Carbon dioxide-expanded liquids for separation and reaction

CO₂ is used to facilitate the distribution of phase-transfer catalysts (PTC) into the aqueous phase in liquid-liquid extraction systems by reducing the polarity of the organic phase. CO₂ can alter the distribution of phase-transfer catalysts between organic phase and aqueous phase so dramatically that even in dilute organic solutions they can be separated selectively from an organic reaction mixture with only a small fraction of the water required in a traditional aqueous extraction. Phase boundary data are measured for the ternary system of carbon dioxide, methanol and hydrogen at 313.2 K to quantify the solubility enhancement of hydrogen gas in CO ₂ expanded methanol at the phase boundary. It is reported for the first time that CO₂ expanded alcohols are catalytic media for cyclohexanone acetal formation and the catalytic capacity can be tuned with CO₂ pressure and temperature, which affords the opportunity to replace some acid catalysts with environmental problems. CO₂ expanded liquids are unique media for amine formation and separation. In the heterogeneous hydrogenation of nitriles in CO₂ expanded ethanol, the primary amines are protected by CO₂ and their yield is greatly increased. In the homogeneous hydrogenation of nitriles and imine in CO₂ expanded THF, the primary amines are separated in situ in the form of solid carbamic acids and/or ammonium carbamates with increased yield while the catalysts remains in the solution.