Transition metal-free 1,3-dimethylimidazolium hydrogen carbonate catalyzed hydration of organonitriles to amides

Article abstract of DOI:10.1039/c2ra22868h

An efficient hydration of organonitriles to the corresponding amides was accomplished using 1,3-dimethylimidazolium hydrogen carbonate as an organocatalyst. The developed catalytic method was also applicable for the synthesis of metal phthalocyanines.

Full text of DOI:10.1039/c2ra22868h

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Transition metal-free 1,3-dimethylimidazolium
hydrogen carbonate catalyzed hydration of
Cite this: RSC Advances, 2013, 3, 895
organonitriles to amides3
Praveen Kumar Verma, Upendra Sharma, Manju Bala, Neeraj Kumar*
and Bikram Singh*
Received 13th November 2012,
Accepted 13th November 2012
An efficient hydration of organonitriles to the corresponding amides was accomplished using 1,3-
dimethylimidazolium hydrogen carbonate as an organocatalyst. The developed catalytic method was also
applicable for the synthesis of metal phthalocyanines.
DOI: 10.1039/c2ra22868h
www.rsc.org/advances
methods have been applied for the synthesis of phthalocya-
nines.
Introduction
Catalytic hydration of nitriles is a sustainable and atom
economic reaction in organic synthesis for the formation of
In recent years, imidazolium based ionic liquids, which are
the precursor of N-heterocyclic carbenes (NHCs), have
emerged as versatile organocatalysts for important organic
1
primary amides. Amides exhibit a broad range of industrial
applications like foam boosting and stabilization, emulsifica-
tion, detergents, viscosity modification, lubricity, antistatic
properties, corrosion inhibition, drug stabilizers, polymers
10
transformations. Nowadays, these imidazolium based NHC
precursors have effectively replaced the conventional inorganic
acids or bases due to several advantages such as stability in
water and air, low volatility, easy separation and immiscibility
2
and are important intermediates in organic synthesis.
Industrially, hydration of acrylonitrile produces more than 2
11
with many organic solvents. NHC-Au complexes have been
5
3–5
6
10 tons of acrylamide annually.
Many efficient catalytic methods based on enzymes and
applied for efficient hydration of organonitriles to the
corresponding amides, but there is no report on the use of
6
7
transition metals (Ni, Pt, Rh, Ir, Mo, Au, Cu, Co, Pd, Ru, Ag)
have been developed for hydration of nitriles. However, the
necessity of special handling of microorganisms (enzymes),
difficulty in catalyst/product separation, high temperature/
pressure and use of costly transition metal complexes limit the
scope of these methods. Hence, the development of metal free
methods is highly desirable.
7b
NHC precursor alone for this trasformation.
Results and discussion
Initially, the effect of different NHC precursors on hydration of
4-nitrobenzonitrile was investigated (Table 1) at 80 uC. No
reaction was observed with 1,3-diisopropylimidazolium chlor-
ide (B) and 1-ethyl-3-methylimidazolium chloride (C), whereas,
full conversion was recorded with 1,3-dimethylimidazolium
hydrogen carbonate (A) (Table 1, entries 1, 2 and 3). As
expected, no conversion was observed without a catalyst
(Table 1, entry 6). Hydration did not proceed at room
temperature (Table 1, entry 4). Water : ethanol (1 : 1) was
taken as a solvent since full conversion was not observed with
water due to the low solubility of the substrate (Table 1, entry
Classically, the hydration of nitriles was accomplished with
8
,9
strong acidic or basic conditions. However, these procedures
are associated with the serious drawbacks of over hydrolysis of
amides to carboxylic acids and formation of salts after
neutralization of the catalyst. In addition, many sensitive
functional groups such as carbon-carbon double bonds and
carbonyls can not tolerate such strong acidic or basic
conditions and results in decreased selectivity for amides.
9
a
9b
Recently, Cs
2
CO
3
/pyrrolidinone and K
2
CO
3
have been
1
2
applied for this transformation but the requirement of excess
amounts of base and high temperatures (up to 150 uC) limit
the scope of these reactions. In addition, none of these
5).
Different concentrations of A were tested to optimize the
minimum effective amount for hydration (Table 1, entries 1
and 7–9). It was observed that 5 mol% of A was sufficient to
effectively catalyze the hydration of 4-nitrobenzonitrile to
Natural Plant Products Division, CSIR-Institute of Himalayan Bioresource
Technology, Palampur, Himachal Pradesh-176 061, India.
4-nitrobenzamide (Table 1, entry 8).
E-mail: neerajnpp@rediffmail.com; bikram_npp@rediffmail.com
To check the scope of present catalytic system various
3
Electronic Supplementary Information (ESI) available: IHBT communication
no. 3423. See DOI: 10.1039/c2ra22868h
organonitriles were studied under optimal reaction conditions
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a
a
Table 1 Screening of NHC precursors for hydration of nitriles
Table 2 Hydration of various nitriles using A
b
Entry
1
Substrate
Time (h)
2.5
Product
Yield (%)
c
99 (97)94
b
Entry NHC precursors Quantity (mol%) Time (h) Yield (%)
1
2
3
4
5
6
7
8
9
A
B
C
A
A
—
A
A
A
25
25
25
25
25
—
2.5
5
10
4
12
12
12
12
12
4
98
2
3
6
6
92 (90)
92 (91)
No reaction
No reaction
No reaction
60
c
d
No reaction
76
98
97
4
4
4
5
6
7
6
5
88 (84)
91
3
a
12
5
2
Reaction conditions: nitrile (1 mmol), A (5 mol%), EtOH : H O
b
c
(
1 : 1, 5 mL), and 80 uC temperature. GC-MS yield. Reaction at
d
room temperature. Reaction in water.
87
(Table 2). Benzonitrile was hydrated to benzamide in 97%
yield (Table 2, entry 1). Halogen substituted benzonitriles were
efficiently hydrated to the corresponding amides without any
dehalogenation (Table 2, entries 2–5). Aldehyde and nitro
substituted benzonitriles were well tolerated and converted
into the corresponding amides with good to excellent yield
c
8
4
99 (96)92
9
5.5
7
88
91
89
(Table 2, entries 7 and 8).
10
The hydration of acrylonitrile is industrially very important
3
–5
1
1
1
2
5
to produce acrylamide.
During this reaction hydration of
carbon-carbon double bonds and the polymerization of
acrylonitrile and/or acrylamide are often observed as side
reactions. However, under present reaction conditions the
hydration of acrylonitrile afforded the acrylamide in quanti-
tative yield without any side reactions (Table 2, entry 9).
The hydration of 2-phenylacetonitrile and propionitrile
afforded the corresponding amide in good yields (Table 2,
entries 10 and 11). NHC precursor (A) successfully catalyzed
the hydration of nitrogen and sulphur containing heterocyclic
nitriles to corresponding amides in high yields (Table 2,
entries 12 and 13).
c
3
4
99 (96)95
13
99 (97)
10
14
12
a
2
Reaction conditions: nitrile (1 mmol), A (5 mol%), EtOH : H O
Very low yield of product was observed in case of
b
(
1 : 1, 5 mL), 80 uC temperature. Isolated yields are given in
c
4-hydroxybenzonitrile and 3-cyanoindole (3–10%) even after
parenthesis. Reaction were carried out with 10 mmol of substrate.
prolonged heating for 12 h (Table 2, entries 6 and 14).
Unfortunately, the present catalytic system was unable to
catalyze the hydration of 1-cyanonaphthalene, 4-carboxyben-
excellent method for the production of phthalimides from
corresponding o-phthalonitriles. 1,3- and 1,4-benzenedinitriles
were hydrated to corresponding diamides in quantitative
yields (Table 3, entries 2 and 3).
Some of the reactions were performed with 10 mmol of
starting substrates and quantitative isolated yields were
obtained in most of these cases, which confirm the applic-
3
zonitrile and 5-cyanophthalide (see ESI , Table S1).
A efficiently catalyzed the double hydration of benzenedi-
nitriles (Table 3). In the case of 1,2-benzenedinitriles double
hydration occurred, and, further, cyclized to the corresponding
phthalimides in quantitative yields (Table 3, entries 1, 4, 5 and
6). Hence, the present catalytic system also provides an
8
96 | RSC Adv., 2013, 3, 895–899
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a
a
Table 3 Hydration of various benzenedinitriles using A
Table 4 NHC precursor (A) catalyzed synthesis of metal phthalocyanines
b
Entry
M
R
1
l
max (nm)
Yield (%)
1
2
3
Co
Fe
Co
H
H
t-Bu
660, 596, 335
659, 602, 332
666, 601, 333
59
54
66
b
Entry
1
Substrate
Time (h)
4
Product
Yield (%)
94 (90)
a
Reaction conditions: nitrile (1 mmol), A (5 mol%), Metal salt (0.25
b
equiv.), EtOH : H
yield.
2
O (1 : 1, 5 mL), 160 uC temperature. Isolated
2
6.5
98 (91)
were also prepared by the present method in fair yields.
Structures of synthesized metal phthalocyanines were con-
firmed by comparing the UV-vis and NMR spectra with
3
4
6.5
5
99 (95)
85
3
literature (see ESI ).
From a mechanistic point of view it is reported that bases
2
catalyzed the hydration of nitriles by generating OH from
water through proton abstraction which undergo nucleophilic
9
addition to the nitrile moiety. In the present case, the counter
2
ion (HCO ) of A abstract the proton from water to generate
3
2
OH which undergoes nucleophilic addition to form an
5
6
5
6
99 (93)
(92)
iminol ion. The iminol ion rearranges and abstracts a proton
from water to form the corresponding amide (Fig. 1). To
confirm the proposed mechanism the reaction was carried
with D O which clearly shows the insertion of two deuterium
2
atoms in the final product and the catalyst A was recovered
after completion of reaction (confirmed by NMR).
a
Reaction conditions: nitrile (1 mmol), A (5 mol%), EtOH : H
2
O
b
Experimental
(1 : 1, 5 mL), 80 uC temperature. Isolated yields are given in
parenthesis.
Metal salts used were purchased from Merck, Germany. Silica
gel (60–120 mesh) used for column chromatography was
purchased from Sisco Research Laboratories Pvt. Ltd. India
and all other chemicals were purchased from Spectrochem,
India, Merck, Germany, and Sigma-Aldrich, USA and were
used without further purification. NMR spectra were recorded
on a Bruker Avance-300 spectrometer. Mass spectra were
recorded on QTOF-Micro of Waters Micromass and Maxis-
ability of the present protocol at large scale (Table 2, entries 1,
8
and 11).
The present catalytic method was also applied for the
synthesis of metal phthalocyanines from o-phthalonitriles
1
3
with slight modification. Earlier reports for organocatalytic
synthesis of metallophthalocyanines suffer from the use of
1
4
additional bases, metal catalyst and additives.
A very
efficiently catalyzed the synthesis of Fe and Co phthalocya-
nines from o-phthalonitriles without the requirement of any
additional base (Scheme 1, Table 4). t-Butyl analogues of CoPc
Scheme 1 NHC precursor (A) catalyzed synthesis of metal phthalocyanines.
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Fig. 1 Plausible reaction mechanism.
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Bruker. The GC-MS analysis was carried out on a Shimadzu
Acknowledgements
(
(
QP 2010) series Gas Chromatogram-Mass Spectrometer
Tokyo, Japan), AOC-20i auto-sampler coupled, and a DB-
Authors are grateful to the Director of the institute for
providing necessary facilities. Mr. P. K. V. and Mr. U. S. are
thankful to CSIR for SRF fellowship.
5MS capillary column, (30 m 6 0.25 mm i.d., 0.25mm). The
initial temperature of the column was 70 uC held for 4 min and
2
1
was programmed to 230 uC at 4 uC min , then held for 15 min
at 230 uC; the sample injection volume was 2 mL in GC grade
dichloromethane. Helium was used as carrier gas at a flow rate
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3
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1
2 Due to low solubility of organonitriles in water, substrates
get deposited on the walls of the reaction flask under
heating and do not participate in the reaction. Therefore,
ethanol was added to solve this issue.
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