Synthesis of aryl nitriles using the stable aryl diazonium silica sulfates

Article abstract of DOI:10.3184/174751912X13450494102019

An efficient method for preparation of aryl nitriles is reported using Cu(I) to catalyse the reaction of aryl diazonium silica sulfates with sodium cyanide under mild conditions at room temperature in water. This method has the advantages of high yields,

Full text of DOI:10.3184/174751912X13450494102019

JOURNAL OF CHEMICAL RESEARCH 2012
OCTOBER, 573–574
RESEARCH PAPER 573
Synthesis of aryl nitriles using the stable aryl diazonium silica sulfates
Davood Habibi*, Somayyeh Heydari and Mahmoud Nasrollahzadeh
Department of Organic Chemistry, Faculty of Chemistry, Bu-Ali Sina University, Hamedan 6517838683, Iran
An efficient method for preparation of aryl nitriles is reported using Cu(I) to catalyse the reaction of aryl diazonium
silica sulfates with sodium cyanide under mild conditions at room temperature in water. This method has the advan-
tages of high yields, simple methodology, short reaction times and easy work-up.
Keywords: aryl diazonium silica sulfates, sodium cyanide, aryl nitriles, Cu(I)
Nitriles are one of a number of important functional groups in
organic synthesis such as esters, amides, carboxylic acids,
amines and nitrogen-containing heterocycles and have been
used in the construction of various pharmaceutically important
(SSA) were used. These are stable at room temperature
and can be stored over the extended periods of time without
2
0
decomposition and can be easily recycled.
In continuation of our recent work on nitriles and the syn-
1
,2
21,25
compounds, agricultural chemicals and functional materials.
thesis of nitrogen-containing compounds,
here we report a
There are several methods for the synthesis of nitriles such
as the dehydration of aromatic amides, the condensation of
carboxylic acids, the nucleophilic substitution of alkyl halides
with inorganic cyanides, the reaction of esters with Me AlNH
mild, efficient and convenient method for the preparation
of nitriles from the reaction between aryl diazonium silica
sulfates as stable reagents with NaCN catalysed by CuCN in
water at room temperature (Scheme 1).
2
2
and the conversion of aromatic bromides. Other procedures
include oxidative conversion of amines using AgO, Pb(OAc)4,
cobalt peroxide, Na S O or (Bu N) S O with metals, NaOCl,
Results and discussion
2
2
8
4
2
2
8
Initially, to determine the optimum reaction conditions, a reac-
tion between p-nitrophenyl- diazonium silica sulfate, NaCN
and CuCN was carried out and it was found that the best condi-
tions are 1.5 mmol of NaCN, 1.0 mmol of aryl diazonium
K Fe(CN) , Cu(I) or Cu(II) with oxygen, PhIO, RuCl and
3
6
3
related Ru reagents and trichloroisocyanuric acid with
3,11
TEMPO. Also, various aromatic bromides and iodides were
converted into the corresponding aryl nitriles with n-BuLi and
silica sulfates, 0.2 mmol of CuCN and 3.0 mL of H O
2
1
2
DMF followed by the reaction with I in aqueous NH . How-
2
3
(
Table 1).
ever, there are several disadvantages in the literature methods
such as the use of expensive and toxic reagents, low yields,
long reaction times, harsh reaction conditions, difficulty in
obtaining the starting materials and tedious work-up.
Aryl diazonium salts are typically more reactive than aryl
halides and have been extensively employed as nitrogen-
The Sandmeyer cyanation of anilines having electron-donat-
18
ing groups was found to be difficult and in a number of cases,
no product was obtained even with the stoichiometric amounts
26
of copper salt. In our method a series of anilines containing
both electron-donating and electron-withdrawing groups were
converted into the corresponding aryl nitriles in high yields
1
3,14
centred radical scavengers
and as sources of aryl radicals
(
Table 2). Different functional groups such as alkyl, nitro and
15
16 17
in the Meerwein, Gomberg–Bachmann, Pschorr, and
halogens remained intact during the reactions. The nature of
the substituent on the aryl diazonium silica sulfate did not
affect the reaction time (Table 2, entries 1–8) and the steric
effects of the ortho-substituents also had no influence on
the reaction time and yields as well (Table 1, entry 7). 1,4-
Diaminobenzene afforded the double substitution product
18
Sandmeyer type reactions. The Sandmeyer reaction has long
been one of the main routes for the synthesis of aryl halides
or cyanides which includes two steps: diazotisation of the
corresponding amines with sodium nitrite in the presence of
hydrochloric or sulfuric acid, and the subsequent reaction with
3
,4
cuprous halides or cyanide. Despite the high yields, the
utility of this method is limited due to disadvantages such as
the formation of phenols in aqueous media at >10 °C, forma-
tion of azophenols by coupling of phenols with diazonium
salts, the use of hydrochloric acid or sulfuric acid (hazardous,
toxic, extremely corrosive and homogeneous reagent, which
cannot easily be recovered), difficulties in the preparation and
storage of diazonium salts (which are synthesised at around
(
Table 2, entry 8).
Due to the high surface area of the aryl diazonium silica
sulfates, reactions were carried out under mild conditions,
1
0 °C and handled below 0 °C to avoid their decomposition),
the instability and explosive nature of the diazonium salts, the
evolution of poisonous gases such as hydrogen cyanide and the
use of low temperatures. Recently, Beletskaya and co-workers
reported the synthesis of aryl nitriles from the reaction of
aryl diazonium salts with KCN in acetonitrile catalysed by
CuCN/phen/Cu(BF ) /dibenzo-18-crown-6 under an inert
atmosphere. However, it is important to note that the aryldia-
zonium salts bearing electron-donating groups led to the
formation of corresponding nitriles in low yields. Therefore,
the pursuit of more convenient and practical synthetic methods
still remains an active research area.
Scheme 1 Preparation of nitriles.
Table 1 Preparation of p-nitrobenzonitrile using varying
amounts of NaCN and CuCN at room temperaturea
4
2
Yield/%b
Entry
NaCN/mmol
CuCN/mmol
19
1
2
3
4
5
6
7
8
1
0
10
13
20
40
55
87
87
87
1.5
2.5
1
0
0
0.1
0.1
0.1
0.2
0.25
1.5
2.5
1.5
1.5
To resolve the problem of the instability of diazonium salts
and to avoid the application of hydrochloric or sulfuric acid,
stable aryl diazonium salts supported on silica sulfuric acid
a
Reaction conditions: p-nitrophenyl diazonium silica sulfates
1 mmol), H O (3 mL), reaction time (10 min).
Isolated yield.
(
2
b
*
Correspondent. E-mail: davood.habibi@gmail.com

5
74 JOURNAL OF CHEMICAL RESEARCH 2012
Table 2 Preparation of aryl nitriles in the presence of CuCN by reaction of aryl diazonium silica sulfate with sodium cyanide at
room temperature
ν/cm−
1a
Yield/%b
M.p./°C (lit.ref/°C)c
Entry
Substrate
Product
CN
1
2
3
4
5
6
7
8
9
C
6
H
5
NH
2
6
C H
5
2229
2360
2225
2233
2234
2229
2235
2232
2225
87
86
83
87
84
85
83
86
82
Oil27
Oil27
p-MeC
p-IC
p-NO
p-OHC
m-BrC
o-Cl-p-NO
p-NH
p-OMeC
6
H
4
NH
NH
NH
NH
NH
NH
NH
NH
2
p-MeC
p-IC
p-NO
p-OHC
m-BrC
o-Cl-p-NO
p-CNC
6
H
4
CN
CN
CN
CN
CN
CN
CN
2
8
7
8
6
H
4
2
6
H
6
4
124–128 (124–128)
C
6
6
H
4
2
2
C
H
4
145–147 (146–148)2
2
2
H
H
4
2
6
H
4
111–112 (110–113)
38–40 (38–40)28
6
4
2
6
H
4
2
C
4
6
H
3
2
2
C
6
H
3
81–83 (commercial, 83–84)
28
2
C
6
H
2
6
H
4
221–225 (221–225)
58–60 (60–62)27
6
H
4
2
p-OMeC
6
H
4
CN
a
−1
IR absorption of nitriles in wavenumbers (cm ).
Yield refers to the pure isolated product.
The compound reported in the literature.
b
c
2
0
short reaction times and gave higher yields. The only by-
products of these reactions are trace amounts of the corre-
sponding phenol derivatives. The products were obtained by
filtration and the subsequent extraction with ethyl acetate. In a
number of cases, short column chromatography is used for the
products purification and recrystallisation is not needed. The
solid-supported acid can be easily recovered after completion
of the reaction and isolation of the product and the diazonium
salts are consumed in the reaction.
We are thankful to the Bu-Ali Sina University, Hamedan
6517838683 Iran, for the support of this work.
Received 16 May 2012; accepted 25 July 2012
Paper 1201316 doi: 10.3184/174751912X13450494102019
Published online: 28 September 2012
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0
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28
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3
0
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32
ions.

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