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Palladium Catalysts on Alkaline‐Earth Supports for Racemization and Dynamic Kinetic Resolution of Benzylic Amines
Author(s) -
Parvulescu Andrei N.,
Jacobs Pierre A.,
De Vos Dirk E.
Publication year - 2007
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.200600899
Subject(s) - racemization , chemistry , kinetic resolution , catalysis , enantiopure drug , hydrogenolysis , palladium , ethylbenzene , amine gas treating , condensation reaction , imine , selectivity , organic chemistry , enantioselective synthesis
Palladium catalysts on alkaline‐earth supports were studied as new heterogeneous catalysts for racemization of chiral benzylic amines such as 1‐phenylethylamine. Particularly 5 % Pd/BaSO 4 and 5 % Pd/CaCO 3 were able to selectively racemize amines, with minimal formation of secondary amines or hydrogenolysis to ethylbenzene. In contrast, these side reactions were pronounced on Pd/C. A reaction mechanism is proposed that is consistent with the reaction kinetics. The catalyst activity was found to depend on the number of available surface Pd atoms, determined by titration with CO. The selectivity crucially depends on the rate of condensation of the amine and the primary imine, which is highest on Pd/C. The racemization catalysts were combined in one pot with an immobilized lipase to perform dynamic kinetic resolution of chiral amines. High yields (up to 88 %) of essentially enantiopure amides were obtained in a single step. The chemo‐enzymatic catalyst system proved to be stable and could be reused without losing the initial activity.