Predictions of thermodynamic properties of energetic materials using COSMO-RS

Abstract In this work, conductor-like screening for real solvents (COSMO-RS) calculations were carried out using COSMOtherm program in conjunction with Gaussian03 packages. The objective was to predict thermodynamic properties for two nitrogen-rich energetic materials which are less harmful for the environment than the conventional ones, namely 3,6-di(hydrazino)-1,2,4,5- tetrazine (DHT) and 3,3’-azo-bis(6-amino-1,2,4,5-tetrazine) (DAAT) for which no experimental data are available to our best knowledge. COSMO-RS approach is a combination of quantum chemical and statistical thermodynamic basis, which allow a physically meaningful description of molecular interactions between pure molecules and solvents in solution. Recently, this approach has been used for the prediction of an enormous number of physicochemical properties especially aqueous solubility, Henry’s law constant, vapor pressure and partition coefficient. The vapor pressure of pure compounds is one of the most important thermodynamic properties required for the chemical process design as well as for the fate assessment of pollutants in the environment. To validate the accuracy of COSMO-RS approach for the two molecules of interest, six reference energetic molecules have been studied, for which experimental data are available, such as cyclotetramethylene-tetranitramine (HMX), 2,4,6-trinitrotoluene (TNT), cyclotrimethylenetrinitramine (RDX), 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (CL-20), 1,1-diamino-2,2-dinitroethylene (FOX-7) and n-methyl-p-nitroaniline (MNA). From predicted results, a good agreement has been noted. DAAT molecule shows a lower volatility in the medium so that a low detectability compared to the DHT and other reference molecules. Both DHT and DAAT showed negative logarithmic values of Octanol-Water partition coefficients, this means that they don’t have the tendency to enhance the bioaccumulation process in soils.