Au/Ag/Cu-Mixed Catalysts for the Eco-Friendly Oxidation of 5-Hydroxymethylfurfural and Related Compounds to Carboxylic Acids under Atmospheric Oxygen in Water

Abstract

A green method for the oxidation of alcohols to carboxylic acids was developed using a novel co-catalytic system based on gold, silver, and copper catalysts. This reaction system was conducted under atmospheric oxygen in water and mild conditions to selectively oxidize 5-hydroxymethylfurfural to 2,5-furandicarboxylic acid, as a building block for polyethylene furanoate, which is a 100% bio-based, future alternative to the petroleum-based polyethylene terephthalate. Furthermore, various primary alcohols were conveniently oxidized to their corresponding carboxylic acids in up to quantitative yields.

Innovative green oxidation of amines to imines under atmospheric oxygen

“…In addition to the catalyst-dissolved ionic liquid, the catalyst recycling for the atmospheric oxygen oxidation of amines to imines was investigated using gold supported on activated carbon (Au/C) and CuO as the catalysts, which were effective for the oxidation of 5-hydroxymethylfurfural to 2,5-furandicarboxylic acid. 34 Both Au/C and CuO are insoluble in organic solvents, which enables easy separation and recovery of the Au/C–CuO mixed catalyst from the reaction mixture. The heterogeneous oxidation of various benzylamines could proceed efficiently in toluene, and the corresponding imines were obtained in up to 100% yields by loading 0.006 mol% of Au/C and 1.25 mol% of CuO under mild conditions.…”

Base‐free synthesis of bio‐derived 2,5‐furandicarboxylic acid using SBA‐15 supported heteropoly acids in ionic liquids

“…Yang and coworkers explored a series of MO x ‐Au/TiO 2 catalysts, from which Au δ ‐O v ‐Ti 3+ was the main active site and provided a FDCA yield of 71.2 % [6] . A green oxidation of HMF to FDCA was developed using a novel co‐catalytic Au/Ag/Cu−O system in basic solution and low O 2 pressure (0.1 MPa), providing 93 % yield [7] . Helapiyumi Weerathunga et al.…”

“…[6] A green oxidation of HMF to FDCA was developed using a novel co-catalytic Au/Ag/CuÀ O system in basic solution and low O 2 pressure (0.1 MPa), providing 93 % yield. [7] Helapiyumi Weerathunga et al reported the oxidative esterification of HMF into FDCÀ Et (corresponding ester) using Au/γ-Al 2 O 3 nanoparticles, leading to 90 % yield in the presence of methanol and 0.5 equivalent base. [8] Noble-metal catalysts are superior in stability, catalytic activity and performance, but hindered to commercial application due to their high cost, poor availability and difficult recycling.…”

Excellent Catalytic Performances of a Au/C–CuO Binary System in the Selective Oxidation of Benzylamines to Imines under Atmospheric Oxygen

“…By developing this new redox system in which the gold and copper catalysts act in concert, the loading of the gold catalyst could be dramatically reduced (0.006 mol %) compared to conventional methods, and the reaction could be conducted under mild conditions. Such a combination of multiple metal reagents in a gold-catalyzed system is very rare, 12 and this method is the first demonstration of the practical and extremely efficient amine oxidation that can be achieved by combining gold catalysts and other metal catalysts. Furthermore, the novel catalyst system for highly selective oxidation of amines to imines has an extremely high catalytic turnover rate (more than 8000 times on a gold basis), and the catalytic activity does not decrease at all even when the catalyst is recovered and reused more than 10 times ( Figure 1 ).…”