Heterogeneous asymmetric reactions Part 17. Asymmetric hydrogenation of 2-methyl-2-pentenoic acid over cinchona modified Pd/Al2O3 catalysts

István Kun, Béla Török, Károly Felföldi, Mihály Bartók

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Abstract

The enantioselective hydrogenation of 2-methyl-2-pentenoic acid (MPA) over a cinchona modified 5% Pd/Al2O3 catalysts is described. The main experimental variables studied were the MPA/catalyst and the cinchonidine (CD)/MPA ratios, the effect of ultrasonic irradiation and the modifier structure. Low MPA/catalyst ratio was found to be advantageous for obtaining enhanced enantioselectivity, while higher CD/MPA ratios resulted in increasing enantioselective according to a saturation type curve. The ultrasonic pretreatment (similarly to α-ketoesters) also slightly increased the enantiomeric excesses. These modifications of the CD-Pd/Al2O3 system, resulted in enantioselectivities up to 66% ee (0°C, 10 min sonication, CD/MPA=0.5, 50 bar H2 pressure) for (S)-2-methyl-pentanoic acid. The variation of the modifier structure provided unique information about the nature of the cinchona-substrate interaction. It has been revealed that the OH group of the alkaloid should be involved in the substrate-modifier interaction which more likely occurs in the liquid phase. An intermediate with refined structure is proposed and the mechanism is suggested to be of stoichiometric nature.

Original languageEnglish
Pages (from-to)71-79
Number of pages9
JournalApplied Catalysis A: General
Volume203
Issue number1
DOIs
Publication statusPublished - Sep 18 2000

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ASJC Scopus subject areas

  • Catalysis
  • Process Chemistry and Technology

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