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1.
Enantioselective catalysts produce organic compounds in enantiomerically enriched form. They are highly efficient tools for the synthesis of biologically active materials, such as pharmaceuticals and crop-protection chemicals, in which enantiomeric purity can be critical. The design of chiral ligands is the key to developing new enantioselective catalysts. Three unusual families of ligands have been used to develop practical technology for enantioselective hydrocyanation of olefins, ring-opening of epoxides, and hydrogenation of various compounds. 相似文献
2.
Solé S Gornitzka H Schoeller WW Bourissou D Bertrand G 《Science (New York, N.Y.)》2001,292(5523):1901-1903
Several (amino)(aryl)carbenes have been shown to be stable at room temperature in solution and in the solid state. Electroneutrality of the carbene center is ensured by the amino group, which has both pi-donor and final sigma-acceptor electronic character. The aryl group remains a spectator substituent, as shown by single-crystal x-ray analysis and by its chemical behavior. Because only one electron-active substituent is needed, numerous stable carbenes will become accessible, which will open the way for new synthetic developments and applications in various fields. 相似文献
3.
Studt F Abild-Pedersen F Bligaard T Sørensen RZ Christensen CH Nørskov JK 《Science (New York, N.Y.)》2008,320(5881):1320-1322
The removal of trace acetylene from ethylene is performed industrially by palladium hydrogenation catalysts (often modified with silver) that avoid the hydrogenation of ethylene to ethane. In an effort to identify catalysts based on less expensive and more available metals, density functional calculations were performed that identified relations in heats of adsorption of hydrocarbon molecules and fragments on metal surfaces. This analysis not only verified the facility of known catalysts but identified nickel-zinc alloys as alternatives. Experimental studies demonstrated that these alloys dispersed on an oxide support were selective for acetylene hydrogenation at low pressures. 相似文献
4.
Selective hydrogenolysis of the aromatic carbon-oxygen (C-O) bonds in aryl ethers is an unsolved synthetic problem important for the generation of fuels and chemical feedstocks from biomass and for the liquefaction of coal. Currently, the hydrogenolysis of aromatic C-O bonds requires heterogeneous catalysts that operate at high temperature and pressure and lead to a mixture of products from competing hydrogenolysis of aliphatic C-O bonds and hydrogenation of the arene. Here, we report hydrogenolyses of aromatic C-O bonds in alkyl aryl and diaryl ethers that form exclusively arenes and alcohols. This process is catalyzed by a soluble nickel carbene complex under just 1 bar of hydrogen at temperatures of 80 to 120°C; the relative reactivity of ether substrates scale as Ar-OAr>Ar-OMe>ArCH(2)-OMe (Ar, Aryl; Me, Methyl). Hydrogenolysis of lignin model compounds highlights the potential of this approach for the conversion of refractory aryl ether biopolymers to hydrocarbons. 相似文献
5.
The selective reduction of a nitro group when other reducible functions are present is a difficult process that often requires stoichiometric amounts of reducing agents or, if H2 is used, the addition of soluble metals. Gold nanoparticles supported on TiO2 or Fe2O3 catalyzed the chemoselective hydrogenation of functionalized nitroarenes with H2 under mild reaction conditions that avoided the accumulation of hydroxylamines and their potential exothermic decomposition. These chemoselective hydrogenation gold catalysts also provide a previously unknown route for the synthesis of the industrially relevant cyclohexanone oxime from 1-nitro-1-cyclohexene. 相似文献
6.
Torres Galvis HM Bitter JH Khare CB Ruitenbeek M Dugulan AI de Jong KP 《Science (New York, N.Y.)》2012,335(6070):835-838
Lower olefins are key building blocks for the manufacture of plastics, cosmetics, and drugs. Traditionally, olefins with two to four carbons are produced by steam cracking of crude oil-derived naphtha, but there is a pressing need for alternative feedstocks and processes in view of supply limitations and of environmental issues. Although the Fischer-Tropsch synthesis has long offered a means to convert coal, biomass, and natural gas into hydrocarbon derivatives through the intermediacy of synthesis gas (a mixture of molecular hydrogen and carbon monoxide), selectivity toward lower olefins tends to be low. We report on the conversion of synthesis gas to C(2) through C(4) olefins with selectivity up to 60 weight percent, using catalysts that constitute iron nanoparticles (promoted by sulfur plus sodium) homogeneously dispersed on weakly interactive α-alumina or carbon nanofiber supports. 相似文献
7.
主要萜类化合物催化加氢研究进展 总被引：1，自引：0，他引：1
付亚 《金陵科技学院学报》2005,21(3):50-55
综述了国内外主要萜类化合物催化加氢研究进展状况.主要介绍蒎烯、双戊烯、香茅醛、柠檬醛、香叶醇和橙花醇等萜类化合物的加氢催化剂种类及其工艺条件. 相似文献
8.
Seayad A Ahmed M Klein H Jackstell R Gross T Beller M 《Science (New York, N.Y.)》2002,297(5587):1676-1678
The selective synthesis of linear amines from internal olefins or olefin mixtures was achieved through a catalytic one-pot reaction consisting of an initial olefin isomerization followed by hydroformylation and reductive amination. Key to the success is the use of specially designed phosphine ligands in the presence of rhodium catalysts. This reaction constitutes an economically attractive and environmentally favorable synthesis of linear aliphatic amines. 相似文献
9.
Teschner D Borsodi J Wootsch A Révay Z Hävecker M Knop-Gericke A Jackson SD Schlögl R 《Science (New York, N.Y.)》2008,320(5872):86-89
Alkynes can be selectively hydrogenated into alkenes on solid palladium catalysts. This process requires a strong modification of the near-surface region of palladium, in which carbon (from fragmented feed molecules) occupies interstitial lattice sites. In situ x-ray photoelectron spectroscopic measurements under reaction conditions indicated that much less carbon was dissolved in palladium during unselective, total hydrogenation. Additional studies of hydrogen content using in situ prompt gamma activation analysis, which allowed us to follow the hydrogen content of palladium during catalysis, indicated that unselective hydrogenation proceeds on hydrogen-saturated beta-hydride, whereas selective hydrogenation was only possible after decoupling bulk properties from the surface events. Thus, the population of subsurface sites of palladium, by either hydrogen or carbon, governs the hydrogenation events on the surface. 相似文献
10.
Younkin TR Connor EF Henderson JI Friedrich SK Grubbs RH Bansleben DA 《Science (New York, N.Y.)》2000,287(5452):460-462
More than half of the 170 million metric tons of polymers produced each year are polyolefins. Current technology uses highly active cationic catalysts, which suffer from an inability to tolerate heteroatoms such as oxygen, nitrogen, and sulfur. These systems require scrupulously clean starting materials and activating cocatalysts. A family of catalysts has been developed whose members are tolerant of both heteroatoms and less pure starting materials. These heteroatom-tolerant neutral late transition metal complexes are in fact highly active systems that produce high-molecular-weight polyethylene, polymerize functionalized olefins, and require no cocatalyst. 相似文献
11.
Supercritical fluids (SCFs), compounds heated and pressurized beyond the critical point, have many unusual properties. Homogeneous molecular catalysts, which have far greater control over selectivity than heterogeneous solid catalysts, are now being tested in SCFs, and early results show that high rates, improved selectivity, and elimination of masstransfer problems can be achieved. As industry moves away from toxic or environmentally damaging solvents, supercritical carbon dioxide may be an ideal replacement medium for nonpolar or weakly polar chemical processes. More than simply substitutes for nonpolar solvents, SCFs can radically change the observed chemistry. Supercritical carbon dioxide is also an excellent medium for its own fixation, as demonstrated by studies of its hydrogenation. 相似文献
12.
A series of free-radical catalysts have been discovered that increase the yield of highly valuable olefins from the cracking of low molecular weight paraffins. For example, catalytic cracking of n-butane, isobutane, and propane over manganese or iron supported on magnesium oxide (MgO) gave product distributions different from those given by thermal (free-radical) cracking or cracking over traditional acid catalysts. With n-butane and propane feeds, the products from catalytic cracking included large amounts of ethylene and ethane; with isobutane feed, propylene was the major product. Physical characterization of the MgO-supported catalyst showed the manganese to be in a 2+ oxidation state in the reduced catalyst and a 4+ oxidation state in the fully oxidized catalyst. Manganese was also shown to be uniformly distributed in the support material with very little enrichment at the surface. Matrix isolation of the gasphase radicals from n-butane feed showed that ethyl and methyl radicals were produced over the active catalysts. In the thermal process, only methyl radicals were produced. The mechanism of the catalytic reaction appears to be selective formation of primary carbanions at the catalyst surface followed by electron transfer and release of primary hydrocarbon radicals to the gas phase. 相似文献
13.
Identification of esters isolated from culture fluids of bacteria growing upon terminal olefins indicates that bacteria oxidize olefins at the saturated methyl group, leaving the double bond intact. The yeast Candida lipolytica produces alpha-glycols from olefins, presumably by attacking the double bond. 相似文献
14.
Liquid alkanes with the number of carbon atoms ranging from C7 to C15 were selectively produced from biomass-derived carbohydrates by acid-catalyzed dehydration, which was followed by aldol condensation over solid base catalysts to form large organic compounds. These molecules were then converted into alkanes by dehydration/hydrogenation over bifunctional catalysts that contained acid and metal sites in a four-phase reactor, in which the aqueous organic reactant becomes more hydrophobic and a hexadecane alkane stream removes hydrophobic species from the catalyst before they go on further to form coke. These liquid alkanes are of the appropriate molecular weight to be used as transportation fuel components, and they contain 90% of the energy of the carbohydrate and H2 feeds. 相似文献
15.
The discovery of distinct modes of asymmetric catalysis has the potential to rapidly advance chemists' ability to build enantioenriched molecules. As an example, the use of chiral cation salts as phase-transfer catalysts for anionic reagents has enabled a vast set of enantioselective transformations. Here, we present evidence that a largely overlooked analogous mechanism wherein a chiral anionic catalyst brings a cationic species into solution is itself a powerful method. The concept is applied to the enantioselective fluorocyclization of olefins with a cationic fluorinating agent and a chiral phosphate catalyst. The reactions proceed in high yield and stereoselectivity, especially considering the scarcity of alternative approaches. This technology can in principle be applied to the large portion of reaction space that uses positively charged reagents and reaction intermediates. 相似文献
16.
A novel concept for performing stoichiometric and catalytic chemical transformations has been developed that is based on the limited miscibility of partially or fully fluorinated compounds with nonfluorinated compounds. A fluorous biphase system (FBS) consists of a fluorous phase containing a dissolved reagent or catalyst and another phase, which could be any common organic or nonorganic solvent with limited or no solubility in the fluorous phase. The fluorous phase is defined as the fluorocarbon (mostly perfluorinated alkanes, ethers, and tertiary amines)-rich phase of a biphase system. An FBS compatible reagent or catalyst contains enough fluorous moieties that it will be soluble only or preferentially in the fluorous phase. The most effective fluorous moieties are linear or branched perfluoroalkyl chains with high carbon number; they may also contain heteroatoms. The chemical transformation may occur either in the fluorous phase or at the interface of the two phases. The application of FBS has been demonstrated for the extraction of rhodium from toluene and for the hydroformylation of olefins. The ability to separate a catalyst or a reagent from the products completely at mild conditions could lead to industrial application of homogeneous catalysts or reagents and to the development of more environmentally benign processes. 相似文献
17.
Reaction-controlled phase-transfer catalysis for propylene epoxidation to propylene oxide 总被引：1，自引：0，他引：1
The epoxidation of olefins with H2O2 was performed with a tungsten-containing catalyst. This insoluble catalyst forms soluble active species by the action of H2O2, and when the H2O2 is used up, the catalyst precipitates for easy recycling. Thus, the advantages of both homogeneous and heterogeneous catalysts are combined in one system through reaction-controlled phase transfer of the catalyst. When coupled with the 2-ethylanthraquinone/2-ethylanthrahydroquinone redox process for H2O2 production, O2 can be used for the epoxidation of propylene to propylene oxide with 85% yield based on 2-ethylanthrahydroquinone without any co-products. This approach avoids the problematic co-products normally associated with the industrial production of propylene oxide. 相似文献
18.
Cytochrome P-450--catalyzed formation of delta 4-VPA, a toxic metabolite of valproic acid 总被引：4，自引：0，他引：4
Liver damage induced by the antiepileptic drug valproic acid (VPA) is believed to be mediated by an unsaturated metabolite of the drug, delta 4-VPA. In studies of the biological origin of this hepatotoxic compound, it was found that liver microsomes from phenobarbital-treated rats catalyzed the desaturation of VPA to delta 4-VPA. Indirect evidence suggested that cytochrome P-450 was the responsible enzyme, a conclusion that was verified by studies with a purified and reconstituted form of the hemoprotein, which catalyzed the oxidation of VPA to 4- and 5-hydroxyvalproic acid and to delta 4-VPA. Desaturation of a nonactivated alkyl substituent represents a novel metabolic function of cytochrome P-450 and probably proceeds via the conversion of substrate to a transient free radical intermediate, which partitions between recombination (alcohol formation) and elimination (olefin production) pathways. These findings have broad implications with respect to the metabolic generation of olefins and may explain the increased hepatotoxic potential of VPA when it is administered in combination with potent enzyme-inducing anticonvulsants such as phenobarbital. 相似文献
19.
The remarkable specificity of an antibody molecule has been used to accomplish highly selective functional group transformations not attainable by current chemical methods. An antibody raised against an amine-oxide hapten catalyzes the reduction of a diketone to a hydroxyketone with greater than 75:1 regioselectivity for one of two nearly equivalent ketone moieties. The antibody-catalyzed reaction is highly stereoselective, affording the hydroxyketone in high enantiomeric excess. Similarly, the reduction of ketones containing branched and aryl substituents, including the highly symmetrical 1-nitrophenyl-3-phenyl-2-propanone, was enantioselective. The simple strategy presented herein may find general applicability to the regio- and stereoselective reduction of a broad range of compounds. 相似文献
20.
本文用固定床反应器考察了Pd/C催化剂硫化前后,在环戊二烯加氢反应中的性能。结果表明环穴二烯的转化率从86.4％上升到98.2％,环戊烯的选择性从86.9％上升到98.8％,确定了最佳硫化条件。应用微型脉冲反应器研究了硫化过程和特性。 相似文献