Fe3O4-Graphene oxide nanocomposite: Synthesis of 5-sulfanyl tetrazole derivatives of alkyls, indoles, and pyrroles

Article abstract of DOI:10.1080/00397911.2018.1519077

In this work, the use of Fe₃O₄/geraphene oxide nanocomposite as an efficient catalyst for the synthesis of 5-sulfanyltetrazole derivatives of indoles, pyrroles, and 5-alkyl sulfanyltetrazoles is described. These compounds are readily

Full text of DOI:10.1080/00397911.2018.1519077

Synthetic Communications
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Fe3O4-Graphene oxide nanocomposite: Synthesis
of 5-sulfanyl tetrazole derivatives of alkyls,
indoles, and pyrroles
Mahrokh Baghershiroudi & Kazem D. Safa
To cite this article: Mahrokh Baghershiroudi & Kazem D. Safa (2018): Fe3O4-Graphene oxide
nanocomposite: Synthesis of 5-sulfanyl tetrazole derivatives of alkyls, indoles, and pyrroles,
Synthetic Communications, DOI: 10.1080/00397911.2018.1519077
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https://doi.org/10.1080/00397911.2018.1519077
Fe3O4-Graphene oxide nanocomposite: Synthesis of
5-sulfanyl tetrazole derivatives of alkyls, indoles,
and pyrroles
Mahrokh Baghershiroudi and Kazem D. Safa
Organosilicon Research Laboratory, Faculty of Chemistry, University of Tabriz, Tabriz, Iran
ABSTRACT
ARTICLE HISTORY
Received 22 June 2018
In this work, the use of Fe3O4/geraphene oxide nanocomposite as an
efficient catalyst for the synthesis of 5-sulfanyltetrazole derivatives of
indoles, pyrroles, and 5-alkyl sulfanyltetrazoles is described. These com-
pounds are readily obtained by the reaction of the starting heterocycles
indoles, N-aryl pyrroles, alkyl thiocyanates, and trimethylsilyl azide in
good to excellent yields. Moreover, Fe3O4/GO nanocomposite could be
easily separated from the reaction mixtures by an external permanent
magnet and reused at least six times continuously without significant
reduction in the product yield and its catalytic activity.
KEYWORDS
Fe3O4/geraphene oxide;
heterogeneous; indoles;
nanocomposite; N-aryl
pyrroles; sulfanyltetrazole
GRAPHICAL ABSTRACT
Introduction
Tetrazole as a five-membered aromatic nitrogen-containing ring is an important hetero-
cyclic scaffold and although not found in nature, it has received much attention in both
CONTACT Kazem D. Safa
dsafa@tabrizu.ac.ir
Department of Organic and Biochemistry, Faculty of Chemistry,
University of Tabriz, Tabriz 51666-14766, Iran.
Supplemental data for this article can be accessed on the publisher’s website.
ß 2018 Taylor & Francis Group, LLC

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M. BAGHERSHIROUDI AND K. D. SAFA
chemistry and biology. Also, it can be considered as carboxylic acid isosteres because of
greater metabolic stability.[1]
Among the tetrazoles family, 5-substituted tetrazoles have been found to be abundant in
active biological compounds.[2] Tetrazole moieties can be used in synthetic organic chemis-
try,[3] coordination chemistry,[4] energetic materials,[5,6] photography,[7] and agriculture.[8]
Sulfanyltetrazoles as a subunit of tetrazoles are increasingly used in drug combina-
tions as a pharmacophore,[9] with applications such as activator in RNA synthesis,[10]
antimycobacterial,[11] antibacterial[12–14] and anti-HIV agents.[15] It has been demon-
strated that compounds containing sulfanyltetrazole structures are significant scaffolds
with great potential for therapeutic activity.[16]
Considering the many applications and development of tetrazoles to a wide variety of bio-
logical agents, there is a big demand for the various methods of synthesizing sulfanyltetra-
zoles. During recent decades, various and practical methods for the synthesis of tetrazole
derivatives have been proposed.[17–21] Due to the lack of publications on the heterogeneous
synthesis of sulfanyltetrazoles,[11,22–27] it would be desirable to attend to the preparation of
these compounds with heterogeneous catalysts. Herein, in continuation of our studies on
the compounds containing sulfanyltetrazole as antibacterial agents[12,13] and focusing on the
potential of these materials for a variety of biological applications, we synthesized 5-sulfanyl
tetrazole derivatives of alkyls as well as indoles and pyrroles, which are rarely reported.[28,29]
In recent years, magnetic nanoparticles have provided new pathways for the
development of recyclable heterogeneous catalysts.[30] In particular, Fe3O4/geraphene
oxide (GO) nanocomposites have received much attention and have been widely used
as nanocatalysts.[31–33]
GO is one of the most important graphene derivatives. It is a good candidate for
supporting metal and metal oxide nanoparticles due to the unique planar structure, high
chemical stability, large surface area, and variety of oxygen-containing functional groups.[34]
N
NH
N
N
SCN
S
R1
R1
R2
R2
N
N
4
H
1
H
N
N
N
S
OR
OR
HN
TMSN3, Fe3O4/GO
SCN
MeOH/DMF (1:9), 80 °C
5
R3
N
2
R3
N
OR
N
OR
N
N
R4
SCN
N
R4
S
H
3
6
Scheme 1. Sulfanyltetrazoles synthesis ctalayzed by Fe3O4@GO nanocomposite

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3
Figure 1. FTIR spectrum of (a) Fe3O4, (b) GO, and (c) Fe3O4/GO.
In this study, we prepared a magnetically recyclable heterogeneous Fe3O4/GO
nanocomposite for the synthesis of some 5-sulfanyl tetrazole derivatives including alkyls,
indoles, and pyrroles. The catalyst produced the desired products with good yields and
could be reused for several cycles with high catalytic activity, which indicates its
applicability as a reusable catalyst for the synthesis of sulfanyltetrazole derivatives.
Results and discussion
Chemistry
Synthesis of sulfanyltetrazoles was achieved through the synthetic pathways as presented
in Scheme 1. As depicted in Scheme 1, the reaction between thiocyanate derivatives and
TMSN3 and Fe3O4@GO nanocomposite in DMF/MeOH (9:1) at 80 ꢀC provided related
sulfanyltetrazoles. Fe3O4@GO nanocomposites were prepared according to a previously
reported procedure with some modifications.[31]
The synthesized nanocomposites were characterized by, FT-IR, powder XRD, VSM,
TEM and SEM analysis.
Figure 1 shows FT-IR spectra for Fe3O4, GO, and Fe3O4-GO, in both cases, show
bands around 585 cmꢁ1, those bands are associated to the stretching vibration modes of
the magnetite Fe–O bonds. There are also present C¼O stretching vibrations
(1716 cmꢁ1) and O–H stretching vibrations (3375 cmꢁ1). Fe3O4-GO spectrum has prom-
inent O–H and C¼O signals, due to the functional groups present on the GO sheets.
Figure 2 shows the XRD pattern of GO and magnetite nanocomposite. As shown in
the XRD pattern of Fe3O4-GO, all the characteristic peaks of nanoparticles and GO

4
M. BAGHERSHIROUDI AND K. D. SAFA
Figure 2. XRD pattern of (a) Fe3O4/GO and (b) GO.
Figure 3. (a) SEM image, (b) and TEM image of Fe3O4/GO.
Figure 4. Vibrating-Sample magnetometer (VSM) patterns of Fe3O4and Fe3O4/GO.
were identified in the spectrum of Fe3O4-GO nanocomposites. The peaks at 2h values
of 30.2ꢀ (200), 35.5ꢀ (311), 43.3ꢀ (400), 53.7ꢀ (422), 57.1ꢀ (511), and 62.9ꢀ (440) were
consistent with the standard XRD data for the magnetite phase (JCPDS no. 19–0629).
However, no diffraction peak of GO is observable for the as-prepared Fe3O4@GO com-
posite, suggesting that the layer stacking of the GO sheets was destroyed by the loading
of Fe3O4 NPs. This confirmed that pure phase Fe3O4-GO was successfully formed.

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5
Table 1. Optimization of the catalyzed formation of sulfanyltetrazole (4a).
Entry
Catalyst(g)
Solvent
Temperature(ꢀC)
Yield(%)[a]
b
2
3
4
5
6
7
8
–
–
DMF/MeOH(9:1)
DMF
80
110
110
90
80
70
60
80
80
80
80
80
80
80
80
80
80
80
80
42
23
77
78
82
67
42
90
90
66
76
Trace
0
0
0
0
0
52
0
Fe3O4/GO(0.03)
Fe3O4/GO(0.03)
Fe3O4/GO(0.03)
Fe3O4/GO(0.03)
Fe3O4/GO(0.03)
Fe3O4/GO(0.05)
Fe3O4/GO(0.03)
Fe3O4/GO(0.01)
Fe3O4/GO(0.03)
Fe3O4/GO(0.03)
Fe3O4/GO(0.03)
Fe3O4/GO(0.03)
Fe3O4/GO(0.03)
Fe3O4/GO(0.03)
Fe3O4/GO(0.03)
Fe3O4(0.03)
DMF/MeOH(9:1)
DMF/MeOH(9:1)
DMF/MeOH(9:1)
DMF/MeOH(9:1)
DMF/MeOH(9:1)
DMF/MeOH(9:1)
DMF/MeOH(9:1)
DMF/MeOH(9:1)
DMF
DMSO
Toluene
THF
H2O
9
10
11
12
13
14
15
16
17
18
19
NMP
Dioxane
DMF/MeOH(9:1)
DMF/MeOH(9:1)
GO(0.03)
[a] Isolated yield.
The morphology of the obtained Fe3O4-GO nanocomposites was also characterized
with scanning electron microscopy (SEM) and transmission electron microscopy
(TEM). As shown in Figure 3, the micrographs of the prepared Fe3O4-GO composites
revealed that Fe3O4 nanoparticles distributed homogeneously in the GO surfaces of the
nanocomposites. Also, TEM images proved that the cubic crystal structure and the
morphology of Fe3O4 NPs on the GO sheets remain unchanged after the recycling.
Next, the magnetic properties of Fe3O4-GO nanocomposite were investigated using
VSM at room temperature (Figure 4). The Fe3O4-GO nanocomposites showed a typical
S-like magnetic hysteresis loop with the specific saturation magnetization (Ms) of
ꢂ26 emu/g. This value exhibits superparamagnetic behavior. These phenomena were
consistent with the results obtained from FT-IR, SEM, TEM, and XRD.
The results of the optimization of reaction conditions are summarized in Table 1. The
control reactions showed that In the absence of a catalyst at 80 and 110ꢀC, no reaction
occurred after 24 h (Table 1, entries 1–2). The effect of temperatures on the reaction was
investigated. Increasing or decreasing the reaction temperature will not dramatically
improve the yield of the reaction (Table 1, entries 3–7). The results on the change of
catalyst loadings showed that catalyst loadings of 0.03 g showed better performance than
that with catalyst loadings of 0.05 g, which had no effect on the yield of the reaction.
Catalyst loading of 0.01 g was not sufficient for the reaction (Table 1, entries 8–10). The
Solvent has a decisive influence on the efficiency of the reaction. The experimental
results show that DMF is good solvent with 76% yield, whereas DMSO, toluene, THF,
H2O, NMP, and dioxane are not suitable for the reaction (Table 1, entries 11–17). Bare
Fe3O4 nanoparticles have been provided 52% product conversion after 24 h. (Table 1,
entry 18). Only GO showed no catalytic activity for this reaction (Table 1, entry19).
Using the results presented in Table 1, we investigated the scope and limitation of the
reaction on a variety of organic thiocyanates. To achieve this goal, a set of 4 Indoles, 3
Pyrroles, and 5 non-aromatic thiocyanate derivatives were subjected to general reaction
conditions. Tetrazole derivatives of indoles and pyrroles were synthesized conveniently

6
M. BAGHERSHIROUDI AND K. D. SAFA
Table 2. Fe3O4/GO catalyzed synthesis of sulfanyltetrazoles[a]
.
Entry
Product
Time(h)
3
Yield(%)[b]
90
1
2
4
92
-
3
4
60
4
5
80
5
3
92
6
7
3
90
91
3.5
(continued)

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7
Table 2. Continued.
Entry
Product
Time(h)
6
Yield(%)[b]
82
8
9
6
8
84
80
10
11
12
24
24
0
0
[a]Thiocyanate (1 mmol), TMSN3 (1.5 mmol), F3O4/GO (0.03 g), DMF/MeOH(9:1) (5 mL), 80 ꢀC.
[b]Isolated yield.
Table 3. The effect of the mass ratio of Fe3O4 to GO on the activity of the catalyst.
The mass ratio of Fe3O4 to GO
Yield of reaction (%)
2
5
10
15
20
47
77
90
88
87
in good to high yields (Table 2, Entries 1–7). With non-aromatic thiocyanates, which
have a thiocyanate substituent at the benzylic position, the reactions did not proceed
(Table 2, Entries 11 and 12). The reaction of (8–10) gave the corresponding tetrazoles in
good to moderate yields, but they need more reaction time to reach completion.
Investigations showed that the Fe3O4 to GO mass ratio in Fe3O4-GO nanocomposite
plays an important role in its catalytic activity. As shown in Table 3, for the reaction of
3-thiocyanato-1H-indole, the reaction efficiency increases with an increase in the mass
ratio of Fe3O4 to GO of 10. Increasing the amount of Fe3O4 does not have a beneficial
effect on improving the reaction efficiency.
A proposed mechanism for the reaction forming 5-substituted sulfanyl tetrazole in
the presence of Fe3O4-GO composites as a catalyst is shown in Scheme 2. At the initial
stage of the catalytic cycle, the reaction of thiocyanates 1 with catalyst produces the
intermediate A; besides, HN3 B forms in situ from the reaction of TMSN3 and MeOH.
[9] The [3 þ 2] cycloaddition between the triple bond of the intermediate A and HN3 B
takes place readily to form the intermediate C. It seems that the triple bond is activated
by forming an A species, which makes the [3 þ 2] cycloaddition feasible. Protonolysis of
the intermediate C affords the 5-substituted sulfanyl tetrazole 3.
The reusability of the catalyst has been studied. For this purpose, the reaction of
3-thiocyanato-1H-indole was carried out under optimized conditions. After carring out

8
M. BAGHERSHIROUDI AND K. D. SAFA
H
R
S
R
S
N
N
NH
N
N
N
N
N
R
SCN
Fe
3O4-GO
R
S C N
H
HN3
TMSN3
+
R
MeOH
S
C
N
N
N
N
TMSOMe
Scheme 2. Proposed mechanism for the synthesis of sulfanyltetrazoles using Fe3O4/GO.
Table 4. Catalyst reusability study.
100
90
90
89
88
88
87
80
60
40
20
0
1
2
3
4
5
6
Cycles
the reaction, the catalyst was centrifuged, washed with ethanol and water (2–3 times)
and dried in vacuum. The catalyst was reused and found not to lose efficiency even
after 6 runs. The results are given in Table 4.
Therefore, Fe3O4-GO shows unique virtues, i.e., not only is the catalytic performance
comparable with homogeneous catalysts, but also the separation and reuse of the
catalyst is easily achieved.
Experimental
Chemicals were either purchased from Merck or synthesized in our laboratory.
Commercial reagents and solvents were used without further purification. The IR spec-
1
tra were recorded on a Bruker Tensor 270 spectrometer using KBr discs. H and 13C
NMR spectra were recorded on a Bruker FT- 400 MHz spectrometer at room tempera-
ture with DMSO-d6 and CDCl3 as solvents. Elemental analyses were performed on an

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SYNTHETIC COMMUNICATIONSV
9
Elementar Vario EL III instrument. X-ray diffraction (XRD) patterns of the samples
were recorded on a Siemens diffractometer with Cu-Ka radiation at 35 kV in the scan
range of 2h from 10ꢀ to 80ꢀ. The surface morphologies of samples were examined by a
scanning electron microscope (SEM) (LEO 1430VP) under vacuum at an operating
voltage of 35 kV. Dried samples were gold coated by sputtering for 15 S. Transmission
electron microscope (TEM) images are recorded by using LEO-906 instrument.
The magnetic properties were analyzed using a vibrating sample magnetometer at room
temperature (VSM; AGFM, Kashan, Iran).
General procedure for the synthesis of the 5-sulfanyltetrazoles
Fe3O4@GO (0.03 g) was added to thiocyanate (alkyl, indole or pyrrole) (1 mmol), trime-
thylsilyl azide (TMSN3) (1.5 mmol), and DMF/MeOH (9:1) (6 mL) and the mixture was
stirred at 80 ꢀC for 6 h. After completion of the reaction (as indicated by TLC), the
catalyst was separated by applying an external magnetic field and washed thrice with
ethanol and water. Then, the reaction mixture was treated with ethyl acetate and 1 N
HCl. The resulting organic layer was separated and dried with anhydrous Na2SO4, and
concentrated. An aqueous solution of NaOH (0.25N) was added to the residue and the
resulting mixture was stirred for 30 min at room temperature. The mixture was washed
with ethyl acetate, and then conc. HCl was added to obtain the pH value of the water
layer to 1. The aqueous layer was extracted with ethyl acetate (ꢃ3) and the combined
organic layers were washed with 1 N HCl. The organic layer was dried over anhydrous
Na2SO4 and concentrated.
Conclusion
In this paper, we reported a simple and practical modification of the sulfanyl tetrazole
synthesis route which leads to 5-sulfenyl tetrazole derivatives of indoles, pyrroles, and
alkyls directly. A sulfanyltetrazole heterogeneous synthesis using a magnetic catalyst has
been developed. Fe3O4-GO nanocomposite shows interesting properties, that is, it has
the ability to separate and reuse, along with performance comparable to homogeneous
catalysts. The chemical efficiency, the low cost of reagents, and the use of environmen-
tally benign catalyst make this process particularly attractive.
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