One of the most significant organic transformations in catalyst technology is the selective oxidation of alcohols. The acceleration of catalyst discovery in this field contributes to the economic and environmental impact in the production of useful materials. Heterogeneous catalysts combined with environmentally benign oxidants, such as molecular oxygen and hydrogen peroxide, are major challenges of exploratory research in the oxidation of alcohols. A wide range of recoverable catalysts has now emerged for these oxidation reactions. In this Focus Review, we present an overview of recent developments in immobilized metal catalysts and evaluate the potential of transition metals in the heterogeneously catalyzed oxidation of alcohols.

Golden capillaries: A gold-immobilized capillary column reactor allows oxidation of alcohols to carbonyl compounds using molecular oxygen. These capillary columns (see picture) can be used for at least four days without loss of activity.

A novel organic-inorganic hybrid ruthenium (HB Ru) catalyst for the oxidation of alcohols with molecular oxygen has been developed. The catalyst was prepared from a polystyrene-based copolymer, which includes a trimethoxysilyl functionality, and dichlorotris(triphenylphosphine)ruthenium, [RuCl2(PPh3)3], as the metal source. A sol-gel process was employed for heterogenization of the catalyst. The choice of both ruthenium species and trialkoxysilyl-bearing monomers was found to be important for high catalytic activity. In the presence of HB Ru corresponding to 5 mol % loading of ruthenium, the alcohols were oxidized with molecular oxygen or air at atmospheric pressure without any additives to afford the corresponding aldehydes or ketones in good to excellent yields. The catalyst could be recovered and reused at least five times without loss of activity.

Goldene Kapillaren: Mit einem goldimmobilisierten Kapillarsäulenreaktor gelingt die Oxidation von Alkoholen mit molekularem Sauerstoff zu Carbonylverbindungen. Diese Kapillarsäulen (siehe Bild) können mindestens vier Tage ohne Aktivitätsverlust verwendet werden.magnified image