4
506
J . Org. Chem. 1999, 64, 4506-4508
Notes
Ta ble 1. DMC Syn th esis fr om CO2 a n d Dim eth yl
Meta l-Ca ta lyzed Dim eth yl Ca r bon a te
Syn th esis fr om Ca r bon Dioxid e a n d Aceta ls
Aceta lsa
R1
R2
yieldb
(%)
Toshiyasu Sakakura,* J un-Chul Choi, Yuko Saito,
Takashi Masuda, Takeshi Sako, and Takeshi Oriyama
National Institute of Materials and Chemical Research,
entry
1c
(see eq 3)
metal complex
additive
Me
Et
Et
Ph
Ph
Ph
Ph
Me
Me
Et
Et
H
H
H
Bu2Sn(OMe)2
Bu2Sn(OMe)2
Bu2Sn(OMe)2
Bu2Sn(OMe)2
Bu2Sn(OMe)2
Cp*2TiCl2
none
none
none
none
Bu4PI
Mg(OMe)2
none
57 (3000)
58 (3380)
26 (1530)
d
2
1
-1 Higashi, Tsukuba, Ibaraki 305-8565, J apan, and
3
4
5
6
7
Ibaraki University, Bunkyo, Mito, Ibaraki 310-8512, J apan
14
7
8
(790)
(430)
(460)
(65)
Received J anuary 27, 1999
The transformation of carbon dioxide, an inexpensive
H
Me
Mg(OMe)2
Bu2Sn(OMe)2
1
and abundant C
1
building block, to useful compounds has
e
8
none
88 (5180)
been a challenge for synthetic chemists and is getting
more important because of its environmentally friendly
nature (nontoxic and nonflammable).1 In particular,
utilization as a phosgene alternative is quite fascinating.
a
Reaction conditions. Acetals (10 mmol), metal complex (0.17
3
mmol), additive (0.17 mmol), methanol (8.1 cm ), CO2 (300 atm),
80 °C, 24 h. Mg(OMe)2 was added as a methanol solution (1.2
1
3
b
cm ). Based on acetals. Figures in parentheses are the yields
based on metal. After 96 h. d After 72 h. e CO2 (2000 atm), 180
°C, 24 h.
c
A significant synthetic target starting from CO
2
is
2
dimethyl carbonate (DMC). A considerable effort has
already been devoted to the straightforward synthesis of
DMC as shown in eq 1 using tin methoxides as a catalyst.
However, the catalytic activity is still at the few turn-
.5 Note that
2
the DMC synthesis from acetals and CO
acetals are much more inexpensive than ortho esters and
easily regenerated from carbonyl compounds (eq 3).
Hence, the reaction can be considered as a formal DMC
3
overs level. This poor yield is ascribed to the formation
of water that decomposes both tin methoxide and DMC.
2
synthesis from CO and MeOH.
In a previous paper, we achieved improved catalytic
efficiencies by reacting trimethyl orthoacetate (a dehy-
drated MeOH derivative) with supercritical CO
2
(eq 2).4
The reaction of acetals takes place under conditions
4
similar to the ortho ester reaction (catalyzed by Bu
2
Sn-
(
OMe) , CO 300 atm, 180 °C, 24 h). Generally speaking,
2
2
acetals derived from dialkyl ketones gave higher yields
than aromatic acetals; the yields under the above condi-
tions were in the order 2,2-dimethoxypropane (26%) )
3
,3-dimethoxypentane (26%) > 1,1-dimethoxycyclohexane
However, ortho esters are relatively expensive as an
industrial raw material. In this paper, we wish to report
(23%) > dimethoxyphenylmethane (14%). Some typical
results are summarized in Table 1. Since the 72 h
reactions gave higher DMC yields compared with the 24
h reactions for the above acetals (e.g., entries 2 and 3),
the relatively low yields of entries 3-7 are not due to
thermodynamic limitations. A rather large MeOH/acetal
molar ratio (e.g., 200/10) was effective to prevent the enol
ether formation. This is probably related to the equilib-
rium between enol ethers and acetals.6
(
2
1) For recent reports for CO conversion by homogeneous catalysis,
see: (a) J essop, P. G.; Ikariya, T.; Noyori, R. Science 1995, 269, 1065-
1
2
2
069. (b) J essop, P. G.; Ikariya, T.; Noyori, R. Chem. Rev. 1995, 95,
59-272. (c) Leitner, W. Angew. Chem., Int. Ed. Engl. 1995, 34, 2207-
221. (d) Morgenstern, D. A.; LeLacheur, R. M.; Morita, D. K.;
Borkowsky, S. L.; Feng, S.; Brown, G. H.; Luan, L.; Gross, M. F.; Burk,
M. J .; Tumas, W. Green Chemistry; Anastas, P. T., Williamson, T. C.,
Eds.; ACS Symposium Series 626; American Chemical Society: Wash-
ington, DC, 1996; pp 132-151. (e) Cheng, M.; Lobkovsky, E. B.; Coates,
G. W. J . Am. Chem. Soc. 1998, 120, 11018-11019. (f) Darensbourg,
D. J .; Holtcamp, M. W.; Struck, G. E.; Zimmer, M. S.; Niezgoda, S. A.;
Rainey, P.; Robertson, J . B.; Draper, J . D.; Reibenspies, J . H. J . Am.
Chem. Soc. 1999, 121, 107-116.
The effect of the catalyst structure is very significant.
Although Bu Sn(OMe) was a productive catalyst, Bu -
2 2 3
Sn(OMe) was almost inactive. The same tendency was
4
(
2) (a) Pacheco, M. A.; Marshall, C. L. Energy Fuels 1997, 11, 2-29.
b) Aresta, M.; Quaranta, E. CHEMTECH 1997, 30-40. (c) Shaikh,
A.-A.; Sivaram, S. Chem. Rev. 1996, 96, 951-976.
3) (a) Kizlink, J .; Pastucha, I. Collect. Czech. Chem. Commun. 1995,
observed in the eq 1 and eq 2 reactions. Other group 14
(
2 2 2
element dialkoxides such as Me Ge(OMe) and Ph Si-
(
6
0, 687-692. (b) Kizlink, J .; Pastucha, I. Collect. Czech. Chem.
(5) A part of the work was presented at the 75th Annual Meeting
of J apan Chemical Society, Sakakura, T.; Saito, Y.; Sako, T., Mat-
suyama, J apan, September 14-19, 1998; J apan Chemical Society;
Abstract 1A604.
(6) Schostakowskii, M. F.; Graccheva, E. P.; Kul’bovskaia, N. K. Zh.
Obshch. Khim. (Engl. Transl.) 1958, 28, 2344-2348.
Commun. 1994, 59, 2116-2118. (c) Kizlink, J . Collect. Czech. Chem.
Commun. 1993, 58, 1399-1402. (d) Yamazaki, N.; Nakahama, S.;
Higashi, F. Rep. Asahi Glass Found. Ind. Technol. 1978, 33, 31-45.
(4) Sakakura, T.; Saito, Y.; Okano, M.; Choi, J .-C.; Sako, T. J . Org.
Chem. 1998, 63, 7095-7096.
1
0.1021/jo990155t CCC: $18.00 © 1999 American Chemical Society
Published on Web 05/18/1999