Gold catalysis oxidation

Weyrauch, J.P., Wolfe, M., Prey, W. and Bats, J.W. (2005) Gold catalysis proof of arene oxides as intermediates in the phenol synthesis. Angewandte Chemie International Edition, 44, 2798. 

Metal oxides of variable oxidation state as supports or support modifiers [202] are well known in gold catalysis. In the previous section we have already indicated some metal-support interactions influencing the electronic state of gold nanoparticles as well as the metallic or ionic state of gold. Of the numerous literatures we have to mention Haruta and Date [169], Bond [195], as well as Goodman works [186,203]. Further results can be found on the iron oxide system in recent literatures [162,204]. 

In the catalysis community, there is considerable interest in the catalytic properties of oxide-supported nanocrystalline gold, which has been found to be remarkably active for the oxidation of CO [Hamta, 1997]. In electrochemistry, the ability of gold to oxidize CO, in the absence of an oxide support, has been known for many years [Roberts and Sawyer, 1964],... 

Tertiary N-butynylamine 48 when oxidized generates an N-oxide intermediate that is cyclized in situ via gold catalysis to give bicyclic piperidone 49 (09JA8394). As amine 48 can be prepared readily, the overall transformation constitutes a formal [4+2] synthesis. 

The oxidation of propene to propene oxide is considered an essential practice in industrial chemistry [1]. Haruta et al. showed that this process can be led by heterogeneous catalysis with gold supported over titania [15, 16]. Another goal in the gold catalysis sequence is the selective oxidation of some alcohols and carbohydrates with molecular oxygen, as studied by Prati and Rossi [17]. 

Hydrochlorination of Alkynes When Thomas and coworkers treated different alkynes in aqueous methanol with HAuC14 and observed the corresponding ketones as major products (Equation 8.28), with less than 5% of methyl vinyl ethers and vinyl chlorides, they were unaware of the fascinating treasure that was in front of them. Some of the most important types of products for gold catalysis were reported in the aforementioned study, but unfortunately at that time this process was believed to be a gold(III) oxidation process, despite the fact that the reaction achieved almost six turnovers. 

Figure 3.1 Four important conditions for catalysis by gold (metal-oxide junction, water, OH- and size of the Au particles or tubes). The figure by each circle is the diameter (nm) of the gold particles or tubes. Gold turns out to be catalytically very active, provided that at least two of the four conditions are fulfilled. For example, in CO oxidation at room temperature even unsupported gold is active in the presence of alkaline (OH-) water (H20).

Ivanova, S., Petit, C., and Pitchon, V. Application of heterogeneous gold catalysis with increased durabilitiy Oxidation of CO hydrocarbons at low temperature. Gold Bulletin, 2006, 39, 3. 

In recent years, the unexpected observation of highly active Au as a low temperature CO oxidation catalyst59,60 has initiated extensive research activity into the use of supported gold for liquid phase oxidation reactions. In general, the adsorption characteristics and catalytic properties of Au depend crucially on particle size, which can be controlled by the preparation method and the support.61-66 The crucial question involving gold catalysis, which as yet has not been fully answered, is the concept of why Au nanoparticles exhibit such radically different behaviour than bulk Au.67-70... 

B. Chen, C. Bai, R. Cook, J. Wright, C. Wang. Gold/cobalt oxide catalysts for oxidative destruction of dichloromethane. Catalysis Today, 30 15-20,1996. 

For instance, the determination of the precise stoichiometry of glucose oxidation by gold catalysis has highlighted the two-electron reduction of oxygen to hydrogen peroxide, according to Eq. (21.1) [8] ... 

The analytical data show that gold catalysis and enzymatic catalysis allow fast and selective aerobic oxidation of glucose according to the same stoichiometry characterized by the formation of hydrogen peroxide as the by-product (Eq. (21.1)) [8]. However, it is not surprising that completely different catalytic systems adopt different reaction mechanisms as shown by the kinetic studies on commercial enzymatic preparations containing /wcose oxidase and catalase [13]. The results of the research support a Michaelis-Menten type mechanism where the kinetic... 

For industrial applications, metal catalysts should be repeatedly recycled or used in continuous mode for a long time. The introduction of gold catalysis in the aerobic oxidation of glucose has opened exciting perspectives Au is a biocompatible, nontoxic metal, which allows even superior productivities with respect to enzymatic catalysis [38], and no leaching problems have been observed using nanometric particles dispersed on different supports [43]. Compared with chemical oxidations, enzymatic catalysis suffers from more plant complexities... 

One of the most problematic questions in heterogeneous catalysis is the cooperative effect of different phases present in a given catalytic system and, in particular, the so-called metal-support interaction [15]. In the case of gold catalysis, interaction of the metal with an oxidic support seems to be of fundamental importance in determining the extraordinary reactivity observed during the low temperature oxidation of CO [14]. 

No doubt exists that gold catalysis for glucose oxidation is one of the most appeaUng goals. A promising future for this new technology, mainly due to better productivity than with enzymatic catalysis, can be predicted (Scheme 13.10). 

Kwon Y, Lai SCS, Rodriguez P, Koper MTM (2011) Electrocatalytic oxidation of alcohols on gold in alkaline media base or gold catalysis J Am Chem Soc 133 6914-6917... 

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