Potential of ionic liquids as co-modifiers in asymmetric hydrogenation on platinum

Publication: Research - peer-reviewJournal article – Annual report year: 2012

Without internal affiliation

  • Author: Sano, Shogo

    Swiss Federal Institute of Technology Zurich, Switzerland

  • Author: Beier, Matthias Josef

    Unknown, Switzerland

  • Author: Mallat, Tamas

    Swiss Federal Institute of Technology Zurich, Switzerland

  • Author: Baiker, Alfons

    Swiss Federal Institute of Technology Zurich, Switzerland

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The enantioselective hydrogenation of methyl benzoylformate on Pt/Al2O3 has been studied in the presence of various ionic liquids (ILs) and three structurally related chiral modifiers: cinchonidine (CD), O-phenyl-cinchonidine (PhOCD), and O-naphthyl-cinchonidine (NaphOCD). Addition of ca. 1% IL to a polar organic solvent – particularly alcohols – improved the enantioselectivity by up to 12% (to 92–93%) in the presence of CD. On the other hand, ILs diminished the reaction rate sometimes dramatically, by two orders of magnitude, and the poisoning effect was even stronger in cyclohexene hydrogenation under identical conditions. Comparative studies revealed that only ILs possessing a heteroaromatic cation interact strongly with Pt or the O-aryl function of PhOCD and NaphOCD. A tentative explanation is the strong π-bonding interaction of ILs with the Pt surface (leading to site blocking and deactivation) and with the O-aryl function of the modifier not involved in the adsorption onto Pt (resulting in a shift in enantioselectivity).
Original languageEnglish
JournalJournal of Molecular Catalysis A: Chemical
Pages (from-to)117-124
StatePublished - 2012
CitationsWeb of Science® Times Cited: 7
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ID: 10208442