Continuous, selective hydroformylation in supercritical carbon dioxide using an immobilised homogeneous catalyst

Ligand modified real heterogeneous catalysts for fixed-bed hydroformylation of propylene

“…One is often referred to anchored catalysts [9], tethered catalysts [10], supported aqueous phase (SAP) catalysts [11,12] and supported ionic liquid phase (SILP) catalysts [13,14] as heterogenized homogeneous catalysts; the other is the biphasic system [15] using aqueous biphase [16], supercritical fluids [17][18][19] and ionic liquids [20]. In these works, interesting concepts have emerged, however, they suffer from low selectivity, reactivity (TOF) and recyclability, high metal leaching, or expensive ligands, and hence, need to be improved for practical applications [21].…”

Fluorinated Silica Gels Doped with TPAP as Effective Aerobic Oxidation Catalysts in Dense Phase Carbon Dioxide

“…[2] Besides the replacement of the volatile organic solvents (VOCs) traditionally used as reaction medium with an environmentally benign solvent, [3] the excellent dense phase CO 2 miscibility with organics and reagents such as O 2 and H 2 , along with ultralow viscosity and superior mass transport properties (absence of a gas-liquid phase boundary) permit one to conduct highly efficient continuous heterogeneous processes (those preferred by industry) [2] in small, high-throughput flow reactors in which the CO 2 is recycled and finally completely removed from the products and from the catalyst by simply reducing the pressure, resulting in a closed-loop system or ™solvent-free∫ reaction. [4] The use of supercritical carbon dioxide in place of traditional organic solvents, however, should not be regarded as a mere replacement of a solvent with another of intermediate liquid/gas properties, as the unique non-uniform distribution of solvent molecules about single solute molecules [5] may eventually alter the reaction pathways observed in the liquid phase, while small changes in temperature or pressure may cause dramatic changes in density, viscosity and dielectric properties making dense phase CO 2 a tunable and versatile solvent; [6] its unique properties, for instance, permit one to achieve high concentrations of H 2 and O 2 in the same pot where they can be catalytically converted to valuable H 2 O 2 . [7] Heterogeneously catalysed oxidations in scCO 2 are particularly attractive and, yet, ™largely unexplored∫; [8] an efficient aerobic alcohol oxidation process would, for example, eliminate altogether the need for potentially polluting organic solvents and stoichiometric chromium, [9a] manganese [9b] oxides or DMSO [9c] employed in current industrial conversions.…”

“…[21] This hypothesis would explain the higher reactivities of catalysts of batch C3-F with lower fluorination. In this case, indeed, the shorter fluoroalkyl chain favours the hydrolysis and slows down the condensation, so that rapid aggregation of the early sol particles is prevented and TFPTMS can fully hydrolyse to CF 3 CH 2 CH 2 -Si(OH) 3 and this copolymerises with the Si(OH) 4 monomers obtained by the parallel (and faster) hydrolysis of TMOS. An open porous network is formed in which most of the TPAP molecules dissolved in the original sol are encapsulated at the surface of the resulting silica cages, where they are accessible for catalysis resulting in gels that are generally more active than those of batch C8-F in which such encapsulation is more difficult due to the high difference in the rate of hydrolysis between TMS and the octylfluoro-derivatised alkoxide.…”

Asymmetric Catalytic Synthesis of Organic Compounds using Metal Complexes in Supercritical Fluids

“…This allowed the removal of the VOCs, but did not greatly assist the catalyst/product separation because both were usually soluble in the scCO 2 . Pressure and temperature swings (the CESS process) [10] were successfully used for selective precipitation of first the catalyst and then the product, but more recently this problem has been addressed by using the scCO 2 as a continuously flowing medium to transport the substrates to and remove the products from the catalyst immobilised either on a solid support [11,12] or in an ionic liquid. [13][14][15][16] Immobilisation by dissolving the catalyst in liquid polymers [17] or in the reaction product [18] has also been demonstrated, but not in asymmetric catalysis.…”