Nitrogen-doped carbon-supported cobalt-catalyzed aerobic oxidation of concentrated acetal-protected 5-HMF solutions to FDCA.

Abstract

Aerobic oxidation of 5-hydroxymethylfurfural (HMF), protected as a six-membered ring acetal with 1,3-propanediol (PDO), was examined using a nitrogen-doped carbon-supported cobalt catalyst in a stepwise approach. Usage of acetal-protected HMF (HMF-acetal) enabled the production of 5-formylfuran-2-carboxylic acid in its acetal form (FFCA-acetal) in 97% yield even in a 20 wt% solution with Ca(OH)₂. The protective PDO was recovered in 94% through acid-catalyzed hydrolysis of FFCA-acetal using HCl in the second step. FFCA in 10 wt% could then be oxidized to 2,5-furan dicarboxylic acid in 96% yield under conditions optimized for this step, enabled through the flexibility of the stepwise approach.