Syntheses and Properties of Methoxy and Nitrile ... - ACS Publications

Article pubs.acs.org/jced

Cite This: J. Chem. Eng. Data XXXX, XXX, XXX−XXX

Syntheses and Properties of Methoxy and Nitrile Functionalized Imidazolium Tris(pentafluoroethyl)trifluorophosphate Ionic Liquids Julius Kim A. Tiongson,† Dwight Angelo V. Bruzon,‡,§ Giovanni A. Tapang,§ and Imee Su Martinez*,†,‡ †

Natural Sciences Research Institute, University of the Philippines Diliman, Quezon City, Philippines, 1101 Institute of Chemistry, University of the Philippines Diliman, Quezon City, Philippines, 1101 § National Institute of the Physics, University of the Philippines Diliman, Quezon City, Philippines, 1101 ‡

S Supporting Information *

ABSTRACT: An alternative and more benign method was employed to synthesize tris(pentafluoroethyl)trifluorophosphate (FAP) ionic liquids (ILs). Ion exchange chromatography was used instead of the typical electrochemical fluorination developed by Ignat’ev and co-workers. The resulting procedure is simple and can be readily performed, as the use of corrosive hydrofluoric acid and the production of toxic and explosive byproducts were circumvented. Functionalization of the alkyl group of the imidazolium cation with a methoxy and a nitrile moiety was employed to observe changes in properties. The success of the synthesis was confirmed by 1H, 19F, and 31P NMR, IR, and UV−vis spectroscopy techniques. Quantitative product yields of approximately 80% (w/w) were obtained. The water content and viscosity values of the synthesized FAP-based ILs were found to be lower compared to other fluorinecontaining ionic liquids. Thermal analyses resulted in high thermal degradation temperatures greater than 573.15 K. Electrochemical analyses showed potential windows of values greater than 5.0 V, indicating electrochemical stability. On the basis of the basic properties observed, the FAP-based ILs synthesized in this study may be useful as gas absorbents, electrolytes, and other applications, especially those involving extended temperature ranges.

1. INTRODUCTION The need for alternative solvents as part of the global campaign toward green chemistry has brought ionic liquids (ILs) in the interest of many.1−4 While ILs are mostly used as solvents for synthesis, their applications have been extended to other forms.5−7 They are either being used or at least being tested for their potential as electrolytes in dye-sensitized solar cells,8−10 lubricant additives,11,12 gas absorbents,13−16 organic catalysts,17,18 and many others. The variety of possible uses has led to the synthesis of ionic liquids with specific applications in mind called “taskspecific” ionic liquids.19,20 Functional groups attached to the cations or anions are altered to tune their physicochemical properties. Tris(pentafluoroethyl)trifluorophosphate or FAP ionic liquids are one of these ILs, which exhibit distinctive properties due to the replacement of hydrogen atoms in their anions with fluorine.21−23 Their hydrophobicity is their distinguishing feature making them ideal systems for solvent extraction.24,25 Because of their wide electrochemical windows, FAP ionic liquids, for example, can be used as chemical agents for alcohol oxidation syntheses.18 They are also predicted to be ideal absorbents for carbon dioxide, such as in the theoretical studies of Rao and co-workers.16 Noncovalent interactions can occur between the fluorine of FAP and CO2 leading to gas solubilization. In terms of thermal stability, these ILs display high degradation temperatures typical of fluorine-containing ionic liquids.26,27 There are still very few experimental studies done on FAPbased ionic liquids due to the complexity involved in the © XXXX American Chemical Society

syntheses. The most cited method is the work of Ignat’ev and co-workers,27 which entails a direct acid−base reaction between Tris(perfluoroalkyl)trifluorophosphoric acid (HFAP) and the chloride precursor of the desired cation. This part of the procedure is simple enough; however, the HFAP used is obtained through the electrochemical fluorination of trialkylphosphines to generate Tris(perfluoroalkyl)difluorophosphorane, which is subsequently reacted with aqueous hydrofluoric acid. This procedure can only be performed with specialized equipment for electrosynthesis and with extreme caution as short chain trialkylphosphines are pyrophoric and HF is quite corrosive. Another electrochemical fluorination method from tris(perfluoroalkyl)phosphine oxides starting material is also quite dangerous as it involves the generation of a highly toxic gas byproduct, oxygen difluoride.28 In addition, the absence of commercially available HFAP is also an issue hindering FAP ionic liquid production. A simpler, safer, and more environmentally benign method is therefore advantageous and more economical. In this particular study, ion exchange chromatography (IEC) was the method of choice due to its success in previous studies in the synthesis of other ionic liquids.29,30 A set of room-temperature imidazolium-based ILs with a common anion tris(pentafluoroethyl)trifluorophosphate and Received: March 20, 2017 Accepted: February 22, 2018

A

DOI: 10.1021/acs.jced.7b00281 J. Chem. Eng. Data XXXX, XXX, XXX−XXX

Journal of Chemical & Engineering Data

Article

Table 1. Cations and Anions Comprising the Ionic Liquids under Study

Table 2. Specifications of the Chemical Samples Used and the Synthesized Ionic Liquids chemical name

source

CASRN

molar mass (g mol−1)

mass fraction purity

82.1 106.593 117.57 88.11 88.106 none 12.01

0.990 0.990 0.980 0.99 0.995 none none

122.593

0.99

none

1

74.12 32.04

0.99 0.998

none none

GCa GCa

394692-83-2

519.15

0.98

none

19

none none none

598.25 609.24 614.25

0.999 0.978 0.994

decolorization using activated charcoal, water extraction, and high vacuum-drying

Sigma-Aldrich

1-chloro-4-methoxybutane

Epochem

17913-18-7

diethyl ether methanol

ACS Reagent

60-29-7 67-56-1

[TMA][FAP]b

Merck KGaA

synthesized samples

a

analysis method H NMR/GCa 1 H NMR/GCa 1 H NMR/GCa GCa GCa none none

616-47-7 543-59-9 6280-87-1 141-78-6 123-91-1 39339-85-0 7440-44-0

[PMIM][FAP] [CNBMIM][FAP] [MOBMIM][FAP]

purification method none none none none none none none

1-methylimidazole 1-chloropentane 5-chlorovaleronitrile ethyl acetate dioxane Amberlyst A-26 activated charcoal

1

H NMR

F and 31P NMR/electropho-resis

1

H NMR H NMR 1 H NMR 1

Gas chromatography. bTetramethylammonium tris(pentafluoroethyl)trifluorophosphate.

product purity. The properties of the ILs such as water content, density, color, viscosity, and thermal and electrochemical stability were then determined.

cations 1-pentyl-3-methylimidazolium [PMIM], 1-(4-methoxybutyl)-3-methylimidazolium [MOBMIM], and 1-(4-cyanobutyl)-3-methylimidazolium [CNBMIM] were synthesized through IEC. Table 1 shows the structure of the cations and the anion of the ILs synthesized and characterized in this study. Cyano and methoxy functional groups were incorporated and were used to replace the terminal methyl of the pentyl chain attached to the imidazolium cation. Changes in properties resulting from the changes made in the structure of the cation were determined, as improved properties such as enhanced thermal and electrochemical stability will make better electrolytes for dye-sensitized solar cells and lithium battery or solvents for CO2.10,15 The ILs were characterized using spectroscopic techniques to determine the success of the syntheses and to assess

2. EXPERIMENTAL METHODS 2.1. Chemical Reagents. Analytical grade reagents were used as received in the syntheses of the ionic liquids. The reagents were purchased from Sigma-Aldrich, except for 1-chloro-4methoxybutane and tetramethylammonium tris(pentafluoroethyl)trifluorophosphate, which were obtained from Epochem and Merck KGaA, respectively. Table 2 shows the chemicals used for the syntheses. 2.2. Synthesis of the Chloride Precursors. The chloride precursors were synthesized based on the works of Zhao B



Article

Figure 1. Syntheses of the different chloride precursors.

and Min.10,31 Direct alkylation of the 1-methylimidazole was performed in order to attach the desired functional groups to the imidazolium ring. Figure 1 shows the reactions involving the syntheses of the chloride precursors. [PMIM]Cl was prepared from 1-methylimidazole (0.20 mol/3.80 mL) and 1-chloropentane (0.22 mol/6.41 mL). The mixture was refluxed at 343.15 K for 72 h, and the resulting product was washed with ethyl acetate. In a similar manner, [CNBMIM]Cl was prepared from 1-methylimidazole (1.00 mol/ 2.50 mL) and 5-chlorovaleronitrile (1.20 mol/4.28 mL). It took only 24 h of refluxing to achieve the desired [CNBMIM]Cl, which was then washed with diethyl ether. The method of preparing [MOBMIM]Cl was identical to that of the [CNBMIM]Cl except for the starting materials, which were 1-methylimidazole (0.030 mol/ 4.00 mL) and 1-chloro-4-methoxybutane (0.030 mol/4.00 mL), and the solvent used for washing, which was dioxane. The washing solvents were removed through rotary evaporation, and the ionic liquid products were purified using activated charcoal. 2.3. Anion Exchange Chromatography. Anion exchange chromatography was used to replace the chloride anion of the precursor with the desired FAP anion. This procedure was based on the work of Alcalde and co-workers in 2012.30 A glass fritted column was packed with wet Amberlyst A-26 in OH− form and then washed with a solution of 1:1 deionized water−methanol. The anion Tris(pentafluoroethyl)trifluorophosphate was then loaded by slowly passing a 1.0% (w/v) [TMA][FAP] solution in methanol. Saturation of the exchange sites with the FAP anion was checked by testing for the presence of OH− in the eluate using a silver nitrate test. The actual ion exchange step was performed by allowing a solution of 0.07 molal of the chloride precursors in methanol to pass through the column. The solution inside the column was continuously replenished until the resulting eluate was chloride free.

The eluates containing the desired ILs were purified in the same manner as the chloride precursors. The purified ionic liquids were mixed with deionized water to remove hydrophilic impurities, such as traces of chloride salts.10,24 As for the [CNBMIM][FAP], its water mixture was heated up to 313.15 K for 10 min while sonicating to further remove traces of chloride impurities. Further purification was done by vacuum-drying the obtained ILs to 1.3 × 10−3 Pascals for 24 h using a modified Schlenk line shown in Figure 2. Removal of volatile impurities such as water and organic solvents was monitored using a residual gas analyzer-quadrupole mass spectrometer (Extorr XT100 SN7236) attached to the high-vacuum preparation line. The samples were evacuated before characterization, unless stated otherwise. 2.4. Characterization of Synthesized FAP Ionic Liquids. 2.4.1. Spectroscopic Methods. The FAP-based ionic liquids were characterized using IR and NMR (1H, 19F, and 31P) spectroscopies. The infrared spectrum of each IL was obtained using a Shimadzu IRAffinity. An Agilent nuclear magnetic resonance spectrometer was used for the NMR measurements, and the frequencies applied were 500 MHz for 1H NMR, 470.18 MHz for 19 F-NMR, and 202.30 MHz for 31P NMR. DMSO-d6 was the solvent used for NMR studies in all the ionic liquids. 2.4.2. Ion Chromatography of FAP-Based ILs and Melting Point Determination of [CNBMIM][FAP]. The chloride content of the synthesized ionic liquids was analyzed using ion chromatography with a Dionex ICS-1000 along with an IonPac AS14A column. This was done to ensure that chloride impurities were not altering the measured properties. The melting point of [CNBMIM][FAP] on the other hand was determined using a Fisher-Johns melting point apparatus. 2.4.3. Water Content Analysis. Karl Fischer titration was performed using an MKS-500 KF moisture titration apparatus to C



Article

Figure 2. Schlenk line with high vacuum pump system and residual gas analyzer.

2.4.8. Electrochemical Stability. Electrochemical stability measurements were obtained using an all Pt three-electrode system. A home-built electrochemical cell was used in order to evacuate the ionic liquids prior to characterization and to perform the experiments in a controlled environment. An eDAQ potentiostat was used with an e-corder 410 interfaced with an EChem software. Cyclic voltammetry was employed to determine the reduction and oxidation limits at a scan rate of 200 mV/s. The working electrode’s electrochemically active surface area was determined using steady state voltammetry of a 2 mM solution of ferrocene in acetonitrile with 0.1 M TBAP as supporting electrolyte.

evaluate the water content of the synthesized ionic liquids. This was also done to ensure that water does not change the measured properties. The samples were analyzed straight after syntheses in ambient conditions. 2.4.4. Density Measurements. The syringe method for measuring density was conducted to minimize sample usage.32 A Hamilton 81301 1000 μL gastight syringe was used to measure the volume of the ionic liquid, while a KERN analytical balance was used to measure its mass. [CNBMIM][FAP], which is solid at ambient conditions, was melted before the measurement was done. Prior to actual experimentation, the syringe was calibrated using common liquids, such as deionized water, ethylene glycol, and glycerol, at 298.15 K.33 Calibration was performed in four trials, and the percentage error of the measured densities was [MOBMIM][FAP]. This is consistent with the study of Gonfa and co-workers46 using cyano-functionalized thiocyanate ILs, which showed that saturated alkyl chain group in ionic liquids resulted in high degradation temperatures compared to their functionalized counterparts, regardless of the anion. The methoxy functionalized IL has the lowest degradation temperature, and this may be attributed to the thermal

Figure 6. Dynamic viscosity (η) of the different fluorine-containing imidazolium ionic liquids (at 298.15 K). *, Performed at 308.15 K; ^, performed at 293.15 K; converted kinematic value to dynamic viscosity; kinematic viscosity (cSt) × density = dynamic viscosity (cP); uncertainty value is not available.

ionic liquids are less viscous than ionic liquids with BF4− and PF6− anion. This may be attributed to the weaker cation−anion interactions due to the large perfluoroethyl groups of FAP−. The large anions will also contribute to a greater free volume increasing mass transfer rate.38 Lowered viscosities of ionic liquids are desired in electrochemical and gas capture applications. 3.6. Thermal Stability. Replacement of the terminal methyl of the alkyl chain with cyano and methoxy functional groups on the imidazolium ring resulted in increased degradation temperatures. The observed temperature trend of the chloride ionic liquids is Td[CNBMIM]Cl > Td[MOBMIM]Cl > Td[PMIM]Cl as shown in the thermograms in Figure 7. The higher degradation temperature of [CNBMIM]Cl is probably due to the presence of a cyano G



Article

Figure 8. TGA curve of the FAP-based ionic liquids. Temperature (T) versus weight loss (w).

instability of butoxymethyl substituents due to the increased acidity of the protons of its terminal carbon.37 The thermal degradation temperatures of the synthesized FAP-based ILs are comparable to those synthesized by Ignat’ev and associates,24 to the cyano-functionalized ionic liquids prepared by Zhang and co-workers,39 to the methoxy-functionalized ionic liquids of Chen and co-workers,44 and to the conventional fluorinated ones made by the group of Huddleston42 as shown in Table 8. A plot is also created to be able to readily compare these values shown in Figure 9. The variation of degradation temperatures of the synthesized [PMIM][FAP] and the [PMIM][FAP] of Ignat’ev and co-workers may be brought about by the difference in water content or experimental parameters in TGA analysis such as heating rate and sample weight.26 Results from the work of Zhang and co-workers39 using [BMIM][BF4] and [C3CNMIM][BF4] ionic liquids have shown that a large decrease in degradation temperatures was observed when functional groups are incorporated into the saturated alkyl group of the imidazolium cation. Their results showed that the temperatures went down from 676.15 to 538.05 K once a −CN functional group replaced the −CH3 moiety. However, the observed difference between the degradation temperatures of the functionalized FAP-based ionic liquids and the saturated alkyl chain ionic liquids in this particular study is not that apparent. The percent difference of the degradation temperature of [CNBMIM][FAP] to [PMIM][FAP] is

Figure 9. Degradation temperature (T) of FAP-based ionic liquids and some published fluorinated ionic liquids. *, synthesized FAP-based ionic liquids. The data are arranged according to anion.

only 1.73%. This means that the FAP anion contributed significantly to the thermal stability of the IL lessening the effect of the cyano group on the cation. This may be attributed to the nature of the FAP anion with its large perfluoroethyl group and its noncoordinative nature.26 3.7. Electrochemical Stability. The synthesized FAP ionic liquids were observed to possess wide electrochemical windows. The nonfunctionalized analogue [PMIM][FAP] has an electrochemical window of 5.25 V, whereas the two functionalized ionic liquids [MOBMIM][FAP] and [CNBMIM][FAP] have electrochemical windows of 5.24 and 5.81 V, respectively. The potential windows were obtained from the voltammograms using the method of Bühlmann and co-workers, which do away with Jcutoff, removing bias in determining electrochemical windows.47 According to their study, this lessens the effect of mass transport, scan rate, and electrode surface area to the determined stabilities. The method involved linear fitting of the current−voltage curve at potentials below and above the onset of electrolyte decomposition and taking the potential where the two lines intersected. The presence of a cyano functional group led to an increase in the measured potential window. The group of Deng and

Table 8. Experimental Degradation Temperature Td of FAP-Based Ionic Liquids and Some Published Fluorinated Ionic Liquidsa ionic liquids

abbreviation

Td/K

literature ref

[1-pentyl-3-methylimidazolium][FAP] [1-(4-cyanobutyl)-3-methylimidazolium][FAP] [1-(4-methoxybutyl)-3-methylimidazolium][FAP] [1-ethyl-3-methylimidazolium][FAP] [1-pentyl-3-methylimidazolium][FAP] [1-hexyl-3-methylimidazolium][FAP] [1-butyl-3-methylimidazolium][BF4] [1-butyl-3-methylimidazolium][PF6] [1-butyl-3-methylimidazolium][Tf2N] [1-(4-cyanopropyl)-3-methylimidazolium][BF4] [1-(4-cyanopropyl)-3-methylimidazolium][PF6] [1-(4-cyanopropyl)-3-methylimidazolium][Tf2N] [1-(4-methoxypropyl)-3-methylimidazolium][Tf2N]

[PMIM][FAP] [CNBMIM][FAP] [MOBMIM][FAP] [EMIM][FAP] [PMIM][FAP] [HMIM][FAP] [BMIM][BF4] [BMIM][PF6] [BMIM][Tf2N] [C3CNMIM][BF4] [C3CNMIM][PF6] [C3CNMIM][TF2N] [C1OC3MIM][Tf2N]

618.3 601.1 588.0 573.2b 573.2b 563.2b 676.2b 622.2b 712.2b 538.0 548.4 657.4 656.4

27 27 27 42 42 42 39 39 39 44

a

The degradation temperatures are obtained at 5% weight loss. The standard uncertainty for the synthesized ILs is u(Td) = 0.1 K. The standard uncertainty value for the published samples is not available. bTemperature onset of degradation. H



I

52 52 52 37 37 48 48 48 Pt Pt Pt Ag+/Ag Ag+/Ag Ag+/Ag Fc/Fc+ Fc/Fc+ Ag/AgCl Ag/AgCl Ag/AgCl Pt Pt Pt GC GC GC Pt Pt GC GC GC 3.72 3.46 3.49 1.12d 1.76d 2.10d 2.1e 2.0e 2.17d 2.03d 2.12d

5.25 5.24b 5.81b 3.24 4.14 4.61 4.8 4.6 5.81 3.98 3.87

working electrode

−1.53 −1.78 −2.32 −2.12d −2.38d −2.51d −2.7e −2.6e −3.64d −1.95d −1.75d

b

Erange/V Eox/V Ered/V

a

[PMIM][FAP] [MOBMIM][FAP] a [CNBMIM][FAP] c [EMIM][BF4] c [EMIM][Tf2N] c [HMIM][Tf2N] a [BMIM][PF6] a [BMIM][BF4] a trihexyl(tetradecyl)phosphonium tris(pentafluoroethyl)trifluorophosphate [P14,6,6,6][FAP] a 4-(2-methoxyethyl)-4-methylmorpholinium tris(pentafluoroethyl)trifluorophosphate [MOEMMor][FAP] a 1-(2-methoxyethyl)-1-methylpiperidinium tris(pentafluoroethyl)trifluorophosphate [MOEMPip][FAP]

4. CONCLUSION A simpler, safer, and more environmentally benign method of synthesizing functionalized imidazolium FAP-based ILs has been developed in this study. Anion exchange chromatography remains to be an attractive solution in IL synthesis for its ease of use. It is, however, recommended that further studies should

a

the three ionic liquids in this study. The acquired electrochemical stability values are comparable to other ionic liquids reported in the literature22,37,48 and are wider than aqueous or other molecular solvents used in electrochemistry.49 However, the working and reference electrodes used from other studies vary, which affected the determined potential windows as shown in Table 9. The prominent oxidation peaks observed in the reverse scan between 0.0 to +1.0 V (vs Pt electrode) for the three ionic liquids were assigned to the oxidation of the imidazolium radical formed at the negative potential limit. This is normally absent in short chain imidazolium ionic liquids, where the favored fate of the imidazolium electrogenerated radical is dimerization.50 The appearance of the voltammograms in this study shows that the favored fate of the electrogenerated imidazolium radicals from the three ionic liquids is the formation of neutral carbene species.49 The generated electroactive carbene species gave back the original cation during an oxidative scan within the range of 0.0 to +1.0 V. The same electrogenerated product was observed in [BMIM][BF4] upon reduction at potentials more negative than −1.9 V (vs Ag reference).51

ionic liquid

Figure 10. Cyclic voltammograms of [PMIM][FAP] (top), [CNBMIM][FAP] (middle), and [MOBMIM][FAP] (bottom) (v = 200 mV/s).

a

Table 9. Experimental Electrochemical Windows of of FAP-Based Ionic Liquids and Some Published Fluorinated Ionic Liquidsa

reference electrode

literature ref

co-workers explained this as the possible passivation of the anodic electrode in the presence of the cyano group as well as the stronger interaction between the cation and anion caused by the CN group.39 Figure 10 shows the cyclic voltammograms of

The standard uncertainty of the synthesized samples is u(E) = 0.01 V. For the published samples, the standard uncertainty values are not available. bIonic liquid was vacuum-dried. cIonic liquid was purged with argon and stirred. dCurrent density limit at 0.5 mA/cm2. eCurrent density limit at 1.0 mA/cm2.

Article



Article

(7) Zhang, S.; Zhang, Q.; Zhang, Y.; Chen, Z.; Watanabe, M.; Deng, Y. Beyond solvents and electrolytes: Ionic liquids-based advanced functional materials. Prog. Mater. Sci. 2016, 77, 80−124. (8) Kuang, D.; Wang, P.; Ito, S.; Zakeeruddin, S. M.; Grätzel, M. Stable mesoscopic dye-sensitized solar cells based on tetracyanoborate ionic liquid electrolyte. J. Am. Chem. Soc. 2006, 128, 7732−7733. (9) Cao, Y.; Zhang, J.; Bai, Y.; Li, R.; Zakeeruddin, S. M.; Grätzel, M.; Wang, P. Dye-sensitized solar cells with solvent-free ionic liquid electrolytes. J. Phys. Chem. C 2008, 112, 13775−13781. (10) Zhao, D.; Fei, Z.; Scopelliti, R.; Dyson, P. J. Synthesis and characterization of ionic liquids incorporating the nitrile functionality. Inorg. Chem. 2004, 43, 2197−2205. (11) Gusain, R.; Gupta, P.; Saran, S.; Khatri, O. P. Halogen-free bis(imidazolium)/bis(ammonium)-di[bis(salicylato)borate] ionic liquids as energy-efficient and environmentally friendly lubricant additives. ACS Appl. Mater. Interfaces 2014, 6, 15318−15328. (12) Otero, I.; López, E. R.; Reichelt, M.; Villanueva, M.; Salgado, J.; Fernández, J. Ionic liquids based on phosphonium cations as neat lubricants or lubricant additives for a steel/steel contact. ACS Appl. Mater. Interfaces 2014, 6, 13115−13128. (13) Brennecke, J. F.; Gurkan, B. E. Ionic Liquids for CO2 capture and emission reduction. J. Phys. Chem. Lett. 2010, 1, 3459−3464. (14) Karadas, F.; Atilhan, M.; Aparicio, S. Review on the use of ionic liquids (ILs) as alternative fluids for CO2 capture and natural gas sweetening. Energy Fuels 2010, 24, 5817−5828. (15) Kanakubo, M.; Makino, T.; Taniguchi, T.; Nokami, T.; Itoh, T. CO2 Solubility in Ether Functionalized Ionic Liquids on Mole Fraction and Molarity Scales. ACS Sustainable Chem. Eng. 2016, 4, 525−535. (16) Rao, S. S.; Gejji, S. P. CO2 Absorption Using Fluorine Functionalized Ionic Liquids: Interplay of Hydrogen and σ-Hole Interactions. J. Phys. Chem. A 2016, 120, 1243−1260. (17) Wasserscheid, P., Welton, T., Eds. Ionic Liquids in Synthesis, 2nd ed.; Wiley-VCH: Weinheim, Germany, 2007; pp 174−287. (18) Freemantle, M. Ionic liquids in organic synthesis. Chem. Eng. News 2004, 82, 44−49. (19) Visser, A. E.; Swatloski, R. P.; Reichert, W. M.; Mayton, R.; Sheff, S.; Wierzbicki, A.; Davis, J. H., Jr.; Rogers, R. D. Task-Specific Ionic Liquids for the Extraction of Metal Ions from Aqueous Solutions. Chem. Commun. 2001, 135−136. (20) H. Davis, J., Jr. Task-specific ionic liquids. Chem. Lett. 2004, 33, 1072−1077. (21) Zein El Abedin, S.; Borissenko, N.; Endres, F. Electropolymerization of benzene in a room temperature ionic liquid. Electrochem. Commun. 2004, 6, 422−426. (22) Buzzeo, M. C.; Hardacre, C.; Compton, R. G. Extended electrochemical windows made accessible by room temperature ionic liquid/organic solvent electrolyte systems. ChemPhysChem 2006, 7, 176−180. (23) Muldoon, M. J.; Aki, S. N. V. K.; Anderson, J. L.; Dixon, J. K.; Brennecke, J. F. Improving carbon dioxide solubility in ionic liquids. J. Phys. Chem. B 2007, 111, 9001−9009. (24) Ignat’Ev, N.; Welz-Biermann, U.; Kucheryna, A.; Bissky, G.; Willner, H. New ionic liquids with tris (perfluoroalkyl) trifluorophosphate (FAP) anions. J. Fluorine Chem. 2005, 126, 1150−1159. (25) Yao, C.; Pitner, W. R.; Anderson, J. L. Ionic Liquids Containing the Tris(pentafluoroethyl)trifluorophosphate Anion: a New Class of Highly Selective and Ultra Hydrophobic Solvents for the Extraction of Polycyclic Aromatic Hydrocarbons Using Single Drop Microextraction. Anal. Chem. 2009, 81, 5054−5063. (26) Maton, C.; De Vos, N.; Stevens, C. V. Ionic liquid thermal stabilities: decomposition mechanisms and analysis tools. Chem. Soc. Rev. 2013, 42, 5963−5977. (27) Ignat’Ev, N.; Sartori, P. Electrochemical fluorination of trialkylphosphines. J. Fluorine Chem. 2000, 103, 57−61. (28) Ignat’ev, N. V. Modern Synthesis Processes and Reactivity of Fluorinated Compounds; Groult, H., Leraux, F. R., Tressaud, A., Eds.; Elsevier: London, 2017; p 71.

be performed on the exchange efficiency of the resin as well as its recyclability. This may lessen operational costs particularly for wide-scale production. The thermal degradation temperatures and electrochemical windows of the FAP-based ionic liquids in this study showed notable thermal and electrochemical stability. In comparison with other fluorine-based ionic liquids, their low viscosity makes them good solvents for gas absorption. Also, these ionic liquids may be useful as hydrophobic solvents and electrolytes for high temperature applications. Adding a −CN functional group to the terminal end of the alkyl chain of the imidazolium cation led to considerable changes in phase, water affinity, viscosity, electrochemical stability, and thermal degradation temperature of the ionic liquid. With the ease of preparation, the use of other functional groups such as −NH2, −COOH, and −SO3H may be performed in the future. Theoretical studies on the properties of FAP-based ionic liquids can also be tested experimentally, and the possible applications of these ionic liquids can be explored.

■

ASSOCIATED CONTENT

* Supporting Information S

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.jced.7b00281.

■

NMR and IR spectra of synthesized ionic liquids (PDF)

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. ORCID

Imee Su Martinez: 0000-0001-9512-4089 Funding

This study was financed by the Natural Sciences Research Institute (NSRI) (Project CHE-15-1-05) of the University of the Philippines-Diliman, the UP Balik PhD Program, OVPAA Emerging Interdisciplinary Research Grant (EIDR) (Grant C02-164), the Office of the Vice Chancellor for Research and Development, UP-Diliman (Grant 131327 PNSE), and the Project VISSER, a collaborative project funded by the Department of Science and Technology (DOST), EIDR, PCIEERD, and ADMATEL-ITDI. Notes

The authors declare no competing financial interest.

■

REFERENCES

(1) Rogers, R. D.; Seddon, K. R. Ionic liquids-Solvents of the Future? Science 2003, 302, 792−793. (2) Canales, R. I.; Brennecke, J. F. Comparison of ionic liquids to conventional organic solvents for extraction of aromatics from aliphatics. J. Chem. Eng. Data 2016, 61, 1685−1699. (3) Kunz, W.; Häckl, K. The hype with ionic liquids as solvents. Chem. Phys. Lett. 2016, 661, 6−12. (4) Hulsbosch, J.; De Vos, D. E.; Binnemans, K. E.; Ameloot, R. Biobased Ionic Liquids: Solvents for a Green Processing Industry? ACS Sustainable Chem. Eng. 2016, 4, 2917−2931. (5) Martins, M. A. P.; Frizzo, C. P.; Moreira, D. N.; Zanatta, N.; Bonacorso, H. G. Ionic liquids in heterocyclic synthesis. Chem. Rev. 2008, 108, 2015−2050. (6) Lu, X.; Luo, Z.; Yu, S.; Fu, X. Lipase-catalyzed synthesis of starch palmitate in mixed ionic liquids. J. Agric. Food Chem. 2012, 60, 9273− 9279. J



Article

(29) Dinarès, I.; Miguel, C. G. D.; Ibáñez, A.; Mesquida, N.; Alcalde, E. Imidazolium ionic liquids: A simple anion exchange protocol. Green Chem. 2009, 11, 1507−1510. (30) Alcalde, E.; Dinarès, I.; Ibáñez, A.; Mesquida, N. A simple halideto-anion exchange method for heteroaromatic salts and ionic liquids. Molecules 2012, 17, 4007−4027. (31) Min, G.-H.; Yim, T.; Lee, H. Y.; Huh, D. H.; Lee, E.; Mun, J.; Oh, S. M.; Kim, Y. G. Synthesis and Properties of Ionic Liquids: Imidazolium Tetrafluoroborates with Unsaturated Side Chains. Bull. Korean Chem. Soc. 2006, 27, 847−852. (32) Burroughs, J. E.; Goodrich, C. P. Rapid method for determining densities of liquids using micro syringes. Anal. Chem. 1974, 46, 1614− 1615. (33) Eshbach, O. W.; Souders, M. Handbook of Engineering Fundamentals; Wiley: New York, 1975; pp 5−6. (34) Fendt, S.; Padmanabhan, S.; Blanch, H. W.; Prausnitz, J. M. Viscosities of Acetate or Chloride-Based Ionic Liquids and Some of Their Mixtures with Water or Other Common Solvents. J. Chem. Eng. Data 2011, 56, 31−34. (35) Holbrey, J. D.; Seddon, K. R. The phase behaviour of 1-alkyl-3methylimidazolium tetrafluoroborates; ionic liquids and ionic liquid crystals. J. Chem. Soc., Dalton Trans. 1999, 13, 2133−2140. (36) 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, 2275−2287. (37) O’Mahony, A. M.; Silvester, D. S.; Aldous, L.; Hardacre, C.; Compton, R. G. Effect of water on the electrochemical window and potential limits of room-temperature ionic liquids. J. Chem. Eng. Data 2008, 53, 2884−2891. (38) Neves, C. M. S. S.; Kurnia, K. A.; Shimizu, K.; Marrucho, I. M.; Rebelo, L. P. N.; Coutinho, J. A. P.; Freire, M. G.; Lopes, J. N. C. The impact of ionic liquid fluorinated moieties on their thermophysical properties and aqueous phase behaviour. Phys. Chem. Chem. Phys. 2014, 16, 21340−21348. (39) Zhang, Q.; Li, Z.; Zhang, J.; Zhang, S.; Zhu, L.; Yang, J.; Zhang, X.; Deng, Y. Physicochemical Properties of Nitrile-Functionalized Ionic Liquids. J. Phys. Chem. B 2007, 111, 2864−2872. (40) Paul, A.; Mandal, P. K.; Samanta, A. On the Optical Properties of the Imidazolium Ionic Liquids. J. Phys. Chem. B 2005, 109, 9148−9153. (41) Billard, I.; Moutiers, G.; Labet, A.; Azzi, A. E.; Gaillard, C.; Mariet, C.; Lützenkirchen, K. Stability of Divalent Europium in an Ionic Liquid: Spectroscopic Investigations in 1-Methyl-3-butylimidazolium Hexafluorophosphate. Inorg. Chem. 2003, 42, 1726−1733. (42) 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, 156−164. (43) Chen, Z. J.; Xue, T.; Lee, J.-M. What causes the low viscosity of ether-functionalized ionic liquids? Its dependence on the increase of free volume. RSC Adv. 2012, 2, 10564−10574. (44) Chen, Z. J.; Huo, Y.; Cao, J.; Xu, L.; Zhang, S. Physicochemical Properties of Ether-Functionalized Ionic Liquids: Understanding Their Irregular Variations with the Ether Chain Length. Ind. Eng. Chem. Res. 2016, 55, 11589−11596. (45) Blake, D. M.; Moens, L.; Rudnicki, D.; Pilath, H. Lifetime of imidazolium salts at elevated temperatures. J. Sol. Energy Eng. 2005, 128, 54−57. (46) Gonfa, G.; Bustam, M. A.; Muhammad, N.; Khan, A. S. Evaluation of Thermophysical Properties of Functionalized Imidazolium Thiocyanate Based Ionic Liquids. Ind. Eng. Chem. Res. 2015, 54, 12428− 12437. (47) Mousavi, M. P. S.; Dittmer, A. J.; Wilson, B. E.; Hu, J.; Stein, A.; Bühlmann, P. Unbiased Quantification of Electrochemical Stability Limits of Electrolytes and Ionic Liquids. J. Electrochem. Soc. 2015, 162, A2250−A2258. (48) Hayyan, M.; Mjalli, F. S.; Hashim, M. A.; Alnashef, I. M.; Mei, T. X. Investigating the electrochemical windows of ionic liquids. J. Ind. Eng. Chem. 2013, 19, 106−112.

(49) Gorodetsky, B.; Ramnial, T.; Branda, N. R.; Clyburne, J. A. C. Electrochemical reduction of an imidazolium cation: Convenient preparation of imidazole-2-ylidenes and their observation in an ionic liquid. Chem. Commun. 2004, 17, 1972−1973. (50) Kroon, M. C.; Buijs, W.; Peters, C. J.; Witkamp, G. J. Decomposition of ionic liquids in electrochemical processing. Green Chem. 2006, 8, 241−245. (51) Feroci, M.; Chiarotto, I.; Forte, G.; Inesi, A. An electrochemical methodology for the cyclic CO2 “catch and release”: The role of the electrogenerated N-heterocyclic carbene in BMIm-BF4. J. CO2 Util. 2013, 2, 29−34. (52) Mousavi, M. P. S.; Wilson, B. E.; Kashefolgheta, S.; Anderson, E. L.; Buhlmann, S.; He, P.; Stein, A. Ionic liquids as electrolytes for electrochemical double-layer capacitors: structures that optimize specific energy. ACS Appl. Mater. Interfaces 2016, 8, 3396−3406.

K


Syntheses and Properties of Methoxy and Nitrile ... - ACS Publications

Recommend Documents