Phosgenation

Phosgenation is a chemical process in which phosgene (COCl2) reacts with nucleophiles such as alcohols, phenols, amines, and carbanions to form carbonyl-containing derivatives. Common products include aryl and alkyl chloroformates (from alcohols or phenols), carbonates (from diols), carbamoyl chlorides (from amines), and isocyanates (via further transformation of carbamoyl chlorides). The reaction proceeds by nucleophilic attack at the carbonyl carbon of phosgene, with chloride acting as the leaving group. Reactions are typically conducted with bases or amines to scavenge the generated HCl.

In laboratory and industrial contexts, phosgenation provides routes to a variety of materials. Phosgene reacts with dihydroxy compounds to form polycarbonates through interfacial polycondensation, a route historically used to make commercial polycarbonates such as those derived from bisphenol A. The process often employs two immiscible phases (water and organic solvent) and bases to neutralize HCl, yielding polymer chains with carbonate linkages. Phosgenation of amines gives carbamoyl chlorides, which can be converted to isocyanates, key intermediates in polyurethane production. Similarly, formation of chloroformates from phenols or alcohols enables subsequent carbonate or urethane chemistries.

Safety and environmental considerations are central to phosgenation. Phosgene is a highly toxic gas and poses severe health risks upon exposure. Industrial implementations rely on closed systems, stringent controls, scrubbers, and regulatory compliance to prevent release and manage neutralization of byproducts such as HCl and CO2.