Novel catalyst based on mono- and di-vanadium substituted Keggin polyoxometalate incorporated in poly(acrylic acid-co-acrylamide) polymer for the oxidation of sulfides

Article abstract of DOI:10.1016/j.mcat.2018.07.016

Composite materials based on [PV_xW_12-xO₄₀]^(3+x)? with x = 1 or 2 (PVW and PV2W respectively), included in poly(acrylic acid-co-acrylamide) gel (PAACA), were synthesized. The samples were characterized by different techniques such as FT-IR, ³¹P MAS-NMR, ⁵¹V-NMR, XRD, DTA-TGA, UV–vis DRS, and the acidic properties were estimated by means of potentiometric titration with n-butylamine. Samples containing 10, 20 and 30% (w/w) of polyoxotungstovanadate (POTV) were prepared by inclusion of the POTV in the polymer during its synthesis. According to Fourier transform infra-red and magic angle spinning-nuclear magnetic resonance studies, the predominat anion present in the samples is [PV_xW_12-xO₄₀]^(3+x)?, and there is no evidence of its decomposition during the synthesis of hybrid materials and the drying step. According to XRD results, these anions are greatly dispersed in the PAACA or present as amorphous phases. UV–vis DRS data reveal that the samples synthesized using POTV with two vanadium atoms (PAACA-PV2W) exhibit lower values of absorption edge energy than those prepared using PVW (PAACA-PVW), which correlates with a higher oxidizing capacity. The potentiometric titration shows strong acid sites of the hybrid materials, and their number increases with the number of vanadium atoms and with the amount of POTV incorporated in the PAACA grid. The hybrid materials prepared by inclusion of POTV during the polymer synthesis exhibit appropriate physicochemical features to catalyze the oxidation of diphenyl sulfide (DPS) to its sulfone employing acetonitrile as solvent H₂O₂ as a green oxidant. The samples with 30% w/w of POVT, which show higher catalytic performance, are suitable for the DPS oxidation and can be reused without remarkable drop of their catalytic activity. Furthermore, they show high activity as a catalyst in the oxidation reaction of 4,4′-diamino diphenyl sulfide to the corresponding sulfone (dapsone) used for malaria treatment.

Full text of DOI:10.1016/j.mcat.2018.07.016

Molecular Catalysis 457 (2018) 8–16
Contents lists available at ScienceDirect
Molecular Catalysis
journal homepage: www.elsevier.com/locate/mcat
Novel catalyst based on mono- and di-vanadium substituted Keggin
polyoxometalate incorporated in poly(acrylic acid-co-acrylamide) polymer
for the oxidation of sulfides
⁎
⁎
Romina A. Frenzel, Gustavo P. Romanelli , Luis R. Pizzio
Centro de Investigación y Desarrollo en Ciencias Aplicadas “Dr. J. J. Ronco” (CINDECA), Departamento de Química, Facultad de Ciencias Exactas, UNLP-CCT La Plata,
CONICET, 47 Nº 257, 1900 La Plata, Argentina
A R T I C L E I N F O
A B S T R A C T
x 12-x
Composite materials based on [PV W O
40](3+x)− with x = 1 or 2 (PVW and PV2W respectively), included in
Keywords:
Keggin polyoxotungstovanadate
Sulfide oxidation
Superabsorbent polymers
Dapsone
poly(acrylic acid-co-acrylamide) gel (PAACA), were synthesized. The samples were characterized by different
31
51
techniques such as FT-IR, P MAS-NMR, V-NMR, XRD, DTA-TGA, UV–vis DRS, and the acidic properties were
estimated by means of potentiometric titration with n-butylamine. Samples containing 10, 20 and 30% (w/w) of
polyoxotungstovanadate (POTV) were prepared by inclusion of the POTV in the polymer during its synthesis.
According to Fourier transform infra-red and magic angle spinning-nuclear magnetic resonance studies, the
(
3+x)−
predominat anion present in the samples is [PV
x
W
12-x
O
40
]
, and there is no evidence of its decomposition
during the synthesis of hybrid materials and the drying step. According to XRD results, these anions are greatly
dispersed in the PAACA or present as amorphous phases.
UV–vis DRS data reveal that the samples synthesized using POTV with two vanadium atoms (PAACA-PV2W)
exhibit lower values of absorption edge energy than those prepared using PVW (PAACA-PVW), which correlates
with a higher oxidizing capacity.
The potentiometric titration shows strong acid sites of the hybrid materials, and their number increases with
the number of vanadium atoms and with the amount of POTV incorporated in the PAACA grid.
The hybrid materials prepared by inclusion of POTV during the polymer synthesis exhibit appropriate phy-
sicochemical features to catalyze the oxidation of diphenyl sulfide (DPS) to its sulfone employing acetonitrile as
2 2
solvent H O as a green oxidant. The samples with 30% w/w of POVT, which show higher catalytic performance,
are suitable for the DPS oxidation and can be reused without remarkable drop of their catalytic activity.
Furthermore, they show high activity as a catalyst in the oxidation reaction of 4,4´-diamino diphenyl sulfide to
the corresponding sulfone (dapsone) used for malaria treatment.
1. Introduction
easy recovery and catalyst reuse, decreased plant corrosion, and more
environmentally safe waste disposal procedures [28–32].
Catalysis by polyoxometalates (POMs) is a field of growing value
The development of new catalytic systems for selective organic
synthesis is one of the principal goals in Organic Chemistry. The pro-
cesses are essential for the conservation of the ecosystems. In the last
years, procedures involving catalysis and green oxidants such as hy-
drogen peroxide, molecular oxygen and organic peroxides have been
developed [33–36]. These are useful systems to oxidize organic sub-
strates and present high efficiency due to their low cost, safety in sto-
rage and operation, and mild reaction conditions.
worldwide. The extensive chemistry of these compounds is related to
the composition of the heteropolyanion [1–3], and the application of
POMs in different fields such as photodegradation, medicine, catalysis
and material science has been reported [4–16]. Their versatility is be-
cause they can act as reversible multielectron oxidants and very strong
acids [17–21]. Taking into account their outstanding catalytic proper-
ties, POMs are used in homogeneous or heterogeneous catalysis and in
bulk or supported form [22–27]. The use of solid acids in organic
transformations has many advantages compared with conventional
acids, including simplified product isolation, mild reaction conditions,
Polymeric materials are a new kind of interesting supports that can
be used when the catalysts are employed in reactions carried out at
relatively low temperatures, due to the relatively low thermal stability
⁎
Corresponding authors.
E-mail addresses: gpr@quimica.unlp.edu.ar (G.P. Romanelli), lrpizzio@quimica.unlp.edu.ar (L.R. Pizzio).
https://doi.org/10.1016/j.mcat.2018.07.016
Received 15 March 2018; Received in revised form 11 July 2018; Accepted 12 July 2018
2468-8231/ © 2018 Elsevier B.V. All rights reserved.

R.A. Frenzel et al.
Molecular Catalysis 457 (2018) 8–16
of some of them [37]. These materials are composed of cross-linked
polymeric chains in the form of a three-dimensional network [38]. They
can absorb and retain large amounts of water, which depends on the
type of monomer, the porosity, the cross-linking degree and the pre-
2.3. Materials characterization
2.3.1. FT-IR analysis
Fourier transform infra-red spectra of POTV, PAACA, PAACA-PVWX
and PAACA-PV2WX materials were obtained in the wavenumber range
sence of hydrophilic groups in the polymer (eCOOH, eCONH
2
, eOH,
−
1
eSO H).
3
400–4000 cm
spectrometer.
using a Bruker IFS 66 Fourier transform infra-red
On the other hand, sulfones are important intermediates in organic
chemistry due to their application in fundamental research and other
extended uses. The most widely used method for the preparation of
sulfones is the oxidation of the corresponding sulfide; some traditional
2.3.2. XRD analysis
XRD diagrams of the materials were recorded employing Philips
PW-1732 equipment, using Cu Ka radiation, nickel filter, 20 mA and
40 kV in the high voltage source, and scanning angle between 5 and 60°
of 2θ at a scanning rate of 2°/min.
oxidizing reagents used for this purpose include HNO
3 2 4 4
, H CrO , KMnO
[
39–41], SeO , MnO , O , NaBO [42], among others [43–45]. For this
2
2
3
3
reason, sulfide oxidation has been the subject of many studies, and
several methods for this transformation have been reported in the lit-
erature [46,47]. Dapsone is very important in the pharmaceutical field
due to its use as a drug for malaria and leprosy treatment, and also in
dermatology for the treatment of different skin diseases [48–52].
In the present work, a polymer (PAACA) composed of acrylic acid
.3.3. 31P and 51V nuclear magnetic resonance (P-NMR and 51V-NMR
2
respectively)
The 31P and 51V magic angle spinning-nuclear magnetic resonance
spectra of the materials were registered with Bruker Avance II-300
equipment (see supplementary information).
(
(
AA) and acrylamide (AM) as monomers, N,N-methylenebisacrylamide
MBA) as a cross-linking agent and ammonium persulfate (APS) as a
polymerization initiator [38] was synthesized and used as support.
The hybrid materials were obtained by inclusion of POTV in the
PAACA during its synthesis, and the materials were characterized by
different physicochemical techniques.
2
.3.4. Diffuse reflectance spectroscopy
UV–vis DRS spectra of the samples were registered using a Perkin
Elmer Lambda 35 spectrophotometer, to which a diffuse reflectance
chamber (Labsphere RSA-PE-20) is attached, in the 200–800 nm wa-
velength range. The absorption edge energy (Eg) was determined from
The aim of this paper is the preparation and characterization of [N
(
4 x 12-x
Prop) ](3+x) [PV W O40] included in superporous polymers to be
diffuse reflectance spectra using the Kubelka–Munk remission function
used as catalysts in the heterogeneous oxidation of diphenyl sulfide to
the corresponding sulfone, with aqueous hydrogen peroxide. The oxi-
dation reaction of diphenyl sulfide (DPS) in homogeneous conditions
using the bulk POMs was also studied for comparatives purposes.
Furthermore, the best conditions found in the oxidation test were used
in the oxidation reaction of 4,4´-diamino diphenyl sulfide to obtain
dapsone, a known drug for malaria treatment (Scheme 1).
1/2
[
F(R ∞)] and [F(R ∞)hυ]
curve [54,55].
2.3.5. TG-DTA
The TG-DTA analyses of the samples were accomplished by a
Shimadzu DT 50 equipment. They were made under Ar atmosphere, in
the temperature range 20–650 °C using 25–50 mg of the solid and a
heating speed of 10 °C/min.
2. Experimental
2.3.6. Acidity measurements
The acid strength and the number of acid sites were estimated from
the n-butylamine potentiometric titration results (for more details
2.1. Synthesis of [N(Prop) ](3+x)[PV W O40] with x = 1 or 2
4 x 12-x
about the technique see supplementary information)
The POTVs were synthesized according to the literature data [53].
NaHPO ·12H O (0.025 mol) was added to an aqueous solution of
Na WO ·2H O (0.019 mol) under continuous stirring, and the pH was
adjusted with HCl (36% v/v) to 2.8. After stirring, 3.75 ml (PVW) or
.00 ml (PV2W) of vanadium stock solution was added dropwise. The
orange color solution was acidified with concentrated HCl to adjust the
pH up to 3.4. The organic salts of POTVs were obtained by the addition
of 0.012 mol of tetrapropylammonium bromide. The yellow (PVW) or
orange (PV2W) solid formed was filtered and dried under vacuum until
constant weight. Vanadium (V) stock solution was prepared by mixing
4
2
2
2
.4. Catalytic test
2
4
2
.4.1. General observations
5
All reagents were acquired from Merck and Aldrich and used
without additional purification. The amount of product was analyzed
by GC, and the reactions were controlled by thin layer chromatography
1
(
TLC). The products were identified by mass spectra or H-NMR
spectra. The yields were estimated after product purification. Aqueous
(35% w/v) was purchased from Merck, and the exact strength at
2 2
H O
4 3
NH VO (0.25 mol) with NaOH (0.50 mol) in 500 ml of distilled water.
the time of utilization was determined by iodometric titration.
2.2. Synthesis of POTV included in a poly (acrylic-co-acrylamide) gel
2.4.2. General test for the oxidation
(PAACA)
Diphenyl sulfide was used as the model reagent for sulfide oxidation
2 2
studies. They were performed with H O (aq. solution) as the oxidant,
The poly (acrylic-co-acrylamide) gel was prepared following the
method described by Dorkoosh [38] (for a typical synthesis of PAACA
see supplementary information).
acetonitrile as the solvent, in a batch reactor at 25 °C, using POTV (PVW
and PV2W) and synthesized hybrid materials (PAACA-PVWX and
PAACA-PV2WX) as homogeneous or heterogeneous catalysts
Scheme 1. Oxidation reaction of 4,4´-diamino
diphenyl sulfide to dapsone.
9

R.A. Frenzel et al.
Molecular Catalysis 457 (2018) 8–16
respectively. We made experiments using excess of H
2
O
2
(10 mmol of
Table 1
Vibration frequencies (cm−1) of PW, PVW and PV2W.
H
2
O
2
per 1 mmol of sulfide). We also tested the oxidation reaction using
lower amount of oxidant (0.3 and 0.5 ml of 35% w/v H ) but very
long reaction times were required to obtain suitable conversion values.
So we decided to use 1 ml of 35% w/v H for the catalytic test. More
2 2
O
Compounds
ν W-Od
ν W-Ob-W
ν W-Oc-W
ν X-Oa
PW
PVW
PV2W
982
963
960
890
889
889
793
810
807
1080
1096, 1070
1095, 1078, 1062
2 2
O
details about the experimental conditions and the identification of the
products were added in the supplementary information.
2
.4.3. Catalyst reuse
Stability tests of the PAACA-PV2W30 catalyst were studied per-
agreement with those previously reported, confirm that the V(V) was
incorporated into the primary structure of the Keggin anion.
Additionally, the FT-IR spectra of PVW and PV2W exhibit the
forming three consecutive reactions, under the same conditions. After
each test, the catalyst was isolated from the reaction mixture, washed
with acetonitrile (2 × 2 mL), dried under vacuum, and then reused.
characteristic bands of organic cation alkyl chains at 1380, 1412, 2880
−1
and 2975 cm
assigned to the vibration of the CeH bonds.
The 31P MAS-NMR spectra corresponding to PVW and PV2W ma-
2
2
(
.4.4. Product identification
terials (Fig. 2) show a single line with a maximum at −14.2 and
.4.4.1. Diphenyl sulfone. Colorless solid. M.p.: 127–129 °C. EM, m/z
−
13.5 ppm respectively, which are in agreement with the values re-
relative intensity): 218 (M+) (36%), 153 (7%), 125 (100%), 97 (12%),
ported in the bibliography [58,59]. The downfield shift observed,
7
7(37%), 51 (23%).
31
compared to the PW (−15.3 ppm), is assigned to the decrease of the
nucleus screening as a result of the replacement of one or two W by V
60].
On the other hand, the 51 V-NMR spectra of PVW and PV2W samples
P
2
.4.4.2. 4,4´-diamino diphenyl sulfone (dapsone). Colorless solid.
[
1
M.p.:174-176 °C. H-NMR: 5.98–6.25 (s, 4H, NH
2
), 6.5–8 (m, 8H,
ArH), CDCl
. Results and discussion
.1. Materials characterization
3
.
display two lines (with maximum at -546 and −550 ppm) and one line
(
with maximum at −552 ppm) respectively, in concordance with the
3
4−
5−
values previously reported for the [PVW11
anions [59,61].
O
40
]
2 10 40
and [PV W O ]
3
The previously mentioned FT-IR characteristic bands of
4−
2 10
and [PV W O
40]5- anions are present in the FT-IR
[
PVW11
O
40
]
The infrared spectra of H
prop) [PV 40] (Fig. 1) show absorption bands characteristic of
the Keggin structure in the range 700-1100 cm , in concordance with
3 4 4
PW12O40, [N(prop) ] [PVW11O40] and [N
spectra of the hybrid materials PAACA-PVWX (Fig. 3) and PAACA-
PV2WX (Fig. 4) overlapping those belonging to the PAACA. Ad-
ditionally, their intensity diminishes due to the decrease of poly-
(
4
]
5
2 10
W O
−
1
3
−
the literature [53,56]. The spectrum of [PW12
O
40
]
anion displays
oxotungstovanadate content.
−
1
bands at 1080, 982, 890, 793, 595 and 524 cm , assigned to the
stretching vibrations PeOa, WeOd, WeObeW, WeOceW, and to the
bending vibration OaePeOa, respectively [57]. The subscripts indicate
oxygen bridging W and the P heteroatom (a), corner sharing (b) and
edge sharing (c), oxygen belonging to WO
oxygen (d).
The spectra of PVW and PV2Wshow that the band at 1080 cm
assigned to the ν3 vibration of the central PO tetrahedron splits into
two (1096 and 1070 cm ) and three (1095, 1078 and 1062 cm
components, respectively, due to the symmetry decrease of the PO
The 31P MAS-NMR spectra of PAACA-PVW10, PAACA-PVW20, and
PAACA-PVW30 samples display a line with a maximum at around
4−
−
14.0 ppm, attributed to the [PVW11
O
40
]
anion [59]. The slight
downfield shift observed, compared to the PVW (−14.2 ppm), can be
ascribed to the interaction between the anion and the eCONH and ]
NH groups present in the PAACA. The interaction can be assumed to be
of the electrostatic type due to the transfer of protons to eCONH and
NH, as has been proposed for the interaction with silica and zirconia
62,63]. Similar results were obtained for the PAACA-PV2W hybrid
6
-octahedra, and terminal
2
−1
2
4
]
−1
−1
)
[
31
4
materials. Their P MAS-NMR spectra reveal the presence of a line at
tetrahedron. Furthermore, the increment of the V atoms in the het-
eropolyanion shifts IR bands to lower frequencies, in particular, the one
assigned to the W-Od band (Table 1). These results, which are in
5−
around −13.1 ppm assignable to the [PV
with the eCONH and ]NH groups.
According to FT-IR and P MAS-NMR results we can establish that
2
W
10
O
40
]
anion interacting
2
31
4
−
5−
the Keggin structure of both [PVW11
O
40
]
2
and [PV W
10
O
40
]
anions
remains unaltered after their inclusion in the polymer matrix.
The TGA diagrams of PVW and PV2W materials show a weight loss
in the range 200–250 °C corresponding to the organic cation decom-
position through a Hoffman´s elimination reaction [64,65]. According
to the DTA diagrams, the thermal decomposition of the Keggin anions
4−
5-
[
PVW11
O
40
]
and [PV
2
W
10
O
40
]
takes place at 450 and 430 °C re-
spectively [66,67].
We previously reported [68] that the DTA diagram of PAACA ex-
hibits two endothermic peaks at 68 °C and 138 °C, which were assigned
to the elimination of moisture and absorbed water respectively, and
may be accompanied by the elimination of residues of the monomer
used in the synthesis [69]. At temperatures higher than 200 °C, three
endothermic peaks due to irreversible chemical changes in the PAACA
(
such as the formation of imides, nitrile groups from the amide groups
of acrylamide and hydrocarbon chain rupture) are present [70,71].
The DTA diagrams of PAACA-PVWX and PAACA-PV2WX hybrid
materials present similar features to those of the PAACA. However, a
new exothermic peak, in the range 400–450 °C, appears in all samples
due to the decomposition of PVW and PV2W anions respectively
[
66,67]. According to the DTA-TGA results, the hybrid materials are
Fig. 1. FT-IR spectra of PW (a), PVW (b) and PV2W (c).
10

R.A. Frenzel et al.
Molecular Catalysis 457 (2018) 8–16
Fig. 2. 31P-NMR of: PW (a), PVW (b) and PV2W (c).
Fig. 3. FT-IR spectrum of: PVW (a), SAP-PVW30 (b), SAP-PVW20 (c), SAP-
Fig. 4. FT-IR spectrum of: PV2W (a), SAP-PV2W30 (b), SAP (c), SAP-PV2W20
PVW10 (d) and SAP (e).
(d) and SAP-PV2W10 (e).
thermally stables till 200 °C. So, they could be used as heterogeneous
catalysts at temperatures higher than 25 °C. However, the H O de-
2 2
composition increased significantly when the temperature was raised.
So we decided to make the oxidation experiments at 25 °C.
indicates the maximum acid strength of the sites. The area under the
curve accounts for the total number of acid sites that the titrated solid
presents. The acid strength of these sites may be classified according to
the following scale: Ei > 100 mV (very strong sites), 0 < Ei < 100 mV
(strong sites), −100 < Ei < 0 (weak sites), and Ei < −100 mV (very
weak sites) [62,63].
According to the potentiometric titration curves (Fig. 6), the acid
strength of the PAACA-PVW10 (Ei = 50 mV), PAACA-PVW20 (Ei =
90 mV) and PAACA-PVW30 (Ei = 138 mV) samples is higher than that
of the PAACA (Ei = −4 mV), but lower than that of bulk PVW (Ei =
172 mV. The same behavior is observed for PAACA-PV2W10 (Ei = 56
mV), PAACA-PV2W20 (Ei = 156 mV) and PAACA-PV2W30 (Ei = 178
The XRD patterns of the PAACA-PVWX and PV2WX (X = 10, 20 and
3
0% w/w) samples are similar to that obtained for the PAACA (Fig. 5).
They do not exhibit any characteristic diffraction lines of PVW or PV2W
72,73]. This is attributable to the fact that both POTVs are highly
[
dispersed in the polymer matrix or present as noncrystalline phases.
The acidity measurements of the catalysts by means of potentio-
metric titration with n-butylamine let us estimate the number of acid
sites and their acid strength. The initial electrode potential (Ei)
11

R.A. Frenzel et al.
Molecular Catalysis 457 (2018) 8–16
Fig. 5. XRD diagrams of: a) SAP, PVW and SAP-PVWX, X = 10, 20 and 30%w/w, b) SAP, PV2W and SAP-PV2WX, X = 10, 20 and 30%w/w.
Fig. 6. Potentiometric titration with n-butylamine of: a) SAP, PVW and SAP-PVWX, X = 10, 20 and 30%w/w, b) SAP, PV2W and SAP-PV2WX, X = 10, 20 and 30%
w/w.
12

R.A. Frenzel et al.
Molecular Catalysis 457 (2018) 8–16
Table 2
The absorption edge energy of PVW, PV2W and the
PAACA-POTV hybrid materials.
Sample
b
E (eV)
PW
PVW
3.02
1.86
1.81
2.25
2.13
2.34
2.23
2.45
2.29
PV2W
PAACA-PVW30
PAACA-PV2W30
PAACA-PVW20
PAACA-PV2W20
PAACA-PVW10
PAACA-PV2W10
vanadium atom per anion increases (Fig. 7) in agreement with previous
reports [75,76].
The UV–vis DRS spectra of the synthesized hybrid materials
PAACA-PVWX and PAACA-PV2WX) show the charge transfer bands
Fig. 7. Uv–vis DRS spectra of PW, PVW and PV2W.
(
previously mentioned (Fig. 8a and b, respectively) superimposed with
those of the PAACA. The intensity of the bands increases with the in-
crement of POTV in the hybrid material.
mV), compared with bulk PV2W (Ei = 213 mV). The acid strength and
the number of sites determined by this technique increase slightly with
increasing amount of POTV in the samples.
The UV–vis DRS spectrum of bulk TPA presents a band at 212 nm
and another broad band that extends from 250 to 450 nm [74] assigned
to the charge transfer from bridging or terminal O 2p to W 5d (WeOeW
and WeOd, respectively).
g
The absorption edge energy (E ) in the UV–vis spectrum reflects the
energy required for ligand-to-metal charge transfer (LMCT) [55,75,76].
It was reported that POM reduction potential increases with decreasing
absorption edge energy [77].
The POMs that are stronger oxidizing agents present absorption
edges at longer wavelength (lower energy), and reduction potentials at
more positive voltages.
The DRS spectra of PVW and PV2W show the absorption threshold
onset continuously shifted to the visible region when the number of
g
The E of the PW, PVW and PV2W (Table 2) decreases in parallel
with the increment of the number of vanadium atom in the Keggin
anion. On the other hand, the hybrid materials (PAACA-PVWX and
PAACA-PV2WX) show absorption edge energy higher than the parent
POTV (PVW and PV2W respectively), which slowly decreases with the
increment of POTV content in the material (Table 2).
3.2. Catalytic studies
First, the catalytic activity of PW, PVW, and PV2W was evaluated in
the diphenyl sulfide oxidation (Scheme 2) under homogeneous condi-
tions. The blank experiment (Table 3, entry 1) was carried out without
2 2
catalyst, using an excess of H O (10 mmol, 35% w/v), and 5 ml of
acetonitrile as reaction solvent at 25 °C. In these conditions, the con-
version was 5% at 24 h, increasing considerably when PVW and PV2W
were used (Table 3, entries 3 and 4), showing 100% of sulfide con-
version at 3 h, with 100% of sulfone selectivity.
Under the same reaction conditions, using PW as catalysts, 98% of
sulfide conversion with a 90% of selectivity to sulfoxide was reached
(
Table 3, entry 2). So, the synthesized materials (PVW and PV2W)
showed better catalytic performance than PW for the studied reaction.
However, they are very soluble in the reaction system, making their
isolation and reuse an exceedingly difficult labor.
Then, with the purpose of evaluating the catalytic performance of
the PAACA-PVWX and PAACA-PV2WX materials, the oxidation of DPS
to the corresponding sulfone in heterogeneous conditions was carried
out under the experimental conditions previously used for PVW and
PV2W, using the weight of PAACA-PVWX (or PAACA-PV2WX) con-
taining 0.01 mmol of PVW (or PV2W). First, we evaluated the activity
of PAACA as catalyst, and we found that it was negligible. The con-
version of DPS using PAACA (under the same experimental condition)
was 5%. This value was similar to the obtained without catalyst
(
Table 3, entry 1).
We evaluated the H
tests. For this purpose, 0.01 mmol of the catalyst, 10 mmol of H O
2 2
2
O
2
decomposition during different catalytic
, and
ml of acetonitrile were added in a test tube. After 24 h at 25 °C, the
decomposition of H was determined using yodometric titration. The
Fig. 8. Uv–vis DRS spectra of the synthesized hybrid materials: a) SAP, PVW
and SAP-PVWX; b) SAP, PV2W and SAP-PV2WX, X = 10, 20 and 30%w/w.
5
2 2
O
13

R.A. Frenzel et al.
Molecular Catalysis 457 (2018) 8–16
Scheme 2. Mild oxidation of diphenyl sulfide
(DPS).
Table 3
Table 5
Selective oxidation of diphenyl sulfide to diphenyl sulfone using PW, PVW and
Selective oxidation of diphenyl sulfide to diphenyl sulfone using PAACA-PVWX
PV2W as catalysts in homogeneous conditions.a
and PAACA-PV2WX, X = 10, 20 and 30%w/w, as catalysts in heterogeneous
a
conditions.
Entry Catalysts Sulfide Conversion
Sulfoxide
Selectivity %
Sulfone Selectivity
%
b
c
d
%
Entry Catalyst
Time Sulfide
Sulfoxide
Selectivity %
Sulfone
c
Selectivity %d
(h)
Conversion %b
1
2
3
4
Nonee
PW
PVW
PV2W
5
98
100
100
100
90
–
–
10
100
100
1
2
3
4
5
6
PAACA-
PVW10
5
7
24
5
7
24
5
7
24
5
7
2
5
7
2
5
7
13
13
29
30
32
42
70
84
93
26
28
41
52
64
100
82
90
100
35
3
65
97
88
85
89
88
100
100
100
69
100
100
100
100
100
90
–
12
15
11
12
–
–
–
31
–
–
–
–
–
10
6
PAACA-
PVW20
a
Reactions were performed by reactivity of sulfide 1 mmol and 1 ml 35%w/
in acetonitrile for 3 h at 25 °C temperature.
Determined by GC on the crude reaction mixture.
Sulfoxide Selectivity = sulfoxide/(sulfoxide + sulfone).
Sulfone Selectivity = sulfone/(sulfoxide + sulfone).
Blank experiment, 24 h.
v H
2
O
2
b
PAACA-
PVW30
c
d
e
PAACA-
PV2W10
4
4
Table 4
PAACA-
PV2W20
Selective oxidation of diphenyl sulfide to diphenyl sulfone using PAACA-PVWX
and PAACA-PV2WX, X = 10, 20 and 30%w/w, as catalysts in heterogeneous
conditions.a
PAACA-
PV2W30
94
100
Entry Catalyst
Sulfide
Conversion %
Sulfoxide
Selectivity%
Sulfone
24
–
b
c
Selectivity %d
a
2 2
Reactions were performed by reacting 1 mmol sulfide, 1 ml 35%w/v H O
1
2
3
4
5
6
PAACA-
PVW10
PAACA-
PVW20
PAACA-
PVW30
PAACA-
PV2W10
PAACA-
PV2W20
PAACA-
PV2W30
6
20
18
17
33
15
14
80
82
83
67
85
86
in acetonitrile (5 ml), 001 mmol catalyst and 25 °C temperature at 5, 7 and 24 h.
b
Determined by GC on the crude reaction mixture.
Sulfoxide Selectivity = sulfoxide/(sulfoxide + sulfone).
Sulfone Selectivity = sulfone/(sulfoxide + sulfone).
30
45
20
35
54
c
d
the samples is strongly affected by their oxidant capacity and acidity,
which increases in parallel with the POTV content.
The catalysts with 30% w/w of bulk PVW and PV2W (PAACA-
PVW30 and PAACA-PV2W30 respectively) showed the best catalytic
performance in the selective oxidation of diphenyl sulfide to the cor-
responding sulfone. Then, the conversion of DPS and the selectivity to
sulfone achieved using longer reaction times were studied. From the
obtained results (Table 5), we can see that the complete conversion of
DPS to sulfone only was achieved after 24 h using PAACA-PV2W20 and
PAACA-PV2W30 catalysts (Table 5, entries 5 and 6, respectively). At
the same reaction time, using PAACA-PVW30 as catalysts, excellent
conversion and selectivity were also obtained (Table 5, entry 3). On the
other hand, after only 7 h of reaction very good conversion (84% and
a
2 2
Reactions were performed by reacting sulfide 1 mmol, 1 ml 35%w/v H O
in acetonitrile (5 ml) for 3 h, catalyst 1% mmol and 25 °C temperature.
b
Determined by GC on the crude reaction mixture.
Sulfoxide Selectivity = sulfoxide/(sulfoxide + sulfone).
Sulfone Selectivity = sulfone/(sulfoxide + sulfone).
c
d
values obtained were in the range 12–15% (they were reported in the
supplementary information, Table S2). Additionally, the values did not
depend on the type (PVW or PV2W) and content of poly-
oxotungstovanadate in the hybrid material.
The obtained results (Table 4) show that the conversion and se-
lectivity achieved using PAACA-PVW and PAACA-PV2W hybrid mate-
rials were lower than those of the parent POTV in homogeneous con-
ditions. However, the main benefit of these catalysts is they are
insoluble in the reaction mixture system. On the other hand, the con-
version increase with the increment of the POTV percentage. As was
mentioned before, the oxidant capacity of the hybrid materials
90%, respectively) and excellent selectivity (96% and 94%, respec-
tively) were achieved using PAACA-PVW30 and PAACA-PV2W30 as
catalysts (Table 5, entries 3 and 6).
After the reaction ended, the catalysts (PAACA-PVW30 and PAACA-
PV2W30) were separated by filtration and reused using the optimized
conditions. Fig. 9 shows three consecutive catalytic cycles in the se-
lective oxidation of DPS to sulfone as a function of reaction time. The
conversion results reached are similar to the ones obtained in the first
use, showing no important loss of catalytic activity after three cycles.
With the object to appreciate the possible POTV solubilization, the
PAACA-PVW30 sample was placed in contact with pure acetonitrile for
(
PAACA-PVWX and PAACA-PV2WX) increased with the increment of
the POTV content. Additionally, their acidity increased in the same
order: PAACA-PVW10 < PAACA-PVW20 < PAACA-PVW30 (the same
behavior was exhibited by the PAACA-PV2WX samples). A. Shaabani
24 h and filtered. The acetonitrile was employed as solvent in a reaction
without incorporate the PAACA-PVW30 catalyst. Using this solvent and
after 20 h of reaction, the DPS conversion was 17%, similar to the value
obtained in the blank experiment (Table 3, entry 1).
2 2
et al. reported that the sulfide oxidation using H O solution was as-
sisted by Brönsted acidity and that acidity influences the formation rate
of peroxo complexes [78,79]. Taking into the account these reports and
our previous results [68], we can suggest that the catalytic activity of
Finally, when we use an excess of aqueous H
2 2
O , the reaction is
highly selective and proceeds in high yield to sulfone, providing an
14

R.A. Frenzel et al.
Molecular Catalysis 457 (2018) 8–16
the polymerization of AA and AM as former monomers, MBA as the
cross-linking agent and APS as the polymerization initiator. The hybrid
materials were reused without loss of their catalytic activity after three
reaction cycles. This indicates that PVW and PV2W are strongly at-
tached to the support. The main advantages of this process are the
operational simplicity, the clearness of reaction and the very good
yields attained. This process can be extended to other sulfides.
The catalyst with better performance for diphenyl sulfone was
chosen for the oxidation of 4,4´-diamino diphenyl sulfide to obtain
dapsone. The catalyst PAACA-PV2W30 showed high conversion and
selectivity values, providing an excellent, easy and clean synthesis
method for such compound.
Acknowledgments
We thank Universidad Nacional de La Plata (X773), CONICET (PIP
0449) and ANPCyT for financial support, and Lilian Osiglio and
Edgardo Soto for their collaboration in the experimental measurements.
Appendix A. Supplementary data
Supplementary material related to this article can be found, in the
online version, at http://dx.doi.org/10.1016/j.mcat.2018.07.016.
References
[
[
[
[
[
[
[
1] D.E. Katsoulis, Chem. Rev. 98 (1998) 359–387.
2] K.C. Dey, V. Sharma, Int. J. ChemTech. Res. 2 (2010) 368–375.
3] Y.P. Jeannin, Chem. Rev. 98 (1998) 51–76.
4] M.A. Rezvani, M. Oveisi, M.A.N. Asli, J. Mol. Catal. A Chem. 410 (2015) 121–132.
5] E. Rafiee, M. Khodayari, J. Mol. Catal. A Chem. 398 (2015) 336–343.
6] S. Gong, J. Lu, H. Wang, L. Liu, Q. Zhang, Appl. Energy 134 (2014) 283–289.
7] E. Nikbakht, B. Yadollahi, M.R. Farsani, Inorg. Chem. Commun. 55 (2015)
1
35–138.
[
8] S. Boudjema, E. Vispe, A. Choukchou-Braham, J.A. Mayoral, R. Bachira,
J.M. Fraileb, RSC Adv. 5 (2015).
Fig. 9. Use and reuse of SAP-PVW30 (a) and SAP-PV2W30 (b) at 25 °C for
sulfide conversion vs. time.
[9] Y. Nishimoto, D. Yokogawa, H. Yoshikawa, K. Awaga, S. Irle, J. Am. Chem. Soc. 136
(2014) 9042–9052.
10] E. Dimitris, K.D. Corning, S. Herrmann, M. Kostrzewa, A. Wierschem, C. Streb,
Angew. Chem. Int. Ed. 53 (2014) 13596–13599.
[
excellent synthesis method for such compounds.
[11] C. Y. Chen, R. L. Giddens, R. D. Carter. Patent No US 7377975 B2, USA, 2008.
[
[
12] H. Sun, N. gao, J. Ren, X. Qu, Chem. Mater. 27 (2015) 7573–7576.
13] I.A. Weinstock, R.H. Atalla, R.S. Reiner, M.A. Moen, K.E. Hammel, C.J. Houtma,
C.L. Hill, N. J. Chem. 20 (1996) 269–275.
Encouraged by the above-mentioned results, we used the same re-
action conditions in the oxidation of 4,4´-diamino diphenyl sulfide to
obtain dapsone. The reaction conditions used were: 1 mmol of sulfide,
[14] A.I. Weinstock, R.H. Atalla, R.S. Reiner, M.A. Moen, K.E. Hammel, J. Mol. Catal. A
Chem. 116 (1997) 59–84.
0.01 mmol of PAACA-PV2W30, 1 ml 35% w/v H
2 2
O , acetonitrile as
[
15] M.S. Saraiva, J.A.F. Gamelas, A.P. Mendes de Sousa, B.M. Reis, J.L. Amaral,
solvent (5 mL) and 25 °C. After 24 h, sulfide conversion was 65% with a
P.J. Ferreira, Materials 3 (2010) 201–215.
78% of selectivity to dapsone.
[16] T. Jeffrey, T. Rhule, C.L. Hill, D.A. Judd, Chem. Rev. 98 (1998) 327–357.
[
17] M.N. Timofeeva, Appl. Catal. A 256 (2003) 19–35.
[
18] S. Shikata, S. Nakata, T. Okuhara, M. Misono, J. Catal. 166 (1997) 263–271.
4. Conclusions
[19] M.E. Chimienti, L.R. Pizzio, C.V. Cáceres, M.N. Blanco, Appl. Catal. A 208 (2001)
–19.
7
[
[
20] A. Micek-Ilnicka, J. Mol. Catal. A Chem. 308 (2009) 1–14.
21] S. Uchida, K. Inumar, M. Misono, J. Phys. Chem. B 104 (2000) 8108–8115.
Polyoxotungstovanadates with Keggin structure were synthesized
and their structure was investigated by diverse techniques. In ac-
[22] C.L. Marcherena, L. Lerici, S. Renzini, L. Pierella, L. Pizzio, Appl. Catal. B 188
2016) 23–30.
23] D. Bennardi, M.N. Blanco, L.R. Pizzio, J.C. Autino, G.P. Romanelli, Curr. Catal. 4
2015) 65–72.
3
1
(
cordance to FT-IR and P-NMR results, the principals species present in
the catalysts PVW, PV2W and the hybrid materials PAACA-PVWX and
[
(
−
4
PAACA-PV2WX (X = 10, 20 and 30% w/w) are [PVW11
O
40
]
and
[24] V.D. Monopoli, L.R. Pizzio, M.N. Blanco, Mater. Chem. Phys. 108 (2008) 331–336.
[25] M.N. Gorsd, M.N. Blanco, L.R. Pizzio, Procedia Mater. Sci. 1 (2012) 432–438.
[
[
-
5
[
PV W O40] , respectively. Conform to XRD results, these species are
2 10
26] M.N. Gorsd, M.N. Blanco, L.R. Pizzio, Mater. Chem. Phys. 171 (2016) 281–289.
27] M.N. Gorsd, G. Sathicg, G.P. Romanelli, M.N. Blanco, L.R. Pizzio, J. Mol. Catal. A
Chem. 420 (2016) 294–302.
highly dispersed in the polymer or appear as noncrystalline phases.
With DTA-TGA results, we could determine that PAACA-POTV
materials do not experiment any notable chemical change up to 200 °C,
being able to be used as catalysts in the oxidation reaction studied.
Additionally, the PAACA-POTV samples exhibit strong acid sites, whose
number increases as the POTV content in them is higher.
These Keggin-type POTVs were used as catalysts for the selective
oxidation of diphenyl sulfide to diphenyl sulfone using a green oxidant
2 2
agent (aqueous H O 35% w/v). The replacement of W atoms by V
enhances their catalytic activity with respect to commercial PW.
With the purpose of recovering the catalyst with easiness after the
reaction and developing an eco-friendly procedure, the POTVs were
included in a novel support, a superabsorbent polymer, synthesized by
[28] K. Tanabe, M. Misono, Y. Ono, H. Hattori, New Solid Acids and Bases: Their
Catalytic Properties, Elsevier, Amsterdam, 1989.
29] D.Y. Ganapati, A.D. Murkute, J. Catal. 224 (2004) 218–223.
30] A. Mitsutami, Catal. Today 73 (2002) 57–63.
[
[
[31] A. Corma, Chem. Rev. 95 (1995) 559–614.
[
[
[
32] C.L. Hil, Chem. Rev. 98 (1998) 1–2.
33] A. Matlack, Introduction to Green Chemistry, CRC Press, Boca Ratón, 2010.
34] P.T. Anastas, J.C. Warner, Green Chemistry, Theory and Practice, Oxford University
Press, New York, 1998.
35] M. Lancaster, “Green chemistry: an introductory text”, Green Chemistry Network,
University of York, Royal Society of Chemistry, 2006.
36] M. Gabriela, T.C. Riberiro, D.A. Costa, A. Machado, Green Chem. Lett. Rev. 3 (2010)
149–159.
[
[
[37] M. Shibayama, T. Tanaka, Adv. Polym. Sci. 109 (1993) 1–62.
15

R.A. Frenzel et al.
Molecular Catalysis 457 (2018) 8–16
[38] F. Dorkoosh, J. Brussee, J. Verhoef, G. Borchard, M. Rafiee-Tehrani, H. Junginger,
[60] M.A. Fedotov, R.I. Maksimovskaya, J. Struct. Chem. 47 (2006) 952–978.
Polymer 41 (2000) 8213–8220.
[61] W. Huang, L. Todaro, G.P. Yap, R. Beer, L.C. Francesconi, T. Polenova, J. Am. Chem.
[
[
[
[
[
[
39] A. Shaabani, F. Tavasoli-Rad, D.G. Lee, Synth. Commun. 35 (2005) 571–580.
40] S. Dash, S. Patel, B.K. Mishra, Tetrahedron 65 (2009) 707–739.
41] D. Goheen, C. Bennett, J. Org. Chem. 26 (1961) 1331–1333.
42] A. Rostami, J. Akradi, Tetrahedron Lett. 51 (2010) 3501–3503.
43] N.J. Leonard, C.R. Johnson, J. Org. Chem. 27 (1962) 282–293.
44] M. Tajbakhsh, R. Hosseinzadeh, A. Shakoori, Tetrahedron Lett. 45 (2004)
Soc. 126 (2004) 11564–11573.
[62] R. Cid, G. Pecchi, Appl. Catal. A Gen. 14 (1985) 15–21.
[63] T.S. Rivera, A. Sosa, G.P. Romanelli, M.N. Blanco, L.R. Pizzio, App. Catal. A Gen.
443-444 (2012) 207–213.
[64] M.R. Udupa, Propellants Explos. Pyrotech. 7 (1982) 155–157.
[65] M. Ralle, J.C. Bryan, A. Habenschuss, B. Wunderlich, Acta Crystall. C Cryst.
Commun. 53 (1997) 488–490.
[66] F. Jing, B. Katryniok, F. Dumeignil, E. Bordes-Richard, S. Paul, J. Catal. 309 (2014)
121–135.
[67] C. Marchal-Roch, N. Laronze, N. Guillow, A. Tezé, G. Hervé, Appl. Catal. A 199
(2000) 33–44.
1
889–1893.
45] A. Rezaeifard, I. Sheikhshoaie, M. Monadi, H. Stoeckli-Evans, Eur. J. Inorg. Chem. 1
2010) 799–806.
46] A.A. Sosa, M.N. Gorsd, M.N. Blanco, L.R. Pizzio, J. Sol Gel Sci. Technol. 83 (2017)
55–365.
47] P. Kowalski, K. Mitka, K. Ossowska, Z. Kolarska, Tetrahedron 61 (2005)
933–1953.
48] J.G. Kublin, F.K. Fraction, K. Dzinjalamala, D.D. Kamwendo, E.M. Malkin,
J.F. Cortese, L.M. Martino, R.A.G. Mukadam, S.J. Rogerson, A.G. Lescano,
M.E. Molyneux, P.A. Winstanley, P. Chimpeni, T.E. Taylor, C.V. Plowe, J. Infect.
Dis. 185 (2002) 380–388.
[
[
[
[
(
3
[68] R. Frenzel, D. Morales, G. Romanelli, G. Sathicq, M. Blanco, L. Pizzio, J. Mol. Catal.
1
A Chem. 40 (2016) 124–133.
[69] S. Dubinsky, G.S. Grader, G.E. Shter, M.S. Silverstein, Polym. Degrad. Stab. 86
(2004) 171–178.
[70] M.J. Caulfield, G.G. Qiao, D.H. Solomon, Chem. Rev. 102 (2002) 3067–3084.
[71] I.C. Mc Neill, S.M.T. Sadeghi, Polym. Degrad. Stab. 29 (1990) 233–246.
[72] X. Tong, N.Q. Tiang, W.M. Zhu, F.H. Cao, W.F. Yan, J. Alloys Compd. 544 (2012)
37–40.
[73] W. Trakarnpruk, J. Jatupisarnpong, Appl. Petroch. Res. 3 (2013) 9–15.
[74] L.R. Pizzio, C.V. Cáceres, M.N. Blanco, Acid catalysts prepared by impregnation of
tungstophosphoric acid solutions on different supports, Appl. Catal. A Gen. 167
(1998) 283–294.
[75] R. de P. F. Bonfim, L.C. de Moura, H. Pizzala, S. Caldarelli, S. Paul, J.G. Eon,
O. Mentré, M. Capron, L. Delevoye, E. Payen, Inorg. Chem. 46 (2007) 7371–7377.
[76] K.P. Barteau, J.E. Lyons, I.K. Song, M.A. Barteau, Top. Catal. 41 (2006) 55–63.
[77] J.H. Choi, J.K. Kim, D.R. Park, T.H. Kang, J.H. Song, I.K. Song, J. Mol. Catal. 371
(2013) 111–117.
[78] A. Shaabani, A.H. Rezayan, Catal. Commun. 8 (2007) 1112–1116.
[79] Y. Ishii, K. Yamawaki, T. Ura, H. Yamada, T. Yoshida, M. Ogawa, J. Org. Chem. 53
(1988) 3581–3593.
[
[
[
[
[
[
[
[
49] A.S. Garret, M.G. Corcos, J. Lepr. Rev. 23 (1952) 106–108.
50] Y.I. Zhu, M.J. Stiller, J. Am. Acad. Dermatol. 45 (2001) 420–434.
51] R.P. Hall, T.J. Lawley, H.R. Smith, S.I. Katz, Ann. Intern. Med. 97 (1982) 165–170.
52] G. Wozel, C. Blasum, Arch. Dermatol. Res. 306 (2014) 103–124.
53] T. Uaeda, M. Komatsu, M. Hojo, Inorg. Chim. Acta 344 (2003) 77–84.
54] P. Kubelka, F. Munk, Z. Tech. Phys. 12 (1931) 593–601.
55] D.R. Park, S. Park, Y. Bang, I.K. Song, Appl. Catal. A 373 (2010) 201–207.
56] F. Jing, B. Katryniok, F. Dumeignil, E. Bordes-Richard, S. Paul, J. Catal. 309 (2014)
1
21–135.
57] L. Yunyan, T. Huang, Q. Wu, H. Ding, W. Yan, A.B. Yaroslavtsev, Mater. Lett. 121
2014) 159–161.
58] B. Ma, Z. Zhang, W. Song, X. Xue, Y. Yu, Z. Zhao, Y. Ding, J. Mol. Catal. A Chem.
68–369 (2013) 152–158.
59] P.J. Domaille, J. Am. Chem. Soc. 106 (1984) 7677–7687.
[
[
[
(
3
16