Extraction of Acids and Bases and the Isolation of Caffeine from Tea

Extraction of Acids and Bases and the Isolation of Caffeine from Tea

Abstract:

Caffeine is classified as an alkaloid. Alkaloids are naturally-occurring molecules that contain basic nitrogen. They have some level of structural complexity that normally involves rings or a number of stereocenter. Like both cocaine and morphine, caffeine can be isolated from plants. Isolating from plants can be difficult because when trying to isolate a single compound from plant material, plant contains a large number of other compounds. To effectively isolate the desired compound one must know the different properties of each component. Properties to examine include polarity and acidity/basicity. In the extraction of caffeine from tea, we will need to consider both polarity and acidity. Extracting caffeine from tea begins by adding hot, basic water to the tea leaves. This process removes all the water soluble components of tea. In addition to caffeine, we remove tannins and small amounts of chlorophyll. Tannins are acidic and will be deprotonated under the basic conditions. The conjugate bases of tannins are anions. Tannins can also decompose in base. The decomposition products are also anions. When water is added to the tea leaves the solution contains caffeine, tannins in the form of anions, and small amounts of chlorophyll. Since caffeine is soluble in organic solvents and the tannin anions are not, we can extract the caffeine into an organic solvent, dichloromethane, and leave the tannin anions behind in the basic aqueous layer. Evaporating the organic solvent will isolate caffeine. Caffeine is a colorless solid, but the caffeine may be greenish due to small amounts of chlorophyll that will also be extracted into the organic solvent. In this lab Caffeine was extracted from instant tea and purified by recrystallization. The yield was determined to be .92 % of caffeine per one gram of instant tea.

Objective:

Numerous purification methods are available to the organic...