Table 6 Knoevenagel condensation of benzaldehyde with ethyl cyanoacetate or ethyl acetoacetate (R \ CN or COMe, respectively) with CsLa/
MCM-41, Na-MCM-41 and Cs-MCM-41 in various reÑuxing protic solvents
Si/Al
ratio
conversion
(% m/m)c
catalysta
Rb
CN
CN
CN
CN
CN
CN
CN
solvent
EtOH
A
/mmol h~1 g~1 d
wt
CsLa/MCM-41A
CsLa/MCM-41A
CsLa/MCM-41A
CsLa/MCM-41Ae
CsLa/MCM-41A
Na-MCM-41f
O
30
O
O
30
13
13
30
86
95
58
46
53
40
55
21
89.2
97.8
51.7
54.3
55.5
30.1
43.3
20.7
EtOH
H OÈTHF
2
H OÈTHF
2
H OÈTHF
2
H OÈTHF
2
Cs-MCM-41f
CsLa/MCM-41A
H OÈTHF
2
COMe
H OÈdioxane
2
a 5% m/m catalyst based on total amount of substrates (10 mmol of each). b Reactant R \ CN is ethyl cyanoacetate and R \ COMe is ethyl
acetoacetate. c Enolate conversion after 1 h. d SpeciÐc activity after 1 h. e 4% m/m re-used CsLa/MCM-41A catalyst after Ðltration and drying.
f Ion-exchanged MCM-41.
having a mild basicity. Their use as basic catalysts in aqueous
media is displayed in the Knoevenagel condensation. The
combination of the CsLaO layer and the mesoporous frame-
x
work alters the product selectivity in the two-step Michael
addition of ethyl acrylate and ethyl cyanoacetate. The cata-
lysts can be re-used after a solvent Ñush and a high tem-
perature cycle without loss of activity.
Scheme 2 Knoevenagel condensation of benzaldehyde with ethyl
cyanoacetate (R \ CN) or ethyl acetoacetate (R \ COMe)
The Knoevenagel condensation of benzaldehyde with ethyl
We thank Dr. A Sinnema for measuring and interpreting the
NMR data, Mr. J.C. Groen for physisorption measurements,
Dr. Y. Pluyto for DTAÈTG measurements and the NIOK
Institute, the Dutch School of Catalysis, for Ðnancial support.
cyanoacetate (pK \ 9) served as a study of the capability of
a
CsLa/MCM-41 to be used in aqueous media (Scheme 2). All
the CsLa/MCM-41A catalysts gave large conversions (Table
6) together with [99% selectivity to the a,b-unsaturated
esters under mild conditions. Interestingly, CsLa/MCM-41A
References
showed a better performance in ethanol than in H OÈTHF.
2
Unexpected solvent e†ects were also found in the Knoevena-
1
2
3
4
5
6
7
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enough to catalyse this reaction also.15 Table 6 illustrates that
8
9
the speciÐc activities A of Na-MCM-41 and Cs-MCM-41 in
wt
H OÈTHF are a little lower than that of CsLa/MCM-41. A
2
I. Rodriguez, H. Cambon, D. Brunel, M. Lasperas and P.
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al.metal
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a
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2
12 C. T. Kresge, M. E. Leonowicz, W. J. Roth, J. C. Vartuli and J. S.
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strated by a similar A after Ðltration (entry 4 in Table 6)
13 J. S. Beck, J. C. Vartuli, W. J. Roth, M. E. Leonowicz, C. T.
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wt
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2
these MCM-41 supported CsLa mixed oxides are easy to
handle, in sharp contrast with La/MCM-41. The lanthana-
supported MCM-41 materials appeared to be inactive in all
the mentioned liquid-phase reactions. This pertains to a much
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Conclusions
42, L1.
Heterogeneous mesoporous stable basic catalysts are prepared
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x
24 Y. S. Tan, L. Q. Dou, D. A. Lu and D. Wu, J. Catal., 1991, 129,
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447.
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x
J. Chem. Soc., Faraday T rans., 1997, V ol. 93
1219