Ecofriendly Claisen rearrangement of allyl-4-tert-butylphenyl ether using heteropolyacid supported on hexagonal mesoporous silica

Article abstract of DOI:10.1021/op050062f

The Claisen rearrangement of allyl phenyl ethers is a valuable reaction in organic synthesis having a variety of applications in perfumes, flavours, pharmaceuticals, and intermediate industries. The replacement of traditional environmentally threatening h

Full text of DOI:10.1021/op050062f

Organic Process Research & Development 2005, 9, 547−554
Full Papers
Ecofriendly Claisen Rearrangement of Allyl-4-tert-butylphenyl Ether Using
Heteropolyacid Supported on Hexagonal Mesoporous Silica
Ganapati D. Yadav* and Sharad V. Lande
Department of Chemical Engineering, UniVersity Institute of Chemical Technology, UniVersity of Mumbai, Matunga,
Mumbai 400 019, India
Abstract:
rearrangement such as Lewis acids (BCl
SnCl , ZnCl , TiCl , AgBF , etc.), Bronsted acids (tri-
fluroacetic acid, H SO , etc.), bases, and transition metal
3 3 3 3
, BF , BBr , AlCl ,
The Claisen rearrangement of allyl phenyl ethers is a valuable
reaction in organic synthesis having a variety of applications
in perfumes, flavours, pharmaceuticals, and intermediate
industries. The replacement of traditional environmentally
threatening homogeneous acid catalysts in organic processes
with solid acid catalysts is an important green chemistry goal.
The Claisen rearrangement of allyl-4-tert-butylphenyl ether to
4
2
4
4
2
4
5
complexes (Rh (I) and Pt(0)). These catalysts are polluting
and lead to several byproduct formations. The Claisen
rearrangement of allyl-4-tert-butylphenyl ether to 2-allyl-4-
tert-butylphenol is an industrially important reaction. 2-Allyl-
4-tert-butylphenol is used as antioxidant, cross linking agent
in polymers, reactive diluents in UV-curable coating com-
position, and intermediate in the preparation of drugs for
the treatment of heart ischemia. It is also used in perfumes,
flavors, and particularly the formulation of products such as
soaps, detergents, air fresheners, as well as in cosmetic
materials. Only a limited amount of information is available
in solid acids on Claisen rearrangement including Al-MCM-
2-allyl-4-tert-butylphenol with 100% selectivity was accom-
plished in an efficient, economically and environmentally
friendly route by employing the solid acid catalysts such as acid-
treated clays, sulphated zirconia, 20% (w/w) dodecatungsto-
phosphoric acid (DTP)/hexagonal mesoporous silica (HMS).
2
0% (w/w) DTP/HMS was found to be superior, reusable
without loss of activity, and 100% selective towards 2-allyl-4-
tert-butylphenol. Based on the experimental data a suitable
mathematical model is proposed to describe the reaction
kinetics. The results are novel.
6
7,8
9
10
41, H-FAU and H-MOR, â-zeolite, mesoporous silica,
1
1
and bentonite, which have been used for allyl phenyl ether
as the reactant.
The field of mesoporous materials has benefited tremen-
dously from the research in supramolecular-templated me-
soporous materials and will continue to grow, especially with
the development of materials of new compositions and
surface modification. Introduction of hexagonally ordered
mesoporous silicates such as FSM-16, HMS (hexagonal
1
. Introduction
The Claisen rearrangement reactions have become one
of the most powerful tools for carbon-carbon bond forma-
tion in organic synthesis. They have widespread synthetic
1
12-15
mesoporous silica) MCM-41,
has resulted in a worldwide
applications due to the simplicity of protocol and high degree
of stereoselectivity and functional group reorganization. The
aliphatic Claisen rearrangement is a [3,3]-sigmatropic re-
arrangement in which an allyl vinyl ether is converted
thermally to an unsaturated carbonyl compound. The aro-
matic Claisen rearrangement is accompanied by a rearoma-
tization, and these are thermally initiated reactions. The initial
(
2) Wipf, P.; Trost, B. M. ComprehensiVe Organic Synthesis; Pergamon
Press: Oxford, 1991; Vol. 5, p 827.
(3) Martin, R. Org. Prep. Proced. Int. 1992, 24, 369.
(4) Cagniant, D. AdV. Heterocycl. Chem. 1975, 18, 358.
(5) Lutz, R. P. Chem. ReV. 1984, 84, 205.
(6) Mathew, N. T.; Khaire, S.; Mayadevi, S.; Jha, R.; Sivasanker, S. J. Catal.
005, 229, 105.
2
(
(
(
7) Elings, J. A.; Downing, R. S.; Sheldon, R. A. Stud. Surf. Sci. Catal. 1995,
94, 487.
8) Sheldon, R. A.; Elings, J. A.; Lee, S. K.; Lempers, H. E. B.; Downing, R.
S. J. Mol. Catal. A: Chem. 1998, 134, 129.
[3,3] step in the Claisen rearrangement of allyl aryl ether
gives an ortho dienone, which rapidly enolizes to a stable
product, an o-allyl phenol. Thus, Claisen rearrangement can
be used to make o-allyl phenols, which are precursors to a
variety of natural products including chromones and
9) Wangikar, S. G.; Mayadevi, S.; Mirajkar, S. P.; Sivasanker, S. In
th
Proceedings onf 14 International Zeolite Conference; van Steen, E.,
Callanan, L., Claeys, M., O’Connor, C. T., Eds.; Cape Town: 2004; p 2731.
(
(
(
10) Sucholeiki, I.; Pavia, M. R.; Kresge, C. T.; Me Cullen, S. B.; Malek, A.;
Schram, S. Mol. DiVersity 1998, 3, 151; C. A. 1999, 129, 202736.
11) Cruz-Almanza, R.; Perez-Flores, F.; Brena, L.; Tapia, E.; Ojeda, R.; Fuentes,
A. J. Heterocycl. Chem. 1995, 32, 219.
12) Beck, J. S.; Vartuli, C.; Roth, W. J.; Leonowicz, M. E.; Kresge, C. T.;
Schmitt, K. D.; Chu, C. T. W.; Olson, D. H.; Sheppard, E. W.; McCullen,
S. B.; Higgins, J. B.; Schlenker, J. L. J. Am. Chem. Soc. 1992, 114, 10834.
2
-4
coumarones.
Several new catalysts with unique acidic
character have been studied for their effectiveness in Claisen
*
To whom correspondence should be addressed. Telephone: 91-22-
4102121, 24145616 (Ext. 291). Fax: 91-22-24102121, 24145614. E-mail:
gdyadav@yahoo.com, gdyadav@udct.org.
2
(13) Kresge, C. T.; Leonowicz, M. E.; Roth, W. J.; Vartuli, J. C.; Beck, J. S.
Nature 1992, 359, 710.
(
1) Rhoads, S. J.; Raulins, N. R. Organic Reactions; Wiley: New York, 1974;
Vol. 22.
(14) Sayari, A. Chem. Mater. 1996, 8, 1840.
1
0.1021/op050062f CCC: $30.25 © 2005 American Chemical Society
Vol. 9, No. 5, 2005 / Organic Process Research & Development
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547
Published on Web 07/08/2005

resurgence in mesoporous material synthesis for catalysis,
adsorption/separation, environmental pollution control, and
intrazeolite fabricating technology. The most striking features
of these novel materials, such as large BET surface area and
pore volume, hydrophobic surface nature, etc., manifest
themselves as selective adsorbents for the removal of volatile
organic compounds (VOCs) present in high-humidity gas
streams or wastewater.
The current study reports the development of an envi-
ronmentally benign route for Claisen rearrangement of allyl-
4-tert-butylphenyl ether to 2-allyl-4-tert-butylphenol using
20% (w/w) DTP/HMS including development of a kinetic
model.
2
. Experimental Section
.1. Chemicals and Catalysts. All chemicals and solvents
2
used in this study were commercially available and used
without further purification. Chlorobenzene, zirconium oxy-
chloride, aqueous ammonia solution, sulfuric acid, and
dodecatungstophosphoric acid (DTP) all of AR grade were
obtained from M/s s.d. Fine Chemicals Pvt. Ltd. Mumbai,
India. Chlorosulfonic acid, dodecylamine, and hexadecy-
lamine were obtained from Spectrochem Ltd., Mumbai. K-10
clay and tetraethyl orthosilicate (TEOS) were obtained from
Fluka, Germany. The catalysts used for the reaction were
The catalytic function of heteropolyacids (HPAs) and
related polyoxometalate compounds has attracted much
attention particularly in the past two decades. It is a field of
increasing importance1
6-22
in which new and promising
developments are being carried out at both research and
technological levels.23 HPAs are widely used as model
systems for fundamental research. They provide good basis
for the molecular design of mixed oxide catalysts, and they
have high capability in particular uses. HPAs are very good
acid catalysts in a homogeneous medium. They catalyze a
wide variety of reactions in a homogeneous phase offering
4
5
dried at 110 °C for 4 h before use. 20% (w/w) DTP/K-10
4
6
and sulfated zirconia were prepared according to a well-
established procedure in our laboratory. 20% (w/w) DTP/
HMS was synthesized as given by Yadav and Manyar.47
Allyl-4-tert-butylphenyl ether was synthesized in our labora-
tory from 4-tert-butylphenol and allyl bromide by using
phase transfer catalysis.
a strong option for efficient and cleaner processing compared
to conventional mineral acids.1
6,20,21,24-26
Though, there are
many advantages, the main disadvantages of HPAs as
catalysts lie in their low thermal stability, low surface area
2
(
1-10 m /g) and separation from reaction mixture. Thus,
2
.2. Preparation of 20% (w/w) DTP/HMS. Hexagonal
the development of a new solid catalyst with advanced
characteristics of strength, surface area, porosity, etc. has
been a challenge for a long time. HPAs on the suitable
support are expected to overcome the mentioned problems
0
0
mesoporous silica (HMS) was synthesized by the neutral S I
templating route, proposed by Tanev and Pinnavaia.48 In a
typical preparation, tetraethyl orthosilicate (TEOS) was added
under vigorous stirring to a solution of dodecylamine (DDA)
in ethanol and deionized water to obtain a gel of composition
1
7,27-28
29
of HPAs. Various supports such as silica,
alumina,
activated carbon,30-32 and MCM-41 have been used for
33
1
2
.0 TEOS:0.27 dodecylamine:9.09 EtOH:50.8 H O. After
supporting HPAs. A number of HPAs supported on K-10
aging for 18 h at ambient temperature, a templated silica
molecular sieve with short-range hexagonal morphology was
recovered. Template removal was achieved by calcination
at 550 °C in air. 20% (w/w) DTP/HMS was prepared by an
incipient wetness technique; a 2 g amount of dry DTP
3
4
clay were reported as novel catalysts by our laboratory,
and 20% dodecatungstophosphoric acid on K-10 has been
found to be a very efficient catalyst for a number of
3
4-44
reactions.
(dodecatungstophosphoric acid) was weighed accurately. This
(15) Tanev, P.; Pinnavaia, T. J. In Access in Nanoporous Materials; Pinnavaia,
was dissolved in 8 mL of methanol. The solution was added
in small aliquots of 1 mL each time to 8 g of HMS with
constant stirring with a glass rod and proper kneading. The
solution was added at time intervals of 2 min. Initially on
addition of the DTP solution, HMS was in a powdery form
but on complete addition it formed a paste. The paste on
further kneading for 10 min resulted in a free flowing
powder. The catalyst was dried at 120 °C and subsequently
calcined at 285 °C for 3 h.
T. J., Thorpe, M. F., Eds.; 1995; p 55.
16) Kozhevnikov, I. V. Russ. Chem. ReV. 1987, 56, 811.
17) Misono, M. Catal. ReV. Sci. Eng. 1987, 29, 269.
(
(
(
18) Misono, M. In New Frontiers in Catalysis; Gutzzi, L., Ed.; Elsevier:
Amsterdam, 1993; Vol. 69.
19) Misono, M.; Nojiri, N. Appl. Catal. 1996, 64, 1.
20) Izumi, Y.; Urabe, K.; Onaka, M. Zeolites Clay and Heteropolyacid in
Organic Reactions: Kodansha: Tokyo, 1992; Vol. 99.
21) Okuhara, T.; Mizuno, N.; Misono, M. AdV. Catal. 1996, 41, 113.
22) Corma, A. Chem. ReV. 1995, 95, 559.
23) Ono, Y. In PerspectiVe in Catalysis; Thomas, J. M., Zamaraev, K. I., Eds.;
Blackwell, Oxford, 1992.
24) Kozhevnikov, I. V.; Matveev, K. I. Appl. Catal. 1983, 5, 135.
25) Kozhevnikov, I. V. Stud. Surf. Sci. Catal. 1994, 21, 90.
26) Kozhevnikov, I. V. Russ. Catal. ReV. Sci. Eng. 1995, 37.
27) Rocchiccioli-Deltcheff, C.; Amirouch, M.; Herve, G.; Fournier, M. Chem.
Tatibouct. J. Mol. Catal. 1990, 126, 591.
(
(
(
(
(
(
(
(
(
(36) Blasco, T.; Corma, A.; Martinez, A.; Martinez-Esolano, P. J. Catal. 1998,
177, 306.
(37) Yadav, G. D.; Bokade, V. V. Appl. Catal. A 1996, 147, 299.
(38) Yadav, G. D.; Kirthivasan, N. Appl. Catal. A 1997, 154, 23.
(39) Yadav, G. D.; Pujari, A. A.; Joshi, A. V. Green Chem. 1999, 1, 269.
(40) Yadav, G. D.; Goel, P. K.; Joshi, A. V. Green Chem. 2001, 3, 92.
(41) Yadav, G. D.; Kirthivasan, N. In Fundamental and Applied Aspects of
Chemically Modified Surfaces; Jonathan, P. B., Charles, B. L., Eds.; Royal
Society of Chemistry, Cambridge, UK, 1999; p 254.
(
(
28) Vazquez, P. G.; Blanco, M. N.; Caceres, C. V. Catal. Lett. 1999, 60, 205.
29) Sawami, S.; Shin-ichi, N.; Okuahar, T.; Misono, M. J. Catal. 1997, 166,
2
63.
(
30) Schwegier, M. A.; Vinke, P.; Vijk, M.; Van der, M.; Bekkum, H. Appl.
Catal. A 1992, 80, 41.
(
(
31) Izumi, Y.; Hasebe, R.; Uraba, K. J. Catal. 1983, 84, 402.
32) Dupont, P.; Vederine, J. C.; Paumard, E.; Hecquet, G.; Lefebve, F. Appl.
Catal. A 1995, 129, 217.
33) Dupont, P.; Lefebve, F. J. Mol. Catal. A: Chem. 1996, 114, 307.
34) Yadav, G. D.; Kirthivasan, N. J. Chem. Soc., Chem. Commun. 1995, 203.
35) Okuhara, T.; Mizuno, N.; Misono, M. In AdVances in Catalysis; Eley, D.
D., Haag, W. O., Gates, B., Eds.; Academic Press: London, 1996; Vol. 41,
p 113.
(42) Yadav, G. D.; Doshi, N. S. Catal. Today 2000, 60, 263.
(43) Yadav, G. D.; Doshi, N. S. Org. Process Res. DeV. 2002, 6, 263.
(44) Yadav, G. D.; Kumar, P. Appl. Catal., A 2005, 286, 61.
(45) Yadav, G. D. Catal. SurV. Asia 2005 9(2), 1.
(
(
(
(46) Kumbhar, P. S.; Yadav, G. D. Chem. Eng. Sci. 1989, 44, 2535.
(47) Yadav, G. D.; Manyar, H. M. Microporous Mesoporous Mater. 2003, 63
(1-2), 85.
(48) Tanev, P. T.; Pinnavaia, T. J. Science 1995, 267, 865.
548
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Vol. 9, No. 5, 2005 / Organic Process Research & Development

Scheme 1. Claisen rearrangement
500) by using a BPX-1 capillary column (250 mm × 30 m)
packed with methyl polysiloxane. The reaction is shown in
Scheme 1.
2
.6. Mechanism of the Claisen Rearrangement Using
2
0% (w/w) DTP/HMS. The mechanism of Claisen re-
arrangement using 20% (w/w) DTP/HMS, with general
acidic site L, is proposed in Scheme 2. According to this
mechanism, the oxygen of the ether having a lone pair of
electrons is chemisorbed on the acidic site, and then the allyl
group migrates to the most favourable ortho position through
intramolecular rearrangement. The product is desorbed
thereby freeing the site for next catalytic cycle.
2
.3. Experimental Procedure and Analysis. The ex-
3
. Results and Discussion
3.1. Catalyst Activity. It was thought desirable to study
perimental setup consisted of a 3 cm i.d. fully baffled
mechanically agitated glass reactor of 50 cm capacity,
3
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
with an accuracy of (1 °C.
the influence of various reaction parameters under otherwise
similar experimental conditions to establish the reaction
mechanism, in the absence of both external mass transfer
and intraparticle diffusion limitations, which will be discussed
later. It was found that only 2-allyl-4-tert-butylphenol product
was formed with a conversion of 85% after 1 h. In the case
of a bulky reactant like allyl-4-tert-butylphenyl ether and a
bulkier 2-allyl-4-tert-butylphenol product, the type of acidity,
its strength, and the pore structure would matter greatly. As
regards the pore structure, the pore size distribution should
be as narrow as possible and in mesoporous range, with a
high coordination number connecting the bulges to throats.
Thus, DTP/HMS was found to be a better catalyst. The large
surface area of silica molecular sieves allows Keggin anions
to dispense uniformly on the surface, and it constitutes a
stable solid acid catalyst system. An important potential
benefit of supporting dodecatungstophosphoric acid on a
silica molecular sieve is enhanced thermal stability which is
A typical reaction mixture consisted of 0.01 mol of allyl-
3
4
-tert-butylphenyl ether in 10 cm of chlorobenzene as a
3
solvent with a catalyst loading of 0.1 g/cm at a agitation
speed of 1000 rpm at 90 °C.
2.4. Analysis. The analysis was done on a gas chromato-
graph (Chemito-8610) equipped with a flame ionisation
detector. A (3.25 mm × 2 m) long stainless steel column
packed with 10% SE-30 supported on chromosorb-WHP was
used for the analysis. The injector and detector were kept at
3
00 °C. The oven temperature was programmed from 130
-
1
°
C (0.5 min) up to 280 °C with a ramp rate of 10 °C min .
Synthetic mixtures were used to calibrate and quantify the
data.
2.5. Isolation of Product: At the end of the reaction, the
4
9-51
reaction mixture was filtered to remove the catalyst DTP/
HMS for further reuse. The clear reaction mixture containing
in agreement with previous work.
HPAs were found to
retain their Keggin-type structure when impregnated on silica
52
2-allyl-4-tert-butylphenol, allyl-4-tert-butylphenyl ether, and
provided its contents are greater than 2% (w/w). There was
thus a synergism between HMS and DTP in the supported
form. However, an independent study was undertaken to
evaluate the stability of the catalyst under experimental
conditions.
chlorobenzene was cooled. The reaction mixture is treated
with 50% aqueous NaOH solution in order to make the
sodium salt of 2-allyl-4-tert-butylphenol. 2-Allyl-4-tert-
butylphenol was isolated by acid hydrolysis of aqueous
phase. The unreacted allyl-4-tert-butylphenyl ether in chlo-
robenzene was obtained by distillation. The isolated product
was confirmed with GC-MS (Perkin Elemer Clarius Model
3.2. Evaluation of Catalyst Stability. The ordered
mesoporous silica molecular sieve with large surface silanol
groups is catalytically inert. The surface acidity of HMS was
Scheme 2. Reaction mechanism on solid acid (L ) acid site)
Vol. 9, No. 5, 2005 / Organic Process Research & Development
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549

modate the bulky molecule. It was found that there was no
other byproduct, and the reaction was facile at much lower
temperatures also. Further experiments were conducted with
2
0% (w/w) DTP/HMS due to excellent reusability and
stability as the catalyst where only one parameter was varied
at a time under otherwise similar experimental conditions.
A brief characterization of this catalyst is presented.
3
.4. Catalyst Characterization. 20% (w/w) DTP/HMS
is completely characterized by FTIR, XRD, SEM, and BET
surface area, and the details were published by us.47 Only a
few salient features are reported here. The framework
IR spectrum of the catalyst exhibits bands at 3450.1,
-
1
1
652.6, 1092.5, 990.7, 893.4, 817.5, and 466.2 cm . The
bands coincide with those reported in the literature for
4
5,53-55
H
3
40
PW12O .
The bands of the DTP supported on HMS
-
1
appear at 1092.5, 990.7, and 893.4 cm . The presence, in
the IR spectra of catalytic samples, of the 817 cm band is
-
1
due to a Si-O bending mode, ν (O-H). The sharp peak in
the region 1600-1700 cm indicates the presence of H O
3
B
Figure 1. Effect of different catalysts. Allyl-4-tert-butylphenyl
ether 0.01 mol, chlorobenzene 10 cm , catalyst 0.1 g/cm .
Temperature 90 °C, speed of agitation 1000 rpm (DTP/HMS
-1
3
3
(
Bronsted acidity). In addition, these materials exhibit a
-
1
strong 3450 cm band, which is associated with silanol
group O-H stretching vibrational mode, ν
(O-H).4
)
20% dodecatungstophosphoric acid on hexagonal mesoporous
silica, DTP/K-10 ) 20% dodecatungstophosphoric acid on K-10
5,53-55
S
clay, SZ- sulfated zirconia).
This band is much broad as compared to the one observed
in case of zeolite molecular sieves which is due to presence
of physisorbed and chemisorbed surface water molecules.
The X-ray diffraction patterns of authentic HMS as well
as 20% (w/w) DTP/HMS were recorded. The XRD patterns
of these materials do not contain any sharp reflections but
only a broad diffuse band similar to that of amorphous
materials. The XRD patterns for DTP supported on silica
were similar to those of the corresponding HMS. In
particular, no crystalline phase could be detected in the case
of DTP supported on silica. This could be attributed to the
due to the HPA. However, it was important to establish the
exact nature of interaction between DTP and silica surface.
If DTP was physically adsorbed on HMS surface, then the
catalyst would not be reused because of leaching out of DTP
into the reaction mixture. It was observed that the DTP/HMS
showed consistent activity up to a minimum of three runs
which suggested that DTP was chemically bonded to the
support. For further confirmation, the stability was evaluated
3
8
by the characteristic heteropoly blue colour test. HPA
solutions develop blue colour when reacted with a mild
reducing agent like ascorbic acid. This property was used
for quantitative determination of leaching, if any. 5 g of 20%
3-
uniform distribution of keggin anion (PW12O40 ) in the
noncrystalline form because of the interaction with the
surface of the silica molecular sieve. These materials are,
hence, completely amorphous without any long range order.
Scanning electron microscopy shows that the average
particle size is in the range 2-4 µm. As is generally observed
in the case of materials synthesized by a sol-gel technique,
these catalytic samples show particles of irregular morphol-
ogy, which are fairly uniform in size.
(w/w) DTP/HMS was refluxed in 25 mL of methanol with
vigorous stirring for 1 h. A 5 mL aliquot of the refluxing
solution was drawn to which 2 mL of 10% ascorbic acid
solution were added. The solution remained clear and
colourless, and there was no development of the blue colour
which otherwise is an instantaneous phenomenon in authentic
HPA solutions. Such a test was also done in acetic acid and
acetic anhydride to find no leaching. The above test was
repeated to confirm the absence of leaching.
2
Characteristic nitrogen BET surface area is 908 m /g. As
observed from BJH adsorption pore size distribution, a major
part of the surface area is contributed by pores with a
diameter characteristic of pores ranging from 17.1 to 33.0
Å. There is also a significant part due to mesopores ranging
from 33.0 to 67.0 Å. The catalyst is essentially mesoporous.
Some of the textural characteristics of these catalytic samples
are given in Table 1.
3.3. Efficacies of Various Catalysts. Different solid acid
catalysts were used to assess their efficacy in this reaction.
3
A 0.1 g/cm loading of catalyst based on the organic volume
of the reaction mixture was employed at 90 °C and an
agitational speed of 1000 rpm. The catalysts used were 20%
(w/w) DTP/HMS, 20% (w/w) DTP/K-10, and sulfated
3
.5. Effect of Speed of Agitation. The effect of speed of
zirconia. It was found that 20% (w/w) DTP/HMS showed
higher conversions compared to other catalysts (Figure 1).
agitation was studied in the range 800-1200 rpm as shown
in Figure 2 for 20% (w/w) DTP/HMS, under otherwise
20% (w/w) DTP/HMS is mesoporous and can easily accom-
(
(
(
49) Moffat, J. B.; Kasztelan, S. J. Catal. 1988, 109, 206.
50) Kasztelan, S.; Payen, E.; Moffat, J. B. J. Catal. 1988, 112, 320.
51) Rocchiccioli-Deltcheff, C.; Thouvenot, R.; Franck, R. Spectrochim. Acta
(53) Okuhara, T.; Mizuno, N.; Misono, M. In AdVances in Catalysis; Eley, D.
D., Haag, W. O., Gates, B., Eds.; Academic Press: London, 1996; Vol. 41;
p 113.
1
976, 32A, 587.
52) Choi, S.; Wang, Y.; Nie, Z.; Liu, J.; Peden, C. H. F. Catal. Today 2000,
5, 117.
(54) Blasco, T.; Corma, A.; Martinez, A.; Martinez-Esolano, P. J. Catal. 1998,
177, 306.
(55) Llewellyn, P. L. Langmuir 1995, 11, 574.
(
5
550
•
Vol. 9, No. 5, 2005 / Organic Process Research & Development

Table 1. Textural characteristics of 20% (w/w) DTP/HMS
single-point
surface area,
BET
Langmuir
BJH adsorption
average
pore diameter
(4V/A) Å
surface area,
surface area,
cumulative pore volume,
2
2
2
3
sample
m /g
m /g
m /g
cm /g
20% (w/w) DTP/HMS
840
909
1264
0.538
26
identical conditions. It was observed that there was no change
in the rate and conversion beyond a speed of 1000 rpm. There
was no external solid-liquid mass transfer resistance to
reactant and product at speeds greater than or equal to 1000
rpm. At lower speeds, there was a likelihood of this
resistance. In further experiments the speed was maintained
at or above 1000 rpm.
constant. It was observed that as the concentration increases
the conversion decreases (Figure 4). The initial rate of
reaction increases linearly with concentration. This suggested
a first-order dependence on catalyst concentration and formed
a basis for the development of kinetics. A plot of initial rate
versus concentration of allyl-4-tert-butylphenyl ether was
made (Figure 5). The initial rate is linear vs concentration
3.6. Effect of Catalyst Loading. In the absence of
external mass transfer resistance, the rate of reaction is
directly proportional to catalyst loading based on the entire
volume of the liquid phase. The catalyst loading was varied
3
over a range of 0.02-0.1 g/cm on the basis of the total
volume of the reaction mixture. Figure 3 shows the effect
of catalyst loading on the conversion of allyl-4-tert-butyl-
phenyl ether. It indicates that as the catalyst loading is
increased, the conversion of allyl-4-tert-butylphenyl ether
increases, which is due to the proportional increase in the
number of active sites. At higher catalyst loading, there were
more catalytic sites than required and thus it does not affect
the rate, and therefore there is no more increase in the rate.
Therefore, all further experiments were carried out at 0.1
3
g/cm catalyst loading. Further, there was no intraparticle
diffusion limitation, which was established by invoking the
Wiesz-Prater criterion based on initial rates of reaction,
particle size, and effective diffusivity of the substrate at 90
°
C. This is omitted for the sake of brevity.
.7. Effect of the Concentration of Allyl-4-tert-bu-
3
Figure 3. Effect of catalyst loading. Allyl-4-tert-butylphenyl
3
tylphenyl Ether. The concentration of allyl-4-tert-butyl-
phenyl ether was varied by taking 0.0025 to 0.02 mol of the
substrate keeping the total volume of reaction mass as
ether 0.01 mol, chlorobenzene 10 cm , temperature 90 °C, speed
of agitation 1000 rpm.
Figure 2. Effect of speed of agitation. Allyl-4-tert-butylphenyl
Figure 4. Effect of concentration of allyl-4-tert-butylphenyl
3
3
ether 0.01 mol, chlorobenzene 10 cm , 20%(w/w) DTP/HMS
ether. Chlorobenzene 10 cm , temperature 90 °C, 20% (w/w)
3
3
0
.1 g/cm , temperature 90 °C.
DTP/HMS 0.1 g/cm , speed of agitation 1000 rpm.
Vol. 9, No. 5, 2005 / Organic Process Research & Development
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551

Figure 5. Plot of initial rate vs concentration of allyl-4-tert-
butylphenyl ether.
Figure 7. Reusability of Catalyst. Allyl-4-tert-butylphenyl ether
3
0
.01 mol, chlorobenzene 10 cm , 20% (w/w) DTP/HMS 0.1
3
g/cm , temperature 90 °C, speed of agitation 1000 rpm.
fresh catalyst, the conversion of allyl-4-tert-butylphenyl ether
was 85.6%. During the third run the conversion decreased
to 72.34% while the selectivity towards 2-allyl-4-tert-
butylphenol remained 100%. The attrition occurs during
agitation, and the fine particles are lost during filtration. No
makeup quantity of catalyst was added in the current studies.
The particle surface area created during attrition does not
lead to enhanced activity, since that surface area of HMS,
which is catalytically inactive. The activity per unit mass of
catalyst remains the same. The catalyst is reusable twice
without loss in activity. This can be assumed to be reason-
able.
Figure 6. Effect of temperature. Allyl-4-tert-butylphenyl ether
3
0
.01 mol, chlorobenzene 10 cm , 20% (w/w) DTP/HMS 0.1
3
g/cm , speed of agitation 1000 rpm.
3
.10. Effect of Different Solvents. We have studied the
effect of different solvents on the rate of the reaction.
Chlorobenzene was found to be the best solvent. It was
observed that, in the case of toluene and mixed xylenes, the
alkylation reaction of the substrate with the solvent takes
place by migration of allyl carbonium ion from allyl-4-tert-
butylphenyl ether to the activated aromatic rings of the
solvent to form allylated toluene and xylenes. This is due to
high acidity of 20% (w/w) DTP/HMS, and it results in the
decrease in selectivity of desired product. Chlorobenzene was
found to be the best solvent, without any byproducts. Both
the reagent and product are solids, and hence use of solvent
was necessary.
of the reactant. It excludes the point at the highest concentra-
tion used in this study. The adsorption term in the denomina-
tor of the typical Langmuir-Hishelwood-Hougen-Watson
model, which will be discussed later, is far less than unity,
and thus, a typical first-order power law model fits the data.
At higher concentration, the terms in the denominator become
comparable to one, and thus, the rate of reaction is lowered,
which leads to the lowering of conversion.
3.8. Effect of Temperature. The effect of temperature
on the rate of reaction was studied by conducting the reaction
at 60, 70, 80, 90, and 100 °C under otherwise similar
conditions as shown in Figure 6. The conversion of allyl-
3
.11. Reaction Kinetics. It is known that in the Claisen
4-tert-butylphenyl ether was found to increase substantially
rearrangement the rate of reaction follows first-order kinetic
with increasing temperature up to 100 °C. In 1 h, the
conversions at higher temperatures were higher.
56
behaviour for thermal reactions. In the absence of any mass
transfer limitations, it is possible to deduce the kinetics. The
mechanism of Claisen rearrangement suggests that a Lang-
muir-Hinshelwood-Hougen-Watson (LHHW) model can
be used with chemisorption, surface reaction, and desorption
steps.
3.9. Reusability of Catalyst. The catalyst reusability of
20% (w/w) DTP/HMS was studied three times, including
the use of fresh catalyst (Figure 7). The catalyst was filtered,
washed with chlorobenzene, and subsequently heated at 285
°
C for 2 h before being reused in subsequent batches. This
reactivation was done to remove the molecules adsorbed on
active sites from the catalyst surface. In the presence of the
(
56) Ghosh, S. General Organic Chemistry A Modern Approach; Books and
Allied (Pvt.) Ltd., 1994; p 578.
552
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For a surface reaction controlled mechanism, the rate of
3
reaction (mol/cm s) is given by
k′ K C C
k K wC
SR A A
SR
A
T
A
-
r ) k′ C
)
)
(1)
A
SR AS
1
+ K C + K C
1 + K C + K C
A A B B
A
A
B
B
where A and B denote the allyl-4-tert-butylphenyl ether and
-allyl-4-tert-butylphenol, respectively.
and K ) adsorption equilibrium constants for A and
B, respectively, cm /mol.
AS ) concentration of adsorbed species A, mol/cm .
2
K
A
B
3
3
C
-
1
k′SR ) reaction rate constant, s .
SR ) reaction rate constant ()Rk′SR), cm /(g of cat ‚ s).
3
k
3
w ) catalyst loading, g-cat/cm liquid phase.
) total catalytic site concentration, mol, () Rw)
C
T
3
R ) constant of proportionality, mol ‚ cm /g of cat.
and C ) bulk concentration of A and B, respectively,
mol/cm .
Equation 1 can be converted in terms of fractional
conversion, X
C
A
B
3
Figure 8. First-order kinetic plot of Claisen rearrangement
of allyl-4-tert-butylphenyl ether.
A
,
k K wC (1 - X )
-
dCA
dt
dXA
dt
SR
A
A
A
0
-
rA )
) CA0
)
(2)
1 + K C (1 - X ) + K C X
A
A
A
A
B
A
0
0
The integration of this equation leads to the following
with appropriate manipulation,
C X (K - K )
A
A
A
B
k K wt
SR A
0
-
ln(1 - X ) +
)
(3)
A
1
+ K CA0
1 + K CA
B
0
B
Equation 3 can be manipulated to get
C (K - K )
-
ln(1 - XA)
k K w
A
0
B
A
SR
A
t
XA
)
+
(4)
XA
(
1 + K CA0
)
1 + K CA
B
0
B
Equation 4 allows us to extract the equilibrium constants
and rate constant from the same data. Thus by making the
A
plot of left-hand side term against t/X , the intercept and
Figure 9. Arrhenius plot.
slopes could be obtained at different w values, to get all three
constants. The above analysis was performed, since there
was a likelihood of strong adsorption of either reactant or
product inhibiting the rate. The adsorption equilibrium
constants for A and B can be compared to get three different
cases as given below:
suggesting very weak adsorption of A and B, leading to a
first-order equation. Thus, a plot of -ln(1 - X ) against time
(t) is shown in Figure 8. It is seen that the data fit very well
and thus validate the model that the reaction is intrinsically
kinetically controlled by the surface reaction on the catalytic
site, with weak adsorption of the reactant and product. An
A
(a) If K
A
> > K
B
-
ln(1 - XA)
t
XA
Arrhenius plot of ln k
the values of the frequency factor k
1
vs I/T (Figure 9) was used to calculate
and the energy of
)
(k K w) - C K
A
(5)
SR
A
A
0
XA
0
4
3
activation as 7.6 × 10 cm /g of cat/min and 10.12 kcal/
mol, respectively. This activation energy also supported the
fact that the overall rate of reaction is not influenced by either
external mass transfer or intraparticle diffusion resistance and
it is an intrinsically kinetically controlled reaction on the
active sites.
(
b) If K
A
< < K
B
C K
B
-
ln(1 - XA)
k K w
A
0
SR
A
t
)
+
(6)
(7)
XA
(
1 + K CA0
)
XA 1 + K C
B
B
A0
A B
c) If K ,K < < 1
4
. Conclusion
-
ln(1 - X ) ) k K wt ) k wt
A SR A 1
Heteropolyacid (HPA) compounds with a Keggin-type
When the LHS term in eqs 5-7 were plotted against the
RHS term involving t, only eq 7 was found to hold, thereby
anion and their derivatives are industrial catalyst precursors
and are used in several catalytic reactions. The major
Vol. 9, No. 5, 2005 / Organic Process Research & Development
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553

drawback of using heteropolyacids in solution phase is that
they become homogeneous with the reaction medium and
create problems as related with homogeneous catalysis. Such
type of problems can be solved by heterogenising the
heteropolyacid by supporting it on an inorganic support or
converting into its salt. The Claisen rearrangement of allyl
NOMENCLATURE
A
B
C
C
C
K
Allyl-4-tert-butylphenyl ether
2-Allyl-4-tert-butylphenol
Concentration of adsorbed species A, mol/cm3
AS
S
Concentration of vacant sites, mol/g-cat.
Total concentration of sites, mol/g-cat.
T
4
-tert-butylphenyl ether was successfully studied by using
environmentally friendly several solid acid catalysts such as
0% (w/w) DTP/HMS, 20% (w/w) DTP/K-10, K-10, and
3
A
, K
B
Adsorption constant for A and B, respectively, cm /mol
3
k
k
k
SR
Reaction rate constant, cm /mol g-cat.min.
2
3
1
Pseudo first-order rate constant, cm /g-cat.min.
sulphated zirconia. The effects of 20% (w/w) DTP/HMS
were found to be superior to others. The effects of various
parameters on the rate of reaction under otherwise similar
conditions were studied. External mass-transfer resistance
was eliminated by providing adequate stirring, and internal
diffusion resistance was also absent due to mesoporosity and
smaller particle size. It was observed that the catalyst has
excellent reusability up to two times, without any makeup
catalyst, and the reaction was 100% selective towards allyl-
3
0
Frequency factor, cm /g-cat.min.
3
-r
Rate of reaction (mol/cm s.)
S
Vacant site
X
A
Fractional Conversion of allyl-4-tert-butylphenyl ether
3
W
Catalyst loading, g/cm liquid phase
Acknowledgment
G.D.Y. acknowledges Darbari Seth Endowment for sup-
porting the Chair and NMITLI CSIR for research funds
which supported S.V.L.
4-tert-butylphenyl ether. There was a loss of catalyst during
filtration, and per unit mass of catalyst the activity was the
same during each reuse. A first-order kinetic model was
developed to analyse the experimental data, and the apparent
activation energy is 10.12 kcal/mol, which also suggested
that the reaction is intrinsically kinetically controlled.
Received for review April 25, 2005.
OP050062F
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