Catalytic Aerobic Oxidation Research Articles

Trinuclear Pd3O2 Intermediate in Aerobic Oxidation Catalysis

AbstractThe activation of O2 is a key step in selective catalytic aerobic oxidation reactions mediated by transition metals. The bridging trinuclear palladium species, [(LPdII)3(μ3‐O)2]2+ (L=2,9‐dimethylphenanthroline), was identified during the [LPd(OAc)]2(OTf)2‐catalyzed aerobic oxidation of 1,2‐propanediol. Independent synthesis, structural characterization, and catalytic studies of the trinuclear compound show that it is a product of oxygen activation by reduced palladium species and is a competent intermediate in the catalytic aerobic oxidation of alcohols. The formation and catalytic activity of the trinuclear Pd3O2 species illuminates a multinuclear pathway for aerobic oxidation reactions catalyzed by Pd complexes.

Biobased Terephthalic Acid Technologies: A Literature Review

Abstract Terephthalic acid (TPA) is a large-volume commodity chemical typically produced via aerobic catalytic oxidation of para-xylene (pX), which is produced from fossil resources. TPA is used primarily as a co-monomer in a condensation with mono ethylene glycol (MEG) to produce polyethylene terephthalate (PET) for plastic containers, fibers, films, and other applications. Condensations of TPA with other glycols produce other polyesters. There is strong interest in improving the environmental profile of TPA, either by improving the environmental aspects of the pX oxidation process and/or producing TPA from renewable resources (biobased TPA) such as carbohydrates, lignin, etc. Currently, biobased PET contains up to 30% biobased materials; the Coca-Cola Company's PlantBottle™ PET, introduced in 2009, is produced using biobased MEG only. Biobased TPA will allow for increasing the biobased content of PET to 100%. Industry and academia are working to develop technology pathways to biobased TPA. For example, ...

Merging Aerobic Oxidation and Enamine Catalysis in the Asymmetric α‐Amination of β‐Ketocarbonyls Using N‐Hydroxycarbamates as Nitrogen Sources

AbstractWe describe herein an unprecedented asymmetric α‐amination of β‐ketocarbonyls under aerobic conditions. The process is enabled by a simple chiral primary amine through the coupling of a catalytic enamine ester intermediate and a nitrosocarbonyl (generated in situ) derived from N‐hydroxycarbamate. The reaction features high chemoselectivity and excellent enantioselectivity for a broad range of substrates.

Merging Aerobic Oxidation and Enamine Catalysis in the Asymmetric α‐Amination of β‐Ketocarbonyls Using N‐Hydroxycarbamates as Nitrogen Sources

We describe herein an unprecedented asymmetric α-amination of β-ketocarbonyls under aerobic conditions. The process is enabled by a simple chiral primary amine through the coupling of a catalytic enamine ester intermediate and a nitrosocarbonyl (generated in situ) derived from N-hydroxycarbamate. The reaction features high chemoselectivity and excellent enantioselectivity for a broad range of substrates.

Novel metal oxide nanocomposite of Au/CuO–ZnO for recyclable catalytic aerobic oxidation of alcohols in water

CuO–ZnO supported gold nanoparticle is introduced as a new, efficient, and recyclable catalyst for the aerobic oxidation of alcohols. The CuO–ZnO support was prepared by co-precipitation and Au nanoparticles were loaded on support by a deposition–precipitation method. The catalyst was characterized by XRD, BET surface area, FESEM, EDS and HRTEM techniques. A wide range of alcohols, including benzylic, primary and secondary alcohols are converted into the corresponding carbonyl derivatives. The experimental procedure with Au/CuO–ZnO catalyst is quite straightforward and the catalyst is recyclable up to 6 consecutive runs by simple filtration.

Efficient catalytic aerobic oxidation of chlorinated phenols with mixed-valent manganese oxide nanoparticles

BACKGROUNDMixed-valence manganese oxide nanoparticles (nano-MnOx) were prepared by the oxidation of Mn (II) with Mn-oxdizing bacteria Pseudomonas sp. G7. The chlorophenols transformation process was studied in detail. RESULTSThe materials were characterized by XRD, TEM-EDX, and XPS measurements. The characterization showed that mixed valence of Mn (II), Mn (III), and Mn (IV) existed in nano-MnOx-1 with the initial Mn (II) dosage of 0.4 mmol L-1. The catalyst was found to be highly effective, stable for catalytic aerobic oxidation of chlorophenols without any Mn (II) release from the catalyst throughout the reaction. Moreover, chlorinated phenols including 2-chlorophenol, 2, 4-dichlorophenol and 2, 4, 6-trichlorophenol, were partly converted into small organic acids. The formation of superoxide radicals (O-2(center dot-)) predominantly came from the interaction of oxygen in air with the reduced manganese in nano-MnOx on the basis of the studies of electron spin resonance and all other information. CONCLUSIONThe mixed valence in nano-MnOx-1 enhanced the formation of O-2(center dot-), resulting in the inhibition of Mn (II) release, maintaining the catalyst stable. Degradation of the tested chlorinated phenols was ascribed to the oxidation of Mn (III/IV) and O-2(center dot-) in nano-MnOx-1 suspension. This finding indicates the potential of nano-MnOx for the elimination of unbiodegradable chemicals in water. (c) 2013 Society of Chemical Industry

Aerobic oxidation catalysis with stable radicals

Selective oxidation reactions are challenging when carried out on an industrial scale. Many traditional methods are undesirable from an environmental or safety point of view. There is a need to develop sustainable catalytic approaches that use molecular oxygen as the terminal oxidant. This review will discuss the use of stable radicals (primarily nitroxyl radicals) in aerobic oxidation catalysis. We will discuss the important advances that have occurred in recent years, highlighting the catalytic performance, mechanistic insights and the expanding synthetic utility of these catalytic systems.

Catalytic aerobic oxidation of renewable furfural to maleic anhydride and furanone derivatives with their mechanistic studies

Using heteropolyacid and copper(ii) as catalysts, renewable furfural has been successfully transformed to maleic anhydride and biologically important 5-acetoxyl-2(5H)-furfuran.

Correction: Catalytic aerobic oxidation of renewable furfural to maleic anhydride and furanone derivatives with their mechanistic studies

Correction: Catalytic aerobic oxidation of renewable furfural to maleic anhydride and furanone derivatives with their mechanistic studies

Continuous gas–liquid aerobic oxidation of toluene catalyzed by [T(p-Cl)PPFe]2O in a series of three stirred tank reactors

The liquid-phase catalytic aerobic oxidation of toluene by [T(p-Cl)PPFe]2O was studied in a series of three stirred tank reactors. The effects of operation mode (including semi-batch and continuous operation), reaction temperature, catalyst concentration, average residence time, and air flow rate on the oxidation process were examined. The experimental results showed that continuous oxidation had no advantage over the total yield and selectivity of benzaldehyde and benzyl alcohol in comparison with semi-batch oxidation. And the reaction temperature was the most significant factor influencing on continuous oxidation of toluene. It is also found that adopting sequentially decreased temperature in the three series reactors could improve the yield and selectivity of benzaldehyde and benzyl alcohol in this process. Under which at the higher conversion of toluene, the total yield to benzaldehyde and benzyl alcohol increased 17.05% or 43.62% respectively in comparison with adopting sequentially increased or same temperature in the three series reactors.

Hierarchically Ordered Nanoporous Pd/SBA-15 Catalyst for the Aerobic Selective Oxidation of Sterically Challenging Allylic Alcohols

The utility of a hierarchically ordered nanoporous SBA-15 architecture, comprising 270 nm macropores and 5 nm mesopores (MM-SBA-15), for the catalytic aerobic selective oxidation of sterically challenging allylic alcohols is shown. Detailed bulk and surface characterization reveals that incorporation of complementary macropores into mesoporous SBA-15 enhances the dispersion of sub 2 nm Pd nanoparticles and thus their degree of surface oxidation. Kinetic profiling reveals a relationship between nanoparticle dispersion and oxidation rate, identifying surface PdO as the catalytically active phase. Hierarchical nanoporous Pd/MM-SBA-15 outperforms mesoporous analogues in allylic alcohol selective oxidation by (i) stabilizing PdO nanoparticles and (ii) dramatically improving in-pore diffusion and access to active sites by sesquiterpenoid substrates such as farnesol and phytol.

ChemInform Abstract: Highly trans‐Stereoselective Synthesis of Bicyclic Isoxazolidines via Copper‐Catalyzed Triple Cascade Catalysis.

A triple cascade was developed using a simple copper catalyst to trans-selectively access bicyclic isoxazolidines in a one-pot synthesis. This strategy features the in situ generation of nitrones and subsequent trapping by [3 + 2] cycloaddition. In this method, copper serves three catalytic functions: as a Lewis acid for the ene reaction, as an organometallic for aerobic oxidation, and as a Lewis acid for an endo-selective [3 + 2] cycloaddition. The successful merging of aerobic oxidation and Lewis acid catalysis demonstrated efficient cascade synergy.

Solvent Effect and Reactivity Trend in the Aerobic Oxidation of 1,3‐Propanediols over Gold Supported on Titania: NMR Diffusion and Relaxation Studies

In recent work, it was reported that changes in solvent composition, precisely the addition of water, significantly inhibits the catalytic activity of Au/TiO2 catalyst in the aerobic oxidation of 1,4-butanediol in methanol due to changes in diffusion and adsorption properties of the reactant. In order to understand whether the inhibition mechanism of water on diol oxidation in methanol is generally valid, the solvent effect on the aerobic catalytic oxidation of 1,3-propanediol and its two methyl-substituted homologues, 2-methyl-1,3-propanediol and 2,2-dimethyl-1,3-propanediol, over a Au/TiO2 catalyst has been studied here using conventional catalytic reaction monitoring in combination with pulsed-field gradient nuclear magnetic resonance (PFG-NMR) diffusion and NMR relaxation time measurements. Diol conversion is significantly lower when water is present in the initial diol/methanol mixture. A reactivity trend within the group of diols was also observed. Combined NMR diffusion and relaxation time measurements suggest that molecular diffusion and, in particular, the relative strength of diol adsorption, are important factors in determining the conversion. These results highlight NMR diffusion and relaxation techniques as novel, non-invasive characterisation tools for catalytic materials, which complement conventional reaction data.

ChemInform Abstract: Selective Catalytic Oxidation of C—H Bonds with Molecular Oxygen

AbstractReview: recent advances in aerobic oxidation catalysis; 284 refs.

Highly trans-Stereoselective Synthesis of Bicyclic Isoxazolidines via Copper-Catalyzed Triple Cascade Catalysis

A triple cascade was developed using a simple copper catalyst to trans-selectively access bicyclic isoxazolidines in a one-pot synthesis. This strategy features the in situ generation of nitrones and subsequent trapping by [3 + 2] cycloaddition. In this method, copper serves three catalytic functions: as a Lewis acid for the ene reaction, as an organometallic for aerobic oxidation, and as a Lewis acid for an endo-selective [3 + 2] cycloaddition. The successful merging of aerobic oxidation and Lewis acid catalysis demonstrated efficient cascade synergy.

Complementary mechanistic properties of Fe- and Mn-doped aluminophosphates in the catalytic aerobic oxidation of hydrocarbons

A comparative computational study of the reaction mechanisms for hydrocarbon oxidations catalysed by Mn- and Fe-doped nanoporous aluminophosphates shows distinctive features for each transition metal depending on its electronic configuration. Preactivation of Mn catalysts is easier due to the higher stability of Mn(II), but its oxidation during propagation requires activation barriers. In contrast, preactivation of Fe is more difficult and avoids a direct Fe reduction because of the low stability of Fe(II). Fe(II) is only produced at the end of the propagation cycle, favoured by an energetic compensation caused by the simultaneous exothermic oxidation of an alcohol molecule. Fe-catalysed propagation is kinetically favoured since it requires lower activation barriers, and is further assisted by higher adsorption energies of the reactants and lower desorption energies of the products on the active site. The mechanistic information gained can be used for the rational design of improved oxidation catalysts.

Catalytic oxidation of rare sugars over gold catalysts

This minireview presents an overview on the recent developments for the heterogeneous catalytic aerobic oxidation of rare sugars over supported gold catalysts. The selective oxidation of several rare sugars; L-arabinose, D-galactose and D-lactose representing pentoses, hexoses and disaccharides, respectively, is reviewed. The critical evaluation of the aerobic oxidation of the different sugars presents a great opportunity to understand the fundamentals of the surprising reactivity and extraordinary properties of gold. This in turn can open up the possibilities for industrial exploitation of sustainable and green processes. Emphasis was put on catalysis, kinetics and mechanistic studies based on understanding of the fundamental reaction engineering.

Electrophilic α-Amination Reaction of β-Ketoesters Using N-Hydroxycarbamates: Merging Aerobic Oxidation and Lewis Acid Catalysis

The copper-catalyzed α-amination of carbonyl compounds using nitrosoformate intermediates as the electrophilic source of nitrogen is reported. The reaction merges aerobic oxidation and Lewis acid catalysis. The scope of the reaction is broad in terms of both the N-substituted hydroxylamines and the β-ketoesters. The new methodology harnesses the power of nitrosoformate intermediates and demonstrates their potential as a viable electrophilic source of nitrogen in α-functionalization reactions.

Synthesis and Characterization of Copper Complexes of a Tetrapyridyl Ligand, and Their Use in the Catalytic Aerobic Oxidation of Benzyl Alcohol

AbstractThe synthesis and characterization of new copper complexes of the tetrapyridyl ligand N,N′‐di(pyridin‐2‐yl)‐2,2′‐bipyridine‐6,6′‐diamine (bapbpy) is reported. The crystal structures of the compounds [Cu(bapbpy)(H2O)]Cl2·H2O (1), [Cu(bapbpy)(H2O)]Br2·H2O (2) and [Cu(bapbpy)(H2O)](NO3)2·H2O (3) have been elucidated and show the copper(II) ions to be in a distorted square‐pyramidal geometry with the tetradentate ligand in the equatorial plane. Conductivity measurements on 1 revealed that it is fully ionized in methanol, i.e., the chloride ions are not coordinated to copper(II) in methanolic solutions. The room temperature electron paramagnetic resonance (EPR) spectra of methanol solutions of the complexes show a copper signal with a giso value of 2.110; it shows hyperfine splitting into four lines (ACu = 77 G) and superhyperfine splitting into nine lines (AN = 12 G) owing to the interaction with the nuclear spin of the four nitrogen donor atoms of the bapbpy ligand. The catalytic activity of 1, 2 and 3 in the aerobic homogeneous oxidation of benzyl alcohol in presence of the TEMPO radical [(2,2,6,6‐tetramethylpiperidin‐1‐yl)oxidanyl] was investigated. Benzaldehyde is obtained selectively and the production of benzoic acid is not observed during 24 h of reaction. EPR analyses, carried out under stoichiometric conditions, show that the TEMPO radical does not interact with the copper centre. These data suggest that oxidation of the substrate may occur in the second coordination sphere of the copper complex.

Selective Catalytic Oxidation of CH Bonds with Molecular Oxygen

AbstractAlthough catalytic reductions, cross‐couplings, metathesis, and oxidation of CC double bonds are well established, the corresponding catalytic hydroxylations of CH bonds in alkanes, arenes, or benzylic (allylic) positions, particularly with O2, the cheapest, “greenest”, and most abundant oxidant, are severely lacking. Certainly, some promising examples in homogenous and heterogenous catalysis exist, as well as enzymes that can perform catalytic aerobic oxidations on various substrates, but these have never achieved an industrial‐scale, owing to a low space‐time‐yield and poor stability. This review illustrates recent advances in aerobic oxidation catalysis by discussing selected examples, and aims to stimulate further exciting work in this area. Theoretical work on catalyst precursors, resting states, and elementary steps, as well as model reactions complemented by spectroscopic studies provide detailed insight into the molecular mechanisms of oxidation catalyses and pave the way for preparative applications. However, O2 also poses a safety hazard, especially when used for large scale reactions, therefore sophisticated methodologies have been developed to minimize these risks and to allow convenient transfer onto industrial scale.