Chemoselective hydrogenation of phenol to cyclohexanol using heterogenized cobalt oxide catalysts

Cobalt oxide nanoparticles (NPs) supported on porous carbon (CoO_x@CN) were fabricated by one-pot method and the hybrids could efficiently and selectively hydrogenate phenol to cyclohexanol with a high yield of 98%.     

Y-Ba-Cu-O mixed oxides for production of diphenols in liquid-solid phase

Superconductor mixed oxides were often used as catalysts at higher temperature in gas phase oxidations, and considered not suitable for lower temperature reactions in the liquid-solid phase; here the catalysis of YBa2Cu3O7+x and Y2BaCuO5+x in the phenol hydroxylation at lower temperature with H2O2 as oxygen donor was studied, and found that the superconductor YBaCu3O7±x has no catalytic activity for phenol hydroxylation, but Y2BaCuO5±x does, even has better catalytic activity and stability than most previously reported ones. With the studies of catalysis of other simple metal oxides and perovskite-like mixed oxides, a radical substitution mechanism is proposed and the experimental facts are explained clearly, and draw a conclusion that the perovskite-like mixed oxides with (AO)(ABO3) and (AO)2(ABO3) structure have better catalytic activity than the simple per-ovskite oxides with (ABO3)3 structure alone, and (AO) structure unit is the key for the mixed oxides to have the phenol hydroxylation activity.     

Catalysis of the rare earth containing mixed oxides Ln2CuO4 in phenol hydroxylation

Mixed oxides Ln₂Cu0_{4 ± λ} (Ln = La, Pr, Nd, Sm, Gd) with K₂NiF₄ structure were prepared. Their crystal structures were studied with XRD and IR spectra. Meanwhile, the average valence of Cu ions and nonstoichiometric oxygen (λ) were determined through chemical analyses. Catalysis of the above-mentioned mixed oxides in the phenol hydroxylation was investigated. Results show that the catalysis of these mixed oxides has close relation with their structures and composition. Substitution of A site atom in Ln₂CuO_4±λ has a great influence on their catalysis in the phenol hydroxylation. Project supported by the National Natural Science Foundation of China.     

Anchoring Fe Ions to Amorphous and Crystalline Oxides: A Means To Tune the Degree of Fe Coordination

We report on an IR spectroscopic study on the room‐temperature adsorption of NO on different iron(II )‐containing siliceous matrices. Fe²⁺ hosted inside the channels of MFI‐type zeolites (Fe‐ZSM‐5 and Al‐free Fe‐silicalite) exhibits pronounced coordinative unsaturation, as witnessed by the capability to form, at 300 K, [Fe²⁺(NO)], [Fe²⁺(NO)₂] and [Fe²⁺(NO)₃] complexes with increasing NO equilibrium pressure. Fe²⁺ hosted on amorphous supports (high surface area SiO₂ and MCM‐41) sinks more deeply into the surface of the siliceous support and thus exhibits less pronounced coordinative unsaturation: only [Fe²⁺(NO)₂] complexes were observed, even at the highest investigated NO equilibrium pressures. Activation at higher temperature (1073 K) of the Al‐free Fe‐silicalite sample resulted in the appearance of Fe²⁺ species similar to those observed on SiO₂ and MCM‐41, and this suggests that local (since not detectable by X‐ray diffraction) amorphisation of the environment around Fe²⁺ anchoring sites occurs. The fact that this behaviour is not observed on the Fe‐ZSM‐5 sample activated at the same temperature suggests that framework Al species (and their negatively charged oxygen environment) have an important role in anchoring extraframework Fe²⁺ species. Such an anchoring phenomenon will prevent a random migration of iron species, with subsequent aggregation and loss of coordinative unsaturation. These observations can thus explain the higher catalytic activity of the Fe‐ZSM‐5 system in one‐step benzene to phenol conversion when compared with the parent, Al‐free, Fe‐silicalite system with similar Fe content. The nature of the support and the activation temperature can therefore be used as effective means to tune the degree of Fe coordination.     

Electronic, magnetic and structural properties of A2VMoO6 perovskites (A=Ca, Sr)

The perovskites Sr₂VMoO₆ and Ca₂VMoO₆ have been synthesized by liquid-mix technique in citrate melts, and their electronic, magnetic and structural properties have been investigated. No signs of V/Mo ordering are seen by synchrotron X-ray powder diffraction, but despite the chemical disorder both oxides are highly conductive and Pauli paramagnetic. Electrical conductivities of these solid solutions are comparable or higher than those reported for polycrystalline AMoO₃ end members. It is suggested that the delocalized metallic conductivity of these compounds with two different transition-metal atoms implies valence equilibrium between the degenerate oxidation-state couples V⁴⁺Mo⁴⁺ and V³⁺Mo⁵⁺.     

A Kinetic Study of Phenolic Oxidation by H2O2 Using the Schiff Base Complexes As Mimetic Peroxidases

The Schiff base complexes containing a transition metal ion, Co^II and Cu^II, were used as mimetic peroxidase in the catalytic oxidation of phenol by H₂O₂. The characteristic spectra of the Schiff base complexes in H₂O₂-buffered solution were recorded and analyzed, respectively. The mechanism and the kinetic mathematic model of the phenol catalytic oxidation were studied. The results showed that the Schiff base complexes containing the transition metal ion, Co^II and Cu^II, as peroxidase mimics exhibited good catalytic activity and the character of the peroxidase in the catalytic oxidation of phenol by H₂O₂ under different conditions.     

Enhancement of Phenol Degradation by Electron Acceptors in Anodic Contact Glow Discharge Electrolysis

Effects of several electron acceptors (Fe³⁺, Cu²⁺, Cr(VI), and H₂O₂) on phenol degradation in anodic contact glow discharge electrolysis have been investigated. Results show that the electron acceptors have positive effects on phenol removal, with the sequence of Fe³⁺?>?Cr(VI)?>?H₂O₂?>?Cu²⁺. Under conditions of voltage 500?V and current 100?mA, 100?mg/L phenol can be removed with 10?min of discharge treatment in the presence of 1.0?mmol/L Fe³⁺, while without any additive only 35?% of phenol is removed in 30?min. The mechanism of the degradation enhancement was discussed based on the reactions taking place in the presence of the different additives.     

Significant roles of oxygen and unbound <Superscript>•</Superscript>OH radical in phenol formation during photo-catalytic degradation of benzene on TiO<Subscript>2</Subscript> suspension in aqueous system

Studies on photo-catalytic degradation of benzene using TiO₂ photo-catalyst as a suspension in water is reported. Degradation studies have been carried out using 350 nm UV light. Phenol, a photo-catalytic product of benzene, was monitored under varying experimental conditions such as amount of TiO₂, concentration of benzene, photolysis time, ambient (air, O₂, Ar, N₂O and N₂O–O₂ mixture), etc. The phenol yields in both aerated and O₂-purged systems increased with the photolysis time. In contrast to oxygenated systems, the yields of phenol in deoxygenated (viz. Ar-purged and N₂O-purged) systems were quite low (~30 μM) and remained steady. H₂O₂ yields in all these systems were also monitored, and found lower than an order of magnitude as compared to phenol yields for the respective systems. The rate of phenol production in aerated 1 mM benzene solution containing 0.05% TiO₂ suspension was evaluated at 12.3 μM min⁻¹ which is lower than the rate obtained in an O₂-saturated system (22.4 μM min⁻¹). The low yields of phenol in both Ar- and N₂O-purged systems, and also the increasing trends in oxygenated systems, together reveal that, for the phenol formation with an enhanced rate, oxygen is essential. In the present study, it is implied that the photo-generated hole, which is mainly an ^•OH radical, is either freely available in the aqueous phase or migrates to the aqueous phase from the catalyst surface, to react with benzene to produce HO-adduct radical. Later, following reaction with oxygen, the adduct produces phenol. On the other hand, h⁺ and surface adsorbed ^•OH radical, being trapped/bonded due to rigid association with the catalyst surface, were not able to generate phenol under similar experimental conditions. The mechanism of phenol formation with TiO₂ photolysis in an aqueous system is rechecked, on the basis of present results on h⁺/surface adsorbed ^•OH radical/unbound ^•OH radical scavenging by benzene, collectively with previous reports on various systems.     

Kinetics and reaction mechanism of phenol hydroxylation catalyzed by La-Cu<Subscript>4</Subscript>FeAlCO<Subscript>3</Subscript>

The present work synthesizes La-Cu₄FeAICO₃ catalyst under microwave irradiation and characterizes its structure using XRD and IR techniques. The results show that the obtained La-Cu₄FeAICO₃ has a hydrotalcite structure. In the phenol hydroxylation with H₂O₂ catalyzed by La-Cu₄FeAICO₃, the effects of reaction time and phenol/H₂O₂ molar ratio on the phenol hydroxylation, and relationships between the initial hydroxylation rate with concentration of the catalyst, phenol, H₂O₂ and reaction temperature are also investigated in details. It is shown the phenol conversion can reach 50.09% (mol percent) in the phenol hydroxylation catalyzed by La-Cu₄FeAICO₃, under the reaction conditions of the molar ratio of phenol/H₂O₂1/2, the amount ratio of phenol/catalyst 20, reaction temperature 343 K, reaction time 120 min, 10 ml_ distilled water as solvent. Moreover, a kinetic equation of v = k[La-Cu₄FeAlCO₃][C₆H₅OH][H₂O₂]. and the activation energy of E _a=58.37 kJ/mol are obtained according to the kinetic studies. Due to the fact that the HO-Cu⁺-OH species are detected in La-Cu₄FeAICO₃/H₂O₂ system by XPS, the new mechanism about the generation of hydroxyl free radicals in the phenol hydroxylation is proposed, which is supposed that HO-Cu⁺-OH species are transition state in this reaction.     

Generation of cyclopropanediazonium and its chemical transformations in the presence of phenol

The reaction of phenol with cyclopropanediazonium ion generated in situ from N-cyclopropyl-N-nitrosourea by the action of K₂CO₃ or Cs₂CO₃ was studied. The main reaction pathway is diazo coupling of cyclopropanediazonium with phenol to give 4-(cyclopropyldiazenyl)phenol, and only traces of isomeric 2-(cyclopropyldiazenyl)phenol were formed. The reaction was accompanied by partial denitrogenation of the diazonium ion with formation of cyclopropyl and allyl cations which gave rise to a number of by-products. All transformation products were characterized by the ¹H and ¹³C NMR spectra with detailed signal assignment.     

Phosphomolybdate clusters as molecular building blocks in the design of one-, two- and three-dimensional organic-inorganic hybrid materials

An attractive approach to the design of inorganic solids exploits the tethering of inorganic clusters through organic spacers to produce hybrid materials with composite properties. We have recently described a modified strategy in which polyoxometalate clusters are linked through organic subunits to give an anionic hybrid substructure which may be further modified through the introduction of secondary metal-ligand complex (SMLC) cations, serving as a third component building block. In this application, the molybdophosphonate cluster {Mo₅O₁₅(O₃PR)₂}⁴⁻ serves as a secondary building unit (SBU) with alkyl (CH₂)_n or aromatic -(C₆H₄)_n- tethers providing one-dimensional structural expansion. A binucleating ligand such as tetrapyridylpyrazine (tpyprz) is used to bridge secondary metal sites into a binuclear {Cu₂(tpyprz)}⁴⁺ SBU which may link phosphomolybdate clusters into two- or three-dimensional structures. The influence of a variety of structural determinants is discussed, including the tether length of the diphosphonate ligand, the coordination preferences of the secondary metal, expansion of the ligand component of the SMLC, and substitution of As for P in the oxide SBU.     

Electrocatalytic Phenol Oxidation on Mixed Pt‐RuO2 Nanoparticle Modified Electrode

Abstract

Nanoscale Pt/RuO₂ colloid with carbon paste support was synthesized and used to prepare a modified electrode for phenol detection. The results showed that the Pt/RuO₂ catalyst has high activity for electrooxidation of phenol with reduced intermediate polymerization due to its significantly low potential for phenol oxidation. The detection limit was as low as 10^?9 mol L^?1 for the polishable Pt/RuO₂/C paste electrode with good reproducibility.     

Reactivity of some vanadium oxides: An EPR and XRD study

V₂O₅, VO₂ and V₂O₃ fresh samples and at different times after purchase or preparation (aged samples) were investigated by chemical analysis, redox treatments, XRD and EPR. The ageing process through a reaction with water and oxygen slowly oxidize crystalline VO₂ and V₂O₃, leading to a quasi-amorphous phase with bariandite structure (V₁₀O₂₄·12H₂O). The role of water is the progressive demolition of the compact structures and formation of hydrated phase. Kinetic study of VO₂ oxidation by O₂ and O₂+H₂O mixture indicates that increasing the temperature up to 723 K the effect of water becomes less important. The reaction leads to partially oxidized products with decreasing water content: bariandite at room temperature, V₃O₇·H₂O at 383 K and V₃O₇ at 723 K. Kinetic investigation of V₂O₅ reduction by CO at 633-723 K showed that the reduction process proceeds trough the formation of V⁴⁺ and of electrons delocalized in the conduction band.     

Bioactive Penta-Coordinated Diorganotin(Iv) Complexes of Pyridoxalimine Schiff Bases

Abstract

Diorganotin(IV) complexes of an extended system derived from the condensation of pyridoxal hydrochloride with 2-amino phenol (H₂L¹), 2-amino-4-methyl phenol (H₂L²), 2-amino-4-chloro phenol (H₂L³), 2-amino-4-nitro phenol (H₂L⁴), 1-amino-2-naphthol hydrochloride (H₂L⁵) have been synthesized by the reaction of dichlorodiorganotin(IV) in a 1:1 molar ratio with these ligands. Spectral studies (IR, ¹H, ¹³C, ¹¹⁹Sn NMR) along with physical data evidenced the formation of penta-coordinated species with the ligands acting as tridentate (ONO) with oxygen occupying the axial positions, and nitrogen at one of the equatorial positions. The ligands and their organotin complexes have been evaluated for antimicrobial activity against phytopathogenic fungi Candida albicans and Aspergillus niger at 25 ± 1 °C and bacteria Bacillus subtilis, Escherichia coli, and Staphylococcus aureus at 37 ± 1 °C. The activities of the ligands have been enhanced on complexation and the results indicate that they exhibit significant antimicrobial properties.

Supplemental materials are available for this article. Go to the publisher's online edition of Phosphorus, Sulfur, and Silicon and the Related Elements to view the free supplemental file.     

Cyclic Voltammetry Study of the Mn‐Substituted Polyoxoanions [MnII4(H2O)2(H4AsW15O56)2]18− and [((MnIIOH2)MnII2PW9O34)2(PW6O26)]17−: Electrodeposition of Manganese Oxides Electrocatalysts for Dioxygen Reduction

The electrochemical behavior of two manganese (Mn)‐substituted polyoxoanions, the dissymmetrical Dawson sandwich‐type [Mn^II₄(H₂O)₂(H₄AsW₁₅O₅₆)₂]^18? and the Keggin sandwich banana‐shaped [((Mn^IIOH₂)Mn^II₂PW₉O₃₄)₂(PW₆O₂₆)]^17? is investigated. At pH 5, the oxidation of the Mn^II‐centers results in one oxidation wave for [Mn^II₄(H₂O)₂(H₄AsW₁₅O₅₆)₂]^18? and two oxidation waves for [((Mn^IIOH₂)Mn^II₂PW₉O₃₄)₂(PW₆O₂₆)]^17?. To the best of our knowledge, presence of the second Mn‐based wave is rarely observed in the electrochemistry of Mn‐containing polyoxometalates. Deposition of Mn‐oxides electrocatalysts for dioxygen reduction is noticed by cyclic voltammetry, which can be distinguished by the significant positive shift in potentials of the dioxygen reduction reaction.     

Vibrational analysis of phenol/(methanol)1

Ab initio calculations at the Hartree-Fock 4-31G* level were performed in order to calculate binding energies and vibrational frequencies of the phenol/CH₃OH-cluster and two deuterated isotopomers (d-phenol/CH₃OD,d-phenol-CD₃OD). The minimum energy structure is trans-linear, as for the phenol/H₂O-cluster. The calculated frequencies of phenol and methanol as well as the intramolecular frequencies of the phenol/CH₃OH-cluster are assigned to experimental values. The calculated intermolecular frequencies of the phenol/CH₃OH-cluster are compared with the available experimental frequencies of theS ₀ (andS ₁)-state of the phenol/methanol-cluster and the similarp-cresol/methanol-cluster. Assignments are suggested for the σ andp ₁-mode. In order to clarify the assignment of the low frequency vibration at 22 cm^?1 anharmonic corrections for the β₂-mode of the phenol/CH₃OH-cluster are calculated. These calculations show only slight anharmonicity compared with the β₂-mode calculations carried out for the phenol/H₂O-cluster.     

Sensitive Phenol Detection Using Tyrosinase‐Based Phenol Oxidation Combined with Redox Cycling of Catechol

This paper reports sensitive phenol detection using (i) tyrosinase (Tyr)‐based oxidation of phenol to catechol, combined with (ii) electrochemical‐chemical‐chemical (ECC) redox cycling involving Ru(NH₃)₆³⁺, catechol, and tris(2‐carboxyethyl)phosphine (TCEP). Phenol is converted into catechol by Tyr in the presence of dissolved O₂. Catechol then reacts with Ru(NH₃)₆³⁺, generating o‐benzoquinone and Ru(NH₃)₆²⁺. o‐Benzoquinone is reduced back to catechol by TCEP, and Ru(NH₃)₆²⁺ is accumulated over the course of the incubation. When Ru(NH₃)₆²⁺ is electrochemically oxidized to Ru(NH₃)₆³⁺, ECC redox cycling occurs. For simple phenol detection, bare ITO electrodes are used without modifying the electrodes with Tyr. The detection limit for phenol in tap water using Tyr‐based oxidation combined with ECC redox cycling is ca. 10^?9 M, while that using only Tyr‐based oxidation is ca. 10^?7 M.     

Electro-catalytic effect of Al2O3 supported onto activated carbon in oxidizing phenol at graphite electrode

In this work, the electro-catalytic oxidation of phenol was studied using the aluminum oxide supported onto activated carbon (Al₂O₃/AC). The later was successfully prepared by impregnating aluminum particles in the activated carbon (AC) using heat treatment. Al₂O₃/AC was characterized by X-ray diffraction (XRD) and infrared spectroscopy (IR). The electro-catalytic performance of the Al₂O₃/AC for phenol oxidation was studied using cyclic voltammetry (CV), chronoamperometry, linear sweep voltammetry polarization, electrochemical impedance spectroscopy and differential pulse voltammetry (DPV) in 0.1 mol L^?1 Na₂SO₄. It has been shown that the proposed catalyst exhibits remarkably an electro-catalytic performance toward phenol oxidation. Moreover, the oxidation peak currents are linearly dependent on the concentration of phenol in the wide ranges from 1.0 × 10^?3 mol L^?1 to 1.0 × 10^?4 mol L^?1 and 8.0 × 10^?5 mol L^?1 to 1.0 × 10^?6 mol L^?1 with a detection limit of 1.51 × 10^?7 mol L^?1 (signal (S) to noise (N) ratio, S/N = 3) and response time of 3 min. The possible interferences were evaluated in 1.0 × 10^?5 mol L^?1 of phenol. The proposed catalyst also indicated suitable repeatability and stability. Moreover, the proposed Al₂O₃/AC–CPE has been successfully applied for the phenol analysis in natural waters and olive oil samples with good recoveries.     

Electronic absorption spectra of phenol(H2O)n and (phenol)n as studied by the MS MPI method

The initial stages of solvation and crystallization were studied in phenol(H₂O)_n and (phenol)_n by the use of the mass-selected MPI method in a supersonic free jet. The spectral position exhibits an irregular shift by the change of the cluster size, which is interpreted in terms of the role of phenol as a proton donor, a proton acceptor or both in the hydrogen bonding. The O⁰₀ band of the phenol—water cluster was found to converge to 276.0 nm. The phenol trimer was concluded to have a cyclic structure.     

Hydrodechlorination of 4-Chlorophenol on Pd-Fe Catalysts on Mesoporous ZrO2SiO2 Support

A mesoporous support based on silica and zirconia (ZS) was used to prepare monometallic 1 wt% Pd/ZS, 10 wt% Fe/ZS, and bimetallic FePd/ZS catalysts. The catalysts were characterized by TPR-H₂, XRD, SEM-EDS, TEM, AAS, and DRIFT spectroscopy of adsorbed CO after H₂ reduction in situ and tested in hydrodechlorination of environmental pollutant 4-chlorophelol in aqueous solution at 30 °C. The bimetallic catalyst demonstrated an excellent activity, selectivity to phenol and stability in 10 consecutive runs. FePd/ZS has exceptional reducibility due to the high dispersion of palladium and strong interaction between FeOx and palladium, confirmed by TPR-H₂, DRIFT spectroscopy, XRD, and TEM. Its reduction occurs during short-time treatment with hydrogen in an aqueous solution at RT. The Pd/ZS was more resistant to reduction but can be activated by aqueous phenol solution and H₂. The study by DRIFT spectroscopy of CO adsorbed on Pd/ZS reduced in harsh (H₂, 330 °C), medium (H₂, 200 °C) and mild conditions (H₂ + aqueous solution of phenol) helped to identify the reasons of the reducing action of phenol solution. It was found that phenol provided fast transformation of Pd⁺ to Pd⁰. Pd/ZS also can serve as an active and stable catalyst for 4-PhCl transformation to phenol after proper reduction.