ISOLATION OF CAFFEINE FROM TEA
EXPERIMENTAL TECHNIQUES REQUIRED
Caffeine is a commonly encountered mild stimulant and a diuretic; it is widely used in proprietary
drugs for the stimulant effect to prevent drowsiness. Caffeine is naturally present in the fruit and bark of a
number of plants, including tea, coffee, and cacao. Tea contains about 30-75 mg and coffee 80-125 mg
in a typical 150 mL (cup) serving. The amount of caffeine in tea varies by brand but the average in
common brands is typically about 30-40 mg caffeine/tea bag.
The January 2005 edition of National Geographic had the cover title "why we love caffeine" and a
30 page article on the "world's most popular psychoactive drug.". In contrast to popular belief it includes
evidence that in moderate amounts, caffeine is not a diuretic. Did you know you can get fabrics with
caffeine woven in and that smokers metabolise caffeine almost twice as fast as non-smokers?
Caffeine belongs to a very important class of compounds called purine alkaloids, a major
component of nucleic acids. Other purine systems are found in naturally occurring compounds, including
uric acid, which is the form in which nitrogen is excreted in non-mammalian animals. The presence of
methyl groups in caffeine is a result of biochemical methylation, a common process in plant metabolism.
The extraction of caffeine from coffee is commercially important as the effects of caffeine are
considered undesirable by some people. Decaffeination used to be carried out by treating the green
coffee beans with a small amount of hot water and then exposing to a solvent (trichloroethylene) until
97% of the caffeine was removed. Residual solvent was removed after extraction by steam distillation.
The process also removes wax from the beans, which are then roasted in the usual way. In these solvent
based methods, the coffee beans are extracted as many as 10 times, maybe for as long as 10 hrs until
the required level of decaffination has been reached. A more common today to use super critical carbon
The extraction of caffeine from tea leaves requires that the caffeine is separated from other
compounds present in the leaves such as cellulose, proteins, amino acids, tannins, saponins and
pigments. It is the differing solubilities of these compounds that we take advantage of to extract the
caffeine. Cellulose is insoluble in water so it is not removed in the initial “brew” and the other compounds
tend to be more water soluble than caffeine itself so they are not extracted by the dichloromethane. The
solubility of caffeine at room temperature is 2.2g/100mL in water at 25 oC (6.7g/100mL at 100 oC) and
18g/100mL in chloroform. Caffeine crystallises readily and it can also be sublimed.
In this experiment the caffeine is first extracted from tea leaves using hot water. This only takes a
few minutes (about 10 minutes), and there is no advantage to leaving it for 20 minutes. This aqueous
solution also contains tannins and other water soluble materials. The caffeine is then recovered from the
aqueous solution by liquid-liquid extraction using dichloromethane. The dichloromethane solution is then
dried, the solvent evaporated, and crude caffeine obtained can be further purified by either careful
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