Association of Tris(pentane-2,4-dionato)chromium(III) with Modifiers of Hydrogen-bond Donors in Supercritical Carbon Dioxide

The solubility of tris(pentane-2,4-dionato)chromium(III) (Cr(acac)3) in supercritical carbon dioxide (SC-CO2) containing organic modifiers (1,1,1,3,3,3-hexafluoro-2-propanol (HFP) and 3,5-bis(trifluoromethyl)phenol (BTMP)) of hydrogen-bond donors was investigated by UV/VIS spectrophotometry. A great solubility enhancement of Cr(acac)3 in SC-CO2 was accomplished by adding HFP and BTMP. The association constant of Cr(acac)3 with HFP and BTMP in SC-CO2 could be determined from the relationship of the solubility enhancement against the concentration of the modifier. The association constant linearly increases with an increase in the acid dissociation constant of the modifiers.