Nanomagnetic-supported Sulfonic Acid: Simple and Rapid Method for the Synthesis of α,α′-Bis-(substituted-benzylidene) Cycloalkanones

Article abstract of DOI:10.1002/jccs.201400377

Nanomagnetic-supported sulfonic acid is found to be a powerful and reusable heterogeneous catalyst for the rapid synthesis of α,α′-bis-(substituted-benzylidene)cycloalkanones under conventional heating and solvent free conditions. High yield, simple work up and easy recovery of the catalyst are the most obvious advantages of this procedure. In this paper, an efficient, sustainable and green procedure for synthesis of α,′α-bis-(substituted-benzylidene) cycloalkanones has been developed using a magnetically separable and easily recyclable nano-γ-Fe₂O₃-SO₃H catalyst in solvent free medium under thermal condition. Easy magnetic separation of the catalyst eliminates the requirement of catalyst filtration after completion of the reaction which is an additional greener attribute of this method.

Full text of DOI:10.1002/jccs.201400377

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Article
Nanomagnetic-supported Sulfonic Acid: Simple and Rapid Method for the Synthesis
of a,a¢-Bis-(substituted-benzylidene) Cycloalkanones
Ali Amoozadeh,* Eskandar Kolvari, Nadiya Koukabi and Somayeh Otokesh
Department of Organic Chemistry, Semnan University, Semnan, Iran
(Received: Sept. 7, 2014; Accepted: Dec. 26, 2014; Published Online: Apr. 17, 2015; DOI: 10.1002/jccs.201400377)
Nanomagnetic-supported sulfonic acid is found to be a powerful and reusable heterogeneous catalyst for
the rapid synthesis of a,a¢-bis-(substituted-benzylidene)cycloalkanones under conventional heating and
solvent free conditions. High yield, simple work up and easy recovery of the catalyst are the most obvious
advantages of this procedure.
Keywords: Nanomagnetic-supported sulfonic acid; Heterogeneous catalyst; Solvent-free route;
a,a´-Bis-(substituted-benzylidene)cycloalkanones.
INTRODUCTION
The a,a´-bis-(substituted-benzylidene) cycloalka-
particles have emerged as viable alternatives to porous ma-
terials for use as robust, readily available, high surface area
heterogeneous catalysts in organic synthesis. Also insolu-
ble and paramagnetic nature of these particles enables mag-
netically recoverable which facilitates reaction work-up
and rapid sample processing, and most importantly reduces
solvent consumption.18-23 For these reasons, it is of interest
to use nanomagnetic-supported sulfonic acid (g-Fe2O3-
SO3H) for synthesis of a,a¢-bis-(substituted-benzylidene)
cycloalkanones under thermal condition (Scheme 1). Na-
no-g-Fe2O3-SO3H has been prepared by the reaction of
chlorosulfonic acid with nano magnetite previously and
was characterized thoroughly and has been used as catalyst
in organic synthesis.24
nones motif is a versatile pharmacophore. This structure
has been widely found in many important biologically ac-
tive compounds. These compounds have shown activities
including cytotoxicty,1 cholesterol-lowering,2 HIV-1 inte-
grate inhibition,3 cancer chemoprevention4 and antioxi-
dant.5 Recently, bis-benzylidene cycloalkanones have been
reported to possess drug resistance reversal.6 They are fre-
quently used for the synthesis a range of organic molecules
with many applications such as precursors to potentially
bioactive pyrimidine derivatives7 and bis-spiropyrrolidines
with antimicrobial and antifungal properties,8 liquid-crys-
talline polymers.9 For these reasons, the synthesis of titled
compounds has attracted much more attention from organic
and medicinal chemistry.
Preparation of a,a´-bis-(substituted-benzyl-
Scheme 1
idene) cycloalkanones
Commonly these compounds are synthesized by
cross-aldol condensation and classically carried out using
strong acid or base. However, in recent years a number of
various catalysts have been used for this reactions such as
wet 2,4,6-trichloro[1,3,5]triazine (TCT),10 (SiO2-R-
SO3H),11 solid base SiO2-OK,12 polymer-supported sul-
phonic acid (NKC-9),13 solid NaOH,14 NaOAc,15 ethanolic
KOH16 and ionic liquids.17 But all them suffer from reverse
and side reactions resulting low yields of the products.
Consume minimal energy, reagents or auxiliaries and mini-
mize waste are the principles of “Green Chemistry” for cat-
alyzed organic reactions. Catalysts, in turn, could meet
these goals. With the advent nanomagnetic catalysts, these
goals can be achieved due to the high activity, easy separa-
tion, and protection of the environment. Magnetic nano-
RESULTS AND DISCUSSION
In this paper, we used for the first time nano magnetic
supported sulfonic acid catalyst for the synthesis of ben-
zylidene. At the first glance, in order to optimize the condi-
tions, the reaction of benzaldehyde, cyclopentanone was
chosen as a model system under thermal conditions (Table
1). The nano-sized particles increase the exposed surface
area of the active component of the catalyst, thereby en-
hancing the contact between reactants so the reaction pro-
cess must be better with nano magnetic catalyst. We tested
* Corresponding author. Tel.: +982333366177; Fax: +98 (23) 33354082; E-mail: aamozadeh@semnan.ac.ir
Supporting information for this article is available on the www under http://dx.doi.org/10.1002/jccs.201400377
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Amoozadeh et al.
Table 1. Iron-based catalyzed synthesis of á,á¢-bis-(substituted-
benzylidene) cycloalkanones[a]
Table 3. The effect of temperature on the synthesis of á,á¢-bis-
(substituted-benzylidene) cycloalkanones[a]
Entry
Catalyst (0.05 g)
Time (min)
Yield (%)[b]
Entry
Temperature (°C)
Time (min)
Yield (%)[b]
1
2
3
4
5
Fe
20
20
20
20
20
-
Trace
35
1
2
3
4
60
80
20
20
20
20
67
80
88
75
FeCl3.6H2O
Bulk-Fe2O3
90
100
Bulk-Fe2O3-SO3H
ã-Fe2O3-SO3H
55
88
[a] Benzaldehyde-cyclopentanone = 2:1, Solvent-free.
[b] Yields refer to isolated products.
[a] Benzaldehyde-cyclopentanone = 2:1, Solvent-free, at 90 °C.
[b] Yields refer to isolated products.
Table 4. Effect of the solvent on the synthesis of the á,á¢-bis-
(substituted-benzylidene) cycloalkanones[a]
Table 2. Influence of the amount of nano-ã-Fe2O3-SO3H on the
synthesis of á,á¢-bis-(substituted-benzylidene) cyclo-
alkanones[a]
Entry
Solvent
Time (min)
Yield (%)[b]
1
2
3
4
5
6
CHCl3
EtOH
20
20
20
20
20
20
42
76
76
65
45
88
Entry
ã-Fe2O3-SO3H (g)
Time (min)
Yield (%)[b]
1
2
3
4
5
6
0.0125
0.025
0.05
0.07
0.1
20
20
20
20
20
20
64
74
88
82
80
73
CH3CN
CH2Cl2
H2O
Solvent free
[a] Benzaldehyde-cyclopentanone = 2:1 at 90 °C.
[b] Yields refer to isolated products.
0.15
[a] Benzaldehyde-cyclopentanone = 2:1, Solvent-free, at 90 °C.
[b] Yields refer to isolated products.
SO3H under solvent free condition. The results are summa-
rized in Table 3. According to the obtained results, 90 °C
was selected for synthesis procedure (Table 3, Entry 3).
After determining the appropriate amount of catalyst
and the optimum temperature and for making sure that sol-
vent free conditions provide the best yields, we have exam-
ined the effect of different solvents by using the same reac-
tion conditions, as shown in Table 4. Moreover, when the
reaction was carried out in solvent-free condition, good
conversion was achieved (Table 4, Entry 5).
the model reaction in the present of different iron-based
catalyst. As indicated from Table 1, the yield of product in-
creases to 88% when used nano-g-Fe2O3-SO3H instead of
Bulk-Fe2O3-SO3H that shows the impact of nano particles
on the reaction. No activity was observed in the presence of
Fe and pure bulk-Fe2O3 (Table 1, Entries 1 and 3). A trace
amount of product also observed when catalyzed by
FeCl3.6H2O (Entry 2). The reaction was clean and fairly
rapid. No side products were detected in these reactions.
The amount of the catalyst is a main factor affecting
the synthesis procedure. To study the required catalyst
load, we explore different reaction condition under solvent
free condition and results are summarized in Table 2. The
results show that the product 3a could be obtained in yield
range 64 to 88%. Hence 0.05 g of nano-g-Fe2O3-SO3H can
be catalyze aldol condensation for synthesis of a,a¢-bis-
(substituted-benzylidene) cycloalkanones (Table 2, Entry
3). It be should noted that more increasing catalyst amount
did not affect the total yield (Table 2, Entries 4-6).
It is important to note that the ferromagnetic property
of nano-g-Fe2O3-SO3H made easy isolation and reuse of
catalyst. After completion of reaction, mixture turned clear
and catalyst was deposited on the magnetic bar, which was
easily removed using an external magnet. After being
washed with acetone and dried in air, the nano-g-Fe2O3-
SO3H can be directly reused without any deactivation even
after five rounds of synthesis of products (Table 5).
In this method under the optimized conditions, we
also examined scope of the reaction by using various aryl
aldehydes with electron-donating and electron-withdraw-
ing groups and cyclic ketones (cyclopentanone, cyclohex-
anone, tert-butylcyclohexanone) and condensation prod-
ucts produced in good yields, the results are summarized in
Table 6. As shown, the reaction works easily for a variety
Afterwards, we investigated the effect of temperature
on the reaction rate as well as the yields of products. To
study the effect of temperature, we explored some reaction
conditions for aldol condensation of cyclopentanone and
benzaldehyde in the presence of 0.05 g nano-g-Fe2O3-
502
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Nanomagnetic-supported Sulfonic Acid
Table 5. Reusability of nano-ã-Fe2O3-SO3H in the synthesis of
á,á¢-bis-benzylidenecycloalkanone[a]
11). It would be interesting to test the reaction on acyclic
ketones as well, but it falls outside the scope of the investi-
gation. On the other hand, compared to different ketones,
cyclohexanone (Table 6, Entries 7-11) reacts faster than
cyclopentanone (Table 6, Entries 1-5).
Run
Time (min)
Yield (%)[b]
1
2
3
4
5
20
20
20
20
20
88
86
84
81
77
Table 7 compares the efficiency of our method with
the efficiency of other published results of the same aldol
reaction. As indicated in Table 7, our method provides high
yield (88%) within 20 minutes (Table 7 Entry 18). The
main advantages of our method are fast reaction time, clean
and environmentally benign reagents and ease of separa-
tion of catalyst with external magnet.
[a] Benzaldehyde-cyclopentanone = 2:1, Solvent-free, at 90 °C.
[b] Yields refer to isolated products.
of aldehydes with both electron-donating and electron-
withdrawing groups to give corresponding a,a¢-bis(sub-
stitutedbenzylidene) cyclohexanones in good to excellent
yields. It is important to note that nature of the substituted
on the aromatic ring had effect on this reaction. In general,
aromatic aldehydes carrying electron-donating groups
(such as methyl and methoxy) (Table 6, Entries 2, 3 and 8,
9) gave cleaner reaction in shorter times than aromatic al-
dehydes carrying electron-withdrawing groups (Table 6,
Entries 4, 5, 6 and 10, 11, 12). Steric effects can play an im-
portant role in rate and yield of reaction, substituent on the
ring at the para position (Table 6, Entries 6, 12 and 17) re-
act faster than ortho position (Table 6, Entries 4, 10 and
EXPERIMENTAL
General: The IR spectra were recorded on a Perkin-Elmer
model 783 spectrophotometer (Waltham, MA, USA). The NMR
spectra were obtained on a Bruker AMX-300 (300 MHz) spec-
trometer (Ettlingen, Germany). The solvent was CDCl3. Tetra
methyl silane (TMS) was used as internal reference.
Typical reaction for the synthesis of 2,5-dibenzylidene-
cyclopentanone (Table 6, Entry 1): A mixture of benzaldehyde
(2 mmol), cyclopentanone (1 mmol), and nano-g-Fe2O3-SO3H
(0.05 g) was heated at 90 °C. After completion of the reaction, hot
ethanol (5 mL) was added to the mixture. In the presence of a
Table 6. Preparation of á,á¢-bis-benzylidenecycloalkanone derivatives by nano-ã-Fe2O3-SO3H[a]
Entry
Ar
R
Product
Time (min) Yield (%)[b] M.p. (°C)
1
C6H5
ñ-MeC6H4
ñ-MeOC6H4
o-ClC6H4
o-O2NC6H4
ñ-ClC6H4
C6H5
CH2
CH2
3a
3b
3c
3d
3e
3f
20
20
20
35
40
35
15
15
20
27
35
30
60
32
15
30
30
60
60
80
100
88
87
85
83
87
89
91
87
94
87
90
95
88
96
91
85
93
85
83
80
84
190-191
245-246
211-213
162-163
168-170
225-226
114-116
162-163
163-165
103-107
158-159
160-162
181-183
152-154
165-168
250-252
146-148
208-211
124-127
208-211
109-111
2
3
CH2
4
CH2
5
CH2
6
CH2
7
CH2CH2
CH2CH2
CH2CH2
CH2CH2
CH2CH2
CH2CH2
CH2CH2
CH2CH2
CH2CH2
CH2CH2
CH2CH2
CH2CH2
CH2CHC(CH3)3
CH2CHC(CH3)3
CO(CH3)2
3g
3h
3i
8
ñ-MeC6H4
ñ-MeOC6H4
o-ClC6H4
o-O2NC6H4
ñ-O2NC6H4
2,6-diClC6H4
ñ-FC6H4
9
10
11
12
13
14
15
16
17
18
19
20
21
3j
3l
3k
3m
3n
3o
3p
3q
3r
ñ-BrC6H4
Me2NC6H4
ñ-ClC6H4
ñ-NCC6H5
C6H5
3s
3t
o-O2NC6H4
C6H5
3u
[a] Aromatic aldehyde-ketone = 2:1, Solvent-free, at 90 °C.
[b] Yields refer to isolated products, which were characterized by comparison of their spectroscopic
and physical data with those of samples synthesized by reported procedures [16, 25,10].
J. Chin. Chem. Soc. 2015, 62, 501-505
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Article
Amoozadeh et al.
Table 7. Comparison of the results obtained for the synthesis á,á¢-bis-(substituted-benzylidene)
cyclopentanone catalyzed by nano-ã-Fe2O3-SO3H with those recently reported catalysts
Entry
Catalyst
Condition
Time (min)
Yield (%)
Ref.
1
I2
KOH
CH2Cl2/r.t.
Ethanol/40 ºC
S.F./90 ºC
270
5
89
98
85
73
90
86
98
87
92
94
97
85
94
96
93
89
92
88
[26]
[16]
2
3
SiO2-R-SO3H
KF/Al2O3
NKC-9
90
[11]
4
MW/450W
5
[27]
5
CHCl3/80 ºC
HOAc/120 °C
Grinding
240
420
5
[13]
6
NaOAc
[15]
7
NaOH
[14]
8
Si2OK
Ethanol/Reflux
S.F./90 ºC
180
20
[12]
9
TCT
[10]
10
11
12
13
14
15
16
17
18
[N2222][EtNHC3SO3]
LiClO4
water/60 ºC
TMSNEt2/r.t.
THF/Reflax
PEG/r.t.
360
7
[28]
[29]
SmI3
360
120
3
[30]
AlCl3
[25]
BDMS
S.F./r.t.
[31]
NH4Cl
EtOH/Reflux
MeOH/ultra son.
[bmim][BF4]/80 ºC
S.F./90 ºC
300
40
[32]
KF/Al2O3
FeCl3.6H2O
ã-Fe2O3-SO3H
[33]
360
20
[34]
This work
magnetic stirrer bar, nano-g-Fe2O3-SO3H moved onto the stirrer
bar steadily and the reaction mixture turned clear within 10 s. The
catalyst can be isolated by simple decantation and the crude prod-
uct was recrystallized from hot EtOH to give a pure product.
Spectra Data
(tert-butyl)cyclohexanone (3t): Yellow powder; M.p. = 208-211
°C 1H NMR (300 MHz, CDCl3, Me4Si): d 7.9 (2H, sbr), 7.37-7.69
(4H, m), 2.18 (2H, m), 2.77 (2H, m) 1.4-1.6 (1H, m), 0.7 (4H,
sbr), 13C NMR (75 MHz, CDCl3): 188.82, 148.19, 137.28, 29.02
ppm. IR (KBr): 3075, 2960, 1674, 1519, 1440 cm–1. Anal. calc.
for C24H24N2O5: C, 68.56; H, 5.75; N, 6.66; O, 19.03%. found: C,
68.33; H, 5.58; N, 6.62; O, 18.93% .
a,a¢-Bis-(4-cyano-benzylidene)cyclohexanone (3r): Yel-
1
low powder; M.p. = 208-211 °C H NMR (300 MHz, CDCl3,
Me4Si): d 7.75 (2H, sbr), 7.70 (4H, dbr, J = 8.20 Hz), 7.53 (4H,
dbr, J = 8.35 Hz), 2.91 (4H, m), 1.83 ppm (2H, m). 13C NMR (75
MHz, CDCl3): d 189.29, 140.20, 138.23, 135.22, 135.18, 132.14,
130.57, 118.51, 112.00, 28.30, 22.56 ppm. IR (KBr): 2223, 1666,
1577, 1500, 1139 cm–1. Anal. calc. for C22H16N2O: C 81.49; H
4.93; N 8.63 %; found: C 81.10; H 4.88; N 8.56 %. a,a¢-bis-(2-ni-
tro-benzylidene)cyclopentanone (3e): Yellow powder; M.p. =
168-170° C 1H NMR (300 MHz, CDCl3, Me4Si): d 7.86 (2H, sbr),
7.52 (4H, J = 6 Hz), 8.11 (4H, J = 6 Hz), 2.88 (4H, sbr), 13C NMR
(75 MHz, CDCl3): d 194.33, 148.86, 140.14 130.59, 125.03,
25.98 ppm. IR (KBr): 3080, 2914, 1691, 1517, 1473 cm–1. Anal.
calc. for C19H14N2O5: C, 65.14; H, 4.03; N, 8.00; O, 22.84%.
found: C, 65.11; H, 3.89; N, 7.93; O, 22.75 %. a,a¢-bis-ben-
zylidene-4-(tert-butyl)cyclohexanone (3s): Yellow powder;
M.p. = 124-127 °C 1H NMR (300 MHz, CDCl3, Me4Si): d 7.78
(2H, sbr), 7.33-7.49 (4H, m), 2.49 (2H, m), 3.20 (2H, m), 1.4-1.6
(1H, m), 0.96 (9H, m), 13C NMR (75 MHz, CDCl3): d 190.64,
136.85, 25.98 ppm. IR (KBr): 3083, 2867, 1660, 1490, 1446 cm–1.
Anal. calc. for C24H26O: C, 87.23; H, 7.93; O, 4.84%. found: C,
86.98; H, 7.71; O, 4.79%. a,a¢-bis-(2-nitrobenzylidene)-4-
CONCLUSIONS
In conclusion, an efficient, sustainable and green pro-
cedure for synthesis of a,a¢-bis-(substituted-benzyli-
dene)cycloalkanones has been developed using a magneti-
cally separable and easily recyclable nano-g-Fe2O3-SO3H
catalyst in solvent free medium under thermal condition.
Easy magnetic separation of the catalyst eliminates the re-
quirement of catalyst filtration after completion of the reac-
tion which is an additional greener attribute of this reac-
tion.
ACKNOWLEDGEMENTS
We thank the Department of Chemistry of Semnan
University for supporting this work.
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