Solvation of Halogens in Fluorous Phases. Experimental and Simulation Data for F2, Cl2, and Br2 in Several Fluorinated Liquids

Abstract

The solubility of halogen gases--fluorine, chlorine and bromine--has been determined experimentally in several fluorinated solvents between 283 and 323 K at atmospheric pressure. The solubility of chlorine was studied in perfluorooctane, perfluorohexane, perfluorohexylethane, perfluoromethylcyclohexane, perfluoro-1,3-dimethylcyclohexane, perfluoro-2-butyltetrahydrofuran, and perfluoroperhydrophenanthrene and was found to be on the order of 10(-2) in mole fraction. The solubility of fluorine in the studied fluorinated solvents at 298 K is 1 order of magnitude lower than the solubility of chlorine. The solubility of bromine was studied as a function of temperature in perfluorooctane, and it was found to be higher than that of chlorine but of the same order of magnitude. The experimental studies were complemented by molecular simulation calculations. The molecular force fields used for the halogen gases and for the fluorinated solvents were taken, when possible, from the literature. An intermolecular potential model had to be developed for perfluoro-2-butyltetrahydrofuran, with a functional form of the Lennard-Jones plus point charges type. The solubility of the three gases was calculated by molecular simulation using Widom test-particle insertion. Dissimilar interaction parameters of 0.89 and 0.75 in the Lennard-Jones well depths between the solute and the solvent had to be introduced to reach agreement with the experimental results for chlorine and fluorine solubilities, respectively. The structure of the solutions was studied by analysis of solute-solvent radial distribution functions. It was found that the preferential solvation sites for the halogen gases are the terminal CF3 groups of the different fluorinated solvents.