Extraction of Caffeine from Tea

Title: The Extraction of Caffeine from Tea

Objective: To Extract Caffeine from Tea Leaves

Theory:

Every day, throughout the world, people start out their morning by extracting a family of natural products called alkaloids from naturally occurring materials and then drinking this extract. The most common of these alkaloids caffeine (C8H10N4O2), 1,3,7 - rimethylxanthine, occurs naturally in coffee beans and tea leaves, but is added to soft drinks and stimulants such as Vivarin and No-Doz, dieting aids such as Dexatrim and Diatac, painkillers such as Anacin and Excedrin, and anti-inflammatory drugs such as Aspirin.

The basic property of alkaloids comes from the lone pair of electrons found on at least one nitrogen. Since they contain nitrogen, they behave like bases (alkalis) and hence, they are termed alkaloids. Other common alkaloids are morphine, quinine, cocaine and codeine. The basic N in caffeine can be used to increase or decrease its water solubility. Acidic conditions will form the conjugate acid salt giving caffeine increased water solubility as a cation. On the other hand if caffeine is in a basic environment it takes the neutral form and is only somewhat polar. Tea leaves contain tannins, which are acidic, as well as a number of colored compounds and a small amount of un-decomposed chlorophyll (soluble in dichloromethane). To ensure that the acidic substance remains water soluble and that the caffeine will be present as the free base, sodium carbonate is added to the extraction medium. In order to successfully extract any substance from one solvent into another, we must maximize differences in solubility. Adding base to the solution has a second important effect. The water solution contains much more than just caffeine and some of these compounds are also soluble in dichloromethane. Making the solution basic forms insoluble tannin salts which removes them from the solution before the caffeine is extracted. The dichloromethane extract will primarily contain caffeine with small amounts of impurities. Caffeine is also water soluble, but by keeping the washing solution basic it minimizes the caffeine lost, while maximizing the removal of impurities.

In this experiment, we will extract caffeine from tea using methylene chloride (CH²Cl²). Methylene chloride is an organic solvent that is somewhat nonpolar. Methylene chloride is a liquid but it isn't like water so they form two layers, just like vinegar and oil. The caffeine molecule is closer in structure to methylene chloride, so it will dissolve in that layer. The two layers can then be separated, and the methylene chloride, which has a very low boiling point, can be evaporated at room temperature, leaving a residue of caffeine.

Procedure:

In a small beaker,