Palladium(II)-catalyzed oxidation of acrylate esters to acetals in supercritical carbon dioxide

Article abstract of DOI:10.1039/a901935i

The development of a new palladium(II)-catalyzed oxidation of methyl acrylate, affording methyl 3,3-dimethoxypropanoate in excellent conversion and selectivity in supercritical CO₂, is presented.

Full text of DOI:10.1039/a901935i

Palladium(ii)-catalyzed oxidation of acrylate esters to acetals in supercritical
carbon dioxide
Lanqi Jia, Huanfeng Jiang* and Jinheng Li
Guangzhou Institute of Chemistry, Chinese Academy of Sciences, PO Box 1122, Guangzhou 510650, China.
E-mail: jhf@mail.gic.ac.cn
Received (in Cambridge, UK) 11th March 1999, Accepted 20th April 1999
The development of a new palladium(ii)-catalyzed oxida-
tion of methyl acrylate, affording methyl 3,3-dimethox-
ypropanoate in excellent conversion and selectivity in
heterogeneous catalysis. Several recent reports have shown that
some interesting results are specifically associated with the use
of scCO
2
as a reaction solvent.11 Here we disclose our work on
II
supercritical CO
2
, is presented.
a Pd -catalyzed terminal olefin oxidation in scCO
2
.‡ Our
results show that Pd -catalyzed oxidation of methyl acrylate
could be successfully processed in scCO to give the dimethyl
II
Alkyl 3,3-dialkoxypropanoates are important intermediates in
organic synthesis and have been used to synthesize a variety of
2
acetal as major product when an excess of MeOH was used
(Scheme 1). Our previous experiments show that it is necessary
to add an excess of MeOH to promote partial dissolution of the
1
2
compounds, including coumarins, porphyrins, spermine me-
3
4
tabolites and loganin. Previously reported methods for the
preparation of alkyl 3,3-dialkoxypropanoates are not sat-
isfactory, due to the high cost of the starting materials and the
2
inorganic catalysts in scCO , since MeOH is miscible in
12
scCO
The catalytic activity of PdCl
oxidation of methyl acrylate were investigated. The reaction
catalyzed by PdCl were slightly faster than that by
PdCl (MeCN) (Table 1, entries 2 and 3).
It has been reported that CuCl was superior to CuCl
2
.
II
low overall yields of the process. The Pd -catalyzed oxidation
2 2 2
and PdCl (MeCN) for
of terminal olefins with water, which is well known as the
5
Wacker reaction, produces methyl ketones. A similar reaction
2
of terminal olefins bearing electron-withdrawing groups upon
2
2
II
treatment of alcohols catalyzed by Pd affords acetals at the
2
as the
Interestingly,
, 0.4 equiv. of CuCl
cocatalyst in the oxidation of acrylate esters.1
in our experiments carried out in scCO
3,6b
terminal carbon in DME. High yields of methyl 3,3-dimethoxy-
propanoate (92%), however, were afforded only in the presence
of HMPA. In the absence of HMPA the yield was only 46%.6
2
2
gave similar or even better results than the same amount of CuCl
(Table 1, entries 8 and 9).
Using supercritical carbon dioxide (scCO
solvent has been attracting extensive attention in recent years.
First, CO
is inexpensive, nonflammable, nontoxic7 and
chemically inert under many conditions. ScCO , as an envir-
onmentally friendly reaction medium, may be a substitute for
2
) as a reaction
Hosokawa reported that the oxidation of methyl acrylate to
6
2
the acetal was carried out at 50 °C in DME. We found that the
2
oxidation reaction could be completed at a lower temperature in
scCO
conversion and selectivity at 40 °C. The reaction was still
smoothly accomplished at 27 °C, at which temperature CO is
2
. In our experiment, the reaction afforded very good
8
2
volatile and toxic organic solvents. Secondly, scCO possesses
hybrid properties of both liquid and gas, to the advantage of
2
9
some reactions involving gaseous reagents. Control of the
a liquid, although the amount of byproducts increased
slightly.
solvent density by variation of the temperature and pressure
enables the solvent properties to be ‘tuned’ to reactants.10
The CO
best results were obtained when the pressure of CO
controlled between 12–13 MPa. As the pressure of CO
2
pressure had a great effect on the selectivity. The
Finally, separating of CO
efficient and simple.
Organic reactions in scCO
organometallic chemistry, particularly in homogeneous and
2
from the reaction mixture is energy-
have facilitated great progress in
2
was
was
2
2
reduced, the conversion and selectivity also declined. For
example, the reaction gave 2 in a yield of only 75.8% and the
Pd , Cu or CuI
II
II
MeO
MeO
MeO
+
+
CO2Me
CO2Me
CO2Me
CO2Me
MeOH/O2 in scCO2
OMe
4
3
1
2
Scheme 1
a
Table 1 Oxidation reaction of methyl acrylate in scCO
2
b
Yield (%)
Selectivity
Entry
Catalyst
T/°C
P
O2/MPa
P
CO2/MPa
Conv.
2
3
4
for 2 (%)
c
d
d
1
2
3
4
5
6
7
8
9
PdCl
PdCl
PdCl
PdCl
PdCl
PdCl
PdCl
PdCl
PdCl
PdCl
2
2
2
2
2
2
2
2
2
2
(MeCN)
2
, CuCl
, CuCl
50
50
50
50
40
27
40
40
40
40
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.5
0.5
1.0
13
13
13
13
12
12
9
13
13
12
99.0
49.4
71.0
98.5
93.0
93.0
92.0
99.1
99.7
99.4
81.1
36.6
42.9
82.7
82.4
75.0
75.8
87.9
86.3
91.7
3.5
5.9
6.6
4.0
2.8
5.1
2.8
1.6
1.5
1.2
8.8
2.7
3.1
3.5
3.0
2.9
3.4
2.5
4.5
2.0
86.8
81.0
81.6
91.7
93.4
90.3
92.4
95.5
93.5
96.6
(MeCN)
2
e
, CuCl
, CuCl
2
2
(MeCN)
2
, CuCl
, CuCl
, CuCl
, CuCl
, CuCl
, CuCl
2
2
2
1
0
2
a
(0.4 equiv.), 12 h. b By GC. c Selectivity = [2/(2
Methyl acrylate (5 mmol), MeOH (1 ml ≈ 24.7 mmol), PdCl
2
or PdCl
(2 mol%). CuCl
2
(MeCN)
2
(3 mol%), CuCl or CuCl
(2 mol%).
2
d
e
+
3 + 4)] 3 100. PdCl
2
(MeCN)
2
(1 mol%), CuCl or CuCl
2
2
Chem. Commun., 1999, 985–986
985

(quantitative analysis) and GC-MS, 1H NMR 13C NMR and IR analysis
amount of other unidentified products increased when 9 MPa
CO was charged in the autoclave.
(identification of products).
2
The oxygen pressure also affected the conversion and
selectivity. Lower oxygen pressure (0.1 MPa) gave satisfactory
conversion but the selectivity to 2 was never higher than 93.4%.
The best selectivity (over 96%) was obtained as the oxygen
pressure was elevated to 1.0 MPa. Using ethyl acrylate as the
substrate, the reaction affords similar results, and the further
experiments are now in progress.
In summary, the oxidation reaction of methyl acrylate
afforded the acetal in high conversion and selectivity at lower
temperature when supercritical carbon dioxide instead of DME
was used as the reaction medium without the presence of
1 D. G. Crosby and R. V. Berthold, J. Org. Chem., 1962, 27, 3083.
2 J. P. Collman, A. O. Chong, G. B. Jameson, R. T. Oakley, E. Rose, E. R.
Schmittou and J. A. Ibers, J. Am. Chem. Soc., 1981, 103, 516.
3
M. Israel, E. C. Zoll, N. Muhammad and E. J. Modest, J. Med. Chem.,
973, 16, 1.
1
4
G. B u¨ chi, J. A. Carlson, J. E. Powell, Jr. and L.-F. Tiztze, J. Am. Chem.
Soc., 1973, 95, 504.
5
6
For a comprehensive review, see: J. Tsuji, Synthesis, 1984, 369.
(a) T. Hosokawa, S. Aoki and S.-I. Murahashi, Synthesis, 1992, 558; (b)
T. Hosokawa, T. Ohta, S. Kanayama and S.-I. Murahashi, Synthesis,
1992, 558; (b) T. Hosokawa, T. Ohta, S. Kanayama and S.-I. Murahashi,
J. Org. Chem., 1987, 52, 1758.
2 2
HMPA. The pressure of CO and O had a remarkable effect on
the conversion and selectivity.
The authors are grateful to the National Natural Science
Foundation of China for financial support of this work
7 For discussions of the advantages of scCO
Bartle, Chem. Ind., 1996, 449; M. Poliakoff and S. Howdle, Chem. Ber.,
995, 31, 118; H. Black, Environ. Sci. Technol., 1996, 30, 124A.
2
, see T. Clifford and K.
1
8
D. A. Morgenstern, R. M. LeLacheur, D. K. Morita, S. L. Borokowsky,
S. Feng, G. H. Brown, L. Luan, M. F. Gross, M. J. Burk and W. Tumas,
ACS Symp. Ser., 1996, 626, 132.
(29772036) and Dr Fangl u¨ Huang for helpful discussions.
Notes and references
9 J. W. Rathke, R. J. Klinger and T. R. Krause, Organometallics, 1991,
1
0, 1350; P. G. Jessop, T. Ikariya and R. Noyori, Nature, 1994, 368,
†
Typical procedure: Reactions were carried out in a HF-25 autoclave. PdII
catalyst (0.15 mmol, 3 mol%), CuCl (4 mmol), MeOH (1 ml, 24.7 mmol)
and acrylate ester (5 mmol) were added into a 25 ml autoclave in sequence.
and then liquid CO were pumped into the autoclave using a cooling
2
31.
2
1
1
0 M. A. Carroll and A. B. Holmes, Chem. Commun., 1998, 1395.
1 M. J. Burk, S. Feng, M. F. Gross and W. Tumas, J. Am. Chem. Soc.,
O
2
2
1
995, 117, 8277.
pump to give the desired pressure. The autoclave was then put into an oil
bath under magnetic stirring for the desired reaction time. After the reaction,
the autoclave was allowed to cool to 230 °C. CO was vented and the
2
surplus was extracted with n-hexane. The extract was filtrated and
condensed under reduced pressure. The product was analyzed using GC
1
1
2 L. Jia, H. Jiang and J. Li, Green Chem., 1999, 91.
3 J. Tsuji, H. Nagashima and H. Nemoto, Org. Synth., 1984, 62, 9.
Communication 9/01935I
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Chem. Commun., 1999, 985–986