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makes it difficult to control the dispersion of the particles.
The second approach is based on the in situ formation of
the guest particles in the presence of the pre-formed
polymer. The drawback of these two first approaches is that
the polymerization of the organic monomer and the for-
mation of the inorganic particles are carried out separately,
so that a uniform particle dispersion and a narrow particle
size distribution are difficult to achieve. The third route
relies on the dispersion of monomer solution in the host
particles (or the precursor of the host matrix), which is then
polymerized. This latter approach, by affording intimate
and even chemical mixing of the two components already
in the starting solution, favors a highly homogeneous dis-
persion of the polymer in the host particle matrix. This
uniform distribution can be further improved by suitable
functionalization of the building blocks and careful opti-
mization of the experimental parameters, such as the molar
ratios among the precursors, the polymerization route and
time. In spite of the advantages of the third way, only a few
studies have been performed in this field.
green medium [25]. Another approach is to develop new
processes involving solvent-free reactions. These methods
have many advantages such as reduced pollution, lower
cost, and simple processing that are beneficial to the
industry as well as to the environment [26]. The use of
environmentally benign solvents like water [27] and the
application of solvent-free reactions represent very pow-
erful green chemical technology procedures from both
economic and synthetic points of view. Not only do they
reduce the burden of organic solvent disposal, but they may
also enhance the rates of many organic reactions. Efforts
have been made to perform the Knoevenagel condensation
in aqueous media as well as in the absence of solvents
[28, 29]. Some of these reactions are performed on solid
supports, promoted by infrared [30], ultrasound, or micro-
wave heating [31].
In this work, we wish to report the synthesis of poly(4-
vinylpyridine) (P4VP) supported on SBA-15 by the poly-
merization of 4-vinylpyridine in the presence of SBA-15.
The use of the poly(4-vinylpyridine)/SBA-15 (P4VP/SBA-
15) composite as an active catalyst in organic synthesis is
also studied. The basic catalytic activity of this novel
organic–inorganic hybrid in the Knoevenagel condensation
reaction when water was used as solvent was tested. The
large surface area of SBA-15 causes this novel compound
to act as an efficient basic catalyst.
Probably the most important advantage of using a
composite functionalized polymer as a reagent or a catalyst
is the simplification of the product work-up, its separation,
and its isolation with high reactivity. On the other hand,
this support has an important role in the activity of the
composite. One of the best supports with large surface area
and catalytic activity is SBA-15. SBA-15 is an inorganic
oxide material in the form of mesoporous silica molecular
sieves with uniform, long, connecting tubular channels
with variable pore sizes (5–30 nm) and a large surface area
[5, 6].
Results and discussion
Reaction process to prepare catalyst P4VP/SBA-15
The Knoevenagel condensation of aldehydes with active
methylene compounds is an important and widely
employed method of carbon-carbon bond formation in
organic synthesis [7–9], with numerous applications in the
synthesis of fine chemicals [10], hetero-Diels–Alder reac-
tions [11], and in the synthesis of carbocyclic as well as
heterocyclic [12] compounds of biological significance.
Homogeneous base catalysts such as ammonia or ammo-
nium salts, primary and secondary amines, pyridine, and
piperidine are usually used for this reaction [13]. Hetero-
geneous catalysts have also been used for the Knoevenagel
reaction, so the reaction has been catalyzed by heteroge-
neous catalysts based on alumina [14, 15], silica [16],
MgO/ZrO2 [17], and other catalysts [18–24], with more or
less success. With the increasing public concern over
environmental degradation, one of the challenges for
chemists is to come up with new approaches that are less
hazardous to human health and the environment. The sol-
vents used in organic synthesis are high on the list of
environmental pollutants because they are employed in
large amounts and are usually volatile liquids. To over-
come this problem, one approach is to select water as a
P4VP/SBA-15 was obtained after hybridizing P4VP with
SBA-15 by in situ polymerization. The procedure used to
prepare P4VP/SBA-15 is given in Scheme 1.
Characterization of the catalyst
Figure 1 shows the FT-IR spectra of mesoporous silica SBA-
15, P4VP, and P4VP/SBA-15. The characteristic band at
1,080 cm-1 is due to Si–O stretching in the Si–O–Si struc-
ture, as seen in Fig. 1a, c. In the FT-IR spectrum of P4VP/
SBA-15 (Fig. 1c), the new bands at 1,602, 1,558, 1,496, and
1,412 cm-1 are the characteristic absorptions of the pyridine
ring. Among them, the band appearing at 1,602 cm-1 is the
absorption due to the stretching vibration of the C–N bond,
and the bands at 1,558, 1,496, and 1,415 cm-1 are attributed
to the stretching vibrations of aromatic C–C bonds. More-
over, the peaks at around 2,800–3,050 cm-1 correspond to
aromatic and aliphatic C–H stretching in P4VP/SBA-15, and
the vibration at 856 cm-1 derives from out-of-plane C–H
deformation. These are in accordance with the spectrum of
P4VP (Fig. 1b).
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