Aerobic diol lactonization by Au-nanoparticles supported onto an anion-exchange resin Original Research Article

Different amounts of AuCl4− (i.e. 3.0, 0.5 and 0.1 wt% of Au) were supported onto the anion-exchange resin Dowex Marathon MSA in its chloride form. A successive rapid reduction of the latter anchored Au-compound with NaBH4 combined with anion exchange reactions (i.e. replacement of chloride by acetate or carbonate) gave resin-stabilized Au-nanoparticles (NPs) of comparable size and size distribution. A screening of the catalytic performance of the obtained heterogenous catalysts in the aerobic oxidation reaction of selected diols to lactones in toluene revealed the carbonate form of the resin bearing 0.1 wt% of Au to be the most active catalytic system. The aerobic oxidation of aliphatic diols led to the formation of the corresponding dicarboxylic acid as side-product, which deactivates the catalyst. By washing the deactivated catalyst after each cycle with a solution of Na2CO3 in water restored the initial catalyst performance for at least four consecutive catalytic cycles.