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  • ethyl pyruvate  (6)
  • Industrial Chemistry and Chemical Engineering  (2)
  • 1
    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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  • 2
    Electronic Resource
    Electronic Resource
    Adsorption mode of ethyl pyruvate on platinum: an in situ XANES study (2000)
    Springer
    Catalysis letters 66 (2000), S. 109-112 
    Details
    ISSN: 1572-879X
    Keywords: ethyl pyruvate ; in situ XANES ; enantioselective hydrogenation ; platinum
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The adsorption of ethyl pyruvate on Pt(111) has been studied by in situ XANES measurements in the presence and absence of hydrogen. Depending on the hydrogen and ethyl pyruvate pressure, the C and O K‐edge spectra exhibit distinctly different angular dependence. Without hydrogen ethyl pyruvate is oriented preferentially perpendicular to the surface, indicating bonding via the O lone pairs. In the presence of hydrogen the mean orientation is more tilted towards the surface. Likely, ethyl pyruvate also interacts with Pt via its π system under these conditions. The observed angle‐dependent shift of the energy of the π* and σ* resonances indicates the coexistence of differently adsorbed ethyl pyruvate species. The experimental findings demonstrate the importance of the in situ approach for unraveling the adsorption mode of ethyl pyruvate in the enantioselective hydrogenation over cinchona‐alkaloid‐modified Pt.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1019047622959
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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
    Chiral nitrogen compounds as new modifiers for the enantioselective hydrogenation of ethyl pyruvate (1995)
    Springer
    Catalysis letters 31 (1995), S. 143-151 
    Details
    ISSN: 1572-879X
    Keywords: enantioselective hydrogenation ; chiral modifier ; ethyl pyruvate ; Pt/alumina
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The enantioselective hydrogenation of ethyl pyruvate to (R)- or (S)-ethyl lactate has been studied over alumina- and carbon-supported Pt-metal catalysts modified by various heterocyclic N-compounds and substituted amides. The reactions were carried out under mild conditions in acetic acid; other solvents had a detrimental effect on enantioselectivity. An enantiomeric excess (ee) of 67% and a rate acceleration by a factor of 6, compared to the unmodified catalyst, was observed with alumina-supported Pt modified by (R)-1-(1-naphthyl)ethylamine. In contrast, carbon-supported Pd, Ru and Rh were non-selective and only little active. The studies indicated that besides naphthyl or quinolyl groups, two separate phenyl groups or one phenyl group together with two amino groups can provide a suitable anchoring of the chiral modifier on the Pt surface. The nature of interaction between the modifiers and ethyl pyruvate is briefly discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00808828
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  • 5
    Electronic Resource
    Electronic Resource
    Enantioselective hydrogenation of ethyl pyruvate in supercritical fluids (1995)
    Springer
    Catalysis letters 34 (1995), S. 1-9 
    Details
    ISSN: 1572-879X
    Keywords: enantioselective hydrogenation ; supercritical fluids ; ethyl pyruvate ; cinchonidine ; Pt/alumina ; CO-poisoning
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The enantioselective hydrogenation of ethyl pyruvate to (R)-ethyl lactate has been studied using gases under supercritical conditions as solvents. The catalyst was a 5 wt% Pt/alumina modified with cinchonidine. In supercritical ethane the reaction time could be reduced by a factor of 3.5 compared to toluene under similar conditions, without any loss in enantioselectivity. A further advantage of ethane is that the enantioselectivity remains high even at high catalyst/reactant ratio, which is interesting in view of a possible application of a continuous fixed-bed reactor for this reaction. A strong catalyst deactivation was observed in supercritical CO2, which is due to the reduction of CO2 on Pt as indicated by FTIR.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00808315
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  • 6
    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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  • 7
    Electronic Resource
    Electronic Resource
    Behavior of three-way catalyst in a hybrid drive system (1996)
    Weinheim : Wiley-Blackwell
    Chemical Engineering & Technology - CET 19 (1996), S. 89-95 
    Details
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The dynamic behavior of a Pt-Rh/CeO2-Al2O3 three-way catalyst (TWC) under pulsed flow operation conditions (intermittent mode), such as occur in a newly developed hybrid drive system, has been studied experimentally in a laboratory apparatus with simulated exhaust gas. The parallel hybrid system is based on the combination of an Otto-cycle engine with an electric motor and a flywheel providing a short-term energy storage. This configuration permits intermittent charging of the flywheel by the combustion engine which runs only during about 10% of the driving time. Each exhaust gas pulse (duration typically ca. 3 s) is proceeded by an air pulse, which results from the filling of the engine cylinders with air at start up and shut off. Experimental studies indicated that the air pulses have a negative impact on the performance of the catalytic converter, reducing the inherent benefits resulting from the intermittent operation mode of the combustion engine.Forced asymmetric λ-cycling during exhaust pulse was found to be most beneficial for improving catalyst performance. A simple reduced kinetic model derived from a Langmuir-Hinshelwood model for CO oxidation, which was extended by introducing CO and O2 equivalents to mimic the complex exhaust gas, was used to describe the dynamic behavior of the TWC. The model proved to be useful for finding the optimal λ-cycling conditions. Experiments with the real Otto-cycle engine exhaust proved that the reduced kinetic model is suitable for use in a closed loop λ-control.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/ceat.270190114
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  • 8
    Electronic Resource
    Electronic Resource
    Selective oxidation of o-xylene to phthalic anhydride over vanadia/titania: A comparative study of integral and recycle reactor operationDedicated to Professor Dr. Manfred Baerns on the occasion of his 60th birthday (1995)
    Weinheim : Wiley-Blackwell
    Chemical Engineering & Technology - CET 18 (1995), S. 17-22 
    Details
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Two vanadia/titania catalysts, containing 1 and 8 wt% vanadia on anatase, have been investigated for the selective oxidation of o-xylene to phthalic anhydride. In a comparative study, activity and selectivity in o-xylene oxidation were measured using an integral reactor and a reactor with external product recirculation, with the objective of studying the influence of backmixing in the latter on the reaction behaviour. Adsorbed surface species were investigated by means of in-situ diffuse reflectance FT-IR spectroscopy, using an environmental chamber which corresponds to an integral reactor. No difference in activity and selectivity in o-xylene oxidation was observed between the two catalysts. FT-IR studies showed adsorbed o-xylene, benzoate and a high concentration of phthalic anhydride on the surface of both catalysts. o-Xylene oxidation follows a sequential reaction path, with o-tolualdehyde as the first intermediate and phthalide, phthalic anhydride and maleic anhydride as sequential products. No evidence was found for a direct oxidation-path of o-xylene to phthalic anhydride. Total oxidation products CO and CO2 are formed by direct oxidation of the o-xylene and by oxidation of the reaction products. Due to greatly reduced concentration and temperature gradients, the recycle reactor proved to be highly suitable for studying the extremely exothermic oxidation of o-xylene.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/ceat.270180105
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