Chemistry Reference
In-Depth Information
4.3.6.3
Triphosgene
Triphosgene has been employed as a phosgene equivalent in the preparation of ben-
zophenones 1284 [959].
O
R
(CCl
3
O)
2
CO
AlCl
3
R
R
1283
1284
R = H, Cl, CH
3
, (CH
3
)
2
N
By adding aluminum trichloride to a solution of triphosgene in chlorobenzene
1285 at 0-10
C and gradually heating to 90
C, a mixture of two benzophenones,
1286 and 1287, is formed [960]. Regioselective formation of 4,4
0
-dichlorobenzo-
phenone can be achieved by the reaction of 4-chlorobenzoyl chloride 1288 with
chlorobenzene.
Cl
O
O
1.
(CCl
3
O)
2
CO
,
AlCl
3
, 0-10°C
Cl
+
2. 90 °C
Cl
Cl
Cl
1286/1287
= 70:30
1285
1286
1287
COCl
AlCl
3
PhCl
Cl
1286/1287
= 96:4
1288
Cl
1285
Triphosgene is able to chlorocarbonylate activated aromatic compounds such as
toluene 1289a, anisole 1289b, 1,4-dimethoxybenzene 1289c, and N-ethyl-N-cyclo-
hexyl aniline 1289d under special conditions (molar excess of triphosgene and
AlCl
3
) to form substituted benzoic acid chlorides 1290a-d in moderate yields (51-
62%, Table 4.44) [961, 962].
This chlorocarbonylation reaction proceeds satisfactorily in refluxing dichloro-
methane, with a molar ratio of 1289/triphosgene/AlCl
3
of 1:2:3, although long re-
action times are required (Table 4.44).
Typical procedure. 2,5-Dimethoxybenzoyl chloride 1290c [962]:
AlCl
3
(4.0 g, 30 mmol)
was suspended in dichloromethane (30 mL). To this mixture, a solution of 1,4-
dimethoxybenzene (1.38 g, 10 mmol) and triphosgene (5.94 g, 20 mmol) in di-
chloromethane (30 mL) was added dropwise over a period of 30 min. The resulting
