Synthesis of peroxy-functionalized magnetic mesoporous silica for epoxidation of vinyl acetate

Article abstract of DOI:10.1016/j.jmmm.2018.11.111

Peroxy-functionalized magnetic mesoporous silica (MMS-PA) composites containing magnetic nanoparticles (MNPs) and peroxy acids were synthesized to be used as an easily reusable heterogeneous oxidant for the epoxidation of alkenes. The presence of peroxy acid functional groups on the composites was confirmed by Fourier transform infrared spectroscopy (FTIR). Transmission electron microscope (TEM) of the MMS-PA composites revealed the irregular structure of porous silica attached with the MNPs. The surface area of the MMS-PA was calculated to be 1089 m² g^?1, which is significantly lower than that of the starting mesoporous silica. As measured using vibrating sample magnetometer (VSM), MMS-PA exhibited saturation magnetization of 0.12 emu/g, indicating that the heterogeneous oxidant could respond to an external magnet. The oxidizing activity of the synthesized MMS-PA composites was investigated using vinyl acetate as a model substrate; the yields of the corresponding epoxide products were measured using nuclear magnetic resonance (NMR) spectroscopy. At room temperature, the freshly prepared MMS-PA gave 52% yield of the product, and the yield decreased only slightly to 47% for the recycled MMS-PA obtained by reactivating the recovered MMS-PA with concentrated H₂O₂ in acidic medium.

Full text of DOI:10.1016/j.jmmm.2018.11.111

JournalofMagnetismandMagneticMaterials475(2019)579–585
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Journal of Magnetism and Magnetic Materials
journal homepage: www.elsevier.com/locate/jmmm
Research articles
Synthesis of peroxy-functionalized magnetic mesoporous silica for
epoxidation of vinyl acetate
⁎
Wishulada Injumpaa, Tanatorn Khotavivattanab, Numpon Insina,c,
a Department of Chemistry, Faculty of Science, Chulalongkorn University, Bangkok 10330, Thailand
b Center of Excellence in Natural Products Chemistry, Department of Chemistry, Faculty of Science, Chulalongkorn University, Bangkok 10330, Thailand
c Center of Excellence in Materials and Bio-interfaces, Chulalongkorn University, Phayathai Road, Pathumwan, Bangkok 10330 Thailand
A R T I C L E I N F O
A B S T R A C T
Keywords:
Peroxy-functionalized magnetic mesoporous silica (MMS-PA) composites containing magnetic nanoparticles
(MNPs) and peroxy acids were synthesized to be used as an easily reusable heterogeneous oxidant for the
epoxidation of alkenes. The presence of peroxy acid functional groups on the composites was confirmed by
Fourier transform infrared spectroscopy (FTIR). Transmission electron microscope (TEM) of the MMS-PA
composites revealed the irregular structure of porous silica attached with the MNPs. The surface area of the
MMS-PA was calculated to be 1089 m2 g−1, which is significantly lower than that of the starting mesoporous
silica. As measured using vibrating sample magnetometer (VSM), MMS-PA exhibited saturation magnetization of
0.12 emu/g, indicating that the heterogeneous oxidant could respond to an external magnet. The oxidizing
activity of the synthesized MMS-PA composites was investigated using vinyl acetate as a model substrate; the
yields of the corresponding epoxide products were measured using nuclear magnetic resonance (NMR) spec-
troscopy. At room temperature, the freshly prepared MMS-PA gave 52% yield of the product, and the yield
decreased only slightly to 47% for the recycled MMS-PA obtained by reactivating the recovered MMS-PA with
concentrated H2O2 in acidic medium.
Heterogeneous oxidizing agent
Magnetic separation
Nanocomposite
Peroxidation
Epoxidation
1. Introduction
the synthesis of many valuable compounds such as pharmaceuticals,
biotechnological products, adhesives or paints [18–21]. Moreover, al-
Magnetic nanoparticles are widely used as additives in many cata-
lysts [1–3] to facilitate the separation from reaction mixtures and
control the movement of the catalysts because of their special character:
superparamagnetism [4–8]. Moreover, the ease of reuse of the magnetic
composite catalysts leads to the improvement in the efficiency of the
magnetic composites because the materials could be recycled for sev-
eral times. For instance, sulfonic acid functionalized silica-coated
crystalline Fe/Fe3O4 core/shell magnetic nanoparticles (MNPs) was
used as a catalyst in transesterification, and the nanoparticles were
separated using a magnet and were reused up to five times [9]. There
are many types of magnetic materials but magnetite (Fe3O4) and ma-
ghemite (γ-Fe2O3) are typically selected because they are stable in
ambient condition, inexpensive, less toxic and easily synthesized
[6,10–13]. In addition, nanostructures of metal ferrites (MFe2O4) are
attractive sorbents for sorption processes due to their high stability,
high surface area and excellent magnetic response [14–17].
kenes, which are the starting materials in this reaction, are also widely
used as common feedstocks in various synthetic protocols [22–24].
Typically for the epoxidation reactions, homogeneous oxidants such as
tert-butyl hydroperoxide (t-BuOOH), m-choloperbenzoic acid (mCPBA)
or other peroxyacids are commonly used [24,25]. Although these re-
agents generally gave high yield, high selectivity and also high effi-
ciency even without catalysts, they are however difficult to separate
from products [26–28].
Recently, there were a few works that demonstrated the in-
corporation of the organic oxidants into particles which were used as
heterogeneous oxidants to simplify the separation or the purification of
both oxidants and products [23,25,29]. However, there is no report that
uses magnetic particles incorporated with an oxidizing agent for
epoxidation. This is probably due to the fact that the strong reaction
conditions (high acid concentration, high temperature and high H2O2
concentration) required for the synthesis of the heterogeneous oxidants
were not compatible with the incorporation of the magnetic particle
[23,29]. However, since magnetic particles could facilitate the
Epoxidation is an important reaction in an industrial process for the
synthesis of the epoxide, a versatile building block and intermediate in
⁎ Corresponding author.
E-mail address: Numpon.I@chula.ac.th (N. Insin).
https://doi.org/10.1016/j.jmmm.2018.11.111
Received 24 June 2018; Received in revised form 22 November 2018; Accepted 22 November 2018
Availableonline23November2018
0304-8853/©2018ElsevierB.V.Allrightsreserved.

W. Injumpa et al.
JournalofMagnetismandMagneticMaterials475(2019)579–585
separation process by using an external magnet [30], which is simpler
and faster than filtration as magnetic separation does not require any
filters or any complicate equipment for separations. Therefore, the
objective of this work is to develop novel magnetic particles which are
stable under strong oxidizing conditions in order to be used as an easily
reusable oxidant in the epoxidation of alkenes. Our strategies include
the selection of magnesium ferrite (MgFe2O4) as magnetic particles for
both metals are in their stable oxidation states, the passivation the
ferrite with a thin silica coating, and the adjustment of conditions for
the peroxidation process.
cooled down to room temperature and diluted. The solid was washed
with DI water until the diluent was neutral. Then, the white powder of
MS-COOH was obtained after dried at 95 °C under vacuum for 12 h.
2.3. Synthesis of magnetic mesoporous silica (MMS-COOH)
MS-COOH (12.0 g) and MNPs (6.0 mL, 31.8 g/mL) were mixed in
hexane [32]. Then, the mixture was stirred overnight, and the mixture
was washed with cyclohexane using centrifugation. Finally, the black
solid of the MNPs and MS-COOH composite was dried at 60 °C in an
oven for 3 h. To ensure the stability of the attachment, the composite
was coated with a thin silica shell using a sol-gel method. 2.5 g of the
composite was dispersed in ethanol (200 mL) before TEOS (1 mL) was
added dropwise for 1.5 h. The mixture was stirred for 24 h, and MMS-
COOH was obtained.
2. Materials and methods
All chemicals were used as received without further purification.
Iron(III) chloride (FeCl3) (99.99%), magnesium chloride anhydrous
(MgCl2) (99.99%), oleic acid (90%), 1-octadecene (90%), sodium hy-
droxide (pellet for analysis), tetraethyl orthosilicate (TEOS; purum >
98%), 2-cyanotriethoxysilane (CTES), ammonium hydroxide (NH4OH;
25%), methanesulfonic acid (reagent grade) were purchased from
Sigma-Aldrich.
2.4. Synthesis of peroxy-functionalized magnetic mesoporous silica (MMS-
PA or MMS-COOOH)
The peroxidation process was adapted from previous works [23,29].
Briefly, MMS-COOH (0.20 g) was mixed with methanesulfonic acid
(2 mL) for 30 min at room temperature. Then, freshly prepared con-
centrated hydrogen peroxide (1 mL) (see Supporting Information for
the preparation of the reagent) was added dropwise into the above
mixture at 5 °C, and then the mixture was stirred for 12 h. Finally, the
mixture was washed using a centrifuge with cold DI-water until the
diluent was neutral. The solid was dried overnight under vacuum at
room temperature. The MMS-PA was obtained and stored at 4 °C before
use. Due to the high reactivity of this composite, the characterizations
using TEM and N2 adsorption-desorption analysis of MMS-PA were
performed only after they were used in the oxidation of alkene. We
called the composite as used MMS-PA for the composite after used for
the first time and recycled MMS-PA for the used MMS-PA that has been
reactivated with peroxidation and has been used for the second time.
2.1. Synthesis of magnetic nanoparticles (MNPs)
Thermal decomposition technique was used for the synthesis of Mg-
doped ferrite with a process previously reported with some modifica-
tions [31]. Fe(oleate)3 and Mg(oleate)2 mixture was first prepared as a
precursor from iron(III) chloride, magnesium chloride and oleic acid.
For the preparation of Fe(oleate)3 and Mg(oleate)2, iron(III) chloride
(0.65 g, 4.0 mmol) and magnesium chloride (0.19 g, 2.0 mmol) were
dissolved de-ionized (DI) water (10.0 mL), and sodium hydroxide
(0.64 g, 16.0 mmol) was dissolved in DI water (10.0 mL). Then oleic
acid (4.52 g, 16.0 mmol) and the sodium hydroxide solution were
added into a round bottom flask, yielding the sodium oleate solution.
Finally, the mixture of iron(III) chloride and magnesium chloride and a
mixture of DI water:ethanol:hexane in the ratio of 12:16:28 by volume
(mL) were added into the oleate solution. The mixture was refluxed at
70 °C for 4 h. Then, the mixture was extracted by of DI water
(3 × 6.0 mL). Fe(oleate)3 and Mg(oleate)2 mixture was then dispersed
in the hexane layer. The Fe(oleate)3 dispersion was collected and was
evaporated to obtain the Fe(oleate)3 and Mg(oleate)2 mixture as dark
brown fluid. For the synthesis of MNPs by thermal decomposition
process, a mixture of oleic acid:Fe(oleate)3 and Mg(oleate)2 mixture:1-
octadecence of 1.0:6.0:38 by mole was prepared. The mixture was
gradually heated as controlled by a temperature controller to 320 °C
with the heating rate of 3.3 °C/min, and the reaction mixture was held
at this temperature for 30 min under inert gas (N2 gas). MNPs disper-
sion was washed several times by 2-propanol then collected using a
centrifuge.
2.5. Epoxidation of vinyl acetate (VA)
The typical procedure for the reaction optimization is as follows:
0.10 g of MMS-PA (2.41 mmol peroxy acid/g, 0.24 mmol) and 1.0 mL of
CDCl3 were first mixed for 1 min. Then, VA (1.72 mg, 0.02 mmol) was
added and allowed to react for 1 h. Toluene (1.84 mg, 0.02 mmol) was
added in the reaction mixture as an internal standard, and the reaction
was attached with a magnet to separate solid from the solution for
2 min before reaction was completed. The solution part was collected
using a syringe and filtered through a syringe filter before determining
the epoxide yield using 1H NMR technique.
2.6. Materials analyses
2.2. Synthesis of mesoporous silica
X-ray diffraction (XRD) patterns of samples were obtained on a
DMAX 2200/Ultima + diffractometer (Rigaku, Tokyo, Japan) using Cu
Kα radiation source and operating at 40 kV and 30 mA. The XRD pat-
terns were collected with a scan range of 20°–70° for MNPs, 0°–10° for
mesoporous silica with a scan speed of 1°/min. Transmission electron
microscopy (TEM) images of particles were obtained using a JEM-2010
microscope at an accelerating voltage of 120 kV (Japan). The dispersed
sample of MMS-COOH and MMS-PA were deposited on a carbon film
with 300 mesh copper grids, and then dried in desiccators at room
temperature. Fourier transform infrared (FTIR) spectra were acquired
using a Nicolet 6700 (Thermo Scientific, MA, USA). A vibrating sample
magnetometer (VSM, Lakeshore 7204) was used to measure the mag-
netic properties of the materials. The Brunauer-Emmett-Teller (BET)
specific surface area and Barrett-Joyner-Halender (BJH) pore size and
volume of the materials were analyzed by nitrogen (N2) adsorption/
desorption using a BEL Japan, BELSORP-mini instrument. The adsorp-
tion isotherms were determined at 77 K using highly pure N2 as an
Sol-gel method was used to synthesize cyano-functionalized silica
(MS-CN) [25,29]. First, the template was prepared using dodecylamine
(30.0 g, 162 mmol) in solution of DI water (318 mL) and ethanol
(312 mL). The mixture was stirred using a mechanical stirrer for 24 h.
Then the mixture of TEOS (61.2 g, 294 mmol) and CTES (32.0 g,
147 mmol) (2:1 in ratio) was added dropwise to the templating mixture.
The mixture was mechanically stirred for 24 h, and a thick white sus-
pension was obtained. The suspension was then filtered, and the white
solid was retained. The white solid was refluxed for three times using
ethanol (600 mL) to remove the templating agent (dodecylamine). Fi-
nally, the white solid was dried at 95 °C under vacuum overnight to
obtain MS-CN (white power).
For the synthesis of carboxyl-functionalized mesoporous silica (MS-
COOH), the fine white solid MS-CN (30.0 g) was stirred with 65%
H2SO4 (300 mL) at 150 °C for 3 h. After hydrolysis, the suspension was
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JournalofMagnetismandMagneticMaterials475(2019)579–585
Fig. 1. Schematic synthesis of peroxy-functionalized magnetic mesoporous silica (MMS-PA).
adsorbate. Each sample (∼0.04 g) was weighted and pretreated at
150 °C for 2 h before each measurement. The crude mixtures obtained
from the epoxidation were characterized by NMR experiments per-
formed on a Bruker Advance (III) 400WB spectrometer, and 1H NMR
data was used to calculate percent yield of the epoxide product.
contained mesoporous silica, and the as-synthesized MNPs could con-
tain magnetite and magnesium ferrite.
The as-synthesized MNPs were characterized further with SEM
equipped with Energy Dispersive X-ray spectrometer (EDX) to estimate
the amount of each element on the particles as shown in Fig. S1. Ac-
cording to the MgFe2O4 formula, if the MNPs are of pure MgFe2O4
phase, the Mg:Fe ratio should be 1:2, but Fig. S1 shows that the average
ratio of Mg:Fe is roughly 1:10 by atom percentage, indicating that the
synthesized MNPs were not pure MgFe2O4. From the observation of
regular distribution of Mg signal in different areas throughout the
samples without distinct phase separation (Fig. S2) and the position of
XRD patterns (Fig. S3) compared with magnetite nanoparticles pre-
pared using the same process with MNPs [31], the synthesized MNPs
should be a solid solution of magnesium-doped iron ferrites. However,
the as-synthesized MNPs can respond with an external magnet, meeting
the requirement for our applications. The morphologies of the materials
were observed using FESEM and TEM. The dispersity of MS-CN and
MMS-COOH are shown in Fig. 3. FESEM images of MS-CN (Fig. 3a) and
TEM image of synthesized MNPs (Fig. 3b) showed that the MNPs were
of spherical shape with diameter of around 12 nm (SD = 1.28 nm, Fig.
S4), while the MS-CN composites were of more irregular shape and
polydispersity with the diameter of around 3.86 µm (SD = 2.18 µm, Fig.
S5). The high magnification TEM images of MMS-COOH (Fig. 3d), used
MMS-PA (Fig. 3e) and recycled MMS-PA (Fig. 2f) showed that the
surface of large particles contained small particles of MNPs [36].
Moreover, for the TEM image of recycled MMS-PA, the small particles
were aggregated, which might be caused by the loss of their surface
stabilizers while exposing with the extreme oxidation conditions in the
peroxidation process.
3. Results and discussion
3.1. MMS-PA synthesis and characterization
Preparation and functionalization of the materials were achieved by
a four-step process (Fig. 1): 1) thermal decomposition of iron-oleate and
magnesium-oleate complexes (synthesis of MNPs), 2) cyano-functio-
nalization of mesoporous silica (synthesis of MS-CN), 3) hydrolysis of
MS-CN (preparation of MS-COOH), 4) preparation of MMS-COOH and
peroxidation of MMS-COOH (synthesis of MMS-PA). Crystalline struc-
tures of the synthesized MNPs, MS-CN and MMS-COOH were char-
acterized by XRD. The resulted XRD patterns were shown in Fig. 2
compared with the standard patterns JCPDS 19-0629, JCPDS 17-0464
and mesoporous silica patterns reported in the previous studies
[23,33–35]. The XRD pattern of the MNPs matched well with a crys-
talline structure of magnetite (Fe3O4), maghemite (γ-Fe2O3) and mag-
nesium ferrite (MgFe2O4), which cannot be differentiated using XRD
pattern. In addition, XRD patterns of the MS-CN and MMS-COOH
(Fig. 2A) showed a broad peak at 2-theta of around 2°–3°, indicating
that these materials contained MCM-type of mesoporous silica as re-
ported in the previous work [23,29]. The diffraction peaks at 2-theta
around 30.0°, 35.0°, 43.0° and 62.0°, which are characteristic peaks of
MNPs (magnetite maghemite and magnesium ferrite), were not ob-
served in the XRD patterns of MMS-COOH, which might be due to the
low amount of MNPs in the composites as observed in TEM images
(Fig. 3c). The XRD results confirmed that MS-CN and MMS-COOH
Additionally, Brunauer-Emmett-Teller (BET) nitrogen adsorption
method was used to calculate surface area of MS-CN, MMS-COOH, used
MMS-PA and recycled MMS-PA as shown in Table 1. Surface areas were
Fig. 2. The XRD patterns of MS-CN and (black A), MMS-COOH (red A) and the synthesized magnetic nanoparticles (MNPs) (green B) comparing with the standard
pattern files JCPDS 19-0629 (black B) of magnetite, JCPDS 17-0464 (red B) of MgFe2O4 and JCPDS 39-1346 (blue B) of maghemite. (For interpretation of the
references to colour in this figure legend, the reader is referred to the web version of this article.)
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JournalofMagnetismandMagneticMaterials475(2019)579–585
Fig. 3. (a) FESEM image of MS-CN; (b) High magnification TEM images of the synthesized MNPs, (c) MS-CN, (d) MMS-COOH, (e) used MMS-PA and (f) recycled
MMS-PA.
Table 1
Textural properties of the materials.
SBET (m2/g)
Pore volumeb (cm3/g)
a
Entry
Materials
1
2
3
4
MS-CN
1294
1076
1089
1025
0.61
0.52
0.35
0.24
MMS-COOH
Used MMS-PA
Recycled MMS-PA
a
Specific surface area obtained by the BET method.
Pore volume calculated from the t-plot.
b
1294 m2/g−1, 1076 m2/g−1, 1089 m2/g−1 and 1025 m2/g−1 for MS-
CN, MMS-COOH, used MMS-PA and recycled MMS-PA, respectively.
Both mesopores and micropores were present in these composites as
calculated using BJH plot and MP plot (Fig. S7 and Table S1), respec-
tively, and the pore width distribution did not alter upon the functio-
nalization and epoxidation processes. Surface area and the pore volume
of MMS-COOH were slightly lower comparing with MS-CN, which
could be caused by the interaction between the –COOH group and
MNPs blocking the N2 adsorption. Moreover, N2 adsorption/desorption
isotherm as shown in Fig. 4 displayed hysteresis loops at a relative
pressure P/P0 of 0.4–0.6, corresponding to Type IV porous materials
and fitted with H1-type hysteresis based on the IUPAC classification,
Fig. 4. N2 adsorption/desorption isotherms of MS-CN (blue), MS-COOH
(black), used MMS-PA (purple) and recycled MMS-PA (red). (For interpretation
of the references to colour in this figure legend, the reader is referred to the web
version of this article.)
indicating that four of the materials (MS-CN, MMS-COOH, used MMS-
PA and recycled MMS-PA) possess mesoporous structure as reported
previously [23,33–35].
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JournalofMagnetismandMagneticMaterials475(2019)579–585
Fig. 5. IR spectra of MS-CN (blue), MS-COOH (pink), MMS-COOH (red) and MMS-PA (green). (For interpretation of the references to colour in this figure legend, the
reader is referred to the web version of this article.)
Functional groups on the magnetic mesoporous silica was identified
using FTIR (Fig. 5). Comparing between MS-CN and MS-COOH, only IR
spectrum of MS-CN showed characteristic –C^N stretching peak at
2251 cm−1, confirming that MS-CN did contain the cyano group (–CN).
After hydrolysis of MS-CN, –CN was expected to become –COOH as
shown in the pink spectrum, showing the peak at 1712 cm−1, which is
–C]O stretching of carboxyl group, and the characteristic peak of –CN
disappeared. The results indicated that the MS-CN was hydrolyzed
completely and became MS-COOH. The spectrum of MMS-COOH (red)
was similar with that of MS-COOH as the typical metal-oxygen (Fe-O) of
Fe3O4 and MgFe2O4 absorption band at ∼560 cm−1 (see Fig. S8 for the
FTIR spectrum of the MNPs) was not observed because of the limitation
of the IR spectrometer. The green spectrum showed the peak at
1761 cm−1, which is the characteristic peak of –C]O stretching of
peroxyl group, indicating that the MMS-PA consisted of peroxy acids.
Moreover, the amount of peroxy on MMS-PA was calculated using io-
dometric titration [25,29] to be 2.41 mmol/g. According to the IR
spectra and the amount of peroxy, it could be confirmed that the het-
erogeneous oxidant (MMS-PA) was successfully synthesized.
Magnetic property of MMS-COOH and MMS-PA before and after
used (used MMS-PA) was measured using a vibrating-sample magnet-
ometer (VSM). The magnetization under different magnetic fields of
MMS-COOH and MMS-PA were as shown in Fig. 6. The saturation
magnetization (Ms) of MMS-COOH is 0.34 emu/g at 25 °C, while Ms of
Fig. 6. Magnetization under a magnetic field of MMS-COOH (blue line) and
MMS-PA before (red line) and after used (used MMS-PA) (green line). (For
interpretation of the references to colour in this figure legend, the reader is
referred to the web version of this article.)
MMS-PA and used MMS-PA are 0.12 emu/g and 0.13 emu/g at 25 °C,
respectively. The low Ms values of these materials compared with Ms of
the synthesized MNPs (Fig. S9) were as expected as the main compo-
nents of the materials were diamagnetic silica. Amount of Fe ion of
pristine MNPs and MMS-COOH were measured using ICP to evaluate
MNPs loading percentage on MMS-COOH. The result shows that MNPs
contain Fe equal to 122 ppm/mg and 0.79% MNPs-loading on MMS-
COOH. The low MNPs-loaded percentage is in agreement with the low
Ms of MMS-COOH compared with pristine MNPs. However, MMS-
COOH can still be successfully removed using an external magnet.
Even though the MMS-PA underwent a harsh acidic and strong
oxidizing condition of peroxidation process, it still showed magnetic
response; however, the Ms of MMS-PA was decreased to roughly half of
the Ms of MMS-COOH. We believe that the decrease in Ms are likely due
to the dissolution and phase changes of the MNPs that were not well
protected by thin silica shells, and we performed further investigation
for this peroxidation process as shown in Table 2. However, the simi-
larity in Ms of MMS-PA and used MMS-PA are likely an indicative of the
similarity in MNPs component incorporated into mesoporous silica
(MS) though the materials have undergone the epoxidation process.
Moreover, hysteresis loops were not observed in these samples, im-
plying a characteristic feature of a superparamagnetic behavior, which
is desired in heterogeneous oxidant and heterogeneous catalyst
applications.
Since the peroxidation process of MMS-COOH is the most important
process that the balance between the oxidizing activity and the mag-
netic responses of MMS-PA, we optimized the condition for this process
by varying the amount of H2O2, time and temperature as shown in
Table 2. At room temperature (Entry 1), the resulted MMS-PA did not
respond to a magnet potentially due to the harsh reaction conditions
causing the digestion of MNPs by MeSO4H. Moreover, some of the
metal ions in MNPs structure might leak out from the structure and
catalyzes H2O2 decomposition [1,37]. The issue was resolved by per-
forming the reaction at lower temperature (5 °C) (Entry 2), yielding
MMS-PA which retained the magnetism and was capable of epoxidizing
VA, although the yield of the epoxide product was only 27%. Increasing
the reaction time from 3 h to 6 h or 12 h did not improve the yield of the
vinyl acetate epoxide product (Entries 2, 3 and 4). Finally, the MMS-PA
with the most epoxidizing property (giving 48% of the epoxide product)
was obtained by increasing the ratio between the H2O2 oxidant and the
amount of the starting MMS-COOH (Entry 5); thus, the conditions
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JournalofMagnetismandMagneticMaterials475(2019)579–585
Table 2
Quantity of materials and condition used in peroxidation of MMS-COOH in relation to the yield of epoxidation.
Entry
MMS-COOH weight (g)
MeSO4H (mL)
Conc.·H2O2 (mL)
Time (h)
T (°C)
Magnetic-response
Epoxide-yielda (%)
1
2
3
4
5
0.5
0.5
0.5
0.5
0.2
2.0
2.0
2.0
2.0
2.0
0.5
0.5
0.5
0.5
1.0
3
3
6
12
12
rt.
5
5
5
5
NO
–
YES
YES
YES
YES
27
19
24
48
a
Yield determined by 1H NMR.
Acknowledgment
Table 3
Epoxidation of VA with MMS-PA.
This work was financially supported by the Asia Research Center of
the Korea Foundation for Advanced Studies at Chulalongkorn
University (Contract Number 009/2561). Injumpa W. is supported by
Science Achievement Scholarship of Thailand (SAST), Support for the
Overseas Presentations of Graduate Level Academic Thesis, Overseas
Research Experience Scholarship for Graduate Student and the 90th
Anniversary of Chulalongkorn University Fund.
Entry
Peroxy/VA (mol/mol)
Time (h)
T (°C)
Epoxide yielda (%)
1
2
3
4
5
6
7
8b
10/1
10/1
10/1
10/1
20/1
20/1
20/1
20/1
0.5
1.0
2.0
3.0
2.0
2.0
2.0
2.0
rt.
rt.
rt.
rt.
rt.
40
50
rt.
22
27
37
38
52
64
59
47
Appendix A. Supplementary data
a
Yield determined by 1H NMR.
Recycled MMS-PA.
b
Supplementary data to this article can be found online at https://
doi.org/10.1016/j.jmmm.2018.11.111.
described in Entry 5 were used for further study.
References
Next, the conditions for the epoxidation of vinyl acetate with the
synthesized MMS-PA were optimized by varying time, temperature and
the amount of MMS-PA (calculated as the overall effective mole of the
peroxy acid presented) as shown in Table 3. The epoxide yield in-
creased with longer reaction time, reaching the maximum yield of 37%
at 2 h (Entries 1–4). The yield further increased to 52% when doubling
the amount of the MMS-PA (Entry 5). Moreover, the yield improved to
64% when the reaction was performed at 40 °C, (Entry 6) and dropped
to 59% at 50 °C (Entry 7), probably due to the decomposition of peroxy
acids on the composites.
In addition, we demonstrated that the MMS-PA can be removed and
recycled. A magnetic field of 3259 Oe from a rare-earth magnet was
used for separating 119.8 mg of MMS-PA in 1 mL of CH2Cl2. After ap-
plying an external magnetic field on the epoxidation vial for 2 min,
94.6 mg of used MMS-PA was recovered from the solution as shown in
Supporting information (Fig. S10) without the leftover Fe and Mg in the
solution as confirmed by ICP measurement. The loss of 21% MMS-PA
was likely due to the transferring and handling of the small quantity of
materials. Upon the treatment of the used particles with the peroxida-
tion conditions, the resulting MMS-PA can be used for the epoxidation
of vinyl acetate, giving only slightly lower the epoxide yield of 47% at
room temperature (Entry 8).
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