Selective oxidation of 5-hydroxymethylfurfural to 5-hydroxymethyl-2-furancarboxylic acid using silver oxide supported on calcium carbonate

This work revealed 5-hydroxymethylfurfural (HMF) oxidation towards 5-hydroxymethyl-2-furancarboxylic acid (HMFCA) employed Ag2O supported on calcium carbonate as heterogeneous catalyst in conventional batch protocols and microwave-assisted batch conditions. Different reaction regimes were investigated, such as catalyst loading, reaction temperature, solvent types and oxidizing agent concentrations. 89 % HMF conversion, 85 % HMFCA yield as well as 95 % HMFCA selectivity achieved under optimum condition (125 mg 20 wt% Ag2O-CaCO3, 2 wt% aq. H2O2 with 0.1 mL min−1 flow rate in 50 min, oil bath 100 ºC). Microwave irradiation (30 W) afforded higher HMF conversion (95 %) as well as HMFCA yield (93 %) with HMFCA selectivity (97 %) under identical condition. Catalyst recycling showed deactivation (64 % HMF conversion and 50 % HMFCA yield in fourth time). Post-characterization was investigated to analyze catalyst deactivation. For instance, EDS and SEM mapping micrographs showed organic moieties deposited on the surface of catalyst. XRD exhibited no CaCO3 crystallographic modification happened after reaction, however, partial reduction of silver (I) to metallic silver (0) happened.