N-Propylsulfamic acid supported onto magnetic Fe3O4 nanoparticles (MNPs-PSA) as a green and reusable heterogeneous nanocatalyst for the chemoselective preparation and deprotection of acylals

Article abstract of DOI:10.1007/s11164-017-3014-4

Abstract: N-propylsulfamic acid supported onto magnetic Fe₃O₄ nanoparticles (MNPs-PSA) was simply synthesized and used as a highly efficient, environmentally friendly, and chemoselective catalyst for the synthesis of 1,1-diacetates (acylals) from the one-pot condensation reaction of various aromatic aldehydes with acetic anhydride, in high yield of products (86–96%) and short reaction time (20–60?min) under solvent-free conditions at room temperature. In addition to these results, we further studied the possibility of deprotection of the resulting acylals into benzaldehyde derivatives in this catalytic system by the addition of water. More importantly, noteworthy advantages of this study are non-use of toxic organic solvents and catalysts, simple work-up procedure, short reaction time, high yield of products, and recovery and reusability of MNPs-PSA by an external magnet. Graphical Abstract: A simple and highly efficient procedure for the protection of various aldehydes with acetic anhydride in the presence of N-propylsulfamic acid supported onto magnetic Fe₃O₄ nanoparticles (MNPs-PSA) is reported. We further studied the possibility of deprotection of the resulting acylals into benzaldehyde derivatives in this catalytic system by the addition of water as a green solvent. The catalyst was reused several times without loss of its catalytic activity.

Full text of DOI:10.1007/s11164-017-3014-4

Res Chem Intermed
DOI 10.1007/s11164-017-3014-4
N-Propylsulfamic acid supported onto magnetic Fe O
3
4
nanoparticles (MNPs-PSA) as a green and reusable
heterogeneous nanocatalyst for the chemoselective
preparation and deprotection of acylals
1
1
Sami Sajjadifar
•
Parastoo Nasri
Received: 18 May 2017 / Accepted: 19 June 2017
Ó Springer Science+Business Media B.V. 2017
Abstract N-propylsulfamic acid supported onto magnetic Fe O nanoparticles (MNPs-
3
4
PSA) was simply synthesized and used as a highly efficient, environmentally friendly,
and chemoselective catalyst for the synthesis of 1,1-diacetates (acylals) from the one-pot
condensation reaction of various aromatic aldehydes with acetic anhydride, in high yield
of products (86–96%) and short reaction time (20–60 min) under solvent-free conditions
at room temperature. In addition to these results, we further studied the possibility of
deprotection of the resulting acylals into benzaldehyde derivatives in this catalytic
system by the addition of water. More importantly, noteworthy advantages of this study
are non-use of toxic organic solvents and catalysts, simple work-up procedure, short
reaction time, high yield of products, and recovery and reusability of MNPs-PSA by an
external magnet.
&
Sami Sajjadifar
sami.sajjadifar@gmail.com; ss_sajjadifar@yahoo.com
1
Department of Chemistry, Payame Noor University, P.O. Box 19395-4697, Tehran, Iran
123

S. Sajjadifar, P. Nasri
Graphical Abstract A simple and highly efficient procedure for the protection of
various aldehydes with acetic anhydride in the presence of N-propylsulfamic acid sup-
ported onto magnetic Fe O nanoparticles (MNPs-PSA) is reported. We further studied
3
4
the possibility of deprotection of the resulting acylals into benzaldehyde derivatives in
this catalytic system by the addition of water as a green solvent. The catalyst was reused
several times without loss of its catalytic activity.
O
R
R= Cl, NO , OH,
H
O
O
2
R
OMe, CN, Br, and
heterocyclic compounds
Me
O
O
Me
8
6-96%
O
O
Me
O
Me
External magnet
No hazardous organic solvent
MNPs-PSA
Using H O for deprotection
2
One-pot procedure
Solvent-free
Keywords NanocatalystÁReusablecatalystÁMagneticnanoparticleÁN-Propylsulfamic
acid Á Acylals Á Solvent-free
Introduction
The selective protection and deprotection of carbonyl groups are one of the most
important and most versatile modern organic reactions. The protection of aldehyde
compounds such as oxathioacetals, dithioacetals, acetals, and acylals are one of the
most important reactions in multi-step syntheses. Among different methods for the
protection of aldehyde, geminal diacetates (acylals) are appropriate candidates for
this aim [1]. Also, geminal diacetate (acylals) from various aldehydes are essential
for the synthesis of other compounds: for instance, as starting materials for Diels–
Alder reactions, as crosslinking reagents for cellulose in cotton, and as useful
intermediates in industries. Moreover, they can be converted to some appropriate
functional groups using appropriate nucleophiles [2–5].
The simple and convenient separation and reusability of the catalysts are the
important and unique factors in the selection of catalytic processes and green
chemistry [6–10]. Application of nanoparticles (NPs), especially iron oxides, have
received special attention in academic research and industry due to their simple and
convenient preparation, their high surface area, low toxicity, abundance, and unique
magnetic properties. In addition, they have characteristics which are useful in
various fields such as magnetic resonance imaging [11], magnetic fluids [12], data
1
23

3 4…
N-Propylsulfamic acid supported onto magnetic Fe O
storage [13], biology and medical applications [14], and environmental remediation
15]. Also, solvent-free reactions and catalysis research are an appropriate direction
[
for the future of organic synthesis, in particular from the point of view of green
chemistry and industry [16–21].
In recent years, several catalysts or reagents such as silica-supported boron
sulfonic acid (SBSA) [22], PEG–SO H [23], silica sulfate [24], titanium-modified
3
MCM-41 [25], LiOTf [26], polymer-supported gadolinium triflate [27], P O /
2
5
Al O [28], In(OTf) [29], solid silica sulfuric acid [30], Fe(NO ) Á9H O [31],
2
3
3
3 3
2
keggin hetero poly acid [32], ZSM-5-SO H [33], sulfuric acid [3-(3-silicapropyl)-
3
TM
2?
[35], Ni @hydroxyapatite-core@shell
sulfanyl]propyl ester [34], selectfluor
c-Fe O nanoparticles [36], 1-methyl-3-(2-(sulfooxy)ethyl)-1H-imidazol-3-ium
2
3
chloride [37], and Fe O @SiO –SO H [38] have been reported for the synthesis
3
4
2
3
of geminal diacetates (acylals) from the reaction between various aldehydes and
acetic anhydride under different reaction conditions. Although some of these
methods are quite useful and satisfactory for the synthesis of geminal diacetates
(
acylals), most of them suffer from disadvantages such as the use of strong acids,
reactions under oxidizing conditions, high toxicity of the reagents, prolonged
reaction time, low yield of products, use of toxic and harmful solvents,
requiringing high temperatures, moisture sensitivity, and the use of unrecyclable
catalysts. Therefore, any effort to find a simple, inexpensive, and green procedure
for the promotion of the acetylation of aldehydes with better yield might be of
high potential and interest. A non-toxic, expensive, and non-recyclable catalyst
(
Lewis and Brønsted acid) is one of most important advantages of this method;
therefore, replacement of these catalysts with magnetic nanoparticles as a reusable
heterogeneous, non-corrosive nature, and eco-friendly catalysts is an area of
current interest. Thus, magnetic nanoparticles can play a significant role in the
development of clean technologies.
Based on our previous research in magnetic nanoparticles and green chemistry,
our group prepared N-propylsulfamic acid supported onto magnetic Fe O
3
4
nanoparticles (MNPs-PSA) (Fig. 1) [39] as a new and heterogeneous magnetic
Brønsted acid catalyst in our laboratory, and reported on the chemoselective
preparation of the gem-diacetates (acylals) from a variety of aldehydes with acetic
anhydride under solvent-free conditions at room temperature, and deprotection of
the corresponding acylals in water using catalytic amounts of MNPs-PSA under
water (Scheme 1).
Fig. 1 N-propylsulfamic acid
supported onto magnetic Fe
nanoparticles (MNPs-PSA)
3 4
O
O
O
Fe O
O Si
N S O H
3
4
H
O
O
123

S. Sajjadifar, P. Nasri
MNPs-PSA (25 mg), solvent free, r.t.
Ar-CHO + AC O
Ar-CH(OAc)2
2
MNPs-PSA (25 mg), H O, r.t.
2
Scheme 1 Synthesis of gem-diacetates and their deprotection using catalyst MNPs-SA
Materials and methods
All chemicals were commercially available and used without further purification.
1
13
The H NMR (400 MHz) and C NMR (100 MHz) were run on a Bruker Avance
DPX-400 FT-NMR spectrometer (d in ppm). Melting points were obtained in open
capillary tubes and were measured on an electrothermal 9200 apparatus. Monitoring
of the reactions and the purity check of the final products were carried out by thin
layer chromatography (TLC) using silica gel-precoated aluminium sheets (60–120
mesh; Merck) and visualization with ultraviolet light at 365 and 254 nm. The
products were characterized by comparing the physical data with those of known
samples or by their spectral data. All yields refer to isolated yields.
Preparation of N-propylsulfamic acid supported onto magnetic Fe O4
3
nanoparticles (MNPs-PSA)
In this research, N-propylsulfamic acid supported onto magnetic Fe O nanopar-
4
3
ticles (MNPs-PSA) was easily prepared via the condensation of MNPs powder with
3-aminopropyl)-trimethoxysilane (APTMS), and then its acidification using
(
chlorosulfuric acid, according to the literature procedure. The mean size and
surface morphology of the MNPs-SA were characterized by transmission electron
microscopy (TEM), scanning electron microscopy (SEM), vibrating-sample mag-
netometry (VSM), X-ray diffraction (XRD) analysis, and Fourier-transform infrared
(
FT-IR) spectroscopy techniques [39, 40] (Scheme 2).
General procedure for the preparation of 1,1-diacetates
To a mixture of a variety of aldehydes (1 mmol) and freshly distilled Ac O
2
(
1.5 mmol) was added MNPs-SA (25 mg), and the whole mixture was stirred in a
round-bottomed flask at room temperature for the appropriate time (Table 3). The
completion of the reaction was monitored by TLC (hexane/ethyl acetate, 5:1). Then,
EtOAc (20 mL) was added to the reaction mixture, and the resulting mixture was
filtered and the extracts concentrated under vacuum. The pure product was isolated
following silica gel column chromatography to afford pure acylals. All the products
1
13
were fully characterized by H NMR, C NMR, IR spectroscopy and melting
points, which were consistent with the literature data.
1
23

3 4…
N-Propylsulfamic acid supported onto magnetic Fe O
OH
HO
HO
HO
OH
OH
MeO
MeO Si
MeO
NH2
FeCl .6H O
3
+
2
NH
4 2
OH, N
Fe
3
O
4
OH
30 min
FeCl .4H O
EtOH
2
2
HO
HO
OH
OH
o
4
0
C, 8h
OH
Si
O
Si
O
O
O
O
O
O
O
O
O
O
O
ClSO
3
H, dry CH
2 2
Cl
Si
O
3
Fe O
O
Si
NH
2
Si
O
Fe O
3
O
Si
3
NSO H
4
4
r.t., 120 oC,
O
O
O
O
O
O
O
O
Si
Si
3 4
Scheme 2 Synthesis of N-propylsulfamic acid supported onto magnetic Fe O nanoparticles (MNPs-
PSA)
General procedure for deprotection of 1,1-diacetates
To a stirred mixture of aldehyde (1 mmol) and acetic anhydride (1.5 mmol), MNPs-
SA (25 mg) was added, and the mixture was stirred at room temperature for the
appropriate time (Table 3). After completion of the protection reaction, water
(
After completion of the cleavage reaction, Et O (20 mL) was added and the reaction
3 mL) was added to the reaction mixture to perform the deprotection reaction.
2
mixture was filtered to separate the catalyst. The solvent was evaporated under
reduced pressure to afford the corresponding aldehydes.
Results and discussion
Recently, Rostami and et al. reported N-propylsulfamic acid supported onto
magnetic Fe O nanoparticles (MNPs-PSA) as a nanocatalyst for the chemoselec-
3
4
tive oxidation of sulfides to sulfoxides in the absence of a solvent at ambient
temperature [34]. Similarly, our group prepared N-propylsulfamic acid supported
onto magnetic Fe O nanoparticles (MNPs-PSA) as a nanocatalyst and its
3
4
applications in another reaction. Here, we wish to report a new, rapid, and eco-
friendly method for the synthesis of 1,1-diacetates (acylals) from the one-pot
condensation reaction of various aromatic aldehydes with acetic anhydride in the
presence of catalytic amounts of N-propylsulfamic acid supported onto magnetic
Fe O nanoparticles (MNPs-PSA) as a new, green and reusable nanocatalyst under
3
4
solvent-free conditions at room temperature.
In the first step, to study the effect of catalyst loading, the reaction between
benzaldehyde (1 mmol) and acetic anhydride (1.5 mmol) in the presence of various
amounts of MNPs-PSA in the absence of a solvent at room temperature was chosen
for the modeling reaction, and the results are summarized in Table 1. In the absence
123

S. Sajjadifar, P. Nasri
Table 1 The effect of catalyst
loading on the synthesis of
phenylmethylene diacetate (3a)
a
Entry
Catalyst loading (mg)
Time (min)
Yield (%)
1
2
3
4
5
6
7
–
24 h
75
Trace
68
5
10
15
20
25
30
50
79
35
88
35
90
20
96
20
92
a
Isolated yield
of the MNPs-PSA, the reaction was slow, boring, and no product was obtained even
after 24 h (Table 1, entry 1). By increasing the amount of the MNPs-PSA,
acceptable reaction times and yields were obtained (Table 1, entries 2–4), but the
acylation of benzaldehyde was incomplete. An excellent yield and short reaction
time was obtained when we used 25 mg of the MNPs-PSA in the same reaction
(Table 2, entry 6). The yield of the compound 3a decreased when 30 mg of the
MNPs-PSA was used (Table 1, entry 7).
In the second step, to study the effect of various solvents, the reaction between
benzaldehyde (1 mmol) and acetic anhydride (1.5 mmol) in the presence of 25 mg
of MNPs-PSA in the various solvents at room temperature was chosen for the
modeling reaction. The results are summarized in Table 2, form which it can be
seen that solvent-free conditions gave the best yield and short reaction time rather
than a solvent.
Hence, under solvent-free conditions at room temperature and 25 mg of MNPs-
PSA, a study to explore the scope of this catalytic system was initiated (Table 3,
entries 1–18). It is noteworthy that the reactions proceeded efficiently in excellent
yields and short reaction times for all varieties of aldehydes (electron-donating and
electron-withdrawing). In this procedure, 1-naphthol gave the corresponding 1,1-
diacetate in a short reaction time and excellent yield (Table 3, entry 9). This
procedure is also efficient for the acetylation of heterocyclic compounds such as
furanaldehyde (Table 3, entry 10) and thiophenealdehyde (Table 3, entry 11).
In the next study, in order to show the chemoselectivity of protection of
aldehydes in the presence of ketones, we investigated the mixture of benzaldehyde
with acetophenone in the presence of MNPs-PSA as a heterogeneous magnetic
Brønsted acid catalyst under solvent-free conditions at room temperature, which
Table 2 The effect of various
solvent on the synthesis of
phenylmethylene diacetate (3a)
a
Entry
Solvent
Time (min)
Yield (%)
1
2
3
4
5
CH COOC
3
2
H
5
120
120
120
90
57
51
40
56
52
CH CN
3
n-Hexane
CH Cl
OC
2
2
C
2
H
5
2
H
5
90
a
Isolated yield
1
23

3 4…
N-Propylsulfamic acid supported onto magnetic Fe O
2
Table 3 Acetylation of various aldehydes using Ac O in the presence of MNPs-PSA at room
temperature
a
b
c
d
Entry Substrate
Products
Time (min) Yield (%) M.p./°C
Found
Reported
1
20
40
95
92
41–43
55–57
44–45 [35]
2
57–58 [35]
3
4
5
6
30
35
25
30
96
90
91
93
97–99
88 –90
81–83
89–91
99–100 [22]
88–89 [28]
80–82 [35]
91–92 [35]
7
25
96
125–127 126–128 [34]
8
9
30
30
91
91
92–94
90–91 [28]
103–105 101–102 [35]
10
11
12
25
20
60
92
92
88
53–54
68–70
92–94
50–52 [35]
65–67 [38]
89–91 [24]
123

S. Sajjadifar, P. Nasri
Table 3 continued
a
b
c
d
Entry Substrate
Products
Time (min) Yield (%) M.p./°C
Found
Reported
1
3
4
40
25
89
89
101–103 102–104 [22]
1
88 –90
91–92 [28]
1
5
6
25
25
86
95
99 –101 100–102 [28]
1
61–62
81–83
63–64 [35]
80–82 [35]
17
20
90
1
1
8
9
25
20
91
93
92–94
92–94
93–94 [28]
90–91 [28]
a
b
c
d
1
13
All the products were characterized by H NMR and C NMR spectroscopy
Reactions were run till the completion as indicated by TLC
Isolated yield
Melting points are uncorrected and compared with those reported in the literature
gave only aldehyde diacetyl. In this comparison, phenylmethylene diacetate was
obtained in a short reaction time and excellent yield (Scheme 3).
The recyclability of the MNPs-PSA is a valuable advantage in green chemistry
and catalysis research, and is also very important from commercial and economical
points of view. In this respect, the recovery and reusability of the MNPs-PSA was
investigated in the synthesis of phenylmethylene diacetate via the reaction between
benzaldehyde (1 mmol) and acetic anhydride (1.5 mmol) with 25 mg of MNPs-PSA
under solvent-free conditions at room temperature (Fig. 2; Table 4). After
completion of the reaction, the MNPs-PSA as a catalyst was filtered by an external
magnet field (Fig. 3), and then washed with ethyl acetate and tested for its activity
1
23

3 4…
N-Propylsulfamic acid supported onto magnetic Fe O
O
O
O
S
O
OAc
OAc
Fe O
O
Si
N
O H
(Cat.)
3
4
96%
0%
H
H
H
O
AC O, solvent free, r.t.
O
2
O
CH3
CH
3
Scheme 3 Chemoslective acetylation of aldehydes in the presence of ketones
Fig. 2 Catalyst reusability
Yield (%)
Time (min)
1
00
90
80
70
60
50
40
30
20
10
0
1
2
3
4
5
6
Yield (%)
95
94
93
93
92
90
Time (min)
20
22
25
28
30
35
Table 4 Calculator of turnover frequency (TOF) and turnover number (TON) for the recyclability of the
MNPs-PSA
Run 1
Run 2
Run 3
Run 4
Run 5
Run 6
a
TON
105.5
5.27
104.4
4.74
103.3
4.22
103.3
3.69
102.2
3.40
100
b
TOF
2.85
a
Turnover number
b
Turnover frequency
in subsequent runs. This process was repeated for 6 cycles, and phenylmethylene
diacetate was obtained in excellent yields after 15 min, without significant loss of its
catalytic activity.
On the other hand, the acidic content of MNPs-PSA was characterized by the
?
determination of its H of the catalyst, through titration with NaOH (0.01 mol/L).
For this purpose, MNPs-PSA (25 mg) was titrated by 0.9 ml of NaOH (0.01 mol/L)
and then the mol % of catalyst was calculated. Turnover frequency (TOF) and
123

S. Sajjadifar, P. Nasri
Fig. 3 Magnetic separation of catalyst by external magnet
turnover number (TON) values for MNPs-PSA were calculated for the recyclability
of the MNPs-PSA in each of the 6 runs. The TOF and TON values are summarized
in Table 4.
In another study, we studied the application of MNPs-PSA for the deprotection of
,1-diacetoxy-1-phenyl methane (Table 3, entry 1) to their corresponding ben-
1
zaldehyde by the addition of water at room temperature. In this method,
benzaldehyde was obtained from the related 1,1-diacetoxy-1-phenyl methane under
mild reaction conditions in a short reaction time and excellent yield (Scheme 4).
As can be seen in Scheme 5, a plausible mechanism for the synthesis of geminal
diacetates (acylals) promoted by N-propylsulfamic acid supported onto magnetic
Fe O nanoparticles (MNPs-PSA) as a Brønsted acidic ionic liquid catalyst under
3
4
solvent-free conditions at room temperature can be selected as the most probable
one.
Comparing the catalytic potentiality of N-propylsulfamic acid supported onto
magnetic Fe O nanoparticles (MNPs-PSA) in the synthesis of 1,1-diacetoxy-1-
3
4
phenyl methane from benzaldehyde with acetic anhydride in the presence of various
catalysts with respect to the amounts of catalyst, reaction time, and the yield of the
products is presented in Table 5. As can be seen, in some methods, toxic solvents
O
O
S
O
O
Fe O
O Si
N
H
O H
(Cat.)
3
4
OAc
OAc
O
H
H
H O, r.t.
2
Scheme 4 Cleavage of acylal to benzaldehyde in water catalyzed by MNPs-PSA
1
23

3 4…
N-Propylsulfamic acid supported onto magnetic Fe O
O
S
O
O
O
H
O
O
S
O
H
O
H
H
O
O
Me
O
Me
Me
O
O
OAc
OAc
O
H
Me
H
O
S
O
O
H
O
O
O
Fe O
O Si
N
H
S
O
O H
3
4
O
Scheme 5 The probable mechanism for the synthesis of geminal diacetates (acylals) N-propylsulfamic
acid supported onto magnetic Fe nanoparticles (MNPs-PSA) as a MNPs catalyst
3 4
O
like CH Cl and n-hexane were used (Table 5, entries 9–12), and on the other hand,
2
2
in some methods, reflux conditions or high temperature were required (Table 5,
entries 7–11). In other methods, using sulphated zirconia (Table 5, entry 8),
TBBDA and PBBS (Table 5, entries 9 and 10), and Cu(OTf) (Table 5, entry 11),
2
the reaction time was longer and boring. Thus, the present procedure with N-
propylsulfamic acid supported onto magnetic Fe O nanoparticles (MNPs-PSA) as a
3
4
catalyst is more convincing in proportion to the above methods in terms of reaction
time and yield of the desired product and conditions of the reaction like solvent,
temperature and catalyst loading.
123

S. Sajjadifar, P. Nasri
Table 5 Comparison of different catalysts
a
Entry
Catalyst
Conditions
Time (min)
Yield (%)
References
b
1
2
3
4
5
6
7
8
9
SBSA
Solvent-free, r.t.
Neat, r.t.
4
97
86
86
99
99
99
90
99
85
85
94
76
90
98
96
[22]
[28]
[35]
[35]
[36]
[37]
[41]
[42]
[43]
[43]
[44]
[45]
[46]
[47]
–
P
2
O
5
/Al
2
O
TM
3
45
70
5
Selectfluor
Selectfluor
Solvent-free, r.t.
Solvent-free, M.W.
Solvent-free, r.t.
Solvent-free, r.t.
Solvent-free, 30 °C
Solvent-free, 0 °C
TM
2?c
c-Fe
2
O
3
@HAp-Ni
d
10
10
[Msei]Cl
g
3
Si-[SbSipim][PF
6
]
g
5
Sulphated zirconia
e
TBBDA
f
PBBS
g
8
CH
CH
CH
2
2
2
Cl
2
Cl
2
Cl
2
, reflux
, reflux
, r.t.
g
5
10
11
12
13
14
15
a
g
4
Cu(OTf)
2
Ruthenium(III) Chloride
Saccharin sulfonic acid
Phospho sulfonic acid
MNPs-PSA
n-hexane, r.t.
10
g
Solvent-free, 90 °C
Solvent-free, r.t.
Solvent-free, r.t.
0.8
5
20
Isolated yield
b
Silica boron sulfonic acid
2?
Ni @hydroxyapatite-core@shellc-Fe
c
2
O
3
nanoparticles
d
1-methyl-3-(2-(sulfooxy)ethyl)-1H-imidazol-3-ium chloride
e
N,N,N0,N0-tetrabromobenzene-1,3-disulfonamide
Poly(N,N0-dibromo-N-ethyl-benzene-1,3-disulfonamide)
In hour
f
g
Conclusion
In summary, an effective, green, and rapid procedure has been developed for the
chemoselective preparation of the geminal diacetates (acylals) from a variety of
aldehydes with acetic anhydride under solvent-free conditions at room temperature and
deperotection of the corresponding acylals in water using catalytic amounts of MNPs-
PSA in water. This method is very selective for the preparation of 1,1-diacetates
(
acylals) from a variety of aldehydes in the presence of ketones (acetophenone). The
simple work-up procedure, non-toxic organic solvents and catalysts, excellent catalytic
capacity, chemoselectivity, short reaction times, high yield of products, and recovery
and reusability of MNPs-PSA by an external magnet are advantages of this method.
Acknowledgement We are grateful to Payame Noor University of Ilam, Iran, for the partial support of
this work.
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3 4…
N-Propylsulfamic acid supported onto magnetic Fe O
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