Acetylation of Alcohols Catalyzed by Heteropolyoxometallates
169
Preparation of Wells–Dawson Heteropolyacid
H P W O
The potassium salt of the Wells–Dawson type heteropolyacid
significant structural changes and the recycled catalyst could
be used several times without any appreciable loss of catalytic
activity.
6
2
18 62
K P W O was prepared and then converted to the corre-
6
2
18 62
+
sponding acid H P W O by passing it through a Dowex -
6
2
18 62
5
0W-X8 ion exchange column. In the final step water was
removed under reduced pressure and the remaining solid was
References
ꢃ
collected and dried overnight at 120 C [30].
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Organic Synthesis, 3rd edn, Wiley, New York
[
2] Chakraborti AK, Nayak MK, Sharma L (2002) J Org
Chem 67: 1776
Preparation of Silica-included 12-Tungstophosphoricacid
H PW O -SiO
3
12 40
2
[3] ChakrabortiAK, SharmaL, SharmaU (2001) Tetrahedron
57: 9343
[4] Vogel A (1996) Textbook of Practical Organic Chemistry,
3
3
A mixture of 36.2cm H O (2.0mol), 18.3 cm , 1-butanol
2
(
0.2mol), and 0.967 g H PW O ꢂ 6.7H O (0.5mmol) was
3
12 40
2
added to 41.6g tetraethyl orthosilicate (0.2mol), and stirred
at 80 C for 3 h. The hydrogel obtained was dehydrated slowly
5
th edn, Longman Group Ltd, London
5] Wright SW, Hageman DL, Wright AS, Mc Clure LD
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5
9] Ishihara K, Ohara S, Yamamoto H (1990) Science 290:
ꢃ
[
[
[
[
[
ꢃ
at 80 C for 1.5 h in vacuo (25 Torr). The dried gel obtained
ꢃ
(
ꢃ
was extracted with water at 80 C for 3 h, and dried at 60 C for
1
2h to give 13.5 g silica-included heteropolyacid (H PW O ,
3 12 40
1
H PW O was vacuum dried (25 Torr) at 150 C for 3 h prior
1.1 wt% estimated by ICP analysis). The silica-included
ꢃ
3
12 40
to use for catalytic reactions.
307
Preparation of H [SiW O ] ꢂ 15H O
4
12 40
2
3
1140
[10] Zhao ZH (2000) J Mol Catal A Chem 154: 131
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611
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Tetrahedron Lett 39: 3263
To 300 cm 2 M aqueous solution of Na WO was added
2
4
3
2
in order to redissolve the local precipitate of tungstic acid.
40 cm 3 M aqueous HCl by fraction with vigorous stirring
[
3
Then 100 cm 0.5 M aqueous solution of sodium metasili-
3
cate was quickly added. A 6 M aqueous HCl (ꢁ20 cm )
9
solution was added to reach pH ¼ 5.5. After standing for
[
0
.5 h, the solution was mixed quickly with another fraction
3
of 6 M HCl (totally 60 cm 6 M HCl added; final pHꢁ1).
3
After concentration to about 400 cm , the solution was fil-
[
[
[
[
[
tered to remove unreacted silica. The pH was adjusted to
about 2 with aqueous 1 M KOH. Addition of 50 g solid
KCl induced the precipitation of ꢀ-K SiW O ꢂ 15H O,
6
4
12 40
2
which was filtered off from warm water and dried in air with-
out preliminary washing (yield: 60% based on W). The ob-
tained precipitate from the saturated aqueous solution of the
above compound was acidified to produce crystals of the
title compound.
(
2
General Procedure for Esterification of Acetic Acid
with Ethanol Catalyzed by Heteropolyacids
To a stirred solution of heteropolyacid (0.037 mmol) in
[20] Iqbal J, Srivastava RR (1992) J Org Chem 57: 2001
[21] Ringold HJ, Loeken B, Rosenkranz G (1956) J Am
Chem Soc 78: 816
[22] Maki-Arfela M, Salmi T, Sundell M, Ekman K,
Peltonen R, Lehtonen J (1999) Appl Catal A Gen
184: 25
3
3
1
(
1.4cm acetic acid (200 mmol), was added 5.9 cm ethanol
100 mmol) and the reaction mixture was allowed to stir at
ꢃ
6
5–70 C [42] for 40min. An open container system was used
to separate products from the reaction mixture. The produced
ester, under reflux, was allowed to pass through a condenser to
be liquefied. Continuous isolation of products from the reac-
tion mixture increased efficiency of the esterification method
[23] Arata K, Hino M (1998) Appl Catal A Gen 173: 121
[24] Heidekum A, Harmer MA, Hoelderich WF (1999)
J Catal 181: 217
[25] Tiofeeva MN, Dimidov AV, Kozhevnikov IV (1979)
J Mol Catal 179: 21
1
0-fold. Progress of the reaction was followed by analysis of
aliquots withdrawn directly from the resolved products. At the
end of the reaction, the reaction mixture was slowly evapo-
[26] Drago RS, Dias JA, Maier T (1997) JAm Chem Soc 119:
7702
[27] Mizuno N, Misono M (1998) Chem Rev 98: 199
[28] Hill CL, Prosser-McCartha GM (1995) Coordn Chem
Rev 143: 407
ꢃ
rated at 50 C, then the recycled catalyst was washed with
ꢃ
CH Cl , dried at 130 C for 1 h, and re-used in another reac-
2
2
tion. The infrared spectrum of the catalyst did not show any