Catalytic asymmetric epoxidation of limonene using manganese Schiff-base complexes immobilized in ionic liquids

The asymmetric epoxidation of limonene has been performed using Jacobsen’s catalyst dissolved in 1-n-butyl-3-methylimidazolium tetrafluoroborate (BMI · BF₄) ionic liquid and with hydrogen peroxide oxidant giving high stereoselectivity. Limonene was selectively converted into 1,2-epoxi-p-ment-8-enes with a diastereoisomeric excess of 74% and conversions up to 70%. Chirality of limonene was found to play an important role in stereochemical formation of new chiral centers because the synthesis occurs with double asymmetric induction.

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Catalytic epoxidation of cyclooctene using molybdenum(VI) compounds and urea-hydrogen peroxide in the ionic liquid [bmim]PF6

Commercially available molybdenum(VI) compounds are shown to be good catalysts in the epoxidation of cyclooctene with the urea-hydrogen peroxide adduct (UHP) in the ionic liquid 1-n-butyl-3-methylimidazolium hexafluorophosphate, [bmim]PF₆. The cyclooctene oxide was isolated by simple extraction with organic solvent and the ionic liquid-catalyst mixture recycled and reused.     

Grafting polyethylene glycols molybdenum(VI) complexes on ZSPP and their catalytic epoxidation of cyclohexene

A new type of inorganic–organic hybrid materials – zirconium oligo-styrenyl phosphonate hydrogen phosphate (ZSPP) was used to prepare heterogeneous catalysts for olefin epoxidation by grafting polyethylene glycols on ZSPP and subsequently coordinating with MoO₂(acac)₂. The catalysts were characterized by IR, Raman, XPS, XRD, TG, BET and elemental analysis. The catalytic activities of the prepared catalysts were evaluated through the epoxidation of cyclohexene using TBHP as oxidant. The results indicated that conversion and selectivity increased at first and then decreased with increasing numbers of O atoms in the ligands, and the catalyst 2b gave the best catalytic results that the conversion and selectivity was up to 98.9% and 97.4%, respectively.     

New molybdenum(VI) complex with ONS-donor thiosemicarbazone ligand: Preparation,structural characterization,and catalytic applications in olefin epoxidation

New dioxomolybdenum(VI) complex was prepared by reacting 1-(2,4-dihydroxybenzylidene)-N-methyl-N-phenylthiosemicarbazone (H₂L) as ligand and [MoO₂(acac)₂] in acetonitrile solution. The doubly deprotonated ligand is coordinated to molybdenum through sulfur atom, hydrazinic nitrogen atom and phenolic oxygen atom. The resulting complex with the formula [MoO₂L(CH₃CN)] which contains an acetonitrile molecule in sixth site of coordination, was characterized by elemental analyses, ¹H NMR, IR and electronic spectroscopic studies and single crystal X-ray diffraction analysis. This complex was tested as a catalyst for the homogeneous epoxidation of olefins using tert-butyl hydrogen peroxide (TBHP) as an oxidant. The catalyst shows efficient reactivity in the olefins epoxidation reactions giving high yield and selectivity under atmospheric conditions, in most cases.     

Electrochemical and spectroscopic studies of molybdenum(VI) complexes with aminopolycarboxylic acids

The complexes of molybdenum(VI) with iminodiacetic acid (IDA), nitrilotriacetic acid (NTA) and ethylenediaminetetraacetic acid (EDTA) were investigated by means of polarographic and spectroscopic methods. The composition of the complexes was determined by the Job's method as following: 1Mo(VI)/1IDA; 1Mo(VI)/1NTA and 2Mo(VI)/1EDTA. The polarographic wave height was fairly dependent on the nature of the complexes. The overall reaction rate for the reduction of Mo(VI)-IDA complex was limited by diffusion. On the other hand, the polarographic reduction of Mo(VI)-NTA and - EDTA complexes were kinetically controlled by the preceding chemical reaction which was composed of protonation, dimerization and substitution of ligands, however, the rate-determining step was the substitution of ligands. The mechanism for the electroreduction of each complex was discussed.     

新型钼(Ⅵ)系配合物MoO2Cl2(OPMePh2)2催化苯乙烯环氧化研究

合成出3种Mo(Ⅵ)配合物MoO2F2(OPMePh2)2、MoO2Cl2(OPMePh2)2、MoO2Cl2(OPPh3)2,并用红外光谱和核磁共振氢谱对其结构进行了表征.首次报道以MoO2Cl2(OPMePh2)2为催化剂、以叔丁基过氧化氢(TBHP)为氧源,催化环氧化苯乙烯反应,反应体系温和有效.研究结果表明,反应温度、反应时间、溶剂种类、氧源用量和催化剂用量等反应条件对苯乙烯环氧化反应具有重要影响.在优化条件下,苯乙烯转化率达到60.07%,环氧化产物选择性达到46.35%.     

Extraction of dioxouranium(VI) in small channels using ionic liquids

The extraction behaviour of dioxouranium(VI) from nitric acid solutions with tributylphosphate (TBP) dissolved (30%, v/v) in room temperature ionic liquids (viz. 1-butyl-3-methylimidazolium bis{(trifluoromethyl)sulfonyl}amide, [C₄mim][NTf₂], 1-decyl-3-methylimidazolium bis{(trifluoromethyl)sulfonyl}amide, [C₁₀mim][NTf₂], and trihexyltetradecylphosphonium bis{(trifluoromethyl)sulfonyl}amide, [P_6 6 6 14][NTf₂]) was investigated. The experiments were performed in a capillary (0.5 mm internal diameter) made of Teflon, operated in the plug flow regime. The effects of ionic liquid type, initial nitric acid concentration, and residence time on dioxouranium(VI) extraction were studied. UV–vis spectroscopy was used for the determination of the dioxouranium(VI) concentration in the ionic liquid phase. For increasing [HNO₃]_aq,init, the %extraction decreased and then increased for [C₄mim][NTf₂], while for the other two ionic liquids it increased. The %extraction also increased with residence time in the channel. Overall mass transfer coefficients were about 0.2 s^–1 in all TBP/ionic liquid systems at the initial nitric acid concentration of 3 M when a 10 cm capillary was used.     

Functionalized chitosan with butylammonium ionic liquids for removal of Cr(VI) from aqueous solution

Environmental pollution by heavy metals is currently a problem of great concern for human health. In this context, this study aims to contribute with the synthesis and characterization of chitosan functionalized with three different ionic liquids (n-butylammonium acetate, sec-butylammonium acetate, and tert-butylammonium acetate) followed by its application in hexavalent chromium effluent treatment. The adsorbents synthesized (ChN, ChS, and ChT) were characterized by SEM, EDS, FTIR, BET, RDD, PSD, and XRD techniques. Afterward, the influences of temperature, contact time, and pH on the Cr(VI) adsorption process were evaluated. The solution with pH 3 displayed the highest adsorption capacities (107.31, 104.60, and 107.97 mg.g^-1 for ChN, ChS, and ChT, respectively). The kinetic data were better adjusted to the Weber-Morris kinetic model with an ideal time of 2 h. Furthermore, the influence of temperature was evaluated using the Freundlich and Langmuir isotherms, with maximum capacities of 142.05 (ChN), 131.58 (ChS), and 146.63 mg.g^-1 (ChT). The adsorbent displayed enhanced adsorption properties in comparison with raw chitosan by an intensification of the electrostatic interaction between amino groups and hexavalent chromium. Finally, the reusability was investigated, and significant results were observed (84.33 ± 4.87%) in the adsorption process after 4 cycles.     

Synthesizing cyclic carbonates from olefin oxides and carbon dioxide. I: Catalysis with ionic liquids

A review of catalytic systems based on ionic liquids used for promoting reactions between olefin oxides and carbon dioxide is presented. It is shown that ionic liquids based on imidazoles, pyridines, quaternary ammonium salts, and other compounds exhibit high activity in these processes and can serve as alternatives to conventional catalysts of cyclocarboxylation of olefin oxides under certain conditions. Specific features of the reactions between oxiranes and carbon dioxide in the presence of ionic liquids are considered, including reactions with the use of promoting additions based on metal salts. Mechanisms of the catalytic action of ionic liquids in syntheses of cyclocarbonates are described. Other works are critically analyzed to develop new lines in the catalysis of cyclocarboxylations of olefin oxides with ionic liquids.     

Extraction behaviour of dioxouranium(VI) cation by two phosphorous-based liquid cation-exchangers in room-temperature ionic liquids

Extraction of uranium with bis-(2-ethylhexyl) phosphonic acid (PC-88A) and bis(2,4,4-trimethylpentyl) phosphinic acid (Cyanex-272) was studied in several imidazolium-based room-temperature ionic liquids (RTILs), C_nmim·X (where n = 4, 6, 8 and X = PF₆ and Tf₂N). The extraction kinetics was slow and about 0.5–1 h equilibration time was required for most of the extraction systems, except in C₈mim·PF₆, where 2 h and 4 h were required to reach the equilibrium values for PC-88A and Cyanex-272, respectively. The extraction of UO₂²⁺ ion by the two ligands was significantly affected by the nature and the composition of the RTILs.     

pH Dependent formations of dinuclear molybdenum(V) and incomplete cubane molybdenum(IV) complexes with nitrilotriacetate

Nitrilotriacetato oxomolybdenum(V) dinuclear complex (NH₄)₄[cis-Mo₂O₄(nta)₂] · 7H₂O (1) (H₃nta = nitrilotriacetic acid) and its incomplete cubane-type trinuclear molybdenum(IV) complex [Mo₃O(OH)₃(Hnta)₃] · Cl · 3H₂O (2) are isolated in a weak acidic and an acidic solutions, respectively (pH 4.5 and 1.0). The nitrilotriacetate ligand in the anion 1 or the cation 2 displays tridentate mode through the nitrogen atom and the oxygen atoms of β-carboxy groups. Unusual protonations of bridged oxygen atoms in 2 have not effect on the skeleton of molybdenum(IV) cap Mo₃O unit. There are obvious dissociations of molybdenum(V) complexes based on ¹³C NMR observations in solution.     

Stability and recycling of polymer-supported Mo(VI) alkene epoxidation catalysts

As a prelude to commissioning a reactive distillation column (RDC) for the continuous epoxidation of cyclohexene using t-butylhydroperoxide and a heterogeneous polymer-supported Mo(VI) catalyst, the long-term stability of three candidate polymer-supported Mo catalysts has been evaluated. The polymer catalysts are a polybenzimidazole-supported species, PBI.Mo, and two poly(styrene-divinylbenzene) resin-based species, Ps.AMP.Mo1 and 2, prepared in-house by amination of vinyl benzyl chloride-containing resins using 2-aminomethyl pyridine, followed by loading with Mo. The stability of each polymer catalyst was assessed by recycling a sample 10 times in small batch reactions using conditions that will form the basis of the continuous process. At the same time the loss of Mo from each support has been investigated by isolating any residue from reaction supernatant solutions, following removal of the heterogeneous polymer catalyst, and then using the residues as potential catalysts in epoxidation reactions. This is a powerful technique for identifying unambiguously loss of catalytically active Mo from the support and is not dependent on Mo analytical procedures. All three polymer catalysts are highly active and selective in 10 consecutive reactions but the supernatant solutions also contain catalytically active Mo residues. In the case of PBI.Mo and Ps.AMP.Mo2 the contribution to catalysis from homogeneous Mo species lost from the supports is all but eliminated after aging through 10 cycles, but in the case of Ps.AMP.Mo1 the contribution from leached Mo species remains significant even after similar aging. The major factor determining this differential behaviour seems to be the mole ratio of polymer-bound ligand to Mo which must be significantly above unity to provide long-term retention of Mo.     

Oxotungsten(VI) complexes with amino(phenolate)alcoholate ligand

The reaction between tungsten(VI) complex [W(eg)₃] (eg = 1,2-ethanediolato dianion) and a phenolic ligand precursor 2,4-di-tert-butyl-6-(((2-hydroxyethyl)(methyl)amino)methyl)phenol (H₂L) affords a monomeric oxotungsten complex [WO(eg)(L)]. This complex reacts further with Me₃SiCl, which leads to the displacement of ethanediolato ligand from the complex unit and formation of cis- and trans-isomers of corresponding dichloro complex [WOCl₂(L)]. Identical dichloro complexes were also prepared by the reaction between H₂L and WOCl₄. Molecular structure of [WO(eg)(L)] was verified by X-ray crystallography.     

水介质中离子液体催化合成四氢喹唑啉

以1-丁基-3-甲基咪唑四氟硼酸盐作为催化剂，以芳香胺和2-氨基苯甲醛为原料，在水介质中通过环化缩合反应，合成了一系列四氢喹唑啉类衍生物。通过对模板反应条件的探究，确定了最优条件为：0.2 mmol 2-（1-吡咯烷基）苯甲醛（Ⅰa），0.4 mmol芳香胺（Ⅱa），30%（以Ⅰa物质的量为基准）的催化剂，1 mL H2O，90 ℃下反应6 h，可得到产率为81%的产物。同时探索了的反应底物普适性，以较好的底物范围合成了19种四氢喹唑啉类衍生物。     

Understanding interfacial behaviors of isobutane alkylation with C4 olefin catalyzed by sulfuric acid or ionic liquids

The interfacial properties between the hydrocarbon phase including isobutane and 2‐butene and the catalyst phase including H₂SO₄ or ionic liquids (ILs) with various alkyl chain length on their imidazolium cations have been investigated using molecular dynamics (MD) simulations. Compared to H₂SO₄, ILs can obviously improve the interfacial width, solubility and diffusion of reactants at the interface. The ILs with longer chains on cations exhibit a significant density enrichment of alkyl chains at the interface and tend to orient themselves with alkyl chains perpendicular to the interface and protruding into the reactant phase, which is in good agreement with the van der Waals energy between the reactants and cations of the ILs. The ILs with longer chains can improve the interfacial width and facilitate the dissolution of isobutane in catalyst phase, and thus exhibit a better catalytic performance, which agrees well with alkylation experiments in this work. © 2017 American Institute of Chemical Engineers AIChE J, 64: 950–960, 2018     

A novel and efficient catalytic epoxidation of monoterpenes by homogeneous and heterogeneous methyltrioxorhenium in ionic liquids

A convenient and efficient synthesis of monoterpene epoxides by application of methyltrioxorhenium and heterogeneous poly(4-vinylpyridine)/methyltrioxorhenium and microencapsulated polystyrene/methyltrioxorhenium catalytic systems in ionic liquids is described here. It was found that even highly sensitive terpenic epoxides were obtained in excellent yields. Environmentally friendly, easily available and low cost (UHP) urea hydrogen peroxide adduct was used as the primary oxidant. Catalysts were stable systems for at least four recycling oxidations. Experimental results showed that the reactions performed in ionic liquids were more selective and efficient than the ones performed in molecular solvents.     

Gas drying with ionic liquids

The gas drying technology with ionic liquids (ILs) was systematically studied ranging from the molecular level to industrial scale. The COSMO‐RS model was first used to screen the suitable IL and provide theoretical insights at the molecular level. Toward CO₂ gas dehydration, we measured the CO₂ solubility in single [EMIM][Tf₂N] and in the [EMIM][Tf₂N] + H₂O mixture, as well as the vapor‐liquid equilibrium (VLE) of [EMIM][Tf₂N] + H₂O system, to justify the applicability of UNIFAC model. Based on the thermodynamic study, the rigorous equilibrium (EQ) stage mathematical model was established for process simulation. The gas drying experiment with IL was also performed and the water content in gas product can be reduced to 375 ppm. It was confirmed that a less flow rate of absorbent, a higher CO₂ recovery ratio and a much lower energy consumption can be achieved with IL than with the conventional triethylene glycol (TEG). © 2017 American Institute of Chemical Engineers AIChE J, 64: 606–619, 2018     

新型离子液体的合成及其阳离子基团缓蚀性能

以高纯环烷酸为原料,合成了一系列含咪唑啉环的新型离子液体Ⅰ～Ⅴ,探讨了阳离子咪唑啉基团中N_（3）原子上取代基与缓蚀性能的关系.采用碳钢挂片失重法和电化学测试法,评价了它们在酸性溶液中的缓蚀性能;采用量子化学法和极化效应指数法,分别计算了离子液体Ⅰ～Ⅴ阳离子咪唑啉基团的前线轨道能量及其相应的PEI等参数.实验结果和理论分析表明：离子液体Ⅰ～Ⅴ阳离子咪唑啉基团的缓蚀效率呈现如下关系,Ⅴ＞Ⅳ＞Ⅲ＞Ⅱ＞Ⅰ;其缓蚀效率与E_HOMO、ΔE_L-H和PEI等参数间均具有良好的线性关系.     

Evaluation and mechanism of cationic/anionic dyes extraction from water by ionic liquids

Dispersive liquid–liquid micro-extraction (DLLME) using three different imidazolium-based ionic liquid (IL) was applied for extraction of recalcitrant dyes, Eriochrome black T (anionic azo dye), and Crystal Violet (cationic triphenylmethane dye) from aqueous solutions, not previously reported. Effects of process parameters such as initial dye concentration, pH of aqueous phase, amount and type of IL on fraction extracted, and distribution ratio of dyes were studied. Further, dyes interaction with ILs and extraction mechanism were explored. Considering the high cost of ILs, regeneration and reuse study for ILs was also performed using reverse DLLME. The fraction extracted for both the dyes with all the ILs varied significantly with pH change. Maximum dyes fraction extracted were observed nearly at neutral pH (pH =7). However, the fraction extracted were different for different IL.     

Electrochemical behavior of several iron complexes in hydrophobic room-temperature ionic liquids

The electrochemical behavior of FeCp₂⁺/FeCp₂ (Cp⁻, cyclopentadienyl), FeCl₄⁻/FeCl₄²⁻, FeBr₄⁻/FeBr₄²⁻ and Fe(CN)₆³⁻/Fe(CN)₆⁴⁻ couples was studied in the hydrophobic room-temperature ionic liquids based on bis(trifluoromethylsulfonyl)imide (TFSI⁻) with 1-n-butyl-1-methylpyrrolidinium (BMP⁺) and other quaternary ammonium cations. The cyclic voltammetric data indicated that these complexes were stable in BMPTFSI and that the redox reactions between trivalent and divalent iron species of these complexes are electrochemically reversible. The diffusion coefficients of these complexes were found to be affected mainly by the size of the species. On the other hand, the redox potential of Fe(CN)₆³⁻/Fe(CN)₆⁴⁻ couple depended on organic cations reflecting the difference in the acceptor properties of the organic cations.