Phenol Conversion Research Articles

Efficient Electrosynthesis of Valuable para‐Benzoquinone from Aqueous Phenol on NiRu Hybrid Catalysts

AbstractElectrocatalytic oxidation of aqueous phenol to para‐benzoquinone (p‐BQ) offers a sustainable approach for both pollutant abatement and value‐added chemicals production. However, achieving high phenol conversion and p‐BQ yield under neutral conditions remains challenging. Herein, we report a Ni(OH)2‐supported Ru nanoparticles (NiRu) hybrid electrocatalyst, which exhibits a superior phenol conversion of 96.5 % and an excellent p‐BQ yield of 83.4 % at pH 7.0, significantly outperforming previously reported electrocatalysts. This exceptional performance benefits from the triple synergistic modulation of the NiRu catalyst, including enhanced phenol adsorption, increased p‐BQ desorption, and suppressed oxygen evolution. By coupling a flow electrolyzer with an extraction‐distillation separation unit, the simultaneous phenol removal and p‐BQ recovery are realized. Additionally, the developed electrocatalytic system with the NiRu/C anode displays good stability, favorable energy consumption, and reduced greenhouse gas emissions for phenol‐containing wastewater treatment, demonstrating its potential for practical applications. This work offers a promising strategy for achieving low‐carbon emissions in phenol wastewater treatment.

Phenol Photostatic Spectra and Quantum‐Classical Photodynamic Deprotonation

ABSTRACTThe spectral‐luminescence properties and photochemical conversions of phenol were analyzed for an isolated molecule as well as in water solvents in a continuum implicit model and explicit atomistic surroundings. This involved employing cut‐edge hybrid quantum‐classical methodologies to generate static optical spectra and the excited dissipative crossing potential energy curves. A combination of electronic excitations, gradient calculations, and embedding electrostatic potential fitting charges on quantum‐classical molecular dynamic propagation trajectories provided statistically averaged absorption spectra. The mixed‐reference spin‐flip multiconfigurational linear response method based on reference triplet preprocessed in the time‐dependent density‐functional theory was utilized to determine conical intersections between the lowest excited and ground states, as well as two‐stage transitions from the second excitation to the ground state. Non‐adiabatic quantum‐classical molecular dynamics defined photodissipative trajectories of excited states, their lifetimes, and crossing points through trajectory surface hopping together with the mixed‐reference spin‐flip and embedding electrostatic potential fitting approaches. Dyson orbitals of the extended Koopmans' theorem were applied to reveal the nature of molecular states at conical intersections and key points on photodynamic trajectories. Potential hydroxyl group cleavage predicted with conical intersections searching turns to “swift” OH deprotonation through |π→⟩ transition along photodynamic propagations in contrast with “long” processes leading to benzene ring deformation with stable OH bond.

Efficient Electrosynthesis of Valuable para-Benzoquinone from Aqueous Phenol on NiRu Hybrid Catalysts.

Electrocatalytic oxidation of aqueous phenol to para-benzoquinone (p-BQ) offers a sustainable approach for both pollutant abatement and value-added chemicals production. However, achieving high phenol conversion and p-BQ yield under neutral conditions remains challenging. Herein, we report a Ni(OH)2-supported Ru nanoparticles (NiRu) hybrid electrocatalyst, which exhibits a superior phenol conversion of 96.5% and an excellent p-BQ yield of 83.4% at pH 7.0, significantly outperforming previously reported electrocatalysts. This exceptional performance benefits from the triple synergistic modulation of the NiRu catalyst, including enhanced phenol adsorption, increased p-BQ desorption, and suppressed oxygen evolution. By coupling a flow electrolyzer with an extraction-distillation separation unit, the simultaneous phenol removal and p-BQ recovery are realized. Additionally, the developed electrocatalytic system with the NiRu/C anode displays good stability, favorable energy consumption, and reduced greenhouse gas emissions for phenol-containing wastewater treatment, demonstrating its potential for practical applications. This work offers a promising strategy for achieving low-carbon emissions in phenol wastewater treatment.

In situ Generation of Cyclohexanone Drives Electrocatalytic Upgrading of Phenol to Nylon‐6 Precursor

AbstractCoupling in situ generated intermediates with other substrates/intermediates is a viable approach for diversifying product outcomes of catalytic reactions involving two or multiple reactants. Cyclohexanone oxime is a key precursor for caprolactam synthesis (the monomer of Nylon‐6), yet its current production uses unsustainable carbon sources, noble metal catalysts, and harsh conditions. Herein, we report the first work to synthesize cyclohexanone oxime through electroreduction of phenol and hydroxylamine. The Faradaic efficiency reached 69.1 % over Cu catalyst, accompanied by a corresponding cyclohexanone oxime formation rate of 82.0 g h−1 gcat−1. In addition, the conversion of phenol was up to 97.5 %. In situ characterizations, control experiments, and theoretical calculations suggested the importance of balanced activation of water, phenol, and hydroxylamine substrates on the optimal metallic Cu catalyst for achieving high‐performance cyclohexanone oxime synthesis. Besides, a tandem catalytic route for the upgrading of lignin to caprolactam has been successfully developed through the integration of thermal catalysis, electrocatalysis, and Beckmann rearrangement, which achieved the synthesis of 0.40 g of caprolactam from 4.0 g of lignin raw material.

Facile One-Pot Conversion of (poly)phenols to Diverse (hetero)aryl Compounds by Suzuki Coupling Reaction: A Modified Approach for the Synthesis of Coumarin- and Equol-Based Compounds as Potential Antioxidants.

A series of 16 (hetero)aryl compounds based on coumarin and equol has been efficiently synthesized by exploring the palladium-catalyzed Suzuki cross-coupling reactions. Polyphenol based on coumarin (4-methyl-7-hydroxy coumarin) was initially converted to corresponding coumarin imidazylate and then subjected to Suzuki coupling reaction with 4-methoxyphenylboronic acid to obtain the coupled product. This modified approach was later developed into a one-pot methodology by directly reacting the polyphenol with 1,1-sulfonyldiimidazole (SDI) and boronic acid in situ to obtain the Suzuki coupled product in one step. Moreover, an array of (poly)phenols based on coumarin and equol were later converted to diverse (hetero)aryl compounds by this optimized step-economic protocol. The synthesized compounds were then subjected to the screening of their potential antioxidant activities by 2,2-diphenyl-1-picrylhydrazyl (DPPH) assay. In our investigation, the compounds 4ah, 4eh, 4gh and 4hh exhibited promising antioxidant potential when compared to the reference standard, butylated hydroxytoluene (BHT). Structure activity relationship (SAR) studies revealed the importance of the presence of electron-donating substituents in enhancing the antioxidant activity of the synthesized compounds.

Improved Photocatalytic Activity of Dion-Jacobson-Type Tantalate Perovskites Modified with FeCl2.

A rapid and feasible approach was used to develop visible-light-driven-type Dion-Jacobson perovskites by the modification of the RbLaTa2O7 host (RbLTO) with FeCl2 through the molten salt route. X-ray diffraction (XRD) characterization showed that FeCl2-modified layered perovskite (e.g., Fe@RbLTO) preserved its lamellar structure. SEM micrographs confirmed the layered morphology of both RbLTO and Fe@RbLTO perovskite materials. The UV-Vis spectra illustrated a significant red shift of the absorption edge after Fe2+ modification, with the band gap energy reducing from 3.88 to 1.82 eV. H2-TPR measurements emphasized the anchorage of Fe2+ species located on the surface of the layered perovskite as well as in the interlayer space. The synthesized materials were valorized as photocatalysts for the degradation of phenol under both Xe lamp and simulated solar irradiation (SSL) conditions. The photocatalytic reaction follows first-order kinetics. By-product formations during phenol (Ph) degradation were identified and quantified using high-performance liquid chromatography (HPLC). Hydroquinone, 1,2-dihydroxi-benzene, benzoquinone, and pyrogallol were identified as the main Ph degradation intermediates. Pristine RbLaTa2O7 exhibited a phenol conversion value of about 17% using an Xe lamp, while a ≈ 11% conversion was achieved under SSL. A substantial increase in Ph conversion and selectivity was perceived after Fe2+ modification. Fe@RbLTO demonstrated superior photocatalytic performances (43% conversion of phenol under an Xe lamp, and 91% selectivity to aromatic intermediate compounds) at optimized reaction conditions. The stability of the Fe@RbLTO photocatalyst when exposed to an Xe lamp was also assessed. These results suggest that the existence of iron species on the layered perovskite's surface is responsible for the improved redox properties of Fe@RbLTO, resulting in a valuable material for environmental applications.

Hydroxylation of Phenol by an Azomethine Quinoxaline Schiff Base Copper (II) Complex

Introduction: A binuclear azomethine quinoxaline Schiff base copper (II) complex, [Cu2LCl2], having square-planar environment around each copper (II), has been synthesized. Method: The coordination of the azomethine quinoxaline Schiff base with copper (II) and its structure was studied by various physicochemical and spectroscopic measurements. Results: Catalytic activity of this complex in phenol hydroxylation reaction has been examined using H2O2 as a green oxidant. Conclusion: Catalytic reaction conditions were optimized and under these conditions, 18.32 % conversion of phenol has been obtained for this catalyst

Co–Fe/Al2O3 catalyst for low-temperature steam reforming of phenol for hydrogen production

In this study, a series of high-efficient catalyst, Co–Fe/Al2O3, were synthesized via the sol-gel method for low-temperature phenol steam reforming (PSR). The optimized catalyst, 15Co–2Fe/Al2O3, exhibited a remarkable phenol conversion of 95.3%, a H2 yield of 92.1% at 450 °C, GHSV = 7500 h−1 and a steam-to-carbon (S/C) ratio of 10. Furthermore, the catalyst activity was maintained for 660 min before a gradual decline was observed. The NH3-TPD analysis revealed that the addition of Fe enhanced the surface acidity of the catalyst, providing more active sites for phenol adsorption and activation. This study aims to address the challenges associated with high reaction temperatures and poor catalyst stability in PSR. Various characterization techniques have been employed to investigate the reaction mechanisms of bimetallic catalysts in low-temperature PSR.

Regulating the electronic state of Pd nanoclusters and Lewis acid density by the carbon doping for synergistically enhancing phenol hydrogenation in green solvent

Pd-based catalysts have been widely applied in selective hydrogenation of phenol. However, avoiding excessive hydrogenation of C=O functional groups is still challenging. Here, we synthesized Pd nanoclusters supported by N-doped C-Al2O3 (Pd/CN-Al2O3) catalyst for phenol hydrogenation. Remarkably, the cyclohexanone yield shows a volcano trend with the doping of carbon content, where Pd/CN-Al2O3 with carbon content of 6.76 % (Pd/CN-Al2O3-2) exhibits the highest cyclohexanone yield. Under the optimized conditions, the phenol conversion and cyclohexanone selectivity over Pd/CN-Al2O3-2 are 99.5 % and 96.7 %, respectively. The corresponding TOF value is 1731.7 h−1, which is 5.8 times higher than that of Pd/Al2O3 (299.7 h−1). Mechanism studies reveal the excellent catalytic performance of Pd/CN-Al2O3-2 is mainly attributed to the synergistic effect of electron-deficient Pd clusters and Lewis acid sites. Pd nanoclusters with moderate electron-deficient state and moderate Lewis acid density are beneficial to the adsorption of phenol and the desorption of cyclohexanone, thereby exhibiting the best phenol conversion and cyclohexanone selectivity. This work provides a carbon modification strategy to regulate the structure of Pd-based catalysts, which is a helpful guide for the hydrogenation reactions.

Impact of H2 Reduction on the Performance and Stability of Phenol Catalytic Wet Air Oxidation (CWAO) Over Cu−Ce/AC Catalysts

AbstractIn this study, we utilized the carbon precursor derived from walnut shells to synthesize a series of Ce‐modified Cu‐based carbon catalysts (Cu−Ce/AC) via the impregnation method. We investigated the performance and stability of Cu−Ce/AC catalysts for CWAO phenol after H2 reduction at various temperatures. The Cu−Ce/AC‐250 catalyst exhibited its highest performance at 250 °C, achieving complete phenol conversion. Characterization results from techniques including XRD, BET, FTIR, ICP‐OES, SEM‐EDS, XPS, and H2‐TPR indicated that the active components of the H2‐reduced catalysts were more evenly distributed across the catalyst surface, thereby enhancing the availability of reactive sites for phenol oxidation. Simultaneously, under the appropriate temperature, the H2 atmosphere can reduce a portion of the Cu2+ on the catalyst surface to Cu+, thereby mitigating the loss of Cu components.

Electrocatalytic Conversion of Phenol to Cyclohexane Using Pt and Ru-Based Catalysts

The production of renewable fuels has become necessary as fossil fuels continue to deplete.1 Pyrolysis of biomass to liquid fuels has emerged as a promising solution due to the possibility of conversion of high carbon content feedstocks into fuel. Pyrolysis oils, however, struggle from low yields and increased heteroatom content.2 In order to solve this problem a second upgrading step is needed to increase the fuel’s hydrogen content and remove heteroatoms. Conventional oil upgrading through thermochemical processes is an option using high temperatures (>300 °C) and high-pressure hydrogen (10-20MPa).3 Electrochemical upgrading of bio-oils represents a novel avenue for the conversion of bio-oils to usable fuels or commodity chemicals under mild condition which requires milder temperatures (30-80 °C) and generates the hydrogen in situ through the water splitting reaction.3 Though initial results on electrocatalytic upgrading have been promising, few studies report appreciable yields of fully deoxygenated products and the efficiency remains low at high current densities.3 This work focuses on the upgrading of phenol as a bio-oil model compound. ECH of phenol was investigated in a custom electrochemical cell (H-Cell), with a solvent trap for the collection and quantification of volatile organic products. Efficient ECH conversion of phenol to cyclohexane was demonstrated and the primary factors impacting the selective production of cyclohexane were studied. Multiple variables, including catalyst type, electrolyte composition and concentration, and cathodic potential were investigated to determine their influence on ECH reaction rate, selectivity, and efficiency. The results obtained show that lab-synthesized, bi-metallic PtRu-C catalyst results in the highest specific ECH rate of 23.52 mol h-1 g-1 metal in comparison to 19.92 mol h-1 g-1 metal, 15.84 mol h-1 g-1 metal and 4.64 mol h-1 g-1 metal, measured with a commercial PtRu-C and mono-metallic Pt-C and Ru-C catalysts, respectively. In addition, the lab synthesized PtRu-C catalyst achieved > 30% selectivity towards cyclohexane, which is among the highest reported in literature to date. Constant potential experiments showed that the cyclohexane was 4.6% higher at -0.46 V vs Ag/AgCl than -0.28 V vs Ag/AgCl indicating cyclohexane selectivity is weakly dependent on cathodic potential. To improve the mechanistic understanding of phenol ECH, operando Raman spectroscopy was explored, finding strong evidence for cyclohexanone reaction intermediates.References(1) Zhang, X.; Lei, H.; Chen, S.; Wu, J. Catalytic Co-Pyrolysis of Lignocellulosic Biomass with Polymers: A Critical Review. Green Chemistry. 2016. https://doi.org/10.1039/c6gc00911e.(2) Zhang, B.; Zhong, Z.; Min, M.; Ding, K.; Xie, Q.; Ruan, R. Catalytic Fast Co-Pyrolysis of Biomass and Food Waste to Produce Aromatics: Analytical Py-GC/MS Study. Bioresour. Technol. 2015, 189. https://doi.org/10.1016/j.biortech.2015.03.092.(3) Chen, G.; Liang, L.; Li, N.; Lu, X.; Yan, B.; Cheng, Z. Upgrading of Bio-Oil Model Compounds and Bio-Crude into Biofuel by Electrocatalysis: A Review. ChemSusChem. 2021. https://doi.org/10.1002/cssc.202002063. Figure 1

In situ Generation of Cyclohexanone Drives Electrocatalytic Upgrading of Phenol to Nylon-6 Precursor.

Coupling in situ generated intermediates with other substrates/intermediates is a viable approach for diversifying product outcomes of catalytic reactions involving two or multiple reactants. Cyclohexanone oxime is a key precursor for caprolactam synthesis (the monomer of Nylon-6), yet its current production uses unsustainable carbon sources, noble metal catalysts, and harsh conditions. Herein, we report the first work to synthesize cyclohexanone oxime through electroreduction of phenol and hydroxylamine. The Faradaic efficiency reached 69.1 % over Cu catalyst, accompanied by a corresponding cyclohexanone oxime formation rate of 82.0 g h-1 gcat -1. In addition, the conversion of phenol was up to 97.5 %. In situ characterizations, control experiments, and theoretical calculations suggested the importance of balanced activation of water, phenol, and hydroxylamine substrates on the optimal metallic Cu catalyst for achieving high-performance cyclohexanone oxime synthesis. Besides, a tandem catalytic route for the upgrading of lignin to caprolactam has been successfully developed through the integration of thermal catalysis, electrocatalysis, and Beckmann rearrangement, which achieved the synthesis of 0.40 g of caprolactam from 4.0 g of lignin raw material.

Unveiling the microbial co-metabolism behavior for electrical-driven degradation of phenol in bioanode

Uncovering the behavior of microbial co-metabolism will provide a vision of microbial mutualistic mechanisms for degrading refractory organics by bioanode and expedite the application of microbial electrochemical technology. Here, microbial co-metabolism is established by adding acetate sodium and is used to stimulate the electrical-driven degradation (e-degradation) of phenol by bioanode. The efficiency of e-degradation for 50 mg L−1 phenol achieved 24.8 % and the total electron recovery was improved by 289 ± 40 % compared with that without microbial co-metabolism. This improvement is found for the e-degradation of 20 mg L−1, 30 mg L−1, and 100 mg L−1 phenol. A big external resistance would inhibit the metabolism of exoelectrogens and lead to a decrease in electron recovery. Abundant exoelectrogens (Geobacter spp. and Pseudomonas spp.) are enriched in bioanode with microbial co-metabolism and the biofilm can perform extracellular electron transport through various pathways with the mid-potential of −0.24 V and −0.42 V, respectively. In addition, elevated amounts of intermediates for phenol e-degradation further demonstrate that microbial co-metabolism stimulates the conversion of phenol in bioanode. The insights gained from this study will assist in disclosing microbial interaction behavior in degrading refectory pollutants by bioanode.

Advancing nanoarchitectures of 2D WO3/MXene photoanode for enhanced photoelectrocatalytic oxidation of phenol and arsenic in synthetic wastewater

The photoelectrocatalytic advanced oxidation process (PEAOP) necessitates high-performing and stable photoanodes for the effective oxidation of complex pollutants in industrial wastewater. This study presents the construction of 2D WO3/MXene heteronanostructures for the development of efficient and stable photoanode. The WO3/MXene heterostructure features well-ordered WO3 photoactive sites anchored on micron-sized MXene sheets, providing an increased visible light active catalytic surface area and enhanced electrocatalytic activities for pollutant oxidation. Phenol, a highly toxic compound, was completely oxidized at an applied potential of 0.8 V vs. RHE under visible light irradiation. Systematic optimization of operational conditions for the photoelectrocatalytic oxidation of phenol was conducted. The phenol oxidation mechanism was elucidated via high-performance liquid chromatography (HPLC) analysis and the identification of intermediate compounds. Additionally, a mixed model of phenol and arsenic (III) in polluted water demonstrated the capability of WO3/MXene photoanode for the simultaneous oxidation of both organic and inorganic pollutants, achieving complete conversion of phenol and As(III) to non-toxic As(V). The WO3/MXene photoanode facilitated water oxidation, generating a substantial amount of O2•– and •OH oxidative species, which are crucial for the concurrent oxidation of phenol and arsenic. Recyclability tests demonstrated a 99% retention of performance, confirming the WO3/MXene photoanode's suitability for long-term operation in PEAOPs. The findings suggest that integrating WO3/MXene photoanodes into water purification systems can enhance economic feasibility, reduce energy consumption, and improve efficiency. This PEAOP offers a viable solution to the critical issue of heavy metal and organic chemical pollution in various water bodies, given its scalability and ability to preserve ecosystems while conserving clean water resources.

Super-Stable Mineralization of Metal Ions from Smelting Wastewater by In Situ Synthesis of NiFe-Based Layered Double Hydroxides for Catalytic Phenol Hydroxylation.

The super-stable mineralization of metal ions from industrial wastewater by in situ synthesis of layered double hydroxides (LDHs) has been regarded as a sustainable approach from environmental protection and resource utilization perspectives. Herein, the study reports a super-stable mineralization of metal ions including Ni, Fe, Cr, Mn, Cu, Ca, Al, etc. from smelting wastewater by in situ synthesis of NiFe-based LDHs through facile coprecipitation. Such approach exhibits superior mineralization efficiency of metal ions simultaneously that can remove hundreds, thousands, or even tens of thousands mg/L of multiple metal ions to below the values of the Chinese National Emission Standards of Pollutants. Furthermore, the obtained NiFe-based LDHs exhibit excellent catalytic performance of phenol hydroxylation due to the mineralization of multiple metals on the laminates, where 48.24% conversion of phenol and 71.58% selectivity of dihydroxybenzenes are realized under room temperature for 3h. This work paves a sustainable strategy for hazardous material disposal and resource utilization.

In Situ Sulfonated Mesoporous Polydivinylbenzene as a Solid Acid Catalyzed the Condensation of Phenol and Acetone

AbstractSulfonated mesoporous polydivinylbenzene solid acid was prepared by in situ sulfonation method, and the physical chemical properties of this solid acid was characterized by XRD, BET, FT‐IR, etc. Acid density of sulfonated mesoporous polydivinylbenzene was characterized by acid base titration, and the result showed that the acid density was 1.58 mmol H+/g. The condensation of phenol and acetone was used as a probe reaction to investigate the catalytic performance of sulfonated mesoporous polydivinylbenzene as a solid acid. Results showed that the phenol conversion rate could approach theoretical conversion rate with Bisphenol‐A selectivity of 91 % at 90 °C. More importantly, sulfonated mesoporous polydivinylbenzene had good stability, and after repeated use for five times, the catalytic performance was not significantly reduced.

Hydrogenation of phenol to cyclohexanone catalyzed by isolated Pd cations in the micropores of zeolite

Cyclohexanone is a key raw material for manufacturing nylon and other chemicals. The sustainable conversion of biomass-derived phenol to cyclohexanone meets the requirements of sustainable development goal but still be challenging. Herein, a catalyst containing isolated Pd cations in zeolite, namely Pd1/ZSM-5, is investigated for the partial hydrogenation of phenol to cyclohexanone. Under 140 °C and 1.5 MPa of initial hydrogen pressure, the conversion of phenol reaches 95.6% with the selectivity to cyclohexanone of 99.9%. Besides, the turnover rate (TOR) of partial hydrogenation of phenol reaches 382.7 h−1. The mild adsorption affinity of cyclohexanone on catalytic sites leads to the high selectivity. Moreover, as unveiled by surface reactivity of phenol monitored by in-situ infrared spectrum, the oxygen atom of phenol hydroxyl group is adsorbed on the Brönsted acid site of Pd1/ZSM-5 as the key reaction step. The reaction intermediate involves the partial hydrogenation of benzene ring of phenol.

Lignin-incorporated Co-MOFs-derived catalysts for selective hydrodeoxygenation of lignin-derived phenols into cyclohexanols

Lignin accounted for the second largest amount in biomass, and was regarded as an important carbon source and important renewable source for value-added chemicals. Herein, a series of lignin-derived carbon-based heterogeneous catalyst was synthesized through a simple hydrothermal method, using Co-MOFs as template. Lignin was introduced as a carbon material into MOF catalysts. Through some characterizations, it has been proven that lignin has been successfully introduced into MOF materials and significantly improved the catalyst performance. Then, lignin-MOF derived catalysts (Co/C-EL-X) were successfully introduced into the catalytic hydrodeoxygenation of lignin-derived phenols. The addition of enzymatic hydrolysis lignin (EL) in catalysts, calcination temperature and some other factors were investigated in detail, considering the catalytic performance during the HDO of vanillin and other typical lignin-derived phenols. Co/C-EL-0.5(500) exhibited the best catalytic performance for the conversion of different kinds of lignin-derived phenols to either 2-methoxy-4-methylphenol (MMP) or cyclohexanol. Under the optimal conditions of 240 °C, 0 MPa N2, and 2 h, the conversion rate of vanillin reached 100 %, and the yield of 4-methyl-2-methoxyphenol (MMP) was up to 92 %. Furthermore, vanillin could also be converted into 4-methylcyclohexanol (MCYL) by changing the initial nitrogen pressure. Also, Co/C-EL-0.5 (500) exhibited high activity for the conversion of other lignin-derived phenols into cyclohexanol (COL). This work provided a novel strategy for the catalytic valorization of lignin sources.

Palladium-Catalyzed Cyanations of Aryl Imidazolylsulfonates with K4[Fe(CN)6]: A Pragmatic Approach to Benzonitriles from Phenols

AbstractA general Pd-catalyzed approach for the conversion of phenols into benzonitriles via aryl imidazolylsulfonates with a non-toxic cyanide source, potassium ferrocyanide, has been developed. Salient features of this method include low palladium precatalyst loadings (as low as 1.0 mol% total Pd), mild reaction conditions, and environmentally benign by-products compared to other (pseudo)halide aryl electrophiles. The initial scope of the reaction on a range of phenolic precursors is demonstrated including a one-pot, two-step approach to convert phenols directly into benzonitriles.

Metal-Organic Framework-Supported Mono Bipyridyl-Iron Hydroxyl Catalyst for Selective Benzene Hydroxylation into Phenol.

Direct hydroxylation of benzene to phenol is more appealing in the industry for the economic and environmentally friendly phenol synthesis than the conventional cumene process. We have developed a UiO-metal-organic framework (MOF)-supported mono bipyridyl-Iron(II) hydroxyl catalyst [bpy-UiO-Fe(OH)2] for the selective benzene hydroxylation into phenol using H2O2 as the oxidant. The heterogeneous bpy-UiO-Fe(OH)2 catalyst showed high activity and remarkable phenol selectivity of 99%, giving the phenol mass-specific activity up to 1261 mmolPhOHgFe-1 h-1 at 60 °C. Bpy-UiO-Fe(OH)2 is significantly more active and selective than its homogeneous counterpart, bipyridine-Fe(OH)2. This enhanced catalytic activity of bpy-UiO-Fe(OH)2 over its homogeneous control is attributed to the active site isolation of the bpy-Fe(OH)2 moiety by the solid MOF that prevents intermolecular decomposition. Moreover, the exceptional selectivity of bpy-UiO-Fe(OH)2 in benzene to phenol conversion is originated via shape-selective catalysis, where the confined reaction space within the porous UiO-MOF prevents the formation of larger overoxidized products such as hydroquinone or benzoquinone, leading to the formation of only smaller-sized phenol after monohydroxylation of benzene. Spectroscopic and controlled experiments and theoretical calculations elucidated the reaction pathway, in which the in situ generated •OH radical mediated by bpy-UiO-FeII(OH)2 is the key species for benzene hydroxylation. This work underscores the significance of MOF-supported earth-abundant metal catalysts for sustainable production of fine chemicals.