FULL PAPERS
Rosaria Ciriminna et al.
purification. Methanol and NaF were purchased from Fluka.
Ultra pure water (Millipore Type 1 quality) was used in all the
preparations.
reaction vessel temperature at 758C, and assuming complete
dissolution of the hydrophobic decane, we varied the CO2
pressure inside the reactor from 140 to 240 bar while analysing
the content at GC in order to check the substrate and product
dissolution which was complete at 220 bar.
Hence, after purging with oxygen (1 bar partial pressure at
ambient temperature), the reaction vessel was sealed and
Instruments
The reaction system employed for oxidations in scCO (a
modified Carlo Erba SFC 3000) was described elsewhere.
placed into an oven thermostatted at 758C. Liquid CO was
2
2
[23]
then pumped into the autoclave using a cryogenic pump to
bring the reactor pressure at 220 bar while the reaction mixture
was kept under stirring at 400 rpm (by means of an alternating
magnetic field stirrer) at the set temperature for the desired
reaction time. Samples withdrawn through the stainless steel
restrictor (kept at 908C) were trapped in dichloromethane
prior to GC analysis; and when the reaction was complete, the
heating was stopped and the system allowed to cool to ambient
temperature. The reactor was thus opened and the CO2
gradually vented off in CH Cl . When the total pressure inside
The stainless steel 10-mL high pressure vessel is connected to a
restrictor through a 6-way HPLC valve for sample withdraw-
ing.
The carbonyl product content was determined by GC
analysis on a Shimadzu chromatograph equipped with a
Supelcowax 10 capillary column (30 m, 0.25 mm ID) using
the internal standard method (with previously calculated
response factors). The N -BET textural values were obtained
2
with a Carlo Erba Instruments Sorptomatic 1900 powder
analyzer, and the Ru content in catalysts and reaction samples
assessed by ICP-MS on an HP 4500 spectrometer.
2
2
the reactor reached the atmospheric value, the product was
extracted with a further amount of CH Cl and the recovered
2
2
catalyst was dried and reused as such in a subsequent reaction
run.
Catalyst Preparation
Several doped ormosils were prepared by sol-gel hydrolysis
and co-polycondensation of MTMS and TMOS in the presence Acknowledgements
of TPAP dissolved in methanol with and without NaF as
polycondensation catalyst and varying the relative amounts of
We thank the CNR for a short-term mobility scholarshipto R. C.
water, co-solvent (batch A, Si:MeOH:H O 1:8:1; batch B,
that allowed her stay at Reading University Catalysis Research
Centre and Dr. S. C. E. Tsang for his kind hospitality. Thanks
are due to Dr. Giuseppe MarcÏ at the University of Palermo for
the SEM pictures.
2
Si:MeOH:H O 1:4:4), and the organosilane/silane ratio.
2
A typical catalyst of batch A obtained with NaF (A-Me1,
Table 1), was prepared by adding MTMS (1.65 mL) and TMOS
(
5.90 mL) to a solution of TPAP (55.5 mg) in MeOH (1.80 mL)
cooled in an ice bath followed by the addition of H O (5.70 mL)
2
and NaF (765 mL, 1 M) under fast stirring. The sol gelled
rapidly and the resulting alcogel was sealed and left to age at
room temperature for 48 h prior to drying in an oven at 508C
until reaching constant weight (5 days). The catalytic xerogel
thus obtained was powdered, washed under reflux (CH Cl Â
References and Notes
[
1] R. A. Sheldon, M. Wallau, I. W. C. E. Arends, U. Schu-
chardt, Acc. Chem. Res. 1998, 31, 485.
2
2
[
2] B. M. Choudary, M. Lakshmi Kantam, P. Lakshmi Kant-
am, Catal. Today 2000, 57, 17.
2
, 408C) and dried at 508C prior to use.
A typical catalyst of batch B such as B-Me3 was obtained by
adding MTMS (4.90 mL) and TMOS (1.95 mL) to a solution of
TPAP (55.5 mg) in MeOH (7.30 mL) cooled in an ice bath
[3] For selected recent examples, see: a) D. R. Jensen, J. S.
Pugsley, M. S. Sigman, J. Am. Chem. Soc. 2001, 123, 7475;
b) G. J. ten Brink, I. W. C. E. Arends, R. A. Sheldon,
Science 2000, 287, 1636; c) J. Takagi, M. Aoki, R. Noyori,
Tetrahedron Lett. 1998, 39, 7549; d) A. Dijksman, A.
Marino-Gonz a¬ lez, A. Mairata i Payeras, I. W. C. E.
Arends, R. A. Sheldon, J. Am. Chem. Soc. 2001, 123,
followed by the addition of H O (2.65 mL) under fast stirring.
2
The sol gelled slowly and the alcogel thereby obtained was
sealed, left to age at room temperature for 48 h and eventually
dried at 508C for 5 days. The resulting powder xerogel was
washed as reported above. A typical catalytic load was
0.05 mmol TPAP/g ormosil.
¬
6
826; e) G. Csjernyik, A. H. Ell, L. Fadini, B. Pugin, J. E.
B‰ckvall, J. Org. Chem. 2002, 67, 1657; f) I. E. Mark o¬ ,
P. R. Giles, M. Tsukazaki, I. Chell e¬ -Regnault, C. J. Urch,
S. M. Brown, J. Am. Chem. Soc. 1997, 119, 12661.
4] For a recent account, see: M. Freemantle, Chem. Eng.
News 2001, 79 (1), 21.
Typical Oxidation Procedure
[
[
Benzyl alcohol (5 mL, 0.5 mmol) and 0.1 equiv. of catalyst
A-Me1 (100 mg) were added along with n-decane (5 mL,
5] a) S. R. Oakes, A. A. Clifford, M. C. Rayner, J. Chem.
Soc. Perkin Trans. 1 2001, 917; b) A. Baiker, Chem. Rev.
1
mmol) as internal standard to the reaction vessel and the
reaction conditions chosen to ensure complete solubility of the
alcohol and of the aldehyde (Scheme 1) in the homogeneous
supercritical phase. In order to do so, we dissolved 0.5 mmol of
substrate and 0.5 mmol of product along with the internal
standard decane in 10 mL CH Cl , analysing its content at GC,
1
5
999, 99, 453; c) S. Kainz, W. Leitner, Catal. Lett. 1998,
5, 223.
[
6] A. D. Curzons, D. J. C. Constable, D. N. Mortimer, V. L.
Cunningham, Green Chem. 2001, 3, 1.
2
2
prior to charging the reactor with the same amounts of
substrate, product and internal standard. Keeping constant the
[7] a) N. J. Meehan, A. J. Sandee, J. N. H. Reek, P. C. J.
Kamer, P. W. N. M. van Leeuwen, M. Poliakoff, Chem.
1266
¹ 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
asc.wiley-vch.de
Adv. Synth. Catal. 2003, 345, 1261 ± 1267