Enantio-differentiating hydrogenation of methyl acetoacetate over modified Raney nickel catalysts prepared by two-step modifications

Two-step modifications of the Raney nickel were examined for the enantio-differentiating hydrogenation of methyl acetoacetate. Among the two-step modifications attempted in this study, the combination of ‘pre-modification with disodium tartrate and NaBr in water’ and ‘in-situ modification with tartaric acid’ resulted in the highest optical yield (84%). This modification process is a greener process than the conventional one carried out under weakly acidic conditions, because this process generated almost no Ni²⁺ ions. The pre-modification with the tartrate and NaBr preferentially eliminated Al³⁺ from the Raney nickel surface.     

Enantio-differentiating hydrogenation of methyl acetoacetate over reduced nickel catalysts pre-modified in methanol

The enantio-differentiating hydrogenation of methyl acetoacetate was carried out over a (R,R)-tartaric acid-NaBr-modified reduced Ni catalyst. Reduced Ni was pre-modified in a methanol solution of tartaric acid and NaBr. It was revealed that the pre-treatment of methanol by molecular sieves was essential for attaining the high enantio-differentiating ability of 80–90% and high durability during repeated uses of the recovered catalyst.     

The hydrogenation of toluene over nickel loaded Y zeolites

The catalytic activities of a range of hydrogen reduced nickel Y zeolites for the hydrogenation of toluene were measured and correlated with the following catalytic parameters: reaction temperature; reaction time; coke deposition. The role of the alkali metal co-cation (Li⁺, Na⁺, K⁺, Rb⁺ or Cs⁺) in influencing the overall hydrogenation activity of the supported nickel metal was probed. The effect of poisoning the surface Bronsted acidity by the adsorption of ammonia is discussed. For comparative purposes, data on the hydrogenation of benzene over the same catalysts are included.     

Progress of enantio-differentiating hydrogenation of prochiral ketones over asymmetrically modified nickel catalysts and a newly proposed enantio-differentiation model

This article reviews the enantio-differentiating hydrogenation of various prochiral ketones over asymmetrically modified Ni catalysts. Development from the discovery to the state of the art of the modified Ni catalyst is surveyed. Understanding and interpretation of this catalyst is discussed and new enantio-differentiation models are proposed. This revised version was published online in June 2006 with corrections to the Cover Date.     

钼改性雷尼镍催化剂的葡萄糖加氢性能

Mo改性雷尼镍是葡萄糖加氢制备山梨醇工业中重要的催化剂。考察了不同Mo含量雷尼镍催化剂的葡萄糖加氢性能。结果表明,Mo改性雷尼镍催化剂的活性和稳定性得到大幅提高,探讨了Mo改性雷尼镍催化剂活性和稳定性提高的原因。Mo改性雷尼镍催化剂活性和稳定性提高的原因是改性催化剂中氧化态的Mo可以作为L酸吸附中心,有利于葡萄糖在催化剂上的吸附,从而提高催化剂活性;Mo的存在,减少了雷尼镍催化剂在反应过程中Al的流失量,是催化剂稳定性提高的主要原因。     

Liquid-phase stereoselective thymol hydrogenation over supported nickel catalysts

The stereoselective hydrogenation of thymol was studied in liquid phase over several nickel catalysts, modified by coimpregnation of inorganic compounds containing chlorine. The total activity of all catalysts studied was decreased and was on the same order of magnitude, indicating that chlorine even after reduction remains on the surface and is responsible for the poisoning effects. Such blocking of accessible sites results in similar reaction rates for the catalysts studied. Selectivity and stereoselectivity to menthols and menthones changed significantly. The modifiers could influence the rate of keto-enol transformations, which is thought to be the key selectivity and stereoselectivity governing step.     

Asymmetric transfer hydrogenation of prochiral ketone catalyzed over Fe-CS/SBA-15 catalyst

A heterogeneous chiral catalyst Fe(III)-CS (chitosan) complex/mesoporous molecular sieve SBA-15 (Santa Barbara Amorphous) was prepared. The asymmetric transfer hydrogenations of prochiral acetophenone and 4-methyl-2-pentanone to corresponding chiral alcohols were carried out on Fe-CS/SBA-15 at atmosphere pressure using 2-propanol as hydrogen donor. Effects of Fe content in catalyst, reaction temperature, reaction time and promoter KOH concentration on the conversion of substrates and enantio-selectivity were investigated. Fe-CS/SBA-15 with 2.2% mass fraction Fe exhibits considerable enantioselectivity and catalytic activity for the asymmetric transfer hydrogenations of aromatic ketone and aliphatic ketone. Under optimal reaction conditions: KOH concentration 0.03 mol/L, reaction temperature 70°C and reaction time 4 h, enantiomer excess (ee) of (R)-1-phenylethanol and conversion of acetophenone can reach 87.4% and 27.7%, respectively. Under the above KOH concentration and reaction temperature and reaction time of 8 h, the ee of (R)-4-methyl-2-pentanol and conversion 4-methyl-2-pentanone amounted to 50.2% and 25.5%, respectively. Translated from Petrochemical Technology, 2006, 35(9): 858–862 [译自: 石油化工]     

Selective hydrogenation of cinnamaldehyde over Raney cobalt catalysts modified with salts of heteropolyacids

The hydrogenation of cinnamaldehyde to cinnamyl alcohol was carried out over Raney cobalt catalysts modified by Cu_3/2PMo₁₂O₄₀. It was found that the conversion of cinnamaldehyde decreases substantially with increases in the amount of Cu_3/2PMo₁₂O₄₀ deposited on Raney cobalt catalysts. The maximum yield of cinnamyl alcohol varies with the amount of deposited Cu_3/2PMo₁₂O₄₀. The more the deposited modifier, the higher the attainable maximum yield of cinnamyl alcohol. With 2.8% Cu_3/2PMo₁₂O₄₀ modified Raney cobalt, the selectivity for cinnamyl alcohol does not change with reaction temperature and reaction time. Thus, it is likely that the selectivity of ca. 80% for cinnamyl alcohol represents a specific value which is related to the nature of the surface modifier, Cu_3/2PMo₁₂O₄₀. The influences of the heteropolyanions and the competitive cations on the conversion and the selectivity were also investigated. It was found that copper salts of different heteropolyacids acting as the modifier of the catalyst bring about different enhancements in the selectivity for cinnamyl alcohol. The order of enhancement of selectivity in terms of heteropolyacid anion is PMo₁₂O³⁻₄₀>SiMo₁₂O⁴⁻₄₀>PW₁₂O³⁻₄₀. There is little difference in selectivity by modification with (NH₄)₆Mo₇O₂₄ and Cu₂SiMo₁₂O₄₀. Raney cobalt catalyst modified by different 12-molybdophosphate containing cations of alkali, alkaline earth and transition metals gives a similar selectivity of about 75%. Among all of the 12-molybdophosphates, that containing the cation Cu²⁺ is the best in improving the selectivity of the catalysts. A selectivity as high as 83% was attained when an amount of 2.8% Cu_3/2PMo₁₂O₄₀ was deposited on the catalyst.     

Asymmetric hydrogenation of prochiral amino ketones to amino alcohols for pharmaceutical use

This Account gives an overview of the homogeneously catalyzed asymmetric hydrogenation of prochiral amino ketones. The preparation of enantiopure arylalkanolamines, which are potent and economically very important pharmaceuticals, is described. Classical routes of synthesis are compared with the new asymmetric hydrogenation route for a number of compounds from the viewpoint of an industrial pharmaceutical chemist.     

Studies of the effects of the modification conditions on the hydrogenation rate for the enantio-differentiating hydrogenation of methyl acetoacetate over a tartaric acid–NaBr-modified nickel catalyst

The effects of the modification conditions on the hydrogenation rate and the enantio-differentiating ability (e.d.a.) for the enantio-differentiating hydrogenation of methyl acetoacetate were studied over an (R, R)-tartaric acid–NaBr-in-situ-modified nickel catalyst. It was revealed that a tartaric acid modification increased the hydrogenation rate irrespective of the presence of the auxiliary modifier, NaBr. In the presence of the tartaric acid, NaBr would have two roles, i.e., Na⁺ activates the enantio-differentiating sites through the interaction with tartaric acid, and Br⁻ deactivates both the enantio-differentiating sites and non-enantio-differentiating sites. The e.d.a. values and the hydrogenation rate would be determined by the combination of these effects of Na⁺ and Br⁻.     

Synthetic natural gas from CO hydrogenation over silicon carbide supported nickel catalysts

Silicon carbide supported nickel catalysts for CO methanation were prepared by impregnation method. The activity of the catalysts was tested in a fixed-bed reactor with a stream of H₂/CO = 3 without diluent gas. The results show that 15 wt.% Ni/SiC catalyst calcined at 550 °C exhibits excellent catalytic activity. As compared with 15 wt.% Ni/TiO₂ catalyst, the Ni/SiC catalyst shows higher activity and stability in the methanation reaction. The characterization results from X-ray diffraction and transmission electron microscopy suggest that no obvious catalyst sintering has occurred in the Ni/SiC catalyst due to the excellent thermal stability and high heat conductivity of SiC.     

Mass transfer and kinetics of the three-phase hydrogenation of a dinitrile over a Raney-type nickel catalyst

The hydrogenation kinetics of a dinitrile over a Raney-type nickel catalyst was evaluated from experiments performed in a fed-batch operating autoclave at 320- and 2- hydrogen pressure. This complex catalytic reaction consists of two main parts: almost 100% selective hydrogenation of the dinitrile to the corresponding aminonitrile and consecutive hydrogenation to either the desired primary diamine or to pyrrolidine via ring formation. An extensive study has been made on the effects of mass transfer in the applied slurry-type reactor for this reaction. The gas-liquid mass transfer is enhanced by the presence of catalyst particles, and at typical hydrogenation conditions, k_La values up to can be reached. A Sherwood correlation for the three-phase reactor showed that important parameters in the gas-liquid mass transfer are stirrer speed and the density and viscosity of the solvent. The kinetic experiments were performed in absence of mass and heat transfer limitations. The kinetic data were modeled using two rate models based on Langmuir-Hinshelwood kinetics, assuming the reaction of dissociatively adsorbed hydrogen and nitrile compound as rate-limiting step. The first model involved competitive adsorption between hydrogen and organic compound and the second model was based on non-competitive adsorption. Both models successfully described both reaction parts. The reaction of dinitrile to aminonitrile is nearly 100% selective due to the relatively strong adsorption of the dinitriles as compared to the aminonitriles. By increasing the hydrogen partial pressure, higher yields of primary amine can be obtained. The models predict that operating in the mass-transfer regime at relatively high temperatures reduces the formation of the primary diamine.     

Enantioselective hydrogenation of α-ketoesters using cinchona modified platinum catalysts and related systems: A review

The state of the art for the heterogeneous enantioselective hydrogenation of α-ketoesters using cinchona modified Pt catalysts and related systems is reviewed. The effect of the following elements of the catalytic system are well known: Catalyst. Supported Pt catalysts with relatively low dispersion (particle diameter >2 nm) are preferred for the hydrogenation of α-ketoacid derivatives, Pd catalysts for functionalized olefins. Most support materials are suitable. Substrate. The reacting function is preferentially a ketone or a C=C bond, a carbonyl group in a-position is necessary for good optical yields. Modifier. The minimal requirements for an efficient modifier for the hydrogenation of α-ketoesters is the presence of a basic nitrogen atom close to one or more stereogenic centers and connected to an extended aromatic system (preferentially quinolyl or naphthyl). The presence of an alcohol or ether in β-position to the basic nitrogen often gives better enantioselectivities. Solvent. Solvents with adielectric constant between 2 and 10 give best selectivities for a-ketoesters with best e.e.'s in acetic acid. For the hydrogenation of substrates with a free acid function aqueous polar solvents are preferred. The highest optical yields for the different substrate types: 95% e.e. for α-ketoesters, 85% for a-ketoacids and 70% for α,)-unsaturated acids. Practical problems for the use of the catalytic system are low e.e.'s at the start of the reaction, the instability of the modifier and some side reactions as well as the purity of the ethyl pyruvate. Mechanistic investigations have established interactions between substrate and modifier in solution and adsorption of the ethyl pyruvate and cinchonidine on the catalyst. The dependence of rate and e.e. on catalyst, cinchonidine, ethyl pyruvate and hydrogen concentration has been established for ethyl pyruvate hydrogenation using Pt/Al₂O₃-cinchona. A Langmuir-Hinshelwood scheme is well suited for explaining the observed kinetic results. Based on the kinetic results, the effect of modifier and substrate structure, and molecular modeling studies, the following mechanistic model has been developed: On the unmodified catalyst, the a-ketoester and hydrogen are reversibly adsorbed and the addition of the first hydrogen atom is rate determining. A modified active site is formed by adsorption of one cinchona molecule. It is postulated that a protonated adsorbed modifier interacts with the α-ketoester and forms a stabilized half hydrogenated intermediate. The rate determining step for the preferred enantiomer is the addition of the second hydrogen. The rate acceleration and the enantiodiscrimination is therefore due to the preferential stabilization of one of the two diastereomeric intermediates. Alternative mechanisms are discussed but considered to be less satisfying.     

Ring hydrogenation of naphthalene and 1-naphthol over supported metal catalysts in supercritical carbon dioxide solvent

Catalytic ring hydrogenations of naphthalene and 1-naphthol were studied over several supported metal catalysts in supercritical carbon dioxide solvent at low temperature. Higher concentration of hydrogen in supercritical carbon dioxide and lower reaction temperature were responsible for higher catalyst activity and selectivities to the desired partial ring hydrogenated products as compared with those observed in organic solvent for the same catalyst.     

Photocatalytic hydrogenation of acetophenone derivatives and diaryl ketones on polycrystalline titanium dioxide

In the absence of molecular oxygen, various aromatic ketones such as acetophenone derivatives and diaryl ketones were photocatalytically hydrogenated on polycrystalline titanium dioxide (Degussa P25) under UV light irradiation (> 340 nm). The desired secondary alcohols were obtained with excellent chemical efficiency (almost 100% yields for 10 examples) by choosing ethanol as a sacrificial hole scavenger, which was oxidized into acetaldehyde.     

Highly dispersed nickel boosts catalysis by Cu/SiO2 in the hydrogenation of CO2-derived ethylene carbonate to methanol and ethylene glycol

The efficient hydrogenation of CO₂-derived ethylene carbonate (EC) to yield methanol (MeOH) and ethylene glycol (EG) is a key process for indirect conversion of CO₂ to MeOH. However, a high H₂/EC molar ratio during the hydrogenation process (usually as 180–300) is generally required to achieve good catalytic performance, resulting in high cost and energy consumption for H₂ circulation in the promising industrial application. Here, we prepared a series of Ni-modified Cu/SiO₂ catalysts and explored the effects of synthesis methods and Ni contents on catalytic performance under different H₂/EC molar ratios. The Cu/SiO₂ catalyst with 0.2% (mass) Ni loading prepared by co-ammonia evaporation method exhibited above 99% conversion of EC, 91% and 98% selectivity to MeOH and EG respectively at H₂/EC ratio of 60. And no significant deactivation was observed within 140 h at a lower H₂/EC of 40. It is demonstrated that a few of Ni addition could not only promote Cu dispersion and increase surface Cu⁺ species due to the strong interaction between Cu and Ni species, but also form uniformly-dispersed CuNi alloy species and thus enhance the adsorption and dissociation of H₂. But the excess Ni species would aggregate and segregate to cover partial surface of Cu nanoparticles, leading to a significantly drop of catalytic performance in EC hydrogenation. These insights may provide guidance for further design of catalysts for the ester hydrogenation reactions.     

胺化反应合成乙二胺催化剂的研究

研究了丝光沸石脱铝及金属改性等对合成乙二胺反应性能的影响,通过X荧光和XRD等手段对所得催化剂进行了表征。实验表明,脱铝改性时HCl溶液的最佳浓度为0.2 mol·L^－1。Cu和Zn改性可极大的提高催化剂的活性和选择性。改性后,催化剂的骨架结构基本维持不变,Cu和Zn高度分散于催化剂中。     

Scaling-out selective hydrogenation reactions: From single capillary reactor to monolith

Selectivity and kinetic studies of the Pd-catalysed hydrogenation of 2-butyne-1,4-diol were performed in a single capillary channel, and monoliths consisting of 1256 capillaries and 5026 capillaries in (I) the pressure range 100-300 kPa (II) the temperature range 298-328 K using a 30% v/v 2-propanol/water solvent. All reactors were operated in downflow mode such that the reaction fluid was in Taylor flow. Transport calculations indicated that liquid-solid transport resistances were low (<5%) and energies of activation were found to be in the range 32-34 kJ mol⁻¹. While the reaction was first order in hydrogen concentration, the order with respect to 2-butyne-1,4-diol changed over the concentration range investigated. A model based upon a Langmuir-Hinshelwood mechanism was applied and found to predict reasonably well the experimental reaction rates. High selectivity values towards the 2-butene-1,4-diol were found in both the single- and multiple-capillary reactors, even at 100% conversion of the alkyne.     

Adsorption of reaction species on raney nickel for slurry-phase hydrogenation of p-nitrotoluene

Adsorption of hydrogen, p-nitrotoluene, p-toluidine and water on Raney nickel from their methanol solutions has been investigated under catalytic conditions. The isotherms of reversible adsorption of hydrogen are linear and the estimated heat of adsorption is 28.9 kJ mol^?1. The amount of hydrogen held irreversibly on the catalyst is very large as compared to that adsorbed reversibly. The isotherms of adsorption of p-nitrotoluene, p-toluidine and water have different shapes (viz. types H3, S1 and L3 respectively). Among the reaction species, p-toluidine is not adsorbed on the catalyst at low concentrations (< 0.8 mmol cm^?3).     

Proline-based amino amide hydrochlorides as ligands for asymmetric transfer hydrogenation of prochiral ketones in water

Chiral amino amide hydrochlorides were synthesized from l-proline and their application to asymmetric transfer hydrogenation of prochiral ketones in aqueous media is described. The ATH reaction could afford excellent conversion rates (up to >99%) and good enantioselectivities (up to 76.9% ee).