Ultralow Tribological Properties of Polymer Composites Containing [BMIm]PF6‐Loaded Multilayer Wall Microcapsule

Multilayer wall microcapsules efficiently loaded with a lubricant (ionic liquid [BMIm]PF₆) are successfully synthesized via a combination of interfacial and in situ polymerization reactions based on lignin nanoparticle–stabilized Pickering emulsion templates. The resulting microcapsules are spherical in shape, with an ideal structure of a rough outer surface and a smooth inner surface. The mean diameter and wall thickness of the resultant microcapsules are 52 ± 18 µm and 3–6 µm. The core fraction is ≈71.29 wt%. Compared with the pure epoxy resin, the friction coefficient of self‐lubricating composites decreases by 83.6% (from 0.55 to 0.09) and the wear rate decreases by 218 times (from 76.8 × 10^?14 to 0.352 × 10^?14 m³ N^?1 m^?1) by incorporating 20 wt% of the resultant microcapsules into the epoxy resin. It is demonstrated that [BMIm]PF₆, a more efficient lubricant, release from the microcapsules during the friction process produced a boundary lubricating film. The bipolar property of [BMIm]PF₆ makes the lubricating film firmer, which can efficiently prevent direct contact between the resin matrix and counterface. Furthermore, the rough poly(urea‐formaldehyde) outer surface of multilayer microcapsules brings in an improved interface property between the microcapsules and resin matrix.     

Enhanced electrical conductivity of polyindole prepared by electrochemical polymerization of indole in ionic liquids

The in situ electrical conductivity (resistance) of electrochemically prepared polyindole (PIn) in ionic liquids was found to be strongly dependent on the nature of the solvents, size of ionic liquid counter ions and preparation technique. Accordingly, the conductivity can be enhanced by about one order of magnitude when using a 1‐butyl‐3‐methylimidazolium tetrafluoroborate [BMIm] [BF₄^‐] or 1‐butyl‐3‐methylimidazolium hexafluorophosphate [BMIm] [PF₆^?] in comparison to acetonitrile (ACN). Moreover, the growth of polyindole in ionic liquid on gold electrode surface is faster than growth of polymer in acetonitrile. Additionally, a significant enhancement of the conductivity by using ionic liquids during the polymerization could be achieved. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40094.     

Negative effect of [bmim][PF6] on the catalytic activity of alcohol dehydrogenase: mechanism and prevention

BACKGROUND: [bmim][PF₆] is a hydrophobic ionic liquid which could be considered as an environmentally friendly solvent for biocatalysis. In pure [bmim][PF₆], however, alcohol dehydrogenase from yeast (YADH) has no catalytic activity. The aim of the present work was (1) to quantitatively study the negative effect of [bmim][PF₆] on the catalytic activity of YADH and the related mechanism and (2) to made an attempt to lessen the negative effect of [bmim][PF₆] on YADH by microemulsifying [bmim][PF₆]. RESULTS: The activity of YADH in the homogeneous solution formed by H₂O, CH₃CH₂OH and [bmim][PF₆] decreased rapidly with the increase of the molar fraction of [bmim][PF₆]. The inhibitory effect of [bmim][PF₆] on YADH was probably caused by the competition of the imidazole group of [bmim][PF₆] with the coenzyme NAD⁺ for the binding sites on YADH. In a water‐in‐[bmim][PF₆] microemulsion, YADH was catalytically active due to the formation of the interfacial membrane of the nonionic surfactant TritonX‐100, which separated YADH from [bmim][PF₆] and avoided the direct inactivation of [bmim][PF₆] on YADH. Under optimal conditions, the activity of YADH was as high as 51 µmol L^?1 min^?1. CONCLUSION: [bmim][PF₆] was an inhibitor of YADH and its negative effect on YADH could be lessened by its microemulsification. Copyright © 2008 Society of Chemical Industry     

Improved activity and stability of pseudomonas capaci lipase in a novel biocompatible ionic liquid, 1‐isobutyl‐3‐methylimidazolium hexafluorophosphate

BACKGROUND: Enzymes may exhibit enhanced activity, stability and selectivity in ionic liquids, depending on the properties of the liquid. The physical–chemical properties of ionic liquids, however, may be modified by altering the anion or cation in the ionic liquid. This feature is a key factor for realizing successful reactions. In this work, a new ionic liquid, 1‐isobutyl‐3‐methylimidazolium hexafluorophosphate (abbreviated as [i‐C₄mim][PF₆]), was synthesized and investigated as a novel medium for the transesterification reaction of 2‐phenylethanol with vinyl acetate catalyzed by pseudomonas capaci lipase. As contrasts, the reaction was also carried out in two reference solvents; the isomeric ionic liquid [i‐C₄mim][PF₆], 1‐butyl‐3‐methylimidazolium hexafluorophosphate (abbreviated as [C₄mim][PF₆]), and hexanes. RESULTS: As reaction medium, [i‐C₄mim][PF₆] was best among the three solvents. The initial reaction rate, the equilibrium conversion of 2‐phenylethanol and the half‐lifetime of the lipase in [i‐C₄mim][PF₆] medium were about 1.5, 1.2 and 3‐fold that obtained in [C₄mim][PF₆] medium, respectively. The lipase in [i‐C₄mim][PF₆] medium was recycled 10 times without substantial diminution in activity. CONCLUSION: The ionic liquid [i‐C₄mim][PF₆] has good biocompatibility, and can be used widely as green media in various biocatalysis reactions to improve the activity and stability of enzymes. Besides hydrophobicity and nucleophilicity, the spatial configuration of ionic liquids is also considered a key factor effecting the behaviour of the enzyme in ionic liquids. Copyright © 2008 Society of Chemical Industry     

Global phase behavior of imidazolium ionic liquids and compressed 1,1,1,2‐tetrafluoroethane (R‐134a)

Novel processes involving ionic liquids with refrigerant gases have recently been developed. Here, the complete global phase behavior has been measured for the refrigerant gas, 1,1,1,2‐tetrafluoroethane (R‐134a) and 1‐n‐alkyl‐3‐methyl‐imidazolium ionic liquids with the anions hexafluorophosphate [PF₆], tetrafluoroborate [BF₄] and bis(trifluoromethylsulfonyl)imide [Tf₂N] from ～0°C to 105°C and to 33 MPa. All of the systems studied were Type V from the classification scheme of Scott‐van Konynenburg with regions of vapor‐liquid equilibrium, miscible/critical regions, vapor‐liquid‐liquid equilibrium, and upper and lower critical endpoints (UCEP and LCEP). The effect of the alkyl chain length has been investigated, for ethyl‐([EMIm]), n‐butyl‐([BMIm]), and n‐hexyl‐([HMIm]). With increasing chain length, the temperature of the lower critical end points increases and pressure at the mixture critical points decrease. With a common cation, the temperature of the LCEP increased and the mixture critical point pressures decreased in the order of [BF₄], [PF₆], and [Tf₂N]. © 2008 American Institute of Chemical Engineers AIChE J, 2009     

Application of hydrophobic ionic liquid [Bmmim][PF6] in solvent extraction for oily sludge

In this study, an ionic liquid (IL), 1-butyl-2,3-dimmmethylimidazolium hexafluorophosphate ([Bmmim][PF₆]), was used in combination with a composite solvent of methyl acetate and n-heptane to enhance the oil extraction from oily sludge. The oil recovery increased by approximately 15% compared with that of solvent extraction without [Bmmim][PF₆] at the optimal ratios of IL to sludge and solvents to sludge, which were at 2:5 (M/M) and 4:1 (V/M), respectively. The saturate, aromatic, resin and asphaltene (SARA) analysis revealed that the recovery of resins and asphaltenes was increased by 14% and 38%, respectively, in the solvent extraction with the addition of [Bmmim][PF₆]. [Bmmim][PF₆] maintained a good performance after its reuse four times. The addition of [Bmmim][PF₆] changed the adhesion forces between oil and soil. The IL-assisted solvent extraction procedure followed the pseudo second-order kinetic model, while the unassisted solvent extraction procedure followed the pseudo first-order kinetic model. The results also demonstrated that [Bmmim][PF₆] decreased the solvent consumption by approximately 60% each time. Additionally, [Bmmim][PF₆] can be easily separated. The results suggested that enhancing the solvent extraction with this IL is a promising way to recover oil from oily sludge with a higher oil recovery rate and lower organic solvent consumption than those with the unassisted solvent extraction method.     

Quantum chemical studies on the simultaneous interaction of thiophene and pyridine with ionic liquid

The simultaneous interaction of thiophene and pyridine with different ionic liquids:1‐butyl‐1‐methylpyrrolidinium tetrafluoroborate([BPYRO][BF₄]),1‐butyl‐1‐methylpyrrolidinium hexafluoro‐phosphate ([BPYRO][PF₆]), 1‐butyl‐4‐methylpyridinium tetrafluoroborate ([BPY][BF₄]), 1‐butyl‐4‐methylpyridinium hexafluorophosphate ([BPY][PF₆]) and 1‐benzyl‐3‐methylimidazolium tetrafluoroborate ([BeMIM][BF₄]) were investigated using quantum chemical calculations. A three‐tier approach comprising of partial charges, interaction energies and sigma profile generation using conductor‐like screening model for real solvents (COSMO‐RS) was chosen to study the systems. A quantitative attempt based on the CH‐π interaction in ionic liquid; thiophene–pyridine complexes gave the interaction energies of ILs in the order: [BPY][BF₄] > [BPYRO][PF₆] > [BeMIM][BF₄] > [BPY][PF₆] > [BPYRO][BF₄]. An inverse relation was observed between the activity coefficient at infinite dilution predicted via COSMO‐RS–based model and interaction energies. The dominance of CH‐π interaction was evident from the sigma profiles of ionic liquid together with thiophene and pyridine. © 2010 American Institute of Chemical Engineers AIChE J, 2011     

Gold Nanoparticles Stabilized by Task-Specific Oligomeric Ionic Liquid for Styrene Epoxidation Without Using VOCs as Solvent

An oligomer of ionic liquid containing imidazolium and disulfide groups, which is miscible with the ionic liquid of [Bmim]PF₆, was synthesized and used to stabilize gold nanoparticles. As such, epoxidation of styrene could be catalyzed by the oligomeric ionic liquid-stabilized gold nanoparticles in the nonvolatile [Bmim]PF₆ without using any VOC as solvent. Under optimum reaction conditions, a styrene conversion of 100% with the selectivity to styrene oxide of 90% was obtained.     

Ab initio calculations of the interaction between thiophene and ionic liquids

The fundamental natures of the interaction between thiophene and ionic liquids of 1-n-butyl-3-methylimidazolium hexafluorophosphate ([BMIM]⁺[PF₆]⁻) and 1-n-butyl-3-methylimidazolium tetrafluoroborate ([BMIM]⁺[BF₄]⁻) were investigated using ab initio calculations and correlated with previous experimental results. The optimized structures show that the anions of the ionic liquids are situated outside the ring plane of the thiophene, with the fluorine atoms interacting with the hydrogen atoms of the thiophene, and the cation of the ionic liquids approaches the thiophene with its positively charged atoms approaching the negatively charged atoms of TS. It is concluded that thiophene molecules interact with the ionic liquids mainly via Coulombian attraction. Further analysis explained the results obtained from an absorption experiment that the molar ratios of the absorbed thiophene to the ionic liquids were approximately 3.5/1 and 2.4/1 for [BMIM]⁺[PF₆]⁻ and [BMIM]⁺[BF₄]⁻, respectively. The strong electron donation of the phosphorus atom to the fluorine atoms in the PF₆⁻ cluster is believed to be the major factor resulting in the higher molar ratio of thiophene/[BMIM]⁺[PF₆]⁻. The other factor is the difference of the compactness between the cation and the anion in the two ionic liquids.     

Asymmetric Glyoxylate-Ene Reactions Catalyzed by Chiral Pd(II) Complexes in the Ionic Liquid [bmim][PF6]

The room temperature ionic liquid [bmim][PF₆] was employed as the reaction medium in the asymmetric glyoxylate-ene reaction of α-methyl styrene (4a) with ethyl glyoxylate using chiral palladium(II) complexes as the catalysts. [Pd(S-BINAP)(3,5-CF₃-PhCN)₂](SbF₆)₂ (1b) showed the highest catalytic activity. Under the reaction conditions of 40 °C, 0.5 h, and 1b/4a molar ratio of 0.05, ethyl α-hydroxy-4-phenyl-4-pentenoate was obtained in excellent chemical yield (94 %) with high enantioselectivity (70 %). Other α-hydroxy esters can also be obtained in high chemical yields and enantioselectities through the glyoxylate-ene reactions of alkenes with glyoxylates catalyzed by 1b in [bmim][PF₆]. Moreover, the ionic liquid [bmim][PF₆] which contained the palladium(II) complex could be recycled and reused several times without significant loss of the catalytic activity.     

Rhodium Acetate Dimer Immobilized in 1‐Butyl‐3‐methylimidazolium Hexafluorophosphate Ionic Liquid: a Novel and Recyclable Catalytic System for the Cyclopropanation of Alkenes

Alkenes undergo smooth cyclopropanation with ethyl diazoacetate using a catalytic amount of rhodium acetate dimer, Rh₂(OAc)₄, immobilized in the air‐ and moisture‐stable 1‐butyl‐3‐methylimidazolium hexafluorophosphate ionic liquid, [bmim]PF₆, to afford cyclopropanecarboxylates in excellent yields with high trans‐selectivity. The recovery of the catalyst is facilitated by the hydrophobic nature of [bmim]PF₆. The recovered ionic liquid containing Rh₂(OAc)₄ can be reused for three to five subsequent runs with only a gradual decrease in activity.     

Recycling Chiral Imidazolidin‐4‐one Catalyst for Asymmetric Diels–Alder Reactions: Screening of Various Ionic Liquids

Various imidazolium ionic liquids such as [Bmim]PF₆, [Bmim]SbF₆, [Bmim]OTf and [Bmim]BF₄ were screened for recycling an organic catalyst [(5S)‐5‐benzyl‐2,2,3‐trimethylimidazolidin‐4‐one ( 1 )] for asymmetric Diels–Alder reactions. Good yields and enantioselectivies (up to 85% yield and 93% ee) were obtained from reactions in [Bmim]PF₆ or [Bmim]SbF₆. However, reactions in [Bmim]OTf or [Bmim]BF₄ gave racemic products in low yields. Isolation of the products by simple extraction using diethyl ether allowed recycling of the ionic liquid containing the immobilized catalyst in subsequent reactions without significant decrease of yields and enantioselectivities.     

Rhodium complexes containing chiral P-donor ligands as catalysts for asymmetric hydrogenation in non conventional media

Abstract  

Rhodium-catalysed asymmetric hydrogenation using P-donor ligands, such as new fluorinated (R)-BINOL and azadioxaphosphabicyclo[3.3.0]octane derivatives was carried out in different reaction media such as organic solvent (CH₂Cl₂), ionic liquid ([BMI][PF₆]), supercritical carbon dioxide (scCO₂) and [BMI][PF₆]/scCO₂ mixture. The best enantioselectivities were obtained in neat [BMI][PF₆], allowing a recycling up to ten times without activity loss. However, the enantioselectivity was lost due to ligand leaching. The ionic liquid phase containing rhodium molecular species was supported on functionalized multi-walled carbon nanotubes in order to improve the recycling, but unfortunately the asymmetric induction was lost upon catalyst immobilization.     

Effect of the ionic liquid [bmim]PF6 on the nonisothermal crystallization kinetics behavior of poly(ether‐b‐amide)

Blending ionic liquid with crystalline polymer permits the design of new high‐performance composite materials. The final properties of these materials are critically depended on the degree of crystallinity and the nature of crystalline morphology. In this work, nonisothermal crystallization behavior of poly(ether‐b‐amide) (Pebax®1657)/room temperature ionic liquid (1‐butyl‐3‐methylimidazolium hexafluorophosphate, [bmim]PF₆) was investigated by differential scanning calorimetry. The presence of [bmim]PF₆ can retard the nucleation of Pebax®1657 and lead to the crystallization depression of the PA block and the crystalline disappearance of the PEO block. However, the dilution effect of the IL results in a higher growth rate of crystallization of PA block. The influence of [bmim]PF₆ content and cooling rate on crystallization mechanism and spherulitc structures was determined by the Avrami equation modified by Jeziorny and Mo's methods, whereas the Ozawa's approach fails to describe the nonisothermal crystallization behavior of Pebax®1657/[bmim]PF₆ blends. In the modified Avrami analysis, the Avrami exponent of PA blocks, n > 3, for pure Pebax®1657, while 3 > n > 2 for Pebax®1657/[bmim]PF₆ blends testifies the transformation of crystallization growth pattern induced by [bmim]PF₆ from three‐dimensional growth of spherulites to a combination of two‐ and three‐dimensional spherulitic growth. Further, lower activation energy for the nonisothermal crystallization of PA blocks of Pebax®1657 can be observed with the increase of [bmim]PF₆ content. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42137.     

Preparation of well-defined dendrimer encapsulated ruthenium nanoparticles and their application as catalyst and enhancement of activity when utilised as SCILL catalysts in the hydrogenation of citral

Silica supported dendrimer encapsulated ruthenium nanoparticles were prepared and evaluated as catalysts in the hydrogenation of citral. The dendrimer encapsulated nanoparticles were prepared using the generation 4 (G4), generation 5 (G5) and generation 6 (G6) hydroxyl-terminated poly(amidoamine) (PAMAM-OH) dendrimers as templating agents with different Ru metal:dendrimer ratios. The effects of ionic liquids as catalyst coatings on the catalytic activity were investigated for the ionic liquids [BMIM][NTf₂], [OMIM][NTf₂], [BMIM][BF₄], [BMIM][PF₆], [EMIM][OcS] and [EMIM][EtS]. An enhancement in catalytic activity was observed when utilising [BMIM][NTf₂] as an ionic liquid coating with selectivity towards citronellal.     

Regioselective acylation of pyridoxine catalyzed by immobilized lipase in ionic liquid

The regioselective acylation of pyridoxine catalyzed by immobilized lipase (Candida Antarctica) in 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM]PF₆) has been investigated, and compared with that in acetonitrile (ACN). The acetylation of pyridoxine using acetic anhydride in [BMIM]PF₆ gave comparable conversion of pyridoxine to 5-monoacetyl pyridoxine with considerably higher regioselectivity (93%–95%) than that in ACN (70%–73%). Among the tested parameters, water activity (a _w) and temperature have profound effects on the reaction performances in either [BMIM]PF₆ or ACN. For the reaction in [BMIM] PF₆, higher temperature (50°C–55°C) and lower a _w (<0.01) are preferable conditions to obtain better conversion and regioselectivity. Mass transfer limitation and intrinsic kinetic from the ionic nature of ionic liquids (ILs) may account for a different rate-temperature profile and a lower velocity at lower temperature in [BMIM]PF₆-mediated reaction. Moreover, consecutive batch reactions for enzyme reuse also show that lipase exhibited a much higher thermal stability and better reusability in [BMIM]PF₆ than in ACN, which represents another advantage of ILs as an alternative to traditional solvents beyond green technology.     

Stability of penicillin G in ionic liquid [Bmim]PF6

The extraction of penicillin G by ionic liquid[Bmim]PF_6 has exhibited promising prospect.The stability of penicillin G is crucial for developing a green ionic liquid-based extraction technology.In this work,the stability of penicillin G in[Bmim]PF_6 was systematically investigated.The results showed the stability of penicillin G was significantly influenced by pH and temperature.It tended to be more stable when pH value increased from 1.5 to 4.0 and the temperature gradually decreased.The half-life(t_(1/2))of penicillin G in[Bmim]PF_6 was 17.7 h in the optimal technological condition(pH 2.0 and 10°C),which is enough for the requirement of extraction technology.The reaction of penicillin G in[Bmim]PF_6 followed the first order kinetics in the pH range 2.0–4.0.Three isomers of penicillin G were found through rearrangement at pH 2.0,and their structures were not affected by temperature.     

Study on Selective Dimerization of α-Methylstyrenes Promoted by Ionic Liquids

The catalytic systems composed of ionic liquids containing BF₄⁻ anion and HBF₄ showed high catalytic activity to produce 4-methyl-2,4-diphenyl-1-pentene (MDP-1) or 1,1,3-trimethyl-3-phenylindan (TPI) under different temperature conditions. Up to 90.8% selectivity to MDP-1 with a 98.7% conversion of α-methylstyrene was obtained at 60 °C in the presence of [HexMIm]BF₄–HBF₄, while exclusive TPI was yielded when the reaction temperature increased to 120 °C. Further studies showed that another ionic liquid, [BMIm]Cl · 2AlCl₃, could act as an excellent catalyst and solvent for the dimerization of α-methylstyrene to produce TPI. The dimerization of α-methylstyrene catalyzed by [HexMIm]BF₄–HBF₄ and [BMIm]Cl · 2AlCl₃ performed the same reaction mechanism and the proton was the active species.     

The functionalized ionic liquid-stabilized palladium nanoparticles catalyzed selective hydrogenation in ionic liquid

The functionalized ionic liquid (2,3-dimethyl-1-[3-N,N-bis(2-pyridyl)-propylamido] imidazolium hexafluorophosphate, [BMMDPA][PF₆]) stabilized and modified palladium nanoparticles were obtained by reducing palladium(II) complex with molecular hydrogen. The as-synthesized palladium nanoparticles have been characterized by different methods. It was demonstrated that the Pd nanoparticles were very efficient catalysts for the selective hydrogenation of the CC bonds of various functionalized alkenes under mild conditions in neat ionic liquid (1-n-butyl-2,3-dimethylimidazolium hexafluorophosphate, [BMMIM][PF₆]). An efficient separation of the products from reaction mixture (ionic liquid phase) was realized and the catalyst’s nano-dispersion and high performance could be preserved.     

Catalytic Activity of Pd(II) Complexes with Triphenylphosphito Ligands in the Sonogashira Reaction in Ionic Liquid Media

The reactivity of palladacycle dimeric complexes with substituted triarylphosphito ligands P(OR)₃ (R = Ph, m-MeC₆H₄, o-MeC₆H₄, C₆H₃-2,4-tBu₂) as well as their non-orthometallated analogues PdCl₂[P(OR)₃]₂ was tested in a copper-free Sonogashira reaction with iodobenzene and phenylacetylene as substrates and imidazolium ionic liquids as the reaction medium. The ionic liquids [bmim][PF₆], [bmim][BF₄] and [emim][SO₄Et] were chosen. The palladium complexes studied showed high activity, and the yield of diphenylacetylene ranged from 31 to 98% in 1 h. The best results were obtained in [bmim][PF₆] for PdCl₂[P(O-m-MeC₆H₄)₃]₂ (84%) and for orthopalladated dimer with the same phosphite (98%).