Synthesis and properties of novel reusable nano-ordered KIT-5-N-sulfamic acid as a heterogeneous catalyst for solvent-free synthesis of 2,4,5-triaryl-1H-imidazoles

Article abstract of DOI:10.1515/chempap-2015-0228

A novel silica-bonded propyl-N-sulfamic acid nanocatalyst (NHSO₃H-KIT-5) supported on modified silica mesopore KIT-5 as an organic-inorganic hybrid with high specific surface area was successfully prepared. The 3-aminopropyltriethoxysilane (APTES) on KIT-5 was reacted with chlorosulfonic acid and accurately characterized by the FT-IR, XRD, SEM, EDAXS, and TGA techniques. This heterogeneous and recyclable catalyst catalyzed one pot, multicomponent condensation of benzil, aromatic aldehydes, and ammonium acetate in the presences of 0.05 g of nanocatalyst under solvent-free conditions to afford triaryl-imidazoles in excellent yields. This catalyst showed high catalytic activity under green conditions. This reaction was performed under open air conditions and required no special reaction conditions or chromatographic separation for purification.

Full text of DOI:10.1515/chempap-2015-0228

Chemical Papers
DOI: 10.1515/chempap-2015-0228
ORIGINAL PAPER
Synthesis and properties of novel reusable nano-ordered
KIT-5- -sulfamic acid as a heterogeneous catalyst
for solvent-free synthesis of 2,4,5-triaryl-1 -imidazoles
c
d
a,bRazieh Mirsafaei, Majid M. Heravi*, Shervin Ahmadi,
cTayebeh Hosseinnejad
aDepartment of Chemistry, Yazd Branch, Islamic Azad University, Yazd, 89168-71967, Iran
bYoung Researcher Club, Shahreza Branch, Islamic Azad University, Shahreza, Isfahan, 63731-93719, Iran
cDepartment of Chemistry, Alzahra University, Vanak, 19938-93973, Tehran, Iran
dIran Polymer and Petrochemical Institute, Tehran, 14977-13115, Iran
Received 16 June 2015; Revised 5 September 2015; Accepted 16 September 2015
A novel silica-bonded propyl-N-sulfamic acid nanocatalyst (NHSO3H-KIT-5) supported on mod-
ified silica mesopore KIT-5 as an organic–inorganic hybrid with high specific surface area was suc-
cessfully prepared. The 3-aminopropyltriethoxysilane (APTES) on KIT-5 was reacted with chloro-
sulfonic acid and accurately characterized by the FT-IR, XRD, SEM, EDAXS, and TGA techniques.
This heterogeneous and recyclable catalyst catalyzed one pot, multicomponent condensation of ben-
zil, aromatic aldehydes, and ammonium acetate in the presences of 0.05 g of nanocatalyst under
solvent-free conditions to afford triaryl-imidazoles in excellent yields. This catalyst showed high
catalytic activity under green conditions. This reaction was performed under open air conditions
and required no special reaction conditions or chromatographic separation for purification.
c
ꢀ 2015 Institute of Chemistry, Slovak Academy of Sciences
Keywords: KIT-5 nanosilica, heterogeneous catalysis, solvent-free conditions, organic–inorganic
hybrids, density functional theory, quantum theory of atoms in molecules
Introduction
lysts. Our group has been engaged in the catalyzed
synthesis of imidazoles using ionic liquids (Siddiqui
et al., 2005), silica sulfuric acid (Shaabani & Rah-
mati, 2006), acetic acid (Sarshar et al., 1996), potas-
sium aluminium sulfate (Mohammadi et al., 2008),
sulfanilic acid (Mohammed et al., 2007), NiCl2 · 6H2O
(Heravi et al., 2007a), H3PO4 (Wang et al., 2012),
L-proline (Samai et al., 2009), zirconium(IV)-modified
silica gel (Sharma & Sharma, 2011), Wells–Dawson
heteropolyacid (Karimi et al., 2010), MCM-41-SO3H
(Mobil Composition of Matter No. 41) (Mahdavinia et
al., 2012), BF3 ·SiO2 (Sadeghi et al., 2008), solid alu-
mina (Li et al., 2012), Zr(acac)4 (Khosropour, 2008),
and I2 (Mazaahir et al., 2007). These methods have
their own advantages and drawbacks. Some of the
Multisubstituted imidazoles are an important het-
erocyclic nucleus due to their well-known biological
properties and play vital roles in biochemical pro-
cesses. The imidazole moiety is present in several pre-
scribed drugs, such as metronidazole, dacarbazine,
cimetidine, thyroliberin, flumazenil, methimazole, and
etomidate (Blotny, 2006; Hamon et al., 2009; Silva et
al., 2001, 2007).
A literature survey revealed an enormous num-
ber of methods for the synthesis of imidazole deriva-
tives via one pot three-component condensation of
appropriate aromatic aldehydes, ammonium acetate,
and benzil/benzoin in the presence of different cata-
*Corresponding author, e-mail: mmh1331@yahoo.com
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Fig. 1. Two effective structure models of supported solid acid aminated KIT-5 nanocatalyst denoted as O-SO3H/KIT-5 (a) and
N-SO3H/KIT-5 (b).
drawbacks are low yields, long reaction times, and
some requires the need of hazardous and hardly af-
fordable catalysts with problematic recovery. Most of
them are carried out in organic solvents and tedious
work-up procedures and purification by expensive col-
umn chromatography were required. Thus, the synthe-
sis and use of novel catalysts, especially nanocatalysts
which may circumvent these problems is desired.
Nowadays, heterogeneous catalysis is an attractive
and superior process in many areas of synthetic or-
ganic chemistry due to its unique properties such as
the ease of separation and reusability (Guisnet et al.,
1988; Tao et al., 2014). In heterogeneous catalysis, the
quality and also the quantity of the surface area for
the catalyst are important. Silica is a good choice as
support for heterogeneous catalysis due to its maxi-
mum surface area. Mesoporous silica materials have
attracted increasing interest in recent years. SBA-16
(Santa Barbara Amorphous-16), SBA-1, and KIT-5
(Korea Institute of Technology No. 5) are good ex-
amples of such porous materials (Bamoharram et al.,
2007; Heravi et al., 2006a). The most common step
toward surface area maximization is employing a sup-
port, a suitable material that the catalysts could be
spread over (Suib, 2013). The three-dimensional pore
architecture is usually the ideal support for this pur-
pose.
et al., 2010; Heravi et al., 2008a). Recently, in situ
prepared copper nanoparticles on modified KIT-5 as
an efficient recyclable catalyst and their application in
click reactions in water have been reported (Mirsafaei
et al., 2015).
Synthesis of heterogeneous catalysts and their ap-
plications in a variety of organic reactions in solvent-
free condition is in the centre of our interest (Heravi
& Sadjadi, 2009; Heravi et al., 2006a, 2006b, 2007b,
2007c, 2007d; Oskooie et al., 2006a); a review, entitled
as “Current advances in the syntheses and biological
potencies of tri- and tetra-substituted 1H-imidazoles”
has also been published (Heravi et al., 2015). In con-
tinuation of our attempts to develop catalyzed syn-
thetic ways (Heravi et al., 2000, 2007a, 2007d, 2008a,
2008b; Davoodnia et al., 2010; Oskooie et al., 2006b;
Zeinali-Dastmalbaf et al., 2011; Moghaddas et al.,
2012), in particular using nanocatalysts (Nemati et
al., 2012; Heravi & Alishiri, 2012; Heravi et al., 2014,
2010, 2009a; Hashemi et al., 2014), and recent suc-
cessful attempts to synthesize modified 3D-nanocage
KIT-5 (Mirsafaei et al., 2015); in this paper, we wish to
report the preparation of an N-sulfamic acid nanocata-
lyst supported on modified 3D-nanocage KIT-5. This
catalyst has been prepared from commercially inex-
pensive commonly purchasable materials.
Many types of N-sulfamic solid acid functional-
ized silica gels have been prepared and applied as
an alternative to conventional sulfonic acid resins
and homogeneous acids used as an efficient catalyst
for different chemical transformations (Zhao et al.,
2014; Khorami & Shaterian, 2014; Nouri Sefat et al.,
2011). These catalysts have been applied to many
acid-catalyzed reactions successfully, for example es-
terification (Schaubroeck et al., 2009, 2010; Silva et
al., 2006), condensation of aldehydes with alcohol
(Shvo & Goldman-Lev, 2002), Beckmann rearrange-
ment (Martín & Garrone, 2003), and imidazole syn-
thesis (Liu et al., 2008; Mannam & Sekar, 2008; Fan
Theoretical
In the next step, comparative assessment of the
chelating behavior of SO3H group onto NH2-KIT-5
was assessed by performing theoretical calculations
using density functional theory (DFT) (Lee et al.,
1988) and quantum theory of atoms in molecules
(QTAIM) (Bader, 1990; Bader & Essén, 1984) ap-
proaches. Strictly speaking, two effective models for
supported solid acid nanocatalyst (as illustrated in
Fig. 1) were employed to comparatively analyze the
preference of sulfur atom of SO3H group in chela-
tion with nitrogen or oxygen atoms onto NH2-KIT-5
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iii
Fig. 2. The energy-minimized structure of O-SO3H/KIT-5 (a) and N-SO3H/KIT-5 (b) together with the calculated O—S and
N—S bond orders obtained at M06/6-31G* level of theory.
Table 1. Mathematical properties of two selected N—S and O-S BCPs in N-SO3H/KIT-5 and O-SO3H/KIT-5; the properties
were obtained by QTAIM analysis on the M06/6-311+G** calculated wave function of electron density (note that all
calculated vaules are in atomic units system)
2
ρb
∇ ρb
Gb
Vb
Hb
|Vb|/Gb
N-SO3H/KIT-5
0.228
0.049
–0.571
0.162
0.120
0.045
–0.383
–0.050
–0.263
–0.005
3.191
1.111
N—S BCP
O-SO3H/KIT-5
O · · · H BCP
(N-SO3H/KIT-5 or O-SO3H/KIT-5). It should be no-
ticed that, from the computational viewpoint, this
model has a reliable comprise between accuracy and
time saving efficiency of the computational procedure.
In this respect, the optimized structure of
N-SO3H/KIT-5 and O-SO3H/KIT-5 was first cal-
culated using DFT computations at M06/6-31G∗
level of theory. It should be stated that M06 func-
tional has been introduced recently as a top per-
former among modern functionals, providing high
performance and accuracy. Moreover, this functional
was recommended for application in organometal-
lic and non-organometallic thermochemistry, kinetic
studies, and noncovalent interactions (Zhao & Truh-
lar, 2008). All DFT computations have been per-
formed using GAMESS suite of programs (Schmidt et
al., 1993). In Fig. 2, the theoretical optimized struc-
tures of N-SO3H/KIT-5 and O-SO3H/KIT-5 com-
pounds are presented. Based on the structural features
of N-SO3H/KIT-5 and O-SO3H/KIT-5 compounds
(Fig. 2), it can be claimed that covalent bond for-
mation between sulfonic acid and NH2 group is more
favorable than that of the OH group onto NH2-KIT-
5 while in O-SO3H/KIT-5, O· · ·H hydrogen bond is
formed instead of O—S covalent bond.
sity was performed. It is important to mention that
the wave functions of electron density are correspond
to M06/6-31G∗ optimized structures of N-SO3H/
KIT-5 and O-SO3H/KIT-5. Thus, electronic energy
density indicators were assessed at some key bond crit-
ical points (BCPs) using AIM2000 program package
(Bader, 2000).
In Table 1, QTAIM calculated values of electron
2
density, ρb, its Laplacian, ∇ ρb, electronic kinetic en-
ergy density, Gb, electronic potential energy density,
Vb, total electronic energy density, Hb, and |Vb|/Gb
ratio are presented at some selected bond criti-
cal points (BCPs) for N-SO3H/KIT-5 and O-SO3H/
KIT-5. It should be noticed that the values of elec-
tron density and the sign of electron density Lapla-
cian at BCPs usually correlate with the strength of
the covalent bond between two atoms. Furthermore, a
good reliable indicator for classifying interatomic in-
teractions as shared, closed-shell, and also hydrogen
bonds is the total electronic energy density defined as
Hb = Gb + Vb at BCPs. In the closed-shell interac-
tions, Hb has a positive value, for shared interactions
it is negative, and for hydrogen bonds, Hb vanishes
where Gb ≈ |Vb|. Based on the QTAIM calculated
data in Table 1, it can be concluded that N—S cova-
lent bond in N-SO3H/KIT-5 is formed with the cor-
In order to present a more concise interpretation of
the chelating behavior of NH2-KIT-5 with sulfur atom
of chlorosulfonic acid, topological analysis of M06/6-
311+G∗∗ calculated wave functions of electron den-
2
responded negative values of ∇ ρb and Hb correlating
with the stabilization of the shared electrons on N—S
BCP while the negative value of Vb together with the
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R. Mirsafaei et al./Chemical Papers
Fig. 3. Preparation of N-sulfamic solid acid nanocatalyst supported on KIT-5 (NHSO3H-KIT-5).
Table 2. Physicochemical properties of mesoporous silica KIT-5 sample
BET surface area
m2 g−1
Pore volume, Vp
cm3 g−1
BJH pore diameter
d111
nm
Unit cell parameter, a0
nm
nm
1090
0.71
2.62
10.38
17.98
low value of Hb on O· · ·H BCP confirm the hydrogen
bond character of O···H in O-SO3H/KIT-5. The calcu-
lated electronic results lead to the fact that the sulfur
atom is chelated with nitrogen atom onto NH2-KIT-5
rather than onto the oxygen atom, which confirms the
experimental observations concerning immobilization
of SO3H inside the mesopores of KIT-5 and prepara-
tion of acid catalysts on N-SO3H/KIT-5.
added dropwise in 5 min and stirred for 2 h. After this
addition was complete, the mixture was stirred for an-
other 2 h at room temperature in order to complete
the elimination of HCl vapors. The mixture was fil-
tered, washed with ethanol (2 × 25 mL), and dried
at room temperature. The sample was denoted as
N-sulfamic acid supported NH2-KIT-5 (NHSO3H-
KIT-5) (5) in form of yellow powder (Fig. 3).
IR spectrum of NH2-KIT-5, νmax/cm−1: 3643.47
(br), 2934.29 (m), 1582.18 (s), 1482.33 (m), 1081.39–
1044.92 (s), 801.07 (s), 694.31 (w), 454.97 (s).
Experimental
All reagents were purchased from Fluka (Ger-
many), Merck (Germany), and Sigma–Aldrich (USA)
companies and used without further purification. All
products were identified by comparison of their spec-
tral and physical data with those of authentic samples
reported. General properties of 3D highly intercon-
nected nanocage-like mesoporous silica of the KIT-5
type, illustrated in Table 2 (Mirsafaei et al., 2015).
IR spectrum of NHSO3H-KIT-5, νmax/cm−1
:
3638.01 (br), 3081.63 (br), 1169.36 (s), 1059.17 (s),
796.21 (w), 587.01 (s), 461.08 (s).
Synthesis of 2,4,5-triphenyl imidazoles
In a round bottomed flask, a mixture of benzil
(1.0 mmol), appropriate aldehyde (1.0 mmol), ammo-
nium acetate (2.0 mmol), and NHSO3H-KIT-5 as a
catalyst (0.05 g) was stirred at room temperature.
Then, the reaction mixture was heated to 120◦C in
an oil bath under solvent-free conditions (Fig. 4) for
the required period of time and monitored by TLC
(ethyl acetate : hexane; ϕr = 7 : 3) as indicated in
Table 3. In order to recover the catalyst, the residue
was stirred in acetone (10 mL) for 10 min, washed
further with acetone, dried under reduced pressured
at 70◦C for 3 h, and stored for another consecutive
reaction run. The filtrate was then evaporated to dry-
ness under reduced pressure to afford the correspond-
ing imidazole as pure crystals which were washed with
10 mL of ether. All imidazoles were known and their
physical data were compared with those of authentic
Catalyst preparation
Aminated KIT-5 was synthesized according to our
previously reported procedure (Mirsafaei et al., 2015).
A suspension of calcined KIT-5 (1.00 g) (1) and
APTES (1.00 g) (2) in toluene (20 mL) as a solvent
was refluxed with continuous stirring under N2 atmo-
sphere for 24 h. The unreacted APTES was removed
by Soxhlet extraction using dry dichloromethane for
20 h and dried at 60◦C. The sample was denoted as
NH2-KIT-5 (3) (Mirsafaei et al., 2015). To this residue
in dry CH2Cl2 (3 mL) in a round-bottomed flask in
an ice bath and under reduced pressure, chlorosulfonic
acid (4) (0.6 mL as a > 97 % standard solution) was
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v
Fig. 4. Synthesis of 2,4,5-triaryl-1H-imidazoles using the NHSO3H-KIT-5 catalyst.
Table 3. Optimized conditions for the synthesis of 2,4,5-triaryl-1H-imidazolesa
Time
min
10
Yieldb
%
M.p./◦C
experimental
Aldehyde
Product
4a
Reference
literature
274–276
Benzaldehyde
90
273–275
Karimi et al. (2010)
3-NO2-Benzaldehyde
4-Cl-Benzaldehyde
4b
4c
4d
4e
4f
4g
4h
4i
20
14
10
11
20
18
14
25
18
11
20
87
89
92
88
85
83
87
88
87
91
83
267–268
260–262
230–231
258–260
230–232
174–175
197–199
235–237
260–262
253–255
228–230
265–267
256–260
228–231
259–262
229–231
174–175
197–199
235–238
259
Karimi et al. (2010)
Karimi et al. (2010)
Karimi et al. (2010)
Heravi et al. (2007a)
Heravi et al. (2007a)
Heravi et al. (2008b)
Heravi et al. (2007a)
Heravi et al. (2007a)
Heravi et al. (2007a)
Bakavoli et al. (2015)
Heravi et al. (2007a)
4-MeO-Benzaldehyde
3-MeO-Benzaldehyde
4-Me-Benzaldehyde
2,4-diCl-Benzaldehyde
2-Cl-Benzaldehyde
4-NO2-Benzaldehyde
4-Br-Benzaldehyde
4-CH(CH3)2-Benzaldehyde
2-NO2-Benzaldehyde
4j
4k
4l
255–257
230–231
a) Reaction conditions: benzil (1.0 mmol), aromatic aldehyde (1.0 mmol), ammonium acetate (2.0 mmol), and NHSO3H-KIT-5 as
a catalyst (0.05 g), solvent-free at 120◦C; b) yield refers to pure and isolated products.
compounds and found to be identical (Karimi et al.,
2010; Heravi et al., 2007a, 2008b).
S 360 (Cambridge, UK) was used to observe the mor-
phology of the modified and unmodified mesoporous
silica materials. Energy dispersive X-ray spectroscopy
(EDXS) Genesis, Iran Polymer and Petrochemical In-
stitute (Iran), with an SUTW detector equipped with
SEM, was used to carry out the EDXS analysis in
order to confirm the presence of silica. Thermal gravi-
metric analysis (TGA) data were obtained by a Se-
taram Labsys TG (STA), Islamic Azad University
(Iran) in the temperature range of 10–700◦C and the
heating rate of 5◦C min−1 under N2 atmosphere.
Fig. 5 shows the wide-angle XRD pattern of the
NH2-KIT-5 (a) and NHSO3H-KIT-5 catalyst (b).
XRD patterns of the catalysts showed a decrease in
the peak intensity due to the presence of a sulfur group
inside the modified mesopores, leading to false diffrac-
tion. The reduced intensity revealed that organic moi-
eties were present in the pores of NH2-KIT-5. More-
over, this observation also confirmed the immobiliza-
tion of SO3H inside the mesopores of KIT-5 and the
preparation of acid catalyst, NHSO3H-KIT-5, which
can be attributed to the symmetry being destroyed by
Spectral (IR and 13C NMR) data for the model
compound (2,4,5-triphenyl-1H-imidazole, 4a) are as
follows: light-yellow solid, m.p. 273–275◦C (274–
276◦C (Karimi et al., 2010)). C21H16N2 composition,
wi/mass %: found C, 85.02; H, 5.1; N, 9.12; computed
C, 85.11, H, 5.44, N, 9.45. IR (KBr), ν/cm−1: 3435,
2993, 2471, 1638, 1215.
Results and discussion
Catalyst characterization
Samples were analyzed by FT-IR spectroscopy us-
ing a Perkin–Elmer 65, Islamic Azad University (Iran)
in a KBr matrix in the range of 4000–400 cm−1
.
X-ray diffraction (XRD) patterns of the materials were
recorded on a Bruker D8 Advanced powder X-ray
diffractometer, Esfahan University (Iran) using CuKα
◦
˚
(λ = 1.54 A) radiation in the 2θ range of 2–80 . A
scanning electron microscope (SEM) Lecia Cambridge
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Fig. 5. WAXRD pattern of the NH2-KIT-5 (a) and NHSO3H-KIT-5 nanocatalyst (b).
Fig. 6. FT-IR spectrum of the NH2-KIT-5 (a) and NHSO3H-KIT-5 catalyst (b).
the hybridization of ordered mesoporous silica loaded
with guest matter.
SO3H moieties. For the sulfamic acid functional group
in the catalyst, the FT-IR spectrum showed over-
lapping asymmetric and symmetric stretching bands
Moreover, conversion of the amino group in
NH2-KIT-5 to NHSO3H-KIT-5 was confirmed by
FT-IR spectra. Fig. 6 shows the IR spectrum be-
fore and after the reaction of NH2-KIT-5 with chloro-
sulfonic acid with the major peaks for silica includ-
ing the broad anti-symmetric stretching Si—O—Si
(1300–1000 cm−1) and the symmetric stretching (820–
740 cm−1) were observed. In the NH2-KIT-5 spec-
trum, the 2935 cm−1 peak can be assigned to the
C—H bond stretching, while the NH2 group showed
two bands for primary amines, the N—H stretching
(3390 cm−1) and the N—H bending (1650 cm−1).
In comparison to the NH2-KIT-5 sample, the distin-
guished features of N-SO3H/KIT-5 were: the presence
of a new absorption peak near 1032 cm−1 assigned
— —
S O with Si—O—Si stretching bands in
— —
of the O
the silica functionalized alkylsulfuric acid. The SO2
asymmetric and symmetric stretching modes were po-
sitioned at 1170 cm−1 and 1060 cm−1, respectively.
The spectrum also showed a broad OH stretching ab-
sorption from 3600 cm−1 to 3200 cm−1. NH stretch-
ing and bending signals appeared at 3420 cm−1 and
1650 cm−1, respectively. In the catalyst spectrum, the
(C—N) peak showed a slight positive shift, indicat-
ing that sulfur is chelated with nitrogen atoms onto
NH2-KIT-5. Therefore, the mesopore support can act
as a chelate, which results in an increase of the amount
of acid groups in the structure of the catalyst.
Morphology of the catalyst surface was analyzed
by a SEM microscope equipped with an energy dis-
persive X-ray analyzer (EDXS). In a previous work,
aminated KIT-5 and the following nanocopper syn-
thesis on this nanosupport was presented (Mirsafaei
—
to the symmetric stretching of the S O bond as a
—
result of the SO3H groups in mesoporous silica, and
an absorption band at 610 cm−1 due to the bending
vibration of the OH groups hydrogen bonded to the
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vii
Fig. 7. SEM images of pure KIT-5 (a), modified KIT-5 (b), and the catalyst (c).
ganic solvents, only the SEM, EDAX, Map, and XRD
analysis techniques could be used for structural elu-
cidation. Fig. 8 shows a Map image of the nanocata-
lyst with the sulfur group homogeneously immobilized
on the modified surface. The map of the catalyst ap-
proved this homogenous dispersion.
EDX data obtained for the catalyst also confirmed
the addition of ClSO3H on the surface of the modi-
fied KIT-5 matrix, suggesting thus the formation of
an N-sulfamic acid linkage to the amine ligand via the
anchored SO3H group (Fig. 9).
Thermal stability of the NH2-KIT-5 and N-sulfo-
namic acid catalyst was initially examined by the
TGA analysis (under flowing of N2), confirming the
incorporation of SO3H groups in NH2-KIT-5. The two
curves observed showed the mass loss of organic ma-
terials as they decomposed upon heating (Fig. 9). As
illustrated in Fig. 10, NH2-KIT-5 showed a slight loss
of mass (about 5 %) below 150◦C, probably due to
the loss of a small quantity of adsorbed water. The
observed mass loss course of N-sulfonamic acid be-
low 150◦C was comparable to that of NH2-KIT-5,
where the mass loss occurred at about 350◦C caused
probably by the decomposition of the aminopropyl
group. Nevertheless, the TGA curve of N-sulfonamic
acid at higher temperatures illustrated a more re-
markable mass loss in comparison to that observed in
NH2-KIT-5. This can be chiefly attributed to the
gradual desorption and thermal decomposition of the
SO3H group. It is expected that the N-sulfamic groups
decompose at lower temperatures in comparison with
APTES. The total percentage of the mass loss of the
catalyst was estimated to be around 18 %, and 7 % in
APTES/KIT-5. Such mass loss in the N-sulfonamic
acid catalyst also proves the presence of N-sulfumic
acid inside the pores. This catalyst is stable up to
220◦C and can be considered as a catalyst of choice
in various organic reactions requiring the temperature
range of 80–140◦C (Kleitz et al., 2003; Sharma et al.,
Fig. 8. Map image of the nanocatalyst.
et al. 2015). Fig. 7 shows the SEM images of pure
KIT-5 (Fig. 7a), aminated KIT-5 (Fig. 7b), and the
catalyst (Fig. 7c). Clear and vivid changes in the SEM
micrographs were observed. The primary structure
of pure KIT-5 was completely changed step by step
(Figs. 7a–7c) after chemical modifications (Fig. 7b)
and nanocatalyst addition (Fig. 7c), the aggregation
of particles was prevented in the NHSO3H-KIT-5 cata-
lyst (Fig. 7c). Fig. 7c clearly demonstrates the changes
in the morphology of the catalyst surface area that
can be mainly attributed to the presence of sulfamic
groups in the catalyst. Consequently, the surface area
of the catalyst was covered uniformly retarding thus
aggregation and increasing the catalytic activity in the
organic transformations. The size of modified KIT-5
(Fig. 7b) was around 21–49 nm.
Due to the catalyst insolubility in all common or-
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R. Mirsafaei et al./Chemical Papers
Fig. 9. EDXS analysis of the NHSO3H-KIT-5 nanocatalys.
Fig. 10. TGA curve of the NH2-KIT-5 (a) and NHSO3H-KIT-5 catalyst (b).
2008). However, NH2-KIT-5 is thermally stable even
up to 400◦C, therefore it is frequently employed as a
thermally stable catalyst support in several organic
transformations.
sults are given in Table 2. A mixture of various alde-
hydes (1 mmol), benzil (1 mmol), ammonium ac-
etate (2 mmol), and NHSO3H-KIT-5 (0.05 g) as the
nanocatalyst were reacted under solvent-free condi-
tions. To find the optimal reaction conditions, the
synthesis of 4a was selected as a model reaction.
This reaction was performed in different solvents such
as H2O, CH3CH2OH, and CH3CN. Interestingly, the
solvent-free system gave the best results in terms of
yield and reaction time (Table 4). As it can be seen,
different solvents (H2O, CH3CH2OH, and CH3CN)
Preparation and characterization
of 2,4,5-triaryl-1H-imidazoles
In order to investigate, the catalytic activity of
the prepared NHSO3H-KIT-5 nanocatalyst, the syn-
thesis of trisubstituted imidazoles was performed; re-
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Table 4. Optimization of conditions for the synthesis of 4a in the presence of the NHSO3H-KIT-5 catalysta
Entry
Solvent and conditions
Catalyst (g)
Time (min)
Yieldb (%)
1
2
3
4
5
6
7
8
9
H2O, reflux
EtOH, reflux
CH3CN, reflux
Solvent-free, 100◦C
Solvent-free, 100◦C
Solvent-free, 100◦C
Solvent-free, 100◦C
Solvent-free, 110◦C
Solvent-free, 120◦C
Solvent-free, 130◦C
0.05
0.05
0.05
0.06
0.05
0.04
0.03
0.05
0.05
0.05
30
35
43
17
17
20
30
16
10
16
63
58
59
75
75
70
70
80
90
90
10
a) Reaction conditions: benzaldehyde (1 mmol), benzil (1 mmol), ammonium acetate (2 mmol) in 2 mL of solvent (in solution
experiment); b) yield refers to isolated and pure product.
Table 5. Comparison of the efficiency of various catalysts with NHSO3H-KIT-5 in the synthesis of 2,4,5-trisubstituted imidazoles
Time
min
Yielda
%
Entry
Catalyst
Conditions
Reference
1
2
3
4
5
6
7
KH2PO4
InCl3 · 3H2O
EtOH/Reflux
MeOH/R.T
EtOH/Reflux
MeOH/60◦C
60
492
120
540
90
89
76
95
87
89
94
90
Heravi and Alishiri (2012)
Heravi et al. (2010)
Khosropour (2008)
Samai et al. (2009)
Heravi et al. (2009a)
Heravi et al. (2009b)
This study
Zr(acac)4
L-proline
NiCl2 · 6H2O/Al2O3
(4-SB)T (4-SPh) PHSO4 (15 mole %)
NHSO3H-KIT-5 (0.05 g)
EtOH/Reflux
Solvent-free /120◦C
Solvent-free /120◦C
15
10
a) Yield refers to isolated and pure product.
the catalyst performance of the presented nanocata-
lyst is quite comparable with those of the already re-
ported ones, regarding the yields and reaction times.
Reusability of the catalyst was also tested
(Fig. 11); the model reaction (synthesis of 4a) was con-
ducted five times with recycled catalysts under similar
conditions and only non-appreciable mass loss was ob-
served in the obtained desired compound. After each
cycle, the catalyst was filtered off, washed with water
(10 mL), dried in an oven at 70◦C and reused in the
next reaction cycle without any further modification.
Fig. 11. Recyclability of the NHSO3H-KIT-5 nanocatalyst in
the preparation of 4a.
Conclusions
were compared with the reaction in solvent-free con-
ditions at different temperatures and with various
amounts of the catalyst. According to the results,
solvent-free conditions were chosen which is dictated
by the green chemistry principles. Optimization of the
amount of the catalyst was also studied. As shown in
Table 4, entry 9, the best result was achieved in the
presence of 0.05 g of NHSO3H-KIT-5 at 120◦C in sol-
vent free conditions.
To show the advantages of NHSO3H-KIT-5 as a
heterogeneous acid nanocatalyst, the reaction condi-
tions of the synthesis of 2,4,5-triphenyl-1H-imidazole
(4a) were compared with those using various catalysts,
reported previously (Table 5). The results showed that
In conclusion, a mild, recoverable and efficient het-
erogeneous catalyst was prepared and employed for
the catalysis of a one-pot multicomponent biologi-
cally important reaction. In the aforementioned re-
action, trisubstituted imidazoles were produced from
benzil, aromatic aldehydes, and ammonium acetate in
the presence of 0.05 g of the catalyst under solvent-
free conditions. A simple and efficient catalyst has
been prepared using a silica type mesoporous mate-
rial, KIT-5, which is the best choice as a support due
to its maximum surface area (1090 m2 g−1). As shown
in Table 1, the catalyst has a large surface area and
highly ordered mesoporous nanocage structure with
cubic Fm3m close packed symmetric ordering, large
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R. Mirsafaei et al./Chemical Papers
pores, and high specific pore volume (Kleitz et al.,
2003). The XRD and SEM results showed the hy-
brid character of KIT-5 supported on APTES as an
organic–inorganic hybrid catalyst. Moreover, based on
DFT computed results, immobilization of SO3H inside
the mesopores of KIT-5 was confirmed. In this respect,
the sulfur atom was proved to be chelated with a ni-
trogen atom on NH2-KIT-5 rather than on an oxygen
atom confirming the effective preparation of acid cata-
lyst on N-SO3H/KIT-5. Therefore, in order to activate
the catalyst surface, an appropriate moiety should be
linked to it. On the other hand, this hybrid catalyst
has better properties than SiO2. The prepared het-
erogeneous catalyst was found stable at high temper-
atures, highly active, and recyclable, which is desired
for catalyzed imidazole reactions in high yields, pro-
viding shorter reaction time than the previously de-
scribed catalysts. It is worthwhile to mention that
this catalyzed reaction is facile, clean, and no tedious
work-up procedure or separation techniques are re-
quired. Therefore, the highly mesoporous silica KIT-5
catalyst should be considered and studied as a smart
support for other nanocatalysts used in various cat-
alyzed organic reactions. The ease of separation along
with its recyclability are the other advantages of this
mesoporous nanocatalyst.
J. J. (2010). Ru(III)-catalyzed oxidation of homopropargyl
alcohols in ionic liquid: an efficient and green route to 1,2-
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tassier, C., & Pérot, G. (Eds.) (1988). Heterogeneous catal-
ysis and fine chemicals (Studies in surface science, Vol. 41).
Amsterdam, The Netherlands: Elsevier.
Hamon, F., Prié, G., Lecornué, F., & Papot, S. (2009). Cyanuric
chloride: an efficient reagent for the Lossen rearrangement.
Tetrahedron Letter, 50, 6800–6802. DOI: 10.1016/j.tetlet.
2009.09.115.
Hashemi, E., Beheshtiha, Y. S., Ahmadi, S., & Heravi, M.
M. (2014). In situ prepared CuI nanoparticles on modified
poly(styrene-co-maleic anhydride): an efficient and recyclable
catalyst for the azide–alkyne click reaction in water. Tran-
sition Metal Chemistry, 39, 593–601. DOI: 10.1007/s11243-
014-9838-5.
Heravi, M. M., Montazeri, N., Rahmizadeh, M., Bakavoli, M.,
& Ghassemzadeh, M. (2000). Zeolite-induced heterocycliza-
tion: a superior method of synthesis of condensed imida-
zoles. Journal of Chemical Research, 2000, 584–585. DOI:
10.3184/030823400103166274.
Heravi, M. M., Rajabzadeh, G., Bamoharram, F. F., & Seifi,
N. (2006a). An eco-friendly catalytic route for synthesis of 4-
amino-pyrazolo[3,4-d]pyrimidine derivatives by Keggin het-
eropolyacids under classical heating and microwave irradia-
tion. Journal of Molecular Catalysis A: Chemical, 256, 238–
241. DOI: 10.1016/j.molcata.2006.04.016.
Heravi, M. M., Tajbakhsh, M., Ahmadi, A. N., & Mohajerani,
B. (2006b). Zeolites. Efficient and eco-friendly catalysts for
the synthesis of benzimidazoles. Monatshefte fu¨r Chemie -
Chemical Monthly, 137, 175–179. DOI: 10.1007/s00706-005-
0407-7.
Heravi, M. M., Bakhtiari, K., Oskooie, H. A., & Taheri, S.
(2007a). Synthesis of 2,4,5-triaryl-imidazoles catalyzed by
NiCl2·6H2O under heterogeneous system. Journal of Molec-
ular Catalysis A: Chemical, 263, 279–281. DOI: 10.1016/j.
molcata.2006.08.070.
Acknowledgements. Professor Heravi is grateful for partial
financial support from the Iran National Science Foundation.
The authors are thankful to the Iran Polymer and Petrochemi-
cal Institute for providing the SEM-EDXS facility, the Kashan
University for providing XRD analysis and the Islamic Azad
Yazd University for providing IR analysis.
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