Abstracts 2003 - 2005

Wyatt, V.T., Bush, D., Lu, J., Hallett, J.P., Liotta, C.L., and Eckert , C.A. , Determination of solvatochromic solvent parameters for the characterization of gas-expanded liquids. Journal of Supercritical Fluids, 2005. 36 (1): p. 16-22.

Solvatochromic shifts of six probe indicators {4-nitroaniline, 4-nitroanisole, 4-nitrophenol, N,N-dimethyl-4-nitroaniline, 4-(2,4,6-triphenylpyridinium)-2,6-diphenylphenoxide and 2,6-dichloro-4-(2,4,6-triphenyl-1-pyridinio)phenolate} have been measured in binary mixtures of carbon dioxide with acetone and methanol at 35 and 40 degrees C over the entire range of solvent composition. The indicators were used to specify the solvatochromic solvent parameters (E-T(30), alpha, beta, and pi*), which were calculated from the solvatochromic shifts of the maximum absorbance peak (v(max)) observed by means of UV-vis spectroscopy. (c) 2005 Elsevier B.V. All rights reserved.

Lazzaroni, M.J., Bush, D., Eckert , C.A. , Frank, T.C., Gupta, S., and Olson, J.D., Revision of MOSCED parameters and extension to solid solubility calculations. Industrial & Engineering Chemistry Research, 2005. 44 (11): p. 4075-4083.

New pure component parameters are presented for the MOSCED limiting activity coefficient model for 133 solvents with an absolute average deviation of 10.6 % to experimental literature data. The MOSCED model has been applied to solid-liquid equilibria correlation and compared with the experimental data available in the literature. The correlation of solubility of 26 solids in organic solvents has an average absolute deviation of 25 %. This compares favorably to the prediction of the modified UNIFAC model.

Xie, X.F., Brown, J.S., Bush, D., and Eckert, C.A., Bubble and dew point measurements of the ternary system carbon dioxide plus methanol plus hydrogen at 313.2 K. Journal of Chemical and Engineering Data, 2005. 50 (3): p. 780-783.

Gas-expanded liquids offer many advantages as superior solvents for asymmetric hydrogenation reactions. To implement such applications, knowledge of the phase behavior of hydrogen with these tunable solvents is imperative. Phase boundary data are reported for the ternary system of carbon dioxide, methanol, and hydrogen at 313.2 K and pressures up to 21.7 MPa. The data were measured in a variable-volume windowed vessel by visual observation of one- to two-phase transitions.

Lazzaroni, M.J., Bush, D., Brown, J.S., and Eckert, C.A., High-pressure vapor-liquid equilbria of some carbon dioxide plus organic binary systems. Journal of Chemical and Engineering Data, 2005. 50 (1): p. 60-65.

Vapor-liquid equilibria, molar volumes, and volume expansion for several binary mixtures of organic solvents with carbon dioxide have been determined using a visual synthetic technique at temperatures from (298 to 333) K. The binary vapor-liquid equilibrium and saturated liquid molar volume of CO2 + acetone, + acetonitrile, + dichloromethane, + nitromethane, + N-methyl-2-pyrrolidone, + perfluorohexane, + 2-propanol, + tetrahydrofuran, + toluene, and + 2,2,2-trifluoroethanol were measured at temperatures from (298.2 to 333.2) K. The VLE correlated well using the Patel-Teja equation of state with Mathias-Klotz-Prausnitz mixing rules. The solubility of CO2 in the various solvents is explained by considering the intermolecular interactions Of CO2 in solution.

Xie, X.F., Liotta, C.L., and Eckert , C.A. , CO2-protected amine formation from nitrile and imine hydrogenation in gas-expanded liquids. Industrial & Engineering Chemistry Research, 2004. 43 (24): p. 7907-7911.

Gas-expanded liquids are tunable media for reaction and separation. We report that gas-expanded liquids under CO2 pressure are unique media for amine formation and separation. In the heterogeneous hydrogenation of benzonitrile and phenylacetonitrile with NiCl2/NaBH4 in CO(2)expanded ethanol, the primary amines are protected by CO2 so that the yield. of the primary amines is greatly increased and the production of the secondary amines is effectively suppressed. In the homogeneous hydrogenation of benzonitrile and phenylacetonitrile with RhH(P-i-Pr-3)(3) and benzophenone imine with Rh(1,5-C8H12){P(C6H5)(3)}(2)]PF6 in CO2-expanded tetrahydrofuran, the primary amines are separated in situ in the form of solid carbamic acids and/or ammonium carbamates with increased yield while the catalyst remains in the solution.. These results demonstrate the potential for using modest pressures Of CO2 to facilitate reactions as well as to separate products.

Eckert , C.A. , Liotta, C.L., Bush, D., Brown, J.S., and Hallett, J.P., Sustainable reactions in tunable solvents. Journal of Physical Chemistry B, 2004. 108 (47): p. 18108-18118.

There are now available a variety of tunable solvents; these have been used extensively for extractions and in a variety of materials applications. Our focus has been to apply these techniques to chemical reactions to take advantage of the special properties available, primarily for sustainable technology, to create processes that are potentially more benign and more advantageous. We report here our work in using supercritical fluids, near-critical fluids, and gas-expanded liquids to couple organic reactions with separations. In this paper, we review applications involving improved transport, catalyst recycling, and product separation as well as the in situ generation of catalysts. Although such tunable solvents are in no way a panacea, they do offer the chemical community alternatives that can often be applied creatively to many reaction opportunities.

Lazzaroni, M.J., Bush, D., Jones, R., Hallett, J.P., Liotta, C.L., and Eckert , C.A. , High-pressure phase equilibria of some carbon dioxide-organic-water systems. Fluid Phase Equilibria, 2004. 224 (1): p. 143-154.

Homogeneous catalysts offer better activity and selectivity than heterogeneous catalysts, but their use is limited by the need to separate them from product and reuse them. Preferential dissolution of gaseous carbon dioxide has been shown to alter phase boundaries and facilitate recovery of such homogenous catalysts. The addition of a polar organic co-solvent to a water/organic biphasic system, coupled with subsequent phase splitting induced by the dissolution of gaseous carbon dioxide creates the opportunity to run homogeneous reactions in an organic/aqueous mixture with a water-soluble catalyst. In homogeneous catalyzed reactions, the catalyst can be tuned to be soluble or insoluble with carbon dioxide present, thus allowing for high catalyst recovery. High-pressure phase equilibria for the systems containing carbon dioxide, an organic (tetrahydrofuran, acetonitrile, or 1,4-dioxane), and water were measured using a variable-volume view cell, by a method capable of rapid and facile measurement of compositions and density in both phases with no sampling or calibration. These systems are well predicted with the Peng-Robinson Equation of State with Huron-Vidal type mixing rules from correlations of the binary systems, with the modified Huron-Vidal 1 (MHV1) and Huron-Vidal-Orbey-Sandler (HVOS) model with UNIQUAC excess energy model performing the best. Applications of the phase behavior on reaction conditions andseparations are addressed. (C) 2004 Elsevier B.V. All rights reserved.

Chamblee, T.S., Weikel, R.R., Nolen, S.A., Liotta, C.L., and Eckert, C.A., Reversible in situ acid formation for beta-pinene hydrolysis using CO2 expanded liquid and hot water. Green Chemistry, 2004. 6 (8): p. 382-386.

Large amounts of waste may result from the neutralization of homogeneous acid catalysts following reaction. Here we present examples of in situ acid formation and self-neutralization, thus eliminating waste and offering advantages for product recovery. The formation of alpha-terpineol ( 2) from beta-pinene ( 1) is a reaction of commercial significance that is typically run with strong acid. We demonstrate that the reaction can be performed under more environmentally benign conditions using the in situ acid formation capabilities of two different green technologies: CO2 expanded liquids and reactions in hot water ( 200 degreesC). This work presents an example of the application of these methods to a reaction that has commercial significance and adds to our knowledge about the benefits and effects of co-solvents. The relative rates and product distributions achieved in each system are presented and discussed.

West, K.N., Hallett, J.P., Jones, R.S., Bush, D., Liotta, C.L., and Eckert, C.A., C02-induced miscibility of fluorous and organic solvents for recycling homogeneous catalysts. Industrial & Engineering Chemistry Research, 2004. 43 (16): p. 4827-4832.

Fluorous biphasic chemistry enables the recovery of homogeneous catalysts but presents engineering challenges because of issues concerning phase contacting and solvent loss. The addition of gaseous CO2 to fluorous-organic biphasic systems results in a single homogeneous liquid phase at temperatures well below the upper critical solution temperature of the binary liquid mixture. This phenomenon is due to the high solubility of CO2 in both organic liquids and fluorocarbons, and it facilitates reactions and can also reduce fluorous solvent losses. We demonstrate two homogeneously catalyzed reactions, a hydrogenation and an epoxidation, which result in an enhancement in the turnover frequency of 70% and 50%, respectively, for the CO2-merged phase relative to the fluorous biphasic system. This creates new opportunities for the use of fluorous-sequestered catalysts.

Xie, X.F., Liotta, C.L., and Eckert , C.A. , CO2-catalyzed acetal formation in CO2-expanded methanol and ethylene glycol. Industrial & Engineering Chemistry Research, 2004. 43 (11): p. 2605-2609.

Gas-expanded liquids are tunable media for reactions and separations. We report for the first time that CO2-expanded alcohols are catalytic media for cyclohexanone acetal formation. This process offers the opportunity to replace some environmentally harmful acid catalysts, as the CO2-based acid catalysts are self-neutralizing and result in no solid waste. We propose that the alkylcarbonic acids formed in situ from CO2 and alcohols are the acid catalysts and that the catalytic capacity can be tuned with CO2 pressure and temperature. The kinetics of cyclohexanone acetal formation in CO2-expanded methanol was investigated under various CO2 pressures over a temperature range of 25-50 degreesC without the addition of acid. Pseudo-first- and second-order rate constants were evaluated. These rate constants go through a maximum and the superficial activation energies go through a minimum between 10 and 40 bar Of CO2.

Levitin, G., Bush, D., Eckert, C.A., and Hess, D.W., Phase behavior and modeling of CO2/methanol/tetramethylammonium bicarbonate and CO2/methanol/tetramethylammonium bicarbonate/water mixtures at high pressures. Journal of Chemical and Engineering Data, 2004. 49 (3): p. 599-606.

High-pressure phase behavior has been measured for CO2/methanol/tetramethylammonium bicarbonate (TMAB) and CO2/methanol/TMAB/water systems at (25 and 70) degreesC and pressures up to 30 MPa. An increase in methanol concentration results in a decrease in the phase-transition pressure due to the higher miscibility of methanol and salt in CO2. At higher methanol concentrations, single phase mixtures could be achieved at moderate pressures with up to 70 mol % CO2. As expected, the addition of water sharply increases the phase transition pressure. The experimental results for the above systems were modeled using the Peng-Robinson equation of state; model predictions were found to be sensitive to adjustable parameters.

Lu, J., Lazzaroni, J., Hallett, J.P., Bommarius, A.S., Liotta, C.L., and Eckert , C.A. , Tunable solvents for homogeneous catalyst recycle. Industrial & Engineering Chemistry Research, 2004. 43 (7): p. 1586-1590.

A novel class of tunable solvents facilitates recycle of homogeneous catalysts for both economic and environmental advantages. In a mixed organic-aqueous tunable solvent (OATS), reactions between water-soluble catalysts and moderately hydrophobic substrates can be run homogeneously, with subsequent phase separation for product purification and catalyst reuse. One example demonstrated is the dimethyl ether (DME)-water system, which has been employed as a benign alternative to organic solvents for alcohol dehydrogenase (ADH)-catalyzed reduction of hydrophobic ketones coupled with regeneration of the cofactor NADH. We also show the feasibility of a biphasic DME -water separation scheme to couple with the biocatalytic reaction. The subsequent downstream processing offers the advantages of easily isolating water-insoluble products from the aqueous phase and recycling enzyme - cofactor. Other OATS systems are discussed where the preferential dissolution of modest pressures of CO2 causes phase separations, which result in very large distribution coefficients of target molecules in the biphasic organic-aqueous system, with substantial promise as tunable solvents for biocatalysis.

Ablan, C.D., Hallett, J.P., West, K.N., Jones, R.S., Eckert , C.A. , Liotta, C.L., and Jessop, P.G., Use and recovery of a homogeneous catalyst with carbon dioxide as a solubility switch. Chemical Communications, 2003(24): p. 2972-2973.

A method for fluorous biphasic catalysis is described, in which the fluorous liquid is replaced by fluorinated silica, the fluorous catalyst is induced to dissolve in the organic solvent by the presence Of CO2, and the recovery of the catalyst after the reaction is achieved by release of the CO2 pressure.

Nolen , S.A. , Liotta, C.L., Eckert , C.A. , and Glaser, R., The catalytic opportunities of near-critical water: a benign medium for conventionally acid and base catalyzed condensations for organic synthesis. Green Chemistry, 2003. 5 (5): p. 663-669.

Near-critical water (NCW; 250-350degreesC, 40-90 bar) provides an environmentally benign alternative medium for conducting organic synthesis. The Claisen-Schmidt condensation of benzaldehyde with 2-butanone was investigated and is used to demonstrate the ability to conduct conventionally acid or base catalyzed reactions homogeneously using NCW without the addition of a catalyst. Kinetic investigations of the Claisen-Schmidt condensation yielded activation energies of 24.7 and 22.6 kJ mol(-1) for the formation of products consistent with those formed under classical acidic and basic conditions, respectively. Investigations of other conventionally base catalyzed condensations were performed in uncatalyzed NCW for completeness, including the self-condensation reaction of butyraldehyde, the benzaldehyde-acetone cross-aldol condensation, the intramolecular Claisen condensations of ethyl-4-acetylbutyrate and ethyl levulinate, as well as the intramolecular Dieckmann condensation of diethyl adipate.

Andrade, G.S., Berkner, J.E., Liotta, C.L., Eckert, C., Schiraldi, D.A., Andersen, A., and Collard, D.M., The one-pot synthesis and Diels-Alder reactivity of 2,5-dihydrothiophene-1,1-dioxide-3-carboxylic acid. Synthetic Communications, 2003. 33 (20): p. 3643-3650.

A one-pot preparation of 2,5-dihydrothiophene-1,1-dioxide-3 carboxylic acid (3-sulfolene-3-carboxylic acid) is reported. The carboxylation of 3-sulfolene, exclusively at the 3-position, using CO2 and DBU proceeds to >90% conversion. A rapid workup gives 3-sulfolene-3-carboxylic acid, a stable precursor to 1,3-butadiene-2-carboxylic acid. High conversions to Diels-Alder adducts were obtained upon treatment of 3-sulfolene-3-carboxylic acid with various dienophiles.

Jayachandran, J.P., Wheeler, C., Eason, B.C., Liotta, C.L., and Eckert , C.A. , Phase transfer catalyzed intramolecular cycloalkylation of phenylacetonitrile with alpha,omega-dibromoalkanes in supercritical ethane. Journal of Supercritical Fluids, 2003. 27 (2): p. 179-186.

An intramolecular cycloalkylation of phenylacetonitrile (PAN) with different alpha,omega-dibromoalkanes in supercritical fluids under phase transfer catalysis (PTC) conditions is reported. In particular, the cycloalkylation of PAN with an excess of 1,4-dibromobutane has been studied in the presence of tetrabutylammonium. bromide and potassium carbonate as a base in supercritical ethane at 70 degreesC and 11.0 MPa. The reaction was complete in less than 6 It yielding selectively the desired cycloadduct in the presence of a PTC, but conversion in the absence of catalyst was low. A cycloalkylation methodology has been developed using several dibromoalkanes, viz., 1,2-dibromoethane, 1,3-dibromopropane, 1,4-dibromobutane, 1,5-dibromopentane, 1,6-dibromohexane and 1,10-dibromodecane. When the cycloalkylation was performed in the presence of supercritical CO2, mono- and di-alkylated products were observed in addition to the cycloadduct. To compare the effect of SC ethane solvent, reactions were also carried out using different conventional solvents such as hexane, tert-butyl methyl ether, ethyl acetate and chlorobenzene. Use of SC ethane gave considerably better yields of products than the other solvents. (C) 2002 Elsevier Science B.V. All rights reserved.

Ngo, T.T., Liotta, C.L., Eckert, C.A., and Kazarian, S.G., Supercritical fluid impregnation of different azo-dyes into polymer: in situ UV/Vis spectroscopic study. Journal of Supercritical Fluids, 2003. 27 (2): p. 215-221.

In situ UV/Vis spectroscopy was used to study supercritical fluid impregnation of azo-dyes with varying functional groups into poly(methyl methacrylate) (PMMA) films. The diffusion and phase behavior of Disperse Orange 25 (DO25) and a dye mixture of Disperse Red I and DO25 in PMMA/CO2 system were studied. Although these azo-dyes are relatively insoluble in supercritical carbon dioxide (scCO(2)) ( < 10(-6) M under conditions of our experiments), the high partition coefficients (approximate to 10(4)-10(5)) between PMMA and scCO(2) phase allow incorporation of similar to 1% of these dyes into PMNIA matrix. The diffusion of azo-dyes in scCO(2)-swollen PMMA film was observed in situ via UV/Vis spectroscopy, and can be tuned simply by changing the CO2 pressure surrounding the polymer film. This article reports the effects Of CO2 pressures and specific intermolecular interactions on the diffusion rate (or diffusivity) and the partitioning of dye solutes between the fluid phase and the PMMA. It also demonstrates a possibility of enhancing diffusion by a dye mixture that is capable of mutual intermolecular interactions and thus reducing interactions with the polymer matrix. (C) 2002 Elsevier Science B.V. All rights reserved.

Glaser, R., Williardt, J., Bush, D., Lazzaroni, M.J., and Eckert , C.A. , Application of high-pressure phase equilibria to the selective oxidation of alcohols over supported platinum catalysts in supercritical carbon dioxide , in Utilization of Greenhouse Gases . 2003. p. 352-364.

At conditions above its critical point, the greenhouse gas carbon dioxide may be used as an environmentally benign, nontoxic medium for organic synthesis. The peculiarities and the prediction of the high-pressure phase behavior of the multicomponent reactant mixture related to the selective oxidation of 2-propanol to acetone by molecular oxygen over a carbon-supported platinum catalyst in high-pressure carbon dioxide at 40degreesC are reported. Very good agreement of vapor-liquid equilibria predictions based on the Patel-Teja equation of state and experimental data obtained with argon as a replacement for oxygen was achieved. From the phase behavior considerations, reaction conditions were derived that ensure single-phase operation for the catalytic 2-propanol oxidation. Optimized product yield and catalyst productivity were reached by balancing the increased reactant concentration, the oxygen/2-propanol ratio and the catalyst deactivation.

Lu, J., Liotta, C.L., and Eckert , C.A. , Spectroscopically probing microscopic solvent properties of room-temperature ionic liquids with the addition of carbon dioxide. Journal of Physical Chemistry A, 2003. 107 (19): p. 3995-4000.

Room-temperature ionic liquids (RTILs) provide an alternative for elimination of solvent emissions to the atmosphere for many reactions, but the subsequent separation of the products by conventional methods can be a challenge. However, the use of supercritical carbon dioxide (scCO(2)) as an extractant offers potential for a novel class of environmentally benign media for chemical reaction and downstream separation. We have investigated the solvent properties of mixtures of 1-butyl-3-methyl imidazolium hexafluorophosphate ([bmim]-[PF6]) and CO2 as functions of temperature (35-50 degreesC) and CO2 pressure (0-230 bar). We report the Kamlet-Taft dipolarity/polarizability parameter, volume expansion, and microviscosity. The results are consistent with a picture of local enhancement of RTIL composition around it chromophore, maintaining solvent strength even at fairly high loadings of CO2, whereas the microviscosity in the vicinity of the solute is dramatically reduced, leading to enhanced mass transport and facilitated separation.

Jessop, P.G., Stanley, R.R., Brown, R.A., Eckert, C.A., Liotta, C.L., Ngo, T.T., and Pollet, P., Neoteric solvents for asymmetric hydrogenation: supercritical fluids, ionic liquids, and expanded ionic liquids. Green Chemistry, 2003. 5 (2): p. 123-128.

Neoteric (new) solvents such as supercritical CO2 (scCO(2)), ionic liquids (ILs), ILs with cosolvents, and CO2-expanded ionic liquids (EILs) offer flexible physical properties, which allow chemists and engineers to select the optimal solvent system for a specific reaction process. Homogeneously-catalyzed asymmetric hydrogenation of alpha,beta-unsaturated carboxylic acids was chosen for its economic interest and its multiple H-2-concentration dependent behaviours. For example, with ruthenium BINAP-type catalysts, type I substrates require high H-2 concentration in solution, while type II require low H-2 concentration. ScCO2, ILs and EILs are highly attractive because of their contrasting properties and their potential flexibility in improving or reducing hydrogen transfer rates and thus concentrations. Several ILs were tested and compared with EILs, IL-cosolvent mixtures, scCO(2), and normal methanol as media for these reactions to establish the most effective system for each substrate type. Atropic acid (type I) was hydrogenated up to 92% ee which is not better than in methanol. However, tiglic acid (type II) was hydrogenated up to 93% ee in the optimized IL system, which is significantly better than was observed in MeOH. CO2-expansion of ionic liquids affected the selectivity for both substrates, improving the selectivity for atropic acid and lowering it for tiglic acid. The solubility of the catalyst in scCO(2) was measured and the antisolvent effect of H-2 in scCO(2) was demonstrated and discussed.

Ngo, T.T., McCarney, J., Brown, J.S., Lazzaroni, M.J., Counts, K., Liotta, C.L., and Eckert, C.A., Surface modification of polybutadiene facilitated by supercritical carbon dioxide. Journal of Applied Polymer Science, 2003. 88 (2): p. 522-530.

The hydrophilicity of polymers can be improved through surface modification, traditionally done with conventional organic solvents, but these may cause the deterioration of polymer bulk properties due to irreversible polymer swelling. However, supercritical carbon dioxide (scCO(2)) not only swells the polymer reversibly, but also acts as a convenient transport medium for monomeric solutes, which may be subsequently polymerized. Thus we are able to modify the polymer surface without affecting its bulk strength and durability. Here we report scCO(2) surface modification of polybutadiene using ultraviolet-visible (UV/Vis) and Fourier transform infrared (FTIR) spectroscopy. Monomers such as 3-vinylbenzoic acid and crotonic acid are used to study the effects of pressure, solute structure, and reaction mechanism on the diffusion rates and partitioning of monomers between the fluid phase and the polymer. (C) 2003 Wiley Periodicals, Inc.

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