Inversion of enantioselectivity for the hydrogenation of ethyl pyruvate in the gas-phase over Pt/SiO2 modified with derivatives of hydroquinidine

N. F. Dummer, R. Jenkins, X. Li, S. M. Bawaked, P. McMorn, A. Burrows, C. J. Kiely, Richard Peter Kerwin Wells, D. J. Willock, G. J. Hutchings

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Abstract

Ethyl pyruvate was hydrogenated as a gas-phase reactant over 2.5% Pt/SiO2 premodified with hydroquinidine 4-chlorobenzoate at two concentrations (0.85 and 8.5 mM g(cat)(-1)). The sense of enantioselectivity changed as a function of the modifier concentration. At low modifier concentrations, the (S)-lactate is the preferred product, and at higher concentrations, (R)-lactate is favoured. The lower concentration yielded an enantiomeric excess (ee) of 15% (S)-ethyl lactate in contrast to 17% (R)-lactate for the higher concentration. A range of hydroquinidine and hydroquinine derivatives were evaluated at these concentrations; the results suggest that the carbonyl group of the ester linkage at the C(9) position was required to promote the observed inversion of enantioselectivity. In a subsequent set of experiments, Bi3+ was adsorbed onto the Pt/SiO2 catalyst before the premodification step; these ions are considered to adsorb preferentially on high-energy surface sites (e.g., corner sites or step edges). Increasing Bi3+ concentration decreased the degree of inversion until the effect was lost. On the basis of high-resolution electron microscopy (HREM) comparisons of these Pt/SiO2 and Bi-PtlSiO(2) catalysts, the inversion effect is discussed in terms of the interaction of the substrate and modifier with the catalyst surface. (c) 2006 Elsevier Inc. All rights reserved.

Original languageEnglish
Pages (from-to)165-170
Number of pages5
JournalJournal of Catalysis
Volume243
DOIs
Publication statusPublished - 2006

Keywords

  • PLATINUM-CATALYZED HYDROGENATION
  • ASYMMETRIC HYDROGENATION
  • ENANTIO SELECTIVITY
  • ORITO-REACTION
  • CINCHONIDINE
  • 1-PHENYLPROPANE-1,2-DIONE
  • KETOPANTOLACTONE
  • KETONES
  • EXCESS
  • SENSE

Cite this

Dummer, N. F., Jenkins, R., Li, X., Bawaked, S. M., McMorn, P., Burrows, A., Kiely, C. J., Wells, R. P. K., Willock, D. J., & Hutchings, G. J. (2006). Inversion of enantioselectivity for the hydrogenation of ethyl pyruvate in the gas-phase over Pt/SiO2 modified with derivatives of hydroquinidine. Journal of Catalysis, 243, 165-170. https://doi.org/10.1016/j.jcat.2006.07.015