Mesostructure organic-inorganic hybrid ionic liquids based on heteropoly acids: Effect of linkage on the molecular structure and catalytic activity

Article abstract of DOI:10.1002/aoc.5170

The new inorganic–organic hybrids based on SO₃H-functionalized ionic liquids (ILs) and Keggin-type heteropoly acids (H₃PW₁₂O₄₀, H₃PMo₁₂O₄₀, and H₄SiW₁₂O₄₀; HPAs) are prepared and characterized by FT-IR, NMR, XRD, CV, SEM/EDX, ICP-OES, BJH and UV. Different molecular structures according to the different inorganic part were also proved. Potentiometric titration showed a good relationship between catalytic activity and acidity of the catalysts. Electrochemical aspects showed electron transfer ability of the compounds. For understanding catalytic activities of the HPA-IL hybrids in N-formylation reaction, effect of catalyst composition, substrate, and reaction conditions were studied. The best SO₃H-functionalized ionic liquid catalyst was readily recovered and reused for four runs. Easy preparation of the catalyst, simple and easy work-up, mild reaction conditions, low cost, excellent yields and short reaction times are the key features of this work.

Full text of DOI:10.1002/aoc.5170

Received: 17 November 2018
DOI: 10.1002/aoc.5170
Revised: 20 June 2019
Accepted: 20 July 2019
F U L L P A P E R
Mesostructure organic‐inorganic hybrid ionic liquids based
on heteropoly acids: Effect of linkage on the molecular
structure and catalytic activity
Shabnam Shahebrahimi1 | Ezzat Rafiee1,2
| Komail Sadrjavadi3
1 Department of Inorganic Chemistry,
The new inorganic–organic hybrids based on SO3H‐functionalized ionic
liquids (ILs) and Keggin‐type heteropoly acids (H3PW12O40, H3PMo12O40, and
H4SiW12O40; HPAs) are prepared and characterized by FT‐IR, NMR, XRD, CV,
SEM/EDX, ICP‐OES, BJH and UV. Different molecular structures according to
the different inorganic part were also proved. Potentiometric titration showed
a good relationship between catalytic activity and acidity of the catalysts. Electro-
chemical aspects showed electron transfer ability of the compounds. For under-
standing catalytic activities of the HPA‐IL hybrids in N‐formylation reaction,
effect of catalyst composition, substrate, and reaction conditions were studied.
The best SO3H‐functionalized ionic liquid catalyst was readily recovered and
reused for four runs. Easy preparation of the catalyst, simple and easy work‐
up, mild reaction conditions, low cost, excellent yields and short reaction times
are the key features of this work.
Faculty of Chemistry, Razi University,
Kermanshah 67149, Iran
2 Institute of Nano Science and Nano
Technology, Razi University, Kermanshah
67149, Iran
3 Pharmaceuticas Sciences Research
Center, School of Pharmacy, Kermanshah
University of Medical Sciences,
Kermanshah, Iran
Correspondence
Ezzat Rafiee, Department of Inorganic
Chemistry, Faculty of Chemistry, Razi
University. Kermanshah, 67149, Iran.
Email: ezzat_rafiee@yahoo.com;
e.rafiei@razi.ac.ir
KEYWORDS
heterogeneous catalyst, Heteropoly acid, mesoporous material, molecular structure, organic–
inorganic hybrid materials
1 | INTRODUCTION
are liquid in a wide temperature range and show interest-
ing electrochemical behaviors.[10] Because of their unique
Hybrid materials are at the interface of the organic and
inorganic domains. These materials offer exceptional op-
portunities not only to combine the important properties
from both material domains but to create completely new
compositions with really unique properties. Hence, due to
these properties of the organic–inorganic hybrids, special
attention is paid to their application in catalysis, more
precisely biphasic and heterogeneous catalysis.[1,2]
Ionic liquids (ILs) exhibit fascinating range of properties
during the course of the last two decades which include
high thermal and chemical stability, un‐flammability, suit-
able solvation behaviors and un‐volatility.[3] Some recent
studies have reported that ILs also show outstanding
dissolving property for some cellulosic derivatives that
insoluble in traditional solvents.[4–9] Additionally, they
properties, IL has become a unique ecologically favorable
access toward modern chemistry to have broad range of
potential uses such as synthesis, catalysis, gas absorption,
and analysis, etc.[11,12] A specific category of ILs, namely
Brønsted acid functionalized ionic liquids (HILs) with
SO3H‐functionalized cations has been reported with high
acidic properties and water solubility.[13,14]
Heteropoly acids (HPAs) constitute a very great and
varied class of polyoxometalates (POMs) widely utilized
as catalysts in many organic reactions because of their
singular structural, acidic and redox properties.[15–18]
However, despite of their main characteristics they ap-
portion common disadvantages such as difficult separa-
tion and reutilization of the catalyst, low surface areas
(5–10 m2/g) tend to decrease the efficiency of active sites,
Appl Organometal Chem. 2019;e5170.
wileyonlinelibrary.com/journal/aoc
© 2019 John Wiley & Sons, Ltd.
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https://doi.org/10.1002/aoc.5170

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RAFIEE ET AL.
unsuitable thermal stability and solubility in polar sol-
vents. These disadvantages can be overcome by dispersal
of HPAs on different supports to improve catalytic perfor-
mances in heterogeneous reaction applications.[1,19]
HPAs‐based hybrid materials are produced by the
combination of organic species with HPAs. Recent pro-
gresses in ILs investigation reported other paths to obtain
organic–inorganic hybrid salts by creation of ionic linkages
between an organic IL cation and an inorganic HPA anion.
HPAs‐based hybrid materials have been widely probed as
solid acid catalysts. These materials are anticipated to pos-
sess low solubility in organic solvents, high melting point
and high mass transfer resistance, and satisfaction as acid
catalysts for organic reactions.[20–23]
Amine formylation to formamides is a key reaction
in organic synthesis due to the many usages of for-
mamides as synthetic intermediates.[24] They have been
widely used in the synthesis of pharmaceutically impor-
tant compounds such as fluoroquinolines, substituted
aryl imidazoles, 1,2‐dihydroquinolines, nitrogen‐bridged
heterocycles, isocyanides, formamidines, oxazolidinones.
In the Vilsmeier reaction, catalyst was used for allylation
and hydrosilylation of carbonyls and also as an important
amino protecting group.[25,26]
double beam UV–vis spectrophotometer (NORDANTEC‐
GmbH) diode‐array spectrometer using quartz cells of
1 cm optical path and the concentration of samples is
0.1 g/l in water. The N2 adsorption–desorption isotherm
and BJH pore diameter distribution were estimated on a
Sorptometer Kelvin 1042 using nitrogen adsorption at
77 K. The electrochemical behavior of the catalyst was
studied in Dimethyl sulfoxide (DMSO) (0.5 M NaClO4).
A glassy carbon electrode was used as the electrode and
Ag/AgCl as the reference electrode. Cyclic voltammo-
grams (CV) were obtained at a scan rate 0.2 V/s and ambi-
ent temperature (20 5 °C). The porosity was measured
with sorptometer kelvin 1042 using nitrogen adsorption
at 77 K. The selected products of N‐formylation were char-
1
acterized by H NMR using a Bruker Avance 400 MHz
NMR spectrometer.
2.2 | Preparation of the catalysts
2.2.1 | Preparation of 4,4′‐bis(3‐
sulfopropyl) bipyridinium (bPyPS) and
4,4′‐bis(4‐sulfobutyl) bipyridinium (bPyBS)
In current research, the combination of the cations
of SO3H‐functionalized ILs by propane sulfonate with
inorganic anionic HPA was used to give composite ILs
(HPA‐ILs) as effective catalysts. Also, we exhibit the use
of special recoverable heterogeneous HPA‐ILs for the
formylation of amines to produce formamides, under sol-
vent free conditions.
4,4′‐bipyridine (1.56 g, 0.01 mol) was solved in 10 ml
dimethyl sulfoxide. Then 0.025 mol 1,3‐propane sultone
(PS) or 1,4‐butane sultone (BS) was added slowly within
5 min and this mixture was stirred for 6 hr at 80 ̊C. The
reaction mixture was distilled to remove dimethyl sulfox-
ide, then washed with diethyl ether five times and dried
at 100 ̊C for 3 hr. The final products denoted as bPyPS
or bPyBS were white powders (Scheme 1).
2 | EXPERIMENTAL
2.1 | Material and methods information
2.2.2 | Preparation of HPA‐ILs
All used substances and solvents were bought from Fluka,
Aldrich or Merck Company and used without further
purification. FT‐IR spectra were recorded as KBr pellets
using a Shimadzu 470 spectrophotometer. TE‐SCAN
Scanning electron microscopy (SEM) and energy disper-
sive X‐ray spectroscopy (EDX) were used to examine the
morphology and composition of the catalyst. Quantitative
bulk elemental composition of the catalyst was evaluated
by inductively coupled plasma optical emission spectros-
copy (ICP‐OES) VARIAN VISTA PRO. X‐ray diffraction
(XRD) patterns were collected with a diffractometer on
For the synthesis of HPA‐IL catalysts, H3PW12O40 (PW),
H3PMo12O40 (PMo) and H4SiW12O40 (SiW) are used as
HPA. The resulting bPyPS (0.004, 0.004 and 0.0027 mol)
was added to an aqueous solution of PW, PMo and SiW
(0.0027, 0.0027 and 0.00133 mol in 10 ml H2O) respectively.
The mixture was stirred at room temperature for 24 hr.
Water was removed in a vacuum to give the final pro-
ducts (bPyPS)3(PW)2, (bPyPS)3(PMo)2 and (bPyPS)2(SiW)2
denoted as bPyPSPW, bPyPSPMo and bPyPSSiW respec-
tively, which are respectively white, green and white pow-
ders. 0.004 mol of bPyBS was added to an aqueous solution
of PW (0.0027 mol in 10 ml H2O) to synthesize bPyBSPW.
Mixture was stirred at room temperature for 24 hr. Final
white product (bPyBS)3PW denoted as bPyBSPW was ob-
tained after water removal.
1
Riguka, Japan, RINT 2500 V using Cu‐Kα radiation. H
NMR spectra data for SO3H functionalized ILs were
recorded by BRUKER 300 MHz AVANCE III. The poten-
tial variation was measured with a Metrohm 713 pH meter.
The absorption spectra of UV–vis were achieved with T80

RAFIEE ET AL.
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SCHEME 1 Structures of the SO3H‐functionalized ILs
silica gel using EtOAc/hexane as eluent. Selected isolated
products gave suitable spectral data (1H NMR) and com-
pared with those reported in literature.[27,28]
2.3 | Acidity measurement
For measurement of the acidity of samples using potentio-
metric titration, 0.05 g of solid catalyst was suspended in
90 ml of acetonitrile and stirred for 3 hr. Then the suspen-
sion was titrated with 0.05 N solution of n‐butylamine in
acetonitrile. The potential variation was evaluated with a
Metrohm 713 pH meter using a double junction electrode.
3 | RESULTS AND DISCUSSION
The HPA‐IL catalysts were synthesized by two‐step reac-
tion (Scheme 1, 2). The zwitterionic‐type compounds were
prepared through one‐step sulfonation, reaction of 4, 4′‐
bipyridine with 1,3‐propane sultone or 1,4‐butane sultone.
The zwitterionic products were analyzed by 1H NMR
2.4 | N‐formylation reactions under
solvent‐free conditions
1
(Figure 1). Based on H NMR results no by‐product was
A blend of aniline (1.0 mmol), aq. formic acid (98%,
2.0 mmol), and HPA‐ILs (0.020 g) was stirred at room tem-
perature under solvent‐free conditions. The progress of
the reaction was continuously monitored by Thin‐Layer
Chromatography (TLC). After the reaction completion, as
indicated by TLC tests, the catalyst was recovered with
addition of ethyl acetate to the reaction mixture and
washed with ethyl acetate. Then the catalyst was dried to
be reused in a new N‐formylation reaction. The isolated
organic phase was washed with a saturated solution of
NaHCO3 and dried over anhydrous Na2SO4. The crude
product was purified by column chromatography on
produced in bPyPS synthesis procedure and present of
two type of aromatic hydrogens shows 1,3‐propane sultone
was connected to each two N atoms in 4, 4′‐bipyridine mol-
ecule. In these spectra, the peaks of the aliphatic hydrogens
of bPyPS were observed in 4.83, 2.97 and 2.47 ppm, related
to CH2‐N, CH2‐S and C‐CH2‐C respectively (Figure 1a).
Nevertheless, in bPyBS product 1,4‐butane sultone was
connected to only one N atom in 4, 4′‐bipyridine molecule
(Figure 1b).
The zwitterion acidification was performed by mixing
of bPyPS with PW, PMo and SiW as well as bPyBS with
PW, which led to the creation of organic–inorganic salts.
SCHEME 2 Preparation of bPyPSPW as
an example

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FIGURE 1 1H NMR spectra of (a)
bPyPS and (b) bPyBS

RAFIEE ET AL.
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FIGURE 2 FT‐IR spectra of (a) bPyPS, (b) PW, (c) bPyPSPW, (d) reused bPyPSPW, (e) bPyBS, (f) bPyBSPW, in left, and (a) bPyPS, (b) PMo,
(c) bPyPSPMo, (d) SiW, (e) bPyPSSiW in right
The procedure of synthesis of bPyPSPW was showed in
Scheme 2 as an example.
UV–vis is a very suitable method to study the electronic
properties of the metal‐center ions. Most of HPAs have
characteristic bands in the middle of the range UV–vis.
The spectra of HPA‐ILs are shown in Figure 3. A distinc-
tive peak of the HPAs in their non‐reduced form was
depended on ligand to metal charge transfer (LMCT) band
that seem in the UV area below 400 nm.[32–34] Radiance
UV light to HPA‐ILs causes the electrons to excite from
the low‐energy electronic levels (O, 2p orbitals) to the
high‐energy levels (metal, d orbitals). The size of the clus-
ter and counter‐cation in HPAs affect their energy of the
electronic transitions. The absorption bands at 205 nm
(bPyPSPW and bPyPSPMo) and 210 nm (bPyBSPW)
related to the O → P transition and the O → Si transition
has the absorbed band at 205 nm (bPyPSSiW). The bands
appear at 255 nm for bPyPSPW and bPyBSPW, and
260 nm for bPyPSSiW are owing to the LMCT of
O2− → W6+ in the Keggin units of HPA.[35–38] The bPyPS
and bPyBS cations have an intense and broad absorption
band at approximately 260 nm, ascribed to the π‐π* tran-
sition of the 4, 4′‐bipyridine. The results indicate that
in four compounds of HPA‐ILs Keggin structure of
HPAs is preserved in spite of interaction with bPyPS and
bPyBS cations.
In our investigations, we made HPA‐ILs with differ-
ent HPA and IL parts, and their structural characteris-
tics were studied using FT‐IR, UV–vis and XRD
techniques. Characteristic peaks of Keggin anions pres-
ent in the HPA‐ILs have been shown in the FT‐IR spec-
tra (Figure 2) which are useful to investigate the
structural and bonding changes of these compounds.
The vibrational bands for [PMo12O40]3−[29] are shown
in 1064 cm−1 (P‐O), 961 cm−1 (Mo = O), 871 cm−1
(Mo‐Oc‐Mo) (corner‐sharing), and 779 cm−1 (Mo‐Oe‐Mo)
(edge sharing). The bands [SiW12O40]4−[30] are placed at
1019 cm−1 (Si‐O), 983 cm−1 (W=O), 924 cm−1 (W‐Oc‐W)
(corner‐sharing), and 781 cm−1 (W‐Oe‐W) (edge sharing).
The typical bands [PW12O40]3‐[31] are illustrated in
1080 cm−1 (P‐O), 984 cm−1 (W=O), 896 cm−1 (W‐Oc‐W),
and 814 cm−1 (W‐Oe‐W) bands. In the HPA‐ILs, the char-
acteristic bands are at the same wavenumbers or with
a small shift according to the interaction HPA with IL.
Moreover, vibrations at 1036 and 1165 cm−1 can be attri-
bute to stretching mode of sulfonic groups in catalysts
and N‐C quaternization stretching frequency at 1640 cm
−1. The results exhibit that the amplification and weaken-
ing of the bonds of the HPAs is due to the interaction
between the SO3H‐functionalized IL cations and the HPAs
(Figure 2).
For more investigation, cyclic voltammetry was used
to study electrochemical behavior of HPA‐ILs. Figure 4
shows the CV of IL, HPA and HPA‐ILs for comparison.

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FIGURE 3 UV–Vis spectra of HPA‐ILs
FIGURE 4 CV of ILs, HPAs and HPA‐ILs (0.03 g) in DMSO (0.5 M NaClO4), scan rate 0.2 V/s, ambient temperature (20
5 ̊C)

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TABLE 1 Electrochemical data
demonstrate that the crystalline structure of HPA as the
result of interaction with IL converted to non‐crystalline
structure.[39]
Potential Shift
Epc
(V)
Epa
(V)
Catalyst
ΔΕpc (V)a
ΔΕpa (V)b
The acidity of HPAs was affected with formation of
HPA‐ILs. Potentiometric titration with an organic base
was used for acidic properties investigations. Titration
curves obtained for different SO3H‐functionalized HPA‐
ILs are presented in Figure 6. It is considered that the
maximum strength of the acid sites is exhibited with the
initial electrode potential (Ei). Value from which the
plateau is reached (mmol amine/mmol catalyst) indicates
the total number of acid sites (na) that are present in the
titrated solid.[40] As shown in Figure 6, all produced HPA‐
ILs displayed very strong acid sites, Ei > 100 mV. Based
on Figure 6a, it seems that IL affect the Ei of PW and
bPyBS decrease Ei of PW more than bPyPS, although
both of bPyBSPW and bPyPSPW are very strong acids
(Ei > 100 mV). According to the titration curves, it was
observed that relative acidic strength of bPyPSPW is more
than bPyBSPW (Figure 6a), bPyPSPMo and bPyPSSiW
(Figure 6b). Strength of acidic sites of produced HPA‐
ILs is as the following trends: bPyPSPW > bPyPSPMo >
bPyPSSiW > bPyBSPW (Ei values for these compounds
are 472.5, 301.0, 293.8, and 222.2 mV respectively). As a
result, probably bPyPSPW may show higher catalytic
activity due to higher acidic strength of this catalyst and
the number of acidic sites (na) of bPyPSPW is 1.8 that is
higher than other HPA‐ILs.
PW
−0.162
−0.732
−1.233
0.733
−0.295
−1.203
bPyPSPW
bPyBSPW
1.532
−0.184
−0.932
−1.272
−2.190
1.542
0.464
−0.104
−1.292
−1.921
0.021
0.200
0.039
0.269
−0.191
−0.089
0.713
0.020
−0.843
−1.451
−2.071
−2.361
−2.870
0.111
0.218
−0.824
−0.379
−2.550
PMo
0.266
0.056
−0.203
−0.662
−1.241
1.503
0.366
−0.083
‐
bPyPSPMo
1.434
0.177
−0.012
−0.391
‐
‐
0.316
−0.152
−0.372
−0.751
−1.260
0.089
0.068
0.188
0.050
0.069
−1.040
−0.201
More investigations on bPyPSPW have been done. The
content of W and S was evaluated quantitatively by
ICP‐OES, which showed 43.93% and 2.34% respectively.
Based on this data, bPyPS to PW molar ratio is 3:2 in
this catalyst that corresponded with neutralization of
electrical charge and possible molecular formula of
[(bPyPS)3(PW)2]. Elemental analysis carried out using
EDX (Figure 7a) showed the presence of C, N, P, W, O
and S. Morphology of bPyPSPW was investigated by SEM
(Figure 7b, 7c).
The porous nature of the best catalyst was studied
using BJH method. The N2 adsorption–desorption iso-
therm and BJH pore diameter distribution are shown in
Figure (7d, 7e) Based on the isotherm curve, bPyPSPW
is mesoporous with the pore diameter of 25 nm.
SiW
1.372
−0.594
−1.143
−2.041
−2.171
1.332
0.733
−0.404
−0.983
−2.431
bPyPSSiW
1.382
−0.863
1.282
0.673
−0.010
0.269
0.050
0.060
−2.181
−2.321
−0.943
−2.401
0.140
0.150
−0.040
−0.030
aEpc (HPA) ‐ Epc (HPA‐IL).
bEpa (HPA) ‐ Epa (HPA‐IL).
The shift in the potential of some redox peak of HPA‐ILs,
clearly shows the interaction between HPA and IL. The
amount of the shifts in different peaks are reported in
Table 1. Investigation of CV of bPyPSPW, bPyPSPMo,
and bPyPSSiW show that their electrochemical synergis-
tic behavior is suitable and keep the electrochemical
property of HPA in the HPA‐ILs. In CV of bPyBSPW,
some peaks have shifted and some merge.
3.1 | Investigation of catalytic activity of
HPA‐ILs in N‐formylation reactions
Catalytic activities of synthesized HPA‐ILs were studied
by N‐formylation reaction. The reaction of aniline with
formic acid was chosen as a model reaction of N‐
formylation (Scheme 3).
The XRD patterns of bPyPS, bPyPSPW, bPyPSPMo,
bPyPSSiW, bPyBS, bPyBSPW, PW, PMo and SiW were
also investigated (Figure 5). XRD patterns of HPA‐ILs

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FIGURE 5 XRD patterns of HPA‐ILs
FIGURE 6 Potentiometric titration curves of different HPA‐ILs, different ILs and HPAs
In an experiment, this reaction was performed in the
lack of HPA‐ILs under solvent‐free conditions that prog-
ress of reaction was 40% (Table 2, entry 1). This reaction
was performed in the attendance of bPyPS and bPyBS as
catalyst (Table 2, entry 2, 3). Considering to acidity prop-
erty of SO3‐functional IL (bPyPS) the reaction efficiency
was relatively high but it is not suitable as catalyst
because of harsh recovery. It should be noted that only
5 wt.% of the bPyPS was recovered. Therefore, organic–
inorganic hybrid salts (HPA‐ILs) can be used to enhance
recycling. Catalytic activity of different HPA‐ILs deter-
mined that bPyPSPW is the best catalyst among other
HPA‐ILs [Table 2, entry 4–7].
Based on obtained results, increase of catalysis activity
bPyPSPW is proportional to its acidity and number of
acidic sites (Figure 8).
Optimum amount of the catalyst was determined
by examination of different amounts of the catalyst
(Table 3, entry 1–5). The results of Table 3 indicated
that optimum amount of bPyPSPW was 0.020 g. Also,
the content of used formic acid is very important. The
usage of additional amount of formic acid under the
same reaction conditions increases time of the reaction
and the yield of the product decreases (Table 3, entries
1, 6–8). The suitable amount of formic acid is 2 mmol.
To study the influence of the solvents, reactions were car-
ried out in ethyl acetate, acetonitrile, dichloromethane,
dimethyl sulfoxide and ethanol (Table 3, entry 9–13). Cat-
alytic performance in solvent system showed very low
yield.
Therefore, 0.020 g of the bPyPSPW and 2 mmol of
formic acid were chosen in solvent free conditions for
further reactions.
A series of aniline derivatives and formic acid were
examined under the optimum conditions and the results
are reported in Table 4.
Activity of the recovered catalyst is an important ad-
vantage when it is introduced for practical application

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FIGURE 7 (a) EDX pattern (b, c) SEM image (d) Nitrogen adsorption–desorption isotherm and (e) BJH plot of bPyPSPW
formylation reaction in solvent free conditions. At the
end of the reaction, bPyPSPW was washed with ethyl ace-
tate, separated by centrifuging and dried under vacuum.
bPyPSPW was 90 wt.% recyclable. The yield of the prod-
uct in model reaction for the first run decreased down
to 80% after fourth run (Figure 9).
SCHEME 3 N‐ formylation of amine in the presence of HPA‐ILs.
in catalytic processes. The recycling performance of
bPyPSPW was investigated in several runs of N‐
The reused catalyst was investigated by SEM/EDX
(Figure 10a, 10b and 10c). Morphology of the reused

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TABLE 2 Investigation of activity of different catalysts in the N‐
TABLE 4 N‐formylation of some amines using bPyPSPW as
formylation reactiona
catalysta
Entry
Catalyst
Time (min)
Yield (%)
Time
Yield
(%)
Entry Substrate
(min) Productb
1
2
3
4
5
6
7
‐
10 (60)
35
40 (40)
75
1
25
25
25
30
90
91
92
84
bPyPS
bPyBS
35
65
2
3
4
bPyPSPW
bPyBSPW
bPyPSPMo
bPyPSSiW
25
90
15 (25)
60
65 (65)
75
60
75
aAniline (1 mmol), formic acid (2 mmol), and catalyst (0.02 g) in solvent free
conditions at r.t.
5
6
7
45
40
60
83
80
72
8
70
70
75
76
66
9
10
160
aAromatic amine (1 mmol), formic acid (2 mmol), and bPyPSPW (0.02 g) in
solvent free conditions at r.t.
bIsolated yield; selected products were identified by comparing their 1H NMR
with those in authentic samples.[27,28]
FIGURE 8 Yield of the product as a function of catalyst acidity
and the number of acidic sites after 25 min
TABLE 3 Optimization of model reaction conditions in the
presence of bPyPSPW
Catalyst
Entry (g)
Formic acid Time Yield
Solvent
Neat
(mmol)
(min) (%)
1
0.010
0.015
0.020
0.025
0.030
0.020
0.020
0.020
0.020
0.020
0.020
0.020
0.020
2
2
2
2
2
1
3
5
2
2
2
2
2
50
70
25
50
40
60
40
90
60
60
60
25
25
45
78
90
81
83
42
89
82
77
65
80
81
79
2
Neat
Neat
3
4
Neat
5
Neat
6
Neat
7
Neat
FIGURE 9 Reusability of bPyPSPW in the model reaction after
40 min
8
Neat
9
EtOH
bPyPSPW compare with bPyPSPW has more uniform
distribution and less agglomeration that was probably
due to abrasion in solvent free conditions. Data of EDX
revealed the presence of several elements including C,
N, P, W, O and S without significant change in weight
percent of the elements.
10
11
12
13
DMSO
CH3CN
Ethylacetate
CH2Cl2
Aniline (1.0 mmol) and formic acid at room temperature.

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FIGURE 10 (a, b) SEM image and (c) EDX pattern (d) Potentiometric titration curves of reused bPyPSPW
Moreover, there is no significant change in the FT‐IR
spectrum (Figure 2d in left). Also, the acidity of reused
bPyPSPW was probed by potentiometric titration
(Figure 10d). Strength of acidic sites of reused bPyPSPW
was decreased toward bPyPSPW (Ei values are 332.5 and
472.5 mV respectively). The reduction in efficiency of
reused bPyPSPW can be justified through reduce in acidic
strength.
due to no damaging volatile solvent is unfastened into
the environment. The isolated catalyst was stable under
the present reaction conditions, could be reused at least
four times with tiny loss of its catalytic activity.
ACKNOWLEDGMENTS
The authors thank the Razi University Research Council
for support of this work.
ORCID
4 | CONCLUSION
Ezzat Rafiee https://orcid.org/0000-0002-6848-9602
In conclusion, we have developed a simple method by
reaction between HPAs and SO3H‐functionalized or-
ganic cations to produce SO3H‐functionalized HPA‐ILs.
The materials showed promising catalytic activity for
N‐formylation reaction in solvent free conditions. The
acidity of different SO3H‐functionalized HPA‐ILs was
probed by potentiometric titration. The results show that
bPyPSPW in comparison with other catalysts exhibited
excellent catalysis activity for production of formamides.
This catalytic reaction was carried out under solvent‐free
conditions that can be considered as “Green procedure”
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