Isolation of Caffeine
References:
Slayden: pp. 47- 49
. Pavia: pp. 24, 73 – 84
Note: These pages are not in the GMU version
of the Pavia text sold in the book, only in
the primary text that we do not use
anymore
1/17/2015
1
Isolation of Caffeine

1/17/2015
Overview
 An aqueous Vivarin/Sodium Carbonate mixture
is extracted with Dichloromethane (Methylene
Chloride)
 The organic fraction is separated from the
aqueous solution and evaporated to dryness
 The product is recrystallized from Acetone
 The mass and % recovery of the product are
determined
 Product identity is verified by Melting Point
2
Isolation of Caffeine

Background
 Caffeine (a stimulant) is a bitter, white
crystalline alkaloid derivative of Xanthine (note
methyl substitution on primary amino groups)


1/17/2015
Caffeine is synthesized from the purine
nucleotides AMP, GMP, and IMP in plants.
These in turn are transformed into Xanthosine
and then Theobromine, the latter being the
penultimate precursor of Caffeine
3
Isolation of Caffeine
The two Amide groups exist as zwitterionic
resonance structures where the Nitrogen and
Carbon atoms are double bonded to each
other so that both of the Nitrogen atoms are
essentially planer (in sp2 orbital hybridization)
 A zwitterion is a neutral molecule with a
positive and a negative electrical charge (not
dipoles) at different locations within that
molecule
 Zwitterions are sometimes also called inner
salts
 The fused ring system therefore contains a
total of ten pi () electrons, thus, according to
Huckel’s rule is aromatic

1/17/2015
4
Isolation of Caffeine
Zwitterionic Resonance
1/17/2015
5
Isolation of Caffeine

Chemical Properties
1/17/2015

Caffeine acts as a general nervous system
stimulant, warding off drowsiness

Caffeine is considered a “psycho active”
substance, but is generally legal and
unregulated

Caffeine is found in varying quantities in the
seeds, leaves, and fruit of some plants, acting
as a natural pesticide by paralyzing and killing
insects

Sources for human use include coffee plants,
tea leaves, and kola nuts
6
Isolation of Caffeine

Procedure
 Obtain 2 Vivarin tablets noting % of active
ingredient
 Determine the mass of the tablets
 Obtain and determine mass of approximately 8 g
of Sodium Carbonate
 Crush the tablets with a pestal & mortor
 Add the crushed sample to a 150 mL beaker
 Add 60 mL of Distilled Water
 Add the Sodium Carbonate (Na2CO3) to the
solution
 Add a Teflon boiling chip
 Heat solution to boiling on a hot plate – maintain
boiling point for 2 minutes
1/17/2015
7
Isolation of Caffeine

1/17/2015
Procedure (Cont’d)

Allow the hot mixture to settle slightly
- some solid particles will remain
undissolved

Attach an iron ring to a ring stand

Insert a 125 ml Separatory Funnel into
the iron ring using a clay triangle if
necessary to support funnel

Adjust height of iron ring so that stem
of separatory funnel fits just inside a
150 ml beaker

Place a glass funnel into the neck of
the separatory funnel

Make a boat of glass wool and place in
the bottom of glass funnel
8
Isolation of Caffeine

Procedure (con’t)
1/17/2015

Decant the sample solution into the glass funnel
allowing the liquid to drain into the 125 mL
Separatory Funnel

Rinse the beaker with a small amount of distilled
water and pass the water through the glass funnel
to the separatory funnel

Allow the filtrate in the Separatory Funnel to cool
to room temperature
9
Isolation of Caffeine

Procedure (con’t)
1/17/2015

Liquid–liquid Extraction, also known as solvent
extraction and partitioning, is a method to
separate two immiscible liquids, usually an
aqueous component and an organic solvent
component

The process involves the extraction of a
substance from one liquid phase into the other
liquid phase utilizing a separatory funnel

Use the following steps to extract the Caffeine
from the aqueous phase into the organic phase
consisting of Methylene Chloride solvent (density –
1.33 g/ml)

Three (3) extractions will be performed
10
Isolation of Caffeine

Procedure (Cont’d)

Add 8.0 mL of Dichloroethane (Methylene
Chloride) to the mixture in the separatory funnel

Place the stopper in the top opening and make
sure it is secure, i.e. won’t leak

Invert the funnel pointing the stopcock end away
from your face

Use “gentle” swirling (avoids formation of an
emulsion) for 10-15 seconds

Slowly open the stopcock to relieve any pressure
1/17/2015
11
Isolation of Caffeine
1/17/2015

Close the stopcock and continuing swirling with
venting every 15 seconds until no more gas is
released (two or three times should be sufficient)

Continue the swirling for a total of 5 minutes

Replace the separatory funnel in the ring stand
and allow the mixture to settle for a few minutes

Remove the stopper from the Separatory Funnel

Open the stopcock slowly and drain the clear
bottom (organic) layer into a clean 150 mL beaker

Repeat the extraction process two more times with
new 8.0 mL aliquots of Methylene Chloride, but
reduce the total swirling time to 2 minutes

Each time, add the clear bottom layer to the 150
mL beaker
12
Isolation of Caffeine

Procedure (Cont’d)
 With the help of the instructor, add Anhydrous
Sodium Sulfate as a drying agent
 Leaving the particles settled on the bottom of the
beaker, slowly pour (decant) the liquid into a
clean, dry, 50 mL beaker
 Rinse the beaker containing the drying agent
particles on the bottom with one additional small
portion of Dichloromethane and add to the sample
beaker
 Evaporate the mixture to dryness in the hood
Note: Set hot plate setting to about 3
Note: Crude yield at this point is roughly 90%
1/17/2015
13
Isolation of Caffeine

Procedure (Cont’d)
 Recrystallization Process using a mixed solvent of
Acetone and Petroleum Ether
 Dissolve the dried product in 12-15 mL cold Acetone
(from ice/water bath)
 Heat solution gently on hot plate
 If solution is incomplete, remove beaker from hot
plate and add more Acetone in 2 mL increments
 Up to 20 mL of additional Acetone may be
required until a clear pale-yellow solution is
obtained
 Remove solution from hot plate and allow to cool
slightly
1/17/2015
14
Isolation of Caffeine

Procedure (Cont’d)

Add Petroleum Ether, drop by drop, with swirling from
a full plastic pipet until the first appearance of
pervasive cloudiness throughout the solution

Continue cooling until crystallization is complete
Note: Maximum yield is obtained when the addition of
Petroleum Ether is stopped at the first appearance of a
pervasive cloudiness throughout the solution
1/17/2015

It may be necessary to boil off a portion of the solution
to effect recrystallization

Separate the crystals from the solution by Vacuum
Filtration rinsing the beaker and crystals in the funnel
with small amounts of Petroleum Ether
15
Isolation of Caffeine

Immerse beaker in an ice-water bath for about a
minute

Air-dry the sample from the evaporation procedure
or the vacuum filtration procedure on a pre-weighed
weighing tray for one week

Compute the mass of the purified sample

Compute the percent recovery of the product
relative to the amount of caffeine indicated in the
tablets

Determine melting point -  236 oC
Note: Decomposition of this crude material occurs
beginning at 236oC over a range of 5oC or so
1/17/2015
16