Enantioselective hydrogenation of α-keto esters over catalyst. Kinetic evidence for the substrate-modifier interaction in the liquid phase

Margitfalvi, József L.; Hegedűs, Mihály; Tfirst, E.

doi:10.1016/0957-4166(96)00041-9

Cited by 66 publications

(61 citation statements)

References 16 publications

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“…In these cases the DHCN binds the EtPy as a nucleophile. The mechanism based on the N fi C@O interaction was previous supported [38][39][40] and later verified by quantum chemical calculations [41] and by hydrogenation of trifluoromethyl ketones [42]. To interpret the enantioselective hydrogenation of EtPy the role of the metalorganic type surface complexes may not be excluded either.…”

Section: Interpretation Of the Results And Conclusionmentioning

confidence: 90%

Enantioselective hydrogenation of ethyl pyruvate catalysed by cinchonine-modified Pt/Al2O3: tilted adsorption geometry of cinchonine

et al. 2005

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The enantioselective hydrogenation of ethyl pyruvate (EtPy) was studied on Pt-alumina catalyst modified by cinchonine (CN) and for comparison by cinchonidine (CD) in toluene and in AcOH. The effects of the modifiers concentration on the reaction rate and the enantioselectivity were examined. Using the Engelhard 4759 catalyst under mild experimental conditions (room temperature, hydrogen pressure 1 bar) in the case of CN (S)-ethyl lactate (EtLt) formed in excess (ee) (in AcOH ee max $ 88%; in toluene ee max $ 72%). In the case of CD (R)-EtLt formed in excess (in AcOH ee max $93%; in toluene ee max $ 84%). The results of H-D exchange measurements and results of modifier mixtures suggest that the compounds responsible for chiral induction are different intermediates, which structure depends mostly on the acidic or non-acidic nature of the hydrogenation medium. The proposed structure of intermediate responsible for enantioselection is an 1:1 CN-or CD-EtPy surface complex in which the quinoline skeleton of CD approximately parallel on the Pt surface while the quinoline plane of CN being tilted relative to the Pt surface under identical experimental conditions.

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Section: Interpretation Of the Results And Conclusionmentioning

confidence: 90%

Enantioselective hydrogenation of ethyl pyruvate catalysed by cinchonine-modified Pt/Al2O3: tilted adsorption geometry of cinchonine

et al. 2005

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“…The RA caused by tertiary amines was interpreted in term of nucleophilic attack of the tertiary nitrogen atom to the carbon atom of the keto group [17,[36][37][38].…”

Section: Kinetic Resultsmentioning

confidence: 99%

“…The above complex requires sufficient room for its accommodation at the Pt sites [15,16]. Contrary to that the ''shielding effect model'' suggests the formation of ''substrate-modifier complex'' in the liquid phase and the hydrogenation of the formed ''supramolecule'' over Pt sites [17][18][19][20]. In the supramolecule the modifier is in closed conformation.…”

Section: Introductionmentioning

confidence: 96%

Anomalous behavior of rigid cinchona alkaloids in the enantioselective hydrogenation of ethyl pyruvate in an aprotic solvent

Margitfalvi

Tálas

2006

Applied Catalysis A: General

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“…The monotonic increase (MI) type ee-conversion (time) dependencies were attributed both to kinetic behavior [6,15] and the experimental artifacts [16]. Our results showed that the monotonic increase type behavior is unavoidable if the steady-state concentration of the substrate-modifier complex formed in the liquid phase cannot be achieved [17], i.e., the monotonic increase character can be induced by both the reaction kinetics and the experimental artifacts.…”

Section: Introductionmentioning

confidence: 63%

Enantioselective hydrogenation of ethyl pyruvate over cinchonidine-Pt/Al2O3 catalyst. A reaction kinetic approach

2006

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A new reaction kinetic approach was used to describe the enantioselective hydrogenation of ethyl pyruvate over cinchona-Pt catalyst. The above reaction was considered as the sum of two parallel reactions: (i) racemic hydrogenation resulting in R-and S-product in equal amount and (ii) enantioselective hydrogenation leading to the exclusive formation of one of the two optically isomers. New terms such as acc diff and k e /k r (where k e and k r are the rate constants of the enantioselective and racemic hydrogenation, respectively) were introduced to characterize the relationship between the enantioselective and the racemic hydrogenation reactions. Results obtained show that the formation of R-product is rate accelerated, while the formation of S-product is decelerated. The results indicate also that the overall rate increase is a kinetic phenomenon and cannot be attributed to the suppression of the poisoning effect of CO or oligomers formed from ethyl pyruvate. The strong rate acceleration effect of achiral tertiary amines (ATAs) added to the reaction mixture was attributed to the decrease of the loss of modifier during the hydrogenation experiments.

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Enantioselective hydrogenation of α-keto esters over catalyst. Kinetic evidence for the substrate-modifier interaction in the liquid phase

Cited by 66 publications

References 16 publications

Enantioselective hydrogenation of ethyl pyruvate catalysed by cinchonine-modified Pt/Al2O3: tilted adsorption geometry of cinchonine

Enantioselective hydrogenation of ethyl pyruvate catalysed by cinchonine-modified Pt/Al2O3: tilted adsorption geometry of cinchonine

Anomalous behavior of rigid cinchona alkaloids in the enantioselective hydrogenation of ethyl pyruvate in an aprotic solvent

Enantioselective hydrogenation of ethyl pyruvate over cinchonidine-Pt/Al2O3 catalyst. A reaction kinetic approach

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