Tunable aryl alkyl ionic liquids (TAAILs) based on 1-aryl-3,5-dimethyl-1H-pyrazoles

Article abstract of DOI:10.1016/j.molliq.2017.10.033

A series of fifteeen new 1-aryl-2,3,5-trimethylpyrazolium salts ([Ph_RC₁pz][X], R: 4-Cl, 4-Br, 4-Me, 4-OMe, 4-NO₂; C₁: methyl, X: methanesulfonate [CH₃SO₃^?], tetrafluoroborate [BF

Full text of DOI:10.1016/j.molliq.2017.10.033

Journal of Molecular Liquids 248 (2017) 314–321
Contents lists available at ScienceDirect
Journal of Molecular Liquids
journal homepage: www.elsevier.com/locate/molliq
Tunable aryl alkyl ionic liquids (TAAILs) based
on 1-aryl-3,5-dimethyl-1H-pyrazoles
⁎
Melek Canbulat Özdemir , Beytiye Özgün
Department of Chemistry, Faculty of Science, Gazi University, 06500 Teknikokullar, Ankara, Turkey
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 10 April 2017
Received in revised form 22 September 2017
Accepted 6 October 2017
Available online 10 October 2017
A series of fifteeen new 1-aryl-2,3,5-trimethylpyrazolium salts ([PhRC1pz][X], R: 4-Cl, 4-Br, 4-Me, 4-OMe, 4-NO2;
C1: methyl, X: methanesulfonate [CH3SO−3 ], tetrafluoroborate [BF4−] and hexafluorophosphate [PF−6 ]) were syn-
thesized and characterized. Thermal properties (Tm/Tg and Td) of all the salts were investigated. Five of the
salts can be classed as ionic liquids since they are liquid at rate time or melt below 100 °C three of which are
room temperature ionic liquids (RTILs). The influence of the substituents at the para position of the aryl ring
was investigated by studying the changes in the melting points of the corresponding methanesulfonate, tetraflu-
oroborate, and hexafluorophosphate salts. The results demonstrate that the electron-withdrawing substituents
tend to higher melting points than electron-donating substituents. Thermophysical properties (density, viscosity,
and refractive index) of the room temperature ionic liquids were measured as a function of temperature. The
electrochemical windows (EW) of all the salts were determined experimentally. The EW values of the salts
were calculated theoretically to make a comparison with the experimentally determined EW values.
© 2017 Elsevier B.V. All rights reserved.
Keywords:
Ionic liquids
Pyrazolium cations [PhRC1pz]+
TAAILs
Substituent effects
1. Introduction
(electron-withdrawing or -donating) and position of the substituents
at the phenyl ring have an influence on the properties of TAAILs [21–24].
Ionic liquids (ILs) are defined as organic molten salts with melting
points below 100 °C. In particular, salts which are even liquid at or
below room temperature are called room temperature ionic liquids
(RTILs) [1–5]. The interest in ILs increased significantly over the last de-
cade, owing to their remarkable properties, such as negligible volatility,
non-flammability, high ionic conductivity, high chemical, thermal, and
electrochemical stability [6–13]. In order for ionic liquids to become
simple and effective replacements for solvents in synthetic chemistry
and also in other areas such as extraction processes, electrochemistry,
lubricants, etc., it is very important that a wide range of salts becomes
available. Thus, the design and synthesis of new ILs for numerous func-
tional applications both in academia and industry is a dynamic area
[14–20].
The physicochemical properties of ILs can be finely tuned for diverse
scientific and technological applications by modifying the structure of
both the cation and anion. In recent years, a new class of ILs called tun-
able aryl alkyl ionic liquids (TAAILs) were synthesized by Strassner and
co-workers [21]. By introducing an aryl part to the imidazole or 1,2,4-
triazole core, researchers achieved to tune the properties of ILs with
mesomeric (+M, −M) and inductive effects (+I, −I). In addition,
the exchange of anion, modification of alkyl chain length and the type
At recent years, it has also been shown that the quantum chemical
calculations are an excellent tool to predict the electrochemical window
of ionic liquids. The results obtained in some of these works could pro-
vide insights on which substituents can be attached to the phenyl ring of
the cations in TAAILs for designing and developing TAAILs with excel-
lent properties such that the electrochemical stability [25,26].
In our previous work, we focused on phenyl/alkyl-3,5-
dimethylpyrazolium based ILs which can be distinguished from the
standard pyrazolium based ionic liquids by the phenyl ring substituted
at the N-1 nitrogen atom of the pyrazole heterocycle. The combination
of sp3-alkyl at the N-2 nitrogen atom, and sp2-phenyl substituent at
the N-1 nitrogen atom on the pyrazole ring allows for additional
mesomeric and inductive effects as well as π-π interactions [27]. In con-
tinuation of our studies, we investigated the influence of the electron
withdrawing (-NO2, -Cl, -Br), and electron donating (−Me, −OMe)
substituents at the para position of phenyl ring on the properties of 1-
aryl-2,3,5-trimethylpyrazolium salts by keeping alkyl part (methyl)
constant for the counter anions [CH3SO−3 ], [BF4−] and [PF6−].
2. Results and discussion
2.1. Synthesis and characterization
⁎
Corresponding author at: Department of Environmental Engineering, Faculty of
The application of MW energy is one of the eco-friendly methods to
accelerate the course of many organic reactions, and having number of
Engineering, Middle East Technical University, 06800 Ankara, Turkey.
E-mail address: ozmelek@metu.edu.tr (M.C. Özdemir).
https://doi.org/10.1016/j.molliq.2017.10.033
0167-7322/© 2017 Elsevier B.V. All rights reserved.

M.C. Özdemir, B. Özgün / Journal of Molecular Liquids 248 (2017) 314–321
315
H3C
O
C
O
C
CH3COOH
R
NH-NH2.HCl
+
N
CH3
MW, 120 o
C
N
H3C
CH3
R
(1a-1e)
R: -Cl, -Br, -CH3, -OCH3, -NO2
H3C
(a) (b) (c) (d) (e)
N
CH3
N
-
BF4
R
HBF4(aq)
RT
CH3
H3C
H3C
O
S
(3a-3e)
[PhRC1pz][BF4
-
]
H3CO
CH3
N
N
R: -Cl, -Br, -CH3, -OCH3, -NO2 C1: methyl
(a) (b) (c) (d) (e)
CH3
CH3
O
N
N
-
CH3SO3
R
MW, 80 o
C
R
CH3
H3C
(1a-1e)
(2a-2e)
[PhRC1pz][CH3SO3
KPF6(aq)
RT
-
N
]
CH3
N
R: -Cl, -Br, -CH3, -OCH3, -NO2 C1: methyl
(a) (b) (c) (d) (e)
R
-
PF6
CH3
(4a-4e)
-
[PhRC1pz][PF6
]
R: -Cl, -Br, -CH3, -OCH3, -NO2 C1: methyl
(a) (b) (c) (d) (e)
Fig. 1. Synthetic pathway for the synthesis of 1-aryl-2,3,5-trimethylpyrazolium ILs/salts.
advantages such as shorter reaction times, enhancement in conversion
and selectivity, higher yields of product, improved reproducibility, re-
duction of side reactions, and high efficiency of heating when compared
to conventional methods [28–30]. Our interest in utilising microwave
radiation is to minimize waste generation and to accelerate both the
synthesis of 1-aryl-3,5-dimethyl-1H-pyrazole compounds and the
quaternisation of these pyrazole compounds which is the first step in
the synthesis of methanesulfonate ionic liquids.
The structures of 1-aryl-2,3,5-trimethylpyrazolium salts were char-
acterized by FTIR, 1H NMR, 13C NMR, 19F NMR (3a–3e and 4a–4e), TOF
MS and elemental analysis.
All the spectral data elucidated the structure of the synthesized
pyrazole salts. The FTIR spectra of all the salts show the characteristic
bands of the pyrazolium moiety as well as those of the corresponding
counterions, where appropriate. In particular, the ν(C = N) and ν(C
= C) absorption bands from the pyrazolium cation appear at ca.
1595–1560 cm−1. Additionally, characteristic bands of the counterions
are also observed. In particular, for [CH3SO−3 ], [BF4−], and [PF6−] salts
The
synthesis
of
1-aryl-2,3,5-trimethylpyrazolium
methanesulfonate ionic liquids was carried out via two-step reaction
(Fig. 1). The first step of the reaction is the synthesis of 1-aryl-3,5-
dimethyl-1H-pyrazole compounds. These compounds were synthe-
sized from aryl hydrazinium hydrochloride derivatives and
acetylacetone under MW irradiation (1a–1e). The second step of the re-
action is alkylation of 1-aryl-3,5-dimethyl-1H-pyrazole compounds
with methyl methanesulfonate in acetonitrile under MW irradiation.
These reactions were yielded 1-aryl-2,3,5-trimethylpyrazolium
methanesulfonate ionic liquids (2a–2e). To achieve the synthesis of 1-
aryl-2,3,5-trimethylpyrazolium tetrafluoroborate salts (3a–3e) and
hexafluorophosphate salts (4a–4e), anion exchange reactions of the
corresponding methanesulfonate salts were performed (Fig. 1).
bands at ca. 1036–1039 cm−1, 1034–1037 cm−1, and 821–832 cm−1
,
corresponding to νs(SO3), ν(BF) and ν(PF) from the corresponding an-
ions [31,32], appear at values that agree with the ionic nature of the
salts. The pyrazole proton was also verified with 1H NMR spectra by
emergence of one singlet around δ 6.43–6.85. In addition, doublets
around δ 7.10–8.59 substantiated the presence of aromatic protons of
aryl ring at the N-1 nitrogen atom of the pyrazole heterocycle. For the
salts 2a–2e one singlet at ca. δ 2.68–2.76 proved three aliphatic protons
Table 1
Thermal properties of the 1-aryl-2,3,5-trimethylpyrazolium ILs/salts.
a
b
c
a
b
c
Entry
salts
Tm
Tg
Td
Entry
Salts
Tm
Tg
Td
(°C)
(°C)
(°C)
(°C)
(°C)
(°C)
1
2
3
4
5
6
7
8
2a
2b
2c
2d
2e
3a
3b
3c
–
76.3
–
−38.8
–
−51.9
−59.7
–
–
–
–
271.1
269.8
291.6
284.2
247.5
368.6
364.5
363.6
9
3d
3e
4a
4b
4c
4d
4e
75.6
–
–
–
–
–
–
–
387.5
328.0
359.8
291.0
305.3
336.4
316.7
10
11
12
13
14
15
166.5
153.9
179.8
138.3
115.6
222.0
–
183.3
133.2
161.2
147.9
a
Tm – melting point.
Tg – glass transition temperature.
Td – decomposition temperature.
b
c
Fig. 2. Melting points of the 1-aryl-2,3,5-trimethylpyrazolium salts.

316
M.C. Özdemir, B. Özgün / Journal of Molecular Liquids 248 (2017) 314–321
Table 2
Cathodic and anodic potentials vs. Ag/Ag+ for EW values of the 1-aryl-2,3,5-trimethylpyrazolium ILs/salts at cut-off current density 1.0 mA/cm2 using GC macro-electrode as a working
electrode at 25 °C.
Entry
Salts
Ecathodic(V)
Eanodic(V)
EW(V)
Entry
Salts
Ecathodic(V)
Eanodic(V)
EW(V)
1
2
3
4
5
6
7
8
2a
2b
2c
2d
2e
3a
3b
3c
−1.37
−0.53
−0.86
−0.71
−1.07
−2.02
−1.60
−2.00
2.44
2.31
2.32
1.73
2.15
2.31
2.65
2.31
3.81
2.84
3.18
2.44
3.22
4.33
4.25
4.31
9
3d
3e
4a
4b
4c
4d
4e
−2.00
−1.05
−1.69
−1.61
−1.71
−1.75
−1.04
1.83
2.51
2.68
2.62
2.68
2.30
2.64
3.83
3.56
4.37
4.23
4.39
4.05
3.68
10
11
12
13
14
15
of methanesulfonate anion. 19F NMR spectra of 3a–3e show two signals
at ca. δ (−148.30)–(−153.94) due to coupling of 19F nucleus with the
two different boron isotopes, 10B and 11B, present in the [BF−4 ] anion,
and the 19F NMR spectra of 4a–4e show typical doublets of [PF−6 ] octa-
hedral structure at ca. δ (−68.90)–(−74.93).
anion generally shows a much weaker coordination to the cation in
comparison to [BF−4 ] and [PF6−] anions and has more available confor-
mations [33,34]. Thus, the methanesulfonate salts (except 2b and 2e)
are in liquid state at room temperature, while all hexafluorophosphate
and tetrafluoroborate salts are in solid state.
The thermal stabilities of the 1-aryl-2,3,5-trimethylpyrazolium salts
were measured by thermogravimetry analysis (TGA). The thermal de-
composition temperatures of the salts are presented in Table 1. All of
the 1-aryl-2,3,5-trimethylpyrazolium salts proved to be stable up to
temperatures between 247.5 and 387.5 °C. The difference between the
thermal stabilities of the [BF4−] and [PF−6 ] containing salts is not notable,
but [CH3SO−3 ] containing salts exhibited much lower thermal stabilities
than the corresponding salts with [BF−4 ] and [PF6−] counterions with al-
most 50 °C difference in the onset of decomposition curves. It was ob-
served that the thermal stability of these salts is significantly
influenced by the nature of the anion similar to that reported previously
[27]. Altogether, the new 1-aryl-2,3,5-trimethylpyrazolium salts are suf-
ficiently stable for most applications, although no long term TGA mea-
surements have yet been performed.
2.2. Thermal properties
Thermal transitions (Tm or Tg) of the 1-aryl-2,3,5-
trimethylpyrazolium salts were determined by differential scanning
calorimetry (DSC), the results of which are summarized in Table 1.
Five of the salts (2a–2d, 3d) can be classed as ionic liquids since they
are liquid at rate time or melt below 100 °C. All of the 1-aryl-2,3,5-
trimethylpyrazolium [PF−6 ] and [BF−4 ] salts (except 3d) and one of the
[CH3SO−3 ] salt (2e) have melting points above 100 °C (Fig. 2, Table 1).
Variation of the substituent (R) on the phenyl ring of the 1-aryl-
2,3,5-trimethylpyrazolium salts leads to different melting points/glass
transitions using the same alkyl chain length and anion depending on
the mesomeric or inductive effects of the substituent. As seen in Fig. 2
and Table 1 electron withdrawing substituents tend to higher melting
points than electron donating substituents at the para position of the
phenyl ring. The electron donating substituents like 4-Me and 4-OMe
have a significant influence on the electronic properties of the aryl
ring. The inductive effect of the methyl group at the para position is
very different compared to the mesomeric effect of the methoxy substit-
uent, which interacts via the π-system. Thus, one can tune the proper-
ties of the salts through the introduction of an electronic variation
through para substitution on the aryl ring. Also, the effect of the coun-
terion can be shown by comparing the pyrazolium salts which have
the same cationic structure (Fig. 2, Table 1). The asymmetric [CH3SO−3 ]
2.3. Electrochemical window (EW)
The
electrochemical
window
of
the
1-aryl-2,3,5-
trimethylpyrazolium salts was assessed by cyclic voltammetry (CV) at
50 mV/s sweep rate, starting from anodic to cathodic potentials and re-
versing back to the initial value. The electrochemical windows of the
salts containing [PF6−] and [BF4−] anions are higher than [CH3SO−3
]
anion containing salts and follow the order of stability [PF−6 ] N [BF4−] N
[CH3SO−3 ] in comparision to the salts having the same cation (Table 2).
Table 3
E
LUMO and EHOMO (eV) of [PhRC1pz][PF6] salts, ELUMO, EHOMO (eV), potentials of cathodic (VCL) and anodic (VAL) limits of individual ions and, electrochemical window (EW) of 1-aryl-2,3,5-
trimethylpyrazole based [CH3SO3−], [BF4−], and [PF−6 ] salts calculated by density functional theory (DFT) calculations at the B3LYP/6–311 + G(d,p) level in gas phase and in solvent
acetonitrile.
In gas phase
In solvent acetonitrile
[PhRC1pz][PF6]
ELUMO
EHOMO
R = Cl
−1.99
−7.91
Br
−1.99
−7.73
CH3
−1.71
−7.80
OCH3
−1.66
−7.17
NO2
−3.64
−8.48
Cl
−1.57
−7.53
Br
−1.56
−7.39
CH3
−1.39
−7.38
OCH3
−1.35
−6.82
NO2
−3.42
−7.92
[PhRC1pz]+
ELUMO
EHOMO
−5.07
−10.51
5.07
−5.06
−10.22
5.06
−4.88
−10.52
4.88
−4.83
−9.78
4.83
−6.08
−11.29
6.08
−1.67
−7.68
1.67
−1.70
−7.53
1.70
−1.52
−7.55
1.52
−1.52
−6.97
1.52
−3.48
−7.07
3.48
V
V
CL/V
AL/V
10.51
10.22
10.52
9.78
11.29
7.68
7.53
7.55
6.97
7.07
Anions
ELUMO
EHOMO
[CH3SO−3
3.39
−1.97
−3.39
1.97
]
[BF−4
4.45
−4.55
−4.45
4.55
]
[PF−6
4.06
−5.54
−4.06
5.54
]
[CH3SO−3
0.20
−6.97
−0.20
6.97
]
[BF−4
0.29
−9.79
−0.29
9.79
]
[PF−6
]
−0.04
−10.28
0.04
V
V
CL/V
AL/V
10.28
EW/V
[PhRC1pz][CH3SO3−
]
−3.1
−0.52
0.47
−3.09
−0.51
0.48
−2.91
−0.33
0.66
−2.86
−0.28
0.71
−4.11
−1.53
−0.54
5.29
6.01
6.01
5.27
5.83
5.83
5.44
6.03
6.03
5.45
5.45
5.45
3.49
3.59
3.59
[PhRC1pz][BF−4
]
[PhRC1pz][PF−6
]

M.C. Özdemir, B. Özgün / Journal of Molecular Liquids 248 (2017) 314–321
317
Table 4
Experimental densities (ρ), dynamic viscosities (η) and refractive indices (nr) of the RTILs
as a function of temperature at atmospheric pressurea.
Aryl alkyl pyrazolium RTILs
T
(K)
ρ
η
nr
(g/cm3)
(mPa.s)
b
2a
298
308
313
333
298
308
313
333
298
308
313
333
1.3046
1.2985
1.2925
1.2776
1.2236
1.2217
1.2066
1.1923
1.2596
1.2561
1.2321
1.2171
–
–
1.5460
1.5430
1.5414
1.5354
1.5339
1.5305
1.5288
1.5237
1.5359
1.5333
1.5320
1.5266
b
2138.88
287.99
b
2c
–
–
b
821.74
148.52
b
2d
–
–
b
1096.01
192.48
Fig. 4. Correlation between calculated and experimental electrochemical windows (units:
V) of 1-aryl-2,3,5-trimethylpyrazolium salts containing [CH3SO−3 ], [BF4−] and [PF6−] anions.
a
Data were measured on samples which had a water content (wt%) in the range of 0.2–0.32
according to coulometric Karl-Fischer titration.
b
Not determined by a viscometer.
the exception of the positions of salts having -Br and -Cl substituents)
it can be found that cathodic stability of the salts against reduction is or-
dered as R = OMe N Me N Cl N Br N NO2 in solvent acetonitrile. Thus, the
substituents at the para position of the phenyl ring of our interested cat-
ions have influence on the EW values of the salts. The electron donating
groups such as -OMe, and -Me groups generally stabilize the cation
(leads to greater EW) while electron-withdrawing groups such as halo-
gen -Br, -Cl and -NO2 groups destabilise the cation (decreases EW).
These results are in well accordance with the results obtained for
para-X-phenyl methylimidazolium ([X − PhMIM]+: X = OCH3, CH3,
and NO2) cations [25]. From HOMO energy of the anions, it is resulted
that anodic stabilities of the anions are in the following order [CH3SO3−
] b [BF−4 ] b [PF−6 ], and are in good agreement with those of calculated
by Ong et al. and Roohi et al. [26,35].
Electrochemical window of the salts, which can be correlated to the
calculated difference in energy level of the lowest unoccupied molecular
orbital (LUMO) of the cation (reductive stability) and the highest occu-
pied molecular orbital (HOMO) of the anion (oxidative stability) were
also calculated theoretically, both in gas phase and in solvent acetoni-
trile for comparison with the experimentally determined EW values.
The HOMO and LUMO energy levels, the potentials of cathodic (VCL
)
and anodic limits (VAL) of the salts were calculated by density functional
theory (DFT) at the B3LYP/6–311 + G(d,p) level in gas phase. All the
computations in solvent acetonitrile were carried out using the Self-
Consistent Reaction Field (SCRF) under the integral equation formalism
polarizable continuum model (IEFPCM). The results are given in Table 3.
EW is estimated from the following expressions;
The EW values calculated theoretically for the [BF−4 ] and [PF6−] salts
in solvent acetonitrile, follow the same order, R = NO2 b OMe b Br
b Cl b Me. Besides, the experimental EW values for the [PF−6 ] salts are
in the same order as their calculated EW values. For the [BF−4 ] salts a
similar order (R = NO2 b OMe b Br b Me b Cl) for their experimentally
determined EW values was observed. Thus, there is a reasonably good
correlation between the theoretical and the experimental EW values
with correlation coefficients of 0.93 and 0.84 for the [PF−6 ] and the
[BF−4 ] salts, respectively (Fig. 4). The calculated EW values for
[CH3SO−3 ] ILs are in the order of R = NO2 b Br b Cl b Me b OMe while
the experimental EW values are found to be in the order of R = OMe
b Br b Me b NO2 b Cl in solvent acetonitrile. So, there is no reasonable
correlation between the calculated and the experimental EW values
for the methanesulfonate ionic liquids (R2: 0.36).
−εHOMO −εLUMO
ε
LUMO−εHOMO
EW ¼ VAL−VCL
¼
−
¼
e
e
e
The LUMO energy levels of the 1-aryl-2,3,5-trimethylpyrazolium
hexafluorophosphate salts and those of their corresponding cations
were calculated in gas phase and in solvent acetonitrile to test the cor-
relation between these two LUMO energy levels. The results are
shown in Table 3. Correlation between LUMO energy of cations and
LUMO energy of [PhRC1pz][PF6] salts in gas phase and in solvent aceto-
nitrile are shown in Fig. 3a and Fig. 3b, respectively, and clearly indicate
that both LUMO energy levels are well correlated. Therefore, it can be
assumed that the LUMO energy level of the cations solely determines
the resistance of these salts against reduction. The cathodic stability of
the salts against reduction is ordered as R = OMe N Me N Br N Cl
N NO2, in gas phase. Similar to the results obtained in gas phase (with
2.4. Thermophysical properties
The thermophysical properties such as density, viscosity, and refrac-
tive index of the three dried 1-aryl-2,3,5-trimethylpyrazolium
methanesulfonate room temperature ionic liquids (2a, 2c, and 2d)
were investigated as a function of temperature from 298 K to 333 K
(Table 4). It is difficult to dry these RTILs rigorously. As a consequnce,
the residual water content may have effect on their thermophysical
properties.
The methanesulfonate RTILs (2a, 2c and 2d) are highly viscous at
room temperature and their viscosities can not be determined by vis-
cometer. As can be seen in Table 4, in the temperature range studied,
the viscosity of these RTILs decreases with increasing temperature.
Within the 1-aryl-2,3,5-trimethylpyrazolium RTILs the ordering of the
viscosities followed is 4-Me b 4-OMe b 4-Cl. This trend may be attribut-
ed to a combination of steric and electronic effects in TAAILs [36].
The experimental densities and refractive indices of 1-aryl-2,3,5-
trimethylpyrazolium methanesulfonate ionic liquids (2a, 2c, 2d) were
plotted as a function of temperature, and are shown in Fig. 5 and
Fig. 3. Linear correlation between LUMO energy of cations versus LUMO energy of 1-aryl-
2,3,5-trimethylpyrazolium hexafluorophosphate salts (4a–4e) in gas phase (a), in solvent
acetonitrile (b).

318
M.C. Özdemir, B. Özgün / Journal of Molecular Liquids 248 (2017) 314–321
Fig. 6, respectively. Both the densities and the refractive indices of
methanesulfonate ionic liquids decrease with increasing temperature
as expected. Consequently, the density, viscosity and refractive indices
of the RTILs were found to depend on temperature.
was prepared in anhydrous acetonitrile and then the solution was
purged with nitrogen for at least 10 min to remove oxygen and
water.
4.2. General procedure for the synthesis of 1-aryl-3,5-dimethyl-1H-
pyrazole compounds (1a–1e)
3. Conclusions
In conclusion, a series of 1-aryl-2,3,5-trimethylpyrazolium salts
comprising three different counterions ([CH3SO−3 ], [BF4−], and [PF6−])
were synthesized and characterized. Thermal properties, electrochemi-
cal windows of all the salts and thermophysical properties (density, vis-
cosity, and refractive index) of the RTILs (2a, 2c, and 2d) were evaluated.
Electrochemical windows of all the salts were calculated theoretically
and compared with the experimentally determined EW values. All the
synthesized 1-aryl-2,3,5-trimethylpyrazolium salts have thermal stabil-
ities in the range of 247.5–387.5 °C. 1-Aryl-2,3,5-trimethylpyrazolium
salts with [BF−4 ], and [PF−6 ] counterions exhibit large electrochemical
window values which make them attractive for their application in elec-
trochemical devices (supercapacitors, batteries), electrochemical syn-
thesis, metal deposition, etc. The RTILs (2a, 2c, and 2d) with high
refractive indices (1.53–1.55) are more environmentally benign than
the vast majority of existing high refractive index immersion fluids.
Therefore, these ionic liquids may be promising alternatives for optical
immersion fluids.
To a mixture of arylhydrazinium hydrochloride (5.0 mmol) in
acetic acid (30.0 mL) acetylacetone (5.0 mmol) was added, and the
mixture was heated at 120 °C under MW irradiation until all the
starting materials were consumed (TLC, 20% EtOAc–hexane). Subse-
quent to completion of the reaction, acetic acid was removed by ro-
tary evaporation. The residue was dissolved in ethyl acetate, and
washed with diluted sodium hydrogen carbonate, water and saturat-
ed brine, respectively. The separated organic phase was dried over
anhydrous sodium sulfate. After removing of ethyl acetate the re-
maining product was purified by column chromatography (silica
gel: 20% EtOAc–hexane).
4.2.1. 1-(4-chlorophenyl)-3,5-dimethyl-1H-pyrazole (1a)
Reaction time: 1.5 min., Yield: 95%, orange oil. 1H NMR (300 MHz,
CDCl3, ppm) δ = 2.29 (s,3H,CH3); 2.30 (s,3H,CH3); 6.0 (s,1H,CH);
7.36–7.43 (m,4H,Ph). 13C NMR(75 MHz, CDCl3, ppm) δ = 12.24;
13.36; 107.41; 125.43; 128.94; 132.47; 138.43; 139.15; 149.05.
4. Experimental section
4.2.2. 1-(4-bromophenyl)-3,5-dimethyl-1H-pyrazole (1b)
Reaction time: 2.0 min.,Yield: 78%, light brown oil. 1H NMR
(300 MHz, CDCl3, ppm): δ = 2.29 (s,3H,CH3); 2.30 (s,3H,CH3); 6.0
(s,1H,CH); 7.31–7.34 (d,2H,Ph,J: 8.8 Hz); 7.55–7.58 (d,2H,Ph,J: 8.8 Hz).
13C NMR(75 MHz CDCl3, ppm) δ = 12.38; 13.46; 107.51; 120.43;
125.73; 131.95; 138.93; 139.13; 149.12.
4.1. General methods
All chemicals were supplied by Acros, Aldrich Fluka, and Merck as
well as other common suppliers and used as received. Microwave-
assisted syntheses were performed with a professional multimode
Microsynth - Milestone oven. A Thermo Scientific Madison 6700
spectrometer with an ATR (Attenuated Total Reflectance) attach-
ment was used to obtain all IR spectra. 1H (300 MHz), 13C
(75 MHz), and 19F (282 MHz) NMR spectra were recorded on
Bruker-Avance-300 MHz spectrometer (in CDCl3 or DMSO-d6). Ele-
mental analysis of the synthesized salts was carried out with a
LECO CHNS-932 elemental analyzer. Mass spectrometry was per-
formed on a Micromass LCT Premier XE (Waters, MS Technologies).
Shimadzu DSC-60 was used to perform differential scanning calo-
rimetry (DSC) experiments, with a ramp temperature of 10
°C min−1 under a nitrogen atmosphere. The thermal stability of all
the salts was investigated on a Shimadzu TA-60WS Thermal Analyz-
er at a heating rate 10 °C min−1 with nitrogen as the purge gas.
The density measurement of RTILs at ambient pressure was carried
out using Anton Paar DMA-4500 M digital densimeter with an
uncertanity of 0.01 K. The DMA-4500 M densimeter protocol includes
an automatic correction for the viscosity of the sample. The apparatus is
precise within 1.0 × 10−5 g/cm3, and the overall uncertainty of the ex-
perimental density measurement at ambient pressure was better than
1.0 × 10−4 g/cm3. Calibration of the densimeter was carried out at at-
mospheric pressure using distilled and degassed water.
4.2.3. 1-(4-methylphenyl)-3,5-dimethyl-1H-pyrazole (1c)
Reaction time: 1.5 min., Yield: 90%, orange oil. 1H NMR (300 MHz,
CDCl3, ppm): δ = 2.28 (s,3H,CH3); 2.30 (s,3H,CH3); 2.40 (s,3H,CH3);
5.98 (s,1H,CH); 7.23–7.25 (d,2H,Ph, J: 8.4 Hz); 7.29–7.32 (d,2H,Ph, J:
8.4 Hz). 13C NMR(75 MHz CDCl3, ppm) δ = 12.27; 13.51; 21.04;
106.60; 124.66; 129.51; 137.07; 137.49; 139.30; 148.63.
4.2.4. 3,5-dimethyl-1-(4-methoxyphenyl)-1H-pyrazole (1d)
Reaction time: 1.0 min.,Yield: 90%, brown oil. 1H NMR (300 MHz,
CDCl3, ppm): δ = 2.25 (s,3H,CH3); 2.29 (s,3H,CH3); 3.84 (s,3H,CH3);
6.0 (s,1H,CH); 6.94–6.97 (d,2H,Ph, J: 8.9 Hz); 7.31–7.34 (d,2H,Ph, J:
8.9 Hz). 13C NMR(75 MHz CDCl3, ppm) δ = 12.12; 13.49; 55.49;
106.24; 114.09; 126.34; 133.10; 139.44; 148.48; 158.76.
4.2.5. 3,5-dimethyl-1-(4-nitrophenyl)-1H-pyrazole (1e)
Reaction time: 2.5 min.,Yield: 85%, yellow solid, m.p: 100.5 °C. 1
H
NMR (300 MHz, CDCl3, ppm): δ = 2.32 (s,3H,CH3); 2.45 (s,3H,CH3);
6.1 (s,1H,CH); 7.68–7.71 (d,2H,Ph, J: 9.2 Hz); 8.32–8.35 (d,2H,Ph, J:
9.2 Hz). 13C NMR(75 MHz CDCl3, ppm) δ = 13.11; 13.48; 109.35;
123.42; 124.67; 139.87; 145.03; 145.51; 150.80.
An Anton Paar Microviscometer (AMVn) was used for measurement
of the dynamic viscosities of the RTILs which is based on falling-ball prin-
ciple. Refractive index measurements of RTILs were conducted with a re-
fractometry DR 6300-TF, A. Krüss Optronic GmbH equipped with a
temperature control using a He\\Ne light source with a wavelength
633 nm.
4.3. General procedure for the synthesis of 1-aryl-2,3,5-
trimethylpyrazolium methanesulfonates (2a–2e)
To a solution of 1-aryl-3,5-dimethyl-1H-pyrazole (5.0 mmol) in ace-
tonitrile (5.0 mL) methyl methanesulfonate (5.0 mmol) was added and
the mixture was heated at 80 °C under MW irradiation for 30 min. The
progress of the reaction was monitored by TLC (80% EtOAc–hexane).
After completion of the reaction, acetonitrile was removed under re-
duced pressure. The resulting product was washed two times with
20.0 mL of hexane and then two times with 20.0 mL of diethyl ether.
Then, active charcoal and 20.0 mL acetonitrile were added and stirred
for 24 h. After filtration the filtrate was dried over anhydrous sodium
The water content of RTILs was determined using coulometric Karl-
Fischer titrator, Cou-Lo Aquamax KF moisture meter.
Cyclic Voltammetry measurements were conducted at 25 °C on
Electrochemical Workstation CHI-660B instrument, using glassy car-
bon macro electrode (surface area: 7.065 × 10−2 cm2) as a working
electrode, Pt as a counter electrode and Ag/AgCl as a reference elec-
trode. 0.1 M solution of the 1-aryl-2,3,5-trimethylpyrazolium salts

M.C. Özdemir, B. Özgün / Journal of Molecular Liquids 248 (2017) 314–321
319
4.3.3. 1-(4-methylphenyl)-2,3,5-trimethylpyrazolium methanesulfonate
(2c)
Yield: 97%, yellow liquid. IR (ATR, cm−1) νmax = 3041, 2970–2929,
1563, 1510, 1195, 1036, 1000–750. 1H NMR (300 MHz, CDCl3, ppm): δ
= 2.23 (s,3H,5-CH3); 2.63 (s,3H,3-CH3); 2.49 (s,3H, PhCH3); 2.76
(s,3H,S-CH3); 3.78 (s,3H,NCH3); 6.49 (s,1H,CH); 7.44–7.47 (d,2H,Ph,J:
8.3 Hz), 7.51–7.54(d,2H,Ph,J: 8.3 Hz). 13C NMR (75 MHz, CDCl3, ppm)
δ = 12.27; 12.35; 21.40; 34.87; 39.30; 108.03; 128.40; 128.51; 131.36;
143.25; 146.62 and 147.78. Analysis: calcd. for C14H20N2O3S: C 56.73,
H 6.80, N 9.45, S 10.82. Found: C 56.39, H 6.83, N 9.39, S 11.2. TOF MS
(ES+) m/z calcd. for C13H17N2: 201.1392. Found: 201.1393. TOF MS
(ES−) m/z calcd. for CH3O3S: 94.9803. Found: 94.9799.
4.3.4. 2,3,5-trimethyl-1-(4-methoxyphenyl)-pyrazolium methanesulfonate
(2d)
Fig. 5. Experimental densities of RTILs (2a, 2c and 2d) as a function of temperature.
Yield: 98%, light brown liquid. IR (ATR, cm−1) νmax = 3063,
2970–2842, 1604, 1563, 1509, 1254, 1194, 1036, 1000–750. 1H NMR
(300 MHz, CDCl3, ppm): δ = 2.23 (s,3H,5-CH3); 2.61 (s,3H,3-CH3);
2.75 (s,3H,S-CH3); 3.77 (s,3H,NCH3); 3.90 (s,3H, PhOCH3); 6.47
(s,1H,CH); 7.12–7.14 (d,2H,Ph,J: 8.3 Hz), 7.58–7.60(d,2H,Ph,J: 8.3 Hz).
13C NMR (75 MHz, CDCl3, ppm) δ = 11,91; 12.18; 34.56; 39.26; 55.74;
107.76; 115.74; 122.98; 130.15; 146.72; 147.37 and 162.12. Analysis:
calcd. for C14H20N2O4S: C 53.83, H 6.45, N 8.97, S 10.26. Found: C
53.52, H 6.48, N 98.92, S 10.59. TOF MS (ES+) m/z calcd. for
sulfate and concentrated. The salts thus obtained were set under vacu-
um for 48 h at 75 °C.
4.3.1. 1-(4-chlorophenyl)-2,3,5-trimethylpyrazolium methanesulfonate
(2a)
Yield: 94%, yellow liquid. IR (ATR, cm−1) νmax = 3054, 2971–2931,
1563, 1491, 1195,1036, 1000–750. 1H NMR (300 MHz, CDCl3, ppm): δ
= 2.24 (s,3H,5-CH3); 2.62 (s,3H,3-CH3); 2.68 (s,3H,S-CH3); 3.80
(s,3H,NCH3); 6.51 (s,1H,CH); 7.63–7.66 (d,2H,Ph,J: 8.4 Hz),
7.74–7.77(d,2H,Ph,J: 8.4 Hz). 13C NMR (75 MHz, CDCl3, ppm) δ =
12.32; 12.40; 35.07; 39.40; 108.24; 129.55; 130.68; 131.03; 138.82;
146.69 and 148.30. Analysis: calcd. for C13H17ClN2O3S: C 49.29, H 5.41,
C
13H17N2O: 217.1341. Found: 217.1338. TOF MS (ES−) m/z calcd. for
CH3O3S: 94.9803. Found: 94.9802.
4.3.5. 2,3,5-trimethyl-1-(4-nitrophenyl)-pyrazolium methanesulfonate
(2e)
N 8.84, S 10.12. Found: C 49.01, H 5.44, N 8.79, S 10.42. TOF MS (ES+
m/z calcd. for C12H14ClN2: 221.0846. Found: 221.0844. TOF MS (ES−
m/z calcd. for CH3O3S: 94.9803. Found: 94.9802.
)
)
Yield: 90%, yellow solid, m.p: 183.3 °C. IR (ATR, cm−1) νmax = 3066,
2970–2930, 1613, 1564, 1532, 1492, 1358, 1199, 1039, 1000–750. 1
H
NMR (300 MHz, CDCl3, ppm): δ = 2.29 (s,3H,5-CH3); 2.65 (s,3H,3-
CH3); 2.72 (s,3H,S-CH3); 3.85 (s,3H,NCH3); 6.57 (s,1H,CH); 8.14–8.17
(d,2H,Ph,J: 8.8 Hz), 8.53–8.56(d,2H,Ph,J: 8.8 Hz). 13C NMR (75 MHz,
CDCl3, ppm) δ = 12.43; 12.49; 35.51; 39.36; 108.73; 125.93; 131.18;
136.13; 146.99; 149.19 and 149.82. Analysis: calcd. for C13H17N3O5S: C
47.70, H 5.23, N 12.84, S 9.80. Found: C 47.44, H 5.27, N 12.77, S 10.08.
TOF MS (ES+) m/z calcd. for C12H17N3O2: 232.1086. Found: 232.1081.
TOF MS (ES−) m/z calcd. for CH3O3S: 94.9803. Found: 94.9800.
4.3.2. 1-(4-bromophenyl)-2,3,5-trimethylpyrazolium methanesulfonate
(2b)
Yield: 92%, yellow solid, m.p: 76.3 °C. IR (ATR, cm−1) νmax = 3056,
2970–2931, 1562, 1489, 1193, 1036, 1000–750. 1H NMR (300 MHz,
CDCl3, ppm): δ = 2.25 (s,3H,5-CH3); 2.62 (s,3H,3-CH3); 2.73 (s,3H,S-
CH3); 3.80 (s,3H,NCH3); 6.51 (s,1H,CH); 7.65–7.68 (d,2H,Ph,J: 8.7 Hz),
7.80–7.83(d,2H,Ph,J: 8.7 Hz). 13C NMR (75 MHz, CDCl3, ppm) δ =
12.31; 12.36; 35.05; 39.32; 108.24; 127.17; 130.03; 130.79; 134.05;
146.68 and 148.26. Analysis: calcd. for C13H17BrN2O3S: C 43.22, H 4.74,
4.4. General synthesis procedure for 1-aryl-2,3,5-trimethylpyrazolium tet-
rafluoroborate salts (3a–3e)
N 7.75, S 8.88. Found: C 43.01, H 4.78, N 7.72, S 9.08. TOF MS (ES+
m/z calcd. for C12H14BrN2: 265.0340. Found: 265.0338. TOF MS (ES−
m/z calcd. for CH3O3S: 94.9803. Found: 94.9804.
)
)
To
a
stirred
solution
of
appropriate
1-aryl-2,3,5-
trimethylpyrazolium methanesulfonate salt (5.0 mmol) in water
(10 mL) was added tetrafluoroboric acid solution (5.0 mmol, 48% in
water) dropwise over 10–15 min at room temperature. Due to the
anion exchange, the product precipitated after a few minutes. The reac-
tion mixture was allowed to stir for 2 h to ensure that the conversion
was complete. Precipitated solid was filtered, recrystallized from etha-
nol and dried under reduced pressure at 75 °C for 48 h.
4.4.1. 1-(4-chlorophenyl)-2,3,5-trimethylpyrazolium tetrafluoroborate
(3a)
Yield: 95%, light yellow solid, m.p: 133.2 °C. IR (ATR, cm−1) νmax
=
3069, 2970–2937, 1561, 1489, 1035, 851. 1H NMR (300 MHz, CDCl3,
ppm): δ = 2.23 (s,3H,5-CH3); 2.56 (s,3H,3-CH3); 3.69 (s,3H,NCH3);
6.49 (s,1H,CH); 7.57–7.60 (d,2H,Ph,J: 8.9 Hz), 7.65–7.68(d,2H,Ph,J:
8.9 Hz). 13C NMR (75 MHz, CDCl3, ppm) δ = 11.83; 12.03; 34.35;
108.19; 129.55; 130.41; 131.05; 138.83; 146.86 and 148.25. 19F NMR
(282 MHz, CDCl3, ppm): δ = −153.88, −153.94. Analysis: calcd. for
Temperature (K)
C
12H14ClN2BF4: C 46.72, H 4.57, N 9.08. Found: C 46.23, H 4.47, N 8.90.
Fig. 6. Experimental refractive indices of RTILs (2a, 2c, and 2d) as a function of
temperature.
TOF MS (ES+) m/z calcd. for C12H14ClN2: 221.0846. Found: 221.0851.

320
M.C. Özdemir, B. Özgün / Journal of Molecular Liquids 248 (2017) 314–321
4.4.2. 1-(4-bromophenyl)-2,3,5-trimethylpyrazolium tetrafluoroborate
4.5.1. 1-(4-chlorophenyl)-2,3,5-trimethylpyrazolium hexafluorophosphate
(4a)
(3b)
Yield: 86%, yellow solid, m.p: 161.2 °C. IR (ATR, cm−1) νmax
=
Yield: 87%, white solid, m.p: 153.9 °C. IR (ATR, cm−1) νmax = 3067,
2973–2933, 1560, 1489, 831, 748. 1H NMR (300 MHz, CDCl3, ppm): δ =
2.22 (s,3H,5-CH3); 2.52 (s,3H,3-CH3); 3.64 (s,3H,NCH3); 6.47 (s,1H,CH);
7.49–7.51 (d,2H,Ph,J: 8.8 Hz), 7.65–7.68(d,2H,Ph,J: 8.8 Hz). 13C NMR
(75 MHz, DMSO-d6, ppm) δ = 11.93; 12.13; 34.85; 108.27; 130.35;
131.12; 131.24; 137.75; 147.16 and 147.96. 19F NMR (282 MHz,
3093, 2971–2932, 1561, 1486, 1035, 850. 1H NMR (300 MHz, CDCl3,
ppm): δ = 2.22 (s,3H,5-CH3); 2.54 (s,3H,3-CH3); 3.67 (s,3H,NCH3);
6.48 (s,1H,CH); 7.49–7.52 (d,2H,Ph,J: 8.5 Hz), 7.79–7.82 (d,2H,Ph,J:
8.5 Hz). 13C NMR (75 MHz, CDCl3, ppm) δ = 11.98; 12.16; 34.47;
108.19; 127.32; 130.08; 130.61; 134.13; 146.71 and 148.27. 19F
NMR (282 MHz, CDCl3, ppm): δ = −153.85, −153.80. Analysis:
calcd. for C12H14BrN2BF4: C 40.83, H 4.00, N 7.94. Found: C 41.14, H
3.91, N 7.97. TOF MS (ES+) m/z calcd. for C12H14BrN2: 265.0340.
Found: 265.0340.
DMSO-d6, ppm):
δ = −68.90, −71.41. Analysis: calcd. for
C
12H14ClN2PF6: C 39.31, H 3.85, N 7.64. Found: C 39.61, H 3.94, N 7.71.
TOF MS (ES+) m/z calcd. for C12H14ClN2: 221.0846. Found: 221.0843.
TOF MS (ES−) m/z calcd. for PF6: 144.9642. Found: 144.9641.
4.5.2. 1-(4-bromophenyl)-2,3,5-trimethylpyrazolium hexafluorophosphate
4.4.3. 1-(4-methylphenyl)-2,3,5-trimethylpyrazolium tetrafluoroborate
(3c)
(4b)
Yield: 79%, white solid, m.p: 179.8 °C. IR (ATR, cm−1) νmax
=
Yield: 90%, yellow solid, m.p: 147.9 °C. IR (ATR, cm−1) νmax = 3072,
2964–2927, 1566, 1512, 1034, 849. 1H NMR (300 MHz, CDCl3, ppm): δ
= 2.14 (s,3H,5-CH3); 2.46 (s,3H,3-CH3); 2.42 (s,3H, PhCH3); 3.58
(s,3H,NCH3); 6.43 (s,1H,CH); 7.34–7.40 (m,4H,Ph). 13C NMR (75 MHz,
CDCl3, ppm) δ = 11.90; 12.11; 21.42; 34.28; 107.92; 128.27; 128.43;
131.37; 143.29; 146.61 and 147.68. 19F NMR (282 MHz, CDCl3, ppm):
δ = −153.82, −153.88. Analysis: calcd. for C13H17N2BF4: C 54.20, H
5.95, N 9.72. Found: C 54.21, H 5.62, N 9.76. TOF MS (ES+) m/z calcd.
for C13H17N2: 201.1392. Found: 201.1388.
3056, 2973–2933, 1561, 1488, 832, 733. 1H NMR (300 MHz, CDCl3,
ppm): δ = 2.22 (s,3H,5-CH3); 2.52 (s,3H,3-CH3); 3.64 (s,3H,NCH3);
6.47 (s,1H,CH); 7.41–7.44 (d,2H,Ph,J: 8.5 Hz), 7.81–7.84 (d,2H,Ph,J:
8.5 Hz). 13C NMR (75 MHz, DMSO-d6, ppm) δ = 11.93; 12.14;
34.88; 108.28; 126.56; 130.79; 131.40; 134.09; 147.11 and 147.98.
19F NMR (282 MHz, DMSO-d6, ppm): δ = −68.90, −71.42. Analysis:
calcd. for C12H14BrN2PF6: C 35.06, H 3.43, N 6.81. Found: C 35.45, H
3.48, N 6.91. TOF MS (ES+) m/z calcd. for C12H14BrN2: 265.0340.
Found: 265.0340. TOF MS (ES−) m/z calcd. for PF6: 144.9642.
Found: 144.9648.
4.4.4. 2,3,5-trimethyl-1-(4-methoxyphenyl)-pyrazolium tetrafluoroborate
(3d)
4.5.3.
1-(4-methylphenyl)-2,3,5-trimethylpyrazolium
hexafluorophosphate (4c)
Yield: 95%, yellow solid, m.p: 75.6 °C. IR (ATR, cm−1) νmax = 3067,
Yield: 80%, yellow solid, m.p: 138.3 °C. IR (ATR, cm−1) νmax
=
2970–2845, 1606, 1563, 1510, 1258, 1034, 850. 1H NMR (300 MHz,
3080, 2970–2930, 1569, 1515, 830, 742. 1H NMR (300 MHz, CDCl3,
ppm): δ = 2.18 (s,3H,5-CH3); 2.48 (s,3H,3-CH3); 2.49 (s,3H,
PhCH3); 3.60 (s,3H,NCH3); 6.44 (s,1H,CH); 7.34–7.37(d,2H,Ph,J:
8.4 Hz), 7.43–7.46 (d,2H,Ph,J: 8.4 Hz). 13C NMR (75 MHz, CDCl3,
ppm) δ = 11.80; 12.08; 21.43; 34.13; 108.0; 128.33; 128.37;
131.48; 143.47; 146.76 and 147.69. 19F NMR (282 MHz, CDCl3,
ppm): δ = −72.41, −74.93. Analysis: calcd. for C13H17N2PF6: C
CDCl3, ppm):
δ = 2.20 (s,3H,5-CH3); 2.53 (s,3H,3-CH3); 3.65
(s,3H,NCH3); 3.90 (s,3H, PhOCH3); 6.45 (s,1H,CH); 7.10–7.13
(d,2H,Ph,J: 8.9 Hz), 7.45–7.48(d,2H,Ph,J: 8.9 Hz). 13C NMR (75 MHz,
CDCl3, ppm) δ = 11.95; 12.15; 34.16; 55.86; 107.79; 115.87; 123.17;
130.18; 146.85; 147.51 and 162.34. 19F NMR (282 MHz, CDCl3, ppm):
δ = −153.82, −153.87. Analysis: calcd. for C13H17N2OBF4:C 51.35, H
5.63, N 9.21. Found: C 50.82, H 5.35, N 9.15. TOF MS (ES+) m/z calcd.
for C13H17N2O: 217.1341. Found: 217.1338.
45.09, H 4.95, N 8.09. Found: C 45.07, H 5.30, N 8.14. TOF MS (ES+
m/z calcd. for C13H17N2: 201.1392. Found: 201.1391. TOF MS (ES−
m/z calcd. for PF6: 144.9642. Found: 144.9643.
)
)
4.4.5. 2,3,5-trimethyl-1-(4-nitrophenyl)-pyrazolium tetrafluoroborate
(3e)
4.5.4.
2,3,5-trimethyl-1-(4-methoxyphenyl)-pyrazolium
hexafluorophosphate (4d)
Yield: 80%, yellow solid, m.p: 166.5 °C. IR (ATR, cm−1) νmax = 3073,
2970–2871, 1614, 1570, 1527, 1496, 1356, 1037, 856. 1H NMR
(300 MHz, CDCl3, ppm): δ = 2.27 (s,3H,5-CH3); 2.60 (s,3H,3-CH3);
3.73 (s,3H,NCH3); 6.54 (s,1H,CH); 7.92–7.95 (d,2H,Ph,J: 8.9 Hz),
8.53–8.56(d,2H,Ph,J: 8.9 Hz). 13C NMR (75 MHz, DMSO-d6, ppm) δ =
12.02; 12.20; 35.24; 108.70; 126.12; 131.27; 136.46; 147.30; 148.69
and 149.97. 19F NMR (282 MHz, DMSO-d6, ppm): δ = −148.30, −
148.36. Analysis: calcd. for C12H14N3O2BF4: C 45.17, H 4.42, N 13.17.
Found: C 45.22, H 3.97, N 13.23. TOF MS (ES+) m/z calcd. for
Yield: 87%, white solid, m.p: 115.6 °C. IR (ATR, cm−1) νmax = 3021,
2958–2850, 1609, 1588, 1520, 1256, 831, 804. 1H NMR (300 MHz,
CDCl3, ppm):
δ = 2.19 (s,3H,5-CH3); 2.49 (s,3H,3-CH3); 3.60
(s,3H,NCH3); 3.90 (s,3H, PhOCH3); 6.43 (s,1H,CH); 7.10–7.13
(d,2H,Ph,J: 8.9 Hz), 7.39–7.42(d,2H,Ph,J: 8.9 Hz). 13C NMR (75 MHz,
CDCl3, ppm) δ = 11.81; 12.08; 39.97; 55.87; 107.86; 115.95; 123.07;
130.06; 146.99; 147.49 and 162.41. 19F NMR (282 MHz, CDCl3, ppm):
δ = −72.41, −74.93. Analysis: calcd. for C13H17N2OPF6: C 43.10, H
4.73, N 7.73. Found: C 43.30, H 4.56, N 7.81. TOF MS (ES+) m/z calcd.
for C13H17N2O: 217.1341. Found: 217.1342. TOF MS (ES−) m/z calcd.
for PF6: 144.9642. Found: 144.9643.
C12H17N3O2: 232.1086. Found: 232.1091.
4.5. General synthesis procedure for 1-aryl-2,3,5-trimethylpyrazolium
hexafluorophosphate salts(4a–4e)
4.5.5. 2,3,5-trimethyl-1-(4-nitrophenyl)-pyrazolium hexafluorophosphate
(4e)
Yield: 78%, yellow solid, m.p: 222.0 °C. IR (ATR, cm−1) νmax = 3080,
2970–2944, 1615, 1568, 1530, 1498, 1357, 821, 750. 1H NMR (300 MHz,
DMSO-d6, ppm): δ = 2.24 (s,3H,5-CH3); 2.53 (s,3H,3-CH3); 3.66
(s,3H,NCH3); 6.85 (s,1H,CH); 8.0–8.03 (d,2H,Ph,J: 8.8 Hz), 8.56–8.59
(d,2H,Ph,J: 8.8 Hz). 13C NMR (75 MHz, DMSO-d6, ppm) δ = 11.98;
12.15; 35.19; 108.69; 126.13; 131.22; 136.46; 147.32; 148.72 and
149.97. 19F NMR (282 MHz, DMSO-d6, ppm): δ = −68.91, −71.43.
Analysis: calcd. for C12H14N3O2PF6: C 38.21, H 3.74, N 11.14. Found: C
38.40, H 3.83, N 11.16. TOF MS (ES+) m/z calcd. for C12H17N3O2:
To
a
stirred
solution
of
appropriate
1-aryl-2,3,5-
trimethylpyrazolium methanesulfonate salt (5.0 mmol) in water
(10 mL) was added potassium hexafluorophosphate solution (prepared
by dissolving 5.0 mmol KPF6 in 5 mL of water) dropwise over 10–15 min
at room temperature. The solid formation was observed after a few mi-
nutes. For completion of the reaction, the reaction mixture was allowed
to stir for 2 h. The resulting solid was filtered, recrystallized from etha-
nol, and dried in vacuo at 75 °C for 48 h.

M.C. Özdemir, B. Özgün / Journal of Molecular Liquids 248 (2017) 314–321
321
232.1086. Found: 232.1086. TOF MS (ES−) m/z calcd. for PF6: 144.9642.
Found: 144.9645.
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Acknowledgements
The authors are grateful to the Research Foundation of Gazi Univer-
sity (Project no. 05/2010-93) for supporting this study. Melek Canbulat
Özdemir is also grateful for the support from TUBITAK (The Scientific
and Technological Research Council of Turkey), namely, the BIDEP
2211 National Doctoral Scholarship Program.
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Appendix A. Supplementary data
This material includes IR, 1H NMR, 13C NMR, 19F NMR, and TOF-MS
spectra; TGA curves, DSC thermograms, Cyclic Voltammograms of all
the 1-aryl-2,3,5-trimethylpyrazolium salts, and details of computational
study. Supplementary data associated with this article can be found in
the online version, at https://doi.org/10.1016/j.molliq.2017.10.033.
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