Commonly used 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, further purification of reagents is often required. A common solvent treatment method is distillation. If the reaction requirement is only anhydrous, a drying tube, oil seal or nitrogen-filled balloon can be added to the condenser tube. If it is necessary to achieve anhydrous and oxygen-free conditions, the solvent needs to be deoxidized. Usually carried out under nitrogen atmosphere.
Purification of reagent-grade solvents Anhydrous reagent-grade solvents are often of sufficient purity and sometimes do not require distillation. To ensure sufficient dryness, active molecular sieves can be added to it during storage. To deoxygenate the solvent, use a syringe or glass tube to blow nitrogen into it for about five minutes. Purification of general solvents Most solvents can be achieved by distilling them from the desiccant in an inert atmosphere. Sufficient purity.
1. Alkane
Such as hexane, pentane, etc. First wash with concentrated sulfuric acid several times to remove olefins, wash with water, dry with CaCl2, dry with sodium wire or P2O5 if necessary, and distill. Store in stoppered reagent bottles.
2. Aromatic hydrocarbons
Such as benzene, toluene, xylene, etc. Dry with CaCl2, dry with sodium wire or P2O5 if necessary, and distill. Store in stoppered reagent bottles.
3. Chlorinated alkanes
Such as dichloromethane, chloroform, carbon tetrachloride, dichloroethane, etc. Wash with water to remove alcohol, etc., dry with CaCl2, and reflux and evaporate in P2O5 or CaH2. Never use sodium wire for drying, otherwise it will explode. Long-term storage should be placed in a sealed bottle and kept in the dark.
4. Ethers and furans
Such as ether, tetrahydrofuran, etc. Many ethers will slowly generate peroxides that are not volatile and have unknown structures when in contact with air. Peroxide easily decomposes and explodes when heated. Therefore, ethers and furans that have been stored for a long time should be tested for the presence of peroxide before use, especially before distillation. Inspection method: Use 1 mL of 10% KI solution containing one drop of starch indicator.body_GB2312; box-sizing: border-box !important; overflow-wrap: break-word !important;">⑴在100mL99%In ethanol, add7gMetal sodium, wait until the reaction is completed, then add27.5gdiethyl phthalate or25gDiethyl oxalate, reflux2~3h, Then distillation takes place.
Although metallic sodium can react with water in ethanol to produce hydrogen and sodium hydroxide, the generated sodium hydroxide reacts in equilibrium with ethanol. Therefore, metallic sodium alone cannot completely remove the water in ethanol. Adding excess high boiling point ester, such as diethyl phthalate, reacts with the generated sodium hydroxide to inhibit the above reaction, thereby achieving the purpose of further dehydration.
⑵at60mL99%In ethanol, add5gMagnesium and0.5giodine, After the magnesium is dissolved to form magnesium alkoxide, add 900mL99%Ethanol, reflux5hAfter distillation, you can get99.9%Ethanol.
Because ethanol is very hygroscopic, you must move quickly during operation and minimize the number of transfers to prevent moisture in the air from entering. At the same time, the instruments used must be dried beforehand.
Note: When using metal compounds as purifiers, the solvent in the distillation bottle should be kept at least during distillation At a quarter of the volume, it is never allowed to evaporate to dryness, otherwise it will be dangerous.
The content of this article comes from the Internet, and the copyright belongs to the original author
The content of this article comes from the Internet, and the copyright belongs to the original author
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