Targeted development of hydrophilic porous polysulfonamide gels with catalytic activity

Article abstract of DOI:10.1016/j.jpcs.2020.109573

We report the use of a template and functional monomers in the synthesis of three novel polysulfonamide gels with new architectures and functional groups. These mesoporous polysulfonamide gels were prepared by the condensation polymerization of benzene-1,3-disulfonyl chloride (as the main precursor), linear monomers, and cross-linkers (as variable precursors) in the presence of a silica template by a combination of sol-gel chemistry and the nanocasting technique. In this synthesis pathway, in situ polymerization onto the template surface led to the construction of a silica/polymer nanocomposite. Next, after removal of the template, the nanocomposite gels were transformed into mesoporous polysulfonamide nanospheres. After the physicochemical identification of the synthesized materials, functionalized polysulfonamides were used as reusable novel catalysts with high efficiency for the Strecker reaction under mild conditions. These polymers have Br?nsted/Lewis acid active sites, a mesoporous structure, and hydrogen bonding. Moreover, since these polymers are hydrogels that can absorb water, they can promote the Strecker reaction through chemical absorption of the generated water as a driving force. Overall, this article describes a novel synthesis procedure and application of porous polysulfonamide gels.

Full text of DOI:10.1016/j.jpcs.2020.109573

Journal of Physics and Chemistry of Solids 146 (2020) 109573
Contents lists available at ScienceDirect
Journal of Physics and Chemistry of Solids
journal homepage: http://www.elsevier.com/locate/jpcs
Targeted development of hydrophilic porous polysulfonamide gels with
catalytic activity
Sedigheh Alavinia, Ramin Ghorbani-Vaghei*
Department of Organic Chemistry, Faculty of Chemistry, Bu-Ali Sina University Hamedan, Iran
A R T I C L E I N F O
A B S T R A C T
Keywords:
We report the use of a template and functional monomers in the synthesis of three novel polysulfonamide gels
with new architectures and functional groups. These mesoporous polysulfonamide gels were prepared by the
condensation polymerization of benzene-1,3-disulfonyl chloride (as the main precursor), linear monomers, and
cross-linkers (as variable precursors) in the presence of a silica template by a combination of sol-gel chemistry
and the nanocasting technique. In this synthesis pathway, in situ polymerization onto the template surface led to
the construction of a silica/polymer nanocomposite. Next, after removal of the template, the nanocomposite gels
were transformed into mesoporous polysulfonamide nanospheres. After the physicochemical identification of the
synthesized materials, functionalized polysulfonamides were used as reusable novel catalysts with high efficiency
for the Strecker reaction under mild conditions. These polymers have Brønsted/Lewis acid active sites, a mes-
oporous structure, and hydrogen bonding. Moreover, since these polymers are hydrogels that can absorb water,
they can promote the Strecker reaction through chemical absorption of the generated water as a driving force.
Overall, this article describes a novel synthesis procedure and application of porous polysulfonamide gels.
Functionalized polysulfonamides
Hydrogen-bonding catalyst
Hydrogels
Heterogeneous catalysis
1. Introduction
of powerful catalysts because of their ease of handling and processing,
high thermal and chemical stabilities, large surface areas, nontoxicity,
New gel structures fabricated with use of organic material via tem-
plates have recently attracted the attention of many researchers. Both
template synthesis and self-organization can be used for structuring
materials with extension scales. These materials have found tremendous
use in basic and applied research, such as sorbents for the adsorption of
gas and the removal of organic compounds from water [1]. Owing to the
specific features of both polymers and porous gels, the design and syn-
thesis of novel porous polymer gels as a catalyst have attracted much
attention. The functional monomers and synthesis processes play an
essential role in the engineering of the surface properties and catalytic
activity [2–5]. Various methods have been reported for preparing
porous polymers; for example, block copolymer self-assembly, template
techniques, and a combination of templating and self-assembly tech-
niques [6]. The template techniques have shown high efficiency for the
direct replication of the inverse structure of the preformed templates
with designed pore architectures as well as pore surface properties and a
customized framework [7,8]. These pathways use hard templates that
can incorporate several chemical functional groups at the pore surface
[6]. Porous cross-linked polymers are excellent candidates for the design
recyclability, and low-cost production [9].
Several attempts have been made to develop bifunctional organo-
catalysts that possess sulfonamide hydrogen-bond donors and a basic
amine moiety for use in asymmetric reactions [10]. Polysulfonamides
are prepared from the reaction between various amines and disulfonyl
chloride [11,12]. Cross-linked polysulfonamides are polymers that form
a gel structure. Although polysulfonamide as a substrate has found po-
tential applications, there is no report focusing on polysulfonamide gel
or cross-linked polysulfonamide in the field of catalysis. Gels are
cross-linked polymers that have the ability to absorb different solvents
[13]. Cross-linked polysulfonamide is a hydrogel that can promote the
Strecker reaction through chemical absorption of the generated water as
a driving force [14]. The development of porous multifunctional poly-
sulfonamide gel such as basic amine moiety organocatalysts with
effective hydrogen bonding and a large surface area can provide inter-
esting applications for catalytic reactions.
The three-component Strecker reaction is one of the most efficient
methods for the synthesis of α-aminonitriles. These materials have been
the subject of intense interest in the chemical study of α-amino acids.
* Corresponding author.
E-mail address: rgvaghei@yahoo.com (R. Ghorbani-Vaghei).
https://doi.org/10.1016/j.jpcs.2020.109573
Received 15 November 2019; Received in revised form 21 May 2020; Accepted 22 May 2020
Available online 20 June 2020
0022-3697/© 2020 Elsevier Ltd. All rights reserved.

S. Alavinia and R. Ghorbani-Vaghei
Journal of Physics and Chemistry of Solids 146 (2020) 109573
Scheme 1. Strecker synthesis of
α
-aminonitrile derivatives and structures of porous cross-linked polysulfonamides. PEA-PSA, poly(ethylene-amine)-poly-
sulfonamide; PEMA-PSA, poly(ethylene-melamine)-polysulfonamide; PPMA-PSA, poly(phenylene-melamine)-polysulfonamide; rt, room temperature; TMSCN,
cyanotetramethylsilane.
Several catalysts have been investigated to promote this reaction to
achieve efficient and novel protocols for producing -aminonitriles
[15–20]. Therefore, further development of environmental methods for
were recorded with a Shimadzu QP 1100 BX mass spectrometer. Melting
points were determined with a Stuart Scientific SMP3 apparatus. Ther-
mogravimetric analysis (TGA) was performed with a PerkinElmer PYRIS
Diamond instrument. The qualitative analysis of the catalysts was per-
formed by energy-dispersive X-ray spectroscopy (EDS) with a Sigma
field-emission scanning electron microscope (Zeiss, Germany). Scanning
electron microscopy (SEM) was performed with China KYKY-EM3200
instrument operated at 30 kV accelerating voltage. Before the surface
area analysis, the samples were activated in a high vacuum at 80 �C for
12 h. All adsorption and desorption measurements were performed at
77 K with a Micromeritics TriStar 3020 version 3.02 (N2) system. The
data were analyzed with TriStar II 3020 version 1.03 (Micromeritics,
Norcross, GA, USA). The pore size distributions were calculated from the
adsorption-desorption isotherms. Wavelength-dispersive X-ray spec-
troscopy was performed with a TESCAN mira3 instrument. The glass
transition temperature (Tg) of the samples was measured by differential
scanning calorimetry (DSC; model PL-DSC, Polymer Laboratory Sys-
tems, UK). DSC analysis was performed at a heating rate of 10 �C/min in
a nitrogen atmosphere with 10.0 mg dried particles.
α
the synthesis of α-aminonitriles is still in great demand. In continuation
of our interest in exploring catalytic methods [21], in this study, an
efficient and straightforward method for the one-pot synthesis of
α
-aminonitriles in the presence of three different porous poly-
sulfonamide gels—poly(ethylene-amine)-polysulfonamide (PEA-PSA),
poly(ethylene-melamine)-polysulfonamide (PEMA-PSA), and poly
(phenylene-melamine)-polysulfonamide (PPMA-PSA)—is described
(Scheme 1).
2. Experimental
2.1. Materials
All commercially available chemicals were obtained from Merck and
Fluka and were used without further purification otherwise stated.
Nuclear magnetic resonance (NMR) spectra were recorded in CDCl3 with
a Bruker Avance 400 MHz spectrometer for 1H NMR and a Bruker
Avance 100 MHz spectrometer for 13C NMR with tetramethylsilane as an
internal standard. Infrared (IR) spectroscopy was conducted with a
PerkinElmer GX Fourier transform IR (FT-IR) spectrometer. Mass spectra
2.2. Gel content
About 0.5 g of polymer (Wi) was added to the solvent and kept at
2

S. Alavinia and R. Ghorbani-Vaghei
Journal of Physics and Chemistry of Solids 146 (2020) 109573
Scheme 2. Preparation of the novel porous polysulfonamide gels with melamine or amine moieties. Formation of self-organized polysulfonamide nanopore: (a)
polymerization of polysulfonamide at the surface of silica nanoparticles; (b) extended polymerization leading to surface deposition; (c) selective dissolution of SiO2
by treatment in 5 vol% hydrofluoric acid. A, poly(ethylene-amine)-polysulfonamide; B, poly(ethylene-melamine)-polysulfonamide; C, poly(phenylene-melamine)-
polysulfonamide.
room temperature for 24 h. After separation of the swollen part via
centrifugation, it was vacuum dried at 40C for 24 h. In the next step,
samples were weighed (Wf) and the gel content was calculated accord-
ing to Eq. (1):
conditions). The nanocomposites were filtered off and washed with
acetonitrile (20 mL) three times and then dried under a vacuum at room
temperature for 12 h.
2.5. Synthesis of porous polysulfonamides
Gel content (%) ¼ Wi/Wf � 100.
(1)
The silica template of the SiO2/polysulfonamide nanocomposite
prepared as described in the previous section was removed selectively
through etching of the SiO2 nanoparticles with an HF aqueous solution.
Then 0.5 g SiO2/polysulfonamide nanoparticle and deionized water (10
mL) were placed in a plastic tube. Next, HF solution (10 mL, 10 wt%)
was added to the mixture, and the resulting mixture was magnetically
stirred for 6 h. The porous gels created were washed with water, dried at
50 �C, and sieved through an 80-mesh screen.
2.3. Synthesis of SiO2 nanoparticles
SiO2 nanoparticles with an average diameter of 20 nm were syn-
€
thesized in ethanol in accordance with the Stober method [22]. In
summary, 100 mL ethanol, 21.6 mL deionized water, and 2.9 mL
aqueous ammonia were added to a round-bottom flask and stirred at
ambient temperature for 10 min. Next, about 4.5 mL tetraethyoxysilane
was slowly added to the solution by a syringe within 30 min and the
reaction was maintained for 10 h. The SiO2 nanoparticles were sepa-
rated by centrifugation, rinsed with water and ethanol, and then dried
under a vacuum at 80 �C for 12 h.
2.6. Synthesis of α-aminonitriles
PEA-PSA, PEMA-PSA, and PPMA-PSA (50 mg) as catalysts were
added to a mixture of substituted benzaldehyde (1 mmol), substituted
anilines (1 mmol), and cyanotetramethylsilane (1.2 mmol) under
solvent-free conditions at room temperature. Once the reaction had
finished, boiling hexane (10 mL) was added to the mixture, and the
catalyst was recovered by washing with acetone and then oven dried at
50C to be used six times. The pure product was obtained by crystalli-
zation from hexane.
2.4. Synthesis of SiO2/polysulfonamide nanocomposites
SiO2 nanoparticles were modified by in situ polymerization of
benzene-1,3-disulfonyl chloride (1) (1 mol), 1,3-phenylenediamine (3),
or ethane-1,2-diamine (NH2CH2CH2NH2) (2) (0.7 mol) and 1,3,5-
triazine-2,4,6-triamine (5) or tris(2-aminoethyl)amine (4) (0.3 mol) in
the presence of SiO2 nanoparticles (0.1 g). For this purpose, 0.1 g SiO2
nanoparticles and starting material were dispersed homogeneously in
30 mL acetonitrile by ultrasonication. After stirring at room temperature
for 6 h, a SiO2/polysulfonamide nanocomposite was obtained (nano-
composites A*, B*, and C* in Scheme 2 were obtained in reflux
3. Results and discussion
3.1. Characterization of porous polymeric gels as a heterogeneous catalyst
Scheme 2 provides a schematic representation of the preparation of
the catalyst. Mesoporous polysulfonamide gels were prepared via the
3

S. Alavinia and R. Ghorbani-Vaghei
Journal of Physics and Chemistry of Solids 146 (2020) 109573
Fig. 1. Field-emission scanning electron microscopy images of (A) porous (A) poly(ethylene-amine)-polysulfonamide gel, (B) porous poly(ethylene-melamine)-
polysulfonamide gel, and (C) porous poly(phenylene-melamine)-polysulfonamide gel.
Fig. 2. Contact angles of nanopore water droplets on (A) poly(ethylene-melamine)-polysulfonamide hydrogel, (B) poly(ethylene-amine)-polysulfonamide hydrogel,
and (C) poly(phenylene-melamine)-polysulfonamide hydrogel.
Fig. 3. Swelling behaviors of porous polysulfonamides in water as a function of cross-linker content: poly(ethylene-amine)-polysulfonamide (PEA-PSA) with 10 wt%
N0, N0-bis(2-aminoethyl)ethane-1,2-diamine and 70 wt% ethylenediamine; poly(ethylene-melamine)-polysulfonamide (PEMA-PSA) with 10 wt% melamine and 70 wt
% ethylendiamine; and poly(phenylene-melamine)-polysulfonamide (PPMA-PSA) with 10 wt% melamine and 70 wt% phenylenediamine.
condensation polymerization of benzene-1,3-disulfonyl chloride (as the
main precursor) and functionalized monomers (as variable precursors)
in the presence of a silica template, followed by template removal with
hydrofluoric acid. In the synthesis of polysulfonamide gels, melamine
and tris(2-aminoethyl)amine were used as cross-linkers. The cross-link is
a bond that links one polymer chain to another [13]. Therefore, the final
structure of the polysulfonamides was controlled by three major factors:
(1) the properties of the silica template such as surface chemistry and
pore size, (2) the cross-linking density of the polymeric framework, and
(3) appropriate selection of the monomers. In this work, we concentrate
4

S. Alavinia and R. Ghorbani-Vaghei
Journal of Physics and Chemistry of Solids 146 (2020) 109573
Fig. 4. Fourier transform infrared spectra of (I) SiO2/poly(ethylene-amine)-polysulfonamide (PEA-PSA) (a) and porous PEA-PSA (b), (II) SiO2/poly(ethylene-mel-
amine)-polysulfonamide (PEMA-PSA) (a) and porous PEMA-PSA (b), and (III) SiO2/poly(phenylene-melamine)-polysulfonamide (PPMA-PSA) (a) and porous PPMA-
PSA (b).
Fig. 5. Energy-dispersive X-ray spectra of the polymeric catalysts. PEA-PSA, poly(ethylene-amine)-polysulfonamide; PEMA-PSA, poly(ethylene-melamine)-poly-
sulfonamide; PPMA-PSA, poly(phenylene-melamine)-polysulfonamide.
mainly on mesoporous multifunctional polysulfonamides as an effective
organocatalyst based on an amine/melamine moiety, acidic sulfon-
amide protons, and sulfonamide hydrogen-bond donors.
3.2. Morphology and wettability of hydrophilic porous polysulfonamide
gels
Morphological characterization of the polysulfonamide gels was
performed by field-emission SEM (FE-SEM). Fig. 1 shows FE-SEM images
5

S. Alavinia and R. Ghorbani-Vaghei
Journal of Physics and Chemistry of Solids 146 (2020) 109573
Fig. 6. N2 adsorption (ADS)-desorption (DES) isotherms for (A) poly(ethylene-amine)-polysulfonamide, (B) poly(ethylene-melamine)-polysulfonamide, and (C) poly
(phenylene-melamine)-polysulfonamide.
polysulfonamides.
Table 1
The wettability was examined by our measuring the contact angle.
Texture parameters obtained from nitrogen adsorption-desorption studies.
Fig. 2 presents the contact angles of water droplet samples. The contact
angle between water and polymers was less than 90�, which indicates
good hydrophilicity behavior. The contact angles are 33�, 43�, and 65�,
respectively, for PEA-PSA (Fig. 2A), PEMA-PSA (Fig. 2B), and PPMA-
PSA (Fig. 2C) [23].
Sample
BET surface area
Pore diameter by BJH
method (nm)
Pore volume
(m2 gÀ 1
)
(cm3 gÀ 1
)
PEA-PSA
PEMA-
PSA
560
381
56.36
48.80
0.43
0.37
PPMA-
PSA
265
39.78
0.24
3.3. Gel content
BET, Brunauer-Emmett-Teller; BJH, Barrett-Joyner-Halenda; PEA-PSA, poly
(ethylene-amine)-polysulfonamide; PEMA-PSA, poly(ethylene-melamine)-
polysulfonamide; PPMA-PSA, poly(phenylene-melamine)-polysulfonamide.
A higher swelling capacity and a higher swelling rate are needed in
real-world applications. The solvent-holding capacity of gels is mostly
attributed to the presence of hydrophilic groups such as amino, sulfon-
amide, and melamine groups in the polymer networks. Our studying gel
content diagrams of the porous polysulfonamide gels revealed good
compatibility with water. According to Fig. 3, the gel content was
increased for a cross-linker concentration ranging from 5% to 10% and
decreased for cross-linker concentrations higher than 10%. According to
these data, with the small amount of cross-linker, the swelling ratio was
low, because a gel with low cross-link density is unable to keep the
absorbed solvent because of insufficient network volume. On increase of
cross-linker concentration, the gel content of the polymers was
of porous cross-linked polysulfonamides. The treated samples exhibited
a porous structure with nanoscale pores. As shown in Fig. 1A, porous
PEA-PSA has the greatest pore volume. According to Fig. 1A, an increase
in pore size and pore volume occurred because of the flexible aliphatic
chain of the polysulfonamide matrix in PEA-PSA. On the other hand,
because of the aromatic framework in PPMA-PSA, the pore size and pore
volume (Fig. 1C) decreased. Therefore, polymer components resulted in
significant changes in the morphology and porosity of the
Fig. 7. Three differential scanning calorimetry scans for samples with various monomers and cross-linkers: (A) poly(ethylene-amine)-polysulfonamide; (B) poly
(ethylene-melamine)-polysulfonamide; (C) poly(phenylene-melamine)-polysulfonamide.
6

S. Alavinia and R. Ghorbani-Vaghei
Journal of Physics and Chemistry of Solids 146 (2020) 109573
Fig. 8. Thermogravimetric analysis thermograms of porous polysulfonamide gels: (A) poly(ethylene-amine)-polysulfonamide; (B) poly(ethylene-melamine)-
polysulfonamide; (C) poly(phenylene-melamine)-polysulfonamide.
PEMA-PSA, and SiO2/PPMA-PSA, respectively [25] (Fig. 4, panels I–III,
Table 2
spectra a). This peak does not appear in the FT-IR spectra of the porous
polysulfonamides (Fig. 4, panels I–III, spectra b) because of the complete
removal of the template from the nanocomposite. The presence of ab-
sorption bands at 1654 and 1684 cmÀ 1 for PEMA-PSA and at 1681 and
1684 cmÀ 1 for PPMA-PSA shows that these polymers were successfully
Optimized results for the synthesis of
α
-aminonitrile 4aa.
Entry
Catalyst
(mg)
Conditions
Time
Yield (%)b PEA-PSA PEMA-
(min)
PSA PPMA-PSA
1
2
3
4
5
6
7
8
9
–
Solvent-free, rt
Solvent-free, rt
Solvent-free, rt
Solvent-free, rt
EtOH
120
60
15
15
30
15
60
60
15
_ _ _c
modified by a cross-linker (melamine) (Fig. 4, panels II and III, spectra
25
50
100
50
50
50
50
50
58 65 70
80 85 92
80 85 92
71 75 80
77 80 83
65 68 75
52 61 65
80 85 92
–
b). The spectra of the porous polymers indicate S O stretching vibra-
–
tions at 1148 and 1334 cmÀ 1 for PEA-PSA, at 1168 and 1312 cmÀ 1 for
PEMA-PSA, and at 1155 and 1333 cmÀ 1 for PPMA-PSA [11,12].
CH3CN
Toluene
H2O
3.5. Energy dispersive X-ray spectra
Solvent-free,
50 �
C
The EDS analysis of the cross-linked polysulfonamides (Fig. 5) re-
veals the signals of sulfur, nitrogen, oxygen, and carbon in the structure
of the polymeric catalyst. Comparison of the EDS results indicated that
the Si atom was removed from the silica particles coated with poly-
sulfonamide by the HF etching.
PEA-PSA, poly(ethylene-amine)-polysulfonamide; PEMA-PSA, poly(ethylene-
melamine)-polysulfonamide;
PPMA-PSA,
poly(phenylene-melamine)-
polysulfonamide; rt, room temperature.
a
Reaction conditions: 1 mmol benzaldehyde, 1 mmol aniline, and 2 mmol
cyanotetramethylsilane under solvent-free condition at room temperature.
b
c
Isolated yield.
No reaction occurred.
3.6. N2 adsorption and desorption
gradually increased such that at 10% cross-linker concentration the
greatest absorbency was achieved. When the cross-linker concentration
was increased to more than 10%, the pores inside the gel became smaller
and, as a result, the gel content decreased. The swelling behavior may be
due to the hydrophilicity and large specific surface area of the synthe-
sized polymeric gels [24] (Fig. 3).
To determine the textural properties, the N2 adsorption-desorption
isotherms of the polysulfonamides were measured (Fig. 6). All of the
N2 isotherms are similar and reveal the typical type IV isotherm with
type H3 hysteresis (defined by IUPAC), which identified the materials as
mesoporous (Fig. 6) [26]. Table 1 summarizes the results of N2
adsorption-desorption, including pore diameters (Barrett-Joyner-Ha-
lenda method), the Brunauer-Emmett-Teller surface area, and the total
pore volume of the samples studied. These results are in good agreement
with the FE-SEM results.
3.4. FT-IR spectra
From Fig. 4, which shows the FT-IR spectra of the SiO2/poly-
sulfonamide and porous polysulfonamide samples, the following can be
(2) successful polymerization; (3) c2ross-linking; and (4) and removal of
the template to create porous polysulfonamides. The characteristic peak
of SiO2 appears at 1112, 1100, and 1150 cmÀ 1, and is attributed to Si–O
stretching vibrations of silica nanoparticles for SiO2/PEA-PSA, SiO2/
3.7. Thermogravimetric properties and DSC results
–
confirmed: (1) the presence of SiO , –S O, and –NH functional groups;
–
Fig. 7 illustrates three DSC scans for the functionalized poly-
sulfonamides. From Fig. 7, all the polysulfonamide samples have a glass
transition temperature. In PEA-PSA (Fig. 7, scan A), with a higher per-
centage of the network and a higher molecular weight, the glass
7

S. Alavinia and R. Ghorbani-Vaghei
Journal of Physics and Chemistry of Solids 146 (2020) 109573
Table 3
Synthesis of
α
-aminonitriles 4a–4x with porous polymeric compositea.
4a
4b
4c
4d
PEA-PSA: 15 min, 80%b
PEMA-PSA: 15 min, 85%
PPMA-PSA: 15 min, 92%
PEA-PSA: 20 min, 78%
PEMA-PSA: 20 min, 85%
PPMA-PSA: 20 min, 90%
PEA-PSA: 20 min, 72%
PEA-PSA: 10 min, 86%
PEMA-PSA: 20 min, 80%
PPMA-PSA: 20 min, 88%
PEMA-PSA: 10 min, 91%
PPMA-PSA: 10 min, 95%
4f
4h
4g
4e
PEA-PSA: 20 min, 80%
PEMA-PSA: 20 min, 88%
PPMA-PSA: 20 min, 92%
PEA-PSA: 25 min, 75%
PEMA-PSA: 25 min, 80%
PPMA-PSA: 25 min, 85%
PEA-PSA: 25 min, 80%
PEMA-PSA: 25 min, 83%
PPMA-PSA: 25 min, 88%
PEA-PSA: 10 min, 82%
PEMA-PSA: 10 min, 88%
PPMA-PSA: 10 min, 95%
4i
4k
4j
4l
PEA-PSA: 25 min, 72%
PEMA-PSA: 25 min, 78%
PPMA-PSA: 25 min, 84%
PEA-PSA: 25 min, 74%
PEMA-PSA: 25 min, 83%
PPMA-PSA: 25 min, 85%
PEA-PSA: 25 min, 70%
PEMA-PSA: 25 min, 77%
PPMA-PSA: 25 min, 80%
PEA-PSA: 25 min, 72%
PEMA-PSA: 25 min, 80%
PPMA-PSA: 25 min, 83%
4o
4p
4m
PEA-PSA: 30 min, 78%
PEMA-PSA: 30 min, 83%
PPMA-PSA: 30 min, 88%
4n
PEA-PSA: 15 min, 87%
PEMA-PSA: 15 min, 90%
PPMA-PSA: 15 min, 94%
PEA-PSA: 25 min, 72%
PEMA-PSA: 25 min, 75%
PPMA-PSA: 25 min, 77%
PEA-PSA: 20 min, 85%
PEMA-PSA: 20 min, 90%
PPMA-PSA: 20 min, 94%
4r
4s
4q
PEA-PSA: 35 min, 73%
PEMA-PSA: 35 min, 80%
PPMA-PSA: 35 min, 86%
PEA-PSA: 30 min, 70%
PEMA-PSA: 30 min, 75%
PPMA-PSA: 30 min, 83%
4t
PEA-PSA: 10 min, 85%
PEMA-PSA: 10 min, 87%
PPMA-PSA: 10 min, 90%
PEA-PSA: 30 min, 72%
PEMA-PSA: 30 min, 80%
PPMA-PSA: 30 min, 84%
4u
4w
4x
4v
PEA-PSA: 10 min, 83%
PEMA-PSA: 10 min, 89%
PPMA-PSA: 10 min, 94%
PEA-PSA: 30 min, 70%
PEA-PSA: 30 min, 72%
PEMA-PSA: 30 min, 82%
PPMA-PSA: 30 min, 87%
PEA-PSA: 40 min, 75%
PEMA-PSA: 40 min, 82%
PPMA-PSA: 40 min, 86%
PEMA-PSA: 30 min, 75%
PPMA-PSA: 30 min, 82%
PEA-PSA, poly(ethylene-amine)-polysulfonamide; PEMA-PSA, poly(ethylene-melamine)-polysulfonamide; PPMA-PSA, poly(phenylene-melamine)-polysulfonamide.
a
Reaction conditions: 1 mmol aldehyde, 1 mmol aniline, and 1.2 mmol cyanotetramethylsilane under solvent-free conditions at room temperature.
b
Isolated yield.
transition temperature shows a gradual rise (71C) [27]. Accordingly, the
reduction in the cross-link density leads to the glass transition shifting to
lower temperatures for PEMA-PSA (Fig. 7, scan B; 64C) and PPMA-PSA
(Fig. 7, scan C; 60C).
basis of our observations, in the absence of the catalyst, the reaction
could not proceed even after a long reaction time (entry 1). So, the
catalyst content was studied, and it found that 50 mg catalyst is the
optimal amount for this reaction (entry 3). A catalyst content less than
50 mg resulted in a low reaction yield (entry 2). In addition, the yield of
the product did not increase when the catalyst content was increased to
more than 50 mg (entry 4). The experimental results in Table 1 revealed
that room temperature and solvent-free conditions were the optimum
reaction variables (entry 3), while use of water, ethanol, toluene, and
acetonitrile as the solvent resulted in reduced yields (entries 5–8).
Further increase of the temperature to 50 �C did not have a significant
effect on the yield (entry 9). This catalytic activity is probably because of
the acidity of –NH, which is controlled by melamine groups and the
resonance effect on SO2, as well as the basicity and hydrogen bonding.
On the basis of the results and reaction yields, the hydrogen acidic
strength and the amount of hydrogen bonds per unit area of the poly-
mers are as follows: PPMA-PSA > PEMA-PSA > PEA-PSA. This could be
due to the high density of hydrogen bonds and more acidic strength in
PPMA-PSA and PEMA-PSA than in PEA-PSA.
Fig. 8 presents the TGA of the prepared polymeric samples. As can be
seen from Fig. 8, a significant weight loss occurs at 210–400C for PEA-
PSA (thermogram A) and at 270–360C for PEMA-PSA (thermogram B)
and PPMA-PSA (thermogram C). This weight loss is mainly due to the
loss of organic moieties [12]. Fig. 8 shows that the thermal stability of
PEMA-PSA and PPMA-PSA is lower than that of PEA-PSA. Hence, it is
concluded that the amount of cross-linked polymer in and the molecular
mass of PPMA-PSA and PEMA-PSA are probably less than those of
PEA-PSA.
3.8. Catalytic activity
The catalytic effect of PEA-PSA, PEMA-PSA, and PPMA-PSA nano-
composites was investigated in the synthesis of 2-phenyl-2-(phenyla-
mino)acetonitrile 4a as a model compound (Table 2). First, on the
8

S. Alavinia and R. Ghorbani-Vaghei
Journal of Physics and Chemistry of Solids 146 (2020) 109573
Scheme 3. Suggested mechanism for the synthesis of
α
-aminonitriles catalyzed by poly(ethylene-melamine)-polysulfonamide. TMSCN, cyanotetramethylsilane.
These results motivated us to examine the generality of this approach
for different aromatic aldehydes and anilines under optimized condi-
tions. According to Table 3, a broad substrate scope is observed for both
Table 4
Comparison of different methods for the synthesis of 2-phenyl-2-(phenylamino)
electron-donating and electron-withdrawing substituents. Overall, it
was observed that substituted aldehydes containing electron-
withdrawing groups reacted faster than aldehydes containing electron-
donating groups. Moreover, substituted aromatic amines with
electron-donating groups react faster than anilines with electron-
acetonitrile 4a.
Catalyst
Conditions
Time
Yielda (%)
Reference
This work
(min)
Cross-linked
Solvent-
free, rt
15
80, 85, 92
polysulfonamide (PEA-
PSA, PEMA-PSA, PPMA-
PSA, 50 mg)
(92, 92, 91,
91, 90, 90)b
Table 5
Fe3O4@ZrO2/SO24À (60 mg)
Sulfated polyborate (5 mol
%)
EtOH, rt
Solvent-
free, rt
30
2
95
98
[19]
[18]
Reusability of poly(ethylene-amine)-polysulfonamide (PEA-PSA) poly(ethylene-
melamine)-polysulfonamide (PEMA-PSA), and poly(phenylene-melamine)-
polysulfonamide (PPMA-PSA) as catalysts in the synthesis of 2-phenyl-2-(phe-
nylamino)acetonitrile.a
Polyboric acid
Solvent-
15
98
89
87
87
[18]
[29]
[30]
[28]
free, 90 �
C
Yield (%)b
PVP-SO2 complex (100 mg)
CH2Cl2, 50
360
15
�C
Run
PEA-PSA
PEMA-PSA
PPMA-PSA
Fe3O4@cellulose-OSO3H
(50 mg)
CH3CN, rt
1
2
3
4
5
6
80
80
80
79
78
78
85
85
83
83
82
82
92
92
91
91
90
90
MNPs with urethane
moieties
Solvent-
30
free, 50 �
C
MNP,
magnetic nanoparticles;
PEA-PSA, poly(ethylene-amine)-poly-
sulfonamide; PEMA-PSA, poly(ethylene-melamine)-polysulfonamide; PPMA-
PSA, poly(phenylene-melamine)-polysulfonamide; PVP, poly(4-vinyl pyri-
dine); rt, room temperature; @, Coated.
a
Reaction conditions: 1 mmol benzaldehyde, 1 mmol aniline, and 1.2 mmol
cyanotetramethylsilane.
a
b
Isolated yield.
b
Recyclability of PPMA-PSA.
Isolated yield.
9

S. Alavinia and R. Ghorbani-Vaghei
Journal of Physics and Chemistry of Solids 146 (2020) 109573
Fig. 9. Fourier transform infrared spectra of (A) poly(ethylene-amine)-polysulfonamide, (B) poly(ethylene-melamine)-polysulfonamide, and (C) poly(phenylene-
melamine)-polysulfonamide after the reaction.
withdrawing groups. All products were examined by means of their
spectroscopic data (mass spectrometry, IR spectroscopy, 13C NMR
spectroscopy, and 1H NMR spectroscopy).
substrate scope, experimental simplicity, reusability of the catalyst, and
solvent-free and metal-free conditions at room temperature. The pres-
ence of cross-linked polysulfonamides in the catalyst matrix seems
absolutely necessary for greater chemical stability of catalysts in com-
parison with other catalysts in the recycled forms because after several
runs, whatever the amount of decomposition, the activity of porous
polysulfonamides is greater.
The proposed reaction mechanism catalyzed by PEMA-PSA is shown
in Scheme 3. Several reports confirmed the presence of a dramatic in-
crease in the catalytic activity owing to the good acidic sulfonamide
protons and hydrogen bonding [10]. PEMA-PSA appears to be an active
catalytic species and is regenerated at the end of the cycle. Initially, the
catalyst activates aldehyde 1 through hydrogen bonding, following by
the nucleophilic addition of aniline 2 to afford the intermediate A, which
can promote imine formation through chemical absorption of the
generated water [14,28]. In the next step, it was speculated that the
catalyst may be effective in activating the imine through hydrogen
bonding [14,28]. At this stage, we speculate that the melamine reacts
with the silicon atom to form a pentacoordinate derivative [28a].
Moreover, the catalyst facilitates the transfer of the cyanide group to the
intermediate B. Finally, it was observed that the nucleophilic attack of
cyanide anion on the intermediate B results in the final product 4 [14,
28]. Once the reaction had finished, boiling hexane (10 mL) was added
to the mixture, the catalyst was recovered by washing with n-hexane and
chloroform, and after separation of the swollen part via centrifugation, it
was vacuum dried at 40 �C for 24 h. In the next step, the catalyst was
weighed (Wf) and the gel content was calculated. The gel contents are as
follows: 80% for PEA-PSA, 70% for PEMA-PSA, and 64% for PPMA-PSA.
These results show that catalyst can promote imine formation through
chemical absorption of the generated water.
3.9. Catalyst recycling
The reusability and catalytic activity of polymeric catalysts were
studied for about six consecutive cycles for the synthesis of 2-phenyl-2-
(phenylamino)acetonitrile 4a (Table 5). From FT-IR analysis, the recy-
cled catalyst has high polymer stability during the recycling procedure
(Fig. 9).
4. Conclusion
In the present work, three novel classes of hydrophilic poly-
sulfonamides containing a melamine and an amine moiety were syn-
thesized with use of
a template and functionalized monomers.
Functionalized polysulfonamides with Brønsted/Lewis acid active sites,
mesoporous structure, and the possibility of hydrogen bonding were
used as a novel reusable catalyst for producing α-aminonitriles with high
efficiency under mild reaction conditions. These polymers (i.e., hydro-
gels with water absorption ability) can accelerate the Strecker reaction
through chemical absorption of the produced water. Overall, this article
describes a novel synthesis procedure and application of porous poly-
sulfonamide gels.
To evaluate the efficiency of the functionalized porous poly-
sulfonamides as catalysts for the Strecker synthesis, the results obtained
were compared with those reported in the literature for other catalysts
(Table 4). The most noteworthy points of this study include broad
10

S. Alavinia and R. Ghorbani-Vaghei
Journal of Physics and Chemistry of Solids 146 (2020) 109573
[7] K. Kim, G. Yoon, S. Baek, J. Rho, H. Lee, ACS Appl. Mater. Interfaces 11 (2019)
26109–26115.
Declaration of competing interest
[8] S. Tanaka, Y.V. Kaneti, R. Bhattacharjee, M.N. Islam, R. Nakahata, N. Abdullah,
S. Yusa, N.T. Nguyen, M.J.A. Shiddiky, Y. Yamauchi, M.S.A. Hossain, ACS Appl.
Mater. Interfaces 10 (2018) 1039–1049.
The authors declare that they have no known competing financial
interests or personal relationships that could have appeared to influence
the work reported in this paper.
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(b) Y. Lei, M. Zhang, Q. Li, Y. Xia, G. Leng, Polymers 11 (2019), 2091–2033;
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(d) Y. Lei, Y. Wan, G. Li, X.-Y. Zhou, Y. Gu, J. Feng, R. Wang, Mater. Chem. Front.
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CRediT authorship contribution statement
�
[10] M. Dajek, R. Kowalczyk, P.J. Boratynski, Catal. Sci. Technol. 8 (2018) 4358–4363.
Sedigheh Alavinia: Conceptualization, Methodology, Software,
Data curation, Writing - original draft, Formal analysis. Ramin Ghor-
bani-Vaghei: Supervision, Conceptualization, Methodology, Valida-
tion, Investigation, Formal analysis, Resources, Data curation, Writing -
review & editing, Project administration.
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Acknowledgments
[17] A.M. Nauth, T. Konrad, Z. Papadopulu, N. Vierengel, B. Lipp, T. Opatz, Green
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The Bu-Ali Sina University and Center of Excellence in Development
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Appendix A. Supplementary data
Supplementary data to this article can be found online at https://doi.
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