Isolation of Caffeine From Tea

1
Isolation of Caffeine From Tea

• Experiment 12A (4th ed.)
• Experiment 11 (3rd ed.)

2
Read Before Class

• 4th ed.Experiment 12
• Techniques 12 17
• 3rd ed.Experiment 11
• Techniques 7 16

3
Overview

• Tea Leaves ? 1Cellulose, 2 Caffeine, 3Tannins
• Glucose polymer not soluble in H2O
• Alkaloid compound soluble in H2O, but more
  soluble in CH2Cl2
• Phenolic compounds all are potentially soluble
  in H2O, and some undergo hydrolysis in H2O

4
Overview

• Tannins that are hydrolyzed when mixed with H2O
  produce glucose gallic acid.
• Adding Na2CO3 makes the acidic solution basic
  converts tannins gallic acid to H2O-soluble
  sodium salts.
• This opens the door for a separation of caffeine
  from the other components via extraction by
  adding CH2Cl2 to the aqueous solution.
• Crude caffeine can then be isolated by
  evaporating off the CH2Cl2 solvent and further
  purified by sublimation or crystallization.

5
Procedural Notes

• Preparing Your Tea Solution
• Get the mass of your tea leaves from me.
• Be very careful not to rupture the tea bag when
  rolling it with your stir rod.
• You want to keep your tea leaves submerged during
  the heating process, so heat a separate beaker of
  hot water along with your tea solutionthis water
  will be used to replenish the supply of water in
  the reaction beaker that has evaporated also
  for heating your flask later.
• Keep your solution temperature around 90oC (just
  below standard b.p. of water) to avoid boiling
  over of the solution.

6
Procedural Notes

• Extraction Purification
• Be sure to vent the centrifuge tubes frequently
  upon addition of Na2CO3 to avoid pressure
  buildups.
• If the CH2Cl2 and water arent separating
  efficiently after shaking the tubes, centrifuge
  them for 1-2 minutes to break up the emulsion.

7
Analysis

• Perform the following analyses on both your crude
  and pure products
• Recovery (NOT Yield!!)
• Melting Pt. (236oC)