UDCaT-5: A novel and efficient solid superacid catalyst for Claisen rearrangement of substituted allyl phenyl ethers

Article abstract of DOI:10.1080/00397910601163810

The Claisen rearrangement of allyl phenyl ethers is a fundamental reaction in organic synthesis with a variety of applications in perfumes, flavors, pharmaceuticals, agrochemicals, polymers, fine chemicals, and intermediate industries. The development of environmentally benign processes using solid acid catalysts is becoming an area of growing interest. It was accomplished in an efficient, economical, environmentally friendly manner and is 100% selective toward alllyl phenols by employing UDCaT-5 as solid acid catalyst. Copyright Taylor & Francis Group, LLC.

Full text of DOI:10.1080/00397910601163810

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UDCaT‐5: A Novel and Efficient Solid
Superacid Catalyst for Claisen Rearrangement
of Substituted Allyl Phenyl Ethers
Ganapati D. Yadav a & Sharad V. Lande a
a Department of Chemical Engineering, University Institute of Chemical
Technology, University of Mumbai, Mumbai, India
Version of record first published: 24 Feb 2007.
To cite this article: Ganapati D. Yadav & Sharad V. Lande (2007): UDCaT‐5: A Novel and Efficient Solid
Superacid Catalyst for Claisen Rearrangement of Substituted Allyl Phenyl Ethers, Synthetic Communications:
An International Journal for Rapid Communication of Synthetic Organic Chemistry, 37:6, 941-946
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Synthetic Communicationsw, 37: 941–946, 2007
Copyright # Taylor & Francis Group, LLC
ISSN 0039-7911 print/1532-2432 online
DOI: 10.1080/00397910601163810
UDCaT-5: A Novel and Efficient Solid
Superacid Catalyst for Claisen
Rearrangement of Substituted Allyl Phenyl
Ethers
Ganapati D. Yadav and Sharad V. Lande
Department of Chemical Engineering, University Institute of Chemical
Technology, University of Mumbai, Mumbai, India
Abstract: The Claisen rearrangement of allyl phenyl ethers is a fundamental reaction
in organic synthesis with a variety of applications in perfumes, flavors, pharmaceuti-
cals, agrochemicals, polymers, fine chemicals, and intermediate industries. The devel-
opment of environmentally benign processes using solid acid catalysts is becoming an
area of growing interest. It was accomplished in an efficient, economical, environmen-
tally friendly manner and is 100% selective toward alllyl phenols by employing
UDCaT-5 as solid acid catalyst.
Keywords: Claisen rearrangement, green chemistry, substituted allyl phenyl ethers,
substituted allyl phenols, UDCaT-5
INTRODUCTION
The Claisen rearrangement reactions have become one of the most powerful
tools for carbon–carbon bond formation in organic synthesis.[1] They have
widespread synthetic applications because of the simplicity of the protocol
and the high degree of stereoselectivity and functional group reorganization.
The (3,3)-sigmatropic shift of allyl phenyl ethers in the Claisen rearrangement
provides convenient ways to o- and p-allyl phenols, which serve as precursors
to a variety of natural products including chromones and coumarones, which
Received in India August 11, 2006
Address correspondence to Ganapati D. Yadav, Department of Chemical Engineer-
ing, University Institute of Chemical Technology, University of Mumbai, Mumbai 400
019, India. E-mail: gdyadav@yahoo.com or gdyadav@udct.org
941

942
G. D. Yadav and S. V. Lande
are used in pharmaceuticals and the intermediate industry.[2] Worldwide
efforts are under way to synthesize new catalysts with unique acidic charac-
ters.[3] Only a limited amount of information is available about solid acids
in Claisen rearrangement, including Al-MCM-41,[4] H-FAU, H-MOR,
b-zeolite,[5] mesoporous silica,[6] and bentonite clay.[7]
A variety of methods have been used to synthesize sulfated zirconia, which
differ mainly in the type of precursors, precipitating agents, sulfation
procedure, and calcination temperature. High sulfur content in the form of
sulfate ions is introduced with H2SO4 as a sulfating agent in comparison
with (NH4)2SO4, (NH4)2S2O3, (NH4)2S, SO3, SO2, H2S, and so forth. Yadav
and Murkute reported for the first time a preparation of sulfated zirconia
with a high sulfur content (9%) that possesses better activity and also
preserves the tetragonal phase by using chlorosulfonic acid as a new source
for the sulfate ion. This new catalyst is designated as UDCaT-5.[8] The abbrevi-
ation UDCaT-5 is used to denote the series of solid acid catalysts developed in
our laboratory, which was formerly known as the University Department of
Chemical Technology (UDCT). This new material is an excellent catalyst for
bulkier molecules and could be used to develop new, greener routes.
The current article is focused on the novelties of UDCaT-5 in the Claisen
rearrangement of substituted allyl phenyl ethers (Scheme 1).
Unlike the thermal Claisen rearrangement, which requires very high
temperatures and results in loss of selectivity,[8] the current process is
simpler, requires mild conditions, and is catalyzed by solid superacid.
EXPERIMENTAL
The experimental setup consisted of a 3-cm-i.d., fully baffled, mechanically
agitated glass reactor of 50 ml capacity, equipped with four baffles and a
six-bladed turbine impeller. The entire reactor assembly was immersed in a
thermostatic water bath, which was maintained at a desired temperature
Scheme 1.

UDCaT-5: Solid Superacid Catalyst
943
with an accuracy of +18C. A typical reaction mixture consisted of 0.01 mol of
allyl phenyl ethers in 10 cm3 of chlorobenzene as a solvent with a catalyst
loading of 0.1 g/cm3 at an agitation speed of 1000 rpm at 908C. The
analysis was done on a gas chromatograph (Chemito-8610) equipped with a
flame ionisation detector. A long stainless steel column (3.25 mm  2 m)
packed with 10% SE-30 supported on chromosorb-WHP was used for the
analysis. The injector and detector were kept at 3008C. The oven temperature
was programmed from 1308C (0.5 min) up to 2808C with a ramp rate of
108C min21. Synthetic mixtures were used to calibrate and quantify the data.
For the isolation of the product, the reaction mixture was filtered to
remove the catalyst UDCaT-5 for further reuse. The clear solution containing
chlorobenzene and substituted phenol on vacuum distillation resulted in a pure
100% selective product. All the isolated products were also confirmed with
GC-MS (Perkin Elemer Clarius model 500) using a BPX-1 capillary
column (250 mm  30 m) packed with methyl polysiloxane. All the
compounds are reported and are shown in Table 1.
A general mechanism for the UDCaT-5 Claisen rearrangement is
proposed in Scheme 2 as follows. The general catalytic site is given by L.
According to this mechanism, the O of the ether, having a lone pair of
electrons, is chemisorbed on the acidic site, and then the allyl group
migrates to the most favorable para position through intramolecular
rearrangement through I–IV. The product is desorbed, thereby freeing the
site for next catalytic cycle.
UDCaT-5 is completely characterized by FT-IR, XRD, BET surface area,
ammonia–TPD, and elemental analysis, and the details were recently
published.[8] UDCaT-5 was prepared by hydrolysis of aqueous zirconium oxy-
.
chloride (ZrOCl2 8H2O) with aqueous ammonia at room temperature at a pH
of 9–10. The precipitated zirconium hydroxide was washed with deionized
water until a neutral filtrate was obtained; the absence of chlorine ion was
detected by phenolphthalein and AgNO3 tests. A material balance on Cl
before and after precipitation and washing shows no retention on the solid.
Zirconium hydroxide was dried in an oven for 24 h at 1008C and was
crushed and sieved through 100 mesh size.
A known amount of Zr(OH)4 was immersed using 15 cm3/g of 0.5 M
soltion of chlorosulfonic acid in ethylene dichloride for 5 min in the solution
under dry conditions without allowing moisture absorption. It was then kept
in an oven, and heating was started to evaporate the solvent to 1208C after
about 30 min. The catalyst was kept in the oven at 1208C for 24 h and then
calcined at 6508C for 3 h to get the active catalyst named UDCaT-5.
The reusability of UDCaT-5 was tested by employing it four times. After
each run, the catalyst was washed thoroughly with chlorobenzene and dried in
an oven at 1208C for 2 h. The catalyst was filtered, dried, and weighed after
each run, and there was up to a 5–10% loss of catalyst during filtration due
to attrition. No additional catalyst was added. Thus, the catalyst was not deac-
tivated, and there is only a marginal decrease in the yield.

944
G. D. Yadav and S. V. Lande
Table 1. Claisen rearrangement of substituted allyl phenyl ethers using UDCaT-5
Time
(min)
Yield
(%)
Entry
1
Reactant
Product
90
92.6
2
3
60
95.5
92.4
60
4
5
90
90
87.6
90.1
6
7
60
45
94.6
93.2
(continued)

UDCaT-5: Solid Superacid Catalyst
945
Table 1. Continued
Time
(min)
Yield
(%)
Entry
8
Reactant
Product
60
60
60
88.6
9
92.46
85.45
10
Reaction condition: Substituted allyl phenyl ethers, 0.01 mol; chlorobenzene (solvent),
10 cm3; UDCaT-5, 0.1 g/cm3; temperature, 908C; speed of agitation, 1000 rpm.
We have studied the effect of different solvents on the rate of the reaction.
Chlorobenzene was found to be the best solvent. In the case of toluene and
mixed xylenes, the alkylation reaction of the substrate with the solvent
takes place by migration of allyl carbonium ions from allyl phenyl ether to
Scheme 2. L ¼ active site.

946
G. D. Yadav and S. V. Lande
the activated aromatic rings of the solvent to form allylated toluene and
xylenes. This is due to high acidity of UDCaT-5, and it results in a decrease
in selectivity of the desired product. Chlorobenzene was found to be the
best solvent, without any by-products. Both the reagent and product are
solids and hence use of solvent was necessary.
The novel solid superacid UDCaT-5 was found to be 100% selective in
the Claisen rearrangement of several substituted allyl phenyl ethers. The
catalyst is environmentally benign and reusable. The process is 100% atom
economical and fits green chemistry protocols.
ACKNOWLEDGMENTS
G. D. Yadav acknowledges Darbari Seth Endowment for supporting the chair
and a research grant from the Council of Scientific and Industrial Research-
New Millenium Indian Technology Leadership Initiative (CSIR-NMITLI).
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