Table 1 Optimization of MTP ozonation in an ionic liquida
[MTP]/mol LÀ1
[O3]/gmÀ3
T/1C
tb/h
Y(HE) (%)
Y(CE) (%)
k1/k2
c
Entry
1
2
3
4
5
6
7
8
9
1
2.5
5
5
5
5
5
5
5
40
40
40
40
40
40
5
25
25
0
25
50
80
25
25
25
2
53
58
68
68
74
72
89
71
72
31
38
11
30
13
28
11
25
27
2.4
3.5
—
3
8d
3
d
7.5
10
1
0.5
4
3
3
d
—
—
d
20
60
6.2
8.3
a
b
c
Reaction conditions: 0.21 mmol minÀ1 O3 flow; [BMPyr][(CN)2N]. Reaction time of maximum hydroxy ester yield. k1 and k2: rate constants
d
of, respectively, the MTP oxidation and the hydroxy ester oxidation (see Scheme 1). Pseudo-first order rate approximation not valid.
Notes and references
w Typical ozonation procedure: the acetal (10 mmol) was dissolved in
2 g IL and ozonized at 0–80 1C (rate of ozone supply: 0.21 mmol min)
for 8 h. Ozone was produced with a Fisher Ozone Generator type OZ
500. After reaction, the excess ozone was removed by flushing the
system with nitrogen. Reaction mixtures in organic solvents were
injected directly in the GC. The solutions in ionic liquids were first
silylated with MSTFA (20 mol MSTFA/hydroxyl group; 80 1C; 2 h)
and extracted with diethyl ether. The ether layer was analyzed with a
Shimadzu 2014 GC equipped with a FID detector and an apolar
CP-Sil 5 CB column. The identity of the reaction products was verified
by GC-MS. An Agilent 6890 gas chromatograph, equipped with a
HP-5MS column, coupled to a 5973 MSD mass spectrometer was
used. NMR spectroscopic measurements: measurements were carried
out with a Bruker AMX-300 at 300 MHz (H) in deuterium oxide
(D2O) and 75.5 MHz (C) in deuterated chloroform (CDCl3) with
tetramethylsilane (TMS) as standard. Additional NMR spectra were
recorded on a Bruker Avance 400 spectrometer.
Fig. 2 Effect of the ozone concentration on the ozonation of MTP
(reaction conditions: [MTP] = 5 mol LÀ1; 25 1C).
1 J A. Wojtowicz, The Kirk-Othmer Encyclopedia of Chemical,
Wiley VCH, New York, 2005, p. 17.
observed. The oxidation of cyclic acetals like MTP and ETF
also proceeded well in a bistriflimide based ionic liquid and in
mixtures of dicyanamide and bistriflimide ionic liquids.
Furthermore, this system proved suitable for ozonation of
b-D-methyl glucopyranoside. Combined with the well-known
cellulose solubilizing power of ILs, this system could be an
interesting approach for the ozonation of cellulose, which is a
structural analogue of the alkyl glucopyranoside.
2 K. Koike, M. Nifuku, K. Izumi, S. Nakamura, S. Fujiwara and
S. Horiguchi, J. Loss Prev. Process Ind., 2005, 18, 465.
3 M. Kanakidou, J. H. Seinfeld, S. N. Pandis, I. Barnes,
F. J. Dentener, M. C. Facchini, R. Van Dingenen, B. Ervens,
A. Nenes, C. J. Nielsen, E. Swietlicki, J. P. Putaud, Y. Balkanski,
S. Fuzzi, J. Horth, G. K. Moortgat, R. Winterhalter, C. E. L.
Myhre, K. Tsigaridis, E. Vignati, E. G. Stephanou and J. Wilson,
Atmos. Chem. Phys., 2005, 5, 1053.
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5 K. R. Seddon, Kinet. Catal., 1996, 37, 693.
6 T. Welton, Chem. Rev., 1999, 99, 2071.
7 N. V. Plechkova and K. R. Seddon, Chem. Soc. Rev., 2008, 37, 123.
8 P. Wasserscheid and T. Welton, Ionic liquids in synthesis,
Wiley-VCH, Weinheim, 2002.
9 P. Wasserscheid and W. Keim, Angew. Chem., Int. Ed., 2000, 39, 3773.
10 J. L. R. Morgan and F. W. Schwartz, J. Am. Chem. Soc., 1911, 33, 1041.
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A. J. Benesi and M. Maroncelli, J. Phys. Chem. B, 2008, 112, 81.
12 P. Deslongchamps and C. Moreau, Can. J. Chem., 1971, 49, 2465.
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C. Moreau, Can. J. Chem., 1974, 52, 3651.
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G. B. Deacon, Chem. Commun., 2001, 1430.
Summarizing, the ionic liquid [BMPyr][(CN)2N] allows to
oxidize cyclic acetals like MTP and ETF selectively to the
corresponding hydroxy esters in a mild and safe way with
ozone as the oxidizing agent. At low ozone concentrations
MTP was fully converted with a hydroxy ester yield of 89%.
The only side product was the overoxidized carboxy ester.
Advantage is taken of the extremely low vapour pressure of
ionic liquids at temperatures below 100 1C, which not only
prevents evaporation of these solvents but also prevents
the formation of explosive mixtures of ozone with organic
vapours.
Financial support from the K.U. Leuven (project IDO/05/005,
CECAT grant and CASAS Methusalem grant) and from the
IWT (Institute for the Promotion of Innovation by Science
and Technology in Flanders) is acknowledged. Support by
IoLiTec (Denzlingen, Germany) is appreciated.
16 J. Pernak and I. Goc, Pol. J. Chem., 2003, 77, 975.
17 J. L. Anthony, J. L. Anderson, E. J. Maginn and J. F. Brennecke,
J. Phys. Chem. B, 2005, 109, 6366.
18 K. Vandersmissen, F. De Smedt and C. Vinckier, Ozone: Sci. Eng.,
2008, 30, 300.
ꢀc
This journal is The Royal Society of Chemistry 2009
Chem. Commun., 2009, 6439–6441 | 6441