Design, characterization and application of silica-bonded imidazolium-sulfonic acid chloride as a novel, active and efficient nanostructured catalyst in the synthesis of hexahydroquinolines

Article abstract of DOI:10.1016/j.apcata.2015.08.004

Abstract novel nanostructured catalyst namely silica-bonded imidazolium-sulfonic acid chloride (SBISAC) was prepared, and fully characterized by several techniques including Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), thermal gravimetric analysis (TGA), differential thermal gravimetric (DTG), scanning electron microscope (SEM), transmission electron microscopy (TEM) and energy dispersive X-ray analysis (EDX). The nano-compound was applied as an efficient and heterogeneous catalyst in the synthesis of hexahydroquinolines via the one-pot multi-component condensation of arylaldehydes with dimedone (5,5-dimethylcyclohexane-1,3-dione), β-ketoesters and ammonium acetate under mild and solvent-free conditions.

Full text of DOI:10.1016/j.apcata.2015.08.004

Accepted Manuscript
Title: Design, characterization and application of
silica-bonded imidazolium-sulfonic acid chloride as a novel,
active and efficient nanostructured catalyst in the synthesis of
hexahydroquinolines
Author: Ahmad Reza Moosavi-Zare Mohammad Ali Zolfigol
Mahmoud Zarei Abdolkarim Zare Javad Afsar
PII:
S0926-860X(15)30099-5
DOI:
Reference:
http://dx.doi.org/doi:10.1016/j.apcata.2015.08.004
APCATA 15498
To appear in:
Applied Catalysis A: General
Received date:
Revised date:
Accepted date:
10-4-2015
21-7-2015
3-8-2015
Please cite this article as: Ahmad Reza Moosavi-Zare, Mohammad Ali Zolfigol,
Mahmoud Zarei, Abdolkarim Zare, Javad Afsar, Design, characterization and
application of silica-bonded imidazolium-sulfonic acid chloride as a novel, active
and efficient nanostructured catalyst in the synthesis of hexahydroquinolines, Applied
Catalysis A, General http://dx.doi.org/10.1016/j.apcata.2015.08.004
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Design, characterization and application of silica-bonded
imidazolium-sulfonic acid chloride as a novel, active and efficient
nanostructured catalyst in the synthesis of hexahydroquinolines
Ahmad Reza Moosavi-Zare,*a Mohammad Ali Zolfigol,*b Mahmoud Zarei,b Abdolkarim Zarec
and Javad Afsarb
aUniversity of Sayyed Jamaleddin Asadabadi, Asadabad, 6541835583, Iran
bFaculty of Chemistry, Bu-Ali Sina University, Hamedan 6517838683, Iran
cDepartment of Chemistry, Payame Noor University, PO BOX 19395-4697, Tehran, Iran
*Corresponding author. Fax: +988118257407, E-mail addresses: moosavizare@yahoo.com,
mzolfigol@yahoo.com.
Graphical abstract
Synthesis and characterization of silica-bonded imidazolium-sulfonic acid chloride as an active
and novel nanostructured heterogeneous catalyst
fx1
Highlights

Design of silica-bonded imidazolium-sulfonic acid chloride (SBISAC) as heterogeneous
nano catalyst.


Characterization of silica-bonded imidazolium-sulfonic acid chloride (SBISAC).
Application of SBISAC in the synthesis of hexahydroquinolines derivatives.
Abstract: A novel nanostructured catalyst namely silica-bonded imidazolium-sulfonic acid
chloride (SBISAC) was prepared, and fully characterized by several techniques including Fourier
transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), thermal gravimetric analysis
1

(TGA), differential thermal gravimetric (DTG), scanning electron microscope (SEM),
transmission electron microscopy (TEM) and energy dispersive X-ray analysis (EDX). The
nano-compound was applied as an efficient and heterogeneous catalyst in the synthesis of
hexahydroquinolines via the one-pot multi-component condensation of arylaldehydes with
dimedone (5,5-dimethylcyclohexane-1,3-dione), β-ketoesters and ammonium acetate under mild
and solvent-free conditions.
Keywords: silica-bonded imidazolium-sulfonic acid chloride (SBISAC), heterogeneous catalyst,
hexahydroquinoline, multi-component reaction.
1. Introduction
Multi-component reactions (MCRs) play a significant role in combinatorial chemistry due to the
ability to prepare target compounds with greater efficiency and atom economy by generating
structural complexity in a single step from three or more reactants. Additionally, MCRs offer
some advantages such as simplicity and synthetic efficiency over conventional chemical
reactions [1-5].
Improvement on the multi-component synthesis of dihydropyridine (DHP) ring, including the
use of hetero atoms or change substituents could not only result in decreased photosensitivity of
these compounds, but also could enrich the diversity of DHPs chemistry, and improve structure-
activity relationship bearing novel aspects into the molecular interactions [6,7]. Moreover,
structural modification on DHP periphery could follow in significant influence in their
pharmacological properties [8-9]. One of the important categories of DHPs with a modified
structural scaffold, is hexahydroquinolines (HHQs) which could be synthesized through the one-
pot four-component condencation reaction between aromatic aldehydes, dimedone (5,5-
dimethylcyclohexane-1,3-dione), β-ketoesters and ammonium acetate (Hantzsch synthesis) using
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various catalysts such as FeF3 [10], K7[PW11CoO40] [11a], PPA-SiO2 [11b] and HClO4-SiO2
[11c]. Moreover, some other methods and catalysts have been introduced for the preparation of
HHQs [12-23]. Quinolines which have a 1,4-dihydropyridine structure are of importance as they
have been extensively used in medicinal chemistry. For example, they have been applied as
antiasthamatic, antibacterial, antihypertensive, anti-inflammatory and antimalarial agents, and as
tyrosine kinase inhibiting compounds [24-29].
Recently, we introduced a new category of acidic ionic liquids (ILs) and solid salts, namely
sulfonic acid-functionalized imidazolium salts (SAFIS) which published in this journal [30], and
applied them as organocatalysts or organoreagents for preparation of 1-amidoalkyl-2-naphthols
[30], N-sulfonyl imines [31], nitro aromatic compounds [32,33], bis(indolyl)methans [34],
benzimidazoles [35], xanthenes [36], 1-carbamatoalkyl-2-naphthols [37], 4,4'-(arylmethylene)-
bis(3-methyl-1-phenyl-1H-pyrazol-5-ol)s [38], t-butyl aryl carbamates [39], 1,2,4,5-
tetrasubstituted imidazoles [40], β-acetamido ketones [41], and hexahydroquinolines [42].
In this work, in continuation of our previous studies on the preparation and applications of acidic
ILs and solid salts in organic transformations [30-42], and also previous works on the synthesis
of silica-bonded imidazolium compounds [43-46], we have synthesized silica-bonded
imidazolium-sulfonic acid chloride (SBISAC) (Figure 1) in which SAFIS have been
immobilized on silica gel, and characterized it by Fourier transform infrared spectroscopy (FT-
IR), X-ray diffraction (XRD), thermal gravimetric analysis (TGA), differential thermal
gravimetric (DTG), scanning electron microscope (SEM), transmission electron microscopy
(TEM) and energy dispersive X-ray analysis (EDX). Then, we have utilized SBISAC as a highly
efficient, stable, reusable and heterogeneous nanocatalyst for the preparation of
hexahydroquinolines at 50 °C under solvent-free conditions (Scheme 1). In this investigation, the
3

catalytic activity of the supported ionic liquid was studied in comparison with the ionic liquid.
We found that the presented nanocatalyst was more efficient with respect to the other catalysts
for the preparation of HHQs, because of increasing effective surface of SBISAC. Furthermore,
the use of solid catalysts in reactions is easier than liquid catalyst. All starting materials for the
synthesis of SBISAC were also available and inexpensive.
2. Experimental
2.1. Materials
All chemicals were purchased from Merck or Fluka Chemical Companies. The known products
were identified by comparison of their melting points and spectral data with those reported in the
literature.
2.2. Catalyst preparation
A mixture of imidazole (0.34 g, 5 mmol), (3-chloropropyl)triethoxysilane (1.125 g, 5 mmol) and
toluene (15 mL) in a 50 mL round-bottomed flask connected to a reflux condenser, was stirred
for 18 hours under reflux conditions. In the next step, the obtained white precipitate, was filtered
to separate from toluene, and reacted with silica (0.3 g, 5 mmol) in ethyl acetate (15 mL) under
reflux conditions for 12 hours to give a solid after removing the ethyl acetate. Then, a solution of
chlorosulfuric acid (5 mmol) in chloroform (10 mL) was added dropwise to the resulted solid at
0 °C (ice-water bath), and stirred for 2 hours. The chloroform was removed, and the residue was
triturated with chloroform (3×10 mL), and dried under powerful vacuum at 90 °C to give silica-
bonded imidazolium-sulfonic acid chloride (SBISAC) as a white precipitate in 95 % yield.
2.3. Catalyst characterization
Progress of the reactions was monitored by TLC using silica gel SIL G/UV 254 plates.
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1
13
The H NMR (500 or 300 MHz) and C NMR (125 or 75 MHz) were run on a Bruker Avance
DPX FT-NMR spectrometer (δ in ppm).
Melting points were recorded on a Büchi B-545 apparatus in open capillary tubes.
Thermal gravimetry (TG) and differential thermal gravimetric (DTG) were analyzed by a Perkin
Elmer (Model: Pyris 1). TG/DTG analysis (25 to 600 °C, temperature increase rate of 10 °C.
min-1, nitrogen atmosphere).
The crystal structure of synthesized materials was determined by an X-ray diffractometer
(Italstructure ADP2000 XRD diffractometer) at ambient temperature.
2.4. Catalytic tests
2.4.1 General procedure for the preparation of hexahydroquinolines
To a mixture of dimedone (0.14 g, 1 mmol), arylaldehyde (1 mmol), β-ketoester (1 mmol) and
ammonium acetate (0.0925 g, 1.2 mmol) in a 25 mL round-bottomed flask, was added SBISAC
(0.005 g), and the resulting mixture was firstly stirred magnetically, and after solidification of the
reaction mixture with a small rod, at 50 ºC. After completion of the reaction, as monitored by
TLC, the reaction mixture was cooled to room temperature. Afterward, ethanol (95%) (20 mL)
was added to the reaction mixture, stirred and refluxed for 3 min, and centrifuged to separate
SBISAC from the mixture [the nanocatalyst isn’t soluble in hot ethanol; however, the product is
soluble in large amount (20 mL ethanol per 1 mmol of the product) of hot ethanol]. The solvent
was evaporated, and the crude product was purified by recrystallization from ethanol (95%). In
this work, the catalyst was recovered, and reused for 5 times without any significant changes in
the yield and the reaction time.
3. Results and Discussion
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At first, imidazole was reacted with (3-chloropropyl)triethoxysilane under reflux conditions to
give I which transformed to II as s white precipitate by releasing of one molecule of HCl. In the
next step, II was reacted with silica in ethyl acetate under reflux conditions for 8 hours to afford
III. Afterward, by the reaction of III with chlorosulfuric, silica-bonded imidazolium-sulfonic
acid chloride (SBISAC) was prepared as a white precipitate (Scheme 2).
The structure of SBISAC was identified by IR, XRD, TG, DTG, EDX, SEM, and TEM.
The IR spectrum of the catalyst showed a broad peak at 2500-3600 cm-1 which could be related
to O-H stretching of SO3H group. Moreover, the two peaks observed at 1046 cm-1 and 1106 cm-1
correspond to vibrational modes of N-SO2 and O-SO2 bonds (Figure 2).
X-ray diffraction analysis (XRD) pattern of SBISAC was studied in domain of 0-90 degree
(Figure 3). As shown in Figure 3, XRD patterns exhibited diffraction lines of a high crystalline
nature at about 2θ ≈ 9.6◦, 12.1◦, 19.5◦, 20.2◦, 22.8◦ and 81.7◦.
Thermal gravimetric analysis (TGA) of SBISAC was also investigated. The corresponding
diagrams are displayed in Figure 4. The thermogravimetry (TG) and differential thermal
gravimetric (DTG) of the catalyst showed weight losses and decomposing in one step, after 325
ºC.
Energy-dispersive X-ray spectroscopy (EDX) of the nanocatalyst (Figure 5) confirmed the
presence of the expected elements in its structure, i.e. carbon, oxygen, nitrogen, sulfur, chlorine
and silicon.
In another investigation, the scanning electron microscope (SEM) micrographs of the catalyst
showed that the particles have not completely agglomerated. Moreover, particles of the catalyst
were observed in nano scale (Figure 6).
To further confirm the nanostructure of silica-bonded imidazolium-sulfonic acid chloride, the
6

corresponding TEM (Figure 7) was studied. The TEM micrograph proves the presence of more
or less spherical nanoparticles with a mean diameter of 12.0 nm.
In the next step, catalytic activity of SBISAC on the preparation of hexahydroquinolines was
studied. For this purpose, as a model reaction, a mixture of dimedone (1 mmol),
4-nitrobenzaldehyde (1 mmol), ethyl acetoacetate (1 mmol) and ammonium acetate (1.2 mmol),
was stirred in the presence of different amounts of SBISAC at range of 25 to 80 °C under
solvent-free conditions. The respective results are depicted in Table 1. As it can be seen in Table
1, 0.005 g of SBISAC was suitable to catalyze the reaction at 50 °C. In this reaction condition,
the expected hexahydroquinoline was efficiently prepared in 93% yield within 6 min (Table 1,
entry 6). The solvent-free condensation was also tested at 50 °C without catalyst in which the
reaction was not progressed even after long reaction time.
To compare the efficiency of the solution versus solvent-free conditions, a mixture of dimedone
(1 mmol), 4-nitrobenzaldehyde (1 mmol), ethyl acetoacetate (1 mmol) and ammonium acetate
(1.2 mmol), as model reaction, using SBISAC (0.005 g) in some various solvents was heated in
an oil-bath (50 °C). Low yields of the product was isolated, even after elongated reaction times.
Using solvents, such as CH2Cl2, CHCl3, EtOAc, EtOH, H2O, acetone and THF, the product was
obtained in low yields (Table 2).
To investigate the efficacy and the generality of the catalyst, dimedone was reacted with various
aromatic aldehydes (benzaldehyde as well as arylaldehyde containing electron-withdrawing
groups, electron-donating groups and halogens), β-ketoesters (ethyl and methyl acetoacetate) and
ammomium acetate under the optimized reaction conditions; the results are displayed in Table 2.
As it is shown in Table 2, all reactions proceeded efficiently to obtain the expected
hexahydroquinoline derivatives in high yields and in short reaction times. Therefore, SBISAC,
7

was a highly efficient and general catalyst for the synthesis of HHQs. The acidic content of
SBISAC was characterized by the determination of its H+ of the catalyst, through titration with
NaOH (0.01 mol/L). For this purpose, SBISAC (0.005 g) was titrated by 0.8 ml of NaOH (0.01
mol/L) and then mol% of catalyst was calculated. Turn over frequency (TOF) and turn over
number (TON) values for SBISAC were calculated by the equations TOF = Yield (%)/[Time
(min)×Catalyst amount (mol%)] and TON = Yield (%)/Catalyst amount (mol%) in this reaction
condition. The TOF and TON values were summarized in Table 2.
To compare the efficiency of our catalyst with the reported catalysts for the synthesis of
hexahydroquinolines, we have tabulated the results of these catalysts to perform the
condensation reaction of dimedone, 4-nitrobenzaldehyde, ethyl acetoacetate and ammonium
acetate, in Table 3. As Table 3 indicates, SBISAC has remarkably improved the synthesis of
hexahydroquinolines. The reaction times were shorter, and the yields were higher when our
catalysts were utilized. Application of SBISAC as a heterogeneous catalyst was also compared
with 3-methyl-1-sulfonic acid imidazolium chloride {[Msim]Cl} as an ionic liquid and
homogenous catalyst in this reaction condition. The result showed that SBISAC is more
successful than [Msim]Cl in terms of reaction time and yield (Table 3).
In a proposed mechanism (Scheme 3) which is supported by the previous literature [22,23,49], at
first dimedone is converted to its enol form using SBISAC as Brønsted acid. By the reaction of
Cl- with enol, enolate produced and reacted with activated aldehyde (by SBISAC) to generate
intermediate I. Also, the activated β-ketoester (by the catalyst) and ammonia (resulted from
ammonium acetate) gives enamine II. Then, the intermediate I and enamine II react with each
other to obtain intermediate III. III is converted to IV by tautomerization, and intermediate IV
gives V by intramolecular nucleophilic attack of the NH2 group to the activated carbonyl group
8

and then removing one molecule H2O. Finally, hexahydroquinonine forms by tautomerization of
V.
In another investigation, recyclability of SBISAC was studied. For this purpose, the reaction of
dimedone (1 mmol) with 4-nitrobenzaldehyde (1 mmol), ethyl acetoacetate (1 mmol) and
ammonium acetate (1.2 mmol) was performed using SBISAC (0.005 g) at 50 °C. After
completion of the reaction, the reaction mixture was cooled to room temperature; ethanol (95%)
(20 mL) was added, stirred and refluxed for 3 min, and centrifused to separate catalyst from
solution of product, and remain the unreacted starting materials and the product. The remained
catalyst was washed with hot ethyl acetate (10 mL), and dried to use for the next run. Catalytic
activity of SBISAC was restored within the limits of the experimental errors for 5 successive
recycle runs (Figure 8). The reused catalyst was also characterized by SEM, IR and CHNS
analysis after its application in the reaction. These SEM image of catalyst was same as this of the
fresh catalyst (Figure 9). Elemental analysis of reused catalyst was investigated by CHNS
analysis and the mass percent of carbon, hydrogen, nitrogen, and sulfur were 17.45, 5.04, 13.88
and 11.45 respectively.
4. Conclusion
In summary, we have synthesized silica-bonded imidazolium-sulfonic acid chloride (SBISAC) as
nanostructured heterogeneous catalyst, and fully characterized it by several techniques including
fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), thermal gravimetric
analysis (TGA), differential thermal gravimetric (DTG), scanning electron microscope (SEM),
transmission electron microscopy (TEM) and energy dispersive X-ray analysis (EDX). SBISAC
was successfully applied as a reusable, stable, general and heterogeneous catalyst for the one-pot
multi-component condensation reaction between dimedone, arylaldehydes, β-ketoesters and
9

ammonium acetate leading to hexahydroquinoliones. Short reaction times, high yields, solvent-
free and mild reaction condition, and reusability of the catalyst are some advantages of this work.
Acknowledgements
The authors gratefully acknowledge the Bu-Ali Sina University Research Council, Center of
Excellence in Development of Environmentally Friendly Methods for Chemical Synthesis
(CEDEFMCS) and University of Sayyed Jamaleddin Asadabadi for providing support to this
work.
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Scheme 1. The one-pot four-component preparation of hexahydroquinolines catalyzed by
SBISAC.
Scheme 2. Preparation of silica-bonded imidazolium-sulfonic acid chloride (SBISAC).
Scheme 3. Proposed mechanism for the synthesis of hexahydroquinonines.
Fig. 1 The structure of silica-bonded imidazolium-sulfonic acid chloride (SBISAC).
Fig. 2 The FT-IR spectrum of SBISAC.
Fig. 3 The XRD diagram of SBISAC in comparison with other components of the catalyst.
Fig. 4 The thermal gravimetric (TG) and derivative thermal gravimetric (DTG) analysis of
SBISAC at range of 25–600 ◦C, with a temperature increase rate of 10 ◦C.
Fig. 5 The energy-dispersive X-ray spectroscopy (EDX) of SBISAC.
Fig. 6 The SEM micrographs of SBISAC.
Fig. 7 The transmission electron micrograph (TEM) of SBISAC.
Fig. 8 The condensation of dimedone with 4-nitrobenzaldehyde, ethyl acetoacetate and
ammonium acetate in the presence of the recycled catalyst.
Fig. 9 The SEM images of reused SBISAC.
14

Table 1. Effect of the catalyst amount and temperature on the reaction between dimedone, 4-
nitrobenzaldehyde, ethyl acetoacetate and ammonium acetate.
Catalyst amount (g) Temp.(ºC) Time (min) Yielda (%)
Entry Catalyst
1
SBISAC
0.005
25
30
60
2
3
SBISAC
SBISAC
0.001
0.005
50
60
22
6
70
93
4
6
7
SBISAC
SBISAC
SBISAC
0.005
0.05
0.005
80
50
50
6
5
6
95
93
93
8
-
-
50
30
28
aIsolated yield.
Table 2. Effect of various solvents on the reaction of dimedone (1 mmol), 4-nitrobenzaldehyde
(1 mmol), ethyl acetoacetate (1 mmol) and ammonium acetate (1.2 mmol) in the presence of
SBISAC (0.005 g).
Entrya
Solvent
CHCl3
EtOAc
EtOH
Temp. (°C)
Time (min)
Yieldb (%)
1
2
3
50
50
50
60
60
60
45
52
39
4
5
CH2Cl2
Hexane
-
Reflux
50
60
60
6
35
39
93
6c
50
aAll reactions were carried out at 50ꢀ°C except entry 4, which was proceeded at reflux condition.
bIsolated yield.
cThe reaction was proceeded in the absence of solvent.
Table 3. The solvent-free synthesis of HHQs from dimedone, arylaldehydes, β-ketoesters and ammonium acetate catalyzed by SBISAC at 50 °C.
Entry
Product
Time (min)a
Yieldb (%)
TONc
TOFd (min-1)
M.p. °C (Lit.)
203-204
(203-205) [10]
1
7
91
113.75
16.25
15

245-246
(242-244) [26]
2
3
6
93
91
116.25
113.75
19.37
11.37
256-258
(257-259) [25]
10
261-262
(260-261) [25]
4
5
9
90
93
112.50
116.25
12.50
11.62
238-240
(232-234) [25]
10
250-253
(255-257) [10]
6
9
91
113.75
12.63
229-231
(235-237) [10]
7
8
10
8
90
93
112.50
116.25
11.25
14.53
247-250
(245-246) [24]
254-256
(256-257) [23]
9
12
10
88
92
110.00
115.00
9.16
243-245
(243-245) [22]
10
11.50
219-220
(211-213) [22]
11
12
13
10
12
10
85
90
91
106.25
112.5
10.62
9.37
257-259
260–262 [23]
228-229
229–231 [23]
113.75
11.37
256-259
14
12
90
112.50
9.37
(257-259) [22]
16

230-233
(235-236) [23]
15
5
90
91
112.50
113.75
22.5
b
232-234
Time
11.37
(min)
Yield
16
10
Reaction Condition
Catalyst loading
Ref.
10
(228) [47]
(%)
FeF3, EtOH, Reflux
5 mol%
60
89
265-268
17
9
91
113.75
12.63
(266-268)
[48,49]
232-234
18
19
12
7
89
93
111.25
116.25
9.27
(232-233) [49]
216-218
16.60
(220) [50]
aFor the calculation of TON and TOF total time and exact time are same.
bIsolated yield.
cTurn over number.
dTurn over frequency.
Table 4. Comparison of the results on the synthesis of hexahydroquinolines catalyzed by our new
catalyst with those obtained by the recently reported catalysts.a
17

K7[PW11CoO40], CH3CN, Reflux
PPA-SiO2, 80 °C
1 mol%
0.03 g
30
40
80
88
11a
11b
HClO4-SiO2, 90 °C
Fe3O4, 50 °C
0.05 g
14
5
90
92
11c
49
5 mol%
[Dsim]HSO4, 50 °C
3 mol %
3 mol %
35
8
93
95
23
22
[pyridine‐SO3H]Cl, 50 °C
c
SBISAC, solvent-free, 50 ºC
[Msim]Cl, solvent-free, 50 ºC
0.005 g
6
93
45
-
0.01 mol%d
10
-
aThe reactions were carried out by the condensation of dimedone with 4-nitrobenzaldehyde, ethyl
acetoacetate and ammonium acetate.
bIsolated yield.
cOur work.
dIn this reaction, the mol% of [Msim]Cl was identical with the applied SBISAC.
Scheme 1.
18

Scheme 2.
Scheme3.
19

Figure.1
Cl
O
O Si
O
SO3H
N
N
20

Figure 2.
.
Figure 3.
21

Figure 4.
Figure 5.
22

Figure 6.
23

Figure 7.
Figure 8.
24

Figure 9.
B
A
C
D
L1= 56.32
L2= 64.32
L3= 76.6
25