Supercritical carbon dioxide environmentally benign solvent

Supercritical carbon dioxide (SC-CO2) is an environmentally benign solvent that is providing a viable alternative to the traditional organic solvents. A Diels-Alder reaction between n-butyl acrylate and cyclopentadiene was investigated with the Lewis acid catalyst scandium tris (trifluoromethanesuffonate), primarily due to its solubility in SC-CO2 (Eq. 10-12) ... 

Supercritical carbon dioxide (SC-CO2) is proving to be a suitable environmentally benign solvent for free radical reactions, providing a unique alternative to many conventional solvents for these reactions which are either carcinogenic or damaging to the environment. Part 1 of this paper examines the implications associated with the use of SC-C02 with regard to issues of solvent effects on chemical reactivity. In Part 2, a new environmentally benign chemical process is described which effects the conversion RH + C=C-C-Br R-C-C=C + HBr via a free radical chain reaction. 

Liquid and supercritical fluid carbon dioxide are an attractive alternative to organic solvents because CO2 is nontoxic, nonflammable, and inexpensive and has a reasonably accessible critical point (7 = 3LC, Pc = 73.8 bar). It is an environmentally benign solvent that is being evaluated as a replacement for organic liquids in numerous applications. However,... 

Another example of an environmentally benign solvent for Heck chemistry is supercritical carbon dioxide (Scheme 44),[ 2],[i93] Undoubtedly, the future need for cleaner chemical processing is great. 

For microencapsulation of inorganic nanoparticles, preparation methods like in situ polymerization may be used [102]. However, these methods often require toxic organic solvents and surfactants. Furthermore, the removal of residual surfactants or solvents is needed, since they cause faults in the product An environmentally benign solvent like supercritical carbon dioxide can be used to encapsulate inorganic nanoparticles. But its use is limited because of the low... 

The use of supercritical fluids, particularly carbon dioxide, as a substitute solvent for chemical synthesis is an area of rapidly growing importance. (1-5) Carbon dioxide, when compressed to a liquid or, al ve its critical point (Jq = 31.rC, Pc = 1071 psi. Pc = 0.468 g/ml), to a supercritical fluid (SCF), represents an environmentally benign alternative to organic solvents. Since C02is nontoxic, nonflammable, inexpensive, and unregulated it can replace hazardous organic solvents and thereby provide a valuable pollution prevention tool. Moreover, as discussed below, there is a significant potential for improved synthetic chemistry via faster rates and/or enhanced selectivity for a number of reactions. 

Carbon dioxide and water are the most commonly used SCFs because they are cheap, nontoxic, nonflammable and environmentally benign. Carbon dioxide has a more accessible critical point (Table 6.13) than water and therefore requires less complex technical apparatus. Water is also a suitable solvent at temperatures below its critical temperature (superheated water). Other fluids used frequently under supercritical conditions are propane, ethane and ethylene. 

The first use of supercritical fluid extraction (SFE) as an extraction technique was reported by Zosel [379]. Since then there have been many reports on the use of SFE to extract PCBs, phenols, PAHs, and other organic compounds from particulate matter, soils and sediments [362, 363, 380-389]. The attraction of SFE as an extraction technique is directly related to the unique properties of the supercritical fluid [390]. Supercritical fluids, which have been used, have low viscosities, high diffusion coefficients, and low flammabilities, which are all clearly superior to the organic solvents normally used. Carbon dioxide (C02, [362,363]) is the most common supercritical fluid used for SFE, since it is inexpensive and has a low critical temperature (31.3 °C) and pressure (72.2 bar). Other less commonly used fluids include nitrous oxide (N20), ammonia, fluoro-form, methane, pentane, methanol, ethanol, sulfur hexafluoride (SF6), and dichlorofluoromethane [362, 363, 391]. Most of these fluids are clearly less attractive as solvents in terms of toxicity or as environmentally benign chemicals. Commercial SFE systems are available, but some workers have also made inexpensive modular systems [390]. 

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... 

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