György Szöllösi

Catalytic transfer hydrogenation of 2-butanone on MgO. New active surface sites generated by treatment with chloroform

In the course of heterogeneous catalytic transfer hydrogenation (CTH) of carbonyl compounds with alcohols on MgO, the catalyst is continuously poisoned, which leads to a complete loss of activity. The main result of the present work is that deactivation may be prevented by treatment with chloroform and the initial activity of MgO is retained for as long as 65 h. Detailed investigations were carried out (activations of MgO, TG, DSC, chloroform treatment, FT-IR spectroscopy, CDCl3 adsorption) in order to identify both types of active centers responsible for poisoning and CTH. Based on our own experimental results as well as on data in the literature, the prerequisites of CTH on MgO appear to be basic (O2−) site and adjacent surface hydroxyl site pairs. Lewis acid centers responsible for poisoning are blocked and active surface hydroxyl groups of weakly acidic character are simultaneously generated by chloroform treatment.

Rigid cinchona conformers in enantioselective catalytic reactions : New cinchona-modified platinum catalysts in the Orito reaction

The use of cinchona alkaloids (cinchonidine, cinchonine, quinine, quinidine, α-isocinchonine, α-isoquinidine, γ-isoquinidine) in the Orito reaction (hydrogenation of ethyl pyruvate and ethyl benzoylformate) strongly supports the structure of the intermediate complex (cinchona alkaloid “anti‐open” conformer–pyruvate 1 : 1 complex); in addition, so far unknown stereochemical conditions have been identified and the utilization of rigid cinchona conformers in the study of asymmetric syntheses have been generalized.

Ultrasonics in asymmetric syntheses. Sonochemical enantioselective hydrogenation of prochiral C=O groups over platinum catalysts

The sonochemical enantioselective hydrogenation of various prochiral carbonyl compounds to the corresponding (R)-hydroxy derivatives over different platinum catalysts using cinchonidine as chiral modifier is described. The carbonyl derivatives studied were trifluoromethyl ketones and α- and β-ketoesters. The sonochemical pretreatment of the catalyst-modifier system was found to be mostly advantageous in increasing the optical yield. Moreover, the ultrasonically promoted reactions provided the best enantiomeric excesses (ee%) ever obtained in this heterogeneous catalytic system (methyl pyruvate 95 ee%, ethyl 4-phenyl-2-oxobutyrate 95 ee%, and ethyl benzoylformate 92 ee%). In a few cases, however, the insonation did not result in enhancement in enantioselectivities. On the basis of the comparison with conventional reactions the limitations of the ultrasonic irradiation in asymmetric hydrogenations are also drawn. Chirality 11:470–474, 1999.

Electrospray ionization mass spectrometry in the heterogeneous catalyzed organic reactions: unknown compounds in the pyruvate hydrogenation

The transformation of cinchonidine was studied in the presence of hydrogen on Pt/alumina by electrospray ionization mass spectrometry using in‐source CID. So far unknown compounds were identified. Further studies on the basis of these new observations may permit to establish a more comprehensive mechanism of enantioselective hydrogenation of α-ketoesters.

Hydrogenation of unsaturated ketones: Selective catalytic transfer hydrogenation of 5-hexen-2-one over MgO

Abstract In the present study the selective catalytic transfer hydrogenation of an unsaturated ketone is described. During the heterogeneous catalytic transfer hydrogenation of 5-hexen-2-one with 2-propanol to 5-hexen-2-ol on MgO, the catalyst was continuously poisoned, which lead to a complete loss of activity. The major point of the present work is that the deactivation can be prevented by treatment with chloromethanes. The best results were obtained on MgO previously treated with chloroform. As a result the selectivity of the formation of 5-hexen-2-ol was close to 100% and no catalyst deactivation was observed during the time period studied. Detailed investigations were carried out (MgO treatment with different organochlorine reagents, FT-IR spectroscopy, CDCl3 adsorption, reaction of chloromethanes with MgO in pulse system) in order to optimize the reaction conditions and to certify the mechanism proposed earlier.

Identification of ethyl pyruvate and dihydrocinchonidine adducts by electrospray ionization mass spectrometry

Several ethyl pyruvate and dihydrocinchonidine adducts, formed by non-covalent interactions with alkali cations, have been identified for the first time using electrospray ionization mass and tandem mass spectrometry. This type of adduct may have an important role in asymmetric reactions of pyruvates in the presence of cinchonas.

Crotonaldehyde hydrogenation over clay-supported platinum catalysts

Abstract Two clay-supported platinum catalysts were prepared by impregnation and tested in the liquid phase hydrogenation of crotonaldehyde. Over both catalysts, the unsaturated alcohol selectivity was increased (to 49%) compared to that obtained over platinum on conventional supports (maximum 20%). The effect of the solvent, the subtrate initial concentration, the hydrogen pressure and the reaction time was studied. The benefic effect of the support was observed only if an alcohol was used as solvent. A deuterium tracer study revealed the coaction of the Lewis acid sites of the clay supports in adsorption of the substrate leading to an increase in the crotyl alcohol selectivity. The self poisoning of the metal over the clay-supported catalysts was supposed to inhibit the CC group hydrogenation.

Role of basic and acidic centers of MgO and modified MgO in catalytic transfer hydrogenation of ketones studied by infrared spectroscopy

Abstract In this study our aim was to identify the active sites and the surface species responsible for deactivation of MgO during catalytic transfer hydrogenations (CTH) of ketones using alcohols as hydrogen donors. Our previous studies showed that deactivation of MgO could be prevented by previous treatment with chloromethanes. Therefore the surface species formed during the reaction were studied before and after treatment with chloroform or chloroform-d by in situ infrared spectroscopy (IR). As a result, it was concluded that the reaction requires the presence of surface basic and acidic centers. The presence of Lewis acid centers was not necessary, the reaction could proceed on weakly acidic surface Bronsted sites, as the alterations in intensity and position of the ν(OH) bands indicated. Modification with chloroform resulted also in the generation of surface OH groups with a proper acidity for the reaction. The shift in carbonyl vibrations led us to the conclusion that Lewis acid and base centers were responsible for the catalyst poisoning, so covering these acid sites by Cl− led to a stable catalyst.

Preparation, Characterization and Application of K-10 Montmorillonite Modified with Chiral Ammonium Halides

Abstract Chiral modification of K-10 montmorillonite was carried out with chiral amine salts. The ion-exchanged K-10 samples were characterized by CHN analysis, XRD, FT-IR and 29Si NMR spectroscopies and tested in catalytic reactions.

Solvent and support effects in the case of acetic acid and alumina: Oxonium cations in asymmetric hydrogenation of ethyl pyruvate over dihydrocinchonidine modified platinum

Abstract Between alumina containing catalysts and acetic acid as solvent a reaction occurs with the formation of + O [ Al ( OAc ) 2 ] 3 . This, until now, unknown support effect gained experimental verification in the enantioselective hydrogenation of ethyl pyruvate in acetic acid, catalyzed by the platinum–alumina–dihydrocinchonidine catalytic system.