ω-Sulfonic-perfluoroalkylated poly(styrene-maleic anhydride)/silica hybridized nanocomposite as a new kind of solid acid catalyst

Article abstract of DOI:10.1016/j.molcata.2012.08.011

A new kind of ω-sulfonic-perfluoroalkylated poly(styrene-maleic anhydride)/silica hybrid nanocomposite FSMA/SiO₂ has been synthesized under mild conditions by perfluoroalkylation of styrene-maleic anhydride copolymer (SMA) with ω-fluorosulfonylperfluorodiacyl peroxides (SFAP), and followed in turn by aminolysis using (3-aminopropyl)triethoxysilane (APTES), alkali hydrolysis, gelation with tetraethoxysilane (TEOS) and finally acidification. The hybrid solid acid FSMA/SiO₂ with terminal perfluoroalkylsulfonic and carboxyl groups was characterized by FTIR, SEM, TEM, TGA, XPS, EDX, acidimetry and nitrogen sorption technique. Its pore structure, acid strength and acid amount were easily modulated by controlling the gelation and perfluoroalkylation conditions. The catalytic activity and selectivity, as well as reusability of FSMA/SiO₂ were tested in three important reactions, namely, cyclization of pseudoionone, condensation of indole and esterification of benzoic acid. Owing to the higher exchange capacity than that of Nafion/SiO₂, and the stronger acidity than that of Amberlyst-15, the nanocomposite FSMA/SiO₂ showed higher activity and selectivity than these commercial solid acids in the reactions.

Full text of DOI:10.1016/j.molcata.2012.08.011

Journal of Molecular Catalysis A: Chemical 365 (2012) 73–79
Contents lists available at SciVerse ScienceDirect
Journal of Molecular Catalysis A: Chemical
journal homepage: www.elsevier.com/locate/molcata
ω-Sulfonic-perfluoroalkylated poly(styrene–maleic anhydride)/silica hybridized
nanocomposite as a new kind of solid acid catalyst
Zhenghuan Lina,b, Limei Huang , Qidan Linga,c,∗, Hong Chen , Chengxue Zhao
a
a
b,∗
a
College of Materials Science and Engineering, Fujian Normal University, Fuzhou 350007, China
Department of Chemistry, Shanghai Jiao Tong University, Shanghai 200240, China
Fujian Key Laboratory of Polymer Materials, Fuzhou 350007, Fujian, China
b
c
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 30 July 2012
Received in revised form 13 August 2012
Accepted 15 August 2012
Available online 24 August 2012
A new kind of ω-sulfonic-perfluoroalkylated poly(styrene–maleic anhydride)/silica hybrid nanocompos-
ite FSMA/SiO2 has been synthesized under mild conditions by perfluoroalkylation of styrene–maleic
anhydride copolymer (SMA) with ω-fluorosulfonylperfluorodiacyl peroxides (SFAP), and followed in
turn by aminolysis using (3-aminopropyl)triethoxysilane (APTES), alkali hydrolysis, gelation with
tetraethoxysilane (TEOS) and finally acidification. The hybrid solid acid FSMA/SiO2 with terminal per-
fluoroalkylsulfonic and carboxyl groups was characterized by FTIR, SEM, TEM, TGA, XPS, EDX, acidimetry
and nitrogen sorption technique. Its pore structure, acid strength and acid amount were easily modu-
lated by controlling the gelation and perfluoroalkylation conditions. The catalytic activity and selectivity,
as well as reusability of FSMA/SiO2 were tested in three important reactions, namely, cyclization of
pseudoionone, condensation of indole and esterification of benzoic acid. Owing to the higher exchange
capacity than that of Nafion/SiO2, and the stronger acidity than that of Amberlyst-15, the nanocomposite
FSMA/SiO2 showed higher activity and selectivity than these commercial solid acids in the reactions.
Keywords:
Solid acid
Sol–gel
Nanocomposite
Perfluoroalkanesulfonic
Superacidity
©
2012 Elsevier B.V. All rights reserved.
1
. Introduction
NR50. The superacidity (H = ∼−12) and high thermostability (sta-
0
◦
ble up to 280 C) of Nafion resins enable them to effectively
Organic/inorganic hybrid materials, a kind of composite, offer
catalyze alkylation of benzene, isomerization, and some select
acylation [27]. However, Nafion NR50 is a kind of gel-type cation-
exchange resin that does not swell in non-polar solvents. This
makes its catalytic activity low in the reactions employing non-
polar solvents due to the low accessibility of acid sites. To
improve the surface area and the accessibility of acid sites, sul-
fonic resins were introduced into the silica skeleton to produce
organic/inorganic hybrid composites [33–42]. For example, Harmer
et al. employed sol–gel technique to prepare Nafion resin/silica
the combinations of the advantages of both organic and inorganic
components such as good mechanical strength, high thermostabi-
lity, easy processability and low cost [1–7]. For allowing designing
and controlling the structure in molecular level, hybrid materi-
als are easily functionalized and widely applied in optics [8,9],
electronic devices [10–12], photochrism [13,14], medicine [15],
separation [16] and catalysis [4,17]. Traditional methods are diffi-
cult to prepare organic/inorganic hybrid materials for the different
nature of two components. Sol–gel technique becomes one of the
important ways to synthesize hybridized materials for its unique
advantages: easy operation, mild reaction condition, high purity of
products, diverse material shape molded for different applications
nanocomposite (Nafion/SiO ) with surface area in the range of
2
2
50–500 m /g which is 1000 times higher than that of Nafion NR50
[33].
However, Nafion resin particles were entrapped within the
porous silica network to produce Nafion/SiO2 hybrid composite
without covalent linkage between organic and inorganic phase.
Due to the aggregation of Nafion resin, the organic particles could
not disperse uniformly in the silica framework, which made cat-
alytic process complex [43]. In this work, we have developed a
kind of ω-sulfonic-perfluoroalkylated poly(styrene–maleic anhy-
[
18–23].
Cation-exchange resins with strong acidity have been widely
used as solid acid catalysts in organic reactions, including alkyl-
ation, transalkylation, isomerization, oligomerization, acylation,
esterification and nitration, etc. [24–32]. There are two main
classes of commercial strong-acid resin: nonfluorinated resin such
as Amberlyst-15 and perfluoroalkylsulfonic resin such as Nafion
dride)/silica hybridized nanocomposites (FSMA/SiO ) originated
2
from SMA in mild condition. FSMA/SiO2 containing both perfluo-
roalkanesulfonic acid and carboxyl acid was synthesized by sol–gel
method with covalent bond linkage between organic and inorganic
∗ Corresponding authors. Tel.: +86 21 54709629; fax: +86 21 54741297.
E-mail addresses: lingqd@fjnu.edu.cn (Q. Ling), cxzhao@sjtu.edu.cn (C. Zhao).
phases. FSMA/SiO was characterized by FTIR, XPS, TGA, SEM, TEM,
2
1
381-1169/$ – see front matter © 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.molcata.2012.08.011

7
4
Z. Lin et al. / Journal of Molecular Catalysis A: Chemical 365 (2012) 73–79
EDX, nitrogen sorption technique and acidimetry, and its catalytic
activity as solid acid in the cyclization of pseudoionone, the con-
densation of indole, and esterification of benzoic acid was also
investigated.
In condensation of indole with acetone, to 10 mol% cata-
lyst (catalyst/acetone = 0.1 mequiv. H /1 mmol) was added indole
+
(2.0 mmol), acetone (1.0 mmol) and 5 mL of CH Cl as solvent. Then
2
2
the mixture was stirred for 12 h at room temperature. The catalyst
was filtered and washed with ethanol three times. The combined
solution was evaporated under reduced pressure. The residue
was purified via column chromatography (silica gel, petroleum
2
. Experimental
ether:ethyl acetate = 4:1) to give dimethyl diindolylmethane: 1
H
2.1. General information
NMR (CDCl , 400 MHz), ı 1.91 (s, 6H), 6.87 (t, 2H), 7.02 (m, 2H),
3
7
.07 (t, 2H), 7.28 (d, 2H), 7.40 (d, 2H), 7.85 (brs, 2H); IR (KBr) ꢀ
BET surface area, pore diameter and BJH cumulative pore
−
1
(cm ), 3440, 2964, 2859, 1659, 1384, 734.
volume were obtained using a Micromeritics instrument (ASAP
Micromeritics 2000). The morphological characteristics were
observed with a SEM (Philips Sirion 200) and a TEM (JEM-2010).
XPS spectra were obtained on an Omicron ESCA spectrome-
ter. Fourier transform infrared spectroscopy (FTIR) using the
KBr pellet was carried out on a Perkin–Elmer 930 spectrome-
ter. The thermogravimetric studies were performed on a TGA 7
Perkin–Elmer). Exchange capacity was determined by acidimetry.
Nuclear magnetic resonance was performed using Varian Mercury
00 spectrometer using CDCl3 as the solvent. Microanalyses were
The esterification of benzoic acid was investigated in a 25 mL
round flask. To the flask was added benzoic acid (0.24 g, 2 mmol),
n-butanol (0.44 g, 6 mmol) and solid catalyst (catalyst/benzoic
acid = 0.1 mequiv. H /1 mmol) in turn. The mixture was stirred at
1
times, and then evaporated under vacuum. The conversion of ben-
zoic acid was obtained from the amount of unreactive benzoic acid
detected by column chromatography.
+
◦
15 C for 6 h, filtered and washed with ethyl acetate for three
(
4
completed on a VARIO EL III elemental analyzer.
3. Results and discussion
SMA containing 12 mol% of maleic anhydride was obtained from
Shanghai Research Institute of Petrochemical Technology (SRIPT).
3.1. Synthesis and physical characterization
The solution of SFAP in F113 (CCl FCClF ) was synthesized by
2
2
following the reported procedure [44] and kept under a freez-
ing condition before use. Other reagents were purchased from
Sinopharm Chemical Reagent Co. and used as received. Amberlyst-
Through five-step reactions, namely, perfluoroalkylation,
aminolysis, hydrolysis, co-gelation and acidification, the target
nanocomposite FSMA/SiO2 was synthesized (Scheme 1). The
perfluoroalkylation of SMA with FSAP was induced via single
electron-transfer (SET) process [45] including a de-electronation
of phenyl ring to yield cation radical, combination of the cation
radical with perfluoroalkane radical to form ı-complex, and depro-
tonation of the complex to give ω-fluorosulfonylperfluoroalkylated
poly(styrene–maleic anhydride) (FSMA). FSMA was further func-
tionalized by aminolysis of maleic anhydride in SMA with coupling
regent APTES. In this step, the loading of APTES had to be controlled
to avoid the gelation in the following hydrolysis under NaOH. Fol-
lowed by alkali hydrolysis, gelation with TEOS and acidification in
HCl, the FSMA/SiO2 was finally obtained.
1
5, Amberlyst-36 and Nafion NR50 were purchased from Aldrich.
The commercial catalysts and Nafion/SiO2 prepared according to
◦
the reported method [33] were dried at 60 C under vacuum
overnight before use.
2.2. Synthesis of FSMA/SiO2
SMA (0.75 g, 7.3 mmol) was dissolved in 5 mL of
dichloromethane, purging with nitrogen for 0.5 h. Cooling to
◦
0
C, F113 solution (0.4 M) of SFAP (9 mL, 3.6 mmol) was added
to the SMA solution under stirring. After 40 h, the solution was
washed with water and dried under vacuum to obtain perflu-
The FTIR spectra of SMA (a), FSMA (b), FSMA/SiO2 (c) and SiO2
19
(d) are shown in Fig. 1. The plot of FSMA shows strong bands
oroalkylated poly(styrene–maleic anhydride) FSMA.
F NMR
−
1
characteristic of the perfluoroalkane group: ꢀ (CF ) at 1310 cm
,
(
−
CDCl , 400 MHz) of FSMA: ı −56.6 (1F, CF O), −38.9 (2F, CF S),
3
3
2
−
1
−1
ꢀ
(CF ) at 1227 cm . The peak at 814 cm characteristic of a
10.4 (3F, CF ), −5.3 to −2.4 (2F, O CF ), 118.4 (1F, SO F).
2
3
2
2
para-disubstituted phenyl ring, as well as carbonyl absorption, pro-
vides strong evidence for para-ω-fluorosulfonylperfluoroalkylation
of SMA. The FTIR spectrum of FSMA/SiO2 shows similar peaks as
that of SiO2 for the high amount of SiO2 in the hybrid materials.
To
a
solution of FSMA in 7 mL of THF, (3-
aminopropyl)triethoxysilane (0.06 g, 0.29 mmol) was added
at room temperature and stirred for 0.5 h. Then, the solution was
added to 15 mL of 5% aqueous NaOH solution and stirred for 5 h at
◦
3
0 C followed by neutralization with HCl. The hydrolyzed FSMA
solution was kept in the freezer.
In a beaker (150 mL) was added TEOS (17.2 g, 80 mmol), water
(
1.8 mL) and 0.2 N aqueous HCl (4.1 mL). The mixture was stirred
for 3 h at room temperature and added to the hydrolyzed FSMA
solution. After stirring for 15 min, 30 mL of 2.6 N ammonia water
was rapidly added to the solution. Within 20 s with shaking, the
mixed solutions gelled to form a hard solid. The solid gel was dried
◦
at 90 C for 24 h, acidified with 6 N aqueous HCl (30 mL) for 36 h,
washed down residue HCl with water to neutral and then dried at
◦
8
0 C under vacuum to a constant weight of FSMA/SiO .
2
2.3. Catalysis studies
Cyclization of pseudoionone was carried out in a two-necked
flask. To a solution of pseudoionone (0.2 mL) in cyclohexane (5 mL),
◦
a solid catalyst (0.1 g) was added under stirring at 80 C. Unreacted
pseudoionone and main products were determined by an Agilent
6
890N GC equipped with a FID detector.
Fig. 1. FT-IR spectra of SMA (a), FSMA (b), FSMA/SiO2 (c) and SiO2 (d).

Z. Lin et al. / Journal of Molecular Catalysis A: Chemical 365 (2012) 73–79
75
Scheme 1. The synthetic sequence of FSMA/SiO2.
Fig. 2 shows TGA plot of SMA and FSMA/SiO2 under heating at
3.2. Pore structure and its controlling
◦
◦
1
0 C/min from room temperature up to about 800 C. In the plot of
◦
SMA, The less than 5% weight loss before 150 C is due to residual
The microstructure and morphology of hybrid materials have
been investigated by using SEM and TEM. The SEM photo (Fig. 6)
at 200,000-fold magnification exhibits that the microstructure of
FSMA/SiO2 is irregularly particulate in nature with primary par-
ticles in the range of 10–30 nm, and that there are plenty of
complex pores between particles with primary pores in the range
of 2–20 nm. The TEM image (see Supporting information, Fig. S1)
of FSMA/SiO2 also shows irregular-shaped particles and poros-
◦
moisture, and the loss (more than 93%) at 390 C is resulted from
polymer decomposition. In the plot of FSMA/SiO , there is a new
2
◦
◦
loss at 283 C before 400 C, which is caused by desulfonation of
perfluoroalkanesulfonic acid.
X-ray photoelectron spectroscopy (XPS) and energy dispersive
X-ray spectroscopy (EDX) were employed to analyzing the compo-
sition and distribution of the element in the surface of FSMA/SiO2.
As shown in XPS spectra (Fig. 3) of FSMA/SiO , there are five kinds
ity. Nitrogen sorption technique analysis of FSMA/SiO gave the
2
2
2
3
of element detected in the surface of the nanocomposites with F1s
at 688.8 eV, O1s at 533.1 eV, C1s at 285.3 eV, Si2p at 103.1 eV, and
N1s at 400.1 eV. S element is not found in XPS spectrum for its low
amount. A similar result is exhibited in the EDX spectrum (Fig. 4)
of FSMA/SiO2 except for a weak peak of S element. Element map-
ping of FSMA/SiO2 shown in Fig. 5 proves a uniform F, O, and Si
distribution across the surface of nanocomposites. The distribution
density of F is less than that of O and Si for its low amount in the
FSMA/SiO2.
porosity with 221 m /g of BET surface area, 0.77 cm /g of BJH pore
volume and 11.3 nm of BJH pore diameter which is consistent with
the result of SEM. The isotherm plot and pore size distribution of
are shown in Fig. S2 and S3 (see Supporting information).
Like Nafion/SiO , the pore structure of FSMA/SiO could be con-
2
2
trolled by varying the sol–gel conditions, such as the concentration
of alkali and the amount of the organic phase. As shown in Table 1,
the alkali (aqueous ammonia) concentration imposes great effects
on all of the pore structure parameters (Entries 1–3). With the
increase in concentration of alkali, the surface area of FSMA/SiO2
decreases dramatically, while pore volume and diameter increase
observably. The effect of the concentration of alkali on adsorption
isotherm and pore size distribution of FSMA/SiO2 was also investi-
gated (see Supporting information, Fig. S4 and S5). It is found that
using higher alkali concentration make the adsorption amount at
the low pressure turn less and pore size distribution shift to the
right, which indicates that the amount of micropore in composite
becomes less, resulting in larger average pore diameter. When the
molar ratio between SFAP and SMA rises from 1:10 to 1:1 (Entries
3
and 4) causing the increase in the content of organic resin, sur-
face area and pore volume of FSMA/SiO2 decrease, and its pore
diameter changes a little. These results keep consistent with that
of Nafion/SiO2 [33].
3.3. The adjustment on exchange capacity of FSMA/SiO2
There are two kinds of acidic groups in FSMA/SiO . One
2
Fig. 2. TGA of FSMA/SiO2 hybrid material.
is perfluoroalkanesulfonic acid (RfSO3H) originated from the

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Z. Lin et al. / Journal of Molecular Catalysis A: Chemical 365 (2012) 73–79
Fig. 3. XPS spectra of FSMA/SiO2 hybridized material.
Fig. 4. Elemental analysis spectrum of the surface of FSMA/SiO2 tested by EDX.
perfluoroalkylation of styrene with SFAP. The other is carboxyl acid
(
CO H) derived from the hydrolysis and aminolysis of maleic anhy-
2
dride. The total amount of the two acids determines the exchange
capacity of FSMA/SiO . Therefore, the exchange capacity can be
2
easily adjusted through changing the using amount of SFAP or the
concentration of maleic anhydride in SMA, instead of varying the
content of polymer resin in the composites, which would simulta-
neously change the porosity of composites. For instance, the surface
area of Nafion/SiO2 dropped rapidly at high loading of Nafion resin
(
such as 60 wt%) [33].
In this work, we have investigated the effect of molar ratio
between SFAP and SMA on the exchange capacity of FSMA/SiO2
with the results shown in the Table 2. The amount of R SO H in
f
3
Fig. 5. Distribution of F, O and Si element in the surface of FSMA/SiO2.
FSMA/SiO could be calculated from the content of F obtained from
2
elemental analysis. With the increase in molar ratio between SFAP
and SMA, the loading of R SO H in FSMA/SiO increase, reaching
f
3
2
Table 1
The effect of sol–gel condition on pore structure of FSMA/SiO2.
a
Entry
Molar ratio
SFAP:SMA)
Concentration of
NH4OH (mol/L)
BET surface
area (m /g)
BJH pore volume
(cm /g)
HJH pore
diameter (nm)
2
3
(
1
2
3
4
1:10
1:10
1:10
1:1
0.5
1.3
2.6
2.6
425
332
289
221
0.48
0.81
0.93
0.77
3.7
6.5
10.5
11.3
a
The molar ratio between TEOS and SMA is 11:1.

Z. Lin et al. / Journal of Molecular Catalysis A: Chemical 365 (2012) 73–79
77
Table 2
The effect of the molar ratio between SMA and SFAP on exchange capacity of FSMA/SiO2.
Entry
Molar ratio
SFAP:SMA)
Content of F
(wt%)
RfSO3H loading
(mmol/g)
CO2H loading
(mmol/g)
Loading ratio
(RfSO3H:CO2H)
Exchange capacity
(mmol/g)b
a
(
1
2
3
4
1:10
1:5
1:2
1:1
0.8
1.0
1.3
3.1
0.05
0.07
0.09
0.20
0.14
0.14
0.16
0.15
1:3
1:2
1:1.5
1:0.8
0.19
0.21
0.25
0.35
a
Calculated from exchange capacity.
Obtained by acidimetry.
b
Scheme 2. Cyclization of pseudoionone.
selectivity except for Nafion NR50 because of its low surface area.
Their excellent activity is attributed to their super-strong acidity
of perfluoroalkanesulfonic acid group (R SO H). It is believed that
f
3
their good selectivity is also ascribed to the bulky, lipophilic and
flexible perfluoroalkyl side chain with ether linkage [46]. Due to
higher surface area and more easily accessible acid sites, nanocom-
posites Nafion/SiO2 and FSMA/SiO2 exhibit higher yield than pure
polymer catalysts. It took FSMA/SiO2 1 h to yield 62% of ˛-ionone
with quantitative conversion and 100% selectivity.
Fig. 6. SEM photo of FSMA/SiO2 hybridized material.
In addition, we have tested the reusability of FSMA/SiO2 in the
cyclization. FSMA/SiO2 recovered by simply washing with ethanol
and drying was reused under the same conditions. In the five
0
.2 mmol/g (Entry 4) at the molar ratio of 1:1 (SFAP:SMA). From the
molar ratio between SMA and APTES, the amount of CO H could be
2
calculated to be 0.25 mmol/g. Thus, the total exchange capacity of
FSMA/SiO2 should be 0.45 mmol/g. However, the acidimetry gives
the exchange capacity of 0.35 mmol/g, which shows maleic anhy-
dride was not hydrolyzed completely. From the measured exchange
runs, FSMA/SiO showed high activity with the conversion of pseu-
2
doionone kept at 100%. In the sixth run, a slight deactivation took
place with 93% of conversion. The result indicates good reusability
of FSMA/SiO2 in the reaction.
capacity of FSMA/SiO , it can be deduced that the actual amount
2
of CO H is approximately 0.15 mmol/g. Through change the molar
2
ratio of SFAP and SMA, the loading ratio between R SO H and CO H
3.5. Condensation of indole
f
3
2
in FSMA/SiO2 is regulated from 1:3 to 1:0.8 with the exchange
capacity adjusted from 0.19 to 0.35 mmol/g.
Diindolylmethane is
a kind of compounds with health-
promoting properties which arise from a beneficial shift in the
balance of the sex hormones, estrogen and testosterone. Tradi-
tionally, diindolylmethane can be synthesized by condensation of
indoles with carbonyl compounds. The condensation of indole with
aldehyde was effectively catalyzed by solid acids to give hexyl diin-
dolylmethanes [47]. However, the activity of the condensation of
indole with ketone is lower than with aldehyde for its higher steric
hindrance. Here, hybrid nanocomposites and pure polymer resins
were employed to catalyze condensation of indole with acetone
3
.4. Cyclization of pseudoionone
The cyclization of pseudoionone (Scheme 2) was investigated
with the FSMA/SiO2 nanocomposite. The conversion of pseu-
doionone and yield of ionone under FSMA/SiO2 are given in
Table 3 with a comparison with the results by using Amberlyst-15,
Amberlyst-36, Nafion NR50 and Nafion/SiO . All of the cata-
lysts containing R SO H (Entries 3–5) show good activity and
2
f
3
Table 3
Cyclization of pseudoionone catalyzed by solid acids based on resins.a
Entry
Catalyst
Time (h)
Conversion (%)
Yield of ionone (%)
˛
ˇ
0
2
.5
.5
11
95
4
26
1
7
1
Amberlyst-15
0
2
28
82
17
32
5
11
2
3
Amberlyst-36
Nafion NR50b
Nafion/SiO2
2
3
0
0
0
1
.5
66
100
39
48
0
0
4
0
1
.5
69
100
37
62
0
0
5
FSMA/SiO2
a
◦
Reactive temperature, 80 C; catalyst/pseudoionone = 0.5 g/1 mL.
To use benzene as solvent.
b

7
8
Z. Lin et al. / Journal of Molecular Catalysis A: Chemical 365 (2012) 73–79
aminolysis with (3-aminopropyl)triethoxysilane, alkali hydrolysis,
gelation using tetraethoxysilane and acidification in aqueous HCl,
we have developed a new kind of ω-sulfonic-perfluoroalkylated
poly(styrene–maleic anhydride)/silica hybrid nanocomposites
FSMA/SiO2 bearing perfluoroalkylsulfonic and carboxyl termi-
nal groups. Compared to Nafion/SiO , FSMA/SiO2 has advantages
2
Scheme 3. Condensation of indole with acetone.
in low cost, mild synthetic conditions, high exchange capacity,
homodispersity of the resin in silica, adjustable acidity and easy
functionalization. The nanocomposite FSMA/SiO2 showed higher
activity and better selectivity than the widely used commer-
cial solid acids catalysts such as Nafion and Amberlyst-15 in the
synthesis of ionone (cyclization), dimethyl diindolylmethane (con-
densation) and butyl benzoate (esterification). The further studies
Table 4
Condensation of indole with acetone catalyzed by solid acids.
a
Entry
Catalyst
Loading of catalyst
mol%)b
Yield (%)
(
1
2
3
4
5
Amberlyst-15
Nafion NR50
FPS
Nafion/SiO2
FSMA/SiO2
10
10
10
5
5
19
21
71
71
via tailoring FSMA/SiO nanocomposite by varying its acid strength
2
and content for particular reactions, are under the way.
5
a
◦
Acknowledgements
Reactive time, 12 h; temperature, 25 C.
Molar ratio (H in catalyst/acetone).
b
+
This work was supported by the National Natural Science Foun-
dation of China (60976019), Specialized Research Fund for the
Doctoral Program of Higher Education (SRFDP 20093223110002),
Program for Innovative Research Team in Science and Technology
in Fujian Province University (IRTSTFJ).
Scheme 4. Esterification of benzoic acid with n-butanol.
Appendix A. Supplementary data
Table 5
a
Esterification of benzyl acid with n-butanol catalyzed by solid acids.
Supplementary data associated with this article can be
found, in the online version, at http://dx.doi.org/10.1016/
j.molcata.2012.08.011.
Entry
Catalyst
Conversion of benzoic
acid (%)
1
2
3
4
5
Amberlyst-15
Amberlyst-36
Nafion NR50
Nafion/SiO2
FSMA/SiO2
69
30
49
81
87
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3
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4
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3
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2
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