Preparation, characterization, and application of 1,1′-disulfo-[2,2′-bipyridine]-1,1′-diium chloride ionic liquid as an efficient catalyst for the synthesis of benzimidazole derivatives

Article abstract of DOI:10.1007/s11164-014-1852-x

In this study, 2,2′-bipyridine was treated with chlorosulfonic acid and 1,1′-disulfo-[2,2′-bipyridine]-1,1′-diium chloride, [BiPy](SO₃H)₂Cl₂, as a new ionic liquid catalyst was obtained and characterized with a variety of techniques including IR, ¹H, and ¹³C NMR, Hammett acidity function as well as mass spectra method. After preparation and characterization, this ionic liquid was used as an efficient catalyst for the green and mild synthesis of benzimidazole derivatives. In addition, this reagent is efficiently able to catalyze the preparation of benzimidazole derivatives from the protected derivatives of aldehydes including oximes and semicarbazones. All reactions are performed under mild conditions in excellent yields.

Full text of DOI:10.1007/s11164-014-1852-x

Res Chem Intermed
DOI 10.1007/s11164-014-1852-x
Preparation, characterization, and application of 1,10-
disulfo-[2,20-bipyridine]-1,10-diium chloride ionic liquid
as an efficient catalyst for the synthesis
of benzimidazole derivatives
•
Farhad Shirini Masoumeh Abedini
•
•
Mohadeseh Seddighi Fatemeh Shaabani Arbosara
Received: 22 August 2014 / Accepted: 17 October 2014
Ó Springer Science+Business Media Dordrecht 2014
Abstract In this study, 2,20-bipyridine was treated with chlorosulfonic acid and
1,10-disulfo-[2,20-bipyridine]-1,10-diium chloride, [BiPy](SO3H)2Cl2, as a new ionic
liquid catalyst was obtained and characterized with a variety of techniques including
1
IR, H, and 13C NMR, Hammett acidity function as well as mass spectra method.
After preparation and characterization, this ionic liquid was used as an efficient
catalyst for the green and mild synthesis of benzimidazole derivatives. In addition,
this reagent is efficiently able to catalyze the preparation of benzimidazole deriv-
atives from the protected derivatives of aldehydes including oximes and semicar-
bazones. All reactions are performed under mild conditions in excellent yields.
Keywords [BiPy](SO3H)2Cl2 ꢀ Ionic liquid ꢀ Benzimidazoles ꢀ Aldehydes ꢀ
Protected aldehydes
Introduction
Ionic liquids (ILs) are compounds with unique properties such as non-flammability,
no miscibility with non-polar solvents, negligible vapor pressure, reasonable
thermal and chemical stability, and the ability to be used many times without
considerable decreasing their activity. Because of these important characteristics,
the use of ILs in organic reactions is under the considerable attention of many
organic chemists. For example, these types of compounds were successfully used
for the acceleration of some of the multi-component reactions [1–6].
F. Shirini (&) ꢀ M. Abedini (&) ꢀ M. Seddighi ꢀ F. S. Arbosara
Department of Chemistry, College of Science, University of Guilan, Post Box 1914, 41335 Rasht,
Iran
e-mail: shirini@guilan.ac.ir
M. Abedini
e-mail: mabedini@guilan.ac.ir
123

F. Shirini et al.
Benzimidazole derivatives are one of the most important classes of heterocyclic
compounds that occur widely in natural products. These heterocycles have shown
different pharmacological and biological activities such as antibacterial, antihyper-
tensives, anticancers, anti-histaminics, anti-HBV activity, anti-inflammatory, anti-
microbial, antiviral, and antitumor [7–15]. Furthermore, these compounds can act as
ligands to transition metals [16].
A wide range of methods are available for the synthesis of benzimidazole
derivatives including condensation of either o-phenylenediamine, o-aminobenze-
nethiol, and/or o-aminophenol with aldehydes, acid chloride, esters, carboxylic
acids, and orthoesters in the presence of various acid catalysts [17–23]. Also,
syntheses of these compounds have been reported using ILs [24–26].
Although these procedures provide improvement, many of these catalysts or
activators suffer from disadvantages such as the use of organic solvents or toxic
reagents, harsh reaction conditions, long reaction times, need to excess amounts of
the reagent, and non-recoverability of the catalyst. Therefore, the introduction of
simple, efficient, and mild procedures with easily separable and reusable solid
catalysts to overcome these problems is still in demand.
In recent years, preparation and use of ILs in organic transformations became an
important part of our ongoing research program [27–30]. Herein, and in
continuation of these studies, we wish to report the preparation and characterization
of 1,10-disulfo-[2,20-bipyridine]-1,10-diium chloride, [BiPy](SO3H)2Cl2, as a new IL
and its applicability in the promotion of the synthesis of benzimidazole derivatives.
Experimental
All chemicals were purchased from Merck, Aldrich, and Fluka Chemical
Companies and used without further purification. Products were characterized by
their physical constants and comparison with authentic samples. Products were
separated and purified by different chromatographic techniques (TLC using silica
gel SIL G/UV 254 plates) and were identified by the comparison of their IR, NMR,
and refractive index with those reported for the authentic samples. All yields refer to
the isolated products.
The IR spectra were recorded on a Perkin Elmer 781 spectrophotometer. In all
the cases, the 1H NMR spectra were recorded with Bruker Avance 400- and
500-MHz instruments. All chemical shifts are quoted in parts per million (ppm)
relative to TMS using deuterated solvent. The 13C NMR data were collected on a
Bruker Avance 400-MHz instrument. MS studies were performed using 5973
network mass selective detector, Agilent Technology (HP) company (ion source:
electroni (EI) 70 eV; ion source temperature: 230 °C; analyzer: quadrupole).
Melting points were recorded on a Bu¨chi B-545 apparatus in open capillary tubes.
Catalyst preparation
Chlorosulfonic acid (1.75 g, 15 mmol) was added dropwise to a round-bottomed
flask (100 ml) containing 2, 20-bipyridine (1.17 g, 7.5 mmol) in dry CH2Cl2
123

Efficient catalyst for the synthesis of benzimidazole derivatives
(50 ml), over a period of 5 min in an ice bath. After the addition was completed, the
reaction mixture was stirred for 2 h, then stood for 5 min, and the solvent was
decanted. The residue was washed with dry diethylether (3 9 50 ml) and dried
under vacuum to give [BiPy](HSO3)2Cl2 as a white solid in 98 % yield (Scheme 1).
Spectroscopic data for [BiPy](SO3H)2Cl2 are as: m.p. 86 °C; MS: 81, 155, 162,
191, 228, 272, 389 m/z; FT-IR (KBr, cm-1) tmax: 3,402, 1,604, 1,513, 1,437, 1,281,
1
1,232, 1,174, 877. H NMR (400 MHz, DMSO-d6): d = 7.92 (1H, ddd, J1 = 8,
J2 = 5.2, J3 = 1.2), 8.46 (1H, td, J1 = 8, J2 = 1.6), 8.70 (1H, d, J = 8), 8.91 (1H,
ddd, J1 = 5.2, J2 = 1.6, J3 = 0.8), 9.58 (1H, OH, s) ppm; 13C NMR (100 MHz,
DMSO-d6) d = 147.84, 147.02, 143.39, 127.66, 124.23 ppm; Elemental analysis:
C, 29.52; H, 3.93; N, 6.39; O, 26.22; S, 14.65.
General procedure for the synthesis of benzimidazole
A mixture of the aldehyde, oxime and/or semicarbazone, 1,2-phenylene diamines
(1 mmol) and [BiPy](HSO3)2Cl2 (10 mg) in EtOH (3 ml) was stirred at room
temperature. After completion of the reaction, monitored by TLC (EtOAc: n-hexane
1:1), the solvent was evaporated and H2O (3 ml) was added and the catalyst was
separated. In continue, the resulting solid product was recrystallized from ethanol to
obtain pure product in good to high yields.
Results and discussion
Catalyst characterization
IR analysis
The infrared spectra of 2-(pyridin-2-yl) pyridine and[BiPy](SO3H)2Cl2 are shown in
Fig. 1. The IR spectrum of the product shows a broad peak at 2,690–3,600 cm-1
,
which can be related to the OH stretching of the SO3H groups. Moreover, the two
peaks observed at 1,174 and 1,281 cm-1 correspond to the O-SO2 symmetric and
asymmetric stretching, respectively, and the other band at 1,068 cm-1 is assigned to
N-SO2 stretching. In addition, C=N and C=C vibrations are observed at 1,604 and
1,513 cm-1 correspondingly [31].
1H NMR analysis
The 1H NMR spectrum of [BiPy](HSO3)2Cl2 in addition to the other protons, shows
the SO3H acidic hydrogen peak at 9.58 ppm. This observation clarifies that
[BiPy](HSO3)2Cl2 is exactly synthesized (Fig. 2).
Mass analysis
The mass spectrum of [BiPy](SO3H)2Cl2 is shown in Fig. 3. In this spectrum the
correct molecular ion peak appears at 389. Other ion peaks are also observed at 272
123

F. Shirini et al.
Scheme 1 Preparation of
[BiPy](HSO3)2Cl2
SO3H
Cl
N
N
2 ClSO3H
Dry CH2Cl2
Ice bath, 2 h
N
N
HO3S
Cl
[BiPy](HSO3)2Cl2
Fig. 1 FT-IR spectra of 2, 20-bipyridine (up) and [BiPy](SO3H)2Cl2(down)
(M?-SO3H and Cl), 228 (M?-2 SO3H), 191 (M?-2 SO3H and Cl), 162 (2 SO3H),
155 (M?-2 SO3H and 2 Cl) and 81 (SO3H).
Acidity of the catalyst
The Hammett acidity method is an effective way to the acidity strength of an acid in
organic solvents, using UV–Vis technique [32]. The Hammett function is defined as:
123

Efficient catalyst for the synthesis of benzimidazole derivatives
Fig. 2 1H NMR spectra of [BiPy](SO3H)2Cl2
Fig. 3 Mass spectra of [BiPy](SO3H)2Cl2
À
Á
H0 = pKðIÞaqþlog ½Iꢁs=½IHþꢁs
where the pK(I)aq is the pKa value of aqueous solution of indicator, [IH?]s and [I]s
are the molar concentrations of protonated and unprotonated forms of the indicator
in the solvent, respectively. According to Lambert–Beer’s Law, the value of [I]s/
[IH?]s can be determined and calculated through the UV–visible spectrum.
123

F. Shirini et al.
2.5
2
(a)
(b)
1.5
1
0.5
0
250
300
350
400
450
Wavelenghth (nm)
Fig. 4 Absorption spectra of 4-nitroaniline (indicator) (a) and [BiPy](HSO3)2Cl2 (catalyst) (b) in CCl4
For this purpose, 4-nitroaniline (pK(I)aq = 0.99) as the basic indicator and CCl4
as the solvent were chosen. As can be seen in Fig. 4, the maximal absorbance of the
unprotonated form of the indicator was observed at 328 nm in CCl4. When
[BiPy](HSO3)2Cl2 as the IL catalyst was added to the indicator solution, the
absorbance of the unprotonated form of the indicator decreased, which indicated
that the indicator was partially in the form of [IH?]. These results that have listed in
Table 1, show the acidity strength of [BiPy](HSO3)2Cl2.
Catalytic activity
On the basis of the obtained information about the structure of [BiPy](HSO3)2Cl2,
we anticipated that this reagent can be used as an efficient catalyst for the
acceleration of the reactions, which need the use of an acidic catalyst to speed up.
So we were interested in investigating the applicability of this reagent in the
synthesis of benzimidazole derivatives.
Initially, the optimization of the reaction conditions was studied with investi-
gating the effect of different molar ratios of the reactants and different solvents and
also solvent-free conditions on the reaction of 4-chlorobenzaldehyde (1 mmol) and
1, 2-phenylene diamine (1 mmol) in terms of time and the product yield (Table 2).
The optimal conditions are shown in Scheme 2.
After optimization of the reaction conditions and in order to show the general
applicability of this method, the protocol was explored with a variety of simple
readily available substrates under the optimal conditions. Using this method, a series
of o-phenylenediamine derivatives reacted with different types of aldehydes and
afforded the respective benzimidazoles in good-to-excellent yields (Table 3, entries
1–15). Furthermore, this method was found to be useful for the synthesis of
benzimidazole derivatives from the reaction of diamines with heteroaromatic
aldehydes or a,b-unsaturated aldehydes in very short reaction times in very
excellent yields (Table 3, entries 16–18). It seems that electronic or strict effect of
123

Efficient catalyst for the synthesis of benzimidazole derivatives
Table 1 Calculation of Hammett acidity function (H0) for [BiPy](HSO3)2Cl2)
Entry
Catalyst
Amax
[I]s %
[IH?]s %
H0
1
2
–
2.2261
1.5984
100
0
–
[BiPy](HSO3)2Cl2
71.80
28.2
1.40
Condition for UV–visible spectrum measurement: solvent: CCl4, indicator: 4- nitroaniline (pK
(I)aq = 0.99), 1.44 9 10-4mol/L (10 ml); catalyst: [BiPy](HSO3)2Cl2 (10 mg), 25 °C
Table 2 Synthesis of
Entry
Catalyst (mg)
Solvent
Time (min)
Yield (%)
benzimidazole derivatives
catalyzed by
[BiPy](SO3H)2Cl2
1
2
3
4
5
6
7
8
EtOH
15
25
30
60
60
30
15
15
15
20
98
98
96
30
70
96
98
98
97
95
H2O
CH2Cl2
Acetone
n-Hexane
EtOH
5
10
15
20
40
EtOH
EtOH
EtOH
9
EtOH
NH2
+ ArCH=X
NH2
Y
[BiPy](HSO3)2Cl2 (10 mg)
Y
N
Ar
EtOH (3 mL), r.t.
X= O, NOH, NHCONH2
N
Scheme 2 The optimal conditions for synthesis of benzimidazole derivatives catalyzed by
[BiPy](HSO3)2Cl2
different substituents on the aromatic ring of aldehydes had no obvious effect on the
yield or reaction time under the optimal conditions.
In 1998, the first example of the synthesis of benzimidazoles using oximes
catalyzed by Ca(OCl)2/Al2O3 was reported by Soufiaoui et al. [33]. Although this
method is useful, it needs a very high temperature (140 °C) for completion.
On the basis of these studies, and after the successful application of
[BiPy](SO3H)2Cl2 in the preparation of benzimidazoles from aldehydes, we were
interested in studying the use of this reagent in the promotion of the synthesis of
benzimidazoles from oximes and semicarbazones as the protected derivatives of
aldehydes (Scheme 2).
It was observed that under the selected conditions, oximes and semicarbazones
containing electron-withdrawing groups as well as electron-donating groups were
easily reacted in short reaction times with good-to-excellent isolated yields
(Table 3, entries 20–29). Also, the obtained results indicated that the protected
aldehydes reacted in longer times compared with the aldehydes.
123

F. Shirini et al.
Table 3 Synthesis of benzimidazole derivatives catalyzed by [BiPy](SO3H)2Cl2
Entry
Aldehyde
Y
Time (min)
Yield (%)
Mp (°C) [Refs.]
1
C6H5CHO
H
10
10
20
15
15
15
20
30
25
15
10
17
25
15
20
15
10
98
98
98
97
96
95
98
98
96
98
95
92
91
94
93
95
95
286–288 [34]
288–290 [35]
220–221 [36]
225–227 [37]
260–262 [38]
240–242 [39]
307–309 [36]
183–185 [36]
222–223 [40]
285–287 [36]
280–282 [38]
301–303 [36]
332–335 [41]
178–180
2
4-ClC6H4CHO
2-ClC6H4CHO
3-ClC6H4CHO
4-BrC6H4CHO
4-FC6H4CHO
H
3
H
4
H
5
H
6
H
7
4-NO2C6H4CHO
3-NO2C6H4CHO
4-MeOC6H4CHO
4-Me2NC6H4CHO
4-HOC6H4CHO
4-ClC6H4CHO
4-NO2C6H4CHO
4-FC6H4CHO
H
8
H
9
H
10
11
12
13
14
15
16
17
H
H
NO2
NO2
CH3
CH3
H
4-MeOC6H4CHO
PhCH=CHCHO
172–174
185–187 [34]
216–218 [26]
H
CHO
CHO
N
O
18
H
20
96
281–282 [35]
19
20
21
22
23
24
25
2-Naphthaldehyde
H
H
H
H
H
H
H
10
120
120
120
120
120
120
98
85
90
95
70
90
95
210–212 [42]
288–290 [35]
220–221 [36]
307–309 [36]
183–185 [36]
185–187 [34]
210–212 [42]
4-ClC6H4CH = NOH
2-ClC6H4CH=NOH
4-NO2C6H4CH=NOH
3-NO2C6H4CH=NOH
PhCH=CHCH=NOH
CH=NOH
26
27
28
29
4-NO2C6H4CH=NNHCONH2
3-NO2C6H4CH=NNHCONH2
4-MeOC6H4CH=NNHCONH2
PhCH=CHCH=NNHCONH2
H
H
H
H
120
120
120
120
80
70
90
75
307–309 [36]
183–185 [36]
222–223 [40]
185–187 [34]
Reaction conditions: aldehyde, oxime and/or semicarbazone (1 mmol), 1,2-phenylene diamines
(1 mmol), [BiPy](HSO3)2Cl2 (10 mg) in EtOH (3 ml) at room temperature
In order to show the efficiency of the present method, we have compared our
result obtained from the reaction between o-phenylenediamine and benzaldehyde in
the presence of [BiPy](SO3H)2Cl2 with some of the other results reported in the
literature (Table 4).
123

Efficient catalyst for the synthesis of benzimidazole derivatives
Table 4 Comparison of the results obtained from the reaction of o-phenylenediamine and benzaldehyde
in the presence of [BiPy](SO3H)2Cl2 with those obtained using some of the other catalysts
Entry Catalyst (mol%)
Reaction conditions Time (h) TOF (h-1
)
Yield (%) [Refs.]
1
2
3
4
5
6
7
8
[Hmim]TFA (10)
[pmim]BF4 (75)
[Msim]Cl (10)
[Dsim]Cl (10)
TBAF (5)
H2O, r.t.
0.167
5
52.7
0.2266
88 [24]
Solvent-free, r.t.
EtOAc, r.t.
85 [25]
0.25
0.2
35.2
45.5
37.6
5.3
88 [26]
EtOAc, r.t.
91 [26]
H2O, Ultrason., r.t.
EtOH, reflux
CH3CN, r.t.
0.5
94 [43]
Nano-ZnO (10)
TBBDA (27)
1.66
0.25
0.167
88 [44]
14.2
228.3
96 [45]
[BiPy](SO3H)2Cl2 (2.57) EtOH, r.t.
98 [This work]
Table 5 Reusability of
[BiPy](SO3H)2Cl2 in the
reaction of 4-bromo
benzaldehyde and 1,2-
phenylene diamine
Run
Time (min)
Yield (%)
1
2
3
4
15
17
22
35
96
95
96
93
This comparison shows the efficiency of [BiPy](HSO3)2Cl2 in the synthesis of
benzimidazoles. In this table, the turnover frequency (TOF) is also compared. As it
is clear, [BiPy](HSO3)2Cl2 is superior in terms of TOF to the compared catalysts.
To check the reusability of the catalyst, the reaction of 4-bromobenzaldehyde and
1, 2-phenylene diamine under optimized reaction conditions was studied again.
When the reaction completed, the solvent was evaporated, H2O (3 ml) was added,
and the catalyst was separated. The solvent of the aqueous phase was evaporated
under reduced pressure to remove the solvents and the resulting IL was reused
directly for the next run. It was found that the catalyst could be recovered and reused
at least for three runs (Table 5).
Conclusions
In this study, we have reported the preparation, characterization, and used
[BiPy](SO3H)2Cl2as a new and highly efficient ILs catalyst for the simple and
efficient synthesis of benzimidazole derivatives. The procedure has several
advantages such as ease of preparation and handling of the catalyst, simple
experimental procedure, high reaction rates, and excellent yields. Furthermore, in
this study different types of protected aldehydes were successfully employed in the
synthesis of benzimidazole and the corresponding products were obtained in high-
to-excellent yields.
Acknowledgments We are thankful to the University of Guilan Research Councils for the partial
support of this work.
123

F. Shirini et al.
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