Hydroxylation Of Benzene Research Articles

Improvement in thermal stability and catalytic activity of titanium containing mordenite by cerium using hydrothermal methods for hydroxylation of benzene into phenol

Cerium–titanium–mordenite (Ce–Ti/Mor) were synthesized using ortho-phenylenediamine (OPDA) as a templating agent, and varying amounts of cerium (0.5–4.0 mol%) have been successfully prepared by direct hydrothermal synthesis. These micropore materials were compared with pure mordenite synthesized at the same conditions. The influence of Ce/Ti–Mor composite on the phase, crystal structure and morphology has been investigated by X-ray diffraction (XRD), scanning electron microscopy and Fourier transform infrared spectroscopy, respectively. The probable assignments of the thermal degradation products of OPDA in Ce–Ti/Mor samples were studied by complementary thermogravimetric analysis and differential scanning calorimetry. XRD appeared of α-quartz (Si3O6) phase in Ti–Mor disappeared by the addition of Ce and reformation of pure mordenite structure. The increase in unit cell parameters observed with replacement Al by Ti is indicative of incorporation of Ti into the framework structure of microporous material mordenite, while a decrease in unit cell by replacement of Ti by Ce attributed to the presence of Ce–O–Ti bond on the surface of mordenite. The hydroxylation of benzene to phenol has been extensively investigated using hydrogen peroxide as an oxidant. All the Ce-supported catalysts exhibited high catalytic activity in the oxidation of benzene.

VxOy Supported on Hydrophobic Poly(Ionic Liquid)s as an Efficient Catalyst for Direct Hydroxylation of Benzene to Phenol

AbstractSupported vanadium oxides (VxOy) on hydrophobic poly(ionic liquid)s (PILs), for which the PILs were obtained by copolymerization of the ionic liquid (IL) 1‐hexadecyl‐3‐vinylimidazolium bromide and the cross‐linker divinylbenzene (DVB), are reported. The VxOy/PIL catalyst was characterized by different techniques, and the performance of the catalyst for the selective oxidation of benzene to phenol was studied with H2O2 as the oxidant. It was demonstrated that VxOy/PIL had much better catalytic performance than the analogous catalyst VxOy/P, prepared with the polymer support (P) obtained from DVB and vinyl imidazole, without the IL. The high activity and selectivity of the VxOy/PIL catalyst could be attributed to the incorporation of the IL during the polymerization, which endowed the VxOy/PIL catalyst with increased specific surface area, stronger absorbent ability, and more active sites than the smooth and bulky VxOy/P. Furthermore, the hydrophobic side chain of the IL in the catalyst was beneficial for the access of benzene and the removal of the generated phenol from the surface of the catalyst, which also played an important role in improving the catalytic performance of VxOy/PIL. Up to 13.4 % yield of phenol was achieved, with a high selectivity of 97.5 %. In addition, the catalyst could be easily separated and recycled at least three times without significant decline in the phenol yield.

Selective Synthesis of Phenol from Benzene with O2 by Switchover of the Reaction Pathway from Complete Oxidation to Selective Hydroxylation by NH3 on Ir/β and Ni/β Catalysts

AbstractNew and selective IrO2 cluster/β and NiO cluster/β catalysts have been synthesized for the direct synthesis of phenol from benzene with O2 in gas‐phase single‐path flow reactions. Phenol is generated by switchover of the reaction pathway from complete oxidation of benzene to selective hydroxylation of benzene by NH3. The active oxide‐cluster structures in the β pores have been characterized by XAFS, XPS, STEM‐EDS, XRD, and DFT calculations. The reaction profile and the role of NH3 in the synthesis of phenol on the proposed Ni4O4 cluster have also been simulated by DFT calculations.

One‐Step Selective Hydroxylation of Benzene to Phenol

AbstractRecent developments in the one‐step thermal and photochemical catalytic hydroxylation of benzene to phenol using various oxidants are described, focusing on the catalytic mechanisms. Hydroxylation of benzene with hydrogen peroxide is catalyzed by homogeneous metal complexes and heterogeneous metal oxides to produce phenol when high‐valent metal‐oxo complexes are reactive species The selective hydroxylation of benzene to phenol is achieved by using mesoporous silica‐alumina as the catalyst support, which prohibits further oxidation of phenol due to the strongly acidic sites. Photocatalytic oxidation of benzene with dioxygen and water is made possible by using organic photocatalysts via photoinduced electron transfer from benzene to the excited states of the photocatalysts, followed by the hydroxylation of the benzene radical cation with water to yield phenol selectively. The further oxidation of phenol is prohibited because of the fast back electron transfer from the one‐electron reduced species of the photocatalyst to the phenol radical cation, whereas back electron transfer from the one‐electron reduced species to the benzene radical cation is slowed down because of the large driving force of the back electron transfer, which is in the Marcus inverted region.

Hierarchically macro/mesostructured porous Au monoliths: simple synthesis, characterization and catalytic performance

We report an efficient, highly selective and low-temperature three-dimensional hierarchically macro/mesostructured porous gold monoliths catalyzed reaction process for one-step oxidation of benzene to phenol with hydrogen peroxide as the green oxidant. The porous catalysts were characterized before calcination by FTIR and TGA and after calcination by XRD, FESEM-EDX and BET techniques. The selectivity of phenol production from the one-step oxidation of benzene over porous gold catalysts can be enhanced by concise tuning of pore diameter and pore surface morphology. From the results obtained, it was concluded that the balance between the decomposition rate of H2O2 and benzene adsorption over the catalyst surface is responsible for the outstanding catalytic performance of the three-dimensional macro/mesoporous gold monoliths. The as-synthesized series of nanoporous gold monoliths were evaluated for the first time as alternative heterogeneous catalysts for the direct catalytic oxidation of benzene to phenol at low temperature. Therefore, it is of great interest to “switch-off” other time- and energy-consuming reactions and promote the hydroxylation of benzene with porous Au catalysts.

Structure of the Active Platinum Cluster and Reaction Pathway of the Selective Synthesis of Phenol from Benzene and Oxygen Regulated with Ammonia on a Platinum Cluster/β-Zeolite Catalyst Studied by DFT Calculations.

DFT calculations were used to investigate the structure of the active Pt cluster and the catalytic reaction pathway for the selective synthesis of phenol from benzene and molecular oxygen regulated with ammonia on a Pt cluster/β-zeolite catalyst that was reported to be active for the selective hydroxylation of benzene only in the coexistence of ammonia. It was found that Pt5-Pt6 clusters were active for the direct synthesis of phenol, and they provided the reaction sites for bond rearrangements among ammonia, oxygen, and benzene; furthermore, the coexistence of ammonia was crucial for the selective oxidation of benzene to phenol, as it suppressed benzene combustion to CO2 and promoted the selective synthesis of phenol. It was further found that water coexisting in the system also played a significant role in desorbing phenol on the Pt cluster surface, which resulted in promotion of the overall selective synthesis of phenol. The energy diagram for the reaction sequences and the structures of the transition states were obtained, which indicated the origin of the Pt/β catalysis.

Liquid phase hydroxylation of benzene to phenol over vanadyl acetylacetonate supported on amine functionalized SBA-15

An efficient catalyst for the direct hydroxylation of benzene to phenol with oxygen as the oxidant was developed by immobilizing the homogeneous vanadyl(IV) acetylacetonate (VO(acac)2) on SBA-15 in which the support surface was functionalized by (3-aminopropyl)triethoxysilane. The as-prepared catalyst was characterized by various techniques including field-emission scanning electron microscopy, X-ray diffraction, nitrogen adsorption and desorption, Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. The results show that the homogeneous vanadium species can be successfully immobilized on the amine functionalized SBA-15 and exhibits better catalytic performance in the hydroxylation of benzene with oxygen compared to other catalysts reported in the literature. The phenol yield significantly depends on the reaction conditions. Under the optimized reaction conditions, the phenol yield can reach 13.3 %, and the as-fabricated V/NH2-SBA-15 shows better stability against leaching owning to strong interaction between vanadium atoms and amine group as compared to the V/SBA-15 sample.

The Effect of Vanadium Oxide on The Catalytic Activity of Titanium Silicalite in Conversion of Benzene to Phenol

Phenol is one of the most important intermediate for petrochemical, agrochemical, and plastics industries<em>. </em>Almost<em> 95% phenol is </em>produced using cumene method. Cumene method is a multi-stage process with many disadvantages including the difficulties to gain phenol product in maximum quantities and production of co-product such as acetone which has great amount in market nowadays. One of the alternative routes to produce phenol which has more advantages is through benzene hydroxylation reaction using H<sub>2</sub>O<sub>2</sub> as oxidant agent and Titanium Silikalit-1 (TS-1) as catalyst. TS-1 catalyst has high catalytic activity and selectivity in selective oxidation reaction of aromatic compounds with H2O2 which important for commercial industries. However, the reaction rate is tend to be low because TS-1 has hydrophobic nature and as the result H2O2 adsorption which has hydrophilic nature towards active sites of TS-1 is also become slower. Addition of metal oxide V2O5 could enhance hydrophilicity of TS-1 catalyst. Liquid phase catalytic benzene hydroxylation using hydrogen peroxide as oxidant was carried out over vanadium (V) oxide-modified TS-1 catalyst (V<sub>2</sub>O<sub>5</sub>/TS-1), that were prepared by impregnation method using vanadium methavanadate as precursor and characterized by pyridine adsorption and hydrophilicity techniques.

Physicochemical Studies and Heterogeneous Hydroxylation of Benzene on FeII, FeIII-Semicarbazone/Zeolite-Y Clathrates

Complexes of Fe(II) and Fe(III) with semicarbazone (SALSC) derived from salicylaldehyde and semicarbazide hydrochloride have been trapped in zeolite-Y super cages using “ship-in-a-bottle technique.” The synthesized new clathrates have been structurally characterized by various physicochemical techniques, in addition to surface area and nitrogen adsorption studies. The Fe(II) and Fe(III) ions inside zeolite-Y are coordinated with SALSC ligand via the (C=N), phenolic (OH), and deprotonated enolized (C=O) groups forming mononuclear structures. The results pointed out that the lattice oxygen zeolite was involved in coordination and the intrazeolitic ferrous and ferric semicarbazone complexes have prevailing octahedral configurations with noticeable high thermal stability. The catalytic activity of the new hybrid materials was checked for hydroxylation of benzene at 80°C using H2O2 as oxidant to give phenol.

Direct hydroxylation of benzene to phenol using hydrogen peroxide catalyzed by nickel complexes supported by pyridylalkylamine ligands.

Selective hydroxylation of benzene to phenol has been achieved using H2O2 in the presence of a catalytic amount of the nickel complex [Ni(II)(tepa)](2+) (2) (tepa = tris[2-(pyridin-2-yl)ethyl]amine) at 60 °C. The maximum yield of phenol was 21% based on benzene without the formation of quinone or diphenol. In an endurance test of the catalyst, complex 2 showed a turnover number (TON) of 749, which is the highest value reported to date for molecular catalysts in benzene hydroxylation with H2O2. When toluene was employed as a substrate instead of benzene, cresol was obtained as the major product with 90% selectivity. When H2(18)O2 was utilized as the oxidant, (18)O-labeled phenol was predominantly obtained. The reaction rate for fully deuterated benzene was nearly identical to that of benzene (kinetic isotope effect = 1.0). On the basis of these results, the reaction mechanism is discussed.

Direct hydroxylation of benzene to phenol over metal oxide supported graphene oxide catalysts

A series of metal oxide (V, Fe, Cu) supported graphene oxide (M/GO) catalysts have been prepared by the impregnation method. The catalysts were characterized by TEM, XRD, FT-IR, and Raman spectroscopies and the results showed that the metal oxide nanoparticles were highly dispersed and successfully incorporated on graphene oxide sheets. Among the catalysts, V/GO exhibited the highest efficiency in direct hydroxylation of benzene using H2O2 as an oxidant in acetic acid solvent with a phenol yield of 22.7% and a selectivity of 98.4% under the optimized condition along with good recycle performance.

Synergistic Effect between Ultrasmall Cu(II) Oxide and CuCr2O4 Spinel Nanoparticles in Selective Hydroxylation of Benzene to Phenol with Air as Oxidant

Phenol is an important commodity chemical, and the catalytic conversion of benzene to phenol by molecular oxygen with minimum waste production is of high significance from an academic as well as industrial point of view. We have developed a facile synthesis method for the preparation of 2–8 nm Cu(II) oxide nanoparticles supported on CuCr2O4 spinel nanoparticles (with size ∼55 nm). Detailed characterization of the material was carried out by XRD, SEM, TEM, XPS, FTIR, TGA, TPR, BET surface area, XANES, and ICP-AES methods. XRD and XPS analyses revealed that the main phase is CuCr2O4 spinel, where a small amount of CuO is dispersed on it. The catalyst was highly active for selective oxidation of benzene to phenol with air as oxidant. The influence of reaction parameters was investigated in detail. The high catalytic performance of the catalyst is due to the ultrasmall size of Cu(II) oxide nanoparticles and the strong synergy between ultrasmall Cu(II) oxide and CuCr2O4 spinel nanoparticles that plays a pivotal role in activating air to generate active oxygen species which accomplishes benzene to phenol conversion (36%) with very high selectivity (78%) in a continuous process.

Study of Benzene Hydroxylation in Liquid Phase Using Mono- and Binuclear Copper Complex Catalysts

Abstract Mono- or binuclear copper homogeneous catalysts with similar coordination environments were used for benzene hydroxylation. The effect of multiple active sites on phenol formation was investigated. The structures of the synthesized mono- and binuclear copper catalysts were confirmed by FT-IR and EXAFS. Molecular oxygen was used as the oxidant and it was found that the binuclear copper catalyst showed better phenols formation than the mononuclear catalyst.

Molecular dynamics simulation to rationalize regioselective hydroxylation of aromatic substrates by soluble methane monooxygenase

Soluble methane monooxygenase (sMMO) is a bacterial multicomponent enzyme that oxidizes a diverse range of substrates, including aromatic hydrocarbons. We have investigated enzyme-substrate interactions that govern oxidation regioselectivity at various sites of aromatic compounds using substrate docking and molecular dynamics (MD) simulations. Here, we studied the hydroxylation of toluene and ethyl benzene by two forms of Methylosinus trichosporium OB3b (sMMO), that is, wild-type (WT) and two active site mutants (L110Y/G). The two substrates, toluene and ethyl benzene, were docked into the active site of the WT and the L110Y/G mutant models of M. trichosporium OB3b sMMO using the available X-ray structure (PDB id 1 MHZ). The trends observed in the formation of the experimental product were highly correlated with the results obtained from the relatively short MD simulation. These results show that our approach could be an attractive computational tool to rationalize the prediction of product ratios and specificities.

ChemInform Abstract: Efficient Hydroxylation of Aromatic Compounds Catalyzed by an Iron(II) Complex with H2O2.

A mononuclear iron(II) complex, Et4N[Fe(C10H6NO2)3], coordinated by three 1-nitroso-2-naphtholate ligands in a fac-N3O3 geometry, was initiated to catalyze the direct hydroxylation of aromatic compounds to phenols in the presence of H2O2 under mild conditions. Various reaction parameters, including the catalyst dosage, temperature, mole ratio of H2O2 to benzene, reaction time and solvents which could affect the hydroxylation activity of the catalyst, were investigated systematically for benzene hydroxylation to obtain ideal benzene conversion and high phenol distribution. Under the optimum conditions, the benzene conversion was 10.2% and only phenol was detected. The catalyst was also found to be active towards hydroxylation of other aromatic compounds with high substrate conversions. The hydroxyl radical formed due to the reaction of the catalyst and H2O2 was determined to be the crucial active intermediate in the hydroxylation. A rational pathway for the formation of the hydroxyl radical was proposed and justified by the density functional theory calculations. Copyright © 2014 John Wiley & Sons, Ltd.

Preparation of Copper-Embedded Graphene Nanocomposites for Catalytic Hydroxylation of Benzene to Phenol

The design and synthesis of graphene-based nanocomposites have drawn enormous attention in recent years owing to their unique structural properties. Here, we describe a simple hydrothermal procedure to fabricate Cu-graphene nanocomposites as a catalyst for direct hydroxylating benzene to phenol in the presence of hydrogen peroxide. The nanocomposites present high catalytic activity and short reaction time, attributing to the uniform diameters of the Cu nanoparticles and their homogeneous distribution on surfaces of graphene sheets. The effects of graphene content, molar ratio of H2O2 to benzene, and reaction temperature on the catalytic performance of the prepared Cu-graphene were studied. Notably, the Cugraphene nanocomposites can contribute a conversion rate of 13.8 % and a phenol selectivity of 92.9 %. In particular, the reaction time was greatly shortened to 0.2 h, which is pretty faster than other reported Cu-based catalysts, indicating the promising application of Cugraphene nanocomposites in the hydroxylation of benzene. Keywords: Cu-graphene nanocomposites, hydroxylation of benzene, phenol.

Synthesis of iron orthophosphate catalysts by solution and solution combustion methods for the hydroxylation of benzene to phenol

Iron orthophosphate was prepared by solution and solution combustion method for use as a catalyst in the hydroxylation of benzene to phenol. The products of each method were structurally identical. The morphology and size of the catalyst were significantly influenced by the synthesis method. The catalytic activity of the catalysts in the liquid phase hydroxylation of benzene was studied. The yields of the solution combustion synthesized and solution synthesized iron orthophosphate were 24.52% and 8.90%, respectively, under optimized conditions. The iron orthophosphate synthesized by the solution combustion method exhibited better catalytic performance characteristics than the one prepared by the solution method.

Controllable synthesis and catalytic performance of mesoporous silica nanotube micro-reactor

We present a robust dual-surfactant strategy to reach full control over the size and morphology of multi-channel mesoporous silica nanotubes, using cetyltrimethylammonium bromide (CTAB) and triblock copolymer PEO20PPO70PEO20 (P123) as co-template. The produced mesoporous silica nanotubes were systematically characterized by XRD, N2 adsorption–desorption, FE-SEM, TEM, UV–vis, ICP and H2-TPR techniques. The experimental results indicated that the sizes of nanotubes can be controlled from the adjustment of the molar ratio of CTAB and P123 under adequate synthesis conditions. We propose that in this dual-surfactant system, CTAB may function as the template to form mesopore structure, while P123 mainly controls the morphology of materials. In addition, we developed the controllable synthesis of copper-doped multi-channel mesoporous silica nanotube micro-reactor, which was successfully utilized to catalyze the catalytic hydroxylation of benzene with hydrogen peroxide as oxidant. Interestingly, it was found that the catalytic activity can be essentially enhanced by the elongating length of micro-reactors of nanotubes, possibly due to the longer contact time of the reactant and the active sites inside. Our controllable synthesis of mesoporous silica nanotube provides a novel approach to rationalize the design of catalysts as well as their catalytic performance.

Aromatic hydroxylation using an oxo-bridged diiron(III) complex: a bio-inspired functional model of toluene monooxygenases.

In biology, aromatic hydroxylation is carried out using a family of heme and nonheme oxygenases, such as cytochrome P450, toluene monooxygenases (TMOs), and methane monooxygenase (MMO). In contrast, a vast majority of synthetic iron based catalysts employed so far in aromatic hydroxylation are monomeric in nature. Herein, we have employed a diferric complex of an aminopyridine ligand ([(bpmen)2Fe2O(μ-O)(μ-OH)](ClO4)3 (2), bpmen = N,N'-dimethyl-N,N'-bis(2-pyridylmethyl)-1,2-diaminoethane) towards aromatic hydroxylation with H2O2 and acetic acid. The diiron(iii) complex shows promising reactivity in the hydroxylation of benzene and alkylbenzenes with a higher selectivity towards aromatic ring hydroxylation over alkyl chain oxidation. The μ-oxo diiron(iii) core has been shown to be regenerated at the end of catalytic turnover. However, mechanistic studies indicate that the diiron(iii) complex undergoes dissociation into its monomeric congener and the resulting iron(iii) complex mitigates aromatic hydroxylation.

Vanadia supported on mesoporous carbon nitride as a highly efficient catalyst for hydroxylation of benzene to phenol

Vanadia supported on mesoporous carbon nitride catalyzed the hydroxylation of benzene with a high conversion of 18%, along with a superior TOF of 1.59 h−1 to other vanadia- and g-C3N4-based catalysts.