Amine grafted Fe3O4 immobilized graphene oxide as a recyclable and effectual nanocomposite for the regioselective ring opening reaction

Article abstract of DOI:10.1007/s11164-021-04509-4

This work describes the synthesis of magnetic graphene oxide (MGO), where iron oxide (Fe₃O₄) nanoparticles were uniformly deposited over the sheets of the graphene oxide (GO). Further, the introduction of aminopropyltrimethoxysilane (APTMS) on the surface of MGO was successfully done and results in the formation of amine-functionalized magnetic graphene oxide (MGO–NH₂). The synthesized heterogeneous magnetic nanocomposite was characterized by numerous physicochemical and morphological techniques such as powder X-ray diffraction, Fourier transform infrared, thermogravimetric analysis, transmission electron microscopy, vibrating sample magnetometer, scanning electron microscopy, CHN analyzer, and energy-dispersive X-ray analysis. The synthesized nanocomposite was proved to be an effectual catalyst in the nucleophilic ring opening reactions of styrene oxide with derivatives of amines under green solvent. The present catalyst displayed good catalytic activity, short reaction time, higher regioselectivity, excellent yields and could be reutilized up to seven catalytic rounds with no substantial loss in its activity. The excellent properties of the catalyst are due to the dual character of acidic groups (existence of carboxyl groups on the sheet edges) and basic groups (amine groups anchored on the surface of GO). On completion of the reaction, the prepared nanocomposite could be effortlessly recovered from the reaction mixture by utilizing an external magnet, owing to the ferromagnetic property of Fe₃O₄. Graphical Abstract: [Figure not available: see fulltext.].

Full text of DOI:10.1007/s11164-021-04509-4

Research on Chemical Intermediates
https://doi.org/10.1007/s11164-021-04509-4
Amine grafted Fe O immobilized graphene oxide
3
4
as a recyclable and eꢀectual nanocomposite
for the regioselective ring opening reaction
1
1
1
1
1
Padmini Gupta · Charu Garkoti · Javaid Shabir · Surabhi · Digvijay Sah ·
Subho Mozumdar1
Received: 1 February 2021 / Accepted: 5 June 2021
©
The Author(s), under exclusive licence to Springer Nature B.V. 2021
Abstract
This work describes the synthesis of magnetic graphene oxide (MGO), where
iron oxide (Fe O ) nanoparticles were uniformly deposited over the sheets of the
3
4
graphene oxide (GO). Further, the introduction of aminopropyltrimethoxysilane
(
APTMS) on the surface of MGO was successfully done and results in the formation
of amine-functionalized magnetic graphene oxide (MGO–NH ). The synthesized
2
heterogeneous magnetic nanocomposite was characterized by numerous physico-
chemical and morphological techniques such as powder X-ray diꢀraction, Fourier
transform infrared, thermogravimetric analysis, transmission electron microscopy,
vibrating sample magnetometer, scanning electron microscopy, CHN analyzer, and
energy-dispersive X-ray analysis. The synthesized nanocomposite was proved to be
an eꢀectual catalyst in the nucleophilic ring opening reactions of styrene oxide with
derivatives of amines under green solvent. The present catalyst displayed good cata-
lytic activity, short reaction time, higher regioselectivity, excellent yields and could
be reutilized up to seven catalytic rounds with no substantial loss in its activity. The
excellent properties of the catalyst are due to the dual character of acidic groups
(
existence of carboxyl groups on the sheet edges) and basic groups (amine groups
anchored on the surface of GO). On completion of the reaction, the prepared nano-
composite could be eꢀortlessly recovered from the reaction mixture by utilizing an
external magnet, owing to the ferromagnetic property of Fe O .
3
4
*
Subho Mozumdar
subhoscom@yahoo.co.in
1
Department of Chemistry, University of Delhi, Delhi 110007, India
Vol.:(012
1
3456789)
3

P. Gupta et al.
Graphical Abstract
Keywords Magnetic graphene oxide · Heterogeneous catalyst · Nanocomposites ·
Green solvent · Regioselective ring opening
Introduction
Recently, substantial attempts have been undertaken to develop various graphene-
based materials [1]. Among them, the most popular precursor, i.e., Graphene oxide
(
GO), a 2-D hexagonal carbon lattice [2] has shown tremendous advantages in the
ꢁ
eld of catalysis due to its various special features like large surface area accessi-
ble for further functionalization, good chemical stability, high adsorption capacity,
extraordinary electrical, thermal, mechanical and structural properties [2–4]. Due
to the existence of diꢀerent functionalities such as carboxyl (–COOH), hydroxyl
(
–OH), and epoxide ( ) groups, GO can provide a necessary platform for the
(
)
incorporation of a large number of inorganic–organic moieties such as metals,
alloys, ꢂuorescent molecules, biomolecules, drugs and inorganic nanoparticles [5].
The various functionalities present on the surface of GO are accountable for ionic
and non-ionic interactions and also explain the oxidizing and acidic eꢀects in vari-
ous reactions [6]. These oxygen functionalities play a vital role as activation sites for
the growth and stabilization of Fe O nanoparticles on the surface of GO [7]. More-
3
4
over, these functionalities enhance the hydrophilic character of the GO sheet which
makes them easily disperse in water [8, 9]. These oxygen-rich functional groups
could be further utilized as reactive sites for required modiꢁcation.
Fe O nanoparticles (NPs) immobilized on GO surface have a wide variety of
3
4
applications in catalysis, magnetic ꢂuids, biomedicine, and environmental remedi-
ation [3, 10]. GO@ Fe O are the magnetic nanocomposites that could aꢀord an
3
4
1
3

Amine grafted Fe O immobilized graphene oxide as a…
3
4
eꢀective approach for recovering by using an external magnetic source. These nano-
composites have both the advantage of magnetic separation and the large accessible
surface area of GO that makes them suitable candidate in the ꢁeld of catalysis [11].
At the present time, the scientiꢁc community has a profound interest in homo-
geneous catalysis due to high activity and selectivity [12, 13]. However, the homo-
geneous catalyst suꢀers from the major disadvantage of arduous separability from
the reaction mixture [8]. To overcome this drawback associated with homogeneous
catalyst, numerous heterogeneous catalytic systems could be designed having the
advantage of easily recoverable catalyst simply by means of centrifugation or ꢁltra-
tion method. Also, it could be reutilized in diꢀerent catalytic cycles. In addition, the
separation of the heterogeneous catalyst from the reaction medium by using centrif-
ugation or ꢁltration method is not always easy and mainly depends upon the size of
the nanoparticles [14, 15]. In continuation of our eꢀorts for the development of het-
erogeneous nanocatalyst [16–18], Herein we report the immobilized Fe O magnetic
3
4
NPs on the surface of GO which enables the easy separation of the catalyst through
a magnet without using the tedious task of centrifugation or ꢁltration method [15].
Further, 3-aminopropyltrimethoxysilane is covalently anchored onto the graphene
oxide. The amine-functionalized magnetic graphene oxide as a heterogeneous cata-
lyst has a large surface area which increases dispersion capacity as well as catalytic
activity.
Epoxides are organic intermediates that are extremely important in the synthe-
sis of several pharmaceutical and medicinal compounds [19]. The synthesis of
β-substituted amino alcohols involves the nucleophilic and regioselective ring open-
ing of various epoxides with derivatives of amines which represents an important
role in the broad range synthesis of various biologically and pharmaceutically active
synthetic and natural products, chiral auxiliaries, and amino acids [20, 21]. This ring
opening reaction of epoxides has been reported with many heterogeneous catalysts
such as NaMCM-22 [19], nano SiO –Cl [22], Nano Fe O [23], Zr–MOR zeolite
2
3
4
[
24], sulfated tungstate [25], silica nanoparticles [26]. The reported catalysts suꢀer
many drawbacks such as lack of appreciable regioselectivity, high catalyst amount,
low yields, high temperature, and use of toxic organic solvent. To address these
issues, the synthesized amine-functionalized magnetic graphene oxide was utilized
as an eꢀectual and heterogeneous catalyst for the regioselective ring opening reac-
tion of styrene oxide with amines which leads to the formation of β-substituted
amino alcohols in the medium of water as a green solvent at 50 °C. Several reports
have been published on a similar type of amine- functionalized magnetic graphene
oxide nanocomposite and employed for catalyzing diꢀerent type of reactions[8,
2
7–30]. However, the reported catalysts were never utilized for catalyzing ring
opening reactions. The synthesized nanocomposite plays an imperative role in the
activation of styrene oxide and increases the regioselectivity in the reaction. The
synthesized catalyst could be eꢀortlessly recovered from reaction medium and recy-
cled for multiple cycles.
1
3

P. Gupta et al.
Experimental section
Materials and methods
Natural ꢂakes of graphite, FeSO ·7H O, and Fe (SO ) were purchased from Sigma-
4
2
2
4 3
Aldrich. 3-aminopropyltrimethoxysilane (APTMS) was provided by Alfa Aesar.
Liquor ammonia (25%) was purchased from Fisher Scientiꢁc. H SO , HCl, H O ,
2
4
2
2
and KMnO were obtained from Spectrochem (India). The rest of the chemicals
4
were used acquired from either Alfa-Aesar, Merck, or Spectrochem (India). All the
purchased chemicals and reagents were not puriꢁed by any methods, they were used
directly.
Preparation of graphene oxide (GO)
GO was prepared by means of an improved Hummers’ process [31]. Typically, a
mixture of H PO /H SO (10: 90 mL) was added to graphite ꢂakes (250 mg). Then,
3
4
2
4
KMnO (2.5 g) was added slowly in the acidic solution and stirred at 50 °C for 12 h.
4
Afterward, the reaction mixture was kept at room temperature then poured into
an ice bath (50 mL) followed by the subsequent addition of H O (0.75 mL). The
2
2
resultant mixture was centrifuged and washed with H O, HCl, MeOH several times
2
and then lastly with diethyl ether. The acquired solid brown color GO was dried
overnight in a vacuum at 60 °C.
Preparation of Fe O nanoparticles immobilized over graphene oxide sheets
3
4
(
MGO)
MGO nanoparticles were prepared through the Chemical deposition method [32].
Typically, GO (80 mg) was dispersed in distilled water (20 mL) in a 100-mL round
bottom ꢂask (solution A) and then ultra-sonicated for an hour. On another 100 ml
round bottom ꢂask, Fe (SO ) (1199.64 mg) and FeSO ·7H O (834.06 mg) were
2
4 3
4
2
dissolved in distilled water (solution B) and stirred vigorously for 15 min till the
solution becomes clear. After stirring, solution B was mixed with solution A at room
temperature. Then, liquor ammonia (25%) was gently added to the above reaction
mixture to maintain the pH of the mixture to 10. Then, the reaction mixture was
vigorously stirred at 60 °C for 2 hours. The precipitated nanoparticles were isolated
via an external magnetic force and washed numerous times using distilled water and
methanol till the pH reached 7. The obtained MGO nanoparticles were parched at
3
0 °C in a vacuum oven.
Preparation of amine‑functionalized magnetic graphene oxide (MGO–NH2)
Typically, toluene (10 mL) was added to the solid magnetic graphene oxide nano-
particles (100 mg) and the mixture was sonicated for 10 min. Then, 3-aminopropyl-
trimethoxysilane (20 mmol) was added to it and the resultant mixture was reꢂuxed at
9
0 °C for 12 h under an inert atmosphere. After 12 h, the ꢁnal catalyst was collected
1
3

Amine grafted Fe O immobilized graphene oxide as a…
3
4
magnetically, washed with toluene and methanol three times, and then dried at 80 °C
for 2 h in a vacuum oven.
Ring opening of styrene Oxide using MGO–NH as nanocatalyst
2
In a typical procedure, a mixture of an amine (1 mmol), styrene oxide (1 mmol),
water (2 ml), and catalyst (7 mg) was taken in a small test tube and kept for stirring
at 50 °C for a suitable time. The completion of the following reaction was tested
using Thin Layer Chromatography. When the reaction was completed, then the cata-
lyst was isolated from the mixture via an external magnetic force and used in the
next reaction to check its recyclability. Then, the mixture was extracted using ethyl
acetate-water and the organic layer part was passed over Na SO . The remaining
2
4
solvent was evaporated under reduced pressure and concentrated in a vacuum to
aꢀord the β-substituted amino alcohol. The products were fully checked by using
1
3
1
C NMR, H NMR, and HR-MS.
Characterization techniques
Powder X-ray diꢀraction (PXRD) patterns were measured by using a Bruker, D8
Discover diꢀractometer with Cu, 3KW radiation in the 2θ region of 5–80° and a
−1
scan rate of 5° min . Fourier transform infrared (FT-IR) spectra were recorded on
−
1
Perkin Elmer Spectrum RXI-Mid IR Spectrometer in the region of 4000–400 cm .
Thermogravimetric (TG) analysis (Perkin Elmer, Pyris diamond) was used for the
thermal decomposition behavior of the MGO–NH nanocomposites. The informa-
2
tion about the morphology and size of the MGO–NH was acquired through scan-
2
ning electron microscopy (SEM) via JEOL Japan Mode: JSM 6610LV electron
microscope and the transmission electron microscopy (TEM) was done through a
2
Tachnai G T30, U‐Twin transmission electron microscope. Vibrating-sample mag-
netometer (VSM) was recorded to study the magnetic behavior of the prepared cata-
lyst at room temperature. Energy-dispersive X-ray spectra (EDX) (equipped with the
1
13
SEM machine) were recorded for elemental analysis. H NMR and C NMR for the
products acquired by the ring opening reactions of styrene oxide with amines were
taken on an instrument Jeol JNM-EXCP 400 at 400 MHz and 100 MHz, respec-
tively. During these characterizations, CDCl was used as solvent, and TMS was
3
used as an internal standard.
Results and discussion
The stepwise procedure for the production of amine-functionalized magnetic gra-
phene oxide (MGO–NH ) has been presented in Scheme 1. Production of graphene
2
oxide was done via an improved Hummers’ method [31]. Fe O nanoparticles
3
4
could be deposited over graphene oxide sheets through the Chemical Deposition
method [32]. The resulting nanosheets of magnetic graphene oxide could be amine
1
3

P. Gupta et al.
Scheme 1 Preparation of amine functionalized magnetic graphene oxide (MGO–NH2)
functionalized through the silylanization of graphene oxide sheets with 3-aminopro-
pyltrimethoxysilane in order to obtain the required catalyst, i.e., amine-functional-
ized magnetic graphene oxide (MGO–NH ).
2
The FT-IR spectra of synthesized GO, MGO, and MGO–NH are displayed in
2
Fig. 1. The FT-IR study of pure GO shows that it contains various functional moie-
−1
ties. The broad band at 3403 cm conꢁrms the presence of stretching O–H vibra-
−1
tional modes. The band at 1740 cm refers to the vibrational stretching mode of
−
1
C=O groups present on GO. The peaks at 1225 cm indicate the presence of epox-
−1
ide moieties [33]. The band at 1626 cm is for aromatic C=C which corresponds
to the unoxidized skeletal vibrations of C=C stretching vibrations. However, the
FT-IR spectrum of MGO was diꢀerent from that of the spectrum of GO. The typical
−1
characteristic band at 570 cm can be ascribed to the stretching Fe–O vibrations
and this conꢁrms the presence of Fe O . The decrease in the broadness of O–H and
3
4
−1
−1
C=O peaks at 3364 cm and 1740 cm conꢁrms that Fe O nanoparticles were
3
4
successfully incorporated over graphene oxide sheets through carboxylate ions.
The FT-IR spectrum of MGO–NH shows the peaks in wide range of
2
−
1
−1
3
363 cm –3404 cm conꢁrms the stretching vibrational mode of (–NH ) and
2
−
1
−1
hydroxyl group. Two peaks at 2927 cm and 2859 cm indicate the stretch-
ing vibrations of asymmetric and symmetric C–H bands of CH –CH moieties
2
2
of the alkyl chains existing in the 3-chloropropyltrimethoxysilane. The existence
of amine groups on GO could be conꢁrmed by the characteristic band of N–H
−
1
−1
bending vibrations at 1560 cm . Moreover, the band at 545 cm refers to the
1
3

Amine grafted Fe O immobilized graphene oxide as a…
3
4
Fig. 1 FT-IR spectra of GO, MGO and MGO–NH2
Fe–O stretching vibrations. Along with, there were also two additional peaks
−
1
−1
at 1103 cm and 1041 cm which could be allotted to the Si–O–C stretching
vibration and O–Si–O asymmetric stretching mode, respectively.
Hence, from the study of FT-IR spectra of MGO and MGO–NH , it was con-
2
cluded that the amine group could be eꢀectively immobilized on the magnetic
surface of graphene oxide sheets.
Patterns of powder X-ray diꢀraction (XRD) reveals the crystallinity of indi-
vidual complex nanocomposite of GO and MGO-NH (Fig. 2a). The analysis of
2
XRD patterns was carried out from 5.0° (2θ) to 80.0° (2θ) in which the broad
bands from 12.0° (2θ) to 29.0° (2θ) were obtained which are indicative of the
amorphous state. A sharp characteristic diꢀraction peak at 2θ = 9.3° highly dem-
onstrates the crystalline nature of graphene oxide which corresponds to the (001)
crystal plane. The band at 43° depicts the crystalline nature of carbon present in
graphene oxide. The XRD analysis of MGO–NH displayed a very broad diꢀrac-
2
tion peak at 2θ = 30°, 35°, 43°, 53.3°, 57° and 62.7° which indicates the crystal-
line nature of cubic Fe O and these could be designated to (220), (311), (400),
3
4
(
422), (511) and (440) crystal planes, respectively [16]. These assigned peaks are
in close agreement with the typical XRD pattern of Fe O having spinel crystal
3
4
1
3

P. Gupta et al.
Fig. 2 a Powder XRD patterns of a GO and b MGO–NH , b Magnetization curves of a MGO and b
2
MGO–NH
2
FCC structure (indexed to JCPDS No. 19–0629). Hence, it could be concluded
that the Fe O strong peak inhibited the GO peak.
3
4
The magnetization behavior of the MGO and MGO–NH at room temperature
2
was determined by VSM with a magnetic ꢁeld from −10000 Oe to+10000 Oe as
presented in Fig. 2b. The saturation magnetization value of MGO was measured
−1
to be 37 emu g whereas there was a little drop in the magnetization values of
−
1
MGO–NH i.e., 30 emu g . This inappreciable decrease in the magnetization value
2
for MGO–NH could be ascribed to the eꢀective immobilization of the amine group
2
over the surface of magnetic graphene oxide (MGO) sheets and it could be eꢀort-
lessly isolated by means of an external magnet from the reaction mixture.
The morphology and shape of MGO–NH nanomaterials were explored by SEM
2
and TEM as shown in Fig. 3. From SEM analysis, it was found that Fe O nano-
3
4
particles were statistically spread over the surface of (a) and (b) GO sheets. The
TEM images of (c) GO show the high surface area having a sheet-like shape for the
immobilization of various groups. Also, the TEM images show a black spot (d) and
(
e) which conꢁrms the presence of Fe O nanoparticles which are well dispersed
3 4
over the GO sheets. Graphene oxide maintains a well-deꢁned sheet-like structure as
no considerable changes were noticed in the morphology of GO sheets. The SAED
(
selected area electron diꢀusion) patterns (f) reveals the crystalline nature of Fe O
3 4
nanoparticles and it could be attributed to its cubic spinel structure. The strong ꢁve
diꢀraction rings in the SAED pattern were allotted to the (220), (311), (400), (511),
and (440) reꢂections of the spinel cubic structure of Fe O nanoparticles, respec-
3
4
tively. These outcomes are very well in agreement with the XRD results.
The energy-dispersive X-ray (EDX) spectroscopy (equipped with the SEM
machine) was utilized for elemental analysis of the MGO–NH nanocomposite
2
(
Fig. 4a). The characteristic peaks of iron, carbon, nitrogen, silicon, and oxygen pre-
sent in the EDX spectrum of MGO–NH conꢁrm the successful immobilization of
2
the amine group over the surface of magnetic graphene oxide (MGO) sheets. Moreo-
ver, CHN analysis was also performed out. The nanocomposites (MGO–NH ) con-
2
tain 1.12, 2.19, and 0.28 mol of carbon, hydrogen, and nitrogen, respectively.
1
3

Amine grafted Fe O immobilized graphene oxide as a…
3
4
Fig. 3 a–b SEM images of MGO-NH , c TEM images of GO, d–e MGO–NH at diꢀerent magniꢁcation
2
2
and f SAED pattern of the Fe O nanoparticles
3
4
The TG analysis was performed to study the thermal decomposition of the pre-
pared nanomaterial MGO–NH (Fig. 4b). The TGA graph for graphene oxide shows
2
a 20% weight loss near the initial heating stage (up to 150 °C) which could be due
to the loss of the absorbed water molecule from the sample as well as from the slow
disintegration of the thermally unstable graphene oxide. At around 150–200 °C, a
sharp weight loss of around 62% occurred which could be ascribed to the ꢂexible
oxygen-containing functional groups that decomposed to carbon dioxide moiety.
Between the temperature range 300 °C and 700 °C, a slow and steady weight loss of
4
% was observed which occurred due to the elimination of the most stable oxygen
functionalities of the GO [17]. In the TGA spectra of MGO–NH , there is a small
2
weight loss near 150 °C which could be due to the loss of some water molecules.
Also, the small weight loss in the region of 300–800 °C could be due to the decom-
position of the most thermally stable amine group over the surface of GO. Hence,
the TG analysis conꢁrms the thermal stability of the amine group over the magnetic
graphene oxide (MGO) sheets.
From the FT-IR, TEM, SEM–EDX, TGA, PXRD, VSM and CHN analysis, it
ultimately proved that the NH group has been statistically anchored over the mag-
2
netic graphene oxide surface.
The catalytic eꢃciency of the prepared catalyst MGO-NH was investigated
2
with the ring opening reactions of styrene oxide. Initially, in order to examine the
diꢀerent reaction conditions, aniline and styrene oxide were employed as sub-
strates for the model reaction (Table 1). Studies with diꢀerent solvents showed
that the excellent product yield (3) could be obtained at 99% when water was
utilized as a solvent at 50 °C (Table 1, entry 5). On the contrary, the product yield
could not found satisfactory when EtOH and CH CN were chosen as solvents
3
(
Table 1, entries 1 and 2). Therefore, water was chosen as the appropriate green
solvent for catalyzing the ring opening reactions. At room temperature, the yield
1
3

P. Gupta et al.
Fig. 4 a EDX spectra of MGO–NH , b TGA curves of a GO and b MGO–NH2
2
of the product was found to be 72%. However, a good amount of product could be
obtained at elevated temperatures (50 °C) (Table 1, entries 5–7). The amount of
catalyst used also aꢀected the yield of the reaction (Table 1, entries 5 and 8). On
optimizing the amount of the catalyst, it could be concluded that the maximum
yield (99%) of the reaction was found with 7 mg of the catalyst (Table 1, entry
5
8
). Although, it also seen that the good yield (90%) of the product (Table 1, entry
) was found with 5 mg of the catalyst. Also, we observed that the product yield
is comparatively less when GO and MGO were used as catalysts even when the
reaction was continued for a prolonged time (Table 1, entry 10–11). Moreover,
in absence of catalyst, a very low yield was obtained even when the reaction per-
sisted for a longer period of time (Table 1, entry 12). Thus, it could be concluded
that the MGO–NH nanocomposites exhibit excellent catalytic activity in terms
2
of catalyst amount and reaction time. These observations conꢁrm that the amine
1
3

Amine grafted Fe O immobilized graphene oxide as a…
3
4
Table 1 Optimization study for MGO–NH2 catalyzed ring opening of styrene oxide by derivatives of
amines
a
Entry
Catalyst
Catalyst amount Solvent
in mg)
Temp (°C)
Time (min)
Yield (%)
(
1
2
3
4
5
6
7
8
9
MGO–NH2
MGO–NH2
MGO–NH2
MGO–NH2
MGO–NH2
MGO–NH2
MGO–NH2
MGO–NH2
MGO–NH2
GO
7
7
7
7
7
7
7
5
7
7
7
–
EtOH
50
50
50
80
50
80
rt
50
50
50
50
50
60
60
60
60
30
30
30
30
50
30
30
45
99
99
72
90
80
60
60
20
CH CN
3
CH Cl
2
2
Toluene
H O
2
H O
2
H O
2
H O
2
Neat
60
10
11
12
H O
120
120
120
2
MGO
Blank
H O
2
H O
2
a
Reaction conditions: Aniline (1 mmol), styrene oxide (1 mmol), solvent (2 mL). Isolated yield
groups which are immobilized on the MGO sheets play a key role in the develop-
ment of catalysts. Amine groups help in activating the epoxide ring for the ring
opening procedure and also increases the regioselectivity of the reaction. There-
fore, the presence of amine functionalities in the MGO–NH could eꢃciently
2
enhance the rate of the reaction.
In order to probe the scope of the MGO–NH catalyst, a variety of amines
2
were used with styrene oxide under the optimized conditions so as to synthesize
various β-subsituted amino alcohols. All the reactions proceeded smoothly to give
β-substituted amino alcohols in excellent yield with high regioselectivity under
extremely shorter reaction times (Table 2). The reaction of various aryl amines with
styrene oxide predominantly gave the corresponding regioselective β-substituted
amino alcohols (3) with a preferably nucleophilic attack at the phenyl position of the
1
styrene oxide following SN mechanism. On the other side, aliphatic amines reacted
with styrene oxide with a nucleophilic attack at a non-benzylic site of the styrene
2
oxide following an SN mechanism [20, 26]. When compared with aniline, ben-
zylamine or cyclohexylamine (Table 2, entries 1, 8–9) gave the major product (4)
in longer reaction intervals. It was also noticed that aromatic amines with electron-
withdrawing groups reacted with longer reaction time and produced lower yields
when compared to those with electron releasing groups.
MGO–NH not only showed the advantage of recyclability when related with
2
other speciꢁed homogeneous catalysts employed for the production of β-substituted
amino alcohols but also displayed higher activity and produced higher yields in
lesser reaction time (Table 3). We have also done the comparison for the recyclabil-
ity of the recovered catalyst with the various reported heterogeneous nanocatalyst
for a similar reaction. The results showed that the MGO–NH was active till the
2
seventh catalytic run with a 91% yield of the reaction.
1
3

P. Gupta et al.
Table 2 Ring opening reactions of styrene oxide catalyzed by MGO–NH2
Entry
Amines
Epoxide
Product
Time (min)
Yielda (%)
1
30
99
2
30
99
3
30
98
4
45
95
5
6
7
50
50
96
95
6
0
95
8
9
40
90
5
4
0
5
90
95
1
0
Reaction conditions: Amines (1 mmol), styrene oxide (1 mmol), MGO–NH (7 mg), water (2 ml), 50 °C.
2
a
Isolated yield
1
3

Amine grafted Fe O immobilized graphene oxide as a…
3
4
Table 3 Comparison of the catalytic eꢃciency of MGO–NH with other reported catalysts for the syn-
2
thesis of β-amino alcohols
Entry Reactants
Catalyst
Reaction conditions
Neat, rt, 15 min
Yield (%) Ref
1
ZrCl (5 mol %)
100
[20]
4
2
3
4
nano SiO –Cl (30 mg) CH Cl , rt
100
[22]
[23]
[25]
2
2
2
Nano Fe O (10 mol
rt to 80 °C, neat, open 99
atmosphere, 20 h
3
4
%)
Sulfated tungstate (10 25 °C, 15 min
wt %)
92
5
6
7
8
Zr–MOR zeolite
25 mg)
313 K, 4 h, solvent
free
93
89
83
98
[24]
(
NaMCM-22 (100 mg) 35 °C, 6 h
[19]
BiX (10%)
25 °C, 7–9 h,
30 min, 50 °C
[34]
3
MGO–NH (7 mg)
Present work
2
Finally, the recyclability for the synthesized catalyst was also considered and the
eꢀects are shown in Fig. 5. In all the steps, the catalyst could be isolated via an
external magnetic force. Subsequently, the recovered catalyst could be washed two
Fig. 5 Recyclability of the
98
MGO–NH nanocomposite in
98
2
96
the ring opening reaction of sty-
95
95
96
94
92
90
88
86
rene oxide with diꢀerent amines
94
92
90
1
2
3
4
5
6
7
No. of Cycles
1
3

P. Gupta et al.
to three times with hot ethanol and kept under vacuum for drying at 50 °C. The
recovered magnetic nanocatalyst could be recycled for at least seven runs without
much considerable loss in their catalytic activity. The ease of recovery of the recy-
cled catalyst through an external magnetic force, suggests that there is not much
metal leaching of Fe O nanoparticles even after seven catalytic runs in the recov-
3
4
ered catalyst.
To check the stability and recyclability of the catalyst, the FT-IR spectra of the
reused catalyst after seven catalytic runs were also tested and matched with the
FT-IR spectra of the fresh catalyst. After recycled up to the seventh usage, there
are not much noteworthy changes in the FT-IR of the reused catalyst (Fig. 6). This
shows that the prepared catalyst could be recycled and stable for up to seven runs
without much major loss in its activity.
Plausible reaction mechanism
An acceptable mechanism for the ring opening reaction of styrene oxide using deriv-
atives of amines is described in Fig. 7. The H of amine groups present at the surface
of GO activates the epoxide ring through an oxygen atom. Starting of the reaction
by the assistance of bronsted acidity of the intrinsic carboxylic acids present on
3
+
the edges of GO and Lewis acidity of Fe due to which the attack is preferentially
1
through the benzylic position of the styrene oxide through SN mechanism for aro-
matic amines and attack at the non-benzylic position for aliphatic amines proceeding
2
through an SN mechanism. This gives the regio-isomer of amino alcohols. After
activation of styrene oxide, epoxide subjected for nucleophilic attack by aromatic
amines through the path (a) and by aliphatic amines through the path (b) leading to
the formation of intermediate (I) through intramolecular proton transfer or interme-
diate (II) through intermolecular proton transfer followed by protonolysis resulting
to the product formation and regeneration of the nanocatalyst.
Fig. 6 FT-IR spectra of fresh catalyst MGO–NH and the resused catalyst after seventh usages
2
1
3

Amine grafted Fe O immobilized graphene oxide as a…
3
4
Fig. 7 Plausible reaction mechanism for the ring opening reactions of styrene oxide with various amines
using the MGO–NH as the nanocatalyst
2
Conclusion
Herein, we have synthesized highly stable and bifunctional amine-functionalized
magnetic graphene oxide (MGO–NH ) as a heterogeneous hybrid nanocomposite.
2
This was further utilized as an eꢀective and recyclable catalyst for the regioselec-
tive ring opening of styrene oxide with amines. The prepared catalyst showed
remarkable catalytic activity in water with low catalyst loading to aꢀord the desir-
able β-substituted amino alcohols of synthetic and biological importance with
good to excellent yield in a shorter reaction time. The amine group increases the
eꢃciency of the reaction and also the catalytic activity of the synthesized mate-
rial. This prepared material could be recovered easily through an external magnet
and reused for up to seven runs with no extensive loss in its catalytic activity. The
presence of carboxylic acid groups and amine groups (acid–base) played a major
role in the activation of the starting material. The catalyst has a large surface area
which increases dispersion capacity as well as catalytic action.
1
3

P. Gupta et al.
Acknowledgements PG thanks to UGC, New Delhi, India for the ꢁnancial support and also USIC-CIF,
University of Delhi, Delhi, India for instrumentation facilities
Declarations
Conꢁict of interest The authors declare that they do not have any conꢂict of interest.
References
1
2
3
4
5
.
.
.
.
.
R. Pasricha, S. Gupta, A.K. Srivastava, Small 5, 20 (2009)
D. Azarifar, M. Khaleghi-Abbasabadi, Res. Chem. Intermed. 45, 2 (2019)
M. Kassaee, E. Motamedi, M. Majdi, Chem. Eng. J. 172, 1 (2011)
S. Rana, S.B. Jonnalagadda, Funct. Nanomater. (2016). https://doi.org/10.5772/65941
S.S. Abbas, G.J. Rees, N.L. Kelly, C.E. Dancer, J.V. Hanna, T., Nanoscale. 10, 34 (2018) https://doi.
org/10.1039/C8NR04781B
6
7
8
9
.
.
.
.
S. Khodabakhshi, F. Marahel, A. Rashidi, M.K. Abbasabadi, J. Chin. Chem. Soc. 62, 5 (2015)
N.A. Zubir, C. Yacou, X. Zhang, J.C.D. da Costa, J. Environ. Chem. Eng. 2, 3 (2014)
S. Rostamizadeh, A. Hemmasi, N. Zekri, Nanochem. Res. 2, 1 (2017)
L. Valentini, S.B. Bon, O. Monticelli, J.M. Kenny, J. Mater. Chem. 22, 13 (2012)
1
0. Y. Zhang, B. Chen, L. Zhang, J. Huang, F. Chen, Z. Yang, J. Yao and Z. Zhang Nanoscale 3, 4
(
2011)
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
1. N. Sui, L. Wang, X. Wu, X. Li, J. Sui, H. Xiao, M. Liu, J. Wan, W.Y. William, RSC Adv. 5, 1 (2015)
2. A. Corma, H. Garcia, Adv. Synth. Catal. 348, 12 (2006)
3. V. Polshettiwar, R. Luque, A. Fihri, H. Zhu, M. Bouhrara, J.-M. Basset, Chem. Rev. 111, 5 (2011)
4. A. Omidvar, B. Jaleh, M. Nasrollahzadeh, H.R. Dasmeh, Chem. Eng. Res. Des. 121, 339 (2017)
5. M. Esmaeilpour, J. Javidi, F. Dehghani, F.N. Dodeji, New J. Chem. 38, 11 (2014)
6. C. Garkoti, J. Shabir, S. Mozumdar, New J. Chem. 41, 17 (2017)
7. C. Garkoti, J. Shabir, P. Gupta, M. Sharma, S. Mozumdar, New J. Chem. 41, 24 (2017)
8. J. Shabir, C. Garkoti, D. Sah, S. Mozumdar, Catal. Lett. 148, 1 (2018)
9. T. Baskaran, A. Joshi, G. Kamalakar, A. Sakthivel, Appl. Catal. A 524, 50 (2016)
0. A.K. Chakraborti, A. Kondaskar, Tetrahedron Lett. 44, 45 (2003)
1. M. Maheswara, K.S.V.K. Rao, J.Y. Do, Tetrahedron Lett. 49, 11 (2008)
2. R. Karimian, F. Piri, B. Karimi, M. Abolghasem, Chin. J. Chem. 29, 5 (2011)
3. A. Kumar, R. Parella, S.A. Babu, Synlett 25, 06 (2014)
4. B. Tang, W.-C. Song, S.-Y. Li, E.-C. Yang, X.-J. Zhao, New J. Chem. 42, 16 (2018)
5. S.P. Pathare, K.G. Akamanchi, Tetrahedron Lett. 54, 48 (2013)
6. B. Sreedhar, P. Radhika, B. Neelima, N. Hebalkar, J. Mol. Catal. A Chem. 272, 1 (2007)
7. V.B. Saptal, T. Sasaki, K. Harada, D. Nishio-Hamane, B.M. Bhanage, Chemsuschem 9, 6 (2016)
8. S. Farhadi, M. Hakimi, M. Maleki, RSC Adv. 8, 13 (2018)
9. M. Pravin, A. Gnanamani, RSC Adv. 8, 67 (2018)
0. M.M. Heravi, B. Baghernejad, H.A. Oskooie, Catalysis lett. 130, 3 (2009)
1. D.C. Marcano, D.V. Kosynkin, J.M. Berlin, A. Sinitskii, Z. Sun, A. Slesarev, L.B. Alemany, W. Lu,
J.M. Tour, ACS Nano 4, 8 (2010)
3
3
3
2. X. Yang, X. Zhang, Y. Ma, Y. Huang, Y. Wang, Y. Chen, J. Mater. Chem. 19, 18 (2009)
3. A. Świetlikowska, M. Gniadek, B. Pałys, Electrochimica. Acta. 98, 75 (2013)
4. T. Ollevier, G. Lavie-Compin, Tetrahedron Lett. 45, 1 (2004)
Publisher’s Note Springer Nature remains neutral with regard to jurisdictional claims in published
maps and institutional aꢃliations.
1
3