Abstract
Dinitropyrazole is an important structure for the design and synthesis of energetic materials. In this work, we reported the first comparative thermal studies of two representative dinitropyrazole-based energetic materials, 4-amino-3,5-dinitropyrazole (LLM-116) and its novel trimer derivative (LLM-226). Both the experimental and theoretical results proved the active aromatic N-H moiety would cause incredible variations in the physicochemical characteristics of the obtained energetic materials. Thermal behaviors and kinetic studies of the two related dinitropyrazole-based energetic structures showed that impressive thermal stabilization could be achieved after the trimerization, but also would result in a less concentrated heat-release process. Detailed analysis of condensed-phase systems and the gaseous products during the thermal decomposition processes, and simulation studies based on ReaxFF force field, indicated that the ring opening of LLM-116 was triggered by hydrogen transfer of the active aromatic N-H moiety. In contrast, the initial decomposition of LLM-226 was caused by the rupture of carbon-nitrogen bonds at the diazo moiety.
Highlights
Thermal property is a key factor for the application of energetic materials [1,2,3,4], which is related to safety production, transportation and storage
Active aromatic N-H moiety widely exists in energetic structures and causes incredible variations in the physicochemical characteristics and detonation performances of corresponding energetic materials [10,11,12]
With a highly acidic aromatic N-H bond, 4-amino-3,5-dinitropyrazole [13,14] (LLM-116) has been successfully applied as an active nucleophile in the design and synthesis of other heterocycle-based energetic materials [15,16]. 4-Diazo-3,5-bis(4-amino-3,5-dinitropyrazol-1-yl)pyrazole (LLM-226) is a novel trimer structure of LLM-116 which was recently beautifully prepared through a selfcoupling reaction [17]. (Figure 1) Compared with LLM-116, the trimerization retains the pyrazole backbones but removes the active H from their aromatic N-H moieties
Summary
Thermal property is a key factor for the application of energetic materials [1,2,3,4], which is related to safety production, transportation and storage. For deep analysis of their condensed-phase products during the thermal decompositions, the structural analysis of LLM-116 and LLM-226 were carried out through in situ FTIR
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