EXTRACTION
- a separation technique
Extraction
• Transferring a solute from one solvent to
another
• Solvents must be immiscible – usually
one is water an one is organic
• Solute (the compound being separated)
must be more soluble in one solvent than
in the other
• Usually uses either a separatory funnel or
conical vial
Separatory Funnel
There are many
different models!
REMEMBER…
- Glass to glass requires (a little) grease!
- Plastic parts should NEVER be put in the oven!
All photos of separatory funnels in this presentation are from the following
site: :http://orgchem.colorado.edu/hndbksupport/ext/extprocedure.html
Using a Separatory Funnel...
1. Filling –
Support funnel.
Stopcock must be closed.
A clean beaker under
funnel –
Do not over-fill!
Using a Separatory Funnel...
2.Holding
Put stopper between
index and middle
finger -– hold bowl of
funnel with thumb and
tips of remaining
fingers
Using a Separatory Funnel...
3. Shaking
Make sure stopcock is
closed – shake with tip
pointed away from
everyone – every few
seconds, vent the
funnel into the hood
Using a Separatory Funnel...
4.Layer
Identification
Usually the more dense
solvent is on the
bottom – To check,
add a few milliliters of
distilled water and
watch where it goes!
Using a Separatory Funnel...
5.Emulsions
Emulsions are collodial
mixtures of the two
solvents. To get rid of
these, either: (a) add a few
mL of sat. NaCl; (b) filter;
(c) add small amount water
soluble detergent; (d) apply
light vacuum; or (e)
change solvent.
Using a Separatory Funnel...
5.Removing one
layer…
Bottom layer is
removed via stopcock
(1)
(1)
Top layer is poured out
(“decanted”) off the top
(2)
(2)
Partition Coefficient
For a solute A, the extracting solvent Sx, and the
original solvent So
Partition (K) =
Coefficient
[A] in Sx
-----------[A] in So
Partition Coefficient
(gm A/molar mass A)
K = [A] in Sx
Liter of Sx
---------- = ------------------[A] in So (gm A/molar mass A)
Liter of So
Molar mass divides out …
Partition Coefficient
• When the volume of two solvents is the
same (V will cancel out), K is reduced to
gm A in Solvent x / gm A in Solvent o
• If K> 1 ... Solute mostly in extracting
solvent (Sx)
• Increasing Volume of Sx, increases gm A
removed but not always practical
Effect of Multiple Extractions
Fn = [ Vo (KVx + Ao) ]n
Fn = fraction of original solute remaining in So after n
extractions with a constant volume of Sx
K = partition coefficient
Vx = volume of extracting solvent
Vo = volume of original solvent
(see page 136-137 of text for derivation/explanation)
Effect of Multiple Extractions
Example:
1 extraction with 30 mL of ether
Fn of 1/16 or 0.0625
3 extractions with 10 mL each of ether
(same total volume)
Fn of 1/216 or 0.00463
Criteria for Extracting Solvent
1. Will not irreversibly alter the solute and
does not react with the other solvent.
2. Immiscible with the original solvent.
3. High K for desired material –
selectively remove desired solute.
4. Readily separated from solute after
removal..
What affects K?
• Relative polarities affect solubility of
solute in each solvent.
• Reversible chemistry can affect
solubility (e.g. protonation/deprotonation).
Effect of pH on Solubility
HA
Add
base
A-
Add acid
WHY??
(the salt is more water soluble)
Add acid
RNH3+
RNH2
Add
base
Extraction Experiment
Dissolve 3 g of 1:1:1 (by mass) mixture of …
(a) benzoic acid
(b) 2-napthol
(c) 1,4-dimethoxybenzene
… in 30 mL of diethyl ether
OCH3
O
pKa ~ 9.5
OH
C
OH
pKa ~ 4.2
2-naphthol
benzoic acid
OCH3
1,4-dimethoxybenzene
Dissolve the 3 g mixture of the above
compounds in 30 mL of diethyl ether
Add 15 mL of saturated NaHCO3 solution
Shake.
Separate layers.
organ
ay e r
o us l
aque
ic lay
pH ~ 8-9
er
compounds remaining
in the organic layer
(what are these compounds?)
Flask A
(what is in Flask A?)
Add 10 mL of 1.5 M
NaOH solution
Shake
Separate layers
Cautiously acidify with HCl
Cool in ice
Isolate solid
s layer
aqueou
SOLID FROM
FLASK A
Flask B
(what is in Flask B?)
Cautiously acidify with HCl
Cool in ice
Isolate solid
organ
ic lay
pH ~ 12-13
er
Dry organic
layer with
Na2SO4.
Decant ether
off drying
agent
Flask C
(what is in Flask C?)
Evaporate
off ether
SOLID FROM
FLASK B
SOLID FROM
FLASK C
To Prepare your NB…
- 10 Compounds needed in Table of Chemical & Physical
Properties: benzoic acid, 2-naphthol, 1,4-dimethoxybenzene,
diethyl ether, sodium bicarbonate, sodium hydroxide, sodium
chloride, water, concentrated hydrochloric acid, anhydrous
sodium sulfate.
- Figures needed:
- Flowchart (can print from these notes and tape into NB)
- Figures 2.60, 2.61, and 2.62 of the text book.
- The Handout (posted on Moodle with Flowchart) is your
procedure for lab. This can also be printed and taped into
your NB, but make sure that you’ve read and understand what
you’re going to be doing in lab!!!
To Prepare your NB… (cont’d)
- There are 4 Chemical Reactions. You need to figure out how
to correctly write these AS CHEMICAL STRUCTURES:
(1) Benzoic Acid + Na(HCO3)  ?? + ??
(2) Sodium benzoate + HCl  ?? + ??
(3) 2-naphthol + NaOH  ?? + ??
(4) Sodium 2-naphtholate + HCl  ?? + ??
To Think About…
-What is the definition of a Bronsted-Lowry Acid?
- How do you identify an “acidic hydrogen?” (Hint: Why type
of atoms are they bonded to before they are pulled off by a
base or “fall off” as H+ ?)
- pKa is a relative measure of acidity. Acidity increases with
decreasing (more negative) pKa values.
- Comparing the pKa of a molecule with the pH of the solution
that it’s dissolved/mixing in will indicate if the molecule is
charged or neutral.
- Remember, that when talking about solubility, “like
dissolves like.” So polar dissolves in polar, and nonpolar
dissolves in nonpolar.
- What is the function of anhydrous sodium sulfate???
Complete the Experiment by..
- Submit the samples of all three solutes which you
recovered by extraction (properly labeled in a vial!)
- Allow the samples to air dry in drawer (for 1 week).
- Weigh and record recovered masses of each compound
next lab period. (Employ weigh-by-difference technique
so pre-weigh empty vials/lid/tape!)
- Calculate exactly how much (grams) of each compound
was in the original ~3 g sample.
- Then, calculate the %-recovery of each compound in Flask
A, B, and C. (Remember, the ~3 g original mixture had a
1:1:1 ratio of the three compounds. Ideally, you should
have retained about the same amount, b/c just separating.)
More info…
• How to test acidity of a solution using
Blue Litmus Paper:
http://www.youtube.com/watch?v=6DCB
WK_Hg5w
• How to dry over anhydrous sodium
sulfate:
http://orgchem.colorado.edu/Technique/P
rocedures/Drying/Drying.html