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The hydrogenative ring-opening reactions of five alkyl-substituted cyclopropanes [ethyl-(ECP), cis -1,2-dimethyl- ( c DMCP) and trans -1,2-dimethyl- ( t DMCP), 1,1-dimethyl-(1,1DMCP) and 1,1,2,2,-tetramethyl- (TMCP) cyclopropane] over Pt/SiO 2 catalyst were studied. The shapes of the curves depicting product formation rate vs. H 2 pressure suggest that CC as well as CH bond rupture occurs upon adsorption. Based on stereochemical considerations and on comparisons of product formation at the maximum rates, it is proposed that c DMCP forms a flat-lying complex over the surface of the catalyst and t DMCP, 1,1DMCP and TMCP react through edge-on surface intermediates. IR measurements concerning the reaction of ECP support the proposed dissociative adsorption.

A study of the sulphuric acid-catalysed dehydrations of 1,1-bishydroxymethyl-cyclopropane, -cyclobutane, - cyclopentane and -cyclohexane (1a–1d) revealed that the product distributions are determined by the relative stabilities of carbenium ions and der kinetic control furnished evidence of a 1,3-hydride shift.

1 Introduction 2 Epoxidation of the CC Bond 3 Epoxidation of the CO Bond 4 Epoxidation of the CN Bond Keywords: epoxidation of CX double bonds; epoxidation of CC bond; peroxy acid epoxidation; metal-catalyzed epoxidations; biological epoxidations; epoxidations by dioxiranes; chemical reactions of oxaziridines; oxaziridine preparation

The reactions of five alkyl-substituted cyclopropanes (ethyl-, cis-1,2-dimethyl-, trans-1,2-dimethyl-, 1,1-dimethyl- and 1,1,2,2-tetramethylcyclopropane) were studied in a hydrogen atmosphere over completely and partially reduced Ni/SiO2 catalyst. The main reaction, hydrogenative ring-opening, is accompanied by hydrogenolysis over the completely reduced catalyst. The hydrogen pressure dependence of this reaction and stereochemical features (i.e. the geometry of the molecules, and differences in the rates of transformations of stereoisomers) were used to acquire mechanistic information. Over the partially reduced Ni/SiO2, isomerization to olefins also occurs. The extent of this pathway increases with decreasing reduction temperature.

The hydrogenolysis of methyloxirane (propylene oxide) was investigated over five Pt/SiO 2 catalysts with different degrees of dispersion (7–100%), at 393 K, with a pulse technique coupled with GC. The number of turnovers per surface atom per pulse (turnover yield) was found to depend on the degree of dispersion. The rate of the ring-opening reaction passed through a maximum at approximately 60% D, which corresponds to a maximum in edge sites on fcc octahedra, or to 2 M sites. The regioselectivity of the ring opening did not depend upon the degree of dispersion, but the formation of the two main products (acetone and 2-propanol) displayed some structure sensitivity. The paper also deals with the interpretation of a recently observed example of structure sensitivity.

Auger electron spectroscopy of an amorphous Cu 61 Zr 39 alloy sample indicates copper and zirconium enrichment on the inner and outer sides, respectively. Dehydrogenation of 2-propanol in hydrogen on this alloy results in bulk crystallization, changes in its surface morphology and a significant copper enrichment on both sides. The increases in the activity and copper surface area of the alloy during the catalytic reaction are explained by copper segregation.

The dehydrogenation of 2-propanol to acetone on Cu 61 Zr 39 alloy has been studied for the first time. The dehydrogenation reaction (flow reactor, 573 K) on as-received or pre- activated (hydrogen, 573 K, 3 h or 473 K, 16 h) alloy brings about a continuous activation of the catalyst. Other types of pretreatment (heat treatment at 800 K for 0.5 h, or treatment with water vapour at 500 K for 24 h) induce an initially high, but unstable, activity. The activity changes parallel changes in the copper surface area (determined via N 2 O decomposition), except for samples prepared by HF dissolution, which results in a highly active and stable catalyst with a low surface area. XRD and DSC indicate crystallisation of the amorphous alloy samples under the given reaction conditions and as a result of pretreatment.

The hydrogenative ring-opening of five alkyl-substituted cyclopropanes and of methyl-oxirane on Pd/SiO2 was studied at different temperatures in a closed circulation reactor. For cyclopropanes, the ring opens through simple hydrogenation, giving exclusively saturated hydrocarbons, whereas alcohols (hydrogenation), oxo compounds (isomerization) and also cracking products are produced from methyloxirane. The substituents exert significant effects on the regioselectivity of the reactions for both type of molecules. For the cyclic hydrocarbons, mechanistic pathways are discussed on the basis of the stereochemistry of the compounds and the characteristic features of the ring-opening rate vs. H2-pressure functions. Finally, a chemical method is proposed for the detection of β-hydride.

The hydrogenations of methyl 2-oxoeyclopentanecarboxylate (1), ethyl 2-oxocyelohexanecarboxylate (3), and 2-methylcyclohexanone (5) on unmodified Raney-Ni catalyst lead predominately to the formation of the cis-hydroxy diastereoisomers of 2, 4, and 6, respectively (Scheme 2). In the asymmetric hydrogenations on catalysts modified with chiral tartaric acid ((R, R )-C4H6O6/Raney-Ni and (R, R)-C4H6O6/NaBr/Raney-Ni), the predominance of the cis-isomer increases significantly. The hydrogenations of β-keto esters 1 and 3 proceed with an enantioselectivity of 10–15% on the modified catalysts, while the similar hydrogenation of 5 yields optically inactive 6. The (1S,2R)-enantiomers of the cis-isomers of 2 and 4 are formed in larger quantity, whereas the (lR,2R)-enantiomers of the corresponding trans-isomers predominate (Scheme 1). The enantioselective formation of trans-2 and trans-4 can be interpreted mainly in terms of the asymmetric hydrogenation of cyclic β-keto esters through the keto form, while that of the corresponding cis-hydroxy esters proceeds through the enol form.

A new method is described for the preparation of Raney Ni catalyst modified with R,R-tartaric acid (MRNi). All experimental conditions which may have a significant impact on the preparation of a reproducible enantioselective catalyst were studied. Experiments were also performed to permit a comparison with literature data.

Substituted cinnamic acids containing a prochiral CC bond, and their Li I , K I , Ni II and Ca II salts, were prepared and their surface complexes on Ni were studied over a Raney-Ni catalyst modified with tartaric acid. The hydrogenation product of sodium cinnamate is optically active. Of the alkali metal salts of ( E )-α-phenylcinnamic acid, the hydrogenation of the Na salt gives the highest optical yield (17%). The solvent used significantly influences the selectivity. The published data for the chiral RH complexes are listed for comparison with the results of the homogeneous and heterogeneous hydrogenations described. The enantioselectivity in the presence of Raney-Ni is the result of a complex formed by the interaction of ( R,R )-tartaric acid with the substrate.

The reactions of four alkyl-substituted cyclopropanes in a hydrogen atmosphere in a closed circulation system have been studied over silica-supported and support-free copper catalysts made by different methods. Both isomerization and direct hydrogen addition occur. The ring opens in both the sterically more hindered and less hindered directions. On the basis of the kinetic data, mechanistic considerations are discussed. The catalysts were studied by N20 titration and TPR (temperature-programmed reduction). The properties of the reactions and the TPR data indicate that the active centers are atomic clusters for the direct hydrogenation and Cu(I) ions for the ring-opening from the sterically hindered direction through the formation of olefinic compounds.

In the reactions of (+)-apopinene (1) in the presence of hydrogen, an optically active hydrocarbon-like layer forms over the surface of Pd catalysts. It is suggested that this layer adsorbs one isomer preferentially, and that it provides the sites for both isomerization and hydrogenation.

The effects of the dehydrogenation of 2-propanol on the structure of an amorphous Cu61Zr39 alloy sample were analysed by means of scanning electron microscopy (SEM), energy dispersive X-ray microanalysis (EDAX), and Auger electron spectroscopy (AES). The inner and outer sides of the as-received amorphous ribbon differed considerably, indicating copper and zirconium enrichment, respectively. During a 24 h reaction dramatic changes in surface morphology and a substantial copper enrichment took place on both sides, resulting in very similar surfaces.

Commercially available copper, nickel, and platinum graphimets prepared from intercalated graphite materials were investigated by XPS, TEM, XRD, DSC and chemisorption techniques. The catalytic activity was tested in hydrogenation reactions. The XPS, TEM and chemisorption data revealed only highly-dispersed platinum particles on the surface of platinum graphimet. Copper oxide was detected on the surface of copper graphimet by means of XPS and XRD, while chemical analysis indicated the presence of residual copper chloride. Nickel graphimet consisted of intercalated nickel chloride, encapsulated metallic nickel and nickel oxide particles. Small nickel particles emerged to the surface of the nickel graphimet after pretreatment in hydrogen at 673 K and pretreatments in oxygen resulted in the aggregation of nickel oxide particles. The catalytic activity is attributed to metallic nickel on the graphite surface.

Evidence supporting a mechanism involving a sterically hindered transition state was found in the dehydrogenation of erythro -2-alkyl-3-dimethylamino-l-phenylpropan-l-ols by using a linear free energy relationship with Charton's steric constants.

Fumonisins were produced in a rice culture infected with Fusarium verticillioides. To decrease the possibility of the formation of artifacts, the fumonisins were analyzed by reversed-phase high-performance liquid chromatography with electrospray ionization ion trap tandem mass spectrometry (RP-HPLC/ESI-IT-MS2) immediately after the extraction of the culture material without any sample clean-up. In addition to already known fumonisins, numerous new fumonisin mycotoxins and fumonisin-like compounds were detected. On the basis of the IT-MS2 data, detailed fragmentation pathways including new mechanisms were proposed for the different series of fumonisins. The retention times, the masses of the protonated molecules and of the product ions including the backbones and the characteristic neutral mass losses from the protonated molecules of the new compounds suggested their structures (applying the well-known designation): iso-FA1a,b, iso-FB1a-d, iso-FB2,3a-e, PHFB2a-c, PHFB4a-d, FB5/iso-FB5a-d, FBK1 2TCA, FBK4 2TCA, FC2, iso-FC2,3, PHFC4, FD and FBX series. The relative quantities of fumonisins and fumonisin-like compounds found in the sample extract were expressed as percentages of FB1 (0.02-100%). The backbone of the compound denoted FD contained fewer carbon atoms than the well-known fumonisins with the C19 or C20 backbone and may well be a precursor of the longer compounds. For the compounds denoted FBX (12 compounds), one or two OH groups attached to the fumonisin backbone were esterified by carboxylic acids other than tricarballylic acid, such as cis-aconitic acid, oxalylsuccinic acid and oxalylfumaric acid.

In order to obtain more information about the structure of transition metal-graphite intercalation compounds, we have studied the active site distribution of Pt-, Pd- and Rh-graphimet before and after medium-temperature pretreatment (MTR, 573 K, 1 h). The surface characterization was performed by 1-butene titration in a flow reactor system. The single turnover method enabled us to distinguish between direct and two-step hydrogenation sites, and isomerization centres. MTR causes a pronounced effect on the active site distribution of all the samples. For Pd- and Rh-graphimet, the decreased number of isomerization and hydrogenation sites observed after MTR is attributed to encapsulation of surface metal into graphite or formation of surface carbon deposits. Pt-graphimet, on the other hand, displays an increased number of active centres following MTR, which make its site distribution similar to that of supported platinum catalysts. The structural change observed may be due to the joint effect of interlayer platinum migration and recrystallization of surface platinum particles.

The heterogeneous catalytic hydrogenation of two isomeric cinchona alkaloids, cinchonidine and cinchonine, was studied over Pt/Al2O3 in 1N H2SO4 solution under 100 bar H2 at 25°C. Cinchonidine was transformed into two diastereomeric hexahydroderivatives by hydrogenation of ring A (with N) of the quinoline moiety (yield over 95%, diastereomeric ratio 2/3), whereas hydrogenation of cinchonine resulted in the formation of three products, the major one being formed by the hydrogenation of ring B (without N) (yield 60%). The isolated hexahydroderivatives were investigated by 1H-, 13C-NMR, 1H-1H COSY, 1H-13C HetCOSY, and NOESY spectroscopy and were used as modifiers in the heterogeneous enantioselective hydrogenation of ethyl pyruvate and as catalysts in the Michael addition of ethyl 2-oxocyclopentanecarboxylate to methyl vinyl ketone. Chirality 15:S82–S89, 2003. © 2003 Wiley-Liss, Inc.

1 Introduction 2 General Characteristics 3 Hydrogenation of CC Bonds 4 Hydrogenation of CO Bonds 5 Hydrogenation of CN Bonds 6 Asymmetric Hydrogenations Keywords: heterogeneous catalytic hydrogenation; platinum, ruthenium and rhodium; shape-selective hydrogenation; cis stereochemistry and Horiuti Polanyi mechanism; new catalysts for alkene hydrogenation; hydrogenation of CO bonds; hydrogenation of ketones; hydrogenation of CN bonds

The reactions of ethyl pyruvate with acetic anhydride and pyridine were studied by electrospray ionization mass spectrometry (ESI-MS). Ethyl 2-acetoxy-2-pyridiniumpropionate (1) (m/z 238) resulting from the reaction of the acetylpyridinium cation with ethyl pyruvate, and the adduct of ethyl 2-acetoxyacrylate with a pyridinium cation (2), bound together by non-covalent interactions (m/z 238), were identified by ESI-MS for the first time. Structures 1 and 2 cannot be distinguished, probably because one may be converted into the other and vice versa.

In the enantioselective hydrogenation of ethyl pyruvate (EtPy) over beta-isocinchonine (beta-ICN) modified Pt-alumina catalysts, the major enantiomer was (R)-ethyl lactate ((R)-EtLt (ee 50%)) in toluene, while in AcOH (S)-EtLt (ee 60%) was formed; the (R) configuration is opposite to what is expected from the absolute configuration of the cinchonine backbone.

Chiral sonochemical hydrogenation of an aliphatic alpha-ketoester, ethyl pyruvate to ethyl lactate was carried out over various platinum catalysts in different solvents under atmospheric hydrogen pressure. The reaction rates and the enantiomeric excesses were determined over Pt/C, Pt/SiO2 and Pt/K-10 catalysts both under conventional and sonochemical conditions. The effect of ultrasounds on the catalytic activity and enantioselectivity was tested applying sonochemical pretreatment before the reaction. The ultrasonic irradiation was found to be highly advantageous in these hydrogenations. After insonation of the catalysts, the enantioselectivity was highly improved over Pt/SiO2 and Pt/K-10 catalysts. In addition, the reactions took place in quantitative yield and with complete chemoselectivity and the hydrogenation rates increased with one order of magnitude despite the very mild (atmospheric hydrogen pressure, room temperature) experimental conditions.

Sonochemical chemo- and enantioselective hydrogenations over supported platinum catalysts are described. We disclose our results with respect to a sonochemical modification of the chemoselective hydrogenation of cinnamaldehyde over supported platinum catalysts, and the asymmetric hydrogenation of ethyl pyruvate promoted by various ultrasonic pretreatments. The ultrasonic pretreatment of the supported platinum catalysts was found to be highly beneficial in almost every case, improving both the catalytic activity and selectivity. The effect of additional experimental variables, such as hydrogen pressure, catalyst support, temperature and the ultrasonic insonation time were also studied. The enantioselectivity of the hydrogenation of ethyl pyruvate increased up to 97.1% ee. In the case of cinnamaldehyde hydrogenation, the selective preparation of cinnamyl alcohol became possible. The theoretical aspects of the working mechanisms in comparison with ‘silent’ reactions will also be provided.

The hydrogenation of unsaturated aldehydes was studied over ultrasonically pretreated silica supported platinum catalyst. In the hydrogenation of cinnamaldehyde a remarkable reaction rate and cinnamyl alcohol selectivity increase was observed. Using other unsaturated aldehydes the reaction rate and unsaturated alcohol selectivity increased moderately.

The sonochemical enantioselective hydrogenation of different α-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.

The sonochemical hydrosilylation of alkyl substituted cyclohexanones catalyzed by Rh(PPh 3 ) 3 Cl is described. The application of ultrasonic irradiation during the reaction highly enhances the reaction rates and produces higher yields than those obtained in silent reactions. The stereoselectivity of the reaction has not been changed, the isomeric distribution, i.e. the cis / trans ratio of the 2-substituted cyclohexanols formed, is very close to those obtained in conventional stirred reactions.

The effect of acid strength of coacids on the enantioselective hydrogenation of ethyl pyruvate over cinchona-modified Pt/Al 2 O 3 catalysts is described. The enantioselectivity passes through a maximum as a function of acid strenght. The best value was obtained using trifluoroacetic acid as additive, which increased the optical yields from 85% to 93% ee. Chiral acids were also studied. It was found, however, that the individual chirality of acids used did not modify the basic characteristics of the outcome of the reactions. The configuration of the products were determined by the cinchona alkaloid. On the basis of separate experiments with cinchona salts a short interpretation of acid-effect is also provided.

The preparation, characterization and application of new clay-supported Pt and Pd catalysts containing cinchonidine as chiral modifier are described. The preparation was carried out by deposition of the metal by impregnation followed by the immobilization of the modifier. The catalysts were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The samples were tested in enantioselective hydrogenation of ethyl pyruvate and 2-methyl-2-pentenoic acid. The catalysts were found to be active in the hydrogenations producing moderate to good enantioselectivities (up to 56% ee for the ( R )- ethyl lactate). Moreover, the Pt catalysts were found to be recyclable. The immobilization of modifier on clay-supported catalysts led us to draw important conclusions concerning the existing mechanistic explanations.

The evolution of the catalytic surface and its main characteristics are investigated in the hydrogenative transformations of cyclohexene over a silica-supported copper catalyst for the first time in a static circulation system and in a flow reactor. The main tools were: (i) restart reactions when aging was studied, (ii) competitive hydrogenation reaction with the cyclopropane molecule known to require very different surface features to be present and (iii) the removal of weakly as well as strongly held carbonaceous species. It was found that in hydrogenative transformations of cyclohexene the presence of hydrogen-rich carbonaceous residues are necessary. Without their formation there is no reaction. As their quantity grows the catalyst becomes more active. They are product precursors and unreacted cyclohexane covering the surface to such an extent that the remaining metal ensembles are not enough for cyclopropane hydrogenation to occur. In restart reactions the catalyst undergoes coking but only to a small extent at 443 K.

Publisher Summary The hydrogenation and isomerization of alkenes can usually be described by the classical Horiuti–Polfinyi mechanism. According to that mechanism, in a deuterium atmosphere, double bond migration incorporates deuterium into the allylic position. Early experiments using (+)-apopinene and deuterium showed, however, that in the isomerized molecules the deuterium content was very low and the isomerization was much faster than deuterium incorporation into the allylic position. Therefore, it seemed probable that isomerization takes place through an intramolecular hydrogen shift. A sigmatropic 1, 3-hydrogen shift was suggested, in which the allylic endo- H shifted ( top shift ). Although this type of reaction is symmetry forbidden in an unadsorbed molecule, theoretical calculations showed that in a molecule adsorbed on transition metals, such a shift is allowed. Later, other theoretical calculations suggested another type of 1, 3-hydrogen shift, one in which the allylic exo -hydrogen is abstracted by the surface from an adsorbed alkene (either 1, 2-diadsorbed or π-complexed) and the resulting π-allyl species move over the abstracted hydrogen in such a way that it adds to the former vinylic position and causes, in effect, a stepwise intramolecular 1,3-hydrogen shift (bottom shift). To distinguish between these two hydrogen shift mechanisms, (1 S )-(-)- exo -2, 4-dideuteroapopinene was constructed as a probe molecule. A top shift of the allylic endo -H will not affect the deuterium content of the molecule and no change should occur in the hydrogen content at any position, but a bottom shift of the allylic exo -D will decrease deuterium in the vinylic position (C2) and increase deuterium in the allylic position (C4).

Temperature dependence and the effects of hydrogen pressure on the rate and regioselectivity were studied in the ring opening of propylcyclobutane over a low-dispersion Pd/SiO2 catalyst. At a certain composition (1.33 kPa of propylcyclobutane and 20 kPa of H2) the reaction rate versus temperature curve was found to pass through a maximum. At each temperature the ring opened selectively (or exclusively at 423 K) in the sterically more hindered direction over the clean surface as well as over the steady-state catalyst, yieldingn-heptane as the major product. The hydrogen pressure versus turnover frequency curves were of saturation type for both products over the initial surface at 523 K. Over the steady-state surface, however, the reaction mechanism changed: ring-opening rate versus hydrogen pressure curve passed through a maximum forn-heptane, while it remained of saturation type for 3-methylhexane. For rationalizing the high regioselectivity towardn-heptane formation, the anchoring effect of the propyl side-chain was suggested.

We have previously studied the use of enantiomeric chiral reducing agents in solution to control the direction of the hydrogenation of the keto group of estrone and estrone-3-methyl ether [1]. The complex catalysts chiral hydrosilane-rhodium-( +)- or (-)-DIOP or (+)- or (-)-BINAP allowed different stereoselectivities in the formation of the 17α- and 17β-alcohols.

Active site formation in the hydrogenative ring opening of propylcyclobutane over Pt/SiO 2 was investigated in a static reactor, mainly at 373 K. Changes in the ring-opening rates and selectivities on variously treated catalyst are described. Three types of treatment were applied: repeated runs with (i) only evacuation or (ii) inter-run reduction (H 2 , 473 K, 0.5 h), or (iii) prepoisoning of the catalyst with propylcyclobutane at 373 K or 673 K. The observed (in some cases dramatic) increase in selectivity towards the formation of heptane (1,2 CC bond scission) is interpreted in terms of the formation of a metal-carbonaceous deposit interface where the deposit provides an anchoring site for the adsorption of the propyl side-chain and the ring opens on the clean Pt atoms. Changes in activity due to the various treatments are also discussed.

The effects of poisons (thiophene and carbon tetrachloride) on the rates of hydrogenation and isomerization of (+)-apopinene on Pt and Pd catalysts were studied. Neither of these poisons completely eliminates hydrogenation activity, but a new phenomenon is observed. A minimum occurs in the plot of the ratio k1/ka (isomerization to addition) vs. the amount of poison on Pd. This minimum may be explained by the different effects of the poisons on the adsorption of apopinene and hydrogen.

A series of variously substituted α,β-unsaturated methyl esters were hydrogenated with deuterium (deuteriumated) over deuterated Raney nickel, modified deuterated Raney nickel, and Pd/C. The deuterated Raney nickel catalysts were prepared by leaching Ni-Al alloy with NaOD in D2O. Each gram of deuterated Raney nickel can furnish approximately 45 to 50 m2L of D2 (STP), which is readily exchanged even from traces of atmospheric water. Deuterium distributions are similar for deuteriumations using either D2 or N2 gas overlaying reaction mixtures of deuterated Raney nickel and substrate in dioxane. However, N2produced less deuterium in the products because of atmospheric water contamination. L-glutamic acid modification of deuterated Raney nickel also produces less deuterium in the products, but deuterium distributions remain unchanged. Raney nickel does not catalyze simple 1,2-cis (syn) addition of deuterium across C=C double bonds but distributes deuterium among carbons contiguous to the double bonds. The distributions are influenced by structure and substituents; however, the results are adequately explained by the half-hydrogenated state mechanism.

The hydrogen pressure dependence of the ring-opening reactions of propylcyclobutane was studied at three different temperatures over Pt/SiO[sub 2] catalyst. At 373 and 573 K, only hydrogenative ring opening occurs, while appreciable amounts of aromatics, ring enlargement, and cracking products are formed at 673 K. At 373 K, the ring opens selectively in the sterically more hindered direction over both the clean and the working catalyst, yielding heptane as the major product. The selectivity is lost at 573 K and 673 K: 2,3 C-C bond scission, i.e., formation of 3-methylhexane occurs with initial rates comparable to that of 1,2 C-C bond scission. Over the working catalyst, the selectivity is close to statistical, with a slight excess of 3-methylhexane. An increase of hydrogen pressure has different effects on the ring-opening reactions, depending on the reaction temperature. The initial rate of product formation vs hydrogen pressure curves exhibit three extremes at 373 K, but they increase monotonously at 573 and 683 K. Over the working catalyst, the hydrogen pressure dependence curves display three extremes at 373 K, pass through a maximum at 573 K, and increase monotonously at 673 K. Mechanisms over both the initial and working catalysts are discussed on themore » basis of regioselectivity data and hydrogen pressure dependence curves. 24 refs., 3 figs., 1 tab.« less

Iron phthalocyanine encapsulated in zeolites was used as oxygen activating cat.lysts in the triple catalytic aerobic oxidation of hydroquinone to benzoquinone, in the allylic oxidation of olefins and in the selective oxidation of terminal olefins to ketones. The catalyst proved active in the above reactions. It is stable towards self-oxidation and can be recovered and reused.

The first direct asymmetric synthesis of chiral alkyl 5-oxo-tetrahydrofuran-2-carboxylates (up to 96% ee), which are important building blocks in the synthesis of natural products by heterogeneous cinchona-modified Pt-catalyzed hydrogenation of α-ketoglutaric acid esters and subsequent cyclization of hydroxy esters is described.

Summary The hydrogenolysis and isomerization of methyloxirane were studied over various Pt catalysts in order to determine the number and nature of the active sites. The steps were found to be the probable active sites and the transformation is structure-sensitive. The regioselectivity is not affected by variation in the catalyst structure, so it is determined by the nature of the metal.

Summary The rearrangement of light and deuterium-labelled cis- and trans-2-methyl-3-phenyloxiranes (1, 2 and 1, 2) was studied on ZnO, A1 2 O 3 , and WO 3 , and in the presence of BF 3. Both in the gas phase (473–673 K) and in the liquid phase (298–413 K), l-phenyl-2-propanone (3) and 2-phenylpropanal (4) were formed with high selectivities (0-90% and 11-80%, respectively). Ring-opening was found to occur by selective fission of the benzyl C-0 bond. Mechanistic studies revealed the formation of an open carbenium ion or a double-bonded surface intermediate. The acidic (electrophilic) and basic characters of the oxides determine the product distributions by affecting the relative importance of the competing mechanisms.