Dicationic imidazolium based ionic liquids: Synthesis and properties

An overview on human exposure, toxicity, solid-phase microextraction and adsorptive removal of perfluoroalkyl carboxylic acids (PFCAs) from water matrices

Perfluoroalkyl carboxylic acids (PFCAs) are sub-class of perfluoroalkyl substances commonly detected in water matrices. They are persistent in the environment, hence highly toxic to living organisms. Their occurrence at trace amount, complex nature and prone to matrix interference make their extraction and detection a challenge. This study consolidates current advancements in solid-phase extraction (SPE) techniques for the trace-level analysis of PFCAs from water matrices. The advantages of the methods in terms of ease of applications, low-cost, robustness, low solvents consumption, high pre-concentration factors, better extraction efficiency, good selectivity and recovery of the analytes have been emphasized. The article also demonstrated effectiveness of some porous materials for the adsorptive removal of the PFCAs from the water matrices. Mechanisms of the SPE/adsorption techniques have been discussed. The success and limitations of the processes have been elucidated.

1-Butyl-3-methylimidazolium methane sulfonate ionic liquid corrosion inhibitor for mild steel alloy: Experimental, optimization and theoretical studies

The current research reports the performance of 1-butyl-3-methylimidazolium methane sulfonate ([C4MIM][OMs](IL)) as effective corrosion inhibitor for mild steel in 1 M H2SO4 electrolyte. For proper evaluation, weight loss, electrochemical study, theoretical modeling and optimization techniques were used. Weight loss and electrochemical methods shows that the inhibition performance of [C4MIM][OMs] on the metal surface strengthens as the concentration increases. Maximum inhibition efficiency of 85.71%, 92.5% and 91.1% at 0.8 g L-1 concentration of [C4MIM][OMs] were obtained from the weight loss, polarization and impedance studies, respectively. In addition, response surface methodology (RSM) a statistical tool was used for modeling and optimization of the empirical data. The RSM model validates the empirical findings. Also, DFT/MD-simulation investigations evidenced that [C4MIM][OMs] forms a barrier film on the mild steel surface. The result shows that the synthesized [C4MIM][OMs] could open up opportunities in corrosion and materials protection for sustainability.

Synthesis and characterization of ammonium-based protic ionic liquids for carbon dioxide absorption

A series of ammonium-based protic ionic liquids (APILs) namely ethanolammonium pentanoate [ETOHA][C5], ethanolammonium heptanoate [ETOHA][C7], triethanolammonium pentanoate [TRIETOHA][C5], triethanolammonium heptanoate [TRIETOHA][C7], tributylammonium pentanoate [TBA][C5] and tributylammonium heptanoate [TBA][C7] was synthesized via proton transfer. Their structural confirmation and physiochemical properties namely thermal stability, phase transition, density, heat capacity (Cp) and refractive index (RI) have been determined. Specifically, [TRIETOHA] APILs have crystallization peaks ranging from -31.67 to -1.00 °C, owing to their large density values. A comparison study revealed the low Cp values of APILs in comparison to monoethanolamine (MEA) which could be advantageous for APILs to be used in CO2 separation during recyclability processes. Additionally, the performance of APILs toward CO2 absorption was investigated by using a pressure drop technique under a pressure range of 1-20 bar at 298.15 K. It was observed that [TBA][C7] recorded the highest CO2 absorption capacity with the value of 0.74 mole fraction at 20 bar. Additionally, the regeneration of [TBA][C7] for CO2 absorption was studied. Analysis of the measured CO2 absorption data showed marginal reduction in the mole fraction of CO2 absorbed between fresh and recycled [TBA][C7] thus proving the promising potential of APILs as good liquid absorbents for CO2 removal.

Hydrophobic ammonium based ionic liquids for efficient extraction of textile dyes from aqueous media: Extraction study and antibacterial evaluation

Alizarin red S (ARS) extraction from aqueous medium was carried out using hydrophobic ionic liquids (ILs) containing trioctylammonium cation paired with 4-tert-butylbenzoate ([TOA][Butbenz] (IL1), 4-phenylbutanoate ([TOA][PheBut] (IL2), 3-4-dimethylbenzoate ([TOA][DMbenz] (IL3), naphthoate, ([TOA][Naph]) (IL4), salicylate ([TOA][Sali]) (IL5) and nonanedioate ([TOA]2[Nona]) (IL6). The findings demonstrated that all of the tested ILs were efficient for extracting ARS, however, [TOA]2[Nona] was more effective than others. For the extraction of ARS from the aqueous phase, the effects of various parameters including the initial pH of the dye solution, contact time, ILs to dye volume ratio (VIL:VW), dye concentration, temperature, and salt effect were investigated. The spontaneity of the liquid-liquid extraction of ARS from the aqueous phase to the IL phase was confirmed by thermodynamic parameters. More than 90% of the ARS was extracted from the aqueous phase to the IL phase throughout all experiments. Interaction of selected IL with dyes were confirmed using FTIR analysis. The standard bacterial strains of Escherichia coli (E. coli) ATCC BAA-2471 (gram negative) and Methicillin-resistant Staphylococcus (MRSA) ATCC 43300 (gram positive) were used for evaluating antibacterial activity. The lower dose (250 ppm), the ILs1, 2, 3, 4, 5, and 6 inhibited 0.40, 1.50, 6.50, 1.50, 2.50, and 0.50 mm growth of E. coli, and 4.0, 2.0, 16.50, 0.40, 5.0, and 3.50 mm growth of MRSA, respectively. The experimental findings confirmed that the present ILs can be utilized as an effective solvent for ARS and other dyes extraction from aqueous media.

Effect of ion structure on the physicochemical properties and gas absorption of surface active ionic liquids

Surface active ionic liquids (SAILs) combine useful characteristics of both ionic liquids (ILs) and surfactants, hence are promising candidates for a wide range of applications. However, the effect of SAIL ionic structures on their physicochemical properties remains unclear, which limits their uptake. To address this knowledge gap, in this work we investigated the density, viscosity, surface tension, and corresponding critical micelle concentration in water, as well as gas absorption of SAILs with a variety of cation and anion structures. SAILs containing anions with linear alkyl chains have smaller molar volumes than those with branched alkyl chains, because linear alkyl chains are interdigitated to a greater extent, leading to more compact packing. This interdigitation also results in SAILs being about two orders of magnitude more viscous than comparable conventional ILs. SAILs at the liquid-air interface orient alkyl chains towards the air, leading to low surface tensions closer to n-alkanes than conventional ILs. Critical temperatures of about 900 K could be estimated for all SAILs from their surface tensions. When dissolved in water, SAILs adsorb at the liquid-air interface and lower the surface tension, like conventional surfactants in water, after which micelles form. Molecular simulations show that the micelles are spherical and that lower critical micelle concentrations correspond to the formation of aggregates with a larger number of ion pairs. CO₂ and N₂ absorption capacities are examined and we conclude that ionic liquids with larger non-polar domains absorb larger quantities of both gases.

Physico-Chemical Properties of Magnetic Dicationic Ionic Liquids with Tetrahaloferrate Anions

A series of imidazolium-based symmetrical and asymmetrical dicationic ionic liquids (DcILs) with alkyl spacers of different length and with [FeCl3 Br]- as counter ion have been synthesized. The synthesized DcILs are characterized by using FTIR and Raman spectroscopy as well as mass spectrometry, along with single-crystal XRD analysis. Physicochemical properties such as solubility, thermal stability and magnetic susceptibility are also measured. These compounds show low melting points, good solubility in water and organic solvents, thermal stability, and paramagnetism. The products of molar susceptibility and temperature (χmol ⋅T) for the synthesized DcILs have been found between 4.05 to 4.79 emu mol-1  K Oe-1 and effective magnetic moment values have also been determined to be compared to that expected from the spin-only approximation.

Understanding X-ray Photoelectron Spectra of Ionic Liquids: Experiments and Simulations of 1-Butyl-3-methylimidazolium Thiocyanate

We demonstrate a combined experimental and computational approach to probe the electronic structure and atomic environment of an ionic liquid, based on core level binding energies. The 1-butyl-3-methylimidazolium thiocyanate [C₄C₁Im][SCN] ionic liquid was studied using ab initio molecular dynamics, and results were compared against previously published and new experimental X-ray photoelectron spectroscopy (XPS) data. The long-held assumption that initial-state effects in XPS dominate the measured binding energies is proven correct, which validates the established premise that the ground state electronic structure of the ionic liquid can be inferred directly from XPS measurements. A regression model based upon site electrostatic potentials and intramolecular bond lengths is shown to account accurately for variations in core-level binding energies within the ionic liquid, demonstrating the important effect of long-range interactions on the core levels and throwing into question the validity of traditional single ion pair ionic liquid calculations for interpreting XPS data.

Efficient Extraction of Methylene Blue from Aqueous Solution Using Phosphine-Based Deep Eutectic Solvents with Carboxylic Acid

Methylene blue (MB), an organic thiazine dye, has numerous industrial and medical applications. However, MB is a wastewater contaminant that is harmful to humans and aquatic life. Hence, its removal from water bodies is essential. In this work, five novel deep eutectic solvents (DESs) were synthesized using different precursors, screened, and studied for the extraction of methylene blue (MB) from aqueous solution using liquid–liquid extraction. The first, TOP-SA, was synthesized using trioctylphosphine (TOP) as a hydrogen bond acceptor (HBA) and 2-hydroxy benzoic acid as a hydrogen bond donor (HBD). Among these, TOP-SA had the highest MB removal efficiency. The effects of pH, contact time, initial MB concentration, volumetric ratio, temperature, and ionic strength were studied and optimized. A 99.3% removal was achieved in 5 min for a 200 mg dm−3 MB solution mixed in a 1:10 ratio with TOP-SA at 25.0 °C. The structural properties of TOP-SA and its interactions with MB were investigated using FTIR. TOP-SA’s toxicity was investigated using human cells in vitro. TOP-SA was found to be comparatively less toxic and is a more efficient MB remover than other literature reported ionic liquids (ILs).

Amine-Based Deep Eutectic Solvents for Alizarin Extraction from Aqueous Media

Alizarin dye is toxic and has a negative influence on human life and the environment. Consequently, the scientific community faces a difficult issue in developing efficient approaches for removing alizarin from water streams. Six distinct deep eutectic solvents (DESs) containing different hydrogen bond acceptors (HBAs), namely trioctylphosphine, trioctylamine and trihexylamine, and two hydrogen bond donors (HBDs), namely salicylic acid and malonic acid, were used to rapidly remove alizarin from high concentration solutions up to 2000 mg/L at room temperature using the liquid–liquid micro-extraction method (LLE). DES-3 had the highest extraction efficiency for alizarin among the other synthesized DESs. The effect of process variables such pH, contact time, dye initial concentration, volume ratio, temperature and salt on alizarin extraction efficiency from water stream was explored, optimized and reported. Statistical analysis was conducted to ensure the accuracy of values for the optimized parameters. For a 1000 mg/L solution of alizarin with a DES/alizarin volume ratio of 1:10 at room temperature, the maximum elimination of 98.02 percent was achieved in 5 min. FTIR was used to analyze the structural properties of DES and the interaction between DES and alizarin. The thermal stability of DES-3 was determined using thermogravimetric analysis (TGA) and indicated that DES-3 has excellent thermal stability up to 320 °C. Human saline was used to test the toxicity of the synthesized DES in vitro. It was determined that synthesized DES is less harmful and more effective at removing alizarin.

Recent Advances in Imidazolium-Based Dicationic Ionic Liquids as Organocatalysts: A Mini-Review

Imidazolium-based dicationic ionic liquids (DILs) are gaining considerable space in the field of organocatalysis mainly due to the opportunities in offering new possible applicable structural variations. In addition to the well-known variables which made the ionic liquids (ILs) famous as the type of cation and anion used, the nature of the molecular spacer moiety turns out a further possibility to improve some physicochemical properties, for example, solubility, acidity, electrochemical behavior, and so on. For this reason, this class of ionic liquids has been considered as possible competitors to their corresponding monocationic salts in replacing common catalysts in organic synthesis, particularly in cases in which their bidentate nature could positively affect the catalytic activity. This mini-review is intended to highlight the progress carried out in the last six years in the field of organocatalysis, including DILs as such and as hybrids with polymers, nanomaterials, and composites.

Chitosan and dicationic ionic liquid intercalated clay-coated solid-phase microextraction fiber for determination of sixteen polycyclic aromatic hydrocarbons in coffee and tea samples

In the present study, solid-phase microextraction (SPME) fiber was prepared by coating clay (MMT)-chitosan (CH) and dicationic ionic liquid (DIL) onto the stainless-steel wire step by step. The characterization of fibers was performed by Fourier transform infrared spectroscopy, thermal analysis, x-ray diffraction analysis, and scanning electron microscopy. The prepared fibers were evaluated for separation and determination of 16 polycyclic aromatic hydrocarbons (PAHs) in coffee and tea samples in headspace- and direct immersion-SPME by coupling with gas chromatography/mass spectrometry. The analytical performance of MMT/CH/DIL fibers was carried out for the extraction of PAHs and compared with the performance of carboxen/polydimethylsiloxane (CAR/PDMS) and divinylbenzene/CAR/PDMS (DVB/CAR/PDMS) fibers under optimized conditions. The wider linear ranges between 0.001 and 25 μg L^-1 with a coefficient of determination above 0.9962, low limits of detection between 0.0001 and 0.05 μg L^-1 and good intra-day repeatability from 2.45 to 6.48 % and fiber-to-fiber reproducibility from 3.19 % to 8.82 % were obtained for all PAHs in both methods with MMT/CH/octyl (O)-DIL fiber. The extraction recoveries of coffee and tea samples ranged from 87.5 to 112 % using the MMT/CH/O-DIL fiber in both SPME methods.

Utilization of montmorillonite nanocomposite incorporated with natural biopolymers and benzyl functionalized dicationic imidazolium based ionic liquid coated fiber for solid-phase microextraction of organochlorine pesticides prior to GC/MS and GC/ECD

A novel montmorillonite clay (MMT) bionanocomposite modified with chitosan (CH), carboxymethyl cellulose (CMC), and benzylimidazolium based dicationic ionic liquid with tetraethylene glycol linker (DIL) was fabricated on stainless steel wire by in situ process. The MMT-CH-CMC-DIL coated solid-phase microextraction (SPME) fiber was examined for the determination of organochlorine pesticides (OCPs) in real samples by HS-SPME-GC method using mass spectrometry (MS) and electron capture detector (ECD). Under optimized conditions, the proposed method exhibited low limits of detection (0.5 ng L^-1 with MS and 0.1 ng L^-1 with ECD detection), good linearities (R² = 0.9972-0.9993 with MS and 0.9987-0.9998 with ECD detection), favorable single-fiber repeatability, and fiber-to-fiber reproducibility (less than 8.2% and 9.9% for both types of detection) and high reusability around 125 cycles. Recovery studies were carried out for OCPs in tap water, green tea, and milk samples to verify the applicability of the developed SPME-GC method.

Scrutinizing Self-Assembly, Surface Activity and Aggregation Behavior of Mixtures of Imidazolium Based Ionic Liquids and Surfactants: A Comprehensive Review

The desire of improving various processes like enhanced oil recovery (EOR), water treatment technologies, biomass extraction, organic synthesis, carbon capture etc. in which conventional surfactants have been traditionally utilized; prompted various researchers to explore the self-assembly and aggregation behavior of different kinds of surface-active molecules. Ionic liquids (ILs) with long alkyl chain present in their structure constitute the advantageous properties of surfactant and ILs, hence termed as surface-active ionic liquids (SAILs). The addition of ILs and SAILs significantly influence the surface-activity and aggregation behavior of industrially useful conventional surfactants. After a brief review of ILs, SAILs and surfactants, the prime focus is made on analyzing the self-assembly of SAILs and the mixed micellization behavior of conventional surfactants with different ILs.

Cation-Anion Interactions, Stability, and IR Spectra of Dicationic Amino Acid-Based Ionic Liquids Probed Using Density Functional Theory

In this work, we have theoretically studied the dicationic ionic liquids (DILs) constructed from geminal methylimidazolium dication with varying amino acid anions and spacers using density functional theory. Amino acid-based DILs form via strong C-H···O hydrogen bonds. These hydrogen bonds have a significant role in stabilizing the DILs. The higher cation-anion interaction energy in the order of covalent bond energy and liquid density of DILs imply higher thermal stability than their mono analogues. The C-H stretching frequencies are above 3100 cm^-1 in all complexes and form a signature for DILs. Interestingly, aliphatic and aromatic amino acid anions show similar molecular properties. Overall, the DILs formed from amino acids exhibit high stability and large surface tension and are chemically non-toxic; hence, they can replace inorganic DILs.

Ionic Liquid-Based Surfactants: Recent Advances in Their Syntheses, Solution Properties, and Applications

The impetus for the expanding interest in ionic liquids (ILs) is their favorable properties and important applications. Ionic liquid-based surfactants (ILBSs) carry long-chain hydrophobic tails. Two or more molecules of ILBSs can be joined by covalent bonds leading, e.g., to gemini compounds (GILBSs). This review article focuses on aspects of the chemistry and applications of ILBSs and GILBSs, especially in the last ten years. Data on their adsorption at the interface and micelle formation are relevant for the applications of these surfactants. Therefore, we collected data for 152 ILBSs and 11 biamphiphilic compounds. The head ions of ILBSs are usually heterocyclic (imidazolium, pyridinium, pyrrolidinium, etc.). Most of these head-ions are also present in the reported 53 GILBSs. Where possible, we correlate the adsorption/micellar properties of the surfactants with their molecular structures, in particular, the number of carbon atoms present in the hydrocarbon "tail". The use of ILBSs as templates for the fabrication of mesoporous nanoparticles enables better control of particle porosity and size, hence increasing their usefulness. ILs and ILBSs form thermodynamically stable water/oil and oil/water microemulsions. These were employed as templates for (radical) polymerization reactions, where the monomer is the "oil" component. The formed polymer nanoparticles can be further stabilized against aggregation by using a functionalized ILBS that is co-polymerized with the monomers. In addition to updating the literature on the subject, we hope that this review highlights the versatility and hence the potential applications of these classes of surfactants in several fields, including synthesis, catalysis, polymers, decontamination, and drug delivery.

Ionic liquids and deep eutectic solvents for the recovery of phenolic compounds: effect of ionic liquids structure and process parameters

Water pollution is a severe and challenging issue threatening the sustainable development of human civilization. Besides other pollutants, waste fluid streams contain phenolic compounds. These have an adverse effect on the human health and marine ecosystem due to their toxic, mutagenic, and carcinogenic nature. Therefore, it is necessary to remove such phenolic pollutants from waste stream fluids prior to discharging to the environment. Different methods have been proposed to remove phenolic compounds from wastewater, including extraction using ionic liquids (ILs) and deep eutectic solvent (DES), a class of organic salts having melting point below 100 °C and tunable physicochemical properties. The purpose of this review is to present the progress in utilizing ILs and DES for phenolic compound extraction from waste fluid streams. The effects of IL structural characteristics, such as anion type, cation type, alkyl chain length, and functional groups will be discussed. In addition, the impact of key process parameters such as pH, phenol concentration, phase ratio, and temperature will be also described. More importantly, several ideas for addressing the limitations of the treatment process and improving its efficiency and industrial viability will be presented. These ideas may form the basis for future studies on developing more effective IL-based processes for treating wastewaters contaminated with phenolic pollutants, to address a growing worldwide environmental problem.

Synthesis, characterization and application of a non-flammable dicationic ionic liquid in lithium-ion battery as electrolyte additive

A novel dicationic room temperature ionic liquid, 1,1′-(5,14-dioxo-4,6,13,15-tetraazaoctadecane-1,18-diyl) bis(3-(sec-butyl)-1H-imidazol-3-ium) bis((trifluoromethyl)-sulfonyl) imide has been synthesized and fully characterized. Its thermal and electrochemical analyses along with transport properties have been studied. We propose it as a potential nominal additive to the commonly used conventional organic carbonate electrolyte mixture and study its adaptability in Lithium-ion batteries which are the prime power sources for ultraportable electronic devices. We have compared the performance characteristics of the full cells made without and with this ionic liquid. The cells comprise lithium nickel cobalt manganese oxide cathode, graphite anode and ethylene carbonate - dimethyl carbonate (1:1, v/v + LiPF₆) mixture electrolyte with nominal amount of ionic liquid as additive. The major concern with conventional electrolytes such as degradation of the materials inside batteries has been addressed by this electrolyte additive. Additionally, this additive is safer at relatively higher temperature. In its presence, the overall battery life is enhanced and it shows good cycling performance and coulombic efficiency with better discharge capacities (22% higher) after 100 cycles. Even after the increase in current rate from 10 mA/g to 100 mA/g, the cell still retains around 73% of capacity.

1, 1'-Sulfinyldiethylammonium Bis (Hydrogen Sulfate) as a Recyclable Dicationic Ionic Liquid Catalyst for the Efficient Solvent-free Synthesis of 3, 4-Dihydropyrimidin-2(1H)-ones via Biginelli Reaction

OBJECTIVE

A facile and efficient method for synthesis of 3, 4-dihydropyrimidin-2(1H)-ones via Biginelli reaction catalyzed by a novel dicationic Brönsted acidic ionic liquid, [(EtNH2)2SO][HSO4]2, has been successfully developed.

MATERIALS AND METHODS

3, 4-Dihydropyrimidin-2(1H)-ones were synthesized through one-pot condensation of aromatic aldehydes, ethyl acetoacetate, and urea under solvent-free conditions using [(EtNH2)2SO][HSO4]2 as a novel catalyst. The progress of the reaction was monitored by thin-layer chromatography (ethyl acetate / n-hexane = 1 / 5). The products have been characterized by IR, 1H NMR, 13C NMR, and also by their melting points.

RESULTS

In this research, a library of dihydropyrimidinone derivatives was synthesized via Biginelli reaction under solvent-free conditions at 120oC using [(EtNH2)2SO][HSO4]2 as a catalyst. Various aromatic aldehydes, as well as heteroaromatic aldehydes, were employed, affording good to high yields of the corresponding products and illustrating the substrate generality of the present method. In addition, the prepared dicationic Brönsted acidic ionic liquid can be easily recovered and reused.

CONCLUSION

1, 1'-Sulfinyldiethylammonium bis (hydrogen sulfate), as a novel dicationic ionic liquid, can act as a highly efficient catalyst for the synthesis of 3, 4-dihydropyrimidin-2(1H)-ones under solvent-free conditions.

Porous ionic liquid polymer: A reusable adsorbent with broad operating pH range for speciation of nitrate and nitrite

Ionic liquids (ILs) are a class of fluids with unique physicochemical properties employing polymeric substances emerging new materials. Solidification of ILs into porous materials generates porous ionic liquid polymers that combine the unique characteristics of ILs with common porous materials and polymers. In this study, it's the first time the porous ionic liquid polymer was chosen as a sorbent for extraction and speciation of nitrite and nitrate. Porous IL was prepared through polymerization of 1-allyl-3-methylimidazolium bromide monomers in the presence of azobisisobutyronitrile (AIBN) and crosslinking of ethylene glycol dimethyl acrylate (EGDMA). Parameters affecting the adsorbent performance were optimized. Under the optimal conditions, correlation coefficient (R²) was 0.9996 and LOD was 0.1 µg L^-1. This method presented the linearity in the concentration range between 0.1-100 µg L^-1 and the relative standard deviation was 3.2%. Finally, the adsorption behavior of the obtained sorbent for nitrate and nitrite determination in various real samples was evaluated. The result indicates that the porous ionic liquid polymer showed high adsorption capacity (233 mg g^-1). The convenient preparation of the porous ionic liquid material, as well as high adsorption capacity for anionic pollutants predicted its broad application potential in anion removal materials.

Physicochemical Properties of Various 2-Hydroxyethylammonium Sulfonate -Based Protic Ionic Liquids and Their Potential Application in Hydrodeoxygenation

In order to obtain the regularities of physicochemical properties of hydroxy protic ionic liquids (PILs) and broaden their potential application, a series of 2-hydroxyethylammonium sulfonate-based PILs were synthesized through proton transfer reaction and characterized by NMR and FT-IR and elemental analysis. Their phase transfer behavior (T _m) and initial decomposition point (T _d) were characterized by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA), respectively. Meanwhile, the regularities of density (ρ), viscosity (η) and electrical conductivity (σ) of synthesized PILs at different temperatures were measured. The results indicated that their physicochemical properties were tightly related with their structures and the interactions between cations and anions. In addition, the dissociation constants (pKa) of synthesized PILs were obtained by acid-base titration, which revealed that all synthesized PILs had pKa exceeding 7 and their cations were the crux of determining the pKa value. Moreover, several synthesized PILs with a low melting temperature also showed potential application in the deoxidation reaction of cyclohexanol, as they had conversion rates approximating 100% and the selectivity of cyclohexane or cyclohexene was about 80%.

Synthesis of novel functional ionic liquids and their application in biomass

A series of dicationic ionic liquids (ILs) including [PF₆][(PYR)C₄(MIM)][Cl], [PF₆][(PYR)C₄(PYR)][Cl], [PF₆][(PYR)C₅(MIM)][Cl], and [PF₆][(PYR)C₅(PYR)][Cl], and monocationic ILs including [(PYR)C₄Cl][PF₆], [(PYR)C₅Cl][PF₆], [(MIM)C₂COOH][PF₆] and [(PYR)C₂COOH][PF₆] were synthesized. Their thermal stability and melting points were determined. Their solubility with organic solvents and the miscibility with water were investigated. These functional ILs are hydrophilic at high temperatures and they are hydrophobic at low temperatures, which enable the effective isolation of the resulting reducing sugar. High yields of reducing sugar were obtained for corn stalk after 8 h (20.73%) and potato starch after 6 h (72.50%) by the treatment with the mixture of [PF₆][(PYR)C₄(PYR)][Cl] and [(PYR)C₂COOH][PF₆]. The reuse of dicationic and monocationic ILs was successfully performed and no significant reduction in yields of reducing sugar was observed. These functional ILs have important implications in the design of homogeneous and heterogeneous systems with water and organic solvents, which could be used to satisfy some specific applications.

A series of dicationic and monocationic ionic liquids (ILs) were synthesized and investigated and it was found that these functional ILs have important implications in the design of homogeneous and heterogeneous systems.

Optical Kerr effect spectroscopy of CS2 in monocationic and dicationic ionic liquids: insights into the intermolecular interactions in ionic liquids

A comparative study of the intermolecular dynamics of CS₂ in monocationic and dicationic ionic liquids (ILs) was performed using optical heterodyne-detected Raman-induced Kerr effect spectroscopy (OHD-RIKES). The reduced spectral densities (RSDs) of mixtures of CS₂ in 1-alkyl-3-methylimidazolium bis[(trifluoromethane)sulfonyl]amide ([C_nC₁im][NTf₂] for n = 3-5) and 1,2n-bis(3-methylimidazolium-1-yl) alkane bis[(trifluoromethane)sulfonyl]amide ([(C₁im)₂C_2n][NTf₂]₂ for n = 3-5) were investigated as a function of concentration at 295 K. An additivity model was used to obtain the CS₂ contribution to the RSD of a mixture in the 0-200 cm^-1 region. One of the aims of this study is to show how CS₂ can be used as a probe of intermolecular/interionic interactions in ILs. The concentrations were chosen such that the CS₂-to-imidazolium ring mole fraction of a mixture with [(C₁im)₂C_2n][NTf₂]₂ (DIL(2n)) is the same as that of a mixture with [C_nC₁im][NTf₂] (MIL(n)). As found previously for CS₂ in monocationic ILs, the intermolecular spectrum of CS₂ in dicationic ILs is lower in frequency and narrower than that of neat CS₂. The new result is that the intermolecular spectrum of CS₂ is higher in frequency in DIL(2n) than in the corresponding MIL(n), indicating that CS₂ molecules experience a stiffer potential in dicationic ILs than in monocationic ILs. The intermolecular dynamics of CS₂ being higher in frequency in DIL(2n) than in MIL(n) is consistent with recent molecular dynamics simulations (Lynden-Bell and Quitevis, J. Chem. Phys., 2018, 148, 193844) that show the stiffer potential is the result of greater confinement of CS₂ in DIL(2n) than in MIL(n). We also show in this study how effects due to dilution and the intermolecular potential seen by a solute molecule in solution are unraveled.

The introduction of two new imidazole-based bis-dicationic Brönsted acidic ionic liquids and comparison of their catalytic activity in the synthesis of barbituric acid derivatives

Two bis-dicationic acidic ionic liquids are prepared, used and compared in the synthesis of barbituric acid derivatives.

Synthesis and properties of novel ammonium-based room-temperature gemini ionic liquids

Ammonium-based room-temperature asymmetrical gemini ionic liquids, 1-trimethylammonium-3-(pyridinium)propane bisdicyanamide ([N₁₁₁C₃Py][DCA]₂) and 1-trimethylammonium-3-(1-methylpiperidinium)propane bisdicyanamide ([N₁₁₁C₃MPi][DCA]₂) were respectively synthesized and structurally characterized by ¹H NMR and ¹³C NMR. Thermal stability of the gemini ionic liquids was determined by thermogravimetric analysis under a pure nitrogen atmosphere. Densities and viscosities of pure GILs and their binary mixtures with acetonitrile (MeCN) were investigated over the entire range of mole fractions at various temperatures, from 288.15 to 333.15 K, under atmospheric pressure. Moreover, the excess molar volumes (V^E_m) and the viscosity deviations (Δη) of the binary mixtures were evaluated and well fitted to the Redlich–Kister polynomial expression. The negative values of V^E_m and Δη result from strong self-association and interaction between the gemini ionic liquid molecules and MeCN. Results are discussed in terms of molecular interactions and structures.

Ammonium-based asymmetrical gemini ionic liquids, 1-trimethylammonium-3-(pyridinium)propane bisdicyanamide and 1-trimethylammonium-3-(1-methylpiperidinium)propane bisdicyanamide were respectively synthesized and characterized by ¹H NMR and ¹³C NMR.

Synthesis of gemini basic ionic liquids and their application in anion exchange membranes

A gemini-type basic morpholine ionic liquid ([Nbmd][OH]) was synthesized via a two-step method with morpholine, bromododecane and 1,4-dibromobutane as raw materials, and its structure was characterized by ¹H NMR and FT-IR spectroscopy. Meanwhile, a series of anion exchange membranes ([Nbmd][OH]_x–QCS) were prepared with quaternized chitosan (QCS) as the polymer matrix and [Nbmd][OH] as the dopant owing to its strong alkalinity and good solubility. The structures of the [Nbmd][OH]_x–QCS composite membranes were characterized in detail by FT-IR spectroscopy, the OH⁻ conductivity by AC impedance spectroscopy, and the morphological features by scanning electron microscopy (SEM), thermal gravity analysis (TGA), etc. The results show that the [Nbmd][OH]_x–QCS composite membranes have uniform surfaces and cross-section morphology. Increasing the content of [Nbmd][OH] not only enhances the thermal stability but also increases the OH⁻ conductivity; the thermal decomposition temperature of the [Nbmd][OH]₄₀–QCS membrane is nearly 20 °C higher than that of the pristine QCS membrane, and the maximum OH⁻ conductivity is approximately 1.37 × 10⁻² S cm⁻² at 70 °C. The methanol permeability of the [Nbmd][OH]₄₀–QCS membrane in 1 M methanol at room temperature is 2.21 × 10⁻⁶ cm⁻² s⁻¹, which is lower than that of Nafion®115, indicating a promising potential use in alkaline direct methanol fuel cells. Moreover, the [Nbmd][OH]₄₀–QCS membrane exhibits the best alkaline stability of all the membranes prepared in this work, retaining approximately 81% of its initial conductivity after immersion in 3 M KOH solution for 120 h at 70 °C.

A gemini-type basic morpholine ionic liquid ([Nbmd][OH]) was synthesized via a two-step method with morpholine, bromododecane and 1,4-dibromobutane as raw materials, and its structure was characterized by ¹H NMR and FT-IR spectroscopy.