Lab 7: Caffeine Extraction 

Pre-Lab:

1. When isolating the caffeine, a base is used for the “digestion” step so that caffeine can be extracted into dichloromethane.  Answer the next several questions in regard to this procedural step so that you can understand the chemistry of digestion. 

• Caffeine is a base.  What functional group in the molecule is basic? The functional group that makes caffeine basic is its amine properties. 

Caffeine is made up of two amide and two amine functional groups. These groups work together to give caffeine its basic qualities.

• All beverages containing caffeine are acidic, having a pH of around 3-4.  This means that the caffeine is in its conjugate acid form within the beverage.  Draw the conjugate acid form of caffeine.

See the image below.

• All beverages are water-based, explain why this form of caffeine, the conjugate acid form, is readily soluble in water and not soluble in dichloromethane.  The molecule is polar because….. 

of its amine and carbonyl functional groups that contribute to it being a very polar molecule. Due to its newly polar form, the conjugate acid form of caffeine isn't soluble in a non-polar non-polar organic like dichloromethane.  

• When the base is added to the beverage, acid/base chemistry occurs between the ionized conjugate acid form of the caffeine and the base.  Draw the acid/base reaction, using curved arrow formalism, that describes the chemistry that happens with the caffeine during digestion.  In your drawing, you can just use “-B” for the base.  

See the image below.

• How should you check to make sure that the digestion solution is actually basic?

You can test the pH of the solution using pH strips. A pH greater than 7 indicates a basic solution.

• After this chemistry happens, why does the caffeine extract into the dichloromethane layer?

Because the chemistry has changed the caffeine from its acidic form into its basic form caffeine is now more soluble in a non-polar organic solvent, dichloromethane than in the polar water. This will cause the caffeine to be extracted into the dichloromethane layer at the bottom of the separatory funnel after separation.  

2. It is very possible during extraction to have an emulsion form.  What is an emulsion?  How can you get rid of an emulsion?

An emulsion is a mixture of two or more liquids that are normally immiscible (unmixable). You can add a bit of saturated salt to the solution to remove the emulsion.

3. The crude caffeine has to be purified by sublimation.  Describe sublimation using your own words in 2-3 sentences.

Sublimation is the process of a chemical undergoing a phase change of a solid directly to a gas without ever entering the liquid phase. This process differs from evaporation in that it happens at high vapor pressures while at room temperature to prevent the solid from entering the liquid phase. An example of sublimation is dry ice!

4. Describe the step-by-step procedure that you will use to isolate caffeine from your source.  The procedure must be written so that anyone in the class could follow your procedure.  Even though you may work with other people and access internet resources to develop your procedure, you cannot copy.  Any procedure that is plagiarized from another source, will not receive any credit.  Please note that even if you take information from a source and then edit it, this is still considered plagiarism.  The best way to avoid accidental plagiarism is to read from a source, close the source and then summarize your thoughts.

1.) Select the type of tea you would like to measure the caffeine content of and grab four tea bags.

2.) Empty the tea bags into a weigh boat and measure the weight of the contents. Afterward, put the tea back into the bags and secure them with staples.

3.) Place these tea bags into a 150 ml beaker. Add 60 ml of DI water and 4.0 g of sodium carbonate. Gently boil the beaker's contents for 10 minutes. If the tea bags float to the surface, occasionally press them down with a glass stirring rod.

4.) Transfer the liquid into a 50 ml Erlenmeyer flask. Add 20 ml of DI water to the beaker and bring it to a boil again. Repeat the transfer process into the 50 ml Erlenmeyer flask. Squeeze the tea bags to extract as much liquid as possible without damaging them and add this liquid to the Erlenmeyer flask. Allow the tea extract to cool to room temperature and discard the tea bags.

5.) Move the tea extract from the 50 ml Erlenmeyer flask to a 125 ml separatory funnel.

6.) Add 5 ml of dichloromethane into the separatory funnel. Invert the funnel, and vent occasionally to relieve pressure.

7.) Allow the contents of the separatory funnel to settle, ensuring there are two distinct, mostly clear layers.

8.) Carefully drain the dichloromethane and caffeine layer into a 25 ml Erlenmeyer flask.

9.) Repeat steps 6 through 8 using another 5 ml portion of dichloromethane.

10.) Add 1.0 g of anhydrous sodium sulfate to the combined dichloromethane extracts in the 25 ml Erlenmeyer flask to absorb any dissolved water.

11.) Test purity using TLC.

Results: 0.05 grams of small, fine, white crystals were obtained during the sublimation process. The percent yield for this experiment was 1.00%.

% yield = (mass recovered/original mass) * 100%

= (0.05g/5.00g) * 100%

= 1.00% yield

Results:

Mass Spec:

The known literature value for a mass spec analysis of pure caffeine is 194.19 g/mol. Our obtained mass value is 195.12 g/mol. For the Westminster mass spec machine, we would expect a result of the literature value of pure caffeine crystals with a +1 value. When run using the mass spec machine the value obtained for pure caffeine was 195.11 g/mol.

TLC Analysis:

Conclusion: According to both the analysis tests performed, we can confidently believe that the caffeine obtained in this experimental procedure was pure. However, due to low yield, the amount of caffeine obtained makes the procedure performed in this lab not very effective.