Covalently anchored organic carboxylic acid on porous silica nano particle: A novel organometallic catalyst (PSNP-CA) for the chromatography-free highly product selective synthesis of tetrasubstituted imidazoles

Article abstract of DOI:10.1016/j.apcata.2013.03.024

A novel organometallic catalyst (PSNP-CA) has been prepared by post synthesis grafting of COOH functionalized organosilane on porous silica nano particle by using surface hydroxyl groups as anchor point. It was characterized by using an array of sophisticated analytical techniques like 13C CP MAS NMR, 29Si MAS NMR, CHN analysis, BET, HR TEM, XRD, TGA, FTIR and pH measurement. The leaching of the active site is greatly avoided as the organic moieties are covalently attached to the inorganic support. This is the first example of organocatalysis promoted by a COOH functionalized porous silica nano particle for the chemoselective synthesis of densely substituted imidazoles. The molecular scaffolds which assimilate bio-active imidazole moiety may be worthwhile molecule from the biological point of view. All the other reported procedures led to the mixture of tri and tetra substituted imidazoles and their proportions were successfully evaluated from crude ¹H NMR spectra. Greenness of the process was well instituted as water was exploited as reaction medium. This catalyst retained its activity after having it exposed to ambient atmosphere for 10 days. There was no deteriorating effect of aerial oxygen or moisture towards the activity of the catalyst.

Full text of DOI:10.1016/j.apcata.2013.03.024

Accepted Manuscript
Title: Covalently anchored organic carboxylic acid on porous
silica nano particle: A novel organometallic catalyst
(PSNP-CA) for the chromatography-free highly product
selective synthesis of tetrasubstituted imidazoles
Author: <ce:author id="aut0005"> Suman Ray<ce:author
id="aut0010"> Paramita Das<ce:author id="aut0015"> Asim
Bhaumik<ce:author id="aut0020"> Arghya Dutta<ce:author
id="aut0025"> Chhanda Mukhopadhyay
PII:
S0926-860X(13)00144-0
DOI:
Reference:
http://dx.doi.org/doi:10.1016/j.apcata.2013.03.024
APCATA 14145
To appear in:
Applied Catalysis A: General
Received date:
Revised date:
Accepted date:
28-11-2012
14-2-2013
21-3-2013
Please cite this article as: S. Ray, P. Das, A. Bhaumik, A. Dutta, C. Mukhopadhyay,
Covalently anchored organic carboxylic acid on porous silica nano particle: a novel
organometallic catalyst (PSNP-CA) for the chromatography-free highly product
selective synthesis of tetrasubstituted imidazoles, Applied Catalysis A, General (2013),
http://dx.doi.org/10.1016/j.apcata.2013.03.024
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1
Research Highlights



 Organic template synthesis of porous silica nanoparticle
 Grafting of –COOH functionalized organosilane on silica nanoparticle
 Selective synthesis of tetrasubstituted imidazoles
Page 1 of 51

2
Covalently anchored organic carboxylic acid on porous silica nano
particle: a novel organometallic catalyst (PSNP-CA) for the
chromatography-free highly product selective synthesis of
tetrasubstituted imidazoles
a
a
b
b
a
Suman Ray , Paramita Das , Asim Bhaumik , Arghya Dutta , Chhanda Mukhopadhyay *
a: Department of Chemistry, University of Calcutta, 92 APC Road, Kolkata-700009, India, E-mail:
cmukhop@yahoo.co.in, Phone: 91-33-23371104
b: Department of Materials Science, Indian Association for the Cultivation of Science, Jadavpur, Kolkata 700 032,
India. E-mail: msab@iacs.res.in
Page 2 of 51

3
Covalently anchored organic carboxylic acid on porous silica nano
particle: a novel organometallic catalyst (PSNP-CA) for the
chromatography-free highly product selective synthesis of
tetrasubstituted imidazoles
a
a
b
b
a
Suman Ray , Paramita Das , Asim Bhaumik , Arghya Dutta , Chhanda Mukhopadhyay *
a: Department of Chemistry, University of Calcutta, 92 APC Road, Kolkata-700009, India, E-mail:
cmukhop@yahoo.co.in, Phone: 91-33-23371104
b: Department of Materials Science, Indian Association for the Cultivation of Science, Jadavpur, Kolkata 700 032,
India. E-mail: msab@iacs.res.in
Abstract: A novel organometallic catalyst (PSNP-CA) has been prepared by post synthesis grafting of –COOH
functionalized organosilane on porous silica nano particle by using surface hydroxyl groups as anchor point. It was
characterized by using an array of sophisticated analytical techniques like 13C CP MAS NMR, 29Si MAS NMR,
CHN analysis, BET, HR TEM, XRD, TGA, FTIR and pH measurement. The leaching of the active site is greatly
avoided as the organic moieties are covalently attached to the inorganic support. This is the first example of
organocatalysis promoted by a –COOH functionalized porous silica nano particle for the chemoselective synthesis
of densely substituted imidazoles. The molecular scaffolds which assimilate bio-active imidazole moiety may be
worthwhile molecule from the biological point of view. All the other reported procedures led to the mixture of tri
1
and tetra substituted imidazoles and their proportions were successfully evaluated from crude H NMR spectra.
Greenness of the process was well instituted as water was exploited as reaction medium. This catalyst retained its
activity after having it exposed to ambient atmosphere for 10 days. There was no deteriorating effect of aerial
oxygen or moisture towards the activity of the catalyst.
Kew words: Organometallic catalyst / post synthesis grafting / porous nanoparticle / product selective / imidazole
1. Introduction
Catalysis lies at the heart of countless chemical protocols. The presence of a catalyst is
mainly required by both modern organic syntheses, and in fine chemical industries [1]. The use
of heterogeneous catalysts in chemical processes would simplify catalyst removal and minimize
the amount of waste formed. However, a substantial decrease in the activity is frequently
observed due to the heterogeneous nature of the supports in reaction media, steric and diffusion
factors. A great proportion of active species are deep inside the supporting matrix and thus
reactants have limited access to catalytic sites [2, 3]. Porous silica nano particle (PSNP) [4-7]
represents some distinctive features like combination of micropores as well as interparticle
mesopores. Indeed, formations of these mesoporous structures are highly favoured as they have a
Page 3 of 51

4
high surface area and large pore [6]. As a result, PSNP offers easy accessibility of the organic
functions within the insoluble solid support. Therefore, PSNP is a very attractive choice for its
use as an insoluble solid support, particularly for liquid–solid phase catalytic reactions. When the
size of the material is decreased to the nanometer scale, the surface area of the NPs increase
dramatically. As a consequence, NPs could have a higher dispersion and greater catalyst loading
capacity than many conventional insoluble matrices, leading to an improved catalytic activity
[3]. Along with these affordable reasons, the deciding factor for solid support ends over the
PSNP. It is well known that smaller-sized silica particles have larger ratio of surface to volume
than large sized ones [8]. But, preparation of small, e.g. <100 nm, silica particle has seldom been
reported [8]. Methods for circumventing the above problems have been suggested by several
research groups [4, 9], such as utilizing functional amines as ‘‘bio”-catalysts, which reduce the
diameter to approximately 50 nm. However, even with the current method, synthesis of spherical
particles smaller than 50 nm remains difficult. Therefore, preparation of nanosized silica material
is a worth investigation.
The imidazole nucleus is a fertile source of biologically important
molecules [10] and is the core structural skeleton in many important biological molecules like
histidine, histamine, and biotin as well as several drug moieties [11,12] such as Trifenagrel,
Eprosartan, and Losartan. Recent development of green chemistry and organometallic chemistry
expands the utility of imidazoles as ionic liquids [13-15] and N-heterocyclic carbenes [13,
1
6,17]. It seems that the highly substituted imidazoles could have novel therapeutic activities
18]. Synthesis of 1,2,4,5-tetrasubstituted imidazoles have been carried out by four-component
condensation of a 1,2-diketone, α-hydroxyketone or α-ketomonoxime with an aldehyde, primary
amine and ammonium acetate using microwaves [18], heteropolyacid [19], BF .SiO [20], silica
gel/NaHSO [21] or HClO –SiO [22] and ionic liquids [23]. In addition, they can also be
[
3
2
4
4
2
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5
synthesized by the cycloaddition reaction of mesoionic 1,3-oxazolium-5-olates with N-
(arylmethylene) benzenesulfonamides [24], hetero-Cope rearrangement [25], condensation of a
1,2-diketone with an aryl nitrile and primaryamine under microwave irradiation [26]. However in
four-component condensation methods imidazoles could be obtained with varying levels of
purity. In addition, highly functionalized synthesis of polar imidazoles in solution requires
laborious work-up and purifications [18].
Inspired by these foregoing discussion and with given our interest and experience in the
area of heterogeneous catalysis in organic synthesis [27-31], we herein report the preparation of
a novel organometallic catalyst (PSNP-CA) by post synthesis grafting of –COOH functionalized
organosilane on porous silica nano particle of 20-25 nm size by using surface hydroxyl groups as
anchor point (Scheme 1).The nano silica particle had nanopores with average diameters of 1.0
nm. Grafting of functional organosilanes by using surface hydroxyl groups as anchor points has
been widely used. Furthermore the leaching of the active site can also be avoided as the organic
moieties are covalently attached to the inorganic support [32].
<
Scheme 1>
Albeit there are plentiful reports on grafting of –SO
3
H group [33-35] on silicas material,
immobilization of organic -COOH on silica is not a common practice. Although SBA-15
supported organic –COOH catalyst is recently reported by A. Bhaumik et.al. [36,37], to the best
of our knowledge there is no report of covalent anchoring of –COOH moiety on porous silica
nanoparticle. This is the first example of organocatalysis promoted by a –COOH functionalized
porous silica nano particle for the synthesis of 1,2,4,5-tetra substituted imidazole (8) in water
(scheme 2) at room temperature addressing the issue of competitive formation of 2,4,5-
trisubstituted imidazole (9) during the 4-MCR involving 1,2-diketone, aldehyde, amine,
Page 5 of 51

6
ammonium carbonate and highlights the influence of this catalyst system in controlling the
selective formation of tetrasubstituted imidazole. Therefore, it opens up a new direction for the
development of catalysts devoid of toxic metals and their further applications in various organic
transformations.
<Scheme 2>
2. Experimental
2.1. Materials and instrumentation
Chemicals were purchased from Aldrich, USA and Spectrochem, India and used without further
purification. TLC was done on glass sheets pre-coated with silica gel (with binder, 300 mesh,
1
13
Spectrochem). The H- and C-NMR analysis were carried out on Bruker-Advance Digital 300
MHz and 75.5 MHz instruments in CDCl and d -DMSO with TMS as an internal reference. The
3
6
chemical shifts were reported as δ values (ppm) relative to TMS. IR spectra were recorded in
KBr pellets in reflection mode on a Perkin Elmer RX-1 FTIR spectrophotometer. CHN analysis
was performed using a Perkin-Elmer 2400 Series II CHN analyzer. X-ray diffraction patterns of
the particle sample were obtained with a Seifert P3000 diffractometer using Cu Kα (λ = 0.15406
nm) radiation. Nitrogen adsorption/desorption isotherms were obtained using a Quantachrome
Autosorb 1C at 77 K. Prior to gas adsorption, all the samples were degassed for 2 h at 403 K.
Transmission electron microscopic images were recorded on a JEOL 2010 TEM operated at 200
kV in Indian Association for the Cultivation of Science, Jadavpur, Kolkata 700 032, India. A
Hitachi S-5200 field-emission scanning electron microscope was used for the determination of
the morphology of the particles. Carbon 13 CP MAS NMR and 29Si MAS NMR was referenced
with respect to external TMS using 7mm zirconia rotor and 2.5–3.5 kHz speed for more than 5 h,
scanning around 5000 scans in NMR Research Centre, IISc, Bangalore-560012.
Page 6 of 51

7
2.2. Preparation of PSNP
PSNP was prepared according to literature procedure reported elsewhere [4] with slight
modification. In a typical procedure, first, a mixed solution was prepared by dissolving 0.1 g
cetyltrimethylammonium bromide (CTAB) in 30 ml of aqueous solution at 60 °C in a three-
necked flask. After a clear solution was obtained, octane, styrene monomer, lysine, tetraethyl
orthosilicate (TEOS), and 2,2'-Azobis (2-methylpropionamide) dihydrochloride (AIBA) were
subsequently added to the system. The reaction was allowed to proceed for 5 h under an N
2
atmosphere at 60 °C. Then, the heating was stopped and the suspension was cooled to room
temperature. The cooled suspension was decanted for about 14 h and purified by centrifugation.
Ethanol was used to wash the centrifuged particle. Finally, the template was completely removed
2
by heat treatment at 800 °C under atmospheric conditions. The mass ratio of H O/TEOS/L-
lysine/CTAB was maintained at 310:8:0.22:1. 0.20 mg/ml of styrene monomer and 0.80 mg/ml
of AIBA were added to the solution.
2.3. Preparation of PSNP supported mercaptopropane (1)
The surface modification of the PSNP by post synthesis grafting method was achieved by
reacting the silanols of the PSNP with MPS (Aldrich) under nitrogen atmosphere. 20 mmol of
MPS was slowly added to a dry toluene solution containing 10 g of PSNP and refluxed for 18 h
under N
toluene and dichloromethane. Soxhlet extraction was carried out for 24 h in dichloromethane
DCM) to remove occluded organosilane. The sample was dried in vacuum for 10 h and
characterized by solid state 13C CP MAS NMR spectra and CHN analysis.
.4. Preparation of surface –CO H functionalized PSNP (3)
2
. The material was filtered after cooling to ambient temperature, washed with dry
(
2
2
Page 7 of 51

8
The surface –CO
2
H functionalized PSNP was prepared by reacting 5g of mercaptopropane
anchored on PSNP (1) with 10 mmol of 2-bromopropionic acid at room temperature. The
liberated HBr was removed through a CaCl drying tube under reduced pressure to a water trap.
Then it was kept in this condition for 1h at room temperature, washed successively with water
10 times), ethanol (3 times) and dried at 110°C for 3h. No precipitate was obtained on treatment
2
(
of silver nitrate solution with the aqueous extract of the solid after washing it ten times with
‒
distilled water. The aforesaid observation conclusively proved the absence of Br on the solid
catalyst after thorough washing with distilled water. The as prepared PSNP supported carboxylic
acid catalyst (3) was abbreviated as PSNP-CA.
2.5. preparation of 1,2,4,5-tetra substituted imidazoles (8)
All the reactions were carried out in a round bottom flask equipped with a magnetic stirrer. In a
typical reaction a mixture of 1,2-diketone (4) (1 mmol), aldehyde (5) (1 mmol), amine (6) (1
4 2 3
mmol), and (NH ) CO (7) (1 mmol) in water (2 ml) were stirred at room temperature till
completion using 10 mg of PSNP-CA (3) (Table 1). The completion of the reaction was
indicated by the disappearance of the starting material in thin layer chromatography. After
completion of the reaction the crude product was taken in ethylacetate and filtered to separate the
products as filtrate from the catalyst (residue). The solvent was evaporated in rotary evaporator
and the crude product was further purified by recrystallization from EtOAc/DCM. The products
1
13
were characterized by IR, H NMR, C NMR, CHN and X-ray single crystal analysis. The
spectral and analytical data of all 19 new compounds are given in this manuscript.
<
Table 1>
Given below is the X-ray single crystal analysis of 1-(3,4-dimethylphenyl)-2-(4-nitrophenyl)-
,5-diphenyl-1H-imidazole (8l) (CCDC 895387) (Figure 1).
4
Page 8 of 51

9
<
Figure 1>
2.6. Reuse of the PSNP-CA catalyst (3)
After crude product was taken in EtOAc and filtered to separate the products
from catalyst. The residue (catalyst) was washed with 15 mL MeOH, 15 ml DCM and then 15
mL diethyl ether. It was dried in vacuum and reused.
3
3
3
. Results and discussion
.1. Characterization of PSNP anchored –COOH (3)
.1.1. 13C CP MAS NMR spectra
The solid state carbon-13 CP MAS NMR spectrum of mercaptopropylsilica (1) (Figure 2, panel
a) showed peaks at δ 26.9 corresponding to (b, c) and at δ 10.7 for (a). The prepared PSNP
supported –COOH catalyst (3) was characterized by comparing the solid state carbon-13 CP
MAS NMR spectrum of the prepared catalyst (3) (panel b) with that of 1 and the normal solution
phase carbon-13 NMR spectrum of 2-bromopropionic acid (2). The normal solution phase
carbon-13 NMR spectrum of 2-bromopropionic acid (2) showed peaks corresponding to δ 21.2
(d), 39.3 (e), 176.3 (f). When the catalyst was prepared, the peak at δ 39.3 corresponding to (e) of
2-bromopropionic acid vanished and appeared at δ 34.1 as (e′). This indicates that bond
formation has taken place through carbon (e) and S atom. The remaining peaks for carbons
showed slight deviations and appeared at δ 11.3 for (a′), 23.0 and 26.7 for (b′, c′), 15.3 (d′), and
the –COOH carbon appeared at the same position at δ 177.6. This confirms the structure of the
prepared surface –COOH functionalized PSNP catalyst (3).
<
Figure 2>
2
9
3
.1.2. Si MAS NMR spectra
Page 9 of 51

1
0
2
9
The Si MAS NMR spectral pattern for PSNP supported carboxylic acid catalyst (PSNP-CA) is
2
3
shown in (Figure 3). Three up resonance peaks assigned to tetrahedral Q (-96 ppm), Q (-101
4
n
ppm) and Q (-111 ppm) silica species [38], respectively where Q = Si(OSi)
n
(OH)4-n, n = 2–4.
4
4
Again the high Q percentage indicated highly condensed network [39]. Such a high Q
concentration is of paramount importance for the catalytic activity of silica based catalyst, since
reduction of surface silanols introduces high hydrophobicity (and thus more affinity towards
organic substrates) [39]. The down field peaks at −58 ppm assigned to Si–OH of RSi(OSi)
2
(OH)
2
3
group (T ) and −66 ppm assigned to R-Si(OSi)
3
group (T ), which provides direct evidence that
the hybrid catalyst (3) consists of a highly condensed siloxane network with an organic group
covalently bonded to the silica gel as a part of the silica wall structure [38].
<
Figure 3>
3.1.3. CHN analysis
In addition to structural confirmation, quantitative determination of covalently anchored -COOH
group onto the surface of catalyst was performed by elemental analysis, ion-exchange pH
analysis and TGA. The elemental analysis of mercaptopropyl silica (1) showed the carbon and
hydrogen content to be 1.37% and 0.27% respectively [27,30]. From this 0.38 mmol/g loading of
the mercaptopropyl group on the silica surface is obtained. In the silica supported -COOH
catalyst (3) the carbon and hydrogen content was found to be 2.59%, and 0.40% respectively
which corresponds to a loading of 0.36 mmol/g. Therefore 95% conversion of the mercapto
group to the S-substituted carboxylic acid is achieved.
3.1.4. HR TEM image of PSNP-CA
Panel a (Figure 4) shows representative TEM image of the PSNP-CA. From this HR TEM
image it is clear that the silica nanoparticles of dimension 20-25 nm are self-aggregated
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1
1
throughout the specimen and in each porous silica nanoparticle randomly distributed micropores
white spots) of dimension ca. 1.0 nm are clearly visible. Therefore, the micropores as well as
(
interparticle mesopores of PSNP host material (panel b) is unaffected by surface modification
with -COOH.
<
Figure 4>
3.1.5 FE-SEM image of PSNP-CA
In the SEM image of PSNP-CA catalyst (Figure 5, panel a) silica nanoparticles of mostly
spherical dimension are quite visible. That they are self-aggregated throughout the specimen is
also evident from this SEM image. Therefore we can say that, the self-aggregated nature of the
parent silica nanoparticles (Figure 5, panel b) survived even after the modification with organic
functional group.
<
Figure 5>
3.1.6. Nitrogen adsorption analysis
Nitrogen adsorption isotherms were applied to investigate the porosity and specific surface area
of the as-synthesized PSNP-CA which suggested that the sample is mostly microporous (Figure
6, panel a). Adsorption/desorption isotherms are of type I corresponding to that of the
microporous materials [40]. Under relative low pressure, the slope of the curves was very small,
which indicated the existence of micropores. When the relative pressure was increased the slope
of the curves increased sharply. Also, hysteresis loops can be observed in the curve of the
sample, which was the evidence of the existence of interparticle mesopore [41]. We can find that
2
-1
2 -
the surface area of the PSNP-CA (302 m g ) decreases when compared to pure PSNP (739 m g
1
)
and pore volume also decreases (Table 2). It is expected for organic-functionalized porous
silica due to the occupation of large organic groups in the small pores, i.e. restricted access to the
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1
2
pores caused by organic functional group. Therefore, the organic acid functionality is grafted
compactly and securely inside the spherical pores while not fully occupying the total available
space, therefore still leaving room for N
distribution result (panel b) wide distribution of pores with peak pore dimension of ca. 1.0 nm.
Figure 6>
Table 2>
2
adsorption and molecular transport. NLDFT pore size
<
<
3.1.7. XRD patterns of the catalyst
In small angle XRD a very broad peak centered at 2.84 degrees of 2θ could originate due to the
formation of self-assembled porous nanoparticles (Figure 7, panel a). No crystalline impurity
was found in the wide angle XRD pattern (Figure 7, panel b).
<
Figure 7>
3.1.8. IR analysis
The chemical structure of PSNP-CA (3) was studied using FT-IR spectroscopy (Figure 8). When
the samples are prepared using the well-known method of KBr pellet, infrared data are useful
only to confirm the existence of the bonded species. Due to the low concentration of the organic
part of modifier on the surface, the intensity of the new bands attesting the presence of organic
–
1
groups is weak [27, 42]. Hardly we observe any differences in the 2800–3000 cm range, where
(C-H) vibrations of the -CH - groups are evidenced [27,42]. The strong and broad band in the
range 3500-3400 cm corresponds to the hydrogen bonded Si-OH groups and adsorbed water
27,43,44]. The thio-propyl groups which is attached to the silicon framework are identified by

2
–1
[
–
1
the methylene C-H stretching bands [27,43] at roughly 2940-2875 cm and another broad at
–
1
1
645 cm is also due to O-H vibration of adsorbed water [27,44]. The weak signal between
–
1
1
2
580-1450 is due to -CH - bending [27,44]. The band at 1222 cm corresponds to the vibration
Page 12 of 51

1
3
–
1
of Si-C bond [27,43] and the sharp features around 1092 cm indicated Si–O–Si stretching
vibrations [27,44]. The most convincing infra red data for the carboxylic acid moiety appeared at
–
1
1
738 cm is due to C=O stretching. These results showed that the silica surface has been
immobilized by covalent bonded organic molecules.
Figure 8>
<
3.1.9. UV-vis spectral analysis
The chemical structure of PSNP-CA (3) was also studied using UV-vis spectroscopy (Figure 9).
*
In the UV-vis spectra of PSNP-CA the peak near 213 nm may be assigned to n-π transition of –
COOH group.
<
Figure 9>
3.1.10. Thermo gravimetric analysis
For PSNP in the room temperature to 150°C interval, a first loss of 2.4% is attributed to
physisorbed water molecules released and a second loss of 2.9% from 150 to 600 °C is attributed
to the condensation of silanol groups bonded to the surface and the remaining water molecules
[27]. Different from PSNP, the silica supported carboxylic catalyst (3) presents an additional
5.29% weight loss, mainly attributed to the organic side arm (Figure 10). From this loss mass of
organic side arm a loading of 0.37 mmol/g is obtained, which is very close to that obtained from
elemental analysis [27].
<
Figure 10>
H
3
.1.11. Ion exchange p analysis
The amounts of acid groups after synthesis of PSNP-CA (3) catalyst was measured by means of
pH measurement. Ion-exchange capacities of the carboxylic acid group were determined using
aqueous solution of sodium chloride as exchange agents. In a typical experiment 1.0 g of the
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1
4
catalyst was added to 100 ml saturated solution of NaCl. The resulting suspension was allowed
to equilibrate for 48 h and then pH of the solution dropped to 4.44 since ion exchange occurred
between sodium ions and protons. From this ion-exchange pH analysis a loading of –COOH of
0
.36 mmol/g on silica surface was obtained which is in good agreement with the result obtained
from TGA and elemental analysis [27, 29, 30].
.2. Catalysis
3
During the 4-MCR involving 1,2-diketone, aldehyde, amine, and ammonia to form
tetrasubstituted imidazole (8) competitive formation of the trisubstituted imidazole (9) was found
to be a potential problem. Therefore, we focussed on this issue of the selectivity of formation of
the tetrasubstituted imidazoles. Proper choice of the catalyst was the critical aspect in controlling
the selectivity. Therefore, we disclose a convergent protocol for selective synthesis of
tetrasubstituted imidazole in eco-compatible solvent water at room temperature.
3.3. Plausible Mechanism
The attenuated acidity of PSNP-CA (3) was found to be crucial for this condensation reaction
but insufficient to affect the acid-sensitive moieties. The imine (10) was obtained through the
reaction between 5 and 6 in the presence of catalyst (3) at room temperature. This compound, on
4 2 3
stirring at room temperature with 1,2-diketone (4) and (NH ) CO (7) in water in the presence of
catalyst (3) afforded the products 8. Thus the intermediacy of 10 in this transformation is clearly
established. The mechanistic formulation was depicted in Scheme 3. The reaction commenced
through the acid catalyzed formation of imine (10) which underwent nucleophilic attack by
ammonia to give the in situ intermediate (11). An acid catalyzed condensation between this
intermediate (11) and diketone (4) produced another in situ intermediate (12) which on
subsequent aromatization produced the tetrasubstitutedimidazole (8) (Scheme 3). The imine (10)
Page 14 of 51

1
5
1
was the only isolable intermediate confirmed from the H NMR spectra of the isolated product
obtained by quenching the reaction after few minutes. The quenching was done by simply
removing the catalyst from the reaction mixture through filtration.
Another notable feature is that albeit the organic precursors like 1,2-diketone (4) and aldehyde
(5) are not soluble in water, they react very efficiently in aqueous medium affording
tetrasubstitutedimidazoles (8) in excellent yields. It can be explained by fact that organic
+
carboxylic acid can easily dissociate in water producing H ion which can protonate the lone
pairs of oxygen on 1,2-diketone (4) and aldehyde (5) resulting positively charged ionic species.
These ions are however soluble in water and thus the reaction in water becomes possible.
<
Scheme 3>
The competitive formation of trisubstituted imidazole (9) can be explained as the aldehyde
undergoes imine formation with ammonia [11, 13, 45] instead of aromatic or aliphatic amine to
afford intermediate 13. This imine (13) undergoes further reaction to produce trisubstituted
imidazole as shown in scheme 4.
<
Scheme 4>
3.4. Comparison of the efficacy of PSNP-CA (3) with other catalysts
We also envisioned that only PSNP-CA (3) drives selectivity towards 1,2,4,5-
tetrasubstituted imidazole (8). Thus, identifying the issue on the competitive formation of
trisubstituted imidazole (9) during the formation of tetrasubstituted imidazole inspired us to
reinvestigate the reported methods (Table 3). It was revealed that all of these reported procedures
led to the mixture of tri (9) and tetrasubstituted imidazole (8). Compared to these reported
catalysts the PSNP supported -COOH catalyst (3) afforded the best results with 100:0
selectivities of 8:9. All the other catalysts catalyzed the reaction albeit in poor selectivity towards
Page 15 of 51

1
6
tetrasubstituted imidazole (8). This comparison was vital to establish the efficacy, selectivity,
environment compatibility and broaden the applicability of the proposed process. Therefore, the
efficacy and superiority of PSNP-CA (3) with respect to other solid acid catalysts have thus been
firmly established. The evaluation tests of the catalyst (3) together with other reported catalysts
(Table 3) in the formation of 8c showed that with PSNP supported –COOH catalyst (3), though
the reaction was slow at room temperature, it allowed reproducibly a better selectivity than the
others.
<
Table 3>
3.5. Evaluation of chemoselectivity
The percentage of the two competitive products as presented in table 3 was evaluated from the
1
crude H NMR spectra. For this purpose two distinct NMR peaks were identified as satellite peak
for tri and tetra substituted imidazoles respectively. In the crude NMR spectra the concentration
1
of 8c was evaluated from the H integration of –CH
3
protons of aromatic amine (Figure 119,
indicated by green colour) and that of 9c from the integration of –NH proton (indicated by pink
colour) in crude 1H NMR spectra. The equation used to evaluate the selectivity of the catalysts
for tetrasubstituted imidazole (8) is represented as
Ctetra
x 100
%
Selectivity =
Ctetra + Ctri
Where, Ctetra and Ctri are concentration of 8 and 9 as determined from crude NMR mixture. One
such crude NMR spectra showing the proportions of 8c (59.4%) and 9c (40.6%) (Table 3, entry
4) is shown here for convenience (Figure 11).
<
Figure 11>
3.6. Origin of chemoselectivity:
Page 16 of 51

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7
Between the two competitive imine intermediates (10 and 13) as we discussed before,
intermediate 10 being more substituted and greater conjugated system is much more stable than
intermediate 13. Therefore, the imine 10 is produced abundantly in the reaction medium leading
to the selective formation of tetrasubstituted imidazole (8). However this is true only when the
reaction is carried out at room temperature where the reaction goes through the more stable
intermediate (10). At high temperature some trisubstituted imidazole is always formed through
the unstable imine (13). In most of the previously reported procedures there is no activation of
aldehyde and keto carbonyl group and the reaction requires either microwave or conventional
heating. Unlike the previously reported catalysts, in case of porous silica nano particle derived
catalyst (PSNP-CA) the carbonyl oxygen coordinates with the silanol [27, 29, 30] groups on
silica surface which increases the electrophilicity of the carbonyl carbon and thereby enables the
reaction to occur at room temperature (Scheme 2). Again the yield was very poor only with
porous silica nano particle which proves that carboxylic acid was essential for this condensation
reaction.
3.7. Monitoring the reaction progress
1
The progress of the reaction was thoroughly monitored by checking the H NMR spectra of the
crude reaction mixture. At any time there were only two detectable species, the imine (10) and
the final product (8). With the pass of time the integration of imine peaks gradually diminishes
1
and that of imidazole gradually intensified in the crude H NMR spectra. In order to draw a
concentration against time curve at any time we need to know concentration of these two species
and for this purpose two distinct NMR peaks were identified as satellite peak: the multiplate
between δ 6.73-6.76 (Figure 12, indicated with green colour) corresponding to two proton
integration was assigned to be the imidazole protons (8k) of aromatic amine moiety and the
Page 17 of 51

1
8
sharp singlet at about δ 8.49 (indicated with pink colour) corresponding to one proton integration
1
was assigned to be olefinic proton of the corresponding imine. The crude H NMR spectra taken
at t = 0.5h, 1h, 1.5h, 2h and 4h for the reaction forming 8k (Figure 12) and also the conversion-
time plot (Figure 13) are presented here for convenience.
<
<
Figure 12>
Figure 13>
3.8. Optimization of amount of catalyst
The reactions were carried out using different amounts of the catalyst and the optimum amount
has been determined, as presented in Table 4. Determination of this optimum amount to achieve
maximum yield was very essential to establish the efficacy and broaden the applicability of the
proposed process. For this purpose the reaction forming 8c was chosen as a test reaction.
<
Table 4>
3.9. General applicability of this protocol to accommodate a variety of substitution pattern
The broad tolerance for various aromatic substituents to the formation of 8 was
investigated (Table 1). The results showed that whether it is electron-donating or
electronwithdrawing substituents on the aromatic ring of precursors 5, the reaction could afford
the corresponding products (8) in good to excellent yields. Acid-sensitive heteroaryl aldehyde,
methoxy substituted aryl aldehyde and aliphatic aldehyde reacted very efficiently with no side
reaction. Electron withdrawing aromatic amine and aliphatic amine also reacted successfully to
afford compound (8). Encouraged by these successful efforts and aiming to demonstrate the
efficiency and generality of this catalyst, we fixed our recent attention to employ other benzil
derivatives in order to get some newly substituted compounds. Quite surprisingly for both
electron withdrawing and donating substituents on aromatic ring of benzil we isolated the
Page 18 of 51

1
9
corresponding compounds in excellent yields. Therefore, the present PSNP-CA (3) catalyzed
protocol has a general applicability accommodating a variety of substitution pattern.
3
3
.10. Recycling experiment
.10.1. Effect of aerial oxygen or moisture towards activity of the catalyst
°
In the presence of PSNP-CA (preheated at 100 C for 4 hours) the reaction between
benzil, 4-cyanobenzaldehyde, 3,4-dimethylaniline and ammonia occurred with 94% yield of 8c
without any formation of 9c or any other side-product. The same reaction in the presence of
PSNP-CA after having it exposed to ambient atmosphere for 10 days produced similar
observation. Obviously, there was no deteriorating effect of aerial oxygen, moisture and heat
towards activity of the catalyst. Therefore, the catalyst had the potential of efficient recycling.
3.10.2. Characterization of the recycled catalyst
The recycled catalyst could be used at least ten times without any further treatment
(Table 5). Detailed characterization of the catalyst after 5th run showed that it was unaffected
under the condition of the reaction. The XRD pattern of the recovered catalyst showed a broad
peak at 2.82° indicating that the self-assembled structure of porous silica nano material still
+
remained intact after recycling. The concentrations of the residual H on the recovered catalyst
after successive experiments were measured and furnished in Table 5. Extremely marginal loss
+
of H was observed. It implied that –CO
2
H moiety was tightly anchored with the silica surface
through a covalent linkage with the oxygen atoms of silanols.
Table 5>
<
It is worthy to mention that our synthesized carboxylic acid functionalized porous silica
nanoparticle (PSNP-CA) is very effective catalyst for this present transformation since it
contains an acidic –COOH group and imidazole formation is an acid catalyzed reaction. The
Page 19 of 51

2
0
presence of -COOH in the catalyst is proved by 13C CP MAS NMR spectra, CHN analysis, IR,
UV and pH measurement. The 29 Si MAS NMR and also the TGA analysis are very essential to
prove the presence of organic group on silica. Again it is highly dispersed in the reaction
medium since the organic group is functionalized on nano silica particle. TEM and SEM image
analysis were essential to measure the nano size of the silica particles. The porous silica
nanoparticle is a very good attractive solid support since they have very high surface area and
large pores. As a result PSNP can offer an easy accessibility of the organic functions within the
2
insoluble solid. The porosity of the material is determined by N adsorption analysis and small
angle XRD pattern. Therefore, all these characterizations were necessary to explain the role of
the catalyst in this present transformation.
4. Conclusion
Therefore, the present method utilized PSNP-CA as a chemically robust, recyclable, organic-
inorganic hybrid Bronsted acid catalyst for the product selective synthesis of tetrasubstituted
imidazole and related derivatives in water at room temperature. The key findings of high
significance described in this work are three-fold. The first one is that the size of the silica
nanoparticle can be arrested between 20-25 nm with a very high surface to volume ratio. The
second key finding in our work is that PSNP-CA enables “sensitive substances” to react under
experimental condition. The third finding in our work is that no trisubstituted imidazole was
formed in reaction affording very high selectivity for tetrasubstituted imidazole. Moreover, the
entire process was highly atom-efficient. So the present protocol minimizes the dispersal of the
harmful chemicals in the environment and maximizes the use of renewable resources. In this
light, this highly efficient catalytic process can also be considered as a green technology.
Spectral and analytical data of all the compounds are given below:
Page 20 of 51

2
1
1
-(3,4-dimethylphenyl)-2-(4-nitrophenyl)-4,5-diphenyl-1H-imidazole 8a (Table 1, entry1):
Yellow solid, mp 170-172°C (CH Cl + EtOAc, equal volumes); IR (KBr): 3434, 3042, 2923,
593, 1509, and 1333 cm ; H NMR (300 MHz, CDCl ) δ: 8.10 (d, J = 8.7 Hz, 2H, aromatic-H),
2
2
-1 1
1
7
7
2
1
1
3
.64 (d, J = 9.0 Hz, 2H, aromatic-H), 7.58 (dd, J = 8.1 Hz and J = 1.2 Hz, 2H, aromatic-H), 7.30-
.21 (m, 6H, aromatic-H), 7.19-7.13 (m, 2H, aromatic-H), 7.06 (d, J = 7.5 Hz, 1H, aromatic-H),
.25 (s, 3H, -CH
37.8, 136.4, 134.0, 133.7, 132,6, 131.0, 130.5, 130.0, 129.0, 128.9, 128.4, 128.3, 128.2, 127.3,
27.0, 125.4, 123.3, 19.7, 19.5; Anal. Calcd for C29 : C, 78.18; H, 5.20; N, 9.43. Found
13
3 3 3
), 2.15 (s, 3H, -CH ); C NMR (75 MHz, CDCl ) δ: 147.0, 144.1, 138.9, 138.1,
23 3 2
H N O
C, 78.18; H, 5.20; N, 9.43.
1
-(3,4-dimethylphenyl)-2-(3-nitrophenyl)-4,5-diphenyl-1H-imidazole 8b (Table 1, entry2):
Yellow solid, mp 180-182°C (CH Cl + EtOAc, equal volumes); IR (KBr): 3435, 3042,
923,1600, 1532, 1503, 1447, and 1344 cm ; H NMR (300 MHz, CDCl
2
2
-1 1
2
1
7
3
) δ: 8.21 (t, J = 1.8 Hz,
H, aromatic-H), 8.01(d, J = 10.2 Hz, 1H, aromatic-H), 7.77 (d, J = 8.1 Hz, 1H, aromatic-H),
.51 (dd, J = 8.4 Hz and J = 1.5 Hz, 2H, aromatic-H), 7.34 (t, J = 7.8, 1H, aromatic-H), 7.22-7.07
(
m, 6H, aromatic-H), 6.98 (d, J = 7.8 Hz, 1H), 6.79-6.73 (m, 2H, aromatic-H), 2.16 (s, 3H, -
13
3 3 3
CH ), 2.07 (s, 3H, -CH ); C NMR (75 MHz, CDCl ) δ: 148.0, 144.1, 138.4, 138.2, 137.8,
1
1
7
34.3, 133.9, 133.7, 132.0, 131.9, 131.0, 130.5, 130.1, 129.0, 128.4, 128.2, 127.3, 126.9, 125.4,
23.3, 122.7, 19.6, 19.5; Anal. Calcd for C29
8.18; H, 5.20; N, 9.43.
23 3 2
H N O : C, 78.18; H, 5.20; N, 9.43. Found C,
4
-(1-(3,4-dimethylphenyl)-4,5-diphenyl-1H-imidazol-2-yl)benzonitrile 8c (Table 1, entry 3):
Cl + EtOAc, equal volumes); IR (KBr): 3432, 3038, 2923,
222, 1603, 1488, and 1439 cm ; H NMR (300 MHz, CDCl ) δ: 7.60-7.50 (m, 6H, aromatic-
H), 7.28-7.13 (m, 8H, aromatic-H), 7.05 (d, J = 7.8 Hz, 1H, aromatic-H), 6.82-6.79 (m, 2H,
White solid, mp 170-172°C (CH
2
2
2
-
1 1
3
1
3
aromatic-H), 2.24 (s, 3H, -CH
3
), 2.14 (s, 3H, -CH
3 3
); C NMR (75 MHz, CDCl ) δ: 144.4, 138.8,
1
1
9
37.9, 137.5, 134.8, 134.1, 134.0, 132.2, 131.7, 131.0, 130.3, 130.1, 128.9, 128.7, 128.3, 128.1,
27.2, 126.8, 125.4, 118.6, 111.2, 19.6, 19.4; Anal. Calcd for C30
.87. Found C, 84.68; H, 5.45; N, 9.87.
23 3
H N : C, 84.68; H, 5.45; N,
2-(4-methoxyphenyl)-4,5-diphenyl-1-p-tolyl-1H-imidazole 8d (Table 1, entry 4): White solid,
mp 176-178°C (CH
2
Cl + EtOAc, equal volumes); IR (KBr): 3434, 3034, 2929, 1605, 1480,
2
-1 1
1439, 1371, and 1251 cm ; H NMR (300 MHz, CDCl
3
) δ: 7.59 (d, J = 7.2 Hz, 2H, aromatic-H),
7.38 (d, J = 8.7 Hz, 2H, aromatic-H), 7.26-7.14 (m, 6H, aromatic-H), 7.11-7.08 (m, 2H,
aromatic-H), 7.03 (d, J = 8.1 Hz, 2H, aromatic-H), 6.89 (d, J = 8.4 Hz, 2H, aromatic-H), 6.76 (d,
1
3
J = 9.0 Hz, 2H, aromatic-H), 3.75 (s, 3H, -OCH
CDCl ) δ: 159.8, 146.8, 138.3, 134.3, 131.2, 130.5, 129.7, 128.3, 128.1, 128.0, 127.5, 126.7,
13.6, 55.2, 21.1; Anal. Calcd for C29 O: C, 83.63; H, 5.81; N, 6.73. Found C, 83.63; H,
.81; N, 6.73.
3 3
), 2.29 (s, 3H, -CH ); C NMR (75 MHz,
3
1
5
24 2
H N
2-(3-nitrophenyl)-4,5-diphenyl-1-m-tolyl-1H-imidazole 8e (Table 1, entry 5): Yellow solid,
mp 154-156°C (CH
2
Cl + EtOAc, equal volumes); IR (KBr): 3435, 3042, 2923,1600, 1532,
2
-1 1
1
8
7
2
3
503, 1447, and 1344 cm ; H NMR (300 MHz, CDCl ) δ: 8.28 (s, 1H, aromatic-H), 8.11 (d, J =
.1 Hz, 1H, aromatic-H), 7.89 (d, J = 7.8 Hz, 1H, aromatic-H), 7.61 (d, J = 6.9 Hz, aromatic-H),
.44 (t, J = 8.1 Hz, aromatic-H), 7.30-7.15 (m, 10H, aromatic-H), 6.92-6.90 (m, 2H, aromatic-H),
13
3 3
.25 (s, 3H, -CH ); C NMR (75 MHz, CDCl ) δ: 148.1, 144.1, 139.8, 138.4, 136.3, 134.4,
Page 21 of 51

2
2
1
1
4
33.6, 132.0, 131.8, 131.1, 129.9, 129.3, 129.1, 128.8, 128.5, 128.4, 128.3, 127.4, 127.1, 125.4,
23.4, 122.9, 21.2; Anal. Calcd for C28
.91; N, 9.74.
21 3 2
H N O : C, 77.94; H, 4.91; N, 9.74. Found C, 77.94; H,
2-(4-bromophenyl)-1-(4-methoxyphenyl)-4,5-diphenyl-1H-imidazole 8f (Table 1, entry 6):
White solid, mp 178-180°C (CH
3
831, 1599, 1507, 1444, and 1246 cm ; H NMR (300 MHz, CDCl ) δ: 7.64 (d, J = 7.5 Hz, 2H,
2
Cl + EtOAc, equal volumes); IR (KBr): 3432, 3049, 2951,
2
-1 1
2
aromatic-H), 7.43-7.40 (m, 4H, aromatic-H), 7.35-7.24 (m, 6H, aromatic-H), 7.14-7.11 (m, 2H,
aromatic-H), 6.97 (d, J = 9.0 Hz, 2H, aromatic-H), 6.80 (d, J = 8.7 Hz, 2H, aromatic-H), 3.79 (s,
1
3
3
1
H, -OCH
31.0, 130.5, 130.3, 129.3, 129.0, 128.4, 128.3, 128.1, 127.4, 126.8, 122.7, 114.5, 55.3; Anal.
O: C, 69.86; H, 4.40; N, 5.82. Found C, 69.86; H, 4.40; N, 5.82.
3 3
); C NMR (75 MHz, CDCl ) δ: 159.3, 145.7, 137.9, 133.8, 131.4, 131.3, 131.1,
Calcd for C28H21BrN
2
1
-(3-methoxyphenyl)-2-(3-nitrophenyl)-4,5-diphenyl-1H-imidazole 8g (Table 1, entry 7):
Yellow solid, mp 198-200°C (CH Cl + EtOAc, equal volumes); IR (KBr): 3434, 3040,
923,1600, 1532, 1503, 1441, and 1341 cm ; H NMR (300 MHz, D
aromatic-H), 8.11 (d, J = 8.1 Hz, 1H, aromatic-H), 7.76 (d, J = 7.2 Hz, 1H, aromatic-H), 7.58-
.47 (m, 4H, aromatic-H), 7.29-7.16 (m, 8H, aromatic-H), 6.97-6.85 (m, 3H, aromatic-H), 3.59
2
2
-1 1
2
6
-DMSO) δ: 8.23 (s, 1H,
7
13
(s, 3H, -OCH
3
); C NMR (75 MHz, D
6
-DMSO) δ: 159.8, 147.7, 143.6, 137.4, 137.3, 134.1,
1
1
7
33.9, 132.2, 131.8, 131.2, 130.3, 130.1, 130.0, 128.7, 128.6, 128.3, 126.8, 126.5, 122.9, 122.4,
20.8, 115.0, 114.6, 55.5; Anal. Calcd for C28
5.15; H, 4.73; N, 9.39.
21 3 3
H N O : C, 75.15; H, 4.73; N, 9.39. Found C,
4
-(4,5-diphenyl-1-p-tolyl-1H-imidazol-2-yl)benzonitrile 8h (Table 1, entry 8): White solid,
Cl + EtOAc, equal volumes); IR (KBr): 3432, 3038, 2224, 1603, 1488, and
439 cm ; H NMR (300 MHz, CDCl ) δ: 7.51-7.42 (m, 5H, aromatic-H), 7.22-7.00 (m, 11H,
aromatic-H), 6.86 (d, J = 8.1 Hz, 2H, aromatic-H), 2.27 (s, 3H, -CH
CDCl ) δ: 144.6, 138.9, 134.8, 134.0, 132.4, 132.2, 131.8, 131.0, 130.1, 129.9, 128.9, 128.7,
28.4, 128.2, 127.9, 127.2, 126.8, 120.9, 118.6, 111.3, 21.1; Anal. Calcd for C29 : C, 84.64;
H, 5.14; N, 10.21. Found C, 84.64; H, 5.14; N, 10.21.
mp 170-172°C (CH
1
2
2
-
1 1
3
1
3
3
); C NMR (75 MHz,
3
1
21 3
H N
2
9
1
7
-(4-methoxyphenyl)-1-(3,4-dimethylphenyl)-4,5-diphenyl-1H-imidazole 8i (Table 1, entry
): White solid, mp 180-182°C (CH Cl + EtOAc, equal volumes); IR (KBr): 3433, 3025, 2921,
595, 1495, and 1447 cm ; H NMR (300 MHz, CDCl ) δ: 7.59 (d, J = 7.2 Hz, 2H, aromatic-H),
.38 (d, J = 8.7 Hz, 2H, aromatic-H), 7.28-7.13 (m, 6H, aromatic-H), 7.06-7.03 (m, 2H,
2
2
-1 1
3
aromatic-H), 6.82-6.79 (m, 2H, aromatic-H), 6.66 (d, J = 9.0 Hz, 2H, aromatic-H), 3.75 (s, 3H, -
1
3
OCH
38.3, 134.3, 131.2, 130.5, 129.7, 128.3, 128.1, 128.0, 127.5, 126.7, 113.6, 55.2, 19.8, 19.6;Anal.
Calcd for C30 O: C, 83.69; H, 6.09; N, 6.51. Found C, 83.69; H, 6.09; N, 6.51.
3 3 3 3
), 2.24 (s, 3H, -CH ), 2.14 (s, 3H, -CH ); C NMR (75 MHz, CDCl ) δ: 160.1, 147.5,
1
26 2
H N
4
,5-bis(4-chlorophenyl)-1-(3,4-dimethylphenyl)-2-(4-nitrophenyl)-1H-imidazole 8j (Table 1,
entry 10): Yellow solid, mp 158-160°C (CH Cl + EtOAc, equal volumes); IR (KBr): 3435,
026, 2919, 1595, 1495, and 1446 cm ; H NMR (300 MHz, CDCl ) δ: 8.23 (d, J = 9.0 Hz, 2H,
aromatic-H), 7.84 (d, J = 8.7 Hz, 2H, aromatic-H), 7.47 (d, J = 8.4 Hz, 2H, aromatic-H), 7.41-
2
2
-1 1
3
3
1
3
7
1
.09 (m, 9H, aromatic-H), 5.13 (s, 2H, -CH
37.0, 136.6, 136.4, 134.2, 132.7, 132.6, 131.4, 130.8, 129.8, 129.5, 129.3, 128,9, 128.7, 128.6,
2 3
); C NMR (75 MHz, CDCl ) δ: 147.3, 145.4,
Page 22 of 51

2
3
1
8
28.4, 127.9, 127.5, 125.9, 123.7, 48.2; Anal. Calcd for C28
.40. Found C, 67.21; H, 3.83; N, 8.40.
2 3 2
H19Cl N O : C, 67.21; H, 3.83; N,
4
1
3
,5-bis(4-chlorophenyl)-1-(3,4-dimethylphenyl)-2-(4-nitrophenyl)-1H-imidazole 8k (Table
, entry11): Yellow solid, mp 196-198°C (CH Cl + EtOAc, equal volumes); IR (KBr): 3434,
022, 2919, 1600, 1495, and 1446 cm ; H NMR (300 MHz, CDCl ) δ: 8.03 (d, J = 9.0 Hz, 2H,
2
2
-1 1
3
aromatic-H), 7.54 (d, J = 8.7 Hz, 2H, aromatic-H), 7.42 (d, J = 8.4 Hz, 2H, aromatic-H), 7.20-
.16 (m, 4H, aromatic-H), 7.04-6.97 (m, 3H, aromatic-H), 6.76-6.73 (m, 2H, aromatic-H), 2.21
7
13
(s, 3H, -CH
3
), 2.10 (s, 3H, -CH
3 3
); C NMR (75 MHz, CDCl ) δ: 147.2, 144.7, 138.5, 138.4,
1
1
4
38.2, 136.2, 134.7, 133.8, 133.0, 132.2, 131.4, 130.8, 130.5, 129.0, 128.9, 128.6, 128.3, 125.4,
23.4, 19.8, 19.6; Anal. Calcd for C29
.11; N, 8.17.
2 3 2
H21Cl N O : C, 67.71; H, 4.11; N, 8.17. Found C, 67.71; H,
4
,5-bis(4-chlorophenyl)-1-(3,4-dimethylphenyl)-2-(3-nitrophenyl)-1H-imidazole 8l (Table 1,
Cl + EtOAc, equal volumes); IR (KBr): 3435,
026, 2919, 1595, 1495, and 1446 cm ; H NMR (300 MHz, CDCl ) δ: 8.15 (s, 1H), 8.07 (d, J =
entry12): Yellow solid, mp 192-194°C (CH
2
2
-1 1
3
9
7
3
.0 Hz, 1H, aromatic-H), 7.95-7.88 (m, 1H, aromatic-H), 7.47-7.34 (m, 4H, aromatic-H), 7.21-
.16 (m, 4H, aromatic-H), 7.05-6.99 (m, 3H, aromatic-H), 6.79-6.75 (m, 2H, aromatic-H), 2.19
13
(
1
1
s, 3H, -CH
3
), 2.10 (s, 3H, -CH
37.8, 134.3, 133.9, 133.7, 132.0, 131.9, 131.0, 130.5, 130.1, 129.0, 128.4, 128.2, 127.3, 126.9,
25.4, 123.3, 122.7, 19.6, 19.5; Anal. Calcd for C29 : C, 67.71; H, 4.11; N, 8.17.
3 3
); C NMR (75 MHz, CDCl ) δ: 148.0, 144.1, 138.4, 138.2,
H
2 3 2
21Cl N O
Found C, 67.71; H, 4.11; N, 8.17.
1
-(3,4-dimethylphenyl)-2-(4-nitrophenyl)-4,5-dip-tolyl-1H-imidazole 8m (Table 1, entry13):
Yellow solid, mp 180-182°C (CH Cl + EtOAc, equal volumes); IR (KBr): 3434, 3042, 2923,
593, 1509, and 1333 cm ; H NMR (300 MHz, CDCl ) δ: 8.01 (d, J = 7.8 Hz, 2H, aromatic-H),
2
2
-1 1
1
3
7.57-7.53 (m, 3H, aromatic-H), 7.34 (d, J = 8.1 Hz, 1H, aromatic-H), 7.18 (s, 1H, aromatic-H),
7.14-7.10 (m, 1H, aromatic-H), 7.04-6.94 (m, 5H, aromatic-H), 6.79-6.73 (m, 2H, aromatic-H),
2
CH
.49-2.47 (m, 3H, -CH
3
), 2.26-2.24 (m, 3H, -CH
3 3
), 2.10-2.18 (m, 3H, -CH ), 2.11-2.08 (m, 3H, -
1
3
3
); C NMR (75 MHz, CDCl ) δ: 149.4, 147.2, 147.1, 144.9, 144.4, 138.8, 138.7, 138.4,
3
1
1
38.2, 137.9, 137.2, 136.7, 136.3, 135.3, 133.9, 133.7, 133.6, 133.3, 132.9, 132.5, 131.3, 130.8,
30.6, 129.4, 129.2, 128.9, 127.4, 126.8, 126.3, 125.4, 123.4, 122.8, 21.3, 21.2, 19.7, 19.5; Anal.
27 3 2
Calcd for C31H N O : C, 78.62; H, 5.75; N, 8.87. Found C, 78.62; H, 5.75; N, 8.87.
1
1
1
7
2
1
-cyclohexyl-4,5-diphenyl-2-propyl-1H-imidazole 8n (Table 1, entry 14): White solid, mp
74-176°C (CH Cl + EtOAc, equal volumes); IR (KBr): 3434, 2931, 2850, 1606, 1502, 1449,
376, 1291, and 1245 cm ; H NMR (300 MHz, CDCl
.11 (m, 3H, aromatic-H), 3.84 (br s, 1H), 2.90 (t, J = 8.1 Hz), 2.00-1.82 (m, 7H), 1.68-1.64 (m,
2
2
-
1 1
3
) δ: 7.49-7.36 (m, 7H, aromatic-H), 7.21-
13
H), 1.25-1.15 (m, 6H); C NMR (75 MHz, CDCl
28.6, 128,4, 128.3, 128.1, 126.8, 126.5, 125.7, 55.6, 32.8, 30.9, 26.2, 25.1, 22.3, 14.9, 14.1;
: C, 83.68; H, 8.19; N, 8.13. Found C, 83.68; H, 8.19; N, 8.13.
3
) δ: 147.5, 136.1, 134.7, 132.4, 131.7, 129.5,
28 2
Anal. Calcd for C24H N
2
-(4-bromophenyl)-1-cyclohexyl-4,5-diphenyl-1H-imidazole 8o (Table 1, entry 15): White
solid, mp 180-182°C (CH Cl + EtOAc, equal volumes); IR (KBr): 3434, 2934, 2850, 1606,
5020, 1449, 1376, 1291, and 1246 cm ; H NMR (300 MHz, CDCl
aromatic-H), 7.51-7.39 (m, 7H, aromatic-H), 7.17-7.06 (m, 3H, aromatic-H), 3.98-3.89 (m, 1H),
2
2
-1 1
1
3
) δ: 7.62 (d, J = 8.4 Hz, 2H,
Page 23 of 51

2
4
1
3
1
.84-1.80 (m, 2H), 1.65-1.43 (m, 5H), 1.09-0.96 (m, 2H), 0.80-0.55 (m, 1H); C NMR (75
MHz, CDCl ) δ: 146.1, 137.2, 133.3, 132.0, 131.6, 130.2, 129.4, 129.1, 128.7, 128.0, 126.8,
26.5, 123.7, 58.7, 33.5, 26.1, 24.9; Anal. Calcd for C27 : C, 70.90; H, 5.51; N, 6.12.
Found C, 70.90; H, 5.51; 6.12.
3
1
H25BrN
2
1
-cyclohexyl-2-(4-methoxyphenyl)-4,5-diphenyl-1H-imidazole 8p (Table 1, entry 16): White
solid, mp 194-196°C (CH Cl + EtOAc, equal volumes); IR (KBr): 3434, 2930, 2851, 1606,
5060, 1441, 1376, 1291, and 1245 cm ; H NMR (300 MHz, CDCl
aromatic-H), 7.48-7.43 (m, 7H, aromatic-H), 7.17-7.08 (m, 3H, aromatic-H), 7.01 (d, J = 8.7 Hz,
2
2
-1 1
1
3
) δ: 7.55 (d, J = 8.1 Hz, 2H,
2
1
1
3
6
H, aromatic-H), 4.01-3.96 (m, 1H), 3.87 (s, 3H, -OCH
3
), 1.85-1.81 (m, 2H), 1.65-1.43 (m, 5H),
.12-0.96 (m, 2H), 0.82-0.68 (m, 1H); C NMR (75 MHz, CDCl ) δ: 160.1, 147.4, 137.1, 134.2,
32.3, 132.0, 131.4, 131.2, 128.9, 128.7, 127.8, 126.7, 126.6, 126.0, 124.2, 113.7, 58.3, 55.2,
1
3
3
3.5, 26.1, 25.0; Anal. Calcd for C28
.91; N, 6.86.
28 2
H N O: C, 82.32; H, 6.91; N, 6.86. Found C, 82.32; H,
4
-(4,5-bis(4-chlorophenyl)-1-(3,4-dimethylphenyl)-1H-imidazol-2-yl)pyridine 8q (Table 1,
Cl + EtOAc, equal volumes); IR (KBr): 3434, 3022,
919, 1600, 1495, and 1446 cm ; H NMR (300 MHz, D -DMSO) δ: 8.54 (d, J = 4.5 Hz, 2H,
aromatic-H), 7.42 (d, J = 8.4 Hz, 2H, aromatic-H), 7.20-7.13 (m, 6H, aromatic-H), 7.04-6.97 (m,
H, aromatic-H), 6.76-6.73 (m, 2H, aromatic-H), 2.21 (s, 3H, -CH ), 2.10 (s, 3H, -CH ); Anal.
: C, 71.49; H, 4.50; Cl, 15.07; N, 8.93. Found C, 71.49; H, 4.50; Cl, 15.07;
entry17): Red solid, mp 179-181°C (CH
2
2
2
-1 1
6
3
3
3
Calcd for C28
N, 8.93.
2 3
H21Cl N
1
1
1
,2-bis(3-nitrophenyl)-4,5-diphenyl-1H-imidazole 8r (Table 1, entry18): Yellow solid, mp
80-182°C (CH Cl + EtOAc, equal volumes); IR (KBr): 3434, 3042, 2923, 1593, 1509, and
333 cm ; H NMR (300 MHz, CDCl ) δ: 8.25-8.12 (m, 4H, aromatic-H), 7.80-7.42 (m, 7H,
2
2
-1 1
3
1
3
aromatic-H), 7.29-7.17 (m, 7H, aromatic-H); C NMR (75 MHz, CDCl
3
) δ: 148.0, 147.8, 144.2,
1
1
3
37.6, 137.3, 135.6, 134.4, 133.9, 132.1, 131.4, 131.3, 131.0, 130.2, 129.7, 129.1, 128.9, 128.6,
28.4, 127.3, 127.0, 126.5, 124.1, 123.9, 128.3, 123.1; Anal. Calcd for C27
.92; N, 12.12. Found C, 70.12; H, 3.92; N, 12.12.
18 4 4
H N O : C, 70.12; H,
1-(3,4-dimethylphenyl)-2-(4-chlorophenyl)-4,5-diphenyl-1H-imidazole
8s
(Table
1,
entry19): Yellow solid, mp 170-172°C (CH
3
2
Cl
042, 2923, 1593, 1509, and 1333 cm ; H NMR (300 MHz, CDCl
aromatic-H), 7.27 (d, J = 8.4 Hz, 2H, aromatic-H), 7.18-7.03 (m, 10H, aromatic-H), 6.90 (d, J =
2
+ EtOAc, equal volumes); IR (KBr): 3434,
-1 1
3
) δ: 7.47 (d, J = 7.8 Hz, 2H,
7
.8 Hz, 1H, aromatic-H), 6.69-6.65 (m, 2H, aromatic-H), 2.12 (s, 3H, -CH
3
), 2.02 (s, 3H, -CH
) δ: 149.7, 138.3, 137.6, 137.0, 134.4, 134.1, 131.3, 131.1, 130.6,
30.2, 129.9, 129.2, 129.1, 128.7, 128.4, 128.2, 128.1, 127.9, 127.3, 126.8, 126.6, 125.5, 19.6,
9.4; Anal. Calcd for C29 : C, 80.08; H, 5.33; N, 6.44. Found C, 80.34; H, 5.33; N, 6.61.
3
);
1
3
C NMR (75 MHz, CDCl
3
1
1
H23ClN
2
Acknowledgements
We acknowledge UGC for financial support (F. No. 37-398 / 2009 (SR) dated 11-01-2010),
CSIR for fellowship (SR) and NMR Research Centre, IISc, Bangalore-560012 for the solid state
Page 24 of 51

2
5
13C CP MAS and 29Si MAS NMR spectrum.
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Figure Captions
2
Scheme 1. Preparation of surface –CO H functionalized PSNP.
Scheme 2. Chemoselective synthesis of tetrasubstituted imidazole.
Scheme 3. Plausible mechanism for tetrasubstituted imidazole (8).
Scheme 4. Plausible mechanism for trisubstituted imidazole (9).
Figure 1. X-ray single crystal structure of 8l (CCDC 895387).
Figure 2. Carbon 13 CP MAS NMR spectra of (a) mercaptopropane functionalized PSNP (1),
and (b) PSNP-CA (3).
Figure 3. 29 Si MAS NMR spectra of PSNP-CA (3).
Figure 4. HRTEM image of (a) PSNP-CA, and (b) PSNP material.
Figure 5. FESEM image of (a) PSNP-CA, and (b) PSNP material.
2
Figure 6. (a) N adsorption isotherm, (b) pore size distribution of PSNP-CA (3).
Figure 7. (a) Small angle XRD pattern, (b) wide angle XRD pattern of PSNP-CA (3).
Figure 8. FTIR spectra of PSNP-CA (3).
Figure 9. UV-vis spectra of PSNP-CA (3).
Figure 10. TGA diagram of PSNP-CA (3) under nitrogen stream.
Figure 11. Crude NMR spectra showing the proportion of 8c and 9c.
1
Figure 12. Crude H NMR spectra taken at different time for the reaction forming 8k.
Figure 13. Effect of time on the yield of 8k.
Table 1. PSNP-CA catalyzed efficient protocol for chemoselective synthesis of 1,2,4,5-
a
tetrasubstituted imidazole.
Table 2. Dependence of porosity on catalyst loadings.
a
Table 3. Performance of other catalysts on the said reaction.
Page 28 of 51

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9
a
Table 4. Optimization of catalyst loading.
Table 5. Recycling experiment
Page 29 of 51