Oxidation of 9-Hydroxyfluorene (Fluorenol) to 9-Fluorenone using Potassium Permanganate Supported on Silica Gel


  1. Evaporate an aqueous slurry of 1 g of potassium permanganate and 10 g of silica gel in a rotary evaporator at 80-90 degrees until it becomes a free-flowing solid.
  2. Pack 1 g into an 8mL SPE tube.
  3. Pass a solution of 10 mg of 9-fluorenol in 1 mL of MTBE over the supported reagent. Wash with another 2 mL of MTBE or suck dry on a vacuum device.
  4. Analyze the product to determine the extent of oxidation.
  5. If oxidation does not seem to be complete, pass the solution over the reagent a second time.
  1. This reagent is an alternative to chromium reagents and avoids their toxicity and waste disposal problems. The reagent is stable and requires no particular storage other than exclusion of moisture. Copper nitrate on silica has also been used, but this reagent is more difficult to prepare.
  2. MTBE is used for an aprotic solvent when possible.
  3. This can be done conveniently using UV or HPLC. 1 g of the reagent can oxidize 50 mg of fluorenol in one pass.

Discussion: This method has also been used to oxidize benzoin to benzil in high yield. The method seems to over-oxidize aliphatic secondary alcohols. Attempts to oxidize 2-methylcyclohexanol and 2-phenylcyclohexanol led to complex product mixtures.

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© February 1996.


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