Over the past two decades, there has been considerable work in the development of insensitive munitions (IM), which exhibit low shock sensitivity and high thermal stability, due to the increased safety and environmental concerns associated with the traditionally used explosives. Contamination of the environment (ground water, soil and sediment) by explosives due to military activities such as weapon production and handling, waste discharge, testing and training of weapons and demilitarization has become a multi-billion dollar problem. Therefore, development of methodologies that can be used to predict the environmental fate of a particular compound before its deployment or even pre-synthesis is of great importance, and could lead to significant long-term cost savings. Molecular simulation has emerged as an attractive tool to study and predict the physicochemical properties of complex species for which little or no experimental data exist. In the case of energetic materials, the use of molecular simulation provides a means to screen candidate molecules for environmental impact prior to synthesis. Such a priori estimates are expected to lead to significant cost savings in the development of green munitions.
In this work, molecular models are developed for mono- and di- nitro aromatic compounds, including 2.4-dinitroanisole (DNAN), N-methyl-p-nitroaniline (MNA), 1,3-dinitrobenzene (13DNB), 1,4-dinitrobenzene (14DNB), 2-nitroanisole (2NAN) and 4-nitroanisole (4NAN), based on the Transferable Potentials for Phase Equilibria (TraPPE) [1,2,3]. These models are used in molecular dynamics to predict physicochemical properties, such as log Kow, KH, crystal density, melting point, vapor pressure and hypothetical vapor-liquid coexistence curves. Molecular dynamics simulations are performed with NAMD using united atom TraPPE force field and SPC/E water model. Absolute values of the 1-octanol/water and air water partition coefficients were calculated directly using the adaptive biasing force method .
1. Martin, M.G.; Siepmann, J.I. J. Phys. Chem. B (1998), 102, 2569.
2. Chen, B.; Potoff, J.J.; Siepmann, J.I. J. Phys. Chem. B (2001), 105, 3093.
3. Wick, C.D.; Stubbs, J.M.; Rai, N.; Siepmann, J.I. J. Phys. Chem. B (2005), 109, 18974
4. Rodriguez-Gomez, D.; Darve, E.; Pohorille, A. J. Chem. Phys. (2004), 120, 3563.