Eco-friendly WO3-ZrO2 solid acid catalyst for acetylation of alcohols and phenols

Article abstract of DOI:10.1081/SCC-120006465

A mild and efficient tungsten promoted zirconia solid acid catalyst has been described for direct acylation of various alcohols and phenols with acetic anhydride into their acetates.

Full text of DOI:10.1081/SCC-120006465

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ECO-FRIENDLY WO3–ZrO2 SOLID ACID CATALYST FOR
ACETYLATION OF ALCOHOLS AND PHENOLS
Benjaram M. Reddy a & Pavani M. Sreekanth a
a Inorganic and Physical Chemistry Division, Indian Institute of Chemical Technology,
Hyderabad, 500 007, India
Published online: 18 Oct 2011.
To cite this article: Benjaram M. Reddy & Pavani M. Sreekanth (2002): ECO-FRIENDLY WO3–ZrO2 SOLID ACID CATALYST FOR
ACETYLATION OF ALCOHOLS AND PHENOLS, Synthetic Communications: An International Journal for Rapid Communication of
Synthetic Organic Chemistry, 32:18, 2815-2819
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SYNTHETIC COMMUNICATIONS
Vol. 32, No. 18, pp. 2815–2819, 2002
ECO-FRIENDLY WO3–ZrO2 SOLID ACID
CATALYST FOR ACETYLATION OF
ALCOHOLS AND PHENOLS
*
Benjaram M. Reddy and Pavani M. Sreekanth
Inorganic and Physical Chemistry Division,
Indian Institute of Chemical Technology,
Hyderabad-500 007, India
ABSTRACT
Amild and efficient tungsten promoted zirconia solid acid
catalyst has been described for direct acylation of various
alcohols and phenols with acetic anhydride into their acetates.
Key Words: Acetylation; Alcohol; Acetic anhydride;
Superacid
Acylation is a fundamental process in organic synthesis. This reaction
is frequently used for derivatization and characterization of alcohols and
also for further transformations.[1] The direct acylation of alcohols can be
brought about with mineral acids, sulfonic acids, and nucleofiles as well as
with bases.[2,3] However, the reaction is reversible and typically large excess
of either of the reactants and elevated conditions are required. The use of
strong mineral acids leads to several disadvantages such as hazardous
*Corresponding author. Fax: þ91-40-717 3387; E-mail: bmreddy@iict.ap.nic.in
2815
DOI: 10.1081/SCC-120006465
Copyright & 2002 by Marcel Dekker, Inc.
0039-7911 (Print); 1532-2432 (Online)
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2816
REDDY AND SREEKANTH
environmental problems due to the generation of acidic waste streams,
recovery of the catalyst and disposal of the used catalyst.
In order to circumvent the problem of equilibria, typically acylation of
alcohols is performed with activated acyl groups such as anhydrides or acid
chlorides with a stoichiometric quantity of amine base in the presence of
basic catalysts such as 4-dimethylaminopyridine (DMAP) or 4-pyrrolidino-
pyridine and phosphenes like tri-butyl phosphene (Bu3P).[3,4] The acylation
of alcohols can also be brought about by the action of Lewis acidic reagents
in conjunction with carboxylic acids, but the Lewis acid is destroyed in the
work-up procedure.[5]
There have been several efforts to introduce solid reagents or
reagents supported on solid phase for easier work-ups which include mon-
tmorillonite K-10 (Ref. [6]) and KSF,[7] silica gel supported NaHSO4,[8]
Zeolite HSZ-360,[9] silica gel supported TaCl5,[10] Nafion-H,[11] Sc(III) or
La(III) triflates.[12] However, most of these catalysts show several disad-
vantages such as a rapid catalyst deactivation, production of wasteful
products, low product yields, and severe reaction conditions. For example,
the zeolite and clay based catalysts are highly susceptible to deactivation
due to pore blocking and hydration. Application of cationic
exchange resins provide better yields, however, most of the cationic
exchange resins are not resistant enough to high temperatures. In view
of the environmental concern, there is a global effort to replace the
conventional catalysts by new solid acids, which can be easily separable
from the products, less toxic, and reusable. In this communication, we
report an efficient WO3–ZrO2 solid acid catalyst for the direct
acylation of various alcohols and phenols with acetic anhydride into
their acetates.
Solid superacids have been found increasing utility in selective
organic transformations.[13] In particular, the importance of sulfated
ZrO2 as a solid superacid for various catalytic applications has been iden-
tified recently.[14] It catalyses alkane isomerization near room
temperature.[15] However, the sulfated ZrO2 catalysts deactivate rapidly
during catalytic runs and tend to leach H2S and SOx during H2 and air
treatments, respectively, and H2SO4 in the presence of H2O. These pro-
cesses cause irreversible loss of catalytic activity and also downstream
containment and corrosion issues. Very recent investigations reveal that
MoO3 or WO3 doped ZrO2 is an alternative catalyst in reactions requiring
stronger acid sites.[16,17] The major advantage associated with these
catalysts is that they do not undergo deactivation due to loss of the
dopents. Although, solid acids of this kind have been attempted in the
petrochemical industries, their application in synthetic organic chemistry
remains unexplored.

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ECO-FRIENDLY WO3–ZrO2 SOLID ACID CATALYST
PREPARATION OF THE CATALYST
2817
To make the WO3–ZrO2 solid acid catalyst, zirconium oxyhydroxide
(ZrOx(OH)4-2x) was prepared from zirconium oxychloride by hydrolysis
with dilute ammonia. In a typical experiment the requisite quantity of
ZrOCl2 Á 8H2O (Aldrich, GR grade) was dissolved (pH 2) in doubly distilled
water and was precipitated with dilute NH4OH solution by adding drop
wise from a burette until the pH of the solution reached 10. The obtained
precipitate was washed several times until free from chloride ions and dried
at 393 K for 48 h. To make the 9 wt.% WO3/ZrO2 catalyst, the rquisite
quantity of ammonium tungstate (J.T. Baker, England; GR grade) was
dissolved in excess water and to which the powdered zirconium oxyhydrox-
ide was added. The excess water was evaporated on a water-bath with
vigorous stirring. The obtained sample was then oven dried at 383 K for
12 h and calcined at 1073 K for 4 h in air atmosphere. The X-ray powder
diffraction analysis of the sample revealed the presence of more tetragonal
zirconia which is known to be responsible for the observed high acidity and
activity of these catalysts.[18,19]
GENERAL PROCEDURE FOR ACYLATION REACTIONS
In a typical reaction procedure a mixture of 1 : 2 molar amounts of
alcohols and acetic anhydride along with the catalyst (0.4 g) were taken into
a round bottom flask and refluxed for various times as mentioned in Table 1.
After completion of the reaction the catalyst was filtered off and the wet
catalyst was used for recycling. No appreciable change in the activity was
noticed. The product was recovered from the filtrate. An aqueous NaHCO3
solution was added to remove the excess acetic anhydride. A20 mL of
CH2Cl2 solution was also added to separate aqueous and organic layers.
The organic layer was decanted into another flask by using separating
funnel and concentrated. The NMR and mass spectrometry techniques
were utilized along with their melting/boiling points for analyzing the prod-
ucts. In the controlled experiments, no reaction was observed in the absence
of WO3–ZrO2 catalyst in the reaction mixture. These results are summarized
in Table 1. The results show that the WO3–ZrO2 catalyst will be ideally
suited for the acylation of alcohols and phenols. Along with O-acetylation,
amines also underwent N-acetylation to give N-acetylated products
(Entries 7 and 8). In conclusion, the use of WO3–ZrO2 solid acid catalyst
for the direct acetylation of alcohols using acetic anhydride as the acetylat-
ing source is an environmentally benign and atom economic process.

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2818
REDDY AND SREEKANTH
Table 1. Acetylation of Alcohols with (Ac)2O Catalyzed by
WO3/ZrO2 Catalyst
Entry
Alcohol
Acetate
Timea/Yieldb
1
2
CH3–OH
CH3–OAc
4/95
2/97
3
4
5
3/92
3/90
3/92
6
7
8
3/89
1/95
1/98
b
aTime in hours; NMR yield.

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©2002 Marcel Dekker, Inc. All rights reserved. This material may not be used or reproduced in any form without the express written permission of Marcel Dekker, Inc.
ECO-FRIENDLY WO3–ZrO2 SOLID ACID CATALYST
2819
The main advantage of this catalyst is easy operation and simplicity in the
work-up, which involves mere filtration of the catalyst and its reusability.
ACKNOWLEDGMENTS
Thanks are due to DST, New Delhi for financial support under SERC
Scheme (SP/S1/H-20/98).
REFERENCES
1. (a) Greene, T.W.; Wuts, P.G.M. Protective Groups in Organic
Synthesis, 2nd Ed.; Wiley: New York, 1991; (b) Kocienski, P.J.
Protecting Groups; Enders, D., Noyori, R., Trost, B.M., Eds.; Thieme:
Stuttgart, 1994; (c) Mulzer, J. Comprehensive Organic Synthesis; Trost,
B.M., Fleming, I., Eds.; Pergmon Press: Oxford, 1991; Vol. 6, p. 323.
2. Trost, B.M. Angew. Chem. Int. Ed. Engl. 1995, 34, 259.
3. Vedejs, E.; Diver, S.T. J. Am. Chem. Soc. 1993, 115, 3358.
4. (a) Scriven, E.F.V. Chem. Soc. Rev. 1983, 12, 129; (b) Hofle, G.;
¨
Steglich, V.; Vorbruggen, H. Angew. Chem. Int. Ed. Engl. 1978, 17, 569.
¨
5. (a) Izumi, J.; Shiina, I.; Mukaiyama, T. Chem. Lett. 1995, 141;
(b) Shiina, I.; Mukaiyama, T. Chem. Lett. 1994, 677.
6. Li, A.-X.; Li, T.-S.; Ding, T.-H. Chem. Commun. 1997, 1389.
7. Bhaskar, P.M.; Loganathan, D. Tetrahedron Lett. 1998, 39, 2215.
8. Breton, G.W. J. Org. Chem. 1997, 62, 8952.
9. Ballini, R.; Bosica, G.; Carloni, S.; Ciaralli, L.; Maggi, R.; Sartori, G.
Tetrahedron Lett. 1998, 39, 6049.
10. Chandrasekahar, S.; Ramachander, T.; Takhi, M. Tetrahedron Lett.
1998, 39, 3263.
11. Kumareswaran, R.; Pachamuthu, K.; Vankar, Y.D. Synlett 2000,
11, 1652.
12. Barrett, A.G.M.; Braddock, D.C. Chem. Commun. 1997, 351.
13. Olah, G.A.; Takashi, K.; David, M. Synthesis 1978, 929.
14. Arata, K. Adv. Catal. 1990, 37, 165 and references therein.
15. Hino, M.; Arata, K. J. Chem. Soc. Chem. Commun. 1980, 851.
16. Hino, M.; Arata, K. Appl. Catal. A: General 1998, 169, 151.
17. Reddy, B.M.; Reddy, V.R. Synth. Commun. 1999, 29, 2789.
18. Scheithauer,M.;Grasselli,R.K.;Knozinger,H.Langmuir1998,14,3019.
¨
19. Reddy, B.M.; Reddy, V.R. J. Mater. Sci. Lett. 2000, 19, 763.
Received in the UK July 16, 2001