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M.C. Ozdemir et al. / Journal of Molecular Structure 1180 (2019) 564e572
565
Milestone) were used for microwave-assisted reactions. FTIR
spectra were obtained from samples with an ATR (Attenuated Total
Reflectance) accessory. NMR spectra were recorded on a Bruker-
Avance-300 MHz spectrometer (at 300 MHz for 1H NMR, 75 MHz
for 13C NMR and 282 MHz for 19F NMR) with TMS as an internal
standard in CDCl3 or DMSO-d6. Elemental analysis was carried out
using a LECO, CHNS-932 elemental analyzer. All melting points
were determined with Electrothermal 9200 melting point appa-
ratus. The thermal stability of the ionic liquids (2e and 3b) was
investigated on a SII Extra TG/DTA 7200 at a heating rate 10 ꢁC
minꢀ1 with nitrogen as the purge gas.
Cyclic Voltammetry experiments were conducted with Elec-
trochemical Workstation CHIe660B instrument at 25 ꢁC. Glassy
carbon macro electrode (surface area: 7.065 ꢂ 10ꢀ2 cm2) was used
as a working electrode. Pt and Ag/AgCl electrodes were used as a
counter and reference electrode, respectively. The solutions of the
synthesized 1-aryl-3,5-dimethylpyrazolium based protic ionic salts
(2ae2e and 3ae3e) with a concentration of 0.1 M were prepared in
anhydrous acetonitrile. Each solution was purged with nitrogen for
at least 10 min to reduce the effect of water and oxygen on cyclic
voltammograms.
CDCl3, ppm):
CH3); 6.0 (s, 1H, CH); 6.94e6.97 (d, 2H, Ph, J: 8.9 Hz); 7.31e7.34 (d,
2H, Ph, J: 8.9 Hz). 13C NMR (75 MHz, CDCl3, ppm) :
d
¼ 2.25 (s, 3H, CH3); 2.29 (s, 3H, CH3); 3.84 (s, 3H,
d
¼ 12.12; 13.49;
55.49; 106.24; 114.09; 126.34; 133.10; 139.44; 148.48; 158.76.
2.2.2. General procedure for the synthesis of 1-aryl-3,5-
dimethylpyrazolium salts
Protic pyrazolium salts were readily prepared according to a
€
Bronsted acid-base reaction carried out in a stoichiometric ratio. To
a stirred solution of 1-aryl-3,5-dimethyl-1H-pyrazole compound
(5 mmol) in a small amount of ethanol (5 mL) at room temperature,
was carefully added concentrated hydrochloric acid (5 mmol, 37%)
for compounds 2ae2e, and tetrafluoroboric acid (5 mmol, 48% in
water) for compounds 3ae3e. The reaction mixture was cooled to
room temperature and stirred for 30 min at room temperature.
After evaporation of solvent the product was washed with hexane
(10 mL) and diethyl ether (10 mL), respectively. The crude product
was dissolved in acetonitrile (10 mL), active charcoal was added
and the mixture was heated under reflux conditions for 2 h. After
filtration, the solvent was removed under reduced pressure. Sub-
sequently, the synthesized salts were recrystallized in ethanol and
dried in vacuum at 75 ꢁC for 48 h.
2.2. Synthesis and characterization
3,5-dimethyl-1-phenylpyrazoliumꢀc1hloride (2a): Yield: 89% (off
2792; 1678; 1588; 1497; 755; 693. 1H NMR (300 MHz, CDCl3, ppm):
¼ 2.37 (s, 3H, 5-CH3); 2.62 (s, 3H, 3-CH3); 6.36 (s, 1H, CH); 7.57
(m, 5H, Ph), 14.5 (brs, 1H, NH). 13C NMR (75 MHz, CDCl3, ppm):
white solid); m.p: 163 ꢁC; IR (ATR, cm
)
nmax ¼ 3254; 3060; 2920-
2.2.1. Synthesis of 1-aryl-3,5-dimethyl-1H-pyrazole compounds
1-aryl-3,5-dimethyl-1H-pyrazole derivatives were synthesized
by a procedure reported in our previous work [26]. In brief, to a
solution of arylhydrazinium hydrochloride (5.0 mmol) in acetic acid
(30 mL), acetylacetone (5.0 mmol) was added with continuous
stirring. The solution was heated at 120 ꢁC under MW irradiation
until all the starting materials were consumed (TLC, 20%
EtOAcehexane). After completion of the reaction, the solvent was
removed under reduced pressure, and the residue was dissolved in
ethyl acetate. The organic layer was washed with diluted sodium
hydrogen carbonate, water, and saturated brine, respectively and
dried over anhydrous sodium sulfate. Then, the solvent was evap-
orated, and the crude product was purified with silica gel column
chromatography.
d
d
¼ 11.36; 12.01; 108.24; 125.96; 130.03; 130.99; 132.95; 144.63;
146.82. Analysis: calcd for C11H13ClN2: C 63.31 H 6.28 N 13.42.
Found: C 62.77 H 6.32 N 13.31.
1-(p-chlorophenyl)-3,5-dimethylpyrazolium chloride (2ꢀb1):
Yield: 90% (milky brown solid); m.p: 139 ꢁC; IR (ATR, cm
)
nmax ¼ 3440; 3107; 2984-2808; 1673; 1571; 1493; 864; 772. 1H
NMR (300 MHz, CDCl3, ppm):
d
¼ 2.37 (s, 3H, 5-CH3); 2.61 (s, 3H, 3-
CH3); 6.32 (s, 1H, CH); 7.52 (m, 4H, Ph), 13.3 (brs, 1H, NH). 13C NMR
(75 MHz, CDCl3, ppm):
d
¼ 11.48; 11.96; 108.29; 127.40; 130.33;
131.51; 137.23; 144.52; 147.31. Analysis: calcd for C11H12Cl2N2: C
54.34 H 4.97 N 11.52. Found: C 53.94 H 5.02 N 11.44.
3,5-dimethyl-1-phenyl-1H-pyrazole (1a): Irradiation time:
1-(p-bromophenyl)-3,5-dimethylpyrazolium chloriꢀd1e (2c):
3268; 3078; 2972-2783; 1703; 1589; 1486; 836; 771. 1H NMR
2.0 min. Yield: 90% (orange oil); 1H NMR (300 MHz, DMSO-d6,
Yield: 92% (milky brown solid); m.p: 142 ꢁC; IR (ATR, cm
)
nmax
¼
ppm):
7.35e7.48 (m, 5H, Ph). 13C NMR (75 MHz, DMSO-d6, ppm):
¼ 12.57; 13.72; 107.55;124.47; 127.32; 129.45; 139.48; 140.16;
148.26.
1-(p-chlorophenyl)-3,5-dimethyl-1H-pyrazole (1b): Irradiation
time: 1.5 min. Yield: 95% (orange oil); 1H NMR (300 MHz, CDCl3,
ppm):
¼ 2.29 (s, 3H, CH3); 2.30 (s, 3H, CH3); 6.0 (s, 1H, CH);
7.36e7.43 (m, 4H, Ph). 13C NMR (75 MHz, CDCl3, ppm):
d
¼ 2.18 (s, 3H, CH3); 2.28 (s, 3H, CH3); 6.05 (s, 1H, CH);
(300 MHz, CDCl3, ppm):
d
¼ 2.35 (s, 3H, 5-CH3); 2.59 (s, 3H, 3-CH3);
d
6.30 (s, 1H, CH); 7.41e7.44 (d, 2H, Ph, J ¼ 8.70); 7.68e7.71 (d, 2H, Ph,
J ¼ 8.70), 13.9 (brs, 1H, NH). 13C NMR (75 MHz, CDCl3, ppm):
d
¼ 11.44; 11.95; 108.30; 125.36; 127.51; 132.0; 133.29; 144.46;
147.28. Analysis: calcd for C11H12BrClN2: C 45.95 H 4.21 N 9.74.
Found: C 45.66 H 4.25 N 9.68.
d
d
¼ 12.24;
1-(p-methylphenyl)-3,5-dimethylpyrazolium chloride (2ꢀd1):
13.36; 107.41; 125.43; 128.94; 132.47; 138.43; 139.15; 149.05.
1-(p-bromophenyl)-3,5-dimethyl-1H-pyrazole (1c): Irradiation
time: 2.0 min. Yield: 78% (light brown oil); 1H NMR (300 MHz,
Yield: 93% (milky brown solid); m.p: 167 ꢁC; IR (ATR, cm
)
nmax ¼ 3426; 3029; 2925-2853; 1642; 1575; 1429; 830; 750. 1H
NMR (300 MHz, CDCl3, ppm):
d
¼ 2.33 (s, 3H, 5-CH3); 2.42 (s, 3H, 3-
CDCl3, ppm):
7.31e7.34 (d, 2H, Ph, J: 8.8 Hz); 7.55e7.58 (d, 2H, Ph, J: 8.8 Hz). 13
NMR (75 MHz, CDCl3, ppm):
¼ 12.38; 13.46; 107.51; 120.43;
125.73; 131.95; 138.93; 139.13; 149.12.
d
¼ 2.29 (s, 3H, CH3); 2.30 (s, 3H, CH3); 6.0 (s, 1H, CH);
CH3); 2.61 (s, 3H, pe(CH3)ePh); 6.27 (s, 1H, CH); 7.37 (m, 4H, Ph).
13C NMR (75 MHz, CDCl3, ppm):
¼ 11.36; 11.84; 21.33; 107.81;
125.80; 130.43; 130.63; 141.60; 144.26; 146.54. Analysis: calcd for
C
d
d
C
12H15ClN2: C 64.71 H 6.79 N 12.58. Found: C 64.2 H 6.82 N 12.48.
1-(p-methylphenyl)-3,5-dimethyl-1H-pyrazole (1d): Irradiation
3,5-dimethyl-1-(p-methoxyphenyl)pyrazolium chloride (2e):
time: 1.5 min. Yield: 90% (orange oil); 1H NMR (300 MHz, CDCl3,
Yield: 95% (light-brown solid); m.p: 62 ꢁC; IR (ATR, cmꢀ1
)
ppm):
5.98 (s, 1H, CH); 7.23e7.25 (d, 2H, Ph, J: 8.4 Hz); 7.29e7.32 (d, 2H,
Ph, J: 8.4 Hz). 13C NMR (75 MHz, CDCl3, ppm):
d
¼ 2.28 (s, 3H, CH3); 2.30 (s, 3H, CH3); 2.40 (s, 3H, CH3);
nmax ¼ 3392; 3065, 2972-2846; 1601; 1514; 1263; 838; 750. 1H
NMR (300 MHz, CDCl3, ppm):
d
¼ 2.32 (s, 3H, 5-CH3); 2.59 (s, 3H,
d
¼ 12.27; 13.51;
3-CH3); 3.87 (s, 3H, pe(OCH3)ePh); 6.24 (s, 1H, CH); 7.03e7.05 (d,
21.04; 106.60; 124.66; 129.51; 137.07; 137.49; 139.30; 148.63.
3,5-dimethyl-1-(p-methoxyphenyl)-1H-pyrazole (1e): Irradia-
tion time: 1.0 min. Yield: 90% (brown oil); 1H NMR (300 MHz,
2H, Ph); 7.42e7.44 (d, 2H, Ph). 13C NMR (75 MHz, CDCl3, ppm):
d
¼ 11.63; 11.92; 55.70; 107.56; 115.07; 126.22; 127.54; 144.0;
146.53; 161.05. Analysis: calcd for C12H15ClN2O: C 60.38 H 6.33 N