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Very Mild Reaction Conditions (very + mild_reaction_condition)
Selected AbstractsHighly efficient and chemoselective acetalization of carbonyl compounds catalyzed by new and reusable zirconyl triflate, ZrO(OTf)2HETEROATOM CHEMISTRY, Issue 3 2009Majid Moghadam Various types of aromatic aldehydes were efficiently converted to their corresponding 1,3-dioxanes and 1,3-dioxolane with 1,3-propanediol and ethylene glycol, respectively, in the presence of catalytic amount of ZrO(OTf)2 in acetonitrile at room temperature. The catalyst can be reused several times without loss of its catalytic activity. Very short reaction times, selective acetalization of aromatic aldehydes in the presence of aliphatic aldehydes and ketones, very mild reaction conditions, reusability of the catalyst, and easy workup are noteworthy advantages of this method. © 2009 Wiley Periodicals, Inc. Heteroatom Chem 20:131,135, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.20523 [source] The First Anionic Thia-Fries Rearrangements at Ferrocene: Ready Access to Trifluoromethylsulfonyl-Substituted Hydroxyferrocenes and an Extremely High Interannular Stereoinduction between Cyclopentadienyl LigandsADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 8 2010Georg Werner Abstract Attempts originally directed towards the generation of ferrocyne (1,2-dehydroferrocene, 4) and ferrocenediyne (1,2,1,,2,-tetradehydroferrocene, 5) by triflate elimination from the respective ferrocenyl triflates led to the discovery of the first anionic thia-Fries rearrangements at a five-membered ring. These reactions take place with remarkable efficiency under very mild reaction conditions and yield the respective trifluoromethylsulfonyl-substituted ferrocenols. Most remarkably, the reaction starting from 1,1,-ferrocenediyl ditriflate (9) adopts an extremely high interannular stereoinduction in that exclusively the meso rearrangement product, meso -2,2,-bis(trifluoromethylsulfonyl)-1,1,-ferrocenediol (16), is formed, the corresponding racemic product 17 is not observed. It is shown that the second anionic thia-Fries rearrangement proceeds at a much larger rate than the first one. The stereochemistry and the high rate of this reaction are explained on the basis of electronic as well as steric considerations. The redox behavior of some of the unprecedented ferrocene derivatives has been characterized by cyclovoltammetry. [source] Hydrogenation of Phenol in Supercritical Carbon Dioxide Catalyzed by Palladium Supported on Al-MCM-41: A Facile Route for One-Pot Cyclohexanone FormationADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 11-12 2009M. Chatterjee Abstract The hydrogenation of phenol has been carried out in supercritical carbon dioxide (scCO2) under very mild reaction conditions at the temperature of 50,°C over palladium supported Al-MCM-41 (metal loading ,1%). This palladium catalyst is shown to be highly active and promotes the selective formation of cyclohexanone (,98%), an industrially important compound, in a "one-pot" way. The effects of different variables like carbon dioxide and hydrogen pressure, reaction time and also silica/alumina ratio of the MCM-41 support along with palladium dispersion are presented and discussed. The pressure effect of carbon dioxide is significantly prominent in terms of conversion and cyclohexanone selectivity. Moreover, the silica/alumina ratio was also found to be an important parameter to enhance the effectiveness of the catalyst as it exhibits a remarkable increase in phenol conversion from 20.6% to 98.4% as the support changes from only silica MCM-41 to Al-MCM-41. A plausible mechanism for the hydrogenation of phenol to cyclohexanone over the palladium catalyst has been proposed. The proposition is validated by transition state calculations using density functional theory (DFT), which reveal that cyclohexanone is a favorable product and stabilized by <19,kcal,mol,1 over cyclohexanol in scCO2 medium. Under similar reaction conditions, phenol hydrogenation was also carried out with rhodium, supported on Al-MCM-41. In contrast to the palladium catalyst, a mixture of cyclohexanone (57.8%) and cyclohexanol (42.2%) was formed. Detailed characterization by X-ray diffraction and transmission electron microscopy confirmed the presence of metal nanoparticles (palladium and rhodium) between 10,20,nm. Both the catalysts exhibit strikingly different product distributions in solventless conditions compared to scCO2. This method can also be successfully applied to the other hydroxylated aromatic compounds. [source] Oxidative processes of desulfurization of liquid fuelsJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 7 2010J.M. Campos-Martin Abstract Environmental concerns have introduced a need to remove sulfur-containing compounds from light oil. As oxidative desulfurization is conducted under very mild reaction conditions, much attention has recently been devoted to this process. In this contribution, the developments in selective removal of organosulfur compounds present in liquid fuels via oxidative desulfurization, including both chemical oxidation and biodesulfurization, are reviewed. At the end of each section, a brief account of the research directions needed in this field is also included. Copyright © 2010 Society of Chemical Industry [source] Rhodium-Catalyzed Formation of Stereocontrolled Trisubstituted Alkenes from Baylis,Hillman AdductsCHEMISTRY - A EUROPEAN JOURNAL, Issue 18 2009Thomas Gendrineau Abstract Efficient and general conditions for the formation of stereodefined trisubstituted alkenes by using the rhodium-catalyzed reaction of unactivated Baylis,Hillman adducts with either organoboronic acids or potassium trifluoro(organo)borates are reported (see scheme). We report here efficient and general conditions for the formation of stereodefined trisubstituted alkenes using the rhodium-catalyzed reaction of unactivated Baylis,Hillman adducts with either organoboronic acids and potassium trifluoro(organo)borates. The use of the [{Rh(cod)OH}2] precursor gave very fast coupling reactions under low catalyst loading, very mild reaction conditions (from room temperature up to 50,°C) and without the need of additional phosphane ligands. Based on the new reaction conditions, the reaction, originally limited to Baylis,Hillman adducts derived from esters, could be extended to a large variety of Baylis,Hillman adducts, bearing either keto, cyano or amido functionalities. Moreover, the reaction of Baylis,Hillman adducts bearing esters functionality was improved and could be conducted at lower temperature using lower catalyst loading. [source] Highly Efficient Redox Isomerization of Allylic Alcohols at Ambient Temperature Catalyzed by Novel Ruthenium,Cyclopentadienyl Complexes,New Insight into the MechanismCHEMISTRY - A EUROPEAN JOURNAL, Issue 20 2005Belén Martín-Matute Dr. Abstract A range of ruthenium cyclopentadienyl (Cp) complexes have been prepared and used for isomerization of allylic alcohols to the corresponding saturated carbonyl compounds. Complexes bearing CO ligands show higher activity than those with PPh3 ligands. The isomerization rate is highly affected by the substituents on the Cp ring. Tetra(phenyl)methyl-substituted catalysts rapidly isomerize allylic alcohols under very mild reaction conditions (ambient temperature) with short reaction times. Substituted allylic alcohols have been isomerized by employing Ru,Cp complexes. A study of the isomerization catalyzed by [Ru(Ph5Cp)(CO)2H] (14) indicates that the isomerization catalyzed by ruthenium hydrides partly follows a different mechanism than that of ruthenium halides activated by KOtBu. Furthermore, the lack of ketone exchange when the isomerization was performed in the presence of an unsaturated ketone (1 equiv), different from that obtained by dehydrogenation of the starting allylic alcohol, supports a mechanism in which the isomerization takes place within the coordination sphere of the ruthenium catalyst. [source] | ||||||||||