Extraction of caffeine from tea (sublimation method)

Principle of experimental method:

Caffeine has the effects of stimulating the heart, exciting brain nerves and diuresis, and is mainly used as a central nervous stimulant. It is also one of the components of compound aspirin (APC) and other drugs. The modern pharmaceutical industry uses synthetic methods to make caffeine. Caffeine is a derivative of purine, and its chemical name is 1,3,7-trimethyl-2,6-dioxopurine, and its structural formula is similar to theophylline and theobromine. Pure coffee is odorless and bitter because of white needle-like crystals; it is easily soluble in water, ethanol, chloroform and acetone; slightly soluble in petroleum ether; hardly soluble in benzene and ether. It is a weakly alkaline substance, and the aqueous solution is neutral to litmus paper.

Experimental material tea

Reagent, kit quicklime powder

Instruments and consumables 1. Evaporating dish 2. Alcohol lamp 3. Tripod 4. Glass rod 5. Platform scale 6. Asbestos net 7. Filter paper 8. Cotton 9. Mortar 10. Pestle

Experimental procedure 1. Weigh 10g tea leaf and 3.5g quick lime mixed into powder, put it in an evaporating dish and put it on an alcohol lamp and roast on a small fire until light yellow, so as to remove all the water.

2. After cooling, wipe off the powder on the edge of the evaporating dish with filter paper to avoid contamination of the product during sublimation.

3. Cover the evaporating dish with a piece of filter paper pierced with many small holes (pinned with a pin), and then cover the glass funnel with a suitable size, and put a little cotton on the neck of the funnel to reduce vapor escape.

4. Heat and sublimate on the asbestos net with an alcohol lamp. The generated steam will rise through the small holes of the filter paper, and after cooling, it will condense on the holes of the filter paper or the wall of the funnel. When white hairy crystals are observed on the paper hole, stop heating and let it cool on its own. If necessary, the outer wall of the funnel can be cooled with a damp cloth. When no steam can be observed in the funnel, the funnel and filter paper can be uncovered, and the caffeine attached to the paper and around the vessel can be carefully scraped off and collected. Weigh and calculate the yield.

Matters needing attention 1. In addition to absorbing water, the function of quicklime can also neutralize and remove some acidic impurities (such as tannic acid). Mix in quicklime to be uniform, and grind carefully and mix well.

2. The key to this experiment is sublimation, and the temperature must be controlled during the sublimation process. It must be heated on a small fire and slowly heated up. It is best that the flame tip of the alcohol lamp just touches the asbestos mesh and is heated slowly for 10-15 minutes. If the flame is too large and the heating is too fast, the filter paper and caffeine will be carbonized and blackened, which will make the product yellow (decompose). ; If the flame is too small and the temperature is too slow, it will waste time. Some caffeine has not yet sublimated, affecting the yield.

3. Be careful when scraping off caffeine to prevent mixing of impurities.

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