Chemistry

EXTRACTION OF CAFFEINE FROM DIFFERENT TEA’S

For this experiment, we will extract caffeine from different tea leaves and we will later analyse the caffeine by TLC (Thin layer Chromatography) and determine the melting point to confirm the caffeine identity. We will also assess two different extracting solvents (dichloromethane and ethyl acetate).

Tea and coffee have been popular beverages for centuries, primarily because they contain the stimulant caffeine, which stimulates respiration, the heart, and the central nervous system. It can cause nervousness and insomnia and, like many drugs, can be addictive making it difficult to reduce daily consumption.

Caffeine belongs to a large class of compounds known as alkaloids. These are of plant origin, contain basic nitrogen, often have a bitter taste, a complex structure and usually have physiological activity. Their names usually end in “ine”; many are quite familiar by name if not chemical structure – nicotine, cocaine, morphine, strychnine.

Structurally, caffeine is 1,3,7-trimethylxanthine. It is also a derivative of purine and is therefore related to the purine bases in nucleic acids and to uric acid.

Two closely related compounds are the dimethylxanthines, theophylline, which occurs along with caffeine in tea, and theobromine, which occurs instead of caffeine in cocoa.

Caffeine is present in tea leaves to the extent of 4-5%. It is soluble in hot water, but soluble in only a few of the common organic solvents. In the present experiment we will extract caffeine from tea leaves with hot water much as is done in the home but in a greater concentration. The amount of caffeine per tea bag will also be calculated.

Preview

• Immerse the tea in boiling water

• Extract the aqueous layer with dichloromethane (or ethyl acetate)

• Wash the organic layer with NaCl

• Dry the organic layer with MgSO4

• Evaporate solvent

• Weigh crude caffeine

• Analyse by TLC and determine the mp

Chemical alert: Dichloromethane is a toxic substance and a skin irritant. Avoid breathing the vapours. Boiling water can cause skin burns. Be careful!

Week 1: Extraction of Caffeine from various tea brands

General Suggestive Procedure

Prepared in advance due to lab time constraints Into a 500ml beaker, 150ml of water is brought to a boil and then 5 tea bags are added. The mixture is left standing for ca. 10 minutes with occasional stirring (careful not to tear the tea bags). The tea bags are squeezed into a Buchner funnel and the solution containing caffeine is collected in a filter flask.

Student: Obtain the amount of caffeine solution specified by the lab instructor and carefully pour it into a 250ml separatory funnel using a liquid funnel. Carefully add 7ml of dichloromethane (or ethyl acetate) to the separatory funnel in the fume hood (to extract the caffeine) and put an adequate piece of cotton in the opening before you head back to your lab bench. Perform the ‘shaking and venting technique’ to extract

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