Abstract
Rearrangement reactions are efficient strategies in organic synthesis and contribute enormously to the development of energetic materials. Here, we report on the preparation of a fused energetic structure of 7-nitro-3,5-dihydro-4H-pyrazolo[4,3-d][1,2,3]triazin-4-one (NPTO) based on a novel Hofmann-type rearrangement. The 1,2,3-triazine unit was introduced into the fused bicyclic skeleton from a pyrazole unit for the first time. The new compound of NPTO was fully characterized using multinuclear NMR and IR spectroscopy, elemental analysis as well as X-ray diffraction studies. The thermal behaviors and detonation properties of NPTO were investigated through a differential scanning calorimetry (DSC-TG) approach and EXPLO5 program-based calculations, respectively. The calculation results showed similar detonation performances between NPTO and the energetic materials of DNPP and ANPP, indicating that NPTO has a good application perspective in insensitive explosives and propellants.
Highlights
As has been well-recognized, rearrangement reactions are the most efficient strategies in organic synthesis, which normally achieve the desired frameworks with remarkably high efficiency [1]
A Curtius rearrangement is one of the most effective methods to convert the carbonyl structures connected to the energetic framework into amino structures, which has been applied to the synthesis of cage-like frameworks and nitrogen-rich aromatic ring energetic materials, such as octanitrocubane (ONC) and 4,4 dinitro-3,3 -diazenofuroxan (DDF) [4,5,6,7]. (Figure 1)
The thermal behaviors of the NPTO·2H2O crystal were investigated based on the TG-DSC experiments. (Figures S1–S3) According to the experimental results, the thermal decomposition of the NPTO·2H2O crystal can clearly be divided into two stages
Summary
As has been well-recognized, rearrangement reactions are the most efficient strategies in organic synthesis, which normally achieve the desired frameworks with remarkably high efficiency [1]. The strong hydrogen bonding effect between -NH2 and other O-rich groups normally plays an important role in achieving insensitivities and heat resistance properties of energetic materials [2,3]. During the past few decades, our research interest was mainly focused on the structural diversity of fused-heterocyclic frameworks in energetic materials, among which, the pyrazolo [4,3-c]pyrazole structure was a successfully applied framework in the construction of 1H,4H-3,6-dinitropyrazolo [4,3-c]pyrazole (DNPP), as well as its insensitive derivative [10,11,12,13], 1,4-diamino-3,6-dinitropyrazolo[4,3-c]pyrazole (LLM-119) [14], which contains both amino and nitro groups. Far, the applications of Hofmann reactions in the synthesis of energetic materials have rarely been reported, especially in the construction of new framework structures. F (000) θ range/(◦) Reflections collected/unique Refinement method GOF on F2 Final R indexes (I > 2σ(I)) Final R indexes (all data) Largest diff peak and hole (e Å−3) GOF on F2 CCDC number
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