Hydrogenation Of Carboxylic Acids Research Articles

Enantioselective synthesis of chiral multicyclic γ-lactones via dynamic kinetic resolution of racemic γ-keto carboxylic acids

Ru-Catalyzed asymmetric transfer hydrogenation of γ-keto carboxylic acids has been achieved, affording chiral multicyclic γ-lactones in high yields with excellent diastereo- and enantioselectivities.

Taming heterogeneous rhenium catalysis for the production of biomass-derived chemicals

Rhenium is one of important components for heterogeneous catalysts, which has been recently used for the catalytic reactions related to the production of biomass-derived chemicals such as deoxydehydration of vicinal OH groups, C-O hydrogenolysis, and hydrogenation of carboxylic acids, and so on. Suitable oxidation state of Re as a catalytic active species is strongly dependent on the catalytic reactions. The control of the oxidation state of Re species on the catalysts is crucial on the catalyst development.

Electrochemical hydrogenation of non-aromatic carboxylic acid derivatives as a sustainable synthesis process: from catalyst design to device construction.

Electrochemical hydrogenation of a carboxylic acid using water as a hydrogen source is an environmentally friendly synthetic process for upgrading bio-based chemicals. We systematically studied electrochemical hydrogenation of non-aromatic carboxylic acid derivatives on anatase TiO2 by a combination of experimental analyses and density functional theory calculations, which for the first time shed light on mechanistic insights for the electrochemical hydrogenation of carboxylic acids. Development of a substrate permeable TiO2 cathode enabled construction of a flow-type electrolyser, i.e., a so-called polymer electrode alcohol synthesis cell (PEAEC) for the continuous synthesis of an alcoholic compound from a carboxylic acid. We demonstrated the highly efficient and selective conversion of oxalic acid to produce glycolic acid, which can be regarded as direct electric power storage into an easily treatable alcoholic compound.

Analysis of Local Structure of Catalysts for Selective Hydrogenation of Carboxylic Acid by XAFS

Analysis of Local Structure of Catalysts for Selective Hydrogenation of Carboxylic Acid by XAFS

Fabrication of highly dispersed Ru nanoparticles stabilized in coated carbon shell via one-pot co-synthesis strategy for aqueous hydrogenation of bio-based itaconic acid

Metal nanoparticles catalysts are widely used in hydrogenation of carboxylic acids and their derivatives, which are significant reactions to produce high-value compounds such as alcohols and lactones. These reactions were usually carried out in liquid phase at harsh conditions with high temperature and pressure, however, catalysts deactivation frequently occurred since small metal NPs were inclined to migrate and aggregate as well as dissolve and leach in such acid systems. Thus, it’s a great challenge to prepare catalysts with highly dispersed small metal NPs with good stability and durability. Herein we propose a novel one-pot co-synthesis method to prepare highly dispersed and stabilized nanometal catalysts that small Ru NPs embedded in carbon species coated on silica nanospheres. Ru precursors were doped directly in the synthesis of RF coated silica spheres along with the polymerization of resorcinol–formaldehyde, and following the process of carbothermal reduction. Aqueous hydrogenation of itaconic acid was used as a probe reaction, which could produce high-value products such as methylsuccinic acid and methyl butyrolactone. The as-prepared catalysts had uniform dispersion of small Ru NPs with core-shell structure of resin coated silica nanospheres, exhibited good hydrogenation activity and stability with no obvious loss of yield for methyl butyrolactone and less sintering in recycling tests.

Hydrogenation of carbonyl compounds of relevance to hydrogen storage in alcohols

Abstract Alcohols are a promising source for the sustainable production of hydrogen that may also serve as rechargeable liquid organic hydrogen carriers (LOHCs). Metal-catalyzed acceptorless dehydrogenation of alcohols produces carbonyl derivatives as H2-depleted by-products, which by means of a hydrogenation reaction can be reconverted to the initial alcohols. Hence, reversible H2-storage systems based on pairs of secondary alcohols/ketones and primary alcohols/carboxylic acid derivatives may be envisaged. In this contribution, the hydrogenation of carbonyl derivatives, including ketones, esters, amides and carboxylic acids, is reviewed from the perspective of the hydrogen storage in alcohols.

Robust cobalt oxide catalysts for controllable hydrogenation of carboxylic acids to alcohols

The selective catalytic hydrogenation of carboxylic acids is an important process for alcohol production, while efficient heterogeneous catalyst systems are still being explored. Here, we report the selective hydrogenation of carboxylic acids using earth-abundant cobalt oxides through a reaction-controlled catalysis process. The further reaction of the alcohols is completely hindered by the presence of carboxylic acids in the reaction system. The partial reduction of cobalt oxides by hydrogen at designated temperatures can dramatically enhance the catalytic activity of pristine samples. A wide range of carboxylic acids with a variety of functional groups can be converted to the corresponding alcohols at a yield level applicable to large-scale production. Cobalt monoxide was established as the preferred active phase for the selective hydrogenation of carboxylic acids.

A theoretical study on the mechanism of hydrogenation of carboxylic acids catalyzed by the Saito catalyst.

The mechanism of the ruthenium carboxylate-catalyzed hydrogenation of carboxylic acids was investigated by using density functional theory (DFT) calculations. The novel mechanism including two hydrogenation cycles was proposed for this reaction. The first cycle is the hydrogenation of the carboxylic acid to an aldehyde, while the second cycle is the hydrogenation of the aldehyde to an alcohol. These two catalytic cycles share similar elementary steps, including H2 heterolysis, hydride migration of the carboxylic acid or aldehyde, and catalyst regeneration. In this hydrogenation mechanism, the carboxylic acid is not only a reactant, but also an important proton source. Furthermore, the noncovalent interaction (e.g. hydrogen bonding interaction) between the ligand and carboxylic acid substrate could promote the hydrogenation of the carboxylic acid through stabilizing the transition state of the most energy-demanding step (i.e., hydride migration in the first catalytic cycle). Besides, the strong electron-donating ability of the dppb ligand could also facilitate the hydride migration.

In situ XAFS Analysis of Local Structure of Pd Alloy Catalysts for Selective Hydrogenation of Carboxylic Acid

In situ XAFS Analysis of Local Structure of Pd Alloy Catalysts for Selective Hydrogenation of Carboxylic Acid

Catalytic hydrogenation of carboxylic acids using low-valent and high-valent metal complexes.

Carboxylic acids are ubiquitous in bio-renewable and petrochemical sources of carbon. The hydrogenation of carboxylic acids to alcohols generates water as the only by-product, and thus represents a sustainable method for the production of these alternative energy carriers/platform chemicals on a large scale. Herein, we offer a brief account of the development of this new concept and molecular insights into cationic mononuclear low- and high-valent transition-metal complexes for the hydrogenation of carboxylic acids.

Selective Hydrogenation of Carboxylic Acids to Alcohols or Alkanes Employing a Heterogeneous Catalyst

The chemoselective hydrogenation of carboxylic acids to either alcohols or alkanes is reported, employing a heterogeneous bimetallic catalyst consisting of rhenium and palladium supported on graphite. α-Chiral carboxylic acids were hydrogenated without loss of optical purity. The catalyst displays a reverse order of reactivity upon hydrogenation of different carboxylic functions with esters being less reactive than amides and carboxylic acids. This allows for chemoselective hydrogenation of an acid in the presence of an ester or an amide function.

Selective hydrogenation of benzoic acid to cyclohexane carboxylic acid over microwave-activated Ni/carbon catalysts

High yields of cyclohexane carboxylic acids were obtained by direct hydrogenation of aromatic carboxylic acids over different Ni/carbon catalysts having distinctive surface properties. The catalysts were characterized by SEM, TEM, H2-TPR and N2 adsorption isotherms for the determination of BET surface area and porosity. The hydrogenation reaction was carried out in batch pressure reactor in gas-liquid phase at 200°C. High selectivity (100%) of cyclohexane carboxylic acids at 86.2mol% conversion of benzoic acid was achieved over microwave-activated biochar supported non-precious metal Ni catalyst. The 10%Ni/CSC-b catalyst has been investigated for hydrogenation of benzoic acid to cyclohexane carboxylic acids and shown little deactivation in stability test. The effects of Ni loading, high dispersion of Ni species, appropriate power of microwave heating and strong interaction of Ni species with carbon are of benefit to the reaction.

Iridium-Catalyzed Asymmetric Hydrogenation of Unsaturated Carboxylic Acids.

Chiral carboxylic acid moieties are widely found in pharmaceuticals, agrochemicals, flavors, fragrances, and health supplements. Although they can be synthesized straightforwardly by transition-metal-catalyzed enantioselective hydrogenation of unsaturated carboxylic acids, because the existing chiral catalysts have various disadvantages, the development of new chiral catalysts with high activity and enantioselectivity is an important, long-standing challenge. Ruthenium complexes with chiral diphosphine ligands and rhodium complexes with chiral monodentate or bidentate phosphorus ligands have been the predominant catalysts for asymmetric hydrogenation of unsaturated acids. However, the efficiency of these catalysts is highly substrate-dependent, and most of the reported catalysts require a high loading, high hydrogen pressure, or long reaction time for satisfactory results. Our recent studies have revealed that chiral iridium complexes with chiral spiro-phosphine-oxazoline ligands and chiral spiro-phosphine-benzylamine ligands exhibit excellent activity and enantioselectivity in the hydrogenation of α,β-unsaturated carboxylic acids, including α,β-disubstituted acrylic acids, trisubstituted acrylic acids, α-substituted acrylic acids, and heterocyclic α,β-unsaturated acids. On the basis of an understanding of the role of the carboxy group in iridium-catalyzed asymmetric hydrogenation reactions, we developed a carboxy-group-directed strategy for asymmetric hydrogenation of olefins. Using this strategy, we hydrogenated several challenging olefin substrates, such as β,γ-unsaturated carboxylic acids, 1,1-diarylethenes, 1,1-dialkylethenes, and 1-alkyl styrenes in high yield and with excellent enantioselectivity. All these iridium-catalyzed asymmetric hydrogenation reactions feature high turnover numbers (up to 10000) and turnover frequencies (up to 6000 h-1), excellent enantioselectivities (greater than 95% ee with few exceptions), low hydrogen pressure (<12 atm), and operational simplicity. These features make chiral iridium catalysts superior or comparable to well-established chiral ruthenium and rhodium catalysts for asymmetric hydrogenation of unsaturated carboxylic acids. A number of chiral natural products and pharmaceuticals have been prepared by concise routes involving an iridium-catalyzed asymmetric hydrogenation of an unsaturated carboxylic acid as a key step. As part of a mechanistic study of iridium-catalyzed asymmetric hydrogenation of unsaturated acids, we isolated, for the first time, the migratory insertion intermediate in the iridium-catalyzed asymmetric hydrogenation of olefins, and this result strongly supports the involvement of an Ir(III)/Ir(V) catalytic cycle. The rigid, bulky scaffold of the chiral spiro-P,N-ligands of the catalysts not only prevents them from undergoing deactivating aggregation under the hydrogenation conditions but also is responsible for the efficient chiral induction. The carboxy group of the substrate acts as an anchor to ensure coordination of the substrate to the iridium center of the catalyst during the reaction and makes the hydrogenation proceed smoothly.

Neutral iridium catalysts with chiral phosphine-carboxy ligands for asymmetric hydrogenation of unsaturated carboxylic acids.

We developed neutral iridium catalysts with chiral spiro phosphine-carboxy ligands (SpiroCAP) for asymmetric hydrogenation of unsaturated carboxylic acids. Different from the cationic Crabtree-type catalysts, the iridium catalysts with chiral spiro phosphine-carboxy ligands are neutral and do not require the use of a tetrakis[3,5-bis(trifluoromethyl)phenyl]borate (BArF-) counterion, which is necessary for stabilizing cationic Crabtree-type catalysts. Another advantage of the neutral iridium catalysts is that they have high stability and have a long lifetime in air. The new iridium catalysts with chiral spiro phosphine-carboxy ligands exhibit unprecedented high enantioselectivity (up to 99.4% ee) in the asymmetric hydrogenations of various unsaturated carboxylic acids, particularly for 3-alkyl-3-methylenepropionic acids, which are challenging substrates for other chiral catalysts.

Mechanism Studies of Ir-Catalyzed Asymmetric Hydrogenation of Unsaturated Carboxylic Acids.

The Ir-catalyzed asymmetric hydrogenation of olefins is widely used for production of value-added bulk and fine chemicals. The iridium catalysts with chiral spiro phosphine-oxazoline ligands developed in our group show high activity and high enantioselectivity in the hydrogenation of olefins bearing a coordinative carboxyl group, such as α,β-unsaturated carboxylic acids, β,γ-unsaturated carboxylic acids, and γ,δ-unsaturated carboxylic acids. Here we conducted detailed mechanistic studies on these Ir-catalyzed asymmetric hydrogenation reactions by using (E)-2-methyl-3-phenylacrylic acid as a model substrate. We isolated and characterized several key intermediates having Ir-H bonds under the real hydrogenation conditions. Particularly, an Ir(III) migratory insertion intermediate was first isolated in an asymmetric hydrogenation reaction promoted by chiral Ir catalysts. That this intermediate cannot undergo reductive elimination in the absence of hydrogen strongly supports the involvement of an Ir(III)/Ir(V) cycle in the hydrogenation. On the basis of the structure of the Ir(III) intermediate, variable-temperature NMR spectroscopy, and density functional theory calculations, we elucidated the mechanistic details of the Ir-catalyzed hydrogenation of unsaturated carboxylic acids and explained the enantioselectivity of the reactions. These findings experimentally and computationally elucidate the mechanism of Ir-catalyzed asymmetric hydrogenation of olefins with a strong coordinative carboxyl group and will likely inspire further catalyst design.

TiO2‐Supported Re as a General and Chemoselective Heterogeneous Catalyst for Hydrogenation of Carboxylic Acids to Alcohols

AbstractInvited for the cover of this issue are the group of Ken‐ichi Shimizu at Hokkaido University and the group of Kazunari Yoshizawa at Kyushu University. The image depicts the latest findings from Hokkaido dealing with selective hydrogenation of carboxylic acids having aromatic moieties to the corresponding alcohols over Re/TiO2. Read the full text of the article at 10.1002/chem.201604762.

Cover Picture: TiO2‐Supported Re as a General and Chemoselective Heterogeneous Catalyst for Hydrogenation of Carboxylic Acids to Alcohols (Chem. Eur. J. 5/2017)

Cover Picture: TiO₂‐Supported Re as a General and Chemoselective Heterogeneous Catalyst for Hydrogenation of Carboxylic Acids to Alcohols (Chem. Eur. J. 5/2017)

TiO2 -Supported Re as a General and Chemoselective Heterogeneous Catalyst for Hydrogenation of Carboxylic Acids to Alcohols.

TiO2 -supported Re, Re/TiO2 , was found to promote selective hydrogenation of carboxylic acids having aromatic and aliphatic moieties to the corresponding alcohols. Re/TiO2 showed superior results compared to other transition-metal-loaded TiO2 and supported Re catalysts for selective hydrogenation of 3-phenylpropionic acid. 3-phenylpropanol was produced in 97 % yield under mild conditions (5 MPa H2 at 140 °C). Contrary to typical heterogeneous catalysts, Re/TiO2 does not lead to the formation of dearomatized byproducts. The catalyst is recyclable and shows a wide substrate scope in the synthesis of alcohols (22 examples; up to 97 % isolated yield).

Inside Cover: Branched Diol Monomers from the Sequential Hydrogenation of Renewable Carboxylic Acids (ChemCatChem 19/2016)

Inside Cover: Branched Diol Monomers from the Sequential Hydrogenation of Renewable Carboxylic Acids (ChemCatChem 19/2016)

Branched Diol Monomers from the Sequential Hydrogenation of Renewable Carboxylic Acids

AbstractA prominent challenge in replacing petrochemical polymers with bioderived alternatives is the efficient transformation of biomass into useful monomers. In this work, we demonstrate a practical process for the synthesis of multifunctional alcohols from five‐ and six‐carbon acids using heterogeneous catalysts in aqueous media. Design of this process was guided by thermodynamic calculations, which indicate the need for two sequential high‐pressure hydrogenations: one, reduction of the acid to a lactone at high temperature; two, further reduction of the lactone to the corresponding diol or triol at low temperature. For example, the conversion of mesaconic acid into (α or β)‐methyl‐γ‐butyrolactone was achieved with 95 % selectivity at a turnover frequency of 1.2 min−1 over Pd/C at 240 °C. Subsequent conversion of (α or β)‐methyl‐γ‐butyrolactone into 2‐methyl‐1,4‐butanediol was achieved with a yield of 80 % with Ru/C at 100 °C. This process is an efficient method for the production of lactones, diols, and triols, all valuable monomers for the synthesis of bioderived branched polyesters.