Sulfonic acid supported on hydroxyapatite-encapsulated-γ-Fe2O3 nanocrystallites as a magnetically Br?nsted acid for N-formylation of amines

Article abstract of DOI:10.1016/j.apcata.2010.01.020

Treatment of aqueous formic acid (85%) with structurally diverse amines in the presence of a catalytic amount of sulfonic acid supported on hydroxyapatite-encapsulated-γ-Fe₂O₃ [HAp@-γ-Fe₂O₃] (0.9 mol.%) as a heterogeneous, reusable and highly efficient catalyst gave the corresponding formamides in good to excellent yields at room temperature. The magnetically catalytic system was recovered by-passing time consuming filtration operation by using an external magnet device. In addition to facility, this methodology, it also enhances product purity and promises economic as well as environmental benefits.

Full text of DOI:10.1016/j.apcata.2010.01.020

Applied Catalysis A: General 377 (2010) 64–69
Contents lists available at ScienceDirect
Applied Catalysis A: General
journal homepage: www.elsevier.com/locate/apcata
Sulfonic acid supported on hydroxyapatite-encapsulated-g-Fe O
2 3
nanocrystallites as a magnetically Brønsted acid for N-formylation of amines
Leila Ma’mani, Mehdi Sheykhan, Akbar Heydari *, Mohammad Faraji, Yadollah Yamini
Chemistry Department, Tarbiat Modares University, Chamran Street, P.O. Box 14155-4838, Tehran, Iran
A R T I C L E I N F O
A B S T R A C T
Article history:
Treatment of aqueous formic acid (85%) with structurally diverse amines in the presence of a catalytic
Received 12 December 2009
Received in revised form 11 January 2010
Accepted 11 January 2010
Available online 22 January 2010
amount of sulfonic acid supported on hydroxyapatite-encapsulated-
g
-Fe
2
O
3
2 3
[HAp@-g-Fe O ]
(
0.9 mol.%) as heterogeneous, reusable and highly efficient catalyst gave the corresponding
a
formamides in good to excellent yields at room temperature. The magnetically catalytic system was
recovered by-passing time consuming filtration operation by using an external magnet device. In
addition to facility, this methodology, it also enhances product purity and promises economic as well as
environmental benefits.
Dedicated to memory of
Baradaraneh Dastvareh.
ß 2010 Elsevier B.V. All rights reserved.
Keywords:
Magnetically catalytic system
Sulfonic acid
Hydroxyapatite-encapsulated-
Formylation
2 3
g-Fe O
1
. Introduction
Due to the high surface area:volume ratios, nanoparticles can
the magnetic dipole–dipole attractions between particles. It was
3 4
also found that pure Fe O NPs were oxidized and easily lost their
magnetism [8]. For many applications it is thus crucial to develop
protection strategies to chemically stabilize the naked magnetic
nanoparticles. It was reported that formation of a passive coating
of magnetic NPs could prevent their aggregation in solutions and
thus improve their chemical stability. The applied coating
strategies can roughly be divided into two major groups: coating
with an organic shell, including surfactants and polymers, or
coating with inorganic components, including silica, carbon,
precious metals and recently, calcium hydroxyapatite [9–16].
Calcium hydroxyapatite, the main component of bone and teeth, is
of considerable interest in many areas because of ion-exchange
ability, adsorption capacity and acid–base properties. It has been
established that the CaHAp surface possess several kinds of P–OH
groups acting as adsorption sites for various molecules such as
effectively improve the loading and the catalytic efficiency of
immobilized catalysts. Therefore the use of nanostructured
materials as supports for different versions of catalyst immobili-
zation is ever-increasing [1,2]. In addition, these particles can be
dispersed into solvents, forming stable dispersions. In spite of the
advantages of heterogenized catalysts, the tedious recycling of
catalysts by filtration and the inevitable loss of some solid catalyst
in the separation process, especially with air sensitive materials,
are some of the drawbacks of the traditional procedures [3,4].
Therefore, there is more interest to introduce more efficient
manners for catalyst recovery, especially from the standpoint of
green chemistry.
Magnetic nanoparticles are receiving increasing interest in
recent years [5–7]. The magnetic nature of these particles allows
for easy recovery and recycling of the catalysts by an external
magnetic field, which may optimize operational cost and enhance
product’s purity. However, an unavoidable problem associated
with ‘‘naked’’ metallic or metal oxide nanoparticles is instability
over longer periods of time due to high initial chemical activity,
easy oxidation in air, loss of magnetism, dispersion and
agglomeration due to the large surface area to volume ratio and
2 3 3 2
H O, CH OH, CH I and CO . The number of surface P–OH groups
determines various surface properties, for instance, acidity and
basicity, affinity and catalytic activity. Due to good chemical
stability, high surface area, easy synthesis hydroxyapatite coated
magnetic nanoparticle has recently been used as heterogonous
catalytic supports.
Solid acids catalysts have served as important functional
materials in industrial processes. In particular, for reactions in
which water participates as a reactant or product, only a few solid
acids show acceptable performance. The development of new
water-tolerant solid acids is expected to have a major impact in
industrial applications as well as for scientific aspects. We have
*
Corresponding author. Tel.: +98 21 44990106; fax: +98 21 44990105.
E-mail address: akbar.heydari@gmx.de (A. Heydari).
0926-860X/$ – see front matter ß 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.apcata.2010.01.020

L. Ma’mani et al. / Applied Catalysis A: General 377 (2010) 64–69
65
overcome this problem by designing a sulfonic acid functionalized
hydroxyapatite-encapsulated- -Fe magnetic nanoparticles.
was complete, the mixture was mechanically stirred vigorously for
6 h until HCl gas evolution was stopped. Then the resulted
magnetic nanoparticles were separated by an external magnet
device and washed with DW until neutral and washed twice with
diethyl ether (100 mL) then dried under vacuum at room
temperature.
g
2 3
O
Formylation of amines is an important process in organic
synthesis with the resulting formamide function being a crossroad
intermediate. N-Formyl compounds have been widely used as
precursor for formamidine and isocyanide preparations [17]. They
are intermediates for mono-methylated amines from primary
amines and are catalysts for allylation and hydrosilylation of
carbonyl compounds [18,19]. In addition, the formyl group is a
useful protecting group, because the selective deprotection
process is possible in the presence of other groups like acetyl or
benzoyl [20]. Furthermore, formamides are very proper reagents in
the Vilsmeier reaction [21] and they have been used in the
synthesis of pharmaceutically important compounds such as
fluoroquinolines [22], 1,2-dihydroquinolines and substituted aryl
imidazoles [23].
2 3 3
2.3. pH-analysis of [g-Fe O @HAp-SO H]
To an aqueous solution of NaCl (1 M, 25 mL) with an initial pH
5.93, the [ -Fe @HAp-SO H] (500 mg) was added and the
g
2
O
3
3
resulting mixture stirred for 3 h after which the pH of solution
À1
decreased to 1.74. This is equal to a loading of 0.9 mmol SO
3
H g
.
Additionally, this result confirmed by back-titration analysis of the
catalyst.
Numerous methods are available for the N-formylation of
amines: in situ formed formic anhydride [24], acetic-formic
anhydride [25,26], chloral [27], activated formic acid using DCC
2.4. Typical experimental protocol for the synthesis of formamides
from amines
[
28] or EDCI [29], activated formic esters [30–32], ammonium
To a solution of amine (1.0 mmol) and aq. formic acid (1.2 mmol)
formate [33], solid supported reagents [34], aq. 85% formic acid
with ZnO [35], and aq. formic acid in protic ionic liquid [36].
However, there are several factors in some of these methods which
limited their applications. In many of these methods, the
applicable reagents are toxic, expensive or out of accessible. Also
long reaction times and by-products formation are other draw-
backs of these protocols. Aqueous formic acid (85%) has previously
been reported as a formylating agent under conventional heating.
However, this method needs a Dean–Stark trap under reflux
conditions in toluene and involves long reaction times. The N-
formylation of anilines having electron-withdrawing groups was
found to be difficult [37]. Regarding the green chemistry’s goals,
iron oxide magnetic nanoparticles open up new avenue to
introduce an amazing and efficient system for facilitating catalyst
recovery in different organic reactions. Therefore, we investigated
a novel design for a powerful recoverable catalytic system to avoid
the above-mentioned drawbacks.
2 3 3 3
was added [g-Fe O @ HAp-SO H] (10 mg = 0.009 mmol of SO H,
0.9 mol.%) and the reaction mixture was stirred at room tempera-
ture. The progress of the reaction was monitored by TLC (see Table
1). The reaction mixture was then separated by an external magnet
and the catalyst was washed and dried to reuse in the next run. The
mixture was extracted with ethyl acetate (3 Â 10 mL). The
2 4
combined organic layer was dried over anhydrous Na SO and
concentrated. All isolated products gave satisfactory spectral data
1
13
( H NMR and C NMR) and compared with those reported in
literature.
2.4.1. Product data
1
1: White solid, mp 46–47 8C, literature [35] 46–48 8C, H NMR
(500 MHz, DMSO): 50:50 (cis/trans), 9.30 (brs, 1H, trans), 8.71 (d,
1H, J = 11.0 Hz, trans), 8.45 (brs, 1H, cis), 8.38 (s, 1H, cis), 7.10–7.56
1
3
(5H, Ar-H). C NMR: 119.1 (CH), 120.6 (CH), 125.3 (CH), 125.6
(CH), 129.4 (CH), 130.2 (CH), 137.3 (C), 137.4 (C), 160.2 (C 55 O),
1
63.8 (C 55 O).
2: White solid, mp 78–80 8C, literature [41] 79–80 8C, H NMR
500 MHz, DMSO): 20:80 (cis/trans), 8.33 (s, 1H, cis), 7.99 (br, 1,
cis), 7.47 (d, 1H, J = 8.9 Hz, trans), 7.06 (d, 1H, J = 8.9 Hz, trans),
1
2
. Experimental
(
2
.1. Synthesis of HAp-encapsulated-g-Fe O [Fe O @HAp]
2 3 2 3
1
3
6
.79 (d, 2H, J = 8.6 Hz), 6.69 (d, 2H, J = 8.6 Hz), 3.79 (s, 3H).
C
Preparation of HAp-encapsulated-
previously reported method. FeCl
FeCl
Á6H
30 mL) under Ar atmosphere at room temperature and the
resulting solution was added to a 25% NH OH solution (10 mL)
with vigorous mechanical stirring (700 rpm). A black precipitate of
g
-Fe
Á4H
2
O
3
was according to the
(1.85 mmol) and
NMR (125 MHz, CDCl ): 55.9 (CH , cis), 56.0 (CH , trans),
3
3
3
2
2
O
114.6 (CH), 122.2 (CH), 140.4 (C), 153.3 (C), 159.3 (C 55 O),
163.4 (C 55 O).
3
2
O (3.7 mmol) were dissolved in deionized water (DW)
1
(
3: Yellow solid, mp 194–195 8C, literature [35] 193–194 8C, H
4
NMR (500 MHz, DMSO): 80:20 (cis/trans), 10.80 (s, 1H, cis), 10.69
(d, 1H, J = 10.0 Hz, trans), 9.04 (d, 1H, J = 10.0 Hz, trans), 8.39 (s, 1H,
1
3
Fe
Fe
3
3
O
O
4
was produced instantly. In order to obtain small and uniform
cis), 8.20 (d, 2H, J = 8.0 Hz), 7.81 (d, 2H, J = 8.0 Hz). C NMR: 116.8
(CH), 119.4 (CH), 124.9 (CH), 125.6 (CH), 143.2 (C), 144.4 (C), 160.0
(C 55 O).
4
particles, the drop rate of NH
4
OH was controlled precisely by
À1
a constant dropper and the drop rate was 1 mL min . After
1
1
5 min, 100 mL of Ca(NO
3
)
2
Á4H
2
O
(33.7 mmol, 0.5 M) and
4: Reddish solid, mp 129–131 8C, literature [35] 128–130 8C, H
(NH HPO (20 mmol, 3.0 M) solutions adjusted to pH 11 were
4
)
2
4
NMR (500 MHz, DMSO): 100:0 (cis/trans), 8.26 (s, 1H), 8.10 (br,
1H), 7.51 (br, 1H), 6.88 (t, 1H, J = 8.0 Hz), 7.03 (d, 1H, J = 8.0 Hz),
added drop-wise to the obtained precipitate over 30 min with
mechanical stirring. The resultant milky solution was heated to
1
3
7.16 (t, 1H, J = 8.0 Hz), 7.18 (d, 1H, J = 8.0 Hz). C NMR (125 MHz,
DMSO): 114.9 (CH), 119.5 (CH), 121.6 (CH), 124.5 (CH), 125.4 (C),
146.6 (C), 160.2 (C 55 O).
9
0 8C. After 2 h, the mixture was cooled to room temperature and
aged overnight. The dark brown precipitate formed was filtered,
washed repeatedly with DW until neutral, and air-dried under
vacuum at room temperature. The as-synthesized sample was
calcined at 300 8C for 3 h, giving a reddish-brown powder.
1
5: White solid, mp 50–54 8C, literature [35] 51–55 8C, H NMR
(500 MHz, DMSO): 50:50 (cis/trans), 8.60 (d, 1H, J = 8.0 Hz,
trans), 8.52 (br, 1H, trans), 8.31 (d, 1H, J = 8.0 Hz, cis), 7.92 (br,
1
H, cis), 7.42 (d, 2H, J = 8.3 Hz, cis), 7.13 (d, 2H, J = 8.3 Hz, trans),
2
.2. Synthesis of sulfonic acid supported on HAp-encapsulated-
g-
7.10 (d, 2H, J = 8.3 Hz, cis), 6.98 (d, 2H, J = 8.3 Hz, trans), 2.31
1
3
Fe -Fe @HAp-SO H]
2
O
3
[g
2
O
3
3
(s, 3H, trans), 2.29 (s, 3H, cis).
3
C NMR (125 MHz, CDCl ):
2
1.2 (CH ), 21.3 (CH ), 119.5 (CH), 120.6 (CH), 130.0 (CH),
3
3
To 1 g
g
-Fe
2
O
3
@HAp, chlorosulfonic acid (ClSO
3
H) 1 g was
130.6 (CH), 134.7–134.9 (CH), 135.5 (C), 159.8 (C 55 O, cis), 163.6
(C 55 O, trans).
added drop-wise at room temperature over 15 min. After addition

6
6
L. Ma’mani et al. / Applied Catalysis A: General 377 (2010) 64–69
Table 1
-Fe
[
g
2
O
3
@HAp-SO
3
H] as a clean and powerful catalytic system for the synthesis of formamides.
a
c
d
À1
Entry
Amine
Time (min)
Yield (%)
TON
TOF (h )
b
b
b
1
20
97 (96, 96, 94) [34]
107 (106, 106, 104)
323 (320, 320, 313)
2
3
4
20
35
30
97 [40]
107
323
94 [34]
92 [34]
104
102
179
207
5
6
15
25
95 [34]
92 [34]
105
102
422
245
7
8
40
60
92 [38]
102
103
153
103
93
9
25
95 [40]
105
253
1
1
0
1
30
60
96 [33]
106
100
213
100
90
1
2
50
93
103
124
1
3
40
95 [39]
105
158

L. Ma’mani et al. / Applied Catalysis A: General 377 (2010) 64–69
67
Table 1 (Continued )
Entry Amine
a
c
d
À1
)
Time (min)
35
Yield (%)
96
TON
106
TOF (h
1
4
5
183
209
1
30
94 [41]
104
a
b
c
Isolated yield.
The yields of three subsequent runs by using the same recovered catalyst.
Turnover number represents the average number of substrate molecules converted into the product per molecule of catalyst.
Turnover number per hour.
d
1
6
: Red solid, mp 67–71 8C, literature [35] 69–73 8C, H NMR
3. Results and discussion
(
(
1
500 MHz, CDCl
m, 4H), 7.18 (d, 2H, J = 7.4 Hz). C NMR (125 MHz, CDCl
30.2 (CH), 140.0 (C), 162.3 (C 55 O).
3
): 8.68 (s, 1H), 7.39–7.43 (m, 4H), 7.27–7.34
13
3
): 125.4–
Recently, based on the demonstrated intense interests in the
fabrication of core–shell magnetic particles, hydroxyapatite has
received considerable attention as one of the most ideal
biocompatible materials for encapsulated iron oxide NPs. These
classes of materials have reliable chemical stability, biocompati-
bility and versatility in surface modification [39]. In this paper, we
have described the preparation of sulfonic acid supported on HAp-
1
7: White solid, mp 60–62 8C, literature [39] 60–61 8C, H NMR
(
500 MHz, DMSO): 85:15 (cis/trans), 8.29 (s, 1H, cis), 8.22 (d, 1H,
J = 12.0 Hz, trans), 7.29 (d, 1H, J = 12.0 Hz, trans), 7.24–7.47 (m, 5H,
Ar-H), 5.75 (s, 1H, cis), 4.51 (d, 2H, J = 6.0 Hz, cis), 4.44 (d, 2H,
J = 6.3 Hz, trans). C NMR (125 MHz, CDCl
13
3 2
): 41.5 (CH ), 126.8
(
CH), 129.1 (CH), 130.6 (CH), 134.1 (C), 162.3 (C 55 O).
encapsulated-
mylation of amines and amine derivatives. The HAp-encapsulated-
-Fe , [ -Fe @HAp] nanocrystallites were prepared according
to the reported procedure and the resulting nanocrystallites
reacted with chlorosulfonic acid (Fig. 1). After 6 h the reddish-
brown powder washed by deionized water (DW) and diethyl ether
and dried under vacuum to obtain sulfonic acid supported on HAp-
2 3
g-Fe O and its potential application in the for-
1
8
: H NMR (500 MHz, CDCl
3
): 8.46 (s, 1H), 7.33–7.43 (m, 10H,
13
Ar-H), 4.46 (s, 2H), 4.30 (s, 2H). C NMR (125 MHz, CDCl
3
): 50.5
), 127.2 (CH), 129.3 (CH), 136.4 (C), 140.6 (C), 163.4
g
2
O
3
g
2 3
O
(
(
CH
C 55 O).
: Colorless oil, [41] H NMR (500 MHz, CDCl
.31–7.37 (m, 5H, Ar-H), 6.78 (br, 1H), 5.18 (m, 1H), 1.5 (d, 3H,
2
), 53.7 (CH
2
1
9
3
): 8.08 (s, 1H),
7
13
J = 7.8 Hz). C NMR (125 MHz, CDCl
3
): 22.3 (CH
CH), 51.6 (CH), 126.5 (CH), 127.7 (CH), 129.0 (CH), 143.4 (C), 147.8
C), 161.2 (C 55 O), 164.9 (C 55 O).
3
), 25.9 (CH
3
), 48.0
encapsulated-
g
-Fe
2
O
3
,
[g
-Fe
2 3 3
O @HAp-SO H] nanocrystallites
(
(
(Scheme 1).
[g-Fe O @HAp-SO H] nanocrystallites were characterized by
2 3 3
1
1
0: Colorless oil, [34] H NMR (500 MHz, CDCl
3
): 8.03 (s, 1H),
IR, TEM (Fig. 1a and b), SEM (Fig. 1c), XRD (Fig. 1d), and ion-
3
3
.67 (t, 2H, J = 4.9 Hz), 3.63 (t, 2H, J = 4.9 Hz), 3.54 (t, 2H, J = 4.9 Hz),
exchange pH-analysis. The ion-exchange pH-analysis demonstrat-
1
3
À1
.37 (t, 2H, J = 4.9 Hz). C NMR (125 MHz, CDCl
), 163.6 (C 55 O).
3
): 40.6 (CH
2
), 66.4
ed a loading of 0.9 mmol SO
3
H g . The characteristic absorption of
(CH
2
the SO
3
H
group correlated to S 55 O stretching appeared at
1
À1
1
1: Colorless oil, H NMR (500 MHz, CDCl
3
): 50:50 (cis/trans)
1255 cm , the stretching and out-of-plane bending of O–H group
appeared at 3400–3500 and 797 cm , respectively. In addition,
À1
8
1
.24 (d, 1H, J = 12.4 Hz, trans), 8.00 (d, 1H, J = 2.4 Hz, cis), 7.51 (brs,
1
3
H, trans), 6.83 (brs, 1H, cis), 1.37 (s, 9H, trans), 1.34 (s, 9H, cis).
C
the well known and characteristic IR adsorption bands due to the
stretching vibrational mode of surface phosphate groups in the
NMR (125 MHz, CDCl
64.3 (C 55 O).
3
): 28.5 (CH ), 30.4 (CH ), 50 (C), 161.3 (C 55 O),
3
3
À1
1
hydroxyapatite cover, was observed at 581 and 617 cm over-
1
1
2: Red oil, H NMR (500 MHz, CDCl
3
/DMSO): 9.33 (s, 1H), 8.35
2 3
lapped with S–O stretching peak. HAp-g-Fe O is subjected to
13
(
(
s, 1H), 2.89 (s, 6H). C NMR (125 MHz, CDCl
C 55 O).
3
): 45.4 (CH
3
), 164.1
further structural characterization with XRD, Fig. 1d. Diffraction
peaks at around 18.48, 30.28, 35.78, 43.68, 63.18 and 56.28
corresponding to the (1 1 1), (2 2 0), (3 1 1), (4 0 0), (5 1 1) and
(4 4 0) are readily recognized from the XRD pattern. The observed
diffraction peaks agree well with the tetragonal structure of
maghemite (1999 JCPDS file No 13-0458). It is clear that no other
phases except the maghemite are detectable. The specific surface
area of the powders was determined by use of the BET method. The
1
1
3: White solid, mp 160–162 8C, literature [40] H NMR
3
(500 MHz, CDCl ): 20:80 (cis/trans), 8.01 (s, 1H, cis), 7.13–7.29 (m,
7
H, Ar-H, NH, CHO, trans), 6.88 (br, 1H, cis), 3.66 (dd, 1H, J = 6.0 Hz,
1
3
J = 8.0 Hz), 3.64 (s, 3H), 3.02 (dd, 1H, J = 6.0 Hz, J = 7.8 Hz). C NMR
125 MHz, CDCl ): 37.7 (CH , cis), 41.0 (CH , trans), 51.8 (CH, cis),
5.8 (CH, trans), 126.8 (CH), 129.4 (CH), 135.8 (C, cis), 137.2 (C,
(
5
3
2
2
2
À1
trans), 160.7 (C 55 O, ester), 171.6 (C 55 O, formyl, cis), 175.3 (C 55 O,
formyl, trans).
BET results showed that the average surface area was 122 m g
for synthetic hydroxyapatite coated magnetic nanoparticle pow-
,
1
2
À1
1
4: White solid, mp 148–151 8C, H NMR (500 MHz, CDCl
3
):
der and 107 m g after functionalization of hydroxyapatite
5
2:48 (cis/trans), 8.69 (s, 1H, cis), 8.37 (s, 1H, trans), 8.08 (br, 1H,
coated magnetic nanoparticle powder. The synthetic powder
showed a type (IV) nitrogen adsorption desorption isotherm
(Fig. 1e).
1
3
cis), 7.36 (br, 1H, trans), 7.09–7.54 (m, 5H, Ar-H).
C NMR
3
(125 MHz, CDCl ): 118.7 (CH, trans), 119.7 (CH, cis), 123.7 (CH, cis),
1
1
24.2 (CH, trans), 124.5 (CH, cis), 125.1 (CH, trans), 128.8 (C, trans),
Aniline was chosen to optimize the reaction conditions, such as
temperature, time and molar ratio of the catalyst to substrate. We
found that 0.9 mol.% of [g-Fe O @HAp-SO H] was sufficient to
2 3 3
obtain the corresponding formamide in 97% yield in 20 min at
room temperature. A variety of amines investigated to confirm the
29.5 (C, cis), 158.6 (C 55 O, cis), 162.1 (C 55 O, trans).
1
1
5: Colorless oil, literature [42] H NMR (500 MHz, DMSO):
1
3
1
1.54 (s, 1H), 8.26 (s, 1H), 8.03 (s, 1H), 7.18 (s, 1H). C NMR
(125 MHz, DMSO): 121.1(CH), 135.1 (CH), 164.1 (C 55 O).

6
8
L. Ma’mani et al. / Applied Catalysis A: General 377 (2010) 64–69
Fig. 1. (a and b) TEM images, (c) SEM photograph, (d) XRD spectra of the
-Fe @HAp-SO H]).
2 3 3 2 3
g-Fe O @HAp-SO H, and (e) nitrogen adsorption desorption isotherm (left [g-Fe O @Hap] and right
[g
O
2 3
3
2 3
Scheme 1. Preparation of sulfonic acid supported on HAp-encapsulated-g-Fe O .
scope and generality of the [
formylation reaction (Scheme 2).
g
-Fe
2
O
3
@HAp-SO
3
H] catalyzed
products under the present reaction conditions. Cyclic amines
(entries 10 and 15), hydrazines (entry 12) and phenylalanine
methyl ester (entry 13) are easily formylated to provide the
corresponding formamides in high yields. The method can be
The amines used for this study included aliphatic, acyclic,
aromatic and heterocyclic compound. Aromatic amines such as
aniline and p-toluidine proceeded quickly to give the correspond-
ing N-formyl compounds in excellent yields (entries 1 and 5);
primary amines were easily formylated to provide alkyl formamide
(
entries 1–5, 7, 9, 12, and 13). Moreover, secondary amines readily
reacted to afford the corresponding formamide in 92–96% yields
entries 6, 8, 10, 14, and 15). It was found that this reaction is
(
chemoselective, and only N-formylation product was formed with
molecules containing both the hydroxyl and the amino group
(entries 4 and 14). O-Formylation of phenols did not take
Scheme 2. The reaction of amines and formic acid which leads to the formamide
place. Thus, the aminophenols furnished only the N-formylation
functionality.

L. Ma’mani et al. / Applied Catalysis A: General 377 (2010) 64–69
69
and inexpensive [
g
-Fe
2
O
3
@HAp-SO
3
H] as catalyst (0.9 mol.%). The
mild reaction conditions, excellent yields, operational simplicity,
practicability and applicability to various substrates renders this
approach as an interesting alternative to previously applied
procedures. Compared with non-magnetic nanoparticle catalytic
system, the presented protocol combines the advantages of solid
Brønsted acid and magnetic nanoparticles. We observed significant
reduction of operation as well as reaction time, product purity and
thus cost effectivity, inclusively the full reusability of the catalyst,
once prepared.
Fig. 2. The comparison of reused results in four runs for the N-formylation of aniline.
Appendix A. Supplementary data
Table 2
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.apcata.2010.01.020.
The comparison of various methods for the N-formylation of aniline.
Entry
Formylating method
Time
Yield
Ref.
References
1
2
3
4
5
6
7
8
9
Vilsmeier–Haack reaction
Acetic-formic anhydride
2 h
75
85
65
80
85
90
92
98
97
[21]
6 h
[26]
DMF–POCl
3
5 h
[28]
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. Conclusion
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We have introduced [
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1