Caffeine Extraction Experiment from Tea Leaves
Caffeine Extraction Experiment from Tea Leaves
This experiment is from the official website of Southern Medical University
Operation method
Caffeine Extraction Experiment from Tea Leaves
Principle
Caffeine (or caffeine) is a cardiac stimulant, cerebral nerve stimulant and diuretic. It is mainly used as a central nervous system stimulant, and is also one of the components of drugs such as compound aspirin (e.g. APC). Caffeine is mostly synthesized in the pharmaceutical industry. Caffeine is a weakly basic compound, soluble in chloroform (12.5%), water (2%), ethanol (2%) and hot benzene (5%) and other solvents, slightly soluble in ether. Caffeine with water of crystallization because of the white needle-like crystals, bitter taste. Loss of water of crystallization at 100 ° C began to sublimate, 120 ° C sublimation is quite significant, 178 ° C above the sublimation of accelerated, anhydrous caffeine melting point of 238 ° C. Caffeine is an alkaloid, which can be precipitated by alkaloid reagents (e.g., ellagic acid, potassium iodide reagent of iodine, etc.) and can also be oxidized by many oxidizing agents (e.g., hydrogen peroxide, etc.). Tea contains a variety of alkaloids. Among them, the caffeine content of 1 to 5% (tannic acid that is, ellagic acid 11 to 12%, pigment, cellulose, protein, etc. about 0.6%). Extraction of caffeine from tea is a suitable solvent in the Soxhlet extractor (shown in Figure 2-24) in continuous heating and extraction, and then concentrated to get crude caffeine (which contains other alkaloids and impurities). Then use the nature of caffeine sublimation for sublimation purification. In this experiment, 95% medical alcohol was used as the solvent to extract caffeine from tea leaves.
Materials and Instruments
Evaporation dish (100mL) 150℃ thermometer Glass funnel Measuring cylinder (100mL) Beaker (50mL) Filter paper cartridge Soxhlet extractor Ordinary distillation apparatus Table scale Analytical balance Filter paper Test tubes Large beaker Evaporation dish Heating jacket Electric stove Water bath device Move I. Caffeine extraction Caveat (1) The filter paper cartridge should be both close to the wall of the apparatus and easy to pick up and put down. The height of the extract can not exceed the siphon, otherwise the extract can not be fully soaked in solvent, affecting the extraction effect. The extract can not leak out of the filter paper cartridge, so as not to block the siphon.(2) lime (CaO) powder to absorb water and neutralization to remove impurities.(3) If there is water, will bring some smoke at the beginning of the next sublimation, contamination of the vessel, affecting the purity of the product.(4) In the case of extraction reflux is sufficient, sublimation operation is the key to the success or failure of the experiment, in the sublimation process should always be strictly control the heating temperature, the temperature is too high, it will make the baked material charring, bring out some of the colored material, so that the product is not pure. Re-sublimation, the heating temperature should also be strictly controlled, otherwise the baked goods a lot of smoke, resulting in product impurity and loss.(5) caffeine can be oxidized by hydrogen peroxide and other oxidizing agents to produce tetramethyl dipurine (which will be evaporated with a water bath to a rose-red color), the latter with the action of ammonia that is a purple ammonium violet ureidoacetic acid. This reaction is a characteristic reaction of purine alkaloids.(6) Caffeine is oxidized and decomposed.(7) Potassium iodide of mercury reagent reacts with alkaloids (e.g., caffeine, etc.) to form molecular complexes. For more product details, please visit Aladdin Scientific website.
1. Extraction
Weigh 8g of tea, loaded into the Soxhlet extractor filter paper cartridge ①, in the extractor flask add 80mL 95% medical alcohol and a few pieces of zeolite, loaded Soxhlet extractor, connected to the condensate, heating, continuous extraction for 1 ~ 1.5 hours (extract can be stopped when the color of the extract is very light), to be condensate is just siphoned off when, immediately stop heating, cooling.
2. Recovery of ethanol
Load the distillation device, water bath heating distillation, recovery of most of the ethanol (boiling point 78 ℃). Then pour the residual liquid (about 15-20mL) into the evaporating dish, the distillation flask with a very small amount of alcohol to wash, the washings are combined in the evaporating dish, and concentrated on a steam bath until the residual liquid is about 10mL or so.
3. Sublimation purification
In the evaporating dish containing the concentrated condensed residue add 4g of quicklime (CaO) powder ②, stir well, and evaporate on a steam bath. Then move the evaporating dish to the asbestos mesh with an alcohol lamp on a small flame baking for a few moments (the flame can not be too large, in order to prevent the sublimation of caffeine), so that all the water removed ③, after cooling, wipe off the powder stained on the edge of the evaporating dish, in order to avoid sublimation of contaminated products.
Take a suitable glass funnel, cover the evaporation dish separated by a filter paper with many small holes (as shown in Figure 2-21), in the asbestos mesh (preferably with a sand bath) continue to sublimation ④ heating over low heat. When white needle-like crystals appear on the filter paper, control the flame appropriately (slow down the rate of sublimation as much as possible to improve the purity of the crystals), and stop heating if you notice brown smoke. After cooling (about 5 min), carefully remove the funnel and filter paper, and carefully scrape the caffeine crystals (white, needle-like) attached to the filter paper and around the vessel with a knife into a dry, clean, weighed 50 mL beaker, and the residue is blended and sublimated by continued heating with a larger flame for one (or two) more times. The sublimations are combined to collect caffeine crystals, which are weighed. The yield is usually around 100 mg, and the melting point of caffeine is 238°C.
Second, the nature of caffeine test
1 in the evaporating dish into the caffeine about 0.05 g, add 8 to 10 drops of 30 % H2O2, then add 5% of dilute hydrochloric acid 4 to 5 drops, placed on the water bath heating and evaporation, the residue shows a beautiful rose red. Add 1 drop of concentrated ammonia to the residue, how does the color change5?
2. Take a test tube and add 8 drops of saturated caffeine solution, 1 drop of 0.5% KMnO4 solution and 3 drops of 5% Na2CO3 solution. Shake the test tube and heat it in a boiling water bath and observe the change in the solution ⑥.
3. Take a test tube and add 5 drops of saturated aqueous solution of caffeine and 3 drops of 10% ellagic acid solution and observe the phenomenon that occurs.
4. Take a test tube, add 1mL of 5% hydrochloric acid solution and a little caffeine solid, shake vigorously to dissolve it into a clear solution (if it is really not soluble, take the clarified solution to do the test), and add 12 drops of potassium mercuric iodide solution (7). Shake the test tube and observe the changes in the solution.
Repeat the above test with your own caffeine extract and compare.