UV Cross-Linked Polymer Stabilized Gold Nanoparticles as a Reusable Dip-Catalyst for Aerobic Oxidation of Alcohols and Cross-Aldol Reactions

Abstract

In this work, a gold nanoparticle (AuNP)-embedded composite polymer membrane for dip-catalysis is developed. Primarily, a polyvinylpyrrolidone-stabilized AuNP (PVP-AuNP) with an average size of 6.50 nm was synthesized by the reduction of a composite solution of Au salt and PVP. Next, the composite membrane was fabricated by simply depositing the PVP-AuNP on the Nylon membrane followed by UV cross-linking. The composite membrane having the cross-linked PVP-AuNP was utilized as a dip-catalyst for the aerobic oxidation of alcohols to carbonyl compounds under oxygen and clean reaction conditions. The catalyst was further tested for performing cross-aldol reactions. The PVP-AuNP-catalyzed oxidation reaction also has other noteworthy characteristics, such as a low catalyst loading (Au, 1.2 mol %), high yield, and selectivity with a broad substrate scope (aliphatic, aromatic, biphenyl, and heterocyclic alcohols). The turnover number (TON) and turnover frequency (TOF) for the oxidation reaction of the alcohol are calculated to be 74.5 and 12.41 h −1 , respectively. The P4VP-AuNP dip-catalysts are highly stable under the reaction conditions without significant leaching of Au into the solution. The dip-catalyst demonstrates outstanding reusability up to 10 catalytic cycles while maintaining high catalytic performance and structural features. It can be easily recovered by simply pulling it out from the reaction mixture once the reaction is complete, followed by washing and drying. The practical usefulness of the suggested method was further demonstrated by the PVP-AuNPcatalyzed gram-scale synthesis of high-value chemicals like acetophenone. Although the AuNPs are already used for different reactions, their integration into dip-catalysts for oxidation of alcohols and cross-aldol reactions with a wide substrate scope is rare. Overall, these findings demonstrate that developing composite dip-catalyst systems is a realistic strategy for creating high-value chemicals in a sustainable and environmentally friendly way.