Synthesis and characterization of 3,6-bis(1H-1,2,3,4-tetrazol-5-ylamino)-1,2,4,5-tetrazine (BTATz): novel high-nitrogen content insensitive high energy material

Carbon-Nitride Popcorn-A Novel Catalyst Prepared by Self-Propagating Combustion of Nitrogen-Rich Triazenes

The interest in development of non-graphitic polymeric carbon nitrides (PCNs), with various C-to-N ratios, having tunable electronic, optical, and chemical properties is rapidly increasing. Here the first self-propagating combustion synthesis methodology for the facile preparation of novel porous PCN materials (PCN3-PCN7) using new nitrogen-rich triazene-based precursors is reported. This methodology is found to be highly precursor dependent, where variations in the terminal functional groups in the newly designed precursors (compounds 3-7) lead to different combustion behaviors, and morphologies of the resulted PCNs. The foam-type highly porous PCN5, generated from self-propagating combustion of 5 is comprehensively characterized and shows a C-to-N ratio of 0.67 (C₃ N_4.45 ). Thermal analyses of PCN5 formulations with ammonium perchlorate (AP) reveal that PCN5 has an excellent catalytic activity in the thermal decomposition of AP. This catalytic activity of PCN5 is further evaluated in a closer-to-application scenario, showing an increase of 18% in the burn rate of AP-Al-HTPB (with 2 wt% of PCN5) solid composite propellant. The newly developed template- and additive-free self-propagating combustion synthetic methodology using specially designed nitrogen-rich precursors should provide a novel platform for the preparation of non-graphitic PCNs with a variety of building block chemistries, morphologies, and properties suitable for a broad range of technologies.

Molecular design of energetic tetrazine-triazole derivatives

Nitrogen-rich compounds are promising candidates for preparing high energetic density materials (HEDMs) and show the potential in the application of propellants, explosives, and pyrotechnics. Two kinds of typical nitrogen-rich compounds, such as tetrazine and triazole, have attracted the attentions in recent years owing to their high densities, good thermal stabilities, and excellent energetic performances. In this work, four series of innovative energetic compounds based on the conjugates of tetrazine and triazole bearing various substituents (-NH₂, -NO₂, and -NHNO₂) were designed. The optimized structures, crystal densities, heats of formation (HOFs) in gas phase and in condensed phase, detonation properties, bond dissociation energies (BDEs), and impact sensitivity (h₅₀) of these compounds were studied systematically via density functional theory (DFT) method. The detonation velocities of four series of compounds are in the range between 7.03 and 8.59 km s^-1 and their detonation pressures are in the range between 20.6 and 33.1 GPa. Results indicated that the linkage of -N=N- bond contributed significantly to HOFs and energy density of the energetic molecules, and 1,2,3-triazole showed better performances than 1,2,4-triazole slightly. As for the same series compounds with different substituents, the compounds with -NHNO₂ possessed the highest HOFs (such as A6, B6, C6, D6). In terms of the energetic properties (D and P), four compounds (A7, B7, C7, and D7) exhibited the comparable performance with the widely used hexa-hydro-1,3,5-trinitro-1,3,5-triazine (RDX) and in the meanwhile displayed superior thermal stability and sensitivity to RDX, which indicated their potential application in the insensitive energetic materials.

A series of guanidine salts of 3,6-bis-nitroguanyl-1,2,4,5-tetrazine: green nitrogen-rich gas-generating agent

Nitrogen-rich energetic materials (EMs) have been widely studied because of their high thermal stability, insensitivity, excellent detonation performance and non-toxic characteristics. In particular, these compounds are well applied as gas-generating agents (GGAs). As a nitrogen-rich heterocyclic framework, 1,2,4,5-tetrazine derivatives have shown great potential in the design of GGAs. The guanidine salts of 3,6-bis-nitroguanyl-1,2,4,5-tetrazine (DNGTz), guanidine (G₂DNGTz) (1), aminoguanidine (AG₂DNGTz) (2), diaminoguanidine (DAG₂DNGTz) (3), and triaminoguanidine (TAG₂DNGTz) (4) have been synthesized and characterized by elemental analysis and FT-IR. The crystal structures of 1 and 2 were obtained by X-ray single crystal diffraction. Crystal analysis shows that 1 and 2 arrange through zigzag-chain-like assembly and face-to-face geometries, which is helpful in decreasing mechanical sensitivity. The thermal stability and thermal decomposition kinetics of these four salts were studied by Differential Scanning Calorimetry (DSC). Furthermore, the thermogravimetry-Fourier transform infrared-mass spectrometry (TG-FTIR-MS) analysis of thermal decomposition products reveals that the main decomposition gaseous products are H₂O, N₂O, CO₂, NO, N₂ and NH₃. Then, the cytotoxicity of the four salts was tested by MTT (3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2-H-tetrazolium bromide) method, and it was found that salts 1–4 show slight cytotoxicity in mouse fibroblasts (L929), at a concentration of 0.125 mg ml⁻¹. The insensitivity, low toxicity, and production of clean gases without solid residue after burning of salt 1 indicate that it can be used as a potential green energetic material for GGAs.

All salts show slight cytotoxicity in mouse fibroblasts and the main decomposition gas products of thermal decomposition are non-toxic.

Properties and Promise of Catenated Nitrogen Systems As High-Energy-Density Materials

The properties of catenated nitrogen molecules, molecules containing internal chains of bonded nitrogen atoms, is of fundamental scientific interest in chemical structure and bonding, as nitrogen is uniquely situated in the periodic table to form kinetically stable compounds often with chemically stable N-N bonds but which are thermodynamically unstable in that the formation of stable multiply bonded N₂ is usually thermodynamically preferable. This unique placement in the periodic table makes catenated nitrogen compounds of interest for development of high-energy-density materials, including explosives for defense and construction purposes, as well as propellants for missile propulsion and for space exploration. This review, designed for a chemical audience, describes foundational subjects, methods, and metrics relevant to the energetic materials community and provides an overview of important classes of catenated nitrogen compounds ranging from theoretical investigation of hypothetical molecules to the practical application of real-world energetic materials. The review is intended to provide detailed chemical insight into the synthesis and decomposition of such materials as well as foundational knowledge of energetic science new to most chemists.

Exploration of High-Energy-Density Materials: Computational Insight into Energetic Derivatives Based on 1,2,4,5-Tetrahydro-1,2,4,5-tetrazine

Density functional theory was employed to investigate ten 1,2,4,5-tetrahydro-1,2,4,5-tetrazine-based energetic materials. The heats of formation and detonation properties were calculated by isodesmic reactions and Kamlet-Jacobs equations. The thermal stabilities and impact sensitivities were also estimated to give a better understanding of their decomposition mechanism. The results indicate that all of the designed compounds have high positive heats of formation ranging from 525.1 to 1639.1 kJ mol-1, moderate detonation properties (heats of detonation of 536.6 to 2187.6 cal g-1, theoretical densities of 1.48 to 2.32 g cm-3, detonation velocities of 7.02 to 12.18 km s-1, and detonation pressures of 19.8 to 75.1 GPa), and acceptable stabilities (bond dissociation energies of 0.8 to 104.9 kJ mol-1). Taking both the detonation properties and the stabilities into consideration, compounds A4 and B4 were finally selected as promising candidates of high-energy-density materials, as their detonation properties and impact sensitivities were superior to those of HMX. Additionally, the frontier molecular orbitals, electronic densities, electrostatic potentials, and thermal dynamic parameters of compounds A4 and B4 were also investigated.

Proposed Proton-Transfer Mechanism for the Initial Decomposition Steps of BTATz

The first steps in the gas-phase decomposition mechanism of N3,N6-bis (1 H-tetrazol-5-yl)-1,2,4,5-tetrazine-3,6-diamine, BTATz, anions and the kinetic isotope effects in these processes were studied using combined multistage mass spectrometry (MS/MS) and computational techniques. Two major fragmentation processes, the exergonic loss of nitrogen molecules and the endergonic loss of hydrazoic acid, were identified. The observation of a primary isotope effect supported by calculations suggests that the loss of a nitrogen molecule from the tetrazole ring involves proton migration, either to or within the terazole ring, as a rate-determining step. The fragmentation of a hydrazoic acid occurs through an asymmetrical retro-pericyclic reaction. Calculations show the relevance of these mechanisms to neutral BTATz. Our findings may contribute to the understanding of decomposition routes in these nitrogen-rich energetic materials and allow tailoring their reactivity and decomposition pathways for better control of performance.

The synthesis, crystal structure and thermal properties of an energetic compound: the hydrated azanium salt of 3,6-bis[(1H-1,2,3,4-tetrazol-5-yl)amino]-1,2,4,5-tetrazine

The energetic ionic salt bis(1-aminoguanidin-2-ium) 5,5'-[1,2,4,5-tetrazine-3,6-diylbis(azanediyl)]bis(1H-1,2,3,4-tetrazol-1-ide) dihydrate, 2CH₇N₄⁺·C₄H₂N₁₄^2-·2H₂O, (I), with a high nitrogen content, has been synthesized and examined by elemental analysis, Fourier transform IR spectrometry, ¹H NMR spectroscopy and single-crystal X-ray crystallography. Compound (I) crystallizes in the monoclinic space group P2₁/c with two water molecules. However, the water molecules are disordered about an inversion centre and were modelled as half-occupancy molecules in the structure. The crystal structure reveals a three-dimensional network of molecules linked through N-H...N, N-H...O, O-H...N and O-H...O hydrogen bonds. Thermal decomposition was investigated by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The exothermic peak temperature is 509.72 K, which indicates that hydrated salt (I) exhibits good thermal stability. Non-isothermal reaction kinetic parameters were calculated via both the Kissinger and the Ozawa methods to yield activation energies of E_k = 239.07 kJ mol^-1, lgA_k = 22.79 s^-1 and E_O = 235.38 kJ mol^-1 for (I). Additionally, the thermal safety was evaluated by calculating critical temperatures and thermodynamic values, viz. T_SADT, T_TIT, T_b, ΔS^≠, ΔH^≠ and ΔG^≠. The results reveal that (I) exhibits good thermal safety compared to other ion salts of 3,6-bis[(1H-1,2,3,4-tetrazol-5-yl)amino]-1,2,4,5-tetrazine (BTATz).

Energetic isomers of 1,2,4,5-tetrazine-bis-1,2,4-triazoles with low toxicity

A series of nitrogen-rich “green” Energetic Materials (EMs), some with improved sensitivity, thermostability, and very low toxicity, were synthesized on the basis of 3,5-diamino-1,2,4-triazole (DAT) and 1,2,4,5-tetrazine building blocks.

The nitration pattern of energetic 3,6-diamino-1,2,4,5-tetrazine derivatives containing azole functional groups

A study of nitration patterns was conducted on 3,6-diamino-1,2,4,5-tetrazines derivatives, revealing the specificity of their nitration, as well as the stability of the formed nitramines towards hydrolysis.

Novel 3,6-unsymmetrically disubstituted-1,2,4,5-tetrazines: S-induced one-pot synthesis, properties and theoretical study

18 unprecedented 3,6-unsymmetrically disubstituted-1,2,4,5-tetrazines were synthesized, and their spectral and electrochemical properties are studied. A systematic theoretical investigation based on DFT calculations was carried out.

Synthesis and characteristics of novel, high-nitrogen 1,2,4-oxadiazoles

Two novel high-nitrogen energetic compounds AOG and AOG₂Tz were prepared with good performance, high thermal stability and low impact sensitivity.

1-[6-(3,5-Di-methyl-pyrazol-1-yl)-1,2,4,5-tetra-zin-3-yl]guanidin-2-ium perchlorate methanol monosolvate

In the title solvated salt, C₈H₁₂N₉⁺·ClO₄⁻·CH₃OH, the dihedral angle between the tetra­zine and pyrazole rings is 26.05 (7)°. The two N atoms bonded to the 1,2,4,5-tetra­zine ring deviate from the plane defined by its four N atoms by 0.234 (2) and 0.186 (2) Å. There is an intra­molecular N—H⋯N hydrogen bond between the protonated guanidine fragment and one of the tetra­zine N atoms. In the crystal, two cations and two perchlorate anions are connected via N—H⋯O hydrogen bonds into centrosymmetric assemblies. These assemblies are further linked into a two-dimensional network parallel to (100) via bifurcated O—H⋯(N,N) hydrogen bonds formed with the bridging methanol mol­ecules.

Theoretical studies on vibrational spectra, thermodynamic properties, and detonation properties for 1,2,4,5-tetrazine derivatives

A density functional theory calculation was performed to study the molecular structures, heats of formation (HOFs), infrared spectra, detonation properties, and thermodynamic properties for five 1,2,4,5-tetrazine derivatives. Based on the full optimized molecular structures at the B3LYP/6-311++G** level, the assigned infrared spectra of the studied compounds were obtained. The isodesmic reaction method was employed to calculate the HOFs of the derivatives. The detonation velocities and pressures were also evaluated by using Kamlet−Jacobs equations with the calculated densities and condensed HOFs. The result shows that 3,6-diazido-1,2,4,5- tetrazine may be a potential candidate of high-energy density materials (HEDMs). Natural bond orbital analysis indicated that the title compounds all have higher bond dissociation energies when compared with 1,3,5,7-tetranitro-1,3,5,7-tetrazocane and 1,3,5-trinitro-1,3,5-triazinane. The results may provide basis information for the molecular design of new HEDMs.

Thermal behaviors, nonisothermal decomposition reaction kinetics, thermal safety and burning rates of BTATz-CMDB propellant

The composite modified double base (CMDB) propellants (nos. RB0601 and RB0602) containing 3,6-bis (1H-1,2,3,4-tetrazol-5-yl-amino)-1,2,4,5-tetrazine (BTATz) without and with the ballistic modifier were prepared and their thermal behaviors, nonisothermal decomposition reaction kinetics, thermal safety and burning rates were investigated. The results show that there are three mass-loss stages in TG curve and two exothermic peaks in DSC curve for the BTATz-CMDB propellant. The first two mass-loss stages occur in succession and the temperature ranges are near apart, and the decomposition peaks of the two stages overlap each other, inducing only one visible exothermic peak appear in DSC curve during 350-550 K. The reaction mechanisms of the main exothermal decomposition processes of RB0601 and RB0602 are all classified as chemical reaction, the mechanism functions are f(alpha)=(1-alpha)(2), and the kinetic equations are dalpha/dt = 10(19.24)(1-alpha)(2)e(-2.32x10(4)/T) and dalpha/dt = 10(20.32)(1-alpha)(2)e(-2.32x10(4)/T). The thermal safety evaluation on the BTATz-CMDB propellants was obtained. With the substitution of 26% RDX by BTATz and with the help of the ballistic modifier in the CMDB propellant formulation, the burning rate can be improved by 89.0% at 8 MPa and 47.1% at 22 MPa, the pressure exponent can be reduced to 0.353 at 14-20 MPa.