Phosgene

Phosgene is the chemical compound with the formula COCl2. This colorless gas gained infamy as a chemical weapon during World War I. It is also a valued industrial reagent and building block in synthesis of pharmaceuticals and other organic compounds. In low concentrations, its odor resembles freshly cut hay or grass.
The primary use of phosgene is in the production of toluene diisocyanate (TDI), a precursor of the polyurethane resins used to make foams, elastomers, and coatings. A rapidly growing use of phosgene is in the manufacture of polymethylene polyphenylisocyanate (PMPPI), which is used in the production of rigid polyurethane foams.