An eco-friendly n-formylation of amines using nano cerium oxide as a recyclable catalyst under solvent-free and ultrasound irradiation conditions at room temperature

Article abstract of DOI:10.2174/157017861131000057

A new method for the synthesis of formamides has been developed by the N-formylation of amines with formic acid in the presence of nano cerium oxide as an efficient and recyclable catalyst under ultrasound irradiation. The reaction system is remarkably simple and environmentally benign.

Full text of DOI:10.2174/157017861131000057

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Letters in Organic Chemistry, 2014, 11, 49-54
49
An Eco-friendly N-formylation of Amines Using Nano Cerium Oxide as
a Recyclable Catalyst Under Solvent-free and Ultrasound Irradiation
Conditions at Room Temperature
a,
b
c
S. Mohammad Sajadi *, Mehdi Maham and Akbar Rezaei
a
Department of Petroleum Geoscience, Faculty of Science, Soran University, PO Box 624, Soran, Kurdistan Regional
b
Government, Iraq; Department of Chemistry, Aliabad Katoul Branch, Islamic Azad University, Aliabad Katoul, Iran;
c
Department of Chemistry, Ahar Branch, Islamic Azad University, Ahar, 5451116714, Iran
Received June 26, 2013: Revised September 01, 2013: Accepted September 02, 2013
Abstract: A new method for the synthesis of formamides has been developed by the N-formylation of amines with formic
acid in the presence of nano cerium oxide as an efficient and recyclable catalyst under ultrasound irradiation. The reaction
system is remarkably simple and environmentally benign.
Keywords: N-Formylation, amine, nano cerium oxide, reusable catalyst, formic acid, ultrasound irradiation.
INTRODUCTION
most of the other N-formylation methods have disadvantages
such as long reaction times, formation of side products,
the use of organic solvents, thermal instability of catalysts
and the use of homogeneous catalysts [14, 15]. Thus,
the development of an efficient and versatile method for
the N-formylation of amines is an active ongoing research
area.
Formamides are valuable intermediates in the synthesis
of pharmaceutically important compounds [1, 2]. In addition,
the formamide moiety has been used to protect the nitrogen
in amines [3] and in the synthesis of formamidines and iso-
cyanides [4]. Also, formamides can act as Lewis base cata-
lysts in reactions such as allylation, synthesis of acid chlo-
rides from carboxylic acids and hydrosilylation of carbonyl
compounds [5].
In recent years there has been a tremendous interest in
various chemical transformations catalyzed by heterogene-
ous catalysis [17]. Among heterogeneous catalysts, metal
nanoparticles have been used widely as efficient catalysts in
organic reactions due to their high catalytic activity, ease of
handling, reusability, and benign character [18]. The applica-
tion of metal oxides, especially ceria, as effective catalysts
Several formylation reagents have been reported in the
literature for the N-formylation of amines such as acetic
formic anhydride [6], chloral [7], activated formic acid using
N,N'-dicyclohexylcarbodiimide [8] or N-(3-Dimethylamino-
propyl)-N'-ethylcarbodiimide hydrochloride [9] activated
formic esters [10] ammonium formate [11], 2,2,2-trifluoro-
ethyl formate [12], Natrolite zeolite [13] and PEG-400 [14].
2
for CO fixation and transalkylation and organic synthesis
has received considerable attention in the recent years due to
their high catalytic activity [19]. Nagarkar and co-workers
recently published Ullmann type coupling between 4-
nitrochlorobenzene and a variety of phenols, amines and
However, there are several obstacles which limit the ap-
plicability of these reagents [15]. In many cases, the reagents
are toxic, sensitive to moisture, expensive or not available
and cannot be stored. Among formylation agents in the N-
formylation of amines, formic acid has received much atten-
tion because it is not explosive, flammable and expensive.
Also, it can be easily stored and is neither moisture sensitive
nor very volatile. Aqueous formic acid (85%) has previously
been reported as a formylating agent under conventional
heating. However, this method needs a Dean-Stark trap un-
der reflux conditions in toluene and involves long reaction
times [16]. Also, the formylation of anilines having electron-
withdrawing groups was found to be difficult [16]. Also,
2
thiophenols in the presence of nano CeO as an efficient,
inexpensive, and environmentally benign heterogeneous
catalyst [20].
In continuation of our recent studies on the application of
heterogeneous catalysts and green chemistry [21], herein we
report the N-formylation of amines using formic acid in the
presence of a catalytic amount of nano cerium oxide [20] as
a heterogeneous catalyst at room temperature under sol-
ventless conditions and ultrasound irradiation in high yields
(
Scheme 1).
CeO nano
2
RR'NH + HCOOH
RR'NCHO
*
Address correspondence to this author at the Department of Petroleum
Solvent-Free
r.t., )))))
Geoscience, Faculty of Science, Soran University, PO Box 624, Soran,
Kurdistan Regional Government; Tel: (964) 6635066660;
Fax: (964) 7703643421; E-mails: phytochem2006@gmail.com and
Mohammad.s@soranu.com
Scheme 1. N-formylation of amines by using formic acid in the
presence of nano cerium oxide.
1
875-6255/14 $58.00+.00
© 2014 Bentham Science Publishers

5
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Letters in Organic Chemistry, 2014, Vol. 11, No. 1
Sajadi et al.
Table 1. The Model Reaction in the Synthesis of N-(3-methylphenyl) Formamide Under Conventional and Ultrasound Irradiation
Conditions at Room Temperature
c
Entry
Method
Catalyst (mol %)
Time (min)
Yield (%)
a
a
a
1
2
3
4
5
6
7
Without US
Without US
Without US
3.0
5.0
7.0
5.0
7.0
0.0
0.0
50
50
33
38
45
96
96
0.0
75
45
b
With US
13
b
With US
13
a
Without US
100
35
b
With US
a
b
c
Reaction under conventional conditions. The ultrasonic power 50 W, irradiation frequency 25 kHz. Isolated yield.
Table 2. N-Formylation of Amines with Formic Acid using CeO
2
Nanoparticles at Room Temperature under Solvent-free and
a
Ultrasound Irradiation Conditions
b
Entry
Amine
Product
Time (min)
Yield (%)
c
1
NH2
NHCHO
4
98, 95
2
3
Me
NH2
Me
NHCHO
NHCHO
NHCHO
2
2
95
96
MeO
NH2
MeO
NH2
4
6
92
OH
OH
5
6
HO
NH2
HO
NHCHO
11
35
93
94
Br
NH2
Br
NHCHO
Cl
Cl
7
8
35
15
93
95
NH2
NHCHO
NHCHO
NHCHO
Cl
NH2
Cl
NH2
9
13
96
Me
Me
NH2
NHCHO
NHCHO
1
1
0
1
85
92
88
O N
O N
2
2
O N
NH2
O N
120
2
2

An Eco-friendly N-formylation of Amines Using Nano Cerium Oxide
Letters in Organic Chemistry, 2014, Vol. 11, No. 1 51
Table 2. Contd…..
b
Entry
Amine
Product
Time (min)
Yield (%)
1
1
2
3
MeOC
NH2
MeOC
NHCHO
NHCHO
90
89
NH2
12
93
1
1
1
4
5
6
O
NH
O
NCHO
NPh
20
50
15
91
93
94
HN
NPh
OHCN
CH NH2
CH NHCHO
2
2
N
N
1
1
7
8
35
91
90
H
CHO
H
N
CHO
N
120
3
NHMe
OH
N(CHO)Me
5
-
89
-
2
2
0
1
No reaction
CH OH
No reaction
-
-
2
2
2
2
3
40
87
82
N
H
N
CHO
HOCH
2
CH
2
NH
2
HOCH
2
CH
2
NHCHO
30
a
b
c
Reaction conditions: amine (1.0 mmol), formic acid (1.2 mmol) and catalyst (5.0 mol %). Yield refers to the pure isolated product. Yield after the third cycle.
RESULTS AND DISCUSSION
a well-established fact that ultrasound irradiation accelerates
the reactions. In addition, the reaction was slow in the ab-
sence of catalyst (Table 3, entry 7), it indicated that combi-
The CeO
2
nanoparticles were prepared by ultrasonically
nano parti-
modified CTAB assisted method [20]. The CeO
2
2
nation method (ultrasound irradiation and CeO nanoparti-
cles were characterized using powder XRD, TEM, SEM and
EDAX [20]. TEM analysis shows particle size 4-5 nm. The
calculated surface area was found to be 214 m /g.
cles) played a significant role on the product yield and reac-
tion time. Based on these results, the best conversion was
observed when the reaction was performed under solvent-
free and ultrasound irradiation conditions in the presence of
2
First of all, the amount of the catalyst was optimized by
reacting 3-methylaniline (1.0 mmol) with formic acid (1.2
mmol) under solvent-free and ultrasound irradiation condi-
tions at room temperature (Table 1). No reaction was ob-
served in the absence of catalyst without ultrasonic irradia-
tion (Table 1, entry 6). When the reaction was carried out at
2
amine (1.0 mmol), formic acid (1.2 mmol) and CeO nano (5
mol%) (Table 1, entry 4) No significant improvement on the
yield was observed using higher amounts of the catalyst (Ta-
ble 1, entry 5). We then used the optimal reaction conditions
for the N-formylation of different amines under solvent-free
and ultrasound irradiation conditions and the results are
shown in (Table 2).
2
room temperature using CeO nanoparticles and in the ab-
sence of ultrasonic irradiation, the product was obtained in
lower yield and longer reaction time (Table 1, entries 1-3),
while in the presence of ultrasonic irradiation, the yield in-
creased and the reaction time reduced (Table 1, entry 4). It is
To study the effects of the nature of the substituents on
the benzene ring of the amines, various formamides were
synthesized from different amines containing both electron-

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2
Letters in Organic Chemistry, 2014, Vol. 11, No. 1
Sajadi et al.
releasing and electron-withdrawing groups in excellent
yields under ultrasound irradiation. We also examined the
scope of this reaction with a series of heterocyclic and ali-
phatic amines. The N-formylation of aliphatic and heterocyc-
lic amines gave the corresponding formamides in high
yields. In contrast with previously reported methods, this
method is applicable for the N-formylation of 4-nitroaniline
•
•
The reaction system is simple and chemoselective and
the yields of the products are very high,
The use of nano cerium oxide as a heterogeneous catalyst
which can easily be recovered and reused.
The possible mechanism for the synthesis of formamides
under ultrasound irradiation is shown in (Scheme 2). The
reaction of amine with formic acid occurs through the activa-
tion of the carbonyl group over surface of the catalyst fol-
lowed by the nucleophilic attack of the amine NH. BET re-
(
Table 2, entry 11). Also, the N-formylation of secondary
amines and steric hindered amines was carried out in high
yield by this method (Table 2, entry 14, 15, 17, 18, 19 and
2
2
2). On the contrary, as seen in (Table 2), the present method
sults show that surface area of nano cerium oxide is 214 m /g
provided high chemoselectivity in N-formylation of amines
containing both the hydroxyl and the amino group (Entry 20
and 21). So, O-Formylation of phenols or alcohols did not
take place under the applied reaction conditions.
[20]. Nano cerium oxide may show complexation towards
carbonyl group of formic acid and thus may enhance the
electrophilic character. The breakdown of C-OH and N-H
bonds in formic acid and amines facilitates the elimination of
H
2
O as by product and the final formamides will be pro-
duced. A similar mechanism has been reported for the N-
formylation of amines using the ZnCl catalyst [15].
To show the merits of our method in comparison with
other reported methods, we compared some of the results for
N-formylation of benzylamine under various conditions. The
results summarized in (Table 3) indicated that, all the reac-
tions catalyzed by nano cerium oxide proceeded with higher
yields and lower reaction times compared with the reactions
catalyzed by other previously reported methods.
2
The catalyst recycling is an important step as it reduces
the cost of the process. We also investigated the recycling of
the nano cerium oxide under solvent-free and ultrasound
irradiation conditions. After completion of the reaction, ethyl
acetate was added and the catalyst was filtered. We found
that catalyst can be reused three times without the loss of
activity (Table 2, entry 1).
Nevertheless some advantages of our work are as below:
•
•
•
•
•
Volatile and toxic organic solvent is not needed,
Short reaction times,
Mild reaction conditions,
The products were characterized by IR, NMR spectros-
copy and from melting points and elemental analysis [13-16,
28]. Disappearance of one strong and sharp absorption band
(
2
-NH stretching band) and appearance of a carbonyl stretch-
The high reaction temperature is not needed,
ing band in the IR spectra, were evidences for the formation
The only by-product of this reaction is H
2
O. So, recrys-
of N-formyl derivatives. IR spectra showed two characteris-
tic peaks, one between 3300 and 3400 cm (secondary NH)
tallization and column chromatography are not needed,
-1
2
Table 3. Comparison of Nano CeO with Reported Catalysts in the N-formylation of Benzylamine
Entry
Formylating Method
HCOOH, Sodium formate
Solvent
Temperature
Time
Yield (%)
Ref.
1
2
3
4
5
6
7
8
9
-
-
r.t.
2.5 h
90 min
2 h
85
90
94
88
42
80
92
49
90
94
22
o
HCOOH, Anhydrous ZnCl
2
70 C
15
Methylformate
PhMe
r.t.
Reflux
r.t.
23
Ammonium formate
HCOOH, PEG
CH
3
CN
6 h
11
-
6 h
14
HCOOH, H
HCOOH, Amberlite IR-120
HC(OEt)
HCOOH
HCOOH, CeO
2
O
2
, Copper salt
MeOH
-
r.t.
75 min
95 min
32 h
24
25
MW, 320 W
o
3
H
2
O
MW, 65 C
26
o
-
-
80 C
60 min
15 min
27
1
0
2
nano
))))), r.t.
This work
CeO
2
C eO
O
CeO
O
2
2
-
�
O
O
-
CeO
2
r.t., ))) ))
Solvent-Free
OH
OH
1 2
R R NC H O
+
C eO
+
2
2
�
2
- H O
H
NR R
1 2
H
OH
H
OH
H
NR
1
R
2
.
.
R R NH
H
1
2
Scheme 2. Proposed mechanism for the N-formylation of amines with formic acid using nano cerium oxide.

An Eco-friendly N-formylation of Amines Using Nano Cerium Oxide
Letters in Organic Chemistry, 2014, Vol. 11, No. 1 53
-
1
and the other between 1640 and 1680 cm (N-formyl, C=O).
ACKNOWLEDGEMENTS
1
The relevant H NMR spectrum shows two distinctive proton
signals; one is related to NH of the N-formamides and an-
The authors wish to thank the research council of Soran
University for financial support.
other belongs to the aldehyde.
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