Homogeneous catalysis in supercritical fluids : hydrogenation of supercritical carbon dioxide to formic acid, alkyl formates, and formamides
17 Jan 1996-Journal of the American Chemical Society (American Chemical Society)-Vol. 118, Iss: 2, pp 344-355
TL;DR: In this article, it was shown that the high rate of reaction is attributed to rapid diffusion, weak catalyst solvation, and the high miscibility of H2 in supercritical state (scCO2).
Abstract: Rapid, selective, and high-yield hydrogenation of CO2 can be achieved if the CO2 is in the supercritical state (scCO2). Dissolving H2, a tertiary amine, a catalyst precursor such as RuH2[P(CH3)3]4 or RuCl2[P(CH3)3]4, and a promoting additive such as water, CH3OH, or DMSO in scCO2 at 50 °C leads to the generation of formic acid with turnover frequencies up to or exceeding 4000 h-1. In general, experiments in which a second phase was formed by one or more reagents or additives had lower rates of reaction. The high rate of reaction is attributed to rapid diffusion, weak catalyst solvation, and the high miscibility of H2 in scCO2. The formic acid synthesis can be coupled with subsequent reactions of formic acid, for example, with alcohols or primary or secondary amines, to give highly efficient routes to formate esters or formamides. With NH(CH3)2, for example 420 000 mol of dimethylformamide/mol of Ru catalyst was obtained at 100 °C. The demonstrated solubility and catalytic activity of complexes of tertiary...
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TL;DR: Reaction Mechanism, Synthesis of Urea and Urethane Derivatives, and Alcohol Homologation 2382 10.1.
Abstract: 4.3. Reaction Mechanism 2373 4.4. Asymmetric Synthesis 2374 4.5. Outlook 2374 5. Alternating Polymerization of Oxiranes and CO2 2374 5.1. Reaction Outlines 2374 5.2. Catalyst 2376 5.3. Asymmetric Polymerization 2377 5.4. Immobilized Catalysts 2377 6. Synthesis of Urea and Urethane Derivatives 2378 7. Synthesis of Carboxylic Acid 2379 8. Synthesis of Esters and Lactones 2380 9. Synthesis of Isocyanates 2382 10. Hydrogenation and Hydroformylation, and Alcohol Homologation 2382
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TL;DR: A critical review of recent developments in hydrogenation reaction, with emphases on catalytic reactivity, reactor innovation, and reaction mechanism, provides an overview regarding the challenges and opportunities for future research in the field.
Abstract: Owing to the increasing emissions of carbon dioxide (CO2), human life and the ecological environment have been affected by global warming and climate changes. To mitigate the concentration of CO2 in the atmosphere various strategies have been implemented such as separation, storage, and utilization of CO2. Although it has been explored for many years, hydrogenation reaction, an important representative among chemical conversions of CO2, offers challenging opportunities for sustainable development in energy and the environment. Indeed, the hydrogenation of CO2 not only reduces the increasing CO2 buildup but also produces fuels and chemicals. In this critical review we discuss recent developments in this area, with emphases on catalytic reactivity, reactor innovation, and reaction mechanism. We also provide an overview regarding the challenges and opportunities for future research in the field (319 references).
2,539 citations
TL;DR: In this paper, the authors present a review of CO2, its synthetic reactions and their possible role in future CO2 mitigation schemes that have to match the scale of man-made CO2 in the atmosphere, which rapidly approaches 1 teraton.
Abstract: The increase in atmospheric carbon dioxide is linked to climate changes; hence there is an urgent need to reduce the accumulation of CO2 in the atmosphere. The utilization of CO2 as a raw material in the synthesis of chemicals and liquid energy carriers offers a way to mitigate the increasing CO2 buildup. This review covers six important CO2 transformations namely: chemical transformations, photochemical reductions, chemical and electrochemical reductions, biological conversions, reforming and inorganic transformations. Furthermore, the vast research area of carbon capture and storage is reviewed briefly. This review is intended as an introduction to CO2, its synthetic reactions and their possible role in future CO2 mitigation schemes that has to match the scale of man-made CO2 in the atmosphere, which rapidly approaches 1 teraton.
1,771 citations
Pacific Northwest National Laboratory1, California Institute of Technology2, Princeton University3, Humboldt University of Berlin4, Pennsylvania State University5, Brookhaven National Laboratory6, University of California, Riverside7, University of Illinois at Urbana–Champaign8, United States Department of Energy9, University of California, Berkeley10, University of Toronto11, University of Michigan12, University of Amsterdam13, Utah State University14, Max Planck Society15, Louisiana State University16
TL;DR: Providing a future energy supply that is secure and CO_2-neutral will require switching to nonfossil energy sources such as wind, solar, nuclear, and geothermal energy and developing methods for transforming the energy produced by these new sources into forms that can be stored, transported, and used upon demand.
Abstract: Two major energy-related problems confront the world in the
next 50 years. First, increased worldwide competition for
gradually depleting fossil fuel reserves (derived from past
photosynthesis) will lead to higher costs, both monetarily and politically. Second, atmospheric CO_2 levels are at their highest recorded level since records began. Further increases are predicted to produce large and uncontrollable impacts on the world climate. These projected impacts extend beyond climate to ocean acidification, because the ocean is a major sink for atmospheric CO2.1 Providing a future energy supply that is secure and CO_2-neutral will require switching to nonfossil energy sources such as wind, solar, nuclear, and geothermal energy and developing methods for transforming the energy produced by these new sources into forms that can be stored, transported, and used upon demand.
1,651 citations
TL;DR: The newly devised [RuCl(2)(phosphane)(2)(1,2-diamine)] complexes are excellent precatalysts for homogeneous hydrogenation of simple ketones which lack any functionality capable of interacting with the metal center.
Abstract: Hydrogenation is a core technology in chemical synthesis. High rates and selectivities are attainable only by the coordination of structurally well-designed catalysts and suitable reaction conditions. The newly devised [RuCl(2)(phosphane)(2)(1,2-diamine)] complexes are excellent precatalysts for homogeneous hydrogenation of simple ketones which lack any functionality capable of interacting with the metal center. This catalyst system allows for the preferential reduction of a C=O function over a coexisting C=C linkage in a 2-propanol solution containing an alkaline base. The hydrogenation tolerates many substituents including F, Cl, Br, I, CF(3), OCH(3), OCH(2)C(6)H(5), COOCH(CH(3))(2), NO(2), NH(2), and NRCOR as well as various electron-rich and -deficient heterocycles. Furthermore, stereoselectivity is easily controlled by the electronic and steric properties (bulkiness and chirality) of the ligands as well as the reaction conditions. Diastereoselectivities observed in the catalytic hydrogenation of cyclic and acyclic ketones with the standard triphenylphosphane/ethylenediamine combination compare well with the best conventional hydride reductions. The use of appropriate chiral diphosphanes, particularly BINAP compounds, and chiral diamines results in rapid and productive asymmetric hydrogenation of a range of aromatic and heteroaromatic ketones and gives a consistently high enantioselectivity. Certain amino and alkoxy ketones can be used as substrates. Cyclic and acyclic alpha,beta-unsaturated ketones can be converted into chiral allyl alcohols of high enantiomeric purity. Hydrogenation of configurationally labile ketones allows for the dynamic kinetic discrimination of diastereomers, epimers, and enantiomers. This new method shows promise in the practical synthesis of a wide variety of chiral alcohols from achiral and chiral ketone substrates. Its versatility is manifested by the asymmetric synthesis of some biologically significant chiral compounds. The high rate and carbonyl selectivity are based on nonclassical metal-ligand bifunctional catalysis involving an 18-electron amino ruthenium hydride complex and a 16-electron amido ruthenium species.
1,630 citations
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TL;DR: The high resolution three-dimensional x-ray structure of the metal sites of bovine heart cytochrome c oxidase is reported, suggesting a dinuclear copper center with an unexpected structure similar to a [2Fe-2S]-type iron-sulfur center.
Abstract: The high resolution three-dimensional x-ray structure of the metal sites of bovine heart cytochrome c oxidase is reported. Cytochrome c oxidase is the largest membrane protein yet crystallized and analyzed at atomic resolution. Electron density distribution of the oxidized bovine cytochrome c oxidase at 2.8 A resolution indicates a dinuclear copper center with an unexpected structure similar to a [2Fe-2S]-type iron-sulfur center. Previously predicted zinc and magnesium sites have been located, the former bound by a nuclear encoded subunit on the matrix side of the membrane, and the latter situated between heme a3 and CuA, at the interface of subunits I and II. The O2 binding site contains heme a3 iron and copper atoms (CuB) with an interatomic distance of 4.5 A; there is no detectable bridging ligand between iron and copper atoms in spite of a strong antiferromagnetic coupling between them. A hydrogen bond is present between a hydroxyl group of the hydroxyfarnesylethyl side chain of heme a3 and an OH of a tyrosine. The tyrosine phenol plane is immediately adjacent and perpendicular to an imidazole group bonded to CuB, suggesting a possible role in intramolecular electron transfer or conformational control, the latter of which could induce the redox-coupled proton pumping. A phenyl group located halfway between a pyrrole plane of the heme a3 and an imidazole plane liganded to the other heme (heme a) could also influence electron transfer or conformational control.
1,319 citations
TL;DR: In this article, the simplest and most studied reactions of CO{sub 2} are the catalytic reactions with H{sub 1} in the presence or absence of other reactive species.
Abstract: Carbon dioxide (CO{sub 2}) is of the greatest interest as a C{sub 1} feedstock because of the vast amounts of carbon which exist in this form and because of the low cost of bulk CO{sub 2}. Currently, toxic carbon monoxide, the main competitor for many processes, is used in industry instead because CO{sub 2} is perceived to be less reactive and its efficient catalytic conversion has remained elusive. Because CO{sub 2} is a highly oxidized, thermodynamically stable compound, its utilization requires reaction with certain high energy substances or electroreductive processes. Catalytic hydrogenation is one of the most promising approaches to CO{sub 2} fixation. Recent research has shown that high catalytic efficiency, yields, and rates of reaction can be obtained from CO{sub 2} with optimum conditions and catalysts. This review will describe the simplest and most studied reactions of CO{sub 2}: the catalytic reactions with H{sub 2} in the presence or absence of other reactive species. The mechanisms of homogeneously catalyzed reactions will be emphasized. Subjects which will not be covered, aside from brief mentions, include stoichiometric reactions of CO{sub 2} with complexes, the reverse water gas shift reaction, hydrosilylation, and electrochemical or photochemical reductions of CO{sub 2}. 132 refs.
870 citations
TL;DR: A review of dihydrogen-dihydride reactions can be found in this article, where the authors present a line-shape analysis of a three-hydrogen system M(H,)H.
630 citations
TL;DR: The use of a supercritical phase, in which hydrogen is highly miscible, leads to a very high initial rate of reaction up to 1,400 moles of formic acid per mole of catalyst per hour as discussed by the authors.
Abstract: THE use of carbon dioxide as a starting material for the synthesis of organic compounds has long been a goal for synthetic chemists. The hydogenation of carbon dioxide to formic acid, methanol and other organic substances is particularly attractive, but has remained difficult. This route to formic acid has been described recently, based on the use of organometallic rhodium catalysts in dimethyl sulphoxideII and aqueous2 solvents. We report here the efficient production of formic acid in a supercritical mixture of carbon dioxide and hydrogen containing a catalytic ruthenium() phosphine complex. The use of a supercritical phase, in which hydrogen is highly miscible, leads to a very high initial rate of reaction up to 1,400 moles of formic acid per mole of catalyst per hour. The same reaction under identical conditions but in liquid organic solvents is much slower. Our results suggest that supercritical fluids represent a promising medium for homogeneous catalysis.
611 citations
TL;DR: In this paper, the system water-carbon dioxide was studied to pressures of 1,600 bars and at temperatures of 110 degrees C to 350 degrees C. The critical curve of the system trends toward higher pressures at lower temperatures and departs strongly from the critical point of pure water.
Abstract: The system water-carbon dioxide was studied to pressures of 1,600 bars and at temperatures of 110 degrees C to 350 degrees C. Preliminary work was done also up to pressures of 3,000 bars. The critical curve of the system trends toward higher pressures at lower temperatures and departs strongly from the critical point of pure water. At low pressures the CO 2 rich phase is the light phase, but at higher pressures this phase is the denser fluid phase. In a natural system of H 2 O-CO 2 complete miscibility will not exist below 265 degrees C; at higher temperatures a completely mixed super-critical fluid may exist, but at lower temperatures this fluid will segregate into two fluid phases.
517 citations