Sulfonic acid-functionalized magnetic nanoparticles as a recyclable and eco-friendly catalyst for atom economical Michael addition reactions and bis indolyl methane synthesis

Article abstract of DOI:10.1039/c4ra11605d

A modified sulfonic acid functionalized magnetic nanoparticle composite (Fe₃O₄@γFe₂O₃-SO₃H) is prepared by the use of ultrasonic irradiation. By this modification, the size of the nano-particles was r

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Sulfonic Acid-Functionalized Magnetic Nanoparticles as a Recyclable and Eco-friendly Catalyst for Atom
Economical Michael Addition Reaction and Bis Indolyl Methane Synthesis
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Journal Name
RSCPublishing
ARTICLE
Sulfonic AcidꢀFunctionalized Magnetic Nanoparticles
as a Recyclable and Ecoꢀfriendly Catalyst for Atom
Economical Michael Addition Reaction and Bis
Indolyl Methane Synthesis
Cite this: DOI: 10.1039/x0xx00000x
Received 00th January 2012,
Accepted 00th January 2012
DOI: 10.1039/x0xx00000x
Hajar Mahmoudia, Abbas Ali Jafari*a, Soroosh Saeedia, and H. Firouzabadi*b
www.rsc.org/
A modified sulfonic acid functionalized magnetic nanoparticle composite (Fe3O4@γFe2O3ꢀSO3H) is
prepared by the use of ultrasonic irradiation. By this modification, the size of the nonoꢀparticles was
reduced and the magnetization of the material was highly improved. This improvement affected
the efficiency and magnetic separation of the material as a catalyst drastically. This new modified
nanomagnetic compound was used as a highly efficient and recyclable catalyst for
functionalization of indole derivatives via Michael addition and FriedelꢀCrafs alkylation
reactions in entirely environmentally friendly media at room temperature. This modified
magnetic material can be easily applied for largeꢀscale operation producing the desired products
in excellent yields in highly pure states.
However; the major problems in using the nanoꢀcatalysts are their
isolation and recovery from the reaction mixture. One of the smart
ways for the isolation and separation of catalysts can be
Introduction
accomplished by their support on the surface of magnetic
nanoparticles (MNPs). By this achievement, the catalyst can be
isolated by an external magnet from the reaction mixture by
minimum contamination of the products. In addition, by adopting
this strategy, easy recycling of the catalyst without using the time
consuming filtration step can be achieved.29ꢀ32 Undoubtedly, the
utilization of MNPs in catalysts separation constitutes the
economically and technologically important application that has
stimulated vast research efforts in this area.33ꢀ36 However, it is
noteworthy to state that, the naked metallic nanoparticles with the
high surface area to volume ratio are highly chemically active and
are easily oxidized in air, resulting generally in loss of magnetism
and disperser of MNPs.37 Hence, for this reason, it is important to
develop a protection strategy for stabilizing the naked MNPs against
degradation during or after the synthesis. This strategy consists of
coating the naked magnetic nanoparticles with polymers or an
inorganic layer such as gold, silica or carbon.38ꢀ43 There is also
notable to declare that, the coating protocol may provide useful sites
for further functionalization of the material. For instance, the strong
acids, known as damaging materials in industry and environment,
can be supported on MNPs. Sulfonic acidꢀfunctionalized magnetic
nanoparticles (SAMN) is known as the recoverable solid strong
acid.44ꢀ46 The SAMN is of great interest in both academic and
Carbonꢀcarbon bond formation reactions are very important
from different aspects, especially in synthetic organic
chemistry. In the last decades, efforts have begun to study the
effect of transition metal catalysts and also different types of
acidic and basic catalysts with the emphasis on green
chemistry.1ꢀ9
The Michael addition reaction and bisindolyl methane synthesis
are important CꢀC bond forming reactions, which have found
wide synthetic applications in material sciences, agrochemicals,
and pharmaceuticals10ꢀ12. Several homogeneous acid and base
catalysts are used to effect these reactions. In the presence of
strong bases or acids, side reactions such as multiple
condensations, polymerizations, and rearrangements are
common to occur.13ꢀ17 Furthermore; many of these procedures
have some drawbacks consisting of corrosive and expensive
reagents, low yield of products, difficult handling, and long
reaction times. To overcome the mentioned difficulties,
chemists investigated a wide range of strategies. One of the
logical solution for the above mentioned problems is to use
heterogeneous catalysts carrying nanoꢀmaterials (NMs).18ꢀ20
Nano scale particles reveal novel properties which are not found in
their macroscopic counterparts. These properties contribute to the
efficiency and capability of nanoꢀcatalysts in the reactions.21ꢀ28
This journal is © The Royal Society of Chemistry 2013
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DOI: 10.1039/C4RA11605D
Fe3O4
SO3
Cl
20.05
19.06
2.01
0
industrial communities due to its economically importance and
environmentally benign features. Nevertheless, up to now, only a
few strategies for the preparation of SAMN have been reported in
the literature. Along of our interest for applying SAMN as a catalyst
in important synthetic reactions,47 now we report a modification for
the preparation of the SAMN by using ultrasound irradiation instead
of vigorous mechanical steering.47 By this modification a promising
advancement in magnetic separation of the material, smaller size of
the nanoꢀparticles and as a result higher catalytic activity has been
observed. This modified SAMN has been used as an effective
catalyst for the high yielding ecoꢀfriendly processes for the
preparation of Michael adducts and also for the preparation of 3ꢀ
substituted indolyl derivatives via FridelꢀCrafts alkylaion reaction of
indole.
20.26
1.66
V2O5
Al2O3
MnO
CaO
CuO
ZnO
*LOI*
Total
0.060
0.031
0.027
0.019
0.010
0.009
35.28
100.05
0.073
0.041
0.034
0.029
0.020
0.009
35.48
100.26
* Loss on Ignition (1000 °C, 2 h)
a ultrasonic irradiation
b vigorous stirring
Results and discussion
The preparation of the modified SAMN material was
accomplished by the assistance of ultrasound irradiation. The
effect of using ultrasound upon the size of the particles from
10ꢀ15 nm47 to 5ꢀ10 nm has been a noticeable phenomenon. This
particle size reduction affects the magnetic separation of the
material much easier and faster in comparison with our
previously reported SAMN47 (Scheme 1).
Figure 1. XRF analysis of SAMN a) by vigorous steering 47 b)
under ultrasonic irradiation
ClSO3H
Vigorous stirring
The results of transmission electron microscopy (TEM)
analysis of the SAMN demonstrate uniformꢀsized particles with
spherical morphology with an average size range of 5–10 nm
(Figure 2). This also shows the effect of ultrasonic irradiation
upon the size of the particles with respect to vigorous stirring
(10ꢀ15nm).47
CH2Cl2
Fe3O4 (10ꢀ15 nm)
Fe3O4
FeCl2.4H2O + 2 FeCl3.6H2O + 8OHꢀ
=SO3H
ClSO3H
rasound
Ult
CH2Cl2
Fe3O4 (5ꢀ10 nm)
Scheme 1
The new SAMN was characterized by XRF, TEM, and VSM
and the amounts of sulfonic acid functional group on magnetic
nanoparticles with maghemite coating supports was determined
by the neutralization titration method to be in the range of 4ꢀ4.5
mmolgꢀ1.
Xꢀray fluorescence analysis (Table 1) confirms the presence of
sulfonic acid on the catalyst surface. The XRF analysis proves
that the use of ultrasonic irradiation, instead of vigorous stirring
in sulfonation process of MNPs, reduces the conversion of
Fe3O4 to γFe2O3. The amount of γFe2O3 on the outer layer of
Fe3O4 is less than that of our previously reported procedure47
(Figure 1).
Table 1.XRF Analysis Results
Figure 2. TEM of SAMN prepared under ultrasound irradiation
Concentration
(%W/W)a
23.50
Concentration
(%W/W)b
42.65
Compound
Fe2O3
2 | J. Name., 2012, 00, 1-3
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The magnetization curves of the Fe3O4 and modified SAMN This modified material has been successfully applied as a
were further recorded at room temperature (Figure 3). The catalyst for Michael addition and Fridel Crafts reactions. In
saturation magnetization value of the modified SAMN is 90 order to optimize the reaction conditions with respect to
emugꢀ1 (Figure 3b). The number is smaller than that of uncoated temperature, time, and the molar ratio of the substrates, the
magnetic nanoparticles which is 93 emugꢀ1 (Figure 3a) and reaction of indole with methyl vinyl ketone as a model reaction
becomes nearly 1.63 times greater than that of our previous was studied. The reaction was proceeded sluggishly and after a
report for the preparation of Fe3O4@γFe2O3ꢀSO3H47 which is prolonged reaction time (5h), the corresponding Michael adduct
55 emugꢀ1 (Figure 3c) and nearly 3.2 times greater than γFe2O3ꢀ was produced in only 20% yield in the absence of the catalyst.
SO3H46 that is 28 emugꢀ1 (Figure 3d).
Then, similar reaction was performed in the presence of
different mol% of the modified SAMN. We observed a drastic
rate enhancement under solvent free conditions and also in
different solvents. Promissing results were obtained at room
temperature when solvent free condition or solvents such as
EtOH, CH3CN,
(Table 2).
nꢀhexane, CH2Cl2 and acetone were used
Table 2. Results of the reaction of indole (1 mmol) with methyl
vinyl ketone (1.1 mmol).
O
O
N
N
H
H
Cat.
(mol %)
ꢀ
Temp.
(◌C)
25
Time
(min)
300
Conversion
Entry
Solvent
(%)
20
100
1
2
ꢀ
ꢀ
Fe3O4 (0.07 g)
25
300
Fe3O4@γFe2O3ꢀSO3H
3
4
ꢀ
ꢀ
25
25
25
25
25
25
100
25
25
25
25
25
30
20
100
100
100
100
100
30
(5)
Fe3O4@γFe2O3ꢀSO3H
(7)
Fe3O4@γFe2O3ꢀSO3H
5
ꢀ
10
(10)
Fe3O4@γFe2O3ꢀSO3H
6
ꢀ
5
(15)
Fe3O4@γFe2O3ꢀSO3H
7
EtOH
H2O
H2O
PEG
180
300
300
300
150
120
120
240
(10)
Fe3O4@γFe2O3ꢀSO3H
8
(10)
Figure 3. Magnetization loops of a) Fe3O4, b) modified SAMN
c) previously reported SAMN47 d) γFe2O3ꢀSO3H.46 All the data
are recorded at room temperature.
Fe3O4@γFe2O3ꢀSO3H
9
70
(10)
Fe3O4@γFe2O3ꢀSO3H
10
11
12
13
14
20
(10)
Fe3O4@γFe2O3ꢀSO3H
(10)
Fe3O4@γFe2O3ꢀSO3H
(10)
Fe3O4@γFe2O3ꢀSO3H
(10)
Fe3O4@γFe2O3ꢀSO3H
(10)
n
ꢀHexan
100
100
100
100
The magnetization curve of the modified SAMN assures that
the use of ultrasonic irradiation produces an agile SAMN which
accumulates in a blink by an external magnetic field from water
(Figure 4).
CH3CN
CH2Cl2
Acetone
In order to show the general applicability of the method, the
reaction of various indoles with α,βꢀunsaturated carbonyl
compounds under solvent free conditions was studied. The
results of this study are tabulated in Table 3.
Table 3. Michael addition of various indoles to α, βꢀunsaturated
ketones [a]
.
Entry
Product
Time (min)
Yield (%)
Figure 4. a) Dispersed modified SAMN in water b) Fast
separation of the modified SAMN with a magnet bar from
water.
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yield after a long reaction time (24h). In the presence of the
modified catalyst, the reaction was progressed well at room
temperature and the desired bisindolyl methane was produced
rapidly (15 min) in a quantitative yield in solvents such as
EtOH, CH3CN, CH2Cl2 and petroleum ether at different
reaction times (Table 4).
1
10
95
Table 4. Results of the reaction of indole (2 mmol) with benzaldehyde
(1 mmol) in different media.
2
60
90
Tem.
(◌C)
25
Time
(h)
24
Conversion
Entry
Cat. (mol %)
Solvent
(%)
30
100
1
2
ꢀ
EtOH
EtOH
3
4
5
180
240
10
93
90
97
Fe3O4
Fe3O4@γFe2O3
SO3H (5)
Fe3O4@γFe2O3
SO3H (7)
Fe3O4@γFe2O3
SO3H (10)
Fe3O4@γFe2O3 ꢀ
SO3H (15)
Fe3O4@γFe2O3
SO3H (10)
Fe3O4@γFe2O3
SO3H (10)
Fe3O4@γFe2O3
SO3H (10)
25
5
ꢀ
ꢀ
ꢀ
3
4
EtOH
EtOH
EtOH
EtOH
H2O
25
25
25
25
25
100
25
25
25
25
1
0.5
0.33
0.25
24
5
100
100
100
100
50
5
6
ꢀ
ꢀ
ꢀ
7
8
H2O
60
9
PEG
24
2.5
6
30
Fe3O4@γFe2O3 ꢀ
SO3H (10)
Fe3O4@γFe2O3 ꢀ
SO3H (10)
Fe3O4@γFe2O3 ꢀ Petroleum
SO3H (10) Ether
10
11
12
CH3CN
CH2Cl2
100
100
100
8
However, in order to show the advancement of the catalytic
activity of the ultrasonically assisted preparation of SAMN
with our previously reported SAMN,47 the reaction of
benzaldehyde with indole was studied (Schemes 2).As it is
evident from the results, the catalytic activity of the modified
SAMN is considerably 18 times greater than the nonꢀmodified
one.
6
7
8
5
95
97
98
120
60
Scheme 2
To demonstrate the general widespread application of the
method, the addition of structurally different indoles to
aldehydes in EtOH at room temperature was studied. The
results of this study are listed in Table 5.
[a] Reaction conditions: indole (1 mmol), α, βꢀunsaturated carbonyl compound (1.1
mmol) and modified SAMN (0.1 mmol, 0.03 g) were mixed and mechanically stirred at
room temperature.
Table 5. Bisindolyl methane synthesis in the presence of the modified
[a]
SAMN
.
In continuation of our studies, FriedelꢀCrafts alkylation reaction
of indole with an aldehyde was also investigated in the presence
of the modified catalyst. At first, the reaction of benzaldehyde
with indole was studied as a model reaction to optimize the
reaction conditions. In the absence of the catalyst, 3, 3'ꢀ
(phenylmethylene)bis(1Hꢀindole) was produced in only 30%
Tim
e
(min
Yiel
d
(%)
Entry
Product
4 | J. Name., 2012, 00, 1-3
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)
1
2
20
95
Scheme 3: Michael addition of indole to methyl vinyl ketone in large
scale catalyzed by modified SAMN catalyst.
HN
NH
H3CO
OCH3
30
91
N
Scheme 4: Bisindolyl methane synthesis in large scale catalyzed by
modified SAMN catalyst.
N
H
H
OH
Efficient recycling of the catalyst is important from
environmental and economic point of views. Therefore,
recycling of this catalyst was studied for the reaction of indole
with methyl vinyl ketone (Figure 5). After completion of each
run, the catalyst was separated by an external magnetic bar and
then was reused for another batch of the reaction. This process
has been repeated for 5 consecutive runs without observable
decrease in catalytic activity of the catalyst (Figure 5). This
observation shows that the morphology and also the size of the
particles of the catalyst should not be changed during different
runs. This observation shows that the morphology and also the
size of the particles of the catalyst should not be changed
during different runs. In order to approve this statement, TEM
image of the catalyst after the first run of recycling was
compared with the TEM image of the catalyst before reaction
(Figure 5) It shows that the size (10ꢀ15nm) and the morphology
(spherical) of the catalyst has been preserved during the
reaction (Figure 6).
OH
3
4
10
20
95
94
HN
NH
OH
HN
NH
F
5
6
20
15
90
93
HN
NH
NO2
N
N
H
H
7
8
5
93
98
N
N
60
Figure 5. Recycling of the modified catalyst for 5 consecutive runs for
Michael addition reaction of indole with methyl vinyl ketone.
HN
NH
[a] Reaction conditions: indole (2 mmol), aldehyde (1 mmol) and modified SAMN (0.1
mmol, 0.03 g) and ethanol (1 mL) were mechanically stirred at room temperature
The high purity of the products with respect to the iron
contamination has been approved by manganometry titration
analysis.
Considering the importance of using catalysts for the large
scale operation and their further applications in industry, we
have studied the use of the catalyst in large scale Michael
addition and FriedelꢀCrafs alkylation reactions with success
under solvent free condition and in EtOH respectively (
Schemes 3 and 4).
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stopped. The resulting modified SAMN material was separated
by an external magnet and washed with dichloromethane (3×5
mL) and finally dried in an oven at 40˚C. A brown solid of the
modified Fe3O4@γFe2O3ꢀSO3H was obtained that was
characterized by XRF, TEM, FTIR.
General procedure for the oneꢀpot reaction of indole with
α, βꢀunsaturated carbonyl compounds:
Modified SAMN (10 mol%, 0.03 g) was added to a stirring
mixture of indole (1 mmol, 0.117 g) and α, βꢀunsaturated
carbonyl compounds (1.1 mmol) at room temperature. The
progress of the reaction was monitored by TLC
(hexane/ethylacetate eluent 5:1). After completion of the
reaction, ethanol (10 mL) was added to the reaction mixture.
The catalyst was separated by a permanent magnet from the
reaction mixture. The desired Michael adducts were obtained
after concentration of the reaction mixture under diminished
pressure as a highly pure crystalline or oily compounds in good
to excellent yields (Table 3).
General procedure for bisindolyl methane synthesis:
A mixture of indole (2 mmol, 0.234), aldehyde (1 mmol) and
modified SAMN (10 mol%, 0.03 g) in ethanol (1 mL) was
mechanically stirred at room temperature. After completion of
the reaction (TLC, hexane/ethylacetate, 4:1), the resulting
mixture was diluted with ethanol (15 mL) and the solid catalyst
was separated by a permanent magnet from the reaction
mixture. Upon evaporation of ethanol under vacuum from the
resulting solution, the desired pure crystalline product was
obtained in high to excellent yields (Table 5).
Figure 6. TEM image of the catalyst after the 1st run of recycling shows
that the size (10ꢀ15nm) and the morphology (spherical) of the catalyst
nano particles are preserved
Experimental Section
General Experimental Methods:
All commercially available chemicals were obtained from
Merck and Fluka Chemical Companies, and used without
further purification unless otherwise stated; Solvents were
distilled before their use. The products were characterized using
FTIR, 1HNMR (500 MHz) and 13CNMR (125 MHz)
spectroscopy. All the reactions are monitored by thin layer
chromatography (TLC) coated with silica gel illuminated with
UV light and iodine as the reagent. All yields refer to the
isolated products.
Conclusions:
In conclusion, the preparation of the modified SAMN material
was accomplished by the assistance of ultrasound irradiation.
The effect of using ultrasound upon the size of the particles
from 10ꢀ15 nm ( our previous work) [47] to 5ꢀ10 nm has been a
noticeable phenomenon. This particle size reduction affects the
magnetic separation of the material much easier and faster in
comparison with the previously reported SAMN 47. The agile
magnetic hydrogen sulfate nanoparticles produced under the
influence of ultrasound irradiation accumulate in a blink with
an external magnetic field from the reaction mixture. This
magnetic separation is facile and eliminates time consuming
filtration process. In the presence of this modified catalyst
under solvent free condition, Michael addition of indols with α,
βꢀunsaturated carbonyl compounds proceeded well and
produced the desired highly pure Michael addition adducts in
excellent yields. The modified SAMN is also an effective
catalyst for FriedelꢀCrafts alkylation reaction. For this purpose,
the reaction of indoles with aldehydes resulted bisindolyl
methane in excellent yields in ethanol as a green solvent. The
protocol is applicable for large scale operation without
difficulties. The catalyst is recyclable with preservation of its
catalytic activity after several reaction runs. The modified
catalyst activity, as observed in a model reaction, is much
higher, 18 times, than our previously reported SAMN[47].
Preparation of the modified Fe3O4 nanoparticles (NPs):
The Fe3O4 NPs were prepared by using the published method48
with modification. FeCl3·6H2O (20 mmol) and FeCl2·4H2O (10
mmol) were added to deionized water (4 mL) under nitrogen
atmosphere with ultrasound irradiation for 15 min at 60 °C.
Then, ammonium hydroxide (15 mL, 28 wt%) was added
rapidly to the resulting solution. The solution was immediately
turned black. The reaction was kept at 60 °C for 20 min under
ultrasound irradiation. The black precipitates were collected
with an external magnet and washed with distilled water. The
resulting Fe3O4 NPs were dried for 12h at room temperature
under vacuum and characterized by XRD, FTIR.
Preparation of the MNHS:
A suction flask was equipped with a constantꢀpressure dropping
funnel and a gas inlet for leading the generated HCl into water.
To this flask, which contains nanoꢀparticles of Fe3O4 (1.00 g) as
described in the preceding paragraph in dichloromethane (20
mL), cholorosulfonic acid (1.0 mL) was added drop wise at
room temperature for 15 min under ultrasound irradiation. The
resulting mixture was sonicated until HCl gas evolution was
Acknowledgements
The authors would like to thank the Research Council of Yazd
University for financial support of this work. H.F. is also
thankful for
a grant (BN048) from the National Elite
Foundation of Iran.
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12, 743ꢀ754.
31. S. Shylesh, V. Schünemann and W. R. Thiel, Angew. Chem.
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