Temperature-Dependent Physicochemical Properties and Solvation Thermodynamics of Nitrotoluenes from Solvation Free Energies

Expanded ensemble molecular dynamics simulations are used to calculate the free energies of hydration and self-solvation of low polarity nitrotoluenes over the temperature range of 273 K to 330 K. From this information the liquid, subcooled, and solid-phase vapor pressures, solubilities, Henry’s law constants, hydration and self-solvation entropies, enthalpies, isobaric heat capacities, and enthalpies of vaporization or sublimation are then computed. The values obtained are compared to the limited experimental data available. At a reference temperature of 300 K, the hydration enthalpies are found to be larger in magnitude than hydration entropies for the nitrotoluenes, and vary with the number of nitro groups, while the hydration entropies are almost unchanged as functions of either the number of nitro groups or the solvent accessible surface area. Consequently the variation in the hydration free energies among the nitrotoluenes is due to the variation in their hydration enthalpies. In contrast, both enthalpies and entropies change with the number of nitro groups in self-solvation, and both contribute to the variation of the self-solvation free energy. Also, the isobaric hydration heat capacities are found to change only slightly with temperature