Chemistry Reference
In-Depth Information
H
N
H
N
H
H
Cl
Cl
Cl
O l
Cl
H
NH
R
R
C
Cl
+
O l
O
O
Cl
Cl
R
Cl
O
O
Cl
O
O
O
Cl
Substrate:Triphosgene 1:1
Substrate:Triphosgene 1:0.33
- CO
2
2 Et
3
N
N
Cl
RNC
R
- 2 HCl
H
The above mechanism is similar to that proposed by Nakajima [13] for the dehy-
dration of primary amides under Swern conditions. There is an obvious analogy
between a sulfoxonium salt and chloroformate:
Me
Me
Me
Me
S
S
S
O
OH
O
Me
O
Me
Cl
RCN
R H
R H
RN
R
2
H
Et
3
N
Therefore, the formation of chloroformate, or compounds of similar structure, as
key intermediates of limited (low) stability is the driving force behind many pro-
cesses involving phosgene or phosgene equivalents.
Triphosgene is quantitatively converted to phosgene by catalysts such as chloride
ion [2-4]. The reaction course has been monitored by IR spectroscopy (React-IR),
which showed diphosgene to be an intermediate. The methanolysis of triphosgene
in deuterated chloroform, as monitored by
1
H NMR spectroscopy, gave as pri-
mary products methyl chloroformate and methyl 1,1,1-trichloromethyl carbonate
in about a 1:1 ratio. The reaction carried out in the presence of a large excess of
Tab. 3.1.
Pseudo-first-order rate constants for the reactions of
phosgene, diphosgene, and triphosgene (0.01
m
) with
) in CDCl
3
at 25
C, calculated from the initial
methanol (0.3
m
rates [4].
Substrate
k
obs
,s
C1
MeOH, 0.3
M
Cl
C
5%
a
MeOH, 0.3
M
Cl
C
10%
a
MeOH, 0.3
M
Phosgene
1.7
10
2
b
b
10
4
10
3
10
3
Diphosgene
9.1
1.0
1.1
Triphosgene
1.0
10
4
2.3
10
4
2.3
10
4
a
added as Bu
4
N
รพ
Cl
;
b
too fast to be measured by NMR
