Catalytic oxidation of 1,2-diols to α -hydroxy -carboxylates with stabilized gold nanocolloids combined with a membrane-based catalyst separation

Gold (Au) nanosols stabilized with poly(vinylalcohol) can be used as homogeneous oxidation catalysts, both in water and in a variety of alcoholic solvents. Under 0.5 MPa O2 pressure, 1,2-diols with varying chain length, such as 1,2-propanediol or 1,2-octanediol, are oxidized to the corresponding α-hydroxy-carboxylates with total chemoselectivity. The activity of the sol is of the same order as previously reported for stabilized nanoparticles deposited on carbon supports. The stabilized sols retain their activity over extended periods. The Au metal colloids can efficiently be recycled by means of a nanofiltration, either from an aqueous reaction medium, or from an organic solvent. The most suitable membranes for the Au sol recuperation are cellulose acetate membranes for the aqueous filtration, and poly(dimethyl)siloxane membranes for the solvent resistant filtration. Recycling tests after nanofiltration show that catalytic activity is largely preserved in consecutive runs.