Isolation of caffeine from soluble coffee (from a commercial product), by extraction with an organic solvent and separation by centrifugation of the aqueous phase and the organic phase obtained.
Caffeine is an alkaloid of the xanthine family. When pure, it is an odorless white solid with a melting point of 234-236 ºC, partially soluble in water (100 mM). As is known, caffeine has a stimulant effect, and is found in plants such as coffee and tea.
Instant coffee or soluble coffee is a product widely spread in the market that is obtained from infusion through the freeze-drying process.
According to the manufacturers, instant coffee contains between 55 and 62 mg of caffeine for each cup prepared with a teaspoon of the product.
In this practice we will proceed to obtain caffeine from an extract obtained from a commercial product.
The isolation of caffeine from soluble coffee is carried out as follows:
In a beaker place 2 g of sodium carbonate and 2 g of instant soluble coffee. Add 9 ml of very hot deionized water and stir the mixture until boiling. The mixture is then allowed to cool to room temperature.
The content of the beaker is poured into a 15 ml centrifuge tube, 2 ml of methylene chloride (CH2Cl2) is added, the tube is closed and shaken vigorously for 1 min. It is then centrifuged for 90 s. The yellowish CH2Cl2 solution is separated from the aqueous phase with the aid of a Pasteur pipette. The operation is repeated two more times.
The organic extracts are pooled and dried over anhydrous sodium sulfate (Na2SO4). The solid is eliminated by filtration by gravity. The desiccant in the paper filter is washed with a few ml more solvent and pooled with the remaining CH2Cl2. The solution is transferred to a previously tared flask, the solvent is removed at the rotary evaporator and finally the flask is weighed and the caffeine obtained is calculated. The caffeine can be purified by EtOH recrystallization.
References and notes
 Process in which the product is frozen and then vacuumed to eliminate water by sublimation.
 In this way we ensure that none of the hydrogens will be protonated, which will facilitate their dissolution in an organic solvent.
 Alternatively, separation of the two phases by decantation can be performed, but is less effective.