The carbon material functionalized with NH2+ and SO3H groups catalyzed esterification with high activity and selectivity

Article abstract of DOI:10.1039/c4gc01395f

A novel carbon-based solid acid was conveniently prepared by heating a mixture of d-glucose, p-toluenesulfonic acid and diphenylammonium tosylate. Its structure was measured by XRD, FT-IR, XPS, ¹³C MAS NMR and EA to illustrate that the carbon material has been functionalized with NH₂⁺ and SO₃H groups and has a strong "hydrophobic effect". It can be used to catalyze the esterification reaction of carboxylic acids with equimolar amounts of sterically demanding and acid-sensitive alcohols with high reactivity (yield up to 90%) and selectivity (up to 95%) in heptane at 80 °C. It could be easily recovered and reused more than ten times without loss of activity.

Full text of DOI:10.1039/c4gc01395f

Green Chemistry
View Article Online
View Journal
COMMUNICATION
+
The carbon material functionalized with NH2 and
SO3H groups catalyzed esterification with high
activity and selectivity†
Cite this: DOI: 10.1039/c4gc01395f
Received 22nd July 2014,
Accepted 28th August 2014
Shaoqi Zhan,a Xiaochun Tao,*a Liangzhen Cai,*a Xiaohui Liua and Taoping Liu*b
DOI: 10.1039/c4gc01395f
www.rsc.org/greenchem
A novel carbon-based solid acid was conveniently prepared by
heating a mixture of D-glucose, p-toluenesulfonic acid and diphenyl-
ammonium tosylate. Its structure was measured by XRD, FT-IR,
XPS, 13C MAS NMR and EA to illustrate that the carbon material has
+
been functionalized with NH2 and SO3H groups and has a strong
“hydrophobic effect”. It can be used to catalyze the esterification
reaction of carboxylic acids with equimolar amounts of sterically
demanding and acid-sensitive alcohols with high reactivity (yield
up to 90%) and selectivity (up to 95%) in heptane at 80 °C. It could
be easily recovered and reused more than ten times without loss
of activity.
Generally, the esterification reaction between carboxylic acids
and alcohols is catalyzed with Brønsted acids such as H2SO4,
p-toluenesulfonic acid, etc.1,2 Although these catalysts show
good activity for esterification reaction, too strong acidity often
leads to low selectivity for some acid-sensitive alcohols, such
as secondary alcohols which can be converted to alkenes in
the presence of a strong acid.3 In 2000, Tanabe et al. developed
a new type of esterification catalyst diphenylammonium
triflate ([Ph2NH2]+[OTf]−),4 which has a weaker acidity and
can be used to catalyze esterification of carboxylic acids with
equimolar amounts of secondary alcohols in high yields.
Subsequently, Ishihara’s group reported that bulky diaryl-
ammonium pentafluorobenzenesulfonates ([Ar2NH2]+[O3SC6F5]−)
were more efficient than [Ph2NH2]+[OTf]− in catalytic activity
and selectivity.3,5–7 They assumed that it is the dimeric cyclic
ion pairs composed of two diarylammonium cations ([Ar2NH2]+)
and two pentafluorobenzenesulfonate anions ([O3SC6F5]−)
which could form a “hydrophobic wall” to promote the esterifi-
cation reactions. Also their steric hindrance could effectively
Scheme 1 Proposed strategy to improve the catalytic activity and
selectivity by a synergistic effect of Ishihara’s and Hara’s catalysts.
suppress the dehydrative elimination of secondary alcohols to
produce alkenes (Scheme 1).6 In order to reuse these catalysts,
several groups had tried to immobilize these types of
ammonium salts on the polymer, but complex synthetic
process and instability of the polymer at high temperatures
limited their application.7–9
In 2005, Hara’s group found a new carbon-based solid sul-
fonic acid, which was prepared by incompletely carbonizing
glucose at high temperatures (over 300 °C) to form a carbon-
based material first, and then sulfonating it with a large
amount of concentrated sulfuric acid.10 Successive research
optimized this preparation method,11–16 including using aryl
sulfonic acid as the resource of sulfonic acid groups to avoid
harsh reaction conditions.17–19 This method is a convenient
and efficient way to immobilize the sulfonic acid groups on
the carbon-based material, and the recyclable catalyst showed
good activity for esterification of simple carboxylic acids (such
as acetic acid, oleic acid, etc.) and alcohols (such as methanol,
ethanol, etc.).20–24 Strong hydrophobic polycyclic aromatic
carbon sheets formed by incomplete carbonizing of organic
matter is the key issue, which can prevent the produced water
aSchool of Chemistry and Molecular Engineering, East China University of Science
and Technology, 130 Meilong Road, Shanghai 200237, P.R. China.
E-mail: xctao@ecust.edu.cn
bSuzhou Eleco Chemical Industry Co., Ltd., 608 Xiao Shu Road, Kunshan,
Jiangsu 215341, P.R. China
†Electronic supplementary information (ESI) available: Experimental details,
XRD pattern, SEM image, TGA pattern, FT-IR spectra, 13C MAS NMR spectrum,
1H NMR spectra, 13C NMR spectra. See DOI: 10.1039/c4gc01395f
This journal is © The Royal Society of Chemistry 2014
Green Chem.

View Article Online
Communication
Green Chemistry
from gaining access to the active site of the catalysts and thus
inhibiting the inactivation of the catalyst by water
(Scheme 1).24,25
Based on that, we assume using polycyclic aromatic carbon
sheets in amorphous carbon to replace the bulky diarylamine
and pentafluorophenyl groups as a “hydrophobic wall”, and
the less bulky diphenylaminium tosylate ([Ph2NH2]+[OTs]−) as
an active site, the new carbon-based solid acid should have
similar catalytic reactivity and selectivity to Ishihara’s
(Scheme 1). Moreover, the salt is embedded into the matrix of
the carbon-based material, so that it can be reused in catalytic
esterification reaction.
Fig. 1 XPS spectra of the GDTCSA.
Here, we report a novel carbon-based solid acid prepared by
introducing [Ph2NH2]+[OTs]− into the carbon-based material
during the process of one-step incomplete carbonization of
glucose and p-toluenesulfonic acid. This carbon-based solid
acid showed high activity and selectivity in the catalytic ester
condensation, and was recycled ten times without losing the
catalytic activity.
The carbon-based solid acid can be readily prepared by
heating a mixture of glucose, p-toluenesulfonic acid and
[Ph2NH2]+[OTs]− at 180 °C for 5 hours under a flow of nitrogen
(Scheme 2). After cooling down to room temperature, the reac-
tion product was washed with hot toluene to remove and
recover the unreacted raw materials, and then the glucose–
diphenylaminium tosylate-derived carbon solid acid (GDTCSA)
was obtained as a black powder.
Fig. 2 13C MAS NMR spectrum of the GDTCSA.
The X-ray diffraction (XRD) pattern of the sample GDTCSA
exhibits two diffraction peaks at 2θ angle of 20° and 45° (see
ESI†), which is typical of amorphous carbon consisting of dis-
ordered polycyclic aromatic carbon sheets26 with a flat struc-
ture. The absorption spectrum of Fourier transform infrared
spectroscopy (FT-IR) for the GDTCSA at 1040 cm−1, 1167 cm−1
carbon sheets with SO3H groups,29 [Ph2NH2]+ (see ref. 7) and
p-toluenesulfonate anions (TsO−).8 In addition, the GDTCSA
also contains phenolic OH (150 ppm) and COOH (180 ppm)
groups. These results show that the carbon-based material is a
polycyclic aromatic plane structure loaded with active Brønsted
acids of [Ph2NH2]+[OTs]− and SO3H groups.
and 1495 cm−1
,
1507 cm−1 confirms the existence of
Table 1 summarizes the structural parameters of the
GDTCSA, including the nominal composition, the acid
amount of [Ph2NH2]+[OTs]− and SO3H groups. The nominal
composition of the GDTCSA suggests that the sulfur com-
ponent is more than nitrogen, which indicates that sulfur not
only existed in the form of p-TsOH to form a salt with diphenyl-
amine, but there is also about 1/4 sulfur attached to the poly-
cyclic aromatic carbon sheets in the form of SO3H groups. The
amount of GDTCSA as a catalyst for the esterification reaction
is based on the acid amount of [Ph2NH2]+[OTs]− and SO3H
groups. GDTCSA was treated with dilute aqueous NaOH
(Scheme 3). The reactant was filtered, the filtered aqueous
[Ph2NH2]+[OTs]− (see ref. 7) and SO3H groups23 (see ESI†). The
X-ray photoelectron spectroscopy (XPS) spectra of the GDTCSA
reveal a single S 2p peak at 168 eV and a single N 1s peak at
401 eV (Fig. 1), which are attributable to sulfur in the SO3H
+ 28
groups27 and nitrogen in the diphenylammonium (Ph2NH2 )
respectively. The 13C magic angle spinning (MAS) nuclear mag-
netic resonance (NMR) spectrum of the GDTCSA is shown in
Fig. 2. The peak at 20 ppm is assigned to CH3 groups on the
polycyclic aromatic rings; 130 ppm is the signal peak of poly-
cyclic aromatic carbon atoms. There are three peaks at 139,
140 and 141 ppm, which are attributable to polycyclic aromatic
Table 1 Structural parameters of the GDTCSA and the GDCSA
Acid amountb
Catalysts
Compositiona
(mmol g−1
)
GDTCSA
GDCSA
CH0.89O0.2N0.03S0.04
CH0.88O0.17N0.03S0.01
2.43
0.61
a The nominal sample composition was determined by elemental
analysis. b The acid amount of [Ph2NH2]+[OTs]− and SO3H groups was
estimated by sulfur elemental analysis.
Scheme 2 Preparation of the GDTCSA.
Green Chem.
This journal is © The Royal Society of Chemistry 2014

View Article Online
Green Chemistry
Communication
Scheme 3 GDTCSA was reacted with dilute aqueous NaOH.
phase was concentrated and then recrystallized by EtOH to
give a white solid (32 wt%), which was confirmed as sodium
p-toluene sulfonate by 1H NMR analysis and melting point
measurement.30 For the black filter residue GDCSA (67 wt%),
the FT-IR absorption spectrum (see ESI†) and the component
(Table 1) show that TsO− was lost from GDTCSA, but diphenyl-
amine groups were still immobilized on the matrix of the
carbon-based material, and there were also small number of
SO3H groups connected with it.
Fig. 3 Esterification of 4-phenylbutyric acid with cyclododecanol cata-
lyzed by various catalysts [Ph2NH2]+[OTs]− (graph A), [Mes2NH2]+-
[O3SC6F5]− (graph B), GTCSA (graph C), and GDTCSA (graph D). The ratio
of cyclododecanol (blue line), cyclododecyl 4-phenylbutyrate (red line)
and cyclododecene (black line) in the reaction mixture over time was
evaluated by 1H NMR analysis. Catalytic activity: [Mes2NH2]+[O3SC6F5]−
≥ [Ph2NH2]+[OTs]− ≥ GDTCSA > GTCSA. Selectivity: GTCSA ≥ GDTCSA ≥
[Mes2NH2]+[O3SC6F5]− > [Ph2NH2]+[OTs]−.
These results illustrate that p-toluenesulfonic acid partici-
pated in the process of incompletely carbonized glucose and
provided the SO3H groups for the polycyclic aromatic carbon
sheets of
a
flat structure. Meanwhile, most of the
[Ph2NH2]+[OTs]− were introduced to the carbonaceous material
and the diphenylamine groups were embedded in the carbon
sheets to provide the NH2+ groups.
According to the Ishihara’s method,3,7 4-phenylbutyric acid
was condensed with an equimolar amount of cyclododecanol
in heating heptane using 5 mol% [Ph2NH2]+[OTs]−,8 dimesityl- immobilized with both NH2 and SO3H groups was more
ammonium pentafluorobenzenesulfonate ([Mes2NH2]+- active than GTCSA containing only SO3H groups in the cata-
[O3SC6F5]−),31 the glucose-TsOH-derived carbon solid acid lytic condensation reaction. The strong “hydrophobic effect” due
(GTCSA),17 and GDTCSA as catalysts respectively to examine to polycyclic aromatic carbon sheets of the carbon solid acid
+
1
their catalytic activities and selectivities in this reaction by H could effectively suppress the dehydrative elimination of sec-
NMR analysis (Fig. 3). First,
a homogeneous catalyst ondary alcohols to produce alkene by comparison between
[Ph2NH2]+[OTs]− was used, cyclododecyl 4-phenylbutyrate GDTCSA and the less bulky [Ph2NH2]+[OTs]−.
(graph A red line) and cyclododecene (graph A black line) were
To explore the generality and scope of the selective esterifi-
produced at 80 °C, and latter conversion was up to 15%, while cation catalyzed by GDTCSA (2 mol%) in heptane at 80 °C, the
the bulky homogeneous catalyst [Mes2NH2]+[O3SC6F5]− condensation was examined with an equimolar mixture of
showed higher catalytic activity (graph B red line) and selecti- various structurally diverse carboxylic acids and alcohols
vity (graph B black line) than [Ph2NH2]+[OTs]−; these results (Table 2). Straight-chain carboxylic acids and alcohols were
were similar to the Ishihara’s report.3,7 The dehydration rate easily condensed to produce the corresponding esters (entries
from cyclododecanol to cyclododecene decreased to 3% (graph 1–6). Sterically demanding pivalic acid and 3-cyclopentene-1-
C black line), but the esterification rate also decreased to 54% carboxylic acid were apt to be condensed to obtain the corres-
(graph C red line) even at heptane reflux (98 °C) with the het- ponding esters (entries 7–9). Benzoic acid and α,β-unsaturated
erogeneous catalyst GTCSA. When the novel carbon-based carboxylic acids were also transformed into the relevant esters
solid acid GDTCSA was used, the catalytic rate was slower (entries 10–12). Allylic alcohol and propargylic alcohol were
initially than the two homogeneous catalysts indicated above. similarly converted into the appropriate esters (entries 13 and
This might be due to physical diffusion barriers of the hetero- 14). In particular, GDTCSA could be used for acid-sensitive
geneous catalyst.32,33 As the reaction progressed, both external and sterically demanding alcohols such as cyclododecanol,
and internal diffusion limitations did not affect the overall cyclohexanol and menthol to give the desired esters in good
reaction rate,32 so the maximum conversion of the ester yields with high selectivity (entries 15–20). The citric acid and
increased to more than 95% (graph D red line) and the cyclo- glycerol could also be esterified completely with the corres-
dodecene was suppressed to less than 5% (graph D black line) ponding alcohol and carboxylic acid respectively (entries 21
at 80 °C. These experimental results showed that GDTCSA and 22).
This journal is © The Royal Society of Chemistry 2014
Green Chem.

View Article Online
Communication
Green Chemistry
Table 2 Esterification reaction between an equimolar mixture of carboxylic acids and alcohols catalyzed by GDTCSAa
Entry
R1CO2R2
Time (h)
Yieldb (%)
Entry
R1CO2R2
Time (h)
Yieldb (%)
1
2
PhCH2CO2C12H25
PhCH2CO2Bn
1
1
94
99
13
14
3
97
90
24
c
3
4
5
6
7
8
Ph(CH2)3CO2C6H13
Ph(CH2)3CO2C8H17
C11H23CO2C6H13
C17H33CO2C6H13
t-BuCO2C6H13
1
1
4
7
6
6
99
98
93
94
94
94
15
16
17
18
19
20
PhCH2CO2C12H23
10
10
7
11
8
97 (98)
95 (98)
97 (99)
91 (99)
92f (99)
94g (99)
c
e
Ph(CH2)3CO2C12H23
d
PhCH2CO2C6H11
C11H23CO2C6H11
PhCH2CO2C10H19
d
e
t-BuCO2C8H17
Ph(CH2)3CO2C10H19
10
9
5
96
21
24
18
95
10
PhCO2C6H13
24
93
22
93
11
12
24
24
95
92
a Unless otherwise noted, a solution of carboxylic acid (2 mmol) and alcohol (2 mmol) in heptane (4 mL) was heated at 80 °C in the presence of
GDTCSA (2 mol%). b Isolated yield of ester. Selectivity in parentheses. c Cyclododecanol (C12H23OH) was used. d Cyclohexanol (C6H11OH) was
used. e (−)-Menthol (C10H19OH) was used. f [a]2D5 −65.8° (c 1.38, CH2Cl2). g [a]D25 −59.2° (c 1.38, CH2Cl2).
Table 3 The cycling experiment of catalytic activitya
without loss of activity, which indicated that the novel material
holds great potential for the green chemical processes.
Experimental section
Run
1
2
3
4
5
6
7
8
9
10
97
Conv.(%)
99
99
99
98
98
98
98
98
97
In a typical synthesis, 3.6 g glucose (20.0 mmol) and 1.9 g
p-toluenesulfonic acid monohydrate (10.0 mmol) were
mixed in toluene, then 3.41 g diphenylammonium tosylate8
(10.0 mmol) prepared in advance was added to the mixture,
under a flow of nitrogen. The water formed during the reaction
and the toluene were distilled off while heating to 180 °C
slowly, after reacting for 5 hours. The product was washed with
hot toluene for 5 × 25 mL (toluene and 1.3 g p-toluenesulfonic
acid were recovered) to obtain a black powder GDTCSA (5.7 g).
The nominal sample composition was determined by elemen-
tal analysis to be CH0.89O0.2N0.03S0.04, and the acid amount of
SO3H groups and [Ph2NH2]+[OTs]− was 2.43 mmol g−1(see
Scheme 2).
a The conversion of hexanyl 4-phenylbutyrate based on hexanol over
time was evaluated by 1H NMR analysis.
The reusability of the carbonaceous material GDTCSA was
measured. After the reaction, the ‘used’ catalyst was recovered
by centrifugation and reused. It was confirmed that the activity
and selectivity remained unchanged, even after the GDTCSA
had been recycled ten times (Table 3).
Conclusions
The reaction mixture, carboxylic acid (2.0 mmol), alcohol
Using polycyclic aromatic carbon sheets formed by incomple-
tely carbonized glucose as a “hydrophobic wall”, along with
simple and inexpensive diphenylaminium tosylate as an active
+
(2.0 mmol), 2 mol% of GDTCSA (2.43 mmol NH2 and SO3H
g−1; 16 mg, 0.04 mmol), and heptane (4 mL), was stirred at
80 °C. Then separation of GDTCSA by filtration and evapor-
ation of heptane in vacuo gave the crude material, which was
purified by column chromatography to give the desired carb-
oxylic ester as colorless oil.
+
site, the novel carbon-based material functionalized with NH2
and SO3H groups has been achieved with one step synthesis by
heating the mixture of D-glucose, p-toluenesulfonic acid and
diphenylammonium tosylate together. And its structure has
been illustrated by a series of tests such as XRD, FT-IR, XPS,
13C MAS NMR and EA. It not only could be used to catalyze the
ester condensation reaction of carboxylic acids with equimolar
amounts of sterically demanding and acid-sensitive alcohols
with high reactivity and selectivity under mild conditions, but
also could be easily recovered and reused more than ten times
Notes and references
1 A. Sakakura, Y. Koshikari and K. Ishihara, Tetrahedron Lett.,
2008, 49, 5017–5020.
2 K. Ishihara, Tetrahedron, 2009, 65, 1085–1109.
Green Chem.
This journal is © The Royal Society of Chemistry 2014

View Article Online
Green Chemistry
Communication
3 K. Ishihara, S. Nakagawa and A. Sakakura, J. Am. Chem. 18 W. L. Zhang, H. X. Tao, B. H. Zhang, J. W. Ren, G. Z. Lu
Soc., 2005, 127, 4168–4169. and Y. Q. Wang, Carbon, 2011, 49, 1811–1820.
4 K. Wakasugi, T. Misaki, K. Yamada and Y. Tanabe, Tetra- 19 Q. B. Fu, B. Gao, H. Dou, L. Hao, X. J. Lu, K. Sun, J. C. Jiang
hedron Lett., 2000, 41, 5249–5252. and X. G. Zhang, Synth. Met., 2011, 161, 373–378.
5 A. Sakakura, H. Watanabe, S. Nakagawa and K. Ishihara, 20 L. Geng, Y. Wang, G. Yu and Y. X. Zhu, Catal. Commun.,
Chem. – Asian J., 2007, 2, 477–483. 2011, 13, 26–30.
6 A. Sakakura, S. Nakagawa and K. Ishihara, Nat. Protoc., 21 S. Suganuma, K. Nakajima, M. Kitano, D. Yamaguchi,
2007, 2, 1746–1751.
7 A. Sakakura, S. Nakagawa and K. Ishihara, Tetrahedron,
2006, 62, 422–433.
8 H. L. Ngo, N. A. Zafiropoulos, T. A. Foglia, E. T. Samulski
and W. B. Lin, Energy Fuels, 2008, 22, 626–634.
9 N. A. Zafiropoulos, H. L. Ngo, T. A. Foglia, E. T. Samulskia
and W. Lin, Chem. Commun., 2007, 3670–3672.
H. Kato, S. Hayashi and M. Hara, J. Am. Chem. Soc., 2008,
130, 12787–12793.
22 X. Z. Liang, M. F. Zeng and C. Z. Qi, Carbon, 2010, 48,
1844–1848.
23 B. V. S. K. Rao, K. C. Mouli, N. Rambabu, A. K. Dalai and
R. B. N. Prasad, Catal. Commun., 2011, 14, 20–26.
24 K. Nakajima and M. Hara, ACS Catal., 2012, 2, 1296–1304.
10 M. Toda, A. Takagaki, M. Okamura, J. N. Kondo, S. Hayashi, 25 M. Okamura, A. Takagaki, M. Toda, J. N. Kondo,
K. Domen and M. Hara, Nature, 2005, 438, 178–178.
11 M. Hara, T. Yoshida, A. Takagaki, T. Takata, J. N. Kondo,
K. Domen, T. Tatsumi, M. Hara and S. Hayashi, Chem.
Mater., 2006, 18, 3039–3045.
S. Hayashi and K. Domen, Angew. Chem., Int. Ed., 2004, 43, 26 N. Tsubouchi, C. B. Xu and Y. Ohtsuka, Energy Fuels, 2003,
2955–2958. 17, 1119–1125.
12 K. Fukuhara, K. Nakajima, M. Kitano, H. Kato, S. Hayashi 27 S. Suganuma, K. Nakajima, M. Kitano, D. Yamaguchi,
and M. Hara, ChemSusChem, 2011, 4, 778–784.
13 S. Suganuma, K. Nakajima, M. Kitano, H. Kato, A. Tamura,
H. Kato, S. Hayashi and M. Hara, Solid State Sci., 2010, 12,
1029–1034.
H. Kondo, S. Yanagawa, S. Hayashi and M. Hara, Micro- 28 M. G. Han, S. K. Cho, S. G. OH and S. S. Im, Synth. Met.,
porous Mesoporous Mater., 2011, 143, 443–450. 2002, 126, 53–60.
14 S. Suganuma, K. Nakajima, M. Kitano, S. Hayashi and 29 X. Zhang and D. H. Solomon, Chem. Mater., 1999, 11,
M. Hara, ChemSusChem, 2012, 5, 1841–1846. 384–391.
15 K. Nakajima, M. Okamura, J. N. Kondo, K. Domen, 30 I. Katash, X. L. Luo and C. N. Sukenik, Langmuir, 2008, 24,
T. Tatsumi, S. Hayashi and M. Hara, Chem. Mater., 2009,
21, 186–193.
16 M. Kitano, K. Arai, A. Kodama, T. Kousaka, K. Nakajima,
S. Hayashi and M. Hara, Catal. Lett., 2009, 131, 242–
249.
10910–10919.
31 Ishihara’s catalyst was purchased from TCI (Shanghai)
Development Co., Ltd, and the synthetic method is pro-
vided in ref. 6.
32 S. H. Ali, A. Tarakmah, S. Q. Merchant and T. A. Sahhaf,
Chem. Eng. Sci., 2007, 62, 3197–3217.
17 B. H. Zhang, J. W. Ren, X. H. Liu, Y. Guo, Y. L. Guo,
G. Z. Lu and Y. Q. Wang, Catal. Commun., 2010, 11, 33 M. J. Lee, H. T. Wu and H. M. Lin, Ind. Eng. Chem. Res.,
629–632.
2000, 39, 4094–4099.
This journal is © The Royal Society of Chemistry 2014
Green Chem.