Thermally decomposed Ni-Fe-hydrotalcite: A highly active catalyst for the solvent-free N-acylation of different amines by acid chlorides

Article abstract of DOI:10.1016/j.catcom.2011.05.015

A composite Ni-Fe catalyst obtained from the thermal decomposition of Ni-Fe-hydrotalcite at 600 °C shows very high activity in the solvent-free N-acylation of amines by different acid chlorides with high product yields under very mild reaction conditions (viz. room temperature, short reaction period and small amount of catalyst). The catalyst also shows excellent reusability in the reaction. The crystalline phases present in the catalyst are mixed oxides and hydroxides of nickel and iron. The high catalytic activity of the decomposed Ni-Fe-hydrotalcite is attributed to the formation of uniformly distributed Ni-Fe metal oxides and hydroxides.

Full text of DOI:10.1016/j.catcom.2011.05.015

Catalysis Communications 12 (2011) 1351–1356
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Catalysis Communications
journal homepage: www.elsevier.com/locate/catcom
Short Communication
Thermally decomposed Ni-Fe-hydrotalcite: A highly active catalyst for the
solvent-free N-acylation of different amines by acid chlorides
⁎
V.R. Choudhary , D.K. Dumbre
Chemical Engineering and Process Development Division, National Chemical Laboratory, Pune, 411008, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 15 April 2011
Received in revised form 12 May 2011
Accepted 15 May 2011
Available online 23 May 2011
A composite Ni–Fe catalyst obtained from the thermal decomposition of Ni-Fe-hydrotalcite at 600 °C shows
very high activity in the solvent-free N-acylation of amines by different acid chlorides with high product
yields under very mild reaction conditions (viz. room temperature, short reaction period and small amount
of catalyst). The catalyst also shows excellent reusability in the reaction. The crystalline phases present in
the catalyst are mixed oxides and hydroxides of nickel and iron. The high catalytic activity of the decomposed
Ni-Fe-hydrotalcite is attributed to the formation of uniformly distributed Ni–Fe metal oxides and hydroxides.
© 2011 Elsevier B.V. All rights reserved.
Keywords:
Amines
Acid chlorides
Ni-Fe-hydrotalcite derived catalyst
Decomposition of Ni-Fe-hydrotalcite
N-acylation of amines
1. Introduction
and, moreover, the reaction involves the use of ethyl acetate (as a
solvent) and expensive acid anhydride. Hence there is a genuine
Acylation of amines is among the most widely used transfor-
mations in organic synthesis. N-acylated amines and their derivatives
are widely used as starting materials for various organic transfor-
mations. The N-acylation of amines also provides an efficient and
inexpensive means to protect their –NH groups in a multistep
organic synthesis [1,2]. Earlier N-acylation was usually carried out
using acylating agents, such as acid anhydrides or acyl chlorides in
presence of organic bases [2–7]. This base catalyzed N-acylation is
slow and requiring harsh and cumbersome procedures. As an
alternative to basic catalysts, recently homogeneous Lewis acid
(such as ZnCl2, FeCl3, MoCl5, B(C6F5)3[8] and anhydrous NiCl2[9]) and
iodine [10] have been reported for the N-acylation under solvent-
free conditions. However, these homogeneous catalysts are difficult
to remove from the reaction mixture and also cannot be reused.
Hence they are not environmentally benign. Moreover, most of them
need expensive acylating agent such as acid anhydride [8,9].
Heterogeneous catalysts, such as magnesium oxide [11] and yttria-
zirconia [12], have also been reported for the N-acylation of amino
compounds. However, although these catalysts can be easily
separated, they require solvent and/or harsh reaction conditions
(higher temperature and/or higher reaction time). Non-catalytic
procedure for N-acylation at room temperature has also been
reported [13]. But in this case, the acylation period is very long
a
b
c
d
b)
a)
e
b’
a
b
c
d
e
2θ
Fig. 1. XRD spectra of catalyst obtained from the thermal decomposition of a) Ni-Fe-HT
and b) Ni(II)-Fe(III) nitrates, at 600 °C [Crystalline phases: a) Fe(OH)3, b) Ni(OH)2,
c) Nioxide-OH-Fe, d) NiO, e) Ni-Fe-Oxide and b') Fe2O3].
⁎
Corresponding author. Tel.: +91 20 25902318; fax: +91 20 25902612.
E-mail addresses: vr.choudhary@ncl.res.in, vrc0001@yahoo.co.in (V.R. Choudhary).
1566-7367/$ – see front matter © 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.catcom.2011.05.015

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V.R. Choudhary, D.K. Dumbre / Catalysis Communications 12 (2011) 1351–1356
need for developing a simple but rapid and environmentally benign
method for the N-acylation of amines.
In this paper we report a solvent-free rapid selective N-acylation of
aliphatic, cyclic and aromatic amines with inexpensive acid chlorides
at room temperature using a highly active solid catalyst derived from
Ni-Fe-hydrotalcite. The catalysts can be easily separated and reused
several times in the reaction.
2. Experimental
The solid catalyst used in this investigation was obtained from the
thermal decomposition of Ni-Fe-hydrotalcite (Ni/Fe mole ratio of 3.0)
in a muffle furnace at 600 °C for 4 h. The resulting mass was finely
powdered. The preparation and characterization of Ni-Fe-hydrotalcite
have been given in our earlier publications [14,15].
The catalyst was characterized for crystalline phases by XRD (using
a Phillips Diffractometer (1730 series) and CuK∝ radiations), particle/
crystal size by SEM (using Stereo Scan 440 made in Cambridge UK).
Its formation was studied by the thermal analysis (TG, DTG and DTA)
of the Ni-Fe-hydrotalcite from 100 °C to 1000 °C at a linear heating
rate of 20 °C/min in air (using Diamond TG/DTA).
The catalytic N-acylation reaction was carried out in a magneti-
cally stirred round bottom flask (capacity: 25 cm3), at the following
reaction conditions: reaction mixture=5 mmol amine+7 mmol
acid chloride+catalyst (10 wt.% w.r.t. amine) at room temperature
(300 K) and reaction time=1–30 min. Reaction was monitored by
TLC. After completion of the reaction, the catalyst was separated by
filtration and the filtrate was treated with a saturated solution of
sodium bicarbonate, followed by extraction with ethyl acetate to give
the crude product, which was subsequently purified by column
chromatography on silica gel with petroleum ether/ethyl acetate as
eluent. The catalyst was further washed with acetone, dried and
reused. The reaction product was isolated by column chromatography
and was confirmed by NMR spectroscopy.
Fig. 2. TG, DTG and DTA of the Ni-Fe-hydrotalcite.
3. Results and discussion
3.1. Catalyst formation and characterization
The catalyst was obtained from the thermal decomposition of Ni-
Fe-HT (Ni/Fe=3, CO32− concentration=0.66 mmol/g, surface area=
60 m2/g) [14] at 600 °C. The XRD of the catalyst (Fig. 1a) revealed that
the hydrotalcite structure is totally destroyed after decomposition
of the Ni-Fe-hydrotalcite. The main crystalline phase present in the
catalyst were found to be uniformly distributed Fe(OH)3, Ni(OH)2, Ni-
oxide-OH-Fe, NiO and Ni-Fe-Oxide. The phases are expected to be
uniformly distributed in the catalyst.
In order to study the catalyst formation, the Ni-Fe-HT was
subjected to thermal analysis from 100 °C to 1000 °C. The TG, DTG
and DTA graphs for the same are presented in Fig. 2. The TG, DTG and
DTA curves indicate that the decomposition is endothermic and it
occurs in two distinct steps- step-I between 100 °Cand 300 °C, with
the DTG and DTA peaks at 185 °C and 200 °C, respectively, and step-II
between 300 °C and 900 °C, with the DTG and DTA peaks at 330 °C
and 340 °C, respectively. The weight loss in step-I and step-II was
about 16% and 67.5%, respectively. The weight loss up to the temper-
ature of 400 °C was quite fast. The weight loss in step-I is expected due
to loss of physically adsorbed water in the hydrotalcite. Whereas,
Fig. 3. SEM Photograph of catalyst obtained from the thermal decomposition of a)Ni-Fe-
HT and b) physically mixed Ni(II)-Fe(III) nitrates (Ni/Fe=3)at 600 °C.
Scheme 1. N-acylation of amines.

V.R. Choudhary, D.K. Dumbre / Catalysis Communications 12 (2011) 1351–1356
1353
Table 1
N-acylation of amines with different acid chlorides at room temperature using thermally decomposed Ni-Fe-HT catalyst, under solvent-free condition.
Entry
Substrate
2
Acid chlorides
Product
4
Reaction time (min)
Isolated product yield (%)
1
1
3
5
1
6
CH3COCl
95
2
CH3COCl
1
97a
3
C6H5COCl
4
95
4
CH3CH2COCl
1
89
5
CH3CH2CH2COCl
2
91
6
4
91
CH3(CH2)3CH2COCl
7
CH3(CH2)5CH2COCl
4
89
(continued on next page)

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V.R. Choudhary, D.K. Dumbre / Catalysis Communications 12 (2011) 1351–1356
Table 1 (continued)
Entry
Substrate
2
Acid chlorides
Product
4
Reaction time (min)
Isolated product yield (%)
1
8
3
5
2
6
CH3COCl
88a
9
CH3COCl
4
88a
10
CH3COCl
3
87a
11
CH3COCl
4
87a
12
CH3COCl
4
89a
13
C6H5COCl
6
85a
14
15
CH3COCl
CH3COCl
5
5
78a
80a

V.R. Choudhary, D.K. Dumbre / Catalysis Communications 12 (2011) 1351–1356
1355
Table 1 (continued)
Entry
1
Substrate
2
Acid chlorides
Product
4
Reaction time (min)
Isolated product yield (%)
3
5
7
6
16
CH3COCl
87a
17
CH3COCl
7
70a
18
CH3COCl
1
64b
19
CH3COCl
1
68c
a
AcCl (3.0 eq.) was used.
Ni-Fe-HT without decomposition was used.
Catalyst obtained from the decomposition of a mixture of Ni(II) nitrate and Fe(III) nitrate (with Ni/Fe mole ratio of 3.0) at 600 °C for 4 h.
b
c
the weight loss in step-II is expected due to the decomposition of
the hydrotalcite, leading to a fast evolution of CO2 at the lower
temperatures (300 °C to 400 °C) followed by a slower dehydroxyla-
tion at the higher temperature (above 400 °C). The presence of dif-
ferent crystalline phases in the catalyst is consistent with this.
The catalyst has also been characterized for its particle/crystal size
by SEM (Fig. 3a). Its crystal size varies from about 0.1 to 2 μm.
Since Ni(II) and Fe(III) are uniformly distributed in the hydro-
talcite, both of them are also expected to be uniformly distributed in
the decomposition product (i.e. the catalyst) from the hydrotalcite.
– The acylation of cyclic amine is slower (entries 1, 12, 13).
– The increase in the relative concentration of acetyl chloride results
in a higher product yield (entries 1, 2). This is expected because of
the high volatility of acetyl chloride.
It may be noted that, when the Ni-Fe-HT was directly used as a
catalyst, the product yield in the same period was much smaller (entry
18). This is expected because of the very strong adsorption of acetyl
chloride on the highly basic hydrotalcite [14]. Also, when the thermally
decomposed (under similar conditions) mixed Ni–Fe nitrates were
used as the catalyst in the acylation, the product yield was much
smaller (entry 19). This may be due to the formation of solid catalyst
with non-uniform distribution of Ni(II) and Fe(III) and/or the presence
of Fe2O3 (which found to be absent in the decomposition product of
the Ni-Fe-HT) in this catalyst. [Fig. 1a, b].
3.2. Catalytic N-acylation of amines
Results of the N-acylation of different aliphatic, cyclic and aromatic
amines by different acid chlorides over the catalyst at room temper-
ature under solvent-free condition (Scheme-1) have been presented
in Table 1. The catalyst showed very high activity and selectivity in all
the cases. The time required for completing the acylation is, however,
found to be dependent upon the acylating agent and/or the substrate,
as follows:
It may also be noted that the catalyst derived from the Ni-Fe-HT
can be easily separated from the reaction mixture. It also shows
Table 2
Reuse of the Ni-Fe-HT catalyst in the N-acetylation of aniline with acetyl chloride.
– The acetylation by acetyl chloride is much faster than the
benzoylation by benzoyl chloride (entries 1 and 3).
– The acylation is slower with increasing the hydrocarbon chain
length of the acid chloride (entries 1, 4–7).
– As expected the electron withdrawing group (NO2) on the benzene
ring causes a large decrease in the acylation rate (entries 9–11).
Reuse of catalyst
Reaction time (s)
Isolated product yield (%)
First reuse
60
60
61
63
65
95
95
95
94
94
Second reuse
Third reuse
Fourth reuse
Fifth reuse

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V.R. Choudhary, D.K. Dumbre / Catalysis Communications 12 (2011) 1351–1356
excellent reusability in the N-acylation; even in the fifth reuse, it does
not loose its initial activity (Table 2). The observed small increase in
the reaction time is expected mostly due to loss of catalyst during its
processing. Thus, this catalyst is much superior to the earlier reported
homogeneous catalysts [8–10]. It also shows much higher activity,
requiring much lesser reaction time and/or temperature in the N-
acylation, than the earlier reported heterogeneous catalysts [11,12].
Acknowledgements
VRC and DKD are grateful to the National Academy of Sciences
(India) for the NASI Sr. Scientist Platinum Jubilee Fellowship and
Project Assistantship, respectively and also to Mr. Jha and Gaikwad
both from NCL, Pune) for their help in the thermal analysis and SEM
studies.
References
4. Conclusions
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in the N-acylation of different aliphatic, cyclic and aromatic amines
with different acid chlorides under solvent-free conditions at room
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