Chiral bis(oxazoline)-copper complex catalyzed Diels-Alder reaction in ionic liquids: remarkable reactivity and selectivity enhancement, and efficient recycling of the catalyst

Ionic liquid was found to be an excellent medium for asymmetric Diels-Alder reaction catalyzed by chiral bis(oxazoline)-copper complex. The reactivity and selectivity of reactions were highly dependent upon the property of the ionic liquids. Reactions of β-substituted acryloyl dienophiles in [Bmim]SbF₆ at ambient temperature provided remarkably enhanced reactivity and stereoselectivity compared to homogeneous reactions in non-ionic liquid solvent at −78 °C. Due to the increased reactivity, the amount of metal catalyst could be reduced down to 0.6 mol % without any significant selectivity compromise. Additionally, recycling of the ligand-metal complex was achieved efficiently up to 18 times.     

Magnetic and calorimetric studies on rare-earth iron borates LnFe3(BO3)4 (Ln=Y, La-Nd, Sm-Ho)

A series of rare-earth iron borates having general formula LnFe₃(BO₃)₄ (Ln=Y, La-Nd, Sm-Ho) were prepared and their magnetic properties have been investigated by the magnetic susceptibility, specific heat, and ⁵⁷Fe Mössbauer spectrum measurements. These borates show antiferromagnetic transitions at low temperatures and their magnetic transition temperatures increase with decreasing Ln³⁺ ionic radius from 22 K for LaFe₃(BO₃)₄ to 40 K for TbFe₃(BO₃)₄. In addition, X-ray diffraction, specific heat, and differential thermal analysis (DTA) measurements indicate that the phase transition occurs for the LnFe₃(BO₃)₄ compounds with Ln=Eu-Ho, Y, and its transition temperature increases remarkably with decreasing Ln³⁺ ionic radius from 88 K for Ln=Eu to 445 K for Ln=Y.     

Synthesis,characterization, and crystal structure of several novel acidic ionic liquids based on the corresponding 1-alkylbenzimidazole with tetrafluoroboric acid

A series of acidic task-specific ionic liquids 1-R₂-2-R₁benzimidazolium tetrafluoroborate (R₁ = Me, R₂ = Me, Et, Pr-n, Bu-n, Pen-n) were prepared by simple acid-base neutralization of the corresponding 1-alkylbenzimidazole and tetrafluoroboric acid. The compounds were characterized by FTIR spectra, elemental analysis, ¹HNMR spectra and thermogravimetric analysis. These new ionic liquids are nonvolatile, and have potential use as alternatives to conventional organic solvents due to their solubility and thermal stability. These novel tetrafluoroborate salts show good catalytic activity to esterification of carboxylic acids with alcohols under mild reaction conditions, which could maintain good catalytic performance after recycling at least six times. Furthermore, a crystal of one compound, [H-bmBim]BF₄, was prepared, with the crystal structure determined by X-ray diffraction analysis. The molecular structure is formed by weak π-π interactions and intermolecular hydrogen bonds between the benzimidazole rings, yielding a three-dimensional net-like supramolecule.     

The effects of substituents,molecular symmetry,ionic radius of the rare earth metal,and macrocycle on the electronic absorption spectra characteristics of sandwich-type bis(phthalocyaninato) and mixed (phthalocyaninato)(porphyrinato) rare earth complexes

The electronic absorption spectroscopic data for two series of 60 unsubstituted/substituted bis(phthalocyaninato) and mixed [tetrakis(4-chlorophenyl)porphyrinato](phthalocyaninato) rare earth complexes M(Pc)₂, M(Pc^∗)₂ and M(TClPP)(Pc) [M = Y, La…Lu except Pm; Pc^∗ = dianion of 2,3,9,10,16,17,23,24-octakis(4-methoxyphenoxy)phthalocyanine [Pc(MeOPhO)₈], dianion of 3(4),12(13),21(22),30(31)-tetra(tert-butyl)phthalocyanine (TBPc) and TClPP = tetra(4-chloro)phenylporphyrin] have been measured in CHCl₃. In this paper, the influence of the symmetry of macrocycle rare earth molecules, the effects of ionic radius of the rare earth metal and the influence of substituent species (tert-butyl and 4-methoxyphenoxy groups) onto the peripheral benzene rings on the electronic absorption characteristics of sandwich-type compounds have also been tentatively studied in detail.     

Solvent-free aza-Markovnikov and aza-Michael additions promoted by a catalytic amount of imidazolide basic ionic liquids

A family of imidazolide ionic liquids were synthesized and characterized. These ionic liquids combined the virtues of strong basicity and relatively good thermal stability. Catalytic properties of these imidazolide ionic liquids were investigated and satisfactory yield was achieved when 2.0 mol % of [Bmim]Im was used as catalyst for aza-Markovnikov addition under solvent-free condition at room temperature in one hour. Experimental results show that a hydrogen bond is not formed between [Bmim]Im/imidazole and vinyl ester, and its existence is not necessary for the [Bmim]Im catalyzed aza-Markovnikov addition either. A possible mechanism for [Bmim]Im-catalyzed aza-Markovnikov addition was proposed. The use of imidazolide ionic liquids in aza-Michael addition was investigated as well.     

Aqueous Geochemistry of Rare Earth Elements and Yttrium. XII: Potentiometric Stability Constant Determination of Bis-Tris Complexes with La, Nd, Eu, Gd, Yb, Dy, Er, Lu, and Y

Conditional stability constants of 2-[bis(2-hydroxyethyl)amino]-2(hydroxymethyl)-1,3-propanediol (BT) complexes of trivalent rare earth element (Ln) ions (La, Nd, Eu, Gd, Yb, Dy, Er, Lu) and Y were determined potentiometrically in aqueous NaCl solutions at 30°C and 0.1 M ionic strength. Least-squares fitting shows that, at <0.04 molal BT, the complex LnBT³⁺ is dominant, with LnBT₂ ³⁺ forming a secondary complex, where:

Facile nucleophilic fluorination by synergistic effect between polymer-supported ionic liquid catalyst and tert-alcohol reaction media system

A highly efficient method was developed for nucleophilic fluorination using an alkali metal fluoride through the synergistic effect of the polymer-supported ionic liquid (PSIL) as a catalyst and tert-alcohol as an alternative reaction media. This PSIL/tert-alcohol system not only enhances the reactivity of alkali metal fluorides and reduces the formation of by-products but also allows the use of a polymer-supported catalyst protocol. As an example, the nucleophilic fluorinations of the model compound, 2-(3-bromopropoxy)naphthalene, with CsF using only tert-amyl alcohol as solvent (for 2 h reaction time), 0.5 equiv of PS[hmim][BF₄] in CH₃CN (for 12 h reaction time), and 0.5 equiv of PS[hmim][BF₄] in tert-amyl alcohol (which is a PSIL/tert-alcohol system for the synergistic effect; for 2 h reaction time) provided 18, 40, and 84% yield, respectively. The characteristics of the nucleophilic fluorination reactions of some halo- and alkanesulfonyloxyalkane systems to the corresponding fluoroalkanes using various alkali metal fluorides are also reported.     

1-Butyl-2,3-trimethyleneimidazolium bis(trifluoromethylsulfonyl)imide ([b-3C-im][NTf2]): a new, stable ionic liquid

Using imidazole as the starting material, the synthesis of a new bicyclic ionic liquid [b-3C-im][NTf₂] is described. Except for the alkylation reaction in the second step (40% yield) of this four-step synthesis of [b-3C-im][NTf₂], others were all high yielding reactions (85-94% isolated yields). We investigated intrinsic reactivity of this and other imidazolium-based ionic liquids and found that, under strongly basic conditions (KOD in CD₃OD/D₂O (1:1) solution), the new ionic liquid was stable to solvent deuterium isotope exchange while the previously reported [bdmim][NTf₂] and [bdmim][PF₆] ionic liquids were 50% deuterium exchanged at its C-2 methyl in 30 min at ambient temperature. At the same experimental condition, the most commonly employed [bmim][PF₆] ionic liquid was deuterium exchanged instantaneously at its C-2 hydrogen. In the absence of bases (CD₃OD/D₂O = 1:1), only [bmim][PF₆] was deuterium exchanged (50% within 1 h) and other ionic liquids gave no detectable exchanges even after one week at ambient temperature. It is therefore concluded that the new [b-3C-im][NTf₂] ionic liquid is far more chemically stable than previously reported [bmim][PF₆], [bdmim][NTf₂], and [bdmim][PF₆].     

Physico-chemical properties and phase behaviour of piperidinium-based ionic liquids

The sufficient review of the existing literature of the 1-alkyl-1-methylppiperidinium-based ionic liquids has been presented. The phase diagrams for the binary systems of {1-butyl-1-methylpiperidinium thiocyanate [BMPIP][SCN] + an alcohol (1-hexanol, 1-heptanol, 1-octanol, 1-nonanol, 1-decanol, 1-dodecanol), or + water, or + aliphatic hydrocarbons (n-hexane, n-heptane, n-octane), or + cyclohexane, or, + cycloheptane, or + aromatic hydrocarbons (benzene, toluene, ethylbenzene)} and for the binary systems of {1-ethyl-1-methylpiperidinium bis{(trifluoromethyl)sulfonyl}imide [EMPIP][NTf₂] + an alcohol (ethanol, 1-propanol, 1-butanol, 1-hexanol, 1-heptanol, 1-octanol, 1-nonanol), or + water} have been determined at atmospheric pressure using a dynamic method. The influence of an alcohol chain length was discussed for these ionic liquids. A systematic decrease in the solubility was observed with an increase of the alkyl chain length of an alcohol. (Solid + liquid) phase equilibria with complete miscibility in the liquid phase region were observed for the systems involving water and the alcohols for the thiocyanate-based ionic liquid. Opposite, the bis{(trifluoromethyl)sulfonyl}imide-based ionic liquid reveal the immiscibility gap in the liquid phase. The correlation of the experimental data has been carried out using the NRTL equation. The phase diagrams reported here have been compared to the systems published earlier with the 1-alkyl-1-methylpiperidinium-based ionic liquids. The influence of the cation and anion on the phase behaviour has been discussed. The basic thermal properties of pure ILs, i.e. melting temperature and the enthalpy of fusion, the solid-solid phase transition temperature and enthalpy have been measured using a differential scanning microcalorimetry technique.     

Thermal stability of ion-exchange Nafion N117CS membranes

The effect of exchanged ions on the thermal stability of Nafion N117CS membranes was investigated by X-ray photoelectron spectra (XPS), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), thermomechanical analysis (TMA), and ion exchange capacity determinations. The ion exchange of alkaline metal ions was effective in improving the thermal stability of the Nafion N117CS membrane. Findings reveal that when Nafion was exchanged for cations with a larger ionic radius, the membrane attained superior thermal stability. On the other hand, we confirmed that the Na-exchange Nafion N117CS membrane possessed a distinctive degree of thermal stability among the alkaline ion-exchange Nafions, although the order of ionic radii is K > Na > Li. Thermal stability improved the most when the Nafion membrane was exchanged for alkaline ions, followed by divalent ions, then trivalent ions. As for the Nafion membrane when it was exchanged for divalent ions or trivalent ions, Nafion following the ion exchange had a thermal stability proportional to an increase in the ionic radius of the cation. This stability may be explained by the reduction of water content and a greater interaction between the sulfonate groups and the cations with larger ionic radii. Since the Al cations acted as a Lewis acid center, the decomposition of the ether bonds of the perfluoroalkylether pendant-chains of the Nafion membrane was observed for the Nafion N117CS membrane that had been exchanged for Al ions. The activation of molecular mobility in Nafion was observed between the decomposition stages of the loss of water and the loss of sulfonic groups. The temperature of activation of cation-exchange Nafion became much higher than that of Nafion in an acid form.     

Synthesis,crystal structure,and characterization of two-dimensional coordination polymers of three heavy rare-earth elements: [RE(5-Nip)(5-HNip)(H<Subscript>2</Subscript>O)<Subscript>2</Subscript>](H<Subscript>2</Subscript>O)<Subscript>2</Subscript> (RE = Y,Ho, Er)

Three new coordination polymers, [RE(5-Nip)(5-HNip)(H₂O)₂)] · 2H₂O (RE = Y (I), Ho (II), and Er (III)) were synthesized by hydrothermal reactions of lanthanide nitrates with 5-nitroisophthalic acid (H₂Nip) and characterized by IR spectra, elemental analysis, and single-crystal X-ray diffraction. X-ray diffraction studies suggest that all the two-dimensional 5-nitroisophthalic complexes crystallize in the P space group and are isomorphic. The two-dimensional layer-like structures are constructed by the lanthanide ions bridged by 5-Nip²⁻ ligands, and the layers further packed into 3D complexes through hydrogen bonds and two kinds of π-π stacking interactions. These complexes exhibit high stabilities up to 465 (1), 518 (2), and 528°C (3), respectively. According to the effective ionic radii of eight-coordinate lanthanide, Y(III) should be arranged before Ho(III) and Er(III), and we obtain a series of lines (except for the RE-OW bonds) in the corresponding RE-O against their ionic radii. In these complexes the yttrium complex could be located before the other two complexes according to the position of its ionic radius, and the ionic radii become a key factor in the formation of these complexes. The text was submitted by the authors in English.     

Solubility of carbon dioxide in the ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide

In this work, the phase behaviour of the binary system of carbon dioxide and the ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([emim][Tf₂N]) has been studied experimentally. The equipment used for the experiments is the Cailletet set-up, based on visual observations of phase transitions of systems with constant overall composition. Results are reported for carbon dioxide concentrations ranging from 12.3 to 59.3 mol%, and within temperature and pressure ranges of 310–450 K and 0–15 MPa, respectively. The data reveal an extremely high capacity of the selected ionic liquid for dissolving CO₂ gas, for example, reaching up to about 60 mol% within the above-mentioned pressure and temperature range. Also, the solubility of CO₂ in the ionic liquid [emim][Tf₂N] is compared to the solubility of CO₂ in the ionic liquid [emim][PF₆], an ionic liquid that shares the same cation.     

Synthesis and phase separation of amine-functional temperature responsive copolymers based on poly(N-isopropylacrylamide)

Free radical copolymerizations of N-isopropyl acrylamide (NIPAM) and cationic N-(3-aminopropyl) methacrylamide hydrochloride (APMH) were investigated to prepare amine-functional temperature responsive copolymers. The reactivity ratios for NIPAM and APMH were evaluated in media of different ionic strength (r_NIPAM = 0.7 and r_APMH = 0.7-1.2). Phase separation behavior of the random copolymers with only 5 mol% of the APMH was found to be suppressed in pure water at temperatures up to 45 °C due to electrostatic repulsion among the cationic amine groups randomly distributed along the copolymer chain. Alternate sequential addition of PNIPAM/APMH mixtures and pure NIPAM was used to provide increased control of the location of APMH units along the chain. Consequently (close to) homo-PNIPAM block(s) were formed as evidenced by its characteristic phase transition at 33 °C. The influences of the monomer feeding time and feeding interval time to the APMH distribution were investigated to prepare copolymers with thermo-induced phase separation under physiologically relevant temperature and to determine the extent of conjugation to poly(ethylene oxide).     

One-pot synthesis of α-aminonitriles using a highly efficient and recyclable silica-based scandium (III) interphase catalyst

Both aryl and alkyl imines, which formed in situ from aldehydes and amines undergo smooth nucleophilic addition with trimethylsilyl cyanide in the presence of a catalytic amount of a silica-based scandium (III) interphase catalyst under mild reaction condition to furnish the corresponding α-aminonitriles in good to excellent yields. The catalyst shows high thermal stability (up to 300 °C) and it could also be recovered and reused for at least 6 reaction cycles without considerable lose of its reactivity.     

Synthesis, polymerization and conducting properties of an ionic liquid-type anionic monomer

The synthesis of a new ionic liquid-type monomer has been performed by association of a methacrylate polymerizable group, a polar tri(ethylene oxide) (TEO) spacer, a trifluoromethane sulfonic (TFSI⁻) anion and a free imidazolium (EMIm⁺) cation. The ionic liquid monomer (ILM) has demonstrated a good thermal stability and a high ionic conductivity around 2.1 × 10⁻³ S cm⁻¹ at 20 °C. The corresponding homopolymer has shown an ionic conductivity closely related to the monomer (6.5 × 10⁻⁴ S cm⁻¹ at 20 °C), which confirms the ILM as a valuable monomer for the formation of polymeric ionic liquid (PIL) materials.     

Transport properties of protic ionic liquids,pure and in aqueous solutions: Effects of the anion and cation structure

Ionic conductivities of twelve protic ionic liquids (PILs) and their mixtures with water over the whole composition range are reported at 298.15 K and atmospheric pressure. The selected PILs are the pyrrolidinium-based PILs containing nitrate, acetate or formate anions; the formate-based PILs containing diisopropylethylammonium, amilaminium, quinolinium, lutidinium or collidinium cations; and the pyrrolidinium alkylcarboxylates, [Pyrr][C_nH_2n+1COO] with n = 5–8. This study was performed in order to investigate the influence of molecular structures of the ions on the ionic conductivities in aqueous solutions. The ionic conductivities of the aqueous solutions are 2–30 times higher than the conductivities of pure PILs. The maximum in conductivity varies from ww=0.41 ??to ??0.74$w_w=0.41\text{\hspace{0.17em}??}\text{to}\text{\hspace{0.17em}??}0.74$ and is related to the nature of cations and anions. The molar conductance and the molar conductance at infinite dilution for (PIL + water) solutions are then determined. Self-diffusion coefficients of the twelve protic ionic liquids in water at infinite dilution and at 298.15 K are calculated by using the Nernst–Haskell, the original and the modified Wilke–Chang equations. These calculations show that similar values are obtained using the modified Wilke–Chang and the Nernst–Haskell equations. Finally, the effective hydrodynamic (or Stokes) radius of the PILs was determined by using the Stokes–Einstein equation. A linear relationship was established in order to predict this radius as a function of the anion alkyl chain length in the case of the pyrrolidinium alkylcarboxylates PILs.     

Ionic liquids accelerate access to N-substituted-1,8-naphthalimides

The synthesis of N-substituted-1,8-naphthalimides is accelerated in the presence of the room temperature ionic liquid [BMIM][NO₃]. Reaction times are reduced from 18 h in volatile organic compounds (VOCs) (PhCH₃, EtOH and THF) to 20 min in the ionic liquid [BMIM][NO₃]. The reaction yields are typically increased to >85% and the products are isolated by ethanol-mediated precipitation direct from the ionic liquid, requiring no further purification.     

Combination of ionic liquid-based dispersive liquid-liquid micro-extraction with stopped-flow spectrofluorometry for the pre-concentration and determination of aluminum in natural waters, fruit juice and food samples

In this research, we combined ionic liquid-based dispersive liquid-liquid micro-extraction (IL-based DLLME) with stopped-flow spectrofluorometry (SFS) to evaluate the concentration of aluminum in different real samples at trace level. 1-Hexylpyridinium hexafluorophosphate [Hpy][PF₆] ionic liquid and 8-hydroxyquinoline (oxine), which forms a highly fluorescent complex with Al³⁺, were chosen as the extraction solvent and chelating agent, respectively. The hydrophobic Al-oxine complex was extracted into the [Hpy][PF₆] and separated from the aqueous phase. Then, the concentration of the enriched aluminum in the sediment phase was determined by SFS. Some effective parameters that influence the SFS signals and the micro-extraction efficiency, such as the suction and sending time, the concentration of the chelating agent, pH, the amount of the ionic liquid, the type of disperser solvent and diluting agent, ionic strength, extraction time, equilibration temperature and centrifugation time were investigated and optimized. In the optimum experimental conditions, the limit of detection (3 s) and enrichment factor were 0.05 μg L⁻¹ and 100, respectively. The relative standard deviation (RSD) for six replicate determinations of 6 μg L⁻¹ Al was 1.7%. The calibration graph using the pre-concentration system was linear in the range of 0.06-15 μg L⁻¹ with a correlation coefficient of 0.9989. The developed method was validated by the analysis of certified reference materials and applied successfully to the determination of aluminum in several water, fruit juice and food samples.     

Poly(ethylene glycol) (PEG) as an efficient and recyclable reaction medium for the synthesis of dibenz[b,f]-1,4-oxazepine

Poly(ethylene glycol) (PEG) has been used as a sustainable, non-volatile, and environmentally friendly reaction solvent for the synthesis of dibenz[b,f]-1,4-oxazepine (2a). PEG-400 as a promoter provided 89% of 2a within 8 h. We compared the reactivity of PEG-400 with 18-crown-6, tetra-n-butylammonium bromide and ionic liquids as phase transfer catalysts. Further, we investigated our protocol with various PEGs, with molecular weight 200, 300, 1000, 2000, 8000, 10,000, and 20,000. The reaction provided excellent yields with low as well as high molecular weight PEGs. We also studied the effect of various organic cosolvents (polar protic/aprotic/non-polar) on the reactivity of PEG-400 for the synthesis of 2a.     

Temperature-controlled highly selective dimerization of α-methylstyrene catalyzed by Brönsted acidic ionic liquid under solvent-free conditions

A temperature-controlled highly selective dimerization of α-methylstyrene to produce 2,4-diphenyl-4-methyl-1-pentene and 1,1,3-trimethyl-3-phenylindan was catalyzed by Brönsted acidic ionic liquid [Hmim]⁺BF₄⁻. At 60 °C, 2,4-diphenyl-4-methyl-1-pentene was formed in 93% selectivity with >92% conversion under a solvent-free condition while 1,1,3-trimethyl-3-phenylindan could be obtained in 100% selectivity when the reaction temperature was increased to 170 °C. The ionic liquid [Hmim]⁺BF₄⁻ could be reused with almost no loss of activity.