Isolation and detection of active principles, caffeine from tea dust

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BACKGROUND

Caffeine is a purine base (1, 3, 7 – trimethylxanthine). This is mostly produced from the tea leaves and leaf buds synthetically. As green tea it is available from China and Japan and as black tea from Sri Lanka and India. Leaves are green in colour, apex is blunt. Tea leaves are the rich source of caffeine which is a weak base. Caffeine is present 1-4% in tea leaves while 1-2% in coffee seed.¹

Aim: Aim of the experiment is to isolate and detect the active constituent, caffeine present in tea dust.

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REQUIREMENTS

Apparatus: Extraction unit,

TLC plate,

Evaporation unit,

Funnel,

Test tube,

Beaker,

Measuring cylinder

Chemicals: Lead acetate,

H₂SO₄,

Charcoal,

Chloroform,

Alcohol,

Ethanol,

MgO,

Acetic acid,

Silica,

HNO₃,

NaOH,

Methanol.

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PROCEDURE

Isolation of caffeine

Tea leaves (coarse powder form) is extracted with boiling water. In that hot condition the aqueous extract is filtered. To precipitate tannin compound, the warm extract sample is treated with lead acetate. By using dilute H₂SO₄ precipitation of excess lead acetate present in sample is done. To remove the colouring matter, the filtered sample is boiled with charcoal and again filtered to remove the charcoal. By using chloroform the filtered decolourized sample is again extracted. After evaporation the combined chloroform extract gives caffeine as a white colour material and by using alcohol again it is re crystallize.
In soxhlet extractor, by using ethanol the coarsely powdered tea leaves are extracted. The extracted sample contains caffeine and it is adsorbed on MgO. After treatment of 10% H₂SO₄ caffeine is disorbed. Finally by using chloroform the sample is extracted and re-crystallized².

Detection of caffeine

Murexide test: Caffeine are treated with a few crystals of HNO₃(3-4 drops) in a porcelain dish and subjected to evaporation for drying. 2 drops of NaOH solution is added to the residue, which gives a purple colour¹.

TLC of caffeine: 1 mg of caffeine is dissolved in 1 ml of methanol or chloroform. Using the solvent (acetate:methanol:acetic acid, 80:10:10) the sample is eluted and spot on the TLC plate. By exposing to vapour of iodine, the dried plates are visualized at an R_f value of 0.40-0.42.²

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CONCLUSION

The active constituent caffeine was isolated and detected from the leaves of tea. It can be used as CNS stimulant, specific analgesic in migraine.

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REFERENCES

Kokate CK, Purohit AP, Gokhale SB. Druds containing alkaloid (caffeine). Text book of Pharmacognosy, 51 edition. Nirali Prakashan, Pune. 2015: 15-74.
Shah B, Seth AK. isolation of phytopharmaceuticals. Text book of Pharmacognosy and Phytochemistry, 2^nd edition. CBS Publishers & Distributors pvt ltd. 2014: 448.