M-Type SrFe12O19Ferrite: An Efficient Catalyst for the Synthesis of Amino Alcohols under Solvent-Free Conditions

Article abstract of DOI:10.1155/2020/7960648

Magnetically separable strontium hexaferrite SrFe12O19 was prepared using the chemical coprecipitation method, and the nanostructured material was characterized by X-ray diffraction, scanning electron microscopy (SEM), energy-dispersive spectrometry (EDS), and BET analysis. The SEM images showed the homogeneity of the chemical composition of SrFe12O19 and uniform distribution of size and morphology. The pore size of the nanomaterial and its specific area were determined by BET measurements. Strontium hexaferrite SrFe12O19 exhibited a strong magnetic field, which is highly suitable in the heterogeneous catalysis as it can be efficiently separated from the reaction. The magnetic nanocatalyst showed high activity and environmentally benign heterogeneous catalysts for the epoxide ring-opening with amines affording β-amino alcohols under solvent-free conditions. When unsymmetrical epoxides were treated in the presence of aromatics amines, the regioselectivity was influenced by the electronic and steric factors. Total regioselectivity was observed for the reactions performed with aliphatic amines. The magnetically SrFe12O19 nanocatalyst showed excellent recyclability with continuously good catalytic activities after four cycles.

Full text of DOI:10.1155/2020/7960648

Hindawi
Journal of Chemistry
Volume 2020, Article ID 7960648, 10 pages
https://doi.org/10.1155/2020/7960648
Research Article
M-Type SrFe12O19 Ferrite: An Efficient Catalyst for the
Synthesis of Amino Alcohols under Solvent-Free Conditions
,
2
,3
MouhsineLaayati,1 AliHasnaoui,1 NayadAbdallah,1 SaadiaOubaassine,1 LahcenFkhar,1
Omar Mounkachi,4 Soufiane El Houssame ,2 Mustapha Ait Ali ,1
and Larbi El Firdoussi
1
1Laboratory of Molecular Chemistry, Coordination Chemistry and Catalysis Team, Cadi Ayyad University,
Faculty of Sciences Semlalia, B.P. 2390–40000, Marrakech, Morocco
2
´
´
Laboratoire de Chimie, Modelisation et Sciences de L’Environnement, Universite Sultan Moulay Slimane,
´
Faculte Polydisciplinaire de Khouribga, B.P. 145, Khouribga 25000, Morocco
3Materials and Nanomaterials Center, MAScIR Foundation, B.P. 10100, Rabat, Morocco
4LaMCScI, B.P. 1014, Faculty of Science Mohammed V, University Rabat, Rabat, Morocco
Correspondence should be addressed to Larbi El Firdoussi; elfirdoussi@uca.ac.ma
Received 1 April 2020; Revised 28 May 2020; Accepted 17 June 2020; Published 11 July 2020
Academic Editor: Andrea Penoni
Copyright © 2020 Mouhsine Laayati et al. (is is an open access article distributed under the Creative Commons Attribution License,
which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Magnetically separable strontium hexaferrite SrFe12O19 was prepared using the chemical coprecipitation method, and the
nanostructured material was characterized by X-ray diffraction, scanning electron microscopy (SEM), energy-dispersive
spectrometry (EDS), and BET analysis. (e SEM images showed the homogeneity of the chemical composition of SrFe12O19 and
uniform distribution of size and morphology. (e pore size of the nanomaterial and its specific area were determined by BET
measurements. Strontium hexaferrite SrFe12O19 exhibited a strong magnetic field, which is highly suitable in the heterogeneous
catalysis as it can be efficiently separated from the reaction. (e magnetic nanocatalyst showed high activity and environmentally
benign heterogeneous catalysts for the epoxide ring-opening with amines affording β-amino alcohols under solvent-free
conditions. When unsymmetrical epoxides were treated in the presence of aromatics amines, the regioselectivity was influenced by
the electronic and steric factors. Total regioselectivity was observed for the reactions performed with aliphatic amines. (e
magnetically SrFe12O19 nanocatalyst showed excellent recyclability with continuously good catalytic activities after four cycles.
homogenous catalysts but suffer from several disadvantages
such as low regioselectivity, toxic solvents, toxic metal ions,
and nonreusable catalysts [8–14].
On the other hand, only a few reports are focused on the
use of heterogeneous catalysts such as silica nanoparticles
[15], Fe-MCM-41 [16], zeolites [17], heteropoly acid, and
MCM-22 [18, 19].
Recently, green chemistry has gained considerable im-
portance in chemical design processes that utilize envi-
ronmental-friendly processes to reduce or eliminate the
generation of toxic by-products [20]. In addition, hetero-
geneous catalysts offer interesting advantages compatible
with the green chemistry approach in catalytic reactions,
such as high activity, atom economy, good regioselectivity,
1. Introduction
β-Amino alcohols are molecules with an interesting role as
intermediates in the synthesis of a wide range of biologically
active natural and synthetic products [1–4]. (e presence of
these functional groups with a defined stereochemistry is of
great importance in the biological activity of these mole-
cules. (ey are also widely used as potential chiral auxiliaries
and chiral ligands in asymmetric synthesis [5]. (e nucle-
ophilic ring-opening of epoxides with amines represents one
of the most important and straightforward methods for the
preparation of the β-amino alcohols [6]. While the classical
methods require a high temperature [7], various method-
ologies developed the epoxide ring-opening using

2
Journal of Chemistry
and especially the reusability of the catalyst. Furthermore,
solvent-free conditions have a supplementary advantage in
avoiding toxic solvents.
reaction mixture on an ISQ LT single quadrupole mass
spectrometer in positive EI mode using a mass scan range of
50 to 400 Da. BET measurements were performed using
3Flex 3500 Micromeritics instruments. (e magnetic pro-
priety was determined by the Quantum Design XL-SQUID
magnetometer.
In recent years, magnetic nanoparticles have emerged as
efficient heterogeneous catalysts in organic synthesis that
offer a major advantage with its easy magnetic separation
[21–25]. In particular, magnetic nano-Fe3O4 and sulfonic
acid-functionalized silica-coated magnetic Fe3O4 were used
as efficient heterogeneous catalysts for the aminolysis of
epoxides by amines [26, 27]. (e same reaction was per-
formed under solvent-free conditions using various spinel
nanoferrites MFe2O4 (M � Co, Ni, Cu, Zn) [28].
2.2. Preparation of the Catalyst. (e M-type hexaferrite
SrFe12O19 was obtained by the co-precipitation method of
Sr2+ and Fe3+ in the presence of NaOH as a precipitate agent
in an aqueous medium. Briefly, stoichiometric amount of
SrCl2 (0.068 g) and FeCl3.6H2O (2 g), were dissolved in
30 mL of deionized water. To the resulting mixture, 100 mL
of NaOH (1.5 M) solution was added dropwise at 60°C. Next,
the temperature was increased to 100°C for 2 hours. (e
precipitated solid was separated magnetically and washed
several times to remove the excess of salts and then dried at
80°C overnight. (e obtained powder was annealed at
1000°C for 6 hours and subjected to various analyses.
Hexagonal strontium hexaferrite (SrFe12O19), known as
M-type strontium hexaferrite (SrM), was discovered in the
1950s by Philips’ laboratories [29]. Strontium hexaferrite is
usually used as magnetic recordings, permanent magnets,
and microwave devices [30–32]. In organic synthesis, it was
applied as a catalyst in the synthesis of 2-amino-4,6-
diphenylnicotinonitrile derivatives [33]. (e magnetic
properties of SrFe12O19 depend on the shape and size of the
particles. Several methods have been used to prepare this
nanomaterial, such as sol-gel [34], hydrothermal [35], salt-
melt methods [36], ball milling [37], self-propagating high-
temperature synthesis [38], and the chemical coprecipitation
method [39]. However, the coprecipitation method is the
most widely used in the synthesis of magnetic oxides due to
its simplicity and good control of the grain size [40].
Previously, we have shown the catalytic efficiency of
calcium trifluoroacetate Ca(CF3CO2)2 as a highly chemo-
selective homogenous catalyst in the epoxide ring-opening
with amines [9]. As part of our studies directed towards the
development of green chemistry protocols by performing
organic transformations under solvent-free conditions
[41, 42], we have focused our attention on the preparation,
characterization, and catalytic application of magnetic
strontium hexaferrite SrFe12O19 nanoparticles. (e magnetic
behavior of SrFe12O19 was evaluated by measurement of the
hysteresis loops at room temperature. Furthermore,
SrFe12O19 nanoparticles were tested as a heterogeneous
catalyst in the ring-opening reactions with various amines.
2.3. Catalytic Activity. In a typical reaction, a mixture of
epoxide (1.02 mmol), amine (1.1 mmol), and SrFe12O19 (9.4
10−3 mmol) was introduced into a 50 mL Rotaflow tube and
stirred at 60°C for 17 hours. (e evolution of the reaction
was monitored by gas chromatography. At the end of the
reaction, the catalyst was easily recovered by applying a
magnetic field, then washed with acetone and distilled water,
and dried in an oven for 6 hours before reuse.
3. Results and Discussion
3.1. Characterization. Figure 1 presents the XRD pattern of
hexagonal SrFe12O19 sample with corresponding diffraction
lines. (e prepared nanomaterial crystallizes in a pure
hexagonal structure with a space group 194/P63 mmc. As
shown in Figure 1, no impurity phases were detected from
the XRD pattern. Rietveld refinement of the sample was
performed by TOPAS software in order to define the lattice
parameters of SrFe12O19 according to JCPDS 01-084-1531.
(e result is presented in Table 1.
2. Experimental Details
To confirm the nanoparticles formation, Debye–Scherrer
formula was used to calculate the crystallite size of the
prepared nanoparticles:
2.1. Materials. All reagents and solvents were purchased
from commercial sources and used as received without
further purification (Aldrich, Acros).
0.9λ
β Cos(θ)
d �
,
(1)
(e synthesized NPs were characterized by X-ray
powder diffraction (XRD) using D8 Discover Bruker (AXS)
˚
with Cu Kα radiation (λCu � 1.5407 A) model. Micro-
where λ is the wavelength (Cu Kα), β is the full width to half-
maximum (FWHM) of line broadening, and θ is the Bragg
angle of diffraction. (e average crystallite size was found to
be 85.4 nm.
structural characterization was performed using a Scanning
Electron Microscope (SEM) (FEI, Quanta FEG 450) from
BRUKER. Aliquots samples from the reaction mixture were
monitored by Shimadzu gas chromatography (GC) with a
flame ionization detector using nitrogen as a carrier gas. GC
parameters for capillary columns BP (25 m × 0.25 mm, SGE)
are injector 250°C; detector 250°C; oven 70°C for 5 min then
3°C/min until 250°C for 30 min; column pressure 20 kPa;
column flow 6.3 mL/min; linear velocity 53.1 cm/s; total flow
138 mL/min. (e products were confirmed by injecting the
(e scanning electron microscope (SEM) shows the
homogeneity of the chemical composition and regular
distribution of size and morphology (Figure 2). EDS results
confirmed the elements that consist of strontium hexaferrite
(Sr, Fe, and O) (Figure 3). (e percentage of elements is in
good agreement with the chemical composition of
SrFe12O19, which confirms the absence of impurities.

Journal of Chemistry
3
20
30
40
50
60
70
80
2θ (degrees)
Figure 1: X-ray patterns of SrFe12O19.
Table 1: Lattice parameters of SrFe12O19.
3
˚
˚
˚
Catalyst
SrFe12O19
Space group
194/P63 mmc
Structure
Hexagonal
a (A)
C (A)
Ddrx (nm)
95.4 ( 0.4)
V (A )
692.1410 ( 0.0056)
5.8856 ( 0.0047)
23.0790 ( 0.0082)
10μm
2μm
(a)
(b)
Figure 2: SEM images of SrFe12O19.
cps/ev
50
40
30
20
10
0
Element
Line s. Mass (%) Mass norm. (%) Atom (%)
Carbon
Oxygen
Iron
K-serie
K-serie
K-serie
6.13
26.78
64.60
10.75
108.26
5.66
24.74
59.67
9.93
14.73
48.33
33.40
3.54
Strontium L-serie
O
100.00
100.00
Fe
Sr
Fe
C
1
2
3
4
5
6
7
8
9
10
Energy (keV)
Figure 3: EDS of SrFe12O19.

4
Journal of Chemistry
22
20
18
16
14
12
10
8
0.006
0.005
0.004
0.003
0.002
0.001
0.000
2
4
6
8
10
12
14
16
Pore width (nm)
6
4
2
0
0.0
0.2
0.4
Relative pressure (p/p°)
Figure 4: N2 adsorption-desorption isotherm and BJH pore diameter distribution of SrFe12O19.
0.6
0.8
1.0
Figure 4 shows the isotherm of M-type hexaferrite
100
80
SrFe12O19 material. According to the IUPAC classification, the
isotherm of the catalyst is assigned to type II, which is
characteristic of nonporous materials, due to the high calci-
nation temperature. (is was confirmed by the pore size
distribution curve determined by the Barrett–Joyner–Halenda
(BJH) method, which showed a centered pore size at 2.21 nm.
(e BETsurface area of the SrFe12O19 material was found to be
25 m2/g.
60
40
20
0
–20
–40
–60
–80
–100
3.2. Magnetic Measurement. (e magnetic propriety of
SrFe12O19 at room temperature was investigated (Figure 5).
(e hysteresis loops of the samples showed that strontium
hexaferrite exhibits a ferrimagnetic behavior characterized
by high coercivity (5.37 KOe), high magnetization saturation
(81.79 emu/g), and remanence magnetization of about 39.74
emu/g. (e values are higher than those found when the
material was prepared by other methods and confirm the
hard magnetic behavior of SrFe12O19 [43–45].
–60000 –40000 –20000
0
20000 40000 60000
Field (Oe)
Figure 5: Hysteresis loop of SrFe12O19.
no reaction took place (entries 4 and 5). In solvent-free
conditions, total conversion and high selectivity were
achieved (entry 1). In the absence of catalysts, only 19% of
selectivity was obtained (entry 6). (e optimal catalytic
amount was found to be 0.92 mol% and the optimum
temperature was 60°C (entry 10).
3.3. Catalytic Application. (e catalytic activity of the
SrFe12O19 nanocatalyst was evaluated for the nucleophilic
ring-opening of cyclohexene oxide with aniline (Scheme 1).
(e scope and limitation of the catalytic system were ex-
amined by testing different parameters (Table 2).
A kinetic study was performed with 0.01 g of the
nanocatalyst SrFe12O19 (Figure 6). Based on Figure 6, the
evolution of the reaction versus time shows that a maximum
of the desired amino alcohol 3a was obtained after 17 h of
reaction time. Under the optimized conditions, various
aromatic and aliphatic amines were examined. (e results
are summarized in Table 3.
Preliminary experiments were conducted at 80°C with
1.02 mmol of cyclohexene oxide (1) and 1.1 mmol of aniline
(2a) catalyzed by SrFe12O19 NPs (0.01 g, 0.92 mol%) in
various solvents or under solvent-free conditions (Table 2).
(e reaction was high stereoselective and afforded the trans
amino alcohol 3a. In protic polar solvents, amino alcohol
derivative 3a was obtained in good yield (entries 2 and 3).
However, in an aprotic solvent such as THF or acetonitrile,
With all amines used, high stereoselectivity was ob-
served. Exclusive trans amino alcohol derivatives were

Journal of Chemistry
5
NH2
NH
SrFe12O19
O
Free solvent, 60°C, 17h
OH
3a
Scheme 1: Catalytic ring-opening of cyclohexene oxide with aniline.
1
2a
Table 2: Catalytic epoxide ring-opening of cyclohexene oxide as symmetric epoxide.
Entry
Solvent
C/S mol (%)
T (°C)
Conversiona (%)
Selectivityb (%)
1
Solvent-free
Water
0.92
0.92
0.92
0.92
0.92
None
0.64
1.38
1.84
0.92
0.92
0.92
0.92
80
80
80
80
80
80
80
80
80
60
50
40
25
100
80
100
80
2
3
Methanol
80
80
4
THF
None
None
19
None
None
19
5
Acetonitrile
Solvent-free
Solvent-free
Solvent-free
Solvent-free
Solvent-free
Solvent-free
Solvent-free
Solvent-free
6
7
28
28
8
96
96
9
79
79
10
11
12
13
100
96
100
96
96
20
95
20
Reaction conditions: solvent (1 mL), reaction time 17 h, cyclohexene oxide (1.02 mmol), and aniline (1.1 mmol). aConversion and bselectivity were determined
by GC.
100
80
60
40
20
0
9
12
14
15
Time (h)
16
17
20
Figure 6: Effect of the reaction time.
Table 3: Catalytic ring-opening of cyclohexene oxide with various amines.
Entry
1
Amine
Product
Conversion (%)a
Yield (%)b
NH2
NH
100
49
97
2a
OH
3a
Cl
NH2
Cl
NH
2
3
49
42
2b
OH
3b
F
NH2
F
NH
42
2c
OH
3c

6
Journal of Chemistry
Table 3: Continued.
Entry
Amine
HN
Product
Conversion (%)a
Yield (%)b
O
O
N
4
5
6
82
82
2d
OH
N
NH
84
84
97
2e
3e
H
N
H3C–NH2
2f
100
10
3f
H
N
2g
N
7
8
9
10
87
95
3g
H
N
NH2
H2N
NH2
2h
90
97
3h
H
N
H2N
2i
3i
Reaction conditions: cyclohexene oxide (1.02 mmol), amine (1.1 mmol), C/S � 0.92 mol%, solvent-free, and 17 h 60°C. aConversion was determined by GC;
bisolated yield.
O
NRR′
OH
R
SrFe12O19 (0,92 mol%)
Free solvent, 60°C, 17 h
OH
NRR′
HN
R′
4
5
5′
Scheme 2: Catalytic ring-opening of styrene oxide with different amines.
obtained in the cleavage of the epoxide ring of cyclohexene
oxide which is in good agreement with the literature [46, 47].
Table 3 shows that electron-withdrawing effects resulted in
the decrease of the nucleophilicity of the aromatic amines
(entries 2 and 3). In the presence of cyclic secondary amines,
a slight decrease in yield was detected (entries 4 and 5). All
the primary amines afford the corresponding amino alcohols
in high yields under solvent-free conditions (entries 6, 8, and
9). Among aliphatic amines, diethylamine exhibited a low
activity due to its low boiling temperature (55°C) (entry 7).

Journal of Chemistry
7
Table 4: Catalytic ring-opening of styrene oxide with various amines.
Selectivity (%)
Yield (%)c 5
b
Entry
1
Amine
Conversion (%)a
Product
5 5′
5′
5
5′
5
5′
NH2
HN
95
74
26
70
12
OH
NH2
F
F
2
3
74
76
83
74
17
26
61
56
10
14
HN
OH
NH2
HN
OH
OH
NH2
4
5
99
85
0
0
100
100
0
0
98
84
NH
OH
HN
O
N
O
OH
NH
6
100
0
100
0
99
N
Reaction conditions: styrene oxide (0.8 mmol), amine (1 mmol), C/S � 0.92 mol%, solvent-free, 17 h, and 60°C. aConversion and bselectivity were determined
c
by GC; isolated yield.
A study on the regioselectivity of the nucleophilic ring-
opening reaction was evaluated in the presence of styrene
oxide 4 as unsymmetrical epoxide with various aromatic and
aliphatic amines (Scheme 2). (e result is summarized in
Table 4.
As was described in the literature with styrene oxide,
the regioselectivity of the reaction is influenced by the
electronic and steric factors associated with the epoxides
and the amines [47]. Table 4 shows that, with aromatic
amines, the reaction afforded the amino alcohols from
nucleophilic attack at the benzylic carbon atom of the
epoxide ring as the major products (entries 1–3). In the
case of aliphatic amines, the major/exclusive product was
the regioisomeric amino alcohol produced by nucleo-
philic attack at the less hindered carbon atom of the
epoxide ring (entries 4–6).
Cat
O
NH2Ar(R)
Ar
O
Cat
O
Ar
H
NHAr(R)
SrFe12O19
Ar
(Cat: SrFe12O19
)
HO
Ar
NHAr(R)
It is commonly recognized that the epoxide ring-opening
reaction under basic or neutral conditions proceeds via the
SN2 mechanism, but under acidic conditions, a borderline
SN2 mechanism has been invoked to justify the electronic
pull on the oxygen by an acid [48, 49].
Scheme 3: Proposed mechanism of the catalytic ring-opening of
styrene oxide.
Sundararajan et al. have discovered that anilines act as
superior ring-opening reagents even when the reactions
were performed with CoCl2.6H2O or under aerobic con-
ditions, thereby ruling out the possibility of the mediation by
free radicals [50]. Moreover, they suggest that CoCl2 co-
ordinates with the oxirane oxygen promote the nucleophilic
attack of the anilines leading to two regioisomers. In the case
of metal coordinated styrene oxide, the positive charge on
oxygen appears to be localized on the more highly
substituted benzylic carbon and the nucleophile attacks the
benzylic carbon of the styrene oxide.

8
Journal of Chemistry
Table 5: Catalyst recycling effect.
25000
20000
15000
10000
5000
0
Entry
Cycle
Conversion (%)a
Selectivity (%)b
1
2
3
4
5
Fresh
100
83
80
75
71
100
83
80
75
71
1
2
3
4
Reaction conditions: cyclohexene oxide (1.02 mmol), aniline (1.1 mmol), C/
S � 0.92 mol%, solvent-free, 17 h, and 60°C. aConversion and bselectivity
were determined by GC.
Element Weight % Atomic %
CK
OK
FeL
SrL
4.29
37.31
45.11
13.30
9.79
63.91
22.14
4.16
20
30
40
50
60
70
80
90
2θ (degrees)
As-prepared
Afer four cycles
Figure 8: DRX patterns of magnetic SrFe12O19 fresh and recycled.
of the oxygen content on the surface of the materials
(Figure 7).
Moreover, XRD analysis of SrFe12O19 nanocatalyst after
five cycles exhibited less intensities of the diffraction planes
compared to the fresh one (Figure 8).
5μm
4. Conclusion
Figure 7: SEM image of magnetic SrFe12O19 after five cycles.
In summary, SrFe12O19 nanoparticles were prepared by
the coprecipitation method and characterized using
various techniques. (e prepared nanomaterial exhibited
a strong magnetic field and marked activity, good reus-
ability, and stability as a heterogeneous catalyst for the
regioselective ring-opening of epoxides with various
amines under free solvent conditions. (e easy magnetic
separation of the catalyst and its good reusability make it a
useful and attractive process for the synthesis of β-amino
alcohols.
Chakraborti et al. have reported that selective for-
mation of the regioisomeric product arising from nu-
cleophilic attack at the benzylic carbon was observed
during the reactions with aromatic amines which are less
nucleophilic [46, 47]. (is preference may be accounted
by the fact that the phenyl group in styrene oxide assists in
the stabilization/accumulation of carbocationic character
at the benzylic carbon. Meanwhile, in the case of aliphatic
amines, a preference for nucleophilic attack at the ter-
minal carbon may be explained by the increased nucle-
ophilicity of aliphatic amines favoring a more SN2
process. According to literature, a similar result was
obtained during our present work and a proposed
mechanism is given in Scheme 3.
Data Availability
SEM, EDS, XRD, BET, and the device types used for re-
cording spectra and other analytical data used to support the
findings of this study are included within the manuscript.
Disclosure
3.4. Recyclability. To investigate the reusability of SrFe12O19
nanoparticles, the catalytic performance in the epoxide ring-
opening reaction of cyclohexene oxide with aniline was
evaluated in five consecutive cycles (Table 5). After each
cycle, the catalyst was separated from the reaction mixture
using an external magnet, washed with water and acetone,
and dried at 100°C for 6 hours while being reused.
(e present research is a part of a Ph.D. thesis work of the
author Mouhsine Laayati.
Conflicts of Interest
(e authors declare that they have no conflicts of interest.
As shown in Table 5, the catalyst still exhibits a good
catalytic activity after the third consecutive cycle. However, a
noticeable drop in cyclohexene oxide conversion was ob-
served after the fourth consecutive run due to agglomerated
particles. SEM image of SrFe12O19 after five cycles showed
particle agglomeration and surface change with an increase
Acknowledgments
(e authors are grateful to the Center for Analysis and
Characterization (CAC) at Cadi Ayyad University, Marra-
kech, for the spectroscopic analysis.

Journal of Chemistry
9
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