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New Journal of Chemistry
Page 3 of 4
DOI: 10.1039/C6NJ03897B
Journal Name
COMMUNICATION
silica source for practical uses. In this context, we applied the azeotropic solvents, or dialkyl carbonates. (iii) The molecular
method developed here to the synthesis of TEOS from a sieves used as the dehydrating agent can be used repeatedly
natural silica substrate (Table 4). Rice hull ash (RHA), which is a via ordinary re-activation methods without observing
a
byproduct of agricultural rice production, is a sustainable silica decrease in the reaction efficiency. This work demonstrates
source.16 RHAs were prepared by calcining rice hulls at various the promising prospect of using silica as a feedstock for
temperatures (500–1000 °C).17 Hereafter, the prepared RHAs producing silicon-containing materials.
are labeled RHA-X, where X is the temperature of calcination.
The specific surface areas of the prepared RHAs were
Acknowledgements
determined from the nitrogen adsorption–desorption
isotherms (using BET method), as shown in Table 4. The
surface areas of the RHAs decreased with increasing
calcination temperature. The reaction of the prepared RHAs
and ethanol in the presence of KOH (10 mol% relative to SiO2)
and molecular sieves was performed using the procedure
described above. The reaction efficiency depended strongly on
the surface area of the RHA. The RHA samples with higher
surface areas gave better yields. A 60% yield, based on the
SiO2 content, was obtained from the RHA-500 sample. By
contrast, RHA-900 or RHA-1000, which featured low surface
areas, displayed a low reactivity, giving only 11 or 6% TEOS
yields. In addition, quartz sand and Celite (prepared from
diatomaceous earth), the surface areas of which were low,
also displayed a low reactivity.
This research was financially supported by Development of
Innovative Catalytic Processes for Organosilicon Functional
Materials Project of NEDO, Japan. We thank Dr. Tadahiro Nitta
for assistance with the experiments.
Notes and references
1
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Organometallics, 2001, 20, 4978-4992.
Table 4 Synthesis of TEOS from natural silica substratesa
Silica
as,BET (m2g-1)
TEOS (%)
Disiloxane (%)
6
R. M. Laine, J. C. Furgal, P. Doan, D. Pan, V. Popova and X.
Zhang, Angew. Chem. Int. Ed., 2016, 55, 1065-1069.
US Pat., 2881198, 1959.
(a) G. B. Goodwin and M. E. Kenney, Inorg. Chem., 1990, 29
1216-1220; (b) US Pat., 4717773, 1988.
RHA-500
RHA-600
RHA-700
RHA-800
RHA-900
RHA-1000
Quartz
224
202
135
28
60
57
44
41
11
6
11
8
7
8
10
3
,
3
0
9
(a) E. Suzuki, M. Akiyama and Y. Ono, Chem. Commun., 1992,
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Mater., 1993, 5, 442-447; (c) L. N. Lewis, F. J. Schattenmann,
0.6
0.8
1
0
3
0
T. M. Jordan, J. C. Carnahan, W. P. Flanagan, R. J. Wroczynski,
J. P. Lemmon, J. M. Anostario and M. A. Othon, Inorg. Chem.,
2002, 41, 2608-2615.
Celite 209
5
0
a The reaction conditions were same as shown in Table 1.
10 N. Fukaya, S. J. Choi, T. Horikoshi, H. Kumai, M. Hasegawa, H.
Yasuda, K. Sato and J.-C. Choi, Chem. Lett., 2016, 45, 828-
830.
11 Laine et al. [ref. 6] mentioned that this reaction can be
considered a "grand challenge" for silicon chemists.
12 R. H. Perry, D. W. Green, Perry's Chemical Engineers'
handbook, McGraw-Hill, New York, 6th edn, 1984.
Finally, we investigated the possibility of scaling-up the
developed method. In a 200 mL inner volume autoclave, 15
mmol silica (10 times scale-up), 10 mol% KOH, and 100 mL
EtOH were added. The reaction was performed at 240 °C using
25 g of molecular sieves 3A. After 6 h, the yield of TEOS was
75%, comparable with above small scale experiments. The
success of TEOS synthesis in scale-up process shows the
potential of our method beyond laboratory research. Such
efforts are currently underway in our group, and we will
discuss the details of these studies elsewhere.
13 (a) D. R. Burfield and R. H. Smithers, J. Org. Chem., 1983, 48
,
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(b) J. C. Moıs̈ e, J. P. Bellat and A. Méthivier, Microporous
Mesoporous Mater., 2001, 43, 91-101.
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and T. Ohmori, Chem. Eng. J., 2012, 181–182, 443-448.
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Wang, Res. Chem. Intermed., 2016, 42, 893-913.
In summary, we developed a simple and practical method for
synthesizing TROS via direct transformation of silica. With our
method, a variety of natural and sustainable silica sources,
such as RHA, were employed for the synthesis. Compared to
conventional methods of preparing TROS, our method is
advantageous and attractive in the following aspects: (i)
Preparation of metallic silicon via the carbothermal reduction
is avoided by directly transforming the silica; (ii) TROS is
synthesized from silica, alcohol and a base catalyst without
using any additive, such as diols for spirocyclic compounds, or
17 The SiO2 content in RHAs was 91-93%, determined by
energy-dispersive X-ray fluorescence analysis.
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