Chemistry Reference
In-Depth Information
carbamoyl chlorides, respectively), in which the main process is chloroformylation,
e.g. reactions involving COCl group transfer. In the present Section, we extend our
survey to chlorination using phosgene or phosgene equivalents.
Chlorination of various monofunctional substrates (e.g. reactions with alcohols
giving alkyl chlorides, or with carboxylic acids giving acid chlorides or anhydrides)
using chlorinated phosgene equivalents (i.e. compounds able to transfer an elec-
trophilic COCl group; chloroformylating agents) is a multi-stage process involving
the formation of chlorocarbonyl functionalized intermediates rather than a one-
step direct substitution reaction. Due to the relatively high reactivity of chloro-
formylated intermediate species, often the literature makes no distinction between
the synthesis of chloroformylated intermediates and their further transformation
into chlorides, carbonates, isocyanates, ureas, etc., as the final ''pseudophosgena-
tion'' reaction products.
The reactivity is typical of that for tricoordinated carbonic acid derivatives, in-
volving an addition-elimination reaction sequence.
CPE
R
O
Cl
R
Cl
R
O
+
CO
2
C
C
C
H
O
1295
1296
1297
C = aliphatic primary, secondary or tertiary carbon atom,
aryl or heteroaryl carbon atom
carbonyl carbon atom
CPE = chlorinated phosgene equivalent
The chlorocarbonyl functionalized intermediates 1296 usually have limited stabil-
ity. Under the reaction conditions, they are not isolable and easily eliminate carbon
dioxide (in the case of O-containing nucleophiles, e.g. alcohols or carboxylic acid
substrates), or benzyl chloride (in the case of N-dealkylation of tertiary benzyl-
amines).
4.4.1
Alkyl Chlorides. Chlorination of Alcohols to give Alkyl Chlorides
A practical and convenient route to a number of chlorinated compounds 1300 is
the direct chlorination of alcohols 1298 [964].
GCl
R
l
R
H
1298
1300
G = H, SOCl, PCl
2
, COCl
Various chlorinating agents, such as thionyl chloride [965], phosphorus trichloride
[966], PPh
3
/tetrachloromethane [967], PPh
3
/hexachloroacetone [968], phosgene
[969-973] or, more economically, phosgene with HCl gas in the presence of an
amine or a quaternary ammonium salt as catalyst [974-977], have been described.
