Work Completed: 01.22.09
Work Submitted: 02.03.09
Synthesis 0732: Isolating Caffeine from Tea
Abstract
Caffeine was extracted from instant tea and purified by recrystallization. The yield was
determined to be 1.2152 % of caffeine per one gram of instant tea.
Introduction
In this experiment, caffeine will be extracted from instant tea. The caffeine will be
purified by recrystallization and the percent mass of caffeine per gram of instant tea will be
determined. Students will perform the following experiment to determine how much
caffeine is in one gram of a typical caffeinated beverage such as instant tea.
Objectives:
1.
2.
3.
4.
5.
To extract caffeine from tea
To perform a vacuum filtration
To separate layers from a crude extract
To purify caffeine by recrystallization
To determine the percent of caffeine per gram of instant tea
Descriptions
Caffeine is a natural product belonging to the alkaloid group. Caffeine is a stimulant
and has some undesirable side effects where an individual has a physical dependence to
this chemical. Many of the earliest isolated pure compounds from plants were alkaloids
because of the ease of isolation. This is because a nitrogen atom generally makes the
compound basic and the compound exists in the plant as a salt. Most alkaloids are
extracted with water or weak acid and recovered as crystalline material by treatment with
base. The following flow chart outlines a typical extraction of the stimulant caffeine from
its natural alkaloid state.
Organic Chemistry II, Lab Report 2
Page 1
Flow chart:
Isolating Caffeine from Tea
Tea + dichloromethane
(DCM) + 2M NaOH
Tea + dichloromethane
(DCM) + 2M NaOH
Extract
Separate
Aqueous Layer –
NaOH
Organic Layer DCM + Caffeine
Discard
Distill
Collect
Excess DCM
Caffeine + small
amount of DCM
Evaporate
Remaining DCM into the
atmosphere
Crude Caffeine
Add 2 – propanol, Heat (hv)
Caffeine +
2-propanol
Cool
Cooled Caffeine +
2-propanol
Add Hexane, Filter
Caffeine Crystals
Structural formulas of some xanthine alkaloids:
O
H
O
H
N
N
N
N
N
N
O
O
O
N
N
N
O
N
O
H
N
H
N
O
N
N
N
N
H
Xanthine
Organic Chemistry II, Lab Report 2
Caffeine
Theophyline
Theobromine
Page 2
Materials:
Figure 1 Distilling Apparatus
Thermometer
Water Out
Condenser
Water In
Hickman Still Head
Conical Vial
Sand Bath
Heat Source
5
4
6
2
1
5
7
3
10
1
4
8
3
9
2
6
7
8
9
1
10
Stirring Apparatus
Students will use the distilling apparatus to separate the caffeine and DCM.
Table 1 List of Materials and Equipment
List of Materials
1. Instant tea
2. Dichloromethane
3. 2M NaOH
4. 2-propanol
5. Hexane
6. Anhydrous sodium
sulfate
To isolate purified
caffeine
To extract the
caffeine
To extract the
caffeine
To recrystallize
To wash the purified
crystals
Drying agent
Organic Chemistry II, Lab Report 2
List of Equipment
1. Round bottom
flask
2. Phase separation
paper
3. Hirsch funnel
with adapter
4. Hot plate
To mix tea, NaOH, and
DCM
To separate the
caffeine from the tea,
NaOH, DCM mixture
To filter crystals
For hot water bath
Page 3
Procedural Steps:
1. Mix tea
2. Separate aqueous and organic layers
3. Distill
4. Evaporate to crude caffeine
5. Dissolve and recrystallize
6. Filter purified caffeine
7. Record mass of crystals
Data and Results
Table 2 Data and Results
Mass Instant Tea
Mass Recovered Caffeine Crystals
1.0122 g
0.0123 g
Calculations:
(Eq. 1)
= 1.2152 %
Discussions and Conclusions
By calculation, the amount of caffeine per one gram of instant tea was determines to
be 1.2152 %. This data may be imprecise because during the extraction of caffeine,
emulsions may have occurred. This happens when an organic compound of one liquid in a
second liquid and the first compound will not mix such as a case with water and oil.
Because of this, during phase separation, a arbitrary amount of caffeine was separated
depending on how gentle students shook the mixture.
In this experiment, caffeine was extracted from instant tea using an aqueous
solution of sodium hydroxide and hexane. Sodium Hydroxide was used to prevent the
extraction of acidic compounds called tannins from the tea leaves. Caffeine is more soluble
in an organic solvent, which is why dichloromethane was used instead of water to extract
the organic solvent and separate it from glucose, tannins, and other water soluble
compounds.
Organic Chemistry II, Lab Report 2
Page 4
References
McMurry, John, Organic Chemistry 7th edition, Thompson Learning Inc. Books/Cole 2008.
Silberman, Robert. “Isolating Caffeine from Tea,” page 65-73, Signature Lab Series, CHE
2403, Cengage Learning. Mason, Ohio: 2008.
Wu, Jennifer CHE 2403 Signature Lab Series Page 65-73.
Organic Chemistry II, Lab Report 2
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