从茶叶中提取咖啡因

用液液萃取分离天然生物碱

Organic Synthesis Advanced (University) 90 分钟 ~$15.00

目标

用二氯甲烷对茶叶进行液液萃取提取咖啡因，演示溶剂萃取和天然产物分离。

背景

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.

安全警告

  • 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

所需PPE

goggles gloves lab_coat

材料

  • 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

设备

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

步骤

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 分钟
2

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

3 分钟
3

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

5 分钟 DCM pressure — vent often
4

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

3 分钟 DCM is the lower layer
5

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

10 分钟
6

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

12 分钟
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 分钟 Fume hood essential — DCM vapors
8

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

5 分钟

预期结果

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.

清理

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

详情

类别
Organic Synthesis
难度
Advanced (University)
时长
90 分钟
预估费用
$15.00
步骤数
8
材料
5

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Frequently Asked Questions

What is the objective of 从茶叶中提取咖啡因?
用二氯甲烷对茶叶进行液液萃取提取咖啡因，演示溶剂萃取和天然产物分离。
How difficult is 从茶叶中提取咖啡因?
This experiment is rated as Advanced (University). It takes approximately 90 minutes to complete.
What safety precautions are needed for 从茶叶中提取咖啡因?
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 从茶叶中提取咖啡因?
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 从茶叶中提取咖啡因?
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.