Lab Experiment: Isolation Of Caffeine From Tea

Experiment #1

Isolation of Caffeine from Tea

Date: 11.09.14
Prepared by: Alibek Abilev

Purpose The aim of the experiment was to isolate crude caffeine from tea leaves by using liquid – liquid extraction with methylene chloride, purify the crude substance by performing sublimation and determine the melting point of both crude and pure caffeine.

Safety
Lab coat, goggles, gloves.
Methylene chloride is a carcinogenic substance, therefore should be kept in a well-ventilated place.
The separatory funnel stem should be pointed away from the human when the pressure is released

Chemicals
1) Methylene chloride – carcinogenic

Procedure
1) Isolation of caffeine 6 tea bags, 5 g of calcium carbonate powder and 180 ml

The solvent was removed using a rotary evaporator. The melting point was estimated. The obtained mass of caffeine was measured. The percentage yield based on the amount of tea originally used was calculated.

2) Purification of caffeine by sublimation The crude caffeine was transferred to Petri dish. Petri dish was placed on a hot plate and covered with three disks of filter paper. Another petri dish filled with ice was placed just on the top of petri dish covered with filter papers. The heat was turned on and sublimation was performed for 5 minutes. The purified caffeine was scraped from the filter papers and its weigh was measured. The melting point of purified caffeine was estimated.

Observations After mixing tea substance with methylene two clearly seen layers were obtained. During rotation of separatory flask the pressure was created inside and after the release of the pressure through the stem a little bump was observed. After the 5 minutes the methanol was rich with caffeine and its previously translucent white color changed to bright green. After the drying the crude caffeine was pale green color.

Leaves containing water-soluble elements were boiled and turned from the solid phase into the liquid phase, boiling water. The calcium carbonate was added to form insoluble calcium salts with the tannins and gallic acid so that after vacuum filtration they would be removed. The sodium chloride salt was added after the vacuum filtration in order to raise the polarity of the water, making less amount of molecules soluble in it. This is because the salt takes the part of the space in water and many compounds become insoluble and are pushed out by the salt. By adding the salt we avoid the situation of getting heavy emulsion when mixing tea with methylene chloride. After separating methylene chloride containing caffeine the magnesium sulfate salt drying agent was added to the methylene chloride solution. After contact with aqueous tea the methylene chloride a bit mixed with water, thus, the added salt is assumed to remove the water present in solution. salt + nH2O ↔ salt •