Sequential Catalytic Condensation-Hydrogenation of Ketones

Article abstract of DOI:10.1021/jo01313a007

Aldol condensation and hydrogenation of the condensation product have been carried out simultaneously by using an immobilized acid catalyst (Nafion-H or Amberlite IR-120) and Pd/C under hydrogen.Acetone was converted to 4-methyl-2-pentanone in a one-pot multistep process at 60-140 deg C and 20-300 psi of hydrogen.The yields of 4-methyl-2-pentanone were higher than the equilibrium-limited yields of mesityl oxide obtained in the absence of the hydrogenation catalyst, demonstrating that the equilibrium to mesityl oxide was shifted by mesityl oxide hydrogenation to 4-methyl-2-pentanone. 2-Propanol was the major byproduct because acetone hydrogenation was competitive with condensation.High-boiling products, found in aldol condensations, were not formed in the condensation-hydrogenation process.Use of RhCl(PPh3)3 or its polymer-bound analogue as the hydrogenation catalyst reduced the amount of acetone hydrogenation but slowed the condensation-hydrogenation reactions.The crossed aldol condensation-hydrogenation of benzaldehyde and acetone gave 4-phenyl-2-butanone with Nafion-H and Pd/C.The major side reaction was the competitive hydrogenation of benzaldehyde to toluene.The intramolecular condensation of 2,5-hexanedione gave mainly 2,5-dimethylfuran while the one-pot condensation-hydrogenation reaction gave 2,5-dimethyltetrahydrofuran.