Magnetic nanocatalyst for the synthesis of maleimide and phthalimide derivatives

Article abstract of DOI:10.1039/c4ra09008j

An efficient and green protocol for the synthesis of N-aryl maleimide and phthalimide derivatives has been developed. The high efficiency of the catalyst was observed due to the homogeneous distribution of the nanoparticles. The catalyst was fully characterised by physicochemical methods such as IR spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction, dynamic light scattering (DLS), energy dispersive X-ray spectrum and zeta potential measurement techniques. The ease of separation of the catalyst from the reaction mixture and its high activity are eco-friendly attributes of this system.

Full text of DOI:10.1039/c4ra09008j

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PAPER
Magnetic nano catalyst for the synthesis of maleimide and phthalimide
derivatives.
Pranila B. Thalea, Pravin N. Borasea, and Ganapati S. Shankarlinga
Cite this: DOI: 10.1039/x0xx00000x
An efficient and green protocol for the synthesis of
Nꢀaryl maleimide
and phthalimide derivatives is developed. The high efficiency of the
catalyst was observed due to homogeneous distribution of the
nanoparticles. Catalyst was fully characterised by physicochemical
methods such as IR spectroscopy, scanning electron microscopy (SEM),
transmission electron microscopy (TEM), Xꢀray diffraction, dynamic
light scattering (DLS), energy dispersive Xꢀray spectrum and zeta
potential measurement techniques. The ease of separation of the catalyst
from the reaction mixture and its high activity are ecoꢀfriendly attribute
Received 00th January 2012,
Accepted 00th January 2012
DOI: 10.1039/x0xx00000x
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of
this
system.
Introduction:
Nanoparticles have emerged as an important tool in catalysis1,2. It acts as a bridge between homogeneous
and heterogeneous catalysis. Nanoparticles can get homogenised in reaction mixture during organic
synthesis to increase catalytic efficiency and it can be easily separated by means of centrifugation or
external magnetic field3. Since past few years, catalyst supported over magnetic nanoparticles have
gained considerable attention in CꢀX coupling and other organic reactions4–8. Hazardous mineral acids are
always in demand for numerous acid catalysed reactions for their excellent catalytic performance9.
However, their sepraration from reaction mixture exhibits limitation on their use due to enviormental
concerns. Such mineral acids after supporting over magnetic nanoparticles, can be eaisly seperated from
reaction mixture without hampering their catalytic activity, which makes the protocol more cost effective
and environmentally benign. NꢀSubstituted imide derivatives find wide application in medicinal
chemistry10,11 biology12,13 material science and polymer chemistry14. Maleimides are backbone of peptideꢀ
conjugate haptens, immune conjugates, and enzyme inhibitors15. In organic synthesis, imide derivatives
play a vital role for protection of amino group16. Despite their wide application, availability of
environmentally benign, inexpensive synthetic protocol for the preparation of imides is limited.
_____________________________________________________________________________________________________________________________________________________________
aDyestuff Technology Department, Institute of Chemical Technology, Mumbai 400019, India.
Corresponding author: Tel: 91ꢀ22ꢀ33612708, Fax: +91ꢀ22ꢀ33611020, Eꢀmail address: gsshankarling@gmail.com
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DOI: 10.1039/C4RA09008J
The conventional methods for synthesis of imide derivatives are the dehydrative condensation of
anhydride and amine in the presence of sulfuric acid17 and Nꢀalkylation of imides promoted by PPh3 in
presence of alcoholic media18. These conventional protocol suffer drawback like high temperature and
longer reaction time. Several attempts have been reported using ionic liquids19,20 as well. Unfortunately,
they also suffer from longer reaction time and tedious product isolation methods. Hence, there is a need
for development of protocol for the synthesis of imide derivatives with a shorter reaction time and easy
separation of products from reaction mass. In current protocol, we have introduced sulphuric acid
functionalised silica supported over magnetite nanoparticles. It provides easy separation of catalyst from
reaction mass and its recyclability induces cost effectiveness to the system.
<Insert Scheme: 1>
Results and discussion:
In the present work, we have reported a simple, efficient and practical approach for the synthesis of Nꢀ
aryl imide derivatives. We have used phthalic anhydride, aniline as standard substrates to screen a
suitable solvent for the reaction. Among the tested solvents, ethanol was the most effective reaction
medium for Nꢀinsertion reaction (Table 1, Entry 6). Low yield of the target product was obtained when
EDC, DMF, toluene, acetone were used as solvents. When the reaction was carried out on bare magnetite
nano particle Fe3O4 (Table 1, Entry 4), as well as on bare silica coated nano particle Fe3O4@SiO2 (Table
1, Entry 5), it resulted in poor yield. Whereas, it gave a good yield with sulfonic acid functionalized silica
coated magnetite nano catalyst. To determine the catalyst loading model reaction of phthalic anhydride
and aniline in ethanol was performed. The reaction occurred smoothly in presence of 20 wt.% of
Fe3O4@SiO2ꢀSO3H, affording a single product (Table 2, entry 4) in 89% yield. Increasing the amount of
catalyst, to more than 20 wt.% showed no substantial improvement in the yield. It is worthy to mention
that, we examined the model reaction without any catalyst in ethanol at reflux temperature and the
product yield did not increased beyond 29% even after prolonged heating (Table 1, Entry 1). The
optimized reaction conditions include 3.37 mmol of phthalic anhydride, 3.37 mmol of aniline and 20
wt.% of Fe3O4@SiO2ꢀSO3H in ethanol at 80°C. Furthermore, for comparison the model reaction was
carried out using amberlyst 15 and silica sulfuric acid under the similar condition which gave the desired
product in 81% and 77% yield respectively (Table 1, Entries 2 and 3) after 8 hr. of heating. This suggests
that, catalyst plays a major role in the reaction. The reaction was faster in case of Fe3O4@SiO2ꢀSO3H
catalyst because of acid active sites and higher surface area of the catalyst due to its nano form. To
investigate the effect of electron donating and withdrawing group on the rate of reaction, we have studied
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DOI: 10.1039/C4RA09008J
different anhydride with various aromatic primary amines (Table 3). In case of electron donating
substituent the reaction was faster and gave better yield whereas, reaction afforded moderate to good
yield when an electron withdrawing substituent was present on the aromatic amine. The proposed reaction
mechanism of the reaction using catalyst is depicted in fig.1.
The catalyst was easily separated from the reaction mixture by magnetic separation method. It was
successfully recycled up to six runs. The catalyst performs well with high turnover number (TON) and
turn over frequency (TOF), which indicates that the catalyst is highly stable and efficient. The quanta of
acid sites determined on the catalyst is 0.4 mmolgꢀ1.
Table 1: Effect of solvent and catalyst on the synthesis of Nꢀphenyl phthalimide.
Time
Entry
Catalyst
Wt.%
Solvent/ Temp
Yield (%)a
(hr.)
4
1
2
ꢀ
ꢀ
Ethanol/80°C
Ethanol/80°C
29%
81%
Amberlyst 15
20%
8
3
4
Silica sulfuric acid
Fe3O4
20%
20%
20%
20%
20%
20%
20%
20%
Ethanol/80°C
Ethanol/80°C
Ethanol/80°C
Ethanol/80°C
Toluene/ 80°C
DMF/80°C
8
1
1
1
1
1
1
1
77%
traces
traces
89%
72%
70%
30%
32%
5
Fe3O4@SiO2
6
Fe3O4@SiO2ꢀSO3H
Fe3O4@SiO2ꢀSO3H
Fe3O4@SiO2ꢀSO3H
Fe3O4@SiO2ꢀSO3H
Fe3O4@SiO2ꢀSO3H
7
8
9
EDC/80°C
Acetone/55°C
10
aisolated yields
Reaction condition: phthalic anhydride: 3.37 mmol; aniline: 3.37 mmol; Solvent: 5ml
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DOI: 10.1039/C4RA09008J
Table 2: Effect of catalyst loading (wt.%) on the synthesis of Nꢀphenyl phthalimide.
Entry
Catalyst wt.% Time (hr.) Yield(%)a
1
2
3
4
5%
5.0
3.0
2.5
1.0
1.0
60%
67%
74%
89%
89%
10%
15%
20%
25%
5
aisolated yield
Reaction condition: phthalic anhydride: 3.37 mmol; aniline: 3.37 mmol; Solvent: ethanol:
5ml; Temp = 80°C.
Table 3: The synthesis of Nꢀaryl imide derivatives in presence of Fe3O4@SiO2ꢀSO3H.
Yield
(%)a
TOFc
Entry
A
Product
Time
2 hr.
TONb
(min. ꢀ1)
41.96
0.34
84%
86%
88%
81%
B
C
D
42.96
43.96
40.46
0.35
0.32
0.29
2 hr.
1 hr. 30
min
O
N
O
2 hr. 15
min
Cl
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O
Cl
2 hr. 45
min
E
F
G
H
I
N
Cl
38.46
39.96
37.96
75.11
0.23
0.29
0.15
1.25
77%
80%
76%
89%
O
2 hr. 15
min
4 hr.
1 hr.
75.95
1.26
1hr.
90%
J
76.80
68.36
1.70
0.75
45 min
91%
81%
K
1hr. 30 min
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DOI: 10.1039/C4RA09008J
L
M
N
67.51
65.83
64.98
0.64
1hr. 45min
80%
78%
77%
O
N
F
0.73
0.43
1hr. 30 min
O
O
2 hr. 30
min
N
NO2
O
aisolated yield
bTON= turn over number
cTOF= turn over frequency
Reaction condition = Temp. 80°C; catalyst loading: 20 wt.% ; Reaction medium: 5 ml ethanol
Characterisation of the catalyst:
TEM image of the catalyst display dark Fe3O4 core surrounded by a lighter amorphous silica shell as
shown in fig. (2b) which confirms that the catalyst has been encapsulated by a thin layer of silica particles
and it has average particle size of 30 nm. The energy dispersive spectrum indicated the presence of Fe, Si
and S (fig.12 supporting information). SEM image of Fe3O4@SiO2ꢀSO3H nanoparticles is shown in fig.
(2a) which shows spherical morphology and it has marked tendency to form large aggregates. The
clustering tendency was observed because of weak hydrogen bonding forces between Fe3O4@SiO2ꢀSO3H
and magnetic characteristic of nanoparticles.
The XRD analysis of Fe3O4, Fe3O4@SiO2, Fe3O4@SiO2ꢀSO3H has been done and its comparative spectra
is depicted in fig.3. The XRD spectrum of Fe3O4 clearly matches with those of the literature report 21. The
XRD pattern of Fe3O4@SiO2, Fe3O4@SiO2ꢀSO3H shows broad band at 2ꢀ =20ꢀ24° which is due to the
presence amorphous silane shell formed around the magnetic core. There is no any other appreciable
shift in the peak positions,which indicates the structural stability of magnetite nanoparticles. The zeta
potential of the Fe3O4, Fe3O4@SiO2 and Fe3O4@SiO2ꢀSO3H samples has been performed to determine the
surface modification of the nanoparticle. The observed zeta potential of the Fe3O4 and Fe3O4@SiO2 were
about ꢀ45mV and ꢀ120mV (fig.8 & 9 supporting information) respectively, which explains that the
surface modification of the nano Fe3O4 has occurred and it is in good agreement with the literature data22.
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The zeta potential distribution for Fe3O4@SiO2ꢀSO3H is positively charged at 25.3mV (82%) and 95.5
mV (18%). It is because of presence of H+ ion on the surface of the catalyst fig. 4. To determine
percentage average particle present in the sample, dynamic light scattering measurement were carried out
as shown in fig. 5 and the observed results were similar to the literature report23. For this, aqueous stock
solution (1 mg/ml of water) was prepared in ultrasonic bath for 30 min.
The IR spectroscopy shows band between 637ꢀ410 cm−1 which corresponds to stretching vibration of Feꢀ
O bond24. The band at 1080 cm−1 corresponds to SiꢀO stretching vibration fig. 6b. The weak band at 814
cm−1 is observed for SiꢀOꢀFe bond fig. 6b which indicates immobilisation of silica on the surface of
Fe3O4 nanoparticle25. This band is shifted to 807 cm−1 in case of Fe3O4@SiO2ꢀSO3H fig 6c. The fig. 6a
and 6b shows broad peak between 3000ꢀ3400 cm−1 and a sharp peak around 1630 cm−1 for the presence
of adsorbed water. The absorption band at 1128 cm−1 corresponds to stretching of SꢀO bond fig 6c, which
justify the presence of the sulfonic acid group on its surface. The broad absorption at 3453 cm−1 and sharp
peak at 1624 cm−1 corresponds to stretching vibration of OH group in the SO3H fig. 6c.
<Insert Figure: 2>
<Insert Figure: 3>
<Insert Figure: 4>
<Insert Figure: 5>
<Insert Figure: 6>
Recyclability study:
The catalyst recyclability study was carried out on phthalic anhydride 3.37 mmol, aniline 3.37 mmol
and catalyst (20 wt.%) in 5 ml ethanol at 80°C. The results are summarised in fig. (7). After completion of
the reaction, catalyst was separated by an external magnet, washed with acetone and dried at 60°C for 1
hr. The recovered catalyst was then used for next batch. It was observed that catalyst could be recycled
efficiently up to six runs. SEM and TEM images of the recycled catalyst were taken fig. (8a and 8b)
which show that, the structural and morphological properties of the catalyst remain unaltered even after
6th recycle. The comparative IR spectra of fresh and reused catalyst shows that there is no change in
functional group values (fig.7 supporting information)
<Insert Figure: 7>
<Insert Figure: 8>
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Determination of acidic sites:
The surfaceꢀbound acidic protons were ion exchanged with a brine solution by sonicating the
Fe3O4@SiO2ꢀSO3H catalyst for 24 hr. The catalyst was separated magnetically, the brine solution was
decanted and titrated with 0.1N NaOH solution to determine the loading of acid sites on the catalyst. The
H+ ions loading was found to be 0.40 mmol gꢀ1.
Experimental:
Materials and Methods:
TEM studies of the nano catalyst were carried out with JEOL JEMꢀ2100 instrument. SEM micrographs
and EDXS data were obtained on JEOL JSM 6380LA instrument. The XRD study was performed on a
Bruker AXS powder diffractometer D8 with Cuꢀkα (1.54°A). The FTꢀIR spectra of the catalyst were
measured with KBr pellets using a BrukerꢀVERTEX 80v vacuum FTIR spectrometer and the IR spectra
of the synthesized compound were recorded on Jasco FTꢀIR ATRꢀPRO/4100 spectrophotometer. 1H
NMR spectra were recorded on Bruker 400 MHz Spectrometer and Agilent 500 MHz spectrometer in
CDCl3 solvent. Mass spectral data were obtained with a Finnigan LCQ Advantage max spectrometer.
Iron(III) chloride hexaꢀhydrate (98%), Iron(II) chloride tetrahydrate (99%), chlorosulfonic acid and other
chemical materials were purchased from S.D. Fine Chemical Ltd., India. and tetra ethyl ortho silicate
were purchased from sigma aldrich Chemicals. Anhydride and aniline were also purchased from S.D.
Fine Chemical Ltd., India.
General procedure for preparation of catalyst:
Fe3O4@SiO2 nanoparticles were prepared by the literature reported method26,27. Under nitrogen
atmosphere, mixture of 5.0 g of ferric chloride and 1.85 g of ferrous chloride salts were dissolved in
distilled water and heated to 90°C. Then aqueous ammonia solution (25%) was added, from which
precipitate of Fe3O4 was obtained. The supernatant was decanted and precipitate was isolated by magnetic
separation. The obtained black powder (Fe3O4) was washed with acetone and dried under vacuum. The
coating of silica on the surface of Fe3O4 nanoparticle was achieved, by diluting 2.0 g of Fe3O4
nanoparticle in water (40 ml), ethanol (120 ml) and aqueous ammonia solution (3.0 ml, 25%). The
resultant dispersion was homogenised by sonicating it for 1 hr. at 40°C. Then subsequently, tetraethyl
orthosilicate diluted in ethanol was charged slowly under continuous mechanical stirring and further the
mixture was stirred for 12 hr. The resultant brown powder was separated magnetically and washed three
times with acetone and then dried.
The immobilization of sulfonic acid group on Fe3O4@SiO2 was done by the literature reported method28.
For preparation of sulfonic acid coated nano catalyst, mixture of silica coated magnetite (2.0 g) and 10 ml
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of nꢀhexane was cooled. Chlorosulfonic acid (1.0 g) was added slowly to the above mixture over a period
of 30 min at room temperature. The resulted sulfonic acid coated magnetic nano particles were separated
and washed repeatedly with ethanol and dried in the oven at 60°C.
General procedure for synthesis of imide derivatives:
In a general procedure, mixture of phthalic anhydride (0.5g, 3.37 mmol), aniline (0.31g, 3.37 mmol) and
Fe3O4@SiO2ꢀSO3H (0.1 g, 20 wt.%) in ethanol (5 ml) was stirred for 60 min at 80°C. After completion of
the reaction (monitored by TLC), the catalyst was separated from the reaction mass by use of an
external magnet. The organic layer was concentrated under reduced pressure to give the desired product
which was subsequently purified in ethanol. The recovered catalyst was washed with acetone and dried at
60°C to give recyclable Fe3O4@SiO2ꢀSO3H. Yield 89%, 0.67 g, m.p. 208°C. All compounds were
analysed by melting point, mass, IR and 1HꢀNMR techniques.
Conclusion:
In conclusion, we have developed an efficient protocol for the synthesis of Nꢀaryl phthalimide and
biphenyl maleimide derivatives using sulphonic acid functionalised silica over magnetite Fe3O4
nanoparticles. These reactions were optimised for various parameters and have been employed for wide
substrates. The advantages offered by this protocol include high TON values, easy separation method and
recyclability of the catalyst up to six runs. This simple, efficient protocol can be explored for other
organic synthesis in future as well.
Acknowledgment:
Authors are thankful to UGCꢀSAP, Technical Education Quality Improvement Programme, for providing
financial assistance and Institute of Intensive Research for Basic Sciences for recording 1H NMR.
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Figure Captions:
Scheme1:
Figure 1: Proposed reaction mechanism.
Figure 2: (a) SEM and (b) TEM images of Fe3O4@SiO2-SO3H catalyst.
Figure 3: XRD spectra of (a) Fe3O4, (b) Fe3O4@SiO2 and (c) Fe3O4@SiO2-SO3H.
Figure 4: Zeta potential of Fe3O4@SiO2-SO3H.
Figure 5: DLS measurement of (1) Fe3O4 (2) Fe3O4@SiO2 and (3) Fe3O4@SiO2-SO3H.
Figure 6: FT-IR spectra of (a) Fe3O4, (b) Fe3O4@SiO2 and (c) Fe3O4@SiO2-SO3H.
Figure 7: Recyclability study of Fe3O4@SiO2-SO3H in the synthesis of N-phenyl phthalimide.
Fig: 8 (a) SEM and (b) TEM images of recovered catalyst after six successive runs of
reaction.
Scheme1:
1

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Figure 1: Proposed reaction mechanism.
Figure 2: (a) SEM and (b) TEM images of Fe3O4@SiO2-SO3H catalyst.
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Figure 3: XRD spectra of (a) Fe3O4, (b) Fe3O4@SiO2 and (c) Fe3O4@SiO2-SO3H.
Figure 4: Zeta potential of Fe3O4@SiO2-SO3H.
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Figure 5: DLS measurement of (1) Fe3O4, (2) Fe3O4@SiO2 and (3) Fe3O4@SiO2-SO3H.
Figure 6: FT-IR spectra of (a) Fe3O4, (b) Fe3O4@SiO2 and (c) Fe3O4@SiO2-SO3H.
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Figure 7: Recyclability study of Fe3O4@SiO2-SO3H in the synthesis of N-phenyl phthalimide.
Fig: 8 (a) SEM and (b) TEM images of recovered catalyst after six successive runs of
reaction.
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Graphical abstract: