1,720,982 research outputs found
Graphene-Based Carbocatalysts for Thermoset Polymers and for Diastereoselective and Enantioselective Organic Synthesis
No full textThis review reports on the catalytic activity of graphene oxide (GO) and high-surface-area graphite (HSAG) for some relevant organic reactions. It is shown that the main drawbacks of graphite-based catalysts, that is, high catalyst loading and generally poor selectivity, can often be removed by operating under solvent-free conditions. Moreover, some reactions that are catalyzed by GO as well as HSAG are presented. For these reactions, stacking of the aromatic substrates with the graphitic planes plays a predominant role in the catalytic activity and the unexpected diastereoselective and enantioselective behaviors
Influence of a remote sulfinyl group on L-proline-catalyzed direct asymmetric aldol addition of acetone
No full textThe addition of acetone to rac-2-methylsulfinyl-benzaldehyde, catalyzed by secondary amines (morpholine, piperidine, L-proline, L-prolinamide and (S)-(–)-α,α-diphenyl-2-pyrrolidinemethanol trimethylsilyl ether), was realized. Interesting aspects, such as 1,4-asymmetric induction by the remote sulfinyl group of the aldehyde but also the stereochemical control and kinetic resolution of the racemic substrate by the chiral organocatalyst were examined. Finally, an unexpected stereoselective retro-aldol reaction catalyzed by L-proline was pointed out
Synthesis of multifunctionalized building blocks via vinylogous addition of Chan's diene to carbonyl and carbonyl-related electrophiles, mediated by molecular iodine
No full textThe synthesis of multifunctionalized β-ketoesters has been achieved by using molecular iodine as a catalyst under very mild conditions. The vinylogous addition of Chan's diene 1 to carbonyl and carbonyl-related compounds (aldehydes, ketones, imines and acetals) occurred with high efficiencies and with complete γ-selectivity, giving a useful method for the synthesis of interesting libraries of different δ-functionalized β-ketoesters. © 2011 Elsevier Ltd. All rights reserved
Edge-oxidation of graphites by hydrogen peroxide
No full textA simple and eco-friendly procedure of edge oxidation of high-surface area graphites, based on hydrogen peroxide treatments at 60 degrees C, is presented. Already, short-term treatments lead to O/C weight ratios higher than 0.1, leaving unaltered interlayer spacing and correlation length. This clearly indicates that all oxidized groups are located on exposed sites (mainly on lateral edges) of the graphitic layers. Short-term H2O2 treatments, as expected, increase hydrophilicity and reduce thermal stability with respect to the starting graphite. Long-term treatments, on the contrary, reduce hydrophilicity and increase thermal stability with respect to the starting graphite, mainly due to surface area reduction associated with the oxidation procedure. Exfoliation of a substantial fraction of the obtained edge-oxidized graphite can be achieved by simple procedures of dispersion and sonication in water
Release of cationic drugs from charcoal
No full textThe goal of this research is to improve preparation of charcoal adducts in a manner suitable for cationic drug release, possibly using an eco-friendly procedure. Charcoal, widely commercialized for human ingestion, is oxidized by hydrogen peroxide in mild conditions. Adducts of a cationic drug (lidocaine hydrochloride, a medication used as local anesthetic) with charcoal are prepared after basification of charcoal and characterized mainly by elemental analysis, wide-angle X-ray diffraction, infrared spectroscopy and thermogravimetry. The drug in the prepared adducts is present in amount close to 30% by weight and can be readily released to both neutral and acidic aqueous solutions. Cation release, as studied by UV spectra of aqueous solutions, is faster in acidic solutions and is faster than for adducts with graphite oxide, which can be prepared only in harsh conditions
Solvent-free organocatalytic Mukaiyama-Michael addition of 2-trimethylsilyloxy furan to nitroalkenes catalyzed by Brønsted acids
No full textThe first organocatalytic Mukaiyama-Michael addition of 2-trimethylsilyloxy furan to nitroalkenes was promoted by Brønsted acids under solvent-free conditions. The conjugate addition took place in moderate to good yields with variously substituted nitroalkenes. The procedure is operationally simple and no workup is required
1-Naphthyl-TADDOL/Emim BF4: A new catalytic system for the asymmetric addition of Chan's diene to aromatic aldehydes
No full textA new organocatalytic system was tested as a promoter for the asymmetric addition of Chan's diene to aldehydes under solvent-free conditions. This new organocatalyst generated in situ by mixing 1-naphthyl-TADDOL derivative and Emim BF4 was able to give enantioenriched vinylogous aldols and hetero-Diels-Alder cycloadducts. A mechanistic investigation through the detection of nonlinear effects confirmed the involvement of the ionic liquid in the formation of a new catalytic supramolecular species. © 2010 Versita Warsaw and Springer-Verlag Wien
New chiral imino- and amino-sulfoxides as activators of allyl trichlorosilane in the asymmetric allylation of aldehydes
No full textChiral 2-methylsulfinyl benzaldehyde proved to be a valuable starting material for a convenient approach towards a variety of imino- and amino-sulfoxides. The catalytic properties of these new ligands, as potential activators of allyl trichlorosilane, have been exploited in new catalytic procedures for the synthesis of enantioenriched homoallylic alcohols. © 2010 Elsevier Ltd. All rights reserved
Epoxy Resin Catalyzed by Graphite-Based Nanofillers
No full textGraphene stacks/epoxy nanocomposites were produced and characterized in order to analyse the effect of different graphene precursors on cure reaction of a model epoxy matrix. A kinetic analysis of the cure mechanism of the epoxy resin associated to the catalytical activity of the graphite based fillers was performed by isothermal DSC measurements. The DSC results showed that the addition of all graphite based fillers greatly increased the enthalpy of epoxy reaction and the reaction rate, confirming the presence of a catalytic activity of graphitic layers on the crosslinking reaction between the epoxy resin components (epoxide oligomer and di-amine). A kinetic modelling analysis, arising from an autocatalyzed reaction mechanism, was finally applied to isothermal DSC data, in order to predict the cure mechanism of the epoxy resin in presence of the graphite based nanofiller
Mukaiyama-Michael vinylogous additions to nitroalkenes under solvent-free conditions
No full textThe first Mukaiyama-Michael vinylogous reaction of a dioxinone-derived silyl ether to nitroalkenes is reported. The conjugate addition is performed in absence of any catalyst under solvent-free conditions, proceeding with satisfactory efficiency with variously substituted nitroalkenes. Moreover, the first organocatalyzed Mukaiyama-Michael vinylogous reaction of trimethylsilyloxyfuran to nitroalkenes is described.The reaction is promoted by Brønsted acids under solvent-free conditions, taking place in moderate to good yield with variously substituted nitroalkenes.. © 2011 Versita Warsaw and Springer-Verlag Wien
- …
