W. R. Thiel et al.
changed from nitromethane to acetone. This reaction path-
way also includes two separate steps: the acid-catalyzed de-
protection of benzaldehyde dimethyl acetal to yield benzal-
dehyde followed by the base-catalyzed aldol condensation
reaction (Scheme 4, Table 6). Similar to the reaction shown
property cannot be controlled completely due to limitations
of the synthesis, a pronounced enhancement of the catalytic
activity can be realized relative to the individual counter-
parts. The successful cohabitation of organic amines and or-
ganic acids on high-surface-area solid supports ensures a
high catalytic activity and a simple catalyst recovery as
À
shown for a series of C C bond-formation reactions. We en-
visage that a successful cohabitation of antagonist groups
like acids and bases within a material can open the way to
new routes for the rational design of morphology-controlled
novel nanomaterials for multifunctional applications.
Experimental Section
General: X-ray powder diffraction (XRD) patterns were obtained on a
Siemens D5005 diffractometer with CuKa radiation. Nitrogen adsorption–
desorption isotherms were measured at 77 K on a Quantachrome Auto-
sorb 1 sorption analyzer after evacuation of the samples at 1208C over-
night. The specific surface areas were calculated by means of the Bruna-
uer–Emmett–Teller (BET) equation in the low relative pressure interval
(<0.3) and the pore size distribution curves were analyzed with the ad-
sorption branch by the BJH method. 13C CP/MAS and 29Si CP/MAS
NMR spectra were recorded on a Bruker DSX Avance spectrometer at
resonance frequencies of 100.6 and 79.5 MHz, respectively. The infrared
spectra were recorded by using a Jasco FT/IR-6100 spectrometer. The
morphology of the mesoporous particles were determined by a field
emission scanning electron microscope with 10 kV acceleration voltage
and 0.005 nA beam current. The reaction product was analyzed by GC–
MS (Varian).
Scheme 4. One-pot deacetalization–aldol cascade reaction.
Table 6. One-pot deacetalization–aldol cascade reaction.[a]
Entry
Catalyst
Conv. of 1 [%]
Yield of 5 [%]
1
2
3
4
5
MSN–NNH2–SO3H
MSN–NH2–SO3H
MSN–SO3H
MSN–NNH2
MSN
58
51
63
40
28
trace
24
8
trace
0
[a] Reaction conditions: benzaldehyde dimethyl acetal (1 mmol),
(CH3)2CO (5 mL), 508C, 24 h.
Tetraethoxysilane (TEOS, 99%), cetyltrimethylammonium bromide
(C16TAB, 95%), and organoalkoxysilanes (APTS, AAPTS, DAPS, CSES)
were purchased from Aldrich chemicals. The aldehydes, benzaldehyde di-
methyl acetal, and nitromethane were purchased from Acros. All chemi-
cals were used as received without further purification.
above, the bifunctional MSN–NNH2–SO3H sample showed
better catalytic conversions to yield the aldol product (dehy-
drated product, 5), whereas the monofunctionalized samples
were unable to complete the reaction process, which again
confirms the acid–base cooperativity that exists in the bi-
functional MSN samples.[24]
Synthesis of bifunctionalized MSN silicas: In a typical synthesis, C16TAB
(2.0 g, 5.4 mmol) was dissolved in deionized water (480 g) containing 2m
NaOH (7 mL) under stirring at room temperature. The temperature of
the solution was then raised to 808C and the solution became clear after
30 min. To this clear solution, TEOS (9.2 g, 44.8 mmol) and the desired
organoalkoxysilane (2 mmol) were added sequentially. For the synthesis
of MSN–NNH2–SO3H, CSES (2 mmol) dissolved in dichloromethane (50/
50 w/w) was added followed by the addition of AAPTS (2 mmol) under
vigorous stirring. White precipitates were obtained after approximately
3 min. The mixtures were then stirred for another 4 h. The products were
then separated by hot filtration, washed with water, and extracted with a
mixture of HCl/EtOH (0.3 g/100 mL) at 608C for 6 h to remove the sur-
The recyclability of the bifunctional catalyst MSN–NNH2–
SO3H was examined by isolating it from the reaction mix-
ture (centrifugation, washing with ethanol and dichlorome-
thane, and drying). Due to the tight anchoring and the spa-
tial separation of the organic functional groups, the catalyst
showed almost no loss in activity in the third run (Table 2,
À
À
factant and to convert SO3Na to SO3H species. The resulting white
solid products were filtered, washed with water and then ethanol, and
dried under vacuum.
1
entry 6). Additionally, the H NMR spectroscopic analysis of
the reaction filtrate gave no hint of leaching of the immobi-
lized organic groups and the elemental analysis of the recov-
ered catalyst confirmed the retention of the organic content
on the mesoporous surface.
Nitroaldol reaction: A mixture of the aldehyde (1 mmol), nitromethane
(10 mL), and the selected catalysts (molar ratio of aldehyde/amine=40)
were kept at 908C under magnetic stirring. The reaction mixture was
then stirred under an atmosphere of nitrogen and aliquots of the sample
mixture were removed with a filter syringe and evaluated by GC–MS to
determine the yield of the nitrostyrene product.
One-pot deacetalization–nitroaldol reaction: A mixture of benzaldehyde
dimethyl acetal (1 mmol), nitromethane (5 mL), and the mesoporous cat-
alyst (0.025 mmol of amine) was kept at 908C under magnetic stirring.
The reaction mixture was then stirred under a nitrogen atmosphere for
5 h and the sample mixture was removed with a filter syringe and evalu-
ated by GC–MS to determine the yield of 2-nitrovinylbenzene.
Conclusion
As a central result, we were able to prove that organic func-
tional groups that cannot coexist in solution can effectively
be utilized for cooperative catalytic reactions by immobiliz-
ing such groups on high-surface-area supports and by con-
trolling their spatial arrangements. Even though the latter
One-pot deacetalization–aldol reaction: A mixture of benzaldehyde di-
methyl acetal (1 mmol), acetone (5 mL), and the mesoporous catalyst
(0.05 mmol of amine) were kept at 508C under magnetic stirring. The re-
7060
ꢀ 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2009, 15, 7052 – 7062