Improvement of glycine preparation experiment

Gu Zhihong Wu Yunkai Anhui Medical University Hefei Anhui 230032

Abstract: This article briefly describes the glycine preparation experiment as a student's experimental advantage, points out the deficiencies in the glycine preparation experiment, gives the improved experimental steps, and emphasizes the key to the success of the experiment.
Keywords: glycine preparation; experimental procedure; experimental improvement

As a good choice for student experiment, glycine preparation experiment has the following advantages:

1. Glycine is an essential amino acid for human body. Glycine is basically used in various amino acid infusion formulas. In addition, as an important fine chemical intermediate, it is widely used in medicine, pesticides, food, electroplating, feed additives and organic synthesis. In other fields, students have a strong interest in this experiment;

2. It is a comprehensive experiment (preparation â†’ purification â†’ inspection â†’ yield calculation), with a complete experimental process;

3. The device is simple and easy to operate, the instruments and drugs used are common, and the pressure of environmental pollution is not large;

4. The accumulated experiment time is about 4 hours, which meets the time required for students to experiment.

In view of this, my teaching and research department decided to classify this experiment as a student experiment in 2007 to replace the toxic and odorous experiment. However, a seemingly simple experiment encountered various difficulties in the implementation process and failed to achieve the desired results. To this end, we have explored and improved, and have now been included as a successful experiment in student experiments in medicine, rehabilitation, oral cavity, anesthesia, imaging, beauty, prevention, women and children, clinical pathology, biomedical engineering, pharmacology, biotechnology, etc. And achieved good results.

1 Question raised

The existing experimental design of the textbook has the following shortcomings: (1) When the excess NH3 is distilled off, the rubber tube connecting the conical flask and the funnel is directly inserted into the container containing dilute hydrochloric acid, which is inconvenient to operate; (2) NH4Cl crystal is easy Precipitation in the tube makes it difficult to continue the experiment; (3) After the crude solution is boiled for 2 to 3 minutes, it is filtered while hot to start the recrystallization process, but at this time the solution is not saturated and no crystals are precipitated.

2 Improved experimental procedures

(1) Weigh 17g of ammonium carbonate in an Erlenmeyer flask, add 15ml of distilled water, and heat in a water bath at 50 ï½ž 60 â„ƒ for about 15min. Cool to room temperature, add 20ml of concentrated ammonia, add 5g of chloroacetic acid, tightly close the rubber stopper, let stand at room temperature for 1 week.

(2) The Erlenmeyer flask is connected to the absorption tube and placed in a water bath (80 ï½ž 100 â„ƒ). The other end of the absorption tube is connected to the funnel and the funnel is inserted into the diluted hydrochloric acid absorption solution. The water bath is heated for about 30 min to evaporate ammonia gas. Transfer the solution in the Erlenmeyer flask to a beaker, add zeolite and activated carbon (about 0.1g), concentrate in a fume hood to 20-25ml, filter while hot, the filtrate is cooled to room temperature, add 30ml of methanol, stir a little, let stand, After the crystals are completely precipitated, they are filtered under reduced pressure and washed with a small amount of methanol for 1-2 times to obtain glycine crystals. Glycine was placed in a drying incubator, dried at 105 â„ƒ for 30min, taken out and cooled to room temperature, weighed to calculate the yield.

(3) The following experiment is carried out with a 1% aqueous solution made of homemade glycine:

â‘ Take 2ml of glycine aqueous solution in a test tube, add 5 drops of ninhydrin solution, heat in boiling water, and observe the color change.
â‘¡Take 2ml of glycine aqueous solution and 10% sodium nitrite solution and place 2ml in a test tube, and then take 2ml of distilled water and 10% sodium nitrite solution 2ml in another test tube, add 5 drops of glacial acetic acid to each test tube, shake, Observe the phenomenon, compare the results, and explain the reasons.

3 Two points to note during the experiment

1. To prevent NH4Cl crystals from evolving out of the rubber tube, making the experiment difficult to continue. This requires that the rubber tube connecting the Erlenmeyer flask and the funnel should not be too long, about 10cm, and the container containing dilute hydrochloric acid should be placed on the water bath to allow NH3 gas to pass through the rubber tube smoothly at 60 â„ƒ.

2. Concentrate the crude product solution to 20-25ml to ensure the formation of a saturated solution.

references

[1] Wei Zhengyou. Medical Organic Chemistry Experiment Course [M]. Anhui: Anhui Science and Technology Press, 2005

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