Magnetically recoverable ferromagnetic 3D hierarchical core-shell Fe3O4@NiO/Co3O4 microspheres as an efficient and ligand-free catalyst for C–S bond formation in poly (ethylene glycol)

Article abstract of DOI:10.1080/17415993.2020.1753743

A simple and efficient protocol for the synthesis of diaryl thioethers from the reaction of thiourea with a wide variety of aryl halides, including aryl iodides, aryl bromides and aryl chlorides in the presence of 3D hierarchical core-shell Fe₃O₄@NiO/Co₃O₄ microspheres has been described. This reaction enables the one-pot synthesis of diaryl thioethers in good to high yields using a non-toxic and magnetically separable catalyst in PEG-400 as an eco-friendly, safe, inexpensive and thermally stable solvent. Magnetic separation and reusability of catalyst for eight times without any significant loss of activity, the use of a commercially available, eco-friendly, cheap and chemically stable sulfur transfer agent and solvent, operational simplicity, environmentally benign, easier work-up procedure and cost efficiency make this method a promising candidate for potential applications in some organic reactions. The catalytic activity of Fe₃O₄@NiO/Co₃O₄ as a novel and inexpensive catalyst was investigated in the C-S cross coupling reaction.

Full text of DOI:10.1080/17415993.2020.1753743

Journal of Sulfur Chemistry
ISSN: 1741-5993 (Print) 1741-6000 (Online) Journal homepage: https://www.tandfonline.com/loi/gsrp20
Magnetically recoverable ferromagnetic 3D
hierarchical core-shell Fe3O4@NiO/Co3O4
microspheres as an efficient and ligand-free
catalyst for C–S bond formation in poly (ethylene
glycol)
Ahad Vatandoust Namanloo, Batool Akhlaghinia & Arezou
Mohammadinezhad
To cite this article: Ahad Vatandoust Namanloo, Batool Akhlaghinia & Arezou Mohammadinezhad
(2020): Magnetically recoverable ferromagnetic 3D hierarchical core-shell Fe3O4@NiO/Co3O4
microspheres as an efficient and ligand-free catalyst for C–S bond formation in poly (ethylene
glycol), Journal of Sulfur Chemistry, DOI: 10.1080/17415993.2020.1753743
To link to this article: https://doi.org/10.1080/17415993.2020.1753743
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JOURNAL OF SULFUR CHEMISTRY
https://doi.org/10.1080/17415993.2020.1753743
Magnetically recoverable ferromagnetic 3D hierarchical
core-shell Fe3O4@NiO/Co3O4 microspheres as an efficient and
ligand-free catalyst for C–S bond formation in poly (ethylene
glycol)
Ahad Vatandoust Namanloo, Batool Akhlaghinia and Arezou Mohammadinezhad
Department of Chemistry, Faculty of Science, Ferdowsi University of Mashhad, Mashhad, Iran
ABSTRACT
ARTICLE HISTORY
Received 5 December 2019
Accepted 6 April 2020
A simple and efficient protocol for the synthesis of diaryl thioethers
from the reaction of thiourea with a wide variety of aryl halides,
including aryl iodides, aryl bromides and aryl chlorides in the pres-
ence of 3D hierarchical core-shell Fe3O4@NiO/Co3O4 microspheres
has been described. This reaction enables the one-pot synthesis
of diaryl thioethers in good to high yields using a non-toxic and
magnetically separable catalyst in PEG-400 as an eco-friendly, safe,
inexpensive and thermally stable solvent. Magnetic separation and
reusability of catalyst for eight times without any significant loss
of activity, the use of a commercially available, eco-friendly, cheap
and chemically stable sulfur transfer agent and solvent, operational
simplicity, environmentally benign, easier work-up procedure and
cost efficiency make this method a promising candidate for potential
applications in some organic reactions.
KEYWORDS
3D hierarchical core-shell
Fe3O4@NiO/Co3O4
microspheres; C–S bond
formation; heterogeneous
catalyst; aryl halides;
thiourea
The catalytic activity of Fe3O4@NiO/Co3O4 as a novel and inex-
pensive catalyst was investigated in the C-S cross coupling reaction.
CONTACT Batool Akhlaghinia
akhlaghinia@um.ac.ir
Department of Chemistry, Faculty of Science, Ferdowsi
University of Mashhad, Mashhad 9177948974, Iran
This article makes reference to supplementary material available on the publisher’s website at
https://doi.org/10.1080/17415993.2020.1753743
© 2020 Informa UK Limited, trading as Taylor & Francis Group

2
A. VATANDOUST NAMANLOO ET AL.
1. Introduction
Today, among the carbon-heteroatom bond-forming reactions, carbon–sulfur bond for-
mation is one of the significant organic transformations and powerful tools in making var-
ious arrangements of target compounds including pharmaceutical to biological molecules
[1–4] and novel precursors in the material science as well [5,6]. Sulfur-containing organic
molecules particularly, diaryl thioethers and their derivatives have been recognized in
numerous drugs, which are used for the cure of some diseases such as Diabete, Alzheimer,
cancer, Parkinson, HIV, and inflammatory and microbial diseases as well. [3,4,7,8] Even
though, several methodologies have been designed for the C–S bond formation (including
reaction of aryl diazoniumfluoroborate with diaryl disulfides [9], coupling of aryl or alkyl
thiols with aryl halides [10,11], cross-coupling reaction of aryl halides and ethyl potassium
xanthogenate [12], reaction of phenolic esters such as acetates, triflates, tosylates and phos-
phonates with alkyl halides by using thiourea as a sulfur source [13], reaction of aryl halides
with aminothiourea [14], oxidative sulfidation of diaryl disulfides with aryltrimethoxysi-
lanes [15], reduction of aryl sulfones or aryl sulfoxides [16,17] and reaction of thiourea
with aryl halides [18–28]), most of them require drastic reaction conditions such as strong
bases, elevated temperatures, strong reducing agents, direct use of volatile, hazardous, and
foul-smelling thiols, toxic and expensive organic solvent, stoichiometric amounts of the
catalyst as well as expensive ligands together with highly toxic metals. Furthermore, it
should be noted that most of the previous methods using homogeneous catalysts (that
cannot be separated and recovered simply), which represent more obstacles for the utility
of this chemistry in parallel synthesis and in the industry. Today, with respect to the impor-
tance of green chemistry legislations, researches in this field of science should be moving
further towards economical, efficient, beneficial and eco-friendly methods and cheap and
safe resources for C–S bond generation.
Metal oxides which are involved in many petrochemicals, intermediates, fine and phar-
maceutical chemicals were found to be one of the most important heterogeneous catalysis
which catalyzed a wide variety of reactions [29,30]. Amongst them, NiO and Co3O4
have possessed increasing consideration due to their commercial and potential applica-
tions in various fields, including catalysis electrode materials, solid-state sensors and super
capacitors [31].
Very recently, due to our interest towards the extension of environmentally friendly
synthetic methods [19,32], the successfully synthesized 3D hierarchical core-shell
Fe3O4@NiO/Co3O4 microspheres (Scheme 1) was efficiently used in the C-P cross-
coupling reaction under mild conditions without using toxic solvent [31]. In the present
study, based on our previous experience for the synthesis of diaryl thioethers [19], we
sought to explore the synthesis of diaryl thioethers from the reaction of aryl halides
with thiourea (as a solid, stable, cheap and odorless sulfur transfer agent) in the pres-
ence of 3D hierarchical core–shell Fe3O4@NiO/Co3O4 microspheres as a magnetically
separable nanostructured heterogeneous catalyst in the absence of an inert atmosphere
(Scheme 2).

JOURNAL OF SULFUR CHEMISTRY
3
Scheme 1. The synthetic route for the preparation of 3D hierarchical core-shell Fe3O4@NiO/Co3O4
microspheres (III).

4
A. VATANDOUST NAMANLOO ET AL.
Scheme 2. C–S coupling reaction in the presence of 3D hierarchical Fe3O4@NiO/Co3O4 microspheres
(III).
2. Results and discussion
To obtain the standard reaction conditions, at the first, a series of experiments were
performed with variation of reaction parameters such as solvent, base, temperature and
catalyst loading (Table 1). Initially, our studies began with the reaction between iodoben-
zene (1.0 mmol) and thiourea (0.5 mmol) in PEG-400 at 110°C under normal atmospheric
conditions. Adjusting the reaction mixture in the absence of catalyst and base/or in the
absence of catalyst /or in the absence of base showed that no product was formed even
after a long reaction time (Table 1, entries1–3). The desired product was obtained in 95%
yield using 3D hierarchical Fe3O4@NiO/Co3O4 microspheres and KOH (Table 1, entry 4).
We then carried out our investigations to identify the best solvent for this reaction. Among
the various solvents screened (PEG, DMF, DMSO, toluene, H2O, THF, EtOH, and solvent
free conditions), PEG-400, with negligible vapor pressure (as an inexpensive, thermally
stable, recoverable, and non-toxic media for environmentally friendly and safe chemical
reactions) was shown to be the best solvent for C–S coupling reaction in the presence of
3D hierarchical Fe3O4@NiO/Co3O4 microspheres and this was then used as a standard
for the optimization of other parameters (Table 1, entries 5–11) [33]. It was evident that
the coupling product could be obtained in DMF, DMSO, and H2O but in lower yield or
after a prolonged reaction time, and a trace amount of product could be detected when
the reaction was carried out in toluene, THF, EtOH and solvent free conditions. Because
of the essential role of base in the C−S coupling reaction, different bases were tested for
this transformation (Table 1, entries 12–15). According to the obtained results, KOH was
specified to be the most efficient base in C−S coupling reaction in the presence of 3D hier-
archical Fe3O4@NiO/Co3O4 microspheres. It was further observed that 4 equivalents of
KOH resulted in the best yield in 20 min at 110°C (Table 1, entries 16–18). Screening was
also performed at different temperatures. (Table 1, entries 19–21) Ultimately, the ideal tem-
perature for the reaction was found to be 100°C. Finally, the effect of catalyst loading on
the yield and reaction rate was also examined (Table 1, entries 22–23). Obtained results
revealed that the amount of catalyst influenced the outcome of C–S coupling reaction and
the higher yield was attained in the presence of 0.01 g (3.2: 2.8 mol% ratio of Ni:Co) of
3D hierarchical Fe3O4@NiO/Co3O4 microspheres. To probe more fully the role of 3D
hierarchical Fe3O4@NiO/Co3O4 microspheres in the C–S coupling reaction, a series of

JOURNAL OF SULFUR CHEMISTRY
5
Table 1. Synthesis of diphenyl sulfide from the reaction of iodobenzene with thiourea catalyzed by 3D
hierarchical core-shell Fe3O4@NiO/Co3O4 microspheres under different reaction conditions.
Molar ratio of
iodoben-
zene/base
Catalyst (mol%
ratio of Ni:Co)a
Temperature
(°C)
Time
(h)
Isolated
yield (%)
Entry
Base
Solvent
1
2
3
4
5
6
7
8
–
–
1/0
1/2
1/0
1/2
1/2
1/2
1/2
1/2
1/2
1/2
1/2
1/2
1/2
1/2
1/2
1/5
1/4
1/3
1/4
1/4
1/4
1/4
1/4
1/4
1/4
1/4
–
KOH
–
PEG-400
PEG-400
PEG-400
PEG-400
DMF
DMSO
Toluene
H2O
110
110
110
110
110
24
24
24
1
3
4
5
5
5
5
5
1.5
3
–
–
–
95
60
95
Trace
95
Trace
Trace
Trace
95
60
20
20
95
95
85
95
95
80
3.2: 2.8
3.2: 2.8
3.2: 2.8
3.2: 2.8
3.2: 2.8
3.2: 2.8
3.2: 2.8
3.2: 2.8
3.2: 2.8
3.2: 2.8
3.2: 2.8
3.2: 2.8
3.2: 2.8
3.2: 2.8
3.2: 2.8
3.2: 2.8
3.2: 2.8
3.2: 2.8
3.2: 2.8
4.4: 3.9
1.92: 1.68
0.01 (g)
3.2
KOH
KOH
KOH
KOH
KOH
KOH
KOH
KOH
K3PO4
K2CO3
NaHCO3
Li2CO3
KOH
KOH
KOH
KOH
KOH
KOH
KOH
KOH
KOH
KOH
KOH
110
Reflux
Reflux
Reflux
Reflux
110
110
110
110
110
110
110
110
120
100
90
100
100
100
9
THF
EtOH
-
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24b
25c
26d
PEG-400
PEG-400
PEG-400
PEG-400
PEG-400
PEG-400
PEG-400
PEG-400
PEG-400
PEG-400
PEG-400
PEG-400
PEG-400
PEG-400
PEG-400
2
45 (min)
20 (min)
20 (min)
20 (min)
20 (min)
20 (min)
20 (min)
20 (min)
20 (min)
2.5
95
85
Trace
60
70
100
100
1.5
1.5
2.8
aThe mol% result was obtained from ICP-OES analysis.
bReaction was performed in the presence of Fe3O4@MAA NPs.
cReaction was performed in the presence of Fe3O4@Co3O4 NPs as catalyst.
dReaction was performed in the presence of Fe3O4@NiO NPs as catalyst.
controlled experiments in the presence of Fe3O4@MAA NPs (I), Fe3O4@Co3O4 NPs and
Fe3O4@NiO NPs, were carried out (Table 1, entries 24-26). It can be seen that trace amount
of desired product was produced after long reaction time using Fe3O4@MAA NPs. Also, in
the presence of Fe3O4@Co3O4 NPs and Fe3O4@NiO NPs, the C–S coupling reaction was
sluggish and gained lower yield of desired product. The results, therefore, suggests that 3D
hierarchical Fe3O4@NiO/Co3O4 microspheres is essential to the success of the reaction.
Next, to explore the scope of the C–S coupling reaction via this modified procedure
(Table 1, entry 20), the reaction of various aryl halides with thiourea (as a commercial
available and economic affordable reagent for the synthesis of aryl sulfides) was studied.
(Table 2) As summarized in Table 2, the electronic nature of substitution played a major
role in governing the reactivity of the aryl halides. Generally, synthesis of aryl thioethers
with electron-withdrawing groups requires shorter reaction time than electron-donating
ones. (Table 2, entries 2–4 vs. entries 5–6, entry 8 vs. entry 9 and entries 13–14 vs. entries

6
A. VATANDOUST NAMANLOO ET AL.
15–16) Our results reveal that aryl chlorides were not as reactive as aryl bromides and aryl
iodides. (Table 2, entries 1–2 and 7–8 vs. entries 12–13) In these cases, the observed yields
are less and there was no improvement in the yields even after prolonged reaction time. As
Table 2. Synthesis of diaryl sulfides from the coupling reaction of aryl halides with thiourea catalyzed
by 3D hierarchical Fe3O4@NiO/Co3O4 microspheres.
Entry
1
Aryl halide
Product
Time (min)
20
Isolated yield (%)
95
2
3
20
15
95
95
4
5
6
7
8
80
60
80
60
60
45
75
70
70
80
9
100
70
10
4.5 (h)
75
(continued).

JOURNAL OF SULFUR CHEMISTRY
7
Table 2. Continued.
Entry
11
Aryl halide
Product
Time (min)
6.5 (h)
Isolated yield (%)
65
12
13
2.5 (h)
2.5 (h)
60
65
14
2.5/7 (h)
15/15
15
16
3.5 (h)
4 (h)
55
45
17
24 (h)
Trace
can be seen, the reaction rate is sensitive to steric effects of the aryl halides. A sterically
hindered ortho-substituted aryl halide proved to be problematic in the presence of 3D
hierarchical core-shell Fe3O4@NiO/Co3O4 microspheres, and no cross-coupled product
was detected even after 24 h (Table 2, entries 16–17). In the case of naphthyl and hetero-
cyclic halides, the reaction time is high to obtain a reasonable yield of the corresponding
symmetrical thioethers (Table 2, entries 10–11). To investigate the chemoselectivity of the
present method, the reaction of 1-chloro-4-iodobenzene (as dihalogenated aryl halide)
with thiourea was also tested which the iodide showed more reactivity (Table 2, entry 4).
This fact was confirmed by the mass spectrometry (Figure 9, Supporting Information file).
In the present study, the progress of the reaction was monitored by disappearance of
aryl halides and formation of C–S coupled product on TLC. All the prepared products were
known compounds and isolated, purified and initially identified by mass spectrometry and
comparison of their melting points with those reported previously or with authentic sam-
ples prepared by the conventional methods. Additionally, the structure of some selected
products was further deduced from 1HNMR and 13CNMR spectral data. The spectral data
of all products are given in ‘Supporting Information’ file.

8
A. VATANDOUST NAMANLOO ET AL.
Scheme 3. Proposed mechanism for synthesis of diaryl thioethers by the reaction of aryl halides with
thiourea in the presence of 3D hierarchical Fe3O4@NiO/Co3O4 microspheres.
Based on the reported pathway in literature and also according to our previous expe-
rience [19,21], a proposed reaction mechanism for C–S coupling reaction of aryl halides
with thiourea in the presence of 3D hierarchical Fe3O4@NiO/Co3O4 microspheres is pre-
sented in Scheme 3. At the outset, through an oxidative addition reaction, the active sites
of catalyst (Ni and Co) inserts into the C-X bond of aryl halide afforded intermediate (I).
Subsequently, upon the reaction of thiourea with intermediate (I) followed by reductive
elimination step, intermediate (II) and intermediate (III) were produced respectively along
with the catalyst. In alkaline media, thiol moiety was generated smoothly and reacted with
the intermediate (I) (which is produced in the oxidative addition step) to afford intermedi-
ate (IV). Finally, the desired C–S coupled product was obtained via a reductive elimination
manner and the catalyst enters the next cycle. The results obtained from Table 1, entries
25–26, revealed that Ni and Co together in the MOF structure enhance the catalytic activ-
ity of 3D hierarchical Fe3O4@NiO/Co3O4 microspheres which accelerate the C–S coupling
reaction.
Particularly, according to the green chemistry viewpoint, the separation of catalyst
using an external magnetic field from the reaction mixture is a very convenient and
efficient process in modern catalysis researches. Magnetic separation of the catalyst as
an attractive alternative to filtration or centrifugation prevents loss of the catalyst and

JOURNAL OF SULFUR CHEMISTRY
9
Figure 1. Reusability of 3D hierarchical Fe3O4@NiO/Co3O4 microspheres in the C–S coupling reaction
under the optimized reaction conditions.
Figure 2. FT-IR spectra of (a) fresh 3D hierarchical Fe3O4@NiO/Co3O4 microspheres (b) and 8th reused
3D hierarchical Fe3O4@NiO/Co3O4 microspheres.
increases its reusability. Due to paramagnetic property, the magnetite Fe3O4 particles
are amenable to magnetic separation. To demonstrate the consistency of 3D hierarchi-
cal Fe3O4@NiO/Co3O4 microspheres in terms of activity and efficiency, the recovery and
reusability of catalyst was studied in model reaction under the optimized reaction con-
ditions. After the completion of the reaction, spent 3D hierarchical Fe3O4@NiO/Co3O4
microspheres was easily separated from the reaction mixture using an external magnetic
field, followed by washing with EtOH (3 × 10 mL), and then dried at 70˚C overnight for the

10
A. VATANDOUST NAMANLOO ET AL.
next run without considerable decrease of its catalytic activity. (Figure 1) As can be seen in
Figure 1 no significant changes in yield of desired product were observed after regeneration
until the 8th cycle.
Fourier transform infrared (FT-IR) spectroscopy was utilized to authenticate the struc-
ture of 3D hierarchical Fe3O4@NiO/Co3O4 microspheres (III) and the 8th recovered
nanocatalyst (Figure 2(a,b)). As it is evident from Figure 2(a), two characteristic absorption
bands at 654 and 593 cm−1 were related to Co3O4, NiO and Fe3O4 stretching vibrations,
respectively [32,34,35]. Furtheremore, the stretching frequencies of hydroxyl groups on
the surface of Fe3O4 NPs and asymmetric and symmetric stretching vibrations of Fe-O-H
bond appeared as broad absorption bands at 3396, 1125 and 864 cm−1, respectively [36],
confirming the structure of 3D hierarchical Fe3O4@NiO/Co3O4 microspheres (III). It is
interesting to note that the shapes, positions, intensities and frequencies of the distinctive
absorption bands are well preserved even after eight recycle runs, as can be seen in Figure
2(b). As well, the obtained ICP-OES results showed that the exact amount of metal ions (Co
and Ni) are 3.2 and 3.2 mmol of cobalt as well as 2.8 and 2.7 mmol of nickel in 1.000 g of the
fresh and the 8th reused 3D hierarchical Fe3O4@NiO/Co3O4 microspheres, respectively.
The catalytic efficiency of 3D hierarchical Fe3O4@NiO/Co3O4 microspheres was com-
pared with some selected previously reported catalysts in preparation of diaryl thioethers
from the reaction of aryl halides with thiourea. (Table 3) It is evident from Table
3 that the reaction of iodobenzene with thiourea in the presence of 3D hierarchical
Fe3O4@NiO/Co3O4 microspheres was completed more quickly than the other catalysts.
More importantly, compared with other catalysts, 3D hierarchical Fe3O4@NiO/Co3O4
microspheres can be easily separated from the reaction mixture by means of a magnetic bar
(Table 3, compare with entries 1–4, 6–8 and 10–11) and reused at least eight times without
any significant loss of its catalytic activity as well (Table 3, entries 6, 7–8 and 11). Notice-
ably, using environmentally friendly solvent is another merit of this catalytic methodology
(Table 3, entries 1, 4–8 and 10–11).
Table 3. Comparison of the catalytic activity of 3D hierarchical core-shell Fe3O4@NiO/Co3O4 micro-
spheres with some literature precedents S-arylation reaction.
Temperature
(°C)
Time
(h)
Yield
(%)
Entry
Catalyst
Solvent
Base
Reusability
Ref.
1
2
3
4
5
6
7
8
CuO nanoparticles
SBA-16/GPTMS-TSC-CuI
CuI
DMSO
–
PEG-200 Na2CO3
DMF/H2O
DMF
DMSO
DMSO
DMSO
H2O
Cs2CO3
KOH
110
110
120
130
120
110
120
120
Reflux
130
120
15
1
4
7
4
6
6
–
–
–
5
4
–
98
95
93
85
94
98
95
65
88
95
96
[18]
[19]
[20]
[21]
[22]
[23]
[24]
[25]
[26]
15
12
12
12
4
24
24
2
Cu(II)-2-MPEa@MCM-41
Magnetic nano CuFe2O4
CuO@GO
KOH
K2CO3
Cs2CO3
NaOEt
Cs2CO3
KOH
GO-N-isatin-Ni (II)
MCM-41-2N-CuI
b
9
10
11
mPANI/pFe3O4
PdNP-PNFc
DMSO
DMSO
KOH
KOH
[27]
[28]
Ni(II)-modified-SBA-15
4
Present
study
12
3D hierarchical core-shell
Fe3O4@NiO/Co3O4
microspheres
PEG-400
KOH
100
20 (min)
8
95
a2-methoxy-1-phenylethanone.
bmesoporous polyaniline/porous magnetic Fe3O4.
cPd nanoparticles on the peptide nanofiber.

JOURNAL OF SULFUR CHEMISTRY
11
3. Conclusion
In summary, 3D hierarchical core–shell Fe3O4@NiO/Co3O4 microspheres was introduced
as a magnetically separable nanostructured heterogeneous catalyst for the one-pot odorless
preparation of diary thioethers from the reaction of aryl halides with thiourea. Experimen-
tal results illustrate that this hierarchical nanostructured catalyst could promote the C–S
cross coupling reaction of a large library of functional substrates including electron-rich
and electron-poor aryl iodides /or aryl bromides /or aryl chlorides with thiourea with a
remarkable yield in a green solvent (PEG-400). The uniqueness and long-term durability
of this catalyst can be related to its small nano crystalline size (10–47 nm, according to
the XRD and TEM data), bimetallic core–shell nanostructure and using cobalt and nickel
species as a low-cost, non-toxic and readily available metal ions in its structure. The notable
features of the present study are as follows: (a) use of readily accessible and non-toxic sulfur
transfer reagent, (b) short reaction times, (c) magnetic separation of the nanocatalyst by
using an external, (d) low environmental impact and high recovery of the nanocatalyst at
least for eight times without a significant decrease in its catalytic activity in the S-arylation
reaction.
4. Experimental
4.1. Material and methods
Iron (III) chloride hexahydrate (FeCl3.6H2O), sodium acetate (NaOAc), nickel (II) nitrate
hexahydrate (Ni(NO3)2.6H2O), cobalt(II) nitrate hexahydrate (Co(NO3)2.6H2O), mer-
capto acetic acid (MMA), benzene-1,3,5-tricarboxylic acid (trimesic acid) (H3BTC), ethy-
lene glycol (99%) and absolute ethanol were purchased from Merck chemical company
and were used as received without further purification. The purity determinations of the
products and the progress of the reactions were accomplished by thin layer chromatog-
raphy on silica gel polygram STL G/UV 254 plates. The melting points of the products
were determined with an Electrothermal Type 9100 melting point apparatus. The FT-IR
spectra were recorded on an AVATAR 370 FT-IR spectrometer (Therma Nicolet spectrom-
eter, USA) using KBr plates at room temperature in the range between 4000 and 400 cm−1
with a resolution of 4 cm−1. Mass spectra were recorded with a CH7A Varianmat Bremen
instrument at 70 eV electron impact ionization, in m/z (rel.%). The NMR spectra were
recorded on a Bruker Avance 400 MHz instrument in CDCl3 and DMSO-d6 as the sol-
vents. Inductively coupled plasma optical emission spectroscopy (ICP-OES) was carried
out on a 76004555 SPECTRO ARCOS ICP-OES analyzer. All yields refer to the isolated
products after purification by thin layer chromatography.
4.2. Synthesis of Fe3O4-MAA NPs (I)
Fe3O4-MAA NPs (I) was synthesized through a simple solvothermal procedure [37].
Accordingly, FeCl3·6H2O (4 mmol, 1.08 g), mercapto acetic acid (MAA) (0.6 mmol,
0.052 g) and sodium acetate (0.1 mol, 8.2 g) were orderly mixed together in 40 mL ethy-
lene glycol at 60°C. The obtained yellow mixture was transferred to a 50 mL Teflon-lined
stainless-steel autoclave and kept at 200°C for 12 h to achieve Fe3O4-MAA NPs (I).

12
A. VATANDOUST NAMANLOO ET AL.
The precipitate was separated by magnetic decantation, washed with deionized water
(3 × 20 mL), ethanol (3 × 20 mL) and dried at 70°C overnight.
4.3. Synthesis of Fe3O4@Ni-Co-BTC NPs (II)
To a suspension of 0.06 g Fe3O4-MAA NPs (I) in ethanol (20 mL) (dispersed in an ultra-
sonic bath for 30 min), a solution of 1.7 mmol of Ni(NO3)2·6H2O (0.494 g) and 3.5 mmol
of Co(NO3)2·6H2O (1.017 g) in 20 mL ethanol was added. The obtained mixture was son-
icated for 30 min. Then, 2.8 mmol of trimesic acid (0.588 g in 20 mL ethanol) was added
to the resulting suspension and the obtained mixture was dispersed again for 30 min. The
mixture was then transferred into a 100 mL Teflon-lined stainless-steel autoclave and main-
tained at 150°C for 12 h. As a final step, the obtained black product (Fe3O4@Ni-Co-BTC
NPs (II)) was separated by magnetic decantation, washed with ethanol for three times and
dried at 60˚C [38].
4.4. Synthesis of 3D hierarchical Fe3O4@NiO/Co3O4 microspheres (III)
To achieve black powder 3D hierarchical Fe3O4@NiO/Co3O4 microspheres (III), the
obtained Fe3O4@Ni-Co-BTC NPs (II) powder was put into an electrical furnace and
annealed in air at 450°C for 2 h with a heating rate of 2°C min−1 [39].
4.5. Typical procedure for the preparation of diphenyl sulfide in the presence of 3D
hierarchical core-shell Fe3O4@NiO/Co3O4 microspheres
To a stirred solution of iodobenzene (1.0 mmol, 0.204 g) and thiourea (0.5 mmol, 0.038 g)
in PEG-400 (3.0 mL) at room temperature, 3D hierarchical core–shell Fe3O4@NiO/Co3O4
microspheres (3.2: 2.8 mol% ratio of Ni: Co, 0.01 g) and KOH (4 mmol, 0.224 g) was added.
The resultant mixture was heated at 100˚C for 20 min. The progress of the reaction was
monitored by TLC. After the reaction was completed, the reaction mixture was allowed
to cool, and diluted by a 1:1 mixture of ethyl acetate/water (6 mL). The catalyst was sep-
arated from the reaction mixture using an external magnetic field, followed by washing
with EtOH (3 × 10 mL), and then dried at 70°C overnight for the next run. The combined
organic extract was separated and dried with anhydrous Na2SO4. Afterwards, the solvent
was completely removed under vacuum to give the crude product, which was purified by
thin layer chromatography (ethyl acetate/ n-hexane, 1:5) to afford diphenyl sulfide in 95%
yield (0.176 g).
4.5.1. Diphenyl sulfide [19] (1a)
Diphenyl sulfide (0.176 g, 95%); Colorless oil; 1H NMR (400 MHz, CDCl3): δ
[ppm] = 7.34-7.31 (m, 5H), 7.29-7.25 (m, 3H), 7.23-7.19 (m, 2H); 13C NMR (100 MHz,
CDCl3): δ [ppm] = 135.9, 131.2, 129.4, 127.2; MS (70 eV, EI); m/z (%): 186 (M+, 12%),
184 (M-2, 100%), 108 (C6H4S, 90%), 76 (C6H4, 42%), 65 (C5H5, 40%), 51 (C4H3, 28%).

JOURNAL OF SULFUR CHEMISTRY
13
4.5.2. 4,4ꢀ-Thiodibenzonitrile [19] (2b)
4,4ꢀ-Thiodibenzonitrile (0.198 g, 84%); Yellow solid; mp 134–135 °C (Lit. 134–135 °C); 1H
NMR (400 MHz, CDCl3): δ [ppm] = 7.43 (d, J = 8.8 Hz, 4 H, Ar-H), 7.19 (d, J = 8.4 Hz,
4 H, Ar-H); 13C NMR (100 MHz, CDCl3): δ [ppm] = 140.6, 133.0, 131.2, 118.2, 111.4.
4.5.3. Bis (4-nitrophenyl) sulfane [19] (3c)
Bis (4-nitrophenyl) sulfane (0.231 g, 84%); Yellow solid; mp 149–150 °C (Lit. 149–150 °C);
1H NMR (400 MHz, DMSO-d6): δ [ppm] = 7 δ 8.25 (dd, J = 8.4, 1.6 Hz, 4H), 7.64 (dd,
J = 8.4, 2.0 Hz, 4H); 13C NMR (100 MHz, DMSO-d6): δ [ppm] = 146.7, 142.2, 131.3,
124.8; MS (70 eV, EI), m/z (%): 276 (M+, 20%), 275 (M-1, 40%), 123 (C6H5NO2, 90%).
4.5.4. Bis (4-chlorophenyl) sulfane [40] (4d)
Bis (4-cholorophenyl) sulfane (0.123 g, 45%); white solid; mp 89–90 °C (Lit. 91–92 °C); MS
(70 eV, EI), m/z (%): 254 (M+,100%), 256 (M + 2,66%), 218 (C12H8ClS,20%), 184 (C12H8S,
82%), 143 (C6H4ClS,18%), 108 (C6H4S,28%).
4.5.5. Di-(p-tolyl) sulfane [19] (5e)
Di-(p-tolyl) sulfane (0.158 g, 74%); Colorless oil; (Lit. 43–46 °C); H NMR (400 MHz,
1
CDCl3): δ [ppm] = 7.23 (d, J = 8.4 Hz, 4 H, Ar-H), 7.10 (d, J = 7.6 Hz, 4H, ArH), 2.32
(s, 6H, CH3); 13C NMR (100 MHz, CDCl3): δ [ppm] = 137.1, 132.8, 131.2, 130.1, 21.3;
MS (70 eV, EI), m/z (%): 212 (M-2, 50%), 91 (C7H7, 67%).
4.5.6. Bis (4-methoxyphenyl) sulfane [19] (6f)
Bis (4-methoxyphenyl) sulfane (0.172 g, 70%); Yellow liquid; 1H NMR (400 MHz, CDCl3):
δ [ppm] = 7.27 (d, J = 8.8 Hz, 4 H, Ar-H), 6.83 (d, J = 8.8 Hz, 4 H, Ar-H), 3.78 (s, 6 H,
OCH3); 13C NMR (100 MHz, CDCl3): δ [ppm] = 159.1, 132.9, 127.6, 114.9, 55.5; MS (70
eV, EI), m/z (%): 246 (M+, 5%), 243 (M-2, 65%), 77 (C6H5, 80).
4.5.7. 4,4ꢀ-Thiodianiline [19] (7g)
4,4ꢀ-Thiodianiline (0.177 g, 82%); Brown solid; mp 107–108 °C (Lit. 107–108 °C); 1H NMR
(400 MHz, CDCl3): δ [ppm] = 7.15 (d, J = 8.0 Hz, 4 H, Ar-H), 6.60 (d, J = 8.0 Hz, 4 H,
Ar-H), 3.67 (s, 4 H, NH2); 13C NMR (100 MHz, CDCl3): δ [ppm] = 145.8, 132.9, 125.2,
115.9.
4.5.8. Di (thiophen-2-yl) sulfane [19] (8h)
Di (thiophen-2-yl) sulfane (0.146 g, 74%); Yellow liquid; 1H NMR (400 MHz, CDCl3): δ
[ppm] = 7.63–7.53 (m, 2H), 7.45–7.34 (m, 2H), 7.27–7.11 (m, 2H); 13C NMR (100 MHz,
CDCl3): δ [ppm] = 135.5, 132.7, 129.6, 137.47.
4.5.9. Di (naphthalen-1-yl) sulfane [27] (9i)
Di (naphthalen-1-yl) sulfane (0.214 g, 75%); White solid; mp 156–157 °C (Lit. 156–158
°C); 1H NMR (400 MHz, CDCl3): δ [ppm] = 8.43–8.40 (m, 2 H, Ar-H), 7.89–7.87 (m, 2
H, Ar-H), 7.78–7.76 (m, 2 H, Ar-H), 7.55–7.51 (m, 4 H, Ar-H), 7.32–7.30 (m, 4 H, Ar-H);
13C NMR (100 MHz, CDCl3): δ [ppm] = 134.3, 132.8, 132.6, 130.1, 128.8, 128.2, 126.9,
126.6, 126.0, 125.3; MS (70 eV, EI), m/z (%): 286 (M+, 8%), 285 (M-1, 52%), 282 (M-4,
90%), 127 (C10H7, 60%).

14
A. VATANDOUST NAMANLOO ET AL.
4.5.10. 4,4ꢀ-Thiodiphenol [19] (11k)
1
4,4ꢀ-Thiodiphenol (0.137 g, 63%); White solid; mp 151–153 °C (Lit. 150–153 °C); H
NMR (400 MHz, DMSO-d6): δ [ppm] = 9.62 (s, 2H), 7.14 (d, J = 8.4 Hz, 4H), 6.73 (d,
J = 8.4 Hz, 4H); 13C NMR (100 MHz, DMSO-d6): δ [ppm] = 157.0, 132.7, 124.7, 116.3.
Acknowledgements
The authors gratefully acknowledge the partial support of this study by Ferdowsi University of
Mashhad Research Council (grant number p/3/51304). Furthermore, it should be noted that
this manuscript is derived from the thesis entitled ‘Ferromagnetic 3D hierarchical core-shell
Fe3O4@NiO/Co3O4 microspheres as an efficient and heterogeneous nanostructured ligand-free
catalyst for C–S bond formation in poly (ethylene glycol).’
Disclosure statement
No potential conflict of interest was reported by the author(s).
Funding
This study was supported by Ferdowsi University of Mashhad [grant number p/3/51304].
ORCID
Batool Akhlaghinia http://orcid.org/0000-0002-9940-5045
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