| Autor: |
Tamás A. Martinek, Mihály Bartók, Katalin Balázsik, Gabriella Fogassy, Imre Bucsi, György Szőllősi, George A. Olah |
| Rok vydání: |
2007 |
| Předmět: |
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| Zdroj: |
Journal of Molecular Catalysis A: Chemical. 272:265-274 |
| ISSN: |
1381-1169 |
| Popis: |
The enantioselective hydrogenations of ethyl pyruvate (EP), methyl benzoylformate (MBF), ketopantolactone (KPL) and pyruvaldehyde dimethylacetal (PADA) were studied on Pt–alumina catalyst modified by a new modifier namely α-isoquinine (α-IQ) with rigid conformation and for comparison by quinine (Q) in toluene and in acetic acid. The effects of modifier concentration, mixtures of modifiers, hydrogenation of α-IQ and theoretical calculations were examined on the interpretation of features of reactions. Using the Engelhard 4759 catalyst under mild experimental conditions (room temperature, 1 bar hydrogen pressure) the ees were lower in the case of α-IQ than for Q. The inversion of enantioselectivity observed in the case of the previously studied β-isocinchonine (β-ICN) containing C8( R ) and C9( S ) atoms in toluene as solvent failed to occur in the presence of α-IQ containing C8( S ) and C9( R ) atoms. Indirect experimental evidence for structure of adsorbed chiral modifier was supported by studies on hydrogenation and relative adsorption strength of α-IQ as well as by theoretical calculations. The significant enantioselectivity changes along the series of otherwise structurally related modifiers (Q, α-IQ and β-ICN) were compared with the ab initio computed geometrical features. The results revealed that besides the effects disclosed up to now in the literature, the orientational angle of the N-lone pair in the quinuclidine moiety relative to the quinoline also influences the structure and the adsorption mode of the intermediate responsible for the enantioselection. |
| Databáze: |
OpenAIRE |
| Externí odkaz: |
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