Properties and preparation of commonly used reagents 2. Ammonia gas for ammonia products is generally contained in a steel cylinder, and gaseous ammonia can be obtained by a pressure reducing device during use. The flow rate of the gas can be controlled by a bubble meter containing a small amount of concentrated potassium hydroxide solution (12 g of potassium hydroxide dissolved in 12 mL of water). A safety bottle should be added between the meter and the reactor. Drying through a drying tower containing loose soda lime or bulk calcium oxide. The Good Bean Sea Salt Chickpeas,Vanilla Bean Salt,The Good Bean Organic Sea Salt Chickpeas,Soaking Beans In Salt Water jiangmen city hongsing food co., ltd. , https://www.jmhongsing.com
Organic chemistry experiments often use a large number of reagents, including inorganic reagents and organic reagents. Commercially available reagents are of analytical grade ( AR ), chemically pure ( CP ), and industrial grade ( TP ), among which the purity of analytical purity is high. Industrial grades carry more impurities. In some organic reactions, the requirements for reagents or solvents are high. Even the presence of trace impurities or moisture will have a certain influence on the reaction rate, yield and product purity. Therefore, it is necessary to master some necessary reagents. Purification methods are necessary.
In actual work, it is often encountered that a certain reagent cannot be purchased or a high-purity reagent cannot be purchased, which affects the normal operation of the experiment. Therefore, it is necessary to understand the preparation methods of some commonly used reagents. In this part, the preparation and purification methods of common organic and inorganic reagents are given, and it is hoped that it will bring some convenience to the experimental work.
The laboratory prepared sodium amide from sodium and liquid ammonia under the catalysis of ferric ions: 300 mL of anhydrous liquid ammonia was added to a 500 mL three-necked flask. The three-necked flask is provided with a glass stopper, a sealed stirring rod, and a reflux condenser equipped with a soda lime drying tube. With stirring, 0.5 g of sodium was added to the solution, and the solution was blue. Then 0.5 g of ferric nitrate powder catalyst was added and 13.3 g of cut sodium was added over 30 minutes. When sodium is converted to sodium amide, the solution is changed from blue to gray suspension, and a sufficient amount of anhydrous diethyl ether is added from the dropping funnel to keep the liquid volume at about 300 mL. The ammonia was distilled off at elevated temperature. After almost all of the ammonia was distilled off, the sodium amide suspension was stirred, heated to reflux for 5 min, and then cooled to room temperature to obtain an ether suspension of 23.4 g of sodium amide, which was almost quantitative.
If a small amount of ammonia is required, it can be prepared by adding concentrated ammonia water to a round bottom flask equipped with a reflux condenser at the upper end, slowly heating, and drying the gas through a drying tower equipped with loose soda lime or massive calcium oxide, and then passed through A safety bottle is introduced into the reaction flask.
3. Benzene <br>Boiling point 80.1 ° C, density d = 0.8791, insoluble in water, can be miscible with ethanol. The melting point is 5.2 ° C. Industrial benzene often contains thiophene, and the boiling point of thiophene (84 ° C) is close to that of benzene and cannot be separated by distillation. Check the presence or absence of thiophene in benzene. Add 5 mL of benzene to a solution of 10 mL of blush and 10 mL of concentrated sulfuric acid. Shake for a while. When thiophene is present, the acid layer will be light blue.
To prepare anhydrous thiophene-free benzene, it is generally possible to wash with concentrated sulfuric acid at room temperature. Take a concentrated sulfuric acid washing with a volume equivalent to 15% by volume of benzene, repeat the operation until the acid layer is colorless or light yellow, then wash with water until neutral, dry with anhydrous calcium chloride, distill, collect 79-81 ° C The fraction is finally dehydrated to anhydrous benzene with sodium metal.
4. Pyridine <br> boiling point 115.5 ℃, a density d = 1.5095, refractive index n 20D = 0.9819. The pure pyridine is analyzed to contain a small amount of water. If an anhydrous pyridine is to be prepared, the pyridine and the granular potassium hydroxide may be refluxed together, and then the moisture is distilled off to be used. The dried pyridine is very absorbent and should be sealed with paraffin when stored.
5. Palladium catalysts Palladium catalysts are very effective hydrogenation catalysts and are relatively expensive. The laboratory can prepare palladium catalyst from palladium chloride.
(1) Preparation of Pd-C (5% Pd): 1.7 g of palladium chloride and 1.7 mL of concentrated hydrochloric acid were added to 20 mL of water, heated in a water bath for 2 hours to dissolve completely, and then it was added to dissolve 30 g in 200 mL of water. In a solution of sodium acetate, it was placed in a 500 mL flask. 20 g of acid washed activated carbon was added and hydrogenated in a hydrogen atmosphere until the end of the reaction. The catalyst was collected by filtration, washed with 5 portions of 100 mL of water and suction filtered. Dry with potassium hydroxide at room temperature or dry with anhydrous calcium chloride in a vacuum desiccator. The catalyst was ground to a powder and stored in a reagent bottle that was stoppered.
(2) Preparation of Pd-C (30% Pd): 8.25 g of palladium chloride and 5 mL of concentrated hydrochloric acid were added to 50 mL of water. Under ice cooling, 50 mL of 40% acetaldehyde solution was added, followed by 11 g of acid washed activated carbon. A solution of 50 g of potassium hydroxide dissolved in 50 mL of water was added under mechanical stirring to maintain the temperature below 50 °C. After the addition, the temperature was raised to 60 ° C for 15 min, and the catalyst was thoroughly washed with water, and then the water was poured out; washed with acetic acid, suction filtered, and washed with water until no Cl- and OH- ions. Dry at 100 ° C and store in a desiccator.
(3) Preparation of palladium black: 5 g of palladium chloride was dissolved in 30 mL of concentrated hydrochloric acid, diluted with 80 mL of water, and 35 mL of 40% acetaldehyde solution was added under cooling with an ice salt bath. Dissolve 35 g of potassium hydroxide in 35 mL of water and add it to the mixture over 30 min with vigorous stirring. After heating to 60 ° C, after 30 min, the water was decanted and the precipitate was washed 6 times with water, filtered onto a crucible, washed with 1 L of water, blotted dry, and dried in a desiccator to yield 3.1 g.
(4) Preparation of Pd-BaSO4 (5% Pd): Add a hot solution of 63.1 g of cesium hydroxide dissolved in 600 mL of water (t=80 °C) in a 2 L beaker, and add 60 mL of 3 mol at a time with rapid stirring. ? L-1 sulfuric acid. Add 3 mol? L-1 sulfuric acid to make the suspension acidic to litmus. Dissolve 4.1 g of palladium chloride in 10 mL of concentrated hydrochloric acid, dilute with 20 mL of water, add barium sulfate solution under mechanical stirring, and then add 4 mL of 40% acetaldehyde solution. Adjust to a weak alkaline with 30% sodium hydroxide solution, continue stirring for 5 min, and let stand. Pour out the upper layer of the night, wash with water, and then let stand, repeat 8 to 10 times. Filter, wash with 5 parts of 25 mL of water, blot as much as possible, dry at 80 ° C, grind fine catalyst, seal in bottle and set aside.
 6 . acetone Â
The boiling point of 56 ° C , density d = 0.7898 , can be miscible with water, ethanol, ether. Industrial acetone contains impurities such as methanol, ethanol, acid, and water. In general, the acetone is purified by refluxing acetone and potassium permanganate until the purple color of the added potassium permanganate is no longer removed, and then the acetone is distilled off, dried with anhydrous potassium carbonate, and then distilled.
7 . glacial acetic acid Â
The boiling point of 117 ° C , the commercially available acetic acid slowly crystallized at 4 ° C , filtered and dried. A small amount of water can be removed by refluxing with phosphorus pentoxide for several hours. Glacial acetic acid has a corrosive effect on the skin. When it touches the skin or splashes on the eyes, it should be washed with plenty of water.
8 . Nitrogen
Nitrogen is generally stored in a cylinder in the form of compressed gas, usually containing traces of oxygen, which can be removed by the following methods: ( 1 ) by an alkali solution of gallic acid ( 15 g gallic acid dissolved in 100 mL of 50% NaOH solution); 2 ) by Fieser solution, the solution preparation method: 20 g of potassium hydroxide is dissolved in 100 mL of water, and 2 g of sodium sulfonate -2- sulfonate and 15 g of sodium hydrogen sulfite are slightly stirred to dissolve, when the blood is red. The solution can be used to cool to room temperature. The solution can absorb 750 mL of oxygen. When the color of the solution changes to brown or a precipitate forms, the solution loses its effect. There are also commercially available high purity nitrogen free of oxygen, but the price is more expensive.
1 . Sodium amide is commercially available as a granular sodium amide having a purity of 80 to 90%. Sodium amide is not easily ground, and is usually ground in a mortar containing a hydrocarbon inert solvent such as toluene, xylene or the like. Exposure of sodium amide to air at room temperature for 2 to 3 days can create a dangerous mixture. For safety, the open sodium amide should be used immediately and the container should not be placed for more than 12 hours. When sodium amide forms an oxide (the color turns yellow or brown) it is very explosive and can no longer be used. A small amount of unused sodium amide was added to toluene to completely cover it, and ethanol diluted with toluene was slowly added under stirring to decompose it.