Decomposition of 2,6‐diamino‐3,5‐dinitropyrazine‐1‐oxide (LLM‐105): From thermodynamics to kinetics

Abstract

The mechanism of initial decomposition of energetic compound is crucial to understand the heat release efficiency, impact sensitivity, toxic emission, and so on. In the present study, we progressively explored the thermodynamic and kinetic features of the decomposition of LLM-105, or 2,6-diamino-3,5dinitropyrazine-1-oxide, a kind of nitro compound in energetic materials using theoretical calculations. The bond dissociation energies (BDEs), bond orders, and the decomposition pathways were investigated by high-level quantum chemical calculations, and the temperature-and pressure-dependent rate coefficients were computed by Rice-Ramsperger-Kassel-Marcus (RRKM)/master equation simulations. Although thermodynamic properties, for example, BDEs and bond orders, provide preliminary estimates on a possible decomposition mechanism including trigger bonds with relatively low computational costs, kinetic studies are necessary to determine all reaction pathways and competition relationships among various pathways. The potential energy surface at the theoretical level of DLPNO-CCSD(T)/CBS//M06-2X-D3/6-311++G(d,p) reveals the complicated decomposition mechanism including the bottlenecks of all channels. The computed rate coefficients showthat the reaction channels yielding NO 2 will dominate the initial decomposition at high temperature (>1000 K), while the NO elimination channels play a controlling role at low temperature (<800 K).

Theoretical Kinetic Studies on Thermal Decomposition of Glycerol Trinitrate and Trimethylolethane Trinitrate in the Gas and Liquid Phases

“…Recently, the rapid development of quantum chemical theories and computer technologies has made high-precision computations of reaction barriers for medium-sized molecules become affordable. 13,14,23 To our surprise, there have been no high level quantum chemical studies on the thermal decomposition of NG and TMETN available, except two DFT studies on NG decomposition. 20,21 The initial decomposition of different phases plays an important role in understanding a range of performance on nitrate esters even EMs, such as safety, 24 combustion, 25 and detonation.…”

“…Quantum chemical methods have been widely used to explore the decomposition mechanism of energetic materials (typically in the gas phase), including nitrate esters. − In 1996, Owens computed the energy barriers of RO-NO 2 bond rupture in a series of R–NO 2 compounds by a semiempirical quantum chemical method – MNDO/3, which was correlated to the susceptibility to high-rate exothermic reactions (detonation) of these molecules . Since the 21st century, density functional theory (DFT) has been widely used to study the decomposition mechanism of nitrate esters, providing more details on competing reaction pathways in addition to the direct bond scission of O–NO 2 . ,− Tsyshevsky et al found large deviations in the reaction barriers of pentaerythritol tetranitrate (PETN) decomposition computed by various DFT methods.…”

“…The largest deviation can even be higher than 10 kcal/mol. Recently, the rapid development of quantum chemical theories and computer technologies has made high-precision computations of reaction barriers for medium-sized molecules become affordable. ,, To our surprise, there have been no high level quantum chemical studies on the thermal decomposition of NG and TMETN available, except two DFT studies on NG decomposition. , …”