Metal-triflate ionic liquid systems immobilized onto mesoporous MS41 materials as new and efficient catalysts for N-acylation

Article abstract of DOI:10.1016/j.jcat.2007.04.022

Two kinds of MS41-immobilized ionic liquids (ILs) based on dihydroimidazolium and pyridinium cation were prepared using a grafting method. The second immobilization of triflate salts on these materials led to the immobilization of metal-triflate complexes into ILs. The materials thus obtained were characterized by ¹H NMR, XRD, N₂-sorption measurements, TG-DTA, DRIFT, XPS, TEM, and ICP-AES. The catalysts were tested in acylation of amines and sulfonamides and proved highly active and selective. For both aromatic and aliphatic amines, acylation with carboxylic acids was possible. For sulfonamides, acylation was possible only with anhydrides. Recycling the catalysts was not accompanied by any leaching of ILs or metal triflate.

Full text of DOI:10.1016/j.jcat.2007.04.022

Journal of Catalysis 249 (2007) 359–369
www.elsevier.com/locate/jcat
Metal-triflate ionic liquid systems immobilized onto mesoporous MS41
materials as new and efficient catalysts for N-acylation
Simona M. Coman a,d,∗, Mihaela Florea a,d, Vasile I. Parvulescu a, Victor David b,
Andrei Medvedovici b, Dirk De Vos c, Pierre A. Jacobs c, George Poncelet d, Paul Grange d
a
University of Bucharest, Faculty of Chemistry, Department of Chemical Technology and Catalysis, Bdul Regina Elisabeta 4-12, Bucharest 70346, Romania
b
University of Bucharest, Faculty of Chemistry, Department of Analytical Chemistry, Bdul Regina Elisabeta 4-12, Bucharest 70346, Romania
c
Katholieke Universiteit Leuven, Centre for Surface Chemistry and Catalysis, Kasteelpark Arenberg 23, B-3001 Leuven, Belgium
Université Catholique de Louvain, Unité de Catalyse et Chimie de Matériaux Divisés, Place Croix du Sud 2/17, B-1348, Belgium
d
Received 9 March 2007; revised 24 April 2007; accepted 26 April 2007
Available online 21 June 2007
Abstract
Two kinds of MS41-immobilized ionic liquids (ILs) based on dihydroimidazolium and pyridinium cation were prepared using a grafting method.
The second immobilization of triflate salts on these materials led to the immobilization of metal-triflate complexes into ILs. The materials thus
1
obtained were characterized by H NMR, XRD, N -sorption measurements, TG–DTA, DRIFT, XPS, TEM, and ICP-AES. The catalysts were
2
tested in acylation of amines and sulfonamides and proved highly active and selective. For both aromatic and aliphatic amines, acylation with
carboxylic acids was possible. For sulfonamides, acylation was possible only with anhydrides. Recycling the catalysts was not accompanied by
any leaching of ILs or metal triflate.
© 2007 Elsevier Inc. All rights reserved.
Keywords: Mesoporous materials; Ionic liquids; Metal triflate; Characterization techniques; Acylation; Amines; Sulfonamides
1. Introduction
use of insoluble solid acids. However, in this case the reaction
rate is small, and the acetylating agent is still acetic anhydride
[6]. Another solution involves metal triflates [7–12]; however,
in this case, although acetic acid is used as acylating agent and
the atom economy is high, the catalyst is soluble and difficult
to recover from the products.
Acylation of sulfonamides also has attracted a special at-
tention in organic syntheses because of the pharmacologic im-
portance of the products [13–15]. As in the case of amines,
most reports describe different approaches using both basic
[16–18] and acidic [19,20] reaction media, with anhydrides, es-
ters, or acyl chlorides as acylating agents. Unfortunately, the
acidic catalysts are sensitive to moisture and are easily decom-
posed or deactivated in the presence of even a small amount
of water. Furthermore, these Lewis acids cannot be recovered
and reused after the reactions are completed. Replacing these
acids with new water-compatible acids poses a significant chal-
lenge. Many organic transformations use rare-earth metal tri-
flates as Lewis acid catalysts [21–23]. Because of the aforemen-
tioned disadvantages, simplification of the acylation reaction
Amides represent an important family of intermediates
widely used in the synthesis of industrial chemicals, drugs, cos-
metics, and food additives. The reaction is usually performed
using acid anhydrides or acyl chlorides in the presence of sto-
ichiometric amounts of amine [1,2]. On the other hand, protic
and Lewis acids are well known to catalyze the acylation re-
action using acetic anhydride as an acetylating agent [3–5].
But using acetic anhydride as acetylating agent and soluble
bases or acids as reagents or catalysts causes important prob-
lems in the recovery of the catalyst and byproducts, leading to
<50% atom economy in the consumption of acetic anhydride.
Consequently, new methods to overcome the aforementioned
problems are of current interest. One such method involves the
*
Corresponding author.
E-mail addresses: s.coman@chem.unibuc.ro, simona_cmn@yahoo.com
(S.M. Coman).
0021-9517/$ – see front matter © 2007 Elsevier Inc. All rights reserved.
doi:10.1016/j.jcat.2007.04.022

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S.M. Coman et al. / Journal of Catalysis 249 (2007) 359–369
through the design of new strong heterogeneous acid catalysts
that can replace the conventional hazardous liquid- or tradi-
tional waste-generating Lewis-acid catalysts is very important.
In this context, room temperature ionic liquids (ILs) have at-
tracted special interest as acid catalysts in organic syntheses
[24–40]. However, the use of biphasic systems requires rela-
tively large amounts of IL, which may create some economic
and toxicologic concerns, because these compounds are expen-
sive in a potential process. Therefore, it is desirable to minimize
the amount of IL used. A solution in that direction is the “immo-
bilization” of ILs on stable, high-surface area materials. Actu-
ally, such an approach would extend the concept introduced by
supported liquid phase (SLP) catalysts [41]. As in that case, im-
mobilization aims to transfer the desired properties (inclusively
catalytic) of the ILs to a solid catalyst.
Several examples of immobilized IL-based catalysts have
been reported in the literature [42–52]. Compared with other
well-known acid catalysts (e.g., silica-alumina, zeolites), im-
mobilized ILs have several advantages. The most important of
these may be the easily tunable acidity, but the possibilities
presented by the choice of the support material and its proper-
ties (e.g., surface area and pore width) should not be neglected.
Furthermore, changing the length of side chains of the organic
cation can enhance the hydrophilicity or hydrophobicity of the
surface. Compared with pure ILs, immobilized ILs offer addi-
tional features; they facilitate the catalyst recovery and can be
used in gas-phase reactions.
MACl) was completely removed by calcination in air at 813 K
(heating rate, 1 K/min) for 10 h.
The grafting of 1-butyl-3-(3ꢀ-triethoxysilylpropyl)-4,5-dihy-
droimidazolium triflate was done in several steps:
Step (a) To 0.05 mol of N-3-(3ꢀ-triethoxysilylpropyl)-4,5-
dihydroimidazole (A), 0.15 mol of chlorobutane was added
dropwise, at room temperature, under stirring and nitrogen at-
mosphere. The mixture was then refluxed at 348 K for 21 h.
Then the volatiles were evaporated under vacuum to remove
any unreacted chlorobutane and imidazole compound. The re-
sulting 1-butyl-3-(3ꢀ-triethoxysilylpropyl)-4,5-dihydroimidaz-
olium chloride (B) was first washed with pentane and dried
under vacuum, and then extracted in dichloromethane and fil-
tered through a bed of active carbon and alumina (previously
dried at 423 K under vacuum). The residual volatile compounds
were removed under reduced pressure (30 mbar) at 353 K.
Step (b) The 1-butyl-3-(3ꢀ-triethoxysilylpropyl)-4,5-dihydro-
imidazolium chloride compound (0.016 mol) was dissolved in
acetonitrile and stirred with 1 equivalent of NaOTf for 4 days
under nitrogen atmosphere, at room temperature. Then the
light-yellow slurry was filtered through a bed of Celite to re-
move the precipitate. After the evaporation of the volatile com-
pounds under reduced pressure at 353 K, the product was ex-
tracted in dichloromethane and filtered through a bed of active
carbon and alumina. Finally, the volatile compounds were re-
moved under reduced pressure at 353 K. The resulting product
was the IL 1-butyl-3-(3ꢀ-triethoxysilylpropyl)-4,5-dihydroim-
idazolium triflate (C).
To avoid the aforementioned problems, the present work
combines the properties of ILs and metal triflates and proposes
new catalysts in which complex metal triflate–IL systems are
immobilized onto MS41 mesoporous supports using a grafting
method. They provide green, stable, recyclable heterogeneous
catalysts for the acylation of amines (with acetic acid) and sul-
fonamides (with acetic anhydride) under green conditions and
with very high atom economy. The synthesis of these green cat-
alysts and their characterization confirming the immobilization
is described.
1
The results of H NMR done on the unsupported IL, 1-bu-
tyl-3-(3ꢀ-triethoxysilylpropyl)-4,5-dihydroimidazolium triflate,
are in agreement with the 1H NMR results of Afeworki et
al. [47] obtained for 1-butyl-3-(3ꢀ-triethoxysilylpropyl)-4,5-
dihydroimidazolium tetrafluoroborate, demonstrating that the
synthesis of the triflate IL was successful: 1H NMR (300
MHz): 0.59 (m, 2H, –CH2–CH2–Si); 0.93 (tr, 3H, J = 8.1 Hz,
CH2–CH2–CH3, n-butyl); 1.20 (tr, 9H, J = 7.6 Hz, CH3–CH2–
O–Si); 1.34 (m, 2H, CH2–CH2–CH3, n-butyl); 1.60 (m, 2H,
CH2–CH2–CH3, n-butyl), 1.70 (m, 2H, CH2–CH2–Si); 3.41
(m, 4H, Si–CH2–CH2–CH2–N; N–CH2–CH2–N–Bu); 3.80 (m,
6H, CH3–CH2–O); 3.88 (m, 4H, N–CH2–CH2–CH2–CH3; N–
CH2–CH2–N–Bu); 7.98 (s, 1H, N–CH–N) ppm.
2. Experimental
2.1. Catalyst preparation
The MCM-41 support was prepared following the well-
reported procedure using cetyltrimethylammoniumchloride
(CTMACl) as a structure-directing agent [53]. The Si:TEAOH
(tetraethylammoniumhydroxide):CTMACl:H2O molar compo-
sition of the gel was 1.00:0.223:1.17:29.125. To 19.27 g of
LUDOX AS-40 (DuPont, 40 wt% colloidal silica in water) were
added 19.43 g of tetraethylammoniumhydroxide (TEAOH)
(20% in water) and 16.16 g of cetyltrimethylammoniumchlo-
ride (CTMACl). The resulting gel was kept for 15 min under
stirring, after which another 32.33 g of CTMACl was added.
The white precipitate was parted in two Teflon-lined autoclaves
and allowed to age for 24 h at 383 K. The solid was filtered
under vacuum, thoroughly washed with water and hot ethanol,
and dried for 24 h at 333 K. The structure-directing agent (CT-
Step (c) First, 1.6 mmol of IL (C) was reacted with 1 g of
MCM-41 support in 100 mL of chloroform at reflux conditions
under stirring for 24 h. The unreacted molecular species were
removed by successive washings of the solid material with pen-
tane, acetonitrile, and diethyl ether. The separated solid was
finally dried under vacuum (30 mbar) at 373 K overnight, re-
sulting in IL-MCM [(D) in Scheme 1].
Step (d) IL-MCM (0.804 mmol IL) was mixed with 1 mmol
of Zn(SO3CF3)2 dissolved in 100 mL of acetonitrile, and stirred
at room temperature for 21 h. The solid thus obtained was sepa-
rated by filtration and washed with large amounts of acetonitrile
to remove weakly bound species. The solid was dried first at

S.M. Coman et al. / Journal of Catalysis 249 (2007) 359–369
361
Scheme 1. Grafting of the imidazolium based ionic liquid onto MCM-41 support (IL-MCM sample).
Scheme 2. Grafting of the pyridinium based ionic liquid onto MCM-41 support (OTf-MCM sample).
room temperature and then at 373 K overnight. The resulting
sample was designated ZnIL-MCM.
A similar procedure was followed for the preparation and
immobilization of scandium triflate in supported 1-butyl-3-
(3ꢀ-triethoxysilylpropyl)-4,5-dihydroimidazolium triflate. This
sample was designated ScIL-MCM.
The chloropropylated solid was then treated with an excess of
pyridine (2 g of pyridine for every 1 g of chloropropylated
solid) and heated under reflux for 24 h. Then the slurry was
cooled to room temperature, at which point the solid was sepa-
rated by filtration, washed with 100 mL of toluene, and finally
dried under ambient conditions. The solid was then treated with
1 equivalent of NaOTf, and the mixture was stirred at room
temperature under nitrogen atmosphere for 4 days. The solid
was filtered, washed with methanol, and dried under reduced
pressure (30 mbar). The resulting sample was designated OTf-
MCM.
2.1.1. Grafting of the (3-chloropropyl)trimethoxysilane
First, 1.6 mmol of (3-chloropropyl) trimethoxysilane was
dissolved in 100 mL of chloroform, and 1 g of MCM-41 was
added. The slurry was heated under reflux for 24 h and then
cooled to room temperature, at which point the solid was sep-
arated by filtration; washed with 50 mL of pentane, 100 mL of
acetonitrile, and 100 mL of diethyl ether; and dried under vac-
uum, resulting in the intermediate Cl-MCM (see Scheme 2).
Scandium triflate and zinc triflate were anchored on OTf-
MCM by treating it with 1 mmol of Sc(SO3CF3)3 [or Zn(SO3-
CF3)2] dissolved in 100 mL of acetonitrile and stirred at room
temperature for 21 h. After reaction, the catalyst was separated

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S.M. Coman et al. / Journal of Catalysis 249 (2007) 359–369
by filtration and washed with large amounts of acetonitrile to
remove weakly bounded species. The solid sample was then
dried at room temperature and at 373 K overnight. These sam-
ples were designated ScOTf-MCM and ZnOTf-MCM.
Elemental analyses were performed by atomic emission spec-
troscopy with inductively coupled plasma atomization (ICP-
AES).
For comparison, the MCM-41 materials impregnated with
scandium and zinc triflate were also tested. The impregnation
procedure was similar to those used for the impregnation of
the IL-MCM and OTf-MCM samples with triflate species. The
resulted samples were designated Sc-MCM and Zn-MCM, re-
spectively. Furthermore, to check whether the porosity of the
support had any influence on the catalytic performance, silica
also was impregnated with the same amounts of triflates. The
samples thus obtained were designated Sc-SiO2 and Zn-SiO2.
2.3. Catalytic tests
Acylation of amines The acylation reactions were carried out
under solvent-free conditions in a closed system (glass vials
with stirring) at amine: acylating agent molar ratio of 1:10. Dif-
ferent amines were used as substrates, including n-butylamine,
1-pentylamine, hexylamine, N-methyl-cyclohexylamine, ani-
line, and 2-ethylaniline. Acetic, propionic, and n-butyric acids
were used as acylating agents. The reaction temperatures were
room temperature and 80 ◦C. After the reaction was stopped,
the catalyst was filtered and the product separated. The product
was then analyzed by GC–MS.
2.2. Catalyst characterization
1H nuclear magnetic resonance of 1-butyl-3-(3ꢀ-triethoxysilyl-
propyl)-4,5-dihydroimidazolium triflate Routine analysis was
performed on a 300-MHz AMX-Bruker spectrometer, with
TMS as the internal standard and CD3CN as the solvent.
Acylation of sulfonamides In a typical procedure, a mixture
of sulfonamide (1.25 mmol), acylating agent (3.75 mmol), and
catalyst (15 mg) in THF or acetonitrile (4 mL) as the solvent,
was stirred at 80 ◦C for 18 h. Different sulfonamides were used
as substrates: benzenesulfonamide, 4-nitrobenzenesulfonamide,
4-methoxybenzenesulfonamide, and N-phenylmethanesulfona-
mide. Acetic acid and acetic anhydride were used as acylating
agents. After the reaction was stopped, the catalyst was filtered
and the product separated from the solvent by vacuum distil-
lation at 80 ◦C. The resulting product, a crystalline solid, was
then redissolved in the HPLC eluent and analyzed. The prod-
ucts were characterized by HPLC–MS.
X-ray diffraction XRD patterns were recorded with a Siemens
D5000 Matic diffractometer equipped with a CuKα radiation
source. The diffractograms were recorded between 1◦ and 35◦
2θ at a scanning speed of 1◦(2θ)/min.
N2 sorption measurements Adsorption and desorption iso-
therms of N2 at 77 K were recorded with a Micromeritics ASAP
2010 device. Before measurement, the samples were outgassed
overnight at 373 K under vacuum.
2.4. Analysis of the reaction products
Diffuse reflectance infrared Fourier transform spectroscopy
DRIFTS spectra were collected with a Bruker IFS88 spectrom-
eter (200 scans with a resolution of 4 cm−1). Pure samples were
placed inside a commercial controlled environment chamber
(Spectra-Tech 0030-103) attached to a diffuse reflectance ac-
cessory (Spectra-Tech collector).
Amine acylation products The analytical system used to fol-
low the changes in the concentrations of the components in the
reaction mixture comprised a Hewlett Packard 5880A gas chro-
matograph equipped with an HP 7673A automatic sample in-
jector, a flame ionization detector (FID), and a capillary column
(50 m long, 0.32 mm i.d., 1.20 µm film thickness). The reaction
products were identified using a MD 800 mass spectrometer
from Fisons Instruments (EI+-ionization at 70 eV, mass max.
500–600) coupled to a gas chromatograph with a Chrompack
CP-SIL 5CB column.
XPS spectroscopy XPS spectra were recorded using a SSI
X-probe FISONS spectrometer (SSX-100/206) with monochro-
mated AlKα radiation. The spectrometer energy scale was cal-
ibrated using the Au4f peak. For calculation of the binding
7/2
energies, the C1s peak of the C–(C, H) component at 284.5 eV
was used as an internal standard. The peaks assigned to the F1s,
O1s, N1s, C1s, S2p, and Si2p levels were quantitatively analyzed.
Sulfonamide acylation products HPLC–MS measurements
were performed with an Agilent 1100 liquid chromatograph
composed of a degasser, quaternary pump, thermostated au-
tosampler, column thermostat, atmospheric pressure chemical
ionization interface (APCI), ion trap mass spectrometric detec-
tor (SL series), and nitrogen generator.
TG–DTA TGA curves were recorded with a SETARAM TGA
92 device (293–1.273 K, 2.5 K/min, 50 mL/min of air).
Transmission electron microscopy Transmission electron mi-
croscopy (TEM) measurements were performed by placing the
materials on a special structured 4-nm-thick carbon support
film. (These thin films are sufficiently stable to cover copper
grids with a mesh of 60 µm without an additional holey organic
film.) The electron microscopy investigation was carried out on
a Siemens Elmiskop 102 instrument.
Chromatographic conditions A monolithic Chromolith Per-
formance RP-18e (Merck, Germany; 100 mm long, 4.6 mm i.d.)
was used. The column was thermostatted at 40 ◦C. Elution was
isocratic with a flow rate of 0.8 mL/min, using a mobile phase
comprising 35% methanol and 65% of 0.1% formic acid solu-
tion.

S.M. Coman et al. / Journal of Catalysis 249 (2007) 359–369
363
Interface parameters The parameters controlling the APCI
interface were as follows: drying gas flow, 10 L/min; drying
gas temperature, 350 ◦C; pressure of the nebulizer gas pressure,
60 psi; capillary voltage, 4500 V; and high-voltage end plate
offset, −500 V. All solvents used were HPLC grade from Merck
KGaA (Darmstadt, Germany).
The tethering of IL induced some slight differences in the
XRD patterns, however. The pattern of the OTf-MCM sample
contained the dominant d100 reflection, but with the long-range
order lines merged together into a broad peak. The lower inten-
sity of the d100 peak compared with MCM-41 is characteristic
of all grafted organo-ordered silicas. Treatment with Sc(OTf)3
or Zn(OTf)2 was not accompanied by any characteristic line of
the metallic compound, indicating that indeed the final material
contained only dispersed docked species. These samples cor-
respond to the textural characteristics of the hybrid materials
presented in Table 1.
Nitrogen adsorption–desorption isotherms of the materials
showed typical type IV shapes as generally reported for meso-
porous materials. However, as for the XRD patterns, differences
among these were observed. These correspond to the values
presented in Table 1. The variation of the surface areas ran par-
allel with the intensity of the d100 line observed in the XRD
patterns. Thus, for sample IL-MCM, a drastic reduction in the
surface area was observed compared with the parent MCM-
41. This drop may be related to the blocking of the pores
by 1-butyl-3-(3ꢀ-triethoxysilylpropyl)-4,5-dihydroimidazolium
triflate IL (which penetrated inside).
3. Results and discussion
1
As shown in Section 2, H NMR analysis of the 1-butyl-3-
(3ꢀ-triethoxysilylpropyl)-4,5-dihydroimidazolium triflate dem-
onstrated successful synthesis of the triflate IL. Powder XRD
patterns of IL-MCM and OTf-MCM, presented in Fig. 1, ex-
hibit only the diffraction lines of the MS41 structure, namely
mesoporous materials with two-dimensional hexagonal sym-
metry (honeycomb structure), providing good evidence that the
structure of the mesoporous materials was preserved through-
out all of the treatments to which these materials were exposed
(i.e., tethering, extraction of the structure directing agent).
The volume developed by the mesopores and the pore di-
ameter decreased in the same way as the surface area. Even
so, after grafting of the IL, the textural characterization indi-
cated that larger mesopores also were created. A reduction in
pore size also occurred. Moreover, during the grafting process,
a fraction of IL may have become attached to the external sur-
face of MCM-41 and part of the mesopores may have been
destroyed in this process, leading to the formation of macro-
pores.
TEM images of the materials confirmed the mesoporous
structure even after grafting of the organic functionality (Figs.
2a and 2b).
DRIFTS analysis of IL-MCM confirmed that the grafting
of IL resulted in functionalized materials with intact organic
groups. Table 2 summarizes all of the bands identified for
MCM-41 and IL-MCM-41.
Fig. 3 shows the change in the Si–OH stretching band at
3745 cm−1 before and after docking of the ILs. The disappear-
ance of this band, accompanied by the appearance of all of the
characteristic bands of IL, constitutes strong evidence for the
nondestructive tethering of these substrates. Moreover, this dis-
appearance indicates full coverage of the MCM support with
the IL.
Table 3 presents the binding energies (in eV) of the main el-
ements of the IL-MCM-41 catalyst, along with the atomic XPS
and chemical F/S, N/S, S/Si, and N/Si ratios. Unfortunately, the
2p1 binding energy of Sc is superimposed with the 1s signal of
N, and the deconvolution of the peaks does not provide accurate
results.
It is already known that the physical and chemical proper-
ties of ILs can be altered by the presence of impurities arising
from their preparation. Thus, purification of the IL is essential.
The main contaminants are halide anions or organic bases that
generally come from unreacted starting material. The halide
impurities can have a detrimental effect on transition metal-
Fig. 1. XRD diffractograms for IL-MCM, ScIL-MCM, ZnIL-MCM and OTf-
MCM samples.
Table 1
Surface area and mesoporous volume of some catalytic samples
Sample
S
V
Pore diameter (nm)
(BJH method)
p meso
3
BET
2
(m /g)
(cm /g)
MCM-41
IL-MCM
OTf-MCM
ScOTf-MCM
544
90
304
258
0.195
0.030
0.110
0.090
2.7
2.2(+3.5)
2.7(+4.2)
2.7(+4.2)

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S.M. Coman et al. / Journal of Catalysis 249 (2007) 359–369
Table 2
Frequency and group assignments for the IL-MCM sample
Wavenumber
Group assignment
MCM-41
Comment
−1
(cm
)
IL-MCM-41
3745 (s)
Free silanol hydroxyl band, str.
Bridged silanols, str.
–
Si–OH stretching (sharp band)
Si–OH groups with strong hydrogen-bonding interaction (broad band)
Molecular adsorbed water
C–H asymmetric stretching
C–H (a)symmetric stretching
3730–3500 (s)
3500–3400
2969 (m)
2937–2882 (m)
1873 (w)
1662 (s)
Bridged silanols, str.
H O–SiOH
–OCH –, asym. str.
–CH – str. (asym. and sym.)
H O –SiOH
2
2
–
–
2
2
–Si–O–, str.
–
–Si–O–, str.
Stretching, combination band
–C=N, str.
1632 (m)
1530
–OH (H O)
–OH (H O)
Bending OH, molecular water
2
2
–
SO CF
3 3
1451
–
–OCH –, str.
2
Asymmetric bending
1250–1000
–Si–O–Si–
–Si–O–Si– and Si–C
Asymmetric stretching mode
(a)
Fig. 3. DRIFT spectra of MCM-41, IL-MCM-41, and OTf-MCM samples.
bonded and that no residual IL remained. The comparison of
the N/Si analytical ratio with the N/Si XPS ratio is consistent
with an agglomeration of the IL on the surface of the meso-
porous support (see Table 3), which is in complete agreement
with expectation and with the XRD and N2 sorption measure-
ments. The F/S ratio of 2.61–2.84, as determined by XPS, also
confirms the preservation of the triflate structure (the theoretical
F/S ratio in the triflate structure is 3) in IL-supported samples
designated as IL-MCM and OTf-MCM.
The triflate anion also could be docked directly to MCM via
ionic interactions with the surface hydroxyl groups, generating
species as in Scheme 3 [54]. Such a direct interaction of the
triflate salt with the support surface determines the increase of
the S/Si XPS ratio (Table 3, entry 10). On the other hand, the
absence of hydroxyl groups after grafting of the IL makes such
interactions impossible. Therefore, the increased S/Si XPS ratio
is merely an indication of the presence of the triflate salt in the
final catalyst, which can be immersed into the grafted IL.
(b)
Fig. 2. TEM microscopy of the MCM-41 (a) and IL-MCM (b) samples.
catalyzed reactions. With respect to this, it is very important
to note that the XPS spectra of the supported ILs showed no
peak that can be associated with the binding energy of chlorine.
This result also demonstrates that all of the IL was covalently

S.M. Coman et al. / Journal of Catalysis 249 (2007) 359–369
365
Moreover, the analytical analysis (ICP-AES) of Sc and Zn
indicated good concordance with the theoretical values. Indeed,
the concentration of these two elements established by ICP-
AES was 3.3 wt% for Sc and 5.1 wt% for Zn, whereas the
theoretical amount corresponding to the metal content in ILs
was 4.0 wt% for Sc and 6.5 wt% for Zn.
Quantitative determination of the organic content in the hy-
brid mesoporous silicas was done by thermogravimetric analy-
sis (TGA) in air. Fig. 4 shows the weight loss curves of the
grafted samples. The large exothermic peak at 370–380 ◦C is
related to decomposition of the organic moiety, with losses of
45.6 wt% for IL-MCM and 59.4 wt% for ScIL-MCM (Fig. 4).
The theoretical amounts of the organic moiety were 43.5 wt%
for IL-MCM and 50.4 wt% for ScIL-MCM. Due to the de-
hydroxylation of the Si–OH groups, a small weight loss was
detected at higher temperatures. Thus, the TGA analysis shows
perfect concordance between the amount of the IL grafted on
the surface and the theoretical amount.
Table 3
Binding energies (eV) of the main elements of the IL-MCM, ScIL-MAM,
ZnIL-MCM and OTf-MCM catalysts, and XPS and calculated N/Si ratio
Element B.E. (eV)
IL-MCM-41 ScIL-MCM-41 ZnIL-MCM-41 OTf-MCM-41
Zn
–
–
1020.6
686.8
531.0
399.2
291.9
167.3
102.8
–
2p
F
687.4
531.5
399.7
291.4
167.6
102.4
686.9
531.3
399.7
291.2
167.6
102.2
687.4
531.4
399.6
291.3
167.7
102.4
1s
O
N
C
1s
1s
1s
S
2p
Si
2p
F/S
2.84
2.64
2.61
2.89
N/S
S/Si
1.85
0.15
0.75
0.45
0.66
0.41
0.89
0.16
Scheme 3. Possible docking of scandium triflate onto MCM-41 surface via ionic
interactions with the surface hydroxyl groups.
Note. N/Si (XPS) = 0.278; N/Si (calc.) = 0.070.
Fig. 4. TGA and DTA curves for ILs grafted onto the surface of the MCM-41 support (IL-MCM: weight loss—45.63%, theoretical—43.46%; ScIL-MCM: weight
loss—59.39%, theoretical—50.97%; OTf-MCM: weight loss—37.72%, theoretical—36.62%).

366
S.M. Coman et al. / Journal of Catalysis 249 (2007) 359–369
Scheme 4 gives a picture of the prepared catalysts based on
The IL-MCM and OTf-MCM catalysts were slightly more
active than the Zn-MCM or Sc-MCM catalysts. No synergistic
effect between metal triflate and IL was observed in this case.
Practically, these results provide no evidence of the contribution
of metal triflate in these reactions. The acylation of aniline in
the presence of immobilized IL led to high selectivity, reaching
100% in the presence of acetic acid, irrespective of the catalysts.
Comparing the results of MCM-immobilized triflates salts
[e.g., Sc-MCM or Zn-MCM (entries 1, 2, 7, 8, 13, and 14 in
Table 5)] and IL-MCM-immobilized triflate salts [e.g., ScIL-
MCM and ZnIL-MCM samples (entries 4, 5, 10, 11, 16, and 17
in Table 5)] shows that after 21 h, higher selectivities were ob-
the results of the characterization techniques.
Table 4 reports the results obtained in the acylation of ani-
line with acetic and propionic acid in the presence of Zn-MCM,
Sc-MCM, Zn-SiO2, and Sc-SiO2 at room temperature. Under
these conditions and with these catalysts, the reaction rate was
quite low; after 23 h, the conversion of aniline was <25%. In
addition, selectivity to the amide was not satisfactory, <90% in
all cases. The data obtained from these reactions gives infor-
mation about the influence of the nature of the support as well.
Therefore, as Table 4 shows, higher conversions are obtained
for the silica-based catalysts than for the MCM-based sam-
ples. The increased conversions obtained for the silica-based
catalysts should be coupled with lower selectivities than those
obtained with MCM-based samples. These results clearly show
that the nature of the support is also important in such reactions.
Heating the mixture at 80 ◦C led to an important increase
of the reaction rate; under these conditions, the reaction with
butyric acid was also possible. Of note, the increased activity
was accompanied by an increase in selectivity, with only the
amide detected (Table 5).
Table 5
Conversion of aniline in the presence of triflate salts-MCM and ionic liquids
◦
based catalysts (aniline/acylating agent = 1/10, 21 h, 80 C)
Entry
Catalyst
Acylating agent
Conversion
Selectivity
(%)
to amide (%)
a
1
2
3
4
5
6
Sc-MCM
Zn-MCM
IL-MCM
ScIL-MCM
ZnIL-MCM
OTf-MCM
Acetic acid
79.5(100)
100
100
100
100
100
100
a
79.2(90.2)
85.8(97.6)
83.3(96.0)
84.2(96.0)
82.1(92.3)
a
a
a
a
Table 4
The acylation of aniline in the presence of MCM-41 and SiO impregnated
with scandium and zinc triflates (RT, aniline/acylating agent molar ratio of 1/10,
23 h)
2
7
8
9
10
11
12
Sc-MCM
Zn-MCM
IL-MCM
ScIL-MCM
ZnIL-MCM
OTf-MCM
Propionic acid
Butyric acid
73.5
72.9
79.2
77.5
78.0
78.7
85.8
81.3
88.2
90.6
92.4
94.2
Entry
Catalyst
Acylating agent
Conversion
(%)
Selectivity
to amide (%)
1
2
3
4
Zn-MCM
Sc-MCM
Acetic acid
17.2
21.2
22.3
24.6
87.8
67.0
51.6
50.1
13
14
15
16
17
18
Sc-MCM
Zn-MCM
IL-MCM
ScIL-MCM
ZnIL-MCM
OTf-MCM
54.7
53.2
58.4
59.8
57.4
55.2
92.3
91.6
93.7
95.0
96.1
95.1
Zn-SiO
2
Sc-SiO
2
5
6
7
8
Zn-MCM
Sc-MCM
Propionic acid
14.7
11.2
18.3
14.9
73.8
21.1
60.1
15.2
Zn-SiO
2
Sc-SiO
2
a
Conversion (%) after 40 h.
Scheme 4. Ideal picture of the catalyst based on the results of the characterization techniques.

S.M. Coman et al. / Journal of Catalysis 249 (2007) 359–369
367
Table 6
◦
Acylation of different kinds of amines in the presence of acetic acid (amine/acetic acid = 1/10, 80 C, 24 h)
Amine
Sc-MCM
IL-MCM
ScIL-MCM
C (%)
C (%)
S (%)
C (%)
S (%)
S (%)
n-Butylamine
n-Pentylamine
n-Hexylamine
2-Ethylaniline
4.24
5.52
4.86
37.66
22.03
83.02
85.14
97.72
97.89
85.88
18.3
6.63
6.66
41.35
20.25
93.58
83.19
89.74
100
100
100
100
45.79
97.32
95.22
96.32
98.18
100
95.94
N-methyl-cyclohexyl-amine
95.60
Table 7
Acylation of sulfonamides
−1 a
Entry
1
R
R
Solvent
TOF (h
)
Yield (%)
1
H
CH CN
161.4
85.0
3
2
3
CH –
CH CN
65.4
68.7
77.6
3
3
H
CH CN
147.6
3
4
5
6
H
H
CH CN
3
159.7
82.8
61.3
73.3
43.4
32.2
THF
THF
CH –
3
7
H
H
THF
THF
79.0
74.4
41.5
39.1
8
a
mmol of transformed substrate/(mmol of active phase × time).
tained with IL-MCM-immobilized triflate salts. As mentioned
above, the reaction was also done with propionic and n-butyric
acids as acylation agents, resulting in satisfactory conversions
and selectivities (e.g., for propionic acid, a conversion of 90–
95% reached after 50 h).
Table 6 gives the results collected for the same catalysts in
the acylation of different acyclic and cyclic amines with acetic
acid. The results demonstrate that conversion depended on the
length of the aliphatic chain. However, for the acylation of
these substrates, a synergistic effect of the presence of IL and
metal triflates was found. Indeed, the conversion was improved
from several percent on Sc-MCM and IL-MCM to 100% on
ScIL-MCM. The best selectivities to N-monoacylamine were
obtained in the presence of ScIL-MCM. The decreased selec-
tivity to N-monoacylamine amide is due to formation of the
N,N-diacylamines.
For the acylation of sulfonamide, an initial screening was
conducted at 80 ◦C using combinations of two solvents (CH3-

368
S.M. Coman et al. / Journal of Catalysis 249 (2007) 359–369
CN and THF), two acylating agents (acetic anhydride and acetic
acid), and six catalysts. Under these conditions, no acylation of
sulfonamide with acetic acid was observed. Using acetic an-
hydride as the acylating agent, the best results were obtained
using ScIL-MCM in CH3CN. These results can be attributed
to the solvent’s ability to stabilize the acylium intermediate.
To provide a general method of access into the acylated sul-
fonamides, this method was applied to a set of sterically and
electronically diverse sulfonamides. As shown in Table 7, the
reaction gave generally high yields and worked on most of the
substrates tested. Generally, the electronic nature of the sulfon-
amide had little effect on the efficiency of the process, whereas
the steric bulk had a greater influence.
Supplementary material
The online version of this article contains additional supple-
mentary material.
Please visit doi:10.1016/j.jcat.2007.04.022
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