Isolation of Caffeine From
“Mountain DewTM” or “CocaColaTM” Syrup
Organic Chemistry Lab I
Fall 2009
Dr. Milkevitch
Oct 19 & 21, 2009
Extraction
Today: Learn a separation method
Extraction: “one of the most common
methods of separating an organic product
from a reaction mixture, or a natural product
from a plant.”
We will be examining liquid-liquid extraction,
attempting to separate caffeine from softdrink syrup.
How Liquid-Liquid Extraction
Works
You have some compound in a solvent
(solute)
Perhaps a reaction product
You add another solvent to this solvent
(which contains the solute)
Solvents must be immiscible
Immiscible: incapable of mixing
Commonly water and a moderately polar/nonpolar
solvent
An equilibrium concentrations of solute is
formed between the immiscible solvents
Extraction, (con’t)
Concentration of solute in each solvent
Depends on the relative solubility of the solute
in each solvent
The solute will be more concentrated in the
solvent in which it is more soluble
Result: You can “move” a compound
from one solvent to another
Followed by purification, characterization, etc.
What Extraction Is Used For
To separate an organic product from water insoluble
impurities
Remember: water + moderately polar/nonpolar solvents are the
most common in extraction
Organic product preferentially drawn into the
organic solvent in which it is more soluble
Other components drawn into or remain in water
Organic component “freed” from water soluble
impurities
Difference Between Extraction
and Washing
Extraction: removing a compound of
interest from a solution or solid mixture
Washing: removing impurities from the
substance of interest
Doing a Miniscale Extraction
Pfft!!!
Stopcock must be closed!
Solvent + compound
VENT!!!
Keep finger on the stopper!
After Initial Venting: Comes the
Pfft!
Shaking!!
!
Followed by venting!!!
Invert multiple times
Do a minimum of 3 times!!!!!!!
After Shaking, Separation!
1) Place separatory funnel back in
Iron ring
2) Let layers separate
3) Drain off lower layer (methylene chloride)
Important Tips Concerning Extraction
Always keep your finger on the glass stopper when
inverting the separatory funnel!
Make sure the stopcock is closed!
Never discard any layer until the experiment is done!
Make certain the phases are thoroughly mixed by
vigorously shaking the separatory funnel
Vent frequently! This will prevent pressure buildup.
If there is only one layer is separatory funnel and
there should be two:
Perhaps a wrong layer was used.
Try adding a little water, and see if 2 layers form
If there is still one layer, add a little organic solvent
Since you didn’t discard anything, you are ok.
More tips
If you get an emulsion:
Emulsion: a yucky suspension
Stir the solution with a glass rod
IF all else fails, add some salt water
OR: filter through filter paper (slow and messy)
OR: In this case, filter through some
magnesium sulfate (will dry at the same
time)
Drying/Breaking Emulsion
Separatory funnel
~ 1 cm layer of magnesium
sulfate
Small piece of cotton
Erlenmeyer flask
Procedure
Measure out 40 ml of Coca-Cola or Mountain Dew syrup (your choice),
transfer to 250 ml flask
Dilute syrup with 40 ml ddH2O
– Add 10 ml ammonium hydroxide
– 40 ml of methylene chloride
Pour solution into a 250 ml separatory funnel
– MUST be supported by a ring stand + iron ring
Stopper funnel, and invert
Extract by invert/revert separatory funnel 3X followed by venting
Do 3 cycles of this
Place back on ring stand, Let layers separate
It may take several minutes for layers to separate
– You will probably see some emulsion
Drain off lower methylene chloride layer into a clean erlenmeyer flask
If you have an emulsion:
– Break emulsion/ dry methylene chloride by passing the methylene chloride
through magnesium sulfate lying on a cotton ball in a powder funnel (see
figure)
– Rinse magnesium sulfate with ~ 2 ml of methylene chloride, let this drain
into the erlenmeyer flask
Repeat the extraction
– Add 40 ml of methylene chloride to the water layer (its remaining in the
separatory funnel)
Procedure (con’t)
Follow same extraction procedure
Drain off the methylene chloride
– Again, if you get an emulsion, drain it through a
fresh portion of magnesium sulfate
Pour your organic (i.e., methylene chloride)
layers in a preweighed erlenmeyer flask (+
boiling chip)
– Evaporate off methylene chloride in the hood
– Let cool
Weight again, calculate weight of caffeine
obtained
Do a TLC of your caffeine
– Check it against a caffeine standard
Results/Conclusions
Report the amount of caffeine that you obtained
Conclusions: things to think about
– Was your extraction successful?
Did you obtain any caffeine?
– What did it look like? (solid/liquid, color, etc)
Any unique observations?
Any problems/challenges?
– If so, how did you deal with them?
– If it wasn’t successful, then why?
What did you think went wrong?
How might you correct it in the future?
Questions to Answer
1) What are 4 characteristics of a good extraction solvent?
2) What is a potential problem of adding too much drying agent to a
solution?
3) When performing an extraction, why must the extraction solvent be
immiscible with the solution that contains your reaction product?
4) We use extraction almost every day in the preparation of foods &
beverages. Give 3 examples of such extractions.
5) Search for a method now commonly used to extract caffeine from
coffee to manufacture decaffeinated coffee. Write a brief description
of this method. You may search the internet or the library. Be sure to
correctly reference your source(s).