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How is phosgene used to make polyurethanes?

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A labeled diagram of the chlorine element from the periodic table shows its atomic number 17, symbol Cl, electron configuration, and atomic weight range. The box is shaded green to indicate chlorine is a halogen, with icons for orthorhombic crystal structure, gas state at room temperature, and strong acidity. A key explains the icons and colors used. — chlorine Properties of chlorine.

Phosgene is a critical chemical intermediate used in the production of polyurethane resins primarily through its role in synthesizing isocyanates.1

The process involves the reaction of primary amines with phosgene ( $C O C l_{2}$ ), which acts as the acid chloride of carbonic acid. Under specific industrial conditions, this reaction converts primary amines into isocyanates according to the following chemical equation:2

$R N H_{2} + C O C l_{2} \to R N = C = O + 2 H C l$

These resulting isocyanates serve as essential building blocks for polyurethane. Because phosgene is a highly toxic gas, its industrial use requires stringent safety protocols to prevent exposure, which can cause severe lung injury. The production of phosgene itself relies on chlorine, as it is manufactured by reacting carbon monoxide with chlorine in the presence of a catalyst.1