Chemistry Letters Vol.33, No.7 (2004)
835
corresponding esters under mild reaction conditions with H2O2
as oxidant and sulphated SnO2 supported on the SBA-1 zeolite
washed with acetone, and then reused as catalyst for the next
run under the same conditions. The reaction results indicate that
there is no difference in either activity or selectivity between the
first and third runs (Entries 1 and 14).
In summary, it was found that several esters can be obtained
in normal yields without any metal catalyst, and a new system
.
as catalyst (the concentration of S SnO2 on the zeolite is
1.5 mmol/g). Furthermore, in the above systems, it was found
that several esters have been obtained in normal yield without
any metal catalyst, and the reports available have not mentioned
this observation.
.
for oxidative esterification of aldehydes, wherein S SnO2/
The oxidative esterification results are shown in Table 1. In
most cases, the desired esters were obtained in poor to normal
yields without any metal catalyst. It is a surprising observation
because H2O2 and metal catalyst are usually used together in
the oxidative esterification systems in the report available.7,10,11
SBA-1 was used as catalyst and H2O2 was used as oxidant,
has been demonstrated. The reaction results indicate that the pro-
cedure is facile, effective and easy to work up and can be used in
.
the preparation of a broad range of esters. Moreover, S SnO2/
SBA-1 catalyst can be easily separated from reaction mixture
and reused at least three times.
.
Using S SnO2/SBA-1 as catalyst, most substrates give good to
excellent yields of corresponding esters. For examples, benzal-
dehyde and straight chain alcohol (including long-chain alcohol)
were oxidized to corresponding esters efficiently (Entries 1–3,
5–8). However, the oxidative esterification result of benzalde-
hyde and 2-propanol was not satisfactory (Entry 4), and no ester
was detected from GC analysis after 6 h. at 323 K when benzal-
dehyde and tert-butanol were used as substrates. This trend indi-
cates that steric effect is an important factor in the reaction sys-
tems. In comparison with benzaldehyde and saturated straight
chain alcohols, benzaldehyde and unsaturated alcohols are less
reactive to oxidative esterification (Entries 9, 10). Besides benz-
aldehyde, this catalytic system is also suitable for unsaturated
and straight chain aldehydes (Entries 11–13). For instance, ex-
cellent results were obtained with pelargonaldehyde as substrate
(Entries 12, 13).
References
1
2
3
4
5
D. R. Williams, F. D. Klingler, E. E. Allen, and F. W.
Lichtenthaler, Tetrahedron Lett., 29, 5087 (1988).
C. Mcdonald, H. Holcomb, K. Kennedy, and E. Kirkpatrick,
J. Org. Chem., 54, 1213 (1989).
S. R. Wilson, S. Tofigh, and R. N. Misra, J. Org. Chem., 47,
1360 (1982).
P. J. Garegg, L. Olsson, and S. Oscarson, J. Org. Chem., 60,
2200 (1995).
E. J. Corey, N. W. Gilman, and E. E. Ganem, J. Am. Chem.
Soc., 90, 5616 (1968).
6
7
M. Okimoto and T. Chiba, J. Org. Chem., 53, 218 (1988).
J. H. Espenson, Z. Zhu, and T. H. Zauche, J. Org. Chem., 64,
1191 (1999).
In above catalytic systems, the reaction can be carried out
even in the absence of any external acid, but the reactions are
rather sluggish. For example, only 45% benzaldehyde was selec-
tively oxidized to methyl benzoate with methanol as solvent in
4 h.
8
9
R. Zhao, Y. Ding, and Z. Peng, Catal. Lett., 87, 81 (2003).
B. R. Travis, M. Sivakumar, G. O. Hollist, and B. Borhan,
Org. Lett., 5, 1031 (2003).
10 R. Gopinath and B. K. Patel, Org. Lett., 2, 577 (2000).
11 R. Gopinath, B. Barkakaty, B. Talukdar, and B. K. Patel,
J. Org. Chem., 68, 2944 (2003).
12 S. P. Chavan, P. K. zubaidha, and S. W. Dantale, Tetrahe-
dron Lett., 37, 233 (1996).
.
Furthermore, S SnO2/SBA-1 is stable and can be reused af-
.
ter oxidative esterification. After reaction, S SnO2/SBA-1 was
separated from the reaction mixture by filtrating, thoroughly
Published on the web (Advance View) June 7, 2004; DOI 10.1246/cl.2004.834
Qian, Guang
