Polymer supported catalysts for oxidation of phenol and cyclohexene using hydrogen peroxide as oxidant

Polymer supported transition metal complexes of N,N′-bis (o-hydroxy acetophenone) hydrazine (HPHZ) Schiff base were prepared by anchoring its amino derivative Schiff base (AHPHZ) on cross-linked (6 wt%) polymer beads and then loading iron(III), copper(II) and zinc(II) ions in methanol. The loading of HPHZ Schiff base on polymer beads was 3.436 mmol g⁻¹ and efficiency of complexation of polymer anchored HPHZ Schiff base for iron(III), copper(II) and zinc(II) ions was 83.21, 83.40 and 83.17%, respectively. The efficiency of complexation of unsupported HPHZ Schiff base for these metal ions was lower than polymer supported HPHZ Schiff base. The structural information obtained by spectral, magnetic and elemental analysis has suggested octahedral and square planar geometry for iron(III) and copper(II) ions complexes, respectively, with paramagnetic behavior, but zinc(II) ions complexes were tetrahedral in shape with diamagnetic behavior. The complexation with metal ions has increased thermal stability of polymer anchored HPHZ Schiff base. The catalytic activity of unsupported and polymer supported HPHZ Schiff base complexes of metal ions was evaluated by studying the oxidation of phenol (Ph) and epoxidation of cyclohexene (CH). The polymer supported metal complexes showed better catalytic activity than unsupported metal complexes. The catalytic activity of metal complexes was optimum at a molar ratio of 1:1:1 of substrate to oxidant and catalyst. The selectivity for catechol (CTL) and epoxy cyclohexane (ECH) in oxidation of phenol and epoxidation of cyclohexene was better with polymer supported metal complexes in comparison to unsupported metal complexes. The energy of activation for oxidation of phenol (22.8 kJ mol⁻¹) and epoxidation of cyclohexene (8.9 kJ mol⁻¹) was lowest with polymer supported complexes of iron(III) ions than polymer supported Schiff base complexes of copper(II) and zinc(II) ions.     

Copper(II) Schiff Base Complex Immobilized on Superparamagnetic Fe3O4@SiO2 as a Magnetically Separable Nanocatalyst for Oxidation of Alkenes and Alcohols

A new heterogeneous catalyst containing a copper(II) Schiff base complex covalently immobilized on the surface of silica‐coated Fe₃O₄ nanoparticles (Fe₃O₄@SiO₂‐Schiff base‐Cu(II)) was synthesized. Characterization of this catalyst was performed using various techniques. The catalytic potential of the catalyst was investigated for the oxidation of various alkenes (styrene, α‐methylstyrene, cyclooctene, cyclohexene and norbornene) and alcohols (benzyl alcohol, 3‐methoxybenzyl alcohol, 3‐chlorobenzyl alcohol, benzhydrol and n ‐butanol) using tert ‐butyl hydroperoxide as oxidant. The catalytic investigations revealed that Fe₃O₄@SiO₂‐Schiff base‐Cu(II) was especially efficient for the oxidation of norbornene and benzyl alcohol. The results showed that norbornene epoxide and benzoic acid were obtained with 100 and 87% selectivity, respectively. Moreover, simple magnetic recovery from the reaction mixture and reuse for several times with no significant loss in catalytic activity were other advantages of this catalyst     

Selective hydrogenation and Suzuki cross‐coupling reactions of various organic substrates using a reusable polymer‐anchored palladium(II) Schiff base complex

A new polymer‐anchored Pd(II) Schiff base complex has been prepared and characterized using scanning electron microscopy, elemental analysis, atomic absorption spectroscopy, TGA and spectrometric methods such as diffuse reflectance spectra of solid and FT‐IR spectroscopy. This polymer‐anchored palladium catalyst shows excellent catalytic activity in the liquid‐phase hydrogenation reaction of styrene oxide to obtain selectively 2‐phenylethanol at normal pressure of hydrogen gas (1 atm.) at room temperature in DMF medium. We have also studied the liquid‐phase hydrogenation reaction of various organic substrates. The catalyst exhibits excellent catalytic activity for the Suzuki cross‐coupling of various substituted and non‐substituted aryl halides. The influences of various parameters were investigated to optimize reaction conditions. The reusability experiments show that the catalyst can be used five times without much loss in catalytic activity. Copyright © 2012 John Wiley & Sons, Ltd.     

Catalytic activities of polymer‐supported metal complexes in oxidation of phenol and epoxidation of cyclohexene

The metal complexes of N, N′‐bis (o‐hydroxy acetophenone) propylene diamine (HPPn) Schiff base were supported on cross‐linked polystyrene beads. The complexation of iron(III), copper(II), and zinc(II) ions on polymer‐anchored HPPn Schiff base was 83.4, 85.7, and 84.5 wt%, respectively, whereas the complexation of these metal ions on unsupported HPPn Schiff base was 82.3, 84.5, and 83.9 wt%. The iron(III) complexes of HPPn Schiff base were octahedral in geometry, whereas copper(II) and zinc(II) ions complexes were square planar and tetrahedral. Complexation of metal ions increased the thermal stability of HPPn Schiff base. Catalytic activity of metal complexes was tested by studying the oxidation of phenol and epoxidation of cyclohexene in the presence of hydrogen peroxide. The polymer‐supported HPPn Schiff base complexes of iron(III) ions showed 73.0 wt% conversion of phenol and 90.6 wt% conversion of cyclohexene at a molar ratio of 1:1:1 of substrate to catalyst and hydrogen peroxide, but unsupported complexes of iron(III) ions showed 63.8 wt% conversion for phenol and 83.2 wt% conversion for cyclohexene. The product selectivity for catechol (CTL) and epoxy cyclohexane (ECH) was 93.1 and 98.3 wt%, respectively with supported HPPn Schiff base complexes of iron(III) ions but was lower with HPPn Schiff base complexes of copper(II) and zinc(II) ions. Activation energy for the epoxidation of cyclohexene and phenol conversion with unsupported HPPn Schiff base complexes of iron(III) ions was 16.6 kJ mol^?1 and 21.2 kJ mol^?1, respectively, but was lower with supported complexes of iron(III) ions. Copyright © 2007 John Wiley & Sons, Ltd.     

Polymer Supported Schiff Base Complexes of Iron(III), Cobalt(II) and Nickel(II) Ions and their Catalytic Activity in Oxidation of Phenol and Cyclohexene

The polymer supported transition metal complexes of N,N′‐bis (o‐hydroxy acetophenone) hydrazine (HPHZ) Schiff base were prepared by immobilization of N,N′‐bis(4‐amino‐o‐hydroxyacetophenone)hydrazine (AHPHZ) Schiff base on chloromethylated polystyrene beads of a constant degree of crosslinking and then loading iron(III), cobalt(II) and nickel(II) ions in methanol. The complexation of polymer anchored HPHZ Schiff base with iron(III), cobalt(II) and nickel(II) ions was 83.30%, 84.20% and 87.80%, respectively, whereas with unsupported HPHZ Schiff base, the complexation of these metal ions was 80.3%, 79.90% and 85.63%. The unsupported and polymer supported metal complexes were characterized for their structures using I.R, UV and elemental analysis. The iron(III) complexes of HPHZ Schiff base were octahedral in geometry, whereas cobalt(II) and nickel(II) complexes showed square planar structures as supported by UV and magnetic measurements. The thermogravimetric analysis (TGA) of HPHZ Schiff base and its metal complexes was used to analyze the variation in thermal stability of HPHZ Schiff base on complexation with metal ions. The HPHZ Schiff base showed a weight loss of 58% at 500°C, but its iron(III), cobalt(II) and nickel(II) ions complexes have shown a weight loss of 30%, 52% and 45% at same temperature. The catalytic activity of metal complexes was tested by studying the oxidation of phenol and epoxidation of cyclohexene in presence of hydrogen peroxide as an oxidant. The supported HPHZ Schiff base complexes of iron(III) ions showed 64.0% conversion for phenol and 81.3% conversion for cyclohexene at a molar ratio of 1∶1∶1 of substrate to catalyst and hydrogen peroxide, but unsupported complexes of iron(III) ions showed 55.5% conversion for phenol and 66.4% conversion for cyclohexene at 1∶1∶1 molar ratio of substrate to catalyst and hydrogen peroxide. The product selectivity for catechol (CTL) and epoxy cyclohexane (ECH) was 90.5% and 96.5% with supported HPHZ Schiff base complexes of iron(III) ions, but was found to be low with cobalt(II) and nickel(II) ions complexes of Schiff base. The selectivity for catechol (CTL) and epoxy cyclohexane (ECH) was different with studied metal ions and varied with molar ratio of metal ions in the reaction mixture. The selectivity was constant on varying the molar ratio of hydrogen peroxide and substrate. The energy of activation for epoxidation of cyclohexene and phenol conversion in presence of polymer supported HPHZ Schiff base complexes of iron(III) ions was 8.9 kJ mol^?1 and 22.8 kJ mol^?1, respectively, but was high with Schiff base complexes of cobalt(II) and nickel(II) ions and with unsupported Schiff base complexes.     

Polymer-anchoring Schiff base ligands and their metal complexes: Investigation of their electrochemical,photoluminescence, thermal and catalytic properties

In this study, we prepared three polymer-anchored Schiff base ligands and their Cu(II), Co(II) and Ni(II) transition metal complexes. For this purpose, we synthesized three Schiff base ligands from the reaction of 2,4-dihydroxybenzaldehyde with diamines in the ethanol solution and characterized by the analytical and spectroscopic methods. We investigated the electrochemical and photophysical properties of the free Schiff base ligands in different solvents and concentrations. In the electrochemical studies, we found that the ligands show the reversible and irreversible redox processes. In order to obtain the polymer-anchored ligands, we used Merrifield’s peptide resin (PS) as solid support. The surface morphologies of the polymer anchored Schiff base ligands were done with the scanning electron microscopy (SEM). We did alkene epoxidation and alkane oxidation reactions of the metal complexes and used the cyclohexene, styrene, cyclohexane and cyclooctane as the substrate and they show the low catalytic activity. The metal complexes have no selectivity in the oxidation reactions. The polymer anchored Schiff base ligands and their metal complexes have high thermal stability at the higher temperatures.     

Heterogeneous Green Catalyst for Oxidation of Cyclohexene and Cyclooctene with Hydrogen Peroxide in the Presence of Host (Nanocavity of Y‐zeolite)/Guest (N4‐Cu(II) Schiff Base Complex) Nanocomposite Material

Copper(II) complex of a Schiff base ligand derived from pyrrolcarbaldehyde and o‐phenylenediamine (H₂L) has been synthesized and encapsulated in Y‐zeolite matrix. The hybrid material has been characterized by elemental analysis, IR and UV‐Vis spectroscopic studies as well as X‐ray diffraction (XRD) pattern. The encapsulated copper(II) catalyst is an active catalyst for the oxidation of cyclooctene and cyclohexene using H₂O₂ as oxidant. Under the optimized reaction conditions 81% conversion of cyclohexene with 65% selectivity for 2‐cyclohexenone formation and 87% conversion of cyclooctene with 46% selectivity for epoxide formation were obtained.     

双氮席夫碱配体对甲基三氧化铼催化烯烃环氧化反应的影响

 利用 2-吡啶甲醛、6-甲基-2-吡啶甲醛或 6-异丙基-2-吡啶甲醛与对甲基苯胺缩合制得双氮席夫碱配体, 考察了席夫碱配体以及溶剂和温度对甲基三氧化铼 (MTO) 催化不同结构烯烃环氧化反应的影响. 结果表明, 这些席夫碱配体与 MTO 构成的催化剂体系在甲醇溶剂中的催化性能最好, 双氮配体能显著提高环氧化反应的选择性. 当以甲醇为溶剂, 环己烯为底物, 在 –10 oC 反应 12 h 时, 环己烯转化率和环氧化物选择性均可达 100%. 席夫碱的配位能力越强, 越有利于提高环氧化物选择性, 而其配位能力取决于吡啶环中 6-位取代基的电子和立体结构. 给电子能力较强和空间位阻较小的烷基对应的配体的配位能力较强.     

高分子希夫碱金属配合物活性中心对催化活化分子氧性能的影响

以交联聚苯乙烯担载酪氨酸希夫碱为配体,制备了其锰、钴、铜高分子金属配合物,分别以环己烯、异丙苯和乙苯为底物,氧气为氧源,研究了温和条件下不同金属中心活化分子氧能力,发现高分子担载铜金属配合物的催化活化分子氧能力最强,对反应机理进行了探讨.     

镍(II)配合物官能化的MCM-41催化分子氧环氧化苯乙烯

制备了镍(II)席夫碱配合物官能化的MCM-41多相催化剂MCM-41-Ni.利用X射线粉末衍射、氮气物理吸附脱附、红外光谱、热重、电感耦合等离子体原子发射光谱、元素分析和透射电镜等方法对催化剂进行了表征.以氧气为氧化剂,MCM-41-Ni在催化环氧化苯乙烯的反应中表现出较高的催化活性;苯乙烯的转化率为95.2%,环氧苯乙烷的选择性为66.7%.系统地研究了反应温度、催化剂用量、溶剂以及反应时间对反应性能的影响.催化剂经过4次循环仍然表现出较好的稳定性和催化活性.     

Preparation and catalytic properties of chitosan bound Schiff base copper complexes

Chitosan, a natural polymer, bound Schiff base copper complexes CT‐She‐Cu, CT‐o‐Bel‐Cu, CT‐m‐Bel‐Cu were prepared and characterize by inductively coupled plasma (ICP), FT‐IR and X‐ray photoelectron spectroscopy (XPS). Their catalytic activity in the oxidation of cyclohexene with molecular oxygen was studied. All the complexes have catalytic activity and the main oxidation products are 2‐cyclohexene‐ol, 2‐cyclohexene‐one and cyclohexene hydroperoxide, which were measured by gas chromatography/mass spectroscopy (GC/MS) and GC/IR. CT‐m‐Bel‐Cu was selected to study the influence of reaction temperature, amount of catalyst and additives such as acid and base on the oxidation of cyclohexene systematically. Copyright © 2004 John Wiley & Sons, Ltd.     

Co(II), Fe(III) or VO(II) Schiff base metal complexes immobilized on graphene oxide for styrene epoxidation

Cobalt(II), iron(III) or oxovanadium(II) Schiff base metal complexes have been covalently grafted onto graphene oxide ( GO ) previously functionalized with 3‐aminopropyltriethoxysilane. Potential catalytic behaviors were tested in the epoxidation of styrene, using air as the oxidant. The catalysts were characterized using infrared (IR) and Raman spectroscopies, thermogravimetric analyses, inductively coupled plasma atomic emission spectrometry (ICP‐AES), X‐ray diffraction, nitrogen adsorption–desorption, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). IR spectroscopy, thermogravimetric analyses and ICP‐AES confirmed the successful incorporation of the metal Schiff base complexes onto GO . X‐ray diffraction, nitrogen adsorption–desorption, Raman spectroscopy, SEM and TEM showed the intact structure of the GO . Co-GO and Fe-GO showed high styrene conversion (90.8 versus 86.7%) and epoxide selectivity (63.7 versus 51.4%). Nevertheless, VO-GO showed poorer catalytic performance compared with Co-GO and Fe-GO . The recycling results of these heterogeneous catalysts showed good recoverability without significant loss of activity and selectivity within four successive runs. Copyright © 2015 John Wiley & Sons, Ltd.     

Covalent supporting of novel dioxo‐molybdenum tetradentate pyrrole‐imine complex on Fe3O4 as high‐efficiency nanocatalyst for selective epoxidation of olefins

A novel Mo(VI) tetradentate Schiff base complex based on two pyrrole‐imine donors was anchored covalently on Fe₃O₄ nanoparticles and characterized using physicochemical techniques. The catalytic epoxidation process was optimized in terms of the effects of solvent, reaction temperature, kind of oxidant and amount of oxidant and catalyst. Then the novel heterogeneous nanocatalyst was used for the efficient and selective catalytic epoxidation of internal alkenes (cyclohexene, cyclooctene, α‐pinene, indene and trans ‐1,2‐diphenylethene) and terminal alkenes (n ‐heptene, n ‐octene, n ‐dodecene and styrene) using tert ‐butyl hydroperoxide (70% in water) as oxidant in 1,2‐dichloroethane as solvent. The prepared nanocatalyst is very effective for the selective epoxidation of cis ‐cyclooctene with 100% conversion, 100% selectivity and turnover frequency of 1098 h⁻¹ in just 30 min. The magnetic nanocatalyst was easily recovered using an external magnetic field and was used subsequently at least six times without significant decrease in conversion.     

Olefin epoxidation with tert-butyl hydroperoxide catalyzed by functionalized polymer-supported copper(II) Schiff base complex

Abstract  

A new polymer-supported Cu(II) Schiff base complex has been synthesized and characterized by elemental (including metal) analysis, FT-IR spectroscopy, UV–Vis diffuse reflectance spectroscopy, thermogravimetric analysis, and scanning electron microscopy. The catalytic performance of this complex was evaluated in the epoxidation of styrene in acetonitrile/N,N-dimethylformamide (9:1) mixture with 70% tert-butyl hydroperoxide as an oxidizing agent under liquid phase reaction conditions for selective synthesis of styrene oxide. Suitable reaction conditions have been optimized by considering the effects of various reaction parameters such as temperature, reaction time, solvent, oxidant, catalyst amount, and styrene to hydroperoxide molar ratio for the maximum conversion of styrene as well as selectivity of styrene oxide. We have also investigated the epoxidation reaction of various olefins under the optimized reaction conditions. Comparison between catalytic activities of the polymer-supported Cu(II) Schiff base complex and its homogeneous analogue showed that the polymer-supported catalyst was more active. This heterogeneous complex was reused for five times. The selectivity of the heterogeneous catalyst does not change even after five times of reusing.     

SYNTHESIS AND CATALYTIC PROPERTY OF POLYSTYRENE SUPPORTED PHENYLALANINE SCHIFF BASE COMPLEX OF Mn(Ⅱ) IN AEROBIC OXIDATION OF CYCLOHEXENE

1. INTRODUCTION The partial oxidation of alkenes (forming acids, aldehydes and alcohols) is of considerable interest to the chemical industry. In most cases, more than one oxygenated product is formed from a given starting material and all products are susceptible to complete oxidation to carbon dioxide and water [1]. As mimetic oxygen carrier or oxidation catalyst, metalloporphyrins have been widly studied [2~7]. Among the non-porphyrin systems, the manganese complexes of Schiff base are…     

Anchoring of copper complex in MCM-41 matrix: a highly efficient catalyst for epoxidation of olefins by tert-BuOOH

A complex moiety containing copper (II) has been anchored covalently into the organic-modified Si-MCM-41 to prepare a new catalyst. The amine group containing organic moiety 3-aminopropyl-triethoxysilane has been first anchored on the surface of Si-MCM-41 via silicon alkoxide route. The amine group upon condensation with salicyldehyde affords a bidentate ligand in the mesoporous matrix for anchoring copper(II) ions. The prepared catalyst has been characterized by UV-vis, electron paramagnetic resonance (EPR), and infrared (IR) spectroscopic analysis, small-angle X-ray diffraction, and N2 sorption study. A remarkable difference in the pore structure has been observed after the immobilization of copper(II) complex in Si-MCM-41. The catalyst showed excellent catalytic efficiency in epoxidation reactions with various olefinic compounds including styrene and allyl alcohol, using tert-BuOOH as oxidant. Notably, styrene shows unprecedented high conversion (97%) as well as epoxide selectivity (89%) with tert-BuOOH over the Cu-MCM-41 catalyst.     

Monomer/polymer Schiff base copper(II) complexes for catalytic oxidative polymerization of 2,2′‐dihydroxybiphenyl

Catalytic oxidative polymerization of 2,2′‐dihydroxybiphenyl (DHBP) was performed by using both the Schiff base monomer‐Cu(II) complex and Schiff base polymer‐Cu(II) complex compounds as catalysts and hydrogen peroxide as oxidant, respectively. The dependence of monomer conversion and molecular weight distribution on various reaction parameters, including time, temperature, solvent as well as the amount of catalyst and oxidant were investigated. The structure of the poly‐2,2′‐dihydroxybiphenyl (PDHBP) was confirmed by UV‐vis, IR, ¹H and ¹³C NMR spectroscopy techniques. The electrochemical and thermal properties of PDHBP were also studied. DSC data revealed that PDHBP was amorphous. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2977–2984, 2009     

Encapsulation of a binuclear manganese(II) complex with an amino acid-based ligand in zeolite Y and its catalytic epoxidation of cyclohexene

A Schiff base ligand was synthesized by the condensation of salicylaldehyde with l-tyrosine. Interaction of this ligand with Mn(II)-exchanged zeolite Y leads to encapsulation of the ligand within the zeolite and complexation of the metal. The encapsulated complex has been characterized by spectroscopic studies and chemical analyses. This material serves as a catalyst for the oxidation of cyclohexene to cyclohexene epoxide and 2-cyclohexene-1-ol using H₂O₂ as oxidant. The reaction conditions have been optimized for solvent, temperature and amount of oxidant and catalyst. The catalyst shows high activity and selectivity toward production of cyclohexene epoxide in acetonitrile at 60 °C with [H₂O₂]/[C₆H₁₀] = 2.5 molar ratio. Comparison of the encapsulated catalyst with the corresponding homogeneous catalyst showed that the heterogeneous catalyst had higher activity and selectivity than the homogeneous catalyst.     

SYNTHESIS AND CATALYTIC PROPERTY OF POLYSTYRENE SUPPORTED PHENYLALANINE SCHIFF BASE COMPLEX OF Mn（Ⅱ） IN AEROBIC OXIDATION OF CYCLOHEXENE

The polystyrene supported phenylalanine Schiff base complex of Mn(Ⅱ)(PS-Sal-Phe-Mn)was prepared with chloromethylated styrene polymer beads, 2,4-dihydroxybenzaldehyde,L-phenylalanine and manganese(Ⅱ)acetate tetrahyrate., The polymeric ligand and the complex were characterized by FT-IR,, small area X-ray photoelectron spectroscopy(XPS), and ICP-AES. In the presence of the manganese complex, cyclohexene(1)was effectively oxidized by molecular oxygen without reductant. The major products of the reaction were 2-cyclohexen-1-ol(2),2-cyclohexen-1-one(3)and 2-cyclohexen-1- hydroperoxide(4), which was different with typical oxidation of cyclohexene. The influence of reaction temperature and additive for oxidation had been studied. The selectivity of 2-cyclohexen-l-hydroperoxide varied with reaction time and different additives. The mechanism of cyclohexene oxidation had also been discussed.     

SYNTHESIS AND CATALYTIC PROPERTY OF POLYSTYRENE SUPPORTED GLUTAMIC ACID SCHIFF BASE COMPLEX OF Mn(Ⅱ)IN AEROBIC OXIDATION OF CYCLOHEXENE

The polystyrene supported glutamic acid Schiff base complex of Mn (Ⅱ) (PS-Sal-Glue-Mn) was prepared with chloromethylated styrene polymer beads,2,4-dihydroxybenzaldehyde, L-glutamic acid and manganese (Ⅱ) acetate tetrahyrate. The polymeric ligand and the complex were characterized by FT-IR, small area X-ray photoelectron spectroscopy (XPS) and ICP-AES. In the presence of the manganese complex, cyclohexene (1) was effectively oxidized by molecular oxygen without reductant. The major products of the reaction were 2-cyclohexen-1-ol (2), 2-cyclohexen-1-one (3) and 2-cyclohexen-1- hydroperoxide (4), which was different with typical oxidation of cyclohexene. The influence of reaction temperature and additive for oxidation had been studied. The selectivity of 2-cyclohexen-1-hydroperoxide varied with reaction time and different additives. The mechanism of cyclohexene oxidation had also been discussed.