Hydroxylation Of Phenol Research Articles

2D RGO nanosheets supported anti-spinel NiFe2O4 nanocubes for efficient hydroxylation of phenol

2D RGO nanosheets supported anti-spinel NiFe2O4 nanocubes for efficient hydroxylation of phenol

Ionic Liquid Templated Ordered Hexagonal Mesoporous Iron Phosphate: A Highly Effective Heterogeneous Catalyst with Remarkable Selectivity for Phenol Hydroxylation Reaction.

A highly organized hexagonal mesoporous iron phosphate framework structure with the designation HMI-41 was successfully synthesized for the first-time in a reproducible way using imidazolium-based ionic liquid as structure directing agent. The unique templating properties of ionic liquid generated a highly ordered well-crystallized mesoporous matrix having high surface area (445 m2g-1), thicker pore wall (2.1 nm) and narrow pore size distribution (3.1 nm). The presence of active sites within a tetrahedral framework structure made the novel HMI-41 catalyst highly effective for phenol hydroxylation in an acidic medium with hydrogen peroxide as the oxidant. The catalyst exhibited outstanding performance, achieving an impressive 80% hydroquinone selectivity and 21% of phenol conversion with a hydroquinone-to-catechol ratio of seven, which is the highest value ever reported.

Fabrication of Fe Single Atoms by Utilizing the Inherent Confined Space for Phenol Hydroxylation

Diphenol is a key chemical product, and the phenol hydroxylation reaction is an important route for the synthesis of diphenol. The Fe sites are well-known active centers for the phenol hydroxylation reaction, and the reaction activity depends on the dispersion of Fe sites; however, facile fabrication of highly dispersed Fe sites remains a big challenge. Here, we provide a simple method for the synthesis of Fe single-atom catalysts (SACs) by utilizing the confined space which exists in template-occupied SBA-15 (TOS). By simple solid phase grinding and subsequent calcination, the Fe precursor was easily introduced into the inherent confined space to form a Fe–O–Si structure. A total of 10 g of SACs can be synthesized easily and efficiently in a single pass via ball milling. The Fe SACs have been applied for the phenol hydroxylation reaction with significantly higher activity than comparison samples without inherent confined space.

Bioorganometallic Chemistry at the Interface with Biocatalysis: Chemoselective Reduction of Biomimetic NAD+ Cofactors with [Cp*Rh(bpy)H]+, Tandem Catalysis with 1,4-NADH-Dependent Enzymes, Chiral Synthesis, Organotin Metabolites, and DFT Mechanism Studies

This Review will focus on our studies of the utilization of the [Cp*Rh(bpy)H]+ complex as a biomimetic hydrogenase, regeneration reagent for chemoselective reduction of biomimetic NAD+ cofactors, N-benzylnicotinamide triflate, 1, β-nicotinamide ribose-5′-methyl phosphate, 2, and natural NAD+, 3, in the conversion to their 1,4-NADH analogues, 1,4-dihydro-N-benzylnicotinamide, 4, and β-1,4-dihydronicotinamide-5′-ribose methyl phosphate, 5, and natural 1,4-NADH, 6, respectively. This regeneration reaction with 1,4-NADH biomimetics 4 and 5 was used in tandem with 1,4-NADH-dependent enzymes for organic synthesis. The enzyme examples will encompass horse liver alcohol dehydrogenase (HLADH) reductions of prochiral ketones to chiral S-alcohols; cytochrome P450 enzymes for selective C–H oxidation reactions of organic compounds, and organometallic substrates, tributyltin acetate and cyclohexyltriphenyltin, with 1,4-NAD(P)H; and the biomimetic 1,4-NADH cofactor, 4, with the 2-hydroxybiphenyl-3-monooxygenase enzyme, HbpA, a FAD-containing monooxygenase enzyme, for hydroxylation of ortho-substituted phenols to catechols. This Review also includes discussions on in-depth DFT mechanism studies, and other chemical mechanistic aspects, of all tandem catalytic reactions that demonstrate, utilizing a simplified model of the HLADH-Zn(II)-mediated enzyme, the unprecedented role of Zn(II) in the hydride transfer reaction. Moreover, site-directed mutagenesis with 1,4-NAD(P)H-dependent cytochrome P450 BM-3 improved the molecular recognition process for biomimetic 1,4-NADH cofactors in organic compound C–H oxidation reactions. The 1,4-NADH-dependent cytochrome P450 CAM recognized the biomimetic 1,4-NADH cofactors; however, site-directed mutagenesis of the putidaredoxin reductase (PdR) component increased the kinetics for the C–H oxidation reaction of camphor. Cyclohexyltriphenyltin demonstrated the differences in hydroxylation regioselectivity, when comparing the cytochrome P450 enzyme with biomimetic P450 porphyrin Fe(III) and Mn(III) models. The biomimetic 1,4-NADH cofactor, 1,4-dihydro-N-benzylnicotinamide, 4, was also utilized as a reducing agent, providing the reduced, chemoselective coenzyme, the FADH– anion, that further reacts with O2/H+ to provide the 4α-hydroperoxide flavin, for the HbpA enzymatic oxidative conversion of ortho-substituted phenols to catechols.

A turn-on fluorescence assay of tyrosinase activity based on an enzyme-triggered hydroxylation of phenol for conformation of silicon nanoparticles

Evolution of fluorometric sensing methods has brought an enormous opportunity and exhibited novel potentials for enzymatic activities determination. Herein, we have established an accurate and straightforward fluorescent sensing approach for tyrosinase (TYR) activity based on the formation of fluorescent silicon nanoparticles (Si NPs). Influenced by TYR-induced hydroxylation of phenol into catechol, and an easy reaction between catechol and 3(2-aminoethylamino) propyl (dimethoxymethylsilane) (AEAPDMMS) to generate Si NPs, we have designed a label-free fluorescence turn-on probe for TYR activity measurement. After optimization of all reaction parameters, the proposed approach could selectively determine TYR activity in the linearity range of 0.08–9 U mL−1 with the limit of detection (LOD) of 0.03 U mL−1. The practicability of the method in real sample was assessed by measuring TYR activity in human serum sample with successful results. In addition, Si NPs were wonderfully acceptable for Hela and SiHa cells imaging by virtue of their tolerable cytotoxicity and impressive biocompatibility. Therefore, the designed fluorescent biosensor exhibited a potential and widespread implementation in clinical diagnoses assays.

Two-step synthesis of Ti-rich surface TS-1 with controllable microenvironment of titanium species

It is significant to improve the catalytic activity of TS-1 by increasing the content of framework titanium and enhancing the accessibility of active titanium sites. However, developing a simple and economical strategy for modulating the coordination environments and the spatial distribution of titanium species is still a challenge. Here, we constructed anatase-free TS-1 with abundant framework titanium species and Ti-rich surface by a simple two-step crystallization strategy. The effects of the crystallization temperature and time of the first stage on the properties of zeolite have been investigated in detail. The TS-1 with a Ti-rich surface showed a higher conversion of phenol and selectivity to dihydroxylbenzene in phenol hydroxylation reaction compared with traditional TS-1, and it still remained the superior catalytic performance after five cycles. The novel strategy will provide a new perspective for the construction of TS-1 with controllable active Ti species.

Synthesis of ultra-fine TS-1 catalyst with high titanium content and its performance in phenol hydroxylation

The study of simultaneous control over framework Ti and particle size was achieved using the incorporation of NH4HCO3 and PVA into the synthesis medium of the TS-1 catalyst.

Catalytic oxidation performance and ion-exchange of Ti-MWW zeolite membrane with dual organic template agents and potassium carbonate

In the absence of boric acid, the tubular Ti-MWW zeolite membranes are prepared with dual organic template agents and potassium carbonate by secondary hydrothermal synthesis. 12MR cage and 10 MR of the MWW zeolite topology structure is stabilized by TMAdaOH and HMI organic template agents, K+ cations is a critical mineralization agent for preparing Ti-MWW zeolite membrane with bi-layer Ti-MWW zeolites layer in this work. Besides, ion-exchange could greatly improve the catalytic performance of the Ti-MWW zeolite membrane for phenol hydroxylation with H2O2, influences of ammonium salt, ion-exchange time and temperature on the micro-structure and catalytic performance are investigated. The upper network-like Ti-MWW zeolite layer could be dissolved and removed by ion-exchange with 0.5 M (NH4)2SO4 solution at 60 °C for 24 h, and the “lying” Ti-MWW zeolites layer is kept on the mullite support. On the other hand, ion-exchange could promote the transformation of hexacoordinated extra-framework titanium species to tetracoordinated state in the framework, part of K+ cations of Ti-MWW zeolites are replaced with NH4+ cations. Total flux and phenol conversion of the ion-exchanged Ti-MWW zeolite membrane are 14.89 kg·m−2·h−1 and 36.49 % for phenol hydroxylation by H2O2 at 50 °C.

Improving the catalytic and mechanical performance of alginate catalyst through functionalization by aminopolycarboxylic acids.

Biomass-based aerogel catalysts have attracted extensive attention due to their high surface aera, continuous porous and environmental friendliness. However, their catalytic activity and mechanical strength are not satisfied for industrial applications. In this work, to solve the above two issues, a new kind of graphene oxide enhancediminodiacetic acid-functionalized Cu-cross-linked alginate (GO-Cu-SA-IDA) aerogel composites were prepared. The physicochemical property of the prepared alginate aerogel composites was characterized systematically, and their catalytic activities were studied in the hydroxylation of phenol. Results illustrated that compared with Cu-SA aerogels (∼16%), the amount of loaded copper ion which played as the active sites in GO-Cu-SA-IDA aerogel composite was increased by 2 times (32.2%). In addition, the mechanical strength of GO-Cu-SA-IDA was increased by 10 times. After functionalization, both the catalytic activity and mechanical strength of prepared alginate aerogel composites were enhanced successfully. In addition, the catalyst had been recycled five times with only 5.8% loss of its catalytic activity, which provided a desirable material for next generation of catalysts.

A Novel Bimetal Cu–Fe Nano-Silica Catalyst Synthesis by Supercritical Method and Its High Catalytic Activity for Phenol Hydroxylation

A Novel Bimetal Cu–Fe Nano-Silica Catalyst Synthesis by Supercritical Method and Its High Catalytic Activity for Phenol Hydroxylation

Recent advances in the synthesis of TS-1 zeolite.

Heteroatomic zeolites as an important class of zeolites, have been widely applied in industrially catalytic processes due to their unique properties. As one of the most representative heteroatomic zeolites, titanosilicate zeolites have been extensively used in the selective oxidations of organic substrates with H2O2 such as cyclohexanone ammoximation, epoxidation of alkenes, and phenol hydroxylation. In this review, recent advances in the synthesis of TS-1 zeolite are briefly summarized, including use of low-cost raw materials (organic templates, silicon, and titanium sources), development of new synthesis routes (post-treatment synthesis, dry-gel conversion synthesis, solvent-free synthesis, and microwave-assisted synthesis), and new strategy for enhanced mass transfer in TS-1 crystals (synthesis of hierarchical and nanosized TS-1 zeolite). This review might help researchers to have a deep understanding on the synthesis of TS-1 zeolite and provide a new opportunity for the design and preparation of highly efficient TS-1 catalysts in the future.

Bulky macroporous titanium silicalite-1 free of extraframework titanium for phenol hydroxylation

A bulky composite material, CaCO 3 @TS-1, was synthesized in a tetrapropylammonium bromide hydrothermal system by adding nanosized CaCO 3 particles of 60–80 nm to a titanium silicalite-1 (TS-1) synthesis gel. The macroporous TS-1 free of extraframework Ti was then obtained by the posttreatment of the CaCO 3 @TS-1 in HCl solution to remove CaCO 3 and extraframework Ti simultaneously. This study demonstrates that this new synthesis route, the acidity posttreatment, can produce a bulky TS-1 with volume-controllable intracrystal macropores. The crystallization mechanism of the macroporous TS-1 was studied systematically. The addition of CaCO 3 accelerates the crystallization of silicon source, and leads to the similar crystallization rates of silicon and titanium sources. Therefore, the formation of extraframework Ti was inhibited, and more Ti ions were inserted into the TS-1 framework. The catalytic performance of macroporous TS-1 was evaluated in the hydroxylation of phenol. An outstanding catalytic activity was obtained due to their enhanced diffusion property and reduced extraframework Ti. • Bulky macroporous TS-1 free of extraframework Ti was obtained by acidity treatment. • The macroporous volume can be controlled by tuning the CaCO 3 adding amount. • The addition of CaCO 3 accelerates the crystallization of silicon source. • An outstanding activity for phenol hydroxylation was obtained on macroporous TS-1.

Computational Investigation of the Bisphenolic Drug Metabolism by Cytochrome P450: What Factors Favor Intramolecular Phenol Coupling.

Intramolecular phenol coupling reactions of alkaloids can lead to active metabolites catalyzed by the mammalian cytochrome P450 enzyme (P450); however, the mechanistic knowledge of such an "unusual" process is lacking. This work performs density functional theory computations to reveal the P450-mediated metabolic pathway leading from R-reticuline to the morphine precursor salutaridine by exploring possible intramolecular phenol coupling mechanisms involving diradical coupling, radical addition, and electron transfer. The computed results show that the outer-sphere electron transfer with a high barrier (>20.0 kcal/mol) is unlikely to happen. However, for inter-sphere intramolecular phenol coupling, it reveals that intramolecular phenol coupling of R-reticuline proceeds via the diradical mechanism consecutively by compound I and protonated compound II of P450 rather than the radical addition mechanism. The existence of a much higher radical rebound barrier than that of H-abstraction in the quartet high-spin state can endow the R-reticuline phenoxy radical with a sufficient lifetime to enable intramolecular phenol coupling, while the H-abstraction/radical rebound mode with a negligible rebound barrier leading to phenol hydroxylation can only happen in the doublet low-spin state. Therefore, the ratio [coupling]/[hydroxylation] can be approximately reflected by the relative yield of the high-spin and low-spin H-abstraction by P450, which thus can provide a theoretical ratio of 16:1 for R-reticuline, which is in accordance with previous experimental results. Especially, the high rebound barrier of the phenoxy radical derived from the weak electron-donating ability of the phenoxy radical is revealed as an intrinsic nature. Therefore, the revealed intramolecular phenol coupling mechanism can be potentially extended to several other bisphenolic drugs to infer groups of unexpected metabolites in organisms.

Engineered Bacterial Flavin-Dependent Monooxygenases for the Regiospecific Hydroxylation of Polycyclic Phenols.

4‐Hydroxyphenylacetate 3‐hydroxylase (4HPA3H), a flavin‐dependent monooxygenase from E. coli that catalyzes the hydroxylation of monophenols to catechols, was modified by rational redesign to convert also more bulky substrates, especially phenolic natural products like phenylpropanoids, flavones or coumarins. Selected amino acid positions in the binding pocket of 4HPA3H were exchanged with residues from the homologous protein from Pseudomonas aeruginosa, yielding variants with improved conversion of spacious substrates such as the flavonoid naringenin or the alkaloid mimetic 2‐hydroxycarbazole. Reactions were followed by an adapted Fe(III)‐catechol chromogenic assay selective for the products. Especially substitution of the residue Y301 facilitated modulation of substrate specificity: introduction of nonaromatic but hydrophobic (iso)leucine resulted in the preference of the substrate ferulic acid (having a guaiacyl (guajacyl) moiety, part of the vanilloid motif) over unsubstituted monophenols. The in vivo (whole‐cell biocatalysts) and in vitro (three‐enzyme cascade) transformations of substrates by 4HPA3H and its optimized variants was strictly regiospecific and proceeded without generation of byproducts.

Monolithic Stirrer Reactors for the Sustainable Production of Dihydroxybenzenes over 3D Printed Fe/γ-Al2O3 Monoliths: Kinetic Modeling and CFD Simulation

The aim of this work is to evaluate the performance of the stirring 3D Fe/Al2O3 monolithic reactor in batch operation applied to the liquid-phase hydroxylation of phenol by hydrogen peroxide (H2O2). An experimental and numerical investigation was carried out at the following operating conditions: CPHENOL,0 = 0.33 M, CH2O2,0 = 0.33 M, T = 75–95 °C, P = 1 atm, ω = 200–500 rpm and WCAT ~ 1.1 g. The kinetic model described the consumption of the H2O2 by a zero-order power-law equation, while the phenol hydroxylation and catechol and hydroquinone production by Eley–Rideal model; the rate determining step was the reaction between the adsorbed H2O2, phenol in solution with two active sites involved. The 3D CFD model, coupling the conservation of mass, momentum and species together with the reaction kinetic equations, was experimentally validated. It demonstrated a laminar flow characterized by the presence of an annular zone located inside and surrounding the monoliths (u = 40–80 mm s−1) and a central vortex with very low velocities (u = 3.5–8 mm s−1). The simulation study showed the increasing phenol selectivity to dihydroxybenzenes by the reaction temperature, while the initial H2O2 concentration mainly affects the phenol conversion.

A bimetallic synergistic effect on the atomic scale of defect-enriched NiV-layered double hydroxide nanosheets for electrochemical phenol hydroxylation

Defect-enriched NiV-LDH-NS with a bimetallic synergistic effect were prepared by a one-step co-precipitation strategy and the electron-rich defects accelerated the formation of hydroxyl radicals (˙OH) to participate in the phenol hydroxylation.

Singlet oxygen synergistic surface-adsorbed hydroxyl radicals for phenol degradation in CoP catalytic photo-Fenton

In recent years, there have been numerous studies on Fenton or Fenton-like reactions mediated by nonfree radicals such as singlet oxygen (1O2); however, there are few studies on the synergistic effect of 1O2 and free radicals on the degradation of organic molecules, such as phenol in Fenton reaction. In this study, a cocatalyst, CoP, commonly used in photocatalysis was synthesized using a simple two-step method, and a CoP/Fe2+/AM1.5 system was constructed by introducing Fe2+ and simulated sunlight (AM1.5) irradiation. The newly constructed CoP/Fe2+/AM1.5 system could effectively degrade various organic pollutants, including dyes, phenols, and antibiotics. Radical quenching experiments and electron paramagnetic resonance detection confirmed that there were three reactive oxygen species (ROS) in the CoP/Fe2+/AM1.5 system, including •OHads, •O2−, and 1O2. Further, combined with the liquid chromatogram of phenol, its intermediate products, and the fluorescence diagram of o-hydroxybenzoic acid, it can be concluded that a synergistic effect exists between 1O2 and the surface-adsorbed ·OHads in the CoP/Fe2+/AM1.5 system. The controllable formation of surface 1O2 and •OHads was achieved through the oxidation (Co3+) and reduction (Pδ−) centers exposed on the CoP surface, and the synergistic effect between them results in phenol's hydroxylation, ring-opening, and degradation. The study of this new mechanism provides a new perspective for revealing the surface interface reaction between ROS and organic pollutants.

Preparation and catalytic performance of TS-2 zeolite membrane

Compact and tubular TS-2 zeolite membrane is successfully fabricated on the mullite support by secondary hydrothermal synthesis. The mullite supports are fully covered by the aggregated walnut-shaped TS-2 zeolite crystals, which are the aggregates of fine and rod-shaped crystals and have high BET surface area, total pore capacity and mesoporous volume by advance isothermal characterization. The incorporation of the Ti atoms in framework positions of the MEL zeolite lattice and mainly form tetrahedrally coordinated titanium. Besides, influence of the crystallization temperature and time on the growth and catalytic performance are investigated in this work. The as-synthesized TS-2 zeolite membrane has a good catalytic performance for phenol hydroxylation by hydrogen peroxide. When the reaction temperature and molar ratio of phenol/hydrogen peroxide are 50 °C and 2, the flux, phenol conversion and dihydroxybenzene selectivity of TS-2 zeoite membrane are 6.43 kg m −2 h −1 , 32.23% and 99.88%, respectively. • Compact and tubular TS-2 zeolite membrane is successfully prepared. • Aggregated walnut-shaped TS-2 zeolites have high BET surface area, total pore capacity and mesoporous volume. • TS-2 zeolite membrane has a good catalytic performance for phenol hydroxylation by hydrogen peroxide. • Flux, phenol conversion and dihydroxybenzene selectivity of TS-2 zeoite membrane are 6.43 kg m −2 h −1 , 32.23% and 99.88%.

One-step controllable strategy for synthesizing hierarchical Fe-MFI/MCM-41 composites using CTAB as a dual-functional template

Hierarchical Fe-doped MFI/MCM-41 composites (Fe-HMZs) were one-pot hydrothermal synthesized by partial transformation strategy using conventional CTAB as a dual-functional template. The hierarchical Fe-doped MFI/MCM-41 composites possess ordered mesopores and crystallized MFI structure. The effect of addition amount of NaOH and CTAB as well as the type of the alkali source on the formation of hierarchical Fe-MFI/MCM-41 composites have been investigated in detail. In addition, the temperature-gradient treatment plays the vital roles in the formation of MFI and the possible formation mechanism has been proposed. The obtained hierarchical Fe-HMZ-40 sample exhibits outstanding catalytic performance for phenol hydroxylation and 48% of phenol conversion as well as 89% of dihydroxybenzene selectivity could be achieved, which are ascribed to the more accessible active sites endowed by the significant diffusion ability of ordered mesopores. Compared with Fe-MCM-41 sample, the hydrothermal stability is improved because of the presence of MFI structure.

A Green Synthesis Technique for Superoxide (O2-) Active Site of Cuxsn100-X Intermetallic Catalysts Prepared by Mechanical Alloying for Phenol Hydroxylation to Catechol: An in Situ Xas Investigation

A Green Synthesis Technique for Superoxide (O2-) Active Site of Cuxsn100-X Intermetallic Catalysts Prepared by Mechanical Alloying for Phenol Hydroxylation to Catechol: An in Situ Xas Investigation