Enhanced Extraction of Tris(pentane-2,4-dionato)cobalt(III) in Supercritical Carbon Dioxide/Water Systems by Association with Fluorinated Phenols

Abstract

The distribution behavior of tris(pentane-2,4-dionato)cobalt(III) [Co(acac)₃] between supercritical carbon dioxide (SC-CO₂) and water was investigated in the absence and presence of fluorine- and trifluoromethyl-substituted phenols (PhOH). The distribution of Co(acac)₃ into SC-CO₂ was enhanced by adding fluorine- and trifluoromethyl-substituted PhOH because of the formation of Co(acac)₃·PhOH association complexes via hydrogen bonding. The Co(acac)₃·PhOH association constant in the biphasic SC-CO₂/water system was determined from the relationship between the distribution enhancement and the PhOH concentration in the supercritical medium. Lower association constants were obtained in the biphasic SC-CO₂/water system compared with those in the single-phase SC-CO₂ system, and this was ascribed to hydrogen bonding inhibition by H₂O molecules dissolved in SC-CO₂. Finally, the thermodynamic parameters and the number of CO₂ molecules released upon the association of Co(acac)₃ and 3,5-bis(trifluoromethyl)phenol were calculated by using data on the formation constant as a function of pressure and temperature.