Isolation of Caffeine in Tea
Today’s world is addicted to coffee and tea for an easy wake up. Both contain caffeine, a drug known for its stimulant properties. Tea, by weight, contains approximately 2-4% caffeine, and the average cup of tea has anywhere from 40 to 120 mg of caffeine (Landgrebe, 327; Mayo Clinic Staff). According to the American Heart Association, caffeine not only stimulates the brain and nervous system, but it releases fatty acids from adipose tissue, and affects the kidneys, increasing urination (Caffeine). Pictured below is the structure of a molecule of caffeine.
Caffeine weighs in at 194.19 g/mole and melts at approximately 227°C. It is known to sublime however at only 178°C, much cooler than the temperature that it melts. Caffeine is considered an alkaloid, a nitrogen containing compound that is found in plant materials (Landgrebe). There are four nitrogens per molecule of caffeine, categorizing well as an alkaloid. Caffeine has a near identical structure to the two chemicals theophylline and theobromine, both shown below according to Clarke Earley. The only differences are the methyl groups attached to two different nitrogens have been replaced by a hydrogen atom in these two variants. Later in the experiment, caffeine reacts with salicylic acid to form caffeine salicylate. The reaction is shown below.
The nitrogen in the caffeine acts as a nucleophile, accepting the acidic proton from the salicylic acid. The Pka of the conjugate acid of caffeine is about 1.22, while the Pka of salicylic acid is 2.97. The reaction normally would be reagent favored, because the conjugate acid formed has a higher Pka than salicylic acid. However, the reaction takes place in a nonpolar, protic solvent, which stabilizes the reaction and pushes it forward. Procedure
Five tea bags were placed in 200mL of distilled water and boiled for approximately 15 minutes. The...
Please join StudyMode to read the full document