Mihály Bartók

Unexpected Inversions in Asymmetric Reactions: Reactions with Chiral Metal Complexes, Chiral Organocatalysts, and Heterogeneous Chiral Catalysts

The recognition of the optical activity of organic compounds, followed by the detailed analysis of optical isomerism,1 laid the foundation for the development of asymmetric syntheses, a group of reactions of fundamental significance. Asymmetric syntheses, available in great varieties, are the indispensable source of a large number of chiral compounds that have become essential for human society. Some of the most important procedures that belong to this group are asymmetric organocatalytic, asymmetric homogeneous and heterogeneous metal catalytic reactions, and enzymecatalyzed procedures. One of the main tasks of pertinent research is the development of chiral catalysts that enable the preparation of the required product in the highest possible enantiomeric excess (ee). The value of ee depends on a number of known and yet unknown factors not only for a given reaction but also for each individual compound within a reaction type.

New Catalytic Materials from Amorphous Metal Alloys

Publisher Summary This chapter focuses on the new catalytic materials from amorphous metal alloys. Amorphous alloys can be produced with wide composition ranges not available in crystalline form, which permits the continuous control of their electronic properties. Their single-phase character and possible lack of surface segregation of the alloying elements ensure thatthe active species are in a uniform dispersion in a chemically homogeneous environment. There are indications that they have a high concentration of coordinatively highly unsaturated sites that makes them easier to study and characterize than ordinary catalysts. Their structure is nonporous, so diffusion limitations, often a problem in traditional heterogeneous catalysis, do not affect the surface reaction. All these features make amorphous alloys attractive materials in heterogeneous catalytic studies. Also, metallic glasses are a kind of missing link in the study of the nature of active sites in catalysis. The common thread running through theories of active sites is the concept of a small cluster of atoms being responsible for catalytic activity. Because metallic glasses have no long-range order, they offer the opportunity to examine reactions requiring little cluster order in the absence of those requiring high order.

Enantiodifferentiation in asymmetric sonochemical hydrogenations

The effect of sonochemical pretreatment on the enantioselectivity of Pt/Al2O3–cinchonidine-catalyzed ethyl pyruvate hydrogenation was studied at different hydrogen pressures in various solvents, mainly in acetic acid. The sonochemical pretreatment of a commercial Pt/Al2O3–cinchonidine catalytic system in acetic acid resulted in enhanced enantioselectivity providing excellent ee values (97% ee) under mild and widely varied experimental conditions. Moreover, the application of ultrasonics provides a possibility of the catalyst recycling without regeneration. The catalyst was tested by transmission electron microscopy to determine the effect of the sonication on the metal particle size morphology.

98% Enantioselectivity in the asymmetric synthesis of a useful chiral building block by heterogeneous method: Enantioselective hydrogenation of ethyl-benzoylformate over cinchona modified Pt/Al2O3 catalysts in the acetic acid

Abstract Extremely high (98%) enantioselectivity of the hydrogenation of ethyl benzoylformate on Pt/Al 2 O 3 modified with dihydrocinchonidine was achieved. The difference between the rates of racemic and enantioselective hydrogenation was less significant than in the case of ethyl pyruvate. This indicates that ligand acceleration is a welcome effect but no necessary prerequisite for achieving high enantioselectivity.

Vapour-phase heterogeneous catalytic transfer hydrogenation of alkyl methyl ketones on MgO: Prevention of the deactivation of MgO in the presence of carbon tetrachloride

Catalytic transfer hydrogenation (henceforth abbreviated CTH) of alkyl methyl ketones (2-butanone, 2-pentanone and 2-hexanone) by 2-propanol was studied on a commercially available MgO catalyst. Pretreatment of MgO, deactivation of the catalyst, temperature dependence of CTH and the effects of the 2-propanol/ketone ratio and of various catalyst modifiers were investigated. An important result of these studies is that the deactivation of MgO may be prevented by treatment with carbon tetrachloride. As a consequence, vapor-phase CTH using commercially available MgO may be economically realized.

Detection and characterization of twenty-eight isomers of fumonisin B1 (FB1) mycotoxin in a solid rice culture infected with Fusarium verticillioides by reversed-phase high-performance liquid chromatography/electrospray ionization time-of-flight and ion trap mass spectrometry

Fumonisin mycotoxins which are hazardous to humans and animals were produced in a Fusarium verticillioides-infected solid rice culture. To decrease the possibility of the formation of artifacts, the fumonisins were analysed by reversed-phase high-performance liquid chromatography/electrospray ionization time-of-flight (RP-HPLC/ESI-TOFMS) and ion trap mass spectrometry (RP-HPLC/ESI-ITMS) immediately after the extraction of the culture material, without any further sample clean-up. The fumonisin isomers were separated by using a flat gradient on a special, high-coverage C(18), narrow-bore HPLC column (YMC-Pack Jsphere ODS H80) suggested for the separation of structural isomers by the manufacturer. Exact mass measurements (TOFMS) of the protonated molecules and extraction of the ion chromatogram corresponding to the empirical formula (C(34)H(59)NO(15)) of FB(1) toxins led to the identification of 29 peaks and shoulders, including those of FB(1). The FB(1) toxin and 28 of its isomers were also detected by ITMS after separation with RP-HPLC. The characteristic m/z values of the product ions, including the backbones obtained by ITMS(2), undoubtedly indicated the structures of the FB(1) isomers for 28 peaks and shoulders. In the MS(2) spectra of the protonated molecules of the FB(1) isomers, with some exceptions, 15 characteristic product ions including the hydrocarbon backbone at m/z 299 were observed. The abundance ratio of the cation at m/z 299 ranged up to 5.8%. The relative quantities of the isomers found in the sample extract were expressed as percentages of the FB(1) content (0.001-0.579%). The total amount of the 28 FB(1) isomers was 2.803% of the quantity of FB(1) that is important from the aspect of food and feed safety.

Asymmetric sonochemical reactions. Enantioselective hydrogenation of α-ketoesters over platinum catalysts

The sonochemical enantioselective hydrogenation of different alpha-ketoesters to the corresponding hydroxy derivatives over cinchona modified Pt catalysts is described. Ultrasonic irradiation was found to be beneficial in improving the optical yields. Besides studying the reaction rates and enantioselectivities, the effect of ultrasonics on the catalyst-modifier system and the scale-up of the process will also be considered.

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.

The modification of CO adlayers on Pt SiO2 catalysts by preadsorbed oxygen: An infrared and pulse microreactor study

Abstract Changes in the structure of CO adlayers as the result of co-adsorbed oxygen on Pt SiO 2 catalysts have been studied using transmission infrared spectroscopy and pulsed microreactor studies. Preadsorbed oxygen was observed to cause a blue shift in the absorption frequency of adsorbed CO. The extent of the blue shift was observed to increase with the severity of the O2 treatment. The origin of this blue shift is explained by invoking an increase in the extent of COCO dipole coupling. Both the infrared and microreactor studies strongly suggest that the increase in dipolar coupling occurs as the result of a compressed CO adlayer in which CO is segregated into isolated patches.