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2.5.10 Phosgenation
[45, Senet, 1997]
Chapter 2
About 300000 tonnes of phosgene is used each year in the manufacture of agrochemicals,
pharmaceuticals, dyestuffs and polymerisation initiators. Phosgene is usually used as a building
block to introduce a carbonyl function or as an agent, e.g. for chlorination or dehydrogenations.
Chemical reaction
Phosgenation follows a nucleophilic or Friedel-Crafts related mechanism, depending on the
conditions:
R – H + COCl2 � R – COCl + HCl
Its use as a chlorination or dehydrogenation agent additionally involves the formation of
stoichiometric amounts of CO2.
Operations
Because phosgenation reactions are diverse in nature, there is no universal method of carrying
them out. The production of each compound is thus considered individually, assessing the
chemical, engineering, and economic factors.
Safety issues
The main safety aspect of the phosgenation reaction is related to the high toxicity of phosgene.
Table 2.15 compares phosgene to some other toxic gases.
Gas Odour identification
ppm
L(CT) 0 – 30 min
exposure
Phosgene 1.5 10
Chlorine 1 873
Carbon monoxide No 4000
Ammonia 5 30000
Table 2.15: Comparison of some toxic gases
Due to these high toxicity properties, the handling and storage of phosgene on an industrial
scale on a site must be strictly treated as a major hazard and such sites may fall – depending on
the amount of phosgene handled – under the regime of the Council Directive 96/82/EC (last
modification by Directive 2003/105/EC) on the control of major accident hazards involving
dangerous substances. Therefore, custom synthesis in specialised companies is a common
practice in this field.
For measures to limit the risks arising from the handling of phosgene, see Section 4.2.30.
OFC_BREF Dezember 2005 55