Synthesis of dioxolanes and oxazolidines by silica gel catalysis (original) (raw)
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Silica Gel-Mediated Organic Reactions under Organic Solvent-Free Conditions
Molecules, 2012
Silica gel was found to be an excellent medium for some useful organic transformations under organic solvent-free conditions, such as (1) the Friedel-Crafts-type nitration of arenes using commercial aqueous 69% nitric acid alone at room temperature, (2) one-pot Wittig-type olefination of aldehydes with activated organic halides in the presence of tributyl-or triphenylphosphine and Hunig's base, and (3) the Morita-Baylis-Hillman reaction of aldehydes with methyl acrylate. After the reactions, the desired products were easily obtained in good to excellent yields through simple manipulation.
2021
In this work, a simple green synthesis of six oxazolidinones derivatives from the reaction of arylamines, diethyl carbonate, ethylene oxide, and ionic liquids was studied. The prepared compounds were firstly purified using the chromatography, then characterized by 1H NMR and 13C NMR. The effect of ionic liquid amount, time, and temperature were examined. The optimal reaction conditions for one-pot conversion of these reactants were 130 °C, 12 h, and 10% amount of catalyst. The results demonstrated that the upper yield of oxazolidinone was provided by anions of ionic liquids with stronger bond basicity, that follows the order OAc->Cl->Br->BF4⎻ below delicate reaction conditions, Bmim OAC was found to be an ideal catalyst for formation of some oxazolidinones in high yields.
Molecules, 2010
The impact of immobilization of oxazaborolidines supported on silica via different substituents on the boron and nitrogen atoms is evaluated in the enantioselective reduction of acetophenone. The performances of the homogeneous analog oxazaborolidines and silica-supported ones are compared by varying different parameters. This article deals with the synthesis, characterization and catalytic evaluation of silicasupported oxazaborolidines, their recycling capabilities and regeneration limitations.
Comptes Rendus Chimie, 2016
High surface area mesoporous silica based catalysts have been prepared by a simple hydrolysis/solegel process without using any organic template and hydrothermal treatment. A controlled hydrolysis of ethyl silicate-40, an industrial bulk chemical, as a silica precursor, resulted in the formation of very high surface area (719 m 2 /g) mesoporous (pore size 67 Å and pore volume 1.19 cc/g) silica. The formation of mesoporous silica has been correlated with the polymeric nature of the ethyl silicate-40 silica precursor which on hydrolysis and further condensation forms long chain silica species which hinders the formation of a close condensed structure thus creating larger pores resulting in the formation of high surface mesoporous silica. Ethyl silicate-40 was used further for preparing a solid acid catalyst by supporting molybdenum oxide nanoparticles on mesoporous silica by a simple hydrolysis solegel synthesis procedure. The catalysts showed very high acidity as determined by NH 3-TPD with the presence of Lewis as well as Brønsted acidity. These catalysts showed very high catalytic activity for esterification; a typical acid catalyzed organic transformation of various mono-and di-carboxylic acids with a range of alcohols. The in situ formed silicomolybdic acid heteropoly-anion species during the catalytic reactions were found to be catalytically active species for these reactions. Ethyl silicate-40, an industrial bulk silica precursor, has shown a good potential for its use as a silica precursor for the preparation of mesoporous silica based heterogeneous catalysts on a larger scale at a lower cost.
The Synthesis and Reactions of Silylaziridines
2000
The reaction of an α-trialkylsilylvinyl carbanion and carboxylic acid derivatives gives α,β-unsaturated carbonyl compounds which, under the conditions of the reaction undergo further conjugate additiorn. The enolate thus formed can also react further, depending upon their reactivity and that of the carboxylic acid derivative. The α-trialkylsilylvinyl carbanion reacted with the α,β-unsaturated ketone to give the 1,4 -addition product. Further acylation of the enolate by acetic anhydride leads to attack at the oxygen while the use of alkyl chloroformates led to attack at the carbon. The reaction of an α-trialkylsilylvinyl carbanion with the α,β-unsaturated ester, formed a product arising from two conjugate additions, irrespective of the ratio of the carbanion to the ester. This product seems to be particularly stable so does not undergo further acylation. We also examined the ability of a silicon to stabilise a positive charge in the α- or β-position. Silanes containing both vinyl and...
Chemical Engineering Journal, 2011
The catalytic conversion of glycerol to acrolein by liquid-phase dehydration over molecular sieves catalysts was studied. In order to understand the role of the acidity, structure and porosity, five structures were synthesized and evaluated. The lower the Si/Al ratio, the higher the activity; large pore molecular sieves, as HY showed high performance (conversion = 89.0%; selectivity to acrolein = 99.5%), while siliceous molecular sieves such as SBA-15 possessing weak acidity, exhibited low conversion (40.6%) and decreased selectivity to acrolein (84.0%). The structure and the acidity govern the selectivity to acrolein and hydroxyacetone, the latter being a by-product mainly dependent on the amount of weak and medium strengths acidic sites, as in the case of H. The activity has almost the same order of the acidity: HY > H > Mor > SBA-15 > ZSM-23. Modifications of the most acidic and active catalysts by silanation (CVD) or Pt incorporation did not result in an enhanced conversion. The studies of reusability and the nature of the coke deposits indicated that heavy polycondensed and cyclic C 6 compounds resulting from the reaction between glycerol and acrolein block the pores and the acidic sites. The blockage was the main cause of deactivation, whereas acidic site poisoning led to a less extensive deactivation of the surface active sites. From these results, it was possible to establish acidity-activity-deactivation relationships that allow to explain the behaviour of the catalysts.
ChemInform, 2008
Ketones Q 0350 New Ionic Liquid-Modified Silica Gels as Recyclable Materials for L-Proline-or H-Pro-Pro-Asp-NH 2-Catalyzed Aldol Reaction.-L-proline and the tripeptide (PEP) are supported, by adsorption, onto the surface of modified silica gels functionalized with a monolayer of covalently attached imidazolium salts. The resulting materials are used as catalyst for the aldol reaction between acetone (III) and substituted benzaldehydes (II). Good yields and enantioselectivities, comparable to or better than those obtained under homogeneous conditions are obtained. In general, the supported tripeptide gives higher enantioselectivities compared to those obtained with supported proline. The materials are easily recovered by filtration.