An imidazolium based ionic liquid supported on Fe3O4@SiO2 nanoparticles as an efficient heterogeneous catalyst for N-formylation of amines

Article abstract of DOI:10.1039/c6nj03985e

An imidazolium based ionic liquid, 1-methyl-3-(3-triethoxysilylpropyl) imidazolium chloride, could be immobilized on the surface of silica-coated ferrite nanoparticles (Fe₃O₄@SiO₂-IL) and could be evaluated as a recyclable catalyst for the N-formylation of amines using formic acid under solvent-free conditions. The prepared organic-inorganic hybrid material could be characterized by various techniques such as Fourier Transform Infrared Spectroscopy (FT-IR), X-Ray Diffraction (XRD), Transmission Electron Microscopy (TEM), Scanning Electron Microscopy (SEM), Energy Dispersive X-Ray Spectroscopy (EDS) and Vibrating Sample Magnetometer (VSM) studies. Utilizing the ferromagnetic nature of Fe₃O₄, the prepared catalyst could be easily recovered after completion of the reaction by using an external magnetic field. The catalyst could be reused for up to five runs with remarkable catalytic activity. The described methodology has various advantages when compared with other methods that rely on homogeneous catalysts.

Full text of DOI:10.1039/c6nj03985e

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ISSN 1144-0546
PAPER
Jason B. Benedict et al.
The role of atropisomers on the photo-reactivity and fatigue of
diarylethene-based metal–organic frameworks
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Received 00th January 20xx,
Accepted 00th January 20xx
Imidazolium Based Ionic Liquid Supported
on Fe O @SiO Nanoparticle as an Efficient
3
4
2
DOI: 10.1039/x0xx00000x
Heterogeneous Catalyst for N-formylation
of Amines
www.rsc.org/
a
a
a
Charu Garkoti, Javaid Shabir and Subho Mozumdar*
Abstract: An imidazolium based ionic liquid, 1-methyl-3-(3-
triethoxysilylpropyl) imidazolium chloride, could be immobilized on the
3 4 2
surface of silica coated ferrite nanoparticle (Fe O @SiO -IL) and could be
evaluated as a recyclable catalyst for the synthesis of N-formylation of
amines using formic acid under solvent-free conditions. The prepared
organic-inorganic hybrid material could be characterized by various
techniques such as Fourier Transform Infrared Spectroscopy (FT-IR), X-Ray
Diffraction (XRD), Transmission Electron Microscopy (TEM), Scanning
Electron Microscopy (SEM), Energy Dispersive X-Ray Spectroscopy (EDS)
and Vibrating Sample Magnetometer (VSM) studies. Utilizing the
3 4
ferromagnetic nature of Fe O , the prepared catalyst could be easily
recovered after completion of reaction by using an external magnetic field.
The catalyst could be reused up to five runs with remarkable catalytic
activity. The described methodology has various advantages when
compared with other methods that rely on homogeneous catalysts.
Keywords: Magnetic nanoparticles, Ionic liquid, N- formylation of Amine,
Solvent-free.
1
. Introduction
In recent years, one of the most important developments in the field of
1
green chemistry has been the use of ionic liquids (ILs) in organic synthesis.
Beyond their use as an alternative reaction media, ionic liquids are
increasingly being explored as task specific catalyst in many of the organic
2
-5
synthesis. In this respect, ionic liquid (IL) based on imidazolium ions have
shown great catalytic performance and have, therefore, received
6
-10
a
considerable interest as eco-friendly catalyst in organic transformations.
Department of Chemistry, University of Delhi, Delhi.India 110007
This is mainly because of their properties, such as non-flammability, low
1
1-16
volatility and high thermal stability.
However, they suffer from high
viscosity and this typically results in only a minor part of ILs taking part in
17-19
the catalyzed reaction.
In addition to their high viscosity, because of
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6
2
their homogeneous nature, imidazolium based ionic liquids also suffer from
the major limitation of their poor recovery from the final reaction
liquid as solvent for N-formylation of Amines under ultrasonic irradiation.
Because of the use of ultrasonic irradiation, the product yield was excellent,
still this protocol suffers from the drawback of higher reaction time and
excessive use of ionic liquid as solvent which is difficult to recycle.
2
0-22
product.
In order to overcome this problem of recoverability of imidazolium based
ionic liquids, the development of a heterogeneous catalytic system is being
worked upon. Numerous methods have been developed to immobilize
ionic liquids on a large variety of solid supports (such as mesoporous
In the recent past, Rostamnia et al and Shirini et al have supported sulfamic
acid and methyl imidazolium based ionic liquids on SBA-15 and nanoporous
sodium montmorillonite clay, respectively. They have employed them as
2
3-27
28-30
31, 32
33-
silica,
amorphous silica,
graphene oxide
and carbon nanotubes
heterogeneous catalyst for N-formylation of amines under solvent free
3
5
61, 63
)
making it very easy and simple to separate these heterogeneous
conditions.
Although the catalyst is recoverable but still there are
catalysts from the reaction mixture and reusing them in subsequent
reactions. Although, all the above mentioned heterogeneous catalyst are
reusable but their recovery from reaction mixture needs tedious procedure
like filtration or centrifugation. In the last couple of years, functionalized
ferrite nanoparticles have emerged as alternatives to conventional
materials because of their high surface area and ability to act as
drawbacks like laborious task of filteration or centrifugation to recycle the
catalyst and requirement of higher temperature to carry out the reaction. In
order to overcome most of the drawbacks related to the use of ionic liquids
as catalyst for N-formylation of amines, we have utilised our prepared ferrite
3 4 2
supported imidazolium based ionic liquids (Fe O @SiO -IL) as magnetically
recoverable catalyst for N-formylation of Amines under solvent free
condition at room temperature. The described method provides some
advantages when compared with other protocols for the same reaction
under solvent free conditions, such as excellent yield at room temperature,
low reaction time and the more importantly magnetic recyclability of the
catalyst for further use upto five catalytic cycles without any appreciable loss
in the catalytic activity. The prepared catalyst acts as an efficient “quasi-
homogeneous” catalyst, which is highly dispersable like homogeneous
catalyst in the reaction system and recoverable as heterogeneous catalyst
by using external magnetic force and reusable for multiple cycles.
36-40
heterogeneous catalyst supports.
In addition, ferrite nanoparticles have
the advantage of being magnetically recoverable from reaction mixture
after the completion of reaction, thereby eliminating the requirement of
catalyst filtration or centrifugation after completion of the reaction as in
the case of other solid support materials. Hence, the major advantage of
these magnetic nanoparticles, apart from their relative non-toxicity, is
their easy accessibility and recyclability. The magnetic nano-catalysts can
be further surface-modified so as to increase their activity and selectivity
41, 42
towards different organic transformations.
In order to address some of the drawbacks related to the use of ionic liquid Furthermore, to the best of our knowledge, this is the first report on the
as homogeneous catalyst, a ferrite nanoparticle supported imidazolium preparation and application of magnetic nanoparticles supported
based ionic liquid (Fe @SiO -IL) has been synthesized. Continuing with the imidazolium based ionic liquid for N-Formylation of amines .
idea of synthesizing effective nano-catalysts for organic transformations,
the prepared Fe @SiO supported ionic liquid (Fe @SiO -IL) was used as
a
3
O
4
2
43-45
3
O
4
2
3
O
4
2
a catalyst for the N–formylation of amines under solvent free conditions. N-
formyl compounds have emerged as an important intermediates in the
4
6, 47
48
preparation of pharmaceutically important compounds,
isocyanides
4
9
and formamidines. They have also been used as a catalyst for some
5
0
46
reactions such as allylation and hydrosilylation of carbonyls. In addition,
5
1
formyl group is an important amino protecting group in peptide synthesis.
Various procedure have been reported where numerous catalyst were used
5
2-56
for N-formylation of amines under solvent free condition.
There are few
reports where ionic liquid has been used as homogeneous catalyst for the
5
7, 58
N-formylation of amines.
Also, there are some reported protocols which
describe the use of imidazolium based ionic liquids with different counter
ions that were employed as homogeneous catalyst for the N-formylation of
5
9-61
amines under solvent free conditions.
However, these protocols have
some limitations, such as inactivity of catalyst at room temperature,
difficulty in the isolation of product and the most important is the non-
recyclability of catalyst. Kamble et al. has used methyl imidazole based ionic
Scheme.1. Preparation of magnetic nanoparticles supported ionic liquid
Fe @SiO -IL).
(
3
O
4
2
2
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reaction, the crude product was recrystallized from n-Hexane/Ethyl acetate
2
. Experimental
1
to afford pure product. The products were characterized by using H NMR
1
3
and C NMR.
2
.1. Materials
3
. Characterisation Techniques
2 3 4 2
Fe (SO4) and FeSO .7H O were purchased from Sigma–Aldrich. TEOS and
FT-IR spectra were recorded by using Perkin Elmer Spectrum RXI-Mid IR
(
3-chloropropyl)triethoxysilane were purchased from Alfa-Aesar. 1-
-
1
spectrometer that was operative in the range of 4000–400 cm .
Methylimidazole and liquid ammonia were purchased from Spectrochem
India. All other chemicals used were purchased from Spectrochem India,
Merck and Alfa-Aesar without any further purification.
Information about size and morphology of the Fe @SiO -IL were
3
O
4
2
obtained through Scanning electron microscopy images using JSL6610LV
and Transmission Electron Microscopy (TEM) using G2T30U-Twin
instrument. Energy-Dispersive X-Ray Spectroscopic (EDS) analysis
2
.2. Preparation of Fe3O4@ SiO
Fe nanoparticles were synthesized by using co-precipitation method.
In a typical procedure Fe (SO4) (3.0 g) and FeSO .7H O (2.1 g) were
2
-coated magnetic nanoparticles:
3
7
3
O
4
(
equipped with the SEM instrument) was performed for the elemental
mapping of Fe @SiO -IL. Powder X-ray Diffraction (XRD) was recorded by
using a Bruker, D8 Discover diffractometer with Cu, 3KW radiation at a
2
3
4
2
3
O
4
2
dissolved in double deionized water (160 ml) and vigorously stirred for one
hour. Then, the pH of the reaction mixture was adjusted to 10 by using 25%
−1
1
13
scanning rate of 4° min in the 2θ range of 10–80°. H NMR and C NMR
spectra of N-Formylation product were recorded on instrument Jeol JNM-
EXCP 400 at 400 MHz and 100MHz respectively.
NH
0°C. The precipitated Fe
external magnetic field and washed several times with distilled water and
4
OH. The reaction mixture was stirred continuously for two hours at
6
3 4
O
nanoparticles were separated by using
3 4
ethanol until the pH becomes neutral. The obtained Fe O
nanoparticles 4. Results and discussion
were dried at 60°C in vacuum oven.
3 4 2
Magnetic nanoparticle supported ionic liquid (Fe O @SiO -IL) was prepared
Silica coating on the Fe
method. In a typical procedure Fe
in ethanol (250 ml) followed by the addition of 25% NH
3 4
O nanoparticles were done by using the sol gel
as shown in Scheme 1. Fe nanoparticles were easily prepared by using
3
O
4
2
+
3+
3
O
4
nanoparticles (1.0 g) were dispersed
OH (6.0 mL) and
co-precipitation method of two different salt of iron (Fe and Fe ions) in
4
basic solution. By using sol-gel procedure, a small layer of silica around
TEOS (2.0 mL). After constantly stirring for 24 h, the brownish precipitates
were collected and washed with water and ethanol for several times and
dried at 60°C in vacuum oven.
Fe
the Fe
N-methyl imidazole with (3-chloropropyl)triethoxysilane at 80°C.
Ionic liquid was immobilized on the surface of Fe @SiO nanoparticles
through covalent bond between the hydroxyl groups on the surface of
Fe @SiO and organosilane group of ionic liquid as shown in Scheme.1.
3 4
O nanoparticle was formed and this prevented the agglomeration of
6
4
3
4
O nanoparticles. The ionic liquid was prepared by the reaction of
6
5
2
.3. Synthesis of 1-methyl-3-(3-triethoxysilylpropyl)-1H-imidazol-3-ium
3
O
4
2
chloride (IL)
A mixture of 1-Methylimidazole (1.26 ml, 15.86 mmol) and (3-chloropropyl)
triethoxysilane (3.82 mL, 15.86 mmol) were stirred at 80°C without using
any solvent for 72h under inert atmosphere. The resulting viscous
yellowish liquid was washed with diethyl ether (3×5mL) to remove any
unreacted material. The resulting product was dried under high vacuum.
3
O
4
2
Fourier Transform Infrared (FT-IR) spectra was recorded to prove the
coating of SiO on the surface of Fe and immobilization of ionic liquid on
the surface of Fe @SiO . The FT-IR spectrum of Fe (Figure.1.a) depicts
2
3 4
O
3
O
4
2
3 4
O
−
1
2
.4.General procedure for the preparation of 1-methyl-3-(3-
triethoxysilylpropyl)-1H-imidazol-3-ium chloride immobilized magnetic
nanoparticles(Fe @SiO -IL).
Finally, ionic liquid was immobilized on Fe
typical procedure, Fe @SiO nanoparticles (1.0 g) were dispersed in 30
ml CHCl by sonicating for hour and 0.28 of 1-methyl-3-(3-
an intense band at 581 cm due to Fe-O vibration and a broad band at
1
3
403 cm- , which is attributed to surface -OH groups. Three additional
−1
−1
−1
3
O
4
2
bands were present around 1080 cm , 960 cm and 800 cm for the
Fe @SiO nanoparticles (Figure.1b). These bands result from Si-O-Si anti
symmetric stretching, Si-O symmetric and Si-O-Si symmetric modes,
respectively. Furthermore, Fe @SiO -IL showed two new peaks around
924 cm and 2852 cm (Figure.1c) which are assigned to the C-H
stretching of alkyl group present on the ionic liquid. FT-IR spectra proved
that SiO was successfully coated on the surface Fe and ionic liquid is
immobilized on the surface of Fe @SiO nanoparticles through covalent
3
4 2
O @SiO nanoparticles. In a
O
3
4
2
3
O
4
2
3
1
g
O
3
4
2
-1
-1
triethoxysilylpropyl)-1H-imidazol-3-ium chloride (1 mmol) was then added
to the solution and the reaction was stirred under reflux condition for 2
days under inert atmosphere. The product was collected magnetically,
2
2
3 4
O
washed three times with CHCl
.5. Procedure for N-formylation product by using Fe
Catalyst.
A mixture of formic acid (3 mmol), amine (1 mmol) and Fe
3
and dried at 60°C in vacuum oven.
3
O
4
2
2
3 4 2
O @SiO -IL as
bond between the hydroxyl groups on the surface of Fe
3 4 2
O @SiO and
organosilane group of ionic liquid.
3
4 2
O @SiO -IL (7
mg) was stirred at room temperature for appropriate time (Table.2). The
progress of the reaction was monitored by TLC. After the completion of the
XRD pattern of Fe
3
O
4
and Fe
3
O
4
@SiO
2
are shown in (Figure.2), the
@SiO (Figure.2b) can be
appearance of broad peak at 2θ = 20–27° of Fe
3
O
4
2
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attributed to the presence of an amorphous silica around the magnetic
Fe nanoparticles. The Bragg’s peak obtained at the same 2θ values in
XRD pattern of Fe @SiO indicates that after coating of SiO layer around
Fe nanoparticles, they retained their crystalline structure. Hence, the
coating of SiO did not induce any phase change in Fe nanoparticles.
The size and morphology of Fe @SiO -IL were analysed by TEM and SEM
Figure.3). From TEM analysis, it was found that the size of particles is
3
O
4
3
O
4
2
2
3
O
4
2
3 4
O
3
O
4
2
(
ranging from 15-20 nm. Although, the exact size of the particles are
difficult to be determined because they aggregate due to their
paramagnetic nature. From SEM picture, it was found that particles are
3 4 2
Figure.3. (a) TEM and (b) SEM Image of Fe O @SiO -IL
3 4 2
roughly spherical in nature. EDX spectra of the Fe O @SiO -IL shown in
(
Figure.4) clearly indicate the presence of Iron, Oxygen, Silicon, Nitrogen,
The room temperature magnetization behaviour of the Fe
and Fe @SiO -IL nanoparticles are shown in (Figure.5). The saturation
magnetization of bare Fe
3 4 2
However, there was a slight decrease in the magnetization of Fe O @SiO
3 4 3 4 2
O , Fe O @SiO
Carbon and Chlorine. The presence of Nitrogen and Chlorine peak in EDX
spectra confirmed the immobilization of ionic liquid on the surface of
3
O
4
2
-1
3
4
O was found to be 50.10 emu g (Figure.5a).
Fe
3
O
4
@SiO
2
.
-
1
-1
(
32.10 emu g ) (Figure.5b) and that of Fe
3
O
4
@SiO
2
-IL (28.45 emu g )
(
Figure.5c). This slight decrease in magnetization of Fe
3
O
4
@SiO can be
2
attributed to the successful coating of SiO
2
layer on surface of Fe
3 4
O
nanoparticles. The decrease in the magnetization of Fe
attributed the successful immobilization of ionic liquid on the surface of
Fe @SiO nanoparticles. From the FT-IR spectra, EDX spectra and
magnetization curves, it was proved that ionic liquid has been successfully
immobilized on the surface of Fe @SiO . Due to the presence of
immobilized ionic liquid and paramagnetic nature of Fe @SiO -IL
nanoparticles, it can be effectively explored in heterogeneous catalysis.
3
O
4
@SiO -IL can be
2
3
O
4
2
3
O
4
2
3
O
4
2
3 4 2
After the characterization of the Fe O @SiO -IL nanoparticles, their
catalytic activity was explored in N-formylation of Amines with formic acid
under different reaction conditions. Table.1 shows the effect of the type of
catalyst, catalyst amount and effect of different solvent on the N-
formylation reaction using aniline and formic acid as model reaction. We
have optimized the amount of catalyst, maximum yield of the product was
reported when 7 mg of catalyst was used under solvent free condition.
When the amount of catalyst was reduced to 3.5 mg and increased to 15
mg, the yield of product was reported as 55% and 99%, respectively. So the
ideal amount of catalyst was found to be 7 mg because decrease in catalyst
amount results in decrease in the yield of product and increase in catalyst
amount has no effect on percentage yield. The yield of product was
maximum when reaction proceed under solvent free condition and when
MeCN, MeOH, THF were used as solvent, the yield of the product
3 4 3 4 2 3 4 2
Figure.1. FT-IR spectra of (a) Fe O (b) Fe O @SiO and (c)Fe O @SiO -IL.
3 4 3 4 2
decreased. When Fe O and Fe O @SiO were used as catalyst under
solvent free conditions, the yield of the product was in trace. So, the
maximum yield was reported only when optimized amount of Fe
3 4 2
O @SiO -
IL was used as catalyst under solvent free condition.
3 4 3 4 2
Figure.2. Powder XRD of (a) Fe O and (b) Fe O @SiO .
4
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With the optimised conditions (Table.1), Fe
3
O
4
@SiO
2
-IL nanocatalyst was
@SiO -IL
explored in N-formylation of Amines with formic acid. The Fe
3
O
4
2
nanocatalyst shows excellent activity with various amines apart from
aniline, where the yield is maximum in short reaction time (Table.2, entry
1
). Aromatic amine with electron donating group furnished desired product
in excellent yields in shorter reaction time without generation of any
detectable side product (Table2, entry 2-3). When aromatic amine having
electron withdrawing group were explored (Table2, entry 4-5), the yield of
the product were found to be excellent but the completion of reaction
takes longer time as compared to aromatic amine having electron donating
group. When different cyclic amines were explored as amine source with
formic acid, the yield of the products were found to be excellent (Table2,
entry 6-8). The catalyst also showed good activity when aliphatic amine
was used with formic acid and the yield of the product was found to be
excellent (Table2, entry10). We have further checked the recyclability and
3 4 2
Figure.4. EDS spectra of Fe O @SiO -IL.
3 4 2
reusability of the Fe O @SiO -IL catalyst for five consecutive catalytic cycles
with aniline and formic acid as model reaction (Figure.6).
3 4 2
After the completion of reaction, Fe O @SiO -IL nanocatalyst was
separated magnetically using external magnet from the reaction mixture
and washed thoroughly with water and ethanol followed by drying in
o
vacuum oven at 60 C and then reused in another catalytic cycle. We found
that the catalyst is magnetically recoverable and reused without any
appreciable loss in catalytic activity for five consecutive catalytic cycles
(Figure.6). In order to investigate the leaching of ionic liquid into the
reaction mixture during the reaction, the catalyst was separated
magnetically from reaction mixture after the completion of almost 50% of
Figure.5. Magnetization curves of (a) Fe
3 4 3 4 2
O (b) Fe O @SiO and (c)
Fe @SiO -IL
3
O
4
2
the
reaction.
Then
the
reaction
was
Table.1. Effect of Catalyst, Catalyst Amount and solvent on N- Formylation
of Amine with Formic acid under different condition.
Catalyst
Amount
(mg)
b
Time
(min)
Yield
(%)
Entry
1
Catalyst
Solvent
Fe
3
Fe
3
Fe
3
Fe
3
Fe
3
Fe
3
Fe
3
Fe
3
O
O
O
O
O
O
O
O
4
4
4
4
4
4
4
4
@SiO
@SiO
@SiO
@SiO
2
2
2
2
-IL
-IL
-IL
3.5
7
5
5
5
5
5
5
5
5
Solvent free
5
9
9
5
9
9
2
3
4
5
6
7
8
Solvent free
Solvent free
Solvent free
Solvent free
15
7
Trace
Trace
7
c
@SiO
@SiO
@SiO
2
2
2
-IL
-IL
-IL
7
MeCN
5
7
5
0
5
5
c
7
MeOH
Figure.6. Recyclability of Fe
3
O
4
@SiO
2
-IL nanocatalyst in the synthesis of N-
c
7
THF
Formylation of aniline with formic acid.
Reaction condition: Aniline (1mmol) and formic acid (3 mmol), rt
b
Isolated yield
Solvent- 3ml
c
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Table.2. N-Formylation of amines with formic acid using Fe
3
O
4
@SiO
2
-IL as
conditions (Table.4). It was found that when unsupported ionic liquid was
used as catalyst, the yield of product was 50% in 5 minutes (Table.4, entry
a nanocatalyst
1
) and when the reaction time was increased to 15 minutes, the yield of
b
Entry Substrate
1
Product
Time
Yield
product was 70% (Table.4, entry 2). When the temperature of the
reaction was increased to 70°C, the yield of the product increased to 99%
(min) (%)
5
99
3 4 2
in 15 minutes(Table.4, entry 3). When Fe O @SiO supported ionic liquid
2
3
4
5
5
98
98
90
90
was used as a catalyst for the same reaction, then reaction completed in
just 5 minutes even at room temperature (Table.4, entry 4). From the
above results, It is observed that the catalytic activity of ionic liquid
increases when it is immobilised on nano-support. At room temperature,
the unsupported ionic liquid is not completely miscible with reaction
mixture and existed as separate phase and therefore only minor portion of
the ionic liquid is able to participate in reaction as a catalyst, which results
a less yield of the product. It is observed that the catalytic activity of ionic
liquid increases when it is immobilised on nano-support. After the
combination of ferrite support and imidazolium ring, the catalyst is highly
dispersible in reaction mixture and can act like “quasi-homogeneous”
catalyst. This increase in catalytic activity is due to the increase in the
number of free active catalytic sites that can participate in reaction as
catalyst with the additional advantages of being easily recyclable by using
external magnet. As the temperature was increased to 70°C, the reaction
completed in 15 minutes, which is due to increase in miscibility of
unsupported ionic liquid with reaction mixture, enabling the ionic liquid to
actively participate in the reaction thus resulting in high yield of the
product.
5
10
10
6
10
92
7
8
10
10
85
85
9
12
5
82
89
1
0
Reaction condition: Amine (1mmol), formic acid (3 mmol), Fe
7 mg), rt
3
O
4
2
@SiO -IL
(
b
Isolated yield
allowed to proceed under similar conditions without any catalyst for
appropriate time and we observed that no considerable reaction progress
was found, which clearly shows that there was no leaching of ionic liquid
3 4 2
moiety into reaction mixture and Fe O @SiO -IL nanocatalyst is most likely
to show its activity under heterogeneous conditions.
We have compared the activity of the prepared ferrite supported ionic
liquid with a number of reported homogeneous as well as heterogeneous
catalyst for N-Formylation of amines under different conditions (Table.3).
As compared to reported homogeneous catalyst, the activity of our catalyst
was found to be excellent at room temperature and then having an
additional advantage of being magnetically recyclable for further use
Table.4. Comparison between unsupported imidazolium based ionic liquid
and Fe
3
O
4
@SiO
2
supported imidazolium based ionic liquid as a catalyst for
b
Catalyst Amount
(mg)
Temp Time
Yield
(%)
Entry
Catalyst
(°C)
(min)
1
2
3
4
[BMIM]Cl
[BMIM]Cl
[BMIM]Cl
7
7
7
7
rt
5
15
15
5
50
70
99
99
(Table.3, Entry 1-5). When compared with reported heterogeneous catalyst
rt
70
rt
for the same reaction (Table.3, Entry 6-7), it was found that although, both
the reported catalyst is recoverable through the means of filtration or
centrifugation and also can be used in further catalytic cycles, but our
prepared catalyst has the advantage of being magnetically recyclable,
which is an easy method compared to tedious procedure like filtration or
centrifugation. In comparison to most of the reported catalysts mentioned
above, the activity of our catalyst is excellent even at room temperature.
3 4 2
Fe O @SiO -IL
the synthesis of N-Formylation of amine.
Reaction conditions: Aniline (1 mmol), Formic acid (3 mmol), Solvent free
b
Isolated yield
4
.1 Comparative Study of the Catalytic Activity of
Fe @SiO -IL and Unsupported Ionic Liquid
3
O
4
2
We have also performed the experiments to compare the catalytic activity
of unsupported and supported imidazole based ionic liquid under different
6
| J. Name., 2012, 00, 1-3
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N eP wl e aJ soe u dr on an lo ot fa dC j uh se t mm i sa rt gr yi ns
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DOI: 10.1039/C6NJ03985E
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ARTICLE
Table.3. Comparison of catalytic efficiency of present protocol with reported catalyst for N-Formylation of aniline.
b
Entry
Catalyst
Catalyst Amount
Temp ( °C)
Time (min)
Solvent
Yield (%)
Ref.
5
6
5
7
0
8
1
2
3
[TBD][TFA]
5 mol%
5 mol%
20 mg
0.5 ml
2 mol%
10 mg
1 mol%
7 mg
rt
10
60
5
Solvent free
Solvent free
Solvent free
98
97
99
99
95
92
97
99
PIL
HIL
-
70
rt
a
62
4
30,)))
70
60
50
rt
15
20
15
240
5
[BMIM]BF
4
5
9
5
6
[MIMPS]
3
PW12
O
40
Solvent free
Solvent free
Solvent free
Solvent free
+
61
63
Na -MMT-[pmim]HSO
SBA-15/PrEn-NHSO
Fe @SiO -IL
4
c
7
3
H
8
3
O
4
2
This work
a
Reaction performed under ultrasonic irradiation
Isolated yield
Ethyl formate is used in place of formic acid
b
c
5
. Proposed Reaction Mechanism
7
, 59
On the basis of previous reports,
we have proposed the reaction
@SiO –IL
mechanism for N–formylation of amine with formic acid using Fe
3
O
4
2
as nanocatalyst (Figure.7). In the first step, C-2 proton of methyl imidazolium
+
cation [MIM] interact with the oxygen atom of the carbonyl group of the
formic acid, thereby increasing the electrophilic character of the carbonyl
group of the formic acid probably through the hydrogen bond formation. The
-
counter ion Cl can interact with proton of amine group and the lone pair of
electron on the nitrogen atom of aniline can then attack to the activated
carbonyl group of formic acid. Finally, dehydration of water molecule leads to
3 4 2
the formation of formanilide, and Fe O @SiO -IL nanocatalyst is regenerated
and reused in other catalytic cycles. The catalyst was prepared under the inert
condition because of the presence of triethoxysilane group in the ionic liquid.
As it is reported that triethoxysilane group is moisture sensitive which can
make it susceptible to rapid hydrolysis. As a result, the Si-O-Si covalent bond
formation between ionic liquid and the solid support can be hindered. Once
the triethoxysilane group present in the ionic liquid is immobilized over the
Figure.7. Proposed reaction mechanism for N- Formylation of
aniline with formic acid using Fe @SiO -IL nanocatalyst.
3
O
4
2
6
. Conclusions
3 4 2
surface of Fe O @SiO through Si-O-Si covalent bonding under inert condition,
then the prepared catalyst (Fe
3
4 2
O @SiO -IL) can remain stable in moisture
In summary, an imidazolium based ionic liquid has been
synthesized and immobilized on the surface of Fe @SiO . The
environment. Thus, the amount of water released during the reaction as shown
in the mechanism (Figure.7) may not affect the chemical stability of the
catalyst and the catalyst can be reused in the number of cycles without any
appreciable loss in catalytic activity.
3
O
4
2
prepared heterogeneous catalyst is being explored for the very
first time for catalysing the N-Formylation of amine with formic
acid under solvent free condition. This heterogeneous catalyst can
be easily recovered by using external magnetic field. It could be
reused in five catalytic cycles without any significant loss in
catalytic activity.
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Acknowledgements
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University of Delhi, Delhi, India for instrumental facility.
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Graphical Abstract
Imidazolium Based Ionic Liquid Supported on
Fe @SiO Nanoparticle as an Efficient
Heterogeneous Catalyst for N-formylation of Amines
3
O
4
2
a
a
*a
Charu Garkoti, Javaid Shabir and Subho Mozumdar
a
Department of Chemistry, University of Delhi, Delhi.India 110007
Ionic liquid supported on silica coated ferrite nanoparticle as
an efficient and reusable catalyst for N-formylation of
amines.
1
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