Synthesis, Characterization and Catalytic Activity of Magnetic KI@Fe3O4 Nanoparticles for Henry Reaction Under Solvent Free Conditions

Article abstract of DOI:10.1007/s10562-019-02814-7

Abstract: In this paper, we, for the first time reported the synthesis of KI loaded Fe₃O₄ nanoparticles (KI@Fe₃O₄ NPs) and investigated its applications in the synthesis of β-nitroalcohol via Henry reaction at room temperature under solvent-free conditions. The synthesized KI@Fe₃O₄ nanoparticle was characterized by SEM, HRTEM, XRD, XPS, EDX, VSM and FT-IR spectroscopy techniques. The XRD peaks at 2θ = 21.9, 25.65, 33.54, 36.35, 40.97, 42.81, 44.79, 54.43, 57.37, 58.83 and 63.13° corresponds to the formation of crystalline KI@Fe₃O₄ NPs. The activity of the catalyst by varying the amount of KI loading on Fe₃O₄ NPs was also investigated. Mild reaction conditions, good yield, short reaction time, solvent-free conditions, easy recoverability and recyclability of the nanocatalysts are the major advantages of our method. Graphical Abstract: [Figure not available: see fulltext.].

Full text of DOI:10.1007/s10562-019-02814-7

Catalysis Letters
https://doi.org/10.1007/s10562-019-02814-7
Synthesis, Characterization and Catalytic Activity of Magnetic KI@
Fe O Nanoparticles for Henry Reaction Under Solvent Free Conditions
3
4
Lalthazuala Rokhum1 · Gunindra Pathak1
Received: 25 January 2019 / Accepted: 8 May 2019
©
Springer Science+Business Media, LLC, part of Springer Nature 2019
Abstract
In this paper, we, for the ꢀrst time reported the synthesis of KI loaded Fe O nanoparticles (KI@Fe O NPs) and investigated
3
4
3
4
its applications in the synthesis of β-nitroalcohol via Henry reaction at room temperature under solvent-free conditions. The
synthesized KI@Fe O nanoparticle was characterized by SEM, HRTEM, XRD, XPS, EDX, VSM and FT-IR spectroscopy
3
4
techniques. The XRD peaks at 2θ=21.9, 25.65, 33.54, 36.35, 40.97, 42.81, 44.79, 54.43, 57.37, 58.83 and 63.13° corre-
sponds to the formation of crystalline KI@Fe O NPs. The activity of the catalyst by varying the amount of KI loading on
3
4
Fe O NPs was also investigated. Mild reaction conditions, good yield, short reaction time, solvent-free conditions, easy
3
4
recoverability and recyclability of the nanocatalysts are the major advantages of our method.
Graphical Abstract
Keywords Magnetic nanocatalyst · KI@Fe O nanoparticles · Nitroalcohol · Solvent-free · Magnetic recoverability
3
4
Electronic supplementary material The online version of this
article (https://doi.org/10.1007/s10562-019-02814-7) contains
supplementary material, which is available to authorized users.
Extended author information available on the last page of the article
Vol.:(0
1
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3

L. Rokhum, G. Pathak
1
Introduction
compounds like epinephrine [24–26]. In recent times many
researchers have performed Henry reaction with diꢂerent
types of catalyst [27–33]. However longer reaction time,
use of hazardous solvent, high temperature and low yields
make these protocol ineꢁcacious and not environmentally
benign. Hence, a simple, mild and eꢁcient procedure for
Henry reaction is always in high demand in the realm of
organic synthesis.
Now a days, the main focus of catalysis research is to
enhance the activity, selectivity and recoverability of a
catalyst used in any chemical transformation. Homogene-
ous catalysis have several advantages such as good cata-
lytic activity and selectivity because they are well deꢀned
on a molecular level and easily soluble in the reaction
medium even under mild conditions, but separation of
the catalyst from the reaction mixture is very diꢁcult
and requires very expensive, time consuming and tedious
procedures. Contrary to this, heterogeneous catalysts can
be easily separated from the reaction medium by simple
washing or ꢀltration [1, 2]. Thus heterogeneous catalysis
is favored over homogeneous catalysis in many circum-
stances and covers a wide range of applications in indus-
tries like chemical manufacturing, energy harvesting and
environmental technologies etc. [3].
In recent times, several research groups have reported an
alkali metal compounds like KF, KNO3 loaded on various
solid supports as an eꢁcient solid base catalyst for stimu-
lating useful chemical transformations such as the Knoev-
enagel condensation, the Michael addition, aldol conden-
sation, Witting-Horner reactions, N–, O– and S-alkylation
reactions, alkene isomerization and biodiesel production
[34–39]. These materials are usually not strongly basic but
when they are subjected to calcination at very high tempera-
ture, a layer of strong basic sites such as K2O were formed
due to decomposition of loaded alkali metal compounds and
have gained high eꢁciency in the catalytic processes [40].
Similarly, it can be presumed that by loading KI on Fe3O4
NPs followed by calcination at very high temperature may
form a layer of strong basic sites due to thermal decompo-
sition of KI to K2O in air and this material can be used as
a basic catalyst in organic transformations. In continuation
of our ongoing interest in Henry reaction [41–44], here we
report the synthesis, characterization and application of a
novel magnetically recoverable KI@Fe3O4 NPs base catalyst
for Henry reaction to aꢂord nitroalcohol in good to excellent
yield. The inꢃuences of various factors on nitroalcohol yield
were also investigated.
Recently, metal nanoparticle (NPs) are getting massive
attraction from researchers mainly due to its easy dispers-
ibility in the reaction medium and high surface area to vol-
ume ratio. Due to its small structure and high surface area,
the interaction between the reactants and the catalyst is
enhanced, resulting in the increase in reaction rate as com-
pared to its homogeneous counterpart. However, conven-
tional ꢀltration is not eꢁcient to separate these nano-sized
catalysts from the reaction mixture [4]. Several time-con-
suming tedious work-up procedures are involved in their
separation, which are not economically and environmen-
tally viable. Therefore, researchers have emphasized more
on the use of magnetic Fe O NPs as their paramagnetic
3
4
nature enables easy recoverability from the reaction mix-
ture by simply applying an external magnet [5–8]. Owing
to this, magnetic Fe O nanocatalyst is widely used as a
2 Experimental Section
3
4
suitable support for preparation of a highly active catalyst
[
9]. Recently, functionalized magnetic Fe O NPs have
2.1 Materials
3
4
found wide range of applications in many areas of science
and technologies such as targeted drug delivery agents
All aldehydes and nitroalkanes were purchased from Spec-
troChem and were used without further puriꢀcation. Solvent
used were extra pure grade purchase from Merck India. Pro-
gress of the reaction was monitored by thin layer chromatog-
raphy (TLC) carried out on glass plates coated with silica
gel G, using the solvent system EtOAc/hexane.
[
10], contrast agents in magnetic resonance imaging [11],
magnetic storage media [12], waste water treatment [13,
4], oxidation [15, 16], reduction [17], transesteriꢀcation
18], coupling and cross coupling reactions [19–21] and
1
[
in the synthesis of various important organic compounds
[
22, 23].
The Henry reaction is one of the most important C–C
2.2 Preparation of Fe3O4 Nanoparticles (Fe3O4 NPs)
bond forming reaction in which β-nitroalcohol is formed
by the reaction of nitroalkanes with carbonyl compounds
in presence of a base catalyst. The product nitroalco-
hol can be used as an intermediate in the formation of
nitroalkenes, α-nitroketones, β-amino alcohol derivatives,
synthesis of aminosugar and antibiotics such as ezomy-
cins and tunicamycin setc and some biologically important
Magnetite nanoparticles (Fe3O4 NPs) were prepared by a
convenient co-precipitation method based on literature [7].
Firstly, FeCl2·4H2O (5 mmol) and FeCl3·6H2O (10 mmol)
2
+
3+
were dissolved in deionized water (Fe :Fe = 1:2 molar
ratio) under nitrogen atmosphere at 90 °C. Ammonium
hydroxide solution was then added drop wise to this solu-
tion with vigorous stirring. The reaction was carried out
1
3

Synthesis, Characterization and Catalytic Activity of Magnetic KI@Fe O Nanoparticles…
3
4
for 60 min until the color of the bulk solution turned black.
The ꢀnal pH value of the aqueous solution was maintained
at about 12.0. Then the mixture was aged for 60 min. The
supernatant liquid was decanted and the black solid was cen-
trifuged and washed with distilled water until the pH value
of ꢀltrate decreased to 7.0. After drying at 60 °C for 24 h,
the precipitate was pulverized.
recorded on a Bruker Avance II (400 MHz), spectrometer
using tetramethylsilane (TMS) as an internal reference.
2.5 General Procedure for Synthesis
of β‑nitroalcohols
To a well-stirred mixture of aldehyde (1 mmol) and nitroal-
kane (1.5 mmol) in a sample vial, 50 mg of KI@Fe O NPs
3
4
2
.3 Preparation of KI@Fe O NPs
(16 wt% of KI) was added at ambient temperature. The reac-
tion mixture was allowed to stir for the time speciꢀed in
Tables 3 and 4. The progress of the reaction was monitored
using TLC. After completion of the reaction (as indicated
by TLC), magnetic catalyst was isolated by an external mag-
net, wash with 3 mL ethyl acetate and the resultant mixture
concentrated in rotary evaporator and puriꢀed by silica gel
column chromatography (10% ethyl acetate in hexane) to
give the corresponding nitroalcohol.
3
4
KI@Fe O NPs was prepared by impregnation method.
3
4
Brieꢃy, 1–5 g of KI was dissolved in 20 mL of distilled
water in ꢀve round bottom ꢃask containing 12.5 g of freshly
prepared magnetic Fe O each (for preparing 8, 16, 24, 32
3
4
and 40% KI loaded Fe O ) and stirred for 30 min. Then the
3
4
excess water was evaporated by rotary evaporator and sub-
sequently dried at 90 °C for 24 h in a hot air oven. Finally,
the dried materials were calcined at 450 °C for 2 h in muꢄe
furnace. The ꢀnal catalysts were stored in a desiccator for
further use.
3 Results and Discussion
2.4 Characterization
3.1 Characterization of Fe O NPs and KI@Fe O NPs
3
4
3 4
The basic strength of the solid catalyst was determined by
using Hammett indicator method. The following Hammett
indicators were used in our experiments: Bromthymol blue
FT-IR analysis of both Fe O and KI@Fe O NPs were
3 4 3 4
performed. The FT-IR analysis showed an intense peak at
−
1
587 cm which is the characteristic peak of Fe O nanopar-
3
4
(
(
(
H_ = 7.2), phenolphthalein (H_ = 9.8), alizarin yellow R
H_=11.0), indigo carmine (H_=12.2), 2,4-dinitroaniline
H_ = 15.0) and nitroaniline (H_ = 18.4). Approximately
ticles, corresponding to the Fe–O bond vibration (Fig. 1).
−
1
−1
The peaks at 3480 cm , 1635 cm were attributed to the
–OH stretching and bending vibration which is due to the
absorption of H O molecule on the surface of the Fe O
2
00 mg of solid catalyst and 1 mL solution of Hammett
2
3
4
indicator diluted by 5 mL of anhydrous methanol was shaken
and settled to equilibrate for 2 h. If the solution exhibit color
change indicates that the basic strength of the catalyst is
stronger than the strength of the indicator used. However,
if the solution does not produce any color change, the basic
strength of the catalyst is weaker than the catalyst used [45].
High resolution transmission electron microscopy
nanoparticles [45–47]. Again in case of KI@Fe O NPs, the
3 4
−
1
−1
FT-IR spectra showed two peaks at 672 cm and 716 cm
due to the stretching vibration of K–O bond which may be
formed by the decomposition of KI to K O in presence of air
2
−
1
[48]. The peaks at 1550, 1370 and 1124 cm corresponds
(
HRTEM) was recorded on an electron microscope JEM-
100, 200 kV, JEOL. Energy dispersive X-ray spectroscopy
2
(
EDX) was also analyzed in the same instrument in EDX
mode with a 0.28sr of solid angle (in HR conꢀguration with
2
a 50 mm detector). Powder X-ray diꢂraction (XRD) patterns
were obtained on a X’Pert Pro, PAN analytical diꢂractom-
eter under the following conditions: K-Alpha1 wavelength
(
λ = 1.54056 Å), K-Alpha2 wavelength (λ = 1.54439 Å),
generator voltage of 40 kV, a tube current of 35 mA and
°
°
°
the count time of 0.5 s per 0.02 in the range of 5 –90 with
copper anode. FTIR Spectra were recorded on a Nicolet
6
700, Nicolet Continuum FTIR Microscope. XPS analysis
+
was carried out on ESCALAB Xi , thermo ꢀsher scientiꢀc
instrument at room temperature. Magnetic measurement was
1
carried out on a Lakeshore VSM 7410 magnetometer. H
1
3
and C NMR spectra of synthesized β-nitroalcohol were
Fig. 1 FTIR spectra of a Fe O and b KI@Fe O
4
3
4
3
1
3

L. Rokhum, G. Pathak
to the stretching and bending vibration of C–O bond of
19-0629). In case of 16 wt% KI loaded Fe O NPs sample
3
4
2
−
CO
which may be formed by the reaction of K O with
calcined at 450 °C (curve b), some new diꢂraction peaks
were observed along with the characteristic peaks of crystal-
line Fe O . The new diꢂraction peaks appeared at 2θ=21.9,
3
2
CO to produce K CO [40].
2
2
3
The crystalline structure of the magnetite nanoparticles
was conꢀrmed by XRD analysis as shown in Fig. 2. From
curve (a) it was seen that the XRD peaks are well matched
with the characteristic peaks of inverse cubic spinal struc-
ture of crystalline Fe O nanoparticles giving 2θ value at
3
4
o
25.65, 42.81, 44.79 and 58.83 were due the presence of
KI molecule loaded over the Fe O surface (JCPDS ꢀle no
3
4
00-004-0471). A new phase of K O was seen in KI@Fe O
2
3
4
NPs at 2θ=28.83, 50.30, 69.41 and 76.61°, which is respon-
sible for high catalytic activity or high basicity of the surface
of the solid catalyst due to the formation of Fe–O–K groups
that act as an active sites for this base catalyzed Henry reac-
tion [47, 48]. The characteristic peaks of Fe O NPs remain
3
4
3
3.54, 36.35, 40.97, 54.43, 57.37 and 63.13° (JCPDS ꢀle no
3
4
unchanged after impregnation with KI.
The surface composition of elements present in KI@
Fe O NPs was investigated by XPS analysis as shown in
3
4
Fig. 3. The general survey spectrum displayed the presence
of Fe2p, O 1s and K2p as a major components and a trace
amount of C1s and I3d were also present on the surface
of KI@Fe O catalyst (Fig. 3a). The Fe2p peak consists
3
4
of two predominant band peaks at 711.5 eV and 724.9 eV
which can be attributed to Fe2p and Fe2p respectively
3
/2
1/2
(
Fig. 3b). These two peaks are the characteristic peaks of
2
+
3+
Fe O structure consists of Fe of FeO and Fe of Fe O
3
3
4
2
[
49]. The O 1s spectrum consists of only one sharp peak
at 530.2 eV, which strongly refers the presence of metal
oxides like Fe O and K O in the prepared KI@Fe O cata-
3
4
2
3
4
Fig. 2 XRD patterns of the a magnetite Fe O and b KI@Fe O NPs
lyst (Fig. 3c). The deconvulated spectrum of K2p showed
3
4
3
4
Fig. 3 KI@Fe O a XPS survey
3
4
spectrum, b Fe2p, c K2p and d
O 1s spectra
1
3

Synthesis, Characterization and Catalytic Activity of Magnetic KI@Fe O Nanoparticles…
3
4
two peaks at binding energies 292.6 eV and 294.9 eV which
indicated the presence of potassium as carbonates and oxides
nanoparticles were covered with mixed KI and K O mol-
2
ecules producing non-uniform aggregated structures. How-
ever, it was diꢁcult to determine the size of the synthesized
catalyst due to agglomeration of the nanoparticles.
(
Fig. 3d). Furthermore, a small peak at 288.6 eV in C 1s
spectrum conꢀrmed the presence of trace amount of metal
carbonates in the catalyst surface. Thus from the XPS data
we conꢀrmed that the surface of Fe O NPs are predomi-
To investigate the size and shape of the synthesized
Fe O NPs, TEM analysis was performed and it was seen
3
4
3
4
nantly covered by potassium oxide, which is responsible for
its high basicity or high catalytic activity towards Henry
reactions.
that quasi-spherical and hexagon shaped nanoparticle with
diameter ranging from 7 to 19 nm were formed (Fig. 5a–c).
A typical HRTEM image recorded from the edge of aggre-
gated particles is shown in (Fig. 5c), which clearly dem-
onstrated that all the primary nanoparticles have parallel
lattice fringes with the lattice spacing of 0.27 nm. The
The surface morphology of the synthesized KI@Fe O
3
4
nano catalyst was investigated by SEM analysis. From the
SEM images (Fig. 4), it was clearly seen that the Fe O
3
4
Fig. 4 SEM images of KI@
Fe O nanoparticles at various
3
4
magniꢀcations (a, b)
Fig. 5 HRTEM images of
Fe O nanoparticles at various
3
4
magniꢀcations (a–c); SAED
pattern (d)
1
3

L. Rokhum, G. Pathak
SAED pattern conꢀrmed the sample is crystalline in nature
which resembled with the results drawn from XRD analysis
There were no distinct diꢂerences in the TEM images of
KI@ Fe O and Fe O NPs (Fig. 7a–c). Only the particle
3
4
3
4
(
Fig. 5d). EDX spectra clearly indicated the existence of Fe
size has increased from 7–19 to 12–21 nm which indicated
a good dispersion of KI on the surface of the nanoparti-
cles. The HRTEM image conꢀrmed the formation of outer
layer over surface of the Fe O nanoparticles (Fig. 7c). The
and O atoms arising from Fe O (Fig. 6).
3
4
3
4
SAED pattern (Fig. 7d) showed the high crystallinity of the
prepared catalyst and the EDX pattern (Fig. 8) showed the
existence of Fe, O, K, I and C in KI@Fe O catalyst. The
3
4
C atom observed in the EDX pattern might has come from
2
−
CO , which might have formed by the reaction of K O
3
2
with atmospheric CO to give K CO during calcination.
2
2
3
The magnetic behavior of the Fe O and KI@ Fe O
3
4
3
4
nanocatalyst were also investigated using VSM (Fig. 9).
From the hysteresis loops it can be seen that, in comparison
to 64.60 emu/g of Fe O , the saturation magnetization of
3
4
KI@Fe O NPs was found to be 46.97 emu/g after being
3
4
impregnated with KI. This may be due to the formation of
an outer layer of KI and K O over the surface of the Fe O
4
2
3
core. Moreover, both the remanence and coercivity value are
almost negligible suggesting that the synthesized Fe O and
3
4
KI@Fe O nanoparticles are superparamagnetic in nature.
3
4
The basic strength of KI@Fe O NPs prepared by load-
3
4
ing 16 wt% of KI on Fe O followed by calcination at 450 °C
3
4
was also investigated by Hammett indicator method. It was
seen that when bromthymol blue indicator solution was mixed
with the catalyst, the color of the solution changes from green
Fig. 6 EDX spectrum of Fe O nanoparticles
3
4
Fig. 7 HRTEM images of KI@
Fe O NPs at various magniꢀ-
3
4
cations (a–c); SAED pattern (d)
1
3

Synthesis, Characterization and Catalytic Activity of Magnetic KI@Fe O Nanoparticles…
3
4
Fe O NPs as a basic catalyst under solvent free conditions
3
4
(
Scheme 1). Optimization of various parameters such as cata-
lyst loading %, catalyst amount and molar ratio of the reactants
were performed to ꢀnd the most suitable conditions for the
synthesis of nitroalcohols via the Henry reaction.
3
.2.1 Optimization of Catalyst Loading
To investigate the inꢃuence of the KI loading on catalytic
activity, a series of catalysts were prepared at diꢂerent KI
loading i.e. 8, 16, 24, 32 and 40 wt% (all samples were cal-
cined at 450 °C for 2 h). The best result was obtained using
catalyst loaded with 16 wt% of KI over magnetic Fe O
3
4
NPs which gave nitroalcohol (2-nitro-1-(4-nitrophenyl)
ethan-1-ol) yield of 99% within 55 min (Fig. 10). The cata-
lyst with 40 wt% gave lowest yield of the desired product.
This is probably due to the fact that the excessive amount
Fig. 8 EDX spectrum of the KI@ Fe O nanoparticles
3
4
of KI loading may result in agglomeration of active K O
2
phase formed during calcination which results in decrease
in surface areas of active components and hence lower in the
catalytic activity [50].
3
.2.2 Optimization of Catalyst Amount
After optimizing the catalyst percentage loading, we inves-
tigated the catalyst amount, by taking 16 wt% of KI@Fe O
3
4
NPs as the optimum loading, for the reaction of 4-nitroben-
zaldehyde and nitromethane with diꢂerent mass of the nano-
catalyst and it was seen that with 50 mg of the catalyst the
reaction took least time to complete with excellent yield
(
Table 1, entry 3).
3
.2.3 Optimization of Molar Ratio of the Reactants
We further optimized the molar ratio of the reagents by tak-
ing diꢂerent equivalent of aldehyde and nitroalkane and it
was found that 1 mmol of 4-nitrobenzaldehyde and 1.5 mmol
of nitromethane (i.e. 1:1.5) was most suitable for this reac-
tion (Table 2, entry 2).
Fig. 9 The magnetic hysteresis loop of Fe O and KI@Fe O nano-
3
4
3
4
particles obtained at room temperature
to yellow. But, when phenolphthalein indicator was used no
color change was observed. Therefore its base strength could
be tentatively denoted as 7.2<H_<9.8.
With the optimized reaction conditions in hand we
decided to investigate the scopes and limitations of the reac-
tion by taking variety of aldehydes with electron-donating
and electron withdrawing groups and the results are sum-
marized in Table 3.
3.2 The Henry Reaction
At the onset, we have performed Henry reaction of 4-nitroben-
zaldehyde with nitromethane as a pilot protocol using KI@
We observed that the reactions were very eꢁcient with
all substituted aldehydes giving good to excellent yield
Scheme 1 Magnetic nanocata-
lyst for Henry reaction
1
3

L. Rokhum, G. Pathak
the eꢂect of substitution pattern in the nitroalkane, we
extended our reaction of aldehyde with nitroethane, as
shown in Table 4.
1
00
9
5
9
0
As the potential to scale-up is very important for any
chemical transformation to be industrially useful, we
ꢀnally tried a 10 mmol scale-up of the Henry reaction.
Here, treatment of 4-nitrobenzaldehyde (1.51 g, 10 mmol),
nitromethane (0.91 g, 15 mmol) and 0.50 g of the catalyst
8
5
8
0
7
5
1
6%
4%
32%
7
0
2
(
KI@Fe O NPs (16 wt% of KI)) in a 50 mL round bottom
3 4
6
5
ꢃask under ambient temperature gave the corresponding
nitroalcohol in almost quantitative yield (99%) after isola-
tion and chromatographic puriꢀcation.
8
0%
%
6
0
4
5
5
Upon generalization, it was observed that the electronic
eꢂects of the substituent in the aromatic aldehydes aꢂected
the reactions in the same way as using nitromethane but
the reactions were slightly slower due to the steric hin-
drance oꢂered by the alkyl group of the nitroethane. It was
pleasing to ꢀnd that the NMR analysis of all the products
revealed exclusive formation of nitroalcohol. A compara-
tive study of some selected literature on Henry reaction
using diꢂerent types of heterogeneous catalyst was sum-
marized in Table 5.
5
0
20
30
40
50
60
Time (min)
Fig. 10 Eꢂects of KI loading on catalytic activity of KI@Fe O NPs
3
4
Table 1 Optimization of weight of catalyst
Entry
Amount (in mg) Time (min)
Yield (%)
1
2
3
4
30
40
50
60
90
75
55
60
79
87
99
92
3.3 Reusability of the Solid Base Catalyst
The reusability of KI@Fe O NPs was examined by car-
3
4
Reaction conditions: 4-nitrobenzaldehyde (1 mmol), nitromethane
1.5 mmol), solvent-free, RT
rying out reaction cycles. Figure 11 depicted the results of
consecutive runs performed by reusing the catalyst under our
optimal reaction conditions. After completion of the reac-
tion, the catalyst was separated by a applying a permanent
magnet. Then it was washed with ethyl acetate and dried at
(
Table 2 Optimization of molar ratio of reagents
Entry
Aldehyde/
Time (min)
Yield (%)
9
5 °C, before being used again in a new reaction. The dried
nitromethane
catalyst was used subsequently in the next reaction cycle
under the same reaction conditions as before. It is found that
the catalyst sustained its catalytic activity even after being
reused for ꢀve times giving up to 90% yield.
1
2
3
4
1:1
1:1.5
1:2
60
55
70
60
91
99
93
24
2:1
To investigate any change in morphology and chemical
composition of the recovered KI@Fe O catalyst after ꢀfth
Reaction conditions: 4-nitrobenzaldehyde (1 mmol), catalyst: KI@
Fe O solvent free, RT
3
4
cycle, FT-IR, SEM, TEM and EDX analysis were performed.
3
4
The IR spectra of the recovered catalyst showed intense
−
1
−1
−1
−1
peaks at 3400 cm , 1557 cm , 1380 cm , 1120 cm ,
−
1
−1
(
entry 1–12). It was found that aldehydes with electron
637 cm and 560 cm , which are almost similar to that
−
1
withdrawing group (Table 3, entries 2–8) were faster and
gave better yield than the reaction of aldehydes with elec-
tron donating groups. This may due to the fact that elec-
tron withdrawing group enhance the electrophilicity of
carbonyl carbons in aldehydes which facilitate the reaction
while electron-donating groups render its electrophilicity
which in turn retarded the reactions (Table 3, entries 9,
of fresh KI@Fe O catalyst. The peak at 637 cm due to
3 4
stretching vibration of K–O bond clearly indicated the pres-
ence of K O molecule in the recovered catalyst, which is
2
responsible for its high basicity even after ꢀfth cycle (Sup-
porting Information Fig. S2a). The SEM and TEM images
of the recovered catalyst revealed irregular quasi spherical
structure similar to that of fresh catalyst (SI Fig. S2b). The
EDX spectrum (SI Fig. S3) also indicated the existence of
Fe, O, K, I and C in the recovered catalyst as in the case of
fresh KI@Fe O nanoparticles.
1
0). Due to the electron donating tendency of alkyl group
the reaction using aliphatic aldehydes was also found to be
slower (Table 3, entry 11, 12). With an interest to perceive
3
4
1
3

Synthesis, Characterization and Catalytic Activity of Magnetic KI@Fe O Nanoparticles…
3
4
Table 3 Henry reactions of
various aromatic and aliphatic
aldehydes with nitromethane
under solvent free conditions
Entry
Aldehyde
Product
Time (min) Yield (%)a
1
85
94
2
3
55
99
60
89
4
60
97
5
6
60
65
96
96
7
8
9
74
92
94
65
70
110
90
1
0
74
1
1
1
2
85
88
92
84
Reaction conditions: aldehyde (1 mmol), nitromethane (1.5 mmol), KI@Fe O (16 wt%, 50 mg) at room
3
4
temperature
a
Yields are calculated from pure isolated product
4
Conclusion
sizes from 12 to 22 nm. The active KI and K2O spe-
cies formed by the reaction of KI and surface hydroxyls,
provided strong basic sites of the catalyst. The catalyst
with 16 wt% KI loading on Fe3O4 nanoparticles and after
calcined at 450 °C for 2 h showed best catalytic activity
for the Henry reactions. Interestingly, we have observed
A nano-magnetic solid base catalyst KI supported on
magnetic Fe O was developed by impregnation method
3
4
and characterized by various analytical techniques.
TEM results indicated that the catalyst has a particle
1
3

L. Rokhum, G. Pathak
Table 4 Henry reactions of
some aromatic aldehydes with
nitroethane under solvent-free
conditions
Entry
Aldehyde
Product
Time (min) Yield (%)a
1
65
70
80
95
99
97
94
83
2
3
4
5
6
7
115
80
77
92
89
87
8
85
90
Reaction conditions: aldehyde (1 mmol), nitroethane (1.5 mmol), KI@Fe O (16 wt%, 50 mg) at room
3
4
temperature
a
Yields are calculated from pure isolated product
Table 5 Comparative study of Henry reaction with diꢂerent catalysts
Entry
Catalyst
Reaction conditions
Yield (%)
References
1
2
3
Fe O /SiO -Met
EtOH, rt, 8 h
EtOH, rt, 2–5 days
65
95
[27]
[28]
[29]
3
4
2
Cu(OAc) ·nH O/Sciꢂ base Ligand
2
2
CuCl ·2H O/phenanthrolinee-quinine ligand
N-Me-morpholine, THF-i-PrOH, 0 °C, 86
2
2
1
4-41 h
4
5
6
7
8
Nickel hydroxyapatite NPs
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Chiral thiourea organocatalyst, Et N
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93
95
98
99
[30]
[31]
[32]
Toluene, THF, EtOH/50–90 °C
CH Cl /rt/24 h
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rt/55 min/solvent-free
[33]
This work
3
4
an exclusive formation of β-nitroalcohols via the Henry
reaction without any formation of side products. Further,
after completion of the reactions the catalyst was easily
separated from the reaction mixture using an external
magnet and reused for five cycles without any significant
loss in its activity.
1
3

Synthesis, Characterization and Catalytic Activity of Magnetic KI@Fe O Nanoparticles…
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4
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L. Rokhum, G. Pathak
Aꢀliations
Lalthazuala Rokhum1 · Gunindra Pathak1
1
*
Lalthazuala Rokhum
Department of Chemistry, National Institute of Technology
Silchar, Assam 788010, India
lalthazualarokhum@gmail.com; rokhum@che.nits.ac.in
1
3