Caffeine From Tea Lab

For the purposes of this lab, only three other chemical constituents of tea were considered during the chemical extraction of caffeine from tea. These chemicals were cellulose, tannins, and chlorophyll. Of course, there are many other chemicals in black tea, including various lipids and carboxylic acids ; however, many of these chemicals are not present in large enough quantities to separate using the methods available to an undergraduate lab, and therefore these chemicals are collectively considered as impurities. Therefore, the procedure and concepts behind the separation of the three aforementioned chemicals, as well as caffeine, from tea will herein be discussed. Cellulose is largely insoluble in water, and only goes into solution at temperatures and pressures much higher than those encountered in boiling tea. Furthermore, a brief literature search suggests that adding a

First off, to separate the tannins from the caffeine, which are both soluble in the nonpolar solvent dichloromethane, one of the chemicals needed to be transformed such that it would extract into a polar, aqueous solvent such as water. By adding sodium carbonate during the initial boiling step, the acidic tannins were deprotonated and thus became ions that were more soluble in water than dichloromethane, allowing the tannins to be separated from caffeine. Furthermore, a base was used to deprotonate the tannins instead of an acid to protonate the basic caffeine because otherwise the caffeine would extract into the aqueous phase and make it more difficult to isolate the crude caffeine using a rotary evaporator since water has a higher boiling point and lower volatility than dichloromethane. Moreover, if one were to remove water from the protonated caffeine to obtain the crude caffeine crystals, the counter ion would likely be present in the crystals as well, adding yet another impurity to the crude