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