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  • ethyl pyruvate  (3)
  • Pt/Al2O3  (2)
  • cinchonidine  (2)
  • 1990-1994  (4)
  • 1
    Electronic Resource
    Electronic Resource
    Enantioselective hydrogenation of ethyl pyruvate on tin promoted Pt/Al2O3 catalysts (1991)
    Springer
    Catalysis letters 10 (1991), S. 325-333 
    Details
    ISSN: 1572-879X
    Keywords: Pt/Al2O3 ; promotion by tin ; modification by tin tetraalkyls ; surface organometallic complexes ; enantioselective hydrogenation ; ethyl pyruvate ; dihydrocinchonidine
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The enantioselective hydrogenation of ethyl pyruvate has been studied on a Pt/Al2O3-dihydrocinchonidine catalyst promoted with different amount of tin. The surface reaction between hydrogen adsorbed on Pt and tin tetraalkyls is used for the tin introduction. This reaction leads to the formation of surface organometallic complexes (I), with SnR(4-x) moieties anchored to the platinum surface. The enantioselectivity of the Pt/Al2O3-dihydrocinchonidine catalyst is found to change only slightly upon promotion with tin, while the rate of ethyl pyruvate hydrogenation depends strongly on the amount and the form of tin introduced. The hydrogenation activity is suppressed completely at relatively low tin coverage (Sn/Pts 〈 0.06). The highest hydrogenation rate is measured over catalysts containing complex (I) (Sn/Pts = 0.025) on the platinum surface. On Sn-Pt alloy type active sites, which are formed after decomposition of (I) in hydrogen, the rate of hydrogŋation is considerably lower than on the unpromoted reference Pt/Al2O3 catalyst.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00769167
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  • 2
    Electronic Resource
    Electronic Resource
    Enantioselective hydrogenation of α-ketoesters over Pt/alumina modified with cinchonidine: theoretical investigation of the substrate-modifier interaction (1994)
    Springer
    Catalysis letters 23 (1994), S. 271-279 
    Details
    ISSN: 1572-879X
    Keywords: Enantioselective hydrogenation ; α-ketoesters ; α-hydroxyesters ; cinchonidine ; modifier ; Pt/alumina ; molecular modelling
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Enantio-differentiation in the asymmetric hydrogenation of α-ketoesters to α-hydroxyesters over platinum catalysts modified with cinchona-alkaloid modifiers occurs through interaction of the ketoester with the cinchona modifier. The structure of the probable transition complex has been calculated for the system methyl pyruvate (substrate) cinchonidine (modifier) using molecular mechanics and quantum chemistry techniques at both ab initio and semiempirical levels. The calculations suggest that protonated cinchonidine is energetically more likely to interact with the substrate and that the crucial interaction occurs via hydrogen bonding of the quinuclidine nitrogen and the oxygen of the α-carbonyl moiety of methyl pyruvate. In this complex the methyl pyruvate is transformed into a half-hydrogenated species which is adsorbed on the platinum surface and on hydrogenation yields the product methyll actate. Theoretical studies indicate that adsorption of the complex leading to (R) -methyl lactate is energetically more favourable than that of the corresponding complex which yields (S) -methyl lactate, which may be the key for the enantio-differentiation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00811362
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  • 3
    Electronic Resource
    Electronic Resource
    Enantioselective hydrogenation of ethyl pyruvate. Influence of oxidative treatment of cinchonidine-modified platinum catalyst and hemiketal formation in alcoholic solvents (1994)
    Springer
    Catalysis letters 29 (1994), S. 115-124 
    Details
    ISSN: 1572-879X
    Keywords: enantioselective hydrogenation ; Pt/alumina ; cinchonidine ; ethyl pyruvate ; protonation ; hemiketal formation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The reasons for the increase in the rate and enantiomeric excess after oxidative (aerobic) treatment of Pt/alumina in ethanol have been investigated. It is demonstrated that this treatment results in the formation of acetic acid and consequently in the protonation of the quinuclidine n1 of cinchonidine. This favours the cinchonidine-pyruvate interaction and improves enantioselectivity. In addition, the reaction rate is enhanced due to acid catalysis of the carbonyl reduction. NMR and UV measurements indicate the rapid transformation of ethyl pyruvate to the corresponding hemiketal in primary alcohols as solvents. It is shown that the possible involvement of this hemiketal (and that formed between cinchonidine and ethyl pyruvate) as an intermediate in the pyruvate hydrogenation mechanism can be excluded.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00814258
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  • 4
    Electronic Resource
    Electronic Resource
    Role of the modifier in the enantioselective hydrogenation of ethyl pyruvate over Pt/Al2O3 catalyst (1990)
    Springer
    Catalysis letters 6 (1990), S. 281-288 
    Details
    ISSN: 1572-879X
    Keywords: Enantioselective hydrogenation ; ethyl pyruvate ; Pt/Al2O3 ; cinchona alkaloids ; modifier
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The time dependence of the conversion and enantioselectivity during the hydrogenation of ethyl pyruvate has been studied over an industrial Pt/Al2O3 catalyst. Various cinchona alkaloids were used as modifier and two different modes were applied for their introduction into the reaction system. The dependence of the enantioselectivity on conversion is strongly influenced by the mode of introduction and the structure of the modifier used. The conversion dependence of the enantioselectivity is attributed to the chemical transformations of the parent alkaloid observed under hydrogenation conditions. Experimental evidence is shown for the dynamic nature of the interaction between the modifier and the catalyst.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00763994
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