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J ¼ 6.7 Hz, 2H), 3.56 (s, 2H, –NH2), 2.32 (s, 3H) ppm. 13C NMR
(100 MHz, CDCl3) d (ppm): 143.9, 129.8, 127.8, 115.3, 20.5.
Experimental
Materials and methods
All the chemicals and solvents were purchased from commer-
cial suppliers (Aldrich, Merck). Melting points, reported without
correction, were measured using a Stuart SMP10 apparatus. The
FT-IR spectra were obtained with a Shimadzu IR prestige 21
spectrophotometer (Columbia, MD, USA). 1H and 13C NMR
spectra were recorded with a Bruker AVANCE III system oper-
ating at 400 MHz, using residual and deuterated solvent peaks
of CDCl3 (dH 7.26; dC 77.0) and DMSO (dH 2.50; dC 39.5) as
reference standards. Elemental analyses were performed on
a Thermo Scientic Flash 2000 CHNS/O analyser and their
results agreed with the calculated values. Raman spectra was
acquired with Thermo Scientic DXR Raman Microscope,
excitation was accomplished by using a single line of 780 nm
wavelength from a frequency-stabilized single mode diode
laser. The incident power was about 20 mW at the sample point.
The density of the DES was measured using a liquid densi-
tometer (Anton Paar DMA4500M). An Abbe type refractometer
(model 2WAJ equipped with a sodium D1 line) was used to
measure the DES refractive. The conductivity and its tempera-
ture dependence were determined using a Jenway 470 portable
conductivity/TDS meter calibrated by measuring the conduc-
tivities of aqueous solutions of KCl at different concentrations.
The variation of the temperature for the determination of the
physical properties was done by using a Lauda Alpha water
circulator. Cyclic voltammetry was carried out using a Gamry
Interface 1000E potentiostat from Gamry Instruments. The
electrochemical measurements were performed in a conven-
tional three-electrode cell, with the 0.071 cm2 Glassy Carbon,
the 0.0314 cm2 Au, the 0.0314 cm2 Pt, and 0.0314 cm2 Sn disks
as the working electrodes, Ag/AgCl as the reference electrode,
and Pt wire as the counter electrode. The working electrodes
were polished with 1 and 0.3 mm g-alumina paste, rinsed and
sonicated for two minutes with deionized water, and dried prior
to all measurements. The experiments were performed at 60 ꢁC
General experimental procedure for the synthesis of N-
arylacetamides 1b–3b, 8b–14b
To an open headspace vial equipped with a magnetic stir bar,
the nitroarene (1.0 mmol) and 1.6 g of SnCl2$2H2O/ChCl (2 : 1
molar ratio) DES were added, and the resulting solution was
then stirred and heated at 80 ꢁC. Aer complete reduction of the
nitroarene (TLC), Ac2O (1.2 mmol) and AcONa$3H2O (2.0 mmol)
in 2 mL water were added and heating was continued until the
reaction was complete (TLC analysis). Next, the reaction mixture
was cooled to room temperature, neutralized with NaHCO3 and
extracted with AcOEt (3 ꢂ 10 mL). Aer drying over anhydrous
Na2SO4 and evaporating the solvent under reduced pressure,
the crude material was puried by column chromatography on
silica gel to afford the desired product.
N-Phenylacetamide (1b). Light yellow solid, mp 112–114 ꢁC.
1
Yield: 92%. H NMR (400 MHz, CDCl3) d (ppm): 8.24 (brs, 1H),
7.54 (d, J ¼ 7.2 Hz, 2H), 7.32–7.28 (m, 2H), 7.12–7.08 (m, 1H),
2.16 (s, 3H). 13C NMR (100 MHz, CDCl3) d (ppm): 169.1, 138.1,
128.9, 124.2, 120.2, 24.4.
N-(4-Bromophenyl)acetamide (14b). Light beige solid, mp
166–169 ꢁC. Yield: 92%. 1H NMR (400 MHz, CDCl3 + DMSO-d6)
d (ppm): 9.37 (br s, 1H), 7.40 (d, J ¼ 6.3 Hz, 2H), 7.29 (d, J ¼
6.0 Hz, 2H), 2.05 (s, 3H). 13C NMR (100 MHz, CDCl3 + DMSO-d6)
d (ppm): 169.0, 138.1, 131.5, 121.3, 115.6, 24.2.
General experimental procedure for the synthesis of
indolo(pyrrolo)[1,2-a]quinoxalines 17a–k and 18a–j
To an open headspace vial equipped with a magnetic stir bar,
the nitroarene 17 or 18 (1.0 mmol), the corresponding aldehyde
(1 mmol) and 2.0 g of SnCl2$2H2O/ChCl (2 : 1 molar ratio) DES
were added, aꢁnd the resulting solution was then stirred and
heated at 110 C. Aer running the reaction to an appropriate
time (TLC analysis), the mixture was allowed to cool to room
temperature, neutralized with NaHCO3 and extracted with
AcOEt (3 ꢂ 10 mL). Aer drying over anhydrous Na2SO4 and
evaporating the solvent under reduced pressure, the crude
material was puried by column chromatography on silica gel
to afford the desired product.
using a scan rate of 100 mV sꢀ1
.
General experimental procedure for the synthesis of
compounds 1a–6a, 10a–16a
To an open headspace vial equipped with a magnetic stir bar,
4-Phenylpyrrolo[1,2-a]quinoxaline (17a). Yellow solid, mp
the nitroarene (1.0 mmol) and 1.6 g of SnCl2$2H2O/ChCl DES 116–119 ꢁC. Yield: 92%. 1H NMR (400 MHz, CDCl3) d (ppm):
were added, and the resulting solution was then stirred and 8.11–8.04 (m, 3H), 7.86 (s, 1H), 7.71 (d, J ¼ 2.8 Hz, 1H), 7.59–7.56
heated at 80 ꢁC. Aer running the reaction to an appropriate (m, 3H), 7.41 (s, 2H), 6.99 (d, J ¼ 4.0 Hz, 1H), 6.82 (d, J ¼ 2.6 Hz,
time (TLC analysis), the mixture was cooled to room tempera- 1H). 13C NMR (100 MHz, CDCl3) d (ppm): 154.2, 138.4, 136.1,
ture, neutralized with NaHCO3 and extracted with AcOEt (3 ꢂ 10 130.0, 129.8, 128.7, 128.6, 127.4, 127.0, 125.2, 125.2, 114.7,
mL). Aer drying over anhydrous Na2SO4 and evaporating the 114.0, 113.6, 108.7. Anal. calcd for C17H12N2: C, 83.58; H,
solvent under reduced pressure, the desired product was ob- 4.95; N, 11.47. Found: C, 83.60; H, 4.91; N, 11.49.
tained in high purity without further purication.
6-(4-Methoxyphenyl)indolo[1,2-a]quinoxaline (18b). Red
p-Aminophenol (3a). Beige solid, mp 187–189 ꢁC. Yield: 93%. solid, mp 165–167 ꢁC. 1H NMR (400 MHz, CDCl3) d (ppm): 8.49
1H NMR (400 MHz, DMSO-d6) d (ppm): 8.49 (brs, 1H), 6.50 (d, J (dd, J ¼ 15.8, 10.0 Hz, 1H), 8.14 (d, J ¼ 8.5 Hz, 1H), 7.86 (d, J ¼
¼ 8.8, 2H), 6.43 (d, J ¼ 8.8, 2H), 4.38 (br s, 2H, –NH2). 13C NMR 8.5 Hz, 1H), 7.71 (d, J ¼ 6.4 Hz, 1H), 7.64 (d, J ¼ 8.7 Hz, 1H), 7.58
(100 MHz, DMSO-d6) d (ppm): 148.7, 141.1, 116.2, 115.7.
(m, 1H), 7.15 (d, J ¼ 8.7 Hz, 2H), 7.03 (d, J ¼ 8.4 Hz, 3H), 6.70 (d,
p-Toluidine (12a). White solid, mp 41–43 C. Yield 94%. H J ¼ 1.4 Hz, 1H), 3.91 (s, 3H). 13C NMR (100 MHz, CDCl3) d (ppm):
1
ꢁ
NMR (400 MHz, CDCl3) d (ppm): 7.04 (d, J ¼ 7.5 Hz, 2H), 6.67 (d, 172.9, 163.0, 134.3, 133.6, 131.9, 131.4, 129.9, 129.4, 128.8,
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RSC Adv., 2020, 10, 40552–40561 | 40559