Gold Nanoparticles Supported on Poly(2,6-dimethyl-1,4-phenylene oxide) as Robust, Selective and Cost-Effective Catalyst for Aerobic Oxidation and Direct Oxidative Esterification of Alcohols

A new catalytic system based on gold nanoparticles (AuNPs) incarcerated in poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) matrix has been synthesized and successfully tested in aerobic oxidation of alkyl alcohols. PPO is a cheap and commercially available polymer, showing nanoporous morphology, high glass transition temperature (T-g =220 degrees C), semi-crystallinity, excellent thermal stability, and interesting chemo-physical properties. The synthesis of the AuNPs-PPO catalyst is simple, cost-effective and allows a fine control of the gold concentration, as well as an optimal dispersion of 7-8 nm sized AuNPs in the polymer matrix. AuNPs-PPO is an efficient, robust and selective catalyst active in the aerobic oxidation and oxidative esterification of alcohols in water under mild reaction conditions (35 degrees C, atmospheric pressure of oxygen). The testing of AuNPs-PPO in aerobic oxidation of 1-phenylethanol to acetophenone, as a benchmark reaction, highlighted that this gold catalyst exhibits activity values among the highest so far reported for polymer-supported AuNPs under mild reaction conditions. The oxidation of primary alcohols, such as benzyl and cinnamyl alcohols, could be addressed to the corresponding aldehyde or carboxylate derivatives. Alkyl cinnamates were obtained with efficiency in the one-pot aerobic oxidation of cinnamyl alcohol in the presence of alkyl alcohols, such as n-butanol or n-hexanol. The role of the polymer matrix and the reaction conditions on both activity and selectivity of the AuNPs-PPO catalyst were also investigated and discussed.