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Oxidation of Alcohols

Oxidation of Alcohols to Aldehydes or Ketones: Experimental Procedure

General procedure for the oxidation of primary alcohols to aldehydes with dipyridine-chromium(VI) oxide.

  • Chromium trioxide (13.6 g) is added in small portions to 100 ml of anhydrous pyridine at 20°C.
  • Red crystalls of pyridine-chromium oxide precipitate after stirring for one hour.
  • The hydroscopic precipitate is filtered under exclusion of air, washed with petroleum ether and dried (the use of high vaccum or acidic drying agents must be avoided to prevent decomposition of the complex).
  • Yield: 30-32 g (85-90%).
  • A freshly prepared, deeply red, 5% solution of pyridine-chromium oxide in dichloromethane is reacted in 5-6 molar excess with the alcohol. The reaction is completed after 5-15 minutes at 25°C. During the reaction, pyridine-chromium oxide is being reduced to a viscous, brown-black polymer.
  • The solution is separated and filtered through a short silica gel column to remove any remaining chromium salts and pyridine.
  • Distillation of the solvent yields the aldehyde.
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