Supercritical fluoroform

In most enzymatic syntheses of polyesters, the polymerization was carried out in organic solvents or bulk. Using supercritical fluoroform as solvent, the polymerization of bis(2,2,2-trichloroethyl) adipate and 1,4-butanediol was demonstrated [60]. The molecular weight increased as a function of the pressure. By changing the pressure, the low-dispersity polymer fractions were separated. 

Critical points vary widely. Table 6.1 shows a representative sample of critical parameters and it is immediately obvious why carbon dioxide is widely used. With a critical temperature just above room temperature and a critical pressure that is relatively low, the amount of energy needed to render carbon dioxide supercritical is comparatively small. Fluoroform (CHF3) and difluoromethane also have easily attainable critical parameters, but they are much more expensive than carbon dioxide. Despite its high critical temperature and pressure, supercritical water (SCH2O) is used widely as a destructive medium since it is highly acidic. 

Shariati, A. and Peters, C. J., High-pressure phase behavior of systems with ionic liquids Measurements and modeling of the binary system fluoroform + l-ethyl-3-methylimidazolium hexafluorophosphate, /. Supercrit. Fluids, 25, 109, 2003. 

Among potentially interesting solvents for enzymatic catalysis, carbon dioxide is the most widely nsed snpercritical fluid. However, there is a growing interest in using other supercritical fluids (e.g., ethylene, fluoroform, ethane, sulfur hexafluoride, and near-critical propane) (Kamat et al., 1995b). 

S. C. Tucker, Solvent density inhomogeneities in supercritical fluids, Chem. Rev., 99 (1999) 391—418 O. Kajimoto, Solvation in supercritical fluids Its effects on energy transfer and chemical reactions, Chem. Rev., 99 (1999) 355-89 S. Nugent and B. M. Ladanyi, The effects of solute-solvent electrostatic interactions on solvatochromic shifts in supercritical C02, J. Chem. Phys., 120 (2004) 874-84 F. Ingrosso and B. M. Ladanyi, Solvation dynamics of C153 in supercritical fluoroform a simulation study based on two-site and five-site models of the solvent, J. Phys. Chem. B, 110 (2006) 10120-29 F. Ingrosso, B. M. Ladanyi, B. Mennucci and G. Scalmani, Solvation of coumarin 153 in supercritical fluoroform, J. Phys. Chem. B, 110 (2006) 4953-62 Y. Kimura and N. Hirota, Effect of solvent density and species on static and dynamic fluorescence Stokes shifts of coumarin 153, J. Chem. Phys., Ill (1999) 5474 ... 

Figure 1 Typical phase diagram for compounds like ethane, fluoroform, and carbon dioxide. The fluid is technically supercritical when T > Tc and P > Pc, but many authors refer to the fluid as supercritical when only the first condition is met. Once the temperature is raised above the Tc, the density can be varied continuously and there is no phase transformation. 

In this chapter, we describe the density- and temperature-dependent behavior of the vibrational lifetime (TO of the asymmetric CO stretching mode of W(CO)6( 2000 cm-1) in supercritical ethane, fluoroform, and carbon dioxide (C02). The studies are performed from low density (well below the critical density) to high density (well above the critical density) at two temperatures one close to the critical temperature and one significantly above the critical temperature (68-70). In addition, experimental results on the temperature dependence of Ti at fixed density are presented. Ti is measured using infrared (IR) pump-probe experiments. The vibrational absorption line positions as a function of density are also reported in the three solvents (68,70) at the two temperatures. 

Figure 3 Vibrational lifetimes for the asymmetric CO stretching mode of W(CO)6 vs. density along two isotherms of three polyatomic supercritical fluids ethane (34°C panel a and 50°C panel b), fluoroform (28°C panel c and 44°C panel d), and carbon dioxide (33°C panel e and 50°C panel f). The upper panel for each solvent is an isotherm at 2°C above the critical temperature. In all six data sets, error bars (representing one standard deviation) are approximately the size of the points.

We have presented experimental and theoretical results for vibrational relaxation of a solute, W(CO)6, in several different polyatomic supercritical solvents (ethane, carbon dioxide, and fluoroform), in argon, and in the collisionless gas phase. The gas phase dynamics reveal an intramolecular vibrational relaxation/redistribution lifetime of 1.28 0.1 ns, as well as the presence of faster (140 ps) and slower (>100 ns) components. The slower component is attributed to a heating-induced spectral shift of the CO stretch. The fast component results from the time evolution of the superposition state created by thermally populated low-frequency vibrational modes. The slow and fast components are strictly gas phase phenomena, and both disappear upon addition of sufficiently high pressures of argon. The vibrational... 

In the present study, we tested the validity of the EOS-Ge models by applying different treatments for 21 binary solid/supercritical fluid systems listed in table 2. In those systems, the supercritical component is one of the following fluids carbon dioxide, ethane, fluoroform and chlorotrifluoromethane and the solid component is either a nonpolar compound... 

SCFs offer a nonaqueous environment which can be desirable for enzymatic catalysis of lipophilic substrates. The lipophilic substance cholesterol is 2 to 3 orders of magnitude more soluble in CX>2-cosolvent blends than in waterQ). In CO2 based blends, it may be oxidized to cholest-4en-3one, a precursor for pharmaceutical production using an immobilized enzyim(22). The enzyme polyphenol oxidase has been found to be catalytically active in supercritical CO2 and fluoroform (22). The purpose of using a SCF is that it is miscible with one of the reactants-oxygen. Lipase may be used to catalyze the hydrolysis and interesterification of triglycerides in supercritical OO2 without severe loss of activity(24). These reactions could be integrated with SCF separations for product recovery. 

Carbon dioxide, water, ethane, ethylene, propane, ammonia, xenon, nitrous oxide, and fluoroform have been considered useful solvents for SEE. Carbon dioxide has so far been the most widely used as a supercritical solvent because of its convenient critical temperature, 304°K, low cost, chemical stability, nonflammability, and nontoxicity. Its polar character as a solvent is intermediate between a truly nonpolar solvent such as hexane and a weakly polar solvent. Moreover, COj also has a large molecular quadrupole. Therefore, it has some limited affinity with polar solutes. To improve its affinity, additional species are often introduced into the solvent as modifiers. For instance, methanol increases C02 s polarity, aliphatic hydrocarbons decrease it, toluene imparts aromaticity, R-2-butanol adds chirality, and tributyl phosphate enhances the solvation of metal complexes. 

Although, supercritical carbon dioxide has the advantage of being nontoxic and abundant, it is practically immiscible with water. Therefore, supercritical fluids used as the reaction medium in enzyme-catalyzed reactions include fluoroform, sulfur hexafluoride, and ethane, while lipases are the enzymes utilized in such reactions. ... 

Chaudhary AK, Kamat SV, Beckman EJ, Nurok D, Kleyle RM, Hadju P, Russell AJ. Control of subtilisin substrate specificity by solvent engineering in organic solvents and supercritical fluoroform. J Am Chem Soc 1996 ... 

Enantioselective esterification can be pressure dependent in supercritical fluoroform. For example, the selectivity of the transesterification of A -acetyl-phenylalanine ethyl ester with methanol catalyzed by Subtilisin Carlsberg was shown by Kamat et al. (26) to be greater at higher pressures than at lower pressures [Eq. (9)] ... 

Mori T, Funasaki M, Kobayashi A, Okahata Y. Reversible activity changes of a lipid-coated lipase for enantioselective esterification in supercritical fluoroform. Chem Commun, 2001 1832-1833. 

Wynne D, Jessop PG. Cyclopropanation enantioselectivity is pressure dependent in supercritical fluoroform. Angew Chem Int Ed Engl 1999 38 1143-1144. 

Parsons DF, Boone BI, Jessop PG, Tucker SC. Electrostriction effects on competing transition states in supercritical fluoroform. J Supercrit Fluids 2002 24 173-181. 

Mikami K, Matsukawa S, Kayaki Y, Ikariya T. Asymmetric Mukaiyama aldol reaction of a ketene silyl acetal of thioester catalyzed by a binaphthol-titanium complex in supercritical fluoroform. Tetrahedron Lett 2000 41 1931-1934. 

Enzyme reactions have been successfully operated in a variety of organic solvents (Table 8.4) as well as in supercritical fluids (e.g., carbon dioxide and fluoroform) and gases. - The latter two categories offer some intriguing possibilities and potential advantages relative to solvents, including enhanced substrate diffusivity, tunable solvent phase properties (via temperature and pressure), reduced solvent... 

Supercritical or near-critical fluids can be used both for extraction and chromatography. Many chemicals, primarily organic species, can be separated and analyzed using this approach [6], which is particularly useful in the food industry. Substances that are useful as supercritical fluids include carbon dioxide, water, ethane, ethene, propane, xenon, ammonia, nitrous oxide, and a fluoroform. Carbon dioxide is most commonly used, typically at a pressure near 100 bar. The required operating pressure ranges from about 43 bar for propane to 221 bar for water. Sometimes a solvent modifier is added (also called an entrainer or cosolvent), particularly when carbon dioxide is used. 

Russell and coworkers [23] conducted an investigation into the condensation reaction between 1,4-butanediol and bis(2,2,2-trichloroethyl) adipate. The authors showed that low-dispersity polymers could be achieved in supercritical fluoroform at 50°C and 372 bar using PCL. Typically, the polymers had a molecular weight less than 1500 Da. This was the first record of biocatalytic polymerization in a supercritical fluid and opened the way for biocatalytic polymerization in these solvents. Almost all polymerization reactions in supercritical fluids to follow were conducted in supercritical C02. 

Mukaiyama aldol reaction. Reasonably good enantioselection is observed when the catalyzed reaction of ketene silyl acetals derived from thioesters with aldehydes is conducted in supercritical fluoroform. ... 

The overall effect of solvent polarity on the solubility of naphthalene follows the same general solubility rule in liquid extractions that like dissolves like . Naphthalene is a nonpolar solid and is most soluble in supercritical ethane. Carbon dioxide behaves as a nonpolar solvent but less so because of its quad-rupole moment [11]. Fluoroform is the most polar solvent because of the elec-... 

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