Magnetically separable nano CuFe2O4: an ef?cient and reusable heterogeneous catalyst for the green synthesis of thiiranes from epoxides with thiourea

Article abstract of DOI:10.1080/17415993.2016.1196691

The magnetically separable nano CuFe₂O₄ was prepared and used as an efficient heterogeneous catalyst for conversion of various epoxides to the corresponding thiiranes with thiourea in refluxing ethanol. The reactions were completed within 34?45 min to give thiiranes in 80?95% yields. The utilized nano CuFe₂O₄ can be reused for several times without losing its activity.

Full text of DOI:10.1080/17415993.2016.1196691

Journal of Sulfur Chemistry
ISSN: 1741-5993 (Print) 1741-6000 (Online) Journal homepage: http://www.tandfonline.com/loi/gsrp20
Magnetically separable nano CuFe2O4: an efficient
and reusable heterogeneous catalyst for the green
synthesis of thiiranes from epoxides with thiourea
Ronak Eisavi, Seiran Ghadernejad, Behzad Zeynizadeh & Farkhondeh
Mohammad Aminzadeh
To cite this article: Ronak Eisavi, Seiran Ghadernejad, Behzad Zeynizadeh & Farkhondeh
Mohammad Aminzadeh (2016): Magnetically separable nano CuFe2O4: an efficient and
reusable heterogeneous catalyst for the green synthesis of thiiranes from epoxides with
thiourea, Journal of Sulfur Chemistry, DOI: 10.1080/17415993.2016.1196691
To link to this article: http://dx.doi.org/10.1080/17415993.2016.1196691
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Date: 21 June 2016, At: 08:58

JOURNAL OF SULFUR CHEMISTRY, 2016
http://dx.doi.org/10.1080/17415993.2016.1196691
Magnetically separable nano CuFe2O4: an efficient and
reusable heterogeneous catalyst for the green synthesis of
thiiranes from epoxides with thiourea
Ronak Eisavia, Seiran Ghadernejada, Behzad Zeynizadehb and Farkhondeh
Mohammad Aminzadehb
aDepartment of Chemistry, Payame Noor Universtiy, Tehran, Iran; bDepartment of Chemistry, Faculty of
Science, Urmia University, Urmia, Iran
ABSTRACT
ARTICLE HISTORY
Received 4 March 2016
Accepted 29 May 2016
The magnetically separable nano CuFe2O4 was prepared and used
as an efficient heterogeneous catalyst for conversion of various
epoxides to the corresponding thiiranes with thiourea in refluxing
ethanol. The reactions were completed within 34−45 min to give thi-
iranes in 80−95% yields. The utilized nano CuFe2O4 can be reused for
several times without losing its activity.
KEYWORDS
Epoxide; CuFe2O4; nano;
thiirane; thiourea
1. Introduction
Thiiranes are valuable synthetic building blocks for the preparation of polymers, phar-
maceuticals, pesticides, and herbicides.[1–3] In addition, thiirane is a fundamental hete-
rocyclic core of various biologically active compounds.[4–7] Transformation of epoxides
to thiiranes by an oxygen–sulfur exchange reaction is an efficient method and has been
achieved with different procedures using sulfur transferring agents.[8–22] However, some
of these methods suffer from disadvantages such as long reaction times, the use of unre-
coverable catalyst, low yield of the products, difficult workup procedures, use of highly
acidic catalysts, rapid increase of pH during the reaction, and the formation of polymeric
by-products.
CONTACT Ronak Eisavi
roonak.isavi@gmail.com
Department of Chemistry, Payame Noor Universtiy, PO BOX
19395-3697, Tehran, Iran
Supplemental data for this article can be accessed here. http://dx.doi.org/10.1080/17415993.2016.1196691
© 2016 Informa UK Limited, trading as Taylor & Francis Group

2
R. EISAVI ET AL.
R
R'
R
R'
NH2CSNH2/Nano CuFe2O4
EtOH, reflux
O
S
R, R' : aryl, alkyl, allyl, H
Scheme 1. Conversion of epoxides to thiiranes with thiourea/nano CuFe2O4 system.
The development and introduction of convenient catalytic procedures, facile recovery of
the catalyst from the reaction medium and recyclability of the catalyst are very significant
tasks in new synthetic chemistry. In recent years, the magnetic nanoparticles based cata-
lysts have been extensively used as heterogeneous catalysts for achieving useful chemical
transformations.[23–33] Among these heterogeneous catalysts, copper/iron oxide-based
catalysts have gained importance in scientific research due to their wide applications in
organic reactions.[34,35] These catalysts are environmentally compatible, air and moisture
insensitive, and because of their magnetic properties, separation and complete recovery
of the catalyst from reaction mixture are very simple and highly possible by magnetiza-
tion with a permanent magnetic field.[36–42] To the best of our knowledge, the reaction
of epoxides with thiourea has not been reported using iron-based nanoparticles/catalysts.
As a part of our research program on the synthesis of thiiranes,[8–11] herein, we report
the magnetic nano CuFe2O4 as efficient and eco-friendly heterogeneous catalysts for the
conversion of structurally different epoxides to thiiranes using thiourea in refluxing EtOH
(Scheme 1).
2. Results and discussion
The optimization experiments showed that the reaction of styrene oxide (1 mmol) with
thiourea (1 mmol) in the presence of nano CuFe2O4 (0.05 mmol, 0.012 g, 5 mol%) was car-
ried out effectively in refluxing EtOH. The epoxide was converted to the corresponding
thiirane in 92% yield within 40 min. The effects of other solvents such as CH3CN, THF,
and MeOH were also investigated for the typical experiment. The results showed that polar
and protic solvents are more effective, and in comparison with EtOH, the reaction times
were longer and the yields of thiiranes were considerably lower in all other solvents. Alco-
holic solvents with hydrogen bonding capability facilitate the ring opening of epoxides
by nucleophilic reagents. On the other hand, between ethanol and methanol, ethanol was
preferred, because of the lower toxicity. The other important parameter for improving the
reaction condition was the amount of CuFe2O4 nanoparticles as catalyst. An increase in the
quantity of CuFe2O4 nanoparticles from 0.03 to 0.05 mmol not only accelerated the rate of
reaction but also increased the product yield. This showed that the quantity of the catalyst
plays a consequential role in the optimization of the product yield. Thus, using 0.05 mmol
of nano CuFe2O4 is a sufficient and appropriate choice to push the reaction forward. More
amounts of nano CuFe2O4 did not improve the yields of products. It is considerable that in
the absence of CuFe2O4 nanoparticles, no conversion of epoxides to thiiranes takes place.
Furthermore, the effect of temperature on the conversion of styrene oxide to styrene episul-
fide was also studied. The results showed that no reaction occurred at room temperature
after 1 h. In addition, performing the reaction in an oil bath (70–80°C) exhibited more
efficiency than room temperature condition (Table 1).

JOURNAL OF SULFUR CHEMISTRY
3
Table 1. Optimization experiments for conversion of styrene oxide to styrene episulfide with thiourea
a
in the presence of nano CuFe2O4 .
Nano CuFe2O4
Entry
(mmol)
Condition
EtOH/reflux
EtOH/reflux
EtOH/reflux
EtOH/reflux
EtOH/reflux
CH3CN/reflux
THF/reflux
MeOH/reflux
EtOH/r.t.
Time (min)
Conversion (%)b
1
2
3
4
5
6
7
8
9
10
–
20
80
40
30
20
50
60
45
60
55
0
100
100
100
100
80
50
90
0
60
0.03 (3 mol%)
0.05 (5 mol%)
0.1 (10 mol%)
0.2 (20 mol%)
0.05 (5 mol%)
0.05 (5 mol%)
0.05 (5 mol%)
0.05 (5 mol%)
0.05 (5 mol%)
Solvent-free/oil bath (70–80°C)
aAll reactions were carried out with 1 mmol of styrene oxide in the presence of thiourea (1 mmol).
bConversion less than 100% was determined on basis of the recovered epoxide.
The ability of this synthetic procedure was further investigated by the reaction of vari-
ous epoxides possessing either electron-donating or -withdrawing substituents, and cyclic
epoxides with thiourea in the presence of nano CuFe2O4 under the optimized condi-
tions. The results are summarized in Table 2. As it is seen, all reactions were carried out
successfully within 34–45 min to give thiiranes in 80–95% yields.
a
Table 2. Conversion of epoxides to thiiranes with thiourea catalyzed by nano CuFe2O4 .
Entry
1
Epoxide (a)
Thiirane (b)
Time (min)
40
Yield (%)b
92
Ph
O
Ph
S
2
3
42
35
85
90
Cl
Cl
O
S
MeO
MeO
O
S
4
5
37
39
95
92
O
O
O
S
Cl
Cl
O
O
O
O
O
O
S
S
6
37
90
NC
NC
(continued).

4
R. EISAVI ET AL.
Table 2. Continued.
Entry
7
Epoxide (a)
Thiirane (b)
Time (min)
35
Yield (%)b
95
MeO
MeO
O
O
O
S
8
9
34
37
85
92
O
O
O
S
O
O
O
S
10
11
12
35
35
36
90
82
90
O
O
O
S
Cl
Cl
O
S
O
O
O
O
O
S
13
14
36
34
90
85
O
S
O
O
S
S
15
16
35
45
80
85
O
S
aAll reactions were carried out with 1 mmol of epoxide in the presence of thiourea (1 mmol) and CuFe2O4 (0.05 mmol,
0.012 g) in refluxing EtOH.
bYields refer to isolated pure products.
2.1. Characterization of the catalyst
CuFe2O4 nanoparticles were synthesized according to the procedure reported by Sun et al.
[38] X-ray diffraction (XRD), scanning electron micrograph (SEM), transmission electron
micrograph (TEM), and FT-IR analyses confirmed the formation of nano CuFe2O4. The
position and relative intensities of all peaks confirm well with standard XRD pattern of
CuFe2O4 (JCPDS card No. 34-0425) indicating characteristic of the tetragonal structure.
The calcinated copper ferrite at 900°C represents a particle size of 110 nm, calculated using
the Scherrer equation (Figure S1). The SEM image shows that there are irregular particles
of various sizes (75–150 nm) in the sample calcinated at 900°C. The large particles are com-
posed of small crystallites (Figure S2). The TEM image of the sample is given in Figure S3
and as can be noticed the particles are of nano sizes. The FT-IR spectrum of CuFe2O4 is
shown in Figure S4. A strong peak appeared at 586 cm−1, corresponding to the vibration

JOURNAL OF SULFUR CHEMISTRY
5
modes of all spinel compounds, which is attributed to the M–O stretching bands in tetrahe-
dral complexes.[43–46] The absorption broad band at 3433 cm−1 represents the stretching
mode of H2O molecules and OH groups. The band around 1627 cm−1 corresponds to the
bending mode of H2O molecules [47] (Figs. S1–S4 in Supporting information).
The green aspect of this method was investigated by recovery of nano CuFe2O4 from the
reaction mixture and then reusing it for the conversion of styrene oxide to styrene episul-
fide. It is notable that the catalyst could be magnetically recovered by an external magnetic
field and washed with ethanol sequentially, then with water and finally dried at 80°C for
2 h. After being dried, it was used for repeating the titled reaction at the optimum condi-
tions. The results showed that the catalyst could be cycled four times without a significant
loss of activity (Table 3).
In addition, the efficiency of our synthetic method was highlighted by comparing
some of our results with the previously reported methods [16–21] (Table 4). A case study
Table 3. Reusability of recovered nano CuFe2O4 in the conversion of
styrene oxide to styrene episulfide by use of thiourea.
Recovery of nano
CuFe2O4 (%)
Run
Yield (%)a
1
2
3
4
5
92
91
91
90
86
98
94
92
90
88
aIsolated yield.
Table 4. Comparison of the conversion of styrene oxide to styrene episulfide with thiourea/CuFe2O4
system and other reported methods.
Entry
Catalyst
Condition
EtOH/reflux
CH3CN/reflux
CH3CN/reflux
CH3CN/reflux
CH3CN/reflux
CH3CN/45°C
Time (min)
Yield (%)a
Ref.
1
2
3
4
5
6
7
Nano CuFe2O4
Ps-AlCl3
40
90
150
60
50
84
92
85
80
98
98
85
65
–
16
17
18
21
19
20
Mg(HSO4)2
SnIV(tpp)(OTf)2
SnIV(tpp)(BF4)2
SiO2–AlCl3
-
Solvent-free/120 °C
15
aIsolated yields.
NH2
NH
+ NH2
R
R
-H2O
:
R
NH2CSNH2
S
S
NH2
O
S
+
O
R
R
OH
-
O
HN=C=NH
+
: Nano CuFe2O4
Scheme 2. A proposed mechanism for conversion of epoxides to thiiranes with thiourea/nano CuFe2O4
system.

6
R. EISAVI ET AL.
shows that the present procedure is more efficient than the reported methods. The exact
mechanism of this synthesis is not known. A possible mechanism is presented in Scheme 2.
3. Conclusions
In summary, we have shown that structurally different epoxides are easily and efficiently
converted to their corresponding thiiranes with thiourea in the presence of nano CuFe2O4
in refluxing EtOH. So, we think that the simple synthesis, reusability, recoverability, non-
toxicity, and cheapness of nano CuFe2O4, short reaction times, and high yields of the
products make this method a useful addition to the present methodologies.
4. Experimental
4.1. General
All reagents and substrates were purchased from commercial sources with the best qual-
1
ity and they were used without further purification. FT-IR and H, 13C NMR spectra
were recorded on Thermo Nicolet Nexus 670 and Bruker Avance (300 MHz) spectrom-
eters, respectively. The products were characterized by their spectra data and comparison
with the reported data in the literature. TLC was applied for the purity determination of
substrates, products, and reaction monitoring over silica gel 60F254 aluminum sheet. The
synthesized nano CuFe2O4 was characterized by XRD on a Bruker D8-Advanced diffrac-
tometer with graphite-monochromatized Cu Kα radiation (λ = 1.54056Å) at room tem-
perature. SEM images were determined on a LEO 1430 VP scanning electron microscopy.
TEM images were recorded with a Philips CM30 at electron energy of 300 keV.
4.2. Preparation of CuFe2O4 nanoparticles
In a typical synthesis, Cu(CH3COO)2·H2O, Fe(NO3)3·9H2O, NaOH, and NaCl were
mixed in a molar ratio (1:2:8:2) and ground together in an agate mortar for 50 min. The
reaction started easily during the mixing process and was accompanied by releasing of heat.
As the reaction proceeded, the mixture became pasty and its color gradually changed from
blue to finally brown. This mixture was washed with distilled water for several times. After
washing, the powders were dried at 80°C for 2 h. Then the powders were calcined at 300°C,
500°C, 700°C, 900°C for 2 h to obtain final powders.[38]
4.3. Conversion of epoxides to thiiranes using thiourea in the presence of nano
CuFe2O4: a general procedure
In a round-bottomed flask (25 mL) equipped with a magnetic stirrer and condenser, a solu-
tion of the epoxide (1 mmol) and thiourea (0.076 g, 1 mmol) in EtOH (3 mL) was prepared.
Nano CuFe2O4 (0.05 mmol) was then added to the resulting solution and the reaction mix-
ture was stirred magnetically under reflux condition for 34–45 min. The progress of the
reaction was monitored by TLC. After completion of the reaction, EtOH was evaporated
and EtOAc (2 × 5 mL) was added to the reaction mixture followed by stirring for 5 min.
In order to separate the catalyst, a magnet was externally appended to the flask, and the
magnetic nano CuFe2O4 was accumulated at the walls of the flask. Then, the mixture was

JOURNAL OF SULFUR CHEMISTRY
7
filtered and the organic layer was washed with water (20 mL) and dried over anhydrous
Na2SO4. The organic solvent was evaporated to give crude thiirane for further purification
by a short-column chromatography over silica gel (80–95% yield) (Table 2). The collected
nano CuFe2O4 was washed with ethanol, then with water and finally dried and preserved
for the next run. All products are known compounds and were identified by compari-
son of their properties (FT-IR, 1H NMR and 13C NMR) with those of authentic samples
[10,12,13,22]; these data were given in the Supporting information.
Acknowledgements
We thank Research Council of Payame Noor University for the financial support of this investigation.
Disclosure statement
No potential conflict of interest was reported by the authors.
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