Chemistry Reference
In-Depth Information
Cl
CCl
4
, 77°C
or without solvent
h
n
O
O
Cl
4 HCl
+
4 Cl
2
+
O
O
Cl
O
O
Cl
O
O
Cl
+
Cl
Cl
Cl
O
The above process was improved by carrying out the photochemical chlorination of
ethylene carbonate in the presence of an initiator, with a high-pressure Hg lamp at
70-100
C, and with continuous circulation of the liquid through an illuminated
side-arm. It has been found that ethylene carbonate can be photochemically con-
verted to the tetrachloro derivative in the absence of a solvent, and the process has
been performed on a 200 L scale.
The reagent is used as a mild substitute for phosgene, thionyl chloride, or phos-
phorus pentachloride. The by-products resulting from the reactions involving ox-
alyl chloride are usually gases (HCl, CO, and CO
2
).
The main applications of oxalyl chloride, as described in Chapter 4, are the
formation of aryl isocyanates and chloroformates (by reactions with amines and
hydroxylic substrates, respectively), and the formation of acyl chlorides from car-
boxylic acids under very mild conditions. Oxalyl chloride reacts with amides to
give acyl isocyanates, and it is used with dimethyl sulfoxide as a mild reagent
for the oxidation of alcohols (Swern-type oxidation). It is also used with N,N-
dimethylformamide as a mild reagent for chlorination and formylation. Oxalyl
chloride is widely used in commercial formulations of speciality polymers, anti-
oxidants, photographic chemicals, X-ray contrasting agents, and chemiluminescent
materials. Other physical properties are presented in Chapter 3.
2.3.2
1,1-Carbonyldiimidazole
1,1-Carbonyldiimidazole (CDI) is a crystalline phosgene substitute (mp 117-122
C) and a preferred reagent for carboxyl activation. Salts (triflate or sulfate) of CDI
are also used as activating agents in peptide and ester formation with retention of
optical activity [104, 105].
CDI is prepared by the phosgenation of 1H-imidazole with phosgene in tetrahy-
drofuran [106] or aromatic solvents [107, 108], or in the presence of tributylamine
[109].
N
COCl
2
solvent
N
N
N
N
H
O
