Hello! I'll be taking an extended break from blogging and temporarily putting a greater focus
If you were to ask any sleep-deprived student what their favorite psychoactive drug is, most would give you a blank stare. Others, however, will say caffeine! Caffeine is an alkaloid, a class of plant-based organic nitrogenous compounds that have a noticeable effect on the body. With caffeine's ability to stimulate the nervous system and make you more alert, humans have come up with many methods of getting the drug into our system. There are brewed beverages, drink mixes, patches, and most importantly for this lab, pills*. Caffeine pills, such as No-Doz, are small capsules of pure caffeine that help people stay awake with powerful single doses. Making these pills, however, requires the isolation of pure caffeine from natural sources or the synthesis of caffeine from reagents. In this lab Organic Chemistry 1 lab, students were able to isolate caffeine from a tea into a powdered solid, helping teach the basic principles of extraction and purification.
*Caffeine is a drug, and taking it in pill form can be extremely harmful and addictive. Please consult a licensed physician before taking caffeine pills (or any supplement for that matter)! This lab also does not purify the caffeine for human consumption, so it is highly discouraged to attempt to ingest any extracted caffeine.
When brewing the tea, the water is going to contain a solution of cellulose, chlorophyll, and tannins. We want to end with pure caffeine, however, so isolation protocols are necessary to remove the byproducts. There are generally 2 routes of going about this: extracting the byproducts from the solution to discard it or extracting the end product directly from the solution.
For this lab, the caffeine will be isolated by dissolving it with dichloromethane (DCM). This solution of DCM and caffeine will then be separated out of the tea solution before the caffeine. Using this method, we can easily avoid picking cellulose and chlorophyll, leaving only tannins as the final byproduct to remove. Despite tannins being slightly soluble in DCM, we can avoid dissolving the tannins by adding sodium carbonate to the tea. This will convert tannins to phenolic anions, making them insoluble in dichloromethane due to polarity.
To then remove the caffeine from the DCM, the solution will be run through a rotary evaporator (rotovap), leaving only a white powdered substance that can be verified to be caffeine via gas chromatography (GC). There are multiple different methods for this last step, but using a rotovap simplifies the process immensely and exists in my high school chemistry lab.
An alternate method to the final step exists in which a beaker of the DCM solution is gently boiled with petroleum being added slowly. The solution would then turn cloudy, indicating the solution should be left to cool. Caffeine crystals would then slowly form and the solution would be filtered to leave only the caffeine.
- Brew a strong tea via a hotplate in an appropriately sized flask using 30mL of DI water and 2g of sodium carbonate. Make sure to cover the beaker with a watch glass to ensure as little water as possible evaporates.
- Decant the tea into a separate beaker and repeat step 1 with only 20mL of DI water. Decant the tea into the same beaker with the 30mL of tea. Discard the tea bags from the previous flask.
- Transfer 50mL of tea to an appropriately sized separatory funnel and add 5mL of DCM. Close the separatory funnel with a stopper and close the stopcock before gently rocking the solution. Release pressure buildup frequently by turning the separatory funnel upside down and opening the stopcock. Make sure to close the stopcock before rocking again.
- Clamp the separatory funnel into a ring stand and allow the solution to separate. Remove the clear bottom solution of DCM into a flask once fully separated and discard the top layer.
- Filter the DCM through cotton and 0.5g of sodium sulfate into a beaker. Transfer the contents of the beaker to an appropriately sized conical vial.
- Rotovap the conical vial until only powder remains. Take a small sample of the powder to GC to verify the end product.
When I conducted the lab, most people ended up with a very small amount of caffeine. While it may be a method to end with powdered caffeine, it certainly isn't the highest-yielding or most efficient method. This doesn't matter for the lab though, since it's really intended to learn basics. This includes allowing students to utilize more advanced glassware not used in courses such as AP Chemistry (Chem 101 at most colleges) or even Chem 102. It also helps the students experience the different reagents used in separation and the basic concepts that can be applied to different scenarios. All in all, it was one of the most satisfying labs I've done.