Oxidation of Alcohols with Molecular Oxygen on Solid Catalysts

Supported gold nanoparticles for aerobic, solventless oxidation of allylic alcohols

After giving some general considerations about the specific properties of nanoparticles below 20 nm, procedures for size stabilization, and the importance of developing green alcohol oxidation reactions, catalytic data are presented showing that gold nanoparticles (3-7 nm) supported on nanoparticulated ceria (4 nm) are far more chemoselective than related palladium catalysts for the aerobic oxidation of allylic alcohols. Using palladium catalysts, in addition to minor oxidation of the alcohol functional group, we have also observed polymerization, 1-2 hydrogen shift, and hydrogenation. In contrast, ceria-supported gold nanoparticles exhibit a remarkable chemoselectivity (in many cases, almost complete) to the alcohol oxidation.

Chiral crystallization of glutamic acid on self assembled films of cysteine

In this article, we describe the preparation and use of chiral surfaces derived from enantiomerically pure crystals of amino acids. For this purpose, we chose to employ a self-assembly process to grow nanoscale chiral films of (+)-L or (-)-D cysteine, onto gold surfaces. We utilized those chiral films as resolving auxiliaries in the crystallization of enantiomers from solutions. To demonstrate the chiral discriminating ability of the chiral surfaces in crystallization processes, we investigated the crystallization of rac-glutamic acid onto the chiral films. Our study demonstrates the potential application of chiral films to control chirality throughout crystallization, where one enantiomer crystallizes on the chiral surfaces with relatively high enantiomeric excess. In addition, crystallization of pure glutamic acid enantiomers, and its racemic compound on to chiral films resulted in crystal morphology modification with preferred crystal orientation, which assists in the interpretation of the ability of our chiral surfaces to function as chiral selectors.

Solvent effect on CO oxidation as a novel diagnosing tool to pin down low-coverage CO at the liquid–solid interface: An in situ infrared study

In situ probing of liquid-solid interfaces is important for understanding heterogeneous liquid-phase catalysis and other interfacial phenomena, but the spectroscopic interference from the bulk is often a problem. Some organics may have infrared features overlapping the adsorbed CO peaks, making the determination of adsorbed CO difficult. In this study, CCl4-flushing was used as a novel diagnosing tool to pin down the low-coverage CO derived from decarbonylation of organics. This diagnosing tool was designed based on our in situ reflection-absorption infrared spectroscopy results reported here that there is a marked solvent effect (water > ethanol > methanol > cyclohexane > benzene approximately carbon tetrachloride) on CO oxidation at the liquid-solid interface. Possible reasons for that solvent effect were discussed.

Discrimination of Active Palladium Sites in Catalytic Liquid-Phase Oxidation of Benzyl Alcohol

Knowledge of the structure of active sites is a prerequisite for the rational design of solid catalysts. Using site-selective blocking by CO and isotope labeling combined with in situ attenuated total reflection infrared (ATR-IR) spectroscopy, we were able to discriminate the different sites involved in the liquid-phase oxidation of benzyl alcohol on Pd/Al(2)O(3). The main reaction, that is, the oxidative dehydrogenation of the alcohol to the corresponding aldehyde, showed only little dependence on structure and occurred on all exposed Pd faces, whereas the undesired product decarbonylation occurred preferentially on hollow sites on (111) Pd faces. This explains why specific blocking of the latter sites, as realized in the industrially used Pd-Bi/Al(2)O(3) catalysts, leads to improved catalytic performance.

Synthetic Scope of Alcohol Transfer Dehydrogenation Catalyzed by Cu/Al2O3: A New Metallic Catalyst with Unusual Selectivity

A method for the anaerobic oxidation of a wide series of alcohols including cyclohexanols and steroidal alcohols, has been set up. It relies on a transfer dehydrogenation reaction from the substrate alcohol to styrene catalyzed by a heterogeneous, reusable copper catalyst under very mild liquid-phase experimental conditions (90 degrees C, N(2)) and shows unusual selectivity. Thus, the method is selective for the oxidation of secondary and allylic alcohols even in the presence of unprotected primary and benzylic alcohols. Electronic effects and the choice of the hydrogen acceptor account for the selectivity observed.

Bis(bismuth)toluene Inverted-Sandwich Complex Supported by Aminetris(phenoxide) Ligands

The reaction of bismuth amides or alkoxides with phenolic ligand precursors yields Bi complexes of aminetris(phenoxide)s, one of which was characterized by X-ray crystallography, revealing monomeric Bi units of the tetradentate NO3 ligand further associated via a symmetrical toluene bridge into a bis(bismuth)toluene inverted-sandwich complex. Synthesis of the analogous Sb complex suggests a markedly different geometric and electronic environment at the metal center, as evidenced by the solid-state molecular structure. Density functional theory calculations of the sandwich bismuth arene complex indicate the presence of a weak sigma*-2pi interaction.

Unique gold chemoselectivity for the aerobic oxidation of allylic alcohols

Gold nanoparticles supported on nanocrystalline ceria has been found to be more active and chemoselective than palladium and gold(core)-palladium(shell) nanoparticles for the aerobic oxidation of allylic alcohols.

In Situ Extended X-ray Absorption Fine Structure Study during Selective Alcohol Oxidation over Pd/Al2O3 in Supercritical Carbon Dioxide

High-pressure in situ X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) data are reported during the selective oxidation of benzyl alcohol to benzaldehyde in supercritical carbon dioxide over a Pd/Al(2)O(3) catalyst (shell impregnated). For this purpose, a continuous-flow system with a spectroscopic cell suitable for in situ X-ray absorption studies on heterogeneous catalysts up to 200 degrees C and 200 bar has been developed. Due to the high contribution of the dense fluid to the overall X-ray absorption, high stability of the process pressure is mandatory, particularly when recording EXAFS spectra. According to EXAFS and XANES results, the palladium particles were fully reduced after exposure to benzyl alcohol in scCO(2). In contrast to Pd-catalyzed liquid-phase oxidation, a higher oxygen tolerance of the catalyst was observed. Palladium was partially oxidized on the surface under typical reaction conditions (0.9 mol % benzyl alcohol/0.5 mol % O(2) in carbon dioxide), which gradually increased when the concentration of oxygen in the feed was raised. Both XANES and EXAFS data uncovered that palladium is mainly oxidized on the surface or within the outermost layers. These results are in accordance with simulations of the XANES data using the FEFF8.20 code (program for ab initio calculations on multiple scattering XAS) and EXAFS data fitting/simulation.

A Solid-Phase Self-Organized Catalyst of Nanopalladium with Main-Chain Viologen Polymers: α-Alkylation of Ketones with Primary Alcohols

[reaction: see text] A novel solid-phase self-organized catalyst of palladium nanoparticles was prepared from PdCl(2) with main-chain viologen polymers via complexation and reduction. This insoluble nanocatalyst nano-Pd-V efficiently promoted alpha-alkylation of ketones with primary alcohols in the presence of Ba(OH)(2).H(2)O under atmospheric conditions without organic solvents. The nano-Pd-V catalyst was reused without loss of catalytic activity.

Solvent-free selective photocatalytic oxidation of benzyl alcohol to benzaldehyde by molecular oxygen using 9-phenyl-10-methylacridinium

9-Phenyl-10-methylacridium ion acts as an effective photocatalyst for solvent free selective photocatalytic oxidation of benzyl alcohol to benzaldehyde under visible light irradiation via efficient photoinduced electron transfer from benzyl alcohol to the singlet excited state of the acridinium ion.

Water-soluble diruthenium complexes bearing acetate and carbonate bridges: highly efficient catalysts for aerobic oxidation of alcohols in water

The aerobic oxidation of alcohols in water can be performed efficiently in the presence of a catalytic amount of the water-soluble diruthenium complex Ru2(micro-OAc)3(micro-CO3) under an atmospheric pressure (1 atm) of O2.

The 3D quadrupole ion trap mass spectrometer as a complete chemical laboratory for fundamental gas-phase studies of metal mediated chemistry

Electrospray ionization provides a "treasure trove" of metal containing ions whose fundamental reactivity can be studied via collision induced dissociation and ion-molecule reactions using the multistage mass spectrometry capabilities of the quadrupole ion trap mass spectrometer. Examples of metal mediated chemistry relevant to catalysis, C-C bond coupling, bioinorganic and supramolecular chemistry are highlighted.

Highly Selective Aerobic Oxidation of Alcohol Catalyzed by a Gold(I) Complex with an Anionic Ligand

Highly selective aerobic oxidation of alcohols to carbonyl compounds was catalyzed by a gold(I) complex with an anionic ligand in solution.

Highly Active, Immobilized Ruthenium Catalysts for Oxidation of Alcohols to Aldehydes and Ketones. Preparation and Use in Both Batch and Flow Systems

A novel, highly active immobilized ruthenium catalyst, which can be successfully used in oxidation of alcohols to aldehydes and ketones, has been developed. In contrast to most immobilized catalysts, the Ru catalyst has activity that is higher than that of the original non-immobilized catalyst. In a batch system, the Ru catalyst was recovered and reused several times without loss of activity. The catalyst was also applied to a flow system, in which excellent conversions and yields were demonstrated. No leaching of Ru was observed in both cases.