Adhesive functionalized ascorbic acid on CoFe2O4: A core-shell nanomagnetic heterostructure for the synthesis of aldoximes and amines

Article abstract of DOI:10.1039/d0ra08244a

This paper reports on the simple synthesis of novel green magnetic nanoparticles (MNPs) with effective catalytic properties and reusability. These heterogeneous nanocatalysts were prepared by the anchoring of Co and V on the surface of CoFe2O4 nanoparticles coated with ascorbic acid (AA) as a green linker. The prepared nanocatalysts have been identified by scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray spectroscopy, X-ray atomic mapping, thermogravimetric analysis, X-ray powder diffraction, vibrating sample magnetometer analysis, coupled plasma optical emission spectrometry and Fourier transform infrared spectroscopy. The impact of CoFe2O4@AA-M (Co, V) was carefully examined for NH2OH·HCl oximation of aldehyde derivatives first and then for the reduction of diverse nitro compounds with sodium borohydride (NaBH4) to the corresponding amines under green conditions. The catalytic efficiency of magnetic CoFe2O4@AA-M (Co, V) nanocatalysts was investigated in production of different aldoximes and amines with high turnover numbers (TON) and turnover frequencies (TOF) through oximation and reduction reactions respectively. Furthermore, the developed environment-friendly method offers a number of advantages such as high turnover frequency, mild reaction conditions, high activity, simple procedure, low cost and easy isolation of the products from the reaction mixture by an external magnetic field and the catalyst can be reused for several consecutive runs without any remarkable decrease in catalytic efficiency.

Full text of DOI:10.1039/d0ra08244a

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PAPER
Adhesive functionalized ascorbic acid on CoFe2O4:
a core–shell nanomagnetic heterostructure for the
synthesis of aldoximes and amines†
Cite this: RSC Adv., 2020, 10, 41336
*
and Roya Mozafari
Serve Sorkhabi,
Mohammad Ghadermazi
This paper reports on the simple synthesis of novel green magnetic nanoparticles (MNPs) with effective
catalytic properties and reusability. These heterogeneous nanocatalysts were prepared by the anchoring
of Co and V on the surface of CoFe2O4 nanoparticles coated with ascorbic acid (AA) as a green linker.
The prepared nanocatalysts have been identified by scanning electron microscopy, transmission electron
microscopy, energy-dispersive X-ray spectroscopy, X-ray atomic mapping, thermogravimetric analysis,
X-ray powder diffraction, vibrating sample magnetometer analysis, coupled plasma optical emission
spectrometry and Fourier transform infrared spectroscopy. The impact of CoFe2O4@AA-M (Co, V) was
carefully examined for NH2OH$HCl oximation of aldehyde derivatives first and then for the reduction of
diverse nitro compounds with sodium borohydride (NaBH4) to the corresponding amines under green
conditions. The catalytic efficiency of magnetic CoFe2O4@AA-M (Co, V) nanocatalysts was investigated
in production of different aldoximes and amines with high turnover numbers (TON) and turnover
frequencies (TOF) through oximation and reduction reactions respectively. Furthermore, the developed
environment-friendly method offers a number of advantages such as high turnover frequency, mild
reaction conditions, high activity, simple procedure, low cost and easy isolation of the products from the
reaction mixture by an external magnetic field and the catalyst can be reused for several consecutive
runs without any remarkable decrease in catalytic efficiency.
Received 26th September 2020
Accepted 6th November 2020
DOI: 10.1039/d0ra08244a
rsc.li/rsc-advances
Fe3O4 MNPs. Among metal ferrite MNPs, cobalt ferrite
(CoFe2O4) MNPs have been recognized interesting due to their
1. Introduction
mechanical hardness high magnetization and high chemical
and thermal stability.11 It is worth noting the organic coat owing
catalytic sites along with structural approach, improve the
catalytic activity of such nanocomposite.12 Vitamin C (ascorbic
acid, AA) as a bio-organic coater is well known for its anti-
oxidant property and is water soluble. Therefore, it is of much
interest to synthesize stable water-soluble magnetic nano-
composite using ascorbic acid.13 The AA is a sugar acid with
a cis-enediol group on the sugar ring and adjacent alcoholic
hydroxyl groups on the side chain available for binding to iron
oxide nanoparticles.14
On the other hand, aldoximes and ketoximes have been widely
used in industry, medicine and analytical chemistry; and they are
very effective and versatile intermediates in synthetic organic
chemistry. The typical synthetic method for oximes is oximation of
aldehydes and ketones with hydroxylamine.15 This method is also
used for the industrial production of 3-caprolactam from cyclo-
hexanone.16 However, hydroxylamine is easily explosive and
unstable during heating. To minimize the risks, hydroxylamine is
oen replaced by diverse salts such as NH2OH$HCl or NH2-
OH$H2SO4.17 Nevertheless, these methodologies show several
shortcomings, such as drastic reaction conditions and compli-
cated operation, which mostly yield many side products and lead
One of the important goals in the eld of catalysis in terms of
green chemistry is to make progress with environmentally
benign, practical, clean, economical and efficient processes for
catalyst separation and recycling.1 From this aspect, nano-
catalysts have exhibited good catalytic activity because of their
large surface area, small size, selectivity, reusability and
recovery from reaction mixtures.2,3 In addition, MNPs have been
used as alternatives to conventional heterogeneous supports.
For this purpose, magnetic ferrite nanoparticles have been
utilized as separable magnetic catalysts as they have large
magnetic anisotropies, high thermal stability, high surface
areas, moderate saturation magnetization and chemical
stability.4,5 A literature review shows that MNPs have been used
in biology,6 biomedicine,7 material sciences,8,9 biochips and
biosensors.10 Bimetal oxide MNPs or metal ferrite nano-
particles, MFe2O4 (M: Mn, Co, Fe, Ni and Zn), are a group of
MNPs which have numerous applications in various elds. They
show a more tunable particle size and better morphology than
Department of Chemistry, University of Kurdistan, P.O. Box 66135-416, Sanandaj,
Iran. E-mail: mghadermazi@yahoo.com; Fax: +98 873324133; Tel: +98 87 33624133
† Electronic supplementary information (ESI) available. See DOI:
10.1039/d0ra08244a
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to drastic environmental contamination.18,19 Hence, it is important oximation and reduction process, suffer from environmental
to prepare efficient and highly selective catalysts that can enhance pollution, the use of hazardous reagents, unsatisfactory yields,
the yield of the corresponding oximes and suppress the formation large amounts, poor recovery of expensive catalysts and long
of side products as much as possible. In recent years, several reaction times, which ultimately lead to the production of large
efficient catalysts were implemented for oximation reaction such amount of toxic waste.
as: [Co(L)2]2Na2[b-Mo8O26]$9H2O and [Fe(L)2]2Na2[b-Mo8O26]$
In continuation of synthesis of task-specic catalysts with
9H2O,20 [K(H2O)6]2[Co(H2O)5]4[WZn3(H2O)2(ZnW9O34)2]$19H2O,21 nanomagnetic properties, herein, we wish to introduce CoFe2-
pyridine-chloroform,22 ethanol-pyridine,23 NaOH with or without O4@AA-M (Co, V) as a novel and active MNPs and concerning
solvent24–27 and hyamine (10 mol%).28 For further reviews on the application of prepared nano catalysts, we have explored
catalytic oximation systems see ref. 29–45. Also, one important their efficacy in the oximation of aldehyde with NH2OH$HCl
class of starting and intermediate materials are aromatic amines and reduction of various nitro compounds to the corresponding
which are used for producing a great diversity of chemicals such as amines with NaBH4 under eco-friendly conditions. It is notable
agrochemicals and rubber materials, pharmaceuticals, biological that, the aim of current work is to introduce magnetic nano-
active molecules, synthetic resins, dyes, plastics and paints.46 ascorbic acid in the trapping and stabilizing of the Co and V
Among some of the reducing agents such as NaBH4, ammonium nanoparticles as a procient, harmless to the environment,
formate, acetic acid, ethylene glycol, hydrazine hydrate, and formic recyclable and magnetic powerful solid catalysts with good
acid as hydrogen sources, NaBH4 showed higher activity compared stability which does not have any of the aforementioned draw-
to the others.47 It is noteworthy that the alone NaBH4 does not backs for the synthesis of mentioned organic reactions.
reduce nitro groups under mild reaction conditions but reducing
ability of this reagent increases dramatically through reduction of
nitro compounds when metal complexes or another promoter are
added. Up to now, some catalytic systems have been reported such
as magnetically nano core–shell Fe3O4@Cu(OH)x/NaBH4,46 bis-
2. Results and discussion
2.1 Catalyst preparation
Development of reusable nanocatalysts and their application in
the progress of organic reaction are our main goal. CoFe2-
O4@AA-M (Co, V) was synthesized as illustrated in Scheme 1.
First, we prepared CoFe2O4 by co-precipitation method. Then to
prepare functionalized magnetic nanocatalysts, the surface of
MNPs was coated using ascorbic acid as green linker. Lastly,
thiourea complexes of bivalent cobalt, nickel, copper and zinc
chlorides48 Ni2B/NaBH4,49 Cu NPs/NaBH4,50 NaBH4/Fe3O4@-
PAMAM/Ni(0)-b-PEG,51 and TiO2@Au/NH2NH2.52 However, to
study more reported reduction protocols see ref. 53–68. In spite of
their merits, the most commonly reported methods in both
Scheme 1 Preparation of CoFe2O4@AA-M (Co, V).
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CoFe2O4@AA-M (Co, V) nanocomposites were generated by conrmed the presence of O, C, Fe, Co, and analysis of CoFe2-
stable interaction of Co and V with functional group of ascorbic O4@AA-V nanocatalyst conrmed the presence of O, C, Fe, Co, V
acid. To conrm the successful synthesis of heterogeneous species in the obtained catalysts (Fig. 2a and b). Also, the X-ray
catalysts, they were identied by several characterization atomic mapping of CoFe2O4@AA-Co and CoFe2O4@AA-V were
equipment such as FT-IR, XRD, FE-SEM, TEM, EDX, TGA, ICP- examined in order to measure the dispersion of Co and V active
OES, X-ray atomic mapping and VSM.
sites anchored over ascorbic acid along with the other core
elements in the catalyst. It was illustrated that the elemental
map images were showed the good dispersion of Co and V on
surface of the catalyst.
2.2 Catalyst characterization
2.2.1 FE-SEM and TEM studies. The morphology of the
CoFe2O4@AA-M (Co, V) catalysts were achieved using scanning
electron microscopy technique. FE-SEM images of these nano-
structures are shown in Fig. 1a and b. As illustrated in this
gure, the prepared compounds were formed with uniform
nanometers-sized particles. It should be noted that the
synthesized samples were obtained with approximately spher-
ical shape. Also, the transmission electron microscopy (TEM)
conrm the core–shell structure and as shown in Fig. 1c the size
of the nanocatalysts is around 50 nm.
2.2.3 TGA-DTA studies. The thermal stability of CoFe2-
O4@AA-M (Co, V) were determined using thermo-gravimetric
analysis (TGA) in the temperature range of 30–700 C (Fig. 3).
ꢀ
The TGA pattern shows an initial small weight loss below
200 ꢀC. In the all samples, the weight loss below 200 ꢀC is
related to the elimination of the chemically and physically
adsorbed solvents or surface hydroxyl groups, and the other
weight loss in the range of 200–500 ꢀC is belonging to the
disintegration of the organic layers on the surface of CoFe2O4
magnetic nanocomposite.69 The reduction of weight in the next
step (500–720 ꢀC) was associating to the further decomposition
of ascorbic acid residues. The TGA prole demonstrate that the
nanocatalysts have a sensible stableness up to 200 ꢀC.
2.2.2 EDX and X-ray atomic map studies. The atomic
percentage of different elements of the synthesized nano-
particles was investigated by energy-dispersive X-ray spectros-
copy (EDX). The EDX analysis of CoFe2O4@AA-Co nanocatalyst
Fig. 1 FE-SEM images of CoFe2O4@AA-Co at (a) 500 nm, (b) 200 nm, FE-SEM images of CoFe2O4@AA-V at (c) 500 nm, (d) 200 nm and TEM
image of CoFe2O4@AA-Co nanocatalyst.
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Fig. 2 EDX spectra and X-ray atomic map analysis of (a) CoFe2O4@AA-Co (b) CoFe2O4@AA-V nanocatalyst.
According to the results of these analyses, the good graing of saturation for CoFe2O4 nanoparticles is higher than that of
AA-M (Co, V) onto the surface of CoFe2O4 nanoparticles is prepared nanocatalysts which is due to the loading of organic
veried.
layers and metal complexes on CoFe2O4 nanoparticles. Despite
2.2.4 XRD studies. XRD prole of CoFe2O4 and CoFe2- the decline in magnetic character of CoFe2O4@AA-M (Co, V), it
O4@AA-M are shown below. XRD analyses were carried out to is sensible enough to be easily separated from the reaction
characterize the phase formation and crystalline structure of mixture by inducing an external magnetic eld.
cobalt ferrite nanoparticles. The pattern conrms formation of
2.2.6 ICP-OES studies. The exact amount of Co and V
pure cubic cobalt ferrite by the peak positions of 2q values at anchored on the surface of modied CoFe2O4 are measured to
22.12ꢀ, 3039ꢀ, 42.18ꢀ, 49.85ꢀ, 61.89ꢀ, 66.79ꢀ and 75.20ꢀ with be 0.52 mmol gꢁ1 and 0.50 mmol gꢁ1 using the ICP atomic
JCPDS 22 1086 (Fig. 4a). As illustrated in XRD pattern of emission spectroscopy method.
CoFe2O4@AA-Co presence of peaks at 2q ¼ 43.6ꢀ and 50.7ꢀ
2.2.7 FT-IR studies. Fig. 6 presents FT-IR spectrum of bare
indicated successful modication of Co and presence of peaks CoFe2O4 nanoparticles (a), CoFe2O4@AA (b), CoFe2O4@AA-Co
at 2q ¼ 44.2ꢀ and 51.3ꢀ indicated successful V at the surface of (c) and CoFe2O4@AA-V (d). Spectrum of the CoFe2O4 clearly
CoFe2O4 nanoparticles (Fig. 4b and c).
shows absorption bands around 586 and 3464 cmꢁ1, which are
2.2.5 VSM studies. To compare magnetic property of bare characteristic of the presence of metal–oxygen bond and
CoFe2O4 with CoFe2O4@AA-M (Co, V) nanoparticles, vibrating hydroxyl functional group (O–H), respectively. As shown in
sample magnetometer (VSM) technique has been used (Fig. 5). Fig. 6b, absorption peaks at approximately 2870–2980 cmꢁ1 (C–
As shown, the saturation magnetization value (Ms) of the bare H stretching vibration) and absorption peak at approximately
CoFe2O4 is 74.4 emu gꢁ1 while aer NPs coating, Ms amount of 1650 cmꢁ1 (C]O stretching vibration) in FT-IR spectrum is due
CoFe2O4@AA-Co and CoFe2O4@AA-V nanoparticles are 33.7 to the loading of ascorbic acid on the surface of the prepared
and 22.8 emu gꢁ1 respectively. It is clear that the magnetic CoFe2O4 nanoparticles. As can be seen from FT-IR spectra of
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Fig.
4
XRD patterns of (a) CoFe2O4, (b) CoFe2O4@AA-Co, (c)
CoFe2O4@AA-V nanocatalyst.
respectively, in the protic solvents such as THF, EtOAc,
CH3CN and EtOH did not take place completely even under
drastic conditions. Interestingly, using H2O as a sole solvent
dramatically accelerated the rate of the oximation process
(entries 8–12, 18 and 22). These observations revealed that H2O
was the best solvent of choice and the best results were achieved
in the presence of 2 mmol hydroxylamine hydrochloride with
20 mg of nano CoFe2O4@AA-M (Co, V) in H2O and at room
temperature condition and it showed a full efficiency for
complete conversion of 1 mmol benzaldehyde to benzaldoxime
immediately (entries 11 and 21).
Fig. 3 TGA-DTA profile of (a) CoFe2O4@AA-Co, (b) CoFe2O4@AA-V
nanocatalyst.
CoFe2O4@AA-Co (c) and CoFe2O4@AA-V (d), the shi on spec-
trum to lower wavenumbers attributed to asymmetrical and
symmetrical modes of the metal–oxygen bonds is happened;
that is because of a robust interaction between the O group of
Co and V complexes on the MNPs.
Furthermore, the progress of the oximation of benzaldehyde
to benzaldoxime with NH2OH$HCl in the presence of CoFe2-
O4@AA-V MNPs was also investigated and conrmed by UV-Vis
analysis using the optimized reaction conditions (mentioned in
Table 1, entry 11). As shown in Fig. 7, during the oximation
reaction, benzaldehyde which is shown by the blue curve
2.3 The catalytic activity
To investigate the catalytic activity of CoFe2O4@AA-Co and
CoFe2O4@AA-V, rst these nanostructures were examined by
NH2OH$HCl oximation of aldehyde derivatives. To optimize the
reaction condition, oximation of benzaldehyde with NH2-
OH$HCl as model substrate was tested. The inuence of
reaction-solvent, temperature and the amount of nanocatalyst.
On the course of the reaction has been illustrated in Table 1.
In spite of the great capabilities of NH2OH$HCl, oximation of
aldehydes with the alone reagent did not proceed at all (entry 1).
Also, CoFe2O4 was not efficient catalyst to progress the reaction
perfectly (entry 2). n-Hexane as aprotic solvent was not able to
progress the reaction well (entries 3 and 13). Entries 4–7 and 13–
17 show that oximation of benzaldehyde with NH2OH$HCl in
the presence of CoFe2O4@AA-Co and CoFe2O4@AA-V
(lmax
¼
250 nm) was fully converted to benzaldoxime
(lmax ¼ 270 nm) which is intimated by the red curve.
It should also be mention that the oximation of benzalde-
hyde to corresponding oxime could be considered as pseudo-
rst-order kinetics because the concentration of NH2OH$HCl
was in excess. Notably, the pseudo-rst-order kinetics equation
can be dened as ln(Ct/C0) ¼ ꢁkappt, where C0 and Ct are the
initial and instantaneous concentration of benzaldehyde,
respectively. As well as the t and kapp stand for the apparent
reaction time and rate constant in turn. Thus, the reaction
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In order to investigate the effects of the NH2OH$HCl amount
on the reaction rate, the concentration of benzaldehyde and
CoFe2O4@AA-Co was kept constant and various amounts of
NH2OH$HCl (1.2, 1.5 and 1.7 mmol) were added to the reaction
vessel. According to the UV-visible spectra (Fig. 9), the reaction
was completed at 20, 15 and 10 s, respectively.
Also, Table 2 shows kapp for these reactions. Based on the
obtained results, we observed that with increasing the concen-
tration of NH2OH$HCl, the amount of the kapp increased.
Notably, although the increase in the amount of NH2OH$HCl
increases, the speed of the oximation reaction, based on the
green chemistry protocols, especially economic efficiency, we
selected 1.2 mmol of the NH2OH$HCl as an optimal amount for
the mentioned reaction.
The effect of various nanocatalyst amounts on the reaction
rate was also studied (Fig. 10). All the other reaction parameters
during the mentioned reaction were kept constant. Based on
the results obtained from Table 3, it can be seen that the kapp
increased from 0.153 to 0.516 sꢁ1 as increasing the concentra-
tion of CoFe2O4@AA-Co from 20 to 30 mg. Notably, the results
clearly showed that the dependence of the reaction rate on
various CoFe2O4@AA-Co amounts is much higher than
NH2OH$HCl various value.
Encouraged by the achieved outcomes, the oximation ability
of NH2OH$HCl/CoFe2O4@AA-M (Co, V) system were examined
for oximation of diverse aldehyde derivatives to the corre-
sponding aldoximes at the optimized reaction conditions. The
outcomes of this examination are shown in Tables 4 and 5.
As illustrated, all reactions were done successfully using the
molar equivalents of aldehyde : NH2OH$HCl (1 : 1.2) in the
presence of 20–40 mg of the nanocatalysts producing the
products in excellent yields within immediate to 7 min. The
result shows that benzaldehyde can be transformed to benzal-
doxime in 96–99% yield (Tables 4 and 3, entry 1). In the case of
electron-releasing substitutions on aromatic rings the corre-
sponding aldoximes can be also obtained in excellent yields. As
well, aromatic aldehydes with electron-withdrawing function-
alities were also successfully changed to the corresponding
aldoximes in high yields using CoFe2O4@AA-M (Co, V) system.
Entry 11 represents that this method is also effective for the
oximation of aliphatic aldehyde to corresponding oxime. The
catalyst turnover frequency (TOF) and turnover number (TON)
are two important factors that are used for measuring the effi-
ciency of the heterogeneous and homogenous catalysts. In
heterogeneous catalytic reactions, the TON and TOF can be
determined on the basis of the amount of product which was
formed.
Fig. 5 Magnetization curves of (a) CoFe2O4, (b) CoFe2O4@AA-Co, (c)
CoFe2O4@AA-V nanocatalyst.
A conceivable mechanism for the nano CoFe2O4@AA-M (Co,
V) catalyzed was shown in Scheme 2. The nanocatalysts simplify
the oximation process via coordination of its M (Co, V) with O of
carbonyl. The condensation made by linkage of R1R2C]O and
O-coordination of hydroxylamine and subsequent intra-
molecular nucleophilic attack. As described, CoFe2O4 was not
capable to progress the reaction perfectly and anchoring Co
and V lead to synthesis efficient nanocatalysts which acceler-
ated the rate of the oximation process. According to these
Fig. 6 FT-IR spectra of (a) CoFe2O4, (b) CoFe2O4@AA, (c) CoFe2-
O4@AA-Co, (d) CoFe2O4@AA-V nanocatalyst.
apparent rate constant (kapp) can be simply calculated with the
slope of ln(Ct/C0) versus reaction time. In this study, the kapp for
oximation of benzaldehyde was 0.153 sꢁ1 (Fig. 8).
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Table 1 Optimization experiments for oximation of benzaldehyde to benzaldoxime with NH2OH$HCl/CoFe2O4@AA-M (Co, V)
Entry
NH2OH$HCl (mmol)
Catalyst (mg)
Conditiona
Time (min)
Conversion (%)
1
2
3
4
5
6
7
8
1.5
1.5
1.2
1.2
1.2
1.2
1.2
1
1.2
1.2
1.2
1.2
1.2
1.2
1.2
1.2
1.2
1
—
H2O/50 ꢀ
H2O/50 ꢀ
C
C
24 h
120
120
25
20
25
20
5
25
10
20 s
10 s
125
28
22
30
23
5
26
10
—
30
30
80
88
88
85
93
85
93
98
99
25
80
87
88
86
90
84
91
96
97
CoFe2O4 (20)
CoFe2O4@AA-Co (20)
CoFe2O4@AA-Co (20)
CoFe2O4@AA-Co (20)
CoFe2O4@AA-Co (20)
CoFe2O4@AA-Co (20)
CoFe2O4@AA-Co (20)
CoFe2O4@AA-Co (10)
CoFe2O4@AA-Co (15)
CoFe2O4@AA-Co (20)
CoFe2O4@AA-Co (25)
CoFe2O4@AA-V (20)
CoFe2O4@AA-V (20)
CoFe2O4@AA-V (20)
CoFe2O4@AA-V (20)
CoFe2O4@AA-V (20)
CoFe2O4@AA-V (20)
CoFe2O4@AA-V (10)
CoFe2O4@AA-V (15)
CoFe2O4@AA-V (20)
CoFe2O4@AA-V (25)
n-Hexane/50 ꢀC
THF/50 ꢀ
EtOAc/50 ꢀ
CH3CN/50 ꢀ
EtOH/50 ꢀ
C
C
C
C
C
H2O/50 ꢀ
H2O/r.t.
H2O/r.t.
H2O/r.t.
H2O/r.t.
9
10
11
12
13
14
15
16
17
18
19
20
21
22
n-Hexane/50 ꢀC
THF/50 ꢀ
EtOAc/50 ꢀ
CH3CN/50 ꢀ
EtOH/50 ꢀ
C
C
C
C
C
H2O/50 ꢀ
H2O/r.t.
H2O/r.t.
H2O/r.t.
H2O/r.t.
1.2
1.2
1.2
1.2
20 s
15 s
a
All reactions were performed with 1 mmol of benzaldehyde, 1.5 mL of solvent.
illustrations, Co and V are the main active sites of the
nanocatalysts.
Thereaer, catalytic activity of CoFe2O4@AA-Co and CoFe2-
O4@AA-V system was distinguished by comparison of the ach-
ieved result for benzaldehyde with other reported oximation
systems. The oximation of benzaldehyde with hydroxylamine
hydrochloride in the presence of diverse catalysts is selected as
reaction model in all cases. The results in Table 6 demonstrate
that in terms of short reaction times, easy work-up procedure,
mild reaction conditions, suppression of any side product,
excellent reusability, handle and inexpensiveness of the nano-
catalysts, the present system illustrates comparable or better
efficiency than the previous reported systems.
Fig. 7 UV-Vis analysis of benzaldehyde oximation under optimized
reaction conditions.
Then the catalytic activity of CoFe2O4@AA-M (Co, V) nano-
particles was examined in NaBH4 reduction of diverse nitro
Fig. 8 Relationship between ln(Ct/C0) and reaction time for the oxi-
mation of benzaldehyde.
Fig. 9 Effect of the concentration of NH2OH$HCl on the reaction rate.
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Table 2 Effect of the concentration of NH2OH$HCl on the reaction
rate
selectivity and the ketones and aldehydes can both be readily
reduced to alcohols (entries 8–10). It is considerable that the
successful reduction of nitroaldehydes and nitroketones
needed higher molar equivalents of NaBH4 and CoFe2O4@AA-M
(Co, V) complexes. A more investigation showed that the present
system was also effective for reduction of aliphatic nitro
compounds (entry 11). The corresponding product were ob-
tained exclusively with high turnover numbers (TON) and
turnover frequencies (TOF).
Entry
NH2OH$HCl (mmol)
Time (s)
kapp (s)
1
2
3
1.2
1.5
1.7
20
15
12
0.153
0.262
0.338
A conceivable mechanism for the nano CoFe2O4@AA-M (Co,
V) catalyzed was shown in Scheme 3. The nanocatalysts facili-
tate the reduction of nitro group. It should be mentioned that
there are four steps in the nitro reduction process.
First hydrogen absorption occurred, then adsorbed on the
metal surfaces. In the thirꢁd stage, electron transfer through
metal surfaces from BH4 to aromatic nitro compounds.
Eventually, aromatic amino compounds desorbed from catalyst
surface. Here the B–H bond cleavage occurs on the surface of
CoFe2O4@AA-M (Co, V) nanocatalysts to give the [M]–H species.
Such high reactive intermediates are responsible for the fast
reduction of nitro compounds into the corresponding phenyl-
hydroxylamine with very rapid reaction kinetics and possibly
skips the compounds intermediate.
Fig. 10 Effect of the concentration of CoFe2O4@AA-Co on the
Thereaer, catalytic activity of CoFe2O4@AA-Co and CoFe2-
O4@AA-V system was distinguished by comparison of the achieved
result for nitrobenzene with other reported reduction systems. The
reduction of nitrobenzene in the presence of different catalysts is
the selected reaction model in all cases. The results in Table 10
indicate that in terms of mild reaction conditions, easy work-up
procedure, short reaction times, high recyclability, suppression
of any side product, handle and inexpensively of the nanocatalysts,
the present system illustrates better or comparable efficiency than
the previous reported systems.
reaction rate.
Table 3 Effect of the concentration of CoFe2O4@AA-Co on the
reaction rate
Entry
CoFe2O4@AA-Co (mg)
Time (s)
kapp (s)
1
2
3
20
25
30
20
12
8
0.153
0.292
0.516
2.4 Recycling CoFe2O4@AA-M (Co, V)
compounds. Reduction of nitrobenzene as a model compound
with NaBH4 was performed under different reaction conditions,
in order to optimize reaction conditions. The results have been
indicated in Table 7. The illustrated results in Table 7 show that
reduction of nitrobenzene with the alone NaBH4 in the absence
of catalyst did not proceed at all (entry 1). Also, CoFe2O4 was not
efficient catalyst to progress the reaction perfectly (entry 2). The
illustrated results show that reduction of nitrobenzene with
NaBH4 in the presence of CoFe2O4@AA-M (Co, V) in aprotic
solvent was not efficient (entries 4 and 13). Analysis of the
results indicates that H2O was the best solvent of choice and the
reaction take place with high speed and the corresponding
product was separated in high yield with 30 mg of the CoFe2O4/
AA-M (Co, V) at room temperature (entries 10 and 19).
In continue, this protocol was used in reduction of diverse
nitro compounds derivatives. The summarized results in
Tables 8 and 9 indicate that reduction of nitro compounds
having electron-releasing or withdrawing functionalities was
accomplished successfully using 2–3 molar equivalents of
NaBH4 and 30–40 mg of CoFe2O4@AA-M (Co, V) within 3–
15 min in H2O at room temperature. Also, the case of nitro-
arenes having carbonyl and nitro groups show did not any
As one of the interesting advantages of nonmagnetic catalysts is
their easy isolation from the reaction mixture by applying an
external magnet, the possibility of the magnetic recycling of
catalysts were also tested. Thus, initially the recovery and
reusability of CoFe2O4@AA-Co and CoFe2O4@AA-V were inves-
tigated towards NH2OH$HCl oximation of benzaldehyde and
then for reduction of nitrobenzene with NaBH4. For this reason,
aer completion of the reactions, the catalysts were easily
separated from the reaction mixture using an external magnet
and washed carefully with ethanol then dried under air atmo-
sphere for additional using at the subsequent runs. It is clear
that the efficiency of the investigated catalysts was restored aer
several successive runs with a low decreasing of its catalytic
activity (Fig. 11 and 12).
In order to identify the changes in the chemical structure of
the catalysts towards NH2OH$HCl oximation of benzaldehyde
during the six cycles, FE-SEM and FT-IR analyses were performed
and the results are demonstrated below (Fig. 13a and b). These
investigations claried that CoFe2O4@AA-M (Co, V) catalysts
retained its chemical structure aer the longevity of experiments.
It is noteworthy that investigation of catalyst reusability aer
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Table 4 Oximation of aldehydes with NH2OH$HCl in the presence of CoFe2O4@AA-Coa,b,c,d,e
CoFe2O4@AA-Co
Entry
1
Substrate
Product
Molar ratio Catalyst (mg) Time (s) Yield (%) TON TOF (hꢁ1
)
Mp (ꢀC)
1 : 1.2
1 : 1.2
20
20
20
15
98
97
23.33 4199
23.09 5541
32 (ref. 70)
2
3
86 (ref. 70)
1 : 1.2
20
20
88
20.95 3771
—
4
5
1 : 1.2
1 : 1.2
20
20
1 min
1 min
86
92
20.47 1228.2
21.90 1314
129 (ref. 71)
70 (ref. 70)
6
1 : 1.2
30
1 min
89
14.12 847.2
179 (ref. 70)
7
1 : 1.2
1 : 1.2
1 : 1.2
1 : 1.2
40
30
20
30
7 min
4 min
2 min
3 min
86
82
90
82
10.11 86.65
13.01 195.15
21.42 642.6
13.01 260.2
58 (ref. 70)
83 (ref. 70)
74 (ref. 30)
—
8
9
10
11
1 : 1.2
20
45
82
19.52 1561.6
—
a
b
c
d
Molar ratio: sub./NH2OH$HCl. Im. means immediately. Yields refer to isolated pure product. TON (turnover number) ¼ [(mol amount of
product)/(mol amount of used catalyst)]. e TOF (turnover frequency) ¼ [(mol amount of product)/(mol amount of used catalyst) ꢂ (time)].
reduction of nitro compounds also display the same results and and the value of V in fresh catalyst and the recycled one aer 6
conrmed the catalyst efficiency aer several runs.
times is 0.50 and 0.47 mmol gꢁ1 respectively which illustrated
the minimal Co and V leaching in the catalytic process
demonstrated the efficiency and stability of the catalyst.
2.5 Catalyst leaching study
The value of Co and V leaching in reduction of nitro compounds
was investigated by comparing the metal anchoring value
2.6 Hot ltration test
before and aer recovering of the catalyst by ICP-OES method. In continuation of current protocol, efficiency of introduced
Result showed that the value of Co in fresh catalyst and the catalysts were examined with hot ltration test. The oximation
recycled one aer 6 times is 0.52 and 0.49 mmol gꢁ1 respectively of benzaldehyde in the presence of reported catalysts was
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Table 5 Oximation of aldehydes with NH2OH$HCl in the presence of CoFe2O4@AA-Va,b,c,d,e
CoFe2O4@AA-V
Entry
Substrate
Product
Molar ratio Catalyst (mg) Time (s) Yield (%) TON TOF (hꢁ1
)
Mp (ꢀC)
1
2
1 : 1.2
1 : 1.2
20
20
20
18
96
94
22.32 4017
21.86 4372
31 (ref. 70)
88 (ref. 70)
3
1 : 1.2
20
30
85
19.76 2371.2
—
4
5
1 : 1.2
1 : 1.2
40
20
3 min
1 min
85
88
9.88
197.6
131 (ref. 71)
70 (ref. 70)
20.46 1227.6
6
1 : 1.2
40
1 min
86
10
600
181 (ref. 70)
7
1 : 1.2
1 : 1.2
1 : 1.2
1 : 1.2
40
40
20
40
7 min
7 min
3 min
4 min
84
82
88
82
9.76
9.53
83.65
81.68
60 (ref. 70)
80 (ref. 70)
76 (ref. 30)
—
8
9
20.46 409.2
10
9.53
142.95
11
1 : 1.2
20
2 min
80
19.06 571.8
—
a
b
c
d
Molar ratio: sub./NH2OH$HCl. Im. means immediately. Yields refer to isolated pure product. TON (turnover number) ¼ [(mol amount of
product)/(mol amount of used catalyst)]. e TOF (turnover frequency) ¼ [(mol amount of product)/(mol amount of used catalyst) ꢂ (time)].
selected to carried out hot ltration test. Under optimized
conditions, oximation of benzaldehyde was proceeded in the
presence of CoFe2O4@AA-Co and CoFe2O4@AA-V in which the
3. Experimental
3.1 Instruments and materials
yields of products in the half time of the reaction were 70 and
68%, respectively. Then the reaction was repeated and the
nanocatalyst was isolated in half time of the reaction. There-
upon, continuous reaction was carried out without CoFe2O4@-
AA-Co and CoFe2O4@AA-V in which the yields of reaction were
73 and 70%, respectively. These observations corroborated that
the leaching of metal has not been happened.
All chemicals and solvents were purchased from Sigma-Aldrich
and Merck chemical companies and were used without extra
purication. The surface morphology and diameter of the
CoFe2O4/AA-M (Co, V) nanocatalysts were studied by scanning
electron microscopy (FE-SEM) analysis data was recorded SEM-
TESCAN MIRA3. Transmission electron microscopy (TEM) was
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samples were determined using a vibrating sample magne-
tometer (VSM) at room temperature (MDKFD, University of
Kashan, Iran). The amounts of Co and V in synthesized the
nanocatalysts were evaluated by plasma-optical emission spec-
trometry (ICP-OES). Infrared (FT-IR) spectra of all samples were
recorded on PerkinElmer Spectrum one instruments, using KBr
pellets in the range of 400–4000 cmꢁ1
.
3.2 Synthesis of CoFe2O4@AA nanocomposite
To synthesize superparamagnetic CoFe2O4 as catalyst support,
a solution of 50 mL of Fe(NO3)3$9H2O (16 mmol, 6.46 g) was
added to a solution of 25 mL of Co(NO3)2$6H2O (8 mmol, 2.32 g)
and the mixture was vigorously stirred. Then, sodium hydroxide
3 M was added dropwise by stirring until the reaction mixture
reached pH ¼ 11–12 then stirring was continued at 80 ꢀC for one
hour. Subsequently, the nal product was isolated using an
external magnet and washed three times with double distilled
hot water and ethanol. At the end, tꢀhe magnetic nano-
composites (CoFe2O4) dried in oven at 60 C.
Scheme 2 A conceivable mechanism for the nano CoFe2O4@AA-M
(Co, V) towards oximation of aldehydes.
carry out using a FEI CM200 eld emission at accelerating
voltage of 80 kV. The XRD was recorded on JEOL JSM-6100
˚
microscope with (Cu Ka radiation, l ¼ 1.54 A). The thermal
gravimetric analysis (TGA) of nanocomposite was carried out on
a Shimadzu analyzer DTG-60. Magnetic properties of the
Table 6 Comparison of the promoter activity of CoFe2O@AA-M/NH2OH$HCl system for oximation of benzaldehyde with other reported
protocols
Entry
Catalyst
Condition
Yield (%)
Time (min)
References
1
2
3
4
5
6
7
SiO2@FeSO4
Bi2O3
Cu–SiO2
Nano Fe3O4
H2C2O4
CoFe2O4@AA-Co
CoFe2O4@AA-V
NH2OH$HCl/s.f/oil bath/70–80 ꢀC
NH2OH$HCl/s.f
96
95
90
100
95
99
96
12
1.5
2–3 h
20
60
34
40
41
33
NH2OH$HCl/aq. EtOH
NH2OH$HCl/s.f/oil bath/70–80 ꢀC
NH2OH$HCl/CH3CN/reux
NH2OH$HCl/H2O/r.t.
35
Immediate
Immediate
This work
This work
NH2OH$HCl/H2O/r.t.
Table 7 Optimization experiments for reduction of nitrobenzene using CoFe2O4@AA-M (Co, V) nanocomposite
Entry
NaBH4 (mmol)
Catalyst (mg)
Conditiona
Time (min)
Conversion (%)
1
2
3
4
5
6
7
8
2.5
2.5
2.5
2.5
2.5
2.5
2.5
1.5
2
—
H2O/50 ꢀC
H2O/50 ꢀC
24 h
120
25
120
20
25
20
10
4
—
40
75
10
78
80
75
91
96
98
98
75
10
76
80
75
90
95
98
98
CoFe2O4 (40)
CoFe2O4@AA-Co (40)
CoFe2O4@AA-Co (40)
CoFe2O4@AA-Co (40)
CoFe2O4@AA-Co (40)
CoFe2O4@AA-Co (40)
CoFe2O4@AA-Co (40)
CoFe2O4@AA-Co (35)
CoFe2O4@AA-Co (30)
CoFe2O4@AA-Co (30)
CoFe2O4@AA-V (40)
CoFe2O4@AA-V (40)
CoFe2O4@AA-V (40)
CoFe2O4@AA-V (40)
CoFe2O4@AA-V (40)
CoFe2O4@AA-V (40)
CoFe2O4@AA-V (35)
CoFe2O4@AA-V (30)
CoFe2O4@AA-V (30)
THF/50 ꢀ
C
n-Hexane/50 ꢀ
EtOAc/50 ꢀ
CH3CN/50 ꢀ
C
C
C
EtOH/50 ꢀ
C
H2O/50 ꢀC
H2O/r.t.
H2O/r.t.
H2O/r.t.
9
10
11
12
13
14
15
16
17
18
19
20
2
5
5
2.5
2.5
2.5
2.5
2.5
2.5
1.5
2
THF/50 ꢀ
C
28
125
22
30
23
11
5
n-Hexane/50 ꢀ
EtOAc/50 ꢀ
CH3CN/50 ꢀ
C
C
C
EtOH/50 ꢀ
C
H2O/50 ꢀC
H2O/r.t.
H2O/r.t.
H2O/r.t.
2
2.5
6
6
a
All reactions were proceeded with 1 mmol of nitrobenzene, 1.5 mL of solvent.
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Table 8 Reduction of nitro compounds with NaBH4 in the presence of CoFe2O4@AA-Co nanocompositea,b,c,d,e
CoFe2O4@AA-Co
Entry
1
Substrate
Product
Molar ratio Catalyst (mg) Time (s) Yield (%) TON
TOF (hꢁ1
)
Mp (ꢀC)
1 : 2
1 : 2
30
30
3
9
98
95
15.55 311
—
2
3
15.07 100.46
14.60 219
172 (ref. 72)
81 (ref. 67)
1 : 2
30
4
92
4
5
1 : 2
1 : 2
30
30
7
9
95
90
15.07 129.17
14.28 95.20
32 (ref. 73)
92 (ref. 73)
6
1 : 2
30
8
90
14.28 107.1
100 (ref. 73)
7
8
9
1 : 2
1 : 3
1 : 3
30
40
40
12
13
15
91
88
90
14.44 72.19
10.23 47.21
10.58 42.32
141 (ref. 67)
83 (ref. 73)
61 (ref. 73)
10
1 : 3
40
30
15
6
90
10.58 42.32
14.76 147.6
68 (ref. 73)
11
1-Nitropentane
1-Aminopentane
1 : 2
93
—
a
b
c
d
Molar ratio: sub./NH2OH$HCl. Im. means immediately. Yields refer to isolated pure product. TON (turnover number) ¼ [(mol amount of
product)/(mol amount of used catalyst)]. e TOF (turnover frequency) ¼ [(mol amount of product)/(mol amount of used catalyst) ꢂ (time)].
Similarly, to produce CoFe2O4@AA, a solution of ascorbic
acid (1 g in 25 mL double distilled water) was added dropwise to
suspensions of 2 g CoFe2O4 in 30 mL double distilled water.
Then, the reaction mixture was stirred for 24 hours at room
temperature. Finally, the prepared nanocomposite was isolated
using an external magnet washed with double distilled water/
3.3 Synthesis of CoFe2O4@AA-Co nanostructure
To expand the scope of the processes, we produced the CoFe2-
O4@AA-Co by blending sonicated CoFe2O4@AA (1 g) in 50 mL of
double distilled water and a solution of 5 mL CoCl2$6H2O
(0.476 g, 2 mmol) was added to mentioned mixture and stirred
under reux for 24 hours. Then, the achieved product was iso-
lated using an external magnet and washed with double
ꢀ
ethanol several times and dried in vacuum oven at 60 C.
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Table 9 Reduction of nitro compounds with NaBH4 in the presence of CoFe2O4@AA-V nanocompositea,b,c,d,e
CoFe2O4@AA-V
Entry
1
Substrate
Product
Molar ratio Catalyst (mg) Time (s) Yield (%) TON
TOF (hꢁ1
)
Mp (ꢀC)
1 : 2
1 : 2
30
30
3
98
95
15.07 301.4
—
2
3
11
14.61
79.69
170 (ref. 72)
83 (ref. 67)
1 : 2
30
6
90
13.84 138.4
14.30 122.57
4
5
1 : 2
1 : 2
30
30
7
93
88
30 (ref. 73)
92 (ref. 73)
10
13.53
13.84
81.18
83.04
6
1 : 2
30
10
90
101 (ref. 73)
7
8
9
1 : 2
1 : 3
1 : 3
30
40
40
13
14
15
90
88
88
13.84
10.23
10.23
63.87
43.84
40.92
139 (ref. 67)
82 (ref. 73)
62 (ref. 73)
10
1 : 3
40
30
15
6
90
10.46
41.84
67 (ref. 73)
11
1-Nitropentane
1-Aminopentane
1 : 2
92
14.15 141.5
—
a
b
c
d
Molar ratio: sub./NH2OH$HCl. Im. means immediately. Yields refer to isolated pure product. TON (turnover number) ¼ [(mol amount of
product)/(mol amount of used catalyst)]. e TOF (turnover frequency) ¼ [(mol amount of product)/(mol amount of used catalyst) ꢂ (time)].
distilled water/ethanol several times then dried in a vacuum washed with double distilled water/ethanol several times and,
ꢀ
ꢀ
oven at 60 C.
nally, dried in a vacuum oven at 70 C.
3.4 Synthesis of CoFe2O4@AA-V nanostructure
3.5 A general procedure for oximation of aldehydes with
NH2OH$HCl in the presence of CoFe2O4@AA-M (Co, V) system
In this step, CoFe2O4@AA (1 g) was dispersed in 50 mL of
double distilled water with ultrasonication for 10 min. Subse- In a round-bottom ask (10 mL) equipped with a magnetic
quently, a solution of 5 mL VCl3 (0.314 g, 2 mmol) was added to stirrer, a solution of aldehyde (1 mmol) in H2O (1.5 mL) was
mentioned mixture and stirred under reux for 24 hours. The provided. Aer 1 min, hydroxylamine hydrochloride (1 mmol,
resultant product separated using an external magnet and 0.069 g) was added and the solution was stirred at room
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completion of the reaction, H2O (3 mL) was added and the
mixture was stirred for 5 min. The aldoxime product was
extracted with EtOAc (2 ꢂ 4 mL) then the organic layer was
dried over anhydrous Na2SO4. Evaporation of the solvent
caused the pure aldoxime in excellent yield (Table 4, entry 1).
The
pure
product
was
obtained
upon
column
chromatography.
3.5.1 Benzaldoxime. Yellow oil; 1H NMR (500 MHz, CDCl3)
d 9.26 (br, 1H), 8.28 (s, 1H), 7.64–7.60 (m, 2H), 7.46–7.43 (m,
3H). 13C NMR (125 MHz, CDCl3) d 153.35, 132.79, 131.05,
129.02, 126.78.
3.5.2 4-Fluorobenzaldoxime. White solid; 1H NMR (500
MHz, CDCl3) d 8.22 (s, 1H), 7.64–7.59 (m, 2H), 7.15–7.1 (m, 2H).
13C NMR (125 MHz, CDCl3) d 164, 162.3, 149.45, 129, 127.89,
115.96.
Scheme 3 A conceivable mechanism for the nano CoFe2O4@AA-M
(Co, V) towards reduction of nitro compounds.
3.5.3 4-Nitrobenzaldoxime. White solid; 1H NMR (500
MHz, DMSO-d6) d 11.8 (br, 1H), 8.27 (s, 1H), 8.32 (d, J 1/4 8.5 Hz,
2H), 7.92 (d, J 1/4 8.5 Hz, 2H). 13C NMR (125 MHz, DMSO-d6)
d 146.75, 147, 140, 127.14, 124.04.
3.5.4 2-Chlorobenzaldoxime. White solid; 1H NMR (500
MHz, CDCl3) d 8.75 (br, 1H), 7.92 (dd, J 1/4 7.5, 1.5 Hz, 1H), 7.43
(dd, J 1/4 7.5, 1.2 Hz, 1H), 7.42 (td, J 1/4 7.5, 1.2 Hz, 1H), 7.36–
7.31 (m, 1H). 13C NMR (125 MHz, CDCl3) d 148.1, 134.06, 130.81,
129.74, 129.8, 126.87, 127.19.
3.6 A general procedure for reduction of nitro compounds
with NaBH4 in the presence of CoFe2O4@AA-M (Co, V) system
In a round-bottom ask (10 mL) equipped with a magnetic
stirrer, a solution of nitrobenzene (1 mmol) in H2O (1.5 mL) was
provided. Aer 1 min, sodium borohydride (2 mmol, 0.076 g)
was added and the solution was stirred at room temperature for
30 s. To the prepared solution CoFe2O4@AA-Co (30 mg) was
added and stirring of the reaction mixture was carried on at
room temperature. Progress of the reaction was monitored
using TLC (eluent: n-hexane/EtOAc: 5/2). Aer completion of the
reaction, H2O (3 mL) was added and the mixture was stirred for
5 min. The aniline product was extracted with EtOAc (2 ꢂ 4 mL)
then the organic layer was dried over anhydrous Na2SO4.
Evaporation of the solvent caused aniline in excellent yield
(Table 8, entry 1) and the column chromatography afforded the
pure aniline.
Fig. 11 Reusability of CoFe2O4@AA-M (Co, V) towards NH2OH$HCl
oximation of benzaldehyde under optimize conditions.
3.6.1 Aniline. Yellow oil; 1H NMR (400 MHz, CDCl3)
d ¼ 3.48 (s, 2H), 6.62–6.79 (m, 3H), 7.14 ppm (t, J ¼ 8 Hz, 2H);
13C NMR (100 MHz, CDCl3) d ¼ 115.1, 117.88, 129.8, 146.5 ppm.
3.6.2 Benzene-1,4-diamine. White solid; 1H NMR
(400 MHz, CDCl3) d ¼ 3.38 (s, 4H), 6.61 (s, 4H); 13C NMR (100
MHz, CDCl3) d ¼ 117.2, 138.7 ppm.
3.6.3 4-Hydroxymethylaniline. Colorless solid; 1H NMR
(CDCl3, 500 MHz): d 7.21–7.18 (m, 2H), 6.72–6.66 (m, 2H), 4.78
(s, 2H) 3.67 (br, 2H); 13C NMR (CDCl3, 125 MHz): d 146.1, 128.9,
128.6, 115.2, 65.1.
Fig. 12 Reusability of CoFe2O4@AA-M (Co, V) for the reduction of
nitrobenzene with NaBH4 under optimized conditions.
3.6.4 2-Amino-phenol. White solid; 1H NMR (500 MHz,
DMSO-d6) d: 8.96 (s, 1H), 6.63–6.61 (m, 1H), 6.54–6.59 (m, 1H),
6.52–6.55 (m, 1H), 6.31–6.35 (m, 1H), 4.40 ppm (s, 2H); 13C NMR
(125 MHz, DMSO-d6) d ¼ 145, 137, 119.8, 116.7, 115, 114.7 ppm.
temperature for 30 s. To the prepared solution CoFe2O4@AA-
Co (30 mg) was added and stirring of the reaction mixture
was carried on at room temperature. Progress of the reaction
was monitored using TLC (eluent: n-hexane/EtOAc: 5/2). Aer
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Table 10 Comparison the reduction of nitrobenzene using CoFe2O@AA-M (Co, V) nanocomposite with other reported protocols
Entry
Catalyst
Condition
Yield (%)
Time (min)
References
1
2
3
4
5
6
7
8
Fe3O4@Cu(OH)x
Fe3O4@PAMAM/Ni(0)-b-PEG
SS-Pd
Ag/a-Fe2O3–rGO
Ag/Fe2O3
Fe–Cu@MCC
Pd-NPs@oak gum
Pd/Fe3O4@C
UiO-66-D-PANI–AgPd
CoPd@CNT
Graphene–ZnO–Au
Pd–NHC–g-Fe2O3–n-butyl SO3H
Fe3O4@APTMS@ZrCp2
Fe3O4@Ni
NaBH4/H2O/55–60 ꢀC
95
91
98
98
99
93
96
100
99
99
97
93
96
95
96
95
3
46
51
54
57
58
59
60
61
62
63
64
65
67
68
NaBH4/H2O/40 ꢀ
C
120
60
30
30
8
60
60
6 h
3
140
3 h
40
25
3
NaBH4/MeOH$H2O/50 ꢀ
N2H4$H2O/H2O/r.t.
C
NaBH4/H2O/100 ꢀ
NaBH4/H2O/r.t.
C
NaBH4/EtOH$H2O/50 ꢀ
C
NaBH4/EtOH/25 ꢀ
C
9
Formic acid/H2O/90 ꢀ
C
10
11
12
13
14
15
16
NaBH4/MeOH : H2O/r.t.
H2O/r.t./(UV-Vis lamp)
NaBH4/EtOH$H2O/r.t.
Glycerol/H2O/r.t.
NaBH4/H2O/r.t.
NaBH4/H2O/r.t.
CoFe2O4@AA-Co
CoFe2O4@AA-V
This work
This work
NaBH4/H2O/r.t.
3
Fig. 13 FE-SEM and FT-IR analyses of reused catalysts for reduction of nitrobenzene with NaBH4 under optimized conditions after 6 runs (a)
CoFe2O4@AA-Co and (b) CoFe2O4@AA-V.
these nanomaterials were identied by FT-IR, FE-SEM, TEM,
EDX, TGA, XRD, VSM, X-ray atomic mapping and ICP-OES
4. Conclusions
techniques. The catalytic status of these nanostructures was
obtained as a recyclable system for the oximation of multiple
aldehyde combinations by hydroxylamine hydrochloride in
H2O/r.t. conditions. Aldoximes were produced in great yields
In present work we successfully exhibited an effectual practice
for the synthesis of two efficient and green reusable heteroge-
neous catalytic system, CoFe2O4@AA-Co and CoFe2O4@AA-V
obtained by anchoring Co or V onto the face of CoFe2O4. Next,
41350 | RSC Adv., 2020, 10, 41336–41352
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within immediate to 7 min. In addition, the catalytic efficiency 12 L. Wu, A. Mendoza-Garcia, Q. Li and S. Sun, Chem. Rev.,
of introduced nanocatalysts were tested toward NaBH4 reduc- 2016, 116, 10473.
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1659.
´
´
´
´
reaction conditions, suppression of any side product and 18 R. Garcıa-Alvarez, A. E. Dıaz-Alvarez, J. Borge, P. Crochet and
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Conflicts of interest
There are no conicts to declare.
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