Synthesis and characterization of MCM-41@XA@Ni(II) as versatile and heterogeneous catalyst for efficient oxidation of sulfides and acetylation of alcohols under solvent-free conditions

Article abstract of DOI:10.1007/s13738-017-1265-z

Herein, Ni(II) immobilized on modified mesoporous silica MCM-41 was designed and synthesized via a facile sequential strategy. The structure of the catalyst was characterized by X-ray diffraction. The thermal property of the as-synthesized materials was studied using thermogravimetric-differential thermal analysis. The average particles size and morphology of MCM-41@XA@Ni(II) were investigated using scanning electron microscopy and transmission electron microscopy. This nanostructure catalyst was effective for the selective oxidation of sulfides and acetylation of alcohols in solvent-free conditions. The easy recyclability of the catalyst and their complete chemoselectivity toward the sulfur group of substrates in the oxidation of sulfides are important “green” attributes of this catalyst.

Full text of DOI:10.1007/s13738-017-1265-z

Journal of the Iranian Chemical Society
https://doi.org/10.1007/s13738-017-1265-z
ORIGINAL PAPER
Synthesis and characterization of MCM‑41@XA@Ni(II) as versatile
and heterogeneous catalyst for efcient oxidation of sulfdes
and acetylation of alcohols under solvent‑free conditions
Somayeh Nazarzadeh1,2 · Arash Ghorbani‑Choghamarani3 · Elham Tahanpesar2
Received: 24 May 2017 / Accepted: 1 December 2017
© Iranian Chemical Society 2017
Abstract
Herein, Ni(II) immobilized on modifed mesoporous silica MCM-41 was designed and synthesized via a facile sequential
strategy. The structure of the catalyst was characterized by X-ray difraction. The thermal property of the as-synthesized
materials was studied using thermogravimetric-diferential thermal analysis. The average particles size and morphology of
MCM-41@XA@Ni(II) were investigated using scanning electron microscopy and transmission electron microscopy. This
nanostructure catalyst was efective for the selective oxidation of sulfdes and acetylation of alcohols in solvent-free condi-
tions. The easy recyclability of the catalyst and their complete chemoselectivity toward the sulfur group of substrates in the
oxidation of sulfdes are important “green” attributes of this catalyst.
Keywords Oxidation · MCM-41@XA@Ni(II) · Xanthine · Sulfde · Sulfoxide · Alcohol
Introduction
ease of product separation with the selectivity founded with
homogeneous complexes. In approaches for catalytic reac-
tions, the recovery and reuse of the catalyst are an impor-
tant factor because of stringent ecological and economic
demands for sustainability [8]. Thus, the development of
efcient catalytic systems for various organic transforma-
tions is an active ongoing research area and the scope for
further improvement toward milder reaction conditions
[9]. Among the mesoporous silica and their hybrid materi-
als, MCM-41 displays a very large specifc surface area of
approximately 1000 m2 g−1 [10]. These characteristics of
MCM-41 make MCM-41 very interesting to be used as an
attractive support for homogeneous catalysts [11].
In recent years, there has been a rapid growth in the devel-
opment of novel supported compounds (such as supported
catalysts, reagents and scavengers) and their applications for
industry and laboratory purposes [1]. In contrast to novel
nanomaterial absorbents, e.g., silica nano-sheets, nanofl-
tration membranes [2–5], a great deal of attention has been
paid to mesoporous silica and their hybrid materials espe-
cially as catalysis and sorption materials due to their large
specifc surface area, high removal efciency for removal
of dye pollutants, high porosity, controlled morphology and
easy functionalization [6, 7].
In the last decade, much efort has been paid to immobi-
lize the homogeneous catalysts onto supports because such
heterogenization of homogeneous catalysts may combine the
The vast chemistry of sulfoxides makes them very useful
reagents in organic synthesis in general and useful synthetic
intermediates for the construction of various chemically and
biologically signifcant molecules in particular [12–15].
Organic sulfoxides are useful and active intermediates in
both laboratory and industry and organic synthesis. There-
fore, the chemoselective oxidation of organic sulfdes to the
corresponding sulfoxides has been the subject of various
studies for the past two decades [16–18]. An additional chal-
lenge in this respect is to make such processes environmen-
tally friendly by strategies such as using nontoxic solvents,
green oxidants and energy-efcient catalytic methods.
* Arash Ghorbani-Choghamarani
arashghch58@yahoo.com; a.ghorbani@ilam.ac.ir
1
2
3
Department of Chemistry, Khuzestan Science and Research
Branch, Islamic Azad University, Ahvaz, Iran
Department of Chemistry, Ahvaz Branch, Islamic Azad
University, Ahvaz, Iran
Department of Chemistry, Faculty of Science, Ilam
University, P. O. Box 69315516, Ilam, Iran
Vol.:(0123456789)
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Journal of the Iranian Chemical Society
Also, protection of functional groups plays an important
role in the synthesis of complex organic molecules such as
natural products. Acetylation has found increasing attention
as highly familiar protocols for the protection of functional
groups in this context [19]. The protection of hydroxyl
groups of alcohols via formation of esters is one of the most
important and used transformations in organic chemistry
[20]. A variety of procedures are routinely performed for
the preparation of acetyl derivatives [21, 22]. However, some
of the reported methods for the acetylation of alcohols sufer
from one or more of the following disadvantages: doing the
reaction in high temperature, harsh reaction conditions, the
formation of undesirable by-products, expensive reagents,
long reaction times and low yields of the desired products.
Thus, the introduction of new catalytic systems for the prep-
aration of esters is still in demand in the chemical process.
Therefore, in continuation of our interest in the develop-
ment of a highly expedient methodology for the synthesis
of fne chemical compounds and the introduction of new
catalysts [23–26], we report here a new and environmentally
friendly protocol for the oxidation of sulfdes and protec-
tion of hydroxyl groups of alcohols catalyzed by MCM-41@
XA@Ni(II) as a recoverable and heterogeneous nanocatalyst
under mild reaction conditions.
Experimental
Synthesis of (3‑chloropropyl)
triethoxysilane‑functionalized MCM‑41 (MCM‑41@
CPTES)
Mesoporous MCM-41 was synthesized using the sol–gel
method according to the previously reported procedure [22].
After synthesis of mesoporous MCM-41, post-synthesis
organic modifcation of the mesoporous material was per-
formed by stirring 2 g of MCM-41 with 3 mL solution of
(3-chloropropyl) triethoxysilane in 100 mL dry toluene for
48 h. The resulting white precipitate was fltered and washed
using dry toluene and dried under vacuum.
Synthesis of xanthine immobilized on the MCM‑41@
CPTES
The as-prepared MCM-41@CPTES was dissolved in dry
toluene, and 2 mmol of xanthine was added to the mix-
ture; then, the mixture was refuxed at 90 °C for 48 h. After
completion of the reaction, the resulting solid was fltered
and washed with ethanol and distilled water. Finally, the
obtained powder dried to obtain xanthine immobilized on
the MCM-41@CPTES (MCM-41@XA.
Scheme 1 Preparation of MCM-41@XA@Ni(II)
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Journal of the Iranian Chemical Society
Synthesis of Ni(II) immobilized on MCM‑41@XA
(MCM‑41@XA@Ni(II))
- -
Si O Si
In the last step, Ni(NO3)2·6H2O (2.5 mmol) and MCM-41@
XA (1 g) in absolute ethanol (100 mL) were added into a
250-mL round-bottom fask; the mixture was refuxed for
24 h. After cooling down, the resulting catalyst was fltered
and washed with ethanol several times. Finally, the obtained
white solid dried under vacuum to obtain MCM-41@XA@
Ni(II).
=
C N
NH
General procedure for the oxidation of sulfdes
to sulfoxides using catalytic amounts of MCM‑41@
XA@Ni(II)
A mixture of sulfde (1 mmol) and H2O2 (0.4 mL) in sol-
vent-free conditions was stirred for an appropriate time at
room temperature in the presence of MCM-41@XA@Ni(II)
(0.01 g). After completion of the reaction, ethylacetate was
added to the reaction mixture and the insoluble catalyst was
fltered. The fltrate washed with water (5 mL) and dried
Fig. 1 Comparison of FTIR spectra of a MCM-41, b MCM-41@
CPTES, c MCM-41@XA and Ni(II) immobilized on MCM-41@XA
Fig. 2 XRD pattern of MCM-41@XA@Ni(II)
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Journal of the Iranian Chemical Society
Fig. 3 a SEM images and b EDS pattern of MCM-41@XA@Ni(II)
over anhydrous Na2SO4. Then, the organic medium was
removed under reduced pressure to give the corresponding
pure sulfoxide in high to excellent yield.
ethylacetate: n-hexane, 3:7), dichloromethane (20 mL) was
added and the catalyst was separated by fltration. Then, the
mixture was diluted with CH2Cl2. The organic phase washed
with 10% aqueous solution of sodium bicarbonate and dried
over Na2SO4. Finally, the organic solvents were evaporated
and the product obtained with high to excellent yield.
General procedure for the preparation of acetate
compounds
Alcohol (1 mmol) was added to a mixture of MCM-41@
XA@Ni(II) (0.03 g) and acetic anhydride (0.4 mL), and the
resulting mixture was stirred at 50 °C in solvent-free condi-
tion. After completion of the reaction (mentioned by TLC,
Selected spectral data
1
2-Phenyleacetate (Table 4, entry 2). HNMR (400 MHz,
CDCl3): δ = 7.2–7.4 (m, 5H), 4.35 (t, J = 3.6 Hz, 2H), 2.95
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Journal of the Iranian Chemical Society
Fig. 4 Transmission electron microscopy (TEM) of MCM-41@XA@Ni(II) catalyst
C–H in all samples. In the FTIR spectrum of MCM-41@
(t, J = 3.6 Hz, 2H), 2.05 (s, 3H) ppm; IR (KBr): 3461, 3087,
3063, 2958, 1741, 1604, 1495, 1453, 1365, 1240, 1032, 912,
749, 751, 700, 641, 496 cm−1.
XA, the stretching vibration bands at 3420 cm−1 (N–H) and
1627 cm−1 (C=N) confrm the presence of xanthine onto the
pores of mesoporous MCM-41. These observations were
shown the immobilization of xanthine and then Ni(II) onto
the surface of the MCM-41 (Fig. 1).
1
4-Methoxybenzylacetate (Table 4, entry 1). HNMR
(400 MHz, CDCl3): δ = 7.28–7.37 (m, 2H), 6.90–6.96 (m,
2H), 5.05 (s, 2H), 3.85 (s, 2H), 2.1 (s, 2H) ppm; IR (KBr):
3060, 2925, 2840, 1739, 1614, 1517, 1464, 1381, 1243,
1176, 1113, 1032, 962, 824 cm−1.
Figure 2 shows the X-ray difraction pattern of MCM-
41@XA@Ni(II) that exhibits the difraction peak corre-
sponding to difraction at (100), (110) and (200) plane of
hexagonal phase. This proves that no change in the XRD
patterns of MCM-41 was observed after functionalization
and the framework structure does not deteriorate seriously
during treatment with organic groups [22].
1
Methylphenyl sulfoxide (Table 2, entry 1). HNMR
(500 MHz, CDCl3): δ = 7.45 (m, 5H), 2.6 (s, 3H) ppm.
1
Dodecylmethyl sulfoxide (Table 2, entry 9). HNMR
(400 MHz, CDCl3): δ = 0.9 (T, J = 3.4 Hz, 3H), 1.2–1.53
(m, 18 H), 1.70–1.83 (m, 2H), 2.64–2.80 (m, 2H), 2.55 (s,
3H) ppm.
The morphology of MCM-41@XA@Ni(II) was investi-
gated using scanning electron microscopy (SEM). Scanning
electron microscopy confrms the presence of uniform par-
ticles size with a spherical shape for the catalyst. Also, the
existence of metallic Ni in nanocatalyst was also confrmed
by the EDS detector coupled to the SEM, which showed the
presence of Ni in functionalized mesoporous MCM-41. In
addition, the exact nickel content of the nanocatalyst was
determined by inductively coupled plasma optical emission
spectroscopy (ICP-OES) analysis that to be 2.6 × 10−3 mol/g
(Figs. 3, 4).
Results and discussion
Scheme 1 shows the schematic illustration for the synthesis
of MCM-41@XA@Ni(II).
The structure of MCM-41@XA@Ni(II) nanocomposite
was fully characterized using FTIR, SEM, TEM, ICP-OES
and XRD techniques.
The average particles size and morphology of the cata-
lyst were investigated by transmission electron microscopy
(TEM). As shown in Fig. 5, the sample is highly ordered;
also the hexagonal structure was still retained for the sup-
ported catalysts. Also, it was found that Ni(II) complex
grafting did not cause a drastic change in the morphology
of MCM-41.
Characterization of MCM‑41@XA@Ni(II)
In order to confrm the existence of organic groups on the
surface of MCM-41, FTIR spectra of MCM-41, MCM-
41@CPTES, MCM-41@XA and MCM-41@XA@
Ni(II) were probed as shown in Fig. 4. The sharp features
around 1085 cm−1 and the absorption peak at 458 cm−1 are
assigned to asymmetric stretching and bending vibration
of Si–O–Si. The presence of the stretching vibration bands
around 2849–2956 cm−1 correspondence to the aliphatic
The thermal analysis of MCM-41@CPTES (curve a)
shows initially a negligible weight loss (2%) in the region
of 90–250 °C because of loss of physically absorbed water
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Journal of the Iranian Chemical Society
Fig. 5 TG–DTG curve of a MCM-41@CPTES and b MCM-41@XA@Ni(II)
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Journal of the Iranian Chemical Society
Table 1 Optimization of the
reaction conditions in the
oxidation of methylphenyl
sulfde
Entry
Substrate
Solvent
Catalyst (g)
Time (min)
Yield (%)a
1
2
3
4
5
6
7
8
Methylphenyl sulfde
Methylphenyl sulfde
Methylphenyl sulfde
Methylphenyl sulfde
Methylphenyl sulfde
Methylphenyl sulfde
Methylphenyl sulfde
Methylphenyl sulfde
Methylphenyl sulfde
Methylphenyl sulfde
Methylphenyl sulfde
EtOH
CH3CN
EtOAc
n-Hexane
CH2Cl2
0.01
0.01
0.01
0.01
0.01
0.01
0.01
0.00
0.003
0.005
0.007
120
120
120
120
120
120
60
60
60
60
60
25
10
30
10
15
15
90
0/00
40
65
85
CHCl3
Solvent free
Solvent free
Solvent free
Solvent free
Solvent free
9
10
11
Reaction condition: sulfde (1 mmol), H2O2 30% (0.4 mL)
aIsolated product
and organic solvents. A second weight loss (14%) occurred
in the temperature range of 280–550 °C, which is attributed
to the loss of immobilized organic groups on the surface of
MCM-41. The weight loss in the third stage (450–700 °C)
is very slight and is about 2%, which may be attributed to
the thermal decomposition of silanol groups. Curve b that
related to MCM-41@XA@Ni(II) which is similar to curve
“a” shows that the small weights loss (4%) in the ranges of
90–150 °C and (~ 2%) in the ranges of 150–250 °C are prob-
ably due to the evaporation of physically adsorbed water and
trapped water and organic solvents, respectively. A weight
loss (~ 24%) is detected in the range of 250–400 °C and
400–650 °C which is predominantly attributed to the decom-
position of organic substances in the synthesized MCM-
41@XA@Ni(II).
Scheme 2 Oxidation reaction of methylphenyl sulfde
Evaluation of the catalytic activity of MCM‑41@XA@
Ni(II)
acetonitrile (Table 1, entries 1–6). Interestingly, the desired
product was achieved in high yield when the reaction was
conducted in the absence of any solvent, i.e., solvent-free
conditions (Table 1, entry 7). The yield and rate of the reac-
tion were also found to be dependent on the concentration
of the catalyst. Thus, to obtain the optimal value of catalyst,
we also investigated the reaction in the presence of diferent
amounts of catalyst. The results are summarized in Table 1.
The results revealed that the best yield of the desired sulfox-
ide was obtained by carrying out the reaction in solvent-free
conditions, in the presence of 0.01 g of the catalyst using
H2O2 as the oxidant (Scheme 2).
To show the efciency of the synthesized nanocatalyst,
the catalytic potential of the MCM-41@XA@Ni(II) was
explored for the oxidation of sulfdes to sulfoxides. In order
to optimize the reaction conditions, the efect of various
parameters on the oxidation of methylphenyl sulfide as
model substrate was investigated. Since solvent has pro-
nounced efect on the outcome of the reaction, the reac-
tion was carried out in the various solvents. As shown in
Table 1, a relatively lower yield was obtained when the
reaction was carried out in organic solvents such as chloro-
form, dichloromethane, ethanol, n-hexane, ethylacetate and
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Journal of the Iranian Chemical Society
Table 2 Oxidation of sulfdes
in the presence of MCM-41@
XA@Ni(II)
Entry
1
Substrate
Product
Time (min)
60
Yield (%)a
90
m.p. [Refs.]
Oil [27]
2
3
60
45
90
95
Oil [27]
Oil [27]
4
5
6
50
90
60
95
88
93
Oil [23]
133–135 [23]
Oil [27]
7
8
50
45
98
95
Oil [28]
Oil [29]
9
CH3(CH2)10CH2SCH3
CH3(CH2)10CH2SOCH3
45
95
56–59 [27]
Reaction condition: sulfde:H2O2:Cat. (1 mmol:0.4 mL:10 mg)
aIsolated product
Scheme 3 General route for the oxidation of sulfdes to sulfoxides
Scheme 4 Acetylation of 4-methoxybenzyl alcohol
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Journal of the Iranian Chemical Society
Table 3 Optimization of the
reaction conditions for the
acetylation of 4-methoxybenzyl
alcohol
Entry
Substrate
Solvent
Catalyst (g)
Time (min)
Yield (%)a
1
2
3
4
5
6
7
8
9
4-Methoxybenzyl alcohol
4-Methoxybenzyl alcohol
4-Methoxybenzyl alcohol
4-Methoxybenzyl alcohol
4-Methoxybenzyl alcohol
4-Methoxybenzyl alcohol
4-Methoxybenzyl alcohol
4-Methoxybenzyl alcohol
4-Methoxybenzyl alcohol
Acetone
CH3CN
EtOAc
n-Hexane
CH2Cl2
Solvent free
Solvent free
Solvent free
Solvent free
0.03
0.03
0.03
0.03
0.03
0.03
0.00
0.01
0.02
360
360
360
360
360
360
360
360
360
N.R.
N.R.
N.R.
N.R.
N.R.
95
16
68
83
Reaction condition: 4-methoxy benzyl alcohol (1 mmol), acetic anhydride (0.4 mL), temperature: 50 °C
aIsolated product
With the optimal reaction conditions in hand, we turned
our attention toward exploring the substrate scope of our
oxidation protocol. As shown in Table 2, this protocol is
rather general for a wide variety of substrates and the reac-
tions went on well to aford products in short times and good
to excellent yields. Therefore, these results show that this
protocol was general and efcient (Scheme 3).
groups are efciently converted to their corresponding ace-
tate compounds in high yields (Table 4; Scheme 5).
The reusability of the catalysts is an important feature
and makes them useful for commercial applications. Thus,
at the end of our experimental work, the reusability of the
MCM-41@XA@Ni(II) was investigated for the oxidation
of methylphenyl sulfde. As shown in Fig. 6, the separated
catalyst was reused for the four consecutive runs and no
signifcant loss of activity was observed.
Encouraged by these results and in the second part of our
studies, we turned our attention toward the acetylation of
alcohols using acetic anhydride as an acetylating agent in
the presence of catalytic amounts of MCM-41@XA@Ni(II)
(Scheme 4). Initially, we studied the reaction of 4-methoxy-
benzyl alcohol with acetic anhydride in the variety of sol-
vents and diferent amounts of catalyst (Table 3). As shown
in Table 3, the use of 0.03 g of MCM-41@XA@Ni(II) under
solvent‐free conditions provided higher yields and shorter
reaction time.
Conclusion
In conclusion, we have shown that MCM-41@XA@Ni(II)
as a heterogeneous catalyst can promote the selective oxida-
tion of a variety of sulfdes into the corresponding sulfoxides
and chemoselective acetylation of alcohols. Although the
literature reports a number of procedures for the oxidation
of sulfdes and acetylation of alcohol, the excellent yields,
Using obtained optimized conditions, variety of primary
alcohols with electron donating and electron withdrawing
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Journal of the Iranian Chemical Society
Table 4 Acetylation of alcohols, phenols and amines in the presence
of MCM-41@XA@Ni(II) under solvent-free conditions
O
O
Cat.;
O
ROCOCH3
ROH
Entry Alcohol
Product
Time Yield
Solvent free, r.t.
(h)
(%)
1
6
95
O
O
O
O
N
H
N
Si
Si
N
N
O
Cat.=
Ni
O
O
O
O
2
3
4
3.5
24
6
87
68
53
NH
N
N
N
H
O
Scheme 5 Acetylation of alcohol using MCM-41@XA@Ni(II)
Recovery
100
80
60
40
20
0
5
1.5
90
1
2
3
4
Run
Fig. 6 Reusability of the MCM-41@XA@Ni(II) in the oxidation
reaction of methylphenyl sulfde
6
7
1.5
24
85
73
heterogeneous conditions, simplicity, easy recyclability of
the catalysts for several catalytic cycles without any change
in activity and selectivity and ease of isolation of the prod-
ucts make our procedure a practical alternative.
Funding Funding was provided by Ahavaz Branch, Islamic Azad
University.
Reaction conditions: alcohol (1 mmol), acetic anhydride (0.4 mL),
temperature: 50 °C
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Journal of the Iranian Chemical Society
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