The potency of γ-valerolactone as bio-sourced polar aprotic organic medium for the electrocarboxlation of furfural by CO2

The reductive electro-carboxylation of furfural at a Pt/C electrode was studied in a bio-sourced gamma-valerolactone (GVL) solvent using linear scan voltammetry, in situ infrared spectroscopy (in situ FTIRS) under electrode potential control and by chrono-amperometry (CA) with analysis of reaction products. In situ FTIRS measurements indicated that GVL reacted at the electrode in the absence of furfural and/or of CO2, while the solvent became much less reactive in the presence of furfural and/or of CO2. It was also found that CO2 was activated from the high cathodic potential of -0.8 V vs SCE (saturated calomel electrode) and that it reacted with furfural. CA measurements at a cell voltage of 2.0 V, corresponding to a cathode potential higher than -1.66 V vs. SHE (standard hydrogen electrode), were performed for 24 h in the presence of CO2 at the cathode. Gas chromatography coupled with mass spectroscopy (GC-MS) analyses revealed the formation of 2-hydroxyvaleric acid (reaction between GVL and residual water) and oxalic acid (coupling reaction of CO2) as main reaction products in the absence of furfural in the reaction medium. In the presence of furfural in the reaction medium, 2-hydroxyvaleric acid and oxalic acid were detected as traces, whereas a new carboxylated specie. 2-furyl(hydroxy)acetic acid, corresponded by far to the main reaction product (ca. 82%). H-1 NMR and LC-MS analyses confirmed the formation of this last compound. Under the experimental conditions described in this article, the electro-activation of CO2 could be performed at high cathode potential in GVL, leading in presence of furfural to the formation of the alpha-hydroxy-acid. (C) 2019 Elsevier B.V. All rights reserved.