Synthesis and characterization of sulfamic acid supported on Fe3O4 nanoparticles: A green, versatile and magnetically separable acidic catalyst for oxidation reactions and Knoevenagel condensation

Article abstract of DOI:10.1002/aoc.3927

Sulfamic acid immobilized on diethylenetriamine functionalized Fe₃O₄ nanoparticles (SA-DETA-Fe₃O₄) was successfully prepared and characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), vibrating sample magnetometer (VSM), thermo gravimetric analysis (TGA), X-Ray diffraction (XRD) and scanning electron microscopy (SEM). The sulfamic acid was found as a magnetically separable and highly active catalyst for the oxidative coupling thiols, oxidation of sulfides. Furthermore, the SA-DETA-Fe₃O₄ showed the high catalytic activity in Knoevenagel condensation of aromatic aldehydes with active methylene compounds (malononitrile and ethyl cynoacetate). The nanosolid catalyst could be easily recovered by a simple magnetic separation and reused for many cycles without deterioration in catalytic activity.

Full text of DOI:10.1002/aoc.3927

Received: 6 February 2017
DOI: 10.1002/aoc.3927
Revised: 24 April 2017
Accepted: 16 May 2017
F U L L PA P E R
Synthesis and characterization of sulfamic acid supported on
Fe3O4 nanoparticles: A green, versatile and magnetically
separable acidic catalyst for oxidation reactions and
Knoevenagel condensation
Lotfi Shiri | Hojatollah Narimani | Mosstafa Kazemi
Department of Chemistry, School of Basic
Sciences, Ilam University, P.O. Box
69315‐516, Ilam, Iran
Sulfamic acid immobilized on diethylenetriamine functionalized Fe3O4
nanoparticles (SA‐DETA‐Fe3O4) was successfully prepared and characterized by
X‐ray diffraction (XRD), Fourier transform infrared spectroscopy (FT‐IR), vibrating
sample magnetometer (VSM), thermo gravimetric analysis (TGA), X‐Ray
diffraction (XRD) and scanning electron microscopy (SEM). The sulfamic acid
was found as a magnetically separable and highly active catalyst for the oxidative
coupling thiols, oxidation of sulfides. Furthermore, the SA‐DETA‐Fe3O4 showed
the high catalytic activity in Knoevenagel condensation of aromatic aldehydes with
active methylene compounds (malononitrile and ethyl cynoacetate). The nanosolid
catalyst could be easily recovered by a simple magnetic separation and reused for
many cycles without deterioration in catalytic activity.
Correspondence
Lotfi Shiri, Department of Chemistry, School
of Basic Sciences, Ilam University, P.O. Box
69315‐516, Ilam, Iran.
Email: lshiri47@gmail.com
Funding information
Ilam University, Ilam, Iran
KEYWORDS
knoevenagel condensation, magnetically separable catalyst, sulfamic acid, sulfides oxidation
thiols coupling
1 | INTRODUCTION
Therefore, the development of new, clean and efficient
protocols (under reusable catalysts and green solvents) for
Sulfoxides and disulfides are two important classes of
organosulfur compounds including category of compounds
possessing a unique exclusive chemistry both in biochemistry
and organic chemistry.[1,2] They exist as important scaffolds
in the structural of many biological and pharmaceutical
active molecules.[3,4] The oxidative coupling of thiols to the
disulfides and oxidation of sulfides to the sulfoxides are
substantial oxidation reactions in organic synthesis, which
has been widely investigated over the years[5] Up to now, a
wide range of catalysts and reagents, for the oxidative
coupling of thiols and oxidation of sulfides, have been
reported in in the literature.[6,7] Unfortunately, most of
methods suffer a series of drawbacks such as tedious work‐
up, long reaction times, high cost, toxicity, use of hazardous
organic solvents as reaction medium.
the oxidative coupling of thiols and oxidation of sulfides is
still an important challenge in organic synthesis. Hydrogen
peroxide due to being its cheap and green is the best oxidant
for these oxidations.[8]
The development of new and efficient nanomaterials as
catalyst supports is a real challenge in modern organic syn-
thesis.[9,10] In this category (nanomaterial supports), in recent
times, magnetic nanoparticles have received an increasing
interest due to their tremendous properties such as simple
preparation and functionalization, large surface area ratio,
low toxicity and cost.[11–16] The simple separation of
MNPs‐supported catalysts from product or mixture reaction
by an external magnet is the most notable advantage of
magnetic nanoparticles.[17–19] According to these fascinating
advantages, magnetic nanoparticles can be considered as a
Appl Organometal Chem. 2017;e3927.
wileyonlinelibrary.com/journal/aoc
Copyright © 2017 John Wiley & Sons, Ltd.
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https://doi.org/10.1002/aoc.3927

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SHIRI ET AL.
promising alternative to other catalyst supports (such as
porous/mesoporous catalyst supports).[20] Among the various
magnetic nanoparticles as the core magnetic support, Fe3O4
nanoparticles have been broadly studied both for their
scientific interests and technological applications.[21]
Since the acids are often liquid and expensive, their
separation from reaction media is the most important concern
of synthetic chemist.[22] Therefore, the designing and synthe-
sizing of strong solid acids and their utilization as catalyst in
synthetic reactions is a nice response of future of organic
synthesis, in particular from the green synthetic chemistry
point of view.[23,24] The immobilization of acidic functional
Catalysis of chemical reactions by acids is always an
important and fascinating research target in organic synthesis.
SCHEME 1 Stepwise preparation of MNPs/DETA‐SA
FIGURE 1 FT‐IR spectra of Fe3O4 NPs
(a), CPTMS‐Fe3O4 (b) and DETA‐Fe3O4 (c)
and SA‐DETA‐Fe3O4 (d)

SHIRI ET AL.
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groups on magnetic nanoparticles and their catalytic utiliza-
tion in organic reactions is an ideal and fascinating solution
to overcome this drawback, because the catalyst can be
readily separated from the reaction media by external
magnet. Inspired by this technique, we synthesized the
diethylenetriamine functionalized Fe3O4 nanoparticles
supported sulfamic acid (SA‐DETA‐Fe3O4) and evaluated
its catalytic activities in the oxidative coupling of thiols and
oxidation of sulfides.
2 | RESULTS AND DISCUSSION
2.1 | Catalyst preparation
The details of applied strategy for the preparation of the
diethylenetriamine functionalized Fe3O4 nanoparticles sup-
ported sulfamic acid (SA‐DETA‐Fe3O4) have presented in
Scheme 1. The magnetic Fe3O4 nanoparticles (Fe3O4 NPs)
were prepared by chemical co‐precipitation procedure[17]
FIGURE 2 SEM images of the SA‐DETA‐Fe3O4

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SHIRI ET AL.
and covered with 3‐chloropropyltrimethoxysilane (CPTMS)
by covalent bonds.[17] The reaction of the supported CPTMS
with diethylenetriamine (DETA) in toluene under reflux
conditions for 42 h produced the DETA functionalized mag-
netic nanoparticles (DETA‐Fe3O4). Ultimately, the reaction
of DETA‐Fe3O4 with chlorosulfonic acid in CH2Cl2 at room
temperature led to sulfamic acid on immobilized on magnetic
nanoparticles (SA‐DETA‐Fe3O4).
The FT‐IR spectrum for the Fe3O4 NPs exhibit a
stretching vibration at 3440 cm−1 which incorporates the
contributions from both symmetrical and asymmetrical
modes of the O‐H bonds which are attached to the surface
iron atoms (Figure 1a). The presence of Fe3O4 NPs was
shown in FT‐IR by strong absorption band at around
560 cm−1, which is attributed to the Fe–O bond of MNPs.
2.2 | Catalyst characterization
As‐prepared nanosolid was characterized by Fourier trans-
form infrared spectroscopy (FT‐IR), scanning electron
microscopy (SEM), Vibrating Sample Magnetometer
(VSM), X‐ray diffraction (XRD) and thermogravimetric
analysis (TGA).
The FT‐IR spectra for the Fe3O4 NPs (a), CPTMS‐Fe3O4
(b) and DETA‐Fe3O4 (c) and SA‐DETA‐Fe3O4 (d) is
displayed in Figure 1.
FIGURE 5 TGA diagram of bare Fe3O4 NPs (black line), CPTMS‐
Fe3O4 (blue line), DETA‐Fe3O4 (redline) and SA‐DETA‐Fe3O4 (green
line)
a
TABLE 1 Optimization of the reaction conditions
Catalyst
(mg)
H2O2
(mL)
Solvent
Time/
min
Yield
(%) b
Entry
(Temp.oC)
1
2
3
4
5
6
7
8
9
3
5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
CH3CN (r.t)
CH3CN (r.t)
CH3CN (r.t)
CH3CN (r.t)
EtOH (r.t)
40
25
91
93
10
15
10
10
10
10
10
15
97*
97
FIGURE 3 Magnetization curves for Fe3O4 NPs (red line) and SA‐
DETA‐Fe3O4 (blue line) at room temperature
15
30
95
Acetone (r.t)
THF (r.t)
35
91
45
95
CH2Cl2 (r.t)
140
110
83
Ethylacetate
(r.t)
91
10
11
12
13
14
10
10
10
10
‐‐
0.3
0.4
0.6
0.5
0.5
CH3CN (r.t)
CH3CN (r.t)
CH3CN (r.t)
CH3CN (40 °C)
CH3CN
70
40
88
92
96
96
5
15
14
120
aReaction conditions: The oxidative coupling of benzo[d]thiazole‐2‐thiol (1 mmol)
using 30% H2O2 in the presence of catalyst and solvent (2 ml).
bIsolated yield.
FIGURE 4 The XRD pattern of the SA‐DETA‐Fe3O4

SHIRI ET AL.
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the Fe3O4 NPs and SA‐DETA‐Fe3O4 have the saturated
magnetization value of 55.1 and 33.2 emu/g, respectively.
The decrease of the saturation magnetization can be related
to the presence of sulfamic acid groups on the surface of
the Fe3O4 nanoparticles supports.
In order to investigate the crystal structure of the obtained
nanocatalyst (SA‐DETA‐Fe3O4), XRD analysis was per-
formed and the resultant pattern of the as‐prepared sample
is shown in Figure 4. As seen in Figure 4, the SA‐
DETA‐Fe3O4 show several characteristic peaks at the 2θ
values of 35.2o, 41.3o, 50.5o, 63.2o, 67.4o and 74.5o (in good
agreement with the standard Fe3O4 NPs XRD spectrum
reported in literature).[11]
Bond formation between the MNPs and the catalyst can
be affirmed by thermogravimetric analysis (TGA). Figure 5
shows the TGA curves for bare Fe3O4 NPs (black line),
CPTMS‐Fe3O4 (blue line), DETA‐Fe3O4 (red line) and SA‐
DETA‐Fe3O4 (green line). The TGA curves of the all sam-
ples shows the small amount of weight loss below 200 °C
is due to desorption of physically adsorbed solvents and
surface hydroxyl groups. Organic groups have been reported
to desorb at temperatures above 260 °C. The CPTMS‐Fe3O4
and DETA‐Fe3O4 have the mass loss, at 5% and 9%, respec-
tively. For the SA‐DETA‐Fe3O4, there is a well‐defined mass
weight loss of 27% between 370 and 520 °C which is related
to the breakdown of the DETA‐SA moieties. As the result of
this analysis, the well grafting of DETA and SA groups on
the Fe3O4 NPs is verified.
SCHEME 2 SA‐DETA‐Fe3O4 catalyzed the oxidative coupling of
thiols to the disulfides
The anchored CPTMS on Fe3O4 NPs is confirmed by C–H
stretching vibrations that appear at 2956–2855 cm−1
(Figure 1b). Also the absorption around at 996 cm−1 is
attributed to Si–O stretching vibration. As shown in
Figure 1c, the functionalized DETA instead of Cl is con-
firmed by N–H stretching vibrations that appear at
3399 cm−1. Reaction of DETA‐Fe3O4 with chlorosufonic
acid produces SA‐DETA‐Fe3O4 (Figure 1d), in which the
presence of SO3H moiety is asserted with 1080, 1131,
and 1212 cm−1 bands in FT‐IR spectra. All of those bands
reveal that the surface of magnetic nanoparticles is success-
fully modified with sulfamic acid.
The morphological and size of the nanosolid was
evaluated using scanning electron microscopy (Figure 2).
The SEM images showed that the SA‐DETA‐Fe3O4 nanopar-
ticles are approximately spherical in shape and tend to
agglomerate into larger aggregates. According to Figure 2,
the diameter average for the SA‐DETA‐Fe3O4 nanoparticles
is about 15 nm.
The magnetic property of Fe3O4 NPs and SA‐DETA‐
Fe3O4 were characterized by VSM. The room temperature
magnetization curves of Fe3O4 NPs and SA‐DETA‐Fe3O4
are shown in Figure 3. The magnetic measurement shows that
The sulfamic acid loading on the surface of nanocompos-
ite was determined by back titration analysis. The data
obtained by back titration showed that the loading amount
of sulfamic acid is 1.1 mmolg−1
.
TABLE 2 SA‐DETA‐Fe3O4 catalyzed the oxidative coupling of thiols to the disulfides in CH3CN at room temperature
a
Entry
1
Thiol
Benzenethiol
Product
2a
Time (min)
Yield (%)
93
Mp (oc) [ref.]
60–62[25]
132–134[4]
56–57[26]
170–172[4]
92–94[4]
40–41[4]
Oil[27]
88–91[26]
82–83[28]
283–286[5]
88–89[26]
160–163[28]
68–71[5]
Oil[5]
45
25
40
15
50
15
15
35
30
25
40
35
50
40
45
2
Naphthalene‐2‐thiol
Pyridine‐2‐thiol
2b
2c
91
3
92
4
Benzo[d]thiazole‐2‐thiol
Benzo[d]oxazole‐2‐thiol
4‐Methylbenzenethiol
4‐Fluorobenzenethiol
4‐Bromobenzenethiol
2‐Aminobenzenethiol
2‐Mercaptobenzoic acid
2,6‐Dichlorobenzenethiol
4,6‐Dimethylpyrimidine‐2‐thiol
Phenylmethanethiol
2d
2e
97
5
85
6
2f
98
7
2g
94
8
2h
2i
97
9
91
10
11
12
13
14
15
2j
96
2k
2l
93
92
2m
2n
2o
90
2‐Mercaptoethanol
2‐Mercaptoacetic acid
93
91
Oil[5]
aIsolated yield.

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SHIRI ET AL.
Table 1. As seen on Table 1, the best results for product 2d
was obtained in the presence of 10 mg SA‐DETA‐Fe3O4
and 0.5 ml of 30% hydrogen peroxide in CH3CN at room
temperature (Table 1, Entry 3).
In order to explore the activity of the catalyst, various
thiols including aromatic and aliphatic thiols with various
functional groups were coupled in the presence of SA‐
DETA‐Fe3O4 under the optimized reaction conditions
(Scheme 2). The obtained results are listed in Table 2. As
shown in Table 2, the corresponding disulfides were obtained
in high yields in less than 50 min.
The proposed mechanism for the oxidative coupling of
thiols is designed in Scheme 3. Combination of H2O2 with
nano‐catalyst would prepare OH radical which would
subsequently react with thiol to form thiol radical, followed
by dimerization to afford final product (disulfide).[7]
SCHEME 3 Proposed mechanism for the oxidative coupling of
thiols using H2O2 catalyzed by SA‐DETA‐Fe3O4
2.3 | Catalytic studies
After the characterization of the nanosolid, the catalytic activ-
ity of sulfamic acid immobilized on diethylenetriamine‐func-
tionalized Fe3O4 nanoparticles (SA‐DETA‐Fe3O4) in the
oxidation reactions have been studied.
2.3.2 | Oxidation of sulfides
The oxidation of methyl phenyl sulfide was chosen as a
simple model reaction to appoint the possibility of the
strategy and optimize the reaction conditions. The collected
results are listed in Table 3. As shown in Table 3, in the
synthesis product 4a, the best results were obtained when
the 15 mg SA‐DETA‐Fe3O4 catalyst and 0.5 ml of 30%
hydrogen peroxide was used in CH3CN at room temperature.
The generality of this approach has been demonstrated by
facile oxidation of various sulfides (Scheme 4). The obtained
2.3.1 | Oxidative coupling of thiols
To evaluate the effect of various parameters (such as solvent
nature, catalyst and oxidant amount) on the system, the
oxidative coupling of benzo[d]thiazole‐2‐thiol as a model
reaction was studied. The obtained results are listed in
a
TABLE 3 Optimization of the reaction conditions
Entry
1
Catalyst (mg)
H2O2 (mL)
0.5
Solvent (Temp.oC)
CH3CN (r.t)
CH3CN (r.t)
CH3CN (r.t)
CH3CN (r.t)
CH3CN (r.t)
Acetone (r.t)
THF (r.t)
Time (min)
Yield (%) b
3
5
95
85
88
90
94
98*
98
82
88
83
94
89
89
94
97
98
10
2
0.5
3
10
15
20
15
15
15
15
15
15
15
15
15
‐‐
0.5
55
4
0.5
30
5
0.5
30
6
0.5
150
130
140
65
7
0.5
8
0.5
CH2Cl2 (r.t)
EtOH (r.t)
9
0.5
10
11
12
13
14
15
0.5
Ethylacetate (r.t)
CH3CN (r.t)
CH3CN (r.t)
CH3CN (r.t)
CH3CN (40 °C)
CH3CN (r.t)
120
70
0.3
0.4
45
0.6
30
0.5
60
0.5
120
aReaction conditions: The oxidation of methyl phenyl sulfide (1 mmol) using 30% H2O2 in the presence of catalyst and solvent (2 ml).
bIsolated yield.

SHIRI ET AL.
7 of 13
SCHEME 4 SA‐DETA‐Fe3O4 catalyzed the oxidation of sulfides to
the sulfoxides
results are listed in Table 4. As shown in Table 4, a variety
of sulfides were successfully oxidixed to the corresponding
sulfoxides in high yields. Thus, the results revealed that this
methodology is effective for the oxidation of a wide range
of sulfides.
As shown in Table 2 and 4, to show the chemoselectivity
of the presented protocol, a broad spectrum of sulfides and
thiols containing other functional groups were subjected to
the oxidation reactions. These functional groups remained
intact during the conversion of thiols to disulfides or sulfides
into sulfoxides. A plausible mechanistic path for the
sulfoxidation reactions is depicted in Scheme 5. Elucidation
for this process is the in situ formation of peroxyacid (A)
by the reaction of MNPs‐NSO3H or OSO3H with hydrogen
peroxide, followed by the oxygen transfer to the organic
substrate.[2]
SCHEME 5 Proposed mechanism for the oxidation of sulfides to
sulfoxide using H2O2 catalyzed by SA‐DETA‐Fe3O4
TABLE 5 OPTIMIZATION of the reaction conditions a
The amount
Solvent
Entry of catalyst (mg) (Temp.oC)
Time/min Yield (%)b
TABLE 4 SA‐DETA‐Fe3O4 catalyzed the oxidation of sulfides into
sulfoxides in ethanol at room temperature
1
3
5
H2O (70 °C)
H2O (70 °C)
H2O (70 °C)
H2O (70 °C)
CH3CN (reflux)
EtOH (reflux)
THF (reflux)
PhMe (reflux)
H2O (reflux)
H2O (60 °C)
H2O (70 °C)
40
30
92
94
2
Mp
3
10
15
10
10
10
10
10
10
‐‐
15
97*
97
Time Yield
(oc)
[ref.]
Product (min) (%)a
4
15
Entry
Sulfide
Oil[5]
5
80
85
1
2
Methyl phenyl sulfide
Benzyl phenyl sulfide
4a
4b
30
55
98
94
6
45
94
114–
116[4]
7
100
115
15
68
Oil[28]
Oil[5]
8
72
3
4
5
Ethyl phenyl sulfide
4c
4d
4e
75
15
45
96
91
90
9
96
Methyl furfuryl sulfide
10
11
30
95
Benzyl 4‐Methylphenyl
sulfide
119–
120[29]
60
Trace
6
7
4‐Chlorobenzyl 4‐
Methylphenyl sulfide
4f
75
45
88
92
155–
aReaction conditions: malononitrile (1.05 mmol) and 4‐chlorobenzaldehyde
(1 mmol) in the presence of catalyst and solvent (2 ml).
bIsolated yield.
158[29]
Benzyl 4‐bromophenyl
sulfide
4g
140–
142[29]
8
2‐(Methylthio)ethanol
2‐(Phenylthio)ethanol
Dibenzyl sulfide
4h
4i
15
25
50
90
89
93
Oil[28]
Oil[5]
9
10
4j
136–
139[4]
11
Dodecyl sulfide
4k
310
86
86–
88[4]
12
13
14
15
Dibutyl sulfide
4l
4m
4n
4o
15
50
60
15
94
93
91
90
Oil[5]
Oil[5]
Oil[5]
Oil[5]
Dipropyl sulfide
Diethyl sulfide
Tetrahydrothiophene
SCHEME 6 Knoevenagel condensation (KC) of active methylene
compounds with aromatic aldehydes catalyzed by SA‐DETA‐Fe3O4
aIsolated yield

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SHIRI ET AL.
and in the synthesis of carbocyclic as well as heterocyclic
compounds of biological significance.[37] Generally, it is the
condensation of aldehydes with active methylene group com-
pounds, which is catalyzed by basic sites to form carbon–
carbon bond.[38] After the observation of excellent obtained
results in the synthesis of 2,3‐dihydroquinazolin‐4(1H)‐ones,
we decide to study the catalytic activity of the SA‐DETA‐
Fe3O4 in the Knoevenagel condensation of aldehydes with
activated methylene groups. In this respect, to establish the
feasibility of the strategy, the reaction condition was
optimized with respect to the quantity of catalyst and solvent
nature as well as temperature by studying the condensation
of malononitrile and 4‐chlorobenzaldehyde as a model reac-
tion. The obtained results are listed in Table 5. As seen on
Table 5, 10 mg SA‐DETA‐Fe3O4 in water at 70 °C was
optimal condition for the desired reaction.
Subsequently, under the optimized reaction conditions,
Knoevenagel condensation of a diverse range of aromatic
aldehydes and two types of active methylene compounds
(malononitrile and ethyl cynoacetate) were investigated
(Scheme 6). The results obtained in the current method are
illustrated in Table 4. As shown in Table 4, all Knoevenagel
products (namely α,β ‐unsaturated products) were obtained
in good to excellent yields.
To show the superiority of this catalyst in comparison
with other reported catalysts, we summarized results for the
synthesis of products 2f, 4a and 6a in Table 6. It is clearly
showed that reaction time and product yield is better than
other protocols reported in literature. Also the new catalyst
is comparable in terms of price, stability, non‐toxicity and
easy separation.
A proposed mechanistic path for the Knoevenagel
condensation (KC) of active methylene compounds with
aldehydes is depicted in Scheme 7.
2.3.3 | Knoevenagel condensation
Knoevenagel condensation is one of the famous
reactions in organic synthesis
Knoevenagel products, namely the α,β ‐unsaturated products,
play a key role in the synthesis of fine chemical,[30] therapeu-
tic drugs,[31] natural products,[32] functional polymers,[33]
cosmetics,[34] perfumes,[35] hetero Diels‐Alder reactions[36]
TABLE 6 Comparison of the activity of various catalysts in the
synthesis of products 2f (Entries 1–5), 4a (Entries 6–10) and 6a
(Entries 11–15)
Time
(min)
Yield
(%)
Entry Product
Catalyst
[ref.]
[6]
1
2
3
4
2f
2f
2f
2f
Ni‐salen‐MCM‐41
Fe NPs@SBA‐15
Zr‐oxide@MCM‐41
25
45
30
72
95
94
98
83
[39]
[5]
[26]
Cu(II) Schiff base
MCM‐41
5
2f
SA‐DETA‐Fe3O4
15
98
This
work
[40]
6
7
8
9
4a
4a
4a
4a
NBS
270
240
156
20
93
88
95
93
[41]
[6]
TsOH
Ni‐salen‐MCM‐41
Cu(II) Schiff base
[26]
MCM‐41
10
4a
SA‐DETA‐Fe3O4
30
98
This
work
[42]
11
12
13
14
15
6a
6a
6a
6a
6a
PVC‐tepa
60
120
60
90
88
SO4−2/ZrO2
Mn salen complex
Lipase
[43]
[44]
[45]
100
94
720
15
SA‐DETA‐Fe3O4
97
This
work
SCHEME 7 Knoevenagel condensation (KC) of active methylene compounds with aldehydes catalyzed by SA‐DETA‐Fe3O4

SHIRI ET AL.
9 of 13
to 6 runs without any significant loss of its catalytic
activity. In addition, one of the attractive features of this
novel catalyst system is the rapid and efficient separation
of the catalyst by using an appropriate external magnet,
which minimizes the loss of catalyst during separation.
2.4 | Reusability of SA‐DETA‐Fe3O4
The recovery and reusability of catalyst is an important
aspect in catalytic processes. In this respect, the reusability
of SA‐DETA‐Fe3O4 was investigated in the synthesis of
products 2f, 4a and 6a. In these experiments, after
completion of the reaction, the catalyst was easily and rap-
idly separated from the product by an external magnet. The
separated magnetic nanocatalyst was further washed with
ethyl acetate to remove residual product. Then, the reaction
vessel was charged with fresh substrate and subjected to the
next. As shown in Figure 6, the catalyst can be recycled up
3 | CONCLUSIONS
In summary, we have demonstrated that SA‐DETA‐Fe3O4 is
a green, versatile and efficient acidic catalyst for the
oxidation of sulfides and oxidative coupling of thiols in
the presence of using H2O2. Furthermore, the SA‐DETA‐
Fe3O4 showed the high catalytic activity in Knoevenagel
condensation of various aromatic aldehydes with two types
of active methylene compounds (malononitrile and ethyl
cynoacetate). The advantages of this protocol are the use
of commercially available materials, ecofriendly conditions,
cheap oxidant, the mild reaction conditions, operational
simplicity, practicability and good to high yields of
reactions. Also the catalyst can be reused for many times
without any significant loss of its activity. More impor-
tance, SA‐DETA‐Fe3O4 has several advantages such as high
surface area, easily and readily available materials to
prepare, thermal and mechanical stability, ease of surface
modification, simple and inexpensive procedure of
preparation.
FIGURE 6 Reusability of SA‐DETA‐Fe3O4 in the synthesis of
products 2f, 4a and 6a
TABLE 7 SA‐DETA‐Fe3O4 catalyzed the one‐pot Knoevenagel condensation in water at 70 °C temperature
Entry
1
Substrate
4‐ClC6H5CHO
4‐OMeC6H5CHO
4‐MeC6H5CHO
4‐FC6H5CHO
4‐NO2C6H5CHO
4‐BrC6H5CHO
4‐(me)2NC6H5CHO
C6H5CHO
X/Y
Cn/Cn
Product
6a
6b
6c
Time (min)
Yield (%)a
97
Mp (oc) [ref.]
158–160[46]
184–186[46]
223–224[46]
197–199[47]
199–200[46]
201–203[47]
208–210[47]
218–220[46]
104–106[47]
107–109[48]
141–143[49]
96–98[50]
15
25
20
10
18
25
20
40
30
20
30
25
35
25
70
50
35
40
45
2
Cn/Cn
90
3
Cn/Cn
92
4
Cn/Cn
6d
6e
97
5
Cn/Cn
93
6
Cn/Cn
6f
91
7
Cn/Cn
6g
6h
6i
90
8
Cn/Cn
94
9
3‐NO2C6H5CHO
3‐BrC6H5CHO
2‐NO2C6H5CHO
2‐ClC6H5CHO
4‐ClC6H5CHO
4‐FC6H5CHO
4‐BrC6H5CHO
4‐MeC6H5CHO
4‐(me)2NC6H5CHO
3‐NO2C6H5CHO
2‐NO2C6H5CHO
Cn/Cn
89
10
11
12
13
14
15
16
17
18
19
Cn/Cn
6j
90
Cn/Cn
6k
6l
87
Cn/Cn
93
CN/CO2Et
CN/CO2Et
CN/CO2Et
CN/CO2Et
CN/CO2Et
CN/CO2Et
CN/CO2Et
6m
6n
6o
6p
6q
6r
85
93–95[47]
92
90–92[51]
90
89–91[47]
94
91–93[47]
87
120–122[47]
128–130[47]
100–102[52]
91
6s
88
aIsolated yield.

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SHIRI ET AL.
and stirred at 100 °C for 30 h under N2 atmosphere. Then,
the prepared functionalized magnetic nanoparticles were
separated by magnetic decantation and washed three times
with ethanol to remove the unattached substrates. The
resulting product was dried at room temperature.
4 | EXPERIMENTAL
4.1 | Materials
Chemicals were purchased from Fisher and Merck. The
reagents and solvents used in this work were obtained
from Sigma‐Aldrich, Fluka or Merck and used without
further purification. The infrared spectra (IR) of samples were
recorded in KBr disks using a NICOLET impact 410
4.5 | Preparation of SA‐DETA‐Fe3O4
The DETA‐Fe3O4 (0.5 g) was dispersed in CH2Cl2 (10 mL)
using an ultrasonic bath for 20 min. Then, chlorosulfonic
acid (1.5 ml) was added dropwise over a period of 20 min,
and the mixture was stirred for 3 h at room temperature.
Functionalized Fe3O4 nanoparticles (SA‐DETA‐Fe3O4) were
separated by magnetic decantation, washed four times with
dry CH2Cl2 and two times with EtOH, and dried at room
temperature.
1
spectrometer. HNMR and 13CNMR spectra were recorded
with a Bruker DRX‐400 spectrometer at 400 and 100 MHz
respectively. Nanostructures were characterized using a
Holland Philips X, pert X‐ray powder diffraction (XRD)
diffractometer (Co Kα, radiation = 0.154056 nm), at a
scanning speed of 2° min−1 from 10° to 80°. Scanning
electron microscope (SEM) was performed on a FEI Quanta
200 SEM operated at a 20 kVaccelerating voltage. The thermo-
gravimetric analysis (TGA) curves are recorded using a PL‐STA
1500 device manufactured by Thermal Sciences. The magnetic
measurements were carried out in a vibrating sample magne-
tometer (VSM, BHV‐55, Riken, Japan) at room temperature.
4.6 | General procedure for the oxidative
coupling of thiols to the disulfides
A mixture of thiol (1 mmol), hydrogen peroxide (0.5 mL) and
SA‐DETA‐Fe3O4 (10 mg) in CH3CN (2 ml) was stirred at
ambient temperature. Reaction progress was monitored by
TLC (acetone: n‐hexane, 2:8). After completion of the reac-
tion, catalyst was separated by external magnet and washed
with ethyl acetate, and next, the product was extracted with
ethyl acetate (5 ml × 4). The organic layer was dried over
anhydrous Na2SO4 (1.5 g). Finally, the organic solvents were
evaporated, and the corresponding disulfides were obtained
in high to excellent yields (90–98%).
4.2 | Preparation of the magnetic Fe3O4
nanoparticles
The mixture of FeCl3.6H2O (5.838 g, 0.0216 mol) and
FeCl2.4H2O (2.147 g, 0.0108 mol) were dissolved in
100 mL of deionized water in a three‐necked bottom
(250 ml) under N2 atmosphere. After that, under rapid
mechanical stirring, 10 mL of NH3 was added into the
solution within 30 min with vigorous mechanical stirring.
After being rapidly stirred for 30 min, the resultant black dis-
persion was heated to 80 °C for 30 min. The black precipitate
formed was isolated by magnetic decantation, washed with
double‐distilled water until neutrality, and further washed
twice with ethanol and dried at room temperature.
4.7 | General procedure for the oxidation of
sulfides to the sulfoxides
Immobilized tribenzyl ammonium‐tribromide on Fe3O4
nanoparticles SA‐DETA‐Fe3O4 (15 mg) was added to
solution of sulfide (1 mmol) and H2O2 (0.5 mL) in CH3CN
(2 ml). The reaction mixture was stirred at room temperature,
and the progress of the reaction was monitored by TLC
(acetone: n‐hexane, 2:8). After completion of the reaction,
catalyst was separated by external magnet and washed with
ethyl acetate, and next, the product was extracted with ethyl
acetate (5 ml × 4). The organic layer was dried over
anhydrous Na2SO4 (1.5 g). Finally, the organic solvents were
evaporated, and the corresponding sulfoxides were obtained
in high to excellent yields (86–98%).
4.3 | Preparation of CPTMS‐Fe3O4
The obtained magnetic nanoparticles (1.5 g) was dispersed in
250 ml ethanol/water (volume ratio, 1:1) by sonication for
30 min, and then CPTMS (2.5 ml) was added to the mixture
reaction. The reaction mixture was stirred using mechanical
stirring under N2 atmosphere at 40 °C for 8 h. then, the
nanoparticles was redispersed in ethanol by sonication for 5
times and separated through magnetic decantation. The
nanoparticles product (CPTMS‐Fe3O4) was dried at room
temperature.
4.8 | General procedure for Knoevenagel
condensation:
4.4 | Preparation of DETA‐Fe3O4
The CPTMS‐Fe3O4 (1.5 g) was dispersed in toluene (50 ml)
A mixture of aldehyde (1 mmol), activated methylene com-
pounds (1.05 mmol) and SA‐DETA‐Fe3O4 (10 mg) in water
(2 ml) was stirred at 70 °C. Reaction progress was monitored
by ultrasonic bath for 10 min. DETA (2 ml) was added

SHIRI ET AL.
11 of 13
by TLC (acetone: n‐hexane, 3:7). After time specified in
Table 7, reaction mass was allowed to cool down to room
temperature. Ethyl acetate (3 × 5 ml) was added to reaction
mixture and the catalyst was separated by an external magnet.
Ethyl acetate was evaporated under reduced pressure to
afford the crude products. The obtained crude products were
further recrystallized from ethanol to get the pure final prod-
ucts (85–97%).
7.47 (d, J = 8 Hz, 2H), 8.03 (s, 1H). 13C–NMR (100 MHz,
DMSO) δ = 15.24 (CH3), 55.31 (CH3O), 65.39 (O‐CH2),
102.33 (C‐CN), 113.77 (CN), 121.36, 126.51, 132.22,
139.33, 152.57, 162.26 (C = O).
ACKNOWLEDGEMENTS
This work was supported by the research facilities of Ilam
University, Ilam, Iran.
4.9 | Spectroscopic data
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How to cite this article: Shiri L, Narimani H,
Kazemi M. Synthesis and characterization of sulfamic
acid supported on Fe3O4 nanoparticles: A green,
versatile and magnetically separable acidic catalyst for
oxidation reactions and Knoevenagel condensation.
Appl Organometal Chem. 2017;e3927. https://doi.org/
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