G Model
CCLET-2685; No. of Pages 4
R. Ghorbani-Vaghei et al. / Chinese Chemical Letters xxx (2013) xxx–xxx
3
X
N
chromatography (packed with silica gel, using n-hexane/ethyl
acetate (8:2) as eluent) to achieve the desired 4-nitrobenzonitrile
with 0.14 g, 95% yield.
X
N
X
N
X
N
X
X
+ :PPh3
X
Ph3P
X
S
S
S
S
O
O
O
O
O
O
O
O
1
2.2. Typical procedure for the conversion of 4-nitrobenzaldehyde
X
X
N
X
oxime to 4-nitrobenzonitrile with TBBDA and PPh
3
1
+ R-CH=N-OH
X
N
H
+
Ph3P O-N =CH-R
S
S
2
O
O
O
3
To the mixture of PPh
.53 mmol) in dry acetonitrile (5 mL), 4-nitrobenzaldehyde oxime
0.166 g, 1 mmol) was added. The mixture was stirred at room
3
(0.525 g, 2 mmol) and TBBDA (0.287 g,
O
0
(
X
O=PPh3 + RCN + HX
Ph3P O-N =C-R
temperature. The progress of the reaction was monitored by TLC.
After completion of the reaction (Table 1), the solvent was
evaporated. The crude products were purified by short-column
chromatography (packed with silica gel, using n-hexane/ethyl
acetate (8:2) as eluent) to achieve the desired 4-nitrobenzonitrile
with 0.13 g, 92% yield.
H
3
Scheme 2. Proposed mechanism for the preparation of nitriles from aldoximes.
The reactions proceeded via combination of TBBDA or TCBDA with
4
-Nitrobenzonitrile (Table 1, entry 7): mp 143–147 8C: IR (KBr,
Ph
(Scheme 1).
In order to optimize the reaction conditions, we first examined
the effect of different molar ratios of TBBDA/triphenylphosphine in
CH CN or TCBDA/triphenylphosphine in CH Cl at room tempera-
ture for the conversion of 4-chlorobenzaldehye oxime to 4-
chlorobenzonitrile as a model reaction. We found that the
optimized molar ratio for transformation was 1/0.32/1.2 (4-
3
P in solvent at room temperature under mild conditions
ꢁ
1
1
cm ): 3106, 2233, 1602, 1525, 1349; H NMR (400 MHz, CDCl
3
d
):
.39 (d, 2H, J = 8.8 Hz), 7.92 (d, 2H, J = 8.8 Hz). C NMR (100 MHz,
CDCl ): 150.06, 133.50, 124.32, 118.36, 116.82.
-Nitrobenzonitrile (Table 1, entry 8): mp 114–117 8C: IR (KBr,
13
8
3
d
3
3
2
2
ꢁ
1
1
cm ): 3110, 2232, 1609, 1525, 1344; H NMR (400 MHz, CDCl
3
):
d
8
.58 (s, 1H), 8.52 (d, 1H, J = 9.6 Hz), 8.03 (d, 1H, J = 8 Hz), 7.78 (t, 1H,
13
J = 8 Hz). C NMR (CDCl
27.56, 127.27, 116.55, 114.18.
-Nitrobenzonitrile (Table 1, entry 9): mp 105–109 8C: IR (KBr,
3
, 100 MHz): d 148.27, 137.61, 130.68,
1
3
chlorobenzaldehye oxime/TCBDA/PPh ) and 1/0.53/2 (4-chloro-
2
benzaldehye oxime/TBBDA/PPh ). This method is general and can
3
ꢁ
1
1
cm ): 3112, 2232, 1613, 1530, 1344; H NMR (400 MHz, CDCl
3
):
.39 (m, 1H), 7.96 (m, 1H), 7.88 (m, 2H). C NMR (100 MHz,
CDCl ): 148.68, 135.63, 134.31, 133.70, 125.60, 114.95, 108.17.
-Methoxybenzonitrile (Table 1, entry 10): mp 57–59 8C: IR
d
be easily applied for the conversion of aldoximes to their
corresponding nitriles using the optimized molar ratios of TCBDA
13
8
3
d
and/or TBBDA and Ph
Dehydration reactions of aldoxime with TBBDA and TCBDA do
not proceed in the absence of PPh . Triphenylphosphine is a
3
P (Table 1).
4
ꢁ1
1
(
7
(
KBr, cm ): 3086, 2972, 2224, 1599; H NMR (400 MHz, CDCl
3
):
.62 (d, 2H, J = 8.8 Hz), 6.98 (d, 2H, J = 8.8 Hz), 3.89 (s, 3H). C NMR
): 162.86, 134.02, 119.27, 114.76, 103.98, 55.57.
,6-Dichlorobenzonitrile (Table 1, entry 13): mp 142–144 8C: IR
d
3
1
3
relatively general reducing agent, and its reactions with N-halo
compounds can lead to the formation of phosphonium inter-
mediates. The phosphorus has positive charge in these inter-
mediates, so its reaction as a strong oxophilic reagent in most cases
is driven to the formation of thermodynamically preferred
3
100 MHz, CDCl d
2
ꢁ
1
1
(
7
1
KBr, cm ): 3092, 2233, 1572, 802; H NMR (400 MHz, CDCl
.53–7.45 (m, 3H). C NMR (100 MHz, CDCl
28.18, 114.47, 113.39.
3
):
d
13
3
): d 138.55, 133.86,
triphenylphosphine oxide. Enthalpies of formation of triphenyl-
0
2
,4-Dichlorobenzonitrile (Table 1, entry 14): mp 56–58 8C: IR
phosphine and triphenylphosphine oxide are
D
f
H = +207.02
ꢁ
1
1
0
(
KBr, cm ): 3066, 2233, 1581, 821; H NMR (400 MHz, CDCl
.65 (d, 1H, J = 8.4 Hz), 7.58 (d, 1H, J = 2 Hz), 7.41 (d, 1H, J = 8.4 Hz).
C NMR (100 MHz, CDCl
27.88, 115.27, 111.91.
3
):
d
kJ/mol and
D
f
H = ꢁ116.41 kJ/mol, respectively [6]. As such, the
P 55 O is the major driving force in the proposed
7
formation of Ph
3
13
3
):
d
140.13, 137.86, 134.61, 130.31,
mechanism (Scheme 2).
1
3
In this potential pathway, triphenylphosphine (PPh ) attacks N-
2
-Nitrocinnamonitrile (Table 1, entry 18): mp 87–90 8C: IR (KBr,
halosufonamide compounds, and leads to intermediate 1 in which
the phosphorus atom is more electrophilic. Then, nucleophilic
attacks of aldoxime 2 on this intermediate give compound 3.
Finally, intermediate 3 can be converted to the product via
formation of triphenylphosphine oxide and HX.
ꢁ
1
1
cm ): 3075, 2226, 1605, 1568, 1523, 1342; H NMR (400 MHz,
CDCl ): 8.16 (d, 1H, J = 9.2 Hz), 8.0 (d, 1H, J = 17.6 Hz), 7.77–7.60
m, 3H), 5.89 (d, 1H, J = 16.4 Hz). C NMR (CDCl
47.48, 146.68, 134.09, 131.36, 129.68, 128.75, 125.36, 116.96,
01.55.
3
d
13
(
1
1
3
, 100 MHz): d
4. Conclusion
3
. Results and discussion
3 3
In conclusion, TBBDA/Ph P and TCBDA/Ph P are mild and
In continuation of our interest in the application of TBBDA and
TCBDA, in organic synthesis [5], herein we report a simple and
improved protocol for the preparation of nitriles from aldoximes.
efficient reagent systems for the conversion of aldoximes into
nitriles. Simple work-up, high yields, short reaction times and mild
reaction temperature could also be considered advantages of this
methodology.
TCBDA or TBBDA/PPh3
RCH=N-OH
RCN
solvent / r.t.
Acknowledgment
R = Ar, alkyl
Br
We are thankful to Bu-Ali Sina University, Center of Excellence
and Development of Chemical Methods (CEDCM) for financial
support.
Cl
Cl
Cl
Br
Br
N
N
N
N
S
S
S
S
Cl
Br
O
O
O
O
O
O
O
O
References
TBBDA
TCBDA
Scheme 1. Synthesis of nitriles from aldoximes.