Exercise 1
ISOLATION OF CAFFEINE
CAFFEINE
white crystalline solid,
odorless, slightly bitter
O
N
N
O
N
N
mp 237⁰C
moderately soluble in
water
belongs to the alkaloid
family
ALKALOIDS
cocaine
nicotine
morphine
caffeine
ALKALOIDS
are a large family of more than 15,000 N-containing
secondary metabolites found in approximately 20%
of vascular plant species.
the N atom in alkaloids is usually part of a
heterocyclic ring (a ring that contains both N and C atoms).
in plants, most alkaloids are believed to function as
defenses against predators because of their general
toxicity and deterrence capability.
nearly all alkaloids are toxic to humans when taken in
sufficient quantity.
Strychnine, atropine and coniine are classic alkaloid
poisoning agents. However, at lower doses they can
be useful pharmacologically.
Morphine, codeine and scopolamine are just a few
of the plant alkaloids currently used in medicine.
Cocaine, nicotine and caffeine enjoy widespread
nonmedical use as stimulants or sedatives.
On a cellular level, the mode of action of alkaloids is
quite variable. Many alkaloids interfere with
components of the nervous system, especially the
chemical transmitters; others affect membrane
transport, protein synthesis, or miscellaneous enzyme
activities.
source of caffeine: TEA LEAVES
The use of tea as a stimulant dates back more
than 2000 years. Its use became widespread in
China around 700 AD and traders introduced
into Europe.
composition of TEA LEAVES
1. CELLULOSE
2.CAFFEINE – 5% by weight
3. TANNINS
4. FLAVONOIDS
5. CHLOROPHYLLS
ISOLATION PROCEDURE
tea bags
+ H2O
Δ
decantate
+ HCl
+15 mL portion of CH2Cl2
AQUEOUS LAYER
+ Na2CO3
+10 mL portions (2X) of CH2Cl2
ORGANIC LAYER
+ drying agent (e.g. Na2SO4)
evaporate CH2Cl2
crude
CAFFEINE
ISOLATION PROCEDURE
1. Steeping of tea bags in hot water
2. Addition of 10% HCl solution
3. Extraction with CH2Cl2
formation of EMULSION during extraction
4. Addition of 10% Na2CO3 solution
5. Extraction with CH2Cl2
6. Removal of water and CH2Cl2
• SOLID – LIQUID EXTRACTION
– extracting solvent: boiling dH2O
– allows the separation of caffeine from the water insoluble
components of tea leaves
• boiling of mixture
• increase in temperature increases solubility of caffeine in
water thus ensuring a maximum yield
• addition of HCl
• protonates caffeine to increase its solubility in the
aqueous layer
• filtration of the mixure
• removes water insoluble products upon acidificarion
• addition of CH2Cl2
• removes CH2Cl2 soluble compounds
• addition of Na2CO3
• converts back caffeine to its molecular form
• LIQUID – LIQUID EXTRACTION
– extracting solvent: dichloromethane
– caffeine is preferentially transferred from water to
dichloromethane layer
– shaking – to hasten the transfer of organic soluble
components to the organic layer
– amount of caffeine transferred is governed by the
distribution coefficient, Kd
• at a given temperature
Kd 
solubility of caffeine in organic solvent
solubility of caffeine in water
• numerators always have higher solubilities, therefore Kd is
always greater than 1
EXTRACTION
solubility
characteristic of a good extracting solvent ?
 high distribution coefficient, KD
KD = DISTRIBUTION / PARTITION COEFFICIENT
constant of a solute at a given temperature
and solvent pair
 KD >1
for caffeine: KD =
1 g is soluble in 5.5 mL CHCl3
1 g is soluble in 46 mL water
• If KD < 1 the substance is mostly soluble in the
original solvent
• If KD > 1 the substance is mostly soluble in the
extracting solvent
• If KD = 1 the substance is mostly soluble in both
Problem 1
Twenty grams of tea leaves was extracted with 175.0 mL water
(20.0g of tea leaves would contain 1.0 g caffeine). The aqueous
extract was then subjected to liquid-liquid extraction using a total
of 60 mL CHCl3. Determine the amount of caffeine isolated using
single and two-step extraction and the % efficiency of the two-step
extraction over the other.
Solubility of caffeine in water and CH3Cl:
1.0 g caffeine / 46.0 mL water, 1.0 g caffeine / 5.5 mL CHCl3
Ans.
Single extraction = 0.74 g caffeine
Two-step extraction = 0.83 g caffeine
% efficiency = 12.2 %
Comparison between single
extraction and two-step extraction
THE SEPARATORY FUNNEL
1.
2.
3.
4.
SHAKE
VENT
STAND
DRAW a small amount of the lower layer on
a watch glass and add water.
5. SEPARATE the organic from the aqueous
layer
6. REPEAT process if extraction will be done
twice, thrice, etc.
problem solving 2 
1. Starting w/ a solution of 1.50 g compound MOO
in 50.0mL water. Calculate the amount that can
be recovered with 30mL ether via single
extraction. KD=3.5
2. What is that total amount of compound MOO that
can be obtained if the extraction was performed with
3 10-mL portions of ether?
Quiz
Starting with 4.5 g of butyric acid present in
water. (Kd = 3.5 at 25 °C)
1. Using 400mL ether, what is the amount of
butyric acid in 400 mL water layer via single step
extraction?
2. What is the total amount of butyric acid
extracted using two successive extractions?
3. Calculate the % efficiency of two-step
extraction over single extraction.