Search

The removal of nitrogen compounds by liquid-liquid extraction using ionic liquids (ILs) as extraction solvents has been limited by the lack of easy-to-prepare, low cost and highly efficient ILs. To overcome this limitation, the present work synthesized protic ILs (PILs) via acid-base reaction and investigated their extraction ability for nitrogen compounds (quinoline, indole and carbazole) from model fuel (n-dodecane). Experimental results suggested that the PIL, triethylammonium p-toluenesulfonate (TEA-TSA), exhibited higher extraction ability for indole and carbazole as compared to the 1-butyl-3-methylimidazolium ([C4mim]+) based ILs due to the stronger π-π interaction between TEA-TSA and nitrogen compounds. Among a number of ILs, TEA-TSA containing a slight excess of p-toluenesulfonic acid (2%, molar percent) was particularly promising as extractant because of its excellent extraction performance for the basic and neutral nitrogen compounds. Furthermore, the suggested PIL could be easily regenerated and reused via a back extraction process. The results showed that extractive denitrogenation using PILs as extractants was a potential technique to produce clean fuel considering their stronger extraction ability, lower-cost and easy-to-prepare characteristics.

Baicalin which has multiple biological activities is the main active component of the root of Scutellaria baicalensis Georgi (SBG). Although its isolation and purification by adsorption methods have aroused much interest of the scientific community, it suffered from the poor selectivity of the adsorbents. In this work, an environmentally benign method was developed to prepare ionic liquids (ILs) grafted silica by using IL 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([C4mim]NTf2) and ethanol as reaction media. The IL 1-propyl-3-methylimidazolium chloride ([C3mim]Cl) grafted silica ([C3mim]+Cl−@SiO2) was used to adsorb and purify baicalin from the root extract of Scutellaria baicalensis Georgi (SBG). Experimental results indicated that the adsorption equilibrium can be quickly achieved (within 10 min). The adsorption behavior of [C3mim]+Cl−@SiO2 for baicalin was in good agreement with Langmuir and Freundlich models and the adsorption was a physisorption process as suggested by Dubinin–Radushkevich model. Compared with commercial resins, [C3mim]+Cl−@SiO2 showed the strongest adsorption ability and highest selectivity. After desorption and crystallization, a purity of baicalin as high as 96.5% could be obtained. These results indicated that the ILs grafted silica materials were promising adsorbents for the adsorption and purification of baicalin and showed huge potential in the purification of other bioactive compounds from natural sources.

The isolation of bioactive compounds from natural sources using conventional solvents has always suffered from the poor extraction ability and tedious extraction procedure. Ionic liquids (ILs) have emerged as the alternatives to conventional solvents due to their high extraction ability and low-toxic nature. In this work, a series of protic ILs was prepared via acid-base reaction using non-to-mild toxic organic acids and bases as starting materials. The synthesized protic ILs in combination with microwave-assisted extraction (ILs-MAE) were used to extract rosmarinic acid (RA) from Perilla seeds. Optimal extraction conditions were 5% of IL concentration, 50 s of microwave irritation time, 350 W of microwave irritation power and 50 g g−1 of liquid–solid ratio. Acidity of ILs and the extraction temperature played an important role in the extraction process. Compared with heating reflux extraction (HRE), ultrasound-assisted extraction (UAE) and maceration (MAC), the IL-MAE exhibited highest extraction ability and fastest extraction rate. After extraction, the IL could be recycled without losing its extraction ability via back extraction of RA with ethyl acetate. The RA in the ethyl acetate extract was further purified by column chromatography and high purity of RA (90.4%) could be obtained. These findings suggest that IL-MAE is promising method for the isolation of bioactive compounds from natural plants.

In Asian, rhizoma smilacis glabrae (RSG) is viewed as traditional food, and herb, and its main bioactive component is astilbin. The extraction of astilbin from RSG by traditional solvents suffers from the lower extraction efficiency, and longer extraction time. In this work, green solvents, vitamin B3-based protic ionic liquids (VB3PILs) were used to extract astilbin from RSG in combination with microwave-assisted extraction (MAE) method. Compared with the traditional solvents, for instance alcohols, and β-cyclodextrin (β-CD) aqueous solution, the VB3PIL, nicotinamidium lactate (NALA), exhibits higher extraction ability, and shorter extraction time (20 s). The extraction ability of VB3PILs depends on their physicochemical properties, such as viscosity, hydrophobicity, and hydrogen-bonding ability. To comprehensively conclude the above results, it can be suggested that VB3PILs are green and, high efficient solvents for the extraction of astilbin from RSG, which may have great potential applications in extracting natural products from plant food sources.

Volume and viscosity data of ionic liquid (IL)-molecular solvent mixtures are very important for the design of process engineering involving these mixtures. In this work, densities and viscosities for the binary solutions of [C n mim]Br (n = 4, 6, 8) ionic liquids with methanol, 1-propanol, and 1-pentanol have been determined at 298.15 K as a function of IL concentrations. From these experimental data, apparent molar volumes, standard partial molar volumes, and viscosity B -coefficient of ILs were derived. The effect of the alkyl chain length in the imidazolium cation and properties of alcohol on the standard partial molar volumes of ILs and viscosity B -coefficient was discussed. In a given alcohol, the standard partial molar volumes of ILs and viscosity B -coefficient increase linearly with increasing alkyl chain length of ILs. For a given IL, unexpectedly, its standard partial molar volume in the three molecular solvents is not a constant, but increases in the order: 1-pentanol > 1-propanol > methanol. The viscosity B -coefficients of a given IL in the alcohols also change in the same sequential order. These results suggest that the interactions between ILs and the alcohols increase with the decrease of alkyl chain length of the alcohols.

Despite the extraction desulfurization of fuel oils using ionic liquids (ILs) as promising alternatives to traditional extractants has attracted worldwide attention, the drawbacks of ILs, such as poor extraction efficiency, high cost and complex preparation, have limited their further application in industrial scale. In this study, a series of trialkylamine-based protic ionic liquids (PILs) were synthesized and characterized, and their extraction desulfurization for thiophene (TH), benzothiophene (BT), and dibenzothiophene (DBT) in model oil was carried out. Effects of PIL species, extraction time, temperature, PIL dosage, and initial sulfuric concentration on desulfurization efficiency were investigated. Experimental results showed that the PILs exhibited higher extraction ability for TH, BT, and DBT as compared to the reported ILs. Under optimal conditions, the removal efficiency of TH, BT, and DBT using tris(3,6-dioxaheptyl) ammonium salicylate ([TDA][SA]) as extractant was 72.68%, 76.31%, and 83.94%, respectively. Finally, the suggested PIL can be easily regenerated and reused via a back extraction process. After 5 extraction cycles, the removal efficiency has no noticeable decrease. With advantages such as higher desulfurization efficiencies, cheap and easily obtained raw materials and simple synthetic process, this study will provide new green solvents for extraction desulfurization process of fuels.

The molecular mechanism of the interaction between pepsin and two typical ionic liquids (ILs), 1-butyl-3-methylimidazolium chloride ([C4mim]Cl) and 1-octyl-3-methylimidazolium chloride ([C8mim]Cl), was investigated with fluorescence spectroscopy, ultraviolet absorption, and circular dichroism spectroscopy at a pH value of 1.6. The results suggest that ILs could quench the intrinsic fluorescence of pepsin, probably via a dynamic quenching mechanism. The fluorescence quenching constants were determined by employing the classic Stern-Volmer equation. The constant values are very small, indicating that only a very weak interaction between ILs and pepsin exists. The Gibbs free-energy change, enthalpy change (ΔH), and entropy change (ΔS) during the interaction of pepsin and ILs were estimated. Positive values of Δ H and ΔS indicate that the interaction between ILs and pepsin is mainly driven by hydrophobic interaction. Synchronous and three-dimensional fluorescence spectra demonstrate that the addition of ILs (0–0.20 mol L−1 for each IL) does not bring apparent changes to the microenvironments of tyrosine and tryptophan residues. Activity experiments show that the activity of pepsin is concentration dependent; higher concentrations of ILs (>0.22 mol L−1 for [C8mim]Cl and >0.30 mol L−1 for [C4mim]Cl) cause the remarkable reduction of enzyme activity. The presence of ILs also does not improve the thermal stability of pepsin.

The interaction between papain and two typical ionic liquids (ILs), 1-octyl-3-methylimidazolium chloride ([C(8)mim]Cl) and 1-butyl-3-methylimidazolium chloride ([C(4)mim]Cl), was investigated by using fluorescence spectroscopy technique at a pH value of 7.4. The results suggested that ILs could quench the intrinsic fluorescence of papain probably via a static quenching mechanism. The binding constants were determined by employing the fluorescence quenching method. They were very small compared with that of volatile organic solvents, indicating that only very weak interaction between ILs and papain existed. The Gibbs free energy change (∆G), enthalpy change (∆H), and entropy change (∆S) during the interaction of papain and ILs were estimated. Negative values of these parameters indicated that the interaction between ILs and papain was a spontaneous process, also implying that hydrogen bonding and van der Waals forces played important roles in the interaction processes.

We have prepared the hydrophobic amino-functionalized ionic liquid (IL) 1-(2-aminoethyl)-3-butylimidazolium hexafluorophosphate and investigated its extraction behavior for copper(II) ion as a model cation. The IL, due to the presence of an amino group, is capable of complexing Cu(II) in a ratio of 6:1. The parameters affecting the extraction efficiency were optimized. The IL-based liquid–liquid microextraction was successfully applied to the analysis of Cu(II) in an environmental water standard reference material. The results are promising in terms of liquid–liquid microextraction, separation, and preconcentration of Cu(II).

In this work, the interaction of an ionic liquid (IL) 1-octyl-3-methylimidazolium chloride ([Omim]Cl) and L-tryptophan was investigated with fluorescence spectroscopic method. The quenching mechanism and binding characteristics of [Omim]Cl with L-tryptophan at different temperatures were studied from fluorescence measurement. The thermodynamic parameters such as free energy change (ΔG), enthalpy change (ΔH) and entropy change (ΔS), were calculated by thermodynamic equations. The experimental results indicated that [Omim]Cl and L-tryptophan had weak interaction and the mechanism of quenching belonged to static quenching. Hydrogen bonds and van der Waals interactions played important roles in the binding of [Omim]Cl with L-tryptophan.

Ionic liquids (ILs), also known as molten salts with low melting points, are receiving an upsurge of interest as green solvents and form an attractive area of research. Within the last few years, research and applications of ILs as extraction solvents in sample pretreatment prior to chromatographic analysis have expanded tremendously. This review presents an overview of IL microextraction-based sample pretreatment techniques for high performance liquid chromatography (HPLC) and gas chromatography (GC).

In this work, ionic liquids/water distribution ratios (D) of azo dyes, including 1-(phenylazo)-2-naphthol, 1-(2-pyridylazo)-2-naphthol, 4-(nitrophenylazo)resorcinol, 4-(2-pyridylazo) resorcinol, and 2-(4-dimethylaminophenylazo) benzoic acid, have been determined experimentally. It was found that the D values are highly influenced by the pH of the water phase and the type of salts added. They increase with increasing alkyl chain length on the cations of the ionic liquids, and the anionic effect follows the order [BF4]− > [PF6]−. Possible extraction mechanism and selective separation of some azo dyes are also investigated. The results suggest that ionic liquids have potential applications in the removal and selective separation of azo dyes from water.

Considering the ionic nature of ionic liquids (ILs), ionic association is expected to be essential in solutions of ILs and to have an important influence on their applications. Although numerous studies have been reported for the ionic association behavior of ILs in solution, quantitative results are quite scarce. Herein, the conductivities of the ILs [Cnmim]Br (n=4, 6, 8, 10, 12), [C4mim][BF4], and [C4mim][PF6] in various molecular solvents (water, methanol, 1-propanol, 1-pentanol, acetonitrile, and acetone) are determined at 298.15 K as a function of IL concentration. The conductance data are analyzed by the Lee-Wheaton conductivity equation in terms of the ionic association constant (KA) and the limiting molar conductance (Lambda(m)(0)). Combined with the values for the Br- anion reported in the literature, the limiting molar conductivities and the transference numbers of the cations and [BF4]- and [PF6]- anions are calculated in the molecular solvents. It is shown that the alkyl chain length of the cations and type of anion affect the ionic association constants and limiting molar conductivities of the ILs. For a given anion (Br-), the Lambda(m)(0) values decrease with increasing alkyl chain length of the cations in all the molecular solvents, whereas the KA values of the ILs decrease in organic solvents but increase in water as the alkyl chain length of the cations increases. For the [C4mim]+ cation, the limiting molar conductivities of the ILs decrease in the order Br- > [BF4]- > [PF6]-, and their ionic association constants follow the order [BF4]- > [PF6]- > Br- in water, acetone, and acetonitrile. Furthermore, and similar to the classical electrolytes, a linear relationship is observed between ln KA of the ILs and the reciprocal of the dielectric constants of the molecular solvents. The ILs are solvated to a different extent by the molecular solvents, and ionic association is affected significantly by ionic solvation. This information is expected to be useful for the modulation of the IL conductance by the alkyl chain length of the cations, type of anion, and physical properties of the molecular solvents.

A number of cinnamic acid derivatives have been synthesised from commercially available aromatic aldehydes and propanedioic acid in a water-insoluble ionic liquid (1-butyl-3-methylimidazolium hexafluorophosphate, [bmim]PF6) in high yields in the presence of small catalytic amounts of piperidine. The ionic liquid can be reused at least five times.

The interaction of an amino-functionalized ionic liquid, 1-(2-aminoethyl)-3-butylimidazolium bromide ([NH(2)C(2)C(4)im]Br) with two enzymes, pepsin and papain was investigated using fluorescence spectroscopic technique. It is found that [NH(2)C(2)C(4)im]Br has strong ability to quench the intrinsic fluorescence of pepsin and papain. Quenching mechanisms are considered as static quenching for papain and dynamic quenching for pepsin, respectively. The binding constants and the number of binding sites (n) of [NH(2)C(2)C(4)im]Br to papain were calculated at different temperatures. The thermodynamic parameters such as free energy change (ΔG), enthalpy change (ΔH) and entropy change (ΔS), were calculated by thermodynamic equations. The values of ΔG, ΔH and ΔS suggest that interaction of [NH(2)C(2)C(4)im]Br with the two enzymes is spontaneous. Hydrogen bonding and van der Waals interactions play important roles in the binding process of [NH(2)C(2)C(4)im]Br to papain. However, hydrophobic interaction is the main driving force for the interaction of [NH(2)C(2)C(4)im]Br with pepsin. The results of three-dimensional fluorescence spectra show that [NH(2)C(2)C(4)im]Br has no obvious effects on the polypeptide structures of the two enzymes. Additionally, the [NH(2)C(2)C(4)im]Br-containing system can slightly increase the activities of the two enzymes.

The title compounds (III) (10 examples) are synthesized by Knoevenagel condensation of commercially available aromatic aldehydes with propanedioic acid using [bmim]PF6 as green solvent.

Densities, conductivities, and polarity indexes of pyrene for aqueous solutions of a series of ionic liquids [C(n)mim]Br (n = 4, 6, 8, 10, 12) and [C4mim][BF4] have been determined at 298.15 K as a function of ionic liquid concentrations. It was shown that possible aggregation appeared for the ionic liquids in aqueous solutions except for [C4mim]Br. The critical aggregation concentration (CAC) of the ionic liquids, the ionization degree of aggregates (beta), the standard Gibbs energy of aggregation (Delta G(m)(o)), the limiting molar conductivity (Lambda(m)(o)), and the standard partial molar volume (V(m)(o)) for the ionic liquids were derived from the experimental data. The dependence of the CAC, Delta G(m)(o), Lambda(m)(o), and V(m)(o) on the length of the alkyl chain of the cations was examined. It was further suggested from volumetric data that a micelle was formed for [C8mim]Br, [C10mim]Br, and [C12mim]Br in aqueous solutions. Their apparent molar volumes at the critical micelle concentration (V Phi,CMC), apparent molar volumes in the micelle phase (V(Phi)(mic)), and the change of their apparent molar volume upon micellization (Delta V Phi,m) were calculated by application of the pseudophase model of micellization. In addition, the average aggregation number of [C(n)mim]Br (n = 8, 10, 12) has been determined by the steady-state fluorescence quenching technique, and predicted from a simple geometrical mode. It is found that the experimental values are in good agreement with the predicted ones.