Nanosized sulfated zirconia as solid acid catalyst for the synthesis of 2-substituted benzimidazoles

Article abstract of DOI:10.2478/s11696-013-0311-2

The condensation reaction of o-phenylenediamine and arylaldehydes was investigated in the presence of nanosized sulfated zirconia (SO ₄ ^2- -ZrO₂) as the solid acid catalyst. Nanosized SO ₄ ^2- -ZrO

Full text of DOI:10.2478/s11696-013-0311-2

Chemical Papers 67 (5) 490–496 (2013)
DOI: 10.2478/s11696-013-0311-2
ORIGINAL PAPER
Nanosized sulfated zirconia as solid acid catalyst for the synthesis
of 2-substituted benzimidazoles
b
aMohammad Abdollahi-Alibeik*, Mohammad Hajihakimi
aDepartment of Chemistry, Yazd University, 89195-741 Yazd, Iran
bDepartment of Chemistry, Payame Noor University, P.O. BOX 19395-3697 Tehran, Iran
Received 6 August 2012; Revised 7 November 2012; Accepted 18 November 2012
The condensation reaction of o-phenylenediamine and arylaldehydes was investigated in the pres-
ence of nanosized sulfated zirconia (SO42−–ZrO2) as the solid acid catalyst. Nanosized SO42−–ZrO2
was prepared and characterized by the XRD, FT-IR, and SEM techniques. The results confirm good
stabilization of the tetragonal phase of zirconia in the presence of sulfate. Reusability experiments
showed partial deactivation of the catalyst after each run; good reusability can be achieved after
calcinations of the recovered catalyst before its reuse.
c
ꢀ 2013 Institute of Chemistry, Slovak Academy of Sciences
Keywords: sulfated zirconia, nanoparticle, solid acid, catalyst, benzimidazole, reusability
Introduction
peratures. The latter method involves two steps that
include the formation of a Schiffs base and then ox-
idative cyclocondensation.
Benzimidazoles and their derivatives have received
considerable attention due to their broad spectrum of
biological and pharmaceutical activities. These com-
pounds have found applications in diverse therapeutic
areas as antitumour (Denny et al., 1990), antipara-
sitic (Valdez et al., 2002), antimicrobial (Fonseca et
al., 2001), antiviral (Song et al., 2005), and antifun-
gal (Katritzky et al., 1998) agents. Moreover, these
compounds are important intermediates in many or-
ganic reactions (Hasegawa et al., 1999) and can also
act as ligands of transition metals for modeling bio-
logical systems (Fekner et al., 2004).
There are two general methods for the syn-
thesis of benzimidazoles including the condensa-
tion of o-phenylenediamines with carboxylic acids
(Dudd et al., 2003), nitriles (Hein et al., 1957),
acid halides (Nadaf et al., 2004), and orthoesters
(Mohammadpoor-Baltork et al., 2007; Karami et al.,
2012) in the presence of strong acids as the cata-
lyst, and the condensation of o-phenylenediamines and
aldehydes (Abdollahi-Alibeik & Moosavifard, 2010) in
the presence of various acid catalysts at elevated tem-
Recently, a variety of catalysts have been used
in the condensation reaction of o-phenylenediamines
and aldehydes including: FeCl3-dopped polyaniline
(Abdollahi-Alibeik & Moosavifard, 2010), FeCl3–
Al2O3 (Chen & Dong, 2012), molecular iodine (Pon-
nala & Prasad Sahu, 2006), L-proline (Varala et
al., 2007), Zn2+-K10-clay (Dhakshinamoorthy et al.,
2011), polyaniline sulfate (Srinivas et al., 2007),
MnAl2O3 (Rekha et al., 2012), and sodium hydrogen
sulfite (Lopez et al., 2009).
Although these methods are suitable under cer-
tain synthesis conditions, sometimes, some drawbacks
such as long reaction times, low yields of the prod-
ucts, the use of an excess amount of the catalyst and
co-occurrence of several side reactions occur. There-
fore, development of new catalytic systems for this
transformation, which are superior to the existing cat-
alysts regarding toxicity, handling, and reusability, is
required.
In recent years, the interest in the replacement
of traditional environmental hazardous and homo-
*Corresponding author, e-mail: abdollahi@yazduni.ac.ir

M. Abdollahi-Alibeik, M. Hajihakimi/Chemical Papers 67 (5) 490–496 (2013)
491
at 600◦C for 4 h to obtain sulfated zirconia nanopar-
ticles.
Typical procedure for 2-arylbenzimidazoles
synthesis
Fig. 1. 2-Arylbenzimidazoles preparation by the condensation
reaction of arylaldehydes with o-phenylenediamine.
A
mixture
containing
o-phenylenediamine
(1 mmol), ethanol (3 mL), and sulfated zirconia
(100 mg) was put in a 10 mL round bottom flask.
To this suspension, a solution containing aldehyde
(1 mmol) in ethanol (2 mL) was added drop-wise and
the suspension was stirred at 50◦C for an appropriate
period of time. After the reaction completion (moni-
tored by TLC, eluent: EtOAC : hexane, ϕr = 1 : 1),
EtOH (5 mL) was added and the solid catalyst was
separated by centrifugation. To the obtained solution,
water (9 mL) was added and the precipitated prod-
uct was filtered. Crude products of high purity were
obtained. Further purification was achieved by recrys-
tallization from an EtOH–H2O solution (ϕr = 3 : 1).
geneous catalysts by heterogeneous solid acid cat-
alysts in organic transformations has been grow-
ing. This is mainly due to the advantages of solid
acids such as the ease of handling, non-toxicity,
non-corrosiveness, simple work-up, and reusability of
the catalysts (Abdollahi-Alibeik & Heidari-Torkabad,
2012; Adam et al., 2012; Wolfson et al., 2009).
Further to our recent studies on the synthe-
sis of heterocyclic compounds (Abdollahi-Alibeik &
Heidari-Torkabad, 2012; Abdollahi-Alibeik et al.,
2008; Abdollahi-Alibeik & Pouriayevali, 2011, 2012;
Abdollahi-Alibeik & Zaghaghi, 2009), in this paper,
we wish to report on the application of sulfated zir-
conia, SO24−–ZrO2 (SZ), nanoparticles as a solid acid
catalyst in the condensation reaction of arylaldehy-
des with o-phenylenediamine in order to synthesize
2-arylbenzimidazoles (Fig. 1).
Physical and spectroscopic data of selected
compounds
2-(3-Chlorophenyl)benzimidazole, (IIIc): M.p:
230–232◦C (Chen & Dong, 2012); 232–233◦C; IR
(KBr) ν˜/cm−1: 1442 (C C aromatic), 1572; H NMR
1
—
—
Experimental
(500 MHz, DMSO-d6), δ: 7.20–7.27 (dd, 2 H, J = 14.89
Hz, J = 8.32 Hz), 7.55–7.61 (m, 3 H), 7.70 (t, 1 H, J
= 7.71 Hz), 8.16 (dd, 1 H, J = 7.32 Hz, J = 1.30 Hz),
8.23 (t, 1 H, J = 1.58 Hz), 13.03 (s, 1 H, NH); 13C
NMR (125 MHz, DMSO-d6), δ: 112.4, 119.9, 122.8,
123.8, 125.9, 126.9, 130.4, 131.8, 133.1, 134.6, 135.9,
144.5, 150.6.
All chemicals were commercial products (Merck,
Germany). All reactions were monitored by TLC and
all yields refer to isolated products. H and 13C NMR
1
spectra were recorded in DMSO-d6 on a Bruker (DRX-
500 AVANCE) 500 MHz spectrometer (Bruker, Ger-
many) and are reported in ppm related to TMS. In-
frared spectra of the catalysts and reaction prod-
ucts were recorded on a Bruker FT-IR Equinax-55
spectrophotometer (Bruker, Germany) in KBr with
the absorption in cm−1. XRD patterns were recorded
on a Bruker D8 ADVANCE X-ray diffractometer
(Bruker, Germany) using nickel filtered CuKα radi-
ation. Morphology of nanoparticles was studied using
a Philips XL30 scanning electron microscope (Philips,
The Netherlands).
2-(2-Furyl)benzimidazole (IIIk): M.p.: 300◦C (Du
& Wang, 2007); 288◦C; IR (KBr) ν˜/cm−1: 1620
1
—
(C N), 3400 (NH); H NMR (500 MHz, DMSO-d ),
—
6
δ: 6.72–6.73 (m, 1 H), 7.18–7.22 (m, 3 H), 7.56 (d, 2
H, J = 3 Hz), 7.94 (d, 1 H, J = 1 Hz), 12.97 (s, 1
1
H); 13C NMR (125.7 MHz, H-decoupled), δ: 111.35,
113.15, 123.03, 144.53, 145.45, 146.48.
Results and discussion
Catalyst preparation
Preparation of sulfated zirconia (SZ)
The preparation of sulfated zirconia can proceed by
the two-step sol–gel process. In general, this process
involves the formation of a sol by the hydrolysis of
zirconium alkoxide as a zirconia precursor and a three-
dimensional network gel of zirconium hydroxide after
the condensation in the first step. This is followed by
the sulfation with sulfuric acid or ammonium sulfate
for the preparation of sulfated zirconia in the second
step (Reddy & Patil, 2009).
ZrCl4 (1.4 g) was dissolved in deionized water
(50 mL) and to this clear solution, dilute aqueous
ammonia (NH4OH, 5 mass %) was added drop-wise
under vigorous stirring until the pH of the solution
reached 9.5. The obtained Zr(OH)4 gel was stirred for
24 h, centrifuged, washed with distilled water to re-
move chloride ions and dried at 120◦C for 12 h. The
uncalcined hydroxide gel (Zr(OH)4) was sulfated by
stirring in concentrated H2SO4 (1 M, 15 mL g−1) for
24 h. The solid was separated by centrifugation and
washed with water, dried at 120◦C for 4 h and calcined
In the present study, ZrCl4 was used as the pre-
cursor of zirconia. The hydrolysis of ZrCl4 was carried
out in aqueous media with pH adjusted up to 9.5 by

492
M. Abdollahi-Alibeik, M. Hajihakimi/Chemical Papers 67 (5) 490–496 (2013)
Fig. 2. SEM Image of ZrO2.
Fig. 4. XRD patterns of SO24−–ZrO2 calcined at 600◦C (a) and
ZrO2 cacined at 600◦C (b).
Catalyst characterization
Particle morphology of the prepared SZ was stud-
ied by scanning electron microscopy (Fig. 2). The SEM
image shows agglomerated ZrO2 nanoparticles with
the size up to 100 nm.
The presence of sulfate in the structure of the cat-
alyst was confirmed by FT-IR spectroscopy. FT-IR
spectra of ZrO2 and SZ are shown in Fig. 3, where line
a, the FT-IR spectrum of SZ, exhibited characteristic
peaks of sulfate at 1244 cm−1, 1136 cm−1, 1082 cm−1
,
and 1043 cm−1, which are attributed to asymmetric
and symmetric stretching frequencies of partially ion-
ized double bond SO and single bond SO, due to the
presence of an inorganic chelating bidentate sulfate
group in the ZrO2 structure (Tyagi et al., 2007).
It is well known from literature that the tetragonal
phase of zirconia is more active in the catalytic pro-
cess (Yamaguchi, 1994). The powder X-ray diffraction
technique was used to describe the crystalline phase
and the effect of sulfate on the phase change of zirconia
(Fig. 4). XRD pattern of ZrO2 exhibited characteris-
tic peaks of both tetragonal and monoclinic phases
(Fig. 4, line a) while that of SZ showed only charac-
teristic peaks of the tetragonal phase at 2θ = 30◦, 35◦,
50◦, 60◦. This indicates that sulfate affects the phase
modification and stabilizes zirconia in the tetragonal
phase. This result is in agreement with literature (Ne-
grón et al., 2005).
Fig. 3. FT-IR spectra of ZrO2 (a) and SO24−–ZrO2 (b).
additions of an ammonia solution. Sulfated zirconia
was prepared by sulfation of dried Zr(OH)4 using 1 M
H2SO4 (15 mL g−1) and calcination of the dried solid
at 600◦C for 4 h.

M. Abdollahi-Alibeik, M. Hajihakimi/Chemical Papers 67 (5) 490–496 (2013)
493
Table 1. Optimization of the catalytic amount of SO24−–ZrO2 in the synthesis of benzimidazole
Catalyst amount
mg
Temperature
◦C
Time
min
Yield
%
Entry
Solvent
1
2
3
4
5
6
7
8
9
100
100
100
25
50
75
150
100
100
100
100
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
CH3CN
CHCl3
CH2Cl2
–
r.t.
reflux
50
50
50
50
50
50
50
45
30
45
70
60
50
30
45
45
45
45
10
65
77
42
65
70
79
65
35
60
10
10
11
50
50
Catalyst activity
rated by centrifugation and the solid was washed by
EtOH. The solution was poured onto crushed ice and
the product precipitated after a few minutes. Crude
products with high purity were obtained by filtration
of the mixture.
To investigate the performance of SO24−–ZrO2 in
the synthesis of benzimidazoles, the reaction of ben-
zaldehyde with o-phenylenediamine was selected as
the model reaction. The effect of different amounts of
catalysts and different reaction temperatures on the
reactivity of SO24−–ZrO2 was investigated and the re-
sults are shown in Table 1 (entries 1–7). To investi-
gate the effect of the solvent on the catalytic reaction,
the model reaction was carried out in the presence of
100 mg of SZ in various solvents and under solvent-
free conditions (Table 1). The results show that EtOH
is the best solvent in terms of time and yield of the
product (Table 1, entries 3, 8–11), it is also suitable
in regard to environmental considerations, and thus it
was selected as the solvent for the reaction.
To study the reusability of the catalyst, the recov-
ered catalyst after used in the reaction of benzalde-
hyde and o-phenylenediamine was reused in the same
reaction. The recovered catalyst for the model reac-
tion was washed with EtOH and dried in an oven at
120◦C for 2 h. The results show that the catalyst ac-
tivity decreased after the first and the second runs
(Table 3, runs 2 and 3). These results suggest that
the deactivation is caused by a blockage of active sites
of the catalyst. The catalyst recovered after the third
run was calcined at 600◦C for 2 h and reused in the
fourth run. The results show that the catalyst activity
increased to nearly the same value as that of the fresh
catalyst (Table 3, run 4). This result is consistent with
a previous report (Negrón et al., 2005).
It is noticeable that experiments on the reusability
of SZ prepared using different methodologies showed
the same results as those for SZ employed in this
work. The yield differences between the first, sec-
ond, and third run in the reusability experiment are
higher than those reported in some other studies
on the SZ reusability in various reactions such as
esterification of acetic acid (Yu et al., 2012), syn-
thesis of 7-isopropyl-1,1-dimethyltetralin by the rear-
rangement of (+)-longifolene (Tyagi et al., 2009) and
Mannich-type reactions between ketene silyl acetals
and aldimines (Du & Wang, 2007). However, differ-
ent results on the decrease in the catalytic activity
after the reuse may be due to the different reaction
media and conditions. Although an exact reusability
study was employed for the model reaction, SZ in the
other reactions including different aldehydes showed
a decrease in its activity after the first run. This de-
crease in the activity is different for various aldehy-
des.
As can be seen from Table 1 (entry 3), the best
reaction conditions were provided by the model with
the molar ratio of aldehyde : diamine of 1 : 1 in the
presence of 100 mg of SO24−–ZrO2 in EtOH as the
solvent at 50◦C.
Considering the optimization results, the reac-
tion of 1 mmol of benzaldehyde and 1 mmol of
o-phenylenediamine in the presence of 100 mg of
SO24−–ZrO2 in EtOH at 50◦C was carried out and
2-phenylbenzimidazole was obtained in a 77 % yield
(Table 2, entry a). In order to investigate the scope
and generality of this method, the reaction of various
types of arylaldehydes with both electron-donating
and electron-withdrawing substituents were carried
out at the same reaction conditions and the corre-
sponding 2-arylbenzimidazoles were obtained in 68–
93 % yields. This method was also successfully used
for the synthesis of heteroaryl benzimidazoles and bis-
benzimidazoles using the heteroaryl aldehydes and
bisaldehyde as starting materials.
Work-up of the reaction is very easy. After the com-
pletion of the reaction (monitored by TLC, eluent;
hexane : EtOAc, ϕr = 2 : 1), the catalyst was sepa-

494
M. Abdollahi-Alibeik, M. Hajihakimi/Chemical Papers 67 (5) 490–496 (2013)
Table 2. Synthesis of benzimidazoles by the reaction o-phenylenediamine and benzaldehyde in the presence of the catalytic amount
of SO24−–ZrO2
Time
min
Yield
%
Entry
Aldehyde (I)
Benzimidazole (III)
a
b
45
50
77
76
c
55
74
d
e
f
50
73
74
76
150
120
ga
60
97
ha
180
40
93
79
70
69
i
j
50
k
60
l
120
70
68
84
m
a) Reactions were performed under reflux condition.
Conclusions
method for the synthesis of 2-substituted benz-
imidazoles by the reaction of aldehydes with o-
phenylenediamine using the catalytic amount of
In conclusion, a mild, convenient and efficient

M. Abdollahi-Alibeik, M. Hajihakimi/Chemical Papers 67 (5) 490–496 (2013)
495
Table 3. Reusability of SO24−–ZrO2 in the reaction of o-
ships for 2-phenylbenzimidazole-4-carboxamides, a new class
of minimal DNA-intercalating agents which may not act via
topoisomerase II. Journal of Medicinal Chemistry, 33, 814–
819. DOI: 10.1021/jm00164a054.
phenylenediamine and benzaldehyde
Time
min
Yield
%
Run
Dhakshinamoorthy, A., Kanagaraj, K.,
& Pitchumani, K.
(2011). Zn2+-K10-clay (clayzic) as an efficient water-tolerant,
solid acid catalyst for the synthesis of benzimidazoles and
quinoxalines at room temperature. Tetrahedron Letters, 52,
69–73. DOI: 10.1016/j.tetlet.2010.10.146.
1
2
3
4a
45
60
70
55
77
69
67
72
Du, L. H., & Wang, Y. G. (2007). A rapid and efficient syn-
thesis of benzimidazoles using hypervalent iodine as oxidant.
Synthesis, 2007, 675–678. DOI: 10.1055/s-2007-965922.
Dudd, L. M., Venardou, E., Garcia-Verdugo, E., Licence, P.,
Blake, A. J., Wilson, C., & Poliakoff, M. (2003). Synthesis of
benzimidazoles in high-temperature water. Green Chemistry,
5, 187–192. DOI: 10.1039/b212394k.
Fekner, T., Gallucci, J., & Chan, M. K. (2004). Ruffling-induced
chirality: Synthesis, metalation, and optical resolution of
highly nonplanar, cyclic, benzimidazole-based ligands. Jour-
nal of the American Chemical Society, 126, 223–236. DOI:
10.1021/ja030196d.
a) Catalyst was calcined at 600◦C for 2 h before use.
SO24−–ZrO2 in EtOH as the solvent was introduced.
The mild reaction conditions, simple experimental
procedure, the ease of the catalyst recovery, as well
as the reusability of the catalyst are some of the ad-
vantages of this method.
Fonseca, T., Gigante, B., & Gilchrist, T. L. (2001). A short
synthesis of phenanthro[2,3-d]imidazoles from dehydroabi-
etic acid. Application of the methodology as a convenient
route to benzimidazoles. Tetrahedron, 57, 1793–1799. DOI:
10.1016/s0040-4020(00)01158-3.
Acknowledgements. The authors are thankful to the Payame
Noor University of Ardakan for partial support of this work.
References
Hasegawa, E., Yoneoka, A., Suzuki, K., Kato, T., Kitazume,
T., & Yanagi, K. (1999). Reductive transformation of α,
β-epoxy ketones and other compounds promoted through
photoinduced electron transfer processes with 1,3-dimethyl-
2-phenylbenzimidazoline (DMPBI). Tetrahedron, 55, 12957–
12968. DOI: 10.1016/s0040-4020(99)00804-2.
Hein, D. W., Alheim, R. J., & Leavitt, J. J. (1957). The use
of polyphosphoric acid in the synthesis of 2-aryl- and 2-
alkyl-substituted benzimidazoles, benzoxazoles and benzoth-
iazoles. Journal of the American Chemical Society, 79, 427–
429. DOI: 10.1021/ja01559a053.
Abdollahi-Alibeik, M., Mohammadpoor-Baltork, I., Zaghaghi,
Z.,
& Yousefi, B. H. (2008). Efficient synthesis of 1,5-
benzodiazepines catalyzed by silica supported 12-tungsto-
phosphoric acid. Catalysis Communications, 9, 2496–2502.
DOI: 10.1016/j.catcom.2008.07.004.
Abdollahi-Alibeik, M., & Zaghaghi, Z. (2009). 1,3-Dibromo-5,5-
dimethylhydantoin as a useful reagent for efficient synthesis
of 3,4-dihydropyrimidin-2-(1H)-ones under solvent-free con-
ditions. Chemical Papers, 63, 97–101. DOI: 10.2478/s11696-
008-0084-1.
Abdollahi-Alibeik, M., & Moosavifard, M. (2010). FeCl3-doped
polyaniline nanoparticles as reusable heterogeneous catalyst
for the synthesis of 2-substituted benzimidazoles. Synthetic
Communications, 40, 2686–2695. DOI: 10.1080/0039791090
3318658.
Abdollahi-Alibeik, M., & Pouriayevali, M. (2011). 12-Tungsto-
phosphoric acid supported on nano sized MCM-41 as an effi-
cient and reusable solid acid catalyst for the three-component
imino Diels–Alder reaction. Reaction Kinetics, Mechanisms
and Catalysis, 104, 235–248. DOI: 10.1007/s11144-011-0345-
9.
Karami, B., Khodabakhshi, S.,
& Haghighijou, Z. (2012).
Tungstate sulfuric acid: preparation, characterization, and
application in catalytic synthesis of novel benzimidazoles.
Chemical Papers, 66, 684–690. DOI: 10.2478/s11696-012-
0152-4.
Katritzky, A. R., Aslan, D. C., & Oniciu, D. C. (1998). Stereose-
lective synthesis of 2-(α-hydroxyalkyl)benzimidazoles. Tetra-
hedron: Asymmetry, 9, 2245–2251. DOI: 10.1016/s0957-
4166(98)00202-x.
Lopez, S. E., Restrepo, J., Perez, B., Ortiz, S., & Salazar,
J. (2009). One pot microwave promoted synthesis of 2-
aryl-1H-benzimidazoles using sodium hydrogen sulfite. Bul-
letin of the Korean Chemical Society, 30, 1628–1630. DOI:
10.5012/bkcs.2009.30.7.1628.
Abdollahi-Alibeik, M., & Heidari-Torkabad, E. (2012). H3PW12
O40/MCM-41 nanoparticles as efficient and reusable solid
acid catalyst for the synthesis of quinoxalines. Comptes Ren-
dus Chimie, 15, 517–523. DOI: 10.1016/j.crci.2012.04.005.
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.
Nadaf, R. N., Siddiqui, S. A., Daniel, T., Lahoti, R. J., &
Srinivasan, K. V. (2004). Room temperature ionic liquid pro-
moted regioselective synthesis of 2-aryl benzimidazoles, ben-
zoxazoles and benzthiazoles under ambient conditions. Jour-
nal of Molecular Catalysis A: Chemical, 214, 155–160. DOI:
10.1016/j.molcata.2003.10.064.
Abdollahi-Alibeik, M.,
& Pouriayevali, M. (2012). Nano-
sized MCM-41 supported protic ionic liquid as an effi-
cient novel catalytic system for Friedlander synthesis of
quinolines. Catalysis Communications, 22, 13–18. DOI:
10.1016/j.catcom.2012.02.004.
Adam, F., Batagarawa, M., Hello, K., & Al-Juaid, S. (2012).
One-step synthesis of solid sulfonic acid catalyst and its ap-
plication in the acetalization of glycerol: crystal structure
of cis-5-hydroxy-2-phenyl-1,3-dioxane trimer. Chemical Pa-
pers, 66, 1048–1058. DOI: 10.2478/s11696-012-0203-x.
Chen, G. F.,
& Dong, X. Y. (2012). Facile and selec-
tive synthesis of 2-substituted benzimidazoles catalyzed by
FeCl3/Al2O3. E-Journal of Chemistry, 9, 289–293. DOI:
10.1155/2012/197174.
Denny, W. A., Rewcastle, G. W., & Baguley, B. C. (1990).
Potential antitumor agents. 59. Structure-activity relation-
Negrón, G. E., Palacios, L. N., Angeles, D., Lomas, L., &
Gavin˜o, R. (2005). A mild and efficient method for the
chemoselective synthesis of acylals from aromatic aldehydes
and their deprotections catalyzed by sulfated zirconia. Jour-

496
M. Abdollahi-Alibeik, M. Hajihakimi/Chemical Papers 67 (5) 490–496 (2013)
nal of the Brazilian Chemical Society, 16, 490–494. DOI:
10.1590/s0103-50532005000300025.
Ponnala, S., Prasad Sahu, D. (2006). Iodine-mediated
synthesis of 2-arylbenzoxazoles, 2-arylbenzimidazoles, and
1,3,5-trisubstituted pyrazoles. Synthetic Communications,
36, 2189–2194. DOI: 10.1080/00397910600638879.
Reddy, B. M., & Patil, M. K. (2009). Organic syntheses and
transformations catalyzed by sulfated zirconia. Chemical Re-
views, 109, 2185–2208. DOI: 10.1021/cr900008m.
Rekha, M., Hamza, A., Venugopal, B. R., & Nagaraju, N.
(2012). Synthesis of 2-substituted benzimidazoles and 1,5-
disubstituted benzodiazepines on alumina and zirconia cat-
alysts. Chinese Journal of Catalysis, 33, 439–446. DOI:
10.1016/s1872-2067(11)60338-0.
Song, X. Q., Vig, B. S., Lorenzi, P. L., Drach, J. C.,
Townsend, L. B., & Amidon, G. L. (2005). Amino acid es-
ter prodrugs of the antiviral agent 2-bromo-5,6-dichloro-1-
(β-D-ribofuranosyl)benzimidazole as potential substrates of
hPEPT1 transporter. Journal of Medicinal Chemistry, 48,
1274–1277. DOI: 10.1021/jm049450i.
Tyagi, B., Mishra, M. K., & Jasra, R. V. (2009). Solvent
free synthesis of 7-isopropyl-1,1-dimethyltetralin by the rear-
rangement of longifolene using nano-crystalline sulfated zir-
conia catalyst. Journal of Molecular Catalysis A: Chemical,
301, 67–78. DOI: 10.1016/j.molcata.2008.11.011.
Valdez, J., Cedillo, R., Hernández-Campos, A., Yépez, L.,
Hernández-Luis, F., Navarrete-Vázquez, G., Tapia, A., Cor-
tés, R., Hernándey, M., & Castillo, R. (2002). Synthesis and
antiparasitic activity of 1H-benzimidazole derivatives. Bioor-
ganic & Medicinal Chemistry Letters, 12, 2221–2224. DOI:
10.1016/s0960-894x(02)00346-3.
Varala, R., Nasreen, A., Enugala, R., & Adapa, S. R. (2007).
L-Proline catalyzed selective synthesis of 2-aryl-1-arylmethyl-
1H-benzimidazoles. Tetrahedron Letters, 48, 69–72. DOI:
10.1016/j.tetlet.2006.11.010.
Wolfson, A., Madhusudhan, R., Shapira-Tchelet, A., & Lan-
dau, M. (2009). Effects of acyl donor type, catalyst type,
and reaction conditions on the activity and selectivity of
Friedel–Crafts acylation. Chemical Papers, 63, 291–297.
DOI: 10.2478/s11696-009-0018-6.
&
Srinivas, U., Srinivas, Ch., Narender, P., Rao, V. J., & Pala-
niappan, S. (2007). Polyaniline-sulfate salt as an efficient and
reusable catalyst for the synthesis of 1,5-benzodiazepines and
2-phenyl benzimidazoles. Catalysis Communications, 8, 107–
110. DOI: 10.1016/j.catcom.2006.05.022.
Yamaguchi, T. (1994). Application of ZrO2 as a catalyst and
a catalyst support. Catalysis Today, 20, 199–217. DOI:
10.1016/0920-5861(94)80003-0.
Yu, S. J., Jiang, P. P., Dong, Y. M., Zhang, P. B., Zhang, Y.,
& Zhang, W. J. (2012). Hydrothermal synthesis of nano-
sized sulfated zirconia as an efficient and reusable cata-
lyst for esterification of acetic acid with n-butanol. Bul-
letin of the Korean Chemical Society, 33, 524–528. DOI:
10.5012/bkcs.2012.33.2.524.
Tyagi, B., Mishra, M. K.,
& Jasra, R. V. (2007). Syn-
thesis of 7-substituted 4-methyl coumarins by Pechmann
reaction using nano-crystalline sulfated-zirconia. Journal
of Molecular Catalysis A: Chemical, 276, 47–56. DOI:
10.1016/j.molcata.2007.06.003.