Santiago M.,ETH Zurich |
Barbera K.,ETH Zurich |
Ferreira C.,Total S.A. |
Curulla-Ferre D.,Total S.A. |
And 2 more authors.
Catalysis Communications | Year: 2012
Co-feeding of two relevant by-products of methanol synthesis, viz. dimethyl ether and methyl formate, in CO + H 2 and CO + CO 2 + H 2 streams was used as a strategy to gain understanding of the reaction over ternary Cu/ZnO/Al 2O 3 and binary Cu/ZnO, Cu/Al 2O 3, and ZnO/Al 2O 3 catalysts. While dimethyl ether does not participate in the process, the addition of methyl formate remarkably increases the MeOH production by its oxygen-assisted split into active intermediate species (CH 3O * and HCOO *). Specifically, a breakthrough role was assigned to ZnO as catalytic partner for methyl formate conversion to methanol, since even the Cu-free ZnO/Al 2O 3 sample shows a considerable MeOH yield on MeF co-feeding. Alternatively, in the Zn-free Cu/Al 2O 3 sample, the presence of carbon dioxide in the inlet mixture was crucial to activate the methyl formate conversion path, likely because CO 2 provides readily available oxygen to the Cu surface. © 2012 Elsevier B.V. All rights reserved.
Spiro- and bicycloannulation of sulfoximine-substituted 2-hydroxy-dihydropyrans: Enantioselective synthesis of spiroketals, spiroethers, and oxabicycles and structure of dihydropyran oxocarbenium ions
Lejkowski M.,RWTH Aachen |
Lejkowski M.,Hte Aktiengesellschaft |
Banerjee P.,RWTH Aachen |
Banerjee P.,Indian Institute of Technology Ropar |
And 2 more authors.
European Journal of Organic Chemistry | Year: 2014
A modular enantioselective synthesis of spiroketals, spiroethers, and oxabicycles, each containing a dihydropyran subunit, is described. It is based on the 2,2-spiro- and 2,6-bicycloannulation of sulfoximine-substituted 2-hydroxy-dihydropyrans. Key steps of the spiroannulations are the ring-closing metathesis of the corresponding 2,2-oxadienyl and 2,6-dienyl dihydropyrans and Prins cyclization of 2-alkenyl 2-hydroxy-dihydropyrans. Ring-closing metathesis of the corresponding 2,6-dienyl dihydropyrans gave oxabicycles with oxabicyclo[4.3.1]decane skeletons. These routes were extended to the synthesis of spiroketals and spiroethers incorporating additional annulated six-membered rings. Diastereoselective Prins cyclization of mono- and bicyclic 2-alkenyl-2-hydroxy-dihydropyrans was highly selective and afforded chloro-substituted spirocycles. Substituted 2-hydroxy-dihydropyrans were obtained through cyclization of δ-hydroxy ketones, which were synthesized from enantiomerically pure sulfoximine-substituted homoallylic alcohols through lithiation and trapping of the α-lithioalkenylsulfoximines with unsaturated aldehydes, followed by allylic oxidation. Inter- and intramolecular glycosidations of the 2-hydroxy-dihydropyrans with O- and C-nucleophiles proceeded with high stereoselectivities and furnished 2,6-trans-configured glycosides. Dihydropyran oxocarbenium ions are most likely intermediates in the glycosidations. According to ab initio calculations, sulfoximine- and trimethyl-substituted dihydropyran oxocarbenium ions adopt a half-chair-like conformation. The energy difference between the oxocarbenium ion with pseudoaxial and the one with pseudoequatorial methyl groups is very small. A transition state model for their reactions with nucleophiles is proposed. It features a half-chair-like conformation, a pseudoequatorial C6 substituent, and an anti-addition of the nucleophile along an axial trajectory to C2 that produces an anti-periplanar lone pair at the O atom. A similar transition state model allows a general explanation for the trans stereoselectivity of the reactions between C6-substituted dihydropyran oxocarbenium ions and nucleophiles. Spiroannulation of 2-hydroxy-dihydropyrans through RCDEM of the corresponding 2,2-dienyl dihydropyrans and Prins cyclization of 2-alkenyl dihydropyrans gave sulfoximine-substituted unsaturated spiroketals and spiroethers. RCDEM of 2,6-dienyl dihydropyrans afforded oxabicycles. A transition state model for the 2,6-trans-stereoselective glycosidation of dihydropyran oxocarbenium ions is proposed. Copyright © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Hte Aktiengesellschaft | Date: 2011-10-17
The present invention relates to a catalysis apparatus for testing catalysts with variable process pressure adjustment over a pressure range from 0.01 millibar to 300 bar. The apparatus preferably has a plurality of reaction chambers (
Hte Aktiengesellschaft | Date: 2012-07-30
The present invention relates to a process for handling product fluid streams which are obtained in the catalytic hydrogenation of liquid feeds in laboratory catalysis apparatuses. The liquid feeds are preferably hydrocarbons comprising sulfur- and nitrogen-comprising compounds as impurities. The hydrogenation serves to convert the impurities into hydrogen sulfide and ammonia which in this form can be readily separated off from the other constituents of the liquid feed. The product fluid streams are contacted with an inert gas stream, with the flow rate of the inert gas being a multiple of the flow rate of the product fluid stream. The formation of deposits in lines of the region on the outlet side of the reaction space can be effectively prevented by means of the process of the invention.
Forster T.,TU Munich |
Schunk S.A.,Hte Aktiengesellschaft |
Jentys A.,TU Munich |
Lercher J.A.,Hte Aktiengesellschaft
Chemical Communications | Year: 2011
Co and Mn polysiloxanes are unique catalyst/initiator systems for the liquid phase oxidation of o-xylene showing higher activity than Co naphthenates, which is related to the weak interaction of the polar products with the hydrophobic surface as well as the absence of hydroxyl groups and surrounding oxygenates limiting radical quenching. © 2011 The Royal Society of Chemistry.