Oppenauer oxidation

Oppenauer oxidation, named after Rupert Viktor Oppenauer [de],^[1] is a gentle method for selectively oxidizing secondary alcohols to ketones.

The reaction is the opposite Meerwein–Ponndorf–Verley reduction.^[2] The alcohol is oxidized with aluminium isopropoxide in excess acetone. This shifts the equilibrium toward the product side.

The oxidation is highly selective for secondary alcohols and does not oxidize other sensitive functional groups such as amines and sulfides.^[3] Though primary alcohols can be oxidized under Oppenauer conditions, primary alcohols are seldom oxidized by this method due to the competing aldol condensation of aldehyde products. The Oppenauer oxidation is still used for the oxidation of acid labile substrates. The method has been largely displaced by oxidation methods based on chromates (e.g. pyridinium chlorochromate) or dimethyl sulfoxide (e.g. Swern oxidation) or Dess–Martin oxidation due to its use of relatively mild and non-toxic reagents (e.g. the reaction is run in acetone/benzene mixtures). The Oppenauer oxidation is commonly used in various industrial processes such as the synthesis of steroids, hormones, alkaloids, terpenes, etc.