ORGANIC cHEMISTRY - Iv

Experiment 1

Principle

Caffeine is a minor constituent of tea, coffee, and other natural plant materials. The major constituent of tea is cellulose which is not water soluble. Caffeine is water soluble but so are some tannins and gallic acid which is formed in the process of boiling tea leaves. The latter two components can be converted to their calcium salts which are insoluble in water. The caffeine can then be extracted from the water by methylene chloride in almost pure form. Some chlorophyll is often extracted at the same time.

Materials required

tea leaves, calcium carbonate/sodium carbonate, dichloromethane, beaker, separating funnel etc

Procedure

Place 15 g of tea leaves, 5 g of calcium carbonate powder and 200 mL of water into a 600 mL beaker. Boil the solution on a hot plate for 20 minutes with occasional stirring. Cool the solution but, while it is still warm, vacuum filter through a Buchner funnel using a fast filter paper, if available. Normally, hot solutions are not vacuum filtered. Rinse the leaves with 50 mL of water. Carefully press out as much filtrate as possible since the caffeine is in the aqueous layer. Rinse again with 50 mL of water. Cool the solution to room temperature and pour it into a 500 mL separatory funnel. Extract with 35 mL of methylene chloride. In a departure from normal procedure, it will be necessary to vigorously shake the separatory funnel in order to extract the caffeine. First, relieve the pressure buildup as soon as you mix the two liquids. Then shake vigorously for 10 seconds and relieve pressure, repeat the shaking two more times. An emulsion will probably form. To break the emulsion formed in the methylene chloride layer, slowly drain the methylene chloride layer through a small amount of anhydrous magnesium sulphate in a powder funnel with a loose cotton plug (a tight plug will prevent drainage). Extract the aqueous solution once again with a 35 mL of methylene chloride, repeating the steps above to collect the lower layer. Combine the organic layers, dry over anhydrous sodium sulphate. Decant the dichloromethane in a 250 mL round bottom flask and distil off the organic solvent on water bath. As the last traces of solvent are distilled off, caffeine crystallizes as an off white or cream colored solid, m.p. 233 – 235 °C.

Calculation

Calculations:

Weight of the product = ________________________(Y) g

Result

1. Weight of the product = _____________________ g

2. % Yield of the product = _____________________

3. Melting Point (M.P.) of the product = ______________________°C

Reference Material

Video link for Extraction of Caffeine from tea leaves.

www.youtube.com/watch?v=sPhJWBL17OQ

Questions

1. Role of sodium carbonate/calcium carbonate in this experiment?

2. Definition of partition coefficient?