Organic Chemistry

How would you purify Fluorene contaminated with ethyl-4-aminobenzoate? What method and solvent you would use? Please help...

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asked by Scott
  1. Fluorene is a polycyclic aromatic hydrocarbon that is soluble in non polar solvents.

    Ethyl 4-amino benzoate is soluble is dilute aqueous acids and solvents like ethyl acetate.

    If you partition the mixture between cold 0.1 M HCl and a nonpolar solvent, say petrolum ether, in a separating funnel. The aqueous layer will contain the amine and the organic layer the fluorene. Separate. Wash the aqueous layer once with petrolum ether. Combine the organics in a separating funnel and wash the mixture again with dilute acid. Evaporate the organic to recover the fluorene.
    If you need to recover the amine. Return the aqueous layer to a separating funnel add base, extract with ethylacetate.

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    posted by Dr Russ
  2. I have just had a few further thoughts. You didn't say how much fluorene you have or the % contamination. If you have a relatively small amount (50 mg - 1g) a small chromatography column would be quick. Pack a small column with silica gel. Take up the mixture in a small volume of petroleum ether (you may need to add a few % of ethyl acetate to get it all in solution). Load onto the column and flush through with petroleum ether. The amine will stick to the origin and the fluorene will pass straight through.

    An even sneakier (quick and dirty) way is to dissolve/suspend the mixture in petroleum ether in a beaker and add silica gel. The amine will stick to the silica. Filter the mixture, wash the silica with petroleum ether. Evaporate the pet ether to recover the fluorene.

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    posted by Dr Russ
  3. thank you so much Dr. Russ...yes the question assumes the containment comprises only a small percentage of the mixture...

    p.s.: do u happen to know the answer to my other question as well? under the same assumptions...

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    posted by Scott

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