L. Wang et al. / Catalysis Communications 15 (2011) 78–81
81
100
80
60
40
20
0
0
1
2
3
4
Number of regeneration
Fig. 5. Changes of PhO conversion with the reaction–regeneration cycles on CNx catalysts.
Reaction conditions: CNx/PhCHO/ethyl cyanoacetate/EtOH=20 mg/2 mmol/2 mmol/5 g;
temperature 353 K; time 2 h. Regeneration: used catalyst was washed with acetone and
dried at 80 °C for 2 h.
Fig. 4. Effect of solvent on the Knoevenagel condensation reaction on CNx catalysts. Re-
action conditions: 2 mmol PhCHO, 2 mmol ethyl cyanoacetate, 5 g solvent, 20 mg cat-
alyst, 353 K, 2 h.
Acknowledgments
those of other solid basic catalysts such as microporous ETS-10 and
NaY zeolites (Entries 1–2).This is probably due to a large amount of
basic sites incorporated in the CNx structure. ETS-10 and NaY both
consisting of 12-membered ring micropores would impose a shape
selective limitation to the adsorption and desorption of the bulky
molecules, which then makes the reaction slower.
This work is supported by the Excellent Youth Teacher Program of
Shanghai (egd08017) and “Shu Guang” project supported by Shang-
hai Municipal Education Commission (09SG54) and Shanghai Educa-
tion Development Foundation.
The efficiency and versatility of the CNx catalyst for the Knoevenagel
condensation on different substituted benzaldehydes using ethylcya-
noacetate were investigated. Various substates got readily condensed
with different conversion efficiencies, but with 100% selectivity (Entries
4–7). 4-Hydroxybenzaldehyde with ethylcyanoacetate conversion was
51.6%, 2-furfural and n-Hexaldehyde with ethylcyanoacetate yielded
50.9% and 81.4% conversion respectively.
Fig. 5 shows catalytic yields of reusable CNx catalyst in the substrate
of benzaldehyde. The experiments were initiated with an enlarged re-
action scale using 1 g of CNx. After the used catalyst was washed with
acetone and dried at 393 K in air, it was subjected to repeated conden-
sation reaction at a constant ratio of catalyst-substrates-solvent. After
four recycles of reaction–regeneration, the conversion of benzaldehyde
is still higher than 90%, indicating its superior stability.
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CNx catalysts with variable basicity were synthesized successfully
and showed higher order of activity for the conversion of C\C bonds
by Knoevenagel condensations with high degree of selectivity. These
CNx catalysts for application of Knoevenagel reactions have the follow-
ing advantages: (a) high catalytic activity under very mild liquid phase
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Table 2
Selective Knoevenagel reaction catalyzed by different solid base catalystsa.
Entry
Catalyst
R
Conv. (mol%)
Sel. (mol%)
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1
2
3
4
5
6
7
ETS-10
NaY
C6H5
C6H5
C6H5
C6H5
4-OHC6H4
C5H4O2
C5H11
60.1
23.4
0
91.7
51.6
50.9
81.4
100
100
0
100
100
100
100
CNT
CNx
CNx
CNx
CNx
a
Reaction conditions: 2 mmol aldehyde, 2 mmol ethyl cyanoacetate, 5 g solvent,
20 mg catalyst, 353 K, 2 h.