Max Muller - Lab 7: Caffeien Extraction

Objective Statement: In this lab, you will apply the lessons learned from extraction to isolate the natural product, caffeine. This lab aims to verify a drink's caffeine content through Mass Spectrometry. Mass spectrometry will both confirm the identity and purity of an isolated chemical. You will develop your laboratory procedure to isolate and purify caffeine, subliminate the caffeine, and then analyze the Caffeine.

Compounds of Study:

Caffeine

Polarity: Partially polar molecule

Mass: 194.19 g/mol

Boiling point: 238 degrees celsius

Sodium Carbonate

Polarity: Polar molecule

Mass: 105.9888 g/mol

Boiling point: 1,600 degrees celsius

Pre-Lab Questions:

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 regarding 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.

The two amide and two amine functional groups give caffeine its basic special properties.

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 drawing 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 the two carbonyl groups that already add to the polarity of the molecule, and then the lone pair of electrons on the nitrogen allows for hydrogen bonding with water to occur. Where this positive charge will make the caffenium ion conjugate acid soluble in water and not a non-polar organic compound 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 drawing below.

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

Understanding the electron pair availability of the digestion solution will determine its basicity. The more available electrons are on atoms, the more ready they are to donate electrons to form bonds during a chemical equation.

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

Caffeine is more soluble in a non-polar organic solvent like dichloromethane than soluble in water. Along with the similar densities of caffeine and the organic layer, both will reside in the bottom layer of a 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 type of mixture of two or more liquids that normally do not mix, but their combination has caused a part of one of those liquids to be 'trapped' in the other. You can get rid of an emulsion by adding salt to increase the ionic strength of the aqueous layer, pushing out the trapped nonaqueous solution.

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

The process of sublimation is transforming a solid into the gas phase without entering the liquid phase. This process is not like evaporation, instead, it happens at high vapor pressures at room temperature to prevent the solid from transitioning into a liquid.

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 can 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.

Add 15g of ground coffee, 10 g of sodium carbonate, and 100 mL of water to a beaker
Bring the solution to a boil for about 15-20 minutes with a watch glass. Limits water loss that the caffeine may have dissolved into
Make sure the solution is not overboiling by turning down the heat when the solution is over bubbling or by removing and swirling the beaker every few minutes.
Remove from heat and let the solution cool.
Use vacuum filtration to remove coffee grounds from the solution and use boiling water to wet filtrate paper and rinse the coffee grounds.
Transfer the solution to a separatory funnel and add 22.5mL of dichloromethane.
Flip the separatory funnel over twenty times very carefully to prevent the formation of emulsions. Every 4 flips, remove the cap and allow for pressure to escape.
Remove the dichloromethane and caffeine organic layer
Repeat steps 6,7 and 8, but this time with 15 mL of dichloromethane.
Transfer the solution to a clean separatory funnel and add some saturated salt solution to remove water from the organic solvent.
Remove the organic solvent and bring it to a light boil ensuring to not burn the caffeine product.
Recrystallize the crude caffeine using a small amount of 95% ethanol.
Vaccum filter the recrystallized solution for a few minutes.
Harvest the isolated recrystallized caffeine on top of the filtration paper and analyze for percent yield.

Procedures:

Activity 1

Added 5.00g of coffee grounds, 60 mL of water, and 5.0 g of sodium carbonate into a beaker with a watch glass on the top. Limits water loss that the caffeine may have dissolved into
Brought the solution to a boil for 15 minutes.
Removed solution from heat and ran through a vacuum filtration setup. To remove coffee grounds.
Added concentrated coffee solution to a separatory funnel with 10 ml of dichloromethane.
Inverted the funnel 15 times, letting out pressure every 3 inversions, and let layers settle for a few minutes.
Separated the organic dichloromethane/caffeine layer from the funnel.
Repeated steps 4-6 with 5 ml of dichloromethane to the same aqueous layer. To extract all the caffeine.
Put the organic dichloromethane/caffeine layer into a new clean seperatory funnel.
Added 7.5 mL of saturated salt solution to the separatory funnel. Washes the organic layer.
Inverted the funnel 15 times, letting out pressure every 3 inversions, and let layers settle for a few minutes.
Added small scoops of magnesium sulfate to the organic layer until the magnesium sulfate no longer clumped together.
Filtered this solution with vacuum filtration. Removes magnesium sulfate, leaving behind a yellow-orangish liquid caffeine/dichloromethane solution.
Put dichloromethane/caffeine solution on a heating mantle on low heat to evaporate the dimethyl chlorine. Left with rust-colored crude caffeine.
The solution was then placed in a round bottom flask with a cold finger inserted into it.
The solution and setup were placed onto the heat and left until sublimation occurred resulting in white crystals appearing on the internal rod of the cold finger insert.
The caffeine crystals were weighed and analyzed by mass spectrometry and a TLC plate with a 95:5 acetate to acetic acid ratio.
0l.15 grams caffeine
TLC ethyl acetate with acetic acid 95:5

Activity 3

1:1 of Hexane: Ethyl Acetate
Dichloromethane to dissolve caffeine into a liquid
distance traveled by the compound/distance traveled by the solvent front
Mass Spec 195.10-195.13 for pure caffeine. Our caffeine was 195.8-195.10
6cm from top to bottom Rf value of standard 5.8cm, our crude caffeine: 5.7cm (one major spot, a lighter one below at 5.4cm

Results:

Crystals after sublimination were opaque white. They were fine and small had slightly shiny.

Mass Recovery: 1.84g after sublimation

% yield = .005g exp/ 5.00g original * 100% = 1% yield

Mass Spectrometry; The literature value of pure caffeine crystals with +1 value due to Westminster's mass spectrometry machine calibrated at 195.11 g/mol.

The P represents the pure caffeine spot while the L is the lab-extracted caffeine crystals.

Solvent Front = 5.4 cm

Pure caffeine spot = 2.1 cm

Rf = (2.1/5.4) = 0.39

Lab caffeine spot =2.1 cm

Rf = (2.1/5.4) = 0.39

Conclusion:

I am confident that my lab group and I extracted pure caffeine. We not only extracted crystals that looked like pure caffeine, but we also analyzed an Rf value the same as the standard on TLC analysis, and a mass spec extremely similar to pure caffeine. The masses are very similar on mass spectrometry, even despite the +1 gram due to the extra proton on the Westminster machine, the mass spectrometry weights were extremely close and resulted in a convenient comparison. I am extremly confident that my group extractyed pure caffeine for all the various reasons.

Reflection:

The process of sublimation took a little time for me to understand during this lab. My group did struggle a little at the start with deciding which sample to use to extract caffeine, but it was difficult for me to understand why and how sublimation worked. We did extract pure caffeine, despite a very low yield percentage, but that was expected. But, that could also be due to using gravity filtration instead of vacuum filtration. This would cause some of our caffeine to be lost into the filter paper as the solution had time to cool and not be a solute when the coffee grounds were seperated from the dissolved caffeine. So in the future, the use of the most effective labrotaroy techniques will be used to ensure the smoothest and most effective laboratory results.