Synthesis of a new schiff base oxovanadium complex with melamine and 2-hydroxynaphtaldehyde on modified magnetic nanoparticles as catalyst for allyl alcohols and olefins epoxidation

Article abstract of DOI:10.1002/aoc.4896

A new magnetically recoverable nanocatalyst designated as Fe₃O₄@SiO₂@PTMS@Mel-Naph-VOcomplex was synthesize by covalent binding of a Schiff base ligand derived from melamine and 2-hydroxy1naphtaldehyde on the surface of silica coated iron oxide magnetic nanoparticles followed by complexation with VO (acac)₂. Characterization of the prepared nanocatalyst was accomplished with FT-IR, XRD, SEM, HRTEM, VSM and atomic absorption techniques. It was found that the epoxidation of geraniol, trans-2-hexen-1-ol, 1-octen-3-ol, norbornene, and cyclooctene is highly selective, affording quantitative yields of the corresponding epoxides with tert-butyl hydroperoxide (TBHP) using Fe₃O₄@SiO₂@Mel-Naph-VOcomplex as catalyst. High reaction yields, short reaction times, simple experimental and work up procedure, catalyst stability and excellent reusability even after five-cycles of usage in the case of geraniol are some advantages of this research.

Full text of DOI:10.1002/aoc.4896

Received: 30 November 2018
DOI: 10.1002/aoc.4896
Revised: 24 January 2019
Accepted: 11 February 2019
F U L L P A P E R
Synthesis of a new schiff base oxovanadium complex with
melamine and 2‐hydroxynaphtaldehyde on modified
magnetic nanoparticles as catalyst for allyl alcohols and
olefins epoxidation
Faezeh Farzaneh
| Zeinab Asgharpour
Alzahra University, Iran
A
new magnetically recoverable nanocatalyst designated as Fe3O4@
Correspondence
Faezeh Farzaneh, Alzahra University,
Iran.
SiO2@PTMS@Mel‐Naph‐VOcomplex was synthesize by covalent binding of
a Schiff base ligand derived from melamine and 2‐hydroxy1naphtaldehyde
on the surface of silica coated iron oxide magnetic nanoparticles followed
by complexation with VO (acac)2. Characterization of the prepared
nanocatalyst was accomplished with FT‐IR, XRD, SEM, HRTEM, VSM and
atomic absorption techniques. It was found that the epoxidation of geraniol,
trans‐2‐hexen‐1‐ol, 1‐octen‐3‐ol, norbornene, and cyclooctene is highly selec-
tive, affording quantitative yields of the corresponding epoxides with tert‐
butyl hydroperoxide (TBHP) using Fe3O4@SiO2@Mel‐Naph‐VOcomplex as
catalyst. High reaction yields, short reaction times, simple experimental and
work up procedure, catalyst stability and excellent reusability even after
five‐cycles of usage in the case of geraniol are some advantages of this
research.
Email: faezeh_farzaneh@yahoo.com;
farzaneh@alzahra.ac.ir
Funding information
Alzahra University
KEYWORDS
epoxidation allylalcohols, melamine, modified magnetic nanoparticles, olefins, vanadium Schiff base
complex
1 | INTRODUCTION
Strecker reactions,[14] olefin polymerization[15] and car-
bon–carbon cleavages.[16]
The enzymatic role and importance of vanadium
compounds in biological catalytic systems such as
bromoperoxidase and nitrogenase has created attention
in the synthesis and catalytic activities of vanadium com-
plexes.[1–4] Catalytic oxidation by metal complexes is one
of the most widely studied reactions in organic chemistry
since epoxides are important synthetic intermediates for a
wide variety of products.[5–8] Oxovanadium complexes
have been widely used as homogeneous and heteroge-
neous catalysts for reactions such as alkene epoxida-
tions,[9] sulfoxidation,[10] alcohol oxidations,[11] oxidative
couplings,[12] oxidative brominations,[13] oxidative
In recent years, different types of vanadium coordina-
tion compounds with Schiff base ligands were synthe-
sized and used as homogeneous and heterogeneous
catalysts in the epoxidation reactions.[17–22] Moreover,
to modify the stabilization and recycling ability of the
homogeneous catalysis systems, they have been
immobilized onto the solid supports. Various organic
polymers[23] and inorganic materials such as silica,
MCM‐41, SBA‐15, zeolites and magnetic nanoparti-
cles[24–28] have been used as support in heterogeneous
catalysis systems. Among them, Fe3O4 magnetic nano-
particles have attracted great interest because of low cost,
Appl Organometal Chem. 2019;e4896.
wileyonlinelibrary.com/journal/aoc
© 2019 John Wiley & Sons, Ltd.
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https://doi.org/10.1002/aoc.4896

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FARZANEH AND ASGHARPOUR
high surface area, low toxicity and easily separation by
applying an external magnetic field.[29,30] In this regard,
vanadium complex with N,N‐bis(3‐salicylidenamino
propyl)amine (salpr),[31] Cu Schiff base complex with
histidine and glutaraldehyde,[32] vanadium Schiff base
complex with histidine and glutaraldehyde[26], vanadium
Schiff base complex with 1,2‐bis(2‐formyl naphthoxy)eth-
ane,[33] manganese Schiff base complex with azo Schiff
base [(Z)‐5‐({2,4‐dichloro‐6‐hydroxyphenyl}diazenyl)‐2‐
hydroxybenzaldehyde,[34] manganese Schiff base complex
with 2, 2‐dimethylpropylenediamine and 5‐bromo‐2‐
hydroxybenzaldehyde,[35] molybdenum Schiff base
complex with terephthaldehyde and thiosemicar
bazide,[36] Cu2+ Schiff base complex with 3‐aminopropyl
(triethoxy) silane and 5‐bromo‐2‐hydroxybenzalde
hyde[37] immobilized on modified Fe3O4 nanoparticles
have been used as catalyst for different organic transfor-
mation reactions. We are pleased to describe the synthe-
sis of a new Schiff base oxovanadium complex with
melamine and 2‐hydroxynaphtaldehyde immobilized on
the modified magnetic nanoparticles and using it as cat-
alyst in the epoxidation of allyl alcohols and olefins.
2 | EXPRIMENTAL
2.1 | Materials and instrumentation
All materials were of commercial reagent grade and used
without further purification. FT‐IR spectra were recorded
on a Bruker Tensor 27 FT‐IR spectrometer using KBr pel-
lets over the range of 4000–400 cm−1. Scanning electron
micrograph (SEM) images were taken by XL‐30 Phillips
(1992). High‐resolution transmission electron microscopy
(HRTEM) images were taken by FEI‐Tecnai F20. Magnetic
susceptibility measurements were carried out using a
vibrating sample magnetometer (VSM) (BHV‐55, Riken,
Tehran, Iran) in the magnetic field range of −8000 to
FIGURE 1 Preparation of
Fe3O4@SiO2@PTMS@Mel‐Naph‐
VOcomplex
FIGURE 2 FT‐IR spectra of (a) Fe3O4, (b) Fe3O4@SiO2, (c) Fe3O4@SiO2@CPTMS, (d) Fe3O4@SiO2@PTMS@Melamine, (e)
Fe3O4@SiO2@PTMS@Mela‐Naph (f) Fe3O4@SiO2@ PTMS @Mel‐NaphVO complex before using and (g) after using as catalyst

FARZANEH AND ASGHARPOUR
3 of 11
8000 Oe at room temperature. The X‐ray powder diffrac-
tion (XRD) data were recorded on a Siefert XRD 3003
PTS diffractometer using Cu Kλ radiation (k = 1.5406 Å).
Vanadium was determined by atomic absorption on a
Chermo double beam instrument. Epoxidation products
were analyzed by GC and GC‐Mass using Agilent 6890
series with a FID detector, HP‐5, 5% phenylmethylsiloxane
capillary and Agilent 5973 network, mass selective detec-
tor, HP‐5 MS 6989 network GC system, respectively.
2.2 | Preparation of modified magnetic
nanoparticles
Fe3O4 as magnetic nanoparticle (MNPs), Fe3O4@SiO2
silica coated magnetic nanoparticle (SCMNPs) and
chlororopropyl
modified
SCMNPs
(Fe3O4@SiO2
@CPTMS) designated as ClpSCMNPs were prepared as
reported before (see also supplementary).[38,39]
2.3 | Preparation of schiff base of
melamine and 2‐hydroxynaphtaldehyde on
the modified magnetic nanoparticles
surface (Fe3O4@SiO2@PTMS@Mel‐Naph)
ClpSCMNPs (1.0 g) was suspended in EtOH (50 ml) and
mixed with melamine (0.13 g, 1 mmol) and the mixture
was heated at reflux for 24 hr. The resultant solid
(Fe3O4@SiO2@PTMS@Melamine) was separated mag-
netically and washed with EtOH and H2O for several
times and dried at room temperature. The obtained
Fe3O4@SiO2@PTMS@Melamine nanoparticles (1.0 g)
was then suspended in EtOH (50 ml) containing 2‐
hydroxy‐1‐naphtaldehyde (0.17 g, 1 mmol) and the mix-
ture was heated at reflux for 24 hr. The obtained solid
(Fe3O4@SiO2@Schiff base) was separated magnetically
and washed with EtOH to remove the unreacted reagent
and then dried in air.
FIGURE 3 XRD pattern of (a) Fe3O4, (b) Fe3O4@SiO2, (c)
Fe3O4@SiO2@CPTMS, (d) Fe3O4@SiO2@PTMS@ Mel‐Naph (e)
Fe3O4@SiO2@PTMS@Mel‐Naph‐VOcomplex before using and (f)
after using as catalyst
2.4 | Preparation of Fe3O4@SiO2@PTMS
@MeL‐Naph‐VOcomplex nanoparticles
Fe3O4@SiO2@Schiff base (1.0 g) was added to a solution of
VO (acac)2 (1 mmol in 50 ml EtOH) and the mixture was
heated at reflux for 12 hr. The solid product was then sep-
arated magnetically, washed with EtOH and dried in air.
2.5 | Catalytic reactions
FIGURE 4 Magnetization curves of (a) Fe3O4, (b) Fe3O4@SiO2,
(c) Fe3O4@SiO2@CPTMS, (d) Fe3O4@SiO2@PTMS@Mel‐Naph
(e) Fe3O4@SiO2@PTMS@Mel‐Naph‐VOcomplex before using and
(f) after using as catalyst
Typically,
a desired amount of catalyst, substrate
(10 mmol), solvent (5 ml) and TBHP (12 mmol) were
mixed in the reaction flask. The suspension was then

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FARZANEH AND ASGHARPOUR
heated at reflux for the desired time. After the separation
of the catalyst using an external magnetic field, the solu-
tion was subjected to GC and GC–MS.
spectrum of Fe3O4@SiO2@PTMS@Melamine, two new
peaks appeared at 1625 and 1541 cm−1 are due to mela-
mine C=N stretching and N‐C‐N bending vibrations
(Figure 2d).[42] Based on these bands, successful grafting
of melamine onto the Fe3O4@SiO2@CPTMS nanoparti-
cles surface is concluded. The formation of Schiff base
ligand on the modified iron magnetic nanoparticles is fur-
ther confirmed by observing a band at 1645 cm−1 due to
the newly formed azomethine C=N and two others at
1564 and 1550 cm−1 for C‐C stretching vibrations
(Figure 2e). After complexation of VO (acac)2 with
Fe3O4@SiO2@Schiff base, appearing NH2 stretch
peaks at 3469, 3419 and 3344 cm−1 and two peaks
attributed to C=O and V=O stretching vibrations
at 1568 and 961 cm−1 prove the formation of
Fe3O4@SiO2@PTMS@Mel‐Naph (Figure 2f).[43–45]
3 | RESULT AND DISCUSSION
3.1 | Synthesis of Fe3O4@SiO2@PTMS
@Mel‐Naph‐VOcomplex
Fe3O4 magnetic nanoparticles (MNPs) were prepared by
precipitation of iron (II) and (III) ions in basic solution
under nitrogen atmosphere. Subsequently, it was coated
with silica to forming Fe3O4@SiO2 core‐shell particles
followed by modification with (3‐chloropropyl)trimetho
xysilane to afford MNPs, designated as ClpSCMNPs
(Fe3O4@SiO2@CPTMS).[26,32] The next step involved
grafting of melamine on the Fe3O4@SiO2@CPTMS sur-
face. Binding of 2‐hydroxy‐1‐naphtaldehyde with
Fe3O4@SiO2@PTMS@Melamine to Schiff base followed
by complexation with VO (acac)2 finally afforded
Fe3O4@SiO2@PTMS@Mel‐Naph‐VOcomplex (Figure 1).
The X‐ray powder diffraction patterns of Fe3O4,
Fe3O4@SiO2, Fe3O4@SiO2@CPTMS, Fe3O4@SiO2@PT
MS@Melamine, Fe3O4@SiO2@PTMS@Mel‐Naph (Fe3O4
@SiO2@Schiff base), Fe3O4@SiO2@PTMS@Mel‐Naph‐
VO (acac) before and after reaction are shown in
Figure 3a‐f respectively. As shown in Figure 3a, it can
3.2 | Charactrization of Fe3O4@SiO2
@PTMS@Mel‐Naph‐vocomplex
FT‐IR spectra of the prepared Fe3O4, Fe3O4@SiO2,
Fe3O4@SiO2@CPTMS Fe3O4@SiO2@PTMS@Melamine,
Fe3O4@SiO2@PTMS@Mel‐Naph (Schiff base), Fe3O4
@SiO2@PTMS@Mel‐Naph‐VOcomplex before and after
reaction, are shown in Figure 2a‐g, respectively. Whereas
the peak observed at 555 cm−1 is attributed to the Fe–O
vibrations of Fe3O4 (MNPs) (Figure 2a), those centered
at 1091 and 805 cm−1 assigned to the asymmetric and
symmetric stretching vibrations of Si–O–Si confirm the
successful coating of magnetite nanoparticles with silica
(Figure 2b).[40] The two obvious bands appearing at
2870 and 2920 cm−1 due to the C‐H stretching vibrations
also confirm the functionalization of the modified
Fe3O4@SiO2 with ClPTMS, which was designated as
Fe3O4@SiO2@CPTMS (Figure 2c).[41] In the FT‐IR
FIGURE 6 The SEM image of Fe3O4@SiO2@PTMS@Mel‐Naph‐
VOcomplex
FIGURE 5 EDX spectra of (a) Fe3O4@SiO2@CPTMS, (b) Fe3O4@SiO2@PTMS@Mel‐Naph, (c) Fe3O4@SiO2@Mel‐Naph‐VO complex

FARZANEH AND ASGHARPOUR
5 of 11
FIGURE 7 The HRTEM image of Fe3O4@SiO2@PTMS@Mel‐Naph‐VOcomplex(a, b) with two different magnification, (c) The dark and
white tissue should be due to core and shell part of single nanoparticle (d) Selected area electron diffraction (SAED) of crystalline phase of
nanoparticles
be seen that the Fe3O4 shows highly crystalline cubic spi-
nel structure which agrees with the standard Fe3O4 (cubic
phase) XRD pattern (JCPDSNo.19–0629).[46,47] The same
set of characteristic peaks were also observed for
Fe3O4@SiO2, Fe3O4@SiO2@CPTMS, Fe3O4@SiO2@PT
MS@Melamine and Fe3O4@SiO2@PTMS @Mela‐Naph
(Schiff base). The obtained results indicate the stability
of crystalline phase of Fe3O4 nanoparticles during the
modification (Figure 3b‐d). Observation of two new
diffraction peaks at 2θ = 12.7 and 2θ = 25.6 confirms
the formation of Fe3O4@SiO2@PTMS@Mel‐Naph‐VO
complex (Figure 3e).
silica coated Fe3O4 magnetite nanoparticles was deter-
mined to be 58.8 emu/g (Figure 4b). The superparamag-
netic behavior of Fe3O4@SiO2@CPTMS and Fe3O4
@SiO2@CPTMS@ Mel‐Naph (Schiff base) were also found
57 emu/g and 47.5 emu/g respectively (Figure 4c,d). After
The magnetic properties of Fe3O4, Fe3O4@SiO2,
Fe3O4@SiO2@CPTMS, Fe3O4@SiO2@PTMS@Mela‐Na
ph, Fe3O4@SiO2@PTMS@Mel‐Naph‐VOcomplex before
and after reaction were examined by vibrating sampling
magnetometry (VSM) at room temperature (Figure 4a‐f).
The magnetization curve of Fe3O4 exhibits superparamag-
netic property with saturation magnetization of about
61 emu/g (Figure 4a). Superparamagnetic behavior of the
FIGURE 8 Conversion and Selectivity of geraniol with different
amounts of Fe3O4@SiO2@PTMS@‐MelNaph‐VOcomplex

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FARZANEH AND ASGHARPOUR
formation of Fe3O4@SiO2@PTMS@Mel‐Naph‐VO (acac),
superparamagnetic behavior was found to be 43 emu/g
(Figure 4e).
3.3 | Catalytic activity of Fe3O4
@SiO2@PTMS@‐Mel‐Naph‐VOcomplex
The catalytic activity of Fe3O4@SiO2@PTMS@‐Mel‐
Naph‐VOcomplex was studied in the epoxidation of some
allyl alcohols and alkenes in acetonitrile. TBHP was used
as oxidant due to its high oxidation selectivity behavior.
Geraniol served for our early exploration of allyl alcohol
epoxidations in order to find the optimum reaction condi-
tions. Various parameters such as the effect of catalyst
amount, reaction time and solvent were evaluated. To
optimize the catalyst amount, reaction was carried out
using 5, 10, 15 and 20 mg of catalyst in acetonitrile while
The EDX for Fe3O4@SiO2@CPTMS, Fe3O4@SiO2
@PTMS@Mel‐Naph and Fe3O4@SiO2@PTMS@Mel‐
Naph‐VOcomplex are shown in Figure 5a‐c, respectively.
Based on the obtained results, characteristic peaks con-
taining C, O, Si, Cl and Fe are indicative of the presence
of these atoms in for Fe3O4@SiO2@CPTMS nanoparticles
(Figure 5a). After formation of Schiff base on the
nanomagnet surface, no peak due to the presence of
chlorine atom is observed but the presence of nitrogen
is considerable (Figure 5b). Based on the obtained
results with EDX, the Cl has been exchanged with
melamine hydrogen. The presence of vanadium deter-
mined in the Fe3O4@SiO2@Mel‐Naph‐VO (acac) EDX
also confirms the formation of the proposed structure
(Figure 5c).
The SEM image of Fe3O4@SiO2@PTMS@Mel‐Naph‐
VOcomplex indicates the morphology of nanoparticles
(Figure 6). HRTEM images of Fe3O4@SiO2@PTMS
@Mel‐Naph‐VOcomplex with two magnification are
shown in Figure 7 a‐b, respectively The obtained results
indicate the formation of core and shell of nanoparticles
with particle size of about 10–15 nm. The dark and white
tissue seen in Figure 7c should be due to core and shell
part of single nanoparticle. Selected area electron diffrac-
tion (SAED) of crystalline phase is shown in Figure 7d.
The ring patterns are due to the crystalline planes of the
prepared nanoparticles.
FIGURE 9 The effect of solvent on the conversion and selectivity
of geraniol using Fe3O4@SiO2@PTMS@Mel‐Naph‐VOcomplex as
catalyst
TABLE 1 Results obtained for the epoxidation of allyl alcohols
Entry
Substrate
Time (h)
Conversiona (%)
Epoxide (%)
TONb
TOFc (h−1
)
1
0.5
1.0
1.5
2.0
85
93
97
100
100
100
100
100
833
417
2
3
0.5
1.0
1.5
2.0
3.0
74
81
87
93
100
100
100
100
100
100
833
833
278
167
1.0
1.5
2.0
3.0
4.0
5.0
67
73
81
91
96
100
100
100
100
100
100
100
aReaction condition: catalyst (20 mg), allyl alchohol (10 mmol), TBHP (12 mmol), in CH3CN, heated to reflux.
bTON is the mmol of epoxide to the mmol of vanadium present in the catalyst.
cTOF: turnover frequency which is calculated by the expression of [epoxide]/[catalyst]time.

FARZANEH AND ASGHARPOUR
7 of 11
Finally, a variety of solvents such as CH3CN, C2H5OH,
CHCl3 and CH2Cl2 were tested for the epoxidation of
geraniol. As seen in Figure 9, the catalytic activity trend
was found to be:
CH3CN~ C2H5OH > CHCl3 > CH2Cl2. Therefore, other
allyl alcohols epoxidation reactions were carried out in
CH3CN. Based on the obtained results, the highest conver-
sion of geraniol epoxidation reaction occurs in CH3CN and
ethanol. The higher boiling points of the solvents seems to
be responsible for solvent trend simply because more gera-
niol conversion occurs at higher temperature.
In the next step, the epoxidation of trans‐2‐ hexen‐1‐ol
and 1‐octen‐3‐ol were investigated in CH3CN using 20 mg
of catalyst within 0.5 to 5 hr. As seen in Figure 10,
trans‐2‐ hexen‐1‐ol and 1‐octen‐3‐ol were converted to
the corresponding epoxides with 100% conversions and
selectivities within 3 and 5 hr, respectively (entries 2–3,
Table 1).
Finally, H2O2 and O2 were used as oxidant in the epox-
idation of geraniol under optimal conditions. It was
found that whereas reaction proceeds about 10% using
H2O2, no conversion occurred in the presence of O2.
The decrease in conversion rates from geraniol to trans‐
2‐hexen‐1‐ol and 1‐octen‐3‐ol may be realized on the basis
of the suggested mechanism shown in Scheme 1. After the
formation of intermediates I and II upon the initial coordi-
nation of TBHP and allyl alcohol to the catalyst vanadium
FIGURE 10 Result of epoxidation of allyl alcohols in presence of
Fe3O4@SiO2@PTMS@‐Mel‐NaphVOcomplex. Reaction condition:
catalyst (20 mg), allyl alchohol (10 mmol), TBHP (12 mmol), solvent
CH3CN
heating at reflux within 2 hr. As seen in Figure 8, increas-
ing the amount of catalyst from 5 to 20 mg increases the
conversion from 90 to 100% with 100% selectivity toward
the formation of geraniol epoxide. Thereafter, all epoxida-
tion reactions were carried out using 20 mg of catalyst.
The effect of time on the geraniol conversion was
investigated using 20 mg of catalyst. Increasing the
reaction time from 0.5 to 2 hr was found to increase the
geraniol conversion from 85 to 100% with 100% selectivity
(entry 1, Table 1).
SCHEME 1 Suggested mechanism for the epoxidation of allyl alcohols

8 of 11
FARZANEH AND ASGHARPOUR
core, the allyl alcohol is subsequently oxygenated by nucle-
ophilic attack of the double bond to the electrophilic oxy-
gen atom of the coordinated TBHP peroxide with
generation of III. In the next step, addition of water to
vanadium in III affords IV. Finally, concomitant elimina-
tion of tert‐butanol and epoxide regenerates the catalyst
(Scheme 1). Since the formation rate of III in the nucleo-
philic attack of double bond to the oxygen electrophile
depends on the number of alkyl substitutions present on
the double bonds,[27] it can be concluded that the geraniol
which contains a trisubstituted double bonds exhibit the
highest epoxidation rate. On the other hand, trans‐2‐
hexen‐1‐ol and 1‐octen‐3‐ol containing disubstituted and
monosubstituted double bonds would undergo epoxida-
tion reactions in lower rates, respectively.
To further support the operation of a concerted mech-
anism, reaction was carried out in the presence of diphe-
nylamine as radical scavenger.[48] Observation of no
conversion inhibition indicated that reaction does not
proceed through a radical mechanism.
SCHEME 2 Suggested mechanism for the epoxidation of alkenes
TABLE 2 result of epoxidation of olefines in different times
Entry
Substrate
Time (h)
Conversiona (%)
Selectivity(%)
TONb
TOFc (h−1
)
1
2
4
6
8
37
50
75
92
100
100
100
100
833
104
2
3
2
4
6
8
32
45
60
80
100
100
100
100
833
583
104
73
2
4
6
8
8
12
16
45d
60
64
65
70
4
2
4
6
8
36
50
64
75e
60
65
67
74
6
77
60
5
2
4
6
8
16
23
31
56f
48
50
56
58
483
aReaction condition: catalyst (20 mg), alkene (10 mmol), TBHP (12 mmol), refluxing CH3CN.
bTON is the mmol of epoxide to the mmol molybdenum present in catalyst.
cTOF: turnover frequency which is calculated by the expression [epoxide]/[catalyst]×time (h−1).
dThe side product is 2‐cyclohexene‐1‐one.
eThe side product is acetophenone.
fThe side product is benzaldyde.

FARZANEH AND ASGHARPOUR
9 of 11
In the next step, alkenes such as norbornene,
cyclooctene, cyclohexene, α‐methyl styrene and styrene
were oxidized with TBHP in acetonitrile using Fe3O4
@SiO2@Mel‐Naph‐VOcomplex as catalyst (Table 2). As
seen in Table 2, whereas norbornene and cyclooctene
exclusively give the corresponding epoxides (entry 1–2,
Table 2), cyclohexene, α‐methyl styrene and styrene epox-
idations afford other side products in addition to epoxides
(entries 3–5, Table 2). Observation of two oxidation paths
in cyclohexene clearly specifies that not only reaction of
alkene double bounds with t‐BuOO radical generate the
corresponding epoxides (Scheme 2a‐e), but also if an
allylic H abstraction occur, it is followed by the formation
of the corresponding allylic radicals. Whereas norbornene
results in the formation of extremely unstable bridgehead
radical (Scheme 2f), cyclooctene generates an unstable
intermediate since the double bond is in one plane and
all other carbons are in another plane (Schemes 2g).[49]
On the other hand and in oppose to cyclooctenyl radical,
cyclohexene partly undergoes allylic‐site oxidation since
the C–H bond is close to parallel to the C=C orbital in
its half‐chair conformation (Scheme 2h).[50] Therefore,
the formation of 2‐cyclohexene‐1‐one identified as the
side products is rationalized (footnote d, Table 2). Finally,
the generation of acetophenone (Scheme 2d) and benzal-
dehyde (Scheme 2e) respectively in the epoxidation of
methylstyrene (footnote e, Table 2) and styrene (footnote
f, Table 2) is not surprising since the partial hydrolysis of
the α‐methyl styrene and styrene epoxides in the aqueous
solution of the used TBHP as oxidant has been reported
previously.[51]
The reusability of the catalyst for epoxidation reaction
of geraniol with TBHP was carried out under the opti-
mized reaction conditions. In this regard, the catalyst
was separated by external magnet from reaction mixture
after completion of the first run. It was washed with ace-
tonitrile and dried before using in the next runs. Based on
the collected data, it was concluded that the catalyst can
be reused for five consecutive cycles with slight decrease
in activity from 99 to 96% (Figure 11).
On the other hand, since no catalytic activity was
observed upon the subjection of the filtrate to the new
epoxidation reaction in the absence of the catalyst, the
heterogeneity of catalyst function was concluded.
The vanadium content of the catalyst before and after
use in reaction was determined as 3.07%. and 3.03%,
respectively. It was concluded that no significant catalyst
FIGURE 11 The effect of recycling on epoxidation of geraniol
TABLE 3 Catalytic activities toward the epoxidation of geraniol of some previously reported heterogeneous catalysts
Entry Catalyst
Conversion (%) Selectivity (%) TON TOF(h−1
)
Ref.
1
Fe3O4 @ SiO2 @ PTMS @ Mel‐Naph‐VO
Osalpr @ SCMNPs
100
100
100
100
80
100
97
98
99
77
97
99
96
97
98
98
81
88
834 417
746 187
199 25
155 155
100 91
This work
[31]
2
[52]
[27]
[53]
[53]
[54]
[54]
[55]
[56]
[57]
[58]
[58]
[59]
[60]
[60]
3
8‐quinolinol oxovanadium (IV) complex @ graphene oxide 83.7
4
Fe3O4@SiO2@APTMS@[VO2(bpca)]
CMK‐3 @ [VO (acac)2]
100
100
98
5
6
CMK3 @ APTES @ [VO (acac)2]with amine
VO (Sa l‐His) @ Al‐MCM‐41
74
68
7
100
27
4040 505
3375 422
1185 184
8
VO @ AlMCM41
9
Fe3O4 @ SiO2 @ APTMS@VMIL‐101
[VO (acac)2] APTES @ SiO2
96
10
11
12
13
14
15
16
100
100
100
100
98
34
60
96
96
96
‐
17
2
2
2
2
‐
Fe2O3 @ SiO2–NH2–Vo (acac)2
[VO (acac)2] @ APTES @ laponite
[VO (acac)2] @ APTES@K10
[VO (acac)2] @ hexagonal mesoporous silica
[VO (acac)2]APTES @ PCH
42
[VO (acac)2]APTES @ SBA‐15
34
‐
‐

10 of 11
FARZANEH AND ASGHARPOUR
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desorption occurs during the course of reaction. More-
over, the similarity observed in the XRD pattern and
FTIR spectrum of the catalyst before and after using in
geraniol epoxidation further revealed the stability and
heterogeneity character of the nanocatalyst.
Finally, comparison of the epoxidation results of gera-
niol catalyzed by Fe3O4@SiO2@CPTMS@‐Mel‐Naph‐
VOcomplex in this work with some previously reported
heterogeneous catalysts provided in Table 3 reveals that
conversion, selectivity, TON and TOF of our catalysis sys-
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4 | CONCLUSION
In conclusion, the synthesis of a new magnetically recov-
erable nanocatalyst with modification of Fe3O4 magnetic
nanoparticles by covalent binding of a Schiff base ligand,
derived from melamine and 2‐hydroxy1naphtaldehyde on
the surface of magnetic nanoparticles followed by com-
plexation with VO (acac)2 was successfully carried out.
After characterization, it was found that several allyl alco-
hols and alkenes can be selectively epoxidized in the pres-
ence of the prepared magnetically nanocatalyst. The
stability, heterogeneity and excellent reusability of the
catalyst even after five‐cycles of usage in the case of gera-
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ACKNOWLEDGEMENT
[24] M. R. Maurya, A. Kumar, J. C. Pessoa, Coord. Chem.Rev. 2315,
2011, 255.
The financial support from Alzahra University is grate-
fully acknowledged.
[25] C. Pereira, A. R. Silva, A. P. Carvalho, J. Pires, C. Freire, J. Mol.
Catal. A: Chem. 2008, 283, 5.
[26] F. Farzaneh, Y. Sadeghi, M. Maghami, Z. Asgharpour,
ORCID
J. Cluster Sci. 2016, 27, 1701.
Faezeh Farzaneh https://orcid.org/0000-0001-5651-8018
[27] Z. Azarkamanzad, F. Farzaneh, M. Maghami, J. Simpson, M.
Azarkish, Appl. Organomet. Chem. 2018, 32, 4168.
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