Impact of the Electrochemically Inert Furan Ring on the Oxidation of the Alcohol and Aldehyde Functional Group of 5-Hydroxymethylfurfural (HMF)

The electrochemical oxidation of bio-based 5-hydroxymethylfurfural (HMF) results in 2,5-furandicarboxylic acid (FDCA), which is a renewable and environmentally friendly alternative to terephthalic acid. Using a gold electrode, we compare the electrochemical oxidation of the aldehyde and alcohol functionality in HMF to the isolated functionalities represented by ethanol and acetaldehyde. Thereby, we investigate the effect of the inert furan ring on the electrochemical reaction. The linear sweep voltammogram (LSV) of HMF in a weakly adsorbing electrolyte differs only marginally from the superposition of LSVs obtained in ethanol and acetaldehyde containing electrolytes. However, in the presence of strong adsorbates, only the kinetics of ethanol and acetaldehyde oxidation but not of HMF oxidation are hampered. We assign this to a stronger adsorption of HMF through the furan ring than through the alcohol and carbonyl functionality of ethanol and acetaldehyde. Hence, HMF is better equipped to compete for adsorption sites than aliphatic compounds. Electrochemically inert furan ring: Current-potential graphs recorded during the 5-hydroxymethylfurfural (HMF), ethanol, and acetaldehyde oxidation show that the oxidation of HMF is less affected by co-adsorption. This indicates an altered adsorption for HMF, presumably by the furan ring. The proposed ring adsorption is stronger and therefore less affected by co-adsorption of strongly adsorbing electrolytes.image