Synthesis of 2-substituted benzimidazoles and 1,5-disubstituted benzodiazepines on alumina and zirconia catalysts

Article abstract of DOI:10.1016/S1872-2067(11)60338-0

In this study, alumina, zirconia, manganese oxide/alumina, and manganese oxide/zirconia have been investigated for their catalytic activity in the condensation reaction between o-phenylenediamine and an aldehyde or a ketone to synthesise 2-substituted benzimidazoles and 1,5-disubstituted benzodiazepines respectively. Surface area, surface acidity, and morphology of the catalysts have been analysed and correlated with their catalytic activity. The isolated yields of 2-substituted benzimidazoles and 1,5-disubstituted benzodiazepines are in the range of 30 to 95. A good correlation between the amount of surface acid sites as well as the surface morphology of the catalysts and the catalytic activity has been observed. This method has been found to be simple and economical. The solid supports could be regenerated and reused without much loss in their activity. Further, the solid supports have been also found to be effective as general catalysts in the condensation of o-phenylenediamine with other substituted aldehydes and ketones.

Full text of DOI:10.1016/S1872-2067(11)60338-0

CHINESE JOURNAL OF CATALYSIS
Volume 33, Issue 3, 2012
Online English edition of the Chinese language journal
Cite this article as: Chin. J. Catal., 2012, 33: 439–446.
ARTICLE
Synthesis of 2-Substituted Benzimidazoles and
1,5-Disubstituted Benzodiazepines on Alumina and Zirconia
Catalysts
M. REKHA1, A. HAMZA1, B. R. VENUGOPAL2, N. NAGARAJU1,*
1Catalysis Research Laboratory, St. Joseph’s College and Research Centre, 39 Lalbagh Road, Shanthinagar, Bangalore 560 027,
India
2Laboratory of Chemistry and Electrochemistry of Surfaces, Facultés Universitaires Notre-Dame de la Paix, Rue de Bruxelles, 61,
B-5000, Namur, Belgium
Abstract: In this study, alumina, zirconia, manganese oxide/alumina, and manganese oxide/zirconia have been investigated for their
catalytic activity in the condensation reaction between o-phenylenediamine and an aldehyde or a ketone to synthesise 2-substituted ben-
zimidazoles and 1,5-disubstituted benzodiazepines respectively. Surface area, surface acidity, and morphology of the catalysts have been
analysed and correlated with their catalytic activity. The isolated yields of 2-substituted benzimidazoles and 1,5-disubstituted benzodi-
azepines are in the range of 30% to 95%. A good correlation between the amount of surface acid sites as well as the surface morphology of
the catalysts and the catalytic activity has been observed. This method has been found to be simple and economical. The solid supports could
be regenerated and reused without much loss in their activity. Further, the solid supports have been also found to be effective as general
catalysts in the condensation of o-phenylenediamine with other substituted aldehydes and ketones.
Key words: 2-substituted benzimidazoles; 1,5-disubstituted benzodiazepines; manganese oxide; alumina; zirconia
For several decades there has been a concern for improving
the chemical processes in industry, with regard to environ-
mental and health related issues, which would also eventually
reduce chemical waste. Catalytic activation of substrates under
heterogeneous conditions using solid acids and bases [1,2] as
catalysts or catalyst supports has been identified as one of the
important ways to make the given process environmentally
benign and efficient. Thus over the years a lot of research has
been focused on the development of greener processes [3].
Benzimidazole derivates exhibit various biological and phar-
maceutical properties [4–7]. Recently it has been found that
benzimidazole derivatives are useful as fluorescent chemo-
sensors for Cu2+ [8]. Benzodiazepine and their derivates are
also interesting class of bioactive compounds widely used in
therapeutics [9] as anti-convulsant, analgesics, anti-anxiety
drugs, sedatives, anti-depressants, and hypnotics [10–12]. One
of the methods commonly reported by several groups for the
synthesis of benzimidazoles and benzodiazepines is the con-
densation reaction between o-phenylenediamine (OPDA) and
an aldehyde [13–15] or a ketone [16–19], respectively.
Catalytic activities of different Lewis acids have been in-
vestigated in the synthesis of benzimidazoles and benzodi-
azepines by different groups highlighting the advantages of
their protocol over the other methods. However, to the best of
our knowledge no attempt has been made to correlate the sur-
face properties of the catalysts and their catalytic activity in the
condensation of aldehydes/ketones with OPDA to synthesise
benzimidazoles and benzodiazepines.
Metal oxides and supported metal oxides are known to
possess surface acidity and/or basicity and activate a number of
industrially important organic transformations [20,21]. Ac-
cordingly the present investigation focuses on the preparation,
Received 22 September 2011. Accepted 7 November 2011.
*Corresponding author. Tel: +91-9886765750; Fax: +91-8022245831; E-mail: nagarajun@yahoo.com
This work was supported by the UGC, New Delhi.
Copyright © 2012, Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by Elsevier BV. All rights reserved.
DOI: 10.1016/S1872-2067(11)60338-0

M. REKHA et al. / Chinese Journal of Catalysis, 2012, 33: 439–446
characterization, and catalytic applications of Al2O3, ZrO2,
(FE-SEM) using JEOL JSM-7500F microscope operating at 20
kV at a working distance of 8 mm. The particle size and dis-
tribution of the materials were studied by low resolution
transmission electron microscopy (TEM) using a TECNAI 10
PHILIPS microscope. Prior to the analysis, the samples were
dispersed in ethanol and a drop of the suspension was deposited
on a holey carbon-coated copper grid.
Manganese oxide/Al2O3 and Manganese oxide/ZrO2. A corre-
lation between the amount of surface acid sites, surface mor-
phology, and the catalytic activity is described.
1 Experimental
1.1 Preparation of the catalyst
1.3 Characterization of the reaction product
Catalysts containing 5% of manganese oxide on Al2O3 and
ZrO2 were prepared by precipitation method. A calculated
quantity of manganese sulphate was dissolved in 500 ml of
distilled water. To this solution, a required amount of Al(OH)3
or Zr(OH)4 powder was added in small portions while the
solution was being stirred (molar ratio of Mn:Al = 0.05:0.95).
Infrared spectra of the products were recorded from a
Nicolet Model Impact 400D FT-IR spectrometer with 4 cm–1
resolution. Sample pellets were made by pressing a mixture of
the sample with KBr in the required ratio. The mass spectra of
the filtrate were recorded on GC-MS Shimadzu QP 5000,
o
1
The mixture was heated to 80 C and 28% NH3 solution was
GC-17A. H NMR spectrum was obtained in DMSO solution
added drop-wise to precipitate manganese as its hydroxide (pH
= 9). A thick brown precipitate thus obtained was digested for 4
h on a water bath, separated by filtration, washed with distilled
at 300 MHz using Bruker Avance NMR spectrometers. Spec-
trum is referenced to transcranial magnetic stimulation (TMS).
o
water, and dried in a hot air oven at 120 C for 12 h and then
1.4 Catalytic activity study
calcined in a furnace at 450 oC for 5 h. Al2O3 and ZrO2 catalysts
without manganese oxide were obtained by drying the com-
mercial Al(OH)3 or Zr(OH)4 at 120 oC followed by calcination
o
Catalytic activity of the catalysts, dried at 120 C and cal-
cined at 450 oC, was investigated in the condensation reaction
between OPDA and benzaldehyde or acetophenone (Scheme 1).
This is used as a model reaction. In a typical procedure a
mixture of OPDA (1 mmol), benzaldehyde (1 mmol) or ace-
tophenone (2.2 mmol), ethanol (5 ml), and the catalyst (0.2 g)
taken in a 100 ml RB flask was heated to 80 oC. The progress of
the reaction was monitored periodically by analysing the reac-
tion mixture by thin layer chromatography using a mixture of
petroleum ether and ethyl acetate in 8:2 ratio. After completion
of the reaction, the reaction mixture was diluted with 10 ml of
ethanol and filtered to recover the solid catalyst. The filtrate
was poured into a beaker containing crushed ice. The solid
product was separated and purified by column chromatography
using silica gel [100–200 mesh] with petroleum ether and ethyl
acetate as solvent. The products were further analyzed by IR,
1H NMR, and GC-MS techniques.
o
at 450 C for 5 h. These catalysts are denoted as Al2O3-120,
MnAl2O3-120,
Al2O3-450,
MnAl2O3-120,
ZrO2-120,
MnZrO2-120, ZrO2-450, and MnZrO2-450.
1.2 Characterization of the catalyst
BET surface area of the catalysts was determined from N2
adsorption data acquired on a Micromeritics TriStar 3000
instrument. Powder X-ray diffraction (XRD) patterns were
recorded on a Panalytical Xpert pro X-ray diffractometer using
Cu Kꢀ radiation (ꢁ = 0.154 nm) in the 2ꢂ range of 5o–70o at 40
kV and at a scanning rate of 2o/min. The amounts of surface
acid sites of the catalysts were determined by N-butylamine
titration method. The surface morphology of the materials were
studied by field-emission scanning electron microscopy
NH2
O
N
0.2 g catalyst
Ethanol, 80 oC
C6H5
+
N
H
C6H5
H
NH2
o-phenylenediamine
Benzaldehyde
2-phenyl-1H-benzimidazole
C6H5
CH3
H
N
NH2
O
0.2 g catalyst
Ethanol, 80 oC
+
CH3
H5C6
NH2
N
C6H5
o-phenylenediamine
Acetophenone
2-methyl-2,4-diphenyl-2,3-dihydro-1H-1,5-benzodiazepine
Scheme 1. The condensation reaction between OPDA and benzaldehyde or acetophenone.

M. REKHA et al. / Chinese Journal of Catalysis, 2012, 33: 439–446
Table 1 BET surface area, amount of surface acid sites in alumina and zirconia catalysts, and their activity in the synthesis of benzimidazole and benzo-
diazepines
Specific surface area
(m2/g)
Surface acidity
(mmol/g)
0.75
Isolated yield (%)
Benzimidazole
Catalyst
Benzodiazepine
Al2O3-120
MnAl2O3-120
Al2O3-450
MnAl2O3-450
ZrO2-120
MnZrO2-120
ZrO2-450
MnZrO2-450
1.38
3.13
30
67
52
90
34
70
65
95
30
60
35
85
47
74
70
93
1.00
1.01
1.25
0.50
1.50
1.25
2.25
262.81
209.67
174.26
154.90
61.39
92.37
2 Results and discussion
phase of alumina was observed which is not observed in
MnAl2O3-120 catalyst. The XRD patterns of ZrO2-120 and
MnZrO2-120 shows no distinct peaks indicating the amorphous
nature of the catalysts (Fig. 1(b)). On calcination the crystal-
linity of both the catalysts has increased. In the case of
ZrO2-450, majority of the ZrO2 is crystallized into tetragonal
phase [24] with small amount of monoclinic phase [25].
However pure tetragonal phase of ZrO2 is formed in the case of
MnZrO2-450 due to phase transition of stable monoclinic to
tetragonal phase transfer is observed on manganese oxide
deposition and calcinations at 450 oC. It is also noteworthy that
upon deposition of manganese oxide on zirconia and calcined
2.1 Catalyst characterization
2.1.1 BET surface area and acidity
The quantitative data on the BET surface area and amount of
surface acid sites of the catalysts are given in the Table 1.
The surface acidities of alumina catalysts followed the
order of MnAl2O3-450 > Al2O3-450 > MnAl2O3-120 >
Al2O3-120. And for the zirconia catalyst, the surface acidities
are MnZrO2-450 > MnZrO2-120 > ZrO2-450 > ZrO2-120. From
the above alumina and zirconia catalysts, MnZrO2-450 catalyst
showed a higher amount of surface acid sites. The surface area
of alumina catalysts followed the order of Al2O3-450 >
MnAl2O3-450 > MnAl2O3-120 > Al2O3-120. And for the
zirconia catalyst, the surface area are ZrO2-120 > MnZrO2-120
> MnZrO2-450 > ZrO2-450. Surface acidity of alumina cata-
lysts is less than that of zirconia catalysts. Calcination in-
creased the surface acidity more in the case of zirconia than
alumina catalysts. MnZrO2-450 catalyst showed the highest
surface acidity of all the catalysts. On calcination the surface
area of alumina catalysts increased significantly whereas it
decreased in the case of zirconia catalysts. MnAl2O3-450
catalyst showed the highest surface area.
(a)
MnAl2O3-450
MnAl2O3-120
Al2O3-450
Al2O3-120
(b)
2.1.2 XRD results
XRD patterns of the catalysts are shown in Fig. 1. It is ob-
served that on calcinations, crystalline nature of alumina
catalysts decreased whereas zirconia sample becomes more
crystalline. This observation clearly accounts for the variation
in the surface area of the respective samples upon calcination
as discussed previously. The highly crystalline XRD pattern of
uncalcined Al2O3 corresponds to the gibbsite phase [22],
however the crystallinity of the catalyst decreased on calcina-
tion with the formation of boehmite phase [23] (Fig. 1(a)).
When manganese oxide is deposited on alumina, the charac-
teristic Hausmannite, Mn3O4 phase along with the Boehmite
MnZrO2-450
MnZrO2-120
ZrO2-450
ZrO2-120
10
20
30 40
2ꢀꢁ(o )
50
60
70
Fig. 1. XRD patterns of alumina (a) and zirconia (b) based catalysts
both calcined and uncalcined samples.

M. REKHA et al. / Chinese Journal of Catalysis, 2012, 33: 439–446
(a)
(b)
(c)
(d)
Fig. 2. SEM images of MnAl2O3-450 (a) and MnZrO2-450 (b) catalysts and TEM images of MnAl2O3-450 (c) and MnZrO2-450 (d) catalysts.
o
at 450 C, no diffraction peaks corresponding to any manga-
nese oxide phases have appeared and catalytically active
tetragonal phase is stabilised.
MnZrO2-450 catalyst showed highest catalytic activity than
other samples (alumina and zirconia based samples). It is in-
teresting to note that a good correlation between the amount of
the acid site and the catalytic activity is observed. Thus, it may
be inferred that the condensation reaction between OPDA and
an aldehyde/ketone is activated by the surface acidity of the
solid catalysts. Further, taking into account of the variation of
other textural properties of the catalyst on calcinations and
incorporation of manganese oxide, it is worthwhile to mention
here that synergistic effects of the following parameters con-
tribute to the overall increase in the catalytic activity of the
solid catalysts: (1) enhancement of the intrinsic surface acid
sites concentration of the supports on calcination; (2) contri-
bution to the additional acidity by the presence of manganese
oxide on alumina and zirconia; (3) stabilisation of catalytically
active tetragonal phase of zirconia on calcination in the pres-
ence of manganese oxide.
It may be noted here that the boehmite phase of alumina and
tetragonal phase of zirconia that are formed upon calcination
are catalytically active for this condensation reaction.
It is evident from the results presented in Table 1, that
5%MnZrO2-450 showed the best results in terms of OPDA
conversion. In order to evaluate the effects of the solvent,
reaction temperature, and amount of catalyst on the product
2.1.3 SEM and TEM image
SEM and TEM images of a few representative catalysts are
shown in the Fig. 2. It is interesting to note that the morphology
of the alumina catalysts is distinctly different from those of
zirconia catalysts. Samples of zirconia exhibited tubular/needle
like shapes with a thickness approximately 30 nm, decorated
with manganese oxide particles.
2.2 Catalytic activity study
The percentage yields of the isolated product in the con-
densation reaction between OPDA and benzalde-
hyde/acetophenone conducted in the presence of solid supports
are given in the Table 1. It is to be noted that the OPDA con-
version in the absence of a solid support was low. However, in
the presence of Al2O3, ZrO2, manganese oxide/Al2O3, and
manganese oxide/ZrO2 catalysts improved the yields. The yield
of the isolated product was in the range 30% to 95%. Pure
Alumina was found to be less active than pure zirconia.

M. REKHA et al. / Chinese Journal of Catalysis, 2012, 33: 439–446
100
90
80
70
60
100
Benzimidazole
Benzodiazepine
75
50
25
Benzimidazole
Benzodiazepine
25
35
45
55
65
75
85
95
105
Temperature (oC)
Fig. 4. Effect of temperature on the activity of MnZrO2-450 catalyst.
Fig. 3. Effect of solvents on the activity of MnZrO2-450 catalyst.
mixture, followed by washing with acetone and drying in oven
at 110 oC for 2 h. Recovery of the catalytic activity of the zir-
conia based catalysts was better than alumina based catalysts.
Zirconia catalysts could be reused upto 5 times without any
significant loss in catalyst efficiency (Table 2).
yield, the following optimisation reactions were conducted
using this catalyst.
2.2.1 Effect of solvent
2.2.4 Generality of the catalytic activity of the catalysts
The isolated yields of the reaction products in the presence
of different solvents are shown in Fig. 3. The yield was high
even in the absence of any solvent but only at high tempera-
tures. The high boiling solvents DMSO and DMF not only
resulted in lower yield but also presented handling problems.
Further, isolation of the products was found to be tedious when
water was used as the solvent. Methanol was not preferred as it
is not safe and is not green. Acetonitrile and chloroform also
resulted in lower yields. Ethanol was found to be the best sol-
vent for this reaction based on its low cost, easy work-up of the
reaction mixture, and good yield of the products. Hence for
further studies in synthesis of substituted benzimidazoles and
benzodiazepines ethanol is used as a solvent.
The activity of our catalyst was further investigated for its
general application in the condensation reaction of OPDA with
other substituted aldehydes and ketones. All the reactions were
conducted with 5% MnZrO2-450 catalyst, using ethanol as the
solvent under refluxing conditions. The results in terms of the
isolated yield of the expected product with various substituted
aldehydes and ketones are presented in the Tables 3 and 4,
respectively. It is noteworthy that an excellent yield of the
expected product could be obtained with in 1–2 h of the reac-
tion. All the isolated products were analysed by their MP, IR,
GC-MS, and 1HNMR techniques. The condensation of OPDA
with aldehydes was more efficient than the ketones in terms of
the duration of the reaction. Thus it may be concluded that
manganese oxide supported on zirconia may be used as general
catalyst to activate the condensation reaction described in this
paper.
2.2.2 Effect of reaction temperature
The results of the experiments conducted at different tem-
peratures are shown in Fig. 4. When the reaction was con-
ducted at room temperature the yield was only 25% to 30%.
However the conversion of OPDA was found to increase with
good selectivity with an increase in the temperature up to 80 oC,
above which the conversion of OPDA remained constant while
the selectivity towards the expected product also decreased.
The spectral data of some representative products are given
below.
Entry 1 in Table 3. 2-Phenyl-1H-benzimidazole: pale yellow
Table 2 Recovery of MnZrO2-450 catalyst in the synthesis of substi-
tuted benzimidazole and benzodiazepine
Isolated yield (%)
Cycle
Benzimidazolea
Benzodiazepineb
2.2.3 Amount and reusability of the catalyst
1
2
3
4
95
90
88
87
93
85
83
75
The condensation reactions were conducted using ethanol as
the solvent at 80 oC and different amounts of 5% MnZrO2-450
catalyst in the range 0.05 to 1 g. The best yield of the reaction
product was obtained with 0.2 g of the catalyst. Higher
amounts of the catalyst did not improve the yield. The catalyst
could be easily recovered by simple filtration of the reaction
aReaction conditions: OPDA (1 mmol), aldehyde (1 mmol), 0.2 g
MnZrO2-450 catalyst, 5 ml ethanol.
bReaction conditions: OPDA (1 mmol), ketone (2.2 mmol), 0.2 g
MnZrO2-450 catalyst, 5 ml ethanol.

M. REKHA et al. / Chinese Journal of Catalysis, 2012, 33: 439–446
Table 3 Condensation of OPDA with various substituted aldehydes in presence of MnZrO2-450 catalyst and ethanol as a solvent
Entry
0
Diamine
Aldehyde
Product
Time (min)
Yield (%)
benzaldehyde
60
95
2
3
4
5
6
7
8
2-methyl-butyraldehyde
2-ethyl-butyraldehyde
4-fluoro-benzaldehyde
4-chloro-benzaldehyde
cinnamic aldehyde
90
90
45
45
35
45
45
87
90
91
85
92
93
90
anisaldehyde
4-cyanobenzaldehyde
solid. mp: 293–296 ºC ; IR (KBr) 3042, 1440, 1403, 1271, 971
DMSO): ꢃ 7.10 (m, 2H), 7.6 (d, 2H, ꢄ = 8.4 Hz), 7.3 (m, 2H),
8.2 (d, 2H, ꢄ = 8.7 Hz), 8.04 (d, 2H, ꢄ = 1.6 Hz).
1
cm–1. MS: m/z = 193(M+). H NMR (300 Hz, DMSO): ꢃ 7.22
(m, 2H), 7.48 (m, 5H), 7.58 (s, IH), 8.04 (d, 2H, ꢄ = 1.6 Hz).
Entry 5 in Table 3. 2-(4-Chlorophenyl)-1H-benzimidazole:
pale yellow solid. mp: 291–293 ºC; IR (KBr) 3039, 1449, 1400,
Entry 7 in Table 3. 2-(4-Methoxyphenyl)-1H-benzimidazole:
yellow solid. mp: 225–226 ºC; IR (KBr) 3478, 2985, 1625,
1
1537, 1341, 1127, 1038, 835 cm–1. MS: m/z = 224 (M+). H
1
1275, 961 cm–1. MS: m/z = 228 (M+). H NMR (300 Hz,
NMR (300 Hz, DMSO): ꢃ 8.00–8.08 (m, 2H), 7.20–7.60 (m,
Table 4 Condensation of OPDA with various substituted ketones in presence of MnZrO2-450 catalyst and ethanol as a solvent
Entry
1
Diamine
Ketone
Product
Time (min)
Yield (%)
acetone
45
93
2
3
4
5
2-butanone
3-pentanone
60
90
90
90
87
92
85
85
cyclopentanone
cyclohexanone
6
7
cycloheptanone
acetophenone
90
60
60
92
90
87
8.
4-nitro-acetophenone

M. REKHA et al. / Chinese Journal of Catalysis, 2012, 33: 439–446
Table 5 Comparison of catalytic activity of MnZrO2-450 catalyst with other reported catalysts
Catalyst
Solvent
ethanol
ethanol
acetic acid
ethanol/water
CH2Cl2
ethanol
ethanol
solvent free
n-hexane
solvent free
Reaction time (h)
Benzimidazole yield (%)
Benzodiazepine yield (%)
Reference
present work
5% MnZrO2
Lewis acid catalysts
Heteropoly acids
Amberlite IR-120
Polyaniline sulphate
5% MnZrO2
MCM-41
Ag3PW12O40
NbCl5
SbCl3-Al2O3
1
85–95
5–93
50–97
70–95
90
—
—
—
—
—
—
—
—
—
85–93
50–60
72–90
85–95
83–90
1–14
3
1.45–6.5
2
1
8
3–7
3–6
3–4
13
15
26
27
present work
28
29
30
31
—
6H), 3.52 (m, 3H).
catalysts in the literature. The importance of the amount of
surface acid sites and morphology of the catalysts in activating
the condensation reaction between OPDA and an alde-
hyde/ketone is made clear.
Entry 1 in Table 4. 2-Methyl-2,4-diphenyl-2,3-dihydro-
1H-1,5-benzodiazepine: yellow solid. mp: 150–152 ºC . IR
(KBr) 3351, 1647, 1593 cm–1. MS: m/z = 188 (M+). H NMR
1
(300 Hz, DMSO): ꢃ 1.73 (s, 3H), 2.95 (d, 2H, ꢄ = 0.17 Hz),
3.12 (d, 2H, ꢄ = 0.17 Hz), 3.38 (br, 1H), 6.80–7.72 (m, 14 H).
Entry 3 in Table 4. 2,2,4,-Triethyl-3-methyl-2,3-dihydro-
1H-1,5-benzodiazepine: yellow solid. mp: 143–145 ºC; IR
Acknowledgements
We thank MRG at St. Joseph’s College and Research Centre,
Bangalore for helping us with XRD measurements. We also
thank UGC, New Delhi for financial assistance.
1
(KBr) 3324, 1637, 1582 cm–1. MS: m/z = 245 (M+). H NMR
(300 Hz, DMSO): ꢃ 0.78–1.75 (m, 14H), 2.63 (m, 2H), 3.13 (q,
1H, ꢄ = 7.0 Hz), 3.69 (br, 1H), 6.71–7.48 (m, 4H).
Entry 7 in Table 4. 2-Methyl-2,4-diphenyl-2-3-dihydro-1H-
1,5-benzodiazepine: yellow solid. mp: 149–151 ºC; IR (KBr)
3349, 1643, 1593 cm–1. MS: m/z = 313 (M+). 1H NMR (300 Hz,
DMSO): ꢃ 1.72 (s, 3H), 2.95 (d, 2H, J = 0.17 Hz), 3.68 (br, 1H),
6.93–7.79 (m, 14H).
References
1
2
Corma A. Chem Rev, 1995, 95: 559
Tanabe K, Misono M, Ono Y, Hattori H. New Solid Acids and
Bases. Kodansha, Tokyo, 1989
3
4
5
6
Clark J H. Pure Appl Chem, 2001, 73: 103
Chen C, Chen Y. Tetrahedron Lett, 2004, 45: 113
Patil A, Ganguly S, Surana S. J Chem Sci, 2010, 122: 443
Valdez J, Cedillo R, Hernandez-Campos A, Yepez L,
Hernandez-Luis F, Navarrete-Vazquez G, Tapia A, Cortes R,
Hernandezc M, Castilloa R. Bioorg Med Chem Lett, 2002, 12:
2221
2.2.5 Comparison of catalytic activity of MnZrO2-450
catalyst with other reported catalysts
A comparison of the catalytic activity of MnZrO2-450 in the
synthesis of benzimidazole and benzodiazepines with those
reported in the literature in terms of percentage yield of the
respective products is given in the Table 5.
7
8
9
Fonseca T, Gigante B, Gilchrist T L. Tetrahedron, 2001, 57:
1793
Wang Y-C, Liu L-Z, Pan Y-M, Wang H-S. Molecules, 2011, 16:
100
3 Conclusions
Strenbach L H. J Med Chem, 1979, 22: 1
10 Schultz H. Benzodiazepines. Heidelberg: Springer, 1982
11 Randall L O, Kappel B, Garattini S, Mussini E, Randall L O
eds. Benzodiazepines. New York: Raven Press, 1973. 27
12 Fryer R I. Bicyclic Diazepines. In: Taylor E C ed. Comprehen-
sive Heterocyclic Chemistry. New York: Wiley, 1991. Volume
50, Chapter II
13 Zhang Z-H, Yin L, Wang Y-M. Catal Commun, 2007, 8: 1126
14 Mohammad A-A, Iraj M-B, Zaghaghi Z, Yousefi B H. Catal
Commun, 2008, 9: 2496
The catalytic activity of alumina, zirconia, and manganese
oxide supported on alumina and zirconia in the condensation
reaction between OPDA and benzaldehyde/acetophenone is
dependent on the amount of surface acid sites of the catalyst,
which is influenced by a synergistic effect of the calcination,
the presence of manganese oxide and the morphology of the
catalysts. Manganese oxide supported on zirconia was found to
be efficient heterogeneous catalyst for the synthesis of
2-substituted benzimidazoles and 1,5-disubstituted benzodi-
azepines by the condensation of o-phenylenediamine with
different substituted aldehydes and ketones. Mild reaction
conditions, easy work up and high yields along with reusability
of the catalyst make it a valuable alternative to the existing
15 Heravi
M M, Sadjadi S, Oskooie H A, Shoar R H,
Bamoharram F F. Catal Commun, 2008, 9: 504
16 Hekmatshoar R, Sajadi S, Heravi M M, Yahya S, and Be-
heshtiha. Synth Commun, 2009, 39: 2549
17 Nagarapu L, Mallepalli R, Aravab G, Yeramanchi L. Eur J
Chem, 2010, 3: 228

M. REKHA et al. / Chinese Journal of Catalysis, 2012, 33: 439–446
18 Kumar R, Chaudhary P, Nimesh S, Verma A K, Chandra R.
Mater Sci, 2008, 17: 62
Green Chem, 2006, 8: 519
25 Breitkopf C, Garsuch A, Papp H. Appl Catal A, 2005, 296: 148
26 Ziarani G M, Badiei A, Abbasi A, Farahani Z. Chin J Chem
2009, 27: 1537
27 Srinivas U, Srinivas Ch, Narender P, Jayathirtha Rao V,
Palaniappan S. Catal Commun, 2007, 8: 107
28 Sucheta K, Vital Rao B. Indian J Chem, 2005, 44B: 2152
29 Yadav J S, Reddy B V S, Kumar P S, Nagaiah K, Lingaiah N,
Saiprasad P S. Synthesis, 2004, 6: 901
30 Gao S-T, Liu W-H, Ma J-J, Wang C, Liang Q. Synth Commun,
2009, 39: 3278
31 Ganai B A, Kumar S, Andotra C S, Kapoor K K. Synth Com-
mun, 2006, 36: 803
19 Suryakiran N, Rajesh K, Prabhakara P, Jon Paul Selvam J,
Venkateswarlu Y. Catal Commun, 2007, 8: 1635
20 Shanty M, Kumara C S, Nagaraju N. J Mol Catal A, 2006,
255: 243
21 Mohamed Shamshuddin S Z, Nagaraju N. J Mol Catal A,
2007, 273: 55
22 Lee S O, Jung K H, Jung Oh C, Lee Y H, Tran T, Kim M J.
Hydrometallurgy, 2009, 98: 156
23 Liu Y, Ma D, Han X, Bao X, Frandsen W, Wang D, Su D. Ma-
ter Lett, 2008, 62: 1297
24 Santos V, Zeni M, Bergmann C P, Hohemberger J M. Rev Adv