Acid and base coexisted heterogeneous catalysts supported on hypercrosslinked polymers for one-pot cascade reactions

Article abstract of DOI:10.1016/j.jcat.2017.02.024

Heterogeneous microporous acid (sulfonic acid) and base (benzylamine) catalysts with high surface areas were synthesized using simple aromatic compounds through one-step external cross-linking reaction. The direct induction and control of catalytic sites were achieved by functionalized monomers using an appropriate amount of acid/base monomers. This strategy provides an easy approach to produce highly stable and acid/base functionalized microporous organic polymers. The structure and composition of the catalysts were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), nitrogen sorption, Fourier transform infrared spectroscopy (FT-IR), solid-state ¹³C cross polarization magic angle spinning (CP/MAS) NMR, thermogravimetric analysis (TGA), and element mapping analysis. The stable porous skeleton and the accurate manipulation of the catalyst structure allowed us to use the obtained polymers as compatible and efficient acid/base co-catalysts for one-pot cascade reactions. We demonstrated the use of these microporous heterogeneous catalysts for the cascade deacetalization/Henry and deacetalization/Knoevenagel reactions. The results demonstrated that preparing microporous materials from simple aromatic compounds through one-step external cross-linking reaction is indeed a cost-effective and easy-to-handle method to produce functionalized heterogeneous catalysts. The microporous heterogeneous catalysts produced by this method are highly stable and the amount of catalytically active sites can easily be controlled to form a catalytic system with two antagonistic centers.

Full text of DOI:10.1016/j.jcat.2017.02.024

Journal of Catalysis 348 (2017) 168–176
Contents lists available at ScienceDirect
Journal of Catalysis
journal homepage: www.elsevier.com/locate/jcat
Acid and base coexisted heterogeneous catalysts supported on
hypercrosslinked polymers for one-pot cascade reactions
a,
Kewei Wang a,b,1, Zhifang Jia a,b,1, Xuekang Yang a, Ling Wang a, Yanlong Gu a, , Bien Tan
⇑
⇑
a Key Laboratory of Material Chemistry for Energy Conversion and Storage, Ministry of Education, Hubei Key Laboratory of Material Chemistry and Service Failure, School of
Chemistry and Chemical Engineering, Huazhong University of Science and Technology, 430074 Wuhan, China
b Department of Chemistry and Chemical Engineering, Shanxi Datong University, Datong 037009, China
a r t i c l e i n f o
a b s t r a c t
Article history:
Heterogeneous microporous acid (sulfonic acid) and base (benzylamine) catalysts with high surface areas
were synthesized using simple aromatic compounds through one-step external cross-linking reaction.
The direct induction and control of catalytic sites were achieved by functionalized monomers using an
appropriate amount of acid/base monomers. This strategy provides an easy approach to produce highly
stable and acid/base functionalized microporous organic polymers. The structure and composition of the
catalysts were characterized by scanning electron microscopy (SEM), transmission electron microscopy
(TEM), nitrogen sorption, Fourier transform infrared spectroscopy (FT-IR), solid-state 13C cross polariza-
tion magic angle spinning (CP/MAS) NMR, thermogravimetric analysis (TGA), and element mapping anal-
ysis. The stable porous skeleton and the accurate manipulation of the catalyst structure allowed us to use
the obtained polymers as compatible and efficient acid/base co-catalysts for one-pot cascade reactions.
We demonstrated the use of these microporous heterogeneous catalysts for the cascade deacetaliza-
tion/Henry and deacetalization/Knoevenagel reactions. The results demonstrated that preparing microp-
orous materials from simple aromatic compounds through one-step external cross-linking reaction is
indeed a cost-effective and easy-to-handle method to produce functionalized heterogeneous catalysts.
The microporous heterogeneous catalysts produced by this method are highly stable and the amount
of catalytically active sites can easily be controlled to form a catalytic system with two antagonistic
centers.
Received 2 October 2016
Revised 15 January 2017
Accepted 20 February 2017
Keywords:
Hypercrosslinked polymers (HCPs)
Heterogeneous catalyst
Monofunctionalized acid and base catalyst
Ó 2017 Elsevier Inc. All rights reserved.
1. Introduction
organic-inorganic hybrid catalyst [12–15], and organic-supported
catalyst [16–18]. However, some issues are accompanied, includ-
Heterogeneous catalysts are preferred over homogeneous sys-
tems for industrial processes because of their easier separation
and recycling ability [1–4]. Multistep organic reactions generally
require different catalysts in various steps, sometimes even coop-
erating catalysts with antagonistic groups. For the continuous reac-
tions, various attempts have been made to develop heterogeneous
catalysts by simulating enzymes, which have both acidic and basic
groups in one molecule and can efficiently catalyze tandem pro-
cesses to produce various biomolecules to improve the overall
reaction efficiency by omitting the separation of catalyst from
the product [5–7]. For this purpose, many heterogeneous catalysts
containing acidic and basic groups immobilized on a carrier have
been designed, including inorganic-supported catalyst [8–11],
ing low catalytic activity due to weak acidity caused by an
unavoidable neutralization between acid and base sites in the
preparing process [10,19], complicated protection and de-
protection operations [16,20], and easy deactivation of basic sites
resulted from strong acid treatment during the base de-
protection process [8,9], all which hampered the researchers to
manipulate the loading and catalytic strength of the active sites.
To overcome these shortcomings, few mono-functionalized cata-
lysts in which acid and base groups located on different supports
have also been employed [17,18]. With this method, it is usually
easier to achieve an adjustable combination of acidic and basic cat-
alytic sites by adding the acid and base components separately.
However, to maximize the efficiency of this method for cascade
reactions, following issues need to be addressed while designing
an acid-base co-catalyst system: (i) generation of acidic and basic
catalytic sites on two separate supports having the similar chemi-
cal/physical properties as much as possible i.e., lipophilicity and
⇑
Corresponding authors. Fax: +86 (0)27 87543632.
E-mail addresses: klgyl@hust.edu.cn (Y. Gu), bien.tan@mail.hust.edu.cn (B. Tan).
1
K. Wang and Z. Jia contributed equally to this work.
http://dx.doi.org/10.1016/j.jcat.2017.02.024
0021-9517/Ó 2017 Elsevier Inc. All rights reserved.

K. Wang et al. / Journal of Catalysis 348 (2017) 168–176
169
porosity rather than on different materials to minimize the mass
transfer issues of reactants and intermediates in liquid phase reac-
tions; (ii) because of the presence of antagonistic species, the sup-
porting material and also the linkers between the catalyst and the
support should have excellent thermal and chemical stability;
otherwise, leaching of one type of catalyst into the reaction solu-
tion will poison another, resulting in rapid deactivation of the cat-
alyst; (iii) to facilitate the manipulation of the reaction selectivity,
the loading of acidic and basic groups and also their strengths
should be controlled precisely. All these factors put together tend
to support the necessity of the development of a suitable method
to prepare acid and base catalysts for establishing a site-isolated
co-catalyst system, which we have now achieved.
Microporous organic polymers (MOPs), as an important class of
microporous materials, have recently emerged as versatile plat-
forms for the development of catalysts because of their unique
properties, including superior chemical and thermal stabilities,
high surface area, and low skeleton density [21–25]. Hyper-
crosslinked polymers (HCPs), a type of MOPs, possess not only
the merits of MOPs but also distinct features of low-cost and facile
preparation, monomer diversity, and tunable pore size [25–27].
The attainment of permanent porosity in HCPs, which is critical
to high efficiency of catalyst, is done by sufficient chemical cross-
linkage that prevents the polymer chains from collapsing into a
dense, nonporous state [28,29]. We recently have reported a series
of cost-effective HCPs-type catalysts using the ‘‘knitting” strategy
in some organic transformations, which testify that HCP material
is a promising catalyst or support for organic catalysis [28,30,31].
Herein, we report a strategy for preparing monofunctionalized
acid and base catalyst (HCP–SO3H and HCP–CH2NH2), in which
the catalytic sites are well-distributed in the backbone of the
microporous polymer (Fig. 1a). The acid and base groups were
induced directly by the monomer, and their loading can also be
controlled precisely. Because the synthesis of catalysts is accom-
plished in only one step, this new synthetic protocol is cost-
effective with readily available starting materials and simple to
operate. Interestingly, because the acid and base groups are located
in the backbone of the polymer matrix, the obtained acid- or
base-functionalized microporous materials are highly stable.
Therefore, these catalysts are capable of catalyzing the following
one-pot tandem reactions: deacetalization-Henry reaction (Fig. 1b)
and deacetalization-Knoevenagel reaction, both which require the
acid-base co-catalyst to synthesize many useful pharmaceutical
intermediates [32,33] and important organic synthesis intermedi-
ates [34,35]. In the selected reactions, the catalysts display good
activity and selectivity, and are easily recovered and reused several
times without significant loss of activity.
2. Results and discussion
The HCPs–SO3H catalyst obtained with different ratios of
benzene to sodium 4-(phenylamino)benzenesulfonate is labeled
as HCPs–SO3H–X, where X refers to the mole fraction of sodium
4-(phenylamino)benzenesulfonate in the substrates. Similarly,
the HCPs–CH2NH2 obtained with different ratios of benzene and
benzylamine are labeled as HCPs–CH2NH2–X, where X refers to
the mole fraction of benzylamine in the substrates (substrates refer
to benzene and acid or base precursor).
The FT-IR spectra of HCPs–SO3H–50 and HCPs–CH2NH2–50 are
shown in Fig. 2. Comparing with the homogeneous counterpart 4
-(phenylamino)benzenesulfonate, the weak C–H stretching
absorption of aromatic rings at 3000–3100 cmꢀ1 in HCPs–SO3H–
50 is absent, while the characteristic peak of benzene skeleton
stretching in the 1450–1600 cmꢀ1 region is visible. In addition,
the characteristic absorption peaks of sulfonic acid group at
1382 cmꢀ1, 1198 cmꢀ1, 1037 cmꢀ1, and 805 cmꢀ1, which are due
to asymmetrical and symmetrical stretching vibrations of S–O,
are retained in HCPs–SO3H–50 [36,37].
A weak peak at
1091 cmꢀ1 can be assigned to C(aromatic)–S stretching vibration
showing the presence of sulfonic acid in the HCPs–SO3H polymer.
Moreover, a broad and a strong band ranging from 3100 to
3650 cmꢀ1 in HCPs–SO3H may be associated with the –OH stretch-
ing vibration. These results indicate that the target HCPs–SO3H–50
catalyst was obtained through the hyper-crosslinking reaction. In
the FTIR spectra of HCPs–CH2NH2, the absorptions at 2917 cmꢀ1
and 2903 cmꢀ1 are clearly visible and account for the –CH2–
Fig. 1. Schematic illustration for (a) the fabrication of HCP–SO3H and HCP–CH2NH2 and (b) the one-pot cascade reaction.

170
K. Wang et al. / Journal of Catalysis 348 (2017) 168–176
content was calculated from EA, indicating that the catalytic sites
Results and Discussion
were induced directly by monomer through crosslinking reaction
and the precise control of catalytic sites was achieved by changing
the amount of monomer according to the specific requirements.
The similar linear relationship also exists between the X of
HCPs–CH2NH2–X catalysts and benzylamine content of the corre-
sponding catalysts (Fig. S4).
Benzylamine
4-(phenylamino)benzenesulfonic acid
-CH
HCPs-CH2NH2-50
HCPs-SO3H-50
S-O
2
-
The thermal stability of HCPs–SO3H and HCPs–CH2NH2 was also
measured by TGA (Fig. S5,6). The TGA curves show that the
obtained HCPs catalysts prepared by hyper-crosslinking reactions
exhibit excellent thermal stability (Tdec > 400 °C), indicating that
the pores, which are desired for mass transfer in organic catalysis,
retain their identity and are not collapsed even at high tempera-
ture. Moreover, as the acidic and basic catalytic sites of catalysts
are anchored firmly in the pore walls formed from stable mono-
mers and are thermally stable, they are not leached from the pore
walls of the catalysts and thus catalyst poisoning is prevented that
in other case would seriously affect the efficiency of such catalysts.
The morphologies and textures of materials were investigated
by FE-SEM and TEM (Fig. 4). The SEM images indicate that HCPs–
SO3H–50 or HCPs–CH2NH2–50 is amorphous in nature (Fig. S7,8).
To prove directly that the –SO3H and –CH2NH2 groups were
introduced successfully in HCPs, a new proof was provided by
the element mapping of SEM images of HCPs–SO3H–50 and
HCPs–CH2NH2–50. From the element mapping images (Fig. 4c
and g), the sulfur and nitrogen contents in the samples are clearly
observed. For further observed the distribution of active groups,
the catalysts HCPs–SO3H–50 and HCPs–CH2NH2–50 were used to
coordinate metal salts BaCl2 [38] and AgNO3 [39], respectively,
which lead to metal-immobilized materials HCPs–SO3H–50–Ba
and HCPs–CH2NH2–50–Ag. The obtained immobilized materials
were then subjected to SEM metal mapping analysis. As shown
in Fig. S9, the metal Ba and Ag in the samples are clearly observed
with uniform distribution, further indicating the uniform distribu-
tions of the sulfonic acid and amine sites in the catalysts. These
results are also in agreement with the finding of the fluorescent
X-ray energy profiles of HCPs–SO3H–50–Ba and HCPs–CH2NH2–
50–Ag (Fig. S10).
The high surface area of HCPs is the key factor for heteroge-
neous catalysis [26]. A series of materials with different SBET sur-
face areas was prepared. As shown in Table S2, with the decrease
of the mole ratio of sodium 4-(phenylamino)benzenesulfonate to
benzene, the SBET surface area of HCPs–SO3H increased from 49
to 820 m2 gꢀ1. The low surface areas of some samples, for example
HCP–SO3H–100, 49 m2 gꢀ1, can be attributed to the partial pore
filling resulted from the more hanging functional groups. On the
other hand, because of the lower activity of sodium 4-(phenyla
mino)benzenesulfonate than that of benzene in the hyper-
crosslinking reaction, the cross-linking degree reduced with the
increase of the mole ratio of 4-(phenylamino)benzenesulfonate
monomer, which results in the significant decreasing of SBET sur-
face areas. And likewise, the SBET surface area of HCP–CH2NH2
increased from 72 to 986 m2 gꢀ1. Taking catalytic performance into
consideration, the HCPs–SO3H–50 and HCP–CH2NH2–50 (Table 1)
catalysts with higher SBET surface area and more catalytic sites
among the obtained samples were employed to catalyze the subse-
quent reactions.
-OH
-NH
2
aromatic ring
4000 3500 3000 2500 2000 1500 1000
Wavenumber cm-1
500
Fig. 2. FT-IR spectra of HCPs–SO3H–50 and HCPs–CH2NH2–50.
symmetrical and asymmetrical stretching vibrations respectively.
Similarly, peaks at 1600 cmꢀ1, 1500 cmꢀ1 and 1450 cmꢀ1 are
attributed to aromatic ring skeleton vibrations. The broad and
strong absorption band ranging from 3100 to 3700 cmꢀ1 is associ-
ated with the OH and NH2 stretching vibration. The FT-IR spectra
of other HCPs–SO3H and HCPs–CH2NH2 catalysts are given in
Fig. S1, 2 (see ESI).
The 13C CP/MAS NMR spectra of HCPs–SO3H–50 and HCPs–CH2-
NH2–50 in Fig. 3 both show that the resonance peaks near 129 ppm
and 124 ppm are due to substituted and non-substituted aromatic
carbons, and the resonance peaks near 28 ppm are assigned to the
methylene carbons formed by the Friedel–Crafts reaction by using
the formaldehyde dimethyl acetal (FDA) linker.
The chemical compositions of the obtained materials were
determined by using a C-H-N-S elemental analyzer (EA). As shown
in Table S1, the sulfur content of the HCPs–SO3H catalysts
increases from 1.3% to 12.3% with the increase of sodium 4-(pheny
lamino)benzenesulfonate ratio from 25% to 100%. Similarly, with
the increase of the ratio of benzylamine from 25% to 100%, the
nitrogen content of HCPs–CH2NH2–X increases from 1.4% to
11.6%. Moreover, a linear relationship (Fig. S3) between the X of
HCPs–SO3H–X catalysts and sulfonic acid content of the corre-
sponding catalyst is also present, among which the sulfonic acid
HCPs-CH2NH2-50
*
The porous properties of HCP–SO3H–50 and HCP–CH2NH2–50
were also determined by nitrogen sorption analysis at 77.3 K. The
nitrogen adsorption and desorption isotherms of two catalysts
(Fig. 5) display Type I curve, which give an indication of microp-
orous materials according to the IUPAC classification [40,41].
Moreover, a steep nitrogen gas uptake in each adsorption isotherm
at low pressure (P/P0 < 0.001) is observed visually confirming
abundant micropores in the structure. An obvious hysteresis loop
in the middle pressure area indicates the presence of a certain
HCPs-SO3H-50
*
200
160
120
80
40
0
Chemical shift (ppm)
Fig. 3. Solid-state 13C CP/MAS for the HCPs–SO3H–50 and HCPs–CH2NH2–50
catalysts.

K. Wang et al. / Journal of Catalysis 348 (2017) 168–176
171
Fig. 4. (a) SEM and (d) TEM images of the HCPs–SO3H–50 catalyst. Element mapping of HCPs–SO3H–50 with (b) C and (c) S elements. (e) SEM and (h) TEM images of the
HCPs–CH2NH2–50. Element mapping of HCPs–CH2NH2–50 with (f) C and (g) N elements.
Table 1
Surface area and porosity of HCP–SO3H–50 and HCP–CH2NH2–50.
M.A.c
m2/g
PVd
MPVe
cm3/g
a
b
Sample
SBET
SL
m2/g
m2/g
cm3/g
HCP–SO3H–50
HCP–CH2NH2–50
627
837
793
1110
360
374
0.48
0.55
0.15
0.16
a
b
c
Surface area calculated from nitrogen adsorption isotherms at 77.3 K using BET equation.
Surface area calculated from nitrogen adsorption isotherms at 77.3 K using Langmuir equation.
t-Plot micropore area.
Total pore volume calculated from nitrogen isotherm at P/P0 = 0.995, 77.3 K.
The micropore volume derived using the t-plot method based on the Halsey thickness equation.
d
e
Fig. 5. (a) Nitrogen adsorption–desorption isotherms of HCP–SO3H–50 and HCP–CH2NH2–50 at 77.3 K. (b) Pore size distribution calculated using DFT methods (slit pore
models, differential pore volumes) of samples.
amount of mesopores, and a sharp rise in high pressure implies the
presence of a spot of macropores in the material (Fig. 5a). The
results are in consistent with the pore-size distribution of HCP–
SO3H–50 and HCP–CH2NH2–50 shown in Fig. 5b. Pore size distribu-
tion shows that the dominant pore sizes of HCP–SO3H–50 are of 5.9
and 12.4 Å and dominant pore sizes of HCP–CH2NH2–50 are of 5.9,
7.3 and 11.8 Å. This similarity of porous structure in acid- and
base- catalysts helps to increase the efficiency of mass transfer
between the liquid phase and the solid catalyst and also between
the two types of catalysts. As shown in Table 1, the BET surface
areas of HCP–SO3H–50 and HCP–CH2NH2–50 are both larger than
600 m2/g, which benefits catalyst activity. Moreover, the hierarchi-
cal pore structure of catalysts is also beneficial to improve catalytic
activity of catalysts because macropore and mesopore can acceler-
ate mass transfer of reactants and products, and micropores can be
used as efficient micro-reactors [28].
In order to quantify the acidity of HCPs–SO3H–50, a conven-
tional titration method [42] was undertaken. As shown in Table 2,

172
K. Wang et al. / Journal of Catalysis 348 (2017) 168–176
Table 2
The amount of acid or base sites of catalysts determined by the back-titration method.a
Entry
Catalyst
Sample weight (mg)
Vconsume (NaOH, mL)
C (mmol/g)
1
2
HCPs–SO3H–50
HCPs–CH2NH2–50
100.4
102.1
7.84
17.86
CSO3H = 0.79
CNH2 = 2.21
a
Indicator: phenolphthalein.
a certain amount of acid sample was impregnated in potassium
chloride standard solution (CKCl = 1.0 mol/L, 20.00 mL) to liberate
all H+ ions of the sample into the solution. After 24 h, the mixture
was centrifuged and all the supernatant liquid was titrated by
sodium hydroxide standard solution (CNaOH = 0.0101 mol/L). Using
this method, the amount of sulfonic acid was determined to be
0.79 mmol/g, which was calculated with the formula (1). The
amount of amino sites of HCPs–CH2NH2–50 was determined to
be 2.21 mmol/g by a back-titration method [43]. A certain amount
of base sample was impregnated in hydrochloric acid standard
solution (CHCl = 0.0203 mol/L, 20.00 mL) for 24 h. The mixture
was centrifuged and all the supernatant liquid was also titrated
by sodium hydroxide standard solution (CNaOH = 0.0101 mol/L).
The amount of base sites was calculated with the formula (2).
These results are nearly identical to those of Element Analysis
(Table S1).
deacetalization and Henry condensation steps, was employed to
investigate the activity of solid catalysts [19,20,44–48]. Among
the two steps, deacetalization requires acid catalyst to give alde-
hyde, while Henry reaction needs a base catalyst.
As shown in Table 3, 2-(2-bromophenyl)-1,3-dioxolane 1 was
chosen as a substrate for the one-pot tandem reaction because
the aromatic aldehydes protected by glycol are more stable at high
temperature than those protected by ethanol or methanol [49,50].
Initially, the reaction was conducted in CH3NO2 at 80 °C in the
presence of HCPs–SO3H–50/HCPs–CH2NH2–50 (1/1, mg/mg), and
the target compound 3 was produced in 72% yield accompanied
by the formation of a certain amount of intermediate products 2
(entry 1). Under catalyst-free conditions, no product
3 was
obtained while only a little 2-bromobenzaldehyde was observed
(entry 2). The formation of intermediate 2 could be the result of
the balance between the starting material and aldehyde in the
presence of water. The reaction was also performed with
CðNaOHÞ ꢁ Vðconsume; NaOHÞ
CSO3H
¼
ð1Þ
HCPs as
a catalyst prepared by benzene, and only a little
mðsolid acidÞ
2-bromobenzaldehyde was detected (entry 3). The results indicate
the necessity of using a catalyst in each tandem step. Inspired by a
fact that the yield of 3 reached up to 72% with HCPs–SO3H–50/
HCPs–CH2NH2–50 (1/1, mg/mg), we then optimized the amount
of the acid/base catalysts (entry 4,5) and found that the yield of
CðHClÞ ꢁ VðHClÞ ꢀ CðNaOHÞ ꢁ Vðconsume; NaOHÞ
mðsolid baseÞ
CNH2
¼
ð2Þ
The goal of the synthesis of monofunctionalization heteroge-
neous catalysts is to improve the efficiency of one-pot continuous
reactions and maintain their activity after various cycles. With the
expected catalysts in hand, a transformation from acetal to
nitroalkene, which is a typical consecutive reaction including
3
reached
95%
with
HCPs–SO3H–50/HCPs–CH2NH2–50
(10 mg/20 mg) under the same conditions. Further investigation
revealed that the reaction was also affected by temperature
and reaction time, and the optimal conditions were as follows:
Table 3
One-pot deacetalization-Henry reaction catalyzed by HCPs–SO3H/HCPs–CH2NH2.
Entrya
Catalyst
Temp. (°C)
Time (h)
Conv. of 1b (%)
Isolated yield (%)
2
3
1c
2
3
HCPs–SO3H–50/HCPs–CH2NH2–50
–
HCPs
HCPs–SO3H–50/HCPs–CH2NH2–50
HCPs–SO3H–50/HCPs–CH2NH2–50
HCPs–SO3H–50/HCPs–CH2NH2–50
HCPs–SO3H–50/HCPs–CH2NH2–50
HCPs–SO3H–50
80
80
80
80
80
60
80
80
80
80
80
80
80
80
80
80
5
5
5
5
5
5
3
5
5
5
5
5
5
5
5
5
100
22
22
100
100
100
100
100
18
35
12
14
62
22
19
18
Trace
30
59
26
94
Trace
12
Trace
12
28
30
31
72
0
0
95
67
23
70
Trace
Trace
17
Trace
Trace
29
4d
5e
6d
7d
8
9
HCPs–CH2NH2–50
10
11
12
13d
14d
15d
16
HCPs–SO3H–50/Bn–NH2
p-TSA/HCPs–CH2NH2–50
p-TSA/Bn–NH2
HZSM–5/MgO
SAPO–34/MgO
75
84
100
41
SSZ–13/MgO
HCPs–SO3H–50/HCPs–CH2NH2–50
49
Trace
95f
a
b
c
d
e
f
1 (0.3 mmol), CH3NO2 (1.0 mL), solid catalyst (10 mg), liquid catalyst (2 mol%), 80 °C, 5 h.
Convertion of 1 determined by GC analysis.
Acid/base catalyst (10 mg/10 mg).
Acid/base catalyst (10 mg/20 mg).
Acid/base catalyst (20 mg/10 mg).
Under 10 mmol scale and acid/base catalyst (0.33 g/0.67 g). (Bn–NH2 = benzylamine, p-TSA = p-toluenesulfonic acid)HCPs–CH2NH2–50. Element mapping of
HCPs–CH2NH2–50 with (f) C and (g) N elements.

K. Wang et al. / Journal of Catalysis 348 (2017) 168–176
173
HCPs–SO3H–50/HCPs–CH2NH2–50 (10 mg/20 mg), 80 °C and 5 h
(entries 6,7). These results manifested that the HCPs–SO3H–50/
HCPs–CH2NH2–50 catalysts display excellent catalytic activity in
the reaction, and the goal of momentarily tuning the ratio of acid
to base according to the requirement of reaction has been achieved
by adding two catalysts simultaneously.
product 3 increases gradually with the progress of the reaction.
The product distributions show that HCPs–SO3H–50/HCPs–CH2-
NH2–50 acted as an acid-base synergetic catalyst in the consecu-
tive reaction, which enabled the reaction to occur and complete.
Synthesis of the solid catalyst was not just to explore a new cat-
alytic system but also to realize the recycling ability of the catalyst.
In order to examine the recyclability of the mixed catalyst, the
model reaction was scaled up to 10 mmol under the optimal con-
ditions, which provided the uniform yield (Table 3, entry 16). After
reaction completion, the solid catalysts were isolated from the
reaction medium by filtration, and then washed with CH3NO2 five
times before dried in a vacuum at 60 °C. The catalysts were sepa-
rated by filtration and washed with EtOH and water, prior to their
use for the next run. As shown in Fig. 7, the mixed catalysts were
recycled easily for at least five times without significant loss in
the product yield. Moreover, the leaching of the –SO3H or –CH2NH2
group was also investigated by the following strategy. When the
yield of product 3 reached 70% under optimal conditions, the reac-
tion was stopped and the mixture was then filtered to remove the
solid catalyst. The obtained mother liquor was continued to react
for 2 h. No significant increase of the yield was observed, indicating
that the mixed solid catalysts were robust heterogeneous catalyst
in the one-pot reaction.
To further investigate the activity and the momentary adjusta-
bility of the mixed catalyst system, the second cascade reaction we
investigated by HCPs–SO3H–50/HCPs–CH2NH2–50 was one-pot
deacetalization-Knoevenagel reaction [10,11,14,15,44,51], includ-
ing deacetalization step catalyzed by acid and nuclearphilic
addition-elimination procedure catalyzed by base (Scheme 1).
Treatment of 2-(2-bromophenyl)-1,3-dioxolane 1 with malononi-
trile in the presence of HCPs–SO3H–50/HCPs–CH2NH2–50 at 90 °C
in toluene for 7 h gave desired product 4 in 97% yield. Comparing
with the one-pot deacetalization-Henry reaction, the more amount
of HCPs–CH2NH2–50 was added, demonstrating the momentary
adjustability of the mixed catalyst according to the specific
requirement. In addition, the good catalytic performance of the
obtained catalyst was further confirmed by the comparison with
other catalytic systems. As shown in Table S3, under the same con-
ditions, no product was detected when the support HCPs were
employed in this reaction (entry 2). Although HCP–SO3H–50 can
catalyze the first reaction, 2 is hardly converted (entry 3) owing
to the low efficiency resulting from the lack of basic sites. Similarly,
no product was generated when HCP–CH2NH2–50 was used as a
catalyst (entry 4). These results manifest that acidic and basic sites
are both needed to ensure the one-pot multistep reaction to be
successful. However, when the catalysts with physical mixture
were used, among which solid acid or base worked in conjunction
with homogeneous base or acid, all the yields reached only
In order to further prove the necessity of designing the mono-
functionalized mixed catalyst and their compatibility, we carried
out a series of experiments with different acids and bases and both
under optimal conditions. HCPs–SO3H–50 gave the low yield
because the Henry reaction did not occur resulting from the lack
of the base catalyst (entry 8). Almost no product 3 was obtained
when only HCPs–CH2NH2–50 was used as catalyst, in which a little
1-nitro-2-phenylethanol could be detected (entry 9). These condi-
tions demonstrate that the one-pot deacetalization-Henry reaction
needed both acid and base catalysts. Importantly, it was inferred
that the opposite functional groups of HCPs–SO3H/HCPs–CH2NH2
mixed system were not neutralized by each other (entry 4). When
HCPs–SO3H–50 was combined with a homogeneous base benzy-
lamine, product 3 was obtained in 17% yield (entry 10). Similar
results were obtained when HCPs–CH2NH2–50 was mixed with a
soluble p-toluenesulfonic acid (p-TSA) (entry 11). Interestingly,
when homogeneous catalysts Bn–NH2 and p-TSA were used
together in the one-pot cascade reaction (entries 12), almost no
desired product 3 was obtained, and only a little intermediate 2
was observed. These results demonstrate that when one or both
catalysts are in homogeneous phase, the neutralization of acid
and base takes place resulting in the cascade reaction failure.
Therefore, it is very important and useful to synthesize such mixed
acid-base co-catalysts that do not affect the catalytic activity of
each catalyst in one-pot reaction. In addition, under the optimal
conditions, the catalytic performances of commercial microporous
catalysts, HZSM–5/MgO, SAPO–34/MgO, SSZ–13/MgO were also
examined (entries 13–15). However, all the yields of 3 were infe-
rior as compared with that of HCPs–SO3H–50/HCPs–CH2NH2–50.
These results indicate that the HCP-type acid-base catalyst with
physical mixture possesses excellent catalytic activity for one-pot
acid-base multistep reactions.
The kinetic curves of the one-pot deacetalization-Henry reac-
tion were also investigated by tracing the reactant conversion
and product distributions with the reaction time by using HCPs–
SO3H–50/HCPs–CH2NH2–50 under the optimal conditions (Fig. 6).
Clearly, the process includes two steps: (i) hydrolysis of starting
material 1 to the aldehyde intermediate 2 and (ii) Henry condensa-
tion of 2 and CH3NO2 to form the final product 3 (as illustrated in
Table 2). The starting material of 1 is completely consumed in the
first 2 h. With the increase of reaction time, yield of the aldehyde 2
increases dramatically first and then decreases, while the yield of
Fig. 6. Kinetic curves of the one-pot deacetalization-Henry reaction catalyzed by
HCPs–SO3H–50/HCPs–CH2NH2–50. (1) Conversion of 2-(2-bromophenyl)-1,3-diox-
olane versus reaction time; (2) yield of 2-bromobenzaldehyde versus reaction time;
(3) yield of bromo-2-(2-nitrovinyl)benzene versus reaction time.
Fig. 7. Recycles of catalysts HCPs–SO3H–50/HCPs–CH2NH2–50.

174
K. Wang et al. / Journal of Catalysis 348 (2017) 168–176
Scheme 1. One-pot deacetalization-Knoevenagel reaction between malononitrile and 2-(2-bromophenyl)-1,3-dioxolane.
approximately 10% (entries 5 and 6). Interestingly, the same condi-
tion over a combination of homogeneous Bn-NH2 and p-TSA gave
no desired product (entry 7). These results also indicate that this
type of mixed acid-base co-catalysts was indeed suitable for pro-
moting the one-pot acid-base multistep reaction. Moreover, com-
pared with commercial catalysts HZSM–5/MgO, SAPO–34/MgO,
SSZ–13/MgO, the HCP catalysts displayed higher catalytic effi-
ciency (entries 8–10). The reaction can also be amplified to
10 mmol with 96% yield (entry 11). The catalysts could be reused
for at least three times without significant loss of the activity under
10 mmol scale (Scheme 1). The results of all selected reactions
show that the mixed catalyst of HCPs–SO3H–50/HCPs–CH2NH2–
(CP/MAS) NMR spectra were recorded on a Bruker Avance II 400
WB 400 MHz spectrometer equipped with 4 mm double-
a
resonance MAS probe and a spinning frequency of 10 kHz.
Benzylamine, sodium 4-(phenylamino)benzenesulfonate, and
formaldehyde dimethyl acetal (FDA, 98%) were purchased from
Aladdin chemical reagent Corp. (Shanghai, China). Anhydrous ferric
chloride (FeCl3), 1,2-dichloroethane (DCE), hydrochloric acid, and
sodium hydroxide were obtained from sinopharm chemical
reagent Co., Ltd (Shanghai, China) and used as received. Unless
otherwise noted, all reagents were obtained from commercial sup-
pliers and used without further purification.
50 is indeed
a robust heterogeneous catalyst for organic
transformations.
4.2. Synthesis of HCPs–SO3H–X
3. Conclusions
(HCPs–SO3H–50 as a model catalyst) FeCl3 (13.75 mmol, 2.23 g)
was added into a solution of sodium 4-(phenylamino)benzenesulfo
nate (2.5 mmol, 0.68 g), benzene (2.5 mmol, 0.20 g), FDA
(13.75 mmol, 1.05 g), and DCE (10 mL). The resulting mixture
was heated at 45 °C for 5 h and then at 80 °C for 19 h. After cooling
to room temperature, the solid product was washed with methanol
several times, and then the precipitate was further purified by
extracting with methanol for 24 h. The product was acidified by
HCl (10% aq, 20 mL) for 24 h, and then washed with water several
times. The catalyst was obtained as a dark brown solid. Yield: 93%.
To summarize, a simple and efficient strategy to synthesize
monofuctionalized acid and base catalysts with similar pore struc-
ture and excellent stability is reported using a one-step hyper-
crosslinked reaction. Using this approach, the acidic and basic
sites of the catalyst were precisely controlled by crosslinking acidic
and basic monomers. The obtained acid-base mixed catalysts were
successfully used as recyclable catalysts for one-pot cascade reac-
tions including deacetalization-Henry and deacetalization-
Knoevenagel reactions in which the amount of acid or base can
be adjusted momentarily according to the requirements of specific
reactions. This study provided not only a choice of heterogeneous
catalysts for the tandem reactions catalyzed by acid/base catalysts
with the advantages of avoiding the acid-base neutralization and
simplifying the separation process for their recycling, but also an
excellent material to achieve the heterogenization of other antag-
onistic species or similar antagonistic complexes.
4.3. Synthesis of HCPs–CH2NH2–X
(HCPs–CH2NH2–50 as a model catalyst) FeCl3 (13.75 mmol,
2.23 g) was added to
a solution of benzylamine (2.5 mmol,
0.27 g), benzene (2.5 mmol, 0.20 g), FDA (13.75 mmol, 1.05 g),
and DCE (10 mL). The resulting mixture was heated at 45 °C for
5 h and then at 80 °C for 19 h. After cooling to room temperature,
the solid product was washed with methanol several times, and
then precipitate was further purified by extracting with methanol
for 24 h. The product was alkalized by NaHCO3 (10% aq, 20 mL) for
24 h and then washed with water several times. The polymer
material was obtained as a dark brown solid. Yield: 95%.
4. Experimental section
4.1. General
The surface areas, N2 adsorption isotherm (77.3 K) and pore size
distributions of HCPs materials were measured using Micromerit-
ics ASAP 2020 M surface area and porosity analyzer. Before analy-
sis, the samples were degassed at 110 °C for 8 h under vacuum
(10ꢀ5 bar). The total pore volume was derived using the Gurvich
method. The FT-IR spectra were recorded by a Bruker VERTEX 70
spectrometer employing the KBr disk method. Elemental analysis
(EA) was determined using a Vario Micro cube Elemental Analyzer
(Elementar, Germany). Thermogravimetric analysis (TGA) was per-
formed on a PerkinElmer Instruments Pyris1 TGA, thermobalance
at a heating rate of 5 °C minꢀ1 under nitrogen. The polymer mor-
phologies were investigated by an FEI Sirion 200 field emission
scanning electron microscope (FE-SEM). Transmission electron
microscopy (TEM) images were obtained on a Tecnai G20 micro-
scope (FEI Corp., USA) operated at an accelerating voltage of
200 kV. The solid-state 13C crosspolarization magic angle spinning
4.4. One-pot deacetalization-Henry reaction
In
a
typical reaction, 2-(2-bromophenyl)-1,3-dioxolane
(0.069 g, 0.3 mmol), HCPs–SO3H–50 (10 mg), and HCPs–CH2NH2–
50 (20 mg) were added in CH3NO2 (1 mL). The resulting solution
was stirred at 80 °C for about 5 h. After reaction, the mixture was
cooled to room temperature and then centrifuged. The supernatant
organic phase was isolated and the bottom solid was washed with
ethanol (4.0 ml ꢁ 3). All organic phase were then combined
together and isolated with preparative TLC (eluting solvent: ethyl
acetate/petroether = 1/5 (v/v)). Then, the desired product, 3, was
obtained in 95% of yield (0.064 g).

K. Wang et al. / Journal of Catalysis 348 (2017) 168–176
175
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4.5. One-pot deacetalization–Knoevenagel reaction
In typical reaction, 2-(2-bromophenyl)-1,3-dioxolane
a
(0.069 g, 0.3 mmol), malononitrile (0.024 g, 0.36 mmol), HCPs–
SO3H–50 (10 mg), and HCPs–CH2NH2–50 (40 mg) were added in
toluene/H2O (1.5 mL/0.06 mL). The resulting solution was stirred
at 90 °C for about 7 h. After reaction, the mixture was cooled to
room temperature and then centrifuged. The supernatant organic
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97% of yield (0.068 g).
4.6. Acidity or alkalinity determination by the back-titration method
HCPs–SO3H–50 (100.4 mg) was impregnated in KCl standard
solution (CKCl = 1.00 mol/L, 10.00 mL) The mixture was stirred
rapidly at room temperature in a sealed V-type reaction tube. After
24 h, the mixture was centrifuged and washed by deionized water
(5.00 mL ꢁ 3). All the supernatant liquids were collected. The
NaOH standard solution (CNaOH = 0.0101 mol/L) as titrant and phe-
nolphthalein ethanol solution (0.50 wt%) as indicator were used to
titrate the mentioned supernatant liquid. (The standard NaOH
solution has been standardized by potassium hydrogen phthalate).
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and washed by deionized water (5.00 mL ꢁ 3). All the supernatant
liquid was also titrated by the NaOH standard solution.
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Acknowledgments
The authors thank for National Natural Science Foundation of
China for the financial support (21474033/51273074/21173089/1
373093) and also for the Analytical and Testing Center of HUST.
Chutian Scholar Program of the Hubei Provincial Government
and the Cooperative Innovation Center of Hubei Province are also
acknowledged. This work is also supported by the Fundamental
Research Funds for the Central Universities of China
(2016JCTD104/2014ZZGH019).
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Appendix A. Supplementary material
Supplementary data associated with this article can be found, in
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