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2. Experimental
2.1. Chemicals and materials
25]. On the other hand, trifluroacetate anion was introduced by neutral-
ization reaction with trifluroacetic acid [26]. All structures of the synthe-
sized ILs were confirmed using 1H and 13C NMR spectroscopy.
The materials and reagents used for this experiment are as follows;
Imidazole (Sigma Aldrich, N99%), Acrylonitrile (Sigma Aldrich, N99%),
2-bromoethyl ethyl ether (Sigma Aldrich, N99%), Trifluoroacetic acid
(Sigma Aldrich, N99%), Lithium bis(trifluoromethanesulfonyl)imide
(Solvionic, N99%), Sodium dicyanamide (Sigma Aldrich, N98%), Silver
nitrate (Merck), Ethyl acetate (Merck), Dichloromethane (HPLC
grade). All the starting materials were used without further purification.
3.2. Thermal profile
Thermal stability and glass transition temperature of the ILs were
measured and the results are shown in Figs. 2 and 3.The water and halide
content of the ILs are shown in Table 1 (Supplementary information).
The water and the halide content in the ILs are below 500 ppm and
1000 ppm respectively. TGA thermogram in Fig. 1 and Table 2 (supple-
mentary info) indicates that the thermal stability of the ILs with [NTf2]
anion is higher compared with other anions. According to previous
studies, thermal stability of ILs depends mainly on the coordinating
nature of the anion [27,28]. For instance, strongly coordinating anions
tend to decrease the decomposition temperature of ILs and poorly coor-
dinating anions ([NTf2] and [N(CN)2]) increases the thermal stability.
Thermal stability of the ILs in this study increases in the order of
[C2CNImEtOEt][CF3COO] b [C2CNImEtOEt][N(CN)2] b [C2CNImEtOEt]
[NTf2]. In addition, the [C2CNImEtOEt] cation with [NTf2] and N(CN)2 an-
ions are thermally less stable compared to the imidazolium ILs with
simple alkyl chains. For example, [C6MIM][NTf2] and [C6MIM][N(CN)2]
showed a decomposition temperature, (Td) of 684.15 K and 503.15 K re-
spectively [27,29] compared to [C2CNImEtOEt][NTf2] and [C2CNImEtOEt]
[N(CN)2] having Td of 596.15 K and 476.15 K respectively. This clearly
indicates that the incorporation of nitrile and ether functionality in the
cation lowered the thermal stability of the dual functionalized ILs. On
another account, [C2CNImEtOEt][NTf2] and [C2CNImEtOEt][N(CN)2] pos-
sess lower Td compared to the imidazolium ILs containing only nitrile
functionality ([C3CNMIm][NTf2] (Td = 657.45 K) and [C3CNMIm]
[N(CN)2] (Td = 551.25 K)]) [25], which might be due to the presence
of the ether functionality on the ILs in this study.
2.2. Characterization
An elemental analyzer (EA-1110) was used to measure carbon, hy-
drogen and nitrogen content of the ILs. Structures of the synthesized
ILs were confirmed by 1H and 13C NMR spectroscopy (Bruker Avance
500 MHz spectrometer). Viscosity and density were measured using
Anton Paar viscometer (model SVM3000) and Anton Paar density
meter (DMA5000) respectively. Coulometric Karl Fischer titrator
(Mettler Toledo, model DL39) was used to analyze the water content
in ILs. The refractive index was measured using refractometer (Mettler
Toledo, RM40) and the surface tension was measured using surface ten-
siometer (model OCA 20) using pendant drop method. Thermal gravi-
metric analyzer (Perkin-Elmer, Pyris V-3.81) with heating profile from
323.15 K to 1073.15 K at a heating rate of 4.72 K·s−1 in inert (nitrogen
atmosphere) condition was used to measure the thermal stability of ILs.
Differential scanning calorimetry (Mettler Toledo, DSC Star 1/500) was
used to measure the glass transition temperature and the melting
point. The samples were heated in an inert atmosphere from 123.15 K
to 403.15 K at a heating rate of 4.72 K·s−1. The uncertainty of the mea-
surement is 0.01 K. Ion chromatogram (Metrohm model 761 Compact
IC) was used to measure the bromide content in the ILs.
The Glass Transition Temperature, (Tg) of the dual functionalized ILs
used in this study are shown in Fig. 3 and Table 2 (Supplementary infor-
mation). The Tg value increases in the order of [C2CNImEtOEt]
[CF3COO] ≈ [C2CNImEtOEt][NTf2] b [C2CNImEtOEt][N(CN)2]. A small dif-
ference in Tg was observed between [CF3COO] and [NTf2] anions, where-
as the lowest Tg was recorded for [N(CN)2] anion. In general, Tg for dual
functionalized ILs are higher than ILs containing only nitrile functional-
ity. For instance, [C2CNImEtOEt][NTf2] has Tg of 212.95 K, while
[C3CNMIm] [NTf2] showed a lower Tg ( 202.45 K). Increase in Tg may
be attributed to the presence of ether group on the cation that promotes
hydrogen bond interactions [30]. Similar results were observed in the
3. Results and discussion
3.1. Synthesis of ILs
The structures of the synthesized ILs in this study are shown in Fig. 1.
The ILs synthesis in this work was conducted into two stages,
namely synthesis of the dual functional cation followed by the introduc-
tion of the desired anion. Michael addition reaction between imidazole
and acrylonitrile was applied to introduce nitrile functionality to the im-
idazole ring [19]. Ether unit was then tethered by SN2 reaction of
imidazol-1-yl-acetonitrile with 2-bromoethyl ether according to previ-
ously published work [23].Three different anions (trifluroacetate,
bis(trifluoromethanesulfonyl)imide and dicyanamide) were used in
this study. Dicyanamide and bis(trifluoromethanesulfonyl)imide an-
ions were introduced through the anion exchange reaction of the halide
precursor ILs with metal salts (Ag or Li) of the corresponding anion [24,
Cation
C
N
N
N
O
Anions
F3C
O
CF3
O
N
N
S
S
NC
CN
O
F3C
O
O O
Fig. 2. TGA profile for ILs:
[C2CNImEtOEt][CF3COO],
[C2CNImEtOEt] [NTf2],
Fig. 1. Overview of the of ILs synthesized in this study.
[C2CNImEtOEt] [N(CN)2].