Name: Kate Alyssa Caton Date Completed: November 26, 2010Partners: Xharisz Yuka Mae Dulin Date Submitted: December 3, 2010

Prem Patrick Parcon

EXPERIMENT 1Isolation of Caffeine from Tea

Objectives: To gain experience in using extraction as a method of separation. To assemble and use a simple distillation setup in the separation of volatile substances from non-

volatile materials. To determine the boiling point of a liquid sample. To isolate caffeine from tea and gain experience in chemical laboratory manipulation of plant

materials.

Results:

Discussion of Results: PARAPHRASE, BITCH.

Tea leafs contain from 2 to 5% caffeine, along with cellulose, tannins, flavonoid pigments and chlorophylls (see structures of caffeine and tannins on next page). The caffeine can be extracted from tea using hot water. However, the tannins, pigments and chlorophylls will also be extracted into the water. The caffeine can then be extracted from the water using methylene chloride (dichloromethane). Since the tannins are acidic, base is added to the aqueous extract in order to ionize the tannins and insure that they remain in the aqueous layer. Along with the caffeine, the chlorophylls (which are present only in small quantities) will also go into the organic layer. Thus, the caffeine that you obtain after evaporating the methylene chloride will not be totally pure. Either sublimation or crystallization can be used to further purify the caffeine. However, we will not do that in this experiment (the caffeine is already close to pure).

The idea in this experiment is to extract the water soluble materials in the tealeaves into hot water. [The solubility of caffeine in water is 22 mg/ml at 25oC, 180 mg/mlat 80oC, and 670 mg/ml at 100oC.] The hot solution is allowed to cool and the caffeine isthen extracted from the water with dichloromethane (methylene chloride), which is anorganic solvent that is insoluble in water. Since caffeine is more soluble indichloromethane (140 mg/ml) than it is in water (22 mg/ml), it readily dissolves in thedichloromethane. However, the tannins are slightly soluble in the dichloromethane. Butwe want to separate the caffeine from the tannins by having the caffeine dissolve in thedichloromethane and the tannins remain in the water. We can do this by takingadvantage of the fact that phenols are acidic enough to be converted to their salts(deprotonation of the -OH group) by reaction with sodium carbonate. So, we will addsodium carbonate to the water and the tannins will be converted to phenolic anions,which are not soluble in the dichloromethane but are soluble in highly polar water.There is one practical disadvantage in converting the tannins to their salts – they becomeanionic surfactants. Detergents and soap are surfactants. It is the purpose of surfactants

to cause materials that do not dissolve in water (like oil, grease and dichloromethane) toform an emulsion with water. We want to be able to separate the aqueous phase fromthe dichloromethane phase, so the last thing we want is an emulsion of the two.

Principle of the experiment:

The technique used to separate an organic compound from a mixture of compounds is called Extraction. Extraction process selectively dis-solves one or more of the mixture compounds into an appropriate solvent. The solution of these dissolved compounds is referred as the Ex-tract. Caffeine is a naturally occurring alkaloid (a class of naturally occurring compounds containing nitrogen and having the properties of an organic amine base) found in coffee, tea, Cocoa, Guarana (Paullinia cupana)  and kola nuts.  

Caffeine belongs to a family of naturally occurring compounds known as xanthines. Caffeine is chemically 1,3,7-trimethylxanthine (C8H10N4O2). Caffeine acts as a stimulant. It stimulates the heart, respiration, the central nervous system, and is a vasodilator (relaxes the blood vessels) as well as a diuretic (increases urination). It is a beverage produced by steeping in freshly boiled water the young leaves and leaf buds of the tea plant, Camellia sinensis. Two principal varieties of tea are used, the small-leaved China plant (C. sinensis) and the large-leaved Assam plant (C. assamica). The leaves may be fermented or left unfermented. Fermented teas are referred to as black tea, unfer-mented teas as green tea, and partially fermented teas as oolong tea. Tea leaves consist mostly of cellulose (a water-insoluble polymer of glucose), caffeine, tannins (phenolic compounds, compounds that have an -OH directly bonded to an aromatic ring) and a small amount of chlorophyll. The solubility of caffeine in water is 22 mg/ml at 25·C, 180 mg/ml at 80·C, and 670 mg/ml at 100·C. Here the organic solvent di-chloromethane is used to extract caffeine from aqueous extract of tea leaves because caffeine is more soluble in dichloromethane (140 mg/ml) than it is in water (22 mg/ml). However, the tannins that are slightly soluble in the dichloromethane can be eliminated by converting it to their salts (phenolic anions by adding sodium carbonate) (tannins are phenolic compounds of high molecular weight and being acidic in nature can be converted to salts by deprotonation of the -OH group) which remain in the water.

Conclusion:

Question & Answers:

A. Discuss briefly the role of the following in the isolation of caffeine: i. sodium carbonate

Sodium carbonate also a base, and it is added in the first extraction to make sure that the caffeine re-mains in the free base form (that is, to prevent it from reacting with any acids that may be present).

If you do not use a base the tannins will also be extracted into the solvent (i.e. methylene chloride) used in the subsequent extraction . The base converts the tannins into their sodium salts - being ionic these salts are not soluble in solvents like methylene chloride so remain in the aqueous layer during extrac-tion. This allows purer caffeine to be extracted.

ii. sodium sulfate

Sodium sulfate serves as a drying agent in most reactions to absorb all excess water from the solution.

A. Give at least three characteristics of chloroform that make it a good extracting solvent for caffeine.Chloroform was chosen as the solvent because Caffeine is very soluble in this substance. Thus, when the separatory funnel is used, the Caffeine in the tea dissolves into the Chloroform and the rest of the tea can be discarded. This is done three times so that the amount of Caffeine left in the discarded tea is minimized. This is followed by two washings with Sodium Hydroxide and one with water. It is believed that the Sodium Hydroxide weakens the attraction Chloroform has on Caffeine, allowing the Caffeine to be isolated more easily later on.

B. How efficient is the extraction of tea leaves containing 1.0 g of caffeine with two 30-mL portions

of chloroform over that of a single step extraction (K25ºC = 8.36)?C. What are emulsions? Why do they form during extractions? How are they minimized?D. Why is it necessary to remove a stopper from a separatory funnel when liquid is being drained

from it through a stopcock.