Chemical synthesis, supercritical carbon dioxide

Supercritical fluids (e.g. supercritical carbon dioxide, scCCb) are regarded as benign alternatives to organic solvents and there are many examples of their use in chemical synthesis, but usually under homogeneous conditions without the need for other solvents. However, SCCO2 has been combined with ionic liquids for the hydroformylation of 1-octene [16]. Since ionic liquids have no vapour pressure and are essentially insoluble in SCCO2, the product can be extracted from the reaction using CO2 virtually uncontaminated by the rhodium catalyst. This process is not a true biphasic process, as the reaction is carried out in the ionic liquid and the supercritical phase is only added once reaction is complete. 

Supercritical Carbon Dioxide as a Substitute Solvent for Chemical Synthesis and Catalysis... 

This book describes green chemistry approaches that employ liquid or supercritical carbon dioxide. Supercritical fluids have been investigated for more than a century however, applications to chemical synthesis and materials processing are relatively new. Since the 1990s, we have witnessed a veritable explosion of increased research activity in the area of chemical reactions and processes in liquid or supercritical carbon dioxide with the... 

Potentially, supercritical carbon dioxide (SCCO2) is the ideal green solvent. It is non-toxic for both humans and the environment. It is chemically inert under most conditions, whether they be non-flammable or non-protic, and it is inert to radical and oxidizing conditions. This gas can be obtained in large quantities as a by-product of fermentation, combustion, and ammonia synthesis and it is relatively cheap, particularly compared with conventional solvents. Supercritical carbon dioxide presents other practical advantages as well, such as the possibility of achieving product isolation to total dryness by simple evaporation. 

Supercritical carbon dioxide as a substitute solvent for chemical synthesis and catalysis [59]... 

In order to optimize and/or improve the behaviour of bioprocesses in ionic liquids/supercritical carbon dioxide biphasic systems, a better understanding of the chemical reaction and mass-transfer phenomena in these biphasic systans is required. In this context, de los Rfos et al. [38] analysed the chemical reaction and the mass-transfer phenomena in the synthesis of bntyl propionate from vinyl propionate and 1-butanol catalysed by CaLB immobilized on dynamic monbranes at... 

Hemdndez FJ, de los Rfos AP, Gomez D et al (2007) Understanding the chemical reaction and mass-transfer phenomena in a recirculating enzymatic membrane reactor for green ester synthesis in ionic Uquid/supercritical carbon dioxide biphasic systems. J Supercrit Flitids 43 303-309... 

The present contribution highlights recent developments in the application of compressed (liquid or supercritical) carbon dioxide as a solvent for chemical reactions. After a brief introduction to the basic physical properties of SCCO2, some practical aspects of the use of compressed gases are discussed. A survey of successful applications of compressed and particularly supercritical CO2 in organic synthesis is provided with an emphasis on metal-catalyzed reactions. 

Applications of Supercritical Carbon Dioxide as a Reaction Medium for Chemical Synthesis... 

Ionic liquids are a new and remarkable class of designer solvents [9] with negligible vapor pressure for chemical syntheses because their properties such as solubility, density, refractive index, and viscosity can be tuned to suit specific requirements [10, 11], Water is a relatively more environmentally friendly alternative for organic synthesis, but its appHcation has been limited so far [6]. Supercritical carbon dioxide is yet another clean solvent but it generally requires a high-pressure reactor [12],... 

Beckman s comprehensive review paper [5] describes chemical reactions in carbon dioxide-based solvents, and evaluates their green character. The title of the paper - Supercritical and near-critical CO2 in green chemical synthesis and processing - is revealing of the new trends in the use of carbon dioxide. 

Supercritical carbon dioxide represents an inexpensive, environmentally benign alternative to conventional solvents for chemical synthesis. In this chapter, we delineate the range of reactions for which supercritical CO2 represents a potentially viable replacement solvent based on solubility considerations and describe the reactors and associated equipment used to explore catalytic and other synthetic reactions in this medium. Three examples of homogeneous catalytic reactions in supercritical CC are presented the copolymerization of CO2 with epoxides, ruthenium>mediated phase transfer oxidation of olefins in a supercritical COa/aqueous system, and the catalyic asymmetric hydrogenation of enamides. The first two classes of reactions proceed in supercritical CO2, but no improvement in reactivity over conventional solvents was observed. Hythogenation reactions, however, exhibit enantioselectivities superior to conventional solvents for several substrates. 

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