Use of (S)-(+)-1-aminoindan, (S)-(+)-1-indanol and (1R, 2S)-(+)-cis-1-amino-2-indanol as chiral modifiers in the enantioselective hydrogenation of ethyl pyruvate with Pt/SiO2 catalysts (original) (raw)
Related papers
Catalysis Today, 2008
The enantioselective hydrogenation of 1-phenyl-1,2-propanodione (PPD) was investigated using cinchonidine-immobilised Pt/TiO 2 catalysts. Prior to metal deposition, TiO 2 was chirally modified by the direct anchoring of cinchonidine (CD) using trimethoxysilane as coupling agent (TMS-CD). The catalysts were prepared using a high H 2 pressure reduction-deposition method and were characterised by elemental analysis (C, H and N), TG, DRIFT, 13 C and 29 Si solid-state NMR, N 2 adsorption-desorption isotherms, XRD, XPS and HR-TEM. The catalytic activity was evaluated in a batch reactor at 298 K and 40 bar using cyclohexane as solvent with various cinchonidine concentrations. The results indicate that the enantioselectivity was sensitive to the CD surface concentration and the enantiomeric excess of the target product, 1-R-phenyl-1-hydroxy-2-propanone, was in the range of 25-51%. The best catalyst was the one supported on TiO 2 with a nominal content of 10 wt% TMS-CD. The effect of the H 2 pressure, the concentration of substrate, solvent and recyclability of the catalyst were studied. The results obtained confirmed that the variation of reaction conditions affects both the activity and enantioselectivity due to the substrate adsorption on the metal active sites. Concerning the solvent effect, the enantiomeric excess decreased non-linearly upon increasing the solvent dielectric constant; this was attributed to the interactions between solvents and TMS-CD on the surface. In the catalyst recycling studies, the enantiomeric excess decreased up to 40% after the 3rd reuse. The drop of activity and enantiomeric excess was attributed to the hydrogenation of the immobilised CD.
Catalysis Today, 2008
The enantioselective hydrogenation of 1-phenyl-1,2-propanodione (PPD) was investigated using cinchonidine-immobilised Pt/TiO 2 catalysts. Prior to metal deposition, TiO 2 was chirally modified by the direct anchoring of cinchonidine (CD) using trimethoxysilane as coupling agent (TMS-CD). The catalysts were prepared using a high H 2 pressure reduction-deposition method and were characterised by elemental analysis (C, H and N), TG, DRIFT, 13 C and 29 Si solid-state NMR, N 2 adsorption-desorption isotherms, XRD, XPS and HR-TEM. The catalytic activity was evaluated in a batch reactor at 298 K and 40 bar using cyclohexane as solvent with various cinchonidine concentrations. The results indicate that the enantioselectivity was sensitive to the CD surface concentration and the enantiomeric excess of the target product, 1-R-phenyl-1-hydroxy-2-propanone, was in the range of 25-51%. The best catalyst was the one supported on TiO 2 with a nominal content of 10 wt% TMS-CD. The effect of the H 2 pressure, the concentration of substrate, solvent and recyclability of the catalyst were studied. The results obtained confirmed that the variation of reaction conditions affects both the activity and enantioselectivity due to the substrate adsorption on the metal active sites. Concerning the solvent effect, the enantiomeric excess decreased non-linearly upon increasing the solvent dielectric constant; this was attributed to the interactions between solvents and TMS-CD on the surface. In the catalyst recycling studies, the enantiomeric excess decreased up to 40% after the 3rd reuse. The drop of activity and enantiomeric excess was attributed to the hydrogenation of the immobilised CD.
Journal of Catalysis, 2001
The previously proposed model for reactant-modifier interaction in the enantioselective hydrogenation of activated carbonyl compounds over platinum chirally modified by cinchona alkaloids has been extended to platinum modified by synthetic pyrrolidinylnaphthyl-ethanol modifiers. As in the case of cinchonidine, the most used modifier, the model predicts enantiomeric excess in nearly quantitative agreement with experiment. Excellent agreement is achieved despite the fact that structural assumptions had to be made and the platinum surface was not explicitly taken into account. The one-to-one interaction between modifier and reactant was calculated at the ab initio level. A comparison of the results for different modifiers leads to the conclusion that steric repulsion caused by the anchoring group plays an important role in the enantiodifferentiating interaction. The favoured formation of the (R)product is traced to the fact that the pro-(S) complex leading to the (S)-product upon hydrogenation is more destabilised due to repulsive interaction than the pro-(R) complex. The model calculations are a useful tool for designing effective modifiers and for gaining insight into the mechanism of enantiodifferentiation.
2006
A new reaction kinetic approach was used to describe the enantioselective hydrogenation of ethyl pyruvate over cinchona-Pt catalyst. The above reaction was considered as the sum of two parallel reactions: (i) racemic hydrogenation resulting in R-and S-product in equal amount and (ii) enantioselective hydrogenation leading to the exclusive formation of one of the two optically isomers. New terms such as acc diff and k e /k r (where k e and k r are the rate constants of the enantioselective and racemic hydrogenation, respectively) were introduced to characterize the relationship between the enantioselective and the racemic hydrogenation reactions. Results obtained show that the formation of R-product is rate accelerated, while the formation of S-product is decelerated. The results indicate also that the overall rate increase is a kinetic phenomenon and cannot be attributed to the suppression of the poisoning effect of CO or oligomers formed from ethyl pyruvate. The strong rate acceleration effect of achiral tertiary amines (ATAs) added to the reaction mixture was attributed to the decrease of the loss of modifier during the hydrogenation experiments.
Enantioselective Hydrogenation of 1Phenyl1,2-propanedione
Journal of Catalysis, 2001
The enantioselective hydrogenation of 1-phenyl-1,2-propanodione (PPD) was investigated using cinchonidine-immobilised Pt/TiO 2 catalysts. Prior to metal deposition, TiO 2 was chirally modified by the direct anchoring of cinchonidine (CD) using trimethoxysilane as coupling agent (TMS-CD). The catalysts were prepared using a high H 2 pressure reduction-deposition method and were characterised by elemental analysis (C, H and N), TG, DRIFT, 13 C and 29 Si solid-state NMR, N 2 adsorption-desorption isotherms, XRD, XPS and HR-TEM. The catalytic activity was evaluated in a batch reactor at 298 K and 40 bar using cyclohexane as solvent with various cinchonidine concentrations. The results indicate that the enantioselectivity was sensitive to the CD surface concentration and the enantiomeric excess of the target product, 1-R-phenyl-1-hydroxy-2-propanone, was in the range of 25-51%. The best catalyst was the one supported on TiO 2 with a nominal content of 10 wt% TMS-CD. The effect of the H 2 pressure, the concentration of substrate, solvent and recyclability of the catalyst were studied. The results obtained confirmed that the variation of reaction conditions affects both the activity and enantioselectivity due to the substrate adsorption on the metal active sites. Concerning the solvent effect, the enantiomeric excess decreased non-linearly upon increasing the solvent dielectric constant; this was attributed to the interactions between solvents and TMS-CD on the surface. In the catalyst recycling studies, the enantiomeric excess decreased up to 40% after the 3rd reuse. The drop of activity and enantiomeric excess was attributed to the hydrogenation of the immobilised CD.
Catalysis Communications, 2008
The effect of the addition of various nitrogen containing and condensed aromatic compounds on both the rate and the enantioselectivity in the hydrogenation of over supported cinchonidine-Pt catalysts has been investigated. The results show that preadsorbed quinoline and acridine cannot be fully replaced from the surface of platinum by cinchonidine. It has been found that the addition of these compounds increases both the reaction rate and the enantioselectivity (both ee max and ee end values). The observation that these additives have no negative effect on the enantioselectivity indicates that generally accepted mechanistic models need some corrections.
Journal of Catalysis, 2004
1-Phenylpropane-1,2-dione was hydrogenated over chirally modified 5% Pt/Al 2 O 3 catalyst at 10 bar H 2 and 15 • C using toluene and acetic acid as solvents. The highest enantiomeric excess for the major product (R)-1-hydroxy-1-phenyl-2-propanone (ee = 57%) was obtained using cinchonidine as the chiral modifier. The presence of the hydroxyl group in the C-9 position of the modifier was important for achieving high enantioselectivity. When the C-9 hydroxyl group of cinchonidine was replaced by a methoxy group enantioselectivity was lost and a small 2% excess of (S)-1-hydroxy-1-phenyl-2-propanone enantiomer was observed. In acetic acid the reaction with cinchonidine proceeded yielding a 7% excess of the (R)-product. Hydrogenation of the intermediate hydroxyketones in acetic acid using cinchonidine or 9-methoxy-10,11dihydrocinchonidine as chiral modifiers gave the corresponding (1S,2R)-diol in 67 and 78% enantiomeric excesses, respectively. By changing the solvent from acetic acid to toluene, an inversion of enantioselectivity took place yielding the (1R,2S)-diol as the main product in 38% ee. A mechanism was proposed involving a two-step cycle (reactant-modifier) and a three-step cycle (reactant-modified acetic acid) in order to account for the observed enantioselectivities. 2004 Elsevier Inc. All rights reserved.
Applied Catalysis A: General, 2013
Chirally modified ␥-Al 2 O 3 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 H 2 at 25 • C and 40 bar. The characterization was carried out by elemental analysis of C, H and N, TG, DRIFT, NMR 13 C and 29 Si on solid state, N 2 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 H 2 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 ␥-Al 2 O 3 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.