COMMUNICATION
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Macroreticular p-(v-sulfonic-perfluoroalkylated) polystyrene
ion-exchange resins: a new type of selective solid acid catalyst
Zhenghuan Lin and Chengxue Zhao*
Received (in Cambridge, UK) 6th April 2005, Accepted 23rd May 2005
First published as an Advance Article on the web 15th June 2005
DOI: 10.1039/b504767f
Macroreticular p-(v-sulfonic-perfluoroalkylated) polystyrene
(
FPS) cation-exchange resins 3 have been synthesized by
sequential p-perfluoroalkylation of macroreticular polystyrene
PS) 1 with v-fluorosulfonylperfluorodiacyl peroxide 2, hydro-
(
lysis and acidification; the fluorinated mesoporous resins
exhibited higher activity and selectivity than commercial
Amberlyst 36 and Nafion NR50 in the cyclization of
pseudoionone.
Since macroreticular polystyrene (PS) 1 resin was invented in the
1
960s, cationic ion-exchange resins as solid acid catalysts have
1–8
been widely employed in organic synthesis for several decades.
The ion-exchange resins used in organic catalysis can be divided
into two categories: macroporous PS sulfonic resin (such as
Amberlyst-15) and perfluorinated sulfonic resin (such as Nafion
NR50). Although the exchange capacity of the former resins is
above 4.2 mmol/g, the temperature of the catalytic process cannot
be higher than 120 uC. In sharp contrast, the latter resins are
Scheme 1
Using as our starting materials two PS resins with different
degrees of crosslinking (PS26, 26%; PS40, 40%), we have
synthesized two macroreticular FPS resins (FPS26 and FPS40).
Their porosity was analyzed by a nitrogen sorption technique
(ASAP Micromeritics 2000). The exchange capacities of FPS26
and FPS40 were determined by acidimetry. As shown in Table 1,
the perfluoroalkylation brought about in the resins significant
changes in specific surface area, pore volume and pore diameter
distribution. The BJH pore diameter data clearly show that the
fluorinated resins are mesoporous in nature. The exchange
capacity of FPS26 is higher than that of FPS40. The high degree
of crosslinking in FPS40 resulted in poor accessibility of 2 to the
benzene ring of polymer substrate 1.
superacid (H 5 y212), and have extremely good chemical
0
resistance and thermostability, but the surface area is too low,
2
down to 0.02 m /g. Although the Nafion nanocomposite with SiO
2
has a greatly increased surface area, exchange capacity is rather
small (0.12 mmol/g). The disadvantages of both types of resins
greatly limit their applications.
9
Recently, Zhao et al. have synthesized a new perfluorodiacyl
peroxide 2 bearing a further convertible v-fluorosulfonyl group.
By using the peroxides, a wide variety of materials with the
v-sulfonic-perfluoroalkyl group, functionally similar to Nafion,
10,11
have been synthesized.
In this communication, we wish to
The TGA (Perkin Elmer TGA 7) of porous PS beads shows a
less than 5% weight loss below 400 uC. This low weight loss was
due to residual moisture. At higher temperature, the polymer chain
began to collapse. In sharp contrast, the macroreticular FPS resin
showed a significant weight loss at 190 uC, mainly due to
desulfonation.
report the preparation of macroreticular p-(v-sulfonic-perfluoroal-
kylated) polystyrene (FPS) resin 3 (Scheme 1) and its application
as a solid acid catalyst in the cyclization of pseudoionone.
Macroreticular FPS resin 3 was prepared by the following
procedure: 5 g PS beads 1 (PS26) were swelled in methylene
dichloride (20 ml) overnight in a glass reactor fitted with a
magnetic stirrer. At 0 uC, 120 ml F113 solution of 2 (0.5 M) were
added to the beads suspension under stirring. After 40 h, the beads
The FTIR spectrum (930-Perkin Elmer Spectrometer) of the
FPS resin (Fig. 1) shows strong bands characteristic of the
3
were filtered and washed in turn with 5% aq. NaHCO , water and
ethanol. Then the beads were hydrolyzed in an excess of 30% aq.
NaOH at 80 uC for 4 h. After washing with water to neutral, the
beads were acidified with an excess of 3 M aq. HCl at room
temperature for 24 h, then washed with water to neutral and dried
at 50 uC under vacuum to constant weight.
Table 1 Porosity characteristics of PS beads (PS26 and PS40) and
FPS resins (FPS26 and FPS40)
Surface Pore
area
(m /g)
Exchange
volume Average pore Pore size capacity
(cm /g) diameter ( A˚ )
2
3
( A˚ )
Resin
(mmol/g)
PS26
128
59
361
0.64
0.31
0.83
0.44
187
188
151
146
10–300
10–220
10–400
10–300
—
1.5
—
Department of Chemistry, Shanghai Jiaotong University, 800
Dongchuan Road, Shanghai, 200240, China.
E-mail: cxzhao@sjtu.edu.cn; Fax: 86-21-54741297; Tel: 86-21-54742824
FPS26
PS40
FPS40 107
1.3
*cxzhao@sjtu.edu.cn
3
556 | Chem. Commun., 2005, 3556–3558
This journal is ß The Royal Society of Chemistry 2005