Ni-SMTU@boehmite: As an efficient and recyclable nanocatalyst for oxidation reactions

Article abstract of DOI:10.1039/c6ra09950e

Boehmite nanoparticles were prepared via a simple and inexpensive procedure in water using commercially available materials, and furthermore a novel type of recoverable nanocatalyst was prepared via immobilization of the S-methylisothiourea complex of nickel on the surface of boehmite nanoparticles (Ni-SMTU@boehmite). This organometallic catalyst was characterized by FT-IR spectroscopy, TGA, XRD, ICP-OES, EDS and SEM techniques. Ni-SMTU@boehmite was applied as an efficient, recoverable and stable heterogeneous organometallic catalyst for the selective oxidation of sulfides to sulfoxides and oxidative coupling of thiols to corresponding disulfides. Metal leaching and heterogeneity test of this catalyst was examined by the ICP-OES technique, which showed that this catalyst can be recovered and reused for several times without significant loss of its catalytic efficiency or nickel leaching.

Full text of DOI:10.1039/c6ra09950e

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Ni-SMTU@boehmite: as an efficient and recyclable
nanocatalyst for the oxidation reactions
Cite this: DOI: 10.1039/x0xx00000x
∗
Arash GhorbaniꢀChoghamarani, Parisa Moradi and Bahman Tahmasbi
Department of Chemistry, Faculty of Science, Ilam University, P. O. Box 69315516, Ilam, Iran.
Received 00th January 2012,
Accepted 00th January 2012
Boehmite nanoparticles were prepared via simple and inexpensive procedure in water using
commercially available materials, and further a novel type of recoverable nanocatalyst was
prepared via immobilization of Sꢀmethylisothiourea complex of nickel on the surface of
boehmite nanoparticles (NiꢀSMTU@boehmite). This organometallic catalyst was characterized
by FTꢀIR spectroscopy, TGA, XRD, ICPꢀOES, EDS and SEM techniques. Niꢀ
SMTU@boehmite applied as an efficient, recoverable and stable heterogeneous organometallic
catalyst for the selective oxidation of sulfides to sulfoxides and oxidative coupling of thiols to
corresponding disulfides. Metal leaching and heterogeneity test of this catalyst was examined
by ICPꢀOES technique, which displayed this catalyst can recovered and reused for several
times without significant loss of its catalytic efficiency or Nickel leaching.
DOI: 10.1039/x0xx00000x
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∗
Address correspondence to A. GhorbaniꢀChoghamarani, Department of Chemistry, Ilam University, P.O. Box
69315516, Ilam, Iran; Tel/Fax: +98 841 2227022; Eꢀmail address: arashghch58@yahoo.com or
a.ghorbani@mail.ilam.ac.ir
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boehmite nanoparticles in this work. In order to regard of this
issue, nickel Sꢀmethylisothiourea complex has been
immobilized on boehmite nanoparticles and further applied as
an excellent nano organometal catalyst for the selective
oxidation of sulfides to sulfoxides and oxidative coupling of
thiols to corresponding disulfides. Because oxidation of sulfides
to sulfoxides and oxidative coupling of thiols into
corresponding disulfides are useful in the synthesis of new
molecules, as well as for various medical, chemical, biological,
materials, and nanotechnological applications [19ꢀ24].
1 Introduction
Nanoparticles due to their high surface area and facile recovery,
have recently emerged as catalyst supports [1, 2]. One of the
novel nanomaterial supports is boehmite (γꢀAlOOH) containing
hydroxyl groups attached to its surface. Boehmite has important
applications in the preparation of catalysts in petrochemical and
petroleum refining processes [3]. Another important application
of boehmite is produce of αꢀAl2O3 by calcinations at high
temperatures [4]. Boehmite is structure consists of double
sheets of octahedral with aluminum ions at their centers and the
sheets themselves are composed of octahedral chains and has a
cubic orthorhombic structure [5]. Boehmite (γꢀAlOOH) is also 2 Results and discussion
used as adsorbent, catalyst, cosmetic products, coatings,
vaccine adjuvants and composite reinforcement material in
2.1 Catalyst preparation
ceramics [6ꢀ8], due to its unique properties such as good In order to preparation of NiꢀSMTU@boehmite, initially the
porosity and thermal stability, high specific surface area (>120 boehmite nanoparticles was prepared according to new reported
m2/g) and mesoporous properties [4, 9]. It is well known that procedure
[25]
and
then
modified
using
(3ꢀ
boehmite is possesses excellent mechanical, electrical, thermal chloropropyl)trimethoxysilane (CPTES). Subsequently, the
and optical properties, excellent biocompatibility, chemical terminal Cl functionals were successfully reacted with Sꢀ
resistance, low cost and corrosion resistance and controllable methylisothiourea hemisulfate salt (SMTU) through substation
synthesis [10, 11].
A
major advantage of boehmite reaction to synthesis of nanoboehmite immobilized Sꢀ
nanoparticles is availability on a large industrial scale [12]. methylisothiourea (SMTU@boehmite). Finally nickel particles
Therefore, several methods have been described for preparation has been grafted on SMTU@boehmite via coordination of
of boehmite nanoparticles such as hydrothermal [13], sol–gel nickel on SMTU@boehmite (Scheme 1). This catalyst has been
[14], and hydrolysis of aluminum [15]. But, most of them have characterized by Fourier transform infrared spectroscopy (FTꢀ
focused on the morphologies, chemical and physical properties IR), thermogravimetric analysis (TGA), scanning electron
of the prepared particles; meanwhile, there is little literatures on microscopy (SEM), energyꢀdispersive Xꢀray spectroscopy
the modification of nanoboehmite surface as heterogeneous (EDS), Xꢀray diffraction (XRD), and inductively coupled
support [16ꢀ18]. Hence, an attempt has been made to modify of plasma atomic emission spectroscopy (ICPꢀOES).
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Scheme 1. Synthesis of NiꢀSMTU@boehmite.
2.2 Catalyst characterizations
The size of the catalyst was evaluated using SEM technique. The
SEM image of NiꢀSMTU@boehmite was shown that the catalyst
was formed of nanometreꢀsized particles (Figure 1).
Also the size and morphology of NiꢀSMTU@boehmite was studied
by TEM technique. As shown in Figure 2, the unit cells of Niꢀ
SMTU@boehmite was obtained in cubic orthorhombic structures
with about 20ꢀ40 nm in size.
Figure 1. SEM image of NiꢀSMTU@boehmite.
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29% and 41% from 200 to 800 °C is occurred for nClꢀPr@boehmite
and SMTU@boehmite, respectively.
100
90
a
80
70
b
c
60
d
50
40
0
200
400
600
800
Temperature(◦C)
Figure 4. TGA diagram of boehmite nanoparticles (a), nClꢀ
Pr@boehmite (b), SMTU@boehmite (c) and NiꢀSMTU@boehmite
(d).
The XRD patterns of boehmite nanoparticles is shown in Figure 5.
As shown in Figure 5, the boehmite phase was characterized by the
Figure 2. TEM images of NiꢀSMTU@boehmite.
To indicate the supporting nickel metal on boehmite surface, the peak positions at 14.41 (0 2 0), 28.40 (1 2 0), 38.56 (0 3 1), 46.45 (1
EDS analysis of NiꢀSMTU@boehmite was carried out. The EDS
patterns of NiꢀSMTU@boehmite is shown in Figure 3. As shown,
EDS spectrum of NiꢀSMTU@boehmite shows the presence of Al, O,
Si, C, S and N and as well as Ni specie in the catalyst. Also, to
obtained amount of nickel in NiꢀSMTU@boehmite, ICPꢀOES
analysis was performed. In this analysis, the amount of nickel in
catalyst was found to be 1.64 × 10ꢀ3 mol gꢀ1 based on ICPꢀOES.
3 1), 49.56 (0 5 1), 51.95 (2 0 0), 56.01 (1 5 1), 59.35 (0 8 0), 65.05
(2 3 1), 65.55 (0 0 2), 68.10 (1 7 1), and 72.40 (2 5 1) from the XRD
patterns, which all the peaks can be confirmed the crystallization of
boehmite with an orthorhombic unit cell [16].
6000
5000
4000
3000
2000
1000
0
0
20 40
2θ / degree
60
80
Figure 5. The XRD pattern of boehmite nanoparticles.
Figure 3. EDX spectrum of NiꢀSMTU@boehmite.
FTꢀIR spectrums of boehmite, nPrꢀCl@boehmite, SMTU@boehmite
and NiꢀSMTU@boehmite are shown in Figure 6. As shown in FTꢀIR
spectrum of the boehmite nanoparticles (Spectrum a), two strong
bands at 3086 and 3308 cm−1 are related to the both symmetrical and
asymmetrical modes of the hydroxyl groups on the surface of
boehmite nanoparticles [27]. In FTꢀIR spectrums aꢀd, several peaks
that appear about 480, 615 and 735 cm−1 can be corresponds to the
absorption of AlꢀO bonds [5]. Also, the nitrate impurity vibration by
a peak at 1637 cm−1 and the hydrogen bands (OH…OH) by two
absorption bands at 1164 and 1069 cmꢀ1 were observed in FTꢀIR
spectrums [7, 8]. In the FTꢀIR spectra of nPrꢀCl@boehmite
In order to determine the percent of organic functional groups
chemisorbed onto the surface of boehmite nanoparticles, the TGA
analysis of NiꢀSMTU@boehmite was performed. Figure 4 shows the
TGA curves for bare boehmite nanoparticles, nClꢀPr@boehmite,
SMTU@boehmite and the NiꢀSMTU@boehmite. In the all samples,
the first step of weight loss (below 200 °C) is owing to the removal
of the surface hydroxyl groups or physically and chemically
adsorbed solvents, and the other weight loss is appeared in the range
of 200ꢀ800 °C corresponds to the decomposition of the organic
fragments and organic ligands on boehmite nanoparticles [26]. The
decomposition of organic layer and Niꢀcomplex on boehmite
nanoparticles (a weight loss about 47%) was occurred in TGA curve
of the catalyst from 200 to 800 °C. Meanwhile, weight loss about
(Spectrum
b),
The
presence
of
the
anchored
chloropropyltrimethoxysilane is authenticated by C–H stretching
vibrations that appears at 2955 cm−1 and also OꢀSi stretching
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vibration modes that appear at 1073 cmꢀ1. In the FTꢀIR spectra of
SMTUꢀboehmite (Spectrum c), the existence of the grafted Sꢀ
methylisothiourea groups is identified by C=N vibrations that appear
at 1638 cm−1.
120
60
0
a
b
0
0.5
1
p/p0
Figure 7. Nitrogen adsorption–desorption isotherms of boehmite
nanoparticles (a) and NiꢀSMTU@boehmite (b).
2.3 Catalytic activity
After characterization of the prepared and characterized of catalyst,
we tested the catalytic activity of NiꢀSMTU@boehmite in the
oxidation of sulfides to sulfoxides (Scheme 2). In order to optimize
the reaction conditions, we examined the oxidation of methyl phenyl
sulfide as a model compound in various solvents, in the presence of
different amount of catalyst and using different amount of hydrogen
peroxide (H2O2). The results of these study are summarized in Table
1. As shown in Table 1, H2O2 (0.4 mL) in the presence of catalytic
amount of NiꢀSMTU@boehmite (0.004 g, 0.66 mol%) under
solventꢀfree condition at room temperature was found to be ideal the
reaction conditions for the conversion of methyl phenyl sulfide to
methyl phenyl sulfoxide. Also, inferior results were obtained in
acetonitrile, ethanol and ethylacetate as solvent.
O
S
Ni-SMTU@boehmite
Figure 6. FTꢀIR spectra of boehmite nanoparticles (a), nClꢀ
Pr@boehmite (b), SMTU@boehmite (c) and NiꢀSMTU@boehmite
(d).
S
R1
R2
R1
R2
H2O2 ,
Solvent Free, r.t.
Scheme 2. NiꢀSMTU@boehmite catalysed the oxidation of sulfides
to sulfoxides.
The nitrogen adsorptionꢀdesorption isotherms of boehmite
nanoparticles and NiꢀSMTU@boehmite are shown in Figure 7. It
can be seen that the BET surface decrease after immobilization of
organic layers and Niꢀcomplex on boehmite nanoparticles. The
decrease in surface area of NiꢀSMTU@boehmite is attributed to the
immobilization of organic layers and Niꢀcomplex on the boehmite.
These results are strong evidences that Niꢀcomplex was bonded on
the boehmite nanoparticles.
Table 1. Optimization of reaction conditions for the oxidation of methylphenyl sulfide in the presence of NiꢀSMTU@boehmite
using H2O2.
Entry NiꢀSMTU@boehmite (mg)
Solvent
H2O2 (mL)
Time
Yield
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(min)
130
75
75
75
70
65
75
75
(%)a
1
2
3
4
5
6
7
8
9
ꢀ
SolventꢀFree
SolventꢀFree
SolventꢀFree
SolventꢀFree
SolventꢀFree
SolventꢀFree
Acetonitrile
Ethanol
0.4
0.4
0.4
0.4
0.4
0.4
0.4
0.4
0.4
0.5
0.3
Traceb
53
2
3
4
5
6
4
4
4
4
4
78
97
96
98
50
81
42
98
Ethyl acetate
SolventꢀFree
SolventꢀFree
75
60
75
10
11
45
a Isolated yield, bthe reaction in the absence of catalyst.
The generality of this approach has been demonstrated by a facile other sulfides with different functional groups were successfully
oxidation of various sulfides. The result of this study was shown in employed to prepare the corresponding sulfoxides in excellent
Table 2. The sulfoxides were obtained in high yields. As shown, a yields. Therefore, the results revealed that this methodology is
variety of sulfides such as dialkyl sulfides, alkyl aryl sulfides, and effective for a wide range of sulfides.
Table 2. Oxidation of sulfides catalyzed by NiꢀSMTU@boehmite using H2O2.
Entry
Sulfide
Time (min)
Yield (%)a
97
Melting Point °C
29ꢀ31
1
75
2
3
4
5
5
97
95
95
Oil
Oil
Oil
10
5
6
15
92
86
134ꢀ136
Oil
120
7
70
89
115ꢀ117
8
9
300
60
90
91
Oil
Oil
a
Isolated
yield
Also, we examined the catalytic activity of Niꢀ dichloromethane, acetonitrile, and as well as solventꢀfree
SMTU@boehmite for the oxidative coupling of thiols into condition were used and the best results were obtained in
corresponding disulfides. Oxidative coupling of thiols into ethanol. As shown in Table 3, 4ꢀmethylthiophenol (1 mmol) in
disulfides using H2O2 in the present of this catalyst was shown the presence of catalytic amount of NiꢀSMTU@boehmite
in Scheme 3. For optimization of the reaction conditions, we (0.008 g, 1.3 mol%) in ethanol using 0.4 mL of H2O2 at room
examined the oxidative coupling of 4ꢀmethylthiophenol as a temperature was found to be ideal the reaction conditions for
model compound in the presence of different amount of catalyst the formation of 1,2ꢀdiꢀpꢀtolyldisulfane (Table 3, entry 2).
and using different amount of H2O2 (Table 3). To choose the
best reaction conditions, various solvents such as ethanol,
Scheme 3. NiꢀSMTU@boehmite catalysed the oxidative coupling of thiols into disulfides.
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Table 3. Optimization of the reaction conditions for the oxidative coupling of 4ꢀMethylthiophenol (1 mmol) in the presence of
different amounts of NiꢀSMTU@boehmite at room temperature in various solvents using H2O2.
Time
(min)
Entry
NiꢀSMTU@boehmite (mg)
Solvent
H2O2 (mL)
Yield (%)a
1
2
3
4
5
6
7
8
7
8
9
8
8
8
8
8
Ethanol
Ethanol
Ethanol
Acetonitrile
CH2Cl2
SolventꢀFree
Ethanol
0.4
0.4
0.4
0.4
0.4
0.4
0.5
0.3
80
80
60
80
80
80
75
80
75
94
95
43
Trace
Trace
96
Ethanol
72
a Isolated yield.
The generality of this approach has been demonstrated by a observed, and all products were obtained in high to excellent
facile oxidative coupling of aromatic and aliphatic thiols as yields in the short reaction time.
shown in Table 4. In all the reactions no any byproducts was
Table 4. Oxidative coupling of thiols catalyzed by NiꢀSMTU@boehmite.
Entry
1
thiol
Time (min)
Yield (%)a
Melting Point °C
SH
80
94
38ꢀ40
H3C
2
3
30
10
91
95
Oil
Oil
4
5
6
90
5
88
93
85
87ꢀ89
174ꢀ175
275ꢀ278
80
7
8
225
125
95
97
57ꢀ59
140ꢀ142
9
15
94
57ꢀ58
a Isolated yield.
To show the chemoselectivity of the presented protocol, the
sulfides and thiols containing other functional groups were
subjected to the oxidation reaction. These functional groups
remained intact during the conversion of sulfides to sulfoxides
and thiols to disulfides (Scheme 4).
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Scheme 4. Chemoselective oxidative coupling of thiols and oxidation of sulfides in the presence of other functional groups using
NiꢀSMTU@boehmite as catalyst.
Because these heterogeneous oxidation systems was performed
in mild conditions, overoxidation for oxidation of sulfides or
oxidative coupling of thiols was not observed (Scheme 5).
Scheme 5. Chemoselective oxidation of sulfides and thiols in the presence NiꢀSMTU@boehmite using H2O2 without
overoxidation.
On the basis of the literatures, a plausible reaction mechanism
A which is converted to active oxidant B. Next, nucleophilic
for oxidation of sulfides and oxidative coupling of thiols in the attack of the sulfide or thiol on this intermediate gives cation
presence of NiꢀSMTU@boehmite is shown in Scheme 6 [28, C1 or C2 which, in turn, produce the corresponding products.
29]. Reaction of H2O2 with Niꢀcatalyst leads to the intermediate
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S
S
R
R
S
O
S
Ni
N
R1
R2
S
Ni-SMTU@boehmite
R
H
H2O2
S
Ni
R1
O
S
S
N
R2
Ni
S
C1
N
O
Ni
R
O
O
S
C2
H
N
H
A
S
Ni
R1
S
O
N
S
R2
+ H2O
Ni
O
N
S
R
H
B
S
R2
R1
Scheme 6. Proposed mechanism for oxidation of sulfides and oxidative coupling of thiols in the presence of NiꢀSMTU@boehmite
using H2O2.
The reusability of the catalysts is one of their most important
advantages, which makes them useful for commercial
100
applications. We have found that NiꢀSMTU@boehmite was
rapidly recovered and demonstrated remarkably excellent
recyclability. In order to investigate this issue, the recyclability
of this catalyst was examined in the oxidation of
tetrahydrothiophene. After the completion of the reaction, the
catalyst was separated, washed with ethanol to remove residual
product and was dried. Then, fresh substrates was added to
remaining catalyst and employed for the next reaction. As
shown in Figure 8, this catalyst can be recycled up to 10 runs
without any significant loss of their catalytic activity or Ni
leaching.
In order to find the leaching of the catalyst, the amount of Ni in
recovered catalyst was calculated by ICPꢀOES after 10 runs
reused. The amount of Ni in recovered catalyst was found to be
1.31 × 10ꢀ3 mol g−1 based on ICPꢀOES after 10 times. Therefore
the catalyst can be reused without any significant leaching of
Nickel metal. Based on ICPꢀOES results, amount of Ni in the
catalyst after 10 runs recycled is comparable with fresh catalyst
(1.64 × 10ꢀ3 mol gꢀ1 for fresh NiꢀSMTU@boehmite) that
confirmed the leaching of Nickel in reaction mixture is
negligible.
80
60
40
20
0
1
2
3
4
5
6
7
8
9
10
Run number
Fig 8. The recycling experiment of NiꢀSMTU@boehmite in the
oxidation of tetrahydrothiophene.
2.4 Comparison of the catalyst
In order to examine the efficiency of this procedure, we compared
the results of the coupling oxidative of methyl(phenyl)sulfide in the
presence of NiꢀSMTU@boehmite with the previous methods in the
literatures (Table 5). It is obvious that described procedure in this
research project shows good reaction time and higher yield than the
other catalysts, which has been reported previously. Also this new
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catalyst is comparable in terms of price, nonꢀtoxicity, stability and catalyst is more than the previously reported catalysts.
easy separation. In addition, the number of the recyclability of this
Table 5. Comparison of NiꢀSMTU@boehmite for the oxidation of methyl(phenyl)sulfide with previously reported procedure.
Entry
Substrate
PhꢀSCH3
PhꢀSCH3
PhꢀSCH3
PhꢀSCH3
PhꢀSCH3
PhꢀSCH3
Catalyst
SiO2–W2–Im
polymerꢀanchored Cu(II)
VO2F(dmpz)2
CdꢀsalenꢀMCMꢀ41
TsOH
NiꢀsalenꢀMCMꢀ41
Heterocyclic amine salts of
Keggin heteropolyacids
NBS
Time (min)
150
Yield a (%) [Reference]
91.9 [30]
90 [31]
1
2
3
4
5
6
180
300
150
240
95[32]
98 [33]
88 [34]
95 [33]
156
7
PhꢀSCH3
120
95 [35]
8
9
10
PhꢀSCH3
PhꢀSCH3
PhꢀSCH3
270
360
75
93 [36]
98 [37]
97 [This work]
DSA@MNPs
NiꢀSMTU@boehmite
3 Conclusions
4.2 General procedure for the oxidation of sulfides
mixture of sulfide (1 mmol), H2O2 (0.4 mL) and Niꢀ
In summary, we have demonstrated that NiꢀSMTU@boehmite can
be used as an efficient and reusable nanocatalyst for the oxidative
coupling of a wide range of thiols into disulfides and also oxidation
of sulfides to sulfoxides using H2O2 at room temperature. This
catalyst can be prepared by a simple procedure from commercially
available and cheap materials. More importance, nanoboehmite is
new support for heterogenization of homogeneous catalysts, which
has several advantages such as high surface area, easily and readily
available material to prepare, thermal and mechanical stability, ease
of surface modification, easy and inexpensive procedure of
preparation. The catalyst has been characterized by SEM, EDS, ICPꢀ
OES, XRD, FTꢀIR and TGA.
A
SMTU@boehmite (0.004 g, 0.66 mol%) was stirred at room
temperature under solventꢀfree condition and the progress of the
reaction was monitored by TLC. After completion of the reaction,
catalyst was separated using filtration and washed with ethyl acetate,
and the product was extracted with ethyl acetate. The organic layer
was dried over anhydrous Na2SO4 (1.5 g). Finally, the organic
solvents were evaporated, and products were obtained in good to
high yield.
4.3 General procedure for the oxidative coupling of thiols
NiꢀSMTU@boehmite (0.008 g, 1.3 mol%) was added to a mixture of
thiol (1 mmol) and H2O2 (0.4 mL) in ethanol (4 mL). Then the
mixture was stirred for the appropriate time at room temperature.
The progress of reaction was monitored by TLC. After completion
of the reaction, the catalyst was separated by filtration and the
mixture was washed with ethyl acetate. The product was extracted
with ethyl acetate. The organic layer was dried over anhydrous
Na2SO4 (1.5 g). The products were obtained in good to high yield.
4 Experimental
4.1 Preparation of catalyst
The solutions of NaOH (6.490 g) in 50 ml of distilled water was
added to solutions of Al(NO3)3.9H2O (20 g) in 30 ml distilled water
as drop to drop under vigorous stirring. The resulting milky mixture
was subjected to mixing in the ultrasonic bath for 3 h at 25 ºC. The
resulted nanoboehmite was filtered and washed by distilled water
and were kept in the oven at 220 ºC for 4 h. The obtained boehmite
nanoparticles (1.5 g) was dispersed in 50 mL toluene by sonication
for 30 min, and then 2.5 mL of (3ꢀcholoropropyl)triethoxysilane
(CPTES) was added to mixture. The reaction mixture was stirred at
40 ºC for 24 h. Then, the prepared nanoparticles (nClꢀPr@boehmite)
was filtered, washed with ethanol and dried at room temperature.
The obtained nClꢀPr@boehmite (1g) were dispersed in 50 mL
ethanol for 20 min, and then Sꢀmethylisothiourea hemisulfate salt
(2.5 mmol) and potassium carbonate (2.5 mmol) were added to the
reaction mixture and stirred for 28 h at 80 ºC. Then, the resulting
nanoparticles (SMTU@boehmite) was filtered, washed with ethanol
and dried at room temperature. The obtained SMTU@boehmite (0.5
g) was dispersed in 25 mL ethanol by sonication for 20 min, and
then Ni(NO3)2.6H2O (1 mmol) was added to the reaction mixture.
The reaction mixture was stirred at 80 ºC for 20 h. The final product
(NiꢀSMTU@boehmite) was filtered, washed by ethanol and dried at
room temperature.
4.4 Selected spectral data:
Tetrahydrothiophene 1-oxide (Table 2, entry 2): H NMR (400
1
MHz, CDCl3): δ = 2.25 (t, J= 7.61 Hz, 2H), 3.06 (t, J= 7.6 Hz, 2H)
ppm.
1
1,2-di-p-tolyldisulfane (Table 4, entry 1): H NMR (400 MHz,
CDCl3): δ = 2.35 (s, 6H), 7.14 (d, J= 7.9 Hz, 4H), 7.42 (d, J= 7.9 Hz,
4H) ppm.
2,2'-Disulfanediyldiethanol (Table 4, entry 3): 1H NMR (400
MHz, CDCl3): δ = 2.60 (br, 2H), 2.89 (t, J= 5.6 Hz, 4H), 3.91 (t, J=
5.6 Hz, 4H) ppm.
Acknowledgements
This work was supported by the research facilities of Ilam
University, Ilam, Iran.
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Graphic Abstract:
Ni-SMTU@boehmite: as an efficient and recyclable nanocatalyst for the
oxidation reactions
Arash Ghorbani-Choghamarani*, Parisa Moradi, Bahman Tahmasbi
An efficient heterogenized nickel catalyst was synthesized on boehmite nanoparticles and
characterized by TGA, FT-IR, XRD, SEM, EDS and ICP-OES techniques. The catalytic activity
of this organometallic catalyst was applied in the selective oxidation of sulfides and oxidative
coupling of thiols in environmentally friendly solvent and solvent-free condition. The catalyst
was reused for several runs without significant loss of its catalytic efficiency or Nickel leaching.