Purification of Triptycene

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Purification of Triptycene
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Agenda

• Purification of Triptycene by a Chemical
  Reaction.
• Characterization of the pure product by
• 1. Thin Layer Chromatography.
• 2. Melting Point.
• 3. 13C NMR spectrum.

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How Did We Make Triptycene ?
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Purification

• Impurities from solid can be removed by
• 1. Extraction.
• 2. Recrystallization
• 3. Column Chromatography.
• But we are going to do a Chemical Reaction to
  remove the impurity !!!

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Possible Impurities

• Anthranilic Acid is cannot be impurity due to the
  following reasons.
• 1. It cannot be the impurity because, we
  converted all of them into very active BENZYNE
  by reacting them with Isoamyl Nitrite.
• 2. The UNREACTED Anthranilic acid must have
  gone with aqueous basic solution.

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Possible Impurities

• Isoamyl Nitrite and 1, 2 Dimethoxyethane are
  also another possible impurities.
• But they are liquids. So they must have gone with
  our filtrate.

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Possible Impurities

• The only reagent left is Anthracene, so our
  impurity must be it.
• We know that anthracene is a diene because it has
  conjugated double bonds.

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Reagent to Remove Impurity

• We are going to use maleic anhydride to remove
  the diene impurity.
• Its a Dieneophile.

Maleic Anhydride
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Theory

• Each compound has different reactivity with
  different chemicals.
• Crude product contain Triptycene and Anthracene.
  
• Anthracene forms an ADDUCT with Maleic Anhydride.
• Triptycene DOES NOT REACT with Maleic Anhydride
  under such conditions.

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Chemical Reaction
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How can we remove the Adduct???
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Procedure

• Take all the crude product and add 20 mL of
  triethylene glycol dimethyl ether.
• Add 1 gram of Maleic Anhydride to the above
  mixture.
• Set up a refluxion apparatus.
• Heat the mixture till its boiling (Boiling Point
  of the solvent is 222 ?C).
• Reflux the mixture for five minutes.

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Procedure

• Cool the mixture for 5 minutes and add
• 1. 10 mL of 95 Ethanol
• 2. 35 mL of 10 NaOH
• Cool the reaction mixture thoroughly with ice
  bath (may be for 10 15 minutes).
• Filter the solid using Buchner funnel and wash
  the solid with chilled Methanol water mixture (
  41)

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Procedure

• Dry the solid using suction pump and then in air
  for 10 minutes.
• Dissolve all the solid in dichloromethane (10 mL
  per gram of the solid).
• Filter them using funnel and cotton plug.
• Rinse the funnel and cotton plug with plenty of
  methylene chloride and pool all of them.

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Procedure

• Take 50 mL RB flask, transfer all the methylene
  chloride solution and gently boil the solution.
• Slowly add methanol into the warm solution (two
  volumes of methanol for each volume of methylene
  chloride) until crystallization begins.
• After seeing the crystal, do not add more methanol

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Procedure

• Slowly cool the solution to room temperature and
  then keep it ice bath for half an hour to
  complete the crystallization.
• Filter the crystals using frit funnel and dry
  them as much as you can using pump.
• Weigh 0.5 gram out of it and transfer into a vial.

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TLC Characterization

• We are going to use the TLC technique to check
  the purity of the compound.
• Take small amount of anthracene, pure triptycene
  and the compound you made it in a separate test
  tube.
• Dissolve them using minimum amount of methylene
  chloride.

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TLC Characterization

• Take a chromatogram of size 8 cm x 3 cm
• Keep tiny spot of all three compound on the line
  of origin.
• Use different capillary for different compounds
• Use hexane as the mobile phase and run the TLC.
• Note Hexane move fast, watch carefully.

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TLC Characterization

• Use UV lamp to visualize your chromatogram.
• Why cant we use Ninhydrin???
• We do not have free NH2 group in the compounds.

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TLC Characterization
Solvent front Line
Pure Anthracene
Pure Triptycene
Line of origin
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Characterization

• Find the melting point.
• Give the dry sample for 13C NMR spectrum.

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Note

• Work in the same group where you were in.
• Make your own capillaries!
• Do not forget to save some triptycene.