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and 298 to 2111 ppm range, corresponding to the T
2
–T
3
and
tetrahedral Ti species around the pore mouth rather than
Q
3
–Q species, confirming that organic fragments were bonded
4
amorphous thick pore wall. Location of such active tetrahedral
Ti species may be responsible for the enhanced catalytic activity
(Table 2).
covalently in the silicate network. The calcined material shows
only one broad peak centered at 2110 ppm, indicating that
organic fragments were removed completely from the silicate
framework. FT-IR spectra of the calcined material showed a
Interestingly, it is seen that the material obtained after
removal of ethylene groups upon calcination is the more active
catalyst. The cyclohexanone and cyclododecanone conversions
were reached at 90.0 mol% and 72.5 mol% respectively.
However, the oximes selectivity was almost comparable in both
cases. This is attributable to the higher surface area, selective
incorporation of isolated tetrahedral titanium atoms at the
internal surface of the silicate framework and uniform pore-size
distribution of the calcined samples. Although the ethane
fragment was completely decomposed at 823 K, the more
hydrophobic features remained and led to improved catalytic
activity. In addition, It is believed that the generation of more
hydrophobic centers via organic ethylene fragments, which
should be an advantage to oxidize bulky organic compounds
which has not been possible in the presence of TS-1 and Ti-
MCM-41 catalysts. The hydrophobic feature was further
2
1
very strong band at 960 cm attributable to the framework Ti–
O–Si vibrations similar to other titanium silicates and is a clear
indication of the incorporation of an isolated tetrahedral Ti
species in the silicate framework.12 The material also showed a
strong UV-Visible absorption band in the 240–260 nm region
indicating the presence of isolated tetrahedral Ti species in the
silicate framework. The characteristics of similar materials have
already been reported in detail in our earlier report.7
,11
Titanium containing ethane bridged hybrid mesoporous
silsesquioxane and its calcined analog were tested for the
ammoximation of cyclohexanone and cyclododecanone sub-
strates using aqueous hydrogen peroxide as oxidant. The
conversion and the selectivity of oximes formation are listed in
Table 2. The reactions were performed in a magnetically stirred
round-bottomed flask fitted with a condenser and placed in a
temperature controlled oil bath. Typically, 0.01 mol of the
substrate was dissolved in 10.0 ml tert-butanol (solvent), and to
this was added the required amount of liquid ammonia (2.5
times the substrates added at different reaction times) and
catalyst (20 wt.% with respect to the substrate) and then the
mixture was preheated to 353 K. The reaction was started when
confirmed by noticeable uptake of H
2
O vapor during water
adsorption measurements at 298K. Compared with pure Ti-
2
1
MCM-41 (V
m m
= 2.73 molecules nm ) a little uptake (V =
2
1
1.45 molecules nm ) was observed for this calcined sil-
sesquioxane at monolayer adsorption (P/P of 0.3), confirming
0
more hydrophobic nature of the material.
In summary, the first example of ammoximation of bulky
ketones over highly hydrophobic titanium incorporated ethane
bridged hybrid mesoporous silsesquioxane with high selectivity
of oximes is presented. The most remarkable features of this
titanium containing organic–inorganic hybrid mesoporous sil-
ica were its high activity and retention of the mesostructure as
well as hydrophobic nature after removal of the organic
ethylene bridge by calcination at high temperature. Further, the
extent of hydrophobicity could be controlled by inserting an
organic molecule of a different nature as an integral part of the
chemical connectivity in the hybrid mesoporous silsesquioxane.
These ammoximation reactions are very important industrially
for the production of caprolactam nylon 6 and nylon 66.
3
0 wt.% H
2
O
2
2
O
was added very slowly for a period of 8 h. The
+NH mole ratio was kept at 1+1.25+2.5 for all
substrate+H
2
3
reactions. 0.5 ml n-heptane was introduced in each of the
reaction mixtures as internal standard. Samples of the reaction
aliquots were taken at regular intervals and after cooling and
filtration the reaction was monitored by GC.
Compared with conventional Ti-MCM-415 and TS-1,14
these novel materials exhibited outstanding catalytic perform-
ance along with very high yield towards oxime products with
,13
1
00% selectivity. The highest loading of Ti reported in Ti-
MCM-41 materials have a Si/Ti mole ratio of 48 in the product.
This sample shows no catalytic activity in the ammoximation
reaction. The ethane-bridged hybrid mesoporous materials
reported in this study contain a large amount of Ti in the silica
framework (Si/Ti mole ratio of ~ 25). This reveals that the
reduction of the charge density of the inorganic phase due to the
introduction of the hydrophobic ethane groups of BTME can
Notes and references
1
B. Notari, Advances in Catalysis, Academic Press, San Diego, CA,
996, 41, 253.
P. T. Tanev, M. Chibwe. and T. J. Pinnavaia, Nature, 1994, 368, 321.
accommodate active tetrahedral Ti species (possibly Ti(O–
1
,12
Si)
3
(OH)7 at the interface of inorganic and surfactant micelle
2
phases. This probably helps to locate the large amount of
3 K. A. Koyano, T. Tatsumi, Y. Tanaka and S. Nakata, J. Phys. Chem. B,
997, 101, 9436.
1
4
A. Corma, J. L. Jordá, M. T. Navarro and F. Rey, Chem. Commun.,
1998, 1899.
Table 2 Ammoximation of ketones over Ti-HMMa
5
A. Bhaumik and T. Tatsumi, J. Catal, 2000, 182, 47–53.
Oximeb
selectivity
6 A. Thangaraj, S. Sivasanker and P. Ratnasamy, J. Catal., 1991, 131,
394.
Material
Substrate
Conversion (mol%) (mol%)
7 M. P. Kapoor, A. Bhaumik, S. Inagaki, K. Kuraoka and T. Yazawa, J.
Mater. Chem., 2002, 12, 3078.
Ti-HMM-Ext Cyclohexanone
Cyclododecanone
63.2
42.0
90.0
72.5
84.2
0.8
No reaction
No reaction
100
100
95.2
100
94.6
100
8 S. Inagaki, S. Guan, Y. Fukushima, T. Ohsuna and O. Terasaki, J. Am.
Chem. Soc., 1999, 121, 9611.
9 T. Asefa, M. J. MacLachlan, N. Coombs and G. A. Ozin, Nature, 1999,
402, 867.
10 S. Inagaki, S. Guan, T. Ohsuna and O. Terasaki, Nature, 2002, 416,
304.
11 M. P. Kapoor, A. K. Sinha, S. Seelan, S. Inagaki, S. Tsubota, H. Yoshida
and M. Haruta, Chem. Commun., 2002, 2902.
12 F. Geobaldo, S. Bordiga, A. Zecchina, E. Giamello, G. Leofanti and G.
Petrini, Catal. Lett., 1992, 16, 109.
Ti-HMM-Calc Cyclohexanone
Cyclododecanone
d
Cyclohexanone
TS-1e
Ti-MCM41
Cyclododecanone
Cyclohexanone
f
Cyclododecanone
a
b
HMM = hybrid mesoporous silsesquioxane material. Oximes refers to
c
cyclohexanoneoxime and cyclododecanoneoxime. Calcined at 823 K for 4
d
e
f
13 T. Blasco, A. Corma, M. T. Navarro and J. P. Pariente, J. Catal., 1995,
h. Isopropylalcohol as solvent instead of tert-butanol. Si/Ti = 27. Si/Ti
48.
1
56, 65.
=
1
4 M. Taramasso, G. Perego and B. Notari, US Pat. 1983, 4 410 501.
CHEM. COMMUN., 2003, 470–471
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