Selective Hydrogenation of Diketones on Supported Transition Metal Catalysts

Abstract

The hydrogenation of α-diketones yields α-hydroxyketones or vic-diols, both compounds of great interest in fine chemistry.The reaction tests were the liquid phase hydrogenation of 2,3-butanedione and 2,3-pentanedione at mild conditions. Theobjectives of this work were evaluating the effect over the activity and selectivity of: (a) different transition metallic phasebased catalysts supported on activated carbon, (b) the symmetry of the reactants and (c) solvents. The physicochemicalcharacterization of the catalysts was carried out by ICP, XRD, TEM, N2adsorption and XPS. The keto-enol equilibrium ofdiketones was studied by 1H-NMR. All the catalysts were active in both reactions. In terms of activity, Pt and Rh were thebest active phases. For both reactants the highest selectivity towards hydroxyketones were achieved with Pd, while Ru wasthe most selective towards the diol. Both the activity and selectivity followed similar patterns in the hydrogenation of bothdiketones. The greater activity of Pt was attributed to the high dispersion of the active metal phase in this catalyst and thehigh efficiency of Pt for C = O bond reduction. The high selectivity of the Pd catalysts towards the intermediate product wasattributed to many effects: (i) a lower interaction of the hydroxyketone with the active site as compared to the diketone, (ii)the easy reducibility of the C = C double bond on Pd, provided by the keto-enol tautomerism of diketones.