Yongxing Tang

Taming of 3,4-Di(nitramino)furazan

Highly energetic 3,4-di(nitramino)furazan (1, DNAF) was synthesized and confirmed structurally by using single-crystal X-ray diffraction. Its highly sensitive nature can be attributed to the shortage of hydrogen-bonding interactions and an interactive nitro chain in the crystal structure. In order to stabilize this structure, a series of corresponding nitrogen-rich salts (3-10) has been prepared and fully characterized. Among these energetic materials, dihydrazinium 3,4-dinitraminofurazanate (5) exhibits a very promising detonation performance (νD = 9849 m s(-1); P = 40.9 GPa) and is one of the most powerful explosives to date. To ensure the practical applications of 5, rather than preparing the salts of 1 through acid-base reactions, an alternative route through the nitration of N-ethoxycarbonyl-protected 3,4-diaminofurazan and aqueous alkaline workup was developed.

1,2,4‐Triazole Links and N‐Azo Bridges Yield Energetic Compounds

Triazole links and polynitropyrazole rings give rise to compounds with energetic properties. These materials were fully characterized by NMR and infrared spectroscopy, elemental analysis, and differential scanning calorimetry (DSC). In addition, the structures of compounds 5 and 8 were confirmed by single-crystal X-ray diffraction analysis. Detonation properties, calculated from heats of formation and experimental densities, thermal stabilities, and impact and friction sensitivities support the potential use of these materials for explosive applications.

Energetic compounds consisting of 1,2,5- and 1,3,4-oxadiazole rings

3-Nitroamino-4-(5-amino-1,3,4-oxadiazol-2-yl)furazan monohydrate (2·H2O), which is a combination of the nitroaminofurazan and 1,3,4-oxadiazole rings, was obtained by the nitration of 3-amino-4-(5-amino-1,3,4-oxadiazol-2-yl)furazan (1) with 100% nitric acid. Several energetic derivatives of 2 were prepared and fully characterized by multinuclear NMR, and IR spectroscopy, as well as elemental analysis. X-ray analyses for 1, 2·H2O and 5·H2O give insight into structural characteristics showing the presence of extensive hydrogen-bonding interactions. Most of these new materials exhibit good thermal stabilities and acceptable sensitivity values. Detonation performance numbers were obtained based on the calculated heats of formation and measured densities indicating that some of these bonded nitroaminofurazan/oxadiazole materials are comparable to RDX.

N-Oxides light up energetic performances: synthesis and characterization of dinitraminobisfuroxans and their salts

4,4′-Diamino-[3,3′-bi(1,2,5-oxadiazole)]-5,5′-dioxide and 4,4′-diamino-[3,3′-bi(1,2,5-oxadiazole)]-2,2′-dioxide were nitrated in 100% HNO3 at −10 °C to give 4,4′-dinitramino-[3,3′-bi(1,2,5-oxadiazole)]-5,5′-dioxide (3) and 4,4′-diamino-[3,3′-bi(1,2,5-oxadiazole)]-2,2′-dioxide (4). Nine nitrogen-rich salts were prepared and were characterized by infrared and multinuclear NMR spectroscopy, elemental analysis, differential scanning calorimetry (DSC) and X-ray single crystal diffraction in some cases. Their detonation properties were evaluated by EXPLO 5 code using the measured density and calculated heat of formation. The sensitivities were determined by standard BAM methods. Several of the new molecules exhibit detonation and other properties which compete with or exceed those of HMX.

Enhancing Energetic Properties and Sensitivity by Incorporating Amino and Nitramino Groups into a 1,2,4‐Oxadiazole Building Block

A single nitrogen-rich heterocyclic ring with many energetic groups is expected to exhibit excellent detonation performance. We report an effective approach for the synthesis of 3-amino-5-nitramino-1,2,4-oxadiazole, which has nitramino and amino groups in the same building block. The single-crystal X-ray structure shows layered hydrogen-bonding pairs as well as the presence of a water molecule which ensure insensitivity. Through incorporation of a cation, the hydrazinium or hydroxylammonium salts exhibit good energetic performance and acceptable sensitivities.

C–N bonded energetic biheterocyclic compounds with good detonation performance and high thermal stability

New C–N bonded energetic biheterocyclic compounds were synthesized using cine substitution of 1,3-dinitro-1,2,4-triazole with different energetic moieties. All the compounds were fully characterized by multinuclear NMR and infrared spectra, and elemental analyses. The structures of 4, 7, 9, and 11 were confirmed by single-crystal X-ray structure analyses. Their physicochemical properties, such as density, thermal stability and sensitivity towards impact and friction, were studied. All of the compounds have high thermal stability. The detonation properties were calculated with EXPLO5 V6.01 based on experimental densities and calculated heats of formation.

Small Cation‐Based High‐Performance Energetic Nitraminofurazanates

Large nitramino-substituted furazan anions were combined with small cations (hydroxylammonium, hydrazinium, and ammonium) to form a series of energetic salts that was fully characterized. The structures of several of the compounds (1 a, 2 a, 3 a, and 4 a) were further confirmed by single-crystal X-ray diffraction. Based on their physiochemical properties, such as density, thermal stability, and sensitivity, together with the calculated detonation properties, it was found that they exhibit good detonation performance and have potential application as high-energy-density materials.

Energized nitro-substituted azoles through ether bridges

A series of ether-bridged energetic compounds was synthesized and fully characterized. All of the compounds melt before thermally decomposing and may have potential as melt-cast explosives based on their properties. Their detonation properties were computed using the EXPLO5 (v6.01) software on the basis of the calculated heats of formation and experimental densities (25 °C). The ether-bridged 5-nitrotetrazole and 5-trinitromethyltetrazole compounds exhibit energetic performance superior to RDX. Impact and friction sensitivities were determined using standard BAM technology. The structures of compounds 1, 4, 5, 7 and 9 were confirmed by single crystal X-ray analyses.

A furazan-fused pyrazole N-oxide via unusual cyclization

6-Nitro-pyrazolo[3,4-c]furazanate 5-oxide, a new fused anion with high energy, was designed and synthesized via an unusual intramolecular cyclization reaction of 3 by using a mixture of 100% nitric acid and trifluoroacetic anhydride followed by KI reduction. The potassium (6) and nitrogen-rich energetic (9–16) salts were prepared, and fully characterized by IR and multinuclear NMR spectroscopy, elemental analysis, and single-crystal X-ray structuring, 6, 9 and 16. Hydroxylammonium salt (10) has excellent detonation performance but high sensitivity, while 13 and 16 have detonation velocities comparable to 1,3,5-trinitro-1,3,5-triazinane (RDX), which suggests they may have potential application as green primary or secondary explosives.

Energetic dinitromethyl group functionalized azofurazan and its azofurazanates

Incorporating explosophore groups such as nitro, dinitromethyl, and azo into furazan results in potential candidates for energetic materials applications. In this study, 3,3′-azofurazan was functionalized with fluorodinitromethyl (2) and dinitromethyl (3) moieties by fluorination and acidification of potassium 4,4′-bis(dinitromethyl)-3,3′-azofurazanate (1), respectively. In addition, 3 was converted to its ammonium (4), hydrazinium (5) and hydroxylammonium (7) salts. All the compounds were fully characterized by multinuclear NMR and IR spectra, and elemental analysis. Compounds 2 and 3 are further supported by X-ray crystallographic analysis. Electronic structures were also studied. In addition, physicochemical properties, such as thermal stability, density, and sensitivity were measured, and energetic properties (e.g., detonation velocities and detonation pressures) were calculated using EXPLO5 code.