Investigation into a Conformationally Locked (Z)-Azidoxime.

High nitrogen compounds find wide use in the development of new propellants and explosives as well as pharmaceutical chemistry as bioisosteres, bacterial stains, and antifungal agents. A class of underexplored high-nitrogen materials includes azidoximes and their 1-hydroxytetrazole isomers. Azidoximes possess an energetic azide group and are quite sensitive to impact, spark, and friction. Therefore, these materials are generated in situ and cyclized under mild acidic conditions to their 1-hydroxytetrazole isomers. Recently, we synthesized a novel 1,2,4-triazine-derived azidoxime; however, upon subjecting this material to established cyclization conditions, no reaction was observed, even after prolonged reaction times with heating. Additional 1,2,4-triazine-derived azidoximes also displayed a similar lack of reactivities. This observation led us to probe the reactivity of these materials with both a DFT investigation and crystallographically based electrostatic potential mapping. In all, the lack of reactivity toward cyclization was found to be due to an inability of 1,2,4-triazine-based azidoximes to isomerize into the reactive (E)-conformation, requiring an activation energy of 26.4 kcal mol-1.

[3+2] click chemistry approach to tetrazine containing polymers.

We report a [3+2] cycloaddition using 3,6-bis-propargyloxy-1,2,4,5-tetrazine and azides to synthesize energetic polymers containing 1,2,4,5-tetrazine within the scaffold. This work also includes [3+2] cycloaddition to crosslink azide containing glycidyl azide polymer (GAP). These reactions provide pathways for incorporation of 1,2,4,5-tetrazine into novel energetic materials using click-chemistry and provide an alternative polymer curing approach.

Lanthanide Complexes of Bis(tetrazolato)amine: A Route to Lanthanide Nitride Foams.

Metal nitrides are strong refractory ceramic materials known for applications in the coatings, catalysis, and semiconductor industries. Lanthanide nitrides are difficult to prepare in high purity and often require high temperatures and sophisticated equipment. In this work, we present an approach to the synthesis of high-purity f-element nitrides through the use of simple lanthanide salts and the nitrogen-rich ligand 5,5'-bis(1H-tetrazolyl)amine (H2BTA) to form lanthanide complexes of 5,5'-bis(tetrazolato)amine (BTA2-). We have demonstrated that, when dehydrated, these types of complexes undergo a self-sustained combustion reaction under an inert atmosphere to yield nanostructured f-element nitride foams for lanthanum and cerium. The synthesis, characterization, and single-crystal X-ray crystallography of the BTA2- complexes of lanthanum, cerium, praseodymium, neodymium, and europium are also discussed.

Azo- and methylene-bridged mixed azoles for stable and insensitive energetic applications.

A simple synthetic strategy for the preparation of high nitrogen content azo- and methylene bridged mixed energetic azoles was used. All new compounds were fully characterized by NMR and infrared spectroscopy, elemental analysis, and differential scanning calorimetry (DSC). In addition, the structures of energetic salts 7 and 10 were confirmed by single-crystal X-ray diffraction analysis. Detonation performances, calculated from heats of formation and experimental densities, thermal stabilities, and impact and friction sensitivities suggest possible applications in the field of insensitive energetic materials.

gem-Dinitromethyl-Functionalized 5-Amino-1,3,4-oxadiazolate Derivatives: Alternate Route, Characterization, and Property Analysis.

A new, safer, and more cost-effective methodology to synthesize salts based on gem-dinitromethyl-functionalized 5-amino-1,3,4-oxadiazolate is given. Cyclization, deprotection, nitration, and neutralization reactions were conducted to obtain products in high yield. All compounds were fully characterized by NMR and IR spectroscopy, elemental analysis, and differential scanning calorimetry. Crystal structure analysis, property tests, and theoretical calculations confirm good detonation performance and high mechanical stabilities of the salts.

Derivatives of 3,6-Bis(3-aminofurazan-4-ylamino)-1,2,4,5-tetrazine: Excellent Energetic Properties with Lower Sensitivities.

To find a balance between energy and safety, a series of compounds based on azo-, azoxy-, 1,4,2,5-dioxadiazene-, and 3,6-diamino-1,2,4,5-tetrazine-bridged bis(aminofurazan) were designed and synthesized. These compounds were analyzed by nitro group charges (Qnitro) and bond dissociation energy (BDE) calculations, which are related to sensitivity and stability. Based on the calculated results, derivatives of 3,6-bis(3-aminofurazan-4-ylamino)-1,2,4,5-tetrazine have the largest values for -Qnitro and BDE of all of the bis(aminofurazan) compounds. This shows that compounds based on 3,6-bis(3-aminofurazan-4-ylamino)-1,2,4,5-tetrazine have the lowest sensitivities and best stabilities, which has been substantiated by experiments. Additionally, their explosive properties remain essentially competitive with compounds based on azo-, azoxy-, and 1,4,2,5-dioxadiazene-bridged bis(aminofurazan). Hirshfeld surface calculations were also performed to better understand the relationship between the molecular structure and stability/sensitivity. This work highlights the value of 3,6-diamino-1,2,4,5-tetrazine as a linker to achieve good balance between safety and energy.

Enforced Planar FOX-7-like Molecules: A Strategy for Thermally Stable and Insensitive π-Conjugated Energetic Materials.

Exploring new energetic derivatives of 1,1-diamino-2,2-dinitroethylene (FOX-7) is still a key aspect in the field of energetic materials. However, so far most of the attention has been focused on modification of FOX-7 via different reaction strategies. Now we report the design of three new FOX-7-like compounds (3-5) where one nitro group in FOX-7 is replaced by a nitrogen-rich heterocyclic ring. Each of them is characterized by single-crystal X-ray crystallography. Electronic structures are studied through computational methods in comparison with FOX-7. In addition, the chemical reactivity of 3 was also investigated. Its hydroxylammonium (7), hydrazinium (8), and ammonium (9) salts were prepared, and the nitrate product (10) was also isolated. Compound 10 has a C-N bond length of 1.577 Å that is one of the longest values found for the C-NO2 bond. It was found that the incorporation of a tetrazole or triazole ring into the backbone of a conjugated nitroenamine does lead to a planar structure, which not only enhances the thermal stability but also improves the sensitivity of the product.

Nitrogen-Rich Tetrazolo[1,5-b]pyridazine: Promising Building Block for Advanced Energetic Materials.

Two metal-free explosives, tetrazolo[1,5-b]pyridazine-containing molecules [6-azido-8-nitrotetrazolo[1,5-b]pyridazine-7-amine (3at) and 8-nitrotetrazolo[1,5-b]pyridazine-6,7-diamine (6)], were obtained via straightforward two-step synthetic routes from commercially available reagents. Compound 3at displays an excellent detonation performance (Dv = 8746 m s-1 and P = 31.5 GPa) that is superior to commercial primary explosives such as lead azide and diazodinitrophenol (DDNP). Compound 6 has superior thermal stability, remarkable insensitivity, and good detonation performance, strongly suggesting it as an acceptable secondary explosive. The initiating ability of compound 3at has been tested by detonating 500 mg of RDX with a surprisingly low minimum primary charge of 40 mg. The extraordinary initiating power surpasses conventional primary explosives, such as commercial DDNP (70 mg) and reported 6-nitro-7-azido-pyrazol[3,4-d][1,2,3]triazine-2-oxide (ICM-103) (60 mg). The outstanding detonation power of 3at contributes to its future prospects as a promising green primary explosive. In addition, the environmentally benign methodology for the synthesis of 3at effectively shortens the time from laboratory-scale research to practical applications.

Synthesis of Erythritol Tetranitrate Derivatives: Functional Group Tuning of Explosive Sensitivity.

Understanding the factors that affect explosive sensitivity is paramount to the safe handling and development of new explosives molecules. Erythritol tetranitrate (ETN) is an explosive that recently has attracted significant attention in the explosives community because of its ease of synthesis and physical properties. Herein, we report the synthesis of ETN derivatives using azide, nitramine, and nitrate ester functional groups. Impact, spark, and friction sensitivity measurements, computationally calculated explosive properties, and the crystal structure analysis of the ETN derivatives are reported. Mixing explosive functional groups led to changes in the explosive sensitivity, explosive performance as well as physical properties including melting point and physical state at room temperature. Overall, we have demonstrated that combining functional groups can enable the tuning of explosive and physical properties of a molecule. This tunability can potentially aid in the development of new explosives in which characteristics are varied to meet certain specifications.

Energetic Derivatives of 8-Nitropyrazolo[1,5-a][1,3,5]triazine-2,4,7-triamine: Achieving Balanced Explosives by Fusing Pyrazole with Triazine.

Using the triazine ring as the stabilizing factor, a series of energy-safety balanced fused ring compounds were successfully studied. Compounds 1, 7, and 9·H2O were further confirmed by single-crystal X-ray diffraction analysis. The detonation performance and safety parameters associated with impact and friction sensitivities were investigated by using EXPLO5 (version 6.01) and BAM methods, respectively. Based on their good detonation properties and high thermal and mechanical stabilities, these materials are potentially high performance insensitive explosives.

Intermolecular Weak Hydrogen Bonding (Het-H-N/O): an Effective Strategy for the Synthesis of Monosubstituted 1,2,4,5-Tetrazine-Based Energetic Materials with Excellent Sensitivity.

A series of monosubstituted 1,2,4,5-tetrazine-based energetic materials was effectively synthesized and fully characterized with IR, multinuclear nuclear magnetic resonance (NMR), and elemental analyses. Heats of formation and detonation performances were determined using Gaussian 03 and EXPLO5 v6.01 programs, which show that 5 and 9 as secondary explosives have detonation velocities superior to the current secondary-explosive benchmark, triaminotrinitrobenzene (TATB). Importantly, compounds 2, 5, and 9 were first characterized with single-crystal X-ray diffraction and Hirshfeld surface calculations, and some intermolecular weak hydrogen bonds (Het-H-N/O) among these compounds illustrate the relationship between these weak interactions and excellent sensitivity of energetic materials. This design method for next-generation energetic materials by incorporating intermolecular weak hydrogen bonds may be of future importance.

Bis(3-nitro-1-(trinitromethyl)-1H-1,2,4-triazol-5-yl)methanone: An Applicable and Very Dense Green Oxidizer.

Ammonium perchlorate (AP) is most often used as a practical solid rocket propellant because of its excellent performance. However, AP has many shortcomings, including instability, high negative enthalpy of formation, and claimed health and environmental issues resulting from its combustion products. The pursuit of highly dense, high-performance, and environmentally friendly oxidizers as solid propellants has long attracted scientists around the world. In this work, bis(3-nitro-1-(trinitromethyl)-1H-1,2,4-triazol-5-yl)methanone (3) was obtained from bis(3-nitro-1H-1,2,4-triazol-5-yl)methane (1) with chloroacetone followed by nitration. The structure of 3 was confirmed by elemental analysis and single-crystal X-ray diffraction. By introducing the carbonyl moiety, the density of 3 was increased to 1.945 g/cm3 and the decomposition temperature increased to 164 °C. Compound 3 is a green energetic oxidizer that has a positive oxygen balance (+8.7%), a high specific impulse (218 s), and an acceptable sensitivity (9 J, 240 N), making it a practical replacement for AP in solid rocket propellant formulations.

C6N10O4: Thermally Stable Nitrogen-Rich Inner Bis(diazonium) Zwitterions.

Two nitrogen-rich inner bis(diazonium) salts, the 4,4'-dinitro-5,5'-diazo-2,2'-bisimidazole (2) and the 4,4'-dinitro-5,5'-diazo-3,3'-bispyrazole (4) zwitterions, are described. Compound 2 was synthesized unexpectedly from the nitration of 4,4'-dinitro-5,5'-diamino-1H,1'H-2,2'-bisimidazole (1) in a mixture of trifluoroacetic anhydride and 100% nitric acid. Both 2 and 4 show good thermal stability, especially 2 has a decomposition temperature of 199 °C, which is the highest one in any of the reported hydrogen-free nitrogen-rich diazonium salts.

Versatile functionalization of 3,5-diamino-4-nitropyrazole for promising insensitive energetic compounds.

Variation of functional groups offers an efficient approach for tuning properties of materials such as thermal stability, and detonation performance while improving sensitivities to mechanical stimuli. Now versatile functionalization of 3,5-diamino-4-nitropyrazole involving the introduction of a tetrazole ring, or a guanyl group, or ring expansion is described. All of the compounds were fully characterized and some of them (2, 9 and 13) were verified by single crystal X-ray diffraction. Based on their good thermal stabilities and high detonation performance as well as insensitive properties, they are potentially insensitive energetic compounds.

Fused rings with N-oxide and -NH2: good combination for high density and low sensitivity energetic materials.

Oxidation reactions of 3,6-diamino-1,2,4-triazolo[4,3-b][1,2,4,5]tetrazine give four N-oxide compounds. Because of the presence of an amino group and the N-oxide moiety, these compounds are extensively hydrogen bonded. Resulting from π-π stacking interactions between the fused rings, compounds 1-3 are impact and friction insensitive, are thermally stable and have good density.

Challenging the Limits of Nitro Groups Associated with a Tetrazole Ring.

To challenge the limits of nitro groups associated with a tetrazole ring, the polynitrotetrazoles, 2,5-bis(dinitromethyl)-2 H-tetrazole, and 2-(dinitromethyl)-5-(trinitromethyl)-2 H-tetrazole as well as their salts, were designed, synthesized, and characterized. The neutral compounds were also studied by natural bonding orbital (NBO) and Hirshfeld surface calculations. The heats of formation were calculated with Gaussian 03 and combined with experimentally determined densities in order to obtain the detonation properties of the energetic materials with the EXPLO5 program. They exhibit high densities, good oxygen balances, positive heats of formation, and excellent detonation properties.

Energetic furazan-triazole hybrid with dinitromethyl and nitramino groups: decreasing sensitivity via the formation of a planar anion.

Energetic salts (4, 5 and 7-11) of 3-(3-dinitromethanide-1H-1,2,4-triazol-5-yl)-4-nitraminofurazanate and the azo compound (15) as well as its ammonium (14), hydrazinium (16) and hydroxylammonium (17) salts were synthesized and fully characterized. The structures of 5 and 15 were confirmed by single crystal X-ray diffraction analysis. The hydroxylammonium salt (5) has a high measured density (1.85 g cm-3) and shows promising properties as a replacement for the traditional explosive (RDX). The anion is planar which suggests that a combination of two heterocyclic five-membered rings with nitramino and dinitromethyl groups could open a new avenue to advanced energetic materials with high detonation performance and good sensitivities.

Green Synthetic Approach for High-Performance Energetic Nitramino Azoles.

A mild and efficient strategy for the nitration of amino-substituted pyrazoles/triazole employing a mixture of potassium nitrate and concentrated sulfuric acid (KNO3/H2SO4) as a nitrating reagent proceeded smoothly to give nitramino-substituted products. These were treated with corresponding bases to give energetic salts 1-10. The compounds were fully characterized, and single crystal X-ray diffraction studies were obtained for 1, 4, 6, and 10. The physical properties and detonation performance were measured or calculated. Salts 1, 2, 6, 8, and 9 exhibited excellent detonation performance and acceptable sensitivities as well as good stabilities, which suggested that they have potential to be useful as high-performance explosives.

Tetrazolyl and dinitromethyl groups with 1,2,3-triazole lead to polyazole energetic materials.

A class of polyazole energetic compounds (combination of tetrazolyl, dinitromethyl and triazole) was obtained from 4,5-dicyanotriazole. All the new compounds were fully characterized by IR, NMR [1H, 13C{1H}], elemental analysis, and differential scanning calorimetry (DSC). Compounds 5, 6 and 8 were further characterized with single-crystal X-ray diffraction studies. Heats of formation and detonation performances were determined using Gaussian 03 and EXPLO5 v6.01 programs, which show that 5 is a promising green primary explosive and 7 as a secondary explosive has a detonation velocity superior to 1,3,5-trinitrotriazacyclohexane (RDX).

Polycyclic N-oxides: high performing, low sensitivity energetic materials.

Polycyclic N-oxides were developed based on the heterocycles 1,2,4,5-tetrazine and 4H,8H-difurazano[3,4-b:3',4'-e]pyrazine. The new compounds are energetic and have excellent explosive properties, while maintaining low mechanical sensitivities. Most notably, compound 7 is thermally stable, insensitive, and has superior detonation properties to the state-of-the-art insensitive high explosive, 1,3,5-triamino-2,4,6-trinitrobenzene.