CeO2-catalyzed one-pot selective synthesis of N-alkyl amides from nitriles, amines and water

Article abstract of DOI:10.1016/j.apcata.2011.12.004

Among 13 kinds of metal oxides, ceria (CeO₂) shows the highest catalytic activity for one-pot selective synthesis of the secondary amide from 2-cyanopyridine and n-octylamine as a test reaction. CeO₂ acts as a reusable heterogeneous catalyst, and it is effective for the secondary amide formation from various nitriles and amines in high yields (73% to >99%). Pharmacologically important products such as heteroaromatic N-alky amides and morpholine amide are effectively synthesized, indicating that CeO₂ can be a practically useful catalyst. A proposed mechanism includes (1) hydration of nitrile to the primary amide and (2) transamidation of the primary amide with amine as the rate-limiting step. This reaction mechanism provides a reason why the present catalytic system gives high selectivity.

Full text of DOI:10.1016/j.apcata.2011.12.004

Applied Catalysis A: General 417–418 (2012) 6–12
Contents lists available at SciVerse ScienceDirect
Applied Catalysis A: General
journal homepage: www.elsevier.com/locate/apcata
CeO2-catalyzed one-pot selective synthesis of N-alkyl amides from nitriles,
amines and water
Masazumi Tamuraa, Takuya Tonomuraa, Ken-ichi Shimizub,∗, Atsushi Satsumaa
a Department of Molecular Design and Engineering, Graduate School of Engineering, Nagoya University, Nagoya 464-8603, Japan
b Catalysis Research Center, Hokkaido University, N-21, W-10, Sapporo 001-0021, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
Among 13 kinds of metal oxides, ceria (CeO2) shows the highest catalytic activity for one-pot selective
synthesis of the secondary amide from 2-cyanopyridine and n-octylamine as a test reaction. CeO2 acts as a
reusable heterogeneous catalyst, and it is effective for the secondary amide formation from various nitriles
and amines in high yields (73% to >99%). Pharmacologically important products such as heteroaromatic N-
alky amides and morpholine amide are effectively synthesized, indicating that CeO2 can be a practically
useful catalyst. A proposed mechanism includes (1) hydration of nitrile to the primary amide and (2)
transamidation of the primary amide with amine as the rate-limiting step. This reaction mechanism
provides a reason why the present catalytic system gives high selectivity.
Received 21 October 2011
Received in revised form
24 November 2011
Accepted 3 December 2011
Available online 9 December 2011
Keywords:
Cerium oxide
Amides
© 2011 Elsevier B.V. All rights reserved.
One-pot synthesis
1. Introduction
separation, use of organic solvent, high price, and low activity for
hydration of heteroaromatic nitriles due to their strong coordina-
The construction of amide bonds is one of the most important
fundamental processes in organic and bioorganic chemistry as pep-
tides and proteins include amide bonds. Synthesis of N-alkyl amides
(secondary and tertiary amides) has been of great interest, because
they are synthetic intermediates of numerous natural products,
polymers, pesticides and pharmaceuticals [1]. Despite their impor-
tance, the majority of amide bond syntheses involve the use of
stoichiometric amounts of coupling reagents, which makes them
expensive and wasteful procedures [2]. Recently, direct amidation
of carboxylic acids with amines by boric acids [3–7] or transamida-
tion of amide with amine by Al(III), Sc(III), group 4 metal complexes
(Ti, Zr, Hf) [8–12] were reported as effective catalytic systems for
the amide bond syntheses. In the view of green chemistry, het-
erogeneous catalyst should be used for the amide bond syntheses.
However, only a few heterogeneous catalysts have been reported
to be effective for direct amidation of carboxylic acids with amines
[13–17]. As an alternative method, catalytic one-pot amidation
from nitriles and amines, first developed by Murahashi et al. [18], is
a potentially useful method for green and economical synthesis of
N-alkyl amides [18–22]. Various catalytic methods using homoge-
neous metal catalysts have been reported [18–20,23,24], though
they have disadvantages including difficulty in catalyst/product
tion to the metal centers. Use of recyclable heterogeneous catalyst
is ideal from environmental and practical viewpoints. However, to
the best of our knowledge, there is only one report on heteroge-
neous catalysts (ZrO2 and Nb2O5) for the amidation from nitriles
and amines [21], which suffers from high reaction temperature
(180–230 ◦C) and low yield. Although heteroaromatic amides are
pharmacologically important [25], there is no report of one-pot
synthesis of them from heteroaromatic nitriles by heterogeneous
catalysts.
CeO2 has acid–base and redox properties and has been used
as an effective catalyst for various organic reactions [26–28] such
as dehydration of alcohols [29–35], alkylation of aromatic com-
pounds [36–38], dimerization of alcohols [39–43], aldehydes, esters
[43] and carboxylic acids [44,45] to ketones, cyclazation of diols
[46], reduction of benzoic acid [47]. Most of CeO2-catalyzed reac-
tions were carried out at high temperature (typically 200–500 ◦C).
In view of the organic synthesis and the green chemistry, it is
important to study CeO2-catalyzed organic reactions below 200 ◦C.
As for CeO2-catalyzed reactions at low temperature (<200 ◦C),
Tomishige et al. recently reported the carbonate synthesis from
CO2 and alcohols at 150 ◦C [48–51]. In this system, nitriles as
dehydration reagents are converted to amide and small amount
of esters. Our research group found that CeO2 acted as a highly
active catalyst for substrate-specific hydration of nitriles at low
temperature (30–100 ◦C) [52]. Kinetic studies showed a mecha-
nism involving nucleophilic attack of OH␦− species to nitriles as a
key step. Based on these findings, we hypothesized that reaction
∗
Corresponding author. Tel.: +81 11 706 9240; fax: +81 11 706 9163.
E-mail addresses: kshimizu@cat.hokudai.ac.jp, kshimizu@apchem.nagoya-
u.ac.jp (K.-i. Shimizu).
0926-860X/$ – see front matter © 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.apcata.2011.12.004

M. Tamura et al. / Applied Catalysis A: General 417–418 (2012) 6–12
7
Table 1
One-pot N-alkyl amide formation from 2-cyanopyridine and n-octylamine by various metal oxides.a
H2O(5 mmol)
O
O
N
CN
N
N
catalyst (25 mg)
N
H
NH2
NH2
+
+
160 oC
1
2
3
Entry
Catalyst
SBET (m2 g−1
)
t (h)
Conv. (%)
Yield (%)
2
Vb (mmol g−1 h−1
)
Selec. (%)c
3
Others
1
2
CeO2
TiO2
81
47
0.33
3
1
3
3
3
3
3
3
3
3
3
3
3
3
1
3
100
100
100
100
92.1
97.0
97.3
100
77.4
75.4
91.7
93.5
94.5
54.7
65.7
6.1
24.2
81.8
32.7
59.5
41.2
33.7
20.0
17.1
13.1
12.9
11.7
7.8
6.8
11.5
8.8
0
10.9
72.1
15.8
37.2
26.6
13.9
3.4
20.0
9.8
12.7
13.4
7.8
5.6
4.2
7.2
6.2
0
14.6
3.7
2.4
72.9
27.4
32.7
20.1
13.7
11.3
6.9
6.0
4.4
4.4
3.9
2.7
2.3
3.8
2.9
–
–
82
–
14.2
13.9
37.0
59.9
57.3
73.1
51.6
49.1
72.2
80.1
83.5
36.0
50.7
6.1
60
45
34
21
17
17
17
13
8
3
4
5
6
7
La2O3
ZrO2
MnO2
SiO2
Pr6O11
Nb2O5
Al2O3
SnO2
18
72
45
300
34
54
124
28
19
9
8
9
10
11
12
13
14
15
MgO
7
21
13
Er2O3
Dy2O3
Blank
51
–
93.1
67.6
–
12
Reaction conditions: 1 (2.5 mmol), n-octylamine (5.0 mmol), CeO2 (25 mg), H2O (5.0 mmol), T = 160 ◦C, in N2. Yields of 2 and 3 were determined by GC.
Initial rate of 2 formation measured under the condition in which yield of 2 were below 50%.
Selectivity of at t = 3 h.
a
b
c
of nitriles with amines might proceed directly to afford N-alkyl
amides.
We report herein that commercial CeO2 acts as a recyclable het-
erogeneous catalyst for one-pot N-alkyl amides formation from
various nitriles and amines at 160 ◦C, which provides a new and
green catalytic system for N-alkyl amides synthesis. Catalytic stud-
ies show that our method is particularly effective for the amidation
of heteroaromatic nitriles. From kinetic studies, a possible reaction
mechanism is proposed.
(Shimazu) or DB-1 (Agilent J&W) using nitrogen as the carrier gas.
All the chemicals for organic reactions were analytical reagent
from chemical products corporation and were used without fur-
ther purification. CeO2 (JRC-CEO3, surface area = 81 m2 g−1) was
supplied from the Catalysis Society of Japan. It was pre-calcined
at 600 ◦C before being supplied. Other metal oxides were commer-
cially available or supplied from the Catalysis Society of Japan [52].
The metal oxides except CeO2 were calcined at 500 ◦C for 3 h before
the reaction.
2. Experimental
2.2. Catalytic experiments
2.1. General
A typical procedure for the N-alkyl amide formation from
nitriles and amines is as follows. CeO2 (25 mg, 5.8 mol.% Ce with
respect to nitrile) was added to the mixture of nitrile (2.5 mmol),
amine (5.0 mmol) and H2O (5.0 mmol) in a reaction vessel equipped
with a condenser under N2. The resulting mixture was vigorously
The GC (Shimadzu GC-14B) and GCMS (Shimazu GCMS-
QP5000) analyses were carried out with Rtx-65 capillary column
100
80
60
40
20
0
2.5
2.0
1.5
1.0
0.5
0
0
1
2
3
0
1
2
3
4
5
6
7
8
9
10 11 12
Time / h
[amine] / [nitrile] molar ratio
Fig. 1. Plots of yield vs. reaction time for one-pot N-alkyl amide formation from
1, n-octylamine and H2O by CeO2 at different temperatures (ꢀ: 160 ◦C, ꢁ: 140 ◦C,
ꢀ: 120 ◦C, ♦: 100 ◦C). Conditions: 1 (2.5 mmol), n-octylamine (5.0 mmol), H2O
(3.0 mmol), CeO2 (25 mg).
Fig. 2. Rate of N-alkyl amide formation vs. amine/nitrile molar ratio. Condi-
tions: 1 (2.5 mmol), n-octylamine (2.5–25.0 mmol), H2O (12.5 mmol), CeO2 (21 mg),
T = 160 ◦C.

8
M. Tamura et al. / Applied Catalysis A: General 417–418 (2012) 6–12
Table 2
One-pot N-alkyl amide formation from various nitriles and n-octylamine by CeO2.a
O
CeO2
H2O
+
+
R
CN
NH2
R
N
H
Entry
Nitrile
Product
t (h)
Yield (%)
O
N
N
CN
N
H
1
2
3
4
5
>99 (>99, >99, >99)c
O
N
CN
N
N
H
5
95
>99
>99
O
CN
N
N
N
N
H
24
24
O
CN
N
H
N
O
N
N
CN
N
N
N
H
5
5
>99
O
O
O
CN
N
H
6
7
5
>99
89
O
O
O
N
O
CN
O
H
24
O
CN
N
H
8b
42
>99
a
Conditions: 1 (2.5 mmol), n-octylamine (5.0 mmol), CeO2 (25 mg), H2O (5.0 mmol), T = 160 ◦C. Yield of the N-alkyl amide was determined by GC.
H2O = 10.0 mmol.
Results of catalyst reuse experiments (successive three cycles after the first run).
b
c
stirred at 160 ◦C. The reaction mixture was analyzed by GC. Conver-
sion and yield of the products were determined based on nitrile and
N-alkyl amide using pentadecane as an internal standard. The prod-
ucts were identified by GCMS or by comparison with commercial
products.
to be the best catalyst for this reaction in terms of activity and
selectivity.
3.2. Effect of reaction conditions
Next, we carried out the optimization of reaction conditions
for CeO2-catalyzed secondary amide formation from nitrile 1, n-
octylamine and H2O. The effect of reaction temperature was tested
in a temperature range of 100–160 ◦C (Fig. 1). Increase in the tem-
perature from 100 ◦C to 160 ◦C increased the reaction rate from 1.4
to 58.6 mmol g−1 h−1. The effect of the molar ratio of n-octylamine
to nitrile 1 was tested using CeO2 catalyst by changing the molar
ratio in a range 1.0–10.0 (Fig. 2). The reaction rate increased lin-
early with increase in the molar ratio. Taking the catalytic and
atom efficiencies into account, the molar ratio of 2 was adopted.
To optimize the amount of H2O, the reaction was carried out by
changing the molar ratios of H2O to nitrile 1 in a range of 1.0–5.0.
As shown in Fig. 3, the reaction rate depended strongly on the
molar ratios of H2O to 1. The reaction rate showed a volcano-type
dependence on the molar ratio, and it showed the maximum value
at the molar ratio of 2.0. Considering the reaction stoichiometry,
one equivalent of H2O is needed, but excess H2O can suppress the
reaction possibly by blocking the active sites on CeO2. Hereafter,
the molar ratio of H2O to nitrile was fixed to 2.0. Next, we opti-
mized the catalyst loading. The experiments were conducted at
four different CeO2 loadings (Fig. 4). The yield of secondary amide
3. Results and discussion
3.1. Comparison of various metal oxides
First, one-pot synthesis of secondary amide from 2-
cyanopyridine
1 with two equivalents of n-octylamine and
H2O at 160 ◦C was chosen as a test reaction to compare the
catalytic activity of various metal oxides (Table 1). The reaction by
CeO2 for 0.33 h resulted in 100% conversion of 1, and the yields
of N-octyl picolinamide 2 and picolinamide 3 were 24.2% and
72.1%, respectively. On the other hand, amide formation hardly
proceeded even in 1 h without a catalyst (entry 14). For various
metal oxides (entries 1–13), the initial rate of the formation of
2 was measured under the condition in which yields of 2 were
below 50%. Among the catalysts tested, CeO2 showed the highest
reaction rate for the direct amidation of 1 with n-octylamine to 2.
In addition, CeO2 showed the highest selectivity for the desired
product, secondary amide 2. From these results, CeO2 is found

M. Tamura et al. / Applied Catalysis A: General 417–418 (2012) 6–12
9
Table 3
One-pot N-alkyl amide formation from 2-cyanopyridine, various amines by CeO2.a
O
N
CN
N
R
CeO2
N
H
+
+
H2O
R NH2
Entry
Amine
Product
t (h)
Yield (%)
O
N
N
N
N
N
H
NH2
1
2
3
5
>99
O
O
O
N
H
NH2
27
48
85
75
N
H
NH2
N
H
NH2
4
5
5
>99
O
O
NH2
N
N
N
H
20
24
77
73
NH
N
O
O
6
a
Reaction conditions: 1 (2.5 mmol), n-octylamine (5.0 mmol), CeO2 (25 mg), H2O (5.0 mmol), T = 160 ◦C. Yield of the N-alkyl amide was determined by GC.
2 after 1 h increased with the amount of the catalyst. After 5 h,
the yield was >99% even with small amount of CeO2 (5.8 mol.%),
corresponding to the TON of 17.3 based on the total number of
Ce atoms in CeO2. Hereafter, the catalyst amount of 5.8 mol.% was
adopted.
nitriles with amines to the corresponding secondary amides as
shown in Table 2. Heteroaromatic nitriles (entries 1–8) such
as 2-cyanopyridine, 4-methyl-2-cyanopyridine, 3-cyanopyridine,
4-cyanopyridine, cyanopyradine, 2-cyanofurane, methoxyacetoni-
trile and phenoxyacetonitrile reacted to afford the corresponding
amides in high yields (89 to >99%). To our knowledge, this is the
first example of one-pot synthesis of heteroaromatic amides from
nitriles by heterogeneous catalyst.
3.3. Efficiency of CeO2-catalyzed one-pot N-alkyl amides
formation
Next, we examined the N-alkyl amide formation from 2-
cyanopyridine and various amines (Table 3). Aliphatic amines
(entries 1 and 2) reacted to afford the corresponding amides in
Under the optimized condition, CeO2 was found to be an
effective catalyst for one-pot selective amidation of various
16
14
12
10
8
100
80
60
40
20
0
6
4
2
0
0
1
2
3
4
5
6
0
1
2
3
4
5
[H2O] / [nitrile] molar ratio
Time / h
Fig. 4. Reaction with various CeO2 contents. ꢀ: 29.0 mol%, ꢁ: 17.4 mol%, ꢀ:
Fig. 3. Rate of N-alkyl amide formation vs. H2O/nitrile molar ratio. Conditions:
(5.0 mmol), n-octylamine (10.0 mmol), H2O (5.0–25.0 mmol), CeO2 (25 mg),
T = 160 ◦C.
5.8 mol%, ᭹: 0 mol%. Conditions:
(5.0 mmol), CeO2, T = 160 ◦C.
1 (2.5 mmol), n-octylamine (5.0 mmol), H2O
1

10
M. Tamura et al. / Applied Catalysis A: General 417–418 (2012) 6–12
O
NH
N
N
N
N
CN
CeO2 or no catalyst
N
N
+
+
H2O
NH2
H
H
2
4
1
O
NH
N
NH2
N
3
5
100
90
80
70
60
50
40
30
20
10
0
(a)
Conversion
2
3
0
1
2
3
4
5
Time / h
100
90
80
70
60
50
40
30
20
10
0
(b)
Conversion
5
4
2
3
0
1
2
3
4
5
6
7
8
9
Time / h
Fig. 5. Conversion and yield for one-pot N-alkyl amide formation with (a) CeO2 (25 mg) and (b) without a catalyst. Conditions: 1 (2.5 mmol), n-octylamine (5.0 mmol), H2O
(5.0 mmol), T = 160 ◦C.
high yields. A branched amine (entry 3) was converted to the cor-
responding amide in moderate yield (75%), which was probably
owing to steric hindrance around the NH2 group of the branched
amine. Amines with an aromatic ring such as benzylamine and
aniline reacted to afford the corresponding amides in good yields
(entries 4 and 5). Morpholine reacted with 2-cyanopyridine to
afford the corresponding tertiary amide (entry 6). Note that such a
morpholine amide is potent histamine H3 antagonist [25,53] and
a synthetically useful compound [54–56]. Therefore, the present
catalytic system may be practically useful in the formation of phar-
macologically important products.
An important advantage of this system is a reusability of CeO2
catalyst. We studied the reuse of CeO2 for the secondary amide
formation reaction (Table 2, entry 1). The catalyst can be easily
retrieved from the reaction mixture by centrifugation. For each suc-
cessive use, the catalyst was washed with acetone three times to
remove the products, followed by calcination in air at 300 ◦C for
1 h. After this treatment, the recovered catalyst was reused at least
three times without any decrease in the yield of 2.
3.4. Reaction mechanism
The effect of reaction time on the CeO2-catalyzed one-pot sec-
ondary amidation of 1 with n-octylamine was investigated as
illustrated in Fig. 5(a). At the initial stage, 2-cyanopyridine was
immediately consumed to produce the corresponding primary
amide 3 (90% yield at t = 10 min). Then, the yield of 3 decreased with
time, while the yield of 2 increased. After 5 h, the yield of 2 reached
>99%, and any by-products were detected by GC. These results
indicate that one-pot secondary amide formation proceeds by two
consecutive steps (route 1 in Scheme 1); (1) hydration of nitrile to
the primary amide and (2) the secondary amide formation from pri-
mary amide and amine. Although we did not have an experimental
evidence of NH3 formation during the reaction, one equivalent of
NH3 should be produced in the second step. The result in Fig. 5(a)
suggests that the latter step is the rate-limiting step. Fig. 5(b) shows
a time-conversion profile for the same reaction without any cata-
lyst. In contrast to the result with CeO2, various by-products were
detected. First, 1 was converted to N-octyl picolinamidine 4. Then

M. Tamura et al. / Applied Catalysis A: General 417–418 (2012) 6–12
11
route 1
O
O
n-Octylamine
-NH3
N
CN
N
N
H2O
CeO2
NH2
N
H
CeO2
3
2
1
route 2
NH
N
N
H
NH
4
N
N
5
Scheme 1. Reaction route of N-alkyl amide formation from 1, n-octylamine and H2O.
of transamidation of picolinamide (66 mmol g−1 h−1). This result
is consistent with the above mechanistic conclusion; transamida-
tion is the rate-limiting step. Note that this reaction mechanism is
different from that of the homogenous catalysts reported by Mura-
hashi and Takaya [19] and Williams et al. [22,24], in which they
have proposed that one-pot alkylamidation of nitrile proceeds by
route 2 via 4 (N-alkyl amidine), a part of which can be converted
to the by-product 5. In contrast, the reaction by CeO2 proceeds by
route 1, which can give high selectivity to N-alkyl amides.
(t = 3 h), the yield of 4 reached the maximum value, and 2, 3 and N,N-
dioctyl picolinamidine 5 were also produced. With further increase
in the reaction time, 4 was converted to 5, while the yields of 2 only
slightly increased with time. This indicates that the hydration of 4
to 2 is much slower than N-alkylation of 4 to 5. The yield of 3 lev-
eled off. From these results, the reaction without a catalyst proceeds
via the following consecutive route (route 2 in Scheme 1); (1) the
addition of amine to nitrile, and (2) hydrolysis of amidine (route
2-a). Even in the presence of catalyst, N-alkylation of N-alkyl ami-
dine to N,N-dialkyl amidine (route 2-b) as side reaction may occur,
which decreases the yield of the desired N-alkyl amide 2. Therefore,
inhibition of the non-catalytic pathway (route 2) increases the N-
alkyl amide yield. Note that most of “other products” in Table 1
were consisted of 4 (N-alkyl amidine) and 5 (N,N-dialkyl amidine).
These compounds were produced with all the metal oxides except
for CeO2. In the case of CeO2, hydration of nitrile is fast and contri-
bution of the route 2 is negligible, leading to the high selectivity of
N-alkyl amides.
From the results in Fig. 5, it is suggested that CeO2-catalyzed
reaction proceeds via route 1 (Scheme 1) and the secondary amide
formation from primary amide and amine (transamidation) is the
rate-limiting step. To estimate the reaction rates of elementary
steps, CeO2-catalyzed hydration of 2-cyanopyridine and transami-
dation of picolinamide with n-octylamine were independently
carried out. As shown in Scheme 2, the rate of hydration of 2-
cyanopyridine (1241 mmol g−1 h−1) is 19 times larger than that
4. Conclusion
We have demonstrated that CeO2 acts as an effective hetero-
geneous catalyst for the direct secondary amide synthesis from
various nitriles and amines. This catalyst provides a clean, conve-
nient and practical route for the direct amide synthesis in view of
the following advantages. (i) The reaction proceeds smoothly and
selectively in the presence of moisture under solventless condition,
producing various secondary amides in high yield. (ii) The catalyst is
stable, reusable and a non-polluting solid that offers easy handling
and ready work-up. (iii) This method is applicable to a wide range
of N-alkyl amides, including pharmaceologically and synthetically
important products (such as heteroaromatic N-alkyl amides and
morpholine amide). (iv) Compared with carboxylic acid or halides,
nitriles are storage-stable and less corrosive reagents. In contrast
to the previously reported catalytic systems, this reaction proceeds
by hydration of nitrile to the primary amide and its transamidation
with amine. This mechanism potentially gives higher selectivity to
N-alkyl amides, because the reaction does not proceed via N-alkyl
amidine.
Hydration of 2-cyanopyridine
n-Octylamine (5.0 mmol)
O
H2O (5.0 mmol)
CeO2 (25mg)
N
CN
N
NH2
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C
V = 1241 mmol g-1 h-1
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O
O
H2O (2.5 mmol)
N
N
CeO2 (25mg)
NH2
N
H
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12
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