Gold Catalysis and Photoactivation: A Fast and Selective Procedure for the Oxidation of Free Sugars

A fast and efficient methodology for the selective oxidation of sugars into corresponding sodium aldonates is herein reported. Hydrogen peroxide was used as a cheap oxidant and electron scavenger, in the presence of only 0.003-0.006 mol % of gold in basic conditions. Three photocatalysts were studied, namely Au/Al2O3, Au/TiO2, and Au/CeO2, the latter being the most efficient (TOF > 750 000 h(-1)) and perfectly selective. Only a 10 min exposition under standard OH OH 0 incident sunlight irradiation (A.M.1.5G conditions, 100 mW/cm(2)) affords total conversion of glucose into the corresponding sodium gluconate. Demonstrating its versatility, this methodology was successfully applied to a variety of oligosaccharides leading to the corresponding aldonates in quantitative yield and high purity (>95%) without any purification step. The photocatalyst was recovered by simple filtration and reused 5 times leading to the same conversion and selectivity after 10 min of illumination.