Oppenauer oxidation

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

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The reaction is the opposite of Meerwein-Ponndorf-Verley reduction. The alcohol is oxidized with Aluminium-tert.-butylate in excess acetone. This shifts the equilibrium toward the product side.

The method has been largely displaced by oxidation methods based on chromates (e.g. PCC) or dimethyl sulfoxide (e.g. Swern oxidation) or Dess-Martin oxidation. It is still used for the oxidation of acid labile substrates. An advantage of the Oppenauer reaction is its use of relatively inexpensive and non-toxic reagents.

A variation that uses trichloroacetaldehyde and aluminium oxide is able to selectively oxidize secondary alcohols, leaving primary alcohols unchanged.

In one modification ^[2] the catalyst is trimethylaluminium and the aldehyde 2-nitrobenzaldehyde for example in the oxidation of isoborneol to camphor:

References