2. Definition
Extraction:
a process that selectively dissolves one or more compounds into an appropriate
solvent. The resulting solution is called an extract.
refers to the transfer of these compounds from one liquid solvent to another
one.
can be used to separate unwanted impurities or to separate mixtures of
compounds.
The two solvents used for extraction must be immiscible.
Washing is the removal of impurities from a solvent containing your compound by a
second immiscible solvent.
Extraction Washing
3. Chemistry of Extraction
Water
Hydrocarbons
Choosing the solvents:
/Ethers
Two immiscible solvents: water vs organic Chlorinated
Water
solvent. solvents
Nonpolar hydrocarbons and ethers (polar)
are less dense than water, so the water
tends to move to the bottom.
Most chlorinated solvents are more dense
than water, so the water will be on top.
Like dissolves like (nonpolar compounds least polar cyclohexane
are more soluble in nonpolar solvents). petroleum ether
To confirm the identities of the layers, add one or hexane
two drops of water to the funnel: toluene
If water mixes with the top layer, then the top diethyl ether
layer is water. dichloromethane
If water falls through the top layer, the bottom ethanol
layer is water. acetone
most polar methanol
4. Acid-Base Extractions Analyzing Reactivity
pKa = - log Ka
Lower pKa = Stronger acid Ka [HA] = [A-] [H+]
O O
OH
OH N
H
p-toluic acid p-tert-butylphenol acetanilide
pK a 4.2 pK a 10.2 pKa 24
O Ka O
+ H+
OH O
O O
+ HCO3 - + H 2 CO 3
OH O
pKa 4.2 pKa 6.4
OH + HCO3 - X O + H 2 CO 3
pKa 10.2 pKa 6.4
Organic-solvent soluble Water soluble
6. Experimental Procedure
Make sure the stopcock of the separatory funnel is closed!
1. Prepare your solution in a beaker. Weigh mixture and mix with TBME.
Transfer the solution into a separatory funnel.
2. Pour a measured amount of extraction liquid.
3. Place stopper securely in the funnel.
7. Experimental Procedure
4. Using your fingers to secure the cover, shake the mixture several times.
5. Vent the pressure by inverting and opening the stopcock. (Vent often!)
NOTE: The cover is always secured
during the whole operation
8. Experimental Procedure
6. Place the separatory funnel in the iron ring.
7. Remove the cover and allow the layers to separate.
8. Identify the layers (solvents). (Don't throw anything away until sure.)
9. Remove bottom solvent by draining through the stopcock. Pour the
upper solvent through the top of the funnel.
9. Macroscale (p.139) ORG 1.3 g of mixture
O O (TA will give you the
OH
OH N breakdown of the
H
p-toluic acid p-tert-butylphenol acetanilide
components!!)
pK a 4.2 pK a 10.2 pKa 24
- dissolve in TBME
-wash with NaHCO3 solution (Weak base only deprotonates the
strong acid)
AQ O
ORG
O
OH
N
O H
- acidify w/ HCl solution to pH ≤ 3 - wash with NaOH solution (Strong base deprotonates
- filter precipitate
the weaker acid)
O
Filtrate O
OH
(discard) AQ
ORG O - heat <60° C in the hood
- then cool in an ice-bath
N
H - acidify w/ HCl dropwise
- transfer to E. flask - vacuum filter
- dry with anhydrous Na2SO4
- decant to a pre-weighed rbf
OH
Filtrate
(discard)
Residue Decantate ORG
(discard) - rotary evaporator distillation – use house
vacuum to remove any residual solvent.
O
N
H Distillate (discard)
10. Miscellaneous Notes
Waste Organic Solvents: a waste bottle will be in the hood that will be
used for all of the organic solvents.
Waste Aqueous Solutions: a waste bottle will be in the hood for the
acid/base solutions from your extractions.
Grading: approximately 2/3 of your grade will be based upon the written
lab report (prelab and postlab questions, experimental procedures,
conclusions, etc.).
11. Make Note of the Following:
Use the Microscale Flow Chart on page 135 as a guide (see the handout), but
use the Macroscale procedure on page 139.
Step 1. The mixture of the three compounds is already prepared for you. (TA will give
you the breakdown of the components!!)
Step 2. Weak base (NaHCO3) only deprotonates the strong acid, which means your
compounds are in both phases.
Step 3. Strong base (NaOH) deprotonates the weaker acid, which means you will again
have compounds in both phases.
Step 4. Isolated p-toluic acid will need to dry in your drawer. Don't forget to pre-weigh
your filter paper.
Step 5. When heating, don't allow the temperature to exceed 60 ºC. Before adding HCl,
cool the solution in an ice bath. Allow the isolated p-tert-butylphenol to dry in
your drawer. (Pre-weigh paper!!) (Heating is done in the hood.)
Step 6. Pre-weigh a round bottomed flask (not a beaker). Perform distillation by rotary
evaporation instead of the evaporation procedure in the lab manual. See 2nd
handout for instructions. Use the house vacuum to remove any residual solvent.
