Rearrangement of allyl phenyl ether over Al-MCM-41

Article abstract of DOI:10.1016/j.jcat.2004.09.027

Claisen rearrangement of allyl phenyl ether to o-allylphenol and a dihydrobenzofuran derivative was investigated over MCM-41 with different Si/Al ratios. Higher aluminum content, higher reaction temperatures, and longer run duration favor the formation of the ring compound 2,3-dihydro-2-methyl benzofuran. There is a close relationship between acidity and conversion, which suggests that the reaction occurs inside the large pores of MCM-41. The influence of temperature and catalyst Si/Al ratio on the reaction are examined by kinetic analysis, under the assumption of a first-order consecutive reaction.

Full text of DOI:10.1016/j.jcat.2004.09.027

Journal of Catalysis 229 (2005) 105–113
www.elsevier.com/locate/jcat
Rearrangement of allyl phenyl ether over Al-MCM-41
Nevin T. Mathew, S. Khaire, S. Mayadevi, R. Jha, S. Sivasanker ∗
National Chemical Laboratory, Pune 411008, India
Received 13 July 2004; revised 29 September 2004; accepted 30 September 2004
Available online 24 November 2004
Abstract
Claisen rearrangement of allyl phenyl ether to o-allylphenol and a dihydrobenzofuran derivative was investigated over MCM-41 with
different Si/Al ratios. Higher aluminum content, higher reaction temperatures, and longer run duration favor the formation of the ring
compound 2,3-dihydro-2-methyl benzofuran. There is a close relationship between acidity and conversion, which suggests that the reaction
occurs inside the large pores of MCM-41. The influence of temperature and catalyst Si/Al ratio on the reaction are examined by kinetic
analysis, under the assumption of a first-order consecutive reaction.
2004 Elsevier Inc. All rights reserved.
Keywords: Claisen rearrangement; Allyl phenyl ether; Al-MCM-41; Molecular rearrangement; Solid acids; Mesoporous material
1. Introduction
Mesoporous molecular sieves of the MCM-41 type have
received much attention because of their large surface area
and the uniform size and shape of the pores over micrometer-
length scales [9,10]. High thermal stability and the advan-
tage of tuning the pore size make these materials interesting
for use as supports and catalysts for various heterogeneously
catalyzed reactions. In the present study, we have explored
the use of Al-MCM-41 with large pores (∼ 30-Å diameter)
as a catalyst in the Claisen rearrangement of APE. The effect
of reaction parameters and catalyst Al content on conversion
and product selectivity has been studied. A kinetic analysis
of the formation of the different products under various re-
action conditions is also presented.
Claisen rearrangement involves the conversion of allyl
phenyl ethers (APEs) to the corresponding o-allylphenols
and is generally performed by heating the ethers at an ele-
vated temperature (> 473 K), but has been reported to be
susceptible to catalysis by Lewis and Brønsted acids [1,2].
Reports of the use of solid acids in the above rearrange-
ment are rather scarce. Pitchumani et al. have observed
shape selectivity in ZSM-5 and ZSM-11 during their study
of photo-assisted Claisen rearrangement [3]. Sheldon et al.
have investigated the use of H-FAU and H-MOR in the re-
arrangement of APE in benzene medium [4,5]. Other solid
catalysts that have been investigated are mesoporous silica
[6] and bentonite [7]. We have already reported our studies
on the use of large-pore zeolites, especially beta, as catalysts
for the rearrangement [8]. As we did not find any meaningful
relationship between acidity and catalytic activity in these
zeolites, we suggested that even over large-pore zeolites, the
rearrangement occurs primarily at the external surface or at
the pore mouth [8].
2. Experimental
Tetraethyl orthosilicate (Aldrich), aluminum sulfate (s.d.
fine chemicals Ltd.), cetyltrimethylammonium bromide
(CTMABr) (Loba Chemie), and tetramethylammonium hy-
droxide (TMAOH) (Aldrich) were used in the synthesis
of the samples. Si-MCM-41 was prepared hydrothermally
in alkaline medium with the use of a gel with the molar
composition 1 SiO2:0.33 TMAOH:0.55 CTMABr:60 H2O.
*
Corresponding author. Fax: +91 20 2589 3761.
E-mail address: siva@cata.ncl.res.in (S. Sivasanker).
0021-9517/$ – see front matter
doi:10.1016/j.jcat.2004.09.027
2004 Elsevier Inc. All rights reserved.

106
N.T. Mathew et al. / Journal of Catalysis 229 (2005) 105–113
Al-MCM-41 with different Si/Al ratios was prepared by
the addition of aluminum sulfate to the Si-MCM-41 gel
to get the molar composition 1 SiO2:0.33 TMAOH:0.55
CTMABr:60 H2O:x Al2O3. Al-MCM-41 with Si/Al ra-
tios of 20, 30, 50, and 100 was prepared by the variation
of x in the gel composition from 0.005 to 0.025 moles.
In all cases, the gel was aged at room temperature for 5 h
with stirring and heated in an autoclave at 383 K for 5 days
under autogenous pressure. The solid product was filtered,
washed, dried, and calcined at 823 K for 8 h to get the final
product. The product was characterized by X-ray diffraction
(XRD) (Rigaku D/MINI-Flex X-ray diffractometer, 40 kV,
20 mA, Ni filtered Cu-Kα), scanning electron microscopy
(JEOL JSM 5200), nuclear magnetic resonance (Brucker
MSL-300), and N2 adsorption. The samples were charac-
terized for their acidity by the temperature-programmed
desorption (TPD) of NH3 (Micromeritics, Autochem Z910).
The standard procedure for TPD measurements involved the
activation of the sample in flowing He at 873 K (3 h), cool-
ing to 298 K, and adsorbing NH3 from a stream of He–NH3
(10%), removing the physically adsorbed NH3 by desorb-
ing in He at 373 K for 1 h, and finally carrying out the TPD
experiment by raising the temperature of the catalyst in a
programmed manner (10 K min−1). The TPD curves were
deconvoluted into two peaks, and the areas under the peaks
were converted into meq NH3 per gram of catalyst based
on injection of known volumes of the He–NH3 mixture un-
der similar conditions. All of the samples were calcined at
823 K for 8 h prior to use in catalytic experiments.
3. Results and discussion
3.1. Physicochemical characterization
3.1.1. X-ray diffraction
The XRD patterns of calcined Si- and Al-MCM-41
are shown in Fig. 1. The physicochemical properties of
MCM-41 with different Si/Al ratios are presented in Ta-
ble 1. The XRD patterns are similar to those reported for
MCM-41 materials [9] and show low angle (110) and (200)
peaks for all of the samples, which is characteristic of long-
range order of crystallinity of the materials. Kresge et al.
[9] indexed these peaks for a hexagonal unit cell, the pa-
rameter for which was calculated with the equation a0 =
√
2d100/ 3 (Table 1). The table shows that the d100 reflection
of Al-MCM-41 is shifted to higher values compared with
its siliceous analogue. This is probably due to the frame-
work substitution of Al in the MCM-41 structure [11]. The
change in the T–O–T bond angle with Al substitution prob-
ably causes long-range disorder in the system and explains
the slightly broader XRD peaks in Al-containing samples
(Fig. 1).
3.1.2. Nuclear magnetic resonance
The 27Al magic-angle spinning nuclear magnetic reso-
nance (MAS NMR) spectrum of calcined Al-MCM-41 with
APE (purity 99%) required for the reaction was synthe-
sized by the reaction of allyl bromide and phenol in ethanol
and purified by standard methods. The reactions were car-
ried out in batch mode in a two-necked round-bottomed
flask (capacity 25 ml) in a nitrogen atmosphere, with the use
of 0.67 g of APE in 10 g of solvent (tetrachloroethylene,
Loba Chemie) with 0.075 g of freshly calcined catalyst.
Aliquots of the reaction mixture were collected at different
time intervals and analyzed by gas chromatography (Var-
ian gas chromatograph; column: CP Sil 5CB, 30 m; i.d.
0.05 mm; FID detector). The products were identified by
gas chromatography-mass spectroscopy (GC-MS) and gas
chromatography-infrared spectroscopy (GC-IR).
Fig. 1. XRD patterns of calcined Si-MCM-41 and Al-MCM-41 with differ-
ent Si/Al ratios.
Table 1
Physicochemical properties of Al-MCM-41 samples
a
b
b
Sample
Si/Al ratio
(XRF)
d
spacing
Unit cell a
parameter (Å)
Surface area
(m /g)
Pore diameter
(Å)
100
0
a
2
(Å)
Si-MCM-41
–
36.78
38.05
39.76
40.49
43.69
40.45
36.92
44.31
44.38
47.19
1094
1219
997
28.58
27.23
30.02
31.44
33.67
Al-MCM-41 (100)
Al-MCM-41 (50)
Al-MCM-41 (30)
Al-MCM-41 (20)
110.1
53.2
31.0
20.8
873
785
a
As-synthesized sample.
Calcined sample.
b

N.T. Mathew et al. / Journal of Catalysis 229 (2005) 105–113
107
a Si/Al ratio of 20 is presented in Fig. 2. It reveals two peaks.
The major peak, with a chemical shift of 52.52 ppm, is as-
signed to tetrahedrally coordinated Al presumably present in
the Al-MCM-41 framework. The small peak at ∼ 0 ppm is
due to octahedrally coordinated (nonframework) Al present
in the material [12]. The spectrum shows that most of the Al
in Al-MCM-41 is tetrahedrally coordinated, even at a high
Al content (Si/Al = 20), and only a small amount of non-
framework Al is present in the material.
3.1.3. Transmission electron microscopy
TEM images of calcined Al-MCM-41 (Si/Al = 50) and
Si-MCM-41 revealed characteristic regular hexagonal arrays
of uniform channels for both Al-MCM-41 (Si/Al = 50) and
Si-MCM-41. The periodicity of the structure was also con-
firmed by the electron diffraction pattern.
3.1.4. Nitrogen sorption
The N2 adsorption–desorptionisotherms of MCM-41 and
Al-MCM-41 were typical for type IV, with a hysteresis
loop characteristic of mesoporous materials (Fig. 3). The
isotherms exhibit three stages. The first stage is due to
monolayer adsorption of nitrogen to the walls of the meso-
27
Fig. 2. Al MAS-NMR spectrum of calcined Al-MCM-41 (Si/Al = 20).
Fig. 3. Nitrogen adsorption isotherms and corresponding pore size distribution of calcined Al-MCM-41 with Si/Al ratios at 20 and 100.

108
N.T. Mathew et al. / Journal of Catalysis 229 (2005) 105–113
pores at a low relative pressure (p/p0 < 0.2). The sec-
ond stage is characterized by a steep increase in adsorp-
tion (p/p0 > 0.2). As the relative pressure increases, the
isotherm exhibits a sharp inflection characteristic of capil-
lary condensation within the uniform mesopores. The p/p0
at the inflection is related to the diameter of the meso-
pore [13], and the steepness of this step indicates the unifor-
mity of pore size distribution. The third stage in the adsorp-
tion isotherm is the gradual increase in volume with p/p0
due to multilayer adsorption on the outer surface of the par-
ticles.
The surface area and average pore diameters of MCM-41
with different Si/Al ratios are given in Table 1. The table
shows that the pore diameter increases with increasing Al
content. The surface area decreases in general with increas-
ing Al content in MCM-41, except in the case of the sample
with Si/Al = 100, which shows a higher SBET value. The
reason for the anomalous behavior of the sample could be
the poor crystallinity of the sample (XRD; Fig. 1).
The pore size distribution of calcined MCM-41 with
Si/Al = 20 and 100 is also presented in Fig. 3. The fig-
ure shows that the materials possess pores of nearly uniform
size with a narrow distribution. However, the distribution be-
comes broader as the Al content increases, because of the
greater disorder caused by Al incorporation.
3.1.5. Temperature-programmed desorption of ammonia
The TPD profiles of Al-MCM-41 with different Si/Al
ratios are presented in Fig. 4. The number and density of
acid sites are expected to increase with the Al content [14].
Fig. 4 shows that the total acidity of MCM-41 increases with
the Al content. The amounts of strong and weak acid sites
in Al-MCM-41 with different Si/Al ratios, estimated from
the deconvoluted TPD profiles, are given in Table 2. The ta-
ble shows that the total number of acid sites (the strong and
the weak acid sites) increases with Al content. The ratio of
strong acid sites to weak acid sites also increases with Al
content. Strong acid sites (Brønsted) are generated by tetra-
hedrally coordinated Al atoms forming Al–O(H)–Si bridges.
The increase in the ratio of strong to weak acid sites with Al
content implies that most of the added Al is tetrahedrally co-
ordinated in the framework. Assuming that the strong acid
sites are directly related to the Al ions in the samples, the
ratio NH3/Al (mole NH3 desorbed per mole Al) was calcu-
lated (Table 2). The results indicate an increase in the ratio
with decreasing Al content, suggesting an increasing disper-
sion of Al at higher Si/Al ratios.
Fig. 4. (a) Temperature programmed desorption of ammonia from
Al-MCM-41 with different Si/Al ratios. (b) Typical deconvoluted plot for
sample with Si/Al = 20.
Table 2
Acidity of Al-MCM-41 with different Si/Al ratios by TPDA
a
Sample
Weak acidity Strong acidity Total acidity NH /Al
3
(mmol/g)
(mmol/g)
(mmol/g)
(mmol/g)
Al-MCM-41 (20) 0.098
0.152
0.250
0.20
Al-MCM-41 (30) 0.091
Al-MCM-41 (50) 0.064
Al-MCM-41 (100) 0.042
0.134
0.093
0.058
0.225
0.157
0.100
0.26
0.30
0.39
a
Moles of NH desorbed/mol of Al in the sample; based on NH from
3
3
strong acid sites.
3.2. Reaction studies
o-allylphenol (o-AP), which cyclizes to give 2,3-dihydro-2-
3.2.1. Claisen rearrangement of allyl phenyl ether
methyl benzofuran (benzofuran).
The catalytic activity of the calcined MCM-41 samples
with different Si/Al ratios was compared for the Claisen
rearrangement of APE. The reaction scheme is shown in
Fig. 5. The ether first undergoes rearrangement to produce
3.2.1.1. Influence of duration of run The effect of run du-
ration (up to 12 h) on conversion and on o-AP and benzo-
furan selectivities over the catalysts (with different Si/Al

N.T. Mathew et al. / Journal of Catalysis 229 (2005) 105–113
109
Fig. 5. Reaction scheme of Claisen rearrangement of allyl phenyl ether: I, allyl phenyl ether; II o-allylphenol; and III, 2,3-dihydro-2-methylbenzofuran.
3.2.1.2. Influence of temperature The influence of tem-
perature on APE conversion and the o-AP and benzofuran
selectivities for the samples with different Si/Al ratios are
presented in Fig. 7. Conversion and ring formation increase
with temperature for all Si/Al ratios, though the effect is less
noticed for the most siliceous sample (Si/Al ∼ 100). o-AP
selectivity increases with increasing Si/Al ratio and decreas-
ing temperature; the influence of temperature is less at higher
Si/Al ratios.
3.2.1.3. Influence of Si/Al ratio Both conversion and se-
lectivity in the Claisen rearrangement are found to be de-
pendent on the Si/Al ratio of MCM-41. Purely siliceous
(Al-free) MCM-41 exhibited negligible conversion. Fig. 8
shows the influence of the Si/Al ratio on the reaction at
different temperatures. The APE conversion decreases with
decreasing aluminum content (increase in the Si/Al ratio)
of the catalyst. The figure shows that a maximum conver-
sion of up to 86.7% can be obtained with Al-MCM-41 with
a Si/Al ratio of 20 at 393 K at the end of a 12-h reaction.
The selectivity for o-AP increases and that for benzofuran
decreases with an increasing Si/Al ratio in Al-MCM-41. As
the reaction is catalyzed by the acid sites of Al-MCM-41, the
observed behavior must be due to the decrease in the acidity
of Al-MCM-41 with increasing Si/Al ratio (Table 2).
A plot of APE conversion and acidity (strong and weak)
versus Al content is shown in Fig. 9a. It is found that both
acidity and conversion increase with Al content. The close
relationship between acidity and conversion suggests that the
reaction occurs inside the pores of MCM-41. In the case of
zeolites, however, the reaction was assumed to occur mainly
on the external surface or at the pore mouth, as no rela-
tion between acidity (or Al content) and conversion was
noticed [8].
The turnover frequency (TOF, mole of APE converted or
product formed per hour per mole of Al present in the sam-
ple) is found to decrease with increasing Al content (for the
samples with Si/Al ≈ 20, 30, and 50) (Fig. 9b). The data
for the sample with Si/Al ≈ 100 do not fall in the above
Fig. 6. Influence of Si/Al ratio and duration of run on the conversion and
selectivity (reaction temperature, 393 K; F, Si/Al 20; 1, Si/Al 30; Q,
Si/Al 50; P, Si/Al 100).
trend because of an unexpectedly small TOF, suggesting the
nonaccessibility of the acid sites to the reactant molecules at
low Al contents. On the other hand, a small increase in the
TOF is noticed with increasing Al content for benzofuran
formation. When the TOF (conversion of APE or formation
ratios) at 393 K are shown in Fig. 6. In general, the con-
version and benzofuran formation increase with duration of
run, whereas o-AP decreases. The activity increases with in-
creasing Al content; the sample with the largest Si/Al ratio
(∼ 100) is the least active.
of o-AP) is calculated based on the total number of acid
sites (moles of NH3 desorbed) in the three samples (Si/Al
≈ 20, 30, and 50), a nearly constant value (TOF = 8
1 mol/(molNH h)) is obtained, revealing a direct relation-
3
ship between acidity and activity in these samples.

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N.T. Mathew et al. / Journal of Catalysis 229 (2005) 105–113
Fig. 7. Influence of temperature on conversion and selectivity over Al-MCM-41 with different Si/Al ratios.
Fig. 8. Influence of Si/Al ratio on conversion and selectivity at different temperatures (reaction time, 12 h; F, 373 K; 1, 383 K; Q, 393 K).

N.T. Mathew et al. / Journal of Catalysis 229 (2005) 105–113
111
(a)
(b)
Fig. 9. Influence of Al-content on (a) APE conversion and catalyst acidity
and (b) on TOF (reaction temperature, 393 K; time, 12 h).
3.2.1.4. Mechanism of the reactions A plausible mecha-
nism for production by the Claisen rearrangement of the allyl
phenol and its subsequent conversion to the ring compound
is presented in Figs. 10a and b. The steps are catalyzed by
acid centers. First the acid site protonates the oxygen of the
ether. This is followed by intramolecular rearrangement of
the protonated (adsorbed) species into the o-allylphenol as
shown in Fig. 10a. The allyl phenol is next protonated at the
allylic double bond to produce the secondary carbenium ion
that reacts again intramolecularly with the phenolic oxygen
to produce the benzofuran (Fig. 10b).
Fig. 10. Plausible mechanism of Claisen rearrangement of APE over solid
acids (Al-MCM-41), for the formation: (a) of o-AP and (b) of ring product.
In the above equations, CA and CA are the concentrations
0
of APE at initial time and at time t, respectively; CR is the
concentration of the intermediate product o-AP at time t;
and k1 and k2 are the rate constants for the first and second
steps, respectively.
3.2.1.5. Kinetic analysis The scheme presented in Fig. 5
shows that the reaction involves two consecutive steps for
the formation of benzofuran. Hence this was treated as a
first-order series reaction with o-AP as the intermediate
product, and the standard equations for a first-order series
reaction were used for the determination of rate constants.
These are
The concentration profiles of APE, o-AP, and benzofu-
ran for two temperatures (383 and 393 K) and Si/Al ra-
tios (Si/Al = 20 and 30) in the Claisen rearrangement of
APE are presented in Fig. 11. The lines represent the the-
oretical profiles. The profiles are those expected for typical
first-order consecutive reactions. The nature of the profile,
especially that for o-AP, depends on the relative values of
k1 and k2. The rate equations and the time tmax, at which
the intermediate o-AP concentration is maximum, are pre-
sented in Table 3. It can be seen from the table that tmax
CA/CA = e−k t
(1)
1
0
and
CR/C = k1(e−k t − e−k t )/(k2 − k1).
(2)
1
2
A0

112
N.T. Mathew et al. / Journal of Catalysis 229 (2005) 105–113
Fig. 11. Parity plots for the Claisen rearrangement of allyl phenyl ether at
two different Si/Al ratios and temperatures. Experimental values are pre-
sented by symbols; bold lines represent profiles based on generated equa-
tions.
Fig. 12. Influence of temperature and Si/Al ratio on the reaction rate con-
stants.
varies with both the reaction temperature and the Si/Al ra-
tio of MCM-41. For a given catalyst, tmax decreases with
increasing temperature and Al content.
The influence of temperature and Si/Al ratio (20 and 30)
on the reaction rate constants, k1 and k2, is presented in
Fig. 12. The figure shows that both k1 and k2 increase with
increasing temperature. It is found that k2 is not much af-
fected by variation in the Si/Al ratio, whereas k1 is sensitive.
The reasons for this are not clear.
The activation energy for the two steps was calculated
with the Arrhenius expression. The activation energy for the
reaction of APE on Al-MCM-41 with a Si/Al ratio of 20
is estimated to be 8.9 kcal/mol. The activation energy for
the formation of benzofuran from o-AP is estimated to be
10.3 kcal/mol. The activation energy of the reactions was
not found to be significantly affected by a change in the
Si/Al ratio.
4. Conclusions
The Claisen rearrangement of APE over Al-MCM-41
proceeds with ease in tetrachloroethane. o-Allyl phenol is
produced initially, which then undergoes cyclization to form
2,3-dihydro-2-methylbenzofuran. The reaction takes place
on the acid sites of the catalyst. Both the catalyst acidity and
substrate conversion increase with the Al content in MCM-
41. There is a close relationship between acidity and conver-
sion, which suggests that the reaction occurs inside the pores
of MCM-41. The conversion and benzofuran formation in-
crease with run duration, whereas the o-AP decreases, as ex-
pected for a consecutive reaction. The temperature effects on
conversion and selectivity are more pronounced at low Si/Al
ratios than at high Si/Al ratios. o-AP selectivity increases
with increasing Si/Al ratio and decreasing temperature. The
reaction kinetics was analyzed under the assumption that it is
Table 3
Results of kinetic analysis for Al-MCM-41 catalysts with Si/Al = 20 and 30
a
c
Si/Al
T
Rate constants
Rate expressions
t
max
b
b
(K)
k
(1/h)
k
(1/h)
2
Eq. (1)
Eq. (2)
(h)
7.55
1
−0.13t
−0.13t
−0.16t
−0.14t
−0.18t
20
383
393
0.13
0.16
0.14
0.18
C /C = e
C /C = 0.13(e
− e
− e
)/0.01
)/0.02
R
A
A
A
0
0
−0.16t
C /C = e
C /C = 0.16(e
5.80
R
A
A
A
0
0
−0.07t
−0.07t
−0.14t
30
a
383
393
0.07
0.10
0.14
0.21
C /C = e
C /C = 0.07(e
− e
− e
)/0.07
)/0.11
10.18
6.58
R
A
A
A
0
0
−0.10t
−0.10t
−0.21t
C /C = e
C /C = 0.10(e
R
A
A
A
0
0
Reaction temperature.
See text, kinetic analysis.
The time at which the concentration of o-AP reaches a maximum value.
b
c

N.T. Mathew et al. / Journal of Catalysis 229 (2005) 105–113
113
a first-order consecutive reaction. On Al-MCM-41, both k1
and k2 increase with increasing temperature. k2 is not much
affected by variation in the Si/Al ratio, whereas k1 is sensi-
tive. The time at which the intermediate o-AP concentration
is maximum, tmax, varies with both the reaction temperature
and the Si/Al ratio of MCM-41. For a given catalyst, tmax
decreases with increasing temperature and Al content.
[5] R.A. Sheldon, J.A. Elings, S.K. Lee, H.E.B. Lempers, R.S. Downing,
J. Mol. Catal. A: Chem. 134 (1998) 129.
[6] I. Sucholeiki, M.R. Pavia, C.T. Kresge, S.B. Mc Cullen, A. Malek, S.
Schram, Mol. Divers. 3 (1998) 151, CA: 129: 202736 (1999).
[7] R. Cruz-Almanza, F. Perez-Flores, L. Brena, E. Tapia, R. Ojeda, A.J.
Fuentes, Heterocycl. Chem. 32 (1995) 219.
[8] S.G. Wagholikar, S. Mayadevi, S.P. Mirajkar, S. Sivasanker, in: E. van
Steen, L. Callanan, M. Claeys, C.T. O’Connor (Eds.), Proceedings of
14th International Zeolite Conference, Cape Town, 2004, p. 2731.
[9] C.T. Kresge, M.E. Leonowicz, W.J. Roth, J.C. Vartuli, J.S. Beck, Na-
ture 359 (1992) 710.
[10] J.S. Beck, J.C. Vartuli, W.J. Roth, M.E. Leonowicz, C.T. Kresge, K.D.
Schmitt, C.T.W. Chu, D.H. Olson, E.W. Scheppard, S.B. MacCullen,
H.B. Higgins, J.L. Schlenker, J. Am. Chem. Soc. 114 (1994) 10834.
[11] R.B. Borade, A. Clearfield, Catal. Lett. 31 (1995) 267.
[12] X. Chen, L. Huang, G. Ding, Q. Li, Catal. Lett. 44 (1997) 123.
[13] S.J. Gregg, K.S.W. Suig, Adsorption, Surface Area and Porosity, Aca-
demic Press, London, 1982, Ch. 4.
References
[1] J. March, Advanced Organic Chemistry, fourth ed., Wiley, New York,
1992.
[2] R.P. Lutz, Chem. Rev. 84 (1984) 205.
[3] K. Pitchumani, M. Warrier, V. Ramamurthy, J. Am. Chem. Soc. 118
(1996) 9428.
[14] H. Kosslick, G. Lischke, B. Parlitz, W. Storek, R. Fricke, Appl. Catal.
A. Gen. 184 (1999) 49.
[4] J.A. Elings, R.S. Downing, R.A. Sheldon, Stud. Surf. Sci. Catal. 94
(1995) 487.