Synthesis of pyridinium-based salts: Catalytic application at the synthesis of six membered O-heterocycles

Article abstract of DOI:10.1016/j.mcat.2019.110403

In this paper, a range of pyridinium-based ionic liquid (IL) and molten salts (MSs) with various counter ions were designed, synthesized and fully characterized. These novel ionic liquid and molten salts were prepared via the reaction of [PySO₃

Full text of DOI:10.1016/j.mcat.2019.110403

MolecularCatalysis475(2019)110403
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Molecular Catalysis
journal homepage: www.elsevier.com/locate/mcat
Synthesis of pyridinium-based salts: Catalytic application at the synthesis of
six membered O-heterocycles
Saeed Babaeea, Mohammad Ali Zolfigola,⁎, Mahmoud Zareia,⁎, Maryam Abbasia, Zahra Najafib
a Department of Organic Chemistry, Faculty of Chemistry, Bu-Ali Sina University, Hamedan 6517838683, Iran
b Department of Medicinal Chemistry, School of Pharmacy, Hamadan University of Medical Sciences, Hamadan, Iran
A R T I C L E I N F O
A B S T R A C T
Keywords:
In this paper, a range of pyridinium-based ionic liquid (IL) and molten salts (MSs) with various counter ions were
designed, synthesized and fully characterized. These novel ionic liquid and molten salts were prepared via the
reaction of [PySO3H]Cl with AlCl3, FeCl3, NaBF4 and KPF6 to produce the desired catalysts [PySO3H]X
(X = AlCl4, FeCl4, BF4 and PF6). The structure of these catalysts were investigated by FT-IR, NMR (1H, 13C, 27Al,
19F) and mass spectra as well as the use of the XRD, SEM, TG, DTG and DTA techniques. Magnetic measurements
(VSM) of [PySO3H]FeCl4 as a magnetic molten salts was also investigated. Three categories of six membered O-
heterocyclic compounds such as 2-amino-4H-chromene, 2-amino-4,8-dihydropyrano and 2-amino-4H-pyrans
were prepared in the presence of a catalytic amount of the above said molten salts. These synthesized O-het-
erocyclic compounds are highly regarded due to their biological activities.
2-Amino-4H-chromene
2-Amino-4,8-dihydropyrano
2-Amino-4H-pyrans
Anion exchange
Drug candidates
Magnetic molten salts
Molten salts
O-heterocyclic compounds
[PySO3H]FeCl4
[PySO3H]AlCl4
[PySO3H]BF4
[PySO3H]PF6
Introduction
heterocyclic structures [22,23]. Cyclic structures with oxygen rings
have been observed in the structures of various pharmaceutical com-
Anion exchange is a subjective way for designing and synthesis of
ionic liquids (ILs) or molten salts (MSs) with a wide range of counter
ions which cannot be directly prepared. Nowadays, the physico-che-
mical properties of ILs and MSs such as: viscosity, melting point, vapor
pressure of fluids and fluorescence had been changed via the ex-
changing of their counter ions [1–4]. By changing physical and che-
mical properties of ILs and MSs, their catalytic ability will be also
change. Ionic liquids and molten salts as efficient catalysts and/or re-
agents were applied for nitration reaction, regioselective sulfonation,
preparation of energetic compounds and other organic synthesis under
milder conditions [5–10].
A variety of compounds have been used for the synthesis of ionic
liquids, which have revealed various catalytic and chemical properties.
Ionic liquids as dual role catalysts with both Brønsted and Lewis acidic
properties have high catalytic abilities [2,5,11–20]. Due to the design
ability of ionic liquids, these catalysts in perennials have been used for
the synthesis of a various kinds of biological and pharmaceutical can-
didate compounds [21].
pounds such as anti-cancer [24], anti-alzheimer [25], anti-malarial [26]
and other biological active compounds [25]. The presence of 2-amino-
4H-chromene, 2-amino-4,8-dihydropyrano and 2-amino-4H-pyrans
rings in the molecular structures, naturally produces a spectrum of
biological properties such as antitumor [27], antioxidants [28] and
antifungal [29]. The presence of these biological properties is the major
reason for the developing of various methodologies at the synthesis of
described valuable compounds [30–36].
Due to the above facts and on the basis of our previous investiga-
tions on the field of ILs and MSs with chlorosulfonic acid [37,38], we
were interested on the development of anion exchange method for the
synthesis of ionic liquid {[PySO3H]BF4, m.p. 85–88 (oC)}, molten salts
{[PySO3H]AlCl4, m.p. > 300 (oC)}, {[PySO3H]PF6, m.p. 258–260 (oC)}
and {[PySO3H]FeCl4, m.p. 266 dec}. The ionic liquid (IL) [PySO3H]BF4
and above said molten salts (MSs) [PySO3H]X (X = FeCl4, AlCl4 and
BF4) were utilized as efficient and reusable catalysts for the preparation
of a wide range of O-heterocyclic compound (2-amino-4H-chromene, 2-
amino-4,8-dihydropyrano and 2-amino-4H-pyrans) through the con-
densation reaction of aldehyde, malononitrile and 2-hydroxynaphtalen-
1,4-dione, 5-Hydroxy-2-(hydroxymethyl)-4H-pyran-4-one or Ethyl
The presence of oxygen atoms in the structure of the heterocyclic
compounds leads to the creation of biological properties of O-
⁎ Corresponding authors.
E-mail addresses: zolfi@basu.ac.ir, mzolfigol@yahoo.com (M.A. Zolfigol), mahmoud8103@yahoo.com (M. Zarei).
https://doi.org/10.1016/j.mcat.2019.110403
Received 24 January 2019; Received in revised form 9 May 2019; Accepted 11 May 2019
2468-8231/©2019PublishedbyElsevierB.V.

S. Babaee, et al.
MolecularCatalysis475(2019)110403
Scheme 1. Synthesis of O-heterocyclic compounds using [PySO3H]X (X = FeCl4 BF4, PF6 or AlCl4).
benzoyl acetate under mild, green and solvent-free conditions (Scheme
1).
ethyl acetate). Then, 10 ml of acetone was added to the reaction mix-
ture and the described catalysts (which are not soluble in the acetone)
were subsequently removed by centrifugation (1000 rpm). Finally, after
the evaporation of the solvent at room temperature, the product was
purified with ethyl acetate (Scheme 1).
Experimental
General procedure for the preparation of molten salts [PySO3H]X
(X = FeCl4, BF4, PF6 or AlCl4)
2. -Amino-5,10-dioxo-4-(p-tolyl)-5,10-dihydro-4H-benzo[g]
chromene-3-carbonitrile (6b)
At first, ionic liquid [PySO3H]Cl was synthesized according to our
previously reported procedure [39]. A mixture of [PySO3H]Cl (5 mmol,
0.975 g) and one of the inorganic salts (AlCl3, FeCl3, NaBF4 or KPF6)
(5 mmol) was placed into a mortar and warmed up to at 60 °C, and the
reaction mixture grinded by a pestle for two hours. After completion of
the reaction, the reaction mixture was cool down to room temperature,
ethanol was used to purify the obtained ILs and MSs. molten salts
[PySO3H]FeCl4, [PySO3H]PF6, [PySO3H]AlCl4 and ionic liquid
[PySO3H]BF4 were obtained in (1.76 g) 99%, (1.46 g) 96%, (1.61 g)
99% and (1.17 g) 95%, yields, respectively (Scheme 2).
Orange solid; Mp: 263–265 °C; IR (KBr): υ (cm−1) = 3400, 3334,
3207, 2962, 2197, 1692, 1670; 1H NMR (300 MHz, DMSO-d6) δ
:
ppm
8.12 - 7.99 (m, 1 H), 7.86 (dtd, J = 8.6, 5.3, 2.0 Hz, 3 H), 7.31 (s, 2 H),
7.19 (d, J =7.8 Hz, 2 H), 7.11 (d, J =7.9 Hz, 2 H), 4.57 (s, 1 H), 2.25 (s,
3 H). 13C NMR (75 MHz, DMSO-d6) δ ppm: 183.0, 177.3, 158.8, 149.2,
141.1, 136.7, 135.0, 134.6, 131.5, 131.1, 129.6, 128.0, 126.5, 126.2,
122.6, 58.1, 36.6, 21.2.
2. -Amino-4-(3,5-difluorophenyl)-5,10-dioxo-5,10-dihydro-4H-
benzo[g]chromene-3-carbonitrile (6i)
General procedure for the synthesis of O-heterocyclic compounds (2-amino-
4H-chromene, 2-amino-4,8-dihydropyrano and 2-amino-4H-pyrans)
Orange solid; Mp: 260–263 °C; IR (KBr): υ (cm−1) = 3396, 3316,
3193, 2199, 1622, 1667, 1622; 1H NMR (400 MHz, DMSO-d6) δ
:
The mixture of O-derivatives (2-hydroxynaphtalen-1,4-dione, 5-
hydroxy-2-(hydroxymethyl)-4H-pyran-4-one or ethyl benzoylacetate)
(1 mmol), malononitrile (1 mmol, 0.066 g) and aldehyde (1 mmol) in
the presence of 10 mol% of molten salts [PySO3H]PF6 (0.03 g),
[PySO3H]AlCl4 (0.033 g), [PySO3H]FeCl4 (0.035 g) or 15 mol% ionic
liquid [PySO3H]BF4 (0.037 g) in a 25 ml round-bottomed flask was
stirred at 90 °C under solvent-free condition. After the completion of the
reactions which were monitored by the TLC technique (4/6 n-hexane:
ppm
8.09–8.05 (m, 1 H), 7.93–7.80 (m, 4 H), 7.43 (s, 1 H), 7.18–7.11 (m,
3 H), 7.11–7.06 (m, 1 H), 4.71 (s, 1 H). 13C NMR (101 MHz, DMSO-d6) δ
ppm: 182.5, 176.7, 163.6, 163.5, 161.2, 161.1, 158.2, 158.2, 149.6,
148.3, 148.2, 148.1, 134.4, 134.1, 130.9, 130.8, 156.0, 125.8, 120.1,
119.0, 119.0, 111.1, 111.0, 110.9, 110.8, 102.8, 102.5, 102.3, 56.6,
36.2.
Scheme 2. Synthesis of ionic liquid and molten salts [PySO3H]X (X = FeCl4, BF4, PF6 or AlCl4).
2

S. Babaee, et al.
MolecularCatalysis475(2019)110403
Scheme 3. Proposed mechanism for the synthesis O-heterocycle compounds using [PySO3H]X (X = FeCl4, AlCl4, BF4 and PF6).
2. -Amino-6-(hydroxymethyl)-4-(4-hydroxyphenyl)-8-oxo-4,8-
dihydropyrano[3,2-b]pyran-3-carbonitrile (7 g)
White solid; Mp: > 300 °C; IR (KBr): υ (cm−1) = 3422, 3350, 3268,
3032, 2923, 2200, 1685, 1657, 1631; 1H NMR (400 MHz, DMSO-d6) δ
ppm: 9.56 (s, 1 H), 7.22 (s, 2 H), 7.11 (d, J =8.6 Hz, 2 H), 6.80 (d, J
=8.5 Hz, 2 H), 6.36 (s, 1 H), 5.74 (s, 1 H), 4.69 (s, 1 H), 4.26 (d, J
=15.9 Hz, 1 H), 4.17 (d, J =15.8 Hz, 1 H). 13C NMR (101 MHz, DMSO-
d6) δ ppm: 169.6, 168.1, 159.1, 157.0, 149.5, 136.0, 131.1, 128.8, 119.4,
115.6, 111.2, 59.1, 56.0, 39.5.
2. -amino-4-(3-ethoxy-4-hydroxyphenyl)-6-(hydroxymethyl)-8-
oxo-4,8-dihydropyrano[3,2-b]pyran-3-carbonitrile (7 h)
1H NMR (400 MHz, DMSO-d6) δ ppm: 9.03 (s, 1 H), 7.19 (s, 2 H), 6.80
(d, J =2.0 Hz, 1 H), 6.78 (d, J =8.1 Hz, 1 H), 6.64 (dd, J = 8.1, 2.0 Hz,
1 H), 6.32 (s, 1 H), 5.71 (t, J =6.1 Hz, 1 H), 4.66 (s, 1 H), 4.19 (qd,
J = 16.1, 6.0 Hz, 2 H), 4.00 (q, J =7.0 Hz, 2 H), 1.32 (t, J =7.0 Hz,
3 H). 13C NMR (101 MHz, DMSO-d6) δ ppm: 169.5, 168.1, 159.1, 149.3,
146.7, 146.4, 136.0, 131.5, 120.0, 119.4, 115.8, 113.1, 111.2, 63.8,
59.1, 55.8, 39.8, 14.6.
Fig. 1. FT-IR of [PySO3H]X (X = FeCl4, BF4, PF6 or AlCl4) and [PySO3H]Cl in
KBr.
2. -Amino-6-(hydroxymethyl)-4-(4-nitrophenyl)-8-oxo-4,8-
dihydropyrano[3,2-b]pyran-3-carbonitrile (7e)
White solid; Mp: > 300 °C; IR (KBr): υ (cm−1) = 3537, 3454, 3328,
3176, 2923, 2195, 1673, 1650, 1520, 1350; 1H NMR (400 MHz, DMSO-
d6) δ ppm: 8.36 (d, J =8.3 Hz, 2 H), 7.72 (d, J =8.2 Hz, 2 H), 7.50 (s,
2 H), 6.45 (s, 1 H), 5.80 (s, 1 H), 5.18 (s, 1 H), 4.26 (q, J =15.6 Hz, 2 H).
13C NMR (101 MHz, DMSO-d6) δ ppm: 169.5, 168.3, 159.3, 147.9, 147.7,
147.1, 136.6, 129.3, 124.1, 118.9, 111.5, 59.0, 54.6, 18.5.
Ethyl 6-amino-5-cyano-4-(4-nitrophenyl)-2-phenyl-4H-pyran-3-carboxylate
(8e)
1H NMR (300 MHz, DMSO-d6) δ ppm: 8.25 (d, J =8.2 Hz, 2 H), 7.58
(d, J =8.2 Hz, 2 H), 7.48 (s, 5 H), 7.20 (s, 1 H), 4.65 (s, 1 H), 3.76 (q, J
=7.1 Hz, 2 H), 0.73 (t, J =6.9 Hz, 3 H). 13C NMR (75 MHz, DMSO-d6) δ
ppm: 165.6, 159.8, 155.0, 152.2, 147.1, 133.3, 130.5, 129.2, 129.0,
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MolecularCatalysis475(2019)110403
Fig. 2. 1HNMR of [PySO3H]X (X = BF4, PF6, AlCl4 or FeCl4) in DMSO-d6.
Fig. 3. 13C NMR of [PySO3H]X (X = BF4, PF6 or AlCl4) in DMSO-d6.
128.5, 127.6, 126.5, 124.4, 108.2, 60.8, 52.2, 25.0, 13.6.
Ethyl 6-amino-5-cyano-4-(3-ethoxy-4-hydroxyphenyl)-2-phenyl-4H-pyran-
3-carboxylate (8i)
Ethyl 6-amino-5-cyano-4-(3,5-difluorophenyl)-2-phenyl-4H-pyran-3-
carboxylate (8 h)
White solid; Mp: 209–211 °C; IR (KBr): υ (cm−1) = 3471, 3387,
3325, 3160, 2979, 2201, 1676; 1H NMR (400 MHz, DMSO-d6) δ
:
ppm
8.86 (s, 1 H), 7.50 - 7.39 (m, 5 H), 6.94 (s, 2 H), 6.78 - 6.71 (m, 2 H),
6.64 (dd, J = 8.1, 2.0 Hz, 1 H), 4.33 (s, 1 H), 3.99 (q, J =7.0 Hz, 2 H),
3.77 (q, J =7.1 Hz, 2 H), 1.32 (t, J =7.0 Hz, 3 H), 0.75 (t, J =7.1 Hz,
3 H). 13C NMR (101 MHz, DMSO-d6) δ ppm: 165.7, 159.0, 153.2, 146.3,
145.9, 134.9, 133.1, 129.8, 128.3, 128.0, 119.8, 119.7, 115.6, 112.9,
109.4, 63.8, 60.1, 57.2, 39.3, 14.7, 13.2.
White solid; Mp: 182–183 °C; IR (KBr): υ (cm−1) = 3411, 3332,
3268, 3226, 2983, 2201, 1702, 1678; 1H NMR (400 MHz, DMSO-d6) δ
ppm: 7.51 - 7.43 (m, 5 H), 7.17 (d, J =3.5 Hz, 2 H), 7.14 (td, J = 9.2,
2.4 Hz, 1 H), 7.00 (dd, J = 8.3, 2.2 Hz, 2 H), 4.57 (s, 1 H), 3.79 (qd,
J = 7.1, 1.0 Hz, 2 H), 0.75 (t, J =7.1 Hz, 3 H). 13C NMR (101 MHz,
DMSO-d6) δ ppm: 165.2, 163.6, 163.5, 161.2, 161.0, 159.1, 159.1,
155.0, 155.0, 148.9, 148.8, 148.7, 132.8, 129.9, 128.5, 127.9, 119.2,
119.2, 110.6, 110.6, 110.4, 110.4, 107.6, 102.9, 102.6, 102.3, 60.2,
55.9, 39.3, 13.1.
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MolecularCatalysis475(2019)110403
Fig. 4. 19F NMR of [PySO3H]X (X = BF4 and PF6) in D2O.
Ethyl 6-amino-5-cyano-2-phenyl-4-(pyridin-3-yl)-4H-pyran-3-carboxylate
(8 j)
White solid; Mp: 200–201 °C; IR (KBr): υ (cm−1) = 3357, 3299,
2987, 2189, 1711, 1678, 1614; 1H NMR (400 MHz, DMSO-d6) δ
:
ppm
8.48 (dd, J = 6.2, 1.5 Hz, 2 H), 7.69 (dt, J = 7.9, 1.9 Hz, 1 H), 7.44 (qq,
J = 7.7, 3.8, 3.0 Hz, 6 H), 7.14 (s, 2 H), 4.52 (s, 1 H), 3.76 (q, J
=6.8 Hz, 2 H), 0.72 (t, J =7.1 Hz, 3 H). 13C NMR (101 MHz, DMSO-d6)
δ
ppm: 165.2, 159.2, 155.0, 148.6, 148.3, 139.6, 135.0, 132.9, 130.0,
128.5, 128.0, 124.0, 119.4, 107.9, 60.2, 56.3, 37.4, 13.1.
Ethyl 6-amino-5-cyano-2-phenyl-4-(4-(trifluoromethyl)phenyl)-4H-pyran-
3-carboxylate (8k)
White solid; Mp: 162–163 °C; IR (KBr): υ (cm−1) = 3416, 3331,
3231, 2981, 2199, 1656, 1329; 1H NMR (400 MHz, DMSO-d6) δ
:
ppm
7.74 (d, J =8.1 Hz, 2 H), 7.54 - 7.40 (m, 7 H), 7.15 (s, 2 H), 4.57 (s,
1 H), 3.76 (q, J =7.1 Hz, 2 H), 0.71 (t, J =7.1 Hz, 3 H). 13C NMR
(101 MHz, DMSO-d6) δ ppm: 165.2, 159.2, 155.0, 148.8, 132.9, 130.0,
128.5, 128.2, 128.0, 127.8, 127.5, 127.2, 125.6, 125.6, 125.6, 125.5,
122.9, 119.4, 108.0, 60.2, 56.2, 39.6, 13.1.
Fig. 5. 27Al NMR of [PySO3H]AlCl4 in DMSO-d6.
Fig. 6. Mass spectra of [PySO3H]BF4.
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MolecularCatalysis475(2019)110403
Fig. 7. Mass spectra of [PySO3H]PF6.
Fig. 8. Mass spectra of [PySO3H]AlCl4.
Table 1
Table 2
XRD data [PySO3H]BF4.
XRD data [PySO3H]PF6.
Entry
2Ɵ
Peak width (degree)
Size [nm]
Inter planer distance [nm]
Entry 2Ɵ Peak width (degree)
Size [nm]
Inter planer distance [nm]
1
2
3
4
5
6
26.35
27.47
32.04
36.77
43.33
43.85
0.15
0.18
0.17
0.26
0.30
0.27
54.49
45.89
49.51
32.31
28.57
36.20
0.338
0.325
0.279
0.244
0.210
0.206
1
15.46
0.12
66.31
60.91
74.49
67.47
59.22
62.05
0.575
0.442
0.348
0.338
0.323
0.301
2
3
4
5
6
20.03
25.50
26.33
27.53
29.71
0.13
0.11
0.12
0.14
0.13
6

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(101 MHz, DMSO-d6) δ ppm: 165.3, 159.1, 154.6, 150.5, 150.4, 149.71,
149.6, 148.1, 148.0, 147.3, 147.1, 142.0, 142.0, 141.9, 132.9, 129.9,
128.5, 128.0, 124.2, 124.2, 124.1, 124.1, 119.4, 117.7, 117.5, 116.5,
116.3, 108.1, 60.2, 56.3, 39.5, 13.2.
Table 3
XRD data [PySO3H]AlCl4.
Entry
2Ɵ
Peak width (degree)
Size [nm]
Inter planer distance [nm]
1
2
3
4
7.91
0.22
0.28
0.43
0.66
36.39
28.28
18.77
12.82
1.24
10.20
23.06
24.46
0.875
0.385
0.365
Ethyl 6-amino-4-(3,5-bis(trifluoromethyl)phenyl)-5-cyano-2-phenyl-4H-
pyran-3-carboxylate (8 m)
White solid; Mp: 185–187 °C; IR (KBr): υ (cm−1) = 3410, 3323,
3294, 3207, 2982, 2201, 1680, 1612; 1H NMR (400 MHz, DMSO-d6) δ
ppm: 8.06 (s, 1 H), 7.95 (s, 2 H), 7.51 - 7.43 (m, 5 H), 7.26 (s, 2 H), 4.84
(s, 1 H), 3.75 (qd, J = 7.1, 1.0 Hz, 2 H), 0.71 (t, J =7.1 Hz, 3 H). 13C
NMR (101 MHz, DMSO-d6) δ ppm: 165.2, 159.3, 155.2, 147.8, 132.6,
130.9, 130.6, 130.3, 130.2, 130.0, 128.4, 128.1, 127.3, 124.6, 121.9,
119.1, 107.3, 60.3, 55.6, 39.1, 13.0.
Table 4
XRD data [PySO3H]FeCl4.
Entry
2Ɵ
Peak width (degree)
Size [nm]
Inter planer distance [nm]
1
2
3
4
5
18.97
22.52
24.57
25.57
27.12
0.65
0.70
0.60
0.48
0.5
12.20
11.49
13.45
16.84
16.23
0.466
0.393
0.361
0.351
0.328
Result and discussion
As mentioned above, the ionic liquid [PySO3H]BF4 and molten salts
[PySO3H]X (X = FeCl4, PF6 and AlCl4) were synthesized by one-pot
reaction of salts (AlCl3, FeCl3, NaBF4 or KPF6) and [PySO3H]Cl under
solvent free condition at 60 °C (Scheme 3). Then, structures of
[PySO3H]X (X = FeCl4, BF4, PF6 and AlCl4) were studied using tech-
niques FT-IR, NMR (1H, 13C, 9F & 27Al) and mass spectra. In the fol-
lowing, morphological and dimensions of the presented IL and MSs
were studied by using of XRD and SEM techniques. Furthermore, TG,
DTG and DTA analysis were used for showing the range of their cor-
responding thermal stability of [PySO3H]X (X = FeCl4, BF4, PF6 and
AlCl4).
The FT-IR spectrum of [PySO3H]Cl and [PySO3H]X (X = FeCl4, BF4,
PF6 and AlCl4) were compared in Fig. 1. FT-IR of the all of the men-
tioned IL and MSs catalyst includes the broad peak of the OeH acid
groups SO3H at 2500–3400 cm−1. In addition, two peaks 1201−1056,
1187−1051, 1176−1071 and 1255−1095 cm−1 have a good corre-
lation with vibrational transplantation of OeS and NeS respectively
(Fig. 1). Hexafluorophosphate [Py-SO3H]PF6 was shown a broad strong
band at 834 cm-1 [39] and tetrafluoroborat [Py-SO3H]BF4 shown broad
band at 1086 cm−1 [40]. The OeH stretching regions in FT-IR (Fig. 1)
are different among for different presented catalysts which are due to
the presence of fluorine within the structure of both of them. These
differences may be due to the intra-molecular hydrogen bonding be-
tween hydrogen of SO3H group with the fluorine of their corresponding
counter ions in the structure of two catalysts [PySO3H]X (X = BF4,
PF6).
Fig. 9. XRD of [PySO3H]X (X = AlCl4, BF4, PF6 and FeCl4).
Ethyl 6-amino-5-cyano-4-(3,4-difluorophenyl)-2-phenyl-4H-pyran-3-
carboxylate (8 l)
White solid; Mp: 185–187 °C; IR (KBr): υ (cm−1) = 3411, 3332,
3295, 2983, 2202; 1H NMR (400 MHz, DMSO-d6) δ ppm: 7.52 - 7.38 (m,
6 H), 7.32 (ddd, J = 11.5, 7.7, 2.2 Hz, 1 H), 7.11 (s, 3 H), 4.51 (s, 1 H),
3.77 (qd, J = 7.2, 1.0 Hz, 2 H), 0.73 (t, J =7.1 Hz, 3 H). 13C NMR
The spectra of NMR (1H, 13C, 19F & 27Al in DMSO-d6 and D2O)
[PySO3H]X (X = BF4, PF6, AlCl4 and FeCl4) was performed the
Fig. 10. SEM of [PySO3H]BF4.
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MolecularCatalysis475(2019)110403
Fig. 11. SEM of [PySO3H]PF6.
Fig. 12. SEM of [PySO3H]AlCl4.
Fig. 13. SEM of [PySO3H]FeCl4.
8

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MolecularCatalysis475(2019)110403
Fig. 14. TG, DTG and DTA analysis of the synthesized [PySO3H]X.
[PySO3H]BF4, [PySO3H]PF6 and [PySO3H]AlCl4 respectively. Also,
peaks (s, -48.10) and (d, 10.07, 1.663, J =756.72 Hz) of [PySO3H]BF4
and [PySO3H]PF6 were related to 19F NMR (84 MHz, D2O), respectively
(Fig. 4). Furthermore, the spectra of 27Al NMR (26 MHz, DMSO-d6) of
[PySO3H]AlCl4 was observed a peak at δ
0.667 (Fig. 5). In con-
tinued, MS m/z (%); found for [PySO3H]BF4: 247.0, [PySO3H]PF6:
305.9, [PySO3H]AlCl4: 327.8 in Figs. 6–8 respectively.
ppm
The particle size and shape as well as the morphology of [PySO3H]X
(X = FeCl4, BF4, PF6 and AlCl4) were studied by XRD (Tables 1–4 and
Fig. 9) and SEM (Figs. 10–13). Characterization was performed by X‐ray
diffraction (XRD) crystalline structure of [PySO3H]X using the tech-
nique XRD (Fig. 9) and calculations Debye-Sherrer equation D = Kλ/
βcosθ and Bragg equation: dhkl = λ/(2sinθ) (Tables 1–4). The size of
the catalysts is in the range of [PySO3H]BF4: 28.57–54.45 nm (Table 1),
[PySO3H]PF6:
59.22–84.03 nm
(Table
2),[PySO3H]AlCl4:
12.82–36.39 nm (Table 3) and [PySO3H]FeCl4: 11–16 nm (Table 4).
The scanning electron microscope (SEM) micrographs of the catalysts
also showed that the particles of [PySO3H]X (X = FeCl4, BF4, PF6 or
AlCl4) that their structures were observed in scale and not completely
agglomerated respectively (Figs. 10–13).
Fig. 15. The vibrating sample magnetometer (VSM) of [PySO3H]FeCl4.
structure of catalyst. The spectra of 1H NMR (400 MHz) shows OeH
peak of acid groups (SO3H) at δ ppm: 7.88 (s, 1H, OH), 11.91 (s, 1H,
OH), 10.68 (s, 1H, OH) and 4.10 (s, 1H, OH) related to [PySO3H]X
(X = BF4, PF6, AlCl4 and FeCl4) respectively (Fig. 2). Peak of CeH
To study the thermal stability of presented IL and MSs the thermal
gravimetric (TG), derivative thermal gravimetric (DTG) and differential
thermal (DTA) analysis were performed. Several degradation stages
were observed for [PySO3H]X (X = BF4, PF6, AlCl4 and FeCl4) in their
obtained profiles patterns (Fig. 14). The first step is the weight loss,
taking place between 25 and 100 °C associated with the removal of
organic solvents which have been used in the course of their prepara-
tion. The main stage of weight loss was related to SO3H release due to
breaking of NeS bond structure of [PySO3H]X. Therefore, about 60%,
50%, 30%, and 50% for [PySO3H]BF4, [PySO3H]PF6, [PySO3H]AlCl4,
and [PySO3H]FeCl4 respectively weight loss were observed. [PySO3H]X
(BF4, PF6, AlCl4 and FeCl4) can be used up to about 250, 211, 160 and
268 °C respectively.
aromatic related to [PySO3H]BF4
δ ppm: 8.94 (d, J =5.6 Hz, 2 H), 8.66
(t, J =7.9 Hz, 1 H), 8.12 (t, J =6.9 Hz, 2 H), [PySO3H]PF6: δ ppm: 8.96
(d, J =5.3 Hz, 2 H), 8.66 (t, J =7.8 Hz, 1 H), 8.12 (t, J =6.9 Hz, 2 H),
[PySO3H]AlCl4: δ ppm: 8.63 (d, J =4.8 Hz, 2 H), 7.90 (td, J = 7.7,
3.8 Hz, 1 H), 7.48 (dd, J = 7.9, 5.3 Hz, 2 H) and [PySO3H]FeCl4: δ
:
ppm
8.81 (s, 2 H), 8.29 (s, 1 H), 7.82 (s, 2 H) (Fig. 2). The 1H NMR analysis
changes of [PySO3H]Cl in comparison with [PySO3H]X displayed the
synthesis of [PySO3H]X.
The spectra of 13C NMR (101 MHz, DMSO-d6) of the above said ILs
and MSs [PySO3H]X (X = BF4, PF6 or AlCl4) were compared in Fig. 3.
Peaks C = C of pyridine (δ ppm: 147.2, 142.3, 127.8), (δ ppm: 146.7,
141.8, 127.3) and (δ ppm: 146.7, 141.6, 127.3) were related to
In another investigation, magnetic measurements of [PySO3H]FeCl4
was investigated at room temperature by using a vibrating sample
9

S. Babaee, et al.
MolecularCatalysis475(2019)110403
Table 5
Effect of different amounts of catalysts, temperature and solvent (5 ml) in the synthesis of 4H-benzo[g]chromene.
Entry
Catalyst (mol%)
([PySO3H]FeCl4)
Temp. (°C)
Solvent
Time (min)
Yield (%)
1
2
3
4
5
6
7
8
–
5
7
90
90
90
90
90
90
90
110
70
–
–
–
–
–
–
–
–
120
50
35
20
20
20
20
20
35
40
65
35
30
30
90
60
Trace
67
79
90
90
88
88
89
74
71
67
71
81
80
–
10
10
15
20
10
10
10
10
10
10
10
10
10
9
–
–
–
H2O
EtOH
CH3CN
n-Hexane
EtOAc
10
11
12
13
14
15
16
50
r.t.
Reflux
Reflux
Reflux
Reflux
Reflux
30
Reaction conditions: 4-nitrobenzaldehyde (1 mmol, 0.151 g), malononitrile (1 mmol, 0.066 g) and 2-hydroxynaphtalen-1,4-dione (1 mmol, 0.174 g).
Table 6
Synthesis of 4H-benzo[g]chromene using [PySO3H]X (X = BF4, PF6, AlCl4 and FeCl4) at 90 °C. (a: [PySO3H]FeCl4, b: [PySO3H]AlCl4, c: [PySO3H]PF6 and d:[PySO3H]
BF4)[41–44].
magnetometer (VSM) in Fig. 15. Based on magnetization curves, the
saturation of the obtained catalyst dropped to 2.2 emu g−1. Therefore,
this amount of magnetic ability is not enough for isolating of [PySO3H]
FeCl4 as a catalyst from the reaction mixture by using an external
magnet. This low paramagnetic property is due to decreasing of the five
unpaired electrons of Fe3+ to one unpaired electron via addition of a
-
chloride (Cl-) ligand to it and formation of FeCl4 counter ion.
After the synthesis and full characterization of [PySO3H]BF4,
[PySO3H]PF6, [PySO3H]AlCl4 and [PySO3H]FeCl4 as catalysts, they
were used for the synthesis of O-heterocyclic compounds (2-amino-4H-
10

S. Babaee, et al.
MolecularCatalysis475(2019)110403
Table 7
Synthesis of 2-amino-4,8-dihydropyrano using [PySO3H]X (X = BF4, PF6, AlCl4 and FeCl4) at 90 °C.(a: [PySO3H]FeCl4, b: [PySO3H]AlCl4, c: [PySO3H]PF6 and d:
[PySO3H]BF4)[45–47].
chromene, 2-amino-4,8-dihydropyrano and 2-amino-4H-pyrans). The
mentioned O-heterocyclic derivatives were synthesized via a con-
densation reaction of suitable starting materials in the presence of
[PySO3H]X (X = BF4, PF6, AlCl4 and FeCl4). The condensation of 4-
nitrobenzaldehyde (1 mmol, 0.151 g), malononitrile (1 mmol, 0.066 g)
and 2-hydroxynaphtalen-1,4-dione (1 mmol, 0.174 g) was selected as
model reaction to optimize the reaction conditions. As shown in the
Table 5, the worthy results were obtained when the reaction was
achieved in the presence of 10 mol% of MSs {[PySO3H]FeCl4 (Table 5,
entry 5). No improvement was detected in the yield of the reaction
using different amounts of the catalyst and temperature (Table 5, en-
tries 2-3 and entries 6-11). Table 5 clearly displayed that in the absence
of catalyst the product was produced in a low yield (Table 5, entry 1).
To investigate the solvent effect on the reaction improvement, several
solvents such as solvent free, H2O, EtOH, CH3CN, n-hexane and EtOAc
(5 ml) were tested and compared with solvent free condition in the
presence of 10 mol% [PySO3H]FeCl4 (Table 5, entries 12-16). The re-
sults are summarized in Table 5.
exposed in the Tables 6–8, the results show that the described meth-
odologies are suitable for the synthesis of a range of O-heterocyclic
derivatives such as 2-amino-4H-chromene, 2-amino-4,8-dihydropyrano
and 2-amino-4H-pyrans in high to excellent yields (70–93%) with in
relatively short reaction times (15–50 min). The results of this study
shows that aldehydes which have electron withdrawing groups to
produce the desired products with high yields and low reaction times in
compared to the electron releasing ones.
Suggested mechanism for the synthesis O-heterocyclic derivatives
(2-amino-4H-chromene, 2-amino-4,8-dihydropyrano and 2-amino-4H-
pyrans) using described catalysts [PySO3H]X (X = BF4, PF6, AlCl4 or
FeCl4) have been summarized in Scheme 5. Initially aldehyde is acti-
vated by the acidic sites of the catalyst, in which malononitrile is re-
acted with aldehyde by removing one water molecule, to afford inter-
mediate (I). For approving the formation of complex A, 4-nitro
benzaldehyde was reacted with [PySO3H]X (X = BF4, PF6, AlCl4 or
FeCl4) at room temperature. Then the FT-IR spectra of the reaction
mixtures were examined: The absorption bond of C]O of the 4-nitro
benzaldehyde at the 1703 cm−1 was changed to 1708, 1708, 1707 and
1708 cm−1 for the complex A respectively (Fig. 16) [49]. Then, inter-
mediate (I) as Michael acceptor to react with nucleophilic substrate (2-
hydroxynaphtalen-1,4-dione, 5-hydroxy-2-(hydroxymethyl)-4H-pyran-
4-one or ethyl benzoylacetate) to afford intermediate (II). Finally, in-
termediate (II) after intramolecular cyclization and tautomerization to
In continuation of our investigations on the scope and limitations of
IL and MSs their efficiency and applicability the reaction of mal-
ononitrile (1 mmol, 0.066 g), O-compounds (5-Hydroxy-2-(hydro-
xymethyl)-4H-pyran-4-one, 2-hydroxynaphtalen-1,4-dione and ethyl
benzoylacetate) (1 mmol) and various aryl aldehydes such as electron-
withdrawing and electron-releasing substituents were checked out. As
11

S. Babaee, et al.
MolecularCatalysis475(2019)110403
Table 8
Synthesis of 2-amino-4H-pyrans using [PySO3H]X (X = BF4, PF6, AlCl4 and FeCl4) at 90 °C. (a: [PySO3H]FeCl4, b: [PySO3H]AlCl4, c: [PySO3H]PF6 and d:[PySO3H]
BF4)[48, 49].
Fig. 16. FT-IR spectra of 4-nitro benzaldehyde and complex A.
12

S. Babaee, et al.
MolecularCatalysis475(2019)110403
Fig. 17. Recyclability of [PySO3H]X (X = BF4, PF6, AlCl4 or FeCl4) for the synthesis O- heterocycle compounds.
and 2-hydroxynaphtalen-1,4-dione (1 mmol, 0.174 g) over [PySO3H]
FeCl4 at 90 ◦C (variation of conversion or yield with time), are shown in
Fig. 18. It was found that after 20 min, the reaction conversion of (1)
was 90%.
To compare the efficiency of [PySO3H]X (X = BF4, PF6, AlCl4 or
FeCl4) with the previously reported catalysts for the synthesis of 4H-
benzo[g]chromene, we have tabulated the results of these catalysts to
perform the condensation of 4-nitrobenzaldehyde (1 mmol, 0.151 g),
malononitrile (1 mmol, 0.066 g) and 2-hydroxynaphtalen-1,4-dione
(1 mmol, 0.174 g), in the Table 9. As Table 9 indicates, [PySO3H]X
(X = BF4, PF6, AlCl4 or FeCl4) have remarkably improved the synthesis
of 4H-benzo[g]chromene in different terms (reaction times and yields).
The presented results of the Table 9 shows those both basic and acidic
properties of applied compounds as catalysts are important for pro-
ceeding of the target reaction. For entry 8 (NaBF4) due to very low
Lewis acidity and basic properties, the efficiency of the reaction was
seriously decreased and the reaction times are also increased.
Fig. 18. Variation of the reaction conversion and yield with time in the
synthesis of 4H-benzo[g]chromene.
Conclusion
In summary, we have synthesized pyridinium-based ionic liquid (IL)
[PySO3H]PF6 and molten salts (MSs) such as [PySO3H]AlCl4, [PySO3H]
BF4, and [PySO3H]FeCl4 via a convenient anion exchange method.
The above mentioned ILs and MSs fully characterized by using
several identification techniques. These molten salts were applied for
one-pot synthesis of O-heterocyclic compounds (2-amino-4H-chromene,
2-amino-4,8-dihydropyrano and 2-amino-4H-pyrans) under mild con-
ditions. The mentioned molecules as biological active and drug candi-
dates have demonstrated that medicinal properties such anti-cancer,
anti-alzheimer, anti-malarial, antitumor, antioxidants and antifungal.
The promising points for the described catalytic methodologies are easy
work-up, recycle and reusability of the catalysts, high efficiency, short
give the desired corresponding O-heterocyclic compounds (Scheme 3).
The recyclability and reusing of the described IL and MSs were also
studied on a model reaction of 4-nitrobenzaldehyde (1 mmol, 0.151 g),
malononitrile (1 mmol, 0.066 g) and 2-hydroxynaphtalen-1,4-dione
(1 mmol, 0.174 g) under the above mentioned optimized reaction
conditions (for fixed time 20 min). As indicated in the Fig. 17, the ap-
plied IL and MSs could be recycled (see experimental for details) and
efficiently reused up to five reaction cycles with a marginal decreasing
their catalytic activities.
The results of catalytic tests in the solvent-free reaction of 4-ni-
trobenzaldehyde (1 mmol, 0.151 g), malononitrile (1 mmol, 0.066 g)
13

S. Babaee, et al.
MolecularCatalysis475(2019)110403
Table 9
Comparison of the previously reported results for the synthesis of 4H-benzo[g]chromene with our new described catalysts.
Entry
Catalyst
Reaction condition
Time (min)
Yield (%)
Reference
1
2
3
4
5
6
7
8
POPINO
MW
[bmim]OH
DBU
Fe3O4/(PEG)
Imidazole
Piperidine
[PySO3H]Cl
[PySO3H]AlCl4
[PySO3H]FeCl4
[PySO3H]PF6
[PySO3H]BF4
AlCl3
Reflux/ H2O
DMF/ HOAc
r.t. / EtOH
Reflux/ H2O
Ultrasonic irradiation/EtOH
Reflux/ EtOH
r.t. / EtOH
Solvent free/ 90 °C
Solvent free/ 90 °C
Solvent free/ 90 °C
Solvent free/ 90 °C
Solvent free/ 90 °C
Solvent free/ 90 °C
Solvent free/ 90 °C
Solvent free/ 90 °C
Solvent free/ 90 °C
Solvent free/ 90 °C
20
5
91
92
91
87
85
93
85
56
87
88
88
89
52
Trace
65
45
65
[31]
[50]
[51]
[52]
[53]
[45]
[54]
a
a
a
a
a
60
60
20
30
15
60
30
30
25
25
45
60
40
60
40
9
10
11
12
13
14
15
16
17
a
a
a
a
NaBF4
FeCl3
KPF6
DABCOb+[PySO3H]FeCl4
a
aOur work.
b1,4-diazabicyclo[2.2.2]octane.
reaction times and high yields of products. The efficacy of the above
mentioned catalysts may be due to the presence both of the proton and
Lewis acidic sites within their structures. Furthermore, the major ad-
vantages of anion exchange method are preparing a good range of novel
molten salts [PySO3H]X (X = FeCl4, AlCl4, BF4 and PF6) as an efficient,
task-specific, recyclable and thermally stable catalysts.
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We thank the Bu-Ali Sina University, National Elites Foundation and
Iran National Science Foundation (INSF) (Grant Number: 96013474)
for financial support.
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Appendix A. Supplementary data
Supplementary material related to this article can be found, in the
online version, at doi:https://doi.org/10.1016/j.mcat.2019.110403.
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