K4[Fe(CN)6] as non-toxic source of cyanide for the cyanation of aryl halides using Pd-Beta zeolite as a heterogeneous catalyst

Article abstract of DOI:10.3184/174751913X13787959859425

A new method for the synthesis of aryl nitriles has been developed by the reaction of aryl halides with K₄Fe(CN)₆ in the presence of Pd-Beta zeolite as efficient and recyclable catalyst.

Full text of DOI:10.3184/174751913X13787959859425

620 RESEARCH PAPER
OCTOBER, 620–622
JOURNAL OF CHEMICAL RESEARCH 2013
K [Fe(CN) ] as non-toxic source of cyanide for the cyanation of aryl halides
using Pd-Beta zeolite as a heterogeneous catalyst
4
6
b
c
S. Mohammad Sajadi*, Mehdi Maham and Sarbast Ahmad Mahmoud
a
Department of Petroleum Geoscience, Faculty of Science, Soran University, Soran, Kurdistan Regional Government, Iraq
Department of Chemistry, Islamic Azad University, Aliabad Katoul, Iran
Department of Biology, Faculty of Science, Soran University, Kurdistan Regional Government, Iraq
b
c
A new method for the synthesis of aryl nitriles has been developed by the reaction of aryl halides with K Fe(CN) in the presence
4
6
of Pd-Beta zeolite as efficient and recyclable catalyst.
Keywords: aryl nitriles, aryl halide, K Fe(CN) , cyanation, palladium, zeolite
4
6
Nitriles are versatile intermediates in organic synthesis,
since they not only constitute key components of a range of
pharmaceuticals, agrochemicals, dyes, but can also easily
the synthesis of aryl nitriles via cyanation of aryl halides using
Pd-zeolite. Among zeolites, Beta zeolite has been reported to
be an efficient catalyst in a number of chemical transformations
1
33,34
be converted into other functional groups such as nitrogen-
including alkylation and acylation.
Its activity arises from
2
,3
containing heterocycles, aldehydes, acids and acid derivatives.
Nitriles are conventionally synthesised by reaction of
its large pore size, high Si/Al ratio, high acid strength, and
thermal stability.
4
,5
aryl halides with stoichiometric amounts of CuCN, the
In continuation of our recent studies on the application of
6
,7
diazotisation of anilines and subsequent Sandmeyer reaction,
the transition metal-catalysed cyanation of aryl halides using
32,35,36
nitriles, zeolites and other natural products,
we report a
new method for the preparation of aryl nitriles via cyanation
8
–13
KCN, NaCN, Me SiCN and Zn(CN) as cyanating agents.
37
3
2
aryl halides with K Fe(CN) in the presence of Pd-Beta zeolite
4
6
However, most of these synthetic methods suffer from different
drawbacks such as employing expensive, moisture sensitive,
toxic and hazardous reagents, use of expensive catalyst or
reagents, several-step methods, long reaction times, low yields
of the products that restrict their usage in practical applications.
as a heterogeneous catalyst.
Pd-zeolite
ArX + K
Fe(CN)
ArCN
4
6
o
DMF, Cs CO , 130 C, 10 h
2
3
X: Br, Cl
Scheme 1
Furthermore, CuCN and Zn(CN) lead to heavy metal waste.
2
Due to safety considerations, we required a method that did
not use of toxic reagents. Therefore, it is desirable to develop a
more efficient and convenient method for the synthesis of aryl
nitriles without the application of expensive, moisture sensitive
and toxic reagents. To resolve this problem, Beller and co-
workers have described a convenient synthesis of nitriles by
potassium hexacyanoferrate (II), K Fe(CN) , as a non-toxic
Results and discussion
In order to find the optimum conditions, we carried out the
reaction of bromobenzene with K Fe(CN) in the presence of
4
6
various solvents and bases using Pd-Beta zeolite (0.025 mmol
Pd) under various temperature conditions. Several organic
solvents such as toluene, methanol, DMF, NMP and acetonitrile
were examined. The data shown in Table 1, revealed that DMF
was the most efficient solvent for this reaction (Table 1, entry
4
6
14,15
cyanide source.
This reagent is commercially available on
ton scale and cheaper than KCN and NaCN and it is even used
in food industry for metal precipitation.
5
). After choosing DMF as the solvent, we examined several
different bases. Our experiments showed that the base was
necessary for the cyanation reaction (Table 1, entry 11). Among
the selected bases, Cs CO acted as the most effective (Table
Homogeneous catalysts have been widely investigated,
among various catalysts for the transition metal-catalysed
16–19
2
3
cyanation of aryl halides with K Fe(CN) ,
Less expensive
4
6
1, entry 5). Moreover, as each mol of K Fe(CN) contains six
4 6
heterogeneous catalysts have received scanter attention.
Thus, the development of a catalytic synthetic method for the
synthesis of nitriles still remains an active research area.
cyanide ions, the ratio of K Fe(CN) to aryl halide was chosen
4
6
0.22:1. We then used the optimum reaction conditions (aryl
2
0–28
halide (1.0 mmol), K Fe(CN) (0.22 mmol), Cs CO (1.0 mmol)
Recent studies of catalysis
have shown that by using
4
6
2
3
and DMF as solvent) for the cyanation of different aryl halides
under thermal conditions. The results are shown in Table 2.
inexpensive and non-corrosive heterogeneous catalysts,
chemicaltransformationsoccurwithbetterefficiency,providing
higher purity of the products, and easier workup, with evident
economic and ecological advantages especially for the industrial
processes. Zeolites are crystalline hydrated aluminosilicates
of the earth alkalines. The application of inorganic solid
acids, especially zeolites, as effective heterogeneous catalysts
for organic synthesis has received considerable attention in
the recent decades due to their microporosity, large surface
Table 1 Optimisation of reaction conditions in cyanation reaction of
bromobenzene with K Fe(CN)
4
6
Entry
Base
Solvent
Temperature/ºC Time/h Yield/%a
1
2
3
4
5
6
7
8
9
Cs CO
Toluene
Reflux
Reflux
Reflux
130
20
20
20
10
10
12
12
10
11
11
20
0
0
0
2
3
3
3
3
3
Cs CO
CH CN
2
3
Cs CO
MeOH
NMP
DMF
DMF
DMF
DMF
DMF
DMF
DMF
2
2
9–32
Cs
2
CO
80
91
21
27
85
79
61
0
area, thermal and chemical stability zeolites.
We recently
Cs CO
130
130
130
130
130
130
130
2
published a synthesis of formamides in high yields using HEU
Et N
32
3
Zeolite as a natural and heterogeneous catalyst. In spite of
these interesting properties of zeolites, there are no reports of
NaF
K CO
2
3
KOAc
10
Na CO
2
3
*
Correspondent.
11
–
E-mail: phytochem2006@gmail.com; mohammad.s@soranu.com
aYields are after work-up.
JCR_1302020_FINAL.indd 620
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JOURNAL OF CHEMICAL RESEARCH 2013 621
a
Table 2 Cyanation reaction of various aryl halides using K Fe(CN) in the presence of Pd-zeolite at 130 °C
4
6
Yield/%b
M.p./°C
Oil
Oil
Oil
59–61
57–59
64–66
84–86
76–78
Oil
59–61
56–58
65–67
221–225
110–115
36–38
Lit.m.p./°C
Ref
Entry
Substrate
C H I
Product
C H CN
7
1
2
3
4
5
6
7
85
80
83
84
87
87
86
79
85
83
82
89
90
91
87
Oil
Oil
Oil
6
5
6
5
7
p-MeC H I
p-MeC H CN
6
4
6
4
3
8
o-MeC H I
o-MeC H CN
6
4
6
4
7
p-MeOC H I
p-MeOC H CN
58–60
6
4
6
4
3
3
3
9
9
9
p-COMeC H I
p-COMeC H CN
56–59
65–67
85–87
6
4
6
4
p-COOMeC H I
p-COOMeC H CN
6
4
6 4
m-OMe-p-OHC H I
p-OH-m-OMeC H CN
6
3
6
3
3
9
8
9
4-IC H N
4-CNC H N
76–79
5
4
5
4
7
C H Br
C H CN
Oil
6
5
6
5
7
3
3
10
p-MeOC H Br
p-MeOC H CN
58–60
56–59
65–67
6
4
6
4
9
9
1
1
p-COMeC H Br
p-COMeC H CN
6
4
6 4
1
2
p-COOMeC H Br
p-COOMeC H CN
6 4
6
4
7
1
3
p-CNC H Br
p-CNC H CN
221–225
6
4
6
4
3
8
1
4
p-BrC H I
p-BrC H CN
110–115
6
4
6
4
3
8
15
1-C H Br
1-C H CN
36–38
10
7
10
7
a
Reaction conditions: Pd-zeolite (0.025 mmol Pd), aryl halide (1 mmol), K Fe(CN) (0.22 mmol), Cs CO
3
4
6
2
(
1.0 mmol), DMF (5 mL), 130 °C, 10 h.
b
Yields are after work-up.
Various aryl nitriles were synthesised from different aryl
halides containing both electron-releasing and electron-
withdrawing groups with K Fe(CN) in DMF in excellent
solution mixture was stirred for 24 h at room temperature, filtered and
–
washed with water until no Cl ion was detectible within the filtrate.
–1
Calcination at 500 °C under pure O (180 mL min ) of the exchanged
2
4
6
palladium zeolite gave the Pd-Beta zeolite. The palladium content
was determined by the inductively coupled plasma (ICP) method,
using a Perkin-Elmer 3300 DV spectroscope, after calcinations of
the sample at 450 °C for 100 min in flowing oxygen. The catalyst was
characterised using the powder XRD, TEM and BET.
yields under thermal conditions. In addition, the reactions
were able to tolerate a wide range of functional groups such
as ketone carbonyl, ester, methoxy, nitrile and hydroxy groups.
The reactions appeared to be insensitive to the steric hindrance
around the reaction site. For instance, 4-iodotoluene gave a
yield of 80%, while 2-iodotoluene with a bigger steric hindrance
around the reaction site also gave a high yield (Table 2, entries 2
and 3). As an example for an electron-poor nitrogen heterocycle
Cyanation of aryl halides with K Fe(CN) ; general procedure
4
6
A mixture of the aryl halide (1.0 mmol), K Fe(CN)6 (0.22 mmol),
4
Cs CO (1.0 mmol), Pd-zeolite (0.025 mmol Pd) and 5 mL of solvent
2
3
(
DMF) was placed in a Schlenk tube (25 mL), and was vigorously
4
-iodopyridine was cyanated in good yield (Table 2, entry 8).
stirred for 10 h at 130 °C. Upon completion, the mixture was cooled to
room temperature, and diluted with ether and water. Organic layer was
High selectivity was observed for 1-bromo-4-iodobenzene
(
Table 2, entry 14).
washed with brine, dried over MgSO , filtered and evaporated under
The products were characterised by melting points, elemental
4
1
13
reduced pressure using rotary evaporator to give the crude product.
The residue was purified by recrystallisation using ethanol and water.
analysis (CHN), IR, H NMR and C NMR. The IR spectra of
the products showed one sharp absorption band in the range of
1
The purity of the compounds was checked by H NMR and yields are
–1
2
225–2360 cm (CN stretching band).
based on aryl halide. All the products are known and the spectroscopic
data (FT-IR and NMR) and melting points were consistent with those
In conclusion, we have developed an efficient procedure for
the ligand-free cyanation of aryl iodides and aryl bromides
using non-toxic K Fe(CN) as the cyanide source and Pd-Beta
4–19,38,39
reported in the literature.
4
6
zeolite as a reusable heterogeneous catalyst under thermal
conditions in DMF. The reactions occurred on the external
surface of the zeolite. This method has the advantages of high
yields, elimination of toxic reagents, simple methodology and
easy work-up. Chromatographic separation was not required to
obtain the pure compounds.
We gratefully acknowledge Soran University for support of this
work.
Received 21 June 2013; accepted 6 August 2013
Paper 1302020 doi:10.3184/174751913X13787959859425
Published online: 7 October 2013
Experimental
All reagents were purchased from the Merck and Aldrich chemical
companies and used without further purification. Products were
characterised by comparison of their physical and spectroscopic data
with authentic samples. The NMR spectra were recorded in DMSO.
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