9-8.7 km/s) and pressures (23.8 - 33.1 GPa). The distribution of frontier molecular orbitals, molecular electrostatic surface potentials, QTAIM topological properties, and noncovalent interactions of designed salts were simulated to understand the electronic structures, charge distribution in molecules, hydrogen bonding, and other nonbond interactions. The predicted safety factor (SF) and impact sensitivity (H50) of designed salts suggest their insensitivity to mechanical stimuli. This work explored the 7H,7'H-[6,6'-bi[1,2,4]triazolo[4,3-b][1,2,4]triazole]-3,3',7,7'-tetramine as a suitable cationic component which could be promising and serve exemplarily in energetic materials.

METHODS

The optimization and energy calculations of all the designed compounds were carried out at the B3LYP/6-311 +  + G(d,p) and M06-2X/def2-TZVPP levels, utilizing the Gaussian software package. The molecular surface electrostatic potential, quantum theory of atoms in molecules (QTAIM), reduced density gradient (RDG), and noncovalent interaction (NCI) analysis were performed by employing Multiwfn software. The EXPLO5 (v 7.01) thermochemical code and PILEM web application were used to predict the detonation properties.

Synthetic approaches and applications of an underprivileged 1,2,5-oxadiazole moiety: A review

1,2,5-oxadiazole belongs to five-membered heterocyclic compounds with two nitrogen and one oxygen atom. In comparison with other heterocyclic moieties, 1,2,5-oxadiazoles moiety is considered as underprivileged as it attracted little attention of the researchers although lot of scopes and possible applications in medicinal, material and agriculture science. 1,2,5-oxadiazole and its derivatives have been reported as good pharmacophores as carbonic anhydrase inhibitors, antibacterial, vasodilating agents, antimalarial, anticancer, etc. In the presented manuscript, we reviewed granted patents and different synthetic strategies which have been reported for the synthesis of 1,2,5-oxadiazoles such as cycloaddition, dimerization, cyclodehydration, condensation, thermolysis, nitration, oxidation and ring-conversion. These synthetic methods have also been analysed for their merits and demerits. The manuscript also highlighted various applications of 1,2,5-oxadiazole and its derivatives. We hope that researchers across the scientific streams will be benefitted from the presented review articles for designing their work related to 1,2,5-oxadiazoles.

A Dihydrazone as a Remarkably Nitrogen-Rich Thermostable and Insensitive Energetic Material

Hydrogen bonds (H-bonds) in energetic compounds have a very pronounced effect on physicochemical properties such as density, thermal stability, sensitivity, and solubility. Now a strategy to synthesize nitrogen-rich energetic materials with overall good properties, which stem from the synergetic effects of inter- or intramolecular H-bonds, is reported. 1,2-Dihydrazono-1,2-di(1H-tetrazol-5-5-yl)ethane (4), a new thermostable and insensitive material, is obtained from the reaction of dioxime (2) with hydrazine hydrate. The exchange of the oxime (NOH) with the hydrazone (NNH2) functionality results in the reduced acidic character and low solubility in water, which make it remarkably suitable for practical use. While the detonation velocity of 4 is comparable with RDX, it has an advantage of high nitrogen content (76%) and high thermal stability (275 °C) and is insensitive toward external stimuli.

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.

Energetic Polymer Possessing Furazan, 1,2,3-Triazole, and Nitramine Subunits

A [3 + 2] cycloaddition reaction using dialkyne and diazide comonomers, both bearing explosophoric groups, to synthesize energetic polymers containing furazan and 1,2,3-triazole ring as well as nitramine group in the polymer chain have been described. The developed solvent- and catalyst-free approach is methodologically simple and effective, the comonomers used are easily available, and the resulting polymer does not need any purification. All this makes it a promising tool for the synthesis of energetic polymers. The protocol was utilized to generate multigram quantities of the target polymer, which has been comprehensively investigated. The resulting polymer was fully characterized by spectral and physico-chemical methods. Compatibility with energetic plasticizers, thermochemical characteristics, and combustion features indicate the prospects of this polymer as a binder base for energetic materials. The polymer of this study surpasses the benchmark energetic polymer, nitrocellulose (NC), in a number of properties.

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.

Synthesis and Crystal Structure of 3-(4-Cyano-3-nitro-1H-pyrazol-5-yl)-4-nitrofurazan: Comparison of the Influence of the NO2 and CN Groups on Crystal Packing and Density

The title compound was synthesized and characterized by IR and NMR spectroscopy and single crystal X-ray diffraction. The analysis of the crystal packing of the title compound and its analog, bearing a nitro group instead of a nitrile one, allowed a direct comparison of two common explosophoric groups: CN and NO2. By using ΔOED-based densification approach, it is shown that the CN group is lighter in mass, less dense, and participates in intermolecular bonding to a lesser extent in comparison to the NO2 group. As a result, the cyano compound has a lower density and a looser crystal packing than the nitro analog.

Energetic [1,2,5]oxadiazolo [2,3-a]pyrimidin-8-ium Perchlorates: Synthesis and Characterization

A convenient method to access the above perchlorates has been developed, based on the cyclocondensation of 3-aminofurazans with 1,3-diketones in the presence of HClO₄. All compounds were fully characterized by multinuclear NMR spectroscopy and X-ray crystal structure determinations. Initial safety testing (impact and friction sensitivity) and thermal stability measurements (DSC/DTA) were also carried out. Energetic performance was calculated by using the PILEM code based on calculated enthalpies of formation and experimental densities at r.t. These salts exhibit excellent burn rates and combustion behavior and are promising ingredients for energetic materials.

Correlated RNN Framework to Quickly Generate Molecules with Desired Properties for Energetic Materials in the Low Data Regime

Motivated by the challenging of deep learning on the low data regime and the urgent demand for intelligent design on highly energetic materials, we explore a correlated deep learning framework, which consists of three recurrent neural networks (RNNs) correlated by the transfer learning strategy, to efficiently generate new energetic molecules with a high detonation velocity in the case of very limited data available. To avoid the dependence on the external big data set, data augmentation by fragment shuffling of 303 energetic compounds is utilized to produce 500,000 molecules to pretrain RNN, through which the model can learn sufficient structure knowledge. Then the pretrained RNN is fine-tuned by focusing on the 303 energetic compounds to generate 7153 molecules similar to the energetic compounds. In order to more reliably screen the molecules with a high detonation velocity, the SMILE enumeration augmentation coupled with the pretrained knowledge is utilized to build an RNN-based prediction model, through which R² is boosted from 0.4446 to 0.9572. The comparable performance with the transfer learning strategy based on an existing big database (ChEMBL) to produce the energetic molecules and drug-like ones further supports the effectiveness and generality of our strategy in the low data regime. High-precision quantum mechanics calculations further confirm that 35 new molecules present a higher detonation velocity and lower synthetic accessibility than the classic explosive RDX, along with good thermal stability. In particular, three new molecules are comparable to caged CL-20 in the detonation velocity. All the source codes and the data set are freely available at https://github.com/wangchenghuidream/RNNMGM.

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.

4,5-Dicyano-1,2,3-Triazole-A Promising Precursor for a New Family of Energetic Compounds and Its Nitrogen-Rich Derivatives: Synthesis and Crystal Structures

The nitrogen-rich compounds and intermediates with structure of monocyclic, bicyclic, and fused rings based on 1,2,3-triazole were synthesized and prepared by using a promising precursor named 4,5-dicyano-1,2,3-triazole, which was obtained by the cyclization reaction of diaminomaleonitrile. Their structure and configurational integrity were assessed by Fourier transform-infrared spectroscopy (FT-IR), mass spectrometry (MS), and elemental analysis (EA). Additionally, fourteen compounds were further confirmed by X-ray single crystal diffraction. Meanwhile, the physical properties of four selected compounds (3·H₂O, 6·H₂O, 10·H₂O, and 16) including thermal stability, detonation parameters, and sensitivity were also estimated. All these compounds could be considered to construct more abundant 1,2,3-triazole-based neutral energetic molecules, salts, and complex compounds, which need to continue study in the future in the field of energetic materials.

3,4-Bis(3-tetrazolylfuroxan-4-yl)furoxan: A Linear C-C Bonded Pentaheterocyclic Energetic Material with High Heat of Formation and Superior Performance

The design and preparation of new nitrogen-rich heterocyclic compounds are of considerable significance for the development of high-performing energetic materials. By combining nitrogen-rich tetrazole and oxygen-rich furoxan, a linear C-C bonded pentaheterocyclic energetic compound, 3,4-bis(3-tetrazolylfuroxan-4-yl) furoxan (BTTFO), was synthesized using a facile and straightforward method. Comprehensive X-ray analysis reveals the key role of hydrogen bonds, π-π interactions, and short contacts in the formation of dense packing of BTTFO and explains why a long chain-shaped molecule has a high density. This multicyclic structure incorporating three furoxan and two tetrazole moieties results in an exceptionally high heat of formation (1290.8 kJ mol^-1) and favorable calculated detonation performances (v _D, 8621 m s^-1, P, 31.5 GPa). The interesting structure and fascinating properties demonstrated the feasibility of a linear multicyclic approach as a high-energy-density skeleton. Additionally, the thermodynamic parameters, electrostatic potential (ESP), and frontier molecular orbitals were also studied to get a better understanding of structure-property correlations.