Role of (3-aminopropyl)tri alkoxysilanes in grafting of chlorosulphonic acid immobilized magnetic nanoparticles and their application as heterogeneous catalysts for the green synthesis of α-aminonitriles

Article abstract of DOI:10.1039/c6ra20095h

The surface modification of SiO₂ coated Fe₃O₄ nanoparticles by grafting silane coupling agents is a highly significant approach to enhancing the interface interaction between the inorganic magnetic core and the organic fun

Full text of DOI:10.1039/c6ra20095h

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Role of (3ꢀaminopropyl) tri alkoxysilanes in grafting of chlorosulphonic acid immobilized
magnetic nanoparticles and their application as heterogeneous catalyst for green synthesis
of αꢀaminonitriles
Harminder Singh, Jaspreet Kaur Rajput#, Priya Arora, Jigyasa
Department of Chemistry, Dr. B R Ambedkar National Institute of Technology, Jalandhar ꢀ144011,
Punjab, India
Corresponding Author: #rajputj@nitj.ac.in, Tel.: +91-181-2690301-2208; fax: +91 181 2690320
Abstract: The surface modification of SiO2 coated Fe3O4 nanoparticles by grafting silane
coupling agents is highly significant approach to enhance the interface interaction between
inorganic magnetic core and organic functionality to be anchored. However the effect of the
grafted molecular structure of silane utilizing different silane alkoxy group has been seldom
investigated on the organicꢀinorganic hybrid magnetic heterogeneous catalysts. The silanization
has carried out on the surface of SiO2 coated Fe3O4 nanoparticles using two different trialkoxy
silanes i.e. 3ꢀaminopropyltriethoxysilane (APTES) and 3ꢀaminopropyltrimethoxysilane
(APMES). The effect of alkoxy silane structure anchored to the surface of silica functionalized
Fe3O4 nanoparticles on their surface area and pore volume has been analyzed by BET analyzer.
The silane functionalization using APTES leads to higher surface area and pore volume than
APTMS. Further chlorosulphonic acid was immobilized on both the APTES and APTMS
functionalized SiO2@Fe3O4 nanoparticles named (AE and AM) and their role as magnetically
separable heterogeneous catalyst for the one pot synthesis of αꢀaminonitriles using water as
solvent has successfully carried out. The chlorofunctionalized nanoparticles, which utilized
APTES as silanizing agent showed better catalytic activity than APTMS in terms of reaction
time and yield. The presented protocol is water based synthesis involving room temperature
conditions along with reusability and recyclability of catalyst. The characterization of the
synthesized catalysts was carried out by using different techniques like FTꢀIR, XRD, TEM, BET,
XPS, VSM and TGAꢀDTA.
1. Introduction
Magnetic nanoparticles has got much attention in academics, research as well as industrial fields
due to its properties like high surface area, high degree of chemical stability, high catalytic
1,2,3
activity, nonswelling in organic solvents,
easily recoverable by an external magnet,
reusability,4 regular shapes, uniform size, low cost of production, non toxic and
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biocompatibility.5 They are also used in other different fields like sealing, oscillation damping,
information storage, electronic devices, etc.5 Under biomedical applications they are used as
biosensors,6 contrasting agents in magnetic resonance imaging (MRI),7 localizer in therapeutic
hyperthermia,8 drug delivery system, etc.9 A number of methods of preparation of magnetic
nanoparticles have been reported like coꢀprecipitation, solvothermal/hyrothermal synthesis,
micro emulsion and thermal decomposition. Due to its simplicity and formation of monodisperse
nanoparticles, coꢀprecipitation method is declared as one of the best method of synthesis.10a
Under the catalytic system, a large number of nanocatalysts are used as heterogeneous
catalyst in many organic synthetic transformation reactions. These have lots of advantages over
the conventional catalyst like their nanoscale size possess a high surface area of active
component which in turn increases the contact between the reactants and the catalyst which
results in a high reaction rate and their high surface to volume ratio increases the catalytic
activity and accessibility of the catalyst. But the nanoscale size of heterogeneous catalysts makes
their recovery difficult from the reaction mixture. Sometimes it becomes more difficult to isolate
or recycle the catalyst by conventional filtration and centrifugation methods. This limitation
obstructs the economic and sustainable growth of these kinds of the protocols. So some
alternatives are in demand to overcome these problems and reuse or recycle them in a highly
efficient manner. Magnetic nanoparticles are the suitable alternatives and are extensively
explored. Paramagnetic nature makes their easy separation from the reaction mixture by using an
external magnet, which in turn increases the recyclability and reusability. Remarkable catalyst
recovery, their non solubility in the reaction medium, green synthesis protocol, minimum waste
production, minimum work up procedure are the important characteristics which make them
more sustainable.10bꢀe
Further application of the magnetic nanoparticles as support has been reported.
Superparamagnetic iron oxide nanoparticles have been studied as magnetic support for the nano
catalytic system. Silica coating on magnetic nanoparticles enhances its dispersibility in liquid
medium by stopping the dipole attractions between the nanoparticles, improves chemical
stability, enhances its performance, protects leaching in an acidic environment, high
hydrothermal stability, protects the further oxidation of bare magnetic nanoparticles, enhances
the textural properties of magnetic nanoparticles, protects against toxicity, presence of a large
number of silanol groups on its surface to make them easy for further functionalization with
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different organic moieties, provides high surface area which enhances the catalytic loading and
activity and also prevents the unwanted interaction between the core, magnetic nanoparticles and
the additional agents linked to silica surface. All these properties render the inert coating of silica
as a solid support for many organic and inorganic moieties. 10fꢀi (3ꢀAminopropyl)ꢀtrialkoxysilanes
are widely used as silanizating agent for the surface modification of the nanoparticles as their
terminal amine group can facilitate the further functionalization of the nanoparticles.
The reaction between aldehyde, an amine and source of cyanide gives rise to the formation of αꢀ
aminonitrile11 is known as Strecker reaction.12,13 Its reliability, versatility of the resulting
products and easy availability of the starting materials are some reasons behind its use in the
formation of large scale production of amino acids, herbicides and chelating agents.14 Further αꢀ
aminonitriles are the important intermediates for the formation of amino acids,15 an important
11
16
synthons of organic chemistry
like nitrogen containing heterocycles
such as imidazole,
thiadiazole, other biological important molecules such as Saframycin A having an anti tumor
activity or phthalascidi,17 manzacidin A, prasugrel, clopidogrel and short acting opioid
analgesics.18 They are also considered as the valuable intermediates in the formation of different
diamines, amides and pharmaceuticals.11 αꢀAmino acids have got immense biological and
economic importance due to their widespread applications in the fields of chemistry and biology.
19
They are also useful as the chiral building blocks in the pharmaceutical industry,
key
precursors for the preparation of protein.11 Recently by using this strategy of the synthesis
20
hepatitis C virus NS3 serine protease inhibitors,
containing retinoids 22 have been reported.
(±)ꢀphthalascidin 62221 and novel boron
In general Strecker reaction involves the nucleophilic addition of the cyanide source to the imine.
12 The common cyanide sources which have been used so far are HCN,11 KCN,23a (EtO)2POCN,
23b
23d
Et2AlCN, 23c BuSnCN.
Since all these mentioned cyanide sources are hazardous, toxic in
nature, require harsh reaction conditions and special handling and care is required during their
24
use. It has been reported that TMSCN, due to its properties like easy handling, effective and
25
safe use makes it one of the best promising cyanide source.
So far many Lewis acids or
26e
bronsted acids like Fe(Cp)2 PF6,26a InCl3,26b RhI3,26c Cu(OTf)2,14 I2 ,26d BiCl3, La(NO3)3.6H2O,
GdCl3.6H2O,26f NiCl2,26g Ga(OTf)3,26h GaCl3,26i CeCl3,26j Pr(OTf)3 ,26k RuCl3,26l FeCl326m,etc.
catalysts have been reported which homogeneously catalyzed this reaction but leaving behind the
limitations like costly, toxic catalytic system, longer reaction time and difficult separation work
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up.26n So it arises the use of heterogeneous catalysts which overcome these problems. Further
supported heterogeneous catalyst has advantages like simple separation method, minimization of
waste, simple recovery, recyclability, reusability and lower contamination of the products.27, 28. 29
Chlorosulphonic acid was used in a wide variety of applications like alkylation, cyclization,
polymerization, halogenations and rearrangement reactions. 29b But direct use of it in water is not
easily feasible as it causes the formation of HCl and H2SO4. So this encouraged us to immobilize
it on another support which promotes its use in various promising applications of sulphamic acid
as an acidic catalyst in reactions like acetalisation, esterification, acetylation of phenols and
alcohols, nitrile formation as chemoselective catalyst in transesterification of βꢀketoesters,
Beckmann rearrangement, etc. 29c
In the present study SiO2@Fe3O4 nanoparticles have been synthesized by Stober’s method.
Further silanization on the surface of hydroxylated SiO2@Fe3O4 nanoparticles was carried out
utilizing two different trialkoxy silanes i.e. 3ꢀaminopropyltriethoxysilane (APTES) and 3ꢀ
aminopropyltrimethoxysilane (APTMS). The APTES functionalized SiO2@Fe3O4 nanoparticles
have obtained higher surface area and pore volume (6.3891 m2/g and 6.03×10ꢀ3cc/g) than
APTMS (1.3220 m2/g and 1.4×10ꢀ3cc/g). Further the chlorosulphonic acid was immobilized on
both NH2ꢀPrꢀ@SiO2@Fe3O4 nanoparticles generated by two different alkoxy silanes i.e. APTES
and APTMS obtained as Fe3O4@SiO2ꢀPrꢀNHꢀSO3H (AE) and Fe3O4@SiO2ꢀPrꢀNHꢀSO3H(AM)
nanoparticles. Further their use in the synthesis of αꢀaminonitriles via coupling of three
components aldehyde, aniline and trimethylsilylcyanide by using water as a green solvent as the
reaction medium has been done. Comparison on reaction time and yield of αꢀaminonitriles has
been carried out. Best results were obtained with AE which encouraged us to focus on AE
10h
nanoparticles. So here in continuation of our previous work on catalysis,
simple and
environmentally friendly work up procedure for the formation of product in high yields has been
developed. All these steps made this protocol eco friendly, cost effective, simple and efficient in
nature.
2. Results and Discussion:
2.1 Characterization of the as prepared catalyst:
FTꢀIR:
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Fig. 1 Comparative study of Fourier transform infrared (FTꢀIR) spectra of Fe3O4 nanoparticles (MNPs),
Fe3O4@SiO2, Fe3O4@SiO2ꢀPrꢀNH2 (APTMS), Fe3O4@SiO2ꢀPrꢀNH2 (APTES), AM and AE
In Fig. 1 the peaks of Fe3O4 nanoparticles were found to be below 700 cmꢀ1, the peak at 600 cmꢀ1
was attributed due to the FeꢀO vibrations; OꢀH deformed vibrations were found near 1646 cmꢀ1
and OꢀH stretching vibrations at 3132 cmꢀ1. The FTꢀIR spectra of Fe3O4@SiO2, consists of the
peaks at 447 cmꢀ1, 954 cmꢀ1 and a sharp peak at 1061 cmꢀ1 which were due to the asymmetric
stretching vibration, symmetric vibration and bending vibration of the all SiꢀOꢀSi groups.
Similarly the OꢀH stretching, vibration near 3100ꢀ 3400 cmꢀ1 and OꢀH deformed vibration near
1630ꢀ1646 cmꢀ1 were present in both cases. 30 The decrease in the intensity of the peak around
600 cmꢀ1 confirmed the coating of silica on Fe3O4 nanoparticles. In the FTꢀIR of Fe3O4@SiO2ꢀ
PrꢀNH2 (APTES) and Fe3O4@SiO2ꢀPrꢀNH2 (APTMS), the introduction of APTES and APTMS
on Fe3O4@SiO2 was confirmed by SiꢀO peak at 1117 cmꢀ1 and 1124 cmꢀ1 and NꢀH broad peak
around 3245 cmꢀ1 and 3358 cmꢀ1 respectively. Further presence of the propyl group was
confirmed by the CꢀH peaks at 2955 cmꢀ1, 2822 cmꢀ1 and 2904 cmꢀ1, 2890 cmꢀ1 for APTES and
APTMS respectively35 In the FTꢀIR spectra of AE, the introduction of the sulphonyl moieties
was confirmed by the bands at 1125 cmꢀ1 and 1250 cmꢀ1 and for AM, at 1147 cmꢀ1 and 1280 cmꢀ
1
.
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Surface area and Pore volume analysis: BET methodology was used extensively for the
estimation of surface area, pore volume of the materials as both are the important parameters
used for the determination of catalytic activity of the catalyst as in Fig. 2.
Fig. 2 (a) Surface area plot of AM (b) Pore volume plot of AM (c) Surface area plot of AE (d) Pore volume
plot of AE
Table 1 Comparison study of surface area and Pore volume
Catalyst Type
Fe3O4
Surface Area (m2/g)
Total Pore Volume (cc/g)
118.0789
0.3047
Fe3O4@SiO2
7.2464
8.5458
13.43
0.0118
0.0299
Fe3O4@SiO2ꢀPrꢀNH2 (APTMS)
Fe3O4@SiO2ꢀPrꢀNH2 (APTES)
0.0433
AM
AE
1.3220
6.3891
0.0014
0.00608
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Here we studied the effect of surface area due to the grafting of APTES and APTMS on
Fe3O4@SiO2 nanoparticles followed by chlorosulphonic acid immobilization. The surface area
was calculated by using the BET equation.31a In the absence of shells, surface area of bare Fe3O4
magnetic nanoparticles was found to be 118.07 m2/g, the high surface area was attributed due to
high porous structure.31b But when the immobilization of different moieties has been done, the
surface area decreased significantly i.e 7.2464 m2/g, 8.5458m2/g, 13.43m2/g, 1.3220 m2/g,
6.3891 m2/g for Fe3O4@SiO2, Fe3O4@SiO2ꢀPrꢀNH2(APTMS), Fe3O4@SiO2ꢀPrꢀNH2(APTES),
AM and AE respectively. This further confirmed the formation of shells on the surface of bare
Fe3O4 nanoparticles. The total pore volume reduced from 0.30473 cc/g for Fe3O4 magnetic
nanoparticles to 0.0118 cc/g, 0.0299 cc/g, 0.0433 cc/g, 0.0014 cc/g, 0.0060cc/g for Fe3O4@SiO2,
Fe3O4@SiO2ꢀPrꢀNH2 (APTMS), Fe3O4@SiOꢀPrꢀNH2 (APTES), AM and AE respectively as in
Table 1. This observation further show that these shells were relatively more dense structure and
possess few pores, which aid in protecting the Fe3O4 magnetic nanoparticles.31c The surface area
and pore volume of AE were obtained higher than AM, which further enhanced the catalytic
properties of AE than AM.
VSM:
Fig. 3 VSM of AE
For MCT (magnetic carrier technology) applications31d, the material must show magnetic
properties. During this investigation magnetic property of the as synthesized catalyst (AE) was
determined by using vibrating sample magnetometer (VSM). The value of saturation
magnetization (Ms) calculated from the plot was found to be 15.42 emu/g as shown in Fig. 3 and
was compared with the value of 46.7 emu/g31e of uncoated Fe3O4 magnetic nanoparticles. The
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lower value of the saturation magnetization (Ms) confirmed the coating of different shells on it.
This value was sufficient for magnetic separation with an external magnet. Furthermore, there
was no hysteresis loss Hc=0 Oe, i.e. this catalyst was superparamagnetic in nature. It was also
clear from the plot that the prepared functionalized magnetic nanoparticles were soft ferrite in
nature.
External
Magnet
Fig. 4 Digital camera images of (a) Dispersed catalyst (b) After applied magnetic field
XRD:
Fig. 5 Comparison study of XRD analysis of (1) Fe3O4 nanoparticles (MNPs), (2) Fe3O4@SiO2, (3)
Fe3O4@SiO2ꢀPrꢀNH2 (APTES), (4) AE.
The XRD patterns of Fe3O4, Fe3O4@SiO2, Fe3O4@SiO2ꢀPrꢀNH2 (APTES), AE has been shown
in Fig 5. In case of Fe3O4, the relative position and intensities of all the diffraction peaks were
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matched with the standard XRD pattern (JCPDS card no. 75ꢀ1609) and the six characteristic
diffraction peaks at 30.0ᵒ, 35.4ᵒ, 43.1ᵒ, 53.7ᵒ, 57.2ᵒ and 63.2ᵒ were observed that corresponds to the
(220), (311), (400), (422), (511) and (440) miller indices respectively. A broad diffraction peak
observed in 20ꢀ25ᵒ indicates the formation of amorphous silane shell around the Fe3O4.32 No
other diffraction peak was observed in both the resulting functionalized magnetic nanoparticles
i.e. functionalization with APTES and chlorosulphonic acid onto the silica coated and propyl
amine coated magnetic nanoparticles respectively. This revealed the retention of the crystalline
spinel ferrite structure during the coating process.30 Furthermore the comparison of the
intensities of the diffraction peaks in all the four cases has been done and it has been observed
that there was a large decrease in intensities in the cases of Fe3O4@SiO2ꢀPrꢀNH2 (APTES) and
AE, which proved the surface coating onto the Fe3O4@SiO2 core shell. By using Scherrer’s
formula, D= kλ/βcosθ, λ was the wavelength, β was the corrected diffraction line fullꢀwidth at
33
halfꢀmaximum, where k was a constant (having value 0.94) and θ was Bragg’s angle, the
average diameter of the AE nanoparticles has been calculated and found to be 13.47 nm.
TEM: Information related to the surface morphology and particle size was provided by using
TEM analysis of the as synthesized nanoparticles.
(a) Fe3O4
(b) Fe3O4@SiO2
(c) Fe3O4@SiO2ꢀPrꢀNH2(APTES)
(d) AE
Core shell
Core shell
Fig. 6 TEM of (a) Fe3O4 nanoparticles, (b) Fe3O4@SiO2, (c) Fe3O4@SiO2ꢀPrꢀNH2 (APTES) (d) AE.
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The particle size calculated for AE nanoparticles from TEM images was 13.5 nm and it was in
agreement with the XRD analysis. The TEM images also confirmed the coating of silica, amine
and chlorosulphonic acid on the bare magnetic nanoparticles by the formation of concentric
circles around it in Fig. 6(b), (c) and (d). Furthermore the spherical functionalized particles have
been observed.
XPS analysis: It was used for the determination of chemical elements on the surface of the
adsorbent. The elements N, S, Si and O were detected on the surface of AE as shown in Fig. 7.
Fig. 7 XPS analysis of AE.
The binding energy for O 1s was found near 532.38 eV for SO3H group while the Si 2p binding
energy at 102.86 eV due to the overlapping of Si 2p3/2 and Si 2p1/2 and at 155.84 eV due to the
presence of Si(2s). The value of the binding energy from 169ꢀ177 eV for S 2p clearly confirmed
the formation of sulphurꢀoxygen bond34aꢀb. The peak near 400.15eV was observed for N 1s
which further proved the formation of NꢀC bond34c. The peaks corresponding to 710.5 and
724.1eV related to Fe 2p3/2 and Fe 2p1/2 for mixed oxides34c and peaks in the range from 56 to 99
eV for Fe 3p and Fe 3s were absent.34a This observation concluded that coating has been done
successfully which also matched with XRD data earlier and further confirmed the formation of
shells on the surface of bare Fe3O4 magnetic nanoparticles as same in TEM images.
Thermal analysis:
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Fig. 8 TGA of AE and AM.
TGA curve gives us information about the thermal stability & weight loss of the material with
temperature. The TGA curves of AM and AE were divided into several parts or regions on the
basis of weight loss. In the initial region up to 174.5oC, the weight loss was 8.1% and 7.0% for
AM and AE respectively, which was attributed due to the loss of water molecules, removal of
physically adsorbed solvent and hydroxyl groups.5 From 260ꢀ531oC weight loss was 4% for AM
and 3% for AE, which was attributed due to the loss of sulphamic acid moieties from the
surface.35 Further loss from 531.7oC to 605oC might be due to the loss of aminopropyl groups
which was found to be 2.3 % for AM and 0.02% for AE. From 605oC to 758oC the weight loss
may be due decomposition of silica shell which was 0.9% and 0.68% for AM and AE
respectively5. From the above discussion, it was clear that AE was more stable than AM in every
region of thermal analysis and also at higher temperatures after decomposition AE remained
about 87.7% and AM was found to be 82.6% as shown in Fig. 8. The above results demonstrated
that our catalyst was stable and it could be used in the organic reactions occurring at higher
temperature.
The formation of synthesized catalyst has been represented diagrammatically as shown in
Scheme 1.
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Fe2SO4+ FeSO4
Sonication, pH 10
NH4OH
Mixed
O
O
NH2
Si
O
OH
OH
R1
Si
OH
Si
Si O
Si
Si
O
HO
HO
OH
OH
NH4OH,
Sonication, H2O
TEOS, EtOH
H2O, NH4OH
SiO2
O
O
O
O
O
2
SiO2
OH
Fe3O4
OH
O
i
HO
HO
HO
HO
Fe3O4
OR2
R2O
R1=
S
-R2OH
OR2
Si
O
Fe3O4
i
S
OH
SiO2
NH2
OH
SiO2
O
R2= ꢀCH3, ꢀC2H5
O
O
O
OH
Si
O
Si
O
ClSO3H,
Sonication, dry
CH2Cl2
-HCl
O
O
NHSO3H
Si
O
Si
Si
O
O
O
O
O
O
SiO2
2
Si
Fe3O4
Si O
Si
SiO2
O
O
O
Si
O
Si
O
O
Scheme 1. Synthesis of Fe3O4 and their functionalization with silica, amine and chlorosulphonic acid moieties.
3. Optimization of various conditions of the model reaction:
Various reaction conditions like different types of catalysts, amount of catalysts, different
solvents, etc. were employed in the model reaction of Benzaldehyde (1mmol), Aniline (1mmol)
and TMSCN (1.3mmol).
CHO
NH2
CN
Catalyst
N
TMSCN
H
Conditions
1aꢀf
2aꢀi
3
4aꢀp
3.1 Effect of different catalysts:
Here the study of the effect of different kinds of coatings on the bare Fe3O4 magnetic
nanoparticles was also elaborated. It was investigated by fixing the amount of catalyst up to 5 mg
and tried the reaction with different kinds of catalysts prepared through step by step. Firstly the
reaction was carried out with bare Fe3O4 magnetic nanoparticles giving rise to 72% of yield and
has taken 155 minutes for its completion. Further silica coated Fe3O4@SiO2 magnetic
nanoparticles were used which completed the reaction in 250 minutes, giving 5% increment in
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yield, i.e. 77% as compared to bare Fe3O4 magnetic nanoparticles. Then the amine coated
catalyst prepared by using two different amines APTES and APTMS was used, i.e. Fe3O4@SiO2ꢀ
PrꢀNH2 (APTES) and Fe3O4@SiO2ꢀPrꢀNH2 (APTMS) and the yields came out to be 90% in 240
minutes and 85% in 84 minutes. Then a further coating of chlorosulphonic acid was employed on
these two different kinds of amine coated catalysts and the resultant catalysts were successfully
used in the reaction. The yields came out by using AE and AM were found to be 99% in 2
minutes and 87% in 40 minutes respectively (Table 2). Catalytic activities of AE and AM were
compared and better results were found (Fig. 9) with AE nanoparticles which concentrated our
study to it.
Table 2 Effect of different as prepared catalysts on reaction yield and timea
CHO
NH2
CN
Catalyst(mg)
rt, water
N
TMSCN
H
1a
2a
3
4a
Entry
1.
Catalyst type
Amount (mg) Time (min) Yield(%)b
Fe3O4 MNPs
5
5
5
5
5
5
155
250
240
84
72
77
90
85
87
99
2.
Fe3O4@SiO2 MNPs
3.
Fe3O4@SiO2@ꢀPrꢀNH2(APTES)
4.
Fe3O4@SiO2@ꢀPrꢀNH2(APTMS)
5.
AM
40
6.
AE
2
aReaction conditions: Benzaldehyde (1mmol), Aniline (1mmol), TMSCN (1.3mmol), catalyst (5mg), water
(1.5ml), room temperature.
bIsolated yield.
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Fig. 9 Yields by catalysts AE and AM respectively.
The reaction was carried out without catalyst which took larger i.e. 210 minutes with 62% of
yield. These results encouraged us to further optimize the amount of catalyst i.e. AE
nanoparticles. Variable amounts of AE and AM (2.5, 5.0, 7.5 and 10.0 mg) were used and yields
of 78, 99, 71 and 78% for AE and 58, 87, 67 and 67 for AM were obtained respectively as in Fig.
9. The difference in yields may be attributed due to the difference of surface area of AE and AM.
The surface area and pore volume obtained by BET plots are 6.3891 m2/g, 6.03×10ꢀ3cc/g and
1.3220 m2/g, 1.4×10ꢀ3cc/g for AE and AM respectively as shown in Fig. 4. Both the higher and
lower amounts of the catalyst were unable to increase the yield and decrease the reaction time.
The present study clearly indicates that the best yield was obtained with 5 mg amount of the
catalyst AE with 99% yield of product, so it was considered as the optimized amount for the
reaction as shown in Table 3.
Table 3 Optimization of the catalytic amount of AEa
CHO
NH2
CN
AE(mg)
rt, water
N
TMSCN
H
1a
2a
3
4a
Entry
AE(mg)
Time(min)
Yield(%)b
1
0
210
22
62
78
2.
2.5
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3.
4.
5.
5
2
99
71
78
7.5
19
10
13
aReaction conditions: Benzaldehyde (1mmol), Aniline (1mmol), TMSCN (1.3mmol), AE (mg), water
(1.5ml), room temperature.
bIsolated yield.
3.2 Screening of the solvent: Different solvents were used in the model reaction for
investigation of the appropriate solvent for the reaction. The reaction was first tried with pure
water as green solvent and it was found that the reaction completed within 2 minutes with 99%
of yield. Other solvents, ethanol and mixture of H2O: EtOH (1:1) were also used, giving 82%
and 35% of yields respectively. The high yield and faster reaction in water may be attributed due
to the high amphoteric nature and high polarizability of water molecules.36 Further the reaction
was tried in pure water and H2O: EtOH (1:1) mixture without catalyst, it was completed in 210
minutes and 29 minutes with 62% and 36% of yields respectively. The reaction was also tried in
solvent free conditions, but it has taken much time i.e. 12 hrs for its completion with 66% of
yield (Table 4).
Table 4 Optimization of the solventa
CHO
NH2
CN
AE(5mg)
rt, solvent
N
TMSCN
H
1a
2a
3
4a
Entry
Solvent(ml)
Catalyst(mg)
Time(min)
Yield(%)b
1
2
3
4
H2O
H2O
5
ꢀ
2
210
4
99
62
82
35
EtOH
5
5
H2O:EtOH
6
5
6
H2O:EtOH
ꢀ
ꢀ
29
36
66
5
12hrs
aReaction conditions: Benzaldehyde (1mmol), Aniline (1mmol), TMSCN (1.3mmol), AE (mg), solvent
(1.5ml), room temperature.
bIsolated yield.
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During the investigation of the formation of different αꢀ aminonitriles, different types of
aldehydes and amines substituted at ortho, meta and para positions were used to react with
TMSCN in water to afford the desired product by using AE (Table 5). The reaction was
successfully completed with electron withdrawing as well as electron releasing groups on
aldehyde and amines. No undesired side product like cyanohydrins, trimethylsilyl ether, etc. was
reported between the reaction of aldehyde and TMSCN, which may be due to the formation of
imine intermediate. The products formed were higher in yield and highly selective in nature. No
further addition of the additives was required to promote the reaction.
The catalytic system was also reacting with acid sensitive 5ꢀmethylfurfuraldehyde giving rise to
the better yield of product, i.e. 94% (Entry 12, Table 5). The effect on yield and reaction time of
different electron withdrawing and releasing groups depends upon the formation of imine
intermediate which play the key role in the formation of products.27
Table 5 Formation of series of derivatives of αꢀaminonitriles by using aldehydes and
aminesa
CHO
NH2
CN
AE(5mg)
rt, water
N
TMSCN
H
1aꢀf
2aꢀi
3
4aꢀp
Time(min) Yield(%)b
Sr
No
Aldehyde
Amine
Product
M.P./Reported
M.P.( oC)
CHO
NH2
1
2
99
87
98
76ꢀ78/
CN
75ꢀ7637
N
H
1a
1a
2a
OCH3
4a
CN
2.
3.
10
15
66ꢀ70
NH2
N
H
OCH3
2b
2c
4b
Cl
NH2
106ꢀ108/108ꢀ
11040
CN
N
H
Cl
1a
4c
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F
4.
NH2
2.5
73
72ꢀ73/
CN
80ꢀ8238
N
H
F
1a
4d
CN
N
2d
CH3
5.
6.
25
2
87
65
60ꢀ62
NH2
1a
1a
CH3
H
2e
4e
H3C
NH2
88ꢀ90
CN
CH3
N
H
4f
2f
OC2H5
NH2
7.
8.
9
99
78
64ꢀ66
CN
N
OC2H5
1a
1a
H
4g
2g
OH
NH2
20
96ꢀ100
CN
N
HO
H
4h
2h
2a
CHO
9.
7
95
69
65
100ꢀ105/
CN
108ꢀ11039
N
Cl
H
Cl
1b
1c
1d
4i
CHO
10.
11.
30
12
94ꢀ96/
CN
94ꢀ9726a
2a
2a
N
H3CO
H
H3CO
4j
H3CO
H3CO
CHO
120ꢀ126/
CN
H3CO
H3CO
134ꢀ13640
N
H
4k
4l
12.
13.
11
35
94
91
102ꢀ105/
CN
108ꢀ11041
H3C
CHO
CHO
O
N
H3C
2a
2a
H
O
1e
121ꢀ122/
CN
120ꢀ12240
N
HO
H
HO
4m
1f
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OCH3
14.
15.
40
90
80
148ꢀ152
CN
NH2
N
H
OCH3
1f
HO
2i
2i
4n
120
80ꢀ82
CN
N
H
1b
OCH3
Cl
4o
CN
16.
180
67
98ꢀ100
N
H
CH3
1b
2e
Cl
4p
aReaction conditions: Aldehyde (1mmol), Amine (1mmol), TMSCN (1.3mmol), AE (5mg), water (1.5 ml), room
temperature.
bIsolated yield.
3.3 Recyclability of the Catalyst:
Fig. 10 Recyclability of AE up to five cycles
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Fig. 11 Comparison study of Fourier transform infrared (FTꢀIR) spectra of fresh AE and reused AE after fifth cycle
Fig. 12 TEM of AE after fifth cycle
Due to the magnetic character, the catalyst was recovered from the reaction mixture after the
completion of the reaction by using an external magnet. The obtained catalyst was washed with
EtOH and dried in an oven at 50oC. After this, it was recycled up to five cycles with very little
loss in activity and percentage yield as shown in Fig. 10. Furthermore to check the stability of ꢀ
SO3H on the surface of the catalyst which was the active site of the catalyst; the resulting
mixture was filtered and washed with distilled water to extract the sulfate ions possibly leached
42
from the catalyst surface. BaCl2 precipitation test was performed and no white precipitation
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occurred; this clearly suggested that there was not any kind of leaching of the catalyst. This test
was also applied to the reaction mixture by putting it for 24 hrs and same observation was
observed. In Fig. 11, FTꢀIR image, peaks belonging to sulphonyl moieties in AE after the fifth
cycle have almost the same position as in fresh AE; no significant change had been occurred.
This observation also further confirmed that there was not any kind of leaching from the surface
of catalyst after being reused. This clearly indicates the stability and reusability of the catalyst.
Fig.12, TEM, of recovered AE after the fifth cycle has been done and particle size observed after
recyclability was little bit increased which could be attributed due to the agglomeration of
magnetic nanoparticles.
3.4 Comparison of catalytic activity with reported catalysts:
A comparison of the catalytic activity of AE was compared with other existing catalysts and
methods for the formation of αꢀaminonitriles. To calculate the number of catalytic active sites (ꢀ
SO3H), acid base titration method was used.42 In a typical experiment 5mg amount of the catalyst
was dissolved in 8.33ml of an aqueous solution of NaHCO3 (5×10ꢀ3mol Lꢀ1) and this mixture was
stirred for 24 hrs. After this, the catalyst was separated by using external magnet and resultant
solution was titrated against HCl (0.1M) by using phenolphthalein as an indicator. The number
of acid sites was investigated by the amount of NaHCO3 consumed and it was found
0.01mmol/g. On the basis of reaction time, yield, very low catalytic amount, use of water as
reaction medium and mild reaction condition makes it superior over the other existing methods
as shown in Table 6.
Table 6 One pot synthesis of αꢀaminonitriles by using different catalysts (comparison
table):
CHO
NH2
CN
AE
N
TMSCN
H
rt, water
1a
2a
3
4a
Catalyst
Amount
5ꢀ6mol%
Solvent Conditions Time(min) %Yield
CH2Cl2 RT 840 94
Ref:
Silicaꢀbased
36
scandium(III)
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Montmorillonite 1g/ mmol
CH2Cl2
RT
RT
RT
RT
RT
RT
RT
RT
330
70
30
20
15
12
10
10
87
97
95
94
94
95
97
93
43
27
MCMꢀ41ꢀSO3H
InI3
1.5 mg
10mol%
5 mol%
1mol%
10 mol%
20mg
MeOH
H2O
26b
26a
37
Fe(Cp)2PF6
TiCl3.4H2O
K2PdCl4
Neat
Neat
H2O
40
SAꢀMNPs
SnHBeta
H2O
Neat
35
2.4
44
mol%/10mg
AE
5µ
H2O
RT
2
99
This work
mol%/5mg
O
O
C
H
H
N
Si
Si
OH
SO2
O
O
Fe3O4
Si
O
H
NHR
C
CN
O
O
O
H
N
O
H
N
Si
Si
OH
(CH3)3SiOH
SO2
O
O
O
Fe3O4
Si
O
C
O
O
O
H
O
H
N
H
N
Si
Si
OH
SO2
O
O
N
C
R
Fe3O4
Si
O
H
H
O
O
R N
O
H
N
H
O
H
N
Si
Si
OH
O
CN
SO2
Me
O
O
Me
Si
O
Fe3O4
Si
TMSCN
O
Me
H
O
O
O
C
NH2R
H
H
H
N
O
H
N
Si
OH
SO2
O
O
O
Fe3O4
Si
N
R
O
H transfer
O
O
H
O
C
H
N
H
N
Si
Si
Si
OH
SO2
H
O
O
Fe3O4
Si
O
O
H
R
O
O
O
H
N
C
N
H
H
OH
Scheme 2. Proposed mechanism of the reaction.
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4. Experimental Section
4.1 Materials
3ꢀAminopropyltriethoxy Silane (APTES) with 99% of purity and 3ꢀAminopropyltriethoxy Silane
(APTMS) with 95% of purity were supplied by Acros Organics, Trimethylsilyl cyanide
(TMSCN) with 90% of purity and chlorosulphonic acid (98%) from Avra Synthesis, Ammonia
solution 30% from Merck, Dichloromethane (DCM) of 99.0% of purity from SDFCL and
Tetraethylorthosilicate (TEOS), 98% from HiMedia. All these were used directly without any
further purification.
4.2 Methods
The crystal structure of prepared magnetic nanoparticles catalyst was investigated by X‐ray
diffraction (XRD) using a Panlytical XPERTPRO (NPD) X‐ray diffractometer with Cu Kα
radiation (λ = 0.154 nm), in the 2θ range 10°–80°. Fourier transform IR (FT‐IR) spectroscopy
was carried out by using Agilent Cary 600 in the range 400–4000 cmꢀ1. The morphology was
studied using transmission electron microscopy (TEM). The sample was prepared by dispersion
of nanoparticles in ethanol, which were deposited on a carbon‐coated Cu grid, and after drying,
analysis was performed using a Hitachi S7500 instrument. The magnetic properties were
measured using a vibrating sample magnetometer (VSM, Princeton Applied Research model155)
at room temperature with a maximum magnetic field range of +1 T to −1 T. Thermogravimetric
analysis (TGA) was performed on the catalyst using an EXSTAR6000TG/DTA 6300 instrument
in the temperature range 50−700oC at a heating rate of 10oC/min under nitrogen atmosphere.
Surface area and pore characteristics were characterized using Quanta Chrome Novaꢀ1000
surface analyzer instrument under liquid nitrogen temperature with vacuum degassing at 110oC
for 3 hrs. The specific surface area was calculated using the BET equation. Surface properties
were studied by using Xꢀray photoelectron spectroscopy (XPS, PHI 5000 Versa Prob II, FEI
1
Inc.). The organic products were characterized by H nuclear magnetic resonance spectroscopy
at 400 MHz with the aid of Advance 400 spectrophotometer using tetramethylsilane as the
internal standard and CDCl3 solvent. Software used for NMR was MNOVA and for drawing
chemical structures were ChemDraw ultra 8.0.
4.3 Synthesis of Fe3O4 magnetic nanoparticles:
The Fe3O4 magnetic nanoparticles were prepared by using coꢀprecipitation method with some
alteration in the reported method. In a typical synthesis, 0.013 moles of Fe2 (SO4)3 were
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dissolved in 10 ml of distilled water and 0.013 moles of FeSO4 was also dissolved in 10 ml of
distilled water. Both solutions were mixed together and the mixture was sonicated up to 15
minutes to get the clear solution. The pH of the mixture was adjusted to 10 by slow drop wise
addition of the ammonium hydroxide solution. Then the mixture was stirred vigorously at 60oC
for 1 hour. The resultant mixture was washed 3ꢀ4 times with distilled water and finally
centrifuged to get the black precipitate of Fe3O4 magnetic nanoparticles.
4.4 Synthesis of Fe3O4@SiO2:
The precursor was prepared by suspending of 1g of Fe3O4 MNPs with 60 ml of EtOH followed
by the addition of 20 ml distilled water and sonicated up to 45 minutes. After mixing, NH4OH (5
ml) and TEOS (31.36 mmol) were added to the mixture and sonicated for 10 minutes again. The
mixture was magnetically stirred at 35oC for 5.5 hrs. Then the resultant mixture was washed 4
times with distilled water and centrifuged. Finally the brown precipitates were dried in an oven at
50oC.45
4.5 Synthesis of Fe3O4@SiO2ꢀPrꢀNH2:
Firstly, a dilution of 0.5 g of Fe3O4@SiO2 was done with the addition of 125 ml of distilled
water. The mixture was then sonicated up to 1 hour. The pH was adjusted up to 10.5 by the slow
drop wise addition of the ammonium hydroxide solution. Then 53.4 mmol of (3ꢀaminopropyl)
triethoxysilane(APTES)/(3ꢀaminopropyl)trimethoxysilane(APTMS) were added to the above
solution separately and again sonicated up to 15 minutes more. The resultant mixture was stirred
at 50oC with 300 RPM for 3.5 hrs. Finally, it was washed 4 times with distilled water,
centrifuged and dried in an oven at 50oC.46
4.6 Synthesis of Fe3O4@SiO2ꢀPrꢀNHꢀSO3H:
The obtained powder of Fe3O4@SiO2@NH2 (0.07272g) was dispersed in DCM (5 ml) by the
ultrasonic bath for 30 minutes. Then 1.74 mmol (0.116 ml) of chlorosulphonic acid was added
drop wise to the constant shaking by hand for 15 minutes in an ice bath. Then there was an
evolution of hydrogen gas from the reaction mixture. Finally mixture was washed 3 times with
dry DCM to remove the unreacted part and kept at room temperature for drying.36
4.7 Synthesis of αꢀaminonitriles:
Aldehyde (1mmol), aniline (1mmol) and TMSCN (1.3mmol, 0.162 ml) were mixed in water (1.5
ml) as solvent at room temperature. Then the appropriate amount of the catalyst was added to the
reaction and then the mixture was stirred. The progress of the reaction was indicated by TLC.
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The solid product separated at the end of the reaction. After this, the reaction product was
dissolved in hot EtOH and catalyst was removed by using an external magnet. Then,
recrystallization was done by using EtOH to afford the pure product.
Spectral data for products:
Table 4, entry 1 (4a): 2ꢀphenylꢀ2ꢀ(phenylamino)acetonitrile
FTꢀIR: 3360, 3024, 2905, 2200, 1600, 1501, 1419, 1321, 1120, 918, 754 cmꢀ1, 1H NMR (CDCl3,
400MHz) δ (ppm): 4.01 (br s, 1H), 5.41(s, 1H), 6.77ꢀ7.00 (d, 3H), 7.26ꢀ7.58 (t, 7H).
Table 4, entry 2 (4b): 2ꢀ(2ꢀmethoxyphenylamino)ꢀ2ꢀphenylacetonitrile
1
FTꢀIR: 3331, 3069, 2958, 2233, 1598, 1508, 1456, 1232, 1120, 1030, 724 cmꢀ1, H NMR
(CDCl3, 400MHz) δ (ppm): 3.83 (s, 3H), 5.46 (s, IH), 6.82ꢀ6.94 (m, 4H), 7.45ꢀ7.48 (m, 3H),
7.61ꢀ7.63 (m, 2H), 8.0ꢀ8.1 (m, 1H).
Table 4, entry 3 (4c): 2ꢀ(4ꢀchlorophenylamino)ꢀ2ꢀphenylacetonitrile
1
FTꢀIR: 3308, 2882, 2255, 1613, 1516, 1486, 1269, 1112, 1008, 754 cmꢀ1, H NMR (CDCl3,
400MHz) δ (ppm): 3.10 (br s, 1H), 5.39 (s, 1H), 6.70ꢀ6.72 (m, 2H), 7.22ꢀ7.23 (m, 2H), 7.44ꢀ7.46
(m, 2H), 7.57ꢀ7.59 (m, 2H), 8.08ꢀ8.10 (m, 1H).
Table 4, entry 4 (4d): 2ꢀ(4ꢀfluorophenylamino)ꢀ2ꢀphenylacetonitrile
1
FTꢀIR: 3346, 3039, 2240, 1605, 1501, 1456, 1299, 1224, 1075, 776 cmꢀ1, H NMR (CDCl3,
400MHz) δ (ppm): 4.25 (br s, 1H), 5.37 (s, 1H), 6.72ꢀ6.76 (m, 2H), 6.98 (t, 2H), 7.45ꢀ7.48 (m,
3H), 7.58ꢀ7.61 (m, 1H), 8.10ꢀ8.12 (m, 1H).
Table 4, entry 5 (4e): 2ꢀ(oꢀtolylamino)ꢀ2ꢀphenylacetonitrile
FTꢀIR: 3368, 3025, 2968, 2240, 1605, 1501, 1446, 1286, 1117, 918, 734 cmꢀ1, 1H NMR (CDCl3,
400MHz) δ (ppm): 2.16 (s, 3H), 3.05 (br s, 1H), 5.46 (s, 1H), 6.85ꢀ6.87 (m, 2H), 7.14 (d, 1H),
7.21 (t, 1H), 7.47ꢀ7.48 (m, 3H), 7.62ꢀ7.63 (m, 1H), 8.0ꢀ8.1 (m,1H).
Table 4, entry 6 (4f): 2ꢀ(mꢀtolylamino)ꢀ2ꢀphenylacetonitrile
FTꢀIR: 3341, 3039, 2920, 2232, 1603, 1487, 1455, 1307, 1165, 906, 764 cmꢀ1, 1H NMR (CDCl3,
400MHz) δ (ppm): 2.32 (s, 3H), 3.50 (br s, 1H), 5.43 (s, 1H), 6.60 (d, 2H), 6.74 (d, 1H), 7.16 (t,
1H), 7.43ꢀ7.48 (m, 3H), 7.59ꢀ7.61 (m, 2H).
Table 4, entry 7 (4g): 2ꢀ(2ꢀethoxyphenylamino)ꢀ2ꢀphenylacetonitrile
FTꢀIR: 3338, 3050, 2977, 2174, 1604, 1507, 1448, 1293, 1128, 914, 730 cmꢀ1, 1H NMR (CDCl3,
400MHz) δ (ppm): 1.39 (t, 3H), 2.40 (br s, 1H), 4.0ꢀ4.1 (m, 2H), 5.48 (s, 1H), 6.80ꢀ6.92(m, 4H),
7.44ꢀ7.47 (m, 3H), 7.61ꢀ7.63 (m, 2H).
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Table 4, entry 8 (4h): 2ꢀ(3ꢀhydoxyphenylamino)ꢀ2ꢀphenylacetonitrile
FTꢀIR: 3301, 3041, 2233, 1619, 1513, 1455, 1273, 1223, 1177, 903, 735 cmꢀ1, 1H NMR (CDCl3,
400MHz) δ (ppm) 4.43 (br s, 1H), 5.33 (s, 1H), 6.70ꢀ6.84 (m, 3H), 7.17ꢀ7.19 (m, 1H), 7.46ꢀ7.58
(m, 3H), 7.88ꢀ7.89 (m, 2H), 8.47 (s, 1H).
Table 4, entry 9 (4i): 2ꢀ(4ꢀchlorophenyl)ꢀ2ꢀ(phenylamino)acetonitrile
1
FTꢀIR: 3353, 3039, 2225, 1605, 1493, 1426, 1284, 1127, 1008, 814 cmꢀ1, H NMR (CDCl3,
400MHz) δ (ppm): 3.48 (br s, 1H), 5.43 (s, 1H), 6.78 (d, 2H), 6.93 (t, 1H), 7.26ꢀ7.30 (m, 2H),
7.42ꢀ7.44 (m, 2H), 7.53ꢀ7.56 (m, 2H).
Table 4, entry 10 (4j): 2ꢀ(4ꢀmethoxyphenyl)ꢀ2ꢀ(phenylamino)acetonitrile
1
FTꢀIR: 3331, 3024, 2935, 2233, 1620, 1501, 1434, 1239, 1157, 1023, 754 cmꢀ1, H NMR
(CDCl3, 400MHz) δ (ppm): 3.82 (s, 3H), 4.00 (br s, 1H), 5.34 (s, 1H), 6.76 (d, 2H), 6.88 (t, 1H),
6.95 (d, 2H), 7.27 (t, 2H), 7.49 (d, 2H).
Table 4, entry11 (4k): 2ꢀ(3, 4ꢀdimethoxyphenyl)ꢀ2ꢀ(phenylamino)acetonitrile
1
FTꢀIR: 3352, 2944, 2233, 1599, 1514, 1307, 1268, 1142, 1023, 755 cmꢀ1, H NMR (CDCl3,
400MHz) δ (ppm): 2.02 ( br s, 1H), 5.36 (s, 1H), 3.89ꢀ3.96 (m, 6H), 6.78 (d, 1H), 6.88ꢀ6.92 (m,
1H), 6.97(d, 1H), 7.05(d, 1H), 7.14ꢀ7.17 (m, 1H), 7.24ꢀ7.30 (m, 1H), 7.40 (d, 1H), 7.44ꢀ7.46(m,
1H).
Table 4, entry 12 (4l): 2ꢀ(5ꢀmethylfuranꢀ2ꢀyl)ꢀ2ꢀ(phenylamino)acetonitrile
1
FTꢀIR: 3333, 3032, 2240, 1600, 1566, 1510, 1438, 1292, 1247, 1097, 1023, 896 cmꢀ1, H NMR
(CDCl3, 400MHz) δ (ppm): 2.32 (s, 3H), 4.15 (br s, 1H), 5.41 (s, 1H), 6.00 (d, 1H), 6.45 (d, 1H),
6.79 (d, 2H), 6.91 (t, 1H), 7.26ꢀ7.29 (m, 2H).
Table 4, entry 13 (4m): 2ꢀ(4ꢀhydoxyphenyl)ꢀ2ꢀ(phenylamino)acetonitrile
FTꢀIR: 3377, 3040, 2197, 1605, 1515, 1443, 1281, 1240, 1157, 978, 761 cmꢀ1, 1H NMR (CDCl3,
400MHz) δ (ppm): 3.97 (br s, 1H), 5.35(s, 1H), 6.69ꢀ6.78 (m, 2H), 6.89ꢀ6.95 (m, 3H), 7.16 (t,
1H), 7.27ꢀ7.30 (m, 1H), 7.32ꢀ7.46 (m, 1H), 7.78ꢀ7.92 (m, 1H), 8.39 (s, 1H).
Table 4, entry 14 (4n): 2ꢀ(2ꢀmethoxyphenylamino)ꢀ2ꢀ(4ꢀhydroxyphenyl)acetonitrile
1
FTꢀIR: 3282, 3025, 2938, 2254, 1602, 1514, 1442, 1225, 1117, 1024, 737 cmꢀ1, H NMR
(CDCl3, 400MHz) δ (ppm): 3.87 (s, 3H), 4.61 (br s, 1H), 5.36 (s, 1H), 6.84ꢀ6.89 (m, 5H), 7.47
(d, 2H), 7.80 (d, 1H), 8.45 (s, 1H).
Table 4, entry 15 (4o): 2ꢀ(2ꢀmethoxyphenylamino)ꢀ2ꢀ(4ꢀchlorophenyl)acetonitrile
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1
FTꢀIR: 3336, 3206, 2941, 2241, 1605, 1509, 1453, 1221, 1119, 1029, 723 cmꢀ1, H NMR
(CDCl3, 400MHz) δ (ppm): 2.12 (br s, 1H), 3.83 (s, 3H), 5.43 (s, 1H), 6.76(t, 1H), 6.84ꢀ6.85 (m,
2H), 6.86ꢀ6.91 (m, 1H), 7.41ꢀ7.43 (m, 2H), 7.54ꢀ7.56 (m, 2H).
Table 4, entry 16 (4p): 2ꢀ(4ꢀchlorophenyl)ꢀ2ꢀ(phenylamino)acetonitrile
FTꢀIR: 3333, 3135, 2921, 2243, 1603, 1497, 1436, 1251, 1093, 1023, 750 cmꢀ1, 1H NMR (CDClꢀ
3, 400MHz) δ (ppm): 2.31 (s, 3H), 4.16 (br s, 1H), 5.40 (s, 1H), 5.99 (d, 1H), 6.43 (d, 1H), 6.77
(d, 2H), 6.90 (t, 1H), 7.14 (t, 1H), 7.26 (t, 2H).
Conclusion: Synthesis of Fe3O4@SiO2ꢀPrꢀNHꢀSO3H (AE) and Fe3O4@SiO2ꢀPrꢀNHꢀSO3H (AM)
nanoparticles was carried out. The effect of grafting with different alkoxy silanes on the catalytic
activity was analyzed. This present methodology offers several advantages, such as excellent
yields, environmentally friendly work up procedure, shorter reaction times, ambient condition in
an open atmosphere, use of green solvent water and a recyclable catalyst with a very easy
separation with an external magnet. In addition, the obtained results indicated that AE can be
used as an inexpensive and effective catalyst for the synthesis of variety of αꢀaminonitriles by
oneꢀpot three component reactions. The catalyst shows high thermal stability, non toxicity,
recyclability and reused up to five reaction cycles without considerable loss in activity.
Acknowledgments: We are thankful to IIT Ropar for XRD, NMR, SAIF, Panjab University,
Chandigarh for TEM, CIL IIT Roorkee for VSM, BIT Bengaluru for BET, IIT Kanpur for XPS,
Department of Chemistry NIT Jalandhar for FTꢀIR, TGA. Three of the authors (H.S., P.A and J.)
are thankful to UGC, MHRD and NIT Jalandhar for providing the research fellowship.
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