Nanoporous TiO2 containing an ionic liquid bridge as an efficient and reusable catalyst for the synthesis of: N, N ′-diarylformamidines, benzoxazoles, benzothiazoles and benzimidazoles

Article abstract of DOI:10.1039/c8nj00171e

In this work, a green and efficient procedure is reported for the preparation of N,N'-diarylformamidines, benzoxazoles, benzothiazoles, and benzimidazoles using nanoporous TiO₂ containing an ionic liquid bridge. This reagent is prepared via the modification of nanoporous TiO₂ with bis-3-(trimethoxysilylpropyl)-ammonium hydrogen sulfate (TiO₂-[bip]-NH₂⁺ HSO₄^-). The procedure gave the products in excellent yields in very short reaction times under solvent-free conditions. The reusability of the catalyst is the other important feature of the reported method.

Full text of DOI:10.1039/c8nj00171e

NJC
View Article Online
View Journal
PAPER
Nanoporous TiO2 containing an ionic liquid bridge
as an efficient and reusable catalyst for the
synthesis of N,N0-diarylformamidines,
benzoxazoles, benzothiazoles and
benzimidazoles†
Cite this:DOI: 10.1039/c8nj00171e
M. Mazloumi, F. Shirini, * O. Goli-Jolodar and M. Seddighi
In this work, a green and efficient procedure is reported for the preparation of N,N’-diarylformamidines,
benzoxazoles, benzothiazoles, and benzimidazoles using nanoporous TiO2 containing an ionic liquid bridge.
This reagent is prepared via the modification of nanoporous TiO2 with bis-3-(trimethoxysilylpropyl)-
Received 11th January 2018,
Accepted 26th February 2018
+
ammonium hydrogen sulfate (TiO2-[bip]-NH2 HSO4ꢀ). The procedure gave the products in excellent
DOI: 10.1039/c8nj00171e
yields in very short reaction times under solvent-free conditions. The reusability of the catalyst is the
other important feature of the reported method.
rsc.li/njc
esters,17 aldehydes,18–25 nitrile oxide,26 dibromomethylarenes27
Introduction
and ortho esters28–34 in the presence of a strong acid is one of the
Formamidines are one of the important intermediates for the methods that has been used for the synthesis of these derivatives.
preparation of heterocyclic and functional group transformations.1
Despite the improved methods, each of them suffer from
In addition, these compounds have many biological and pharma- disadvantages such as long reaction times, harsh reaction condi-
ceutical properties including antimicrobial, antiviral and anti- tions, need for excess amounts of reagents, use of organic solvents,
hypertension activities.2,3 Also, they have been employed as use of toxic reagents, and non-recoverability of the catalyst. Due to
protecting groups for primary amines and as building blocks in these problems it would be interesting to provide a simple and
polymer synthesis.4,5 On the other hand, N,N0-diarylform- effective method for the synthesis of these compounds.
amidines (ArN = CHNHAr) and their anions have been widely
In the last few decades, immobilized ionic liquids have
used in coordination chemistry by coordination with metal become attractive because the immobilization of ionic liquids
centers to form chelating, bridging and chelating/bridging on solid surfaces is a useful method for the preparation of solid
bonding modes.6–8 The general procedure for the synthesis and heterogeneous catalysts. These types of catalysts retain the
of formamidines involves the reaction between two moles of benefits of ionic liquids, including excellent flexibility, heat
aniline derivatives and one mole of ethyl orthoformate in the resistance, non-volatility, non-corrosiveness, slight vapor pressure
presence of an acidic catalyst.9–11
and tunable polarity with common organic solvents.35 Furthermore,
Benzimidazole, benzoxazole, benzothiazole and their derivatives the immobilization of ionic liquids removes some defects, such
are important classes of heterocyclic compounds showing con- as improving the recovery and reusability of the catalyst and
siderable biological properties. They are important intermediates decreasing the amount of IL utilized and its cost.
for the synthesis of some drugs, for example a benzimidazole
Among various substrates, metal oxides are one of the suitable
framework exists in the structure of vitamin B12.12 Furthermore, substrates for the immobilization of ionic liquids. TiO2 nano-
these heterocyclic compounds can be extensively used as ligands particles due to their low cost, easy synthesis and high thermal
for transition metals.13
stability can efficiently be used for this purpose.36
Condensation of o-aminobenzenethiol, o-aminophenol or
In this study and in continuation of our previous reports on
o-phenylenediamine with acid chlorides,14 carboxylic acids,15,16 the preparation and application of nano catalysts in organic
transformations,37–39 nanoporous TiO2 modified with bis-3-
(trimethoxysilylpropyl)-amine is easily prepared and character-
ized using different techniques such as FT-IR, X-ray diffraction
(XRD), field emission scanning electron microscopy (FESEM)
and thermogravimetric analysis (TGA). Its application in the
Department of Chemistry, College of Sciences, University of Guilan, Rasht,
41335-19141, Iran. E-mail: shirini@guilan.ac.ir; Fax: +98 131 3233262;
Tel: +98 131 3233262
† Electronic supplementary information (ESI) available: FT-IR, 1H NMR and 13C
NMR of the new products. See DOI: 10.1039/c8nj00171e
This journal is © The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2018
New J. Chem.

View Article Online
Paper
NJC
synthesis of N,N0-diarylformamidines, benzoxazoles, benzo- and the resulting mixture was stirred at 60 1C for the appro-
thiazoles, and benzimidazoles is then studied.
priate time. After completion of the reaction as indicated by
TLC [EtOAc : n-hexane (1 : 1)], ethyl acetate (20 mL) was added
and the catalyst was separated by filtration. The organic phase
was washed with brine and dried over Na2SO4. Then the solvent
was removed under reduced pressure. Subsequently, the product
was purified by recrystallization from n-hexane to afford the
desired product in good to high yields. The spectral data of the
prepared new compounds are as follow:
Experimental
All the chemicals were purchased from Fluka, Merck, and Aldrich
chemical companies. All yields refer to the isolated products. The
products were characterized by comparison of their physical
constants, and IR and NMR spectra with authentic samples
and those reported in the literature. The purity determination
of the substrate and reaction monitoring were performed by
TLC on silicagel polygram SILG/UV 254 plates.
N,N0-Bis(3,4-dimethoxyphenyl)formimidamide: IR (KBr) n = 3439,
3071, 2997, 2916, 2833, 1670, 1599, 1512, 1449, 1307, 1238, 1141,
1023, 841, 799, 765 cmꢀ1; 1H NMR (DMSO-d6, 400 MHz) d = 3.71
(6H, s, OCH3), 3.76 (6H, s, OCH3), 6.75 (2H, s), 6.86 (4H, d, J = 8),
8.09 (1H, s, CH), 9.40 (1H, s, NH) ppm; 13C NMR (DMSO-d6,
100 MHz): d = 55.90, 59.37, 104.50, 110.68, 113.24, 144.92,
147.97, 149.70 ppm.
Preparation of nanoporous TiO2
The required amount of titanium tetraisopropoxide (TTIP)
(a TTIP : EtOH volume ratio of 1 : 6) was mixed with ethanol.
Then, deionized water was slowly added to the resulting
mixture (TTIP:water with a ratio of 1:60) to cause the hydrolysis
of TTIP and stirring was maintained for 2 h to hydrolyze TTIP
completely. The prepared material was separated by filtration,
washed with water, and dried at 80 1C. Finally, the obtained solid
was calcinated at 500 1C for 3 h to obtain nanoporous TiO2.40
N,N0-Bis(2,6-difluorophenyl)formimidamide: IR (KBr) n = 3403,
3019, 2936, 2887, 1667, 1582, 1482, 1314, 1210, 994, 770 cmꢀ1
;
1H NMR (DMSO-d6, 400 MHz) d = 7.12 (6H, s), 8.04 (1H, s, CH),
9.48 (1H, s, NH) ppm; 13C NMR (DMSO-d6, 100 MHz): d = 112.21,
112.27, 112.38, 112.45, 123.88, 155.20, 157.65 ppm.
General procedure for the synthesis of benzimidazole,
benzoxazole, and benzothiazole derivatives
Preparation of nanoporous TiO2 modified with bis-3-
1,2-Phenylenediamine, 2-aminophenol, or 2-aminothiophenol
(1 mmol) was added to a mixture of TiO2-[bip]-NH2+ HSO4ꢀ (10 mg)
and the corresponding ortho ester (trimethyl orthoformate, triethyl
orthoformate, or triethyl orthoacetate) (1.5 mmol), and the
resulting mixture was stirred at 90 1C for the appropriate time.
After completion of the reaction, which was monitored by TLC
[EtOAc : n-hexane (1 : 1)], ethyl acetate (20 mL) was added and
the catalyst was separated by filtration. The organic phase was
washed with brine and dried over Na2SO4. Then, the solvent
was removed under reduced pressure. If necessary the product
was purified by recrystallization from n-hexane to afford the
desired product in good to high yield.
(trimethoxysilylpropyl)ꢀ-ammonium hydrogen sulfate
+
(TiO2-[bip]-NH2 HSO4
)
Bis-3-(trimethoxysilylpropyl)-amine (5 mmol) was added to 5 g of
TiO2 in 25 mL of ethanol and the reaction mixture was refluxed
with stirring for 3 days. After cooling to room temperature, the
mixture was filtered and the product was washed with 10 mL of
Et2O and dried under vacuum. Subsequently, the reaction pro-
duct (6.5 g) was suspended in 20 mL of dry CH2Cl2. Then, under
vigorous stirring in an ice bath (0 1C), 5 mmol concentrated
H2SO4 (97%) was added dropwise to the mixture. The mixture
was refluxeꢀd with stirring for 24 h. After filtration, TiO2-[bip]-
+
NH2 HSO4 was obtained as a white solid (Scheme 1).
General procedure for the synthesis of
N,N0diphenylformamidines
Results and discussion
Instrumentation
An aromatic amine (2 mmol) was added to a mixture of TiO2-
[bip]-NH2+ HSO4ꢀ (10 mg) and triethyl orthoformate (1.5 mmol),
FT-IR spectra were recorded on a VERTEX 70 (Brucker,
Germany) instrument using KBr pellets for solid samples and
neat for liquid samples in the range of 4000–400 cmꢀ1. X-ray
diffraction (XRD) analysis was performed on an X’Pert MPD
diffractometer using Cu Ka radiation (l: 1.78897 Å). Field
Emission Scanning Electron Microscopy (FESEM) images were
obtained using a TE-SCAN model MIRA3 microscope. Thermo-
gravimetric Analysis (TGA) was performed using a TGA-DTA
METTLER TGA/STTA 851 analyzer (swiss).
Catalyst characterization
+
The FT-IR spectra of TiO2, TiO2-[bip]-NH and TiO2-[bip]-NH2
ꢀ
HSO4 are compared in Fig. 1. In the spectrum of TiO2 the
peaks at 3402 and 1630 cmꢀ1 are related to the hydroxyl groups
of TiO2 and adsorbed water, respectively.41 Also, the vibration
+
ꢀ
.
Scheme 1 Preparation of TiO2-[bip]-NH2 HSO4
New J. Chem.
This journal is © The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2018

View Article Online
NJC
Paper
+
ꢀ
.
Fig. 1 FT-IR spectra of TiO2, TiO2-[bip]-NH and TiO2-[bip]-NH2 HSO4
modes of the Ti–O–Ti band appeared at 650 cm .
ꢀ1 42 In the case
of TiO2-[bip]-NH, the peak at 2930 cmꢀ1 is attributed to the C–H
stretching vibrations and the peak at 1121 cmꢀ1 is assigned to
the C–C–C bending vibrations. Furthermore, in this spectrum
the peak at 1037 cmꢀ1 can be assigned to the stretching modes
of the Si–O band.43
In the FTIR spectrum of TiO2-[bip]-NH2+ HSO4ꢀ the stretch-
ing modes of the SQO band of HSO4ꢀ appeared at 1219 cmꢀ1 44
.
X-ray diffraction (XRD) analysis was performed in order to
+
determine the structure and phase of TiO2 and TiO2-[bip]-NH2
HSO4ꢀ (Fig. 2). In the XRD pattern of TiO2, five peaks appeared
at around 2y = 25.08, 37.51, 47.96, 54.11 and 62.30 that
corresponded to the (101), (004), (200), (105) and (211) facets
in the anatase crystal.45 The XRD pattern of TiO2-[bip]-NH2
+
ꢀ
HSO4 shows that the immobilization of an ionic liquid on
+
ꢀ
.
Fig. 2 XRD patterns of TiO2 and TiO2-[bip]-NH2 HSO4
TiO2 did not change its phase.
The thermogravimꢀetric analysis (TGA) curves of TiO2 and
+
TiO2-[bip]-NH2 HSO4 are shown in Fig. 3. The TGA curve of
TiO2 shows a slight weight loss (2%) which indicates the high to the removal of the adsorbed water and destruction of the –OH
thermal stability of this reagent. The TGA curve of the catalyst groups. Two weight losses observed at about 240 and 390 1C can
displays a completely different curve from TiO2, which is the be correlated with the decomposition of organic moieties.
result of the modification of its surface during the applied
procedure. In this curve the lost weight below 240 1C is related and TiO2-[bip]-NH2 HSO4 samples were observed using field
The surface morphology and particle size of the TiO2
+
ꢀ
This journal is © The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2018
New J. Chem.

View Article Online
Paper
NJC
cause ion–ion attraction and/or hydrogen bonding between the
prepared particles.
Catalytic activity
After careful identification of the prepared reagent and on the
basis of its determined formula, it is suggested that this reagent
may be able to promote reactions that need an acidic catalyst to
speed them up.
At first and in order to confirm this suggestion, the synthesis
of N,N0-diarylformamidines was studied. In this regard, the
condensation of aniline with triethyl orthoformate to its corres-
ponding formamidine was chosen as a model reaction and the
effect of the amount of catalyst, the amount of orthoformate
and the temperature was examined.
After careful studies as tabulated in Table 1, the optimal
reaction conditions were obtained as: 2 mmol aniline, 1.5 mꢀmol
+
ꢀ
.
Fig. 3 TGA curves of TiO2 and TiO2-[bip]-NH2 HSO4
+
triethyl orthoformate and 10 mg of TiO2-[bip]-NH2 HSO4 at
emission scanning electron microscopy (FESEM) (Fig. 4). The 60 1C (Table 1, entry 4) (Scheme 2).
FESEM images show that the TiO2 particles are spherical. In the
After the optimization of the reaction conditions and in
catalyst, the particles are aggregated and their sizes are order to reveal the generality of this method, we explored the
increased. This is because the presence of ionic groups can protocol with a variety of simple readily available amines under
+
ꢀ
Fig. 4 FESEM images of TiO2 (a and b) and TiO2-[bip]-NH2 HSO4 (c and d).
New J. Chem.
This journal is © The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2018

View Article Online
NJC
Table 1 Optimization of the reaction conditions catalyzed by TiO2-[bip]-NH2 HSO4
Paper
+
ꢀ
Entry
Catalyst (mg)
Triethyl orthoformate (mmol)
Temperature (1C)
Time (min)
Conversion (%)
1
2
3
4
5
6
7
8
40
30
20
10
5
10
10
20
20
10
10
1.5
1.5
1.5
1.5
1.5
1.5
1.5
1.5
1.5
2
60
60
60
60
60
40
30
40
30
60
60
4
4.5
5
5
8
10
15
7
10
6
100
100
100
100
100
100
100
100
100
100
100
9
10
11
1
9
+
ꢀ
.
Scheme 2 Synthesis of N,N0-diarylformamidine derivatives catalyzed by TiO2-[bip]-NH2 HSO4
+
ꢀa
Table 2 Synthesis of various N,N0-diphenylformamidines catalyzed by TiO2-[bip]-NH2 HSO4
Melting point (1C)
Entry
1
Amine
Product
Time (min)
5
Yieldb (%)
93
Found
Reported
134–136
137–13946
2
3
4
4
93
92
112–114
124–126
114–11649
126–12850
4
4
91
98–100
108–11049
5
6
3
5
92
93
177–179
183–185
182–183.549
186–18750
7
5
91
135–137
141–14346
This journal is © The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2018
New J. Chem.

View Article Online
Paper
NJC
Table 2 (continued)
Melting point (1C)
Entry
8
Amine
Product
Time (min)
5
Yieldb (%)
90
Found
Reported
116–118
118–11949
9
15
15
89
83
110–112
109–110
113–11549
113–11549
10
11
12
20
30
93
88
195–197
133–135
—
—
13
14
40
1 h
3
Mixture of products
—
—
0
—
—
—
—
100
15
0
—
—
a
+
ꢀ
Reaction conditions: aromatic amine (2 mmol), triethyl orthoformate (1.5 mmol), and TiO2-[bip]-NH2 HSO4 (10 mg) under solvent-free
b
conditions at 60 1C. Isolated yields.
the selected conditions, and the results are collected in Table 2. of compounds. In this regard, the selectivity of this method was
As can be seen, aromatic amines having various substituents at checked by the competitive reaction of 4-chloro aniline and
different positions of the benzene ring were efficiently con- benzylamine under the selected conditions. The obtained
verted to their corresponding N,N0-diarylformamidine deriva- result confirms that 4-chloro aniline was selectively converted
tives in very short reaction times in high-to-excellent yields to the corresponding product (Table 2, entry 15).
(Table 2, entries 1–12). Under the optimal reaction conditions
the synthesis of the unsymmetrical diarylformamidines or aniline with orthoformate in the presence of TiO2-[bip]-NH2
aliphatic formamidines was unsuccessful (Table 2, entries 13–14). HSO4 with some of those reported in the literature (Table 3)
A comparison of the obtained result from the reaction of
+
ꢀ
So this method is not useful for the preparation of these types shows that the present method is superior in terms of efficiency,
New J. Chem.
This journal is © The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2018

View Article Online
NJC
Paper
Table 3 Comparison of the obtained results from the reaction of aniline and orthoformate catalyzed by TiO2-[bip]-NH2+ HSO4ꢀ with some of the best
results reported in the references
Entry
Catalyst [ref.]
Reaction conditions
Time (min)
Yield (%)
1
2
3
4
5
6
7
Acetic acid7
Solvent-free/140–160 1C
Solvent-free/40 1C
HFIP/r.t.
3–4 h
12 h
3 h
4 h
2 h
2 h
5 min
50–80
97
95
95
90
92
93
SO42ꢀ/ZrO2 (13 mg)47
HFIP (1 mL)46
g-Fe2O3@SiO2–HBF4 (2.5 mol%)48
Nano TiO2 (10 mg) [this work]
TiO2-[bip]-NH (10 mg) [this work]
Solvent-free/r.t.
Solvent-free/60 1C
Solvent-free/60 1C
Solvent-free/60 1C
+
ꢀ
TiO2-[bip]-NH2 HSO4 (10 mg) [this work]
+
ꢀ
Scheme 3 Synthesis of benzoxazole, benzothiazole and benzimidazole derivatives catalyzed by TiO2-[bip]-NH2 HSO4
.
Table 4 Synthesis of benzimidazole, benzoxazole, and benzothiazole derivatives catalyzed by TiO2-[bip]-NH2 HSO4 as the catalysta
Melting point (1C)
+
ꢀ
Entry
Amine
Orthoester
Product
Time (min)
Yieldb (%)
Found
Reported
1
CH(OEt)3
4
94
168–170
170–17146
2
3
CH(OMe)3
5
7
92
90
168–170
168–170
170–17146
172–17451
CH3CH(OEt)3
4
5
6
7
CH(OEt)3
10
15
20
30
95
89
93
90
109–111
194–196
203–205
203–205
112–11451
198–20051
201–20252
201–20252
CH3CH(OEt)3
CH(OEt)3
CH(OMe)3
This journal is © The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2018
New J. Chem.

View Article Online
Paper
NJC
Table 4 (continued)
Melting point (1C)
Entry
8
Amine
Orthoester
Product
Time (min)
35
Yieldb (%)
89
Found
Reported
CH3CH(OEt)3
220–222
227–22852
9
CH(OEt)3
2
2
2
5
7
2
95
92
93
92
91
91
Oil
Oil
Oil
Oil
Oil
Oil
Oil53
Oil53
Oil53
Oil [53]
Oil53
Oil53
10
11
12
13
CH(OMe)3
CH3CH(OEt)3
CH(OEt)3
CH(OMe)3
CH3CH(OEt)3
14
Reaction conditions: substrate (1 mmol), triethyl orthoformate (1.5 mmol), and TiO2-[bip]-NH2+ HSO4ꢀ (10 mg) under solvent-free conditions at
a
b
90 1C. Isolated yields.
+
ꢀ
Table 5 Comparison of the obtained results from the reaction of 1,2-phenylenediamine and orthoformate catalyzed by TiO2-[bip]-NH2 HSO4 with
some of the best reported results in the literature
Entry
Catalyst [Ref.]
Reaction conditions
Time (min)
Yield (%)
1
2
3
4
5
6
7
8
9
KSF (1 g)27
Toluene/reflux
CH3OH/r.t.
CH3OH/r.t.
HFIP
U.S./45 1C
Solvent free/80 1C
Solvent free/80 1C
Solvent-free/90 1C
Solvent-free/90 1C
Solvent free/90 1C
12 h
1 h
2 h
2 h
20
50
8
1 h
30
4
79
98
93
92
86
94
90
90
93
94
Sulfamic acid (5 mol%)29
ZrCl4 (10 mol%)30
Hexafluoroisopropanol (HFIP) (1 ml)31
[EtNH3][NO3]32
HBF4–SiO2 (40 mg)33
Silica tungstic acid (50 mg)34
Nano TiO2 (10 mg) [this work]
TiO2-[bip]-NH (10 mg) [this work]
+
ꢀ
10
TiO2-[bip]-NH2 HSO4 (10 mg) [this work]
reaction time and catalyst amount. As it can be seen, TiO2 and long reaction times, so we increased the amount of catalyst and
TiO2-[bip]-NH are also able to catalyze these types of reactions, the temperature. Although by increasing the temperature, the
but in longer reaction times than TiO2-[bip]-NH2+ HSO4ꢀ (Table 3, reaction time is reduced, increasing the amount of catalyst
entries 5 and 6). These results are clear evidence to confirm the did not have a considerable effect on the reaction time. Thꢀe
important role of the preformed modification in the catalyst to best result was obtained using 10 mg of TiO2-[bip]-NH2+ HSO4
obtain the best performance.
at 90 1C (Scheme 3).
After the successful application of TiO2-[bip]-NH2+ HSO4ꢀ as
Under these optimal reaction conditions, different ortho-
the catalyst in the synthesis of N,N0-diarylformamidines, we esters (including trimethyl orthoformate, triethyl orthoformate,
decided to use this reagent for the promotion of the synthesis and triethyl orthoacetate) were used and a variety of benzimid-
of benzoxazoles, benzothiazoles, and benzimidazoles. The azole, benzoxazole and benzothiazole derivatives were obtained
obtained results showed that the synthesis of benzimidazole in good to excellent yields (Table 4). It is apparent that
using the previous reaction conditions can be performed in 1,2-phenylene diamines containing electron-donating groups gave
New J. Chem.
This journal is © The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2018

View Article Online
NJC
Paper
Scheme 4 The proposed mechanism of the studied reactions.
the desired products in excellent yields (Table 4, entries 4 and 5), (20 mmol) and triethyl orthoformate (15 mmol) using 0.1 g of
+
ꢀ
whereas 1,2-phenylene diamines with electron-withdrawing TiO2-[bip]-NH2 HSO4 at 60 1C. The reaction was completed
groups reacted at longer reaction times (Table 4, entries 6–8). within 3 min, and the desired product was obtained in 90% yield,
The method was also found to be useful for the synthesis of almost similarly in all respects with the 1 mmol scale entry
benzothiazoles and benzoxazoles derivatives, in very short (Table 2, entry 5). The above result indicated that a large-scale
reaction times (Table 4, entries 9–14).
reaction is achievable using TiO2-[bip]-NH2+ HSO4ꢀ as the catalyst.
In order to show the efficiency of the present method,
we have compared our obtained results from the reaction of
1,2-phenylenediamineꢀand orthoformate in the presence of
+
TiO2-[bip]-NH2 HSO4 with some of the reported results in
the literature and also with the obtained results using nano
TiO2 and TiO2-[bip]-NH (Table 5). It is definite that the present
method is superior in terms of the reaction times, efficiency
and catalyst amount.
The proposed mechanism of the studied reactions in the
+
ꢀ
presence of TiO2-[bip]-NH2 HSO4 as the catalyst is shown in
+
Scheme 4. On the basis of this mechanism, TiO2-[bip]-NH2
HSO4 acts as a Bronsted acidic catalyst to activate the ortho
ꢀ
¨
ester against nucleophilic attack.
We also examined the possibility of using the present method
for a large-scale reaction via the reaction of 4-chlorobeaniline
Fig. 5 Reusability of the catalyst.
This journal is © The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2018
New J. Chem.

View Article Online
Paper
To check the recovery capability of the catalyst, the reaction
of aniline with triethyl orthoformate under the optimized
reaction conditions was studied again. After completion of
the reaction, ethyl acetate was added and the catalyst was
separated by filtration. This process was repeated more than
eight times and all the reactions were well done without
significant changes in the reaction time and yield, which clearly
shows the practical recyclability of this catalyst (Fig. 5).
NJC
14 R. S. Pottorf, N. K. Chadha, M. Katkevics, V. Ozola, E. Suna,
H. Ghane, T. Regberg and M. R. Player, Tetrahedron Lett.,
2003, 44, 175.
15 K. Mickeviciene, A. Voskiene and V. Mickevicius, Res. Chem.
Intermed., 2014, 40, 1619.
16 X. Wen, J. E. Bakali, R. Deprez-Poulain and B. Deprez,
Tetrahedron Lett., 2012, 53, 2440.
17 H. Matsushita, S. Lee, M. Joung, B. Clapham and
K. D. Janda, Tetrahedron Lett., 2004, 45, 313.
18 M. Kalhor, A. Mobinikhaledi and J. Jamshidi, Res. Chem.
Intermed., 2013, 39, 3127.
Conclusions
In conclusion, in this study TiO2-[bip]-NH2+ HSO4ꢀ is prepared,
identified and used as a highly powerful catalyst for the simple
and efficient synthesis of N,N0-diarylformamidines, benzoxazoles,
benzothiazoles, and benzimidazoles. The procedure has several
advantages such as high reaction rates, ease of preparation and
handling of the catalyst, a simple and green experimental
procedure and the use of an inexpensive and reusable catalyst.
We believe that this process can be a useful and attractive
strategy in view of its economic and environmental advantages.
19 L. M. Dudd, E. Venardou, E. Garcia-Verdugo, P. Licence,
A. J. Blake, C. Wilson and M. Poliakoff, Green Chem., 2003,
5, 187.
20 B. F. Mirjalili, A. Bamoniri and M. R. Kazerouni, Chem.
Heterocycl. Compd., 2014, 50, 35.
21 Y. Riadi, R. Mamouni, R. Azzalou, M. E. Haddad, S. Routier,
G. Guillaumet and S. Lazar, Tetrahedron Lett., 2011,
52, 3492.
22 R. Azzallou, R. Mamouni, K. Stieglitz, N. Saffaj, M. E. Haddad
and S. Lazar, Int. J. Org. Chem., 2013, 3, 151.
23 D. Yang, P. Liu, N. Zhang, W. Wei, M. Yue, J. You and
H. Wang, ChemCatChem, 2014, 6, 3434.
Conflicts of interest
24 D. Yang, X. Zhu, W. Wei, N. Sun, L. Yuan, M. Jiang, J. Youac
and H. Wang, RSC Adv., 2014, 4, 17832.
There are no conflicts to declare.
25 M. Kidwai, V. Bansal, A. Saxena, S. Aerryb and S. Mozumdar,
Tetrahedron Lett., 2006, 47, 8049.
Acknowledgements
26 I. A. S. Smellie, A. Fromm, F. Fabbiani, I. D. H. Oswald,
F. J. Whitea and R. M. Paton, Tetrahedron, 2010, 66, 7155.
27 C. Siddappa, V. Kambappa, M. Umashankara and
K. S. Rangappa, Tetrahedron Lett., 2011, 52, 5474.
28 D. Villemin, M. Hammadi and B. Martin, Synth. Commun.,
1996, 26, 2895.
The authors are grateful to the Guilan University Research
Council for partial support of this work.
References
29 M. M. Heravi, N. Montazeri, M. Rahmizadeh, M. Bakavoli
and M. J. Ghassemzadeh, Acc. Chem. Res., 2000, 12, 584.
30 Z. Zhang, T. Li and J. Li, Monatsh. Chem., 2007, 138, 89.
31 Z. Zhang, L. Yin and Y. Wang, Catal. Commun., 2007,
8, 1126.
1 S. H. Kwak and Y.-D. Gong, Tetrahedron, 2013, 69, 7107.
2 S. Delarue, S. Girault, F. D. Ali, L. Maes, P. Grellier and
C. Sergheraert, Chem. Pharm. Bull., 2001, 49, 933.
3 S. Khaksar, A. Heydari, M. Tajbakhsh and S. M. Vahdat,
J. Fluorine Chem., 2010, 131, 1377.
32 S. Khaksar, A. Heydari, M. Tajbakhsh and S. M. Vahdat,
J. Fluorine Chem., 2010, 131, 1377.
33 G. Aridoss and K. K. Laali, Eur. J. Org. Chem., 2011, 2827.
34 A. V. Patil, B. P. Bandgar and S. Lee, Bull. Korean Chem. Soc.,
2010, 31, 1719.
4 H. Rudyk, M. H. Knaggs, S. Vasiljevic, J. Hope, C. Birkett and
I. H. Gilbert, Eur. J. Med. Chem., 2003, 38, 567.
5 P. S. Furth, M. S. Reitman and A. F. Cook, Tetrahedron Lett.,
1997, 38, 5403.
6 Y. Wu, C. Yeh, Z. Chan, C. Lin, C. Yang, J. Chen and J. Wang,
J. Mol. Struct., 2008, 890, 48.
7 S. J. Archibald, N. W. Alcock, D. H. Busch and D. R. Whitcomb,
Inorg. Chem., 1999, 38, 5571.
8 D. Y. Melgarejo, G. M. Chiarella and J. P. Fackler Jr., Inorg.
Chim. Acta, 2011, 378, 297.
9 V. L. Claisen, Ann, 1895, 287, 360.
10 R. M. Roberts and P. J. Vogt, J. Am. Chem. Soc., 1956,
78, 4778.
11 R. M. Roberts and R. H. DeWolfe, J. Am. Chem. Soc., 1954,
76, 2411.
12 G. Yadav and S. Ganguly, Eur. J. Med. Chem., 2015, 97, 419.
13 T. Fekner, J. Gallucci and M. K. Chan, J. Am. Chem. Soc.,
2004, 126, 223.
35 B. Garg and Yong-Chien Ling, Tetrahedron Lett., 2012,
53, 5674.
36 I. M. Gindri, C. P. Frizzo, C. R. Bender, A. Z. Tier, M. A. P.
Martins, M. A. Villetti, G. Machado, L. C. Rodriguez and
D. C. Rodrigues, ACS Appl. Mater. Interfaces, 2014, 6, 11536.
37 F. Shirini, S. V. Atghia and M. G. Jirdehi, Catal. Commun.,
2012, 18, 5.
38 F. Shirini, M. Seddighi, M. Mazloumi, M. Makhsous and
M. Abedini, J. Mol. Liq., 2015, 208, 291.
39 F. Shirini, M. Mazloumi and M. Seddighi, Res. Chem.
Intermed., 2016, 42, 1759.
40 M. Seddighi, F. Shirini and O. G. Jolodar, RSC Adv., 2016,
6, 23564.
New J. Chem.
This journal is © The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2018

View Article Online
NJC
Paper
41 N. P. Hung, N. T. V. Hoan and N. V. Nghia, Nanosci. 47 M. Sheykhan, M. Mohammadquli and A. Heydari, J. Mol.
Nanotechnol., 2013, 3, 19. Struct., 2012, 1027, 156.
42 D. A. Kumar, J. M. Shyla and F. P. Xavier, Appl. Nanosci., 48 C. Lin, C. Tsai and H. Chang, Catal. Lett., 2005, 104, 135.
2012, 2, 429.
49 M. Seddighi, F. Shirini and M. Mamaghani, J. Iran.
Chem. Soc., 2015, 12, 433.
50 D. R. Patil and D. S. Dalal, Chin. Chem. Lett., 2012, 23, 1125.
43 M. H. Baki, F. Shemirani, R. Khani and M. Bayat, Anal.
Methods, 2014, 6, 1875.
44 Y. Shao, H. Wan, J. Miao and G. Guan, React. Kinet., Mech. 51 I. Mohammadpoor-Baltork, A. R. Khosropour and S. F. Hojati,
Catal., 2013, 109, 149. Monatsh. Chem., 2007, 138, 663.
45 S. Ambika and M. Sundrarajan, J. Mol. Liq., 2016, 221, 52 Z.-H. Zhang, J.-J. Li, Y.-Z. Gao and Y.-H. Liu, J. Heterocycl.
986. Chem., 2007, 44, 1509.
46 S. Khaksar, A. Heydari, M. Tajbakhsh and S. M. Vahdat, 53 I. Mohammadpoor-Baltork, A. R. Khosropour and S. F. Hojati,
J. Fluorine Chem., 2010, 131, 1377. Catal. Commun., 2007, 8, 1865.
This journal is © The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2018
New J. Chem.