Extractions
Mixture of benzoic acid, anthracene, and
p-nitroaniline
O
COH
NH2
NO2
Mixture of methylene chloride and water
Density of CH2Cl2 is 1.33 g/mL
H2O
CH2Cl2
If we dissolve NaCl in this mixture
which phase has the highest salt
concentration?
Salts concentrate in
the water layer
If we dissolve benzoic acid in this mixture
in which phase would it concentrate?
Salts
Neutral organic compounds
concentrate in the organic
phase
Salts in water phase
Water
Neutral organic
compounds in the
organic phase
CH2Cl2
Treatment of benzoic acid with
sodium hydroxide converts it into
the salt, sodium benzoate.
COOH + Na OH
Benzoic Acid
COO Na
Sodium Benzoate
COOH + Na OH
COO Na
O2N
NH2 + HCl
O2N
NH3 Cl
Use separatory funnel for separations.
Shake to be sure phases
equilibrate
Hold stopper
and stopcock
Vent frequently
benzoic Acid
p-nitroaniline
anthracene
HCl
CH2Cl2
Benzoic acid
O2N
NH3 Cl
Anthracene
benzoic Acid
anthracene
CH2Cl2
NaOH
COO
Na
anthracene
O2N
NH3 Cl
NaOH
O2N
Filter
wash
dry
weigh
NH2
COO
Na
HCl
COOH
Filter
wash
dry
weigh
Dry
filter
evaporate
weigh
Addition of acid to
the sodium benzoate
solution causes
benzoic acid to
precipitate.
The benzoic acid is
filtered, washed, and
dried.
Weigh the benzoic
acid and measure its
melting point.
NaOH
O2N
NH3 Cl
O2N
Cool to complete precipitation
NH2
Dry the methylene chloride solution
of anthracene with a small amount of
sodium sulfate.
Remove the drying agent by filtration
through a fluted filter paper.
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
for K = 1, 2 and 4