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Wednesday, November 28, 2012

Sublimation - Extraction Caffeine from Tea Leaves - Techniques in Organic Chemistry



Caffeine is a bitter, white crystalline xanthine alkaloid that acts as a stimulant drug. 


Caffeine is found in varying quantities in the seeds, leaves, and fruit of some plants, where it acts as a natural pesticide that paralyzes and kills certain insects feeding on the plants. It is most commonly consumed by humans in infusions extracted from the seed of the coffee plant and the leaves of the tea bush.

In humans, caffeine acts as a CNS (central nervous system stimulant), temporarily warding off drowsiness and restoring alertness. It is the world's most widely consumed psychoactive drug, but, unlike many other psychoactive substances, it is both legal and unregulated in nearly all parts of the world. 


Product Name
Serving Size
Caffeine(mg)/serve
Caffeine(mg/L)
Coffee, decaffeinated
207 mL (7.0 US fl oz)
5–15
24–72
Coffee, espresso
44–60 mL (1.5–2.0 US fl oz)
100
1,691–2,254
Tea – black, green, and other types, – steeped for 3 min.
177 millilitres (6.0 US fl oz)
22–74
124–416
Guayakí yerba mate (loose leaf)
6 g (200 US fl oz)
85
approx. 358
Coca-Cola Classic
355 mL (12.0 US fl oz)
34
96
 References from Wikipedia

 
Chemical:
Dichloromethane: 20mL
Sodium carbonate monohydrate: ~7g
Tea leaf (High Mountain Oolong Tea): 10.00g

Magnesium sulfate anhydrous: Some

Procedure:

Extraction of Crude Caffeine from Tea Leaves
1.      Weight about 10g of tea leaves (precise to 0.01g).

 
2.      Dissolve sodium carbonate in 50mL water.



3.      Pour the solution onto tea leaves
4.      Boil the cup of tea for 20~30 minutes.

 At the beginning of heating

5.      Cool the solution to below 20 in ice bath
6.      Decant the thick, dark solution into a separatory funnel.

 Very Thick Tea

7.      Add another 10mL water to wash the tea leaves and also decant into the separatory funnel.
8.      Add 10mL dichloromethane into the separatory funnel to extract caffeine from aqueous layer.

 
9.      Add another 10mL dichloromethane to extract caffeine again and combine it with the other extraction.
10.  Pour the dichloromethane solution in to a flask.

 We can clearly see, there are still some aqueous in the solution

11.  Add enough  magnesium sulfate to remove water from the organic solvent.

We added some magnesium sulfate to remove water

12. Separate the desiccant(magnesium sulfate) from the solution.

 Use a pill of cotton and a funnel could remove desiccant faster than a filter paper
 
13.  Use a rotary to evaporate all the solvent dichloromethane.


14.  Now we get the crude caffeine


The sublimation of crude caffeine
1.      Take our crude caffeine in to a flask
2.      Put on a stop with a hole with a test tube and the test tube is filled with iced water.
3.      Put the apparatus onto a hot plate and control the surface temperature around 180(because the sublimation point of caffeine is 178under an atmosphere)


4.      Keep the water in the test tube cold.

 Caffeine start deposition on a cold surface(the test tube)

5.      After no longer substance sublimating, take the apparatus from the hot plate.
6.      Collect all the sublimated caffeine from the vessel

 Collect the caffeine from the test tube

 Total caffeine which was purified from sublimation

 Analysis

Name
Unit
Weight of Tea Leaves (g)
10.140
Weight of Crude Caffeine (g)
0.050
Weight of Sublimated Caffeine (g)
0.020
Crude Caffeine / Tea Leaves (g/g)
0.005
Sublimated Caffeine / Tea Leaves (g/g)
0.002




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