An efficient hydration of nitriles to amides in aqueous media by hydrotalcite-clay supported nickel nanoparticles

Article abstract of DOI:10.1016/j.catcom.2012.09.014

Hydrotalcite-clay supported nickel nanoparticles catalyze hydration of nitriles to amides in aqueous media. This Ni NPs/HT system is efficient for the synthesis of a diverse range of amides and affords the expected products with good yields in aqueous media. The synthesized nickel nanoparticles are characterized by UV-DRS, powder XRD, SEM and HRTEM. The catalyst is reused at least three times and a plausible mechanism is proposed. This fast, simple, effective and environmentally benign heterogeneous protocol provides a safer alternative to hazardous, corrosive and more polluting conventional catalysts.

Full text of DOI:10.1016/j.catcom.2012.09.014

Catalysis Communications 29 (2012) 109–113
Contents lists available at SciVerse ScienceDirect
Catalysis Communications
journal homepage: www.elsevier.com/locate/catcom
Short Communication
An efficient hydration of nitriles to amides in aqueous media by hydrotalcite-clay
supported nickel nanoparticles
⁎
Thirumeni Subramanian, Kasi Pitchumani
School of Chemistry, Madurai Kamaraj University, Madurai-625021, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 24 July 2012
Received in revised form 12 September 2012
Accepted 13 September 2012
Available online 20 September 2012
Hydrotalcite-clay supported nickel nanoparticles catalyze hydration of nitriles to amides in aqueous media.
This Ni NPs/HT system is efficient for the synthesis of a diverse range of amides and affords the expected
products with good yields in aqueous media. The synthesized nickel nanoparticles are characterized by
UV-DRS, powder XRD, SEM and HRTEM. The catalyst is reused at least three times and a plausible mechanism
is proposed. This fast, simple, effective and environmentally benign heterogeneous protocol provides a safer
alternative to hazardous, corrosive and more polluting conventional catalysts.
Keywords:
Hydration
Nitriles
© 2012 Elsevier B.V. All rights reserved.
Amides
Hydrotalcite
Ni nanoparticles
Water
1. Introduction
the way to advance the hydration reaction in aqueous medium, the
protocol still needs traditional workup, using organic solvents to
The amide bond is a ubiquitous functional group in contemporary
chemistry. It is essential to sustain life, making up the peptide bonds in
proteins such as enzymes [1], present in many natural products and is
one of the most prolific moieties in many pharmaceuticals. Among the
many ways of constructing the amide bonds, use of metal-catalyzed
methods are of growing interest. Acids and esters have been used for
preparation of amides in coupling reaction with amines, but aldehydes
and alcohols are also used in oxidative couplings [2]. The use of nitriles
and oximes as starting materials for amide formation is emerging areas
of interest [3–6]. However, the synthesis of amides from aldoximes is
challenging and involves the use of reagents in stoichiometric quantities
or more. The most common traditional method for the synthesis of
the amides is treatment of activated carboxylic acid with amines.
Hydration of nitriles is an important reaction because of their
usefulness in a wide variety of applications in organic syntheses
[7–10]. For example, hydration of acrylonitrile produces annually
more than 2×105 t of acrylamide [11]. Homogeneous hydration of
nitriles is traditionally carried out with acids such as H2SO4 [12].
Several homogeneous metal and metal oxide catalysts, such as Ru
[13–18], Rd [19,20], Au [21], Os [22], Pt [23], Pd [24], Ir [25], Mo
[26,27], Fe [28], Co [29], Cu [30], Ag [31] and CeO2 [32] have also
been reported for the hydration of nitriles. However, these systems
have drawbacks such as difficulty in catalyst/product separation
and very limited scope in catalyst reuse. Although these works led
isolate the product.
Nanoparticles have emerged as sustainable alternatives to con-
ventional materials, as robust, high surface area heterogeneous cata-
lysts [33,34] and catalyst supports [35,36]. The nano-sized particles
possess higher surface, thereby enhancing the contact between reac-
tants and catalyst dramatically. In recent years, work in the field of
metal and metal oxide nanoparticles such as Au, Ag and Pd as cata-
lysts in synthetic organic chemistry has gained much attention
[37–39]. However Au NPs are highly expensive and Ag NPs are mois-
ture and light sensitive. On the other hand, Ni NPs are found to be
more specific and are complementary to their Pd analogues. Due to
their air stability, ease of preparation and separation of the catalyst
mixture from the products at the end of the reaction sequence, ease
of recyclability and smaller size compared to Pd [40], Ni NPs have
been found to be better catalysts than Pd.
HT is a multifunctional material which has cation-exchange abil-
ity in the brucite layer, an anion-exchange ability in the interlayer
and a tunable basicity of the surface [41–46]. Thus, the interaction
of the introduced metal cations (M1) with other cations (M2)
through M1\O\M2 bonds would lead to unique catalytic reactions in-
volving functionalised hydrotalcites. Recently, new strategies for the
design of solid heterogeneous catalysts by utilizing HTs supported
metal nanoparticles for various organic transformations such as dehy-
drogenation of alcohols (Cu, Ag, Au) [47–49], synthesis of ammonia
(Ru) [50] and alkyne semihydrogenation (Pd) [51]. Kaneda et.al. [52]
have reported hydroxyapatite-supported silver nanoparticles as cata-
lysts for hydration of nitriles to amides in water. Along with other the
⁎
Corresponding author. Tel.: +91 0452 2456614.
E-mail address: pit12399@yahoo.com (K. Pitchumani).
1566-7367/$ – see front matter © 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.catcom.2012.09.014

110
T. Subramanian, K. Pitchumani / Catalysis Communications 29 (2012) 109–113
Table 1
transition metals, nickel nanoparticles, with their well known magnetic,
electronic and catalytic activities, enjoy significant advantages and ap-
plications [53–55].
Optimization of reaction conditions in synthesis of benzamide from benzonitrile.a
Our interest in development of heterogeneous catalyst supports
[56,57] as inexpensive and green reagents for organic transforma-
tions [58] which enjoy advantages such as a fast and simple isolation
of the reaction products by filtration, recyclability and minimization
of metallic waste, prompted us to report, for the first time, the use
of Ni nanoparticles supported on HT, as a heterogeneous and reusable
catalyst for hydration of nitriles to amides in the presence of water
with complete absence of explosive, hazardous and carcinogenic or-
ganic solvents. In comparison with other inflammable and toxic or-
ganic solvents, water serves as a superior solvent which is safe to
use in organic reactions.
Entry
Catalyst
Temp (°C)
Time (h)
Yield (%)b
TONc
1d
None
Mg(NO3)2·6H2O
MgCl2
MgO
Al(NO3)3·9H2O
Al2O3
AlCl3·6H2O
Al2(SO4)3·16H2O
TiO2
Mg–Al HT
Ni(OAc)2·4H2O
NiCl2·6H2O
Ni(NO3)2·6H2O
Ni–Y zeolite
Ni–K10-clay
Ni–Al–MCM-41
Ni/HT
Ni NPs/HT
Ni NPs/HT
Ni NPs/HT
Ni NPs/HT
Ni NPs/HT
Ni NPs/HT
Ni NPs/HT
Ni NPs/K10-clay
140
120
120
120
120
120
120
120
120
120
120
120
120
120
120
120
120
30
24
15
15
15
15
15
15
15
15
15
15
15
15
15
15
15
15
10
10
10
10
10
10
5
Nil
b10
10
Nil
15
Nil
12
10
21
23
28
30
24
33
31
35
41
Nil
23
Nil
b10
43
85
48
65
–
1
1
–
2
–
1
2
3
3
1
2
2
9
6
7
8
–
5
–
2
9
17
8
12
2e
3e
4e
5e
6e
7e
8e
9
10f
11e
12e
13e
14f
15f
16f
17f
18
19
20g
21h
22i
23j
24j
25
2. Experimental
2.1. General remarks
All reagents and starting materials were obtained commercially
from Aldrich and used without any further purification.
80
120
120
120
120
120
120
2.2. Preparation of hydrotalcite (HT) clay
Al(NO3)3·9H2O (0.01 mol) and Mg(NO3)2·6H2O (0.05 mol) are
dissolved in deionised water (100 ml) and added slowly to a solution
(60 ml) of Na2CO3 (0.03 mol) and NaOH (0.07 mol) with effective
stirring. The resulting mixture is heated at 65 °C for 18 h with vigor-
ous stirring. The white slurry is then cooled to room temperature, fil-
tered, washed well with deionised water and dried overnight at
110 °C.
10
a
Reaction conditions: benzonitrile 1 mmol, catalyst 50 mg, water 4 ml.
Isolated yield.
The moles of amides formed per mole of catalyst.
Without catalyst.
Reaction carried with 30 mg of aluminum and magnesium salts.
50 mg of the catalyst used.
Without solvent.
10 mg of the catalysts used.
30 mg of the catalysts used.
50 mg of the catalysts used.
b
c
d
e
f
g
h
i
j
2.3. Synthesis of hydrotalcite supported Ni nanoparticles (Ni NPs/HT)
To prepare the catalyst, 1.0 g of the HT is added to 10 ml of a
0.8 mmol of nickel nitrate in 50 ml of deionized water, then the pH is
adjusted to 8.0 with a solution of ammonia (25 wt.%), after which the
heterogeneous mixture is stirred for 5 h at room temperature. The
resulting slurry is filtered, washed thoroughly with deionized water
and dried in vacuum at room temperature to yield a green powder.
The HT-supported Ni2+ ions are reduced with sodium borohydride
(1 mmol) at 80 °C for 1 h. The color changes from green to black,
which indicates the formation of Ni(0)-HT nanoparticles. Nickel
nanoparticles supported on hydrotalcite are characterized by EDAX,
UV-DRS, XRD, SEM and HRTEM (Figs. S.2–S.5, supporting information).
3. Results and discussion
The Ni content in Ni NPs/HT about 5.83 atom % is obtained, deter-
mined by energy dispersive X-ray analysis (EDX). The average diam-
eter of Ni nanoparticles is estimated to be in the range of 1–4 nm
from HRTEM images.
After synthesis and characterization of hydrotalcite supported
nickel nanoparticles which are subsequently used for hydration of ni-
triles, the reaction parameters are optimized using benzonitrile as a
model substrate. Typical reaction parameters including various nickel
catalysts, time and temperature are screened and the results are sum-
marized in Table 1. Without any catalyst (Table 1, entry 1) and
2.4. Typical procedure for the Ni NPs/HT catalyzed hydration of nitriles to
amides
Table 2
Effect of solvents in the hydration of benzonitrile using Ni NPs/HT catalyst.a
Ni NPs/HT (0.05 g) is placed in a heavy-walled pressure tube,
followed by the addition of water (4 ml) and benzonitrile (1 mmol),
and the reaction mixture is vigorously stirred at 120 °C in an oil bath
for the specified time in tables. The progress of the reaction in each
case was monitored by TLC analysis. After completion of the reaction,
the reaction mixture is extracted with ethyl acetate, after the extraction,
the catalyst is removed by filtration, and the filtrate is cooled to 0 °C,
and white crystals are precipitated from the filtrate. The crystalline
product was obtained by simple filtration and dried in vacuo at room
temperature to give analytically amide product. In cases where the
product not precipitated out, the reaction mixture was extracted with
ethyl acetate, subsequent purification by column chromatography on
silica gel provided amide product.
Entry
Solvent
Time (h)
Yield (%)b
TONc
1
2
3
4
5
6
7
8
9
10
n-Hexane
Toluene
Acetonitrile
Dichloromethane
THF
Ethanol
Methanol
Ethanol/water (2/3)
Methanol/water (2/3)
Water
12
12
12
12
12
10
10
10
10
10
–
–
–
–
–
–
–
–
–
–
12
16
71
73
85
2
3
14
15
17
a
Reaction conditions: benzonitrile 1 mmol, Ni NPs/HT 50 mg, solvent 4 ml at 120 °C.
Isolated yield.
Moles of benzamide formed per mole of the catalyst.
b
c

T. Subramanian, K. Pitchumani / Catalysis Communications 29 (2012) 109–113
111
Table 3
Table 4
Hydrotalcite supported Ni nanoparticles (Ni NPs/HT) catalyzed hydration of nitriles to
Sheldon testa.
amides.a
Catalyst Ni NPs/HT
Time
6 h
48
6+6 h (without Ni NPs/HT catalyst)
49
Yield (%)b
a
Reaction conditions: benzonitrile 1 mmol, Ni NPs/HT 50 mg, water 4 ml at 120 °C.
Isolated yield.
b
Entry Nitrile
1
Amide
Time/h Yield (%)b TONc
(2a)
(2b)
10
15
85, 86d
17
16
solvents employed to optimize the reaction conditions (Table 2),
only water has the highest activity (Table 2, entry 10).
79
2
Under the optimized reaction conditions, the protocol is also extend-
ed to various nitriles. A large numbers of aromatic nitriles (Table 3, en-
tries 1–15) as well as an aliphatic nitrile (Table 3, entry 15) are
smoothly hydrated to the corresponding amide in excellent yield. Aro-
matic nitriles carrying either electron-donating such as p-methyl and
p-methoxy or electron-withdrawing such as p-bromo, chloro and
p-nitro groups exhibit comparable reactivity and react efficiently to
yield the final product. Usually, the hydration of heteroaromatic nitriles
is more difficult and the reaction rates are much lower than those of
common nitriles because of their strong coordination to the metal cen-
ters. In the present study, hydration of 3-cyano (87%) and
2-cyanopyridines (90%) and also 2-thiophenecarbonitrile (87%)
afforded the corresponding amides in near quantitative yields
(Table 3, entries 11–13). Hydration was found to be difficult with
bulkier organonitrile (Table 3, entry 14). Notably, the industrially
important hydration of acrylonitrile proceeded efficiently to afford
quantitative yield of acrylamide. Neither hydration of the carbon–
carbon double bond nor polymerization of acrylonitrile and/or acryl-
amide occurred (Table 3, entry 15). As it is important to justify that the
observed catalytic conversion is caused by solid Ni NPs/HT rather than
leached nickel species, the following control experiments were carried
out. The reaction stopped at 6 h, catalyst and the product are removed
from the reaction mixture by filtration. The filtrate is again heated for
another 6 h at 120 °C. No amide formation is observed (Table 4). The
observed results indicate that no appreciable leaching of metal ions in
the filtrate in the present reaction condition. It is also relevant to note
that, this heterogeneous Ni NPs/HT catalyst can be reused three times
with only a marginal loss of activity (Table 5).
(2c)
(2d)
(2e)
(2f)
(2g)
(2h)
(2i)
(2j)
(2k)
(2l)
15
17
15
17
15
14
24
17
10
10
80
77
75
71
81
84
72
65
87
90
80
70
88
16
16
15
14
17
17
15
13
18
18
16
14
18
3
4
5
6
7
8
9
10
11
12
13
14
(2m) 10
(2n)
(2o)
15
10
15
On the basis of the above results and also in accordance with ear-
lier literature reports [50,59], a plausible reaction pathway involving
the coordination of water and an aromatic nitrile on the Ni NPs sur-
face is proposed as shown in Scheme 1. In the first step of the mech-
anism, nitrile initially binds with Ni(0) species in the η2-mode (I) that
is typical for Ni(0) complexes [9]. This side on coordination of the ni-
trile groups on Ni nanoparticles on HT, is supported by shift of C`N
stretching vibration to higher frequency compared to their liquid
forms. Subsequent binding of water to Ni(0) (II) and nucleophilic at-
tack on C`N bond leads to intermediate (III). Tautomerism of the co-
ordinated imines produces the amide, which are readily removed
from Ni(0). Support for binding in η2-mode (π-binding) with Ni(0)
and unchanged oxidation state of nickel center in water media is
also reported in an earlier work by Garcia et. al. [9]. It is also relevant
to note that there is neither a change in color nor absorption spectra
noticed in the present study.
a
Reaction conditions: Substrate 1 mmol, Ni NPs/HT 50 mg, water 4 ml at 120 °C.
Isolated yield.
The moles of the amides formed per mole of the catalyst.
Yield of gram-scale reaction with benzonitrile (10 mmol).
b
c
d
catalyst alone without any solvent (Table 1, entry 19) no reaction oc-
curred at 120 °C. With various aluminium and magnesium catalysts
which are the sources for the preparation of hydrotalcite, the yield
of the desired product is very low (Table 1, entries 2–8). The catalytic
activity for the hydration of nitrile to amide in water at 120 °C is stud-
ied with magnesium and aluminium metal oxides with various nickel
salts such as nickel acetate, nickel chloride and nickel nitrate and poor
yields are obtained (Table 1, entries 10–12). We have also used het-
erogeneously supported nickel catalyst such as Ni–Y zeolite, Ni–Al–
MCM-41 and Ni–K10-clay and lesser amount (33%, 31% and 35% re-
spectively) of the product is observed (Table 1, entries 13–15).
When the hydration of benzonitrile is carried out at room tempera-
ture for 15 h using Ni NPs/HT, no reaction occurs. However, when
the reaction temperature is increased to 80 °C, the reaction proceeds
slowly with 23% conversion (Table 1, entry 18). When the tempera-
ture is increased to 120 °C, the product formation increased further
to 85% (Table 1, entry 22). When the amount of catalyst is varied
from 10, 30 to 50 mg, conversion of the hydration reaction is im-
proved significantly (Table 1, entries 20–22). Among the different
Table 5
Reusability of Ni NPs/HT catalyzed hydration of benzonitrilea.
Run
First (TON)b
80 (17)
Second (TON)b
77 (16)
Third (TON)b
75 (15)
Yield (%)c
a
Reaction conditions: benzonitrile 1 mmol, Ni NPs/HT 50 mg, water 4 ml at 120 °C.
The moles of the amides formed per mole of the catalyst.
Isolated yield.
b
c

112
T. Subramanian, K. Pitchumani / Catalysis Communications 29 (2012) 109–113
Table 6
Comparison with reported catalytic systems for hydration of nitriles.
Entry
Catalyst
Solvent
Temp (°C)
Time (h)
Yield (%)
Reusability of catalyst
1
2
3
4
5
6
7
8
Nanoferrite–[Ru(OH)]x [13]
[RuCl2(η6C6Me6)(PTA-Bn)] [16]
Ag NPs/HAP (0.1 g) [52]
[(IPr)Au(NTf2)] (2 mol%) [21]
CeO2 (0.03 g) [32]
H2O
H2O
H2O
H2O/THF
H2O/EtOH
DME
120 (MW)
100a
140–180
140 (MW)
30–100
180
0.5
61–85
>90
>90
39–99
5–99
>90
>90
>70
>90
>70
>90
>70
>70
3
1
4
1–4
0.5–6
2
1–24
0.3
6–18
12
24–72
24
NRb
3
Ru(acac)2(PPh2Py)2 (0.002 mmol) [17]
[(PCy3)(CO)RuH]4(0.034 g) [15]
Pd(OAc)2(10 mol%) [24]
[{Rh(OMe)(cod)}2]/PCy3 [11]
[RhOMe)(cod)]2Cy3P [19]
Ru(OH)x/Al2O3 (4 mol%) [14]
TFA-H2SO4 [12]
NR
NR
6
NR
4
2
NR
3
H2O
80–90
Refluxc
25d
H2O/EtOH
H2O+i-ProH
H2O+i-ProH
H2O
H2O
H2O
9
10
11
12
13
25e
140
RT
120
6–24
4–8
10–17
Ni NPs/HTf
a
5 mol% of the catalyst was used under N2 atmosphere.
Not reported.
PPh3(20 mol%) was used.
0.005 mol of catalyst used.
0.02 mol% of catalyst and benzoic acid (1%)/Na2CO3 (2.5%) used as additive.
Reaction conditions: benzonitrile 1 mmol, Ni NPs/HT 50 mg, water 4 ml at 120 °C.
b
c
d
e
f
Data on reaction conditions, activity and efficiency of the different
4. Conclusions
metal and metal nanoparticles for hydration of nitriles are given in
Table 6. Comparison of the results indicates that our catalytic system
(entry 13) exhibits better catalytic performance compared to other
conventional catalysts such as Ru, Ag, Pd, Ce, Au and TFA. These sys-
tems require additives (entry 10), external solvent (entries 9 and
10), higher reaction time (entries 5, 7, 9 and11), higher quantity of
catalyst (entry 3), higher temperature (entries 3, 6 and 1) and poor
reusability (entries 2, 4, 6, 7, 9, 11 and 12).
We have developed an efficient, atom economical and environmen-
tally friendly method for the synthesis of amides from nitriles using
nickel nanoparticles supported on heterogeneous hydrotalcite clay. A
suitable mechanism is proposed. Also this novel heterogeneous catalyst
reported for the first time is found to have advantages over the conven-
tional catalysts, due to their unique properties such as reusability, ease
of handling, cost effectiveness and environmental friendliness. This
Scheme 1. Plausible mechanism for HT supported nickel nanoparticles catalyzed hydration of nitriles to amides.

T. Subramanian, K. Pitchumani / Catalysis Communications 29 (2012) 109–113
113
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