Studies On Asymmetric Hydrogenations Of Acetophenone And Its Derivatives Catalyzed By Ru-Rh/γ-Al₂O₃ Catalyst And Selective Hydrogenation Of α, β-unsaturated Carbonyl Compounds Over Ru/γ-Al₂O₃

The hydrogenations of ketones to corresponding alcohols are an important reaction in the field of pharmaceuticals and fine chemicals. The homogeneous hydrogenation catalyzed by organometallic complexes exhibits generally the high catalytic activity and selectivity under mild conditions, but the difficult separation of catalyst from products greatly blocks the industrial application. The catalyst of heterogeneous hydrogenation is of the advantages of the easy separation and reuse, but its catalytic activity and selectivity are often low. So how to combine their advantages of homogeneous and heterogeneous catalysis has been paid more and more attention in the recent years.Ruthenium-rhodium, ruthenium and rhodium supported on alumina catalysts stabilized by TPP(teiphenylphosphine) and reduced by formaldehyde in lower temperature have been prepared with an improved method. The results indicated that bimetallic catalyst Ru-Rh/γ-Al₂O₃ stabilized by TPP catalyst exhibits the higher catalytic activity and enantioselectivity in the presence of(S, S)-1,2-diphenyl-1,2-ethylene diamine((1S, 2S)-DPEN) for the asymmetric hydrogenation of acetophenone and its derivatives than monometallic catalyst Ru/γ-Al₂O₃ or Rh/γ-Al₂O₃. Ruthenium and rhodium loaded on alumina show obviously the synergistic effect. Chiral modifier DPEN does not only cause a good enantiodifferentiating ability, but it also lead to a considerable accelerating effect for the hydrogenation. Under the optimum conditions, the conversions of acetophenone, ethyl-phenyl-ketone and isopropyl-phenyl-ketone are near 100% and the enantioselectivities of products are up to 79.6%, 81.2% and 81.4%, respectively.Monometallic catalyst Ru/γ-Al₂O₃ stabilized by TPP was used for the selective hydrogenation of trans-4-phenyl-3-butene-2-one and cinnamaldehyde in the presence of KOH and diamines or aromatic 1,2-diamines. RU/2TPP-γ-Al₂O₃ showed an excellent activity and high selectivity for C=O hydrogenation. When DPEN was used as a modifier, under the conditions of the reaction temperature of 35℃, H₂ pressure of 4.0 MPa, KOH concentration of 0.04 mol/L, and reaction time of 3h, the conversion of trans-4-phenyl-3-butene-2-one was 100% and the selectivity for unsaturated alcohol trans-4-phenyl-3-butene-2-ol was more than 99%. Similarly, the conversion of cinnamaldehyd could be up to 96.0% and the selectivity for cinnamyl alcohol was over 94%. At the same time, the synergistic effect between DPEN and KOH, which could significantly accelerate the reaction rate and enhance the selectivity for C=O hydrogenation, was observed...