Full Papers
doi.org/10.1002/cctc.202100424
ChemCatChem
was transferred into the teflon-lined autoclave to crystallization for
versatile quinoline skeletons among various synthetic routes to
quinolines, undergoing aza-heterocyclic and subsequent aroma-
tization processes.[29] In general, traditionally homogeneous
catalysts were usually employed in quinolines synthetic reac-
tions, such as, sulfuric acid, muriatic acid, metal salt and ionic
liquids.[30–33] Nevertheless, the homogeneous catalytic process
caused several significant problems. For example, a larger
amount of acid wastewater is brought out and the complicated
separation of homogeneous catalysts after reaction is required.
Alternatively, heterogeneous catalysts are easier separated from
the reaction system, which is more environmentally-friendly
than the homogeneous ones. In recent years, just several
heterogeneous catalysts, liking InCl3/SiO2, montmorillonite and
phosphotungstic acid, have been explored for the reaction of
Doebner-Miller reaction to quinolines,[34–37] and these catalysts
existed short lifetimes because of the loss of active ingredients
and/or rapid inactivation during quinolines synthetic reaction.
Therefore, the further development of a novel type of green
heterogeneous catalysts owning high activity as well as
excellent stability for Doebner-Von Miller reaction to quinoline
is still highly desired.
In this work, a novel gemini sulfonic ionic liquid immobi-
lized on MCM-41 was prepared as effective and recyclable
heterogeneous catalyst, and employed to catalyze the domino
reaction of aniline and acrolein dimethyl acetal to quinoline, via
hydrolysis-heterocyclic-aromatization processes. Accordingly,
2,2’-bipyridine-based gemini sulfonic ionic liquid was firstly
prepared and then immobilized on MCM-41 mesoporous
materials. The obtained IL-immobilized MCM-41 materials were
characterized, and the catalytic activities were evaluated
systematically in Doebner-Von Miller reaction. Further, the
reusability of the IL-immobilized MCM-41 catalysts were also
investigated.
°
24 h at 100 C. The resultant solid was collected by filtration,
°
washing with distilled water and then vacuum drying at 60 C.
Finally, the mesoporous MCM-41 material was obtained via
°
calcining for 6 hours at 550 C in an air flow.
Preparation of Gemini Sulfonic Ionic Liquid
A typical procedure of gemini sulfonic ionic liquid’ synthesis is
given, as depicted in Figure 1S(a). 2,2’-bipyridine and 1,4-butane
sultone were mixed completely without using solvent; and stirred
°
violently for 24 h at 60 C. Subsequently, the sulfuric acid (98%) was
added slowly into the reaction system and then kept stirring
magnetically for 12 h at room temperature. The forming liquid was
washed repeatedly with ethyl acetate and dried in vacuum
°
condition at 60 C for 24 h. the as-obtained ionic liquid was named
as IL1. As comparison, a typical imidazole-type sulfonic ionic liquid
was also ready according to the above method, using N-methyl
imidazole and 1,4-butane sultone as reagents, as showed in
Figure 1S(b), which was defined as IL2.
Immobilization of Ionic Liquid on MCM-41
Immobilization of ionic liquid on MCM-41 was prepared using the
convenient impregnation method. In a typical preparation, the as-
prepared IL1 or IL2 was dissolved into absolute ethyl alcohol. Then,
the MCM-41 powder was added into and the formed suspension
kept strongly stirring for 12 h at room temperature. After that, the
°
resulting suspension was dried at 60 C for 24 h in the vacuum
environment to remove absolute ethyl alcohol. The obtained IL-
immobilized catalysts were denoted respectively as IL1/MCM-41
and IL2/MCM-41.
Catalysts Characterization
X-ray diffraction (XRD) spectroscopy for catalysts was performed
with a Bruker D8-Advance diffractometer, using the conditions as
follow: Cu target Kα radiation (λ=1.54187 Å), scanning voltage
(40 kV), scanning speed (0.5 s), scanning current (40 mA); scanning
°
step (0.02 ).
Experimental
Fourier transform infrared (FT-IR) spectra for catalysts was recorded
on a Varian 3100 spectrometer, equipped with a DTGS detector.
The sample and KBr were initially mixed thoroughly and then
positioned in the holder to mount in sample cavity of the
spectrometer. The data were recorded at a scanning number of 32
Chemicals
All the chemicals, tetraethoxysilane (Sinopharm Chemical Reagent
Co., Ltd; TEOS), cetylpyridinium chloride (Sinopharm Chemical
Reagent Co., Ltd. CPCl), acetic acid and sodium hydroxide
(Sinopharm Chemical Reagent Co., Ltd.), 2,2’-bipyridine, 1-meth-
ylimidazole and 1,4-butane sultone (Aladdin Chemical Reagent Co.,
Ltd.); aniline and Acrolein diethyl acetal (Xilong Chemical Co., Ltd.),
were commercially available and had an analytic purity.
as well as a resolution of 2 cmÀ 1
.
Scanning electron microscopy (SEM) for catalysts was conducted on
a JEOL JSM 6700F apparatus, using an accelerating voltage of
10 kV. The sample was initially dispersed adequately in alcohol via
ultrasonication and then placed on the silicon chip.
Transmission Electron Microscope (TEM) for catalysts was recorded
with a JEM-2100F apparatus, using an accelerating voltage of
200 kV. The sample was firstly ultrasonic treated to disperse in
ethanol and then dropped on the carbon-coated copper grid.
Catalyst Preparation
Preparation of MCM-41
N2-physisorption for catalysts was measured on a Quantachrome
Autosorb-1 apparatus at liquid nitrogen temperature. Prior to
The synthesis method of MCM-41 was used as in previous
literatures.[38,39] In a typical preparation, the aqueous solution
containing cetylpyridinium chloride (CPCl) and ammonia (NH3 H2O,
.
°
measurement, the sample was firstly outgassed at 300 C for 8 h
under a 10À 8 Torr vacuum. The specific surface area was obtained
via the multipoint BET equation, and the average mesopore size
was calculated via BJH method using desorption isotherms.
25 wt.%) was stirring for 30 min, and then tetraethoxysilane (TEOS)
was dropwise into the aqueous solution. The mixture was further
stirring at room temperature for 30 min to form an expectant
homogeneization gel. The synthesis gel had the molar composition:
X-ray photoelectron spectroscopy (XPS) for catalysts was performed
on a PHI Quantum 2000 apparatus, using the Al Ka radiation source.
.
1TEOS: 9.2NH3 H2O: 0.5CPCl: 130H2O. Subsequently, the formed-gel
ChemCatChem 2021, 13, 1–10
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