Purification of Common Organic Reagents

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Purification of Common Organic Reagents – Propanone (2002-12-1). Boiling point: 56.2°C; refractive index: 1.3588; relative density: 0.7899. Ordinary propylene typically contains small amounts of water as well as reducing impurities such as methanol and acetaldehyde. The purification methods include: (1) Adding 2.5 g of potassium permanganate to 250 mL of acetone and heating under reflux; if the purple color of potassium permanganate disappears quickly, a small amount more of potassium permanganate is added and heating continues until the purple color no longer fades. Then propylene is distilled off, dried with anhydrous potassium carbonate or anhydrous calcium sulfate, filtered, and distilled again, with the fraction collected at 55–56.5°C. When purifying propanol using this method, it is necessary to ensure that there are not too many reducing substances present in propanol; otherwise, excessive amounts of potassium permanganate and propanol will be consumed, prolonging the processing time. ⑵Transfer 100 mL of the organic solvent into a separatory funnel. First, add 4 mL of 10% silver nitrate solution, then add 3.6 mL of 1 mol/L sodium hydroxide solution. Shake for 10 minutes, separate the organic layer, and then dry it using anhydrous potassium sulfate or anhydrous calcium sulfate. Finally, the fraction at 55–56.5°C is collected by distillation. This method is faster than Method ⑴, but silver nitrate is expensive, making it suitable only for small-scale purification. Purification of common organic solvents – **Furan: Boiling point 67°C (64.5°C), refractive index 1.4050, relative density 0.8892. **Furan is miscible with water and often contains small amounts of moisture and peroxides. To obtain anhydrous **furan**, lithium aluminum hydride can be used to remove the water and peroxides present under an atmosphere free from moisture (usually, 2–4 g of lithium aluminum hydride is required for 1000 mL of the substance), followed by distillation. The fraction at 66°C should be collected; during distillation, it is not necessary to evaporate everything dry – just pour out the remaining small amount of residue. The refined liquid should be mixed with sodium wire and stored under a nitrogen atmosphere. When handling **furan**, it is necessary to first conduct tests with a small amount; only after confirming that there is only a small amount of water and peroxides and that the reaction will not be too intense can purification proceed. **Peroxides in furans can be detected using an acidified potassium iodide solution. If there is an excess of peroxides, it is advisable to handle it separately. Purification of common organic solvents – Dioxane: Boiling point 101.5°C, melting point 12°C, refractive index 1.4424, relative density 1.0336. Dioxane mixes freely with water; it often contains small amounts of diethanol acetal along with water. Dioxane that has been stored for a long time may contain peroxides (for identification and removal, see ether). The purification method for dioxane involves adding 8 mL of concentrated hydrochloric acid and 50 mL of water to 500 mL of dioxane, then heating the mixture under reflux for 6–10 hours. During this reflux process, nitrogen gas is slowly introduced to remove the acetaldehyde that is formed. After cooling, solid potassium hydroxide is added until no further dissolution occurs; the aqueous layer is separated, and the mixture is dried with solid potassium hydroxide for 24 hours. Then filter, heat under reflux for 8–12 hours in the presence of metallic sodium, and finally distill in the presence of metallic sodium before sealing it in glass vials for storage. Refined 1,4-dioxane should be kept away from air. Purification of common organic solvents – Pyridine has a boiling point of 115.5°C, a refractive index of 1.5095, and a relative density of 0.9819. Analytically pure pyridine contains a small amount of moisture and is suitable for general experiments. To obtain anhydrous pyridine, pyridine can be refluxed with granular potassium (sodium) hydroxide, and then distilled under an airtight condition for later use. Dry pyridine has a high water absorption capacity, so the container opening should be sealed with paraffin when storing it. Purification of common organic solvents – Petroleum ether. Petroleum ether is a light petroleum product, which is a mixture of alkanes with low relative molecular mass. Its boiling range is 30–150°C, with the temperature range for collection generally around 30°C. There are petroleum ethers in boiling range specifications such as 30–60°C, 60–90°C, and 90–120°C. It contains a small amount of unsaturated hydrocarbons, has a boiling point similar to that of alkanes, and cannot be separated by distillation. The purification of petroleum ether typically involves washing it 2–3 times with concentrated sulfuric acid, corresponding to its volume, and then washing it with a saturated solution prepared from potassium permanganate and 10% sulfuric acid, until the purple color in the water layer disappears. It is then washed with water, dried over anhydrous calcium chloride, and distilled. If absolutely dry petroleum ether is required, sodium wire can be added (the same as for purified anhydrous diethyl ether). Purification of common organic solvents – Methanol: boiling point 64.96°C, refractive index 1.3288, relative density 0.7914. Ordinary, unrefined methanol contains 0.02% propanone and 0.1% water. In industrial methanol, the content of these impurities ranges from 0.5% to 1%. To obtain methanol with a purity of over 99.9%, methanol can be distilled using a distillation column. Collect the fraction at 64°C, and then dehydrate it with magnesium (in the same way as for preparing anhydrous ethanol). Methanol is toxic; care should be taken to avoid inhaling its vapors when handling it. Purification of common organic solvents – Ethyl acetate has a boiling point of 77.06°C, a refractive index of 1.3723, and a relative density of 0.9003. The typical content of ethyl acetate is 95%–98%, with small amounts of water, ethanol, and acetic acid present. Purification can be carried out as follows: Add 100 mL of acetic anhydride to 1000 mL of ethyl acetate, along with 10 drops of concentrated sulfuric acid; heat under reflux for 4 hours to remove impurities such as ethanol and water, and then proceed with distillation. The distillate is shaken with 20–30 g of anhydrous potassium carbonate, and then distilled again. The boiling point of the product is 77°C, with a purity of over 99%. Purification of common organic solvents – Diethyl ether: boiling point 34.51°C, refractive index 1.3526, relative density 0.71378. Ordinary diethyl ether usually contains 2% ethanol and 0.5% water. Ether that has been stored for a long time often contains small amounts of peroxides. Testing and removal of peroxides: In a clean test tube, add 2–3 drops of concentrated sulfuric acid, 1 mL of a 2% potassium iodide solution (if the potassium iodide solution has been oxidized by air, dilute sodium sulfite solution can be added until the yellow color disappears), and 1–2 drops of starch solution. After mixing well, ether is added to the mixture; the appearance of blue color indicates the presence of peroxides. Peroxides can be removed using a freshly prepared dilute solution of ferrous sulfate (prepared by mixing 60 g of FeSO4·H2O, 100 mL of water, and 6 mL of concentrated sulfuric acid). Place 100 mL of ether and 10 mL of the freshly prepared ferrous sulfate solution in a separatory funnel and wash several times until no peroxides remain. Testing and removal of alcohols and water: Add a small amount of potassium permanganate powder and a pellet of sodium hydroxide to ether. After placement, brown resin adheres to the surface of sodium hydroxide, indicating the presence of alcohol. The presence of water is tested with anhydrous copper sulfate. Most of the water is first removed using anhydrous calcium chloride, followed by drying with metallic sodium. The method is as follows: Place 100 mL of ether in a dry conical flask, add 20–25 g of anhydrous calcium chloride, seal the flask with a cork, leave it there for more than a day while shaking it occasionally, and then distill it to collect the fraction at 33–37°C. 1 g of metallic sodium was directly pressed into sodium wire using a sodium press and placed in a bottle containing diethyl ether, which was then sealed with a cork equipped with a calcium chloride desiccant tube. Or, insert a glass tube with one end drawn into a capillary into the cork; this prevents moisture from entering while allowing any gases that are produced to escape. It can be used once no bubbles are formed ； After placement, if the surface of the sodium wire has turned yellow and thickened, it must be steamed again before being pressed into shape. Purification of common organic solvents – Ethanol: boiling point 78.5°C, refractive index 1.3616, relative density 0.7893. There are many methods for preparing anhydrous ethanol, and different methods are chosen depending on the requirements regarding the quality of the anhydrous ethanol. To obtain 98%~99% ethanol, the following method can be used: (1) Utilizing the property that benzene, water, and ethanol form azeotrope mixtures, benzene is added to ethanol and fractional distillation is carried out. At 64.9°C, the ternary azeotrope mixture of benzene, water, and ethanol is vaporized; excess benzene forms a binary azeotrope mixture with ethanol and is vaporized as well, with ethanol being vaporized last. This method is widely used in industry. ⑵Dehydrate using quicklime. 20 g of fresh bulk quicklime was added to 100 mL of 95% ethanol, and the mixture was refluxed for 3–5 hours before distillation. To obtain ethanol with a purity of over 99%, the following method can be used: (1) Add 7 g of metallic sodium to 100 mL of 99% ethanol; after the reaction is complete, add 27.5 g of diethyl phthalate or 25 g of diethyl oxalate, then reflux for 2–3 hours, and finally proceed with distillation. Although metallic sodium can react with the water in ethanol to produce hydrogen and sodium hydroxide, the sodium hydroxide formed then undergoes a equilibrium reaction with ethanol. Therefore, the use of metallic sodium alone cannot completely remove the water from ethanol; an excess of high-boiling-point esters, such as diethyl phthalate, must be added to react with the generated sodium hydroxide and suppress the aforementioned reaction, thereby achieving further dehydration. ⑵To 60 mL of 99% ethanol, add 5 g of magnesium and 0.5 g of iodine; after the magnesium dissolves to form magnesium alkoxide, add 900 mL of 99% ethanol. After refluxing for 5 hours, distillation yields 99.9% ethanol. Due to ethanol’s very strong hygroscopicity, quick actions are required during handling to minimize the number of transfers and prevent moisture from the air from entering; meanwhile, the instruments used must be dried in advance. Purification of common organic solvents – DMSO has a boiling point of 189°C, a melting point of 18.5°C, a refractive index of 1.4783, and a relative density of 1.100. Dimethyl sulfoxide can mix with water and can be dried by long-term storage using molecular sieves. Then, vacuum distillation is performed, and the fraction at 76°C/1600 Pa (12 mmHg) is collected. During distillation, the temperature must not exceed 90°C; otherwise, a disproportionation reaction will occur, producing dimethyl sulfone and dimethyl sulfide. It can also be dried using calcium oxide, calcium hydride, barium oxide, or anhydrous barium sulfate, followed by vacuum distillation. It can also be purified by partial crystallization. Dimethyl sulfoxide can explode when mixed with certain substances; care should be taken, for example, with sodium hydride, periodic acid, or magnesium perchlorate. Purification of common organic solvents – DMF, N,N-Dimethylformamide: Boiling point 149–156°C, refractive index 1.4305, relative density 0.9487. A colorless liquid that mixes freely with most organic solvents and water, and has good dissolving power for organic and inorganic compounds. N,N-dimethylformamide contains a small amount of moisture. Some decomposition occurs during atmospheric distillation, producing dimethylamine and carbon monoxide. The decomposition accelerates in the presence of acid or base. Therefore, upon adding solid potassium (sodium) hydroxide and leaving it at room temperature for several hours, partial decomposition occurs. Therefore, calcium sulfate, magnesium sulfate, barium oxide, silica gel, or molecular sieves are most commonly used for drying, followed by vacuum distillation to collect the fraction at 76°C/4800 Pa (36 mmHg). If it contains a high amount of water, 1/10 volume of benzene can be added; the water and benzene are then removed under normal pressure at temperatures below 80°C. After that, it is dried using anhydrous magnesium sulfate or barium oxide, and finally subjected to vacuum distillation. Purified N,N-dimethylformamide should be stored in the dark. If free amines are present in N,N-dimethylformamide, their presence can be detected by the formation of color using 2,4-dichlorofluobenzene. Purification of common organic solvents – Dichloromethane has a boiling point of 40°C, a refractive index of 1.4242, and a relative density of 1.3266. Using dichloromethane is safer than chloroform, so it is often used as a substitute for chloroform as an extractant that is denser than water. Ordinary dichloromethane can generally be used directly as an extractant. For purification, it can be washed with a 5% sodium carbonate solution, then with water, and dried over anhydrous calcium chloride. The fraction collected at 40–41°C is distilled and stored in a brown bottle. Purification of common organic solvents – Carbon disulfide has a boiling point of 46.25°C, a refractive index of 1.6319, and a relative density of 1.2632. Carbon disulfide is a toxic compound that can poison the nervous tissue in the blood. It has a high degree of volatility and flammability; therefore, contact with its vapors should be avoided during use. For experiments where high purity of carbon disulfide is not required, a small amount of anhydrous calcium chloride is added to the carbon disulfide and the mixture is dried for several hours; thereafter, distillation is carried out under heating in a water bath at 55°C to 65°C, and the distilled product is collected. To prepare purer carbon disulfide, add an 0.5% potassium permanganate aqueous solution to the reagent-grade carbon disulfide and wash it three times. Remove hydrogen sulfide and then continuously shake with mercury to remove sulfur. Finally, it is washed with a 2.5% mercuric sulfate solution to remove all hydrogen sulfide (until no foul odor remains), then dried over calcium chloride and collected by distillation. Purification of common organic solvents – Chloroform: boiling point 61.7°C, refractive index 1.4459, relative density 1.4832. Chloroform is easily oxidized by sunlight to chlorine, hydrogen chloride, and phosgene (highly toxic); therefore, it should be stored in brown bottles. Chloroform available on the market is often stabilized with 1% alcohol to eliminate the phosgene that is produced. The detection of ethanol in chloroform can be done using the iodoform reaction ； The detection of free hydrogen chloride can be done using an alcoholic solution of silver nitrate. Ethanol is removed, and chloroform is separated from the lower layer by shaking with half its volume of water several times; it is then dried over calcium chloride for 24 hours and distilled. Another purification method: Vibrate chloroform with a small amount of concentrated sulfuric acid two or three times. To every 200 mL of chloroform, add 10 mL of concentrated sulfuric acid; after separating the acid layer, the chloroform is washed with water, dried, and then distilled. Anhydrous chloroform, free of ethanol, should be stored in a brown bottle away from light to prevent the formation of phosgene due to photochemical reactions. Purification of common organic solvents – Benzene: boiling point 80.1°C, refractive index 1.5011, relative density 0.87865. Ordinary benzene often contains small amounts of water and thiophene; thiophene has a boiling point of 84°C, which is close to that of benzene, and it cannot be removed by distillation. Test for thiophene: Add 1 mL of benzene to 2 mL of concentrated sulfuric acid containing 2 mg of indoloquinone, shake briefly; if the acid layer turns blue-green, it indicates the presence of thiophene. Removal of thiophene and water: Pour benzene into a separatory funnel, add concentrated sulfuric acid in an amount equal to one seventh of the volume of the benzene, shake to sulfonate the thiophene, discard the acidic solution, then add more concentrated sulfuric acid and repeat this process several times until the acid layer becomes colorless or pale yellow and no thiophene is detected. The above-mentioned thiophene-free benzene is successively washed with 10% sodium carbonate solution and water until neutralized, then dried with calcium chloride, distilled, and the fraction at 80°C is collected; finally, trace amounts of water are removed using metallic sodium to obtain anhydrous benzene.