Piperazine-functionalized ordered mesoporous polymer as highly active and reusable organocatalyst for water-medium organic synthesis

Article abstract of DOI:10.1039/c3gc40215k

A piperazine-functionalized mesoporous polymer (PP-MPs) was synthesized through a one-step surfactant-directed phenol-formaldehyde- piperazinecarbaldehyde oligomer self-assembly approach. This novel PP-MP catalyst exhibited highly catalytic reactivity and selectivity for water-medium Knoevenagel reaction, water-medium [3 + 3] cycloaddition reaction and intermolecular cross-conjugated addition reaction. The excellent performance could be attributed to its high dispersion of piperazine active sites and ordered mesoporous structure, which effectively diminished the steric hindrance and diffusion limitation. Moreover, its pure organic framework could enhance surface hydrophobicity, which promoted organic reactant molecule adsorption, especially in water. Meanwhile, piperazine functional groups embedded in the polymeric framework could inhibit the leaching of active species and thus resulted in the excellent durability without significant loss of activity for recovery and recycling at least four times.

Full text of DOI:10.1039/c3gc40215k

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Piperazine-functionalized Ordered Mesoporous Polymer as
Highly Active and Reusable Organocatalyst for Water-medium
Organic Synthesis
Fang Zhang*, Xushi Yang, Chao Liang, Ruixing Zhu and Hexing Li*
The Education Ministry Key Laboratory of Resource Chemistry and Shanghai Key
Laboratory of Rare Earth Functional Materials, Shanghai Normal University,
Shanghai 200234, China
Corresponding author: zhangfang@shnu.edu.cn; HeXing-Li@shnu.edu.cn
Abstract
Piperazine-functionalized mesoporous polymers (PP-MPs) were synthesized
through one-step surfactant-directed phenol-formaldehyde-piperazinecarbaldehyde
oligomer self-assembly approach. This novel PP-MPs catalyst exhibited highly
catalytic reactivity and selectivity in water-medium Knoevenagel reaction,
water-medium [3+3] cycloaddition reaction and intermolecular cross-conjugated
addition reaction. The excellent performance could be attributed to its high dispersion
of piperazine active sites and ordered mesoporous structure, which effectively
diminished the steric hindrance and diffusion limitation. Moreover, its pure organic
framework could enhance surface hydrophobicity, which promoted organic reactant
molecules adsorption, especially in water. Meanwhile, piperazine functional groups
embedded in the polymeric framework could inhibit the leaching of active species and
thus resulted in the excellent durability without significant loss of activity for recover
and recycle at least four times.

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Introduction
The development of more green and safer chemical transformations for effective
synthesis of fine chemicals is an important goal in our society.1 The use of water as a
sole medium of organic reactions would greatly contribute to the development of
environmentally friendly processes.2 Most of this research has been focused on
homogeneous catalytic processes. Although highly active and selective, homogeneous
catalysts are difficult for handling and separation, leading to significant economical
and ecological disadvantages.3 Recently, the use of heterogeneous catalysts in
water-medium organic transformations seems a promising strategy to overcome the
inherent problems in the homogeneous catalytic system.4 To date, various catalytic
active species attached to either inorganic or organic materials, such as silica,5 layered
clays,6 carbon,7 polymers8 and metal-organic frameworks (MOFs),9 have been
successfully fabricated by using covalent and non-covalent immobilization approach.
Although these catalytic systems are effective, one critical issue associated with using
expensive and toxic metal-based active species is always believed as a most
challenging obstacle in the future.10 Therefore, new and general paradigms for
preparing metal-free heterogeneous catalysts for aqueous organic synthesis are
urgently needed.
In the last decade, organocatalysts have gained tremendous importance from the
synthetic community because they are less expensive, non-toxic, readily available,
and environmentally friendly.11 Accordingly, considerable efforts have been made in
developing water-compatible organocatalysts for performing organic transformations

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in water.12 Although homogeneous organocatalysts with high reactivity and selectivity,
most of them suffered from high catalyst loadings (typically 10-20%) and tedious
separation from the products, which raised significant concerns regarding its practical
applications and feasibility on a large scale preparation.13 To circumvent this difficulty,
the development of recoverable and reusable organocatalysts appears as one of the
most advantageous strategies.14 Most attempts to gain the advantage of
water-compatible heterogeneous organocatalysts have so far been directed toward the
anchoring of efficient soluble organic active sites on insoluble polymer matrixes.15
However, such polymer-supported organocatalysts often suffered from tedious
synthetic routes, less and inhomogeneously distributed active sites, poor stability, as
well as low efficiency in mass transport, especially in water.16
Recently, a novel phenol-formaldehyde polymer with ordered mesoporous
structure and high surface area, offers a potential to serve as an alternative solid
support for catalyst immobilization and improves the catalyst activity.17 In our group,
we have synthesized mesoporous polymer-supported organometallic catalysts, which
displayed comparable activity and selectivity to that of homogenous organometallic
complex in a wide of water-medium organic reactions.18 Encouraged by these
successful efforts and aiming to develop a stable and highly active solid
organocatalyst, we report for the first time the bottom-up construction of a robust
ordered mesoporous polymer-supported piperazine organocatalyst (PP-MPs) by using
one-step surfactant-directed phenol-formaldehyde-piperazinecarbaldehyde oligomer
self-assembly approach. The obtained PP-MPs catalysts possessed the highly ordered

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mesostructure, large surface area and uniform pore size. In the water-medium
Knoevenagel reaction and [3+3] cycloaddition reaction and intermolecular
cross-conjugated addition reaction, PP-MPs catalyst exhibited almost the same
catalytic reactivity and selectivity with that of homogeneous piperazine catalyst,
which was maybe attributed to the high dispersion organoamine group in the
mesoporous polymer framework and the intrinsic hydrophobic microenvironment
around the active sites. Moreover, this heterogeneous organocatalyst can be recycled
and reused for several times without loss of catalytic efficiency.
Experimental
Synthesis of piperazine-derived oligomers (PP-ROs)
The piperazine-derived polymer precursor was obtained through base-catalyzed
polymerization with phenol, formaldehyde and 1-piperazinecarbaldehyde. In a typical
synthesis, 61 mg 1-piperazinecarbaldehyde and 4.2 g 37 wt% formaldehyde aqueous
solution were mixed at 40oC and then allowed the mixture to reflux at 70oC for 0.5 h.
Following that, the solution pH value was adjusted to 10.0 by adding certain amount
20 wt% NaOH. Then, 2.4 g phenol was introduced in the above solution and stirred
for another 2.0 h. Finally, the solution pH value was adjusted to 7.0 by using 2.0 M
HCl
and
then
removed
water
by
rotary
evaporator
to
give
phenol-formaldehyde-piperazinecarbaldehyde oligomer. The final oligomer could be
defined as PP-ROs-1, PP-ROs-2 and PP-ROs-3, corresponding to
1-piperazinecarbaldehyde/formaldehyde molar ratio of 2.0%, 4.0%, and 6.0% in the

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initial mixture, respectively.
Synthesis of piperazine-functionalized mesoporous polymer
The PP-MPs was prepared by one-step surfactant-directed evaporation induced
self-assembly (EISA) approach using PP-ROs precursor and triblock copolymer F127
(Scheme 1). In a typical synthetic procedure, 1.0 g F127 was added into 25 ml ethanol
solution composing of 1.2 g PP-ROs and stirred for 1.0 h to form a clear solution. The
mixture was transferred into dishes and exposed in air at 30oC for 12 h to evaporate
ethanol and further thermo-polymerized at 120oC for 96 h. The as-made materials
were calcined in a tubular furnace at 350oC for 6.0 h in argon atmosphere to remove
F127 template. The final products were denoted as PP-MPs-1, PP-MPs-2 and
PP-MPs-3, which involved with three corresponding PP-ROs precursor as functional
building blocks.
Characterization
Small-angle X-ray diffraction (XRD) patterns were conducted on Rigaku D/maxr
B diffractometer with Cu Kα radiation (40 kV, 20 mA). N2 sorption isotherms were
measured at 77
K
on Quantachrome NOVA 4000e analyzer. The
Brunauer-Emmett-Teller (BET) method was utilized to calculate the specific surface
areas. Transmission electron microscopy (TEM) experiments were performed on
JEM2011 microscope operated at 200 kV. The sample for TEM measurement was
13
suspended in ethanol and supported onto a holey carbon film on a Cu grid. C Solid
nuclear magnetic resonance (NMR) spectra were recorded on Bruker DRX-400 NMR

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spectrometer under the condition of magic angle spinning (MAS), and the spectra
were collected at room temperature at a frequency of 100.6 MHz. The surface
electronic states were analyzed by X-ray photoelectron spectroscopy (XPS,
Perkin-Elmer PHI 5000C ESCA). All of the binding energy values are calibrated by
using C1S = 284.6 eV as a reference. The nitrogen content was determined by
elemental analysis using an Element Vario EL III analyzer. Water and toluene vapour
absorption measurements were carried out on a intelligent gravimetric analyse (Hiden
Isochema IGA-002) by introducing a dosed amount of high-purity vapor directly into
the sample chamber and recording the weight change after stable equilibrium pressure
was reached.
Activity test
All these reactions were carried out in a 10 ml round-bottomed flask. The
reaction conditions and the product analysis methods were described in Reaction I and
II. The reproducibility was checked by repeating experiments at least three times and
was found to be within acceptable limits (± 5 %).
Reaction I. In a typical run of water-medium Knoevenagel condensation reaction,
0.20 mmol ethyl cyanoacetate, 0.24 mmol benzaldehyde, 0.15 mmol n-decane as
internal standard, 5.0 ml distilled water and a catalyst containing 0.020 mmol
piperazidine were mixed and allowed to stir at 40oC for 3.0 h. After extracted with
ethyl acetate, the products were analyzed on a gas chromatograph (GC, Agilent 1790)
equipped with a JWDB-5, 95% dimethyl 1-(5%)-diphenylpolysiloxane column and a

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FID detector.
Reaction II. In each run of intermolecular cross-conjugated addition reactions, 0.50
mmol -methyl--nitrostyrene, 1.0 mmol 1, 3-diphenyl-2-propenone, 0.50 mmol
DMAP and 3.0 ml DMSO, and a catalyst containing 0.050 mmol piperazidine were
mixed. After reaction under vigorous stirring for 16 h, the catalyst was removed by
centrifugation and washed with CH2Cl2 for 3 times. The organic layer is diluted with
CH2Cl2 10 ml, followed by washing with water and brine subsequently. After being
dried in anhydrous sodium sulfate, the solvent is distilled under reduced pressure.
Then, the solid product is dissolved in 10 ml THF, followed by quantitatively
analyzing to determine conversion, selectivity and yield to target product. The product
analysis was performed on a HPLC-MS (Agilent 6410B) by using the external
standard. The conversion was calculated based on α-methyl-β-nitrostyrene since the
ketone compounds are excess. Selectivity was calculated from the relative peak area
ratio of the product and byproduct, which was calibrated by using experimental data
reported by Shi et al.19 There were four enantiomers of the target product. The
HPLC-MS could not distinguish R, R and S, S enantiomers or R, S and S, R
enantiomers, but the R, R and S, S enantiomers could be easily distinguished from R,
S and S, R enantiomers. The diastereomeric ratio (d.r.) refers to the molar ratio
between syn-isomers (R, R + S, S) and trans- enantiomers (R, S + S, R), which could
be calculated based on the respective peak areas.
Reaction III. In a typical run of water-medium [3+3] cycloaddition reactions, a catalyst
containing 0.050 mmol piperazidine, 0.50 mmol 1,3-Cyclohexanedione and 0.50 mmol

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α,β-unsaturated aldehydes, 5.0 ml H2O were mixed and allowed to stir at 20oC for 12 h. The
products were extracted with methanol, followed by analysis on High-performance liquid
chromatography (Agilent 6410 Series Triple Quad) equipped with Agilent C18 20 cm*Ф5mm
column.
Determination of catalyst leaching and durability
In order to determine the catalyst durability, the heterogeneous catalyst was
centrifuged after each run of the reactions and the clear supernatant liquid was
decanted slowly. The residual solid catalyst was washed thoroughly with distilled
water and ethyl acetate, followed by drying at 80oC for 8.0 h under vacuum condition.
Then, the catalyst was re-used with fresh charge of solvent and reactants for
subsequent recycle runs under the same reaction conditions.
Results and Discussion
Elemental analysis revealed that the nitrogen content in a series of PP-MPs
samples was in the range from 0.090 wt% to 1.1 wt% (Table 1), indicating the
existence of organoamine species. The chemical composition of the representative
PP-MPs-2 was further investigated by solid NMR spectroscopy. As shown in Figure 1,
the 13C CP-MAS NMR spectra of non-functionalized mesoporous polymer (MPs)
displayed two peaks around 149 and 128 ppm, which belonged to -OH substituted
carbon in phenol and other aromatic carbons. A shoulder peak around 119 ppm could
be assigned to the non-substituted aromatic ortho carbons. Meanwhile, the broad

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overlapping signals at 36 ppm and 69 ppm could be attributed to methylene linkages
between phenolic rings and benzyl hydroxyl groups, respectively.20 The peaks around
175 and 75 ppm marked with asterisks were considered as rotational sidebands, which
had been confirmed by changing rotational speed. In comparison with MPs, the
PP-MPs-2 sample displayed one addition peak around 48 ppm, which could be
assigned to the methylene carbon in the piperazine units,21 demonstrating the
successful incorporation of piperazine functional group in the mesoporous polymeric
framework. According to IR and NMR data, the introduction of piperazine species in
the mesoporous polymer framework could be achieved through base catalyzed
condensation reaction between 1-piperazinecarbaldehyde, formaldehyde and phenol
and thus the obtained soluble oligomers were further interacted with surfactant to give
the functionalized mesoporous polymer since the oligomers have a large number of
hydroxy groups.17 Meanwhile, the XPS analysis (Figure 2) demonstrated that nitrogen
species in the PP-MPs-2 was present in negative trivalence state, corresponding to the
binding energy of 399.7 eV in N1s level.22 As expected, the binding energy value of
PP-MPs-2 sample was much the same with that of piperazine, suggesting the
chemical structure of piperazine could be well retained after supramolecular
self-assembly and thermal co-polymerization processes.
Figure 3 showed small-angle XRD patterns for PP-MPs with different piperazine
contents. All the PP-MPs samples exhibited a well resolved peak at 2 = 0.75o
characteristic of the (100) diffraction, suggesting the formation of ordered
2-dimensional p6mm hexagonal mesoporous structure.23 The XRD peak intensity

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decreased with the increase of piperazine content due to the decrease in ordering
degree of mesoporous structure, which revealed that more piperazine units in the
precursor maybe disturbed the effective assembly between triblock co-polymer and
the hydrophilic phenolic -OH groups. TEM image (inset) of the representative
PP-MPs-2 sample further confirmed it exhibited a two-dimensional hexagonal
arrangement of one-dimensional channels with uniform size.24 Ordered mesoporous
morphology can be observed in large domains, without distinct defects. The pore
structure of these samples was further characterized using nitrogen sorption
experiments. All the PP-MPs materials displayed typical type IV N2
adsorption-desorption isotherms with H1-type hysteresis loop characteristic of
mesoporous structure (Figure 4). The BET surface areas, average pore size, and pore
volume of these functionalized mesoporous polymers were summarized in Table 1.
Increase with piperazine content resulted in the decrease of SBET, DP and VP due to the
decreased ordered degree of the mesoporous structure. This phenomenon was maybe
due to the reduced hydrophilic -OH groups in the PP-ROs with more piperazine units,
which was unfavorable for -OH groups to interact with EO block to form the final
ordered mesostructures during solvent evaporation induced self-assembly process.
Based on these results, it can be safely concluded that the current approach for the
introduction of piperazine functional groups in the mesoporous polymer framework
could effectively avoid the degradation of the original mesoporosity and mesoscopic
ordering.
Water-medium Knoevenagel condensation reaction was used to evaluate the

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catalytic performance of piperazine-functionalized mesoporous polymer. As
summarized in Table 1, a series of PP-MPs displayed highly catalytic reactivity,
indicating piperazine functional group was indeed catalytically active site. Firstly, we
investigated the effect of nitrogen content on the catalytic activity in the condensation
of benzaldehyde with ethyl cyanoacetate. The results showed that the yield of ethyl
a-cyanocinnamate increased from 82% to 92% with the increase of nitrogen content
from to 0.090 to 0.33 wt%. However, the yield drastically dropped to 87% when
nitrogen content increased to 1.1 wt%. The inferior catalytic reactivity of PP-MPs-1
could be attributed to the lower active site density, which reduced the requisite
substance contact. While the decreased ordered degree of pore structure of PP-MPs-3
disfavored the transport limitation and/or the interaction between organic piperazine
species and the reactants, which resulted in the reduced catalytic efficiency.
Furthermore, we examined the difference in catalytic activity between PP-MPs-2 and
homogeneous catalyst (Table 2). Notably, we found that PP-MPs-2 exhibited similar
catalytic reactivity to that of piperazine, confirming its almost unchanged chemical
microenvironment. Meanwhile, the pure organic framework of PP-MPs-2 catalyst
guaranteed the surface hydrophobicity, leading to the deceased mass transport
limitation in water. To gain precise insight into the hydrophobic effect, both toluene
and water vapor absorption tests were employed to test the hydrophobicity of
PP-MP-2 catalyst (Figure 5). All the isotherms were of type V indicative of weak
absorbent-absorbate interaction.25 However, the adsorption capacity of PP-MP-2 for
toluene (13 wt.%) was much higher than that of water (5.7 wt.%). This result

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demonstrated that its mesopore surface was hydrophobic, leading to selective
adsorption for organic reactants. Next, we tested a series of the electron donor and
withdrawing capability of substituent in the benzene ring of derivatives under the
same reaction conditions. As expected, a benzaldehyde derivative with electron
withdrawing substituent (-NO2) in its benzene ring was conducive to Knoevenagel
reaction and 99% yield of the condensation product was obtained. On the contrary, the
existence of electron donor substituent (-OCH3) led to a lower 77% yield.
With the aim of examining the possibility of the wide use of PP-MPs-2 catalyst,
intermolecular cross-conjugated addition reaction between α-methyl-β-nitrostyrene
and 1, 3-diphenyl-2-propenone was chosen as a probe to test its catalytic efficiency.
Besides the target product, two byproducts were also detected by HPLC-MS. One was
resulted from the isomerization of α-methyl-β-nitrostyrene and the other was due to
the self-coupling reaction of α-methyl-β-nitrostyrene (see the reaction equations in
Scheme 2). As shown in Table 3, the conversion increased with the increase of either
the reaction temperature or the reaction time but the selectivity and d.r. value
remained almost identical. The optimum reaction conditions was determined as 40oC
and 16 h, corresponding to the yield of 83% to the target product, which was almost
the same as that obtained in the presence of homogeneous piperazine organocatalyst.
Moreover, we also extended this system to water-medium [3+3] cycloaddition
reaction for constructing pyranyl heterocycle, which is one of the most common
structural subunits in nature products and biological active compounds.26 The results
was summarized in Table 4. PP-MPs-2 catalyst could efficiently catalyze all the

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α,β-unsaturated aldehydes to react with 1,3-cyclohexanedione and obtained their corresponding
pyranyl-containing compounds. Meanwhile, we also found that it displayed almost the same
catalytic performances with homogeneous piperazine catalyst. Interestingly, even for
3-(anthracen-10-yl)acrylaldehyde with relative large molecular size, PP-MPs-2 also exhibited
comparable catalytic reactivity with that of piperazine. The high activity and selectivity
of PP-MPs-2 catalyst could be attributed to the similar Lewis base strength and
chemical microenvironment of piperazine active sites to free piperazine. Meanwhile,
the large surface area and the ordered mesoporous channels of mesoporous polymer
support facilitated the diffusion and adsorption of reactant molecules.
To ensure the reactivity originated from the immobilized piperazine other than
from dissolved piperazine either from the absorbed piperazine or from catalyst
leaching, the following procedure, proposed by Sheldon et al. was carried out.27 After
reaction for 1.5 h that the conversion exceeded 45% in water-medium Knoevenagel
reaction between benzaldehyde and ethyl cyanoacetate, the mixture was filtered to
remove the solid catalyst and then allowed the mother liquor to react for another 3.0 h
under the same reaction conditions. No significant activity was observed,
demonstrating that the active species were not the dissolved piperazine leached from
PP-MPs-2 catalyst. Therefore, it was reasonable to suggest that the present catalysis
was heterogeneous in nature.
An important merit of heterogeneous catalysts is that they should be
conveniently recycled and reused. Firstly, we examined the durability of PP-MPs-2
catalyst in water-medium Knoevenagel reaction between benzaldehyde and ethyl

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cyanoacetate. As shown in Figure 6a, no significant decrease could be found in either
the activity or the selectivity after being used repetitively for 6 times. Then we further
determined the lifetime of PP-MPs-2 catalyst in intermolecular cross-conjugated
addition reaction between α-methyl-β-nitrostyrene and 1, 3-diphenyl-2-propenone. As
shown in Figures 6b, PP-MPs-2 catalyst could be used repetitively for more than 4
times without significant deactivation. Elemental analysis revealed that after being
used, the nitrogen content in the recycled PP-MP-2 catalyst remained almost the same
(0.32 wt%), indicating mesoporous polymers framework could effectively inhibit the
leaching of active sites. Furthermore, XPS data displayed the similar nitrogen binding
energy value (Figure 7), suggesting the unchanged chemical microenvironment. In
addition, N2 sorption isotherm (Figure 8a) and low-angle XRD pattern (Figure 8b) as
well as TEM image (inset) confirmed that the ordered mesoporous structure of the
urea-MP-2 was well preserved after being reused, resulting in its excellent stabilty.
Conclusion
In summary, we demonstrated the synthesis of piperazine-functionalized
mesoporous polymers through one-step solvent evaporation induced self-assmbly
approach. This heterogeneous organocatalyst showed high reactivity, selectivity and
stability in the water-medium Knoevengel reaction, water-medium [3+3]
cycloaddition reaction and intermolecular cross-conjugated addition reaction,
presumably as a result of the ordered mesoporous structure and favorable
hydrophobic micro-environment. This facile self-assembly route is of great potential

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in the controlled synthesis of high active mesoporous polymer-supported
organocatalysts for various chemical transformations.
Acknowledgements
This work was supported by the National Natural Science Foundation of China
(21107071 and 51273112), Shanghai Government (10dj1400100, 12CG52, 11YZ88,
and ssd10014).
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Table 1 Structural parameters and catalytic performances of PP-MPs catalysts with different
piperazidine content in water-medium Knoevenagel condensation reactiona
N loading
(wt%)
0.090
0.33
SBET
Dp
Vp
Conv. Select. Yield
Catalyst
(m2/g) (nm) (cm3/g) (%)
(%)
99
(%)
82
PP-MPs-1
PP-MPs-2
PP-MPs-3
155
132
100
3.2
3.1
2.9
0.23
0.21
0.18
83
93
87
99
92
1.1
99
86
aRection conditions: a catalyst containing 0.020 mmol piperazidine, 0.20 mmol ethyl cyanoacetate,
0.24 mmol benzaldehyde, 5.0 ml distilled water, t = 3.0 h, T = 40oC.
Table 2 Catalytic performances of PP-MPs-2 and piperazidine catalysts in water-medium
Knoevenagel condensation reactiona
O
COOEt
CN
H
NC COOEt
+
R
R
Catalyst
R
H
Conv. (%)
Select. (%) Yield (%)
PP-MPs-2
piperazidine
PP-MPs-2
93
97
99
99
99
99
99
99
92
96
77
81
98
99
78
OCH3
NO2
piperazidine
PP-MPs-2
82
99
piperazidine
100
aRection conditions are given in Table 1.

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Table 3 Catalytic performances of PP-MPs and piperazidine catalysts in the intermolecular cross-
conjugated addition reactiona
Catalyst
T (oC)
t (h)
Conv. (%)
Select. (%) Yield (%) d.r. (syn/anti)
PP-MPs-2
PP-MPs-2
PP-MPs-2
PP-MPs-2
PP-MPs-2
piperazidine
30
40
50
40
40
40
16
16
16
8
86
95
98
53
99
97
88
87
87
89
86
89
76
83
85
47
85
86
1:1.2
1:1.2
1:1.2
1:1.2
1:1.2
1:1.2
24
16
aReaction conditions:
a
catalyst containing 0.050 mmol piperazidine, 0.50 mmol
α-methyl-β-nitrostyrene, 1.0 mmol 1, 3-diphenyl-2-propenone, 0.50 mmol DMAP, 3.0 ml DMSO.
Table 4 Catalytic performances of PP-MPs-2 and piperazidine catalysts in water-medium [3+3]
cycloaddition reaction between 1,3-Cyclohexanedione and various α,β-unsaturated aldehydesa
O
O
O
+
R1
R2
R1
R2
O
O
Conv. Select. Yield
Catalyst
Aldehyde
Product
(%)
84.3
88.5
80.5
82.8
78.0
79.6
60.2
(%)
99
99
99
99
99
99
99
(%)
83.3
88.4
80.4
82.7
77.9
79.5
60.1
PP-MPs-2
piperazidine
PP-MPs-2
piperazidine
PP-MPs-2
piperazidine
PP-MPs-2
piperazidine
65.3
99
65.2
aReaction conditions:
a
catalyst containing 0.050 mmol piperazidine, 0.50 mmol
1,3-Cyclohexanedione, 0.50 mmol aldehyde, 5.0 ml distilled water, t = 12 h, T = 20oC.

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Scheme 1 llustration of the preparation of the PP-MPs catalyst.

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Scheme
2
Reaction equations between α-methyl-β-nitrostyrene and 1,
3-diphenyl-2-propenone.

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Figure 1 13C CP MAS NMR spectra of PP-MPs-2 and MPs samples.

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Figure 2 XPS spectra of piperazidine aldehyde and PP-MPs-2 samples.

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Figure 3 XRD patterns of PP-MPs samples with different piperazine contents and
TEM image (inset) of representative PP-MPs-2 sample.

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Figure 4 N2 sorption isotherms of PP-MPs samples with different piperazine contents.

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Figure 5 Toluene and water vapor absorption tests of PP-MPs-2 catalyst.

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Figure 6 Recycling test of PP-MPs-2 catalyst in water-medium Knoevenagel reaction
(a, reaction I), intermolecular cross-conjugated addition reaction (b, reaction II).
Reaction conditions are given in experimenal section.

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Figure 7 XPS spectrum of PP-MPs-2 catalyst after being reused for 6 times in
water-medium Knoevenagel reaction.

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Figure 8 N2 sorption isotherm (a), XRD patteren (b) and TEM image (inset) of
PP-MPs-2 catalyst after being reused for 6 times in water-medium Knoevenagel
reaction.