Plant sterols, a mixture of several des-4-methyl sterols, were hydrogenated over a Pd/C catalyst by varying catalyst amount and stirring rate. Reactions were carried out under kinetic regime and under the influence of external mass transfer limitations. All reaction were done in the absence of internal diffusion limitations. Under external mass transfer limitations of hydrogen more byproducts due to hydrogenolysis and double bond migration were formed. Under mass transfer limited reactions higher catalyst amounts led to a more extensive byproduct formation. Because of double bond migration two very similar byproducts from sitosterol were formed having trans- and cis-fused rings. Interestingly hydrogenolysis also resulted in two similar stereoisomers of sitostane, in the same way as sitostanone, indicating that the hydrogenolysis occurred during the double bond migration when the double bond is in the Delta 3 position. An intermediate product of stigmasterol was observed, in which the ring structure is hydrogenated but the alkyl chain double bond is intact, proving that the ring double bond is hydrogenated prior to alkyl chain double bond hydrogenation. The results show that under mass transfer limitation an optimal amount of catalyst should be used to minimize unwanted byproduct formation.

Hydrogenation of seven prochiral vicinal diketones over heterogeneous cinchona alkaloid modified Pt catalyst is reviewed. Cinchona alkaloids induce enantioselectivity among product hydroxyketones and diols. Effect of modifier structure, reaction parameters (concentration, solvent, hydrogen pressure, temperature) and transient operation is reported. Presence of two reactive carbonyl groups complicate reaction scheme and increase number of possible reactant-modifier diastereomeric complexes. Both regio- and diastereoselctivity aspects are involved. For maximum enantiomeric excess (ee) relatively high molar modifier-to-surface Pt ratios (2–3:1) are required. Non-polar solvents give high ee while acetic acid has a negative effect on the ee. Modifier structure-selectivity correlations are quite specific. Presence of C9–OH group is important to achieve high ee. The highest ee has been obtained with 11-(triethylsilyl)-10,11-dihydrocinchonidine modifier giving 70 % ee at 50 % 1-phenyl-1,2-propanedione (A) conversion. Parameters and structural aspects that result in optimal enantioselectivity are reviewed. The highest ever reported ee = 77 % (at maximum yield of 66 %) in the hydrogenation of A was obtained applying transient operation in continuous fixed bed reactor.

Direct catalytic valorization of bioethanol to 1-butanol over different alumina supported catalysts was studied. Thirteen (13) heterogeneous catalysts were screened in search for the optimal material composition for direct one-pot conversion of ethanol to 1-butanol. For the most promising catalyst, a 25% ethanol conversion with 80% selectivity (among liquid carbon products) to 1-butanol could be reached at 250 °C. Additionally, the reaction kinetics and mechanisms were further investigated upon use of the most suitable catalyst candidate.

Transient techniques are frequently used for catalytic gas-phase processes, but the application of transient techniques on catalytic three-phase systems is very scarce. Transient kinetic experiments provide valuable additional information about the behaviour of complex organic reaction systems, which was illustrated here with continuous enantioselective three-phase hydrogenation of ethyl benzoylformate over supported Pt catalyst particles in a fixed bed. The catalyst stability and the details of the adsorption–desorption behaviour of the reaction participants were revealed by transient experiments. Quantitative modelling of the data was based on kinetic experiments and characterisation of the reactor flow pattern by an inert tracer. Both liquid-phase species and adsorbed surface species were included in the modelling. The model predicted correctly the dynamic behaviour of the complex organic system under transient conditions. The approach is generally applicable to complex organic systems undergoing catalytic transformations.

One-pot synthesis of R-1-phenylethyl acetate was investigated starting from acetophenone hydrogenation performed over Pd/Al2O3 and PdZn/Al2O3 catalysts followed by acylation of the intermediate secondary alcohol, R-1-phenylethanol, over an immobilized lipase. Furthermore, the performance of a third type of catalyst, Ru supported on hydroxyapatite (HAP) was evaluated for racemization of S-1-phenylethanol in one pot together with the two other catalysts. The main objectives of this work were to separate the effects of different catalysts and to reveal the reaction mechanism. For this purpose not only acetophenone, but also (R,S)-1-phenylethanol, S-1-phenylethanol, R-1-phenylethyl acetate, and styrene were used as reactants in combination with Pd/Al2O3, lipase and Ru/HAP as catalysts. The results revealed that the main side product, ethylbenzene, was formed in two different ways, via dehydration of (R,S)-1-phenylethanol to styrene, followed by its rapid hydrogenation to ethylbenzene, and via debenzylation of the desired product, R-1-phenylethyl acetate to ethylbenzene. The true one-pot synthesis, however, was demonstrated over Shvo’s catalyst, but Ru/HAP was not sufficiently active in the racemization step. Ru/Al2O3 was a promising catalyst for racemization of S-1-phenylethanol and for dynamic kinetic resolution of (R,S)-1-phenylethanol, when using only small amounts of the acyl donor ethyl acetate. The challenge in racemization is that the activity of heterogeneous Ru catalysts was inhibited by esters.

E Toukoniitty*, D. Kumar Madnani, K. Kordas, J.-P. Mikkola Abo Akademi University, Laboratory of Industrial Chemistry and Reaction Engineering, FI20500 Turku-Abo, (Finland); University of Oulu, Microelectronics and Materials Physics Laboratories, Department of Electrical and Information Engineering, FI-90014 University of Oulu (Finland); Umea University, Department of Chemistry, Technical Chemistry, 90187 Umea (Sweden) *Esa.Toukoniitty@abo.fi

The use of ionic liquids in catalysis is attracting ever more attention in chemical engineering. In line with this research we have studied supported ionic liquid catalysts (SILCAs) which consist of immobilized catalytic species, e.g., transition metal particles residing in an ionic liquid layer immobilized on a solid support, in batch mode operations. In this study the same concept was successfully applied in continuous mode applying a three-phase structured reactor in the hydrogenation of citral.

Assessing the origin of asymmetric induction in heterogeneously catalyzed hydrogenation is a challenging task. In this work, hydrogenation of a chiral compound, (R)-1-hydroxy-1-phenyl-2-propanone [(R)-PAC], in toluene over cinchonidine modified and unmodified Pt/Al(2)O(3) was studied. To reveal the detailed reaction mechanism and the origin of stereoselectivity in the Pt-catalyzed hydrogenation of the CO double bond, the structures and energies of several adsorption modes of (R)-PAC as well as whole reaction paths for hydrogenation were investigated on Pt(111) by density functional theory (DFT). In agreement with experimental results, the theoretically obtained potential energy profiles for the studied hydrogenation mechanisms implied that (1R,2S)-1-phenyl-1,2-propanediol is formed in excess with respect to the other diastereomeric product diol, (1R,2R)-1-phenyl-1,2-propanediol. Generally, if the elementary hydrogen addition step was thermodynamically more favorable on one of the two diastereotopic faces, it was also kinetically preferred on the same face, and vice versa. Pairwise addition of hydrogen was the most energetically favorable mechanism. Adsorption and hydrogenation of other structurally similar chiral alpha-hydroxyketones, (R)-3-hydroxy-2-butanone and (R)-2-hydroxy-1-cyclohexanone, were also studied computationally on Pt(111). The results showed that cluster model DFT calculations can be used to assess (dia)stereoselectivity in metal-catalyzed hydrogenation of even such complex organic molecules as studied here.

Structures and conformational behavior of several cinchona alkaloid O-ethers in the solid state (X-ray), in solution (NMR and DFT), and in the gas phase (DFT) were investigated. In the crystal, O-phenylcinchonidine adopts the Open(3) conformation similar to cinchonidine, whereas the O-methyl ether derivatives of both cinchonidine and cinchonine are packed in the Closed(1) conformation. Dynamic equilibria in solutions of the alkaloids were revealed by combined experimental-theoretical spin simulation/iteration techniques for the first time. In the (1)H NMR spectra in CDCl3 and toluene-d8 at room temperature, Closed(1) conformation was observed for the O-silyl ethers as a separate set of signals. For O-methyl ether derivatives Closed(1) could be separated only at -30 degrees C in CDCl3 or toluene-d8 and for O-phenylcinchonidine at -70 degrees C in CDCl3/CD2Cl2. The ratio between the Closed(2) and Open(3) conformers was estimated by analyzing the vicinal coupling constant (3)J(H9,H8) at ambient and low temperatures. The observed conformational equilibria of O-(tert-butyldimethylsilyl)cinchonidine in CDCl 3 and toluene-d8 are in good agreement with the theoretically estimated equilibrium populations of the conformations according to Boltzmann statistics. The conformational equilibria of four cinchona alkaloid O-ether solutes in CDCl3 and toluene-d8 are discussed in the light of their relevance to the mechanism of 1-phenyl-1,2-propanedione (PPD) hydrogenation over cinchona alkaloid modified heterogeneous platinum catalysts. It was demonstrated that the conformation found to be abundant in the liquid phase has no direct correlation with the enantioselectivity of the PPD hydrogenation reaction.

Nine cinchona alkaloid O-ethers together with cinchonidine and cinchonine were studied as chiral modifiers in the enantioselective hydrogenation of 1-phenyl-1,2-propanedione over Pt/Al2O3. The influence of the O-substituent on the reaction rate, selectivity and product distribution was investigated. Apparent rate constants for all hydrogenation steps were calculated using a first-order kinetic approach resulting in a good agreement between the experimentally recorded and predicted concentrations. The experimentally observed structure–selectivity effects indicate that the mechanisms of enantiodifferentiation over the catalyst modified by parent cinchona alkaloids and their ether derivatives differ from each other. Moreover, the modifier structure–selectivity dependence and the solvent effect were different for enantio- and diastereoselection in the 1-phenyl-1,2-propanedione and 1-hydroxyketone hydrogenations. Correlation between the modifier substituent bulkiness and diastereoselectivity of the 1-hydroxyketone hydrogenation was observed. Data on the inversion of enantioselectivity of 1-phenyl-1,2-propanedione hydrogenation, diastereoselectivity and the sense of kinetic resolution of the 1-hydroxyketones were presented. Due to the complexity of the reaction network, several competing mechanistic pathways may be present in a single reaction system.

Enantioselective hydrogenation of 1-phenyl-1,2-propanedione (PPD) over cinchona-modified oxide-supported platinum catalysts represents an extension to the well-known Orito reaction with methyl and ethyl pyruvates (EtPy) as typical substrates for the asymmetric reduction. In this paper, the adsorption of PPD and cinchonidine on a Pt catalyst was studied by diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). The catalyst preparation and the adsorption of the reactant and modifier were carried out according to the procedure generally used in catalysis under actual reaction conditions. The catalysts with adsorbed species were analyzed ex situ. The selective deposition of cinchonidine and PPD on the metal surface was confirmed by parallel experiments with alumina samples and by analyzing the platinum adsorption sites with carbon monoxide as a probe molecule. Among the IR visible adsorbed species, eta(1)(O2)-configuration of PPD was found as the most populated on Pt surface under the conditions of ex situ measurements. New data on the mutual interactions among cinchonidine, PPD, and the Pt catalyst are presented. Tilted pi-bonded cinchonidine was detected on the surface under the modifier concentration profile used for obtaining high enantioselectivity in the hydrogenation of PPD. Hydrogen bonding between adsorbed cinchonidine and PPD was also detected.

Enantioselective and racemic hydrogenation of ethyl pyruvate over Pt/Al2O3 catalyst was investigated under conventional and microwave dielectric heating. Experiments were carried out in a single-mode microwave loop reactor, equipped with a heating band, to directly compare the efficiency of the conventional convective/conductive heating and microwave dielectric heating. A sequence of kinetic experiments was performed, varying the microwave power input and the solvent. A catalyst deactivation study was conducted by recycling the catalyst. The choice of solvent significantly affected reaction rate and enantioselectivity. The highest reaction rate and enantioselectivity (75%) was achieved in toluene. In this solvent, the kinetics and enantioselectivity was unaffected by the mode of heating. In case of ethyl alcohol as solvent, the reaction rate remained the same for conventional and dielectric heating. However, the enantioselectivity dramatically decreased under microwave irradiation. The spent and fresh catalysts were characterized by scanning electron microscopy (SEM), nitrogen physisorption and direct current plasma (DCP) technique. Based on the SEM images and nitrogen physisorption analyses, slight sintering of catalyst surface was observed under microwave irradiation.

Hydrogenation of the prochiral diketone, 1,2-indanedione was for the first time investigated using cinchonidine-modified Pt/Al2O3 as a catalyst. The influence of the reaction parameters on catalyst activity, regio- and enantioselectivity was studied revealing fully regioselective hydrogenation of the C(2)-keto group. Enantioselectivities of the (R)- versus (S)-2-hydroxy-1-indanone varied from low to moderate in favor of the (R)-enantiomer.

The impact of nanoscience on heterogeneous catalysis is discussed with the emphasis on enantioselective hydrogenation. Experimental data on liquid-phase hydrogenation reactions of 1-phenyl-1,2-propanedione are presented, demonstrating that the size of nanoparticles should account for the explanation of activity, regio- and enantioselectivity.

Different γ-Al2O3 supported Ir, Pd, Ru, Rh and Pt catalysts were tested in enantioselective 1-phenylpropane-1,2-dione hydrogenation using cinchona alkaloid modifiers. Activity and enantioselectivity over Ir and Ru catalysts were low. Pd catalyst was active in the hydrogenation of 1-phenylpropane-1,2-dione, however, the enantioselectivity over this catalyst was almost negligible. Over Pd hydrogenation proceeded mainly via hydrogenation of the C1O1 carbonyl group, which is attached to the phenyl ring. Hydrogenation over Pd did not proceed in the second hydrogenation step via an enol form as found for ethyl pyruvate hydrogenation over Pd. The structure-selectivity relationship and solvent effects are similar over Pt and Rh in the first hydrogenation step. However, in the second hydrogenation step of hydroxyketones to diols large mechanistical differences between Pt and Rh were observed. Although the activity over Rh catalysts was lower than over Pt after optimization the best result obtained with Rh/γ-Al2O3 (5754 Lancaster) was 60% ee in toluene at maximum yield of 28%, which makes Rh a promising metal for enantioselective hydrogenation.

The nonlinear behavior of modifier mixtures has been discussed for heterogeneous enantioselective catalysis. A kinetic model is developed, which is based on molecular mechanism. Numerical calculations as well as comparison with experimental data on ketopantolactone, isophorone and 4-methoxy-6-methyl-2-pyrone hydrogenation demonstrate applicability of the model to explain nonlinear phenomenon. Within the framework of the advanced model, which has several simplifications, an attempt is made to analyze striking nonlinear phenomena in terms of rate constants and adsorption enthalpies. In order to account for this behavior solely based on adsorption enthalpy (i.e., neglecting the possible difference between adsorption entropy) corresponding difference between two modifiers should be 8–17 kJ mol−1. Alternatively, the reaction rates should have two to three orders of magnitude difference over different modifiers in order to observe strong nonlinear phenomena in a system with modifier mixtures.