A density functional theory study of the decomposition mechanism of nitroglycerin

Abstract

The detailed decomposition mechanism of nitroglycerin (NG) in the gas phase was studied by examining reaction pathways using density functional theory (DFT) and canonical variational transition state theory combined with a small-curvature tunneling correction (CVT/SCT). The mechanism of NG autocatalytic decomposition was investigated at the B3LYP/6-31G(d,p) level of theory. Five possible decomposition pathways involving NG were identified and the rate constants for the pathways at temperatures ranging from 200 to 1000 K were calculated using CVT/SCT. There was found to be a lower energy barrier to the β-H abstraction reaction than to the α-H abstraction reaction during the initial step in the autocatalytic decomposition of NG. The decomposition pathways for CHOCOCHONO (a product obtained following the abstraction of three H atoms from NG by NO) include O-NO cleavage or isomer production, meaning that the autocatalytic decomposition of NG has two reaction pathways, both of which are exothermic. The rate constants for these two reaction pathways are greater than the rate constants for the three pathways corresponding to unimolecular NG decomposition. The overall process of NG decomposition can be divided into two stages based on the NO concentration, which affects the decomposition products and reactions. In the first stage, the reaction pathway corresponding to O-NO cleavage is the main pathway, but the rates of the two autocatalytic decomposition pathways increase with increasing NO concentration. However, when a threshold NO concentration is reached, the NG decomposition process enters its second stage, with the two pathways for NG autocatalytic decomposition becoming the main and secondary reaction pathways.

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

“…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. 26 In particular, the researchers have made great progress in studying the surface decomposition mechanisms of condensed phases, which supports a lot for the hot spot theory of energetic materials.…”

“…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. , …”

“…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.…”