Extractions
Mixture of benzoic acid, anthracene, and
p-nitroaniline
Mixture
O
COH
NH2
NO2
Methylene Chloride and Water
Density of CH2Cl2 is 1.33 g/mL
H2O
CH2Cl2
Add Salt
If we dissolve NaCl in
this mixture which
phase has the highest
salt concentration?
Salts concentrate in
the water layer
Add Benzoic Acid
If we dissolve benzoic
acid in this mixture in
which phase would it
concentrate?
Neutral organic
compounds concentrate
in the organic phase
Salts
Phases
Salts in water phase
Water
Neutral organic
compounds in the
organic phase
CH2Cl2
Sodium Benzoate
Treatment of benzoic acid with
sodium hydroxide converts it
into the salt, sodium benzoate.
COOH + Na OH
Benzoic Acid
COO Na
Sodium Benzoate
Salts in Water Phase
COOH + Na OH
COO Na
Ammonia and Acid
NH3 + HCl
Base
Acid
NH4
+
Salt
Cl
Aniline and Acid
O2N
NH2 + HCl
O2N
NH3 Cl
Separatory Funnel
Use separatory
funnel for
separating liquid
phases.
Shake to be sure
phases equilibrate
Hold stopper
and stopcock
Vent frequently
Extract with HCl
benzoic Acid
p-nitroaniline
anthracene
HCl
CH2Cl2
Benzoic acid
O2N
NH3 Cl
Anthracene
Extract with NaOH
benzoic Acid
anthracene
NaOH
COO
CH2Cl2
Na
anthracene
Extraction Summary
O2N
NH3 Cl
NaOH
O2N
Filter
wash
dry
weigh
NH2
COO
Na
HCl
COOH
Filter
wash
dry
weigh
Dry
filter
evaporate
weigh
Precipitate Benzoic Acid
Addition of acid to
the sodium
benzoate solution
causes benzoic acid
to precipitate.
Purify Benzoic Acid
The benzoic acid is
filtered, washed,
and dried.
Weight, m.p.
Weigh the benzoic
acid and measure its
melting point.
Precipitate p-Nitroaniline
NaOH
O2N
NH3 Cl
O2N
Cool to complete precipitation
NH2
Dry Methylene Chloride
Dry the
methylene
chloride
solution of
anthracene
with a small
amount of
sodium sulfate.
Filter
Remove the
drying agent by
filtration
through a fluted
filter paper.
Remove Methylene
Chloride
Evaporate the
methylene chloride
on a steam bath.
Use an inverted
funnel connected to
the vacuum line to
collect the vapor.
Weigh your products and measure
their melting points.
Put your samples in labeled vials
and give them to your TA.
Partition Coefficients
10 g t-butyl alcohol
100 mL ether
100 mL water
10 grams t-butyl alcohol
2.2 =
x g / 200 mL
( 10 - x)g /100 mL
x = 8.1 grams
Which is better?
Extract once with 200 mL or twice with 100 mL?
If K = 1.0, a = 10 grams, S2 = 100 mL
Extract once with 200 mL yields 6.7 grams
Extract once with 100 mL yields 5.0 grams
Second extraction with 100 mL yields 2.5 grams
Total 2 extractions with 100 mL = 7.5 grams
Grams extracted vs. number of
extractions