Water Sorption in Functionalized Ionic Liquids: Kinetics and

IL–D2O systems are used to simulate the interactions of IL–H2O systems. ... Unexpectedly, no significant difference exists in νO–H between [aEM...
0 downloads 0 Views 2MB Size
Download PDF
Article pubs.acs.org/IECR

Water Sorption in Functionalized Ionic Liquids: Kinetics and Intermolecular Interactions Yuanyuan Cao, Yu Chen, Liyi Lu, Zhimin Xue, and Tiancheng Mu* Department of Chemistry, Renmin University of China, Beijing 100872, China S Supporting Information *

ABSTRACT: The water sorption by nine functionalized imidazolium based ionic liquids (ILs) with the effects of temperature and relative humidity were investigated. Three kinds of parameters (sorption capacity, sorption rate, and sorption equilibrium) were derived to comprehensively characterize the sorption processes. A sorption triangle was proposed to correlate these kinds of parameters, which were the corresponding three vertices of this triangle. The sorption triangle has three effective categories numbered types 1, 2, and 3. The hydrophilicity of the ILs was sorted into four levels according to the steady-state water sorption capacity. The sorption results were consistent with the water−IL interaction investigation with attenuated total refletance infrared (ATR-IR) and nuclear magnetic resonance (NMR) spectra. The functionalized ILs investigated in this study are more hydrophilic than conventional ILs from a statistical view. concentration.24,35,36 Water molecules are adsorbed in the surface of ILs due to physical attractive forces such as van der Waals or hydrogen bonds.25 The kinetics of water absorption was investigated through near infrared (NIR) spectrometry,33 a gravimetric method,26 and a theoretical model.21 These investigations gave us fundamental knowledge on water sorption of mainly the conventional ILs; the corresponding research on functionalized ILs has not been published as far as we know. The water sorption and water−IL interactions of allyl- and amine-functionalized ILs were investigated in this study because they possessed many potential applications. Several examples are given below. Allyl-functionalized ILs have been applied to dissolve biomass, such as cellulose,3,37 chitin,38 chitosan,38 and sucrose.39 The allyl moiety is also helpful to the syntheses of multiwalled carbon nanotube composite fibers.40 Also, allyl-based ILs could modify the silica stationary phase in the reverse-phase liquid chromatography, which favors the investigation of π−π and ion-dipole interactions.41 Aminefunctionalized ILs are mainly used to absorb sour gases, such as CO2.5,7,42−44 Also, amine functionalization is favorable for chemical reactions or synthesis as catalyst or solvent, such as the asymmetric Michael addition of cyclohexanone,45 stable gold nanoparticles synthesis,46 and Knoevenagel condensation of aromatic aldehydes.47 On the basis of our previous research on the water sorption by eighteen conventional ILs,21 we further investigated the kinetics of water sorption by nine functionalized ILs. Seven allyl functionalized imidazolium ILs were selected to investigate the effect of alkyl chain length at imidazolium ring ([AMIM][Cl], [ABIM][Cl]) and anion type ([AMIM][Cl], [AMIM][BF4], and [AMIM][PF6] with the same cation [AMIM] and [ABIM][Cl], [ABIM][NO3], [ABIM][BF4], and [ABIM][PF6]

1. INTRODUCTION Room temperature ionic liquids (ILs) have attracted increasing attention and made tremendous growth in both academia and industry since the first report of water-stable ILs in 1992.1 The motivation of the booming research on ILs is not only the combination of various cation and anion moieties (described as “designer solvents”2), but also the incorporation of functional groups on cation or anion (so-called “functionalized” or “task specific”). The incorporation of functional groups, such as allyl group,3 guanidine,4 amine,5−7 acids,8 and hydroxyl group,9 generates dramatic property advantages. The functionalized ILs have been applied for extraction,10,11 dissolution,3,4,12 gas absorption,5−7,13−15 material science,16,17 and so on. Several reviews have been published on the functionalized ILs.18−20 However, most of the ILs are hygroscopic.21,22 On one hand, ILs absorb water from the atmosphere or wet surfaces.23−26 On the other hand, the presence of water is inevitable during the synthesis, storage, and application procedures of ILs.27 The existence of water has significant influence on the physical properties (e.g., density, viscosity, surface tension, and conductivity),23,27 solubility power,28,29 reactivity, and selectivity30,31 of ILs. For example, sulfonic acid-functionalized ILs were used as solvent and catalyst for esterification reaction, while the presence of a threshold quantity of water induced to higher dehydration reaction yields;8 and the role of water was not clear yet. The viscosity of gas-complexed ILs (e.g., CO2 with amine-functionalized) has greatly decreased with trace of water.6 Since the water sorption, the water−IL interactions, and the correlations between the sorption and the interactions are very important, investigations on these topics have been carried out, and the following conclusions have been drawn.21−23,26,32 Water preferentially interacts with anion, which is the key factor to determine water sorption, followed by the alkyl side chain length at the cation and cation type.21,23,33,34 Water molecules prefer to be in the free state at a low water concentration; while they are hydrogen-bonded among themselves at a higher water © 2013 American Chemical Society

Received: Revised: Accepted: Published: 2073

October 18, 2012 January 11, 2013 January 11, 2013 January 11, 2013 dx.doi.org/10.1021/ie302850z | Ind. Eng. Chem. Res. 2013, 52, 2073−2083

Industrial & Engineering Chemistry Research

Article

Table 1. Name and Structure of Nine ILs Investigated

with the same cation [ABIM]). Amino functionalized imidazolium ILs [aEMIM][BF4] and [aEMMIM][BF4] were used to study the effect of C2 methylation at imidazolium ring. The effects of temperature and relative humidity were studied also. The ILs used are listed in Table 1. Three kinds of parameters (sorption capacity (W3h, W∞), sorption rate (1000kW∞, 1000/t0.01), and sorption equilibrium (1/k)) derived from the modified two-step sorption mechanism21 were used to analyze the sorption processes. The relations among those parameters were summed up by a sorption triangle (Scheme 1). The attenuated total reflectance infrared (ATR-IR) and 1H nuclear magnetic resonance (NMR) spectra were used to investigate the water−IL interactions, and the interaction results coincide with the water sorption results.

Scheme 1. Proposed Sorption Triangle for Water Sorption by ILs

2. EXPERIMENTAL SECTION 2.1. Materials. The ILs listed in Table 1 (≥99%) were purchased from Lanzhou Greenchem ILs, LICP, CAS (Lanzhou, China). The ILs were dried at 50 °C and for 96 h in vacuum drying oven with P2O5 desiccant nearby before use. The 1H and 13C NMR analysis (Bruker AM 400 MHz spectrometer) indicated that no detectable impurities and degradants existed in the ILs. Inductively coupled plasma

optical emission spectrometry (ICP-OES) with a Varian Vista MPX gave the contents of Li and Na ( [ABIM][BF4] > [ABIM][PF6]. More chemical shifts to the upfield of C2−H mean stronger interactions between water and ILs,58 thus [ABIM][Cl] has the strongest interaction with water and [ABIM][PF6] has the least. This corroborates the sorption capacity results. The most upfield chemical shifts of δC2−H and the three types of sorption parameters also have a good linear correlation (Figure 7b). It shows that water sorption capacity increases (−0.6722%/ppm) more than sorption rate (−0.5885%/ppm) with the chemical shifts down fielding, making the sorption equilibrium more difficult to reach as suggested by the type 2 sorption triangle. Anion is the most important factor for water sorption. Supporting Information Table S2 shows that W3h ranges ca. 0.39−14.14% w/w for ILs varying in anion. Anions have largest effects on water sorption compared to the alkyl chain length, C2 methylation, temperature, and relative humidity. The effect of anions must be given full consideration in case applying ILs in a damp environment. Enthalpies of solution of water in ILs primarily depend on the anion identity,59 which corroborates the importance of the anion. Previous study on water sorption by conventional ILs also supported the significant effect of anion.21 3.2.3. Effect of C2 Methylation at the Imidazolium Ring. [aEMIM][BF4] (with C2 methylation) has greater sorption capacity, larger sorption rate, and smaller time to reach sorption equilibrium, compared to [aEMMIM][BF4] (non-C2 methylation) at 25 °C and 52% relative humidity (Figure 1 and 8a). The easier to reach sorption equilibrium is caused by more increase in sorption rate than sorption capacity [C+, R++, E+], i.e., the type 3 sorption triangle. [BMIM][BF4] (non-C2 methylation) and [BMMIM][BF4] (with C2 methylation) also have a same rule for water sorption.21 The lower viscosity of [aEMIM][BF4] contributes to a favorable interaction with water, thus leading to a greater sorption capacity and faster sorption rate. The sorption rate

length have a reverse trend compared to the solubility of water in ILs. Alcohols dissolve more in the ILs with a longer alkyl chain.55 It may be attributed to the increase of van der Waals interaction.55 Likewise, solubility of CO2 is greater in ILs with a longer alkyl chain in the cation, which might be ascribed to a greater free volume for the longer alkyl chain ILs.13 [AMIM][Cl] and [ABIM][Cl] fit a type 1 sorption triangle [C+, R−, E+]. Greater sorption capacity and slower sorption rate lead to longer sorption equilibrium time. The alkyl chain length of [AMIM][Cl] is shorter than [ABIM][Cl], while [AMIM][Cl] has a greater sorption capacity and slower sorption rate, thus making the sorption equilibrium more difficult to reach. 3.2.2. Effect of Anion. Figure 5a shows that water absorption of [AMIM]-based ILs follows the order: [AMIM][Cl] > [AMIM][NO3] > [AMIM][BF4] > [AMIM][PF6]. [AMIM]based ILs follows same order ([AMIM][Cl] > [AMIM][BF4] > [AMIM][PF6]) (Figure 5b). Conventional [BMIM]-based ILs present the same order for water21 or vinyl chloride56,57 sorption, i.e., [BMIM][Cl] > [BMIM][NO3] > [BMIM][BF4] > [BMIM][PF6]. More interestingly, the sorption capacity, sorption equilibrium, and sorption rate have the same tendency (Figure 1). It could be explained by the type 2 sorption triangle. Equilibrium is suppressed by the higher increase in sorption rate than in sorption capacity (Scheme 2b). It was also verified by the IR and NMR investigation, with the [ABIM]-based ILs varying in anion selected as a representation. Figure 6 presents the IR spectra of OH and C2−H of [ABIM]-based ILs. A stronger interaction between water and ILs induces lower vibrational frequency of OH (νOH),24 thus the νOH values indicate that the interactions of [ABIM]-based ILs with water follow the order: [ABIM][Cl] > [ABIM][NO3] > [ABIM][BF4] > [ABIM][PF6] (Figure 6a). This coincides with the water sorption results. Figure 6b shows that νOH and the three types of sorption parameters have good linear correlations. The blue shifts of another IR absorption peak νC2−H are ordered as: [ABIM][Cl] > [ABIM][NO3] > [ABIM][BF4] ≈ [ABIM][PF6], also has similar order as the water sorption capacity, sorption rate, and sorption equilibrium (Figure 6c). Larger νC2−H58 value indicates stronger interaction between ILs and water. 2079

dx.doi.org/10.1021/ie302850z | Ind. Eng. Chem. Res. 2013, 52, 2073−2083

Industrial & Engineering Chemistry Research

Article

gives us a hint that storage of ILs at relatively lower temperature is a good way to prevent the moisture uptake. 3.3.2. Effect of Relative Humidity. Relative humidity measures the ratio of vapor pressure in the air to the amount of saturated vapor pressure of water at a given temperature. A larger value of relative humidity means a larger amount of water vapor in the air and consequently that hydration of ILs should be easy. Figure 1 shows that the water sorption capacity of [ABIM][Cl] at 15 °C increases with the increasing of relative humidity from 45% to 52%. This situation is adapted to the type 1 sorption triangle. Our previous report on conventional ILs (e.g., [BMIM][BF4]) for water sorption showed a different result when increasing relative humidity: a greater increase in sorption capacity than sorption rate leads to more time to reach sorption equilibrium, which could be expressed as a type 2 sorption triangle.21 The difference might be due to the fact that [ABIM][Cl] is more sensitive to relative humidity for water sorption capacity and less sensitive to sorption rate than [BMIM][BF4]. 3.4. Hydrophilicity of Functionalized ILs. The quantitative scale of hydrophilicity of functionalized ILs (HPI) is important. The Kyte−Doolittle61 and Rose scales62 are the most widely used hydrophilicity scales. They are complicated and only indicate parts of the interactions. Water sorption capacity 100W∞ derived from the modified two-step sorption mechanism is an indicator of the ILs’ affinity with water (HPI).21 It reflects total interactions between water and ILs. It is more direct and convenient to indicate the hydrophilicity of ILs. Simply, four levels of hydrophilicity of ILs, i.e., superhigh hydrophilicity (level 1: 15 ≤ HPI), high hydrophilicity (level 2: 7.5 ≤ HPI < 15), medium hydrophilicity (level 3: 2.5 ≤ HPI < 7.5), and low hydrophilicity (level 4: HPI ≤ 2.5), are defined.21 Figure 10a shows that the anion effect on the hydrophilicity of both [ABIM]- and [AMIM]-based ILs is ordered as follows: [Cl] > [NO3] > [BF4] > [PF6]. ILs with C2 methylation and longer chain length at imidazolium ring are less hydrophilic. Among all of the nine ILs considered, [AMIM][Cl] has greatest hydrophilicity, while [AMIM][PF6] has the least. The anion plays a more important role in determining the hydrophilicity of ILs than the chain length at imidazolium ring, then C2 methylation. This is consistent with previous reports.23,33,34 The effect of anions on the hygroscopicity of ILs covers three levels (for [ABIM]) or four levels (for [AMIM]). The effect of chain length extends to two levels (levels 1 and 2), while the effect of C2 methylation only fluctuates within level 2. It corroborates again the statement that anion is the foremost factor on water sorption. Interestingly, more functionalized ILs have superhigh or high hydrophilicity than conventional ILs from a statistical view. Figure 10b gives the relative frequency of number of ILs having different hydrophilicity. The relative frequency is expressed by the number of ILs within the hydrophilicity level divided by the total number of ILs investigated. The statistics provides a hint on the higher hydrophilicity of functionalized ILs than that of conventional ILs. This indicates a high probability of functionalized ILs absorbing water from the ambient environment when being stored or transported.

might be more apparent than the sorption capacity; therefore resulting faster sorption equilibrium. Another piece of evidence from the cation−anion interaction strength, i.e., [BMIM] > [BMMIM], results from ESI-MS/MS experiments.34 Stronger cation−anion interaction hints a greater hydrogen bonding strength between water and cation,34 thus corroborating the water sorption capacity and sorption rate. Enthalpy of solution for non-C2 methylation [BMIM][PF6] is 5 kJ/mol lower than the C2 methylation counterpart [BMMIM][PF6], providing a third piece of evidence for the stronger interaction between water and the non-C2 methylation IL.59 Unexpectedly, no significant difference exists in νO−H between [aEMIM][BF4] and [aEMMIM][BF4] when interacting with water (Figure 8b). It shows that νO−H is not a perfect indicator for the interaction between water and ILs. After all, wavenumber shift of νO−H is only a part of interactions that IR implicates. Other interactions, e.g., columbic force, are beyond the detection of IR spectra. Moreover, the amine identity NH2 tethered to the imidazolium cation, both for [aEMIM][BF4] and [aEMMIM][BF4] possess a stronger hydrogen bonding with water, which would weaken the hydrogen bonding between water and C2−H. Thus, we must be aware of the effect of νO−H, with which we identify the interaction between water and ILs. 3.3. Effects of External Factors on the Water Sorption. 3.3.1. Effect of Temperature. The water sorption by [ABIM][Cl] at 15 and 25 °C with the relative humidity 52% was investigated to classify the effect of temperature. Figure 9

Figure 9. Effect of temperature on water sorption of [ABIM][Cl] at relative humidity 52%.

shows that higher temperature favors more water sorption for [ABIM][Cl]. A lower viscosity induced by a higher temperature of IL is favorable for water sorption; however, in view of thermodynamics, a higher temperature is unfavorable for water sorption. For [ABIM][Cl], the viscosity factor dominates the water sorption at different temperatures. The decrease of 1/k at higher temperature indicates easier phase equilibrium (Figure 1). It could be explained by the more increase in sorption rate than sorption capacity [C+, R++, E−], shown in Scheme 2c as the type 3 sorption triangle. Similar rules were obtained for [Tf2N]-based ILs59,60 at 15 and 45 °C and [BMIM][BF4]21 at 23 and 30 °C. The kinetics of water sorption by ILs is complicated.34 The physical properties of ILs may change after the sorption of water, which in turn affects the water sorption.33 The structure of ILs and water, the inherent factor influences on water sorption, is dependent on the concentration of water.33,34 It

4. CONCLUSIONS The sorption triangle proposed in this study can be used to explain the relationship among three kinds of parameters (sorption capacity, sorption rate, and sorption equilibrium) derived from the modified two-step sorption mechanism for 2080

dx.doi.org/10.1021/ie302850z | Ind. Eng. Chem. Res. 2013, 52, 2073−2083

Industrial & Engineering Chemistry Research

Article

Figure 10. Hydrophilicity of ILs (HPI) (a) and relative frequency distribution (b) of ILs. The value of HPI in (a) was calculated based on the real value of 100W∞. The first two and the last two numbers after the name of ILs refer to temperature and relative humidity, respectively. Relative frequency of conventional ILs was from ref 21.

■

ACKNOWLEDGMENTS This work was supported by the National Natural Science Foundation of China (21173267) and the Basic Research Funds in Renmin University of China from the Central Government (12XNLL05).

water sorption by functionalized ILs varying in structure and external factors (temperature and relative humidity). ATR-IR and NMR measurements corroborated the sorption kinetics. Relative humidity and alkyl chain length, C2 methylation and anion, and temperature can be classified as type 1, type 2, and type 3 sorption triangles, respectively. The sorption triangle provides a simple way to qualitatively analyze the correlation among the sorption capacity, sorption rate, and sorption equilibrium. Functionalized ILs have a higher hydrophilicity and are more hygroscopic than conventional ILs. Water sorption by ILs should be observed impartially. On the negative side, this causes problems such as a dramatic change in physical properties or a great hindrance in IL usages as solvent or catalyst for the application of ILs. On the positive side, it provides a fascinating way to new usage of ILs, such as acting as a water sensor, or to serve for the drying agent, which is on the way of our study. The results show that water sorption by functionalized ILs is so important that we should pay more attention to it in both experimental research and industrial applications.

■

■

ASSOCIATED CONTENT

S Supporting Information *

Equilibrium relative humidity for saturated salt solutions (Table S1). Sorption capacity, sorption equilibrium, and sorption rate of the ILs (Table S2). This material is available free of charge via the Internet at http://pubs.acs.org.

■

REFERENCES

(1) Wilkes, J. S.; Zaworotko, M. J. Air and Water Stable 1-Ethyl-3Methylimidazolium Based Ionic Liquids. J. Chem. Soc., Chem. Commun. 1992, 965. (2) Earle, M. J.; Seddon, K. R. Ionic Liquids. Green Solvents for the Future. Pure Appl. Chem. 2000, 72, 1391. (3) Zhang, H.; Wu, J.; Zhang, J.; He, J. 1-Allyl-3-Methylimidazolium Chloride Room Temperature Ionic Liquid: A New and Powerful Nonderivatizing Solvent for Cellulose. Macromolecules 2005, 38, 8272. (4) Wu, W.; Han, B.; Gao, H.; Liu, Z.; Jiang, T.; Huang, J. Desulfurization of Flue Gas: SO2 Absorption by an Ionic Liquid. Angew. Chem., Int. Ed. 2004, 43, 2415. (5) Bates, E. D.; Mayton, R. D.; Ntai, I.; Davis, J. H. CO2 Capture by a Task−Specific Ionic Liquid. J. Am. Chem. Soc. 2002, 124, 926. (6) Goodrich, B. F.; de la Fuente, J. C.; Gurkan, B. E.; Lopez, Z. K.; Price, E. A.; Huang, Y.; Brennecke, J. F. Effect of Water and Temperature on Absorption of CO2 by Amine-Functionalized AnionTethered Ionic Liquids. J. Phys. Chem. B 2011, 115, 9140. (7) Xue, Z.; Zhang, Z.; Han, J.; Chen, Y.; Mu, T. Carbon Dioxide Capture by a Dual Amino Ionic Liquid with Amino−Functionalized Imidazolium Cation and Taurine Anion. Int. J. Greenhouse Gas Control 2011, 5, 628. (8) Cole, A. C.; Jensen, J. L.; Ntai, I.; Tran, K. L. T.; Weaver, K. J.; Forbes, D. C.; Davis, J. H., Jr Novel Brønsted Acidic Ionic Liquids and Their Use as Dual Solvent-catalysts. J. Am. Chem. Soc. 2002, 124, 5962. (9) Huang, Q.; Li, Y.; Jin, X. B.; Zhao, D.; Chen, G. Z. Chloride Ion Enhanced Thermal Stability of Carbon Dioxide Captured by Monoethanolamine in Hydroxyl Imidazolium Based Ionic Liquids. Energy Environ. Sci. 2011, 4, 2125. (10) Zhao, Q. C.; Anderson, J. L. Task-Specific Microextractions Using Ionic Liquids. Anal. Bioanal. Chem. 2011, 400, 1613. (11) Visser, A. E.; Swatloski, R. P.; Reichert, W. M.; Mayton, R.; Sheff, S.; Wierzbicki, A.; Davis, J. H., Jr; Rogers, R. D. Task-Specific

AUTHOR INFORMATION

Corresponding Author

*Tel.: +86-10-62514925. Fax: +86-10-62516444. E-mail: [email protected]. Notes

The authors declare no competing financial interest. 2081

dx.doi.org/10.1021/ie302850z | Ind. Eng. Chem. Res. 2013, 52, 2073−2083

Industrial & Engineering Chemistry Research

Article

Solubilities of Water-Imidazolium-Based Ionic Liquids Systems. Fluid Phase Equilib. 2007, 261, 449. (35) Moreno, M.; Castiglione, F.; Mele, A.; Pasqui, C.; Raos, G. Interaction of Water with the Model Ionic Liquid [bmim][BF4]: Molecular Dynamics Simulations and Comparison with NMR Data. J. Phys. Chem. B 2008, 112, 7826. (36) Takamuku, T.; Kyoshoin, Y.; Shimomura, T.; Kittaka, S.; Yamaguchi, T. Effect of Water on Structure of Hydrophilic Imidazolium−Based Ionic Liquid. J. Phys. Chem. B 2009, 113, 10817. (37) Wu, J.; Zhang, J.; Zhang, H.; He, J.; Ren, Q.; Guo, M. Homogeneous Acetylation of Cellulose in a New Ionic Liquid. Biomacromolecules 2004, 5, 266. (38) Xie, H.; Zhang, S.; Li, S. Chitin and Chitosan Dissolved in Ionic Liquids as Reversible Sorbents of CO2. Green Chem. 2006, 8, 630. (39) Wu, B.; Zhang, Y. M.; Wang, H. P. Aqueous Biphasic Systems of Hydrophilic Ionic Liquids + Sucrose for Separation. J. Chem. Eng. Data 2008, 53, 983. (40) Zhang, H.; Wang, Z.; Zhang, Z.; Wu, J.; Zhang, J.; He, J. Regenerated-Cellulose/Multiwalled Carbon Nanotube Composite Fibers with Enhanced Mechanical Properties Prepared with the Ionic Liquid 1-Allyl-3-Methylimidazolium Chloride. Adv. Mater. 2007, 19, 698. (41) Qiu, H. D.; Takafuji, M.; Liu, X.; Jiang, S. X.; Ihara, H. Investigation of pi-pi and Ion-Dipole Interactions on 1-Allyl-3Butylimidazolium Ionic Liquid-Modified Silica Stationary Phase in Reversed-Phase Liquid Chromatography. J. Chromatogr. A 2010, 1217, 5190. (42) Gutowski, K. E.; Maginn, E. J. Amine−Functionalized Task− Specific Ionic Liquids: a Mechanistic Explanation for the Dramatic Increase in Viscosity upon Complexation with CO2 from Molecular Simulation. J. Am. Chem. Soc. 2008, 130, 14690. (43) Zhang, Y.; Zhang, S.; Lu, X.; Zhou, Q.; Fan, W.; Zhang, X. P. Dual Amino Functionalised Phosphonium Ionic Liquids for CO2 Capture. Chem.Eur. J. 2009, 15, 3003. (44) Schneider, W. F.; Gurkan, B. E.; de la Fuente, J. C.; Mindrup, E. M.; Ficke, L. E.; Goodrich, B. F.; Price, E. A.; Brennecke, J. F. Equimolar CO2 Absorption by Anion−Functionalized Ionic Liquids. J. Am. Chem. Soc. 2010, 132, 2116. (45) Qian, Y. B.; Xiao, S. Y.; Liu, L.; Wang, Y. M. A Mild and Efficient Procedure for Asymmetric Michael Additions of Cyclohexanone to Chalcones Catalyzed by an Amino Acid Ionic Liquid. Tetrahedron−Asymmetry 2008, 19, 1515. (46) Wang, Z. J.; Zhang, Q. X.; Kuehner, D.; Ivaska, A.; Niu, L. Green Synthesis of 1−2 nm Gold Nanoparticles Stabilized by AmineTerminated Ionic Liquid and Their Electrocatalytic Activity in Oxygen Reduction. Green Chem. 2008, 10, 907. (47) Cai, Y. Q.; Peng, Y. Q.; Song, G. H. Amino-Functionalized Ionic Liquid as an Efficient and Recyclable Catalyst for Knoevenagel Reactions in Water. Catal. Lett. 2006, 109, 61. (48) Wink, W. A. Determining Moisture Equilibrium Curves of Hygroscopic Materials. Ind. Eng. Chem. Anal. Edi. 1946, 18, 251. (49) Zhang, Q.; Wang, N.; Wang, S.; Yu, Z. Hydrogen Bonding Behaviors of Binary Systems Containing the Ionic Liquid 1-Butyl-3Methylimidazolium Trifluoroacetate and Water/Methanol. J. Phys. Chem. B 2011, 115, 11127. (50) Zhang, Q. G.; Wang, N. N.; Yu, Z. W. The Hydrogen Bonding Interactions between the Ionic Liquid 1-Ethyl-3-Methylimidazolium Ethyl Sulfate and Water. J. Phys. Chem. B 2010, 114, 4747. (51) Mu, T.; Han, B.; Zhang, J.; Li, Z.; Liu, Z.; Du, J.; Liu, D. Hydrogen Bonding of Acetic Acid in CO2 + n-Pentane Mixed Fluids in the Critical Region. J. Supercrit. Fluid. 2004, 30, 17. (52) Bini, R.; Bortolini, O.; Chiappe, C.; Pieraccini, D.; Siciliano, T. Development of Cation/Anion ″Interaction″ Scales for Ionic Liquids through ESI-MS Measurements. J. Phys. Chem. B 2007, 111, 598. (53) Huddleston, J. G.; Visser, A. E.; Reichert, W. M.; Willauer, H. D.; Broker, G. A.; Rogers, R. D. Characterization and Comparison of Hydrophilic and Hydrophobic Room Temperature Ionic Liquids Incorporating the Imidazolium Cation. Green Chem. 2001, 3, 156.

Ionic Liquids for the Extraction of Metal Ions from Aqueous Solutions. Chem. Commun. 2001, 135. (12) Ohno, H.; Fukaya, Y. Task Specific Ionic Liquids for Cellulose Technology. Chem. Lett. 2009, 38, 2. (13) Chen, Y.; Han, J.; Wang, T.; Mu, T. Determination of Absorption Rate and Capacity of CO2 in Ionic Liquids at Atmospheric Pressure by Thermogravimetric Analysis. Energy Fuel 2011, 25, 5810. (14) Yang, Z. Z.; Zhao, Y. N.; He, L. N. CO2 Chemistry: TaskSpecific Ionic Liquids for CO2 Capture/Activation and Subsequent Conversion. RSC Adv. 2011, 1, 545. (15) Palomar, J.; Gonzalez-Miquel, M.; Bedia, J.; Rodriguez, F.; Rodriguez, J. J. Task-Specific Ionic Liquids for Efficient Ammonia Absorption. Sep. Purif. Technol. 2011, 82, 43. (16) Zakeeruddin, S. M.; Grätzel, M. Solvent-Free Ionic Liquid Electrolytes for Mesoscopic Dye-Sensitized Solar Cells. Adv. Funct. Mater. 2009, 19, 2187. (17) Armand, M.; Endres, F.; MacFarlane, D. R.; Ohno, H.; Scrosati, B. Ionic-Liquid Materials for the Electrochemical Challenges of the Future. Nat. Mater. 2009, 8, 621. (18) Lee, S.-g. Functionalized Imidazolium Salts for Task-Specific Ionic Liquids and Their Applications. Chem. Commun. 2006, 1049. (19) Chaturvedi, D. Recent Developments on Task Specific Ionic Liquids. Curr. Org. Chem. 2011, 15, 1236. (20) Giernoth, R. Task-Specific Ionic Liquids. Angew. Chem., Int. Ed. 2010, 49, 2834. (21) Cao, Y.; Chen, Y.; Sun, X.; Zhang, Z.; Mu, T. Water Sorption in Ionic Liquids: Kinetics, Mechanisms and Hydrophilicity. Phys. Chem. Chem. Phys. 2012, 14, 12252. (22) Roth, C.; Rose, A.; Ludwig, R. Ionic Liquids Can be More Hydrophobic than Chloroform or Benzene. ChemPhysChem 2012, 13, 3102. (23) Seddon, K. R.; Stark, A.; Torres, M. J. Influence of Chloride, Water, and Organic Solvents on the Physical Properties of Ionic Liquids. Pure Appl. Chem. 2000, 72, 2275. (24) Cammarata, L.; Kazarian, S.; Salter, P.; Welton, T. Molecular States of Water in Room Temperature Ionic Liquids. Phys. Chem. Chem. Phys. 2001, 3, 5192. (25) Cuadrado-Prado, S.; Dominguez-Perez, M.; Rilo, E.; GarciaGarabal, S.; Segade, L.; Franjo, C.; Cabeza, O. Experimental Measurement of the Hygroscopic Grade on Eight Imidazolium Based Ionic Liquids. Fluid Phase Equilib. 2009, 278, 36. (26) Di Francesco, F.; Calisi, N.; Creatini, M.; Melai, B.; Salvo, P.; Chiappe, C. Water Sorption by Anhydrous Ionic Liquids. Green Chem. 2011, 13, 1712. (27) Torrecilla, J. S.; Rafione, T.; Garcia, J.; Rodriguez, F. Effect of Relative Humidity of Air on Density, Apparent Molar Volume, Viscosity, Surface Tension, and Water Content of 1-Ethyl-3Methylimidazolium Ethylsulfate Ionic Liquid. J. Chem. Eng. Data 2008, 53, 923. (28) Blanchard, L. A.; Gu, Z.; Brennecke, J. F. High−Pressure Phase Behavior of Ionic Liquid/CO2 Systems. J. Phys. Chem. B 2001, 105, 2437. (29) Najdanovic-Visak, V.; Rebelo, L. P. N.; da Ponte, M. N. Liquid− Liquid Behaviour of Ionic Liquid−1-Butanol−Water and High Pressure CO2−Induced Phase Changes. Green Chem. 2005, 7, 443. (30) Sheldon, R. A.; Lau, R. M.; Sorgedrager, M. J.; van Rantwijk, F.; Seddon, K. R. Biocatalysis in Ionic Liquids. Green Chem. 2002, 4, 147. (31) Hanke, C.; Lynden-Bell, R. A Simulation Study of WaterDialkylimidazolium Ionic Liquid Mixtures. J. Phys. Chem. B 2003, 107, 10873. (32) Köddermann, T.; Wertz, C.; Heintz, A.; Ludwig, R. The Association of Water in Ionic Liquids: a Reliable Measure of Polarity. Angew. Chem., Int. Ed. 2006, 45, 3697. (33) Tran, C. D.; Lacerda, S. H. D.; Oliveira, D. Absorption of Water by Room−Temperature Ionic Liquids: Effect of Anions on Concentration and State of Water. Appl. Spectrosc. 2003, 57, 152. (34) Freire, M. G.; Santos, L. M. N. B. F.; Fernandes, A. M.; Coutinho, J. A. P.; Marrucho, I. M. An Overview of the Mutual 2082

dx.doi.org/10.1021/ie302850z | Ind. Eng. Chem. Res. 2013, 52, 2073−2083

Industrial & Engineering Chemistry Research

Article

(54) Lovelock, K. R. J.; Smith, E. F.; Deyko, A.; Villar-Garcia, I. J.; Licence, P.; Jones, R. G. Water Adsorption on a Liquid Surface. Chem. Commun. 2007, 4866. (55) Aki, S. N. V. K.; Mellein, B. R.; Saurer, E. M.; Brennecke, J. F. High−pressure Phase Behavior of Carbon Dioxide with Imidazolium− Based Ionic Liquids. J. Phys. Chem. B 2004, 108, 20355. (56) Cheng, X.; Yang, G.; Mu, T.; Guo, X.; Wang, X. Absorption of Vinyl Chloride by Room Temperature Ionic Liquids. Clean−Soil, Air, Water 2009, 37, 245. (57) Cheng, X.; Mu, T.; Wang, X.; Guo, X.; Zou, L. Low Pressure Solubilities of Vinyl Chloride in Ionic Liquids. J. Chem. Eng. Data 2008, 53, 2807. (58) Gao, Y.; Zhang, L.; Wang, Y.; Li, H. Probing Electron Density of H-Bonding between Cation−Anion of Imidazolium-Based Ionic Liquids with Different Anions by Vibrational Spectroscopy. J. Phys. Chem. B 2010, 114, 2828. (59) Freire, M. G.; Neves, C. M. S. S.; Carvalho, P. J.; Gardas, R. L.; Fernandes, A. M.; Marrucho, I. M.; Santos, L. M.; Coutinho, J. A. P. Mutual Solubilities of Water and Hydrophobic Ionic Liquids. J. Phys. Chem. B 2007, 111, 13082. (60) Aki, S. N. V. K.; Brennecke, J. F.; Samanta, A. How Polar are Room−Temperature Ionic Liquids? Chem. Commun. 2001, 413. (61) Kyte, J.; Doolittle, R. F. A Simple Method for Displaying the Hydropathic Character of a Protein. J. Mol. Biol. 1982, 157, 105. (62) Rose, G. D.; Geselowitz, A. R.; Lesser, G. J.; Lee, R. H.; Zehfus, M. H. Hydrophobicity of Amino Acid Residues in Globular Proteins. Science 1985, 229, 834.

2083

dx.doi.org/10.1021/ie302850z | Ind. Eng. Chem. Res. 2013, 52, 2073−2083