On-line Raman spectroscopy combined with multivariate curve resolution-alternating least squares (MCR-ALS) to investigate the synthesis mechanism of 3,5-diamino-1,2,4-triazole (DAT)

The precise and accurate synthesis mechanism of typical energetic materials (EMs) intermediate is extremely important for the optimization of synthesis technology of EMs. In this research, on-line Raman spectroscopy technique combined with multivariate curve resolution-alternating least squares(MCR-ALS) method was proposed and used to investigate the synthesis mechanism of EMs intermediate (3,5-diamino-1,2,4-triazole, DAT). Initially, on-line Raman spectroscopy was applied to collect the Raman spectral data of DAT synthesis process. Secondly, principal component analysis (PCA), coupled with singular value decomposition (SVD) were used to determine the number of component of the reaction system and the components was 5. Thirdly, MCR-ALS was used to extract the pure Raman spectra and concentration curves of each substance of DAT synthesis process. During the MCR-ALS operation, evolving factor analysis (EFA) was choose to acquire the initial concentration estimation for MCR-ALS. Several constraints were selected to apply to ALS optimization including non-negative, closure, equality and correlation constraint. And the correlation coefficient between the Raman spectra and the actual Raman spectra of the hydrazine hydrochloride, dicyandiamide and DAT was calculated, their correlation coefficient R² were 0.9522, 0.9446, 0.9908 respectively which showed a good data fit of MCR-ALS method. Finally, according to the results of MCR-ALS analysis, the structure of the synthetic intermediates was successfully deduced and the mechanism of DAT synthesis was proposed. Hence, a precise and comprehensive method for analyzing the DAT synthesis reaction mechanism is proposed, which is helpful to provide a new idea for the analysis of the synthesis reaction mechanism of energetic materials.

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.

Studies on the synthesis and properties of nitramino compounds based on tetrazine backbones

In this paper, a series of novel energetic compounds based on the backbone of the tetrazine-triazole structure were successfully synthesized. N,N'-((1,2,4,5-Tetrazine-3,6-diyl)bis(1,2-dihydro-3H-1,2,4-triazole-5-yl-3-ylidene))dinitramino (4) was prepared by the nitration of 5,5'-(1,4-dihydro-1,2,4,5-tetrazine-3,6-diyl)bis(1H-1,2,4-triazol-3-amine) (3) with 100% nitric acid and its energetic salts (6-14) were also prepared. All the compounds were fully characterized. The structures of 4 and 5 were further confirmed by single crystal X-ray diffraction analysis. The results show that these compounds have high heats of formation ranging from 2.09 to 3.95 kJ g^-1, good detonation pressures and detonation velocities and acceptable sensitivities. Among them, compound 4, with low sensitivities (IS: 20 J and FS: 270 N) and excellent detonation properties (v_D = 9100 m s^-1; P = 34.1 GPa) shows potential for application in the field of highly energetic and insensitive explosives. The hydroxylammonium salt (7) exhibits promising energetic properties, which, in some cases, are superior to those of octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX).