Hydroxylation Of Phenol Research Articles

A Heme Peroxidase with a Functional Role as an l-Tyrosine Hydroxylase in the Biosynthesis of Anthramycin

We report the first characterization and classification of Orf13 (S. refuineus) as a heme-dependent peroxidase catalyzing the ortho-hydroxylation of L-tyrosine to L-DOPA. The putative tyrosine hydroxylase coded by orf13 of the anthramycin biosynthesis gene cluster has been expressed and purified. Heme b has been identified as the required cofactor for catalysis, and maximal L-tyrosine conversion to L-DOPA is observed in the presence of hydrogen peroxide. Preincubation of L-tyrosine with Orf13 prior to the addition of hydrogen peroxide is required for L-DOPA production. However, the enzyme becomes inactivated by hydrogen peroxide during catalysis. Steady-state kinetic analysis of L-tyrosine hydroxylation revealed similar catalytic efficiency for both L-tyrosine and hydrogen peroxide. Spectroscopic data from a reduced-CO(g) UV-vis spectrum of Orf13 and electron paramagnetic resonance of ferric heme Orf13 are consistent with heme peroxidases that have a histidyl-ligated heme iron. Contrary to the classical heme peroxidase oxidation reaction with hydrogen peroxide that produces coupled aromatic products such as o,o'-dityrosine, Orf13 is novel in its ability to catalyze aromatic amino acid hydroxylation with hydrogen peroxide, in the substrate addition order and for its substrate specificity for L-tyrosine. Peroxygenase activity of Orf13 for the ortho-hydroxylation of L-tyrosine to L-DOPA by a molecular oxygen dependent pathway in the presence of dihydroxyfumaric acid is also observed. This reaction behavior is consistent with peroxygenase activity reported with horseradish peroxidase for the hydroxylation of phenol. Overall, the putative function of Orf13 as a tyrosine hydroxylase has been confirmed and establishes the first bacterial class of tyrosine hydroxylases.

A Novel Dual-Membrane Reactor for Continuous Heterogeneous Oxidation Catalysis

A novel dual-membrane reactor is proposed for heterogeneous catalysis over ultrafine catalyst particles. In this reactor, one tubular porous ceramic membrane is employed as a distributor controlling the supply of reactant, while the other is employed as a membrane separator for in situ separation of ultrafine catalysts from the products. To evaluate the feasibility and the performance of the dual-membrane reactor, phenol hydroxylation with hydrogen peroxide (H2O2) over TS-1 catalyst was selected as a model reaction. As compared to traditional H2O2 feeding modes, the use of the porous ceramic membrane distributor allows a uniform injection of H2O2 into the reaction system, and as a result significantly promotes the dihydroxybenzene selectivity. The phenol conversion and the DHB selectivity above 15% and about 95%, respectively, can be achieved in a continuous operation of 30 h. TS-1 catalysts can be retained almost completely in the reactor system by the membrane separator. Our study demonstrates the advan...

Hydroxylation of phenol over rare earth exchanged iron pillared montmorillonites

Iron pillared montmorillonite prepared by partial hydrolysis method was exchanged with La, Ce and Th metal salts. The pillared montmorillonite showed considerable increase in basal spacing and surface area. EDAX showed presence of about 2% rare earth metals. 27Al and 29Si NMR spectra showed relaxation effects due to iron paramagnetic centres. The prepared systems are excellent catalysts for hydroxylation of phenol underlining the use of environmentally friendly clay catalysts for effective removal of pollutants. A detailed study of reaction variables suggests that oxidation of phenol increases with temperature and maximum conversion is obtained at 80 °C. Hydroquinone selectivity increases with phenol and solvent concentrations but decreases with time.

Self-assembly of copper and cobalt complexes with hierarchical size and catalytic properties for hydroxylation of phenol

A feasible and effective self-assembly method to synthesize different scale coordination polymers in highly dilute solution (from nanocrystals to microcrystals and to bulk crystals) without any blocking agent has been described. The growth of crystalline particles was controlled by removing the particles at different reaction times to interrupt the growth at the desired size. The nano and microscale particles show better catalytic conversions and selectivities in the hydroxylation of phenols than the bulk crystals.

Fe-containing nickel phosphate molecular sieves as heterogeneous catalysts for phenol oxidation and hydroxylation with H2O2

Fe-containing nickel phosphate molecular sieves (Fe-VSB-5) were hydrothermally synthesized in weak basic conditions under microwave irradiation and characterized by SEM, XRD, N2-adsorption/desorption, DRS-UV–vis, and FT-IR spectroscopy using PhCN and CDCl3 as probe molecules. The catalytic activity of Fe-VSB-5 was tested for the phenol hydroxylation and wet phenol oxidation with H2O2. The increase in iron content in Fe-VSB-5 leds to an increase in the reaction rates. The increases in activity can be explained by the role of the Fe species, which increases the generation of radicals. The Fe-VSB-5 samples were stable against the leaching out of Fe ions. The catalytic activity of Fe-VSB-5 was compared to the catalytic activity of traditional Fe-containing materials.

Synthesis and Catalytic Properties of FeZSM-35 Zeolites Directed by Alkyl-polyamine Triethylene-tetramine

Using a long alkyl-polyamine triethylene-tetramine as structure-directing agent, FeZSM-35 zeolites were synthesized and characterized by XRD, SEM, FTIR and TG-DTA techniques. EDS and ICP-AES indicate that the transition metal iron ions were framework elements and the mass fraction was 0.48%. The catalytic activity of as-synthesized crystals was examined for the aqueous hydroxylation of phenol with hydrogen peroxide. The phenol conversion was 18.8% and the selectivity on catechol and hydroquinone was ca. 69.1% and 30.9%, respectively. The as-synthesized FeZSM-35 zeolites show relative high selectivity towards catechol and could be a promising catalyst.

Synthesis of Titanium Silicalite-1 with Small Crystal Size by Using Mother Liquid of Titanium Silicalite-1 As Seed

Titanium silicalite-1 (TS-1) with small crystal size was synthesized in a TPABr-ethylamine system using the mother liquid of nanosized TS-1 as seed. The as-synthesized small-crystal TS-1, the size of which was about 600 nm × 400 nm × 250 nm was characterized with X-ray diffraction (XRD), Fourier transform-infrared (FT-IR), ultraviolet–visible (UV–vis), UV-Raman, N2 sorption, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Its catalytic performance was evaluated in the epoxidation of propylene and the hydroxylation of phenol. The conversion of hydrogen peroxide and selectivity of propylene oxide (PO) in the propylene epoxidation reached 92 and 98 mol %, respectively. In the hydroxylation of phenol, small-crystal TS-1 also resulted in a high conversion of phenol.

Tale of a Twist: Magnetic and Optical Switching in Copper(II) Semiquinone Complexes

An intermediate (C) that is observed in both phenol hydroxylation and catechol oxidation with the side-on peroxide species [Cu(2)O(2)(DBED)(2)](2+) (DBED = N(1),N(2)-di-tert-butylethane-1,2-diamine) is identified as a copper(II) semiquinone species ([1](+)) through independent synthesis and characterization. The reaction of the redox-active 3,5-di-tert-butylquinone ligand with [(DBED)Cu(I)(MeCN)](+) yields a copper(II) semiquinone [1](+) complex with a singlet ground state and an intense purple chromophore (ε(580) ~ 3500 M(-1) cm(-1)). All other copper(II) semiquinone complexes characterized to date are paramagnetic and weakly colored (ε(800) ~ 500 M(-1) cm(-1)). Antiferromagnetic coupling between the Cu(II) center and the semiquinone radical in [1](+) is characterized by paramagnetic (1)H NMR and SQUID magnetometry. Comparative X-ray crystal structures along with density functional theory calculations correlate the geometric structures of copper(II) semiquinone complexes with their magnetic and optical properties. The unique observable properties of [1](+) originate from an increase in the overlap of the Cu 3d and semiquinone π orbitals resulting from a large rhombic distortion in the structure with a twist of 51°, attributable to the large isotropic demands of the tert-butyl substituents of the DBED ligand. Independent characterization of [1](+) allows the spectroscopic yields of intermediate C to be quantified in this intriguing hydroxylation reaction.

Synthesis of mesoporous zeolite single crystals with cheap porogens

Mesoporous zeolite (silicalite-1, ZSM-5, TS-1) single crystals have been successfully synthesized by adding soluble starch or sodium carboxymethyl cellulose (CMC) to a conventional zeolite synthesis system. The obtained samples were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), nitrogen sorption analysis, 27Al magic angle spinning nuclear magnetic resonance ( 27Al MAS NMR), temperature-programmed desorption of ammonia (NH 3-TPD) and ultraviolet–visible spectroscopy (UV–vis). The SEM images clearly show that all zeolite crystals possess the similar morphology with particle size of about 300 nm, the TEM images reveal that irregular intracrystal pores are randomly distributed in the whole crystal. 27Al MAS NMR spectra indicate that nearly all of the Al atoms are in tetrahedral co-ordination in ZSM-5, UV–vis spectra confirm that nearly all of titanium atoms are incorporated into the framework of TS-1. The catalytic activity of meso-ZSM-5 in acetalization of cyclohexanone and meso-TS-1 in hydroxylation of phenol was also studied. The synthesis method reported in this paper is cost-effective and environmental friendly, can be easily expended to prepare other hierarchical structured zeolites.

수열 합성법과 마이크로파 가열법으로 제조한 TS-1 촉매에 의한 페놀 수산화 반응: 용매의 영향

수열 합성법과 마이크로파 가열법으로 제조한 TS-1의 촉매 성능 평가를 과산화수소수를 이용한 페놀 수산화 반응 에서 수행하였는데 아세톤과 메탄올 및 물의 세 가지 용매를 사용하여 각 용매에서의 페놀 전환율과 생성물의 선택도 변화를 관찰하였다. 수열 합성법으로 제조한 TS-1과 마이크로파 가열법으로 합성한 TS-1의 XRD, EDS, SEM, BET 흡착/탈착 시험을 통해 촉매의 특성을 비교.분석하였고 마이크로파 가열법으로 합성한 TS-1이 수열 합성으로 제조한 TS-1과 상이한 페놀 전환율과 생성물의 선택도를 보이는 이유에 대해서 설명하였다. Catalytic activity such as conversion and selectivity on the phenol hydroxylation over TS-1 prepared by hydrothermal method and microwave heating method, respectively, was compared and discussed for understanding the dependence of solvent such as water, methanol, acetone, respectively, during phenol hydroxylation, with hydrogen peroxide. Basic physical properties such as XRD, EDS, SEM and <TEX>$N_{2}$</TEX> adsorption/desorption were determined and compared. The relationship between catalytic activity and physical properties of TS-1 was explained.

Hydroxylation of phenol with hydrogen peroxide in protic and aprotic solvents on TS-1 catalyst

Hydroxylation of phenol with a 25% aqueous solution of hydrogen peroxide in polar protic and aprotic solvents on TS-1 heterogeneous catalyst under various conditions was studied. The major reaction products (hydroquinone, pyrocatechol) and their ratio were determined. A kinetic model describing the hydroxylation in accordance with the Rideal-Eley mechanism was chosen.

Photocatalytic hydroxylation of phenol with Fe–Al-silicate photocatalyst: A clean and highly selective synthesis of dihydroxybenzenes

Abstract Photocatalytic hydroxylation of phenol to catechol and hydroquinone in liquid phase over a novel heterogeneous photocatalyst Fe–Al-silicate was investigated with the assistance of UV irradiation at 365 nm at room temperature. The catalyst was characterized by BET, BJH, FT-IR, UV–vis DRS and XRD. The effects of various parameters (types and amount of co-solvent, amount of catalyst, reaction time and amount of H 2 O 2 ) on photocatalytic hydroxylation of phenol were studied to explore the better reaction conditions. In this study, phenol conversion could reach high up to 64.9%, with a total selectivity of 95% and the yield of 39.3%, 22.3% for catechol and hydroquinone, respectively.

Mordenite modification and utilization as supports for iron catalyst in phenol hydroxylation

The goal of this work was to synthesize mordenite in sodium form (NaMOR) using rice husk silica; modify by leaching with acid, base or both; and use the obtained zeolites as supports for iron (Fe) catalysts in phenol hydroxylation. All MOR zeolites were characterized by X-ray diffraction (XRD), nitrogen adsorption/desorption and the Si/Al ratios were determined by Inductively Coupled Plasma-Mass Spectrometry (ICP-MS). The influence of zeolite modification to the phenol hydroxylation was also studied. All modified zeolites still exhibited MOR phase with higher surface area than that of the parent NaMOR. Only the sample leached by acid and base (ABMOR) showed a significant change in adsorption–desorption isotherm from type I to type IV, a characteristic of mesoporous materials. The major forms of Fe (5 wt.%) in all catalysts confirmed by XRD and X-ray Absorption Near Edge Structure (XANES) were Fe 2O 3. Because mesopores were generated in ABMOR to facilitate diffusion of reactants, the fastest reaction was obtained on Fe/ABMOR catalyst. The conversion was also highest on this catalyst probably because Fe was dispersed on the support with the highest surface area. However, the presence of mesopores did not improve the selectivity and the products observed were catechol and hydroquinone.

Microporous carbon molecular sieve as a novel catalyst for the hydroxylation of phenol

A series of microporous carbon-based catalysts were prepared by acidification and/or oxidization treatment of a commercially available carbon molecular sieve (CMS). The resultant samples were characterized by Boehm titration, X-photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), point of zero charge (pH PZC) test, N 2 adsorption, and inductively coupled plasma atomic emission spectrometry (ICP-AES), and employed as catalysts for phenol hydroxylation with H 2O 2. It is found that the acidic functional groups of CMSs play an important role for the catalytic performance. The effects of solvents, reaction temperature, ratio of phenol/catalyst, ratio of phenol/H 2O 2 and reaction time were investigated. Over the sample with the strongest surface acidity among the studied CMSs, the phenol conversion, the selectivity to dihydroxybenzene, and the effective utilization of H 2O 2 reach 29.6%, 85.1% and 80%, respectively under optimal reaction condition. The catalyst is stable in the recycling test. Furthermore, due to its easy physical separation, environmental benignity and low cost, the microporous CMSs is promising for industrial application.

Catalytic activity of unsaturated coordinated Cu-MOF to the hydroxylation of phenol

A 2D metal-organic framework [Cu 2 (BPTC) (Im) 4(H 2O) (DMF)] n ( 1) with unsaturated coordinated Cu(II) sites has been prepared under solvothermal condition, and applied to the hydroxylation of phenol after activating. The catalytic results indicate that 1a (the activated 1) exhibits an obvious activity for phenol hydroxylation at 40 °C for 4 h. Compared to the control experiments where the free Cu(II) (from Cu(OAc) 2 salt) has been utilized as the catalysts, 1a shows the higher selectivity to diphenols. This suggests that the coordinated environment of unsaturated coordinated Cu(II) sites in the 2D layer play the key role in the phenol hydroxylation.

Hydroxylation of Phenol with Hydrogen Peroxide over the Ti-MWW Catalyst in the Presence of Acetonitrile

AbstractThis work presents the results of phenol hydroxylation with hydrogen peroxide over the Ti-MWW catalyst. The studies were carried out under autogenic pressure and in the presence of acetonitrile as a solvent. The influence of the following technological parameters on the course of hydroxylation was examined: the temperature in the range of 100-150 °C, the molar ratio of phenol/H

One-step synthesis of Ti-MSU and its catalytic performance on phenol hydroxylation

In this study, high-quality Ti-MSU was synthesized by a convenient one-step hydrothermal synthesis procedure. This is the first detailed study on the role of addition time of a Ti source. We found that the addition time of the Ti source can effectively influence the structure and morphology of the product by adjusting the balance of hydrolysis–polymerization and nucleation–aggregation in different self-assembly steps. The optimum synthesized Ti-SMU sample showed a good catalytic performance on the phenol hydroxylation.

Facile Synthesis of Bi2O3/TiO2−xNx and its Direct Solar‐Light‐Driven Photocatalytic Selective Hydroxylation of Phenol

AbstractMesoporous Bi2O3/TiO2−xNx nanocomposites (BiNT) have been synthesized by using a template‐free homogeneous coprecipitation technique. X‐ray diffraction, X‐ray photoelectron spectroscopy, high‐resolution transmission electron microscopy, UV/Vis diffuse reflectance spectroscopy, and photoluminescence studies are adapted to characterize the structural, electronic, and optical properties of the composites. The photocatalytic activities of the catalysts are evaluated for the hydroxylation of phenol under direct solar irradiation. The BiNT materials show excellent catalytic activity for selective phenol hydroxylation without using any oxidant. Notably, one of the nanocomposites shows a very high activity and results in a phenol conversion of 99 % in aqueous medium with 100 % selectivity towards hydroquinone and, in general, excellent selectivity is found for dihydroxybenzene compounds. The heterogeneous catalysts exhibit a successive slight decrease in catalytic activity if reused for five or more times.

One-Pot Synthesis and Characterization of Cu-SBA-16 Mesoporous Molecular Sieves as an Excellent Catalyst for Phenol Hydroxylation

Cu-SBA-16 has been prepared by one-pot synthesis method, and Characterized by XRD, TEM, and N2 adsorption measurements. An extended study about the nature of copper species in the Cu-SBA-16 has been performed by FT-IR, UV-DRS, H2-TPR and XPS. The copper species is mainly present on the mesoporous SBA-16 in the form of isolated mononuclear Cu2+ ions and highly dispersive CuO nanoclusters. The excellent catalytic activity has been obtained for phenol hydroxylation due to the presence of high amount of highly dispersive Cu species. The conversion to phenol and selectivity to diphenol are 29.4 and 91.5%, respectively. A simple EISA strategy for direct synthesis of mesoporous Cu-SBA-16 containing isolated mononuclear Cu2+ ions and highly dispersive CuO clusters which shows an excellent catalytic performance for phenol hydroxylation.

Comparasion of Different Catalysts on Phenol Hydroxylation

Fe2O3,heteropoly salt and Fe/ZrO2 exhibited high catalytic activity toward phenol hydroxylation using H2 O2 as oxidant.A rapid hydroxylation of phenol was observed after an induction period in the hydroxylation of phenol catalyzed by Fe2 O3;however,a slow hydroxylation of phenol was observed and the induction period disappeared in the same system catalyzed by heteropoly salt or Fe/ZrO2.The results suggest that,first,an induction period in hydroxylation of phenol is related to the formation of active species Fe3+and Fe2+ from Fe2O3;and second,the slow hydroxylation is related to the surface catalysis reaction on heteropoly salt or Fe/ZrO2,leading to the disappearance of the induction period.