Nitrile-functionalized azepanium ionic liquids: Synthesis characterization and thermophysical properties

Article abstract of DOI:10.1016/j.molliq.2016.06.092

The synthesis of nitrile-functionalized azepanium ionic liquids such as 1-butyl-1-(2-cyano-ethyl)-azepanium bromide, [C_4CNAzp][Br], 1-butyl-1-(2-cyano-ethyl)azepanium trifluoroacetate, [C_4CNAzp][TFA], 1-butyl-1-(2-cyano-ethyl)-azepanium methanesulfonate [C_4CNAzp][CH₃SO₃], 1-butyl-1-(2-cyano-ethyl)azepanium trifluoromethanesulfonate [C_4CNAzp][CF₃SO₃], 1-butyl-1-(2-cyano-ethyl)azepaniummethanesulfate[C_4CNAzp][CH₃SO₄],1-butyl-1-(2-cyano-ethyl) azepanium p-toluenesulfonate [C_4CNAzp][PTS] were performed. The synthesis of ionic liquids was performed in three steps. ¹H, ¹³C and CHNS elemental analysis were used to characterize the synthesized ionic liquids. The thermal stability, melting point and glass transition temperature of the ionic liquids were determined. The nitrile-functionalized ionic liquids showed good thermal stability.

Full text of DOI:10.1016/j.molliq.2016.06.092

Journal of Molecular Liquids 221 (2016) 1140–1144
Contents lists available at ScienceDirect
Journal of Molecular Liquids
journal homepage: www.elsevier.com/locate/molliq
Nitrile-functionalized azepanium ionic liquids: Synthesis
characterization and thermophysical properties
a,b,
b
b
Kallidanthiyil Chellappan Lethesh ⁎, Syed Nasir Shah , Olumide Bolarinwa Ayodele ,
c
a
M.I. Abdul Mutalib , Yoshimitsu Uemura
Center for Biofuel and Biochemical Research, Universiti Teknologi PETRONAS, Bandar Seri Iskandar, 32610-Perak, Malaysia
Center of Research In Ionic Liquids, Universiti Teknologi PETRONAS, Bandar Seri Iskandar, 32610-Perak, Malaysia
Department of Chemical Engineering, Universiti Teknologi PETRONAS, Bandar Seri Iskandar, 32610-Perak, Malaysia
a
b
c
a r t i c l e i n f o
a b s t r a c t
Article history:
The synthesis of nitrile-functionalized azepanium ionic liquids such as 1-butyl-1-(2-cyano-ethyl)-
azepanium bromide, [C4CNAzp][Br], 1-butyl-1-(2-cyano-ethyl)azepanium trifluoroacetate,
Received 19 October 2015
Received in revised form 23 May 2016
Accepted 27 June 2016
[
1
C
4CNAzp][TFA], 1-butyl-1-(2-cyano-ethyl)-azepanium methanesulfonate [C4CNAzp][CH
-(2-cyano-ethyl)azepanium trifluoromethanesulfonate [C4CNAzp][CF SO ], 1-butyl-1-(2-cyano-
ethyl)azepaniummethanesulfate[C4CNAzp][CH SO ],1-butyl-1-(2-cyano-ethyl) azepanium p-toluenesulfonate
4CNAzp][PTS] were performed. The synthesis of ionic liquids was performed in three steps. H, C and CHNS
3 3
SO ], 1-butyl-
3
3
Available online 01 July 2016
3
4
1
13
[C
Keywords:
Azepane
elemental analysis were used to characterize the synthesized ionic liquids. The thermal stability, melting point
and glass transition temperature of the ionic liquids were determined. The nitrile-functionalized ionic liquids
showed good thermal stability.
Nitrile functionality
Biomass dissolution
Ionic liquids
Thermal stability
Melting point
© 2016 Published by Elsevier B.V.
1
. Introduction
Ionic liquids (ILs) are organic salt consisting entirely of ions [1]. If
thermal stability [27]. The nitrile-functionalized ILs with five and six
ring systems (imidazolium, pyrrolidinium, pyridinium and
pypiridinium) were investigated for various applications [27–30].
However, there is no report regarding nitrile-functionalized ILs with
seven membered ring (azepane) systems. The azepanium based ILs
were first introduced by Belhocine et al. [7,9]. They reported
the thermophysical properties of azepanium ILs having side chains
such as butyl, hexyl, methoxyethyl and 1-ethoxy-2-methoxy-ethane
with various anions such as bistriflimide, trifluoroacetate and
trifluoromethanesulfonate. Azepanium based ILs also been reported
for other applications such as electrolyte for high voltage super capaci-
tors, and electro chemistry [8,9,31–33]. In this work, the synthesis and
characterization of nitrile-functionalized azepanium ILs with various
anions such as trifluoro acetate, methanesulfonate, and methane sulfate
were reported. These ILs were developed in order to explore their po-
tential in biomass dissolution. The biomass dissolution experiments
are currently in progress in our laboratory. Preliminary results showed
that nitrile functionalized ILs, especially triflate and trifluoro acetate
anion containing ILs, are promising solvents for the dissolution of
biomass.
they are liquids at ambient conditions, they can be termed as room tem-
perature ionic liquids (RTILs). Most of the ILs are synthesized from five
and six membered aromatic or non-aromatic cyclic compounds con-
taining a nitrogen atom [2–4] For instance, the most extensively studied
ILs are based on 1-alkyl-3-methylimidazolium cation. Although ILs with
bicyclic ring systems was reported [5,6], there is only limited number of
ILs with seven membered heterocyclic systems [5,7–9]. The properties
of ILs can be adjusted by the careful section of the constituent ions. Be-
cause of this properties ILs find applications in different areas such as
separation [10–14], electrochemistry [15], biomass dissolution [16–
1
9], and organic synthesis [20,21]. The properties can be enhanced by
the incorporation of functional groups. The class of ILs with functional
groups is known as functionalized ionic liquids. The functional groups
can be introduced either to cation or to anion or on both. In 1998,
Davis et al. reported the synthesis first functionalized ILs from micona-
zole [22]. After this report, many functionalized ILs were synthesized
for various applications [2,23–26]. Among the functionalized ILs ni-
trile-functionalized ILs have special place because of their higher
2. Experimental
⁎
Corresponding author at: Center for Biofuel and Biochemical Research, Universiti
The starting materials and reagents were purchased from Acros Or-
Teknologi PETRONAS, Bandar Seri Iskandar, 32610-Perak, Malaysia.
E-mail address: letheshkc@gmail.com (K.C. Lethesh).
ganics. All the starting materials were used without further purification.
http://dx.doi.org/10.1016/j.molliq.2016.06.092
0167-7322/© 2016 Published by Elsevier B.V.

K.C. Lethesh et al. / Journal of Molecular Liquids 221 (2016) 1140–1144
1141
An elemental analyzer (EA-1110) was used to measure carbon, hydro-
6
(DMSO, d ): 12.4, 19.6, 21.9, 23.2, 26.4, 28. 1, 56.0, 60. 1, 62.3, 117.7.
128.3(q), 178.6. CHN elemental analysis: Calculated: C; 55.89, H; 7.82,
N; 8.69. Experimental: C; 55.84, H; 7.89, N; 8.78.
1
13
gen and nitrogen content of the ionic liquids. H and C NMR spectra
were recorded on a Bruker Avance 500 spectrometer. The thermal de-
composition temperature was measured using a thermal gravimetric
analyzer (Perkin-Elmer, Pyris V-3.81). The samples were heated in an
inert atmosphere from 50 °C to 750 °C at a heating rate of 10 °
2.4. 1-Butyl-1-(2-cyano-ethyl)-azepanium methanesulfonate
3 3
[C4CNAzp][CH SO ]
−
1
C min . The uncertainty of the measurement is ± 1 °C. Melting point
and glass transition temperature was measured using differential scan-
ning calorimetry (DSC; PerkinElmer, model Pyris1).
[C4CNAzp][CH
3
3
SO ] was synthesized by the same procedure de-
scribed for [C4CNAzp][TFA] using [C4CNAzp][Br] (10 g, 34.57 mmol) and
1
sodiummethanesulfonate (4.49 g, 38.02 mmol). Yield = 8 g (76%). H
2
.1. Synthesis of 3-Azepan-1-yl-propionitrile
6
NMR (DMSO, d ): δ = ) δ =0.90 (t, 3H), 1.35 (m, 2H), 1.78 (m, 6H),
1
.22 (m, 4H), 3.10 (m, 6H), 3.28 (m, 2H), 3.58 (m, 2H), 3.91 (s, 3H).
C NMR (DMSO, d ): 12.1, 19.5, 21.8, 23.2, 26.4, 28. 3, 58.10, 56.0, 60.
6
1
3
To a solution of Azepane (2 g, 20.16 mmol), acrylonitrile was added
and stirred at room temperature for 24 h. The reaction mixture was
poured into water and the organic layer was extracted with dichloro-
methane (3 × 10 mL). The combined organic layer was evaporated
1, 62.3, 117.7. CHN elemental analysis: Calculated: C; 55.23, H; 9.27,
N; 9.20. Experimental: C; 55.29, H; 9.21, N; 9.15.
using a rotary evaporator to obtain 3-Azepan-1-yl-propionitrile as a
2.5. 1-Butyl-1-(2-cyano-ethyl)azepanium trifluoromethanesulfonate
[C4CNAzp][OTf]
1
pale yellow liquid. Yield = 2.7 g (88%). H NMR (DMSO,d
6
): δ: 1.21
1
3
(
m, 4H), 1.40 (m, 4H), 2.41 (m, 4H), 2.55 (t, 2H), 2.80 (t, 2H).
NMR, DMSO (d ): δ: 17.2, 26.4, 29.6, 49.4, 117.2. CHN elemental analy-
sis: Calculated: C; 71.01, H; 10.59, N; 18.40. Experimental: C; 69.98, H;
C
6
3 3
[C4CNAzp][CF SO ] was synthesized by the same procedure de-
scribed for [C4CNAzp][TFA] using [C4CNAzp][Br] (6 g, 20.74 mmol) and
1
0.66, N; 18.34.
potassium trifluoro methanesulfonate (4.29 g, 22.81 mmol). Yield =
1
5
g (67%). H NMR (DMSO, d
6
):δ =
N
:
0.90 (t, 3H), 1.35 (m, 2H), 1.78
13
2
.2. Synthesis of 1-butyl-1-(2-cyano-ethyl)-azepanium bromide
4CNAzp][Br]
(m, 6H), 1.22 (m, 4H), , 3.10 (m, 6H), 3.28 (m, 2H), 3.58 (m, 2H).
NMR (DMSO, d ): 12.4, 19.6, 21.9, 23.2, 26.4, 28. 1, 56.0, 60. 1, 62.3,
17.7. 125.3(q). CHN elemental analysis: Calculated: C; 46.91, H; 7.03,
C
[C
6
1
To a solution of 3-Azepan-1-yl-propionitrile (3 g, 19.70 mmol) in
N; 7.82. Experimental: C; 46.85, H; 7.09, N; 7.86.
acetonitrile (15 mL), 1-bromobutane (3.24 g, 23.64 mmol) was added
and stirred at 55 °C for 48 h. The acetonitrile was evaporated using a ro-
tary evaporator and the solid obtained was washed with ethyl acetate
2.6. 1-Butyl-1-(2-cyano-ethyl)azepanium methanesulfonate
3 4
[C4CNAzp][CH SO ]
(
3 × 15 mL). The residual solvent was removed using rotary evaporator
and the product was further dried in vacuum oven at 50 °C for 24 h.
[C4CNAzp][CH
3
4
SO ] was synthesized by the same procedure de-
1
Yield = 3.5 g (61%). H NMR (DMSO, d
6
): δ = 0.90 (t, 3H), 1.35 (m,
scribed for [C4CNAzp][TFA] using [C4CNAzp][Br] (6 g, 20.74 mmol) and
2
2
6
9
H), 1.78 (m, 6H), 1.22(m, 4H), 3.10(m, 6H), 3.28 (m, 2H), 3.58 (m,
sodiummethanesulfonate (3.05 g, 22.81 mmol). Yield = 5.2 g
13
1
6
H). C NMR (DMSO, d ): 12.8, 19.2, 21.1, 24.2, 26.2, 28. 5, 56.2, 60. 9,
6
(66%). H NMR (DMSO, d ):δ = = 0.90 (t, 3H), 1.35 (m, 2H), 1.78 (m,
3.2, 117.2. CHN elemental analysis: Calculated: C; 53.98, H; 8.71, N;
.68. Experimental: C; 54.14, H; 8.89, N; 9.61.
6H), 1.22(m, 4H), 3.10(m, 6H), 3.28 (m, 2H), 3.58 (m, 2H)., 3.81(s,
3H). 13C NMR (DMSO, d
): 12.1, 19.5, 21.8, 23.2, 26.4, 28. 3, 56.10,
6.0, 60. 1, 62.3, 117.7. CHN elemental analysis: Calculated: C; 52.47,
6
5
2
.3. 1-Butyl-1-(2-cyano-ethyl)azepanium trifluoroacetate [C4CNAzp][TFA]
H; 8.81, N; 8.74. Experimental: C; 52.39, H; 8.91, N; 8.68.
To a solution of [C4CNAzp][Br] (5 g, 17.27 mmol) in dichloromethane
25 mL), sodium trifluoroacetate (2.58 g, 19.0 mmol) was added and
2.7. 1-Butyl-1-(2-cyano-ethyl)azepanium p-toluenesulfonate
[C4CNAzp][PTS]
(
stirred at room temperature for 24 h. The precipitate formed was fil-
tered off and the organic phase was washed several times with ice
cold water. The dichloromethane was removed using rotary evaporator
and the product obtained was further dried in vacuum oven at 50 °C for
1H NMR (DMSO, d
1.22 (m, 4H), 2.35 (s, 3H), 3.10 (m, 6H), 3.28 (m, 2H), 3.58 (m, 2H),
7.31 (d, 2H), 7.89 (d, 2H). 13C NMR (DMSO, d
): 12.8, 19.2, 20.8, 21.1,
): δ = 0.90 (t, 3H), 1.35 (m, 2H), 1.78 (m, 6H),
6
6
2
4 h. The [C4CNAzp][TFA] obtained as a pale yellow solid. Yield = 5 g
24.2, 26.2, 28. 5, 56.2, 60. 9, 63.2, 117.2, 125.4, 130.8, 135.9. CHN elemen-
tal analysis: Calculated: C; 63.60, H; 9.15, N; 7.06. Experimental: C;
63.51, H; 9.11, N; 7.15.
1
(
6
89%). H NMR (DMSO, d ): δ = 0.90 (t, 3H), 1.35 (m, 2H), 1.78 (m,
13
6
H), 1.22 (m, 4H), , 3.10 (m, 6H), 3.28 (m, 2H), 3.58 (m, 2H). C NMR
Scheme 1. Synthesis route for nitrile-functionalized azepanium ILs.

1142
K.C. Lethesh et al. / Journal of Molecular Liquids 221 (2016) 1140–1144
Table 1
Thermal decomposition temperature (T
ature (T ) of the ILs.
d m
), melting point (T ) and glass transition temper-
g
ILs
T
d
(°C)
Tm (°C)
g
T (°C)
[C
[C
[C
[C
[C
[C
4CNAzp][Br]
4CNAzp][TFA]
4CNAzp][CH SO
4CNAzp][OTf]
4CNAzp][CH SO
4CNAzp][PTS]
216
176
220
332
234
240
164
80
142.9
104.6
168.4
158.6
nd
−60
−10
−82
−20
nd
3
3
4
]
]
3
3
. 2. Results and discussion
The synthesis of nitrile-functionalized ILs was performed in three
steps according to the Scheme 1.
In the first step, nitrile-functionality was introduced by the reaction
of azepane with acrylonitrile at room temperature in solvent free condi-
tion. The reaction mixture was poured into to water and the product
was extracted using dichloromethane. The solvent was removed using
rotary evaporator and Azepanepropionitrile was obtained as a pale yel-
low liquid in excellent yield (98%). In the second step, the bromide salt
was synthesized by the reaction of 3-Azepan-1-yl-propionitrile with 1-
bromobutane at 55 °C for 48 h. Acetonitrile was used as the solvent.
After the removal of the solvent and washing with ethyl acetate,
Fig. 2. TGA profile of the synthesized ILs: [C4CNAzp][OTf], [C4CNAzp][PTS],
[C4CNAzp][CH SO ], [C4CNAzp][CH SO ], [C4CNAzp][Br], [C4CNAzp][TFA].
3
4
3
3
solvent residual peak (DMSO) and another singlet at 3.33 corresponds
to the water in the DMSO.
[
C
4
CNAzp][Br] was obtained as a white solid. The third step was the in-
The thermal stability of the synthesized ILs were determined using
thermo gravimetric analysis (TGA) and the results are given in Table 1
and Fig. 2.
Among all the ILs studied, [C4CNAzp][OTf] showed the highest ther-
mal stability (332 °C). The azepanium ILs with simple alky groups also
showed similar thermal behavior [7]. For instance, the methylazepanium
cation with butyl group with [OTf] anion (1-butyl-1-methyl azepanium
triflate, [C mAzp][OTf]) is thermally stable up to 310 °C, which is only
4
about 20 °C lower than [C4CNAzp][OTf]. Similar results were obtained
when the alkyl group on the azepanium ring was changed to hexyl
troduction of various anions by the ion exchange reaction of the bro-
mide precursor ILs with the metal salts of the desired anions. The
reaction was performed at room temperature in dichloromethane for
2
4 h. The precipitate formed was filtered off and the solution was
washed with several times with aliquot of cold water to remove the re-
maining halide impurities. The halide content was measured using ion
chromatogram and was found to be below 250 ppm. The nitrile-func-
tionalized azepanium ILs obtained as solids at room temperature. The
structure, name and abbreviations of the synthesized ILs is given in
Table 1.
6
group. 1-Hexyl-1-methyl azepanium triflate, [C mAzp][OTf] is also stable
1
1
The synthesized ILs were mainly characterized using H NMR. H
NMR spectrum of [C4CNAzp][Br] is shown in Fig. 1.
up to 310 °C. [C4CNAzp][TFA] showed a thermal stability of 176 °C, which
is comparable to the thermal stability of azepanium ILs with simple alkyl
side chain having the similar anion [34]. For instance, the thermal stabil-
A triplet at δ = 0.90 corresponds to the three protons on methyl (–
CH
3
) group at the end of the carbon in the alkyl chain (marked a in
ity of 1-butyl-1-methyl azepanium trifluoroacetate, [C
C. Similar results were observed in the case of azepanium cation
with hexyl group, [C Azp][TFA], which is also stable up to 170 °C.
Azepanium based protic ILs with trifluoroacetate anion, [Azp][TFA] is
thermally more stable (239 °C) than [C Azp][TFA] and [C4CNAzp][TFA]
[8]. The thermal stability of the synthesized ILs follows the order
4
Azp][TFA] is 170 °
the structure). The multiplets at δ = 1.35, corresponds to the b. The
multiplet at around δ = 1.3 corresponds to i and c. The multiplets at
δ = 1.78 represents the hydrogen atoms h. Another multiplet at δ =
6
3
3
.1 corresponds to g and f. The multiplets at around δ = 3.2 and δ =
.4 represents e and d respectively. The peak at 2.5 corresponds to the
6
Fig. 1. 1H NMR spectrum of [C4CNAzp][Br].

K.C. Lethesh et al. / Journal of Molecular Liquids 221 (2016) 1140–1144
1143
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4
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. Conclusion
Nitrile-functionalized azepanium ILs with different anions were syn-
8955–8958.
[
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1
13
thesized and characterized. H NMR, C NMR and CHN elemental anal-
ysis were used to characterize ILs. The melting point, glass transition
and thermal decomposition temperature of the ILs were determined
using thermo gravimetric analysis (TGA) and Differential scanning calo-
rimetry (DSC). All the ILs showed good thermal stability. 1-butyl-1-(2-
cyano-ethyl)azepanium trifluoromethanesulfonate, [C4CNAzp][OTf],
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Acknowledgement
[
[
This work was supported by Short Term Internal Research Grant
1
5876–15882.
(
(
STIRF, cost center: 0153AA-C31) from Universiti Teknologi PETRONAS
UTP).
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