Stable poly (ionic liquids) with unique cross‐linked mesoporous‐macroporous structure as efficient catalyst for alkylation of o‐xylene and styrene

In this work, using divinylbenzene (D), 1‐vinylimidazole (V) and 1‐vinyl‐3‐butylimidazolium bromide ([VBIM][Br]) as monomers, the binary‐monomer poly (ionic liquids) (PILs) and ternary‐monomer PILs were successfully synthesized, via hydrothermal polymerization and anion exchange, sequentially. Compared with each other, the ternary polymeric acidic IL catalyst has a clear spongy porous structure, while having a more stable macroporous structure, a larger specific surface area, more acidic groups and more active sites. Catalytic performance of catalyst was investigated through the alkylation of o‐xylene and styrene. The effect of the amount of IL added and the length of the cation chain on the ternary polymerization of acidic IL was systematically investigated. Under optimal reaction conditions (molar ratio of monomers was D:V:[VBIM][Br] = 2:1:1, the most suitable cation chain length was C₄), the synthesized MPD‐[C₄V]‐[VBIM][SO₃CF₃] has a larger specific surface area (89.47 m²/g), large pore volume (0.29 cm³/g), and abundant mesopores and macropores, which help to improve the contact between the active site and reactants. Moreover, the catalyst could maintain a relatively high conversion of styrene (99.0%), 1,2‐diphenylethane yield (98.7%) and high thermostability under reaction and be easily be divided from the solution, which is critical for heterogeneous solid catalysts.     

Gas‐phase dissociation of ionic liquid aggregates studied by electrospray ionisation mass spectrometry and energy‐variable collision induced dissociation

Positive singly charged ionic liquid aggregates [(C_nmim)_m+1(BF₄)_m]⁺ (mim = 3‐methylimidazolium; n = 2, 4, 8 and 10) and [(C₄mim)_m+1(A)_m]⁺ (A = Cl⁻, BF₄⁻, PF₆⁻, CF₃SO₃⁻ and (CF₃SO₂)₂N⁻) were investigated by electrospray ionisation mass spectrometry and energy‐variable collision induced dissociation. The electrospray ionisation mass spectra (ESI‐MS) showed the formation of an aggregate with extra stability for m = 4 for all the ionic liquids with the exception of [C₄mim][CF₃SO₃]. ESI‐MS‐MS and breakdown curves of aggregate ions showed that their dissociation occurred by loss of neutral species ([C_nmim][A])_a with a ≥ 1. Variable‐energy collision induced dissociation of each aggregate from m = 1 to m = 8 for all the ionic liquids studied enabled the determination of E_{cm, 1/2} values, whose variation with m showed that the monomers were always kinetically much more stable than the larger aggregates, independently of the nature of cation and anion. The centre‐of‐mass energy values correlate well with literature data on ionic volumes and interaction and hydrogen bond energies. Copyright © 2008 John Wiley & Sons, Ltd.     

High Catalytic Performance of Mesoporous Dual Brønsted Acidic Ternary Poly (Ionic Liquids) for Friedel‐Crafts Alkylation

A newfangled cross‐linked dual Brønsted acidic ternary mesoporous poly (ionic liquids)(MPILs) with mesoporous structure was successfully synthesized with divinylbenzene as cross linker, 1‐vinyl‐3‐butyl imidazole bromide and sodium p‐styrene sulfonate as functional group through an ordinary post‐modification method and anion exchange process. A sponge‐like mesoporous tunnel structure was observed and the obtained P (BVS‐SO₃H)‐SO₃CF₃ sample appeared a relatively high thermal stability, a large surface area (up to 286.8 m²/g) and great pore volume (0.73 cm³/g). The abundant dual acidic group of sulfonic acid and trifluoromethanesulfonic acid of the composite in the polymer framework impart Brønsted acidity. For the sake of demonstrating our claims, the sample has been used as a novel solid acid catalyst for the reaction of alkylation of o‐xylene with styrene to 1‐diphenylethane (PXE). Under optimal reaction conditions (reaction under 120 °C for 3 hr, catalyst amount was 0.5 wt% of the reaction system, and the mass ratio of o‐xylene/styrene was 7.5:1, a 100% conversion of styrene and 93.7% PXE yield was acquired. After four times recycle, the yield remains 53.3%. Comparing with the commercial liquid acid catalyst, it processing a higher catalytic property and recyclability. Moreover, this fresh dual acidic heterogeneous catalyst owning a promising future applied in other acidic catalytic reactions and provide a new method to modify catalyst.     

Synthesis of Pyrazolo[3,4‐d]pyrimidin‐4‐ones Catalyzed by Br?nsted‐acidic Ionic Liquids as Highly Efficient and Reusable Catalysts

A convenient and efficient method for the synthesis of pyrazolo[3,4‐d]pyrimidin‐4‐ones via heterocyclization reaction of 5‐amino‐1H‐pyrazole‐4‐carboxamides with triethyl orthoesters using two Br?nsted‐acidic ionic liquids, 3‐methyl‐1‐(4‐sulfonic acid)butylimidazolium hydrogen sulfate [MIM⁺(CH₂)₄SO₃H][HSO₄^?] or N‐(4‐sulfonic acid)butyl triethylammonium hydrogen sulfate [Et₃N⁺(CH₂)₄SO₃H][HSO₄^?], as efficient homogeneous catalysts under solvent‐free conditions is described.     

Functional mesoporous poly (ionic liquid) derived from P123: From synthesis to catalysis and alkylation of styrene and o‐xylene

A novel strategy was proposed for the fabrication of high‐performance acidic mesoporous poly ionic liquids catalyst. In this work, mesoporous poly ionic liquids (MPILs) were synthesized with P123 (PEO₂₀PPO₇₀PEO₂₀) served as pore‐forming agent. Then, MPILs were treated with PW^3? anion exchange, thereby fabricating PW/MPIL‐S(x). MPIL and PW/MPIL‐S(x) were characterized by scanning electron microscope (SEM), transmission electron microscopy (TEM), Thermogravimetric analysis (TA), N₂ adsorption–desorption and Fourier transform infrared (FT‐IR) spectra and X‐ray photoelectron spectroscopy (XPS) spectra. The effect of solvent and concentration of P123 on the morphology and mesoporous structure of MPILs were investigated systematically. And the results show that MPILs were featured with mesoporous channel structure, high surface area (up to 737 m²/g) and large pore volumes (1.16 cm³/g), which benefit heterogeneous phase reaction (such as, alkylation of styrene with o‐xylene). In the alkylation reaction, under optimal reaction conditions, the catalyst PW/MPIL‐THF (4.0 g) shows high conversion of styrene (100%) and PXE yield (96.21%), demonstrating the excellent catalytic activities. Furthermore, PW/MPIL‐S(x) are easy to be separated from the catalytic system by filtration and show no obvious decrease in catalytic activity after 6 cycle runs. The obtained PW/MPIL‐S(x) catalyst exhibit high thermal and mechanical stability as well, indicating extensive application in high temperature acidic catalysis. This work might open up a new method for the synthesizing of porous polymer catalysts in the future.     

D,L‐α‐Tocopherol Synthesis Catalyzed by the Brønsted Acidic Ionic Liquids

Abstract

The synthesis of D,L‐α‐tocopherol from trimethylhydroquinone and isophytol using the Brønsted acidic SO₃H‐functionalized ionic liquids as catalysts was explored. The catalytic activities of the SO₃H‐functionalized ionic liquids were dependent on their anions. The yield of D,L‐α‐tocopherol also depended on the solvent, which was the reaction medium. A yield of 94.3% was obtained using the SO₃H‐functionalized ionic liquid with [BF₄ ^?] anion as catalyst in propylene carbonate/heptane. The reaction mixture exhibited good biphasic behaviors, so that the produced D,L‐α‐tocopherol could be separated by decantation. The SO₃H‐functionalized ionic liquids could be reused after the removal of water.     

Water in Ionic Liquids: Correlation between Anion Hydrophilicity and Near‐Infrared Fingerprints

We show that fingerprints of the different states of water association can be clearly distinguished in the range of the first overtone of water′s symmetric O‐H stretching in the spectra of water‐saturated [EMIm]⁺‐based ionic liquids with anions of substantially different hydrophilicity, such as hydrophobic [(CF₃SO₂)₂N]^?, moderately hydrophilic [CF₃SO₃]^?, and highly hydrophilic [HSO₄]^?.     

Effect of Ionic Liquid Anion Type in the Performance of Solid Polymer Electrolytes Based on Poly(Vinylidene fluoride‐trifluoroethylene)

The effect of different anions within the ionic liquid in the characteristics of solid polymer electrolytes (SPEs) based on P(VDF‐TrFE) has been investigated. 1‐ethyl‐3‐methylimidazolium acetate, [C₂mim][OAc], 1‐ethyl‐3‐methylimidazolium triflate, [C₂mim][(CF₃SO₃)], 1‐ethyl‐3‐methylimidazolium lactate, [C₂mim][Lactate], 1‐ethyl‐3‐methylimidazolium thiocyanate, [C₂mim][SNC] and 1‐ethyl‐3‐methylimidazolium hydrogen sulfate [C₂mim][HSO₄] have been used in SPE prepared by solvent casting. The polymer phase, thermal and electrochemical properties of the SPE have been determined. The thermal and electrical properties of the SPEs strongly depend on the selected IL, as determined by their different interactions with the polymer matrix. The room temperature ionic conductivity increases in the following way for the different anions: [SNC]>[CF₃SO₃)]>[HSO₄]>[Lactate]>[OAc], which is mainly dependent on the viscosity of the ionic liquid.     

The Synthesis of Anatase TiO2 Nanoparticles by Solvothermal Method using Ionic Liquid as Additive

The solvothermal reactions of Ti(OiPr)₄ in alcohol using ionic liquid as additive were investigated. In the presence of [BMIM][Cl], [BMIM][Br], [BMIM][NTf₂], [BMIM][SO₃Me], [BMIM][SO₄Me], or [BMIM][OTf] (BMIM = 1‐Butyl‐3‐methylimidazolium), pure anatase nanoparticles were obtained. The controlled hydrolysis of Ti(OiPr)₄ in the presence of ionic liquids to form titanium oxo clusters plays a key role in the formation of anatase nanostructures, and ionic liquids can be repeatedly used to synthesise anatase nanoparticles. However, in the presence of [BMIM][PF₆], [BMIM]₂[Ti(OH)₆] was obtained by an anion exchange reaction.     

Ferrocene‐tagged ionic liquid stabilized on silica‐coated magnetic nanoparticles: Efficient catalyst for the synthesis of 2‐amino‐3‐cyano‐4H‐pyran derivatives under solvent‐free conditions

An advanced novel magnetic ionic liquid based on imidazolium tagged with ferrocene, a supported ionic liquid, is introduced as a recyclable heterogeneous catalyst. Catalytic activity of the novel nanocatalyst was investigated in one‐pot three‐component reactions of various aldehydes, malononitrile and 2‐naphthol for the facile synthesis of 2‐amino‐3‐cyano‐4H‐pyran derivatives under solvent‐free conditions without additional co‐catalyst or additive in air. For this purpose, we firstly synthesized and investigated 1‐(4‐ferrocenylbutyl)‐3‐methylimidazolium acetate, [FcBuMeIm][OAc], as a novel basic ferrocene‐tagged ionic liquid. This ferrocene‐tagged ionic liquid was then linked to silica‐coated nano‐Fe₃O₄ to afford a novel heterogeneous magnetic nanocatalyst, namely [Fe₃O₄@SiO₂@Im‐Fc][OAc]. The synthesized novel catalyst was characterized using ¹H NMR, ¹³C NMR, Fourier transform infrared and energy‐dispersive X‐ray spectroscopies, X‐ray diffraction, and transmission and field emission scanning electron microscopies. Combination of some unique characteristics of ferrocene and the supported ionic liquid developed the catalytic activity in a simple, efficient, green and eco‐friendly protocol. The catalyst could be reused several times without loss of activity.     

Comparative Investigation of the Ionicity of Aprotic and Protic Ionic Liquids in Molecular Solvents by using Conductometry and NMR Spectroscopy

Electrical conductivity (σ), viscosity (η), and self‐diffusion coefficient (D) measurements of binary mixtures of aprotic and protic imidazolium‐based ionic liquids with water, dimethyl sulfoxide, and ethylene glycol were measured from 293.15 to 323.15 K. The temperature dependence study reveals typical Arrhenius behavior. The ionicities of aprotic ionic liquids were observed to be higher than those of protic ionic liquids in these solvents. The aprotic ionic liquid, 1‐butyl‐3‐methylimidazolium tetrafluoroborate, [bmIm][BF₄], displays 100 % ionicity in both water and ethylene glycol. The protic ionic liquids in both water and ethylene glycol are classed as good ionic candidates, whereas in DMSO they are classed as having a poor ionic nature. The solvation dynamics of the ionic species of the ionic liquids are illustrated on the basis of the ¹H NMR chemical shifts of the ionic liquids. The self‐diffusion coefficients D of the cation and anion of [HmIm][CH₃COO] in D₂O and in [D₆]DMSO are determined by using ¹H nuclei with pulsed field gradient spin‐echo NMR spectroscopy.     

SET‐LRP of acrylonitrile in ionic liquids without any ligand

Use of ionic liquids as reaction media was investigated in the design of an environmentally friendly single electron transfer‐living radical polymerization (SET‐LRP) for acrylonitrile (AN) without any ligand by using Fe(0) wire as catalyst and 2‐bromopropionitrile as initiator. 1‐Methylimidazolium acetate ([mim][AT]), 1‐methylimidazolium propionate ([mim][PT]), and 1‐methylimidazolium valerate ([mim][VT]) were applied in this study. First‐order kinetics of polymerization with respect to the monomer concentration, linear increase of the molecular weight, and narrow polydispersity with monomer conversion showed the controlled/living radical polymerization characters. The sequence of the apparent polymerization rate constant of SET‐LRP of AN was k_app ([mim][AT]) > k_app ([mim][PT]) > k_app ([mim][VT]). The living feature of the polymerization was also confirmed by chain extensions of polyacrylonitrile with methyl methacrylate. All three ionic liquids were recycled and reused and had no obvious effect on the controlled/living nature of SET‐LRP of AN. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

NMR Diffusion Measurements as a Simple Method to Examine Solvent–Solvent and Solvent–Solute Interactions in Mixtures of the Ionic Liquid [Bmim][N(SO2CF3)2] and Acetonitrile

The self‐diffusion coefficients of each component in mixtures of 1‐butyl‐3‐methylimidazolium bis(trifluoromethanesulfonyl)imide ([Bmim][N(SO₂CF₃)₂]) and acetonitrile were determined. The results suggest that the hydrodynamic boundary conditions change from “stick” to “slip” as the solvent composition transitions from “ionic liquid dissolved in acetonitrile” (χ_IL<0.4) to “acetonitrile dissolved in ionic liquid” (χ_IL>0.4). At higher χ_IL, the acetonitrile species are affected by “cage” and “jump” events, as the acetonitrile molecules reside nearer to the charged centre on the ions than in the “non‐polar” regions. The self‐diffusion coefficients of hexan‐1‐amine, dipropylamine, 1‐hexanol and dipropylether in mixtures of [Bmim][N(SO₂CF₃)₂] and acetonitrile were determined. In general, the nitrogen‐containing solutes were found to diffuse slower than the oxygen‐containing solutes; this indicates that there are greater ionic liquid–N interactions than ionic liquid–O interactions. This work demonstrates that the self‐diffusion coefficients of species can provide valuable information about solvent–solvent and solvent–solute interactions in mixtures containing an ionic liquid.     

Abrasive Stripping Voltammetric Studies of Lignin and Lignin Model Compounds

Lignin is potentially a major renewable, nonfossil source of aromatic and cyclohexyl compounds. In this study, we have investigated the abrasive stripping voltammetry of lignin and four lignin model compounds in the room temperature ionic liquids (RTILs) [C₄mim][NTf₂], [N_6,2,2,2][NTf₂] and [C₄mim][OTf] (where [C₄mim]⁺=1‐butyl‐3‐methylimidazolium, [N_6,2,2,2]⁺=n‐hexyltriethylammonium, [NTf₂]^?=bis(trifluoromethanesulfonyl)imide and [OTf]^? =trifluoromethanesulfonate) on a gold macrodisk and in 0.1 M H₂SO₄ and 0.1 M NaOH on a boron‐doped diamond (BDD) macroelectrode, with the hope of using the voltammetry to fingerprint the functional groups within the lignin molecule. The use of RTILs on metal electrodes, or either acidic or basic media in combination with BDD electrodes allows solvent systems with wide electrochemical potential windows, useful for studying voltammetry which may be difficult to observe in systems where early breakdown of the solvent occurs.     

Coordination environment of [UO2Br4] in ionic liquids and crystal structure of [Bmim]2[UO2Br4]

The complex formed by the reaction of the uranyl ion, UO₂²⁺, with bromide ions in the ionic liquids 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([Bmim][Tf₂N]) and methyl-tributylammonium bis(trifluoromethylsulfonyl)imide ([MeBu₃N][Tf₂N]) has been investigated by UV–Vis and U L_III-edge EXAFS spectroscopy and compared to the crystal structure of [Bmim]₂[UO₂Br₄]. The solid state reveals a classical tetragonal bipyramid geometry for [UO₂Br₄]²⁻ with hydrogen bonds between the Bmim⁺ and the coordinated bromides. The UV–Vis spectroscopy reveals the quantitative formation of [UO₂Br₄]²⁻ when a stoichiometric amount of bromide ions is added to UO₂(CF₃SO₃)₂ in both Tf₂N-based ionic liquids. The absorption spectrum also suggests a D_4h symmetry for [UO₂Br₄]²⁻ in ionic liquids, as previously observed for the [UO₂Cl₄]²⁻ congener. EXAFS analysis supports this conclusion and demonstrates that the [UO₂Br₄]²⁻ coordination polyhedron is maintained in the ionic liquids without any coordinating solvent or water molecules. The mean U–O and U–Br distances in the solutions, determined by EXAFS, are, respectively, 1.766(2) and 2.821(2) Å in [Bmim][Tf₂N], and, respectively, 1.768(2) and 2.827(2) Å, in [MeBu₃N][Tf₂N]. Similar results are obtained in both ionic liquids indicating no significant influence of the ionic liquid cation either on the complexation reaction or on the structure of the uranyl species.     

Influence of FeCl3‐modified chloroaluminate ionic liquids on long‐chain alkenes alkylation

The influence of anhydrous ferric chloride on the catalytic properties of chloroaluminate ionic liquids catalyst for Friedel–Crafts alkylation was investigated. The catalysts were characterized by Fourier‐transform infrared (FT‐IR) (acetonitrile molecule as probe), specific gravity, and ²⁷Al NMR. Besides, the effect of the mass ratio of FeCl₃ to AlCl₃, catalysts dosage, toluene/olefin molar ratio, reaction temperature, and reaction time on long‐chain alkenes alkylation were investigated thoroughly. And bromine value and high‐performance liquid chromatography (HPLC) were employed as the evaluation method for alkylation products. It was observed that the addition of anhydrous ferric chloride results in improvement in terms of Lewis acid and its catalytic recyclability. Among these catalysts studied, the catalyst modified with 1.0 wt.% anhydrous FeCl₃ showed the best catalytic performance in terms of yield and stability, which can be attributed to the formation of new stronger acidic ions [Al₂FeCl_l0]^? when the added ferric chloride reacts with acidic ions [Al₂Cl₇]^?.     

Speciation of Aluminium in Mixtures of the Ionic Liquids [C3mpip][NTf2] and [C4mpyr][NTf2] with AlCl3: An Electrochemical and NMR Spectroscopy Study

This paper reports on the electrodeposition of aluminium on several substrates from the air‐ and water‐stable ionic liquids 1‐propyl‐1‐methylpiperidinium bis(trifluoromethylsulfonyl)amide ([C₃mpip][NTf₂]) and 1‐butyl‐1‐methylpyrrolidinium bis(trifluoromethylsulfonyl)amide ([C₄mpyr][NTf₂]), which contain anhydrous AlCl₃. At an AlCl₃ concentration of 0.75 molal, no evidence for aluminium electrodeposition was observed in either system at room temperature. However, aluminium electrodeposition becomes feasible upon heating the samples to 80 °C. Aluminium electrodeposition from bis(trifluoromethylsulfonyl)amide‐based ionic liquids that contain AlCl₃ has previously been shown to be very dependent upon the AlCl₃ concentration and has not been demonstrated at AlCl₃ concentrations below 1.13 molal. The dissolution of AlCl₃ in [C₃mpip][NTf₂] and [C₄mpyr][NTf₂] was studied by variable‐temperature ²⁷Al NMR spectroscopy to gain insights on the electroactive species responsible for aluminium electrodeposition. A similar change in the aluminium speciation with temperature was observed in both ionic liquids, thereby indicating that the chemistry was similar in both. The electrodeposition of aluminium was shown to coincide with the formation of an asymmetric four‐coordinate aluminium‐containing species with an ²⁷Al chemical shift of δ=94 and 92 ppm in the [C₃mpip][NTf₂]–AlCl₃ and [C₄mpyr][NTf₂]–AlCl₃ systems, respectively. It was concluded that the aluminium‐containing species that give rise to these resonances corresponds to the electroactive species and was assigned to [AlCl₃(NTf₂)]^?.     

Living/controlled radical copolymerization of N‐substituted maleimides with styrene in 1‐butyl‐3‐methylimidazolium hexafluorophosphate and anisole

The atom transfer radical copolymerization of N‐substituted maleimides such as N‐phenylmaleimide (PhMI), N‐cyclohexylmaleimide (ChMI), and N‐butylmaleimide (NBMI) with styrene initiated with dendritic polyarylether 2‐bromoisobutyrates in an ionic liquid, 1‐butyl‐3‐methylimidazolium hexafluorophosphate ([bmim][PF₆]), at room temperature and anisole at 110 °C was investigated. The dendritic‐linear block copolymers obtained in ionic liquid possessed well‐defined molecular weight and low polydispersity (1.05 < M_w/M_n < 1.32) and could be used as a macroinitiator for chain‐extension polymerization, suggesting the living nature of the reaction system. The ionic liquids containing catalyst could be recycled in the atom transfer radical polymerization systems without further treatment. Compared with polymerization conducted in anisole, the polymerization in ionic liquid had a stronger tendency for alternation. The tendency for alternation decreased in the order PhMI > NBMI > ChMI in [bmim][PF₆] and PhMI > ChMI > NBMI in anisole. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 2156–2165, 2003     

SO3H-Functionalized Ionic Liquids: Green, Efficient and Reusable Catalysts for the Facile Dehydration of Aldoximes into Nitriles

Easily synthesized aldoximes have been converted to the corresponding nitriles under very mild conditions by a simple reaction using two halogen‐free SO₃H‐functionalized ionic liquids, 3‐methyl‐1‐(4‐sulfonic acid)butylimi‐ dazolium hydrogen sulfate [MIM(CH₂)₄SO₃H][HSO₄] and 1‐(4‐sulfonic acid)butylpyridinium hydrogen sulfate [PY(CH₂)₄SO₃H][HSO₄], as catalyst and reaction medium without any additional organic solvent. The method was equally effective for aromatic aldoximes bearing electron‐donating and electron‐withdrawing substituents. Taking into account environmental and economical consideration, the protocol presented here has the merits of environmentally friendly, simple operation, easy work‐up and very good yields. The catalysts could be recycled and reused for several times without noticeably decreasing in their catalytic activities.     

以N为中心的阴离子离子液体的合成、表征及应用

首次通过不同阴离子的钾盐和不同的季铵化的咪唑,吡咯溴盐/氯盐进行离子交换,合成了一系列含氰基官能团的阴离子功能化离子液体。通过红外、核磁共振、质谱对离子液体的结构进行表征;通过TGA对离子液体的热稳定性进行测定,结果发现功能化离子液体具有良好的热稳定性,其分解温度在224-289℃范围内。将功能化离子液体[EMIm][N(CN)COC2H5]作为配体应用于无膦配体的Suzuki偶联反应,发现在反应中加入功能化离子液体[EMIm][N(CN)COC2H5]可以使反应收率提高10-20%。