Fluorination effects on rotational correlation times of tris(β-diketonato)aluminum(III) in CO2 by 27Al NMR relaxation measurements.

(27)Al NMR longitudinal relaxation times, T(1,obs)((27)Al), of [Al(acac)(3)] and [Al(hfa)(3)] (Hacac = acetylacetone, Hhfa = hexafluoroacetylacetone) in CH(3)CN and CO(2) were measured over a wide range of temperature and pressure. The rotational correlation times, τ(r), of the tris(β-diketonato)aluminum(III) complexes were determined from T(1,obs)((27)Al) using (27)Al quadrupole coupling constants, eQq/h((27)Al), which were also obtained to be 3.11 and 3.

Preparation of silica sphere with porous structure in supercritical carbon dioxide.

Silica sphere with porous structure has been synthesized in supercritical carbon dioxide. The structure originates from a delicate CO(2) trapping phenomenon intended for void formation in the inorganic framework. Silicate polymerization and subsequent removal of CO(2) by depressurization leaves the porous architecture.

Development of a novel catalytic membrane reactor for heterogeneous catalysis in supercritical CO₂.

A novel type of high-pressure membrane reactor has been developed for hydrogenation in supercritical carbon dioxide (scCO(2)). The main objectives of the design of the reactor are the separate feeding of hydrogen and substrate in scCO(2) for safe reactions in a continuous flow process, and to reduce the reaction time. By using this new reactor, hydrogenation of cinnamaldehyde into hydrocinnamaldehyde has been successfully carried out with 100% selectivity at 50 degrees C in 10 MPa (H(2): 1 MPa, CO(2): 9 MPa) with a flow rate of substrate ranging from 0.

Amphiphilic block copolymer-stabilized gold nanoparticles for aerobic oxidation of alcohols in aqueous solution.

Stable Au nanoparticles in P123 aqueous solution using a simple method have been developed and the colloidal Au nanoparticles were successfully applied for the effective oxidation of various alcohols using molecular O2 as oxidant at 30 degrees C in aqueous solution.

Applications of environmentally benign supercritical water to organic syntheses.

Supercritical water (scH(2)O) is utilized for organic synthesis as an acid- or a base-catalyst as well as a useful replacement for organic solvents. There have been few works on the use of scH(2)O for acid- or base-catalyzed organic synthesis, because the ion product of scH(2)O is much lower than liquid water under certain conditions. Our recent studies by in situ Raman and IR spectroscopic measurements were allowed to expect the occurrence of acid- or base-catalysis of scH(2)O.

Temperature dependence of local density augmentation for acetophenone N,N,N',N'-tetramethylbenzidine exciplex in supercritical water.

Local density augmentation around exciplex between acetophenone and N,N,N',N'-tetramethylbenzidine in supercritical water was measured by observing the peak shift of transient absorption spectrum at temperatures from 380 to 410 degrees C and at pressures from 6 to 37 MPa. Large local density augmentation was observed at lower solvent densities. Local density augmentation was evaluated by the excess density, which was defined as the difference between local density and bulk density, and the density enhancement factor, which was defined by the ratio of the local density to the bulk density.

Facile "green" synthesis, characterization, and catalytic function of beta-D-glucose-stabilized Au nanocrystals.

We present a straightforward, economically viable, and "green" approach for the synthesis and stabilization of relatively monodisperse Au nanocrystals with an average diameter of 8.2 nm (standard deviation, SD=2.3 nm) by using nontoxic and renewable biochemical of beta-D-glucose and by simply adjusting the pH environment in aqueous medium.

Polar attributes of supercritical carbon dioxide.

Supercritical carbon dioxide (scCO(2)) is increasingly promoted as an environmentally benign alternative to conventional organic solvents. The supercritical state bridges the gap between liquid and gaseous states by offering gaslike diffusion rates and liquidlike solvent densities, thereby enabling potential opportunities as a reaction and separation medium in chemical industry. Understanding the solvent behavior of liquid and scCO(2) is of critical importance to enable the design of CO(2)-philic molecular systems and to expand the use of these solvent systems to a wider range of chemical processes.

Self-assembly of beta-D glucose-stabilized Pt nanocrystals into nanowire-like structures.

In this work we demonstrate the self-assembly of beta-D glucose-protected Pt nanocrystals (average particle size = 4.1 nm) into nanowire-like assemblies under ambient conditions.

Synthesis of Ag and AgI quantum dots in AOT-stabilized water-in-CO2 microemulsions.

Silver and silver iodide nanocrystals have been synthesized in the water-in-CO(2) reverse microemulsions formed by the commonly used surfactant, sodium bis(2-ethylhexyl)sulfosuccinate (AOT), in the presence of 2,2,3,3,4,4,5,5-octafluoro-1-pentanol as cosurfactant. The nanometer-sized aqueous domains in the microemulsion cores not only act as nanoreactors, but the surfactant interfacial monolayer also helps the stabilization of the metal and semiconductor nanoparticles. The transmission electron microscopy results show that silver and silver iodide nanocrystals with average diameters of 6.

Synthesis of Ag2S quantum dots in water-in-CO2 microemulsions.

Ag2S nanocrystals with a mean diameter of 5.9 nm (sigma= 1.65 nm) and characteristic surface plasmon resonance absorption at 330 nm have been synthesized in water-in-supercritical CO2 reverse microemulsion using the commonly used AOT surfactant with 2,2,3,3,4,4,5,5-octafluoro-1-pentanol (F-pentanol) as cosurfactant.

Carbon dioxide-expanded liquid substrate phase: an effective medium for selective hydrogenation of cinnamaldehyde to cinnamyl alcohol.

It has been shown that CO(2)-expanded cinnamaldehyde liquid phase is a unique and effective medium for cinnamaldehyde hydrogenation to cinnamyl alcohol, due to interactions between the C[double bond, length as m-dash]O group of the substrate and CO(2) molecules and increased solubility of H(2).

Heck coupling reaction of iodobenzene and styrene using supercritical water in the absence of a catalyst.

Heck coupling reaction of iodobenzene and styrene proceeds rapidly and selectively in supercritical water even without any catalyst in the presence of base. Both the choice of base and the reaction conditions had a significant effect on the conversion and the selectivity of the coupling products. The addition of a relatively mild base such as potassium acetate facilitated the cross-coupling reaction, while the hydrolysis of phenyl halide was favored in the presence of a strong base.

Control of self-aldol condensation by pressure manipulation under compressed CO2.

Under supercritical CO2 conditions, simple adjustment of the pressure was found to successfully control the ratio of aldol to enal product in the self-aldol condensation of aldehyde, in which the enal product was obtained in a maximum selectivity of 94% at the critical pressure of 12MPa, whereas 85% selectivity to the aldol product was achieved at the subcritical region.

A rapid and effective synthesis of propylene carbonate using a supercritical CO2-ionic liquid system.

The synthesis of propylene carbonate from propylene oxide and carbon dioxide under supercritical conditions in the presence of 1-octyl-3-methylimidazolium tetrafluoroborate was achieved in nearly 100% yield and 100% selectivity within 5 minutes, whose TOF value is 77 times larger than those so far reported.

Innovation in a chemical reaction process using a supercritical water microreaction system: environmentally friendly production of epsilon-caprolactam.

Our microreaction system using supercritical water solutions achieves nearly 100% yield and 100% selectivity for epsilon-caprolactam production at reaction times shorter than 1 s.