86
M. B. M. Reddy et al.
Yield (%) [Ref.]
Table 3 Comparison of nano-
MgO catalyzed N-formylation
with other methods
Entry
Formylation reagent/catalyst/solvent/condition
Time (h/min)
a
b
c
d
e
f
HCOOH/PEG-400/RT
4–6 h
79–93 [23]
25–99 [17]
60–99 [21]
94–98 [24]
63–91 [18]
90–98a
Ammonium formate/Toluene/heat
HCOOH-ZnO/heat (70 °C)
HCOOH/IL/RT
4–9 h
10–720 min
5–30 min
12 h
a
Reaction conditions: aromatic
amine (2 mmol), formic acid
(3 mmol) and nano-MgO
(20 mg), MW (320 W) under
solvent-free condition
NH4COOH/Neat/CH3CN-reflux
HCOOH/nano-MgO/solvent-free-MWI
1–2 min
O
N
H
H
Scheme 2 Plausible
mechanism for the N-
formylation of amines on nano-
MgO surface
O
H
H
O
Ph
H
H
O
H
+
N
H
H
H
Ph
O
Ph
Ph
+
H
N
_
N
. .
O
H
O
H
O
H
H
H
2+
Mg
2-
O
2-
O
2-
O
2-
O
2-
O
2-
O
2-
O
2-
O
2+
Mg
2-
O
2+
Mg
2+
Mg
2+
Mg
2+
Mg
2+
Mg
2+
Mg
catalytic nano-MgO at 100 °C for about 30 min, gave the
corresponding formamide in low yield (3a, 50%).
(90–98%) of high purity and the reusability of the solid basic
catalyst after separation followed by thermal activation.
When compared with other reported methods (Table 3,
entries a–e with f), we have found, nano-MgO to be an
efficient catalyst for the rapid synthesis of formamides in
excellent yields within 1–2 min, under solvent-free MWI;
the results of this study are presented in Table 3.
Acknowledgements G.T.C. gratefully acknowledges the financial
support from the Department of Science and Technology, NSTI
Phase-IV, Government of India, New Delhi. We also acknowledge
the help of Prof. Jai Prakash, Bangalore Institute of Technology, for
providing surface area measurement facility and MW reactor. One of
the authors M.S. Reddy also wishes to thank Dr. D.N. Sathyanara-
yana, Professor (Retired) Department of Inorganic and Physical
Chemistry, I. I. Sc, Bengaluru, India, for constant encouragement.
3.1 Recyclability of the Catalyst
Reusability of the catalyst was examined employing the
reaction between 1a and 2 to obtain 3a under identical
reaction conditions. The catalyst was easily recovered from
the mixture by filtration. It was washed with distilled water
and ethyl acetate repeatedly, and dried for 2–3 h under
vacuum. The recycled catalyst was used five times to
obtain N-formamide without appreciable decrease in the
yield 98, 93, 95, 90 and 95%, respectively, for 1–5 cycles.
After every reaction, the catalyst was recovered from the
reaction mixture and regenerated as described above.
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4 Conclusions
In conclusion, nano-MgO is an active and reusable catalyst
for the rapid N-formylation of arylamines by formic acid
under microwave irradiation. The salient features of this
protocol are enhanced reaction rate; and experimental ease.
The significance of the study lies in the solvent-free eco-
nomical synthesis of N-formamides in excellent yield
123