Synthesis of the sulfonated condensed polynuclear aromatic (S-COPNA) resins as strong protonic acids

Article abstract of DOI:10.1016/j.tet.2010.11.077

The mixture (PXG/PR=1.00) of pyrene (PR) and p-xylylene glycol (1,4-benzenedimethanol) (PXG) in the presence of 5 wt % of p-toluenesulfonic acid (TsOH) was heated at 140 °C for 45 min under nitrogen to give the highly viscous condensed polynuclear aromatic (COPNA) resin. It was converted into an infusible and insoluble solid by further heating at 300 °C for 1 h. The obtained material was treated with fuming sulfuric acid at 80 °C for 15 h under nitrogen to give the sulfonated COPNA resin. The similar acidic resin was prepared by the reaction of phenanthrene or naphthalene with PXG in the presence of TsOH followed by sulfonation. The performance of the sulfonated polymers as the strong protonic acids was evaluated.

Full text of DOI:10.1016/j.tet.2010.11.077

Tetrahedron 67 (2011) 1314e1319
Contents lists available at ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Synthesis of the sulfonated condensed polynuclear aromatic (S-COPNA) resins
as strong protonic acids
,
a
a
b
Kiyoshi Tanemura a , Tsuneo Suzuki , Yoko Nishida , Takaaki Horaguchi
*
a School of Life Dentistry at Niigata, Nippon Dental University, Hamaura-cho, Niigata 951-8580, Japan
b Department of Chemistry, Faculty of Science, Niigata University, Ikarashi, Niigata 950-2181, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 10 August 2010
Received in revised form 18 November 2010
Accepted 18 November 2010
Available online 27 November 2010
The mixture (PXG/PR¼1.00) of pyrene (PR) and p-xylylene glycol (1,4-benzenedimethanol) (PXG) in the
presence of 5 wt % of p-toluenesulfonic acid (TsOH) was heated at 140 ꢀC for 45 min under nitrogen to
give the highly viscous condensed polynuclear aromatic (COPNA) resin. It was converted into an infusible
and insoluble solid by further heating at 300 ꢀC for 1 h. The obtained material was treated with fuming
sulfuric acid at 80 ꢀC for 15 h under nitrogen to give the sulfonated COPNA resin. The similar acidic resin
was prepared by the reaction of phenanthrene or naphthalene with PXG in the presence of TsOH fol-
lowed by sulfonation. The performance of the sulfonated polymers as the strong protonic acids was
evaluated.
Keywords:
COPNA resin
Acid catalysts
Protonic acids
Sulfonation
Ó 2010 Elsevier Ltd. All rights reserved.
Sulfonated polymers
1. Introduction
quite insoluble to boiling water and many hot organic solvents.
Furthermore, these can be employed at high temperature and
Sulfonated polymers have attracted considerable attention for
a wide range of potential usefulness as solid acid catalysts, con-
ductive polymers, and materials for making fuel cell membranes.1
Cation exchange resins, such as Amberlyte are superior acid cata-
lysts easy to synthesize, however, these polymers cannot be
employed at high temperature. Nafion-H is typically used as the
polymeric superacid, however, it is difficult to synthesize and its
acid activity is low. Recently, the sugar catalyst, which was a new
class of sulfonated carbons derived from incomplete carbonization
and sulfonation of simple sugars, has been devised.2,3 Sulfonated
poly(1,4-diphenoxyphenylene)4 and sulfonated carbon material
derived from polynuclear aromatic compounds, such as naphtha-
lene,5 have been prepared. The advantage utilizing polynuclear
aromatic compounds as the starting material is that sulfonated
polymers with various substituents can be designed.
showed high acid activities. In this paper, we wish to report the
synthesis and evaluation of the S-COPNA resins.
2. Results and discussions
2.1. Synthesis of the S-COPNA resins
First, synthesis of the S-COPNA(PR) resin (PXG/PR¼1.25 in the
molar ratio) (PR¼pyrene) was investigated as the model case. By
Otani’s method,6 the mixture of pyrene, PXG, and p-TsOH (5 wt % of
[PXGþPR]) was heated at 140 ꢀC for 45 min under nitrogen to give
a highly viscous yellow melt (called as a B-stage resin). The melt
was converted into an infusible and insoluble black solid by sub-
sequent post-curing at 300 ꢀC for 1 h under nitrogen.
The post-cured COPNA(PR) resin was sulfonated by fuming sul-
furic acid (15 wt % SO3) at 80 ꢀC for 15 h under nitrogen to give the
S-COPNA(PR) resin as the black powder (Table 1, entry 2). The plau-
sible structural model of the S-COPNA(PR) resin was shown in Fig. 1.
Acid density was determined by acid titration. The rate constant (k)
for the esterification of acetic acid with EtOH was determined by acid
titration of remaining acetic acid included in the reaction mixture.
Although sulfonation at 150 ꢀC affordedthe materialwith thehighest
acid density, k was smaller than that of 80 ꢀC (entries 1 and 2).
Weconsidered that the approach ofsubstrates mightbedifficult with
the decrease of hydrophobic nature of the catalyst by the
Otani et al. have reported the synthesis of the condensed poly-
nuclear aromatic (COPNA) resins with extremely high thermosta-
bility through the dehydration reaction between fused aromatic
hydrocarbons (Aro) and p-xylylene glycol (1,4-benzenedimethanol)
(PXG) catalyzed by p-toluenesulfonic acid (TsOH).6e10
These results prompted us to study the synthesis of the
sulfonated COPNA (S-COPNA) resins. The obtained materials were
* Corresponding author. Fax: þ81 25 267 1134; e-mail address: tanemura@
ngt.ndu.ac.jp (K. Tanemura).
0040-4020/$ e see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2010.11.077

K. Tanemura et al. / Tetrahedron 67 (2011) 1314e1319
1315
Table 1
Table 3
Sulfonation of the post-cured COPNA(PR) resin by fuming sulfuric acida
Sulfonation of the COPNA(PR) resins treated at various curing temperature by
fuming sulfuric acida
Entry Temp (ꢀC) Time (h) Acid density (mmol gꢂ1
)
kcꢁ10ꢂ4 Solubilityd
b
Entry Curing
temp (ꢀC)
400
Temp (ꢀC) Acid
density (mmol gꢂ1
4.96
kcꢁ10ꢂ4 Solubilityd
1
2
3
150
80
25
150
80
25
15
15
24
15
15
24
6.01
5.12
4.44
5.70
4.44
0.30
4.63
6.59
5.43
3.66
3.44
0.63
þ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
b
)
1
2
3
4
80
80
80
80
25
25
25
6.98
7.08
7.84
8.56
7.98
8.59
9.35
ꢂ
4e
5e
6e
300
200
none
400
300
5.18
5.51
5.33
4.93
5.04
5.23
ꢂ
ꢂ
ꢂ
5e
6e
7e
þ
a
Reagents and conditions: the post-cured COPNA(PR) resin (PXG/PR¼1.25 in the
molar ratio, post-cured at 300 ꢀC for 1 h) 2.5 g, fuming sulfuric acid (15 wt % SO3)
20 mL, N2.
ꢂ
none
þþ
b
a
Determined by titration.
Rate constant for the esterification of acetic acid with EtOH.
Reagents and conditions: the COPNA(PR) resin (PXG/PR¼1.00 in the molar ratio)
c
2.5 g, fuming sulfuric acid (15 wt % SO3) 20 mL, 15 h, N2.
d
b
Solubility to boiling water: ꢂ(insoluble)<þ<þþ(partially soluble).
Determined by titration.
Rate constant for the esterification of acetic acid with EtOH.
e
c
Sulfuric acid (20 mL) was used.
d
Solubility to boiling water: ꢂ(insoluble) <þ<þþ(partially soluble).
e
Sulfonated by chlorosulfonic acid in dichloromethane.
sulfuric acid, a color change from yellow to black was observed,
suggesting that aromatization of the carbon skeleton may occur
during sulfonation. Although the obtained resin possessed the
highest activity, it required long time to filter the precipitate and
the sedimentation in water was slow (entry 4). Post-curing, espe-
cially at 300 ꢀC, was effective for quick filtration and fast sedi-
mentation (entry 2). Sulfonation of the COPNA(PR) resin with
and without post-curing by ClSO3H in dichloromethane gave the
S-COPNA(PR) resins with high activities (entries 5e7). The color
change of the precipitate from brown to black during work-up,
especially heating at 150 ꢀC, was observed. However, it was difficult
to exclude adsorbed chlorosulfonic acid. Therefore, complex ex-
perimental procedures were required.
Table 4 shows the analytical data and catalytic activities of the
S-COPNA(PR) resins synthesized by the different sulfonating agents.
Rate constants were correlated with the degree of sulfonation cal-
culated from chemical composition. Acid densities of the sulfonated
resins determined by titration were larger than the degree of sul-
fonation. Especially, there was a large difference in the sulfonated
resin prepared by the reaction with sulfuric acid (entry 2). It will be
because of containing weakly acidic functional groups, such as
phenolic hydroxyl groups. However, it was difficult to discuss the
detailed structure of the sulfonated resins, since IR spectra of the S-
COPNA(PR) resin prepared by the sulfonation with sulfuric acid was
almost the same as the others except for the appearance of the new
absorption at 1560 cmꢂ1 due to the benzene ring.
Next, we prepared the post-cured COPNA resins consisting of
the other condensed polynuclear aromatic structure. The results
are shown in Table 5. The post-cured COPNA(PH) (PH¼phenan-
threne) and the COPNA(NP) (NP¼naphthalene) resins were pre-
pared in good yields by the similar procedure with the post-cured
COPNA(PR) resin (curing temp 300 ꢀC) (entries 2 and 5). Attempts
to prepare the COPNA(AT) (AT¼anthracene) resin failed because the
mixture of PXG, anthracene, and 5 wt % of TsOH did not make the
uniform melt even at 260 ꢀC because of the high melting point of
anthracene (218 ꢀC)11 (entries 3 and 4). Table 6 shows the results for
the sulfonation of the various post-cured COPNA resins by fuming
sulfuric acid. Although sulfonation of the post-cured COPNA(PH)
resin at 150 ꢀC gave the solid with higher acid density, the activity
was lower than that of the solid sulfonated at 80 ꢀC (entries 2 and
3). In addition, it was partially soluble to boiling water. Sulfonation
at 80 ꢀC led to the most active material (entry 3). The rate constant
(k¼6.22ꢁ10ꢂ4) of the S-COPNA(PH) resin was smaller than that of
the S-COPNA(PR) resin (k¼7.08ꢁ10ꢂ4) (entries 1 and 3). Similarly,
the S-COPNA(NP) resin was obtained by the sulfonation of the post-
cured COPNA(NP) resin at 150 ꢀC (entry 5). The rate constant
(k¼4.87ꢁ10ꢂ4) of the S-COPNA(NP) resin was smaller than those
of the S-COPNA(PR) and the S-COPNA(PH) resins. The obtained
S-COPNA resins were insoluble to boiling water and many hot
Fig. 1. Schematic model of the S-COPNA(PR) resin.
introduction of the hydrophilic SO3H group. In addition, it was par-
tially soluble to boiling water. When sulfonation was carried out by
concentrated sulfuric acid, rate constants were smaller than those by
fuming sulfuric acid (entries 4e6). It is interesting to note that the
rate constant (k¼5.43ꢁ10ꢂ4) of the material sulfonated by fuming
sulfuric acid at 25 ꢀC was larger than that by concentrated sulfuric
acid at 80 ꢀC (k¼3.44ꢁ10ꢂ4) in spite of the same acid density
(4.44mmolgꢂ1)(entries3and 5). TheS-COPNA(PR)resinobtainedby
the reaction at 80 ꢀC in fuming sulfuric acid was the most active
material (entry 2).
Table 2 summarizes the results for sulfonation of the post-cured
COPNA(PR) resins with various molar ratios PXG/PR. We chose the
post-cured COPNA(PR) resins with PXG/PR¼1.00, 1.25, and 1.50,
which were suitable for the formation of the B-stage resin.6 The
best result was obtained by the sulfonation of the post-cured
COPNA resin with PXG/PR¼1.00 (entry 1).
The influence of post-curing temperature on the activity of the
S-COPNA resin was explored (Table 3, entries 1e4). When the
COPNA(PR) resin without post-curing was treated with fuming
Table 2
Sulfonation of the post-cured COPNA(PR) resins with various molar ratios by fuming
sulfuric acida
b
Entry
PXG/PR
Acid density (mmol gꢂ1
)
kcꢁ10ꢂ4
Solubilityd
1
2
3
1.00
1.25
1.50
5.18
5.12
4.67
7.08
6.59
5.08
ꢂ
ꢂ
ꢂ
a
Reagents and conditions: the post-cured COPNA(PR) resin (post-cured at 300 ꢀ
for 1 h) 2.5 g, fuming sulfuric acid (15 wt % SO3) 20 mL, 80 ꢀC, 15 h, N2.
C
b
Determined by titration.
Rate constant for the esterification of acetic acid with EtOH.
Solubility to boiling water: ꢂ(insoluble) <þ<þþ(partially soluble).
c
d

1316
K. Tanemura et al. / Tetrahedron 67 (2011) 1314e1319
Table 4
Analytical data and catalytic activities of the S-COPNA(PR) resins
d
e
Entry
Sulfonating agent
Chemical composition
SO3H (mmol$gꢂ1
)
Acid density (mmol gꢂ1
)
kfꢁ10ꢂ4
7.08
3.50
8.59
Solubilityg
1
2
3
Fuming sulfuric acida
CH0.725O0.396S0.088
CH0.438O0.265S0.030
CH0.671O0.312S0.086
4.02
1.70
4.21
5.18
4.88
5.04
ꢂ
ꢂ
ꢂ
Sulfuric acidb
Chlorosulfonic acidc
a
Reagents and conditions: the post-cured COPNA resin (PXG/Aro¼1.00 in the molar ratio, post-cured at 300 ꢀC for 1 h) 2.5 g, fuming sulfuric acid (15 wt % SO3) 20 mL, 80 ꢀC,
15 h, N2.
b
c
Reagents and conditions: the post-cured COPNA resin (PXG/Aro¼1.00 in the molar ratio, post-cured at 300 ꢀC for 1 h) 2.5 g, sulfuric acid 20 mL, 150 ꢀC, 15 h, N2.
Reagents and conditions: the post-cured COPNA resin (PXG/Aro¼1.00 in the molar ratio, post-cured at 300 ꢀC for 1 h) 2.5 g, chlorosulfonic acid 3.9 mL, dichloromethane
22.5 mL, 25 ꢀC, 24 h, N2.
d
Calculated from chemical composition.
Determined by titration.
Rate constant for the esterification of acetic acid with EtOH.
Solubility to boiling water: ꢂ(insoluble) <þ<þþ(partially soluble).
e
f
g
decomposition process was observed for all polymers. For the
S-COPNA(PR) resin, the decomposition reaction started at around
190 ꢀC, while for the S-COPNA(PH) and the S-COPNA(NP) resins, the
reactions started at 240e250 ꢀC. In the case of the S-COPNA(NP)
resin, the weight decreased largely at 510e530 ꢀC. Heating these
polymers above 480e530 ꢀC resulted in a rapid decrease in weight.
Table 5
Synthesis of the various post-cured COPNA(Aro) resinsa
Entry
Aro
Temp (ꢀC)
Time (h)
Yield (%)
1
2
3
4
5
PR
PH
AT
140
130
260
180
120
0.75
2
2
2
3.5
91
89
0
0
81
NP
2.2. Evaluation of the S-COPNA resins
a
Reagents and conditions: Aro (100 mmol), PXG (100 mmol), TsOH (5 wt % of
[PXGþAro]), post-cured at 300 ꢀC for 1 h, N2.
Rate constants for esterification of carboxylic acids and hydro-
lysis of esters were summarized in Table 7. Fig. 3a shows the rate
constants for the formation of ethyl acetate (80 ꢀC) on the most
active S-COPNA(PR) and the easily accessible S-COPNA(NP) resins
(200 mg). These catalysts exhibited higher activities than conven-
tional solid acids, such as mordenite, Montmorillonite K10, Nafion
NR50, Nafion SAC-13, and Amberlyst 15. The rate constant
(k¼7.08ꢁ10ꢂ4) of the S-COPNA(PR) resin was 1.8 times larger than
that of the sugar catalyst (k¼4.04ꢁ10ꢂ4). The S-COPNA(PR) and the
S-COPNA(NP) resins showed high activities for the formation of
ethyl benzoate (80 ꢀC), while conventional solid acids were inert for
the reaction (Fig. 3b). For the hydrolysis of cyclohexyl acetate and
oleyl acetate, activities of the S-COPNA(PR) resin were considerably
higher than those of the other acidic catalysts including sulfuric
acid (Fig. 3c and d).
Table 6
Sulfonation of the various post-cured COPNA(Aro) resins by fuming sulfuric acida
Entry Aro Temp (ꢀC) Time (h) SO3H
(mmol$gꢂ1
4.02
Acid density kdꢁ10ꢂ4 Solubilitye
b
c
)
(mmol gꢂ1
)
1
2
3
4
5
6
7
PR 80
PH 150
80
25
NP 150
80
15
15
15
24
15
15
24
5.18
5.20
3.62
0.58
4.92
2.53
0.53
7.08
6.10
6.22
1.35
4.87
3.44
1.33
ꢂ
þ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
2.42
3.42
25
a
Reagents and conditions: the post-cured COPNA resin (PXG/Aro¼1.00 in the
molar ratio, post-cured at 300 ꢀC for 1 h) 2.5 g, fuming sulfuric acid (15 wt % SO3)
20 mL, N2.
b
In order to check the reusability of the catalysts, the catalysts
were removed by decantation and used for the next experiment.
The catalysts were reused without significant loss of activities
(Table 8).
Calculated from chemical composition.
Determined by titration.
Rate constant for the esterification of acetic acid with EtOH.
Solubility to boiling water: ꢂ(insoluble) <þ<þþ(partially soluble).
c
d
e
organic solvents, such as benzene, THF, chloroform, ethanol, ace-
tone, EtOAc, CH3CN, DMF, and DMSO.
3. Conclusions
The thermal stability of the S-COPNA resins was examined by
thermogravimetric analysis (TGA) in air atmosphere (Fig. 2). The
thermal stability increased in the order: the S-COPNA(NP) resin-
>the S-COPNA(PH) resin>the S-COPNA(PR) resin. After an initial
weight loss due to evaporation of absorbed water, the two-step
We synthesized the S-COPNA resins by the reactions of poly-
nuclear aromatic compounds and PXG in the presence of TsOH
followed by sulfonation. It is noteworthy that synthetic procedures
are quite simple because preparations of the COPNA resins
are conducted by only mixing and heating of the substrates. The
S-COPNA resins exhibited the higher performance than conven-
tional solid acids. The activities of the S-COPNA(PR) resin were
higher than those of the S-COPNA(NP) resin. The S-COPNA(NP)
resin will be also useful because of the lower price of naphthalene.
The S-COPNA resins can be easily removed by simple decantation
from the reaction mixture.
4. Experimental
4.1. General methods
IR spectra were recorded on a JEOL FT/IR-620 spectrophotom-
eter. UV spectra were recorded on a Shimadzu UVevis spectro-
photometer UV-2550. Thermogravimetric analysis (TGA) in air
atmosphere was carried out on a Rigaku Thermo Plus 2 station
Fig. 2. TGA curves in air of the S-COPNA resins.

K. Tanemura et al. / Tetrahedron 67 (2011) 1314e1319
1317
Table 7
Rate constants for various reactions
Catalyst
CH3COOHþEtOH
PhCOOHþEtOH
CyOAcþH2O
OleOAcþH2O
a
b
c
d
(ꢁ10ꢂ4 mol dm3 minꢂ1
)
(ꢁ10ꢂ5 mol dm3 minꢂ1
)
(ꢁ10ꢂ4 mol dm3 minꢂ1
)
(ꢁ10ꢂ5 mol dm3 minꢂ1
)
S-COPNA(PR)
S-COPNA(NP)
Mordenite
Montmorillonite K10
Nafion NR50
Nafion SAC-13
Amberlyst 15
Sulfuric acid
7.08
4.87
0.11
1.63
0.56
0.79
2.33
46.00
3.33
1.15
0.00
0.00
0.00
0.00
0.00
15.50
10.30
3.47
0.04
0.03
0.25
0.15
0.26
0.80
3.41
1.23
0.15
0.00
0.00
0.00
0.08
1.00
a
Reagents and conditions: EtOH (1.0 mol), CH3COOH (0.1 mol), catalyst (200 mg), 80 ꢀC.
Reagents and conditions: EtOH (1.0 mol), PhCOOH (0.1 mol), catalyst (200 mg), 80 ꢀC.
Reagents and conditions: CyOAc (4.4 mmol), H2O (3.3 mol), catalyst (200 mg), 90 ꢀC.
Reagents and conditions: OleOAc (4.4 mmol), H2O (3.3 mol), catalyst (200 mg), 100 ꢀC.
b
c
d
TG-DTA TG 8120 at a heating rate of 10 ꢀC/min. All samples were
evacuated at 150 ꢀC for 1 h under reduced pressure prior to the
measurement of TGA. The grinding was conducted by Wonder
Blender WB-1 (Osaka Chemical Co., purchased from AS ONE Co.).
140 ꢀC for 45 min in a stream of nitrogen to produce a highly viscous
material. The yield was 31.6 g (93%); IR (KBr) nmax 3437 (OH), 3036
(ArH), 2903, 2850 (CH2), 1602, 1508, 841, 817, 748 cmꢂ1 (ArH).
The obtained material was converted into an infusible and in-
soluble solid by further heating at 300 ꢀC for 1 h under nitrogen.
The obtained solid was ground to a powder by the mill. The yield
was 30.7 g (91%); IR (KBr) nmax 3448 (OH), 3040 (ArH), 2925 (CH2),
1637, 1508, 839 cmꢂ1 (ArH). The nominal sample composition was
4.2. Preparation of the post-cured COPNA(PR) resin
The mixture of pyrene (20.2 g, 100 mmol), PXG (13.8 g,
determined by elemental analysis to be CH0.675O0.010
.
100 mmol), and TsOH (1.70 g, 5 wt % of [PXGþpyrene]) was heated at
Fig. 3. Acid-catalyzed liquid-phase reactions: (a) Rate constants for the formation of ethyl acetate (80 ꢀC); (b) Rate constants for the formation of ethyl benzoate (80 ꢀC); (c) Rate
constants for the hydrolysis of cyclohexyl acetate (90 ꢀC); (d) Rate constants for the hydrolysis of oleyl acetate (100 ꢀC).

1318
K. Tanemura et al. / Tetrahedron 67 (2011) 1314e1319
Table 8
4.7. Preparation of the S-COPNA(NP) resin
Recycle experiments of the formation of ethyl acetate catalyzed by the S-COPNA(PR)
or the S-COPNA(NP) resina
Post-cured COPNA(NP) (7.5 g) was added to fuming sulfuric acid
(15 wt % SO3) (60 mL). The mixture was stirred at 150 ꢀC for 15 h
under nitrogen. The mixture was poured into distilled water
(400 mL). The precipitate was collected by filtration and washed
repeatedly with hot distilled water (>80 ꢀC) until the wash water
reached a pH of 7. The precipitate was dried at 150 ꢀC for 3 h under
reduced pressure. The S-COPNA(NP) resin (10.5 g) was obtained as
the hygroscopic black powder; IR (KBr) nmax 2921 (CH2), 1619 (ArH),
1168, 1029 cmꢂ1 (SO3H). The nominal sample composition was
Cycle
First
Second
Third
Fourth
Fifth
S-COPNA(PR), 4 h Conv. (%)b
90
76
88
73
90
73
90
75
88
74
S-COPNA(NP), 4 h Conv. (%)b
a
Reagents and conditions: EtOH (1.0 mol), CH3COOH (0.1 mol), catalyst (200 mg),
80 ꢀC, 4h.
b
Determined by titration.
4.3. Preparation of the post-cured COPNA(PH) resin
determined by elemental analysis to be CH0.918O0.576S0.085
.
The mixture of phenanthrene (17.8 g, 100 mmol), PXG (13.8 g,
100 mmol) and TsOH (1.58 g, 5 wt %) was heated at 130ꢀC for 2 h
under nitrogen to produce a highly viscous material. It was con-
verted into an infusible and insoluble solid by further heating at
300 ꢀC for 1 h. The obtained solid was ground to a powder. The yield
was 28.0 g (89%); IR (KBr) nmax 3436 (OH), 3017 (ArH), 2915 (CH2),
1618, 1508, 885, 803, 742, 721 cmꢂ1 (ArH). The nominal sample
composition was determined by elemental analysis to be
4.8. Sulfonation of the post-cured COPNA(PR) resin by
sulfuric acid
Post-cured COPNA(PR) (2.5 g) was added to sulfuric acid
(20 mL). The mixture was stirred at 150 ꢀC for 15 h under nitrogen.
The mixture was poured into distilled water (133 mL). The pre-
cipitate was collected by filtration and washed repeatedly with hot
distilled water (>80 ꢀC) until the wash water reached a pH of 7. The
precipitate was dried at 150 ꢀC for 3 h under reduced pressure. The
S-COPNA(PR) resin (2.9 g) was obtained as the hygroscopic black
powder; IR (KBr) nmax 2923 (CH2),1637,1560 (ArH),1170,1026 cmꢂ1
(SO3H). The nominal sample composition was determined by ele-
CH0.734O0.012
.
4.4. Preparation of the post-cured COPNA(NP) resin
The mixture of naphthalene (15.4 g, 120 mmol), PXG (16.6 g,
120 mmol), and TsOH (1.60 g, 5 wt %) was heated at 120 ꢀC for 3.5 h
under nitrogen to produce a highly viscous material. It was con-
verted into an infusible and insoluble solid by further heating at
300 ꢀC for 1 h. The obtained solid was ground to a powder. The yield
was 25.5 g (81%); IR (KBr) nmax 3432 (OH), 3043, 3005 (ArH), 2901
(CH2), 1596, 1508, 780 cmꢂ1 (ArH). The nominal sample composi-
mental analysis to be CH0.438O0.265S0.030
.
4.9. Sulfonation of the post-cured COPNA(PR) resin by
chlorosulfonic acid
A
solution of chlorosulfonic acid (3.9 mL, 60 mmol) in
dichloromethane (7.5 mL) was slowly added to the mixture of post-
cured COPNA(PR) (2.5 g) in dichloromethane (15 mL) with stirring
under nitrogen. The mixture was stirred at 25 ꢀC for 24 h. The
precipitate was collected by filtration and washed with dichloro-
methane. The precipitate was dispersed in distilled water (100 mL).
The mixture was filtered and the precipitate was washed with hot
distilled water (>80 ꢀC) until the wash water reached a pH of 7.
Procedures of heating at 150 ꢀC for 30 min, dispersion in distilled
water (100 mL), and filtration were repeated until hydrogen chlo-
ride does not evolve. The precipitate was dried at 150 ꢀC for 3 h
under reduced pressure to give the sulfonated polymer. The yield
was 3.0 g; IR (KBr) nmax 2925 (CH2), 1637 (ArH), 1166, 1020 cmꢂ1
(SO3H). The nominal sample composition was determined by ele-
tion was determined by elemental analysis to be CH0.789O0.010
.
4.5. Preparation of the S-COPNA(PR) resin
Post-cured COPNA(PR) (7.5 g) was added to fuming sulfuric acid
(15 wt % SO3) (60 mL). The mixture was stirred at 80 ꢀC for 15 h
under nitrogen. The mixture was poured into distilled water
(400 mL). The precipitate was collected by filtration and washed
repeatedly with hot distilled water (>80 ꢀC) until the wash water
reached a pH of 7. The precipitate was dried at 150 ꢀC for 3 h under
reduced pressure. The S-COPNA(PR) resin (10.5 g) was obtained as
the hygroscopic black powder; IR (KBr) nmax 2925 (CH2),1636 (ArH),
1165, 1023 cmꢂ1 (SO3H). The nominal sample composition was
mental analysis to be CH0.671O0.312S0.086
.
determined by elemental analysis to be CH0.725O0.396S0.088
.
4.10. Determination of the rate constant (k) for the
esterification of carboxylic acids and hydrolysis of esters
Acid density was determined by titration using the following
procedure. The sulfonated polymer (168 mg) was placed in 0.1 M
aqueous NaOH solution (20 mL), and the mixture was kept at room
temperature for 1 day. The precipitate was filtered, and the filtrate
was then back titrated with 0.1 M aqueous potassium hydrogen
phthalate solution using phenolphthalein as an indicator.
Esterification of acetic acid with ethanol was typically carried
out at 80 ꢀC in the mixture of ethanol (56.80 mL, 1.0 mol), acetic
acid (5.71 mL, 0.1 mol), and the catalyst (200 mg). The reaction
mixture at 10, 20, 30, 40, 50, 60, 80, 100, 120, and 140 min was
analyzed by titration with 0.1 M aqueous NaOH solution. In the
actual experiment, a blank sample containing EtOH (62.51 mL) and
the catalyst (200 mg) without acetic acid was also titrated. From the
difference in titrant volume required to reach the endpoint for the
blank, the concentration of acetic acid was calculated. Rate con-
stants were determined by the plots between time versus [1/(aꢂb)]
ln[b(aꢂx)/a(bꢂx)] (the second order reaction) using the method of
least squares. The rate constant of sulfuric acid was determined in
the early stage of the reaction (10 min). The S-COPNA resins were
dried at 150 ꢀC for 1 h under reduced pressure prior to the reaction.
Esterification of benzoic acid with ethanol was carried out in the
mixture of ethanol (56.80 mL, 1.0 mol) and benzoic acid (12.2 g,
0.1 mol) at 80 ꢀC. The reaction mixture at 10, 20, 40, 60, 100, 140,
4.6. Preparation of the S-COPNA(PH) resin
Post-cured COPNA(PH) (2.5 g) was added to fuming sulfuric acid
(15 wt % SO3) (20 mL). The mixture was stirred at 80 ꢀC for 15 h
under nitrogen. The mixture was poured into distilled water
(133 mL). The precipitate was collected by filtration and washed
repeatedly with hot distilled water (>80 ꢀC) until the wash water
reached a pH of 7. The precipitate was dried at 150 ꢀC for 3 h under
reduced pressure. The S-COPNA(PH) resin (3.0 g) was obtained as
the hygroscopic black powder; IR (KBr) nmax 2925 (CH2),1637 (ArH),
1170, 1033 cmꢂ1 (SO3H). The nominal sample composition was
determined by elemental analysis to be CH0.914O0.262S0.045
.

K. Tanemura et al. / Tetrahedron 67 (2011) 1314e1319
1319
180, 220, 260, 300, 340, and 380 min was analyzed by titration with
0.1 M aqueous NaOH solution.
AcOH with 0.1 M aqueous NaOH solution. The catalyst was re-
covered by decantation and reused repeatedly for the next reaction.
Hydrolysis of cyclohexyl acetate was carried out in the mixture
of cyclohexyl acetate (0.64 mL, 4.4 mmol) and distilled water
(59.40 mL, 3.3 mol) at 90 ꢀC. The reaction mixture at 10, 20, 30, 40,
50, 60, 80, 100, 120, and 140 min was analyzed by titration with
0.05 M aqueous NaOH solution.
Hydrolysis of oleyl acetate was carried out in the mixture of
oleyl acetate (1.57 mL 4.4 mmol) and distilled water (59.40 mL,
3.3 mol) at 100 ꢀC. The reaction mixture at 10, 20, 30, 40, 50, 60, 80,
100, 120, 140, 160, and 180 min was analyzed by titration with
0.05 M aqueous NaOH solution.
Acknowledgements
We thank the Division of Chemical Analysis, the Institute of
Physical and Chemical Research (RIKEN) for elemental analyses. We
thank the Research Promotion Grant (NDUF-10-11) from Nippon
Dental University.
References and notes
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After esterification of acetic acid with ethanol for 4 h, the con-
version of acetic acid was determined by acid titration of remaining