E25 ISOLATION OF A BIOLOGICALLY ACTIVE COMPOUND The isolation of caffeine from tea leaves

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1 E25 ISLATI F A BILGICALLY ACTIVE CMPUD The isolation of caffeine from tea leaves ITRDUCTI The overwhelmin majority of bioloically active molecules are oranic compounds, e.. alcohol, salicylic acid and tetrahydrocannabinol (THC). aturally occurrin oranic amines, such as caffeine, are called alkaloids and are amonst the most interestin and widely varied of all naturally occurrin compounds. H CH H salicylic acid tetrahydrocannabinol (THC) caffeine C 7 H 6 3 C 21 H 30 2 C 8 H Caffeine is an alkaloid that occurs in tea, coffee and several carbonated soft-drinks. It is one of the alkaloids easiest to isolate and, in this experiment, is extracted from tea leaves, alon with other compounds like tannic acids, usin hot water. Calcium hydroxide is added to the tea leaves durin the extraction process to deprotonate the tannic acids, thus increasin their water solubility and facilitatin their separation from the caffeine. Dichloromethane is added to the water - the caffeine is preferentially soluble in the dichloromethane and is thus transferred from a lare volume of water to a small volume of oranic solvent. Sodium chloride is added to help prevent the formation of an emulsion. The dichloromethane solvent is subsequently removed by evaporation to leave crude caffeine. You will analyse the purity of your product in a later laboratory session (E29) usin thin layer chromatoraphy and compare it to that of a commercial source of caffeine. (Purification of an oranic solid is often accomplished usin column chromatoraphy. You will come across this technique in 3 rd year.) SAFETY Materials ature hot water sodium chloride calcium hydroxide celite dichloromethane caffeine Indicate, by sinin, that you have understood the information in the safety table. I understand the safety information Demonstrator s Initials E25-1

2 E25-2 LAB-WRK Date 20 1) Place a clean 500 ml conical flask with a lare plastic funnel (provided near the balances) sittin in the top, onto a balance. Tare the balance. Usin the scoop provided, carefully pour approximately 20 of dry tea leaves directly into the flask. Record the exact mass weihed out. Add 200 ml of hot water from the hot-water tap at the back of the lab (ensure that the water runnin is hot!). Leave the flask on a heat-proof mat on your bench while you weih out the solids in step 2 and set up your equipment for step 3. Allow the tea to brew, swirlin it occasionally, for at least 7 minutes. Mass of tea leaves 2) Tare a 100 ml beaker and weih into it approximately 2 of calcium hydroxide. Tare a 250 ml beaker and weih into it approximately 50 of sodium chloride. After the tea has brewed, add these two solids to the tea mixture, swirl the flask for 1 minute and leave it to rest until you are ready to filter. 3) Set up a filtration apparatus as shown below: About ¾-fill a 100 ml beaker with celite 1. Clamp a clean, 500 ml filter flask to a retort stand (this flask does T need to be dry why do you think this is?). Place a clean, lare Büchner funnel with rubber seal attached, into the flask and fit a filter paper which lies flat to cover all the holes. Dampen the paper with a few drops of water to form a seal between the paper and the funnel. Apply a entle vacuum 2 to the flask and ensure there is a ood seal between the flask and the funnel. Transfer the celite into the funnel - there should be enouh to create a layer which is about 1 cm thick. Place a small piece of filter paper on top. (This paper prevents the tea solution disruptin the celite layer.) lare Büchner funnel 4) Filter the tea mixture (after doin step 2) throuh the celite. Add brine 3 (20 ml) to the conical flask with residual tea leaves in it, swirl it and filter this throuh the Büchner funnel too. Disconnect the vacuum and discard the waste tea leaves and celite toether in the waste bin located in the front fumehood. Feel the side of the filter flask. If it feels warm to touch, cool it briefly in an ice bath 4. 1 Celite is diatomaceous earth, a hih-porosity powder. It is used to filter out very fine particles in the tea mixture which would otherwise block the filter paper. 2 Test the vacuum by touchin your thumb with the vacuum tubin. The vacuum should just be able to hold the tube onto your thumb. If you use a stroner vacuum you may rupture the filter paper and will have to set up the filtration apparatus aain. 3 Brine is a saturated aqueous solution of sodium chloride. This has been prepared for you. 4 An ice bath is a mixture of ice and water. The contact between the flask and the cold water is much reater than that between the flask and solid ice allowin for more efficient conduction of heat.

3 E25-3 5) Support a 250 ml separatin funnel on a retort stand and rin. Ensure that the tap is closed. Transfer the filtrate into the separatin funnel and add dichloromethane (30 ml). 6) Stopper the funnel, invert it and immediately relieve the pressure by openin the tap. Close the tap and while inverted, ently swirl the mixture for 2-3 seconds only and aain, relieve the pressure immediately. (Violent shakin will emulsify the dichloromethane and the separation of the layers will be difficult.) Repeat this procedure of swirlin followed by the reular release of pressure three times. Put the funnel on the stand and allow the layers to separate. Remove the stopper and run off the lower dichloromethane layer into a clean, dry, 250 ml conical flask. If there is an emulsion, run this off into the conical flask as well. 7) Leave the coloured water layer in the separatin funnel. Add fresh dichloromethane (30 ml) to the separatin funnel and repeat step 6 above, runnin off the dichloromethane layer into the same conical flask as before. Dispose of the coloured aqueous layer into the tea leaves waste in the fumehood. Pour the combined dichloromethane extracts back into the separatin funnel and ently swirl it to allow the emulsion to separate. Drain the lower dichloromethane layer, only, into a clean, dry, 250 ml conical flask. Leave any coloured layer or emulsion behind in the separatin funnel and dispose of it in the tea leaves waste. Holdin a separatory funnel durin shakin; Always point the stem away from others durin ventin (openin the tap to reduce pressure) 8) Dry the dichloromethane layer over sodium sulfate. To do this, add a spatula-load of anhydrous sodium sulfate. If the solution is wet, the sodium sulfate will absorb the water and clump toether in the bottom of the flask. Continue to add spatula-loads of sodium sulfate until it runs freely. If you think you need to add more than 4 spatula-loads, consult your demonstrator. Allow the mixture to settle. Usin a dry 500 ml beaker as a support vessel, determine the mass of a clean, dry, 100 ml round-bottom flask containin two anti-bumpin ranules (record this value on the next pae). Decant your dichloromethane solution throuh a small plastic funnel into the pre-weihed round-bottom flask. Ensure you do not et any sodium sulfate into the flask.

4 E25-4 9) Distil the solution to dryness on a steam bath, collectin the dichloromethane distillate in a clean, dry 100 ml conical flask. Dispose of the distillate into the dichloromethane waste drum in the front fumehood. The solid residue in the round bottom flask is your crude caffeine. Allow the flask to cool to room temperature. (If the product is reen, add some hexane and shake well. The caffeine is insoluble but the impurities dissolve in the hexane and can be removed with a clean dry pipette.) 10) Reweih the flask and calculate the mass of crude caffeine. Usin a spatula, transfer a small portion of your product into a plastic sample vial and clearly label it with your name, lab and bench number. Hand-in your sample vial to your demonstrator. You will test the purity of your product in a future laboratory session when you do E29. Mass of flask + caffeine Mass of flask Mass of caffeine Demonstrator s Initials

5 E25-5 PST-WRK Calculate the percentae by weiht of caffeine in tea leaves. Complete the followin table which lists some of the common oranic solvents. For those solvents that are immiscible with water indicate whether they form the upper or the lower layer when mixed with water. Solvent Constitutional formula Boilin point ( C) Density ( ml 1 ) upper/lower/ miscible diethyl ether acetone ethyl acetate ethanol chloroform dichloromethane Demonstrator s Initials