Direct Hydroxylation Of Benzene Research Articles

Fragmentation engineering on the edge of hydroxy-functional COFs for the enhanced photocatalytic production of H2O2 and direct photo-oxidation of benzene to phenol in aqueous systems

Structural design is important and challenging for the fabrication of covalent organic frameworks (COFs) in the photocatalytic applications. Hydroxyl groups have been found to be the active sites for O2 adsorption and promote the electron-donating conjugation effects, which favorable for the oxygen reduction reaction (ORR) in photocatalytic hydrogen peroxide (H2O2) evolution. This study reports the preparation of “fragmentized” COFs (TxHy-COFs) photocatalysts and their application in H2O2 synthesis, as well as the direct hydroxylation of benzene to phenol. The results demonstrate that the functional design of surface hydroxyl (–OH) modification on fragmentized TxHy-COFs was achieved by varying the feed ratio of TAPT and THTA monomers, which greatly enhances surface hydrophilicity and effectively improves the separation and transfer of photoexcited electrons and holes. Under visible light irradiation without sacrificial agents, the fragmentized T1H1.8-COF exhibits a boosting H2O2 yield of 2567 μmol g−1h−1, which is 4.2 times higher than the original T1H1-COF. Furthermore, the introduction of metal ions (Fe3+ etc.) into the COF framework through the impregnation method enables the in situ activation of H2O2, allowing the direct hydroxylation of benzene to phenol in aqueous systems, with yield of 9.4 % and selectivity of 99 %. The results of this work demonstrate that the prepared photocatalyst exhibits high stability and photocatalytic activity by structural design optimization, showing great potential for industrial applications in H2O2 production and direct photo-oxidation.

G-C3N4-modified Zr-Fc MOFs as a novel photocatalysis-self-Fenton system toward the direct hydroxylation of benzene to phenol.

In order to explore a green, economic, and sustainable phenol production process, a heterojunction semiconductor materials g-C3N4/Zr-Fc MOF was synthesized via an in situ synthesis method. With the synergistic effect of photocatalysis and the Fenton effect, the composite could effectively catalyze the direct hydroxylation of benzene to phenol under visible light irradiation. The yield of phenol and the selectivity were 13.84% and 99.38% under the optimal conditions, respectively, and it could still maintain high photocatalytic activity after 5 photocatalytic cycles. Therefore, the designed photocatalysis-self-Fenton system has great potential in the field of the direct hydroxylation of benzene to phenol.

An efficient photocatalysis-self-Fenton system based on Fe(ii)-MOF/g-C3N4for direct hydroxylation of benzene to phenol

With the synergistic effect of photocatalysis and the Fenton effect, the Fe(ii)-MOF/g-C3N4 could achieve efficient direct hydroxylation of benzene to phenol.

Combined computational and experimental investigation on the Fenton reagent catalysed hydroxylation of benzene

BackgroundPhenol is one of the most important chemicals in industry, generally produced from benzene in cumene processes. Alternatively, the direct hydroxylation of benzene catalysed by Fenton reagent has been a potentially sustainable process for the production of phenol. MethodsComputational calculation method combined with experiments were both employed to investigate the Fenton reagent catalysed hydroxylation of benzene. Significant findingsComputational calculation turned out that the H migration National Institutes of Health (NIH) shift in the benzene hydroxylation reaction including intramolecular immigration and an intermolecular process. The activation energy (ΔG) for the H migration between IM2 molecules was 17.5 kcal mol−1, while the ΔG for the intramolecular H transfer was 49.4 kcal mol−1. The crucial intermediates in the direct hydroxylation reaction were characterised by a variety of analysis methods. There were three types of C-C bonds in IM1 with Mayer bond order (MBO) equivalent to 1.272, 1.581, and 1.041 respectively, and the C-C bonds in IM2 were not equal based on the localised orbitals and orbital composition analysis and a series of electronic structure information. Moreover, the global electron delocalisation analysis visually demonstrated an uneven distribution of π electron, revealing the aromaticity of these two intermediates. These two intermediates exhibited both aromaticity and antiaromaticity features under external magnetic conditions. Notably, the nuclear magnetic resonance results showed the existence of one of the prominent intermediates.

Highly Dispersed Vanadia Anchored on Protonated g-C3N4 as an Efficient and Selective Catalyst for the Hydroxylation of Benzene into Phenol

The direct hydroxylation of benzene is a green and economical-efficient alternative to the existing cumene process for phenol production. However, the undesired phenol selectivity at high benzene conversion hinders its wide application. Here, we develop a one-pot synthesis of protonated g-C3N4 supporting vanadia catalysts (V-pg-C3N4) for the efficient and selective hydroxylation of benzene. Characterizations suggest that protonating g-C3N4 in diluted HCl can boost the generation of amino groups (NH/NH2) without changing the bulk structure. The content of surface amino groups, which determines the dispersion of vanadia, can be easily regulated by the amount of HCl added in the preparation. Increasing the content of surface amino groups benefits the dispersion of vanadia, which eventually leads to improved H2O2 activation and benzene hydroxylation. The optimal catalyst, V-pg-C3N4-0.46, achieves 60% benzene conversion and 99.7% phenol selectivity at 60 oC with H2O2 as the oxidant.

Direct Hydroxylation of Benzene with Hydrogen Peroxide Using Fe Complexes Encapsulated into Mesoporous Y-Type Zeolite.

Mesoporous Y-type zeolite (MYZ) was prepared by an acid and base treatment of commercial Y-type zeolite (YZ). The mesopore volume of MYZ was six times higher than that of YZ. [Fe(terpy)2]2+ complexes encapsulated into MYZ and YZ with different Fe contents (Fe(X)L-MYZ and Fe(X)L-YZ; X is the amount of Fe) were prepared and characterized. The oxidation of benzene with H2O2 using Fe(X)L-MYZ and Fe(X)L-YZ catalysts was carried out; phenol was selectively produced with all Fe-containing zeolite catalysts. As a result, the oxidation activity of benzene increased with increasing iron complex content in the Fe(X)L-MYZ and Fe(X)L-YZ catalysts. The oxidation activity of benzene using Fe(X)L-MYZ catalyst was higher than that using Fe(X)L-YZ. Furthermore, adding mesopores increased the catalytic activity of the iron complex as the iron complex content increased.

La-Cu based heterogeneous perovskite catalyst for highly selective benzene hydroxylation under mild conditions.

Direct hydroxylation of benzene towards phenol with high conversion and selectivity remains a great challenge. We report herein an efficient La2 CuO4 perovskite catalyst for one-step oxidation of benzene using hydrogen peroxide under mild conditions. The catalyst was characterized using XRD, TEM, XPS, TG-DTA, and other advanced techniques. The one-pot hydroxylation reaction carried out at 60 °C under optimum reaction conditions in the presence of catalytic material shows benzene to phenol transformation with 51% conversion with >99% selectivity with 65 percent peroxide efficiency, respectively. The influence of reaction conditions such as temperature, amount of oxidant, reaction time and mode of addition of the oxidant was crucial in selectivity optimization.

A metal-/additive-free system for oxygen-mediated hydroxylation of benzene over polyfuran-functionalized hydrothermal carbocatalyst

Direct benzene hydroxylation with dioxygen (O2) is among the most promising alternative pathways for green phenol production, but efficient catalysis systems usually involve metal species or other additives such as sacrificial agents. In this work, we designed a carbon catalyst from the hydrothermal treatment of biomass-derived sucrose and constructed a metal-/additive free heterogeneous catalytic system for benzene hydroxylation to phenol with O2. The champion carbon sample gave a high phenol yield of 13.4%. The catalyst was facilely recovered and reused without apparent deactivation. There abundant oxygen functional groups such as phenolic and quinone carbonyl groups served as the active sites and polyfuran units accelerated the O2 adsorption and activation. The synergistic effect of these surficial organic groups is conducive to the formation of reactive oxygen species, hydroxyl radicals, which effectively oxidized the benzene to phenol.

Direct Benzene Hydroxylation with Dioxygen Induced by Copper Complexes: Uncovering the Active Species by DFT Calculations.

The direct oxidation of benzene into phenol using molecular oxygen at very mild temperatures can be promoted in the presence of the copper complex TpBr3Cu(NCMe) in the homogeneous phase in the presence of ascorbic acid as the source of protons and electrons. The stoichiometric nature, relative to copper, of this transformation prompted a thorough DFT study in order to understand the reaction pathway. As a result, the dinuclear species TpBr3CuII(μ-O•)(μ-OH)CuIITpBr3 is proposed as the relevant structure which is responsible for activating the arene C–H bond leading to phenol formation.

Selective oxidation of benzene by an iron oxide carbonaceous nanocatalyst prepared from iron perchlorate salts and hydrogen peroxide in benzene and acetonitrile

Direct benzene hydroxylation under mild conditions using hydrogen peroxide can be essential in producing phenol. A new iron oxide-carbonaceous nanocatalyst (Fe-oxide CNC) is prepared in situ using a precursor of Fe(ClO4)2 and H2O2 in benzene and CH3CN. The obtained Fe-oxide CNC can efficiently catalyze benzene oxidation to phenol using H2O2(aq) in CH3CN. The highest phenol production was achieved with the turnover number (TON) of 122 in unit iron content and selectivity of 96% at 60 °C. The catalyst was characterized by SEM, TEM, XAS, XPS, Raman, XRD, BET, and TGA techniques.Interestingly, materials identification and characterization of the Fe-oxide CNC provided evidence to support the presence of Fe2O3. In addition, the carbonaceous moieties mainly consisted of branched aliphatic hydrocarbons on the iron oxide surface, which enhance the catalytic performance for benzene oxidation to phenol. The Fe-oxide CNC can be recycled three times with comparable catalytic efficiency. Using H218O2 as an oxidant, the phenol product with highly enriched 18O-atom indicates that the reactive oxygen species (ROS) activated by H2O2(aq) is crucial for aromatic oxidation. Time-resolved spin trapping experiments displayed the formation of the intermediate adducts consisting of 5,5-dimethyl-1-pyrroline N-oxide (DMPO) and reactive oxygenated radicals. For 3‒24 h durations, higher steady-state concentrations of the oxygenated intermediates observed at 25 °C than 60 °C indicate that the catalytic oxidation of benzene mediated by Fe-oxide CNC performs much faster kinetics at 60 °C than the ambient condition.

An efficient photocatalyst based on H5PMo10V2O40/UiO-66-NH2 for direct hydroxylation of benzene to phenol by H2O2.

To realize the direct hydroxylation of benzene to phenol by hydrogen peroxide, an efficient photoactive catalyst system was prepared by the recombination of H5PMo10V2O40 and UiO-66-NH2. The heterpolyacid was uniformly distributed on the UiO-66-NH2, and the combination was stable. The composite could effectively photocatalyze the direct hydroxylation of benzene to phenol by H2O2 in the mixture solution of acetonitrile and acetic acid. The yield and selectivity were 14.08% and 98.8% under the optimum condition, respectively. The performance of the catalyst still maintained well after 5 catalytic cycles. Hence, the investigated catalyst system might be applied in the field of hydroxylation of benzene to phenol.

Enhanced Hydroxylation of Benzene to Phenol with Hydrogen Peroxide over g-C3N4 Quantum Dots-Modified Fe-SBA-15 Catalysts: Synergistic Effect Among Fe Species, g-C3N4 QDs, and Porous Structure

g-C3N4 quantum dots (QDs) attract considerable attention due to its remarkable applications in various fields such as catalysis, ion detection, and biosensors. Herein, the inner surface of the hexagon channels of Fe-SBA-15 was adorned by g-C3N4 QDs to enhance direct hydroxylation of benzene with H2O2 to afford phenol. The crystal texture, porous properties, inner structure, morphology, elemental distribution, chemical composites, and bonding energy of the synthesized CN-QDs/Fe-SBA-15 were thoroughly analyzed and characterized using X-ray diffraction, N2 adsorption–desorption, transmission electron microscopy (TEM), scanning electron microscopy–energy-dispersive X-ray spectroscopy, high-resolution transmission electron microscopy, high-angle annular dark-field scanning TEM, X-ray photoelectron spectroscopy, and UV–vis and Fourier-transform infrared spectroscopies. The catalytic performance of the synthesized g-C3N4 QD-decorated Fe-SBA-15 was explored for one-step direct oxidation of benzene, with H2O2 as a green oxidant to obtain phenol. The structural characterization and catalytic investigation revealed that benzene molecules were adsorbed on the surface of CN-QDs by noncovalent interactions and activated by the terminal groups, that is, N-defects/C–OH present on the edges of CN-QDs. Then, the activated benzene was attacked by the hydroxyl radical generated by iron-peroxo-capturing hydrogen ion to produce phenol. The mesoporous structure of Fe-SBA-15 not only deals with the stability and aggregation of g-C3N4 QDs but also ensures the uniform dispersion of Fe species on the inner surface of the channel. The maximum yield of phenol obtained was 41.2% in this catalytic system, which is crucially dependent on the synergic effect between g-C3N4 QDs and Fe-SBA-15.

One-pot synthesis of highly active Fe-containing MWW zeolite catalyst: Elucidation of Fe species and its impact on catalytic performance

Fe-containing MWW zeolite catalysts in the absence (Fe-MWW) or presence of Al atoms (Fe,Al-MWW) were directly prepared by the hydrothermal synthesis approach. The nature of Fe species was systematically analyzed by UV–vis, in-situ NO adsorption FTIR spectroscopy, and H2-TPR technology. The presence of Al atoms in the synthesis gel seriously affected the chemical composition, textural properties, and the states of Fe species, hence made the catalytic activity in hydroxylation of benzene with H2O2 worse than the one without Al. Moreover, we found that the states of Fe species could be adjusted by changing the calcination temperature. The catalytic activity of Fe-MWW was improved by increasing the calcination temperature, while that of Fe,Al-MWW was weakened due to the degeneration of texture properties and the transformation of Fe species. Fe-MWW zeolite calcined at 750 °C exhibited the highest 8.3% yield and 94% selectivity to phenol in direct hydroxylation of benzene with H2O2.

Oxo-vanadium (IV) phthalocyanine implanted onto the modified SBA-15 as a catalyst for direct hydroxylation of benzene to phenol in acetonitrile-water medium: A kinetic study

Direct hydroxylation of benzene using molecular oxygen is an engaged approach to yield of phenol as a valuable compound with numerous applications. In the present research, highly selective benzene hydroxylation was successfully carried out in the presence of O2 using vanadyl phthalocyanine implanted onto the chloro-functionalized SBA-15 as a robust catalyst. Also, the effect of water as a co-solvent was investigated and it was concluded that the mixed solvent (CH3CN-H2O) can play a remarkable role in the development of the reaction progress due to its ability to act as an axial ligand. Then, the oxidation of benzene using CH3CN and CH3CN-H2O was kinetically investigated.

Light-Induced Efficient Hydroxylation of Benzene to Phenol by Quinolinium and Polyoxovanadate-Based Supramolecular Catalysts.

Direct Hydroxylation of benzene to phenol with high yield and selectivity has been the goal of phenol industrial production. Photocatalysis can serve as a competitive method to realize the hydroxylation of benzene to phenol owing to its cost-effective and environmental friendliness, however it is still a forbidding challenge to obtain good yield, high selectivity and high atom availability meanwhile. Here we show a series of supramolecular catalysts based on alkoxohexavanadate anions and quinolinium ions for the photocatalytic hydroxylation of benzene to phenol under UV irradiation. We demonstrate that polyoxoalkoxovanadates can serve as efficient catalysts which can not only stabilize quinolinium radicals but also reuse H2 O2 produced by quinolinium ions under light irradiation to obtain excellent synergistic effect, including competitive good yield (50.1 %), high selectivity (>99 %) and high atom availability.

Rational Designed Polymer as a Metal-Free Catalyst for Hydroxylation of Benzene to Phenol with Dioxygen

Direct hydroxylation of benzene to phenol with dioxygen is a green route for synthesis of phenol. The higher bonding energies of C–H in benzene and O–O in dioxygen make metal-free catalysis a challenge. A novel metal-free catalyst of quinone-cylcohexanone-formaldehyde polymer was rationally designed and prepared. The polymer was characterized with FT-IR, XRD, Raman, SEM, 13C NMR and XPS. Abundant oxygen functional groups of cyclic ketonic, quinone carbonyl and hydroquinone were found on the surface of polymer. The catalytic performances for hydroxylation of benzene to phenol with dioxygen over the metal-free catalyst were investigated and a phenol yielding of 11.4% was achieved. Moreover, the reaction mechanism was proposed.

Selective Hydroxylation of Benzene to Phenol over Fe Nanoparticles Encapsulated within N-Doped Carbon Shells

Iron-containing heterogeneous catalysts hold great promising for the direct hydroxylation of benzene to phenol. However, their catalytic performance is greatly hampered by the inherent drawbacks of iron-containing solids, in particular their hydrophilic surface structure and inevitable leaching of iron species during the Fenton process, which result in poor selectivity and durability toward phenol production. Herein, we demonstrate that the encapsulation of iron nanoparticles with N-doped carbon layer as core–shell nanostructures (Fe@NC) is a promising synthetic strategy to advance iron-containing solids for benzene hydroxylation. The rigid carbon shells conformably coating on iron cores not only protect iron from leaching but also facilitate the selective adsorption of benzene molecules on Fe@NC because of their excellent stability against acid etching and hydrophobic surface with the unique π-conjugated electron system. As a result, Fe@NC exhibit a robust catalytic durability and good yield with high selectivity for the direct hydroxylation of benzene to phenol. Benefiting from their unique core–shell nanostructures and strong host–guest electron interaction between metals and carbons, Fe@NC are expected to be promising also for other liquid-phase organic synthesis.

Systematic Evolution of Decoy Molecules for the Highly Efficient Hydroxylation of Benzene and Small Alkanes Catalyzed by Wild-Type Cytochrome P450BM3

Highly effective dipeptidic decoy molecules, which stimulate the direct hydroxylation of benzene by wild-type cytochrome P450BM3, were successfully developed through a rationally designed screening...

On the Ability of Nickel Complexes Derived from Tripodal Aminopyridine Ligands to Catalyze Arene Hydroxylations.

The development of catalysts for the selective hydroxylation of aromatic C-H bonds is an essential challenge in current chemical research. The accomplishment of this goal requires the discovery of powerful metal-based oxidizing species capable of hydroxylating inert aromatic bonds in a selective manner, avoiding the generation of non-selective oxygen-centered radicals. Herein we show an investigation on the ability of nickel(ii) complexes supported by tripodal tetradentate aminopyridine ligands to catalyze the direct hydroxylation of benzene to phenol with H₂O₂ as oxidant. We have found that modifications on the ligand structure of the nickel complex do not translate into different reactivity, which differs from previous findings for nickel-based arene hydroxylations. Besides, several nickel(ii) salts have been found to be effective in the oxidation of aromatic C-H bonds. The use of fluorinated alcohols as solvent has been found to result in an increase in phenol yield; however, showing no more than two turn-overs per nickel. These findings raise questions on the nature of the oxidizing species responsible for the arene hydroxylation reaction.

Vanadium Oxyacetylacetonate Grated on Metal Organic Framework as Catalyst for the Direct Hydroxylation of Benzene to Phenol

AbstractA high‐performance NH2‐MIL‐88B(Fe)‐SA−V for the direct catalytic oxidation of benzene hydroxylation using hydrogen peroxide as the oxidant was designed and prepared. The synthesized material was characterized by scanning electron microscopy, x‐ray powder diffraction, flourier transform infrared spectroscopy and nitrogen adsorption‐desorption. The influence of different parameters on the catalytic performance of NH2‐MIL‐88B(Fe)‐SA−V for benzene hydroxylation was researched. Under optimized condition, the high yield of 22.2% and selectivity of 98.6% were obtained, while the pure NH2‐MIL‐88B(Fe) only gained the yield of 1.2%. Furthermore, the V/Fe3O4 catalyst was obtained by calcination of NH2‐MIL‐88B(Fe)‐SA−V in N2 for photocatalytic recycle, and the yield and selectivity of phenol were 20.2% and 98.2% respectively. And the V/Fe3O4 has good photocatalytic efficiency after several recycling tests in the acid reaction condition.