Chemistry Reference
In-Depth Information
alcohols, phenols, and aldehydes [74-77]. In the entire period up to 1980, only a
dozen papers and patents appeared, whereas in the last decade their number has
grown exponentially. Several literature contributions have reviewed the synthetic
possibilities of this reagent, and have thereby opened up many synthetic oppor-
tunities for pharmaceutical and agrochemical applications [10-19, 78, 79].
2.2.2.1
Triphosgene as a Phosgene Equivalent or Phosgene Source
Triphosgene is used as a phosgene equivalent [10-19, 78, 79] or as a source of
phosgene [3, 69, 80, 81].
Triphosgene may have an important role to play in evaluating the use of phos-
gene in a synthesis. One of the recent developments in current use, tested some
years ago in various laboratories, is the pre-packaged cartridge for ''intelligent''
phosgene production based on triphosgene ''depolymerization'' using a solid cata-
lyst containing one or several nitrogen atoms with a pair of deactivated electrons.
Dr. Eckert GmbH have designed a process based on downstream demand, in which
triphosgene is employed as a phosgene source [3, 80-84] (see also Chapter 7).
The method may be classified within the group of ''methods using compounds as
in situ phosgene source (precursor)'' (see Chapter 3) and has important advantages
over the traditional methods of phosgene manufacture in small- and medium-scale
phosgenations, considering the very mild and highly versatile conditions of opera-
tion based on established chemistry, and the ready availability of the high turnover
catalyst (owner Dr. Eckert GmbH [82]).
2.2.2.2
Stability : Thermally and Chemically Induced Decomposition
In spite of the growing interest in synthetic applications, no systematic investi-
gation on triphosgene stability has yet been reported. Since its first preparation,
bis(trichloromethyl)carbonate has been regarded as a stable solid compound. How-
ever, Hood [51] noted a marked decomposition into diphosgene and phosgene
when the product was distilled. A decomposition route via a four-membered tran-
sition state, akin to that depicted for diphosgene in Section 2.2.1, can be envisaged.
Cl
O
l
O
Cl
O
l
O
CCl
O
D
Cl
Cl
O
Cl
Cl
Cl
Cl
+
Cl
O
Cl
Cl
CI
Cl
O
O
CI
Cl
Grignard [70], Kling [85], and Marotta [86] have studied the thermal decomposi-
tion of triphosgene, and, although their results were somewhat divergent, high
thermal stability up to 300
C was claimed.
The thermogram obtained by differential scanning calorimetry (DSC) shows a
melting peak at 82.4
C and an exothermal decomposition peak starting at 160
C
(
200 J g
1
). Tests on an accelerating rate calorimeter (ARC) showed the
onset of decomposition at 130
C, with
D
H
dec
¼
278 J g
1
, and a final temperature
of 179
C. The accumulated data do not support the originally claimed stability
D
H
dec
¼
