Gold nanoclusters as colloidal catalysts for oxidation of long chain aliphatic 1,2-diols in alcohol solvents

Long chain aliphatic 1,2-diols like 1,2-hexanediol and 1,2-octanediol can be converted to the corresponding alpha-hydroxy-alkanoates with total chemoselectivity, in an oxidation catalyzed by an aqueous gold sol under O-2 atmosphere. The sol is stabilized with poly(vinylalcohol), and the reaction is performed in alcohol solvents. Two methods are proposed for the efficient recycling of the colloidal Au catalyst. Firstly a solvent-resistant membrane filtration can be applied. As the membrane material, poly(dimethylsiloxane) is chosen. Secondly, in appropriate conditions, the reaction proceeds in the liquid biphasic mode, and the aqueous Au sol can be recycled by phase separation. Using either of both approaches, the colloidal stability and catalytic activity can be preserved over several recycles.