H.S. Rama

Bio: H.S. Rama is an academic researcher from Maharaja Sayajirao University of Baroda. The author has contributed to research in topics: Catalysis & Styrene. The author has an hindex of 6, co-authored 6 publications receiving 133 citations.

Catalytic oxidation by polymer-supported copper(II)-L-valine complexes

Abstract: Anchoring of an amino acid l -valine on cross-linked styrene–divinyl benzene was carried out in presence of a base. Reaction of cupric acetate with the polymeric ligand resulted in chelate formation with Cu(II) ion. The immobilized Cu(II) catalysts were characterized by elemental analyses, IR, UV-Vis, SEM, ESR and thermal analysis. Physico-chemical properties like surface area, apparent bulk density, pore volume, etc. have been determined. The supported Cu(II) complexes behave as versatile catalysts in the oxidation of various substrates such as benzyl alcohol, cyclohexanol and styrene in presence of t -butyl hydroperoxide as oxidant. The effect of reaction conditions on conversion and selectivity to products has been studied in detail. Preliminary kinetic experiments reveal that the Cu(II) complexes attached to polymer matrix can be recycled about four times with no major loss in activity.

Catalytic oxidation of alkanes and alkenes by polymer-anchored amino acid-ruthenium complexes

Abstract: A synthetic strategy was developed to anchor an amino acid, l -valine, on to chloromethylated styrene–divinyl benzene co-polymer beads with 6% and 8% cross-linking. The polymeric ligands containing bidentate N,O donor sites were treated with a solution of ruthenium(III)chloride to form the metal complex on the support. These immobilized Ru(III) complexes were characterized by elemental analyses, FT-IR, ESR, SEM and thermal analysis. Physico-chemical properties of the supported catalysts were also studied. The catalytic oxidation of cyclohexane and toluene were investigated using the catalysts in presence of tert -butyl hydroperoxide as the terminal oxidant at ambient and at 45 °C. In the case of cyclohexane the formation of cyclohexanol and cyclohexanone were observed. Benzaldehyde was selectively obtained with toluene as substrate. The catalysts are also active in the epoxidation of olefins such as styrene and norbornylene. Recycling studies indicate that the catalyst can be recycled three to four times without significant degradation of polymer matrix. The probable mechanistic pathway has been described.

A study of synthesis, characterization and catalytic hydrogenation by polymer anchored Pd(II)-amino acid complexes

Abstract: l -Valine was anchored to 6% and 8% cross-linked poly(styrene-divinyl benzene) resin and its complex with palladium chloride was prepared. The newly synthesized catalysts were characterized by various techniques such as elemental analysis, FT-IR, DRS, SEM and TGA. Physico-chemical properties like surface area, swelling behavior in different solvents, bulk density, etc. have been determined. The polymer supported Pd complexes behave as versatile and recyclable catalysts for the hydrogenation of 1-octene, cyclohexene, acetophenone and nitrobenzene. Kinetics of hydrogenation of 1-octene has been investigated in detail. The influence of different reaction parameters on conversion and selectivity to products are reported.

Catalytic Asymmetric Epoxidation of Unfunctionalized Olefins by Supported Cu(II)-Amino Acid Complexes

Abstract: Polymer-supported Cu(II) complexes with L-phenyl alanine and L-valine were used as chiral catalysts for asymmetric epoxidation of nonfunctionalized straight-chain terminal olefins viz. 1-octene, 1-hexene, 2-methyl-1-pentene and 4-methyl-1-pentene using m-chloroperbenzoic acid (m-CPBA) as oxidant giving high conversions and selectivity. Enantiomeric yields, though moderate, are comparable with the best-reported ees using homogeneous catalysts. All catalysts displayed good recycling efficiency. Variations in percent ee have been discussed on the basis of the structural geometry of the supported catalysts and the trajectory of the olefin approach to the active oxo-intermediate.

Catalytic epoxidation of olefins by polymer-anchored amino acid ruthenium complexes

Abstract: A synthetic strategy was developed to anchor an amino acid l -valine on to styrene–divinylbenzene co-polymer beads with 8% and 6% cross linking. The polymeric ligands containing bidentate N,O donor sites were treated with a solution of ruthenium(III) chloride to form the metal complex on the support. These immobilized Ru(III) complexes were characterized by elemental analysis, FT-IR, UV–visible diffuse reflectance, ESR, SEM and thermal analysis. The catalytic epoxidation of styrene, norbornylene, cyclooctene, and cyclohexene were investigated using the supported catalysts in the presence of tert.-butyl hydroperoxide as the terminal oxidant. Selective epoxide formation was observed with norbornylene and cis-cyclooctene whereas in the case of styrene the corresponding epoxide, benzaldehyde and acetophenone were obtained. Amongst the olefins screened, good activity was observed in the case of cyclohexene. The effect of various reaction parameters as well as some aspects of catalyst recycling and possible mechanistic pathways has also been investigated.

Advances in Homogeneous and Heterogeneous Catalytic Asymmetric Epoxidation

Abstract: Laboratory for Advanced Materials and New Catalysis, School of Chemistry and Materials Science, Hubei University, Wuhan 430062, China,Laboratory of Natural Gas Utilization and Applied Catalysis, Dalian Institute of Chemical Physics of Chinese Academy of Sciences, Dalian 116023,China, and Jingmen Technological College, Jingmen 448000, ChinaReceived June 30, 2004

Enantioselective Epoxidation of Terminal Alkenes to (R)- and (S)-Epoxides by Engineered Cytochromes P450 BM-3

Abstract: Cytochrome P450 BM-3 from Bacillus megaterium was engineered for enantioselective epoxidation of simple terminal alkenes. Screening saturation mutagenesis libraries, in which mutations were introduced in the active site of an engineered P450, followed by recombination of beneficial mutations generated two P450 BM-3 variants that convert a range of terminal alkenes to either (R)- or (S)-epoxide (up to 83 % ee) with high catalytic turnovers (up to 1370) and high epoxidation selectivities (up to 95 %). A biocatalytic system using E. coli lysates containing P450 variants as the epoxidation catalysts and in vitro NADPH regeneration by the alcohol dehydrogenase from Thermoanaerobium brockii generates each of the epoxide enantiomers, without additional cofactor.