Synthesis of 2-nitroalkanols by Mg-Al-O-t-Bu hydrotalcite

Henry (nitroaldol) reactions were performed with Mg-Al-O-t-Bu hydrotalcite as catalyst in quantitative yields in liquid phase under mild reaction conditions at a faster rate. Exclusive synthesis of 2-nitroalkanols (3) is realised by compatible basic sites of Mg-Al-O-t-Bu hydrotalcite

Solid base catalysts in organic synthesis

The basic and catalytic properties of hydrotalcites, supported fluorides and mixed oxides are reviewed, with a special emphasis on C-C bond forming reactions. Relatively strong basicity can be induced on hydrotalcites by calcination followed by rehydration. In that case the shift from Lewis to Bronsted basicity has strong influence on the catalytic properties. The basicity is further enhanced by introduction of t-butoxide or fluoride anions in place of hydroxyls, while chloride anions inhibit activity. Excellent yields have been reported, by fine-tuning of basic sites of the hydrotaclites, supported fluorides and mixed oxides as exemplified in aldol, Henry, Knoevenagel, Michael, trans-esterification Wadsworth- Emmons and N-oxidation reactions. In many cases the catalysts can be recycled

Enantioselective Michael addition reactions catalyzed by a new heterobimetallic asymmetric complex

A heterobimetallic catalyst obtained by reaction of LiAlH<SUB>4</SUB> with aminodiol derived from natural (+)-tartaric acid promotes asymmetric Michael addition of malonic esters, thiophenols and nitro alkanes to cyclic and acyclic enones with excellent yields albeit low enantiomeric excess

Highly efficient "tight fit" immobilization of α-chymotrypsin in mesoporous MCM-41: a novel approach using precursor immobilization and activation

The zymogen α-chymotrypsinogen A is bound to mesoporous silica MCM-41 with a protein loading of 170 mg/g solid (MCM-Z) by a simple stirring in aqueous tris-HCl buffer (pH 7.2). The bound zymogen is then activated with trypsin to obtain α-chymotrypsin immobilized on MCM-41 (MCM-E.I) that displays an effective enzyme activity corresponding to 65 mg protein/g of solid support (3250 BTEE units/g). A direct immobilization of commercially available α-chymotrypsin (MCM-E.II) gives lower loading (1250 BTEE units/g). Protein content of the solid support after immobilization is confirmed by thermogravimetric analysis (TGA). The enzyme is tightly bound to the support and can be used over 100 recycles over 1 week in aqueous as well as reverse micellar media. The immobilized enzyme (MCM-E.I) has been used for resolution of N-acetyl-dl-amino acid esters and racemic trans-4-methoxy-3-phenylglycidic acid (PGA) methyl ester

Change of Dye Bath for Sensitisation of Nanocrystalline TiO Films: Enhances Performance of Dye-Sensitized Solar Cells

The photovoltaic performance of the heteroleptic H102 and HRD2 sensitizers was measured in DSSC and compared with that of reference N719 under similar fabrication and evaluation conditions. The Dye-Sensitised TiO2 electrodes were prepared by staining the electrodes in ethanol bath and 1/1 v/v acetonitrile/tert-butanol (binary liquid) mixture bath separately and the DSSCs based on these sensitizers show that the change of dye bath from ethanol to the binary liquid mixture enhances the photocurrent action spectrum and solar-to-electricity conversion efficiencies, (η). Using ethanol for sensitisation of TiO2 electrodes, the efficiencies obtained for H102, HRD2 and N719 are 4.31%, 4.62%, and 5.46%, respectively, while in binary liquid mixture bath, the corresponding values are enhanced to 5.89%, 4.87%, and 7.23%, respectively, under comparable conditions

Epoxidations of olefins catalysed by new Mn(II) salen immobilized mesoporous materials

Covalently anchored Mn(II) salen complexes on mesoporous materials have been prepared by direct condensation of prefabricated Mn complex on the support or via ensembling step-wise salen entities on the support and subsequent complexation. The resultant anchored complexes have been compared with the immobilised Mn(II) salen complexes on mesoporous materials prepared by the process of cationic exchange of a Mn(II) salen complex for the epoxidation of styrene and cyclic olefins with different oxidizing agents such as PhIO and m-chloroperbenzoic acid. Both types of samples show comparable structures but the anchored complexes can be recycled with perbenzoic acid as oxidant

Montmorillonite substrate selectivity in alcohol oxidation

An unusual display of sequential and preferential molecular recognition in favour of trans-tert-butyl-cyclohexanols 1, primary alcohols 3 and o-benzyl alcohols as against cis-tent-butylcyclohexanols 2, secondary alcohols 4 and p-benzylalcohols, respectively, is described