The purpose of this lab is to utilize extraction techniques to remove and purify caffeine. Different extraction practices have been practiced in the lab throughout this year, allowing us to refer to them and build our own procedure. This extraction practice first isolates the caffeine through digestion and extraction, then isoalotes the compound through sublimation.

1. (12 pts)  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 regards 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 contains two amine and two amide functional groups which makes the molecule basic.

• 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.

Drawn below(a)

• 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….. (finish sentence)

The molecule is polar because the molecule gains a positive charge in it's conjugate acid form on the Nitrogen atom allowing for hydrogen bonding to occur.

• 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.  

Drawn Below(b)

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

The solution can be tested to be basic with a pH strip which should result in a pH of greater than 7.

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

The caffeine extracts into the dichloromethane layer because it has become a base again and can no longer bond with the polar water. In its original form, it's non-polar so it's miscible in dichloromethane.

2.  (4 pts) It is very possible during extraction to have an emulsion form.  What is an emulsion?  How can you get rid of an emulsion?

Emulsion is the dispersion of small droplets into a solution where they're not miscible.  An emulsion can be eliminated using a saturated salt solution to increase the ionic strength of the aqueous layer forcing separation to occur.

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

Sublimation is taking a substance from the solid phase to gaseous phase while bypassing the liquid phase. Taking the compound of interest from a solid to gas ensures purification within the gas as the impurities have a different boiling point so the vapor at a certain temperature will be all one substance.

4.  (4 pts) 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. Open 4 tea bags and weigh the tea.

2. Staple the tea back into the bags then combine with 4.0 grams of sodium carbonate and 60 mL of DI water.

3. Bring the solution to a boil for about 10 minutes then remove the liquid into a 50 mL Erlenmeyer flask.

4. Add another 20 mL of DI water into the beater  and boil again also removing the liquid into the same flask.

5. Add the tea extract to a separatory funnel and add 10 mL of dichloromethane then invert the funnel. Repeat this step twice.

6. Wait for the layers to fully separate then drain the dichloromethane(bottom) layer into a 25 mL Erlenmeyer flask.

7. Add 1.0 grams of anhydrous sodium sulfate to the flask to remove traces of water.

8. Bring the solution to a boil then add petroleum ether until the solution becomes cloudy.

9. Set the solution aside to cool, caffeine crystals will form as the solution cools down.

10. Filter the crystals using vacuum filtration, washing them with the dichloromethane solution.

11. Extract the crystals and set them aside to dry.

• 5.00 grams of coffee grounds were weighed out.

• 5.00 grams of sodium carbonate and 60 mL of water were measured.

• All the weighed contents were added to a beaker which was then placed on a hot plate on setting 6.

• Once it was brought to boil, it was left to boil for about 10 minutes.

• After 10 minutes, the coffe grounds were extracted out of the mixture using vacuum filtration.

• The solution was added into the separatory funnel along with 10 mL of dichloromethane.

• The funnel was inverted and, once seperated, the dichloromethane layer which was the bottom was dumped.

• 10 more mL of dichloromethane was added and the same steps were repeated to ensure caffeine was extracted.

• Anhydrous sodium sulfate was added to the dichloromethane solution until it flowed in the solution to dry the mixture.

• The sodium sulfate was vaccum filtered out of the solution.

• The dichloromethane solvent was evaporated from the solution on low heat.

• The solution was then placed in a round bottom flask with a cold finger inserted into it.

• The solution and set up was placed onto heat and left until sublimation occured resulting in white crystals apperaring on the internal rod fo the cold finger insert.

• The caffeine crystals were weighed and analyzed by mass spectrometry and a TLC plate with a 95:5 ethyl acetate to acetic acid ratio.

Observations and color of the caffeine crystals

The crystals purified from solution were completly white. They were very fine and small crystals that had some shine to them.

Mass recovery

The mass recovered was 0.05 grams of caffeine.

The avg. caffeine content for 5 grams of ground coffee is 0.06 grams

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

= (0.05g/0.06g) * 100%

= 83.3% yeild

Mass Spectrometry

The literature value of pure caffeine crystals with a +1 value due to the Westminster mass spec. macheine callibration is 195.11g/mol

TLC analysis

Looking at the various forms of analysis of the lab isolated caffiene, I'm confident we isolated pure caffeine. Looking at the isolated crystals, they were white and fine which is also the qualitative qualities of oure caffeine. Analyzing the compound by mass spec, it matched the mass of vcaffeine. The pure caffeine substnace had a mass of 195.11 g/mol, including the +1 mass from the calibration of the macheine. When our compound was ran through the macheine, the mass was 195.12 g/mol. The similarity of these masses shows that pore, or mostly pure, caffeine was present under mass spec analysis. The graph also shows only one large peak which demonstartes that no other major impurities were present in the compound further leading to the conclusion that pure caffeine was present.

Lastly, looking at the TLC analysis, the spots of the lab isolated and pure caffeine are almost the same with the Rf values being the same. Examining the various forms of analysis of the pure and lab isolated  caffeine, I'm confident pure caffeine was isolated in this lab.

In this lab, the process of sublimation of a compound was utilized to extract caffeine from coffee ground. This lab went very well as pure caffeine was isolated from this procedure. My group had a bit of trouble starting the lab as we tried tea first then utilized gravity filtration instead of vaccum filtration. This made it so a lot of our compound was lot of the absorbition of the filter paper. We also didn't get the mass yeild we expectd from coffee grounds.

In the furture, I would always utilize vaccum filtration even on a low setting as it speeds up the process and less mixture is lost from absorbition. I would also boil the coffee grouns mutliple times to ensure most or all of the caffeine was extracted.