Solubility enhancement in supercritical carbon dioxide by fluorination effect

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In this study, solubilities of fluorinated compounds were measured to examine the fluorination effect on the solubility in supercritical carbon dioxide. Further, the mechanism of solubility enhancement was discussed by a molecular simulation and the following results were obtained.The solubilities of Rh complexes, which are used as catalysts for hydroformylation, in supercritical carbon dioxide were measured. As a ligand, triphenylphosphine (TTP) and tris (p-Trifluoromethylphenyl) phosphine (TTFMPP) were adopted. The solubilities were determined by IR absorbance. It is found that the solubilities of the ligand and the complex fluorinated, TTFMPP and Rh-TTFMPP, can be enhanced compared to non-fluorinated TPP and Rh-TPP.2-,3-trifluoromethyl benzoic acids, which are fluorinated compounds, were adopted as model substances and its sublimation pressures were measured. The sample was set in an equilibrium cell and the vapor phase concentration was determined by UV absorbance. The sublimation pressures were determined by using the equation of state for ideal gas. Reliable sublimation pressure data can be obtained based on the present experimental procedure. The sublimation pressures of 2-,3-trifuloromethyl benzoic acids show the cross point near 314K.MD simulation was performed for the supercritical carbon dioxide + fluorinated compounds mixtures. 2-,3-,4-,trifluoromethyl benzoic acids and 2-,3-,4-methyl benzoic acids were studied. It is found that carbon dioxide molecules are solvated around trifluoromethyl group and this fact is the reason for the solubility enhancement.As mentioned above, fluorination is effective to enhance the solubility in supercritical carbon dioxide and the mechanism is due to solvation.