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In the laboratory, don’t we often encounter situations like this: when conducting a certain experiment, using reagents from different brands, or even different batches of the same brand, yields completely different results. The only thing these different results have in common is that they’re so extraordinary that they could potentially win a Nobel Prize... Then, after purchasing reagents with higher purity for use in the experiment, the results become normal... The common reagents provided by chemical suppliers can only meet the requirements of ordinary chemical reactions. To ensure the smooth progress of certain organic synthesis reactions, it is often necessary to further purify the reagents. The commonly used solvent treatment method is distillation. If the reaction merely requires an anhydrous environment, a drying tube, oil seal, or nitrogen balloon can be attached to the condenser. However, if both anhydrous and oxygen-free conditions are required, the solvent must be degassed. It is generally carried out under a nitrogen atmosphere. Purification of reagent-grade solvents: Anhydrous reagent-grade solvents often have sufficient purity; sometimes distillation is not necessary. To ensure adequate dryness, active molecular sieves can be added during storage. To deoxygenate the solvent, nitrogen can be blown into it using a syringe or glass tube for about five minutes. Purification of common solvents: For most solvents, sufficient purity can be achieved by distilling them from a desiccant under an inert atmosphere. 1. Alkanes such as hexane, pentane, etc. First, wash several times with concentrated sulfuric acid to remove the olefins, then wash with water, dry over CaCl2, and if necessary, dry over sodium wire or P2O5, followed by distillation. Stored in a stoppered reagent bottle. 2. Aromatic hydrocarbons, such as: benzene, toluene, xylene, etc. Dry with CaCl2; if necessary, dry with sodium wire or P2O5, then distill. Stored in a stoppered reagent bottle. 3. Chloroalkanes such as: dichloromethane, chloroform, carbon tetrachloride, dichloroethane, etc. Washing removes alcohols and the like, drying with CaCl2, and then distillation under reflux in P2O5 or CaH2. It must never be dried with sodium wire, otherwise an explosion will occur. For long-term storage, it should be placed in a sealed bottle and kept in the dark. 4. Ethers and furans such as ether, **furan, etc. Many ethers, upon contact with air, gradually form non-volatile peroxides of unknown structure. Peroxides decompose easily and explode when heated. Therefore, ether and furan compounds that have been stored for too long should be tested for the presence of peroxides before use, especially before distillation. Test method: Mix 1 mL of 10% KI solution containing a drop of starch indicator with 10 mL of ether solution; if no color change occurs, then there is no peroxide present. Or test using an 1% ammonium ferrous sulfate solution, as well as a solution of ferrous sulfate and potassium thiocyanate. If present, add 5% FeSO4 or sodium bisulfite solution to the ether and shake to decompose the peroxides. CaCl2 is pre-dried and then distilled off by refluxing in sodium wire or LiAlH4. Store in a sealed bottle and keep in a cool, dark place. 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 stored for a long time often contains small amounts of peroxides. Detection and removal of peroxides: In a clean test tube, add 2–3 drops of concentrated sulfuric acid, 1 mL of 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, add ether; 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 FeSO4·7H2O with 100 mL of water and 6 mL of concentrated sulfuric acid). Place 100 mL of ether and 10 mL of a 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 particles adhered 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 – **Furan (THF): 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 present 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 them separately. CuCl can be used in reflux to remove large amounts of peroxides. 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. 5. Amides such as dimethylformamide, dimethylacetamide, HMPT, etc. Add CaH2 and reflux; evaporate under reduced pressure, otherwise it tends to decompose. Add the newly activated molecular sieve, store it in a bottle, and indicate the date. Purification of common organic solvents: N,N-Dimethylformamide – DMF. The boiling point of N,N-dimethylformamide is 149–156°C, its refractive index is 1.4305, and its relative density is 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-difluorobenzene. 6. Dimethyl sulfoxide is added to CaH2 and stirred overnight, followed by vacuum distillation. Add newly activated molecular sieves, store them in vials, and label with the date. 7. Pyridine can be treated with KOH, NaOH, CaO, BaO or sodium, and then distilled off. Add the newly activated 5Å molecular sieve, store it in a sealed container, and indicate the date. 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 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. 8. Ethanol: The main impurities are fusel oils, aldehydes, alcohols, and water. The available purification methods are magnesium shavings and iodine reflux, along with refluxing with CaO and evaporation. Add newly activated 3A molecular sieve and store it in a small bottle. 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; once 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. ⑵In 60 mL of 99% ethanol, 5 g of magnesium and 0.5 g of iodine are added. After the magnesium dissolves to form magnesium alkoxide, 900 mL of 99% ethanol is added. After refluxing for 5 hours, distillation is carried out to obtain 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. Note: When using metal compounds as purifying agents, the volume of solvent in the distillation flask should be maintained at at least one-quarter during distillation; it is absolutely not allowed to let it evaporate completely, as this can be dangerous.