Acidic polymer containing sulfunic acid and carboxylic acid groups heterogenized with natural clay: A novel metal free and heterogeneous catalyst for acid-catalyzed reactions

Article abstract of DOI:10.1016/j.poly.2020.114375

A novel metal-free solid acid catalyst, PHSA, has been designed and synthesized through facile and environmentally benign procedure via using halloysite nanoclay as a natural and biocompatible support. The synthetic protocol included co-polymerization of

Full text of DOI:10.1016/j.poly.2020.114375

Journal Pre-proofs
Acidic polymer containing sulfunic acid and carboxylic acid groups heterogen-
ized with natural clay: a novel metal free and heterogeneous catalyst for acid-
catalyzed reactions
Samahe Sadjadi, Maryam Akbari, Fatemeh Ghoreyshi Kahangi, Majid M.
Heravi
PII:
S0277-5387(20)30032-2
DOI:
https://doi.org/10.1016/j.poly.2020.114375
POLY 114375
Reference:
Polyhedron
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Revised Date:
Accepted Date:
19 September 2019
7 January 2020
15 January 2020
Please cite this article as: S. Sadjadi, M. Akbari, F.G. Kahangi, M.M. Heravi, Acidic polymer containing sulfunic
acid and carboxylic acid groups heterogenized with natural clay: a novel metal free and heterogeneous catalyst for
acid-catalyzed reactions, Polyhedron (2020), doi: https://doi.org/10.1016/j.poly.2020.114375
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Acidic polymer containing sulfunic acid and carboxylic acid groups
heterogenized with natural clay: a novel metal free and heterogeneous catalyst
for acid-catalyzed reactions
Samahe Sadjadi*a, Maryam Akbarib, Fatemeh Ghoreyshi Kahangic, Majid, M. Heravib
a Gas Conversion Department, Faculty of Petrochemicals, Iran Polymer and Petrochemicals
Institute, PO Box 14975-112, Tehran, Iran. Tel.: +982148666; Fax: +982144787021-3; E-mail:
samahesadjadi@yahoo.com and s.sadjadi@ippi.ac.ir
bDepartment of Chemistry, School of Science, Alzahra University, PO Box 1993891176, Vanak,
Tehran, Iran. Tel.: +98 21 88044051; fax: +982188041344; E-mail: mmh1331@yahoo.com and
m.heravi@alzahra.ac.ir
c Department of Chemistry, University Campus 2, University of Guilan, Rasht, Iran
Abstract
A novel metal-free solid acid catalyst, PHSA, has been designed and synthesized through facile
and environmentally benign procedure via using halloysite nanoclay as a natural and
biocompatible support. The synthetic protocol included co-polymerization of 2-acrylamido-2-
methylpropane sulfonic acid and acrylic acid in the presence of vinyl functionalized halloysite.
The metal-free solid catalyst that contained both carboxylic acid and sulfonic acid functionality
exhibited high catalytic activity for catalyzing both Knoevenagel condensation and Xanthenes
synthesis under mild reaction conditions in aqueous media. The presence of halloysite in the
1

structure of PHSA rendered the catalyst heterogeneous and facilitated its recovery and
recyclability compared to the halloysite-free homogeneous counterpart. High catalytic activity and
recyclability of the catalyst, simplicity of the preparation procedure, using available and natural
clay as a support are the merits of this new metal-free solid acid catalyst.
Keywords: Halloysite, Polymer, Metal free catalyst, Knoevenagel condensation, Xanthenes.
1. Introduction:
Environmental considerations and safety concerns have motivated researchers to find solid acids
as alternatives for corrosive and hazardous liquid-acid catalysts. Although traditional liquid-acid
catalysts are highly efficient, they are difficult to separate from the homogeneous reaction mixture,
resulting in non-recyclable acid waste. Acidic polymers are solid acids that can effectively catalyze
a wide range of organic reactions. Many organic reactions can be typically promoted by acid
catalysts, including synthesis of α,β-unsaturated materials and Xanthene. The Knoevenagel
condensation is the general and primitive route for the synthesis of α,β-unsaturated compounds
by condensation of aldehydes or ketones with a C–H acidic methylene group-containing
compounds [1]. It is also regarded as a key step for the synthesis of fine chemicals,
therapeutic drugs (e.g. niphendipine and nitrendipine) and functional polymers [2]. Xanthenes
are also fertile sources of biologically important molecules possessing various important
pharmacological properties such as antiviral, antibacterial and anti-inflammatory [3, 4]. In
addition, Xanthene derivatives are one of the most important classes of drugs in photodynamic
therapy and antagonists for paralyzing the action of zoxazolamine [5, 6]. Furthermore, extensive
studies have revealed that these compounds exhibit many other range of applications from utilizing
as dyes, pH-sensitive fluorescent materials for the visualization of biomolecular assemblies and
laser technology [7]. Consequently, development of various protocols for the synthesis of
2

Xanthene derivatives, particularly based on the use of heterogeneous catalysts has been found as
the subject of research of some organic and medicinal chemists in recent years. To date, several
catalysts have been reported for Knoevenagel condensation, including TiCl4 [8], MOF [9],
polyacrylonitrile fiber [10]and amine functionalized montmorillonite [11]. Synthesis of Xanthenes
has also been promoted by using various catalysts such as TiO2-SO3H [12], ionic liquid [13] and
acid functionalized SiO2 [14-16].
Although the abovementioned catalytic routes have provided significant achievements, some of
the methods are plagued by some limitations in terms of yields, long reaction times, and excess of
organic solvent, high temperatures, harsh reaction conditions and catalyst reusability. Considering
the great achievements of metal-free catalyzed reactions over the past decade and the intrinsic
advantages of these catalysts compared to metal catalysts such low cost, development of new solid
acids is of interest.
Halloysite clay (Hal) is a tubular natural clay with chemical composition similar to Kaolin [17].
The discovery of this clay dated back to many years ago. However, it has received tremendous
attention in recent decade and research groups disclosed its utilities for catalysis, cleaning, material
science and drug delivery [18-26]. Hal can be applied both in its bare form and composite with
other compounds such as dendrimers and polymers. Moreover, the properties of Hal can be tuned
via surface functionalization [27].
Pursuing our research on the development of heterogeneous Hal-based catalysts [28, 29], herein,
we disclose the synthesis of a novel metal-free acidic catalyst, PHSA, using Hal as a
biocompatible, naturally occurring and available clay. The catalyst has been prepared through co-
polymerization of 2-acrylamido-2-methylpropane sulfonic acid (AMPS) and acrylic acid (AA) in
the presence of vinyl functionalized Hal. The catalyst that possessed both carboxyl acid and -SO3H
3

groups showed high catalytic activity for promoting two types of acid catalyzed reactions,
Knoevenagel condensation and synthesis of Xanthenes. Compared to Hal-free counterpart, PHSA
was heterogeneous and could be recovered and recycled easily for five reaction runs.
2. Experimental
2.1.
The materials applied for the synthesis of the catalyst included, acrylic acid (AA), Hal, ammonium
persulfate (APS), 2-acrylamido-2-methylpropane sulfonic acid (AMPS) and
Materials
vinyltrimethoxysilane. To evaluate the catalytic activity of the catalyst, two organic
transformations, i.e. synthesis of Xanthenes and Knoevenagel condensation were targeted. To
perform these reactions, aldehydes, malononitrile and dimedone were utilized. All the chemicals
and solvents used for this research were provided from Sigma-Aldrich and used as received.
2.2.
Instruments
To confirm the formation of the catalyst, PHSA, it was analyzed via XRD, TGA, SEM,
TEM, BET, TPD and FTIR. The FTIR spectrum of PHSA was recorded by using PERKIN-
ELMER-Spectrum 65 instrument. The used XRD instrument was Siemens, D5000. Cu Kα
radiation from a sealed tube. To investigate the thermal stability of PHSA, its thermogram
was recorded via METTLER TOLEDO thermogravimetric analysis apparatus. The TG
analysis was performed under inert atmosphere and scanning rate of 10 °C.min-1. The
textural features of the PHSA was studied by accomplishing BET analysis using a Belsorp
Mini II instrument. In this analysis, the catalyst was degassed at 100 °C for 2 h. SEM images
of PHSA were recorded via a Tescan instrument, using Au-coated samples and acceleration
4

voltage of 20 kV. Transmission electron microscope (TEM) images of the catalyst were obtained
using a CM30300Kv field emission transmission electron microscope.
2.3.
Synthesis of the catalyst
2.3.1. Vinyl functionalization of Hal: synthesis of Hal-V
In order to functionalize Hal surface, Hal (1g) was dispersed in dry toluene (30 mL) via ultrasonic
irradiation for 15 min (power 100 W). Then, vinyltrimethoxysilane (2 mL) was slowly added to
the abovementioned suspension and the resulting mixture was refluxed under inert atmosphere for
24 h. At the end of the reaction, the precipitate was simply separated via filtration and washed
three times with dry toluene. The purified product was then dried in oven at 100 °C for 12 h.
2.3.2. Synthesis of PHSA
To synthesis the catalyst, PHSA, AMPS (1 g) and Hal-V (1 g) were dissolved in 25 mL of distilled
water. Subsequently, APS aqueous solution (0.1 g in 5 mL H2O) as an initiator was added in a
dropwise manner into the reaction mixture. After 30 min, AA (1g) was added slowly into the
mixture and then the resulting mixture was stirred for 24 h at 50 °C. After the completion of the
reaction, the mixture was precipitated using large volume of acetone at room temperature. The
obtained PHSA was washed at least two times to remove the unreacted monomers and then dried
in oven at 100 °C. Noteworthy, to synthesis the control catalyst, PSA, the same procedure was
followed, except, Hal-V was not applied. The procedures of the synthesis of the catalyst and
control catalyst are depicted in Figure 1.
2.4.
Evaluation of catalytic activity:
2.4.1. Knoevenagel condensation:
5

In a typical procedure, a mixture of aldehyde (1 mmol), malononitrile (1.2 mmol), catalyst (0.03
g) and H2O (3 mL) was stirred at ambient temperature for 2 h. At the end of the reaction (monitored
by TLC), EtOH (20 mL) was introduced and the catalyst was separated via simple filtration. To
reuse PHSA, it was washed with ethanol and water and dried at 100 °C in an oven. The purification
of the resulting product was accomplished by recrystallization from EtOH. The physical and
spectral data of the compounds were in agreement with those of the authentic samples, Figures S1-
S17.
2.4.2. General procedure for the synthesis of 1,8-dioxo-octahydroxanthenes derivative:
Typically, aldehyde (1 mmol), dimedone (2 mmol), catalyst (0.03 g) were mixed in H2O (3 mL)
as solvent. The resulting mixture was then stirred at room temperature for 3 h. After completion
of the reaction (traced by TLC), EtOH (20 mL) was added to the reaction mixture and PHSA was
filtered. The product was purified by recrystalization from EtOH to afford the pure products in
good to high yields.
Figure 1.
3. Result and discussion
3.1.
Verification of PHSA formation
To verify the formation of PHSA, it was subjected to XRD analysis. As illustrated in Figure 2, the
XRD patterns of PHSA and pristine Hal are similar and both showed the bands at 2θ = 11.5°,
20.2°, 26.7°, 35.4°, 55.6° and 62.1° that are the characteristic bands of Hal, JCPDS No. 29-1487
[30, 31]. Notably, the comparison of the XRD patterns of Hal and PHSA showed the lower
intensities of the bands of the latter. According to the literature, this issue can be assigned to the
presence of polymeric counterpart [32]. It is worth noting that the absence of any shift or
6

displacement of the characteristic bands PHSA compared to Hal can indicate that the polymeric
chain did not penetrate into the Hal lumen [27].
Figure 2.
To further verify the formation of PHSA, the TG analysis was performed. First, to confirm the
functionalization of Hal with silane, the thermogram of PHSA was recorded and compared with
that of Hal Figure 3. As shown, the thermal stability of Hal is slightly higher than that of Hal-V.
More precisely, Hal-V showed three weight losses at 170, 320 and 540 °C, related to the loss of
the structural water, decomposition of silane group and Hal dehydroxylation respectively [33, 34],
while Hal showed only two losses due to the loss of water and dehydroxylation. Comparing these
two thermograms, the content of silane functionality on Hal was measured to be ~ 4 wt%.
Subsequently, the thermogram of PHSA was recorded. As shown the thermal stability of PHSA
was lower than that of Hal and Hal-V and showed an additional weight loss step (about 340 °C)
due to the decomposition of polymeric component. The content of polymer on Hal was calculated
to be 15 wt%.
To provide more insight into the role of incorporation of Hal in the thermal stability of polymer,
the thermal stability of Hal-free control sample, PSA, was also recorded and compared with that
of PHSA, Figure 3. As shown, the incorporation of Hal can dramatically enhance the thermal
stability of the final catalyst.
Figure 3.
The FTIR spectrum of PHSA was also recorded and compared with that of PSA and Hal. As
shown, the FTIR spectrum of PHSA contained two types of the characteristic bands, i.e. the
characteristic bands of Hal and PSA. The characteristic bands of PSA are observed at 3372 cm-1 (-
7

-
OH), 2900 cm-1 (-CH2), 1737 cm-1 (-C=O), 1108 (SO3 stretching) and 1039 cm-1 (O=S=O
stretching in SO3H) [35] and the characteristic bands of Hal are appeared at 580 cm-1 (Al-O-Si
vibration), 3695 and 3622 cm-1 (inner –OH) and1035 cm-1 (Si–O stretching).
Figure 4.
To investigate the effect of functionalization on the textural properties of Hal, the N2-adsorption
desorption isotherms of Hal, Hal-V and PHSA were recorded and compared. From the isotherm
of Hal, Figure S18, it was found that the isotherm was of type II and the specific surface area of
Hal was 48.1 m2g-1. The measurement of the specific surface area of Hal-V showed that this value
(35 m2g-1) for Hal-V was lower than that of Hal. This issue can confirm the conjugation of V on
the Hal surface. Notably, the N2-adsorption desorption isotherm of Hal-V was of type II. The N2-
adsorption -desorption isotherm of PHSA, Figure 5, showed that upon introduction of the polymer,
the specific surface area decreased remarkably and reached to 4.9 m2g-1. This observation can
confirm the coverage of Hal surface area with polymer. It is worth noting that the isotherm of
PHSA was of type II, Figure 5, similar to that of Hal and Hal-V.
Figure 5.
Recording SEM and TEM images, the morphology of PHSA was studied. As illustrated in Figure
6. the Hal tubes are detectable in both TEM and SEM images of PHSA. In the SEM images, it can
be seen that incorporation of polymer on Hal can lead to the packing of Hal tubes. This can stem
from the interactions between the polymer functionalities. In the TEM image of the catalyst, it can
be seen that the Hal tubes are covered with polymer.
Figure 6.
8

Finally, to investigate the acidic property of PHSA, it was subjected to NH3-TPD analysis. The
temperature programmed desorption of NH3 (NH3-TPD) is depicted in Figure 7. As illustrated,
PHSA showed two broad peaks distributed in the region of 200-300 °C and 450 - 600 °C,
indicating two types of acid sites in PHSA. According to the previous reports [36], the low-
temperature desorption peak observed at 200-300 °C confirms the presence of weak acidic sites
on the catalyst. On the other hand, the high temperature desorption peak (450 – 600 °C), is
representative of the strong acidic sites on PHSA. This observation confirmed the acidic nature of
PHSA.
Figure 7.
3.2.
Investigation of the
catalytic activity of PHSA
To commence the study of the catalytic activity of PHSA, a classic acid catalyst reaction,
Knoevenagel condensation of benzaldehyde and malononitrile was targeted. First, the reaction was
performed in the absence of the catalyst at room temperature (Table 1, entry 7). The result
confirmed the necessity of the use of the catalyst for promoting this reaction. Next, the reaction
was carried out under solvent free condition with the use of 30 mg PHSA at room temperature
(Table 1, entry 6). As shown, solvent free condition was not efficient condition and moderate yield
of the desired product was furnished after 2 h. Repeating this reaction in water as solvent
remarkably increased the reaction yield and high yield of the reaction was achieved after 1h (Table
1, entry 5). Prolonging the reaction for 2 h under the aforementioned condition led to the
quantitative yield and conversion (Table 1, entry 4). Noteworthy, increase of the reaction
temperature lingered the reaction (Table 1, entry 2). Regarding the catalyst amount, use of lower
mount of the catalyst (Table 1, entry 3) led to the lower yield of the product and 91% of the product
9

was furnished after 5 h. On the other hand, increase of the used catalyst from 30 mg to 40 mg
(Table 1, entry 1) did not accelerate the reaction. Considering all these results, the best reaction
condition was use of water as solvent, 30 mg of catalyst at room temperature.
Table 1.
Finding the optimum reaction condition, the contribution of Hal to the catalysis was investigated.
To this purpose, the model Knoevenagel condensation was performed in the presence of similar
amount of Hal and PSA (Hal free catalyst, see Experimental section) as catalysts under the similar
reaction condition. The results, Table 2, showed that Hal in its bare form showed moderate
catalytic activity and could promote the reaction to furnish the product in 45% yield. PSA control
catalyst, on the other hand, showed similar catalytic activity compared to PHSA. However, PSA
was soluble in aqueous media and formed a homogeneous catalyst with tedious recyclability,
while, PHSA was heterogeneous and could be easily recovered and recycled. This can confirm
that incorporation of Hal can improve the catalytic recovery and recyclability. However, the results
showed that the role of Hal is not limited to this extent. In more detail, Hal in its individual form
can exhibit the catalytic activity and contribute to the catalysis. For that reason, in PHSA that
contained only 15 wt% PSA, the catalytic activity was similar to that of PSA. Taking these results
into account, PHSA was selected as the catalyst of the choice.
Table 2.
Motivated by high catalytic activity of PHSA as heterogeneous catalyst, the generality of the
developed protocol for the Knoevenagel condensation reaction was studied by using various
aldehydes as starting materials. As tabulated in Table 2, it can be concluded that PSHA can
efficiently promote the reaction of various substrates with different electronic properties (having
10

electron withdrawing and electron donating groups). Moreover, the heterocyclic aldehydes as well
as ketones could tolerate this reaction to furnish the corresponding products in high to excellent
yields.
The plausible reaction mechanism for Knoevenagel condensation is depicted in Figure 8. It is
postulated that the acidic groups, -SO3H and –CO2H, on the structure of PHSA, could activate
-
-
aldehyde and result in the formation of –SO3 and –CO2 groups that could activate malononitrile.
Subsequently, the reaction of both activated substrates resulted in an intermediate that could
tolerate dehydration to form the desired product [37].
Figure 8
Following the study of the catalytic activity of PHSA, it was investigated whether this solid acid
catalyst could catalyze other acid-catalyzed reaction. In this line, the synthesis of Xanthene
derivatives from reaction of aldehydes and dimedone in the presence of PHSA was examined.
Interestingly, the results, Table 3, confirmed that various aldehydes could undergo this reaction in
the presence of PHSA (30 mg) in water as solvent to furnish the corresponding products after 3 h
in high to excellent yields. Notably, furfural as heterocyclic aldehyde could also tolerate this
reaction. However, the reaction time for this substrate was longer (4 h).
Table 3.
To show the merit of this protocol for promoting Knoevenagel condensation and Xanthene
synthesis, the catalytic activity of PHSA was compared with some of the previously reported
catalysts used for catalyzing these two chemical transformations, Tables 4 and 5.
Comparing the catalytic activity of the catalyst with the reported catalysts for Knoevenagel
condensation, Table 4, it can be seen that various catalysts, including metal free and metallic
11

catalysts have been reported for promoting this reaction. As an example of metallic catalyst,
PdNi@GO can be mentioned. Despite high catalytic activity, use of precious metal and
graphenoxide (GO) as support is not economically and environmentally attractive. Use of metal
organic frameworks, MOF (Table 4, entry 1), led to high yield. However, the reaction time was
relatively high. On the other hand, the synthesis of MOF is mostly costly and time consuming. Use
of bio-based catalysts such as chitosan is environmentally interesting. However, the reaction time
was relatively long. Ionic liquids are also efficient for promoting this reaction. However, most of
them are homogeneous. Considering all of these results, it can be concluded that PHSA can be
classified as an efficient catalyst for Knoevenagel condensation.
Table 4. [38-41]
The comparison of the catalytic activity of PHSA for the Xanthene synthesis with other catalysts
also confirmed high catalytic activity of the catalyst. More precisely, compared with silica-bonded
S-sulfonic acid, PHSA can promote the reaction at lower reaction temperature and shorter reaction
time. Fe3O4@SiO2–SO3H led to the desired product in high yield in short reaction time. However,
the reaction temperature and the used catalyst amount were higher than PHSA. Some metallic
catalysts such as Nano-ZnO and Nano-NiO were not efficient for this reaction and led to very low
yields. Fe2(SO4)3.7H2O is another catalyst reported for the synthesis of Xanthenes. The yield of
the model product is lower than that of PHSA and the reaction temperature was relatively high.
Similarly, the efficiency of n-TSA was lower than PHSA and higher temperature was required for
promoting the reaction.
Table 5. [12, 14, 15, 42]
3.3.
Recovery of PHSA
12

The final part of this research is devoted to the study of the recyclability of PHSA. This issue is
important from both economic and environmental points of view. The recyclability study followed
the standard recycling test. Briefly, PHSA was recovered after the first run of model Knoevenagel
condensation and after washing and drying (Experimental section), it was re-used for the next run
of reaction. This process was repeated for six consecutive reaction runs under exactly similar
reaction condition (the optimum condition). The study of the yield of Knoevenagel condensation
after each reaction run disclosed that use of PHSA for the second run of the reaction resulted in
the quantitative yield of the desired product and the catalytic activity of PHSA did not decreased.
However, further recycling up to five reaction runs led to slight decrease of the catalytic activity.
Recycling for the sixth run, however, caused a remarkable loss of the catalytic activity and the
desired product was furnished only in 61%, Figure 9.
Figure 9.
To elucidate whether recycling can affect the structure of the catalyst, the FTIR spectrum of the
recycled catalyst after six reaction runs was compared with that of fresh PHSA, Figure 10. The
comparison of both spectra confirmed that the recycling did not destruct the structure of PHSA
and the catalyst was stable.
Figure 10.
To further investigate the recycling effect on the catalyst, the XRD pattern of the recycled catalyst
after six runs was recorded and compared with that of the fresh catalyst, Figure 11. As depicted in
Figure 11, the catalyst characteristic bands can be observed in the XRD pattern of the recycled
catalyst. Moreover, no shift in the position of the bands was observed. This can indicate the fact
that PHSA was stable and preserved its structure in the course of recycling.
13

Figure 11.
It is worth noting that the measurement of the specific surface area of the catalyst after six runs,
showed that this value slightly decrease (from 4.9 for the fresh catalyst to 3.1 m2g-1). To investigate
whether recycling can induce any change in the morphology of the catalyst, the SEM image of the
catalyst after six runs of recycling was recorded, Figure 12. Similar to the fresh PHSA, in the SEM
image of the recycled catalyst the Hal tubes can be observed. However, it can be seen that the
recycled catalyst showed more packed morphology.
Figure 12.
To elucidate whether the reagents could adsorb the protons, the pH of the reaction mixture was
examined in each reaction cycle. Notably, the fresh catalyst in aqueous media led to the acidic
media (pH = 3). Interestingly, upon recycling, the pH of the reaction mixture did not change
significantly. This observation ruled out the possibility of adoption of the protons by reagents.
Considering the results, the lower catalytic activity of the catalyst after six reaction runs can be
attributed to the partial aggregation of the Hal tubes that resulted in lower specific surface area.
This may hinder the accessibility of the reagents to the catalytic active sites.
Conclusion
PHSA as a metal free solid acid was simply prepared through vinyl functionalization of Hal
followed by co-polymerization of 2-acrylamido-2-methylpropane sulfonic acid and acrylic acid in
its presence. The study of the catalytic activity of PHSA confirmed its high catalytic activity,
superior to that of some of the previously reported catalysts for Knoevenagel condensation and
Xanthenes synthesis under mild reaction condition in aqueous media. Noteworthy, use of Hal that
is a natural and biocompatible clay in the structure of the catalyst rendered PHSA heterogeneous
14

and easy to recover (it can be recycled for six consecutive reaction runs with slight loss of the
catalytic activity). On the other hand, Hal exhibited the catalytic activity and contributed to the
catalysis. The present protocol benefits from some advantages including, facile preparation of the
catalyst using natural and biocompatible clay, high catalytic activity and recyclability, broad scope
of the reaction and environmentally benign reaction condition.
Conflicts of interest
There are no conflicts to declare.
Acknowledgment
The authors appreciate the partial supports from Iran Polymer and Petrochemical Institute, Alzahra
University and Iran National Science Foundation (INSF).
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18

Table 1. The study on the optimum condition of Knoevenagel condensation of benzaldehyde and
malononitrile in the presence of PHSA catalyst.
Temp.
PHSA
(mg)
Yield
(%)a
Entry
Solvent
Time (h)
(°C)
1
2
3
4
5
6
7
40
30
20
30
30
30
-
H2O
H2O
H2O
H2O
H2O
-
r.t.
60
r.t.
r.t.
r.t.
r.t.
r.t.
5
5
5
2
1
2
2
100
100
91
100
82
45
H2O
-
aIsolated Yield.
19

Table 2. Comparison of the catalytic activities of Hal, PSA and PHSA and study of the
generality of the PHSA-catalyzed Knoevenagel condensation
NC
CN
CHO
PHSA (30 mg)
H
NC
CN
+
H2O, r.t.
2 h
R
R
Entry
Catalyst
Hal
Substrate
Yield (%)
45
1
2
Benzaldehyde
Benzaldehyde
100
100
100
96
PSA
3
PHSA
PHSA
Benzaldehyde
4
4-NO2-benzaldehyde
3-NO2-benzaldehyde
4-Me-benzaldehyde
4-MeO-benzaldehyde
2-MeO-benzaldehyde
4-Cl-benzaldehyde
Furfural
PHSA
PHSA
PHSA
PHSA
PHSA
PHSA
PHSA
5
98
6
94
7
91
8
100
90
9
10
83
11
Acetophenone a
a 83% in 5h ( 43% in 2h).
Table 3. Synthesis of various derivatives of Xanthenes under PHSA catalysis.
20

R
O
O
O
CHO
PHSA (30 mg)
2
+
H2O, r.t.
3 h
O
R
O
Entry
Substrate
Yield (%)
100
1
2
3
4
5
6
7
8
Benzaldehyde
4-NO2-benzaldehyde
3-NO2-benzaldehyde
4-Me-benzaldehyde
4-MeO-benzaldehyde
2-MeO-benzaldehyde
4-Cl-benzaldehyde
Furfural a
100
100
96
100
93
100
91
a 91% in 4 h (65% in 3h).
Table 4. The comparison of the catalytic activity of PHSA with some of the previously reported
catalysts for the synthesis of 2-(phenylmethylene) malononitrile.
21

NC
CN
H
CHO
+
NC
CN
Entry
Catalyst [Ref.]
Quantity a Solvent
Temp. Time Yield
(°C)
(%)
Activated Hf-UiO-66-
1
0.02 g
EtOH
r.t.
4h
98
[38]
N2H3
PdNi@GO[39]
CS[40]
0.02 g
H2O/EtOH 25
8 min 95
2
3
0.025 g
EtOH
40
25
6h
98
[H3N+-CH2-CH2-
OH][CH3COO-] IL[41]
Solvent
free
4 drop
<1h
90.9
4
5
PHSA
0.03 g
H2O
r.t.
2 h
100
a The catalyst quantity was measured for 1 mmol benzaldehyde.
22

Table 5. The comparison of the catalytic activity of PHSA with some of the previously reported
catalysts for the synthesis of 3,4,6,7-Tetrahydro-3,3,6,6-tetramethyl-9-phenyl-2H-xanthene1,8-
(5H,9H)-dione.a
O
O
O
CHO
2
+
O
O
Entry
Catalyst [Ref.]
Quantity Solvent Temp.
(°C)
Time
Yield
(%)
h:min
Silica-bonded S-sulfonic acid
(SBSSA) [15]
1
0.03g
EtOH
reflux
10:00
98
97
2
3
4
Fe3O4@SiO2–SO3H [14]
Nano-ZnO [12]
0.05g
-
-
-
110
100
100
00.04
2:00
2:00
10 mol%
10 mol%
Trace
Nano-NiO [12]
Trace
91
Nano titania-supported sulfonic
acid (n-TSA) [12]
5
0.013g
-
90
1:10
6
6
Fe2(SO4)3.7H2O[42]
PHSA
10 mol%
0.03g
-
120
r.t.
1:30
3:00
86
H2O
100
a The catalyst quantity was measured for 1 mmol benzaldehyde.
23

Author’s contribution
Samahe Sadjadi: Designing the work, writing the manuscript, revising and editing, Financially
supporting.
Akbari and Ghoreyshi Kahangi: Doing experiments
Heravi: Partial financial support
24

Figure 1.The schematic procedure of the synthesis of PHSA and PSA.
25

Figure 2. XRD patterns of pristine Hal and PHSA.
26

Figure 3. TGA thermograms of Hal, Hal-V, PSA and PHSA.
27

Figure 4. FTIR spectra of Hal, PSA and PHSA.
28

Figure 5. The N2-adsorption-desorption isotherm of PHSA.
29