Bis(4‐nitraminofurazanyl‐3‐azoxy)azofurazan and Derivatives: 1,2,5‐Oxadiazole Structures and High‐Performance Energetic Materials

Bis(4‐nitraminofurazanyl‐3‐azoxy)azofurazan ( 1 ) and ten of its energetic salts were prepared and fully characterized. Computational analysis based on isochemical shielding surface and trigger bond dissociation enthalpy provide a better understanding of the thermal stabilities for nitramine‐furazans. These energetic compounds exhibit good densities, high heats of formation, and excellent detonation velocity and pressure. Some representative compounds, for example, 1 (v_D: 9541 m s^?1; P: 40.5 GPa), and 4 (v_D: 9256 m s^?1; P: 38.0 GPa) exhibit excellent detonation performances, which are comparable with current high explosives such as RDX (v_D: 8724 m s^?1; P: 35.2 GPa) and HMX (v_D: 9059 m s^?1; P: 39.2 GPa).     

High‐Oxygen‐Balance Furazan Anions: A Good Choice for High‐Performance Energetic Salts

3,4‐Diaminofurazan was conveniently converted into energetic salts of 3,4‐dinitraminofurazan that were paired with nitrogen‐rich cations in fewer than three steps. Seven energetic salts were prepared and fully characterized by multinuclear (¹H, ¹³C) NMR and IR spectroscopy, differential scanning calorimetry (DSC), and elemental analysis. In addition, the structures of the ammonium salt ( 2 ), hydrazinium salt ( 4 ), hydroxylammonium salt ( 5 ), aminoguanidinium salt ( 7 ), diaminoguanidinium salt ( 8 ) and triaminoguanidinium salt of 3,4‐dinitraminofurazan ( 9 ) were further confirmed by single‐crystal X‐ray diffraction. The densities of these salts were between 1.673 ( 8 ) and 1.791 g cm^?3 ( 5 ), whilst their oxygen balances were between ?48.20 % ( 9 ) and ?6.25 % ( 5 ). These salts showed high thermal stabilities, with decomposition temperatures between 179 ( 5 ) and 283 °C ( 6 ). Their sensitivities towards impact and friction were measured by BAM equipment to be between <1 J ( 9 ) and >40 J ( 6 – 8 ) and 64 N ( 9 ) and >360 N ( 6 ), respectively. The detonation performance of these compounds, which was calculated by using the EXPLO5 program, revealed detonation pressures of between 28.0 ( 6 ) and 40.5 GPa ( 5 ) and detonation velocities of between 8404 ( 6 ) and 9407 m s^?1 ( 5 ).     

Energetic Salts Based on Monoanions of N,N‐Bis(1H‐tetrazol‐5‐yl)amine and 5,5′‐Bis(tetrazole)

High‐density energetic salts that contain nitrogen‐rich cations and the 5‐(tetrazol‐5‐ylamino)tetrazolate (HBTA^?) or the 5‐(tetrazol‐5‐yl)tetrazolate (HBT^?) anion were readily synthesized by the metathesis reactions of sulfate salts with barium compounds, such as bis[5‐(tetrazol‐5‐ylamino)tetrazolate] (Ba(HBTA)₂), barium iminobis(5‐tetrazolate) (BaBTA), or barium 5,5′‐bis(tetrazolate) (BaBT) in aqueous solution. All salts were fully characterized by IR spectroscopy, multinuclear (¹H, ¹³C, ¹⁵N) NMR spectroscopy, elemental analyses, density, differential scanning calorimetry (DSC), and impact sensitivity. Ba(HBTA)₂ ? 4 H₂O crystallizes in the triclinic space group P$\bar 1$ , as determined by single‐crystal X‐ray diffraction, with a density of 2.177 g cm^?3. The densities of the other organic energetic salts range between 1.55 and 1.75 g cm^?3 as measured by a gas pycnometer. The detonation pressure (P) values calculated for these salts range from 19.4 to 33.6 GPa, and the detonation velocities (ν_D) range from 7677 to 9487 m s^?1, which make them competitive energetic materials. Solid‐state ¹³C NMR spectroscopy was used as an effective technique to determine the structure of the products that were obtained from the metathesis reactions of biguanidinium sulfate with barium iminobis(5‐tetrazolate) (BaBTA). Thus, the structure was determined as an HBTA salt by the comparison of its solid‐state ¹³C NMR spectroscopy with those of ammonium 5‐(tetrazol‐5‐ylamino)tetrazolate (AHBTA) and diammonium iminobis(5‐tetrazolate) (A₂BTA).     

4‐Nitro‐3‐(5‐tetrazole)furoxan and Its Salts: Synthesis,Characterization, and Energetic Properties

A series of new energetic salts based on 4‐nitro‐3‐(5‐tetrazole)furoxan (HTNF) has been synthesized. All of the salts have been fully characterized by nuclear magnetic resonance (¹H and ¹³C), infrared (IR) spectroscopy, elemental analysis, and differential scanning calorimetry (DSC). The crystal structures of neutral HTNF ( 3 ) and its ammonium ( 4 ) and N‐carbamoylguanidinium salts ( 9 ) have been determined by single‐crystal X‐ray diffraction analysis. The densities of 3 and its nine salts were found to range from 1.63 to 1.84 g cm^?3. Impact sensitivities have been determined by hammer tests, and the results ranged from 2 J (very sensitive) to >40 J (insensitive). Theoretical performance calculations (Gaussian 03 and EXPLO 5.05) provided detonation pressures and velocities for the ionic compounds 4 – 12 in the ranges 25.5–36.2 GPa and 7934–8919 m s^?1, respectively, which make them competitive energetic materials.     

Thermally Stable 3,6‐Dinitropyrazolo[4,3‐c]pyrazole‐based Energetic Materials

3,6‐Dinitropyrazolo[4,3‐c]pyrazole was prepared using an efficient modified process. With selected cations, ten nitrogen‐rich energetic salts and three metal salts were synthesized in high yield based on the 3,6‐dinitropyrazolo[4,3‐c]pyrazolate anion. These compounds were fully characterized by IR and multinuclear NMR spectroscopies, as well as elemental analyses. The structures of the neutral compounds 4 and its salt 16 were confirmed by single‐crystal X‐ray diffraction showing extensive hydrogen‐bonding interactions. The neutral pyrazole precursor and its salts are remarkably thermally stable. Based on the calculated heats of formation and measured densities, detonation pressures (22.5–35.4 GPa) and velocities (7948–9005 m s^?1) were determined, and they compare favorably with those of TNT and RDX. Their impact and friction sensitivities range from 12 to >40 J and 80 to 360 N, respectively. These properties make them competitive as insensitive and thermally stable high‐energy density materials.     

Nitrogen‐Rich Energetic Monoanionic Salts of 3,4‐Bis(1 H‐5‐tetrazolyl)furoxan

3,4‐Bis(1H‐5‐tetrazolyl)furoxan (H₂BTF, 2 ) and its monoanionic salts that contain nitrogen‐rich cations were readily synthesized and fully characterized by multinuclear NMR (¹H, ¹³C) and IR spectroscopy, differential scanning calorimetry (DSC), and elemental analyses. Hydrazinium ( 3 ) and 4‐amino‐1,2,4‐triazolium ( 7 ) salts crystallized in the monoclinic space group P2(1)/n and have calculated densities of 1.820 and 1.764 g cm^?3, respectively. The densities of the energetic salts range between 1.63 and 1.79 g cm^?3, as measured by a gas pycnometer. Detonation pressures and detonation velocities were calculated to be 23.1–32.5 GPa and 7740–8790 m s^?1, respectively.     

Insensitive and Thermostable Energetic Materials Based on 3‐Ureido‐4‐tetrazole‐furazan: Synthesis,Characterization, and Properties

Energetic salts composed of ureido, furazan, and tetrazole were prepared by simple and efficient chemical routes to explore new insensitive and thermostable energetic materials. 3‐Ureido‐4‐tetrazole‐furazan ( 3 ) and its ammonium salt ( 5 ) and hydrazinium salt ( 6 ) were confirmed by single‐crystal X‐ray diffraction. The thermal stabilities of the synthesized salts were studied using differential scanning calorimetry, and the detonation performances of these salts were calculated using EXPLO 5 V6.01. All the salts exhibit good thermal stability (Td: 148–259 °C) and mechanical sensitivities (IS > 40 J, FS > 360 N), and their detonation velocities range from 7316 to 8655 m · s^–1. Compounds 6 and 10 are potential candidates as novel insensitive and heat‐resistant explosives because of their high detonation temperatures of 247 and 256 °C, good detonation velocities of 8432 and 8523 m · s^–1, and good detonation pressures of 25.6 and 26.8 GPa.     

Energetic Salts Based on Furazan‐Functionalized Tetrazoles: Routes to Boost Energy

Based on the backbone of the furazan‐tetrazole structure, routes were developed to improve the properties of energetic materials. Two types of high‐density energetic salts were designed, prepared, and fully characterized. Single‐crystal X‐ray analyses support the structural characteristics for two amino salts. A majority of the salts exhibited good detonation properties, high thermal stabilities, and relatively low impact and friction sensitivities. Hydroxylammonium and hydrazinium salts, 1 – 3 and 1 – 4 , which have relatively high densities (1.84 and 1.74 g cm^?3,, respectively), acceptable impact and friction sensitivities (14 J, 160 N and 28 J, 360 N), and good detonation pressures (38.3 and 32.2 GPa) and velocities (9323 and 9094 m s^?1), have performance properties superior to 1,3,5‐trinitro‐1,3,5‐triazinane (RDX) and triaminotrinitrobenzene (TATB).     

3,4,5‐Trinitropyrazole‐Based Energetic Salts

High‐density energetic salts that are comprised of nitrogen‐rich cations and the 3,4,5‐trinitropyrazolate anion were synthesized in high yield by neutralization or metathesis reactions. The resulting salts were fully characterized by ¹H, ¹³C NMR, and IR spectroscopy; differential scanning calorimetry; and elemental analysis. Additionally, the structures of the 3,5‐diaminotriazolium and triaminoguanidinium 3,4,5‐trinitropyrazolates were confirmed by single‐crystal X‐ray diffraction. Based on the measured densities and calculated heats of formation, the detonation performances (pressure: 23.74–31.89 GPa; velocity: 7586–8543 ms^?1; Cheetah 5.0) of the 3,4,5‐trinitropyrazolate salts are comparable with 1,3,5‐triamino‐2,4,6‐trinitrobenzene (TATB; 31.15 GPa and 8114 ms^?1). Impact sensitivities were determined to be no less than 35 J by hammer tests, which places these salts in the insensitive class.     

Energetic Salts Based on an Oxygen‐Containing Cation: 2,4‐Diamino‐1,3,5‐triazine‐6‐one

A family of energetic salts with high thermal stability and low impact sensitivity based on an oxygen‐containing cation, 2,4‐diamino‐1,3,5‐triazine‐6‐one, were synthesized and fully characterized by IR and multinuclear (¹H, ¹³C) NMR spectroscopy, elemental analysis, and differential scanning calorimetry. Insights into their sensitivities towards impact, friction, and electrostatics were gained by submitting the materials to standard tests. The structures of 2,4‐diamino‐1,3,5‐triazine‐6‐one nitrate, 2,4‐diamino‐1,3,5‐triazine‐6‐one sulfate, 2,4‐diamino‐1,3,5‐triazine‐6‐one perchlorate, 2,4‐diamino‐1,3,5‐triazine‐6‐one 5‐nitrotetrazolate were determined by single‐crystal X‐ray diffraction; their densities are 1.691, 1.776, 1.854, and 1.636 g cm^?3, respectively. Most of the salts decompose at temperatures over 180 °C; in particular, the salts 2,4‐diamino‐1,3,5‐triazine‐6‐one nitrate and 2,4‐diamino‐1,3,5‐triazine‐6‐one perchlorate, which decompose at 303.3 and 336.4 °C, respectively, are fairly stable. Furthermore, most of the salts exhibit excellent impact sensitivities (>40 J), friction sensitivities (>360 N), and are insensitive to electrostatics. The measured densities of these energetic salts range from 1.64 to 2.01 g cm^?3. The detonation pressure values calculated for these salts range from 14.6 to 29.2 GPa, and the detonation velocities range from 6536 to 8275 m s^?1; these values make the salts potential candidates for thermally stable and insensitive energetic materials.     

Nitrogen‐rich Salts based on 3‐Dinitromethyl‐[1,2,4]triazine: Synthesis,Characterization, and Performance

1,1‐Diamino‐2,2‐dinitroethylene (FOX‐7), one of the most well‐known energetic materials, has attracted broad attention around the world. To extend the chemistry of FOX‐7, we present here a series of energetic salts based on 3‐dinitromethyl‐[1,2,4]triazine, which is prepared from FOX‐7. All these salts were fully characterized using ¹H NMR, ¹³C NMR, IR, and elemental analysis. In addition, the potassium salt ( 2 ), ammonium salt ( 5 ), and guanidinium salt ( 7 ) were further confirmed by single‐crystal X‐ray diffraction. Extensive hydrogen bonds were observed in these salts. The salts exhibit moderate densities varying from 1.63 to 1.76 g · cm^–3. All the compounds possess good thermal stability with decomposition temperatures from 118 to 267 °C. The detonation performance for salts were calculated by using EXPLO 5, their detonation velocities are in the range from 6807 to 8614 m · s^–1 and detonation pressures fall between 18.8 to 31.6 GPa. All the salts exhibit very low mechanical sensitivity, which indicates their potential application as insensitive energetic materials.     

Nitrogen‐Rich Energetic Dianionic Salts of 3, 4‐Bis(1H‐5‐­tetrazolyl)furoxan with Excellent Thermal Stability

Nitrogen‐rich 3, 4‐bis(1H‐tetrazol‐5‐yl)furoxan (H₂BTF, 2 ) and its energetic salts with excellent thermal stability were successfully synthesized and fully characterized by ¹H, and ¹³C NMR, and IR spectroscopy, differential scanning calorimetry (DSC), and elemental analyses. Additionally, the structures of barium ( 3 ) and 1‐methyl‐3, 4, 5‐triamino‐triazolium ( 10 ) salts were confirmed by single‐crystal X‐ray diffraction. The densities of the energetic salts paired with organic cations range between 1.56 and 1.85 g · cm^–3 as measured by a gas pycnometer. Based on the measured densities and calculated heats of formation, the detonation pressures and velocities are calculated to be in the range 23.4–32.0 GPa and 7939–8915 m · s^–1, which make them competitive energetic materials.     

Energetic N,N′‐Ethylene‐Bridged Bis(nitropyrazoles): Diversified Functionalities and Properties

A new class of N,N′‐ethylene‐bridged bis(nitropyrazoles) was synthesized and fully characterized. The highly efficient formation of the N,N′‐ethylene bridge was accomplished using dibromoethane and ammonium or potassium pyrazolate. Further functional‐group transformations of diaminobis(pyrazole) and dichlorobis(pyrazole) gave rise to diversified derivatives, including dinitramino‐, diazido‐ and hexanitrobis(pyrazole). Single‐crystal X‐ray diffractions were obtained for hexanitro and diazido derivatives to illustrate the structural characteristics. Heats of formation and detonation performance were calculated by using Gaussian 03 and EXPLO5 v6.01 programs, respectively. Because of the different functionalized groups, the impact and friction sensitivities of these new compounds range from insensitive to sensitive. Among them, the hexanitro derivative displays the most promising overall energetic properties (density (ρ)=1.84 g cm^?3; decomposition temperature (T_d)=250 °C; detonation pressure (P)=34.1 GPa; detonation velocity (v_D)=8759 m s^?1; impact sensitivity (IS)=25 J; friction sensitivity (FS)=160 N), which is competitive with those of 1,3,5‐trinitrotriazacyclohexane (ρ=1.80 g cm^?3; T_d=205 °C; P=35.0 GPa; v_D=8762 m s^?1; IS=7 J; FS=120 N).     

Synthesis of Amino,Azido, Nitro,and Nitrogen‐Rich Azole‐Substituted Derivatives of 1H‐Benzotriazole for High‐Energy Materials Applications

The amino, azido, nitro, and nitrogen‐rich azole substituted derivatives of 1H‐benzotriazole have been synthesized for energetic material applications. The synthesized compounds were fully characterized by ¹H and ¹³C NMR spectroscopy, IR, MS, and elemental analysis. 5‐Chloro‐4‐nitro‐1H‐benzo[1,2,3]triazole ( 2 ) and 5‐azido‐4,6‐dinitro‐1H‐benzo[1,2,3]triazole ( 7 ) crystallize in the Pca2₁ (orthorhombic) and P2₁/c (monoclinic) space group, respectively, as determined by single‐crystal X‐ray diffraction. Their densities are 1.71 and 1.77 g cm^?3, respectively. The calculated densities of the other compounds range between 1.61 and 1.98 g cm^?3. The detonation velocity (D) values calculated for these synthesized compounds range from 5.45 to 8.06 km s^?1, and the detonation pressure (P) ranges from 12.35 to 28 GPa.     

Syntheses of Energetic cyclo‐Pentazolate Salts

Three energetic salts of cyclo‐N₅^? were synthesized via a metathesis reaction of barium pentazolate and sulfates which was driven by the precipitation of BaSO₄. All the energetic cyclo‐N₅^? salts were characterized by single‐crystal X‐ray diffraction, infrared (IR), ¹H and ¹³C multinuclear NMR spectroscopies, thermal analysis (TGA and DSC), and elemental analysis. The salts exhibit relatively good detonation performance with low sensitivities and good thermal stabilities. This new method opens the door to exploring more pentazolate anion‐containing high‐performance energetic materials.     

Stabilization of the Pentazolate Anion in Three Anhydrous and Metal‐Free Energetic Salts

According to previous reports, metal cations or water molecules are necessary for the stabilization of pentazolate anion (cyclo‐N₅^?) at ambient temperature and pressure. Seeking a new method to stabilize N₅^? is a big challenge. In this work, three anhydrous, metal‐free energetic salts based on cyclo‐N₅^? 3,9‐diamino‐6,7‐dihydro‐5 H‐bis([1,2,4]triazolo)[4,3‐e:3′,4′‐g][1,2,4,5] tetrazepine‐2,10‐diium, N‐carbamoylguanidinium, and oxalohydrazinium (oxahy⁺) pentazolate were synthesized and isolated. All salts were characterized by elemental analysis, IR spectroscopy, ¹H, ¹³C, and (in some cases) ¹⁵N NMR spectroscopy, thermal analysis (TGA and DSC), and single‐crystal XRD analysis. Computational studies associated with heats of formation and detonation performance were performed by using Gaussian 09 and Explo5 programs, respectively. The sensitivity of the salts towards impact and friction was determined, and overall the real N₅ explosives showed promising energetic properties.     

Synthesis,Structure, and Energetic Properties of 1,5‐Diaminotetrazolium Sulfate Salts

1,5‐diaminotetrazolium chloride (DATC) and 1,5‐diaminotetrazolium sulfate (DATS) were synthesized in this work. The structures of DATS and DATC were characterized. The single crystal of DATS was first cultured, and its structure was analyzed. The thermal behavior of DATS was investigated. The activation energy and pro‐exponential factor were calculated, E_k = 120.86 KJ/mol, A_k = 10^12.96 s^?1. The density, heat of formation, detonation pressure, and detonation velocity of DATS were first calculated. The detonation pressure and detonation velocity of DATS are P = 11.877 GPa, D = 5.617 km s^?1, which are smaller than those of 1,5‐diaminotetrazolium nitrate (DATN) (P = 33.3GPa, D = 8.77 km s^?1).     

1,5‐Diamino‐4‐methyltetrazolium 5‐Nitrotetrazolate – Synthesis,Testing and Scale‐up

1,5‐Diamino‐4‐methyltetrazolium 5‐nitrotetrazolate ( 2b ) was synthesized in high yield from 1,5‐diamino‐4‐methyltetrazolium iodide ( 2a ) and highly sensitive silver 5‐nitrotetrazolate (AgNT). A safer synthesis, suitable for scale‐up, is introduced involving reaction of the previously unreported 1‐amino‐5‐imino‐4‐methyltetrazole free base ( 2 ) with ammonium 5‐nitrotetrazolate. Both new compounds ( 2 and 2b ) were fully characterized using vibrational (IR and Raman) and multinuclear NMR spectroscopy (¹H, ¹³C, ¹⁴N, ¹⁵N), elemental analysis and single crystal X‐ray diffraction. The hydrogen‐bonding networks of both materials are described in terms of their graph‐sets. Compound 2b is hydrolytically stable with a high melting point and concomitant decomposition at 160 °C. The sensitivity of the energetic salt 2b towards impact (>30 J) and friction (>360 N) was tested. The constant volume energy of combustion (Δ_cU) of 2b was measured experimentally using bomb calorimetry. In addition, the detonation parameters (detonation pressure and velocity) of the nitrotetrazolate salt were calculated from the energy of formation, the crystal density and the molecular formula using the EXPLO5 computer code (P = 15.5·GPa, D = 6749 m s^?1) and are similar to that of TNT and nitroguanidine making 2b of prospective interest in propellant charge formulations or, in combination with a suitable oxidizer, as a solid propellant.     

Synthesis,Characterization and Explosive Properties of 1,3‐Dimethyl‐5‐amino‐1H‐tetrazolium 5‐Nitrotetrazolate

1,3‐Dimethyl‐5‐amino‐1H‐tetrazolium 5‐nitrotetrazolate ( 5b ) was synthesized in high yield from 1,4‐dimethyl‐5‐amino‐1H‐tetrazolium iodide ( 5a ) and silver 5‐nitrotetrazolate. Both new compounds ( 5a and 5b ) were characterized using vibrational (IR and Raman) and multinuclear NMR spectroscopy (¹H, ¹³C and ¹⁵N), elemental analysis and single‐crystal X‐ray diffraction. 5a crystallizes in an orthorhombic cell: Pbca, a = 11.5016(4), b = 13.7744(5), c = 13.7744(5) Å, V = 1638.2(1) ų, Z = 8, ρ = 1.955 g cm^?3, R₁ = 0.0210 (F > 4σ(F)), wR₂ (all data) = 0.0542; whereas 5b crystallizes in a monoclinic cell: C1c, a = 14.5228(8), b = 5.0347(2), c = 13.7217(7) Å, β = 112.11(1)°, V = 929.6(2) ų, Z = 4, ρ = 1.630 g cm^?3, R₁ = 0.0279 (F > 4σ(F)), wR₂ (all data) = 0.0585. The sensitivity of 5b to classical stimuli was determined by using standard BAM tests and its thermal stability was assessed by DSC measurements. In addition, its heat of combustion was determined by bomb calorimetry measurements. The EXPLO5 was used to calculate the detonation pressure (P) and velocity (D) of 5b (P = 13.3 GPa and D = 6379 m s^?1), as well as those of its mixtures with ammonium nitrate (P = 23.2 GPa and D = 7862 m s^?1) and ammonium dinitramide (P = 29.6 GPa and D = 8594 m s^?1). Compound 5b is a hydrolytically stable solid with a high melting point (160 °C) and thermally stable to 190 °C with a very low sensitivity to friction (>360 N) and impact (>30 J) and good performance in combination with an oxidizer making it of interest in new environmentally friendly, insensitive explosive formulations.     

Tetraanionic Nitrogen‐Rich Tetrazole‐Based Energetic Salts

1,1,3,3‐Tetra(1H‐tetrazol‐5‐yl)propane‐based energetic salts were synthesized in a simple and straightforward manner. The structures of these new salts were determined by ¹H and ¹³C NMR spectroscopy, IR spectroscopy, MS, and elemental analysis. All of these compounds showed good thermal stabilities above 180 °C, as confirmed by thermogravimetric–differential thermal analysis (TG–DTA) measurements. Moreover, these salts also exhibited high positive enthalpies of formation, high nitrogen content, good thermal stabilities, and moderate detonation properties.