Synthesis of Polyurethane Raw Material Using CO₂ as a Resource

Abstract

Production of useful chemicals using CO₂ as a resource is attracting attention as a technology to reduce CO₂ emissions and contribute to the prevention of global warming. Isocyanates, the raw material for polyurethanes that are mass-produced and used for long periods of time, are one of the ideal core chemicals as a target for this technology. Therefore, organic carbamates, which give isocyanates through pyrolysis, are focused attention as an intermediate compound for the synthesis of isocyanates from CO₂. In this paper, we introduce the efficient and environmentally benign synthesis methods for organic carbamates from CO₂ using regenerable metal alkoxides, such as dialkyltin dialkoxides R₂Sn(OR’)₂, titanium tetraalkoxides Ti(OR’)₄, and tetraalkyl orthosilicates Si(OR’)₄, which we have previously reported. By using these regenerable reagents, we have achieved the synthesis of a polyurethane raw material that consumes practically only amines and CO₂, with H₂O as the only byproduct. In particular, the reaction using Si(OMe)₄ has succeeded in highly efficient synthesis of precursors of the industrially important polyurethane raw materials (MDI, TDI, and HDI) using 1 atm of CO₂.