Measurement of solubilities for rhodium complexes and phosphine ligands in supercritical carbon dioxide

The solubilities of phosphine ligands and rhodium (Rh) complexes in supercritical carbon dioxide were measured with Fourier transform infrared (FT-IR) spectroscopy at 320 and 333 K and several pressures. Triphenylphosphine (TPP) and tris(p-trifluoromethylphenyl)-phosphine (TTFMPP) were selected as ligands for the Rh complex. The solubilities of the fluorinated ligands and complexes were compared with those of the non-fluorinated compounds. The solubilities of ligand increased up to 10 times by the fluorination. It was found that the solubilities of Rh complexes were enhanced up to 30 times by introducing trifluoromethyl group to the ligand. The experimental data was correlated by the Chrastil equation. The correlated results were in good agreement with the experimental data. Furthermore, the solvation numbers of carbon dioxide around the ligands and Rh complexes were obtained from the slope of the Chrastil equation. The solvation number for the fluorinated compounds was about two and five times higher than those of the non-fluorinated ligand and complex, respectively.