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Selective Hydrogenation (selective + hydrogenation)
Selected AbstractsSelective Hydrogenation of Amides using Ruthenium/ Molybdenum CatalystsADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 5 2010Graham Beamson Abstract Recyclable, heterogeneous bimetallic ruthenium/molybdenum catalysts, formed in situ from triruthenium dodecacarbonyl [Ru3(CO)12] and molybdenum hexacarbonyl [Mo(CO)6], are effective for the selective liquid phase hydrogenation of cyclohexylcarboxamide (CyCONH2) to cyclohexanemethylamine (CyCH2NH2), with no secondary or tertiary amine by-product formation. Variation of Mo:Ru composition reveals both synergistic and poisoning effects, with the optimum combination of conversion and selectivity at ca. 0.5, and total inhibition of catalysis evident at ,1. Good amide conversions are noted within the reaction condition regimes 20,100,bar hydrogen and 145,160,°C. The order of reactivity of these catalysts towards reduction of different amide functional groups is primary>tertiary,secondary. In situ HP-FT-IR spectroscopy confirms that catalyst genesis occurs during an induction period associated with decomposition of the organometallic precursors. Ex situ characterisation, using XRD, XPS and EDX-STEM, for active Mo:Ru compositions, has provided evidence for intimately mixed ca. 2.5,4,nm particles that contain metallic ruthenium, and molybdenum (in several oxidation states, including zero). [source] Selective Hydrogenation of 5-Ethoxymethylfurfural over Alumina-Supported Heterogeneous CatalystsADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 18 2009Erik-Jan Ras Abstract We report here the synthesis and testing of a set of 48 alumina-supported catalysts for hydrogenation of 5-ethoxymethylfurfural. This catalytic reaction is very important in the context of converting biomass to biofuels. The catalysts are composed of one main metal (gold, copper, iridium, nickel, palladium, platinum, rhodium, ruthenium) and one promoter metal (bismuth, chromium, iron, sodium, tin, tungsten). Using a 16-parallel trickle-flow reactor, we tested all 48 catalyst combinations under a variety of conditions. The results show that both substrate conversion and product selectivity are sensitive towards temperature changes and solvent effects. The best results of >99% yield to the desired product, 5-ethoxymethylfurfuryl alcohol, are obtained using an iridium/chromium (Ir/Cr) catalyst. The mechanistic implications of different possible reaction pathways in this complex hydrogenation system are discussed. [source] Tuning Selectivity in Terpene Chemistry: Selective Hydrogenation versus Cascade Reactions over Copper CatalystsADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 9 2005F. Zaccheria Abstract The selectivity of Cu/Al2O3 under very mild catalytic hydrogenation conditions can be tuned only by switching the solvent. Geraniol can be converted in a one-pot one-step process into a mixture of citronellol and menthol in hydrocarbon solvents or reduced to citronellol with 98% selectivity in 2-propanol without any additive. Both reactions can be applied to essential oils or synthetic mixtures containing geraniol, citronellal and nerol. [source] Atomically Precise Au25(SR)18 Nanoparticles as Catalysts for the Selective Hydrogenation of ,,,-Unsaturated Ketones and Aldehydes,ANGEWANDTE CHEMIE, Issue 7 2010Yan Zhu Dr. Eine glänzende Gelegenheit: Eine Erklärung für den chemoselektiven Verlauf der Hydrierung ,,,-ungesättigter Ketone (oder Aldehyde) zu ungesättigten Alkoholen mit monodispersen Au25(SR)18 -Partikeln als Katalysator wird vorgeschlagen (siehe Bild). Dank der nun bekannten Struktur dieser Nanopartikel können Struktur-Aktivitäts-Beziehungen aufgestellt werden. [source] Selective Hydrogenation of 4-Substituted Phenols to the Cyclohexanone Analogues , Catalyst Optimization and KineticsCHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 5 2003M. Wydra 4-position substituted cyclohexanones are of great importance as key intermediates for the synthesis of liquid-crystal materials. Unsubstituted cyclohexanone can be manufactured by the selective hydrogenation of phenol. Industrial processes exist, in which phenol is hydrogenated by a heterogeneous catalyst in the vapor or liquid phase melt with high selectivity leading to high amounts of cyclohexanone. However, very little kinetic data exists to date for the selective hydrogenation of phenol and the cresols in an inert solvent. The aim of this work is to optimize the selective liquid-phase hydrogenation of 4-(4,-trans-n-propylcyclohexyl)-phenol. [source] ChemInform Abstract: Highly Selective Hydrogenation of Aromatic Chloronitro Compounds to Aromatic Chloroamines with Ionic-Liquid-Like Copolymer Stabilized Platinum Nanocatalysts in Ionic Liquids.CHEMINFORM, Issue 26 2010Xiao Yuan Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] ChemInform Abstract: Selective Hydrogenation of Aromatic Aminoketones by Pd/C Catalysis.CHEMINFORM, Issue 6 2009Rui Du Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] ChemInform Abstract: Selective Hydrogenation of Unsaturated Aldehydes in a Poly(ethylene glycol)/Compressed Carbon Dioxide Biphasic System.CHEMINFORM, Issue 6 2009Ruixia Liu Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] A Novel Catalyst for the Selective Hydrogenation of Furfural to Furfuryl Alcohol.CHEMINFORM, Issue 49 2005Xiang-Ying Hao Abstract For Abstract see ChemInform Abstract in Full Text. [source] Selective Hydrogenation of Aromatic Compounds Containing Epoxy Group over Rh/Graphite.CHEMINFORM, Issue 10 2003Yoshinori Hara Abstract For Abstract see ChemInform Abstract in Full Text. [source] Highly Selective Hydrogenation of Carbon,Carbon Multiple Bonds Catalyzed by the Cation [(C6Me6)2Ru2(PPh2)H2]+: Molecular Structure of [(C6Me6)2Ru2(PPh2)(CHCHPh)H]+, a Possible Intermediate in the Case of Phenylacetylene HydrogenationCHEMISTRY - A EUROPEAN JOURNAL, Issue 1 2007Mathieu J.-L. Abstract The dinuclear cation [(C6Me6)2Ru2(PPh2)H2]+ (1) has been studied as the catalyst for the hydrogenation of carbon,carbon double and triple bonds. In particular, [1][BF4] turned out to be a highly selective hydrogenation catalyst for olefin functions in molecules also containing reducible carbonyl functions, such as acrolein, carvone, and methyljasmonate. The hypothesis of molecular catalysis by dinuclear ruthenium complexes is supported by catalyst-poisoning experiments, the absence of an induction period in the kinetics of cyclohexene hydrogenation, and the isolation and single-crystal X-ray structure analysis of the tetrafluoroborate salt of the cation [(C6Me6)2Ru2(PPh2)(CHCHPh)H]+ (2), which can be considered as an intermediate in the case of phenylacetylene hydrogenation. On the basis of these findings, a catalytic cycle is proposed which implies that substrate hydrogenation takes place at the intact diruthenium backbone, with the two ruthenium atoms acting cooperatively in the hydrogen-transfer process. [source] Synthesis of cis-Hedione® and Methyl Jasmonate via Cascade Baylis,Hillman Reaction and Claisen Ortho Ester RearrangementHELVETICA CHIMICA ACTA, Issue 12 2005Christian Chapuis The exocyclically unsaturated conjugated keto esters 10, obtained via a Claisen ortho ester rearrangement of the allylic hydroxy ketones 9, were either directly hydrogenated or partially isomerized into the endocyclically unsaturated tetrasubstituted didehydrojasmonoid intermediates 14, prior to a more selective hydrogenation with Pd/C in cyclohexane to the disubstituted oxocyclopentaneacetates 15 (Scheme,2). The key intermediates 9 were obtained either by a four-step sequence, including acetal protection/deprotection from enone 1, in the specific case of hydroxy ketone 9a (Scheme,1), or more directly and generally by a Baylis,Hillman reaction from cyclopent-2-en-1-one (16) and the appropriate aldehydes 17 (Scheme,2). The judicious choice of these aldehydes opens versatile modifications for the stereoselective introduction of the partially cis - or epimerized trans -C(2) jasmonoid side chain, while the Baylis,Hillman reaction, catalyzed by chiral [1,1,-binaphthalene]-2,2,-diols (BINOLs) 19 (Scheme,3), may be efficiently conducted in a one-pot cascade fashion including the ortho ester Claisen rearrangement. [source] Donor-Stabilized Phosphenium Adducts as New Efficient and Immobilizing Ligands in Palladium-Catalyzed Alkynylation and Platinum-Catalyzed Hydrogenation in Ionic LiquidsADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 10 2009Samer Saleh Abstract The straightforward synthesis of a new donor-stabilized phosphenium ligand 3d by addition of bromodifurylphosphine to 1,3-dimethylimidazolium-2-carboxylate 1 is described. The obtained ligand exhibits a very strong ,-acceptor character, comparable to that of triphenyl phosphite [P(OPh)3] or of tris-halogenophosphines, with a ,CO(A1) at 2087,cm,1 for its nickel tricarbonyl complex. This ligand, as well as the related 3a which was obtained from chlorodiphenylphosphine, were tested in palladium-catalyzed aryl alkynylation and in the platinum-catalyzed selective hydrogenation of chloronitrobenzenes, both in an ionic liquid phase. In CC bond cross-coupling we observed that the increase of the ,-acceptor character in ligand 3d, due to the introduction of an additional electron-withdrawing group, provides a very efficient catalyst in the alkynylation reaction of aryl bromides with phenylacetylene, including the deactivated 4-bromoanisole or the sterically hindered 2-bromonaphthalene. The catalytic activity decreases with recycling due to the sensitiveness of ligands to protonation in the ionic phase. Conversely, a multiple recycling of the metal/ligand system in non-acidic media was achieved from platinum-catalyzed hydrogenation of m- chloronitrobenzene. The catalytic results obtained by employing the complex of platinum(II) chloride with 3a [trans -PtCl2(3a)2] in comparison with the non-ionic related trans -tris(triphenylphosphine)platinum dichloride [trans -PtCl2(PPh3)2] complex clearly indicate that the simultaneous existence of a strong ,-acceptor character and a positive charge within the ligand 3a significantly increases the life-time of the platinum catalyst. The selectivity of the reaction is also improved by decreasing the undesirable formation of dehalogenation products. This cationic platinum complex trans -PtCl2(3a)2 is the first example of a highly selective catalyst for hydrogenation of chloronitroarenes immobilized in an ionic liquid phase. The system was recycled six times without noticeable metal leaching in the organic phase, and no loss of activity. [source] Carbon-Carbon Double Bond versus Carbonyl Group Hydrogenation: Controlling the Intramolecular Selectivity with Polyaniline-Supported Platinum CatalystsADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 9 2008Martin Steffan Abstract The use of polyaniline (PANI) as catalyst support for heterogeneous catalysts and their application in chemical catalysis is hitherto rather poorly known. We report the successful synthesis of highly dispersed PANI-supported platinum catalysts (particle sizes between 1.7 and 3.7,nm as revealed by transmission electron microscopy, TEM) choosing two different approaches, namely (i) deposition-precipitation of H2PtCl6 onto polyaniline, suspended in basic medium (DP method) and, (ii) immobilization of a preformed nanoscale platinum colloid on polyaniline (sol-method). The PANI-supported platinum catalysts were applied in the selective hydrogenation of the ,,,-unsaturated aldehyde citral. In order to benchmark their catalytic performance, citral hydrogenation was also carried out by using platinum supported on the classical support materials silica (SiO2), alumina (Al2O3), active carbon and graphite. The relations of the structural characteristics and surface state of the catalysts with respect to their hydrogenation properties have been probed by EXAFS and XPS. It is found that the DP method yields chemically prepared PtO2 on polyaniline and, thus, produces a highly dispersed and immobilized Adams catalyst (in the ,-PtO2 form) which is able to efficiently hydrogenate the conjugated CC bond of citral (selectivity to citronellal=87%), whereas reduction of the CO group occurs with polyaniline-supported platinum (selectivity to geraniol/nerol=78%) prepared via the sol-method. The complete reversal of the selectivity between the preferred hydrogenation of the conjugated CC or CO group is not only particularly useful for the selective hydrogenation of ,,,-unsaturated aldehydes but also unveils the great potential of conducting polymer-supported precious metals in the field of hitherto barely investigated chemical catalysis. [source] Study of the preparation and composition of the metallic function for the selective hydrogenation of CO2 to gasoline over bifunctional catalysts,JOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 2-3 2003Javier Ereña Abstract Bifunctional catalysts for the transformation of carbon dioxide and hydrogen into gasoline have been prepared by conventional and novel processes and characterized by measurement of BET surface area and volume and distribution of pores, and by X-ray diffraction, FTIR spectroscopy and X-ray fluorescence. The effects of the preparation conditions and of the atomic ratios between the metals on the structure and on the properties of the catalysts were studied. © 2003 Society of Chemical Industry [source] Magnetism in hydro- and dehydrogenated benzenePHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 10 2009J. A. Vergés Abstract Recently, it has been shown that selective hydrogenation of Polycyclic Aromatic Hydrocarbons (PAH) can lead to high spin molecules. In particular, this is the case of some forms of hydrogenated coronene and coranulenne. In this work, mono- and multi-determinantal methods are used to show that hydrogenation of benzene, and dehydrogenation of benzene and coronene (a highly unlikely process), may lead to species whose ground states are characterized by a large spin degeneracy. Results for dehydrogenated coronene can be explained by Lieb's theorem for bipartite lattices. On the other hand, the theorem does not predict the correct spin of ground states for various forms of hydrogenated and dehydrogenated benzene (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Homogeneous Stabilization of Pt Nanoparticles in Dendritic Core,Multishell Architectures: Application in Catalytic Hydrogenation Reactions and RecyclingCHEMCATCHEM, Issue 7 2010Juliane Keilitz Abstract Core,multishell architectures are a new approach to homogeneously stabilize metal nanoparticles for harsh conditions. Herein, we present the synthesis and stabilization of Pt nanoparticles in dendritic core,multishell polymers and their application in hydrogenation reactions. The successful recycling of the catalyst was demonstrated for the hydrogenation of methyl crotonate 1 and was either achieved by ultrafiltration or in a two-phase system for at least 14,cycles. Thereby, the total turnover number (TON) was increased to 22,000. In the recycling experiments, low metal leaching into the product (as low as 0.3,ppm) was detected. Additionally, the selective hydrogenation of isophorone 3 was investigated and selectivities of 99:1 for CC versus CO hydrogenation were achieved. [source] Liquid-Phase Hydrogenation of Unsaturated Aldehydes: Enhancing Selectivity of Multiwalled Carbon Nanotube-Supported Catalysts by Thermal ActivationCHEMCATCHEM, Issue 2 2010Bruno Abstract Platinum and iridium organometallic precursors are used to prepare nanosized, thermally stable multiwalled carbon nanotube-supported catalysts. The materials are characterized by N2 adsorption at 77,K, temperature-programmed desorption coupled with mass spectrometry, H2 chemisorption, transmission electron microscopy and thermogravimetric analysis; they are tested in the selective hydrogenation of cinnamaldehyde to cinnamyl alcohol under mild conditions (363,K and 1,MPa). A thermal activation at 973,K is found to have a very positive effect over both activity and selectivity, leading to selectivities of approximately 70,%, at 50,% conversion, regardless of the active metal phase (Pt or Ir). Since no noticeable differences in the metal particle sizes are detected, the results are interpreted in light of an enhanced metal/support interaction. This effect, induced by the removal of oxygenated surface groups, is thought to change the adsorption mechanism of the cinnamaldehyde molecule. [source] Comparison of Selective Gas Phase- and Liquid Phase Hydrogenation of (Cyclo-)Alkadienes towards Cycloalkenes on Pd/Alumina Egg-Shell CatalystsCHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 12 2006N. Wuchter Abstract The hydrogenation of dienes such as 1,3-butadiene, cyclooctadiene, and of acetylenic hydrocarbons on Pd catalysts shows high reaction rates and consequently, a strong influence of mass transfer on the selectivity of the intermediate alkene or cycloalkene product. 100,% selectivity towards (cyclo)-alkene hydrogenation is achieved for the gas phase when the Thiele modulus is , where L is the thickness of the active layer and Deff is the effective diffusion coefficient of the diene. The interdependencies expressed by this formula were studied in detail using model catalysts with regular pores of uniform length and diameter and perpendicular to the surface. These catalysts were prepared by anodic oxidation of aluminium wires and immobilization of the active Pd. For the liquid phase procedure of selective hydrogenation, a reaction mass transfer model has been derived in order to compare the gas phase and liquid phase procedures, in particular with respect to the selectivity. The hydrogenation of 1,3-cyclooctadiene and of 1,3-butadiene were studied for both procedures employing the same catalyst. The rate of hydrogenation can be represented for both cases by the identical kinetic equation r1,=,k1,cH2. This result is interpreted by assuming that the access of hydrogen to the surface through the dense layer of adsorbed diene is the rate determining step. [source] Selective Hydrogenation of 4-Substituted Phenols to the Cyclohexanone Analogues , Catalyst Optimization and KineticsCHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 5 2003M. Wydra 4-position substituted cyclohexanones are of great importance as key intermediates for the synthesis of liquid-crystal materials. Unsubstituted cyclohexanone can be manufactured by the selective hydrogenation of phenol. Industrial processes exist, in which phenol is hydrogenated by a heterogeneous catalyst in the vapor or liquid phase melt with high selectivity leading to high amounts of cyclohexanone. However, very little kinetic data exists to date for the selective hydrogenation of phenol and the cresols in an inert solvent. The aim of this work is to optimize the selective liquid-phase hydrogenation of 4-(4,-trans-n-propylcyclohexyl)-phenol. [source] Colloidal Noble-Metal and Bimetallic Alloy Nanocrystals: A General Synthetic Method and Their Catalytic Hydrogenation PropertiesCHEMISTRY - A EUROPEAN JOURNAL, Issue 21 2010Shuyan Song Dr. Abstract A general single-step strategy has been developed for the direct thermal decomposition of noble-metal salts in octadecylamine to synthesize octahedron- and rod-shaped noble-metal aggregates and monodisperse noble-metal or bimetallic alloy nanocrystals without introducing any additive into the system. It has presented a facile and economic way to fabricate these nanocrystals, especially alloy nanocrystals, which does not require a post-synthesis solid-state annealing process. The morphology of the nanocrystals can be easily controlled by tuning the synthetic temperature. Their ability to catalyze heterogeneous Suzuki coupling reactions has been investigated and showed satisfactory catalytic activity. The catalytic performance of the monometallic and bimetallic alloy nanocrystals were also evaluated in the selective hydrogenation of citral in a conventional organic solvent (toluene) and a green solvent (supercritical carbon dioxide, scCO2). Interestingly, the catalysts performed differently to each other when they were in scCO2 owing to the different morphology, which should be readily optimized for further use. [source] | ||||||||||||||||||||||