Extraction of Organic Mixture

Extraction and Separation of
Benzoic Acid, 2-Naphthol and

Naphthalene
Part B - Two base extraction, p. 158
Important Concepts
• Extraction technique for isolating organic compounds
• Solvent polarity “like dissolves like”
• Acid base theory: pKa’s
• Density
• Partition Coefficient
• Rotory Evaporator
Chem 341 - Extraction, Copyright - D.J. Dyer & SIUC 1
Introduction to Extractions
- A technique for the isolation and purification of organic compounds.
- Solvents A and B are NOT miscible (like oil

and water).
Separatory Funnel
- Usually one is organic (i.e. nonpolar) and
A
one is aqueous (i.e. polar).
Less Dense - The organic layer may or may not be the top
B layer. This depends on density, or the ratio
of mass to volume in g/ml.
More Dense Stopcock
- The more dense solvent will go to the
bottom:
Density of water = 1.0 g/ml
Density of diethyl ether = 0.706 g/ml
Density of dichloromethane = 1.325 g/ml
(methylene chloride)
- How can you determine which solvent is more dense?

How Does an Extraction Work?
Suppose you have three compounds (1, 2 & 3) that are dissolved in solvent A, but
compound 3 is more soluble in solvent B.
1. Stopper and Shake the 3. Allow contents to settle, then

flask to mix contents. open stopcock and let bottom
1 2 solvent drain into flask or
A3 1 2 beaker. 1 2
B 1
3 3
2
2. Vent the flask to release

pressure, then close
stopcock.
†
Flask 3
- Now compound 3 (a solute) has

been separated (i.e. extracted) from
solvent A into solvent B.
Chem 341 - Extraction, Copyright - D.J. Dyer & SIUC Photo source: †-http://orgchem.colorado.edu 3
Theory of Extraction
The partition coefficient (K) defines the solubility of a compound (solute) in a
particular solvent according to the following equation: [Sx ] S = extracting solvent
K= x
So = original solvent
[So]
K>1 Solute will prefer Sx provided volumes are similar.
Single extraction (K = 5) Extract 3 times with 10 ml each (K = 5)
So
Sx
1 x 30 ml
1 x 10 ml 2 x 10 ml 3 x 10 ml
Extracted ~ 94% Same volume but extracted ~ 99.5%

Criteria for a Good Extracting Solvent
- Must not react in an irreversible way with the solute.
- Must be immiscible with the original solvent.
- The extracting solvent should selectively remove the desired

compound (i.e. K for solute is large, whereas K for all other
compounds is small).
- Extracting solvent should be easily separated from the solute (e.g.

distill off a low boiling organic solvent such as diethyl ether).
- Extracting solvent is nontoxic and environmentally benign

(unfortunately most organic solvents are not benign and so we try
to recover it for safe disposal).
Our Extraction Scheme
Naphthalene Benzoic Acid 2-Naphthol
O
1:1:1 mixture by weight is OH
OH
dissolved in diethyl ether + +
aq. NaHCO3
aqueous organic
O
OH
O- Na+ +
aq. NaOH
H3O+ aqueous organic
O
O- Na+
OH
H3O+
Recrystallize each product after recovery. OH

Extraction 1: Sodium Bicarbonate (NaHCO3)
- Sodium bicarbonate is a weak base, which means that it can deprotonate a strong acid but
not a weak acid. (Note: this seems counter-intuitive but in fact, a strong acid easily gives up
its proton, whereas a weak acid holds on to its proton more tightly)
O
OH
O (aqueous layer)
OH
O-Na+ O
OH Aq. NaHCO3
+ CO2 + H2O
HO OH
Sodium Benzoate Carbonic Acid
+
O
HCl - acidification OH
(ether)
(ether)
Recrystallize from ethanol/water
- The pKa is a figure of merit that tells us the strength of a particular acid: A pKa < 20
indicates an acidic proton and the lower the pKa, the more acidic:
pKa
Strong acid
Caution: The formation of CO2 builds up pressure,
Benzoic acid ~ 4
2-Naphthol ~ 9.5 Weak acid so vent the separatory funnel frequently. And point
the end away from you or others around you.
Extraction 2: Sodium Hydroxide (NaOH)
- Sodium hydroxide is a strong base, which means that it can deprotonate a weak acid but it
can also deprotonate a strong acid. Therefore it is important to extract with the weak base
first, otherwise NaOH would deprotonate both benzoic acid and 2-naphthol at the same time
and bring both into the aqueous phase.
(ether)
OH (aqueous layer) (ether) 1. Rotovap
O-Na+
Aq. NaOH
+ 2. Recrystallize from
ethanol
HCl
Acidification
OH
Recrystallize from 95% ethanol/water (dissolve in hot ethanol, add charcoal, filter, then add water
- After the 2nd extraction, dry the ether solution with anhydrous sodium sulfate (Na2SO4) to
remove residual amounts of water. Swirl the flask and let sit for 5 minutes before filtering
off the drying agent. Put the ether into a round-bottomed flask and then evaporate off the
solvent on the rotovap.
How do we Remove the Organic Solvent?
- use a rapid distillation method to evaporate solvent by reducing pressure.
Rotary Evaporation Procedure

1. Your compound is dissolved in an organic solvent with a To Rotary Evaporator †
relatively low b.p. and placed in a flask. Vacuum (Rotovap)
2. The flask is mounted onto the rotovap with a Keck clamp.
Note: we generally place a trap between the flask and Air Condenser
rotovap to prevent cross-contamination. Inlet
Spin Control
3. The spin dial is adjusted to spin the flask at a rapid pace. Flask
Confirm that coolant is flowing through condenser. w/compound
and initial
4. Make sure the vacuum pump is on and properly adjusted,
solvent
then close air inlet to apply vacuum. Note: the air inlet can
be used to control vacuum (e.g. partially open for less
vacuum).
5. Lower flask into the water bath. Note: the temperature
should be adjusted for appropriate solvent b.p. (e.g. for Receiving
ether room temp is fine) Flask
6. When evaporation is complete, open air inlet and turn
vacuum pump off. Raise the flask and turn the spinner and Water Bath
water bath off. Finally, remove flask and scrape out
contents.
Chem 341 - Extraction, Copyright - D.J. Dyer & SIUC Photo source: †-http://www.buchi.com 9
Required Data
- Fill out the data requested in the worksheet.
Data: - m.p. of purified compounds

- mass of purified compounds
- % recovery for each compound
% Recovery Calculation
Assuming 0.9 g total for the crude solid, then 1/3 would be due
to each compound or 0.3 g. Now if we recovered 0.1 g of
naphthalene, then:
0.1g
%Recovery = "100 = 33%
0.3g
Note: do not get m.p. of crude solid.

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Extraction and Separation of

Benzoic Acid, 2-Naphthol and

- Solvents A and B are NOT miscible (like oil

- How can you determine which solvent is more dense?

1. Stopper and Shake the 3. Allow contents to settle, then

2. Vent the flask to release

- Now compound 3 (a solute) has

Extracted ~ 94% Same volume but extracted ~ 99.5%

- Must be immiscible with the original solvent.

- The extracting solvent should selectively remove the desired

- Extracting solvent should be easily separated from the solute (e.g.

- Extracting solvent is nontoxic and environmentally benign

H3O+ aqueous organic

Recrystallize each product after recovery. OH

Chem 341 - Extraction, Copyright - D.J. Dyer & SIUC 6

Recrystallize from ethanol/water

Rotary Evaporation Procedure

Data: - m.p. of purified compounds

Note: do not get m.p. of crude solid.

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