Plants and other natural materials are sources of many chemicals. Sometimes you want to isolate just one of the thousands that may be present. Here is an example of the use of solvent extraction to isolate and purify caffeine from tea. The same principle can be used to extract other chemicals from natural sources.
Caffeine in tea: List of materials
- 2 tea bags
- NaOH 0,2 M (hydroxyde de sodium)
- Celite (diatomaceous earth – silicon dioxide)
- diethyl ether
- 2-propanol (isopropyl alcohol)
- Open the tea bags and weigh the contents. This will help you determine how well your procedure has worked.
- Place the tea leaves in a 125 ml Erlenmeyer flask.
- Add 20 ml of dichloromethane and 10 ml of 0.2 M NaOH.
- Extraction: Seal the bottle and shake gently for 5 to 10 minutes to allow the solvent mixture to penetrate the leaves. Caffeine dissolves in the solvent, unlike most other compounds found in the leaves. In addition, caffeine is more soluble in dichloromethane than in water.
- Filtration: Use a Büchner funnel, filter paper and Celite to use vacuum filtration to separate the tea leaves from the solution. To do this, moisten the filter paper with dichloromethane, add a Celite pad (about 3 grams of celite). Turn on the vacuum cleaner and slowly pour the solution over the celite. Rinse the Celite with 15 ml of dichloromethane. At this point, you can discard the tea leaves. Save the liquid you have collected – it contains caffeine.
- In a hood, gently heat a 100 ml beaker containing the washes to evaporate the solvent.
The solid that remains after the solvent evaporates contains caffeine and several other compounds. You must separate the caffeine from these compounds. One method is to use the different solubility of caffeine compared to other compounds to purify it.
- Let the beaker cool. Wash the raw caffeine with 1 ml portions of a 1: 1 mixture of hexane and diethyl ether.
- Use a pipette carefully to remove the liquid. Keep the caffeine solid.
- Dissolve the impure caffeine in 2 ml of dichloromethane. Filter the liquid through a thin layer of cotton in a small test tube. Rinse the beaker twice with 0.5 ml portions of dichloromethane and filter the liquid through the cotton to minimize the loss of caffeine.
- In a hood, heat the test tube in a hot water bath (50-60 ° C) to evaporate the solvent.
- Leave the test tube in the hot water bath. Add 2-propanol one drop at a time until the solid dissolves. Use the minimum amount required. This should not exceed 2 milliliters.
- Now you can remove the test tube from the water bath and allow it to cool to room temperature.
- Add 1 ml of hexane to the test tube. This will cause the caffeine to crystallize out of the solution.
- Carefully remove the liquid using a pipette, leaving the caffeine purified.
- Wash the caffeine with 1 ml of a 1: 1 mixture of hexane and diethyl ether. Use a pipette to remove the liquid. Allow the solid to dry before weighing it to determine your yield.
- With any purification, it is a good idea to check the melting point of the sample. This will give you an idea of its purity. The melting point of caffeine is 234 ° C.
Another way to extract caffeine from tea is to make tea in hot water, let it cool to room temperature or below, and add dichloromethane to the tea. Caffeine dissolves preferentially in dichloromethane, so if you swirl the solution and let the layers of solvent separate. you will get caffeine in the heavier dichloromethane layer. The top layer is decaffeinated tea. If you remove the dichloromethane layer and evaporate the solvent, you will get a slightly yellowish and impure crystalline caffeine.
Risk associated with these products :
There are risks associated with these products and all chemicals used in a laboratory procedure. Be sure to read the MSDS for each chemical and wear safety glasses, a lab coat, gloves and other appropriate laboratory clothing. In general, be aware that solvents are flammable and should be kept away from open flames.
A hood is used because the chemicals can be irritating or toxic. Avoid contact with the sodium hydroxide solution, as it is caustic and may cause chemical burns on contact. Although you will find caffeine in coffee, tea and other foods, it is toxic in relatively low doses. Don’t taste your product!
- What is caffeine and how does it work?
- How to prepare a sodium hydroxide solution
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