Tungstate sulfuric acid: Preparation, characterization, and application in catalytic synthesis of novel benzimidazoles

Article abstract of DOI:10.2478/s11696-012-0152-4

Tungstate sulfuric acid (TSA) was prepared, characterized, and applied for direct synthesis of novel and known benzimidazoles through a condensation reaction of o-phenylenediamines with orthoesters under solvent-free conditions. TSA was characterized by powdered X-ray diffraction (XRD), X-ray fluorescence (XRF), and FTIR spectroscopy. This novel and eco-friendly method is very cheap and has many advantages such as excellent yields, recyclable and eco-friendly catalyst, and simple work-up procedure.

Full text of DOI:10.2478/s11696-012-0152-4

Chemical Papers 66 (7) 684–690 (2012)
DOI: 10.2478/s11696-012-0152-4
ORIGINAL PAPER
Tungstate sulfuric acid: preparation, characterization,
and application in catalytic synthesis of novel benzimidazoles
Bahador Karami*, Saeed Khodabakhshi, Zahra Haghighijou
Department of Chemistry, Yasouj University, 75918-74831 Yasouj, P.O. Box 353, Iran
Received 17 September 2011; Revised 3 January 2012; Accepted 4 January 2012
Tungstate sulfuric acid (TSA) was prepared, characterized, and applied for direct synthesis of
novel and known benzimidazoles through a condensation reaction of o-phenylenediamines with
orthoesters under solvent-free conditions. TSA was characterized by powdered X-ray diffraction
(
XRD), X-ray fluorescence (XRF), and FTIR spectroscopy. This novel and eco-friendly method is
very cheap and has many advantages such as excellent yields, recyclable and eco-friendly catalyst,
and simple work-up procedure.
ꢀ
c 2012 Institute of Chemistry, Slovak Academy of Sciences
Keywords: orthoesters, o-phenylenediamine, tungstate sulfuric acid, benzimidazole, catalyst
Introduction
pivotal focal point of research activity in the field of
modern organic synthesis. Until now, several meth-
ods for the synthesis of benzimidazoles have been re-
ported. However, the most commonly used method is
the condensation of an o-aryldiamine with a carbonyl
equivalent (Wright, 1951; Preston, 1974). Also, esters,
lactones, and anhydrides are able to produce benzim-
idazoles through the cyclization of amide (Niknam &
Fatehi-Raviz, 2007). It should be mentioned that some
of the reported methods suffer from drawbacks such
as the use of toxic and expensive catalysts or organic
solvents, long reaction times, low yield of the prod-
ucts, and difficult work-up procedures (Sharma et al.,
2009; Howarth & Hanlon, 2001; Reddy et al., 1983).
Catalytic technology plays an important role in
many recent organic reactions (especially synthesis
of heterocyclic compounds), therefore, preparing and
employing a green catalyst can be extremely valuable
(
Davoodnia et al., 2011). Among heterocycles contain-
ing a nitrogen atom, benzimidazole and its deriva-
tives are very useful intermediates for the develop-
ment of molecules of pharmaceutical and biological
interest (Ogurtsov et al., 2003). For example, some
benzimidazoles showed a relatively high biological ac-
tivity as anti herpes (Migawa et al., 1998), anti in-
fluenza (Tamm, 1957), anti fungal agents (Ku ¸s & Al-
tanlar, 2003), and RAF (rapidly accelerated fibrosar-
coma) kinase inhibitor (Buchstaller et al., 2011). The
most prominent benzimidazole compound in nature
is N-ribosyl-dimethylbenzimidazole (5,6-dimethyl-1-
α-D-ribofuranosyl-1H-benzimidazole) which serves as
an axial ligand for cobalt in vitamin B12 (Barker
et al., 1960). Moreover, benzimidazole derivatives
are efficiently used in material science (Maiti et al.,
Experimental
All chemicals were purchased from Merck Co.
(Germany), and Sigma–Aldrich Co. (USA). The re-
actions were monitored by TLC (silica-gel 60 F254,
1-hexane–ethyl acetate). IR spectra were recorded on
a FTIR Shimadzu-470 spectrometer at the scanning
−
1
2
009), corrosion science (Roquea et al., 2008), cataly-
sis (Tarte et al., 2008), etc.
range of 400–4000 cm (Shimadzu, Japan) and the
1
H NMR spectra were obtained on a Bruker instru-
The discovery of novel synthetic methodologies fa-
cilitating the preparation of compound libraries is a
ment (400 MHz) DPX-400 Avance 2 model (Bruker,
USA). Chemical shifts (δ) are reported in ppm. X-ray
*Corresponding author, e-mail: karami@mail.yu.ac.ir

B. Karami et al./Chemical Papers 66 (7) 684–690 (2012)
685
Fig. 1. Preparation of TSA (I).
diffraction (XRD) pattern was obtained by a Philips
X Pert Pro X diffractometer operated with an Ni-
filtered CuKα radiation source 9 (PANalytical, the
Netherlands). X-ray fluorescence (XRF) spectra were
recorded by an X-ray fluorescence analyzer, Bruker,
S4 (Pioneer, Germany). All products (except novel
compounds) were characterized by comparison of their
spectra and physical data with those reported in lit-
erature.
At first, 25 mL of dry 1-hexane were put in a
1
00 mL round bottom flask equipped with an ice bath
Fig. 2. Powder X-ray diffraction pattern of TSA.
Table 1. XRF data of TSA; LOI = loss on ignition
and an overhead stirrer, 0.588 g (2.00 mmol) of anhy-
drous sodium tungstate was added to the flask, and
then, 0.266 mL (4.00 mmol) of chlorosulfonic acid was
added dropwise to the flask in 30 min. This solution
was stirred for 1.5 h. Afterwards, the reaction mixture
was gradually poured into 25 mL of chilled distilled
water under agitation. The yellowish solid which sep-
arated out was filtered. Then, the catalyst was washed
with distilled water five times until the filtrate showed
Mass fraction
Compound
%
WO4
SO3
Na2O
Cl
19.49
0.317
0.190
0.056
0.023
0.015
0.014
99.93
79.82
◦
negative test for the chloride ion, and dried at 120 C
for 5 h. The catalyst was obtained in a 98 % yield as
a yellowish solid decomposing at 285 C.
◦
CuO
Fe O
A mixture of orthoester (1.1 mmol), o-phenylene-
2
3
diamine (1.0 mmol), and tungstate sulfuric acid (0.1
eq.) was stirred and heated at 80 C in a preheated
CaO
Total
LOI
◦
oil bath for appropriate time. After completion of the
reaction as indicated by TLC (ethyl acetate–1-hexan,
ϕr = 1 : 2), the reaction mixture was dissolved in
hot ethyl acetate and the catalyst was separated by
filtration. The solvent was evaporated and the crude
product was purified by recrystallization in ethyl ac-
etate. The separated catalyst was washed with diethyl
ꢀ
Recently, silica sulfuric acid and Nafion-H (Zol-
figol, 2001; Olah et al., 1978) have been used in a wide
variety of reactions (Zolfigol et al., 2002; Zolfigol &
Bamoniri, 2002). Accordingly, in our previous studies,
the synthesis and application of TSA in some organic
transformations was described; however, this method
has drawbacks such as low yield of the product in long
reaction time and difficult work-up procedure (Karami
et al., 2005, 2006a, 2006b). In present work, it was
found that anhydrous sodium tungstate reacts with
chlorosulfonic acid (1 : 2 mole ratio) to give tungstate
sulfuric acid (TSA, I ). The reaction is easy and clean
and no gas is generated during the reaction (Fig. 1).
◦
ether, dried at 70 C for 45 min, and reused in another
reaction.
Results and discussion
The challenge to develop practical methods, reac-
tion media, conditions, and/or materials based on the
idea of green chemistry is one of the important issues
in the scientific community. However, the concept of
“
green chemistry” has emerged as one of the guid-
ing principles of environmentally friendly organic syn-
thesis. In fact, from the economic and environmental
point of view, a solvent-free or solid state reaction re-
duce pollution and decrease handling costs due to the
simplification of the experimental procedure, work-up
techniques, and savings in labor, which is especially
important in industrial production.
Characterization of catalyst
Fig. 2 shows the XRD patterns of TSA. It was
reported that high degree of mixing of W–S in chloro-
sulfonic acid often leads to the absence of the XRD
pattern for anhydrous sodium tungstate.

6
86
B. Karami et al./Chemical Papers 66 (7) 684–690 (2012)
Table 2. Optimization of the catalyst amount for the synthe-
◦
sis of benzimidazole IVa at 80 C under solvent-free
conditions
Catalyst
eq.
Time
min
Yielda
%
Entry
1
2
3
4
–
540
45
15
50b
70
90
90
0.05
0.10
0.20
30
a) Isolated yields; b) not completed.
Table 3. Optimization of reaction temperature for synthesis of
benzimidazole IVa using TSA (0.1 eq.) under solvent-
free conditions
Fig. 3. FTIR spectra of TSA.
Temperature
Time
min
Yielda
%
Entry
◦
◦
C
The broad peak around 25.7 (2θ) (θ is the Bragg’s
angle) from the smaller inset was attributed to the
presence and linking of WO3 to the chlorosulfonic acid
1
2
3
4
25
60
80
540
70
15
30b
70
90
50
(
Santato et al., 2001). The XRF data of TSA indicate
the presence of WO4 and SO3 in the catalyst (Table 1).
FTIR spectra of anhydrous sodium tungstate and
TSA are shown in Fig. 3. The spectrum of TSA shows
characteristic bonds of anhydrous sodium tungstate
and chlorosulfonic acid. The absorption at 3406 cm
820 cm , 1725 cm , 1702 cm , 1620 cm
290 cm , 1060 cm , 1005 cm , and 860 cm
in the catalyst spectrum reveals both bonds in anhy-
drous sodium tungstate and —OSO3H group.
According to many reports on the application of
solid acids as efficient catalysts in organic transfor-
mations (Martin & Kalevaru, 2010; Romanelli et al.,
008, 2010; Tamaddon & Tavakoli, 2001; Marziano et
al., 2005), and to our recent studies on the synthe-
sis of organic compounds (Karami & Khodabakhshi,
011; Karami et al., 2006a, 2006b; Mallakpour et al.,
998; Heydari et al., 2000; Damavandi et al., 2002), it
was found that TSA can be used as efficient and safe
catalyst for the condensation of orthoesters (II ) and
o-phenylenediamines (III ) under thermal and solvent-
free conditions to afford benzimidazole derivatives
120
25
a) Isolated yields; b) not completed.
−
−1
−1
1
,
,
−
1
−1
−1
−1
−1
1
1
Interest in the environmental control of chemical
processes has increased remarkably during the last
three decades as a response to public concern about
the use of hazardous chemicals. Therefore, to improve
the effectiveness of this method in preventing chemical
waste, it is important to investigate optimal reaction
conditions. To determine simple and suitable condi-
tions for the preparation of benzimidazole derivatives
using TSA as a solid acid catalyst, the treatment of tri-
ethyl orthoformate with o-phenylenediamine was cho-
sen as a model reaction. At first, it was found that in
the absence of the catalyst, the reaction was not com-
pleted even at high temperatures. After applying var-
ious amounts of TSA according to Table 2, and a wide
range of temperatures (Table 3), it was found that the
condensation reaction can be efficiently carried out by
−
1
2
2
1
◦
(
IV ) in good to excellent yields (Fig. 4).
adding 0.1 equivalents of the catalyst at 80 C under
Fig. 4. Synthesis of benzimidazole derivatives using TSA.

B. Karami et al./Chemical Papers 66 (7) 684–690 (2012)
687
◦
Table 4. Synthesis of benzimidazole derivatives IV using TSA (0.1 eq.) at 80 C under solvent-free conditions
Time
min
Yieldb
%
M.p.
Producta
R1
R2
G
◦
C
c
IVa
IVb
IVc
IVd
IVe
IVf
IVg
IVh
IVi
IVj
IVj
IVk
IVl
H
Me
Et
H
Me
Et
H
Me
Et
H
Et
Me
Et
Et
Me
Et
Et
Me
Et
H
H
H
Me
Me
15
15
30
35
35
25
12
10
15
30
40
35
40
90
92
85
75
90
85
90
92
85
85
80
85
90
170–172, 170–172
c
176–178,172–174
166–168, 163–165
108–110, 112–114
198–200, 198–200
165–167, 160–163
208–210, 206–208
225–227, 225–227
177–179, 177–179
136–138
c
c
c
c
c
c
c
Me
NO2
NO2
NO2
PhCO
PhCO
PhCO
PhCO
Et
H
Me
Et
Me
Me
Et
136–138
168–170
140–142
a) Identified by comparison with authentic samples; b) refers to isolated yields; c) Mohammadpoor-Baltork et al. (2007).
◦
Fig. 5. Synthesis of novel benzimidazole derivatives using TSA. Reaction conditions used: solvent-free, 80 C, 0.1 eq. TSA.
solvent-free conditions in a short time span of 15 min.
The use of excess amounts of the catalyst did not
have marked influence on the product yield and reac-
tion rate. The probable reason for this is the coordi-
nation of excessive catalyst to the diamine.
tives such as IVj, IVk, and IVl were synthesized under
the same conditions and results obtained are summa-
rized in Table 4.
Spectral data of the novel products are summa-
1
rized in Tables 5. The H NMR (CDC13, 400 MHz)
Also, as can be seen in Table 3, further increase
of temperature did not improve the yield. In or-
der to prove general applicability of this method, af-
ter optimization of the reaction conditions, different
orthoesters were treated with o-phenylenediamines
bearing electron withdrawing and donating groups un-
der solvent-free and thermal conditions. The results
are summarized in Table 4.
spectrum of IVl exhibited a triplet of the methyl group
protons (δ = 1.47), a quartet of the methylene group
protons (δ = 3.00), and three multiplet signals (δ =
7.82–7.45) and a singlet signal (δ = 7.23–7.27) corre-
sponding to the aromatic protons. Also, the resonance
1
of the NH proton in the H NMR spectrum of IVl ap-
peared at δ = 10.80–10.40 as a broad signal. Position
of the hydrogen atom of benzimidazoles is not easily
determined. NMR spectra point out to fluxional be-
In another variation, using 4-benzoyl-1,2-phenyl-
enediamine (Fig. 5), three novel benzimidazole deriva-
havior. Resonances of th ecarbonyl groups in the 13
C

6
88
B. Karami et al./Chemical Papers 66 (7) 684–690 (2012)
Table 5. Spectral data of newly prepared compounds
Compound
Spectral data
−
IVj
IVk
IVl
IR, ν˜ /cm 1: 3250–2300, 1650, 1615, 1450, 1100, 950, 870, 690
1
H NMR (CDCl3), δ: 8.22 (s, 1H, Harom), 8.18 (s, 1H, —N—C—CH), 7.84 (ddd, J = 9.4 Hz, J = 1.2 Hz, 3H,
Harom), 7.72 (d, J = 8.4 Hz, 1H, Harom), 7.60 (dd, J = 7.2 Hz, 1H, Harom), 7.49 (dd, J = 8.0 Hz, 2H, Harom)
C NMR (CDCl3), δ: 197.31, 157.80, 143.20, 138.11, 132.46, 132.34, 130.05, 128.32, 125.29, 115.12
MS, m/z: 222 (M+
13
)
IR, ν˜ /cm 1: 3200, 2350, 1665, 1620, 1510, 1320, 1020, 820, 720
−
1
H NMR (CDC13), δ: 8.04 (s, 1H, Harom), 7.81 (d, J = 7.6 Hz, 2H, Harom), 7.75 (d, J = 8 Hz, 1H, Harom), 7.57 (d,
J = 7.2 Hz, 2H, Harom), 7.47 (dd, J = 7.2 Hz, 2H, Harom), 2.67 (s, 3H, CH3)
C NMR (CDCl3), δ: 197.51, 154.42, 138.28, 132.24, 131.64, 130.02, 128.27, 124.94, 15.17
MS, m/z: 236 (M+
13
)
IR, ν˜ /cm 1: 3300–2300, 1650, 1620, 1540, 1475, 1400, 1100, 960, 870,700
−
1
H NMR (CDC13), δ: 10.70 (s, 1H, NH), 8.06 (s, 1H, Harom), 7.78 (d, J = 8.1 Hz, 3H, Harom), 7.58 (ddd, J =
6
.6 Hz, J = 1.2 Hz, 2H, Harom), 7.47 (dd, J = 7.6 Hz, 2H, Harom), 3.02 (q, J = 7.6 Hz, 2H, CH2), 1.47 (t, J =
.6 Hz, 3H, CH3)
7
13
C NMR (CDC13), δ: 197.62, 159.75, 138.30, 132.21, 131.51, 129.97, 128.25, 124.86, 118.16, 114.27, 22.81, 12.32
MS, m/z: 250 (M+
)
◦
Table 6. Recyclability of TSA I as the catalyst for the synthesis of IVa at 80 C under solvent-free conditions
Time
min
Isolated yield
%
Entry
Cycle
1
2
3
4
1
2
3
4
15
18
20
25
90
87
85
80
Fig. 6. Proposed mechanism for the o-pehenylenediamines condensation with orthoesters using TSA.
NMR spectrum of IVl appeared at δ = 197.62.
It should be noted that the main disadvantage of
many of the reported methods for the synthesis of
benzimidazoles is that the employed catalysts are de-
stroyed in the work-up procedure and cannot be recov-
ered or reused. In this process, as shown in Table 3,
the recycled catalyst was used in four cycles during
which an insignificant loss in the catalytic activity was
observed.
As shown in Fig. 6, a plausible mechanism for

B. Karami et al./Chemical Papers 66 (7) 684–690 (2012)
689
the synthesis of benzimidazoles IV and recyclability
of TSA was proposed. TSA acts as a Brønsted acid
so that it can release a proton and activate the or-
thoester; thus, the energy of the transition state de-
creases and the rate of the nucleophilic displacement
increases. In general, TSA has valuable and special
features including: a) reaction carried out under sol-
vent free conditions; b) high thermal stability; c) small
amount of catalyst used making this reaction eco-
nomic and eco-friendly.
site strain NF54. Tetrahedron Letters, 42, 751–754. DOI:
0.1016/s0040-4039(00)02106-7.
Karami, B., Damavandi, A. J., Bayat, M., & Montazerzohori,
M. (2006a). A new role of N-arylbenzoquinoneimine N-oxides
in the von Richter reaction. Journal of the Serbian Chemical
Society, 71, 27–30. DOI: 10.2298/jsc0601027k.
Karami, B., & Khodabakhshi, S. (2011). A facile synthesis of
phenazine and quinoxaline (new 1,4-benzo diazine) deriva-
tives using magnesium sulfate heptahydrate as a catalyst.
Journal of the Serbian Chemical Society, 76, 1191–1198.
DOI: 10.2298/jsc100801104k.
Karami, B., Montazerozohori, M., & Habibi, M. H. (2005).
Tungstate sulfuric acid (TSA)/NaNO2 as a novel heteroge-
neous system for the N-nitrosation of secondary amines under
mild conditions. Bulletin of the Korean Chemical Society, 26,
1
Conclusions
1
125–1128. DOI: 10.5012/bkcs.2005.26.7.1125.
In summary, a useful application of tungstate sul-
furic acid as a powerful solid acid catalyst in the con-
densation of orthoesters with o-phenylenediamines un-
der solvent-free conditions was presented. Simple ex-
perimental procedure, utilization of a clean and re-
cyclable catalyst, the use of ready available starting
materials, short period of reaction and good to excel-
lent yields make this method a valid contribution to
the existing methodologies. In fact, this method may
contribute to the development of green chemistry be-
cause it proceeds under solvent-free conditions. Also,
the presence of transformable functionalities of the
novel products makes them potentially valuable from
the aspect of further synthetic manipulations.
Karami, B., Montazerozohori, M., & Habibi, M. H. (2006b).
Tungstate sulfuric acid: A novel and efficient solid acidic
reagent for the oxidation of thiols to disulfides and the
oxidative demasking of 1,3-dithianes. Phosphorous, Sulfur,
and Silicon and the Related Elements, 181, 2825–2831. DOI:
10.1080/10426500600864965.
Ku ¸s , C., & Altanlar, N. (2003). Synthesis of some new benz-
imidazole carbamate derivatives for evaluation of antifungal
activity. Turkish Journal of Chemistry, 27, 35–40.
Maiti, D. K., Halder, S., Pandit, P., Chatterjee, N., De Joarder,
D, Pramanik, N., Saima, Y., Patra, A., & Maiti, P. K.
(2009). Synthesis of glycal-based chiralbenzimidazoles by
VO(acac)2–CeCl3 combo catalyst and their self-aggregated
nanostructured materials. The Journal of Organic Chem-
istry, 74, 8086–8097. DOI: 10.1021/jo901458k.
Mallakpour, S. E., Karami-Descho, B., & Sheikholeslami, B.
(1998). Polymerization of 1-methyl-2,5-bis[1-(4-phenylurazo-
lyl)] pyrrole dianion with alkyldihalides. Polymer Interna-
tional, 45, 98–102. DOI: 10.1002/(SICI)1097-0126(199801)45:
Acknowledgements. The authors gratefully acknowledge
partial support of this work by the Yasouj University, Iran.
1
<98::AID-PI895>3.0.CO;2-3.
References
Martin, A., & Kalevaru, N. V. (2010). Heterogeneously cat-
alyzed ammoxidation: A valuable tool for one-step synthesis
of nitriles. ChemCatChem, 2, 1504–1522. DOI: 10.1002/cctc.
Barker, H. A., Smyth, R. D., Weissbach, H., Toohey, J. I., Ladd,
J. N., & Volcani, B. E. (1960). Isolation and properties of
crystalline cobamide coenzymes containing benzimidazole or
201000173.
Marziano, N. C., Ronchin, L., Tortato, C., Ronchin, S., & Vava-
sori, A. (2005). Selective oxidations by nitrosating agents:
Part 2: Oxidations of alcohols and ketones over solid acid
catalysts. Journal of Molecular Catalysis A: Chemical, 235,
5
,6-dimethylbenzimidazole. The Journal of Biological Chem-
istry, 235, 480–488.
Buchstaller, H. P., Burgdorf, L., Finsinger, D., Stieber, F., Sir-
renberg, C., Amendt, C., Grell, M., Zenke, F., & Krier, M.
2011). Design and synthesis of isoquinolines and benzim-
idazoles as RAF kinase inhibitors. Bioorganic & Medicinal
Chemistry Letters, 21, 2264–2269. DOI: 10.1016/j.bmcl.2011.
26–34. DOI: 10.1016/j.molcata.2005.03.008.
(
Migawa, M. T., Girardet, J. L., Walker, J. A., Koszalka,
G. W., Chamberlain, S. D., Drach, J. C., & Townsend,
L. B. (1998). Design, synthesis, and antiviral activity of
α-nucleosides: D- and L-isomers of lyxofuranosyl- and (5-
deoxylyxofuranosyl)benzimidazoles. Journal of Medicinal
Chemistry, 41, 1242–1251. DOI: 10.1021/jm970545c.
Mohammadpoor-Baltork, I., Khosropour, A. R., & Hojati, S.
F. (2007). ZrOCl2·8H2O as an efficient, environmentally
friendly and reusable catalyst for synthesis of benzoxazoles,
benzothiazoles, benzimidazoles and oxazolo[4,5-b]pyridines
under solvent-free conditions. Catalysis Communications, 8,
1865–1870. DOI: 10.1016/j.catcom.2007.02.020.
02.108.
Damavandi, J. A., Karami, B., & Zolfigol, M. A. (2002). Se-
lective oxidation of N-alkyl imines to oxaziridines using
UHP/maleic anhydride system. Synlett, 2002, 933–934. DOI:
0.1055/s-2002-31903.
Davoodnia, A., Allameh, S., Fazli, S., & Tavakoli-Hoseini, N.
2011). One-pot synthesis of 2-amino-3-cyano-4-arylsubstitu-
ted tetrahydrobenzo[b]pyrans catalysed by silica gel-suppor-
ted polyphosphoric acid (PPA–SiO2) as an efficient and
reusable catalyst. Chemical Papers, 65, 714–720. DOI:
1
(
Niknam, K.,
& Fatehi-Raviz, A. (2007). Synthesis of 2-
1
0.2478/s11696-011-0064-8.
substituted benzimidazoles and bis-benzimidazoles by mi-
crowave in the presence of alumina-methanesulfonic acid.
Journal of the Iranian Chemical Society, 4, 438–443.
Ogurtsov, V. A., Rakitin, O. A., Rees, C. W., & Smolentsev, A.
A. (2003). 4,5-Dichloro-1,2-dithiole-3-thione in the synthesis
of benzimidazole, benzoxazole and benzothiazole derivatives
of 1,3-dithioles. Mendeleev Communications, 13, 50–51. DOI:
10.1070/mc2003v013n02abeh001750.
Heydari, A., Larijani, H., Emami, J., & Karami, B. (2000).
Lithium perchlorate/diethylether-catalyzed three-compo-
nent coupling reactions of aldehydes, hydroxylamines and
trimethylsilyl cyanide leading to α-cyanohydroxylamines.
Tetrahedron Letters, 41, 2471–2473. DOI: 10.1016/s0040-
4039(00)00182-9.
Howarth, J., & Hanlon, K. (2001). Novel N-ferrocenylmethyl,
N -methyl-2-substituted benzimidazolium iodide salts with
in vitro activity against the P. falciparum malarial para-
ꢀ
Olah, G. A., Molhotra, R., & Narang, S. C. (1978). Aromatic
substitution. 43. Perfluorinated resinsulfonic acid catalyzed

6
90
B. Karami et al./Chemical Papers 66 (7) 684–690 (2012)
nitration of aromatics. The Journal of Organic Chemistry,
3, 4628–4630. DOI: 10.1021/jo00418a019.
Preston, P. N. (1974). Synthesis, reactions, and spectroscopic
properties of benzimidazoles. Chemical Reviews, 74, 279–314.
DOI: 10.1021/cr60289a001.
Tamaddon, F., & Tavakoli, F. (2011). One-pot synthesis of
4
N-tert-butyl amides from alcohols, ethers and esters using
ZnCl2/SiO2 as a recyclable heterogeneous catalyst. Jour-
nal of Molecular Catalysis A: Chemical, 337, 52–55. DOI:
10.1016/j.molcata.2011.01.013.
Reddy, V. P., Prasunamba, P. L., Reddy, P. S. N., & Ratnam, C.
V. (1983). Synthesis of quinazolin-4-ones and benzimidazoles:
fusion of 2 aminobenzamide and 1,2-diaminobenzene with
organic acids. Indian Journal of Chemistry – Section B, 22B,
Tamm, I. (1957). Ribonucleic acid synthesis and infulenza virus
multiplication. Science, 126, 1235–1236. DOI: 10.1126/sci-
ence.126.3285.1229.
Tarte, N. H., Woo, S. I., Cui, L., Gong, Y D., & Hwang,
Y. H. (2008). Novel non-chelated cobalt(II) benzimida-
zole complex catalysts: Synthesis, crystal structures and
cocatalyst effect in vinyl polymerization of norbornene.
Journal of Organometallic Chemistry, 693, 729–736. DOI:
10.1016/j.jorganchem.2007.12.001.
917–918.
Romanelli, G. P., Bennardi, D. O., Autino, J. C., Baronetti,
G. T., & Thomas, H. J. (2008). A simple and mild acylation
of alcohols, phenols, amines, and thiols with a reusable het-
eropoly acid catalyst (H6P2W18O62·24H2O). E-Journal of
Chemistry, 5, 641–647.
Wright, J. B. (1951). Errata and addenda – the chemistry of
the benzimidazoles. Chemical Reviews, 49, 397–541. DOI:
10.1021/cr60153a603.
Romanelli, G. P., Ruiz, D. M., Autino, J. C., & Giaccio,
H. E. (2010). A suitable preparation of N-sulfonyl-1,2,3,4-
tetrahydroisoquinolines and their ring homologs with
reusable Preyssler heteropolyacid as catalyst. Molecular Di-
versity, 14, 803–807. DOI: 10.1007/s11030-009-9173-5.
a
Zolfigol, M. A. (2001). Silica sulfuric acid/NaNO2 as a novel
heterogeneous system for production of thionitrites and disul-
fides under mild conditions. Tetrahedron, 57, 9509–9511.
DOI: 10.1016/s0040-4020(01)00960-7.
Roquea, J. M., Pandiyana, T., Cruz, J., & García-Ochoa, E.
(
2008). DFT and electrochemical studies of tris(benzimida-
Zolfigol, M. A., & Bamoniri, A. (2002). Silica sulfuric acid/
NaNO2 as a novel heterogeneous system for the chemose-
lective N-nitrosation of secondary amines under mild condi-
tions. Synlett, 2002, 1621–1624. DOI: 10.1055/s-2002-34230.
Zolfigol, M. A., Shirin, F., Choghamarani, G. A., & Mohammad-
poor-Baltork, I. (2002). Silica modified sulfuric acid/NaNO2
as a novel heterogeneous system for the oxidation of 1,4-
dihydropyridines under mild conditions. Green Chemistry,
4, 562–564. DOI: 10.1039/b208328k.
zole-2-ylmethyl)amine as an efficient corrosion inhibitor for
carbon steel surface. Corrosion Science, 50, 614–624. DOI:
1
Santato, C., Odziemkowski, M., Ulmann, M., & Augustynski,
J. (2001). Crystallographically oriented mesoporous WO3
Films: Synthesis, characterization, and applications. Journal
of the American Chemical Society, 123, 10639–10649. DOI:
0.1016/j.corsci.2007.11.012.
1
0.1021/ja011315x.
Sharma, S., Gangal, S.,
&
Rauf, A. (2009). Convenient
one-pot synthesis of novel 2-substituted benzimidazoles,
tetrahydrobenzimidazoles and imidazoles and evaluation of
their in vitro antibacterial and antifungal activities. Euro-
pean Journal of Medicinal Chemistry, 44, 1751–1757. DOI:
10.1016/j.ejmech.2008.03.026.