Novel catalytic acetylation of alcohols with Preyssler's anion, [NaP 5Wa30O110]14-1

Article abstract of DOI:10.1023/A:1025142101029

Sodium 30-tungstopentaphosphate, the so-called Preyssler's anion with a formula of [NaP₅W₃₀O₁₁₀]^14- (I) catalyzes the acetylation of alcohols (C_nH_{2n + 1}OH, n = 2, 3, 4, 5) with acetic acid. High yield is obtained with I as pure acid or supported on silica. Both homogeneous and heterogeneous catalysts are discussed and compared. H₁₄[NaP₅W₃₀O₁₁₀], abbreviated as H₁₄-P₅, under homogeneous conditions, as well as supported on silica (heterogeneous conditions) is found to be an excellent catalyst. Our data indicate that, when the ammonium salt of I is employed as the catalyst, the yield increases as the alcohol carbon-chain is increased. This behavior is found to be quite general. The catalysts can be easily recovered and recycled with retention of their initial structure and activity.

Full text of DOI:10.1023/A:1025142101029

Kinetics and Catalysis, Vol. 44, No. 4, 2003, pp. 524–528. From Kinetika i Kataliz, Vol. 44, No. 4, 2003, pp. 574–579.
Original English Text Copyright © 2003 by Alizadeh, Razavi, Farrash Bamoharram, Hassanzadeh, Khoshnavazi, Mohammadi Zonoz.
Novel Catalytic Acetylation of Alcohols with Preyssler’s Anion,
1
[NaP5Wa30O110]14–
M. H. Alizadeh**, H. Razavi***, F. Farrash Bamoharram*,
M. K. Hassanzadeh**, R. Khoshnavazi*, and F. Mohammadi Zonoz*
* Department of Chemistry, Ferdowsi University of Mashhad, Iran
** Department of Pharmaceutical Chemistry, School of Pharmacy, Mashhad University of Medical Sciences. Mashhad, Iran
*** Department of Chemistry, Georgetown University, USA
Received August 19, 2002
Abstract—Sodium 30-tungstopentaphosphate, the so-called Preyssler’s anion with a formula of
[NaP5W30O110]
14– (I) catalyzes the acetylation of alcohols (CnH2n + 1OH, n = 2, 3, 4, 5) with acetic acid. High
yield is obtained with I as pure acid or supported on silica. Both homogeneous and heterogeneous catalysts are
discussed and compared. H14[NaP5W30O110], abbreviated as H14-P5, under homogeneous conditions, as well as
supported on silica (heterogeneous conditions) is found to be an excellent catalyst. Our data indicate that, when
the ammonium salt of I is employed as the catalyst, the yield increases as the alcohol carbon-chain is increased.
This behavior is found to be quite general. The catalysts can be easily recovered and recycled with retention of
their initial structure and activity.
1
1. INTRODUCTION
the application of Preyssler’s anion has been very lim-
ited, with only a few demonstrations of catalytic activ-
ity [22]. In some cases there have been reports of no
catalytic capability [23]. One of the more recent reports
of reactions involving Preyssler’s anion is its use for
radioactive waste treatment [24].
Esters are commercially important. Sulfuric, hydro-
chloric, and hydrofluoric acids are the most commonly
used homogeneous catalysts in the esterification of car-
boxylic acids. However, these catalysts are toxic and
corrosive.
Recently, they have been replaced by other acid cat-
alysts such as sulfonic and heteropoly acids [1, 2]. In
homogeneous catalysis, p-toluene sulfonic acid is well
known. There are many heterogeneous catalysts: SO3H
resins, Nafion-H, the zirconium oxide–sulfate ion, the
titanium oxide–sulfate ion, silica–alumina, zeolite HY,
cation exchange resins, niobic acid, titanium alkoxide,
alumina, and zirconium alkoxide supported on silica
[3–6].
The interesting feature of this heteropolyanion (of
high surface area) is its hydrolytic stability, which is
very important in catalytic processes [25]. In continua-
tion of our research on the synthesis and application of
heteropoly anions in organic syntheses [26], we hereby
report the applicability of a novel and recyclable cata-
lyst (sodium30-tungstopentaphosphate) for efficient
esterification of acetic acid.
We have studied the pure and supported acid and
salts of Preyssler’s anion. They exhibit high selectivity
and good yield in the esterification reaction. Some
important features of this heteropolyanion are:
The synthesis of some of these catalysts is difficult,
and there is the fear of unfavorable side reactions such
as dehydration. Heteropoly compounds, on the other
hand, provide a framework of mixed-oxide catalysts of
high efficiency and favorable practical characteristics.
The catalytic capability of heteropoly compounds has
attracted much attention in the last two decades. They
are used in solution as well as in the solid state [7–9].
Many important industrial reactions are facilitated by
the use of these compounds [10–14].
(1) Its stability in the pH range from 0 to 12, thus
encompassing a wide range of acid and/or alcohol con-
centrations [25].
(2) The anion is not sensitive to water and the ester-
ification does not require water-free conditions [27].
Most catalytic research is focused on the Keggin
and Dawson structures of heteropolyanions such as
[PW12O40]3–, [PMo12O40]3–, [P2W18O62]6–, [P2Mo18O62]6–,
etc. [14, 15–21]. Although Keggin and Dawson type
polyoxoanions have widely been studied as catalysts,
(3) The anion is thermally stable, rendering high-
temperature reactions practical [27].
(4) Both pure and supported catalysts can be easily
recovered and recycled without degradation and loss of
activity.
1
This article was submitted by the authors in English.
0023-1584/03/4404-0524$25.00 © 2003 MAIK “Nauka /Interperiodica”

NOVEL CATALYTIC ACETYLATION OF ALCOHOLS
Table 1. Esterification in the liquid phase by NH4-P5
525
2. RESULTS AND DISCUSSION
2.1. Acetylation of Alcohols
Entry
Alcohol
Ethanol
% Yield
by (NH4)14[NaP5W30O110], NH4-P5
1*
2
7
25
63
68
In order to achieve heterogeneous catalysis and
avoid strong acid strength on the surface, the esterifica-
tion was carried out by NH4-P5. The anion has an
approximate D5h symmetry and consists of a cyclic
assembly of five PW6O22 units, each derived from the
Keggin anion, [PW12O40]3–, by the removal of two sets
of three corner-shared WO6 octahedra. A sodium ion is
located within the polyanion on the fivefold axis and
1.25 Å above the pseudomirror plane that contains the
five-phosphorus atoms (Fig. 1) [25].
In esterification of acetic acid by ethanol, propanol,
butanol, and pentanol, a molar ratio of (acetic acid/cat-
alyst) 467 was used. The yields of esters are shown in
Table 1. The results show that the reactivities of alco-
hols were increased as the carbon chain of the alcohol
grew longer. The yield of esters increased in this order:
ethylacetate < propylacetate < butylacetate < pentyl-
acetate.
Propanol
Butanol
Pentanol
3
4
–5
Note: Reaction conditions: Catalyst: 3.75 × 10 mol, acetic acid:
–2
1.75 × 10 mol, alcohol (29 ml), reflux for 4–6 h.
* Toluene (20 ml) was added, alcohol (7 ml).
Table 2. Esterification in the liquid phase by H14-P5/NH4-P5
and P-tolu/NH4-P5
% Product yield
Entry
Alcohol
Ethanol
H14-P5/NH4-P5 P-tolu/NH4-P5
1*
2
47
52
71
92
70
81
86
90
Propanol
Butanol
Pentanol
3
In other words, NH4-P5 is a better catalyst for ester-
ification of acetic acid by pentanol, whereas in the
esterification by ethanol, shows a relatively poor activ-
ity. This trend may be general with any catalyst. How-
ever, what is of interest to us is the fact that Preyssler’s
anion is an effective catalyst for each esterification
reaction studied.
4
Note: Reaction conditions: Catalyst: H -P /NH -P : 3.75 ×
14
5
–5
4
5
–5
10 mol and P-tolu/NH -P : 3.75 × 10 mol, acetic acid:
4
5
–2
1.75 × 10 mol, alcohol (29 ml), reflux for 4–6 h.
* Toluene (20 ml) was added, alcohol (7 ml).
Another effective way to generate a larger external
surface area is generating supported heteropoly acids
[28]. We examined H14-P5 in conjunction with NH4-P5
and p-toluene sulfonic acid, P-tolu (an inorganic and
organic catalyst). H14-P5 and P-tolu were placed in the
reaction system on an NH4–P5 support as the heteroge-
neous catalyst. The results are shown in Table 2.
Table 3. Comparison between NH4-P5, NH4-PW12, and
NH4-SiW12 (liquid phase)
% Product yield
Entry
Alcohol
NH4–P5
NH4-PW12 NH4-PW12
In order to compare several catalytic systems, we
selected (NH4)3[PW12O40], NH4-P, (NH4)4[SiW12O40],
NH4-Si, and NH4-P5. The reaction results are summa-
rized in Table 3. They show that the catalyst has a dra-
matic effect on the esterification yield. As expected, a
series of control experiments with different concentra-
tions of alcohols indicated that the yield of the esters
produced is decreased with decreasing alcohol concen-
tration.
1*
2
Ethanol
Propanol
Butanol
Pentanol
7
25
63
68
Trace
4
Trace
3
3
22
18
4
36
44
–5
Note: Reaction conditions: Catalyst: 3.75 × 10 mol, acetic acid:
–2
1.75 × 10 mol, alcohol (29 ml), reflux for 4–6 h.
* Toluene (20 ml) was added, alcohol (7 ml).
2.2. Acetylation of Alcohols by H14-P5
In esterification reactions, there is a strong demand
for new solid acids with favorable characteristics to
replace conventional liquid and solid catalysts such as
sulfuric acid, hydrochloric acid, and ion-exchange res-
ins [14]. Sulfuric acid poses serious environmental and
operational problems. Acidic ion-exchange resins such
as Amberlyst-15 are widely employed. They are useful
only at temperatures below 100°C due to their low ther-
mal stability. It should be noted that, in the reactions
where water may be present (as a product or otherwise),
criteria for activity and stability. To avoid these prob-
lems, we selected pure H14-P5. To enhance the acid
strength, solid H14-P5 catalyst was dehydrated under
vacuum at 150–300°C for 1–2 h [16].
The results of the liquid-phase esterification of ace-
tic acid with ethanol, propanol, butanol, and pentanol in
the presence of H14-P5 are listed in Table 4. The molar
there are only a few solid acid catalysts that meet the ratio of acetic acid to heteropolyanion was 467.
KINETICS AND CATALYSIS Vol. 44 No. 4 2003

526
ALIZADEH et al.
interact. This would lead to a diminished availability
due to this extra ionic interaction [29].
The results of the comparison between H14-P5,
H14-P5/NH4-P5, and H14-P5/SiO2 are shown in Fig. 2.
Although H14-P5/SiO2 and H14-P5/NH4-P5 are less active
than the homogeneous H14-P5, they can be easily sepa-
rated from the reaction mixture and reused (by filter-
ing).
2.4. Recycling of the Catalyst
One of the most desirable properties for a catalyst is
the ease of its recovery. We have found that Preyssler’s
anion can be reused several times without any apprecia-
ble loss of activity. In this study, at the termination of
each reaction, the catalyst was recovered. In the heter-
ogeneous case, the catalyst was simply filtered and
dried. In the homogeneous catalysis, the reaction mix-
ture was distilled and dried. IR spectra of the resulting
solids are shown in Fig. 3. They indicate that the cata-
lyst can be recovered without structural degradation.
The recovered solids were reused as catalyst for new
reactions. The recovery had only slightly decreased
their catalytic activity, pointing to the stability and
retention capability of this useful polyanion.
Fig. 1. Structure of Preyssler’s anion.
The results show that H14-P5 produces a higher ester
yield than does its ammonium salt. It seems clear that
the acid strength of the protons on H14-P5 is sufficient to
catalyze the esterification reaction and potentially all
protons are active sites. In other words, the acid
strength of the solid H14-P5 is comparable to that of liq-
uid H2SO4.
3. CONCLUSIONS
Efficient acetylation of ethanol, propanol, butanol,
and pentanol have been studied for the first time by an
inexpensive, recyclable, and easily prepared Preyssler’s
anion with high selectivity. Important features of this
catalyst are high thermal and hydrolytic stability
throughout a wide pH range. Thus, a wide range of cat-
alytic reactions can be effected without loss of structure
and activity.
Among the different forms of Preyssler’s anions
(H14-P5, NH4-P5, H14-P5/SiO2, and H14-P5/NH4-P5)
that were studied, H14-P5 was found to produce the
highest yield of esters. Comparison between H14-P5,
H14-P5/SiO2, and H14-P5/NH4-P5 (unsupported and sup-
ported polyacid) indicated that the activity was always
higher with the unsupported catalyst.
2.3. Supported Heteropoly Acids
versus Homogeneous Conditions
The reactivities of H14-P5/NH4-P5 and H14-P5/SiO2
(supported acid on H14-P5 and SiO2) have been studied.
In all cases, the supported polyacid is less active than
the unsupported one (Table 5). One plausible interpre-
tation of this observation is that, in H14-P5/SiO2, there
are polyanion-support interactions of an acid–base
nature. Some protons of the polyacid and some basic
sites of the support (for example hydroxyl groups) can
Table 4. Esterification in the liquid phase by H14-P5
Table 5. Esterification in the liquid phase by H14-P5/SiO2
Entry
Alcohol
Ethanol
% Yield
Entry
Alcohol
Ethanol
% Yield
1*
2
78
83
96
1*
2
66
80
86
Propanol
Butanol
Pentanol
Propanol
Butanol
3
3
4
99
4
Pentanol
90
–5
–2
–5
–2
Note: Catalyst: 3.75 × 10 mol, acetic acid: 1.75 × 10 mol, alco-
Note: Catalyst: 3.75 × 10 mol, acetic acid: 1.75 × 10 mol, alco-
hol (29 ml), reflux for 4–6 h.
hol (29 ml), reflux for 4–6 h.
* Toluene (20 ml) was added, alcohol (7 ml).
* Toluene (20 ml) was added, alcohol (7 ml).
KINETICS AND CATALYSIS Vol. 44 No. 4 2003

NOVEL CATALYTIC ACETYLATION OF ALCOHOLS
527
16
100
90
80
70
60
50
40
30
20
10
0
12
8
4
H14-P5/NH4-P5 H14-P5/SO2
H14-P5
Fig. 2. Comparison between H -P /NH -P , H -P /SiO ,
14
5
4
5
14
5
2
0
and H -P as catalyst in esterification reactions.
Etha-
14
5
nol;
propanol;
butanol;
pentanol.
1200
1000
800
600
ν, cm–1
The catalyst in both homogeneous and heteroge-
neous conditions can be recovered and reused without
loss of structure and activity. The reactivities of alco-
hols were increased as the carbon chain of the alcohols
grew longer.
By using the ammonium salt of Preyssler’s anion,
the yield of esters increased in this order: ethylacetate <
propylacetate < butylacetate < pentylacetate. Compari-
son of NH4-P5, NH4-PW12, and NH4-SiW12 showed that
the activity was always higher for NH4-P5.
The highly efficient esterification of acetic acid,
accomplished via a simple experimental setup and pro-
cedure, makes this method a useful addition to the
present methodologies. Furthermore, this method dem-
onstrates the applicability of Preyssler’s anion for some
reactions that require solid catalysts with strong acidic
strength, highly thermal stability and functionality over
a wide range of pH.
Fig. 3. IR spectrum of catalyst (Preyssler’s anion) at the end
of reaction.
a column (50 × 1 cm) of Dowex 50W × 8 in the H+
form and evaporation of the elute to dryness under
vacuum [25].
Supported heteropoly acid catalysts were prepared
by impregnating a support in the form of powder (SiO2)
with an aqueous solution of the heteropoly acid. After
stirring the heterogeneous solution–support mixture,
the solvent was evaporated. Samples were dried at 120–
140°C, and the catalysts were calcined at 300°C in a
furnace prior to use.
The Keggin-type heteropoly acids were of commer-
cially available purity. Their ammonium salts were pre-
pared by adding ammonium chloride powder to an
aqueous solution of the heteropoly acid. The white pre-
cipitate was filtered and dried under vacuum.
In a typical reaction, a catalyst (3.75 × 10–5 mol) was
added to a solution of 1-pentanol (29 ml) in acetic acid
(1.75 × 10–2 mol). The reaction mixture was stirred and
refluxed for 4–6 h. After filtering the catalyst, the prod-
ucts were analyzed by gas chromatography and the
yields were determined by the External Standard
Method (calibration curves were drawn with 5, 10, 15,
20, and 30 mmol of pure esters).
4. EXPERIMENTAL SECTION
Materials. Acetic acid, alcohols, and solvents were
commercially available, and their purity was monitored
by gas chromatography. The reaction products were
characterized by comparing their spectroscopic proper-
ties and retention times with those of authentic sam-
ples. All yields were determined by calibration curves
(External Standard Procedure).
Instruments. 1H-NMR spectra were recorded on a
FT-NMR Bruker 100 MHz Aspect 3000 spectrometer
(with tetramethylsilane as an internal standard).
IR spectra were obtained with a Buck 500 scientific
spectrometer (KBr pellets). GLC analysis was per-
formed on a Sigma 300 Perkin-Elmer gas chromato-
graph. Nitrogen was used as the carrier gas with FID
detector; the GC column used for analysis was OV-1.
REFERENCES
1. Schweglen, M.A., van Bekkum, H., and de Munck, N.A.,
Appl. Catal., 1991, vol. 74, no. 2, p. 191.
2. Patent 907.368 FR, 1990.
3. Olah, G.A., Keumi, T., and Meidar, D., Synthesis, 1978,
no. 12, p. 929.
4. Hino, M. and Arata, K., Chem. Lett., 1981, no. 12,
Catalysts preparation. The ammonium and potas-
sium salts of Preyssler’s anion were prepared according
to the literature [25]. The free acid was prepared by pas-
sage of a solution of the potassium salt in water through
p. 1671.
5. Santacesaria, E., Gelosa, D., Danise, P., and Carra, S.,
J. Catal., 1983, vol. 80, no. 2, p. 427.
KINETICS AND CATALYSIS Vol. 44 No. 4 2003

528
ALIZADEH et al.
6. Chen, Z., Iizuka, T., and Tanabe, K., Chem. Lett., 1984, 20. Sato, S., Furuta, H., Sodesawa, O., and Nozaki, F.,
no. 7, p. 1085.
J. Chem. Soc., Perkin Trans., 1993, no. 3, p. 385.
7. Okuhara, O., Mizuno, N., and Misono, M., Adv. Catal.,
21. Timofeeva, M. N. and Kozhevnikov, I.V., React. Kinet.
Catal. Lett., 1995, vol. 54, no. 2, p. 413.
1996, vol. 41, p. 113.
8. Misono, M., Catal. Lett., 1992, vol. 12, nos. 1–3, p. 963.
9. Misono, M., Catal. Rev. Sci. Eng., 1988, vol. 30, p. 339.
22. Harrup, M.K. and Hill, C.L., Inorg. Chem., 1994,
vol. 33, no. 24, p. 5448.
10. Ono, Y. and Thomas, J.M., In: Zamaraev, K.I., Perspec-
tives in Catalysis, London: Blackwell, 1992.
23. Fox, M.A., Cardona, R., and Gaillard, E., J. Am. Chem.
Soc., 1987, vol. 109, no. 21, p. 6347.
11. Kozhevnikov, I.V. and Matveev, K.I., Appl. Catal., 1983,
24. Kim, K.N., Dickman, M.H., Wassermann, K., Pope, M.O.,
Department of Chemistry, BOX 571227, Georgetown
University, Washington, DC 20057.
vol. 5, no. 2, p. 135.
12. Izumi, Y., Urabe, K., and Onaka, A., Zeolite, Clay, and
Heteropoly Acids in Organic Chemistry, Tokyo-VCH,
Weinheim: Kodansha, 1992.
25. Alizadeh, M.H., Harmalker, S.P., Jeannin, Y., and
Pope, M.T., J. Am. Chem. Soc., 1985, vol. 107, no. 9,
p. 2662.
13. Kozhevnikov, I.V., Catal. Rev.–Sci. Eng., 1995, vol. 37,
no. 2, p. 311.
26. Alizadeh, M.H., Razavi, H., Mohammadi Zonoz, F., and
14. Misono, M. and Noriji, N., Appl. Catal., 1990, vol. 64,
Mohammadi, M.R., Polyhedron., 2002 (in press).
nos. 1–2, p. 1.
15. Pope, M.T., Heteropoly and Isopoly Oxometalatest, Ber- 27. Alizadeh, M.H., Ph.D. Dissertation, Washengton: Geor-
lin: Springer, 1983.
getown University, 1985.
16. Kozhevnikov, I.V., Russ. Chem. Rev., 1987, vol. 56,
28. Nowinska, K., Fiedorow, R., and Adamiec, J., J. Chem.
Soc., Faraday Trans., 1991, vol. 87, no. 5, p. 749; Brück-
man, K., Haber, J., Lalik, E., and Serwicka, E.M., Catal.
Lett., 1988, vol. 1, nos. 1–3, p. 35; Serwicka, E.M.,
Brückman, K., Haber, J., et al., Appl. Catal., 1991,
vol. 73, no. 2, p. 153.
p. 811.
17. Hu, C., Hashimoto, M., Okuhara, T., and Misono, M.,
J. Catal., 1993, vol. 143, no. 2, p. 437.
18. Izumi, Y., Matsuo, E., and Urabe, K., J. Mol. Catal.,
1983,vol. 18, no. 3, p. 229.
19. Sato, S., Sakurai, C., Furuta, H., et al., J. Chem. Soc. 29. Lefebvre, F., J. Chem. Soc., Chem. Commun., 1992,
Chem. Commun., 1991, no. 19, p. 1327.
no. 10, p. 756.
KINETICS AND CATALYSIS Vol. 44 No. 4 2003