Novel evidence on the role of the nucleophilic intermediate complex in the orito-reaction: Unexpected inversion in the enantioselective hydrogenation of 2,2,2-trifluoroacetophenone on Pt-Cinchona chiral catalyst using continuous-flow fixed-bed reactor

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Abstract

The enantioselective hydrogenation of 2,2,2,- trifluoroacetophenone over Pt/Al 2 O 3 catalysts modified by cinchona alkaloids was investigated for the first time using continuous-flow fixed-bed reactor system in toluene/AcOH 9/1 solvent mixture in absence and presence of 0.1 v/v% trifluoroacetic acid (TFA). The enantioselective hydrogenations yielded the (R)-product in excess on Pt-CD, Pt-CN, Pt-QN and Pt-QD catalysts in toluene/AcOH mixture; consequently, unexpected inversion took place on the Pt-CN and Pt-QD catalysts. Hydrogenation in the presence of 0.1% (v/v) TFA follows the general rule of the Orito reaction, according to which the products formed in excess are (R)-alcohols on Pt-CD and Pt-QN and (S)- alcohols on Pt-CN and Pt-QD. Since there is no inversion in the presence of TFA, the observed unexpected inversion can be interpreted on the basis of the nucleophilic intermediate complex.

Original languageEnglish
Pages (from-to)264-269
Number of pages6
JournalCatalysis Letters
Volume134
Issue number3-4
DOIs
Publication statusPublished - Feb 2010

Keywords

  • Asymmetric hydrogenation
  • Cinchona alkaloids
  • Continuous-flow fixed-bed reactor
  • Platinum
  • Trifluoroacetophenone
  • Unexpected inversion

ASJC Scopus subject areas

  • Catalysis
  • Chemistry(all)

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