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LIQUID-LIQUID EXTRACTIONS

Chemistry 227 Laboratory. LIQUID-LIQUID EXTRACTIONS. The separation of A solid organic acid, A liquid organic base, and a solid neutral compound by changing polarities. Important Concepts:. What d’ya mean: POLAR??. Some important Acid - Base Concepts. Preparation of the mixture.

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LIQUID-LIQUID EXTRACTIONS

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  1. Chemistry 227 Laboratory LIQUID-LIQUID EXTRACTIONS The separation of A solid organic acid, A liquid organic base, and a solid neutral compound by changing polarities.

  2. Important Concepts: What d’ya mean: POLAR??

  3. Some important Acid-BaseConcepts

  4. 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.

  5. Preparation of the extractionsolvents: Prepare about 50 grams each of: 10% HCl and 10% NaOH as shown above.

  6. PART A-Separation of the Acid Provide a separatory funnel, the mixture, and the 10% NaOH

  7. Be sure your stopcock is assembled properly. Tighten the blue retaining nut. Test for leaks with a bit of water.

  8. Transfer the mixture into the separatory funnel Add about 15mLs of 10% NaOH . . . It will form a separate UPPER layer

  9. Gently rock the funnel back and forthto agitate the mixture. Open the stopcock occasionally to release the pressure.

  10. Draw off the lower organic layer. It contains the aniline and the p-dichlorobenzene in CH2Cl2.

  11. 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.

  12. PART B– Recovery of the free acid. Add conc HCl until CongoRed paper turns DARK BLUE or Alkacid paper turns PURPLE.. STIR THOROUGHLY BEFORE TESTING! The acid separates as a white solid!

  13. Collect the crude acid on Buchner w/ suction. Do not purify the acid! Next year’s class will recrystallize it.

  14. Part C-Separation of the base. Transfer the organic layer back into the separatory funnel.

  15. Add about 15 mLs of 10% HCl. The aqueous acid forms the upper layer. Provide a vessel labeled “HCl Extracts”

  16. Gently rock the funnel back and forthto agitate the mixture. Open the stopcock occasionally to release the pressure.

  17. Draw off the lower, organic layer. It contains the neutral p-dichlorobenzene dissolved in methylene chloride.

  18. 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.

  19. 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.

  20. 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!

  21. 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.

  22. THE BACK EXTRACTION:(Zubrick, p. 135) Transfer the aniline mixture “back” into the separatory funnel.

  23. NOTE that the aniline is the upper layer. Obtain about 45-50 mLs of methylene chloride.

  24. Transfer 15-20 mLs of methylene chloride into the funnel The methylene chloride with the aniline NOW FORMS THE LOWER LAYER.

  25. Gently rock the funnel back and forthto agitate the mixture Open the stopcock occasionally to release the pressure.

  26. Draw off the lower organic layer of anilinein 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.

  27. 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” . . .

  28. 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.

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