Catalytic application of sulfamic acid-functionalized magnetic Fe3O4nanoparticles (SA-MNPs) for protection of aromatic carbonyl compounds and alcohols: Experimental and theoretical studies

Article abstract of DOI:10.1039/d0ra09087e

Protection techniques of functional groups within the structure of organic compounds are important synthetic methods against unwanted attacks from various reagents during synthetic sequences. Acetal and thioacetal groups are well known as protective funct

Full text of DOI:10.1039/d0ra09087e

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Catalytic application of sulfamic acid-
functionalized magnetic Fe3O4 nanoparticles (SA-
MNPs) for protection of aromatic carbonyl
compounds and alcohols: experimental and
theoretical studies†
Cite this: RSC Adv., 2020, 10, 44946
ab
a
b
*
Avat Arman Taherpour
*
Sepideh Khaef,
and Meysam Yarie
Mohammad Ali Zolfigol,
a
Protection techniques of functional groups within the structure of organic compounds are important
synthetic methods against unwanted attacks from various reagents during synthetic sequences. Acetal
and thioacetal groups are well known as protective functional groups in organic reactions. In this study,
acetalization of carbonyl compounds with diols and dithiols and methoxymethylation of alcohols with
formaldehyde dimethyl acetal (FDMA) have been carried out using sulfamic acid-functionalized magnetic
Fe3O4 nanoparticles (SA-MNPs) as a heterogeneous solid acid catalyst. Products were characterized by
FT-IR and NMR spectroscopies. The structural and electronic properties of some products were
computed by quantum mechanical (QM) methods. Depending on the stereochemistry and electronic
properties that were obtained by computational results, we have suggested that hyperconjugation plays
a key role in the structural properties of 2-phenyl-1,3-dioxolane derivatives, and also the electron
transfer between p-electrons of the aromatic ring with the 3d orbital of S-atoms influences the 2-
phenyl-1,3-dithiane derivatives' structure.
Received 24th October 2020
Accepted 4th December 2020
DOI: 10.1039/d0ra09087e
rsc.li/rsc-advances
instead of aldehydes was called ketalization in this kind of
reaction.5–7
Introduction
Due to the great importance of these fundamental reactions,
various catalysts have been designed and used for carbonyl
protection. Fig. 1, portrayed varied catalytic systems including
photons,8 electrochemical,9 bases10 and acids, like solid acids,11
organocatalysts,12 polymers,13 nanomagnetic catalyst,14 metal–
organic framework,15 graphene oxide,16 transition metal salts17
and ion liquids18 in this eld.
Protection strategies of carbonyl compounds are well known as
one of the most important branches of organic chemistry in the
eld of multistep total synthesis of enantiomerically pure
natural and non-natural compounds.1 For example, protection
strategies were applied in the synthetic processes of (ꢀ)-dihy-
droaatoxin D2,2 (ꢀ)- & (+)-microminutinin,2 optically active
vitamin E3 and bryostatin 1 (ref. 4) (Scheme 1).
On the other hand, one of the most important purposes in
new science is the application of easily separable catalysts
which follows the green chemistry principles. Nano magnetic
catalysts have been recently known as useful catalysts due to
easy separation, reusability and fully dispersion in reaction
media.19 The surface functionalization of magnetic nano-
particles is a well-designed method to convert homogeneous
catalysts to heterogeneous ones.20 Acidic-functionalized
magnetic nanoparticles are known as efficient acidic catalysts
applied for a variety of organic reactions which need acidic
conditions.21
Several methods have been reported for protection of alco-
hols with formaldehyde dimethoxy acetal (FDMA).22 The trace
and impact of anomeric effect can be observed in methox-
ymethylation of alcohols. For example, the catalytic activity of
silica sulfuric acid (SSA) was investigated for the chemoselective
The known protecting groups of carbonyl compounds are
acetals, ketals, dithianes and acylals. One of the most useful
protective groups in synthetic reactions are acetals.5 Due to the
relatively stable toward a variety of reagents, these intermedi-
ates are noticeable and also, cyclic acetals are generally much
easier to construct than open-chain acetals.6 Acetalization per-
formed by reaction between an aldehyde with two equivalents
(or an excess amount) of an alcohol, or a diol and elimination of
water in acidic conditions. Likewise, using ketone derivatives
aDepartment of Organic Chemistry, Faculty of Chemistry, Bu-Ali Sina University,
Hamedan, Iran. E-mail: zol@basu.ac.ir; mzolgol@yahoo.com
bDepartment of Organic Chemistry, Faculty of Chemistry, Razi University,
Kermanshah, Iran. E-mail: avat.taherpour@gmail.com
† Electronic supplementary information (ESI) available. See DOI:
10.1039/d0ra09087e
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Scheme 1 Samples of compounds where protection strategies take place in their synthesis.
Fig. 1 Varied catalytic systems applied for protection of carbonyls.8–18
methoxymethylation of benzylic alcohols. It is suggested that empty antibonding orbital, has made a stabilized molecule by
the anomeric effect leads to activation of FDMA for protection of hyperconjugation concept (Fig. 3).24a
alcohols. In this case, the anomeric effect (nO / s*CꢀO) leads to
Classical anomeric effect is one of the well-known stereo-
weakening of C–O bond and facilitates the protection process electronic effects which is dened as the tendency of electro-
(Scheme 2).22a It is worthy to mention that due to the resonance negative heteroatomic substituents positioned next to
phenomenon, the phenolic hydroxy group is a weaker nucleo- a heteroatom within a cyclohexane ring to prefer an axial rather
phile than its alcoholic (benzylic hydroxy group) ones.
than an equatorial position.24a,25 In the anomeric theory it is
Commonly, preparation of methoxymethyl ethers from suggested that the existence of a stabilizing interaction between
hydroxylic compounds has been carried out by formaldehyde the lone pair of ring heteroatom and the anti-periplanar anti-
dimethyl acetal (FDMA) used as a stable, low-cost, and acces- bonding s* orbital of the axial substituent bond at the
sible compound.23
anomeric carbon (nX / s*CꢀY) leads to weakening of C–Y bond
Hyperconjugation theorem enriches the concept of the and increase negative charge on Y. Also, predicted dipole–
molecular stabilizing effect which is occurred with interactions dipole repulsion between the two electronegative atoms that
between electronic orbitals.24 In general, hyperconjugation was one part of the ring and the other exocyclic, causes the prefer-
well dened as the interaction between electronic orbitals, for ence for the smallest dipole moment with the axial conforma-
example by the use of conjugation between 2p and s-bond tion (Scheme 3).25a Many experimental and computational
molecular orbital. Few important examples of hyper- evidence proved the stereoelectronic nature of the anomeric
conjugation's patterns were shown in Fig. 2.24a
effect.25
Due to the interaction between two-electrons of the lower
energy orbital (s-bond or a lone pair) with the higher energy
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Scheme 2 Chemoselective methoxymethylation of benzylic alcohols and its hydrolysis process.
Fig. 2 Examples of delocalizing interactions of hyperconjugation.24a
Computational methods and modeling
details
In this study which is about the synthesis of acetals and thio-
acetals, some of the appropriate quantum mechanical (QM)
methods were applied, in order to determine the most stable
structure of the products. The DFT-B3LYP method was per-
formed by Spartan'10 package.26 In this molecular modeling,
the structures were minimized and optimized by B3LYP levels
with the 6-31G* basis sets. The structural and electronic prop-
erties of some products (2-phenyl-1,3-dioxolane and 2-phenyl-
Fig. 3 Energy lowering due to hyperconjugative interaction between
sC–H and s*CꢀX orbitals.24a
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Scheme 3 Factors make the anomeric effect.25a
Scheme 4 Stable and unstable forms of 2-phenyl-1,3-dioxolane derivatives and phenyl cyclopentane.
1,3-dithiane derivatives) like energy level differences between and vibrational frequencies of H1 and H8 were calculated as
the stable form to unstable form, bond length of C7–H8, C7–H1 well. The results are demonstrated in the schemes and the
(see Schemes 4 and 5 respectively) and C1–C7, dihedral angle of related tables (Schemes 4 and 5, Tables 5 and 6).
H1 and H8 with aromatic ring, Mullikan charges of H1 & H8,
Scheme 5 Stable and unstable forms of 2-phenyl-1,3-dithiane derivatives and phenyl cyclohexane.
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Table 1 The reaction of 4-nitrobenzaldehyde (1 mmol) with ethylene Table 2 The reaction of benzyl alcohol (1 mmol) with formaldehyde
glycol (2 mmol) in the presence of various catalysts at room temper- dimethyl acetal (FDMA) (10 mmol) in the presence of catalysts at room
ature (25 ꢁC) under solvent-free conditions for 1 hour
temperature (25 ꢁC) under solvent-free conditions for 2 hours
Amounts of
Entry
Catalyst
cat. (g)
Yield (%)
Amount of
cat. (g)
Yield
(%)
1
2
3
4
5
6
7
8
Al(HSO4)3
Zn(HSO4)2
Fe(HSO4)3
Ca(HSO4)2
Trityl chloride
Trityl bromide
Silica sulfuric acid
Sulfamic acid
Hydroxylamine-O-sulfonic acid
SA-MNPs
0.2
0.2
0.2
0.2
0.1
0.1
0.2
0.1
0.1
0.025
0.05
0.1
0.2
85
81
85
83
78
75
90
81
73
74
82
97
85
Entry
Catalyst
1
2
3
4
5
6
7
8
Al(HSO4)3
Zn(HSO4)2
Fe(HSO4)3
Ca(HSO4)2
0.2
0.2
0.2
0.2
81
83
82
78
10
76
76
87
74
57
81
(NH4)2SO4
0.2
Trityl chloride
Trityl bromide
Silica sulfuric acid
Sulfamic acid
Hydroxylamine-O-sulfonic acid
Pyridinium hydrogen
sulphateb
0.1a
0.12a
0.2
9
10
11
12
13
SA-MNPs
SA-MNPs
SA-MNPs
9
10
11
0.1
0.1
0.12a
12
1,10-Phenanthroline-based
molten saltc
—
SA-MNPs
SA-MNPs
0.16
62
13
14
15
16
17
0.0
0
phenanthroline-based molten salt as a bifunctional sulfonic
acid, which was synthesized by Babaee and co-workers has
shown a yield about 62% (entry 12).28 The reaction failed in the
absence of a catalyst (entry 13). The SA-MNPs catalyst was found
to be the most effective solid acid for cyclic acetalization and
thioacetalization. In order to study the best amount of SA-MNPs
catalyst, it was examined 0.025, 0.05, 0.1 and 0.2 g of the catalyst
(entries 14–17). Whenever the amount of catalyst was increased,
the yield of desired product increased as well, but the excess
amount of the catalyst caused a decrease in the reaction yield
(entry 17). So, the amount of the catalyst should be optimized.
The results demonstrated that 0.1 g of SA-MNPs catalyst with
the yield of 95% was the optimum amount of catalyst for ace-
talization reaction (Table 1, entry 16).
Various organic and inorganic solid acid catalysts were
tested for methoxymethylation in the reaction of benzyl alcohol
(0.103 mL, 1 mmol) with the excess of formaldehyde dimethyl
acetal (FDMA) (0.88 mL, 10 mmol) in order to have a compar-
ison with the efficiency of SA-MNPs catalyst (Table 2). Hydrogen
sulfate as solid acidic salts such as: Al(HSO4)3, Zn(HSO4)2,
Fe(HSO4)3 and Ca(HSO4)2 were tested for methoxymethylation
reaction and their yields are shown in Table 2 (entries 1–4). The
organic solid Lewis acids, trityl chloride and trityl bromide were
also utilized for methoxymethylation reaction and the desired
product was obtained in 78% and 75% yields, respectively
(entries 5 and 6). The reaction was done in the presence of silica
sulfuric acid and had the yield of 90% (entry 7). When the
reaction was accomplished with sulfamic acid, the yield was
observed 81% (entry 8). Hydroxylamine-O-sulfonic acid was
another organic solid acid, which was used for methox-
ymethylation and the desired product was obtained in 73%
0.025
0.05
0.1
52
71
95
82
SA-MNPs
SA-MNPs
0.2
a
c
40 mol%. b Ref. 27. Ref. 28.
Results and discussion
To compare the efficiency of SA-MNPs catalyst for acetalization
reaction, different organic and inorganic solid acid catalysts
were examined upon the reaction of 4-nitrobenzaldehyde
(0.151 g, 1 mmol) with ethylene glycol (0.11 mL, 2 mmol)
(Table 1). Acidic solid salts Al(HSO4)3, Zn(HSO4)2, Fe(HSO4)3,
Ca(HSO4)2 were tested in cyclic acetalization reaction and they
had the yield about 80% but with (NH4)2SO4, the yield of the
reaction strongly decreased (entries 1–5 in Table 1). Trityl (tri-
phenylmethyl) chloride and trityl bromide were also examined
as solid acids for described reaction and the desired product
was obtained in 76% yield (entries 6 and 7). The reaction was
performed in the presence of silica sulfuric acid and the yield of
the reaction improved (entry 8), while the reaction was carried
out with sulfamic acid the crude yield was 74% (entry 9).
Hydroxylamine-O-sulfonic acid with acidic characteristic which
is another inorganic compound, was also tested for acetaliza-
tion of nitrobenzaldehyde and the yield of desired product
decreased up to 57% (entry 10). Pyridinium hydrogen sulphate
was synthesized using the reported procedure by Moosavi-Zare
and co-workers.27 It was tested for this reaction and the desired
product was obtained in 81% yield (entry 11). Employing 1,10-
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Table 3 Conversion of carbonyl compounds to acetals and thioacetals using SA-MNPs at room temperature, under solvent-free conditionsa
a
b
Carbonyl compound (1 mmol), diol or dithiol (3 mmol) and SA-MNPs (0.1 g). Under reux in acetonitrile.
yield (entry 9). To nd the optimum amount of catalyst for process with pentaerythritol and 4-nitrobenzaldehyde and 3-
preparation of MOM-ethers, 0.025, 0.05, 0.1 g of SA-MNP cata- nitrobenzaldehyde and 1-phenyl-1,2-ethanediol with 4-nitro-
lyst were applied (entries 10–13). Whenever the amount of benzaldehyde were also performed under reux conditions in
catalyst decreased, the yield of the desired product decreased as acetonitrile for 6 hours with good yields (Table 3, 1e–1g). The
well, but the excess amount of catalyst had negative effect (entry thioacetalization reaction with 1,3-propanedithiol with benzal-
13). The results demonstrated that 0.1 g of SA-MNPs catalyst dehyde derivatives and 2-naphthaldehyde were achieved (Table
with the yield of 97% was the optimum amount for methox- 3, 2a–2h). Moreover, the products of 4-nitroacetophenone with
ymethylation reaction (Table 2, entry 12).
ethylene glycol and 1,3-propanedithiol as examples of ketali-
Aer the amount of SA-MNPs catalyst was optimized to zation were occurred aer 2 hours (Table 3, 1d, 2i). As Table 3
protect carbonyl compounds at room temperature under indicates, the aromatic aldehyde derivatives possessing
solvent-free conditions (Table 1, entry 16), the efficiency of SA- electron-withdrawing and halogen substituents afforded the
MNPs was explored for the acetalization and thioacetalization desired products with the short reaction times in excellent
reactions of different aromatic carbonyl derivatives with various yields. Due to the characteristics of electron-withdrawing
diols and/or dithiol. The results are displayed in Table 3. The groups, the carbon of aldehydes is more positive and more
acetalization reaction with ethylene glycol via benzaldehyde susceptible of diol's attacking (Table 3, 1a–1c, 2a–2c), whereas
derivatives were carried out (Table 3, 1a–1c). The acetalization
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Table 4 Methoxymethylation of alcohols with SA-MNPs under solvent-free conditions at room temperaturea
a
Benzyl alcohol (1 mmol), formaldehyde dimethyl acetal (FDMA) (10 mmol, 0.88 mL) and SA-NMPs (0.1 g). b n-Butanol is an example of alcohol has
been participated in methoxymethylation reaction.
Table 5 Selected structural data of stable forms of 2-phenyl-1,3-dioxolane derivatives
Energy difference
2-Phenyl-1,3-
dioxolane
derivatives (R¼)
between stable form
Dihedral angle of
to unstable forma
H1 with aromatic ring [C3]
Bond length
of C7–H1 (A)
Bond length
of C4–C7 (A)
Mullikan charge
of H1 (esu)
Frequency of
(kcal molꢀ1
)
in stable form (qꢁ)
H1 (cmꢀ1
)
ꢀ
ꢀ
(1a) NO2
(1c) CF3
Cl
OH
3.80
4.09
4.01
3.99
4.15
4.03
1.21
81.50
81.86
80.04
78.86
78.03
77.58
0.93
1.099
1.098
1.098
1.098
1.098
1.098
1.099
1.526
1.525
1.524
1.522
1.524
1.523
1.515
0.161
0.158
0.156
0.150
0.153
0.151
0.125
3043
3049
3050
3052
3051
3052
3024
H
CH3
Phenyl cyclopentaneb
a
In unstable form of 2-phenyl-1,3-dioxolane derivatives, dihedral angle of H8 with aromatic ring force to be almost q ¼ 0ꢁ. b Red numbers related to
phenylcyclopentane derivative model.
the aldehyde with the electron-donating groups needed more withdrawing substituents and phenols as weak nucleophiles
time to complete the reaction (Table 3, 2d–2h).
had no yield in methoxymethylation reaction (Table 4, 3i–3k).
Aer the optimization of the amount of SA-MNPs for
Cyclic acetals and thioacetals are suitable candidates for
methoxymethylation reaction at room temperature (25 ꢁC) development of stereoelectronic effects.29 In continuation our
under solvent-free conditions (Table 2, entry 12), the efficiency previous computational investigations of stereoelectronic
of this catalyst was studied by the preparation of methox- effects within the structures of suitable molecules,30 herein we
ymethyl ethers (MOM-ethers). The results are displayed in Table wish to study the role of hyperconjugation and anomeric effect
4. Benzyl alcohol derivatives with electron-donating and at the structures of desired products via computational calcu-
halogen substituents, afforded the desired products with short lations. The obtained theoretical results of the synthesized
reaction times in good to excellent yields (Table 4, 3a–3g). Also, products (based on Tables 5 and 6) show different structural,
alkyl alcohol such as n-butanol gave the corresponding product stereochemistry and electronic properties of 2-phenyl-1,3-
in good yield (Table 4, 3h). But, benzyl alcohol with electron dioxolane derivatives in comparison with the 2-phenyl-1,3-
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Table 6 Selected structural data of stable forms of 2-phenyl-1,3-dithiane derivatives
2-Phenyl-1,3-dithiane Energy difference
Dihedral angle of H8
derivatives
(R¼)
between stable form to
with aromatic ring [C3] Bond length
Bond length Mullikan charge Frequency of
unstable forma (kcal molꢀ1
)
in stable form (qꢁ)
of C7–H8 (A) of C4–C7 (A) of H8 (esu)
H8 (cmꢀ1
)
ꢀ
ꢀ
(2a) NO2
(2c) CF3
(2d) Cl
(2e) OH
(2g) H
3.38
3.45
3.42
3.65
3.62
3.64
3.02
ꢀ0.37
0.55
0.00
0.00
0.00
0.14
ꢀ7.70
1.094
1.094
1.094
1.094
1.094
1.094
1.101
1.510
1.510
1.510
1.509
1.511
1.510
1.520
0.193
0.191
0.190
0.187
0.188
0.188
0.119
3075
3075
3076
3076
3079
3075
3006
(2f) CH3
Phenyl cyclohexaneb
a
In unstable form of 2-phenyl-1,3-dithiane derivatives, dihedral angle of H8 with aromatic ring force to be almost q ¼ 90ꢁ. b Red numbers related to
phenyl cyclohexane derivative model.
Previous computational studies on 1,3-dioxolane's proper-
ties show that it is puckered molecule because of lone pairs,
thus the geometries of 1,3-dioxolane's conformers do not seem
to be appropriate for anomeric (n–s*) interactions.31
The authors believe that the hyperconjugation effect
between C–H1 and aromatic ring (2p1 of CAr) in diols has made
this stable conformational structure and stereo electronical
properties. Also, electron transfer between p-electrons of
aromatic ring with 3d orbital space of S-atoms in the 2-phenyl-
1,3-dithiane derivatives and electrostatic repulsion have made
this stereochemistry. The predicted model of hyperconjugation
between C–H and aromatic ring in one of the diol's derivatives
Scheme 6 The predicted model of hyperconjugation between C–H
and aromatic ring in 4NO2-2-phenyl-1,3-dioxolane.
and the predicted model of electron transfer between p-elec-
trons of aromatic ring and 3d orbital space of S-atoms in one of
the dithiol's derivatives have been modeled in Schemes 6 and 7
dithiane derivatives, phenylcyclohexane and phenyl-
cyclopentane molecules. In 2-phenyl-1,3-dioxolane derivatives
H1 is nearly orthogonal toward aromatic ring (dihedral angle of
H1 with aromatic ring [C3] in stable forms of derivatives is
almost q ¼ 80ꢁ), whereas dihedral angle of H1 with aromatic
ring [C3] in phenyl cyclopentane is almost q ¼ 0ꢁ (Scheme 4 and
Table 5). It shows that maybe oxygen atoms have inuence on
stereo electronical properties of the structures.
respectively.
Spectral analysis to prove the predicted computational model
In addition to computational study, in 13C-NMR spectrum of
4CF3-2-phenyl-1,3-dioxolane, the C–H to C–H2 ratio is approxi-
mately 1 : 3. But, in 13C-NMR spectrum of 2-(naphthalen-2-yl)-
1,3-dithiane which is guessed to be inuenced by NOE effect
with CH aromatic ring, the C–H to C–H2 ratio is approximately
Scheme 7 The predicted model of electron transfer between p-electrons of aromatic ring and 3d orbital space of S-atoms in 4NO2-2-phenyl-
1,3-dithiane.
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Fig. 4 Comparing NOE effect in 13C-NMR spectrum of products. ((a) Part of 13C-NMR spectrum of 2-(naphthalen-2-yl)-1,3-dithiane (1c). (b) Part
of 13C-NMR spectrum of 4CF3-2-phenyl-1,3-dioxolane (2h)).
Conclusion
Sulfamic acid-functionalized magnetic Fe3O4 nanoparticles (SA-
MNPs) was applied in protection reactions of some carbonyl
compounds with diols and dithiols and the reaction of alcohols
with FDMA with good to excellent yields. Moreover, structural
and electronic properties of some of the products were
computed by DFT-B3LYP/6-31G* method. The experimental
and theoretical investigation demonstrated that electronic
effects like hyperconjugation and electron transfer, has made 2-
phenyl-1,3-dioxolane and 2-phenyl-1,3-dithiane conformers
become stabilized respectively. Also analysis of 13C-NMR spec-
Fig. 5 Reusability of the SA-MNPs catalyst for eight reaction runs.
trum of 2-(naphthalen-2-yl)-1,3-dithiane which is guessed to be
inuenced by NOE effect demonstrated that the predicted
model which claims that C–H8 is almost parallel with C–H
aromatic ring in 2-phenyl-1,3-dithiane derivatives, could be
abundant conformers. The results show that the reusability of
the SA-MNPs catalyst could be used for eight similar cycles of
1 : 2. Therefore, the predicted model which claims that C–H of
dithiane is parallel with C–H aromatic ring, could be abundant
conformer of 2-(naphthalen-2-yl)-1,3-dithiane molecule (Fig. 4).
the reaction.
The reusability of SA-MNPs catalyst was investigated for
acetalization reaction of 4-nitrobenzaldehyde with ethylene
glycol for eight runs under the optimized reaction conditions.
Experimental
The data are displayed in Fig. 5. The catalyst was separated from General
the reaction mixture by using an external magnet, repeatedly
All chemicals and solvents used in this article were purchased
washed with di-isopropyl ether, dried and reused in the next
from Merck and Aldrich. The progress of the reaction and the
run. It shows that the performance of the catalyst doesn't drop
purity of the products were determined using TLC performed
aer eight sequential runs.
with SIL G/UV 254 silica gel plates. All experiments were carried
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Scheme 8 Synthesis of SA-MNPs according to the Kassaee and co-workers' reported method.21f
out under an atmosphere of air. 13C NMR spectra were reported decanted. The organic solvent was evaporated at room
in ppm relative to residual DMSO (39.52 ppm) that were ob- atmosphere.
1
tained with H-decoupling and described in terms of chemical
1
shi (d in ppm). Data for H-NMR are described as following:
chemical shi (d in ppm), multiplicity (s, singlet; d, doublet; t,
Conflicts of interest
triplet; q, quartet; quin, quintet; sx, sextet; m, multiplet; app,
apparent; br, broad signal), coupling constant (Hz), integration.
There are no conicts to declare.
NMR data were given in University of Isfahan (Bruker-400 MHz).
Acknowledgements
General procedure for preparation of sulfamic acid-
functionalized magnetic Fe3O4 nanoparticles (SA-MNPs)
We thank Bu-Ali Sina University and Iran National Science
Foundation (INSF) (grant number: 98001912) for nancial
support to our research group.
The SA-MNPs catalyst was synthesized by Kassaee and co-
workers in 2011 and was produced according to their protocol
and it is worthy to mention that, since the catalyst structure is
similar to the previously reported catalyst, therefore, we did not
characterize it again (Scheme 8).21f
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