pressure regulator (JASCO, SCF-Bpg). The product sample was mixed
with a known amount of mesitylene (internal standard substance) and
analysed by GC (Shimadzu, GC-17A) equipped with a flame ionisa-
tion detector and a DB-1 column (J&W Scientific, catalog no.
polarised silica surface also seems to be important for the
smooth desorption of the water by-product. Actually, the
constant conversions were observed for 6 h time-on-stream
with the silica catalysts (entries 3, 5, 8 and 11), demonstrating
that water desorption occurred smoothly over the silica
catalysts, leading to the constant regeneration of the active
silica surface. Over ALO-6 and SAL-2, on the other hand, the
water should be strongly adsorbed, acting as an inhibitor or
even a poison.
122-1032, 30
m
ꢂ
0.25 mm). The column temperature was
programmed as follows: 50 1C (5 min) - 15 1C minꢁ1 - 250 1C
(12 min), where methanol, DMEDA and DMI appeared at a retention
time of ca. 1.9, 4.7 and 11.1 min, respectively. Since the selectivity
for DMI was always 100%, the conversion was calculated by the
following equation:
Conv. (%) = (mmol DMI)/[(mmol DMEDA)
+ (mmol DMI)] ꢂ 100
In summary, we have found that silica catalysts, particularly
those bearing regularly ordered mesopores, as well as high
surface areas, are highly effective for the continuous catalytic
synthesis of DMI from DMEDA and CO2 under supercritical
conditions. This could be one of the most important examples
of catalysis making the best use of the unique structural
properties of MCM-41- and HMS-type mesoporous silicas.
A part of the experimental work was performed at the group
of Prof. Dr Masaki Okamoto (Tokyo Institute of Technology)
with the help of his students. This work was partially
supported by a grant-in-aid from the Japan Society for
the Promotion of Science (project code 070300000755), the
Ministry of Education, Culture, Sports, Science and Techno-
logy of Japan (grant no. 18065017; ‘‘Chemistry of Concerto
Catalysis’’), and the GCOE program.
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Notes and references
y Catalysts and reagents: Q-30 (amorphous silica; CARiACT Q-30; lot
no. C81206) was supplied by Fuji Silysia. A-P (amorphous silica;
catalog no. 37049-10; lot no. 305F1374) was purchased from Kanto
Chemical. MCM-41-type mesoporous silica with a hexagonal frame-
work (catalog no. 643645; batch no. 01215KH) and HMS-type
mesoporous silica with a wormhole framework (catalog no. 541036;
batch no. 18704TI) were purchased from Aldrich. SAL-2 (silica–
alumina; JRC-SAL-2; 13.8 wt% Al2O3) and ALO-6 (g-Al2O3; JRC-
ALO-6) were supplied by the Catalysis Society of Japan. The A-P,
MCM-41, HMS and SAL-2, received in fine powder form, were
converted to larger particles (size 500–850 mm) by pelletization at
20 MPa and subsequent sieving to avoid catalyst efflux during the
continuous flow operations. The WO3/Q-30 was prepared by adding
Q-30 to the WO3-dispersed de-ionized water, followed by washing
with de-ionized water, drying at 110 1C and calcination at 500 1C.
Liquid CO2 (99.9%; water content o20 ppm) was purchased from
Taiyo Nippon Sanso and used as received. DMEDA (catalog no.
D157805; 99%) and dehydrated methanol (catalog no. 25506,
Z99.8%) were purchased from Aldrich and Kanto Chemical,
respectively, and used as received.
5 M. G. Hitzler, F. R. Smail, S. K. Ross and M. Poliakoff, Org.
Process Res. Dev., 1998, 2, 137.
6 The use of methanol would not be a hindrance to commercializa-
tion, because it can be recycled after separation from the
product mixture by distillation. Solvents other than methanol
(e.g., DMI) could also be used successfully, although we only used
methanol.
z SAFETY NOTE: Operators handling high pressure equipment for
reactions in scCO2 should take proper precautions to minimise the risk of
personal injury.
The reaction procedures were as follows: 1.0 g of catalyst was activated
at 500 1C for 2 h in a stream of dry air (Taiyo Nippon Sanso; dew
point ꢁ40 1C) and placed in a tubular reactor (inner diameter
10 mm; length 135 mm) under an Ar atmosphere. Then, the spaces
in the reactor, both above and below the catalyst bed, were compen-
sated with stainless steel balls (diameter 1.5 mm). The reactor was
connected to the continuous flow reactor system and heated to the
reaction temperature in an oven (Shimadzu, GC-14B). Liquid CO2,
DMEDA and methanol were fed with an HPLC pump (JASCO,
PU-2080). The product downstream was expanded with a back
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ꢀc
This journal is The Royal Society of Chemistry 2009
Chem. Commun., 2009, 349–351 | 351