Aluminium dodecatungstophosphate (AlPW12O40) as a highly efficient catalyst for the selective acetylation of -OH, -SH and -NH2 functional groups in the absence of solvent at room temperature

Article abstract of DOI:10.1039/b300775h

AlPW₁₂O₄₀ was found to be an effective catalyst for the selective acetylation of alcohols, thiols, and amines in the absence of solvent at room temperature.

Full text of DOI:10.1039/b300775h

Aluminium dodecatungstophosphate (AlPW12O40) as a highly efficient
catalyst for the selective acetylation of –OH, –SH and –NH2 functional
groups in the absence of solvent at room temperature
Habib Firouzabadi,* Nasser Iranpoor,* Farhad Nowrouzi and Kamal Amani
Department of chemistry, Shiraz University, Shiraz 71454, Iran. E-mail: Firouzabadi@ chem.susc.ac.ir
Iranpoor@ chem.susc.ac.ir; Fax: +98-711-2280926; Tel: +98-711-2284822
Received (in Cambridge, UK) 21st January 2003, Accepted 11th February 2003
First published as an Advance Article on the web 25th February 2003
AlPW12O40 was found to be an effective catalyst for the
selective acetylation of alcohols, thiols, and amines in the
absence of solvent at room temperature.
yields in short reaction times by 3, 4.5, and 6 mmol of acetic
anhydride for acetylation of all hydroxy groups present in the
molecules respectively (Table 1, entries 24–26). We observed
that -(+)-ascorbic acid requires a higher molar ratio of acetic
L
Heteropoly acids (HPAs) have been extensively studied as acid
and oxidation catalysts for many reactions and found industrial
application in several processes.1 HPAs are promising solid
acids to replace environmentally harmful liquid acid catalysts
such as H2SO4.1c–f The Keggin type H3PW12O40 is more active
than conventional solid acids such as SiO2–Al2O3, H3PO4–
SiO2, and zeolites.1c,f Solid acid catalysts are harmless to the
environment with respect to corrosiveness, safety, quantity of
waste, and separability.
Protection of alcohols, amines, and thiols by acetyl chloride
or acetic anhydride is an important transformation reaction in
organic synthesis.2 For this purpose, acetic anhydride or acetyl
chloride in the presence of stoichiometric amounts of amine
bases, such as tertiary amines, 4-(dimethylamino)pyridine
(DMAP) and tributylphosphine have been used.3 Protic or
Lewis acids have also been used to catalyze acetylation of
alcohols.4
anhydride (8 mmol) in order to acetylate all four hydroxy
groups of the molecule (Table 1, entry 27). We found that this
method was also suitable for the acetylation of amines and thiols
and they were converted to their corresponding acetamides and
thioacetates respectively in short reaction times in excellent
yields (Table 1, entries 28–35).
In order to show the scope and limitation of this catalytic
system, we have studied several competitive reactions under
similar reaction conditions. The results of this study are shown
in Table 2.
In a typical procedure, a mixture of benzyl alcohol (5 mmol,
0.54 g), acetic anhydride (7.5 mmol, 0.7 ml) and AlPW12O40
(0.005 mmol, 0.015 g) was stirred at room temperature for 4 min
(monitored by TLC and GC). The reaction mixture was diluted
Table 1 Acetylation of alcohols, amines and thiols using Ac2O in the
presence of AlPW12O40 as a catalysta
Preparation
of
aluminium
dodecatungstophosphate
(AlPW12O40) was reported in 1982 by Ono by the reaction of
aluminium nitrate and dodecatungstophosphoric acid in a
quantitative yield. We have also prepared this compound by the
addition of aluminium nitrate or by aluminium carbonate to the
aqueous solution of tungstophosphoric acid which on complete
evaporation of water gave the desired compound as a white
powder in a quantitative yield. AlPW12O40 prepared by both
protocols gave satisfactory analytical results within the range of
the experimental errors. This salt is a water stable and a non-
hygroscopic compound. To the best of our knowledge there is a
report available in the literature, which deals with the
conversion of methanol into hydrocarbons using this compound
as a catalyst.5 In continuation of our interest to study the
catalytic activities of heteropolyacids,6 now in this communica-
tion, we describe the use of a catalytic amount (0.1 mol%) of
AlPW12O40 as an effective catalyst for the acetylation of
alcohols, thiols and amines in the presence of acetic anhydride
at room temperature (Scheme 1).
Acetylation of benzylic, primary, secondary, hindered terti-
ary alcohols and phenols were proceeded efficiently in high
isolated yields using 1.5 mmol of acetic anhydride (Table 1,
entries 1–20). Sensitive alcohols towards acidic conditions were
also acetylated under similar reaction conditions in high yields
in short reaction times without giving by-products (Table 1,
entries 21–23). Hydroquinone, glycerol, and pentaerithrotriol
were also converted to their corresponding acetates in excellent
Entry
Substrate
Time/min
Yield (%)b
1
2
3
4
5
6
7
8
9
PhCH2OH
4
1
5
8
8
94
93
94
88
94
91
96
95
96
89
87
92
94
92
91
90
88
92
95
92
91
93
92
88
89
94
93
96
98
89
91
92
96
91
89
4-OMeC6H4CH2OH
PhCH(OH)CH3
PhCH(OH)Ph
Octan-1-ol
1,4-Butandiol
Norborneol
(2)-Menthol
Octan-2-ol
Benzoin
Cholesterol
Adamantanol
tert-Butyl alcohol
Terpineol
(Ph)2C(OH)CH3
PhOH
4-NO2C6H4OH
4-ClC6H4OH
2,6-Dicholorophenol
2-Naphthol
3-Methyl-2-buten-1-ol
1-Octen-3-ol
3-Hexyne- 2,5-diol
Hydroquinone
Glycerol
5
12
11
18
95
22
100
120
140
200
3
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
12
4
3
15
12
5
15
12
37
35
120
1
Pentaerithrotriol
L
-(+)-Ascorbic acid
PhNH2
2-Me-C6H4NH2
4-NO2-C6H4NH2
PhNH(Me)
Cyclohexylamine
NH(CH2Ph)2
PhSH
1
12
10
3
10
2
PhCH2SH
3
a All products were identified by their 1H NMR spectra. b Isolated yield.
Scheme 1
764
CHEM. COMMUN., 2003, 764–765
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Table 2 Competitive acetylation reactions of alcohols and amines using
Ac2O in the presence of AlPW12O40 at room temperature under solvent-free
conditionsa
In conclusion, in this study, we have introduced aluminium
dodecatungstophosphate (AlPW12O40) as a new highly effec-
tive non-hygroscopic, heterogeneous, non-corrosive and envir-
onmentally benign catalyst for the efficient conversion of a
variety of alcohols, phenols, amines, and thiols to their acetic
esters, acetamides, and thioacetates in the absence of solvent.
Extensive studies upon applications of this catalyst in organic
reactions such as Friedel–Crafts, Fries and Beckmann re-
arrangements, Diels–Alder, Michael and aldol condensation
reactions are underway in our laboratories.
Notes and references
1 (a) T. Okuhara, N. Mizuno and M. Misono, Appl. Catal., A, 2001, 22, 63;
(b) M. Misono, Chem. Commun., 2001, 1141; (c) I. V. Kozhevnikov,
Chem. Rev., 1998, 98, 171; (d) Y. Izumi, K. Urabeand and M. Onaka
Zeolite, Clay and Heteropoly Acids in Organic Synthesis, Kodansha/
VCH, Tokyo, 1992; (e) I. V. Kozhevnikov, Catal. Rev. Sci. Eng., 1995,
37, 311; (f) T. Okuhara, N. Mizuno and M. Misono, Adv. Catal., 1996, 41,
113; (g) M. Misono and N. Nojiri, Appl. Catal., 1990, 64, 641; (h) K.
Sano, H. Uchida and S. Wakabayashi, Catal. Surv. Jpn., 1999, 3, 55.
2 (a) T. W. Greene and P. G. M. Wuts, Protective Groups in Organic
Synthesis, Wiley, New York, 1999, 3rd ed; (b) J. R. Hanson, Protecting
Groups in Organic Synthesis, Blackwell Science, Inc., Malden, MA,
1999, 1st edn.
3 (a) W. Steglich and G. Höfle, Angew. Chem., Int. Ed. Engl., 1969, 8, 981;
(b) Review: G. Höfle, W. Steglich and H. Vorbrüggen, Angew. Chem.,
Int. Ed. Engl., 1978, 17, 569.
4 (a) Cu(OTf)2: P. Saravanan and V. K. Singh, Tetrahedron Lett., 1999, 40,
2611; (b) In(OTf)3: K. K. Chauhan, C. G. Frost, L. Love and D. Waite,
Synlett, 1999, 1743; (c) Sc(OTf)3: K. Ishihara, M. Kubota, H. Kurihara
and H. Yamamoto, J. Org. Chem., 1996, 61, 4560; (d) A. Orita, C.
Tanahashi, A. Kakuda and J. Otera, Angew. Chem., Int. Ed., 2000, 39,
2877; (e) M. D. Carrigan, D. A. Freiberg, R. C. Smith, H. M. Zerth and
R. S. Mohan, Synthesis, 2001, 2091 and references therein.
5 (a) T. Baba, J. Sakai and Y. Ono, Bull. Chem. Soc. Jpn, 1982, 55, 2657;
(b) T. Baba, H. Watanabe and Y. Ono, J. Phys. Chem., 1983, 87,
2406.
6 (a) H. Firouzabadi, N. Iranpoor and K. Amani, Green Chem., 2000, 3,
131; (b) H. Firouzabadi, N. Iranpoor and K. Amani, Synthesis, 2002, 59;
(c) H. Firouzabadi, N. Iranpoor and K. Amani, J. Mol. Catal., 2002, in the
press; (d) H. Firouzabadi, N. Iranpoor, K. Amani and F. Nowrouzi, J.
Chem. Soc., Perkin Trans. 1, 2002, 2601; (e) H. Firouzabadi, N. Iranpoor
and K. Amani, Synthesis, 2003, , 408.
a The percentage of the products in the reaction mixture was determined by
GC analysis. b Products were separated by plate in ethylacetate–n-
hexane(9+1).
7 Spectral data for protected ascorbic acid: 1H NMR (250 MHz, CDCl3): d
with n-hexane (10 ml) and filtered. The filter cake was also
washed with another portion of n-hexane (10 ml). The filtrates
were combined together and the resulting organic phase was
washed with an aqueous solution of NaHCO3 (20%, 23 10 ml).
The organic layer was separated, dried over anhydrous Na2SO4
and filtered. Evaporation of the solvent gave the desired pure
product without further purification.7
=
6.82(d,1H), 5.6(d, 1H), 3.84–4.16(m,2H), 2(s,3H),1.83(s,3H),
1.79(s,3H), 1.78(s,3H). 13CNMR (250 MHz, CDCl3): d = 175.4, 172.2,
171.3, 170.6, 145, 75, 69, 64, 21, 20.8, 20.2, 18. IR (KBr): 1800, 1751,
1741, 1373, 1226, 1161, 1056. 3a(Table 2): 1H NMR (250 MHz,
CDCl3):
d
=
7–7.4(m,5H), 5.3(s,1H), 3.65(m,2H), 3.75(m,2H),
1.95(s,3H). 13CNMR (250 MHz, CDCl3): d = 20.84, 55, 60, 125, 127,
129, 143, 172. IR (KBr): 3430, 1650. 1595, 1496, 1409, 1330, 1074.
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