In this experiment, caffeine is iso

In this experiment, caffeine is isolated from tealeaves. The chief problem with the isolation is that caffeine does not exist alone in the tealeaves, but other natural substances from which it must be separated accompany it. The main component of tealeaves is cellulose, which is a polymer of glucose. Since cellulose is virtually insoluble in water, it presents no problems in the isolation procedure. Caffeine, on the other hand, is somewhat water-soluble and is one of the main substances extracted into the solution called tea. Caffeine constitutes as much as 5% by mass of the leaf material in tea plants.
Tannins also dissolve in the hot water used to extract tealeaves. The term tannin does not refer to a single homogenous compound, or even to substances that have similar chemical structure. It refers to a class of compounds that have certain properties in common. Tannins are phenolic compounds having molecular masses between 500 and 3000. They are widely used to “tan” leather. They precipitate alkaloids and proteins from aqueous solutions. Tannins are usually divided into two classes: those that can be hydrolyzed (react with water) and those that cannot. Tannins of the first type that are found in tea generally yield glucose and gallic acid when they are hydrolyzed. These tannins are esters of gallic acid and glucose. They represent structures in which some of the hydroxyl groups in glucose have been esterified by digalloyl groups. The nonhydrolyzable tannins found in tea are condensation polymers of catechin. These polymers are not uniform in structure; catechin molecules are usually linked at ring positions 4 and 8.