Summary of Common Organic Solvent Purification Methods Used in Laboratories

Figure 1: Extraction of Essential Oils from Natural Sources

Common reagents provided by chemical suppliers typically meet general needs for chemical reactions. However, to ensure the success of certain organic synthesis reactions, further purification of reagents is often necessary. The most common purification method for solvents is distillation. If the reaction only requires anhydrous conditions, a drying tube, oil seal, or nitrogen gas balloon can be added to the condenser. If oxygen-free conditions are required, solvents need to undergo deoxygenation, usually performed under a nitrogen atmosphere.

Reagent-grade solvents often have sufficient purity and may not require distillation. To ensure adequate dryness, active molecular sieves can be added during storage. For deoxygenation, nitrogen gas can be injected into the solvent for about five minutes using a syringe or glass tube. Most solvents can achieve adequate purity by distilling them from a drying agent in an inert atmosphere.

1. Alkanes: For example, hexane and pentane should be washed several times with concentrated sulfuric acid to remove alkenes, followed by water washing, drying with CaCl2, and if necessary, with sodium wire or P2O5 before distillation.

2. Aromatic Hydrocarbons: For instance, benzene, toluene, and xylene should be dried with CaCl2 and, if necessary, with sodium wire or P2O5 before distillation.

3. Chlorinated Alkanes: Such as dichloromethane, chloroform, carbon tetrachloride, and dichloroethane should be washed with water to remove alcohols, dried with CaCl2, and distilled over P2O5 or CaH2. Sodium wire should never be used for drying due to explosion risk.

4. Ethers and Furan: For example, diethyl ether and tetrahydrofuran can form non-volatile peroxides upon exposure to air, which can decompose explosively upon heating. Therefore, ethers and furan should be checked for peroxides before use, particularly before distillation.

5. Amides: For instance, dimethylformamide and dimethylacetamide can be purified by refluxing with CaH2 and then reduced pressure distillation.

6. Dimethyl Sulfoxide (DMSO): Can be purified by stirring with CaH2 overnight followed by reduced pressure distillation.

7. Pyridine: Can be purified with KOH, NaOH, CaO, BaO, or sodium before distillation.

8. Ethanol: The main impurities include fusel oil, aldehydes, and water. Purification methods include refluxing with magnesium shavings and iodine or with CaO, followed by storage with activated molecular sieves.

Each solvent has specific methods for purification that are tailored to their chemical properties and potential impurities, ensuring optimal results for laboratory applications.