Friedel-Crafts alkylation of anisole in supercritical carbon dioxide: A comparative study of catalysts

Article abstract of DOI:10.1021/op050044y

The Friedel-Crafts alkylation of anisole with n-propanol was carried out over five different Bronsted solid acid catalysts using supercritical carbon dioxide as the reaction medium. The reaction temperature and pressure were evaluated in terms of selectivity for the monoalkylated products, conversion of the starting material, and the products' isomeric ratio. Desulfonation of the catalysts was observed when the temperature was increased above 150°C for the organic supported catalysts investigated Amberlyst 15 and Purolite CT-175, and above 200 to 250°C for the inorganic supported catalysts Nafion SAC-13 and Deloxan ASP I/7. A decrease in the catalytic performance of organic supported catalysts was observed with increasing pressure. This decrease was related to the phase behaviour of the reaction.

Full text of DOI:10.1021/op050044y

Organic Process Research & Development 2005, 9, 451−456
Friedel-Crafts Alkylation of Anisole in Supercritical Carbon Dioxide: A
Comparative Study of Catalysts
†
†
‡
§
,†
Rodrigo Amandi, Peter Licence, Stephen K. Ross, Olli Aaltonen, and Martyn Poliakoff*
School of Chemistry, UniVersity of Nottingham, UniVersity Park, Nottingham NG7 2RD, UK, Thomas Swan & Co. Ltd.,
Crookhall, Consett, Co. Durham DH8 7ND, UK, and VTT Processes, P.O. Box 1602 FIN-02044 VTT, Finland
9
Abstract:
modified with trifluoroacetic acid (TFA) or water, rare earth
1
0,11
The Friedel-Crafts alkylation of anisole with n-propanol was
carried out over five different Brønsted solid acid catalysts using
supercritical carbon dioxide as the reaction medium. The
reaction temperature and pressure were evaluated in terms of
selectivity for the monoalkylated products, conversion of the
starting material, and the products’ isomeric ratio. Desulfona-
tion of the catalysts was observed when the temperature was
increased above 150 °C for the organic supported catalysts
investigated Amberlyst 15 and Purolite CT-175, and above 200
to 250 °C for the inorganic supported catalysts Nafion SAC-13
and Deloxan ASP I/7. A decrease in the catalytic performance
of organic supported catalysts was observed with increasing
pressure. This decrease was related to the phase behaviour of
the reaction.
metal trifluoromethanesulfonates
catalysis and mesoporous molecular sieves,
all as homogeneous
1
2,13
organic
1
4,15
16
17,18
4,13
resins,
sulfated metal oxides, clays,
and zeolites
for heterogeneously catalysed Friedel-Crafts alkylation
reactions.
The advantages of using heterogeneous catalysts include
reduced equipment corrosion, ease of product separation, less
potential contamination in waste streams, recycling of the
catalysts, and also the possibility of carrying out Friedel-
Crafts reactions continuously with a fixed catalyst bed rather
Continuous reactors are
generally smaller and safer than batch reactors with equiva-
lent production capacity. In addition, batch reactions in
scCO are relatively difficult to scale up as a result of the
14,19
than in traditional batch reactors.
2
0
2
high cost associated with the high-pressure vessels needed.
Continuous fixed-bed catalytic flow reactors, using scCO
as the reaction medium, have already been scaled up to
commercial scale by Thomas Swan & Co. Ltd. This facility
is a multipurpose plant; thus, changing the catalyst within
the reactor changes the chemistry.
To investigate whether the catalytic activity of heteroge-
neous catalysts changes under supercritical conditions is of
crucial importance for the chemical manufacturer in the event
of scaling-up a particular process. In this investigation, the
2
1
. Introduction
21
The Friedel-Crafts alkylation reaction is among the most
fundamental and useful reactions for carbon-carbon bond
formation in aromatic systems. Although Friedel-Crafts
chemistry is one of the most wasteful in terms of byproduct
formation, atom efficiency, and catalyst usage, it is widely
applied in the fine chemicals industry. Typically, the reaction
is performed using an alkyl halide in the presence of Lewis
acids, such as AlCl
concentrated H SO . In particular, anhydrous AlCl has
2 4 3
1
2
3
4
2
effect of scCO on the catalytic activity of a variety of
5
3
or BF
3
, or protic acids, such as HF or
commercially available solid acid catalysts, by varying the
reaction p and T, was evaluated for the alkylation of anisole
with n-propanol (Scheme 1).
6
maintained its wide use in solution chemistry since it was
introduced by Friedel and Crafts in 1877.7
Due to the importance of the Friedel-Crafts alkylation
reaction in industry, a variety of new, more environmentally
friendly and efficient catalysts have been reported in the
(
9) Olah, G.; Torok, B.; Prakash, S. Appl. Catal., A 1996, 146, 107-117.
4
(10) Kawada, A.; Mitamura, S.; Matsuo, J.; Tsuchiya, T.; Kobayashi, S. Bull.
Chem. Soc. Jpn. 2000, 73, 2325-2333.
11) Kobayashi, S.; Sugiura, M.; Kitagawa, H.; Lam, W. W. L. Chem. ReV. 2002,
(
literature. Examples of these include p-toluensulfonic acid
102, 2227-2302.
8
(12) Selvaraj, M.; Pandurangan, A.; Seshadri, K. S.; Sinha, P. K.; Krisnashami,
monohydrate (TsOH), trifluoromethanesulfonic acid (TFSA)
V.; Lal, K. B. J. Mol. Catal. A: Chem. 2002, 186, 173-186.
(
13) Clark, M. C.; Subramaniam, B. Ind. Eng. Chem. Res. 1998, 37, 1243-
*
Corresponding author. Telephone: +44 (0)115 951 3520. Fax: +44 (0)-
1250.
1
15 951 3058. E-mail address: Martyn.Poliakoff@nottingham.ac.uk.
(14) Harmer, M. A.; Sun, Q. Appl. Catal., A 2001, 221, 45-62.
(15) Hart, M.; Fuller, G.; Brown, D. R.; Park, C.; Keane, M. A.; Dale, J. A.;
Fougret, C. M.; Cockman, R. W. Catal. Lett. 2001, 72, 135-139.
(16) Ginosar, D. M.; Thompson, D. N.; Coates, K.; Zalewski, D. J. Ind. Eng.
Chem. Res. 2002, 41, 2864-2873.
(17) Cseri, T.; Bekassy, S.; Kenessey, G.; Liptay, G.; Figueras, F. Thermochim.
Acta 1996, 288, 137-154.
(18) Miller, J. M.; Goodchild, M.; Lakshmi, L. J.; Wails, D.; Hartman, J. S.
Mater. Lett. 2000, 44, 164-169.
(19) Haag, J. S. Handbook of Heterogeneous Catalysis; Wiley-VCH: Weinheim,
1997; Vol. 5.
†
University of Nottingham.
Thomas Swan & Co. Ltd.
VTT Processes.
‡
§
(
1) Olah, G. A. Friedel-Crafts and Related Reactions; Wiley: New York, 1963-
964; Vol. I-IV.
2) Constable, D. J. C.; Curzons, A. D.; Cunningham, V. L. Green Chem. 2002,
1
(
4
, 521-527.
(
(
(
(
3) Sheldon, R. A. CHEMTECH 1994, 24, 38-47.
4) Tanabe, K.; H o¨ lderich, W. F. Appl. Catal., A 1999, 181, 399-434.
5) Singh, R. P.; Singh, V. K. Tetrahedron 2000, 57, 241-247.
6) Harmer, M. A.; Sun, Q.; Vega, A. J.; Farneth, W. E.; Heidekum, A.;
Hoelderich, W. F. Green Chem. 2000, 2, 7-14.
(20) Tundo, P. Continuous Methods in Organic Synthesis; Ellis Horwood:
Chichester, 1991.
(21) Licence, P.; Ke, J.; Sokolova, M.; Ross, S. K.; Poliakoff, M. Green Chem.
2003, 5, 99-104.
(
(
7) Friedel, C.; Crafts, J. M. Comptes Rendus 1877, 84, 1392-1450.
8) Mahindaratne, M.; Wimalasena, K. J. Org. Chem. 1998, 63, 2858-2866.
1
0.1021/op050044y CCC: $30.25 © 2005 American Chemical Society
Vol. 9, No. 4, 2005 / Organic Process Research & Development
•
451
Published on Web 05/12/2005

Scheme 1. Friedel-Crafts alkylation of anisole, 1, with
n-propanol over solid acid catalysts to form
o-isopropylanisole, 2, p-isopropylanisole, 3, and polyalkylated
derivatives, 4
Table 1. Supplier and properties of the commercially
available catalysts investigated
surface
typical
area
loading T stability
amount
2
a
catalyst
supplier
(m /g) (meq/g)
(°C)
loaded (g)
Amberlyst 15b
Purolite CT-175
Nafion SAC-13
Deloxan ASP I/7d Degussa
Rohm & Haas
Purolite Int.
DuPont
47
30
200
510
660
4.80
5.00
0.15
1.10
1.60
130
150
280
200
-
4.8
5.7
3.7
4.7
3.3
b
c
e
Zeolyst CBV 600
Zeolyst Int.
The catalysts investigated included the following: com-
mercially available organic acidic ion-exchange resins (Am-
berlyst 15 and Purolite CT-175), inorganic supported cata-
lysts (Nafion SAC-13 and Deloxan ASP I/7) in addition to
a
Amount needed to fill a 10-mL reactor volume. b Organic supported catalysts
as a result of the copolymerisation of styrene and DVB. The degree of cross-
c
linking was 20-25%. Silica composite with 13% w/w of Nafion particles
d
entrapped within the porous framework. Deloxan is a macroporous polysiloxane
with alkylsulfonic acid groups. This catalyst was manufactured by Degussa, but
2
a zeolite (Zeolyst CBV 600). The use of scCO as a solvent
sadly, it is no longer available. e Type Y zeolite (H ) with a Si/Al ratio of 5.2.
+
in our reactions may offer the following advantages: en-
22
hancement of the reaction rate and selectivity, enhancement
of mass and heat transfer rates, an increase in the catalyst
lifetime due to the extraction of coke precursors, and easier
of the organic mixture in the scCO
otherwise stated.
2
was 10%w/w unless
2
3
separation of the products from the solution after reaction.
2.1. Catalysts. Five commercially available Brønsted-type
There have been a small number of published examples
solid acid catalysts have been studied in this research,
Amberlyst 15, Purolite CT-175, Nafion SAC-13, Deloxan
ASP I/7, and Zeolyst CBV 600. Table 1 shows some of their
properties as well as the different suppliers. Samples of
of continuous alkylation reactions using heterogeneous
catalysts in scCO
2
in the literature,1
6,24,25
which demonstrated
that aromatic substrates could undergo continuous and
sustainable Friedel-Crafts alkylation in supercritical fluids
over solid acid heterogeneous catalysts with high selectivity
towards the product of interest. However, although the
literature shows that Friedel-Crafts alkylation reactions can
be carried out in the supercritical phase and in the presence
of heterogeneous catalysts, there is no true understanding
of the reaction parameters required to perform more produc-
tive and selective alkylations.
“
fresh” catalyst were used to study the performance of the
different catalysts across the temperature range at different
pressures.
The catalysts were loaded into the reactor and used “as
supplied” by the manufacturer. Before pumping of the
organic substrate was started, the catalysts were dried in situ
by flowing scCO at the reaction temperature for a period
2
of 1 h. This pretreatment should, in principle, remove any
water entrapped within the catalyst particles.
To achieve a highly selective Friedel-Crafts alkylation
in scCO
and optimised; namely, pressure (p), temperature (T), alky-
lating agent, flow rates of scCO and substrate, choice of
catalyst, and the effect of scCO on their catalytic activity.
2
, a large number of parameters must be investigated
2
.2. Supercritical Fluid Continuous Flow Apparatus.
A diagram of the supercritical fluid continuous flow ap-
paratus is shown in Figure 1. The scCO pump compresses
the CO to above the desired system pressure. The system
2
2
2
2
Minor modification of the reaction conditions could lead to
dramatic changes to the outcome of the reaction, mainly in
terms of selectivity and conversion. For this reason, a deeper
knowledge and control of the process is highly desirable from
both an industrial and academic point of view.
pressure is then controlled by the pressure regulator. The
organic substrate is pumped using a standard HPLC pump.
The supercritical fluid and the organic substrate are mixed
in a static mixer, before entering the reactor, which contains
the catalyst. The catalyst is held inside the reactor by a frit
placed at the bottom of the reactor. Thermocouples placed
inside the catalyst bed, in the reactor heating block and in
the product stream, are used to monitor the reaction. The
pressure is then reduced stepwise to separate the product(s)
from the fluid using an expansion module. The flow of the
exhaust gases is measured by a flowmeter which is connected
to the vent line. The flow rate of the gases was set to 0.65
The main chemical challenge in conventional Friedel-
Crafts alkylation reactions is to achieve selective monoalky-
lation of the substrate. Unfortunately, the addition of the first
alkyl group activates the substrate so that subsequent
26
alkylation is made easier. Consequently, reaction parameters
have to be controlled precisely, often with high dilution and
low temperatures to minimise the formation of polyalkylated
2
5
products.
L/min of CO
corresponds to 1.06 g/min.
.3. Characterisation Techniques. The identification and
2
at room temperature and pressure which
2
. Experimental Section
All of the experiments reported were carried out using 1
2
quantification of the products obtained in all the experiments
reported were carried out using GC and GC-MS. The GC
analysis was carried out using a Shimadzu GC-17a with an
AOC 20i autosampler. Helium was used as carrier gas, and
the detector was an FID. The GC-MS instrument employed
was a Thermo-Finnegan Polaris Q ion trap GC-MSn. The
column used in both instruments was a RTX-5 (30 m length,
0.52 mm i.d. and 0.25 µm film thickness).
and n-propanol in a molar ratio of 3:1, and the concentration
(
(
22) Baiker, A. Chem. ReV. 1999, 99, 453-473.
23) Hyde, J. R.; Licence, P.; Carter, D. N.; Poliakoff, M. Appl. Catal., A 2001,
2
22, 119-131.
(
24) Santana, G. M.; Akgerman, A. Ind. Eng. Chem. Res. 2001, 40, 3879-3882.
(25) Hitzler, M. G.; Smail, F. R.; Ross, S. K.; Poliakoff, M. Chem. Commun.
1
998, 359-360.
(26) Vollhardt, K. P.; Schore, N. E. Organic Chemistry, 2nd ed.; W. H. Freeman
and Company: New York, 1994.
452
•
Vol. 9, No. 4, 2005 / Organic Process Research & Development

Figure 1. Schematic of the supercritical fluid continuous flow equipment.
Scheme 2. Formation of phenol 5 and Fries rearrangement
of 1 to form o-cresol, p-cresol, and m-cresol in the presence
of an acid catalyst
Figure 2. Conversion of 1 (0), selectivity for 2 and 3 (9), and
ratio of 2 to 3 (2) for the alkylation of 1 with n-propanol over
Amberlyst 15 at 200 bar in scCO
3. Results and Discussion
2
.
The influence of the reaction temperature and pressure
2
8
on the catalyst performance was evaluated in terms of the
selectivity for monoalkylated products (2 + 3), the absolute
conversion of 1, and the isomeric ratio for monoalkylated
species (2 and 3).
al. The formation of propylene was also observed as a result
of the formation of the carbocation and the subsequent
elimination of a proton to form the double bond.
Figure 2 shows the catalytic activity of Amberlyst 15 for
the alkylation reaction at 200 bar and across the range of
temperatures. The conversion of 1 was maximized at 150
3
.1. Effect of Temperature. The range of temperatures
at which the catalysts were investigated was from 100 to
50 °C. As a general observation, formation of phenol 5 and
2
°
C, although the selectivity for monoalkylated products was
cresols occurred (Scheme 2). The formation of these deriva-
tives, particularly 5, increased significantly when the tem-
perature was raised above 200 °C.
poor. Above 150 °C the conversion of 1 dropped dramatically
with the reaction running time, as a result of a desulfonation
29
process of the catalyst.
Formation of cresols was a result of protonation of the
O-Me group and the rearrangement of 1 (Fries rearrange-
ment) in the presence of an acid catalyst. In some cases, the
Sulfur microanalysis measurements on a sample of
untreated catalyst and catalyst exposed to the reaction
conditions confirmed the desulfonation of the catalyst (Table
2
7
reaction can proceed by simple heating without a catalyst.
2
). The loading found for the untreated sample of catalyst
The phenol formed can also react with n-propanol to form
phenol-alkylated products, thereby decreasing the overall
selectivity for 2 and 3. The formation of ethers (N-n-propyl
ether and n-propyl-isopropyl ether) was also observed when
the reaction was performed at mild temperatures (100-150
was 4.3 mequiv/g of -SO H groups (13.67% S), whereas
the loading for the catalysts after use at 150 °C and 200 °C
were 10% and nearly 50% lower, respectively. Purolite CT
3
1
1
75 showed a behavior similar to that shown by Amberlyst
5. However, no reaction was observed at low temperatures
°
C). Formation of ethers from alcohols in the presence of a
solid acid catalyst in scCO was first described by Gray et
2
(28) Gray, W. K.; Smail, F. R.; Hitzler, M. G.; Ross, S. K.; Poliakoff, M. J. Am.
Chem. Soc. 1999, 121, 10711-10718.
(29) Rhodes, C. N.; Brown, D. R.; Plant, S.; Dale, J. A. React. Funct. Polym.
1999, 40, 187-193.
(
27) March, J. AdVances in Organic Chemistry; Wiley-Interscience: New York,
1
985.
Vol. 9, No. 4, 2005 / Organic Process Research & Development
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453

Table 2. Sulfur content by microanalysis in untreated and
treated samples of Amberlyst 15
sulfur detected
(%)
3
meq of -SO H/
catalyst
untreated
g catalyst
13.67
12.33
6.90
4.3
3.9
2.2
150 °C/200 bar
00 °C/200 bar
2
Figure 4. Effect of pressure on the conversion of 1 at 200 °C
over inorganic supported catalysts in scCO
2
.
Figure 3. Conversion of 1 (0), selectivity for 2 and 3 (9), and
ratio of 2 to 3 (2) for the Friedel-Crafts alkylation of 1 with
n-propanol at 200 bar in scCO and using Nafion SAC-13 as
2
catalyst.
(100 °C) most likely due to the high moisture content of
this catalyst (∼53%w/w).
Desulfonation of the catalyst also occurred above 150 °C,
leading to a poor conversion of 1. In contrast, the inorganic
supported catalysts showed a higher optimum temperature
range than that observed for the organic supported catalysts.
Figure 3 shows that a 90% conversion of 1 and 60%
selectivity for 2 plus 3 was achieved at 200 °C using Nafion
SAC-13 as catalyst. However, at temperatures above 250
Figure 5. Effect of pressure on the selectivity for 2 + 3 at 200
C over Nafion SAC-13 Deloxan ASP I/7 and Zeolyst CBV 600
in scCO
°
2
.
°C desulfonation of the catalyst was observed. Deloxan ASP
I/7 showed an optimum reaction temperature of 200 °C;
however, desulfonation was noted at temperatures above that
temperature. Finally, maximum conversion of 1 (73%) was
achieved at 200 °C using Zeolyst CBV 600, but selectivity
to 2 + 3 decreased to 60%.
3.2. Effect of Pressure. An increase in the system
pressure causes an increase in the CO density as well as an
2
increase in the mean residence time of the organic substrate
in the catalyst bed. This effect might be expected to increase
the absolute conversion of the starting material and decrease
the selectivity for the product(s), but only if the reaction has
not reached its final conversion inside the catalyst bed at
the reference conditions. This was observed for the inorganic
supported catalysts investigated (Figures 4 and 5), but the
organic supported catalysts showed the opposite effect
Figure 6. Effect of pressure on the conversion of 1 at 150 °C
over Amberlyst 15 and Purolite CT-175 in scCO
2
.
plasticization.30,31 A plasticization process may also have
been taking place in the catalysts investigated in the presence
of scCO
interact with CO
A decrease in the T
2
, since they possess a polymeric matrix which could
with a decrease in the T of the polymer.
of the polymer might modify the
2
g
g
(
Figures 6 and 7).
A possible explanation for this effect on both parameters,
polymer matrix decreasing the number of available acidic
groups which in turn would impair the catalyst performance
could be related to the different nature of the support of these
catalysts under high pressure. Recent studies have shown
when the amount of CO
CO can dissolve polystyrene (PS) at pressures above 500
bar and 100 °C if the molecular weight of the PS is less
2
in our system increased. However,
2
3
2
the ability of scCO
CO causes swelling and changes in the mechanical and
physical properties of the polymer. The most important result
is a reduction in the glass transition temperature (T ) of glassy
polymers in the presence of scCO . This is generally termed
2
to diffuse into a polymeric matrix. The
2
(30) Kazarian, S. G.; Vincent, M. F.; Bright, F. V.; Liotta, C. L.; Eckert, C. A.
J. Am. Chem. Soc. 1996, 118, 1729-1736.
(
(
31) Kazarian, S. G. Polym. Sci., Ser. C 2000, 42, 78-101.
32) McHugh, M. A.; Krukonis, V. J. Supercritical Fluid Extraction: Principle
and Practice, 2nd ed.; Butterworth-Heinemann: Boston, 1994.
g
2
454
•
Vol. 9, No. 4, 2005 / Organic Process Research & Development

anisole but to a decrease in the selectivity for the desired
products. An increase in pressure (300-400 bar) leads to a
single-phase system, in which all the organics would be
2
dissolved and diluted within the scCO . The diffusion
resistance of this single phase into the catalytic active sites
would determine the overall rate. An increase in pressure
from 300 to 400 bar would increase the residence time across
the catalyst bed leading to an increase in the conversion of
the starting material. The selectivity for the reaction could
be explained as follows: in the two-phase region, the organic
material, in the liquid phase, would take longer to diffuse
into the polymeric matrix, react. and diffuse back out to the
reaction stream, allowing further alkylation reactions and
other side reactions to take place. By contrast, in the one-
phase region, the diffusion of the organic material into the
polymeric particles would occur more rapidly since the
Figure 7. Effect of pressure on the selectivity for 2 + 3 at 150
C over Amberlyst 15 and Purolite CT-175 and across the
pressure range in scCO
°
2
.
organic material is dissolved in the scCO
2
. The inorganic
supported catalysts may not display such a marked pseudocon-
centration effect at low pressures, since the surface may not
be so easily wetted when the reaction mixture is biphasic.
Consequently, an increase in the working pressure should
increase the conversion of the starting material due to the
longer residence time across the catalyst bed. In the single
phase, the diffusion into the active sites would probably be
the rate-determining step, as all the organic material would
Figure 8. Phase diagram showing the effect of %w/w of
organic material in scCO at 150 °C (2), 175 °C (b), and 200
C (0). The organic mixture is for the alkylation of 1 with
n-propanol at 3:1 molar ratio at different temperatures in
scCO . The phase measurements were conducted in a variable
2
be dissolved and diluted within the scCO .
2
°
4
. Conclusions
2
volume view cell with a visual inspection of the cell contents
via a boroscope and a video camera system.
The organic supported catalysts investigated, Amberlyst
5 and Purolite CT-175, performed best within the temper-
1
ature range from 100 to 150 °C. Above 150 °C, a decrease
in the conversion of the starting material with time occurred
as a result of desulfonation of the catalyst. By contrast, the
inorganic supported catalysts, Nafion SAC-13, Deloxan ASP
I/7, and Zeolyst CBV 600, showed a higher optimum
temperature range. As a general trend, the higher the reaction
temperature, within the optimum temperature range found
for each catalyst, the higher the conversion of the starting
material. However, the reaction became less selective towards
the monoalkylated products.
The effect of pressure on the reaction performance was
found to correlate with the phase behaviour of the reaction.
Thus, when the organic supported catalysts were employed
in the reaction in the two-phase region, a pseudoconcentra-
tion effect appeared to modify the behaviour of the catalyst
bed, thus increasing the reaction rate for all processes leading
to a higher conversion of 1 and decreasing the selectivity
for monoalkylated products. In the single-phase region, the
than 1000. In contrast, PS of a higher molecular weight
-
1
(106 000 gmol ) shows very low solubility even at 225 °C
and 2100 bar which demonstrates that a plasticization process
is unlikely to be happening to our catalyst due to the low
solubility that scCO exhibited in PS.
2
Phase behaviour studies of our reaction (see Figure 8)
suggested why lower pressures (100 bar) might lead to an
apparent increase in the activity of the organic supported
catalysts leading to an increase in the conversion of the
starting material and a decrease in selectivity for the products
of interest. The low solubility of the reactants (1 +
2
n-propanol) in scCO and the lipophilicity of the catalysts
due to their organic nature (styrene-divinylbenzene copoly-
mer (S-DVB)) could favour the formation of a thin film of
3
3
the organic material on the surface of the catalyst. Thus,
an increase in the concentration of organic material in the
proximity of the catalyst active sites would occurred
(
pseudoconcentration effect).34
2
organic material would be dissolved and diluted with scCO .
Furthermore, at low pressures, the reactor would operate
The diffusion of the single phase into the catalytic active
sites would determine the overall rate of the reaction.
However, when inorganic supported catalysts were em-
ployed, increases in the working pressure produced corre-
sponding increases in the conversion of the starting material
as a consequence of an increase in the residence time across
as a trickle bed reactor, in which the residence time of the
liquid phase across the catalyst bed would be longer than
the residence time of the single supercritical phase formed
at higher pressures. In this way, the reaction rate of all
processes will increase, leading to a higher conversion of
the catalyst bed. Furthermore, the acidic terminal -CF
2 2
CF -
(
(
33) Desikan, S.; Doraiswamy, L. K. Chem. Eng. Sci. 2000, 55, 6119-6127.
34) Hodge, P. Chem. Soc. ReV. 1997, 26, 417-424.
SO H group in Nafion SAC-13, has been shown to be scCO -
3
2
Vol. 9, No. 4, 2005 / Organic Process Research & Development
•
455

philic,35 and therefore an enhancement in the diffusion of
the single phase formed by the organic material dissolved
within the scCO into the catalytic sites would be expected.
2
selectivities for the product(s) of interest. Phase behavior
measurements have proved to be of crucial importance to
truly understand and predict the reaction outcome when
employing supercritical fluids as the reaction media.
An extensive catalyst lifetime investigation, however, is
required to scale up this process to commercial scale.
Despite the high surface area of Deloxan ASP I/7, this
catalyst behaved very similarly to the organic supported
catalysts previously described, when the pressure was varied.
The low conversion of the starting material achieved across
the temperatures and pressures tested was a result of the low
loading of the catalyst. The o-/p- ratio was found to be largely
independent of temperature, pressure, and catalyst type.
This investigation has shown that Friedel-Crafts alky-
lation of simple aromatics, such as anisole, can successfully
be carried out over Brønsted-type solid acid catalysts with
Acknowledgment
We thank J. R. Hyde, D. N. Carter, F. R. Smail, and E.
Garcia-Verdugo for their help and J. A. Dale and L. Froment
from Purolite International for kindly providing some of the
catalysts investigated. Finally, we thank Thomas Swan &
Co. Ltd., EPSRC, EUFP5 project “CPFCO2”, and the Marie
Curie Programme for funding.
2
different catalytic supports, in scCO , with very high
conversion of starting material in conjunction with high
Received for review March 17, 2005.
OP050044Y
(35) Harmer, M. A.; Hutchenson, K. W. Chem. Commun. 2002, 18-19.
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