Question

Introduction:

The technique used to separate an organic compound from a mixture of compounds is called Extraction. Extraction process selectively dissolves one or more of the mixture compounds into a suitable solvent. The solution of these dissolved compounds is referred to as the Extract. Here the organic solvent dichloromethane is used to extract caffeine from an aqueous extract of tea leaves because caffeine is more soluble in dichloromethane (140 mg/ml) than it is in water (22 mg/ml). However, there are other compounds also present in tea that would come together with caffeine, they are called tannins. Tannins are slightly soluble in dichloromethane but can be eliminated by converting them to their salts or phenolic

anions by adding sodium carbonate. The solvent that is used for an extraction must be immisciblewith the other liquid. Immiscible liquids are two liquids which are not soluble. In other words, when they are mixed together they separate into two layers. The denser liquid will form the bottom layer in a separation funnel.

An average bag of 30g of tea can contain 20-ll0 mg of caffeine thereby making tea a significant source of caffeine compared to other beverages, make sure you inquire about the concentration of caffeine in the bags provided to you, this would give you an idea, as a good chemist, of how much caffeine you would expect from this process. Caffeine can stimulate nervous system and can cause relaxation of respiratory and cardiac muscles. Caffeine is well known to increase both the alertness level and attention span. But like all other addictive molecules, tea also shows withdrawal symptoms like headache, nervousness and insomnia for a regular consuming person. Caffeine, 1,3,7-trimethylxanthine, belongs to a wide class of compounds known as alkaloids. These are plant derived compounds with complex structure containing nitrogen, and usually have roles in physiological activity.

Equipment / Materials:

•  Hot plate

•  Benson burner

•  Beakers

 Tea bags, Sodium Carbonate (Na2CO3), Sodium Sulfate Anhydrous (Na2SO4(anh) .

Experimental procedures:

 Separating funnel

 Solvents: DCM, H2O

caffeine

1. Take 3 tea bags.

2. Take a 250 ml beaker and add 80 to 100ml of distilled water to it. Now place the tea bags in

   this beaker.

3. Add 2g of sodium carbonate into the beaker with water and tea bags.

4. Place a watch glass on the top of the beaker and gently boil the contents using a hot plate for

   about 10 minutes.

1. Allow the mixture to cool for 5 minutes and then decant the mixture into another beaker.

2. Gently squeeze the tea bags to liberate the rest of the water and get the most caffeine

   possible. (Do not get burned!!!), and you can discard the tea into regular garbage waste.

Isolation of Caffeine from tea leaves.

3. Cool the aqueous solution to near room temperature.

4. Once the temperature has dropped to almost room temperature, slowly add one by one cube

   or ice until it is cold, you could break the glassware if you add too much ice and you must start

   over.

5. Extract the solution three times with 15-mL portions of dichloromethane (CH2Cl2). Do not get

   dichloromethane on your hands. The procedure of how to perform an extraction is not outlined here, you performed and extraction last week and if you need to follow the procedure you can turn your lab notebook into the corresponding page where you have this information. Note that dichloromethane is more dense than water.

6. Dry the combined dichloromethane solutions or in other words, your organic phases combined with anhydrous Sodium sulfate. Make sure the crystals are free flowing. (Add about 1 teaspoon of the drying agent until it no longer clumps together at the bottom of the flask). Mix well and leave it for 10 minutes while you weigh an empty round bottom flask RBF.

7. Decant the dichloromethane into the round bottom flask, because not all the solvent can be decanted into the round bottom flask, you can always rinse the sodium sulfate crystals with 2- 3 mL to allow more compound to be recovered and have the minimum lost.

8. Evaporate the dichloromethane solvent using the rotoevaporator or rotovap. (follow instructions from your AI about how to properly use the apparatus).

9. Once the solvent has been removed, observe your residue.

10. Weight the flask after the organic solvent has been evaporated. Make sure you dry the outer

    surface of the flask or you will have an error in your calculations.

11. Record the weight of your impure caffeine (this is the difference of the clean RB flask and

    evaporated organic phase in the flask).

To further purify your caffeine, perform a sublimation procedure.

12. Carefully transfer the content of the round bottom flask into a petri dish with about 2 mL and rinse the flask with another 2mLs of DCM. (if you don’t have one in your drawer, you must check it out from the stockroom).

13. Allow the few milliliters of DCM to completely evaporate.

14. If you have very little amount of caffeine you are allowed to use of caffeine for your sublimation

    (up to 30 mg). Your percent yield should be modified to accommodate this.

15. Weigh the lid of the petri dish.

16. Cover your petri dish with the lid and on top of the lid place and appropriately sized beaker

    with ice (crushed, or small pieces), a beaker of smaller circumference than your petri dish.

17. Place the petri dish on a hot plate and heat until sublimation occurs. (Caffeine melts at 238C and sublimes at 178C, if you heat too much you will burn or melt your caffeine). Sublimation usually looks like fog inside of the dish, very carefully remove your petri dish from the heat (be

    careful the petri dish is hot, you must use long tongs).

18. Remove the beaker with ice and allow glassware to cool down.

19. Carefully open your petri dish and flip the lid upside-down. Now with all your precious

    sublimated caffeine, carefully dry the lid. (You dry it now so that the fine crystals of caffeine stay in the lid, if not, you will push them into the petri dish and your recovered material won’t be as much.

Isolation of Caffeine from tea leaves.

20. Weigh the lid of the petri dish with your purified caffeine. Annotate your observations and calculate your percent yield. (based on how much caffeine you expected per bag and the amount of bags used you should have an idea of the amount of caffeine expected)

21. DO NOT INGEST YOUR SAMPLE!
22. Obtain a clean IR spectrum and add the printed version to your LCC.

1a) (2)In the experiment you also used Sodium sulfate anhydrous. If you find that you have ran out of it, Could you use Sodium Sulfate pentahydrate instead? Why, or why not?

1a) (2)Describe the desirable properties of an extraction solvent.

1b) (2)What did you do to successfully extract caffeine without carrying other impurities from tea?

1c) (2)Why is methylene chloride used for the extraction rather than methanol?

1d) (2)Explain why caffeine migrates to methylene chloride from aqueous phase during the liquid-

liquid extraction, how is this ratio called?.

1e) (1)Why does the tea need to be cooled to room temperature before methylene chloride was

added?

Answer 1

1(a) I) Immiscibility. II) Dissolves the compound to be extracted. Iii) Does not dissolve impurities. IV) Volatile. V) Not toxic, not flammable.

1(b) liquid-liquid extraction followed by sublimation.

1(c) Methanol is miscible with water, hence methanol would not be useful for extraction process.

1(d) Caffeine being more soluble in methylene chloride than in water migrates to organic phase from aqueous phase. This ratio is called partition coefficient.

1(e) The boiling point of methylene chloride is 39.6 ^oC. If methylene chloride is added to hot tea extract, it will get evaporated making extraction process inefficient.