Application of the Density Functional Theory (DFT) to Study the Decomposition Pathway of Nitroarenes

The 1,3,5-triamino-2,4,6-trinitrobenzene (TATB) and 1,3-Diamino-2,4,6-trinitrobenzene (DATB) belong to the family of Nitroarenes and are considered thermally stable explosives. In fact, they are more stable at elevated temperatures and applications are found in modern Ordnance, Space and Nuclear fields. Studies regarding the decomposition mechanisms of these compounds have been rather underestimated and the knowledge related to reactive hazards of those compounds is very limited. Indeed, these could be considered as the main causes of related process safety incidents.

Computational quantum chemistry methods have been developed in a way that allows estimation of thermodynamic (e.g. enthalpy, entropy and Gibbs free energy) and kinetic parameters (e.g. activation energy and pre-Exponential factor). These methods are based on molecular quantum theory where the motion and distribution of electrons is described in terms of electron probability distributions or molecular orbitals. Among the most known techniques are ab initio, Density Functional Theory (DFT), and semi-empirical methods. However, the calculations will be performed using DFT approach mainly for two reasons; first, this method is able to represent complex molecules and second, previous researches have shown to be accurate when applied to Nitroarenes compounds.

This research aims to gain the fundamental understanding of TATB and DATB decomposition processes based on the principles mentioned. This study will simulate the decomposition reactions and enhance the understanding of the decomposition reaction mechanisms of these molecules. With this study, the decomposition mechanisms will be proposed using the most common channels for Nitroarenes. Previous researches proposed several decomposition mechanisms, these will be included in this study, some of them are: Homolysis of C-NO2 and C-NH2, Nitro/Nitrite Isomerization, Inter- or intramolecular hydrogen transfer and formation of benzo-furazan and benzo-furoxan which are modeled using DFT with B3LYP functional and 6-311+G** basis set in Gaussian 09 software.

Each one of these calculations will be carried out in gas phase due to the simplicity and that it is a necessary part in all studies of thermally induced decomposition of nitro compounds. Thermodynamic and kinetic parameters will be computed using DFT.