Hierarchically Pore Structure poly 2-(Dimethyl amino) ethyl methacrylate/Hi-ZSM-5: A Novel Acid–Base Bi-functional Catalyst as Heterogeneous Platform for a Tandem Reaction

Article abstract of DOI:10.1007/s10562-018-2301-z

Abstract: A simple method is developed to prepare an efficient and low cost acid–base bifunctional catalyst by using poly 2-(dimethyl amino) ethyl methacrylate as a basic part and hierarchical ZSM-5 as an acidic part of the catalyst. Tandem reaction of deacetalization–Knoevenagel condensation was selected to evaluate the prepared catalyst and the outcomes were excellent. Graphical Abstract: [Figure not available: see fulltext.].

Full text of DOI:10.1007/s10562-018-2301-z

Catalysis Letters
https://doi.org/10.1007/s10562-018-2301-z
Hierarchically Pore Structure poly 2-(Dimethyl amino) ethyl
methacrylate/Hi-ZSM-5: A Novel Acid–Base Bi-functional Catalyst
as Heterogeneous Platform for a Tandem Reaction
Roozbeh Javad Kalbasi1 · Anahita Khojastegi1
Received: 13 October 2017 / Accepted: 7 January 2018
© Springer Science+Business Media, LLC, part of Springer Nature 2018
Abstract
A simple method is developed to prepare an efficient and low cost acid–base bifunctional catalyst by using poly 2-(dime-
thyl amino) ethyl methacrylate as a basic part and hierarchical ZSM-5 as an acidic part of the catalyst. Tandem reaction of
deacetalization–Knoevenagel condensation was selected to evaluate the prepared catalyst and the outcomes were excellent.
Graphical Abstract
Keywords Acid–base bifunctional catalyst · Hierarchical zeolite · Tandem reaction · Deacetalization–Knoevenagel
condensation
1 Introduction
In recent years researchers have paid great attention to one-
pot, multi-step reactions due to higher efficiency, reduction
in the synthesis steps such as isolation of intermediates,
purification, lower cost and decrease in waste [1–3]. For
this purpose, design and synthesis of catalysts that contain
two or three kinds of active sites are required. Particularly,
acid–base bifunctional catalysts, which have the ability
to interact with both nucleophiles and electrophiles, have
attracted great attention. Immobilization of acid and base
Electronic supplementary material The online version of this
article (https://doi.org/10.1007/s10562-018-2301-z) contains
supplementary material, which is available to authorized users.
* Roozbeh Javad Kalbasi
rkalbasi@gmail.com
1
Faculty of Chemistry, Kharazmi University, Tehran, Iran
Vol.:(0123456789)
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R. Javad Kalbasi, A. Khojastegi
groups on a solid support is one of the best and most effi-
cient methods for the preparation of acid–base bifunctional
catalysts [4–7]. The common strategy to synthesize bifunc-
tional catalyst is the functionalization of a solid support with
the organosilane precursors, which have an acidic group
(–SO3H) and basic group (–NH2) [8–12]. Using this method
poses serious problems such as using the highly toxic raw
materials, synthetic procedure complexity, high-cost pro-
cess and relatively lower activity and selectivity. Thus,
there is considerable demand for producing an acid–base
bifunctional catalyst by facile, straightforward and low-
cost methods. In recent years, some acid–base bifunctional
catalysts are prepared without using expensive materials
such as organosilanes or bridged organosilanes and there
is still much effort to prepare novel, efficient and low cost
acid–base bifunctional catalysts. In this regard, Zhang group
prepared an acid–base bifunctional catalyst by dual func-
tionalization of porous aromatic frameworks through step-
wise post-synthetic modification [13]. In other work, Li et al.
have prepared a core–shell structured nanocomposite, based
on LDHs and Al-mesoporous silica [14]. Banerjee group
reported a polymeric crystalline organo-catalytic porous
COF (2,3-DhaTph) as an acid–base bifunctional catalyst
by polymerization of acidic catechol and basic porphyrin
[15]. Sun et al. prepared a bifunctional catalyst by func-
tionalization of heteropolyacid (HPA) nanospheres (as the
acid sites) with lysine (as the basic site). The activity of the
catalyst was tested in cascade isomerization/dehydration of
glucose to 5-hydroxymethylfurfural or levulinic acid [16].
Wu group developed a hierarchically core–shell structured
acid–base bifunctional catalyst (ZSM-5@Mg3Si4O9(OH)4)
by hydrothermal treatment of ZSM-5 with magnesium
cations. ZSM-5 zeolite in core served as the acid site and
Mg3Si4O9(OH)4 in outer shell acted as the basic site in deac-
etalization–Knoevenagel reaction [17].
Modification of surface by a polymer is one of the most
efficient procedures to change the properties of surface
which can be extensively applied to various functional pol-
ymers change. In our previous works, we prepared various
polymer-inorganic basic nanocomposites with different basic
nature and structure through in-situ polymerization [25, 26].
These nanocomposites showed excellent catalytic activity
as heterogeneous catalysts in various organic reactions.
In continuation of our previous works, in this study, poly
2-(dimethyl amino) ethyl methacrylate/hierarchical ZSM-5
(PDMAEMA/Hi-ZSM-5) was prepared as a novel acid–base
bifunctional catalyst through a simple route. Hierarchical
ZSM-5 (Hi-ZSM-5) has been used as the acid sites and
catalyst support whereas the PDMAEMA polymer with the
basic functional group in the side branch acted as the basic
sites. This method can be used to prepare various kinds of
bifunctional catalysts and it can be a good replacement for
the previous complicated, high-cost methods. The activity
of the catalyst was assayed in the tandem reaction of deac-
etalization–Knoevenagel condensation.
2 Experimental Method
2.1 Instruments and Characterization
The catalyst was characterized using: BET specific surface
areas and BJH pore size distribution (Series BEL SORP 18,
at 77 K), FT-IR spectroscopy (using a Perkin Elmer RXI in
KBr matrix in the range of 4000–400 cm−1), scanning elec-
tron microscopy (SEM) (Hitachi S4160 FESEM), the X-ray
powder diffraction (XRD) (using a X-ray diffractometer, Cu
Kα radiation) and transmission electron microscopy (TEM)
(Philips CM30 electron microscope). The products were
identified by 1H and 13C NMR techniques (Burker Advanced
300 spectrometer at 300.1 and 75 MHz, respectively).
Zeolites have been used as a catalyst in petroleum refin-
ing and chemical processes because of having excellent
thermal stability, high acidity, and regular pore structure.
However, relatively small, fine zeolites pores, significantly
affect mass transfer in many catalytic reactions. These
problems have restricted the application of zeolite cata-
lysts. Many approaches have been proposed to improve the
performance of zeolite [18]. Mesoporous materials with a
larger pore size (2–50 nm) and high surface area provide a
way to solve the problem of the micropores. However, the
mesoporous material has a lower thermal and mechanical
stability than the zeolite because of the amorphous nature
of the walls. Hierarchically mesoporous zeolites are the new
development of microporous zeolites with combination of
thermal/hydrothermal stability of the zeolites and fast mass
transportation of mesoporous materials. They not only have
larger pores and crystalline framework but also have strong
acidity which can use as acid catalysts [19–24].
2.2 Preparation of poly 2‑(Dimethyl amino) ethyl
methacrylate/Hi‑ZSM‑5 Nanocomposite
Hierarchical ZSM-5 was synthesized according to the
procedure published in advance [27]. To prepare the cata-
lyst, Hi-ZSM-5 (0.25 g), 2-(dimethyl amino) ethyl meth-
acrylate (0.25 g, 1.59 mmol) and divinyl benzene (10 mol
%, 0.0205 g) in 6 mL of water/ethanol binary solvent (1/1
by volume) were added in a flask and the suspension was
stirred and refluxed for 6 h under nitrogen atmosphere. Then,
AIBN (3 mol %, 0.008 g) was added as a radical initiator
and the mixture was stirred under N2 gas in 70–75 °C for
48 h [28]. Finally, the solvent was removed under vacuum to
gain cream colored powder of poly 2-(dimethyl amino) ethyl
methacrylate/Hi-ZSM-5 (PDMAEMA/Hi-ZSM-5).
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Hierarchically Pore Structure poly 2-(Dimethyl amino) ethyl methacrylate/Hi-ZSM-5: A Novel…
(C=C alkene, C=C aromatic); 1H NMR (300 MHz, CDCl3)
2.3 General Procedure for Tandem Reaction
of Deacetalization–Knoevenagel Condensation
δ ppm 8.70 (ArH, t, J = 1.8 Hz, 1H), 8.45–8.38 (ArH, m,
2H), 8.32 (=CH, s, 1H), 7.74 (ArH, t, J=8.1 Hz, 1H), 4.43
(CH2, d, J=7.1 Hz, 2H), 1.42 (CH3, t, J=7.1 Hz, 3H); 13
C
In a typical method, a mixture of benzaldehyde dimethy-
lacetal (1.87 mmol), ethyl cyanoacetate (1.87 mmol) and
PDMAEMA/Hi-ZSM-5 catalyst (0.07 g) in water (5 mL)
was placed in a two necked flask. The mixture was stirred at
60 °C for 150 min. The reaction was followed by thin layer
chromatography, using hexane–ethyl acetate (4:1). The reac-
tion was worked-up after cooling down to 10 °C and after
that, the mixture was filtered and then rinsed with boiling
ethanol. After crystallization, the product was separated to
obtain a pure product. The products were characterized by
1H-NMR, 13C-NMR (see Figs. S1–S20 in Supporting Infor-
mation), and FT-IR spectroscopy methods.
NMR (75 MHz, CDCl3) δ ppm 161.44, 151.84, 148.55,
135.13, 132.83, 130.53, 127.06, 126.05, 114.53, 106.58,
63.33, 14.10.
2.3.5 (E)-Ethyl 2-cyano-3-(2,6-dichlorophenyl)acrylate (5a)
FT-IR (KBr, cm−1): 3036 (=CH, Ar, str), 2981 (CH, str),
2235 (CN), 1722 (C=O), 1476–1621 (C=C alkene, C=C
aromatic); 1H NMR (300 MHz,DMSO) δ ppm 8.47 (=CH,
s, 1H), 7.67–7.63 (ArH, m, 2H), 7.57–7.52 (ArH, m, 1H),
4.35 (CH2, q, J=7.1 Hz, 2H), 1.31 (CH3, t, J=7.1 Hz, 3H);
13C NMR (75 MHz, DMSO) δ ppm 160.00, 152.33, 132.75,
132.55, 130.25, 128.72, 128.10, 113.35, 63.04, 13.84.
2.3.1 (E)-Ethyl 2-cyano-3-phenylacrylate (1a, 2b)
FT-IR (KBr, cm−1): 3029 (=CH, Ar, str), 2979 (CH, str),
2223 (CN), 1725 (C=O), 1446–1606 (C=C alkene, C=C
aromatic); 1H NMR (300 MHz, CDCl3) δ ppm 8.26 (=CH,
s, 1H), 8.00-7.98 (ArH, d, J=6.2, 2H), 7.61–7.43 (ArH, m,
3H), 4.39 (CH2, q, J=7.1 Hz, 2H), 1.41 (CH3, t, J=7.1 Hz,
3H); 13C NMR (75 MHz, CDCl3) δ ppm 162.43, 155.01,
133.26, 131.41, 131.03, 129.23,115.88, 102.95, 62.70,
14.12.
2.3.6 (E)-Ethyl 2-cyano-3-(p-tolyl)acrylate (6a)
FT-IR (KBr, cm−1): 3029 (=CH, Ar, str), 2985 (CH, str),
2217 (CN), 1722 (C=O), 1463–1598 (C=C alkene, C=C
aromatic); 1H NMR (300 MHz, CDCl3) δ ppm 8.22 (=CH, s,
1H), 7.91 (ArH, d, J=8.2 Hz, 2H), 7.31 (ArH, d, J=8.1 Hz,
2H), 4.38 (CH2, q, J=7.1 Hz, 2H), 2.44 (CH3, s, 3H), 1.40
(CH3, t, J=7.1 Hz, 3H); 13C NMR (75 MHz, CDCl3) δ ppm
162.76, 155.00, 144.64, 131.24, 130.01, 128.84, 115.78,
101.53, 62.58, 21.87, 14.17.
2.3.2 (E)-Ethyl 2-cyano-3-(4-nitrophenyl)acrylate (2a)
FT-IR (KBr, cm−1): 3096 (=CH, Ar, str), 2992 (CH, str),
2226 (CN), 1720 (C=O), 1445–1616 (C=C alkene, C=C
aromatic), 1346–1515 (N=O); 1H NMR (300 MHz, DMSO)
δ ppm 8.54 (=CH, s, 1H), 8.39 (ArH, d, J = 8.8 Hz, 2H),
8.23 (ArH, d, J=8.8 Hz, 2H), 4.34 (CH2, q, J=7.1 Hz, 2H),
1.32 (CH3, t, J=7.1 Hz, 3H); 13C NMR (75 MHz, DMSO)
δ ppm 161.11, 152.65, 149.21, 137.25, 131.65, 124.13,
114.92, 106.64, 62.72, 13.93.
2.3.7 (E)-Ethyl 2-cyano-3-(4-hydroxyphenyl)acrylate (7a)
FT-IR (KBr, cm−1): 3289 (O-H, str), 3022 (=CH, Ar, str),
2987 (CH, str), 2231 (CN), 1714 (C=O), 1443–1587 (C=C
1
alkene, C=C aromatic); H NMR (300 MHz, DMSO) δ
ppm 10.82 (OH, br, 1H), 8.22 (=CH, s, 1H), 7.98 (ArH, d,
J=8.8 Hz, 2H), 6.94 (ArH, d, J=8.8 Hz, 2H), 4.27 (CH2,
q, J=7.1 Hz, 2H), 1.28 (CH3, t, J=7.1 Hz, 3H); 13C NMR
(75 MHz, DMSO) δ ppm 162.95, 162.61, 154.68, 133.99,
122.48, 116.48, 116.39, 96.98, 61.94, 14.05.
2.3.3 (E)-Ethyl 2-cyano-3-(4-chlorophenyl)acrylate (3a)
FT-IR (KBr, cm−1): 3035 (=CH, Ar, str), 2989 (CH, str),
2223 (CN), 1723 (C=O), 1491–1612 (C=C alkene, C=C
aromatic); 1H NMR (300 MHz, CDCl3) δ ppm 8.20 (=CH, s,
1H), 7.94 (ArH, d, J=8.6 Hz, 2H), 7.48 (ArH, d, J=8.6 Hz,
2H), 4.39 (CH2, q, J=7.1 Hz, 2H), 1.40 (CH3, t, J=7.1 Hz,
3H); 13C NMR (75 MHz, CDCl3) δ ppm 162.19, 153.75,
139.56, 132.17, 129.82, 129.63, 115.24, 103.43, 62.85,
14.12.
2.3.8 (E)-Ethyl 2-cyano-3-(4-hydroxy-3-methoxyphenyl)
acrylate (9a)
FT-IR (KBr, cm−1): 3376 (O–H, str), 3071 (=CH, Ar, str),
2988 (CH, str), 2219 (CN), 1701 (C=O), 1469–1574 (C=C
alkene, C=C aromatic); 1H NMR (300 MHz, CDCl3) δ ppm
8.15 (=CH, s, 1H), 7.86 (ArH, d, J=2.0 Hz, 1H), 7.40 (ArH,
dd, J=8.1, 2.2 Hz, 1H), 7.01 (ArH, d, J=8.3 Hz, 1H), 5.91
(OH, br, 1H), 4.38 (CH2, q, J=7.1 Hz, 2H), 3.99 (CH3, s,
3H), 1.39 (CH3, d, J = 7.1 Hz, 3H); 13C NMR (75 MHz,
CDCl3) δ ppm 163.11, 154.83, 150.82, 146.78, 128.79,
124.26, 116.42, 114.88, 111.11, 99.01, 62.43, 56.14, 14.21.
2.3.4 (E)-Ethyl 2-cyano-3-(3-nitrophenyl)acrylate (4a)
FT-IR (KBr, cm−1): 3071 (=CH, Ar, str), 2988 (CH, str),
2226 (CN), 1718 (C=O), 1355–1529 (N=O), 1471–1606
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R. Javad Kalbasi, A. Khojastegi
2.3.9 (E)-Ethyl 2-cyano-3-(furan-3-yl)acrylate (10a)
The N2 adsorption–desorption isotherms of Hi-ZSM-5
and PDMAEMA/Hi-ZSM-5 samples are shown in Fig. 2.
Both samples show type IV isotherm with hysteresis loop
H3, which demonstrates the mesoporous structure with uni-
form size distributions according to the IUPAC classifica-
tion. The surface area and total pore volume of Hi-ZSM-5
obtained from BET method are 273 m2 g−1 and 0.75 cm2 g−1,
respectively (Table 1). After in-situ polymerization of
DMAEMA in the pores of Hi-ZSM-5, PDMAEMA/Hi-
ZSM-5 still has a reasonable surface area (120 m2 g−1) and
pore volume (0.5 cm2 g−1) which is decreased in comparison
with Hi-ZSM-5. Actually, the decrease of pore volume may
be related to the existence of some polymers inside the pore
of Hi-ZSM-5. As can be seen, after the incorporation of the
polymer into the pores of Hi-ZSM-5 the catalyst still has
reasonable surface area and pore volume.
FT-IR (KBr, cm−1): 3129 (=CH, str, Ar), 3039 (CH, str),
2987 (CH, str), 2222 (CN), 1715 (C=O), 1464–1620 (C=C
alkene, C=C aromatic); 1H NMR (300 MHz, CDCl3) δ ppm
8.02 (=CH, s, 1H), 7.76 (ArH, d, J=1.5 Hz, 1H), 7.40 (ArH,
d, J=3.7 Hz, 1H), 6.67 (ArH, dd, J=3.6, 1.7 Hz, 1H), 4.36
(CH2, q, J=7.1 Hz, 2H), 1.38 (CH3, t, J=7.1 Hz, 3H); 13
C
NMR (75 MHz, CDCl3) δ ppm 162.57, 148.72, 148.21,
139.46, 121.70, 115.33, 113.82, 98.62, 62.56, 14.16.
2.3.10 2-Benzylidenemalononitrile (1b)
FT-IR (KBr, cm−1): 3059 (=CH, str, Ar), 3032 (CH, str),
2935 (CH, str), 2222 (CN), 1450–1591 (C=C alkene, C=C
aromatic); 1H NMR (300 MHz, CDCl3) δ ppm 7.92 (ArH, d,
J=7.4 Hz, 2H), 7.79 (=CH, s, 1H), 7.70–7.50 (ArH, m, 3H);
13C NMR (75 MHz, CDCl3) δ ppm 159.91, 134.58, 130.84,
130.67, 129.56, 113.65, 112.49, 82.75.
The pore size distribution of Hi-ZSM-5 and PDMAEMA/
Hi-ZSM-5 samples calculated by BJH method are shown
in Fig. 3. Moreover, the results are presented in Table 1.
According to the results, Hi-ZSM-5 exhibits relatively nar-
row pore size distribution with average pore dimensions of
3.9 nm. After incorporation of the polymer in the pores of
Hi-ZSM-5, the average pore diameter reduced to 3.1 nm and
it’s an irrefutable evidence for successful synthesis of poly-
mer inside the pores of Hi-ZSM-5. Due to the possibility of
hyper-branching of the polymer [29], the results display that
the polymer was synthesized relatively linear and regular
within the pores.
3 Results and Discussion
3.1 Catalyst Characterization
The X-ray diffraction patterns of Hi-ZSM-5, PDMAEMA/
Hi-ZSM-5, and PDMAEMA materials are presented in
Fig. 1. The XRD pattern of Hi-ZSM-5 shows the intense
peaks at 2Ɵ = 7.9, 8.8, 23.3, 23.7, 24 which represent the
high crystallinity of Hi-ZSM-5 (Fig. 1). The broad peak of
PDMAEMA at 2Ɵ=7.5–17.5 shows the amorphous struc-
ture of the polymer which overlaps with intense peaks of Hi-
ZSM-5 in the catalyst, confirming the existence of polymer
on the surfaces of the zeolite.
Moreover, MP-Plot and t-Plot methods were utilized
to study of micropores of the catalyst (Table 1). The total
surface area of PDMAEMA/Hi-ZSM-5 reduced from 273
to 120 m2 g−1 while the surface area of micropores did
not reduce. In addition, from the curve of PDMAEMA/
Hi-ZSM-5 in Fig. 2, we do not observe the N2 adsorption
Fig. 1 XRD patterns of Hi-ZSM-5, PDMAEMA/Hi-ZSM-5, and
Fig. 2 N2 adsorption–desorption isotherms of Hi-ZSM-5 and
PDMAEMA
PDMAEMA/Hi-ZSM-5
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Hierarchically Pore Structure poly 2-(Dimethyl amino) ethyl methacrylate/Hi-ZSM-5: A Novel…
Table 1 Physicochemical
a
a
b
c
d
d
c
Sample
Smesopore
Vmesopore
Dmesopore
(nm)
Smicropore
Smicropore
Vmicropore
Dmicropore
(nm)
properties of PDMAEMA/
Hi-ZSM-5
(m2 g−1
)
(cm3 g−1
)
(m2 g−1
)
(m2 g−1
)
(cm3 g−1
)
Hi-ZSM-5
237
0.75
0.5
3.9
3.1
272
256
195
157
0.12
0.13
0.7
1.7
PDMAEMA/ 120
Hi-ZSM-5
aCalculated by BET method
bAverage pore sizes determined by using BJH method from the adsorption branch of the isotherm curves
cCalculated by Mp-Plot method
dCalculated by t-plot method
Fig. 3 Average pore size distributions of Hi-ZSM-5 and
PDMAEMA/Hi-ZSM-5
Fig. 4 FT-IR spectra of Hi-ZSM-5 and PDMAEMA/Hi-ZSM-5
amount of micropores which can be seen in the curve of Hi-
ZSM-5 (control). Therefore, the micropores of PDMAEMA/
Hi-ZSM-5 originally come from the mesopores of Hi-
ZSM-5 which were reduced upon incorporation of the poly-
mer within the mesopores of Hi-ZSM-5 (not from Hi-ZSM-5
micropores).
is related to CH3 bending vibrations which corresponds to
methyl groups in the side branches of the polymer and also
the band in 1457 cm−1 is correlated to CH2 bending vibra-
tion of methylene groups of the polymer. As a matter of fact,
all of these bands, which mentioned above, are characteris-
tics of PDMAEMA in the structure of the catalyst. In addi-
tion, looking at the FT-IR spectrum of DMAEMA monomer
(Fig. S21) it can be found that the band at 1720 cm−1 belongs
to carbonyl bond is shifted to 1726 cm−1 after polymeriza-
tion of monomer. Actually, carbonyl bond of ester in the
monomer is conjugated to C=C but after polymerization,
the C=C bond is consumed and this conjugation is removed.
Therefore, the carbonyl band is shifted to higher frequency
(1726 cm−1). Overall, the existence of the above bands in the
FT-IR spectrum of the catalyst is an evidence for successful
synthesis of PDMAEMA/Hi-ZSM-5.
The FT-IR spectra of Hi-ZSM-5 and PDMAEMA/Hi-
ZSM-5 are presented in Fig. 4. The FT-IR spectrum of
Hi-ZSM-5 displays the characteristic bands around 1090,
800 and 470 cm−1, corresponding to bending and stretch-
ing vibrations of Si–O–Si and Si–O–Al groups, which are
attributed to the Hi-ZSM-5 framework. Absorption bands
in the region of 1636 and 3422 cm−1 are ascribed to the
bending and stretching vibration of O–H groups, which are
resulting from adsorbed water on the surface of the zeolite
as well as hydroxyl groups of zeolite structure. Also, these
bands can be seen in the FT-IR spectrum of PDMAEMA/
Hi-ZSM-5. Moreover, the sharp band at 1726 cm−1 belongs
to C=O stretching vibration and the band around 2984 cm−1
is assigned to the aliphatic C–H stretching related to ali-
phatic sp3 carbon-hydrogen bond in the backbone and side
branches of PDMAEMA. The band in the region 1387 cm−1
The SEM images of Hi-ZSM-5 and PDMAEMA/
Hi-ZSM-5 are demonstrated in Fig. 5. As can be seen,
Hi-ZSM-5 has a cubic morphology (with 5 µm average
size) the same as KIT-6. In addition, some amorphous
phases can be seen in the SEM images of Hi-ZSM-5 and
PDMAEMA/Hi-ZSM-5 which is belonged to KIT-6 and
1 3

R. Javad Kalbasi, A. Khojastegi
Fig. 5 SEM images of the Hi-ZSM-5 (a, b), PDMAEMA/Hi-ZSM-5 (c, d)
it is normal because KIT-6 was served as the silica origin
for preparation of Hi-ZSM-5 (Fig. 5a, b). Furthermore,
looking at the SEM images of PDMAEMA/Hi-ZSM-5
present that the cubic morphology of Hi-ZSM-5 is pre-
served after polymerization and also some of the polymer
chains are located inside the Hi-ZSM-5 pores (Fig. 5c, d).
However, some of the polymer chains may be distributed
on the outer surface of Hi-ZSM-5.
3.2 Catalytic Activity
The acidic and basic properties of the bifunctional cata-
lyst were evaluated in the tandem reaction of deacetaliza-
tion–Knoevenagel condensation in the presence of aqua as
a green, cheap and accessible solvent. This cascade reaction
involves two separate reactions that are performed in a con-
tainer. The acid sites catalyze the deprotection reaction and
hydrolysis of benzaldehyde dimethyl acetal to benzaldehyde
intermediate and subsequently the basic sites catalyze Kno-
evenagel condensation via active methylene compound and
benzaldehyde (Scheme 1). The mechanistic insight of the
reaction was surveyed based on experiments and the litera-
ture and the detailed mechanism is illustrated in Scheme 2.
In this catalyst the acid site is originated from bronsted
acids on Al–O–Si bridges in the tetrahedral framework of
the zeolite [30, 31] and the basicity is provided by tertiary
amino groups in the side branches of the PDMAEMA. The
catalyst is assembled from the reaction of the monomers
within the zeolite network and the polymer is synthesized
directly inside the hierarchical zeolite pores. In this condi-
tion, the polymer is disabled to get out of the pores due to
enormous volume, numerous interactions like dipole–dipole
interactions, inductions, and hydrogen bonds [32]. As a
matter of fact, there is not any covalent bonding between
The TEM technique was used to characterize the tex-
tural properties of samples. The images of Hi-ZSM-5
and PDMAEMA/Hi-ZSM-5 are depicted in Fig. 6. The
TEM images revealed a perfect mesopore structure and
channels of Hi-ZSM-5. As can be seen, the images of
the catalyst represent the elegant and admirable structure
of PDMAEMA/Hi-ZSM-5 and imply that after polym-
erization, the mesoporous structure of Hi-ZSM-5 is still
retained and pore blockage cannot be seen. It should be
mentioned that the polymerization condition was suitably
mild and did not damage the structure of the hierarchical
zeolite. Representative images signify that the polymers
are distributed orderly and systematic in the pores of Hi-
ZSM-5. Besides, the nanocomposite has pore diameter
around 6 nm which is a prominent feature for the catalyst.
These outcomes are in accordance with previous results
obtained from BET, FT-IR, and XRD.
1 3

Hierarchically Pore Structure poly 2-(Dimethyl amino) ethyl methacrylate/Hi-ZSM-5: A Novel…
Fig. 6 TEM images of Hi-
ZSM-5 (a), PDMAEMA/Hi-
ZSM-5 (b–d)
deacetalization–Knoevenagel condensation and the out-
comes are demonstrated in Table 2. For this purpose, three
catalysts with different polymer/zeolite weight ratio were
prepared and the free basic sites of these catalysts were cal-
culated by back titration (Table 2). The results represented
that in comparison with theoretical calculations; the cata-
lysts have possessed about 70% of free basic sites. It is natu-
ral that some of the basic and acidic sites in an acid–base
bifunctional catalyst are neutralized with each other. How-
ever, 70% free basic sites in the catalyst, is a remarkable
achievement because it shows a good basic activity of the
catalyst. In fact, a great number of tertiary amine groups of
the polymer cannot react or interact with the acid sites of the
zeolite because of the strain effect of tertiary amines and low
spaces in the pores of the zeolite.
Scheme 1 Tandem reaction of deacetalization–Knoevenagel conden-
sation
polymer and zeolite surface and the polymer chains are just
encapsulated and trapped in the pores of the zeolite by non-
covalent bonding. This synthesis method can be named as a
ship in a bottle which is a superior method due to cheapness
and easiness [33, 34]. The catalyst profits the tunable pore
size, high thermal and mechanical stability of the hierarchi-
cal zeolite, the specific functionality and high flexibility of
the polymer. Our prospect for this concept was to design
a novel acid–base bifunctional catalyst that contained sev-
eral active sites to gain a robust catalyst. A hierarchical acid
support with high surface area (hierarchical ZSM-5) and a
polymer that contain numerous basic sites (PDMAEMA)
were utilized to increase the acidic and basic sites to pro-
mote the catalytic performance. Moreover, the tertiary amine
moiety of the polymer is a stronger base than conventional
–NH2 groups which have been employed in many acid–base
bifunctional catalysts.
The hierarchical ZSM-5 is abundant in three-dimensional
pores and channels some of which are unreachable for poly-
mer chains (mostly micropores). Therefore, a great number
of acidic sites do not neutralize and it is a great achievement
in comparison with other catalysts for which neutralization
happens to them due to the proximity of acid sites with basic
groups. On the other hand, the existence of hierarchical
ZSM-5 zeolite in the structure of the catalyst, which has a
high surface area and a large dimension mesopores, redound
to get the extra access of reactants to acidic and basic sites.
In summary, based on the results obtained from Table 2,
all the catalysts had excellent yields and short reaction
times. However, the catalyst with 1:1 weight ratio (ZSM-5
to monomer) showed higher activity and less reaction time
The impact of the basic sites of the catalyst on the
catalytic activity was examined in the tandem reaction of
1 3

R. Javad Kalbasi, A. Khojastegi
Scheme 2 A possible mecha-
nism of tandem reaction of
deacetalization–Knoevenagel
condensation
Table 2 Effect of the amount
of acidic and basic sites on
the catalytic activity of the
PDMAEMA/Hi-ZSM-5
Entry
Monomer (g)/
zeolite (g)
Weight ratio
Time (min)
Isolated yielda Free basic
(monomer:zeolite)
(%)
sitesb
(mmol g−1
)
1
2
3
0.25/0.25
0.125/0.25
0.0625/0.25
1:1
1:2
1:4
40
55
75
95
91
89
2.1
1.4
1.2
Reaction condition: benzaldehyde dimethyl acetal (1.87 mmol), ethylcyanoacetate (1.87 mmol), catalyst
(0.1 g) and H2O (5 mL), reflux
aIsolated yield after work up
bCalculated by back titration method
than the others. The experimental observations demon-
strated that the rates of the first step of the reaction were
almost identical for all catalysts. Thanks to the high sur-
face area and large pores of the catalyst, the acidic sites
are readily accessible and with a small amount of catalyst,
this reaction could be easily accomplished. However, for
the second step, the number of basic sites is absolutely
crucial when it was increased; acceleration in the reaction
rate was observed because with increasing the amount of
the polymer, free basic sites have been rising too.
Table 3 Effect of temperature on the catalytic activity of the
PDMAEMA/Hi-ZSM-5
Entry
Temperature (°C)
Time (min)
Isolated
yielda (%)
1
2
3
4
Reflux
60
40
40
60
180
540
95
95
79
55
25
Reaction condition: benzaldehyde dimethyl acetal (1.87 mmol), ethyl-
cyanoacetate (1.87 mmol), catalyst (0.1 g) and H2O (5 mL)
aIsolated yield after work up
1 3

Hierarchically Pore Structure poly 2-(Dimethyl amino) ethyl methacrylate/Hi-ZSM-5: A Novel…
In order to monitor the effect of temperature on the rate
and yield, the reaction was carried out at different tempera-
tures (Table 3). Observations reveal that the decrease in tem-
perature adversely affected the rate of both reaction steps.
By Increasing temperature from 25 to 60 °C the duration of
reaction is decreased from 9 to 1 h and the yield increased
from 55 to 95%. In the higher temperatures, the yield was
constant. Thus, 60 °C was selected as the best temperature
for the reaction.
shortest reaction time. Also, about benzaldehyde dimethyl
acetal derivatives with electron donating substitution, yield
was excellent but the reaction time was longer. Thus, a large
amount of catalyst (0.07 g) was required. Moreover, the reac-
tion was perfectly 10 times scaled-up, which represents the
superior activity of the catalyst.
Also, these reactions with a variation of active meth-
ylene compound and benzaldehyde dimethyl acetal were
performed (Table 6). Malononitrile which is a more active
methylene compound, showed short reaction time and excel-
lent yield. Furthermore, cyclic active methylene compound
like 1,3 dimethyl barbituric acid exhibited excellent activity
in tandem reaction.
The amount of catalyst is one of the determining factors
to assess the catalytic activity of the materials (Table 4). To
investigate this factor, various mass of catalyst from 0.02
to 0.1 g was used for the tandem reaction while the other
parameters remained constant. The results showed that with
decreasing the catalyst from 0.1 to 0.07 g, the yield and time
of the reaction were constant. Furthermore, by reducing the
amount of the catalyst to 0.02 g, the yield was still excellent
though the reaction time became longer. Actually, decreas-
ing the amount of the catalyst causes to diminish the amount
of acid–base sites and an increase in the reaction time, but
the yield is still reasonable owing to high surface area and
large pore dimension of the catalyst that reflected in its per-
formance. Accordingly, from the point of economic view,
0.02 g of the catalyst was found as the best weight for the
tandem reaction of deacetalization–Knoevenagel condensa-
tion at 60 °C.
In order to prove the cooperative behavior of the acidic
support and the basic polymer, the performance of the
catalyst in the tandem reaction was compared with differ-
ent blank materials. No conversion of benzaldehyde dime-
thyl acetal to benzaldehyde was shown in the absence of
the catalyst (Table 7, entry 1). By using Hi-ZSM-5, ben-
zaldehyde dimethyl acetal was deprotected after 40 min
(Table 7, entry 2), which is the same as PDMAEMA/Hi-
ZSM-5. This indicated that the acid sites were not covered
with or occupy by the polymer, because the Hi-ZSM-5 has
high surface area, which still is accessible after incorpora-
tion of polymers. By utilization of KIT-6, which has weak
acid sites on silanol surface, 100% benzaldehyde was gener-
ated after 2 h (Table 7, entry 3). All the reactions continued
for 72 h and no product of Knoevenagel condensation was
observed (Table 7, entries 1–3). By using PDMAEMA as
the catalyst, the benzaldehyde intermediate was not gener-
ated and as a result, the benzylidene product was not dis-
played (Table 7, entry 4). No improvement in the tandem
reaction was achieved in the cases above, which implied
that PDMAEMA/Hi-ZSM-5 is a bifunctional catalyst. These
results suggested that the acid sites (Hi-ZSM-5) had no role
in the subsequent step progressing of the cascade reaction.
Consequently, it confirmed the proposed mechanism for the
reaction (Scheme 2).
Tandem reaction of deacetalization–Knoevenagel con-
densation was considered for the reaction of benzaldehyde
dimethyl acetals with different substitution and ethylcy-
anoacetate in water (Table 5). The yields and reaction times
are satisfied in all cases even with a large substitution that
signifies mass transport of the catalyst. As expected, a pro-
tected aromatic aldehyde with electron withdrawing group
substitution was more active than those with electron donat-
ing group, except in 2,6-dichlorobenzaldehydedimethylac-
etal because of having two large chlorine substitution in the
ortho position, which makes it difficult to access to the car-
bonyl group. Subsequently, the reaction time was longer than
other substitutions. 4-nitrobenzaldehydedimethylacetal with
strong electron withdrawing group has the best yield and
To compare the efficacy of PDMAEMA/Hi-ZSM-5 and
the PDMAEMA, in the second stage of the tandem reaction,
benzaldehyde was used instead of benzaldehyde dimethyl
acetal and the reaction was performed under optimum con-
ditions (Table 7, entry 5). Interestingly, the results showed
that even though the polymer containing numerous basic
groups, after about 2 h, the desired product was not gener-
ated. Actually, the cyclic conformation is a favor conforma-
tion for PDMAEMA, because of the interaction of nitrogen
electron pair with the carbonyl group of ester (Scheme 3,
down) [38]. Therefore, this conformation causes to reduce
the basic property and activity of PDMAEMA. In contrast,
in the case of PDMAEMA/Hi-ZSM-5 as catalyst, owing to
the interaction of nitrogen electron pairs with protons on the
surface of the zeolite, side branches of the polymer prefer
Table 4 Effect of amount of catalyst on tandem reaction of deacetali-
zation–Knoevenagel condensation
Entry
Catalyst amount
(g)
Time (min)
Isolated
yielda (%)
1
2
3
4
0.1
60
95
125
150
95
95
90
90
0.07
0.05
0.02
Reaction condition: benzaldehyde dimethyl acetal (1.87 mmol), ethyl-
cyanoacetate (1.87 mmol) and H2O (5 mL), 60 °C.
aIsolated yield after work up
1 3

R. Javad Kalbasi, A. Khojastegi
Table 5 Tandem reaction of deacetalization–Knoevenagel condensation of different benzaldehyde dimethyl acetal and ethylcyano acetate cata-
lyzed by PDMAEMA/Hi-ZSM-5
Entry
Benzaldehyde dimethyl acetal
Product
Isolated
Time (h)
Melting point (˚C)
yielda (%)
found
48–49
Reported (Ref.)
1a
90
2.5
4
48–50 [35]
85b
93
2a
3a
4a
2
165–167
90–92
166–168 [35]
91
91
2.5
2.5
92–93 [35]
130–131
131–132 [35]
5a
80
91
24
4
70–73
92–94
_
6ac
93–94 [35]
7ac
8ac
9ac
89
87
89
6
6
7
167–169
84–87
170–171 [35]
87–89 [35]
102–104
99–101 [36]
1 3

Hierarchically Pore Structure poly 2-(Dimethyl amino) ethyl methacrylate/Hi-ZSM-5: A Novel…
Table 5 (continued)
Entry
Benzaldehyde dimethyl acetal
Product
Isolated
Time (h)
2
Melting point (˚C)
yielda (%)
found
92–93
Reported (Ref.)
93–93 [35]
10ac
95
Reaction condition: benzaldehydedimethylacetal (1.87 mmol), ethylcyanoacetate (1.87 mmol), catalyst (0.02 g) and H2O (5 mL), 60 °C
aIsolated yield after work up
bReaction condition: benzaldehydedimethylacetal (18.7 mmol), ethylcyanoacetate (18.7 mmol), catalyst (0.2 g) and H2O (25 mL), 60 °C
cCatalyst (0.07 g)
Table 6 Tandem reaction of deacetalization–Knoevenagel condensation of benzaldehyde dimethyl acetal and active methylene compounds cata-
lyzed by PDMAEMA/Hi-ZSM-5
Entry
Active methylene compound
Product
Isolated yield Time (h)
(%)a
Melting point (˚C)
found
80–81
Reported (Ref.)
1b
95
1.2
80–82 [35]
2b
3b
90
2.5
48–49
49–50 [35]
90
3
153–156
159–160 [37]
Reaction condition: benzaldehydedimethyl acetal (1.87 mmol), active methylene compound (1.87 mmol), catalyst (0.02 g) and H2O (5 mL),
60 °C
aIsolated yield after work up
stretched conformation and basic sites are more available
(Scheme 3, up). The intimacy of acid–base site has been
found so prominent for the catalyst and recommended the
cooperative effect of acid–base sites.
Table 7 Tandem reaction of deacetalization–Knoevenagel condensa-
tion with other materials
Entry Catalyst
Time (min) Benzalde- Benzylidene ethyl
hyde (%) cyanoacetateb (%)
By increasing the amount of PDMAEMA from 0.02 to
0.07 g, the second step of the reaction has progressed after
24 h to 70% yield (Table 7, entry 5). This observation pecu-
liarly proved that the PDMAEMA has not much catalytic
activity. Indeed, these outcomes clarify the importance of
embedding polymer into the hierarchical zeolite.
1
2
3
–
150
40
180
150
150
–
–
–
–
–
–
70
Hi-ZSM-5
KIT-6
PDMAEMA
PDMAEMA
100
100
–
–
–
4
5a
24 h
One major concern about heterogeneous catalyst is
active site leaching during the reaction. In order to exam-
ine leaching possibility of the polymer during the tandem
reaction, the hot filtration was carried out. The catalyst
was removed in the middle of the process and the reaction
Reaction condition: benzaldehyde dimethyl acetal (1.87 mmol), ethyl-
cyanoacetate (1.87 mmol), catalyst (0.02 g) and H2O (5 mL), 60 °C
aReaction condition: benzaldehyde (1.87 mmol), ethylcyanoacetate
(1.87 mmol), catalyst (0.02 g) and H2O (5 mL), 60 °C
bIsolated yield after work up
1 3

R. Javad Kalbasi, A. Khojastegi
Scheme 3 Polymer side
branches conformations in the
PDMAEMA/Hi-ZSM-5 (up)
and PDMAEMA (down)
carried out without the catalyst for 5 h. After removal of
the catalyst, no significant change was observed in the
final product yield and the amount of intermediate. These
results confirm that the catalyst is really heterogeneous
and leaching of the polymer during the reaction did not
occur.
The reusability of the catalyst is very important for the
industrial application. For this purpose, the reaction was
performed and the catalyst was separated and rinsed vari-
ous times with diethyl ether then it was dried at 70 °C. The
recycled catalyst was used in the reaction for five times and
it had acceptable catalytic activity. The catalyst was found
recoverable, reusable and marginal decrease in activity and
selectivity (Fig. 7). Moreover, the back titration results were
confirmed a minute change in the number of free basic sites
of the recovered catalyst after five cycles, which approved
the permanence of the polymer in the structure of the cata-
lyst during the reaction step.
Fig. 7 Reusability of PDMAEMA/Hi-ZSM-5 in tandem reaction
under optimized condition
Moreover, SEM image of recycled catalyst (Fig. 8) in
comparison with fresh catalyst indicates that the catalyst has
high stability during the reaction and the morphology of the
catalyst has not changed.
indicated the presence of the amorphous polymer in the
structure of Hi-ZSM-5 after five cycles and showed that
the polymer was not leached during the reaction. Indeed,
the polymer has a great stability in both hierarchical zeo-
lite and reaction.
The XRD pattern of the reused catalyst (Fig. 9) dem-
onstrated no significant changes in comparison with
fresh catalyst. The intense peaks in the XRD pattern of
the recycled catalyst represented that the crystallinity
of the Hi-ZSM-5 is still retained. Also, the broad peaks
1 3

Hierarchically Pore Structure poly 2-(Dimethyl amino) ethyl methacrylate/Hi-ZSM-5: A Novel…
and reusability. The present work is one of the pioneers in
the field of polymer-composite material as the acid–base
bifunctional catalyst and benefits from the advantages of
the tunable pore size, high thermal stability and the crystal-
line walls of the hierarchical zeolite and unique properties
of polymers such a great assortment of functional groups.
Our methodology for the preparation of this catalyst was
widespread and with a variety of polymer and zeolite, a wide
diversity of high-performance bifunctional acid–base cata-
lyst can be achieved.
Acknowledgements The support from Kharazmi University, Tehran,
Iran is greatly appreciated by the authors.
Fig. 8 SEM image of five times recycled catalyst
Compliance with Ethical Standards
Conflict of interest The authors declare that they have no conflict of
interest.
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