(556a) Synthetic Reactions In a Biphasic System of Emulsified Water and Supercritical CO2

A biphasic system of supercritical carbon dioxide and liquid water has been developed in a batch reactor which offers an effective environmentally friendly route to the synthesis of organic compounds with differing polarities. This system side-steps the problems associated with the solubility of polar compounds in supercritical CO₂. A CO₂/water emulsion was created by an ultrasonic probe which facilitated the contact between the organic reactants compounds dissolved in the two phases. The emulsions were created in a 1-litre high-pressure reactor and were visualized under a microscope. The average size of the emulsion droplets was 10 micron; pressure and emulsification time did not affect the size significantly. The efficacy of the reactor toward organic synthesis was tested by undertaking one basic and one acidic reaction. The tested basic reaction was the Suzuki-Miyaura which tended to proceed unfavourably due to the low pH drop of the water-CO₂ system. The acidic reaction, a reductive amination however, showed improved results.reaction. Both reactions are important in the synthesis of pharmaceutical intermediates. Reactants were selected with a range of different polarities and were subjected to reactions at 80 to 120 °C, and pressures between 80 bar and 150 bar. The presence of the catalyst particles in the Suzuki-Miyaura reaction was found to stabilise the emulsions by pickering stabilisation. Following the reaction, the emulsions were broken by adjusting the pressure. The products and un-reacted compounds were analysed by GC and HPLC and the conversions were compared with values from conventional synthesis methods. The results showed that the supercritical CO₂/water emulsion route gave comparable, and sometimes improved, conversions with high selectivities and offers an alternative to synthesis in the presence of organic solvents.