Solvation of benzene derivatives in SC-CO2: a molecular dynamics study of fluorination effectsElectronic supplementary information (ESI) available: structures and interaction energies of X-Benz(CO2)n aggregates in the gas phase and table of force field parameters. See http://www.rsc.org/suppdata/nj/b3/b304300b/

Abstract

According to a molecular dynamics study of benzene (C6H6) and its derivatives C6F6, CH3–C6H5 and CF3–C6H5 in SC-CO2 solution, the fluoro compounds are better solvated than the H analogs. This is supported by the analysis of average solute-solvent interaction energies and by free energy perturbation simulations at 305 and 350 K. Stepwise model building of C6X6(CO2)n aggregates (X = H and F) in the gas phase, however, indicates that up to n = 6, interactions with CO2 are stronger with benzene, while perfluorobenzene becomes better solvated at higher coordination numbers. Thus, the enhancement of the CO2-philicity upon fluorination does not stem from enhanced individual interactions with the CO2 molecule, but from the higher coordination number, due to the increase of solvent accessible surface. Finally, simulations of C6H6 and C6F6 at the CO2–water interface reveal that the former is somewhat surface active due to specific O–H⋯π facial interactions between interfacial water molecules, while C6F6 mostly sits in the CO2 phase, in keeping with its larger CO2-philicity.