Antal Tungler

Catalysis with supported palladium metal, selectivity in the hydrogenation of C=C, C=O and C=N bonds, from chemo- to enantioselectivity

Abstract The selectivity characteristics of Pd catalysts in heterogeneous hydrogenations are discussed, especially the stereochemical issues in the reduction of Cue605C, Cue605O and Cue605N bonds. Special attention was paid to diastereoselective and enantioselective reactions.

(S)-Proline based chiral modifiers

(S)-Proline esters and amides containing condensed aromatic rings were synthesised in order to use them as chiral modifiers in the enantioselective heterogeneous catalytic hydrogenation of isophorone and ethyl pyruvate. The (S)-proline 2-(2-naphthyl)-ethyl ester resulted in 23% enantiomeric excess of (S)-dihydroisophorone in methanol. 5% optical purity was obtained with the (S)-proline 3-ethyl-indolamide in the hydrogenation of ethyl pyruvate in acetic acid.

Diastereoselective heterogeneous catalytic hydrogenation of N-heterocycles. Part I. Hydrogenation of pyridines

Abstract High diastereoselectivities were obtained in the heterogeneous catalytic hydrogenation of chiral picolinic and nicotinic acid derivatives with complete conversion, in non-acidic medium. The effects of catalytic metals, solvents, temperature and pressure on the conversion and the diastereomeric excess (d.e.) were investigated. The hydrogenation of N-picolinoyl-(S)-proline methyl ester (1) resulted in 79% d.e. over 10% Pd/C, in methanol, at moderate pressure and temperature (50xa0bar, 50°C). Very high d.e. (94%) was achieved in the saturation of N-nicotinoyl-(S)-proline methyl ester (2) under similar conditions. The hydrogenation of quaternized 1 took place already at room temperature (RT) and 20xa0bar with almost complete diastereoselectivity (98%), over palladium on carbon, in methanol. These are successful examples of a diastereoselection in the hydrogenation of prochiral pyridines.

(S)-α,α-diphenyl- and (S)-α,α-dinaphthyl-2-pyrrolidinemethanol as chiral modifiers in asymmetric heterogeneous catalytic hydrogenation of isophorone

The use of DPPM and DNPM as chiral modifiers in asymmetric heterogeneous catalytic hydrogenation of isophorone is reported. The effect of solvents and the concentration of reactant, modifiers and catalysts on the enantioselectivity are described. Circular dichroism spectroscopy was used to detect the interaction between the chiral modifier and the substrate.

Enantioselective hydrogenation of exocyclic α, β-unsaturated ketones. Part II. Hydrogenation in the presence of (S)-proline

In the asymmetric synthesis of chiral compounds, the reduction of prochiral unsaturated reactants has a great importance. (S)-proline as a chiral auxiliary is used in the hydrogenations of exocyclic α,β-unsaturated ketones with palladium on carbon catalysts, producing the corresponding saturated ketones with an optical purity up to 20%. The influence of the parameters (solvents, additives) on the optical yield is also investigated. The highest enantioselectivity was obtained in ethyl acetate and acetonitrile (ee 20%), at atmospheric pressure and room temperature.

Enantioselective hydrogenation of isophorone over Pd catalysts in the presence of(-)-dihydroapovincaminic acid ethyl ester the effect of reduction method of Pd blacks on the enantiomeric excess

The enantioselective heterogeneous catalytic hydrogenation of isophorone in the presence of apovincaminic acid ethyl ester was investigated. Various Pd black catalysts differing in their preparation method were studied. The catalysts were characterized by different methods such as physical adsorption and chemisorption, SEM and XPS. An explanation was created for the different enantioselectivity of the catalysts being precipitated by different reducing agents.

n-Octane reforming over modified catalysts: I. The role of Sn, Te and Bi under industrial conditions

Abstract A Pt-Sn/γ-Al 2 O 3 bifunctional catalyst was modified by tin, bismuth and tellurium using metal adsorption technique. The parent and the modified catalysts were tested in n -octane reforming under conditions similar to industrial applications. The added tin decreased the reformate yield a little, the aromatic content decreased and the isoparaffin content increased, the research octane number remained high. Tellurium and bismuth deposited greatly deactivated the metal function of the catalyst; the liquid yield of the product is far less than that over the parent platinum–tin catalyst. The isoparaffin and aromatic selectivity however changed favourably. More isoparaffin hydrocarbon was found in the liquid product over the modified catalysts. The reforming function of the metal was suppressed and, therefore, the reactions of alkenes occurring on the acid sites of the catalyst became dominant.

Solvent and support effects in enantioselective hydrogenation of isophorone with (s)-α,α -diphenyl-2-pyrrolidinemethanol modified palladium

Asymmetric heterogeneous catalytic hydrogenation of isophorone has been investigated over (S)-α,α-diphenyl-2-pyrrolidinemethanol modified Pd. The influence of solvent and support effects is discussed. The impact of water, acidic and basic additives on enantioselectivity is described.

Enantioselective hydrogenation of exocyclic α,β-unsaturated ketones: Part III. Hydrogenation with Pd in the presence of cinchonidine

Abstract Cinchonidine as a chiral modifier was used in the hydrogenation of exocyclic α,β-unsaturated ketones with palladium black catalyst, producing the corresponding saturated ketones up to 54% optical purity (2-benzyl-1-benzosuberone) in toluene under 50xa0bar hydrogen pressure. The influence of different parameters (solvent, catalyst) on the optical yield was investigated.

Enantioselective hydrogenation of isophorone with titania supported Pd catalysts modified by (-)-dihydroapovincaminic acid ethyl ester effect of the support and the reduction method

Abstract Enantioselective hydrogenation of isophorone was investigated over Pd/TiO 2 catalysts in the presence of (−)-dihydroapovincaminic acid ethyl ester. The used supports were different in crystalline form and in surface area. The influence of the catalyst preparation method on the optical purity was studied. The catalysts were characterized by H 2 adsorption and SEM.