Chemistry Reference
In-Depth Information
with oximes (HNu is HO
a
N
b
CR
2
), mixtures of products arising from routes b and
a/c have been recovered [63].
H
O
O
Cl
O
Cl
O
Cl
O
a
Cl
Cl
Cl
Cl
Cl
+
Cl
Cl
Cl
Nu
Nu
Cl
O
CI
NuH
Cl
O
-
H
Cl
Cl
O
HNu:
H
Cl
O
Cl
O
b
Cl
c
Cl
Cl
Cl
O
Nu
-
H
Cl
Cl
O
Nu
H
O
Cl
O
Cl
O
O
Cl
O
Cl
Cl
Cl
a
Cl
Cl
Cl
R
R
+
Cl
N
Cl
O
CI
Cl
O
N
R
Cl
CI
Cl
O
NH
R
N
Cl
R
R
Diphosgene has been used as a phosgene source in many applications. The chlori-
nation of carboxylic acids in the presence of dimethylformamide as catalyst is an
e
cient route to highly pure acid chlorides [64]. In a practical method for the
chlorination of carboxylic acids, diphosgene is conveniently converted into phos-
gene by dissolving it in tetrachloromethane containing a basic catalyst (diphosgene
in CCl
4
:pyridine, 400:1, for 30 min; yields 90%) [65]. Several nitrogen compounds,
e.g. pyridine, quinoline, tetramethyl urea, or tertiary amines, have also been re-
ported to catalyze the quantitative decomposition of diphosgene into phosgene
[66, 67].
Diphosgene decomposes very rapidly and quantitatively in the presence of a
nucleophile such as a ''naked'' chloride anion [68, 69]. Nucleophilic attack at the
carbonyl atom, which is the origin of the molecule-catalyzed ''decomposition'' and
of phosgene release, can be generalized according to the scheme below. In many
cases, in situ generated phosgene reacts very rapidly with the nucleophile, which
acts as a ''phosgene scavenger'' affording chlorocarbonyl or nucleophilic dis-
ubstituted derivatives, respectively, as the reaction products.
Cl
O
O
O
Cl
Cl
+
Nu:
+
Cl
O
Nu
Cl
Cl
Cl
Cl
Cl
O
Cl
Cl
O
CI
Cl
O
Cl
O
O
O
Cl
Cl
Cl
Cl
or
+
+
Cl
Nu:
Cl
O
Nu
Nu
Cl
Cl
Cl
Nu
Cl
O
The stability of diphosgene in the presence of various metal (Fe, Al, V) oxides and
chlorides has been extensively investigated in order to find practical routes for
quantitative decomposition or to establish the compatibility of the reagent with
various materials [51].
Diphosgene was first prepared by Hentschel, who obtained a mixture of chlori-
