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Experimental report on extracting caffeine from tea
1. Learn the principle and method of solid-liquid extraction by extracting caffeine from tea.
2. Master the principle and function of Soxhlet extractor.
3. Master the sublimation principle and operation.
Second, the experimental principle
Tea contains a variety of alkaloids derived from xanthine, the main component is caffeine (also known as caffeine), the content is about 1%~5%, there are a small amount of theophylline and theobromine, and the content is about1%~12%, and the content is about 0.6%.
The chemical name of caffeine is 1, 3,7-trimethyl-2,6-dioxpurine, and its structure is:
Pure caffeine has white needle-like crystals, which are tasteless and bitter, and it is weathered in the air. Soluble in water, ethanol, chloroform and acetone, slightly soluble in petroleum ether, insoluble in benzene and ether, it is a weakened substance, and its aqueous solution is neutral to litmus test paper. Caffeine loses its crystal water at C and begins to sublimate. C sublimates significantly, sometimes quickly. The melting point of anhydrous caffeine is.
Caffeine can stimulate the heart, excite the brain and induce diuresis, so it can be used as a formula of related drugs alone. Caffeine can be obtained by artificial synthesis or extraction. In this experiment, caffeine was extracted from tea by Soxhlet extraction. Taking advantage of the characteristics that caffeine is easily soluble in ethanol and easy to sublimate, 95% ethanol is used as solvent, continuous extraction is carried out with Soxhlet extractor (or reflux), then crude caffeine is obtained by concentration and roasting, and then purified caffeine is obtained by sublimation extraction.
Third, the experimental device
1. Soxhlet extractor: See Figure 2- 17.
2. Reflux extraction device: Soxhlet extractor is not required for reflux condensation device (Figure 3- 13). However, the general reflux condensation device has a large amount of solvent, and the extraction effect is poor with Bison extractor.
3. Sublimation device: A solid substance with high vapor pressure is heated below the melting point and directly turned into vapor without melting. The process of vapor condensing into a solid is called sublimation. High purity products can be obtained by sublimation, but this method has great losses.
Add the fully dried substance to be sublimated into the evaporating dish, cover the evaporating dish with a piece of filter paper with dense holes, and then invert a slightly smaller glass funnel of aperture ratio evaporating dish. To avoid steam escaping, put a small cotton ball on the neck of the funnel. Figure 4-3 1 shows the atmospheric sublimation device.
Four, reagents and equipment
Reagent: tea, 95% ethanol, quicklime.
Equipment: a set of 60mL Soxhlet extractor, evaporating dish, glass funnel, distillation head, receiving tube, 50mL conical flask and direct condensing tube.
Verb (abbreviation of verb) experimental steps
Weigh 5g of tea powder, put the tea leaves into a filter paper sleeve, carefully insert the filter paper sleeve into a Soxhlet extractor, add 50ml of 95% ethanol into a 60mL flat-bottomed flask, and add a few grains of zeolite to install the device as shown in Figure 2- 17. After heating in water bath and continuous extraction for 2~2.5h, the color of the extract becomes pale. When the solution just siphoned back into the flask, stop heating immediately.
Install a distillation device (see Figure 3-2), and conduct distillation in a water bath to evaporate most of the ethanol and recover it. Pour the residual liquid (about 5~ 10mL) into an evaporating dish, add 2g of finely ground quicklime powder, and evaporate the solvent in a steam bath under the constant stirring of a glass rod. Then carefully dry the solid on the asbestos net with a small torch.
Take a suitable glass funnel and cover it on the evaporating dish separated by filter paper with many holes (Figure 4-3 1). Be careful to heat and sublimate with small fire. If there is steam on the funnel, dry it with filter paper. When white needles appear on the filter paper, stop heating, cool slightly and carefully collect caffeine crystals on the front and back of the filter paper. After mixing, the residue can be sublimated again with a slightly larger fire. After mixing the products, weigh and measure the melting point. The yield is about 20 ~ 30 mg.
Matters needing attention about intransitive verbs
1. Add quicklime to neutralize and remove acidic substances such as tannic acid. Quicklime must be ground fine.
2. When ethanol is about to evaporate, solids are easy to overflow from the tray, so pay attention to fire prevention.
3. Water must be completely removed before sublimation, otherwise water droplets will appear in the funnel during sublimation. In this case, the water droplets are quickly dried with filter paper, and baking is continued for a period of time before sublimation.
4. The heating temperature must be strictly controlled during sublimation.
Seven. Experimental results and discussion
Pure coffee is a white needle-like crystal, and the experimental results can be weighed by electronic balance. In this experiment, if there is no Soxhlet extractor, caffeine can also be extracted by reflux method.
Eight, thinking about the problem
1. What is the principle of Soxhlet extractor? What are the advantages compared with direct solvent reflux extraction?
2. What is the function of adding quicklime before sublimation?
3. What is the principle of sublimation operation?
4. Why in sublimation operation, the heating temperature must be controlled below the melting point of the sublimate?
5. Why should water be removed before sublimation?
6. Besides sublimation, what other methods can be used to extract caffeine?
Determination of Caffeine B by Infrared Absorption Spectrometry
First, the experimental purpose
1. Understand the working principle of Fourier transform infrared spectrometer and learn how to use AVATAR360FT-IR.
2. Master the commonly used infrared sample preparation method of solid matter-potassium bromide tabletting method.
3. Learn the method of qualitative identification of organic compounds by infrared absorption spectrum.
Second, the experimental principle
1. infrared absorption spectrum is one of the important methods to identify the structure of organic compounds, which can mainly provide information such as functional groups contained in organic compounds. See section 4.2.3 for the basic principle of infrared absorption spectrum.
2. When measuring infrared spectrum, different types of samples must adopt different sample preparation methods. Generally, solid samples can be made by tabletting and pasting methods. The tabletting method is to mix and grind the sample with potassium bromide powder, and then press it into a transparent sheet with a thickness of about 65438±0mm; The sticking method is to grind the sample into fine enough powder, then make it into paste with liquid paraffin or carbon tetrachloride, and then spread the paste thinly and evenly on the potassium bromide disc. Because paraffin or carbon tetrachloride itself has absorption in the infrared spectrum, the absorption peak generated by paraffin or carbon tetrachloride should be deducted when analyzing the spectrum. Figure 4-32 shows the infrared absorption spectra of liquid paraffin and carbon tetrachloride.
3. Drawing the infrared spectrum of the sample is only the first step for the firm work of the compound structure, and it is more important to analyze the infrared spectrum. There are many absorption peaks in infrared spectrum, which contain rich structural information, but many absorption peaks cannot be accurately explained. Beginners should master the regression of absorption peaks in the characteristic frequency range of 4000~ 1500 functional groups and some important absorption peaks below 1500, and learn how to consult infrared standard spectra or search standard spectra library by computer.
Third, instruments and reagents
1.AVATAR360FT-IR spectrometer or other infrared spectrometer.
2. Infrared drying lamp, stainless steel tweezers and sample scraper, agate mortar, sample paper, compression molding machine, tablet press, magnetic sample rack, absorbent cotton soaked in anhydrous alcohol, etc.
3. Samples and reagents: caffeine and potassium bromide powder extracted in experiment 17A.
Fourth, experimental methods.
1. Open the instrument, start the computer and enter the OMNIC window (see section 4.2.3).
2. Tablet preparation: put 1~2mg dry sample into agate mortar, add about 100mg potassium bromide powder, and grind it evenly. Place the base, bottom die, sample paper and die body of the die in the order shown in Figure 4-33. Then, carefully put the ground potassium bromide powder with the sample into the hole in the center of the sample paper, insert the pressure bar into the die body, insert it at the bottom, and rotate it gently to make the potassium bromide powder evenly dispersed. Place the whole mold on the workbench pad of the tablet press (see Figure 4-34), rotate the compression screw handwheel to compress the mold, and rotate the oil drain valve clockwise to the end. Then, slowly press the dynamic handle up and down to observe the pressure gauge. When the pressure reaches (about 100~ 120), stop pressurizing for 2~3min, rotate the oil drain valve counterclockwise, release the pressure, return the pointer of the pressure gauge to "0", unscrew the handwheel of the pressure screw, and take out the mold to obtain the transparent disc fixed in the sample paper hole. Carefully place the sample paper in the middle of the magnetic sample holder and press the magnetic sheet. The prepared samples are used to collect the sample map in the next step.
3. Draw the infrared spectrum of caffeine in the sample and search the standard library (see section 4.2.3 for details). The whole process includes (1) setting acquisition parameters; (2) collecting background; (3) collecting sample drawings; (4) carrying out baseline correction, peak labeling and other processing on the spectrogram of the obtained sample; (5) standard library retrieval; (6) Print spectrogram.
4. After collecting the sample diagram, you can take out the sample rack from the sample room. Clean used mortar, tweezers, scraper, mold, etc. Soak absorbent cotton in absolute ethanol and dry it under infrared drying lamp to prepare the next sample.
V. Spectrum Analysis
1. According to the structure of the sample, the absorption peaks in the infrared spectrum were assigned. Every peak in the region of 4000~ 1500 should be discussed, and the absorption peak less than 1500 mainly belongs to it. See Figure 4-20 and Appendix 3 for attributes.
2. Record the retrieval results of computer library, and evaluate and discuss the retrieval results.
Matters needing attention about intransitive verbs
1. When making samples, the number of samples must be appropriate. There are too many samples, and the prepared sample wafer is too "thick" and has poor light transmittance, resulting in strong peaks beyond the detection range in the collected spectrogram; The sample size is too small, the wafer is too "thin", and the signal-to-noise ratio of the collected spectrum is poor.
2. The infrared spectrum experiment should be carried out in a dry environment, because some light-transmitting parts in the infrared spectrometer are made of water-soluble substances such as potassium bromide, which are easy to be damaged in a humid environment. In addition, water itself can absorb infrared light to produce a strong absorption peak, which interferes with the spectrogram of the sample.
Seven. Thinking and discussing
How is the infrared spectrum of 1. compound produced? What important structural information can it provide?
2. Why does the stretching vibration of methyl appear in the high frequency region?
3. Can we get the exact structure of an unknown object only by infrared spectrum analysis? Why?
4. Can the infrared spectrum of water-containing samples be directly determined? Why?
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