Ether Functionalized Choline Tethered Amino Acid Ionic Liquids for

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Ether Functionalized Choline Tethered Amino Acid Ionic Liquids for Enhanced CO2 Capture Shubhankar Bhattacharyya, and Faiz Ullah Shah ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/ acssuschemeng.6b00824 • Publication Date (Web): 29 Aug 2016 Downloaded from http://pubs.acs.org on August 31, 2016

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ACS Sustainable Chemistry & Engineering

Ether Functionalized Choline Tethered Amino Acid Ionic Liquids for Enhanced CO2 Capture

Shubhankar Bhattacharyya* and Faiz Ullah Shah* Chemistry of Interfaces Lulea University of Technology SBN, Lulea-97187, Sweden E-mail: [email protected]; [email protected]

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Abstract

Amino acid ionic liquids (ILs) are the most interesting and effective for CO2 capture due to their low toxicity, biodegradability and fast reactivity towards CO2. Ionic nature of amino acid ILs can raise an environmental issue if the cation counterpart becomes toxic to the aquatic ecosystems and can become potential atmospheric pollutant. In this regard, choline based ILs are known to be promising scaffolds for the development of less toxic amino acid ILs. However, the existing choline amino acid ILs are highly viscous limiting their applicability as solvents. Ether functionalized choline based amino acid ILs with novel series of less toxic green ILs were explored with reduced viscosity and high CO2 capture capacity. A simple, economic, clean and environmentally benign method was utilized for the synthesis of novel choline based amino acid ILs using a commercially available and economical starting material 2-(dimethylamino)ethanol (deanol, a human dietary food supplement). These ILs have low viscosity with high CO2 capture capacity (1.62 mol of CO2 /mol of IL, 4.31 mol of CO2/kg of IL, 19.02 wt.% of CO2). Mechanism of [N1,1,6,2O4][Lys]+CO2 reaction and adduct structure was proposed by using DFT calculations, and IR and NMR spectroscopic techniques.

Keywords: Bio-ionic liquids, Carbon storage, Lysine, Carbamate, Deanol, Etherification, Carbon capture

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Introduction The success of CO2 Capture and Storage (CCS) technology has allowed researchers to continue exploring strategies for limiting CO2 emissions and thus to improve sustainability of the use of coal in power generation. The development of efficient and green CO2 sorbents has become one of the most challenging facets in current science. In the recent years ionic liquids (ILs) appeared to be excellent replacements for the conventional amine solutions that are widely used in postcombustion CO2 capture from flue gas.[1-5] The unique properties of ILs such as high thermal stability, low vapour pressure, wide liquid range and structural functionality makes them highly versatile and tunable sorbents for CO2 capture from power plant flue gases. However, development of novel, effective ILs with reduced toxicity still remains a challenge and can fall under the banner of Green Chemistry.[6]

Recently, amino acid based ILs have been attracted to chemists for their low toxicity and high reactivity towards CO2.[7-16] Amino acid based ILs comprise amino acids as anions in combination with various cations, such as phosphonium, imidazolium, choline, cyclic and acyclic quaternary ammonium cations. However, it has been found that most of the ILs have very low vapour pressure due to which they can become potential atmospheric pollutants.[17-19] Furthermore, their hydrophilic as well as ionic nature makes most of them highly soluble in water, can also raise an environmental issue in case they become toxic to the organisms inhabiting aquatic ecosystems. Nevertheless, recently toxicological and biodegradability studies of the choline based ILs have reported

[20-22]

but no such reports have been established for other

cations. Yang et al. have recently reported new insights into CO2 absorption mechanism of amino

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acid ILs with [P6,6,6,14] cation but there are very few reports that explore new cations in the ILs field.[16] Therefore, ILs containing choline based cations as scaffold of biorenewable materials can shed some light in the identification of less toxic and more promising ILs for optimal CO2 capture in the field of green technology. However, development of choline based ILs with high CO2 capture capacity and low viscosity is a challenging task. There are few published reports about choline based amino acid ILs,[23-26] however, to the best of our knowledge there is no publication that explores functionalization of choline cation in combination with amino acid anion.

In this work, we report on a series of structurally diverse novel ILs containing choline based ether as well as non-ether functionalized cations with various amino acid anions for effective CO2 capture performance. The synthesized ILs can be easily accessed using 2-(dimethylamino)ethanol as the starting material, which is commercially available in a bargain price. Additionally, 2(dimethylamino)ethanol, commercially known as deanol has also been used as human dietary food supplement.[27-28] Keeping in mind the greener character of this compound, it was further functionalized for the preparation of new ILs. The CO2 capture capacity of these ILs was measured at atmospheric pressure and variable temperature. Detailed DFT calculations, IR and NMR spectroscopic characterization were performed to understand the mechanism of CO2 absorption mechanism of these ionic liquids.

Results and Discussion Our approach intended towards choline based amino acid ILs, we started the reaction with deanol 1 and alkyl bromide at 50-60 °C under solventless condition (Scheme 1). Progress of the reaction

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was monitored by TLC with MeOH: CHCl3 (9:1) as the mobile phase. Rate of alkylation of deanol depends upon the size of the alkyl bromide as well as the reaction temperature. It was observed that high reaction temperature increase contamination in the products due to slow decomposition of alkyl bromides. Further removal of impurities required use of toxic solvents accompanied by loss of product in waste solvent, thus, making the synthetic protocol against environmentally benign. Therefore, 50-60 °C was found to be the optimum reaction temperature for the quaternization of deanol. The higher alkyl bromides (>C-7) required longer reaction time (>5 h) in contrast to the lower alkyl bromide (200 cP at the same temperature[7]. At 60 °C, the viscosity was slightly high (583 cP) with CO2 capture capacity 0.90 mol of CO2 per mol of IL which increased to 1.2 mol at 40 °C. This could be due to the desorption occurring at high temperature. Figure 1, also revealed that temperature has strong influence on CO2 capture capacity of [N1,1,6,2O4][Lys]. At 20 °C, IL showed very fast CO2 capture kinetics compared to higher temperature. It absorbed 0.93 mol within first 10 minutes at 20 °C whereas the CO2 capture capacity was 0.73 and 0.62 mol at 40 °C and 60 °C respectively. However, the absorption slowed down later due to the increased viscosity of the reaction mixture with time. The high viscosity of reaction mixture would resist further diffusion of CO2 into ILs. Thus, IL [N1,1,6,2O4][Lys] absorbed 1.62 mol of CO2/mol of ILs (19.02 wt.% of CO2) and achieved equilibrium after 200 minutes at 20 °C. It is also found that IL [P6,6,6,14][Lys] and [N6,6,6,14][Lys] took 48 hours and 24 hours respectively to reached equilibrium condition. Whereas in the case of [N1,1,6,2O4][Lys] it took ~3.5 hrs. This is probably due to larger cation can shielded lysine anion more efficiently than smaller anion. Thus with smaller cation, CO2 can approach more efficiently to amino groups of lysine anion and as a result equilibrium condition can achieved easily. To explore more, we measured the viscosity parameter of structurally diverse choline based ILs (Figure 2). The viscosity increased rapidly with increasing alkyl chain length on N atom. At 40 ° C, viscosity of [N1,1,10,2OH][Threo] is 7478 cP whereas [N1,1,4,2OH][Threo] is 3621 cP and it goes further down to 1133 cP for [N1,1,4,2O4][Threo] on etherification.

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The density measurement also showed decrease in density of lysine based ILs upon ether functionalization (density of [N1,1,6,2OH][Lys] at 20 °C is 1.0023 gm/ml). Furthermore, the density of ILs decreased with increase in temperature and alkyl chain length on N atom as shown in SI (SI, S6). To get a deeper insight into the mechanism of the CO2 interaction with ILs, NMR spectroscopy was employed to monitor the reaction of [N1,1,6,2OH][Lys] with CO2. 1H and

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C NMR spectra

were recorded in D2O prior as well as after CO2 capture experiment at 20 °C (Figure 3 & 5). In the 1H NMR, methylene protons (H2N-CH2-) attached to terminal -NH2 group shifted from 2.79 ppm to 2.99 ppm after CO2 capture. The α-proton signal shifted from 3.25 ppm to 3.52 – 3.58 ppm region after carbamic acid formation (Figure 3). The peak position of α-proton after CO2 capture was located on the basis of 1H-1H COSY NMR experiment. Before CO2 capture, the triplet of methylene proton (H2N-CH2-) at 2.79 ppm and α-proton at 3.25 ppm of [N1,1,6,2OH][Lys] coupled with aliphatic multiplets at 1.52 – 1.63 ppm (Figure 4). However, the methylene proton (H2N-CH2-) shifted to 2.99 ppm and coupled with multiplets at 1.69 ppm after CO2 capture. But the α-proton merged in the region of 3.52-3.58 ppm showing correlation with multiplets at 1.76 ppm. This new correlation also confirmed the peak assignment of α-proton of [N1,1,6,2O4][Lys] after CO2 absorption (Figure 4). The

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C NMR showed the carboxylate carbon of amino acid at 183.32 ppm which is shifted to

181.20 ppm after CO2 capture because of strong intramolecular hydrogen bonding of carboxylate oxygen anion and H-N- proton of carbamic acid. Appearance of an additional peak at 178.0 ppm could be due to intermolecular hydrogen bonding of carboxylate anion. Further, two additional carbonyl signals at 160.89 ppm and 163.71 ppm observed after CO2 capture implies formation of

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carbamic acid and carbamate anion respectively (Figure 5). Further in the aliphatic region carbon peak assignment was difficult due to little differences in chemical shifts. The alpha carbon shows signal at 55.75 ppm, which is further shifted to 56.31 ppm and 54.87 ppm. This is most probably due to formation of carbamate as well as carbamic acid to the adjacent amino group. In the same way terminal methylene carbon (H2N-CH2-) is also shifted from 39.80 to 39.93 and 39.03 ppm. It could be due to formation for carbamate and ammonium species to adjacent amino group. The present NMR data also shows good agreement with previously published data on CO2 capture by amino acid ILs.[10] Noticeably, the data also indicates the formation of [N1,1,6,2O4][Anion]-CO2 adduct (Figure 6). To understand more mechanistic insight of the reaction, infrared spectroscopy was used to investigate any structural change in [N1,1,6,2OH][Lys] before and after CO2 capture at 20 °C (SI, S4). The lysine anion showed strong band at 1579 cm-1 due to carboxylate carbonyl and due to – NH2 at 3280 cm-1. However, after CO2 capture, the primary amine band at 3280 cm-1 disappeared and carboxyl band shifted to 1569 cm-1. Additionally, one more band appeared at 1632 cm-1 due to formation of different hydrogen bonded carboxyl acid species. Current IR data also suggested formation of ILs-CO2 adduct as reported earlier.[7] The thermogravimetric analysis (TGA) of [N1,1,6,2O4][Lys] implies lower thermal degradation (~170 °C) as compared to [N1,1,4,2OH][Threo] which has ~190 °C (SI, S3). This is may be due to the less stable flexible amine side chain contain lysine anion. In order to improve CO2 capture capacity of ILs and develop a simple, nontoxic, selective ILs for optimum CO2 capture, it is necessary to understand the total course of the reaction of ionic liquid with CO2 thoroughly. For this purpose, computational chemistry techniques have been

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demonstrated to be an adequate complementary tool to explain, guide and design the optimum ILs for CO2 capture. In the current study, we have adopted Density functional theory (DFT) method using B3LYP functional together with the 6-31+G (d,p) basis set using Gaussian 09 programme.[37] Optimization were performed for the reactants, transition states, intermediates and products of [N1,1,6,2O4][Lys] and CO2 reaction. However, solvent model and cations are not included in the current calculations as solvent properties and diffraction data are not available for ILs structure. All the transition states have been confirmed by the presence of one imaginary frequency. Reactants, intermediates and products are confirmed as stationary points by the presence of all real frequency. Each transition state (TS) has been confirmed by Intrinsic reaction coordinate (IRC) calculation by connecting the corresponding product and reactants in the respective potential energy surface. Lysine has two –NH2 groups one is alpha and another is terminal. The DFT studies show slightly different reactivity of these two –NH2 groups at room temperature. The reaction of lysine anion and CO2 can proceeds via two way, either first carbamate formation at α-NH2 followed by terminal –NH2 group (Path A) or vice-versa (Path B) (Figure 7). But, strong hydrogen bond formation between oxygen atom of carboxylate anion and N-H of carbamic acid in the first transition state (TS-A1) and in the corresponding product (IM-A2) is the key parameter for faster reactivity of alpha –NH2 group rather than the terminal one (Figure 8). It can be easily observed that the hydrogen bond becomes stronger in transition state TS-A1 (OƟ….H-Nα is 1.90Å) rather than carbamic acid IM-A2 (OƟ….H-Nα is 1.96Å).

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Apart from the hydrogen bond involvement, oxygen atom of carboxylate anion acts as a Lewis base towards –NH2 proton and increases the charge density on nitrogen atom of TS-A1 (charge density of α-N atom -0.632) rather than nitrogen atom of TS-B1 (charge density of terminal N atom -0.614). Though, the first transition states of both the path (TS-A1 & TS-B1) differ by 5.5 Kcal/mol only (Figure 7) which is very low for room temperature reactions. Thus, due to negligible differences in ∆G# value, both the paths (Path A & Path B) are equally probable at room temperature. The DFT calculations also suggested that stability of the product formed after CO2 capture, can be achieved by strong hydrogen bonding between oxygen atom of carboxylate anion and -N-H of carbamic acid (Figure 8). Further, DFT calculation also complies with reported adduct structure of lysine anion with CO2 molecule. It was also found that two amino groups shows different reactivity in lysine anion. Theoretically, the IL:CO2 ratio in the case of [N1,1,6,2O4][Lys]+CO2 system should be 1:2 at 20°C temperature. However, we found experimentally that IL:CO2 ratio is 1:1.6 (~1.5). From DFT studies we observed that reactivity of two amino groups is not same. Alpha amino group has faster reactivity than the terminal amino group. It could be noted that in [N1,1,6,2O4][Lys]+CO2 adduct structure, all the alpha amino group is carboxylated whereas the terminal amino group is partially carboxylated. Thus ionic liquid [N1,1,6,2O4][Lys] shows 1: 1.5 IL: CO2 ratio at 20 °C temperature.

Conclusions Ether functionalized choline based amino acid ILs were explored to accomplish less toxic and low viscous ionic liquids with high CO2 capture capacity. In this work, eighteen new structurally diverse choline based amino acid ILs are reported. The reported ILs could be easily synthesized

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from commercially available starting material 2-(dimethylamino) ethanol, which is also commercially known as deanol, a human dietary food supplement. In addition to this, all ionic liquids are prepared without using any toxic solvents and further prepared choline based cations that comparatively more greener than earlier reported cations. The 1H NMR data clearly showed purity of ILs and cation-anion in 1:1 ratio. Ether functionalization drastically reduced the viscosity as well as density of the resulting ILs. Amongst all the synthesized ILs, [N1,1,6,2O4][Lys] exhibited highest CO2 capture capacity, up to 1.62 mol of CO2 per mol of IL (4.31 mol of CO2 per kg of IL, 19.02 wt.% of CO2). Further, mechanistic studies of carbamate formation were proposed using NMR & IR spectroscopic technique. Density functional theory (DFT) studies have also been incorporated to understand complete course of the carbamate formation reaction at molecular level. The future of the choline based ILs is highly promising and paradigm of new door of research field on “natural-ILs” or “bio-ILs” in comparison to the conventional tetraalkyl phosphonium and ammonium cation.

Experimental Section General Reagents were obtained from commercial supplier, and used without further purification. TLC analysis was done using silica gel 60 Å F-254 thin layer plates with KMnO4 charing solution. 1H and

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C NMR spectra were recorded on a Bruker Ascend Aeon WB 400 spectrometer. Spectra

were run at 25 °C using standard Bruker pulse programs. Chemical shifts were expressed in parts per millions (δ) downfield from tetramethylsilane with the solvent resonance as the internal standard (D2O, δ = 4.79 and CDCl3, δ = 7.26) and were reported as s (singlet), d (doublet), t

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(triplet), q (quartet), br (broad) and m (multiplet). All coupling constants (J) are reported in Hertz (Hz). Mass spectra were obtained using Waters QTOF XEVO-G2 High Resolution Mass Spectrometer with positive as well as negative ESI mode. Infrared spectra were recorded on a Bruker Vertex 80v FTIR spectrometer equipped with a Zincselenide crystal as ATR accessory. The thermogravimetric analysis of ionic liquids was measured by Netzsch STA 409 instrument from 20 °C to 550 °C with a heating ramp 10 °C/min under nitrogen atmosphere.

Density Measurements An Anton-Paar DMA 4100M density meter was used to measure densities of choline based ILs in a temperature range from 20 °C to 80 °C. The density meter was calibrated before the measurements using ultra high pure water with a density of 0.998 g cm3 at 20 °C. Before measuring density all the samples were dried under vacuum at 60 °C for 2 days.

Viscosity Measurements Viscosity was measured with Lovis 2000 ME Automated Microviscometer (Anton-Paar falling ball type viscometer with 2.50 mm glass capillary, viscosity range 10-10000 cP) in a temperature range from 20 °C to 80 °C using a sealed sample tube. Before measuring viscosity all the samples were dried under vacuum at 60 °C for 2 days.

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CO2 Absorption Measurements CO2 absorption experiments were performed using 0.7 -1 g of neat choline based amino acids ILs in a 5 ml closed test tube and CO2 gas (99.9 %) was purged through the liquid with 2.1 x 80 mm size needle at temperatures 20 °C, 40 °C and 60 °C under atmospheric pressure with ocational stirring. The CO2 absorption capacity of the ILs was measured with Mettler Toledo gravimetric balance (0.1 mg accuracy) by weighing the test tube periodically during the CO2 absorption capacity experiments.[7, 38, 39] General method of preparation for choline base amino acid ILs (4a -4m) Deanol (1 equivalent) and alkyl bromide (1.2 equivalent) were stirred for 3-5 hours at 50-60 °C under nitrogen atmosphere. Progress of the reaction was monitored by TLC with MeOH: CHCl3 (1:1) as the mobile phase. After completion of the reaction, a solid mass was obtained and further evaporation of unreacted alkyl bromide under rotary evaporator afforded quaternary bromide salt of deanol. Next, the bromide salt was dissolved in water and stirred overnight with prewashed Amberlite IRN-78 (basic) resin. Further, on passing the aqueous solution through Amberlite IRN78 (basic) resin column gave quaternary ammonium hydroxide solution. Next, the ammonium hydroxide solution was neutralized with equivalent amount amino acid and after evaporation of water gave choline based amino acid ionic liquid. The excess of unreacted amino acid was removed by adding excess of MeOH or ACN and stored over night at 0 °C.

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General method of preparation for ether functionalized choline based amino acid ILs (8a8e) Method A: deanol (1 equivalent), alkyl chloride (1.1 equivalent), Aliquat® 336 (5 mol%) and 3.5 equivalent aqueous NaOH solution (solution was prepared by dissolving 3.5 eq. NaOH in minimum volume of water) were mixed and heated for 6-7 hours at 50-60 °C. Progress of the reaction was monitored by TLC with MeOH: CHCl3 (9:1) as the mobile phase. After completion of the reaction, organic layer was extracted with dichloromethane and on evaporation of solvent gave ether functionalized amine. Further, quaternary bromide salt of ether functionalized amine was prepared by heated at 60-70 °C with alkyl bromide (1.2 equivalent) for 3-5 hours under solventless condition to get ether functionalized quaternary ammonium salt. Progress of the reaction was monitored by TLC with MeOH: CHCl3 (1:1) as the mobile phase. Next, on passing through prewashed Amberlite IRN-78 (basic) resin column gave ether functionalized quaternary ammonium hydroxide solution. Neutralization of the ammonium hydroxide solution with equivalent amount amino acid gave ether functionalized choline based amino acid ionic liquid. The excess of unreacted amino acid was removed by adding excess of MeOH or ACN and stored over night at 0 °C.

Method B: deanol (1 equivalent) and alkyl chloride (1.2 equivalent) were stirred for 7-8 hours at 50-60 °C under nitrogen atmosphere. Progress of the reaction was monitored by TLC with MeOH: CHCl3 (1:1) as the mobile phase. After completion of the reaction, a solid mass was obtained and further evaporation of unreacted alkyl chloride under rotary evaporator afforded quaternary chloride salt of deanol as a waxy solid. Further, quaternary chloride salt was heated at

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60-70 °C with 3.5 equivalent of aqueous NaOH solution (solution was prepared by dissolving 3.5 eq. NaOH in minimum volume of water) and alkyl chloride (1.5 equivalent) for 4-6 hrs to get ether functionalized quaternary ammonium salt. Next, on passing through prewashed Amberlite IRN-78 (basic) resin column gave ether functionalized quaternary ammonium hydroxide solution. Neutralization of the ammonium hydroxide solution with equivalent amount amino acid gave ether functionalized choline based amino acid ionic liquid. The excess of unreacted amino acid and salts were removed by adding excess of MeOH or ACN and stored over night at 0 °C.

Spectroscopic Characterization data [N1,1,4,2OH][Threo] (4a): colourless oil; yield 96%; 1H NMR (400 MHz, D2O): δ 0.95 (t, 3H, J= 7.4Hz), 1.20 (d, 3H, J= 6.8Hz), 1.34-1.43 (m, 2H), 1.72-1.80 (m, 2H), 3.10 (d, 1H, J=8Hz), 3.13 (s, 6H), 3.35-3.39 (m, 2H), 3.47-3.49 (m, 2H), 3.91-3.98 (m, 1H), 4.02-4.06 (m, 2H); 13C NMR (100.6 MHz, D2O) δ 180.57, 69.45, 65.28, 64.80, 61.88, 55.31, 51.32, 51.28, 51.24, 23.90, 19.07, 19.03, 12.74; HRMS (ESI) m/z: calcd for [C8H20NO]+ 146.1545; found 146.1545, calcd for [C4H8NO3]- 118.0504; found 118.0505. [N1,1,5,2OH][Threo] (4b): colourless oil; yield 94%; 1H NMR (400 MHz, D2O): δ 0.90 (t, 3H, J= 7.2Hz), 1.20 (d, 3H, J=6.4Hz), 1.33-1.38 (m, 4H), 1.74-1.82 (m, 2H), 3.09-3.10 (d, 1H) 3.12 (s, 6H), 3.35-3.38 (m, 2H), 3.46-3.49 (m, 2H), 3.91-3.97 (m, 1H), 4.01-4.04 (m, 2H);

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C NMR

(100.6 MHz, D2O) δ 180.57, 69.45, 65.46, 64.78, 61.88, 55.31, 51.31, 51.27, 51.23, 27.60, 21.57, 21.45, 19.08, 12.99; HRMS (ESI) m/z: calcd for [C9H22NO]+ 160.1701; found 160.1705, calcd for [C4H8NO3]- 118.0504; found 118.0504.

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[N1,1,5,2OH][Ser] (4c): colourless oil; yield 95%; 1H NMR (400 MHz, D2O): δ 0.90 (t, 3H, J= 7.2Hz), 1.32-1.38 (m, 4H), 1.74-1.82 (m, 2H), 3.12 (s, 6H), 3.34-3.38 (m, 3H), 3.46-3.49 (m, 2H), 3.67-3.77 (m, 2H), 4.01-4.05 (m, 2H); 13C NMR (100.6 MHz, D2O) δ 180.12, 65.46, 64.79, 64.49, 57.47, 55.31, 51.31, 51.27, 51.24, 27.60, 21.57, 21.45, 13.00; HRMS (ESI) m/z: calcd for [C9H22NO]+ 160.1701; found 160.1705, calcd for [C3H6NO3]- 104.0348; found 104.0347. [N1,1,6,2OH][Ser] (4d): colourless oil; yield 93%; 1H NMR (400 MHz, D2O): δ 0.87 (t, 3H, J= 7.2Hz), 1.30-1.36 (m, 6H), 1.73-1.79 (m, 2H), 3.12 (s, 6H), 3.33-3.38 (m, 3H), 3.46-3.48 (m, 2H), 3.67-3.78 (m,2H), 4.01-4.03 (m, 2H); 13C NMR (100.6 MHz, D2O) δ 179.89, 65.47, 64.77, 64.36, 57.44, 55.30, 51.31, 51.27, 51.24, 30.36, 25.08, 21.80, 21.65, 13.16; HRMS (ESI) m/z: calcd for [C10H24NO]+

174.1858; found 174.1856, calcd for [C3H6NO3]- 104.0348; found

104.0347. [N1,1,7,2OH][Threo] (4e): colourless viscous oil; yield 94%; 1H NMR (400 MHz, D2O): δ 0.87 (t, 3H, J= 7.2Hz), 1.20-1.21 (d, 3H, J=6.4Hz), 1.29-1.37 (m, 8H), 1.76-1.80 (m, 2H), 3.09-3.13 (m, 7H), 3.34-3.39 (m, 2H), 3.47-3.49 (m, 2H), 3.90-3.98 (m,1H), 4.02-4.05 (m, 2H);

13

C NMR

(100.6 MHz, D2O) δ 180.43, 69.39, 65.49, 64.78, 61.85, 55.33, 51.33, 51.30, 51.26, 30.72, 27.78, 25.37, 21.85, 21.83, 19.09, 13.31; HRMS (ESI) m/z: calcd for [C11H26NO]+ 188.2014; found 188.2014, calcd for [C4H8NO3]- 118.0504; found 118.0502. [N1,1,7,2OH][Ser] (4f): colourless viscous oil; yield 96%; 1H NMR (400 MHz, D2O): δ 0.87 (t, 3H, J= 7.2Hz), 1.29-1.37 (m, 8H), 1.76-1.80 (m, 2H), 3.12 (s, 6H), 3.34-3.39 (m, 3H), 3.47-3.49 (m, 2H), 3.70-3.79 (m,2H), 4.03 (br s, 2H);

13

C NMR (100.6 MHz, D2O) δ 179.71, 65.48, 64.77,

64.24, 57.41, 55.32, 51.32, 51.28, 51.25, 30.71, 27.78, 25.36, 21.84, 21.82, 13.29; HRMS (ESI)

18


Page 19 of 41

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m/z: calcd for [C11H26NO]+ 188.2014; found 188.2013, calcd for [C3H6NO3]- 104.0348; found 104.0346. [N1,1,10,2OH][Threo] (4g): colourless viscous oil; yield 95%; 1H NMR (400 MHz, D2O): δ 0.88 (t, 3H, J= 6.4Hz), 1.19-1.21 (d, 3H, J=6.4Hz), 1.29-1.36 (m, 14H), 1.75-1.79 (m, 2H), 3.09-3.13 (m, 7H), 3.34-3.39 (m, 2H), 3.47-3.49 (m, 2H), 3.91-3.97 (m, 1H), 4.02-4.04 (m, 2H);

13

C NMR

(100.6 MHz, D2O) δ 180.43, 69.41, 65.35, 64.87, 61.85, 55.33, 51.36, 31.41, 28.88, 28.77, 28.74, 28.40, 25.64, 22.24, 22.01, 19.11, 13.60; HRMS (ESI) m/z: calcd for [C14H32NO]+ 230.2484; found 230.2485, calcd for [C4H8NO3]- 118.0504; found 118.0504. [N1,1,14,2OH][Threo] (4h): Solid; yield 91%; 1H NMR (400 MHz, D2O): δ 0.78 (t, 3H, J= 6.8Hz), 1.14-1.25 (br m, 25H), 1.67 (m, 2H), 3.06 (s, 7H), 3.23 (s, 1H), 3.28-3.32 (m, 2H), 3.39-3.42 (m, 2H), 3.91-3.93 (m, 2H); 13C NMR (100.6 MHz, D2O) δ 181.41, 69.59, 65.12, 65.04, 61.52, 55.41, 51.52, 31.91, 29.82, 29.73, 29.63, 29.49, 29.41, 29.02, 26.10, 22.59, 22.37, 13.84; HRMS (ESI) m/z: calcd for [C18H40NO]+ 286.3110; found 286.3105, calcd for [C4H8NO3]- 118.0504; found 118.0503. [N1,1,6,2OH][Lys] (4i): Solid; yield 93%; 1H NMR (400 MHz, D2O): δ 0.81 (t, 3H, J=7.2Hz), 1.10-1.31 (m, 10H), 1.69-1.73 (m, 2H), 2.74-2.94 (m, 2H), 3.06 (s, 6H), 3.28-3.32 (m, 2H), 3.403.43 (m, 3H), 3.56-3.61 (m,2H), 3.97 (br s, 2H);

13

C NMR (100.6 MHz, D2O) δ 181.44, 65.47,

64.76, 57.40, 55.96, 55.30, 51.26, 51.23, 31.57, 30.36, 25.07, 21.79, 21.64, 16.76, 13.13; HRMS (ESI) m/z: calcd for [C10H24NO]+ 174.1858; found 174.1855, calcd for [C6H13N2O2]- 145.0977; found 145.0976. [N1,1,5,2OH][Ala] (4j): colourless oil; yield 91%; 1H NMR (400 MHz, D2O): δ 0.89 (t, 3H, J= 7.2Hz), 1.23 (d, 3H, J= 7.2Hz), 1.32-1.38 (m, 4H), 1.74-1.82 (m, 2H), 3.12 (s, 6H), 3.33-3.38 (m,

19



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Page 20 of 41

3H), 3.46-3.49 (m, 2H), 4.02-4.04 (m, 2H), 13C NMR (100.6 MHz, D2O) δ 183.69, 65.46, 64.78, 55.31, 51.32, 51.27, 51.23, 27.59, 21.56, 21.45, 19.92, 12.99; HRMS (ESI) m/z: calcd for [C9H22NO]+ 160.1701; found 160.1703, calcd for [C3H6NO2]- 88.0399; found 88.0398. [N1,1,6,2OH][Tau] (4k): colourless oil; yield 95%; 1H NMR (400 MHz, D2O): δ 0.88 (t, 3H, J= 7.2Hz), 1.31-1.37 (m, 6H), 1.74-1.82 (m, 2H), 3.02-3.04 (m, 4H), 3.13 (s, 6H), 3.35-3.39 (m, 2H), 3.47-3.50 (m, 2H), 4.03-4.04 (m, 2H);

13

C NMR (100.6 MHz, D2O) δ 65.49, 64.78, 55.32,

53.02, 51.32, 51.28, 51.25, 36.46, 30.37, 25.09, 21.81, 21.66, 13.16; HRMS (ESI) m/z: calcd for [C10H24NO]+ 174.1858; found 174.1859, calcd for [C2H6NO3S]- 124.0068; found 124.0070. [N1,1,6,2OH][β-Ala] (4l): colourless viscous oil; yield 90%; 1H NMR (400 MHz, D2O): δ 0.87 (t, 3H, J= 7.2Hz), 1.30-1.36 (m, 6H), 1.73-1.81 (m, 2H), 2.35 (t, 2H, J= 6.4Hz), 2.85 (t, 2H, J= 6.4Hz), 3.13 (s, 6H), 3.34-3.38 (m, 2H), 3.46-3.49 (m, 2H), 4.02-4.04 (m, 2H); 13C NMR (100.6 MHz, D2O) δ 181.16, 65.47, 64.77, 55.30, 51.26, 39.47, 37.68, 30.36, 25.07, 21.80, 21.65, 13.13; HRMS (ESI) m/z: calcd for [C10H24NO]+ 174.1858; found 174.1859, calcd for [C3H6NO2]88.0399; found 88.0399. [N1,1,7,2OH][4-Am-CO2] (4m): colourless viscous solid; yield 90%; 1H NMR (400 MHz, D2O): δ 0.87 (t, 3H, J= 7.2Hz), 1.29-1.37 (m, 8H), 1.72-1.80 (m, 4H), 2.22 (t, 2H, J= 7.4Hz), 2.70 (t, 2H, J= 7.4Hz), 3.13 (s, 6H), 3.34-3.39 (m, 2H), 3.47-3.49 (m, 2H), 4.02-4.04 (m, 2H);

13

C NMR

(100.6 MHz, D2O) δ 182.87, 65.49, 64.78, 55.32, 51.33, 51.29, 51.26, 40.17, 34.93, 30.71, 27.78, 27.51, 25.36, 21.85, 21.82, 13.30; HRMS (ESI) m/z: calcd for [C11H26NO]+ 188.2014; found 188.2015, calcd for [C4H8NO2]- 102.0555; found 102.0554. [N1,1,4,2O4][Threo] (8a): colourless oil; yield 81%; 1H NMR (400 MHz, D2O): δ 0.90 (t, 3H, J= 7.2Hz), 0.95 (t, 3H, J= 7.2Hz), 1.20 (d, 3H, J= 6.4Hz), 1.32-1.40 (m, 4H), 1.56-1.59 (m, 2H),

20


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1.73-1.77 (m, 2H), 3.11-3.12 (m, 7H), 3.33-3.38 (m, 2H), 3.53-3.59 (m, 4H), 3.91-3.97 (m, 3H), 13

C NMR (100.6 MHz, D2O) δ 180.17, 71.03, 69.26, 65.24, 63.78, 62.81, 61.80, 51.30, 30.68,

23.94, 19.09, 19.05, 18.72, 13.03, 12.76; HRMS (ESI) m/z: calcd for [C12H28NO]+ 202.2171; found 202.2176, calcd for [C4H8NO3]- 118.0504; found 118.0505. [N1,1,4,2O4][Lys] (8b): colourless viscous solid; yield 80%; 1H NMR (400 MHz, D2O): δ 0.880.97 (m, 6H), 1.32-1.40 (m, 6H), 1.49-1.62 (m, 6H), 1.73-1.75 (m, 2H), 2.75 (t, 2H, J= 7.2Hz), 3.11 (s, 6H), 3.24 (t, 1H, J=6.4Hz), 3.33-3.38 (m, 2H), 3.53-3.59 (m, 4H), 3.90-3.92 (m, 2H); 13C NMR (100.6 MHz, D2O) δ 183.32, 71.03, 65.24, 63.78, 62.81, 55.80, 51.30, 39.92, 34.10, 30.68, 29.73, 23.94, 22.16, 19.05, 18.72, 13.03, 12.75; HRMS (ESI) m/z: calcd for [C12H28NO]+ 202.2171; found 202.2172, calcd for [C6H13N2O2]- 145.0977; found 145.0979. [N1,1,6,2O4][Lys] (8c): colourless oil; yield 81%; 1H NMR (400 MHz, D2O): δ 0.86-0.92 (m, 6H), 1.30-1.39 (m, 10H), 1.52-1.65 (m, 6H), 1.74-1.78 (m, 2H), 2.79 (t, 2H, J= 7.2Hz), 3.11 (s, 6H), 3.25 (t, 1H, J=6.4Hz), 3.33-3.37 (m, 2H), 3.53-3.58 (m, 4H), 3.91 (br s, 2H);

13

C NMR (100.6

MHz, D2O) δ 183.14, 71.04, 65.39, 63.81, 62.75, 55.75, 51.32, 39.80, 33.98, 30.70, 30.41, 29.18, 25.12, 22.11, 21.86, 21.69, 18.74, 13.17, 13.04; HRMS (ESI) m/z: calcd for [C14H32NO]+ 230.2484; found 230.2482, calcd for [C6H13N2O2]- 145.0977; found 145.0977. [N1,1,6,2O12][Lys] (8d): colourless viscous oil; yield 83%; 1H NMR (400 MHz, D2O): δ 0.86-0.95 (m, 6H), 1.29-1.36 (m, 27H), 1.46-1.80 (m, 7H), 2.69 (t, 1H, J= 7.2Hz), 3.10-3.15 (m, 5H), 3.22 3.39(m, 3H), 3.49-3.59 (m, 3H), 3.88-3.89 (br m,1H);

13

C NMR (100.6 MHz, D2O) δ 183.40,

71.14, 64.44, 62.32, 61.48, 55.87, 52.03, 40.11, 34.29, 32.01, 31.97, 31.11, 30.03, 29.96, 29.88, 29.85, 29.57, 29.47, 26.47, 25.78, 22.61, 22.40, 22.34, 22.26, 13.80, 13.74; HRMS (ESI) m/z:

21



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Page 22 of 41

calcd for [C22H48NO]+ 342.3736; found 342.3731, calcd for [C6H13N2O2]- 145.0977; found 145.0977. [N1,1,14,2O12][Lys] (8e): white solid; yield 82%; 1H NMR (400 MHz, CDCl3): δ 0.85-0.88 (m, 6H), 1.24-1.72 (br m, 52H), 2.65-2.68 (m, 1H), 3.18 (d, 1H, J=7.6Hz), 3.32 -3.47 (m, 9H), 3.86 (br s, 2H), 3.98-4.00 (br m,2H);

13

C NMR (100.6 MHz, CDCl3) δ 181.31, 71.96, 66.17, 65.13,

63.22, 62.95, 57.36, 51.77, 45.69, 42.22, 36.50, 34.24, 32.95, 32.05, 29.80, 29.78, 29.75, 29.65, 29.62, 29.55, 29.49, 29.34, 26.48, 26.38, 25.93, 24.02, 23.00, 22.82, 14.25; HRMS (ESI) m/z: calcd for [C30H64NO]+ 454.4988; found 454.4982, calcd for [C6H13N2O2]- 145.0977; found 145.0977.

Associated Content Supporting Information 1

H and

13

C NMR spectra of all the synthesized ionic liquids, TGA curves of selected ionic

liquids, weight % of CO2 absorption kinetics, density as a function of temperature for

selected ionic liquids, FTIR spectra before and after CO2 capture and computational data. This material is available free of charge via the Internet at http://pubs.acs.org.

Acknowledgements The Norrbotten Research Council (NoFo) and the Swedish Research Council are gratefully acknowledged for the financial support of this project.

22


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imidazolium-based

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Scheme 1

R N

OH

1

H2 C Br

R1

IRN-78

N

solventless

R CH2 OH 3

2

R1

HO2C

N

H2O

OH

Br

50-60 °C

1

Amberlite R1

CH2

OH

NH2

O

CH2 N

R

OH O

H2O

NH2

4

Deanol Scheme 1: Synthesis of choline based amino acid ionic liquids from deanol

Scheme 2

N

OH 1

Deanol

R2 H2 CH2 R2 C Cl N solventless 50-60 °C

Cl 5

R2 R3 Cl , H2O OH

NaOH (3.5 eq)

R2

CH2 R IRN-78 3

N

O

R CH2 N

Cl

OH

6

7

O

R3

HO2C H2O

Scheme 2: Synthesis of ether functionalized amino acid ionic liquids from deanol

29


R2 NH2

CH2 N

O

O

R

O

NH2

R3 8


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Page 30 of 41

Table 1: Structure and abbreviation of prepared ionic liquids

HO

HO (H2C)2

O

OH

(H2C)3 N

N

OH

4a

O

NH2 4b

[N1,1,4,2OH][Threo]

O

OH

(H2C)3

O

OH

NH2

[N1,1,5,2OH][Threo]

4c

O

OH

4d

O

N

4f

O OH

(H2C)8 N

O

NH2 4g

[N1,1,7,2OH][Ser] O

(H2C)4

O

N 4k

OH

N NH2

O

4l

[N1,1,6,2OH][Tau]

N

O O

8c

(CH2)4

C4H9 O

[N1,1,6,2O4][Lys]

O

OH

O

NH2

O OH

OH

NH2 4h

[N1,1,10,2OH][Threo]

4m

[N1,1,6,2OH][β-Ala]

NH2

OH

O

N

OH

O

NH2 (H2C)2 N

O

[N1,1,7,2OH][4-Am-CO2]

(H2C)4 N

O

8a

8d

O

(CH2)4

O

NH2

C12H25

NH2

O

OH (H2C)2 N

C4H9 O

O

NH2

[N1,1,4,2O4][Threo]

8b

NH2

Table 1: Structure and abbreviation of prepared ILs


O

(CH2)4

O

NH2

C4H9

[N1,1,4,2O4][Lys] H2N

(H2C)12 N

[N1,1,6,2O12][Lys]

30

O

[N1,1,5,2OH][Ala]

4j

[N1,1,6,2OH][Lys]

4i

[N1,1,7,2OH][Threo]

NH2

O

NH2

H2N

O OH

O

O

N

OH

O

(H2C)3

(CH2)4

O

(H2C)4


(H2C)5 N

OH

4e

H 2N

H2N

H2N (H2C)4

(H2C)12 N

(H2C)4

S

OH

O

OH

NH2

[N1,1,6,2OH][Ser]

HO (H2C)5

O

N

NH2

[N1,1,5,2OH][Ser]

(H2C)5

O

N

N

OH

(H2C)4

O

8e

O

O

(CH2)4

O

NH2

C12H25

[N1,1,14,2O12][Lys]

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Table 2. CO2 absorption capacity (in mol of CO2/mol of ILs, Wt. % in parentheses) of choline based amino acid ILs

Name of ionic liquid

20 °C

40 °C

60 °C

[N1,1,4,2OH][Threo]

1.06 (17.57)

0.53 (8.84)

0.34 (5.69)

[N1,1,7,2OH][Threo]

0.72 (10.43)

0.59 (8.53)

0.57 (8.24)


0.61 (7.72)

0.47 (5.97)

0.46 (5.89)

[N1,1,6,2OH][Tau]

0.67 (9.28)

0.60 (8.95)

0.57 (8.44)

[N1,1,6,2O4][Lys]

1.62 (19.02)

1.20 (14.12)

0.90 (10.59)

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Figure Captions

Figure 1. Time-course CO2 absorption study of choline based amino acid ILs as function of time at 20°C (green), 40°C (blue) and 60°C (red)

Figure 2. Viscosity as a function of temperature for selected Ils

Figure 3. 1H NMR study of [N1,1,6,2O4][Lys] and CO2 reaction at 20 °C. (a) before CO2 reaction (b) after 5 mins (c) after complete reaction

Figure 4. 1H-1H cosy of [N1,1,6,2O4][Lys] and CO2 reaction at 20 °C. (a) before (b) after

Figure 5.

13

C NMR study of [N1,1,6,2O4][Lys] (a) before and (b) after CO2 capture at 20 °C

Figure 6. Proposed structure of anion in [N1,1,6,2O4][Lys]+CO2 adduct at 20 °C

Figure 7. Energy profile diagrame for the reaction of lysine anion and CO2

Figure 8. DFT optimised structure of (a) TS-B1 and (b) TS-A1 and (c) product

32


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Figure 1:

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Figure 2.

34


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Figure 3.

c

b

a

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Figure 4.

(a)

(b)

36


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Figure 5.

b

a

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Figure 6. 2H

O

O

H

O

(H2C)4

O

H

O

NH

NH3

N O

O 2C

(CH2)4 O2C

(N1162O4)2

N H

38


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Figure 7.

39



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Figure 8.

(b) (a)

(c)

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TOC

Ether Functionalized Choline Tethered Amino Acid Ionic Liquids for Enhanced CO2 Capture Shubhankar Bhattacharyya, Faiz Ullah Shah Bio-renewable materials inspired environmentally benign approach for high CO2 capture

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Ether Functionalized Choline Tethered Amino Acid Ionic Liquids for

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