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.     

Synthesis, Characterization and Thermal Properties of Energetic Compounds Derived from 3-Amino-4-(tetrazol-5-yl)furazan

Five energetic compounds, 3,3‐bis(tetrazol‐5‐yl)‐4,4‐azofurazan (DTZAF), 3‐nitro‐4‐(tetrazol‐5‐yl)furazan (NTZF), hydrazinium 3‐amino‐4‐(tetrazol‐5‐yl)furazan (HATZF), triaminoguanidinium 3‐amino‐4‐(tetrazol‐ 5‐yl)furazan (TAGATZF) and guanylureaium 3‐amino‐4‐(tetrazol‐5‐yl)furazan (MATZF), were prepared using 3‐amino‐4‐(tetrazol‐5‐yl)furazan (ATZF) as starting material and their structures were characterized by FT‐IR, ¹H NMR, ¹³C NMR and elemental analysis. The properties of NTZF were estimated:density is 1.67 g/cm³, enthalpy of formation +415.41 kJ/mol and detonation velocity 8257.83 m/s. The main thermal properties of four compounds, DTZAF, HATZF, TAGATZF and MATZF, were analyzed by TG and DSC techniques and the results showed that their melting points are 251.9, 159.7, 205.4 and 211.4°C, respectively, and their first decomposition temperatures are 256.7, 258.6, 231.7 and 268.6°C, respectively. The fact that their decomposition temperatures were over 230°C showed that they exhibit better thermal stability.     

Magnesium Azotetrazole‐1,1′‐dioxide: Synthesis and Promising Properties of Green Insensitive Energetic Materials

Magnesium azotetrazole‐1,1′‐dioxide ( 1 ) was first prepared and intensively characterized by single‐crystal X‐ray diffraction, IR spectroscopy, mass spectrometry, elemental analysis, and DSC measurements. The heat of formation was calculated using the atomization energy method based on quantum chemistry and the heat of detonation was also predicted. The NBO analysis was performed for inspecting charge distributions. The sensitivities towards impact and friction were tested using the BAM standard. The high detonation performance (5289 kJ · kg^–1), good thermal stabilities (245.5 °C) and excellent insensitivity (39.2 J and >360 N) as well as clean decomposition products supports it of great interest as a promising candidate of green insensitive energetic materials.     

Furazan‐Functionalized Tetrazolate‐Based Salts: A New Family of Insensitive Energetic Materials

Insensitive energetic salts : A series of furazan‐functionalized tetrazolate‐based energetic salts (see figure) were synthesized and characterized. All of the salts exhibit excellent thermal stabilities and high positive heats of formation.

     

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).     

Energetic Materials Based on the 5‐Azido‐3‐nitro‐1, 2,4‐tri­azolate Anion

This study presents the preparation of 5‐azido‐3‐nitro‐1H‐1, 2,4‐triazole ( 1 ) in both good yield and high purity, starting from commercially available chemicals in a three step synthesis. Furthermore, several metal and nitrogen‐rich salts with sodium ( 3 ), potassium ( 4 ), cesium ( 5 ), silver ( 6 ), lead ( 7 ), ammonium ( 8 ), guanidinium ( 9 ), and aminoguanidinium ( 10 ) were prepared by simple acid‐base reactions. All compounds were well characterized by various means, including vibrational (IR, Raman) and multinuclear (¹H, ¹³C, ¹⁴N, ¹⁵N) NMR spectroscopy, mass spectrometry, and DSC. Additionally the structure of 7 was determined by single‐crystal X‐ray diffraction. The sensitivities towards various outer stimuli (impact, friction, electrostatic discharge) were determined according to BAM standards. The metal salts were tested as potential primary explosives utilizing various preliminary tests.     

Synthesis,Structure, and Characterization of 3, 4′‐Bis‐1H‐1, 2,4‐triazolium Picrate Salt: A New High‐Energy Density Material

The environmentally friendly high‐energy density salt (TRTR)(PA) (TRTR = 3, 4′‐bis‐1, 2,4‐1H‐triazole, PA = 2, 4,6‐trinitrophenol, picric acid) was synthesized and characterized. The X‐ray single crystal diffraction results illustrate that the structure of title salt belongs to the monoclinic system, space group P2₁/c. Many parallel relationships exist in the molecule, as well as a strong intramolecular π–π stacking interaction. The DSC result shows only one exothermal decomposition step at 229.1 °C. The TG‐DTG curve demonstrates a 75.9 % mass loss from 180 °C to 300 °C at a rate of 3.01 % · K^–1. Experimental data show that the combustion heat approximately equals to TNT (–15.22 MJ · kg^–1) and the enthalpy of formation is +332.2 kJ · mol^–1. Non–isothermal kinetic and thermodynamic parameters were obtained by two methods (Kissinger and Ozawa). Detonation pressure and velocity were calculated to be 23.4 GPa and 7.32 km · s^–1, respectively. Additionally, the sensitivities towards impact and friction were assessed with relevant standard methods.     

2‐(Dinitromethylene)‐1‐nitro‐1, 3‐diazacyclopentane‐Based Energetic Salts

Energetic salts that contain nitrogen‐rich cations and the 2‐(dinitromethyl)‐3‐nitro‐1, 3‐diazacyclopent‐1‐ene anion were synthesized in high yield by direct neutralization reactions. The resulting salts were fully characterized by multinuclear NMR spectroscopy (¹H and ¹³C), vibrational spectroscopy (IR), elemental analysis, density and differential scanning calorimetry (DSC), and elemental analysis. Additionally, the structures of the ammonium ( 1 ) and isopropylideneaminoguanidinium ( 9 ) 2‐(dinitromethyl)‐3‐nitro‐1, 3‐diazacyclopent‐l‐ene salts were confirmed by single‐crystal X‐ray diffraction. Solid‐state ¹⁵N NMR spectroscopy was used as an effective technique to further determine the structure of some of the products. The densities of the energetic salts paired with organic cations fell between 1.50 and 1.79 g · cm^–3 as measured by a gas pycnometer. Based on the measured densities and calculated heats of formation, detonation pressures and velocities were calculated using Explo 5.05 and found to to be 25.2–35.5 GPa and 7949–9004 m · s^–1, respectively, which make them competitive energetic materials.     

Perchlorate‐Free Pyrotechnic Formulations Utilizing Energetic Chlorine Donors: 1‐CDN, 11‐CDN, 13‐CDN

Several novel materials were investigated as energetic chlorine donors, specifically for the preparation of perchlorate‐free pyrotechnic formulations with low‐smoke output. The novel compounds, 2‐chloromethyl‐2‐methyl‐5,5‐dinitro‐1,3‐dioxane (1‐CDN), 2,2‐bis(chloromethyl)‐5,5‐dinitro‐1,3‐dioxane (13‐CDN), and 2‐(dichloromethyl)‐2‐methyl‐5,5‐dinitro‐1,3‐dioxane (11‐CDN), were formulated with a variety of fuels and oxidizers and their resulting colored flames analyzed for color quality. The preparation and preliminary characterization of these energetic chlorine donors are described.     

High‐ and low‐temperature phases in isostructural 4‐chloro‐3‐nitroaniline and 4‐iodo‐3‐nitroaniline

The structures of 4‐chloro‐3‐nitroaniline, C₆H₅ClN₂O₂, (I), and 4‐iodo‐3‐nitroaniline, C₆H₅IN₂O₂, (II), are isomorphs and both undergo continuous (second order) phase transitions at 237 and 200 K, respectively. The structures, as well as their phase transitions, have been studied by single‐crystal X‐ray diffraction, Raman spectroscopy and difference scanning calorimetry experiments. Both high‐temperature phases (293 K) show disorder of the nitro substituents, which are inclined towards the benzene‐ring planes at two different orientations. In the low‐temperature phases (120 K), both inclination angles are well maintained, while the disorder is removed. Concomitantly, the b axis doubles with respect to the room‐temperature cell. Each of the low‐temperature phases of (I) and (II) contains two pairs of independent molecules, where the molecules in each pair are related by noncrystallographic inversion centres. The molecules within each pair have the same absolute value of the inclination angle. The Flack parameter of the low‐temperature phases is very close to 0.5, indicating inversion twinning. This can be envisaged as stacking faults in the low‐temperature phases. It seems that competition between the primary amine–nitro N—H...O hydrogen bonds which form three‐centred hydrogen bonds is the reason for the disorder of the nitro groups, as well as for the phase transition in both (I) and (II). The backbones of the structures are formed by N—H...N hydrogen bonding of moderate strength which results in the graph‐set motif C(3). This graph‐set motif forms a zigzag chain parallel to the monoclinic b axis and is maintained in both the high‐ and the low‐temperature structures. The primary amine groups are pyramidal, with similar geometric values in all four determinations. The high‐temperature phase of (II) has been described previously [Garden et al. (2004). Acta Cryst. C 60 , o328–o330].     

The Pyridazine Scaffold as a Building Block for Energetic Materials: Synthesis,Characterization, and Properties

In the present studies, the synthesis of new energetic materials based on the pyridazine scaffold and their characterization is the main subject. For this purpose, desired 3,5‐dimethoxy‐4,6‐dinitropyridazine‐1‐oxide ( 7 ) was synthesized in the first instance. The persubstituted pyridazine precursor laid the groundwork for further preparative modification. The targeted functionalization through the regioselective introduction of various smaller amine nucleophiles such as methylamine or 2‐aminoethanol gave several new energetic materials. Among them are 3,5‐bis(methylamino)‐4,6‐dinitropyridazine‐1‐oxide ( 8 ), 3,5‐bis(methylnitramino)‐4,6‐dinitropyridazine‐1‐oxide ( 9 ), 3,5‐bis(dimethylamino)‐4,6‐dinitropyridazine‐1‐oxide ( 10 ), and 3,5‐bis((2‐hydroxyethyl)amino)‐4,6‐dinitropyridazine‐1‐oxide ( 11 ). With the aim of increasing the detonation performance, compound 8 was additionally nitrated and 3,5‐bis(methylnitramino)‐4,6‐dinitropyridazine‐1‐oxide ( 9 ) was obtained. These new energetic materials were characterized and identified by multinuclear NMR (¹H, ¹³C, ¹⁴N, ¹⁵N) and IR spectroscopy, elemental analysis and mass spectrometry. In addition, their sensitivities toward impact, friction and electrostatic discharge were thoroughly examined. Furthermore, obtained single‐crystals of the substances were characterized by low‐temperature single‐crystal X‐ray diffraction.     

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.     

Synthesis,Characterization, and Energetic Properties of 6‐Amino‐tetrazolo[1,5‐b]‐1,2,4,5‐tetrazine‐7‐N‐oxide: A Nitrogen‐Rich Material with High Density

The synthesis and energetic properties of a novel N‐oxide high‐nitrogen compound, 6‐amino‐tetrazolo[1,5‐b]‐1,2,4,5‐tetrazine‐7‐N‐oxide, are described. Resulting from the N‐oxide and fused rings system, this molecule exhibits high density, excellent detonation properties, and acceptable impact and friction sensitivities, which suggests potential applications as an energetic material. Compared to known high‐nitrogen compounds, such as 3,6‐diazido‐1,2,4,5‐tetrazine (DiAT), 2,4,6‐tri(azido)‐1,3,5‐triazine (TAT), and 4,4′,6,6′‐tetra(azido)azo‐1,3,5‐triazine (TAAT), a marked performance and stability increase is seen. This supports the superior qualities of this new compound and the advantage of design strategy.     

Two Energetic Salts based on 5,5′‐Bitetrazole‐1,1′‐diolate: Syntheses,Characterization, and Properties

Two salts based on 1H,1′H‐5,5′‐bitetrazole‐1,1′‐diolate (BTO) anion with pyrazole ( 1 ) and imidazole ( 2 ) cations were synthesized with metathesis reactions. Structural characterization was accomplished for them by using the element analysis, Fourier transform infrared spectroscopy (FT‐IR), NMR and mass spectrum, and X‐ray single crystal diffraction. Thermal analysis for the title salts were determined by means of differential scanning calorimetry (DSC) and thermogravimetry‐derivative thermogravimetry (TG‐DTG) as well as the calculation of non‐isothermal kinetic parameters. Consequently, both salts shown acceptable thermal stabilities as the decomposition temperatures were over 200 °C. The enthalpies of formation were calculated for these salts using the measured combustion energies with a result of 70.6 kJ · mol^–1 for 1 and –47.8 kJ · mol^–1 for 2 , respectively. Impact and friction sensitivities were also tested and the results indicated that these salts both have low sensitivities (>40 J, 120 N). The title energetic salts possess acceptable performance, they can therefore be applied in the field of energetic materials.     

Synthesis and Characterization of Salts of the 3,6‐Dinitro‐[1,2,4]triazolo[4,3‐b][1,2,4]triazolate Anion: Insensitive Energetic Materials Available From Economical Precursors

In this work, the treatment of 3,6,7‐triamino‐[1,2,4]triazolo[4,3‐b][1,2,4]triazole (TATOT)^[1] with sulfuric acid and sodium nitrite results in elimination of the N‐amine and the formation of the new energetic anion 3,6‐dinitro‐[1,2,4]triazolo[4,3‐b][1,2,4]triazolate (DNTT) via nitro‐Sandmeyer chemistry. This new energetic anion is available in a convenient and inexpensive three‐step process from inexpensive commercial starting materials. Several nitrogen rich salts of this material have been prepared and their chemical (infrared, Raman, NMR, single‐crystal X‐ray) and energetic (impact, friction, thermal) properties determined. As a rule, this class of energetic salts are insensitive energetic materials.     

Synthesis,Crystal Structure,and Properties of Energetic Copper(II) Complex based on 3,5‐Dinitrobenzoic Acid and 1,5‐Diaminotetrazole

Energetic copper(II) complexes based on 3,5‐dinitrobenzoic acid (HDNBA) and 1,5‐diaminotetrazole (DAT), Cu(DNBA)₂(H₂O)₂ ( 1 ) and Cu(DAT)₂(DNBA)₂ ( 2 ) were synthesized and characterized by elemental analysis, IR spectroscopy, single‐crystal and powder X‐ray diffraction. In both complexes, Cu^II was coordinated to a plane tetragon, by four oxygen atoms from two DNBA^– ions and two coordinated H₂O molecules for 1 , and by two oxygen atoms and two nitrogen atoms from different DNBA^– ions and DAT ligands for 2 . Differential scanning calorimetry (DSC) and thermogravimetry (TG) analyses were employed to measure the thermal decomposition processes and non‐isothermal kinetics parameters of the complexes. The thermal decomposition onset temperatures of 1 and 2 are 321 and 177 °C. The apparent activation energies of the first exothermic decomposition peaks of 1 and 2 are 247.2 and 185.2 kJ · mol^–1. Both 1 (35 J, > 360 N) and 2 (12.5 J, > 360 N) are less sensitive than RDX. The catalytic effects on the decomposition of ammonium perchlorate (AP) of 1 and 2 were studied by DSC. All results supported the potential applications of the energetic complexes as additives of solid rocket propellants.     

3‐Nitramino‐4‐nitrofurazan: Enhancing the Stability and Energetic Properties by Introduction of Alkylnitramines

Nitration of 3‐amino‐4‐nitrofurazan with N₂O₅ yielded the corresponding nitramine. 3‐Nitramino‐4‐nitrofurazan is a very promising explosive regarding detonation performance but it suffers from its hygroscopicity, low thermal stability, and high sensitivity to external stimuli. The introduction of other nitramine groups either by alkylation with 1‐chloro‐2‐nitrazapropane or by combination of two 3‐nitramino‐4‐nitrofurazans yielded the corresponding more stable and non‐hygroscopic open‐chain nitramines. Their molecular structures were investigated by single‐crystal X‐ray diffraction. The remarkable difference of their impact sensitivities were evaluated by calculation of their electrostatic potential of the molecular surfaces. Furthermore, the detonation parameters and combustion parameters of the open‐chain nitramines were computed with the EXPLO5 (v. 6.02) computer code.     

Synthesis and Characterization of 3‐(5‐(Fluorodinitromethyl)‐1H‐1,2,4‐triazol‐3‐yl)‐4‐nitrofurazan: A Novel Promising Energetic Component of Boron‐based Fuels for Rocket Ramjet Engines

The synthesis of a new energetic 1,2,4‐triazole compound bearing nitrofurazanyl and fluorodinitromethyl units, which may find use as a component for rocket ramjet engines (RRE), is described. The target product was prepared in a four‐step process applying oxidation/nitration/decarboxylation/fluorination reactions and is fully characterized. Its density and structural features were uniquely determined by X‐ray analysis. It is shown that replacing HMX with the compound of this study in boron‐based fuels gives an increase in energy.     

pH Dependent Synthesis of Two Manganese Compounds based on 5‐(2‐Pyrimidyl)tetrazole‐1‐acetic Acid

Reactions of Hpymtza [Hpymtza = 5‐(2‐pyrimidyl)tetrazole‐1‐acetic acid] with MnCl₂ · 4H₂O under different pH conditions, afforded the complexes [Mn(pymtza)₂(H₂O)₄] ( 1 ) and [Mn₂(pymtza)₂Cl₂(EtOH)] · H₂O ( 2 ). The compounds were structurally characterized by elemental analysis, IR spectroscopy and single‐crystal X‐ray diffraction. Compound 1 shows a mononuclear structure, whereas complex 2 has a 1D chain structure. In compound 1 , the pymtza ligand only acts in a monodentate manner to coordinate to one central Mn^II atom by one carboxylate atom, In 2 , pymtza acts as tetradentate ligand to connect three Mn^II ions. Compounds 1 and 2 display 3D networks by hydrogen bonding interactions. Furthermore, the luminescence properties of Hpymtza as well as compounds 1 and 2 were investigated at room temperature in the solid state.