Aqueous-supercritical carbon dioxide

Antibody catalysts, role in environmentally benign synthesis of chemicals, 125-126 Aqueous-supercritical carbon dioxide medium, phase-transfer catalytic oxidation, 144-145 Arene cw-dihydrodiols, biocatalytic conversion of aromatics to optically pure synthons for pharmaceutical industry, 180-195... 

SAP supported-aqueous-phase scC02 supercritical carbon dioxide... 

Another environmental issue is the use of organic solvents. The use of chlorinated hydrocarbons, for example, has been severely curtailed. In fact, so many of the solvents favored by organic chemists are now on the black list that the whole question of solvents requires rethinking. The best solvent is no solvent, and if a solvent (diluent) is needed, then water has a lot to recommend it. This provides a golden opportunity for biocatalysis, since the replacement of classic chemical methods in organic solvents by enzymatic procedures in water at ambient temperature and pressure can provide substantial environmental and economic benefits. Similarly, there is a marked trend toward the application of organometal-lic catalysis in aqueous biphasic systems and other nonconventional media, such as fluorous biphasic, supercritical carbon dioxide and ionic liquids. ... 

Leitner W (1999) In Knochel P (ed) Reactions in Supercritical Carbon Dioxide (scC02) in Modern Solvent Systems. Top Curr Chem 206 107 Morita DK, David SK (1998) Chem Commun, p 1397 Wegner A, Leitner W (1999) Chem Commun, p 1583 Sellin M, Cole-Hamilton DJ (2000) J Chem Soc, Dalton Trans, p 1681 Solinas M, Pfaltz A, Leitner W (2004) J Am Chem Soc 126 16124 Leitner W, Scurto AM (1998) Imobilization of Organometallic Catalysts using Supercritical Fluids. In Cornils B, Herrmann WA (eds) Aqueous Organometallic Catalysis. WUey, Weinheim, p 664... 

Supercritical carbon dioxide has been used as a dispersing medium for the manufacture and processing of polymeric materials. The process allows for the synthesis of high molar mass acrylic polymers in the form of micrometer-sized particles with a narrow size distribution. This procedure represents an environmentally responsible alternative to aqueous and organic dispersing media for heterogeneous dispersion polymerizations (Fox, 1994). 

Water in supercritical carbon dioxide microemulsions spectroscopic investigation of a new environment for aqueous inorganic chemistry... 

Water in Supercritical Carbon Dioxide Microemulsions—Spectroscopic Investigation of a New Environment for Aqueous Inorganic Chemistry (Clarke et al., 1997a)... 

Romack, T. J. DeSimone, J. M. Synthesis of Tetrafluoroethylene-Based, Non-aqueous Fluoropolymers in Supercritical Carbon Dioxide. Macromolecules 1995, 28, 8429-8431. 

Erkey, C. (2000), Supercritical Carbon Dioxide Extraction of Metals from Aqueous Solutions a Review, J. Supercrit. FI. 17, 259-287. 

Mochizuki, S., Wada, N., Smith, R. L., Inomata, H. (1999), Perfluorocarboxylic acid Counter ion Enhanced Extraction of Aqueous Alkali Metal Ions with Supercritical Carbon Dioxide, Analyst 124, 1507-1511. 

Experimental results are presented for high pressure phase equilibria in the binary systems carbon dioxide - acetone and carbon dioxide - ethanol and the ternary system carbon dioxide - acetone - water at 313 and 333 K and pressures between 20 and 150 bar. A high pressure optical cell with external recirculation and sampling of all phases was used for the experimental measurements. The ternary system exhibits an extensive three-phase equilibrium region with an upper and lower critical solution pressure at both temperatures. A modified cubic equation of a state with a non-quadratic mixing rule was successfully used to model the experimental data. The phase equilibrium behavior of the system is favorable for extraction of acetone from dilute aqueous solutions using supercritical carbon dioxide. 

In Figure 7, we present the w/w concentration of acetone in the supercritical phase on a C02-free basis versus the corresponding concentration of acetone in the liquid phase. The curve shows a broad maximum at a range of concentrations of acetone in the aqueous phase between 2% and 15% w/w. The maximum concentration of acetone in the supercritical phase is close to 95% w/w. We can, therefore, obtain almost pure acetone from a dilute aqueous solution using a single-step extraction with supercritical carbon dioxide. 

In biphasic reactors or two-phase partitioning bioreactors (TPPB), the substrate is located mostly in the immiscible phase and diffuses to the aqueous phase. The enzyme catalyzes conversion of the substrate at the interface and/or in the aqueous phase. The product/s of the reaction then may partition to the organic phase. The system is self-regulated, as the substrate delivery to the aqueous phase is only directed by the partitioning ratio between the two phases and the enzymatic reaction rate [53]. The use of ionic liquid/supercritical carbon dioxide for enzyme-catalyzed transformation is gaining attention [69]. 

The recovery and purification of furfural from aqueous effluents by high-pressure extraction is of technical interest. Alternative extraction tests with supercritical carbon dioxide were carried out [1,2]. Further research [3-5] led to the conclusion that carbon dioxide is a good alternative to organic solvents with comparable and even better extraction results. For all these experiments the system furfural - water without acetic acid was used. 

The employment of catalytic methodologies - homogeneous, heterogeneous and enzymatic - in water or supercritical carbon dioxide as the reaction medium holds much promise for the development of a sustainable chemical manufacturing industry. Water is cheap, abundantly available, non-toxic and non-inflammable and the use of aqueous biphasic catalysis provides an ideal basis for recovery... 

Even in its simplified form, the Nelson protocol will deter the most enthusiast natural-product chemist. Unsurprisingly, alternative protocols have been described in the proprietary literature, and their sheer number testify to the ingenuity and commitment of chemists to solve what is still today a daunting task. Some modern modifications to the Nelson method from the proprietary literature include the use of supercritical carbon dioxide to reduce the extraction of pigments in the preparation of the oleoresin [54], and the recourse to macroporous adsorption resins [55] or to repeated extraction with aqueous silver nitrate to trap capsaicinoids and reduce the number of partition steps [56]. 

Several alternative polymerization media have been proposed for reducing the amount of unstable end groups in poly(tetrafluoroethylene). These include chlorofluorocarbons, which are detrimental to the environment, perfluoro-carbons, hydrofluorocarbons, and perfluoroalkyl sulfide acids, which are all expensive. Supercritical carbon dioxide has been identified as a viable alternative to aqueous and fluorocarbon reaction media [31]. Further more, mixing... 

In this special volume on polymer particles, recent trends and developments in the synthesis of nano- to micron-sized polymer particles by radical polymerization of vinyl monomers in environmentally friendly heterogeneous aqueous and supercritical carbon dioxide fluid media are reviewed by prominent worldwide researchers. Polymer particles are prepared extensively as synthetic emulsions and latexes, which are applied as binders in the industrial fields of paint, paper and inks, and films such as adhesives and coating materials. Considerable attention has recently been directed towards aqueous dispersed systems due to the increased awareness of environmental issues. Moreover, such polymer particles have already been applied to more advanced fields such as bio-, information, and electronic technologies. In addition to the obvious commercial importance of these techniques, it is of fundamental scientific interest to completely elucidate the mechanistic details of macromolecule synthesis in the microreactors that the polymer particles in these heterogeneous systems constitute. 

Recent developments in phosphine synthesis have allowed for catalysis to be carried out in nontraditional media, such as aqueous and fluorous solvents, as well as in supercritical carbon dioxide. Horvath and Gladysz have... 

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