Search results for "SELE"
showing 10 items of 4721 documents
Dual stereocontrolled alkylation of aldehydes with polystyrene-supported nickel complexes derived from α-amino amides
2015
Nickel(II) complexes derived from α-amino amide ligands anchored to gel-type and monolithic polymers act as efficient catalysts for the enantioselective addition of dialkylzinc reagents to aldehydes. Similar to the analogous homogeneous systems, dual stereocontrol in addition products can be achieved by controlling the stoichiometry of the immobilized nickel complex. Aromatic and aliphatic aldehydes were alkylated in good yields with enantioselectivities comparable to those obtained with the homogeneous analogues. These polymer-supported catalysts offer significant advantages as no metal leaching is observed and they can be easily recovered from the reaction mixture by simple filtration and…
Potent affinity material for tracing acetone and related analytes based on molecular recognition by halogen bonds.
2014
Affinity materials based on halogen bonds turned out to be a powerful tool for the molecular recognition of acetone or related carbonyl compounds in the presence of ubiquitous protic molecules. The superior selectivity and sensitivity were found by the gravimetric detection of volatile organic compounds by quartz crystal microbalances.
A solvent-free regioselective iodination route of ortho-carboranes.
2006
Tetraiodo-ortho-carborane based X-ray contrast agents can be readily prepared in a high yield, fast, clean, regioselective fashion by a solvent-free reaction of ortho-carboranes with iodine in sealed tubes.
Literature survey of on-line elemental speciation in aqueous solutions.
2001
The literature about the on-line speciation in water has been comprehensively studied. Critical examination of this subject reveals that a great deal of work has been performed in this area for inorganic metal species and some organic compounds. The topic studied mainly includes the speciation of chromium, selenium, copper, arsenic, lead, cadmium, mercury, iron, aluminium, nickel, tin, antimony, phosphorus, nitrogen and others. The present literature survey includes also comments about the possibilities and problems of speciation as a function of analytical steps, general strategies involved and methods proposed in the literature for each element or a series of elements.
Gravimetric determination of palladium with biguanide sulfate
1986
Abstract Biguanides are interesting reagents for the determination of palladium owing to their solubility, chemical resistance, and selectivity in moderately acidic solutions. A procedure for the gravimetric determination of palladium(II) in the form of Pd(HL)2SO4, where HL = biguanide, is proposed and the conditions of precipitation, treatment of the precipitate, precision, accuracy, and selectivity of the procedure are discussed.
In-situ synthesis of hydrogen peroxide in tandem with selective oxidation reactions: A mini-review
2014
7 Figuras, 6 Tablas
Supported Ionic Liquid Asymmetric Catalysis. A New Method for Chiral Catalysts Recycling. The Case of Proline-Catalyzed Aldol Reaction.
2004
A new method for chiral catalysts recycling, based on the supported ionic liquid asymmetric catalysis concept, has been developed. This concept involves the treatment of a monolayer of covalently attached ionic liquid on the surface of silica gel with additional ionic liquid. These layers serve as the reaction phase in which the homogeneous chiral catalyst is dissolved. As first application of this concept the L-proline-catalyzed aldol reaction has been carried out. Good yields and ee values, comparable with those obtained under homogeneous conditions have been obtained. Moreover, this material shows high regenerability.
Advances towards highly active and stereoselective simple and cheap proline-based organocatalysts
2010
Ten 4-acyloxy-L-prolines were screened as catalysts at loadings of 2–0.1 mol-% for the direct asymmetric aldol reaction in water by using variable amounts of water. Among them, a new catalyst, the L-proline carrying a trans-4-(2,2-diphenylacetoxy) group, and a catalyst previously synthesized by us, the L-proline carrying a trans-4-(4-phenylbutanoyloxy) group, were found to be excellent catalysts for the aldol reaction between cyclohexanone or cyclopentanone and substituted benzaldehydes when employed in only 1 and 0.5 mol-%,respectively, at room temperature without additives. For such catalysts, high turnover numbers were obtained, which are among the highest values obtained for enamine org…
Gold(I)-catalyzed intermolecular oxyarylation of alkynes: unexpected regiochemistry in the alkylation of arenes.
2009
The reaction between acetylenes and sulfoxides, studied as a test case for gold-catalyzed intermolecular addition, provides the oxyarylation compounds 3 in good yields. Unpredictably, in all cases a single regioisomer arising from the electrophilic aromatic alkylation at the position adjacent to the sulfur atom is obtained instead of the expected Friedel−Crafts regioisomer. A new concerted mechanism based on DFT calculations is proposed to account for the products in this intermolecular gold(I)-catalyzed reaction.
Enhanced Heterogeneous Catalytic Conversion of Furfuryl Alcohol into Butyl Levulinate
2014
We study the catalytic condensation of furfuryl alcohol with 1-butanol to butyl levulinate. A screening of several commercial and as-synthesized solid acid catalysts shows that propylsulfonic acid-functionalized mesoporous silica outperforms the state-of-the-art phosphotungstate acid catalysts. The catalyst is prepared via template-assisted sol-gel polycondensation of TEOS and MPTMS. It gives 96 % yield (and 100 % selectivity) of butyl levulinate in 4h at 110 °C. Reaction profiles before and after a hot filtration test confirm that the active catalytic species do not leach into the solution. The catalyst synthesis, characterization, and mode of operation are presented and discussed. Sour ca…