Phosgene

Phosgene, also known as carbonic dichloride, colorless, extremely toxic gas of formula COCl₂ with an unpleasant, irritating odor 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 edema of the lungs within a few hours. It was used in World War I (1914-1918) as a poison gas (see Chemical Warfare). It was later used 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).