Green solvents supercritical carbon dioxide

Often a safer solvent can be substituted for a more hazardous solvent. Safer can be either, or both, of the goals of reducing flammability or toxicity. Two publications have described green solvents. Supercritical carbon dioxide has proved to be an excellent substitute for some organic solvents, particularly if newly designed polymers are added, which can increase solute solubility. ... 

Environmentally green solvents. Supercritical carbon dioxide presents an environmentally benign medium for polymerizations (and other chemical operations), minimizing pollution from organic solvents and facilitating the isolation of the polymeric product. 

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. 

Solvent-assisted decaffeination of coffee can result in residues of solvent reaching the consumer.208 The use of chlorinated hydrocarbon solvents such as chloroform,209 methylene chloride, trichloroethylene,208 and difluoromonochloromethane (Freon),210 will probably be replaced by compounds already found in roasted coffee. The use of an ethyl acetate and 2-butanone mixture leaves a 26-ppm residue in green coffee, but zero residue in roasted coffee.211 Other solvent compounds used or suggested for coffee improvement or decaffeination include propane, butane,212 carbon dioxide,213 214 acetone215 dimethyl succinate,2161,1-dimethoxymethane, and 1,1-dimethoxyethane.217 Of all these, supercritical carbon dioxide, ethyl acetate, and methylene chloride are the solvents most used currently in decaffeination processes. 

Thus, the use of catalysts in new green reaction media such as ionic liquids, fluorous solvents, and supercritical carbon dioxide has become a viable alternative to those discussed within the chapters. 

Coordination ROP can be carried out in bulk and in organic solvents. Particular attention has to be paid to supercritical carbon dioxide because it is a green. 

Matsudo s team uses the bacterium Bacillus megaterium in supercritical carbon dioxide at temperatures of about 100°F (40°G) and 100 atmospheres of pressure to bring about carboxylation. The process illustrates yet one more way of using more than one green chemistry principle in a process the use of a safer catalyst as well as a safer solvent. (The role of supercriticial carbon dioxide as a solvent will be discussed in the next section.)... 

After performing the bioconversion in an ionic liquid, the product needs to be recovered and the biocatalyst and the ionic liquid recycled. Relatively volatile products can be removed by evaporation. Alternatively, immiscible organic solvents can be used to extract the product, and the biocatalyst can be recycled as a suspension in the ionic liquid phase [58]. A more elegant, green method, which avoids the use of volatile organic solvents altogether, involves the use of supercritical carbon dioxide as the extractive phase [96, 147, 148]. 

Fluoromethylbenzoic acids, metallation, 9, 26-27 Fluoro(phenyl) complexes, with platinum(II), 8, 482 Fluorosilanes, elimination in fluorinated alkene activation, 1, 732 in fluorinated aromatic activation, 1, 731 and hydrodefluorination, 1, 748 Fluorosilicate anions, hypercoordinated anions, 3, 484 Fluorotoluenes, metallation, 9, 21 Fluorous alkylstannanes, preparation, 3, 820 Fluorous biphasic system, as green solvent, 12, 844 Fluorous ligands, with supercritical carbon dioxide, 1, 82 Fluorous media... 

Supercritical carbon dioxide is considered a "green" solvent because it is made of nothing more than carbon dioxide, a substance naturally present on Earth. Currently, supercritical carbon dioxide is used to decaffeinate coffee beans, extract new scents for perfume, and clean clothes. 

Wang J-Q, Cai F, Wang E et al (2007) Supercritical carbon dioxide and poly(ethylene glycol) an environmentally benign biphasic solvent system for aerobic oxidation of styrene. Green Chem 9(8) 882-887... 

Du Y, Cai F, Kong D-L et al (2005) Organic solvent-free process for the synthesis of propylene carbonate from supercritical carbon dioxide and propylene oxide catalyzed by insoluble ion exchange resins. Green Chem 7(7) 518-523... 

Nalawade SP, Picchioni F, Janssen LPBM (2006) Supercritical carbon dioxide as a green solvent for processing polymer melts processing aspects and applications. Prog Polym Sci 31(1) 19—43... 

Removal of stimulants like caffeine from (green) coffee beans and black tealeafs is practised since the beginning of the century because of potential health hazards to consumers Since about 15 years supercritical Carbon dioxide is used as solvent. 

Several features of scC02 make it an interesting solvent in the context of green chemistry and catalysis. For carbon dioxide the critical pressure and temperature are moderate 74 bar and 31 °C, respectively. Hence the amount of energy required to generate supercritical carbon dioxide is relatively small. 

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