Highly efficient, green, rapid, and chemoselective oxidation of sulfur-containing compounds in the presence of an MCM-41@creatinine@M (M = la and Pr) mesostructured catalyst under neat conditions

Article abstract of DOI:10.1039/c7nj05189a

In the present study, we report the synthesis of two green recoverable catalysts by covalent linking of the creatinine La and Pr complexes on an MCM-41 mesostructure with the commercially available materials and via a simple and inexpensive procedure. These heterogeneous catalysts were characterized by Fourier transform infrared spectroscopy, energy-dispersive X-ray spectroscopy, scanning electron microscopy, N₂ adsorption and desorption, inductively coupled plasma optical emission spectroscopy, and thermogravimetric analysis. The obtained mesostructures act as active and reusable catalysts for the oxidation of sulfides and oxidative coupling of thiols under neat conditions. More importantly, significant practical advantages of this environmentally friendly process include high efficiency, good reaction times, and convenient recovery and reusability for several times without any significant loss of activity of the catalyst.

Full text of DOI:10.1039/c7nj05189a

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PAPER
Jason B. Benedict et al.
The role of atropisomers on the photo-reactivity and fatigue of
diarylethene-based metal–organic frameworks
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A highly efficient, green, rapid, and chemoselective
oxidation of sulfur containing compounds in presence
of MCM-41@creatinine@M (M= La and Pr)
mesostructured catalyst under neat conditions
Received 00th January 20xx,
Accepted 00th January 20xx
DOI: 10.1039/x0xx00000x
Taiebeh Tamoradi,a Mohammad Ghadermazi,a,* Arash Ghorbaniꢀ
www.rsc.org/
Choghamaranib,*
In the present study, we report the synthesis of two green recoverable catalysts by covalent
linking of creatinine La and Pr complexes on MCMꢀ41 mesostructured via commercially
available materials and simple and inexpensive procedure. These heterogeneous catalysts were
characterized by Fourier transform infrared spectroscopy, energyꢀdispersive Xꢀray
spectroscopy, scanning electron microscopy, N2 adsorption and desorption, inductively
coupled plasma optical emission spectroscopy and thermal gravimetric analysis. The obtained
mesostructures act as active and reusable catalysts for oxidation of sulfides and oxidative
coupling of thiols under neat conditions. More importantly, significant practical advantages of
this environmentꢀfriendly process are high efficiency, good reaction times, convenient
recovery and reusability for several times without any significant loss of activity.
developed for the construction of organic compounds and
synthetic intermediates, which most of these supports exhibit
1 Introduction
disadvantages such as expensive, use of atmosphere or high
temperature for calcination or preparation, unstable and tedious
recycling procedures [14ꢀ16]. In the recent years, considerable
research was paid towards development of mesoporous
nanoparticles, especially mesoporous silica nanoparticles
(MSNs) with a diameter below 200 nm as immobilized support.
It should be noted that the mesoporous silica materials with
nanoꢀsized pores and controllable porous structure and pore
volume can use as a suitable catalyst support for organic
transformations. Also, silica mesoporous nanocomposite in
particular MCMꢀ41 was represented several significant features
in comparison with its heterogeneous catalysts [17ꢀ20]. Indeed,
among the different types of mesoporous supports, mesoporous
MCMꢀ41 has excellent properties such as high activity,
uniform pore structure, excellent stability (chemical and
thermal), good accessibility, lager surface area, associated with
high thioresistance for the hydrogenation of aromatics found in
diesel fuels, and inert environment for immobilization of
transition metal nanoparticles [21ꢀ25]. It is noteworthy that the
ability to stabilize reactive metal ions in mesoporous silica
framework due to their low toxicity and low cost has made
them unique in heterogeneous catalysis. The walls of the porous
system of MCMꢀ41 can be easily modified with anchoring of
different ligands into the hexagonal channels [26,27]. On the
other hand, mesostructured catalysts can be used as recoverable
and reusable heterogeneous catalysts in the oxidation of
sulfides, oxidative coupling of thiols [28ꢀ30]. Disulfides and
sulfoxides, among organic sulfur compounds, have attracted
great interest because of the large number of applications, such
as precursors or intermediates in the synthesis of natural
products and valuable physiologically and pharmacologically
active molecules as well as important integral and
supplementary parts in many pharmaceutical and biological
During the recent years, ‘‘Green Chemistry’’ has received
considerable importance in several key research areas, such as
catalysis, the design of safer chemicals and environmentally
benign solvents [1]. Therefore, significant progress has been
made in several key research areas, such as catalysis, the design
of safer chemicals and environmentally benign solvents in order
to increasing attention to problems of chemical pollution and
resource depletion that minimize the use and generation of
hazardous substances [2ꢀ4] .In this regard, the heterogeneous
catalysts has attracted a great deal of attention in recent times,
since the potential advantages of these materials such as
simplified recovery and providing improved reusability in the
designed systems can have positive environmental effects.
Indeed, the use of reusable heterogeneous catalysts is important
issues in organic synthesis because of their chemical, economic,
environmental, and industrial aspects [5ꢀ9]. Despite the
widespread applications of the heterogeneous catalysts, these
catalysts have lower catalytic activities than their hemogeneous
counterparts. To overcome these drawbacks, in order to
combine the advantages of both homogeneous and
heterogeneous catalysis, immobilization of homogeneous
catalysts on heterogeneous nanomaterials can use as an
efficiently bridge the gap between homogeneous and
heterogeneous catalysis [10ꢀ13]. Up to now, a diverse range of
supports such as zeolite, carbon nanotubes, graphene,
heteropolyacids, ionic liquids or some polymers have been
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active molecules such as cystine, DTNB (Ellman’s reagent or
5,50ꢀdithioꢀbis(2ꢀnitrobenzoic acid), omeprazole and fipronil
[31ꢀ33]. In the present work, we report synthesis of La and Pr
complex supported on mesoporous silica by anchoring of
creatinine on the wall of functionalized MCMꢀ41, then reacted
with La (NO3)2.6H2O and Pr(NO3)2.5H2O, respectively. On the
other hand, the prepared catalysts were investigated for
oxidation of sulfides and oxidative coupling of thiols, which
exhibit a high stability and catalytic activity in these reactions.
High surface area, convenient recovery and reusability for
several times without any significant loss of activity, the use of
a commercially available, ecoꢀfriendly, cheap and chemically
stabile reagents, good reaction times and simple practical
methodology; makes this protocol both attractive and
economically viable.
2.2 Catalyst characterization
These prepared heterogeneous catalysts were characterized by
Fourier transform infrared spectroscopy, scanning electron
microscopies, energyꢀdispersive Xꢀray spectroscopy, inductively
coupled plasma optical emission spectroscopy, Xꢀray diffraction,
thermal gravimetric analysis, and N2 adsorption and desorption, and
by their comparisons with that of authentic sample. Afterward, the
structure of obtained catalyst was characterized by FTꢀIR, TGA,
ICPꢀOES, EDX, XRD and SEM.
2.2.1 Thermogravimetric analysis
Fig. 1 showed the quantitative determination of lanthanum and
praseodymium complexes onto the surface of organically modified
mesoporous silica by thermoꢀgravimetric analysis (TGA). It should
be noted that the first weight loss below 200 °C might be due to
removal of hydroxyl groups and adsorbed solvents. More
importantly, the thermal analysis further demonstrates that the
imobilization of lanthanum and praseodymium complexes were
successfully occurred on MCMꢀ41 structure. Therefore, the second
weight loss in the range of 200–600 °C may be associated the
decomposition process of immobilized organic spaces on calcined
MCMꢀ41 surface. Based on TGA data, the weight losses of MCMꢀ
41 from 200 to 600 °C is 3 %. It can be seen that TGA curves of the
MCMꢀ41@creatinine@La and MCMꢀ41@creatinine@Pr were
shown a weight loss 16 % from 200 to 600 °C. Also, based on ICP,
La and Pr content of described catalyst were 6.4 and 5.8 %,
respectively. It can be concluded that the MCMꢀ41 content of MCMꢀ
41@creatinine@La and MCMꢀ41@creatinine@Pr was 77.6 and
2 Results and discussion
2.1 Catalyst preparation
Following the method reported on application of heterogeneous
catalyst in for oxidation of sulfides and oxidative coupling of
thiols [34ꢀ37], we decided to prepare two novel and green
heterogeneous catalysts for this purpose. Initially, MCMꢀ41
particles were prepared according to a previous report by
Hajjami et al [38] and subsequently coated with 3ꢀ
chloropropyltrimethoxysilane (CMTS). Also, immobilized
creatinine ligand on mesostructured MCMꢀ41 was successfully
synthesized by using the surface modification strategy as
depicted in Scheme 1. Then, MCM
‐41@creatinine@La and
MCM 41@creatinine@Pr catalysts were prepared using stable
‐
interaction between the N and O atoms of creatinine and M 78.2 %, respectively. Therefore, these results were confirmed that La
(M=La and Pr). The proposed structure is designed according to and Pr complexes have been anchored on the surface of MCMꢀ41.
recently reported procedure [39]. It should be noted that
creatinine was chosen as a green, available, cheap and readily
available chelating ligand.
HO
HO
HO
Condensation of silica
Calcination
Fig. 1 TGA curves of MCM‐41, MCMꢀ41@creatinine@La and
MCMꢀ41@creatinine@Pr.
CPTMS
Toluene,
Reflux, 24h
2.2.2 N2 adsorption–desorption studies
M(NO3)3
Creatinine
M= La or Pr
In the field of solid catalysis, the nitrogen adsorption and desorption
isotherms have been a powerful tool for determine the textural
properties of nano or mesoporous material. The N2 adsorption–
desorption measurements (BET and BJH methods) of MCM‐41,
MCMꢀ41@creatinine@La and MCMꢀ41@creatinine@Pr are shown
in Fig. 2. On the basis of this observation, the BET analysis of
MCMꢀ41 was shown a surface area of 1113.7 m2 gꢀ1, whereas the
BET analysis of MCMꢀ41@creatinine@La and MCMꢀ
41@creatinine@Pr were shown a surface area of 584.79 and 620.22
m2 gꢀ1, respectively. It was observed that the pore diameter and
volume drastically decreased with the incorporation of La and Pr
complexes into the MCMꢀ41 sample (Table 1). We can conclude
that the immobilization of La and Pr complexes have taken place
substantially inside the pore channels of MCMꢀ41.
EtOH,
Reflux, 16h
Toluene,
Reflux, 48h
O
O
N
N
M
N
N
Cl
Si
H
H
N
N
Si
Si
O
O
O
O
O
O
O
O
O
MCM-41@creatinine
MCM-41@creatinine@M
MCM-41-Cl
Scheme 1 Synthesis of MCM‐41@creatinine@M (M=La and
Pd).
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Table 1
Texture parameters obtained from nitrogen adsorption studies.
Sample
SBET (m2 gꢀ1)
Pore diameter by BJH
Pore volume
method (nm)
2.39
(cm3 gꢀ1)
1.39
MCMꢀ41
1113.7
584.79
620.22
MCMꢀ41@creatinine@La
MCMꢀ41@creatinine@Pr
1.01
0.673
0.714
1.21
Fig. 2 Nitrogen adsorption/desorption isotherms of MCM‐41 (a), MCM‐41@creatinine@La and MCM‐41@creatinine@Pr.
2.2.3 X-ray diffraction
The crystalline structures of the MCMꢀ41, and MCM‐
41@creatinine@La and MCM‐41@creatinine@Pr were determined
by powder Xꢀray diffraction (XRD). In all materials, well‐resolved
peaks with very intense diffraction peaks indicated that can be
indexed as (100), (110), and (200) reflections attributed to the
presence a hexagonal space group symmetry P6mm. After the
immobilization of La and Pr complexes on the wall of functionalized
MCMꢀ41, an overall decrease in diffraction (100), (110) and (200)
reflections was noticed that is due to the difference in the scattering
contrast of the pores and the walls of nanochannels of MCMꢀ41 (Fig.
3). Also, the peak shifting at (100) plane can be observed after
immobilization of La and Pr complexes on the inner channel pores.
Therefore, it can be concluded that the formation of the catalyst has
taken place preferentially inside the pore system of the MCMꢀ41.
Fig. 3 Small angle XRD patterns of MCM 41 (blue), MCM
41@creatinine@La (red) and MCM 41@creatinine@Pr (green).
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were made up of quite homogeneous and uniform spherical particles
and no significant changes in the morphology occurred after
anchoring of lanthanum and praseodymium complexes onto the
2.2.4. FT-IR spectroscopy
Fig.4 shows the FTꢀIR spectra of MCM‐41, MCM‐41@Cl, MCMꢀ
41@creatinine,
MCMꢀ41@creatinine@La
and
MCMꢀ surface of mesoporous MCMꢀ41 silica.
41@creatinine@Pd in the 400–4000 cmꢀ1. It should be mentioned
that the Fourier transform infrared spectroscopy is helpful to
examine the synthesis process. The presence of peaks at 481, 820
and 1079 to 1225 cmꢀ1 was most probably due to the symmetric and
asymmetric stretching vibrations of framework and terminal Si–O
groups (Fig. 1a). Also, the presence of peaks at 2950 and 2850 cmꢀ1
was most probably due to the C–H stretching vibrations (Fig. 4b).
The CꢀN and C=O stretching peaks at 1250 and 1710 cm−1 indicate
that the surface of silica is successfully modified by creatinine ligand
(Fig 4c). On the basis of these observations, Fig. 1d and 1e indicate
that the bending vibration absorption band of N–H is shifted to lower
wavenumbers, which is perhaps due to the robust interaction
between the N groups of La and Pr complexes on the MCMꢀ41.
Fig. 5 FESEM images of MCM‐41 (a), MCMꢀ41@creatinine@La
(b) and MCMꢀ41@creatinine@Pd (c) at 500 nm (top) and 1 µm
(down).
It should be noted that the immobilization of La and Pr complexes
on mesoporous MCMꢀ41 were confirmed through the presence of N,
O, C, Si, La and Pr species in EDX analysis of these synthesized
catalyst (Fig. 6). Also, the exact amount of La and Pr loaded on
surface of modified mesoporous silica are found to be 0.46 and 0.41
mmol gꢀ1 using the ICP atomic emission spectroscopy technique.
More importantly, interpretations made on the basis of ICP results
are supported by the EDX data.
Fig. 6 EDX spectrum of MCMꢀ41@creatinine@La (a) and MCMꢀ
41@creatinine@Pd (b).
2.3 Catalytic studies
Fig. 4 FTꢀIR spectrum for bare of MCM‐41 (a), MCM‐41@Cl (b),
MCMꢀ41@creatinine (c), MCMꢀ41@creatinine@La (d) and MCMꢀ
41@creatinine@Pr (e).
After characterization of the MCM‐41@creatinine@La (I) and
MCM‐41@creatinine@Pr (II), we examined the catalytic activity of
these catalysts as efficient, stable, recyclable and commercially
viable catalysts in the oxidation of sulfides to sulfoxides (Scheme 2)
and oxidative coupling of thiols to disulfides (Scheme 4) in the
present of H2O2 (30%) as oxidant under neat conditions at room
temperature. In order to find the best reaction conditions, the
oxidation of methylphenyl sulfide using H2O2 (30%) was selected as
a model compound in the presence of different amounts of MCM‐
2.2.5 Scanning electron microscopy
Fig. 5 shows the FESEM images of the MCMꢀ41 (a), MCMꢀ
41@creatinine@La (b) and MCMꢀ41@creatinine@Pr (c) for
investigation of the surface morphology of the obtained
nanostructure. According to the FESEM images, prepared samples
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41@creatinine@Pr in various solvents as well as solventꢀfree
conditions. The results of observation are summarized in Table 2. In
initial experiments, the solvent effect was examined that good yields As it is evident from Tables 3, under the obtained optimized
were obtained in solventꢀfree. Then, the amount of catalyst was also conditions, the various sulfides including several of functional
examined, and 0.005 g of MCM‐41@creatinine@Pr was found to be groups were successfully employed to prepare the corresponding
optimal. Also, it was found that a lower yield was observed when the sulfoxides in the presence of MCM‐41@creatinine@La (I) and
amount of the catalyst was decreased. Finally, the amount of H2O2 MCM‐41@creatinine@Pr (II) as catalyst. All products are obtained
was examined that optimization condition were obtained in 0.4 mL in the short reaction time and in good to excellent yields. Also, we
H2O2 for in the synthesis of methylphenyl sulfoxide. More
importantly, because of mild conditions of described heterogeneous
found that the coupling reaction yield and time was susceptible to
type of catalyst. It is important to note that these results were
systems, there is no overoxidation to sulfone for oxidation of obtained by comparing the effect of prepared catalysts trough the
sulfides.
oxidation of sulfide to corresponding sulfoxides. As listed in Table
3, the effect of catalyst was carefully investigated and the best results
were obtained in the presence of MCM‐41@creatinine@Pr. The
obtained results are summarized in table 3.
Scheme 2. Oxidation of sulfides to the corresponding sulfoxides.
Table 2 Optimization of reaction conditions for the oxidation
of methylphenyl sulfide in the presence of MCM‐
41@creatinine@Pr using H2O2.
Catalyst
(mg)
H2O2
Time
(min)
35
35
35
35
35
35
35
Entry
Solvent
Yield (%)a
(mL)
0.4
0.4
0.4
0.4
0.4
0.4
0.4
0.5
0.3
0.4
1
2
3
4
5
6
8
9
5
5
5
5
4
6
3
5
5
0
EtOH
63
42
38
94
73
95
49
95
63
Ethyl acetate
Acetonitrile
SolventꢀFree
SolventꢀFree
SolventꢀFree
SolventꢀFree
SolventꢀFree
SolventꢀFree
SolventꢀFree
35
35
10 h
10
11
Trace
a Isolated yield.
Table 3 Oxidation of sulfides to the sulfoxides in the presence of prepared catalysts.
Entry Substrate
Product
Time (min)
Yield (%)a
TOF (hꢀ1)
Cat (I)
Cat (II)
35
Cat (I) Cat (II) Cat (I)
Cat (II)
786.06
1
2
3
40
55
35
92
96
95
94
95
600
2a
2b
2c
50
35
455.34
708.07
556.1
97
91
722.98
4
5
45
55
35
50
87
91
504.35
431.62
760.97
544.39
2d
2e
93
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6
7
5
5
99
89
96
5165.22
273.15
5619.5
2f
85
80
92
336.58
2g
8
55
35
96
91
455.34
760.97
2h
9
50
75
45
70
91
93
92
95
474.78
323.48
598.37
397.21
2i
2j
10
11
75
70
75
60
87
93
90
313.04
351.22
439.02
2k
2l
12
90 346.58
aIsolated yield
Finally, a plausible reaction mechanism for oxidation of sulfides in conditions for the oxidative coupling of 4ꢀmethylbenzenethiol. Also,
the presence of catalyst is proposed on the basis of the literatures because of mild conditions of described heterogeneous systems, all
(Scheme 3) [8].
the reactions take place with total selectivity. The results of this
study are summarized in Table 4.
Scheme 4. Oxidative coupling of thiols into disulfides.
Table
4
Optimization of oxidative coupling of 4ꢀ
methylthiophenol using MCM 41@creatinine@Pr under
various conditions.
Catalyst
(mg)
H2O2 Time
Entry
Solvent
Yield (%)a
(min)
(mL)
1
2
3
4
5
6
7
8
9
5
5
5
5
4
3
5
6
5
0
SolventꢀFree
Ethyl acetate
Acetonitrile
EtOH
0.4
0.4
0.4
0.4
0.4
0.4
0.5
0.4
0.3
0.4
40
40
40
40
40
40
40
40
40
71
47
58
97
78
48
97
98
77
Scheme 3 Proposed mechanism for the oxidation of sulfides
presence of catalyst.
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
As the second part of our organic study, we also studied the
synthesis of disulfide compounds from reaction of 4ꢀ
methylbenzenethiol (1 mmol) and H2O2 as a model reaction. Hence,
the reaction conditions in the synthesis of disulfide derivatives were
optimized for above mentioned reaction under the influence of
different amounts of MCM‐41@creatinine@Pr as catalyst in various
solvents as well as solventꢀfree conditions. It was observed that
0.005 g MCM‐41@creatinine@Pr catalyst in the presence of 0.4 mL
H2O2 in EtOH at room temperature was found to be ideal reaction
10
10 h
Trace
a Isolated yield.
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Then, under the optimized reaction conditions, we shown the
generality of this approach by a facile oxidation of various sulfides. Therefore, based on theoretical principles and proposed mechanisms
As shown in Table 5, a variety of sulfides with different functional in Scheme and 5, the catalytic activity of MCMꢀ
3
groups were successfully employed to prepare the corresponding 41@creatinine@Pr is better than the MCMꢀ41@creatinine@La.
sulfoxides. It can be seen that the sulfoxides were obtained in high
yields in the presence of MCM‐41@creatinine@La (I) and MCM‐
41@creatinine@Pr (II) as catalyst. It should be noted that the effect
of catalyst was carefully investigated and the best results were
obtained in the presence of MCM‐41@creatinine@Pr. MCM
41@creatinine@La and MCM 41@creatinine@Pr were acted as
Lewis acids. Pr and La were metals in the 4f block lanthanide series.
More importantly, MCMꢀ41@creatinine@Pr is a stronger Lewis
acid than MCM 41@creatinine@La.
Table 5 Oxidation of sulfides to the sulfoxides in the presence of prepared catalysts.
Yield
Entry Substrate
Product Time (min)
TOF (hꢀ1)
(%)a
Cat (I) Cat (II)
Cat (I) Cat(II)
96 91
97
Cat(I)
Cat(II)
443.9
1
2
65
50
60
45
3 85.28
495.65
2a
2b
95
630.89
794.42
3
4
35
45
35
91
95
92
678.26
562.32
2c
40
97
637.17
2d
5
6
7
55
55
35
50
93
88
90
91
87
441.1
532.68
565.85
917.07
2e
2f
45
417.39
670.81
30
94
2g
8
50
65
40
45
60
40
95
85
91
87
495.65
341.14
593.48
565.85
439.02
680.49
2h
2i
9
90
10
93
90
91
2j
11
50
60
45
93
90
485.22
391.3
585.36
484.26
2k
2l
12
55
aIsolated yield.
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It should be mentioned that proposed mechanism for this process
using H2O2 as oxidant in the presence catalyst is outlined in Scheme
5 [8].
H
+
S
O
R
O
M
S
N
R
S
S
R
O
R
H
N
N
N
M
H
N
H
N
M=La or Pr
H2O2
Fig. 7 Reusability of MCM‐41@creatinine@Pr in the oxidation of
methyl phenyl sulfide and MCM‐41@creatinine@La in oxidative
coupling of 2ꢀnaphthalenethiol.
S
R
H
N
H
O
N
H
3.5 Catalyst leaching study
N
M
Finally, using ICPꢀOEIS technique, the exact amount of metal
leaching was studied by checking the amount of metal loading on
modified MCMꢀ41 before and after recycling of the catalyst. Based
on ICPꢀOEIS analysis of the prepared catalysts, the recycled MCM‐
41@creatinine@Pr in the oxidation of methyl phenyl sulfide and the
recycled MCM‐41@creatinine@La in oxidative coupling of 2ꢀ
naphthalenethiol after several times recycling is 0.31 and 0.28 mmol
gꢀ1, respectively. Also, the oxidative of methyl phenyl sulfide in the
presence of MCM‐41@creatinine@Pr and oxidative coupling of 2ꢀ
mercaptoethanol in the presence of has been investigated to perform
hot filtration experiment under optimized reaction conditions. In the
oxidation of methylphenyl sulfide and oxidative coupling of 2ꢀ
mercaptoethanol, we found the yield of product under optimized
conditions in half time of the reaction that it was 67 and 58 %,
respectively. Then, described reactions were repeated and in half
time of the reaction, the catalysts were separated from reaction
mixture and allowed the iltrate to react further under identical
reaction conditions. The yield of reaction in this stage was 70 and 62
% the oxidation of methylphenyl sulfide and oxidative coupling of 2ꢀ
mercaptoethanol, respectively, that confirmed the leaching of metal
hasn’t been occurred.
N
N
O
N
O
M
O
O
H
Scheme 5. Proposed mechanism for oxidative coupling of thiols in
presence of catalyst.
3.4 Reusability of the catalyst
One of outstanding advantages of these heterogeneous catalysts over
its homogeneous counterpart is its easy separation from reaction
media and the possibility of reusing the catalyst after reaction.
Therefore, in continuation of our studies in the introduction of novel
and green catalysts, the reusability of described catalysts was
examined using the synthesis of methylphenyl sulfoxide and 1,2ꢀ
di(naphthalenꢀ2ꢀyl)disulfane in after several reaction cycles. In this
procedure, after completion of each reaction, the recovered catalyst
was washed with ethyl acetate to remove residual product and the
catalyst reused for next reactions for several times without any
significant loss of its catalytic activity or metal leaching (Fig.7).
3.6 Comparison of the catalyst
To show the merit of prepared catalysts in comparison with other
reported catalysts, the activity of described catalysts in comparison
with the best of the reported data in the literatures was evaluated
(Table 6). It is observed that all synthesized mesostructured catalysts
showed good reaction time and better performance than the wellꢀ
known catalyst from the literature as out lined in the Table 6. In
these nanohybrid robust catalysts represents the attractive features
including operational simplicity, facile synthesis, environmental
friendliness, and recyclability of the catalyst by simple filteration as
well as the ability to tolerate a wide variety of substitutions in the
reagents.
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Table 6 Comparison results of prepared catalysts with other catalysts in the oxidation reaction.
Substrate
Entry
Catalyst
Time (h)
1.58
Yield (%)
TOF (hꢀ1)
Refs.
[40]
[41]
methylphenyl sulfide
1
3
Niꢀcomplexꢀboehmite
RuII(TMP)(CO)
98
90
213.43
270
methylphenyl sulfide
methylphenyl sulfide
methylphenyl sulfide
methylphenyl sulfide
methylphenyl sulfide
methylphenyl sulfide
methylphenyl sulfide
methylphenyl sulfide
1.5
4
22.8
178.2
ꢀ
[42]
SiO2–2ꢀImSiO2–2ꢀIm
Mn(III)–salphen
2.5
0.53
1
86
95
23
14
89
90
92
5
[43]
6
This work
This work
This work
This work
This work
This work
MCMꢀ41
7
ꢀ
MCMꢀ41@creatinine
creatinine@La
1
8
579.9
745.4
600
0.68
0.61
0.66
9
creatinine@Pr
10
11
MCMꢀ41@creatinine@La
786.06
methylphenyl sulfide
4ꢀMethylbenzenthiol
4ꢀMethylbenzenthiol
MCMꢀ41@creatinine@Pr
NiꢀSMTU@boehmite
Fe3O4ꢀAdenineꢀZn
Fe NPs @ SBAꢀ15
0.58
1.33
1.5
94
94
99
94
97
19
10
92
93
95
97
12
13
53.95
[8]
235.71
[13]
4ꢀMethylbenzenthiol
4ꢀMethylbenzenthiol
14
15
0.75
0.25
1
29.19
[45]
[46]
165.12
Fe3O4/salen of Cu(II)
MCMꢀ41
4ꢀMethylbenzenthiol
4ꢀMethylbenzenthiol
4ꢀMethylbenzenthiol
4ꢀMethylbenzenthiol
4ꢀMethylbenzenthiol
4ꢀMethylbenzenthiol
16
17
18
19
20
21
ꢀ
This work
This work
This work
This work
This work
This work
MCMꢀ41@creatinine
creatinine@La
1
ꢀ
0.80
0.71
0.83
0.66
472.5
609.1
495.65
630.89
creatinine@Pr
MCMꢀ41@creatinine@La
MCMꢀ41@creatinine@Pr
a Isolated yield.
Tetraethylorthosilicate (TEOS), cetyl trimethylammonium
bromide (CTAB), creatinine dipropylsulfide, diethylsulfide,
dibenzylsulfide, benzylphenylsulfide, tetrahydrothiophene,
3 Conclusions
In this work, we reported two novel and green recoverable
heterogeneous catalytic system by simple and inexpensive
procedure. Then, these nanohybrids were carefully
characterized by FTꢀIR, XRD, TGA, BET, SEM and ICPꢀOES
techniques. It was be found that heterogeneous catalysts could
be easily separated by applying a simple filteration and reused
several consecutive runs without appreciable change in its
catalytic activity. These mesostructures were exhibited
enhanced catalytic performance compared to other similar
reported catalysts, and has been successfully utilized for the
oxidation of sulfur containing compounds using urea hydrogen
peroxide (UHP) under condition under mild conditions. More
importantly, these nanohybrid robust catalysts has excellent
advantages such as high surface area, the use of a commercially
available, chemically stabile reagents, ecoꢀfriendly, low cost,
operational simplicity, good reaction times and high efficiency
in the aboveꢀmentioned reactions.
dodecyl
methylsulfide,
methylphenylsulfide,
2ꢀ
(phenylthio)ethanol, diphenyl sulfide, benzo[d]thiazoleꢀ2ꢀthiol,
benzyl mercaptan, 4ꢀmethylbenzenethiol, naphthaleneꢀ2ꢀthiol,
2ꢀmercaptopyridine, thiophenol, benzo[d]oxazoleꢀ2ꢀthiol, 2ꢀ
mercaptoacetic
acid,
4ꢀbromothiophenol,
3ꢀ
chloropropyltrimethoxysilane (CPTMS), triethylamine, H2O2
(33 %), La (NO3)3.6H2O and Pr(NO3)3.5H2O and all solvents
used in this work are purchased from Merck, Flucka or Aldrich
and used without further purification.
4.2 Measurement
Infrared sample spectra were examined on a Bruker VERTEX
80 v model using the KBr pellets in the range of 400˗4000 cmꢀ
1.The elemental analysis of the samples was done by Energyꢀ
dispersive Xꢀray spectroscopy (EDAX, TSCAN). Measuring
the Amount of metal in synthesized nanostructure was
investigated by inductively coupled plasma optical emission
spectrometry (ICPꢀOES). Powder Xꢀray diffraction (XRD)
measurements were done using Co radiation source with a
4 Experimental
4.1 Materials
wavel length
= 1.78897 Å, 40 kV at various points.
Thermogravimetric analysis (TGA) was carried out on
Shimadzu DTGꢀ60 instrument in different temperatures. The
surface morphology of synthesized nanostructural material
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1
were investigated by measuring SEM using FESEMꢀTESCAN
MIRA3.
Dibenzyl sulfoxide (Table 3, entry 4). H NMR (400 MHz,
CDCl3): δH= 3.90 (d, 2H, J= 12.8 Hz), 3.95 (d, 2H, J= 12.8 Hz),
7.29ꢀ7.43 (m, 10H) ppm.
4.3 Preparation of MCM‐41@creatinine
1
Dodecyl methyl sulfoxide (Table 3, entry 10). H NMR (400
Mesoporous MCMꢀ41 was synthesized through the solꢀgel
method by previous report by Hajjami et al [38].
Cetyltrimethylammonium bromide (CTAB), as structure
directing template agent, was dissolved in a solution containing
3.5 mL of NaOH solution (2 M) and deionized water (480 mL)
at 80 °C under stirring condition. After TEOS (5 mL) as the
silica source was gradually added to the solution and the
mixture stirred at the same temperature for 2 h. Finally, the
solid product wasrecovered by filtration and washed with
deionized water and dried in an oven at 60 ˚C followed by
calcination at at 823 K for 5 h at a rate of 2 °C/ min to remove
the residual surfactants. The collected product affords pure
silica MCMꢀ41. Additionally, the reaction mixture was
filteration and washed with nꢀhexane and dried under vacuum
to obtain chlorꢀfunctionalized MCMꢀ41 (MCMꢀ41ꢀCl). Then,
creatinine (0.226 g) was added to a suspension of the MCMꢀ41ꢀ
Cl (1 g) in toluene (30 mL). The resulting mixture stirred under
reflux conditions for 48 h, filtered, washed thoroughly with
ethanol/water and dried in vacuum.
MHz, DMSO): δH= 0.87 (t,
J=6.8, 3H), 1.26–1.71 (m, 20H),
2.58(s, 3H), 3.09 (t, =8, 2H) ppm.
J
1,2-Bis(4-bromophenyl)disulfane (Table 5, entry 10
)
.
1H
= 8, Hz, 4H), 7.53 (t, J
NMR (400 MHz, CDCl3): δH= 7.44 (t,
= 8, Hz,4H) ppm.
J
1,2-Di(naphthalen-2-yl)disulfane (Table 5, entry 11). 1H
NMR (400 MHz, DMSO): δH= 7.50–7.57 (m, 4H), 7.67–7.75
(m, 2H), 7.89–7.93 (m, 4H), 7.96ꢀ8.00 (m, 2H), 8 (s, 2H) ppm.
1,2-Bis(4,6-dimethylpyrimidin-2-yl)disulfane (Table 5, entry
12). 1H NMR (400 MHz, CDCl3, ppm): δH
= 2.50 (s, 12H), 6.87
(s, 2H) ppm.
Acknowledgements
We gratefully acknowledge the support of this work by
University of Kurdistan and University of Ilam.
4.4 Preparation of MCM
‐
‐
41@creatinine@La
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DOI: 10.1039/C7NJ05189A
Graphical abstract
A highly efficient, green, rapid, and chemoselective oxidation of sulfur
containing compounds in presence of MCM-41@creatinine@M (M= La and
Pr) mesostructured catalyst under neat conditions
Taiebeh Tamoradi,a Mohammad Ghadermazi,a,∗ Arash Ghorbani-Choghamarani b,∗
MCM-41@creatinnine@M (M= La and Pr) as highly efficient and reusable
heterogeneous catalyst prepared by a simple procedure for the oxidation of
sulfur containing compounds.
∗
Address correspondence to University of Kurdistan, Department of Chemistry, Faculty of Science,
Sanandaj, Iran.; e-mail: mghadermazi@yahoo.com (M. Ghadermazi) or Department of Chemistry,
Faculty of Science , Ilam University, P.O. Box 69315516, Ilam, Iran; Tel/Fax: +98 841 2227022; E-mail
address: arashghch58@yahoo.com or a.ghorbani@ilam.ac.ir (A. Ghorbani-Choghamarani).