How does phosgene convert primary amines into isocyanates?

The reaction between phosgene ($COC{l}_2$) and primary amines is a process of significant industrial importance, primarily used to produce isocyanates.

While phosgene can react with primary amines to form ureas, the reaction is typically carried out under specific conditions that favor the formation of isocyanates. The chemical equation for this conversion is:

$$RN{H}_2+COC{l}_2\to RN=C=O+2HCl$$

In this reaction, the primary amine reacts with phosgene—the acid chloride of carbonic acid—resulting in the formation of the isocyanate group ($RN=C=O$) and the release of hydrochloric acid as a byproduct. These resulting isocyanates are highly reactive and serve as essential building blocks for the production of polyurethane resins.14