TLDR;
This video provides a step-by-step guide on how to extract caffeine from tea using a separatory funnel and dichloromethane (DCM). It covers the initial brewing of tea, the extraction process using DCM, drying the organic layer with anhydrous sodium sulfate, filtering to remove the drying agent, and finally, evaporating the DCM to obtain crude caffeine.
- Brewing tea to increase caffeine solubility.
- Using DCM in a separatory funnel to extract caffeine.
- Drying the organic layer to remove water.
- Evaporating DCM to isolate crude caffeine.
Introduction to Caffeine Extraction [0:02]
The video introduces the process of extracting caffeine from tea. It begins by placing a 250ml beaker on a hot plate and adding approximately 150ml of distilled water. Several tea bags are opened and their contents are placed into the beaker. A watch glass is placed over the beaker to minimise water evaporation while heating.
Brewing the Tea [0:18]
The water is heated to a boil, then removed from the hot plate and allowed to cool. This step is crucial as increasing the temperature of the water increases caffeine's solubility due to its polar groups.
Macro Scale Extraction with a Separatory Funnel [0:36]
20ml of the brewed tea is added to a separatory funnel, ensuring the stopcock is closed. The video explains how to verify the stopcock is closed by checking the position of the hole in the plastic. The extraction process requires a solvent in which caffeine is more soluble than water and that can separate from the tea.
Choosing the Solvent: Dichloromethane (DCM) [0:57]
The video highlights the use of dichloromethane (DCM), also known as methylene chloride, as the organic solvent. The structure of caffeine suggests it will be soluble in certain organic solvents. DCM is compared to water, implying its suitability for extracting caffeine. 20ml of DCM is added to the funnel, and it's noted that the solvent sinks to the bottom.
Performing the Extraction [1:41]
A cap is placed on the funnel, and the mixture is gently shaken to mix the two solvents. The funnel is inverted, and the valve is slowly opened to vent any pressure build-up. This shaking and venting process is repeated to maximise the yield. The funnel is then placed back on the stand, and the layers are allowed to separate, which may take a few minutes.
Separating the Layers [2:16]
If bubbles form between the layers, a clean glass rod can be used to pop them, speeding up the separation. The bottom layer, which is the organic layer in this case, is collected by opening the stopcock and draining it into a collection vessel. The collection is done quickly at first, then slowed down as the tea layer approaches the bottom. The extraction with DCM is repeated one to two more times, collecting into the same vessel.
Drying with Anhydrous Sodium Sulphate [2:45]
Even with careful separation, some of the aqueous layer (tea water) may transfer. Anhydrous sodium sulphate is used as a drying agent to remove this remaining water. A small, spatula-sized amount is added to the flask and swirled to trap the water. More sodium sulphate is added until all the water is contained.
Gravity Filtration [3:17]
The dried material is transferred to another flask using standard gravity filtration. Filter paper is folded and placed in a funnel, and the mixture is slowly poured through. A glass rod is used to hold the filter paper down and direct the flow into the funnel.
Evaporation of DCM [3:42]
In a fume hood, the DCM is heated on a hot plate at a very low heat. Due to DCM's low boiling point, it evaporates quickly. As the DCM evaporates, the remaining caffeine is left behind, forming a crude solid. This crude caffeine can then be further purified.
