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.