EXPERIMENT 1: ISOLATION OF CAFFEINE FROM A TEA BAG

OBJECTIVES: To determine the amount of caffeine in a tea bag.

INTRODUCTION:

Structure of caffeineCaffeine belongs to the family of heterocyclic compounds known as purines. It has the systematic name 3,7-dihydro-1,3,7-trimethyl-1H-purine-2,6-dione; it is also known as 1,3,7-trimethylxanthine, and 1,3,7-trimethyl-2,6-dioxopurine. Caffeine can be classified as analkaloid, a term used for substances produced as end products of nitrogenmetabolismin some plants. The chemical formula is C8H10N4O2. Caffeine has a molar mass of 194.19 grams (6.85 ounces). It is soluble in water and in many organic solvents, and it appears in pure form as white crystals. Caffeine can be prepared by extraction from natural sources or bysynthesisfrom uric acid. More than sixty plants, including those that give us coffee, tea, cola, and cacao, produce caffeine from the purine xanthine. Whereas caffeine is a natural constituent in coffee, tea, chocolate, and some cola drinks, it is added to consumer products such as soft drinks, diet pills, andanalgesics. Caffeine is said to be the most widely used drug in the world, and more than 100 million people in the United States consume caffeine each day. It has pharmacological uses: as a cardiac and respiratory stimulant and as an agent that promotes kidney diuresis. A therapeutic dose of caffeine is about the same as the amount found in an average cup of coffee, between 100 and 200 milligrams (0.0071 ounces). Decaffeinated coffee can be prepared through extraction with a solvent (such as methylene chloride), water extraction, or steam extraction.Caffeine enters the bloodstream about ten minutes after its ingestion and stays in the body for up to twelve hours. Like other alkaloids, caffeine has powerful physiological effects on humans and animals. It stimulates heart muscle and relaxes certain structures that contain smooth muscle, including the coronary arteries and the bronchi. It is a diuretic. Theophylline and theobromine, two other plant alkaloid derivatives of xanthine, have physiological effects similar to those of caffeine.Caffeine acts as a stimulant of the central nervous system (CNS) through several proposed mechanisms. The most important seems to be its interference with the ability of the neurotransmitter adenosine to bind to its nerve cellreceptor. Also, caffeine inhibits the enzyme cyclic nucleotide phosphodiesterase, which breaks down intracellular cyclic adenosine monophosphate (cAMP), another messenger involved in the transmission of nerve signals from hormones originating outside the central nervous systemTo separate caffeine from tea solution extraction technique was used. Liquid-liquid extractions using aseparatory funnelare essentially the only kind of extraction performed in the organic teaching labs. Liquid-liquid means that two liquids are used in the extraction procedure. The liquids must be immiscible: this means that they will form two layers when added together, like oil and water. Some compounds are more soluble in the organic layer and compounds are more soluble in the aqueous layer.

APPARATUS: Beaker, small conical flask, separatory funnel, cotton, rotary evaporator, dropper. MATERIAL: distilled water, sodium carbonate, methylene chloride, anhydrous sodium sulphate. PROCEDURE:1. A 100 mL beaker was used and 50 mL of water was added inside the beaker to make the tea solution2. Then, the hot tea solution was transferred into a small conical flask.3. 0.5 g of sodium bicarbonate (Na2CO3) was added into the tea solution.4. The solution was filtered using cotton into small separatory funnel.5. 15 mL of methylene chloride was added into and the extraction begins.6. The lower methylene chloride layer was drain off and 10 mL of fresh methylene chloride was added.7. The step of adding methylene chloride was repeated 2 times.8. Combined all methylene chlorine solution and dried it with anhydrous sodium sulphate.9. Dried methylene chloride was transferred into a pre-weighted small round bottom flask and the solution was evaporated using the rotary-evaporator.

RESULT:Weight of empty beaker= 49.33 gWeight of Na2CO3= 0.51 gWeight beaker+anhydrous+ organic layer= 63.46 gMass of teabag = 2.17 gMelting point= 213.7 CMass of dry caffeine+beaker= 49.43 gMass of caffeine= 0.10 g

DISCUSSION:Caffeine is a common substance and is found in coffee, tea, soft drinks and chocolates. It can be isolated from natural sources like tea leaves, cola nuts and cacao beans. Caffeine is an alkaloid, and more specifically, a member of the methlxanthines.Caffeine has been found to act as receptor antagonists by inhibiting the effect of adenosine.Adenosine is a modulator that regulates sleep and other neural phenomena in human.This inhibitory effect of caffeine makes it a central nervous system stimulant. High doses of caffeine in human adult can be fatal. The acute lethal dose of caffeine in human adult has been estimated to be 10 g/person.To isolate caffeine from tea, extraction is used to separate the caffeine from other components of tea. Extraction is a separation technique based on the differences in the solubility of substances in two immiscible solvents.For the purpose of this experiment, methylene chloride was used as the solvent because caffeine is more soluble in methylene chloride than in water. Caffeine was extracted by adding 15 ml of methylene chloride to the tea solution. 0.5g of sodium carbonate was also added to the mixture. Sodium carbonate was added in order to convert tannins and gallic acid to sodium salts which are soluble in water. When the extraction was carried out, an emulsion was formed. An emulsion is dispersion of liquid in another liquid. The emulsion was broken into two layers by centrifugation. The organic layer which is denser than water settled on the bottom of the tube, while the aqueous layer was on top. The high density of the organic layer is because of the two chlorine atoms bonded to an alkyl group in methylene chloride. The organic layer was separated from the aqueous layer and dried by adding sodium sulfate. Drying is complete when the sodium sulfate clumps together. When this had occurred, the organic layer is separated from the hydrated sulfate using a Pasteur pipet.The dry organic layer was then evaporated by heating using rotary-evaporator. After the methylene chloride had evaporated, solid caffeine was collected which had some greenish stains on the solid crystals. The melting point of the crude crystal was found is 213.7 0C. This suggested that the crystals contained impurity. The crude crystal weighed 0.10 g. This mass was calculated by subtracting the mass of the beaker from the mass of the beaker when it contained crude caffeine crystal. The crude crystal was purified by sublimation under reduced pressure. The pure crystal recovered was whitish and had a powdery texture. The percent recovery was calculated by dividing 0.10 g which is the amount recovered by 2.17 g, amount of impure crystal and multiplying the result by 100. Percentage of recovery (Caffeine) = X 100= 4. 608 %The melting point of the recovered crystal lied between 213.7 0C. This range differed from the pure range of 235.30C-238.50C. The literature melting of caffeine is 236 0C. The difference in melting point was as a result of operator error and the crystal absorbing moisture from the ice cooled tube used in the set up and from surrounding air.CONCLUSION:From this experiment, the amount caffeine required from the tea solution is 0.10 g. The percentage of caffeine recovery was 4.608 %.

REFERENCES:(1) Pavia, D.; Lampman, G et al. Organic Lab.Tech. 3rded.; Cengage: Belmont, 2011, 77.(2) Isolation of caffeine from tea,http://www.oxford.net/~mavarod/portal/school/caffeine.html(accessed 22/05/2015)(3) Role and Reg. of adenosine,http://www.cscb.northwestern.edu/jcpdfs/dunwiddie01.pdf.(accessed 25/03/2015)(4) Nawrot, P.; Eastwood, J, e tal. Food Additives And Contaminant[online], 2003, Vol. 20, 2.http://ehis.ebscohost.com.db20.linccweb.org/ehost/pdfviewer/pdfviewer?vid=3&sid=4415681e-3b1b-4d6a-bda9-f720bd9c776d%40sessionmgr10&hid=16(accessed 25/3/2015)(5) Extraction,http://chemistry.csudh.edu/faculty/noel/CHE317L/Extraction%20Experiment.htm (accessed 22/03/2015)

Question:1. Why was the sodium carbonate added in experiment 11A and 11B?Sodium carbonate was added in order to convert tannins and gallic acid to sodium salts which are soluble in water.2. The crude caffeine isolated from the tea has a green tinge. Why?Because the tea leaves have chlorophyll and chlorophyll color is green based on studies.3. What are some possibilities explanations for why melting points of your isolated caffeine may be lower than the true value (236 degree celcius)?

The difference in melting point was as a result of operator error and the crystal absorbing moisture from the ice cooled tube used in the set up and from surrounding air.4. What would happen to the caffeine if the sublimation step was performed at atmospheric pressure?Caffeine would decomposed and produce less yield and more heat required.5. Use flow chart to outline the separation technique