Tetrahedron Letters
Fe3+-exchanged clay catalyzed transamidation of amides with amines
under solvent-free condition
Md. Ayub Ali a, S. M. A. Hakim Siddiki b, Kenichi Kon a, Ken-ichi Shimizu a,b,
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a Catalysis Research Center, Hokkaido University, N-21, W-10, Sapporo 001-0021, Japan
b Elements Strategy Initiative for Catalysts and Batteries, Kyoto University, Katsura, Kyoto 615-8520, Japan
a r t i c l e i n f o
a b s t r a c t
Fe3+-exchanged montmorillonite is shown to be an effective and reusable heterogeneous catalyst for the
transamidation of various amides and amines under solvent-free condition. The catalyst shows high
yields and wide substrate scope.
Article history:
Received 11 November 2013
Revised 9 December 2013
Accepted 26 December 2013
Available online xxxx
Ó 2014 Elsevier Ltd. All rights reserved.
Keywords:
Heterogeneous catalysis
Amides
Transamidation
Iron
Introduction
Our group reported the first successful example of heterogeneous
catalysis for transamidation under solvent-free conditions using
The amide bond is a fundamental component of biological and
synthetic polymers (i.e., proteins and nylons) and constitutes an
important functional group in organic chemistry.1 The most com-
mon way to make an amide bond is based on the coupling of acti-
vated carboxylic acid derivatives and amines, but there are
limitations such as the lability of the activated acid derivatives
and tedious procedures.2,3 Among various catalytic methods of
amide bond formation,4 transamidation of amides with amines is
potentially an attractive alternative method of the direct amide
bond formation. Due to the high stability of carboxyamide groups,
thermal transamidation requires high temperatures (>180 °C) or
microwave heating, which leads to a limited substrate scope.5,6 En-
zyme-mediated transformation is also known, but it has limited
scope and requires highly evolved enzymes as well as long reaction
time.7 To overcome these detriments new homogeneous8–17 and
heterogeneous18–20 catalysts for transamidation are recently reported.
Stahl8,9 and Mayers10 reported pioneering works and showed possi-
bility of transamidation under mild conditions, but the methods
suffer from low yield or use of excess amount of activation reagents.
Recently, Beller (copper acetate)11 and Williams12,13 (hydroxyl-
amine hydrochloride and zirconocene dichloride) have developed
effective homogeneous catalysts for transamidation. However,
these homogeneous catalysts suffer from difficulty in catalyst re-
cycle, necessity of the solvent, and low turnover number (TON).
CeO2 as reusable catalyst.19 More recently, Akamanchi et al. re-
ported sulfated tungstate as a solid catalyst, but it required solvent
and the reusability was not studied.20 As part of our continuing
interests in the heterogeneous catalysis for transamidation19 and
heterogeneous Lewis acid catalysis,21,22 we report herein the effi-
cient transamidation of amides with amines under solvent-free con-
dition using Fe3+-exchanged montmorillonite (Fe-mont). We will
show that Fe-mont as a cheap and reusable heterogeneous catalyst
exhibits higher activity and wider substrate scope than CeO2.
Results and discussion
We performed the reaction of benzamide and n-octylamine as a
model reaction to optimize the catalytic parameters. Table 1 sum-
marizes the results of the initial catalyst screening test under the
solvent-free condition (140 °C, 30 h, under N2) using different cata-
lysts including CeO2. Note that CeO2 showed the highest activity for
transamidation among 11 kinds of metal oxides tested in our previ-
ous study.19 Among the catalysts in Table 1, Fe-mont showed the
highest yield of the corresponding alkylamide. Thermal transamida-
tion hardly proceeded without any catalyst at 140 °C. Using Fe-
mont, increase in the amide/amine ratio from 1/1.1 to 1.1/1 resulted
in a decrease of the yield from 98% to 69%. This result suggests stron-
ger interaction of amide with the active site (Fe3+ Lewis acid site)
than amine during the reaction. From the time–yield profile
(Fig. S1), we adopted the reaction time of 30 h. Stoichiometric
amount of NH3 is produced and is mostly present in gas phase.
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Corresponding author. Tel.: +81 11 706 9240; fax: +81 11 706 9163.
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