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

• Published in: Catalysis letters Vol. 134; no. 3-4; pp. 264 - 269
• Main Authors: SZOLLOSI, György, CSERENYI, Szabolcs, BARTOK, Mihály
• Format: Journal Article
• Language: English
• Published: Boston Springer US 01.02.2010; Springer; Springer Nature B.V
• Subjects: Alcohol; Alcohols; Alkaloids; Aluminum oxide; Catalysis; Catalysts; Chemistry; Chemistry and Materials Science; Enantiomers; Exact sciences and technology; General and physical chemistry; Hydrogenation; Industrial Chemistry/Chemical Engineering; Organometallic Chemistry; Physical Chemistry; Theory of reactions, general kinetics. Catalysis. Nomenclature, chemical documentation, computer chemistry; Toluene; Asymmetric hydrogenation; Continuous-flow fixed-bed reactor; Cinchona alkaloids; Unexpected inversion; Platinum; Trifluoroacetophenone; Binary compound; Cinchona; Enantioselectivity; Alcohol; Hydrogenation; Supported catalyst; Alkaloid; Dicotyledones; Angiospermae; Rubiaceae; Hydrocarbon; Toluene; Fixed bed reactor; Transition metal; Complexes; Heterogeneous catalysis; Acids; Benzenic compound; Spermatophyta; Alumina; Catalyst
• ISSN: 1011-372X; 1572-879X
• DOI: 10.1007/s10562-009-0242-2

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. Graphical Abstract