Functionalization of mesoporous carbon with superbasic MgO nanoparticles for the efficient synthesis of sulfinamides

Article abstract of DOI:10.1002/chem.201002885

Highly basic MgO nanoparticles with different sizes have been successfully immobilized over mesoporous carbon with different pore diameters by a simple wet-impregnation method. The prepared catalysts have been characterized by various sophisticated techniques, such as XRD, nitrogen adsorption, electron energy loss spectroscopy, high-resolution TEM, X-ray photoelectron spectroscopy, and the temperature-programmed desorption of CO₂. XRD results reveal that the mesostructure of the support is retained even after the huge loading of MgO nanoparticles inside the mesochannels of the support. It is also demonstrated that the particle size and dispersion of the MgO nanoparticles on the support can be finely controlled by the simple adjustment of the textural parameters of the supports. Among the support materials studied, mesoporous carbon with the largest pore diameter and large pore volume offered highly crystalline small-size cubic-phase MgO nanoparticles with a high dispersion. The basicity of the MgO-supported mesoporous carbons can also be controlled by simply changing the loading of the MgO and the pore diameter of the support. These materials have been employed as heterogeneous catalysts for the first time in the selective synthesis of sulfinamides. Among the catalysts investigated, the support with the large pore diameter and high loading of MgO showed the highest activity with an excellent yield of sulfinamides. The catalyst also showed much higher activity than the pristine MgO nanoparticles. The effects of the reaction parameters, including the solvents and reaction temperature, and textural parameters of the supports in the activity of the catalyst have also been demonstrated. Most importantly, the catalyst was found to be highly stable, showing excellent activity even after the third cycle of reaction. Reuse and recycle: Highly basic MgO-functionalized mesoporous carbon with different pore diameters has been prepared (see picture). The material showed a much higher performance in the synthesis of sulfinamides than pure MgO nanoparticles. The catalyst was also highly stable and could be reused several times without affecting its activity. Copyright

Full text of DOI:10.1002/chem.201002885

FULL PAPER
DOI: 10.1002/chem.201002885
Functionalization of Mesoporous Carbon with Superbasic MgO
Nanoparticles for the Efficient Synthesis of Sulfinamides
Rajashree Chakravarti,[a] Ajayan Mano,[a] Hideo Iwai,[b] Salem S. Aldeyab,[d]
R. Pradeep Kumar,[a] M. Lakshmi Kantam,[c] and Ajayan Vinu*[a]
Abstract: Highly basic MgO nanoparti-
cles with different sizes have been suc-
cessfully immobilized over mesoporous
carbon with different pore diameters
by a simple wet-impregnation method.
The prepared catalysts have been char-
acterized by various sophisticated tech-
niques, such as XRD, nitrogen adsorp-
tion, electron energy loss spectroscopy,
high-resolution TEM, X-ray photoelec-
tron spectroscopy, and the tempera-
ture-programmed desorption of CO2.
XRD results reveal that the mesostruc-
ture of the support is retained even
after the huge loading of MgO nano-
particles inside the mesochannels of
the support. It is also demonstrated
that the particle size and dispersion of
the MgO nanoparticles on the support
can be finely controlled by the simple
adjustment of the textural parameters
of the supports. Among the support
materials studied, mesoporous carbon
with the largest pore diameter and
large pore volume offered highly crys-
talline small-size cubic-phase MgO
nanoparticles with a high dispersion.
The basicity of the MgO-supported
mesoporous carbons can also be con-
trolled by simply changing the loading
of the MgO and the pore diameter of
the support. These materials have been
employed as heterogeneous catalysts
for the first time in the selective syn-
thesis of sulfinamides. Among the cata-
lysts investigated, the support with the
large pore diameter and high loading
of MgO showed the highest activity
with an excellent yield of sulfinamides.
The catalyst also showed much higher
activity than the pristine MgO nano-
particles. The effects of the reaction pa-
rameters, including the solvents and re-
action temperature, and textural pa-
rameters of the supports in the activity
of the catalyst have also been demon-
strated. Most importantly, the catalyst
was found to be highly stable, showing
excellent activity even after the third
cycle of reaction.
Keywords: carbon · heterogeneous
catalysis · magnesium · mesoporous
materials · nanoparticles
Introduction
synthesis of inorganic metal oxides.[1–7] Various synthetic ap-
proaches including sacrificial inorganic metal oxide templat-
ing, physical and chemical activation of carbons, and the car-
bonization of polymer blends have been used for the fabri-
cation of mesoporous carbons. Among the preparation
methods, templating with inorganic metal oxides including
zeolites, colloidal crystals, and mesoporous silica with differ-
ent structure is quite attractive as it can offer a material
with well-ordered porous structure and excellent textural
characteristics. Knox et al. first realized the inorganic tem-
plating process to make mesoporous carbon materials by
simply impregnating silica gel or porous glass with phenolic
resin, followed by the carbonization of the resin and the re-
moval of the template.[8] Using the same approach, Kyotani
and co-workers prepared mesoporous carbon with high sur-
face area by using zeolite as template.[9] In 1999, two
Korean researchers followed a similar approach for the fab-
rication of well-ordered mesoporous carbon materials by
using highly ordered mesoporous silicas as templates.[10,11]
However, unlike other carbon materials, the resultant mate-
rials exhibit a well-ordered porous structure with uniform
pore size distribution and large accessible mesopore volume
for large biomolecules.[7,12,13] These exciting features of the
materials paved the way for creating various well-ordered
mesoporous carbons with different pore diameters and
In recent years, highly ordered mesoporous carbon materials
have attracted tremendous attention for their possible appli-
cations as adsorbents for large and small biomolecules, cata-
lytic supports, electrode materials, and templates for the
[a] Dr. R. Chakravarti, A. Mano, R. P. Kumar, Prof. A. Vinu
World Premier International Center for Materials Nanoarchitectonics
National Institute for Materials Science (NIMS)
Tsukuba, Ibaraki 305-0044 (Japan)
Fax : +(81)29-860-4706
E-mail: vinu.ajayan@nims.go.jp
[b] Dr. H. Iwai
Materials Analysis Station, Department of Materials Infrastructure,
NIMS
1-2-1, Sengen, Tsukuba, Ibaraki 305-0047 (Japan)
[c] Dr. M. L. Kantam
NIMS-IICT Materials Research Center, Physical Chemistry Division
Indian Institute for Chemical Technology
Hyderabad 500 007 (India)
[d] Prof. S. S. Aldeyab
Department of Chemistry, Petrochemicals Research Chair
Faculty of Science, King Saud University
Riyadh 11451 (Kingdom of Saudi Arabia)
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.201002885.
Chem. Eur. J. 2011, 17, 6673 – 6682
ꢀ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
6673

structures by using different mesoporous silica templates
with different structures and pore diameters, which were
used for the adsorption and separation of large biomolecules
including vitamins, proteins, and amino acids.[7,12,13] Al-
though these materials demonstrated excellent adsorption
capability for various biomolecules, their inert nature and
the hydrophobic surface of the mesoporous carbons limit
the range of application possibilities mainly to the fields of
catalysis, fuel cells, and sensors.
To widen the scope of the materials for a wide range of
applications including acid–base catalysis, it is vital that new
properties should be introduced in the mesochannels of the
mesoporous carbon materials. This can be achieved by
either introducing different functional groups through sur-
face modification or the addition of metal or metal oxide
nanoparticles inside the mesochannels of the mesoporous
carbons. Acidic or basic functions on the surface of the
phosphites as the reducing agent.[34] However, the attempts
of this group to prepare sulfinamides were not successful.
Later, Toru and co-workers introduced the synthesis of sulfi-
nate esters by using triarylphosphines as reductants.[35] Re-
cently, Harmata et al. have reported the synthesis of sulfina-
mides from sulfonyl chlorides, with triphenylphosphine as a
reductant and triethylamine as the base.[33] Unfortunately,
most of the synthetic methods developed so far for the prep-
aration of sulfinamides are homogeneously catalyzed pro-
cesses, which have several disadvantages such as difficulty in
separation of the product from the reaction mixture, poor
recyclability, and the requirement for
a stoichiometric
amount of catalyst. To the best of our knowledge, no reports
of the heterogeneously catalyzed synthesis of sulfinamides
from the corresponding sulfonyl chlorides are available in
the literature.
Herein, we report the results on the encapsulation of su-
perbasic MgO nanoparticles in mesoporous carbon by the
wet-impregnation method (Scheme 1). We also show that
mesoACHTUNGTRENNUNGporous carbon materials can be introduced by simply
modifying the surface with carboxyl or amine groups, which
was first realized by Vinu et al.[13] However, the textural pa-
rameters of the materials were significantly affected after
the chemical modification due to defects in the carbon wall
structure. On the other hand, some researchers tried to im-
mobilize ultrasmall metal or metal oxide nanoparticles in
the mesoporous channels to introduce new functions by
taking advantage of their excellent pore structural order and
textural parameters because the size and dispersion of the
nanoparticles can be directed.[14,15] Although a few reports
are available on the preparation of mesoporous carbon
loaded with metal and metal oxide nanoparticles, which
were limited to only transition-metal oxide nanoparti-
cles,[14,15] the encapsulation of basic metal oxides, such as
MgO, which is considered as a superbasic oxide, in the
mesoACHTUNGTRENNUNGchannels of mesoporous carbons has rarely been re-
ported. However, various mesoporous metal oxides includ-
ing MgO have been synthesized by using mesoporous
carbon as template.[16,17] Unfortunately, the resulting meso-
porous MgO possesses much lower surface area than the
template, which makes it less attractive for various applica-
tions.
Scheme 1. Synthesis of pure mesoporous carbon and mesoporous carbon
with encapsulated MgO nanoparticles.
the crystallite size of the MgO in the pore channels of the
mesoporous carbon can be controlled by the simple adjust-
ment of the pore diameter of the support. The mesoporous
carbons with different pore diameters and encapsulated su-
perbasic MgO have been characterized by XRD, nitrogen
adsorption, X-ray photoelectron spectroscopy (XPS), high-
resolution TEM (HRTEM), electron energy loss spectrosco-
py (EELS), and temperature-programmed desorption
(TPD) of CO2. We also report here for the first time the
synthesis of aromatic sulfinamides by reductive amination
from the corresponding aromatic sulfonyl chlorides with tri-
phenylphosphine as a reductant and the MgO-nanoparticle-
supporting mesoporous carbon as the base catalyst
(Scheme 2). The roles of the pore diameter of the support
and the size and basicity of the MgO nanoparticles, which
affect the yield of the synthesized aromatic sulfinamides,
have also been studied. In addition, the recycling capability
of the MgO-loaded mesoporous carbon has been studied
Sulfinamides are an important class of organic compounds
that play a key role in modern organic chemistry.[18,19] They
are useful compounds and can easily be transformed into a
number of other important functional groups, such as sulfon-
ACHTUNGTRENNUNG
imidoyl chlorides.[20,21] Furthermore, sulfinamides can also
act as an N-sulfinyl protecting group, which can be easily re-
moved under mild conditions.[22–24] Various procedures have
been reported for the preparation of sulfinamides from sul-
finic acids,[25] sulfinates,[26–29] sulfinyl chlorides,[30] disul-
fides,[31] and by hemolytic substitution at the sulfur atom.[32]
However, these reactions often require two or more synthet-
ic steps. To render this reaction more useful in the area of
sulfinamide chemistry, an elegant single-step process is de-
sired.[33] Recently, much effort has been directed towards a
mild synthesis of sulfinamides. Sharpless and Klunder re-
ported the synthesis of sulfinate esters from sulfonyl chlor-
ides by a one-pot reductive esterification reaction using
6674
www.chemeurj.org
ꢀ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2011, 17, 6673 – 6682

Functionalization of Mesoporous Carbon with MgO Nanoparticles
FULL PAPER
of the CMK-3-150-Y samples in comparison with the pris-
tine CMK-3-150. As can be seen, all the MgO-loaded CMK-
3-150 samples exhibit a sharp peak at lower angle, thus con-
firming that the hexagonally ordered mesoporous structure
with p6mm symmetry is retained even after loading more
than 50 wt% of the MgO nanoparticles. However, the inten-
sity of the lower-angle peak decreases with increased load-
ing of the MgO nanoparticles, thereby revealing the pres-
ence of MgO nanoparticles in the mesochannels of the sam-
ples.
Scheme 2. Synthesis of sulfinamides by using mesoporous carbon (CMK-
3) with encapsulated MgO nanoparticles.
and it has been found that the catalyst can be reused several
times without much affecting its catalytic activity.
The wide-angle powder XRD patterns of the CMK-3-150-
Y samples are shown in Figure 1B. All the samples exhibit
several peaks, which can be indexed as (111), (200), (220),
(331), and (222) of the crystalline cubic structure of the
MgO nanoparticles. The peaks of other phases of MgO were
not observed for all the samples, which indicates that pure
cubic MgO nanocrystals without any impure phase in the
pore channels of the CMK-3 can be prepared by a simple
wet-impregnation method. This also further confirms the
conversion of the Mg salt into MgO during the high-temper-
ature treatment. It is interesting to note that as the loading
of MgO on the pore channels of the CMK-3-150 increases,
the intensity of the (200) and (220) peaks increases, whereas
a decrease in the full width at half maximum (FWHM) was
observed for the same samples, thus indicating the dense
packing of the MgO nanoparticles in the case of CMK-3-
150-50. The crystallite size of the MgO nanoparticles was
calculated by using the using Debye–Scherrer formula D=
0.9l/bcosq, in which l is the wavelength of the CuKa radia-
tion, q is the angle of diffraction, D is the average crystallite
size measured in a direction perpendicular to the surface of
the specimen, and b is the FWHM. The crystallite size of
the MgO increases from 11.6 to 12.2 nm with increasing
loading of MgO nanoparticles in the mesochannels of CMK-
3-150 from 20 to 50 wt%. This may be ascribed to the ag-
gregation of the small nanoparticles on the external surface
of the support when the loading of MgO is high. It should
be noted that the crystallite size of the MgO nanoparticles is
much larger than that of the pore diameter of the CMK-3-
150. It is a well-known fact that when the crystallite domain
size is not defined properly, the value of the crystallite size
derived from the Scherrerꢁs formula should be treated as a
rough estimate.[16,17]
Results and Discussion
CMK-3 materials with different pore diameters were pre-
pared by using silica SBA-15 templates synthesized at differ-
ent temperatures, and the samples were denoted CMK-3-X
in which X denotes the synthesis temperature of the SBA-15
template. MgO nanoparticles at different weight percentages
were then encapsulated inside the mesochannels of CMK-3
with different pore diameters by a wet-impregnation tech-
nique, followed by calcination at 5008C under a nitrogen at-
mosphere. The samples are denoted as CMK-3-X-Y in
which Y denotes the weight percentage of MgO with respect
to the mesoporous carbon. To check whether the encapsula-
tion process makes any structural defects in the mesoporous
carbon support, the mesoporous carbons loaded with MgO
nanoparticles were characterized by low-angle powder XRD
measurements. Figure 1A shows the powder XRD patterns
The retention of the mesostructure of the CMK-3 support
and the presence of the MgO particles in the mesochannels
are confirmed by HRTEM. Figure 2 shows the representa-
tive HRTEM images of CMK-3-150-50. The sample exhibits
a well-ordered mesoporous structure with a linear array of
mesopores that are arranged in regular intervals, thus re-
vealing that the mesostructure of the sample is completely
retained even after the encapsulation of basic MgO nano-
particles. It can also be seen from these images that the
MgO nanoparticles are highly dispersed on the surface of
the support with a few agglomerated MgO nanoparticles.
MgO particles with a size similar to that of the pore diame-
ter of the support can also be clearly seen from the
HRTEM images. However, XRD data reveal the presence
Figure 1. A) Low- and B) wide-angle powder XRD patterns of mesopo-
rous carbons with different weight percentages of encapsulated MgO
nanoparticles: a) CMK-3-150, b) CMK-3-150-20, c) CMK-3-150-30, and
d) CMK-3-150-50.
Chem. Eur. J. 2011, 17, 6673 – 6682
ꢀ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
6675

A. Vinu et al.
even after the loading of about 50 wt% of MgO nanoparti-
cles. However, the amount of nitrogen adsorption decreased
with increasing loading of the MgO nanoparticles, which
was mainly due to the occupation of the surface and the
mesochannels of the support by the MgO nanoparticles. The
specific surface area, specific pore volume, and pore diame-
ter of the samples before and after loading of different
weight percentages of the MgO nanoparticles are given in
Table 1. It can be seen that the specific surface area and the
specific pore volume of the sample were drastically de-
creased upon loading of the MgO nanoparticles. The specific
surface area decreases from 1350 to 879 m2 gÀ1 upon increas-
ing the loading of MgO from 20 to 50 wt%, whereas the
specific pore volume decreases from 1.60 to 1.34 cm3 gÀ1 for
the same samples. These results further confirm the occupa-
tion of the pores by the MgO nanoparticles. However, not
much change in the pore diameter of the sample after MgO
Figure 2. Representative HRTEM images of CMK-3-150-50.
of large crystallites, which indi-
cates the presence of MgO
nanoparticles with different size
on both the mesochannels and
the external surface of the
sample. The presence of Mg, O,
and C was also confirmed by
EELS (Figure 3A). Mg, O, and
C elemental mapping of the
sample is displayed in Fig-
ure 3B. The distribution of the
Mg and
O elements in the
maps reveals that MgO nano-
particles are uniformly distrib-
uted on the surface of the
CMK-3-150 support.
The effect of the MgO nano-
particle loading on the textural
parameters of the CMK-3-150
sample
was
investigated.
Figure 4 shows the nitrogen ad-
sorption–desorption isotherms
of CMK-3-150 loaded with dif-
ferent weight percentages of
MgO nanoparticles in compari-
son to the pristine CMK-3-150.
All the MgO-loaded samples
show a type IV adsorption iso-
therm with H1 hysteresis loop
and a sharp capillary condensa-
tion step, which is a characteris-
tic of well-ordered mesoporous
materials. It was found that the
shape and position of the capil-
lary condensation step, which
directly gives the dimension of
the pore diameter, were not
changed at all. This result re-
veals that the mesostructure of
Figure 3. A) EELS and B) elemental mapping of mesoporous carbon CMK-3-150-50 with encapsulated MgO
the material was not collapsed nanoparticles.
6676
www.chemeurj.org
ꢀ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2011, 17, 6673 – 6682

Functionalization of Mesoporous Carbon with MgO Nanoparticles
FULL PAPER
smallest pore diameter, is much larger than that formed on
the surface of CMK-3-150. This is mainly because the pore
diameter of the CMK-3-100 is too small to accommodate
the large MgO nanoparticles, which trigger agglomeration
and the formation of large crystals on the external surface.
The textural parameters and the porosity of the resulting
MgO-loaded CMK-3 samples with different pore diameters
were further obtained from the nitrogen adsorption–desorp-
tion isotherms (Figure 2S, Supporting Information). All sam-
ples were found to exhibit a type IV isotherm with H1 hys-
teresis loop, a characteristic of the parent CMK-3 material.
The capillary condensation step shown in the isotherms
clearly points out that no major pore blockage has occurred
in the MgO-loaded samples, even though a significant
amount of MgO has been dispersed onto the surface of the
CMK-3. This is also proved from the presence of the well-
defined low-angle peak in the powder XRD pattern. But
the decrease in surface area, as well as the pore diameters
in the modified samples, suggests that the pore cavities are
indeed occupied by the MgO particles even though they are
not blocked completely. It should be mentioned that the re-
duction in the pore volume, surface area, and pore diameter
of the support after the encapsulation of MgO nanoparticles
is more pronounced for CMK-3-150 than for other supports.
This is mainly due to the fact that the excellent textural pa-
rameters together with the large pore diameter of the CMK-
3-150 offer easy diffusion of MgO nanoparticles inside the
channels and limit the agglomeration of the particles both in
the pore entrance and on the porous surface of the support.
These results suggest that a support with large pore diame-
ter and large pore volume is crucial to obtain well-dispersed
MgO nanoparticles on the surface of the CMK-3 support.
The nature of the MgO nanoparticles and their interac-
tion with the mesoporous carbon support were investigated
by XPS. The XPS spectra of the calcined CMK-3-MgO
showed peaks for the binding energies of the core shell elec-
trons in the Mg, C, and O species. A careful FWHM-based
deconvolution of the resulting peaks provides information
about the presence of various species of Mg in the pore
channels of CMK-3 as well as on the surface of the materi-
al.[36] Figure 5 shows the XPS survey spectrum of CMK-3-
150-50. The peaks related to Mg, O, and C are clearly visible
in the survey spectrum. C1s, O1s, and Mg2p curve-fit spectra
are also displayed in Figure 5B–D, respectively. To obtain
clear details about the nature of the MgO species in the
samples, the spectra were deconvoluted into Gaussian–Lor-
entzian shapes. As shown in Figure 5D, the sample exhibits
a sharp peak at 50.47 eV which is attributed to MgO and
Mg(OH)2; the ratio between the two components is deter-
mined from the O1s curve-fit result and another small peak
that may be assigned to MgCO3. The intensity of the MgO
peak is higher than that of the other peaks, which suggests
the formation of a huge amount of MgO in the samples. The
presence of the Mg(OH)2 and MgCO3 peaks may be attrib-
uted to the surface reaction of MgO nanoparticles with at-
mospheric moisture and CO2 molecules. It is also possible
that some of the Mg(OH)2 was not converted fully into
Figure 4. Nitrogen adsorption isotherms of pure mesoporous carbon and
*
mesoporous carbon with encapsulated MgO nanoparticles: ( ) CMK-3-
~
&
^
150, ( ) CMK-3-150-20, ( ) CMK-3-150-30, and ( ) CMK-3-150-50.
Table 1. Textural parameters of the pure mesoporous carbon with differ-
ent pore diameters and of the mesoporous carbon with encapsulated
MgO nanoparticles.
[b]
[c]
[d]
A[a]
[m2 gÀ1
Vpore
[cm3 gÀ1
Dpore
[nm]
Crystallite
size [nm]
VCO
2
G
]
G
]
[mmolgÀ1
ACHTUNGTERNNUNG ]
CMK-3-100- 938
50
CMK-3-130- 832
50
CMK-3-150- 879
50
CMK-3-150- 1030
30
1.02
1.08
1.17
1.31
1.34
3.5
4.2
5.8
5.8
5.8
15.5
12.9
12.2
11.6
11.6
0.15
0.21
1.31
0.74
0.13
CMK-3-150- 1052
20
CMK-3-100
CMK-3-130
CMK-3-150
1260
1250
1350
1.10
1.30
1.60
3.3
4.3
6.5
–
–
–
NA
NA
0.03
[a] Surface area. [b] Pore volume. [c] Pore diameter. [d] Total volume of
CO2 desorbed. NA: not applicable.
loading was observed (Table 1). In addition, the sample still
exhibits a huge accessible pore volume even after loading
50 wt% of MgO, which indicates that the pores are not com-
pletely blocked by the MgO nanoparticles and the basic
active sites can be available for molecules involved in organ-
ic transformations.
To find out the role of the pore diameter of the mesopo-
rous carbon support, we also attempted to load the MgO
nanoparticles inside the mesochannels of CMK-3 with differ-
ent pore diameters. CMK-3-100, CMK-3-130, and CMK-3-
150, which have different pore diameters, obtained from
SBA-15 templates synthesized at different temperatures,
were loaded with 50 wt% of MgO in a similar way and the
effects were observed by thorough characterization. Fig-
ure 1S in the Supporting Information shows powder XRD
patterns of CMK-3 samples with different pore diameters
and immobilized MgO. It was found that a well-ordered
mesostructure is maintained for all the samples, thus indicat-
ing a 2D hexagonal mesoporous structure with p6mm sym-
metry. The formation of the MgO nanoparticles was also
confirmed by wide-angle powder XRD patterns. It is inter-
esting to note that the crystallite size of the MgO nanoparti-
cles formed on the surface of the CMK-3-100, which has the
Chem. Eur. J. 2011, 17, 6673 – 6682
ꢀ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
6677

A. Vinu et al.
was tested in the synthesis of
sulfonamides, which require
basic sites to trigger the re-
AHCTUNGTRENNUNG
action.[33] The reactivity of the
catalyst was also compared with
that of commercially available
MgO (surface area: 25 m2 gÀ1)
and MgO-supported activated
carbon with high specific sur-
face area. It was observed that
a mere 20% of the desired
product could be isolated when
commercial MgO was used as
the catalyst in the reaction of p-
toluenesulfonyl chloride with
benzylamine in the presence of
triphenylphosphine as reducing
agent. On the other hand,
MgO-supported
activated
carbon gave a yield of isolated
product of only 29% (19% sul-
fonamide and 10% sulfina-
mide), which is much lower
Figure 5. XPS data of mesoporous carbon with encapsulated MgO nanoparticles: A) survey, B) C1s, C) O1s,
and D) Mg2p spectra of CMK-3-150-50.
MgO during the carbonization process as it was carried out
in a nitrogen atmosphere. From the C1s and O1s spectra, it
can be suggested that the carbon support is strongly bonded
with the oxygen from the MgO nanoparticles, which is ex-
pected to provide high stability and avoid the agglomeration
of the nanoparticles.
The main idea behind the loading of the MgO nanoparti-
cles inside the mesochannels of CMK-3 is to create superba-
sic oxide sites and to utilize them for basic organic catalytic
transformations. Before proceeding into the reaction part,
the basicity of the CMK-3 with different pore diameters and
different MgO nanoparticle loadings was determined by
using TPD of CO2 molecules and the results were compared
with those for the pristine CMK-3 support. Figure 6 shows
the TPD profiles of CMK-3 with different pore diameters
loaded with different weight percentages of MgO nanoparti-
cles. The TPD measurements were carried out up to 5008C
as it is believed that the carbon will be decomposed above
this temperature. These CO2 desorption temperatures cou-
pled with the amount of CO2 desorbed per gram of the
sample (Table 1) gives a clear picture of the basicity of the
samples. From the TPD profile, it can be seen that all the
samples showed a major peak at approximately 2008C and a
broad peak above 4008C. These results suggest that MgO-
loaded samples possess both weakly and moderately basic
sites. It should also be mentioned that the basicity of the
MgO-loaded samples is significantly higher than that of the
pristine CMK-3 support. Among the samples studied, CMK-
3-150-50 showed the highest basicity due to the highly dis-
persed MgO nanoparticles with a small size.
Figure 6. A) TPD profiles of different weight percentages of MgO nano-
particles over CMK-3-150: a) CMK-3-150-50, b) CMK-3-150-30, c) CMK-
3-150-20, and d) CMK-3-150. B) TPD profiles of MgO nanoparticles en-
capsulated over mesoporous carbon with different pore diameters:
a) CMK-3-150-50, b) CMK-3-130-50, and c) CMK-3-100-50.
than that obtained for MgO-supported mesoporous carbon
CMK-3-150. Interestingly, the yield of the corresponding
product was 72% when CMK-3-150-50 was used as the cata-
lyst. This greater reactivity may be attributed to the higher
surface area, well-ordered mesoporous structure, and the
large pore diameter of the support, which offer high disper-
Finally, the basic catalytic activity of the CMK-3-150-50,
which has the highest basicity among the samples studied,
6678
www.chemeurj.org
ꢀ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2011, 17, 6673 – 6682

Functionalization of Mesoporous Carbon with MgO Nanoparticles
FULL PAPER
sion of small MgO basic nanoparticles and provide a greater
number of basic sites to catalyze the reaction more efficient-
ly. Although the specific surface area of the activated
carbon support is as high as that of the mesoporous carbon
support, the former suffered from a disordered porous struc-
ture and registered a poor activity. This may be attributed to
the presence of hidden pores in the activated carbon, which
do not favor the high dispersion of the MgO nanoparticles
on the porous surface and their accessibility for the re-
agent in all the reactions. Under these optimized reaction
conditions, a variety of amines of various classes, such as ali-
phatic, aromatic, cyclic, and amino acid derivatives, were
made to undergo this reaction. The results are summarized
in Table 2.
The synthesis of sulfinamides of p-toluenesulfonyl chlo-
ride with various amines proceeded smoothly to afford the
desired products in moderate to good yields. In most of the
cases aryl sulfonamides were formed as a minor side prod-
uct. 1H NMR spectroscopy, 13C NMR spectroscopy, and
mass spectrometry of the resulting compounds revealed that
benzylamine gave 72% of the desired product in a very
short reaction time (Table 2, entry 1). Other aliphatic
amines, such as butylamine, showed a good selectivity to-
wards the formation of the sulfinamide (Table 2, entry 2).
Sterically hindered secondary amines like dibutylamine af-
forded a moderate yield of the sulfinamide product. This
may be attributed to its slow reaction with the correspond-
ing sulfonyl chloride (Table 2, entry 3).[34] Good yields of the
aryl sulfinamides were also obtained in the case of cyclic pri-
mary amines, with which the aryl sulfonamides were formed
in a very small amount of merely 10% (Table 2, entry 4). Pi-
peridine afforded a poor yield of the desired sulfinamide,
even though the same reaction conditions were followed.
Morpholine, on the other hand, showed a much higher se-
lectivity towards the formation of the corresponding sulfina-
mide (Table 2, entries 5 and 6). On the other hand, aniline
and the substituted anilines showed excellent selectivity to-
wards the formation of sulfinamides without any formation
of sulfonamides (Table 2, entries 8–11). Proline methyl ester
showed a poor selectivity towards the formation of the cor-
responding sulfinamide (Table 2, entry 12) in which the for-
mation of the diastereoselective products was not observed.
Various substituted arylsulfonyl chlorides yielded the corre-
sponding sulfinamides in moderate to good yields when sub-
jected to reductive amination with a series of amines. The
results are summarized in Table 3.
From the results, it was observed that benzenesulfonyl
chloride shows a moderate selectivity towards the formation
of the corresponding sulfinamides (Table 3, entries 1 and 2).
Comparatively, a lesser amount of aryl sulfinamide forma-
tion was found in the case of both ortho- and para-substitut-
ed nitrobenzenesulfonyl chlorides (Table 3, entries 3–6).
2,4,6-Triisopropyl benzenesulfonyl chloride, on the other
hand, afforded the desired product in good yield. Therefore,
it can be concluded that the electron-donating groups when
attached to the phenyl ring assist the formation of the de-
sired product.
After the reaction, the catalyst was separated by simple
filtration and washed several times with ethyl acetate to
remove any traces of organic compounds. The sample was
dried in a hot-air oven and subjected to recalcination at
5008C under a nitrogen atmosphere for 5 h before use for
the second cycle in order to burn out traces of any remain-
ing organic compounds occluding the mesopore channels of
the material, the adsorbed HCl gases (the byproduct of the
reaction), and to activate the recycled catalyst. The catalytic
ACHTUNGTRENNUNG
catalyst, CMK-3-100, CMK-3-130, and CMK-3-150 loaded
with 50 wt% MgO were used to catalyze the reaction
(Table 1S, Supporting Information). Among the catalysts
studied, CMK-3-150-50 registered the highest activity with
an excellent yield of sulfinamides. As mentioned before, the
large pore volume, high surface area, and large pore diame-
ter of the support, which offer high dispersion of the MgO
nanoparticles and facilitate the easy passage of comparative-
ly bulkier molecules like triphenylphosphine,[37] are responsi-
ble for its high activity. As CMK-3-150-50 was found to be
the most active catalyst in the synthesis of sulfinamides, this
catalyst was used for further studies. The screening of vari-
ous solvents for this reaction showed that a very low yield
of the desired sulfinamide was realized in THF, acetonitrile,
and chloroform whereas the reaction in toluene showed
only a trace amount of conversion of the starting materials.
However, when dichloromethane was used as the solvent,
the catalyst showed the highest activity with p-toluenesul-
fonyl chloride, benzylamine, and triphenylphosphine as the
model substrates (Table 2S, Supporting Information).
To optimize the yield of the desired product, three differ-
ent methods of addition of substrates were adopted. In the
first, all the reactants were placed consecutively in a round-
bottomed flask and then the catalyst was added. The mix-
ture was then stirred at 08C for 1 h. In the second method,
p-toluenesulfonyl chloride and triphenylphosphine were
placed in a round-bottomed flask and the catalyst was
added. To this stirred reaction mixture, benzylamine was
added slowly over 30 min. In the third method, a solution of
benzylamine and triphenylphosphine in dichloromethane
was added slowly over 30 min to a stirred solution of p-tol-
uenesulfonyl chloride and the catalyst in dichloromethane.
It was found that the maximum amount of sulfinamide was
formed when the third method of addition was followed.
Therefore, this method was used for all other reactions.
When the reaction was carried out at room temperature, the
selectivity to the sulfinamide was completely lost and sulfo-
namide appeared as the major product. However, at À108C
the reaction became very sluggish and resulted in a conver-
sion of a mere 40% after 3 h (Table 3S, Supporting Informa-
tion). The optimum yield of the desired product sulfinamide
was obtained when the reaction was conducted at 08C. It
should also be mentioned that the use of two equivalents of
the reductant triphenylphosphine did not help to improve
the yield of the corresponding sulfinamide. Therefore, one
equivalent of triphenylphosphine was used as the reducing
Chem. Eur. J. 2011, 17, 6673 – 6682
ꢀ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
6679

A. Vinu et al.
Table 2. Synthesis of a series sulfinamides from p-toluenesulfonyl chloride and various amines by using CMK-
lyst, after recalcining each time
under the above conditions,
showed comparable yields of
3-150-50.[a]
Entry
Substrate
Amine
Sulfinamide 1
(Yield[b] [%])
Sulfinamide 2
(Yield[b] [%])
A
ACHTUNGTRENNUNG
the products, though only
a
little decrease in the yield was
observed. XRD and nitrogen
sorption studies of the used cat-
alyst showed a robust structure
of the catalyst, and not much
change in the structural order
of the recycled catalyst was ob-
served even after three consec-
utive cycles of the reaction.
These results reveal that the
catalyst loaded with MgO nano-
particles is highly stable and
can be reused several times
without sacrificing the catalytic
efficiency.
1
(72)
(70)
(8)
(5)
2
3
(51)
(22)
4
5
6
(70)
(25)
ACHTUNGTRENNUNG
Conclusion
We have strikingly demonstrat-
ed the preparation of mesopo-
rous carbons with different
pore diameters loaded with
highly basic MgO nanoparticles
by a wet-impregnation method.
The prepared catalysts have
been characterized by sophisti-
cated techniques such as XRD,
nitrogen adsorption, EELS,
HRTEM, XPS, and TPD of
CO2. It has been found that the
pore diameter of the support
plays a critical role in control-
ling the crystallite size and the
dispersion of the basic MgO
nanoparticles inside the meso-
channels and the surface of the
supports. Among the support
materials studied, the support
with the largest pore diameter
and large pore volume offered
highly crystalline small-size
cubic-phase MgO nanoparticles
with a high dispersion and ex-
tremely high basicity. We also
demonstrated that the basicity
of the materials could be tuned
by simply changing the loading
of the MgO nanoparticles and
the pore diameter of the sup-
port. All the materials have
(66)
ACHTUNGTRNE(NUNG trace)
7
(67)
(84)
(12)
(0)
8
9
(86)
(78)
(0)
(0)
10
11
12
(55)
(32)
(0)
(40)
[a] Reaction conditions: p-toluenesulfonyl chloride (1 mmol), triphenylphosphine (1 mmol), amine (1 mmol),
catalyst (50 mg), dichloromethane (4 mL), stirred at 08C for 1 h. [b] Yields of isolated product.
activity of the recycled catalysts is given in Table 4. Studies
over three cycles of the same reaction with the same cata-
been employed as basic heterogeneous catalysts for the se-
lective synthesis of sulfinamides. Among the catalysts stud-
6680
www.chemeurj.org
ꢀ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2011, 17, 6673 – 6682

Functionalization of Mesoporous Carbon with MgO Nanoparticles
FULL PAPER
Table 3. Synthesis of a series sulfinamides with various arylsulfonyl chlorides and amines by using CMK-3-
150-50.[a]
found to be the best, affording
high selectivity to sulfinamide.
We have also demonstrated the
applicability of the catalyst in
the synthesis of sulfinamides by
using various arylsulfonyl chlor-
ides and amines. Most impor-
tantly, the catalyst was found to
be highly stable, showing excel-
lent activity even after the third
cycle of reaction. Since these
catalysts are highly active and
selective, and the nanoparticles
formed inside the mesochannels
of the support are highly crys-
talline with cubic phase and
basic in nature, we strongly be-
lieve that the catalytic system
can be applied to a series of
base-catalyzed transformations
involving bulky molecules for
fine chemical production and
can replace the existing highly
hazardous homogeneous solu-
ble base catalysts.
Entry
Substrate
Amine
Sulfinamide
Sulfinamide
A
ACHTUNGTRENNUNG
1
(74)
(68)
(8)
2
3
(10)
(48)
(13)
4
5
6
(45)
(58)
(15)
(14)
(55)
(78)
(68)
(16)
(6)
7
8
Experimental Section
Typical experimental procedure for
catalytic reactions: A solution of tri-
phenylphosphine (262 mg, 1 mmol)
and benzylamine (107 mg, 1 mmol) in
dichloromethane (2 mL) was added
with a syringe over a period of 30 min
(8)
to
AHCTUNGTRENNUNG
a
stirred solution of p-tolu-
[a] Reaction conditions: arylsulfonyl chloride (1 mmol), triphenylphosphine (1 mmol), amine (1 mmol), cata-
lyst (50 mg), dichloromethane (4 mL), stirred at 08C for 1 h. [b] Yields of isolated product.
and catalyst containing encapsulated
MgO nanoparticles (50 mg) in di-
chloromethane (2 mL) at 08C. The re-
action was monitored by TLC for the
complete conversion of the p-toluene-
sulfonyl chloride. After completion of
the reaction, the mixture was filtered
Table 4. Recovery and reuse of CMK-3-MgO catalyst for reductive ami-
nation of p-toluene sulfonyl chloride with aniline.[a]
Entry
No. of cycles
Yield[b] [%]
to remove the catalyst and washed several times with ethyl acetate. The
combined organic extracts were concentrated under reduced pressure
and subjected to purification by column chromatography over silica gel
(60–120 mesh; eluent: 20% ethyl acetate/hexane) to afford the pure
product as a white solid. The catalyst was dried at 1008C in a hot-air
oven and preserved for the next run. The products were identified by
NMR spectroscopy and mass spectrometry and the results were com-
pared with data available in the literature.[33] The data for a representa-
tive example are given below.
N-Benzyl-p-toluenesulfinamide (Table 3, entry 1): White solid; 1H NMR
(400 MHz, CDCl3): d=7.62 (d, J=8.4 Hz, 2H), 7.18–7.31 (m, 7H), 4.24–
4.30 (t, J=5.5 Hz, 1H), 4.14 (dd, J=4.8, 13.2 Hz, 1H), 3.76 (dd, J=7.3,
13.5 Hz, 1H), 2.35 ppm (s, 3H); 13C NMR (100 MHz, CDCl3): d=140.8,
140.2, 137.3, 129.3, 128.3, 127.8, 126.9, 125.4, 44.0, 20.9 ppm; ESI-MS (rel-
ative intensity): m/z (%): 246 [M+1] (43). Data for selected compounds
are given in the Supporting Information.
1
2
3
1
2
3
84
75
73
[a] Reaction conditions: p-toluenesulfonyl chloride (1 mmol), triphenyl-
phosphine (1 mmol), aniline (1 mmol), catalyst (50 mg), dichloromethane
(4 mL), stirred at 08C for 1 h. In the case of subsequent cycles the
amount of substrate was adjusted according to the amount of catalyst re-
covered. [b] Unoptimized yields of isolated product (Æ3%).
ied, CMK-3-150-50 showed the highest activity with an ex-
cellent yield of sulfinamides. It has also been found that the
solvent plays a critical role in controlling the activity of the
catalysts. Of the solvents studied, dichloromethane was
Chem. Eur. J. 2011, 17, 6673 – 6682
ꢀ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
6681

A. Vinu et al.
[15] Y. Cao, J. Cao, M. Zheng, J. Liu, G. Ji, J. Solid State Chem. 2007,
180, 792.
Acknowledgements
[16] J. Roggenbuck, G. Koch, M. Tiemann, Chem. Mater. 2006, 18, 4151.
[17] J. Roggenbuck, M. Tiemann, J. Am. Chem. Soc. 2005, 127, 1096.
[18] J. A. Ellman, Pure Appl. Chem. 2003, 75, 39.
[19] C. H. Senanayake, D. Krishnamurthy, Z.-H. Lu, Z. Han, I. Gallou,
Aldrichimica Acta 2005, 38, 93.
[20] J. G. Tillet in The Chemistry of Sulphinic Acids, Esters and their De-
rivatives (Ed.: S. Patai), Wiley, New York, 1990, pp. 603–622.
[21] M. Reggelin, B. Junker, Chem. Eur. J. 2001, 7, 1232.
[22] T. P. Tang, S. K. Volkman, J. A. Ellman, J. Org. Chem. 2001, 66,
8772.
This work was partially supported by the Ministry of Education, Culture,
Sports, Science, and Technology (MEXT) under the Strategic Program
for Building an Asian Science and Technology Community Scheme and
World Premier International Research Center (WPI) Initiative on Mate-
rials Nanoarchitectonics, MEXT, Japan. We also thank the CSIR, India,
for financial support and R.C. thanks NIMS for the Internship award and
support for the research.
[1] A. Vinu, Adv. Funct. Mater. 2008, 18, 816.
[23] J. Hannam, T. Harrison, F. Heath, A. Madin, K. Merchant, Synlett
2006, 833.
[2] X. Jin, V. V. Balasubramanian, S. T. Selvan, D. P. Sawant, M. A.
Chari, G. Q. Lu, A. Vinu, Angew. Chem. 2009, 121, 8024; Angew.
Chem. Int. Ed. 2009, 48, 7884.
[3] S. H. Joo, S. J. Choi, I. Oh, J. Kwak, Z. Liu, O. Terasaki, R. Ryoo,
Nature 2001, 412, 169.
[4] D. Lee, J. Lee, J. Kim, J. Kim, H. B. Na, B. Kim, C. H. Shin, J. H.
Kwak, A. Dohnalkova, J. W. Grate, T. Hyeon, H. S. Kim, Adv.
Mater. 2005, 17, 2828.
[24] K. W. Kells, J. M. Chong, Org. Lett. 2003, 5, 4215.
[25] M. Furukawa, T. Okawara, Synthesis 1976, 339.
[26] T. Billard, A. Greiner, B. R. Langlois, Tetrahedron 1999, 55, 7243.
[27] F. A. Davis, Y. Zhang, Y. Andemichael, T. Fang, D. L. Fanelli, H.
Zhang, J. Org. Chem. 1999, 64, 1403.
[28] F. A. Davis, R. E. Reddy, J. M. Szewczyk, G. V. Reddy, P. S. Portono-
vo, H. Zhang, D. Fanelli, R. T. Reddy, P. Zhou, P. J. Carroll, J. Org.
Chem. 1997, 62, 2555.
[29] P. Zhou, B.-C. Chen, F. A. Davis, Tetrahedron 2004, 60, 8003.
[30] M. Uchino, M. Sekiya, Chem. Pharm. Bull. 1980, 28, 126.
[31] A. Cogan, G. Liu, K. Kim, B. A. Backes, J. A. Ellman, J. Am. Chem.
Soc. 1998, 120, 8011.
[32] J. Coulomb, V. Certal, L. Fensterbank, E. Lacꢂte, M. Malacria,
Angew. Chem. 2006, 118, 649; Angew. Chem. Int. Ed. 2006, 45, 633.
[33] M. Harmata, P. Zheng, C. Huang, M. G. Gomes, W. Ying, K. O. Ra-
nyanil, G. Balan, N. L. Calkins, J. Org. Chem. 2007, 72, 683.
[34] J. M. Klunder, K. B. Sharpless, J. Org. Chem. 1987, 52, 2598.
[35] Y. Watanabe, N. Mase, M. Tateyama, T. Toru, Tetrahedron: Asym-
metry 1999, 10, 737.
[5] M. Hartmann, Chem. Mater. 2005, 17, 4577.
[6] H. S. Zhou, S. M. Zhu, M. Hibino, I. Honma, M. Ichihara, Adv.
Mater. 2003, 15, 2107.
[7] a) A. Vinu, M. Miyahara, K. Ariga, Stud. Surf. Sci. Catal. 2005,
158B, 971; b) A. Vinu, M. Miyahara, K. Ariga, J. Phys. Chem. B
2005, 109, 6436; c) Y. Huang, H. Cai, T. Yu, X. Sun, B. Tu, D. Zhao,
Chem. Asian J. 2007, 2, 1282.
[8] J. H. Knox, B. Kaur, G. R. Millward, J. Chromatogr. 1986, 352, 3.
[9] T. Kyotani, T. Nagai, S. Inoue, A. Tomita, Chem. Mater. 1997, 9, 609.
[10] J. Lee, S. Yoon, T. Hyeon, S. M. Oh, K. B. Kim, Chem. Commun.
1999, 2177.
[11] R. Ryoo, S. H. Joo, S. Jun, J. Phys. Chem. B 1999, 103, 7743.
[12] a) A. Vinu, K. Z. Hossain, G. Satish Kumar, K. Ariga, Carbon 2006,
44, 530; b) M. Hartmann, A. Vinu, G. Chandrasekar, Chem. Mater.
2005, 17, 829.
[36] H. B. Yao, Y. Li, A. T. S. Wee, Appl. Surf. Sci. 2000, 158, 112.
[37] A. Taguchi, F. Schuth, Microporous Mesoporous Mater. 2005, 77, 1.
[13] A. Vinu, K. Z. Hossian, P. Srinivasu, M. Miyahara, S. Anandan, N.
Gokulakrishnan, T. Mori, K. Ariga, V. V. Balasubramanian, J. Mater.
Chem. 2007, 17, 1819.
Received: October 7, 2010
Revised: January 22, 2011
[14] H. Huwe, M. Frçba, Carbon 2007, 45, 304.
Published online: April 27, 2011
6682
www.chemeurj.org
ꢀ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2011, 17, 6673 – 6682