Effect of PEG-based triazolyl substituents of copper-catalyzed aerobic alcohol oxidation

Abstract

Oxidation of alcohols to aldehydes is one of the most fundamental and important organic reactions with wide industrial applications. However, alcohol oxidation reactions usually require toxic oxidizing agents such as NaOCl, HClO4, and H2O2 under harsh conditions. Recently, Cu-catalyzed aerobic alcohol oxidation has attracted a considerable interest due to its high catalytic efficiency under mild reaction conditions. To further reduce environmental impacts, we wish to develop copper catalyst systems that are water soluble and recyclable. In this work, a series of bis(amine-triazole) ligands featuring n-hexyl and water-soluble poly(ethylene glycol) (PEG) substituents with different chain lengths (PEG200 and mPEG550) were prepared and used as Cu catalyst supports. Catalytic studies toward aerobic oxidation of benzyl alcohol and its derivatives in H2O as well as CH3CN were carried out using the catalyst system [Cu]/ligand/TEMPO/base (TEMPO = 2,2,6,6-tetramethylpiperidinyl-1-oxyl). In particular, the effects of triazolyl substituent's chain length on catalytic oxidation activities were examined.