R EFERENCES
3.2 Experiments
3.2.4. Composition Analysis
1H-nuclear magnetic resonance (NMR) spectroscopy was used for the composition anal- ysis. 1H-NMR spectrum provides the information regarding the number of different types of hydrogen atoms present in the molecule as well as the electronic environment for the different types of hydrogen. Each group of chemically equivalent hydrogen gives rise to a unique peak in the NMR spectrum. Further different groups provide different chemical shift within the NMR spectra. The number of hydrogen atoms cor- responding to each peak is identified by the integration (relative area) of the peak for each group.Thus, the area under each peak is proportional to the number of hydro- gen atoms within the peak. This is used for the determination of the composition of each component present in the mixture. In this work, 1H-NMR spectra were recorded by both 400 MHz (Varian) and 600 MHz (Bruker) NMR spectrometers. NMR spectra are recorded in solution and it is assumed that solvent protons do not interfere with the compound spectra. Therefore, deuterated solvents are used for NMR. In this work, deuterated dimethyl sulfoxide (DMSO-D6), was used.
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Chapter-3 Table 3.1.:Chemicals Source, Purification Method, Purity and Analysis Method
Sl. Chemical Purification Purity
no. Name Source Method (Mass fraction) Analysis Method
1 Acetic acid Merck, India None > 0.99 density method and1H NMRa
2 Furfural SRL Pvt. Ltd., India None > 0.99 density method and1H NMR
3 Acetol Alfa Aesar, UK None 0.95 density method and1H NMR
4 Ethyl acetate Merck, India None 0.995 density method and1H NMR
5 n-propyl acetate Alfa Aesar, UK None 0.99 density method and1H NMR
6 n-butyl acetate Alfa Aesar, UK None > 0.99 density method and1H NMR
7 Chloroform Merck, India None > 0.99 density method and1H NMR
8 [EMIM][Tf2N]b Merck, Germany Vacuum drying > 0.98 density method and1H NMR 9 [BMIM][Tf2N]c Merck, Germany Vacuum drying > 0.98 density method and1H NMR
10 DMSO-D6 Merck, Germany None 0.998 None
a1H NMR =1H Nuclear Magnetic Resonance spectroscopy
b [EMIM][Tf2N] = 1-Ethyl-3-Methylimidazolium bis (trifluoromethylsulfonyl) imide
c[BMIM][Tf2N] = 1-Butyl-3-Methylimidazolium bis (trifluoromethylsulfonyl) imide
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Chapter-3
Table 3.2.:Density(ρ) of acetic acid, acetol, furfural, ethyl acetate,n-propyl acetate, n-butyl acetate, chloroform, [EMIM][Tf2N] and [BMIM][Tf2N] as a function of temperature at atmospheric pressure (p = 0.1 Mpa)
Acetic acid Acetol
T (K) ρ(g/cm3) T (K) ρ(g/cm3)
293.15 1.04975 293.15 1.08013
298.15 1.04407 298.15 1.07492
303.15 1.03839 303.15 1.06967
308.15 1.03272 308.15 1.06431
313.15 1.02705 313.15 1.05871
Ethyl acetate 318.15 1.05313
293.15 0.90048 323.15 1.04755
298.15 0.89436 328.15 1.04201
303.15 0.88819 333.15 1.03662
308.15 0.88198 n-butyl acetate
313.15 0.87573 293.15 0.88061
n-propyl acetate 298.15 0.87545
293.15 0.88780 303.15 0.87027
298.15 0.88219 308.15 0.86508
303.15 0.87656 313.15 0.85986
308.15 0.87090 Chloroform
313.15 0.86521 293.15 1.4800
Furfural 298.15 1.4710
298.15 303.15 1.4605
313.15 313.15 1.4415
[EMIM][Tf2N] [BMIM][Tf2N]
293.15 1.5326 293.15 1.4495
298.15 1.5277 298.15 1.4447
303.15 1.5227 303.15 1.4400
308.15 1.5180 308.15 1.4352
313.15 1.5128 313.15 1.4305
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Chapter-3 A sample of 0.10 ml from each phase was collected using 1 ml syringe (needle size 0.45 x 13 mm; Hindustan Syringes & Medical devices Ltd., Faridabad, India) and mixed with 0.5 ml of NMR solvent (DMSO-d6) in NMR tube (thrift grade, Sigma Aldrich). The tube was placed on Spinix Vortex Shaker (TARSONS) for mixing the sample and NMR sol- vent. Then, tubes were placed in NMR spectrophotometer and reference peak for NMR solvent was recorded (2.5 ppm for DMSO-d6). In each NMR spectroscopy experiment, a free induction decay (fid) data file is generated. All fid files were analysed using a freeware namely, ACD/NMR Processor Academic Edition software (www.acdlabs.com) for the calculation of mole-fraction of each component in respective phase. Peaks were analyzed for the calculation of mole fraction of each component in respective phase.
1H NMR peak values for all the components studied in this work are reported in Figure 3.1. Methyl group of acetic acid showed a peak at 1.9 ppm which was considered for the quantification of acetic acid in both the phases. Peak at 5.0 ppm and 1.16 ppm was used for the quantification of acetol and ethyl acetate respectively. Peak at 0.85 ppm due to three H-atoms was used for the quantification of n-propyl acetate and n-butyl acetate. Chloroform (CHCl3) spectra has single peak at 8.26 due to single H-atom which was used for the composition estimation of chloroform. NMR spectra of furfural showed four different peaks. Peak at 8.0 ppm due to single H-atom was used for the quantification of furfural in both the phases. Peak at 9.0 ppm due to single H-atom was used for the quantification of [EMIM][Tf2N] and [BMIM][Tf2N]. The water in DMSO- d6 showed peak at 3.3-4.0 ppm.
To verify the reliability of 1H NMR spectroscopy, solutions of known compositions of IL-acetic acid-water was prepared and analyzed by 1H NMR spectroscopy. The results obtained were in good agreement with the known compositions (± 0.001 mole frac- tion). Further we have carried out the composition analysis for binary mixtures of [BMIM][Tf2N]-water at T = 298.15 K and atmospheric pressure.1H-NMR spectrum of water phase is dominated by water peak where the mole fraction of IL is 0.004 (Fig- ure 3.2). In a similar manner the mole fraction of water in IL-phase is 0.3169 (Figure 3.3). These values are tabulated in Table 3.3 and compared with existing experimental
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Chapter-3 data. The comparison clearly shows the reliability of1H-NMR determined composition.
Further the water mole fractions in both the phases were confirmed by a Karl Fisher Titrator (MetroOhm 787 KF Titrino).
Table 3.3.:Benchmarking Studies of IL-Water mixtures using1H-NMR spectroscopy at T = 298.15 K and pressure p = 0.1 Mpa
water in IL-phase
[BMIM][Tf2N] This Work 1/2 3
Mole fraction 0.3169 0.2700 (0.23-0.31) 0.2568
IL in water phase
Mole fraction 0.0004 0.0003 0.0003
1 = [Crosthwaite et al., 2004]
2 = [Chapeaux et al., 2007]
3 = [Freire et al., 2008]
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Chapter-3 Figure 3.1.:1H NMR peak values (in ppm) of chemical compounds studied in this work.
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Chapter-3 Figure 3.2.:1H NMR spectra of water rich-Phase for [BMIM][Tf2N] + WATER
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Chapter-3 Figure 3.3.:1H NMR spectra of IL rich-Phase for [BMIM][Tf2N] + WATER
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Chapter-3