CoOOH-catalyzed anodic oxidation of 5-(hydroxymethyl)-furfural under non-alkaline conditions†

Abstract

The oxidation of 5-(hydroxymethyl)-furfural (HMF), a platform chemical of biogenic origin, to 2,5-furandicarboxylic acid (FDCA) is a reaction of high relevance for sustainable production of polymers like polyethylene furanoate. However, a majority of the oxidation processes published to date rely on alkaline conditions, in which the instability of HMF and a resource intensive separation of FDCA are major obstacles for technological realization. In this study, we present the electrochemical oxidation of HMF in non-alkaline acetate and phosphate buffers (pH 5–7) on CoOOH modified electrodes. Current-controlled batch experiments were performed, to obtain optimal conditions with respect to the catalyst loading, current density and reaction temperature. Under optimized conditions, a FDCA yield of 94.7% in the acetate buffer (pH 5) was achieved. Through interval sampling, we were able to observe a consecutive oxidation mechanism during the optimized reaction, which mainly proceeded via the intermediate products 2,5-diformylfuran (DFF) and 5-formyl-2-furancarboxylic acid (FFCA). Furthermore, we observed that humic substances formed during the first reaction steps could also be oxidized to FDCA towards the end of the reaction.