Z. Sharifzadeh et al.
Ultrasonics Sonochemistry 73 (2021) 105499
the synthesis of stable chiral catalysts and asymmetric catalysis owing to
their features such as polarity, basicity, and large cavity. They have
stable catalytic centers in their structures and in fact, they are not an
inert material. To chiralize active surfaces of these polymers, we have
also chosen CMNPs as the core, [62,63] that are prepared by using L-
at 40/60 kHz). A horn-type tube Pyrex reactor was custom-made and
fitted to the sonicator bath.
3. Preparation of CMNPs/1,3-Zbtb & CMNPs/1,4-Zbtb
composites via solvothermal strategy.
(
+)-tartaric acid (chiral carboxylic acid) stabilized nano-magnetite with
high chirality induction[64]. As above mentioned, three synthetic
methods were employed to synthesize these chiral magnetic materials
by encapsulation of CMNPs. The results showed that the best method is
using ultrasonic irradiation. However, in several reports, the effect of
ultrasonic in encapsulation of various molecules has been shown and
proved [48,58,65,66]. In fact, carrying out reactions in ultrasonic-bath
not only leads to the dispersion of magnetic NPs and especially mag-
netic NPs, but also causes accelerates binding of metal to organic linkers
around NPs. Therefore, we observed that in the absence of ultrasonic
The CMNPs (as reported in S1) (0.04 mmol) were well dispersed (10
mL DMF) by ultrasonic irradiation. Then the solution of 1,4-btmbenzene
ligand (1 mmol) (or 1,3-btmbenzene, S2) in DMF (15 mL) and meth-
anolic solution (5 mL) of Zn(NO
3
)
2
⋅6H
2
O (296 mg, 1 mmol) were added
to dispersed nanoparticles. This mixture was transferred to a 30 mL
◦
Teflon-lined stainless-steel vessel, sealed, and heated at 120 C for 12 h.
3.1. Preparation of CMNPs/1,3-Zbtb & CMNPs/1,4-Zbtb composites via
mechanical stirring method
3 4
irradiation, functionalized-Fe O nanoparticles definitely cannot well
disperse well and the majority of them are located on the outer surface of
hollow spherical polymers. The produced catalysts by sonochemical
synthesis have smaller dimension and higher active surface than two
other synthetic methods. So, these features can induce high catalytic
performance to chiral ICPs and show the effect of ultrasonic irradi-
ation on the structure, respectively. Fig. 2 shows the schematic diagram
of the preparation process for CMNPs/1,4-Zbtb as the main catalyst.
Since, it showed better results than CMNPs/1,3-Zbtb, preserving its
structural integrity and catalytic activity (synthesis of CMNPs/1,3-Zbtb
similar to CMNPs/1,4-Zbtb). Apart from the presence of unsaturated Zn
atoms at the shell that can act as active acidic centers in the oxidation,
nitroaldole reaction (as a type of C–C bond-forming) reaction can be
proceeded by Lewis-acid or base [67–71]. To the best of our knowledge,
this is the first example of chiral ICP in asymmetric catalysis with high
enantiomeric excess [72,73] by chiral agent protection.
The CMNPs (0.04 mmol) were fully dispersed in DMF (10 mL) by
ultrasonic irradiation. Then the solution of 1,4-btmbenzene ligand (1
mmol) (or 1,3-btmbenzene, S2) in DMF (15 mL) was added to it. Then,
during stirring by a mechanical stirrer, a methanolic solution (5 mL) of
Zn (NO ) ⋅6H O (296 mg, 1 mmol) was added dropwise to them. After
3
2
2
stirring for one hour, the produced product was separated and washed
with methanol and DMF.
3.2. Preparation of CMNPs/1,3-Zbtb & CMNPs/1,4-Zbtb composites by
using of ultrasonic irradiation
The CMNPs (0.04 mmol) was dispersed well in DMF (10 mL) by use
of ultrasonic irradiations. Then the solution of 1,4-btmbenzene ligand
(1 mmol) in DMF (15 mL) was added to dispersed nanoparticles and then
both of them were sonicated for specific times (30–45 min) at room
temperature. After homogenization, a methanolic solution (5 mL) of Zn
2
. Experimental section
(NO
3
)
2
⋅6H
2
O (296 mg, 1 mmol) was added dropwise to the mixture of
CMNPs and ligand in the ultrasonic bath. Subsequently, the light-brown
micro sphere-like polymers as shell with chiral magnetic nanoparticles
within their core were generated. Finally, they were purified by mag-
netic separation and washed with DMF through filtration-redispersion
2
.1. Materials and instrumentation
Materials: L-(+)-Tartaric acid ((2R,3R)-(+)-tartaric acid, >99%,
ꢀ 1
Merck), iron(III) chloride hexahydrate (FeCl
3
⋅6H
2
O, 98% Fluka),
cycles.IR data ( /cm ):427 (s), 657 (w), 777 (w), 1106 (w), 1430
υ
diethylene glycol (99%, Merck), 1,4-phenylenediacetonitrile and 1,3-
phenylenediacetonitrile were purchased from Sigma–Aldrich (Mil-
waulkee, WI, USA). Sodium azide and zinc bromide were commercially
obtainable from Merck Company (Darmstadt, Germany) and other re-
agents and solvents were purchased and used without further purifica-
tion from commercial suppliers (Sigma Aldrich, Alfa Aesar, TCI, and
others).
(m), 1658 (s), 1732 (s), 2349 (w), 2830 (w), 2935 (w), 3428 (m).
Preparation of CMNPs/1,3-Zbtb was similar to CMNPs/1,4-Zbtb without
any change in ratios. IR data ( /cm-1):446 (w), 690 (w), 765 (m), 1108
υ
(m), 1434 (m), 1653 (s), 1730 (s), 2351 (w), 2810 (m), 2920 (m) and
3430 (m).
3.3. Typical reaction procedure of Henry reaction
IR spectra were recorded using a Nicolet 100 Fourier Transform IR
ꢀ
1
spectrometer in the range of 500–4000 cm using the KBr disk tech-
nique. The inductively coupled plasma (ICP) analyses were achieved on
a Varian ICP-OES VISTA-PRO CCD instrument. Melting points were
measured on an Electrothermal 9100 apparatus. UV–vis absorption
spectra were obtained by UV–vis Perkin Elmer Lambda 25 spectropho-
tometer. CD spectra were recorded on a Jasco J-715 spectropolarimeter
In a typical reaction, chiral catalyst (CMNPs/1,3-Zbtb & CMNPs/1,4-
Zbtb) (0.05 g) was added to a solution of MeOH (5 mL) in 5 mL screw-
capped vial. Afterwards, benzaldehyde (2 mmol) and nitromethane (5
mmol) were added into above solution. The reaction mixture was
◦
allowed to stir at 70 C. After that, upon filtration by an external magnet,
the catalyst was separated and washed with MeOH. The solution was
collected and analyzed by chiral GC.
(
Japan). Gas chromatography (GC) runs were performed on an Echrom
GC A90 gas chromatograph. The samples were also characterized by
using a field emission scanning electron microscope (FE-SEM) TESCAN
MIRA with gold coating. TEM (transmission electron microscopy)
analysis was performed on a JEOL 2100 electron microscope at an
operating voltage of 200 kV. Powder X-ray diffraction (PXRD) mea-
3.4. Recycling of catalyst
After the first step of the catalytic cycle, the heterogeneous catalyst
was separated by external magnet, rinsed several times by MeOH and
′
◦
surements were performed using a Philips X pert diffractometer with
dried for 5 h in oven (80 C). Then, the recovered catalyst was reused in
monochromated Cu-K
α
(λ = 1.54056 Å) radiation. The contact angle
the subsequent recycling experiments under identical reaction
conditions.
was measured by using an OCA 15 plus apparatus. Magnetic measure-
ments were performed with a Quantum Design vibrating sample
magnetometer (VSM) at room temperature in an applied magnetic field
sweep. Ultrasonic generation was carried out in an ultrasonic bath
SONICA-2200 EP (frequency of 40 kHz). The sonicator used in this study
was a SONICA-2200 EP with adjustable power output (maximum 305 W
3.5. Typical reaction procedure of benzyl alcohol oxidation to
benzaldehyde
In a typical procedure, BzOH (2 mmol) and deionized water (5 mL),
3