Chemistry Reference
In-Depth Information
Fe
2
O
3
, or active charcoal
2 COCl
2
or AlCl
3
, or FeCl
3
CCl
3
OCOCl
Al
2
O
3
CO
2
+ CCl
4
Two different diphosgene decomposition routes have also been noted in the pres-
ence of aluminum(III) chloride, one giving hexachloroethane and carbon dioxide and
the second giving trichloroacetyl chloride and phosgene [61].
Cl
Cl
Cl
+ CO
2
Cl
Cl
O
Cl
Cl
AlCl
3
Cl
Cl
O
Cl
Cl
O
Cl
Cl
+
Cl
Cl
Cl
O
The thermal decomposition of a series of compounds containing the trichloromethyl
group, generating two or three moles of phosgene per mole of starting material,
has been reported [55, 57, 59, 62].
Thermal or catalytic
decomposition
Cl
O
O
O
Cl
+
Cl
O
R
Cl
Cl
Cl
R
R = alkyl, Cl or OCCl
3
Therefore, diphosgene can be regarded as being equivalent to two molecules of
phosgene, into which it is slowly decomposed when pure [58]. One of the internal
trichloromethyl chlorine atoms probably plays the Nu role in a four-membered cy-
clic transition state. A continuous stream of phosgene is also emitted when tri-
chloromethyl chloroformate is simply heated under reflux [55].
O
> 100°C
heat under reflux
Cl
O
O
O
Cl
Cl
Cl
+
Cl
O
Cl
O
Cl
Cl
Cl
Cl
Cl
Cl
Nucleophilic reactions of diphosgene highlight its reactivity as a tricoordinated
carbonic acid derivative. Its phosgene equivalence can be rationalized in terms of
the mechanistic scheme shown below (e.g. route a with a dialkylamine as HNu),
whereby a mole of phosgene is released during the nucleophilic substitution. Sev-
eral examples of route b have also been reported. From the reaction of diphosgene
