Chemistry Reference
In-Depth Information
O
Ts-Cl
O
O
O
O
N
N
H
H
pyridine
Et
3
N
40°C, 40 min
23 %
1744
1743
Typical procedure. Bis(2-vinyloxyethyl)carbodiimide 1744 [1280]:
To a vigorously
stirred solution of the urea 1743 (4.99 g) in pyridine (50 mL) and triethylamine (14
mL), p-toluenesulfonyl chloride (9.52 g) was added in small portions. (Spontane-
ous heating of the reaction mixture to 41
C was observed.) Stirring was continued
for a further 40 min. The precipitated salts, i.e. triethylammonium tosylate and
triethylammonium chloride, were filtered off, the solvent was removed from the
filtrate, and the residue was distilled in vacuo to give 1.02 g (23%) of the carbodi-
imide 1744;bp82
C (0.5 mmHg); IR: n
max
2130 cm
1
. On storage under nor-
mal conditions, carbodiimide 1744 is stable for several months.
A method has been described for the preparation of carbodiimides 1699 by de-
hydration of ureas 1696 with p-tosyl chloride under solid-liquid phase-transfer
catalytic (PTC) conditions using solid potassium carbonate as a base and a lipo-
philic quaternary ammonium salt as a catalyst. The method is generally applicable
for the synthesis of disubstituted carbodiimides, but is especially useful for un-
symmetrically substituted carbodiimides. Yields of the resulting carbodiimides
1699 vary depending on the solvent (usually used at reflux temperature); in ben-
zene or toluene yields of 66-98% are achieved, while in chloroform they are only
30-50% [1281].
¼
General procedure. Carbodiimides 1699 from ureas [1281]:
A solution of disubsti-
tuted urea 1696 (10 mmol) and p-toluenesulfonyl chloride (10 mmol) in benzene
or toluene (70 mL) is stirred at reflux temperature for 1-5 h in the presence of
potassium carbonate (3.53 g, 40 mmol) and benzyltriethylammonium chloride
(TEBAC) (0.23 g, 1 mmol).
O
Ts-Cl
R
R
R´
N
N
H
H
R´
toluene or benzene
TEBAC, K
2
CO
3
reflux, 1-5 h
66-98 %
1699
1696
The reaction is monitored by TLC. The resultant precipitate is filtered off, and the
filtrate is washed with water (2
10 mL). The organic layer is dried with magne-
sium sulfate and concentrated to give the carbodiimide 1699 as an oily residue
(66-98% yield), which is generally pure or can be distilled in vacuo.
CDC (2-Chloro-1,3-dimethylimidazolinium chloride)
The versatile dehydration reagent CDC has also been employed to prepare carbo-
diimides 1699 from the corresponding thioureas 1740 in yields of 40-88% [1137].
