Selective Oxidation Of Phenol Research Articles

Zeolite encapsulated host-guest Cu(II) Schiff base complexes: Superior activity towards oxidation reactions over homogenous catalytic systems

Crystalline copper Schiff base complexes of general formula [CuL1NO3]n(1) and [CuL2Cl] (2) (where HL1 = 1-[(3-dimethylaminopropylimino)-methyl]-naphthalen-2-ol and HL2 = 3-[(3-dimethylamino-2,2-dimethyl-propylimino)-methyl]-naphthalen-2-ol) were prepared and well characterized. The guest, metal complexes were entrapped in the supercages of NaY zeolite (host) in the solvent phase through two stage process (i) ion exchange of the selected transition metal (Cu(II)-salt) in the porous structure and (ii) encapsulation of Schiff-base ligands (HL1/HL2) in Cu(II) exchanged zeolite. The novel Cu(II) complexes as well as host-guest catalysts were characterized using various physicochemical [Single crystal XRD, elemental analysis, EDX, scanning electron microscopy (FE-SEM), the Brunauer-Emmet-Teller (BET) adsorption technique (N2 gas), Inductively coupled plasma (ICP-MS), powder X-ray diffraction (PXRD), thermal analysis (TGA), cyclic voltametry] and spectroscopic techniques [1H and 13C NMR, FT-IR, ESI-MS, electro spin resonance (ESR), diffuse reflectance spectroscopy (DRS), FT-Raman and GC-MS]. Herein, this study reveals the advantage of heterogeneous catalytic methods for the stability of metal complexes into the supercages of zeolite-Y and the selective oxidation of phenol, styrene and cyclohexene in presence of H2O2 at mild reaction conditions. The catalytic activities of the zeolite entrapped Cu(II) complexes were tested with their homogeneous analogous as well. The heterogeneous catalyst can be re-used after recovering for several cycles without decay of activity which was confirmed by PXRD, cyclic voltammetry, SEM and FTIR studies.

Investigation on Preparation of p-Benzoquinone through the Organoselenium-Catalyzed Selective Oxidation of Phenol

Investigation on Preparation of p-Benzoquinone through the Organoselenium-Catalyzed Selective Oxidation of Phenol

Software Module of Mathematical Chemistry Web-Laboratory for Studying the Kinetics of Oxidation of 4-tert-Butyl-phenol by Aqueous Solution of H2O2 in the Presence of Titanosilicates

Selective oxidation of phenols is of great interest in terms of practically valuable hydroquinone and pyrocatechin. purpose of this paper is to investigate the kinetics of the oxidation reaction of 4-tert-butylphenol by an aqueous solution of hydrogen peroxide using titanosilicates and a Macrokinetic model of experimental data was obtained. To minimize the relative error in the population at different temperature we use Genetic Algorithm and simulated Annealing methods to solve the resulting optimization problems. To perform the experimental calculation a separate software module the Web-laboratory of mathematical chemistry was developed. A Sub module The inverse for the solving the inverse kinetic problem with the use of Java-interface for Octave was designed.

Zeolite-Y enslaved manganese(III) complexes as heterogeneous catalysts

Traditional catalytic procedures for oxidation of phenol produce environmentally undesirable wastes. As a consequence, there is a clear demand for development of an environmentally benign catalytic route for the selective oxidation of phenol. A series of zeolite-Y enslaved Mn(III) complexes with Schiff bases derived from vanillin furoic-2-carboxylic acid hydrazone (VFCH), vanillin thiophene-2-carboxylic acid hydrazone (VTCH), ethylvanillin thiophene-2-carboxylic acid hydrazone (EVTCH), and/or ethylvanillin furoic-2-carboxylic acid hydrazone have been synthesized and characterized by physico-chemical techniques. Catalytic oxidations of phenol using 30% H2O2 as an oxidant over [Mn(VTCH)2·2H2O]+-Y, [Mn(VFCH)2·2H2O]+-Y, and [Mn(EVTCH)2·2H2O]+-Y under mild conditions were studied. These zeolite-Y enslaved Mn(III) complexes are stable and recyclable under current reaction conditions.

Effect of steaming on the catalytic performance of ZSM-5 zeolite in the selective oxidation of phenol by nitrous oxide

Gas-phase oxidation of phenol to dihydroxybenzenes (DHB) with nitrous oxide was performed over a set of ZSM-5 zeolites steamed at different temperatures in the range from 550 to 750°C. The best of the catalysts demonstrated 70% N2O conversion and a more than 90% selectivity for DHB. However, significant differences were observed in DHB isomer distribution and catalyst deactivation due to changes in the acidity of the zeolites. The steaming procedure reduces the concentration of Bronsted acid sites, thus allowing a decrease in coke loading. Simultaneously, a substantial decline in the molar ratio of hydroquinone to catechol in the reaction products was observed, mainly due to the increased selectivity to the ortho isomer – catechol. These results can be used to control the selectivity for different DHB isomers in the title reaction by varying steaming severity.

Synthesis and Characterization of Fe,Cr or Sn-MSU-X and Catalytic Applications

Iron, chromium or tin containing mesoporous materials MSU-X were synthesized using Pluronic F127 as templating agent under the neutral pH condition by one-step method. The samples were characterized by XRD, N2 adsorption, TEM, FT-IR, UV-Vis. The surface acid nature of Sn-MSU-X was investigated by FT-IR of pyridine adsorption. The results indicate that Fe, Cr and Sn have been successfully incorprated into the framework of the MSU-X samples. And these samples have an uniform pore size distribution. Fe-MSU-X and Cr-MSU-X exhibit disordered worm-like mesostructure. However, Sn-MSU-X exhibits highly ordered hexagonal-pores mesostructure. The Fe-MSU-X and Cr-MSU-X catalysts are more active for the selective oxidation of phenol and cyclooctane, respectively.There are both Lewis and Brönsted acid sites on the surface of Sn-MSU-X.

Selective oxidation of phenol and benzoic acid in water via home-prepared TiO2 photocatalysts: Distribution of hydroxylation products

The hydroxylation of phenol (a substrate containing an electron donor group) and of benzoic acid (a substrate containing an electron withdrawing group) has been carried out by the photocatalytic method in aqueous suspensions containing commercial or home prepared TiO2 samples. The aim of the work was to study the distribution of hydroxylation products when different photocatalysts were used and to correlate the selectivity to some physico-chemical features of the powders. The samples were characterized by X-ray diffraction, thermogravimetry, determination of crystalline phase percentage, specific surface area and zero charge point. The photoreactivity results indicate that the products of the primary oxidation of phenol are the ortho- and para-mono-hydroxy derivatives while those of benzoic acid are all the mono-hydroxy derivatives independently of the catalyst. The selectivity toward mono-hydroxy derivatives shows a strong dependence on catalyst hydroxylation and crystallinity degrees: the highest selectivity values were obtained by using the commercial samples that resulted the least hydroxylated and the most crystalline ones. A kinetic model, taking into account the mineralization and the partial oxidation reaction routes, is proposed by using the Langmuir–Hinshelwood model.

Selective Oxidation of Phenol in the Presence of Transition-Metal Substituted Polyoxometalates

Tetrabutylammonium salts of lacunary Keggin anions with supported Co and Mn cations soluble in organic solvents were prepared and characterized by thermogravimetric analysis, FTIR spectroscopy and X-ray diffraction. These salts were applied as catalysts for phenol oxidation in acetonitrile solution with iodosobenzene diacetate as single oxygen donor. Deposition of cobalt ions in the lacunary Keggin anions strongly increases the catalytic activity. The conversion of phenol is proportional to concentrations of catalyst and single oxygen donor. The dependence of the conversion of phenol on time indicates that the reaction is 1st order with respect to phenol. The catalyst retains its activity after recycling. On the basis of catalytic results reaction mechanism was elucidated.

Selective oxidation of phenol with hydrogen peroxide using two types of catalytic microreactor

Selective oxidation of phenol with hydrogen peroxide over titanium silicalite-1 (TS-1) was performed using two types of catalytic microreactor: a packed bed microreactor and a catalytic wall microreactor. The reaction rates were markedly faster in both microreactors than in flasks due to improvement of the contact efficiency between reactant and catalyst. However, using a packed bed microreactor, phenol conversion and yields of benzenediols decreased gradually with time course. Therefore, we developed a catalytic wall microreactor in which catalyst elements could be exchanged easily. Use of this new catalytic wall reactor suppressed catalyst deactivation. In addition, the regioselectivity of hydroxylation, i. e., the molar ratio of para-diol (hydroquinone)/ ortho-diol (catechol) changed remarkably. A higher degree of para-selectivity was achieved with the wall type reactor than the packed bed type reactor.

Direct synthesis, characterization of Cu-SBA-15 and its high catalytic activity in hydroxylation of phenol by H 2O 2

Transition metal copper substituted mesoporous silica (Cu-SBA-15) was synthesized using triblock copolymers surfactant as template agent under acidic condition. The result Cu-SBA-15 was characterized with XRD, ICP-AES, FT-IR and N 2 adsorption–desorption measurements, which prove that Cu(II) was mainly incorporated into the framework of Cu-SBA-15. Its catalytic activity was studied for phenol hydroxylation using H 2O 2 (30%). The substituting element (Cu 2+) is incorporated into the framework position forming a new type of active site which raises the phenol conversion to 62.4% and the diphenol (the mixture of catechol (CAT) and hydroquinone (HQ)) selectivity to 97%. The Cu-SBA-15 has very high selectivity for catechol (about 71% selectivity), which is completely different from that of the microporous titanium silicalite zeolites (47.1% phenol conversion and about 50% selectivity to CAT under same reaction conditions). The results obtained indicate that the selective oxidation of phenol with H 2O 2 by a radical substitution mechanism.

Computational Study of Benzene-to-Phenol Oxidation Catalyzed by N2O on Iron-Exchanged Ferrierite

An Fe(II) ion at an α-cation exchange position of ferrierite, (Fe)α, was taken as a model for the active site in nitrous oxide decomposition and in the selective oxidation of phenol with nitrous oxide. The oxygen that is deposited via the decomposition of N2O is commonly referred to as α-oxygen, (O)α. Comparison with the results of cluster model calculations was performed for reaction of benzene-to-phenol oxidation. Periodic calculations predict the same reaction path for benzene oxidation as does the cluster model study. Differences in the adsorption modes for both types of calculations were analyzed and discussed.

Cluster Model DFT Study of the Intermediates of Benzene to Phenol Oxidation by N2O on FeZSM-5 Zeolites

An Fe(II) ion at an α-cation exchange position of ZSM-5 zeolite (Fe/Z) was taken as a model for the active site in the nitrous oxide decomposition and in the selective oxidation of phenol with nitrous oxide. The oxygen deposited by decomposition of N2O is commonly referred to as α-oxygen (OFe/Z). Cluster model DFT calculations show that the interaction of the OFe/Z center with benzene resulted easily in arene oxide formation. The results indicate a rather low activation energy for this step. Possible transformations of the adsorbed arene oxide are considered and the experimental evidence for the absence of the kinetic H/D isotope effect in phenol formation is discussed. It is concluded that the rate-limiting step for the in situ oxidation of benzene to phenol is the desorption of the product.

Selective oxidation of phenol and anisole derivatives to quinones with hydrogen peroxide and polymer-supported methylrhenium trioxide systems

A convenient and efficient application of heterogeneous poly(4-vinylpyridine)/methyl rhenium trioxide (PVP/MTO) systems for the selective oxidation of substituted phenol and anisole derivatives to benzoquinones is described. Environment friendly, easily available, and low cost H 2O 2 was used as the oxygen atom donor. All catalysts were stable systems for at least five recycling experiments. In the oxidation of some natural phenols such as cardanol derivatives higher conversion and yields of benzoquinones were observed with respect to MTO in homogeneous phase suggesting a support-mediated molecular recognition process based on hydrogen-bonding interactions.

Selective hydroxylation of phenol employing Cu–MCM-41 catalysts

We studied the oxidation reaction of phenol in aqueous and acetonitrile media under mild conditions, employing Cu-modified MCM-41 mesoporous catalysts. The stability of the catalysts under reaction conditions was confirmed by XRD, UV–VIS and FTIR techniques. Results obtained indicate that the selective oxidation of phenol with H2O2 by a radical substitution mechanism produces three main reaction products: catechol, hydroqinone and benzoquinone.

Structure and Redox Behavior of Zirconium in Microporous Zr-Silicalites Studied by EXAFS and ESR Techniques

The local environment of zirconium in Zr-silicalite with MEL structure has been studied using the EXAFS technique. The structural parameters indicate the presence of tetrahedrally coordinated, isolated zirconium sites with Si–O–Zr linkages. The experimental results support the location of Zr4+ ions at edge- or corner-sharing positions (N(Zr–O)=3.9 and N(Zr–Si)=1.2), rather than in regular substitutional positions. The isolated Zr4+ ions could be reduced to the Zr3+ state on treatment with H2 followed by UV irradiation. The ESR spectra of reduced Zr-silicalite samples of both MFI and MEL structures reveal a distorted tetrahedral geometry around Zr3+ and a dx2−y2 orbital ground state. The ESR results are consistent with EXAFS findings. The role of these active Zr species in the selective oxidation of phenol is investigated by ESR after interaction of the samples with aqueous H2O2. The formation of a Zr4+–O−•2 radical species, and the variation in the g parameter under the influence of solvents such as water, acetonitrile, and methanol are reported. The results confirm the role of Zr4+ as active centers. The coordination of solvent molecules around Zr centers affects the catalytic activity to different extents, in agreement with the difference in ESR signal intensity of the radical species. These isolated active sites are responsible for the formation of superoxide/hydroperoxide species through which the oxygen is transferred to the substrate in the hydroxylation of phenol.

Selective oxidation of phenols using copper complexes encapsulated in zeolites

The oxidation and hydroxylation of phenols to dihydroxy aromatic compounds have been investigated using phthalocyanines and substituted (chloro- and nitro-) phthalocyanines of copper encapsulated in zeolites (X and Y). H 2O 2 has been used as oxidant. At ambient conditions, the encapsulated copper chloro- and nitro phthalocyanine complexes, unlike their unsubstituted analogs, are able to oxidise, selectively, phenol to catechol and hydroquinone. The catalytic efficiency (turnover number) of the copper atoms are higher in the encapsulated state compared to that in the “neat” complex. The solid catalysts have been characterised by IR, UV, ESR and ESCA spectroscopy. The influence of various process parameters (like temperature, reaction time, substrate/oxidant ratio, catalyst weight etc.) on the conversion and product distribution is also illustrated and discussed.