Preparation of magnetically recoverable Fe3O4–graphene oxide catalyst by green method and its application for reduction of nitropyrimidine in aqueous medium

Article abstract of DOI:10.1007/s11164-018-3527-5

Magnetic graphene oxide (GO)/amino-functionalized Fe₃O₄ nanocomposite was prepared using tannic acid as binder. For this purpose, Fe₃O₄ nanoparticles were modified by phenylenediamine and GO was partially reduced and modified in presence of tannic acid. Nanocomposites were prepared under three different synthesis conditions. The morphology and chemical structure of the magnetic GO nanocomposites were studied by means of Fourier-transform infrared spectroscopy, X-ray powder diffraction, transmission electron microscopy, scanning electron microscopy, thermogravimetric analysis, and vibrating-sample magnetometry. The catalytic activity of the optimal GO/Fe₃O₄ nanocomposite was then studied using reduction of 2,4-dichloro-6-methyl-5-nitropyrimidine at different catalyst doses. The reaction time was probed using ultraviolet–visible (UV–Vis) absorption spectroscopy and thin-layer chromatography (TLC) analysis. The results demonstrated that, on increasing the catalyst dose from 1 to 7?mg, the reaction time decreased from 20 to 5?min. The synthesized product was also confirmed by nuclear magnetic resonance. The very low catalyst dose required, green media, and low temperature demonstrate that the as-prepared magnetic GO catalyst has high catalytic activity for reduction of nitropyrimidine to aminopyrimidine in aqueous medium.

Full text of DOI:10.1007/s11164-018-3527-5

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Preparation of magnetically recoverable Fe3O4–graphene
oxide catalyst by green method and its application
for reduction of nitropyrimidine in aqueous medium
Mahdieh Namvar-Mahboub1 Elaheh Khodeir1 Azam Karimian2
•
•
Received: 23 January 2018 / Accepted: 9 July 2018
Ó Springer Nature B.V. 2018
Abstract
Magnetic graphene oxide (GO)/amino-functionalized Fe3O4 nanocomposite was
prepared using tannic acid as binder. For this purpose, Fe3O4 nanoparticles were
modified by phenylenediamine and GO was partially reduced and modified in
presence of tannic acid. Nanocomposites were prepared under three different syn-
thesis conditions. The morphology and chemical structure of the magnetic GO
nanocomposites were studied by means of Fourier-transform infrared spectroscopy,
X-ray powder diffraction, transmission electron microscopy, scanning electron
microscopy, thermogravimetric analysis, and vibrating-sample magnetometry. The
catalytic activity of the optimal GO/Fe3O4 nanocomposite was then studied using
reduction of 2,4-dichloro-6-methyl-5-nitropyrimidine at different catalyst doses.
The reaction time was probed using ultraviolet–visible (UV–Vis) absorption spec-
troscopy and thin-layer chromatography (TLC) analysis. The results demonstrated
that, on increasing the catalyst dose from 1 to 7 mg, the reaction time decreased
from 20 to 5 min. The synthesized product was also confirmed by nuclear magnetic
resonance. The very low catalyst dose required, green media, and low temperature
demonstrate that the as-prepared magnetic GO catalyst has high catalytic activity
for reduction of nitropyrimidine to aminopyrimidine in aqueous medium.
Keywords Magnetic GO Á Catalysis Á Nanocomposite Á Reduction reaction
&
Mahdieh Namvar-Mahboub
Namvar@gonabad.ac.ir; namvarmahboob@yahoo.com
1
2
Department of Chemical Engineering, University of Gonabad, Gonabad, Iran
Department of Chemistry, University of Gonabad, Gonabad, Iran
123

M. Namvar-Mahboub et al.
Introduction
Aminopyrimidines are a group of key intermediate compounds employed to
produce many marketed drugs such as nucleoside antibiotics, antiinflammatory
drugs, and antibacterial and cardiovascular agents, owing to their biological
properties [1, 2]. There are various protocols to synthesize these compounds,
including one-pot synthesis from ketones, arylacetylenes, and guanidines [2],
reduction of nitro compounds [3, 4], etc. However, development of highly selective,
low-cost, easily scalable, and safe methods remains a major challenge for design of
appropriate and economical production lines. Based on literature reports, it seems
that synthetic transformation of nitropyrimidines to aminopyrimidines in presence
of suitable reagents via reduction reaction can meet the mentioned conditions [4–6].
Regarding industrial aspects, application of a nontoxic, stable, highly active catalyst
is essential for the above-mentioned organic synthesis. In this regard, carbon-based
catalysts such as graphene, its derivatives, and hybrid forms have been considered
as environmentally friendly catalysts and/or adsorbents over recent decades [7].
GO is one of the graphene derivatives which has abundant oxygenated functional
groups, including hydroxyl and epoxy groups (both on the basal plane) as well as
carbonyl and carboxyl groups (both at sheet edges). The mentioned functional
groups are responsible for its high hydrophilicity. The two-dimensional lamellar
structure and high surface area accompanied with full accessibility and edge
reactivity make it favorable for assembly of graphene-based hybrid nanomaterials
[8–11]. Over the past decade, GO-based nanocomposites have been considered as
potential materials for applications such as drug delivery [12–14], water purification
[15, 16], catalytic processes [7, 17–19], biosensing [20, 21], polymer composites
[22], etc. To date, depending on the application, different substances including Pd
[23], Pt [24], Au [25], Ag [26], TiO2 [27], SnO2 [28], Fe3O4 [29], and Co-Fe2O4
[30] have been assembled onto inorganic GO sheets to obtain nanocomposites with
novel or enhanced properties. Among GO nanocomposites with catalytic applica-
tions, GO–Fe3O4 has drawn attention from researchers due to the biocompatibility
and catalytic activity of Fe3O4, as well as its magnetic property, which simplifies
separation of such nanocatalysts from the reaction system using an external
magnetic field. To date, the catalytic activity of magnetic GO nanocomposite has
been studied for reduction of nitrophenol [31, 32], oxidation of 2,4 dichlorophenol
[33], Suzuki and Heck cross-coupling reactions [19], and A3 coupling reaction of
aldehyde, amine, and alkyne [34].
Commonly, Fe3O4 nanoparticles can attach to a GO layer via in situ reduction of
iron salt precursors [19, 35–38]. In this case, magnetite may be physically adsorbed
on the GO surface or via electrostatic interaction. This method faces major
challenges, including high synthetic temperature, difficulty in controlling the Fe3O4
loading, weak GO–Fe3O4 interaction, and leaching of magnetic nanoparticles
[35, 36]. Accordingly, in recent years, covalent attachment of Fe3O4 nanoparticles
onto GO has been developed to obtain nanocomposites with high stability and better
performance [12, 29, 39]; For instance, He et al. [29] reported fabrication of an
Fe3O4/GO nanocomposite using a covalent process. They modified Fe3O4 using
123

Preparation of magnetically recoverable Fe3O4–graphene…
tetraethylorthosilicate and (3-aminopropyl)triethoxysilane to react with the car-
boxylic groups of GO with the aid of 1-ethyl-3-(3-dimethylaminopropyl)carbodi-
imide (EDC) and N-hydroxysuccinimide (NHS). In addition, Li et al. [39] used
EDC and NHS to form carboxamide bonds between amino groups of Fe3O4/SiO2
core–shell nanoparticles and carboxylic groups of GO. Xi et al. [36] loaded amino-
modified Fe3O4 nanoparticles onto the surface of GO sheets. They functionalized
GO sheets by SOCl2 to obtain GO with acid chloride groups, which can react with
amino groups of modified Fe3O4. Yang et al. [12] prepared a magnetic GO
nanocomposite by covalent attachment of dopamine-coated Fe3O4 and acyl
chloride-functionalized GO. In all such literature reports, different chemical groups
were introduced to achieve covalent attachment between magnetite and GO.
Although reported results confirm appropriate covalent bonding, the multiplicity of
toxic modifiers applied make such methods less desirable. It seems that use of
nonhazardous attachment agents should be considered.
Accordingly, in the current study, we developed a novel, green method to prepare
a covalently bonded GO–Fe3O4 nanocomposite, then studied its catalytic applica-
tion. For this purpose, GO was modified in presence of tannic acid as reactive
coating agent, then interacted with amino-functionalized magnetic nanoparticles
through individual bonds, as probed by Fourier-transform infrared (FTIR) analysis.
Additionally, the prepared magnetic nanocomposite was characterized by energy-
dispersive X-ray spectroscopy (EDS), scanning electron microscopy (SEM),
transmission electron microscopy (TEM), vibrating-sample magnetometry (VSM),
and X-ray diffraction (XRD) analyses. The catalytic activity of the prepared
magnetic GO nanoparticles was investigated via aminolysis reaction of 2,4-
dichloro-6-methyl-5-nitropyrimidine in water as green solvent. The reaction time
was probed at different catalyst doses, and the results compared with literature
reports.
Materials and methods
Chemicals
Graphene oxide powder (99%) with average particle size of 40 nm and Fe3O4
nanoparticles (99%, 20–40 nm) were supplied by USNANO Co. (USA). Tannic
acid and 1,2-phenylenediamine used as modifiers and sodium borohydride (NaBH4)
were obtained from Sigma Aldrich. Methanol (Merck) and deionized water were
used as solvents.
2,4-Dichloro-6-methyl-5-nitropyrimidine was synthesized in our laboratory
according to the procedure reported by Karimian et al. [40]. Analytical TLC was
performed on Merck DC precoated TLC plates with 0.25-mm Kieselgel 60 F254.
Amino functionalization of Fe3O4 nanoparticles
To create strong bonding between GO and Fe3O4 nanoparticles, both of them were
functionalized with appropriate chemical groups. In this study, Fe3O4 nanoparticles
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M. Namvar-Mahboub et al.
were amino-functionalized using phenylenediamine according to the following
procedure: Firstly, 100 mg Fe3O4 was added to 20 ml methanol and stirred at 50 °C
for 30 min. Then 100 mg phenylenediamine was added to the suspension. After
12 h, nanoparticles were centrifuged and rinsed several times with deionized water
and ethanol to remove excess phenylenediamine. Finally, the resulting amino-
functionalized nanoparticles were dried in oven at 70 °C.
Preparation of tannic acid-coated GO
GO nanosheets (5 mg) were suspended in 5 ml deionized water. Separately, 10 mg
tannic acid was dissolved in 8 ml deionized water. These two solutions were mixed
and stirred for 1 h at ambient temperature. Unreacted tannic acid was removed from
functionalized GO by washing with deionized water, and the resulting modified GO
was dried in oven at 70 °C.
Preparation of GO–Fe3O4 nanocomposite
Amino-functionalized Fe3O4 nanoparticles and TA–GO at a certain mass ratio were
dispersed in deionized water and stirred at constant temperature for 60 h to ensure
reaction completion. The as-prepared nanocomposite was then separated magnet-
ically, rinsed with deionized water, and dried in oven at 70 °C. Using this
procedure, three different nanocomposite samples were prepared under different
conditions (Table 1).
Characterization of GO–Fe3O4 nanocomposite
To study the morphology of the as-prepared nanocomposites, transmission electron
microscopy (Leo 912 AB, Germany) and scanning electron microscopy (Leo
1450VP, Germany) equipped with EDS analysis were applied. XRD analysis was
˚
conducted using an X-ray diffractometer with Cu Ka radiation (k = 1.541874 A) in
the range from 9.995° and 70.005°. Chemical bonds of nanocomposite were
investigated via FTIR analysis. FTIR spectra were collected using a Thermo Nicolet
AVATAR 370 FT-IR (USA) in the range from 4000 to 400 cm-1 at resolution of
4 cm-1. Vibrating-sample magnetometry (BHV-55, Riken, Japan) was used to
determine the magnetic property of the as-prepared material at room temperature.
Thermogravimetric analysis was carried out using a Shimadzu TGA-50 from 23 to
800 °C under air atmosphere.
Table 1 Synthesis conditions
for GO–Fe3O4 nanocomposite
samples
Sample code
Stirring temperature (°C)
GO/Fe3O4 mass ratio
MGO-1
MGO-2
MGO-3
25
50
25
1:1
1:1
3:1
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Preparation of magnetically recoverable Fe3O4–graphene…
Catalytic reduction of 2,4-dichloro-6-methyl-5-nitropyrimidine
Reduction of 2,4-dichloro-6-methyl-5-nitropyrimidine was carried out in a
conventional round-bottomed flask according to the following procedure: 15 mg
(0.072 mmol) 2,4-dichloro-6-methyl-5-nitropyrimidine was dissolved in 5 ml
deionized water. Then, 2.1 mmol NaBH4 and different amounts (1, 3, 5, and
7 mg) of GO–Fe3O4 catalyst were added to the solution and stirred at ambient
temperature. Sampling from the mixture was performed after 1, 5, and 10 min to
monitor reaction progress via ultraviolet–visible (UV–Vis) spectrophotometry
(Photonix Ar). For this purpose, each sample was diluted in deionized water.
Adsorption spectra were collected in the range of 200–400 nm. The concentration
change of 2,4-dichloro-6-methyl-5-aminopyrimidine was represented by the change
of the adsorption peak at wavelength of 235 nm. In addition, reaction completion
was confirmed by thin-layer chromatography (TLC) using chloroform/methanol
(10:1) as eluent after 10 min. After reaction completion, the nanomagnetic catalyst
was separated from the reaction mixture by applying an external magnetic field. To
extract product from deionized water, 5 ml ethyl acetate (EtOAc) was added to the
resultant solution. The organic phase was separated from water in decanter, dried
over Na2SO4, and allowed to evaporate to give crude solid 2,4-dichloro-6-
methylpyrimidin-5-amine in yield of 98% as red powder; m.p. 102–103 °C; H NMR
(CDCl3): d 2.32 (s, 3H, CH3), 6.08 (s, 2H, NH2, D2O exchangeable); IR: m 3472,
3371, 1621, 1555, 1527 cm-1; MS (m/z) 178 (M?), 180 (M? ?2). Anal. Calcd. for
C5H5Cl2N3: C, 33.73; H, 2.83; N, 23.60. Found: C, 33.71; H, 2.83; N, 23.59.
Results and discussion
FTIR analysis of GO–Fe3O4 nanocomposite
The preparation procedure for the magnetic GO catalyst is described in Scheme 1,
according to which it is expected that tannic acid will provide a large number of
active sites leading to formation of covalent bonding, hydrogen bonding, and p–p
interactions between TA–GO and amino-functionalized Fe3O4. FTIR analysis was
carried out to confirm the chemical structure of each as-prepared nanocomposite, as
presented in Scheme 1.
Figure 1a, b shows the FTIR spectra of tannic acid-functionalized–GO (TA–GO),
NH2–Fe3O4, and as-prepared magnetic nanocomposites, respectively. As seen from
Fig. 1a, for TA–GO, the characteristic band at 3454 cm-1 is ascribed to O–H
stretching of GO. The bands at 2954 and 2912 cm-1 correspond to symmetric and
antisymmetric vibrations of CH2. The band observed at 1764 cm-1 can be assigned
to stretching vibration of ester O–C=O in the structure of both GO and tannic acid.
The band at 1078 cm-1 corresponds to stretching vibration of ester C–O of tannic
acid. The bands at 1627, 1444, 1288, and 900 cm-1 correspond to stretching
vibrations of aromatic C=C, stretching vibrations of esteric carbonyl groups, and
stretching vibration of phenolic OH and c(C–H) of aromatic rings [41–43]. In the
case of amino-functionalized Fe3O4 (NH2–Fe3O4), the strong band at 3457 cm-1 is
123

M. Namvar-Mahboub et al.
Scheme1 Preparation procedure for magnetic GO nanocomposite catalyst
attributed to stretching of NH2 of amine group and OH group. The bands at 1604
and 1545 cm-1 arise from deformations of water and bending of N–H, respectively.
The band with strong intensity observed at 642 cm-1 corresponds to Fe–O bond
[44].
Figure 1b presents the FTIR spectra of the GO–Fe3O4 nanocomposites MGO-1,
MGO-2, and MGO-3, revealing main characteristic bands of GO and Fe3O4 in the
spectra for all three samples. The band at around 3500 cm-1 is assigned to the
overlap of amide groups of Fe3O4 and OH groups. Thus, the more intense band is
observed when compared with that of GO. Moreover, the band intensity decreased
with increasing GO/Fe3O4 ratio. Additionally, main characteristic bands of TA–GO
and NH2–Fe3O4 shifted to new values, confirming hydrogen bonding and p–p
interaction between functionalized nanoparticles [34]. The aromatic carboxylic
groups of tannic acid can also react with amine group of Fe3O4 [45–47]. In this case,
characteristic band of C=N is observed at wavenumber of 1550 cm-1. As can be
seen, with increasing synthesis temperature, the intensity of the band at 640 cm-1
corresponding to Fe–O, increased.
,
Morphology of as-prepared nanocomposite
TEM and SEM images of GO–Fe3O4 nanocomposite are shown in Fig. 2, clearly
illustrating Fe3O4 nanoparticles distributed in GO nanosheets. The TEM images
show magnetic nanoparticles with spherical structure and diameter of about 20 nm,
anchored onto the surface of GO nanosheets. Additionally, the SEM image confirms
presence of Fe3O4 nanoparticles, distinguished by their white color on GO sheets.
The EDS spectra and elemental analysis results for MGO-1 and MGO-3 are
presented in Fig. 3. For both samples, peaks corresponding to Fe, O, and C were
observed, indicating correct formation of GO–Fe3O4 nanocomposites. However, the
123

Preparation of magnetically recoverable Fe3O4–graphene…
Fig. 1 FTIR spectra of a tannic acid-modified GO sample and amine-modified Fe2O3 nanoparticles, and
b GO–Fe3O4 nanocomposites
Fe peak intensity decreased for MGO-3 compared with MGO-1. The elemental
analysis data are consistent with the EDS results. As can be seen, the Fe content of
MGO-2 was about 16.9%, while the Fe content of MGO-3 was about 4.1%. This
trend can be ascribed to the reduction of the Fe3O4 dose in the initial solution for
MGO-3.
The XRD patterns of GO–Fe3O4 nanocomposites obtained using different ratios
of GO to Fe3O4 are presented in Fig. 4. For both MGO-1 and MGO-3, the original
characteristic peak of GO can be observed at around 2h of 11°, being related to
(001) plane of GO [43]. Due to the interaction with metal oxide, the mentioned
diffraction peak is broader for the GO nanocomposite compared with pure GO [34].
The peaks appearing at around 30°, 35°, 42°, 57°, and 63° are due to (220), (311),
(400), (511), and (440) planes of Fe3O4 [48]. The presence of the above-mentioned
peaks indicate that the nanocomposites show characteristic peaks of magnetite. As
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M. Namvar-Mahboub et al.
Fig. 2 a TEM images of GO–Fe3O4 nanocomposite (MGO-1 sample) at two magnifications, b SEM
image of GO–Fe3O4 nanocomposite (MGO-1)
Fig. 3 EDS analysis of GO–Fe3O4 nanocomposites at two ratios of GO to Fe3O4
123

Preparation of magnetically recoverable Fe3O4–graphene…
Fig. 4 XRD spectra of GO–Fe3O4 nanocomposites obtained using two ratios of GO to Fe3O4
stated by Mandal and Chattopadhyay [34], the intensity of diffraction peaks of iron
oxide may be reduce due to formation of a GO–Fe3O4 composite compared with
pure Fe3O4. However, there is no clear difference between the XRD spectra of the
two samples. The same effect was observed by Jusin et al. [49].
20
15
10
5
0
-5
MGO-1
MGO-2
MGO-3
-10
-15
-20
-10000 -7500 -5000 -2500
0
2500 5000 7500 10000
Applied field (Oe)
Fig. 5 Magnetization curves of as-prepared GO–Fe3O4 nanocomposites
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M. Namvar-Mahboub et al.
Magnetic property of as-prepared nanocomposite
Vibrating-sample magnetometry was used to measure the magnetization curves of
the as-prepared nanocomposites in the range of -10,000 to 10,000 Oe. Figure 5
illustrates the hysteresis loop of magnetization (M, emu/g) versus magnetic field (H,
Oe). As can be seen, the saturation magnetization (Ms) was 15, 12, and 9 emu/g for
MGO-2, MGO-1, and MGO-3, respectively. Note also that these Ms values of the
as-prepared samples are less than that for pure Fe3O4 due to the composite structure
of the magnetic GO materials. Additionally, the remanent magnetization was found
to be about zero for all samples.
The obtained values show that all the samples exhibited supermagnetic
properties. From these results, it is obvious that lower Fe3O4 loading led to lower
magnetic strength. Moreover, at the same magnetite loading, higher magnetic
property was observed for MGO-2, which was produced at higher temperature. This
trend is consistent with the FTIR results, which confirm greater interaction between
GO and Fe3O4. As stated above, NH2 group of functionalized magnetite can
covalently bond to tannic acid-functionalized GO via the OH group of its aromatic
section. Such covalent bonding occurs more efficiently at higher temperature. In the
case of MGO-2, a higher mixing temperature was applied compared with MGO-1
but at the same ratio of GO to Fe3O4. Therefore, the number and strength of Fe3O4–
GO bonds will increase.
TGA results
The composition of the magnetic catalysts was analyzed using TGA; the resulting
spectra for both GO and MGO-2 are presented in Fig. 6. As shown in this figure, for
GO, weight loss occurred in three steps. The weight loss below 100 °C corresponds
to evaporation of adsorbed water. Decomposition of oxygen-containing functional
groups of GO at 183 °C led to 29% weight loss. Up to 600 °C, about 98% weight
loss was observed, due to decomposition of GO. In the case of MGO-2, the
decomposition temperature changed to 191 °C with about 53% weight loss up to
800 °C, which can be assigned to the Fe3O4 composition.
120
GO
100
MGO
80
60
40
20
0
0
Fig. 6 TGA results for GO and MGO
123
200
400
600
800
Temperature (˚C)

Preparation of magnetically recoverable Fe3O4–graphene…
Catalytic activity of GO–Fe3O4 nanocomposite
The applicability of the as-prepared nanocomposite was investigated using the
hydrolysis reaction of a synthesized nitropyrimidine compound with excess NaBH4.
For this purpose, MGO-2 was used due to its appropriate magnetic property and Fe–
GO connection. 2,4-Dichloro-6-methyl-5-nitropyrimidine was conveniently synthe-
sized according to the published procedure [25]. The nitro group of this compound
was reduced by treatment with GO–Fe3O4 nanocomposite at room temperature to
give 2,4-dichloro-6-methylpyrimidin-5-amine (Scheme 2).
As there is no side reaction during reduction of the nitro compound, UV–Vis
absorption spectroscopy can potentially be used to probe the time dependence of the
reaction progress. As stated above, sampling from the reaction mixtures was carried
out at specified time intervals. The UV–Vis spectra of diluted solutions of
nitropyrimidine compound as reactant and product are depicted in Fig. 7. This
figure reveals that aqueous solution of 2,4-dichloro-5-nitro-6-methylpyrimidine
showed two kmax signals at 210 and 265 nm. However, for samples of the reaction
mixture at different times, new peaks were seen at around 235 and 313 nm. These
peaks increased with increasing reaction time, implying that a reaction took place.
To investigate the effect of the catalyst dose on the reaction time, the aminolysis
reaction was also performed at 1, 3, 5, and 7 mg with fixed amount of other
components. The resulting UV–Vis absorption curves are shown in Fig. 8.
As expected, on increasing the nanocatalyst dose, the reaction time decreased
from about 20 min for 1 mg catalyst to about 5 min for 7 mg catalyst. It can be
concluded that there was no change in the UV spectra between the last two time
intervals. It should also be stated that reduction of nitropyrimidine is kinetically
restricted when no catalyst is present in the reaction medium.
To confirm reaction completion, two samples using each catalyst dose were taken
at the two last intervals and analyzed by TLC without dilution with chloroform/
methanol mixture (10:1) as eluent. Figure 8 shows the TLC results for the extracted
product compared with the reactant. As can be seen, the spot which featured the
product can be clearly distinguished from the reactant by TLC (Fig. 9).
These results show that a small amount of magnetic GO catalyst assisted
production of the mentioned aminopyrimidine at room temperature. Note also that
water was used as green solvent for the reaction medium. As stated by Li et al. [49],
GO has high adsorptive capacity for nitro compounds such as nitrophenol due to
hydrogen bonding, hydrophobic interactions, and p–p interactions of their
functional groups. On the other hand, Fe3O4 has high catalytic capability for
Scheme 2 Reduction reaction of 2,4-dichloro-6-methyl-5-nitropyrimidine to 2,4-dichloro-6-
methylpyrimidin-5-amine in presence of GO–Fe3O4 nanocomposite
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M. Namvar-Mahboub et al.
Fig. 7 UV–Vis absorption
spectra of reactant
(nitropyrimidine) and product
(aminopyrimidine)
Product
Reactant
200
250
300
350
400
Wavelength (nm)
Fig. 8 UV–Vis absorption spectra of reduction reaction at different doses of GO–Fe3O4 nanocomposite
as catalyst: a 1 mg, b 3 mg, c 5 mg, and d 7 mg (25 °C)
reduction of nitro compounds. However, Fe3O4 nanoparticles tend to agglomerate.
Their attachment to GO can result in enhanced catalytic activity of the
nanocomposite catalyst due to the decreased agglomeration effect.
To confirm the superiority of the as-prepared nanocatalyst, the reaction time,
catalyst dose, and reaction medium used in this study were compared with the best
results of other researchers for the same nitro compounds, as summarized in
Table 2. In addition, literature results from previous investigations into the catalytic
123

Preparation of magnetically recoverable Fe3O4–graphene…
Fig. 9 TLC results of 2,4-
dichloro-6-methyl-5-
aminopyrimidine as product and
2,4-dichloro-6-methyl-5-
nitropyrimidine as reactant
[chloroform/methanol mixture
(10:1) as eluent]
Table 2 Comparison of performance of catalyst introduced in this study with literature results
Catalyst
Temperature
(°C)
Solvent
mcatalyst/mreactant (g/ Reaction time
g)
Ref.
(min)
Magnetic GO 25
Water
Water
0.067–0.47
20–5
This
study
Fe–Ni
Fe
50
25
2.32
1.19
10
[4]
Acetic
acid
120
[40]
Magnetic
GOa
98
Ethanol
0.041
17
[51]
aReaction data for aniline reduction
123

M. Namvar-Mahboub et al.
activity of magnetic GO for reduction of other nitro compounds were compared
with the results of this study.
As reported by Karimian et al. [40], when Fe was used as catalyst to produce
aminopyrimidine from nitropyrimidine, the time required for reaction completion
exceeded 2 h. However, Rezazadeh et al. [4] reported that use of a reaction mixture
including bimetallic Fe–Ni as nanocatalyst at 90 °C could reduce the reaction time
to 10 min. However, high temperature was required when this highly active
bimetallic catalyst was utilized in the reaction medium. The low reaction time,
temperature, and catalyst dose herein indicate that GO–Fe3O4 is a unique candidate
for production of this intermediate compound.
Confirmation of product structure via spectroscopic and microanalytical data
Spectroscopic and microanalytical data confirmed reduction of the nitro group of
2,4-dichloro-6-methyl-5-nitropyrimidine to 2,4-dichloro-6 methylpyrimidin-5-
amine; For instance, the FTIR spectrum of compound 2,4-dichloro-6-methylpyrim-
idin-5-amine showed definite stretching vibration bands at m of 3472 and
3371 cm-1, indicating presence of NH2 group in the product. The vibration band
at m of 1621 cm-1 corresponds to C=N of pyrimidine ring. The FTIR spectra of 2,4-
Dichloro-6-methyl-5-nitropyrimidine and 2,4-dichloro-6 methylpyrimidin-5-amine
are compared in Figs. 10 and 11. The 1H NMR spectrum of the synthesized
compound showed the signal of methyl group of pyrimidine moiety at d of
2.32 ppm and a D2O exchangeable signal at d 6.20 ppm belonging to NH2 group.
The mass spectrum also showed the molecular ion peak of the compound at m/z of
Fig. 10 FTIR spectrum of 2,4-dichloro-6-methyl-5-nitropyrimidine
123

Preparation of magnetically recoverable Fe3O4–graphene…
Fig. 11 FTIR spectrum of 2,4-dichloro-6 methylpyrimidin-5-amine
178 (M?), corresponding to the molecular formula C5H5Cl2N3. Elemental analysis
also confirmed the molecular formula of this compound.
Reaction mechanism
The reduction of nitropyrimidine by NaBH4 in presence of GO–Fe3O4 nanocom-
posite as catalyst may proceed according to a mechanism suggested by Verakumar
et al. [50] (Scheme 3). Firstly, BH4- reacts with Fe3O4 nanoparticles, and metal
hydride is generated on the surface of the catalyst. Simultaneously, nitropyrimidine
molecules adsorb on the surface of the catalyst. Nitroso compound and water
molecules are the product of this step. Then, nitroso compound reacts with more
hydrogen molecules to form hydroxyl amine. Subsequently, hydroxyl amine group
is converted to amine group, and finally aminopyrimidine is produced with water as
byproduct.
Conclusions
Magnetic GO nanocomposite was prepared by a new method and employed as
catalyst for production of 2,4-dichloro-6 methylpyrimidin-5-amine as an interme-
diate compound for use in drug synthesis. Amino-functionalized Fe3O4 was
covalently bonded to GO using tannic acid as binder. As-prepared nanocomposites
obtained under different synthesis conditions were characterized by FTIR, XRD,
TEM, SEM, EDS, and VSM. The results showed that synthesis using GO/Fe3O4
123

M. Namvar-Mahboub et al.
Scheme 3 Suggested mechanism for reduction of nitropyrimidine compound in presence of borohydride
and GO–Fe3O4 nanocatalyst
ratio of 1:1 (w/w) at 50 °C resulted in higher magnetic strength and GO–Fe3O4
interactions. The catalytic activity of the optimal GO/Fe3O4 nanocomposite was
then investigated in reduction of 2,4-dichloro-6-methyl-5-nitropyrimidine. Probing
of the reaction medium via UV–Vis absorption spectroscopy and TLC analysis
revealed that the reaction completed after 10 min. According to the results, the as-
prepared magnetic GO catalyst has the ability to reduce nitropyrimidine to
aminopyrimidine. These unique advantages, including green (aqueous) reaction
medium, low reaction temperature, and rapid reaction, make GO/Fe3O4 a special
candidate for production of aminopyrimidines.
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