Hydrogenation Of Esters Research Articles

Design and Synthesis of Pyrrolidinyl Ferrocene-Containing Ligands and Their Application in Highly Enantioselective Rhodium-Catalyzed Olefin Hydrogenation.

Herein, we report the design and synthesis of a series of chiral pyrrolidine-substituted ferrocene-derived ligands. The proficiency of this novel structural motif was demonstrated in the Rh-catalyzed asymmetric hydrogenation of dehydroamino acid esters and α-aryl enamides. The products were obtained with full conversions and excellent levels of enantioselectivities of up to >99.9% ee and 97.7% ee, respectively, using a BINOL-substituted phosphine-phosphoaramidite ligand which possesses planar, central, and axial chirality elements.

Performance and sulfur poisoning of SiO2, γ-Al2O3, and SiO2-Al2O3-supported bimetallic Pd-Pt catalysts in selective hydrogenation of soybean oil-derived fatty acid methyl esters

Selective hydrogenation of soybean oil-derived fatty acid methyl esters (FAMEs) with low oxidative stability over supported Pd catalysts is crucial to the production of monounsaturated counterparts (mono-FAME), whose oxidative stability and cold flow properties are suitable for producing fuels with high blend ratios. However, supported Pd catalysts are easily deactivated by sulfur-containing FAMEs. Herein, the performance and sulfur poisoning of Pd-Pt/SiO2, Pd-Pt/γ-Al2O3, and Pd-Pt/SiO2-Al2O3 bimetallic catalysts containing 3–10 nm Pt-Pd alloy particles and possessing surface acidity of 0.1–2.4 mmol NH3 g−1 were examined. Pd-Pt/SiO2 with large Pd-Pt alloy particles (10 nm) and weak acidity (0.1 mmol NH3 g−1) favored the selective hydrogenation of polyunsaturated-FAME (poly-FAME) to mono-FAME, while Pd-Pt/γ-Al2O3 and Pd-Pt/SiO2-Al2O3 with smaller Pd-Pt alloy particles and stronger acidity favored the formation of saturated-FAME. These Pd-Pt catalysts were poisoned when using FAME containing 3.4–5.3 ppm of sulfur. However, the performance of the Pd-Pt/SiO2 catalyst physically mixed with γ-Al2O3 did not deteriorate when using a feedstock containing 5.3 ppm of sulfur because the acidic γ-Al2O3 support could adsorb sulfur. Thus, the combination of acidic γ-Al2O3 and Pd-Pt/SiO2 catalysts can be efficiently used to produce mono-FAME through the selective hydrogenation of commercial biodiesel fuels containing high poly-FAME concentrations.

Highly efficient axially biscarboline ethers as catalysts used in 1,2- and 1,4-transfer hydrogenations of ketimines and β-enamino esters

A series of new axial chiral biscarboline ethers were synthesized using L-tryptophan aminoacid after dehydrogenation and oxidations using m-CPBA. These diastereoisomers can be obtained by column chromatography and used as catalysts in asymmetric hydrogenation reactions of β-enamine esters and ketimines. Chiral catalysts 6 and 7 exhibited very high enantioselectivity in the reactions. For example, high up to 98%ee was achieved in the enantioselective hydrogenations when only 1%mol of catalyst was used.

Roles of N on the N-doped Ru/AC catalyst in the hydrogenation of phthalate esters

Roles of N on the N-doped Ru/AC catalyst in the hydrogenation of phthalate esters

The importance of Brønsted acid sites on C[sbnd]O bond rupture selectivities during hydrogenation and hydrogenolysis of esters

Esters represent an important class of reagents and intermediates for the production of fine chemicals and polymers. In prior studies of homogeneous catalysis, molecular complexes have been reported to selectively cleave either carbonyl CO or acyl CO bonds of ester to ether or alcohols, respectively. In contrast, reactions of esters and H2 upon heterogeneous catalysts typically cleave acyl CO bonds and produce alcohols. Here, we demonstrate that the proximity of Brønsted acid sites to Pd nanoparticles and the thermodynamic strength of these Brønsted acid sites influence the rates and selectivities toward CO bond cleavage pathways either to ethers or alcohols during reactions of esters over bifunctional solid catalysts. The combined results from rate measurements as functions of H2 pressure, ester conversion, and methods to combine Pd nanoparticles and acidic supports; kinetic isotope effects; in situ Brønsted acid site titrations; and calorimetric assessments of Brønsted acid strength provide evidence for bifunctional pathways that require proximity between Brønsted acid sites and Pd atoms to form ethers. These findings suggest that Brønsted acid sites near Pd nanoparticles and with lower deprotonation energies promote the direct reduction of esters to ethers by cleaving the carbonyl CO bond. Taken together, these data indicate that direct reduction of esters to ethers involves the hydrogenation of the ester reactant to form hemiacetal at Pd nanoparticles, followed by dehydration of the hemiacetal at proximal acid sites, and subsequent hydrogenation of the enol ether. In comparison, hydrogenolysis of acyl CO bonds of the ester reactant involves the reaction of a hydrogenated intermediate (plausibly hemiacetal) upon Pd nanoparticles to form the corresponding alcohol and aldehyde products. Among the materials examined, Pd nanoparticles supported on WO3 catalyze the direct reduction of esters and lactones to corresponding ethers and remain stable over extended periods of time on stream (∼42 h). These findings offer a foundation for further design and improvement of heterogeneous catalysts for the selective reduction of esters and other challenging hydrogenations.

Partial Hydrogenation of Soybean and Waste Cooking Oil Biodiesel over Recyclable-Polymer-Supported Pd and Ni Nanoparticles

Biodiesel obtained through the transesterification in methanol of vegetable oils, such as soybean oil (SO) and waste cooking oil (WCO), cannot be used as a biofuel for automotive applications due to the presence of polyunsaturated fatty esters, which have a detrimental effect on oxidation stability (OS). A method of upgrading this material is the catalytic partial hydrogenation of the fatty acid methyl ester (FAME) mixture. The target molecule of the partial hydrogenation reaction is monounsaturated methyl oleate (C18:1), which represents a good compromise between OS and the cold filter plugging point (CFPP) value, which becomes too high if the biodiesel consists of unsaturated fatty esters only. In the present work, polymer-supported palladium (Pd-pol) and nickel (Ni-pol) nanoparticles were separately tested as catalysts for upgrading SO and WCO biodiesels under mild conditions (room temperature for Pd-pol and T = 100 °C for Ni-pol) using dihydrogen (p = 10 bar) as the reductant. Both catalysts were obtained through co-polymerization of the metal containing monomer M(AAEMA)2 (M = Pd, Ni; AEEMA− = deprotonated form of 2-(acetoacetoxy)ethyl methacrylate)) with co-monomers (ethyl methacrylate for Pd and N,N-dimethylacrilamide for Ni) and cross-linkers (ethylene glycol dimethacrylate for Pd and N,N’-methylene bis-acrylamide for Ni), followed by reduction. The Pd-pol system became very active in the hydrogenation of C=C double bonds, but poorly selective towards the desirable C18:1 product. The Ni-pol catalyst was less active than Pd-pol, but very selective towards the mono-unsaturated product. Recyclability tests demonstrated that the Ni-based system retained its activity and selectivity with both the SO and WCO substrates for at least five subsequent runs, thus representing an opportunity for waste biomass valorization.

Basic Promotors Impact Thermodynamics and Catalyst Speciation in Homogeneous Carbonyl Hydrogenation.

Homogeneously catalyzed reactions often make use of additives and promotors that affect reactivity patterns and improve catalytic performance. While the role of reaction promotors is often discussed in view of their chemical reactivity, we demonstrate that they can be involved in catalysis indirectly. In particular, we demonstrate that promotors can adjust the thermodynamics of key transformations in homogeneous hydrogenation catalysis and enable reactions that would be unfavorable otherwise. We identified this phenomenon in a set of well-established and new Mn pincer catalysts that suffer from persistent product inhibition in ester hydrogenation. Although alkoxide base additives do not directly participate in inhibitory transformations, they can affect the equilibrium constants of these processes. Experimentally, we confirm that by varying the base promotor concentration one can control catalyst speciation and inflict substantial changes to the standard free energies of the key steps in the catalytic cycle. Despite the fact that the latter are universally assumed to be constant, we demonstrate that reaction thermodynamics and catalyst state are subject to external control. These results suggest that reaction promotors can be viewed as an integral component of the reaction medium, on its own capable of improving the catalytic performance and reshaping the seemingly rigid thermodynamic landscape of the catalytic transformation.

Nickel-Catalyzed Asymmetric Hydrogenation of γ-Keto Acids, Esters, and Amides to Chiral γ-Lactones and γ-Hydroxy Acid Derivatives.

A highly efficient asymmetric hydrogenation of a series of γ-keto acid derivatives, including γ-keto acids, esters, and amides, using a Ni-(R,R)-QuinoxP* complex as the catalyst has been developed to afford chiral γ-hydroxy acid derivatives with excellent enantioselectivities, up to 99.9% ee. This method provides not only an economical one-pot approach for the synthesis of chiral γ-lactones but also access to (S)-norfluoxetine, an inhibitor of neural serotonin reuptake and an essential intermediate for pharmaceutical synthesis.

Synthesis of organobentonite-supported Pd composite catalyst used for the catalytic transfer hydrogenation of polyunsaturated fatty acid methyl ester

Synthesis of organobentonite-supported Pd composite catalyst used for the catalytic transfer hydrogenation of polyunsaturated fatty acid methyl ester

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 CO 2 -derived ethylene carbonate (EC) to yield methanol (MeOH) and ethylene glycol (EG) is a key process for indirect conversion of CO 2 to MeOH. However, a high H 2 /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 H 2 circulation in the promising industrial application. Here, we prepared a series of Ni-modified Cu/SiO 2 catalysts and explored the effects of synthesis methods and Ni contents on catalytic performance under different H 2 /EC molar ratios. The Cu/SiO 2 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 H 2 /EC ratio of 60. And no significant deactivation was observed within 140 h at a lower H 2 /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 H 2 . 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.

Leveraging Chiral Zr(IV)-Based Metal-Organic Frameworks To Elucidate Catalytically Active Rh Species in Asymmetric Hydrogenation Reactions.

One of the most widely employed strategies to produce chiral molecules involves the asymmetric hydrogenation of functionalized olefins using rhodium catalysts. Despite their excellent performance, the exact identity of the active Rh species is still ambiguous as each site may plausibly feature one or two phosphorus ligands. In this work, we used a sequential postsynthetic modification approach to successfully incorporate single-site Rh species into a zirconium-based metal-organic framework comprised of chiral spinol-based ligands. These Rh species feature one phosphorus ligand per Rh, which contrasts with the molecular analogue that contains two phosphorus ligands per Rh site. Following extensive characterization of the Rh-monophosphorus material using techniques including solid-state NMR and extended X-ray absorption fine-structure (EXAFS) spectroscopy, we studied their catalytic performance in the asymmetric hydrogenations of enamides and α-dehydroamino acid esters and observed excellent yields and enantioselectivities (up to 99.9% ee). Notably, the Rh-monophosphorus catalyst is 5 times more active than the homogeneous Rh-biphosphorus control, which we attributed to the higher activity of the single-site Rh-monophosphorus species and the confined MOF cavities that can enrich reactants. In addition, we observed a unique topology-dependent behavior in which linker expansion leads to the formation of a novel Zr-MOF with a distinct 4,8-connected net that cannot be phosphorylated, presumably due to intense tensile strain and steric repulsion present within this framework. Finally, we demonstrate the utility of this single-site Rh-monophosphorus catalyst in the gram-scale synthesis of (R)-cinacalcet hydrochloride, a first-in-class drug in the therapy of secondary hyperparathyroidism and parathyroid carcinoma, with 99.1% ee.

Atomic ruthenium stabilized on vacancy-rich boron nitride for selective hydrogenation of esters

Constructing and taming metal–support interaction of atoms and/or clusters has emerged as a promising protocol to maximize the catalytic performance of noble metal-based materials. Here, we report atomic ruthenium (Ru) with the oxidized state immobilized on defect-rich hexagonal boron nitride (d-BN) nanosheets and the essential interfacial electronic effect on Ru deduced from B- and N-vacancies for superior selective hydrogenation of esters. Experimental results indicate that strong electronic interplay exists between vacancies and atomic Ru species. Unlike defect-free commercial hexagonal BN (h-BN), d-BN can highly stabilize the active Ru species in atomic scale with oxidation state, and the obtained Ru/d-BN significantly increases the catalytic activity and durability. Specifically, the turnover frequency of Ru/d-BN is more than one order of magnitude higher than that of the conventional optimized Ag/SiO2 catalyst for the selective hydrogenation of dimethyl oxalate to methyl glycol. Systematic characterizations show that the Ru on B- and N-vacancies, and the defective BN serves as electron acceptor. The findings demonstrate the overall electronic effect on the electron-rich feature of Ru on d-BN, such that the electronic metal–support interactions cause the Ru species to favor the adsorption and selective scission of C–O bonds in esters, revealing a highly efficient hydrogenation catalysis.

Hydrogenation of Esters by Manganese Catalysts

AbstractThe hydrogenation of esters catalyzed by a manganese complex of phosphine‐aminopyridine ligand was developed. Using this protocol, a variety of (hetero)aromatic and aliphatic carboxylates including biomass‐derived esters and lactones were hydrogenated to primary alcohols with 63–98% yields. The manganese catalyst was found to be active for the hydrogenation of methyl benzoate, providing benzyl alcohol with turnover numbers (TON) as high as 45,000. Investigation of catalyst intermediates indicated that the amido manganese complex was the active catalyst species for the reaction.magnified image

Facile preparation of PVA hydrogels with adhesive, self-healing, antimicrobial, and on-demand removable capabilities for rapid hemostasis.

Multifunctional and smart hydrogel-based hemostatic materials are of great significance in the field of medical care. In this paper, a facile method for the preparation of self-healing, adhesive and on-demand removable PBO hydrogels was established with a simple mixture of polyvinyl alcohol (PVA), borax and oligomeric procyanidin (OPC). In this hydrogel system, borax and OPC were used as dynamic crosslinkers to connect the PVA macromolecules through reversible borate ester bonds and hydrogen bonds, resulting in hydrogels that possess good self-healing and adhesive abilities. Furthermore, the PBO hydrogel displayed excellent antimicrobial activity against Escherichia coli and Staphylococcus aureus. In addition, thanks to the adhesive property of the hydrogel and the inherent hemostatic activity of OPC, this hydrogel showed rapid hemostasis performance as concluded from the in vivo experiments of mouse liver incision, tail amputation and femoral artery models. Benefitting from the fast degradation in water, this hydrogel could be easily removed on-demand within 10 min. Therefore, this well-designed PBO hydrogel offers an important prospect as a rapid hemostatic dressing.

B(C6F5)3-Catalyzed transfer hydrogenation of esters and organic carbonates towards alcohols with ammonia borane.

Herein, we report an efficient metal-free system for the transfer hydrogenation of esters and carbonates by-passing the otherwise ubiquitous formation of transesterification side-products. The Lewis acid B(C6F5)3 is used as catalyst and ammonia borane as hydrogen donor. This methodology shows broad substrate scope and functional group tolerance in excellent yields at very mild conditions.

Mild and highly selective hydrogenation of cyclohexyl acetate to cyclohexanol over Cu(i) coordinated amino-functionalized poly(ionic liquid)s

Cu(i) coordinated amino-functionalized poly(ionic liquid)s exhibited an unprecedented performance for mild and highly selective hydrogenation of esters.

Copper-Based Catalysts Confined in Carbon Nanocage Reactors for Condensed Ester Hydrogenation: Tuning Copper Species by Confined SiO2 and Methanol Resistance

Copper-Based Catalysts Confined in Carbon Nanocage Reactors for Condensed Ester Hydrogenation: Tuning Copper Species by Confined SiO₂ and Methanol Resistance

Alkali Metal Alkoxides in Noyori‐Type Hydrogenations

AbstractThis minireview discusses the accelerative role of alkali metal alkoxides in two important catalytic processes: hydrogenation of ketones and esters with Noyori‐type molecular catalysts. Here I offer my perspective on the unique mechanistic aspects of these reactions – a subject that remains controversial and often misunderstood.

Intensification of catalytic transfer hydrogenation of fatty acid methyl esters by using ultrasound

Ultrasound was applied to intensity the catalytic transfer hydrogenation (CTH) of highly unsaturated fatty acid methyl esters (FAMEs) to realize the effective hydrogenation of FAMEs under mild conditions. Under the optimum reaction conditions of ultrasound-assisted CTH using La-doped nickel-boride amorphous alloy (Ni–La–B) as catalyst, sodium borohydride as hydrogen donor and water as solvent, a high conversion ratio of hydrogenation for polyunsaturated FAMEs could be easily realized at 35 °C at 120 min (ca. 78.66%). It was found that ultrasound presented a significant intensification effect on the CTH of FAMEs; different from the conventional and ultrasound approaches, by using ultrasound-assisted approach of CTH, deep hydrogenation could be avoided to a certain extent even under the high conversion ratio of hydrogenation, and the hydrogenated product with good performance was easily gained. The self-purification function of ultrasound on the catalyst played the most important positive effect on the intensification of CTH of FAMEs. Overall, the ultrasound-assisted approach played an effective process intensification on the CTH of FAMEs to produce high-quality products under mild conditions.

New derivatives of the iridoid specioside from fungal biotransformation.

Iridoids are widely found from species of Bignoniaceae family and exhibit several biological activities, such as anti-inflammatory, antimicrobial, antioxidant, and antitumor. Specioside is an iridoid found from Tabebuia species, mainly in Tabebuia aurea. Thus, here fungus-mediated biotransformation of the iridoid specioside was investigated by seven fungi. The fungus-mediated biotransformation reactions resulted in a total of nineteen different analogs by fungus Aspergillus niger, Aspergillus flavus, Aspergillus japonicus, Aspergillus terreus, Aspergillus niveus, Penicillium crustosum, and Thermoascus aurantiacus. Non-glycosylated specioside was the main metabolite observed. The other analogs were yielded from ester hydrolysis, hydroxylation, methylation, and hydrogenation reactions. The non-glycosylated specioside and coumaric acid were yielded by all fungi-mediated biotransformation. Thus, fungus applied in this study showed the ability to perform hydroxylation and glycosidic, as well as ester hydrolysis reactions from glycosylated iridoid. KEY POINTS: • The biotransformation of specioside by seven fungi yielded nineteen analogs. • The non-glycosylated specioside was the main analog obtained. • Ester hydrolysis, hydroxylation, methylation, and hydrogenation reactions were observe.