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SYNTHESIS OF MONOGLYCERIDES WITH MESOPOROUS SULFONIC ACIDS
157
HMS-SH by co-condensation. HMS-SH was synthe-
sized at room temperature from a gel containing 0.8 TEOS,
0.2 MPTS, 0.275 n-dodecylamine, 8.9 EtOH, 29.4 H2O. The
amine was first dissolved in the alcohol–water mixture.
Then the TEOS-MPTS mixture was added and the mix-
ture was stirred for 24 h. The amine template was extracted
from the as-synthesized HMS-SH with boiling EtOH.
SCHEME 1
components include Ludox AS 40, 25% cetyltrimethy-
lammonium chloride (CTMACl, Aldrich), and 20 wt%
tetraethylammonium hydroxide (TEAOH, Aldrich). In the
standard procedure 19.43 g TEAOH, 16.16 g CTMACl, and
20 ml H2O were added to 19.27 g Ludox AS 40 under stir-
ring (200 rpm). After 15 min, 32.33 g CTMACl and 20 ml
H2O were added to the reagent mixture. The synthesis gel
was agitated for another 15 min and divided over two auto-
claves. The hydrothermal step was carried out dynamically
at 383 K. The resulting white product was filtered, washed
extensively with hot H2O and EtOH, dried at 333 K in air,
and finally calcined at 823 K for 12 h.
Oxidation procedure and acidification. Materials with
immobilized mercaptopropyl groups were oxidized with
H2O2 in a methanol–water mixture. Typically, 2.04 g of
aqueous 35% H2O2 dissolved in three parts of methanol
was used per g of material. After 24 h, the suspension was
filtered, and washed with H2O and EtOH. The wet ma-
terial was resuspended (1 wt% ) in acidified H2O (H2SO4;
0.1 M) for another 4 h. Finally, the materials were exten-
sively rinsed with H2O, dried at 333 K, and stored in a desic-
cator. These acid-activated materials are denoted with the
suffix -SO3H. The oxidation procedure is slightly different
from the one published previously (14). 13C-MAS-NMR
proves that the current procedure leaves no –SH or –S-S-
groups on the surface; the only signals are those of hetero-
genized -(CH2)3SO3H.
Propylsulfonic acid mesoporous silicas. Mesoporous
silicas were modified with a 3-mercaptopropyl group using
(3-mercaptopropyl)trimethoxysilane (MPTS, Fluka) as the
organosulfonic acid precursor (see Scheme 1). Deposition
of MPTS in toluene onto a support with controlled water
content results in a “coated” material with a monolayer of
MPTSmoieties, while less-covered “silylated” materialsare
obtained in dry conditions. Alternatively, in the synthesis
of a HMS (hexagonal mesoporous silica), organofunctional
groups are directly incorporated by “co-condensation” of
MPTS and the main Si source (TEOS) in the presence of a
neutral surfactant. Representative recipes for the different
synthesis procedures are based on literature examples (14,
15, 18, 19) and are given below.
Catalyst recuperation for reuse. After reaction the cata-
lyst was allowed to sink to the bottom of the reactor at
333 K. After 5 h, the reaction liquor was decanted. The
catalyst was resuspended in EtOH and centrifugated. This
washing procedure was repeated five times, and the catalyst
was finally dried at 333 K.
Characterization. XRD analyses were performed with
a Siemens D5000 diffractometer. Loadings with organic
groups (meq g 1) were routinely determined from ther-
mogravimetric analysis and were calculated based on the
weight loss between 423 and 573 K. A Coulter Omnisorp
100 apparatus was employed for N2 sorption experiments.
A combination of XRD and sorption experiments was used
throughout to evaluate the materials after modification or
after reaction. XRD proved that the hexagonal structure
of the ordered mesoporous materials did not undergo ma-
jor changes. Some sorption characteristics are included in
Table 1.
Coated MCM-41-SH. Calcined MCM-41 (3.5 g) is hy-
drated by refluxing for 3 h in 500 ml water and removed
from the suspension by filtration. The wet filter cake is sus-
pended in toluene (300 ml) in a Dean Stark apparatus, and
H2O/toluene is removed until a translucent suspension is
obtained (approximately 100–150 ml). An excess of MPTS
(20.0 g) is added and after stirring overnight without heat-
ing, the suspension is refluxed for 3 h. The coated material
is then washed in a soxhlet extractor with CH2Cl2/Et2O
(50/50) for 24 h and air-dried.
Other solid Brønsted acid catalysts. H-USY (CBV 720
from PQ; Si/Al = 14.5) was activated in a quartz tube under
1
an air flow. The zeolite was heated with a slope of 1 K min
Silylated MCM-41-SH. Calcined MCM-41 (3.5 g) is
evacuated (overnight, 393 K, <10 Pa) and added to a solu-
tion of MPTS (7.4 g) in 300 ml toluene. Toluene was dried
over zeolite 4A before use. After 4 h refluxing, the powder
is collected and subjected to the same soxhlet purification
as the previous material.
and kept at 773 K for 12 h. Amberlyst-15 was a commercial
product from Fluka (4.6 meq g 1). This sulfonic acid resin
was thoroughly washed with H2O to remove all residual
homogeneous acid and dried after Dean Stark extraction
with toluene.
Esterification Procedures
Coated silica gel-SH. This was prepared by modifying
a chromatographic silica gel 60 (70–230 mesh, Fluka) with
MPTS following the same method as used to coat MCM-41. 1 : 1) were added to a 100-ml round bottom flask. After
First, 12.6 g glycerol and 27.4 g lauric acid (molar ratio =