Transamidation catalysed by a magnetically separable Fe3O4 nano catalyst under solvent-free conditions

Article abstract of DOI:10.1039/c6ra07149j

An environmentally benign protocol for transamidation of carboxamides with different amines under solvent free conditions using magnetically separable nano Fe₃O₄ as a heterogeneous catalyst is developed. The series of aryl and alkyl amines with long chain alkyl substituents have been selectively converted into transamide products. The current protocol offers a diverse substrate scope with good yield of the product. The Fe₃O₄ nano catalyst has also been used for formylation of amines via transamidation of dimethyl formamide. Efficient transamidation, ease of work up, simple separation and reusability of the catalyst for up to six runs are the important highlights of this process.

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Transamidation catalysed by magnetically separable Fe3O4 nano
catalyst under solvent-free condition
Received 00th January 20xx,
Accepted 00th January 20xx
a
Pranila B. Thale‡ , Pravin N. Borase‡a and Dr. Ganapati S. Shankarling*a.
An environmentally benign protocol for transamidation of carboxamides with different amines under solvent free
condition using magnetically separable nano Fe3O4 as a heterogeneous catalyst is developed. The series of aryl and alkyl
amines with long chain alkyl substituents have been selectively converted into transamide products. The current protocol
offers diverse substrate scope with good yield of the product. Fe3O4 nano catalyst have also been used for formylation of
amines via transamidation of dimethyl formamide. Efficient transamidation, ease of work up, simple separation and
DOI: 10.1039/x0xx00000x
www.rsc.org/
reusability
of
catalyst
up
to
six
runs
are
the
important
highlights
of
this
process.
Beckmann rearrangement31,32, amidation of thio acids with
azides33and aminocarbonylation process. Most of these
methods suffer from limitations such as harsh reaction
conditions, tedious work up procedure and low reactivity.
Therefore, transamidation has gained considerable interest as
the most convenient route for the synthesis of secondary or
tertiary amines through tandom process. Unfortunately,
transamidation is a fairly unusual reaction because of high
stability and inert nature of amides. Usually, high temperature
and long reaction time is required to cleave the amide bond.
There are several reports for transamidation using new
homogeneous and heterogeneous catalysts34–38. Stahl et al.
have reported Al (III), Sc(III) and group 4 metal complex as a
homogeneous catalyst which works under milder conditions.
Despite the advances achieved by all these methods, there is
difficulty in the separation, recycle and reuse of these catalysts
from the product. Copper diacetate39 and boric acid40 have
also been reported as homogeneous catalysts for effective
transamidation. Nevertheless, their major shortcomings are
long reaction time and difficulty in recycling. To overcome the
issue of separation, Shi et al41 have reported HfCl4 supported
heterogeneous catalyst. This method also has limitations like
need of the strong base and limited substrate scope as it has
been reported that reactions were unproductive with aliphatic
amines.
1. Introduction:
There is an increasing need of a sustainable, efficient and
greener route for the development of high quality products1.
In this respect, nanoparticles have emerged as an important
tool in many organic reactions2–4. The use of nano catalysts for
different organic reactions is ever increasing. But, the major
problem in the use of nano catalysts is its tedious recycling
procedure and loss of the catalyst in the handling process.
Superparamagnetic Fe3O4 nanoparticles have attracted
considerable attention all over the world due to wide
biological5–7 and technological applications8,9. It has significant
characteristics such as ease of separation from the reaction
media by use of a simple magnet and facile recycling process10-
12. Therefore, there is growing interest for the use of Fe3O4
nanoparticles
as
a
catalyst
in
many
organic
transformations13,14
.
Amide functionality is one of the fundamental building block
found in nature15,16. It is commonly present in natural products
and synthetic compounds17. It is useful as a versatile building
block in the preparation of bioactive products such as
peptides, peptidomimetics and in proteins to make up the
peptide bonds. It is also used in drugs or drug intermediates,
polymers, agrochemicals and in organic materials18–21. There
are several synthetic routes available for their synthesis.
Generally, synthesis of amide involves reaction of activated
carboxylic acid derivatives such as chloride, anhydride or ester
with amines22,23. Other reactions include hydroamination of
Although, there are efficient reports to dictate transamidation,
little attention has been given for the development of
heterogeneous, recyclable catalysts. In continuation of our
efforts on the development of green and sustainable
methods42 herein, we report a simple and efficient protocol for
transamidation of carboxamides and phthalimide with various
amines in the presence of Fe3O4 nano catalyst. We have also
described the application of Fe3O4 nano catalyst for the direct
formylation of various amines using N,N- dimethyl formamide
(DMF) as a formylation agent.
alkynes24–26, hydration of nitriles27–29 Schmidt reaction30,
,
a Dyestuff Technology Department,
Institute of Chemical Technology, Mumbai 400019, India.
Tel: 91-22-33612708, Fax: +91-22-33611020
E-mail address: gsshankarling@gmail.com
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aReaction condition: amide (1 mmol), amine (1.2 mmol); catalyst: 20 wt. %,
solvent 2ml, in a seal tube, 8h, bisolated yields.; cReaction time 24 h for entry 1;
dReaction performed with 10, 15 and 25 wt. % of the catalyst in entries 9-11;
eReaction performed in absence of the catalyst.
2. Result and discussion:
In the present study, we have reported an efficient and
industrially viable method for transamidation. Initially, we
began our study with benzamide and benzyl amine as a model
⁰
With these optimised conditions in hand, the general
applicability and efficiency of this protocol was demonstrated
by a wide substrate study with various amines. As shown in
table 2, both electron donating and withdrawing groups
present on the benzyl amine provided good to excellent yield
of the transamidation product (76-93%). Reaction of
benzamide with dodecyl amine and butyl amine gave the
desired product in 87% and 90% yield respectively in 3 h.
However, the reaction rate was found to be slow between
benzamide and less nucleophilic amines, giving 68 to 70%
yield, in 24 h.
substrate using nano-Fe3O4 as a catalyst in toluene at 120 C
but no product formation was observed after 24 h (Table 1,
entry 1). Reactions were performed in different solvents such
as xylene, DMSO, diglyme, water and chlorobenzene but, no
improvement in the yield was observed (Table 1, entry 2-6). To
our delight, when we performed the reaction under neat
⁰
condition at 120 C, 29% yield of the product was observed
⁰
(Table 1, entry 7). On increasing the temperature to 140 C,
increase in the yield to 91% was noted (Table 1, entry 8). We
have also performed the catalyst loading study, but decrease
in the yield was observed on decreasing the catalyst loading
(Table 1, entry 9, 10). Whereas, on increasing the amount of
the catalyst to more than 20 wt. %, no improvement in the
yield was observed (Table 1, entry 11). Hence, the optimised
Table 2: Scope of transamidation of benzamide with various aminesa.
⁰
reaction conditions include 20 wt. % catalyst, at 140 C for 8 h
under neat condition. Furthermore for comparison, the model
reactions were carried out in presence of different catalysts
such as Al2O3, MgO, ZnO under similar reaction conditions but
no appreciable yield was observed (Table 1, entry 12-14).
⁰
When the reaction was performed without catalyst at 140 C,
only 28% of the desired product was obtained. This suggests
that the catalyst plays a major role in the reaction. The rate of
reaction was faster due to the nano form of the catalyst. When
the reaction is performed under a neat condition, better
diffusion of nano Fe3O4 catalyst in the reaction mixture was
observed. Due to which substrate are directly adsorbed on the
surface of the catalyst resulting in increased rate of the
reaction and higher yield of the product. However, in presence
of different solvents, comparatively less active sites are
available because of which traces yield of the product were
obtained.
aReaction condition: amide (1 mmol), amine (1.2 mmol), 20 wt. % catalyst,
⁰
seal tube, time: 8 h, temperature: 140 C, isolated yield; btemperature: 100
°C, bReaction time: 3h; cReaction time: 24 h.
Table 1: Optimisation of reaction conditiona.
Table 3: Scope of transamidation of aliphatic amide with various aminesa.
Isolated
Entry
Catalyst
Temperature
Solvent
Yieldb
Nil
1c
2
3
4
5
6
7
8
Fe3O4
Fe3O4
Fe3O4
Fe3O4
Fe3O4
Fe3O4
Fe3O4
Fe3O4
Fe3O4
Fe3O4
Fe3O4
Al2O3
MgO
ZnO
120
120
130
130
110
120
120
140
140
140
140
140
140
140
140
Toluene
Xylene
DMSO
Diglyme
Nil
traces
traces
Nil
Water
Chlorobenzene
Traces
29%
91%
70%
79%
91%
78%
82%
80%
28%
-
-
-
-
-
-
-
-
-
9d
10d
11d
12
13
14
15e
aReaction condition: aliphatic amide (1mmol), amine (1.2mmol), 20 wt.
catalyst, seal tube, time: 1 h, temperature: 100 °C, isolated yield.
%
-
To ascertain the scope of the transamidation process, we
carried out the reaction of aliphatic amide namely, formamide
and acetamide with different amines Table
3 (electron
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donating and electron withdrawing). The reaction proceeded
⁰
smoothly under milder condition at 100 C in 1 h. Under this
condition, aliphatic amides like acetamide and formamide
were reacted with various amines to obtain the desired
products in good to excellent yields (76-92%).
Phthalimide is a potential precursor in pesticide, medicine and
many dye intermediates. Thus, after successful transamidation
of benzamide, we attempted transamidation of phthalimide
with different amines (benzyl, aliphatic and cyclic amines)
(Table 4). All the amines reacted smoothly and gave the
Figure 1: Recyclability study of the Fe3O4 nano catalyst.
corresponding N-substituted derivative in good yield (75-91%).
Table 5: Scope of N-formylation of amines using N,N-dimethylformamide
Thus, this methodology has broad applicability.
as formylation agenta.
Table 4: Transamidation of phthalimide with various aminesa.
Scheme-5
O
Scheme - 4
N
H
H
N
Fe3O4, DMF
140oC, 18h
R1
R1 NH2
N
H
O
O
H
O
R1
H
Fe3O4 (20%)
(5a-5h)
NH
N
H
N
R1 NH3
O
O
O
Neat, 140oC, 5h
O
O
N
H
H
N
H
N
H
H
H
(4a-4f)
O
F
5a; 91%
O
N
O
N
O
5c; 89%
O
5b; 76%
O
O
H
N
N
H
H
NH
N
H
H
O
O
O
O
4a; 90%
4b; 91%
4c; 84%
O
F
5f; 85%
O
5e; 78%
NC
5d; 87%
H
O
N
O
O
N
O
O
N
N
H
N
H
10
H
O
O
5h; 72%
5g; 93%
4e; 90%
4d; 75%
4f; 89%
aReaction condition: amine (1.5 mmol), DMF: 2ml, 20 wt. % catalyst, seal tube,
time: 18 h, temperature: 140 °C, isolated yield.
aReaction condition: phthalimide (1 mmol), amine (1.2 mmol), 20 wt. % catalyst,
⁰
seal tube, time: 5 h, temperature: 140 C, isolated yield.
To assess the recyclability of the catalyst, we examined the
After efficacious transamidation of benzamide under neat transamidation of benzamide with benzyl amine under the
condition, we were keen to know whether N,N-dimethyl optimised condition. The results are summarised in figure 1.
formamide (DMF) could be used for direct formylation of After completion of the reaction, the catalyst was separated by
⁰
include an external magnet, washed with methanol and dried at 60 C
amines.
Recent
literature
reports
44
HCONH2/NH2OH.HCl43, HCONH2/Cp2ZrCl2
and use of for 1 h. The recovered catalyst was then used for the next
carboxylic acid in presence of protic ionic liquids45. However, batch. It was observed that catalyst could be recycled
these methods require longer reaction time, high catalyst efficiently up to six runs. This study indicates potential
loading or anhydrous condition for the reaction. Hence, we application of nano Fe3O4 as a heterogeneous catalyst for
prophesied that Fe3O4 mediated transamidation using DMF transamidation reaction with wide substrate scope under neat
may be advantageous for direct formylation of amines. condition. Figure 2 and 3 show TEM and SEM images of the
Therefore, we have performed the reaction of benzyl amine in fresh and reused catalyst. Although, slight aggregation of the
presence of DMF with 20 wt. % of the Fe3O4 catalyst. The catalyst was observed in the SEM image due its magnetic
reaction was completed in 18 h. In this reaction, DMF plays a nature, there is no change in the surface morphology and size
of the catalyst after 6th recycle.
dual role of solvent as well as formylation agent. The reaction
was performed with various aliphatic, aromatic amines in
presence of DMF and Fe3O4 as a catalyst (Table 5). In the
formylation of benzyl amine derivatives, the electronic effect
of the substituent had no effect on the yield of product. It
offered good to excellent yield of the targeted product (72-
93%).
Figure 2: TEM images of Fe3O4 nano catalyst before use (a) and after six runs (b)
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O
O
H
N
R
R2
NH3
+
R
N
H
R1
Fe3O4
R1
H
O
H
R
N
H
R2
H
N
N
R
H
O
Fe3O4
Fe3O4
R1
H
N
Intermediate Step- III
R2
Intermediate Step- I
Fe3O4
Figure 3: SEM images of Fe3O4 nano catalyst before use (a) and after six runs (b).
-
3. Characterisation of the catalyst:
The Fe3O4 nano catalyst was prepared according to previously
O
R1
H
H
+
N
N
R
reported literature method46
The XRD pattern of the Fe3O4
.
R2
H
Intermediate Step- II
nanoparticle is shown in Figure 4. A number of Bragg
reflections by their indices (220), (311), (400), (422), (551) and
(440) indicate the cubic crystal phase of Fe3O447. TEM image of
the catalyst displays dark Fe3O4 core with spherical surface
morphology and average particle size between 13-15 nm
(Figure 2a). This nano size of Fe3O4 provides higher surface
area and active sites, resulting in faster reaction rate. The SEM
image of the Fe3O4 nano particles is shown in Figure 3a. It
shows that they have spherical morphology and it has marked
tendency to form large aggregates due to magnetic
characteristics.
Figure 5: Plausible reaction mechanism
5. Conclusion:
In summary, we have developed an efficient protocol for
transamidation of carboximide under solvent free condition
using heterogeneous nano catalyst. A wide range of aliphatic,
aromatic and benzylic amines could be efficiently converted
into their transamidation products with good to excellent
yield. Along with this, the ease of separation and reusability of
the catalyst are the added advantages of this process. The
developed protocol is simple, green and economically viable.
Experimental:
General procedure for transamidation:
A mixture of amide (1 mmol), amine (1.2 mmol) and Fe3O4 (20
wt.%) was stirred in a sealed tube at specified temperature for
specified reaction time (scheme 1-4). After completion of the
reaction (monitored by TLC), the reaction mixture was cooled
to room temperature and dissolved in ethyl acetate. The
catalyst was separated from the reaction mixture by an
external magnet. The crude reaction mass was concentrated
and then purified by column chromatography using hexane
and ethyl acetate as eluent.
Figure 4: XRD images of Fe3O4 nano catalyst
General procedure for formylation using DMF:
4. Plausible reaction Mechanism:
A mixture of benzyl amine (1.5 mmol), N, N- dimethyl
⁰
formamide and Fe3O4 (20 wt. %) was stirred at 140 C for 18 h
Based on the present experimental results and literature
reports40,43,48, it is supposed that catalytically active site of
Fe3O4 is Fe3+ which behaves as Lewis acid and coordinates to
the carbonyl group of amide to form intermediate step-I. Then,
nucleophilic attack by an amine at the carbonyl centre of the
activated amide intermediate step-I generates intermediate
step-II. It is subsequently followed by a rearrangement to give
intermediate step-III, which is then followed by elimination of
ammonia to yield the desired product, thus regenerating the
Fe3O4 catalyst (Figure 5).
in a sealed tube (scheme 5). After completion of the reaction
(monitored by TLC), the reaction mixture was cooled to room
temperature and dissolved in dichloromethane. The catalyst
was separated from the reaction mass by an external magnet.
Water was then added to the reaction mixture to remove
excess of DMF and then reaction mass was extracted into
dichloromethane. The combined organic layer was dried over
anhydrous Na2SO4 and concentrated. The residue was
subjected to column chromatography to obtain the pure
desired product (eluent hexane and ethyl acetate).
Acknowledgements
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Authors are thankful to UGC-SAP, Technical Education Quality
Improvement Programme, for providing financial assistance.
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DOI: 10.1039/C6RA07149J
Transamidation catalysed by magnetically separable Fe3O4 nano catalyst under solvent-
free condition.
Graphical abstract