LIQUID-LIQUID EXTRACTIONS

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LIQUID-LIQUID EXTRACTIONS
Chemistry 227 Laboratory

• The separation of
• A solid organic acid,
• A liquid organic base, and
• a solid neutral compound by changing polarities.

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Important Concepts

• What dya mean POLAR??

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Some important Acid-Base Concepts
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Preparation of the mixture

• In about 50 mLs of methylene chloride, dissolve
  2-3 g of benzoic acid, 10-15 mLs of aniline, and
  4-5 g of p-dichlorobenzene.

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Preparation of the extraction solvents

• Prepare about 50 grams each of
• 10 HCl and 10 NaOH as shown above.

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PART A- Separation of the Acid

• Provide a separatory funnel, the mixture, and the
  10 NaOH

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Be sure your stopcock is assembled properly.

• Tighten the blue retaining nut.
• Test for leaks with a bit of water.

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Transfer the mixture into the separatory funnel

• Add about 15mLs of 10 NaOH . . .
• It will form a separate UPPER layer

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Gently rock the funnel back and forth to agitate
the mixture.

• Open the stopcock occasionally to release the
  pressure.

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Draw off the lower organic layer.

• It contains the aniline and the
• p-dichlorobenzene in CH2Cl2.

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Pour the remaining aqueous layer into a vessel
labeled NaOH Extracts

• Repeat the extraction twice more, with 10 NaOH.
• Finally, wash with 10 mLs of water, combining all
  four aqueous layers.

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PART B Recovery of the free acid.

• Add conc HCl until Congo Red paper turns DARK
  BLUE or Alkacid paper turns PURPLE. .
• STIR THOROUGHLY BEFORE TESTING!
• The acid separates as a white solid!

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Collect the crude acid on Buchner w/ suction.

• Do not purify the acid! Next years class will
  recrystallize it.

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Part C- Separation of the base.

• Transfer the organic layer back into the
  separatory funnel.

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Add about 15 mLs of 10 HCl.

• The aqueous acid forms the upper layer. Provide a
  vessel labeled HCl Extracts

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Gently rock the funnel back and forth to agitate
the mixture.

• Open the stopcock occasionally to release the
  pressure.

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Draw off the lower, organic layer.

• It contains the neutral p-dichlorobenzene
  dissolved in methylene chloride.

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Pour the remaining aqueous layer into a vessel
labeled HCl Extracts.

• Repeat the extraction twice more, with 10 HCl.
• Finally, wash with 10 mLs of water, combining all
  four aqueous layers.

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Part E- Separation of the neutral compound.

• Pour the organic layer into a flask that can be
  stoppered. It is the
• p-dichlorobenzene dissolved in wet methylene
  chloride.

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Add 1-2 g of anhydous magnesium sulfate stopper
the flask and swirl the contents occasionally.

• Meanwhile, proceed with Part D, the Recovery of
  the Free base and the back extraction.
• Read Zubrick, p. 135!

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Part D- Recovery of the base.

• Add 50 NaOH until red (pink) litmus paper
• or alkacid paper turns BLUE.
• STIR and TEST with a stirring rod.
• The aniline separates as an oily upper layer.

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THE BACK EXTRACTION(Zubrick, p. 135)

• Transfer the aniline mixture back into the
  separatory funnel.

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NOTE that the aniline is the upper layer.

• Obtain about 45-50 mLs of methylene chloride.

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Transfer 15-20 mLs of methylene chloride into the
funnel

• The methylene chloride with the aniline NOW FORMS
  THE LOWER LAYER.

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Gently rock the funnel back and forth to agitate
the mixture

• Open the stopcock occasionally to release the
  pressure.

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Draw off the lower organic layer of aniline in
methylene chloride. Put the upper, aqueous layer
back into the sep funnel.

• Extract the aqueous layer 2 3 more times with
  small portions of methylene chloride.

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To the combined extracts of wet methylene
chloride, add 1-2 g of anhydrous magnesium
sulfate.

• Stopper the flask tightly, and swirl the contents
  occasionally. Prepare to perform a flash
  evaporation . . .

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At this point, you should be able to account for
the following items.

• If you have all three of the above items
  everything else can be discarded.
• Prepare for the FLASH EVAPORATION.