Original Title: Summary of Purification Methods for Common Organic Solvents Used in the Laboratory “ Do you often encounter this situation in the laboratory: do an experiment, use different brands or even different batches of reagents of the same brand, can make completely different results, the only common point of different results is that they can win the Nobel Prize.. Then I bought a more pure reagent to do it, and the result was normal. ” The common reagents provided by chemical suppliers can only meet the needs of general chemical reactions. In order to ensure the smooth progress of some organic synthesis reactions, reagents are often further purified. A common method of solvent treatment is distillation. If the reaction requires only no water, a drying tube, an oil seal or a nitrogen-filled balloon can be added to the condenser tube. If it is necessary to achieve water-free and oxygen-free conditions, the solvent needs to be deoxygenated. Typically under a nitrogen atmosphere. Purification of Reagent Grade Solvents Anhydrous reagent grade solvents are often of sufficient purity to sometimes dispense with distillation. To ensure sufficient dryness, active molecular sieves may be added during storage. To deoxidize the solvent, nitrogen gas is bubbled through it for about five minutes using a syringe or a glass tube. Purification of General Solvents Most solvents can be sufficiently pure by distilling them from the desiccant in an inert atmosphere. 1. Alkane Uch as hexane, pentane, and the like. It is first washed several times with concentrated sulfuric acid to remove olefins, washed with water, dried with CaCl2 and, if necessary, with sodium wire or P2O5, and distilled. Store in a stoppered reagent bottle. 2. Aromatic hydrocarbons Uch as benzene, toluene, xylene and the like. Drying with CaCl2, drying with sodium wire or P2O5 if necessary, and distilling. Store in a stoppered reagent bottle. 3. Chlorinated alkanes Uch as dichloromethane, chloroform, carbon tetrachloride, dichloroethane and the like. Washing with water to remove alcohol, drying with CaCl2, and refluxing and evaporating in P2O5 or CaH2. Never use sodium wire to dry, otherwise it will explode. Long-term storage should be in a closed bottle and kept in the dark. 4. Ethers and Furans Expand the full text Uch as ether, tetrahydrofuran and the like. Many ethers will slowly form peroxides which are not volatile and have unknown structure when they come into contact with air. Peroxide is easy to decompose and explode when heated. Therefore, ethers and furans stored for a long time should be tested for the presence of peroxides before use, especially before distillation. Method of test: Mix 1 mL of 10% KI solution containing a drop of starch indicator with 10 mL of ether solution. If there is no color change, there is no peroxide. Or 1% ferrous ammonium sulfate solution, ferrous sulfate and potassium thiocyanate solution. If any, add 5% FeSO4 or sodium metabisulfite solution in ether and shake to decompose the peroxide. Pre-drying CaCl2, and refluxing and evaporating in sodium wire or LiAlH4. Store in a tightly closed bottle and keep in a cool, dark place. Purification of common organic solvents-ether boiling point 34.51 ℃, refractive index 1.3526, relative density 0.71378. Ordinary ether usually contains 2% ethanol and 0.5% water. The long-stored ether often contains a small amount of peroxide. Inspection and removal of peroxide: put 2 ~ 3 drops of concentrated sulfuric acid, 1mL of 2% potassium iodide solution (if the potassium iodide solution has been oxidized by air, dilute sodium sulfite solution can be used until the yellow color disappears) and 1 ~ 2 drops of starch solution into a clean test tube, mix them evenly and then add ether. If blue color appears, it indicates the presence of peroxide. The peroxide can be removed by using a newly prepared dilute solution of ferrous sulfate (the preparation method is 60 G of FeSO47H2O, 100 mL of water and 6 mL of concentrated sulfuric acid). Wash 100 mL of diethyl ether and 10 mL of freshly prepared ferrous sulfate solution in a separatory funnel several times until no peroxide is present. Examination and removal of alcohol and water: put a little potassium permanganate powder and a grain of sodium hydroxide in ether. The presence of alcohol is evidenced by the presence of brown particles on the surface of the sodium hydroxide after standing. The presence of water was tested with anhydrous copper sulfate. Most of the water is removed with anhydrous calcium chloride and then dried with sodium metal. The method comprises the following steps of: putting 100mL of diethyl ether into a dry conical flask, adding 20 to 25g of anhydrous calcium chloride, tightly plugging the mouth of the conical flask with a cork, standing for more than one day, discontinuously shaking, distilling, and collecting a fraction at the temperature of between 33 and 37 deg C. Use a sodium press to directly press 1G of sodium metal into sodium wire, put it into a bottle containing ether, and plug it with a cork with a calcium chloride drying tube. Or insert a glass tube with the end drawn into a capillary tube in the cork, so that moisture can be prevented from entering and the gas produced can escape. It can be used after it is placed until there is no bubble; after it is placed, if the surface of the sodium wire has become yellow and thick, it must be steamed again, and then the sodium wire is pressed in. Purification of common organic solvents-Tetrahydrofuran (THF) boiling point 67 ℃ (64.5 ℃), refractive index 1.4050, relative density 0.8892. Tetrahydrofuran is miscible with water and often contains small amounts of water and peroxides. If anhydrous tetrahydrofuran is to be prepared, lithium aluminum hydride can be used to remove water and peroxide by refluxing under moisture isolation (usually 2 to 4 G of lithium aluminum hydride is needed for 1000 mL), and then distillation is carried out to collect the fraction at 66 ℃ (do not evaporate to dryness during distillation, and pour out the remaining small amount of residue). The refined liquid is added to the sodium wire and should be stored in a nitrogen atmosphere. When handling tetrahydrofuran, a small amount should be tested first, and purification should not be carried out until it is confirmed that only a small amount of water and peroxide are present and the action is not too intense! Peroxides in tetrahydrofuran can be tested with an acidified potassium iodide solution. If the peroxide is too much, it should be treated separately. A large amount of peroxide can be removed by refluxing with CuCl. Purification of common organic solvents — — dioxane: boiling point 101.5 ℃, melting point 12 ℃, refractive index 1.4424, relative density 1.0336. Dioxane can be mixed freely with water and usually contains small amounts of diethyl acetal and water. Long-stored dioxane may contain peroxides (see Ether for identification and removal). The purification method of dioxane is as follows: add 8 mL of concentrated hydrochloric acid and 50 mL of water into 500 mL of dioxane, and reflux for 6 ~ 10 H. During the reflux process, slowly introduce nitrogen to remove the generated acetaldehyde. After cooling, solid potassium hydroxide was added until it could no longer be dissolved, rotovap distillation ,rotary vacuum evaporator, the water layer was removed, and then dried with solid potassium hydroxide for 24 H. Then filtering, heating and refluxing for 8 to 12 hours in the presence of metal sodium, finally distilling in the presence of metal sodium, and pressing into the silk for sealed storage. The purified 1,4-dioxane should be kept out of contact with air. 5. Amide Uch as dimethylformamide, dimethylacetamide, HMPT and the like. CaH2 is added for refluxing, and the mixture is distilled out under reduced pressure, otherwise, the mixture is easy to decompose. Add the freshly activated molecular sieve and store in a bottle with the date. Purification of common organic solvents, N, N-dimethylformamide-DMF N, N-dimethylformamide boiling point 149 ~ 156 ℃, refractive index 1.430 5, relative density 0.9487. Colorless liquid, can be mixed with most organic solvents and water at will, and has good solubility for organic and inorganic compounds. N, N-dimethylformamide contains a small amount of water. Some decomposition occurs during atmospheric distillation, producing dimethylamine and carbon monoxide. In the presence of acid or base, the decomposition is accelerated. Therefore, after adding solid potassium hydroxide (sodium hydroxide) and standing at room temperature for several hours, it is partially decomposed. Therefore, it is most commonly dried with calcium sulfate, magnesium sulfate, barium oxide, silica gel, or molecular sieve and then distilled under reduced pressure to collect a 76 ° C/4800 Pa (36 mmHg) fraction. If the water content is large, 1/10 volume of benzene can be added, water and benzene are distilled off at normal pressure and below 80 deg C, then anhydrous magnesium sulfate or barium oxide is used for drying, and finally reduced pressure distillation is carried out. The purified N, N-dimethylformamide should be stored away from light. The presence of free amine in N, N-dimethylformamide can be checked by the color produced by 2,4-dinitrofluorobenzene. 6. Dimethyl sulfoxide CaH2 was added and stirred overnight, then fractionated under reduced pressure. Add the freshly activated molecular sieve and store in a vial with a date. 7 Pyridine KOH, NaOH, CaO, BaO or sodium can be used and then distilled off. Add freshly activated 55Å molecular sieve and store in a sealed container with date. Purification of common organic solvents-pyridine boiling point 115.5 ℃, refractive index 1.5095, relative density 0.9819. The analytically pure pyridine contains a small amount of water and can be used for general experiments. If anhydrous pyridine is to be prepared, the pyridine and potassium (sodium) hydroxide can be refluxed together, and then the pyridine and potassium (sodium) hydroxide are separated from moisture and evaporated for later use. Dry pyridine has strong water absorption, so the container mouth should be sealed with paraffin when it is stored. 8. Ethanol The main impurities are fusel oil, aldehydes, alcohols, ketones and water. A useful purification method is refluxing magnesium chips and iodine, refluxing with CaO and distilling off. Add freshly activated 3A molecular sieve and store in a vial. Purification of common organic solvents-ethanol boiling point 78.5 ℃, refractive index 1.3616, relative density 0.7893. There are many methods to prepare anhydrous ethanol, and different methods are selected according to different requirements for the quality of anhydrous ethanol. If 98% to 99% ethanol is required, the following methods may be used: (1) According to the property that benzene, water and ethanol form a low azeotropic mixture, benzene is added into ethanol for fractionation. A ternary azeotropic mixture of benzene, water and ethanol is distilled out at 64.9 ℃. Excess benzene is distilled out at 68.3 ℃ to form a binary azeotrope with ethanol. Finally, ethanol is distilled out. This method is widely used in industry. (2) Dewatering with quicklime. 20g of fresh lumpy quicklime is added into 100mL of 95% ethanol, refluxed for 3 to 5 hours, and then distilled. If more than 99% ethanol is required, the following methods can be used: (1) Add 7 G of metal sodium into 100 mL of 99% ethanol. After the reaction is completed, add 27.5 G of diethyl phthalate or 25 G of diethyl oxalate, reflux for 2 ~ 3 H, and then distill. Although sodium metal can react with the water in ethanol to produce hydrogen and sodium hydroxide, the produced sodium hydroxide has an equilibrium reaction with ethanol. Therefore, sodium metal alone cannot completely remove the water in ethanol. It is necessary to add excessive high-boiling esters, such as diethyl phthalate, to react with the produced sodium hydroxide to inhibit the above reaction, so as to achieve the purpose of further dehydration. (2) Add 5 G magnesium and 0.5 G iodine into 60 mL 99% ethanol. After magnesium is dissolved to produce magnesium alkoxide, add 900 mL 99% ethanol, reflux for 5 H, and then distill to obtain 99.9% ethanol. As ethanol has a very strong hygroscopicity, it should be operated quickly and the number of transfers should be minimized to prevent moisture from entering the air, and the instruments used must be dried in advance. Note: When metal compounds are used as purifiers,decarboxylation after extraction, the solvent in the distillation flask should be kept at least a quarter of the volume during distillation, and it is not allowed to evaporate to dryness, otherwise it will be dangerous. Source: Modern Laboratory Equipment Network Return to Sohu to see more Responsible Editor:. toptiontech.com