Chemistry Letters 2000
999
should be cyano group to realize enough reactivity in this system.
Malononitrile reacted with less reactive acetophenone while ethyl
cyanoacetate did not (Entries 5–7). However, both malononitrile
and ethyl cyanoacetate reacted with aliphatic ketone such as
cyclohexanone (Entries 8–10).
In summary, unexpectedly high catalytic activity of quater-
nary ammonium-ordered porous silicate composite materials for
Knoevenagel condensation has been found and investigated.
Although these materials are not to be utilized for “shape-selec-
tive” purposes, they still should be useful for general heteroge-
neous catalysis, particularly for the synthesis of fine-chemicals
under mild conditions in non-polar media.
(TBMP2+)–[Si]–BEA, whereas only little Si(3-OSi, 1-OH) reso-
nance can be seen in the spectrum of (TEA+F–)–[Si]–BEA, which
is consistent with the reported results.13,16,19,20 Therefore, it is
suggested that the actual catalytic sites are basic (SiO)3SiO– moi-
eties in the composite materials. Metal oxides, hydroxide ions
and organic amines are absent in this reaction system. It seems
that the SiO– moiety is an effective base in a non-polar medium
with the assistance of quaternary ammonium cation. This is
essentially different situation from the case that hydroxide or
alkoxide could be generated from metal cation in aqueous or
alcoholic media and function as a base. The basic function is
located on the side of parent silicate framework unlike the case in
which mobile hydroxide or alkoxide could take part in the reac-
tion mechanism as a base.
References and Notes
1
S. I. Zones and M. E. Davis, Curr. Opin. Solid State Mater. Sci., 1, 107
(1996); D. Zhao, P. Yang, Q. Huo, B .F. Chmelka, and G. D. Stucky,
Curr. Opin. Solid State Mater. Sci., 3, 111 (1998).
2
3
H. Hattori, Stud. Surf. Sci. Catal., 78, 35 (1993).
G. Jones, “Organic Reactions,” ed. by A. C. Cope, John Wiley & Sons,
New York (1967), Vol. 15, pp. 204–599.
Nitrogen adsorption measurement of active (HDTMA+)–
[Si]–MCM-41 did not give Type-IV isotherm and BET surface
area was 14 m2 g–1, whereas the typical Type IV isotherm and a
large BET surface area (1013 m2 g–1) were obtained from catalyti-
cally inactive [Si]–MCM-41. This indicates that the large surface
area and complete porosity are not essential in this reaction sys-
tem. The reaction should be taking place at around pore-mouth of
the silicates, not deeply inside the pore. The efficient catalysis by
MCM-41-based material may be due to the more exposed catalyt-
ic sites at pore-mouth compared to zeolite-based materials.
It should be noted that (HDTMA+)–[Si]–MCM-41 was
reusable. Almost no loss of activity was observed even at the
third use. It was confirmed by means of XRD, elemental analysis,
and TGA that the framework structure and organic content in the
recovered catalysts were unchanged. In contrast to the recovered
catalyst, the filtered reaction mixture demonstrated no activity
after adding fresh substrates. Therefore, the probability of homo-
geneous catalysis by any leached species (including amine) was
excluded.
4
E. Angeletti, C. Canepa, G. Martinetti, and P. Venturello, J. Chem. Soc.,
Perkin Trans. 1, 1989, 105.
5
6
D. J. Macquarrie, Green Chemistry, 1999, 195.
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(1992); W. Richardhein and J. Melvin, J. Org. Chem., 26, 4874 (1961).
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10 A. Corma and R. M. Martin-Aranda, J. Catal., 130, 130 (1991).
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Figueras, Chem. Commun., 1998, 1033.
12 An exceptionally mild condition is reported in Ref. 11, which is as mild
as that in this work.
13 C.-Y. Chen, H.-X. Li, and M. E. Davis, Micropor. Mater., 2, 17 (1993).
14 M. K. Rubin, U. S. Patent, 5164169 (1992); Chem. Abstr., 118, 41807s
(1993).
15 K. Tsuji and M. E. Davis, Micropor. Mesopor. Mater., 11, 53 (1997).
16 M. A. Camblor, A. C. Corma, and S. Valencia, Chem. Commun., 1996,
2365.
17 The procedure (2)-(b) of Ref. 13 was exactly followed to synthesize the
(HDTMA+)-[Si]-MCM-41.
18 On the basis of elemental analysis, 0.33 mmol of HDTMA+ cation is
occluded in 200 mg of (HDTMA+)–[Si]–MCM-41 catalyst.
19 C. W. Jones, K. Tsuji, and M. E. Davis, Nature, 393, 52 (1998).
20 E. J. R. Sudhölter, R. Huis, G. R. Hays, and N. C. M. Alma, J. Colloid
Sci., 103, 554 (1985).
Lower reactivity was observed for bulkier esters of cyano-
acetic acid, and higher temperature was needed to obtain high
yield (Table 2, Entries 2, 3). Diethyl malonate hardly reacted
with benzaldehyde (Entry 4), suggesting that either R3 or R4