Enantioselective hydrogenation of 1-phenyl-1,2-propanedione over Pt on immobilized cinchonidine on γ-Al₂O₃ catalysts

Chirally modified γ-Al₂O₃ containing different amounts of cinchonidine were prepared by the chemical modification of cinchonidine with trimethoxysilane (TMS-CD). These solids were used as support of Pt catalysts containing 1 wt% Pt by chemical reduction of the hexachloroplatinic acid with H₂ at 25°C and 40 bar. The characterization was carried out by elemental analysis of C, H and N, TG, DRIFT, NMR ¹³C and ²⁹Si on solid state, N₂ adsorption-desorption at 77 K, XDR, XPS and TEM. The catalytic activity was evaluated in the hydrogenation of 1-phenyl-propane-1,2-dione in a batch reactor at 298 K and 40 bar. The effect of H₂ pressure, concentration substrate, catalyst mass, solvents effect and recycles, of the catalyst with the major enantiomeric excess was studied. It was found that all catalysts were active in the reaction being the enantiomeric excess of the target product, 1-R-phenyl-1-hydroxy-2-propanone in the range 30-44% and the best catalyst is that supported on γ-Al₂O₃ with a nominal content of 5 wt% TMS-CD. The results obtained in this study confirm that the variation of reaction conditions show a dependence on the activity and enantioselectivity for substrate adsorption in the metal active sites. In the solvent effect, enantiomeric excess decreased non-linearly with an increasing solvent dielectric and we could be attributed to the interactions between solvents and TMS-CD in the surface. In the recycles studies enantiomeric excess was achieved as 40% even after 3rd reuse with a slight loss in activity and enantiomeric excess.