Mesoporous carbon as an efficient catalyst for alcoholysis and aminolysis of epoxides

Article abstract of DOI:10.1016/j.apcata.2012.06.036

The ring opening reaction of epoxides by alcohols and amines using mesoporous activated carbon as efficient and environmentally friendly heterogeneous catalyst is reported. Carbon xerogels were synthesized by polymerization of resorcinol and formaldehyde. The surface of the activated carbon was oxidized in liquid phase with HNO₃ and then functionalized with H₂SO₄. Chemical and textural characterization by elemental analysis, pH_PZC, TPD, BET and XPS indicates that oxidation in liquid phase is effective in the introduction of strong acid groups in the carbon surface. The functionalization with H₂SO₄ led to more acid functional groups, as expected. The activated carbons were tested in alcoholysis and aminolysis of epoxides, having been obtained excellent results of conversion and selectivity, both over 95%.

Full text of DOI:10.1016/j.apcata.2012.06.036

Applied Catalysis A: General 439–440 (2012) 24–30
Contents lists available at SciVerse ScienceDirect
Applied Catalysis A: General
journal homepage: www.elsevier.com/locate/apcata
Mesoporous carbon as an efficient catalyst for alcoholysis and aminolysis of
epoxides
a,∗
a
b
c
Inês Matos , Paulo Duarte Neves , José Eduardo Castanheiro , Elena Perez-Mayoral ,
c
d
a
e
a,∗
Rosa Martin-Aranda , Carlos Duran-Valle , Joaquim Vital , Ana M. Botelho do Rego , Isabel M. Fonseca
a
REQUIMTE/CQFB, Faculdade de Ciências e Tecnologia, Universidade Nova de, Lisboa, 2829-516 Caparica, Portugal
Centro de Química de Évora, Departamento de Química, Universidade de Évora, 7000-671 Évora, Portugal
Departamento de Química Inorgánica y Química Técnica, Facultad de Ciencias, UNED, Paseo Senda del Rey 9, 28040 Madrid, Spain
Departamento de Química Orgânica e Inorgánica, Universidad de Extremadura, Avda de Elvas, s/n, E-06006 Badajoz, Spain
b
c
d
e
CQFM and IN, Technical University of Lisbon, IST, Av. Rovisco Pais, 1049-001 Lisboa, Portugal
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 2 March 2012
Received in revised form 28 May 2012
Accepted 21 June 2012
Available online 30 June 2012
The ring opening reaction of epoxides by alcohols and amines using mesoporous activated carbon as effi-
cient and environmentally friendly heterogeneous catalyst is reported. Carbon xerogels were synthesized
by polymerization of resorcinol and formaldehyde. The surface of the activated carbon was oxidized in
liquid phase with HNO3 and then functionalized with H2SO4.
Chemical and textural characterization by elemental analysis, pHPZC, TPD, BET and XPS indicates that
oxidation in liquid phase is effective in the introduction of strong acid groups in the carbon surface. The
functionalization with H2SO4 led to more acid functional groups, as expected. The activated carbons were
tested in alcoholysis and aminolysis of epoxides, having been obtained excellent results of conversion
and selectivity, both over 95%.
Keywords:
Ring opening
Mesoporous carbon
Alcoholysis of epoxides
Aminolysis of epoxides
© 2012 Elsevier B.V. All rights reserved.
1
. Introduction
For the sustainability of our ever evolving modern world it is
for the pharmaceutical industry for their role as treatment agents
of several human disorders [4–6].
Among the possible synthetic approaches yielding these prod-
ucts, the ring opening reaction appears as a very attractive method
due to its simplicity leading to the corresponding ␤-substituted
alcohols in high yields.
necessary to keep looking for new and diverse ways to optimize the
available resources. In this sense the development of new and less
expensive heterogeneous catalysts and their application in reac-
tions with synthetic interest such as the ring opening of epoxides
is an important challenge with industrial repercussions.
Epoxides are versatile and valuable intermediates in organic
synthesis. These oxygen heterocycles are significantly more reac-
tive than other ethers due to the strain induced by the presence
of the three-membered ring; thus, epoxides undergo ring-opening
reactions with alcohols to give ␤-alkoxy alcohols [1,2], which may
result in valuable organic solvents or be used as a synthetic route
for the synthesis of relevant compounds such as antitumorals or
immunosuppressives [3].
Suitable epoxide ring opening catalysts include Lewis acids and
bases, Brönsted acids, porphyrin complexes [1], triflates [7] and
perchlorates [8] in homogeneous phase. Heterogeneous catalysts
have also been reported among them polymer supported ferric
chloride [9], aluminumdodecatungstophosphate [10] and AlKIT-5
[11].
Other methods used include electrochemical reaction with tri-
organylborane [12] and microwave assisted synthesis [13–15].
All these catalysts used in the alcoholysis or aminolysis of epox-
ides show some disadvantages such as high reaction temperature,
prolonged reaction time, non-catalytic nature of the reagent, low
conversion and low regioselectivity. Furthermore, some of them
may become explosive, are expensive, need special conditions for
their preparation and, in homogenous phase, have some problems
for the separation, isolation and purification of the product. Thus,
the development of new catalytic methods for the reaction under
study is highly desirable.
It is also possible to synthesize amino alcohols by the amina-
tion of epoxides, where the cleavage of the C O bond occurs in the
presence of an amine. ␤-Amino alcohols are of growing importance
∗ Corresponding authors. Tel.: +351 212948385; fax: +351 212948385.
E-mail addresses: ines.matos@fct.unl.pt (I. Matos), blo@fct.unl.pt (I.M. Fonseca).
0
926-860X/$ – see front matter © 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.apcata.2012.06.036

I. Matos et al. / Applied Catalysis A: General 439–440 (2012) 24–30
25
In recent years, heterogeneous catalysts [16,17] and among
them activated carbon [18,19], have attracted much attention as
catalysts for various organic transformations as well as process
related to fine-chemical synthesis in the scope of green chemistry.
Activated carbons with microporous structure have been
employed successfully in several catalytic reactions [20–24].
However, mesoporous carbon has the advantage of presenting
meso and macro porous [25] which may result in more efficient
selectivity toward products.
Otherwise, carbon gels are inexpensive materials and have
relatively simple synthesis, so these porous materials are impor-
tant heterogeneous catalysts that display very interesting features
about their structural characteristics because they are very sen-
sitive to the conditions used during gel synthesis and processing
isotherms by Barrett–Joyner–Halenda (BJH) method. The meso-
porous volume was obtained by DFT method using a micromeritics
software DataMaster version 4. Microporous volume and meso-
porous surface area were determined by the t-method, using a
standard isotherm proposed by Greeg and Sing [30].
Temperature-programmed desorption analyses (TPD-MS) were
carried out using a Micromeritics TPD/TPR 2900 instrument, with
the evolution of CO (m/z 28) and CO2 (m/z 44) being monitored
by mass spectrometry using a Fisons MD800 (Leicestershire, UK)
instrument. Prior to analysis, the sample (ca. 50 mg) was placed
in a fixed bed U-shaped quartz tubular micro-reactor and dried at
383 K in flowing He, overnight. The temperature was then increased
3
at a rate of 10 K/min to 1273 K, under a flow of helium (25 cm /min,
0.1 MPa).
[
26,27].
Even though carbon gels are obtained through different
Chemical composition. Elemental analysis of the carbons was car-
ried out in a CHNS Analyser (Thermofinnigan Flash, EA, 1112 series).
Oxygen content was obtained by the difference between the total
percentage (100 wt%) and the sum of percentages (wt%) of nitrogen,
carbon, hydrogen and sulfur.
Carbon acidity. The pH at the point of zero charge (pHPZC) was
determined by reverse mass titration, following the method pro-
posed by Noh and Schwarz [31].
XPS measurements. The XPS instrument used was an XSAM800
(Kratos) X-ray spectrometer operated in the fixed analyzer
transmission mode, with a pass energy of 20 eV, and the non
monochromated Mg K␣ X-radiation (hꢀ = 1253.7 eV). Power was
130 W (13 V × 10 mA). Details about data acquisition and treatment
can be found elsewhere [32]. For quantitative purposes, the follow-
ing sensitivity factors, provided by Kratos, were used: C 1s: 0.25; O
procedures, the preparation has to account for 3 phases: gel syn-
thesis, with the formation of a three-dimensional polymer in
a solvent; gel drying, for removing the solvent; and pyrolysis
under an inert atmosphere to form the porous carbon material.
Resorcinol–formaldehyde (RF) aqueous gels are among the most
studied systems [28]. Several thermal and chemical processes can
be used to tailor the porous structure and the type and concentra-
tion of specific oxygen surface groups.
In this context we report here the ring opening reaction of epox-
ides by alcohols and amines using mesoporous activated carbon
functionalizated with sulfonic acids as efficient and environmen-
tally friendly heterogeneous catalyst.
1
s: 0.66.
2
. Experimental
2.1. Preparation of the catalysts
2.3. Catalytic experiments
All reagents and solvents used in the preparation of RF aque-
ous gels and surface functionalization of the carbon xerogels were
purchase from Aldrich and used as received.
The catalysts samples were prepared according Lin and Rit-
ter [29] by sol–gel technique. In more detail, solution containing
% (w/v) solids was prepared, in which the R/F mole ratio was
The catalytic experiments were carried out in a stirred batch
reactor with reflux, at different temperatures. In a typical exper-
iment, the reactor was loaded with 3 cm3 of alcohol, 1.5 mmol of
styrene oxide and 0.1 g of catalyst.
Particle sizes of the catalysts were maintained between 25
and 20 mesh, since preliminary tests with smaller particle sizes
revealed no change in conversion. Stirring rate was kept at high
values (>1000 rpm) to minimize external mass transfer limitations.
Samples were taken periodically and analyzed by GC, using a
KONIC HRGC-3000C instrument equipped with a 30 m × 0.25 mm
DB-1 column.
5
fixed at 1:2 and the R/C (resorcinol/sodium carbonate) mole ratio
was fixed at 50:1. The initial pH of the solution was adjusted
to 6.10–6.20 with diluted HNO . After curing for one week in
3
◦
an oven at 85 C the washed gel was dried under N atmo-
sphere using a heating rate of 0.5 C/min until 65 C and then
held there for 5 h. Subsequently, it was heated to 110 C and
2
◦
◦
◦
then held there for another 5 h. Finally, the carbon xerogel was
3
. Results and discussion
◦
formed by pyrolysis of the dried gel at 800 C for 3 h in a N atmo-
2
◦
sphere with both heating and cooling rates set at 0.5 C/min (CM).
3.1. Catalyst characterization
The carbon xerogel (CM) was refluxed with a nitric acid solu-
3
tion (13 M) for 6 h (1 g/20 cm ) then washed with deionized water
Table
1
shows the textural characterization of the car-
nitrogen
◦
in soxhlet until pH 7 and then dried in oven at 110 C (carbon
bon samples. The synthesized carbons present
a
CMN).
adsorption–desorption isotherm type IV (according to IUPAC
nomenclature) with a type H3 hysteresis loop typical of materi-
als with mesoporosity. However they can also be considered as a
combination of type I and type IV isotherms [26,33].
The two catalysts were prepared in consecutive batches, starting
from the same initial carbon followed by the treatment with nitric
acid and then sulfuric acid.
◦
The oxidized carbon (CMN) was heated at 150 C with con-
centrated sulfuric acid solution (1 g Carbon/20 cm sulfuric acid
3
solution) for 13 h under N2 atmosphere, washed with deionized
◦
water in soxhlet until pH 7 and then dried in oven at 110 C (carbon
CMNS).
2
.2. Characterization of the catalyst
The textural properties of the different samples were not modi-
fied significantly by the two treatments. The oxidation of the carbon
with nitric acid had no meaningful effect on the BET area, but some
decrease of the mesoporous volume is observed. This may be due
to the presence of functional groups in the entrance of the pores
blocking the accessibility. In any case Fig. 1 shows that the oxi-
dation step does not change the size of the mesoporous [34]. The
N2 adsorption. Textural characterization was performed by
N2 adsorption at 77 K on an ASAP 2010 V1.01 B Micromerit-
ics. The specific surface area was calculated using the
Brunauer–Emmett–Teller (BET) method. The pore size distri-
butions were obtained from desorption branch of the nitrogen

2
6
I. Matos et al. / Applied Catalysis A: General 439–440 (2012) 24–30
Table 1
Textural properties.
−1
Vmicro (cm3
t method
−1
Vmeso (cm3
−1
Vmacro (cm3
−1
VT (cm3
Gurvitsh
−1
)
Catalyst
SBET (m2
BET
g
)
g
)
g
)
g
)
g
Dp (Å)
BJH method
DFT Method
Vtotal − Vmicro − Vmeso
CM
CMN
CMNS
771
760
797
0.18
0.19
0.20
0.5
0.32
0.51
0.08
0.08
0.08
0.76
0.59
0.79
65.4
51.6
74.5
0
,02
The TPD analysis of the samples is presented in Fig. 3. From
the deconvolution of TPD curves presented in Fig. 3a and b into
the various contributions from the different surface groups fol-
lowing the method presented in previous reports [37,38], it is
possible to obtain the summarized conclusions (Fig. 3c). The results
obtained with TPD are in quite accordance with the XPS and AE
analysis. There is a great difference in the chemical surface char-
acteristics between the original carbon and the modified ones. A
pronounced increase in the functional group content of the samples
after oxidation with HNO3 was observed. Phenols and carboxylic
groups are the most abundant species in the surface of the oxi-
dized carbons and are responsible for the acidity of the sample [39].
However the carbon functionalized with sulfonic groups (CMNS)
exhibits smaller amount of carboxylic acids which confirms that
the increase in acidity is due to the presence of sulfonic anchored
groups. The decomposition of the sulfonic groups was detected as
SO2 (m/z 64) above 530 K.
CM
0
0
,015
CMN
CMNS
0
,01
,005
0
2
0
200
Pore Width (Å)
Fig. 1. Pore size distribution by BJH method desorption branch.
posterior treatment with concentrated sulfuric acid may have
caused the formation of new pores and the widening of existing
pores which explains the difference in the pore size distribution
obtained for catalyst CMNS.
The surface chemistry was characterized by TPD-MS, elemental
analysis, XPS and pHPZC. The results summarized in Table 2 show
that there is an increase of the total amount of oxygen in the sam-
ple treated with the HNO3 meaning that the surface oxidation was
successful. When treated with sulfuric acid the value of pHPZC of the
resulting catalyst is smaller indicating an increase in acidity. This
effect is probably not due to the increase of oxygen but to the pres-
ence of sulfonic groups at the surface which were detected using
XPS (BE = 168.5 eV).
The O/C ratio detected by XPS is just slightly smaller than the
value obtained by elemental analysis. This means that it was pos-
sible to obtain material presenting a homogeneous distribution of
the oxygen groups throughout the carbon, although some oxygen
may be located inside the pores and was not accessible for detec-
tion by XPS. After peak fitting of the XPS C 1s peak, it was possible
to establish the presence of different carbon containing groups,
Fig. 2. The major contribution is from the peak at binding energy
3
3
.2. Catalytic study
.2.1. Alcoholysis of epoxides
Mesoporous carbons CMN and CMNS were tested as catalysts
in the ring opening reaction of epoxides. The effect of different
reaction conditions on conversion and selectivity was evaluated. In
general, when epoxides react with an alcohol, two different reac-
tion products can be obtained (Scheme 1). Traditionally these are
considered to be SN2 type reactions, where the alcohol attacks the
most substituted carbon in the case of the split of the epoxide cat-
alyzed by acid or attacks the less substituted carbon in the case of
the split catalyzed by base, resulting in two different products.
In order to compare our results with those reported in the liter-
ature it was carried out an experiment at room temperature using
styrene oxide and ethanol. For both catalysts, CMN and CMNS, high
conversions and good selectivity are observed, being 2-ethoxy-
2
3
-phenylethanol (1b) the major product. For catalyst CMNS only
0 min of reaction time at room temperature attained almost 100%
conversion, selectivity to 1b being 97%. Duran-Valle et al. [40]
reported that for microporous carbon treated with a sulfonitric acid
mixture, the total conversion for the compound 1b was obtained
only after 1 h of reaction time. These results reflect the catalytic
enhancement due to the changes in the textural characteristics of
the catalyst such as pore size, suggesting that they play an impor-
tant role on promoting the accessibility to the active centers of the
catalyst. On the other hand the value of selectivity remained very
high meaning that it was possible to favor conversion with no lost in
selectivity. It is important to note that the mesoporous carbon with
no surface oxidation treatment revealed no activity in this reaction.
When comparing the two catalysts developed, although both of
them are active in the ring opening reaction, the functionalized car-
bon with sulfonic groups, CMNS, presents higher reactivity. While
2
84.8 eV which can be assigned to a mixture of C C bonds of the
∼
graphite-like structure of the carbon (BE = 284.3 eV) [35], and the
C and C H groups involving sp3 carbon atoms (BE = 285.0 eV)
∼
C
[
36]. The other 4 peaks can be assigned to different oxygen con-
taining functional groups present in the surface of the catalysts.
The peak centered at 286.6 ± 0.2 eV, has the second largest contri-
bution and is attributed to the C O bond in alcohols and/or ethers.
The other components can be associated to C O and/or O
C O at
2
88.4 ± 0.2 eV to more oxidize species such as OC O in carboxylic
acids and/or esters and, finally, at 291.9 ± 0.2 eV, the ␲ → ␲* exci-
tation associated to the graphitic carbon.
Table 2
◦
the reaction between styrene oxide and butanol at 80 C catalyzed
Surface chemistry characterization.
by CMN presents 99% of conversion and 83% of selectivity to com-
pound 1b during 180 min of reaction time, when using CMNS the
corresponding product was isolated with analogous conversion and
selectivity in only 15 min (Table 3). These results seem to indicate a
direct influence of the active sites present in the catalyst. According
to TPD results, the main difference in the oxidized groups between
Sample
O/C
O/C
Total oxygen
EA (at.%)
pHPZC
XPS (atomic ratio)
EA (atomic ratio)
CM
CMN
CMNS
0.06
0.20
0.19
0.075
0.25
0.29
6.3
16.0
20.2
9.7
3.2
2.4

I. Matos et al. / Applied Catalysis A: General 439–440 (2012) 24–30
27
8
6
4
2
000
000
000
000
0
8000
CMN (C)
CMNS (C)
6000
4000
2000
0
2
95
290
285
280
295
290
285
280
B.E. [eV]
B.E. [eV]
Fig. 2. XPS spectrum of the samples CMN and CMNS displaying the C 1s peak after peak fitting (BE = 284.8 ± 0.2 eV, BE = 286.6 ± 0.2 eV, BE = 288.4 ± 0.2 eV, BE = 290.0 ± 0.2 eV
and BE = 291.9 ± 0.2 eV).
0
0
0
0
.3
.2
.1
.0
0.3
0.2
0.1
0.0
CM
CMN
CMNS
CM
CMN
CMNS
a)
b)
4
00
600
800
1000
1200
400
600
800
1000
1200
T [K]
T [K]
CM
c)
CMN
CMNS
Free
Carboxylic
Acid
Lactone Phenol Carboxilic Carbonyl,
Anhydride Quinone
and Ether
Fig. 3. TPD study of the 3 mesoporous carbon. (a) CO TPD spectra of CM, CMN and CMNS; (b) CO2 TPD spectra of CM, CMN and CMNS; (c) amount of oxygen containing
surface groups determined by integration of the TPD deconvoluted curves.
Scheme 1. Reaction of epoxides with alcohols.

2
8
I. Matos et al. / Applied Catalysis A: General 439–440 (2012) 24–30
Table 3
Ring opening of substituted epoxide with different alcohols. Effect of the alcohol chain.
◦
Epoxide
Alcohol
T ( C)
Time (min)
Conversion (%)
Selectivity to b (%)
O
O
O
O
r.t.
50
30
15
5
99
99
99
97
96
94
EtOH
80
r.t.
50
60
30
15
99
99
99
97
99
91
1
1
-PrOH
-BuOH
80
r.t.
50
60
30
15
99
99
97
92
95
84
80
i-PrOH
50
30/60
70/97
95/84
O
r.t.
50
24 h
180
45
78
99
94
100
100
83
Ciclohexanol
80
r.t.
80
120
30
89
99
100
100
EtOH
EtOH
O
O
r.t.
80
24 h
4 h
38
97
57
52
CH
3
Conditions: catalyst CMNS 0.1 g, 3 ml of alcohol, and 1.5 mmol of epoxide.
CMN and CMNS, apart from the presence of sulfonic groups, is the
amount of carboxylic groups. The carbon modified with sulfonic
groups presents a lower value of carboxylic groups then CMN and
all the other functional groups are present in a comparable value.
As so, a decrease in activity should be expected, but on the contrary,
the observed increase in activity must be due to the new sulfonic
groups (strong acids) introduced in the structure, even if present in
only small amount.
an increase of the temperature reaction generally reduced the time
necessary to achieve the same conversion values, but a negative
effect on the selectivity was observed. This effect can be explained
considering a SN2 borderline mechanism for the ring opening reac-
tion as shown in Scheme 2. First step consisting of the protonation
of oxygen atom of the epoxide leading to the intermediate specie
(I); nucleophilic attack on (I) occurs through the best carbon accom-
modating the positive charge, in this particular case the carbon
supporting the phenyl group, promoting the ring opening of the
epoxide giving compounds 1b–5b at lowest temperatures. Delo-
calization of positive charge on the aromatic group, Ph, supposes
the additional stabilization of the intermediate specie. However, at
In order to study the influence of the alcohol hydrocarbon chain
in the ring opening reaction different alcohols were tested. Table 3
shows the results obtained for linear or branch alcohols at differ-
ent temperatures using CMNS as the most efficient catalyst for this
transformation. Then, the three linear alcohols lead to quantita-
tive conversions, selectivity to compounds 1b–3b being in a range
of 84–99%. Comparing the results obtained at the same tempera-
ture, as the alkyl group of the alcohol becomes bulkier, the time
of reaction increases probably because of the lower diffusion rate
of the corresponding reagents and products. This reactive behavior
is much more pronounced when starting from branched alcohols
such as i-propanol or cyclohexanol. Thus, the reaction of styrene
◦
the highest temperature, 80 C, it is possible the formation of the
compounds a due to additional energetic requirements (Scheme 2).
Thus, optimum reaction conditions may represent a compromise
between reaction time, selectivity and temperature, so that the
desired products b can be obtained in as mild conditions as
possible.
◦
oxide and i-propanol at 50 C affords the corresponding alkoxy
alcohol 4b in 70% of conversion and high selectivity (95%) after
3
0 min of reaction time. Remarkably an increment of the reaction
time, additionally 30 min, produces an increase of conversion, as
expected, but also decreases the selectivity. Due to the six member
ring present in the cyclohexyl alcohol, this substrate exhibits the
lowest reactivity; in all studied cases at different temperatures, it
was necessary the use of longer reaction times to give conversions
higher than 78% and also high selectivities. It suggests that alcohols
with larger molecular sizes exhibit higher steric hindrance to access
to the active sites present in the porous structure of the carbon.
Nevertheless, there were no significant changes in the selectivity
between all 5 alcohols.
The effect of temperature on the conversion and selectivity for
the reaction under study was also evaluated. For the same alcohol,
Scheme 2. SN2 mechanism on ring opening reaction of styrene oxide.

I. Matos et al. / Applied Catalysis A: General 439–440 (2012) 24–30
29
Table 4
Effect of catalyst amount in the reaction of styrene oxide and n-butanol.
Table 5
Aminolysis of epoxides. Ring opening of styrene oxide with aniline.
◦
Entry
Amount of catalyst (mg)
Conversion (%)
Selectivity to 3b (%)
Catalyst
CMN
T ( C)
Time (h)
Conversion (%)
1
2
3
25
50
100
4
6
97
74
74
84
r.t.
80
24
24
49
91
r.t.
80
24
24
46
96
◦
CMNS
Conditions: catalyst CMNS in the reaction of styrene oxide with n-BuOH at 80 C,
during 15 min.
Conditions: catalyst 0.1 g, 3 ml of ciclohexane, 1.5 mmol of epoxide, and 1.5 mmol
of aniline.
In order to widen the scope of the study, the ring opening
reactions of other two epoxides with ethanol were evaluated.
For cyclohexene oxide the reaction proceeds with high conver-
sion and rather small reaction times even at room temperature
affording compound 6b with total selectivity. However, when
1
,2-epoxihexane was used, the reaction requires higher reaction
temperature and the selectivity drops drastically.
As mentioned above, in both cases the lower reactivity observed
for both epoxides, cyclohexene oxide and 1,2-epoxihexane, is prob-
ably due to the diffusion problem of the reagents and products.
The lowest selectivity to product 7b in the case of using 1,2-
epoxihexane, it is probably related with small differences of the
activation barrier for both pathways. Thus, substitution over the
three member ring is an important limiting factor influencing both
the conversion and selectivity to products for the reaction. In this
sense, while Ph group stabilizes the intermediate specie (I) afford-
ing preferentially compounds 1b–5b regardless the alcohol used,
the substitution by a alkyl chain affects the conversion and selectiv-
ity of the reaction leading to mixtures of compound 7a and 7b and
therefore observing a decrease of the selectivity (approximately
Scheme 3. Reaction of styrene oxide with aniline.
carbon surface even after 3 consecutive runs, indicating that no sig-
nificant leaching of the sulfonic groups is observed. TPD studies of
the catalyst sample CMNS confirmed this result, since it was possi-
ble to detect sulfonic groups in the sample. On the other hand, TPD
of both catalysts samples after reaction showed a decrease in the
amount of carboxylic groups.
Concerning the textural properties, the samples analyzed after
reaction revealed a slight increase of the average pore size diameter
91 A˚ ) and a reduction of the microporosity probably due to some
(
blockage of the microporous.
A different approach is to consider the regeneration of the car-
bon catalyst. When the carbon CMN recovered from the reaction
was re-oxidized with nitric acid, the catalyst regained its initial
activity and selectivity. Although it seems not profitable to reuse
the catalyst directly from the reaction media, the oxidation of the
used catalyst proved to be an efficient method for reusability.
5
0%).
The optimum catalyst amount was studied in the reaction of
styrene oxide with n-BuOH, using different amounts of catalyst,
◦
CMNS, at 80 C (Table 4). The 3 different amounts of catalyst used
did not modify notably the selectivity but have a significant impact
on the conversion. Using 25 or 50 mg (entries 1 and 2) results were
in very low yields, however an increase for 100 mg shows a total
conversion of 99% with the highest selectivity to compound 3b. In
view of these results, the amount of catalyst used in this study was
fixed at 100 mg.
3
.2.2. Aminolysis of epoxides
The ring opening of styrene oxide with aromatic amines was also
studied in the presence of both catalysts, CMN and CMNS. The reac-
tion was carried out in ciclohexane at two different temperatures,
According to the mechanism presented in Scheme 2 it is nec-
essary to occur the adsorption of styrene oxide on the active sites,
similarly to an Eley–Rideal mechanism. Due to the hydrophilicity of
the catalyst surface, the alcohol in excess adsorbs on the active sites
and will act as a weak acid. This may explain the lower values of
conversion observed with lower amounts of catalyst. When the cat-
alyst loading increases, there are more active sites available and the
styrene oxide adsorption is favored leading to higher conversion.
Considering that one of the most important features of hetero-
geneous catalyst is easy recover and possible reutilization, it is very
important to assess this characteristics. Reutilization studies were
performed with both catalysts where CMNS and CMN stability and
reusability were evaluated. For this purpose, 3 different catalytic
runs were carried out reacting ethanol and styrene oxide at room
temperature, using the same catalyst sample. A drop in conversion
was observed, and both catalysts lost 60% of its activity probably
because of the esterification reaction of the acidic groups over the
catalyst with ethanol. In the second and third consecutive runs the
activity presented by catalyst CMNS remained higher than the one
for catalyst CMN, indicating that probably the most affected groups
by deactivation are the carboxylic groups present in both catalysts
as mentioned earlier in the TPD analysis.
◦
room temperature and 80 C (Table 5; Scheme 3).
For all these reactions only one product was found. Both
catalysts were able to catalyze the amination reaction yielding
selectively ␤-amino alcohol 8c. Even though the conversion is not
◦
very high at room temperature, at 80 C almost quantitative con-
versions were obtained after 24 h. For this reaction it seems that the
presence of the sulfonic groups is not so important for the aminol-
ysis reaction as for the alcoholysis since no significative difference
was observed between the two catalysts.
4
. Conclusions
Mesoporous activated carbon proved to be effective catalysts for
the ring opening reaction of epoxides affording the corresponding
-substituted alcohols with high conversion values and very good
␤
selectivity. The mesoporosity of these materials seems to have a
significant role on the performance. The introduction of sulfonic
groups attached to the surface of the carbon resulted in better cat-
alysts with enhanced activity than the oxidized with nitric acid.
Also the application of the catalysts reported here simplifies the
experimental procedure, and allows the use of mild conditions for
ring opening reactions from epoxides. It was possible to regener-
ate the catalyst CMN and thus restore the original activity. The ring
opening reaction with amines, although not so effective, was also
catalyzed by the mesoporous carbon catalysts.
In the third reutilization of sample CMNS the drop in activity was
not very pronounced, suggesting that there are still active sites in
the catalyst. XPS studies of the CMNS sample after the three reuti-
lization runs showed that the sulfonic groups remain present in the

3
0
I. Matos et al. / Applied Catalysis A: General 439–440 (2012) 24–30
Acknowledgments
[17] I. Matos, E. Pérez-Mayoral, E. Soriano, A. Zukal, R.M. Martín-Aranda, A.J. López-
Peinado, I. Fonseca, J. Cˇ ejka, Chem. Eng. J. 161 (2010) 377–383.
[
18] P. Ferreira, I.M. Fonseca, A.M. Ramos, J. Vital, J.E. Castanheiro, Catal. Commun.
I. Matos thanks Funda c¸ ão para Ciência e Tecnologia for grant
SFRH/BPD/34659/2007.
12 (2011) 573–576.
[19] V. Calvino-Casilda, R.M. Martin-Aranda, A.J. Lopez-Peinado, A.C. Duran Valle,
Catal. Rev. Sci. Eng. 52 (2010) 325–380.
[
E.P-M. and R.M-A. works have been supported in part by MICINN
20] J. Rubio-Gómez, R.M. Martín-Aranda, M.L. Rojas-Cervantes, J. de D. López-
González, J.L.G. Fierro, Carbon 37 (1999) 213–219.
(
projects CTQ2009-10478 and CTQ2010-18652).
This work has been supported by Funda c¸ ão para a Ciência e a
Tecnologia through grant no. PEst-C/EQB/LA0006/2011.
[21] V. Calvino-Casilda, A.J. López-Peinado, R.M. Martín-Aranda, Appl. Catal. 240
(2002) 287–293.
[
22] J.M. López-Pesta n˜ a, M.J. Ávila-Rey, R.M. Martín-Aranda, Green Chem. 4 (2002)
6
28–630.
References
[23] J.M. López-Pesta n˜ a, J. Díaz-Terán, M.J. Ávila-Rey, M.L. Rojas-Cervantes,
R.M. Martín-Aranda, Micropor. Mesopor. Mater. 67 (1) (2004)
87–94.
[1] S. Zakavi, G. Karimipour, N. Gholami Gharab, Catal. Commun. 10 (2009)
3
88–390.
[24] C.J. Durán-Valle, I. Fonseca, V. Calvino-Casilda, M. Picallo, A.J. López-Peinado,
R.M. Martín-Aranda, Catal. Today 107–108 (2005) 500–506.
[25] I. Matos, S. Fernandes, L. Guerreiro, S. Barata, A.M. Ramos, J. Vital, I.M. Fonseca,
Micropor. Mesopor. Mater. 92 (2006) 38–46.
[26] L. Zubizarreta, A. Arenillas, J.-P. Pirard, J.J. Pis, N. Job, Microp. Mesop. Mater. 115
(2008) 480–490.
[27] R.W. Pekala, D.W. Schaefer, Macromolecules 26 (1993) 5487–5493.
[28] S.A. Al-Muhtaseb, J.A. Ritter, Adv. Mater. 15 (2003) 101–114.
[29] C. Lin, J.A. Ritter, Carbon 35 (1997) 1271–1278.
[30] S.J. Gregg, K.S.W. Sing, Adsorption, Surface Area and Porosity, Academic Press,
London, 1982.
[31] J.S. Noh, J.A. Schwarz, J. Colloid Interface Sci. 130 (1989) 157–164.
[32] J.R.C. Salgado, R.G. Duarte, L.M. Ilharco, A.M. Botelho do Rego, A.M. Ferraria,
M.G.S. Ferreira, Appl. Catal. B: Environ. 102 (2011) 496–504.
[33] N. Job, R. Pirard, J. Marien, J.-P. Pirar, Carbon 42 (2004) 619–628.
[34] S. Lambert, N. Job, L. D’Souza, M.F. Ribeiro Pereira, R. Pirard, B. Heinrichs, J.L.
Figueiredo, J.-P. Pirard, J.R. Regalbuto, J. Catal. 261 (2009) 23–33.
[35] A.P. Terzyk, Colloid Surf. A 177 (2001) 23–45.
[
[
2] Y. Liu, Q. Liu, Z. Zhang, J. Mol. Catal. A: Chem. 296 (2008) 42–46.
3] C. Baylon, G. Prestat, M.P. Heck, C. Mioskowski, Tetrahedron Lett. 41 (2000)
3
4] E.J. Corey, F.Y. Zhang, Angew. Chem. Int. Ed. 38 (1999) 1931–1934.
5] A.A. Jafari, Moradgholi, Synth. Commun. 41 (2011) 594–602.
6] Y. Li, Y. Tan, E. Herdtweck, M. Cokoja, F.E. Kühn, Appl. Catal. A: Gen. 384 (2010)
833–3835.
[
[
[
1
71–176.
[
[
7] P.R. Likhar, M.P. Kumar, A.K. Bandyopadhyay, Synlett (2001) 836–839.
8] P. Salehi, B. Seddighi, M. Irandoost, F.K. Behbahani, Synth. Commun. 30 (2000)
2
967–2973.
9] R.V. Yarapathi, S.M. Reddy, S. Tammishetti, React. Funct. Polym. 64 (2005)
57–161.
10] H. Firouzabadi, N. Iranpoor, A. Ali Jafari, S. Makarem, J. Mol. Catal. A: Chem. 250
2006) 237–242.
[
1
[
[
[
[
[
[
[
(
11] R. Chakravarti, H. Oveisi, P. Kalita, R.R. Pal, S.B. Halligudi, M.L. Kantam, A. Vinu,
Micropor. Mesopor. Mater. 123 (2009) 338–344.
12] J.H. Choi, S.J. Lee, C.R. Joo, J.S. Kim, D.J. Baek, Bull. Korean Chem. Soc. 20 (1999)
1
384–1386.
[36] G. Beamson, D. Briggs, High Resolution XPS of Organic Polymers: The Scienta
ESCA300 Database, John Wiley & Sons Ltd., New York, 1992.
[37] A. Valente, C. Palma, I.M. Fonseca, A.M. Ramos, J. Vital, Carbon 41 (2003)
2793–2803.
[38] J.L. Figueiredo, M.F.R. Pereira, M.M.A. Freitas, J.J.M. Orfão, Carbon 37 (1999)
1379–1389.
[39] N. Mahata, M.F.R. Pereira, F. Suarez-Garcia, A. Martinez-Alonso, J.M.D. Tascon,
J.L. Figueiredo, J. Colloid Interface Sci. 324 (2008) 150–155.
[40] C.J. Duran-Valle, J.A. Garcıa-Vidal, Catal. Lett. 130 (2009) 37–41.
13] R.I. Kureshy, I. Ahmad, K. Pathak, N.H. Khan, S.H.R. Abdi, H.C. Bajaj, E. Suresh,
Res. Lett. Org. Chem. (2009) 1–5 (Article ID 109717).
14] M.M. Mojtahedi, M.H. Ghasemi, M. Saeed Abaee, M. Bolourtchian, ARKIVOC XV
(
2005) 68–73.
15] J.A. Garcıa-Vidal, C.J. Duran-Valle, S. Ferrera-Escudero, Appl. Surf. Sci. 252
2006) 6064–6066.
(
16] D.S. Pita, I. Matos, I.M. Fonseca, A.M. Ramos, J. Vital, J.E. Castanheiro, Appl. Catal.
A: Gen. 373 (2010) 140–146.