Synthesis, characterization and application of nano-CoAl2O4 as an efficient catalyst in the preparation of hexahydroquinolines

Article abstract of DOI:10.1002/aoc.3815

In this work, nano-CoAl₂O₄ was prepared and characterized by FT-IR, energy dispersive X-ray analysis (EDX), X-ray diffraction patterns (XRD), scanning electron microscopy (SEM), vibrating sample magnetometer (VSM) and transmission el

Full text of DOI:10.1002/aoc.3815

Received: 5 January 2017
DOI: 10.1002/aoc.3815
Revised: 3 March 2017
Accepted: 5 March 2017
F U L L PA P E R
Synthesis, characterization and application of nano‐CoAl2O4 as an
efficient catalyst in the preparation of hexahydroquinolines
Ardeshir Khazaei1
Ahmad Reza Moosavi‐Zare2
| Leila Jafari‐Ghalebabakhani1 | Esmaeil Ghaderi1 | Mahsa Tavasoli1 |
1 Bu‐Ali Sina University, Hamedan
6517838683, Iran
2 Sayyed Jamaleddin Asadabadi University,
Asadabad 6541835583, I. R. Iran
In this work, nano‐CoAl2O4 was prepared and characterized by FT‐IR, energy
dispersive X‐ray analysis (EDX), X‐ray diffraction patterns (XRD), scanning
electron microscopy (SEM), vibrating sample magnetometer (VSM) and transmission
electron microscopy (TEM). Nano‐CoAl2O4 was applied for the synthesis of
hexahydroquinoline derivatives by the condensation reaction between ethyl
acetoacetate, dimedone and various aldehydes. These reactions were carried out at
80 °C under solvent‐free conditions.
Correspondence
Ardeshir Khazaei, Bu‐Ali Sina University,
Hamedan, 6517838683, Iran.
Email: Khazaei_1326@yahoo.com
Ahmad Reza Moosavi‐Zare, Sayyed
Jamaleddin Asadabadi University, Asadabad,
6541835583, I. R. Iran.
KEYWORDS
Email: moosavizare@yahoo.com
hantzsch synthesis, hexahydroquinoline, multi‐component reaction, nano‐CoAl2O4, solvent‐free
Funding Information
Research Affairs Office of Bu-Ali Sina Uni-
versity and Iran National Science Foundation
(INSF)
1 | INTRODUCTION
with high stability, reusability and simple recyclability.[14]
Some methods for the preparation of polyhydroquinolines
Multi‐component reactions have an important role in
combinatorial chemistry because of the ability to give desired
products with high efficiency and atomic economy by the
reaction of three or more compounds together in a one step.
Additionally, MCRs improve simplicity and synthetic
efficiency on the conventional organic synthesis.[1]
Nano Cobalt aluminate (nano‐CoAl2O4) is introduced
as a catalyst, pigment layer on luminescent materials and
color filter for automotive lamps.[2] Coloration of plastics,
fibers, rubber, glass, ceramic bodies, paint and porcelain
are other uses of this material because this nano‐catalyst
is a thermally and chemically stable pigment.[3] For the
synthesis of cobalt aluminate oxide several techniques such
as sol–gel,[4] EDTA chelating precursor,[5] polymer aerosol
pyrolysis,[6] reverse micelle processes,[7,8] oil‐in‐water,[9]
molten salt,[10] hydrothermal,[11] combustion,[12] and
Pechini[13] are reported. Heterogeneous catalyst (nano‐
CoAl2O4) has many advantages including good selectivity
have been reported. The three‐component condensation
reaction of aldehyde with ethyl acetoacetate and ammonia
in acetic acid or alcohol are classical method for the
synthesis of these compounds.[15–17] Lower yields of the
products, usage of an excess of organic solvent and long
reaction times are disadvantages of this method. Recently,
some investigations have been introduced in order to
improve the efficiency of Hantzsch DHPs synthesis, such
as [pyridine‐SO3H]Cl,[18] threo‐(1S,2S)‐2‐amino‐1‐(4′‐
nitrophenyl)‐1,3‐propanediol,[19] iron (III) trifluoroacetate,[20]
ionic liquid,[21] cerium(IV) ammonium nitrate[22] and
Sc(OTf)3.[23] But, some drawbacks still present, for
example longer reaction time, non‐recyclable catalysts and
tedious work‐up procedures, low yield that limit the use
of these methods.[24] Solvent‐free method is an efficient
technique for various organic transformations instead of
using harmful organic solvents.[25–27] In this work, we have
reported a green solvent‐free procedure for the synthesis of
Appl Organometal Chem. 2017;e3815.
wileyonlinelibrary.com/journal/aoc
Copyright © 2017 John Wiley & Sons, Ltd.
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https://doi.org/10.1002/aoc.3815

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KHAZAEI ET AL.
SCHEME 1 The preparation of
hexahydroquinolines catalyzed by Nano‐
CoAl2O4
polyhydroquinolines using nano‐CoAl2O4 with some
advantages including short reaction times, high yields,
simplicity of workup and reusability of the catalyst
(Scheme 1).
2 | EXPERIMENTAL
2.1 | General
All materials were purchased from Merck and Fluka
Chemical Companies. The known products were identified
by comparison of their melting points and spectral data with
those reported in the literature. The chemical reactions were
monitored by TLC using silica gel SIL G/UV 254 plates.
1
The H NMR (400 MHz) and 13C NMR (100 MHz) were
run on Bruker Avance DPX FTNMR spectrometers. Melting
points were recorded on a Büchi B‐545 apparatus in open
capillary tubes.
2.2 | Procedure for the preparation of nano‐
CoAl2O4
A solution of metal sulfates was prepared by dissolving
CoSO4.7H2O (3.5 gr, 0.012 mol) and Al2 (SO4)3.18H2O
(16.5 g, 0.0495 mol) in 100 ml water with the molar ratio of
Co+2/Al+3 1:2 at 50
̊
̊
FIGURE 1 The synthesis of nano‐CoAl2O4 powder
When the solution was stirred, aqueous sodium hydroxide
(12 g, 0.3 mol) was added to the obtained mixture. Purple pre-
cipitate was formed immediately. The precipitate compound
(Nano‐CoAl2O4) was collected by centrifuge and was washed
with cold water. Nano CoAl2O4 was calcinated when it was
was added to the reaction mixture and heated to dissolve
the crude product and starting materials. Then, the nano‐
CoAl2O4 catalyst was partly recovered by centrifuge, and
the product was purified by the recrystallization in ethanol.
The recovered catalyst was reused for four times without
reducing the efficiency of the catalyst in the yield of products
and reaction times. The spectral data of compounds have
been reported in supporting information.
put in the furnace (800 ̊C) for 6 hours (Figure 1).
2.3 | General procedure for the synthesis of
hexahydroquinolines under solvent‐free
conditions
The mixture of the dimedone (1 mmol), ammonium acetate
(1.2 mmol), aldehydes (1 mmol), ethyl acetoacetate (1 mmol)
and nano‐CoAl2O4 (0.005 g) as catalyst was stirred at 80 °C
for specific time in a 25 ml round‐bottomed flask connected
to a reflux condenser. Completion of the reaction was identi-
fied by TLC (n‐hexane/ethyl acetate: 7/3). Ethanol (20 ml)
3 | RESULTS AND DISCUSSION
Nano‐CoAl2O4 was synthesized and characterized by
FT‐IR, EDX, XRD, SEM, UV–Vis, VSM and TEM analysis.

KHAZAEI ET AL.
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FIGURE 2 FT‐IR spectra of the synthesized nano‐CoAl2O4 after calcinations at 600 °C (a) and 800 °C (b) for 6 h
In the IR spectrum of the new catalyst, the stretching
vibration of the hydrogen‐bonded OH groups was appeared
at 3470 cm−1. C–H stretching vibration of absorption band
appeared at 2960 cm−1 (organic compounds).[28] All of the
peaks related to the organic species disappear while the
temperature is increased and the rest of absorption peaks
related to metal oxygen vibrations become much sharper.[29]
The bands at 667.24, 569.24 and 506.14 cm−1 of the calcined
powders indicate the formation of metal oxide (Co–O and
Al–O stretching vibrations).[28] The bending vibration of
water molecules appeared at 1654 (Figure 2).[28]
and 64.8° are shown in Figure 5. Also, the XRD data, includ-
ing 2θ, peak width, size of particles and inter planar distance
are extracted and shown in Table 1. As shown in Table 1, the
SEM and TEM analysis of the catalyst are given in
figures 3 and 4. As SEM images, indicates that the size
of the particles is less than 50 nm. Also, the transmission
electron microscopy (TEM) analysis approves the same
result which was obtained for SEM. So these observations
confirm the morphology of the nano catalyst.
XRD pattern of cobalt aluminate was also investigated
(Figure 5). Diffraction peaks at various 2θ values including
18.5°, 30.8°, 36.4°, 43.8°, 44.3°, 51.1°, 55.2°, 58.6°, 58.9°
FIGURE 4 The transmission electron microscopy images of the
catalyst
FIGURE 3 The scanning electron microscopy (SEM) of the nano‐
CoAl2O4
FIGURE 5 The X‐ray diffraction (XRD) pattern of nano‐CoAl2O4

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KHAZAEI ET AL.
TABLE 1 XRD data for the nano‐CoAl2O4
Peak width
[FWHM]
(degree) (Debye–Scherrer‐nm)
Inter
planer distance
(nm)
Crystal size
Entry 2ϴ
1
2
3
4
5
6
7
8
9
10
18.5
30.8
36.4
43.8
44.3
51.1
55.5
58.6
58.9
64.8
0.2
0.33
0.3
0.2
0.3
0.1
0.2
0.9
0.4
0.6
40.25
24.97
27.87
39.18
28.59
88
0.479034
0.30131
0.246534
0.206441
0.204226
0.178532
0.289898
0.157341
0.156612
0.143703
44
FIGURE 7 Magnetization curve of the prepared catalyst
10.12
22.81
15.68
120 °C under solvent‐free conditions. Table 2 shows the
results of these optimization experiments. As the results of
these reactions, indicates that a catalyst loading of 0.005
size of the size of the crystals is calculated from 10 to 88 nm
according to Debye–Scherrer equation.
Energy dispersive spectroscopy (EDS) spectrum of nano‐
CoAl2O4 was shown in Figure 6. As it is shown in Figure 6,
indicates that the existence of cobalt, aluminium and oxygen
in the nano‐CoAl2O4.
TABLE 2 Effect of the catalyst amount and temperature on the
reaction between dimedone, ethyl acetoacetate, benzaldehyde, and
ammonium acetate
Entry Catalyst amount (g) Temp. (̊
C) Time (min) Yielda (%)
The magnetization curve that is shown in Figure 7 deter-
mined the values of magnetic moment of nano‐CoAl2O4. The
saturation magnetization of nano‐CoAl2O4 was 11 emu/g.
The catalytic activity of nano‐CoAl2O4 was tested for
the synthesis of hexahydroquinolines. The multi‐component
reaction of ethyl acetoacetate (1 mmol), dimedone (0.14 g,
1 mmol), benzaldehyde (1 mmol) and ammonium acetate
(0.0925 g, 1.2 mmol) was selected as a model reaction.
The model reaction was tested in the presence of different
amounts of nano‐CoAl2O4, and in the range of 25 to
1
2
3
4
5
6
7
8
9
0.001
0.005
0.008
0.012
0.017
0.001
0.001
0.001
0.001
80
80
5
3
71
91
90
90
91
45
79
90
90
80
4
80
4
80
3
25
25
9
60
100
120
4
4
aIsolated yield.
TABLE 3 Effect of different solvents on the reaction of dimedone,
benzaldehyde and ammonium acetate in the presence of nano‐CoAl2O4
(3 mol%)
Entry
Solvent
Yielda (%)
Time (min)
Temp. (̊C)
1
2
3
4
5
6
7
8
H2O
70
50
55
43
63
61
43
91
60
60
60
60
60
60
60
3
80
CH2Cl2
CHCl3
n‐Hexan
EtOH
EtOAC
CH3CN
‐
reflux
reflux
reflux
reflux
reflux
reflux
80
FIGURE 6 The energy‐dispersive X‐ray spectroscopy (EDX) of the
nano‐CoAl2O4
aIsolated yield.

KHAZAEI ET AL.
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TABLE 4 Synthesis of hexahydroquinoline derivatives catalyzed by nano‐CoAl2O4 under solvent‐free conditions
Entry
Product
Time (min)
Yield (%)
M.p. ̊C (lit.)
1
3
91
229–231 (203–205) [30]
2
4
81
244–245 (242–244) [31]
3
4
4
8
90
90
263–265 (257–259) [32]
266–268 (260–261) [32]
5
6
7
4
8
5
75
90
85
234–236 (232–234) [32]
256–258 (255–257) [30]
230–231 (235–237) [30]
8
9
2
8
87
86
243–245 (243–245) [18]
246–248 (245–246) [33]
(Continues)

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KHAZAEI ET AL.
TABLE 4 (Continued)
Entry
Product
Time (min)
Yield (%)
M.p.
̊C (lit.)
10
5
92
249–251 (256–257) [34]
11
12
11
90
85
242–245 (245) [35]
8
235–238 (232–233) [36]
13
7
86
202–205 (207) [35]
14
15
3
3
82
81
235–237 (238–240) [35]
214–217 (205–207) [37]
16
17
7
2
85
84
260–261 (266–268) [36]
186–189 (179–181) [18]
18
6
86
201–202 (200–202) [38]
(Continues)

KHAZAEI ET AL.
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TABLE 4 (Continued)
Entry
Product
Time (min)
Yield (%)
M.p. ̊C (lit.)
19
7
89
206–208 (202–204) [24]
20
21
7
4
85
79
214–215
157–160
22
23
3
2
83
89
242–245
233–235
TABLE 5 The reusability of the catalyst
gram of catalyst at 80 °C was the best reaction conditions
(Table 2, entry 2).
Run
Time (min)
Yielda (%)
Table 3 shows the comparison of the efficiency of the
solution versus solvent‐free conditions using a variety of
different solvents at 80 °C. Low yields of the products were
shown in all of the solvent condition.
1
2
3
4
3
3
2
3
91
89
91
90
Dimedone was reacted with a series of different aryl
aldehydes (possessing halogens, electron‐donating groups
and electron‐ withdrawing groups), ammonium acetate and
ethyl acetoacetate under the optimized reaction conditions.
Table 4 shows the results of these reactions. High yields over
short reaction times are the main advantages of this method.
As we have already tested the recyclability of the nano‐
CoAl2O4 in terms of its advantage as a catalyst (0.005 g) to
the multi‐component reaction of ethyl acetoacetate (1 mmol),
ammonium acetate (1.2 mmol), dimedone (1 mmol), and
benzaldehyde (1 mmol) at 80 °C. when the reaction was
finished, ethanol was added and heated to dissolve the crude
product and starting materials. Then the nano‐CoAl2O4
catalyst was partly recovered by centrifuge. The collected cat-
alyst was washed with ethanol, dried and used again in the
aIsolated yield.
next reaction. The catalyst was successfully reused for four
times (Table 5).
4 | CONCLUSION
In this work, nano‐CoAl2O4 as a recoverable heterogeneous
catalyst was prepared and characterized by FT‐IR, energy‐
dispersive x‐ray spectroscopy (EDX), X‐ray diffraction pat-
terns (XRD), scanning electron microscopy (SEM), vibrat-
ing sample magnetometer (VSM) and transmission electron

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KHAZAEI ET AL.
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̊
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of the presented method are high yield, short reaction time,
generality, cleaner reaction profile, efficiency, simplicity and
reusability of the catalyst.
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The authors gratefully acknowledge partial support of this
work by the Research Affairs Office of Bu‐Ali Sina
University and Iran National Science Foundation (INSF) for
financial support to our research groups.
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SUPPORTING INFORMATION
Additional Supporting Information may be found online in
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How to cite this article: Khazaei A, Jafari‐
Ghalebabakhani L, Ghaderi E, Tavasoli M, Moosavi‐
Zare AR. Synthesis, characterization and application
of nano‐CoAl2O4 as an efficient catalyst in the
preparation of hexahydroquinolines. Appl
Organometal Chem. 2017;e3815. https://doi.org/
10.1002/aoc.3815
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