Recyclable fluorous gold nanoparticles as catalysts in the biphasic oxidation of 1-octene

Abstract

A fluorous biphasic approach as a green strategy for the facile recycling of noble metal catalysts has been probed. A library of monodispersed fluorous-stabilized Au nanoparticles (NPs) were successfully synthesized using one of two synthetic methods i.e., a micelle-templated strategy, and a direct method employing two fluorous stabilizers. The fluorous-stabilized AuNPs were evaluated in the fluorous biphasic oxidation of 1-octene as the model substrate, in conjunction with O2, H2O2 and tertbutyl hydroperoxide (TBHP) as oxidants. All the fluorous-stabilized AuNPs which were evaluated were active in the oxidation of 1-octene achieving ± 50% conversions. Irrespective of the fluorous ligand or solvent employed in the oxidation reaction, the catalytic system exhibited an overwhelming degree of selectivity for epoxy-1,2-octane (> 60%) with a slight amount of the 1-octanal and 1-octanoic acid products being produced. More pertinently, the catalyst recycling presented auspicious results pertaining to a possible greener chemical approach to catalytic oxidation. The fluorous-stabilized AuNPs were recycled up to five times in the oxidation of 1-octene, with a negligible decrease in the catalytic conversion for each subsequent recycling run. Therefore, the fluorous biphasic method afforded a highly recyclable noble metal catalytic system, resulting in an increasingly cost-effective approach to catalysis. In an attempt to rationalize the products obtained from the oxidation process, a nanoparticle-assisted oxidation mechanism was proposed. The feasibility of the mechanism was probed through qualitative analysis by gas chromatography – mass spectrometry (GC-MS), which provided analytical evidence to consider the proposed mechanism as viable.