Hydrogenation Of Cyclohexanone Research Articles

SiO2-supported Pd nanoparticles for highly efficient, selective and stable phenol hydrogenation to cyclohexanone

Cyclohexanone is significant chemical reagent for organic synthesis, so it is key to design and prepare a highly active and environmentally friendly catalyst for the conversion of phenol to cyclohexanone. The results in this work show that the Pd-based supported nanocatalysts (Pd/SiO2) with various Pd contents (Pd/SiO2–1 with 0.16 wt% Pd, Pd/SiO2–2 with 0.26 wt% Pd, Pd/SiO2–3 with 0.52 wt% Pd, Pd/SiO2–4 with 2.60 wt% Pd) have high conversion and selectivity in phenol selective hydrogenation to cyclohexanone under relatively moderate reaction parameters, Pd/SiO2–2 with the highest conversion of 80.6%, selectivity of 92.1% and turnover frequency (TOF) of 1106.1 h−1. This excellent activity is attributed to the highly dispersed Pd nanoparticles (NPs) on silica with high surface area. The Pd/SiO2 catalysts are with high Pd dispersion and strong interaction of Pd-SiO2, which have been proved by XRD, XPS, BET, TEM, HRTEM, STEM, STEM-EDS elemental analysis techniques. The as-prepared materials have good catalytic behaviors in the selective hydrogenation of phenol and good stability, facilitating phenol hydrogenation to cyclohexanone and preventing the excessive hydrogenation of cyclohexanone to cyclohexanol.

Superior catalytic performance of intermetallic CaPt2 nanoparticles supported on titanium group oxides in hydrogenation of ketones to alcohols.

Intermetallic CaPt2 nanoparticles, supported on titanium group oxides, were prepared using a molten salt method with CaH2 as both the reducing agent and the calcium source. The nanoparticles exhibited superior catalytic activity compared to a commercial Pt/C catalyst in the hydrogenation of ketones to alcohols, which could be promoted by electron-rich Pt sites in CaPt2.

Intermetallic YIr2 nanoparticles with negatively charged Ir active sites for catalytic hydrogenation of cyclohexanone to cyclohexanol

Negatively charged iridium species in Laves phase YIr2 as highly active sites for hydrogenation of cyclohexanone to cyclohexanol.

Atypical and Asymmetric 1,3-P,N Ligands: Synthesis, Coordination and Catalytic Performance of Cycloiminophosphanes.

Novel seven‐membered cyclic imine‐based 1,3‐P,N ligands were obtained by capturing a Beckmann nitrilium ion intermediate generated in situ from cyclohexanone with benzotriazole, and then displacing it by a secondary phosphane under triflic acid promotion. These “cycloiminophosphanes” possess flexible non‐isomerizable tetrahydroazepine rings with a high basicity; this sets them apart from previously reported iminophophanes. The donor strength of the ligands was investigated by using their P‐κ1‐ and P,N‐κ2‐tungsten(0) carbonyl complexes, by determining the IR frequency of the trans‐CO ligands. Complexes with [RhCp*Cl2]2 demonstrated the hemilability of the ligands, giving a dynamic equilibrium of κ1 and κ2 species; treatment with AgOTf gives full conversion to the κ2 complex. The potential for catalysis was shown in the RuII‐catalyzed, solvent‐free hydration of benzonitrile and the RuII‐ and IrI‐catalyzed transfer hydrogenation of cyclohexanone in isopropanol. Finally, to enable access to asymmetric catalysts, chiral cycloiminophosphanes were prepared from l‐menthone, as well as their P,N‐κ2‐RhIII and a P‐κ1‐RuII complexes.

Half-sandwich ruthenium(II) complexes containing 4-substituted aniline derivatives: structural characterizations and catalytic properties in transfer hydrogenation of ketones

Four half-sandwich Ru(II) complexes (1)–(4) with the general formulae [Ru(η6-p-cymene)(L)Cl2] were synthesized by the reaction of one equivalent of the Ru(II) p-cymene dimer with two equivalents of a p-substituted aniline derivative L (where L is p-methyl, p-isopropyl, p-methoxy, or p-hydroxy aniline). The structures of complexes (2)–(4) were determined by single-crystal X-ray diffraction studies. The structural analysis revealed piano-stool geometry at the Ru(II) ions which are coordinated to the η6-p-cymene, two chloride anions and the amine group of the aniline ligand. In the structure of (2)–(4), the coordinated chloride ions make intermolecular hydrogen bonding with the –NH2 group of an adjacent molecules (NH–Cl) resulting in hydrogen bond networks. The catalytic activities of the complexes in transfer hydrogenation of acetophenone were studied. Complex [Ru(η6-p-cymene)(p-methylaniline)Cl2] (1) showed the best catalytic performance in the transfer hydrogenation of acetophenone. The presence and positions of methyl and bromide groups on the acetophenone have an impact on the catalytic activity in transfer hydrogenation properties of the complex (1). Moreover, catalytic activity of the complex (1) is significantly higher in the transfers hydrogenation of cyclohexanone than 2-hexanone.

Mild-temperature hydrogenation of carbonyls over Co-ZIF-9 derived Co-ZIF-x nanoparticle catalyst

Benzimidazole and metal cobalt salts were employed in the synthesis of Co-ZIF-9 by solvothermal crystallization. Highly active catalysts for selective hydrogenation of carbonyl compounds were developed. The optimal nanocatalyst Co-ZIF-350 manifested remarkable activity and selectivity for the hydrogenation of cyclohexanone under mild conditions. Catalytic conversion of cyclohexanone reached the highest over the catalyst of Co-ZIF-9-pyrolyzed at 350 °C for 2 h, in which the conversion of cyclohexanone was 100 % and the selectivity of cyclohexanol was ＞99 % at 50 °C. A wide scope of ketones/aromatic aldehydes could be selectively reduced to the corresponding alcohols with high yields. Importantly, the nanocatalyst Co-ZIF-350 presented good tolerance of substrates with various functional groups under mild conditions.

Selective Hydrogenation of Phenol to Cyclohexanol over Ni/CNT in the Absence of External Hydrogen

Transfer hydrogenation is a novel and efficient method to realize the hydrogenation in different chemical reactions and exploring a simple heterogeneous catalyst with high activity is crucial. Ni/CNT was synthesized through a traditional impregnation method, and the detailed physicochemical properties were performed by means of XRD, TEM, XPS, BET, and ICP analysis. Through the screening of loading amounts, solvents, reaction temperature, and reaction time, 20% Ni/CNT achieves an almost complete conversion of phenol after 60 min at 220 °C in the absence of external hydrogen. Furthermore, the catalytic system is carried out on a variety of phenol derivatives for the generation of corresponding cyclohexanols with good to excellent results. The mechanism suggests that the hydrogenation of phenol to cyclohexanone is the first step, while the hydrogenation of cyclohexanone for the generation of cyclohexanol takes place in a successive step. Moreover, Ni/CNT catalyst can be magnetically recovered and reused in the next test for succeeding four times.

Poisoning and competitive adsorption effects during phenol hydrogenation on platinum in water-alcohol mixtures

The effect of other bio-oil components on the aqueous phase hydrogenation of phenol on a Pt/C catalyst was investigated at a temperature of 353 K and a total pressure of 250 psi. Cyclohexanone and cyclohexanol were primary products; cyclohexanone was further converted to cylcohexanol. Methanol or ethanol as additives in water could completely stop ring hydrogenation in phenol (and in other test compounds: benzene, toluene) and decelerated the hydrogenation of cyclohexanone. Formic acid also suppressed hydrogenation reactions. The poisoning effect resulted from CO, formed by decomposition of alcohols or formic acid on platinum. Ab initio density-functional theory calculations afforded adsorption geometries, binding energies and diffusion barriers of relevant species. Phenol hydrogenation on platinum is more susceptible to CO poisoning than cyclohexanone hydrogenation because it needs a large ensemble site. The poisoning effect of alcohols can be avoided by mixing the components in a specific order.

Low temperature hydrogenation and hydrodeoxygenation of oxygen-substituted aromatics over Rh/silica: part 1: phenol, anisole and 4-methoxyphenol

The hydrogenation and competitive hydrogenation of anisole, phenol and 4-methoxyphenol was studied in the liquid phase over a Rh/silica catalyst at 323 K and 3 barg hydrogen pressure. The rate of conversion of the reactants to products gave an order of anisole ≫ phenol > 4-methoxyphenol with hydrogenation and hydrodeoxygenation products being produced. Anisole, the most reactive substrate, was rapidly converted to methoxycyclohexane, cyclohexane, cyclohexanone and cyclohexanol, while phenol was hydrogenated to cyclohexanone, cyclohexanol and cyclohexane. In both cases cyclohexanol was produced as a secondary product from cyclohexanone hydrogenation. The yield of cyclohexane, the hydrodeoxygenation (HDO) product was > 20% from both reactants and was formed as a primary product from the aromatic species. Hydrogenation of 4-methoxyphenol was selective to 4-methoxycyclohexanone with no alcohol formation, while the hydrogenolysis products revealed that the catalyst was more active for demethoxylation than dehydroxylation. A comparative strength of adsorption was determined from competitive hydrogenation and gave an order of anisole > phenol > 4-methoxyphenol. Competitive, pair hydrogenation inhibited HDO and stopped cyclohexane from being produced from phenol and 4-methoxyphenol, although it was still produced from anisole. An increased rate of hydrogenation for 4-methoxyphenol was observed for competitive reactions with phenol and anisole but not when all three reactants were present. In contrast to the pair reactions, when all three reactants were present HDO occurred with all aromatics producing cyclohexane. Replacing hydrogen with deuterium revealed an inverse kinetic isotope effect for ring hydrogenation of 4-methoxyphenol but not phenol or anisole, which both had a positive KIE.

Hydrogenation of Phenol to Cyclohexanone over Bifunctional Pd/C-Heteropoly Acid Catalyst in the Liquid Phase

Cyclohexanone is an important intermediate in the manufacture of polyamides in chemical industry, but direct selective hydrogenation of phenol to cyclohexanone under mild conditions is a challenge. Hydrogenation of phenol to cyclohexanone has been investigated in the presence of the composite catalytic system of Pd/C-heteropoly acid. 100% conversion of phenol and 93.6% selectivity of cyclohexanone were achieved within 3 h under 80 °C and 1.0 MPa hydrogen pressure. It has been found that a synergetic effect of Pd/C and heteropoly acid enhanced the catalytic performance of the composite catalytic system which suppressed the hydrogenation of cyclohexanone to cyclohexanol.

Photocatalytic Selective Ring Hydrogenation of Phenol to Cyclohexanone over a Palladium‐Loaded Titanium(IV) Oxide under Hydrogen‐Free Conditions

AbstractPhotocatalytic ring hydrogenation of phenol proceeded in an aqueous suspension of palladium‐loaded TiO2 at room temperature in the presence of oxalic acid as a hole scavenger, and cyclohexanone was produced in a high yield (90 %) without the use of hydrogen gas. Cyclohexanone was formed via keto‐enol tautomerism of cyclohexenol. The effects of hole scavengers and solvents on the hydrogenation of phenol can be explained by the adsorption behaviour of phenol and hole scavengers in the solvents. Over a Pd‐TiO2 photocatalyst, the apparent activation energy (Ea) in the ring hydrogenation of phenol and the Ea value in the hydrogenation of cyclohexanone were estimated to be 25 kJ mol−1 and 36 kJ mol−1, respectively, as calculated by using the Arrhenius equation. We concluded that the difference in the Ea values is attributable to the selective production of cyclohexanone and the decreased production of cyclohexanol in the ring hydrogenation of phenol over a Pd‐TiO2 photocatalyst.

Hydrogen-free ring hydrogenation of phenol to cyclohexanol over a rhodium-loaded titanium(IV) oxide photocatalyst

Since photocatalytic reactions are almost consistent with the concept of green chemistry, substance conversion using photocatalysts has recently attracted the attention of researchers in the fields of organic chemistry, physical chemistry and material chemistry. We investigated photoinduced ring hydrogenation of phenol over a metal-loaded titanium(IV) oxide (TiO2) photocatalyst without the use of H2 gas and we report here the effects of various parameters, including the type and amount of metal co-catalyst loaded on TiO2 and the kinds of solvents and hole scavengers, on the ring hydrogenation. We found that the combination of an Rh co-catalyst, water and oxalic acid resulted in the highest yield of cyclohexanol. Detailed analyses revealed that phenol was first hydrogenated to cyclohexanone via keto-enol tautomerism of cyclohexenol followed by hydrogenation of cyclohexanone to cyclohexanol and that adsorption of phenol onto Rh-TiO2 is a factor of great importance for the ring hydrogenation.

A Pd/Monolayer Titanate Nanosheet with Surface Synergetic Effects for Precise Synthesis of Cyclohexanones

A catalyst composed of monolayer nonstoichiometric titanate nanosheets (denoted as TN) and Pd clusters is constructed for precise synthesis of cyclohexanone from phenol hydrogenation with high conversion (>99%) and selectivity (>99%) in aqueous media under light irradiation. Experimental and DFT calculation results reveal that the surface exposed acid and basic sites on TN could interact with phenol molecules in a nonplanar fashion via a hexahydroxy hydrogen-bonding ring to form a surface coordination species. This greatly facilitates the adsorption and activation of phenol molecules and suppresses the further hydrogenation of cyclohexanone. Moreover, the surface Pd clusters serve as the active sites for the adsorption and dissociation of hydrogen molecules to provide active H atoms. The synergistic effect of the surface coordination species, TN and Pd clusters remarkably facilitate the high yield of cyclohexanone in photocatalysis. Finally, the possible thermo/photocatalytic mechanisms on Pd/TN are propo...

Enhanced Selectivity of Phenol Hydrogenation in Low-Pressure CO2 over Supported Pd Catalysts

Selective hydrogenation of phenol to cyclohexanone is an important process in both chemical industry and renewable feedstock processing. However, direct hydrogenation of phenol to cyclohexanone under mild conditions over catalysts with high reactivity, selectivity, and facile preparation is still a challenge. In the present study, we report that 99% conversion and 99% selectivity can be achieved over as-prepared Pd/γ-Al2O3 catalyst under the medium of low-pressure CO2 (0.05–0.2 MPa) and H2O at 373 K. According to experiment results, ab initio calculations and in situ high-pressure FTIR measurements indicated enhanced selectivity of cyclohexanone in low-pressure CO2; this result originated from the molecular interaction between cyclohexanone and CO2 and can prevent the further hydrogenation of cyclohexanone. Notably, enhancement of selectivity to cyclohexanone in low-pressure CO2 was also achieved using commercial Pd/γ-Al2O3 and Pd/C catalysts.

Water-Assisted Selective Hydrodeoxygenation of Guaiacol to Cyclohexanol over Supported Ni and Co Bimetallic Catalysts

Hydrodeoxygenation (HDO) of guaiacol, a typical lignin-derived phenolic compound, at relatively mild conditions was studied over γ-Al2O3 and ZSM-5 supported catalysts with Ni and/or Co as active metal. Among various catalysts, NiCo/γ-Al2O3 catalysts exhibited better guaiacol conversion up to 96.1% with cyclohexanol as the main product in aqueous, due to the proper acidity and interaction between metal particles and support. The effects of process parameters on guaiacol conversion and product distribution were investigated in detail associated with solvent effect. The cleavage of C–O bonds in guaiacol was investigated over NiCo/γ-Al2O3 catalysts in aqueous phase. Phenol was found as the main intermediate with 1-methyl-1,2-cyclohexanediol as another intermediate instead of 2-methoxy-cyclohexanol. The demethoxylation first happened to form phenol, and then, the aromatic ring was hydrogenated to give cyclohexanol after further hydrogenation of cyclohexanone.

Synthesis and characterization of half-sandwich ruthenium(II) complexes with N-alkyl pyridyl-imine ligands and their application in transfer hydrogenation of ketones

A series of new arene ruthenium(II) complexes were prepared by reaction of ruthenium(II) precursors of the general formula [(η6-arene)Ru(μ-Cl)Cl]2 with N,N′-bidentate pyridyl-imine ligands to form complexes of the type [(η6-arene)RuCl(C5H4N-2-CH=N-R)]PF6, with arene = C6H6, R = iso-propyl (1a), tert-butyl (1b), cyclohexyl (1c), cyclopentyl (1d) and n-butyl (1e); arene = p-cymene, R = iso-propyl (2a), tert-butyl (2b). The complexes were fully characterized by 1H NMR and 13C NMR, UV–Vis and IR spectroscopies, elemental analyses, and the single-crystal X-ray structures of 2a and 2b have been determined. The single-crystal molecular structure revealed both compounds with a pseudo-octahedral geometry around the Ru(II) center, normally referred to as a piano stool conformation, with the pyridyl-imine as a bidentate N,N ligand. The activity of all complexes in the transfer hydrogenation of cyclohexanone in the presence of NaOH and iso-propanol is reported, the compounds showing turnover numbers of close to 1990 and high conversions. Complex 2b was also shown to be very effective for a range of aliphatic and cyclic ketones, giving conversions of up to 100 %.

Amidinatogermylene Metal Complexes as Homogeneous Catalysts in Alcoholic Media

A series of transition-metal complexes containing the bulky amidinatogermylene Ge(tBu2bzam)tBu (1; tBu2bzam = N,N′-bis(tert-butyl)benzamidinate) as a ligand have been prepared and characterized. While the hydrolytic degradation of the germylene ligand of the square-planar complexes [MCl(η4-cod){Ge(tBu2bzam)tBu}] (M = Rh (2), Ir (3); cod = 1,5-cyclooctadiene) and [PdCl(η3-metallyl){Ge(tBu2bzam)tBu}] (4; metallyl = 2-methylallyl) is slow but clearly evident in carefully dried aprotic solvents, the octahedral complexes [RuCl2(η6-cym){Ge(tBu2bzam)tBu}] (5; cym = p-cymene) and [IrCl2(η5-Cp*){Ge(tBu2bzam)tBu}] (6; Cp* = pentamethylcyclopentadienyl) have proven to be stable even in alcoholic solvents. These latter complexes have been tested as catalyst precursors of reactions involving alcohols as substrates and/or solvents, and remarkably, they have been found to be active in the transfer hydrogenation of cyclohexanone with isopropyl alcohol (5 and 6), the N-alkylation of aniline with benzyl alcohol (5 and 6), ...

Mechanistic Insights into Transfer Hydrogenation Catalysis by [Ir(cod)(NHC)2]+Complexes with Functionalized N-Heterocyclic Carbene Ligands

The synthesis of unbridged biscarbene iridium(I) [Ir(cod)(MeIm∩Z)2]+ complexes having N- or O-functionalized NHC ligands (∩Z = 2-methoxybenzyl, pyridin-2-ylmethyl, quinolin-8-ylmethyl) is described. The molecular structures of the complexes show an antiparallel disposition of the carbene ligands that minimize the steric repulsions between the bulky substituents. However, the complexes were found to be dynamic in solution, due to the restricted rotation about the C(carbene)–Ir bond that results in two interconverting diasteromers having different dispositions of the functionalized NHC ligands. A rotational barrier of around 80 kJ mol–1 (298 K) has been determined by 2D EXSY NMR spectroscopy. The iridium(III) dihydride complex [IrH2(MeIm∩Z)2]+ (∩Z = pyridin-2-ylmethyl) has been prepared by reaction of the corresponding iridium(I) complex with molecular hydrogen. These complexes efficiently catalyzed the transfer hydrogenation of cyclohexanone using 2-propanol as a hydrogen source and KOH as base at 80 °C with average TOF values of 117–155 h–1 at 0.1 mol % iridium catalyst loading. All of the catalyst precursors showed comparable activity independent of both the wingtip type at the NHC ligands and the counterion. Mechanistic studies support the involvement of diene free bis-NHC iridium(I) intermediates in these catalytic systems. DFT calculations have shown that a MPV-like concerted mechanism (Meerwein–Ponndorf–Verley mechanism), involving the direct hydrogen transfer at the coordination sphere of the iridium center, might compete with the well-established hydrido mechanism. Indirect evidence of a MPV-like mechanism has been found for the catalyst precursor having NHC ligands having with a pyridin-2-ylmethyl wingtip.

Impact of solvent for individual steps of phenol hydrodeoxygenation with Pd/C and HZSM-5 as catalysts

Impacts of water, methanol, and hexadecane solvents on the individual steps of phenol hydrodeoxygenation are investigated over Pd/C and HZSM-5 catalyst components at 473K in presence of H2. Hydrodeoxygenation of phenol to cyclohexane includes four individual steps of phenol hydrogenation to cyclohexanone on Pd/C, cyclohexanone hydrogenation to cyclohexanol on Pd/C, cyclohexanol dehydration to cyclohexene on HZSM-5, and cyclohexene hydrogenation to cyclohexane on Pd/C. Individual phenol and cyclohexanone hydrogenation rates are much lower in methanol and hexadecane than in water, while rates of cyclohexanol dehydration and cyclohexene hydrogenation are similar in three solvents. The slow rate in methanol is due to the strong solvation of reactants and the adsorption of methanol on Pd, as well as to the reaction between methanol and the cyclohexanone intermediate. The low solubility of phenol and strong interaction of hexadecane with Pd lead to the slow rate in hexadecane. The apparent activation energies for hydrogenation follow the order Ea phenol>Ea cyclohexanone>Ea cyclohexene, and the sequences of individual reaction rates are reverse in three solvents. The dehydration rates 1.1–1.8×103molmolBAS-1h-1 and apparent activation energies (115–124kJmol−1) are comparable in three solvents. In situ liquid-phase IR spectroscopy shows the rates consistent with kinetics derived from chromatographic evidence in the aqueous phase and verifies that hydrogenation of phenol and cyclohexanone follows reaction orders of 1.0 and 0.55 over Pd/C, respectively. Conversion of cyclohexanol with HZSM-5 shows first-order dependence in approaching the dehydration–hydration equilibrium in the aqueous phase.

Understanding the catalytic activity of single‐chain polymeric nanoparticles in water

ABSTRACTThe structuring role of benzene‐1,3,5‐tricarboxamide (BTA) groups for the catalytic activity of single chain polymeric nanoparticles in water was investigated in the transfer hydrogenation of ketones. To this end, a set of segmented, amphiphilic copolymers was prepared, which comprised oligo(ethylene glycol) side chains to impart water solubility, BTA and/or lauryl side chains to induce hydrophobicity and diphenylphosphinostyrene (SDP) units in the middle part as a ligand to bind a ruthenium catalyst. All copolymers were obtained by reversible addition‐fragmentation chain transfer (RAFT) polymerization and showed low dispersities (Mw/Mn = 1.23–1.38) and controlled molecular weights (Mn = 44–28 kDa). A combination of circular dichroism (CD) spectroscopy and dynamic light scattering (DLS) showed that all copolymers fold into a single chain polymeric nanoparticles (SCPNs) as a result of the helical self‐assembly of the pendant BTA units and/or hydrophilic–hydrophobic phase separation. To create catalytic sites, RuCl2(PPh3)3 was incorporated into the copolymers. The Cotton effects of the copolymers before and after Ru(II) loading were identical, indicating that the helical self‐assembly of the BTA units and the complexation of SDP ligands and Ru(II) occurs in an orthogonal manner. DLS revealed that after Ru(II) loading, SDP‐bearing copolymers retained their single chain character in water, while copolymers lacking SDP units clustered into larger aggregates. The Ru(II) loaded SCPNs were tested in the transfer hydrogenation of cyclohexanone. This study reveals that BTA induced stack formation is not crucial for SCPN formation and catalytic activity; SDP‐bearing copolymers folded by Ru(II) complexation and hydrophobic pendants suffice to provide hydrophobic, isolated reaction pockets around Ru(II) complexes. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014, 52, 12–20