ScCO2-Soluble Catalysts

For the homogeneously catalyzed cycloaddition in SCCO2, the catalysts and the starting materials, epoxides and scCOj, form a homogeneous mixture, but the resultant carbonate is not soluble in scCOj. Hence, while running the reaction, the product is automatically separated from the reaction mixture. Thus, the development of an scC02-soluble catalyst is necessary. In this case, the SCCO2-soluble catalysts remain in the CO2 phase and can be recycled [72]. 

A new SCCO2 soluble Rh catalyst supported on fluoroacrylate copolymers was synthesized. The catalysts were active for hydrogenation of 1-octene and cyclohexene. The optimal Rh to copolymer molar ratio was 3. Using... 

This new catalytic system was then tested for oxidation of various alkyl aromatic hydrocarbons (Table 12.3). The result showed that the selectivity of a conventional homogenous oxidation, which induces oxidative a-P carbon bond cleavages, could be influenced by utilizing this microemulsion method in SCCO2 (only partial oxidation took place). The different observed selectivity toward partial oxidation products can be explained in terms of solvent polarity. This approach makes the C02-soluble partial oxidation products less accessible to the water-soluble catalyst, preventing over-oxidations. The catalytic system was... 

Recently, Song et al. [74] provided a simple way for performing the homogeneous catalyzed cycloaddition in SCCO2 with the direct and spontaneous separation of the carbonate. The solubility of the catalysts could be enhanced by the incorporation of the fluorinated chain in the polymer, and phosphonium salts acted as a homogeneous C02-soluble catalyst and promoted the cycloaddition very well. Through the release of CO2, the catalyst could be recovered and reused and kept satisfactory catalytic activity. 

The cationic rhodium catalyst in Scheme 8.8 is rendered soluble in SCCO2 by the anion, BArF, a perfluorinated tetraphenylborate counter-anion (Figure 8.9). 

Processes in which catalysts immobilized in ionic liquids have been combined with product extraction using SCCO2 show considerable promise [20], The ionic liquids are poorly soluble in the SCCO2 which allows products to be extracted without contamination from the ionic liquid or the catalyst. 

Catalyst Separation and Recycling Using SCCO2 as Solubility Switch. 93... 

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