Catalysis studies of macroreticular polystyrene cation-exchange resin with terminal perfluoroalkanesulfonic acids

Article abstract of DOI:10.1002/jccs.201200431

Macroreticular p-(ω-sulfonic-perfluoroalkylated) polystyrene (FPS) resin with the advantages of both sulfonic polystyrene (such as macroreticular Amberlyst-15) and perfluoroalkanesulfonic resin (such as superacidic Nafion NR50) has exhibited excellent catalytic selectivity and activity in cyclization of pseudoionone and condensation of indole. In this paper, FPS was characterized by XPS, nitrogen sorption technique, FESEM and Hammett indicator method, and employed as the solid acid catalyst in the esterification, acylation and alkylation reactions. The FPS resin showed better activity than commercial solid acid catalysts (Amberlyst-15 and Nafion NR50) owing to its high surface area and strong acidity close to superacidity.

Full text of DOI:10.1002/jccs.201200431

JOURNAL OF THE CHINESE
CHEMICAL SOCIETY
Article
Catalysis Studies of Macroreticular Polystyrene Cation-exchange Resin with Terminal
Perfluoroalkanesulfonic Acids
Zhenghuan Lin,a,b Chuanjin Guan,c Limei Huang,a Wen Wang,a Qidan Linga,d,* and
Chengxue Zhaob,*
aCollege of Materials Science and Engineering, Fujian Normal University, Fuzhou 350007, China
bDepartment of Chemistry, Shanghai Jiao Tong University, Shanghai 200240, China
cDepartment of Environmental Engineering, Shanghai Second Polytechnic University, Shanghai 201209, China
dFujian Key Laboratory of Polymer Materials, Fuzhou 350007, Fujian, P. R. China
(Received: Aug. 6, 2012; Accepted: Oct. 31, 2012; Published Online: Dec. 20, 2012; DOI: 10.1002/jccs.201200431)
Macroreticular p-(w-sulfonic-perfluoroalkylated) polystyrene (FPS) resin with the advantages of both
sulfonic polystyrene (such as macroreticular Amberlyst-15) and perfluoroalkanesulfonic resin (such as
superacidic Nafion NR50) has exhibited excellent catalytic selectivity and activity in cyclization of
pseudoionone and condensation of indole. In this paper, FPS was characterized by XPS, nitrogen sorption
technique, FESEM and Hammett indicator method, and employed as the solid acid catalyst in the
esterification, acylation and alkylation reactions. The FPS resin showed better activity than commercial
solid acid catalysts (Amberlyst-15 and Nafion NR50) owing to its high surface area and strong acidity
close to superacidity.
Keywords: Macroreticular; Solid acid; Cation-exchange resin; Perfluoroalkanesulfonic.
INTRODUCTION
Organic reactions catalyzed by acids have widely ex-
media (aqueous, non-aqueous; polar and non-polar), and
their high selectivity which enables them to be used in sep-
aration of the mixtures with close boiling temperatures12
and in fixed bed reactor.13,14 There are two kinds of com-
mercial cation-exchange resins: non-fluorinated macro-
reticular sulfonic resins (such as Amberlyst-15) and per-
fluoroalkylsulfonic resins (such as Nafion NR50). They
have own advantages and disadvantages. For example,
Amberlyst-15 is of high surface area and exchange capac-
ity (4.2 mmol/g) with low usage temperature up to 120 oC.
Nafion NR50 is superacid (H0 = ~ -12), and has extremely
good chemical resistance and thermostability with low sur-
face area of 0.02 m2/g and exchange capacity of 0.9 mmol/
g. Although the Nafion nanocomposite with silica (Nafion/
SiO2) has expanded the surface area, its exchange capacity
turns less to 0.12 mmol/g.15,16
isted in every aspect of laboratorial research and industrial
application. There are so many kinds of acids used in or-
ganic reactions: liquid and solid acids (different phase); in-
organic and organic acids (different composition); weak,
strong and super acids (different acidity); Brønsted and
Lewis acids (different catalytic process).1 Generally, cata-
lytic activity of liquid acids is higher than that of solid acids
for homogeneous reaction. However, its disadvantages of
high toxicity, difficult separation and recovery, environ-
mental pollution and equipment corrosion greatly limit its
further applications in organic synthesis.2-4 Therefore, it is
desirable in the chemical transformation employing acids
as catalysts to replace liquid acids with more environmen-
tally friendly solid acids such as zeolites, metal salts, ox-
ides, clays, heteropolyacids and sulfides, etc.1 However,
the properties and structure of solid acids still need to be
improved, like stability, acidity, accessibility of acidic
sites,5 synthetic method, deactivation of catalysts, water-
tolerance, etc.2
Recently, Zhao et al.17 reported a kind of fluorinated
sulfonic resin FPS (Scheme I) composed of macroreticular
polystyrene skeleton and perfluoroalkanesulfonic side
chain. Due to its unique structure, FPS exhibits some ad-
vantages of both Amberlyst and Nafion resins, such as high
exchange capacity of 2.0 mmol/g, surface area of 107 m2/g,
Since macroreticular polystyrene resins were synthe-
sized in 1960s, cation-exchange resins as solid acid cata-
lysts have received more and more interests6-11 for their sta-
ble structure which enables them to be used in all kinks of
o
thermostability (stable up to 190 C) and strong acidity.
FPS resins have shown higher activity than commercial
solid acids in cyclization of pseudoionone into a-ionone
* Corresponding author. Tel: +86 591 22868666; Fax: +86 591 22868666; E-mail: lingqd@fjnu.edu.cn (Qidan Ling);
Tel: +86 21 54709629; Fax: +86 21 54741297; E-mail: cxzhao@sjtu.edu.cn (Chengxue Zhao)
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Lin et al.
Table 1. Acidic strength of FPS resin[a]
Scheme I Structure of cation-exchange resins
p-Nitrochloro-
benzene
Anthraquinone p-Nitrotoluene
Resin
(H0, -8.2)
(-11.35)
(-12.7)
Amberlyst-15
FPS
-
+
+
-
±
+
-
-
±
Nafion NR50
and condensation of indole with aldehyde or imine.18 In
this work, Hammett indicators and XPS were employed to
determine the acid strength and element composition on the
surface of FPS. The porosity of FPS was analyzed by nitro-
gen sorption technique and FESEM. We tested further the
catalytic activity of FPS in other organic reactions, like
esterification, acylation and alkylation.
[a] (+) Color changed clearly; (-) Color unchanged; (±) Color
changed unclearly.
The acidic strength of FPS was determined by ob-
serving the color change of the indicator adsorbed on the
surface of the sample. The indicators used in this work are
anthraquinone (H0 = -8.20), p-nitrotoluene (H0 = -11.35)
and p-nitrochlorobenzene (H0 = -12.70). The solvent used
in the experiment is n-heptane. The results were listed in
the Table 1. The H0 value of FPS is approximately -11.4,
which is close to the superacidity (H0 = -12).
RESULTS AND DISCUSSION
Structure and property of FPS
FPS resin has been synthesized by following perfluo-
roalkylation of w-fluorosulfonylperfluorodiacyl peroxides
(SFAP) with polystyrene (PS), alkali hydrolysis and acidi-
fication. X-ray photoelectron spectroscopy (XPS) was em-
ployed to analyzing the element composition in the surface
of macroreticular PS and FPS. As shown in Fig. 1, XPS
spectra of FPS show one peak of F1s at 688.1 eV, one peak
of S2p at 168.5 eV, two peaks of C1s at 284.5 eV and 290.1
eV for two kinds of carbon atoms in FPS: the hydrogenated
carbon (284.5 eV) in the main chain and the fluorinated
carbon (290.1 eV) in the side chain. There is only one C1s
peak at 284.5 eV in the XPS spectra of polystyrene. The
XPS results provided the evidence that the perfluoroalkyl-
sulfonic groups were introduced successfully into the sur-
face of polystyrene to produce FPS.
The porosity of FPS was characterized by nitrogen
sorption technique. Fig. 2 gives the adsorption and desorp-
tion isotherm of FPS. The adsorption curve displays a type
II isotherm with a similar H3 hysteresis typical of disorder
slit pores caused by particles accumulation. At low pres-
sures, the gradual adsorption curve shows first an adsor-
bate monolayer is formed on the pore surface, which is fol-
lowed by the multilayer formation. At high pressures, the
steep adsorption step indicates the relatively large pore size
and narrow pore size distribution of FPS, which is matched
with the pore size distribution shown in Fig. 3. Compared
to PS, the pore size of FPS turns less for some pores occu-
pied by perfluoroalkanesulfonic chain. Their pore parame-
ters (shown in Table 2) were obtained by BET and BJH
methods. High resolution field emission scanning electron
microscopy (HR-FESEM) was used to observe the micro-
structure and morphology of FPS. The HR-FESEM photo
Fig. 2. Adsorption and desorption isotherm of FPS.
Fig. 1. XPS spectra of polystyrene (PS) and FPS.
262
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CHEMICAL SOCIETY
Macroreticular Perfluoroalkanesulfonic Resin
Table 2. Physical characteristics of various resins
BJH pore
diameter
(nm)
Exchange
capacity
BET surface area BJH pore volume
(cm3/g)
Resin
H0
(m2/g)
(mmol/g)
Amberlyst-15
Amberlyst-36
Nafion NR50
Nafion/SiO2
FPS
42
35
0.36
0.28
/
34.3
32.9
/
4.8
5.3
0.9
0.15
1.3
/
-2.2
-2.2
-12.7
-12
0.02
88
0.56
0.44
0.83
21.8
14.6
15.1
107
361
-11.4
/
PS
(Fig. 4) at 40,000-fold magnification exhibits that the
microstructure of FPS is irregular particulate in nature and
that there are plenty of complex and disorder slit pores
between particles. The result is consistent with adsorption
isotherm.
change resins have attracted much attention for their high
activity and stability.10,19-24 In this work, the esterification
of benzoic acid with n-butanol was investigated with FPS,
Amberlyst-15, Amberlyst-36, Nafion NR50 and its nano-
composite Nafion/SiO2. Table 3 gives the conversion rate
of benzoic acid catalyzed by these solid acids. FPS (Entry
5) exhibits best catalytic activity in the reaction with 91%
of conversion of benzoic acid for being of the advantages
of both Amberlyst-15 and Nafion NR50 resins such as big
surface area, easy accessibility of acidic sites and super-
acidity. Owing to forming big surface area through intro-
ducing Nafion resin into silica framework, benzoic acid’s
conversion is greatly improved from 49% under Nafion
NR50 to 81% under Nafion/SiO2. FPS was also used to cat-
alyze benzoic acid with different alkyl alcohols with the re-
sults listed in Table 4. FPS also exhibits high activity with
the conversion rate of aryl acid in the range of 89-95%, ex-
cept for isoamyl alcohol with 74% of conversion rate of
benzoic acid, because there is bigger steric hindrance of
OH group in isoamyl alcohol than in primary alcohol.
For benzyl alcohol being prone to dehydrate to pro-
duce benzyl ether, its esterification was employed to deter-
mine the selectivity and activity of solid acids at low tem-
perature. Table 5 shows the result of esterification of ben-
zyl alcohol with acetic acid catalyzed by 10 mol% of solid
acids (Amberlyst-15, Nafion NR50 and FPS) at 78 oC. Like
the esterification of benzoic acid, FPS presents the best ac-
Catalytic activity of FPS
The Physical characteristics of FPS and commercial
cation-exchange resins were listed in Table 2. For the com-
bination of advantages of both Amberlyst and Nafion resin,
FPS has behaved excellent activity as the solid catalyst in
the cyclization of pseudoionone into a-ionone and conden-
sation of indole with aldehyde or imine.18 The catalytic ac-
tivity of FPS was evaluated further in the esterification,
acylation and alkylation.
Esterification of acids with alcohols
Recently, the esterifications catalyzed by cation-ex-
Fig. 3. Pore size distribution of PS and FPS.
Table 3. Esterification of benzoic acid with n-butanol catalyzed
by solid acids
Conversion of benzoic acid
Entry
Catalyst
(%)
1
2
3
4
5
Amberlyst-15
Amberlyst-36
Nafion NR50
Nafion/SiO2
FPS
69
30
49
81
91
Fig. 4. HR-FESEM photo of PS (a) and FPS (b).
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Lin et al.
Table 4. Esterification of benzoic acid with different alcohols
catalyzed by FPS
Table 6. Acylation of different arenes catalyzed by solid acids
Entry
Substrate
Acylating agent
Yield (%)[a]
Entry
Alcohol
Conversion of acid (%)
1
2
3
4
5
6
toluene
anisole
Ph-COCl
Ph-COCl
84
92
87
89
72
19
1
2
3
4
5
6
n-C4H9OH
n-C5H11OH
i-C5H11OH
n-C6H13OH
n-C12H25OH
n-C4H9OH[a]
91
90
74
89
90
95
m-xylene
mesitylene
toluene
Ph-COCl
Ph-COCl
(CH3CO)2O
(CH3CO)2O
benzene
[a] Isolated yield.
[a] Esterification of phenylacetic acid with n-butanol.
Table 7. Alkylation of toluene with isopropanol catalyzed by
solid acids
Table 5. Esterification of benzyl alcohol with acetic acid cata-
lyzed by solid acids
Entry
Resin
Yield of cymene[a]
Conversion of
Yield of
Selectivity of
ester (%)
Resin
1
2
3
4
Amberlyst-15
Amberlyst-36
Nafion NR50
FPS
7
8
benzyl alcohol (%) ester (%)[a]
Amberlyst-15
Nafion NR50
FPS
40
74
89
5
12
20
11
6
15
10
10
[a] Isolated yield.
[a] Isolated yield.
or contaminate the environment for polymerization or gen-
erating HX. Relatively, alkylating reaction with alcohols
has attracted much attention for its safety and cleanliness.26
The alkylation of toluene with isopropanol was investi-
gated with non-fluorinated sulfonic resin (Amberlyst-15
and Amberlyst-36), perfluorosulfonic resin (Nafion NR50)
and fluorinated sulfonic resin (FPS). From the results
shown in Table 7, all of these resins give isopropyltoluene
in low yield up to 10%, because most of isopropanol under-
went a dehydrolysis process to yield propene which es-
capes from the reaction medium. The result is consistent
with one reported in the literature.26 The formation of pro-
pene was confirmed by bubbling the gas effluent into a so-
lution of Br2/CCl4. However, FPS resin gives the highest
yield of isopropyltoluene in the alkylation for its unique
structure and strong acidity.
tivity in low temperature with 89% of conversion of benzyl
alcohol and similar selectivity as Amberlyst-15. In these
solid acids, Nafion NR50 exhibits best selectivity and good
activity with 15% of yield of ester and 74% of conversion.
Acylation of arenes
Friedel-Crafts acylation, one of frequently used reac-
tion in organic synthesis, is an important method of synthe-
sizing arone which is a crucial intermediate in the industry
of fine chemicals.19,25 We used FPS to catalyze the acyla-
tion of different arenas with benzoyl chloride or acetic an-
hydride. From Table 6, it is found that the benzoyl chloride
(Entry 1-4) gives higher yield (above 84%) than acetic an-
hydride for its strong electrophilicity, which is favorable
for the acylation reaction according to electrophilic substi-
tution mechanism. The substituent groups in the phenyl
ring have big effect on the yield. The acylation of anisole
gets high yield up to 92% for strong electron-donating abil-
ity of the methoxy group. Though the acylating ability of
acetic anhydride is lower than that of benzoyl chloride, the
acylating yield of toluene with acetic anhydride can reach
72%, which prove that FPS is a kind of high effective
catalyst.
EXPERIMENTAL
Materials
Organic reagents used in catalysis studies were purchased
from Sinopharm Chemical Reagent Co. without further purifica-
tion before use. FPS was synthesized from polystyrene (PS, 36%
of crosslink degree) by following the reported procedure.18
Amberlyst-15, Amberlyst-36 and Nafion NR50 were purchased
from Aldrich. The commercial catalysts and Nafion/SiO2 nano-
composites (13% of Nafion resin) prepared according to the re-
ported method15 were dried at 60 oC under vacuum overnight be-
fore use.
Alkylation of toluene
Alkylation of arene with alkylating reagents (like
alkene, halohydrocarbon and alcohol) is one of the impor-
tant reaction synthesizing aromatic derivatives. However,
alkene or halohydrocarbon makes alkylation turn complex
264
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CHEMICAL SOCIETY
Macroreticular Perfluoroalkanesulfonic Resin
Characterization
(s, 2H), 2.33 (s, 3H), 2.08 (s, 6H).
1H NMR of acetyltoluene (CDCl3, 400 MHz): d 7.80 (m,
XPS spectra were obtained on an Omicron ESCAspectrom-
eter. Acid strength was determined by Hammett indicator method
in vacuo. Nuclear magnetic resonance was performed using
Varian Mercury 400 spectrometer. Adsorption isotherm and pore
size distribution were obtained by using a Micromeritics instru-
ment (ASAP Micromeritics 2000). The morphological character-
istics were observed with a high resolution field emission scan-
ning electron microscope (Philips Sirion 200).
2H), 7.27 (m, 2H), 2.57 (s, 3H), 2.43 (m, 3H).
1H NMR of acetylbenzene (CDCl3, 400 MHz): d 7.95 (m,
2H), 7.58 (m, 1H), 7.44 (m, 2H), 2.61 (s, 3H).
The alkylation of toluene with isopropanol was carried out
in a 25 mL three-neck flask connected with a bubbler loaded with
the solution of Br2/CCl4. To 3 mL of toluene was added isopro-
panol (0.12 g, 2 mmol) and 10 mol% of catalyst. The mixture was
stirred at 80 oC for 5 h, filtered and washed with ethyl acetate for
three times. The combined solution was evaporated under re-
duced pressure. The residue was purified via column chromatog-
Catalysis studies
The esterification of aryl acid was carried out in a 25 mL
round flask. To the flask was added aryl acid (2 mmol), alkanol (6
mmol) and 10 mol% of solid catalyst in turn. The mixture was
stirred at 115 oC for 6 h, filtered and washed with ethyl acetate for
three times, and then evaporated under vacuum. The residue was
analyzed by column chromatography to give the conversion of
aryl acid.
1
raphy. H NMR of isopropyltoluene (CDCl3, 400 MHz): d 7.86
(m, 2H), 7.25 (m, 2H), 2.58 (s, 3H), 2.41 (m, 1H), 1.26 (m, 6H).
CONCLUSION
The surface composition and acidity of FPS resin
bearing terminal perfluoroalkanesulfonic groups was ana-
lyzed by XPS and Hammett indicator method, respectively.
The XPS spectra show that the perfluoroalkanesulfonic
group was successfully introduced into the surface of FPS.
By Hammett indicator method, the acidity of FPS, H0 = -11,
was determined. Owing to the nearly superacidity and easy
accessibility of the acid sites, the FPS resin behaved supe-
rior activity over other commercial solid acid catalysts in
some reactions, like esterification, acylation and alkyla-
tion. For example, the esterification of aromatic acids with
primary alcohols can smoothly proceed by using FPS cata-
lyst with high conversion of the acids over 89%. It is ex-
pected that FPS may be used as an efficient catalyst in
various reactions.
In the esterification of benzyl alcohol with acetic acid, to 10
mol% of solid catalyst was added acetic acid (0.12 g, 2.0 mmol),
benzyl alcohol (0.22 g, 2.0 mmol). Then the mixture was stirred
for 6 h at 78 oC. The catalyst was filtered and washed with ethyl
acetate three times. The combined solution was evaporated under
reduced pressure. The residue was purified via column chroma-
1
tography (silica gel, petroleum ether: ethyl acetate = 5:1). H
NMR of benzyl acetate (CDCl3, 400 MHz): d 7.37 (m, 1H), 7.26
(d, 2H), 7.17 (m, 2H), 4.04 (s, 2H), 2.4 (s, 3H).
The acylation of arene with benzoyl chloride or acetic an-
hydride was investigated in a 25 mL round flask. Benzoyl chlo-
ride (0.4 g, 2.8 mmol) or acetic anhydride (0.29 g, 2.8 mmol), and
10 mol% of catalyst were added to 15 mL of arene under a nitro-
gen atmosphere. The mixture was stirred for 8 h under refluxing.
The catalyst was filtered and washed with toluene three times.
The combined solution was evaporated under reduced pressure.
The residue was purified via column chromatography (silica gel,
petroleum ether: ethyl acetate = 20:1).
1H NMR of tolylphenylmethanone (CDCl3, 400 MHz): d
7.81~7.77 (m, 2H), 7.73~7.71 (d, 2H), 7.58~7.53 (m, 1H), 7.47~
7.44 (m, 2H), 7.29~7.25 (d, 2H), 2.43 (s, 3H).
1H NMR of methoxyphenyl phenylmethanone (CDCl3, 400
MHz): d 7.8 (m, 2H), 7.7 (d, 2H), 7.6 (m, 1H), 7.5 (m, 2H), 7.3 (d,
2H), 2.4 (s, 3H).
ACKNOWLEDGEMENTS
This work was supported by the National Natural Sci-
ence Foundation of China (60976019), Specialized Re-
search Fund for the Doctoral Program of Higher Education
(SRFDP 20093223110002), Program for Innovative Re-
search Team in Science and Technology in Fujian Province
University (IRTSTFJ), Key Programs of Fujian Educa-
tional Committee (JA12059).
1H NMR of (2,4-dimethylphenyl)phenylmethanone (CDCl3,
400 MHz): d 7.80~7.76 (m, 2H), 7.58~7.50 (m, 1H), 7.45~7.39
(m, 2H), 7.24~7.20 (m, 1H), 7.10~7.02 (d, 2H), 2.38 ~2.31 (m,
6H).
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