Abstracts 2000-2002

Jessop, P.G., Eckert, C.A., Liotta, C.L., Bonilla, R.J., Brown, J.S., Brown, R.A., Pollet, P., Thomas, C.A., Wheeler, C., and Wynne, D., Catalysis using supercritical or subcritical inert gases under split-phase conditions , in Clean Solvents . 2002. p. 97-112.

Compressed CO2 and other gases can serve as media for catalysis in a number of different ways. While use of such gases as supercritical fluids (SCFs) under single-phase conditions has been studied intensively over the past decade, the use of inert gases under split phase conditions has received less attention. Having a condensed phase such as water, an ionic liquid, or even a solid below a SCF allows one to perform reactions combined with simultaneous or subsequent separation of product from catalyst or excess reagent. Performing a reaction in a condensed phase below a subcritical gas allows one to modify the reaction behaviour by adjusting the choice of inert gas or pressure of the gas. Examples of these possibilities are described, with an emphasis. on applications to homogeneous hydrogenation and phase-transfer catalysis.

Jessop, P.G., Olmstead, M.M., Ablan, C.D., Grabenauer, M., Sheppard, D., Eckert, C.A., and Liotta, C.L., Carbon dioxide as a solubility "switch" for the reversible dissolution of highly fluorinated complexes and reagents in organic solvents: Application to crystallization. Inorganic Chemistry, 2002. 41 (13): p. 3463-3468.

Highly fluorinated organic or organometallic solid compounds can be made to dissolve in liquid hydrocarbons by the application of 20-70 bar of CO2 gas, Subsequently releasing the gas causes the compounds to precipitate or crystallize, giving quantitative recovery of the solid. The resulting crystals can be of sufficient quality for single-crystal X-ray crystallography; the structures of Rh-2(O2CCF2CF2CF3)(4)(DMF)(2), Rh-2(O2C(CF2)(9)F)(4)(MeOH)(2), Cr(hfacac)(3), and P{C6H3(3,5-CF3)(2)}(3) have been determined from crystals grown in this manner.

Lu, J., Brown, J.S., Boughner, E.C., Liotta, C.L., and Eckert , C.A. , Solvatochromic characterization of near-critical water as a benign reaction medium. Industrial & Engineering Chemistry Research, 2002. 41 (12): p. 2835-2841.

Near-critical water (liquid water between 200 and 374 degreesC) offers an environmentally benign alternative for the replacement of undesirable solvents and catalysts. This work characterizes the solvent strength of liquid water at saturation pressure from ambient temperature to 275 degreesC in terms of its Kamlet-Taft dipolarity/polarizability, hydrogen-bond-donating acidity, and hydrogen-bond-accepting basicity using in situ UV-vis spectroscopy. The results suggest that near-critical water exhibits a wide range of polarity and hydrogen-bond-donor ability for tailoring chemical reactions and separations. These Kamlet-Taft solvent parameters can be used to correlate kinetic properties for reactions in water. As model reactions, the temperature-dependent kinetics of the hydrolyses of two nitroaromatic compounds, 4-nitroaniline and N,N-dimethyl nitroaniline, were determined in NCW in the temperature range of 200-275 degreesC. The hydronium ion dissociated from water promotes the initial hydrolysis reaction without the addition of any acid. Solvent effects on the rate constant were correlated with Kamlet-Taft solvent parameters based on a linear solvation energy relationship (LSER).

Lu, J., Boughner, E.C., Liotta, C.L., and Eckert , C.A. , Nearcritical and supercritical ethanol as a benign solvent: polarity and hydrogen-bonding. Fluid Phase Equilibria, 2002. 198 (1): p. 37-49.

Nearcritical (NC) and supercritical (SC) ethanol may offer novel media for both chemical reactions and separations as a replacement for environmentally undesirable organic solvents. We investigated the dipolarity/polarizability, hydrogen-bond donating acidity and accepting basicity in terms of Kamlet-Taft solvatochromism parameters pi*. a and beta in saturated liquid ethanol from 25 to 225 degreesC and in gaseous and SC ethanol at 250 degreesC as a function of pressure. Reichardt's E-T(30) scale was determined for ethanol under the same conditions. NC and SC ethanol has a wide range of solvent strength. which can be readily and continuously tuned by temperature and pressure. Liquid ethanol becomes nearly nonpolar as the temperature increases towards its critical point. The dipolarity/polarizability for SC ethanol ranges from gas-like to nonpolar liquid-like with increasing pressure. On the other hand. ethanol maintains significant hydrogen-bond donating acidity even under the supercritical conditions at 250 degreesC and at pressures up to 18.7 MPa. The hydrogen-bond accepting basicity, however. is considerably weakened at elevated temperatures. These well-established solvent parameters greatly improve our understanding of hot compressible ethanol, and allow us to explore the feasibility of using it in a variety of benign processes. (C) 2002 Elsevier Science B.V. All rights reserved.

Xie, X.F., Brown, J.S., Joseph, P.J., Liotta, C.L., and Eckert , C.A. , Phase-transfer catalyst separation by CO2 enhanced aqueous extraction. Chemical Communications, 2002(10): p. 1156-1157.

CO2 is used to enhance the environmentally benign and efficient recovery of phase transfer catalysts with aqueous extraction; this method can alter the distribution of phase transfer catalysts so dramatically that even in dilute organic solutions they can be separated selectively from an organic reaction mixture with only a small fraction of the water required in a traditional aqueous extraction.

Wheeler, C., Lamb, D.R., Jayachandran, J.P., Hallett, J.P., Liotta, C.L., and Eckert, C.A., Phase-transfer-catalyzed alkylation of phenylacetonitrile in supercritical ethane. Industrial & Engineering Chemistry Research, 2002. 41 (7): p. 1763-1767.

The first example of a phase-transfer-catalyzed alkylation reaction under supercritical fluid conditions is reported. The reaction is that of phenylacetonitrile and ethyl bromide in the presence of tetrabutylammonium bromide and potassium carbonate in supercritical ethane at 45, 60, and 75 degreesC and 138 bar. Results show that the reaction will go to completion in less than 24 h in the presence of the catalyst but that only a few percent conversion is achieved without it during the same period of time. The effects of catalyst concentration, temperature, and cosolvents are investigated. Catalyst solubility estimates and kinetic analyses suggest that the reaction takes place on the surface of the potassium carbonate particles. When the same reaction is attempted in supercritical carbon dioxide, both carboxylation and alkylation are observed. Cycloalkylation reactions between phenylacetonitrile and dibromoalkanes are also discussed.

Nolen, S.A., Lu, J., Brown, J.S., Pollet, P., Eason, B.C., Griffith, K.N., Glaser, R., Bush, D., Lamb, D.R., Liotta, C.L., Eckert, C.A., Thiele, G.F., and Bartels, K.A., Olefin epoxidations using supercritical carbon dioxide and hydrogen peroxide without added metallic catalysts or peroxy acids. Industrial & Engineering Chemistry Research, 2002. 41 (3): p. 316-323.

An alternative means of epoxidation is reported that uses environmentally benign supercritical carbon dioxide as both a solvent and reactant in combination with aqueous H2O2, which is made possible through the in situ formation of peroxycarbonic acid. Experiments were conducted at 40 degreesC and 120 bar in which cyclohexene was epoxidized to 1,2-cyclohexene oxide and 1,2-cyclohexanediol in this aqueous-organic biphasic system. Through the addition of NaHCO3 and the hydrophilic cosolvent dimethylformamide, the conversion increased from 0.4 mol % (without additives) to 12.6 mol % (with 0.1 mol % NaHCO3 and 13 mol % dimethylformamide). The results suggest that the reaction occurs within the aqueous phase, which led to investigations using the water-soluble olefin 3-cyclohexen-1-carboxylate sodium salt as a means of verifying the reaction location. Epoxidation of 3-cyclohexen-1-carboxylate sodium salt went to completion in less than 20 h at 40 degreesC and 120 bar with an epoxide yield of 89 mol % and diol Yield of 11 mol %.

Patrick, H.R., Griffith , K., Liotta, C.L., Eckert , C.A. , and Glaser, R., Near-critical water: A benign medium for catalytic reactions. Industrial & Engineering Chemistry Research, 2001. 40 (26): p. 6063-6067.

Environmentally benign near-critical water offers substantial advantages over traditional organic solvents. In this work we use the hydrolyses of several substituted benzoate esters and a series of substituted anisoles as probes to elucidate the activity of the two ionic species in near-critical water. Each of these hydrolyses can run via both acid- and base-catalyzed pathways, as well as an S(N)2 pathway. An analysis of Hammett plots suggests that the benzoate esters hydrolyze autocatalytically, following an acid-catalyzed mechanism, whereas the anisoles are hydrolyzed via the S(N)2 mechanistic pathway. This work suggests that near-critical. water offers significant potential, both as a benign solvent and as a reaction medium that does not require neutralization with acid or base after the desired reaction is complete.

Ngo, T.T., Bush, D., Eckert , C.A. , and Liotta, C.L., Spectroscopic measurement of solid solubility in supercritical fluids. Aiche Journal, 2001. 47 (11): p. 2566-2572.

Different in situ spectroscopic techniques, including infrared, ultraviolet, and fluorescence, were developed to measure the solubility of organic solids in supercritical carbon dioxide (scCO(2)). These techniques are applicable over a wide range of concentrations, as low as 10 (-6) or 10 (-7) mol fraction, where the conventional flow method is ineffective and less accurate. No separate calibration is required; in fact, the molar absorptivity is determined at the saturation point as an additional benefit. While this technique requires more time per data point, it is more accurate and unbiased than traditional methods at lower concentrations. The Patel-Teja equation of state was used to correlate the data and expand the data for the ternary system. Data are reported for anthracene, 1,4-naphthoquinone, and 2-naphthol in scCO(2) and CO2 with methanol cosolvent at 313 K and a pressure range from 7 to 21 MPa.

Milani, M., Schork, F.J., Liotta, C.L., and Poehlein, G.W., Model compound studies of the devulcanization of rubber via phase transfer catalysis. Polymer Reaction Engineering, 2001. 9 (1): p. 19-36.

It has been estimated that 240 million automobile tires must be disposed of annually in the United States alone (Korte, 1988). Presently, most of these tires are not being recycled but are instead being stockpiled across the country. One of the difficulties in recycling the tires arises from the vulcanized nature of the styrene-butadiene rubber (SBR). One route for recycling these tires is to cleave the sulfur crosslinks so that uncrosslinked chains can then be remolded into new tires and revulcanized. To date this route has not been shown to be completely feasible. This paper focuses on initial efforts to develop a low cost process using phase transfer catalysis to cleave the sulfur crosslinks in vulcanized rubber via phase transfer catalysis (PTC). Model compounds as well as SBR were used to study the cleavage of both disulfide and monosulfide bond via PTC. Although the chemistry proved to be capable of cleaving sulfur bonds in model compounds, the work on SBR was inconclusive.

Connor, D.M., Allen, S.D., Collard, D.M., Liotta, C.L., and Schiraldi, D.A., Effect of comonomers on the rate of crystallization of PET U-turn comonomers. Journal of Applied Polymer Science, 2001. 81 (7): p. 1675-1682.

The effect of incorporating phthalate, 1,8-naphthalenedicarboxylate, and 1,8-anthracenedicarboxylate structural units on the crystallization rate of PET are evaluated by isothermal and dynamic calorimetry. Although all of the comonomers retard crystallization, the 1,8-naphthalene unit shows no concentration dependence between 2.5 and 10% incorporation, in contrast to the smaller phthalate and larger anthracene units. The greater rate at which the 1,8-naphthalene copolymer crystallizes, relative to that of the other copolymers, is consistent with the notion that the U-turn geometry induces chain folding and nucleates crystallization. (C) 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 1675-1682, 2001.

Wheeler, C., West, K.N., Liotta, C.L., and Eckert , C.A. , Ionic liquids as catalytic green solvents for nucleophilic displacement reactions. Chemical Communications, 2001(10): p. 887-888.

We demonstrate the use of room-temperature ionic liquids as a catalytic, environmentally benign solvent for the cyanide displacement on benzyl chloride, replacing phase-transfer catalyzed biphasic systems and thus eliminating the need for a volatile organic solvent and hazardous catalyst disposal.

West, K.N., Wheeler, C., McCarney, J.P., Griffith, K.N., Bush, D., Liotta, C.L., and Eckert, C.A., In situ formation of alkylcarbonic acids with CO2. Journal of Physical Chemistry A, 2001. 105 (16): p. 3947-3948.

The mutual solubility of carbon dioxide and alcohols over a wide range of temperature and pressure provides a useful and tunable medium for reactions and separations. For many years, researchers have used alcohols as cosolvents in supercritical CO2, and recently CO2-swollen alcohols have been used for antisolvent crystallization and as mobile phases for chromatography. However, little consideration has been given to chemical interaction between the alcohols and CO2. We have confirmed that such an interaction does exist and can create an acidic environment. By isolating reaction products we have demonstrated that alcohol-CO2 complexes react similarly to carboxylic acids with diazodiphenylmethane, a compound typically used to evaluate acid strengths. Our evidence indicates that the behavior of CO2-alcohol systems is comparable to that of CO2-water systems, where carbonic acid is formed.

Connor, D.M., Allen, S.D., Collard, D., Liotta, C.L., and Schiraldi, D.A., Effect of linear comonomers on the rate of crystallization of copolyesters. Journal of Applied Polymer Science, 2001. 80 (14): p. 2696-2704.

Small amounts of dimethyl-4,4'-biphenyldicarboxylate, 2,7-dimethyl-4,5,9,10-tetrahydropyrenedicarboxylate, and dimethyl-2,7-pyrenedicarboxylate have been copolymerized into poly(ethylene) terephthalate (PET). The thermal transitions of the copolymers have been characterized, and the crystallization rates have been measured isothermally. Avrami analysis indicates that all the copolymers crystallized at a slower rate than that of the PET homopolymer. Addition of perylene to the copolymers containing pyrene enhanced the rate of crystallization, which could be the consequence of stacked arene assemblies serving as templates for crystal formation. (C) 2001 John Wiley & Sons, Inc.

Lu, J., Brown, J.S., Liotta, C.L., and Eckert , C.A. , Polarity and hydrogen-bonding of ambient to near-critical water: Kamlet-Taft solvent parameters. Chemical Communications, 2001(7): p. 665-666.

The Kamlet-Taft solvent parameters pi*, alpha, and beta of saturated liquid water have been determined from 25 to 275 degreesC based on solvatochromic measurements and indicate that the polarity and hydrogen-bonding of water are highly tunable properties with temperature.

Eckert , C.A. , Bush, D., Brown, J.S., and Liotta, C.L., Tuning solvents for sustainable technology. Industrial & Engineering Chemistry Research, 2000. 39 (12): p. 4615-4621.

The key to sustainable technology is achieving an economic benefit for environmental improvements. The tunability of benign compounds such as CO2 and water as supercritical and near-critical fluids offers improved performance and greater flexibility for separation and reaction processes, leading to economic advantages. Examples of such behavior are supercritical CO2 extractions and separations, CO2-expanded polar liquids for separations, and reactions in near-critical water. In each case the tunability is achieved through density changes or cosolvents and may augment product yield, quality, or rates.

Brown, J.S., Hallett, J.P., Bush, D., and Eckert , C.A. , Liquid-liquid equilibria for binary mixtures of water plus acetophenone, plus 1-octanol, plus anisole, and plus toluene from 370 K to 550 K. Journal of Chemical and Engineering Data, 2000. 45 (5): p. 846-850.

Liquid-liquid equilibria are reported for binary mixtures of water with acetophenone, 1-octanol, anisole, and toluene in the temperature range of 370 K to 550 K. The data were measured in a variable-volume windowed vessel by a traditional cloud point technique. These results are in good agreement with data reported in the literature. Above 450 K binary data for the water + anisole and water + acetophenone systems have not been reported previously.

Brown, J.S., Glaser, R., Liotta, C.L., and Eckert , C.A. , Acylation of activated aromatics without added acid catalyst. Chemical Communications, 2000(14): p. 1295-1296.

Phenol and resorcinol can be acetylated to the corresponding esters and ketones in aqueous and neat acetic acid at high temperature (250-300 degrees C) to substantial equilibrium conversion without any added acid catalyst.

Brantley , N.H. , Kazarian, S.G., and Eckert , C.A. , In situ FTIR measurement of carbon dioxide sorption into poly(ethylene terephthalate) at elevated pressures. Journal of Applied Polymer Science, 2000. 77 (4): p. 764-775.

Knowledge of the sorption rate and solubility of CO2 in polymers are of great importance for developing technologies utilizing high-pressure and supercritical CO2-assisted processes. Many conventional techniques for measuring gas sorption have inherent complications when used at elevated pressures. In this work, we demonstrate the use of near-IR spectroscopy as an accurate method to measure CO2 sorption kinetics and solubility in PET at elevated pressures. Sorption kinetics and solubility are measured at 0, 28, and 50 degrees C between pressures of 57.1 and 175.2 atm. Both initially amorphous and initially partially crystalline samples of PET are studied, and the effects of the initial crystallinity are determined. In addition, the effects of CO2 processing on the final crystallinities of our samples are measured. Crystallization was induced in PET at 28 and 50 degrees C over the range of pressures studied. However, at 0 degrees C, no detectable crystallization occurred in PET, even in the presence of high pressures of CO2. The method demonstrated in this work could easily be extended to directly measure CO2 sorption in other polymers. (C) 2000 John Wiley & Sons, Inc.

Vargas, M., Collard, D.M., Liotta, C.L., and Schiraldi, D.A., Photocrosslinkable copolyesters: Poly(alkylene terephthalate-co-1,4-phenylene bisacrylate). Journal of Polymer Science Part a-Polymer Chemistry, 2000. 38 (12): p. 2167-2176.

1,4-Phenylene bis(acrylic acid) is a thermally stable diacid, which can be incorporated into polyesters. The phenylene bisacrylate structural units undergo rapid photochemical reaction in the solid state to form crosslinks. This constitutes a feasible approach to polyesters, which can be photochemically thermoset after fabrication as films and fibers. (C) 2000 John Wiley & Sons, Inc.

Connor, D.M., Kriegel, R.M., Collard, D.M., Liotta, C.L., and Schiraldi, D.A., Pyrene and anthracene dicarboxylic acids as fluorescent brightening comonomers for polyester. Journal of Polymer Science Part a-Polymer Chemistry, 2000. 38 (8): p. 1291-1301.

Diacids of fused arenes have been prepared for use as covalently bound fluorescent optical brightening agents in condensation polymers. The monomers: dimethyl 1,6-pyrene dicarboxylate, dimethyl 1,8-pyrenedicarboxylate, dimethyl 2,7-pyrenedicarboxylate, 1,8-bis(2-carboxybenzoyl)pyrene dimethyl ester, dimethyl 2,6-anthracenedicarboxylate, dimethyl 2,7-anthracenedicarboxylate and dimethyl 9,10-anthracenedicarboxylate are copolymerized with poly(ethylene terephthalate) and their optical properties are assessed. All of the polymers give blue fluorescence, with the copolymer containing dimethyl 1,6-pyrenedicarboxylate being the brightest. (C) 2000 John Wiley & Sons, Inc.

Jones, J.R., Liotta, C.L., Collard, D.M., and Schiraldi, D.A., Photochemical cross-linking of poly(ethylene terephthalate-co-2,6-anthracenedicarboxylate). Macromolecules, 2000. 33 (5): p. 1640-1645.

Poly(ethylene terephthalate) copolymers containing 2,6-anthracenedicarboxylate structural units are chain extended and cross-linked by irradiation at 350 nm. The cross-linked materials were characterized by NMR, UV-vis, DSC, and dilute solution viscometry. The cross-linking is attributed to face-to-face dimerization of the anthracene units and radical reactions. Model anthracene photodimers are cleaved in solid films of PET by irradiation at 254 nm, but polymeric anthracene photodimerization reactions are irreversible under these conditions. The combination of irreversible anthracene photodimerization and irreversible radical reactions renders the cross-links permanent.

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