EXPERIMENT 1 ISOLATION OF CAFFEINE FROM TEA
In this experiment you will isolate caffeine from tea leaves and prepare the salicylate derivative.
Introduction This experiment illustrates the isolation of a naturally occurring product from plant material -- caffeine from tea leaves. The experiment will provide experience in handling relatively small amounts of material and at the same time you will be exposed to several techniques and procedures which are fundamental for survival in an organic chemistry lab.
You have been exposed to most of them during your CHEM 250 laboratory session. Please refer to the Laboratory Techniques TECH 1 to 7 and familiarize yourself with the content. For example during this lab you will be
doing extraction and TECH 6 describes the theory behind it and how to handle separatory funnel. using a drying agent and in TECH 6-5 you will read about the use of drying agents doing a distillation and the procedure can be found in TECH 5-2 and the apparatus set up in TECH 5-4 carrying out gravity filtration using fluted filter paper and TECH 3-6 shows you how to flute the filter paper. using the rotary Evaporator (Rotavap) to evaporate solvent at a lower temperature ( Appendix A)
Make sure you are familiar with the above techniques and the apparatus set up.
Caffeine is an alkaloid, a class of naturally occurring compounds
containing nitrogen and having the properties of an organic amine base [alkaline, hence, alkaloid]. Typical alkaloids are caffeine, nicotine, morphine, codeine, and cocaine. RO O N CH3 C HO Caffeine
CH3 N N
CH3 CO2CH3 N N CH3 O H O
O N N CH3 is found
nicotine (from tobacco)
(-) cocaine (from coca plant)
morphine, R = H codeine, R = CH3
leaves, coffee beans, kola nuts, and cocoa beans. The table belowgives the amount of caffeine in the various beverages prepared from these natural products.
One can develop both a tolerance and a dependence on caffeine. The dependence is real, and a heavy [> 5 cups of coffee per day] user will experience lethargy, headache, and perhaps nausea after about 18 hours abstinence. An excessive intake of caffeine may lead to restlessness, irritability, insomnia, and muscular tremor. Caffeine can be toxic, but it has been estimated that to achieve a lethal dose of caffeine one would have to drink about 100 cups of coffee over a relatively short time.
Table The amount of caffeine found in beverages*
60−100 mg/100 mL
* The average cup of coffee or tea contains about 150 mL of liquid. The average bottle of Coke contains about 350 mL of liquid.
Because of the central nervous system effects that caffeine causes, many persons prefer to use decaffeinated coffee. The caffeine is removed from coffee by extracting the whole beans with trichloroethylene at 71 °C. Following this, the solvent is drained off, and the beans are steamed to remove any residual solvent. Then, the beans are dried and roasted to bring out the flavor.
Decaffeination reduces the caffeine content of coffee from a range of 2% to 5% to the range of 0.03% to 1.2% caffeine.
The isolation of caffeine from tea leaves presents the chemist with a major problem: caffeine does not occur alone in tea leaves, but is accompanied by other natural substances from which it must be separated. The major components of tea leaves are:
Cellulose − the major structural material of all plant cells. Since cellulose is virtually insoluble in water it presents no problems in the isolation procedure. Caffeine − one of the major water soluble substances present in tea leaves. Caffeine comprises as much as 5% by weight of the leaf material in tea plants. Tannins − high molecular weight, water soluble compounds that are responsible for the color...