A guide to the selection of switchable functional groups for CO2-switchable compounds.

Many CO2-responsive species, including many of the CO2-switchable surfactants, solvents, solutes, gels, colloids, and surfaces, rely on the ability of CO2 to lower the pH of water. Uncharged basic groups on the CO2-responsive species are therefore converted from a neutral state to a protonated cationic state (a bicarbonate salt), which causes dramatic and useful changes to the properties of the species. However, this switching process only works correctly if a basic group of appropriate basicity has been selected. This article presents a comprehensive guide to the selection of basic groups for CO2-switchable species for use in water. The appropriate basicity, as measured by the pKaH (the pKa of the protonated compound), is a function of the concentration of the switchable species, the temperature, the pressure of CO2, the presence or absence of an organic liquid phase, and the solubility of the neutral form of the compound.

Homogeneous catalysis in supercritical fluids.

Supercritical fluids (SCFs), compounds heated and pressurized beyond the critical point, have many unusual properties. Homogeneous molecular catalysts, which have far greater control over selectivity than heterogeneous solid catalysts, are now being tested in SCFs, and early results show that high rates, improved selectivity, and elimination of masstransfer problems can be achieved. As industry moves away from toxic or environmentally damaging solvents, supercritical carbon dioxide may be an ideal replacement medium for nonpolar or weakly polar chemical processes. More than simply substitutes for nonpolar solvents, SCFs can radically change the observed chemistry. Supercritical carbon dioxide is also an excellent medium for its own fixation, as demonstrated by studies of its hydrogenation.

Piperylene sulfone: a labile and recyclable DMSO substitute.

The properties and uses of piperylene sulfone as a new, recyclable dipolar, aprotic solvent for conducting organic reactions are presented.

Cyclopropanation enantioselectivity is pressure dependent in supercritical fluoroform.

The tunable dielectric constant ε of supercritical fluoroform is the explanation for pressure-dependent enantioselectivity in a reaction conducted at low pressure. For the cyclopropanation of styrene and methyl phenyldiazoacetate with a dirhodium catalyst, the enantioselectivity was significantly higher at 52 bar than above 80 bar (see plot).

Phosphonium ionic liquids for degradation of phenol in a two-phase partitioning bioreactor.

Six ionic liquids (ILs), which are organic salts that are liquid at room temperature, were tested for their biocompatibility with three xenobiotic-degrading bacteria, Pseudomonas putida, Achromobacter xylosoxidans, and Sphingomonas aromaticivorans. Of the 18 pairings, seven were found to demonstrate biocompatibility, with one IL (trihexyl(tetradecyl)phosphonium bis(trifluoromethylsulfonyl) amide) being biocompatible with all three organisms. This IL was then used in a two-phase partitioning bioreactor (TPPB), consisting of 1 l aqueous phase loaded with 1,580 mg phenol and 0.25 l IL, inoculated with the phenol degrader P. putida. This initially toxic aqueous level of phenol was substantially reduced by phenol partitioning into the IL phase, allowing the cells to utilize the reduced phenol concentration. The partitioning of phenol from the IL to the aqueous phase was driven by cellular demand and thermodynamic equilibrium. All of the phenol was consumed at a rate comparable to that of previously used organic-aqueous TPPB systems, demonstrating the first successful use of an IL with a cell-based system. A quantitative (31)P NMR spectroscopic assay for estimating the log P values of ILs is under development.