Ionic liquid promoted synthesis of heterocycle-fused pyrimidine-2,4(1H,3H)-diones utilising CO2

An efficient ionic liquid system was developed for the preparation of various heterocycle-fused pyrimidine-2, 4(1H,3H)-diones in moderate to excellent yields (52–95%). It was found that [HDBN⁺][TFE^?], a simple and easily prepared ionic liquid, could act as both the solvent and reaction promoter, and that the reactions could be efficiently carried out at atmospheric pressures of CO₂.     

Effects of temperature and anion species on CO2 permeability and CO2/N2 separation coefficient through ionic liquid membranes

The permeability of carbon dioxide (CO₂) through imidazolium-based ionic liquid membranes was measured by a sweep gas method. Six species of ionic liquids were studied in this work as follows: [emim][BF₄], [bmim][BF₄], [bmim][PF₆], [bmim][Tf₂N], [bmim][OTf], and [bmim][dca]. The ionic liquids were supported with a polyvinylidene fluoride porous membrane. The measurements were performed at T = (303.15 to 343.15) K. The partial pressure difference between feed and permeate sides was 0.121 MPa. The permeability of the CO₂ increases with temperature for the all ionic liquid species. Base on solution diffusion theory, it can be explained that the diffusion coefficient of CO₂ in an ionic liquid affects the temperature dependence more strongly than the solubility coefficient. The greatest permeability was obtained with the [bmim][Tf₂N] membrane. The membrane of [bmim][PF₆] presents the lowest permeability.The separation coefficient between CO₂ and N₂ through the ionic liquid membranes was also investigated at the volume fraction of CO₂ at feed side 0.10. The separation coefficient decreases with the increase of temperature for the all ionic liquid species. The membrane of [emim][BF₄] and [bmim][BF₄] gives the highest separation coefficient at constant temperature. The lowest separation coefficient was obtained from [bmim][Tf₂N] membrane which presents the highest permeability of CO₂.     

Task-specific ionic liquid and CO2-cocatalysed efficient hydration of propargylic alcohols to α-hydroxy ketones

The hydration of propargylic alcohols is a green route to synthesize α-hydroxy ketones. Herein a CO₂-reactive ionic liquid (IL), [Bu₄P][Im], was found to display high performance for catalyzing the hydration of propargylic alcohols in the presence of atmospheric CO₂, and a series of propargylic alcohols could be converted into the corresponding α-hydroxy ketones in good to excellent yields. In the IL/CO₂ reaction system, CO₂ served as a cocatalyst by forming α-alkylidene cyclic carbonates with propargylic alcohols, and was released via the rapid hydrolysis of the carbonates catalysed by the IL. This is the first example of the efficient hydration of propargylic alcohols under metal-free conditions.     

A novel ionic liquids-based scrubbing process for efficient CO2 capture

A novel alkanolamine-based ionic liquid, N-methyl-diethanolammonium tetrafluoroborate ([MDEA][BF₄]), was synthesized in our laboratory. The ionic liquid-based composite solution consisting of N-methyl-diethanolamine (MDEA), [MDEA][BF₄], piperazine (PZ) and H₂O was investigated for CO₂ capture. The optimal performance for CO₂ capture was found at 45 °C, 1.50 MPa, probably due to a synergistic action of the reaction and the transport. No apparent corrosion was found on stainless and carbon steel with the above composite solution. This finding is very significant to the promotion of its engineering application.     

Improving CO2 selectivity in polymerized room-temperature ionic liquid gas separation membranes through incorporation of polar substituents

Solid, polymer membranes fabricated from room-temperature ionic liquid monomers containing oligo(ethylene glycol) or nitrile-terminated alkyl substituents tethered to imidazolium cations were found to exhibit ideal CO₂/N₂ and CO₂/CH₄ separation factors significantly greater than those with comparable length n-alkyl substituents, with similar CO₂ permeability. Polymers containing these functional groups exhibited CO₂/N₂ gas separation performance exceeding the “upper bound” of a “Robeson Plot”.     

离子液体中电生成CoIL催化行为研究

在离子液体中, 研究了CoL(钴希夫碱配合物)的电化学行为, 并进一步探讨了其对氯苄还原以及PhCH₂Cl与CO₂反应的催化特性. CoL在离子液体中呈现一对由扩散控制的单电子可逆氧化还原峰. 通过电化学行为研究发现, 其氧化还原峰电位不易随金属有机配合物的配体和离子液体阴离子的变化而变化, 并求得了相应的扩散系数. 同时, 循环伏安图表明该体系能对PhCH₂Cl的还原起催化作用, 反应经历一个ECE过程. 另外, 该体系还能催化PhCH₂Cl与CO₂反应, 通过恒电位电解得到(PhCH₂)₂CO, 说明常温常压下, CO₂可以通过CoL催化在离子液体中进行固定, 得到新的有机化合物.     

Predictions of cation and anion effects on solubilities,selectivities and permeabilities for CO2 in ionic liquid using COSMO based activity coefficient model

The solubilities and selectivities for CO₂, N₂ and CH₄ in ionic liquid were predicted using a COSMO based activity coefficient model, COSMO-SAC method. The 1-alkyl-3-methylimidazolium cations were focused in this work. The anion species include tetrafluoroborate [BF₄], hexafluorophosphate [PF₆], triflate [OTf], dicyanamide [dca] and bis(trifluoromethane)-sulfonimide [Tf₂N]. The predicted results of the solubilities of CO₂ in the ionic liquids by COSMO-SAC method are in agreement with the experimental data within the averaged deviation of 0.0017 in mole fraction. The predicted results of selectivities for CO₂/N₂ and CO₂/CH₄ represent the effects of anion species qualitatively. Permeability through supported liquid membrane can be presented by solubility and diffusion coefficients in the liquid. The permeabilities of CO₂ through the ionic liquid membranes were also predicted by a solution-diffusion model with COSMO-SAC method. The predicted results of the CO₂ permeabilities through the ionic liquids represent the experimental data within the order of the permeabilities.     

Confinement of Ionic Liquids in Nanocages: Tailoring the Molecular Sieving Properties of ZIF‐8 for Membrane‐Based CO2 Capture

Fine‐tuning of effective pore size of microporous materials is necessary to achieve precise molecular sieving properties. Herein, we demonstrate that room temperature ionic liquids can be used as cavity occupants for modification of the microenvironment of MOF nanocages. Targeting CO₂ capture applications, we tailored the effective cage size of ZIF‐8 to be between CO₂ and N₂ by confining an imidazolium‐based ionic liquid [bmim][Tf₂N] into ZIF‐8’s SOD cages by in‐situ ionothermal synthesis. Mixed matrix membranes derived from ionic liquid‐modified ZIF‐8 exhibited remarkable combinations of permeability and selectivity that transcend the upper bound of polymer membranes for CO₂/N₂ and CO₂/CH₄ separation. We observed an unusual response of the membranes to varying pressure, that is, an increase in the CO₂/CH₄ separation factor with pressure, which is highly desirable for practical applications in natural gas upgrading.     

Osmium catalyzed asymmetric dihydroxylation of methyl trans-cinnamate in ionic liquids, followed by supercritical CO2 product recovery

In this work, osmium-catalyzed asymmetric dihydroxylation (AD) of methyl trans-cinnamate was studied. Osmium and chiral ligand catalysts were immobilized in ionic liquid only, without any other reaction solvents, while the recovery of the product was performed by extraction with supercritical CO₂, and compared with results obtained by extractions with organic solvents such as hexane and diethyl ether. In supercritical CO₂ extraction experiments, optimal extraction pressure was found and ionic liquid chosen, so that the highest reaction yields coupled with lowest osmium content in the crude product can be achieved. Finally, recycle experiments of the same (ionic liquid + catalytic system) mixture were successfully conducted. Application of ionic liquids and supercritical CO₂ in osmium catalyzed AD allows for the isolation of the diol basically without contamination with osmium, in high yield and enantiomeric excess, and it makes possible the efficient reuse of ionic liquid solvent and the catalytic system.     

Extraction and mechanism investigation of trace roxithromycin in real water samples by use of ionic liquid-salt aqueous two-phase system

The ionic liquid, as a green solvent, has several advantages over the organic solvents in traditional liquid-liquid extraction. Aqueous two-phase system (ATPS) consisting of a hydrophilic ionic liquid (1-butyl-3-methylimidazolium tetrafluoraborate, [Bmim]BF₄) and Na₂CO₃, which is a novel, simple, non-toxic and effective sample pretreatment technique coupled with molecular fluorescence spectrophotometry, was developed for the simultaneous separation, enrichment and rapid analysis of roxithromycin. The extraction yield of roxithromycin in [Bmim]BF₄-Na₂CO₃ aqueous two-phase system is influenced by the types of salts, concentrations of Na₂CO₃ and [Bmim]BF₄, as well as the extracting temperature. Under the optimum conditions, the average extraction efficiency is up to 90.7%. The mechanism of ionic liquid-salt ATPS formation was discussed by hydration theory, and the extraction mechanism of the [Bmim]BF₄-salt ATPS was investigated by FT-IR spectroscopy and UV-vis spectroscopy. The results demonstrate that no chemical (bonding) interactions are observed between ionic liquid and roxithromycin, while the nature properties of the roxithromycin are not altered. This method was practical when applied to the analysis of roxithromycin in real water samples with the detection limit of 0.03 μg mL⁻¹, relative standard deviation (RSD) of 1.9% (n = 13), and linear ranges of 1.00-20.00 μg mL⁻¹. The proposed extraction technique will be promising in the separation of other small biomolecules.     

Actinide(III) carbonate complexation

The following equations have been developed to estimate trivalent actinide and lanthanide carbonate stability constants: log B₁⁰ = −6.128+35.206R−21.557R²; log B₂⁰ = 14.797+7.945R−10.304R², where B₁⁰ = aMCO₃⁺/(aM³⁺aCO₃²⁻, B₂⁰ = aM(CO₃)₂⁻(aM³⁺(aCO₃²⁻), aX is the activity of ion X, M indicates a metal ion and R is the effective ionic radius of the metal ion in six-fold coordination. These equations describe carbonate stability constants for cerium, europium and ytterbium at zero ionic strength. Constants at zero ionic strength were estimated from experimental determinations made in 0.68 molal NaClO₄ by accounting for medium effects.     

Computer‐Assisted Design of Imidazolate‐Based Ionic Liquids for Improving Sulfur Dioxide Capture,Carbon Dioxide Capture,and Sulfur Dioxide/Carbon Dioxide Selectivity

A new strategy involving the computer‐assisted design of substituted imidazolate‐based ionic liquids (ILs) through tuning the absorption enthalpy as well as the basicity of the ILs to improve SO₂ capture, CO₂ capture, and SO₂/CO₂ selectivity was explored. The best substituted imidazolate‐based ILs as absorbents for different applications were first predicted. During absorption, high SO₂ capacities up to ≈5.3 and 2.4 mol mol_IL⁻¹ could be achieved by ILs with the methylimidazolate anions under 1.0 and 0.1 bar (1 bar=0.1 MPa), respectively, through tuning multiple N ⋅⋅⋅ S interactions between SO₂ and the N atoms in the imidazolate anion with different substituents. In addition, CO₂ capture by the imidazolate‐based ILs could also be easily tuned through changing the substituents of the ILs, and 4‐bromoimidazolate IL showed a high CO₂ capacity but a low absorption enthalpy. Furthermore, a high selectivity for SO₂/CO₂ could be reached by IL with 4,5‐dicyanoimidazolate anion owing to its high SO₂ capacity but low CO₂ capacity. The results put forward in this work are in good agreement with the predictions. Quantum‐chemical calculations and FTIR and NMR spectroscopy analysis methods were used to discuss the SO₂ and CO₂ absorption mechanisms.     

Reduction of Carbon Dioxide to Formate at Low Overpotential Using a Superbase Ionic Liquid

A new low‐energy pathway is reported for the electrochemical reduction of CO₂ to formate and syngas at low overpotentials, utilizing a reactive ionic liquid as the solvent. The superbasic tetraalkyl phosphonium ionic liquid [P₆₆₆₁₄][124Triz] is able to chemisorb CO₂ through equimolar binding of CO₂ with the 1,2,4‐triazole anion. This chemisorbed CO₂ can be reduced at silver electrodes at overpotentials as low as 0.17 V, forming formate. In contrast, physically absorbed CO₂ within the same ionic liquid or in ionic liquids where chemisorption is impossible (such as [P₆₆₆₁₄][NTf₂]) undergoes reduction at significantly increased overpotentials, producing only CO as the product.     

Multi‐Molar Absorption of CO2 by the Activation of Carboxylate Groups in Amino Acid Ionic Liquids

A new strategy for multi‐molar absorption of CO₂ is reported based on activating a carboxylate group in amino acid ionic liquids. It was illustrated that introducing an electron‐withdrawing site to amino acid anions could reduce the negative inductive effect of the amino group while simultaneously activating the carboxylate group to interact with CO₂ very efficiently. An extremely high absorption capacity of CO₂ (up to 1.69 mol mol^?1) in aminopolycarboxylate‐based amino acid ionic liquids was thus achieved. The evidence of spectroscopic investigations and quantum‐chemical calculations confirmed the interactions between two kinds of sites in the anion and CO₂ that resulted in superior CO₂ capacities.     

CO<Subscript>2</Subscript>-responsive Polymeric Fluorescent Sensor with Ultrafast Response

Abstract Response speed is one of the most important evaluation criteria for CO₂ sensors. In this work, we report an ultrafast CO₂ fluorescent sensor based on poly[oligo(ethylene glycol) methyl ether methacrylate]-b-poly[N,N-diethylaminoethyl methacrylate-r-4-(2-methylacryloyloxyethylamino)-7-nitro-2,1,3-benzoxadiazole] [POEGMA-b-P(DEAEMA-r-NBDMA)], in which DEAEMA units act as the CO₂-responsive segment and 4-nitrobenzo-2-oxa-1,3-diazole (NBD) is the chromophore. The micelles composed of this copolymer could disassemble in 2 s upon CO₂ bubbling, accompanying with enhanced fluorescence emission with bathochromic shift. Furthermore, the quantum yield of the NBD chromophore increases with both the CO₂ aeration time and the NBD content. Thus we attribute the fluorescent enhancement to the inhibition of the photo-induced electron transfer between unprotonated tertiary amine groups and NBD fluorophores. The sensor is durable although it is based on “soft” materials. These micellar sensors could be facilely recycled by alternative CO₂/Ar purging for at least 5 times, indicating good reversibility.     

Poly(ionic liquid)s as new materials for CO2 absorption

A series of imidazolium‐based ionic liquid monomers and their corresponding polymers (poly(ionic liquid)s) were synthesized, and their CO₂ sorption was studied. The poly(ionic liquid)s had enhanced CO₂ sorption capacities and fast sorption/desorption rates compared with room temperature ionic liquids. The effects of the chemical structures, including the types of anion, cation, and backbone of the poly(ionic liquid)s on their CO₂ sorption have been discussed. In contrast to room temperature ionic liquids, the polymer with PF anions had the highest CO₂‐sorption capacity, while those with BF or Tf₂N^? anions had the same capacities. The CO₂ sorption and desorption of the polymers were fast and reversible, and the sorption was selective over H₂, N_2, and O₂. The measured Henry's constants of P[VBBI][BF₄] and P[MABI][BF₄] were 26.0 bar and 37.7 bar, which were lower than those of similar room temperature ionic liquids. The preliminary study of the mechanism indicated that the CO₂ sorption of the polymer particles was more absorption (the bulk) but less adsorption (the surface). © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 5477–5489, 2005     

Determination of the upper limits, benchmarks, and critical properties for gas separations using stabilized room temperature ionic liquid membranes (SILMs) for the purpose of guiding future research

The literature reports that supported ionic liquid membranes (SILMs) outperform standard polymers for the separations of CO₂/N₂ and CO₂/CH₄, even under continuous flow mixed gas conditions. Before the expenditure of more resources to develop new room temperature ionic liquids (RTILs) and SILMs, it is time to consider what benchmarks for SILM performance exist and if upper limits could be projected based on the physical chemistry of RTILs. At this juncture, we should ask if the current research efforts are properly focused based on the successes and failures in the literature. We summarize literature data, along with adding new data, on the SILM permeabilities and selectivities for the following gas pairs: CO₂/N₂, CO₂/CH₄, O₂/N₂, ethylene/ethane, propylene/propane, 1-butene/butane, and 1,3-butadiene/butane. The analysis predicts a maximum CO₂-permeability for SILMs and an upper bound for permeability selectivity vs. CO₂-permeability with respect to the CO₂/N₂ and CO₂/CH₄ separations. Also summarized are the representative successes and failures for improving the separation performance of SILMs via functionalization and facilitated transport in the context of the CO₂/N₂, CO₂/CH₄, and olefin/paraffin separations. In the context of the CO₂-separations, the analysis recommends a number of future research foci including research into SILMs cast from RTILs with smaller molar volumes. In the context of olefin/paraffin separations, the preliminary data is encouraging when considering the use of facilitated transport via silver carriers. Since RTIL-solvent/solvent interactions dominate in terminating the overall SILM performance, past attempts at enhancing solute/solvent interactions via the addition of functional groups to the RTILs have not produced SILMs with better separation performance compared to the unfunctionalized RTILs. Future research into functionalized RTILs needs to consider the changes to the dominant solvent/solvent interactions and not just the solute/solvent interactions.     

Ionic Liquids and Water: Hydrophobicity vs. Hydrophilicity

Many chemical processes rely extensively on organic solvents posing safety and environmental concerns. For a successful transfer of some of those chemical processes and reactions to aqueous media, agents acting as solubilizers, or phase-modifiers, are of central importance. In the present work, the structure of aqueous solutions of several ionic liquid systems capable of forming multiple solubilizing environments were modeled by molecular dynamics simulations. The effect of small aliphatic chains on solutions of hydrophobic 1-alkyl-3-methylimidazolium bis(trifluoromethyl)sulfonylimide ionic liquids (with alkyl = propyl [C₃C₁im][NTf₂], butyl [C₄C₁im][NTf₂] and isobutyl [iC₄C₁im][NTf₂]) are covered first. Next, we focus on the interactions of sulphonate- and carboxylate-based anions with different hydrogenated and perfluorinated alkyl side chains in solutions of [C₂C₁im][C_nF_2n+1SO₃], [C₂C₁im][C_nH_2n+1SO₃], [C₂C₁im][CF₃CO₂] and [C₂C₁im][CH₃CO₂] (n = 1, 4, 8). The last system considered is an ionic liquid completely miscible with water that combines the cation N-methyl-N,N,N-tris(2-hydroxyethyl)ammonium [N_{1 2OH 2OH 2OH}]⁺, with high hydrogen-bonding capability, and the hydrophobic anion [NTf₂]^–. The interplay between short- and long-range interactions, clustering of alkyl and perfluoroalkyl tails, and hydrogen bonding enables a wealth of possibilities in tailoring an ionic liquid solution according to the needs.     

Acidic ionic liquid [NMP]H2PO4 as dual solvent-catalyst for synthesis of β-alkoxyketones by the oxa-Michael addition reactions

Acidic ionic liquid N-methyl-2-pyrrolidonium dihydrogen phosphate [NMP]H₂PO₄ was prepared and used as efficient catalyst and reaction medium to synthesize β-alkoxyketones by the oxa-Michael addition reactions for the first time. The effect of anions and cations, amount of ionic liquid on the reaction was investigated. Various alcohols and phenols proceeded smoothly and led to corresponding β-alkoxyketones with high yields under mild reaction conditions, O-selectivity addition of aminoethanols was also achieved in this paper. Compared with traditional imidazolium ionic liquids, [NMP]H₂PO₄ gave the better results. The ionic liquid was stable and could be reused at least five times with a slight loss of activity.     

Probing the Reorganization of Ionic Liquids’ Structure Induced by CO2 Sorption

The sorption of CO₂ is often used to modify the macroscopic properties of liquids and solids. In the particular case of ionic liquids, different from molecular liquids, the sorption of CO₂ may not induce volume expansions due to the strong Coulombic interactions between the ions of the fluid. However, a considerable viscosity decrease has been systematically observed. In order to understand the mechanisms of properties modifications in ionic fluids, herein we used Raman spectroscopy to probe the effect of CO₂ on the structure of ionic liquids. It is shown that CO₂ perturbs the electrostatic interactions between cations and anions, thus inducing a change in the polar domain of ionic liquids. It is observed that ionic liquids having bulkier ions are more prone to be perturbed by CO₂ in comparison to ionic liquids having smaller ions. These results reveal new means of controlling the electrostatic forces between the ions and contributes to the mechanistic understanding of the modification of the macroscopic properties of ionic liquids by CO₂ sorption.