Catalysis and reaction mechanisms of N-formylation of amines using Fe(III)-exchanged sepiolite

Article abstract of DOI:10.2478/s11696-013-0484-8

This study presents a rapid, economical and "green" N-formylation of anilines with formic acid (FA) using Fe(III)-exchanged sepiolite (IES) as a catalyst. The IES exhibited excellent catalytic properties and the reactions were complete within 20-90 min to afford products with high yields. The adsorption mechanism of FA on the IES sample was studied by infrared (IR) spectroscopy at a temperature range of 120-400°C. The thermal desorption of pyridine was detected by the IR technique to estimate the acidity of IES. Lewis acid-bound pyridine bands at 1618-1631 cm^-1 and 1443-1445 cm ^-1 were observed even after the IES sample was heated above 400°C.

Full text of DOI:10.2478/s11696-013-0484-8

Chemical Papers 68 (5) 584–590 (2014)
DOI: 10.2478/s11696-013-0484-8
ORIGINAL PAPER
Catalysis and reaction mechanisms of -formylation of amines using
Fe(III)-exchanged sepiolite
Bilge Eren*, Reyhan Aydin, Erdal Eren
Department of Chemistry, Faculty of Science and Arts, Bilecik University, 11210, Bilecik, Turkey
Received 2 April 2013; Revised 15 July 2013; Accepted 21 July 2013
This study presents a rapid, economical and “green” N-formylation of anilines with formic acid
(
FA) using Fe(III)-exchanged sepiolite (IES) as a catalyst. The IES exhibited excellent catalytic
properties and the reactions were complete within 20–90 min to afford products with high yields.
The adsorption mechanism of FA on the IES sample was studied by infrared (IR) spectroscopy
◦
at a temperature range of 120–400 C. The thermal desorption of pyridine was detected by the IR
−
1
technique to estimate the acidity of IES. Lewis acid-bound pyridine bands at 1618–1631 cm and
−
1
◦
1
443–1445 cm were observed even after the IES sample was heated above 400 C.
ꢀ
c 2013 Institute of Chemistry, Slovak Academy of Sciences
Keywords: sepiolite, ion-exchanged, N-formylation, formic acid, catalysis
Introduction
lene glycol (PEG-400) (Das et al., 2008), formic acid
and toluene (Jung et al., 2002), formic acid in the pres-
ence of TiO2–SO2 (Krishnakumar & Swaminathan,
−
Due to its structural characteristics and physico-
chemical properties, sepiolite has recently been used
as a catalyst support (Aramendía et al., 1994; Shimizu
et al., 2004; Milt et al., 2010; Letaief et al., 2011; Kara-
manis et al., 2011). Also, the reactants are readily
changed into activated complexes when the reactants
are adsorbed due to basic [MgO6] and acidic [SiO4]
centres on a sepiolite surface. The reactions catalysed
by sepiolite are usually carried out under mild condi-
tions with high yields and high selectivities and the
procedure for these reactions is very simple.
N-Formylation of amines is an important reaction
in synthetic organic chemistry. N-Formyl compounds
are key intermediates in the synthesis of various phar-
maceutical compounds (Chen et al., 2000). They are
also useful reagents as Lewis base catalysts in allyla-
tion (Kobayashi & Nishio, 1994) and hydrosilylation of
carbonyl compounds (Kobayashi et al., 1996). Various
methods have been developed for the N-formylation of
amines using different reagents such as ammonium for-
mate (Reddy et al., 2000), formic acid and polyethy-
4
2011), and formic acid using Zn metal as a catalyst
under solvent-free conditions (Kim & Jang, 2010).
In the last decade, the modification of clays with
Fe(III) species has been investigated in order to obtain
Fe(III)-exchanged or Fe(III)-pillared materials. These
materials have shown important potential applications
as catalysts in organic synthesis (Dorado et al., 2006;
Skoularikis et al., 1988; Long & Yang, 2000). To date,
the synthesis of N-formyl compounds directly catal-
ysed by raw or modified sepiolites has not been re-
ported. Accordingly, an easy and efficient procedure
for the synthesis of N-formyl compounds catalysed by
Fe(III)-exchanged sepiolite (IES) is reported here. To
explain the mechanism of reaction in the presence of
the IES catalyst, infrared (IR) spectra of formic acid
on IES were used to obtain information on the nature
of the surface species and their mode of coordination.
In addition, the acidic sites of IES were investigated
using the IR spectroscopy technique with pyridine as
a molecular probe.
*Corresponding author, e-mail: bilge.eren@bilecik.edu.tr

B. Eren et al./Chemical Papers 68 (5) 584–590 (2014)
585
Table 1. N-Formylation of various anilines with formic acid using raw sepiolite (RS) and Fe(III)-exchanged sepiolite (IES)
◦
Entry
1
Compound
R
H
M.p./ C
Catalyst
Time/min
Conversion/%
4
4
6–47
6–47a
RS
IES
30
30
20
95
I
5
5
1–53
RS
IES
20
20
15
96
2
3
4
5
II
III
IV
V
CH3
OCH3
NO2
Cl
0–54a
7
7
9–80
RS
IES
20
20
15
92
9–80a
1
1
95–198
94–195a
RS
IES
90
90
10
75
1
01–105
RS
IES
55
55
20
95
–
a) M.p. reported by Ma’mani et al. (2010).
Experimental
All reagents used, such as formic acid, pyridine,
and FeCl3 were of analytical grade. Double-distilled
water was used in the preparation of all solutions. Raw
sepiolite (RS) was obtained from the Eski ¸s ehir region,
Turkey. The RS was washed thoroughly with double-
Fig. 1. Formylation of amines.
distilled water to remove the foreign matter, dried at
◦
◦
6
0 C for 24 h, then pulverised in an agate mortar to
and 400 C). Specimens for measurement were pre-
pared by mixing 0.9 mg of the powdered sample with
70 mg of KBr and pressing the mixture into a pellet.
The interaction between the gaseous phase of
formic acid and sepiolite samples’ surface was accom-
plished in desiccators at ambient temperature for 2 h.
After adsorption studies, desorption experiments were
pass through a 200 mesh sieve. Fe(III)-exchanged sepi-
olite was obtained by using a liquid-to-solid ratio of 10
and 0.1 M of FeCl3 at ambient temperature for 24 h.
−
1
The resulting mixtures were centrifuged at 3000 min
for 5 min until the chloride ion-free form was obtained.
The IR spectra were recorded on a Perkin–Elmer
Spectrum-100 FTIR spectrometer in the range of
◦
also performed at elevated temperatures (120–400 C)
for 10 min.
−
1
1
2
300–1700 cm
with 64 scans and a resolution of
−
1
cm . The chemical analyses of sepiolite samples
Aniline (1 mmol) was added to a stirred mix-
ture of IES (0.1 g) and formic acid (1–3 mmol) in
toluene (5 mL), and stirring continued using a Dean–
Stark trap for an appropriate time (Table 1). After
completion of the reaction (monitored by TLC), the
formic acid was neutralised with a 10 % aqueous solu-
tion of NaHCO3 and the product was extracted with
ethyl acetate (2 × 10 mL). The combined organic
phases were washed with brine (2 × 5 mL) and dried
(Na2SO4). Evaporation of the solvent under reduced
pressure afforded almost pure N-formylated anilines
I–V (Fig. 1). These are all known compounds, hence
they were identified by comparison of their physi-
cal and spectral data with those of authentic sam-
ples.
were carried out using a Rigaku ZSX Primus model
XRF instrument. Data on the surface characteristics
of the sepiolite samples were obtained with a Quan-
tachrome NOVA 2200e Surface Area Analyser. For
surface analysis, a certain amount of sepiolite was de-
◦
gassed at 120 C for 24 h, then the sorption isotherm
was obtained with various doses of N2 at 77 K. The
surface areas of the adsorbents were calculated using
the BET equation. In addition, the t-plot method was
applied to calculate their micropore areas and micro-
pore volumes.
The Brønsted and Lewis acid sites were determined
by IR spectroscopy with chemisorbed pyridine. For
this purpose, the sepiolite samples were dried in a hot
◦
air oven at 120 C for 24 h prior to pyridine treatment
for IR measurements. The samples (50 mg each) were
poured loosely into a sample cup. The loosely-packed
sample was brought into direct contact with the pyri-
dine (0.1 mL). The sample cup was then held in a hot
Results and discussion
Surface acidity of IES sample
◦
air oven at 100 C for 1 h to remove the physisorbed
Table 2 shows the chemical composition of RS and
IES. The results indicate that the content of iron in
IES increased from 0.22 % to 18.42 %, while the rel-
ative proportions of Mg, Si and Ca decreased. In the
pyridine. After cooling to ambient temperature, the
sample of the adsorbed pyridine was evacuated for 20
◦
◦
◦
min at several temperatures (120 C, 200 C, 300 C,

5
86
B. Eren et al./Chemical Papers 68 (5) 584–590 (2014)
Table 2. Chemical composition of sepiolite samples
Sample
MgO
Al2O3
SiO2
Fe2O3
CaO
NiO
SO3
K2O
Na2O
P2O5
LOI
RS
IES
30.24
18.75
0.42
0.54
54.81
53.93
0.22
18.42
0.43
0.04
0.25
0.25
0.02
0.07
0.05
0.06
–
2.23
0.01
0.01
13.56
5.7
RS sample, the total content of SiO2 and MgO was
8
1
5.05 % and the content ratio of MgO to SiO2 was
.81. In the IES sample, the total content of MgO
and SiO2 was 72.68 % and the corresponding ratio
of MgO to SiO2 was 2.88. Mg, Al, and Fe are the
main constituents of the octahedral sheets of sepio-
lite. The relative content of Al2O3 obtained by XRF
increased with the dissolution of Mg and Ca. More-
over, the contents of MgO and CaO decreased sharply
with the Fe(III)-exchange process, whereas Al2O3 was
more difficult to remove than MgO and CaO (Harja
et al., 2013). This is attributed to the fact that Al oc-
cupied the centre and Mg exclusively the edges of the
octahedral ribbons of sepiolite.
−
1
The IR spectra in the region of 1400–1700 cm af-
ter pyridine adsorption and thermal desorption at dif-
ferent temperatures for 20 min of pyridine adsorbed
on IES are presented in Fig. 2. The IR absorption
bands were assigned according to the literature (Jóna
et al., 2005; Reddy et al., 2007; Figueiredo et al., 2009;
Horňáček et al., 2009). The IR spectra of the adsorbed
pyridine exhibited the absorption bands at 1618–
−
−
1
−1
−1
−1
1
1
1
631 cm , 1594–1597 cm , 1490 cm
and 1443–
1
−1
445 cm . The bands at 1443 cm , 1490 cm
,
−
1
−1
−1
576 cm , 1594 cm and 1618 cm were assigned
to Lewis acid-bound pyridine. It was observed that
the intensities of the Lewis acid-bound pyridine peaks
decreased with the increasing temperature but shifted
to a higher wavelength, suggesting that the IES sam-
ple possessed a strong Lewis acid site. Following the
desorption of pyridine at different temperatures, the
−
1
−1
−1
bands at 1597 cm , 1576 cm and 1491 cm re-
◦
◦
sisted up to 300 C and disappeared at 400 C, whereas
the intensities of the other bands (1618 cm
−
1
and
−
1
1
443 cm ) were unaffected by the increasing tem-
◦
◦
perature from 200 C to 300 C but decreased signifi-
Fig. 2. Desorption of pyridine from IES after thermal treat-
◦
◦
◦
cantly at 400 C. After heating at 300 C, the pyridine
bands observed at 1444 cm , 1576 cm , 1597 cm
and 1624 cm indicated four types of pyridine which
are directly coordinated to the Fe(III) ion. The very
broad band at approximately 1620–1630 cm
cluded the vibration of water and the interaction of
ment (120–400 C).
−
1
−1
−1
−
1
Adsorption and desorption of formic acid on
IES surface
−
1
in-
−
◦
1
pyridine with the Lewis sites. The bands at 1443 cm
The IR spectra recorded for formic acid-adsorbed
RS (RS/FA) and IES (IES/FA) surfaces at different
temperatures are shown in Fig. 3. After heating to
higher temperatures, some changes were observed in
−
1
and 1631 cm
were stable to outgassing at 400 C.
−
1
The intensity of the band at 1490 cm correspond-
ing to the combined Brønsted and Lewis-bonded pyri-
dine acid sites was reduced significantly after heating
−
1
the shape of the peaks located between 1300 cm
◦
−1
−1
at 200 C. These results affirm that the acid sites of
and 1700 cm . The peaks at 1566–1581 cm
and
correspond to formate OCO asym-
−
1
IES were predominantly Lewis acidic in nature. This
means that the metal cation acts as an electron pair
acceptor.
1337–1356 cm
metric and symmetric stretching, respectively (Ivanov
et al., 2009; Borowiak et al., 2000; Flaherty et al.,

B. Eren et al./Chemical Papers 68 (5) 584–590 (2014)
587
2
010; Miller et al., 2011; Eren et al., 2012, 2013). Af-
◦
◦
ter heating from 120 C to 200 C, the formate OCO
asymmetric peak was shifted from 1587 cm
1
1
1
−
1
to
−
1
591 cm , the formate OCO symmetric peak at
−
1
371 cm
broadened, and also split into peaks at
−
1
−1
−1
−1
366 cm , 1374 cm , 1381 cm
and 1404 cm .
The formate bonding geometries on the surfaces were
determined from the difference in the OCO antisym-
metric and symmetric stretching frequencies of for-
mate (∆νas−s) relative to the aqueous ionic formate
−
1
(
∆νionic = 201 cm ). Miller et al. (2011) described
the correlations between ∆νas−s and adsorption geom-
etry as follows: ∆νas−s > ∆νionic = monodentate co-
ordination; ∆νas−s < ∆νionic = chelating or bidentate
bridging; ∆νas−s ꢀ ∆νionic = bidentate chelating. Af-
◦
−1
ter heating at 120 C, the broad band at 1587 cm
showed the formate OCO asymmetric band of formic
acid overlapped with the HOH bending vibration band
of the zeolitic water molecules. The spectral decon-
volution revealed that the formate OCO asymmetric
−
1
band was at 1580 cm as shown in Fig. S1 (Appendix
A; see Supplementary data). After applying the de-
convolution method for the broad band, the ∆νas−s
−
1
was calculated as 209 cm . This result means that
the monodentate formate forms on the IES surface
(Fig. 4).
Catalyst test – IES-catalysed N-formylation of
aniline with formic acid
The reaction conditions were optimised by evalu-
ating the influence of different amounts of formic acid
and catalyst on the time and product yield in the N-
Fig. 3. IR spectra of FA species adsorbed on IES after thermal
◦
treatment (120–400 C).
−
Fig. 4. Possible configurations for HCOOH and HCOO species bonded to iron cation(s).

5
88
B. Eren et al./Chemical Papers 68 (5) 584–590 (2014)
Table 3. Optimisation of amount of formic acid (FA) and cat-
dicate that IES is an efficient heterogeneous catalyst.
The BET specific surface area of IES showed an in-
crease over the parent RS (Table 5). This result was
attributed to the increase in the porosity of the se-
piolite because of the presence of Fe(III) ions on the
outer surfaces of the sepiolite particles. This structure
enables the diffusion of both reagents and products
into and out of the pores of IES, and also controls
the possible reaction intermediates formed within the
pores (Isahak et al., 2012). The plausible mechanism
for the N-formylation of aniline catalysed by IES is
shown in Fig. 5. The strength and number of the acid
sites of sepiolite are important in the reactivity and
selectivity of sepiolite. The activity of the IES in the
Lewis acid-catalysed N-formylation of anilines origi-
nates from the Fe(III) ions which have a tendency
to acquire a pair of electrons to fill its vacant p or-
bitals. This mechanism of the N-formylation reaction
involves the complexation of the Fe(III) ion with the
formic acid (Fe(III) acting as a Lewis acid to coordi-
nate the carbonyl oxygen of formic acid) and the nu-
cleophilic attack of the lone pair of electrons present
in the aniline on the carbonyl carbon of formic acid
followed by the dehydration to give an N-formyl prod-
uct.
alyst (IES) for N-formylation of aniline (1 mmol) at
◦
8
0 C
FA/mmol Catalyst IES/g Time/min Conversion/%
RS
IES
10
60
1
2
3
3
3
0.1
0.1
30
30
30
30
30
RS
IES
10
75
RS
IES
20
95
0.1
RS
IES
10
85
0.02
0.05
RS
IES
15
92
formylation of aniline. The results are shown in Ta-
ble 3. The optimum amount was 3 mmol of HCOOH
in the presence of 0.1 g of IES. In order to further
investigate the scope and limitations of this reaction,
different aniline derivatives and formic acid were sub-
jected to the N-formylation reaction under similar re-
action conditions. The results are presented in Table 1.
It is evident that the reactions proceeded well irrespec-
tive of the substituents and the conversions were com-
pleted within 20–90 min. It is also clear that anilines
containing electron-donating substituents such as CH3
and OCH3 (entries 2 and 3) and electron-withdrawing
groups such as NO2 and Cl (entries 4 and 5) afforded
the corresponding N-formamides with excellent yields.
Table 4 shows a comparison of the performances of IES
and various catalysts used previously. The results in-
Conclusions
A very simple and highly efficient protocol for
the N-formylation of anilines using non-toxic and in-
expensive IES was developed. The design of the N-
formylation reaction mixtures is simple and highly
convenient; in many cases, the products are obtained
with high purity. Furthermore, the IES used as a cat-
alyst in the formylation reaction can also be recovered
and reused.
Table 4. Comparative performance of various methods in N-formylation of aniline
Formylation method
Time/h
Yield/%
Catalyst amount/g
Reference
Ammonium formate
HCOOH/PEG
11
1
96
90
0.473
2
Reddy et al., 2000
Das et al., 2008
HCOOH/toluene/reflux
3
99
–
Jung et al., 2002
HCOOH/3 %-TiO2-SO2
−
0.5
0.5
0.5
98.2
96
0.1
0.013
0.1
Krishnakumar & Swaminathan, 2011
Kim & Jang, 2010
Present study
4
HCOOH/activated Zn
HCOOH/IES
a
95
a) Yields from three subsequent runs using the same recovered catalyst were 95 %, 90 %, and 90 %.
Table 5. Porous structure parameters of RS and IES samples
SBET/(m2
g
−1
)
Smic/(m2
g
−1
)
Smeso and Smac/(m2
g
−1
)
Vt/(cm3
g
−1
)
Vmic/(cm3
g
−1
)
D /nm
a
Sample
p
RS
IES
161.25
211.62
75.71
–
85.54
211.62
0.124
0.185
0.0362
–
3.083
3.492
a) 4V/A by BET.

B. Eren et al./Chemical Papers 68 (5) 584–590 (2014)
589
Fig. 5. Plausible mechanism for N-formylation of aniline catalysed by IES.
Acknowledgements. The authors wish to express their grat-
itude to Dr. Turgay Tay (University of Anadolu, Turkey) for
the surface area measurements and to the reviewers for their
remarks and corrections of the manuscript.
pillared clays: Study of the influence of the synthesis con-
ditions on the activity for the selective catalytic reduction of
NO with C3H6. Applied Catalysis A: General, 305, 189–196.
DOI: 10.1016/j.apcata.2006.03.022.
Eren, E., Gumus, H., & Sarihan, A. (2012). An investigation of
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ganese oxide coated sepiolite surfaces. Appied Clay Science,
Supplementary data
6
2–63, 1–7. DOI: 10.1016/j.clay.2012.04.013.
Supplementary data associated with this article
deconvoluted IR spectrum of formic acid adsorbed
on the IES sample) can be found in the online version
of this paper (DOI: 10.2478/s11696-013-0484-8).
Eren, E., Gumus, H., Eren, B., & Sarihan, A. (2013). Surface
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