Magnetic BaFe12O19/Al2O3: An Efficient Heterogeneous Lewis Acid Catalyst for the Synthesis of α-Aminophosphonates (Kabachnik–Fields Reaction)

Article abstract of DOI:10.1007/s10562-019-02910-8

Abstract: The design and application of environmentally friendly catalysts to reduce the quantity of toxic wastes is critical for improving?the chemical synthesis process. Therefore, BaFe₁₂O₁₉/Al₂O₃, a magnetic mesoporous nanocomposites, were designed synthesized and characterized using different techniques such as energy dispersive X-ray (EDX) spectroscopy, X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), field emission scanning electron microscopy (FESEM), Brunauer–Emmett–Teller?(BET) adsorption method, and vibrating sample magnetometry (VSM). The prepared BaFe₁₂O₁₉/Al₂O₃ display a high surface area (1773.22?m²/g) with an average pore diameter of 3.946?nm from nitrogen sorption analysis. In addition, the synthesized nanocomposites prove to be an active heterogeneous Lewis acid catalyst for the solvent free synthesis of α-aminophosphonates at ambient temperature, through three-component reaction of aldehydes/ketones, amines and triethyl phosphite. The use of this catalyst results in an effortless magnetic recoverability and recyclability, high yield and short reaction time under solvent-free conditions. Graphic Abstract: [Figure not available: see fulltext.].

Full text of DOI:10.1007/s10562-019-02910-8

Catalysis Letters
https://doi.org/10.1007/s10562-019-02910-8
Magnetic BaFe12O19/Al2O3: An Efcient Heterogeneous Lewis Acid
Catalyst for the Synthesis of α‑Aminophosphonates (Kabachnik–Fields
Reaction)
Tayebeh Piri1 · Reza Peymanfar1 · Shahrzad Javanshir1 · Sara Amirnejat1
Received: 14 March 2019 / Accepted: 20 July 2019
© Springer Science+Business Media, LLC, part of Springer Nature 2019
Abstract
The design and application of environmentally friendly catalysts to reduce the quantity of toxic wastes is critical for improv-
ing the chemical synthesis process. Therefore, BaFe12O19/Al2O3, a magnetic mesoporous nanocomposites, were designed
synthesized and characterized using diferent techniques such as energy dispersive X-ray (EDX) spectroscopy, X-ray dif-
fraction (XRD), Fourier transform infrared spectroscopy (FT-IR), feld emission scanning electron microscopy (FESEM),
Brunauer–Emmett–Teller (BET) adsorption method, and vibrating sample magnetometry (VSM). The prepared BaFe12O19/
Al2O3 display a high surface area (1773.22 m2/g) with an average pore diameter of 3.946 nm from nitrogen sorption analysis.
In addition, the synthesized nanocomposites prove to be an active heterogeneous Lewis acid catalyst for the solvent free
synthesis of α-aminophosphonates at ambient temperature, through three-component reaction of aldehydes/ketones, amines
and triethyl phosphite. The use of this catalyst results in an efortless magnetic recoverability and recyclability, high yield
and short reaction time under solvent-free conditions.
Graphic Abstract
O
EtO
EtO
P
ArCHO
1a-l
Ar
N
H
NH2
2a-b
BaFe12O19/Al2O3
4a-p
EtO OEt
P
or
or
OEt
r.t.
Solvent
Free,
O
P
O
R'
OEt
OEt
1m
3
NH
4q
Electronic supplementary material The online version of this
article (https://doi.org/10.1007/s10562-019-02910-8) contains
supplementary material, which is available to authorized users.
Extended author information available on the last page of the article
Vol.:(0123456789)
1 3

T. Piri et al.
Keywords Heterogeneous catalysis · Amination · Magnetic separation · Mesoporous materials · Lewis acid · Kabachnik–
felds reaction
1 Introduction
2 Experimental
The synthesis of α-aminophosphonates, known as bio-
isosteres of alpha-amino acids, has gained great interest
because of their varied pharmacological properties like
anticancer, antiviral, herbicides, fungicides, bactericides,
peptide mimetic and enzyme inhibitor [1–4]. Consider-
ing their multipurpose pharmaceutical importance, vari-
ous methods have been developed for the synthesis of
α-aminophosphonates [5]. Of these, the Kabachnik–Fields
reaction of aldehydes/ketones, amines, and phosphites is
of great interest [6–8]. Abundant protocols for this conven-
tional synthesis include employment of various catalytic
systems such as Lewis acids [9–11], Brønsted acids [12],
heterogeneous catalysts [13], have been developed. Owing
to their synthetic and biological values, there is still need
to develop new accessible, environmentally benign and ef-
cient protocol for the preparation of α-aminophosphonates.
In recent years, the use of γ-Al2O3 as a support for catalytic
applications has led to a new generation of heterogeneous
“nanocatalyst.” [14] Such catalysts are preferable to con-
ventional catalysts because of numerous aspects such as
greater surface area; higher activity; higher selectivity and
longer life and thus, developing a newer type of sustainable
environmentally friendly catalysts which may fnd a wide
range of applications in the area of fne and bulk chemi-
cal industries, pharmaceuticals, and many other felds.
Although the problem of their separation from the reaction
medium is partly solved, but their separation and recycling
involves the use of methods such as fltering or centrifuga-
tion which prolong the process. Also, these methods make
part of the catalysts disappear and causes impurities to
remain in the reaction environment.
2.1 Chemicals and Instruments
All of the reagents and solvents used in this work were
achieved from Fluka or Merck and used without further
purifcation. Fourier transform infrared spectroscopy (FT-
IR) measurements were performed using KBr disk on a
Shimazdu spectrometer. Ray X-ray analysis was performed
by using Philips analyzer. Ultrasonic bath used for syn-
thesis of catalyst from Elmasonic, Which produced 60 Hz
frequency and maintained a temperature up to a maximum
temperature of 80 °C. calcination of catalyst performed by
Exciton oven. A vibrating-sample magnetometer (VSM)
model MDKFD (Danesh Pajohan Kavir Co). Scanning
electron microscope (SEM) used for analyses from Czech
Republic. The 1H- and 13C-spectra were measured at 500 and
125 MHz, respectively, on a Bruker DRX 500-Avance FT-
NMR instrument with CDCl3 solvent. Melting point meas-
ured by Electro thermal 9100. The Brunauer–Emmett–Teller
(BET) surface area measurements of the catalyst were car-
ried out using ASAP 2020 instrument.
2.2 Synthesis of Barium Hexaferrite Magnetic
Nanoparticles (BaFe12O19)
For the preparation of barium ferrite, Ba(NO3)2 (0.52 g,
1.99 mmol) and of Fe(NO3)3·9H2O (9.6 g, 23.76 mmol)
were poured into a 250 ml round-bottomed fask contain-
ing 100 ml of double-distilled water, followed by the addi-
tion of citric acid (4.5 g, 23.42 mmol). The mixture was
then sonicated in an ultrasonic bath for 15 min to attain a
homogenous dispersion. Then, aqueous ammonia solution
(25%) was added to the dispersed solution until the pH value
reached 8. After subsequent washing and drying, the prod-
uct was calcined at 1000 °C for 2 h to obtain the desired
magnetic nanoparticles of barium hexaferrite.
In the current paper, magnetic nanoparticles of barium
hexaferrite supported on gamma-aluminum oxide were
prepared and used as heterogeneous Lewis acid catalyst
in Kabachnik -Fields reaction. A very simple protocol
was followed in the reaction process for the synthesis of
α-aminophosphonates via the addition of triethylphosphite
to the double bond of imines, formed from the reaction
between diverse aldehydes and aniline derivatives. The
reaction proceeded smoothly at ambient temperature under
solvent free conditions, at the same time the issues of sepa-
ration and recycling of the catalyst is excluded due to its
magnetic properties [15, 16].
2.3 Synthesis of BaFe12O19/Al2O3 Magnetic
Nanocomposites
Aluminum nitrate (16.5 g, 77.93 mmol) and citric acid
(9.2 g, 47.9 mmol) were dissolved in H2O/EtOH (2:1,
45 ml). Then, ammonia solution (25%) was added dropwise
to the solution until pH 8 was reached and then barium fer-
rite (0.7 g, 0.63 mmol) was added under sonication con-
ditions. In the next step, in order to utterly evaporate the
1 3

Magnetic BaFe12O19/Al2O3: An Efcient Heterogeneous Lewis Acid Catalyst for the…
FT-IR spectra
solvent, the mixture was stirred at 80 °C. The magnetic
nanocomposites BaFe12O19/Al2O3 were achieved after cal-
cination treatment at 750 °C for 5 h.
BaFe12O19
BaFe12O19/Al2O3
2.4 General Procedure for the Synthesis
of α‑aminophosphonates (4a‑4q)
For the synthesis of α-aminophosphonates, triethylphosphite
3900
3400
2900
2400
1900
1400
900
400
Wavenumber (cm-1
)
(0.199 mg, 1.2 mmol), aniline derivatives (1 mmol), alde-
hydes (or ketones) (1 mmol), and BaFe12O19/Al2O3 magnetic
Fig. 2 The FT-IR spectra of BaFe12O19 and BaFe12O19/Al2O3
nanocomposites (35 mg) were added into a test tube at room
temperature under solvent-free condition. The mixture was
stirred up to perform reaction at required time. The reaction
was monitored by TLC (eluent: EtOAc/n-hexane, 1:3). At
the end of the procedure the catalyst was removed from the
reaction mixture by an external magnet, to be reused in the
next cycle after being sufciently washed with EtOH, n-hex-
ane and ethyl acetate. The magnetic property of the catalyst
was checked with magnet, which was desirable (Fig. 1).
to Al-O and peak at 550 cm−1 was attributed to the bend-
ing vibration of the O–Al–O. One strong absorption band
at 250–550 cm−1 was attributed to vibrations of Fe–O in
barium hexaferrite structure.
The XRD patterns of the BaFe12O19 nanoparticles and
BaFe12O19/Al2O3 nanocomposite were shown in Fig. 2. As
can be seen, the presence of all the crystal planes such as
(110), (107), (114), (203), (217), (2011), and (220) ascribed
to the crystal structure of hexaferrite of barium proves that
BaFe12O19 nanoparticles were synthesized and that its crys-
talline structure was maintained after its composition by
Al2O3 nanoparticles. The presence of difraction peaks at
45.7° and 66.6° corresponding to (400) and (440) lattice
planes related to the γ-Al2O3 structure in the BaFe12O19/
Al2O3 nanocomposite. The BaFe12O19 and Al2O3 nanoparti-
cles were characterized by [01-072-0738] and [00-001-1308]
standard carts, respectively.
3 Results and Discussion
The prepared BaFe12O19/Al2O3 nanohybrid was character-
ized using Fourier transform infrared (FTIR), X-ray Difrac-
tion XRD, vibrating sample magnetometer (VSM), scanning
electron microscopy (SEM), energy dispersive X-ray (EDX)
spectroscopy, and Brauner Emette Teller (BET) surface area
analysis.
The FT-IR spectra of BaFe12O19/Al2O3 was studied and
shown in Fig. 2. The broad band at 3200–3700 cm−1 was
assigned to the OH stretching vibration and 1640 cm−1 to the
bending vibrations of H2O [15]. Peak at 880 cm−1 attributed
Figure 3 shows VSM curves of BaFe12O19 nanoparti-
cles and BaFe12O19/Al2O3. The magnetic saturation (Ms)
remanent magnetization (Mr) of M-type barium hexafer-
rite as a ferrimagnetic nanoparticles was 52.04 emu/g and
28.43 emu/g respectively, while Ms and Mr of BaFe12O19/
Al2O3 nanocomposite are shifted to 11.18 emu/g and
6.05 emu/g respectively (Fig. 4) due to the mass fraction
of non-magnetic Al2O3 nanoparticles in the nanocomposite.
Both BaFe12O19/Al2O3 and BaFe12O19 nanomaterials show
a hard-magnetic behavior conferring to their broad hyster-
esis loops. The increase in coercivity (Hc) in BaFe12O19/
Al2O3 nanocomposite is due to the surface spin efect and
the dipole–dipole interaction between BaFe12O19 and Al2O3.
The morphologies of the BaFe12O19 nanoparticles and
BaFe12O19/Al2O3 nanocomposite were investigated by SEM
micrographs. As shown in Fig. 5a, BaFe12O19 magnetic
nanoparticles synthesized by sol–gel method had a hexago-
nal and uniform lace-like morphology. The SEM images of
BaFe12O19/Al2O3 nanocomposite illustrated in Fig. 4b show
well that Al2O3 sheets were almost uniformly covered by
BaFe12O19 nanoparticles.
Also, the EDX of BaFe12O19/Al2O3 nanocomposites dis-
closes the presence of O, Al, Fe and Ba in the structure of
this material (Fig. 6).
Fig. 1 Separation of magnetic BaFe12O19/Al2O3 catalyst by exter-
nal magnet
1 3

T. Piri et al.
Figure 7 depicts an adsorption/desorption isotherm of
BaFe12O19/Al2O3 nanocomposites determined by BET
method s at 77 K. The isotherm of the BaFe12O19/Al2O3
sample was a typical mesoporous material with pore size
between 2 and 50 nm. The BET surface area (SBET) was
1773.22 m2/g, average pore diameter was 3.946 nm, and the
total volume of pore was 1.749 cm3/g.
3.1 Evaluation the Catalytic Activity of BaFe12O19/
Al2O3 Magnetic Nanocomposites Through
Synthesis of α‑aminophosphonates
We studied the catalytic activity of heterogeneous Lewis
acid BaFe12O19/Al2O3 magnetic nanocomposites in one-
pot three-component synthesis of α-aminophosphonates,
through the reaction of aromatic aldehydes (and ketone), tri-
ethyl phosphite and aniline derivatives. In order to establish
the optimum reaction conditions, we used 4-chlorobenzal-
dehyde, triethyl phosphite and aniline as model substrates.
The reaction was studied under diferent conditions and the
results of these comparative experiments are summarized
in Table 1.
At the frst, the reaction carried out in solvent-free and
temperature (80 °C) in the presence of 10 mg of catalyst with
57% isolated yield. The reaction was carried out in various
organic solvents such as Ethanol, Water, and Acetonitrile.
The best yield achieved in solvent-free condition, thus the
efect of various temperature checked out, while in room
temperature yield of the reaction improved. By increasing
the temperature (60, 80,100 °C) lower yields were observed.
This is typical for any equilibrium where the direct reaction
is exothermic. To probe the efect of the catalyst concen-
tration, regular studies were carried out in the presence of
diferent amounts of the catalyst (15, 25, 35 mg), giving
α-aminophosphonates with 73%, 79% and 90% isolated
yields, individually. Thus, the best yield is accessible in the
presence of just 35 mg catalyst, and use of higher amounts
of the catalyst did not increase the result to a signifcant
level. Therefore the best results appeared in solvent-free,
at room temperature in the presence of 35 mg catalyst. In
the absence of catalyst the reaction did not proceed even
after 24 h at room temperature. Although in the presence of
Nano BaFe12O19 or Al2O3 as catalyst the yield of reaction
was improved, but high product yield was obtained using
BaFe12O19/Al2O3 magnetic nanocomposites. (Table 1, entry
11).
Fig. 3 XRD patterns of a standard BaFe12O19 nanoparticles and b
synthesized BaFe12O19 and BaFe12O19/Al2O3 nanocomposites
In the absence of the catalyst the reaction did not proceed
even after 24 h at room temperature. Although in the pres-
ence of Nano BaFe12O19 or Al2O3 as catalyst the yield of
reaction was improved, but high product yield was obtained
using BaFe12O19/Al2O3 magnetic nanocomposites (Table 2,
entry 4).
Fig. 4 Magnetic hysteresis loops of the BaFe12O19 nanoparticles and
BaFe12O19/Al2O3 nanocomposite
1 3

Magnetic BaFe12O19/Al2O3: An Efcient Heterogeneous Lewis Acid Catalyst for the…
Fig. 5 SEM images of a BaFe12O19 nanoparticles and b BaFe12O19/Al2O3 nanocomposite
Fig. 6 EDX spectrum of BaFe12O19/Al2O3
Under the optimal reaction conditions, a range of alde-
hydes were used with diferent anilines and triethyl phos-
phite in order to examine the three-component reaction.
Several representative models are summarized in Table 3.
Variety of functional groups present in the aryl aldehydes
such as halogen, methoxy, hydroxyl groups were toler-
ated (see Table 3). It was found that most of the reac-
tions proceeded smoothly to achieve the derivatives of
α-aminophosphonates in good yields (74–90%). Reaction
with dialkyl phosphiste was also performed using dimethyl
phosphite (DMP) as the P-component. The results shown
that the reaction was slower, the yield is very low even
after 1 day, and the condensation was not complete.
Fig. 7 Langmuir surface area plot for BaFe12O19/Al2O3
A conceivable mechanism for the synthesis of
α-aminophosphonates is suggested in Scheme 1. According
to the mechanism, the catalyst activated the carbonyl group
enabling the generation of the imine which is attacked by the
triethyl phosphite to give the α-aminophosphonates. Lewis
acid catalyst is envisioned to activate the imine to nucleo-
philic attack. [32–36].
To survey the recyclability of the catalysts BaFe12O19/Al2O3
magnetic nanocomposites was removed from the mixture of
reaction by external magnet, washed plenty with ethanol, ethyl
1 3

T. Piri et al.
Table 1 Optimization of catalyst loading and solvent for the synthesis of α-aminophosphonates
O
P
NH2
CHO
OEt
EtO
OEt
EtO
Catalyst (35mg)
Solvent free, r. t.
P
N
H
+
+
OEt
Cl
Cl
Entry
Temperature(°C)
Solvent
Catalyst(mg)
Time(h)
Yield (%)
1
2
3
4
5
6
7
8
80
80
80
80
r.t
60
100
r.t
Ethanol
Water
Acetonitrile
10
10
10
10
10
10
10
15
25
35
50
1
1
1
1
1
1
1
1
1
1
1
51
Nil
43
57
65
60
55
73
79
90
92
–
–
–
–
–
–
–
–
9
10
11
r.t
r.t
r.t
Reaction conditions: 4-chlorobenzaldehyde (1 mmol), triethyl phosphite (1.2 mmol), aniline, catalyst (35 mg), room temperature
Table 2 Screening of catalyst conditions in synthesis of
It has been proved to be highly active catalyst towards the
synthesis of α-aminophosphonates via one-pot three-com-
ponent coupling reaction of carbonyl, triethylphosphite, and
amine under solvent-free condition at room temperature. The
prepared catalyst ofers several advantages including high
concentration of catalytically active sites with high surface
area as well as ease of separation, and the recyclability of the
catalyst as the environmental and economic requirements.
Diethyl ((5-bromo 2-hydrox y phenyl)(phenylamino)
methyl)phosphonate, white crystalline solid, m.p.
136–138 °C. 1HNMR (500 MHz, CDCl3, 25 °C):
δ=1.253–1.331 (m, 6H), 4.055–4.152 (m, 4H), 4.951–5.029
(d, 2JPH = 39, 1H), 6.694–6.843 (m, 4H), 7.153–7.276 (m,
3H), 7.361 (s, 1H).13CNMR (125 MHz, CDCl3, 25 °C):
δ=16.22–16.42 (t, J=0.061 Hz), 63.72–63.81 (d, J=0.092),
64.21–64.31 (d, J= 0.098), 112.23 (s), 114.60 (s), 119.65
(s), 123.70 (s), 129.35 (s), 131.17 (s), 132.14 (s), 154.96 (s);
31PNMR(200 MHz, 35); Anal. Calcd. For C17H21BrNO4P
(413.039): C, 49.29; H, 5.11; N, 3.38; Fund C, 49.31; H,
5.08; N, 3.41.
α-aminophosphonates a
Entry
Catalyst
Catalyst(mg)
Time(h)
Yield (%)
1
2
3
4
–
–
24
1
1
Nil
48
61
90
Nano BaFe12O19
Al2O3
BaFe12O19/Al2O3
35
35
35
1
acetate and normal hexane. After drying at room temperature
for several hours (or oven-dried at 50 °C for 10 min), the recy-
cled catalyst was reused in the subsequent experiments. The
results indicate that the catalyst is able to be used successfully
in four sequential cycles without a signifcant change in cata-
lytic activity (Fig. 8).
For comparison purposes, the catalytic performance of the
present catalysts was compared with that of earlier reported
catalysts used in Kabachnik–Fields reaction and exhibited in
Table 4. BaFe12O19/Al2O3 in comparison with other reported
catalyst is exhibited in Table 4, interestingly, shows better cata-
lytic performances in Kabachnik–Fields Reaction.
Diethyl ((4-chlorophenyl)((2-hydroxyphenyl)amino)
methyl)phosphonate, white crystalline solid, m.p.
146–148 °C.1 HNMR (500 MHz, CDCl3): δ = 1.18 (t,
J = 7.5 Hz, 3H, OCH2CH3), 1.33 (t, J = 7.5 Hz, 3H,
OCH2CH3), 3.74–3.79 (q, J=6.25, 1H, OCH2), 3.98–4.02
(q, J = 5, 1H, OCH2), 4.26–4.32 (m, 2H), 4.86–4.91(d,
2JPH =25, 1H, PCH)), 5.69 (s, 1H, NH), 6.45–6.80 (m, 4H,
ArH)), 7.13–7.15 (m, 2H, ArH), 7.36–7.38(m, 2H, ArH),
9.10 (s, 1H, OH). 13CNMR (125 MHz, CDCl3, 25 °C):
4 Conclusion
This study displays the potential for the synthesis and use
of BaFe12O19/Al2O3 mesoporous superparamagnetic nano-
composites as a novel heterogeneous Lewis acid catalyst.
1 3

Magnetic BaFe12O19/Al2O3: An Efcient Heterogeneous Lewis Acid Catalyst for the…
Table 3 One-pot solvent-free synthesis of α-aminophosphonates using magnetic Lewis acid catalyst BaFe12O19/Al2O3 at room temperature
ArCHO
1a-l
NH2
O
O
EtO
EtO
EtO
EtO
BaFe12O19/Al2O3
Solvent Free, r.t.
EtO
OEt
P
P
or
P
or
OEt
N
Ar
N
O
H
R'
H
4a-q
1m
2a-b
3
4r
Entry Carbonyl
Amine
Product
Time (min) Yield (%) m.p
m.p[ref.]
1
2
3
C6H5-CHO
Aniline
Aniline
Aniline
45
50
35
86
85
90
88–89
87–89 [14]
O
OEt
P
OEt
HN
4a
4b
2-Cl-C6H4-CHO
4-Cl-C6H4-CHO
99–101
55–57
98–100 [15]
57–58 [17]
O
OEt
P
OEt
HN
Cl
NH
EtO
EtO
P
O
Cl
4c
4d
4
5
2,4-(Cl)2-C6H3-CHO
2-NO2-C6H4-CHO
Aniline
Aniline
55
55
81
87
63–65
65–67 [18]
Cl
NH
EtO
EtO
P
O
Cl
155–157 154–156 [19]
O
P
OEt
OEt
NO2 NH
4e
1 3

T. Piri et al.
Table 3 (continued)
Entry Carbonyl
Amine
Product
Time (min) Yield (%) m.p
m.p[ref.]
61–62[20]
6
4-Me-C6H4-CHO
Aniline
50
85
60–62
O
P
EtO
OEt
HN
4f
7
8
2-OMe-C6H4-CHO
Aniline
Aniline
40
55
85
90
100–102 99–100 [21]
MeO
O
P
EtO
OEt
HN
4 g
3-NO2-C6H4-CHO
130–131 126–128 [3]
NO2
O
P
OEt
OEt
NH
4 h
9
4-F-C6H4-CHO
Aniline
Aniline
50
45
87
85
84–85
78–79 [14]
F
O
P
OEt
OEt
NH
4i
10
3-OH-C6H4-CHO
93
93[22]
OH
O
P
OEt
OEt
NH
4j
1 3

Magnetic BaFe12O19/Al2O3: An Efcient Heterogeneous Lewis Acid Catalyst for the…
Table 3 (continued)
Entry Carbonyl
Amine
Product
Time (min) Yield (%) m.p
m.p[ref.]
–
a11
5-Br-2-OH-C6H4-CHO Aniline
45
85
136–138
Br
O
P
OEt
OEt
HO
Br
NH
4 k
OEt
12
13
3-Br-C6H4-CHO
4-Cl-C6H4-CHO
Aniline
45
40
85
81
97–99
96–98[23]
O
P
P
OEt
NH
4 l
4-(Br)-Aniline
125–127 124–126[24]
OEt
OEt
O
NH
Cl
Br
4 m
14
C6H5CHO
4-(Br)-Aniline
60
84
123–124 121–123[25]
OEt
OEt
O
P
NH
Br
4o
15
Furfural
Aniline
60
35
83
92
51–52
53–55[3]
O
P
OEt
OEt
O
NH
4p
a16
2-aminophenol
146–148
–
Cl
O
P
OEt
OEt
NH
HO
4q
1 3

T. Piri et al.
Table 3 (continued)
Entry Carbonyl
Amine
Product
Time (min) Yield (%) m.p
m.p[ref.]
104 [26]
a17
Cyclohexanone
Aniline
65
74
108
O
P
OEt
OEt
NH
4r
Reaction conditions: carbonyl (1 mmol), triethyl phosphite (1.2 mmol), amine (1 mmol), BaFe12O19/Al2O3 (35 mg)
aNew compounds
Scheme 1 Plausible mecha-
nism for the synthesis of
α-aminophosphonates
O
R
R1
NH2
R2
R2
O
-H2O
R1
R2
R1
N
R
R NH
R1
P
P
OH
OEt
OEt
OEt
EtO
EtO
H2O
R2
O
P
OEt
EtO
100
90
89
86
83
80
60
40
20
0
Table 4 Catalytic Performance of BaFe12O19/Al2O3 in comparison
with other reported catalyst
Entry Catalyst
Temp (°C) Time (min) Yield Ref.
1
2
3
4
Al2O3
(10 mol%)
110
90
130
61
81
[27]
[28]
TiO2–SiO2
90
1
(15 mol%)
2
3
4
Al2O3/
r.t.
240–480
120
59-80 [27]
86 [29]
Run #
NH4HCO2
γ-Fe2O3@SiO2- 80
Fig. 8 Recyclability of catalyst
PA
5
6
7
Fe/SWCNTs
CeCl3.7H2O
50
r.t.
r.t.
180
540
35–65
80-95 [30]
90 [31]
74–92 This work
δ=16.07 (d, 3JPC =6.13), 16.32(d, 3JPC =5.82), 54.79, 56.02,
2
63.69 (d, JPC = 7.5 Hz, OCH2), 64.38 (d,2JPC = 10 Hz,
BaFe12O19/
Al2O3
OCH2), 111.97, 114.41, 118.54, 119.97, 128.67, 129.35
1 3

Magnetic BaFe12O19/Al2O3: An Efcient Heterogeneous Lewis Acid Catalyst for the…
2
16. Peymanfar R, Rahmanisaghieh M (2018) Mater Res Express
(d, JPC = 6.25 Hz, CHCAr), 134.37, 134.65, 145.10
(d,3JPC =11.25 Hz, NHCAr); 31PNMR (200 MHz, CDCl3):
δ=35; Anal. Calcd. For C17H21ClNO4P (369.08): C, 55.22;
H, 5.72; N, 3.79. Found: C, 55.14; H, 5.63; N, 3.67.
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Acknowledgements The authors gratefully acknowledge the support
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jurisdictional claims in published maps and institutional afliations.
Afliations
Tayebeh Piri1 · Reza Peymanfar1 · Shahrzad Javanshir1 · Sara Amirnejat1
1
* Shahrzad Javanshir
Heterocyclic Chemistry Research Laboratory, Department
shjavan@iust.ac.ir
of Chemistry, Iran University of Science and Technology,
Tehran 16846-13114, Iran
1 3