Hydroxylation Of Benzene Research Articles

Photochemical Formation of Hydroxyl Radical from Effluent Organic Matter

The photochemical formation of hydroxyl radical (HO•) from effluent organic matter (EfOM) was evaluated using three bulk wastewater samples collected at different treatment facilities under simulated sunlight. For the samples studied, the formation rates of HO•(R(HO•)) were obtained from the formation rate of phenol following the hydroxylation of benzene. The values of R(HO•) ranged from 2.3 to 3.8 × 10(-10) M s(-1) for the samples studied. The formation rate of HO• from nitrate photolysis (R(NO3)(HO•)) was determined to be 3.0 × 10(-7) M(HO)• M(NO3)(-1) s(-1). The HO• production rate from EfOM (R(EfOM)(HO•)) ranged from 0.76 to 1.3 × 10(-10) M s(-1). For the wastewater samples studied, R(EfOM)(HO•) varied from 1.5 to 2.4 × 10(-7) M(HO)• M(C)(-1) (s-1) on molarcarbon basis, which was close to HO• production from nitrate photolysis. The apparent quantum yield for the formation of HO• from nitrate (Φ(NO3-HO•)(a)) was determined as 0.010 ± 0.001 for the wavelength range 290-400 nm in ultrapure water. The apparent quantum yield for HO• formation in EfOM (Φ(EfOM-HO•)(a)) ranged from 6.1 to 9.8 × 10(-5), compared to 2.99 to 4.56 × 10(-5) for organic matter (OM) isolates. The results indicate that wastewater effluents could produce significant concentrations of HO•, as shown by potential higher nitrate levels and relatively higher quantum yields of HO• formation from EfOM.

Selectivity of gold nanoparticles on the photocatalytic activity of TiO2 for the hydroxylation of benzene by water

The influence of gold nanoparticles on the photocatalytic activity (500W-medium pressure Hg lamp) of TiO2 anatase for the conversion of benzene to phenol has been studied. Au/TiO2 samples (Au loading ranging from 0.25 to 2.20wt%) were prepared by the deposition–precipitation method and characterized by chemical analysis, TEM, XRD, and Raman spectroscopy. Photocatalytic tests revealed that the presence of gold nanoparticles initially decreases the reaction rate but for longer reaction times it becomes beneficial and promotes phenol formation almost doubling the reaction yield with respect to unmodified TiO2, without increasing the percentage of hydroquinone, resorcinol and benzoquinone byproducts.

Hybrid compounds of Schiff base Cu, Fe, Co complexes with molybdovanadophoric heteropolyacids: synthesis, characterization and their catalytic performance to hydroxylation of benzene with H2O2

Hybrid compounds of molybdovanadophoric heteropolyacids and a Schiff base transition metal complex, M‐saldmp or M‐fpdmp (M = Fe(II), Co(II), Cu(II)), were successfully prepared and found to be effective catalysts for direct hydroxylation of benzene with H2O2. The synergistic effect between Schiff base metal complex and heteropolyacid plays an important role in the promotion of catalytic activity. Copyright © 2012 John Wiley & Sons, Ltd.

Catalytic Hydroxylation of Benzene to Phenol with Vanadium Containing Hexagonal Mesoporous Silica

Vanadium containing hexagonal mesoporous silica(V-HMS) catalysts with different vanadium contents were prepared by sol-gel method with ammonium metavanadate used as the starting material of vanadium,and the obtained catalysts were characterized by powder X-ray diffraction(XRD),N2-adsorption techniques and H2-temperature programmed reduction(H2-TPR).The catalytic performance for hydroxylation of benzene with H2O2 to phenol was investigated.The results indicated that vanadium species was successfully incorporated into the framework of HMS,and a uniform mesoporous structure and good dispersion were found.Meanwhile,V-HMS exhibited superior catalytic performance in the hydroxylation of benzene to phenol.The good dispersion and isolated vanadium species were beneficial to the high catalytic activity of hydroxylation of benzene to phenol.When the mass fraction of V(5.8% mass fraction)-HMS was 2%,the reaction temperature was 60 ℃,and the reaction time was 5 h,the yield and selectivity of phenol achieved 18.55% and 100%,respectively.

Catalytic Hydroxylation of Benzene to Phenol with Hydrogen Peroxide over Cesium Salts of Keggin-type Heteropoly Acids

Catalytic Hydroxylation of Benzene to Phenol with Hydrogen Peroxide over Cesium Salts of Keggin-type Heteropoly Acids

Elucidating active species and mechanism of the direct oxidation of benzene to phenol with hydrogen peroxide catalyzed by vanadium-based catalysts using DFT calculations

The mechanism by which benzene is converted to phenol through hydroxylation, catalyzed by vanadium in CH3CN is explored at the B3LYP(IEF-PCM)//B3LYP/6-311G(2d,2p) level. Three candidate catalysts are used to simulate the catalytic cycle. The solvent effectively reduces the free energy barriers of the C–H bond activation step. The binuclear vanadium species is predicted to be the main form of the operative catalyst. The cooperative role of the two vanadium centres and the dynamic charge distribution of the binuclear vanadium species are found to increase the catalytic activity. The conservation of aromaticity for the phenyl ring in the benzene or phenyl ligand is essential for the benzene hydroxylation.

Performance of vanadium based catalyst in a membrane contactor for the benzene hydroxylation to phenol

Phenol production through the direct hydroxylation of benzene with hydrogen peroxide, as oxidant, using a vanadium catalyst in a membrane reactor has been studied. The reaction was carried out in mild condition in a liquid–liquid biphasic system separated by a polypropylene membrane. This system showed high selectivity to phenol, minimizing its over-oxidation to over-oxygenated by-products. The influence of various reaction parameters such as the addition of hydrogen peroxide mode, catalyst and sulphuric acid amounts, temperature and reducing agent effects were investigated. The vanadium catalyst avoided tar formation in all the investigated experimental conditions compared to the previous system where an iron-based catalyst was used. Use of (C5H8O2)2VO as catalyst, 18mmol of hydrogen peroxide as oxidant pumped for 4h in the aqueous phase with the step-by-step feeding mode gave the best system performance in terms of yield (63.2%), selectivity to phenol (97.0%), and extraction quotient (76.4%).

Kinetics of the gas‐phase reactions of OH radicals with a series of trimethylphenols

AbstractThe kinetics of the reactions of hydroxyl (OH) radicals with 2,3,5‐trimethylphenol (235TMP), 2,3,6‐trimethylphenol (236TMP), 2,4,5‐trimethylphenol (245TMP), 2,4,6‐trimethylphenol (246TMP), and 3,4,5‐trimethylphenol (345TMP) have been investigated at 298 ± 2 K and atmospheric pressure of air using a relative rate method. The experiments were performed in a 1080 L volume photoreactor using in situ FTIR analysis to monitor the decay of the trimethylphenols and the reference compounds. The following rate coefficients (in cm3 molecule−1 s−1) were obtained at 298 ± 2 K and 1 atm of air: k(235TMP) = (1.48 ± 0.42) × 10−10; k(236TMP) = (1.35 ± 0.39) × 10−10; k(245TMP) = (1.23 ± 0.48) × 10−10; k(246TMP) = (1.67 ± 0.48) × 10−10; k(345TMP) = (1.55 ± 0.43) × 10−10. The present kinetic data are discussed in terms of OH addition reactivity trends, and comparisons are made with the reactivity trends observed for successive methylation of benzene and phenol and successive hydroxylation of benzene. © 2011 Wiley Periodicals, Inc. Int J Chem Kinet 44: 117–124, 2012

The effect of TEMPO in the hydroxylation of benzene to phenol on the [(CH 3) 4N] 4PMo 11VO 40/ascorbic acid/TEMPO/O 2 catalytic system: Formation of ascorbic acid radicals through hydrogen exchange of ascorbic acid and TEMPO

Hydroxylation of benzene to phenol in the [(CH 3) 4N] 4PMo 11VO 40/ascorbic acid/TEMPO/O 2 catalytic system was carefully investigated. UV–vis, ESR and 1H NMR studies showed ascorbic acid radicals were formed through the hydrogen exchange of ascorbic acid with TEMPO (2,2,6,6-tetramethyl-1-piperidine-N-oxyl radicals) during the reaction. In acetonitrile, the ascorbic acid would be partly oxidized to 2-hydroxy-2-buten-4-olide (α-tetronic acid, isotetronic acid, compound 1) without TEMPO. The interaction of TEMPO and ascorbic acid restrained the oxidative dissociation of ascorbic acid and promoted the rate of the hydroxylation. Aqueous acetic acid solvent can also restrain the oxidative dissociation of ascorbic acid. In aqueous acetic acid, the yield of phenol could reach 18.9% in the [(CH 3) 4N] 4PMo 11VO 40/ascorbic acid/TEMPO/O 2 catalytic system with sufficient ascorbic acid after 400 min.

Electrochemical Oxidation of Benzene to Phenol

Gas-phase electrochemistry: The direct hydroxylation of benzene to phenol was investigated using an electrochemical cell. The production of phenol over a VO(x) anode was found to be significant at 50 °C. The resultant current efficiency for phenol production and selectivity toward phenol reached 76.5 and 94.7 %, respectively.

Effect of semi-batch reactor configuration on aromatic hydroxylation reactions

Phenol, toluene and ethyl benzene hydroxylation were studied to investigate the potential benefits of semi-batch operation on aromatic hydroxylation reactions. Small crystallites of TS-1 and Al-free Ti-Beta were used as catalysts either in closed batch reactors or in a semi-batch system with the hydrogen peroxide added slowly over time. Water and methanol were used as solvents for all substrates and acetonitrile and solvent free systems were investigated additionally for toluene and ethylbenzene. It was seen that tar formation was higher when more H 2O 2 was present. For phenol hydroxylation, semi-batch operation significantly improved reaction performance with specific catalyst/solvent combinations. The best results were seen with Al-free Ti-Beta using the methanol solvent. This was attributed to increased formation of di(hydro)peroxo species in the pores of Al-free Ti-Beta, particularly in the presence of the methanol. In all cases, the lifetime of the catalyst was observed to increase when using semi-batch operation due to the decreased tar formation. Semi-batch operation also improved the catalyst lifetime for toluene hydroxylation as well as improving the reaction activity and selectivity in select cases.

Advanced Materials for Sustainable Energy and a Greener Environment

Advanced Materials for Sustainable Energy and a Greener Environment

2,2,6,6-Tetramethylpiperidine-1-Oxyl-Promoted Hydroxylation of Benzene to Phenol over a Vanadium-Based Catalyst Using Molecular Oxygen

Rapid benzene hydroxylation was achieved using a reaction system that consisted of a vanadium-based catalyst, ascorbic acid, and 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) with molecular oxygen as the oxidant. The hydroxyl radicals that form by a Fenton-type process attack the benzene ring to produce a hydroxycyclohexadienyl radical. The hydroxyl hydrogen is then abstracted quickly in the presence of TEMPO and phenol forms by the transfer of a hydrogen atom from the benzene ring to oxygen. Over the [(CH3)4N]4-PMo11VO40 catalyst the phenol yield reached 8.3% with a selectivity of 95% in 1 h while trace amounts of phenol were obtained in the normal system without TEMPO.

Hydrogen-terminated silicon nanowire photocatalysis: Benzene oxidation and methyl red decomposition

Hydrogen-terminated silicon nanowires (H-SiNWs) were used as heterogeneous photocatalysts for the hydroxylation of benzene and for the decomposition of methyl red under visible light irradiation. The above reactions were monitored by GC–MS and UV–Vis spectrophotometry, respectively, which shows 100% selectivity for the transformation of benzene to phenol. A complete decomposition of a 2 × 10 −4 M methyl red solution was achieved within 30 min. The high selectivity for the hydroxylation of benzene and the photodecomposition demonstrate the catalytic activity of ultrafine H-SiNWs during nanocatalysis.

Heteropolyanion-based ionic hybrid solid: A green bulk-type catalyst for hydroxylation of benzene with hydrogen peroxide

A novel heteropolyanion-based ionic hybrid was prepared by combining the divalent ionic liquid (IL) cation of 1,1′-(butane-1,4-diyl)-bis(3-methylimidazolium) with the Keggin-structured V-containing heteropolyanion, and characterized by 1H NMR, FT-IR, ESI-MS, XRD, SEM, TG, BET surface area, melting point, and elemental analysis. Its catalytic activity was evaluated in the hydroxylation of benzene with aqueous H 2O 2, including the testing of the influence of organic cations, catalytic reusability and optimization of reaction conditions. This hybrid is characterized to be semi-amorphous nanoparticles with a IL-like composition. The hybrid catalyst leads to the liquid–solid biphasic reaction system for hydroxylation of benzene with H 2O 2, presenting such advantages as high catalytic activity, convenient recovery, and steady reuse. The strong ionic interaction between the divalent IL cation and the heteropolyanion is responsible for the catalyst's solid nature and insolubility, and moreover, the bulk-type catalysis involving the V 5+/V 4+ redox pairs as active centers accounts for the hybrid's excellent catalytic performance.

Liquid phase hydroxylation of benzene to phenol over vanadium substituted Keggin anion supported on amine functionalized SBA-15

The Keggin type vanadium substituted molybdophosphoric acid (H 5PMo 10V 2O 40) supported on amine functionalized SBA-15 was tested in direct hydroxylation of benzene to phenol in the liquid phase. The catalyst was characterized by various techniques such as X-ray diffraction, FT-IR spectroscopy, thermogravimetric analysis (TGA), N 2 absorption–desorption surface area measurement and SEM. Gas chromatography of products showed high catalytic activity and selectivity to phenol. As we expected, the leaching of heteropoly acid from support during the reaction was negligible, because of strong interaction between heteropoly acid and amine groups of surface. The influence of reaction temperature, reaction time, amount of catalyst and H 2O 2 were investigated. Under optimized conditions 20% conversion of benzene and 95% selectivity to phenol was achieved.

Direct Synthesis of Phenol from Benzene on an Activated Carbon Catalyst Treated with Nitric Acid

Commercially available coal-based activated carbon was treated by nitric acid with different concentrations and the resultant samples were used as catalysts for the direct hydroxylation of benzene to phenol in acetonitrile. Boehm titration, X-ray photoelectron spectroscopy, scanning electron microscope coupled with an energy dispersive X-ray microanalyzer, and Brunauer-Emmett-Teller method were used to characterize the samples. The number of carboxyl groups on the surface was found to be the main factor affecting the catalytic activity. An optimum catalytic performance with a yield of 15.7% and a selectivity of 87.2% to phenol was obtained.

Bicomponent VO 2-defects/MWCNT catalyst for hydroxylation of benzene to phenol: Promoter effect of defects on catalytic performance

A novel bicomponent catalyst, VO 2 supported on multi-walled carbon nanotubes (MWCNTs) with defects as promoter (VO 2-defects/MWCNTs) was synthesized for the hydroxylation of benzene to phenol. In the bicomponent system, VO 2 nanoparticles with 2–10 nm were prepared by the spontaneous redox between V 5+ and defects of MWCNTs. Moreover, defects of MWCNTs were firstly used as promoters for preventing the oxidation of phenol and transferring electrons in the catalysis. Thus, compared with other vanadium catalysts, VO 2-defects/MWCNTs show excellent catalytic performance for the hydroxylation of benzene to phenol, which indicates defects as promoter are quite promising for catalyzing the hydroxylation of benzene.

Vanadium Contribution to the Surface Modification of Titanium Silicalite for Conversion of Benzene to Phenol

Vanadium oxide supported on the surface of titanium silicalite was investigated in benzene hydroxylation to determine its activity as heterogeneous catalyst. Effect of vanadium loading on structure and activity of titanium silicalite was investigated. On the basis of X-ray diffraction and infrared spectroscopy techniques, it was found that the titanium structure was remained on the modified catalyst. The catalytic activity of the modified catalyst was observed to be higher than that of parent catalyst.

Hydroxylation of Benzene Catalyzed by Supported Phthalocyanine Catalysts

Phthalocyanine catalysts were synthesized and supported matel phthalocyanines were found to be good catalysts for benzene hydroxylation to phenol. Matel phthalocyanines were characterized by N2 absorption-desorption, FT-IR spectroscopy, and tranmsission electron microscopy. The experimental results suggested that the supported matel phthalocyanines were good catalysts for benzene hydoxylation reaction. Supported vanadium phthalocyanine performed the best catalytic activity, on which 11.6% of phenol yield and 100% of selectivity were obtained. And it was proved to be reusable in this reaction.