An efficient and one-pot synthesis of benzimidazoles, benzoxazoles, benzothiazoles and quinoxalines catalyzed via nano-solid acid catalysts

Article abstract of DOI:10.1016/j.molcata.2013.02.030

A simple highly versatile and efficient synthesis of benzimidazoles, benzoxazoles, benzothiazoles, and quinoxalinesis achieved from carbonyl compounds and o-substituted aminoaromatics using nano-sulfated zirconia, nano-structured ZnO, nano-γ-alumina and nano-ZSM-5 zeolites, as the catalyst. The characteristic structural features of the materials were determined by techniques, such as XRD, FT-IR and SEM. The advantages of method are short reaction times and milder conditions and easy work-up. The catalysts can be recovered for the subsequent reactions and reused without any appreciable loss of efficiency.

Full text of DOI:10.1016/j.molcata.2013.02.030

Journal of Molecular Catalysis A: Chemical 373 (2013) 38–45
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Journal of Molecular Catalysis A: Chemical
journal homepage: www.elsevier.com/locate/molcata
An efficient and one-pot synthesis of benzimidazoles, benzoxazoles,
benzothiazoles and quinoxalines catalyzed via nano-solid acid catalysts
a,∗
b
a
c
Abbas Teimouri , Alireza Najafi Chermahini , Hossien Salavati , Leila Ghorbanian
a
Chemistry Department, Payame Noor University, Tehran 19395-4697, Iran
Department of Chemistry, Isfahan University of Technology, Isfahan 841543111, Iran
Materials Engineering Department, Isfahan University of Technology, Isfahan, Iran
b
c
a r t i c l e i n f o
a b s t r a c t
Article history:
A simple highly versatile and efficient synthesis of benzimidazoles, benzoxazoles, benzothiazoles, and
quinoxalinesis achieved from carbonyl compounds and o-substituted aminoaromatics using nano-
sulfated zirconia, nano-structured ZnO, nano-␥-alumina and nano-ZSM-5 zeolites, as the catalyst. The
characteristic structural features of the materials were determined by techniques, such as XRD, FT-IR
and SEM. The advantages of method are short reaction times and milder conditions and easy work-up.
The catalysts can be recovered for the subsequent reactions and reused without any appreciable loss of
efficiency.
Received 9 December 2012
Received in revised form 6 February 2013
Accepted 23 February 2013
Available online 14 March 2013
Keywords:
Benzimidazoles
Benzoxazoles
Published by Elsevier B.V.
Nano-sulfated zirconia
Nano-sized ZnO
Nano-␥-alumina
Nano-ZSM-5 zeolites
1
. Introduction
The benzoxazoles, benzothiazoles, benzimidazoles and quinox-
also been found applications as building blocks in the synthesis of
organic semiconductors [30], rigid subunits in macrocyclic recep-
tors or molecular recognition [31], and chemically controllable
switches [32].
aline have attracted much interest in diverse areas of chemistry [1].
These heterocycles have shown different pharmacological activi-
ties such as antibacterial, antiulcers, antihypertensives, antivirals,
antifungals, anticancers, and antihistaminics [2–7]. These com-
pounds are also used as ligands for asymmetric transformations
A number of methods have been reported for the synthesis
of the benzimidazole [33], benzothiazole [34] and benzoxazole
[35] by condensing benzene-1,2-diamine, 2-aminophenol and 2-
aminobenzenethiol with acyl chlorides or aldehydes. Recently,
some other methods for the preparation of quinoxaline derivatives
have been reported [36].
However, most of the traditional processes suffer from one or
more of the following drawbacks such as strong acidic conditions,
pollution, high cost, low yields of the products, requirements for
long reaction time, and tedious work-up procedures, need to excess
amounts of reagent and the use of toxic reagents, catalysts and/or
solvents. Therefore, there is a strong demand for a highly efficient
and environmentally benign method for the synthesis of these het-
erocycles.
In the recent years, the use of nano-structured ZnO [37],
nano-sulfated zirconia [38], nano-␥-alumina [39] and nano-ZSM-5
zeolite [40], catalysts has received considerable interest in organic
synthesis. This extensive application of heterogeneous catalysts in
synthetic organic chemistry can make the synthetic process more
efficient from both environmental and economic point of view [41]
and used-catalyst can be easily recycled.
[
8], exhibit nonlinear optical [9] and luminescent [10] /fluores-
cent [11]. Benzimidazole derivatives exhibit significant activity
against several viruses such as HIV [12,13], herpes (HSV-1) [14],
RNA [15], potential antitumor agents [16], antimicrobial agents [17]
and influenza [18]. They also act as topoisomerase inhibitors [19],
selective neuropeptide YY1 receptor antagonists [20], angiotensin
II inhibitors [21], and smooth muscle cell proliferation inhibitors
[
22] and have much more importance in organic synthesis [23].
Quinoxaline and its derivatives are an important class of ben-
zoheterocycles displaying a broad spectrum of biological activities
which have made them privileged structures in pharmacologically
active compounds [24–27] and catalytic systems [28,29]. They have
∗ Corresponding author at: Department of Chemistry, Payame Noor University
(
PNU), Isfahan P.O. Box 81395-671, Iran. Tel.: +98 311 3521804;
fax: +98 311 3521802.
E-mail addresses: a teimoory@yahoo.com, ateimouri@pnu.ac.ir,
a teimouri@pnu.ac.ir, ateimoory@yahoo.com (A. Teimouri).
Very recently we have developed a convenient and efficient pro-
cedure for the synthesis of 2,4,5-trisubstituted imidazoles using
1
381-1169/$ – see front matter. Published by Elsevier B.V.
http://dx.doi.org/10.1016/j.molcata.2013.02.030

A. Teimouri et al. / Journal of Molecular Catalysis A: Chemical 373 (2013) 38–45
39
clays, zeolite, nano-crystalline sulfated zirconia (SZ) as catalyst
42]. In the present study, we report the synthesis of benzim-
idazoles, benzoxazoles, benzothiazoles, by the condensation of
,2-diaminobenzene, 2-aminophenol, or 2-aminothiophenol and
substituted aldehydes and the synthesis of quinoxalines derivatives
by the condensation of 1,2-diaminobenzene and 1,2-dicarbonyl in
ethanol using nano-structured ZnO, nano-sulfated zirconia, nano-
mixture was stirred for 4 h. The digested precipitates were filtered
and re-dispersed again in hot 2 l of deionized water, filtered and
finally washed with ethanol first followed by acetone to avoid con-
tamination of ‘Na’ ions; and air dried at room temperature. The
[
1
◦
dried precipitates were calcined in a furnace at 550 C for 5 h to
produce nano-sized ␥-Al O3 powders.
2
␥-alumina and nano-ZSM-5 zeolites, as the catalyst.
2.2.4. Synthesis of nano-ZSM-5
For synthesis of nano-ZSM-5, tetrapropyl ammonium hydroxide
2
. Experimental
and tetra ethyl ortho silicate were the sources of aluminum and sil-
icon, respectively. nano-ZSM-5 Zeolite was synthesized according
to the procedure described in advance. [39] The components were
mixed with constant stirring. After adding all the ingredients the
solution was left to hydrolyze at room temperature for 48 h. The gel
2.1. Instruments and characterization
Diethanolamine (DEA), zinc acetate dehydrate, aluminum
nitrate, sodium carbonate, tetrapropyl ammonium hydroxide and
tetra ethyl ortho silicate and other reagents were purchased from
Merck and Aldrich and used without further purification.
◦
thus obtained was heated at 80 C to evaporate water and ethanol
formed during reaction. The obtained solution was charged into
a Teflon-lined stainless-steel autoclave under pressure and static
Products were characterized by spectroscopy data (FTIR, 1H
◦
conditions at 170 C for of 48 h. The solid phase obtained was fil-
1
3
NMR and C NMR spectra), elemental analysis (CHN) and melting
points. A JASCO FT/IR-680 PLUS spectrometer was used to record IR
spectra using KBr pellets. NMR spectra were recorded on a Bruker
◦
tered, washed with distilled water several times, dried at 120 C
and then calcined at 550 C for 12 h.
◦
4
00 Ultrasheild NMR and DMSO-d6 was used as solvent. Melting
2
.2.5. Characterization
X-ray diffraction pattern were recorded on diffractometer
points reported were determined by open capillary method using a
Galen Kamp melting point apparatus and are uncorrected. The total
surface acidity of catalysts, was measured by a Micromeritics Pulse
Chemisorb instrument by means of NH3 adsorption-desorption.
Mass Spectra were recorded on a Shimadzu Gas Chromatograph
Mass Spectrometer GCMS-QP5050A/Q P5000 apparatus.
(
Philips X’pert) using CuK␣ radiation (ꢁ = 1.5405 A˚ ), Crystallite size
of the crystalline phase was determined from the peak of max-
imum intensity by using Scherrer formula [46], with a shape
factor (K) of 0.9, as below: Crystallite size = K·ꢁ/W·cos ꢂ, where,
W = W − Ws and W is the broadened profile width of experimen-
b
b
tal sample and Ws is the standard profile width of reference silicon
2
2
.2. Catalyst preparation
sample. FT-IR spectra of the catalysts were recorded by FT-IR spec-
trophotometer in the range of 400–4000 cm with a resolution of
4
volume and pore size distribution of samples calcined at 600 C
were determined from N adsorption–desorption isotherms at 77K
−
1
.2.1. Synthesis of nano-crystalline sulfated zirconia
−
1
cm by mixing the sample with KBr. Specific surface area, pore
Nano-crystalline sulfated zirconia has been prepared by one
◦
step sol–gel technique [43]. A typical synthesis involves the
addition of concentrated sulfuric acid (1.02 ml) to zirconium n-
propoxide precursor (30 wt%) followed by the hydrolysis with
water. After 3 h aging at room temperature, the resulting gel was
dried at 110 C for 12 h followed by calcination at 600 C for 2 h. The
bulk sulfur of the sulfated zirconia after calcination at 600 C was
2
(ASAP 2010 Micromeritics). Surface area was calculated by using
BET equation; pore volume and pore size distribution were cal-
culated by BJH method [47]. The samples were degassed under
vacuum at 120 C for 4 h, prior to adsorption measurement to evac-
◦
◦
◦
◦
uate the physisorbed moisture. The detailed imaging information
about the morphology and surface texture of the catalyst was
provided by SEM (Philips XL30 ESEM TMP), a part of the spectra
data has been published in our previous work [42]. The total sur-
face acidity of catalysts was measured by a Micromeritics Pulse
Chemisorb instrument by means of NH3 adsorption–desorption.
The bulk sulfur (wt%) retained in sulfated zirconia samples before
3
.2 wt% as measured by elemental analyzer.
2.2.2. Synthesis of nano-sized ZnO
Nano-structure ZnO has been prepared by one step sol–gel
technique [44]. In a typical procedure, mixtures of ethanol,
diethanolamine (DEA) and zinc acetate dihydrate, were prepared.
The concentration of zinc acetate dihydrate in solvent was 0.2 M.
The molar ratios of zinc acetate dehydrate and diethanolamine was
◦
and after calcination at 600 C was analyzed by C H N S/O elemental
analyzer.
1
.0. Then the pH of the mixture was reached to about 9. When the
zinc acetate crystals were dissolved completely, sodium hydroxide
NaOH) pellets were added to the solution to increase the pH of the
mixture to about 11. Then, the washed precipitates were dried at
(
2.3. General procedure for the synthesis of benzimidazoles
derivatives
◦
◦
1
30 C and calcined at 600 C for 15 min in a oven to obtain white
nano-sized ZnO particles.
In a 50 mL round bottom flask aldehyde (1 mmol) and 1,2-
diaminobenzene, 2-aminophenol, or 2-aminothiophenol (1 mmol)
were thoroughly mixed in ethanol (10 mL) then catalyst (10 mol%)
was added, and the solution was refluxed for appropriate time. The
progress of the reaction was monitored by TLC. After completion of
the reaction, the reaction mixture was cooled to room temperature
and the resulting solid was collected by filtration and dissolved
in 20 mL ethyl acetate. The catalyst was recovered by filtration.
After evaporation of the solvent, the resulting solid product was
recrystallized from ethanol to obtain pure product.
2.2.3. Synthesis of nano-ꢀ-Al O3 catalyst
2
The nano-␥-Al O3 was prepared by sol–gel method according
2
to a procedure described [45]. In a typical experiment, Aluminum
nitrate (15.614 g) was added to 400 ml of deionized water. Similarly
solution of sodium carbonate is prepared by dissolving (7.95 g) in
4
00 ml of deionized water. 200 ml of deionized water is taken in
a 2 L capacity round-bottom flask and stirred well using magnetic
stirrer. Then sodium carbonate and aluminum nitrate solutions are
added to 200 ml of deionized water (from separate burettes) drop
wise.
◦
−1
Compound 1a: Mp 292–294 C. FTIR (KBr, cm ): 3452, 1618,
−
1
1
1460 cm
;
H NMR (400 MHz, DMSO-d6): ı 7.18–7.22 (m, 5H),
◦
13
The temperature was maintained 70 C during experiment. The
7.52–7.59 (m, 4H), 12.81 (s, 1H); C NMR (400 MHz, DMSO-d6):
pH after precipitation was found to be in the range of 7.5–8.5. The
ı116.3 (2C), 123.5 (2C), 127.5 (2C), 128.6, 129.3 (2C), 130.6, 138.9

4
0
A. Teimouri et al. / Journal of Molecular Catalysis A: Chemical 373 (2013) 38–45
+
◦ −1
Compound 2f: Mp 126–128 C. FTIR (KBr, cm ): 3440, 1646,
1461 cm ; H NMR (400 MHz, DMSO-d6): ı 2.31 (s, 3H), 7.26–7.37
(
2C), 152.9; ESI MS (m/z): 194.08 (M ); Anal. Calcd. for C13H10N :
2
−
1 1
C, 80.39; H, 5.19; N, 14.42. Found: C, 80.11; H, 4.89; N, 14.10.
Compound 1b: Mp 290–292 C. FTIR (KBr, cm ): 3446, 1628,
477 cm ; H NMR (400 MHz, DMSO-d6): ı 7.28 (d, 2H), 7.30–7.34
◦
−1
(d, 2H), 7.41–7.49 (m, 1H), 7.56–7.65 (d, 2H), 7.24–7. 74 (m, 1H),
−1
1
13
1
8.06–8.22 (m, 2H); C NMR (400 MHz, DMSO-d6): ı 21.3, 110.7,
(
m, 2H), 7.38–7.42 (m, 1H), 7.62–7.66 (m, 1H), 8.56 (d, 2H), 12.13
119.6, 123.4, 124.8, 126.4, 127.4 (2C), 129.6 (2C), 138.4, 141.5, 150.4,
162.2; ESI MS (m/z): 209.08 (M ); Anal. Calcd for C14H11NO: C,
+
+
(
s, 1H); ESI MS (m/z): 228.05 (M ); Anal. Calcd for C13H ClN : C,
9
2
6
8.28; H, 3.97; N, 15.50. Found: C, 67.86; H, 3.59; N, 15.16.
80.36; H, 5.30; N, 6.69. Found: C, 79.98; H, 5.02; N, 6.32.
◦
−1
◦ −1
Compound 2g: Mp 96–98 C. FTIR (KBr, cm ): 3448, 1651,
Compound 1c: Mp 268–270 C. FTIR (KBr, cm ): 3438, 1635,
−1
1
−1
1
1
434 cm ; H NMR (400 MHz, DMSO-d6): ı 7.32 (d, 2H), 7.38–7.42
1462 cm ; H NMR (400 MHz, DMSO-d6): ı 3.64 (s, 3H), 7.28–7.39
(
m, 2H), 7.46–7.50 (m, 1H), 7.66–7.70 (m, 1H), 8.44 (d, 2H), 12.53
(d, 2H), 7.44–7.52 (m, 1H), 7.54–7.63 (d, 2H), 7.33–7.53 (m, 1H),
8.11–8.27 (m, 2H); C NMR (400 MHz, DMSO-d6): ı 54.3, 110.7,
+
13
(
s, 1H); ESI MS (m/z): 271.95 (M ); Anal. Calcd for C13H BrN : C,
9
2
5
7.18; H, 3.32; N, 29.26. Found: C, 56.89; H, 3.09; N, 28.87.
116.4 (2C), 118.5, 121.3, 122.4, 124.7, 127.6 (2C), 142.2, 150.4, 161.4,
◦
−1
+
Compound 1d: Mp 318–320 C. FTIR (KBr, cm ): 3448, 1626,
164.7;ESI MS (m/z): 225.08 (M ); Anal. Calcd for C14H11NO : C,
2
−1
1
1
587, 1529, 1356 cm
;
H NMR (400 MHz, DMSO-d6): ı 7.26 (d,
74.65; H, 4.92; N, 6.22. Found: C, 74.22; H, 4.62; N, 6.02.
◦ −1
Compound 3a: Mp 110–112 C. FTIR (KBr, cm ): 3426, 1658,
2
H), 7.34–7.38 (m, 2H), 7.42–7.48 (m, 1H), 7.58–7.63 (m, 1H), 8.62
+
−1
1
(
d, 2H), 12.28 (s, 1H); ESI MS (m/z): 239.08 (M ); Anal. Calcd for
1448 cm
; H NMR (400 MHz, DMSO-d6): ı 7.38–7.42 (m, 5H),
13
C13H N O : C, 65.27; H, 3.79; N, 17.56. Found: C, 65.06; H, 3.39; N,
7.66–7.73 (m, 4H); C NMR (400 MHz, DMSO-d6): ı 121.8, 122.2,
9
3
2
1
7.19.
123.5, 125.6 (2C), 126.6, 129.2 (2C), 132.3, 135.3, 151.1, 154.2,
◦
−1
+
Compound 1e: Mp 288–290 C. FTIR (KBr, cm ): 3561, 3434,
166.3;ESI MS (m/z): 211.05 (M ); Anal. Calcd for C13H NS: C, 73.90;
9
−1
1
1
7
2
621, 1463 cm
;
H NMR (400 MHz, DMSO-d6): ı 7.23 (d, 2H),
H, 4.59; N, 6.63. Found: C, 73.56; H, 3.86; N, 6.44.
◦ −1
Compound 3b: Mp 106–108 C. FTIR (KBr, cm ): 3456, 1638,
.29–7.33 (m, 2H), 7.38–7.42 (m, 1H), 7.64–7.68 (m, 1H), 8.44 (d,
+
−1
1
H), 9.58 (s, 1H), 12.32 (s, 1H); ESI MS (m/z): 210.07 (M ); Anal.
1445 cm
; H NMR (400 MHz, DMSO-d6): ı 7.24–7.35 (d, 2H),
Calcd for C13H10N O: C, 74.27; H, 4.79; N, 13.33. Found: C, 74.06;
7.48–7.56 (m, 1H), 7.62–7.71 (d, 2H), 7.40–7. 81 (m, 1H), 8.31–8.48
2
+
H, 4.38; N, 13.88.
(m, 2H); ESI MS (m/z): 245.01 (M ); Anal. Calcd for C13H ClNS: C,
8
◦
−1
Compound 1f: Mp 260–262 C. FTIR (KBr, cm ): 3432, 1622,
63.54; H, 3.28; N, 5.70. Found: C, 63.11; H, 2.94; N, 5.42.
−1
1
◦ −1
Compound 3c: Mp 102–104 C. FTIR (KBr, cm ): 3450, 1644,
1
456 cm
;
H NMR (400 MHz, DMSO-d6): ı 2.35 (s, 3H), 7.16 (d,
−
1
1
2
H), 7.32–7.38 (m, 2H), 7.43–7.49 (m, 1H), 7.61–7.64 (m, 1H), 8.09
1432 cm
; H NMR (400 MHz, DMSO-d6): ı 7.31–7.42 (d, 2H),
1
3
(
(
d, 2H), 12.80 (s, 1H); C NMR (400 MHz, DMSO-d6): ı 24.3, 115.3
2C), 123.0 (2C), 127.4 (2C), 127.7, 129.6 (2C), 137.4, 138.7 (2C),
7.50–7.58 (m, 1H), 7.64–7.73 (d, 2H), 7.48–7. 88 (m, 1H), 8.26–8.32
+
(m, 2H); ESI MS (m/z): 288.96 (M ); Anal. Calcd for C13H BrNS: C,
8
+
1
52.9; ESI MS (m/z): 208.01 (M ); Anal. Calcd for C14H12N : C, 80.74;
58.93; H, 2.78; N, 4.83. Found: C, 58.46; H, 2.34; N, 4.56.
2
◦ −1
Compound 3d: Mp 228–230 C. FTIR (KBr, cm ): 3446, 1576,
H, 5.81; N, 13.45. Found: C, 80.21; H, 5.39; N, 13.08.
◦
−1
−1
1
Compound 1g: Mp 180–182 C. FTIR (KBr, cm ): 3443, 1627,
1537, 1352 cm
; H NMR (400 MHz, DMSO-d6): ı 7.25–7.36 (d,
−1 1
1
459 cm
;
H NMR (400 MHz, DMSO-d6): ı 3.81 (s, 3H), 7.22 (d,
2H), 7.45–7.53 (m, 1H), 7.62–7.71 (d, 2H), 7.48–7.98 (m, 1H),
+
2
H), 7.38–7.47 (m, 2H), 7.48–7.55 (m, 1H), 7.58–7.75 (m, 1H), 7.92
8.28–8.44 (m, 2H); ESI MS (m/z): 256.03 (M ); Anal. Calcd for
1
3
(
d, 2H), 12.93 (s, 1H); C NMR (400 MHz, DMSO-d6): ı 55.6, 114.6
C13H N O S: C, 60.93; H, 3.15; N, 10.93. Found: C, 69.44; H, 2.91;
8
2
2
(
1
2C), 115.3 (2C), 123.0 (2C), 123.2, 128.5 (2C), 138.7 (2C), 152.8,
N, 10.62.
Compound 3e: Mp 224–226 C. FTIR (KBr, cm ): 3536, 3441,
+
◦
−1
60.7; MS (m/z): 224.08 (M ); Anal. Calcd for C14H12N O: C, 74.98;
2
−
1
1
H, 5.39; N, 12.48. Found: C, 74.34; H, 5.06; N, 11.98.
1652, 1448 cm
; H NMR (400 MHz, DMSO-d6): ı 7.10–7.21 (d,
◦
−1
Compound 2a: Mp 100–102 C. FTIR (KBr, cm ): 3456, 1638,
2H), 7.32–7.40 (m, 1H), 7.51–7.60 (d, 2H), 7.46–7.96 (m, 1H),
−1
1
+
1
7
1
1
454 cm
;
H NMR (400 MHz, DMSO-d6): ı 7.23–7.27 (m, 5H),
.51–7.58 (m, 4H); C NMR (400 MHz, DMSO-d6): ı 121.6, 122.3,
8.19–8.35 (m, 2H) 11.3 (s, 1H); ESI MS (m/z): 227.04 (M ); Anal.
1
3
Calcd for C13H NOS: C, 68.70; H, 3.99; N, 6.16. Found: C, 68.36; H,
9
23.5, 124.6 (2C), 125.4, 129.4 (2C), 132.3, 138.5, 150.6, 154.2,
3.62; N, 5.86.
+
◦ −1
Compound 3f: Mp 82–84 C. FTIR (KBr, cm ): 3437, 1648,
62.2;MS (m/z): 195.07 (M ); Anal. Calcd for C13H NO: C, 79.98;
9
−
1 1
H, 4.65; N, 7.16. Found: C, 79.61; H, 3.28; N, 6.84.
1452 cm ; H NMR (400 MHz, DMSO-d6): ı 2.31 (s, 3H), 7.18–7.29
◦
−1
Compound 2b: Mp 146–148 C. FTIR (KBr, cm ): 3451, 1632,
(d, 2H), 7.40–7.48 (m, 1H), 7.54–7.63 (d, 2H), 7.42–7.92 (m, 1H),
−1
1
13
1
458 cm
;
H NMR (400 MHz, DMSO-d6): ı 7.28–7.39 (d, 2H),
8.21–8.37 (m, 2H); C NMR (400 MHz, DMSO-d6): ı 21.3, 121.7,
7
.52–7.60 (m, 1H), 7.65–7.74 (d, 2H), 7.35–7. 86 (m, 1H), 8.11–8.19
123.2, 125.2, 125.5 (2C), 126.4, 132.9, 133.5, 135.1, 138.9 (2C), 154.1,
168.7;ESI MS (m/z): 225.06 (M ); Anal. Calcd for C14H11NS: C, 74.63;
+
+
(m, 2H); MS (m/z): 229.03 (M ); Anal. Calcd for C13H ClNO: C, 67.99;
8
H, 3.51; N, 6.10. Found: C, 67.64; H, 3.18; N, 5.92.
H, 4.92; N, 6.22. Found: C, 69.34; H, 4.58; N, 5.82.
◦
−1
◦ −1
Compound 3g: Mp 118–120 C. FTIR (KBr, cm ): 3432, 1646,
Compound 2c: Mp 142–144 C. FTIR (KBr, cm ): 3456, 1642,
−1
1
−1
1
1
463 cm
;
H NMR (400 MHz, DMSO-d6): ı 7.32–7.43 (d, 2H),
1458 cm ; H NMR (400 MHz, DMSO-d6): ı 3.85 (s, 3H), 7.15–7.26
7
.54–7.62 (m, 1H), 7.63–7.72 (d, 2H), 7.30–7. 81 (m, 1H), 8.09–8.17
(d, 2H), 7.42–7.50 (m, 1H), 7.56–7.65 (d, 2H), 7.48–7.98 (m, 1H),
8.16–8.32 (m, 2H); C NMR (400 MHz, DMSO-d6): ı 54.3, 121.8,
+
13
(m, 2H); ESI MS (m/z): 272.98 (M ); Anal. Calcd for C H BrNO: C,
13
8
5
6.97; H, 2.94; N, 5.11. Found: C, 56.46; H, 2.58; N, 4.78.
123.7, 125.8, 126.7, 127.4 (2C), 130.3 (2C), 135.4, 137.4, 144.4, 154.2,
166.4;ESI MS (m/z): 241.06 (M ); Anal. Calcd for C14H11NOS: C,
69.68; H, 4.59; N, 5.80. Found: C, 69.34; H, 4.18; N, 5.62.
◦
−1
+
Compound 2d: Mp 262–264 C. FTIR (KBr, cm ): 3448, 1587,
−1
1
1
2
8
531, 1354 cm
;
H NMR (400 MHz, DMSO-d6): ı 7.30–7.41 (d,
H), 7.50–7.58 (m, 1H), 7.62–7.71 (d, 2H), 7.33–7. 84 (m, 1H),
+
.10–8.18 (m, 2H); ESI MS (m/z): 240.05 (M ); Anal. Calcd for
C13H N O : C, 65.01; H, 3.36; N, 11.76. Found: C, 64.74; H, 3.08;
2.4. General procedure for the synthesis of quinoxalines
derivatives
8
2
3
N, 11.72.
Compound 2e: Mp 282–284 C. FTIR (KBr, cm ): 3541, 3448,
◦
−1
−
1
1
1
2
8
647, 1454 cm
;
H NMR (400 MHz, DMSO-d6): ı 7.27–7.38 (d,
To a mixture of 1,2-diaminobenzene (1 mmol) and 1,2-
H), 7.42–7.50 (m, 1H), 7.56–7.65 (d, 2H), 7.41–7. 57(m, 1H),
.16–8.32 (m, 2H)), 9.42 (s, 1H); MS (m/z): 211.05 (M ); Anal. Calcd
dicarbonyl compound (1 mmol) in ethanol (10 mL), catalyst
(10 mol%) was added and the solution was refluxed for appro-
priate time. The progress of the reaction was monitored by TLC.
After completion of the reaction, ethyl acetate was added to the
+
for C13H NO : C, 73.91; H, 4.59; N, 6.63. Found: C, 73.64; H, 3.96;
9
2
N, 6.42.

A. Teimouri et al. / Journal of Molecular Catalysis A: Chemical 373 (2013) 38–45
41
Table 2
solidified mixture and the insoluble catalyst was separated by fil-
tration. After evaporation of the solvent, the resulting solid product
was recrystallized from ethanol to obtain pure product.
Effect of various solvents on the reaction times and yields using nano SZ as the
catalysts.
◦
−1
Entry
Solventa
Time (min)b
Yield (%)c
Compound 4a: Mp 130–132 C. FTIR (KBr, cm ): 3052, 1646,
−
1
1
1
(
344 cm
;
H NMR (400 MHz, DMSO-d6): ı 7.41 (m, 6H), 7.55
1
2
3
4
5
6
H O
90
90
90
90
90
90
75
92
80
75
65
60
2
13
m, 4H), 7.79 (d, 2H), 8.18 (d, 2H); C NMR (400 MHz, DMSO-d6):
EtOH
MeOH
CH3CN
1,4-Dioxan
THF
ı 128.30, 128.83, 129.05, 129.23, 129.87, 129.99, 134.90, 139.10,
+
1
41.24, 153.49;ESI MS (m/z): 282.12 (M ); Anal. Calcd for C20H14N :
2
C, 85.08; H, 5.01; N, 9.92. Found: C, 84.84; H, 4.78; N, 9.62.
◦
−1
Compound 4b: Mp 192–194 C. FTIR (KBr, cm ): 3038, 1642,
a
Reaction was performed with benzaldehyde (2.0 mmol), benzene-1,2-diamine
2.0 mmol) in the presence of 10 mg nano SZ as the catalyst in various solvents.
−
1 1
1
4
336 cm
;
H NMR (400 MHz, DMSO-d6): ı 6.74 (d, 4H), 7.68 (d,
H), 7.58 (d, 2H), 8.26 (d, 2H); ESI MS (m/z): 350.05 (M ); Anal. Calcd
(
+
b
Reaction time monitored by TLC.
Isolated yield.
c
for C20H12Cl N : C, 68.39; H, 3.44; N, 7.98. Found: C, 68.08; H, 3.11;
2
2
N, 7.58.
Compound 4c:Mp 132–134 C. FTIR (KBr, cm ): 3044, 1645,
◦
−1
In order to optimize the reaction conditions, including solvents
−
1 1
1
4
352 cm
;
H NMR (400 MHz, DMSO-d6): ı 6.78 (d, 4H), 7.70 (d,
and temperature, the reaction of benzaldehyde (2 mmol) and 1,2-
diaminobenzene (2 mmol) was optimized by time of the reaction
and using various solvents such as H O, EtOH, MeOH, CH CN, 1,4-
+
H), 7.56 (d, 2H), 8.22 (d, 2H); ESI MS (m/z): 318.01 (M ); Anal. Calcd
for C20H12F N : C, 75.46; H, 3.80; N, 8.80. Found: C, 75.13; H, 3.62;
2
2
2
3
N, 8.48.
Compound 4d: Mp 128–130 C. FTIR (KBr, cm ): 3034, 1641,
Dioxan, and THF in the presence of nano SZ as the catalyst. (Table 2,
entries 1–6). Reaction in 1,4-Dioxan, and THF solvent gave low
product yields even after 120 min (Table 2, entries 5 and 6). The
yields were moderate in case of methanol and acetonitrile under
reflux condition. (Table 2, entries 3 and 4). The best results were
obtained when the reaction was carried out in ethanol at reflux
◦
−1
−
1 1
1
347 cm
; H NMR (400 MHz, DMSO-d6): ı 2.42 (s, 6H), 6.76 (d,
4
H), 7.73 (d, 4H), 7.55 (d, 2H), 8.21 (d, 2H); ESI MS (m/z):310.15
+
(
M ); Anal. Calcd for C22H18N : C, 85.13; H, 5.85; N, 9.03. Found: C,
2
8
4.91; H, 5.51; N, 8.68.
Compound 4e: Mp 148–150 C. FTIR (KBr, cm ): 3042, 1626,
◦
−1
9
0 min in the presence of catalyst (Table 2, entry 2). Therefore,
−
1 1
1
345 cm
; H NMR (400 MHz, DMSO-d6): ı 3.81 (s, 6H), 6.89 (d,
ethanol was selected as a solvent for this reaction. The reaction
of benzil with 1,2-diaminobenzene was chosen as a model reaction
to study the effect of various solvents on the yield of quinoxaline.
Among the solvents examined, ethanol was found to be the most
effective solvent.
4
H), 7.50 (d, 4H), 7.65 (d, 2H), 8.16 (d, 2H); ESI MS (m/z): 342.18
+
(
M ); Anal. Calcd for C22H18N O : C, 77.17; H, 5.30; N, 8.18. Found:
2
2
C, 76.87; H, 5.08; N, 7.72.
3
. Results and discussion
Although water is a desirable solvent for chemical reactions for
reasons of cost, safety and environmental concerns, we found that
using water in this reaction gave moderate yields of products under
reflux condition after long reaction times.
Synthesis of benzimidazoles, benzoxazoles, benzothiazoles,
by condensation of 1,2-diaminobenzene, 2-aminophenol, or
2-aminothiophenol and substituted aldehydes and the synthe-
sis of quinoxalines derivatives by the condensation of 1,2-
diaminobenzene and 1,2-dicarbonyl in ethanol using (Tables 4–7)
preferred values of catalysts achieved. In all reactions good to
excellent yields was obtained. The isolated compounds were char-
acterized using spectroscopic and physical methods and compared
with those data in literature.
In the reaction between aldehydes and 1,2-diaminobenzene, 2-
aminophenol, or 2-aminothiophenol and 1,2-diaminobenzene and
,2-dicarbonyl compounds effect of the catalyst amount was inves-
tigated.
To minimize the formation of byproducts and to achieve good
1
yield of the desired product, the reaction is optimized by varying
the amount of catalyst,the percentage yield of the product with 5,
1
0 and 15 mg of nano-sulfated zirconia as a catalyst are 80%, 92%
and 70%, respectively (Table 1, entries 2–4). The percentage yield
of the product with 5, 10 and 15 mol% of nano-ZnO as a catalyst
are 75%, 80% and 65%, respectively (Table 1, entries 5–7). For the
nano-␥-alumina and nano-ZMS-5 as the catalyst, when the catalyst
content was increased to 15 mg,the product yield decreased to 70%
The total acidity of catalysts was determined by temperature-
programmed description of ammonia (TPD). The catalysts were
◦
(Table 1, entry 10) and 65% (Table 1, entry 13) respectively.
treated under helium at 200 C for 1 h, and then treated with a
◦
It is noteworthy to mention that in the absence of catalyst, no
NH3 flow for 5 min at 100 C. The excess physisorbed ammonia
◦
product was found even after 24 h. These results indicate that the
catalyst exhibits a high catalytic activity in this transformation.
was flushed out with pure He gas flow at 120 C for 1 h and the
temperature subsequently raised up to 600 C at 10 /min. The total
◦
◦
Table 1
Effect of type and amount of catalyst on the synthesis of benzimidazoles derivatives.
Entry
Catalyst
Catalyst loading
Catalyst (mol%)
Time (h)
Yield (%)a
1
2
3
4
5
6
7
8
9
0
1
2
3
None
Nano-SZ
Nano-SZ
Nano-SZ
Nano-ZnO
Nano-ZnO
Nano-ZnO
Nano-␥-alumina
Nano-␥-alumina
Nano-␥-alumina
Nano-ZMS-5
Nano-ZMS-5
Nano-ZMS-5
–
5 (mg)
–
5
10
15
5
10
15
5
10
15
5
24
5
5
5
5
5
5
5
5
5
5
5
5
No reaction
80
92
70
75
80
65
75
85
70
73
75
65
10 (mg)
15 (mg)
5 (mol%)
10 (mol%)
15 (mol%)
5 (mg)
10 (mg)
15 (mg)
5 (mg)
1
1
1
1
10 (mg)
15 (mg)
10
15
a
Yields after isolation of product.

4
2
A. Teimouri et al. / Journal of Molecular Catalysis A: Chemical 373 (2013) 38–45
Table 3
Summary of acidic measured by NH3-TPD of synthesized catalysts.
Catalyst
Acidic sites (mmol NH3/g)
◦
◦
T1 (<200 C)
T2 (>500 C)
Total
Nano-crystalline SZ
Nano-␥-Al2O3
Nano-ZMS-5
0.223
0.197
0.186
0.173
0.199
0.175
0.172
0.142
0.402
0.372
0.358
0.315
Nano size-ZnO
evacuation of NH3 from the catalysts was measured. The results of
the TPD measurements are summarized in Table 3.
In view of the above results obtained, it has now become clear
that all four catalysts have both Bronsted and Lewis acid sites.
The total number of acid sites, nano-crystalline SZ was found to
have 0.402 mmol/g whereas the nano ␥-Al O , nano-ZMS-5 and
Fig. 2. XRD pattern of nano-ZnO catalyst.
2
3
nano size-ZnO have 0.372, 0.358 and 0.315 mmol/g, respectively.
Sulfated zirconia possesses stronger surface acidity due to the pres-
ence of sulfate group binding with zirconia surface. The highest
catalytic activity for sulfated zirconia could be attributed to its
stronger surface acidity compared to other studied catalysts. There-
fore, nano-crystalline SZ had the largest acidity and nano size-ZnO
had the smallest acidity as compared to the other catalysts. These
results are in good agreement with previous works [48].
◦
The FT-IR spectra of alumina samples calcined at 600 C (Fig. 1)
−
1
showed an intense band centered around 3500 cm and a broad
−1
band at 1650 cm , these are assigned to stretching and bending
modes of adsorbed water. The Al–O–Al bending stretching vibra-
−1
tions observed at around 1150 cm
are due to symmetric and
asymmetric bending modes, respectively. The OH torsional mode
Fig. 3. SEM micrograph of nano-␥-alumina catalyst.
−1
observed at 800 cm overlaps with Al–O stretching vibrations. The
−
1
weak band at 2091 cm is assigned to a combination band. The
−1
bands observed at 617 and 481 cm are attributable to stretching
and bending modes of AlO6 [49].
The XRD patterns of nano-sized ZnO powders obtained. All
nano-ZnO samples exhibited a hexagonal structure. Characteristic
peaks of ZnO appeared at 31.7, 34.5, 36.2 and 56.5. (Fig. 2) The mor-
phology of the as prepared nano-size-␥-Al O3 and nano-sized ZnO
2
powders analyzed by SEM is shown in Figs. 3 and 4. The SEM image
demonstrates clearly the formation of spherical ZnO nanoparticles.
The ␥-Al O powders indicated strong agglomeration of particles
2
3
with varied spherical sizes.
One of the most important advantages of heterogeneous cataly-
sis over the homogeneous counterpart is the possibility of reusing
the catalyst by simple filtration, without loss of activity. The recov-
ery and reusability of the catalyst was investigated in the product
formation. After completion of the reaction, the catalyst was sep-
arated by filtration, washed 3 times with 5 ml acetone, then with
Fig. 4. SEM micrograph of nano-ZnO catalyst.
◦
doubly distilled water several times and dried at 110 C. Then the
recovered catalyst was used in the next run. The results of three
consecutive runs showed that the catalyst could be reused several
times without significant loss of its activity (see Fig. 5).
To generalize the scope and versatility of this protocol, differ-
ent substituted arylaldehydes are used for the synthesis of these
products. Aldehyde compounds which have electron donating or
electron withdrawing groups were used and as expected it gives
good yield of products, it can be seen that electron donating and
electron withdrawing groups does not show any difference on the
reaction yields (Tables 4–7). This indicates that the present cata-
lyst efficiently makes the condensation reaction much faster with
increased yields (Fig. 6).
The method described here for synthesis of quinoxalines
derivatives can be compared with other catalysts that reported
literature [59–61]. To account for the facile formation of benzimi-
dazoles, benzoxazoles and benzothiazoles, by the condensation of
Fig. 1. FT-IR spectra nano-␥-alumina catalyst.

A. Teimouri et al. / Journal of Molecular Catalysis A: Chemical 373 (2013) 38–45
43
Table 4
a
Acid-catalyzed synthesis of benzimidazoles derivatives.
H
N
NH2
Catalyst
+
Ar CHO
Ar
EtOH, reflux
NH2
N
Time (min)/yield (%)b
MP C (lit.) [Ref.]
◦
Entry/product
Ar
Nano-ZnO
Nano-␥-alumina
Nano-ZMS-5
Nano-crystalline SZ
1
2
3
4
5
6
7
(1a)
(1b)
(1c)
(1d)
(1e)
(1f)
(1g)
C6H5
100/88
100/70
90/72
95/64
80/65
90/74
80/70
90/88
80/82
85/76
90/74
80/82
90/78
85/74
85/90
85/85
90/84
80/82
80/80
75/84
70/82
45/92
60/88
75/81
70/90
85/82
90/92
90/85
292–294 (290–293) [50]
290–292 (288–291) [51]
4-ClC6H5
4-BrC6H5
4-NO2C6H5
4-OHC6H5
4-CH3C6H5
4-OCH3C6H5
268–270 (261.5–263.5) [52]
318–320 (322–323) [50]
288–290 (265–267) [52]
260–262 (264–265) [50]
180–182 (223–226) [53]
a
The products were characterized by IR, 1H NMR, 13C NMR and mass spectroscopy.
Isolated yields.
b
Table 5
a
Acid-catalyzed synthesis of benzoxazoles derivatives.
NH2
N
Catalyst
Ar CHO
Ar
+
EtOH, reflux
OH
O
Time (min)/Yield (%)b
MP C (lit.) [Ref.]
◦
Entry/product
Ar
Nano-ZnO
Nano-␥-alumina
Nano-ZMS-5
Nano-crystalline SZ
1
2
3
4
5
6
7
(2a)
(2b)
(2c)
(2d)
(2e)
(2f)
(2g)
C6H5
4-ClC6H5
4-BrC6H5
4-NO2C6H5
4-OHC6H5
4-CH3C6H5
4-OCH3C6H5
100/86
100/70
95/76
90/70
85/75
90/76
85/75
90/88
80/80
80/77
95/78
80/78
95/78
80/80
80/90
85/80
80/82
80/82
90/80
70/80
75/84
45/86
60/86
60/85
75/84
80/85
85/87
90/87
100–102 (102–103) [50]
146–148 (149–150) [50]
142–144
262–264 (266–267) [50]
282–284 (287–289) [54]
126–128 (100–101) [54]
96–98 (100–101) [50]
a
The products were characterized by IR, 1H NMR, 13C NMR and mass spectroscopy.
Isolated yields.
b
Table 6
a
Acid-catalyzed synthesis of benzothiazoles derivatives.
NH2
N
Catalyst
+
Ar CHO
Ar
EtOH, reflux
S
SH
Time (min)/Yield (%)b
MP C (lit.) [Ref.]
◦
Entry/product
Ar
Nano-ZnO
Nano-␥-alumina
Nano-ZMS-5
Nano-crystalline SZ
1
2
3
4
5
6
7
(3a)
(3b)
(3c)
(3d)
(3e)
(3f)
(3g)
C6H5
4-ClC6H5
4-BrC6H5
4-NO2C6H5
4-OHC6H5
4-CH3C6H5
4-OCH3C6H5
100/86
90/75
80/72
95/72
80/70
95/76
80/70
90/87
80/80
85/78
95/78
90/76
95/80
85/76
85/92
80/84
90/82
90/80
80/78
75/82
70/80
45/92
60/94
60/85
75/91
80/92
85/92
90/90
110–112(112–114) [55]
108–110 (103–104) [56]
102–104
228–230 (230–231) [57]
224–226 (227) [57]
82–84 (85) [57]
118–120 (120–121) [55]
a
The products were characterized by IR, 1H NMR, 13C NMR and mass spectroscopy.
Isolated yields.
b
1
,2-diaminobenzene, 2-aminophenol, or 2-aminothiophenol and
acid sites, followed by the nucleophilic attack on the diketone and
then followed by dehydration to give a carbocation intermediate
and elimination of a proton to give quinoxaline products as shown
in Fig. 7. A similar mechanism has been proposed for this reaction
[62].
substituted aldehydes, the following mechanism (Fig. 7) is pro-
posed. The reaction between an aldehyde and aromatic amine leads
to the formation of Schiff base which is stabilized by catalyst. Then
intramolecular attack by the second group on C N double bond to
give the final product. This reaction is likely to follow the proposed
mechanism of acid-catalyzed coordination of a 1,2-dicarbonyl onto
In conclusion, a one-pot, multicomponent methodology has
been developed for the synthesis of, benzimidazoles, benzoxazoles,

4
4
A. Teimouri et al. / Journal of Molecular Catalysis A: Chemical 373 (2013) 38–45
Table 7
Acid-catalyzed synthesis of quinoxalines derivatives.
a
Ar
O
H N
N
N
2
Ar
Ar
Catalyst
+
EtOH, reflux
Ar
O
H N
2
Time (min)/Yield (%)b
MP C (lit.) [Ref.]
◦
Entry/product
Ar
Nano-ZnO
Nano-␥-alumina
Nano-ZMS-5
Nano-crystalline SZ
1
(4a)
(4b)
(4c)
(4d)
(4e)
C6H5
4-ClC6H5
4-BrC6H5
4-NO2C6H5
4-OHC6H5
70/86
80/72
90/76
95/76
80/75
70/88
70/80
85/78
90/80
80/82
75/90
65/85
90/84
80/82
80/80
30/92
20/94
25/90
20/88
15/88
130–132 (128–129) [58]
192–194 (195–196) [58]
132–134 (135–137) [58]
128–130
2
3
4
5
148–150 (151–152.5) [58]
a
The products were characterized by IR, 1H NMR, 13C NMR and mass spectroscopy.
Isolated yields.
b
benzothiazolesand quinoxalines derivatives catalyzed by nano-
sulfated zirconia, nano-structured ZnO, nano-␥-alumina and
nano-ZSM-5 zeolites with the nano-sulfated zirconia exhibiting
greater activity has also been demonstrated. Compared to previ-
ously reported methods, Moreover, the mild reaction conditions,
easy work-up, clean reaction profiles, lower catalyst loading and
cost efficiency render this approach as an interesting alternative to
the existing methods.
Acknowledgements
Supports from the Payame Noor University in Isfahan research
council and helps of Isfahan University of technology are grate-
fully acknowledged. Thanks are also due to Mrs. Shahraki and Mr.
Narimani for recording the FT-IR spectra of the compound.
Fig. 5. The results obtained from catalyst reuse in the product formation.
Ar CHO
O
Ar
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H
H
H
H
[
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