Aerobic copper/TEMPO-catalyzed oxidation of primary alcohols to aldehydes using a microbubble strategy to increase gas concentration in liquid phase reactions

Abstract

An efficient method for the synthesis of aldehydes was achieved by using air-microbubble techniques in aerobic copper/TEMPO-catalyzed oxidation of primary alcohols. Use of air-microbubbles to improve gas absorption into liquid phase is proven to be highly beneficial for gas/liquid phase reactions.

Aerobic oxidation catalysis with stable radicals

“…However, the most well-known and widely studied system employs copper complexes combined with TEMPO, which was first reported by Semmelhack and co-workers in 1984. 21 Since that report, numerous studies have explored this catalyst system, investigating ligands, 22 neoteric solvent systems, 23 immobilisation, 24 reaction engineering 25 and oxidation of renewable substrates. 26 However, we wish to focus on the recent reports, primarily from the Stahl Group, which exemplify the potential of Cu/nitroxyl catalysis for synthesis and also give further mechanistic insights.…”

Synthesis of UiO-66-NH2 derived heterogeneous copper (II) catalyst and study of its application in the selective aerobic oxidation of alcohols

“…Semmelhack pioneered homogeneous copper catalysis work since 1984, in which he reported a CuCl/TEMPO system using molecular oxygen [10]. To date, the Cu/TEMPO system has been extensively studied by several research groups [11][12][13][14]. However, despite the high activity achieved by these homogeneous copper catalysts, they suffered from inherent problems in separation, deactivation and recycling [15].…”

Recent advances in green catalytic oxidations of alcohols in aqueous media

“…This copper centered dehydrogenation mechanism, in which a copper coordinated TEMPO ligand plays the same role as a coordinated tyrosine radical in the galactose oxidase mechanism, differs totally from the oxoammonium type mechanism originally proposed by Semmelhack [71] for the Cu/TEMPO system. The aerobic Cu/TEMPO system was further improved by using air-microbubble techniques to facilitate gas absorption into the liquid phase [72]. It was also shown [73] that Cu(I) salts give better results than Cu(II) salts in a system using TEMPO and bipy in combination with N-methylimidazole as a base.…”