Chemistry Reference
In-Depth Information
10
C and the reaction time could be
reduced drastically to less than 1 min [1103]. A 15% improvement in the yield from
67 to 82% could be achieved by using 1,2-dibromotetrachloroethane instead of tet-
rachloromethane in the dehydration of carbaldoxime 1453 to the cyanide 1454 with
triphenylphosphine.
perature could be lowered significantly to
Typical procedure. 5-Benzoxycarbonyl-2-cyano-4-(2-methoxycarbonylethyl)-3-methoxycar-
bonylmethylpyrrole 1454 [1103]:
To a mixture of the oxime 1453 (402 mg, 1.0
mmol) and triphenylphosphine (524 mg, 2.0 mmol) in dry 1,2-dichloroethane
(20 mL), a solution of 1,2-dibromotetrachloroethane (652 mg, 2 mmol) and tri-
ethylamine (0.56 mL, 4.0 mmol) in dichloroethane (10 mL) was added at
10
C.
Removal of the precipitate by filtration and evaporation of the solvent under re-
duced pressure left an oily residue, which was passed through a short column of
silica gel eluting with petroleum ether (bp 40-60
C)/diethyl ether (1:2). Crystalli-
zation from ligroin afforded 1454; yield: 316 mg (82%); mp 116
C; IR (KBr):
n
max
¼
2215 cm
1
(CN).
CO
2
Me
Ph
3
P
BrCl
2
C-CCl
2
Br
CO
2
Me
CO
2
Me
CO
2
Me
Et
3
N
dichloroethane
- 10°C, < 1 min
BnO
2
C
N
H
BnO
2
C
CN
H
OH
1453
82 %
1454
Thionyl chloride
An often used dehydrating agent is thionyl chloride. It is very volatile, and thus any
excess can easily be removed. However, its decomposition product is gaseous sul-
fur dioxide, which is severely disadvantageous owing to its ecological impact (see
also Chapter 6). An Organic Synthesis procedure is given for the production of 2-
ethylhexanonitrile 1456 in yields of 86-94% [1104].
CH
3
(CH
2
)
3
CH(C
2
H
5
)CONH
2
+
SOCl
2
→
CH
3
(CH
2
)
3
CH(C
2
H
5
)
CN
+ SO
2
+ 2 HCl
1455
1456
Typical procedure. 2-Ethylhexanonitrile 1456 [1104]:
In a 1-L round-bottomed flask,
fitted with an e
cient reflux condenser, were placed 2-ethylhexaneamide 1455
(286 g, 2mol), dry benzene (300mL), and thionyl chloride (357 g, 218mL, 3mol). The
flask was placed in a water bath, which was quickly heated to 75-80
C and main-
tained at that temperature for 4.5 h. The reaction mixture was then transferred to a
1.5-L beaker and cooled in an ice bath. A mixture of crushed ice (100 g) and water
(100 mL) was added to decompose the excess thionyl chloride. Cold 50% aq. po-
tassium hydroxide solution was then added in small portions with stirring until the
