Oxidation supercritical carbon dioxide

Crowe TD and White PJ. 2003. Oxidation, flavor, and texture of walnuts reduced in fat content by supercritical carbon dioxide. J Am Oil Chem Soc 80(6) 569-574. 

Ashraf-Khorassani M, Taylor LT, Zimmerman P. Nitrous oxide versus carbon dioxide for supercritical fluid extraction and chromatography of amines. Anal. Chem. 1990 62 1177-1180. 

Hawthorne et al. [77] compared supercritical chlorodifluoromethane, nitrous oxide and carbon dioxide for the extraction of polychlorobiphenyls from sediments. Chlorodifluoromethane provided the highest recoveries,... 

Sun, Z., et al., Coating carbon nanotubes with metal oxides in a supercritical carbon dioxide-ethanol solution. Carbon, 2007. 45(13) p. 2589-2596. 

T0755 Supercritical Carbon Dioxide Extraction—General T0827 U.S. Filter/Zimpro Products, Wet Air Oxidation... 

T0755 Supercritical Carbon Dioxide Extraction—General T0756 Supercritical Water Oxidation—General T0770 Terra Systems, Inc., In Situ Bioremediation (ISB)... 

T0755 Supercritical Carbon Dioxide Extraction—General T0756 Supercritical Water Oxidation—General T0759 Surfactants—General... 

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The process employs the supercritical fluid carbon dioxide as a solvent. When a compound (in this case carbon dioxide) is subjected to temperatures and pressures above its critical point (31°C, 7.4 MPa, respectively), it exhibits properties that differ from both the liquid and vapor phases. Polar bonding between molecules essentially stops. Some organic compounds that are normally insoluble become completely soluble (miscible in all proportions) in supercritical fluids. Supercritical carbon dioxide sustains combustion and oxidation reactions because it mixes well with oxygen and with nonpolar organic compounds. 

Cyclohexane oxidation has been studied in supercritical carbon dioxide medium for homogenizing the initial reaction mixture to produce cyclohexanone and cyclohex-anol as the chief reaction products. Conversions obtained are low compared to the liquid phase oxidation because of dilute concentrations of the reactants. Cyclohexanone is more selectively formed and favored by both pressure and temperature. Results suggest that the reaction in supercritical CO2 medium can be gready manipulated (Srinivas and Mukhopadhyay, 1994). 

Environmental applications of SFE appear to be the most widespread in the literature. A typical example is the comparison of extraction efficiency for 2,3,7,8 -tetrachlorodibenzo-p-dioxin (2,3,7,8-TCDD) from sediment samples using supercritical fluid extraction and five individual mobile phases with Soxhlet extraction was made (101). The mobile phases, carbon dioxide, nitrous oxide, pure and modified with 2% methanol as well as sulfur hexafluoride were examined. Pure nitrous oxide, modified carbon dioxide and modified nitrous oxide systems gave the recoveries in the acceptable range of 80 to 100%. Carbon dioxide and sulfur hexafluoride showed recoveries of less than 50% under identical conditions. Classical Soxhlet recoveries by comparison illustrated the poorest precision with average extraction efficiencies of less than 65%. Mobile phase choice, still as yet a major question in the science of supercritical fluid extraction, seems to be dependent upon several factors polarity of the solute of interest, stearic interactions, as well as those between the matrix and the mobile phase. Physical parameters of the solute of interest, as suggested by King, must also be considered. Presently, the science behind the extraction of analytes of interest from complex matrices is not completely understood. 

Uncatalysed oxidation of cycloalkanes and alkylarenes by molecular oxygen with acetaldehyde as sacrificial co-reductant occurs efficiently in supercritical carbon dioxide under mild multiphase conditions.252... 

An efficient and convenient methodology for the aerobic oxidation of alcohols catalysed by sol-gel trapped perruthenate and promoted by an encapsulated ionic liquid in supercritical carbon dioxide solution has been reported. The reaction is highly selective and useful for substrates otherwise difficult to oxidize.263 A four-component system consisting of acetamido-TEMPO-Cu(C104)2-TMDP-DABCO has been developed for aerobic alcohol oxidation at room temperature. The catalytic system shows excellent selectivity towards the oxidation of benzylic and allylic alcohols and is not deactivated by heteroatom-containing (S, N) compounds. The use of DMSO as the reaction medium allows the catalysts to be recycled and reused for three runs with no significant loss of catalytic activity.264... 

Trofimov, T.I. Samsonov, M.D. Kulyako, Y.M. Myasoedov, B.F. Dissolution and extraction of actinide oxides in supercritical carbon dioxide containing the complex of tri-n-butylphosphate with nitric acid, C.R. Chimie 7 (2004) 1209-1213. 

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