Rare earth(III) perfluorooctanesulfonates catalyzed Friedel-Crafts alkylation in fluorous biphase system

Article abstract of DOI:10.1016/j.jfluchem.2005.03.010

The catalyst of rare earth(III) perfluorooctanesulfonates (RE(OSO ₂C₈F₁₇)₃, RE = Sc, Y, La-Lu) were prepared from either rare earth chlorides(III) or oxides and perfluorooctanesulfonic acid. The perflates thus obtained act as novel catalysts for Friedel-Crafts alkylation in fluorous biphasic system. Perfluorohexane (C₆F₁₄), perfluoromethylcyclohexane (C₇F ₁₄), perfluorotoluene (C₇F₈), perfluorooctane (C₈F₁₈), perfluorooctyl bromide (C₈F ₁₇Br) and perfluorodecalin (C₁₀F₁₈, cis- and trans-mixture) can be used as fluorous solvents for this reaction. By simple separation of the fluorous phase containing only catalyst, alkylation can be repeated many times.

Full text of DOI:10.1016/j.jfluchem.2005.03.010

Journal of Fluorine Chemistry 126 (2005) 831–833
www.elsevier.com/locate/fluor
Rare earth(III) perfluorooctanesulfonates catalyzed Friedel–Crafts
alkylation in fluorous biphase system
*
Wen-Bin Yi , Chun Cai
Chemical Engineering College, Nanjing University of Science and Technology, Nanjing 210094, China
Received 13 January 2005; received in revised form 26 February 2005; accepted 7 March 2005
Available online 28 April 2005
Abstract
The catalyst of rare earth(III) perfluorooctanesulfonates (RE(OSO2C8F17)3, RE = Sc, Y, La–Lu) were prepared from either rare earth
chlorides(III) or oxides and perfluorooctanesulfonic acid. The perflates thus obtained act as novel catalysts for Friedel–Crafts alkylation in
fluorous biphasic system. Perfluorohexane (C6F14), perfluoromethylcyclohexane (C7F14), perfluorotoluene (C7F8), perfluorooctane (C8F18),
perfluorooctyl bromide (C8F17Br) and perfluorodecalin (C10F18, cis- and trans-mixture) can be used as fluorous solvents for this reaction. By
simple separation of the fluorous phase containing only catalyst, alkylation can be repeated many times.
# 2005 Elsevier B.V. All rights reserved.
Keywords: Friedel–Crafts alkylation; Fluorous biphasic catalysis; Rare earth(III) perfluorooctanesulfonates; Perfluorocarbons
1. Introduction
under homogeneous conditions. When the reaction is
finished the fluorous phase containing only catalyst is
easily recovered through simple phase-separation, and can
be reused without further treatment in a new reaction cycle
[5]. Therefore, we believe that Lewis acids RE(O-
SO2C8F17)3 can catalyze Friedel–Crafts alkylation in
FBS. In this paper, a green process of Friedel–Crafts
alkylation in FBS was studied.
Friedel–Crafts alkylation is a key process in the catalytic
manufacturing of semiproducts for the synthesis of drugs,
pesticides and dyes. However, the large-scale synthesis,
involving more than stoichiometrical amount of Lewis acids
such as aluminum trichloride (AlCl3), makes alkylation one
of the most environmentally harmful processes. Recently,
many papers related with the Lewis acids of rare earth(III)
perfluorooctane sulfonates (RE(OSO2C8F17)3) have been
published [1–4]. The characteristic features of the catalyst
include low hygroscopicity, ease of handling, robustness for
the recycling using and high solubility in fluorous solvent
[2–4]. Shi and Cui reported in 2002 that RE(OSO2C8F17)3
could catalyze Friedel–Crafts acylation effectively [4]. As
the same time, researchers have found many reactions can be
carried out in fluorous biphasic system (FBS) proposed by
Horvath and Rabai [5]. FBS is a new separation and
immobilization technique. By choosing a perfluorocar-
bon(PFC)/organic solvent couple that shows a thermally
controlled miscibility, it is possible to carry out the reaction
2. Results and discussion
The reaction of anisole with benzyl alcohol was adopted
for the investigate of catalysts and solvents (Scheme 1).
Table 1 shows the catalytic activity of sixteen RE(O-
SO2C8F17)3 (RE = Sc, Y, La–Lu) complexes in perfluor-
odecalin (C10F18, cis- and trans-mixture) fluorous solvent.
Among these catalysts, Sc(OSO2C8F17)3 and Yb(O-
SO2C8F17)3 are the most active catalysts in this reaction.
The control experiment elucidates that only 6% product of
alkylation could be obtained in the absence of catalyst and
fluorous solvent. In addition, we found that, only 0.2 mol%
catalyst loading was required in the alkylation. We even tried
heptadecafluorooctanesulfonic acid (C8F17SO3H) itself
* Corresponding author. Fax: +86 25 84315030.
E-mail address: yiwenbin5@163.com (W.-B. Yi).
0022-1139/$ – see front matter # 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.jfluchem.2005.03.010

832
W.-B. Yi, C. Cai / Journal of Fluorine Chemistry 126 (2005) 831–833
Scheme 1.
Scheme 2.
Table 1
temperature, so it is impossible to recover fluorous phase by
phase-separation. At the same time, we found that during
repeated alkylation reactions the loss of fluorous solvent is
very serious when using perfluoromethyl-cyclohexane
(C7F14) as a fluorous solvent because it is very volatile
(bp 76 8C). Therefore, perfluorodecalin (C10F18, cis- and
trans-mixture) is the best fluorous solvent for alkylation.
Thus, in order to seek out a pratical, useful Friedel–Crafts
alkylation, we decided to use the relatively cheap and
Effect of catalysts for alkylation of anisole with benzalcohol
Entry
Catalyst
Sc(OSO2C8F17 3
Y(OSO2C8F17 3
La(OSO2C8F17 3
Ce(OSO2C8F17 3
Pr(OSO2C8F17 3
Nd(OSO2C8F17 3
Sm(OSO2C8F17 3
Eu(OSO2C8F17 3
Gd(OSO2C8F17 3
Tb(OSO2C8F17 3
Dy(OSO2C8F17 3
Ho(OSO2C8F17 3
Er(OSO2C8F17 3
Tm(OSO2C8F17 3
Yb(OSO2C8F17 3
Lu(OSO2C8F17 3
C8F17SO3H
Yield (%)a
Ratio of o:m:pb
1
2
)
98
72
53
52
91
40
60
91
86
31
56
90
67
59
96
94
92
34:trace:66
32:trace:68
31:trace:69
30:trace:70
39:trace:61
36:trace:64
34:trace:66
32:trace:68
34:trace:66
30:trace:70
35:trace:65
39:trace:61
36:trace:64
31:trace:69
33:trace:67
32:trace:68
39:trace:61
)
3
)
4
)
5
)
6
)
7
)
8
)
similarly active Yb(OSO2C8F17)3 as
a catalyst and
9
)
perfluorodecalin (C10F18, cis and trans-mixture) as a
fluorous solvent for alkylation in FBS (Scheme 2). The
alkylations of various aromatics with alkylating agents have
been tested. As shown in Table 3, Friedel–Crafts alkylation
can be carried out effectively in FBS. When the reaction was
finished, the reaction mixture was cooled to room
temperature. The fluorous phase is not miscible with
aromatic substrates and dissolves only the catalysts. The
fluorous phase can be easily separated from the reaction
mixture and reused for the next alkylation. The fluorous
phase containing only catalyst could be simply reused many
times with a little decrease in activity. For example, in the
Yb(OSO2C8F17)3 catalyzed reaction of anisole with benzyl
alcohol in perfluorodecalin (C10F18, cis and trans-mixture),
the yields of alkylation from the first run to the fifth run are
96, 94, 95, 94 and 92%, respectively. This may partly be
attributed to the water-repellent nature of the perfluoroalk-
ane chain ‘‘(ÀCF2ÀCF2À)n’’ of RE(OSO2C8F17)3 which
refuses the approach of water molecules to the central metal
cation, thus maintaining its high Lewis acidity [2].
10
11
12
13
14
15
16
17
)
)
)
)
)
)
)
All reactions were carried out in perfluorodecalin(C10F18, cis and trans-
mixture); temperature of reaction was 100 8C; time of reaction was 12 h.
Isolated yields based on the alkylating agent.
a
b
All ratios of o:m:p were determined by GC.
(Table 1, entry 17), finding that the catalyst also can promote
reaction greatly, but it can dissolved in water, which results
in the great loss of catalyst when reusing fluorous phase.
Next perfluorohexane (C6F14), perfluoromethylcyclo-
hexane (C7F14), perfluorotoluene (C7F8), perfluorooctane
(C8F18) and perfluorooctyl bromide (C8F17Br) were also
selected as fluorous solvents and the effect of such solvents
was examined for the Friedel–Crafts alkylation (Table 2).
The results showed that the yields of alkylation in
perfluorooctane (C8F18) and perfluorooctyl bromide
(C8F17Br) are lower than other solvents. It was observed
that perfluorohexane (C6F14) and perfluorotoluene (C7F8)
are in fact miscible with aromatic substrates at room
In conclusion, RE(OSO2C8F17)3 are demonstrated to be
new and highly effective catalysts for Friedel–Crafts
alkylation in FBS. By simple separation of the fluorous
phase containing only catalyst, alkylation can be repeated
many times. Further study on the application of FBS to other
Table 3
Table 2
Friedel–Crafts alkylations in FBS
Effect of solvents for alkylation of anisole with benzalcohol
Entry
Aromatics
Alkyltion agents
Yield (%)a
Ratio of o:m:pb
Entry
PFC
Yield (%)a
Ratio of o:m:pb
1
2
C6H6
PhCH2OH
PhCH2OH
PhCH2OH
PhCH2OH
PhCH2OH
PhCH2OH
Cyclohexanol
(CH3)2CHOH
PhCH2Cl
48
95
87
82
18
84
62
41
14
58
46
–
1
2
CF3(CF2)4CF3
88
99
40:trace:60
46:trace:54
PhMe
PhEt
26:6:68
20:2:78
11:trace:89
6:trace:94
4:trace:96
44:trace:56
41:4:55
–
3
4
i-Pr-Ph
PhCl
3
99
42:trace:58
5
6
PhF
4
5
6
CF3(CF2)6CF3
82
74
96
34:trace:66
28:trace:72
33:trace:67
7
PhOMe
PhOMe
C6H6
CF3(CF2)6CF2Br
8
9
10
11
PhMe
PhOMe
PhCH2Cl
4:trace:96
1:trace:99
PhCH2Cl
All reactions were carried out in the presence of Yb(OSO2C8F17)3 catalyst;
temperature of reaction was 100 8C; time of reaction was 12 h.
Isolated yields based on the alkylating agent.
Temperature of all reactions was 100 8C; time of all reaction was 12 h.
Isolated yields based on the alkylating agent.
a
a
b
b
All ratios of o:m:p were determined by GC.
All ratios of o:m:p were determined by GC.

W.-B. Yi, C. Cai / Journal of Fluorine Chemistry 126 (2005) 831–833
833
reactions, which can promote by such Lewis acids is under
way in this laboratory.
p-Benzyltoluene A colorless liquid; 1H NMR (300 MHz,
TMS, CDCl3) d 2.30 (3H, s, CH3), 3.85 (2H, s, CH2), 6.81–
7.12 (9H, m, Ar). MS (EI) m/z 182 (M+).
( p-Benzyl)ethylbenzene A colorless liquid; 1H NMR
(300 MHz, TMS, CDCl3) d 1.27–1.38 (3H, t, CH3), 2.21–
2.62 (2H, m, CH2), 3.82 (2H, s, CH2), 6.82–7.18 (9H, m, Ar).
MS (EI) m/z 196 (M+).
3. Experimental
3.1. General
( p-Benzyl)i-propyllbenzene A colorless liquid; 1H NMR
(300 MHz, TMS, CDCl3) d 1.12ꢀ1.29 (6H, d, CH3), 2.50–
3.01 (H, m, CH), 3.80 (2H, s, CH2), 6.79–7.19 (9H, m, Ar).
MS (EI) m/z 196 (M+).
MPs were obtained with Shimadzu DSC-50 thermal
analyzer. IR spectra were recorded on a Bumem MB154S
infrared analyzer. 1H NMR spectra were measured on Bruke
Advance DMX500. Mass spectra were recorded with a
Saturn 2000GC/MS instrument. Inductively coupled plasma
(ICP) spectra were measured on Ultima2C apparatus.
Elemental analyses were performed on a Yanagimoto
MT3CHN corder. The orientation of alkylation was
determined by HP4890 GC analyzer with HP-5 silica
chromatography column. Commercially available reagents
were used without further purification.
( p-Benzyl)chlorobenzene A colorless liquid; 1H NMR
(300 MHz, TMS, CDCl3) d 3.90 (2H, s, CH2), 6.98–7.22 (5H,
m, Ar), 7.32–7.70 (4H, m, Ar). MS (EI) m/z 202 204 (M+).
( p-Benzyl)fluorobenzene A colorless liquid; 1H NMR
(300 MHz, TMS, CDCl3) d 3.92 (2H, s, CH2), 6.96–7.24
(5H, m, Ar), 7.36–7.62 (4H, m, Ar). MS (EI) m/z 186 (M+).
p-Cyclohexylanisole
A
colorless solid; 1H NMR
(300 MHz, TMS, CDCl3) d 1.15–1.68 (10H, d, (CH2)5),
1,74 (1H, m, CH) 2.24 (3H, s, CH3), 6.84–7.21 (4H, m, Ar).
MS (EI) m/z 190 (M+).
3.2. Typical procedure for preparation of RE(OSO2C8F17)3
p-(i-Propyl)anisole
A
colorless liquid; 1H NMR
RE(OSO2C8F17)3 was prepared according to the litera-
tures [2] (Method A). The mixture of C8F17SO3H solution
(aq) and YbCl3Á6H2O solution (aq) was stirred at room
temperature (Method B). The mixture of C8F17SO3H
solution (aq) and Yb2O3 powder was stirred at boiling. In
both methods, the resulting gelatin-like solid was collected,
washed and dried at 150 8C in vacuo to give a white solid,
which does not have a clear melting point up to 500 8C, but
shrinks around 380 and 450 8C. IR (KBr) y1 237 (CF3), 1
152 (CF2), 1 081 (SO2), 1 059 (SO2), 747 (S–O) and 652 (C–
S) cmÀ1. ICP: Calcd for C24O9F51SYb: Yb, 10.30%. Found:
Yb, 9.88%. Anal. Calcd for C24O9F51SYbÁH2O: C, 17.21%;
H, 0.10%. Found: C, 17.03%; H, 0.40%.
(300 MHz, TMS, CDCl3) d 2.20 (3H, s, CH3), 2.48–3.10
(H, m, CH), 6.70–7.06 (4H, m, Ar). MS (EI) m/z 150 (M+).
Acknowledgements
We thank the National Defence Committee of Science
and Technology (40406020103) for financial support. We
also thank the Zhen-Ya Rare Earth Co. Ltd. for providing
several kinds of rare earth oxides.
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1
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A
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