Nano-sized glass as an economically viable and eco-benign support to anchor heteropolyacids for green and sustainable chemoselective oxidation of sulfides to sulfoxides

Article abstract of DOI:10.1007/s12039-017-1348-5

Abstract: In this work, glass wastes were employed as cost-effective supports for the immobilization of phosphomolybdic acid (5–25 wt.% PMA) through an impregnation method. The highly efficient and retrievable nanocatalyst named nano-glass waste-supported phosphomolybdic acid (n-GW/PMA) was fully characterized by several techniques such as: XRD, FE-SEM, EDX, FT-IR and TGA. The catalytic performance of the as-synthesized heterogeneous nanocatalyst was effectively investigated for the chemoselective oxidation of sulfides to sulfoxides in the presence of 30% H ₂O ₂ as an oxidant at room temperature under solvent-free condition. Optimization of the reaction conditions was performed by means of central composite design (CCD), which is one of the powerful response surface methodologies. Based on the results obtained under the optimum condition, the sample of 16 wt.% of PMA loading offered high conversion rates and yields (97%). Besides, the beneficial points of the prepared catalyst were its recoverability and reusability for several reaction cycles, low-cost and toxicity, easy availability and facile production. Graphical abstract: Nano-glass waste-supported phosphomolybdic acid (n-GW/PMA) was synthesized as a novel, highly efficient and retrievable nanocatalyst for the chemoselective, green and rapid oxidation of sulfides to sulfoxides through an experimental design (CCD) approach. The prepared catalyst was characterized by FT-IR, TGA, XRD, FE-SEM and EDX techniques. [Figure not available: see fulltext.].

Full text of DOI:10.1007/s12039-017-1348-5

J. Chem. Sci.
© Indian Academy of Sciences
DOI 10.1007/s12039-017-1348-5
REGULAR ARTICLE
Nano-sized glass as an economically viable and eco-benign support
to anchor heteropolyacids for green and sustainable
chemoselective oxidation of sulfides to sulfoxides
∗
SOMAYEH ZOLFAGHARINIA, ESKANDAR KOLVARI , NADIYA KOUKABI
and MALIHEH M HOSSEINI
Department of Chemistry, Semnan University, Semnan, Iran
E-mail: kolvari@semnan.ac.ir
MS received 11 December 2016; revised 17 April 2017; accepted 17 June 2017
Abstract. In this work, glass wastes were employed as cost-effective supports for the immobilization of
phosphomolybdic acid (5–25 wt.% PMA) through an impregnation method. The highly efficient and retrievable
nanocatalyst named nano-glass waste-supported phosphomolybdic acid (n-GW/PMA) was fully characterized
by several techniques such as: XRD, FE-SEM, EDX, FT-IR and TGA. The catalytic performance of the as-
synthesized heterogeneous nanocatalyst was effectively investigated for the chemoselective oxidation of sulfides
to sulfoxides in the presence of 30% H2O2 as an oxidant at room temperature under solvent-free condition.
Optimization of the reaction conditions was performed by means of central composite design (CCD), which is
one of the powerful response surface methodologies. Based on the results obtained under the optimum condition,
the sample of 16 wt.% of PMA loading offered high conversion rates and yields (97%). Besides, the beneficial
points of the prepared catalyst were its recoverability and reusability for several reaction cycles, low-cost and
toxicity, easy availability and facile production.
Keywords. Nano-glass; phosphomolybdic acid; impregnation method; nanocatalyst; sulfide oxidation;
reusability.
1
. Introduction
limitation in the amounts of wastes produced have been
accomplished. However, in such heterogeneous sys-
tems, catalystrecoverythroughfiltrationorprecipitation
would be a major issue because of considerable time-
and energy-consumption. Additionally, on account of
the heterogeneous nature of the support materials in
reaction media, steric and diffusion factors, the immobi-
lized catalysts show a substantial decrease in the activity
During the last decades, in the light of green chem-
istry approaches, implementation of more sustainable
practices in industries has been undergoing consider-
able alteration. Green chemistry strives to protect the
health and the environment in a cost-effective manner. In
this context, significant improvement has been made for
designing safer chemicals and eco-friendly solvents and
catalysts. Catalysis is the central focus of green chem-
1,2
and selectivity. Besides, in the systems where a great
proportion of active species are deep inside the sup-
porting matrix, the reactants encountered difficulties for
st
istry research in 21 century due to its applications in
3
various systems with reduced toxicity, renewable and
benign energy, and high reaction efficiency. Based on
these facts, preparation of heterogeneous analogues of
the most commonly used soluble and homogeneous cat-
alysts can be approached through their immobilization
on different insoluble supports. In the light of this sit-
uation, the simplification of catalyst removal and the
accessing to the catalytic active sites. Hence, for the
economic viability preservation, the designed heteroge-
neous systems must exhibit the advantages with respect
to minimization of waste formation, comparable or
higher catalytic activities and selectivity over the exist-
ing homogenous routes. To address these challenges,
nanoparticles (NPs), the alternative soluble matrixes,
*
For correspondence
Electronic supplementary material: The online version of this article (doi:10.1007/s12039-017-1348-5) contains supplementary material,
which is available to authorized users.

Somayeh Zolfagharinia et al.
have been applied to support homogeneous catalysts or Glass in many forms such as packaging or container
reagents. The advantages of the support materials lie glass (bottles and jars), flat glass (windows and wind-
with increasing the surface area on the basis of their screens), bulb glass (light globes) and cathode ray tube
nanometer sizes, higher catalyst loading capacity and glass (TV screens, monitors, etc.), have a limited life.
dispersion comparable to the most common support Therefore, it is essential to reuse or recycle them so
4
–6
matrixes.
as to prevent environmental problems related to their
19
Polyoxometallates (POMs) stand for a diverse fam- stockpiling or sending to the landfill. As a result, we
ily of anionic metal oxide molecular species, which thought that the utilization of nano-glass waste for sup-
span a rich variety of sizes and shapes, with outstand- porting heteropolyacids could go a long way towards
ing properties and functions as acid and redox catalysts the simultaneous reaching the above-mentioned tar-
7
both in the homogeneous and heterogeneous media.
gets. In this context, recently we reported nano-glass
Heteropolyacids (HPAs), an extremely large and var- waste-supported sulfonic acid as an accessible, sta-
ied class of polyoxometalates, as powerful oxidants, ble, recoverable, non-toxic and inexpensive solid acid
20
can display fast reversible multi-electron redox transfor- nanocatalyst for multicomponent reactions. However,
8
mation under mild condition. Thanks to their unique to the best of our knowledge there are no literature
properties, heteropolyacids can open up the opportu- reports on the exploitation of glass wastes for the immo-
nity for catalyzing the reactions in both solution and bilization of the highly applicable heteropolyacids.
solid state lowering the production of wastes or by- Among heteropolyacids, we chose phosphomolybdic
products. There is a plethora of large scale industrial acid (PMA) because it is one of the least expensive
transformations catalyzed by HPAs including alcohol commercially available one. In continuation of our
dehydration, alkylation and esterification, etc.9 How- attempts for the preparation of different solid acid cat-
,10
21–28
ever, the main drawbacks of HPA are pertained to their alyst,
the present study consists of the synthesis
low surface areas and high solubility in polar solvents of a novel solid acid nanocatalyst named nano-glass
which render difficulties in respect of their recovery waste-supported phosphomolybdic acid (n-GW/PMA)
and catalytic useful life. Addressing these issues, such and its application for the facile, fast, highly efficient,
catalytically efficient HPAs are frequently immobilized and chemoselective oxidation of sulfides to sulfoxides in
onto the insoluble, easily separable solid matrixes with the presence of H O as oxidant under solvent-free con-
2
2
high surface areas7
,11–13
The attractive feature related ditions. Afterwards, the newly synthesized n-GW/PMA
to the supported HPAs is the fact that they are more was fully characterized through FT-IR, EDX, FE-SEM
active than typical solid acids. So far, numerous support and TGA techniques. The specific advantages of the cat-
1
4
15
16
materials such as silica, zeolite, alumina, active alyst are related to its high stability, facile recoverability,
17
18
carbon and ion-exchange resin have been employed reusability, easy accessibility and low cost.
for the immobilization of HPAs. However, the alterna-
tive routes show some problems including the formation
of deposit (coke) on the catalyst surface which makes
2
. Experimental
these types of supported catalysts to be susceptible
7
against deactivation during organic reaction In addi-
2.1 Chemicals and apparatus
tion, HPAs supported on solid matrixes are prone to
leaching in polar solvents which limit their reusability.
All the chemicals were purchased from Merck and Aldrich
Therefore, there is still much room for the improvement companies and used without any further purification. Glass
of such systems through the application and design of wastes were provided from Sandis (Iran). Powder making
stable, inexpensive, active and available solid support of the glass waste was carried out through a two-cup plan-
etary ball mill. The products purity was checked through
for binding of HPAs. In this context, we postulated that
thin layer chromatography (TLC) on glass plates coated with
the application of waste materials or products as solid
silica gel 60 F254 using n-hexane/ethyl acetate mixture as
supports for the immobilization of HPAs could provide
mobile phase. All yields refer to the isolated products after
a golden chance which one could achieve three goals,
purification. Products were characterized by melting points
at the same time: (i) The waste materials or products
1
13
and spectroscopic data (FTIR, H NMR and C NMR spec-
tra). Melting points were determined in open capillaries using
an Electrothermal 9100 without further corrections. Fourier
transform infrared spectroscopy (FT-IR) was recorded on
a Shimadzu 8400 s spectrometer using KBr pressed pow-
can be recycled and in the subsequent step, the drastic
impacts on the environment can be mitigated. (ii) An
efficient solid heterogeneous catalyst can be prepared
through the heterogenization of HPAs. (iii) An organic
1
13
transformation can be rapidly catalyzed in a mild reac- der discs. H- and C-NMR spectra were recorded with a
tion condition. Bruker Avance 400 Ultrashield NMR spectrometer, in pure

Nano-sized glass supported heteropolyacids
Table 1. Oxidation of sulfides to sulfoxides in the presence of n-GW/PMAa.
Entry
Sulfide
Sulfoxide
T [min] Yield [%]b Selectivity (%)
1
25
15
91
100
2
96
100
3
4
10
10
95
95
100
100
5
65
83
100
6
7
10
20
97
95
100
100
8
9
25
88
100
50
60
91
92
100
100
10
aReaction condition: sulfide (1 mmol), 30% H2O2 (2.4 eq.) and n-GW/PMA 16. Wt. % (12 mg), solvent
free, r.t.
b
Yields refer to isolated products.

Somayeh Zolfagharinia et al.
deuterated chloroform with tetramethylsilane (TMS) as the
internal standard. Thermogravimetric analyses (TGA) were
performed on a DuPont 2000 thermal analysis apparatus at
◦
−1
a heating rate of 5 C min under air atmosphere. X-ray
diffraction (XRD) was recorded by Philips using Cu-Kα radi-
ation of wavelength 1.54 Å. Field emission scanning electron to sulfoxides using H O .
Scheme 1. Nano-GW/PMA catalyzed oxidation of sulfides
2
2
microscope (FE-SEM) images were obtained through Tescan-
vega II XMU Digital Scanning Microscope. The EDX spectra
were acquired with the aid of a Mira 3-XMU scanning elec-
tron microscope equipped with an energy dispersive X-ray
spectrometer operating. A central composite design (CCD)
was performed to optimize the reaction condition for the
oxidation method. 20 data analyses were carried out using
Design-Expert trial version 7.0.0. (Stat-Ease Inc., Minneapo-
lis).
2
.4b dibenzo[b,d]thiophene 5-oxide (Table 1, entry
◦
−1
:
1
0): White solid, M.p.: 215–217 C. IR (KBr) ν/cm
1
3
083, 2982, 1591, 1452, 1288, 1164, 1047, 711, 698;
H-NMR (CDCl , 400 MHz) δH (ppm): 7.5–7.8 (m, 8H).
3
1
3
C NMR (CDCl , 400 MHz): δC (ppm):120.57, 121.132,
3
129.35, 130.57, 132.87, 136.65.
2.2 Preparation of the neat glass waste powder
2.5 Investigation of the catalytic activity of
n-GW/PMA for the oxidation of sulfides to sulfoxides
After washing glass wastes with 200 mL methanol and
ethanol, they were turned into fine powder. Then, the pre-
pared powder (20 g) was carefully washed with excess amount
of distilled water three times. Afterwards, precipitated glass
powder was filtered and rinsed with excess amount of water
Owing to the fact that organic sulfoxides have been widely
used in variable pharmaceutical and agrochemical sectors, the
selective oxidation of sulfides to sulfoxides are considered as
29,30
an important transformation in organic synthesis.
As a
◦
and then dried at 120 C.
consequence, we were inspired by the investigation of the
catalytic activities of our synthesized n-GW/PMA as a het-
erogeneous nanocatalyst for the chemoselective oxidation of
structurally diverse sulfides to sulfoxides in the presence of
2.3 Synthesis of the glass waste-supported
phosphomolybdic acid
3
0% H2O2 as an oxidant (Scheme 1).
Aiming at establishing the optimum reaction condition, we
The n-GW/PMA with the loadings of 5–25 wt.% were
prepared by the aid of the wetness impregnation method. Typ-
ically, 2 g of n-GW was impregnated with an aqueous solution
of PMA (0.06–0.375 g in 10–50 mL double distilled water).
The mixture was vigorously stirred overnight at room tem-
perature. Then, the water was completely evaporated using
a rotary evaporator and the green sample was prepared after
studied the model reaction of 4, 4’-thiodiphenol oxidation. At
first, we tested the model reaction without any catalyst but
the results were unsatisfactory (i.e., the yields were negligi-
ble (28%) in the prolonged reaction time (2 h)). Therefore, it
was understood that the presence of the catalyst in the reac-
tion was essential. Then, for acquiring the best condition for
the oxidation reaction, central composite design (CCD) was
chosen. When the number of effective parameters are lower
than/or equal to four, central composite design (CCD), as
one of the most applicable types of response surface model
◦
drying and calcination at 150 C for 2 h.
2.4 General procedure for the catalytic oxidation of
sulfides
(RSM), could be helpful.
To a reactor equipped with a stirrer bar, a mixture of sulfide
At the outset, preliminary experiments were performed
(
(
1 mmol), 30% H2O2 (2.4 eq.) and the n-GW/PMA 16Wt.% for the evaluation of the suitable parameters and for the
12 mg) was added and allowed to be stirred at room tempera- determination of the experimental domain. Considering these
ture for appropriate time indicated in the Table 1. The progress experiments, the effects of catalyst amount (A), PMA load-
of the reaction was monitored by TLC (n-hexane: EtOAc, 9: ing (B) and H O concentration (C), were studied on reaction
2
2
1). After the reaction was completed, the mixture was diluted yield as response in 10 min. Optimization is performed in
with Et2O (10 mL) and the catalyst was separated through condition at which the optimal parameters can be employed
centrifugation. Then, the combined organic layers were dried for all of the used derivatives. Since time was variable about
over anhydrous Na2SO4 and diethyl ether was evaporated each derivatives, it was not optimized. Therefore, in the opti-
under reduced pressure to afford the pure products in 83–97% mization process, each run was tested in 10 min. A five-level
yields.
CCD of three independent variables with their corresponding
values was displayed in Table S1 in Supporting Information.
Based on the CCD method, total number of experiments
2
.4a 4, 4’-sulfinyldiphenol (Table 1, entry 6): IR
−1
(
KBr) ν/cm : 3236, 2923, 1583, 1496, 1438, 1365, 1139, was found to be twenty, which were comprised of eight full
1
1
1
4
000, 721, 690; H-NMR (DMSO-d , 400 MHz) δH (ppm): factorial points, six axial points and six central points. Con-
6
1
3
0.08 (s, 2H), 6.8–7.7 (dd, 8H); C NMR (DMSO-d , ditions of 20 trials in addition to their respective yields are
6
00 MHz): δC (ppm):116.52, 127.04, 135.41, 160.07.
shown in Table S2 (See Supporting Information).

Nano-sized glass supported heteropolyacids
With the aid of performing analysis of variance (ANOVA) H2O2 were the optimum conditions for the synthesis of 4,
on the model, valuable information about significance of fitted 4’-sulfinyldiphenol (Figure S19).
model and its terms were achieved. According to the Table S3
In order to study the effects of solvents on the reaction
(Supporting Information), the model p-value and lack of fit efficiency, the model reaction was carried out under optimum
were lower and higher than 0.05, respectively indicating the condition in the presence of EtOH, MeOH, CH3CN, H2O,
fact that, fitted model was significant in confidence level of and CH2Cl2. However, the best results in terms of reaction
9
5% and it was not needed to reduce to lower orders. Besides, yields and time were related to the reactions operated under
the amounts of R-squared and adj R-squared were above solvent free conditions.
.9 and close to each other which was a testimony for the The obtained results encouraged us to extent the appli-
0
high accuracy and reliability of the fitted model in predic- cation of this optimized catalytic protocol to the oxidation
tion of the reaction yield. It was meant that there was a good of various sulfides (Table 1). As could be observed from the
agreement between experimental and the predicted responses table 1, a variety of sulfides like dialkyl sulfides, alkyl aryl sul-
which approved the suitability of the following fitted model fides and other sulfides with different functional groups could
regarding the significantly linear, quadratic and interaction yield the corresponding sulfoxides with high conversion rate
terms based on their p-values.
and outstanding selectivity. Additionally, under the designed
reaction condition in the presence of the novel n-GW/PMA
Y = +1.90313 + 6.42339 A + 4.54018 B + 16.29883 C catalyst, the oxidation reactions were carried out smoothly
without detecting any over oxidation products such as sul-
+
−
0.030000 AB − −0.16667 AC − 0.50000 BC
2 2 2
fones. Moreover, the steric effects of some sulfide derivatives
were clear in this catalytic system. For example, the oxida-
tion of diphenyl sulfide in comparison with isopropyl sulfide
was performed in much longer reaction time which afforded
a much lower reaction yields (Table 1, entries 4 and 5). The
structures of some of the products were well characterized by
0.27761 A − 0.11497 B − 1.07532 C
It can be found from the response equation that the three A, B
and C parameters showed a linear effect on the product yield,
therefore all factors (i.e., the amount of catalyst, PMA loading
and H2O2 concentration) were important in progressing of the
reaction. In order to investigate the main interaction effects
between two parameters on the yield of reaction, three and
two dimensional profile of yield versus a pair of parameters
were used (Figure S18 in Supporting Information).
Based on their p-values, it could be realized that the inter-
action of AB, AC and BC were significant; therefore, the
simultaneous changing in the catalyst amount, PMA loading
and H2O2 concentration could alter the product yield. When
catalyst amount (12 mg), PMA loading (16 wt.%) and H2O2
1
13
using H-NMR and C-NMR spectral data.
3
. Results and Discussion
The novel nano-glass waste supported phosphomolyb-
dic acid (n-GW/PMA) was synthesized through impreg-
nation method as briefly showed in Scheme 2. In order to
(
2.4 equiv.) were applied in the reaction, the product yields synthesize the desired novel catalyst, firstly, nano-glass
and the desirability were 96.92% and 0.99, respectively. The waste was prepared by crushing and powder making of
main target of this design was to optimize and maximize the the glass waste provided. Afterwards, an impregnation
yield of the reaction corresponded to the conditions of an
reaction occurred between the n-glass waste and PMA.
experiment in which the response equation was maximized.
At the subsequent step, the obtained catalyst was dried
and calcinated at 150 C for 2 h and allowed to cool to
In this work, determination of the optimal conditions was
done with the help of desirability function by using Design-
Expert 7.0.0. It was initially selected desired goals for each
factor and for response to obtain the maximum product yield
withhighdesirabilityfunction(closetoone). Then, conditions
possessing high desirability were tested three times. Negligi-
ble difference between the average yields and the prediction
values of software, confirms the high accuracy and precision
◦
room temperature. In order to explore the best amounts
of PMA loaded on the n-GW support, a series of cata-
lysts containing 5–25 wt.% PMA was synthesized. The
results obtained showed that the catalyst with 16 wt.%
loading exhibited better performance compared to the
other catalysts. The newly prepared catalyst was charac-
of optimum conditions. The results showed that 12 mg of terized through FT-IR, FE-SEM, XRD, EDX and TGA
the catalyst, 16 wt.% of PMA loading and 2.4 equivalent of techniques.
H PMo O
3
12 40
Nano-glass waste
H O, r.t.
Nano-glass waste
2
n-GW
n-GW/PMA
PMA
Scheme 2. Preparation of nano-glass waste-supported phosphomolybdic acid.

Somayeh Zolfagharinia et al.
3
.1 Characterization of n-GW/PMA
.1a FT-IR spectra of the samples: FT-IR spectra
3
were employed to establish the presence of PMA on
the n-glass waste support. Figure 1 showed the FT-
IR spectra of the n-GW, n-GW/PMA (10, 16 and
2
5 wt.%) and PMA. Curve (a) in Figure 1 shows
the infrared spectrum of n-GW. About Figure 1a, the
−1
bands appeared at 3523 and 1623 cm are respec-
tively assigned to the stretching and bending modes of
the SiOH groups and the adsorbed water. The strong
−1
absorbance at 1066, 775 and 468 cm are related to
the asymmetric stretching, symmetric stretching and
31
bending modes of SiO , respectively The FT-IR spec-
2
trum of n-GW/PMA displayed the absorbance at 1058,
−1
9
62, 882 and 792 cm which are attributed to the the
symmetric stretching of the central-atom–oxygen (P–O)
bond of the PO tetrahedron, the asymmetric stretching
4
of the peripheral-atom-terminal-oxygen (Mo–O) bond,
and the Mo–O-Mo stretching of the inter- and intraoc-
tahedral bridges of the trimetallic group, respectively
32
(
Figure 1c). These observations confirmed the fact
that the existence of PMA on support was in the Keggin
structure.The vibrations due to molecular water present
in the n-glass waste support and phosphomolybdic acid
−1
are identified at about 1627 and 3560 cm . The FT-
IR spectrum of PMA (Figure 1e) reveals that the bands
in n-GW/PMA are corresponded to those for the PMA
−1
(
i.e., the peaks at 1064, 960, 880 and 779 cm ). The
FT-IR spectra of the different loading of PMA into n-
GW indicated that most of characteristic bands of the
parent Keggin structure could be found in PMA finger-
−1
print region (1250–500 cm ). These findings clearly
confirmed that the phosphomolybdic acid molecules are
covalently bound to the n-GW support.
Figure 1. FT-IR spectra of (a) n-GW, (b–d) n-GW/PMA
0–25 wt.% and (e) PMA.
1
3
.1b X-ray diffraction analysis: Figure 2 shows the
XRD patterns of n-GW, pure PMA and 16 wt.% PMA
supported on n-GW. According to Figure 2a, n-GW pos-
sessed the amorphous structure with the broad peak
◦
33
around 2θ equal to 27 . As can be seen from Fig-
ure 2c, the crystalline peaks appeared between 2θ equal
◦
to 10–45 are attributed to the purely crystalline form of
34
PMA. The XRD pattern of n-GW/PMA 16% shows
◦
some reflections of Keggin structure PMA at 20–35
(2θ) (Figure 2b). From the XRD analysis, it can be con-
cluded that the Keggin structure of the H PMo O was
3
12 40
maintained after supporting on n-GW.
3
.1c Thermogravimetric (TGA) analysis: Thermo-
gravimetric analysis (TGA) was used for the evalua-
tion of materials in terms of their thermal stability, Figure 2. XRD spectra of (a) n-GW, (b) n-GW/PMA 16
wt.% and (c) bulk PMA.
chemisorption and bond formation. Figure 3 shows

Nano-sized glass supported heteropolyacids
support shows a mass loss of about 4 wt.% in the
◦
temperature up to 100 C relating to the loss of phys-
ically adsorbed water. The steadily dehydroxilaytion of
◦
n-GW was occurred at the temperature lower than 600 C
35
which caused 2 wt.% loss. According to Figure 3b, n-
GW/PMA exhibited the weight loss of 3.5 wt.% up to
◦
1
00 C, attributed to removal of the physisorbed water.
The second loss of weight (about 1 wt.%) between
◦
1
30–300 C was ascribed to the dehydroxylation of
chemisorbed water and the strongly adsorbed water on
36
the n-GW support. The continuous weight loss (1
wt.%) observed with further heating up to 800 C was
due to the loss of water of the supported heteropoly-
Figure 3. TGA curves of (a) n-GW and (b) n-GW/PMA 16
wt.%.
◦
the TGA results for the n-GW and n-GW/PMA 16 acid and decomposition of the keggin units to give
◦
37,38
wt.% in the temperature ranging from 30 to 800 C. MoO
.
The results showed that the thermal stability
3
◦
As can be observed from Figure 3a, the naked n-GW of n-GW/PMA was more than 300 C which could be
Figure 4. FE-SEM images of n-GW (a, b), and n-GW/PMA (c, d).

Somayeh Zolfagharinia et al.
Figure 5. The EDX spectrum of n-GW/PMA 16 wt.%.
Table 2. Comparison of n-GW/PMA for the oxidation of methyl phenyl sulfide with other reported
procedures.
Entry
Reagent
T [min]
Yield [%]
Ref.
3
4
4
4
4
9
0
1
2
3
1
2
3
4
5
6
Thiourea dioxide/TBHP
NaBO3.4H2O/Silica Sulfuric acid/ KBr
Borax/H2O2
210
840
360
300
150
15
93
55
35
35
90
96
Clay-supported ceric ammonium nitrate (CAN)/O2
SiO2-W2-Py/H O2
2
n-GW/PMA/H2O2
Present work
safely employed in organic reactions at temperatures up 3.1e Energy-dispersive X-ray spectroscopy (EDX):
◦
to 350 C.
The elemental composition of the n-GW/PMA from the
EDX spectrum is depicted in the Figure 5. As it is obvi-
ous, the O, Si, Al, Ca, Fe, Ti, Na, P and Mo elements ae
present in the structure of the as-synthesized catalyst.
Table 2 displays the efficiency of our designed cat-
alytic system in comparison with those reported in the
literature. The result for the preparation of (methyl-
sulfinyl benzene) in the presence of n-GW/PMA are
compared with the data from the literature, which shows
that the n-GW/PMA is superior to most of the others
regarding the reaction times and product yields. There-
fore, it could be concluded that n-GW/PMA is a very
beneficial and efficient catalyst for the sulfide oxidation.
3
(
.1d Field emission scanning electron microscopy:
FE-SEM): FE-SEM images were employed in order
to study the surface morphology, particle shape and
size distribution of the as-synthesized materials (Fig-
ures 4a–e). Figures 6a and b show the SEM images
of the n-GW which indicated that the material con-
sisted of some particles on the surface. These non-
homogeneous particles have the sizes in the range of
5
0 nm to 2 µm. On the other hand, as displayed
in the Figures 4c and d, n-GW/PMA had completely
different morphology and size ranges. As it was obvi-
ous in the micrographs, after the modification of
n-GW with PMA, the obtained material had aggre-
gated particles with quasi-spherical shape. Besides, the
size distribution of the catalyst particles was nearly
3.2 Plausible mechanism for the oxidation of sulfides
to sulfoxides catalyzed by n-GW/PMA
homogeneous and their diameter sizes were around 5– Based on earlier reports,44,45 we propose a mechanism
1 nm. for the oxidation of sulfides to sulfoxides in the presence
1

Nano-sized glass supported heteropolyacids
recyclability has been one of the important criteria
for organic transformations, we examine our new n-
GW/PMA catalyst for its recyclability and reusability
in the optimum reaction condition of selective sulfide
oxidation. After each run, the catalyst was simply sepa-
rated from the product by adding diethyl ether and, then
by centrifugation. After that, the recovered catalyst was
◦
washed with extra amounts of ether and dried at 100 C.
The dried recovered catalyst was capable to efficiently
run the oxidation reaction for five runs without losing its
activity. The yields in the first 5 runs were as follows: 97,
9
6, 94, 93 and 93%. These results indicated the fact of
tight immobilization of the PMA function on the n-GW
support.
The identity of the recovered catalyst was checked
by FE-SEM which suggested that the nature of the cat-
alyst remained intact and there was no change in the
morphology during the reaction and recycling stages as
compared to the fresh catalyst (Figure 6). Additionally,
Scheme 3. Plausible mechanism for the oxidation of sul-
fides to sulfoxides in the presence of n-GW/PMA.
ofn-GW/PMA(Scheme3). Thereactionisinitiatedwith
the nucleophilic attack of H O on the oxo ligands of
2
2
Mo(VI) atom on the n-GW surface (i.e., species 1) to
form the octahedral hydroperoxymolybdate (2). Then,
monoperoxo species (3) is generated, followed by a loss
ofawatermolecule. Asaconsequence, theperoxogroup
is electrophilically activated through the coordination to
the high-valent molybdenum atom. Finally, the sulfox-
ide product (5) is formed when the sulfur atom in the
organosulfur compounds (4) attacks on a peroxo group
of intermediate (3) and regenerates polymolybdate or
monoperoxo species.
3.3 Reusability of the designed catalyst
On account of the fact that the development of novel Figure 7. XRD spectra of n-GW/PMA (a) before use and
b) after reuse for five times.
(
heterogeneous catalysts with the capability of good
th
Figure 6. FE-SEM images of (a) fresh n-GW/PMA and (b) after 5 run.

Somayeh Zolfagharinia et al.
6. Zhu Y, Lee C N, Kemp R A, Hosmane N S and Maguire J
the XRD patterns of the catalyst after five cycles were
similar to the corresponding pattern before catalytic
reaction which confirmed the existence of heteropoly-
acid groups on the surface of catalyst (Figure 7).
A 2008 Latest developments in the catalytic application
of nanoscaled neutral group 8–10 metals Chem. Asian J.
3
650
7
. Kozhevnikov I V 1998 Catalysis by heteropoly acids and
multicomponent polyoxometalates in liquid-phase reac-
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. Misono M 2001 Unique acid catalysis of heteropoly
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Chem. Commun. 1141
4
. Conclusions
8
In conclusion, n-GW/PMA was synthesized as the
eco-friendly, heterogeneous solid acid catalyst through
the utilization of n-glass waste as an accessible and
9
inexpensive solid support for the immobilization of 10. Palermo V, Villabrille P I, Vazquez P G, Caceres C V,
Tundo P and Romanelli G P 2013 Role of vanadium and
phosphomolybdic acid. The strong binding of the PMA
pyridine in heteropolycompounds for selective oxidation
of alcohols with hydrogen peroxide J. Chem. Sci. 125
molecules on the surface of the n-GW/PMA caused
the novel catalyst to show extraordinary activity and
1375
chemoselectivity for the synthesis of sulfoxides through
the oxidation of sulfides. The designed reaction was
green and economical since this transformation pos-
sessed several advantages, such as, short reaction times,
high reaction yields, application of low amount of cat-
alyst, solvent-free condition at room temperature, use
of waste material as catalyst support, and utilization of
H O as the green oxidant.
1
1. Damyanova S, Fierro J L G, Sobrados I and Sanz J
1999 Surface behavior of supported 12-heteropoly acid
as revealed by nuclear magnetic resonance, X-ray pho-
toelectron spectroscopy, and Fourier transform infrared
techniques Langmuir 15 469
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2. Kim H J, Chu Y H, Moon J H, Han H S and Shul Y
G 2001 Preparation of heteropoly acid entraped in nano
silica matrix Mol. Cryst. Liq. Cryst. 371 131
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2
Supplementary Information (SI)
All additional information pertaining to characterization of
some of the products (Table 1) using IR spectra (Figures S1,
1
4. Yan X M, Lei J H, Liu D, Wu Y C and Liu W 2007
Synthesis and catalytic properties of mesoporous phos-
photungstic acid/SiO2 in a self-generated acidic environ-
ment by evaporation-induced self-assembly Mater. Res.
Bull. 42 1905
1
S3, S7, S10 and S15), H NMR spectra (Figures S2, S4, S8,
S11 and S16) and 13C MNR spectra (Figures S13 and S17),
and details for the optimization of the reaction conditions by
CCD method (Figures S18 and S19 and Tables S1, S2 and S3)
are given in the Supporting Information, which is available at
www.ias.ac.in/chemsci.
1
5. Dubey N, Rayalu S S, Labhsetwar N K and Devotta S
2
008 Visible light active zeolite-based photocatalysts for
hydrogen evolution from water Int. J. Hydrogen Energy
3 5958
6. Abdollahi-Alibeik
3
1
M,
Zaghaghi
Z
and
Acknowledgements
Mohammadpoor-Baltork I 2008 Alumina Supported 12-
Tungstophosphoric Acid as an Efficient and Reusable
Catalyst for Synthesis of 1, 5-Benzodiazepines J. Chin.
Chem. Soc. 55 1
The authors would like to thank Semnan University Research
Council for the financial support of this work.
1
7. Dupont P, Védrine J C, Paumard E, Hecquet G and
Lefebvre F 1995 Heteropolyacids supported on activated
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