1216
Y.-L. Zhang et al. / Catalysis Communications 12 (2011) 1212–1217
Table 2
The charts of various substrates and corresponding Knoevenagel condensation products.
Run
1
Substrates
Products
Conversion (%)
97.0
benzaldehyde
2-(Benzylmethylene)malononitrile
CN
O
CN
CN
CN
2
3
Cyclohexanone
Furfural
2-Cyclohexylidenemalononitrile
2-(Furylmethylene)malononitrile
92.6
95.1
CN
O
O
CHO
CN
CN
CN
4
4-Nitrobenzaldehyde
2[(4-Nitrophenyl)methylene]malononitrile
88.3
CHO
O2N
O2N
CN
CHO
OH
5
6
7
Salicylaldehyde
Pentanal
2-[(2-Hydroxyphenyl)methylene]malononitrile
2-(Pentylmethylene)malononitrile
81.9
94.5
84.3
CN
OH
CN
CHO
CN
CN
n-Hexaldehyde
2-(Hexylmethylene)malononitrile
CHO
CN
is inactive to the reaction due to the absence of basic sites. Conventional
solid base catalysts of magnesium oxide and Mg–Al hydrotalcite show
the yields of 35.5% and 22.5% after activation. The relatively low
conversion is attributed to their limitation of exposed active sites on the
surface. However, PDVB-VP-n samples exhibit much higher yields (38–
97%). Particularly, PDVB-VP-20 and PDVB-VP-30 give the yields of 97.0
and 97.1%. Kinetic studies show that when the reaction time reaches
120 min, all the samples give their highest yields (Fig. S4). The
difference in catalytic activities is reasonably assigned to homoge-
neous-like feature of PDVB-VP-n in the solvent of cyclohexane where
each of pyridine groups is completely exposed to the reactants.
Additionally, PVP in the solvent of cyclohexane also gives low
conversion (33.2%) due to its poor dissolution. When PVP dissolved in
ethanol as a homogeneous catalyst, the yield of 97% is obtained, which is
similar to the value of PDVB-VP-20 (96%). These results confirm that
PDVB-VP-20 is a homogeneous-like base catalyst. Fig. 5c shows catalytic
yields of reusable PDVB-VP-20 catalyst in the substrate of benzaldehyde.
After recycling for 5 times, the conversion of benzaldehyde is still higher
than 96%, indicating its superior stability. N2 isotherm of PDVB-VP-20
recycled for 5 times shows similar textural parameters to fresh PDVB-
VP-20, indicating its excellent stability of porous structure during
reactions (Table 1, Fig. S5). Furthermore, various substrates aromatic,
aliphatic and heteroatamatic aldehydes have been used to react with
malononitrile over PDVB-VP-20 catalyst (Fig. 5d and Table 2). All
substrates exhibit high conversions to the corresponding products. For
example, cyclohexanone and furfural give the yields of 92.6 and 95.1%,
respectively.
Acknowledgments
This work was supported by theState Basic Research Project of
China (2009CB623507), Sinopec, and the National Natural Science
Foundation of China (20773049). We also acknowledge the financial
support from NSFC under grant nos. 61008014.
Appendix A. Supplementary data
Supplementary data to this article can be found online at
doi:10.1016/j.catcom.2011.04.020.
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4. Conclusions
In summary, we have demonstrated a preparation of swelling porous
polymers with pyridine groups. These novel polymers are designed as
homogeneous-like base catalysts, which exhibit outstanding catalytic
activities and long catalyst life in the Knoevenagel condensation of
malononitrile and various aldehydes. The development of homogeneous-
like solid catalysts might bring out a new concept for designing efficient
heterogeneous catalysts.