Table 3 Results of the amidation of palmitic acid with various amines
a marvellous catalyst which is highly active, recoverable and
reusable.
over MCM-41 catalysta
Entry
Amines
Yieldb/%
Experimental
1
2
3
4
5
6
Aniline
93 (trace)
92 (42)
59 (8)
0 (0)
3 (trace)
94 (50)
Benzylamine
Cyclohexylamine
Tert-butylamine
N,N-Dihexylamine
Pyrrolidine
A round-bottom flask containing the mixture of fatty acid
(3 mmol), amine (3 mmol) and MCM-41 (20 wt%) in toluene
(15 ml) equipped with a Dean–Stark apparatus was heated at
azeotropic reflux temperature for 6 h. After cooling to ambient
temperature, the suspended MCM-41 was removed by filtration
and rinsed with CHCl3. A small portion was taken from the
collected filtrate to determine the conversion and yield by gas
chromatography (Shimadzu 18A, column: Ultra ALLOY+-65).
Purification was carried out by column chromatography using
hexane–EtOAc (3/1) as an eluent, and the isolated products were
identified by both 1H and 13C NMR (ECA-500 NMR, JEOL).
Note: The utilization of toxic chloroform, through extremely
undesirable, was necessary to estimate accurate yields of amides
by GC due to their poor solubility.
a Reaction was carried out by using acid (3 mmol) and amine (3 mmol)
in the presence of 20 wt% of MCM-41 in toluene (15 ml) at reflux for
12 h. b Isolated yield. The values in parentheses are yields of control
experiments (without MCM-41 catalyst).
of pyrrolidine, because the reaction moderately proceeded even
in the absence of MCM-41 catalyst. These results suggest that
MCM-41 effectively catalyzed the reaction for less sterically
hindrance substrates.
The amidation of fatty acids and long-chain aliphatic amines
catalyzed by MCM-41 gave an excellent opportunity for practi-
cal applications that are green, environmentally benign and atom
economical. Then we have attempted to examine the recyclability
and reusability of the MCM-41 catalyst and have demonstrated
this by the reaction of palmitic acid with hexylamine as a
model reaction. The results are given in Fig. 1. The MCM-41
catalyst can be completely recovered from the reaction mixture
by filtration, and the collected catalyst was treated in two
different manners prior to use in the next reaction; calcination
at 550 ◦C under air flow (black bar in Fig. 1), or rinsed with
chloroform and dried at 60 ◦C for overnight (white bar in
Fig. 1). When treated by rinsing with CHCl3, the yield of amide
declined to 67% after the 1st reuse, however, further reuse until
the 4th repeat did not significantly drop the yield. TG-DTA
analysis of used catalyst revealed an exothermic peak at 300 ◦C
corresponding to the decomposition and/or the combustion of
organic compounds adsorbed on the pore wall surface. Thus
we carried out calcination of the used MCM-41 and utilized
it for repeat experiments, which resulted in excellent yields of
amide until the 4th time reuse. This suggests that MCM-41 is
Conclusions
Amide compounds can be excellently prepared by MCM-41
catalyst from the mixture of an equimolar amount of long-chain
aliphatic acids and amines. The MCM-41 catalyst is non-toxic
and safe, and further it can be recovered and reused without
loss of its catalytic activity. Hence, this offers a great advantage
for a green chemical process with highly atom economy. Further
research is ongoing and we will report in near future.
Notes and references
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Fig. 1 Results of reuse experiments of MCM-41 catalyst. Reaction was
performed with palmitic acid (3 mmol), n-hexylamine (3 mmol) and
MCM-41 (20 wt%) in toluene (15 mL) at reflux for 6 h. Black bar:
calcination; white bar: rinse with CHCl3.
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830 | Green Chem., 2011, 13, 828–831
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