Extraction de la Caféine du Thé

Isolement d'un alcaloïde naturel par extraction liquide-liquide

Organic Synthesis Advanced (University) 90 min ~$15,00

Objectif

Extraire la caféine des feuilles de thé par extraction liquide-liquide au dichlorométhane, démontrant l'extraction par solvant et l'isolement de produits naturels.

Contexte

Tea contains 2-4% caffeine by dry weight. After brewing a concentrated tea, caffeine is extracted into dichloromethane (DCM), which is immiscible with water. Sodium carbonate is added to convert tannins to sodium salts, keeping them in the aqueous layer while caffeine partitions into DCM.

Avertissements de sécurité

  • DCM is a volatile organic solvent — work in fume hood
  • DCM is denser than water (lower layer in separating funnel)
  • Avoid inhaling DCM vapors
  • Do not use open flames near DCM

EPI requis

goggles gloves lab_coat

Matériaux

  • Tea bags (black tea) (4 bags)
    Strong black tea
  • Dichloromethane (DCM) (60 mL)
    Extraction solvent
  • Sodium carbonate (Na₂CO₃) (5 g)
    To deprotonate tannins
  • Anhydrous sodium sulfate (5 g)
    Drying agent
  • Hot water (200 mL)
    Freshly boiled

Équipement

250 mL beaker Separating funnel Ring stand Evaporating dish Hot plate Buchner funnel

Procédure

1

Brew a strong tea by steeping 4 tea bags in 200 mL of hot water for 10 minutes. Squeeze out the bags and allow to cool.

15 min
2

Add 5 g Na₂CO₃ to the tea. Stir until dissolved.

3 min
3

Transfer the tea to the separating funnel. Add 20 mL DCM. Shake gently with frequent venting.

5 min DCM pressure — vent often
4

Allow the layers to separate. Drain the lower DCM layer into a clean flask.

3 min DCM is the lower layer
5

Repeat the DCM extraction two more times with fresh 20 mL portions. Combine all DCM extracts.

10 min
6

Dry the combined DCM extracts over anhydrous Na₂SO₄ for 10 minutes. Filter.

12 min
7

Carefully evaporate the DCM in a fume hood using a warm water bath (not a hot plate directly). White caffeine crystals should remain.

15 min Fume hood essential — DCM vapors
8

Weigh the crude caffeine. Calculate the yield per gram of tea.

5 min

Résultats attendus

White to off-white crystalline caffeine, typically 20-50 mg from 4 tea bags. The crystals should have a bitter taste. If a melting point apparatus is available, pure caffeine melts at 235-238°C.

Nettoyage

Evaporate remaining DCM in fume hood before disposing of waste. Rinse glassware with acetone then water. Dispose of DCM waste in halogenated solvent container.

Détails

Catégorie
Organic Synthesis
Difficulté
Advanced (University)
Durée
90 min
Coût estimé
$15,00
Étapes
8
Matériaux
5

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Frequently Asked Questions

What is the objective of Extraction de la Caféine du Thé?
Extraire la caféine des feuilles de thé par extraction liquide-liquide au dichlorométhane, démontrant l'extraction par solvant et l'isolement de produits naturels.
How difficult is Extraction de la Caféine du Thé?
This experiment is rated as Advanced (University). It takes approximately 90 minutes to complete.
What safety precautions are needed for Extraction de la Caféine du Thé?
Key safety precautions include: DCM is a volatile organic solvent — work in fume hood; DCM is denser than water (lower layer in separating funnel); Avoid inhaling DCM vapors.
What materials are needed for Extraction de la Caféine du Thé?
The main materials required are: Tea bags (black tea), Dichloromethane (DCM), Sodium carbonate (Na₂CO₃), Anhydrous sodium sulfate, Hot water.
What results should I expect from Extraction de la Caféine du Thé?
White to off-white crystalline caffeine, typically 20-50 mg from 4 tea bags. The crystals should have a bitter taste. If a melting point apparatus is available, pure caffeine melts at 235-238°C.