Phosgene

Phosgene, also known as carbonic dichloride, colourless, extremely toxic gas of formula COCl₂ with an unpleasant, irritating odour at high concentrations. It is prepared by the reaction of carbon monoxide with chlorine in the presence of a catalyst. Phosgene is poisonous in concentrations above 50 parts per million of air, and if inhaled, it causes severe and often fatal oedema of the lungs within a few hours. It was used in World War I as a poison gas but today is used principally as an intermediate in the synthesis of organic compounds, including carbonic esters, isocyanates, polyurethanes, and dyes.

Phosgene is 3.43 times heavier than air; the gas melts at -118° C (-180.4° F) and boils at 8.3° C (46.9° F).