Gold, alkene oxidation

Alkene Oxidation over Copper, Silver, and Gold Catalysts... 

The selectivity of palladium and gold for alkene oxidation to aldehydes 28,29,170) was attributed initially to adsorption strength. However, electrooxidation in the presence of palladium ions indicates possible homogeneous alkene insertion, similar to the Wacker process 304). Homogeneous reaction is also involved in redox oxidations of hydrocarbons. In this case, the nature of the metal ions is expected to control selectivity. Indeed, toluene yields 20% benzaldehyde in electrolytes containing Ce salts, while oxidation proceeds to benzoic acid with Cr redox catalysts 311). In addition, the concentration of redox catalysts appears to affect yields in nonelectrochemical oxidation of ethylene large amounts of palladium chloride promote butene formation at the expense of acetaldehyde 312). Finally, the role of the electrolyte and solvent should not be ignored. For instance, electrooxidation of ethylene on carbon, in aqueous solution of acetic acid yields acetaldehyde 313) in the... 

It is well established that ultrasmall metal clusters on supports have catalytic properties distinct from those properties of large bulk-like particles, as illustrated by the selective oxidation of propylene to propylene oxide by gold, alkene and arene hydrogenation catalysis,and CO oxidation. In these examples, the catalytic properties improve as the clusters become smaller. On the other hand, a reduction in size of the metal cluster can lead to less desirable catalytic properties as seen for ammonia synthesis on iron. Various explanations have been offered to account for the unique properties of nanoscaled metal catalysts, however, much remains to be understood. Clearly, experimental and theoretical studies will be required to develop an in-depth under-... 

The Haruta s discovery that nanosized gold particales adsorbed on metal-oxide powders facilitate a wide class of reactions under near-ambient conditions has attracted a worldwide interest [1]. It is known that gold is very inert in bulk phase. However, small gold clusters possess high reactivity in selective methane and alkenes oxidation and hydrogenation of linear alkenes [2]. So, gold nanoparticles have been found to be active catalysts for many reactions of industrial and environmental interest. 

Other researchers [69, 70] have shown that polymer-immobilized nano-gold particles had unprecedented catalytic activity for activation of carbon dioxide and high turnover frequency (TOF) for the synthesis of cyclic carbonates. Moreover, Xiang et al. [69] have reported a novel and convenient route for the direct synthesis of cyclic carbonates that avoids the preliminary synthesis and isolation of intermediate alkene oxide, coupling the two sequential reactions of epoxidation of alkene and cycloaddition of CO to epoxide into one pot. It is still not clear at this stage about the reaction mechanism. Shi et al. [70] proposed that the activation of... 

Zhang G, Cui L, Wang Y, Zhang L. Homogeneous gold-catalyzed oxidative carboheterofunctionalization of alkenes. 

Despite its apparent noble character, gold catalysts have been recently found to be active in many homogeneous and heterogeneous catalytic processes such as oxidation reactions, nucleophilic additions, cross-coupling reactions, and alkene and imine hydrogenations (69—71). Corma and co-workers showed that Au... 

The first experiments in this area were carried out by Thomas et al. in 1974 [52], inspired by their earlier work on similar reactions from alkynes and cydopro-panes [53]. However, in the case of alkenes a stoichiometric amount of gold was indeed needed for the process gold was an oxidant and not a catalyst. 

It has recently been found that NEt3 is a gas-phase promoter for propene epoxidation by supported gold catalysts [245]. In more recent studies, Hughes et al. reported that catalytic amounts of peroxides could initiate the oxidation of alkenes with 02, without the need for sacrificial H2 [243]. The process worked for a range of substrates (cyclohexene, ds-stilbene, styrene and so on) and even in the absence of solvent hence, we may refer to this as green technology. 

Gold NPs deposited on carbons are active and selective for mild oxidations in liquid phase although they exhibit almost no catalytic activity in the gas phase. Examples are aerobic oxidation of mono-alcohols, diols, glycerol, glucose, alkenes and alkanes. 

About the only catalytic use for silver is in the conversion of ethylene to ethylene oxide by the action of oxygen.42 This reaction is very specific. Other alkenes are oxidized to CO2 and H2O with no epoxide formation observed. Gold is generally inactive as a catalyst for most reactions but it has found some use in catalytic oxidations. 43... 

Thiol monolayers are not removed by solvents, but by sulfur-active chemicals which pass through the surface monolayers. Laser desorption mass spectrometry has shown that thiolate molecules are intact on the gold surface, but through air oxidation, some sulfonates develop. The relative stability of alkanethiol SAMs on gold to air oxidation is to be expected due to the covalent nature of the S—Au bond. Photooxidation via UV excitation of electrons in the metal surface is, however, possible and leads to sulfonate salts which have again been characterized by mass spectrometry as well as by XPS . Alkene-thiolate monolayers can best be desorbed from gold by a one-electron reductive path. Stable monolayers on gold were also obtained with benzenesulfinate. 

Vajda S, Ballentine GE, Mucherie S, Marshall CL, Elam JW, Pellin MJ, Lee B, Lo CT, Seifert S, Winans RE, Calo JM (2007) Highly selective oxidation reactions Oxidative dehydrogenation of propane (ODHP) by size-selected platinum catalysts and oxidation of alkenes on size-selected silver and gold clusters and nanoparticles. Am Chem Soc Div Petrol Chem 52... 

Key Words Direct propylene epoxidation. Propylene oxide, Gold, Titanium, Propene, Au/Ti catalysts. Catalysis by gold. Titanium silicalite, TS-1, Gold/TS-1, Hydrogen peroxide, Kinetics, Design of experiments, Deposition-precipitation, Ammonium nitrate, Selective oxidation, Alkene epoxidation, Density functional theory, DFT calculations, QM/MM calculations. 2008 Elsevier B.v. 

Besides organocatalysts, metal complexes show catalytic activities in various types of [3+2]cycloaddition. Thus Ru complex 140 performs a role in the reaction of nitrile oxides with enals, and gold(l) benzoate complex of Cy-SEGPHOS is involved in the reaction of miinchnones with alkenes. "... 

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