Charles A. Eckert

Green chemistry: Reversible nonpolar-to-polar solvent

Imagine a smart solvent that can be switched reversibly from a liquid with one set of properties to another that has very different properties, upon command. Here we create such a system, in which a non-ionic liquid (an alcohol and an amine base) converts to an ionic liquid (a salt in liquid form) upon exposure to an atmosphere of carbon dioxide, and then reverts back to its non-ionic form when exposed to nitrogen or argon gas. Such switchable solvents should facilitate organic syntheses and separations by eliminating the need to remove and replace solvents after each reaction step.

Solvents for sustainable chemical processes

The properties and some key applications of solvents such as (1) supercritical fluids (SCFs), (2) gas-expanded liquids (GXLs) and organic-aqueous tunable solvents (OATS), (3) water at elevated temperature (WET), and (4) switchable solvents like reversible ionic liquids (RevILs) are discussed in this review. Each system offers a unique set of properties to enable alternative strategies for varied applications. These applications range from chemical transformations, product separation, catalyst recycling, nanomaterial processing, and CO2 capture. For each application, however, the common thrust is to enable greener and sustainable solutions for chemical processes.

Generalized reference fugacities for phase equilibrium thermodynamics

Abstract The reference fugacity for the liquid-phase activity coefficient of any component is chosen as the fugacity of pure liquid of that component at the temperature of the solution and at zero pressure. When suitably non-dimensionalized,this reference fugacity is a function only of reduced temperature and acentric factor; using Pitzers tables reduced reference fugacities are calculated from a reduced temperature of 0·56 to 1·0 and, by extrapolation, to 1·5. For non-condensable components it is necessary to know the partial molar volume in liquid solution and an approximate correlation for this quantity is presented. The results of this work should be useful for the systematic interpretation and correlation of phase equilibrium data.

In situ Spectroscopy of Polymers Subjected to Supercritical CO2: Plasticization and Dye Impregnation

In situ FT-IR spectroscopy has been used to study poly(methyl methacrylate) films subjected to high-pressure and supercritical CO2. Spectral changes indicate increased molecular mobility of ester groups due to the plasticization effect of CO2 on PMMA. This increase in PMMA segmental mobility has been used to impregnate Disperse Red 1 dye (DR1) into polymer film from a supercritical fluid solution. The enhanced diffusion process was observed in situ via FT-IR and UV/vis spectroscopy.

The use of partial molal volume data to evaluate equations of state for supercritical fluid mixtures

Abstract Infinite dilution partial molal volumes have been measured for heavy organic solids in supercritical fluid solvents. The results are highly negative in the region of greatest compressibility and, when combined with solubility data, serve as a base for stringen testing of phase equilibrium models. Comparisons are made with some of the common cubic equations of state as well as for an ideal chemical theory approach.

The catalytic opportunities of near-critical water: a benign medium for conventionally acid and base catalyzed condensations for organic synthesis

Near-critical water (NCW; 250–350 °C, 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.

Neoteric solvents for asymmetric hydrogenation: supercritical fluids, ionic liquids, and expanded ionic liquids

Neoteric (new) solvents such as supercritical CO2 (scCO2), 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 α,β-unsaturated carboxylic acids was chosen for its economic interest and its multiple H2-concentration dependent behaviours. For example, with ruthenium BINAP-type catalysts, type I substrates require high H2 concentration in solution, while type II require low H2 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, scCO2, 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 scCO2 was measured and the antisolvent effect of H2 in scCO2 was demonstrated and discussed.

Partitioning of solutes and cosolvents between supercritical CO2 and polymer phases

Abstract In situ Fourier transform IR and UV–vis spectroscopy have been used for partitioning of solutes between supercritical (sc) CO2 and polymer phases. Partitioning of deuterated water and azo-dyes between poly(methyl methacrylate) and scCO2 have been measured. Despite the low solubilities of polar azo-dyes in scCO2 the partition coefficient of these dyes is ca. 104. In addition, the degree of partitioning of cosolvents methanol and acetone from scCO2 into cross-linked poly(dimethylsiloxane) as well as the pressure dependence of the partition coefficient have been determined. Specific intermolecular interactions have been identified and related to the cosolvent partitioning between scCO2 and polymer phases.

Reversible in situ acid formation for β-pinene hydrolysis using CO2 expanded liquid and hot water

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 α-terpineol (2) from β-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 °C). 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.

Supercritical fluid dyeing of PMMA films with azo-dyes

In situ ultraviolet–visible spectroscopy has been used to study diffusion of two azo-dyes in a CO2-swollen matrix of poly(methyl methacrylate) (PMMA). The diffusivity of both dyes can be tuned simply be changing the system pressure. Higher pressure of CO2 enhances diffusion of a dye in PMMA. The diffusion of dyes in CO2-swollen PMMA can also be influenced by specific interactions. The partitioning of the dyes between the polymer phase and the fluid phase was measured, and the partition coefficients are large (104–105). Thus, supercritical fluid dyeing is possible, although the solubility of the dyes in the fluid phase is low.