2004 Volume 37 Issue 2 Pages 310-317
We have been studying the reduction of carbonyl compounds by using heterogeneous catalysts in the liquid phase. The reducing reagents were simple primary or secondary alcohols, e.g. 2-propanol. The supported Sn and Zr oxides catalysts were active and selective for the reduction of crotonaldehyde (C4-unsaturated aldehyde: CH3CH=CHCHO) to crotyl alcohol (the corresponding unsaturated alcohol: CH3CH=CHCH2OH) with 2-propanol or 2-butanol as a reducing reagent. The reaction proceeded via hydrogen transfer from alcohol to carbonyl compounds. The reagent, 2-propanol, was converted to only acetone, which could be regenerated by a simple hydrogenation reaction over a conventional metallic catalyst. Silica and MCM-41 supports were superior to TiO2 and Al2O3 for the reaction. This suggests that the surface of porous support should be inert for the hydrogen transfer reaction. The reduction of the Sn catalysts in H2 was necessary for the reaction. The Sn and Zr oxide catalysts were available to the selective reduction of cinnamaldehyde, acrolein, leaf aldehyde, and acetophenone. The corresponding alcohols were selectively formed over the supported Sn and Zr oxide catalysts. The hydrogen transfer reaction will provide various unsaturated alcohols in high selectivity without toxic reducing agents. These results indicate that the hydrogen transfer reaction is one of the Green Sustainable Processes for the production of various alcohols.
