The isolation of caffeine from tea leaves
The overwhelming majority of biologically active molecules are organic compounds; for example, ethanol, salicylic acid and tetrahydrocannabinol (THC). Naturally occurring organic amines are called alkaloids and are amongst the most interesting and widely varied of all naturally occurring compounds.
Salicylic Acid |
Tetrahydrocannabinol |
Caffeine |
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Caffeine is an alkaloid that occurs in tea, coffee and several carbonated soft-drinks. It is one of the alkaloids easiest to isolate and, in this practical exercise, is extracted from tea leaves by treating them with dichloromethane. Calcium hydroxide is added to the tea leaves during the extraction process to neutralise the tannic acids that would otherwise be difficult to separate from the caffeine.
After evaporation of the dichloromethane solvent, the crude caffeine is purified by thin-layer chromatography (see E29).
Final purification of an organic solid is nearly always accomplished by recrystallisation (see E24 for more information concerning this procedure).