One-pot synthesis of nitriles from aldehydes catalyzed by deep eutectic solvent

Article abstract of DOI:10.1055/s-0033-1339904

The choline chloride-urea (1:2) based deep eutectic mixture as an efficient and ecofriendly catalyst for the one-pot synthesis of nitriles from aldehydes under solvent-free conditions under both conventional and microwave irradiation; the products were obtained in good to excellent yields. Georg Thieme Verlag Stuttgart New York.

Full text of DOI:10.1055/s-0033-1339904

PAPER
▌3295
pOapnere-Pot Synthesis of Nitriles from Aldehydes Catalyzed by Deep Eutectic
Solvent
One-Pot Synthesis of Nitriles from Aldehydes
Umakant B. Patil, Suresh S. Shendage, Jayashree M. Nagarkar*
Department of Chemistry, Institute of Chemical Technology, N. Parekh Marg, Matunga, Mumbai 400 019, India
Fax +91(22)33611020; E-mail: jayashreenagarkar@yahoo.co.in; E-mail: jm.nagarkar@ictmumbai.edu.in
Received: 11.07.2013; Accepted after revision: 11.09.2013
have garnered attention as a green solvent as well as a cat-
alyst for many organic transformations. Negligible vapor
pressure, nonflammability, nontoxic, biodegradable na-
ture, low cost, and thermal stability are the important
properties of deep eutectic solvents. Deep eutectic sol-
vents are used as co-solvents for enzyme-catalyzed epox-
Abstract: The choline chloride–urea (1:2) based deep eutectic mix-
ture as an efficient and ecofriendly catalyst for the one-pot synthesis
of nitriles from aldehydes under solvent-free conditions under both
conventional and microwave irradiation; the products were ob-
tained in good to excellent yields.
Key words: nitriles, deep eutectic solvent, aldehydes, hydroxyl-
amine hydrochloride, microwave
1
9
ide hydrolysis, catalyst for nitroaldol formation via
2
0
hydrogen bond activation, C–C bond formation reac-
2
1
22
tions, and N-alkylation of primary amines. Abbott et
al. have extensively studied the applications of deep eu-
Organic functional groups play a vital role in synthetic or-
ganic chemistry and particularly the nitrile group is an im-
portant and productive functional group in research and
industrial chemistry.
2
3
tectic solvents. Usually, aldehydes are readily available
and can be easily converted into nitriles.
The use of a choline chloride based deep eutectic solvent
as both the solvent and catalyst for the transformation of
aldehydes into nitriles is a potentially greener synthetic
route. This can be extended to industrial applications due
to the ready availability of aldehydes. An most important
aspect of these reactions is the cyanide-free cyanation,
which can be carried out without base and oxidant.
Nitriles are an important precursor in the synthesis of
nitrogen-containing heterocyclic compounds, amides,
1
,2
amines, carboxylic acids, esters, and aldehydes. Trans-
formation of a carbon equivalent functional group into a
3
nitrile is an important synthetic route. Generally nitriles
are prepared by: (1) reaction of alkyl and aryl halides with
metal cyanides; (2) oxidation of amines; or (3) dehydra- The application of this conversion can be expanded by us-
tion of amides and aldoximes.4 Various methods for the ing milder and greener reaction conditions. Since we are
,5
2
4
direct synthesis of nitriles from aldehydes using either hy- interested in developing oxime chemistry, we attempted
droxylamine hydrochloride or ammonia in combination to prepare nitriles from oximes. A mixture of benzaldox-
with a variety of activating reagents have been reported. ime (0.121 g, 1 mmol) and 15 mol% deep eutectic solvent
The reagents u6sed for this transformation are was added into a 10-mL round-bottomed flask and the re-
7
8
9
10
CuCl /NaOMe/O , Pb(OAc) , Oxone, H O , I ,
action mass was heated to 100 °C for eight hours, which
2
1
2
4
2
2
2
1
12
13
14
NBS, IBX, NaICl , KF/Al O , ethyl dichlorophos- gave the corresponding benzonitrile in 94% yield. After
2
2
3
phate/DBU,15 and graphite; triflic acid using sodium this inspiring result, we carried out the one-pot synthesis
16a
azide as the nitrogen source for cyanation is also report- of nitriles from aldehydes using a deep eutectic solvent.
1
6b
ed. Also nitriles have been synthesized in ionic liq- We studied the synthesis of nitriles from aldehydes under
uids.17 All of the above-mentioned reagents are either the microwave irradiation and by conventional methods
selective with respect to certain groups or required harsh using reusable biodegradable choline chloride–urea (1:2)
reaction conditions.
based deep eutectic solvent as both the solvent and cata-
lyst (Scheme 1). The deep eutectic solvent was prepared
There are some reports of the microwave-assisted synthe-
sis of nitriles from aldehydes using HY-zeolite, silica gel
supported sodium hydrogen sulfate, and ammonium ace-
tate catalysts. But these catalysts decomposed under mi-
crowave irradiation and also they cannot be stored for
extended periods. Herein we report a greener route for the
synthesis of nitriles from aldehydes using choline chlo-
ride–urea (1:2) based deep eutectic solvent.
2
5
by a previously reported method.
1
8
CN
CHO
choline chloride–urea (1:2)
MW (10 min), 100 °C, 12 h
+
2
NH OH⋅HCl
Scheme 1 Synthesis of nitriles from aldehyde by using choline chlo-
ride–urea (1:2) based deep eutectic solvent (DES)
The properties of deep eutectic solvent (DES) are similar
to that of an ionic liquid. Therefore deep eutectic solvents
The model reaction was carried out by using different
choline-based eutectic mixtures such as choline chloride–
glycerol and choline chloride–malonic acid. It is clear that
the choline chloride–urea (1:2) based deep eutectic sol-
SYNTHESIS 2013, 45, 3295–3299
Advanced online publication: 26.09.2013
0
0
3
9
-
7
8
8
1
1
4
3
7
-
2
1
0
X
DOI: 10.1055/s-0033-1339904; Art ID: SS-2013-Z0471-OP
Georg Thieme Verlag Stuttgart · New York
©

3296
U. B. Patil et al.
PAPER
Table 1 Synthesis of Nitrile by Using Different DESa
DES
Choline chloride–urea
Choline chloride–glycerol
Choline chloride–malonic acid
molar ratio
1:2
95
1:2
25
1:2
yield (%)b
trace
a
Reaction conditions: benzaldehyde (1 mmol), hydroxylamine hydrochloride (1.2 mmol), 15 mol% catalyst (DES), 140 °C, 10 min, MW irra-
diation.
Isolated yield.
b
vent gave the maximum yield of the desired product (Ta- was found that benzaldehydes can be transformed into the
ble 1).
desired nitriles in good to excellent yield by using a deep
eutectic solvent as both the catalyst and solvent (Table 2).
The deep eutectic solvent can be exploited for the prepa-
ration of nitriles under microwave irradiation and also by
We have also explored the applicability of this protocol to
the synthesis of various substituted benzonitriles and it
Table 2 Synthesis of Nitriles from Various Aldehydes by Using Choline Chloride–Urea Based DESa
b
Entry Substrate
Product
Time
Yield (%)
c
Conventional (h)
MW irradiation (min)
Conventional MW irradiation
116
12
10
92
95
CHO
CHO
CN
OMe
OMe
CN
214
326c
418
12
12
12
10
10
10
89
90
87
92
94
90
H NH C
2
2
CHO
H2NH2C
Cl
CN
Cl
CHO
CN
518
Cl
CHO
12
12
12
12
84
85
89
91
Cl
CN
CN
626b
Br
F
CHO
Br
F
726a
12
12
10
10
82
77
89
81
CHO
N
CN
OHC
NC
813
N
913
CH CHO
12
12
10
10
73
75
77
81
2
CH2CN
Cl
CH CHO
2
Cl
CH CN
1
016b
2
MeO
MeO
1
1
126d
12
12
10
5
82
68
87
70
CH2CHO
CH2CN
CHO
CN
226e
a
b
c
Reaction conditions: aldehyde (1 mmol), hydroxylamine hydrochloride (1.2 mmol), 15 mol% catalyst, 100 °C.
Isolated yield of product.
Reaction carried out at 140 °C under MW irradiation.
Synthesis 2013, 45, 3295–3299
© Georg Thieme Verlag Stuttgart · New York

PAPER
One-Pot Synthesis of Nitriles from Aldehydes
3297
conventional heating. The yields of the products obtained In this transformation, during the synthesis of nitriles
by microwave irradiation are higher than by conventional from aldehydes and hydroxylamine hydrochloride, initial-
heating. Benzaldehydes having electron-donating or elec- ly an aldoxime was obtained that was converted into the
tron-withdrawing groups gave good to excellent yield of nitrile after dehydration (Scheme 2).
products (entries 2–7). Also pyridine-3-carbaldehyde was
In conclusion, we have developed a simple, greener, and
transformed into 3-cyanopyridine in good yield (entry 8),
atom-economical procedure for the synthesis of nitriles
whereas aliphatic aldehydes gave the corresponding ni-
using an environmentally friendly deep eutectic solvent.
The deep eutectic solvent can be efficiently used for these
triles in moderate yields (entries 9–12).
transformations for the synthesis of nitriles under micro-
wave irradiation and by conventional heating. Microwave
Table 3 Reusability Study of Catalysta
b
Entry
No. of cycles
Yield (%)
irradiation is extremely efficient compared to convention-
al heating with respect to time. These transformations
avoid the use of acidic, high-cost and highly toxic re-
agents as the catalyst. Additionally, mild reaction condi-
tions, good to excellent yields, the use of a reusable
biodegradable choline chloride–urea mixture as solvent
and catalyst, low cost, and easy workup are the major ad-
vantages of this transformation.
1
2
3
4
1
2
3
4
5
95
92
88
82
79
5
a
Reaction conditions: benzaldehyde (1 mmol), hydroxylamine hy-
drochloride (1.2 mmol), 15 mol% catalyst, 140 °C, 10 min, MW irra-
diation.
Preparation of Deep Eutectic Solvent (Choline Chloride–Urea)
Choline chloride (1 mmol) and urea (2 mmol) were added to a
round-bottom flask and heated up to 100 °C for 30 min to give col-
orless transparent liquid. This was used as a eutectic solvent after
cooling.
b
Isolated yield of product.
The reusability of the catalyst was also examined. After
completion of the reaction, ethyl acetate was added to the
reaction mass and it was stirred for five minutes. The ethyl Conventional method: A mixture of benzaldehyde (0.106 g, 1
acetate layer was separated and the recovered deep eutec-
tic solvent was dried under vacuum at 80 °C and then re-
used. It was found that the deep eutectic solvent can be
reused for up to five successive cycles (Table 3) with a
gradual decrease in the product yield.
Benzonitrile by One-Pot Synthesis from Benzaldehyde; Typical
Procedures
mmol), hydroxylamine hydrochloride (0.083 g, 1.2 mmol), and cat-
alyst (15 mol%) was taken in a 25-mL round-bottom flask and heat-
ed at 100 °C for 12 h under vigorous stirring. After completion of
the reaction, the reaction mass was cooled to r.t. The product was
extracted into EtOAc. The solid product was obtained after evapo-
ration of EtOAc. The obtained solid was purified by column chro-
matography (silica gel).
Microwave irradiation: A mixture of benzaldehyde (0.106 g, 1
mmol), hydroxylamine hydrochloride (0.083 g, 1.2 mmol) and cat-
alyst (15 mol%) was irradiated in microwave oven at 140 °C for 10
min. The progress of the reaction was monitored by TLC. After
completion of the reaction, the reaction mass was cooled to r.t. The
product was extracted into EtOAc. The solid product was obtained
after evaporation of EtOAc. The obtained solid was purified by col-
umn chromatography (silica gel). The pure product was character-
+N
+N
O
O
O
–
-
Cl–
Cl
H
H
H
H
N
H
N
H
N
H
N
H
OH
OH
-
O
H
1
ized by GC-MS and H NMR.
R
H
NH OH. HCl
R
+NOH
H
2
Benzonitrile16
Colorless liquid; yield: 0.0979 g (95%); bp 188–190 °C.
–
1
IR (neat): 2224 cm .
H
R
N
1
O
H NMR (300 MHz, CDCl ): δ = 7.67–7.58 (m, 3 H), 7.50–7.45 (m,
3
–
H2O
+N
– H2O
R
N
H
2 H).
H
Cl–
N
O
H
R
N
+
H
GC-MS: m/z (%) = 103 (M , 100), 76 (40), 50 (13).
OH
H
2-Methoxybenzonitrile14
Colorless liquid; yield: 0.122 g (92%); bp 134 °C.
OH
H
O
N
H
1
H NMR (300 MHz, CDCl ): δ = 7.57–7.52 (m, 2 H), 7.03–6.97 (m,
3
2
H), 3.93 (s, 3 H).
GC-MS: m/z (%) = 133 (M , 100), 132 (29), 104 (84), 90 (41), 76
19), 63 (27).
R = Ph
+
(
Scheme 2 Plausible mechanism for nitrile synthesis using a deep eu-
tectic solvent [choline chloride–urea (1:2)] as catalyst
-(Aminomethyl)benzonitrile26c
4
Pale yellow liquid; yield: 0.124 g (94%); bp 160–162 °C.
1
H NMR (300 MHz, CDCl ): δ = 7.52 (d, 2 H), 7.41 (d, 2 H), 4.30
3
(m 2 H).
©
Georg Thieme Verlag Stuttgart · New York
Synthesis 2013, 45, 3295–3299

3298
U. B. Patil et al.
PAPER
+
GC-MS: m/z (%) = 131 (M , 100), 104 (52), 30 (58).
Acknowledgment
3
-Chlorobenzonitrile18
The authors are thankful to UGC-SAP, New Delhi, India for the
award of fellowship.
Crystalline white; yield: 0.123 g (90%); mp 38–40 °C.
1
H NMR (300 MHz, CDCl ): δ = 7.65–7.58 (d, 2 H), 7.56–7.27 (d,
3
2
H).
Supporting Information for this article is available online at
13
C NMR (100 MHz, CDCl ): δ = 135.1, 133.1, 131.8, 130.3, 117.3,
3
http://www.thieme-connect.com/ejournals/toc/synthesis.SnoIufproi
m
tgioSrantnugIifoop
r
itmnatr
113.8.
+
GC-MS: m/z (%) = 137 (M , 100), 139 (33), 102 (36), 75 (20), 50
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© Georg Thieme Verlag Stuttgart · New York

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One-Pot Synthesis of Nitriles from Aldehydes
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©
Georg Thieme Verlag Stuttgart · New York
Synthesis 2013, 45, 3295–3299