The purpose of this experiment was to practice fundamental laboratory techniques by isolation of caffeine, from tea leaves.
Camellia sinensis (tea) Caffeine
Analysis (Isolation of Caffeine)
This experiment was conducted to study the simple isolation of an alkaloid and to train with fundamental laboratory equipment like the separatory funnel and distillation apparatus. Ten commercial tea bags (23.06 grams) were used for the extraction. Boiling water (~275 mL) was used to extract caffeine from the solid leaves. This was the most efficient solvent because water causes tea to swell, allowing for a caffeine solubility of 670 mg/mL. Sodium carbonate was added to the tea/water solution to ensure that caffeine remained in its free base form and to keep acidic tannins water soluble. The mixture was decanted after seven minutes and cooled.
In a separatory funnel, the water solution and dichloromethane (30 mL) were gently mixed. The dichloromethane solvent was used because caffeine is basically the only substance from the water solution that will dissolve in it. After mixing, the two layers began to separate. At the point of separation an emulsion began to form. The emulsion looked foamy and grew quite large (1/8 of the volume). The emulsion dwindled after a half an hour. The solutions were separated and the water solution was added to dichloromethane (30 mL) in the funnel once more to ensure maximum recovery of caffeine. In effort to prevent another emulsion, a highly saturated solution of salt water was also added to the solutions. After mixing the separatory funnel, an emulsion formed, but it was not nearly as large as before. The second volume of dichloromethane was separated from the water solution and added to the first volume.
To ensure that no water remained in the dichloromethane solution, Calcium Chloride pellets were added. These pellets are very hydrophilic. The pellets left the dichloromethane solution crystal clear. Now the solution should have contained only the solvent and caffeine. To isolate caffeine, the solution was filtered through silicon paper (another drying agent) into a distillation apparatus. The solvent boiled away leaving a fine white powder, caffeine.
Table A: Percent Recovery of Caffeine
|Mass of Tea||Mass of Crude Caffeine||Anticipated Mass of Crude Caffeine||Percent Recovery of Caffeine|
|23.06 grams||21 milligrams||~23 milligrams||91%|
Williamson, author of Organic Experiments, anticipates that this exercise should yield a mg/gram of tea (see Table A). At this standard, the experiment had 91% recovery of the caffeine. However, Williamson also describes the caffeine as greenish in appearance, which was not seen in the experiment. The experiment seemed highly successful in isolating the alkaloid.