Renewable Terephthalates and Aromatic Diisocyanates from Galactose

Abstract

Aromatic diisocyanates, invaluable commodity chemicals for polymer manufacturing, are produced annually on megaton scales from petroleum-derived diamines via phosgenation. Existing routes toward renewable alternatives are sparse and limited by access to functionalized aromatic starting materials, such as terephthalates. Herein, we report the development of a robust route to renewable terephthalates and aromatic diisocyanates from D-galactose via Eastwood olefination and Diels–Alder cycloaddition, followed by a mild electrochemical decarboxylative aromatization. This process was developed and applied on gram-scale to synthesize terephthalates, which were transformed into aromatic diisocyanates via Curtius rearrangement in flow. We demonstrate gram-scale preparation of 1,4-phenylene diisocyanate and 2,5-toluene diisocyanate and formulation of these monomers to prepare fully renewable thermoplastic polyurethanes. Preparation of these renewable aromatic diisocyanates proceeds without the use of high-pressure gases or costly transition-metals and represents a novel route to fully renewable aromatic diisocyanates.