3.6 Uses
Phosgene is a widely used chemical intermediate, primarily manufactured for the
synthesis of isocyanate-based polymers, carbonic acid esters and acid chlorides. It is
also used in the manufacture of dyestuffs, some insecticides and pharmaceuticals and
in metallurgy.
Phosgene consumption is summarized below:
Practically all phosgene manufacture is captive; it is used in the manufacture
of other chemicals within the plant boundary. Globally, approximately 75% of
phosgene is consumed for isocyanates, 20% for polycarbonates, and about
5% for fine chemicals.
TDI Reaction: The overall reaction of toluene diamine with phosgene to form
toluene diisocyanate (TDI) is shown below:
CH3-C6H3(NH2)2+ 2 COCl2 ----- > CH3-C6H3(NCO)2 + 4 HCI
Toluene diamine Phosgene TDI HCI
MDI Reaction: The overall reaction of Diaminodiphenyl methane with phosgene
to form Methyldiphenyl diisocyanate (MDl) is shown below:
2(C6H4)-CH2-2(NH2) + 2 COCl2 ----- > 2(C6H4)-CH2-2(NCO) + 4 HCI
Diaminodiphenyl methane Phosgene MDI HCl
Polycarbonate Reaction: The reaction of Bisphenol-A with phosgene gives the
very hard and strong polycarbonate plastics that can be molded and extruded.
x(HO-C6H4-C(CH3)2-C6H4-OH) + x(COCl2) - > 2x HCI + [-OCO-O-C6H4-C(CH3)2-C6H4-]x
Bisphenol-A Phosgene HCl Polycarbonate
When phosgene reacts with alcohols, the alkyl chloroformate is formed first and further
reaction gives the alkyl carbonate.
COCl2 + C2H5OH --- > ClCOOC2H5 + HCI
Phosgene Ethyl chloroformate
CICOOC2H5 + C2H5OH--- > OC(OC2H5)2 + HCl
Ethyl carbonate