Polyoxometalate compound: a highly efficient heterogeneous catalyst for aerobic alcohol oxidation

Oxidation of alcohols to aldehydes and ketones has been studied using atmospheric oxygen and a catalytic amount of Na_6.3Fe_0.9[AlMo₁₁O₃₉]·2H₂O in toluene under heating (80 or 110 °C) in high yields. Secondary alcohols can be chemoselectively converted into ketones in the presence of primary hydroxyl groups.     

Highly efficient, organocatalytic aerobic alcohol oxidation

5-Fluoro-2-azaadamantane N-oxyl (5-F-AZADO) realizes a simple, organocatalytic aerobic alcohol oxidation system that has a wide scope under mild conditions at ambient pressure and temperature and is weakly acidic and halogen- and transition-metal-free. The oxoammonium nitrate (5-F-AZADO(+)NO(3)(-)) works as a bifunctional catalyst of 5-F-AZADO and NO(x) that enables the catalytic aerobic oxidation of alcohols by itself (a metal-salt-free system).     

高效多羟胺有机催化剂选择性催化分子氧氧化研究进展

基于氧气(空气)为氧源的选择性催化分子氧氧化技术在制备含氧精细化学品或食品添加剂与医药等的重要中间体方面一直受到科学界的广泛关注.由于碳氢化合物中碳氢键的反应惰性和分子氧的自旋禁阻作用,设计与开发高效催化剂或催化体系以实现碳氢化合物的选择性氧化是当前催化氧化领域的研究热点.在已发展的过渡金属盐、仿生催化剂、有机催化剂、酶、碳材料和卤化物等众多催化剂中,以N-羟基邻苯二甲酰亚胺(NHPI)为代表的羟胺有机催化剂由于在温和条件下的卓越催化性能而备受瞩目.尽管基于羟胺有机催化剂的催化体系具有良好的工业应用前景,但仍存在催化剂高温易分解、使用量较大和可回收性较差等缺点.近年来,许多实验与理论工作围绕改进这些缺点展开,设计了一系列羟胺有机催化剂及其协同催化体系,如在NHPI结构中修饰疏水链基团、吸电子基团、N-烷氧基团和离子液体,或固载金属-有机框架材料、无机物和聚合物,或组合光催化剂.尽管已有大量综述总结了相关研究进展,但尚未见到有关近年来发展的多羟胺有机催化剂及其高效催化氧化性能的综述报道.本文综述了近15年来多羟胺有机催化剂选择性催化分子氧氧化碳氢化合物的研究进展.首先,简要概述了N,N-二羟基邻苯二甲酰亚胺(NDHPI)和N,N',N"-三羟基异氰基尿酸(THICA)两种多羟胺有机催化剂的合成方法,系统介绍了它们在各类碳氢化合物氧化中的高效催化性能,并与普遍应用的NHPI的催化性能进行对比.由于NDHPI与THICA具有多羟胺的独特结构,它们只需要比NHPI更少的用量便可获得比NHPI更高的催化氧化效率,可以直接利用高压空气实现对碳氢化合物的选择性催化氧化,并且在较高温度下依然具有较好的催化效果.在此基础上,介绍了联系实验与理论之间的重要工作,总结了多羟胺有机催化剂的合理设计策略.理论计算研究揭示了NDHPI与THICA的催化性能优于NHPI的主要原因是具有类似于吸电子效应的多羟胺与多氮氧自由基结构能显著增强催化剂的夺氢活性.通过对NDHPI结构的进一步修饰和夺氢活性研究,提出了该类催化剂的合理设计策略:在芳环体系中增加共轭的羟胺基团数量,或在NDHPI苯环中掺杂N原子或引入离子对基团都能提高催化剂的夺氢活性;增大芳环共轭体系对催化剂的夺氢活性影响较小,但该活性仍高于NHPI.这也为基于碳材料的非均相共轭多羟胺有机催化剂的开发提供了理论依据.最后,结合羟胺有机催化剂的发展现状和上述设计策略,设计了基于金属卟啉/席夫碱等仿生催化剂、(含离子对结构)聚合物、非均相碳材料和多N-烷氧基团等几种具有潜在发展前景的模型多羟胺有机催化剂,分别讨论了这些催化剂的优点和局限性,并展望了多羟胺有机催化剂的可能应用及其在催化氧化过程中仍需系统研究的方向.     

Size-specific catalytic activity of polymer-stabilized gold nanoclusters for aerobic alcohol oxidation in water

Gold nanoclusters (phi = 1.3 nm) stabilized by poly(N-vinyl-2-pyrrolidone) (Au:PVP NCs) readily oxidize benzylic alcohols to the corresponding aldehydes and/or carboxylic acids under ambient temperature in water. Kinetic measurement revealed that smaller Au:PVP NCs exhibit higher catalytic activity than larger (9.5 nm) homologues and, more surprisingly, than Pd:PVP NCs of comparable size (1.5 and 2.2 nm). On the basis of the marked difference in the kinetic isotope effect and activation energy between Au:PVP and Pd:PVP NCs, a reaction mechanism for alcohol oxidation catalyzed by Au:PVP NCs is proposed in which a superoxo-like molecular oxygen species adsorbed on the surface of the small Au NCs abstracts a hydrogen atom from the alkoxide.     

A highly efficient and recyclable silica-supported palladium catalyst for alcohol oxidation reaction

A silica supported palladium catalyst (SiO₂@APTES-Pd) showed excellent activity and reusability for selective oxidation of alcohols to corresponding carbonyl compounds with H₂O₂ as oxidant under base free environment. A wide range of alcohols including aliphatic alcohols are tolerated as substrates with a low loading of palladium (0.1 mol %).     

Reaction-driven surface restructuring and selectivity control in allylic alcohol catalytic aerobic oxidation over Pd

Synchronous, time-resolved DRIFTS/MS/XAS cycling studies of the vapor-phase selective aerobic oxidation of crotyl alcohol over nanoparticulate Pd have revealed surface oxide as the desired catalytically active phase, with dynamic, reaction-induced Pd redox processes controlling selective versus combustion pathways.     

Rh-catalyzed alkene oxidation: a highly efficient and selective process for preparing N-alkoxysulfonyl aziridines

Unique alkoxysulfonyl aziridine heterocycles were prepared through selective intra- and intermolecular alkene oxidation reactions. These methods are general and perform efficiently at low Rh-catalyst loadings (1-2 mol %) with only a slight excess of an inexpensive commercial oxidant, PhI(OAc)₂. For intermolecular processes, trichloroethylsulfamate was identified as a novel and markedly effective N-atom source, allowing reactions to be conducted with limiting amounts of the olefin substrate. The aziridine products submit to facile, nucleophilic ring opening; these processes are regioselective and can be used to prepare polyfunctionalized amines, including α-aminoketones via the direct addition of Me₂SO.     

Transition-metal-free highly efficient synthesis of 2-pyridones from β-keto amides and ynals

A convenient and efficient annulation reaction was developed, affording 2-pyridones in good to excellent yields. A variety of substituted β-keto amides and ynals were well tolerated, and especially the transformation produced water as only by-product under transition-metal-free conditions. Furthermore, the conjugated enyneamides were achieved from β-cyano amides and ynals in high yields.     

Zeolite-confined Nano-RuO(2): A green,selective, and efficient catalyst for aerobic alcohol oxidation

The development of green, selective, and efficient catalysts, which can aerobically oxidize a variety of alcohols to their corresponding aldehydes and ketones, is of both economic and environmental significance. We report here the synthesis of a novel aerobic oxidation catalyst, a zeolite-confined nanometer-sized RuO(2) (RuO(2)-FAU), by a one-step hydrothermal method. Using the spatial constraints of the rigid zeolitic framework, we sucessfully incorporated RuO(2) nanoparticles (1.3 +/- 0.2 nm) into the supercages of faujasite zeolite. Ru K-edge X-ray absorption fine structure results indicate that the RuO(2) nanoclusters anchored in the zeolite are structurally similar to highly hydrous RuO(2); that is, there is a two-dimensional structure of independent chains, in which RuO(6) octahedra are connected together by two shared oxygen atoms. In our preliminary catalytic studies, we find that the RuO(2) nanoclusters exhibit extraordinarily high activity and selectivity in the aerobic oxidation of alcohols under mild conditions, for example, air and ambient pressure. The physically trapped RuO(2) nanoclusters cannot diffuse out of the relatively narrow channels/pores of the zeolite during the catalytic process, making the catalyst both stable and reusable.     

FluoRuGel: a versatile catalyst for aerobic alcohol oxidation in supercritical carbon dioxide

FluoRuGel--a hybrid fluorinated silica glass doped with TPAP (tetra-n-propylammonium perruthenate)--is a versatile catalyst for the aerobic oxidation of different alcohols in dense phase CO(2) with marked stabilization and activity enhancement of perruthenate upon its confinement in the sol-gel fluorinated silica matrix. A brief competitive analysis shows large potential rewards.     

泡沫铜无溶剂催化氧化苄醇的应用研究

本文报道了在模拟的鼓泡床反应器中,以1-甲基咪唑(NMI)和2,2,6,6-四甲基-1-哌啶基氧基(TEMPO)作为助催化剂,空气泵鼓入空气作为氧源,泡沫铜作为催化剂,室温、无溶剂条件下催化氧化苄醇的应用研究.具体优化条件为:以50 mmol苯甲醇为反应底物,2.5 mmol泡沫铜,0.625 mmol NMI,2.5...     

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.     

A highly selective aerobic oxidation process catalyzed by electron-deficient nitroarenes via single electron transfer processes

A versatile and simple method for aerobic oxidation of various aromatics containing an oxygen-functionalized benzylic carbon is reported. Results from oxidation experiments with methyl aryl ketones, benzaldehydes, benzylic alcohols, and mandelic acid are reported; all provide high yields of the corresponding aromatic carboxylic acids. By means of response surface methodology and mechanistic interpretation it is revealed that the oxidation process operates catalytically using electron-deficient nitroarenes, such as 1,3-dinitrobenzene, 1,2,3-trifluoro-4-nitrobenzene, and 2,4-difluoro-1-nitrobenzene, with molecular oxygen as the terminal oxidant. The reaction is carried out in a basic solution of potassium tert-butoxide in tert-butyl alcohol. Since the terminal oxidant is molecular oxygen and only 5-10 mol % of, e.g., 1,3-dinitrobenzene as catalyst is used, the new method represents an environmentally benign alternative to, for example, the well-known haloform reaction. The method is also a convincing alternative when transition metal free conditions are required.     

Efficient NO equivalent for activation of molecular oxygen and its applications in transition-metal-free catalytic aerobic alcohol oxidation

tert-Butyl nitrite (TBN) was identified as an efficient NO equivalent for the activation of molecular oxygen. The unique property of TBN enabled TEMPO-catalyzed aerobic alcohol oxidation to be performed in high-volume efficiency. Up to a 16,000 turnover number was achieved in this transition-metal-free aerobic catalytic system. Under the optimal reaction conditions, various alcohols were converted into their corresponding carbonyl compounds with TEMPO/HBr/TBN as catalyst. The newly developed method was suitable for the oxidation of solid substrate alcohols with high melting point and/or low solubility under the help of minimum solvent to form a slurry.     

A phototriggered molecular spring for aerobic catalytic oxidation reactions

The first catalytic oxidation reactions with cofacial bisporphyrins using molecular oxygen as the terminal oxidant are presented. The photocatalytic reactions proceed under mild conditions (ambient temperature and pressure) without the need for a co-reductant. A systematic reactivity study of the photooxidation of dimethyl sulfide (DMS) with a homologous series of bisiron(III) mu-oxo porphyrins containing dibenzofuran, xanthene, or no bridge reveals that the facility of these processes is markedly dependent on the vertical flexibility of the catalyst to provide a phototriggered molecular spring.     

Hexabromoacetone and ethyl tribromoacetate: a highly efficient reagent for bromination of alcohol

A new and efficient method for the bromination of alcohols utilizing Br₃CCOCBr₃/PPh₃ and Br₃CCO₂Et/PPh₃ is described. Various alcohols can be converted smoothly into their corresponding alkyl bromides in high yields under mild conditions with short reaction times. Based upon ¹H NMR studies using competitive reactions between selected brominating agents and Cl₃CCN, Br₃CCOCBr₃ displays the highest reactivity approximately nine times that of CBr₄.     

Efficient ruthenium-catalyzed aerobic oxidation of alcohols using a biomimetic coupled catalytic system

Efficient aerobic oxidation of alcohols was developed via a biomimetic catalytic system. The principle for this aerobic oxidation is reminiscent of biological oxidation of alcohols via the respiratory chain and involves selective electron/proton transfer. A substrate-selective catalyst (ruthenium complex 1) dehydrogenates the alcohol, and the hydrogens abstracted are transferred to an electron-rich quinone (4b). The hydroquinone thus formed is continuously reoxidized by air with the aid of an oxygen-activating Co[bond]salen type complex (6). Most alcohols are oxidized to ketones in high yield and selectivity within 1-2 h, and the catalytic system tolerates a wide range of O(2) concentrations without being deactivated. Compared to other ruthenium-catalyzed aerobic oxidations this new catalytic system has high turnover frequency (TOF).     

Selective aerobic oxidation of hydroxy compounds catalyzed by photoactivated ruthenium-salen complexes (selective catalytic aerobic oxidation)

Selective oxidation of alcohols to the corresponding carbonyl compounds is one of the most fundamental reactions in organic synthesis. Traditional methods for this transformation generally rely on stoichiometric amount of oxidants represented by Cr(VI) or DMSO reagents, though their synthetic utility is encumbered by unpleasant waste materials. From ecological and atom-economic viewpoints, catalytic aerobic oxidation is much more advantageous because molecular oxygen is ubiquitous and the byproduct is basically non-toxic water or hydrogen peroxide. On the other hand, phenol derivatives undergo oxidative coupling, forming C-C or C-O bond, through radical intermediates coupled with an electron-transfer process. Molecular oxygen is also well known to serve as electron acceptor in this reaction. Thus, a variety of transition metal complexes have so far been examined for aerobic oxidations of alcohols and phenols, and high catalytic activities have been achieved in some cases. However, stereo- and chemo-selective aerobic oxidations are still limited in number and are of current interest. Presented in this paper is our recent studies on catalytic aerobic oxidations with photoactivated nitrosyl ruthenium-salen complexes, including asymmetric oxidation of secondary alcohols to ketones (kinetic resolution), enantioselective oxidative coupling of 2-naphthols to binaphthols and oxygen-radical bicyclization of 2,2'-dihydroxystilbene, chemoselective oxidation of primary alcohols to aldehydes and diols to lactols, and asymmetric desymmetrization of meso-diols to lactols.     

New efficient catalysts for the aerobic oxidation of ethers

Some nickel, copper, and silver salts or complexes are efficient catalysts for the oxidation of benzylic ethers with oxygen in 1,2-dimethoxyethane. Salts of the weakly coordinating anion trifluoroacetate are particularly efficient, approaching (and, in some cases, improving) the yields obtained with cobalt(II) chloride, the best catalyst so far reported.     

Transition-metal- and organic-solvent-free: a highly efficient anaerobic process for selective oxidation of alcohols to aldehydes and ketones in water

A new system, I2-KI-K2CO3-H2O, selectively oxidized alcohols to aldehydes and ketones under anaerobic condition in water at 90 degrees C with excellent yields. The process is green, mild and inexpensive.